Fix /\p{pkg::User-defined}/i

[perl5.git] / regcomp.c

/*    regcomp.c
 */

/*
 * 'A fair jaw-cracker dwarf-language must be.'            --Samwise Gamgee
 *
 *     [p.285 of _The Lord of the Rings_, II/iii: "The Ring Goes South"]
 */

/* This file contains functions for compiling a regular expression.  See
 * also regexec.c which funnily enough, contains functions for executing
 * a regular expression.
 *
 * This file is also copied at build time to ext/re/re_comp.c, where
 * it's built with -DPERL_EXT_RE_BUILD -DPERL_EXT_RE_DEBUG -DPERL_EXT.
 * This causes the main functions to be compiled under new names and with
 * debugging support added, which makes "use re 'debug'" work.
 */

/* NOTE: this is derived from Henry Spencer's regexp code, and should not
 * confused with the original package (see point 3 below).  Thanks, Henry!
 */

/* Additional note: this code is very heavily munged from Henry's version
 * in places.  In some spots I've traded clarity for efficiency, so don't
 * blame Henry for some of the lack of readability.
 */

/* The names of the functions have been changed from regcomp and
 * regexec to pregcomp and pregexec in order to avoid conflicts
 * with the POSIX routines of the same names.
*/

#ifdef PERL_EXT_RE_BUILD
#include "re_top.h"
#endif

/*
 * pregcomp and pregexec -- regsub and regerror are not used in perl
 *
 *      Copyright (c) 1986 by University of Toronto.
 *      Written by Henry Spencer.  Not derived from licensed software.
 *
 *      Permission is granted to anyone to use this software for any
 *      purpose on any computer system, and to redistribute it freely,
 *      subject to the following restrictions:
 *
 *      1. The author is not responsible for the consequences of use of
 *              this software, no matter how awful, even if they arise
 *              from defects in it.
 *
 *      2. The origin of this software must not be misrepresented, either
 *              by explicit claim or by omission.
 *
 *      3. Altered versions must be plainly marked as such, and must not
 *              be misrepresented as being the original software.
 *
 *
 ****    Alterations to Henry's code are...
 ****
 ****    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 ****    2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
 ****    by Larry Wall and others
 ****
 ****    You may distribute under the terms of either the GNU General Public
 ****    License or the Artistic License, as specified in the README file.

 *
 * Beware that some of this code is subtly aware of the way operator
 * precedence is structured in regular expressions.  Serious changes in
 * regular-expression syntax might require a total rethink.
 */
#include "EXTERN.h"
#define PERL_IN_REGCOMP_C
#include "perl.h"

#ifndef PERL_IN_XSUB_RE
#  include "INTERN.h"
#endif

#define REG_COMP_C
#ifdef PERL_IN_XSUB_RE
#  include "re_comp.h"
EXTERN_C const struct regexp_engine my_reg_engine;
#else
#  include "regcomp.h"
#endif

#include "dquote_inline.h"
#include "invlist_inline.h"
#include "unicode_constants.h"

#define HAS_NONLATIN1_FOLD_CLOSURE(i) \
 _HAS_NONLATIN1_FOLD_CLOSURE_ONLY_FOR_USE_BY_REGCOMP_DOT_C_AND_REGEXEC_DOT_C(i)
#define HAS_NONLATIN1_SIMPLE_FOLD_CLOSURE(i) \
 _HAS_NONLATIN1_SIMPLE_FOLD_CLOSURE_ONLY_FOR_USE_BY_REGCOMP_DOT_C_AND_REGEXEC_DOT_C(i)
#define IS_NON_FINAL_FOLD(c) _IS_NON_FINAL_FOLD_ONLY_FOR_USE_BY_REGCOMP_DOT_C(c)
#define IS_IN_SOME_FOLD_L1(c) _IS_IN_SOME_FOLD_ONLY_FOR_USE_BY_REGCOMP_DOT_C(c)

#ifndef STATIC
#define STATIC  static
#endif

#ifndef MIN
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#endif

#ifndef MAX
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#endif

/* this is a chain of data about sub patterns we are processing that
   need to be handled separately/specially in study_chunk. Its so
   we can simulate recursion without losing state.  */
struct scan_frame;
typedef struct scan_frame {
    regnode *last_regnode;      /* last node to process in this frame */
    regnode *next_regnode;      /* next node to process when last is reached */
    U32 prev_recursed_depth;
    I32 stopparen;              /* what stopparen do we use */
    U32 is_top_frame;           /* what flags do we use? */

    struct scan_frame *this_prev_frame; /* this previous frame */
    struct scan_frame *prev_frame;      /* previous frame */
    struct scan_frame *next_frame;      /* next frame */
} scan_frame;

/* Certain characters are output as a sequence with the first being a
 * backslash. */
#define isBACKSLASHED_PUNCT(c)                                              \
                    ((c) == '-' || (c) == ']' || (c) == '\\' || (c) == '^')


struct RExC_state_t {
    U32         flags;                  /* RXf_* are we folding, multilining? */
    U32         pm_flags;               /* PMf_* stuff from the calling PMOP */
    char        *precomp;               /* uncompiled string. */
    char        *precomp_end;           /* pointer to end of uncompiled string. */
    REGEXP      *rx_sv;                 /* The SV that is the regexp. */
    regexp      *rx;                    /* perl core regexp structure */
    regexp_internal     *rxi;           /* internal data for regexp object
                                           pprivate field */
    char        *start;                 /* Start of input for compile */
    char        *end;                   /* End of input for compile */
    char        *parse;                 /* Input-scan pointer. */
    char        *adjusted_start;        /* 'start', adjusted.  See code use */
    STRLEN      precomp_adj;            /* an offset beyond precomp.  See code use */
    SSize_t     whilem_seen;            /* number of WHILEM in this expr */
    regnode     *emit_start;            /* Start of emitted-code area */
    regnode     *emit_bound;            /* First regnode outside of the
                                           allocated space */
    regnode     *emit;                  /* Code-emit pointer; if = &emit_dummy,
                                           implies compiling, so don't emit */
    regnode_ssc emit_dummy;             /* placeholder for emit to point to;
                                           large enough for the largest
                                           non-EXACTish node, so can use it as
                                           scratch in pass1 */
    I32         naughty;                /* How bad is this pattern? */
    I32         sawback;                /* Did we see \1, ...? */
    U32         seen;
    SSize_t     size;                   /* Code size. */
    I32                npar;            /* Capture buffer count, (OPEN) plus
                                           one. ("par" 0 is the whole
                                           pattern)*/
    I32         nestroot;               /* root parens we are in - used by
                                           accept */
    I32         extralen;
    I32         seen_zerolen;
    regnode     **open_parens;          /* pointers to open parens */
    regnode     **close_parens;         /* pointers to close parens */
    regnode     *opend;                 /* END node in program */
    I32         utf8;           /* whether the pattern is utf8 or not */
    I32         orig_utf8;      /* whether the pattern was originally in utf8 */
                                /* XXX use this for future optimisation of case
                                 * where pattern must be upgraded to utf8. */
    I32         uni_semantics;  /* If a d charset modifier should use unicode
                                   rules, even if the pattern is not in
                                   utf8 */
    HV          *paren_names;           /* Paren names */

    regnode     **recurse;              /* Recurse regops */
    I32         recurse_count;          /* Number of recurse regops */
    U8          *study_chunk_recursed;  /* bitmap of which subs we have moved
                                           through */
    U32         study_chunk_recursed_bytes;  /* bytes in bitmap */
    I32         in_lookbehind;
    I32         contains_locale;
    I32         contains_i;
    I32         override_recoding;
#ifdef EBCDIC
    I32         recode_x_to_native;
#endif
    I32         in_multi_char_class;
    struct reg_code_block *code_blocks; /* positions of literal (?{})
                                            within pattern */
    int         num_code_blocks;        /* size of code_blocks[] */
    int         code_index;             /* next code_blocks[] slot */
    SSize_t     maxlen;                        /* mininum possible number of chars in string to match */
    scan_frame *frame_head;
    scan_frame *frame_last;
    U32         frame_count;
#ifdef ADD_TO_REGEXEC
    char        *starttry;              /* -Dr: where regtry was called. */
#define RExC_starttry   (pRExC_state->starttry)
#endif
    SV          *runtime_code_qr;       /* qr with the runtime code blocks */
#ifdef DEBUGGING
    const char  *lastparse;
    I32         lastnum;
    AV          *paren_name_list;       /* idx -> name */
    U32         study_chunk_recursed_count;
    SV          *mysv1;
    SV          *mysv2;
#define RExC_lastparse  (pRExC_state->lastparse)
#define RExC_lastnum    (pRExC_state->lastnum)
#define RExC_paren_name_list    (pRExC_state->paren_name_list)
#define RExC_study_chunk_recursed_count    (pRExC_state->study_chunk_recursed_count)
#define RExC_mysv       (pRExC_state->mysv1)
#define RExC_mysv1      (pRExC_state->mysv1)
#define RExC_mysv2      (pRExC_state->mysv2)

#endif
    bool        seen_unfolded_sharp_s;
    bool        strict;
};

#define RExC_flags      (pRExC_state->flags)
#define RExC_pm_flags   (pRExC_state->pm_flags)
#define RExC_precomp    (pRExC_state->precomp)
#define RExC_precomp_adj (pRExC_state->precomp_adj)
#define RExC_adjusted_start  (pRExC_state->adjusted_start)
#define RExC_precomp_end (pRExC_state->precomp_end)
#define RExC_rx_sv      (pRExC_state->rx_sv)
#define RExC_rx         (pRExC_state->rx)
#define RExC_rxi        (pRExC_state->rxi)
#define RExC_start      (pRExC_state->start)
#define RExC_end        (pRExC_state->end)
#define RExC_parse      (pRExC_state->parse)
#define RExC_whilem_seen        (pRExC_state->whilem_seen)

/* Set during the sizing pass when there is a LATIN SMALL LETTER SHARP S in any
 * EXACTF node, hence was parsed under /di rules.  If later in the parse,
 * something forces the pattern into using /ui rules, the sharp s should be
 * folded into the sequence 'ss', which takes up more space than previously
 * calculated.  This means that the sizing pass needs to be restarted.  (The
 * node also becomes an EXACTFU_SS.)  For all other characters, an EXACTF node
 * that gets converted to /ui (and EXACTFU) occupies the same amount of space,
 * so there is no need to resize [perl #125990]. */
#define RExC_seen_unfolded_sharp_s (pRExC_state->seen_unfolded_sharp_s)

#ifdef RE_TRACK_PATTERN_OFFSETS
#define RExC_offsets    (pRExC_state->rxi->u.offsets) /* I am not like the
                                                         others */
#endif
#define RExC_emit       (pRExC_state->emit)
#define RExC_emit_dummy (pRExC_state->emit_dummy)
#define RExC_emit_start (pRExC_state->emit_start)
#define RExC_emit_bound (pRExC_state->emit_bound)
#define RExC_sawback    (pRExC_state->sawback)
#define RExC_seen       (pRExC_state->seen)
#define RExC_size       (pRExC_state->size)
#define RExC_maxlen        (pRExC_state->maxlen)
#define RExC_npar       (pRExC_state->npar)
#define RExC_nestroot   (pRExC_state->nestroot)
#define RExC_extralen   (pRExC_state->extralen)
#define RExC_seen_zerolen       (pRExC_state->seen_zerolen)
#define RExC_utf8       (pRExC_state->utf8)
#define RExC_uni_semantics      (pRExC_state->uni_semantics)
#define RExC_orig_utf8  (pRExC_state->orig_utf8)
#define RExC_open_parens        (pRExC_state->open_parens)
#define RExC_close_parens       (pRExC_state->close_parens)
#define RExC_opend      (pRExC_state->opend)
#define RExC_paren_names        (pRExC_state->paren_names)
#define RExC_recurse    (pRExC_state->recurse)
#define RExC_recurse_count      (pRExC_state->recurse_count)
#define RExC_study_chunk_recursed        (pRExC_state->study_chunk_recursed)
#define RExC_study_chunk_recursed_bytes  \
                                   (pRExC_state->study_chunk_recursed_bytes)
#define RExC_in_lookbehind      (pRExC_state->in_lookbehind)
#define RExC_contains_locale    (pRExC_state->contains_locale)
#define RExC_contains_i (pRExC_state->contains_i)
#define RExC_override_recoding (pRExC_state->override_recoding)
#ifdef EBCDIC
#   define RExC_recode_x_to_native (pRExC_state->recode_x_to_native)
#endif
#define RExC_in_multi_char_class (pRExC_state->in_multi_char_class)
#define RExC_frame_head (pRExC_state->frame_head)
#define RExC_frame_last (pRExC_state->frame_last)
#define RExC_frame_count (pRExC_state->frame_count)
#define RExC_strict (pRExC_state->strict)

/* Heuristic check on the complexity of the pattern: if TOO_NAUGHTY, we set
 * a flag to disable back-off on the fixed/floating substrings - if it's
 * a high complexity pattern we assume the benefit of avoiding a full match
 * is worth the cost of checking for the substrings even if they rarely help.
 */
#define RExC_naughty    (pRExC_state->naughty)
#define TOO_NAUGHTY (10)
#define MARK_NAUGHTY(add) \
    if (RExC_naughty < TOO_NAUGHTY) \
        RExC_naughty += (add)
#define MARK_NAUGHTY_EXP(exp, add) \
    if (RExC_naughty < TOO_NAUGHTY) \
        RExC_naughty += RExC_naughty / (exp) + (add)

#define ISMULT1(c)      ((c) == '*' || (c) == '+' || (c) == '?')
#define ISMULT2(s)      ((*s) == '*' || (*s) == '+' || (*s) == '?' || \
        ((*s) == '{' && regcurly(s)))

/*
 * Flags to be passed up and down.
 */
#define WORST           0       /* Worst case. */
#define HASWIDTH        0x01    /* Known to match non-null strings. */

/* Simple enough to be STAR/PLUS operand; in an EXACTish node must be a single
 * character.  (There needs to be a case: in the switch statement in regexec.c
 * for any node marked SIMPLE.)  Note that this is not the same thing as
 * REGNODE_SIMPLE */
#define SIMPLE          0x02
#define SPSTART         0x04    /* Starts with * or + */
#define POSTPONED       0x08    /* (?1),(?&name), (??{...}) or similar */
#define TRYAGAIN        0x10    /* Weeded out a declaration. */
#define RESTART_PASS1   0x20    /* Need to restart sizing pass */
#define NEED_UTF8       0x40    /* In conjunction with RESTART_PASS1, need to
                                   calcuate sizes as UTF-8 */

#define REG_NODE_NUM(x) ((x) ? (int)((x)-RExC_emit_start) : -1)

/* whether trie related optimizations are enabled */
#if PERL_ENABLE_EXTENDED_TRIE_OPTIMISATION
#define TRIE_STUDY_OPT
#define FULL_TRIE_STUDY
#define TRIE_STCLASS
#endif



#define PBYTE(u8str,paren) ((U8*)(u8str))[(paren) >> 3]
#define PBITVAL(paren) (1 << ((paren) & 7))
#define PAREN_TEST(u8str,paren) ( PBYTE(u8str,paren) & PBITVAL(paren))
#define PAREN_SET(u8str,paren) PBYTE(u8str,paren) |= PBITVAL(paren)
#define PAREN_UNSET(u8str,paren) PBYTE(u8str,paren) &= (~PBITVAL(paren))

#define REQUIRE_UTF8(flagp) STMT_START {                                   \
                                     if (!UTF) {                           \
                                         assert(PASS1);                    \
                                         *flagp = RESTART_PASS1|NEED_UTF8; \
                                         return NULL;                      \
                                     }                                     \
                             } STMT_END

/* Change from /d into /u rules, and restart the parse if we've already seen
 * something whose size would increase as a result, by setting *flagp and
 * returning 'restart_retval'.  RExC_uni_semantics is a flag that indicates
 * we've change to /u during the parse.  */
#define REQUIRE_UNI_RULES(flagp, restart_retval)                            \
    STMT_START {                                                            \
            if (DEPENDS_SEMANTICS) {                                        \
                assert(PASS1);                                              \
                set_regex_charset(&RExC_flags, REGEX_UNICODE_CHARSET);      \
                RExC_uni_semantics = 1;                                     \
                if (RExC_seen_unfolded_sharp_s) {                           \
                    *flagp |= RESTART_PASS1;                                \
                    return restart_retval;                                  \
                }                                                           \
            }                                                               \
    } STMT_END

/* This converts the named class defined in regcomp.h to its equivalent class
 * number defined in handy.h. */
#define namedclass_to_classnum(class)  ((int) ((class) / 2))
#define classnum_to_namedclass(classnum)  ((classnum) * 2)

#define _invlist_union_complement_2nd(a, b, output) \
                        _invlist_union_maybe_complement_2nd(a, b, TRUE, output)
#define _invlist_intersection_complement_2nd(a, b, output) \
                 _invlist_intersection_maybe_complement_2nd(a, b, TRUE, output)

/* About scan_data_t.

  During optimisation we recurse through the regexp program performing
  various inplace (keyhole style) optimisations. In addition study_chunk
  and scan_commit populate this data structure with information about
  what strings MUST appear in the pattern. We look for the longest
  string that must appear at a fixed location, and we look for the
  longest string that may appear at a floating location. So for instance
  in the pattern:

    /FOO[xX]A.*B[xX]BAR/

  Both 'FOO' and 'A' are fixed strings. Both 'B' and 'BAR' are floating
  strings (because they follow a .* construct). study_chunk will identify
  both FOO and BAR as being the longest fixed and floating strings respectively.

  The strings can be composites, for instance

     /(f)(o)(o)/

  will result in a composite fixed substring 'foo'.

  For each string some basic information is maintained:

  - offset or min_offset
    This is the position the string must appear at, or not before.
    It also implicitly (when combined with minlenp) tells us how many
    characters must match before the string we are searching for.
    Likewise when combined with minlenp and the length of the string it
    tells us how many characters must appear after the string we have
    found.

  - max_offset
    Only used for floating strings. This is the rightmost point that
    the string can appear at. If set to SSize_t_MAX it indicates that the
    string can occur infinitely far to the right.

  - minlenp
    A pointer to the minimum number of characters of the pattern that the
    string was found inside. This is important as in the case of positive
    lookahead or positive lookbehind we can have multiple patterns
    involved. Consider

    /(?=FOO).*F/

    The minimum length of the pattern overall is 3, the minimum length
    of the lookahead part is 3, but the minimum length of the part that
    will actually match is 1. So 'FOO's minimum length is 3, but the
    minimum length for the F is 1. This is important as the minimum length
    is used to determine offsets in front of and behind the string being
    looked for.  Since strings can be composites this is the length of the
    pattern at the time it was committed with a scan_commit. Note that
    the length is calculated by study_chunk, so that the minimum lengths
    are not known until the full pattern has been compiled, thus the
    pointer to the value.

  - lookbehind

    In the case of lookbehind the string being searched for can be
    offset past the start point of the final matching string.
    If this value was just blithely removed from the min_offset it would
    invalidate some of the calculations for how many chars must match
    before or after (as they are derived from min_offset and minlen and
    the length of the string being searched for).
    When the final pattern is compiled and the data is moved from the
    scan_data_t structure into the regexp structure the information
    about lookbehind is factored in, with the information that would
    have been lost precalculated in the end_shift field for the
    associated string.

  The fields pos_min and pos_delta are used to store the minimum offset
  and the delta to the maximum offset at the current point in the pattern.

*/

typedef struct scan_data_t {
    /*I32 len_min;      unused */
    /*I32 len_delta;    unused */
    SSize_t pos_min;
    SSize_t pos_delta;
    SV *last_found;
    SSize_t last_end;       /* min value, <0 unless valid. */
    SSize_t last_start_min;
    SSize_t last_start_max;
    SV **longest;           /* Either &l_fixed, or &l_float. */
    SV *longest_fixed;      /* longest fixed string found in pattern */
    SSize_t offset_fixed;   /* offset where it starts */
    SSize_t *minlen_fixed;  /* pointer to the minlen relevant to the string */
    I32 lookbehind_fixed;   /* is the position of the string modfied by LB */
    SV *longest_float;      /* longest floating string found in pattern */
    SSize_t offset_float_min; /* earliest point in string it can appear */
    SSize_t offset_float_max; /* latest point in string it can appear */
    SSize_t *minlen_float;  /* pointer to the minlen relevant to the string */
    SSize_t lookbehind_float; /* is the pos of the string modified by LB */
    I32 flags;
    I32 whilem_c;
    SSize_t *last_closep;
    regnode_ssc *start_class;
} scan_data_t;

/*
 * Forward declarations for pregcomp()'s friends.
 */

static const scan_data_t zero_scan_data =
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ,0};

#define SF_BEFORE_EOL           (SF_BEFORE_SEOL|SF_BEFORE_MEOL)
#define SF_BEFORE_SEOL          0x0001
#define SF_BEFORE_MEOL          0x0002
#define SF_FIX_BEFORE_EOL       (SF_FIX_BEFORE_SEOL|SF_FIX_BEFORE_MEOL)
#define SF_FL_BEFORE_EOL        (SF_FL_BEFORE_SEOL|SF_FL_BEFORE_MEOL)

#define SF_FIX_SHIFT_EOL        (+2)
#define SF_FL_SHIFT_EOL         (+4)

#define SF_FIX_BEFORE_SEOL      (SF_BEFORE_SEOL << SF_FIX_SHIFT_EOL)
#define SF_FIX_BEFORE_MEOL      (SF_BEFORE_MEOL << SF_FIX_SHIFT_EOL)

#define SF_FL_BEFORE_SEOL       (SF_BEFORE_SEOL << SF_FL_SHIFT_EOL)
#define SF_FL_BEFORE_MEOL       (SF_BEFORE_MEOL << SF_FL_SHIFT_EOL) /* 0x20 */
#define SF_IS_INF               0x0040
#define SF_HAS_PAR              0x0080
#define SF_IN_PAR               0x0100
#define SF_HAS_EVAL             0x0200
#define SCF_DO_SUBSTR           0x0400
#define SCF_DO_STCLASS_AND      0x0800
#define SCF_DO_STCLASS_OR       0x1000
#define SCF_DO_STCLASS          (SCF_DO_STCLASS_AND|SCF_DO_STCLASS_OR)
#define SCF_WHILEM_VISITED_POS  0x2000

#define SCF_TRIE_RESTUDY        0x4000 /* Do restudy? */
#define SCF_SEEN_ACCEPT         0x8000
#define SCF_TRIE_DOING_RESTUDY 0x10000
#define SCF_IN_DEFINE          0x20000




#define UTF cBOOL(RExC_utf8)

/* The enums for all these are ordered so things work out correctly */
#define LOC (get_regex_charset(RExC_flags) == REGEX_LOCALE_CHARSET)
#define DEPENDS_SEMANTICS (get_regex_charset(RExC_flags)                    \
                                                     == REGEX_DEPENDS_CHARSET)
#define UNI_SEMANTICS (get_regex_charset(RExC_flags) == REGEX_UNICODE_CHARSET)
#define AT_LEAST_UNI_SEMANTICS (get_regex_charset(RExC_flags)                \
                                                     >= REGEX_UNICODE_CHARSET)
#define ASCII_RESTRICTED (get_regex_charset(RExC_flags)                      \
                                            == REGEX_ASCII_RESTRICTED_CHARSET)
#define AT_LEAST_ASCII_RESTRICTED (get_regex_charset(RExC_flags)             \
                                            >= REGEX_ASCII_RESTRICTED_CHARSET)
#define ASCII_FOLD_RESTRICTED (get_regex_charset(RExC_flags)                 \
                                        == REGEX_ASCII_MORE_RESTRICTED_CHARSET)

#define FOLD cBOOL(RExC_flags & RXf_PMf_FOLD)

/* For programs that want to be strictly Unicode compatible by dying if any
 * attempt is made to match a non-Unicode code point against a Unicode
 * property.  */
#define ALWAYS_WARN_SUPER  ckDEAD(packWARN(WARN_NON_UNICODE))

#define OOB_NAMEDCLASS          -1

/* There is no code point that is out-of-bounds, so this is problematic.  But
 * its only current use is to initialize a variable that is always set before
 * looked at. */
#define OOB_UNICODE             0xDEADBEEF

#define CHR_SVLEN(sv) (UTF ? sv_len_utf8(sv) : SvCUR(sv))
#define CHR_DIST(a,b) (UTF ? utf8_distance(a,b) : a - b)


/* length of regex to show in messages that don't mark a position within */
#define RegexLengthToShowInErrorMessages 127

/*
 * If MARKER[12] are adjusted, be sure to adjust the constants at the top
 * of t/op/regmesg.t, the tests in t/op/re_tests, and those in
 * op/pragma/warn/regcomp.
 */
#define MARKER1 "<-- HERE"    /* marker as it appears in the description */
#define MARKER2 " <-- HERE "  /* marker as it appears within the regex */

#define REPORT_LOCATION " in regex; marked by " MARKER1    \
                        " in m/%"UTF8f MARKER2 "%"UTF8f"/"

/* The code in this file in places uses one level of recursion with parsing
 * rebased to an alternate string constructed by us in memory.  This can take
 * the form of something that is completely different from the input, or
 * something that uses the input as part of the alternate.  In the first case,
 * there should be no possibility of an error, as we are in complete control of
 * the alternate string.  But in the second case we don't control the input
 * portion, so there may be errors in that.  Here's an example:
 *      /[abc\x{DF}def]/ui
 * is handled specially because \x{df} folds to a sequence of more than one
 * character, 'ss'.  What is done is to create and parse an alternate string,
 * which looks like this:
 *      /(?:\x{DF}|[abc\x{DF}def])/ui
 * where it uses the input unchanged in the middle of something it constructs,
 * which is a branch for the DF outside the character class, and clustering
 * parens around the whole thing. (It knows enough to skip the DF inside the
 * class while in this substitute parse.) 'abc' and 'def' may have errors that
 * need to be reported.  The general situation looks like this:
 *
 *              sI                       tI               xI       eI
 * Input:       ----------------------------------------------------
 * Constructed:         ---------------------------------------------------
 *                      sC               tC               xC       eC     EC
 *
 * The input string sI..eI is the input pattern.  The string sC..EC is the
 * constructed substitute parse string.  The portions sC..tC and eC..EC are
 * constructed by us.  The portion tC..eC is an exact duplicate of the input
 * pattern tI..eI.  In the diagram, these are vertically aligned.  Suppose that
 * while parsing, we find an error at xC.  We want to display a message showing
 * the real input string.  Thus we need to find the point xI in it which
 * corresponds to xC.  xC >= tC, since the portion of the string sC..tC has
 * been constructed by us, and so shouldn't have errors.  We get:
 *
 *      xI = sI + (tI - sI) + (xC - tC)
 *
 * and, the offset into sI is:
 *
 *      (xI - sI) = (tI - sI) + (xC - tC)
 *
 * When the substitute is constructed, we save (tI -sI) as RExC_precomp_adj,
 * and we save tC as RExC_adjusted_start.
 *
 * During normal processing of the input pattern, everything points to that,
 * with RExC_precomp_adj set to 0, and RExC_adjusted_start set to sI.
 */

#define tI_sI           RExC_precomp_adj
#define tC              RExC_adjusted_start
#define sC              RExC_precomp
#define xI_offset(xC)   ((IV) (tI_sI + (xC - tC)))
#define xI(xC)          (sC + xI_offset(xC))
#define eC              RExC_precomp_end

#define REPORT_LOCATION_ARGS(xC)                                            \
    UTF8fARG(UTF,                                                           \
             (xI(xC) > eC) /* Don't run off end */                          \
              ? eC - sC   /* Length before the <--HERE */                   \
              : xI_offset(xC),                                              \
             sC),         /* The input pattern printed up to the <--HERE */ \
    UTF8fARG(UTF,                                                           \
             (xI(xC) > eC) ? 0 : eC - xI(xC), /* Length after <--HERE */    \
             (xI(xC) > eC) ? eC : xI(xC))     /* pattern after <--HERE */

/* Used to point after bad bytes for an error message, but avoid skipping
 * past a nul byte. */
#define SKIP_IF_CHAR(s) (!*(s) ? 0 : UTF ? UTF8SKIP(s) : 1)

/*
 * Calls SAVEDESTRUCTOR_X if needed, then calls Perl_croak with the given
 * arg. Show regex, up to a maximum length. If it's too long, chop and add
 * "...".
 */
#define _FAIL(code) STMT_START {                                        \
    const char *ellipses = "";                                          \
    IV len = RExC_precomp_end - RExC_precomp;                                   \
                                                                        \
    if (!SIZE_ONLY)                                                     \
        SAVEFREESV(RExC_rx_sv);                                         \
    if (len > RegexLengthToShowInErrorMessages) {                       \
        /* chop 10 shorter than the max, to ensure meaning of "..." */  \
        len = RegexLengthToShowInErrorMessages - 10;                    \
        ellipses = "...";                                               \
    }                                                                   \
    code;                                                               \
} STMT_END

#define FAIL(msg) _FAIL(                            \
    Perl_croak(aTHX_ "%s in regex m/%"UTF8f"%s/",           \
            msg, UTF8fARG(UTF, len, RExC_precomp), ellipses))

#define FAIL2(msg,arg) _FAIL(                       \
    Perl_croak(aTHX_ msg " in regex m/%"UTF8f"%s/",         \
            arg, UTF8fARG(UTF, len, RExC_precomp), ellipses))

/*
 * Simple_vFAIL -- like FAIL, but marks the current location in the scan
 */
#define Simple_vFAIL(m) STMT_START {                                    \
    Perl_croak(aTHX_ "%s" REPORT_LOCATION,                              \
            m, REPORT_LOCATION_ARGS(RExC_parse));                       \
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL()
 */
#define vFAIL(m) STMT_START {                           \
    if (!SIZE_ONLY)                                     \
        SAVEFREESV(RExC_rx_sv);                         \
    Simple_vFAIL(m);                                    \
} STMT_END

/*
 * Like Simple_vFAIL(), but accepts two arguments.
 */
#define Simple_vFAIL2(m,a1) STMT_START {                        \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1,              \
                      REPORT_LOCATION_ARGS(RExC_parse));        \
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL2().
 */
#define vFAIL2(m,a1) STMT_START {                       \
    if (!SIZE_ONLY)                                     \
        SAVEFREESV(RExC_rx_sv);                         \
    Simple_vFAIL2(m, a1);                               \
} STMT_END


/*
 * Like Simple_vFAIL(), but accepts three arguments.
 */
#define Simple_vFAIL3(m, a1, a2) STMT_START {                   \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2,          \
            REPORT_LOCATION_ARGS(RExC_parse));                  \
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL3().
 */
#define vFAIL3(m,a1,a2) STMT_START {                    \
    if (!SIZE_ONLY)                                     \
        SAVEFREESV(RExC_rx_sv);                         \
    Simple_vFAIL3(m, a1, a2);                           \
} STMT_END

/*
 * Like Simple_vFAIL(), but accepts four arguments.
 */
#define Simple_vFAIL4(m, a1, a2, a3) STMT_START {               \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2, a3,      \
            REPORT_LOCATION_ARGS(RExC_parse));                  \
} STMT_END

#define vFAIL4(m,a1,a2,a3) STMT_START {                 \
    if (!SIZE_ONLY)                                     \
        SAVEFREESV(RExC_rx_sv);                         \
    Simple_vFAIL4(m, a1, a2, a3);                       \
} STMT_END

/* A specialized version of vFAIL2 that works with UTF8f */
#define vFAIL2utf8f(m, a1) STMT_START {             \
    if (!SIZE_ONLY)                                 \
        SAVEFREESV(RExC_rx_sv);                     \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1,  \
            REPORT_LOCATION_ARGS(RExC_parse));      \
} STMT_END

#define vFAIL3utf8f(m, a1, a2) STMT_START {             \
    if (!SIZE_ONLY)                                     \
        SAVEFREESV(RExC_rx_sv);                         \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2,  \
            REPORT_LOCATION_ARGS(RExC_parse));          \
} STMT_END

/* These have asserts in them because of [perl #122671] Many warnings in
 * regcomp.c can occur twice.  If they get output in pass1 and later in that
 * pass, the pattern has to be converted to UTF-8 and the pass restarted, they
 * would get output again.  So they should be output in pass2, and these
 * asserts make sure new warnings follow that paradigm. */

/* m is not necessarily a "literal string", in this macro */
#define reg_warn_non_literal_string(loc, m) STMT_START {                \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                       "%s" REPORT_LOCATION,            \
                                  m, REPORT_LOCATION_ARGS(loc));        \
} STMT_END

#define ckWARNreg(loc,m) STMT_START {                                   \
    __ASSERT_(PASS2) Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),        \
                                          m REPORT_LOCATION,            \
                                          REPORT_LOCATION_ARGS(loc));   \
} STMT_END

#define vWARN(loc, m) STMT_START {                                      \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                       m REPORT_LOCATION,               \
                                       REPORT_LOCATION_ARGS(loc));      \
} STMT_END

#define vWARN_dep(loc, m) STMT_START {                                  \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_DEPRECATED),       \
                                       m REPORT_LOCATION,               \
                                       REPORT_LOCATION_ARGS(loc));      \
} STMT_END

#define ckWARNdep(loc,m) STMT_START {                                   \
    __ASSERT_(PASS2) Perl_ck_warner_d(aTHX_ packWARN(WARN_DEPRECATED),  \
                                            m REPORT_LOCATION,          \
                                            REPORT_LOCATION_ARGS(loc)); \
} STMT_END

#define ckWARNregdep(loc,m) STMT_START {                                    \
    __ASSERT_(PASS2) Perl_ck_warner_d(aTHX_ packWARN2(WARN_DEPRECATED,      \
                                                      WARN_REGEXP),         \
                                             m REPORT_LOCATION,             \
                                             REPORT_LOCATION_ARGS(loc));    \
} STMT_END

#define ckWARN2reg_d(loc,m, a1) STMT_START {                                \
    __ASSERT_(PASS2) Perl_ck_warner_d(aTHX_ packWARN(WARN_REGEXP),          \
                                            m REPORT_LOCATION,              \
                                            a1, REPORT_LOCATION_ARGS(loc)); \
} STMT_END

#define ckWARN2reg(loc, m, a1) STMT_START {                                 \
    __ASSERT_(PASS2) Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),            \
                                          m REPORT_LOCATION,                \
                                          a1, REPORT_LOCATION_ARGS(loc));   \
} STMT_END

#define vWARN3(loc, m, a1, a2) STMT_START {                                 \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_REGEXP),               \
                                       m REPORT_LOCATION,                   \
                                       a1, a2, REPORT_LOCATION_ARGS(loc));  \
} STMT_END

#define ckWARN3reg(loc, m, a1, a2) STMT_START {                             \
    __ASSERT_(PASS2) Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),            \
                                          m REPORT_LOCATION,                \
                                          a1, a2,                           \
                                          REPORT_LOCATION_ARGS(loc));       \
} STMT_END

#define vWARN4(loc, m, a1, a2, a3) STMT_START {                         \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                       m REPORT_LOCATION,               \
                                       a1, a2, a3,                      \
                                       REPORT_LOCATION_ARGS(loc));      \
} STMT_END

#define ckWARN4reg(loc, m, a1, a2, a3) STMT_START {                     \
    __ASSERT_(PASS2) Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),        \
                                          m REPORT_LOCATION,            \
                                          a1, a2, a3,                   \
                                          REPORT_LOCATION_ARGS(loc));   \
} STMT_END

#define vWARN5(loc, m, a1, a2, a3, a4) STMT_START {                     \
    __ASSERT_(PASS2) Perl_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                       m REPORT_LOCATION,               \
                                       a1, a2, a3, a4,                  \
                                       REPORT_LOCATION_ARGS(loc));      \
} STMT_END

/* Macros for recording node offsets.   20001227 mjd@plover.com
 * Nodes are numbered 1, 2, 3, 4.  Node #n's position is recorded in
 * element 2*n-1 of the array.  Element #2n holds the byte length node #n.
 * Element 0 holds the number n.
 * Position is 1 indexed.
 */
#ifndef RE_TRACK_PATTERN_OFFSETS
#define Set_Node_Offset_To_R(node,byte)
#define Set_Node_Offset(node,byte)
#define Set_Cur_Node_Offset
#define Set_Node_Length_To_R(node,len)
#define Set_Node_Length(node,len)
#define Set_Node_Cur_Length(node,start)
#define Node_Offset(n)
#define Node_Length(n)
#define Set_Node_Offset_Length(node,offset,len)
#define ProgLen(ri) ri->u.proglen
#define SetProgLen(ri,x) ri->u.proglen = x
#else
#define ProgLen(ri) ri->u.offsets[0]
#define SetProgLen(ri,x) ri->u.offsets[0] = x
#define Set_Node_Offset_To_R(node,byte) STMT_START {                    \
    if (! SIZE_ONLY) {                                                  \
        MJD_OFFSET_DEBUG(("** (%d) offset of node %d is %d.\n",         \
                    __LINE__, (int)(node), (int)(byte)));               \
        if((node) < 0) {                                                \
            Perl_croak(aTHX_ "value of node is %d in Offset macro",     \
                                         (int)(node));                  \
        } else {                                                        \
            RExC_offsets[2*(node)-1] = (byte);                          \
        }                                                               \
    }                                                                   \
} STMT_END

#define Set_Node_Offset(node,byte) \
    Set_Node_Offset_To_R((node)-RExC_emit_start, (byte)-RExC_start)
#define Set_Cur_Node_Offset Set_Node_Offset(RExC_emit, RExC_parse)

#define Set_Node_Length_To_R(node,len) STMT_START {                     \
    if (! SIZE_ONLY) {                                                  \
        MJD_OFFSET_DEBUG(("** (%d) size of node %d is %d.\n",           \
                __LINE__, (int)(node), (int)(len)));                    \
        if((node) < 0) {                                                \
            Perl_croak(aTHX_ "value of node is %d in Length macro",     \
                                         (int)(node));                  \
        } else {                                                        \
            RExC_offsets[2*(node)] = (len);                             \
        }                                                               \
    }                                                                   \
} STMT_END

#define Set_Node_Length(node,len) \
    Set_Node_Length_To_R((node)-RExC_emit_start, len)
#define Set_Node_Cur_Length(node, start)                \
    Set_Node_Length(node, RExC_parse - start)

/* Get offsets and lengths */
#define Node_Offset(n) (RExC_offsets[2*((n)-RExC_emit_start)-1])
#define Node_Length(n) (RExC_offsets[2*((n)-RExC_emit_start)])

#define Set_Node_Offset_Length(node,offset,len) STMT_START {    \
    Set_Node_Offset_To_R((node)-RExC_emit_start, (offset));     \
    Set_Node_Length_To_R((node)-RExC_emit_start, (len));        \
} STMT_END
#endif

#if PERL_ENABLE_EXPERIMENTAL_REGEX_OPTIMISATIONS
#define EXPERIMENTAL_INPLACESCAN
#endif /*PERL_ENABLE_EXPERIMENTAL_REGEX_OPTIMISATIONS*/

#define DEBUG_RExC_seen() \
        DEBUG_OPTIMISE_MORE_r({                                             \
            PerlIO_printf(Perl_debug_log,"RExC_seen: ");                    \
                                                                            \
            if (RExC_seen & REG_ZERO_LEN_SEEN)                              \
                PerlIO_printf(Perl_debug_log,"REG_ZERO_LEN_SEEN ");         \
                                                                            \
            if (RExC_seen & REG_LOOKBEHIND_SEEN)                            \
                PerlIO_printf(Perl_debug_log,"REG_LOOKBEHIND_SEEN ");       \
                                                                            \
            if (RExC_seen & REG_GPOS_SEEN)                                  \
                PerlIO_printf(Perl_debug_log,"REG_GPOS_SEEN ");             \
                                                                            \
            if (RExC_seen & REG_RECURSE_SEEN)                               \
                PerlIO_printf(Perl_debug_log,"REG_RECURSE_SEEN ");          \
                                                                            \
            if (RExC_seen & REG_TOP_LEVEL_BRANCHES_SEEN)                         \
                PerlIO_printf(Perl_debug_log,"REG_TOP_LEVEL_BRANCHES_SEEN ");    \
                                                                            \
            if (RExC_seen & REG_VERBARG_SEEN)                               \
                PerlIO_printf(Perl_debug_log,"REG_VERBARG_SEEN ");          \
                                                                            \
            if (RExC_seen & REG_CUTGROUP_SEEN)                              \
                PerlIO_printf(Perl_debug_log,"REG_CUTGROUP_SEEN ");         \
                                                                            \
            if (RExC_seen & REG_RUN_ON_COMMENT_SEEN)                        \
                PerlIO_printf(Perl_debug_log,"REG_RUN_ON_COMMENT_SEEN ");   \
                                                                            \
            if (RExC_seen & REG_UNFOLDED_MULTI_SEEN)                        \
                PerlIO_printf(Perl_debug_log,"REG_UNFOLDED_MULTI_SEEN ");   \
                                                                            \
            if (RExC_seen & REG_GOSTART_SEEN)                               \
                PerlIO_printf(Perl_debug_log,"REG_GOSTART_SEEN ");          \
                                                                            \
            if (RExC_seen & REG_UNBOUNDED_QUANTIFIER_SEEN)                               \
                PerlIO_printf(Perl_debug_log,"REG_UNBOUNDED_QUANTIFIER_SEEN ");          \
                                                                            \
            PerlIO_printf(Perl_debug_log,"\n");                             \
        });

#define DEBUG_SHOW_STUDY_FLAG(flags,flag) \
  if ((flags) & flag) PerlIO_printf(Perl_debug_log, "%s ", #flag)

#define DEBUG_SHOW_STUDY_FLAGS(flags,open_str,close_str)                    \
    if ( ( flags ) ) {                                                      \
        PerlIO_printf(Perl_debug_log, "%s", open_str);                      \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_FL_BEFORE_SEOL);                     \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_FL_BEFORE_MEOL);                     \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_IS_INF);                             \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_HAS_PAR);                            \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_IN_PAR);                             \
        DEBUG_SHOW_STUDY_FLAG(flags,SF_HAS_EVAL);                           \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_DO_SUBSTR);                         \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_DO_STCLASS_AND);                    \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_DO_STCLASS_OR);                     \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_DO_STCLASS);                        \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_WHILEM_VISITED_POS);                \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_TRIE_RESTUDY);                      \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_SEEN_ACCEPT);                       \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_TRIE_DOING_RESTUDY);                \
        DEBUG_SHOW_STUDY_FLAG(flags,SCF_IN_DEFINE);                         \
        PerlIO_printf(Perl_debug_log, "%s", close_str);                     \
    }


#define DEBUG_STUDYDATA(str,data,depth)                              \
DEBUG_OPTIMISE_MORE_r(if(data){                                      \
    PerlIO_printf(Perl_debug_log,                                    \
        "%*s" str "Pos:%"IVdf"/%"IVdf                                \
        " Flags: 0x%"UVXf,                                           \
        (int)(depth)*2, "",                                          \
        (IV)((data)->pos_min),                                       \
        (IV)((data)->pos_delta),                                     \
        (UV)((data)->flags)                                          \
    );                                                               \
    DEBUG_SHOW_STUDY_FLAGS((data)->flags," [ ","]");                 \
    PerlIO_printf(Perl_debug_log,                                    \
        " Whilem_c: %"IVdf" Lcp: %"IVdf" %s",                        \
        (IV)((data)->whilem_c),                                      \
        (IV)((data)->last_closep ? *((data)->last_closep) : -1),     \
        is_inf ? "INF " : ""                                         \
    );                                                               \
    if ((data)->last_found)                                          \
        PerlIO_printf(Perl_debug_log,                                \
            "Last:'%s' %"IVdf":%"IVdf"/%"IVdf" %sFixed:'%s' @ %"IVdf \
            " %sFloat: '%s' @ %"IVdf"/%"IVdf"",                      \
            SvPVX_const((data)->last_found),                         \
            (IV)((data)->last_end),                                  \
            (IV)((data)->last_start_min),                            \
            (IV)((data)->last_start_max),                            \
            ((data)->longest &&                                      \
             (data)->longest==&((data)->longest_fixed)) ? "*" : "",  \
            SvPVX_const((data)->longest_fixed),                      \
            (IV)((data)->offset_fixed),                              \
            ((data)->longest &&                                      \
             (data)->longest==&((data)->longest_float)) ? "*" : "",  \
            SvPVX_const((data)->longest_float),                      \
            (IV)((data)->offset_float_min),                          \
            (IV)((data)->offset_float_max)                           \
        );                                                           \
    PerlIO_printf(Perl_debug_log,"\n");                              \
});

/* =========================================================
 * BEGIN edit_distance stuff.
 *
 * This calculates how many single character changes of any type are needed to
 * transform a string into another one.  It is taken from version 3.1 of
 *
 * https://metacpan.org/pod/Text::Levenshtein::Damerau::XS
 */

/* Our unsorted dictionary linked list.   */
/* Note we use UVs, not chars. */

struct dictionary{
  UV key;
  UV value;
  struct dictionary* next;
};
typedef struct dictionary item;


PERL_STATIC_INLINE item*
push(UV key,item* curr)
{
    item* head;
    Newxz(head, 1, item);
    head->key = key;
    head->value = 0;
    head->next = curr;
    return head;
}


PERL_STATIC_INLINE item*
find(item* head, UV key)
{
    item* iterator = head;
    while (iterator){
        if (iterator->key == key){
            return iterator;
        }
        iterator = iterator->next;
    }

    return NULL;
}

PERL_STATIC_INLINE item*
uniquePush(item* head,UV key)
{
    item* iterator = head;

    while (iterator){
        if (iterator->key == key) {
            return head;
        }
        iterator = iterator->next;
    }

    return push(key,head);
}

PERL_STATIC_INLINE void
dict_free(item* head)
{
    item* iterator = head;

    while (iterator) {
        item* temp = iterator;
        iterator = iterator->next;
        Safefree(temp);
    }

    head = NULL;
}

/* End of Dictionary Stuff */

/* All calculations/work are done here */
STATIC int
S_edit_distance(const UV* src,
                const UV* tgt,
                const STRLEN x,             /* length of src[] */
                const STRLEN y,             /* length of tgt[] */
                const SSize_t maxDistance
)
{
    item *head = NULL;
    UV swapCount,swapScore,targetCharCount,i,j;
    UV *scores;
    UV score_ceil = x + y;

    PERL_ARGS_ASSERT_EDIT_DISTANCE;

    /* intialize matrix start values */
    Newxz(scores, ( (x + 2) * (y + 2)), UV);
    scores[0] = score_ceil;
    scores[1 * (y + 2) + 0] = score_ceil;
    scores[0 * (y + 2) + 1] = score_ceil;
    scores[1 * (y + 2) + 1] = 0;
    head = uniquePush(uniquePush(head,src[0]),tgt[0]);

    /* work loops    */
    /* i = src index */
    /* j = tgt index */
    for (i=1;i<=x;i++) {
        if (i < x)
            head = uniquePush(head,src[i]);
        scores[(i+1) * (y + 2) + 1] = i;
        scores[(i+1) * (y + 2) + 0] = score_ceil;
        swapCount = 0;

        for (j=1;j<=y;j++) {
            if (i == 1) {
                if(j < y)
                head = uniquePush(head,tgt[j]);
                scores[1 * (y + 2) + (j + 1)] = j;
                scores[0 * (y + 2) + (j + 1)] = score_ceil;
            }

            targetCharCount = find(head,tgt[j-1])->value;
            swapScore = scores[targetCharCount * (y + 2) + swapCount] + i - targetCharCount - 1 + j - swapCount;

            if (src[i-1] != tgt[j-1]){
                scores[(i+1) * (y + 2) + (j + 1)] = MIN(swapScore,(MIN(scores[i * (y + 2) + j], MIN(scores[(i+1) * (y + 2) + j], scores[i * (y + 2) + (j + 1)])) + 1));
            }
            else {
                swapCount = j;
                scores[(i+1) * (y + 2) + (j + 1)] = MIN(scores[i * (y + 2) + j], swapScore);
            }
        }

        find(head,src[i-1])->value = i;
    }

    {
        IV score = scores[(x+1) * (y + 2) + (y + 1)];
        dict_free(head);
        Safefree(scores);
        return (maxDistance != 0 && maxDistance < score)?(-1):score;
    }
}

/* END of edit_distance() stuff
 * ========================================================= */

/* is c a control character for which we have a mnemonic? */
#define isMNEMONIC_CNTRL(c) _IS_MNEMONIC_CNTRL_ONLY_FOR_USE_BY_REGCOMP_DOT_C(c)

STATIC const char *
S_cntrl_to_mnemonic(const U8 c)
{
    /* Returns the mnemonic string that represents character 'c', if one
     * exists; NULL otherwise.  The only ones that exist for the purposes of
     * this routine are a few control characters */

    switch (c) {
        case '\a':       return "\\a";
        case '\b':       return "\\b";
        case ESC_NATIVE: return "\\e";
        case '\f':       return "\\f";
        case '\n':       return "\\n";
        case '\r':       return "\\r";
        case '\t':       return "\\t";
    }

    return NULL;
}

/* Mark that we cannot extend a found fixed substring at this point.
   Update the longest found anchored substring and the longest found
   floating substrings if needed. */

STATIC void
S_scan_commit(pTHX_ const RExC_state_t *pRExC_state, scan_data_t *data,
                    SSize_t *minlenp, int is_inf)
{
    const STRLEN l = CHR_SVLEN(data->last_found);
    const STRLEN old_l = CHR_SVLEN(*data->longest);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_SCAN_COMMIT;

    if ((l >= old_l) && ((l > old_l) || (data->flags & SF_BEFORE_EOL))) {
        SvSetMagicSV(*data->longest, data->last_found);
        if (*data->longest == data->longest_fixed) {
            data->offset_fixed = l ? data->last_start_min : data->pos_min;
            if (data->flags & SF_BEFORE_EOL)
                data->flags
                    |= ((data->flags & SF_BEFORE_EOL) << SF_FIX_SHIFT_EOL);
            else
                data->flags &= ~SF_FIX_BEFORE_EOL;
            data->minlen_fixed=minlenp;
            data->lookbehind_fixed=0;
        }
        else { /* *data->longest == data->longest_float */
            data->offset_float_min = l ? data->last_start_min : data->pos_min;
            data->offset_float_max = (l
                          ? data->last_start_max
                          : (data->pos_delta > SSize_t_MAX - data->pos_min
                                         ? SSize_t_MAX
                                         : data->pos_min + data->pos_delta));
            if (is_inf
                 || (STRLEN)data->offset_float_max > (STRLEN)SSize_t_MAX)
                data->offset_float_max = SSize_t_MAX;
            if (data->flags & SF_BEFORE_EOL)
                data->flags
                    |= ((data->flags & SF_BEFORE_EOL) << SF_FL_SHIFT_EOL);
            else
                data->flags &= ~SF_FL_BEFORE_EOL;
            data->minlen_float=minlenp;
            data->lookbehind_float=0;
        }
    }
    SvCUR_set(data->last_found, 0);
    {
        SV * const sv = data->last_found;
        if (SvUTF8(sv) && SvMAGICAL(sv)) {
            MAGIC * const mg = mg_find(sv, PERL_MAGIC_utf8);
            if (mg)
                mg->mg_len = 0;
        }
    }
    data->last_end = -1;
    data->flags &= ~SF_BEFORE_EOL;
    DEBUG_STUDYDATA("commit: ",data,0);
}

/* An SSC is just a regnode_charclass_posix with an extra field: the inversion
 * list that describes which code points it matches */

STATIC void
S_ssc_anything(pTHX_ regnode_ssc *ssc)
{
    /* Set the SSC 'ssc' to match an empty string or any code point */

    PERL_ARGS_ASSERT_SSC_ANYTHING;

    assert(is_ANYOF_SYNTHETIC(ssc));

    ssc->invlist = sv_2mortal(_new_invlist(2)); /* mortalize so won't leak */
    _append_range_to_invlist(ssc->invlist, 0, UV_MAX);
    ANYOF_FLAGS(ssc) |= SSC_MATCHES_EMPTY_STRING;  /* Plus matches empty */
}

STATIC int
S_ssc_is_anything(const regnode_ssc *ssc)
{
    /* Returns TRUE if the SSC 'ssc' can match the empty string and any code
     * point; FALSE otherwise.  Thus, this is used to see if using 'ssc' buys
     * us anything: if the function returns TRUE, 'ssc' hasn't been restricted
     * in any way, so there's no point in using it */

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_ANYTHING;

    assert(is_ANYOF_SYNTHETIC(ssc));

    if (! (ANYOF_FLAGS(ssc) & SSC_MATCHES_EMPTY_STRING)) {
        return FALSE;
    }

    /* See if the list consists solely of the range 0 - Infinity */
    invlist_iterinit(ssc->invlist);
    ret = invlist_iternext(ssc->invlist, &start, &end)
          && start == 0
          && end == UV_MAX;

    invlist_iterfinish(ssc->invlist);

    if (ret) {
        return TRUE;
    }

    /* If e.g., both \w and \W are set, matches everything */
    if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)) {
        int i;
        for (i = 0; i < ANYOF_POSIXL_MAX; i += 2) {
            if (ANYOF_POSIXL_TEST(ssc, i) && ANYOF_POSIXL_TEST(ssc, i+1)) {
                return TRUE;
            }
        }
    }

    return FALSE;
}

STATIC void
S_ssc_init(pTHX_ const RExC_state_t *pRExC_state, regnode_ssc *ssc)
{
    /* Initializes the SSC 'ssc'.  This includes setting it to match an empty
     * string, any code point, or any posix class under locale */

    PERL_ARGS_ASSERT_SSC_INIT;

    Zero(ssc, 1, regnode_ssc);
    set_ANYOF_SYNTHETIC(ssc);
    ARG_SET(ssc, ANYOF_ONLY_HAS_BITMAP);
    ssc_anything(ssc);

    /* If any portion of the regex is to operate under locale rules that aren't
     * fully known at compile time, initialization includes it.  The reason
     * this isn't done for all regexes is that the optimizer was written under
     * the assumption that locale was all-or-nothing.  Given the complexity and
     * lack of documentation in the optimizer, and that there are inadequate
     * test cases for locale, many parts of it may not work properly, it is
     * safest to avoid locale unless necessary. */
    if (RExC_contains_locale) {
        ANYOF_POSIXL_SETALL(ssc);
    }
    else {
        ANYOF_POSIXL_ZERO(ssc);
    }
}

STATIC int
S_ssc_is_cp_posixl_init(const RExC_state_t *pRExC_state,
                        const regnode_ssc *ssc)
{
    /* Returns TRUE if the SSC 'ssc' is in its initial state with regard only
     * to the list of code points matched, and locale posix classes; hence does
     * not check its flags) */

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_CP_POSIXL_INIT;

    assert(is_ANYOF_SYNTHETIC(ssc));

    invlist_iterinit(ssc->invlist);
    ret = invlist_iternext(ssc->invlist, &start, &end)
          && start == 0
          && end == UV_MAX;

    invlist_iterfinish(ssc->invlist);

    if (! ret) {
        return FALSE;
    }

    if (RExC_contains_locale && ! ANYOF_POSIXL_SSC_TEST_ALL_SET(ssc)) {
        return FALSE;
    }

    return TRUE;
}

STATIC SV*
S_get_ANYOF_cp_list_for_ssc(pTHX_ const RExC_state_t *pRExC_state,
                               const regnode_charclass* const node)
{
    /* Returns a mortal inversion list defining which code points are matched
     * by 'node', which is of type ANYOF.  Handles complementing the result if
     * appropriate.  If some code points aren't knowable at this time, the
     * returned list must, and will, contain every code point that is a
     * possibility. */

    SV* invlist = NULL;
    SV* only_utf8_locale_invlist = NULL;
    unsigned int i;
    const U32 n = ARG(node);
    bool new_node_has_latin1 = FALSE;

    PERL_ARGS_ASSERT_GET_ANYOF_CP_LIST_FOR_SSC;

    /* Look at the data structure created by S_set_ANYOF_arg() */
    if (n != ANYOF_ONLY_HAS_BITMAP) {
        SV * const rv = MUTABLE_SV(RExC_rxi->data->data[n]);
        AV * const av = MUTABLE_AV(SvRV(rv));
        SV **const ary = AvARRAY(av);
        assert(RExC_rxi->data->what[n] == 's');

        if (ary[1] && ary[1] != &PL_sv_undef) { /* Has compile-time swash */
            invlist = sv_2mortal(invlist_clone(_get_swash_invlist(ary[1])));
        }
        else if (ary[0] && ary[0] != &PL_sv_undef) {

            /* Here, no compile-time swash, and there are things that won't be
             * known until runtime -- we have to assume it could be anything */
            invlist = sv_2mortal(_new_invlist(1));
            return _add_range_to_invlist(invlist, 0, UV_MAX);
        }
        else if (ary[3] && ary[3] != &PL_sv_undef) {

            /* Here no compile-time swash, and no run-time only data.  Use the
             * node's inversion list */
            invlist = sv_2mortal(invlist_clone(ary[3]));
        }

        /* Get the code points valid only under UTF-8 locales */
        if ((ANYOF_FLAGS(node) & ANYOFL_FOLD)
            && ary[2] && ary[2] != &PL_sv_undef)
        {
            only_utf8_locale_invlist = ary[2];
        }
    }

    if (! invlist) {
        invlist = sv_2mortal(_new_invlist(0));
    }

    /* An ANYOF node contains a bitmap for the first NUM_ANYOF_CODE_POINTS
     * code points, and an inversion list for the others, but if there are code
     * points that should match only conditionally on the target string being
     * UTF-8, those are placed in the inversion list, and not the bitmap.
     * Since there are circumstances under which they could match, they are
     * included in the SSC.  But if the ANYOF node is to be inverted, we have
     * to exclude them here, so that when we invert below, the end result
     * actually does include them.  (Think about "\xe0" =~ /[^\xc0]/di;).  We
     * have to do this here before we add the unconditionally matched code
     * points */
    if (ANYOF_FLAGS(node) & ANYOF_INVERT) {
        _invlist_intersection_complement_2nd(invlist,
                                             PL_UpperLatin1,
                                             &invlist);
    }

    /* Add in the points from the bit map */
    for (i = 0; i < NUM_ANYOF_CODE_POINTS; i++) {
        if (ANYOF_BITMAP_TEST(node, i)) {
            invlist = add_cp_to_invlist(invlist, i);
            new_node_has_latin1 = TRUE;
        }
    }

    /* If this can match all upper Latin1 code points, have to add them
     * as well.  But don't add them if inverting, as when that gets done below,
     * it would exclude all these characters, including the ones it shouldn't
     * that were added just above */
    if (! (ANYOF_FLAGS(node) & ANYOF_INVERT) && OP(node) == ANYOFD
        && (ANYOF_FLAGS(node) & ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER))
    {
        _invlist_union(invlist, PL_UpperLatin1, &invlist);
    }

    /* Similarly for these */
    if (ANYOF_FLAGS(node) & ANYOF_MATCHES_ALL_ABOVE_BITMAP) {
        _invlist_union_complement_2nd(invlist, PL_InBitmap, &invlist);
    }

    if (ANYOF_FLAGS(node) & ANYOF_INVERT) {
        _invlist_invert(invlist);
    }
    else if (new_node_has_latin1 && ANYOF_FLAGS(node) & ANYOFL_FOLD) {

        /* Under /li, any 0-255 could fold to any other 0-255, depending on the
         * locale.  We can skip this if there are no 0-255 at all. */
        _invlist_union(invlist, PL_Latin1, &invlist);
    }

    /* Similarly add the UTF-8 locale possible matches.  These have to be
     * deferred until after the non-UTF-8 locale ones are taken care of just
     * above, or it leads to wrong results under ANYOF_INVERT */
    if (only_utf8_locale_invlist) {
        _invlist_union_maybe_complement_2nd(invlist,
                                            only_utf8_locale_invlist,
                                            ANYOF_FLAGS(node) & ANYOF_INVERT,
                                            &invlist);
    }

    return invlist;
}

/* These two functions currently do the exact same thing */
#define ssc_init_zero           ssc_init

#define ssc_add_cp(ssc, cp)   ssc_add_range((ssc), (cp), (cp))
#define ssc_match_all_cp(ssc) ssc_add_range(ssc, 0, UV_MAX)

/* 'AND' a given class with another one.  Can create false positives.  'ssc'
 * should not be inverted.  'and_with->flags & ANYOF_MATCHES_POSIXL' should be
 * 0 if 'and_with' is a regnode_charclass instead of a regnode_ssc. */

STATIC void
S_ssc_and(pTHX_ const RExC_state_t *pRExC_state, regnode_ssc *ssc,
                const regnode_charclass *and_with)
{
    /* Accumulate into SSC 'ssc' its 'AND' with 'and_with', which is either
     * another SSC or a regular ANYOF class.  Can create false positives. */

    SV* anded_cp_list;
    U8  anded_flags;

    PERL_ARGS_ASSERT_SSC_AND;

    assert(is_ANYOF_SYNTHETIC(ssc));

    /* 'and_with' is used as-is if it too is an SSC; otherwise have to extract
     * the code point inversion list and just the relevant flags */
    if (is_ANYOF_SYNTHETIC(and_with)) {
        anded_cp_list = ((regnode_ssc *)and_with)->invlist;
        anded_flags = ANYOF_FLAGS(and_with);

        /* XXX This is a kludge around what appears to be deficiencies in the
         * optimizer.  If we make S_ssc_anything() add in the WARN_SUPER flag,
         * there are paths through the optimizer where it doesn't get weeded
         * out when it should.  And if we don't make some extra provision for
         * it like the code just below, it doesn't get added when it should.
         * This solution is to add it only when AND'ing, which is here, and
         * only when what is being AND'ed is the pristine, original node
         * matching anything.  Thus it is like adding it to ssc_anything() but
         * only when the result is to be AND'ed.  Probably the same solution
         * could be adopted for the same problem we have with /l matching,
         * which is solved differently in S_ssc_init(), and that would lead to
         * fewer false positives than that solution has.  But if this solution
         * creates bugs, the consequences are only that a warning isn't raised
         * that should be; while the consequences for having /l bugs is
         * incorrect matches */
        if (ssc_is_anything((regnode_ssc *)and_with)) {
            anded_flags |= ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER;
        }
    }
    else {
        anded_cp_list = get_ANYOF_cp_list_for_ssc(pRExC_state, and_with);
        if (OP(and_with) == ANYOFD) {
            anded_flags = ANYOF_FLAGS(and_with) & ANYOF_COMMON_FLAGS;
        }
        else {
            anded_flags = ANYOF_FLAGS(and_with)
            &( ANYOF_COMMON_FLAGS
              |ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER
              |ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP);
            if (ANYOFL_UTF8_LOCALE_REQD(ANYOF_FLAGS(and_with))) {
                anded_flags &=
                    ANYOFL_SHARED_UTF8_LOCALE_fold_HAS_MATCHES_nonfold_REQD;
            }
        }
    }

    ANYOF_FLAGS(ssc) &= anded_flags;

    /* Below, C1 is the list of code points in 'ssc'; P1, its posix classes.
     * C2 is the list of code points in 'and-with'; P2, its posix classes.
     * 'and_with' may be inverted.  When not inverted, we have the situation of
     * computing:
     *  (C1 | P1) & (C2 | P2)
     *                     =  (C1 & (C2 | P2)) | (P1 & (C2 | P2))
     *                     =  ((C1 & C2) | (C1 & P2)) | ((P1 & C2) | (P1 & P2))
     *                    <=  ((C1 & C2) |       P2)) | ( P1       | (P1 & P2))
     *                    <=  ((C1 & C2) | P1 | P2)
     * Alternatively, the last few steps could be:
     *                     =  ((C1 & C2) | (C1 & P2)) | ((P1 & C2) | (P1 & P2))
     *                    <=  ((C1 & C2) |  C1      ) | (      C2  | (P1 & P2))
     *                    <=  (C1 | C2 | (P1 & P2))
     * We favor the second approach if either P1 or P2 is non-empty.  This is
     * because these components are a barrier to doing optimizations, as what
     * they match cannot be known until the moment of matching as they are
     * dependent on the current locale, 'AND"ing them likely will reduce or
     * eliminate them.
     * But we can do better if we know that C1,P1 are in their initial state (a
     * frequent occurrence), each matching everything:
     *  (<everything>) & (C2 | P2) =  C2 | P2
     * Similarly, if C2,P2 are in their initial state (again a frequent
     * occurrence), the result is a no-op
     *  (C1 | P1) & (<everything>) =  C1 | P1
     *
     * Inverted, we have
     *  (C1 | P1) & ~(C2 | P2)  =  (C1 | P1) & (~C2 & ~P2)
     *                          =  (C1 & (~C2 & ~P2)) | (P1 & (~C2 & ~P2))
     *                         <=  (C1 & ~C2) | (P1 & ~P2)
     * */

    if ((ANYOF_FLAGS(and_with) & ANYOF_INVERT)
        && ! is_ANYOF_SYNTHETIC(and_with))
    {
        unsigned int i;

        ssc_intersection(ssc,
                         anded_cp_list,
                         FALSE /* Has already been inverted */
                         );

        /* If either P1 or P2 is empty, the intersection will be also; can skip
         * the loop */
        if (! (ANYOF_FLAGS(and_with) & ANYOF_MATCHES_POSIXL)) {
            ANYOF_POSIXL_ZERO(ssc);
        }
        else if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)) {

            /* Note that the Posix class component P from 'and_with' actually
             * looks like:
             *      P = Pa | Pb | ... | Pn
             * where each component is one posix class, such as in [\w\s].
             * Thus
             *      ~P = ~(Pa | Pb | ... | Pn)
             *         = ~Pa & ~Pb & ... & ~Pn
             *        <= ~Pa | ~Pb | ... | ~Pn
             * The last is something we can easily calculate, but unfortunately
             * is likely to have many false positives.  We could do better
             * in some (but certainly not all) instances if two classes in
             * P have known relationships.  For example
             *      :lower: <= :alpha: <= :alnum: <= \w <= :graph: <= :print:
             * So
             *      :lower: & :print: = :lower:
             * And similarly for classes that must be disjoint.  For example,
             * since \s and \w can have no elements in common based on rules in
             * the POSIX standard,
             *      \w & ^\S = nothing
             * Unfortunately, some vendor locales do not meet the Posix
             * standard, in particular almost everything by Microsoft.
             * The loop below just changes e.g., \w into \W and vice versa */

            regnode_charclass_posixl temp;
            int add = 1;    /* To calculate the index of the complement */

            ANYOF_POSIXL_ZERO(&temp);
            for (i = 0; i < ANYOF_MAX; i++) {
                assert(i % 2 != 0
                       || ! ANYOF_POSIXL_TEST((regnode_charclass_posixl*) and_with, i)
                       || ! ANYOF_POSIXL_TEST((regnode_charclass_posixl*) and_with, i + 1));

                if (ANYOF_POSIXL_TEST((regnode_charclass_posixl*) and_with, i)) {
                    ANYOF_POSIXL_SET(&temp, i + add);
                }
                add = 0 - add; /* 1 goes to -1; -1 goes to 1 */
            }
            ANYOF_POSIXL_AND(&temp, ssc);

        } /* else ssc already has no posixes */
    } /* else: Not inverted.  This routine is a no-op if 'and_with' is an SSC
         in its initial state */
    else if (! is_ANYOF_SYNTHETIC(and_with)
             || ! ssc_is_cp_posixl_init(pRExC_state, (regnode_ssc *)and_with))
    {
        /* But if 'ssc' is in its initial state, the result is just 'and_with';
         * copy it over 'ssc' */
        if (ssc_is_cp_posixl_init(pRExC_state, ssc)) {
            if (is_ANYOF_SYNTHETIC(and_with)) {
                StructCopy(and_with, ssc, regnode_ssc);
            }
            else {
                ssc->invlist = anded_cp_list;
                ANYOF_POSIXL_ZERO(ssc);
                if (ANYOF_FLAGS(and_with) & ANYOF_MATCHES_POSIXL) {
                    ANYOF_POSIXL_OR((regnode_charclass_posixl*) and_with, ssc);
                }
            }
        }
        else if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)
                 || (ANYOF_FLAGS(and_with) & ANYOF_MATCHES_POSIXL))
        {
            /* One or the other of P1, P2 is non-empty. */
            if (ANYOF_FLAGS(and_with) & ANYOF_MATCHES_POSIXL) {
                ANYOF_POSIXL_AND((regnode_charclass_posixl*) and_with, ssc);
            }
            ssc_union(ssc, anded_cp_list, FALSE);
        }
        else { /* P1 = P2 = empty */
            ssc_intersection(ssc, anded_cp_list, FALSE);
        }
    }
}

STATIC void
S_ssc_or(pTHX_ const RExC_state_t *pRExC_state, regnode_ssc *ssc,
               const regnode_charclass *or_with)
{
    /* Accumulate into SSC 'ssc' its 'OR' with 'or_with', which is either
     * another SSC or a regular ANYOF class.  Can create false positives if
     * 'or_with' is to be inverted. */

    SV* ored_cp_list;
    U8 ored_flags;

    PERL_ARGS_ASSERT_SSC_OR;

    assert(is_ANYOF_SYNTHETIC(ssc));

    /* 'or_with' is used as-is if it too is an SSC; otherwise have to extract
     * the code point inversion list and just the relevant flags */
    if (is_ANYOF_SYNTHETIC(or_with)) {
        ored_cp_list = ((regnode_ssc*) or_with)->invlist;
        ored_flags = ANYOF_FLAGS(or_with);
    }
    else {
        ored_cp_list = get_ANYOF_cp_list_for_ssc(pRExC_state, or_with);
        ored_flags = ANYOF_FLAGS(or_with) & ANYOF_COMMON_FLAGS;
        if (OP(or_with) != ANYOFD) {
            ored_flags
            |= ANYOF_FLAGS(or_with)
             & ( ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER
                |ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP);
            if (ANYOFL_UTF8_LOCALE_REQD(ANYOF_FLAGS(or_with))) {
                ored_flags |=
                    ANYOFL_SHARED_UTF8_LOCALE_fold_HAS_MATCHES_nonfold_REQD;
            }
        }
    }

    ANYOF_FLAGS(ssc) |= ored_flags;

    /* Below, C1 is the list of code points in 'ssc'; P1, its posix classes.
     * C2 is the list of code points in 'or-with'; P2, its posix classes.
     * 'or_with' may be inverted.  When not inverted, we have the simple
     * situation of computing:
     *  (C1 | P1) | (C2 | P2)  =  (C1 | C2) | (P1 | P2)
     * If P1|P2 yields a situation with both a class and its complement are
     * set, like having both \w and \W, this matches all code points, and we
     * can delete these from the P component of the ssc going forward.  XXX We
     * might be able to delete all the P components, but I (khw) am not certain
     * about this, and it is better to be safe.
     *
     * Inverted, we have
     *  (C1 | P1) | ~(C2 | P2)  =  (C1 | P1) | (~C2 & ~P2)
     *                         <=  (C1 | P1) | ~C2
     *                         <=  (C1 | ~C2) | P1
     * (which results in actually simpler code than the non-inverted case)
     * */

    if ((ANYOF_FLAGS(or_with) & ANYOF_INVERT)
        && ! is_ANYOF_SYNTHETIC(or_with))
    {
        /* We ignore P2, leaving P1 going forward */
    }   /* else  Not inverted */
    else if (ANYOF_FLAGS(or_with) & ANYOF_MATCHES_POSIXL) {
        ANYOF_POSIXL_OR((regnode_charclass_posixl*)or_with, ssc);
        if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)) {
            unsigned int i;
            for (i = 0; i < ANYOF_MAX; i += 2) {
                if (ANYOF_POSIXL_TEST(ssc, i) && ANYOF_POSIXL_TEST(ssc, i + 1))
                {
                    ssc_match_all_cp(ssc);
                    ANYOF_POSIXL_CLEAR(ssc, i);
                    ANYOF_POSIXL_CLEAR(ssc, i+1);
                }
            }
        }
    }

    ssc_union(ssc,
              ored_cp_list,
              FALSE /* Already has been inverted */
              );
}

PERL_STATIC_INLINE void
S_ssc_union(pTHX_ regnode_ssc *ssc, SV* const invlist, const bool invert2nd)
{
    PERL_ARGS_ASSERT_SSC_UNION;

    assert(is_ANYOF_SYNTHETIC(ssc));

    _invlist_union_maybe_complement_2nd(ssc->invlist,
                                        invlist,
                                        invert2nd,
                                        &ssc->invlist);
}

PERL_STATIC_INLINE void
S_ssc_intersection(pTHX_ regnode_ssc *ssc,
                         SV* const invlist,
                         const bool invert2nd)
{
    PERL_ARGS_ASSERT_SSC_INTERSECTION;

    assert(is_ANYOF_SYNTHETIC(ssc));

    _invlist_intersection_maybe_complement_2nd(ssc->invlist,
                                               invlist,
                                               invert2nd,
                                               &ssc->invlist);
}

PERL_STATIC_INLINE void
S_ssc_add_range(pTHX_ regnode_ssc *ssc, const UV start, const UV end)
{
    PERL_ARGS_ASSERT_SSC_ADD_RANGE;

    assert(is_ANYOF_SYNTHETIC(ssc));

    ssc->invlist = _add_range_to_invlist(ssc->invlist, start, end);
}

PERL_STATIC_INLINE void
S_ssc_cp_and(pTHX_ regnode_ssc *ssc, const UV cp)
{
    /* AND just the single code point 'cp' into the SSC 'ssc' */

    SV* cp_list = _new_invlist(2);

    PERL_ARGS_ASSERT_SSC_CP_AND;

    assert(is_ANYOF_SYNTHETIC(ssc));

    cp_list = add_cp_to_invlist(cp_list, cp);
    ssc_intersection(ssc, cp_list,
                     FALSE /* Not inverted */
                     );
    SvREFCNT_dec_NN(cp_list);
}

PERL_STATIC_INLINE void
S_ssc_clear_locale(regnode_ssc *ssc)
{
    /* Set the SSC 'ssc' to not match any locale things */
    PERL_ARGS_ASSERT_SSC_CLEAR_LOCALE;

    assert(is_ANYOF_SYNTHETIC(ssc));

    ANYOF_POSIXL_ZERO(ssc);
    ANYOF_FLAGS(ssc) &= ~ANYOF_LOCALE_FLAGS;
}

#define NON_OTHER_COUNT   NON_OTHER_COUNT_FOR_USE_ONLY_BY_REGCOMP_DOT_C

STATIC bool
S_is_ssc_worth_it(const RExC_state_t * pRExC_state, const regnode_ssc * ssc)
{
    /* The synthetic start class is used to hopefully quickly winnow down
     * places where a pattern could start a match in the target string.  If it
     * doesn't really narrow things down that much, there isn't much point to
     * having the overhead of using it.  This function uses some very crude
     * heuristics to decide if to use the ssc or not.
     *
     * It returns TRUE if 'ssc' rules out more than half what it considers to
     * be the "likely" possible matches, but of course it doesn't know what the
     * actual things being matched are going to be; these are only guesses
     *
     * For /l matches, it assumes that the only likely matches are going to be
     *      in the 0-255 range, uniformly distributed, so half of that is 127
     * For /a and /d matches, it assumes that the likely matches will be just
     *      the ASCII range, so half of that is 63
     * For /u and there isn't anything matching above the Latin1 range, it
     *      assumes that that is the only range likely to be matched, and uses
     *      half that as the cut-off: 127.  If anything matches above Latin1,
     *      it assumes that all of Unicode could match (uniformly), except for
     *      non-Unicode code points and things in the General Category "Other"
     *      (unassigned, private use, surrogates, controls and formats).  This
     *      is a much large number. */

    U32 count = 0;      /* Running total of number of code points matched by
                           'ssc' */
    UV start, end;      /* Start and end points of current range in inversion
                           list */
    const U32 max_code_points = (LOC)
                                ?  256
                                : ((   ! UNI_SEMANTICS
                                     || invlist_highest(ssc->invlist) < 256)
                                  ? 128
                                  : NON_OTHER_COUNT);
    const U32 max_match = max_code_points / 2;

    PERL_ARGS_ASSERT_IS_SSC_WORTH_IT;

    invlist_iterinit(ssc->invlist);
    while (invlist_iternext(ssc->invlist, &start, &end)) {
        if (start >= max_code_points) {
            break;
        }
        end = MIN(end, max_code_points - 1);
        count += end - start + 1;
        if (count >= max_match) {
            invlist_iterfinish(ssc->invlist);
            return FALSE;
        }
    }

    return TRUE;
}


STATIC void
S_ssc_finalize(pTHX_ RExC_state_t *pRExC_state, regnode_ssc *ssc)
{
    /* The inversion list in the SSC is marked mortal; now we need a more
     * permanent copy, which is stored the same way that is done in a regular
     * ANYOF node, with the first NUM_ANYOF_CODE_POINTS code points in a bit
     * map */

    SV* invlist = invlist_clone(ssc->invlist);

    PERL_ARGS_ASSERT_SSC_FINALIZE;

    assert(is_ANYOF_SYNTHETIC(ssc));

    /* The code in this file assumes that all but these flags aren't relevant
     * to the SSC, except SSC_MATCHES_EMPTY_STRING, which should be cleared
     * by the time we reach here */
    assert(! (ANYOF_FLAGS(ssc)
        & ~( ANYOF_COMMON_FLAGS
            |ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER
            |ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP)));

    populate_ANYOF_from_invlist( (regnode *) ssc, &invlist);

    set_ANYOF_arg(pRExC_state, (regnode *) ssc, invlist,
                                NULL, NULL, NULL, FALSE);

    /* Make sure is clone-safe */
    ssc->invlist = NULL;

    if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)) {
        ANYOF_FLAGS(ssc) |= ANYOF_MATCHES_POSIXL;
    }

    if (RExC_contains_locale) {
        OP(ssc) = ANYOFL;
    }

    assert(! (ANYOF_FLAGS(ssc) & ANYOF_LOCALE_FLAGS) || RExC_contains_locale);
}

#define TRIE_LIST_ITEM(state,idx) (trie->states[state].trans.list)[ idx ]
#define TRIE_LIST_CUR(state)  ( TRIE_LIST_ITEM( state, 0 ).forid )
#define TRIE_LIST_LEN(state) ( TRIE_LIST_ITEM( state, 0 ).newstate )
#define TRIE_LIST_USED(idx)  ( trie->states[state].trans.list         \
                               ? (TRIE_LIST_CUR( idx ) - 1)           \
                               : 0 )


#ifdef DEBUGGING
/*
   dump_trie(trie,widecharmap,revcharmap)
   dump_trie_interim_list(trie,widecharmap,revcharmap,next_alloc)
   dump_trie_interim_table(trie,widecharmap,revcharmap,next_alloc)

   These routines dump out a trie in a somewhat readable format.
   The _interim_ variants are used for debugging the interim
   tables that are used to generate the final compressed
   representation which is what dump_trie expects.

   Part of the reason for their existence is to provide a form
   of documentation as to how the different representations function.

*/

/*
  Dumps the final compressed table form of the trie to Perl_debug_log.
  Used for debugging make_trie().
*/

STATIC void
S_dump_trie(pTHX_ const struct _reg_trie_data *trie, HV *widecharmap,
            AV *revcharmap, U32 depth)
{
    U32 state;
    SV *sv=sv_newmortal();
    int colwidth= widecharmap ? 6 : 4;
    U16 word;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_DUMP_TRIE;

    PerlIO_printf( Perl_debug_log, "%*sChar : %-6s%-6s%-4s ",
        (int)depth * 2 + 2,"",
        "Match","Base","Ofs" );

    for( state = 0 ; state < trie->uniquecharcount ; state++ ) {
        SV ** const tmp = av_fetch( revcharmap, state, 0);
        if ( tmp ) {
            PerlIO_printf( Perl_debug_log, "%*s",
                colwidth,
                pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth,
                            PL_colors[0], PL_colors[1],
                            (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                            PERL_PV_ESCAPE_FIRSTCHAR
                )
            );
        }
    }
    PerlIO_printf( Perl_debug_log, "\n%*sState|-----------------------",
        (int)depth * 2 + 2,"");

    for( state = 0 ; state < trie->uniquecharcount ; state++ )
        PerlIO_printf( Perl_debug_log, "%.*s", colwidth, "--------");
    PerlIO_printf( Perl_debug_log, "\n");

    for( state = 1 ; state < trie->statecount ; state++ ) {
        const U32 base = trie->states[ state ].trans.base;

        PerlIO_printf( Perl_debug_log, "%*s#%4"UVXf"|",
                                       (int)depth * 2 + 2,"", (UV)state);

        if ( trie->states[ state ].wordnum ) {
            PerlIO_printf( Perl_debug_log, " W%4X",
                                           trie->states[ state ].wordnum );
        } else {
            PerlIO_printf( Perl_debug_log, "%6s", "" );
        }

        PerlIO_printf( Perl_debug_log, " @%4"UVXf" ", (UV)base );

        if ( base ) {
            U32 ofs = 0;

            while( ( base + ofs  < trie->uniquecharcount ) ||
                   ( base + ofs - trie->uniquecharcount < trie->lasttrans
                     && trie->trans[ base + ofs - trie->uniquecharcount ].check
                                                                    != state))
                    ofs++;

            PerlIO_printf( Perl_debug_log, "+%2"UVXf"[ ", (UV)ofs);

            for ( ofs = 0 ; ofs < trie->uniquecharcount ; ofs++ ) {
                if ( ( base + ofs >= trie->uniquecharcount )
                        && ( base + ofs - trie->uniquecharcount
                                                        < trie->lasttrans )
                        && trie->trans[ base + ofs
                                    - trie->uniquecharcount ].check == state )
                {
                   PerlIO_printf( Perl_debug_log, "%*"UVXf,
                    colwidth,
                    (UV)trie->trans[ base + ofs
                                             - trie->uniquecharcount ].next );
                } else {
                    PerlIO_printf( Perl_debug_log, "%*s",colwidth,"   ." );
                }
            }

            PerlIO_printf( Perl_debug_log, "]");

        }
        PerlIO_printf( Perl_debug_log, "\n" );
    }
    PerlIO_printf(Perl_debug_log, "%*sword_info N:(prev,len)=",
                                (int)depth*2, "");
    for (word=1; word <= trie->wordcount; word++) {
        PerlIO_printf(Perl_debug_log, " %d:(%d,%d)",
            (int)word, (int)(trie->wordinfo[word].prev),
            (int)(trie->wordinfo[word].len));
    }
    PerlIO_printf(Perl_debug_log, "\n" );
}
/*
  Dumps a fully constructed but uncompressed trie in list form.
  List tries normally only are used for construction when the number of
  possible chars (trie->uniquecharcount) is very high.
  Used for debugging make_trie().
*/
STATIC void
S_dump_trie_interim_list(pTHX_ const struct _reg_trie_data *trie,
                         HV *widecharmap, AV *revcharmap, U32 next_alloc,
                         U32 depth)
{
    U32 state;
    SV *sv=sv_newmortal();
    int colwidth= widecharmap ? 6 : 4;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_DUMP_TRIE_INTERIM_LIST;

    /* print out the table precompression.  */
    PerlIO_printf( Perl_debug_log, "%*sState :Word | Transition Data\n%*s%s",
        (int)depth * 2 + 2,"", (int)depth * 2 + 2,"",
        "------:-----+-----------------\n" );

    for( state=1 ; state < next_alloc ; state ++ ) {
        U16 charid;

        PerlIO_printf( Perl_debug_log, "%*s %4"UVXf" :",
            (int)depth * 2 + 2,"", (UV)state  );
        if ( ! trie->states[ state ].wordnum ) {
            PerlIO_printf( Perl_debug_log, "%5s| ","");
        } else {
            PerlIO_printf( Perl_debug_log, "W%4x| ",
                trie->states[ state ].wordnum
            );
        }
        for( charid = 1 ; charid <= TRIE_LIST_USED( state ) ; charid++ ) {
            SV ** const tmp = av_fetch( revcharmap,
                                        TRIE_LIST_ITEM(state,charid).forid, 0);
            if ( tmp ) {
                PerlIO_printf( Perl_debug_log, "%*s:%3X=%4"UVXf" | ",
                    colwidth,
                    pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp),
                              colwidth,
                              PL_colors[0], PL_colors[1],
                              (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0)
                              | PERL_PV_ESCAPE_FIRSTCHAR
                    ) ,
                    TRIE_LIST_ITEM(state,charid).forid,
                    (UV)TRIE_LIST_ITEM(state,charid).newstate
                );
                if (!(charid % 10))
                    PerlIO_printf(Perl_debug_log, "\n%*s| ",
                        (int)((depth * 2) + 14), "");
            }
        }
        PerlIO_printf( Perl_debug_log, "\n");
    }
}

/*
  Dumps a fully constructed but uncompressed trie in table form.
  This is the normal DFA style state transition table, with a few
  twists to facilitate compression later.
  Used for debugging make_trie().
*/
STATIC void
S_dump_trie_interim_table(pTHX_ const struct _reg_trie_data *trie,
                          HV *widecharmap, AV *revcharmap, U32 next_alloc,
                          U32 depth)
{
    U32 state;
    U16 charid;
    SV *sv=sv_newmortal();
    int colwidth= widecharmap ? 6 : 4;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_DUMP_TRIE_INTERIM_TABLE;

    /*
       print out the table precompression so that we can do a visual check
       that they are identical.
     */

    PerlIO_printf( Perl_debug_log, "%*sChar : ",(int)depth * 2 + 2,"" );

    for( charid = 0 ; charid < trie->uniquecharcount ; charid++ ) {
        SV ** const tmp = av_fetch( revcharmap, charid, 0);
        if ( tmp ) {
            PerlIO_printf( Perl_debug_log, "%*s",
                colwidth,
                pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth,
                            PL_colors[0], PL_colors[1],
                            (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                            PERL_PV_ESCAPE_FIRSTCHAR
                )
            );
        }
    }

    PerlIO_printf( Perl_debug_log, "\n%*sState+-",(int)depth * 2 + 2,"" );

    for( charid=0 ; charid < trie->uniquecharcount ; charid++ ) {
        PerlIO_printf( Perl_debug_log, "%.*s", colwidth,"--------");
    }

    PerlIO_printf( Perl_debug_log, "\n" );

    for( state=1 ; state < next_alloc ; state += trie->uniquecharcount ) {

        PerlIO_printf( Perl_debug_log, "%*s%4"UVXf" : ",
            (int)depth * 2 + 2,"",
            (UV)TRIE_NODENUM( state ) );

        for( charid = 0 ; charid < trie->uniquecharcount ; charid++ ) {
            UV v=(UV)SAFE_TRIE_NODENUM( trie->trans[ state + charid ].next );
            if (v)
                PerlIO_printf( Perl_debug_log, "%*"UVXf, colwidth, v );
            else
                PerlIO_printf( Perl_debug_log, "%*s", colwidth, "." );
        }
        if ( ! trie->states[ TRIE_NODENUM( state ) ].wordnum ) {
            PerlIO_printf( Perl_debug_log, " (%4"UVXf")\n",
                                            (UV)trie->trans[ state ].check );
        } else {
            PerlIO_printf( Perl_debug_log, " (%4"UVXf") W%4X\n",
                                            (UV)trie->trans[ state ].check,
            trie->states[ TRIE_NODENUM( state ) ].wordnum );
        }
    }
}

#endif


/* make_trie(startbranch,first,last,tail,word_count,flags,depth)
  startbranch: the first branch in the whole branch sequence
  first      : start branch of sequence of branch-exact nodes.
               May be the same as startbranch
  last       : Thing following the last branch.
               May be the same as tail.
  tail       : item following the branch sequence
  count      : words in the sequence
  flags      : currently the OP() type we will be building one of /EXACT(|F|FA|FU|FU_SS|L|FLU8)/
  depth      : indent depth

Inplace optimizes a sequence of 2 or more Branch-Exact nodes into a TRIE node.

A trie is an N'ary tree where the branches are determined by digital
decomposition of the key. IE, at the root node you look up the 1st character and
follow that branch repeat until you find the end of the branches. Nodes can be
marked as "accepting" meaning they represent a complete word. Eg:

  /he|she|his|hers/

would convert into the following structure. Numbers represent states, letters
following numbers represent valid transitions on the letter from that state, if
the number is in square brackets it represents an accepting state, otherwise it
will be in parenthesis.

      +-h->+-e->[3]-+-r->(8)-+-s->[9]
      |    |
      |   (2)
      |    |
     (1)   +-i->(6)-+-s->[7]
      |
      +-s->(3)-+-h->(4)-+-e->[5]

      Accept Word Mapping: 3=>1 (he),5=>2 (she), 7=>3 (his), 9=>4 (hers)

This shows that when matching against the string 'hers' we will begin at state 1
read 'h' and move to state 2, read 'e' and move to state 3 which is accepting,
then read 'r' and go to state 8 followed by 's' which takes us to state 9 which
is also accepting. Thus we know that we can match both 'he' and 'hers' with a
single traverse. We store a mapping from accepting to state to which word was
matched, and then when we have multiple possibilities we try to complete the
rest of the regex in the order in which they occurred in the alternation.

The only prior NFA like behaviour that would be changed by the TRIE support is
the silent ignoring of duplicate alternations which are of the form:

 / (DUPE|DUPE) X? (?{ ... }) Y /x

Thus EVAL blocks following a trie may be called a different number of times with
and without the optimisation. With the optimisations dupes will be silently
ignored. This inconsistent behaviour of EVAL type nodes is well established as
the following demonstrates:

 'words'=~/(word|word|word)(?{ print $1 })[xyz]/

which prints out 'word' three times, but

 'words'=~/(word|word|word)(?{ print $1 })S/

which doesnt print it out at all. This is due to other optimisations kicking in.

Example of what happens on a structural level:

The regexp /(ac|ad|ab)+/ will produce the following debug output:

   1: CURLYM[1] {1,32767}(18)
   5:   BRANCH(8)
   6:     EXACT <ac>(16)
   8:   BRANCH(11)
   9:     EXACT <ad>(16)
  11:   BRANCH(14)
  12:     EXACT <ab>(16)
  16:   SUCCEED(0)
  17:   NOTHING(18)
  18: END(0)

This would be optimizable with startbranch=5, first=5, last=16, tail=16
and should turn into:

   1: CURLYM[1] {1,32767}(18)
   5:   TRIE(16)
        [Words:3 Chars Stored:6 Unique Chars:4 States:5 NCP:1]
          <ac>
          <ad>
          <ab>
  16:   SUCCEED(0)
  17:   NOTHING(18)
  18: END(0)

Cases where tail != last would be like /(?foo|bar)baz/:

   1: BRANCH(4)
   2:   EXACT <foo>(8)
   4: BRANCH(7)
   5:   EXACT <bar>(8)
   7: TAIL(8)
   8: EXACT <baz>(10)
  10: END(0)

which would be optimizable with startbranch=1, first=1, last=7, tail=8
and would end up looking like:

    1: TRIE(8)
      [Words:2 Chars Stored:6 Unique Chars:5 States:7 NCP:1]
        <foo>
        <bar>
   7: TAIL(8)
   8: EXACT <baz>(10)
  10: END(0)

    d = uvchr_to_utf8_flags(d, uv, 0);

is the recommended Unicode-aware way of saying

    *(d++) = uv;
*/

#define TRIE_STORE_REVCHAR(val)                                            \
    STMT_START {                                                           \
        if (UTF) {                                                         \
            SV *zlopp = newSV(UTF8_MAXBYTES);                              \
            unsigned char *flrbbbbb = (unsigned char *) SvPVX(zlopp);      \
            unsigned const char *const kapow = uvchr_to_utf8(flrbbbbb, val); \
            SvCUR_set(zlopp, kapow - flrbbbbb);                            \
            SvPOK_on(zlopp);                                               \
            SvUTF8_on(zlopp);                                              \
            av_push(revcharmap, zlopp);                                    \
        } else {                                                           \
            char ooooff = (char)val;                                           \
            av_push(revcharmap, newSVpvn(&ooooff, 1));                     \
        }                                                                  \
        } STMT_END

/* This gets the next character from the input, folding it if not already
 * folded. */
#define TRIE_READ_CHAR STMT_START {                                           \
    wordlen++;                                                                \
    if ( UTF ) {                                                              \
        /* if it is UTF then it is either already folded, or does not need    \
         * folding */                                                         \
        uvc = valid_utf8_to_uvchr( (const U8*) uc, &len);                     \
    }                                                                         \
    else if (folder == PL_fold_latin1) {                                      \
        /* This folder implies Unicode rules, which in the range expressible  \
         *  by not UTF is the lower case, with the two exceptions, one of     \
         *  which should have been taken care of before calling this */       \
        assert(*uc != LATIN_SMALL_LETTER_SHARP_S);                            \
        uvc = toLOWER_L1(*uc);                                                \
        if (UNLIKELY(uvc == MICRO_SIGN)) uvc = GREEK_SMALL_LETTER_MU;         \
        len = 1;                                                              \
    } else {                                                                  \
        /* raw data, will be folded later if needed */                        \
        uvc = (U32)*uc;                                                       \
        len = 1;                                                              \
    }                                                                         \
} STMT_END



#define TRIE_LIST_PUSH(state,fid,ns) STMT_START {               \
    if ( TRIE_LIST_CUR( state ) >=TRIE_LIST_LEN( state ) ) {    \
        U32 ging = TRIE_LIST_LEN( state ) *= 2;                 \
        Renew( trie->states[ state ].trans.list, ging, reg_trie_trans_le ); \
    }                                                           \
    TRIE_LIST_ITEM( state, TRIE_LIST_CUR( state ) ).forid = fid;     \
    TRIE_LIST_ITEM( state, TRIE_LIST_CUR( state ) ).newstate = ns;   \
    TRIE_LIST_CUR( state )++;                                   \
} STMT_END

#define TRIE_LIST_NEW(state) STMT_START {                       \
    Newxz( trie->states[ state ].trans.list,               \
        4, reg_trie_trans_le );                                 \
     TRIE_LIST_CUR( state ) = 1;                                \
     TRIE_LIST_LEN( state ) = 4;                                \
} STMT_END

#define TRIE_HANDLE_WORD(state) STMT_START {                    \
    U16 dupe= trie->states[ state ].wordnum;                    \
    regnode * const noper_next = regnext( noper );              \
                                                                \
    DEBUG_r({                                                   \
        /* store the word for dumping */                        \
        SV* tmp;                                                \
        if (OP(noper) != NOTHING)                               \
            tmp = newSVpvn_utf8(STRING(noper), STR_LEN(noper), UTF);    \
        else                                                    \
            tmp = newSVpvn_utf8( "", 0, UTF );                  \
        av_push( trie_words, tmp );                             \
    });                                                         \
                                                                \
    curword++;                                                  \
    trie->wordinfo[curword].prev   = 0;                         \
    trie->wordinfo[curword].len    = wordlen;                   \
    trie->wordinfo[curword].accept = state;                     \
                                                                \
    if ( noper_next < tail ) {                                  \
        if (!trie->jump)                                        \
            trie->jump = (U16 *) PerlMemShared_calloc( word_count + 1, \
                                                 sizeof(U16) ); \
        trie->jump[curword] = (U16)(noper_next - convert);      \
        if (!jumper)                                            \
            jumper = noper_next;                                \
        if (!nextbranch)                                        \
            nextbranch= regnext(cur);                           \
    }                                                           \
                                                                \
    if ( dupe ) {                                               \
        /* It's a dupe. Pre-insert into the wordinfo[].prev   */\
        /* chain, so that when the bits of chain are later    */\
        /* linked together, the dups appear in the chain      */\
        trie->wordinfo[curword].prev = trie->wordinfo[dupe].prev; \
        trie->wordinfo[dupe].prev = curword;                    \
    } else {                                                    \
        /* we haven't inserted this word yet.                */ \
        trie->states[ state ].wordnum = curword;                \
    }                                                           \
} STMT_END


#define TRIE_TRANS_STATE(state,base,ucharcount,charid,special)          \
     ( ( base + charid >=  ucharcount                                   \
         && base + charid < ubound                                      \
         && state == trie->trans[ base - ucharcount + charid ].check    \
         && trie->trans[ base - ucharcount + charid ].next )            \
           ? trie->trans[ base - ucharcount + charid ].next             \
           : ( state==1 ? special : 0 )                                 \
      )

#define MADE_TRIE       1
#define MADE_JUMP_TRIE  2
#define MADE_EXACT_TRIE 4

STATIC I32
S_make_trie(pTHX_ RExC_state_t *pRExC_state, regnode *startbranch,
                  regnode *first, regnode *last, regnode *tail,
                  U32 word_count, U32 flags, U32 depth)
{
    /* first pass, loop through and scan words */
    reg_trie_data *trie;
    HV *widecharmap = NULL;
    AV *revcharmap = newAV();
    regnode *cur;
    STRLEN len = 0;
    UV uvc = 0;
    U16 curword = 0;
    U32 next_alloc = 0;
    regnode *jumper = NULL;
    regnode *nextbranch = NULL;
    regnode *convert = NULL;
    U32 *prev_states; /* temp array mapping each state to previous one */
    /* we just use folder as a flag in utf8 */
    const U8 * folder = NULL;

#ifdef DEBUGGING
    const U32 data_slot = add_data( pRExC_state, STR_WITH_LEN("tuuu"));
    AV *trie_words = NULL;
    /* along with revcharmap, this only used during construction but both are
     * useful during debugging so we store them in the struct when debugging.
     */
#else
    const U32 data_slot = add_data( pRExC_state, STR_WITH_LEN("tu"));
    STRLEN trie_charcount=0;
#endif
    SV *re_trie_maxbuff;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_MAKE_TRIE;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif

    switch (flags) {
        case EXACT: case EXACTL: break;
        case EXACTFA:
        case EXACTFU_SS:
        case EXACTFU:
        case EXACTFLU8: folder = PL_fold_latin1; break;
        case EXACTF:  folder = PL_fold; break;
        default: Perl_croak( aTHX_ "panic! In trie construction, unknown node type %u %s", (unsigned) flags, PL_reg_name[flags] );
    }

    trie = (reg_trie_data *) PerlMemShared_calloc( 1, sizeof(reg_trie_data) );
    trie->refcount = 1;
    trie->startstate = 1;
    trie->wordcount = word_count;
    RExC_rxi->data->data[ data_slot ] = (void*)trie;
    trie->charmap = (U16 *) PerlMemShared_calloc( 256, sizeof(U16) );
    if (flags == EXACT || flags == EXACTL)
        trie->bitmap = (char *) PerlMemShared_calloc( ANYOF_BITMAP_SIZE, 1 );
    trie->wordinfo = (reg_trie_wordinfo *) PerlMemShared_calloc(
                       trie->wordcount+1, sizeof(reg_trie_wordinfo));

    DEBUG_r({
        trie_words = newAV();
    });

    re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
    assert(re_trie_maxbuff);
    if (!SvIOK(re_trie_maxbuff)) {
        sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
    }
    DEBUG_TRIE_COMPILE_r({
        PerlIO_printf( Perl_debug_log,
          "%*smake_trie start==%d, first==%d, last==%d, tail==%d depth=%d\n",
          (int)depth * 2 + 2, "",
          REG_NODE_NUM(startbranch),REG_NODE_NUM(first),
          REG_NODE_NUM(last), REG_NODE_NUM(tail), (int)depth);
    });

   /* Find the node we are going to overwrite */
    if ( first == startbranch && OP( last ) != BRANCH ) {
        /* whole branch chain */
        convert = first;
    } else {
        /* branch sub-chain */
        convert = NEXTOPER( first );
    }

    /*  -- First loop and Setup --

       We first traverse the branches and scan each word to determine if it
       contains widechars, and how many unique chars there are, this is
       important as we have to build a table with at least as many columns as we
       have unique chars.

       We use an array of integers to represent the character codes 0..255
       (trie->charmap) and we use a an HV* to store Unicode characters. We use
       the native representation of the character value as the key and IV's for
       the coded index.

       *TODO* If we keep track of how many times each character is used we can
       remap the columns so that the table compression later on is more
       efficient in terms of memory by ensuring the most common value is in the
       middle and the least common are on the outside.  IMO this would be better
       than a most to least common mapping as theres a decent chance the most
       common letter will share a node with the least common, meaning the node
       will not be compressible. With a middle is most common approach the worst
       case is when we have the least common nodes twice.

     */

    for ( cur = first ; cur < last ; cur = regnext( cur ) ) {
        regnode *noper = NEXTOPER( cur );
        const U8 *uc = (U8*)STRING( noper );
        const U8 *e  = uc + STR_LEN( noper );
        int foldlen = 0;
        U32 wordlen      = 0;         /* required init */
        STRLEN minchars = 0;
        STRLEN maxchars = 0;
        bool set_bit = trie->bitmap ? 1 : 0; /*store the first char in the
                                               bitmap?*/

        if (OP(noper) == NOTHING) {
            regnode *noper_next= regnext(noper);
            if (noper_next != tail && OP(noper_next) == flags) {
                noper = noper_next;
                uc= (U8*)STRING(noper);
                e= uc + STR_LEN(noper);
                trie->minlen= STR_LEN(noper);
            } else {
                trie->minlen= 0;
                continue;
            }
        }

        if ( set_bit ) { /* bitmap only alloced when !(UTF&&Folding) */
            TRIE_BITMAP_SET(trie,*uc); /* store the raw first byte
                                          regardless of encoding */
            if (OP( noper ) == EXACTFU_SS) {
                /* false positives are ok, so just set this */
                TRIE_BITMAP_SET(trie, LATIN_SMALL_LETTER_SHARP_S);
            }
        }
        for ( ; uc < e ; uc += len ) {  /* Look at each char in the current
                                           branch */
            TRIE_CHARCOUNT(trie)++;
            TRIE_READ_CHAR;

            /* TRIE_READ_CHAR returns the current character, or its fold if /i
             * is in effect.  Under /i, this character can match itself, or
             * anything that folds to it.  If not under /i, it can match just
             * itself.  Most folds are 1-1, for example k, K, and KELVIN SIGN
             * all fold to k, and all are single characters.   But some folds
             * expand to more than one character, so for example LATIN SMALL
             * LIGATURE FFI folds to the three character sequence 'ffi'.  If
             * the string beginning at 'uc' is 'ffi', it could be matched by
             * three characters, or just by the one ligature character. (It
             * could also be matched by two characters: LATIN SMALL LIGATURE FF
             * followed by 'i', or by 'f' followed by LATIN SMALL LIGATURE FI).
             * (Of course 'I' and/or 'F' instead of 'i' and 'f' can also
             * match.)  The trie needs to know the minimum and maximum number
             * of characters that could match so that it can use size alone to
             * quickly reject many match attempts.  The max is simple: it is
             * the number of folded characters in this branch (since a fold is
             * never shorter than what folds to it. */

            maxchars++;

            /* And the min is equal to the max if not under /i (indicated by
             * 'folder' being NULL), or there are no multi-character folds.  If
             * there is a multi-character fold, the min is incremented just
             * once, for the character that folds to the sequence.  Each
             * character in the sequence needs to be added to the list below of
             * characters in the trie, but we count only the first towards the
             * min number of characters needed.  This is done through the
             * variable 'foldlen', which is returned by the macros that look
             * for these sequences as the number of bytes the sequence
             * occupies.  Each time through the loop, we decrement 'foldlen' by
             * how many bytes the current char occupies.  Only when it reaches
             * 0 do we increment 'minchars' or look for another multi-character
             * sequence. */
            if (folder == NULL) {
                minchars++;
            }
            else if (foldlen > 0) {
                foldlen -= (UTF) ? UTF8SKIP(uc) : 1;
            }
            else {
                minchars++;

                /* See if *uc is the beginning of a multi-character fold.  If
                 * so, we decrement the length remaining to look at, to account
                 * for the current character this iteration.  (We can use 'uc'
                 * instead of the fold returned by TRIE_READ_CHAR because for
                 * non-UTF, the latin1_safe macro is smart enough to account
                 * for all the unfolded characters, and because for UTF, the
                 * string will already have been folded earlier in the
                 * compilation process */
                if (UTF) {
                    if ((foldlen = is_MULTI_CHAR_FOLD_utf8_safe(uc, e))) {
                        foldlen -= UTF8SKIP(uc);
                    }
                }
                else if ((foldlen = is_MULTI_CHAR_FOLD_latin1_safe(uc, e))) {
                    foldlen--;
                }
            }

            /* The current character (and any potential folds) should be added
             * to the possible matching characters for this position in this
             * branch */
            if ( uvc < 256 ) {
                if ( folder ) {
                    U8 folded= folder[ (U8) uvc ];
                    if ( !trie->charmap[ folded ] ) {
                        trie->charmap[ folded ]=( ++trie->uniquecharcount );
                        TRIE_STORE_REVCHAR( folded );
                    }
                }
                if ( !trie->charmap[ uvc ] ) {
                    trie->charmap[ uvc ]=( ++trie->uniquecharcount );
                    TRIE_STORE_REVCHAR( uvc );
                }
                if ( set_bit ) {
                    /* store the codepoint in the bitmap, and its folded
                     * equivalent. */
                    TRIE_BITMAP_SET(trie, uvc);

                    /* store the folded codepoint */
                    if ( folder ) TRIE_BITMAP_SET(trie, folder[(U8) uvc ]);

                    if ( !UTF ) {
                        /* store first byte of utf8 representation of
                           variant codepoints */
                        if (! UVCHR_IS_INVARIANT(uvc)) {
                            TRIE_BITMAP_SET(trie, UTF8_TWO_BYTE_HI(uvc));
                        }
                    }
                    set_bit = 0; /* We've done our bit :-) */
                }
            } else {

                /* XXX We could come up with the list of code points that fold
                 * to this using PL_utf8_foldclosures, except not for
                 * multi-char folds, as there may be multiple combinations
                 * there that could work, which needs to wait until runtime to
                 * resolve (The comment about LIGATURE FFI above is such an
                 * example */

                SV** svpp;
                if ( !widecharmap )
                    widecharmap = newHV();

                svpp = hv_fetch( widecharmap, (char*)&uvc, sizeof( UV ), 1 );

                if ( !svpp )
                    Perl_croak( aTHX_ "error creating/fetching widecharmap entry for 0x%"UVXf, uvc );

                if ( !SvTRUE( *svpp ) ) {
                    sv_setiv( *svpp, ++trie->uniquecharcount );
                    TRIE_STORE_REVCHAR(uvc);
                }
            }
        } /* end loop through characters in this branch of the trie */

        /* We take the min and max for this branch and combine to find the min
         * and max for all branches processed so far */
        if( cur == first ) {
            trie->minlen = minchars;
            trie->maxlen = maxchars;
        } else if (minchars < trie->minlen) {
            trie->minlen = minchars;
        } else if (maxchars > trie->maxlen) {
            trie->maxlen = maxchars;
        }
    } /* end first pass */
    DEBUG_TRIE_COMPILE_r(
        PerlIO_printf( Perl_debug_log,
                "%*sTRIE(%s): W:%d C:%d Uq:%d Min:%d Max:%d\n",
                (int)depth * 2 + 2,"",
                ( widecharmap ? "UTF8" : "NATIVE" ), (int)word_count,
                (int)TRIE_CHARCOUNT(trie), trie->uniquecharcount,
                (int)trie->minlen, (int)trie->maxlen )
    );

    /*
        We now know what we are dealing with in terms of unique chars and
        string sizes so we can calculate how much memory a naive
        representation using a flat table  will take. If it's over a reasonable
        limit (as specified by ${^RE_TRIE_MAXBUF}) we use a more memory
        conservative but potentially much slower representation using an array
        of lists.

        At the end we convert both representations into the same compressed
        form that will be used in regexec.c for matching with. The latter
        is a form that cannot be used to construct with but has memory
        properties similar to the list form and access properties similar
        to the table form making it both suitable for fast searches and
        small enough that its feasable to store for the duration of a program.

        See the comment in the code where the compressed table is produced
        inplace from the flat tabe representation for an explanation of how
        the compression works.

    */


    Newx(prev_states, TRIE_CHARCOUNT(trie) + 2, U32);
    prev_states[1] = 0;

    if ( (IV)( ( TRIE_CHARCOUNT(trie) + 1 ) * trie->uniquecharcount + 1)
                                                    > SvIV(re_trie_maxbuff) )
    {
        /*
            Second Pass -- Array Of Lists Representation

            Each state will be represented by a list of charid:state records
            (reg_trie_trans_le) the first such element holds the CUR and LEN
            points of the allocated array. (See defines above).

            We build the initial structure using the lists, and then convert
            it into the compressed table form which allows faster lookups
            (but cant be modified once converted).
        */

        STRLEN transcount = 1;

        DEBUG_TRIE_COMPILE_MORE_r( PerlIO_printf( Perl_debug_log,
            "%*sCompiling trie using list compiler\n",
            (int)depth * 2 + 2, ""));

        trie->states = (reg_trie_state *)
            PerlMemShared_calloc( TRIE_CHARCOUNT(trie) + 2,
                                  sizeof(reg_trie_state) );
        TRIE_LIST_NEW(1);
        next_alloc = 2;

        for ( cur = first ; cur < last ; cur = regnext( cur ) ) {

            regnode *noper   = NEXTOPER( cur );
            U8 *uc           = (U8*)STRING( noper );
            const U8 *e      = uc + STR_LEN( noper );
            U32 state        = 1;         /* required init */
            U16 charid       = 0;         /* sanity init */
            U32 wordlen      = 0;         /* required init */

            if (OP(noper) == NOTHING) {
                regnode *noper_next= regnext(noper);
                if (noper_next != tail && OP(noper_next) == flags) {
                    noper = noper_next;
                    uc= (U8*)STRING(noper);
                    e= uc + STR_LEN(noper);
                }
            }

            if (OP(noper) != NOTHING) {
                for ( ; uc < e ; uc += len ) {

                    TRIE_READ_CHAR;

                    if ( uvc < 256 ) {
                        charid = trie->charmap[ uvc ];
                    } else {
                        SV** const svpp = hv_fetch( widecharmap,
                                                    (char*)&uvc,
                                                    sizeof( UV ),
                                                    0);
                        if ( !svpp ) {
                            charid = 0;
                        } else {
                            charid=(U16)SvIV( *svpp );
                        }
                    }
                    /* charid is now 0 if we dont know the char read, or
                     * nonzero if we do */
                    if ( charid ) {

                        U16 check;
                        U32 newstate = 0;

                        charid--;
                        if ( !trie->states[ state ].trans.list ) {
                            TRIE_LIST_NEW( state );
                        }
                        for ( check = 1;
                              check <= TRIE_LIST_USED( state );
                              check++ )
                        {
                            if ( TRIE_LIST_ITEM( state, check ).forid
                                                                    == charid )
                            {
                                newstate = TRIE_LIST_ITEM( state, check ).newstate;
                                break;
                            }
                        }
                        if ( ! newstate ) {
                            newstate = next_alloc++;
                            prev_states[newstate] = state;
                            TRIE_LIST_PUSH( state, charid, newstate );
                            transcount++;
                        }
                        state = newstate;
                    } else {
                        Perl_croak( aTHX_ "panic! In trie construction, no char mapping for %"IVdf, uvc );
                    }
                }
            }
            TRIE_HANDLE_WORD(state);

        } /* end second pass */

        /* next alloc is the NEXT state to be allocated */
        trie->statecount = next_alloc;
        trie->states = (reg_trie_state *)
            PerlMemShared_realloc( trie->states,
                                   next_alloc
                                   * sizeof(reg_trie_state) );

        /* and now dump it out before we compress it */
        DEBUG_TRIE_COMPILE_MORE_r(dump_trie_interim_list(trie, widecharmap,
                                                         revcharmap, next_alloc,
                                                         depth+1)
        );

        trie->trans = (reg_trie_trans *)
            PerlMemShared_calloc( transcount, sizeof(reg_trie_trans) );
        {
            U32 state;
            U32 tp = 0;
            U32 zp = 0;


            for( state=1 ; state < next_alloc ; state ++ ) {
                U32 base=0;

                /*
                DEBUG_TRIE_COMPILE_MORE_r(
                    PerlIO_printf( Perl_debug_log, "tp: %d zp: %d ",tp,zp)
                );
                */

                if (trie->states[state].trans.list) {
                    U16 minid=TRIE_LIST_ITEM( state, 1).forid;
                    U16 maxid=minid;
                    U16 idx;

                    for( idx = 2 ; idx <= TRIE_LIST_USED( state ) ; idx++ ) {
                        const U16 forid = TRIE_LIST_ITEM( state, idx).forid;
                        if ( forid < minid ) {
                            minid=forid;
                        } else if ( forid > maxid ) {
                            maxid=forid;
                        }
                    }
                    if ( transcount < tp + maxid - minid + 1) {
                        transcount *= 2;
                        trie->trans = (reg_trie_trans *)
                            PerlMemShared_realloc( trie->trans,
                                                     transcount
                                                     * sizeof(reg_trie_trans) );
                        Zero( trie->trans + (transcount / 2),
                              transcount / 2,
                              reg_trie_trans );
                    }
                    base = trie->uniquecharcount + tp - minid;
                    if ( maxid == minid ) {
                        U32 set = 0;
                        for ( ; zp < tp ; zp++ ) {
                            if ( ! trie->trans[ zp ].next ) {
                                base = trie->uniquecharcount + zp - minid;
                                trie->trans[ zp ].next = TRIE_LIST_ITEM( state,
                                                                   1).newstate;
                                trie->trans[ zp ].check = state;
                                set = 1;
                                break;
                            }
                        }
                        if ( !set ) {
                            trie->trans[ tp ].next = TRIE_LIST_ITEM( state,
                                                                   1).newstate;
                            trie->trans[ tp ].check = state;
                            tp++;
                            zp = tp;
                        }
                    } else {
                        for ( idx=1; idx <= TRIE_LIST_USED( state ) ; idx++ ) {
                            const U32 tid = base
                                           - trie->uniquecharcount
                                           + TRIE_LIST_ITEM( state, idx ).forid;
                            trie->trans[ tid ].next = TRIE_LIST_ITEM( state,
                                                                idx ).newstate;
                            trie->trans[ tid ].check = state;
                        }
                        tp += ( maxid - minid + 1 );
                    }
                    Safefree(trie->states[ state ].trans.list);
                }
                /*
                DEBUG_TRIE_COMPILE_MORE_r(
                    PerlIO_printf( Perl_debug_log, " base: %d\n",base);
                );
                */
                trie->states[ state ].trans.base=base;
            }
            trie->lasttrans = tp + 1;
        }
    } else {
        /*
           Second Pass -- Flat Table Representation.

           we dont use the 0 slot of either trans[] or states[] so we add 1 to
           each.  We know that we will need Charcount+1 trans at most to store
           the data (one row per char at worst case) So we preallocate both
           structures assuming worst case.

           We then construct the trie using only the .next slots of the entry
           structs.

           We use the .check field of the first entry of the node temporarily
           to make compression both faster and easier by keeping track of how
           many non zero fields are in the node.

           Since trans are numbered from 1 any 0 pointer in the table is a FAIL
           transition.

           There are two terms at use here: state as a TRIE_NODEIDX() which is
           a number representing the first entry of the node, and state as a
           TRIE_NODENUM() which is the trans number. state 1 is TRIE_NODEIDX(1)
           and TRIE_NODENUM(1), state 2 is TRIE_NODEIDX(2) and TRIE_NODENUM(3)
           if there are 2 entrys per node. eg:

             A B       A B
          1. 2 4    1. 3 7
          2. 0 3    3. 0 5
          3. 0 0    5. 0 0
          4. 0 0    7. 0 0

           The table is internally in the right hand, idx form. However as we
           also have to deal with the states array which is indexed by nodenum
           we have to use TRIE_NODENUM() to convert.

        */
        DEBUG_TRIE_COMPILE_MORE_r( PerlIO_printf( Perl_debug_log,
            "%*sCompiling trie using table compiler\n",
            (int)depth * 2 + 2, ""));

        trie->trans = (reg_trie_trans *)
            PerlMemShared_calloc( ( TRIE_CHARCOUNT(trie) + 1 )
                                  * trie->uniquecharcount + 1,
                                  sizeof(reg_trie_trans) );
        trie->states = (reg_trie_state *)
            PerlMemShared_calloc( TRIE_CHARCOUNT(trie) + 2,
                                  sizeof(reg_trie_state) );
        next_alloc = trie->uniquecharcount + 1;


        for ( cur = first ; cur < last ; cur = regnext( cur ) ) {

            regnode *noper   = NEXTOPER( cur );
            const U8 *uc     = (U8*)STRING( noper );
            const U8 *e      = uc + STR_LEN( noper );

            U32 state        = 1;         /* required init */

            U16 charid       = 0;         /* sanity init */
            U32 accept_state = 0;         /* sanity init */

            U32 wordlen      = 0;         /* required init */

            if (OP(noper) == NOTHING) {
                regnode *noper_next= regnext(noper);
                if (noper_next != tail && OP(noper_next) == flags) {
                    noper = noper_next;
                    uc= (U8*)STRING(noper);
                    e= uc + STR_LEN(noper);
                }
            }

            if ( OP(noper) != NOTHING ) {
                for ( ; uc < e ; uc += len ) {

                    TRIE_READ_CHAR;

                    if ( uvc < 256 ) {
                        charid = trie->charmap[ uvc ];
                    } else {
                        SV* const * const svpp = hv_fetch( widecharmap,
                                                           (char*)&uvc,
                                                           sizeof( UV ),
                                                           0);
                        charid = svpp ? (U16)SvIV(*svpp) : 0;
                    }
                    if ( charid ) {
                        charid--;
                        if ( !trie->trans[ state + charid ].next ) {
                            trie->trans[ state + charid ].next = next_alloc;
                            trie->trans[ state ].check++;
                            prev_states[TRIE_NODENUM(next_alloc)]
                                    = TRIE_NODENUM(state);
                            next_alloc += trie->uniquecharcount;
                        }
                        state = trie->trans[ state + charid ].next;
                    } else {
                        Perl_croak( aTHX_ "panic! In trie construction, no char mapping for %"IVdf, uvc );
                    }
                    /* charid is now 0 if we dont know the char read, or
                     * nonzero if we do */
                }
            }
            accept_state = TRIE_NODENUM( state );
            TRIE_HANDLE_WORD(accept_state);

        } /* end second pass */

        /* and now dump it out before we compress it */
        DEBUG_TRIE_COMPILE_MORE_r(dump_trie_interim_table(trie, widecharmap,
                                                          revcharmap,
                                                          next_alloc, depth+1));

        {
        /*
           * Inplace compress the table.*

           For sparse data sets the table constructed by the trie algorithm will
           be mostly 0/FAIL transitions or to put it another way mostly empty.
           (Note that leaf nodes will not contain any transitions.)

           This algorithm compresses the tables by eliminating most such
           transitions, at the cost of a modest bit of extra work during lookup:

           - Each states[] entry contains a .base field which indicates the
           index in the state[] array wheres its transition data is stored.

           - If .base is 0 there are no valid transitions from that node.

           - If .base is nonzero then charid is added to it to find an entry in
           the trans array.

           -If trans[states[state].base+charid].check!=state then the
           transition is taken to be a 0/Fail transition. Thus if there are fail
           transitions at the front of the node then the .base offset will point
           somewhere inside the previous nodes data (or maybe even into a node
           even earlier), but the .check field determines if the transition is
           valid.

           XXX - wrong maybe?
           The following process inplace converts the table to the compressed
           table: We first do not compress the root node 1,and mark all its
           .check pointers as 1 and set its .base pointer as 1 as well. This
           allows us to do a DFA construction from the compressed table later,
           and ensures that any .base pointers we calculate later are greater
           than 0.

           - We set 'pos' to indicate the first entry of the second node.

           - We then iterate over the columns of the node, finding the first and
           last used entry at l and m. We then copy l..m into pos..(pos+m-l),
           and set the .check pointers accordingly, and advance pos
           appropriately and repreat for the next node. Note that when we copy
           the next pointers we have to convert them from the original
           NODEIDX form to NODENUM form as the former is not valid post
           compression.

           - If a node has no transitions used we mark its base as 0 and do not
           advance the pos pointer.

           - If a node only has one transition we use a second pointer into the
           structure to fill in allocated fail transitions from other states.
           This pointer is independent of the main pointer and scans forward
           looking for null transitions that are allocated to a state. When it
           finds one it writes the single transition into the "hole".  If the
           pointer doesnt find one the single transition is appended as normal.

           - Once compressed we can Renew/realloc the structures to release the
           excess space.

           See "Table-Compression Methods" in sec 3.9 of the Red Dragon,
           specifically Fig 3.47 and the associated pseudocode.

           demq
        */
        const U32 laststate = TRIE_NODENUM( next_alloc );
        U32 state, charid;
        U32 pos = 0, zp=0;
        trie->statecount = laststate;

        for ( state = 1 ; state < laststate ; state++ ) {
            U8 flag = 0;
            const U32 stateidx = TRIE_NODEIDX( state );
            const U32 o_used = trie->trans[ stateidx ].check;
            U32 used = trie->trans[ stateidx ].check;
            trie->trans[ stateidx ].check = 0;

            for ( charid = 0;
                  used && charid < trie->uniquecharcount;
                  charid++ )
            {
                if ( flag || trie->trans[ stateidx + charid ].next ) {
                    if ( trie->trans[ stateidx + charid ].next ) {
                        if (o_used == 1) {
                            for ( ; zp < pos ; zp++ ) {
                                if ( ! trie->trans[ zp ].next ) {
                                    break;
                                }
                            }
                            trie->states[ state ].trans.base
                                                    = zp
                                                      + trie->uniquecharcount
                                                      - charid ;
                            trie->trans[ zp ].next
                                = SAFE_TRIE_NODENUM( trie->trans[ stateidx
                                                             + charid ].next );
                            trie->trans[ zp ].check = state;
                            if ( ++zp > pos ) pos = zp;
                            break;
                        }
                        used--;
                    }
                    if ( !flag ) {
                        flag = 1;
                        trie->states[ state ].trans.base
                                       = pos + trie->uniquecharcount - charid ;
                    }
                    trie->trans[ pos ].next
                        = SAFE_TRIE_NODENUM(
                                       trie->trans[ stateidx + charid ].next );
                    trie->trans[ pos ].check = state;
                    pos++;
                }
            }
        }
        trie->lasttrans = pos + 1;
        trie->states = (reg_trie_state *)
            PerlMemShared_realloc( trie->states, laststate
                                   * sizeof(reg_trie_state) );
        DEBUG_TRIE_COMPILE_MORE_r(
            PerlIO_printf( Perl_debug_log,
                "%*sAlloc: %d Orig: %"IVdf" elements, Final:%"IVdf". Savings of %%%5.2f\n",
                (int)depth * 2 + 2,"",
                (int)( ( TRIE_CHARCOUNT(trie) + 1 ) * trie->uniquecharcount
                       + 1 ),
                (IV)next_alloc,
                (IV)pos,
                ( ( next_alloc - pos ) * 100 ) / (double)next_alloc );
            );

        } /* end table compress */
    }
    DEBUG_TRIE_COMPILE_MORE_r(
            PerlIO_printf(Perl_debug_log,
                "%*sStatecount:%"UVxf" Lasttrans:%"UVxf"\n",
                (int)depth * 2 + 2, "",
                (UV)trie->statecount,
                (UV)trie->lasttrans)
    );
    /* resize the trans array to remove unused space */
    trie->trans = (reg_trie_trans *)
        PerlMemShared_realloc( trie->trans, trie->lasttrans
                               * sizeof(reg_trie_trans) );

    {   /* Modify the program and insert the new TRIE node */
        U8 nodetype =(U8)(flags & 0xFF);
        char *str=NULL;

#ifdef DEBUGGING
        regnode *optimize = NULL;
#ifdef RE_TRACK_PATTERN_OFFSETS

        U32 mjd_offset = 0;
        U32 mjd_nodelen = 0;
#endif /* RE_TRACK_PATTERN_OFFSETS */
#endif /* DEBUGGING */
        /*
           This means we convert either the first branch or the first Exact,
           depending on whether the thing following (in 'last') is a branch
           or not and whther first is the startbranch (ie is it a sub part of
           the alternation or is it the whole thing.)
           Assuming its a sub part we convert the EXACT otherwise we convert
           the whole branch sequence, including the first.
         */
        /* Find the node we are going to overwrite */
        if ( first != startbranch || OP( last ) == BRANCH ) {
            /* branch sub-chain */
            NEXT_OFF( first ) = (U16)(last - first);
#ifdef RE_TRACK_PATTERN_OFFSETS
            DEBUG_r({
                mjd_offset= Node_Offset((convert));
                mjd_nodelen= Node_Length((convert));
            });
#endif
            /* whole branch chain */
        }
#ifdef RE_TRACK_PATTERN_OFFSETS
        else {
            DEBUG_r({
                const  regnode *nop = NEXTOPER( convert );
                mjd_offset= Node_Offset((nop));
                mjd_nodelen= Node_Length((nop));
            });
        }
        DEBUG_OPTIMISE_r(
            PerlIO_printf(Perl_debug_log,
                "%*sMJD offset:%"UVuf" MJD length:%"UVuf"\n",
                (int)depth * 2 + 2, "",
                (UV)mjd_offset, (UV)mjd_nodelen)
        );
#endif
        /* But first we check to see if there is a common prefix we can
           split out as an EXACT and put in front of the TRIE node.  */
        trie->startstate= 1;
        if ( trie->bitmap && !widecharmap && !trie->jump  ) {
            U32 state;
            for ( state = 1 ; state < trie->statecount-1 ; state++ ) {
                U32 ofs = 0;
                I32 idx = -1;
                U32 count = 0;
                const U32 base = trie->states[ state ].trans.base;

                if ( trie->states[state].wordnum )
                        count = 1;

                for ( ofs = 0 ; ofs < trie->uniquecharcount ; ofs++ ) {
                    if ( ( base + ofs >= trie->uniquecharcount ) &&
                         ( base + ofs - trie->uniquecharcount < trie->lasttrans ) &&
                         trie->trans[ base + ofs - trie->uniquecharcount ].check == state )
                    {
                        if ( ++count > 1 ) {
                            SV **tmp = av_fetch( revcharmap, ofs, 0);
                            const U8 *ch = (U8*)SvPV_nolen_const( *tmp );
                            if ( state == 1 ) break;
                            if ( count == 2 ) {
                                Zero(trie->bitmap, ANYOF_BITMAP_SIZE, char);
                                DEBUG_OPTIMISE_r(
                                    PerlIO_printf(Perl_debug_log,
                                        "%*sNew Start State=%"UVuf" Class: [",
                                        (int)depth * 2 + 2, "",
                                        (UV)state));
                                if (idx >= 0) {
                                    SV ** const tmp = av_fetch( revcharmap, idx, 0);
                                    const U8 * const ch = (U8*)SvPV_nolen_const( *tmp );

                                    TRIE_BITMAP_SET(trie,*ch);
                                    if ( folder )
                                        TRIE_BITMAP_SET(trie, folder[ *ch ]);
                                    DEBUG_OPTIMISE_r(
                                        PerlIO_printf(Perl_debug_log, "%s", (char*)ch)
                                    );
                                }
                            }
                            TRIE_BITMAP_SET(trie,*ch);
                            if ( folder )
                                TRIE_BITMAP_SET(trie,folder[ *ch ]);
                            DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"%s", ch));
                        }
                        idx = ofs;
                    }
                }
                if ( count == 1 ) {
                    SV **tmp = av_fetch( revcharmap, idx, 0);
                    STRLEN len;
                    char *ch = SvPV( *tmp, len );
                    DEBUG_OPTIMISE_r({
                        SV *sv=sv_newmortal();
                        PerlIO_printf( Perl_debug_log,
                            "%*sPrefix State: %"UVuf" Idx:%"UVuf" Char='%s'\n",
                            (int)depth * 2 + 2, "",
                            (UV)state, (UV)idx,
                            pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), 6,
                                PL_colors[0], PL_colors[1],
                                (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                                PERL_PV_ESCAPE_FIRSTCHAR
                            )
                        );
                    });
                    if ( state==1 ) {
                        OP( convert ) = nodetype;
                        str=STRING(convert);
                        STR_LEN(convert)=0;
                    }
                    STR_LEN(convert) += len;
                    while (len--)
                        *str++ = *ch++;
                } else {
#ifdef DEBUGGING
                    if (state>1)
                        DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"]\n"));
#endif
                    break;
                }
            }
            trie->prefixlen = (state-1);
            if (str) {
                regnode *n = convert+NODE_SZ_STR(convert);
                NEXT_OFF(convert) = NODE_SZ_STR(convert);
                trie->startstate = state;
                trie->minlen -= (state - 1);
                trie->maxlen -= (state - 1);
#ifdef DEBUGGING
               /* At least the UNICOS C compiler choked on this
                * being argument to DEBUG_r(), so let's just have
                * it right here. */
               if (
#ifdef PERL_EXT_RE_BUILD
                   1
#else
                   DEBUG_r_TEST
#endif
                   ) {
                   regnode *fix = convert;
                   U32 word = trie->wordcount;
                   mjd_nodelen++;
                   Set_Node_Offset_Length(convert, mjd_offset, state - 1);
                   while( ++fix < n ) {
                       Set_Node_Offset_Length(fix, 0, 0);
                   }
                   while (word--) {
                       SV ** const tmp = av_fetch( trie_words, word, 0 );
                       if (tmp) {
                           if ( STR_LEN(convert) <= SvCUR(*tmp) )
                               sv_chop(*tmp, SvPV_nolen(*tmp) + STR_LEN(convert));
                           else
                               sv_chop(*tmp, SvPV_nolen(*tmp) + SvCUR(*tmp));
                       }
                   }
               }
#endif
                if (trie->maxlen) {
                    convert = n;
                } else {
                    NEXT_OFF(convert) = (U16)(tail - convert);
                    DEBUG_r(optimize= n);
                }
            }
        }
        if (!jumper)
            jumper = last;
        if ( trie->maxlen ) {
            NEXT_OFF( convert ) = (U16)(tail - convert);
            ARG_SET( convert, data_slot );
            /* Store the offset to the first unabsorbed branch in
               jump[0], which is otherwise unused by the jump logic.
               We use this when dumping a trie and during optimisation. */
            if (trie->jump)
                trie->jump[0] = (U16)(nextbranch - convert);

            /* If the start state is not accepting (meaning there is no empty string/NOTHING)
             *   and there is a bitmap
             *   and the first "jump target" node we found leaves enough room
             * then convert the TRIE node into a TRIEC node, with the bitmap
             * embedded inline in the opcode - this is hypothetically faster.
             */
            if ( !trie->states[trie->startstate].wordnum
                 && trie->bitmap
                 && ( (char *)jumper - (char *)convert) >= (int)sizeof(struct regnode_charclass) )
            {
                OP( convert ) = TRIEC;
                Copy(trie->bitmap, ((struct regnode_charclass *)convert)->bitmap, ANYOF_BITMAP_SIZE, char);
                PerlMemShared_free(trie->bitmap);
                trie->bitmap= NULL;
            } else
                OP( convert ) = TRIE;

            /* store the type in the flags */
            convert->flags = nodetype;
            DEBUG_r({
            optimize = convert
                      + NODE_STEP_REGNODE
                      + regarglen[ OP( convert ) ];
            });
            /* XXX We really should free up the resource in trie now,
                   as we won't use them - (which resources?) dmq */
        }
        /* needed for dumping*/
        DEBUG_r(if (optimize) {
            regnode *opt = convert;

            while ( ++opt < optimize) {
                Set_Node_Offset_Length(opt,0,0);
            }
            /*
                Try to clean up some of the debris left after the
                optimisation.
             */
            while( optimize < jumper ) {
                mjd_nodelen += Node_Length((optimize));
                OP( optimize ) = OPTIMIZED;
                Set_Node_Offset_Length(optimize,0,0);
                optimize++;
            }
            Set_Node_Offset_Length(convert,mjd_offset,mjd_nodelen);
        });
    } /* end node insert */

    /*  Finish populating the prev field of the wordinfo array.  Walk back
     *  from each accept state until we find another accept state, and if
     *  so, point the first word's .prev field at the second word. If the
     *  second already has a .prev field set, stop now. This will be the
     *  case either if we've already processed that word's accept state,
     *  or that state had multiple words, and the overspill words were
     *  already linked up earlier.
     */
    {
        U16 word;
        U32 state;
        U16 prev;

        for (word=1; word <= trie->wordcount; word++) {
            prev = 0;
            if (trie->wordinfo[word].prev)
                continue;
            state = trie->wordinfo[word].accept;
            while (state) {
                state = prev_states[state];
                if (!state)
                    break;
                prev = trie->states[state].wordnum;
                if (prev)
                    break;
            }
            trie->wordinfo[word].prev = prev;
        }
        Safefree(prev_states);
    }


    /* and now dump out the compressed format */
    DEBUG_TRIE_COMPILE_r(dump_trie(trie, widecharmap, revcharmap, depth+1));

    RExC_rxi->data->data[ data_slot + 1 ] = (void*)widecharmap;
#ifdef DEBUGGING
    RExC_rxi->data->data[ data_slot + TRIE_WORDS_OFFSET ] = (void*)trie_words;
    RExC_rxi->data->data[ data_slot + 3 ] = (void*)revcharmap;
#else
    SvREFCNT_dec_NN(revcharmap);
#endif
    return trie->jump
           ? MADE_JUMP_TRIE
           : trie->startstate>1
             ? MADE_EXACT_TRIE
             : MADE_TRIE;
}

STATIC regnode *
S_construct_ahocorasick_from_trie(pTHX_ RExC_state_t *pRExC_state, regnode *source, U32 depth)
{
/* The Trie is constructed and compressed now so we can build a fail array if
 * it's needed

   This is basically the Aho-Corasick algorithm. Its from exercise 3.31 and
   3.32 in the
   "Red Dragon" -- Compilers, principles, techniques, and tools. Aho, Sethi,
   Ullman 1985/88
   ISBN 0-201-10088-6

   We find the fail state for each state in the trie, this state is the longest
   proper suffix of the current state's 'word' that is also a proper prefix of
   another word in our trie. State 1 represents the word '' and is thus the
   default fail state. This allows the DFA not to have to restart after its
   tried and failed a word at a given point, it simply continues as though it
   had been matching the other word in the first place.
   Consider
      'abcdgu'=~/abcdefg|cdgu/
   When we get to 'd' we are still matching the first word, we would encounter
   'g' which would fail, which would bring us to the state representing 'd' in
   the second word where we would try 'g' and succeed, proceeding to match
   'cdgu'.
 */
 /* add a fail transition */
    const U32 trie_offset = ARG(source);
    reg_trie_data *trie=(reg_trie_data *)RExC_rxi->data->data[trie_offset];
    U32 *q;
    const U32 ucharcount = trie->uniquecharcount;
    const U32 numstates = trie->statecount;
    const U32 ubound = trie->lasttrans + ucharcount;
    U32 q_read = 0;
    U32 q_write = 0;
    U32 charid;
    U32 base = trie->states[ 1 ].trans.base;
    U32 *fail;
    reg_ac_data *aho;
    const U32 data_slot = add_data( pRExC_state, STR_WITH_LEN("T"));
    regnode *stclass;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_CONSTRUCT_AHOCORASICK_FROM_TRIE;
    PERL_UNUSED_CONTEXT;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif

    if ( OP(source) == TRIE ) {
        struct regnode_1 *op = (struct regnode_1 *)
            PerlMemShared_calloc(1, sizeof(struct regnode_1));
        StructCopy(source,op,struct regnode_1);
        stclass = (regnode *)op;
    } else {
        struct regnode_charclass *op = (struct regnode_charclass *)
            PerlMemShared_calloc(1, sizeof(struct regnode_charclass));
        StructCopy(source,op,struct regnode_charclass);
        stclass = (regnode *)op;
    }
    OP(stclass)+=2; /* convert the TRIE type to its AHO-CORASICK equivalent */

    ARG_SET( stclass, data_slot );
    aho = (reg_ac_data *) PerlMemShared_calloc( 1, sizeof(reg_ac_data) );
    RExC_rxi->data->data[ data_slot ] = (void*)aho;
    aho->trie=trie_offset;
    aho->states=(reg_trie_state *)PerlMemShared_malloc( numstates * sizeof(reg_trie_state) );
    Copy( trie->states, aho->states, numstates, reg_trie_state );
    Newxz( q, numstates, U32);
    aho->fail = (U32 *) PerlMemShared_calloc( numstates, sizeof(U32) );
    aho->refcount = 1;
    fail = aho->fail;
    /* initialize fail[0..1] to be 1 so that we always have
       a valid final fail state */
    fail[ 0 ] = fail[ 1 ] = 1;

    for ( charid = 0; charid < ucharcount ; charid++ ) {
        const U32 newstate = TRIE_TRANS_STATE( 1, base, ucharcount, charid, 0 );
        if ( newstate ) {
            q[ q_write ] = newstate;
            /* set to point at the root */
            fail[ q[ q_write++ ] ]=1;
        }
    }
    while ( q_read < q_write) {
        const U32 cur = q[ q_read++ % numstates ];
        base = trie->states[ cur ].trans.base;

        for ( charid = 0 ; charid < ucharcount ; charid++ ) {
            const U32 ch_state = TRIE_TRANS_STATE( cur, base, ucharcount, charid, 1 );
            if (ch_state) {
                U32 fail_state = cur;
                U32 fail_base;
                do {
                    fail_state = fail[ fail_state ];
                    fail_base = aho->states[ fail_state ].trans.base;
                } while ( !TRIE_TRANS_STATE( fail_state, fail_base, ucharcount, charid, 1 ) );

                fail_state = TRIE_TRANS_STATE( fail_state, fail_base, ucharcount, charid, 1 );
                fail[ ch_state ] = fail_state;
                if ( !aho->states[ ch_state ].wordnum && aho->states[ fail_state ].wordnum )
                {
                        aho->states[ ch_state ].wordnum =  aho->states[ fail_state ].wordnum;
                }
                q[ q_write++ % numstates] = ch_state;
            }
        }
    }
    /* restore fail[0..1] to 0 so that we "fall out" of the AC loop
       when we fail in state 1, this allows us to use the
       charclass scan to find a valid start char. This is based on the principle
       that theres a good chance the string being searched contains lots of stuff
       that cant be a start char.
     */
    fail[ 0 ] = fail[ 1 ] = 0;
    DEBUG_TRIE_COMPILE_r({
        PerlIO_printf(Perl_debug_log,
                      "%*sStclass Failtable (%"UVuf" states): 0",
                      (int)(depth * 2), "", (UV)numstates
        );
        for( q_read=1; q_read<numstates; q_read++ ) {
            PerlIO_printf(Perl_debug_log, ", %"UVuf, (UV)fail[q_read]);
        }
        PerlIO_printf(Perl_debug_log, "\n");
    });
    Safefree(q);
    /*RExC_seen |= REG_TRIEDFA_SEEN;*/
    return stclass;
}


#define DEBUG_PEEP(str,scan,depth) \
    DEBUG_OPTIMISE_r({if (scan){ \
       regnode *Next = regnext(scan); \
       regprop(RExC_rx, RExC_mysv, scan, NULL, pRExC_state); \
       PerlIO_printf(Perl_debug_log, "%*s" str ">%3d: %s (%d)", \
           (int)depth*2, "", REG_NODE_NUM(scan), SvPV_nolen_const(RExC_mysv),\
           Next ? (REG_NODE_NUM(Next)) : 0 ); \
       DEBUG_SHOW_STUDY_FLAGS(flags," [ ","]");\
       PerlIO_printf(Perl_debug_log, "\n"); \
   }});

/* The below joins as many adjacent EXACTish nodes as possible into a single
 * one.  The regop may be changed if the node(s) contain certain sequences that
 * require special handling.  The joining is only done if:
 * 1) there is room in the current conglomerated node to entirely contain the
 *    next one.
 * 2) they are the exact same node type
 *
 * The adjacent nodes actually may be separated by NOTHING-kind nodes, and
 * these get optimized out
 *
 * XXX khw thinks this should be enhanced to fill EXACT (at least) nodes as full
 * as possible, even if that means splitting an existing node so that its first
 * part is moved to the preceeding node.  This would maximise the efficiency of
 * memEQ during matching.  Elsewhere in this file, khw proposes splitting
 * EXACTFish nodes into portions that don't change under folding vs those that
 * do.  Those portions that don't change may be the only things in the pattern that
 * could be used to find fixed and floating strings.
 *
 * If a node is to match under /i (folded), the number of characters it matches
 * can be different than its character length if it contains a multi-character
 * fold.  *min_subtract is set to the total delta number of characters of the
 * input nodes.
 *
 * And *unfolded_multi_char is set to indicate whether or not the node contains
 * an unfolded multi-char fold.  This happens when whether the fold is valid or
 * not won't be known until runtime; namely for EXACTF nodes that contain LATIN
 * SMALL LETTER SHARP S, as only if the target string being matched against
 * turns out to be UTF-8 is that fold valid; and also for EXACTFL nodes whose
 * folding rules depend on the locale in force at runtime.  (Multi-char folds
 * whose components are all above the Latin1 range are not run-time locale
 * dependent, and have already been folded by the time this function is
 * called.)
 *
 * This is as good a place as any to discuss the design of handling these
 * multi-character fold sequences.  It's been wrong in Perl for a very long
 * time.  There are three code points in Unicode whose multi-character folds
 * were long ago discovered to mess things up.  The previous designs for
 * dealing with these involved assigning a special node for them.  This
 * approach doesn't always work, as evidenced by this example:
 *      "\xDFs" =~ /s\xDF/ui    # Used to fail before these patches
 * Both sides fold to "sss", but if the pattern is parsed to create a node that
 * would match just the \xDF, it won't be able to handle the case where a
 * successful match would have to cross the node's boundary.  The new approach
 * that hopefully generally solves the problem generates an EXACTFU_SS node
 * that is "sss" in this case.
 *
 * It turns out that there are problems with all multi-character folds, and not
 * just these three.  Now the code is general, for all such cases.  The
 * approach taken is:
 * 1)   This routine examines each EXACTFish node that could contain multi-
 *      character folded sequences.  Since a single character can fold into
 *      such a sequence, the minimum match length for this node is less than
 *      the number of characters in the node.  This routine returns in
 *      *min_subtract how many characters to subtract from the the actual
 *      length of the string to get a real minimum match length; it is 0 if
 *      there are no multi-char foldeds.  This delta is used by the caller to
 *      adjust the min length of the match, and the delta between min and max,
 *      so that the optimizer doesn't reject these possibilities based on size
 *      constraints.
 * 2)   For the sequence involving the Sharp s (\xDF), the node type EXACTFU_SS
 *      is used for an EXACTFU node that contains at least one "ss" sequence in
 *      it.  For non-UTF-8 patterns and strings, this is the only case where
 *      there is a possible fold length change.  That means that a regular
 *      EXACTFU node without UTF-8 involvement doesn't have to concern itself
 *      with length changes, and so can be processed faster.  regexec.c takes
 *      advantage of this.  Generally, an EXACTFish node that is in UTF-8 is
 *      pre-folded by regcomp.c (except EXACTFL, some of whose folds aren't
 *      known until runtime).  This saves effort in regex matching.  However,
 *      the pre-folding isn't done for non-UTF8 patterns because the fold of
 *      the MICRO SIGN requires UTF-8, and we don't want to slow things down by
 *      forcing the pattern into UTF8 unless necessary.  Also what EXACTF (and,
 *      again, EXACTFL) nodes fold to isn't known until runtime.  The fold
 *      possibilities for the non-UTF8 patterns are quite simple, except for
 *      the sharp s.  All the ones that don't involve a UTF-8 target string are
 *      members of a fold-pair, and arrays are set up for all of them so that
 *      the other member of the pair can be found quickly.  Code elsewhere in
 *      this file makes sure that in EXACTFU nodes, the sharp s gets folded to
 *      'ss', even if the pattern isn't UTF-8.  This avoids the issues
 *      described in the next item.
 * 3)   A problem remains for unfolded multi-char folds. (These occur when the
 *      validity of the fold won't be known until runtime, and so must remain
 *      unfolded for now.  This happens for the sharp s in EXACTF and EXACTFA
 *      nodes when the pattern isn't in UTF-8.  (Note, BTW, that there cannot
 *      be an EXACTF node with a UTF-8 pattern.)  They also occur for various
 *      folds in EXACTFL nodes, regardless of the UTF-ness of the pattern.)
 *      The reason this is a problem is that the optimizer part of regexec.c
 *      (probably unwittingly, in Perl_regexec_flags()) makes an assumption
 *      that a character in the pattern corresponds to at most a single
 *      character in the target string.  (And I do mean character, and not byte
 *      here, unlike other parts of the documentation that have never been
 *      updated to account for multibyte Unicode.)  sharp s in EXACTF and
 *      EXACTFL nodes can match the two character string 'ss'; in EXACTFA nodes
 *      it can match "\x{17F}\x{17F}".  These, along with other ones in EXACTFL
 *      nodes, violate the assumption, and they are the only instances where it
 *      is violated.  I'm reluctant to try to change the assumption, as the
 *      code involved is impenetrable to me (khw), so instead the code here
 *      punts.  This routine examines EXACTFL nodes, and (when the pattern
 *      isn't UTF-8) EXACTF and EXACTFA for such unfolded folds, and returns a
 *      boolean indicating whether or not the node contains such a fold.  When
 *      it is true, the caller sets a flag that later causes the optimizer in
 *      this file to not set values for the floating and fixed string lengths,
 *      and thus avoids the optimizer code in regexec.c that makes the invalid
 *      assumption.  Thus, there is no optimization based on string lengths for
 *      EXACTFL nodes that contain these few folds, nor for non-UTF8-pattern
 *      EXACTF and EXACTFA nodes that contain the sharp s.  (The reason the
 *      assumption is wrong only in these cases is that all other non-UTF-8
 *      folds are 1-1; and, for UTF-8 patterns, we pre-fold all other folds to
 *      their expanded versions.  (Again, we can't prefold sharp s to 'ss' in
 *      EXACTF nodes because we don't know at compile time if it actually
 *      matches 'ss' or not.  For EXACTF nodes it will match iff the target
 *      string is in UTF-8.  This is in contrast to EXACTFU nodes, where it
 *      always matches; and EXACTFA where it never does.  In an EXACTFA node in
 *      a UTF-8 pattern, sharp s is folded to "\x{17F}\x{17F}, avoiding the
 *      problem; but in a non-UTF8 pattern, folding it to that above-Latin1
 *      string would require the pattern to be forced into UTF-8, the overhead
 *      of which we want to avoid.  Similarly the unfolded multi-char folds in
 *      EXACTFL nodes will match iff the locale at the time of match is a UTF-8
 *      locale.)
 *
 *      Similarly, the code that generates tries doesn't currently handle
 *      not-already-folded multi-char folds, and it looks like a pain to change
 *      that.  Therefore, trie generation of EXACTFA nodes with the sharp s
 *      doesn't work.  Instead, such an EXACTFA is turned into a new regnode,
 *      EXACTFA_NO_TRIE, which the trie code knows not to handle.  Most people
 *      using /iaa matching will be doing so almost entirely with ASCII
 *      strings, so this should rarely be encountered in practice */

#define JOIN_EXACT(scan,min_subtract,unfolded_multi_char, flags) \
    if (PL_regkind[OP(scan)] == EXACT) \
        join_exact(pRExC_state,(scan),(min_subtract),unfolded_multi_char, (flags),NULL,depth+1)

STATIC U32
S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan,
                   UV *min_subtract, bool *unfolded_multi_char,
                   U32 flags,regnode *val, U32 depth)
{
    /* Merge several consecutive EXACTish nodes into one. */
    regnode *n = regnext(scan);
    U32 stringok = 1;
    regnode *next = scan + NODE_SZ_STR(scan);
    U32 merged = 0;
    U32 stopnow = 0;
#ifdef DEBUGGING
    regnode *stop = scan;
    GET_RE_DEBUG_FLAGS_DECL;
#else
    PERL_UNUSED_ARG(depth);
#endif

    PERL_ARGS_ASSERT_JOIN_EXACT;
#ifndef EXPERIMENTAL_INPLACESCAN
    PERL_UNUSED_ARG(flags);
    PERL_UNUSED_ARG(val);
#endif
    DEBUG_PEEP("join",scan,depth);

    /* Look through the subsequent nodes in the chain.  Skip NOTHING, merge
     * EXACT ones that are mergeable to the current one. */
    while (n
           && (PL_regkind[OP(n)] == NOTHING
               || (stringok && OP(n) == OP(scan)))
           && NEXT_OFF(n)
           && NEXT_OFF(scan) + NEXT_OFF(n) < I16_MAX)
    {

        if (OP(n) == TAIL || n > next)
            stringok = 0;
        if (PL_regkind[OP(n)] == NOTHING) {
            DEBUG_PEEP("skip:",n,depth);
            NEXT_OFF(scan) += NEXT_OFF(n);
            next = n + NODE_STEP_REGNODE;
#ifdef DEBUGGING
            if (stringok)
                stop = n;
#endif
            n = regnext(n);
        }
        else if (stringok) {
            const unsigned int oldl = STR_LEN(scan);
            regnode * const nnext = regnext(n);

            /* XXX I (khw) kind of doubt that this works on platforms (should
             * Perl ever run on one) where U8_MAX is above 255 because of lots
             * of other assumptions */
            /* Don't join if the sum can't fit into a single node */
            if (oldl + STR_LEN(n) > U8_MAX)
                break;

            DEBUG_PEEP("merg",n,depth);
            merged++;

            NEXT_OFF(scan) += NEXT_OFF(n);
            STR_LEN(scan) += STR_LEN(n);
            next = n + NODE_SZ_STR(n);
            /* Now we can overwrite *n : */
            Move(STRING(n), STRING(scan) + oldl, STR_LEN(n), char);
#ifdef DEBUGGING
            stop = next - 1;
#endif
            n = nnext;
            if (stopnow) break;
        }

#ifdef EXPERIMENTAL_INPLACESCAN
        if (flags && !NEXT_OFF(n)) {
            DEBUG_PEEP("atch", val, depth);
            if (reg_off_by_arg[OP(n)]) {
                ARG_SET(n, val - n);
            }
            else {
                NEXT_OFF(n) = val - n;
            }
            stopnow = 1;
        }
#endif
    }

    *min_subtract = 0;
    *unfolded_multi_char = FALSE;

    /* Here, all the adjacent mergeable EXACTish nodes have been merged.  We
     * can now analyze for sequences of problematic code points.  (Prior to
     * this final joining, sequences could have been split over boundaries, and
     * hence missed).  The sequences only happen in folding, hence for any
     * non-EXACT EXACTish node */
    if (OP(scan) != EXACT && OP(scan) != EXACTL) {
        U8* s0 = (U8*) STRING(scan);
        U8* s = s0;
        U8* s_end = s0 + STR_LEN(scan);

        int total_count_delta = 0;  /* Total delta number of characters that
                                       multi-char folds expand to */

        /* One pass is made over the node's string looking for all the
         * possibilities.  To avoid some tests in the loop, there are two main
         * cases, for UTF-8 patterns (which can't have EXACTF nodes) and
         * non-UTF-8 */
        if (UTF) {
            U8* folded = NULL;

            if (OP(scan) == EXACTFL) {
                U8 *d;

                /* An EXACTFL node would already have been changed to another
                 * node type unless there is at least one character in it that
                 * is problematic; likely a character whose fold definition
                 * won't be known until runtime, and so has yet to be folded.
                 * For all but the UTF-8 locale, folds are 1-1 in length, but
                 * to handle the UTF-8 case, we need to create a temporary
                 * folded copy using UTF-8 locale rules in order to analyze it.
                 * This is because our macros that look to see if a sequence is
                 * a multi-char fold assume everything is folded (otherwise the
                 * tests in those macros would be too complicated and slow).
                 * Note that here, the non-problematic folds will have already
                 * been done, so we can just copy such characters.  We actually
                 * don't completely fold the EXACTFL string.  We skip the
                 * unfolded multi-char folds, as that would just create work
                 * below to figure out the size they already are */

                Newx(folded, UTF8_MAX_FOLD_CHAR_EXPAND * STR_LEN(scan) + 1, U8);
                d = folded;
                while (s < s_end) {
                    STRLEN s_len = UTF8SKIP(s);
                    if (! is_PROBLEMATIC_LOCALE_FOLD_utf8(s)) {
                        Copy(s, d, s_len, U8);
                        d += s_len;
                    }
                    else if (is_FOLDS_TO_MULTI_utf8(s)) {
                        *unfolded_multi_char = TRUE;
                        Copy(s, d, s_len, U8);
                        d += s_len;
                    }
                    else if (isASCII(*s)) {
                        *(d++) = toFOLD(*s);
                    }
                    else {
                        STRLEN len;
                        _to_utf8_fold_flags(s, d, &len, FOLD_FLAGS_FULL);
                        d += len;
                    }
                    s += s_len;
                }

                /* Point the remainder of the routine to look at our temporary
                 * folded copy */
                s = folded;
                s_end = d;
            } /* End of creating folded copy of EXACTFL string */

            /* Examine the string for a multi-character fold sequence.  UTF-8
             * patterns have all characters pre-folded by the time this code is
             * executed */
            while (s < s_end - 1) /* Can stop 1 before the end, as minimum
                                     length sequence we are looking for is 2 */
            {
                int count = 0;  /* How many characters in a multi-char fold */
                int len = is_MULTI_CHAR_FOLD_utf8_safe(s, s_end);
                if (! len) {    /* Not a multi-char fold: get next char */
                    s += UTF8SKIP(s);
                    continue;
                }

                /* Nodes with 'ss' require special handling, except for
                 * EXACTFA-ish for which there is no multi-char fold to this */
                if (len == 2 && *s == 's' && *(s+1) == 's'
                    && OP(scan) != EXACTFA
                    && OP(scan) != EXACTFA_NO_TRIE)
                {
                    count = 2;
                    if (OP(scan) != EXACTFL) {
                        OP(scan) = EXACTFU_SS;
                    }
                    s += 2;
                }
                else { /* Here is a generic multi-char fold. */
                    U8* multi_end  = s + len;

                    /* Count how many characters are in it.  In the case of
                     * /aa, no folds which contain ASCII code points are
                     * allowed, so check for those, and skip if found. */
                    if (OP(scan) != EXACTFA && OP(scan) != EXACTFA_NO_TRIE) {
                        count = utf8_length(s, multi_end);
                        s = multi_end;
                    }
                    else {
                        while (s < multi_end) {
                            if (isASCII(*s)) {
                                s++;
                                goto next_iteration;
                            }
                            else {
                                s += UTF8SKIP(s);
                            }
                            count++;
                        }
                    }
                }

                /* The delta is how long the sequence is minus 1 (1 is how long
                 * the character that folds to the sequence is) */
                total_count_delta += count - 1;
              next_iteration: ;
            }

            /* We created a temporary folded copy of the string in EXACTFL
             * nodes.  Therefore we need to be sure it doesn't go below zero,
             * as the real string could be shorter */
            if (OP(scan) == EXACTFL) {
                int total_chars = utf8_length((U8*) STRING(scan),
                                           (U8*) STRING(scan) + STR_LEN(scan));
                if (total_count_delta > total_chars) {
                    total_count_delta = total_chars;
                }
            }

            *min_subtract += total_count_delta;
            Safefree(folded);
        }
        else if (OP(scan) == EXACTFA) {

            /* Non-UTF-8 pattern, EXACTFA node.  There can't be a multi-char
             * fold to the ASCII range (and there are no existing ones in the
             * upper latin1 range).  But, as outlined in the comments preceding
             * this function, we need to flag any occurrences of the sharp s.
             * This character forbids trie formation (because of added
             * complexity) */
#if    UNICODE_MAJOR_VERSION > 3 /* no multifolds in early Unicode */   \
   || (UNICODE_MAJOR_VERSION == 3 && (   UNICODE_DOT_VERSION > 0)       \
                                      || UNICODE_DOT_DOT_VERSION > 0)
            while (s < s_end) {
                if (*s == LATIN_SMALL_LETTER_SHARP_S) {
                    OP(scan) = EXACTFA_NO_TRIE;
                    *unfolded_multi_char = TRUE;
                    break;
                }
                s++;
            }
        }
        else {

            /* Non-UTF-8 pattern, not EXACTFA node.  Look for the multi-char
             * folds that are all Latin1.  As explained in the comments
             * preceding this function, we look also for the sharp s in EXACTF
             * and EXACTFL nodes; it can be in the final position.  Otherwise
             * we can stop looking 1 byte earlier because have to find at least
             * two characters for a multi-fold */
            const U8* upper = (OP(scan) == EXACTF || OP(scan) == EXACTFL)
                              ? s_end
                              : s_end -1;

            while (s < upper) {
                int len = is_MULTI_CHAR_FOLD_latin1_safe(s, s_end);
                if (! len) {    /* Not a multi-char fold. */
                    if (*s == LATIN_SMALL_LETTER_SHARP_S
                        && (OP(scan) == EXACTF || OP(scan) == EXACTFL))
                    {
                        *unfolded_multi_char = TRUE;
                    }
                    s++;
                    continue;
                }

                if (len == 2
                    && isALPHA_FOLD_EQ(*s, 's')
                    && isALPHA_FOLD_EQ(*(s+1), 's'))
                {

                    /* EXACTF nodes need to know that the minimum length
                     * changed so that a sharp s in the string can match this
                     * ss in the pattern, but they remain EXACTF nodes, as they
                     * won't match this unless the target string is is UTF-8,
                     * which we don't know until runtime.  EXACTFL nodes can't
                     * transform into EXACTFU nodes */
                    if (OP(scan) != EXACTF && OP(scan) != EXACTFL) {
                        OP(scan) = EXACTFU_SS;
                    }
                }

                *min_subtract += len - 1;
                s += len;
            }
#endif
        }
    }

#ifdef DEBUGGING
    /* Allow dumping but overwriting the collection of skipped
     * ops and/or strings with fake optimized ops */
    n = scan + NODE_SZ_STR(scan);
    while (n <= stop) {
        OP(n) = OPTIMIZED;
        FLAGS(n) = 0;
        NEXT_OFF(n) = 0;
        n++;
    }
#endif
    DEBUG_OPTIMISE_r(if (merged){DEBUG_PEEP("finl",scan,depth)});
    return stopnow;
}

/* REx optimizer.  Converts nodes into quicker variants "in place".
   Finds fixed substrings.  */

/* Stops at toplevel WHILEM as well as at "last". At end *scanp is set
   to the position after last scanned or to NULL. */

#define INIT_AND_WITHP \
    assert(!and_withp); \
    Newx(and_withp,1, regnode_ssc); \
    SAVEFREEPV(and_withp)


static void
S_unwind_scan_frames(pTHX_ const void *p)
{
    scan_frame *f= (scan_frame *)p;
    do {
        scan_frame *n= f->next_frame;
        Safefree(f);
        f= n;
    } while (f);
}


STATIC SSize_t
S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp,
                        SSize_t *minlenp, SSize_t *deltap,
                        regnode *last,
                        scan_data_t *data,
                        I32 stopparen,
                        U32 recursed_depth,
                        regnode_ssc *and_withp,
                        U32 flags, U32 depth)
                        /* scanp: Start here (read-write). */
                        /* deltap: Write maxlen-minlen here. */
                        /* last: Stop before this one. */
                        /* data: string data about the pattern */
                        /* stopparen: treat close N as END */
                        /* recursed: which subroutines have we recursed into */
                        /* and_withp: Valid if flags & SCF_DO_STCLASS_OR */
{
    /* There must be at least this number of characters to match */
    SSize_t min = 0;
    I32 pars = 0, code;
    regnode *scan = *scanp, *next;
    SSize_t delta = 0;
    int is_inf = (flags & SCF_DO_SUBSTR) && (data->flags & SF_IS_INF);
    int is_inf_internal = 0;            /* The studied chunk is infinite */
    I32 is_par = OP(scan) == OPEN ? ARG(scan) : 0;
    scan_data_t data_fake;
    SV *re_trie_maxbuff = NULL;
    regnode *first_non_open = scan;
    SSize_t stopmin = SSize_t_MAX;
    scan_frame *frame = NULL;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_STUDY_CHUNK;


    if ( depth == 0 ) {
        while (first_non_open && OP(first_non_open) == OPEN)
            first_non_open=regnext(first_non_open);
    }


  fake_study_recurse:
    DEBUG_r(
        RExC_study_chunk_recursed_count++;
    );
    DEBUG_OPTIMISE_MORE_r(
    {
        PerlIO_printf(Perl_debug_log,
            "%*sstudy_chunk stopparen=%ld recursed_count=%lu depth=%lu recursed_depth=%lu scan=%p last=%p",
            (int)(depth*2), "", (long)stopparen,
            (unsigned long)RExC_study_chunk_recursed_count,
            (unsigned long)depth, (unsigned long)recursed_depth,
            scan,
            last);
        if (recursed_depth) {
            U32 i;
            U32 j;
            for ( j = 0 ; j < recursed_depth ; j++ ) {
                for ( i = 0 ; i < (U32)RExC_npar ; i++ ) {
                    if (
                        PAREN_TEST(RExC_study_chunk_recursed +
                                   ( j * RExC_study_chunk_recursed_bytes), i )
                        && (
                            !j ||
                            !PAREN_TEST(RExC_study_chunk_recursed +
                                   (( j - 1 ) * RExC_study_chunk_recursed_bytes), i)
                        )
                    ) {
                        PerlIO_printf(Perl_debug_log," %d",(int)i);
                        break;
                    }
                }
                if ( j + 1 < recursed_depth ) {
                    PerlIO_printf(Perl_debug_log, ",");
                }
            }
        }
        PerlIO_printf(Perl_debug_log,"\n");
    }
    );
    while ( scan && OP(scan) != END && scan < last ){
        UV min_subtract = 0;    /* How mmany chars to subtract from the minimum
                                   node length to get a real minimum (because
                                   the folded version may be shorter) */
        bool unfolded_multi_char = FALSE;
        /* Peephole optimizer: */
        DEBUG_STUDYDATA("Peep:", data, depth);
        DEBUG_PEEP("Peep", scan, depth);


        /* The reason we do this here we need to deal with things like /(?:f)(?:o)(?:o)/
         * which cant be dealt with by the normal EXACT parsing code, as each (?:..) is handled
         * by a different invocation of reg() -- Yves
         */
        JOIN_EXACT(scan,&min_subtract, &unfolded_multi_char, 0);

        /* Follow the next-chain of the current node and optimize
           away all the NOTHINGs from it.  */
        if (OP(scan) != CURLYX) {
            const int max = (reg_off_by_arg[OP(scan)]
                       ? I32_MAX
                       /* I32 may be smaller than U16 on CRAYs! */
                       : (I32_MAX < U16_MAX ? I32_MAX : U16_MAX));
            int off = (reg_off_by_arg[OP(scan)] ? ARG(scan) : NEXT_OFF(scan));
            int noff;
            regnode *n = scan;

            /* Skip NOTHING and LONGJMP. */
            while ((n = regnext(n))
                   && ((PL_regkind[OP(n)] == NOTHING && (noff = NEXT_OFF(n)))
                       || ((OP(n) == LONGJMP) && (noff = ARG(n))))
                   && off + noff < max)
                off += noff;
            if (reg_off_by_arg[OP(scan)])
                ARG(scan) = off;
            else
                NEXT_OFF(scan) = off;
        }

        /* The principal pseudo-switch.  Cannot be a switch, since we
           look into several different things.  */
        if ( OP(scan) == DEFINEP ) {
            SSize_t minlen = 0;
            SSize_t deltanext = 0;
            SSize_t fake_last_close = 0;
            I32 f = SCF_IN_DEFINE;

            StructCopy(&zero_scan_data, &data_fake, scan_data_t);
            scan = regnext(scan);
            assert( OP(scan) == IFTHEN );
            DEBUG_PEEP("expect IFTHEN", scan, depth);

            data_fake.last_closep= &fake_last_close;
            minlen = *minlenp;
            next = regnext(scan);
            scan = NEXTOPER(NEXTOPER(scan));
            DEBUG_PEEP("scan", scan, depth);
            DEBUG_PEEP("next", next, depth);

            /* we suppose the run is continuous, last=next...
             * NOTE we dont use the return here! */
            (void)study_chunk(pRExC_state, &scan, &minlen,
                              &deltanext, next, &data_fake, stopparen,
                              recursed_depth, NULL, f, depth+1);

            scan = next;
        } else
        if (
            OP(scan) == BRANCH  ||
            OP(scan) == BRANCHJ ||
            OP(scan) == IFTHEN
        ) {
            next = regnext(scan);
            code = OP(scan);

            /* The op(next)==code check below is to see if we
             * have "BRANCH-BRANCH", "BRANCHJ-BRANCHJ", "IFTHEN-IFTHEN"
             * IFTHEN is special as it might not appear in pairs.
             * Not sure whether BRANCH-BRANCHJ is possible, regardless
             * we dont handle it cleanly. */
            if (OP(next) == code || code == IFTHEN) {
                /* NOTE - There is similar code to this block below for
                 * handling TRIE nodes on a re-study.  If you change stuff here
                 * check there too. */
                SSize_t max1 = 0, min1 = SSize_t_MAX, num = 0;
                regnode_ssc accum;
                regnode * const startbranch=scan;

                if (flags & SCF_DO_SUBSTR) {
                    /* Cannot merge strings after this. */
                    scan_commit(pRExC_state, data, minlenp, is_inf);
                }

                if (flags & SCF_DO_STCLASS)
                    ssc_init_zero(pRExC_state, &accum);

                while (OP(scan) == code) {
                    SSize_t deltanext, minnext, fake;
                    I32 f = 0;
                    regnode_ssc this_class;

                    DEBUG_PEEP("Branch", scan, depth);

                    num++;
                    StructCopy(&zero_scan_data, &data_fake, scan_data_t);
                    if (data) {
                        data_fake.whilem_c = data->whilem_c;
                        data_fake.last_closep = data->last_closep;
                    }
                    else
                        data_fake.last_closep = &fake;

                    data_fake.pos_delta = delta;
                    next = regnext(scan);

                    scan = NEXTOPER(scan); /* everything */
                    if (code != BRANCH)    /* everything but BRANCH */
                        scan = NEXTOPER(scan);

                    if (flags & SCF_DO_STCLASS) {
                        ssc_init(pRExC_state, &this_class);
                        data_fake.start_class = &this_class;
                        f = SCF_DO_STCLASS_AND;
                    }
                    if (flags & SCF_WHILEM_VISITED_POS)
                        f |= SCF_WHILEM_VISITED_POS;

                    /* we suppose the run is continuous, last=next...*/
                    minnext = study_chunk(pRExC_state, &scan, minlenp,
                                      &deltanext, next, &data_fake, stopparen,
                                      recursed_depth, NULL, f,depth+1);

                    if (min1 > minnext)
                        min1 = minnext;
                    if (deltanext == SSize_t_MAX) {
                        is_inf = is_inf_internal = 1;
                        max1 = SSize_t_MAX;
                    } else if (max1 < minnext + deltanext)
                        max1 = minnext + deltanext;
                    scan = next;
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SCF_SEEN_ACCEPT) {
                        if ( stopmin > minnext)
                            stopmin = min + min1;
                        flags &= ~SCF_DO_SUBSTR;
                        if (data)
                            data->flags |= SCF_SEEN_ACCEPT;
                    }
                    if (data) {
                        if (data_fake.flags & SF_HAS_EVAL)
                            data->flags |= SF_HAS_EVAL;
                        data->whilem_c = data_fake.whilem_c;
                    }
                    if (flags & SCF_DO_STCLASS)
                        ssc_or(pRExC_state, &accum, (regnode_charclass*)&this_class);
                }
                if (code == IFTHEN && num < 2) /* Empty ELSE branch */
                    min1 = 0;
                if (flags & SCF_DO_SUBSTR) {
                    data->pos_min += min1;
                    if (data->pos_delta >= SSize_t_MAX - (max1 - min1))
                        data->pos_delta = SSize_t_MAX;
                    else
                        data->pos_delta += max1 - min1;
                    if (max1 != min1 || is_inf)
                        data->longest = &(data->longest_float);
                }
                min += min1;
                if (delta == SSize_t_MAX
                 || SSize_t_MAX - delta - (max1 - min1) < 0)
                    delta = SSize_t_MAX;
                else
                    delta += max1 - min1;
                if (flags & SCF_DO_STCLASS_OR) {
                    ssc_or(pRExC_state, data->start_class, (regnode_charclass*) &accum);
                    if (min1) {
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);
                        flags &= ~SCF_DO_STCLASS;
                    }
                }
                else if (flags & SCF_DO_STCLASS_AND) {
                    if (min1) {
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &accum);
                        flags &= ~SCF_DO_STCLASS;
                    }
                    else {
                        /* Switch to OR mode: cache the old value of
                         * data->start_class */
                        INIT_AND_WITHP;
                        StructCopy(data->start_class, and_withp, regnode_ssc);
                        flags &= ~SCF_DO_STCLASS_AND;
                        StructCopy(&accum, data->start_class, regnode_ssc);
                        flags |= SCF_DO_STCLASS_OR;
                    }
                }

                if (PERL_ENABLE_TRIE_OPTIMISATION &&
                        OP( startbranch ) == BRANCH )
                {
                /* demq.

                   Assuming this was/is a branch we are dealing with: 'scan'
                   now points at the item that follows the branch sequence,
                   whatever it is. We now start at the beginning of the
                   sequence and look for subsequences of

                   BRANCH->EXACT=>x1
                   BRANCH->EXACT=>x2
                   tail

                   which would be constructed from a pattern like
                   /A|LIST|OF|WORDS/

                   If we can find such a subsequence we need to turn the first
                   element into a trie and then add the subsequent branch exact
                   strings to the trie.

                   We have two cases

                     1. patterns where the whole set of branches can be
                        converted.

                     2. patterns where only a subset can be converted.

                   In case 1 we can replace the whole set with a single regop
                   for the trie. In case 2 we need to keep the start and end
                   branches so

                     'BRANCH EXACT; BRANCH EXACT; BRANCH X'
                     becomes BRANCH TRIE; BRANCH X;

                  There is an additional case, that being where there is a
                  common prefix, which gets split out into an EXACT like node
                  preceding the TRIE node.

                  If x(1..n)==tail then we can do a simple trie, if not we make
                  a "jump" trie, such that when we match the appropriate word
                  we "jump" to the appropriate tail node. Essentially we turn
                  a nested if into a case structure of sorts.

                */

                    int made=0;
                    if (!re_trie_maxbuff) {
                        re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
                        if (!SvIOK(re_trie_maxbuff))
                            sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
                    }
                    if ( SvIV(re_trie_maxbuff)>=0  ) {
                        regnode *cur;
                        regnode *first = (regnode *)NULL;
                        regnode *last = (regnode *)NULL;
                        regnode *tail = scan;
                        U8 trietype = 0;
                        U32 count=0;

                        /* var tail is used because there may be a TAIL
                           regop in the way. Ie, the exacts will point to the
                           thing following the TAIL, but the last branch will
                           point at the TAIL. So we advance tail. If we
                           have nested (?:) we may have to move through several
                           tails.
                         */

                        while ( OP( tail ) == TAIL ) {
                            /* this is the TAIL generated by (?:) */
                            tail = regnext( tail );
                        }


                        DEBUG_TRIE_COMPILE_r({
                            regprop(RExC_rx, RExC_mysv, tail, NULL, pRExC_state);
                            PerlIO_printf( Perl_debug_log, "%*s%s%s\n",
                              (int)depth * 2 + 2, "",
                              "Looking for TRIE'able sequences. Tail node is: ",
                              SvPV_nolen_const( RExC_mysv )
                            );
                        });

                        /*

                            Step through the branches
                                cur represents each branch,
                                noper is the first thing to be matched as part
                                      of that branch
                                noper_next is the regnext() of that node.

                            We normally handle a case like this
                            /FOO[xyz]|BAR[pqr]/ via a "jump trie" but we also
                            support building with NOJUMPTRIE, which restricts
                            the trie logic to structures like /FOO|BAR/.

                            If noper is a trieable nodetype then the branch is
                            a possible optimization target. If we are building
                            under NOJUMPTRIE then we require that noper_next is
                            the same as scan (our current position in the regex
                            program).

                            Once we have two or more consecutive such branches
                            we can create a trie of the EXACT's contents and
                            stitch it in place into the program.

                            If the sequence represents all of the branches in
                            the alternation we replace the entire thing with a
                            single TRIE node.

                            Otherwise when it is a subsequence we need to
                            stitch it in place and replace only the relevant
                            branches. This means the first branch has to remain
                            as it is used by the alternation logic, and its
                            next pointer, and needs to be repointed at the item
                            on the branch chain following the last branch we
                            have optimized away.

                            This could be either a BRANCH, in which case the
                            subsequence is internal, or it could be the item
                            following the branch sequence in which case the
                            subsequence is at the end (which does not
                            necessarily mean the first node is the start of the
                            alternation).

                            TRIE_TYPE(X) is a define which maps the optype to a
                            trietype.

                                optype          |  trietype
                                ----------------+-----------
                                NOTHING         | NOTHING
                                EXACT           | EXACT
                                EXACTFU         | EXACTFU
                                EXACTFU_SS      | EXACTFU
                                EXACTFA         | EXACTFA
                                EXACTL          | EXACTL
                                EXACTFLU8       | EXACTFLU8


                        */
#define TRIE_TYPE(X) ( ( NOTHING == (X) )                                   \
                       ? NOTHING                                            \
                       : ( EXACT == (X) )                                   \
                         ? EXACT                                            \
                         : ( EXACTFU == (X) || EXACTFU_SS == (X) )          \
                           ? EXACTFU                                        \
                           : ( EXACTFA == (X) )                             \
                             ? EXACTFA                                      \
                             : ( EXACTL == (X) )                            \
                               ? EXACTL                                     \
                               : ( EXACTFLU8 == (X) )                        \
                                 ? EXACTFLU8                                 \
                                 : 0 )

                        /* dont use tail as the end marker for this traverse */
                        for ( cur = startbranch ; cur != scan ; cur = regnext( cur ) ) {
                            regnode * const noper = NEXTOPER( cur );
                            U8 noper_type = OP( noper );
                            U8 noper_trietype = TRIE_TYPE( noper_type );
#if defined(DEBUGGING) || defined(NOJUMPTRIE)
                            regnode * const noper_next = regnext( noper );
                            U8 noper_next_type = (noper_next && noper_next != tail) ? OP(noper_next) : 0;
                            U8 noper_next_trietype = (noper_next && noper_next != tail) ? TRIE_TYPE( noper_next_type ) :0;
#endif

                            DEBUG_TRIE_COMPILE_r({
                                regprop(RExC_rx, RExC_mysv, cur, NULL, pRExC_state);
                                PerlIO_printf( Perl_debug_log, "%*s- %s (%d)",
                                   (int)depth * 2 + 2,"", SvPV_nolen_const( RExC_mysv ), REG_NODE_NUM(cur) );

                                regprop(RExC_rx, RExC_mysv, noper, NULL, pRExC_state);
                                PerlIO_printf( Perl_debug_log, " -> %s",
                                    SvPV_nolen_const(RExC_mysv));

                                if ( noper_next ) {
                                  regprop(RExC_rx, RExC_mysv, noper_next, NULL, pRExC_state);
                                  PerlIO_printf( Perl_debug_log,"\t=> %s\t",
                                    SvPV_nolen_const(RExC_mysv));
                                }
                                PerlIO_printf( Perl_debug_log, "(First==%d,Last==%d,Cur==%d,tt==%s,nt==%s,nnt==%s)\n",
                                   REG_NODE_NUM(first), REG_NODE_NUM(last), REG_NODE_NUM(cur),
                                   PL_reg_name[trietype], PL_reg_name[noper_trietype], PL_reg_name[noper_next_trietype]
                                );
                            });

                            /* Is noper a trieable nodetype that can be merged
                             * with the current trie (if there is one)? */
                            if ( noper_trietype
                                  &&
                                  (
                                        ( noper_trietype == NOTHING)
                                        || ( trietype == NOTHING )
                                        || ( trietype == noper_trietype )
                                  )
#ifdef NOJUMPTRIE
                                  && noper_next == tail
#endif
                                  && count < U16_MAX)
                            {
                                /* Handle mergable triable node Either we are
                                 * the first node in a new trieable sequence,
                                 * in which case we do some bookkeeping,
                                 * otherwise we update the end pointer. */
                                if ( !first ) {
                                    first = cur;
                                    if ( noper_trietype == NOTHING ) {
#if !defined(DEBUGGING) && !defined(NOJUMPTRIE)
                                        regnode * const noper_next = regnext( noper );
                                        U8 noper_next_type = (noper_next && noper_next!=tail) ? OP(noper_next) : 0;
                                        U8 noper_next_trietype = noper_next_type ? TRIE_TYPE( noper_next_type ) :0;
#endif

                                        if ( noper_next_trietype ) {
                                            trietype = noper_next_trietype;
                                        } else if (noper_next_type)  {
                                            /* a NOTHING regop is 1 regop wide.
                                             * We need at least two for a trie
                                             * so we can't merge this in */
                                            first = NULL;
                                        }
                                    } else {
                                        trietype = noper_trietype;
                                    }
                                } else {
                                    if ( trietype == NOTHING )
                                        trietype = noper_trietype;
                                    last = cur;
                                }
                                if (first)
                                    count++;
                            } /* end handle mergable triable node */
                            else {
                                /* handle unmergable node -
                                 * noper may either be a triable node which can
                                 * not be tried together with the current trie,
                                 * or a non triable node */
                                if ( last ) {
                                    /* If last is set and trietype is not
                                     * NOTHING then we have found at least two
                                     * triable branch sequences in a row of a
                                     * similar trietype so we can turn them
                                     * into a trie. If/when we allow NOTHING to
                                     * start a trie sequence this condition
                                     * will be required, and it isn't expensive
                                     * so we leave it in for now. */
                                    if ( trietype && trietype != NOTHING )
                                        make_trie( pRExC_state,
                                                startbranch, first, cur, tail,
                                                count, trietype, depth+1 );
                                    last = NULL; /* note: we clear/update
                                                    first, trietype etc below,
                                                    so we dont do it here */
                                }
                                if ( noper_trietype
#ifdef NOJUMPTRIE
                                     && noper_next == tail
#endif
                                ){
                                    /* noper is triable, so we can start a new
                                     * trie sequence */
                                    count = 1;
                                    first = cur;
                                    trietype = noper_trietype;
                                } else if (first) {
                                    /* if we already saw a first but the
                                     * current node is not triable then we have
                                     * to reset the first information. */
                                    count = 0;
                                    first = NULL;
                                    trietype = 0;
                                }
                            } /* end handle unmergable node */
                        } /* loop over branches */
                        DEBUG_TRIE_COMPILE_r({
                            regprop(RExC_rx, RExC_mysv, cur, NULL, pRExC_state);
                            PerlIO_printf( Perl_debug_log,
                              "%*s- %s (%d) <SCAN FINISHED>\n",
                              (int)depth * 2 + 2,
                              "", SvPV_nolen_const( RExC_mysv ),REG_NODE_NUM(cur));

                        });
                        if ( last && trietype ) {
                            if ( trietype != NOTHING ) {
                                /* the last branch of the sequence was part of
                                 * a trie, so we have to construct it here
                                 * outside of the loop */
                                made= make_trie( pRExC_state, startbranch,
                                                 first, scan, tail, count,
                                                 trietype, depth+1 );
#ifdef TRIE_STUDY_OPT
                                if ( ((made == MADE_EXACT_TRIE &&
                                     startbranch == first)
                                     || ( first_non_open == first )) &&
                                     depth==0 ) {
                                    flags |= SCF_TRIE_RESTUDY;
                                    if ( startbranch == first
                                         && scan == tail )
                                    {
                                        RExC_seen &=~REG_TOP_LEVEL_BRANCHES_SEEN;
                                    }
                                }
#endif
                            } else {
                                /* at this point we know whatever we have is a
                                 * NOTHING sequence/branch AND if 'startbranch'
                                 * is 'first' then we can turn the whole thing
                                 * into a NOTHING
                                 */
                                if ( startbranch == first ) {
                                    regnode *opt;
                                    /* the entire thing is a NOTHING sequence,
                                     * something like this: (?:|) So we can
                                     * turn it into a plain NOTHING op. */
                                    DEBUG_TRIE_COMPILE_r({
                                        regprop(RExC_rx, RExC_mysv, cur, NULL, pRExC_state);
                                        PerlIO_printf( Perl_debug_log,
                                          "%*s- %s (%d) <NOTHING BRANCH SEQUENCE>\n", (int)depth * 2 + 2,
                                          "", SvPV_nolen_const( RExC_mysv ),REG_NODE_NUM(cur));

                                    });
                                    OP(startbranch)= NOTHING;
                                    NEXT_OFF(startbranch)= tail - startbranch;
                                    for ( opt= startbranch + 1; opt < tail ; opt++ )
                                        OP(opt)= OPTIMIZED;
                                }
                            }
                        } /* end if ( last) */
                    } /* TRIE_MAXBUF is non zero */

                } /* do trie */

            }
            else if ( code == BRANCHJ ) {  /* single branch is optimized. */
                scan = NEXTOPER(NEXTOPER(scan));
            } else                      /* single branch is optimized. */
                scan = NEXTOPER(scan);
            continue;
        } else if (OP(scan) == SUSPEND || OP(scan) == GOSUB || OP(scan) == GOSTART) {
            I32 paren = 0;
            regnode *start = NULL;
            regnode *end = NULL;
            U32 my_recursed_depth= recursed_depth;


            if (OP(scan) != SUSPEND) { /* GOSUB/GOSTART */
                /* Do setup, note this code has side effects beyond
                 * the rest of this block. Specifically setting
                 * RExC_recurse[] must happen at least once during
                 * study_chunk(). */
                if (OP(scan) == GOSUB) {
                    paren = ARG(scan);
                    RExC_recurse[ARG2L(scan)] = scan;
                    start = RExC_open_parens[paren-1];
                    end   = RExC_close_parens[paren-1];
                } else {
                    start = RExC_rxi->program + 1;
                    end   = RExC_opend;
                }
                /* NOTE we MUST always execute the above code, even
                 * if we do nothing with a GOSUB/GOSTART */
                if (
                    ( flags & SCF_IN_DEFINE )
                    ||
                    (
                        (is_inf_internal || is_inf || (data && data->flags & SF_IS_INF))
                        &&
                        ( (flags & (SCF_DO_STCLASS | SCF_DO_SUBSTR)) == 0 )
                    )
                ) {
                    /* no need to do anything here if we are in a define. */
                    /* or we are after some kind of infinite construct
                     * so we can skip recursing into this item.
                     * Since it is infinite we will not change the maxlen
                     * or delta, and if we miss something that might raise
                     * the minlen it will merely pessimise a little.
                     *
                     * Iow /(?(DEFINE)(?<foo>foo|food))a+(?&foo)/
                     * might result in a minlen of 1 and not of 4,
                     * but this doesn't make us mismatch, just try a bit
                     * harder than we should.
                     * */
                    scan= regnext(scan);
                    continue;
                }

                if (
                    !recursed_depth
                    ||
                    !PAREN_TEST(RExC_study_chunk_recursed + ((recursed_depth-1) * RExC_study_chunk_recursed_bytes), paren)
                ) {
                    /* it is quite possible that there are more efficient ways
                     * to do this. We maintain a bitmap per level of recursion
                     * of which patterns we have entered so we can detect if a
                     * pattern creates a possible infinite loop. When we
                     * recurse down a level we copy the previous levels bitmap
                     * down. When we are at recursion level 0 we zero the top
                     * level bitmap. It would be nice to implement a different
                     * more efficient way of doing this. In particular the top
                     * level bitmap may be unnecessary.
                     */
                    if (!recursed_depth) {
                        Zero(RExC_study_chunk_recursed, RExC_study_chunk_recursed_bytes, U8);
                    } else {
                        Copy(RExC_study_chunk_recursed + ((recursed_depth-1) * RExC_study_chunk_recursed_bytes),
                             RExC_study_chunk_recursed + (recursed_depth * RExC_study_chunk_recursed_bytes),
                             RExC_study_chunk_recursed_bytes, U8);
                    }
                    /* we havent recursed into this paren yet, so recurse into it */
                    DEBUG_STUDYDATA("set:", data,depth);
                    PAREN_SET(RExC_study_chunk_recursed + (recursed_depth * RExC_study_chunk_recursed_bytes), paren);
                    my_recursed_depth= recursed_depth + 1;
                } else {
                    DEBUG_STUDYDATA("inf:", data,depth);
                    /* some form of infinite recursion, assume infinite length
                     * */
                    if (flags & SCF_DO_SUBSTR) {
                        scan_commit(pRExC_state, data, minlenp, is_inf);
                        data->longest = &(data->longest_float);
                    }
                    is_inf = is_inf_internal = 1;
                    if (flags & SCF_DO_STCLASS_OR) /* Allow everything */
                        ssc_anything(data->start_class);
                    flags &= ~SCF_DO_STCLASS;

                    start= NULL; /* reset start so we dont recurse later on. */
                }
            } else {
                paren = stopparen;
                start = scan + 2;
                end = regnext(scan);
            }
            if (start) {
                scan_frame *newframe;
                assert(end);
                if (!RExC_frame_last) {
                    Newxz(newframe, 1, scan_frame);
                    SAVEDESTRUCTOR_X(S_unwind_scan_frames, newframe);
                    RExC_frame_head= newframe;
                    RExC_frame_count++;
                } else if (!RExC_frame_last->next_frame) {
                    Newxz(newframe,1,scan_frame);
                    RExC_frame_last->next_frame= newframe;
                    newframe->prev_frame= RExC_frame_last;
                    RExC_frame_count++;
                } else {
                    newframe= RExC_frame_last->next_frame;
                }
                RExC_frame_last= newframe;

                newframe->next_regnode = regnext(scan);
                newframe->last_regnode = last;
                newframe->stopparen = stopparen;
                newframe->prev_recursed_depth = recursed_depth;
                newframe->this_prev_frame= frame;

                DEBUG_STUDYDATA("frame-new:",data,depth);
                DEBUG_PEEP("fnew", scan, depth);

                frame = newframe;
                scan =  start;
                stopparen = paren;
                last = end;
                depth = depth + 1;
                recursed_depth= my_recursed_depth;

                continue;
            }
        }
        else if (OP(scan) == EXACT || OP(scan) == EXACTL) {
            SSize_t l = STR_LEN(scan);
            UV uc;
            if (UTF) {
                const U8 * const s = (U8*)STRING(scan);
                uc = utf8_to_uvchr_buf(s, s + l, NULL);
                l = utf8_length(s, s + l);
            } else {
                uc = *((U8*)STRING(scan));
            }
            min += l;
            if (flags & SCF_DO_SUBSTR) { /* Update longest substr. */
                /* The code below prefers earlier match for fixed
                   offset, later match for variable offset.  */
                if (data->last_end == -1) { /* Update the start info. */
                    data->last_start_min = data->pos_min;
                    data->last_start_max = is_inf
                        ? SSize_t_MAX : data->pos_min + data->pos_delta;
                }
                sv_catpvn(data->last_found, STRING(scan), STR_LEN(scan));
                if (UTF)
                    SvUTF8_on(data->last_found);
                {
                    SV * const sv = data->last_found;
                    MAGIC * const mg = SvUTF8(sv) && SvMAGICAL(sv) ?
                        mg_find(sv, PERL_MAGIC_utf8) : NULL;
                    if (mg && mg->mg_len >= 0)
                        mg->mg_len += utf8_length((U8*)STRING(scan),
                                              (U8*)STRING(scan)+STR_LEN(scan));
                }
                data->last_end = data->pos_min + l;
                data->pos_min += l; /* As in the first entry. */
                data->flags &= ~SF_BEFORE_EOL;
            }

            /* ANDing the code point leaves at most it, and not in locale, and
             * can't match null string */
            if (flags & SCF_DO_STCLASS_AND) {
                ssc_cp_and(data->start_class, uc);
                ANYOF_FLAGS(data->start_class) &= ~SSC_MATCHES_EMPTY_STRING;
                ssc_clear_locale(data->start_class);
            }
            else if (flags & SCF_DO_STCLASS_OR) {
                ssc_add_cp(data->start_class, uc);
                ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);

                /* See commit msg 749e076fceedeb708a624933726e7989f2302f6a */
                ANYOF_FLAGS(data->start_class) &= ~SSC_MATCHES_EMPTY_STRING;
            }
            flags &= ~SCF_DO_STCLASS;
        }
        else if (PL_regkind[OP(scan)] == EXACT) {
            /* But OP != EXACT!, so is EXACTFish */
            SSize_t l = STR_LEN(scan);
            const U8 * s = (U8*)STRING(scan);

            /* Search for fixed substrings supports EXACT only. */
            if (flags & SCF_DO_SUBSTR) {
                assert(data);
                scan_commit(pRExC_state, data, minlenp, is_inf);
            }
            if (UTF) {
                l = utf8_length(s, s + l);
            }
            if (unfolded_multi_char) {
                RExC_seen |= REG_UNFOLDED_MULTI_SEEN;
            }
            min += l - min_subtract;
            assert (min >= 0);
            delta += min_subtract;
            if (flags & SCF_DO_SUBSTR) {
                data->pos_min += l - min_subtract;
                if (data->pos_min < 0) {
                    data->pos_min = 0;
                }
                data->pos_delta += min_subtract;
                if (min_subtract) {
                    data->longest = &(data->longest_float);
                }
            }

            if (flags & SCF_DO_STCLASS) {
                SV* EXACTF_invlist = _make_exactf_invlist(pRExC_state, scan);

                assert(EXACTF_invlist);
                if (flags & SCF_DO_STCLASS_AND) {
                    if (OP(scan) != EXACTFL)
                        ssc_clear_locale(data->start_class);
                    ANYOF_FLAGS(data->start_class) &= ~SSC_MATCHES_EMPTY_STRING;
                    ANYOF_POSIXL_ZERO(data->start_class);
                    ssc_intersection(data->start_class, EXACTF_invlist, FALSE);
                }
                else {  /* SCF_DO_STCLASS_OR */
                    ssc_union(data->start_class, EXACTF_invlist, FALSE);
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);

                    /* See commit msg 749e076fceedeb708a624933726e7989f2302f6a */
                    ANYOF_FLAGS(data->start_class) &= ~SSC_MATCHES_EMPTY_STRING;
                }
                flags &= ~SCF_DO_STCLASS;
                SvREFCNT_dec(EXACTF_invlist);
            }
        }
        else if (REGNODE_VARIES(OP(scan))) {
            SSize_t mincount, maxcount, minnext, deltanext, pos_before = 0;
            I32 fl = 0, f = flags;
            regnode * const oscan = scan;
            regnode_ssc this_class;
            regnode_ssc *oclass = NULL;
            I32 next_is_eval = 0;

            switch (PL_regkind[OP(scan)]) {
            case WHILEM:                /* End of (?:...)* . */
                scan = NEXTOPER(scan);
                goto finish;
            case PLUS:
                if (flags & (SCF_DO_SUBSTR | SCF_DO_STCLASS)) {
                    next = NEXTOPER(scan);
                    if (OP(next) == EXACT
                        || OP(next) == EXACTL
                        || (flags & SCF_DO_STCLASS))
                    {
                        mincount = 1;
                        maxcount = REG_INFTY;
                        next = regnext(scan);
                        scan = NEXTOPER(scan);
                        goto do_curly;
                    }
                }
                if (flags & SCF_DO_SUBSTR)
                    data->pos_min++;
                min++;
                /* FALLTHROUGH */
            case STAR:
                if (flags & SCF_DO_STCLASS) {
                    mincount = 0;
                    maxcount = REG_INFTY;
                    next = regnext(scan);
                    scan = NEXTOPER(scan);
                    goto do_curly;
                }
                if (flags & SCF_DO_SUBSTR) {
                    scan_commit(pRExC_state, data, minlenp, is_inf);
                    /* Cannot extend fixed substrings */
                    data->longest = &(data->longest_float);
                }
                is_inf = is_inf_internal = 1;
                scan = regnext(scan);
                goto optimize_curly_tail;
            case CURLY:
                if (stopparen>0 && (OP(scan)==CURLYN || OP(scan)==CURLYM)
                    && (scan->flags == stopparen))
                {
                    mincount = 1;
                    maxcount = 1;
                } else {
                    mincount = ARG1(scan);
                    maxcount = ARG2(scan);
                }
                next = regnext(scan);
                if (OP(scan) == CURLYX) {
                    I32 lp = (data ? *(data->last_closep) : 0);
                    scan->flags = ((lp <= (I32)U8_MAX) ? (U8)lp : U8_MAX);
                }
                scan = NEXTOPER(scan) + EXTRA_STEP_2ARGS;
                next_is_eval = (OP(scan) == EVAL);
              do_curly:
                if (flags & SCF_DO_SUBSTR) {
                    if (mincount == 0)
                        scan_commit(pRExC_state, data, minlenp, is_inf);
                    /* Cannot extend fixed substrings */
                    pos_before = data->pos_min;
                }
                if (data) {
                    fl = data->flags;
                    data->flags &= ~(SF_HAS_PAR|SF_IN_PAR|SF_HAS_EVAL);
                    if (is_inf)
                        data->flags |= SF_IS_INF;
                }
                if (flags & SCF_DO_STCLASS) {
                    ssc_init(pRExC_state, &this_class);
                    oclass = data->start_class;
                    data->start_class = &this_class;
                    f |= SCF_DO_STCLASS_AND;
                    f &= ~SCF_DO_STCLASS_OR;
                }
                /* Exclude from super-linear cache processing any {n,m}
                   regops for which the combination of input pos and regex
                   pos is not enough information to determine if a match
                   will be possible.

                   For example, in the regex /foo(bar\s*){4,8}baz/ with the
                   regex pos at the \s*, the prospects for a match depend not
                   only on the input position but also on how many (bar\s*)
                   repeats into the {4,8} we are. */
               if ((mincount > 1) || (maxcount > 1 && maxcount != REG_INFTY))
                    f &= ~SCF_WHILEM_VISITED_POS;

                /* This will finish on WHILEM, setting scan, or on NULL: */
                minnext = study_chunk(pRExC_state, &scan, minlenp, &deltanext,
                                  last, data, stopparen, recursed_depth, NULL,
                                  (mincount == 0
                                   ? (f & ~SCF_DO_SUBSTR)
                                   : f)
                                  ,depth+1);

                if (flags & SCF_DO_STCLASS)
                    data->start_class = oclass;
                if (mincount == 0 || minnext == 0) {
                    if (flags & SCF_DO_STCLASS_OR) {
                        ssc_or(pRExC_state, data->start_class, (regnode_charclass *) &this_class);
                    }
                    else if (flags & SCF_DO_STCLASS_AND) {
                        /* Switch to OR mode: cache the old value of
                         * data->start_class */
                        INIT_AND_WITHP;
                        StructCopy(data->start_class, and_withp, regnode_ssc);
                        flags &= ~SCF_DO_STCLASS_AND;
                        StructCopy(&this_class, data->start_class, regnode_ssc);
                        flags |= SCF_DO_STCLASS_OR;
                        ANYOF_FLAGS(data->start_class)
                                                |= SSC_MATCHES_EMPTY_STRING;
                    }
                } else {                /* Non-zero len */
                    if (flags & SCF_DO_STCLASS_OR) {
                        ssc_or(pRExC_state, data->start_class, (regnode_charclass *) &this_class);
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);
                    }
                    else if (flags & SCF_DO_STCLASS_AND)
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &this_class);
                    flags &= ~SCF_DO_STCLASS;
                }
                if (!scan)              /* It was not CURLYX, but CURLY. */
                    scan = next;
                if (!(flags & SCF_TRIE_DOING_RESTUDY)
                    /* ? quantifier ok, except for (?{ ... }) */
                    && (next_is_eval || !(mincount == 0 && maxcount == 1))
                    && (minnext == 0) && (deltanext == 0)
                    && data && !(data->flags & (SF_HAS_PAR|SF_IN_PAR))
                    && maxcount <= REG_INFTY/3) /* Complement check for big
                                                   count */
                {
                    /* Fatal warnings may leak the regexp without this: */
                    SAVEFREESV(RExC_rx_sv);
                    Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),
                        "Quantifier unexpected on zero-length expression "
                        "in regex m/%"UTF8f"/",
                         UTF8fARG(UTF, RExC_precomp_end - RExC_precomp,
                                  RExC_precomp));
                    (void)ReREFCNT_inc(RExC_rx_sv);
                }

                min += minnext * mincount;
                is_inf_internal |= deltanext == SSize_t_MAX
                         || (maxcount == REG_INFTY && minnext + deltanext > 0);
                is_inf |= is_inf_internal;
                if (is_inf) {
                    delta = SSize_t_MAX;
                } else {
                    delta += (minnext + deltanext) * maxcount
                             - minnext * mincount;
                }
                /* Try powerful optimization CURLYX => CURLYN. */
                if (  OP(oscan) == CURLYX && data
                      && data->flags & SF_IN_PAR
                      && !(data->flags & SF_HAS_EVAL)
                      && !deltanext && minnext == 1 ) {
                    /* Try to optimize to CURLYN.  */
                    regnode *nxt = NEXTOPER(oscan) + EXTRA_STEP_2ARGS;
                    regnode * const nxt1 = nxt;
#ifdef DEBUGGING
                    regnode *nxt2;
#endif

                    /* Skip open. */
                    nxt = regnext(nxt);
                    if (!REGNODE_SIMPLE(OP(nxt))
                        && !(PL_regkind[OP(nxt)] == EXACT
                             && STR_LEN(nxt) == 1))
                        goto nogo;
#ifdef DEBUGGING
                    nxt2 = nxt;
#endif
                    nxt = regnext(nxt);
                    if (OP(nxt) != CLOSE)
                        goto nogo;
                    if (RExC_open_parens) {
                        RExC_open_parens[ARG(nxt1)-1]=oscan; /*open->CURLYM*/
                        RExC_close_parens[ARG(nxt1)-1]=nxt+2; /*close->while*/
                    }
                    /* Now we know that nxt2 is the only contents: */
                    oscan->flags = (U8)ARG(nxt);
                    OP(oscan) = CURLYN;
                    OP(nxt1) = NOTHING; /* was OPEN. */

#ifdef DEBUGGING
                    OP(nxt1 + 1) = OPTIMIZED; /* was count. */
                    NEXT_OFF(nxt1+ 1) = 0; /* just for consistency. */
                    NEXT_OFF(nxt2) = 0; /* just for consistency with CURLY. */
                    OP(nxt) = OPTIMIZED;        /* was CLOSE. */
                    OP(nxt + 1) = OPTIMIZED; /* was count. */
                    NEXT_OFF(nxt+ 1) = 0; /* just for consistency. */
#endif
                }
              nogo:

                /* Try optimization CURLYX => CURLYM. */
                if (  OP(oscan) == CURLYX && data
                      && !(data->flags & SF_HAS_PAR)
                      && !(data->flags & SF_HAS_EVAL)
                      && !deltanext     /* atom is fixed width */
                      && minnext != 0   /* CURLYM can't handle zero width */

                         /* Nor characters whose fold at run-time may be
                          * multi-character */
                      && ! (RExC_seen & REG_UNFOLDED_MULTI_SEEN)
                ) {
                    /* XXXX How to optimize if data == 0? */
                    /* Optimize to a simpler form.  */
                    regnode *nxt = NEXTOPER(oscan) + EXTRA_STEP_2ARGS; /* OPEN */
                    regnode *nxt2;

                    OP(oscan) = CURLYM;
                    while ( (nxt2 = regnext(nxt)) /* skip over embedded stuff*/
                            && (OP(nxt2) != WHILEM))
                        nxt = nxt2;
                    OP(nxt2)  = SUCCEED; /* Whas WHILEM */
                    /* Need to optimize away parenths. */
                    if ((data->flags & SF_IN_PAR) && OP(nxt) == CLOSE) {
                        /* Set the parenth number.  */
                        regnode *nxt1 = NEXTOPER(oscan) + EXTRA_STEP_2ARGS; /* OPEN*/

                        oscan->flags = (U8)ARG(nxt);
                        if (RExC_open_parens) {
                            RExC_open_parens[ARG(nxt1)-1]=oscan; /*open->CURLYM*/
                            RExC_close_parens[ARG(nxt1)-1]=nxt2+1; /*close->NOTHING*/
                        }
                        OP(nxt1) = OPTIMIZED;   /* was OPEN. */
                        OP(nxt) = OPTIMIZED;    /* was CLOSE. */

#ifdef DEBUGGING
                        OP(nxt1 + 1) = OPTIMIZED; /* was count. */
                        OP(nxt + 1) = OPTIMIZED; /* was count. */
                        NEXT_OFF(nxt1 + 1) = 0; /* just for consistency. */
                        NEXT_OFF(nxt + 1) = 0; /* just for consistency. */
#endif
#if 0
                        while ( nxt1 && (OP(nxt1) != WHILEM)) {
                            regnode *nnxt = regnext(nxt1);
                            if (nnxt == nxt) {
                                if (reg_off_by_arg[OP(nxt1)])
                                    ARG_SET(nxt1, nxt2 - nxt1);
                                else if (nxt2 - nxt1 < U16_MAX)
                                    NEXT_OFF(nxt1) = nxt2 - nxt1;
                                else
                                    OP(nxt) = NOTHING;  /* Cannot beautify */
                            }
                            nxt1 = nnxt;
                        }
#endif
                        /* Optimize again: */
                        study_chunk(pRExC_state, &nxt1, minlenp, &deltanext, nxt,
                                    NULL, stopparen, recursed_depth, NULL, 0,depth+1);
                    }
                    else
                        oscan->flags = 0;
                }
                else if ((OP(oscan) == CURLYX)
                         && (flags & SCF_WHILEM_VISITED_POS)
                         /* See the comment on a similar expression above.
                            However, this time it's not a subexpression
                            we care about, but the expression itself. */
                         && (maxcount == REG_INFTY)
                         && data && ++data->whilem_c < 16) {
                    /* This stays as CURLYX, we can put the count/of pair. */
                    /* Find WHILEM (as in regexec.c) */
                    regnode *nxt = oscan + NEXT_OFF(oscan);

                    if (OP(PREVOPER(nxt)) == NOTHING) /* LONGJMP */
                        nxt += ARG(nxt);
                    PREVOPER(nxt)->flags = (U8)(data->whilem_c
                        | (RExC_whilem_seen << 4)); /* On WHILEM */
                }
                if (data && fl & (SF_HAS_PAR|SF_IN_PAR))
                    pars++;
                if (flags & SCF_DO_SUBSTR) {
                    SV *last_str = NULL;
                    STRLEN last_chrs = 0;
                    int counted = mincount != 0;

                    if (data->last_end > 0 && mincount != 0) { /* Ends with a
                                                                  string. */
                        SSize_t b = pos_before >= data->last_start_min
                            ? pos_before : data->last_start_min;
                        STRLEN l;
                        const char * const s = SvPV_const(data->last_found, l);
                        SSize_t old = b - data->last_start_min;

                        if (UTF)
                            old = utf8_hop((U8*)s, old) - (U8*)s;
                        l -= old;
                        /* Get the added string: */
                        last_str = newSVpvn_utf8(s  + old, l, UTF);
                        last_chrs = UTF ? utf8_length((U8*)(s + old),
                                            (U8*)(s + old + l)) : l;
                        if (deltanext == 0 && pos_before == b) {
                            /* What was added is a constant string */
                            if (mincount > 1) {

                                SvGROW(last_str, (mincount * l) + 1);
                                repeatcpy(SvPVX(last_str) + l,
                                          SvPVX_const(last_str), l,
                                          mincount - 1);
                                SvCUR_set(last_str, SvCUR(last_str) * mincount);
                                /* Add additional parts. */
                                SvCUR_set(data->last_found,
                                          SvCUR(data->last_found) - l);
                                sv_catsv(data->last_found, last_str);
                                {
                                    SV * sv = data->last_found;
                                    MAGIC *mg =
                                        SvUTF8(sv) && SvMAGICAL(sv) ?
                                        mg_find(sv, PERL_MAGIC_utf8) : NULL;
                                    if (mg && mg->mg_len >= 0)
                                        mg->mg_len += last_chrs * (mincount-1);
                                }
                                last_chrs *= mincount;
                                data->last_end += l * (mincount - 1);
                            }
                        } else {
                            /* start offset must point into the last copy */
                            data->last_start_min += minnext * (mincount - 1);
                            data->last_start_max =
                              is_inf
                               ? SSize_t_MAX
                               : data->last_start_max +
                                 (maxcount - 1) * (minnext + data->pos_delta);
                        }
                    }
                    /* It is counted once already... */
                    data->pos_min += minnext * (mincount - counted);
#if 0
PerlIO_printf(Perl_debug_log, "counted=%"UVuf" deltanext=%"UVuf
                              " SSize_t_MAX=%"UVuf" minnext=%"UVuf
                              " maxcount=%"UVuf" mincount=%"UVuf"\n",
    (UV)counted, (UV)deltanext, (UV)SSize_t_MAX, (UV)minnext, (UV)maxcount,
    (UV)mincount);
if (deltanext != SSize_t_MAX)
PerlIO_printf(Perl_debug_log, "LHS=%"UVuf" RHS=%"UVuf"\n",
    (UV)(-counted * deltanext + (minnext + deltanext) * maxcount
          - minnext * mincount), (UV)(SSize_t_MAX - data->pos_delta));
#endif
                    if (deltanext == SSize_t_MAX
                        || -counted * deltanext + (minnext + deltanext) * maxcount - minnext * mincount >= SSize_t_MAX - data->pos_delta)
                        data->pos_delta = SSize_t_MAX;
                    else
                        data->pos_delta += - counted * deltanext +
                        (minnext + deltanext) * maxcount - minnext * mincount;
                    if (mincount != maxcount) {
                         /* Cannot extend fixed substrings found inside
                            the group.  */
                        scan_commit(pRExC_state, data, minlenp, is_inf);
                        if (mincount && last_str) {
                            SV * const sv = data->last_found;
                            MAGIC * const mg = SvUTF8(sv) && SvMAGICAL(sv) ?
                                mg_find(sv, PERL_MAGIC_utf8) : NULL;

                            if (mg)
                                mg->mg_len = -1;
                            sv_setsv(sv, last_str);
                            data->last_end = data->pos_min;
                            data->last_start_min = data->pos_min - last_chrs;
                            data->last_start_max = is_inf
                                ? SSize_t_MAX
                                : data->pos_min + data->pos_delta - last_chrs;
                        }
                        data->longest = &(data->longest_float);
                    }
                    SvREFCNT_dec(last_str);
                }
                if (data && (fl & SF_HAS_EVAL))
                    data->flags |= SF_HAS_EVAL;
              optimize_curly_tail:
                if (OP(oscan) != CURLYX) {
                    while (PL_regkind[OP(next = regnext(oscan))] == NOTHING
                           && NEXT_OFF(next))
                        NEXT_OFF(oscan) += NEXT_OFF(next);
                }
                continue;

            default:
#ifdef DEBUGGING
                Perl_croak(aTHX_ "panic: unexpected varying REx opcode %d",
                                                                    OP(scan));
#endif
            case REF:
            case CLUMP:
                if (flags & SCF_DO_SUBSTR) {
                    /* Cannot expect anything... */
                    scan_commit(pRExC_state, data, minlenp, is_inf);
                    data->longest = &(data->longest_float);
                }
                is_inf = is_inf_internal = 1;
                if (flags & SCF_DO_STCLASS_OR) {
                    if (OP(scan) == CLUMP) {
                        /* Actually is any start char, but very few code points
                         * aren't start characters */
                        ssc_match_all_cp(data->start_class);
                    }
                    else {
                        ssc_anything(data->start_class);
                    }
                }
                flags &= ~SCF_DO_STCLASS;
                break;
            }
        }
        else if (OP(scan) == LNBREAK) {
            if (flags & SCF_DO_STCLASS) {
                if (flags & SCF_DO_STCLASS_AND) {
                    ssc_intersection(data->start_class,
                                    PL_XPosix_ptrs[_CC_VERTSPACE], FALSE);
                    ssc_clear_locale(data->start_class);
                    ANYOF_FLAGS(data->start_class)
                                                &= ~SSC_MATCHES_EMPTY_STRING;
                }
                else if (flags & SCF_DO_STCLASS_OR) {
                    ssc_union(data->start_class,
                              PL_XPosix_ptrs[_CC_VERTSPACE],
                              FALSE);
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);

                    /* See commit msg for
                     * 749e076fceedeb708a624933726e7989f2302f6a */
                    ANYOF_FLAGS(data->start_class)
                                                &= ~SSC_MATCHES_EMPTY_STRING;
                }
                flags &= ~SCF_DO_STCLASS;
            }
            min++;
            if (delta != SSize_t_MAX)
                delta++;    /* Because of the 2 char string cr-lf */
            if (flags & SCF_DO_SUBSTR) {
                /* Cannot expect anything... */
                scan_commit(pRExC_state, data, minlenp, is_inf);
                data->pos_min += 1;
                data->pos_delta += 1;
                data->longest = &(data->longest_float);
            }
        }
        else if (REGNODE_SIMPLE(OP(scan))) {

            if (flags & SCF_DO_SUBSTR) {
                scan_commit(pRExC_state, data, minlenp, is_inf);
                data->pos_min++;
            }
            min++;
            if (flags & SCF_DO_STCLASS) {
                bool invert = 0;
                SV* my_invlist = NULL;
                U8 namedclass;

                /* See commit msg 749e076fceedeb708a624933726e7989f2302f6a */
                ANYOF_FLAGS(data->start_class) &= ~SSC_MATCHES_EMPTY_STRING;

                /* Some of the logic below assumes that switching
                   locale on will only add false positives. */
                switch (OP(scan)) {

                default:
#ifdef DEBUGGING
                   Perl_croak(aTHX_ "panic: unexpected simple REx opcode %d",
                                                                     OP(scan));
#endif
                case SANY:
                    if (flags & SCF_DO_STCLASS_OR) /* Allow everything */
                        ssc_match_all_cp(data->start_class);
                    break;

                case REG_ANY:
                    {
                        SV* REG_ANY_invlist = _new_invlist(2);
                        REG_ANY_invlist = add_cp_to_invlist(REG_ANY_invlist,
                                                            '\n');
                        if (flags & SCF_DO_STCLASS_OR) {
                            ssc_union(data->start_class,
                                      REG_ANY_invlist,
                                      TRUE /* TRUE => invert, hence all but \n
                                            */
                                      );
                        }
                        else if (flags & SCF_DO_STCLASS_AND) {
                            ssc_intersection(data->start_class,
                                             REG_ANY_invlist,
                                             TRUE  /* TRUE => invert */
                                             );
                            ssc_clear_locale(data->start_class);
                        }
                        SvREFCNT_dec_NN(REG_ANY_invlist);
                    }
                    break;

                case ANYOFD:
                case ANYOFL:
                case ANYOF:
                    if (flags & SCF_DO_STCLASS_AND)
                        ssc_and(pRExC_state, data->start_class,
                                (regnode_charclass *) scan);
                    else
                        ssc_or(pRExC_state, data->start_class,
                                                          (regnode_charclass *) scan);
                    break;

                case NPOSIXL:
                    invert = 1;
                    /* FALLTHROUGH */

                case POSIXL:
                    namedclass = classnum_to_namedclass(FLAGS(scan)) + invert;
                    if (flags & SCF_DO_STCLASS_AND) {
                        bool was_there = cBOOL(
                                          ANYOF_POSIXL_TEST(data->start_class,
                                                                 namedclass));
                        ANYOF_POSIXL_ZERO(data->start_class);
                        if (was_there) {    /* Do an AND */
                            ANYOF_POSIXL_SET(data->start_class, namedclass);
                        }
                        /* No individual code points can now match */
                        data->start_class->invlist
                                                = sv_2mortal(_new_invlist(0));
                    }
                    else {
                        int complement = namedclass + ((invert) ? -1 : 1);

                        assert(flags & SCF_DO_STCLASS_OR);

                        /* If the complement of this class was already there,
                         * the result is that they match all code points,
                         * (\d + \D == everything).  Remove the classes from
                         * future consideration.  Locale is not relevant in
                         * this case */
                        if (ANYOF_POSIXL_TEST(data->start_class, complement)) {
                            ssc_match_all_cp(data->start_class);
                            ANYOF_POSIXL_CLEAR(data->start_class, namedclass);
                            ANYOF_POSIXL_CLEAR(data->start_class, complement);
                        }
                        else {  /* The usual case; just add this class to the
                                   existing set */
                            ANYOF_POSIXL_SET(data->start_class, namedclass);
                        }
                    }
                    break;

                case NPOSIXA:   /* For these, we always know the exact set of
                                   what's matched */
                    invert = 1;
                    /* FALLTHROUGH */
                case POSIXA:
                    if (FLAGS(scan) == _CC_ASCII) {
                        my_invlist = invlist_clone(PL_XPosix_ptrs[_CC_ASCII]);
                    }
                    else {
                        _invlist_intersection(PL_XPosix_ptrs[FLAGS(scan)],
                                              PL_XPosix_ptrs[_CC_ASCII],
                                              &my_invlist);
                    }
                    goto join_posix;

                case NPOSIXD:
                case NPOSIXU:
                    invert = 1;
                    /* FALLTHROUGH */
                case POSIXD:
                case POSIXU:
                    my_invlist = invlist_clone(PL_XPosix_ptrs[FLAGS(scan)]);

                    /* NPOSIXD matches all upper Latin1 code points unless the
                     * target string being matched is UTF-8, which is
                     * unknowable until match time.  Since we are going to
                     * invert, we want to get rid of all of them so that the
                     * inversion will match all */
                    if (OP(scan) == NPOSIXD) {
                        _invlist_subtract(my_invlist, PL_UpperLatin1,
                                          &my_invlist);
                    }

                  join_posix:

                    if (flags & SCF_DO_STCLASS_AND) {
                        ssc_intersection(data->start_class, my_invlist, invert);
                        ssc_clear_locale(data->start_class);
                    }
                    else {
                        assert(flags & SCF_DO_STCLASS_OR);
                        ssc_union(data->start_class, my_invlist, invert);
                    }
                    SvREFCNT_dec(my_invlist);
                }
                if (flags & SCF_DO_STCLASS_OR)
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);
                flags &= ~SCF_DO_STCLASS;
            }
        }
        else if (PL_regkind[OP(scan)] == EOL && flags & SCF_DO_SUBSTR) {
            data->flags |= (OP(scan) == MEOL
                            ? SF_BEFORE_MEOL
                            : SF_BEFORE_SEOL);
            scan_commit(pRExC_state, data, minlenp, is_inf);

        }
        else if (  PL_regkind[OP(scan)] == BRANCHJ
                 /* Lookbehind, or need to calculate parens/evals/stclass: */
                   && (scan->flags || data || (flags & SCF_DO_STCLASS))
                   && (OP(scan) == IFMATCH || OP(scan) == UNLESSM))
        {
            if ( !PERL_ENABLE_POSITIVE_ASSERTION_STUDY
                || OP(scan) == UNLESSM )
            {
                /* Negative Lookahead/lookbehind
                   In this case we can't do fixed string optimisation.
                */

                SSize_t deltanext, minnext, fake = 0;
                regnode *nscan;
                regnode_ssc intrnl;
                int f = 0;

                StructCopy(&zero_scan_data, &data_fake, scan_data_t);
                if (data) {
                    data_fake.whilem_c = data->whilem_c;
                    data_fake.last_closep = data->last_closep;
                }
                else
                    data_fake.last_closep = &fake;
                data_fake.pos_delta = delta;
                if ( flags & SCF_DO_STCLASS && !scan->flags
                     && OP(scan) == IFMATCH ) { /* Lookahead */
                    ssc_init(pRExC_state, &intrnl);
                    data_fake.start_class = &intrnl;
                    f |= SCF_DO_STCLASS_AND;
                }
                if (flags & SCF_WHILEM_VISITED_POS)
                    f |= SCF_WHILEM_VISITED_POS;
                next = regnext(scan);
                nscan = NEXTOPER(NEXTOPER(scan));
                minnext = study_chunk(pRExC_state, &nscan, minlenp, &deltanext,
                                      last, &data_fake, stopparen,
                                      recursed_depth, NULL, f, depth+1);
                if (scan->flags) {
                    if (deltanext) {
                        FAIL("Variable length lookbehind not implemented");
                    }
                    else if (minnext > (I32)U8_MAX) {
                        FAIL2("Lookbehind longer than %"UVuf" not implemented",
                              (UV)U8_MAX);
                    }
                    scan->flags = (U8)minnext;
                }
                if (data) {
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SF_HAS_EVAL)
                        data->flags |= SF_HAS_EVAL;
                    data->whilem_c = data_fake.whilem_c;
                }
                if (f & SCF_DO_STCLASS_AND) {
                    if (flags & SCF_DO_STCLASS_OR) {
                        /* OR before, AND after: ideally we would recurse with
                         * data_fake to get the AND applied by study of the
                         * remainder of the pattern, and then derecurse;
                         * *** HACK *** for now just treat as "no information".
                         * See [perl #56690].
                         */
                        ssc_init(pRExC_state, data->start_class);
                    }  else {
                        /* AND before and after: combine and continue.  These
                         * assertions are zero-length, so can match an EMPTY
                         * string */
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &intrnl);
                        ANYOF_FLAGS(data->start_class)
                                                   |= SSC_MATCHES_EMPTY_STRING;
                    }
                }
            }
#if PERL_ENABLE_POSITIVE_ASSERTION_STUDY
            else {
                /* Positive Lookahead/lookbehind
                   In this case we can do fixed string optimisation,
                   but we must be careful about it. Note in the case of
                   lookbehind the positions will be offset by the minimum
                   length of the pattern, something we won't know about
                   until after the recurse.
                */
                SSize_t deltanext, fake = 0;
                regnode *nscan;
                regnode_ssc intrnl;
                int f = 0;
                /* We use SAVEFREEPV so that when the full compile
                    is finished perl will clean up the allocated
                    minlens when it's all done. This way we don't
                    have to worry about freeing them when we know
                    they wont be used, which would be a pain.
                 */
                SSize_t *minnextp;
                Newx( minnextp, 1, SSize_t );
                SAVEFREEPV(minnextp);

                if (data) {
                    StructCopy(data, &data_fake, scan_data_t);
                    if ((flags & SCF_DO_SUBSTR) && data->last_found) {
                        f |= SCF_DO_SUBSTR;
                        if (scan->flags)
                            scan_commit(pRExC_state, &data_fake, minlenp, is_inf);
                        data_fake.last_found=newSVsv(data->last_found);
                    }
                }
                else
                    data_fake.last_closep = &fake;
                data_fake.flags = 0;
                data_fake.pos_delta = delta;
                if (is_inf)
                    data_fake.flags |= SF_IS_INF;
                if ( flags & SCF_DO_STCLASS && !scan->flags
                     && OP(scan) == IFMATCH ) { /* Lookahead */
                    ssc_init(pRExC_state, &intrnl);
                    data_fake.start_class = &intrnl;
                    f |= SCF_DO_STCLASS_AND;
                }
                if (flags & SCF_WHILEM_VISITED_POS)
                    f |= SCF_WHILEM_VISITED_POS;
                next = regnext(scan);
                nscan = NEXTOPER(NEXTOPER(scan));

                *minnextp = study_chunk(pRExC_state, &nscan, minnextp,
                                        &deltanext, last, &data_fake,
                                        stopparen, recursed_depth, NULL,
                                        f,depth+1);
                if (scan->flags) {
                    if (deltanext) {
                        FAIL("Variable length lookbehind not implemented");
                    }
                    else if (*minnextp > (I32)U8_MAX) {
                        FAIL2("Lookbehind longer than %"UVuf" not implemented",
                              (UV)U8_MAX);
                    }
                    scan->flags = (U8)*minnextp;
                }

                *minnextp += min;

                if (f & SCF_DO_STCLASS_AND) {
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &intrnl);
                    ANYOF_FLAGS(data->start_class) |= SSC_MATCHES_EMPTY_STRING;
                }
                if (data) {
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SF_HAS_EVAL)
                        data->flags |= SF_HAS_EVAL;
                    data->whilem_c = data_fake.whilem_c;
                    if ((flags & SCF_DO_SUBSTR) && data_fake.last_found) {
                        if (RExC_rx->minlen<*minnextp)
                            RExC_rx->minlen=*minnextp;
                        scan_commit(pRExC_state, &data_fake, minnextp, is_inf);
                        SvREFCNT_dec_NN(data_fake.last_found);

                        if ( data_fake.minlen_fixed != minlenp )
                        {
                            data->offset_fixed= data_fake.offset_fixed;
                            data->minlen_fixed= data_fake.minlen_fixed;
                            data->lookbehind_fixed+= scan->flags;
                        }
                        if ( data_fake.minlen_float != minlenp )
                        {
                            data->minlen_float= data_fake.minlen_float;
                            data->offset_float_min=data_fake.offset_float_min;
                            data->offset_float_max=data_fake.offset_float_max;
                            data->lookbehind_float+= scan->flags;
                        }
                    }
                }
            }
#endif
        }
        else if (OP(scan) == OPEN) {
            if (stopparen != (I32)ARG(scan))
                pars++;
        }
        else if (OP(scan) == CLOSE) {
            if (stopparen == (I32)ARG(scan)) {
                break;
            }
            if ((I32)ARG(scan) == is_par) {
                next = regnext(scan);

                if ( next && (OP(next) != WHILEM) && next < last)
                    is_par = 0;         /* Disable optimization */
            }
            if (data)
                *(data->last_closep) = ARG(scan);
        }
        else if (OP(scan) == EVAL) {
                if (data)
                    data->flags |= SF_HAS_EVAL;
        }
        else if ( PL_regkind[OP(scan)] == ENDLIKE ) {
            if (flags & SCF_DO_SUBSTR) {
                scan_commit(pRExC_state, data, minlenp, is_inf);
                flags &= ~SCF_DO_SUBSTR;
            }
            if (data && OP(scan)==ACCEPT) {
                data->flags |= SCF_SEEN_ACCEPT;
                if (stopmin > min)
                    stopmin = min;
            }
        }
        else if (OP(scan) == LOGICAL && scan->flags == 2) /* Embedded follows */
        {
                if (flags & SCF_DO_SUBSTR) {
                    scan_commit(pRExC_state, data, minlenp, is_inf);
                    data->longest = &(data->longest_float);
                }
                is_inf = is_inf_internal = 1;
                if (flags & SCF_DO_STCLASS_OR) /* Allow everything */
                    ssc_anything(data->start_class);
                flags &= ~SCF_DO_STCLASS;
        }
        else if (OP(scan) == GPOS) {
            if (!(RExC_rx->intflags & PREGf_GPOS_FLOAT) &&
                !(delta || is_inf || (data && data->pos_delta)))
            {
                if (!(RExC_rx->intflags & PREGf_ANCH) && (flags & SCF_DO_SUBSTR))
                    RExC_rx->intflags |= PREGf_ANCH_GPOS;
                if (RExC_rx->gofs < (STRLEN)min)
                    RExC_rx->gofs = min;
            } else {
                RExC_rx->intflags |= PREGf_GPOS_FLOAT;
                RExC_rx->gofs = 0;
            }
        }
#ifdef TRIE_STUDY_OPT
#ifdef FULL_TRIE_STUDY
        else if (PL_regkind[OP(scan)] == TRIE) {
            /* NOTE - There is similar code to this block above for handling
               BRANCH nodes on the initial study.  If you change stuff here
               check there too. */
            regnode *trie_node= scan;
            regnode *tail= regnext(scan);
            reg_trie_data *trie = (reg_trie_data*)RExC_rxi->data->data[ ARG(scan) ];
            SSize_t max1 = 0, min1 = SSize_t_MAX;
            regnode_ssc accum;

            if (flags & SCF_DO_SUBSTR) { /* XXXX Add !SUSPEND? */
                /* Cannot merge strings after this. */
                scan_commit(pRExC_state, data, minlenp, is_inf);
            }
            if (flags & SCF_DO_STCLASS)
                ssc_init_zero(pRExC_state, &accum);

            if (!trie->jump) {
                min1= trie->minlen;
                max1= trie->maxlen;
            } else {
                const regnode *nextbranch= NULL;
                U32 word;

                for ( word=1 ; word <= trie->wordcount ; word++)
                {
                    SSize_t deltanext=0, minnext=0, f = 0, fake;
                    regnode_ssc this_class;

                    StructCopy(&zero_scan_data, &data_fake, scan_data_t);
                    if (data) {
                        data_fake.whilem_c = data->whilem_c;
                        data_fake.last_closep = data->last_closep;
                    }
                    else
                        data_fake.last_closep = &fake;
                    data_fake.pos_delta = delta;
                    if (flags & SCF_DO_STCLASS) {
                        ssc_init(pRExC_state, &this_class);
                        data_fake.start_class = &this_class;
                        f = SCF_DO_STCLASS_AND;
                    }
                    if (flags & SCF_WHILEM_VISITED_POS)
                        f |= SCF_WHILEM_VISITED_POS;

                    if (trie->jump[word]) {
                        if (!nextbranch)
                            nextbranch = trie_node + trie->jump[0];
                        scan= trie_node + trie->jump[word];
                        /* We go from the jump point to the branch that follows
                           it. Note this means we need the vestigal unused
                           branches even though they arent otherwise used. */
                        minnext = study_chunk(pRExC_state, &scan, minlenp,
                            &deltanext, (regnode *)nextbranch, &data_fake,
                            stopparen, recursed_depth, NULL, f,depth+1);
                    }
                    if (nextbranch && PL_regkind[OP(nextbranch)]==BRANCH)
                        nextbranch= regnext((regnode*)nextbranch);

                    if (min1 > (SSize_t)(minnext + trie->minlen))
                        min1 = minnext + trie->minlen;
                    if (deltanext == SSize_t_MAX) {
                        is_inf = is_inf_internal = 1;
                        max1 = SSize_t_MAX;
                    } else if (max1 < (SSize_t)(minnext + deltanext + trie->maxlen))
                        max1 = minnext + deltanext + trie->maxlen;

                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SCF_SEEN_ACCEPT) {
                        if ( stopmin > min + min1)
                            stopmin = min + min1;
                        flags &= ~SCF_DO_SUBSTR;
                        if (data)
                            data->flags |= SCF_SEEN_ACCEPT;
                    }
                    if (data) {
                        if (data_fake.flags & SF_HAS_EVAL)
                            data->flags |= SF_HAS_EVAL;
                        data->whilem_c = data_fake.whilem_c;
                    }
                    if (flags & SCF_DO_STCLASS)
                        ssc_or(pRExC_state, &accum, (regnode_charclass *) &this_class);
                }
            }
            if (flags & SCF_DO_SUBSTR) {
                data->pos_min += min1;
                data->pos_delta += max1 - min1;
                if (max1 != min1 || is_inf)
                    data->longest = &(data->longest_float);
            }
            min += min1;
            if (delta != SSize_t_MAX)
                delta += max1 - min1;
            if (flags & SCF_DO_STCLASS_OR) {
                ssc_or(pRExC_state, data->start_class, (regnode_charclass *) &accum);
                if (min1) {
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);
                    flags &= ~SCF_DO_STCLASS;
                }
            }
            else if (flags & SCF_DO_STCLASS_AND) {
                if (min1) {
                    ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &accum);
                    flags &= ~SCF_DO_STCLASS;
                }
                else {
                    /* Switch to OR mode: cache the old value of
                     * data->start_class */
                    INIT_AND_WITHP;
                    StructCopy(data->start_class, and_withp, regnode_ssc);
                    flags &= ~SCF_DO_STCLASS_AND;
                    StructCopy(&accum, data->start_class, regnode_ssc);
                    flags |= SCF_DO_STCLASS_OR;
                }
            }
            scan= tail;
            continue;
        }
#else
        else if (PL_regkind[OP(scan)] == TRIE) {
            reg_trie_data *trie = (reg_trie_data*)RExC_rxi->data->data[ ARG(scan) ];
            U8*bang=NULL;

            min += trie->minlen;
            delta += (trie->maxlen - trie->minlen);
            flags &= ~SCF_DO_STCLASS; /* xxx */
            if (flags & SCF_DO_SUBSTR) {
                /* Cannot expect anything... */
                scan_commit(pRExC_state, data, minlenp, is_inf);
                data->pos_min += trie->minlen;
                data->pos_delta += (trie->maxlen - trie->minlen);
                if (trie->maxlen != trie->minlen)
                    data->longest = &(data->longest_float);
            }
            if (trie->jump) /* no more substrings -- for now /grr*/
               flags &= ~SCF_DO_SUBSTR;
        }
#endif /* old or new */
#endif /* TRIE_STUDY_OPT */

        /* Else: zero-length, ignore. */
        scan = regnext(scan);
    }
    /* If we are exiting a recursion we can unset its recursed bit
     * and allow ourselves to enter it again - no danger of an
     * infinite loop there.
    if (stopparen > -1 && recursed) {
        DEBUG_STUDYDATA("unset:", data,depth);
        PAREN_UNSET( recursed, stopparen);
    }
    */
    if (frame) {
        depth = depth - 1;

        DEBUG_STUDYDATA("frame-end:",data,depth);
        DEBUG_PEEP("fend", scan, depth);

        /* restore previous context */
        last = frame->last_regnode;
        scan = frame->next_regnode;
        stopparen = frame->stopparen;
        recursed_depth = frame->prev_recursed_depth;

        RExC_frame_last = frame->prev_frame;
        frame = frame->this_prev_frame;
        goto fake_study_recurse;
    }

  finish:
    assert(!frame);
    DEBUG_STUDYDATA("pre-fin:",data,depth);

    *scanp = scan;
    *deltap = is_inf_internal ? SSize_t_MAX : delta;

    if (flags & SCF_DO_SUBSTR && is_inf)
        data->pos_delta = SSize_t_MAX - data->pos_min;
    if (is_par > (I32)U8_MAX)
        is_par = 0;
    if (is_par && pars==1 && data) {
        data->flags |= SF_IN_PAR;
        data->flags &= ~SF_HAS_PAR;
    }
    else if (pars && data) {
        data->flags |= SF_HAS_PAR;
        data->flags &= ~SF_IN_PAR;
    }
    if (flags & SCF_DO_STCLASS_OR)
        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) and_withp);
    if (flags & SCF_TRIE_RESTUDY)
        data->flags |=  SCF_TRIE_RESTUDY;

    DEBUG_STUDYDATA("post-fin:",data,depth);

    {
        SSize_t final_minlen= min < stopmin ? min : stopmin;

        if (!(RExC_seen & REG_UNBOUNDED_QUANTIFIER_SEEN)) {
            if (final_minlen > SSize_t_MAX - delta)
                RExC_maxlen = SSize_t_MAX;
            else if (RExC_maxlen < final_minlen + delta)
                RExC_maxlen = final_minlen + delta;
        }
        return final_minlen;
    }
    NOT_REACHED; /* NOTREACHED */
}

STATIC U32
S_add_data(RExC_state_t* const pRExC_state, const char* const s, const U32 n)
{
    U32 count = RExC_rxi->data ? RExC_rxi->data->count : 0;

    PERL_ARGS_ASSERT_ADD_DATA;

    Renewc(RExC_rxi->data,
           sizeof(*RExC_rxi->data) + sizeof(void*) * (count + n - 1),
           char, struct reg_data);
    if(count)
        Renew(RExC_rxi->data->what, count + n, U8);
    else
        Newx(RExC_rxi->data->what, n, U8);
    RExC_rxi->data->count = count + n;
    Copy(s, RExC_rxi->data->what + count, n, U8);
    return count;
}

/*XXX: todo make this not included in a non debugging perl, but appears to be
 * used anyway there, in 'use re' */
#ifndef PERL_IN_XSUB_RE
void
Perl_reginitcolors(pTHX)
{
    const char * const s = PerlEnv_getenv("PERL_RE_COLORS");
    if (s) {
        char *t = savepv(s);
        int i = 0;
        PL_colors[0] = t;
        while (++i < 6) {
            t = strchr(t, '\t');
            if (t) {
                *t = '\0';
                PL_colors[i] = ++t;
            }
            else
                PL_colors[i] = t = (char *)"";
        }
    } else {
        int i = 0;
        while (i < 6)
            PL_colors[i++] = (char *)"";
    }
    PL_colorset = 1;
}
#endif


#ifdef TRIE_STUDY_OPT
#define CHECK_RESTUDY_GOTO_butfirst(dOsomething)            \
    STMT_START {                                            \
        if (                                                \
              (data.flags & SCF_TRIE_RESTUDY)               \
              && ! restudied++                              \
        ) {                                                 \
            dOsomething;                                    \
            goto reStudy;                                   \
        }                                                   \
    } STMT_END
#else
#define CHECK_RESTUDY_GOTO_butfirst
#endif

/*
 * pregcomp - compile a regular expression into internal code
 *
 * Decides which engine's compiler to call based on the hint currently in
 * scope
 */

#ifndef PERL_IN_XSUB_RE

/* return the currently in-scope regex engine (or the default if none)  */

regexp_engine const *
Perl_current_re_engine(pTHX)
{
    if (IN_PERL_COMPILETIME) {
        HV * const table = GvHV(PL_hintgv);
        SV **ptr;

        if (!table || !(PL_hints & HINT_LOCALIZE_HH))
            return &PL_core_reg_engine;
        ptr = hv_fetchs(table, "regcomp", FALSE);
        if ( !(ptr && SvIOK(*ptr) && SvIV(*ptr)))
            return &PL_core_reg_engine;
        return INT2PTR(regexp_engine*,SvIV(*ptr));
    }
    else {
        SV *ptr;
        if (!PL_curcop->cop_hints_hash)
            return &PL_core_reg_engine;
        ptr = cop_hints_fetch_pvs(PL_curcop, "regcomp", 0);
        if ( !(ptr && SvIOK(ptr) && SvIV(ptr)))
            return &PL_core_reg_engine;
        return INT2PTR(regexp_engine*,SvIV(ptr));
    }
}


REGEXP *
Perl_pregcomp(pTHX_ SV * const pattern, const U32 flags)
{
    regexp_engine const *eng = current_re_engine();
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_PREGCOMP;

    /* Dispatch a request to compile a regexp to correct regexp engine. */
    DEBUG_COMPILE_r({
        PerlIO_printf(Perl_debug_log, "Using engine %"UVxf"\n",
                        PTR2UV(eng));
    });
    return CALLREGCOMP_ENG(eng, pattern, flags);
}
#endif

/* public(ish) entry point for the perl core's own regex compiling code.
 * It's actually a wrapper for Perl_re_op_compile that only takes an SV
 * pattern rather than a list of OPs, and uses the internal engine rather
 * than the current one */

REGEXP *
Perl_re_compile(pTHX_ SV * const pattern, U32 rx_flags)
{
    SV *pat = pattern; /* defeat constness! */
    PERL_ARGS_ASSERT_RE_COMPILE;
    return Perl_re_op_compile(aTHX_ &pat, 1, NULL,
#ifdef PERL_IN_XSUB_RE
                                &my_reg_engine,
#else
                                &PL_core_reg_engine,
#endif
                                NULL, NULL, rx_flags, 0);
}


/* upgrade pattern pat_p of length plen_p to UTF8, and if there are code
 * blocks, recalculate the indices. Update pat_p and plen_p in-place to
 * point to the realloced string and length.
 *
 * This is essentially a copy of Perl_bytes_to_utf8() with the code index
 * stuff added */

static void
S_pat_upgrade_to_utf8(pTHX_ RExC_state_t * const pRExC_state,
                    char **pat_p, STRLEN *plen_p, int num_code_blocks)
{
    U8 *const src = (U8*)*pat_p;
    U8 *dst, *d;
    int n=0;
    STRLEN s = 0;
    bool do_end = 0;
    GET_RE_DEBUG_FLAGS_DECL;

    DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log,
        "UTF8 mismatch! Converting to utf8 for resizing and compile\n"));

    Newx(dst, *plen_p * 2 + 1, U8);
    d = dst;

    while (s < *plen_p) {
        append_utf8_from_native_byte(src[s], &d);
        if (n < num_code_blocks) {
            if (!do_end && pRExC_state->code_blocks[n].start == s) {
                pRExC_state->code_blocks[n].start = d - dst - 1;
                assert(*(d - 1) == '(');
                do_end = 1;
            }
            else if (do_end && pRExC_state->code_blocks[n].end == s) {
                pRExC_state->code_blocks[n].end = d - dst - 1;
                assert(*(d - 1) == ')');
                do_end = 0;
                n++;
            }
        }
        s++;
    }
    *d = '\0';
    *plen_p = d - dst;
    *pat_p = (char*) dst;
    SAVEFREEPV(*pat_p);
    RExC_orig_utf8 = RExC_utf8 = 1;
}



/* S_concat_pat(): concatenate a list of args to the pattern string pat,
 * while recording any code block indices, and handling overloading,
 * nested qr// objects etc.  If pat is null, it will allocate a new
 * string, or just return the first arg, if there's only one.
 *
 * Returns the malloced/updated pat.
 * patternp and pat_count is the array of SVs to be concatted;
 * oplist is the optional list of ops that generated the SVs;
 * recompile_p is a pointer to a boolean that will be set if
 *   the regex will need to be recompiled.
 * delim, if non-null is an SV that will be inserted between each element
 */

static SV*
S_concat_pat(pTHX_ RExC_state_t * const pRExC_state,
                SV *pat, SV ** const patternp, int pat_count,
                OP *oplist, bool *recompile_p, SV *delim)
{
    SV **svp;
    int n = 0;
    bool use_delim = FALSE;
    bool alloced = FALSE;

    /* if we know we have at least two args, create an empty string,
     * then concatenate args to that. For no args, return an empty string */
    if (!pat && pat_count != 1) {
        pat = newSVpvs("");
        SAVEFREESV(pat);
        alloced = TRUE;
    }

    for (svp = patternp; svp < patternp + pat_count; svp++) {
        SV *sv;
        SV *rx  = NULL;
        STRLEN orig_patlen = 0;
        bool code = 0;
        SV *msv = use_delim ? delim : *svp;
        if (!msv) msv = &PL_sv_undef;

        /* if we've got a delimiter, we go round the loop twice for each
         * svp slot (except the last), using the delimiter the second
         * time round */
        if (use_delim) {
            svp--;
            use_delim = FALSE;
        }
        else if (delim)
            use_delim = TRUE;

        if (SvTYPE(msv) == SVt_PVAV) {
            /* we've encountered an interpolated array within
             * the pattern, e.g. /...@a..../. Expand the list of elements,
             * then recursively append elements.
             * The code in this block is based on S_pushav() */

            AV *const av = (AV*)msv;
            const SSize_t maxarg = AvFILL(av) + 1;
            SV **array;

            if (oplist) {
                assert(oplist->op_type == OP_PADAV
                    || oplist->op_type == OP_RV2AV);
                oplist = OpSIBLING(oplist);
            }

            if (SvRMAGICAL(av)) {
                SSize_t i;

                Newx(array, maxarg, SV*);
                SAVEFREEPV(array);
                for (i=0; i < maxarg; i++) {
                    SV ** const svp = av_fetch(av, i, FALSE);
                    array[i] = svp ? *svp : &PL_sv_undef;
                }
            }
            else
                array = AvARRAY(av);

            pat = S_concat_pat(aTHX_ pRExC_state, pat,
                                array, maxarg, NULL, recompile_p,
                                /* $" */
                                GvSV((gv_fetchpvs("\"", GV_ADDMULTI, SVt_PV))));

            continue;
        }


        /* we make the assumption here that each op in the list of
         * op_siblings maps to one SV pushed onto the stack,
         * except for code blocks, with have both an OP_NULL and
         * and OP_CONST.
         * This allows us to match up the list of SVs against the
         * list of OPs to find the next code block.
         *
         * Note that       PUSHMARK PADSV PADSV ..
         * is optimised to
         *                 PADRANGE PADSV  PADSV  ..
         * so the alignment still works. */

        if (oplist) {
            if (oplist->op_type == OP_NULL
                && (oplist->op_flags & OPf_SPECIAL))
            {
                assert(n < pRExC_state->num_code_blocks);
                pRExC_state->code_blocks[n].start = pat ? SvCUR(pat) : 0;
                pRExC_state->code_blocks[n].block = oplist;
                pRExC_state->code_blocks[n].src_regex = NULL;
                n++;
                code = 1;
                oplist = OpSIBLING(oplist); /* skip CONST */
                assert(oplist);
            }
            oplist = OpSIBLING(oplist);;
        }

        /* apply magic and QR overloading to arg */

        SvGETMAGIC(msv);
        if (SvROK(msv) && SvAMAGIC(msv)) {
            SV *sv = AMG_CALLunary(msv, regexp_amg);
            if (sv) {
                if (SvROK(sv))
                    sv = SvRV(sv);
                if (SvTYPE(sv) != SVt_REGEXP)
                    Perl_croak(aTHX_ "Overloaded qr did not return a REGEXP");
                msv = sv;
            }
        }

        /* try concatenation overload ... */
        if (pat && (SvAMAGIC(pat) || SvAMAGIC(msv)) &&
                (sv = amagic_call(pat, msv, concat_amg, AMGf_assign)))
        {
            sv_setsv(pat, sv);
            /* overloading involved: all bets are off over literal
             * code. Pretend we haven't seen it */
            pRExC_state->num_code_blocks -= n;
            n = 0;
        }
        else  {
            /* ... or failing that, try "" overload */
            while (SvAMAGIC(msv)
                    && (sv = AMG_CALLunary(msv, string_amg))
                    && sv != msv
                    &&  !(   SvROK(msv)
                          && SvROK(sv)
                          && SvRV(msv) == SvRV(sv))
            ) {
                msv = sv;
                SvGETMAGIC(msv);
            }
            if (SvROK(msv) && SvTYPE(SvRV(msv)) == SVt_REGEXP)
                msv = SvRV(msv);

            if (pat) {
                /* this is a partially unrolled
                 *     sv_catsv_nomg(pat, msv);
                 * that allows us to adjust code block indices if
                 * needed */
                STRLEN dlen;
                char *dst = SvPV_force_nomg(pat, dlen);
                orig_patlen = dlen;
                if (SvUTF8(msv) && !SvUTF8(pat)) {
                    S_pat_upgrade_to_utf8(aTHX_ pRExC_state, &dst, &dlen, n);
                    sv_setpvn(pat, dst, dlen);
                    SvUTF8_on(pat);
                }
                sv_catsv_nomg(pat, msv);
                rx = msv;
            }
            else
                pat = msv;

            if (code)
                pRExC_state->code_blocks[n-1].end = SvCUR(pat)-1;
        }

        /* extract any code blocks within any embedded qr//'s */
        if (rx && SvTYPE(rx) == SVt_REGEXP
            && RX_ENGINE((REGEXP*)rx)->op_comp)
        {

            RXi_GET_DECL(ReANY((REGEXP *)rx), ri);
            if (ri->num_code_blocks) {
                int i;
                /* the presence of an embedded qr// with code means
                 * we should always recompile: the text of the
                 * qr// may not have changed, but it may be a
                 * different closure than last time */
                *recompile_p = 1;
                Renew(pRExC_state->code_blocks,
                    pRExC_state->num_code_blocks + ri->num_code_blocks,
                    struct reg_code_block);
                pRExC_state->num_code_blocks += ri->num_code_blocks;

                for (i=0; i < ri->num_code_blocks; i++) {
                    struct reg_code_block *src, *dst;
                    STRLEN offset =  orig_patlen
                        + ReANY((REGEXP *)rx)->pre_prefix;
                    assert(n < pRExC_state->num_code_blocks);
                    src = &ri->code_blocks[i];
                    dst = &pRExC_state->code_blocks[n];
                    dst->start      = src->start + offset;
                    dst->end        = src->end   + offset;
                    dst->block      = src->block;
                    dst->src_regex  = (REGEXP*) SvREFCNT_inc( (SV*)
                                            src->src_regex
                                                ? src->src_regex
                                                : (REGEXP*)rx);
                    n++;
                }
            }
        }
    }
    /* avoid calling magic multiple times on a single element e.g. =~ $qr */
    if (alloced)
        SvSETMAGIC(pat);

    return pat;
}



/* see if there are any run-time code blocks in the pattern.
 * False positives are allowed */

static bool
S_has_runtime_code(pTHX_ RExC_state_t * const pRExC_state,
                    char *pat, STRLEN plen)
{
    int n = 0;
    STRLEN s;
    
    PERL_UNUSED_CONTEXT;

    for (s = 0; s < plen; s++) {
        if (n < pRExC_state->num_code_blocks
            && s == pRExC_state->code_blocks[n].start)
        {
            s = pRExC_state->code_blocks[n].end;
            n++;
            continue;
        }
        /* TODO ideally should handle [..], (#..), /#.../x to reduce false
         * positives here */
        if (pat[s] == '(' && s+2 <= plen && pat[s+1] == '?' &&
            (pat[s+2] == '{'
                || (s + 2 <= plen && pat[s+2] == '?' && pat[s+3] == '{'))
        )
            return 1;
    }
    return 0;
}

/* Handle run-time code blocks. We will already have compiled any direct
 * or indirect literal code blocks. Now, take the pattern 'pat' and make a
 * copy of it, but with any literal code blocks blanked out and
 * appropriate chars escaped; then feed it into
 *
 *    eval "qr'modified_pattern'"
 *
 * For example,
 *
 *       a\bc(?{"this was literal"})def'ghi\\jkl(?{"this is runtime"})mno
 *
 * becomes
 *
 *    qr'a\\bc_______________________def\'ghi\\\\jkl(?{"this is runtime"})mno'
 *
 * After eval_sv()-ing that, grab any new code blocks from the returned qr
 * and merge them with any code blocks of the original regexp.
 *
 * If the pat is non-UTF8, while the evalled qr is UTF8, don't merge;
 * instead, just save the qr and return FALSE; this tells our caller that
 * the original pattern needs upgrading to utf8.
 */

static bool
S_compile_runtime_code(pTHX_ RExC_state_t * const pRExC_state,
    char *pat, STRLEN plen)
{
    SV *qr;

    GET_RE_DEBUG_FLAGS_DECL;

    if (pRExC_state->runtime_code_qr) {
        /* this is the second time we've been called; this should
         * only happen if the main pattern got upgraded to utf8
         * during compilation; re-use the qr we compiled first time
         * round (which should be utf8 too)
         */
        qr = pRExC_state->runtime_code_qr;
        pRExC_state->runtime_code_qr = NULL;
        assert(RExC_utf8 && SvUTF8(qr));
    }
    else {
        int n = 0;
        STRLEN s;
        char *p, *newpat;
        int newlen = plen + 6; /* allow for "qr''x\0" extra chars */
        SV *sv, *qr_ref;
        dSP;

        /* determine how many extra chars we need for ' and \ escaping */
        for (s = 0; s < plen; s++) {
            if (pat[s] == '\'' || pat[s] == '\\')
                newlen++;
        }

        Newx(newpat, newlen, char);
        p = newpat;
        *p++ = 'q'; *p++ = 'r'; *p++ = '\'';

        for (s = 0; s < plen; s++) {
            if (n < pRExC_state->num_code_blocks
                && s == pRExC_state->code_blocks[n].start)
            {
                /* blank out literal code block */
                assert(pat[s] == '(');
                while (s <= pRExC_state->code_blocks[n].end) {
                    *p++ = '_';
                    s++;
                }
                s--;
                n++;
                continue;
            }
            if (pat[s] == '\'' || pat[s] == '\\')
                *p++ = '\\';
            *p++ = pat[s];
        }
        *p++ = '\'';
        if (pRExC_state->pm_flags & RXf_PMf_EXTENDED)
            *p++ = 'x';
        *p++ = '\0';
        DEBUG_COMPILE_r({
            PerlIO_printf(Perl_debug_log,
                "%sre-parsing pattern for runtime code:%s %s\n",
                PL_colors[4],PL_colors[5],newpat);
        });

        sv = newSVpvn_flags(newpat, p-newpat-1, RExC_utf8 ? SVf_UTF8 : 0);
        Safefree(newpat);

        ENTER;
        SAVETMPS;
        save_re_context();
        PUSHSTACKi(PERLSI_REQUIRE);
        /* G_RE_REPARSING causes the toker to collapse \\ into \ when
         * parsing qr''; normally only q'' does this. It also alters
         * hints handling */
        eval_sv(sv, G_SCALAR|G_RE_REPARSING);
        SvREFCNT_dec_NN(sv);
        SPAGAIN;
        qr_ref = POPs;
        PUTBACK;
        {
            SV * const errsv = ERRSV;
            if (SvTRUE_NN(errsv))
            {
                Safefree(pRExC_state->code_blocks);
                /* use croak_sv ? */
                Perl_croak_nocontext("%"SVf, SVfARG(errsv));
            }
        }
        assert(SvROK(qr_ref));
        qr = SvRV(qr_ref);
        assert(SvTYPE(qr) == SVt_REGEXP && RX_ENGINE((REGEXP*)qr)->op_comp);
        /* the leaving below frees the tmp qr_ref.
         * Give qr a life of its own */
        SvREFCNT_inc(qr);
        POPSTACK;
        FREETMPS;
        LEAVE;

    }

    if (!RExC_utf8 && SvUTF8(qr)) {
        /* first time through; the pattern got upgraded; save the
         * qr for the next time through */
        assert(!pRExC_state->runtime_code_qr);
        pRExC_state->runtime_code_qr = qr;
        return 0;
    }


    /* extract any code blocks within the returned qr//  */


    /* merge the main (r1) and run-time (r2) code blocks into one */
    {
        RXi_GET_DECL(ReANY((REGEXP *)qr), r2);
        struct reg_code_block *new_block, *dst;
        RExC_state_t * const r1 = pRExC_state; /* convenient alias */
        int i1 = 0, i2 = 0;

        if (!r2->num_code_blocks) /* we guessed wrong */
        {
            SvREFCNT_dec_NN(qr);
            return 1;
        }

        Newx(new_block,
            r1->num_code_blocks + r2->num_code_blocks,
            struct reg_code_block);
        dst = new_block;

        while (    i1 < r1->num_code_blocks
                || i2 < r2->num_code_blocks)
        {
            struct reg_code_block *src;
            bool is_qr = 0;

            if (i1 == r1->num_code_blocks) {
                src = &r2->code_blocks[i2++];
                is_qr = 1;
            }
            else if (i2 == r2->num_code_blocks)
                src = &r1->code_blocks[i1++];
            else if (  r1->code_blocks[i1].start
                     < r2->code_blocks[i2].start)
            {
                src = &r1->code_blocks[i1++];
                assert(src->end < r2->code_blocks[i2].start);
            }
            else {
                assert(  r1->code_blocks[i1].start
                       > r2->code_blocks[i2].start);
                src = &r2->code_blocks[i2++];
                is_qr = 1;
                assert(src->end < r1->code_blocks[i1].start);
            }

            assert(pat[src->start] == '(');
            assert(pat[src->end]   == ')');
            dst->start      = src->start;
            dst->end        = src->end;
            dst->block      = src->block;
            dst->src_regex  = is_qr ? (REGEXP*) SvREFCNT_inc( (SV*) qr)
                                    : src->src_regex;
            dst++;
        }
        r1->num_code_blocks += r2->num_code_blocks;
        Safefree(r1->code_blocks);
        r1->code_blocks = new_block;
    }

    SvREFCNT_dec_NN(qr);
    return 1;
}


STATIC bool
S_setup_longest(pTHX_ RExC_state_t *pRExC_state, SV* sv_longest,
                      SV** rx_utf8, SV** rx_substr, SSize_t* rx_end_shift,
                      SSize_t lookbehind, SSize_t offset, SSize_t *minlen,
                      STRLEN longest_length, bool eol, bool meol)
{
    /* This is the common code for setting up the floating and fixed length
     * string data extracted from Perl_re_op_compile() below.  Returns a boolean
     * as to whether succeeded or not */

    I32 t;
    SSize_t ml;

    if (! (longest_length
           || (eol /* Can't have SEOL and MULTI */
               && (! meol || (RExC_flags & RXf_PMf_MULTILINE)))
          )
            /* See comments for join_exact for why REG_UNFOLDED_MULTI_SEEN */
        || (RExC_seen & REG_UNFOLDED_MULTI_SEEN))
    {
        return FALSE;
    }

    /* copy the information about the longest from the reg_scan_data
        over to the program. */
    if (SvUTF8(sv_longest)) {
        *rx_utf8 = sv_longest;
        *rx_substr = NULL;
    } else {
        *rx_substr = sv_longest;
        *rx_utf8 = NULL;
    }
    /* end_shift is how many chars that must be matched that
        follow this item. We calculate it ahead of time as once the
        lookbehind offset is added in we lose the ability to correctly
        calculate it.*/
    ml = minlen ? *(minlen) : (SSize_t)longest_length;
    *rx_end_shift = ml - offset
        - longest_length + (SvTAIL(sv_longest) != 0)
        + lookbehind;

    t = (eol/* Can't have SEOL and MULTI */
         && (! meol || (RExC_flags & RXf_PMf_MULTILINE)));
    fbm_compile(sv_longest, t ? FBMcf_TAIL : 0);

    return TRUE;
}

/*
 * Perl_re_op_compile - the perl internal RE engine's function to compile a
 * regular expression into internal code.
 * The pattern may be passed either as:
 *    a list of SVs (patternp plus pat_count)
 *    a list of OPs (expr)
 * If both are passed, the SV list is used, but the OP list indicates
 * which SVs are actually pre-compiled code blocks
 *
 * The SVs in the list have magic and qr overloading applied to them (and
 * the list may be modified in-place with replacement SVs in the latter
 * case).
 *
 * If the pattern hasn't changed from old_re, then old_re will be
 * returned.
 *
 * eng is the current engine. If that engine has an op_comp method, then
 * handle directly (i.e. we assume that op_comp was us); otherwise, just
 * do the initial concatenation of arguments and pass on to the external
 * engine.
 *
 * If is_bare_re is not null, set it to a boolean indicating whether the
 * arg list reduced (after overloading) to a single bare regex which has
 * been returned (i.e. /$qr/).
 *
 * orig_rx_flags contains RXf_* flags. See perlreapi.pod for more details.
 *
 * pm_flags contains the PMf_* flags, typically based on those from the
 * pm_flags field of the related PMOP. Currently we're only interested in
 * PMf_HAS_CV, PMf_IS_QR, PMf_USE_RE_EVAL.
 *
 * We can't allocate space until we know how big the compiled form will be,
 * but we can't compile it (and thus know how big it is) until we've got a
 * place to put the code.  So we cheat:  we compile it twice, once with code
 * generation turned off and size counting turned on, and once "for real".
 * This also means that we don't allocate space until we are sure that the
 * thing really will compile successfully, and we never have to move the
 * code and thus invalidate pointers into it.  (Note that it has to be in
 * one piece because free() must be able to free it all.) [NB: not true in perl]
 *
 * Beware that the optimization-preparation code in here knows about some
 * of the structure of the compiled regexp.  [I'll say.]
 */

REGEXP *
Perl_re_op_compile(pTHX_ SV ** const patternp, int pat_count,
                    OP *expr, const regexp_engine* eng, REGEXP *old_re,
                     bool *is_bare_re, U32 orig_rx_flags, U32 pm_flags)
{
    REGEXP *rx;
    struct regexp *r;
    regexp_internal *ri;
    STRLEN plen;
    char *exp;
    regnode *scan;
    I32 flags;
    SSize_t minlen = 0;
    U32 rx_flags;
    SV *pat;
    SV *code_blocksv = NULL;
    SV** new_patternp = patternp;

    /* these are all flags - maybe they should be turned
     * into a single int with different bit masks */
    I32 sawlookahead = 0;
    I32 sawplus = 0;
    I32 sawopen = 0;
    I32 sawminmod = 0;

    regex_charset initial_charset = get_regex_charset(orig_rx_flags);
    bool recompile = 0;
    bool runtime_code = 0;
    scan_data_t data;
    RExC_state_t RExC_state;
    RExC_state_t * const pRExC_state = &RExC_state;
#ifdef TRIE_STUDY_OPT
    int restudied = 0;
    RExC_state_t copyRExC_state;
#endif
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_RE_OP_COMPILE;

    DEBUG_r(if (!PL_colorset) reginitcolors());

    /* Initialize these here instead of as-needed, as is quick and avoids
     * having to test them each time otherwise */
    if (! PL_AboveLatin1) {
#ifdef DEBUGGING
        char * dump_len_string;
#endif

        PL_AboveLatin1 = _new_invlist_C_array(AboveLatin1_invlist);
        PL_Latin1 = _new_invlist_C_array(Latin1_invlist);
        PL_UpperLatin1 = _new_invlist_C_array(UpperLatin1_invlist);
        PL_utf8_foldable = _new_invlist_C_array(_Perl_Any_Folds_invlist);
        PL_HasMultiCharFold =
                       _new_invlist_C_array(_Perl_Folds_To_Multi_Char_invlist);

        /* This is calculated here, because the Perl program that generates the
         * static global ones doesn't currently have access to
         * NUM_ANYOF_CODE_POINTS */
        PL_InBitmap = _new_invlist(2);
        PL_InBitmap = _add_range_to_invlist(PL_InBitmap, 0,
                                                    NUM_ANYOF_CODE_POINTS - 1);
#ifdef DEBUGGING
        dump_len_string = PerlEnv_getenv("PERL_DUMP_RE_MAX_LEN");
        if (   ! dump_len_string
            || ! grok_atoUV(dump_len_string, (UV *)&PL_dump_re_max_len, NULL))
        {
            PL_dump_re_max_len = 0;
        }
#endif
    }

    pRExC_state->code_blocks = NULL;
    pRExC_state->num_code_blocks = 0;

    if (is_bare_re)
        *is_bare_re = FALSE;

    if (expr && (expr->op_type == OP_LIST ||
                (expr->op_type == OP_NULL && expr->op_targ == OP_LIST))) {
        /* allocate code_blocks if needed */
        OP *o;
        int ncode = 0;

        for (o = cLISTOPx(expr)->op_first; o; o = OpSIBLING(o))
            if (o->op_type == OP_NULL && (o->op_flags & OPf_SPECIAL))
                ncode++; /* count of DO blocks */
        if (ncode) {
            pRExC_state->num_code_blocks = ncode;
            Newx(pRExC_state->code_blocks, ncode, struct reg_code_block);
        }
    }

    if (!pat_count) {
        /* compile-time pattern with just OP_CONSTs and DO blocks */

        int n;
        OP *o;

        /* find how many CONSTs there are */
        assert(expr);
        n = 0;
        if (expr->op_type == OP_CONST)
            n = 1;
        else
            for (o = cLISTOPx(expr)->op_first; o; o = OpSIBLING(o)) {
                if (o->op_type == OP_CONST)
                    n++;
            }

        /* fake up an SV array */

        assert(!new_patternp);
        Newx(new_patternp, n, SV*);
        SAVEFREEPV(new_patternp);
        pat_count = n;

        n = 0;
        if (expr->op_type == OP_CONST)
            new_patternp[n] = cSVOPx_sv(expr);
        else
            for (o = cLISTOPx(expr)->op_first; o; o = OpSIBLING(o)) {
                if (o->op_type == OP_CONST)
                    new_patternp[n++] = cSVOPo_sv;
            }

    }

    DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log,
        "Assembling pattern from %d elements%s\n", pat_count,
            orig_rx_flags & RXf_SPLIT ? " for split" : ""));

    /* set expr to the first arg op */

    if (pRExC_state->num_code_blocks
         && expr->op_type != OP_CONST)
    {
            expr = cLISTOPx(expr)->op_first;
            assert(   expr->op_type == OP_PUSHMARK
                   || (expr->op_type == OP_NULL && expr->op_targ == OP_PUSHMARK)
                   || expr->op_type == OP_PADRANGE);
            expr = OpSIBLING(expr);
    }

    pat = S_concat_pat(aTHX_ pRExC_state, NULL, new_patternp, pat_count,
                        expr, &recompile, NULL);

    /* handle bare (possibly after overloading) regex: foo =~ $re */
    {
        SV *re = pat;
        if (SvROK(re))
            re = SvRV(re);
        if (SvTYPE(re) == SVt_REGEXP) {
            if (is_bare_re)
                *is_bare_re = TRUE;
            SvREFCNT_inc(re);
            Safefree(pRExC_state->code_blocks);
            DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log,
                "Precompiled pattern%s\n",
                    orig_rx_flags & RXf_SPLIT ? " for split" : ""));

            return (REGEXP*)re;
        }
    }

    exp = SvPV_nomg(pat, plen);

    if (!eng->op_comp) {
        if ((SvUTF8(pat) && IN_BYTES)
                || SvGMAGICAL(pat) || SvAMAGIC(pat))
        {
            /* make a temporary copy; either to convert to bytes,
             * or to avoid repeating get-magic / overloaded stringify */
            pat = newSVpvn_flags(exp, plen, SVs_TEMP |
                                        (IN_BYTES ? 0 : SvUTF8(pat)));
        }
        Safefree(pRExC_state->code_blocks);
        return CALLREGCOMP_ENG(eng, pat, orig_rx_flags);
    }

    /* ignore the utf8ness if the pattern is 0 length */
    RExC_utf8 = RExC_orig_utf8 = (plen == 0 || IN_BYTES) ? 0 : SvUTF8(pat);

    RExC_uni_semantics = 0;
    RExC_seen_unfolded_sharp_s = 0;
    RExC_contains_locale = 0;
    RExC_contains_i = 0;
    RExC_strict = cBOOL(pm_flags & RXf_PMf_STRICT);
    pRExC_state->runtime_code_qr = NULL;
    RExC_frame_head= NULL;
    RExC_frame_last= NULL;
    RExC_frame_count= 0;

    DEBUG_r({
        RExC_mysv1= sv_newmortal();
        RExC_mysv2= sv_newmortal();
    });
    DEBUG_COMPILE_r({
            SV *dsv= sv_newmortal();
            RE_PV_QUOTED_DECL(s, RExC_utf8, dsv, exp, plen, 60);
            PerlIO_printf(Perl_debug_log, "%sCompiling REx%s %s\n",
                          PL_colors[4],PL_colors[5],s);
        });

  redo_first_pass:
    /* we jump here if we have to recompile, e.g., from upgrading the pattern
     * to utf8 */

    if ((pm_flags & PMf_USE_RE_EVAL)
                /* this second condition covers the non-regex literal case,
                 * i.e.  $foo =~ '(?{})'. */
                || (IN_PERL_COMPILETIME && (PL_hints & HINT_RE_EVAL))
    )
        runtime_code = S_has_runtime_code(aTHX_ pRExC_state, exp, plen);

    /* return old regex if pattern hasn't changed */
    /* XXX: note in the below we have to check the flags as well as the
     * pattern.
     *
     * Things get a touch tricky as we have to compare the utf8 flag
     * independently from the compile flags.  */

    if (   old_re
        && !recompile
        && !!RX_UTF8(old_re) == !!RExC_utf8
        && ( RX_COMPFLAGS(old_re) == ( orig_rx_flags & RXf_PMf_FLAGCOPYMASK ) )
        && RX_PRECOMP(old_re)
        && RX_PRELEN(old_re) == plen
        && memEQ(RX_PRECOMP(old_re), exp, plen)
        && !runtime_code /* with runtime code, always recompile */ )
    {
        Safefree(pRExC_state->code_blocks);
        return old_re;
    }

    rx_flags = orig_rx_flags;

    if (rx_flags & PMf_FOLD) {
        RExC_contains_i = 1;
    }
    if (   initial_charset == REGEX_DEPENDS_CHARSET
        && (RExC_utf8 ||RExC_uni_semantics))
    {

        /* Set to use unicode semantics if the pattern is in utf8 and has the
         * 'depends' charset specified, as it means unicode when utf8  */
        set_regex_charset(&rx_flags, REGEX_UNICODE_CHARSET);
    }

    RExC_precomp = exp;
    RExC_precomp_adj = 0;
    RExC_flags = rx_flags;
    RExC_pm_flags = pm_flags;

    if (runtime_code) {
        assert(TAINTING_get || !TAINT_get);
        if (TAINT_get)
            Perl_croak(aTHX_ "Eval-group in insecure regular expression");

        if (!S_compile_runtime_code(aTHX_ pRExC_state, exp, plen)) {
            /* whoops, we have a non-utf8 pattern, whilst run-time code
             * got compiled as utf8. Try again with a utf8 pattern */
            S_pat_upgrade_to_utf8(aTHX_ pRExC_state, &exp, &plen,
                                    pRExC_state->num_code_blocks);
            goto redo_first_pass;
        }
    }
    assert(!pRExC_state->runtime_code_qr);

    RExC_sawback = 0;

    RExC_seen = 0;
    RExC_maxlen = 0;
    RExC_in_lookbehind = 0;
    RExC_seen_zerolen = *exp == '^' ? -1 : 0;
    RExC_extralen = 0;
    RExC_override_recoding = 0;
#ifdef EBCDIC
    RExC_recode_x_to_native = 0;
#endif
    RExC_in_multi_char_class = 0;

    /* First pass: determine size, legality. */
    RExC_parse = exp;
    RExC_start = RExC_adjusted_start = exp;
    RExC_end = exp + plen;
    RExC_precomp_end = RExC_end;
    RExC_naughty = 0;
    RExC_npar = 1;
    RExC_nestroot = 0;
    RExC_size = 0L;
    RExC_emit = (regnode *) &RExC_emit_dummy;
    RExC_whilem_seen = 0;
    RExC_open_parens = NULL;
    RExC_close_parens = NULL;
    RExC_opend = NULL;
    RExC_paren_names = NULL;
#ifdef DEBUGGING
    RExC_paren_name_list = NULL;
#endif
    RExC_recurse = NULL;
    RExC_study_chunk_recursed = NULL;
    RExC_study_chunk_recursed_bytes= 0;
    RExC_recurse_count = 0;
    pRExC_state->code_index = 0;

    /* This NUL is guaranteed because the pattern comes from an SV*, and the sv
     * code makes sure the final byte is an uncounted NUL.  But should this
     * ever not be the case, lots of things could read beyond the end of the
     * buffer: loops like
     *      while(isFOO(*RExC_parse)) RExC_parse++;
     *      strchr(RExC_parse, "foo");
     * etc.  So it is worth noting. */
    assert(*RExC_end == '\0');

    DEBUG_PARSE_r(
        PerlIO_printf(Perl_debug_log, "Starting first pass (sizing)\n");
        RExC_lastnum=0;
        RExC_lastparse=NULL;
    );
    /* reg may croak on us, not giving us a chance to free
       pRExC_state->code_blocks.  We cannot SAVEFREEPV it now, as we may
       need it to survive as long as the regexp (qr/(?{})/).
       We must check that code_blocksv is not already set, because we may
       have jumped back to restart the sizing pass. */
    if (pRExC_state->code_blocks && !code_blocksv) {
        code_blocksv = newSV_type(SVt_PV);
        SAVEFREESV(code_blocksv);
        SvPV_set(code_blocksv, (char *)pRExC_state->code_blocks);
        SvLEN_set(code_blocksv, 1); /*sufficient to make sv_clear free it*/
    }
    if (reg(pRExC_state, 0, &flags,1) == NULL) {
        /* It's possible to write a regexp in ascii that represents Unicode
        codepoints outside of the byte range, such as via \x{100}. If we
        detect such a sequence we have to convert the entire pattern to utf8
        and then recompile, as our sizing calculation will have been based
        on 1 byte == 1 character, but we will need to use utf8 to encode
        at least some part of the pattern, and therefore must convert the whole
        thing.
        -- dmq */
        if (flags & RESTART_PASS1) {
            if (flags & NEED_UTF8) {
                S_pat_upgrade_to_utf8(aTHX_ pRExC_state, &exp, &plen,
                                    pRExC_state->num_code_blocks);
            }
            else {
                DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log,
                "Need to redo pass 1\n"));
            }

            goto redo_first_pass;
        }
        Perl_croak(aTHX_ "panic: reg returned NULL to re_op_compile for sizing pass, flags=%#"UVxf"", (UV) flags);
    }
    if (code_blocksv)
        SvLEN_set(code_blocksv,0); /* no you can't have it, sv_clear */

    DEBUG_PARSE_r({
        PerlIO_printf(Perl_debug_log,
            "Required size %"IVdf" nodes\n"
            "Starting second pass (creation)\n",
            (IV)RExC_size);
        RExC_lastnum=0;
        RExC_lastparse=NULL;
    });

    /* The first pass could have found things that force Unicode semantics */
    if ((RExC_utf8 || RExC_uni_semantics)
         && get_regex_charset(rx_flags) == REGEX_DEPENDS_CHARSET)
    {
        set_regex_charset(&rx_flags, REGEX_UNICODE_CHARSET);
    }

    /* Small enough for pointer-storage convention?
       If extralen==0, this means that we will not need long jumps. */
    if (RExC_size >= 0x10000L && RExC_extralen)
        RExC_size += RExC_extralen;
    else
        RExC_extralen = 0;
    if (RExC_whilem_seen > 15)
        RExC_whilem_seen = 15;

    /* Allocate space and zero-initialize. Note, the two step process
       of zeroing when in debug mode, thus anything assigned has to
       happen after that */
    rx = (REGEXP*) newSV_type(SVt_REGEXP);
    r = ReANY(rx);
    Newxc(ri, sizeof(regexp_internal) + (unsigned)RExC_size * sizeof(regnode),
         char, regexp_internal);
    if ( r == NULL || ri == NULL )
        FAIL("Regexp out of space");
#ifdef DEBUGGING
    /* avoid reading uninitialized memory in DEBUGGING code in study_chunk() */
    Zero(ri, sizeof(regexp_internal) + (unsigned)RExC_size * sizeof(regnode),
         char);
#else
    /* bulk initialize base fields with 0. */
    Zero(ri, sizeof(regexp_internal), char);
#endif

    /* non-zero initialization begins here */
    RXi_SET( r, ri );
    r->engine= eng;
    r->extflags = rx_flags;
    RXp_COMPFLAGS(r) = orig_rx_flags & RXf_PMf_FLAGCOPYMASK;

    if (pm_flags & PMf_IS_QR) {
        ri->code_blocks = pRExC_state->code_blocks;
        ri->num_code_blocks = pRExC_state->num_code_blocks;
    }
    else
    {
        int n;
        for (n = 0; n < pRExC_state->num_code_blocks; n++)
            if (pRExC_state->code_blocks[n].src_regex)
                SAVEFREESV(pRExC_state->code_blocks[n].src_regex);
        if(pRExC_state->code_blocks)
            SAVEFREEPV(pRExC_state->code_blocks); /* often null */
    }

    {
        bool has_p     = ((r->extflags & RXf_PMf_KEEPCOPY) == RXf_PMf_KEEPCOPY);
        bool has_charset = (get_regex_charset(r->extflags)
                                                    != REGEX_DEPENDS_CHARSET);

        /* The caret is output if there are any defaults: if not all the STD
         * flags are set, or if no character set specifier is needed */
        bool has_default =
                    (((r->extflags & RXf_PMf_STD_PMMOD) != RXf_PMf_STD_PMMOD)
                    || ! has_charset);
        bool has_runon = ((RExC_seen & REG_RUN_ON_COMMENT_SEEN)
                                                   == REG_RUN_ON_COMMENT_SEEN);
        U8 reganch = (U8)((r->extflags & RXf_PMf_STD_PMMOD)
                            >> RXf_PMf_STD_PMMOD_SHIFT);
        const char *fptr = STD_PAT_MODS;        /*"msixn"*/
        char *p;

        /* We output all the necessary flags; we never output a minus, as all
         * those are defaults, so are
         * covered by the caret */
        const STRLEN wraplen = plen + has_p + has_runon
            + has_default       /* If needs a caret */
            + PL_bitcount[reganch] /* 1 char for each set standard flag */

                /* If needs a character set specifier */
            + ((has_charset) ? MAX_CHARSET_NAME_LENGTH : 0)
            + (sizeof("(?:)") - 1);

        /* make sure PL_bitcount bounds not exceeded */
        assert(sizeof(STD_PAT_MODS) <= 8);

        Newx(p, wraplen + 1, char); /* +1 for the ending NUL */
        r->xpv_len_u.xpvlenu_pv = p;
        if (RExC_utf8)
            SvFLAGS(rx) |= SVf_UTF8;
        *p++='('; *p++='?';

        /* If a default, cover it using the caret */
        if (has_default) {
            *p++= DEFAULT_PAT_MOD;
        }
        if (has_charset) {
            STRLEN len;
            const char* const name = get_regex_charset_name(r->extflags, &len);
            Copy(name, p, len, char);
            p += len;
        }
        if (has_p)
            *p++ = KEEPCOPY_PAT_MOD; /*'p'*/
        {
            char ch;
            while((ch = *fptr++)) {
                if(reganch & 1)
                    *p++ = ch;
                reganch >>= 1;
            }
        }

        *p++ = ':';
        Copy(RExC_precomp, p, plen, char);
        assert ((RX_WRAPPED(rx) - p) < 16);
        r->pre_prefix = p - RX_WRAPPED(rx);
        p += plen;
        if (has_runon)
            *p++ = '\n';
        *p++ = ')';
        *p = 0;
        SvCUR_set(rx, p - RX_WRAPPED(rx));
    }

    r->intflags = 0;
    r->nparens = RExC_npar - 1; /* set early to validate backrefs */

    /* setup various meta data about recursion, this all requires
     * RExC_npar to be correctly set, and a bit later on we clear it */
    if (RExC_seen & REG_RECURSE_SEEN) {
        Newxz(RExC_open_parens, RExC_npar,regnode *);
        SAVEFREEPV(RExC_open_parens);
        Newxz(RExC_close_parens,RExC_npar,regnode *);
        SAVEFREEPV(RExC_close_parens);
    }
    if (RExC_seen & (REG_RECURSE_SEEN | REG_GOSTART_SEEN)) {
        /* Note, RExC_npar is 1 + the number of parens in a pattern.
         * So its 1 if there are no parens. */
        RExC_study_chunk_recursed_bytes= (RExC_npar >> 3) +
                                         ((RExC_npar & 0x07) != 0);
        Newx(RExC_study_chunk_recursed,
             RExC_study_chunk_recursed_bytes * RExC_npar, U8);
        SAVEFREEPV(RExC_study_chunk_recursed);
    }

    /* Useful during FAIL. */
#ifdef RE_TRACK_PATTERN_OFFSETS
    Newxz(ri->u.offsets, 2*RExC_size+1, U32); /* MJD 20001228 */
    DEBUG_OFFSETS_r(PerlIO_printf(Perl_debug_log,
                          "%s %"UVuf" bytes for offset annotations.\n",
                          ri->u.offsets ? "Got" : "Couldn't get",
                          (UV)((2*RExC_size+1) * sizeof(U32))));
#endif
    SetProgLen(ri,RExC_size);
    RExC_rx_sv = rx;
    RExC_rx = r;
    RExC_rxi = ri;

    /* Second pass: emit code. */
    RExC_flags = rx_flags;      /* don't let top level (?i) bleed */
    RExC_pm_flags = pm_flags;
    RExC_parse = exp;
    RExC_end = exp + plen;
    RExC_naughty = 0;
    RExC_npar = 1;
    RExC_emit_start = ri->program;
    RExC_emit = ri->program;
    RExC_emit_bound = ri->program + RExC_size + 1;
    pRExC_state->code_index = 0;

    *((char*) RExC_emit++) = (char) REG_MAGIC;
    if (reg(pRExC_state, 0, &flags,1) == NULL) {
        ReREFCNT_dec(rx);
        Perl_croak(aTHX_ "panic: reg returned NULL to re_op_compile for generation pass, flags=%#"UVxf"", (UV) flags);
    }
    /* XXXX To minimize changes to RE engine we always allocate
       3-units-long substrs field. */
    Newx(r->substrs, 1, struct reg_substr_data);
    if (RExC_recurse_count) {
        Newxz(RExC_recurse,RExC_recurse_count,regnode *);
        SAVEFREEPV(RExC_recurse);
    }

  reStudy:
    r->minlen = minlen = sawlookahead = sawplus = sawopen = sawminmod = 0;
    DEBUG_r(
        RExC_study_chunk_recursed_count= 0;
    );
    Zero(r->substrs, 1, struct reg_substr_data);
    if (RExC_study_chunk_recursed) {
        Zero(RExC_study_chunk_recursed,
             RExC_study_chunk_recursed_bytes * RExC_npar, U8);
    }


#ifdef TRIE_STUDY_OPT
    if (!restudied) {
        StructCopy(&zero_scan_data, &data, scan_data_t);
        copyRExC_state = RExC_state;
    } else {
        U32 seen=RExC_seen;
        DEBUG_OPTIMISE_r(PerlIO_printf(Perl_debug_log,"Restudying\n"));

        RExC_state = copyRExC_state;
        if (seen & REG_TOP_LEVEL_BRANCHES_SEEN)
            RExC_seen |= REG_TOP_LEVEL_BRANCHES_SEEN;
        else
            RExC_seen &= ~REG_TOP_LEVEL_BRANCHES_SEEN;
        StructCopy(&zero_scan_data, &data, scan_data_t);
    }
#else
    StructCopy(&zero_scan_data, &data, scan_data_t);
#endif

    /* Dig out information for optimizations. */
    r->extflags = RExC_flags; /* was pm_op */
    /*dmq: removed as part of de-PMOP: pm->op_pmflags = RExC_flags; */

    if (UTF)
        SvUTF8_on(rx);  /* Unicode in it? */
    ri->regstclass = NULL;
    if (RExC_naughty >= TOO_NAUGHTY)    /* Probably an expensive pattern. */
        r->intflags |= PREGf_NAUGHTY;
    scan = ri->program + 1;             /* First BRANCH. */

    /* testing for BRANCH here tells us whether there is "must appear"
       data in the pattern. If there is then we can use it for optimisations */
    if (!(RExC_seen & REG_TOP_LEVEL_BRANCHES_SEEN)) { /*  Only one top-level choice.
                                                  */
        SSize_t fake;
        STRLEN longest_float_length, longest_fixed_length;
        regnode_ssc ch_class; /* pointed to by data */
        int stclass_flag;
        SSize_t last_close = 0; /* pointed to by data */
        regnode *first= scan;
        regnode *first_next= regnext(first);
        /*
         * Skip introductions and multiplicators >= 1
         * so that we can extract the 'meat' of the pattern that must
         * match in the large if() sequence following.
         * NOTE that EXACT is NOT covered here, as it is normally
         * picked up by the optimiser separately.
         *
         * This is unfortunate as the optimiser isnt handling lookahead
         * properly currently.
         *
         */
        while ((OP(first) == OPEN && (sawopen = 1)) ||
               /* An OR of *one* alternative - should not happen now. */
            (OP(first) == BRANCH && OP(first_next) != BRANCH) ||
            /* for now we can't handle lookbehind IFMATCH*/
            (OP(first) == IFMATCH && !first->flags && (sawlookahead = 1)) ||
            (OP(first) == PLUS) ||
            (OP(first) == MINMOD) ||
               /* An {n,m} with n>0 */
            (PL_regkind[OP(first)] == CURLY && ARG1(first) > 0) ||
            (OP(first) == NOTHING && PL_regkind[OP(first_next)] != END ))
        {
                /*
                 * the only op that could be a regnode is PLUS, all the rest
                 * will be regnode_1 or regnode_2.
                 *
                 * (yves doesn't think this is true)
                 */
                if (OP(first) == PLUS)
                    sawplus = 1;
                else {
                    if (OP(first) == MINMOD)
                        sawminmod = 1;
                    first += regarglen[OP(first)];
                }
                first = NEXTOPER(first);
                first_next= regnext(first);
        }

        /* Starting-point info. */
      again:
        DEBUG_PEEP("first:",first,0);
        /* Ignore EXACT as we deal with it later. */
        if (PL_regkind[OP(first)] == EXACT) {
            if (OP(first) == EXACT || OP(first) == EXACTL)
                NOOP;   /* Empty, get anchored substr later. */
            else
                ri->regstclass = first;
        }
#ifdef TRIE_STCLASS
        else if (PL_regkind[OP(first)] == TRIE &&
                ((reg_trie_data *)ri->data->data[ ARG(first) ])->minlen>0)
        {
            /* this can happen only on restudy */
            ri->regstclass = construct_ahocorasick_from_trie(pRExC_state, (regnode *)first, 0);
        }
#endif
        else if (REGNODE_SIMPLE(OP(first)))
            ri->regstclass = first;
        else if (PL_regkind[OP(first)] == BOUND ||
                 PL_regkind[OP(first)] == NBOUND)
            ri->regstclass = first;
        else if (PL_regkind[OP(first)] == BOL) {
            r->intflags |= (OP(first) == MBOL
                           ? PREGf_ANCH_MBOL
                           : PREGf_ANCH_SBOL);
            first = NEXTOPER(first);
            goto again;
        }
        else if (OP(first) == GPOS) {
            r->intflags |= PREGf_ANCH_GPOS;
            first = NEXTOPER(first);
            goto again;
        }
        else if ((!sawopen || !RExC_sawback) &&
            !sawlookahead &&
            (OP(first) == STAR &&
            PL_regkind[OP(NEXTOPER(first))] == REG_ANY) &&
            !(r->intflags & PREGf_ANCH) && !pRExC_state->num_code_blocks)
        {
            /* turn .* into ^.* with an implied $*=1 */
            const int type =
                (OP(NEXTOPER(first)) == REG_ANY)
                    ? PREGf_ANCH_MBOL
                    : PREGf_ANCH_SBOL;
            r->intflags |= (type | PREGf_IMPLICIT);
            first = NEXTOPER(first);
            goto again;
        }
        if (sawplus && !sawminmod && !sawlookahead
            && (!sawopen || !RExC_sawback)
            && !pRExC_state->num_code_blocks) /* May examine pos and $& */
            /* x+ must match at the 1st pos of run of x's */
            r->intflags |= PREGf_SKIP;

        /* Scan is after the zeroth branch, first is atomic matcher. */
#ifdef TRIE_STUDY_OPT
        DEBUG_PARSE_r(
            if (!restudied)
                PerlIO_printf(Perl_debug_log, "first at %"IVdf"\n",
                              (IV)(first - scan + 1))
        );
#else
        DEBUG_PARSE_r(
            PerlIO_printf(Perl_debug_log, "first at %"IVdf"\n",
                (IV)(first - scan + 1))
        );
#endif


        /*
        * If there's something expensive in the r.e., find the
        * longest literal string that must appear and make it the
        * regmust.  Resolve ties in favor of later strings, since
        * the regstart check works with the beginning of the r.e.
        * and avoiding duplication strengthens checking.  Not a
        * strong reason, but sufficient in the absence of others.
        * [Now we resolve ties in favor of the earlier string if
        * it happens that c_offset_min has been invalidated, since the
        * earlier string may buy us something the later one won't.]
        */

        data.longest_fixed = newSVpvs("");
        data.longest_float = newSVpvs("");
        data.last_found = newSVpvs("");
        data.longest = &(data.longest_fixed);
        ENTER_with_name("study_chunk");
        SAVEFREESV(data.longest_fixed);
        SAVEFREESV(data.longest_float);
        SAVEFREESV(data.last_found);
        first = scan;
        if (!ri->regstclass) {
            ssc_init(pRExC_state, &ch_class);
            data.start_class = &ch_class;
            stclass_flag = SCF_DO_STCLASS_AND;
        } else                          /* XXXX Check for BOUND? */
            stclass_flag = 0;
        data.last_closep = &last_close;

        DEBUG_RExC_seen();
        minlen = study_chunk(pRExC_state, &first, &minlen, &fake,
                             scan + RExC_size, /* Up to end */
            &data, -1, 0, NULL,
            SCF_DO_SUBSTR | SCF_WHILEM_VISITED_POS | stclass_flag
                          | (restudied ? SCF_TRIE_DOING_RESTUDY : 0),
            0);


        CHECK_RESTUDY_GOTO_butfirst(LEAVE_with_name("study_chunk"));


        if ( RExC_npar == 1 && data.longest == &(data.longest_fixed)
             && data.last_start_min == 0 && data.last_end > 0
             && !RExC_seen_zerolen
             && !(RExC_seen & REG_VERBARG_SEEN)
             && !(RExC_seen & REG_GPOS_SEEN)
        ){
            r->extflags |= RXf_CHECK_ALL;
        }
        scan_commit(pRExC_state, &data,&minlen,0);

        longest_float_length = CHR_SVLEN(data.longest_float);

        if (! ((SvCUR(data.longest_fixed)  /* ok to leave SvCUR */
                   && data.offset_fixed == data.offset_float_min
                   && SvCUR(data.longest_fixed) == SvCUR(data.longest_float)))
            && S_setup_longest (aTHX_ pRExC_state,
                                    data.longest_float,
                                    &(r->float_utf8),
                                    &(r->float_substr),
                                    &(r->float_end_shift),
                                    data.lookbehind_float,
                                    data.offset_float_min,
                                    data.minlen_float,
                                    longest_float_length,
                                    cBOOL(data.flags & SF_FL_BEFORE_EOL),
                                    cBOOL(data.flags & SF_FL_BEFORE_MEOL)))
        {
            r->float_min_offset = data.offset_float_min - data.lookbehind_float;
            r->float_max_offset = data.offset_float_max;
            if (data.offset_float_max < SSize_t_MAX) /* Don't offset infinity */
                r->float_max_offset -= data.lookbehind_float;
            SvREFCNT_inc_simple_void_NN(data.longest_float);
        }
        else {
            r->float_substr = r->float_utf8 = NULL;
            longest_float_length = 0;
        }

        longest_fixed_length = CHR_SVLEN(data.longest_fixed);

        if (S_setup_longest (aTHX_ pRExC_state,
                                data.longest_fixed,
                                &(r->anchored_utf8),
                                &(r->anchored_substr),
                                &(r->anchored_end_shift),
                                data.lookbehind_fixed,
                                data.offset_fixed,
                                data.minlen_fixed,
                                longest_fixed_length,
                                cBOOL(data.flags & SF_FIX_BEFORE_EOL),
                                cBOOL(data.flags & SF_FIX_BEFORE_MEOL)))
        {
            r->anchored_offset = data.offset_fixed - data.lookbehind_fixed;
            SvREFCNT_inc_simple_void_NN(data.longest_fixed);
        }
        else {
            r->anchored_substr = r->anchored_utf8 = NULL;
            longest_fixed_length = 0;
        }
        LEAVE_with_name("study_chunk");

        if (ri->regstclass
            && (OP(ri->regstclass) == REG_ANY || OP(ri->regstclass) == SANY))
            ri->regstclass = NULL;

        if ((!(r->anchored_substr || r->anchored_utf8) || r->anchored_offset)
            && stclass_flag
            && ! (ANYOF_FLAGS(data.start_class) & SSC_MATCHES_EMPTY_STRING)
            && is_ssc_worth_it(pRExC_state, data.start_class))
        {
            const U32 n = add_data(pRExC_state, STR_WITH_LEN("f"));

            ssc_finalize(pRExC_state, data.start_class);

            Newx(RExC_rxi->data->data[n], 1, regnode_ssc);
            StructCopy(data.start_class,
                       (regnode_ssc*)RExC_rxi->data->data[n],
                       regnode_ssc);
            ri->regstclass = (regnode*)RExC_rxi->data->data[n];
            r->intflags &= ~PREGf_SKIP; /* Used in find_byclass(). */
            DEBUG_COMPILE_r({ SV *sv = sv_newmortal();
                      regprop(r, sv, (regnode*)data.start_class, NULL, pRExC_state);
                      PerlIO_printf(Perl_debug_log,
                                    "synthetic stclass \"%s\".\n",
                                    SvPVX_const(sv));});
            data.start_class = NULL;
        }

        /* A temporary algorithm prefers floated substr to fixed one to dig
         * more info. */
        if (longest_fixed_length > longest_float_length) {
            r->substrs->check_ix = 0;
            r->check_end_shift = r->anchored_end_shift;
            r->check_substr = r->anchored_substr;
            r->check_utf8 = r->anchored_utf8;
            r->check_offset_min = r->check_offset_max = r->anchored_offset;
            if (r->intflags & (PREGf_ANCH_SBOL|PREGf_ANCH_GPOS))
                r->intflags |= PREGf_NOSCAN;
        }
        else {
            r->substrs->check_ix = 1;
            r->check_end_shift = r->float_end_shift;
            r->check_substr = r->float_substr;
            r->check_utf8 = r->float_utf8;
            r->check_offset_min = r->float_min_offset;
            r->check_offset_max = r->float_max_offset;
        }
        if ((r->check_substr || r->check_utf8) ) {
            r->extflags |= RXf_USE_INTUIT;
            if (SvTAIL(r->check_substr ? r->check_substr : r->check_utf8))
                r->extflags |= RXf_INTUIT_TAIL;
        }
        r->substrs->data[0].max_offset = r->substrs->data[0].min_offset;

        /* XXX Unneeded? dmq (shouldn't as this is handled elsewhere)
        if ( (STRLEN)minlen < longest_float_length )
            minlen= longest_float_length;
        if ( (STRLEN)minlen < longest_fixed_length )
            minlen= longest_fixed_length;
        */
    }
    else {
        /* Several toplevels. Best we can is to set minlen. */
        SSize_t fake;
        regnode_ssc ch_class;
        SSize_t last_close = 0;

        DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log, "\nMulti Top Level\n"));

        scan = ri->program + 1;
        ssc_init(pRExC_state, &ch_class);
        data.start_class = &ch_class;
        data.last_closep = &last_close;

        DEBUG_RExC_seen();
        minlen = study_chunk(pRExC_state,
            &scan, &minlen, &fake, scan + RExC_size, &data, -1, 0, NULL,
            SCF_DO_STCLASS_AND|SCF_WHILEM_VISITED_POS|(restudied
                                                      ? SCF_TRIE_DOING_RESTUDY
                                                      : 0),
            0);

        CHECK_RESTUDY_GOTO_butfirst(NOOP);

        r->check_substr = r->check_utf8 = r->anchored_substr = r->anchored_utf8
                = r->float_substr = r->float_utf8 = NULL;

        if (! (ANYOF_FLAGS(data.start_class) & SSC_MATCHES_EMPTY_STRING)
            && is_ssc_worth_it(pRExC_state, data.start_class))
        {
            const U32 n = add_data(pRExC_state, STR_WITH_LEN("f"));

            ssc_finalize(pRExC_state, data.start_class);

            Newx(RExC_rxi->data->data[n], 1, regnode_ssc);
            StructCopy(data.start_class,
                       (regnode_ssc*)RExC_rxi->data->data[n],
                       regnode_ssc);
            ri->regstclass = (regnode*)RExC_rxi->data->data[n];
            r->intflags &= ~PREGf_SKIP; /* Used in find_byclass(). */
            DEBUG_COMPILE_r({ SV* sv = sv_newmortal();
                      regprop(r, sv, (regnode*)data.start_class, NULL, pRExC_state);
                      PerlIO_printf(Perl_debug_log,
                                    "synthetic stclass \"%s\".\n",
                                    SvPVX_const(sv));});
            data.start_class = NULL;
        }
    }

    if (RExC_seen & REG_UNBOUNDED_QUANTIFIER_SEEN) {
        r->extflags |= RXf_UNBOUNDED_QUANTIFIER_SEEN;
        r->maxlen = REG_INFTY;
    }
    else {
        r->maxlen = RExC_maxlen;
    }

    /* Guard against an embedded (?=) or (?<=) with a longer minlen than
       the "real" pattern. */
    DEBUG_OPTIMISE_r({
        PerlIO_printf(Perl_debug_log,"minlen: %"IVdf" r->minlen:%"IVdf" maxlen:%"IVdf"\n",
                      (IV)minlen, (IV)r->minlen, (IV)RExC_maxlen);
    });
    r->minlenret = minlen;
    if (r->minlen < minlen)
        r->minlen = minlen;

    if (RExC_seen & REG_GPOS_SEEN)
        r->intflags |= PREGf_GPOS_SEEN;
    if (RExC_seen & REG_LOOKBEHIND_SEEN)
        r->extflags |= RXf_NO_INPLACE_SUBST; /* inplace might break the
                                                lookbehind */
    if (pRExC_state->num_code_blocks)
        r->extflags |= RXf_EVAL_SEEN;
    if (RExC_seen & REG_VERBARG_SEEN)
    {
        r->intflags |= PREGf_VERBARG_SEEN;
        r->extflags |= RXf_NO_INPLACE_SUBST; /* don't understand this! Yves */
    }
    if (RExC_seen & REG_CUTGROUP_SEEN)
        r->intflags |= PREGf_CUTGROUP_SEEN;
    if (pm_flags & PMf_USE_RE_EVAL)
        r->intflags |= PREGf_USE_RE_EVAL;
    if (RExC_paren_names)
        RXp_PAREN_NAMES(r) = MUTABLE_HV(SvREFCNT_inc(RExC_paren_names));
    else
        RXp_PAREN_NAMES(r) = NULL;

    /* If we have seen an anchor in our pattern then we set the extflag RXf_IS_ANCHORED
     * so it can be used in pp.c */
    if (r->intflags & PREGf_ANCH)
        r->extflags |= RXf_IS_ANCHORED;


    {
        /* this is used to identify "special" patterns that might result
         * in Perl NOT calling the regex engine and instead doing the match "itself",
         * particularly special cases in split//. By having the regex compiler
         * do this pattern matching at a regop level (instead of by inspecting the pattern)
         * we avoid weird issues with equivalent patterns resulting in different behavior,
         * AND we allow non Perl engines to get the same optimizations by the setting the
         * flags appropriately - Yves */
        regnode *first = ri->program + 1;
        U8 fop = OP(first);
        regnode *next = regnext(first);
        U8 nop = OP(next);

        if (PL_regkind[fop] == NOTHING && nop == END)
            r->extflags |= RXf_NULL;
        else if ((fop == MBOL || (fop == SBOL && !first->flags)) && nop == END)
            /* when fop is SBOL first->flags will be true only when it was
             * produced by parsing /\A/, and not when parsing /^/. This is
             * very important for the split code as there we want to
             * treat /^/ as /^/m, but we do not want to treat /\A/ as /^/m.
             * See rt #122761 for more details. -- Yves */
            r->extflags |= RXf_START_ONLY;
        else if (fop == PLUS
                 && PL_regkind[nop] == POSIXD && FLAGS(next) == _CC_SPACE
                 && nop == END)
            r->extflags |= RXf_WHITE;
        else if ( r->extflags & RXf_SPLIT
                  && (fop == EXACT || fop == EXACTL)
                  && STR_LEN(first) == 1
                  && *(STRING(first)) == ' '
                  && nop == END )
            r->extflags |= (RXf_SKIPWHITE|RXf_WHITE);

    }

    if (RExC_contains_locale) {
        RXp_EXTFLAGS(r) |= RXf_TAINTED;
    }

#ifdef DEBUGGING
    if (RExC_paren_names) {
        ri->name_list_idx = add_data( pRExC_state, STR_WITH_LEN("a"));
        ri->data->data[ri->name_list_idx]
                                   = (void*)SvREFCNT_inc(RExC_paren_name_list);
    } else
#endif
        ri->name_list_idx = 0;

    if (RExC_recurse_count) {
        for ( ; RExC_recurse_count ; RExC_recurse_count-- ) {
            const regnode *scan = RExC_recurse[RExC_recurse_count-1];
            ARG2L_SET( scan, RExC_open_parens[ARG(scan)-1] - scan );
        }
    }
    Newxz(r->offs, RExC_npar, regexp_paren_pair);
    /* assume we don't need to swap parens around before we match */
    DEBUG_TEST_r({
        PerlIO_printf(Perl_debug_log,"study_chunk_recursed_count: %lu\n",
            (unsigned long)RExC_study_chunk_recursed_count);
    });
    DEBUG_DUMP_r({
        DEBUG_RExC_seen();
        PerlIO_printf(Perl_debug_log,"Final program:\n");
        regdump(r);
    });
#ifdef RE_TRACK_PATTERN_OFFSETS
    DEBUG_OFFSETS_r(if (ri->u.offsets) {
        const STRLEN len = ri->u.offsets[0];
        STRLEN i;
        GET_RE_DEBUG_FLAGS_DECL;
        PerlIO_printf(Perl_debug_log,
                      "Offsets: [%"UVuf"]\n\t", (UV)ri->u.offsets[0]);
        for (i = 1; i <= len; i++) {
            if (ri->u.offsets[i*2-1] || ri->u.offsets[i*2])
                PerlIO_printf(Perl_debug_log, "%"UVuf":%"UVuf"[%"UVuf"] ",
                (UV)i, (UV)ri->u.offsets[i*2-1], (UV)ri->u.offsets[i*2]);
            }
        PerlIO_printf(Perl_debug_log, "\n");
    });
#endif

#ifdef USE_ITHREADS
    /* under ithreads the ?pat? PMf_USED flag on the pmop is simulated
     * by setting the regexp SV to readonly-only instead. If the
     * pattern's been recompiled, the USEDness should remain. */
    if (old_re && SvREADONLY(old_re))
        SvREADONLY_on(rx);
#endif
    return rx;
}


SV*
Perl_reg_named_buff(pTHX_ REGEXP * const rx, SV * const key, SV * const value,
                    const U32 flags)
{
    PERL_ARGS_ASSERT_REG_NAMED_BUFF;

    PERL_UNUSED_ARG(value);

    if (flags & RXapif_FETCH) {
        return reg_named_buff_fetch(rx, key, flags);
    } else if (flags & (RXapif_STORE | RXapif_DELETE | RXapif_CLEAR)) {
        Perl_croak_no_modify();
        return NULL;
    } else if (flags & RXapif_EXISTS) {
        return reg_named_buff_exists(rx, key, flags)
            ? &PL_sv_yes
            : &PL_sv_no;
    } else if (flags & RXapif_REGNAMES) {
        return reg_named_buff_all(rx, flags);
    } else if (flags & (RXapif_SCALAR | RXapif_REGNAMES_COUNT)) {
        return reg_named_buff_scalar(rx, flags);
    } else {
        Perl_croak(aTHX_ "panic: Unknown flags %d in named_buff", (int)flags);
        return NULL;
    }
}

SV*
Perl_reg_named_buff_iter(pTHX_ REGEXP * const rx, const SV * const lastkey,
                         const U32 flags)
{
    PERL_ARGS_ASSERT_REG_NAMED_BUFF_ITER;
    PERL_UNUSED_ARG(lastkey);

    if (flags & RXapif_FIRSTKEY)
        return reg_named_buff_firstkey(rx, flags);
    else if (flags & RXapif_NEXTKEY)
        return reg_named_buff_nextkey(rx, flags);
    else {
        Perl_croak(aTHX_ "panic: Unknown flags %d in named_buff_iter",
                                            (int)flags);
        return NULL;
    }
}

SV*
Perl_reg_named_buff_fetch(pTHX_ REGEXP * const r, SV * const namesv,
                          const U32 flags)
{
    AV *retarray = NULL;
    SV *ret;
    struct regexp *const rx = ReANY(r);

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_FETCH;

    if (flags & RXapif_ALL)
        retarray=newAV();

    if (rx && RXp_PAREN_NAMES(rx)) {
        HE *he_str = hv_fetch_ent( RXp_PAREN_NAMES(rx), namesv, 0, 0 );
        if (he_str) {
            IV i;
            SV* sv_dat=HeVAL(he_str);
            I32 *nums=(I32*)SvPVX(sv_dat);
            for ( i=0; i<SvIVX(sv_dat); i++ ) {
                if ((I32)(rx->nparens) >= nums[i]
                    && rx->offs[nums[i]].start != -1
                    && rx->offs[nums[i]].end != -1)
                {
                    ret = newSVpvs("");
                    CALLREG_NUMBUF_FETCH(r,nums[i],ret);
                    if (!retarray)
                        return ret;
                } else {
                    if (retarray)
                        ret = newSVsv(&PL_sv_undef);
                }
                if (retarray)
                    av_push(retarray, ret);
            }
            if (retarray)
                return newRV_noinc(MUTABLE_SV(retarray));
        }
    }
    return NULL;
}

bool
Perl_reg_named_buff_exists(pTHX_ REGEXP * const r, SV * const key,
                           const U32 flags)
{
    struct regexp *const rx = ReANY(r);

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_EXISTS;

    if (rx && RXp_PAREN_NAMES(rx)) {
        if (flags & RXapif_ALL) {
            return hv_exists_ent(RXp_PAREN_NAMES(rx), key, 0);
        } else {
            SV *sv = CALLREG_NAMED_BUFF_FETCH(r, key, flags);
            if (sv) {
                SvREFCNT_dec_NN(sv);
                return TRUE;
            } else {
                return FALSE;
            }
        }
    } else {
        return FALSE;
    }
}

SV*
Perl_reg_named_buff_firstkey(pTHX_ REGEXP * const r, const U32 flags)
{
    struct regexp *const rx = ReANY(r);

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_FIRSTKEY;

    if ( rx && RXp_PAREN_NAMES(rx) ) {
        (void)hv_iterinit(RXp_PAREN_NAMES(rx));

        return CALLREG_NAMED_BUFF_NEXTKEY(r, NULL, flags & ~RXapif_FIRSTKEY);
    } else {
        return FALSE;
    }
}

SV*
Perl_reg_named_buff_nextkey(pTHX_ REGEXP * const r, const U32 flags)
{
    struct regexp *const rx = ReANY(r);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_NEXTKEY;

    if (rx && RXp_PAREN_NAMES(rx)) {
        HV *hv = RXp_PAREN_NAMES(rx);
        HE *temphe;
        while ( (temphe = hv_iternext_flags(hv,0)) ) {
            IV i;
            IV parno = 0;
            SV* sv_dat = HeVAL(temphe);
            I32 *nums = (I32*)SvPVX(sv_dat);
            for ( i = 0; i < SvIVX(sv_dat); i++ ) {
                if ((I32)(rx->lastparen) >= nums[i] &&
                    rx->offs[nums[i]].start != -1 &&
                    rx->offs[nums[i]].end != -1)
                {
                    parno = nums[i];
                    break;
                }
            }
            if (parno || flags & RXapif_ALL) {
                return newSVhek(HeKEY_hek(temphe));
            }
        }
    }
    return NULL;
}

SV*
Perl_reg_named_buff_scalar(pTHX_ REGEXP * const r, const U32 flags)
{
    SV *ret;
    AV *av;
    SSize_t length;
    struct regexp *const rx = ReANY(r);

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_SCALAR;

    if (rx && RXp_PAREN_NAMES(rx)) {
        if (flags & (RXapif_ALL | RXapif_REGNAMES_COUNT)) {
            return newSViv(HvTOTALKEYS(RXp_PAREN_NAMES(rx)));
        } else if (flags & RXapif_ONE) {
            ret = CALLREG_NAMED_BUFF_ALL(r, (flags | RXapif_REGNAMES));
            av = MUTABLE_AV(SvRV(ret));
            length = av_tindex(av);
            SvREFCNT_dec_NN(ret);
            return newSViv(length + 1);
        } else {
            Perl_croak(aTHX_ "panic: Unknown flags %d in named_buff_scalar",
                                                (int)flags);
            return NULL;
        }
    }
    return &PL_sv_undef;
}

SV*
Perl_reg_named_buff_all(pTHX_ REGEXP * const r, const U32 flags)
{
    struct regexp *const rx = ReANY(r);
    AV *av = newAV();

    PERL_ARGS_ASSERT_REG_NAMED_BUFF_ALL;

    if (rx && RXp_PAREN_NAMES(rx)) {
        HV *hv= RXp_PAREN_NAMES(rx);
        HE *temphe;
        (void)hv_iterinit(hv);
        while ( (temphe = hv_iternext_flags(hv,0)) ) {
            IV i;
            IV parno = 0;
            SV* sv_dat = HeVAL(temphe);
            I32 *nums = (I32*)SvPVX(sv_dat);
            for ( i = 0; i < SvIVX(sv_dat); i++ ) {
                if ((I32)(rx->lastparen) >= nums[i] &&
                    rx->offs[nums[i]].start != -1 &&
                    rx->offs[nums[i]].end != -1)
                {
                    parno = nums[i];
                    break;
                }
            }
            if (parno || flags & RXapif_ALL) {
                av_push(av, newSVhek(HeKEY_hek(temphe)));
            }
        }
    }

    return newRV_noinc(MUTABLE_SV(av));
}

void
Perl_reg_numbered_buff_fetch(pTHX_ REGEXP * const r, const I32 paren,
                             SV * const sv)
{
    struct regexp *const rx = ReANY(r);
    char *s = NULL;
    SSize_t i = 0;
    SSize_t s1, t1;
    I32 n = paren;

    PERL_ARGS_ASSERT_REG_NUMBERED_BUFF_FETCH;

    if (      n == RX_BUFF_IDX_CARET_PREMATCH
           || n == RX_BUFF_IDX_CARET_FULLMATCH
           || n == RX_BUFF_IDX_CARET_POSTMATCH
       )
    {
        bool keepcopy = cBOOL(rx->extflags & RXf_PMf_KEEPCOPY);
        if (!keepcopy) {
            /* on something like
             *    $r = qr/.../;
             *    /$qr/p;
             * the KEEPCOPY is set on the PMOP rather than the regex */
            if (PL_curpm && r == PM_GETRE(PL_curpm))
                 keepcopy = cBOOL(PL_curpm->op_pmflags & PMf_KEEPCOPY);
        }
        if (!keepcopy)
            goto ret_undef;
    }

    if (!rx->subbeg)
        goto ret_undef;

    if (n == RX_BUFF_IDX_CARET_FULLMATCH)
        /* no need to distinguish between them any more */
        n = RX_BUFF_IDX_FULLMATCH;

    if ((n == RX_BUFF_IDX_PREMATCH || n == RX_BUFF_IDX_CARET_PREMATCH)
        && rx->offs[0].start != -1)
    {
        /* $`, ${^PREMATCH} */
        i = rx->offs[0].start;
        s = rx->subbeg;
    }
    else
    if ((n == RX_BUFF_IDX_POSTMATCH || n == RX_BUFF_IDX_CARET_POSTMATCH)
        && rx->offs[0].end != -1)
    {
        /* $', ${^POSTMATCH} */
        s = rx->subbeg - rx->suboffset + rx->offs[0].end;
        i = rx->sublen + rx->suboffset - rx->offs[0].end;
    }
    else
    if ( 0 <= n && n <= (I32)rx->nparens &&
        (s1 = rx->offs[n].start) != -1 &&
        (t1 = rx->offs[n].end) != -1)
    {
        /* $&, ${^MATCH},  $1 ... */
        i = t1 - s1;
        s = rx->subbeg + s1 - rx->suboffset;
    } else {
        goto ret_undef;
    }

    assert(s >= rx->subbeg);
    assert((STRLEN)rx->sublen >= (STRLEN)((s - rx->subbeg) + i) );
    if (i >= 0) {
#ifdef NO_TAINT_SUPPORT
        sv_setpvn(sv, s, i);
#else
        const int oldtainted = TAINT_get;
        TAINT_NOT;
        sv_setpvn(sv, s, i);
        TAINT_set(oldtainted);
#endif
        if (RXp_MATCH_UTF8(rx))
            SvUTF8_on(sv);
        else
            SvUTF8_off(sv);
        if (TAINTING_get) {
            if (RXp_MATCH_TAINTED(rx)) {
                if (SvTYPE(sv) >= SVt_PVMG) {
                    MAGIC* const mg = SvMAGIC(sv);
                    MAGIC* mgt;
                    TAINT;
                    SvMAGIC_set(sv, mg->mg_moremagic);
                    SvTAINT(sv);
                    if ((mgt = SvMAGIC(sv))) {
                        mg->mg_moremagic = mgt;
                        SvMAGIC_set(sv, mg);
                    }
                } else {
                    TAINT;
                    SvTAINT(sv);
                }
            } else
                SvTAINTED_off(sv);
        }
    } else {
      ret_undef:
        sv_setsv(sv,&PL_sv_undef);
        return;
    }
}

void
Perl_reg_numbered_buff_store(pTHX_ REGEXP * const rx, const I32 paren,
                                                         SV const * const value)
{
    PERL_ARGS_ASSERT_REG_NUMBERED_BUFF_STORE;

    PERL_UNUSED_ARG(rx);
    PERL_UNUSED_ARG(paren);
    PERL_UNUSED_ARG(value);

    if (!PL_localizing)
        Perl_croak_no_modify();
}

I32
Perl_reg_numbered_buff_length(pTHX_ REGEXP * const r, const SV * const sv,
                              const I32 paren)
{
    struct regexp *const rx = ReANY(r);
    I32 i;
    I32 s1, t1;

    PERL_ARGS_ASSERT_REG_NUMBERED_BUFF_LENGTH;

    if (   paren == RX_BUFF_IDX_CARET_PREMATCH
        || paren == RX_BUFF_IDX_CARET_FULLMATCH
        || paren == RX_BUFF_IDX_CARET_POSTMATCH
    )
    {
        bool keepcopy = cBOOL(rx->extflags & RXf_PMf_KEEPCOPY);
        if (!keepcopy) {
            /* on something like
             *    $r = qr/.../;
             *    /$qr/p;
             * the KEEPCOPY is set on the PMOP rather than the regex */
            if (PL_curpm && r == PM_GETRE(PL_curpm))
                 keepcopy = cBOOL(PL_curpm->op_pmflags & PMf_KEEPCOPY);
        }
        if (!keepcopy)
            goto warn_undef;
    }

    /* Some of this code was originally in C<Perl_magic_len> in F<mg.c> */
    switch (paren) {
      case RX_BUFF_IDX_CARET_PREMATCH: /* ${^PREMATCH} */
      case RX_BUFF_IDX_PREMATCH:       /* $` */
        if (rx->offs[0].start != -1) {
                        i = rx->offs[0].start;
                        if (i > 0) {
                                s1 = 0;
                                t1 = i;
                                goto getlen;
                        }
            }
        return 0;

      case RX_BUFF_IDX_CARET_POSTMATCH: /* ${^POSTMATCH} */
      case RX_BUFF_IDX_POSTMATCH:       /* $' */
            if (rx->offs[0].end != -1) {
                        i = rx->sublen - rx->offs[0].end;
                        if (i > 0) {
                                s1 = rx->offs[0].end;
                                t1 = rx->sublen;
                                goto getlen;
                        }
            }
        return 0;

      default: /* $& / ${^MATCH}, $1, $2, ... */
            if (paren <= (I32)rx->nparens &&
            (s1 = rx->offs[paren].start) != -1 &&
            (t1 = rx->offs[paren].end) != -1)
            {
            i = t1 - s1;
            goto getlen;
        } else {
          warn_undef:
            if (ckWARN(WARN_UNINITIALIZED))
                report_uninit((const SV *)sv);
            return 0;
        }
    }
  getlen:
    if (i > 0 && RXp_MATCH_UTF8(rx)) {
        const char * const s = rx->subbeg - rx->suboffset + s1;
        const U8 *ep;
        STRLEN el;

        i = t1 - s1;
        if (is_utf8_string_loclen((U8*)s, i, &ep, &el))
                        i = el;
    }
    return i;
}

SV*
Perl_reg_qr_package(pTHX_ REGEXP * const rx)
{
    PERL_ARGS_ASSERT_REG_QR_PACKAGE;
        PERL_UNUSED_ARG(rx);
        if (0)
            return NULL;
        else
            return newSVpvs("Regexp");
}

/* Scans the name of a named buffer from the pattern.
 * If flags is REG_RSN_RETURN_NULL returns null.
 * If flags is REG_RSN_RETURN_NAME returns an SV* containing the name
 * If flags is REG_RSN_RETURN_DATA returns the data SV* corresponding
 * to the parsed name as looked up in the RExC_paren_names hash.
 * If there is an error throws a vFAIL().. type exception.
 */

#define REG_RSN_RETURN_NULL    0
#define REG_RSN_RETURN_NAME    1
#define REG_RSN_RETURN_DATA    2

STATIC SV*
S_reg_scan_name(pTHX_ RExC_state_t *pRExC_state, U32 flags)
{
    char *name_start = RExC_parse;

    PERL_ARGS_ASSERT_REG_SCAN_NAME;

    assert (RExC_parse <= RExC_end);
    if (RExC_parse == RExC_end) NOOP;
    else if (isIDFIRST_lazy_if(RExC_parse, UTF)) {
         /* Note that the code here assumes well-formed UTF-8.  Skip IDFIRST by
          * using do...while */
        if (UTF)
            do {
                RExC_parse += UTF8SKIP(RExC_parse);
            } while (isWORDCHAR_utf8((U8*)RExC_parse));
        else
            do {
                RExC_parse++;
            } while (isWORDCHAR(*RExC_parse));
    } else {
        RExC_parse++; /* so the <- from the vFAIL is after the offending
                         character */
        vFAIL("Group name must start with a non-digit word character");
    }
    if ( flags ) {
        SV* sv_name
            = newSVpvn_flags(name_start, (int)(RExC_parse - name_start),
                             SVs_TEMP | (UTF ? SVf_UTF8 : 0));
        if ( flags == REG_RSN_RETURN_NAME)
            return sv_name;
        else if (flags==REG_RSN_RETURN_DATA) {
            HE *he_str = NULL;
            SV *sv_dat = NULL;
            if ( ! sv_name )      /* should not happen*/
                Perl_croak(aTHX_ "panic: no svname in reg_scan_name");
            if (RExC_paren_names)
                he_str = hv_fetch_ent( RExC_paren_names, sv_name, 0, 0 );
            if ( he_str )
                sv_dat = HeVAL(he_str);
            if ( ! sv_dat )
                vFAIL("Reference to nonexistent named group");
            return sv_dat;
        }
        else {
            Perl_croak(aTHX_ "panic: bad flag %lx in reg_scan_name",
                       (unsigned long) flags);
        }
        NOT_REACHED; /* NOTREACHED */
    }
    return NULL;
}

#define DEBUG_PARSE_MSG(funcname)     DEBUG_PARSE_r({           \
    int num;                                                    \
    if (RExC_lastparse!=RExC_parse) {                           \
        PerlIO_printf(Perl_debug_log, "%s",                     \
            Perl_pv_pretty(aTHX_ RExC_mysv1, RExC_parse,        \
                RExC_end - RExC_parse, 16,                      \
                "", "",                                         \
                PERL_PV_ESCAPE_UNI_DETECT |                     \
                PERL_PV_PRETTY_ELLIPSES   |                     \
                PERL_PV_PRETTY_LTGT       |                     \
                PERL_PV_ESCAPE_RE         |                     \
                PERL_PV_PRETTY_EXACTSIZE                        \
            )                                                   \
        );                                                      \
    } else                                                      \
        PerlIO_printf(Perl_debug_log,"%16s","");                \
                                                                \
    if (SIZE_ONLY)                                              \
       num = RExC_size + 1;                                     \
    else                                                        \
       num=REG_NODE_NUM(RExC_emit);                             \
    if (RExC_lastnum!=num)                                      \
       PerlIO_printf(Perl_debug_log,"|%4d",num);                \
    else                                                        \
       PerlIO_printf(Perl_debug_log,"|%4s","");                 \
    PerlIO_printf(Perl_debug_log,"|%*s%-4s",                    \
        (int)((depth*2)), "",                                   \
        (funcname)                                              \
    );                                                          \
    RExC_lastnum=num;                                           \
    RExC_lastparse=RExC_parse;                                  \
})



#define DEBUG_PARSE(funcname)     DEBUG_PARSE_r({           \
    DEBUG_PARSE_MSG((funcname));                            \
    PerlIO_printf(Perl_debug_log,"%4s","\n");               \
})
#define DEBUG_PARSE_FMT(funcname,fmt,args)     DEBUG_PARSE_r({           \
    DEBUG_PARSE_MSG((funcname));                            \
    PerlIO_printf(Perl_debug_log,fmt "\n",args);               \
})

/* This section of code defines the inversion list object and its methods.  The
 * interfaces are highly subject to change, so as much as possible is static to
 * this file.  An inversion list is here implemented as a malloc'd C UV array
 * as an SVt_INVLIST scalar.
 *
 * An inversion list for Unicode is an array of code points, sorted by ordinal
 * number.  The zeroth element is the first code point in the list.  The 1th
 * element is the first element beyond that not in the list.  In other words,
 * the first range is
 *  invlist[0]..(invlist[1]-1)
 * The other ranges follow.  Thus every element whose index is divisible by two
 * marks the beginning of a range that is in the list, and every element not
 * divisible by two marks the beginning of a range not in the list.  A single
 * element inversion list that contains the single code point N generally
 * consists of two elements
 *  invlist[0] == N
 *  invlist[1] == N+1
 * (The exception is when N is the highest representable value on the
 * machine, in which case the list containing just it would be a single
 * element, itself.  By extension, if the last range in the list extends to
 * infinity, then the first element of that range will be in the inversion list
 * at a position that is divisible by two, and is the final element in the
 * list.)
 * Taking the complement (inverting) an inversion list is quite simple, if the
 * first element is 0, remove it; otherwise add a 0 element at the beginning.
 * This implementation reserves an element at the beginning of each inversion
 * list to always contain 0; there is an additional flag in the header which
 * indicates if the list begins at the 0, or is offset to begin at the next
 * element.
 *
 * More about inversion lists can be found in "Unicode Demystified"
 * Chapter 13 by Richard Gillam, published by Addison-Wesley.
 * More will be coming when functionality is added later.
 *
 * The inversion list data structure is currently implemented as an SV pointing
 * to an array of UVs that the SV thinks are bytes.  This allows us to have an
 * array of UV whose memory management is automatically handled by the existing
 * facilities for SV's.
 *
 * Some of the methods should always be private to the implementation, and some
 * should eventually be made public */

/* The header definitions are in F<invlist_inline.h> */

PERL_STATIC_INLINE UV*
S__invlist_array_init(SV* const invlist, const bool will_have_0)
{
    /* Returns a pointer to the first element in the inversion list's array.
     * This is called upon initialization of an inversion list.  Where the
     * array begins depends on whether the list has the code point U+0000 in it
     * or not.  The other parameter tells it whether the code that follows this
     * call is about to put a 0 in the inversion list or not.  The first
     * element is either the element reserved for 0, if TRUE, or the element
     * after it, if FALSE */

    bool* offset = get_invlist_offset_addr(invlist);
    UV* zero_addr = (UV *) SvPVX(invlist);

    PERL_ARGS_ASSERT__INVLIST_ARRAY_INIT;

    /* Must be empty */
    assert(! _invlist_len(invlist));

    *zero_addr = 0;

    /* 1^1 = 0; 1^0 = 1 */
    *offset = 1 ^ will_have_0;
    return zero_addr + *offset;
}

PERL_STATIC_INLINE void
S_invlist_set_len(pTHX_ SV* const invlist, const UV len, const bool offset)
{
    /* Sets the current number of elements stored in the inversion list.
     * Updates SvCUR correspondingly */
    PERL_UNUSED_CONTEXT;
    PERL_ARGS_ASSERT_INVLIST_SET_LEN;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    SvCUR_set(invlist,
              (len == 0)
               ? 0
               : TO_INTERNAL_SIZE(len + offset));
    assert(SvLEN(invlist) == 0 || SvCUR(invlist) <= SvLEN(invlist));
}

#ifndef PERL_IN_XSUB_RE

STATIC void
S_invlist_replace_list_destroys_src(pTHX_ SV * dest, SV * src)
{
    /* Replaces the inversion list in 'src' with the one in 'dest'.  It steals
     * the list from 'src', so 'src' is made to have a NULL list.  This is
     * similar to what SvSetMagicSV() would do, if it were implemented on
     * inversion lists, though this routine avoids a copy */

    const UV src_len          = _invlist_len(src);
    const bool src_offset     = *get_invlist_offset_addr(src);
    const STRLEN src_byte_len = SvLEN(src);
    char * array              = SvPVX(src);

    const int oldtainted = TAINT_get;

    PERL_ARGS_ASSERT_INVLIST_REPLACE_LIST_DESTROYS_SRC;

    assert(SvTYPE(src) == SVt_INVLIST);
    assert(SvTYPE(dest) == SVt_INVLIST);
    assert(! invlist_is_iterating(src));
    assert(SvCUR(src) == 0 || SvCUR(src) < SvLEN(src));

    /* Make sure it ends in the right place with a NUL, as our inversion list
     * manipulations aren't careful to keep this true, but sv_usepvn_flags()
     * asserts it */
    array[src_byte_len - 1] = '\0';

    TAINT_NOT;      /* Otherwise it breaks */
    sv_usepvn_flags(dest,
                    (char *) array,
                    src_byte_len - 1,

                    /* This flag is documented to cause a copy to be avoided */
                    SV_HAS_TRAILING_NUL);
    TAINT_set(oldtainted);
    SvPV_set(src, 0);
    SvLEN_set(src, 0);
    SvCUR_set(src, 0);

    /* Finish up copying over the other fields in an inversion list */
    *get_invlist_offset_addr(dest) = src_offset;
    invlist_set_len(dest, src_len, src_offset);
    *get_invlist_previous_index_addr(dest) = 0;
    invlist_iterfinish(dest);
}

PERL_STATIC_INLINE IV*
S_get_invlist_previous_index_addr(SV* invlist)
{
    /* Return the address of the IV that is reserved to hold the cached index
     * */
    PERL_ARGS_ASSERT_GET_INVLIST_PREVIOUS_INDEX_ADDR;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    return &(((XINVLIST*) SvANY(invlist))->prev_index);
}

PERL_STATIC_INLINE IV
S_invlist_previous_index(SV* const invlist)
{
    /* Returns cached index of previous search */

    PERL_ARGS_ASSERT_INVLIST_PREVIOUS_INDEX;

    return *get_invlist_previous_index_addr(invlist);
}

PERL_STATIC_INLINE void
S_invlist_set_previous_index(SV* const invlist, const IV index)
{
    /* Caches <index> for later retrieval */

    PERL_ARGS_ASSERT_INVLIST_SET_PREVIOUS_INDEX;

    assert(index == 0 || index < (int) _invlist_len(invlist));

    *get_invlist_previous_index_addr(invlist) = index;
}

PERL_STATIC_INLINE void
S_invlist_trim(SV* invlist)
{
    /* Free the not currently-being-used space in an inversion list */

    /* But don't free up the space needed for 0 UV that is always at the
     * beginning of the list, nor the trailing NUL */
    const UV min_size = TO_INTERNAL_SIZE(1) + 1;

    PERL_ARGS_ASSERT_INVLIST_TRIM;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    SvPV_renew(invlist, MAX(min_size, SvCUR(invlist) + 1));

}

PERL_STATIC_INLINE void
S_invlist_clear(pTHX_ SV* invlist)    /* Empty the inversion list */
{
    PERL_ARGS_ASSERT_INVLIST_CLEAR;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    invlist_set_len(invlist, 0, 0);
    invlist_trim(invlist);
}

#endif /* ifndef PERL_IN_XSUB_RE */

PERL_STATIC_INLINE bool
S_invlist_is_iterating(SV* const invlist)
{
    PERL_ARGS_ASSERT_INVLIST_IS_ITERATING;

    return *(get_invlist_iter_addr(invlist)) < (STRLEN) UV_MAX;
}

PERL_STATIC_INLINE UV
S_invlist_max(SV* const invlist)
{
    /* Returns the maximum number of elements storable in the inversion list's
     * array, without having to realloc() */

    PERL_ARGS_ASSERT_INVLIST_MAX;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    /* Assumes worst case, in which the 0 element is not counted in the
     * inversion list, so subtracts 1 for that */
    return SvLEN(invlist) == 0  /* This happens under _new_invlist_C_array */
           ? FROM_INTERNAL_SIZE(SvCUR(invlist)) - 1
           : FROM_INTERNAL_SIZE(SvLEN(invlist)) - 1;
}

#ifndef PERL_IN_XSUB_RE
SV*
Perl__new_invlist(pTHX_ IV initial_size)
{

    /* Return a pointer to a newly constructed inversion list, with enough
     * space to store 'initial_size' elements.  If that number is negative, a
     * system default is used instead */

    SV* new_list;

    if (initial_size < 0) {
        initial_size = 10;
    }

    /* Allocate the initial space */
    new_list = newSV_type(SVt_INVLIST);

    /* First 1 is in case the zero element isn't in the list; second 1 is for
     * trailing NUL */
    SvGROW(new_list, TO_INTERNAL_SIZE(initial_size + 1) + 1);
    invlist_set_len(new_list, 0, 0);

    /* Force iterinit() to be used to get iteration to work */
    *get_invlist_iter_addr(new_list) = (STRLEN) UV_MAX;

    *get_invlist_previous_index_addr(new_list) = 0;

    return new_list;
}

SV*
Perl__new_invlist_C_array(pTHX_ const UV* const list)
{
    /* Return a pointer to a newly constructed inversion list, initialized to
     * point to <list>, which has to be in the exact correct inversion list
     * form, including internal fields.  Thus this is a dangerous routine that
     * should not be used in the wrong hands.  The passed in 'list' contains
     * several header fields at the beginning that are not part of the
     * inversion list body proper */

    const STRLEN length = (STRLEN) list[0];
    const UV version_id =          list[1];
    const bool offset   =    cBOOL(list[2]);
#define HEADER_LENGTH 3
    /* If any of the above changes in any way, you must change HEADER_LENGTH
     * (if appropriate) and regenerate INVLIST_VERSION_ID by running
     *      perl -E 'say int(rand 2**31-1)'
     */
#define INVLIST_VERSION_ID 148565664 /* This is a combination of a version and
                                        data structure type, so that one being
                                        passed in can be validated to be an
                                        inversion list of the correct vintage.
                                       */

    SV* invlist = newSV_type(SVt_INVLIST);

    PERL_ARGS_ASSERT__NEW_INVLIST_C_ARRAY;

    if (version_id != INVLIST_VERSION_ID) {
        Perl_croak(aTHX_ "panic: Incorrect version for previously generated inversion list");
    }

    /* The generated array passed in includes header elements that aren't part
     * of the list proper, so start it just after them */
    SvPV_set(invlist, (char *) (list + HEADER_LENGTH));

    SvLEN_set(invlist, 0);  /* Means we own the contents, and the system
                               shouldn't touch it */

    *(get_invlist_offset_addr(invlist)) = offset;

    /* The 'length' passed to us is the physical number of elements in the
     * inversion list.  But if there is an offset the logical number is one
     * less than that */
    invlist_set_len(invlist, length  - offset, offset);

    invlist_set_previous_index(invlist, 0);

    /* Initialize the iteration pointer. */
    invlist_iterfinish(invlist);

    SvREADONLY_on(invlist);

    return invlist;
}
#endif /* ifndef PERL_IN_XSUB_RE */

STATIC void
S_invlist_extend(pTHX_ SV* const invlist, const UV new_max)
{
    /* Grow the maximum size of an inversion list */

    PERL_ARGS_ASSERT_INVLIST_EXTEND;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    /* Add one to account for the zero element at the beginning which may not
     * be counted by the calling parameters */
    SvGROW((SV *)invlist, TO_INTERNAL_SIZE(new_max + 1));
}

STATIC void
S__append_range_to_invlist(pTHX_ SV* const invlist,
                                 const UV start, const UV end)
{
   /* Subject to change or removal.  Append the range from 'start' to 'end' at
    * the end of the inversion list.  The range must be above any existing
    * ones. */

    UV* array;
    UV max = invlist_max(invlist);
    UV len = _invlist_len(invlist);
    bool offset;

    PERL_ARGS_ASSERT__APPEND_RANGE_TO_INVLIST;

    if (len == 0) { /* Empty lists must be initialized */
        offset = start != 0;
        array = _invlist_array_init(invlist, ! offset);
    }
    else {
        /* Here, the existing list is non-empty. The current max entry in the
         * list is generally the first value not in the set, except when the
         * set extends to the end of permissible values, in which case it is
         * the first entry in that final set, and so this call is an attempt to
         * append out-of-order */

        UV final_element = len - 1;
        array = invlist_array(invlist);
        if (array[final_element] > start
            || ELEMENT_RANGE_MATCHES_INVLIST(final_element))
        {
            Perl_croak(aTHX_ "panic: attempting to append to an inversion list, but wasn't at the end of the list, final=%"UVuf", start=%"UVuf", match=%c",
                     array[final_element], start,
                     ELEMENT_RANGE_MATCHES_INVLIST(final_element) ? 't' : 'f');
        }

        /* Here, it is a legal append.  If the new range begins with the first
         * value not in the set, it is extending the set, so the new first
         * value not in the set is one greater than the newly extended range.
         * */
        offset = *get_invlist_offset_addr(invlist);
        if (array[final_element] == start) {
            if (end != UV_MAX) {
                array[final_element] = end + 1;
            }
            else {
                /* But if the end is the maximum representable on the machine,
                 * just let the range that this would extend to have no end */
                invlist_set_len(invlist, len - 1, offset);
            }
            return;
        }
    }

    /* Here the new range doesn't extend any existing set.  Add it */

    len += 2;   /* Includes an element each for the start and end of range */

    /* If wll overflow the existing space, extend, which may cause the array to
     * be moved */
    if (max < len) {
        invlist_extend(invlist, len);

        /* Have to set len here to avoid assert failure in invlist_array() */
        invlist_set_len(invlist, len, offset);

        array = invlist_array(invlist);
    }
    else {
        invlist_set_len(invlist, len, offset);
    }

    /* The next item on the list starts the range, the one after that is
     * one past the new range.  */
    array[len - 2] = start;
    if (end != UV_MAX) {
        array[len - 1] = end + 1;
    }
    else {
        /* But if the end is the maximum representable on the machine, just let
         * the range have no end */
        invlist_set_len(invlist, len - 1, offset);
    }
}

#ifndef PERL_IN_XSUB_RE

IV
Perl__invlist_search(SV* const invlist, const UV cp)
{
    /* Searches the inversion list for the entry that contains the input code
     * point <cp>.  If <cp> is not in the list, -1 is returned.  Otherwise, the
     * return value is the index into the list's array of the range that
     * contains <cp>, that is, 'i' such that
     *  array[i] <= cp < array[i+1]
     */

    IV low = 0;
    IV mid;
    IV high = _invlist_len(invlist);
    const IV highest_element = high - 1;
    const UV* array;

    PERL_ARGS_ASSERT__INVLIST_SEARCH;

    /* If list is empty, return failure. */
    if (high == 0) {
        return -1;
    }

    /* (We can't get the array unless we know the list is non-empty) */
    array = invlist_array(invlist);

    mid = invlist_previous_index(invlist);
    assert(mid >=0);
    if (mid > highest_element) {
        mid = highest_element;
    }

    /* <mid> contains the cache of the result of the previous call to this
     * function (0 the first time).  See if this call is for the same result,
     * or if it is for mid-1.  This is under the theory that calls to this
     * function will often be for related code points that are near each other.
     * And benchmarks show that caching gives better results.  We also test
     * here if the code point is within the bounds of the list.  These tests
     * replace others that would have had to be made anyway to make sure that
     * the array bounds were not exceeded, and these give us extra information
     * at the same time */
    if (cp >= array[mid]) {
        if (cp >= array[highest_element]) {
            return highest_element;
        }

        /* Here, array[mid] <= cp < array[highest_element].  This means that
         * the final element is not the answer, so can exclude it; it also
         * means that <mid> is not the final element, so can refer to 'mid + 1'
         * safely */
        if (cp < array[mid + 1]) {
            return mid;
        }
        high--;
        low = mid + 1;
    }
    else { /* cp < aray[mid] */
        if (cp < array[0]) { /* Fail if outside the array */
            return -1;
        }
        high = mid;
        if (cp >= array[mid - 1]) {
            goto found_entry;
        }
    }

    /* Binary search.  What we are looking for is <i> such that
     *  array[i] <= cp < array[i+1]
     * The loop below converges on the i+1.  Note that there may not be an
     * (i+1)th element in the array, and things work nonetheless */
    while (low < high) {
        mid = (low + high) / 2;
        assert(mid <= highest_element);
        if (array[mid] <= cp) { /* cp >= array[mid] */
            low = mid + 1;

            /* We could do this extra test to exit the loop early.
            if (cp < array[low]) {
                return mid;
            }
            */
        }
        else { /* cp < array[mid] */
            high = mid;
        }
    }

  found_entry:
    high--;
    invlist_set_previous_index(invlist, high);
    return high;
}

void
Perl__invlist_populate_swatch(SV* const invlist,
                              const UV start, const UV end, U8* swatch)
{
    /* populates a swatch of a swash the same way swatch_get() does in utf8.c,
     * but is used when the swash has an inversion list.  This makes this much
     * faster, as it uses a binary search instead of a linear one.  This is
     * intimately tied to that function, and perhaps should be in utf8.c,
     * except it is intimately tied to inversion lists as well.  It assumes
     * that <swatch> is all 0's on input */

    UV current = start;
    const IV len = _invlist_len(invlist);
    IV i;
    const UV * array;

    PERL_ARGS_ASSERT__INVLIST_POPULATE_SWATCH;

    if (len == 0) { /* Empty inversion list */
        return;
    }

    array = invlist_array(invlist);

    /* Find which element it is */
    i = _invlist_search(invlist, start);

    /* We populate from <start> to <end> */
    while (current < end) {
        UV upper;

        /* The inversion list gives the results for every possible code point
         * after the first one in the list.  Only those ranges whose index is
         * even are ones that the inversion list matches.  For the odd ones,
         * and if the initial code point is not in the list, we have to skip
         * forward to the next element */
        if (i == -1 || ! ELEMENT_RANGE_MATCHES_INVLIST(i)) {
            i++;
            if (i >= len) { /* Finished if beyond the end of the array */
                return;
            }
            current = array[i];
            if (current >= end) {   /* Finished if beyond the end of what we
                                       are populating */
                if (LIKELY(end < UV_MAX)) {
                    return;
                }

                /* We get here when the upper bound is the maximum
                 * representable on the machine, and we are looking for just
                 * that code point.  Have to special case it */
                i = len;
                goto join_end_of_list;
            }
        }
        assert(current >= start);

        /* The current range ends one below the next one, except don't go past
         * <end> */
        i++;
        upper = (i < len && array[i] < end) ? array[i] : end;

        /* Here we are in a range that matches.  Populate a bit in the 3-bit U8
         * for each code point in it */
        for (; current < upper; current++) {
            const STRLEN offset = (STRLEN)(current - start);
            swatch[offset >> 3] |= 1 << (offset & 7);
        }

      join_end_of_list:

        /* Quit if at the end of the list */
        if (i >= len) {

            /* But first, have to deal with the highest possible code point on
             * the platform.  The previous code assumes that <end> is one
             * beyond where we want to populate, but that is impossible at the
             * platform's infinity, so have to handle it specially */
            if (UNLIKELY(end == UV_MAX && ELEMENT_RANGE_MATCHES_INVLIST(len-1)))
            {
                const STRLEN offset = (STRLEN)(end - start);
                swatch[offset >> 3] |= 1 << (offset & 7);
            }
            return;
        }

        /* Advance to the next range, which will be for code points not in the
         * inversion list */
        current = array[i];
    }

    return;
}

void
Perl__invlist_union_maybe_complement_2nd(pTHX_ SV* const a, SV* const b,
                                         const bool complement_b, SV** output)
{
    /* Take the union of two inversion lists and point <output> to it.  *output
     * SHOULD BE DEFINED upon input, and if it points to one of the two lists,
     * the reference count to that list will be decremented if not already a
     * temporary (mortal); otherwise just its contents will be modified to be
     * the union.  The first list, <a>, may be NULL, in which case a copy of
     * the second list is returned.  If <complement_b> is TRUE, the union is
     * taken of the complement (inversion) of <b> instead of b itself.
     *
     * The basis for this comes from "Unicode Demystified" Chapter 13 by
     * Richard Gillam, published by Addison-Wesley, and explained at some
     * length there.  The preface says to incorporate its examples into your
     * code at your own risk.
     *
     * The algorithm is like a merge sort.
     *
     * XXX A potential performance improvement is to keep track as we go along
     * if only one of the inputs contributes to the result, meaning the other
     * is a subset of that one.  In that case, we can skip the final copy and
     * return the larger of the input lists, but then outside code might need
     * to keep track of whether to free the input list or not */

    const UV* array_a;    /* a's array */
    const UV* array_b;
    UV len_a;       /* length of a's array */
    UV len_b;

    SV* u;                      /* the resulting union */
    UV* array_u;
    UV len_u;

    UV i_a = 0;             /* current index into a's array */
    UV i_b = 0;
    UV i_u = 0;

    /* running count, as explained in the algorithm source book; items are
     * stopped accumulating and are output when the count changes to/from 0.
     * The count is incremented when we start a range that's in the set, and
     * decremented when we start a range that's not in the set.  So its range
     * is 0 to 2.  Only when the count is zero is something not in the set.
     */
    UV count = 0;

    PERL_ARGS_ASSERT__INVLIST_UNION_MAYBE_COMPLEMENT_2ND;
    assert(a != b);

    len_b = _invlist_len(b);
    if (len_b == 0) {

        /* Here, 'b' is empty.  If the output is the complement of 'b', the
         * union is all possible code points, and we need not even look at 'a'.
         * It's easiest to create a new inversion list that matches everything.
         * */
        if (complement_b) {
            SV* everything = _new_invlist(1);
            _append_range_to_invlist(everything, 0, UV_MAX);

            /* If the output didn't exist, just point it at the new list */
            if (*output == NULL) {
                *output = everything;
                return;
            }

            /* Otherwise, replace its contents with the new list */
            invlist_replace_list_destroys_src(*output, everything);
            SvREFCNT_dec_NN(everything);
            return;
        }

        /* Here, we don't want the complement of 'b', and since it is empty,
         * the union will come entirely from 'a'.  If 'a' is NULL or empty, the
         * output will be empty */

        if (a == NULL) {
            *output = _new_invlist(0);
            return;
        }

        if (_invlist_len(a) == 0) {
            invlist_clear(*output);
            return;
        }

        /* Here, 'a' is not empty, and entirely determines the union.  If the
         * output is not to overwrite 'b', we can just return 'a'. */
        if (*output != b) {

            /* If the output is to overwrite 'a', we have a no-op, as it's
             * already in 'a' */
            if (*output == a) {
                return;
            }

            /* But otherwise we have to copy 'a' to the output */
            *output = invlist_clone(a);
            return;
        }

        /* Here, 'b' is to be overwritten by the output, which will be 'a' */
        u = invlist_clone(a);
        invlist_replace_list_destroys_src(*output, u);
        SvREFCNT_dec_NN(u);

        return;
    }

    if (a == NULL || ((len_a = _invlist_len(a)) == 0)) {

        /* Here, 'a' is empty.  That means the union will come entirely from
         * 'b'.  If the output is not to overwrite 'a', we can just return
         * what's in 'b'.  */
        if (*output != a) {

            /* If the output is to overwrite 'b', it's already in 'b', but
             * otherwise we have to copy 'b' to the output */
            if (*output != b) {
                *output = invlist_clone(b);
            }

            /* And if the output is to be the inversion of 'b', do that */
            if (complement_b) {
                _invlist_invert(*output);
            }

            return;
        }

        /* Here, 'a', which is empty or even NULL, is to be overwritten by the
         * output, which will either be 'b' or the complement of 'b' */

        if (a == NULL) {
            *output = invlist_clone(b);
        }
        else {
            u = invlist_clone(b);
            invlist_replace_list_destroys_src(*output, u);
            SvREFCNT_dec_NN(u);
        }

        if (complement_b) {
            _invlist_invert(*output);
        }

        return;
    }

    /* Here both lists exist and are non-empty */
    array_a = invlist_array(a);
    array_b = invlist_array(b);

    /* If are to take the union of 'a' with the complement of b, set it
     * up so are looking at b's complement. */
    if (complement_b) {

        /* To complement, we invert: if the first element is 0, remove it.  To
         * do this, we just pretend the array starts one later */
        if (array_b[0] == 0) {
            array_b++;
            len_b--;
        }
        else {

            /* But if the first element is not zero, we pretend the list starts
             * at the 0 that is always stored immediately before the array. */
            array_b--;
            len_b++;
        }
    }

    /* Size the union for the worst case: that the sets are completely
     * disjoint */
    u = _new_invlist(len_a + len_b);

    /* Will contain U+0000 if either component does */
    array_u = _invlist_array_init(u, (len_a > 0 && array_a[0] == 0)
                                      || (len_b > 0 && array_b[0] == 0));

    /* Go through each list item by item, stopping when exhausted one of
     * them */
    while (i_a < len_a && i_b < len_b) {
        UV cp;      /* The element to potentially add to the union's array */
        bool cp_in_set;   /* is it in the the input list's set or not */

        /* We need to take one or the other of the two inputs for the union.
         * Since we are merging two sorted lists, we take the smaller of the
         * next items.  In case of a tie, we take the one that is in its set
         * first.  If we took one not in the set first, it would decrement the
         * count, possibly to 0 which would cause it to be output as ending the
         * range, and the next time through we would take the same number, and
         * output it again as beginning the next range.  By doing it the
         * opposite way, there is no possibility that the count will be
         * momentarily decremented to 0, and thus the two adjoining ranges will
         * be seamlessly merged.  (In a tie and both are in the set or both not
         * in the set, it doesn't matter which we take first.) */
        if (array_a[i_a] < array_b[i_b]
            || (array_a[i_a] == array_b[i_b]
                && ELEMENT_RANGE_MATCHES_INVLIST(i_a)))
        {
            cp_in_set = ELEMENT_RANGE_MATCHES_INVLIST(i_a);
            cp= array_a[i_a++];
        }
        else {
            cp_in_set = ELEMENT_RANGE_MATCHES_INVLIST(i_b);
            cp = array_b[i_b++];
        }

        /* Here, have chosen which of the two inputs to look at.  Only output
         * if the running count changes to/from 0, which marks the
         * beginning/end of a range in that's in the set */
        if (cp_in_set) {
            if (count == 0) {
                array_u[i_u++] = cp;
            }
            count++;
        }
        else {
            count--;
            if (count == 0) {
                array_u[i_u++] = cp;
            }
        }
    }

    /* Here, we are finished going through at least one of the lists, which
     * means there is something remaining in at most one.  We check if the list
     * that hasn't been exhausted is positioned such that we are in the middle
     * of a range in its set or not.  (i_a and i_b point to the element beyond
     * the one we care about.) If in the set, we decrement 'count'; if 0, there
     * is potentially more to output.
     * There are four cases:
     *  1) Both weren't in their sets, count is 0, and remains 0.  What's left
     *     in the union is entirely from the non-exhausted set.
     *  2) Both were in their sets, count is 2.  Nothing further should
     *     be output, as everything that remains will be in the exhausted
     *     list's set, hence in the union; decrementing to 1 but not 0 insures
     *     that
     *  3) the exhausted was in its set, non-exhausted isn't, count is 1.
     *     Nothing further should be output because the union includes
     *     everything from the exhausted set.  Not decrementing ensures that.
     *  4) the exhausted wasn't in its set, non-exhausted is, count is 1;
     *     decrementing to 0 insures that we look at the remainder of the
     *     non-exhausted set */
    if ((i_a != len_a && PREV_RANGE_MATCHES_INVLIST(i_a))
        || (i_b != len_b && PREV_RANGE_MATCHES_INVLIST(i_b)))
    {
        count--;
    }

    /* The final length is what we've output so far, plus what else is about to
     * be output.  (If 'count' is non-zero, then the input list we exhausted
     * has everything remaining up to the machine's limit in its set, and hence
     * in the union, so there will be no further output. */
    len_u = i_u;
    if (count == 0) {
        /* At most one of the subexpressions will be non-zero */
        len_u += (len_a - i_a) + (len_b - i_b);
    }

    /* Set result to final length, which can change the pointer to array_u, so
     * re-find it */
    if (len_u != _invlist_len(u)) {
        invlist_set_len(u, len_u, *get_invlist_offset_addr(u));
        invlist_trim(u);
        array_u = invlist_array(u);
    }

    /* When 'count' is 0, the list that was exhausted (if one was shorter than
     * the other) ended with everything above it not in its set.  That means
     * that the remaining part of the union is precisely the same as the
     * non-exhausted list, so can just copy it unchanged.  (If both list were
     * exhausted at the same time, then the operations below will be both 0.)
     */
    if (count == 0) {
        IV copy_count; /* At most one will have a non-zero copy count */
        if ((copy_count = len_a - i_a) > 0) {
            Copy(array_a + i_a, array_u + i_u, copy_count, UV);
        }
        else if ((copy_count = len_b - i_b) > 0) {
            Copy(array_b + i_b, array_u + i_u, copy_count, UV);
        }
    }

    if (a != *output && b != *output) {
        *output = u;
    }
    else {
        /*  Here, the output is to be the same as one of the input scalars,
         *  hence replacing it.  The simple thing to do is to free the input
         *  scalar, making it instead be the output one.  But experience has
         *  shown [perl #127392] that if the input is a mortal, we can get a
         *  huge build-up of these during regex compilation before they get
         *  freed.  So for that case, replace just the input's interior with
         *  the output's, and then free the output */

        assert(! invlist_is_iterating(*output));

        if (! SvTEMP(*output)) {
            SvREFCNT_dec_NN(*output);
            *output = u;
        }
        else {
            invlist_replace_list_destroys_src(*output, u);
            SvREFCNT_dec_NN(u);
        }
    }

    return;
}

void
Perl__invlist_intersection_maybe_complement_2nd(pTHX_ SV* const a, SV* const b,
                                               const bool complement_b, SV** i)
{
    /* Take the intersection of two inversion lists and point <i> to it.  *i
     * SHOULD BE DEFINED upon input, and if it points to one of the two lists,
     * the reference count to that list will be decremented if not already a
     * temporary (mortal); otherwise just its contents will be modified to be
     * the intersection.  The first list, <a>, may be NULL, in which case an
     * empty list is returned.  If <complement_b> is TRUE, the result will be
     * the intersection of <a> and the complement (or inversion) of <b> instead
     * of <b> directly.
     *
     * The basis for this comes from "Unicode Demystified" Chapter 13 by
     * Richard Gillam, published by Addison-Wesley, and explained at some
     * length there.  The preface says to incorporate its examples into your
     * code at your own risk.  In fact, it had bugs
     *
     * The algorithm is like a merge sort, and is essentially the same as the
     * union above
     */

    const UV* array_a;          /* a's array */
    const UV* array_b;
    UV len_a;   /* length of a's array */
    UV len_b;

    SV* r;                   /* the resulting intersection */
    UV* array_r;
    UV len_r;

    UV i_a = 0;             /* current index into a's array */
    UV i_b = 0;
    UV i_r = 0;

    /* running count, as explained in the algorithm source book; items are
     * stopped accumulating and are output when the count changes to/from 2.
     * The count is incremented when we start a range that's in the set, and
     * decremented when we start a range that's not in the set.  So its range
     * is 0 to 2.  Only when the count is 2 is something in the intersection.
     */
    UV count = 0;

    PERL_ARGS_ASSERT__INVLIST_INTERSECTION_MAYBE_COMPLEMENT_2ND;
    assert(a != b);

    /* Special case if either one is empty */
    len_a = (a == NULL) ? 0 : _invlist_len(a);
    if ((len_a == 0) || ((len_b = _invlist_len(b)) == 0)) {
        if (len_a != 0 && complement_b) {

            /* Here, 'a' is not empty, therefore from the enclosing 'if', 'b'
             * must be empty.  Here, also we are using 'b's complement, which
             * hence must be every possible code point.  Thus the intersection
             * is simply 'a'. */

            if (*i == a) {  /* No-op */
                return;
            }

            /* If not overwriting either input, just make a copy of 'a' */
            if (*i != b) {
                *i = invlist_clone(a);
                return;
            }

            /* Here we are overwriting 'b' with 'a's contents */
            r = invlist_clone(a);
            invlist_replace_list_destroys_src(*i, r);
            SvREFCNT_dec_NN(r);
            return;
        }

        /* Here, 'a' or 'b' is empty and not using the complement of 'b'.  The
         * intersection must be empty */
        if (*i == NULL) {
            *i = _new_invlist(0);
            return;
        }

        invlist_clear(*i);
        return;
    }

    /* Here both lists exist and are non-empty */
    array_a = invlist_array(a);
    array_b = invlist_array(b);

    /* If are to take the intersection of 'a' with the complement of b, set it
     * up so are looking at b's complement. */
    if (complement_b) {

        /* To complement, we invert: if the first element is 0, remove it.  To
         * do this, we just pretend the array starts one later */
        if (array_b[0] == 0) {
            array_b++;
            len_b--;
        }
        else {

            /* But if the first element is not zero, we pretend the list starts
             * at the 0 that is always stored immediately before the array. */
            array_b--;
            len_b++;
        }
    }

    /* Size the intersection for the worst case: that the intersection ends up
     * fragmenting everything to be completely disjoint */
    r= _new_invlist(len_a + len_b);

    /* Will contain U+0000 iff both components do */
    array_r = _invlist_array_init(r, len_a > 0 && array_a[0] == 0
                                     && len_b > 0 && array_b[0] == 0);

    /* Go through each list item by item, stopping when exhausted one of
     * them */
    while (i_a < len_a && i_b < len_b) {
        UV cp;      /* The element to potentially add to the intersection's
                       array */
        bool cp_in_set; /* Is it in the input list's set or not */

        /* We need to take one or the other of the two inputs for the
         * intersection.  Since we are merging two sorted lists, we take the
         * smaller of the next items.  In case of a tie, we take the one that
         * is not in its set first (a difference from the union algorithm).  If
         * we took one in the set first, it would increment the count, possibly
         * to 2 which would cause it to be output as starting a range in the
         * intersection, and the next time through we would take that same
         * number, and output it again as ending the set.  By doing it the
         * opposite of this, there is no possibility that the count will be
         * momentarily incremented to 2.  (In a tie and both are in the set or
         * both not in the set, it doesn't matter which we take first.) */
        if (array_a[i_a] < array_b[i_b]
            || (array_a[i_a] == array_b[i_b]
                && ! ELEMENT_RANGE_MATCHES_INVLIST(i_a)))
        {
            cp_in_set = ELEMENT_RANGE_MATCHES_INVLIST(i_a);
            cp= array_a[i_a++];
        }
        else {
            cp_in_set = ELEMENT_RANGE_MATCHES_INVLIST(i_b);
            cp= array_b[i_b++];
        }

        /* Here, have chosen which of the two inputs to look at.  Only output
         * if the running count changes to/from 2, which marks the
         * beginning/end of a range that's in the intersection */
        if (cp_in_set) {
            count++;
            if (count == 2) {
                array_r[i_r++] = cp;
            }
        }
        else {
            if (count == 2) {
                array_r[i_r++] = cp;
            }
            count--;
        }
    }

    /* Here, we are finished going through at least one of the lists, which
     * means there is something remaining in at most one.  We check if the list
     * that has been exhausted is positioned such that we are in the middle
     * of a range in its set or not.  (i_a and i_b point to elements 1 beyond
     * the ones we care about.)  There are four cases:
     *  1) Both weren't in their sets, count is 0, and remains 0.  There's
     *     nothing left in the intersection.
     *  2) Both were in their sets, count is 2 and perhaps is incremented to
     *     above 2.  What should be output is exactly that which is in the
     *     non-exhausted set, as everything it has is also in the intersection
     *     set, and everything it doesn't have can't be in the intersection
     *  3) The exhausted was in its set, non-exhausted isn't, count is 1, and
     *     gets incremented to 2.  Like the previous case, the intersection is
     *     everything that remains in the non-exhausted set.
     *  4) the exhausted wasn't in its set, non-exhausted is, count is 1, and
     *     remains 1.  And the intersection has nothing more. */
    if ((i_a == len_a && PREV_RANGE_MATCHES_INVLIST(i_a))
        || (i_b == len_b && PREV_RANGE_MATCHES_INVLIST(i_b)))
    {
        count++;
    }

    /* The final length is what we've output so far plus what else is in the
     * intersection.  At most one of the subexpressions below will be non-zero
     * */
    len_r = i_r;
    if (count >= 2) {
        len_r += (len_a - i_a) + (len_b - i_b);
    }

    /* Set result to final length, which can change the pointer to array_r, so
     * re-find it */
    if (len_r != _invlist_len(r)) {
        invlist_set_len(r, len_r, *get_invlist_offset_addr(r));
        invlist_trim(r);
        array_r = invlist_array(r);
    }

    /* Finish outputting any remaining */
    if (count >= 2) { /* At most one will have a non-zero copy count */
        IV copy_count;
        if ((copy_count = len_a - i_a) > 0) {
            Copy(array_a + i_a, array_r + i_r, copy_count, UV);
        }
        else if ((copy_count = len_b - i_b) > 0) {
            Copy(array_b + i_b, array_r + i_r, copy_count, UV);
        }
    }

    if (a != *i && b != *i) {
        *i = r;
    }
    else {
        /*  Here, the output is to be the same as one of the input scalars,
         *  hence replacing it.  The simple thing to do is to free the input
         *  scalar, making it instead be the output one.  But experience has
         *  shown [perl #127392] that if the input is a mortal, we can get a
         *  huge build-up of these during regex compilation before they get
         *  freed.  So for that case, replace just the input's interior with
         *  the output's, and then free the output.  A short-cut in this case
         *  is if the output is empty, we can just set the input to be empty */

        assert(! invlist_is_iterating(*i));

        if (! SvTEMP(*i)) {
            SvREFCNT_dec_NN(*i);
            *i = r;
        }
        else {
            if (len_r) {
                invlist_replace_list_destroys_src(*i, r);
            }
            else {
                invlist_clear(*i);
            }
            SvREFCNT_dec_NN(r);
        }
    }

    return;
}

SV*
Perl__add_range_to_invlist(pTHX_ SV* invlist, const UV start, const UV end)
{
    /* Add the range from 'start' to 'end' inclusive to the inversion list's
     * set.  A pointer to the inversion list is returned.  This may actually be
     * a new list, in which case the passed in one has been destroyed.  The
     * passed-in inversion list can be NULL, in which case a new one is created
     * with just the one range in it */

    SV* range_invlist;
    UV len;

    if (invlist == NULL) {
        invlist = _new_invlist(2);
        len = 0;
    }
    else {
        len = _invlist_len(invlist);
    }

    /* If comes after the final entry actually in the list, can just append it
     * to the end, */
    if (len == 0
        || (! ELEMENT_RANGE_MATCHES_INVLIST(len - 1)
            && start >= invlist_array(invlist)[len - 1]))
    {
        _append_range_to_invlist(invlist, start, end);
        return invlist;
    }

    /* Here, can't just append things, create and return a new inversion list
     * which is the union of this range and the existing inversion list.  (If
     * the new range is well-behaved wrt to the old one, we could just insert
     * it, doing a Move() down on the tail of the old one (potentially growing
     * it first).  But to determine that means we would have the extra
     * (possibly throw-away) work of first finding where the new one goes and
     * whether it disrupts (splits) an existing range, so it doesn't appear to
     * me (khw) that it's worth it) */
    range_invlist = _new_invlist(2);
    _append_range_to_invlist(range_invlist, start, end);

    _invlist_union(invlist, range_invlist, &invlist);

    /* The temporary can be freed */
    SvREFCNT_dec_NN(range_invlist);

    return invlist;
}

SV*
Perl__setup_canned_invlist(pTHX_ const STRLEN size, const UV element0,
                                 UV** other_elements_ptr)
{
    /* Create and return an inversion list whose contents are to be populated
     * by the caller.  The caller gives the number of elements (in 'size') and
     * the very first element ('element0').  This function will set
     * '*other_elements_ptr' to an array of UVs, where the remaining elements
     * are to be placed.
     *
     * Obviously there is some trust involved that the caller will properly
     * fill in the other elements of the array.
     *
     * (The first element needs to be passed in, as the underlying code does
     * things differently depending on whether it is zero or non-zero) */

    SV* invlist = _new_invlist(size);
    bool offset;

    PERL_ARGS_ASSERT__SETUP_CANNED_INVLIST;

    _append_range_to_invlist(invlist, element0, element0);
    offset = *get_invlist_offset_addr(invlist);

    invlist_set_len(invlist, size, offset);
    *other_elements_ptr = invlist_array(invlist) + 1;
    return invlist;
}

#endif

PERL_STATIC_INLINE SV*
S_add_cp_to_invlist(pTHX_ SV* invlist, const UV cp) {
    return _add_range_to_invlist(invlist, cp, cp);
}

#ifndef PERL_IN_XSUB_RE
void
Perl__invlist_invert(pTHX_ SV* const invlist)
{
    /* Complement the input inversion list.  This adds a 0 if the list didn't
     * have a zero; removes it otherwise.  As described above, the data
     * structure is set up so that this is very efficient */

    PERL_ARGS_ASSERT__INVLIST_INVERT;

    assert(! invlist_is_iterating(invlist));

    /* The inverse of matching nothing is matching everything */
    if (_invlist_len(invlist) == 0) {
        _append_range_to_invlist(invlist, 0, UV_MAX);
        return;
    }

    *get_invlist_offset_addr(invlist) = ! *get_invlist_offset_addr(invlist);
}

#endif

PERL_STATIC_INLINE SV*
S_invlist_clone(pTHX_ SV* const invlist)
{

    /* Return a new inversion list that is a copy of the input one, which is
     * unchanged.  The new list will not be mortal even if the old one was. */

    /* Need to allocate extra space to accommodate Perl's addition of a
     * trailing NUL to SvPV's, since it thinks they are always strings */
    SV* new_invlist = _new_invlist(_invlist_len(invlist) + 1);
    STRLEN physical_length = SvCUR(invlist);
    bool offset = *(get_invlist_offset_addr(invlist));

    PERL_ARGS_ASSERT_INVLIST_CLONE;

    *(get_invlist_offset_addr(new_invlist)) = offset;
    invlist_set_len(new_invlist, _invlist_len(invlist), offset);
    Copy(SvPVX(invlist), SvPVX(new_invlist), physical_length, char);

    return new_invlist;
}

PERL_STATIC_INLINE STRLEN*
S_get_invlist_iter_addr(SV* invlist)
{
    /* Return the address of the UV that contains the current iteration
     * position */

    PERL_ARGS_ASSERT_GET_INVLIST_ITER_ADDR;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    return &(((XINVLIST*) SvANY(invlist))->iterator);
}

PERL_STATIC_INLINE void
S_invlist_iterinit(SV* invlist) /* Initialize iterator for invlist */
{
    PERL_ARGS_ASSERT_INVLIST_ITERINIT;

    *get_invlist_iter_addr(invlist) = 0;
}

PERL_STATIC_INLINE void
S_invlist_iterfinish(SV* invlist)
{
    /* Terminate iterator for invlist.  This is to catch development errors.
     * Any iteration that is interrupted before completed should call this
     * function.  Functions that add code points anywhere else but to the end
     * of an inversion list assert that they are not in the middle of an
     * iteration.  If they were, the addition would make the iteration
     * problematical: if the iteration hadn't reached the place where things
     * were being added, it would be ok */

    PERL_ARGS_ASSERT_INVLIST_ITERFINISH;

    *get_invlist_iter_addr(invlist) = (STRLEN) UV_MAX;
}

STATIC bool
S_invlist_iternext(SV* invlist, UV* start, UV* end)
{
    /* An C<invlist_iterinit> call on <invlist> must be used to set this up.
     * This call sets in <*start> and <*end>, the next range in <invlist>.
     * Returns <TRUE> if successful and the next call will return the next
     * range; <FALSE> if was already at the end of the list.  If the latter,
     * <*start> and <*end> are unchanged, and the next call to this function
     * will start over at the beginning of the list */

    STRLEN* pos = get_invlist_iter_addr(invlist);
    UV len = _invlist_len(invlist);
    UV *array;

    PERL_ARGS_ASSERT_INVLIST_ITERNEXT;

    if (*pos >= len) {
        *pos = (STRLEN) UV_MAX; /* Force iterinit() to be required next time */
        return FALSE;
    }

    array = invlist_array(invlist);

    *start = array[(*pos)++];

    if (*pos >= len) {
        *end = UV_MAX;
    }
    else {
        *end = array[(*pos)++] - 1;
    }

    return TRUE;
}

PERL_STATIC_INLINE UV
S_invlist_highest(SV* const invlist)
{
    /* Returns the highest code point that matches an inversion list.  This API
     * has an ambiguity, as it returns 0 under either the highest is actually
     * 0, or if the list is empty.  If this distinction matters to you, check
     * for emptiness before calling this function */

    UV len = _invlist_len(invlist);
    UV *array;

    PERL_ARGS_ASSERT_INVLIST_HIGHEST;

    if (len == 0) {
        return 0;
    }

    array = invlist_array(invlist);

    /* The last element in the array in the inversion list always starts a
     * range that goes to infinity.  That range may be for code points that are
     * matched in the inversion list, or it may be for ones that aren't
     * matched.  In the latter case, the highest code point in the set is one
     * less than the beginning of this range; otherwise it is the final element
     * of this range: infinity */
    return (ELEMENT_RANGE_MATCHES_INVLIST(len - 1))
           ? UV_MAX
           : array[len - 1] - 1;
}

STATIC SV *
S_invlist_contents(pTHX_ SV* const invlist, const bool traditional_style)
{
    /* Get the contents of an inversion list into a string SV so that they can
     * be printed out.  If 'traditional_style' is TRUE, it uses the format
     * traditionally done for debug tracing; otherwise it uses a format
     * suitable for just copying to the output, with blanks between ranges and
     * a dash between range components */

    UV start, end;
    SV* output;
    const char intra_range_delimiter = (traditional_style ? '\t' : '-');
    const char inter_range_delimiter = (traditional_style ? '\n' : ' ');

    if (traditional_style) {
        output = newSVpvs("\n");
    }
    else {
        output = newSVpvs("");
    }

    PERL_ARGS_ASSERT_INVLIST_CONTENTS;

    assert(! invlist_is_iterating(invlist));

    invlist_iterinit(invlist);
    while (invlist_iternext(invlist, &start, &end)) {
        if (end == UV_MAX) {
            Perl_sv_catpvf(aTHX_ output, "%04"UVXf"%cINFINITY%c",
                                          start, intra_range_delimiter,
                                                 inter_range_delimiter);
        }
        else if (end != start) {
            Perl_sv_catpvf(aTHX_ output, "%04"UVXf"%c%04"UVXf"%c",
                                          start,
                                                   intra_range_delimiter,
                                                  end, inter_range_delimiter);
        }
        else {
            Perl_sv_catpvf(aTHX_ output, "%04"UVXf"%c",
                                          start, inter_range_delimiter);
        }
    }

    if (SvCUR(output) && ! traditional_style) {/* Get rid of trailing blank */
        SvCUR_set(output, SvCUR(output) - 1);
    }

    return output;
}

#ifndef PERL_IN_XSUB_RE
void
Perl__invlist_dump(pTHX_ PerlIO *file, I32 level,
                         const char * const indent, SV* const invlist)
{
    /* Designed to be called only by do_sv_dump().  Dumps out the ranges of the
     * inversion list 'invlist' to 'file' at 'level'  Each line is prefixed by
     * the string 'indent'.  The output looks like this:
         [0] 0x000A .. 0x000D
         [2] 0x0085
         [4] 0x2028 .. 0x2029
         [6] 0x3104 .. INFINITY
     * This means that the first range of code points matched by the list are
     * 0xA through 0xD; the second range contains only the single code point
     * 0x85, etc.  An inversion list is an array of UVs.  Two array elements
     * are used to define each range (except if the final range extends to
     * infinity, only a single element is needed).  The array index of the
     * first element for the corresponding range is given in brackets. */

    UV start, end;
    STRLEN count = 0;

    PERL_ARGS_ASSERT__INVLIST_DUMP;

    if (invlist_is_iterating(invlist)) {
        Perl_dump_indent(aTHX_ level, file,
             "%sCan't dump inversion list because is in middle of iterating\n",
             indent);
        return;
    }

    invlist_iterinit(invlist);
    while (invlist_iternext(invlist, &start, &end)) {
        if (end == UV_MAX) {
            Perl_dump_indent(aTHX_ level, file,
                                       "%s[%"UVuf"] 0x%04"UVXf" .. INFINITY\n",
                                   indent, (UV)count, start);
        }
        else if (end != start) {
            Perl_dump_indent(aTHX_ level, file,
                                    "%s[%"UVuf"] 0x%04"UVXf" .. 0x%04"UVXf"\n",
                                indent, (UV)count, start,         end);
        }
        else {
            Perl_dump_indent(aTHX_ level, file, "%s[%"UVuf"] 0x%04"UVXf"\n",
                                            indent, (UV)count, start);
        }
        count += 2;
    }
}

void
Perl__load_PL_utf8_foldclosures (pTHX)
{
    assert(! PL_utf8_foldclosures);

    /* If the folds haven't been read in, call a fold function
     * to force that */
    if (! PL_utf8_tofold) {
        U8 dummy[UTF8_MAXBYTES_CASE+1];

        /* This string is just a short named one above \xff */
        to_utf8_fold((U8*) HYPHEN_UTF8, dummy, NULL);
        assert(PL_utf8_tofold); /* Verify that worked */
    }
    PL_utf8_foldclosures = _swash_inversion_hash(PL_utf8_tofold);
}
#endif

#if defined(PERL_ARGS_ASSERT__INVLISTEQ) && !defined(PERL_IN_XSUB_RE)
bool
Perl__invlistEQ(pTHX_ SV* const a, SV* const b, const bool complement_b)
{
    /* Return a boolean as to if the two passed in inversion lists are
     * identical.  The final argument, if TRUE, says to take the complement of
     * the second inversion list before doing the comparison */

    const UV* array_a = invlist_array(a);
    const UV* array_b = invlist_array(b);
    UV len_a = _invlist_len(a);
    UV len_b = _invlist_len(b);

    UV i = 0;               /* current index into the arrays */
    bool retval = TRUE;     /* Assume are identical until proven otherwise */

    PERL_ARGS_ASSERT__INVLISTEQ;

    /* If are to compare 'a' with the complement of b, set it
     * up so are looking at b's complement. */
    if (complement_b) {

        /* The complement of nothing is everything, so <a> would have to have
         * just one element, starting at zero (ending at infinity) */
        if (len_b == 0) {
            return (len_a == 1 && array_a[0] == 0);
        }
        else if (array_b[0] == 0) {

            /* Otherwise, to complement, we invert.  Here, the first element is
             * 0, just remove it.  To do this, we just pretend the array starts
             * one later */

            array_b++;
            len_b--;
        }
        else {

            /* But if the first element is not zero, we pretend the list starts
             * at the 0 that is always stored immediately before the array. */
            array_b--;
            len_b++;
        }
    }

    /* Make sure that the lengths are the same, as well as the final element
     * before looping through the remainder.  (Thus we test the length, final,
     * and first elements right off the bat) */
    if (len_a != len_b || array_a[len_a-1] != array_b[len_a-1]) {
        retval = FALSE;
    }
    else for (i = 0; i < len_a - 1; i++) {
        if (array_a[i] != array_b[i]) {
            retval = FALSE;
            break;
        }
    }

    return retval;
}
#endif

/*
 * As best we can, determine the characters that can match the start of
 * the given EXACTF-ish node.
 *
 * Returns the invlist as a new SV*; it is the caller's responsibility to
 * call SvREFCNT_dec() when done with it.
 */
STATIC SV*
S__make_exactf_invlist(pTHX_ RExC_state_t *pRExC_state, regnode *node)
{
    const U8 * s = (U8*)STRING(node);
    SSize_t bytelen = STR_LEN(node);
    UV uc;
    /* Start out big enough for 2 separate code points */
    SV* invlist = _new_invlist(4);

    PERL_ARGS_ASSERT__MAKE_EXACTF_INVLIST;

    if (! UTF) {
        uc = *s;

        /* We punt and assume can match anything if the node begins
         * with a multi-character fold.  Things are complicated.  For
         * example, /ffi/i could match any of:
         *  "\N{LATIN SMALL LIGATURE FFI}"
         *  "\N{LATIN SMALL LIGATURE FF}I"
         *  "F\N{LATIN SMALL LIGATURE FI}"
         *  plus several other things; and making sure we have all the
         *  possibilities is hard. */
        if (is_MULTI_CHAR_FOLD_latin1_safe(s, s + bytelen)) {
            invlist = _add_range_to_invlist(invlist, 0, UV_MAX);
        }
        else {
            /* Any Latin1 range character can potentially match any
             * other depending on the locale */
            if (OP(node) == EXACTFL) {
                _invlist_union(invlist, PL_Latin1, &invlist);
            }
            else {
                /* But otherwise, it matches at least itself.  We can
                 * quickly tell if it has a distinct fold, and if so,
                 * it matches that as well */
                invlist = add_cp_to_invlist(invlist, uc);
                if (IS_IN_SOME_FOLD_L1(uc))
                    invlist = add_cp_to_invlist(invlist, PL_fold_latin1[uc]);
            }

            /* Some characters match above-Latin1 ones under /i.  This
             * is true of EXACTFL ones when the locale is UTF-8 */
            if (HAS_NONLATIN1_SIMPLE_FOLD_CLOSURE(uc)
                && (! isASCII(uc) || (OP(node) != EXACTFA
                                    && OP(node) != EXACTFA_NO_TRIE)))
            {
                add_above_Latin1_folds(pRExC_state, (U8) uc, &invlist);
            }
        }
    }
    else {  /* Pattern is UTF-8 */
        U8 folded[UTF8_MAX_FOLD_CHAR_EXPAND * UTF8_MAXBYTES_CASE + 1] = { '\0' };
        STRLEN foldlen = UTF8SKIP(s);
        const U8* e = s + bytelen;
        SV** listp;

        uc = utf8_to_uvchr_buf(s, s + bytelen, NULL);

        /* The only code points that aren't folded in a UTF EXACTFish
         * node are are the problematic ones in EXACTFL nodes */
        if (OP(node) == EXACTFL && is_PROBLEMATIC_LOCALE_FOLDEDS_START_cp(uc)) {
            /* We need to check for the possibility that this EXACTFL
             * node begins with a multi-char fold.  Therefore we fold
             * the first few characters of it so that we can make that
             * check */
            U8 *d = folded;
            int i;

            for (i = 0; i < UTF8_MAX_FOLD_CHAR_EXPAND && s < e; i++) {
                if (isASCII(*s)) {
                    *(d++) = (U8) toFOLD(*s);
                    s++;
                }
                else {
                    STRLEN len;
                    to_utf8_fold(s, d, &len);
                    d += len;
                    s += UTF8SKIP(s);
                }
            }

            /* And set up so the code below that looks in this folded
             * buffer instead of the node's string */
            e = d;
            foldlen = UTF8SKIP(folded);
            s = folded;
        }

        /* When we reach here 's' points to the fold of the first
         * character(s) of the node; and 'e' points to far enough along
         * the folded string to be just past any possible multi-char
         * fold. 'foldlen' is the length in bytes of the first
         * character in 's'
         *
         * Unlike the non-UTF-8 case, the macro for determining if a
         * string is a multi-char fold requires all the characters to
         * already be folded.  This is because of all the complications
         * if not.  Note that they are folded anyway, except in EXACTFL
         * nodes.  Like the non-UTF case above, we punt if the node
         * begins with a multi-char fold  */

        if (is_MULTI_CHAR_FOLD_utf8_safe(s, e)) {
            invlist = _add_range_to_invlist(invlist, 0, UV_MAX);
        }
        else {  /* Single char fold */

            /* It matches all the things that fold to it, which are
             * found in PL_utf8_foldclosures (including itself) */
            invlist = add_cp_to_invlist(invlist, uc);
            if (! PL_utf8_foldclosures)
                _load_PL_utf8_foldclosures();
            if ((listp = hv_fetch(PL_utf8_foldclosures,
                                (char *) s, foldlen, FALSE)))
            {
                AV* list = (AV*) *listp;
                IV k;
                for (k = 0; k <= av_tindex(list); k++) {
                    SV** c_p = av_fetch(list, k, FALSE);
                    UV c;
                    assert(c_p);

                    c = SvUV(*c_p);

                    /* /aa doesn't allow folds between ASCII and non- */
                    if ((OP(node) == EXACTFA || OP(node) == EXACTFA_NO_TRIE)
                        && isASCII(c) != isASCII(uc))
                    {
                        continue;
                    }

                    invlist = add_cp_to_invlist(invlist, c);
                }
            }
        }
    }

    return invlist;
}

#undef HEADER_LENGTH
#undef TO_INTERNAL_SIZE
#undef FROM_INTERNAL_SIZE
#undef INVLIST_VERSION_ID

/* End of inversion list object */

STATIC void
S_parse_lparen_question_flags(pTHX_ RExC_state_t *pRExC_state)
{
    /* This parses the flags that are in either the '(?foo)' or '(?foo:bar)'
     * constructs, and updates RExC_flags with them.  On input, RExC_parse
     * should point to the first flag; it is updated on output to point to the
     * final ')' or ':'.  There needs to be at least one flag, or this will
     * abort */

    /* for (?g), (?gc), and (?o) warnings; warning
       about (?c) will warn about (?g) -- japhy    */

#define WASTED_O  0x01
#define WASTED_G  0x02
#define WASTED_C  0x04
#define WASTED_GC (WASTED_G|WASTED_C)
    I32 wastedflags = 0x00;
    U32 posflags = 0, negflags = 0;
    U32 *flagsp = &posflags;
    char has_charset_modifier = '\0';
    regex_charset cs;
    bool has_use_defaults = FALSE;
    const char* const seqstart = RExC_parse - 1; /* Point to the '?' */
    int x_mod_count = 0;

    PERL_ARGS_ASSERT_PARSE_LPAREN_QUESTION_FLAGS;

    /* '^' as an initial flag sets certain defaults */
    if (UCHARAT(RExC_parse) == '^') {
        RExC_parse++;
        has_use_defaults = TRUE;
        STD_PMMOD_FLAGS_CLEAR(&RExC_flags);
        set_regex_charset(&RExC_flags, (RExC_utf8 || RExC_uni_semantics)
                                        ? REGEX_UNICODE_CHARSET
                                        : REGEX_DEPENDS_CHARSET);
    }

    cs = get_regex_charset(RExC_flags);
    if (cs == REGEX_DEPENDS_CHARSET
        && (RExC_utf8 || RExC_uni_semantics))
    {
        cs = REGEX_UNICODE_CHARSET;
    }

    while (RExC_parse < RExC_end) {
        /* && strchr("iogcmsx", *RExC_parse) */
        /* (?g), (?gc) and (?o) are useless here
           and must be globally applied -- japhy */
        switch (*RExC_parse) {

            /* Code for the imsxn flags */
            CASE_STD_PMMOD_FLAGS_PARSE_SET(flagsp, x_mod_count);

            case LOCALE_PAT_MOD:
                if (has_charset_modifier) {
                    goto excess_modifier;
                }
                else if (flagsp == &negflags) {
                    goto neg_modifier;
                }
                cs = REGEX_LOCALE_CHARSET;
                has_charset_modifier = LOCALE_PAT_MOD;
                break;
            case UNICODE_PAT_MOD:
                if (has_charset_modifier) {
                    goto excess_modifier;
                }
                else if (flagsp == &negflags) {
                    goto neg_modifier;
                }
                cs = REGEX_UNICODE_CHARSET;
                has_charset_modifier = UNICODE_PAT_MOD;
                break;
            case ASCII_RESTRICT_PAT_MOD:
                if (flagsp == &negflags) {
                    goto neg_modifier;
                }
                if (has_charset_modifier) {
                    if (cs != REGEX_ASCII_RESTRICTED_CHARSET) {
                        goto excess_modifier;
                    }
                    /* Doubled modifier implies more restricted */
                    cs = REGEX_ASCII_MORE_RESTRICTED_CHARSET;
                }
                else {
                    cs = REGEX_ASCII_RESTRICTED_CHARSET;
                }
                has_charset_modifier = ASCII_RESTRICT_PAT_MOD;
                break;
            case DEPENDS_PAT_MOD:
                if (has_use_defaults) {
                    goto fail_modifiers;
                }
                else if (flagsp == &negflags) {
                    goto neg_modifier;
                }
                else if (has_charset_modifier) {
                    goto excess_modifier;
                }

                /* The dual charset means unicode semantics if the
                 * pattern (or target, not known until runtime) are
                 * utf8, or something in the pattern indicates unicode
                 * semantics */
                cs = (RExC_utf8 || RExC_uni_semantics)
                     ? REGEX_UNICODE_CHARSET
                     : REGEX_DEPENDS_CHARSET;
                has_charset_modifier = DEPENDS_PAT_MOD;
                break;
              excess_modifier:
                RExC_parse++;
                if (has_charset_modifier == ASCII_RESTRICT_PAT_MOD) {
                    vFAIL2("Regexp modifier \"%c\" may appear a maximum of twice", ASCII_RESTRICT_PAT_MOD);
                }
                else if (has_charset_modifier == *(RExC_parse - 1)) {
                    vFAIL2("Regexp modifier \"%c\" may not appear twice",
                                        *(RExC_parse - 1));
                }
                else {
                    vFAIL3("Regexp modifiers \"%c\" and \"%c\" are mutually exclusive", has_charset_modifier, *(RExC_parse - 1));
                }
                NOT_REACHED; /*NOTREACHED*/
              neg_modifier:
                RExC_parse++;
                vFAIL2("Regexp modifier \"%c\" may not appear after the \"-\"",
                                    *(RExC_parse - 1));
                NOT_REACHED; /*NOTREACHED*/
            case ONCE_PAT_MOD: /* 'o' */
            case GLOBAL_PAT_MOD: /* 'g' */
                if (PASS2 && ckWARN(WARN_REGEXP)) {
                    const I32 wflagbit = *RExC_parse == 'o'
                                         ? WASTED_O
                                         : WASTED_G;
                    if (! (wastedflags & wflagbit) ) {
                        wastedflags |= wflagbit;
                        /* diag_listed_as: Useless (?-%s) - don't use /%s modifier in regex; marked by <-- HERE in m/%s/ */
                        vWARN5(
                            RExC_parse + 1,
                            "Useless (%s%c) - %suse /%c modifier",
                            flagsp == &negflags ? "?-" : "?",
                            *RExC_parse,
                            flagsp == &negflags ? "don't " : "",
                            *RExC_parse
                        );
                    }
                }
                break;

            case CONTINUE_PAT_MOD: /* 'c' */
                if (PASS2 && ckWARN(WARN_REGEXP)) {
                    if (! (wastedflags & WASTED_C) ) {
                        wastedflags |= WASTED_GC;
                        /* diag_listed_as: Useless (?-%s) - don't use /%s modifier in regex; marked by <-- HERE in m/%s/ */
                        vWARN3(
                            RExC_parse + 1,
                            "Useless (%sc) - %suse /gc modifier",
                            flagsp == &negflags ? "?-" : "?",
                            flagsp == &negflags ? "don't " : ""
                        );
                    }
                }
                break;
            case KEEPCOPY_PAT_MOD: /* 'p' */
                if (flagsp == &negflags) {
                    if (PASS2)
                        ckWARNreg(RExC_parse + 1,"Useless use of (?-p)");
                } else {
                    *flagsp |= RXf_PMf_KEEPCOPY;
                }
                break;
            case '-':
                /* A flag is a default iff it is following a minus, so
                 * if there is a minus, it means will be trying to
                 * re-specify a default which is an error */
                if (has_use_defaults || flagsp == &negflags) {
                    goto fail_modifiers;
                }
                flagsp = &negflags;
                wastedflags = 0;  /* reset so (?g-c) warns twice */
                break;
            case ':':
            case ')':
                RExC_flags |= posflags;
                RExC_flags &= ~negflags;
                set_regex_charset(&RExC_flags, cs);
                if (RExC_flags & RXf_PMf_FOLD) {
                    RExC_contains_i = 1;
                }
                if (PASS2) {
                    STD_PMMOD_FLAGS_PARSE_X_WARN(x_mod_count);
                }
                return;
                /*NOTREACHED*/
            default:
              fail_modifiers:
                RExC_parse += SKIP_IF_CHAR(RExC_parse);
                /* diag_listed_as: Sequence (?%s...) not recognized in regex; marked by <-- HERE in m/%s/ */
                vFAIL2utf8f("Sequence (%"UTF8f"...) not recognized",
                      UTF8fARG(UTF, RExC_parse-seqstart, seqstart));
                NOT_REACHED; /*NOTREACHED*/
        }

        RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
    }

    vFAIL("Sequence (?... not terminated");
}

/*
 - reg - regular expression, i.e. main body or parenthesized thing
 *
 * Caller must absorb opening parenthesis.
 *
 * Combining parenthesis handling with the base level of regular expression
 * is a trifle forced, but the need to tie the tails of the branches to what
 * follows makes it hard to avoid.
 */
#define REGTAIL(x,y,z) regtail((x),(y),(z),depth+1)
#ifdef DEBUGGING
#define REGTAIL_STUDY(x,y,z) regtail_study((x),(y),(z),depth+1)
#else
#define REGTAIL_STUDY(x,y,z) regtail((x),(y),(z),depth+1)
#endif

PERL_STATIC_INLINE regnode *
S_handle_named_backref(pTHX_ RExC_state_t *pRExC_state,
                             I32 *flagp,
                             char * parse_start,
                             char ch
                      )
{
    regnode *ret;
    char* name_start = RExC_parse;
    U32 num = 0;
    SV *sv_dat = reg_scan_name(pRExC_state, SIZE_ONLY
                                            ? REG_RSN_RETURN_NULL
                                            : REG_RSN_RETURN_DATA);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_HANDLE_NAMED_BACKREF;

    if (RExC_parse == name_start || *RExC_parse != ch) {
        /* diag_listed_as: Sequence \%s... not terminated in regex; marked by <-- HERE in m/%s/ */
        vFAIL2("Sequence %.3s... not terminated",parse_start);
    }

    if (!SIZE_ONLY) {
        num = add_data( pRExC_state, STR_WITH_LEN("S"));
        RExC_rxi->data->data[num]=(void*)sv_dat;
        SvREFCNT_inc_simple_void(sv_dat);
    }
    RExC_sawback = 1;
    ret = reganode(pRExC_state,
                   ((! FOLD)
                     ? NREF
                     : (ASCII_FOLD_RESTRICTED)
                       ? NREFFA
                       : (AT_LEAST_UNI_SEMANTICS)
                         ? NREFFU
                         : (LOC)
                           ? NREFFL
                           : NREFF),
                    num);
    *flagp |= HASWIDTH;

    Set_Node_Offset(ret, parse_start+1);
    Set_Node_Cur_Length(ret, parse_start);

    nextchar(pRExC_state);
    return ret;
}

/* Returns NULL, setting *flagp to TRYAGAIN at the end of (?) that only sets
   flags. Returns NULL, setting *flagp to RESTART_PASS1 if the sizing scan
   needs to be restarted, or'd with NEED_UTF8 if the pattern needs to be
   upgraded to UTF-8.  Otherwise would only return NULL if regbranch() returns
   NULL, which cannot happen.  */
STATIC regnode *
S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp,U32 depth)
    /* paren: Parenthesized? 0=top; 1,2=inside '(': changed to letter.
     * 2 is like 1, but indicates that nextchar() has been called to advance
     * RExC_parse beyond the '('.  Things like '(?' are indivisible tokens, and
     * this flag alerts us to the need to check for that */
{
    regnode *ret;               /* Will be the head of the group. */
    regnode *br;
    regnode *lastbr;
    regnode *ender = NULL;
    I32 parno = 0;
    I32 flags;
    U32 oregflags = RExC_flags;
    bool have_branch = 0;
    bool is_open = 0;
    I32 freeze_paren = 0;
    I32 after_freeze = 0;
    I32 num; /* numeric backreferences */

    char * parse_start = RExC_parse; /* MJD */
    char * const oregcomp_parse = RExC_parse;

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REG;
    DEBUG_PARSE("reg ");

    *flagp = 0;                         /* Tentatively. */

    /* Having this true makes it feasible to have a lot fewer tests for the
     * parse pointer being in scope.  For example, we can write
     *      while(isFOO(*RExC_parse)) RExC_parse++;
     * instead of
     *      while(RExC_parse < RExC_end && isFOO(*RExC_parse)) RExC_parse++;
     */
    assert(*RExC_end == '\0');

    /* Make an OPEN node, if parenthesized. */
    if (paren) {

        /* Under /x, space and comments can be gobbled up between the '(' and
         * here (if paren ==2).  The forms '(*VERB' and '(?...' disallow such
         * intervening space, as the sequence is a token, and a token should be
         * indivisible */
        bool has_intervening_patws = paren == 2 && *(RExC_parse - 1) != '(';

        assert(RExC_parse < RExC_end);

        if ( *RExC_parse == '*') { /* (*VERB:ARG) */
            char *start_verb = RExC_parse + 1;
            STRLEN verb_len;
            char *start_arg = NULL;
            unsigned char op = 0;
            int arg_required = 0;
            int internal_argval = -1; /* if >-1 we are not allowed an argument*/

            if (has_intervening_patws) {
                RExC_parse++;   /* past the '*' */
                vFAIL("In '(*VERB...)', the '(' and '*' must be adjacent");
            }
            while (RExC_parse < RExC_end && *RExC_parse != ')' ) {
                if ( *RExC_parse == ':' ) {
                    start_arg = RExC_parse + 1;
                    break;
                }
                RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
            }
            verb_len = RExC_parse - start_verb;
            if ( start_arg ) {
                if (RExC_parse >= RExC_end) {
                    goto unterminated_verb_pattern;
                }
                RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                while ( RExC_parse < RExC_end && *RExC_parse != ')' )
                    RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                if ( RExC_parse >= RExC_end || *RExC_parse != ')' )
                  unterminated_verb_pattern:
                    vFAIL("Unterminated verb pattern argument");
                if ( RExC_parse == start_arg )
                    start_arg = NULL;
            } else {
                if ( RExC_parse >= RExC_end || *RExC_parse != ')' )
                    vFAIL("Unterminated verb pattern");
            }

            /* Here, we know that RExC_parse < RExC_end */

            switch ( *start_verb ) {
            case 'A':  /* (*ACCEPT) */
                if ( memEQs(start_verb,verb_len,"ACCEPT") ) {
                    op = ACCEPT;
                    internal_argval = RExC_nestroot;
                }
                break;
            case 'C':  /* (*COMMIT) */
                if ( memEQs(start_verb,verb_len,"COMMIT") )
                    op = COMMIT;
                break;
            case 'F':  /* (*FAIL) */
                if ( verb_len==1 || memEQs(start_verb,verb_len,"FAIL") ) {
                    op = OPFAIL;
                }
                break;
            case ':':  /* (*:NAME) */
            case 'M':  /* (*MARK:NAME) */
                if ( verb_len==0 || memEQs(start_verb,verb_len,"MARK") ) {
                    op = MARKPOINT;
                    arg_required = 1;
                }
                break;
            case 'P':  /* (*PRUNE) */
                if ( memEQs(start_verb,verb_len,"PRUNE") )
                    op = PRUNE;
                break;
            case 'S':   /* (*SKIP) */
                if ( memEQs(start_verb,verb_len,"SKIP") )
                    op = SKIP;
                break;
            case 'T':  /* (*THEN) */
                /* [19:06] <TimToady> :: is then */
                if ( memEQs(start_verb,verb_len,"THEN") ) {
                    op = CUTGROUP;
                    RExC_seen |= REG_CUTGROUP_SEEN;
                }
                break;
            }
            if ( ! op ) {
                RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                vFAIL2utf8f(
                    "Unknown verb pattern '%"UTF8f"'",
                    UTF8fARG(UTF, verb_len, start_verb));
            }
            if ( arg_required && !start_arg ) {
                vFAIL3("Verb pattern '%.*s' has a mandatory argument",
                    verb_len, start_verb);
            }
            if (internal_argval == -1) {
                ret = reganode(pRExC_state, op, 0);
            } else {
                ret = reg2Lanode(pRExC_state, op, 0, internal_argval);
            }
            RExC_seen |= REG_VERBARG_SEEN;
            if ( ! SIZE_ONLY ) {
                if (start_arg) {
                    SV *sv = newSVpvn( start_arg,
                                       RExC_parse - start_arg);
                    ARG(ret) = add_data( pRExC_state,
                                         STR_WITH_LEN("S"));
                    RExC_rxi->data->data[ARG(ret)]=(void*)sv;
                    ret->flags = 1;
                } else {
                    ret->flags = 0;
                }
                if ( internal_argval != -1 )
                    ARG2L_SET(ret, internal_argval);
            }
            nextchar(pRExC_state);
            return ret;
        }
        else if (*RExC_parse == '?') { /* (?...) */
            bool is_logical = 0;
            const char * const seqstart = RExC_parse;
            const char * endptr;
            if (has_intervening_patws) {
                RExC_parse++;
                vFAIL("In '(?...)', the '(' and '?' must be adjacent");
            }

            RExC_parse++;           /* past the '?' */
            paren = *RExC_parse;    /* might be a trailing NUL, if not
                                       well-formed */
            RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
            if (RExC_parse > RExC_end) {
                paren = '\0';
            }
            ret = NULL;                 /* For look-ahead/behind. */
            switch (paren) {

            case 'P':   /* (?P...) variants for those used to PCRE/Python */
                paren = *RExC_parse;
                if ( paren == '<') {    /* (?P<...>) named capture */
                    RExC_parse++;
                    if (RExC_parse >= RExC_end) {
                        vFAIL("Sequence (?P<... not terminated");
                    }
                    goto named_capture;
                }
                else if (paren == '>') {   /* (?P>name) named recursion */
                    RExC_parse++;
                    if (RExC_parse >= RExC_end) {
                        vFAIL("Sequence (?P>... not terminated");
                    }
                    goto named_recursion;
                }
                else if (paren == '=') {   /* (?P=...)  named backref */
                    RExC_parse++;
                    return handle_named_backref(pRExC_state, flagp,
                                                parse_start, ')');
                }
                RExC_parse += SKIP_IF_CHAR(RExC_parse);
                /* diag_listed_as: Sequence (?%s...) not recognized in regex; marked by <-- HERE in m/%s/ */
                vFAIL3("Sequence (%.*s...) not recognized",
                                RExC_parse-seqstart, seqstart);
                NOT_REACHED; /*NOTREACHED*/
            case '<':           /* (?<...) */
                if (*RExC_parse == '!')
                    paren = ',';
                else if (*RExC_parse != '=')
              named_capture:
                {               /* (?<...>) */
                    char *name_start;
                    SV *svname;
                    paren= '>';
                /* FALLTHROUGH */
            case '\'':          /* (?'...') */
                    name_start = RExC_parse;
                    svname = reg_scan_name(pRExC_state,
                        SIZE_ONLY    /* reverse test from the others */
                        ? REG_RSN_RETURN_NAME
                        : REG_RSN_RETURN_NULL);
                    if (   RExC_parse == name_start
                        || RExC_parse >= RExC_end
                        || *RExC_parse != paren)
                    {
                        vFAIL2("Sequence (?%c... not terminated",
                            paren=='>' ? '<' : paren);
                    }
                    if (SIZE_ONLY) {
                        HE *he_str;
                        SV *sv_dat = NULL;
                        if (!svname) /* shouldn't happen */
                            Perl_croak(aTHX_
                                "panic: reg_scan_name returned NULL");
                        if (!RExC_paren_names) {
                            RExC_paren_names= newHV();
                            sv_2mortal(MUTABLE_SV(RExC_paren_names));
#ifdef DEBUGGING
                            RExC_paren_name_list= newAV();
                            sv_2mortal(MUTABLE_SV(RExC_paren_name_list));
#endif
                        }
                        he_str = hv_fetch_ent( RExC_paren_names, svname, 1, 0 );
                        if ( he_str )
                            sv_dat = HeVAL(he_str);
                        if ( ! sv_dat ) {
                            /* croak baby croak */
                            Perl_croak(aTHX_
                                "panic: paren_name hash element allocation failed");
                        } else if ( SvPOK(sv_dat) ) {
                            /* (?|...) can mean we have dupes so scan to check
                               its already been stored. Maybe a flag indicating
                               we are inside such a construct would be useful,
                               but the arrays are likely to be quite small, so
                               for now we punt -- dmq */
                            IV count = SvIV(sv_dat);
                            I32 *pv = (I32*)SvPVX(sv_dat);
                            IV i;
                            for ( i = 0 ; i < count ; i++ ) {
                                if ( pv[i] == RExC_npar ) {
                                    count = 0;
                                    break;
                                }
                            }
                            if ( count ) {
                                pv = (I32*)SvGROW(sv_dat,
                                                SvCUR(sv_dat) + sizeof(I32)+1);
                                SvCUR_set(sv_dat, SvCUR(sv_dat) + sizeof(I32));
                                pv[count] = RExC_npar;
                                SvIV_set(sv_dat, SvIVX(sv_dat) + 1);
                            }
                        } else {
                            (void)SvUPGRADE(sv_dat,SVt_PVNV);
                            sv_setpvn(sv_dat, (char *)&(RExC_npar),
                                                                sizeof(I32));
                            SvIOK_on(sv_dat);
                            SvIV_set(sv_dat, 1);
                        }
#ifdef DEBUGGING
                        /* Yes this does cause a memory leak in debugging Perls
                         * */
                        if (!av_store(RExC_paren_name_list,
                                      RExC_npar, SvREFCNT_inc(svname)))
                            SvREFCNT_dec_NN(svname);
#endif

                        /*sv_dump(sv_dat);*/
                    }
                    nextchar(pRExC_state);
                    paren = 1;
                    goto capturing_parens;
                }
                RExC_seen |= REG_LOOKBEHIND_SEEN;
                RExC_in_lookbehind++;
                RExC_parse++;
                assert(RExC_parse < RExC_end);
                /* FALLTHROUGH */
            case '=':           /* (?=...) */
                RExC_seen_zerolen++;
                break;
            case '!':           /* (?!...) */
                RExC_seen_zerolen++;
                /* check if we're really just a "FAIL" assertion */
                skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                        FALSE /* Don't force to /x */ );
                if (*RExC_parse == ')') {
                    ret=reganode(pRExC_state, OPFAIL, 0);
                    nextchar(pRExC_state);
                    return ret;
                }
                break;
            case '|':           /* (?|...) */
                /* branch reset, behave like a (?:...) except that
                   buffers in alternations share the same numbers */
                paren = ':';
                after_freeze = freeze_paren = RExC_npar;
                break;
            case ':':           /* (?:...) */
            case '>':           /* (?>...) */
                break;
            case '$':           /* (?$...) */
            case '@':           /* (?@...) */
                vFAIL2("Sequence (?%c...) not implemented", (int)paren);
                break;
            case '0' :           /* (?0) */
            case 'R' :           /* (?R) */
                if (*RExC_parse != ')')
                    FAIL("Sequence (?R) not terminated");
                ret = reg_node(pRExC_state, GOSTART);
                    RExC_seen |= REG_GOSTART_SEEN;
                *flagp |= POSTPONED;
                nextchar(pRExC_state);
                return ret;
                /*notreached*/
            /* named and numeric backreferences */
            case '&':            /* (?&NAME) */
                parse_start = RExC_parse - 1;
              named_recursion:
                {
                    SV *sv_dat = reg_scan_name(pRExC_state,
                        SIZE_ONLY ? REG_RSN_RETURN_NULL : REG_RSN_RETURN_DATA);
                     num = sv_dat ? *((I32 *)SvPVX(sv_dat)) : 0;
                }
                if (RExC_parse >= RExC_end || *RExC_parse != ')')
                    vFAIL("Sequence (?&... not terminated");
                goto gen_recurse_regop;
                /* NOTREACHED */
            case '+':
                if (!(RExC_parse[0] >= '1' && RExC_parse[0] <= '9')) {
                    RExC_parse++;
                    vFAIL("Illegal pattern");
                }
                goto parse_recursion;
                /* NOTREACHED*/
            case '-': /* (?-1) */
                if (!(RExC_parse[0] >= '1' && RExC_parse[0] <= '9')) {
                    RExC_parse--; /* rewind to let it be handled later */
                    goto parse_flags;
                }
                /* FALLTHROUGH */
            case '1': case '2': case '3': case '4': /* (?1) */
            case '5': case '6': case '7': case '8': case '9':
                RExC_parse = (char *) seqstart + 1;  /* Point to the digit */
              parse_recursion:
                {
                    bool is_neg = FALSE;
                    UV unum;
                    parse_start = RExC_parse - 1; /* MJD */
                    if (*RExC_parse == '-') {
                        RExC_parse++;
                        is_neg = TRUE;
                    }
                    if (grok_atoUV(RExC_parse, &unum, &endptr)
                        && unum <= I32_MAX
                    ) {
                        num = (I32)unum;
                        RExC_parse = (char*)endptr;
                    } else
                        num = I32_MAX;
                    if (is_neg) {
                        /* Some limit for num? */
                        num = -num;
                    }
                }
                if (*RExC_parse!=')')
                    vFAIL("Expecting close bracket");

              gen_recurse_regop:
                if ( paren == '-' ) {
                    /*
                    Diagram of capture buffer numbering.
                    Top line is the normal capture buffer numbers
                    Bottom line is the negative indexing as from
                    the X (the (?-2))

                    +   1 2    3 4 5 X          6 7
                       /(a(x)y)(a(b(c(?-2)d)e)f)(g(h))/
                    -   5 4    3 2 1 X          x x

                    */
                    num = RExC_npar + num;
                    if (num < 1)  {
                        RExC_parse++;
                        vFAIL("Reference to nonexistent group");
                    }
                } else if ( paren == '+' ) {
                    num = RExC_npar + num - 1;
                }

                ret = reg2Lanode(pRExC_state, GOSUB, num, RExC_recurse_count);
                if (!SIZE_ONLY) {
                    if (num > (I32)RExC_rx->nparens) {
                        RExC_parse++;
                        vFAIL("Reference to nonexistent group");
                    }
                    RExC_recurse_count++;
                    DEBUG_OPTIMISE_MORE_r(PerlIO_printf(Perl_debug_log,
                        "%*s%*s Recurse #%"UVuf" to %"IVdf"\n",
                              22, "|    |", (int)(depth * 2 + 1), "",
                              (UV)ARG(ret), (IV)ARG2L(ret)));
                }
                RExC_seen |= REG_RECURSE_SEEN;
                Set_Node_Length(ret, 1 + regarglen[OP(ret)]); /* MJD */
                Set_Node_Offset(ret, parse_start); /* MJD */

                *flagp |= POSTPONED;
                nextchar(pRExC_state);
                return ret;

            /* NOTREACHED */

            case '?':           /* (??...) */
                is_logical = 1;
                if (*RExC_parse != '{') {
                    RExC_parse += SKIP_IF_CHAR(RExC_parse);
                    /* diag_listed_as: Sequence (?%s...) not recognized in regex; marked by <-- HERE in m/%s/ */
                    vFAIL2utf8f(
                        "Sequence (%"UTF8f"...) not recognized",
                        UTF8fARG(UTF, RExC_parse-seqstart, seqstart));
                    NOT_REACHED; /*NOTREACHED*/
                }
                *flagp |= POSTPONED;
                paren = '{';
                RExC_parse++;
                /* FALLTHROUGH */
            case '{':           /* (?{...}) */
            {
                U32 n = 0;
                struct reg_code_block *cb;

                RExC_seen_zerolen++;

                if (   !pRExC_state->num_code_blocks
                    || pRExC_state->code_index >= pRExC_state->num_code_blocks
                    || pRExC_state->code_blocks[pRExC_state->code_index].start
                        != (STRLEN)((RExC_parse -3 - (is_logical ? 1 : 0))
                            - RExC_start)
                ) {
                    if (RExC_pm_flags & PMf_USE_RE_EVAL)
                        FAIL("panic: Sequence (?{...}): no code block found\n");
                    FAIL("Eval-group not allowed at runtime, use re 'eval'");
                }
                /* this is a pre-compiled code block (?{...}) */
                cb = &pRExC_state->code_blocks[pRExC_state->code_index];
                RExC_parse = RExC_start + cb->end;
                if (!SIZE_ONLY) {
                    OP *o = cb->block;
                    if (cb->src_regex) {
                        n = add_data(pRExC_state, STR_WITH_LEN("rl"));
                        RExC_rxi->data->data[n] =
                            (void*)SvREFCNT_inc((SV*)cb->src_regex);
                        RExC_rxi->data->data[n+1] = (void*)o;
                    }
                    else {
                        n = add_data(pRExC_state,
                               (RExC_pm_flags & PMf_HAS_CV) ? "L" : "l", 1);
                        RExC_rxi->data->data[n] = (void*)o;
                    }
                }
                pRExC_state->code_index++;
                nextchar(pRExC_state);

                if (is_logical) {
                    regnode *eval;
                    ret = reg_node(pRExC_state, LOGICAL);

                    eval = reg2Lanode(pRExC_state, EVAL,
                                       n,

                                       /* for later propagation into (??{})
                                        * return value */
                                       RExC_flags & RXf_PMf_COMPILETIME
                                      );
                    if (!SIZE_ONLY) {
                        ret->flags = 2;
                    }
                    REGTAIL(pRExC_state, ret, eval);
                    /* deal with the length of this later - MJD */
                    return ret;
                }
                ret = reg2Lanode(pRExC_state, EVAL, n, 0);
                Set_Node_Length(ret, RExC_parse - parse_start + 1);
                Set_Node_Offset(ret, parse_start);
                return ret;
            }
            case '(':           /* (?(?{...})...) and (?(?=...)...) */
            {
                int is_define= 0;
                const int DEFINE_len = sizeof("DEFINE") - 1;
                if (RExC_parse[0] == '?') {        /* (?(?...)) */
                    if (   RExC_parse < RExC_end - 1
                        && (   RExC_parse[1] == '='
                            || RExC_parse[1] == '!'
                            || RExC_parse[1] == '<'
                            || RExC_parse[1] == '{')
                    ) { /* Lookahead or eval. */
                        I32 flag;
                        regnode *tail;

                        ret = reg_node(pRExC_state, LOGICAL);
                        if (!SIZE_ONLY)
                            ret->flags = 1;

                        tail = reg(pRExC_state, 1, &flag, depth+1);
                        if (flag & (RESTART_PASS1|NEED_UTF8)) {
                            *flagp = flag & (RESTART_PASS1|NEED_UTF8);
                            return NULL;
                        }
                        REGTAIL(pRExC_state, ret, tail);
                        goto insert_if;
                    }
                    /* Fall through to ‘Unknown switch condition’ at the
                       end of the if/else chain. */
                }
                else if ( RExC_parse[0] == '<'     /* (?(<NAME>)...) */
                         || RExC_parse[0] == '\'' ) /* (?('NAME')...) */
                {
                    char ch = RExC_parse[0] == '<' ? '>' : '\'';
                    char *name_start= RExC_parse++;
                    U32 num = 0;
                    SV *sv_dat=reg_scan_name(pRExC_state,
                        SIZE_ONLY ? REG_RSN_RETURN_NULL : REG_RSN_RETURN_DATA);
                    if (   RExC_parse == name_start
                        || RExC_parse >= RExC_end
                        || *RExC_parse != ch)
                    {
                        vFAIL2("Sequence (?(%c... not terminated",
                            (ch == '>' ? '<' : ch));
                    }
                    RExC_parse++;
                    if (!SIZE_ONLY) {
                        num = add_data( pRExC_state, STR_WITH_LEN("S"));
                        RExC_rxi->data->data[num]=(void*)sv_dat;
                        SvREFCNT_inc_simple_void(sv_dat);
                    }
                    ret = reganode(pRExC_state,NGROUPP,num);
                    goto insert_if_check_paren;
                }
                else if (RExC_end - RExC_parse >= DEFINE_len
                        && strnEQ(RExC_parse, "DEFINE", DEFINE_len))
                {
                    ret = reganode(pRExC_state,DEFINEP,0);
                    RExC_parse += DEFINE_len;
                    is_define = 1;
                    goto insert_if_check_paren;
                }
                else if (RExC_parse[0] == 'R') {
                    RExC_parse++;
                    parno = 0;
                    if (RExC_parse[0] >= '1' && RExC_parse[0] <= '9' ) {
                        UV uv;
                        if (grok_atoUV(RExC_parse, &uv, &endptr)
                            && uv <= I32_MAX
                        ) {
                            parno = (I32)uv;
                            RExC_parse = (char*)endptr;
                        }
                        /* else "Switch condition not recognized" below */
                    } else if (RExC_parse[0] == '&') {
                        SV *sv_dat;
                        RExC_parse++;
                        sv_dat = reg_scan_name(pRExC_state,
                            SIZE_ONLY
                            ? REG_RSN_RETURN_NULL
                            : REG_RSN_RETURN_DATA);
                        parno = sv_dat ? *((I32 *)SvPVX(sv_dat)) : 0;
                    }
                    ret = reganode(pRExC_state,INSUBP,parno);
                    goto insert_if_check_paren;
                }
                else if (RExC_parse[0] >= '1' && RExC_parse[0] <= '9' ) {
                    /* (?(1)...) */
                    char c;
                    UV uv;
                    if (grok_atoUV(RExC_parse, &uv, &endptr)
                        && uv <= I32_MAX
                    ) {
                        parno = (I32)uv;
                        RExC_parse = (char*)endptr;
                    }
                    else {
                        vFAIL("panic: grok_atoUV returned FALSE");
                    }
                    ret = reganode(pRExC_state, GROUPP, parno);

                 insert_if_check_paren:
                    if (UCHARAT(RExC_parse) != ')') {
                        RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                        vFAIL("Switch condition not recognized");
                    }
                    nextchar(pRExC_state);
                  insert_if:
                    REGTAIL(pRExC_state, ret, reganode(pRExC_state, IFTHEN, 0));
                    br = regbranch(pRExC_state, &flags, 1,depth+1);
                    if (br == NULL) {
                        if (flags & (RESTART_PASS1|NEED_UTF8)) {
                            *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                            return NULL;
                        }
                        FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"",
                              (UV) flags);
                    } else
                        REGTAIL(pRExC_state, br, reganode(pRExC_state,
                                                          LONGJMP, 0));
                    c = UCHARAT(RExC_parse);
                    nextchar(pRExC_state);
                    if (flags&HASWIDTH)
                        *flagp |= HASWIDTH;
                    if (c == '|') {
                        if (is_define)
                            vFAIL("(?(DEFINE)....) does not allow branches");

                        /* Fake one for optimizer.  */
                        lastbr = reganode(pRExC_state, IFTHEN, 0);

                        if (!regbranch(pRExC_state, &flags, 1,depth+1)) {
                            if (flags & (RESTART_PASS1|NEED_UTF8)) {
                                *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                                return NULL;
                            }
                            FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"",
                                  (UV) flags);
                        }
                        REGTAIL(pRExC_state, ret, lastbr);
                        if (flags&HASWIDTH)
                            *flagp |= HASWIDTH;
                        c = UCHARAT(RExC_parse);
                        nextchar(pRExC_state);
                    }
                    else
                        lastbr = NULL;
                    if (c != ')') {
                        if (RExC_parse >= RExC_end)
                            vFAIL("Switch (?(condition)... not terminated");
                        else
                            vFAIL("Switch (?(condition)... contains too many branches");
                    }
                    ender = reg_node(pRExC_state, TAIL);
                    REGTAIL(pRExC_state, br, ender);
                    if (lastbr) {
                        REGTAIL(pRExC_state, lastbr, ender);
                        REGTAIL(pRExC_state, NEXTOPER(NEXTOPER(lastbr)), ender);
                    }
                    else
                        REGTAIL(pRExC_state, ret, ender);
                    RExC_size++; /* XXX WHY do we need this?!!
                                    For large programs it seems to be required
                                    but I can't figure out why. -- dmq*/
                    return ret;
                }
                RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                vFAIL("Unknown switch condition (?(...))");
            }
            case '[':           /* (?[ ... ]) */
                return handle_regex_sets(pRExC_state, NULL, flagp, depth,
                                         oregcomp_parse);
            case 0: /* A NUL */
                RExC_parse--; /* for vFAIL to print correctly */
                vFAIL("Sequence (? incomplete");
                break;
            default: /* e.g., (?i) */
                RExC_parse = (char *) seqstart + 1;
              parse_flags:
                parse_lparen_question_flags(pRExC_state);
                if (UCHARAT(RExC_parse) != ':') {
                    if (RExC_parse < RExC_end)
                        nextchar(pRExC_state);
                    *flagp = TRYAGAIN;
                    return NULL;
                }
                paren = ':';
                nextchar(pRExC_state);
                ret = NULL;
                goto parse_rest;
            } /* end switch */
        }
        else if (!(RExC_flags & RXf_PMf_NOCAPTURE)) {   /* (...) */
          capturing_parens:
            parno = RExC_npar;
            RExC_npar++;

            ret = reganode(pRExC_state, OPEN, parno);
            if (!SIZE_ONLY ){
                if (!RExC_nestroot)
                    RExC_nestroot = parno;
                if (RExC_seen & REG_RECURSE_SEEN
                    && !RExC_open_parens[parno-1])
                {
                    DEBUG_OPTIMISE_MORE_r(PerlIO_printf(Perl_debug_log,
                        "%*s%*s Setting open paren #%"IVdf" to %d\n",
                        22, "|    |", (int)(depth * 2 + 1), "",
                        (IV)parno, REG_NODE_NUM(ret)));
                    RExC_open_parens[parno-1]= ret;
                }
            }
            Set_Node_Length(ret, 1); /* MJD */
            Set_Node_Offset(ret, RExC_parse); /* MJD */
            is_open = 1;
        } else {
            /* with RXf_PMf_NOCAPTURE treat (...) as (?:...) */
            paren = ':';
            ret = NULL;
        }
    }
    else                        /* ! paren */
        ret = NULL;

   parse_rest:
    /* Pick up the branches, linking them together. */
    parse_start = RExC_parse;   /* MJD */
    br = regbranch(pRExC_state, &flags, 1,depth+1);

    /*     branch_len = (paren != 0); */

    if (br == NULL) {
        if (flags & (RESTART_PASS1|NEED_UTF8)) {
            *flagp = flags & (RESTART_PASS1|NEED_UTF8);
            return NULL;
        }
        FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"", (UV) flags);
    }
    if (*RExC_parse == '|') {
        if (!SIZE_ONLY && RExC_extralen) {
            reginsert(pRExC_state, BRANCHJ, br, depth+1);
        }
        else {                  /* MJD */
            reginsert(pRExC_state, BRANCH, br, depth+1);
            Set_Node_Length(br, paren != 0);
            Set_Node_Offset_To_R(br-RExC_emit_start, parse_start-RExC_start);
        }
        have_branch = 1;
        if (SIZE_ONLY)
            RExC_extralen += 1;         /* For BRANCHJ-BRANCH. */
    }
    else if (paren == ':') {
        *flagp |= flags&SIMPLE;
    }
    if (is_open) {                              /* Starts with OPEN. */
        REGTAIL(pRExC_state, ret, br);          /* OPEN -> first. */
    }
    else if (paren != '?')              /* Not Conditional */
        ret = br;
    *flagp |= flags & (SPSTART | HASWIDTH | POSTPONED);
    lastbr = br;
    while (*RExC_parse == '|') {
        if (!SIZE_ONLY && RExC_extralen) {
            ender = reganode(pRExC_state, LONGJMP,0);

            /* Append to the previous. */
            REGTAIL(pRExC_state, NEXTOPER(NEXTOPER(lastbr)), ender);
        }
        if (SIZE_ONLY)
            RExC_extralen += 2;         /* Account for LONGJMP. */
        nextchar(pRExC_state);
        if (freeze_paren) {
            if (RExC_npar > after_freeze)
                after_freeze = RExC_npar;
            RExC_npar = freeze_paren;
        }
        br = regbranch(pRExC_state, &flags, 0, depth+1);

        if (br == NULL) {
            if (flags & (RESTART_PASS1|NEED_UTF8)) {
                *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                return NULL;
            }
            FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"", (UV) flags);
        }
        REGTAIL(pRExC_state, lastbr, br);               /* BRANCH -> BRANCH. */
        lastbr = br;
        *flagp |= flags & (SPSTART | HASWIDTH | POSTPONED);
    }

    if (have_branch || paren != ':') {
        /* Make a closing node, and hook it on the end. */
        switch (paren) {
        case ':':
            ender = reg_node(pRExC_state, TAIL);
            break;
        case 1: case 2:
            ender = reganode(pRExC_state, CLOSE, parno);
            if (!SIZE_ONLY && RExC_seen & REG_RECURSE_SEEN) {
                DEBUG_OPTIMISE_MORE_r(PerlIO_printf(Perl_debug_log,
                        "%*s%*s Setting close paren #%"IVdf" to %d\n",
                        22, "|    |", (int)(depth * 2 + 1), "", (IV)parno, REG_NODE_NUM(ender)));
                RExC_close_parens[parno-1]= ender;
                if (RExC_nestroot == parno)
                    RExC_nestroot = 0;
            }
            Set_Node_Offset(ender,RExC_parse+1); /* MJD */
            Set_Node_Length(ender,1); /* MJD */
            break;
        case '<':
        case ',':
        case '=':
        case '!':
            *flagp &= ~HASWIDTH;
            /* FALLTHROUGH */
        case '>':
            ender = reg_node(pRExC_state, SUCCEED);
            break;
        case 0:
            ender = reg_node(pRExC_state, END);
            if (!SIZE_ONLY) {
                assert(!RExC_opend); /* there can only be one! */
                RExC_opend = ender;
            }
            break;
        }
        DEBUG_PARSE_r(if (!SIZE_ONLY) {
            DEBUG_PARSE_MSG("lsbr");
            regprop(RExC_rx, RExC_mysv1, lastbr, NULL, pRExC_state);
            regprop(RExC_rx, RExC_mysv2, ender, NULL, pRExC_state);
            PerlIO_printf(Perl_debug_log, "~ tying lastbr %s (%"IVdf") to ender %s (%"IVdf") offset %"IVdf"\n",
                          SvPV_nolen_const(RExC_mysv1),
                          (IV)REG_NODE_NUM(lastbr),
                          SvPV_nolen_const(RExC_mysv2),
                          (IV)REG_NODE_NUM(ender),
                          (IV)(ender - lastbr)
            );
        });
        REGTAIL(pRExC_state, lastbr, ender);

        if (have_branch && !SIZE_ONLY) {
            char is_nothing= 1;
            if (depth==1)
                RExC_seen |= REG_TOP_LEVEL_BRANCHES_SEEN;

            /* Hook the tails of the branches to the closing node. */
            for (br = ret; br; br = regnext(br)) {
                const U8 op = PL_regkind[OP(br)];
                if (op == BRANCH) {
                    REGTAIL_STUDY(pRExC_state, NEXTOPER(br), ender);
                    if ( OP(NEXTOPER(br)) != NOTHING
                         || regnext(NEXTOPER(br)) != ender)
                        is_nothing= 0;
                }
                else if (op == BRANCHJ) {
                    REGTAIL_STUDY(pRExC_state, NEXTOPER(NEXTOPER(br)), ender);
                    /* for now we always disable this optimisation * /
                    if ( OP(NEXTOPER(NEXTOPER(br))) != NOTHING
                         || regnext(NEXTOPER(NEXTOPER(br))) != ender)
                    */
                        is_nothing= 0;
                }
            }
            if (is_nothing) {
                br= PL_regkind[OP(ret)] != BRANCH ? regnext(ret) : ret;
                DEBUG_PARSE_r(if (!SIZE_ONLY) {
                    DEBUG_PARSE_MSG("NADA");
                    regprop(RExC_rx, RExC_mysv1, ret, NULL, pRExC_state);
                    regprop(RExC_rx, RExC_mysv2, ender, NULL, pRExC_state);
                    PerlIO_printf(Perl_debug_log, "~ converting ret %s (%"IVdf") to ender %s (%"IVdf") offset %"IVdf"\n",
                                  SvPV_nolen_const(RExC_mysv1),
                                  (IV)REG_NODE_NUM(ret),
                                  SvPV_nolen_const(RExC_mysv2),
                                  (IV)REG_NODE_NUM(ender),
                                  (IV)(ender - ret)
                    );
                });
                OP(br)= NOTHING;
                if (OP(ender) == TAIL) {
                    NEXT_OFF(br)= 0;
                    RExC_emit= br + 1;
                } else {
                    regnode *opt;
                    for ( opt= br + 1; opt < ender ; opt++ )
                        OP(opt)= OPTIMIZED;
                    NEXT_OFF(br)= ender - br;
                }
            }
        }
    }

    {
        const char *p;
        static const char parens[] = "=!<,>";

        if (paren && (p = strchr(parens, paren))) {
            U8 node = ((p - parens) % 2) ? UNLESSM : IFMATCH;
            int flag = (p - parens) > 1;

            if (paren == '>')
                node = SUSPEND, flag = 0;
            reginsert(pRExC_state, node,ret, depth+1);
            Set_Node_Cur_Length(ret, parse_start);
            Set_Node_Offset(ret, parse_start + 1);
            ret->flags = flag;
            REGTAIL_STUDY(pRExC_state, ret, reg_node(pRExC_state, TAIL));
        }
    }

    /* Check for proper termination. */
    if (paren) {
        /* restore original flags, but keep (?p) and, if we've changed from /d
         * rules to /u, keep the /u */
        RExC_flags = oregflags | (RExC_flags & RXf_PMf_KEEPCOPY);
        if (DEPENDS_SEMANTICS && RExC_uni_semantics) {
            set_regex_charset(&RExC_flags, REGEX_UNICODE_CHARSET);
        }
        if (RExC_parse >= RExC_end || UCHARAT(RExC_parse) != ')') {
            RExC_parse = oregcomp_parse;
            vFAIL("Unmatched (");
        }
        nextchar(pRExC_state);
    }
    else if (!paren && RExC_parse < RExC_end) {
        if (*RExC_parse == ')') {
            RExC_parse++;
            vFAIL("Unmatched )");
        }
        else
            FAIL("Junk on end of regexp");      /* "Can't happen". */
        NOT_REACHED; /* NOTREACHED */
    }

    if (RExC_in_lookbehind) {
        RExC_in_lookbehind--;
    }
    if (after_freeze > RExC_npar)
        RExC_npar = after_freeze;
    return(ret);
}

/*
 - regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 *
 * Returns NULL, setting *flagp to RESTART_PASS1 if the sizing scan needs to be
 * restarted, or'd with NEED_UTF8 if the pattern needs to be upgraded to UTF-8
 */
STATIC regnode *
S_regbranch(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, I32 first, U32 depth)
{
    regnode *ret;
    regnode *chain = NULL;
    regnode *latest;
    I32 flags = 0, c = 0;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGBRANCH;

    DEBUG_PARSE("brnc");

    if (first)
        ret = NULL;
    else {
        if (!SIZE_ONLY && RExC_extralen)
            ret = reganode(pRExC_state, BRANCHJ,0);
        else {
            ret = reg_node(pRExC_state, BRANCH);
            Set_Node_Length(ret, 1);
        }
    }

    if (!first && SIZE_ONLY)
        RExC_extralen += 1;                     /* BRANCHJ */

    *flagp = WORST;                     /* Tentatively. */

    skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                            FALSE /* Don't force to /x */ );
    while (RExC_parse < RExC_end && *RExC_parse != '|' && *RExC_parse != ')') {
        flags &= ~TRYAGAIN;
        latest = regpiece(pRExC_state, &flags,depth+1);
        if (latest == NULL) {
            if (flags & TRYAGAIN)
                continue;
            if (flags & (RESTART_PASS1|NEED_UTF8)) {
                *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                return NULL;
            }
            FAIL2("panic: regpiece returned NULL, flags=%#"UVxf"", (UV) flags);
        }
        else if (ret == NULL)
            ret = latest;
        *flagp |= flags&(HASWIDTH|POSTPONED);
        if (chain == NULL)      /* First piece. */
            *flagp |= flags&SPSTART;
        else {
            /* FIXME adding one for every branch after the first is probably
             * excessive now we have TRIE support. (hv) */
            MARK_NAUGHTY(1);
            REGTAIL(pRExC_state, chain, latest);
        }
        chain = latest;
        c++;
    }
    if (chain == NULL) {        /* Loop ran zero times. */
        chain = reg_node(pRExC_state, NOTHING);
        if (ret == NULL)
            ret = chain;
    }
    if (c == 1) {
        *flagp |= flags&SIMPLE;
    }

    return ret;
}

/*
 - regpiece - something followed by possible [*+?]
 *
 * Note that the branching code sequences used for ? and the general cases
 * of * and + are somewhat optimized:  they use the same NOTHING node as
 * both the endmarker for their branch list and the body of the last branch.
 * It might seem that this node could be dispensed with entirely, but the
 * endmarker role is not redundant.
 *
 * Returns NULL, setting *flagp to TRYAGAIN if regatom() returns NULL with
 * TRYAGAIN.
 * Returns NULL, setting *flagp to RESTART_PASS1 if the sizing scan needs to be
 * restarted, or'd with NEED_UTF8 if the pattern needs to be upgraded to UTF-8
 */
STATIC regnode *
S_regpiece(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
{
    regnode *ret;
    char op;
    char *next;
    I32 flags;
    const char * const origparse = RExC_parse;
    I32 min;
    I32 max = REG_INFTY;
#ifdef RE_TRACK_PATTERN_OFFSETS
    char *parse_start;
#endif
    const char *maxpos = NULL;
    UV uv;

    /* Save the original in case we change the emitted regop to a FAIL. */
    regnode * const orig_emit = RExC_emit;

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGPIECE;

    DEBUG_PARSE("piec");

    ret = regatom(pRExC_state, &flags,depth+1);
    if (ret == NULL) {
        if (flags & (TRYAGAIN|RESTART_PASS1|NEED_UTF8))
            *flagp |= flags & (TRYAGAIN|RESTART_PASS1|NEED_UTF8);
        else
            FAIL2("panic: regatom returned NULL, flags=%#"UVxf"", (UV) flags);
        return(NULL);
    }

    op = *RExC_parse;

    if (op == '{' && regcurly(RExC_parse)) {
        maxpos = NULL;
#ifdef RE_TRACK_PATTERN_OFFSETS
        parse_start = RExC_parse; /* MJD */
#endif
        next = RExC_parse + 1;
        while (isDIGIT(*next) || *next == ',') {
            if (*next == ',') {
                if (maxpos)
                    break;
                else
                    maxpos = next;
            }
            next++;
        }
        if (*next == '}') {             /* got one */
            const char* endptr;
            if (!maxpos)
                maxpos = next;
            RExC_parse++;
            if (isDIGIT(*RExC_parse)) {
                if (!grok_atoUV(RExC_parse, &uv, &endptr))
                    vFAIL("Invalid quantifier in {,}");
                if (uv >= REG_INFTY)
                    vFAIL2("Quantifier in {,} bigger than %d", REG_INFTY - 1);
                min = (I32)uv;
            } else {
                min = 0;
            }
            if (*maxpos == ',')
                maxpos++;
            else
                maxpos = RExC_parse;
            if (isDIGIT(*maxpos)) {
                if (!grok_atoUV(maxpos, &uv, &endptr))
                    vFAIL("Invalid quantifier in {,}");
                if (uv >= REG_INFTY)
                    vFAIL2("Quantifier in {,} bigger than %d", REG_INFTY - 1);
                max = (I32)uv;
            } else {
                max = REG_INFTY;                /* meaning "infinity" */
            }
            RExC_parse = next;
            nextchar(pRExC_state);
            if (max < min) {    /* If can't match, warn and optimize to fail
                                   unconditionally */
                if (SIZE_ONLY) {

                    /* We can't back off the size because we have to reserve
                     * enough space for all the things we are about to throw
                     * away, but we can shrink it by the amount we are about
                     * to re-use here */
                    RExC_size += PREVOPER(RExC_size) - regarglen[(U8)OPFAIL];
                }
                else {
                    ckWARNreg(RExC_parse, "Quantifier {n,m} with n > m can't match");
                    RExC_emit = orig_emit;
                }
                ret = reganode(pRExC_state, OPFAIL, 0);
                return ret;
            }
            else if (min == max && *RExC_parse == '?')
            {
                if (PASS2) {
                    ckWARN2reg(RExC_parse + 1,
                               "Useless use of greediness modifier '%c'",
                               *RExC_parse);
                }
            }

          do_curly:
            if ((flags&SIMPLE)) {
                if (min == 0 && max == REG_INFTY) {
                    reginsert(pRExC_state, STAR, ret, depth+1);
                    ret->flags = 0;
                    MARK_NAUGHTY(4);
                    RExC_seen |= REG_UNBOUNDED_QUANTIFIER_SEEN;
                    goto nest_check;
                }
                if (min == 1 && max == REG_INFTY) {
                    reginsert(pRExC_state, PLUS, ret, depth+1);
                    ret->flags = 0;
                    MARK_NAUGHTY(3);
                    RExC_seen |= REG_UNBOUNDED_QUANTIFIER_SEEN;
                    goto nest_check;
                }
                MARK_NAUGHTY_EXP(2, 2);
                reginsert(pRExC_state, CURLY, ret, depth+1);
                Set_Node_Offset(ret, parse_start+1); /* MJD */
                Set_Node_Cur_Length(ret, parse_start);
            }
            else {
                regnode * const w = reg_node(pRExC_state, WHILEM);

                w->flags = 0;
                REGTAIL(pRExC_state, ret, w);
                if (!SIZE_ONLY && RExC_extralen) {
                    reginsert(pRExC_state, LONGJMP,ret, depth+1);
                    reginsert(pRExC_state, NOTHING,ret, depth+1);
                    NEXT_OFF(ret) = 3;  /* Go over LONGJMP. */
                }
                reginsert(pRExC_state, CURLYX,ret, depth+1);
                                /* MJD hk */
                Set_Node_Offset(ret, parse_start+1);
                Set_Node_Length(ret,
                                op == '{' ? (RExC_parse - parse_start) : 1);

                if (!SIZE_ONLY && RExC_extralen)
                    NEXT_OFF(ret) = 3;  /* Go over NOTHING to LONGJMP. */
                REGTAIL(pRExC_state, ret, reg_node(pRExC_state, NOTHING));
                if (SIZE_ONLY)
                    RExC_whilem_seen++, RExC_extralen += 3;
                MARK_NAUGHTY_EXP(1, 4);     /* compound interest */
            }
            ret->flags = 0;

            if (min > 0)
                *flagp = WORST;
            if (max > 0)
                *flagp |= HASWIDTH;
            if (!SIZE_ONLY) {
                ARG1_SET(ret, (U16)min);
                ARG2_SET(ret, (U16)max);
            }
            if (max == REG_INFTY)
                RExC_seen |= REG_UNBOUNDED_QUANTIFIER_SEEN;

            goto nest_check;
        }
    }

    if (!ISMULT1(op)) {
        *flagp = flags;
        return(ret);
    }

#if 0                           /* Now runtime fix should be reliable. */

    /* if this is reinstated, don't forget to put this back into perldiag:

            =item Regexp *+ operand could be empty at {#} in regex m/%s/

           (F) The part of the regexp subject to either the * or + quantifier
           could match an empty string. The {#} shows in the regular
           expression about where the problem was discovered.

    */

    if (!(flags&HASWIDTH) && op != '?')
      vFAIL("Regexp *+ operand could be empty");
#endif

#ifdef RE_TRACK_PATTERN_OFFSETS
    parse_start = RExC_parse;
#endif
    nextchar(pRExC_state);

    *flagp = (op != '+') ? (WORST|SPSTART|HASWIDTH) : (WORST|HASWIDTH);

    if (op == '*') {
        min = 0;
        goto do_curly;
    }
    else if (op == '+') {
        min = 1;
        goto do_curly;
    }
    else if (op == '?') {
        min = 0; max = 1;
        goto do_curly;
    }
  nest_check:
    if (!SIZE_ONLY && !(flags&(HASWIDTH|POSTPONED)) && max > REG_INFTY/3) {
        SAVEFREESV(RExC_rx_sv); /* in case of fatal warnings */
        ckWARN2reg(RExC_parse,
                   "%"UTF8f" matches null string many times",
                   UTF8fARG(UTF, (RExC_parse >= origparse
                                 ? RExC_parse - origparse
                                 : 0),
                   origparse));
        (void)ReREFCNT_inc(RExC_rx_sv);
    }

    if (*RExC_parse == '?') {
        nextchar(pRExC_state);
        reginsert(pRExC_state, MINMOD, ret, depth+1);
        REGTAIL(pRExC_state, ret, ret + NODE_STEP_REGNODE);
    }
    else if (*RExC_parse == '+') {
        regnode *ender;
        nextchar(pRExC_state);
        ender = reg_node(pRExC_state, SUCCEED);
        REGTAIL(pRExC_state, ret, ender);
        reginsert(pRExC_state, SUSPEND, ret, depth+1);
        ret->flags = 0;
        ender = reg_node(pRExC_state, TAIL);
        REGTAIL(pRExC_state, ret, ender);
    }

    if (ISMULT2(RExC_parse)) {
        RExC_parse++;
        vFAIL("Nested quantifiers");
    }

    return(ret);
}

STATIC bool
S_grok_bslash_N(pTHX_ RExC_state_t *pRExC_state,
                regnode ** node_p,
                UV * code_point_p,
                int * cp_count,
                I32 * flagp,
                const bool strict,
                const U32 depth
    )
{
 /* This routine teases apart the various meanings of \N and returns
  * accordingly.  The input parameters constrain which meaning(s) is/are valid
  * in the current context.
  *
  * Exactly one of <node_p> and <code_point_p> must be non-NULL.
  *
  * If <code_point_p> is not NULL, the context is expecting the result to be a
  * single code point.  If this \N instance turns out to a single code point,
  * the function returns TRUE and sets *code_point_p to that code point.
  *
  * If <node_p> is not NULL, the context is expecting the result to be one of
  * the things representable by a regnode.  If this \N instance turns out to be
  * one such, the function generates the regnode, returns TRUE and sets *node_p
  * to point to that regnode.
  *
  * If this instance of \N isn't legal in any context, this function will
  * generate a fatal error and not return.
  *
  * On input, RExC_parse should point to the first char following the \N at the
  * time of the call.  On successful return, RExC_parse will have been updated
  * to point to just after the sequence identified by this routine.  Also
  * *flagp has been updated as needed.
  *
  * When there is some problem with the current context and this \N instance,
  * the function returns FALSE, without advancing RExC_parse, nor setting
  * *node_p, nor *code_point_p, nor *flagp.
  *
  * If <cp_count> is not NULL, the caller wants to know the length (in code
  * points) that this \N sequence matches.  This is set even if the function
  * returns FALSE, as detailed below.
  *
  * There are 5 possibilities here, as detailed in the next 5 paragraphs.
  *
  * Probably the most common case is for the \N to specify a single code point.
  * *cp_count will be set to 1, and *code_point_p will be set to that code
  * point.
  *
  * Another possibility is for the input to be an empty \N{}, which for
  * backwards compatibility we accept.  *cp_count will be set to 0. *node_p
  * will be set to a generated NOTHING node.
  *
  * Still another possibility is for the \N to mean [^\n]. *cp_count will be
  * set to 0. *node_p will be set to a generated REG_ANY node.
  *
  * The fourth possibility is that \N resolves to a sequence of more than one
  * code points.  *cp_count will be set to the number of code points in the
  * sequence. *node_p * will be set to a generated node returned by this
  * function calling S_reg().
  *
  * The final possibility is that it is premature to be calling this function;
  * that pass1 needs to be restarted.  This can happen when this changes from
  * /d to /u rules, or when the pattern needs to be upgraded to UTF-8.  The
  * latter occurs only when the fourth possibility would otherwise be in
  * effect, and is because one of those code points requires the pattern to be
  * recompiled as UTF-8.  The function returns FALSE, and sets the
  * RESTART_PASS1 and NEED_UTF8 flags in *flagp, as appropriate.  When this
  * happens, the caller needs to desist from continuing parsing, and return
  * this information to its caller.  This is not set for when there is only one
  * code point, as this can be called as part of an ANYOF node, and they can
  * store above-Latin1 code points without the pattern having to be in UTF-8.
  *
  * For non-single-quoted regexes, the tokenizer has resolved character and
  * sequence names inside \N{...} into their Unicode values, normalizing the
  * result into what we should see here: '\N{U+c1.c2...}', where c1... are the
  * hex-represented code points in the sequence.  This is done there because
  * the names can vary based on what charnames pragma is in scope at the time,
  * so we need a way to take a snapshot of what they resolve to at the time of
  * the original parse. [perl #56444].
  *
  * That parsing is skipped for single-quoted regexes, so we may here get
  * '\N{NAME}'.  This is a fatal error.  These names have to be resolved by the
  * parser.  But if the single-quoted regex is something like '\N{U+41}', that
  * is legal and handled here.  The code point is Unicode, and has to be
  * translated into the native character set for non-ASCII platforms.
  */

    char * endbrace;    /* points to '}' following the name */
    char *endchar;      /* Points to '.' or '}' ending cur char in the input
                           stream */
    char* p = RExC_parse; /* Temporary */

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_GROK_BSLASH_N;

    GET_RE_DEBUG_FLAGS;

    assert(cBOOL(node_p) ^ cBOOL(code_point_p));  /* Exactly one should be set */
    assert(! (node_p && cp_count));               /* At most 1 should be set */

    if (cp_count) {     /* Initialize return for the most common case */
        *cp_count = 1;
    }

    /* The [^\n] meaning of \N ignores spaces and comments under the /x
     * modifier.  The other meanings do not, so use a temporary until we find
     * out which we are being called with */
    skip_to_be_ignored_text(pRExC_state, &p,
                            FALSE /* Don't force to /x */ );

    /* Disambiguate between \N meaning a named character versus \N meaning
     * [^\n].  The latter is assumed when the {...} following the \N is a legal
     * quantifier, or there is no '{' at all */
    if (*p != '{' || regcurly(p)) {
        RExC_parse = p;
        if (cp_count) {
            *cp_count = -1;
        }

        if (! node_p) {
            return FALSE;
        }

        *node_p = reg_node(pRExC_state, REG_ANY);
        *flagp |= HASWIDTH|SIMPLE;
        MARK_NAUGHTY(1);
        Set_Node_Length(*node_p, 1); /* MJD */
        return TRUE;
    }

    /* Here, we have decided it should be a named character or sequence */

    /* The test above made sure that the next real character is a '{', but
     * under the /x modifier, it could be separated by space (or a comment and
     * \n) and this is not allowed (for consistency with \x{...} and the
     * tokenizer handling of \N{NAME}). */
    if (*RExC_parse != '{') {
        vFAIL("Missing braces on \\N{}");
    }

    RExC_parse++;       /* Skip past the '{' */

    if (! (endbrace = strchr(RExC_parse, '}'))  /* no trailing brace */
        || ! (endbrace == RExC_parse            /* nothing between the {} */
              || (endbrace - RExC_parse >= 2    /* U+ (bad hex is checked... */
                  && strnEQ(RExC_parse, "U+", 2)))) /* ... below for a better
                                                       error msg) */
    {
        if (endbrace) RExC_parse = endbrace;    /* position msg's '<--HERE' */
        vFAIL("\\N{NAME} must be resolved by the lexer");
    }

    REQUIRE_UNI_RULES(flagp, FALSE); /* Unicode named chars imply Unicode
                                        semantics */

    if (endbrace == RExC_parse) {   /* empty: \N{} */
        if (strict) {
            RExC_parse++;   /* Position after the "}" */
            vFAIL("Zero length \\N{}");
        }
        if (cp_count) {
            *cp_count = 0;
        }
        nextchar(pRExC_state);
        if (! node_p) {
            return FALSE;
        }

        *node_p = reg_node(pRExC_state,NOTHING);
        return TRUE;
    }

    RExC_parse += 2;    /* Skip past the 'U+' */

    /* Because toke.c has generated a special construct for us guaranteed not
     * to have NULs, we can use a str function */
    endchar = RExC_parse + strcspn(RExC_parse, ".}");

    /* Code points are separated by dots.  If none, there is only one code
     * point, and is terminated by the brace */

    if (endchar >= endbrace) {
        STRLEN length_of_hex;
        I32 grok_hex_flags;

        /* Here, exactly one code point.  If that isn't what is wanted, fail */
        if (! code_point_p) {
            RExC_parse = p;
            return FALSE;
        }

        /* Convert code point from hex */
        length_of_hex = (STRLEN)(endchar - RExC_parse);
        grok_hex_flags = PERL_SCAN_ALLOW_UNDERSCORES
                           | PERL_SCAN_DISALLOW_PREFIX

                             /* No errors in the first pass (See [perl
                              * #122671].)  We let the code below find the
                              * errors when there are multiple chars. */
                           | ((SIZE_ONLY)
                              ? PERL_SCAN_SILENT_ILLDIGIT
                              : 0);

        /* This routine is the one place where both single- and double-quotish
         * \N{U+xxxx} are evaluated.  The value is a Unicode code point which
         * must be converted to native. */
        *code_point_p = UNI_TO_NATIVE(grok_hex(RExC_parse,
                                         &length_of_hex,
                                         &grok_hex_flags,
                                         NULL));

        /* The tokenizer should have guaranteed validity, but it's possible to
         * bypass it by using single quoting, so check.  Don't do the check
         * here when there are multiple chars; we do it below anyway. */
        if (length_of_hex == 0
            || length_of_hex != (STRLEN)(endchar - RExC_parse) )
        {
            RExC_parse += length_of_hex;        /* Includes all the valid */
            RExC_parse += (RExC_orig_utf8)      /* point to after 1st invalid */
                            ? UTF8SKIP(RExC_parse)
                            : 1;
            /* Guard against malformed utf8 */
            if (RExC_parse >= endchar) {
                RExC_parse = endchar;
            }
            vFAIL("Invalid hexadecimal number in \\N{U+...}");
        }

        RExC_parse = endbrace + 1;
        return TRUE;
    }
    else {  /* Is a multiple character sequence */
        SV * substitute_parse;
        STRLEN len;
        char *orig_end = RExC_end;
        char *save_start = RExC_start;
        I32 flags;

        /* Count the code points, if desired, in the sequence */
        if (cp_count) {
            *cp_count = 0;
            while (RExC_parse < endbrace) {
                /* Point to the beginning of the next character in the sequence. */
                RExC_parse = endchar + 1;
                endchar = RExC_parse + strcspn(RExC_parse, ".}");
                (*cp_count)++;
            }
        }

        /* Fail if caller doesn't want to handle a multi-code-point sequence.
         * But don't backup up the pointer if the caller want to know how many
         * code points there are (they can then handle things) */
        if (! node_p) {
            if (! cp_count) {
                RExC_parse = p;
            }
            return FALSE;
        }

        /* What is done here is to convert this to a sub-pattern of the form
         * \x{char1}\x{char2}...  and then call reg recursively to parse it
         * (enclosing in "(?: ... )" ).  That way, it retains its atomicness,
         * while not having to worry about special handling that some code
         * points may have. */

        substitute_parse = newSVpvs("?:");

        while (RExC_parse < endbrace) {

            /* Convert to notation the rest of the code understands */
            sv_catpv(substitute_parse, "\\x{");
            sv_catpvn(substitute_parse, RExC_parse, endchar - RExC_parse);
            sv_catpv(substitute_parse, "}");

            /* Point to the beginning of the next character in the sequence. */
            RExC_parse = endchar + 1;
            endchar = RExC_parse + strcspn(RExC_parse, ".}");

        }
        sv_catpv(substitute_parse, ")");

        RExC_parse = RExC_start = RExC_adjusted_start = SvPV(substitute_parse,
                                                             len);

        /* Don't allow empty number */
        if (len < (STRLEN) 8) {
            RExC_parse = endbrace;
            vFAIL("Invalid hexadecimal number in \\N{U+...}");
        }
        RExC_end = RExC_parse + len;

        /* The values are Unicode, and therefore not subject to recoding, but
         * have to be converted to native on a non-Unicode (meaning non-ASCII)
         * platform. */
        RExC_override_recoding = 1;
#ifdef EBCDIC
        RExC_recode_x_to_native = 1;
#endif

        if (node_p) {
            if (!(*node_p = reg(pRExC_state, 1, &flags, depth+1))) {
                if (flags & (RESTART_PASS1|NEED_UTF8)) {
                    *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                    return FALSE;
                }
                FAIL2("panic: reg returned NULL to grok_bslash_N, flags=%#"UVxf"",
                    (UV) flags);
            }
            *flagp |= flags&(HASWIDTH|SPSTART|SIMPLE|POSTPONED);
        }

        /* Restore the saved values */
        RExC_start = RExC_adjusted_start = save_start;
        RExC_parse = endbrace;
        RExC_end = orig_end;
        RExC_override_recoding = 0;
#ifdef EBCDIC
        RExC_recode_x_to_native = 0;
#endif

        SvREFCNT_dec_NN(substitute_parse);
        nextchar(pRExC_state);

        return TRUE;
    }
}


/*
 * reg_recode
 *
 * It returns the code point in utf8 for the value in *encp.
 *    value: a code value in the source encoding
 *    encp:  a pointer to an Encode object
 *
 * If the result from Encode is not a single character,
 * it returns U+FFFD (Replacement character) and sets *encp to NULL.
 */
STATIC UV
S_reg_recode(pTHX_ const U8 value, SV **encp)
{
    STRLEN numlen = 1;
    SV * const sv = newSVpvn_flags((const char *) &value, numlen, SVs_TEMP);
    const char * const s = *encp ? sv_recode_to_utf8(sv, *encp) : SvPVX(sv);
    const STRLEN newlen = SvCUR(sv);
    UV uv = UNICODE_REPLACEMENT;

    PERL_ARGS_ASSERT_REG_RECODE;

    if (newlen)
        uv = SvUTF8(sv)
             ? utf8n_to_uvchr((U8*)s, newlen, &numlen, UTF8_ALLOW_DEFAULT)
             : *(U8*)s;

    if (!newlen || numlen != newlen) {
        uv = UNICODE_REPLACEMENT;
        *encp = NULL;
    }
    return uv;
}

PERL_STATIC_INLINE U8
S_compute_EXACTish(RExC_state_t *pRExC_state)
{
    U8 op;

    PERL_ARGS_ASSERT_COMPUTE_EXACTISH;

    if (! FOLD) {
        return (LOC)
                ? EXACTL
                : EXACT;
    }

    op = get_regex_charset(RExC_flags);
    if (op >= REGEX_ASCII_RESTRICTED_CHARSET) {
        op--; /* /a is same as /u, and map /aa's offset to what /a's would have
                 been, so there is no hole */
    }

    return op + EXACTF;
}

PERL_STATIC_INLINE void
S_alloc_maybe_populate_EXACT(pTHX_ RExC_state_t *pRExC_state,
                         regnode *node, I32* flagp, STRLEN len, UV code_point,
                         bool downgradable)
{
    /* This knows the details about sizing an EXACTish node, setting flags for
     * it (by setting <*flagp>, and potentially populating it with a single
     * character.
     *
     * If <len> (the length in bytes) is non-zero, this function assumes that
     * the node has already been populated, and just does the sizing.  In this
     * case <code_point> should be the final code point that has already been
     * placed into the node.  This value will be ignored except that under some
     * circumstances <*flagp> is set based on it.
     *
     * If <len> is zero, the function assumes that the node is to contain only
     * the single character given by <code_point> and calculates what <len>
     * should be.  In pass 1, it sizes the node appropriately.  In pass 2, it
     * additionally will populate the node's STRING with <code_point> or its
     * fold if folding.
     *
     * In both cases <*flagp> is appropriately set
     *
     * It knows that under FOLD, the Latin Sharp S and UTF characters above
     * 255, must be folded (the former only when the rules indicate it can
     * match 'ss')
     *
     * When it does the populating, it looks at the flag 'downgradable'.  If
     * true with a node that folds, it checks if the single code point
     * participates in a fold, and if not downgrades the node to an EXACT.
     * This helps the optimizer */

    bool len_passed_in = cBOOL(len != 0);
    U8 character[UTF8_MAXBYTES_CASE+1];

    PERL_ARGS_ASSERT_ALLOC_MAYBE_POPULATE_EXACT;

    /* Don't bother to check for downgrading in PASS1, as it doesn't make any
     * sizing difference, and is extra work that is thrown away */
    if (downgradable && ! PASS2) {
        downgradable = FALSE;
    }

    if (! len_passed_in) {
        if (UTF) {
            if (UVCHR_IS_INVARIANT(code_point)) {
                if (LOC || ! FOLD) {    /* /l defers folding until runtime */
                    *character = (U8) code_point;
                }
                else { /* Here is /i and not /l. (toFOLD() is defined on just
                          ASCII, which isn't the same thing as INVARIANT on
                          EBCDIC, but it works there, as the extra invariants
                          fold to themselves) */
                    *character = toFOLD((U8) code_point);

                    /* We can downgrade to an EXACT node if this character
                     * isn't a folding one.  Note that this assumes that
                     * nothing above Latin1 folds to some other invariant than
                     * one of these alphabetics; otherwise we would also have
                     * to check:
                     *  && (! HAS_NONLATIN1_FOLD_CLOSURE(code_point)
                     *      || ASCII_FOLD_RESTRICTED))
                     */
                    if (downgradable && PL_fold[code_point] == code_point) {
                        OP(node) = EXACT;
                    }
                }
                len = 1;
            }
            else if (FOLD && (! LOC
                              || ! is_PROBLEMATIC_LOCALE_FOLD_cp(code_point)))
            {   /* Folding, and ok to do so now */
                UV folded = _to_uni_fold_flags(
                                   code_point,
                                   character,
                                   &len,
                                   FOLD_FLAGS_FULL | ((ASCII_FOLD_RESTRICTED)
                                                      ? FOLD_FLAGS_NOMIX_ASCII
                                                      : 0));
                if (downgradable
                    && folded == code_point /* This quickly rules out many
                                               cases, avoiding the
                                               _invlist_contains_cp() overhead
                                               for those.  */
                    && ! _invlist_contains_cp(PL_utf8_foldable, code_point))
                {
                    OP(node) = (LOC)
                               ? EXACTL
                               : EXACT;
                }
            }
            else if (code_point <= MAX_UTF8_TWO_BYTE) {

                /* Not folding this cp, and can output it directly */
                *character = UTF8_TWO_BYTE_HI(code_point);
                *(character + 1) = UTF8_TWO_BYTE_LO(code_point);
                len = 2;
            }
            else {
                uvchr_to_utf8( character, code_point);
                len = UTF8SKIP(character);
            }
        } /* Else pattern isn't UTF8.  */
        else if (! FOLD) {
            *character = (U8) code_point;
            len = 1;
        } /* Else is folded non-UTF8 */
#if    UNICODE_MAJOR_VERSION > 3 /* no multifolds in early Unicode */   \
   || (UNICODE_MAJOR_VERSION == 3 && (   UNICODE_DOT_VERSION > 0)       \
                                      || UNICODE_DOT_DOT_VERSION > 0)
        else if (LIKELY(code_point != LATIN_SMALL_LETTER_SHARP_S)) {
#else
        else if (1) {
#endif
            /* We don't fold any non-UTF8 except possibly the Sharp s  (see
             * comments at join_exact()); */
            *character = (U8) code_point;
            len = 1;

            /* Can turn into an EXACT node if we know the fold at compile time,
             * and it folds to itself and doesn't particpate in other folds */
            if (downgradable
                && ! LOC
                && PL_fold_latin1[code_point] == code_point
                && (! HAS_NONLATIN1_FOLD_CLOSURE(code_point)
                    || (isASCII(code_point) && ASCII_FOLD_RESTRICTED)))
            {
                OP(node) = EXACT;
            }
        } /* else is Sharp s.  May need to fold it */
        else if (AT_LEAST_UNI_SEMANTICS && ! ASCII_FOLD_RESTRICTED) {
            *character = 's';
            *(character + 1) = 's';
            len = 2;
        }
        else {
            *character = LATIN_SMALL_LETTER_SHARP_S;
            len = 1;
        }
    }

    if (SIZE_ONLY) {
        RExC_size += STR_SZ(len);
    }
    else {
        RExC_emit += STR_SZ(len);
        STR_LEN(node) = len;
        if (! len_passed_in) {
            Copy((char *) character, STRING(node), len, char);
        }
    }

    *flagp |= HASWIDTH;

    /* A single character node is SIMPLE, except for the special-cased SHARP S
     * under /di. */
    if ((len == 1 || (UTF && len == UVCHR_SKIP(code_point)))
#if    UNICODE_MAJOR_VERSION > 3 /* no multifolds in early Unicode */   \
   || (UNICODE_MAJOR_VERSION == 3 && (   UNICODE_DOT_VERSION > 0)       \
                                      || UNICODE_DOT_DOT_VERSION > 0)
        && ( code_point != LATIN_SMALL_LETTER_SHARP_S
            || ! FOLD || ! DEPENDS_SEMANTICS)
#endif
    ) {
        *flagp |= SIMPLE;
    }

    /* The OP may not be well defined in PASS1 */
    if (PASS2 && OP(node) == EXACTFL) {
        RExC_contains_locale = 1;
    }
}


/* Parse backref decimal value, unless it's too big to sensibly be a backref,
 * in which case return I32_MAX (rather than possibly 32-bit wrapping) */

static I32
S_backref_value(char *p)
{
    const char* endptr;
    UV val;
    if (grok_atoUV(p, &val, &endptr) && val <= I32_MAX)
        return (I32)val;
    return I32_MAX;
}


/*
 - regatom - the lowest level

   Try to identify anything special at the start of the pattern. If there
   is, then handle it as required. This may involve generating a single regop,
   such as for an assertion; or it may involve recursing, such as to
   handle a () structure.

   If the string doesn't start with something special then we gobble up
   as much literal text as we can.

   Once we have been able to handle whatever type of thing started the
   sequence, we return.

   Note: we have to be careful with escapes, as they can be both literal
   and special, and in the case of \10 and friends, context determines which.

   A summary of the code structure is:

   switch (first_byte) {
        cases for each special:
            handle this special;
            break;
        case '\\':
            switch (2nd byte) {
                cases for each unambiguous special:
                    handle this special;
                    break;
                cases for each ambigous special/literal:
                    disambiguate;
                    if (special)  handle here
                    else goto defchar;
                default: // unambiguously literal:
                    goto defchar;
            }
        default:  // is a literal char
            // FALL THROUGH
        defchar:
            create EXACTish node for literal;
            while (more input and node isn't full) {
                switch (input_byte) {
                   cases for each special;
                       make sure parse pointer is set so that the next call to
                           regatom will see this special first
                       goto loopdone; // EXACTish node terminated by prev. char
                   default:
                       append char to EXACTISH node;
                }
                get next input byte;
            }
        loopdone:
   }
   return the generated node;

   Specifically there are two separate switches for handling
   escape sequences, with the one for handling literal escapes requiring
   a dummy entry for all of the special escapes that are actually handled
   by the other.

   Returns NULL, setting *flagp to TRYAGAIN if reg() returns NULL with
   TRYAGAIN.
   Returns NULL, setting *flagp to RESTART_PASS1 if the sizing scan needs to be
   restarted, or'd with NEED_UTF8 if the pattern needs to be upgraded to UTF-8
   Otherwise does not return NULL.
*/

STATIC regnode *
S_regatom(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
{
    regnode *ret = NULL;
    I32 flags = 0;
    char *parse_start;
    U8 op;
    int invert = 0;
    U8 arg;

    GET_RE_DEBUG_FLAGS_DECL;

    *flagp = WORST;             /* Tentatively. */

    DEBUG_PARSE("atom");

    PERL_ARGS_ASSERT_REGATOM;

  tryagain:
    parse_start = RExC_parse;
    assert(RExC_parse < RExC_end);
    switch ((U8)*RExC_parse) {
    case '^':
        RExC_seen_zerolen++;
        nextchar(pRExC_state);
        if (RExC_flags & RXf_PMf_MULTILINE)
            ret = reg_node(pRExC_state, MBOL);
        else
            ret = reg_node(pRExC_state, SBOL);
        Set_Node_Length(ret, 1); /* MJD */
        break;
    case '$':
        nextchar(pRExC_state);
        if (*RExC_parse)
            RExC_seen_zerolen++;
        if (RExC_flags & RXf_PMf_MULTILINE)
            ret = reg_node(pRExC_state, MEOL);
        else
            ret = reg_node(pRExC_state, SEOL);
        Set_Node_Length(ret, 1); /* MJD */
        break;
    case '.':
        nextchar(pRExC_state);
        if (RExC_flags & RXf_PMf_SINGLELINE)
            ret = reg_node(pRExC_state, SANY);
        else
            ret = reg_node(pRExC_state, REG_ANY);
        *flagp |= HASWIDTH|SIMPLE;
        MARK_NAUGHTY(1);
        Set_Node_Length(ret, 1); /* MJD */
        break;
    case '[':
    {
        char * const oregcomp_parse = ++RExC_parse;
        ret = regclass(pRExC_state, flagp,depth+1,
                       FALSE, /* means parse the whole char class */
                       TRUE, /* allow multi-char folds */
                       FALSE, /* don't silence non-portable warnings. */
                       (bool) RExC_strict,
                       TRUE, /* Allow an optimized regnode result */
                       NULL,
                       NULL);
        if (ret == NULL) {
            if (*flagp & (RESTART_PASS1|NEED_UTF8))
                return NULL;
            FAIL2("panic: regclass returned NULL to regatom, flags=%#"UVxf"",
                  (UV) *flagp);
        }
        if (*RExC_parse != ']') {
            RExC_parse = oregcomp_parse;
            vFAIL("Unmatched [");
        }
        nextchar(pRExC_state);
        Set_Node_Length(ret, RExC_parse - oregcomp_parse + 1); /* MJD */
        break;
    }
    case '(':
        nextchar(pRExC_state);
        ret = reg(pRExC_state, 2, &flags,depth+1);
        if (ret == NULL) {
                if (flags & TRYAGAIN) {
                    if (RExC_parse >= RExC_end) {
                         /* Make parent create an empty node if needed. */
                        *flagp |= TRYAGAIN;
                        return(NULL);
                    }
                    goto tryagain;
                }
                if (flags & (RESTART_PASS1|NEED_UTF8)) {
                    *flagp = flags & (RESTART_PASS1|NEED_UTF8);
                    return NULL;
                }
                FAIL2("panic: reg returned NULL to regatom, flags=%#"UVxf"",
                                                                 (UV) flags);
        }
        *flagp |= flags&(HASWIDTH|SPSTART|SIMPLE|POSTPONED);
        break;
    case '|':
    case ')':
        if (flags & TRYAGAIN) {
            *flagp |= TRYAGAIN;
            return NULL;
        }
        vFAIL("Internal urp");
                                /* Supposed to be caught earlier. */
        break;
    case '?':
    case '+':
    case '*':
        RExC_parse++;
        vFAIL("Quantifier follows nothing");
        break;
    case '\\':
        /* Special Escapes

           This switch handles escape sequences that resolve to some kind
           of special regop and not to literal text. Escape sequnces that
           resolve to literal text are handled below in the switch marked
           "Literal Escapes".

           Every entry in this switch *must* have a corresponding entry
           in the literal escape switch. However, the opposite is not
           required, as the default for this switch is to jump to the
           literal text handling code.
        */
        RExC_parse++;
        switch ((U8)*RExC_parse) {
        /* Special Escapes */
        case 'A':
            RExC_seen_zerolen++;
            ret = reg_node(pRExC_state, SBOL);
            /* SBOL is shared with /^/ so we set the flags so we can tell
             * /\A/ from /^/ in split. We check ret because first pass we
             * have no regop struct to set the flags on. */
            if (PASS2)
                ret->flags = 1;
            *flagp |= SIMPLE;
            goto finish_meta_pat;
        case 'G':
            ret = reg_node(pRExC_state, GPOS);
            RExC_seen |= REG_GPOS_SEEN;
            *flagp |= SIMPLE;
            goto finish_meta_pat;
        case 'K':
            RExC_seen_zerolen++;
            ret = reg_node(pRExC_state, KEEPS);
            *flagp |= SIMPLE;
            /* XXX:dmq : disabling in-place substitution seems to
             * be necessary here to avoid cases of memory corruption, as
             * with: C<$_="x" x 80; s/x\K/y/> -- rgs
             */
            RExC_seen |= REG_LOOKBEHIND_SEEN;
            goto finish_meta_pat;
        case 'Z':
            ret = reg_node(pRExC_state, SEOL);
            *flagp |= SIMPLE;
            RExC_seen_zerolen++;                /* Do not optimize RE away */
            goto finish_meta_pat;
        case 'z':
            ret = reg_node(pRExC_state, EOS);
            *flagp |= SIMPLE;
            RExC_seen_zerolen++;                /* Do not optimize RE away */
            goto finish_meta_pat;
        case 'C':
            vFAIL("\\C no longer supported");
        case 'X':
            ret = reg_node(pRExC_state, CLUMP);
            *flagp |= HASWIDTH;
            goto finish_meta_pat;

        case 'W':
            invert = 1;
            /* FALLTHROUGH */
        case 'w':
            arg = ANYOF_WORDCHAR;
            goto join_posix;

        case 'B':
            invert = 1;
            /* FALLTHROUGH */
        case 'b':
          {
            regex_charset charset = get_regex_charset(RExC_flags);

            RExC_seen_zerolen++;
            RExC_seen |= REG_LOOKBEHIND_SEEN;
            op = BOUND + charset;

            if (op == BOUNDL) {
                RExC_contains_locale = 1;
            }

            ret = reg_node(pRExC_state, op);
            *flagp |= SIMPLE;
            if (RExC_parse >= RExC_end || *(RExC_parse + 1) != '{') {
                FLAGS(ret) = TRADITIONAL_BOUND;
                if (PASS2 && op > BOUNDA) {  /* /aa is same as /a */
                    OP(ret) = BOUNDA;
                }
            }
            else {
                STRLEN length;
                char name = *RExC_parse;
                char * endbrace;
                RExC_parse += 2;
                endbrace = strchr(RExC_parse, '}');

                if (! endbrace) {
                    vFAIL2("Missing right brace on \\%c{}", name);
                }
                /* XXX Need to decide whether to take spaces or not.  Should be
                 * consistent with \p{}, but that currently is SPACE, which
                 * means vertical too, which seems wrong
                 * while (isBLANK(*RExC_parse)) {
                    RExC_parse++;
                }*/
                if (endbrace == RExC_parse) {
                    RExC_parse++;  /* After the '}' */
                    vFAIL2("Empty \\%c{}", name);
                }
                length = endbrace - RExC_parse;
                /*while (isBLANK(*(RExC_parse + length - 1))) {
                    length--;
                }*/
                switch (*RExC_parse) {
                    case 'g':
                        if (length != 1
                            && (length != 3 || strnNE(RExC_parse + 1, "cb", 2)))
                        {
                            goto bad_bound_type;
                        }
                        FLAGS(ret) = GCB_BOUND;
                        break;
                    case 'l':
                        if (length != 2 || *(RExC_parse + 1) != 'b') {
                            goto bad_bound_type;
                        }
                        FLAGS(ret) = LB_BOUND;
                        break;
                    case 's':
                        if (length != 2 || *(RExC_parse + 1) != 'b') {
                            goto bad_bound_type;
                        }
                        FLAGS(ret) = SB_BOUND;
                        break;
                    case 'w':
                        if (length != 2 || *(RExC_parse + 1) != 'b') {
                            goto bad_bound_type;
                        }
                        FLAGS(ret) = WB_BOUND;
                        break;
                    default:
                      bad_bound_type:
                        RExC_parse = endbrace;
                        vFAIL2utf8f(
                            "'%"UTF8f"' is an unknown bound type",
                            UTF8fARG(UTF, length, endbrace - length));
                        NOT_REACHED; /*NOTREACHED*/
                }
                RExC_parse = endbrace;
                REQUIRE_UNI_RULES(flagp, NULL);

                if (PASS2 && op >= BOUNDA) {  /* /aa is same as /a */
                    OP(ret) = BOUNDU;
                    length += 4;

                    /* Don't have to worry about UTF-8, in this message because
                     * to get here the contents of the \b must be ASCII */
                    ckWARN4reg(RExC_parse + 1,  /* Include the '}' in msg */
                              "Using /u for '%.*s' instead of /%s",
                              (unsigned) length,
                              endbrace - length + 1,
                              (charset == REGEX_ASCII_RESTRICTED_CHARSET)
                              ? ASCII_RESTRICT_PAT_MODS
                              : ASCII_MORE_RESTRICT_PAT_MODS);
                }
            }

            if (PASS2 && invert) {
                OP(ret) += NBOUND - BOUND;
            }
            goto finish_meta_pat;
          }

        case 'D':
            invert = 1;
            /* FALLTHROUGH */
        case 'd':
            arg = ANYOF_DIGIT;
            if (! DEPENDS_SEMANTICS) {
                goto join_posix;
            }

            /* \d doesn't have any matches in the upper Latin1 range, hence /d
             * is equivalent to /u.  Changing to /u saves some branches at
             * runtime */
            op = POSIXU;
            goto join_posix_op_known;

        case 'R':
            ret = reg_node(pRExC_state, LNBREAK);
            *flagp |= HASWIDTH|SIMPLE;
            goto finish_meta_pat;

        case 'H':
            invert = 1;
            /* FALLTHROUGH */
        case 'h':
            arg = ANYOF_BLANK;
            op = POSIXU;
            goto join_posix_op_known;

        case 'V':
            invert = 1;
            /* FALLTHROUGH */
        case 'v':
            arg = ANYOF_VERTWS;
            op = POSIXU;
            goto join_posix_op_known;

        case 'S':
            invert = 1;
            /* FALLTHROUGH */
        case 's':
            arg = ANYOF_SPACE;

          join_posix:

            op = POSIXD + get_regex_charset(RExC_flags);
            if (op > POSIXA) {  /* /aa is same as /a */
                op = POSIXA;
            }
            else if (op == POSIXL) {
                RExC_contains_locale = 1;
            }

          join_posix_op_known:

            if (invert) {
                op += NPOSIXD - POSIXD;
            }

            ret = reg_node(pRExC_state, op);
            if (! SIZE_ONLY) {
                FLAGS(ret) = namedclass_to_classnum(arg);
            }

            *flagp |= HASWIDTH|SIMPLE;
            /* FALLTHROUGH */

          finish_meta_pat:
            nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
            break;
        case 'p':
        case 'P':
            RExC_parse--;

            ret = regclass(pRExC_state, flagp,depth+1,
                           TRUE, /* means just parse this element */
                           FALSE, /* don't allow multi-char folds */
                           FALSE, /* don't silence non-portable warnings.  It
                                     would be a bug if these returned
                                     non-portables */
                           (bool) RExC_strict,
                           TRUE, /* Allow an optimized regnode result */
                           NULL,
                           NULL);
            if (*flagp & RESTART_PASS1)
                return NULL;
            /* regclass() can only return RESTART_PASS1 and NEED_UTF8 if
             * multi-char folds are allowed.  */
            if (!ret)
                FAIL2("panic: regclass returned NULL to regatom, flags=%#"UVxf"",
                      (UV) *flagp);

            RExC_parse--;

            Set_Node_Offset(ret, parse_start);
            Set_Node_Cur_Length(ret, parse_start - 2);
            nextchar(pRExC_state);
            break;
        case 'N':
            /* Handle \N, \N{} and \N{NAMED SEQUENCE} (the latter meaning the
             * \N{...} evaluates to a sequence of more than one code points).
             * The function call below returns a regnode, which is our result.
             * The parameters cause it to fail if the \N{} evaluates to a
             * single code point; we handle those like any other literal.  The
             * reason that the multicharacter case is handled here and not as
             * part of the EXACtish code is because of quantifiers.  In
             * /\N{BLAH}+/, the '+' applies to the whole thing, and doing it
             * this way makes that Just Happen. dmq.
             * join_exact() will join this up with adjacent EXACTish nodes
             * later on, if appropriate. */
            ++RExC_parse;
            if (grok_bslash_N(pRExC_state,
                              &ret,     /* Want a regnode returned */
                              NULL,     /* Fail if evaluates to a single code
                                           point */
                              NULL,     /* Don't need a count of how many code
                                           points */
                              flagp,
                              RExC_strict,
                              depth)
            ) {
                break;
            }

            if (*flagp & RESTART_PASS1)
                return NULL;

            /* Here, evaluates to a single code point.  Go get that */
            RExC_parse = parse_start;
            goto defchar;

        case 'k':    /* Handle \k<NAME> and \k'NAME' */
      parse_named_seq:
        {
            char ch;
            if (   RExC_parse >= RExC_end - 1
                || ((   ch = RExC_parse[1]) != '<'
                                      && ch != '\''
                                      && ch != '{'))
            {
                RExC_parse++;
                /* diag_listed_as: Sequence \%s... not terminated in regex; marked by <-- HERE in m/%s/ */
                vFAIL2("Sequence %.2s... not terminated",parse_start);
            } else {
                RExC_parse += 2;
                ret = handle_named_backref(pRExC_state,
                                           flagp,
                                           parse_start,
                                           (ch == '<')
                                           ? '>'
                                           : (ch == '{')
                                             ? '}'
                                             : '\'');
            }
            break;
        }
        case 'g':
        case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
            {
                I32 num;
                bool hasbrace = 0;

                if (*RExC_parse == 'g') {
                    bool isrel = 0;

                    RExC_parse++;
                    if (*RExC_parse == '{') {
                        RExC_parse++;
                        hasbrace = 1;
                    }
                    if (*RExC_parse == '-') {
                        RExC_parse++;
                        isrel = 1;
                    }
                    if (hasbrace && !isDIGIT(*RExC_parse)) {
                        if (isrel) RExC_parse--;
                        RExC_parse -= 2;
                        goto parse_named_seq;
                    }

                    if (RExC_parse >= RExC_end) {
                        goto unterminated_g;
                    }
                    num = S_backref_value(RExC_parse);
                    if (num == 0)
                        vFAIL("Reference to invalid group 0");
                    else if (num == I32_MAX) {
                         if (isDIGIT(*RExC_parse))
                            vFAIL("Reference to nonexistent group");
                        else
                          unterminated_g:
                            vFAIL("Unterminated \\g... pattern");
                    }

                    if (isrel) {
                        num = RExC_npar - num;
                        if (num < 1)
                            vFAIL("Reference to nonexistent or unclosed group");
                    }
                }
                else {
                    num = S_backref_value(RExC_parse);
                    /* bare \NNN might be backref or octal - if it is larger
                     * than or equal RExC_npar then it is assumed to be an
                     * octal escape. Note RExC_npar is +1 from the actual
                     * number of parens. */
                    /* Note we do NOT check if num == I32_MAX here, as that is
                     * handled by the RExC_npar check */

                    if (
                        /* any numeric escape < 10 is always a backref */
                        num > 9
                        /* any numeric escape < RExC_npar is a backref */
                        && num >= RExC_npar
                        /* cannot be an octal escape if it starts with 8 */
                        && *RExC_parse != '8'
                        /* cannot be an octal escape it it starts with 9 */
                        && *RExC_parse != '9'
                    )
                    {
                        /* Probably not a backref, instead likely to be an
                         * octal character escape, e.g. \35 or \777.
                         * The above logic should make it obvious why using
                         * octal escapes in patterns is problematic. - Yves */
                        RExC_parse = parse_start;
                        goto defchar;
                    }
                }

                /* At this point RExC_parse points at a numeric escape like
                 * \12 or \88 or something similar, which we should NOT treat
                 * as an octal escape. It may or may not be a valid backref
                 * escape. For instance \88888888 is unlikely to be a valid
                 * backref. */
                while (isDIGIT(*RExC_parse))
                    RExC_parse++;
                if (hasbrace) {
                    if (*RExC_parse != '}')
                        vFAIL("Unterminated \\g{...} pattern");
                    RExC_parse++;
                }
                if (!SIZE_ONLY) {
                    if (num > (I32)RExC_rx->nparens)
                        vFAIL("Reference to nonexistent group");
                }
                RExC_sawback = 1;
                ret = reganode(pRExC_state,
                               ((! FOLD)
                                 ? REF
                                 : (ASCII_FOLD_RESTRICTED)
                                   ? REFFA
                                   : (AT_LEAST_UNI_SEMANTICS)
                                     ? REFFU
                                     : (LOC)
                                       ? REFFL
                                       : REFF),
                                num);
                *flagp |= HASWIDTH;

                /* override incorrect value set in reganode MJD */
                Set_Node_Offset(ret, parse_start);
                Set_Node_Cur_Length(ret, parse_start-1);
                skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                        FALSE /* Don't force to /x */ );
            }
            break;
        case '\0':
            if (RExC_parse >= RExC_end)
                FAIL("Trailing \\");
            /* FALLTHROUGH */
        default:
            /* Do not generate "unrecognized" warnings here, we fall
               back into the quick-grab loop below */
            RExC_parse = parse_start;
            goto defchar;
        } /* end of switch on a \foo sequence */
        break;

    case '#':

        /* '#' comments should have been spaced over before this function was
         * called */
        assert((RExC_flags & RXf_PMf_EXTENDED) == 0);
        /*
        if (RExC_flags & RXf_PMf_EXTENDED) {
            RExC_parse = reg_skipcomment( pRExC_state, RExC_parse );
            if (RExC_parse < RExC_end)
                goto tryagain;
        }
        */

        /* FALLTHROUGH */

    default:
          defchar: {

            /* Here, we have determined that the next thing is probably a
             * literal character.  RExC_parse points to the first byte of its
             * definition.  (It still may be an escape sequence that evaluates
             * to a single character) */

            STRLEN len = 0;
            UV ender = 0;
            char *p;
            char *s;
#define MAX_NODE_STRING_SIZE 127
            char foldbuf[MAX_NODE_STRING_SIZE+UTF8_MAXBYTES_CASE];
            char *s0;
            U8 upper_parse = MAX_NODE_STRING_SIZE;
            U8 node_type = compute_EXACTish(pRExC_state);
            bool next_is_quantifier;
            char * oldp = NULL;

            /* We can convert EXACTF nodes to EXACTFU if they contain only
             * characters that match identically regardless of the target
             * string's UTF8ness.  The reason to do this is that EXACTF is not
             * trie-able, EXACTFU is.
             *
             * Similarly, we can convert EXACTFL nodes to EXACTFLU8 if they
             * contain only above-Latin1 characters (hence must be in UTF8),
             * which don't participate in folds with Latin1-range characters,
             * as the latter's folds aren't known until runtime.  (We don't
             * need to figure this out until pass 2) */
            bool maybe_exactfu = PASS2
                               && (node_type == EXACTF || node_type == EXACTFL);

            /* If a folding node contains only code points that don't
             * participate in folds, it can be changed into an EXACT node,
             * which allows the optimizer more things to look for */
            bool maybe_exact;

            ret = reg_node(pRExC_state, node_type);

            /* In pass1, folded, we use a temporary buffer instead of the
             * actual node, as the node doesn't exist yet */
            s = (SIZE_ONLY && FOLD) ? foldbuf : STRING(ret);

            s0 = s;

          reparse:

            /* We look for the EXACTFish to EXACT node optimizaton only if
             * folding.  (And we don't need to figure this out until pass 2).
             * XXX It might actually make sense to split the node into portions
             * that are exact and ones that aren't, so that we could later use
             * the exact ones to find the longest fixed and floating strings.
             * One would want to join them back into a larger node.  One could
             * use a pseudo regnode like 'EXACT_ORIG_FOLD' */
            maybe_exact = FOLD && PASS2;

            /* XXX The node can hold up to 255 bytes, yet this only goes to
             * 127.  I (khw) do not know why.  Keeping it somewhat less than
             * 255 allows us to not have to worry about overflow due to
             * converting to utf8 and fold expansion, but that value is
             * 255-UTF8_MAXBYTES_CASE.  join_exact() may join adjacent nodes
             * split up by this limit into a single one using the real max of
             * 255.  Even at 127, this breaks under rare circumstances.  If
             * folding, we do not want to split a node at a character that is a
             * non-final in a multi-char fold, as an input string could just
             * happen to want to match across the node boundary.  The join
             * would solve that problem if the join actually happens.  But a
             * series of more than two nodes in a row each of 127 would cause
             * the first join to succeed to get to 254, but then there wouldn't
             * be room for the next one, which could at be one of those split
             * multi-char folds.  I don't know of any fool-proof solution.  One
             * could back off to end with only a code point that isn't such a
             * non-final, but it is possible for there not to be any in the
             * entire node. */

            assert(   ! UTF     /* Is at the beginning of a character */
                   || UTF8_IS_INVARIANT(UCHARAT(RExC_parse))
                   || UTF8_IS_START(UCHARAT(RExC_parse)));

            for (p = RExC_parse;
                 len < upper_parse && p < RExC_end;
                 len++)
            {
                oldp = p;

                /* White space has already been ignored */
                assert(   (RExC_flags & RXf_PMf_EXTENDED) == 0
                       || ! is_PATWS_safe((p), RExC_end, UTF));

                switch ((U8)*p) {
                case '^':
                case '$':
                case '.':
                case '[':
                case '(':
                case ')':
                case '|':
                    goto loopdone;
                case '\\':
                    /* Literal Escapes Switch

                       This switch is meant to handle escape sequences that
                       resolve to a literal character.

                       Every escape sequence that represents something
                       else, like an assertion or a char class, is handled
                       in the switch marked 'Special Escapes' above in this
                       routine, but also has an entry here as anything that
                       isn't explicitly mentioned here will be treated as
                       an unescaped equivalent literal.
                    */

                    switch ((U8)*++p) {
                    /* These are all the special escapes. */
                    case 'A':             /* Start assertion */
                    case 'b': case 'B':   /* Word-boundary assertion*/
                    case 'C':             /* Single char !DANGEROUS! */
                    case 'd': case 'D':   /* digit class */
                    case 'g': case 'G':   /* generic-backref, pos assertion */
                    case 'h': case 'H':   /* HORIZWS */
                    case 'k': case 'K':   /* named backref, keep marker */
                    case 'p': case 'P':   /* Unicode property */
                              case 'R':   /* LNBREAK */
                    case 's': case 'S':   /* space class */
                    case 'v': case 'V':   /* VERTWS */
                    case 'w': case 'W':   /* word class */
                    case 'X':             /* eXtended Unicode "combining
                                             character sequence" */
                    case 'z': case 'Z':   /* End of line/string assertion */
                        --p;
                        goto loopdone;

                    /* Anything after here is an escape that resolves to a
                       literal. (Except digits, which may or may not)
                     */
                    case 'n':
                        ender = '\n';
                        p++;
                        break;
                    case 'N': /* Handle a single-code point named character. */
                        RExC_parse = p + 1;
                        if (! grok_bslash_N(pRExC_state,
                                            NULL,   /* Fail if evaluates to
                                                       anything other than a
                                                       single code point */
                                            &ender, /* The returned single code
                                                       point */
                                            NULL,   /* Don't need a count of
                                                       how many code points */
                                            flagp,
                                            RExC_strict,
                                            depth)
                        ) {
                            if (*flagp & NEED_UTF8)
                                FAIL("panic: grok_bslash_N set NEED_UTF8");
                            if (*flagp & RESTART_PASS1)
                                return NULL;

                            /* Here, it wasn't a single code point.  Go close
                             * up this EXACTish node.  The switch() prior to
                             * this switch handles the other cases */
                            RExC_parse = p = oldp;
                            goto loopdone;
                        }
                        p = RExC_parse;
                        if (ender > 0xff) {
                            REQUIRE_UTF8(flagp);
                        }
                        break;
                    case 'r':
                        ender = '\r';
                        p++;
                        break;
                    case 't':
                        ender = '\t';
                        p++;
                        break;
                    case 'f':
                        ender = '\f';
                        p++;
                        break;
                    case 'e':
                        ender = ESC_NATIVE;
                        p++;
                        break;
                    case 'a':
                        ender = '\a';
                        p++;
                        break;
                    case 'o':
                        {
                            UV result;
                            const char* error_msg;

                            bool valid = grok_bslash_o(&p,
                                                       &result,
                                                       &error_msg,
                                                       PASS2, /* out warnings */
                                                       (bool) RExC_strict,
                                                       TRUE, /* Output warnings
                                                                for non-
                                                                portables */
                                                       UTF);
                            if (! valid) {
                                RExC_parse = p; /* going to die anyway; point
                                                   to exact spot of failure */
                                vFAIL(error_msg);
                            }
                            ender = result;
                            if (IN_ENCODING && ender < 0x100) {
                                goto recode_encoding;
                            }
                            if (ender > 0xff) {
                                REQUIRE_UTF8(flagp);
                            }
                            break;
                        }
                    case 'x':
                        {
                            UV result = UV_MAX; /* initialize to erroneous
                                                   value */
                            const char* error_msg;

                            bool valid = grok_bslash_x(&p,
                                                       &result,
                                                       &error_msg,
                                                       PASS2, /* out warnings */
                                                       (bool) RExC_strict,
                                                       TRUE, /* Silence warnings
                                                                for non-
                                                                portables */
                                                       UTF);
                            if (! valid) {
                                RExC_parse = p; /* going to die anyway; point
                                                   to exact spot of failure */
                                vFAIL(error_msg);
                            }
                            ender = result;

                            if (ender < 0x100) {
#ifdef EBCDIC
                                if (RExC_recode_x_to_native) {
                                    ender = LATIN1_TO_NATIVE(ender);
                                }
                                else
#endif
                                if (IN_ENCODING) {
                                    goto recode_encoding;
                                }
                            }
                            else {
                                REQUIRE_UTF8(flagp);
                            }
                            break;
                        }
                    case 'c':
                        p++;
                        ender = grok_bslash_c(*p++, PASS2);
                        break;
                    case '8': case '9': /* must be a backreference */
                        --p;
                        /* we have an escape like \8 which cannot be an octal escape
                         * so we exit the loop, and let the outer loop handle this
                         * escape which may or may not be a legitimate backref. */
                        goto loopdone;
                    case '1': case '2': case '3':case '4':
                    case '5': case '6': case '7':
                        /* When we parse backslash escapes there is ambiguity
                         * between backreferences and octal escapes. Any escape
                         * from \1 - \9 is a backreference, any multi-digit
                         * escape which does not start with 0 and which when
                         * evaluated as decimal could refer to an already
                         * parsed capture buffer is a back reference. Anything
                         * else is octal.
                         *
                         * Note this implies that \118 could be interpreted as
                         * 118 OR as "\11" . "8" depending on whether there
                         * were 118 capture buffers defined already in the
                         * pattern.  */

                        /* NOTE, RExC_npar is 1 more than the actual number of
                         * parens we have seen so far, hence the < RExC_npar below. */

                        if ( !isDIGIT(p[1]) || S_backref_value(p) < RExC_npar)
                        {  /* Not to be treated as an octal constant, go
                                   find backref */
                            --p;
                            goto loopdone;
                        }
                        /* FALLTHROUGH */
                    case '0':
                        {
                            I32 flags = PERL_SCAN_SILENT_ILLDIGIT;
                            STRLEN numlen = 3;
                            ender = grok_oct(p, &numlen, &flags, NULL);
                            if (ender > 0xff) {
                                REQUIRE_UTF8(flagp);
                            }
                            p += numlen;
                            if (PASS2   /* like \08, \178 */
                                && numlen < 3
                                && isDIGIT(*p) && ckWARN(WARN_REGEXP))
                            {
                                reg_warn_non_literal_string(
                                         p + 1,
                                         form_short_octal_warning(p, numlen));
                            }
                        }
                        if (IN_ENCODING && ender < 0x100)
                            goto recode_encoding;
                        break;
                      recode_encoding:
                        if (! RExC_override_recoding) {
                            SV* enc = _get_encoding();
                            ender = reg_recode((U8)ender, &enc);
                            if (!enc && PASS2)
                                ckWARNreg(p, "Invalid escape in the specified encoding");
                            REQUIRE_UTF8(flagp);
                        }
                        break;
                    case '\0':
                        if (p >= RExC_end)
                            FAIL("Trailing \\");
                        /* FALLTHROUGH */
                    default:
                        if (!SIZE_ONLY&& isALPHANUMERIC(*p)) {
                            /* Include any left brace following the alpha to emphasize
                             * that it could be part of an escape at some point
                             * in the future */
                            int len = (isALPHA(*p) && *(p + 1) == '{') ? 2 : 1;
                            ckWARN3reg(p + len, "Unrecognized escape \\%.*s passed through", len, p);
                        }
                        goto normal_default;
                    } /* End of switch on '\' */
                    break;
                case '{':
                    /* Currently we don't warn when the lbrace is at the start
                     * of a construct.  This catches it in the middle of a
                     * literal string, or when it's the first thing after
                     * something like "\b" */
                    if (! SIZE_ONLY
                        && (len || (p > RExC_start && isALPHA_A(*(p -1)))))
                    {
                        ckWARNregdep(p + 1, "Unescaped left brace in regex is deprecated, passed through");
                    }
                    /*FALLTHROUGH*/
                default:    /* A literal character */
                  normal_default:
                    if (! UTF8_IS_INVARIANT(*p) && UTF) {
                        STRLEN numlen;
                        ender = utf8n_to_uvchr((U8*)p, RExC_end - p,
                                               &numlen, UTF8_ALLOW_DEFAULT);
                        p += numlen;
                    }
                    else
                        ender = (U8) *p++;
                    break;
                } /* End of switch on the literal */

                /* Here, have looked at the literal character and <ender>
                 * contains its ordinal, <p> points to the character after it.
                 * We need to check if the next non-ignored thing is a
                 * quantifier.  Move <p> to after anything that should be
                 * ignored, which, as a side effect, positions <p> for the next
                 * loop iteration */
                skip_to_be_ignored_text(pRExC_state, &p,
                                        FALSE /* Don't force to /x */ );

                /* If the next thing is a quantifier, it applies to this
                 * character only, which means that this character has to be in
                 * its own node and can't just be appended to the string in an
                 * existing node, so if there are already other characters in
                 * the node, close the node with just them, and set up to do
                 * this character again next time through, when it will be the
                 * only thing in its new node */
                if ((next_is_quantifier = (   LIKELY(p < RExC_end)
                                           && UNLIKELY(ISMULT2(p))))
                    && LIKELY(len))
                {
                    p = oldp;
                    goto loopdone;
                }

                /* Ready to add 'ender' to the node */

                if (! FOLD) {  /* The simple case, just append the literal */

                    /* In the sizing pass, we need only the size of the
                     * character we are appending, hence we can delay getting
                     * its representation until PASS2. */
                    if (SIZE_ONLY) {
                        if (UTF) {
                            const STRLEN unilen = UVCHR_SKIP(ender);
                            s += unilen;

                            /* We have to subtract 1 just below (and again in
                             * the corresponding PASS2 code) because the loop
                             * increments <len> each time, as all but this path
                             * (and one other) through it add a single byte to
                             * the EXACTish node.  But these paths would change
                             * len to be the correct final value, so cancel out
                             * the increment that follows */
                            len += unilen - 1;
                        }
                        else {
                            s++;
                        }
                    } else { /* PASS2 */
                      not_fold_common:
                        if (UTF) {
                            U8 * new_s = uvchr_to_utf8((U8*)s, ender);
                            len += (char *) new_s - s - 1;
                            s = (char *) new_s;
                        }
                        else {
                            *(s++) = (char) ender;
                        }
                    }
                }
                else if (LOC && is_PROBLEMATIC_LOCALE_FOLD_cp(ender)) {

                    /* Here are folding under /l, and the code point is
                     * problematic.  First, we know we can't simplify things */
                    maybe_exact = FALSE;
                    maybe_exactfu = FALSE;

                    /* A problematic code point in this context means that its
                     * fold isn't known until runtime, so we can't fold it now.
                     * (The non-problematic code points are the above-Latin1
                     * ones that fold to also all above-Latin1.  Their folds
                     * don't vary no matter what the locale is.) But here we
                     * have characters whose fold depends on the locale.
                     * Unlike the non-folding case above, we have to keep track
                     * of these in the sizing pass, so that we can make sure we
                     * don't split too-long nodes in the middle of a potential
                     * multi-char fold.  And unlike the regular fold case
                     * handled in the else clauses below, we don't actually
                     * fold and don't have special cases to consider.  What we
                     * do for both passes is the PASS2 code for non-folding */
                    goto not_fold_common;
                }
                else /* A regular FOLD code point */
                    if (! (   UTF
#if    UNICODE_MAJOR_VERSION > 3 /* no multifolds in early Unicode */   \
   || (UNICODE_MAJOR_VERSION == 3 && (   UNICODE_DOT_VERSION > 0)       \
                                      || UNICODE_DOT_DOT_VERSION > 0)
                            /* See comments for join_exact() as to why we fold
                             * this non-UTF at compile time */
                            || (   node_type == EXACTFU
                                && ender == LATIN_SMALL_LETTER_SHARP_S)
#endif
                )) {
                    /* Here, are folding and are not UTF-8 encoded; therefore
                     * the character must be in the range 0-255, and is not /l
                     * (Not /l because we already handled these under /l in
                     * is_PROBLEMATIC_LOCALE_FOLD_cp) */
                    if (IS_IN_SOME_FOLD_L1(ender)) {
                        maybe_exact = FALSE;

                        /* See if the character's fold differs between /d and
                         * /u.  This includes the multi-char fold SHARP S to
                         * 'ss' */
                        if (UNLIKELY(ender == LATIN_SMALL_LETTER_SHARP_S)) {
                            RExC_seen_unfolded_sharp_s = 1;
                            maybe_exactfu = FALSE;
                        }
                        else if (maybe_exactfu
                            && (PL_fold[ender] != PL_fold_latin1[ender]
#if    UNICODE_MAJOR_VERSION > 3 /* no multifolds in early Unicode */   \
   || (UNICODE_MAJOR_VERSION == 3 && (   UNICODE_DOT_VERSION > 0)       \
                                      || UNICODE_DOT_DOT_VERSION > 0)
                                || (   len > 0
                                    && isALPHA_FOLD_EQ(ender, 's')
                                    && isALPHA_FOLD_EQ(*(s-1), 's'))
#endif
                        )) {
                            maybe_exactfu = FALSE;
                        }
                    }

                    /* Even when folding, we store just the input character, as
                     * we have an array that finds its fold quickly */
                    *(s++) = (char) ender;
                }
                else {  /* FOLD, and UTF (or sharp s) */
                    /* Unlike the non-fold case, we do actually have to
                     * calculate the results here in pass 1.  This is for two
                     * reasons, the folded length may be longer than the
                     * unfolded, and we have to calculate how many EXACTish
                     * nodes it will take; and we may run out of room in a node
                     * in the middle of a potential multi-char fold, and have
                     * to back off accordingly.  */

                    UV folded;
                    if (isASCII_uni(ender)) {
                        folded = toFOLD(ender);
                        *(s)++ = (U8) folded;
                    }
                    else {
                        STRLEN foldlen;

                        folded = _to_uni_fold_flags(
                                     ender,
                                     (U8 *) s,
                                     &foldlen,
                                     FOLD_FLAGS_FULL | ((ASCII_FOLD_RESTRICTED)
                                                        ? FOLD_FLAGS_NOMIX_ASCII
                                                        : 0));
                        s += foldlen;

                        /* The loop increments <len> each time, as all but this
                         * path (and one other) through it add a single byte to
                         * the EXACTish node.  But this one has changed len to
                         * be the correct final value, so subtract one to
                         * cancel out the increment that follows */
                        len += foldlen - 1;
                    }
                    /* If this node only contains non-folding code points so
                     * far, see if this new one is also non-folding */
                    if (maybe_exact) {
                        if (folded != ender) {
                            maybe_exact = FALSE;
                        }
                        else {
                            /* Here the fold is the original; we have to check
                             * further to see if anything folds to it */
                            if (_invlist_contains_cp(PL_utf8_foldable,
                                                        ender))
                            {
                                maybe_exact = FALSE;
                            }
                        }
                    }
                    ender = folded;
                }

                if (next_is_quantifier) {

                    /* Here, the next input is a quantifier, and to get here,
                     * the current character is the only one in the node.
                     * Also, here <len> doesn't include the final byte for this
                     * character */
                    len++;
                    goto loopdone;
                }

            } /* End of loop through literal characters */

            /* Here we have either exhausted the input or ran out of room in
             * the node.  (If we encountered a character that can't be in the
             * node, transfer is made directly to <loopdone>, and so we
             * wouldn't have fallen off the end of the loop.)  In the latter
             * case, we artificially have to split the node into two, because
             * we just don't have enough space to hold everything.  This
             * creates a problem if the final character participates in a
             * multi-character fold in the non-final position, as a match that
             * should have occurred won't, due to the way nodes are matched,
             * and our artificial boundary.  So back off until we find a non-
             * problematic character -- one that isn't at the beginning or
             * middle of such a fold.  (Either it doesn't participate in any
             * folds, or appears only in the final position of all the folds it
             * does participate in.)  A better solution with far fewer false
             * positives, and that would fill the nodes more completely, would
             * be to actually have available all the multi-character folds to
             * test against, and to back-off only far enough to be sure that
             * this node isn't ending with a partial one.  <upper_parse> is set
             * further below (if we need to reparse the node) to include just
             * up through that final non-problematic character that this code
             * identifies, so when it is set to less than the full node, we can
             * skip the rest of this */
            if (FOLD && p < RExC_end && upper_parse == MAX_NODE_STRING_SIZE) {

                const STRLEN full_len = len;

                assert(len >= MAX_NODE_STRING_SIZE);

                /* Here, <s> points to the final byte of the final character.
                 * Look backwards through the string until find a non-
                 * problematic character */

                if (! UTF) {

                    /* This has no multi-char folds to non-UTF characters */
                    if (ASCII_FOLD_RESTRICTED) {
                        goto loopdone;
                    }

                    while (--s >= s0 && IS_NON_FINAL_FOLD(*s)) { }
                    len = s - s0 + 1;
                }
                else {
                    if (!  PL_NonL1NonFinalFold) {
                        PL_NonL1NonFinalFold = _new_invlist_C_array(
                                        NonL1_Perl_Non_Final_Folds_invlist);
                    }

                    /* Point to the first byte of the final character */
                    s = (char *) utf8_hop((U8 *) s, -1);

                    while (s >= s0) {   /* Search backwards until find
                                           non-problematic char */
                        if (UTF8_IS_INVARIANT(*s)) {

                            /* There are no ascii characters that participate
                             * in multi-char folds under /aa.  In EBCDIC, the
                             * non-ascii invariants are all control characters,
                             * so don't ever participate in any folds. */
                            if (ASCII_FOLD_RESTRICTED
                                || ! IS_NON_FINAL_FOLD(*s))
                            {
                                break;
                            }
                        }
                        else if (UTF8_IS_DOWNGRADEABLE_START(*s)) {
                            if (! IS_NON_FINAL_FOLD(EIGHT_BIT_UTF8_TO_NATIVE(
                                                                  *s, *(s+1))))
                            {
                                break;
                            }
                        }
                        else if (! _invlist_contains_cp(
                                        PL_NonL1NonFinalFold,
                                        valid_utf8_to_uvchr((U8 *) s, NULL)))
                        {
                            break;
                        }

                        /* Here, the current character is problematic in that
                         * it does occur in the non-final position of some
                         * fold, so try the character before it, but have to
                         * special case the very first byte in the string, so
                         * we don't read outside the string */
                        s = (s == s0) ? s -1 : (char *) utf8_hop((U8 *) s, -1);
                    } /* End of loop backwards through the string */

                    /* If there were only problematic characters in the string,
                     * <s> will point to before s0, in which case the length
                     * should be 0, otherwise include the length of the
                     * non-problematic character just found */
                    len = (s < s0) ? 0 : s - s0 + UTF8SKIP(s);
                }

                /* Here, have found the final character, if any, that is
                 * non-problematic as far as ending the node without splitting
                 * it across a potential multi-char fold.  <len> contains the
                 * number of bytes in the node up-to and including that
                 * character, or is 0 if there is no such character, meaning
                 * the whole node contains only problematic characters.  In
                 * this case, give up and just take the node as-is.  We can't
                 * do any better */
                if (len == 0) {
                    len = full_len;

                    /* If the node ends in an 's' we make sure it stays EXACTF,
                     * as if it turns into an EXACTFU, it could later get
                     * joined with another 's' that would then wrongly match
                     * the sharp s */
                    if (maybe_exactfu && isALPHA_FOLD_EQ(ender, 's'))
                    {
                        maybe_exactfu = FALSE;
                    }
                } else {

                    /* Here, the node does contain some characters that aren't
                     * problematic.  If one such is the final character in the
                     * node, we are done */
                    if (len == full_len) {
                        goto loopdone;
                    }
                    else if (len + ((UTF) ? UTF8SKIP(s) : 1) == full_len) {

                        /* If the final character is problematic, but the
                         * penultimate is not, back-off that last character to
                         * later start a new node with it */
                        p = oldp;
                        goto loopdone;
                    }

                    /* Here, the final non-problematic character is earlier
                     * in the input than the penultimate character.  What we do
                     * is reparse from the beginning, going up only as far as
                     * this final ok one, thus guaranteeing that the node ends
                     * in an acceptable character.  The reason we reparse is
                     * that we know how far in the character is, but we don't
                     * know how to correlate its position with the input parse.
                     * An alternate implementation would be to build that
                     * correlation as we go along during the original parse,
                     * but that would entail extra work for every node, whereas
                     * this code gets executed only when the string is too
                     * large for the node, and the final two characters are
                     * problematic, an infrequent occurrence.  Yet another
                     * possible strategy would be to save the tail of the
                     * string, and the next time regatom is called, initialize
                     * with that.  The problem with this is that unless you
                     * back off one more character, you won't be guaranteed
                     * regatom will get called again, unless regbranch,
                     * regpiece ... are also changed.  If you do back off that
                     * extra character, so that there is input guaranteed to
                     * force calling regatom, you can't handle the case where
                     * just the first character in the node is acceptable.  I
                     * (khw) decided to try this method which doesn't have that
                     * pitfall; if performance issues are found, we can do a
                     * combination of the current approach plus that one */
                    upper_parse = len;
                    len = 0;
                    s = s0;
                    goto reparse;
                }
            }   /* End of verifying node ends with an appropriate char */

          loopdone:   /* Jumped to when encounters something that shouldn't be
                         in the node */

            /* I (khw) don't know if you can get here with zero length, but the
             * old code handled this situation by creating a zero-length EXACT
             * node.  Might as well be NOTHING instead */
            if (len == 0) {
                OP(ret) = NOTHING;
            }
            else {
                if (FOLD) {
                    /* If 'maybe_exact' is still set here, means there are no
                     * code points in the node that participate in folds;
                     * similarly for 'maybe_exactfu' and code points that match
                     * differently depending on UTF8ness of the target string
                     * (for /u), or depending on locale for /l */
                    if (maybe_exact) {
                        OP(ret) = (LOC)
                                  ? EXACTL
                                  : EXACT;
                    }
                    else if (maybe_exactfu) {
                        OP(ret) = (LOC)
                                  ? EXACTFLU8
                                  : EXACTFU;
                    }
                }
                alloc_maybe_populate_EXACT(pRExC_state, ret, flagp, len, ender,
                                           FALSE /* Don't look to see if could
                                                    be turned into an EXACT
                                                    node, as we have already
                                                    computed that */
                                          );
            }

            RExC_parse = p - 1;
            Set_Node_Cur_Length(ret, parse_start);
            RExC_parse = p;
            skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                    FALSE /* Don't force to /x */ );
            {
                /* len is STRLEN which is unsigned, need to copy to signed */
                IV iv = len;
                if (iv < 0)
                    vFAIL("Internal disaster");
            }

        } /* End of label 'defchar:' */
        break;
    } /* End of giant switch on input character */

    return(ret);
}


STATIC void
S_populate_ANYOF_from_invlist(pTHX_ regnode *node, SV** invlist_ptr)
{
    /* Uses the inversion list '*invlist_ptr' to populate the ANYOF 'node'.  It
     * sets up the bitmap and any flags, removing those code points from the
     * inversion list, setting it to NULL should it become completely empty */

    PERL_ARGS_ASSERT_POPULATE_ANYOF_FROM_INVLIST;
    assert(PL_regkind[OP(node)] == ANYOF);

    ANYOF_BITMAP_ZERO(node);
    if (*invlist_ptr) {

        /* This gets set if we actually need to modify things */
        bool change_invlist = FALSE;

        UV start, end;

        /* Start looking through *invlist_ptr */
        invlist_iterinit(*invlist_ptr);
        while (invlist_iternext(*invlist_ptr, &start, &end)) {
            UV high;
            int i;

            if (end == UV_MAX && start <= NUM_ANYOF_CODE_POINTS) {
                ANYOF_FLAGS(node) |= ANYOF_MATCHES_ALL_ABOVE_BITMAP;
            }

            /* Quit if are above what we should change */
            if (start >= NUM_ANYOF_CODE_POINTS) {
                break;
            }

            change_invlist = TRUE;

            /* Set all the bits in the range, up to the max that we are doing */
            high = (end < NUM_ANYOF_CODE_POINTS - 1)
                   ? end
                   : NUM_ANYOF_CODE_POINTS - 1;
            for (i = start; i <= (int) high; i++) {
                if (! ANYOF_BITMAP_TEST(node, i)) {
                    ANYOF_BITMAP_SET(node, i);
                }
            }
        }
        invlist_iterfinish(*invlist_ptr);

        /* Done with loop; remove any code points that are in the bitmap from
         * *invlist_ptr; similarly for code points above the bitmap if we have
         * a flag to match all of them anyways */
        if (change_invlist) {
            _invlist_subtract(*invlist_ptr, PL_InBitmap, invlist_ptr);
        }
        if (ANYOF_FLAGS(node) & ANYOF_MATCHES_ALL_ABOVE_BITMAP) {
            _invlist_intersection(*invlist_ptr, PL_InBitmap, invlist_ptr);
        }

        /* If have completely emptied it, remove it completely */
        if (_invlist_len(*invlist_ptr) == 0) {
            SvREFCNT_dec_NN(*invlist_ptr);
            *invlist_ptr = NULL;
        }
    }
}

/* Parse POSIX character classes: [[:foo:]], [[=foo=]], [[.foo.]].
   Character classes ([:foo:]) can also be negated ([:^foo:]).
   Returns a named class id (ANYOF_XXX) if successful, -1 otherwise.
   Equivalence classes ([=foo=]) and composites ([.foo.]) are parsed,
   but trigger failures because they are currently unimplemented. */

#define POSIXCC_DONE(c)   ((c) == ':')
#define POSIXCC_NOTYET(c) ((c) == '=' || (c) == '.')
#define POSIXCC(c) (POSIXCC_DONE(c) || POSIXCC_NOTYET(c))
#define MAYBE_POSIXCC(c) (POSIXCC(c) || (c) == '^' || (c) == ';')

#define WARNING_PREFIX              "Assuming NOT a POSIX class since "
#define NO_BLANKS_POSIX_WARNING     "no blanks are allowed in one"
#define SEMI_COLON_POSIX_WARNING    "a semi-colon was found instead of a colon"

#define NOT_MEANT_TO_BE_A_POSIX_CLASS (OOB_NAMEDCLASS - 1)

/* 'posix_warnings' and 'warn_text' are names of variables in the following
 * routine. q.v. */
#define ADD_POSIX_WARNING(p, text)  STMT_START {                            \
        if (posix_warnings && (   posix_warnings != (AV **) -1              \
                               || (PASS2 && ckWARN(WARN_REGEXP))))          \
        {                                                                   \
            if (! warn_text) warn_text = newAV();                           \
            av_push(warn_text, Perl_newSVpvf(aTHX_                          \
                                             WARNING_PREFIX                 \
                                             text                           \
                                             REPORT_LOCATION,               \
                                             REPORT_LOCATION_ARGS(p)));     \
        }                                                                   \
    } STMT_END

STATIC int
S_handle_possible_posix(pTHX_ RExC_state_t *pRExC_state,

    const char * const s,      /* Where the putative posix class begins.
                                  Normally, this is one past the '['.  This
                                  parameter exists so it can be somewhere
                                  besides RExC_parse. */
    char ** updated_parse_ptr, /* Where to set the updated parse pointer, or
                                  NULL */
    AV ** posix_warnings       /* Where to place any generated warnings, or -1
                                  if to output them, or NULL */
)
{
    /* This parses what the caller thinks may be one of the three POSIX
     * constructs:
     *  1) a character class, like [:blank:]
     *  2) a collating symbol, like [. .]
     *  3) an equivalence class, like [= =]
     * In the latter two cases, it croaks if it finds a syntactically legal
     * one, as these are not handled by Perl.
     *
     * The main purpose is to look for a POSIX character class.  It returns:
     *  a) the class number
     *      if it is a completely syntactically and semantically legal class.
     *      'updated_parse_ptr', if not NULL, is set to point to just after the
     *      closing ']' of the class
     *  b) OOB_NAMEDCLASS
     *      if it appears that one of the three POSIX constructs was meant, but
     *      its specification was somehow defective.  'updated_parse_ptr', if
     *      not NULL, is set to point to the character just after the end
     *      character of the class.  See below for handling of warnings.
     *  c) NOT_MEANT_TO_BE_A_POSIX_CLASS
     *      if it  doesn't appear that a POSIX construct was intended.
     *      'updated_parse_ptr' is not changed.  No warnings nor errors are
     *      raised.
     *
     * In b) there may be warnings and even errors generated.  What to do about
     * these is determined by the 'posix_warnings' parameter.  If it is NULL,
     * this call is treated as a check-only, scouting-out-the-territory call,
     * and no warnings nor errors are generated at all.  Otherwise, any errors
     * are raised if found.  If 'posix_warnings' is -1 (appropriately cast),
     * warnings are generated and displayed (in pass 2), just as they would be
     * for any other message of the same type from this file.  If it isn't NULL
     * and not -1, warnings aren't displayed, but instead an AV is generated
     * with all the warning messages (that aren't to be ignored) stored into
     * it, so that the caller can output them if it wants.  This is done in all
     * passes.  The reason for this is that the rest of the parsing is heavily
     * dependent on whether this routine found a valid posix class or not.  If
     * it did, the closing ']' is absorbed as part of the class.  If no class
     * or an invalid one is found, any ']' will be considered the terminator of
     * the outer bracketed character class, leading to very different results.
     * In particular, a '(?[ ])' construct will likely have a syntax error if
     * the class is parsed other than intended, and this will happen in pass1,
     * before the warnings would normally be output.  This mechanism allows the
     * caller to output those warnings in pass1 just before dieing, giving a
     * much better clue as to what is wrong.
     *
     * The reason for this function, and its complexity is that a bracketed
     * character class can contain just about anything.  But it's easy to
     * mistype the very specific posix class syntax but yielding a valid
     * regular bracketed class, so it silently gets compiled into something
     * quite unintended.
     *
     * The solution adopted here maintains backward compatibility except that
     * it adds a warning if it looks like a posix class was intended but
     * improperly specified.  The warning is not raised unless what is input
     * very closely resembles one of the 14 legal posix classes.  To do this,
     * it uses fuzzy parsing.  It calculates how many single-character edits it
     * would take to transform what was input into a legal posix class.  Only
     * if that number is quite small does it think that the intention was a
     * posix class.  Obviously these are heuristics, and there will be cases
     * where it errs on one side or another, and they can be tweaked as
     * experience informs.
     *
     * The syntax for a legal posix class is:
     *
     * qr/(?xa: \[ : \^? [:lower:]{4,6} : \] )/
     *
     * What this routine considers syntactically to be an intended posix class
     * is this (the comments indicate some restrictions that the pattern
     * doesn't show):
     *
     *  qr/(?x: \[?                         # The left bracket, possibly
     *                                      # omitted
     *          \h*                         # possibly followed by blanks
     *          (?: \^ \h* )?               # possibly a misplaced caret
     *          [:;]?                       # The opening class character,
     *                                      # possibly omitted.  A typo
     *                                      # semi-colon can also be used.
     *          \h*
     *          \^?                         # possibly a correctly placed
     *                                      # caret, but not if there was also
     *                                      # a misplaced one
     *          \h*
     *          .{3,15}                     # The class name.  If there are
     *                                      # deviations from the legal syntax,
     *                                      # its edit distance must be close
     *                                      # to a real class name in order
     *                                      # for it to be considered to be
     *                                      # an intended posix class.
     *          \h*
     *          [:punct:]?                  # The closing class character,
     *                                      # possibly omitted.  If not a colon
     *                                      # nor semi colon, the class name
     *                                      # must be even closer to a valid
     *                                      # one
     *          \h*
     *          \]?                         # The right bracket, possibly
     *                                      # omitted.
     *     )/
     *
     * In the above, \h must be ASCII-only.
     *
     * These are heuristics, and can be tweaked as field experience dictates.
     * There will be cases when someone didn't intend to specify a posix class
     * that this warns as being so.  The goal is to minimize these, while
     * maximizing the catching of things intended to be a posix class that
     * aren't parsed as such.
     */

    const char* p             = s;
    const char * const e      = RExC_end;
    unsigned complement       = 0;      /* If to complement the class */
    bool found_problem        = FALSE;  /* Assume OK until proven otherwise */
    bool has_opening_bracket  = FALSE;
    bool has_opening_colon    = FALSE;
    int class_number          = OOB_NAMEDCLASS; /* Out-of-bounds until find
                                                   valid class */
    AV* warn_text             = NULL;   /* any warning messages */
    const char * possible_end = NULL;   /* used for a 2nd parse pass */
    const char* name_start;             /* ptr to class name first char */

    /* If the number of single-character typos the input name is away from a
     * legal name is no more than this number, it is considered to have meant
     * the legal name */
    int max_distance          = 2;

    /* to store the name.  The size determines the maximum length before we
     * decide that no posix class was intended.  Should be at least
     * sizeof("alphanumeric") */
    UV input_text[15];

    PERL_ARGS_ASSERT_HANDLE_POSSIBLE_POSIX;

    if (p >= e) {
        return NOT_MEANT_TO_BE_A_POSIX_CLASS;
    }

    if (*(p - 1) != '[') {
        ADD_POSIX_WARNING(p, "it doesn't start with a '['");
        found_problem = TRUE;
    }
    else {
        has_opening_bracket = TRUE;
    }

    /* They could be confused and think you can put spaces between the
     * components */
    if (isBLANK(*p)) {
        found_problem = TRUE;

        do {
            p++;
        } while (p < e && isBLANK(*p));

        ADD_POSIX_WARNING(p, NO_BLANKS_POSIX_WARNING);
    }

    /* For [. .] and [= =].  These are quite different internally from [: :],
     * so they are handled separately.  */
    if (POSIXCC_NOTYET(*p)) {
        const char open_char  = *p;
        const char * temp_ptr = p + 1;
        unsigned int len      = 0;

        /* These two constructs are not handled by perl, and if we find a
         * syntactically valid one, we croak.  It looks like just about any
         * byte can be in them, but they are likely very short, like [.ch.] to
         * denote a ligature 'ch' single character.  If we find something that
         * started out to look like one of these constructs, but isn't, we
         * break so that it can be checked for being a class name with a typo
         * of '.' or '=' instead of a colon */
        while (temp_ptr < e) {
            len++;

            /* qr/[[.].]]/, for example, is valid.  But otherwise we quit on an
             * unexpected ']'.  It is possible, it appears, for such a ']' to
             * be not in the final position, but that's so unlikely that that
             * case is not handled. */
            if (*temp_ptr == ']' && temp_ptr[1] != open_char) {
                break;
            }

            /* XXX this could be cut down, but this value is certainly large
             * enough */
            if (len > 10) {
                break;
            }

            if (*temp_ptr == open_char) {
                temp_ptr++;
                if (*temp_ptr == ']') {
                    temp_ptr++;
                    if (! found_problem && posix_warnings) {
                        RExC_parse = (char *) temp_ptr;
                        vFAIL3("POSIX syntax [%c %c] is reserved for future "
                               "extensions", open_char, open_char);
                    }

                    /* Here, the syntax wasn't completely valid, or else the
                     * call is to check-only */
                    if (updated_parse_ptr) {
                        *updated_parse_ptr = (char *) temp_ptr;
                    }

                    return OOB_NAMEDCLASS;
                }
            }
            else if (*temp_ptr == '\\') {

                /* A backslash is treate as like any other character, unless it
                 * precedes a comment starter.  XXX multiple backslashes in a
                 * row are not handled specially here, nor would they ever
                 * likely to be handled specially in one of these constructs */
                if (temp_ptr[1] == '#' && (RExC_flags & RXf_PMf_EXTENDED)) {
                    temp_ptr++;
                }
                temp_ptr++;
            }
            else if (*temp_ptr == '#' && (RExC_flags & RXf_PMf_EXTENDED)) {
                break;  /* Under no circumstances can we look at the interior
                           of a comment */
            }
            else if (*temp_ptr == '\n') {   /* And we don't allow newlines
                                               either as it's extremely
                                               unlikely that one could be in an
                                               intended class */
                break;
            }
            else if (UTF && ! UTF8_IS_INVARIANT(*temp_ptr)) {
                /* XXX Since perl will never handle multi-byte locales, except
                 * for UTF-8, we could break if we found a byte above latin1,
                 * but perhaps the person intended to use one. */
                temp_ptr += UTF8SKIP(temp_ptr);
            }
            else {
                temp_ptr++;
            }
        }
    }

    /* Here, we think there is a possibility that a [: :] class was meant, and
     * we have the first real character.  It could be they think the '^' comes
     * first */
    if (*p == '^') {
        found_problem = TRUE;
        ADD_POSIX_WARNING(p + 1, "the '^' must come after the colon");
        complement = 1;
        p++;

        if (isBLANK(*p)) {
            found_problem = TRUE;

            do {
                p++;
            } while (p < e && isBLANK(*p));

            ADD_POSIX_WARNING(p, NO_BLANKS_POSIX_WARNING);
        }
    }

    /* But the first character should be a colon, which they could have easily
     * mistyped on a qwerty keyboard as a semi-colon (and which may be hard to
     * distinguish from a colon, so treat that as a colon).  */
    if (*p == ':') {
        p++;
        has_opening_colon = TRUE;
    }
    else if (*p == ';') {
        found_problem = TRUE;
        p++;
        ADD_POSIX_WARNING(p, SEMI_COLON_POSIX_WARNING);
        has_opening_colon = TRUE;
    }
    else {
        found_problem = TRUE;
        ADD_POSIX_WARNING(p, "there must be a starting ':'");

        /* Consider an initial punctuation (not one of the recognized ones) to
         * be a left terminator */
        if (*p != '^' && *p != ']' && isPUNCT(*p)) {
            p++;
        }
    }

    /* They may think that you can put spaces between the components */
    if (isBLANK(*p)) {
        found_problem = TRUE;

        do {
            p++;
        } while (p < e && isBLANK(*p));

        ADD_POSIX_WARNING(p, NO_BLANKS_POSIX_WARNING);
    }

    if (*p == '^') {

        /* We consider something like [^:^alnum:]] to not have been intended to
         * be a posix class, but XXX maybe we should */
        if (complement) {
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

        complement = 1;
        p++;
    }

    /* Again, they may think that you can put spaces between the components */
    if (isBLANK(*p)) {
        found_problem = TRUE;

        do {
            p++;
        } while (p < e && isBLANK(*p));

        ADD_POSIX_WARNING(p, NO_BLANKS_POSIX_WARNING);
    }

    if (*p == ']') {

        /* XXX This ']' may be a typo, and something else was meant.  But
         * treating it as such creates enough complications, that that
         * possibility isn't currently considered here.  So we assume that the
         * ']' is what is intended, and if we've already found an initial '[',
         * this leaves this construct looking like [:] or [:^], which almost
         * certainly weren't intended to be posix classes */
        if (has_opening_bracket) {
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

        /* But this function can be called when we parse the colon for
         * something like qr/[alpha:]]/, so we back up to look for the
         * beginning */
        p--;

        if (*p == ';') {
            found_problem = TRUE;
            ADD_POSIX_WARNING(p, SEMI_COLON_POSIX_WARNING);
        }
        else if (*p != ':') {

            /* XXX We are currently very restrictive here, so this code doesn't
             * consider the possibility that, say, /[alpha.]]/ was intended to
             * be a posix class. */
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

        /* Here we have something like 'foo:]'.  There was no initial colon,
         * and we back up over 'foo.  XXX Unlike the going forward case, we
         * don't handle typos of non-word chars in the middle */
        has_opening_colon = FALSE;
        p--;

        while (p > RExC_start && isWORDCHAR(*p)) {
            p--;
        }
        p++;

        /* Here, we have positioned ourselves to where we think the first
         * character in the potential class is */
    }

    /* Now the interior really starts.  There are certain key characters that
     * can end the interior, or these could just be typos.  To catch both
     * cases, we may have to do two passes.  In the first pass, we keep on
     * going unless we come to a sequence that matches
     *      qr/ [[:punct:]] [[:blank:]]* \] /xa
     * This means it takes a sequence to end the pass, so two typos in a row if
     * that wasn't what was intended.  If the class is perfectly formed, just
     * this one pass is needed.  We also stop if there are too many characters
     * being accumulated, but this number is deliberately set higher than any
     * real class.  It is set high enough so that someone who thinks that
     * 'alphanumeric' is a correct name would get warned that it wasn't.
     * While doing the pass, we keep track of where the key characters were in
     * it.  If we don't find an end to the class, and one of the key characters
     * was found, we redo the pass, but stop when we get to that character.
     * Thus the key character was considered a typo in the first pass, but a
     * terminator in the second.  If two key characters are found, we stop at
     * the second one in the first pass.  Again this can miss two typos, but
     * catches a single one
     *
     * In the first pass, 'possible_end' starts as NULL, and then gets set to
     * point to the first key character.  For the second pass, it starts as -1.
     * */

    name_start = p;
  parse_name:
    {
        bool has_blank               = FALSE;
        bool has_upper               = FALSE;
        bool has_terminating_colon   = FALSE;
        bool has_terminating_bracket = FALSE;
        bool has_semi_colon          = FALSE;
        unsigned int name_len        = 0;
        int punct_count              = 0;

        while (p < e) {

            /* Squeeze out blanks when looking up the class name below */
            if (isBLANK(*p) ) {
                has_blank = TRUE;
                found_problem = TRUE;
                p++;
                continue;
            }

            /* The name will end with a punctuation */
            if (isPUNCT(*p)) {
                const char * peek = p + 1;

                /* Treat any non-']' punctuation followed by a ']' (possibly
                 * with intervening blanks) as trying to terminate the class.
                 * ']]' is very likely to mean a class was intended (but
                 * missing the colon), but the warning message that gets
                 * generated shows the error position better if we exit the
                 * loop at the bottom (eventually), so skip it here. */
                if (*p != ']') {
                    if (peek < e && isBLANK(*peek)) {
                        has_blank = TRUE;
                        found_problem = TRUE;
                        do {
                            peek++;
                        } while (peek < e && isBLANK(*peek));
                    }

                    if (peek < e && *peek == ']') {
                        has_terminating_bracket = TRUE;
                        if (*p == ':') {
                            has_terminating_colon = TRUE;
                        }
                        else if (*p == ';') {
                            has_semi_colon = TRUE;
                            has_terminating_colon = TRUE;
                        }
                        else {
                            found_problem = TRUE;
                        }
                        p = peek + 1;
                        goto try_posix;
                    }
                }

                /* Here we have punctuation we thought didn't end the class.
                 * Keep track of the position of the key characters that are
                 * more likely to have been class-enders */
                if (*p == ']' || *p == '[' || *p == ':' || *p == ';') {

                    /* Allow just one such possible class-ender not actually
                     * ending the class. */
                    if (possible_end) {
                        break;
                    }
                    possible_end = p;
                }

                /* If we have too many punctuation characters, no use in
                 * keeping going */
                if (++punct_count > max_distance) {
                    break;
                }

                /* Treat the punctuation as a typo. */
                input_text[name_len++] = *p;
                p++;
            }
            else if (isUPPER(*p)) { /* Use lowercase for lookup */
                input_text[name_len++] = toLOWER(*p);
                has_upper = TRUE;
                found_problem = TRUE;
                p++;
            } else if (! UTF || UTF8_IS_INVARIANT(*p)) {
                input_text[name_len++] = *p;
                p++;
            }
            else {
                input_text[name_len++] = utf8_to_uvchr_buf((U8 *) p, e, NULL);
                p+= UTF8SKIP(p);
            }

            /* The declaration of 'input_text' is how long we allow a potential
             * class name to be, before saying they didn't mean a class name at
             * all */
            if (name_len >= C_ARRAY_LENGTH(input_text)) {
                break;
            }
        }

        /* We get to here when the possible class name hasn't been properly
         * terminated before:
         *   1) we ran off the end of the pattern; or
         *   2) found two characters, each of which might have been intended to
         *      be the name's terminator
         *   3) found so many punctuation characters in the purported name,
         *      that the edit distance to a valid one is exceeded
         *   4) we decided it was more characters than anyone could have
         *      intended to be one. */

        found_problem = TRUE;

        /* In the final two cases, we know that looking up what we've
         * accumulated won't lead to a match, even a fuzzy one. */
        if (   name_len >= C_ARRAY_LENGTH(input_text)
            || punct_count > max_distance)
        {
            /* If there was an intermediate key character that could have been
             * an intended end, redo the parse, but stop there */
            if (possible_end && possible_end != (char *) -1) {
                possible_end = (char *) -1; /* Special signal value to say
                                               we've done a first pass */
                p = name_start;
                goto parse_name;
            }

            /* Otherwise, it can't have meant to have been a class */
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

        /* If we ran off the end, and the final character was a punctuation
         * one, back up one, to look at that final one just below.  Later, we
         * will restore the parse pointer if appropriate */
        if (name_len && p == e && isPUNCT(*(p-1))) {
            p--;
            name_len--;
        }

        if (p < e && isPUNCT(*p)) {
            if (*p == ']') {
                has_terminating_bracket = TRUE;

                /* If this is a 2nd ']', and the first one is just below this
                 * one, consider that to be the real terminator.  This gives a
                 * uniform and better positioning for the warning message  */
                if (   possible_end
                    && possible_end != (char *) -1
                    && *possible_end == ']'
                    && name_len && input_text[name_len - 1] == ']')
                {
                    name_len--;
                    p = possible_end;

                    /* And this is actually equivalent to having done the 2nd
                     * pass now, so set it to not try again */
                    possible_end = (char *) -1;
                }
            }
            else {
                if (*p == ':') {
                    has_terminating_colon = TRUE;
                }
                else if (*p == ';') {
                    has_semi_colon = TRUE;
                    has_terminating_colon = TRUE;
                }
                p++;
            }
        }

    try_posix:

        /* Here, we have a class name to look up.  We can short circuit the
         * stuff below for short names that can't possibly be meant to be a
         * class name.  (We can do this on the first pass, as any second pass
         * will yield an even shorter name) */
        if (name_len < 3) {
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

        /* Find which class it is.  Initially switch on the length of the name.
         * */
        switch (name_len) {
            case 4:
                if (memEQ(name_start, "word", 4)) {
                    /* this is not POSIX, this is the Perl \w */
                    class_number = ANYOF_WORDCHAR;
                }
                break;
            case 5:
                /* Names all of length 5: alnum alpha ascii blank cntrl digit
                 *                        graph lower print punct space upper
                 * Offset 4 gives the best switch position.  */
                switch (name_start[4]) {
                    case 'a':
                        if (memEQ(name_start, "alph", 4)) /* alpha */
                            class_number = ANYOF_ALPHA;
                        break;
                    case 'e':
                        if (memEQ(name_start, "spac", 4)) /* space */
                            class_number = ANYOF_SPACE;
                        break;
                    case 'h':
                        if (memEQ(name_start, "grap", 4)) /* graph */
                            class_number = ANYOF_GRAPH;
                        break;
                    case 'i':
                        if (memEQ(name_start, "asci", 4)) /* ascii */
                            class_number = ANYOF_ASCII;
                        break;
                    case 'k':
                        if (memEQ(name_start, "blan", 4)) /* blank */
                            class_number = ANYOF_BLANK;
                        break;
                    case 'l':
                        if (memEQ(name_start, "cntr", 4)) /* cntrl */
                            class_number = ANYOF_CNTRL;
                        break;
                    case 'm':
                        if (memEQ(name_start, "alnu", 4)) /* alnum */
                            class_number = ANYOF_ALPHANUMERIC;
                        break;
                    case 'r':
                        if (memEQ(name_start, "lowe", 4)) /* lower */
                            class_number = (FOLD) ? ANYOF_CASED : ANYOF_LOWER;
                        else if (memEQ(name_start, "uppe", 4)) /* upper */
                            class_number = (FOLD) ? ANYOF_CASED : ANYOF_UPPER;
                        break;
                    case 't':
                        if (memEQ(name_start, "digi", 4)) /* digit */
                            class_number = ANYOF_DIGIT;
                        else if (memEQ(name_start, "prin", 4)) /* print */
                            class_number = ANYOF_PRINT;
                        else if (memEQ(name_start, "punc", 4)) /* punct */
                            class_number = ANYOF_PUNCT;
                        break;
                }
                break;
            case 6:
                if (memEQ(name_start, "xdigit", 6))
                    class_number = ANYOF_XDIGIT;
                break;
        }

        /* If the name exactly matches a posix class name the class number will
         * here be set to it, and the input almost certainly was meant to be a
         * posix class, so we can skip further checking.  If instead the syntax
         * is exactly correct, but the name isn't one of the legal ones, we
         * will return that as an error below.  But if neither of these apply,
         * it could be that no posix class was intended at all, or that one
         * was, but there was a typo.  We tease these apart by doing fuzzy
         * matching on the name */
        if (class_number == OOB_NAMEDCLASS && found_problem) {
            const UV posix_names[][6] = {
                                                { 'a', 'l', 'n', 'u', 'm' },
                                                { 'a', 'l', 'p', 'h', 'a' },
                                                { 'a', 's', 'c', 'i', 'i' },
                                                { 'b', 'l', 'a', 'n', 'k' },
                                                { 'c', 'n', 't', 'r', 'l' },
                                                { 'd', 'i', 'g', 'i', 't' },
                                                { 'g', 'r', 'a', 'p', 'h' },
                                                { 'l', 'o', 'w', 'e', 'r' },
                                                { 'p', 'r', 'i', 'n', 't' },
                                                { 'p', 'u', 'n', 'c', 't' },
                                                { 's', 'p', 'a', 'c', 'e' },
                                                { 'u', 'p', 'p', 'e', 'r' },
                                                { 'w', 'o', 'r', 'd' },
                                                { 'x', 'd', 'i', 'g', 'i', 't' }
                                            };
            /* The names of the above all have added NULs to make them the same
             * size, so we need to also have the real lengths */
            const UV posix_name_lengths[] = {
                                                sizeof("alnum") - 1,
                                                sizeof("alpha") - 1,
                                                sizeof("ascii") - 1,
                                                sizeof("blank") - 1,
                                                sizeof("cntrl") - 1,
                                                sizeof("digit") - 1,
                                                sizeof("graph") - 1,
                                                sizeof("lower") - 1,
                                                sizeof("print") - 1,
                                                sizeof("punct") - 1,
                                                sizeof("space") - 1,
                                                sizeof("upper") - 1,
                                                sizeof("word")  - 1,
                                                sizeof("xdigit")- 1
                                            };
            unsigned int i;
            int temp_max = max_distance;    /* Use a temporary, so if we
                                               reparse, we haven't changed the
                                               outer one */

            /* Use a smaller max edit distance if we are missing one of the
             * delimiters */
            if (   has_opening_bracket + has_opening_colon < 2
                || has_terminating_bracket + has_terminating_colon < 2)
            {
                temp_max--;
            }

            /* See if the input name is close to a legal one */
            for (i = 0; i < C_ARRAY_LENGTH(posix_names); i++) {

                /* Short circuit call if the lengths are too far apart to be
                 * able to match */
                if (abs( (int) (name_len - posix_name_lengths[i]))
                    > temp_max)
                {
                    continue;
                }

                if (edit_distance(input_text,
                                  posix_names[i],
                                  name_len,
                                  posix_name_lengths[i],
                                  temp_max
                                 )
                    > -1)
                { /* If it is close, it probably was intended to be a class */
                    goto probably_meant_to_be;
                }
            }

            /* Here the input name is not close enough to a valid class name
             * for us to consider it to be intended to be a posix class.  If
             * we haven't already done so, and the parse found a character that
             * could have been terminators for the name, but which we absorbed
             * as typos during the first pass, repeat the parse, signalling it
             * to stop at that character */
            if (possible_end && possible_end != (char *) -1) {
                possible_end = (char *) -1;
                p = name_start;
                goto parse_name;
            }

            /* Here neither pass found a close-enough class name */
            return NOT_MEANT_TO_BE_A_POSIX_CLASS;
        }

    probably_meant_to_be:

        /* Here we think that a posix specification was intended.  Update any
         * parse pointer */
        if (updated_parse_ptr) {
            *updated_parse_ptr = (char *) p;
        }

        /* If a posix class name was intended but incorrectly specified, we
         * output or return the warnings */
        if (found_problem) {

            /* We set flags for these issues in the parse loop above instead of
             * adding them to the list of warnings, because we can parse it
             * twice, and we only want one warning instance */
            if (has_upper) {
                ADD_POSIX_WARNING(p, "the name must be all lowercase letters");
            }
            if (has_blank) {
                ADD_POSIX_WARNING(p, NO_BLANKS_POSIX_WARNING);
            }
            if (has_semi_colon) {
                ADD_POSIX_WARNING(p, SEMI_COLON_POSIX_WARNING);
            }
            else if (! has_terminating_colon) {
                ADD_POSIX_WARNING(p, "there is no terminating ':'");
            }
            if (! has_terminating_bracket) {
                ADD_POSIX_WARNING(p, "there is no terminating ']'");
            }

            if (warn_text) {
                if (posix_warnings != (AV **) -1) {
                    *posix_warnings = warn_text;
                }
                else {
                    SV * msg;
                    while ((msg = av_shift(warn_text)) != &PL_sv_undef) {
                        Perl_warner(aTHX_ packWARN(WARN_REGEXP),
                                    "%s", SvPVX(msg));
                        SvREFCNT_dec_NN(msg);
                    }
                    SvREFCNT_dec_NN(warn_text);
                }
            }
        }
        else if (class_number != OOB_NAMEDCLASS) {
            /* If it is a known class, return the class.  The class number
             * #defines are structured so each complement is +1 to the normal
             * one */
            return class_number + complement;
        }
        else if (posix_warnings) {

            /* Here, it is an unrecognized class.  This is an error (unless the
            * call is to check only, which we've already handled above) */
            const char * const complement_string = (complement)
                                                   ? "^"
                                                   : "";
            RExC_parse = (char *) p;
            vFAIL3utf8f("POSIX class [:%s%"UTF8f":] unknown",
                        complement_string,
                        UTF8fARG(UTF, RExC_parse - name_start - 2, name_start));
        }
    }

    return OOB_NAMEDCLASS;
}
#undef ADD_POSIX_WARNING

STATIC unsigned  int
S_regex_set_precedence(const U8 my_operator) {

    /* Returns the precedence in the (?[...]) construct of the input operator,
     * specified by its character representation.  The precedence follows
     * general Perl rules, but it extends this so that ')' and ']' have (low)
     * precedence even though they aren't really operators */

    switch (my_operator) {
        case '!':
            return 5;
        case '&':
            return 4;
        case '^':
        case '|':
        case '+':
        case '-':
            return 3;
        case ')':
            return 2;
        case ']':
            return 1;
    }

    NOT_REACHED; /* NOTREACHED */
    return 0;   /* Silence compiler warning */
}

STATIC regnode *
S_handle_regex_sets(pTHX_ RExC_state_t *pRExC_state, SV** return_invlist,
                    I32 *flagp, U32 depth,
                    char * const oregcomp_parse)
{
    /* Handle the (?[...]) construct to do set operations */

    U8 curchar;                     /* Current character being parsed */
    UV start, end;                  /* End points of code point ranges */
    SV* final = NULL;               /* The end result inversion list */
    SV* result_string;              /* 'final' stringified */
    AV* stack;                      /* stack of operators and operands not yet
                                       resolved */
    AV* fence_stack = NULL;         /* A stack containing the positions in
                                       'stack' of where the undealt-with left
                                       parens would be if they were actually
                                       put there */
    IV fence = 0;                   /* Position of where most recent undealt-
                                       with left paren in stack is; -1 if none.
                                     */
    STRLEN len;                     /* Temporary */
    regnode* node;                  /* Temporary, and final regnode returned by
                                       this function */
    const bool save_fold = FOLD;    /* Temporary */
    char *save_end, *save_parse;    /* Temporaries */
    const bool in_locale = LOC;     /* we turn off /l during processing */
    AV* posix_warnings = NULL;

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_HANDLE_REGEX_SETS;

    if (in_locale) {
        set_regex_charset(&RExC_flags, REGEX_UNICODE_CHARSET);
    }

    REQUIRE_UNI_RULES(flagp, NULL);   /* The use of this operator implies /u.
                                         This is required so that the compile
                                         time values are valid in all runtime
                                         cases */

    /* This will return only an ANYOF regnode, or (unlikely) something smaller
     * (such as EXACT).  Thus we can skip most everything if just sizing.  We
     * call regclass to handle '[]' so as to not have to reinvent its parsing
     * rules here (throwing away the size it computes each time).  And, we exit
     * upon an unescaped ']' that isn't one ending a regclass.  To do both
     * these things, we need to realize that something preceded by a backslash
     * is escaped, so we have to keep track of backslashes */
    if (SIZE_ONLY) {
        UV depth = 0; /* how many nested (?[...]) constructs */

        while (RExC_parse < RExC_end) {
            SV* current = NULL;

            skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                    TRUE /* Force /x */ );

            switch (*RExC_parse) {
                case '?':
                    if (RExC_parse[1] == '[') depth++, RExC_parse++;
                    /* FALLTHROUGH */
                default:
                    break;
                case '\\':
                    /* Skip past this, so the next character gets skipped, after
                     * the switch */
                    RExC_parse++;
                    if (*RExC_parse == 'c') {
                            /* Skip the \cX notation for control characters */
                            RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                    }
                    break;

                case '[':
                {
                    /* See if this is a [:posix:] class. */
                    bool is_posix_class = (OOB_NAMEDCLASS
                            < handle_possible_posix(pRExC_state,
                                                RExC_parse + 1,
                                                NULL,
                                                NULL));
                    /* If it is a posix class, leave the parse pointer at the
                     * '[' to fool regclass() into thinking it is part of a
                     * '[[:posix:]]'. */
                    if (! is_posix_class) {
                        RExC_parse++;
                    }

                    /* regclass() can only return RESTART_PASS1 and NEED_UTF8
                     * if multi-char folds are allowed.  */
                    if (!regclass(pRExC_state, flagp,depth+1,
                                  is_posix_class, /* parse the whole char
                                                     class only if not a
                                                     posix class */
                                  FALSE, /* don't allow multi-char folds */
                                  TRUE, /* silence non-portable warnings. */
                                  TRUE, /* strict */
                                  FALSE, /* Require return to be an ANYOF */
                                  &current,
                                  &posix_warnings
                                 ))
                        FAIL2("panic: regclass returned NULL to handle_sets, "
                              "flags=%#"UVxf"", (UV) *flagp);

                    /* function call leaves parse pointing to the ']', except
                     * if we faked it */
                    if (is_posix_class) {
                        RExC_parse--;
                    }

                    SvREFCNT_dec(current);   /* In case it returned something */
                    break;
                }

                case ']':
                    if (depth--) break;
                    RExC_parse++;
                    if (*RExC_parse == ')') {
                        node = reganode(pRExC_state, ANYOF, 0);
                        RExC_size += ANYOF_SKIP;
                        nextchar(pRExC_state);
                        Set_Node_Length(node,
                                RExC_parse - oregcomp_parse + 1); /* MJD */
                        if (in_locale) {
                            set_regex_charset(&RExC_flags, REGEX_LOCALE_CHARSET);
                        }

                        return node;
                    }
                    goto no_close;
            }

            RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
        }

      no_close:
        /* We output the messages even if warnings are off, because we'll fail
         * the very next thing, and these give a likely diagnosis for that */
        if (posix_warnings) {
            SV * msg;
            while ((msg = av_shift(posix_warnings)) != &PL_sv_undef) {
                Perl_warner(aTHX_ packWARN(WARN_REGEXP), "%s", SvPVX(msg));
                SvREFCNT_dec_NN(msg);
            }
            SvREFCNT_dec_NN(posix_warnings);
        }

        FAIL("Syntax error in (?[...])");
    }

    /* Pass 2 only after this. */
    Perl_ck_warner_d(aTHX_
        packWARN(WARN_EXPERIMENTAL__REGEX_SETS),
        "The regex_sets feature is experimental" REPORT_LOCATION,
        REPORT_LOCATION_ARGS(RExC_parse));

    /* Everything in this construct is a metacharacter.  Operands begin with
     * either a '\' (for an escape sequence), or a '[' for a bracketed
     * character class.  Any other character should be an operator, or
     * parenthesis for grouping.  Both types of operands are handled by calling
     * regclass() to parse them.  It is called with a parameter to indicate to
     * return the computed inversion list.  The parsing here is implemented via
     * a stack.  Each entry on the stack is a single character representing one
     * of the operators; or else a pointer to an operand inversion list. */

#define IS_OPERATOR(a) SvIOK(a)
#define IS_OPERAND(a)  (! IS_OPERATOR(a))

    /* The stack is kept in Łukasiewicz order.  (That's pronounced similar
     * to luke-a-shave-itch (or -itz), but people who didn't want to bother
     * with pronouncing it called it Reverse Polish instead, but now that YOU
     * know how to pronounce it you can use the correct term, thus giving due
     * credit to the person who invented it, and impressing your geek friends.
     * Wikipedia says that the pronounciation of "Ł" has been changing so that
     * it is now more like an English initial W (as in wonk) than an L.)
     *
     * This means that, for example, 'a | b & c' is stored on the stack as
     *
     * c  [4]
     * b  [3]
     * &  [2]
     * a  [1]
     * |  [0]
     *
     * where the numbers in brackets give the stack [array] element number.
     * In this implementation, parentheses are not stored on the stack.
     * Instead a '(' creates a "fence" so that the part of the stack below the
     * fence is invisible except to the corresponding ')' (this allows us to
     * replace testing for parens, by using instead subtraction of the fence
     * position).  As new operands are processed they are pushed onto the stack
     * (except as noted in the next paragraph).  New operators of higher
     * precedence than the current final one are inserted on the stack before
     * the lhs operand (so that when the rhs is pushed next, everything will be
     * in the correct positions shown above.  When an operator of equal or
     * lower precedence is encountered in parsing, all the stacked operations
     * of equal or higher precedence are evaluated, leaving the result as the
     * top entry on the stack.  This makes higher precedence operations
     * evaluate before lower precedence ones, and causes operations of equal
     * precedence to left associate.
     *
     * The only unary operator '!' is immediately pushed onto the stack when
     * encountered.  When an operand is encountered, if the top of the stack is
     * a '!", the complement is immediately performed, and the '!' popped.  The
     * resulting value is treated as a new operand, and the logic in the
     * previous paragraph is executed.  Thus in the expression
     *      [a] + ! [b]
     * the stack looks like
     *
     * !
     * a
     * +
     *
     * as 'b' gets parsed, the latter gets evaluated to '!b', and the stack
     * becomes
     *
     * !b
     * a
     * +
     *
     * A ')' is treated as an operator with lower precedence than all the
     * aforementioned ones, which causes all operations on the stack above the
     * corresponding '(' to be evaluated down to a single resultant operand.
     * Then the fence for the '(' is removed, and the operand goes through the
     * algorithm above, without the fence.
     *
     * A separate stack is kept of the fence positions, so that the position of
     * the latest so-far unbalanced '(' is at the top of it.
     *
     * The ']' ending the construct is treated as the lowest operator of all,
     * so that everything gets evaluated down to a single operand, which is the
     * result */

    sv_2mortal((SV *)(stack = newAV()));
    sv_2mortal((SV *)(fence_stack = newAV()));

    while (RExC_parse < RExC_end) {
        I32 top_index;              /* Index of top-most element in 'stack' */
        SV** top_ptr;               /* Pointer to top 'stack' element */
        SV* current = NULL;         /* To contain the current inversion list
                                       operand */
        SV* only_to_avoid_leaks;

        skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                TRUE /* Force /x */ );
        if (RExC_parse >= RExC_end) {
            Perl_croak(aTHX_ "panic: Read past end of '(?[ ])'");
        }

        curchar = UCHARAT(RExC_parse);

redo_curchar:

        top_index = av_tindex(stack);

        switch (curchar) {
            SV** stacked_ptr;       /* Ptr to something already on 'stack' */
            char stacked_operator;  /* The topmost operator on the 'stack'. */
            SV* lhs;                /* Operand to the left of the operator */
            SV* rhs;                /* Operand to the right of the operator */
            SV* fence_ptr;          /* Pointer to top element of the fence
                                       stack */

            case '(':

                if (   RExC_parse < RExC_end - 1
                    && (UCHARAT(RExC_parse + 1) == '?'))
                {
                    /* If is a '(?', could be an embedded '(?flags:(?[...])'.
                     * This happens when we have some thing like
                     *
                     *   my $thai_or_lao = qr/(?[ \p{Thai} + \p{Lao} ])/;
                     *   ...
                     *   qr/(?[ \p{Digit} & $thai_or_lao ])/;
                     *
                     * Here we would be handling the interpolated
                     * '$thai_or_lao'.  We handle this by a recursive call to
                     * ourselves which returns the inversion list the
                     * interpolated expression evaluates to.  We use the flags
                     * from the interpolated pattern. */
                    U32 save_flags = RExC_flags;
                    const char * save_parse;

                    RExC_parse += 2;        /* Skip past the '(?' */
                    save_parse = RExC_parse;

                    /* Parse any flags for the '(?' */
                    parse_lparen_question_flags(pRExC_state);

                    if (RExC_parse == save_parse  /* Makes sure there was at
                                                     least one flag (or else
                                                     this embedding wasn't
                                                     compiled) */
                        || RExC_parse >= RExC_end - 4
                        || UCHARAT(RExC_parse) != ':'
                        || UCHARAT(++RExC_parse) != '('
                        || UCHARAT(++RExC_parse) != '?'
                        || UCHARAT(++RExC_parse) != '[')
                    {

                        /* In combination with the above, this moves the
                         * pointer to the point just after the first erroneous
                         * character (or if there are no flags, to where they
                         * should have been) */
                        if (RExC_parse >= RExC_end - 4) {
                            RExC_parse = RExC_end;
                        }
                        else if (RExC_parse != save_parse) {
                            RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
                        }
                        vFAIL("Expecting '(?flags:(?[...'");
                    }

                    /* Recurse, with the meat of the embedded expression */
                    RExC_parse++;
                    (void) handle_regex_sets(pRExC_state, &current, flagp,
                                                    depth+1, oregcomp_parse);

                    /* Here, 'current' contains the embedded expression's
                     * inversion list, and RExC_parse points to the trailing
                     * ']'; the next character should be the ')' */
                    RExC_parse++;
                    assert(UCHARAT(RExC_parse) == ')');

                    /* Then the ')' matching the original '(' handled by this
                     * case: statement */
                    RExC_parse++;
                    assert(UCHARAT(RExC_parse) == ')');

                    RExC_parse++;
                    RExC_flags = save_flags;
                    goto handle_operand;
                }

                /* A regular '('.  Look behind for illegal syntax */
                if (top_index - fence >= 0) {
                    /* If the top entry on the stack is an operator, it had
                     * better be a '!', otherwise the entry below the top
                     * operand should be an operator */
                    if (   ! (top_ptr = av_fetch(stack, top_index, FALSE))
                        || (IS_OPERATOR(*top_ptr) && SvUV(*top_ptr) != '!')
                        || (   IS_OPERAND(*top_ptr)
                            && (   top_index - fence < 1
                                || ! (stacked_ptr = av_fetch(stack,
                                                             top_index - 1,
                                                             FALSE))
                                || ! IS_OPERATOR(*stacked_ptr))))
                    {
                        RExC_parse++;
                        vFAIL("Unexpected '(' with no preceding operator");
                    }
                }

                /* Stack the position of this undealt-with left paren */
                fence = top_index + 1;
                av_push(fence_stack, newSViv(fence));
                break;

            case '\\':
                /* regclass() can only return RESTART_PASS1 and NEED_UTF8 if
                 * multi-char folds are allowed.  */
                if (!regclass(pRExC_state, flagp,depth+1,
                              TRUE, /* means parse just the next thing */
                              FALSE, /* don't allow multi-char folds */
                              FALSE, /* don't silence non-portable warnings.  */
                              TRUE,  /* strict */
                              FALSE, /* Require return to be an ANYOF */
                              &current,
                              NULL))
                {
                    FAIL2("panic: regclass returned NULL to handle_sets, "
                          "flags=%#"UVxf"", (UV) *flagp);
                }

                /* regclass() will return with parsing just the \ sequence,
                 * leaving the parse pointer at the next thing to parse */
                RExC_parse--;
                goto handle_operand;

            case '[':   /* Is a bracketed character class */
            {
                /* See if this is a [:posix:] class. */
                bool is_posix_class = (OOB_NAMEDCLASS
                            < handle_possible_posix(pRExC_state,
                                                RExC_parse + 1,
                                                NULL,
                                                NULL));
                /* If it is a posix class, leave the parse pointer at the '['
                 * to fool regclass() into thinking it is part of a
                 * '[[:posix:]]'. */
                if (! is_posix_class) {
                    RExC_parse++;
                }

                /* regclass() can only return RESTART_PASS1 and NEED_UTF8 if
                 * multi-char folds are allowed.  */
                if (!regclass(pRExC_state, flagp,depth+1,
                                is_posix_class, /* parse the whole char
                                                    class only if not a
                                                    posix class */
                                FALSE, /* don't allow multi-char folds */
                                TRUE, /* silence non-portable warnings. */
                                TRUE, /* strict */
                                FALSE, /* Require return to be an ANYOF */
                                &current,
                                NULL
                                ))
                {
                    FAIL2("panic: regclass returned NULL to handle_sets, "
                          "flags=%#"UVxf"", (UV) *flagp);
                }

                /* function call leaves parse pointing to the ']', except if we
                 * faked it */
                if (is_posix_class) {
                    RExC_parse--;
                }

                goto handle_operand;
            }

            case ']':
                if (top_index >= 1) {
                    goto join_operators;
                }

                /* Only a single operand on the stack: are done */
                goto done;

            case ')':
                if (av_tindex(fence_stack) < 0) {
                    RExC_parse++;
                    vFAIL("Unexpected ')'");
                }

                 /* If at least two thing on the stack, treat this as an
                  * operator */
                if (top_index - fence >= 1) {
                    goto join_operators;
                }

                /* Here only a single thing on the fenced stack, and there is a
                 * fence.  Get rid of it */
                fence_ptr = av_pop(fence_stack);
                assert(fence_ptr);
                fence = SvIV(fence_ptr) - 1;
                SvREFCNT_dec_NN(fence_ptr);
                fence_ptr = NULL;

                if (fence < 0) {
                    fence = 0;
                }

                /* Having gotten rid of the fence, we pop the operand at the
                 * stack top and process it as a newly encountered operand */
                current = av_pop(stack);
                if (IS_OPERAND(current)) {
                    goto handle_operand;
                }

                RExC_parse++;
                goto bad_syntax;

            case '&':
            case '|':
            case '+':
            case '-':
            case '^':

                /* These binary operators should have a left operand already
                 * parsed */
                if (   top_index - fence < 0
                    || top_index - fence == 1
                    || ( ! (top_ptr = av_fetch(stack, top_index, FALSE)))
                    || ! IS_OPERAND(*top_ptr))
                {
                    goto unexpected_binary;
                }

                /* If only the one operand is on the part of the stack visible
                 * to us, we just place this operator in the proper position */
                if (top_index - fence < 2) {

                    /* Place the operator before the operand */

                    SV* lhs = av_pop(stack);
                    av_push(stack, newSVuv(curchar));
                    av_push(stack, lhs);
                    break;
                }

                /* But if there is something else on the stack, we need to
                 * process it before this new operator if and only if the
                 * stacked operation has equal or higher precedence than the
                 * new one */

             join_operators:

                /* The operator on the stack is supposed to be below both its
                 * operands */
                if (   ! (stacked_ptr = av_fetch(stack, top_index - 2, FALSE))
                    || IS_OPERAND(*stacked_ptr))
                {
                    /* But if not, it's legal and indicates we are completely
                     * done if and only if we're currently processing a ']',
                     * which should be the final thing in the expression */
                    if (curchar == ']') {
                        goto done;
                    }

                  unexpected_binary:
                    RExC_parse++;
                    vFAIL2("Unexpected binary operator '%c' with no "
                           "preceding operand", curchar);
                }
                stacked_operator = (char) SvUV(*stacked_ptr);

                if (regex_set_precedence(curchar)
                    > regex_set_precedence(stacked_operator))
                {
                    /* Here, the new operator has higher precedence than the
                     * stacked one.  This means we need to add the new one to
                     * the stack to await its rhs operand (and maybe more
                     * stuff).  We put it before the lhs operand, leaving
                     * untouched the stacked operator and everything below it
                     * */
                    lhs = av_pop(stack);
                    assert(IS_OPERAND(lhs));

                    av_push(stack, newSVuv(curchar));
                    av_push(stack, lhs);
                    break;
                }

                /* Here, the new operator has equal or lower precedence than
                 * what's already there.  This means the operation already
                 * there should be performed now, before the new one. */

                rhs = av_pop(stack);
                if (! IS_OPERAND(rhs)) {

                    /* This can happen when a ! is not followed by an operand,
                     * like in /(?[\t &!])/ */
                    goto bad_syntax;
                }

                lhs = av_pop(stack);

                if (! IS_OPERAND(lhs)) {

                    /* This can happen when there is an empty (), like in
                     * /(?[[0]+()+])/ */
                    goto bad_syntax;
                }

                switch (stacked_operator) {
                    case '&':
                        _invlist_intersection(lhs, rhs, &rhs);
                        break;

                    case '|':
                    case '+':
                        _invlist_union(lhs, rhs, &rhs);
                        break;

                    case '-':
                        _invlist_subtract(lhs, rhs, &rhs);
                        break;

                    case '^':   /* The union minus the intersection */
                    {
                        SV* i = NULL;
                        SV* u = NULL;
                        SV* element;

                        _invlist_union(lhs, rhs, &u);
                        _invlist_intersection(lhs, rhs, &i);
                        /* _invlist_subtract will overwrite rhs
                            without freeing what it already contains */
                        element = rhs;
                        _invlist_subtract(u, i, &rhs);
                        SvREFCNT_dec_NN(i);
                        SvREFCNT_dec_NN(u);
                        SvREFCNT_dec_NN(element);
                        break;
                    }
                }
                SvREFCNT_dec(lhs);

                /* Here, the higher precedence operation has been done, and the
                 * result is in 'rhs'.  We overwrite the stacked operator with
                 * the result.  Then we redo this code to either push the new
                 * operator onto the stack or perform any higher precedence
                 * stacked operation */
                only_to_avoid_leaks = av_pop(stack);
                SvREFCNT_dec(only_to_avoid_leaks);
                av_push(stack, rhs);
                goto redo_curchar;

            case '!':   /* Highest priority, right associative */

                /* If what's already at the top of the stack is another '!",
                 * they just cancel each other out */
                if (   (top_ptr = av_fetch(stack, top_index, FALSE))
                    && (IS_OPERATOR(*top_ptr) && SvUV(*top_ptr) == '!'))
                {
                    only_to_avoid_leaks = av_pop(stack);
                    SvREFCNT_dec(only_to_avoid_leaks);
                }
                else { /* Otherwise, since it's right associative, just push
                          onto the stack */
                    av_push(stack, newSVuv(curchar));
                }
                break;

            default:
                RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
                vFAIL("Unexpected character");

          handle_operand:

            /* Here 'current' is the operand.  If something is already on the
             * stack, we have to check if it is a !. */
            top_index = av_tindex(stack);   /* Code above may have altered the
                                             * stack in the time since we
                                             * earlier set 'top_index'. */
            if (top_index - fence >= 0) {
                /* If the top entry on the stack is an operator, it had better
                 * be a '!', otherwise the entry below the top operand should
                 * be an operator */
                top_ptr = av_fetch(stack, top_index, FALSE);
                assert(top_ptr);
                if (IS_OPERATOR(*top_ptr)) {

                    /* The only permissible operator at the top of the stack is
                     * '!', which is applied immediately to this operand. */
                    curchar = (char) SvUV(*top_ptr);
                    if (curchar != '!') {
                        SvREFCNT_dec(current);
                        vFAIL2("Unexpected binary operator '%c' with no "
                                "preceding operand", curchar);
                    }

                    _invlist_invert(current);

                    only_to_avoid_leaks = av_pop(stack);
                    SvREFCNT_dec(only_to_avoid_leaks);
                    top_index = av_tindex(stack);

                    /* And we redo with the inverted operand.  This allows
                     * handling multiple ! in a row */
                    goto handle_operand;
                }
                          /* Single operand is ok only for the non-binary ')'
                           * operator */
                else if ((top_index - fence == 0 && curchar != ')')
                         || (top_index - fence > 0
                             && (! (stacked_ptr = av_fetch(stack,
                                                           top_index - 1,
                                                           FALSE))
                                 || IS_OPERAND(*stacked_ptr))))
                {
                    SvREFCNT_dec(current);
                    vFAIL("Operand with no preceding operator");
                }
            }

            /* Here there was nothing on the stack or the top element was
             * another operand.  Just add this new one */
            av_push(stack, current);

        } /* End of switch on next parse token */

        RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
    } /* End of loop parsing through the construct */

  done:
    if (av_tindex(fence_stack) >= 0) {
        vFAIL("Unmatched (");
    }

    if (av_tindex(stack) < 0   /* Was empty */
        || ((final = av_pop(stack)) == NULL)
        || ! IS_OPERAND(final)
        || SvTYPE(final) != SVt_INVLIST
        || av_tindex(stack) >= 0)  /* More left on stack */
    {
      bad_syntax:
        SvREFCNT_dec(final);
        vFAIL("Incomplete expression within '(?[ ])'");
    }

    /* Here, 'final' is the resultant inversion list from evaluating the
     * expression.  Return it if so requested */
    if (return_invlist) {
        *return_invlist = final;
        return END;
    }

    /* Otherwise generate a resultant node, based on 'final'.  regclass() is
     * expecting a string of ranges and individual code points */
    invlist_iterinit(final);
    result_string = newSVpvs("");
    while (invlist_iternext(final, &start, &end)) {
        if (start == end) {
            Perl_sv_catpvf(aTHX_ result_string, "\\x{%"UVXf"}", start);
        }
        else {
            Perl_sv_catpvf(aTHX_ result_string, "\\x{%"UVXf"}-\\x{%"UVXf"}",
                                                     start,          end);
        }
    }

    /* About to generate an ANYOF (or similar) node from the inversion list we
     * have calculated */
    save_parse = RExC_parse;
    RExC_parse = SvPV(result_string, len);
    save_end = RExC_end;
    RExC_end = RExC_parse + len;

    /* We turn off folding around the call, as the class we have constructed
     * already has all folding taken into consideration, and we don't want
     * regclass() to add to that */
    RExC_flags &= ~RXf_PMf_FOLD;
    /* regclass() can only return RESTART_PASS1 and NEED_UTF8 if multi-char
     * folds are allowed.  */
    node = regclass(pRExC_state, flagp,depth+1,
                    FALSE, /* means parse the whole char class */
                    FALSE, /* don't allow multi-char folds */
                    TRUE, /* silence non-portable warnings.  The above may very
                             well have generated non-portable code points, but
                             they're valid on this machine */
                    FALSE, /* similarly, no need for strict */
                    FALSE, /* Require return to be an ANYOF */
                    NULL,
                    NULL
                );
    if (!node)
        FAIL2("panic: regclass returned NULL to handle_sets, flags=%#"UVxf,
                    PTR2UV(flagp));

    /* Fix up the node type if we are in locale.  (We have pretended we are
     * under /u for the purposes of regclass(), as this construct will only
     * work under UTF-8 locales.  But now we change the opcode to be ANYOFL (so
     * as to cause any warnings about bad locales to be output in regexec.c),
     * and add the flag that indicates to check if not in a UTF-8 locale.  The
     * reason we above forbid optimization into something other than an ANYOF
     * node is simply to minimize the number of code changes in regexec.c.
     * Otherwise we would have to create new EXACTish node types and deal with
     * them.  This decision could be revisited should this construct become
     * popular.
     *
     * (One might think we could look at the resulting ANYOF node and suppress
     * the flag if everything is above 255, as those would be UTF-8 only,
     * but this isn't true, as the components that led to that result could
     * have been locale-affected, and just happen to cancel each other out
     * under UTF-8 locales.) */
    if (in_locale) {
        set_regex_charset(&RExC_flags, REGEX_LOCALE_CHARSET);

        assert(OP(node) == ANYOF);

        OP(node) = ANYOFL;
        ANYOF_FLAGS(node)
                |= ANYOFL_SHARED_UTF8_LOCALE_fold_HAS_MATCHES_nonfold_REQD;
    }

    if (save_fold) {
        RExC_flags |= RXf_PMf_FOLD;
    }

    RExC_parse = save_parse + 1;
    RExC_end = save_end;
    SvREFCNT_dec_NN(final);
    SvREFCNT_dec_NN(result_string);

    nextchar(pRExC_state);
    Set_Node_Length(node, RExC_parse - oregcomp_parse + 1); /* MJD */
    return node;
}
#undef IS_OPERATOR
#undef IS_OPERAND

STATIC void
S_add_above_Latin1_folds(pTHX_ RExC_state_t *pRExC_state, const U8 cp, SV** invlist)
{
    /* This hard-codes the Latin1/above-Latin1 folding rules, so that an
     * innocent-looking character class, like /[ks]/i won't have to go out to
     * disk to find the possible matches.
     *
     * This should be called only for a Latin1-range code points, cp, which is
     * known to be involved in a simple fold with other code points above
     * Latin1.  It would give false results if /aa has been specified.
     * Multi-char folds are outside the scope of this, and must be handled
     * specially.
     *
     * XXX It would be better to generate these via regen, in case a new
     * version of the Unicode standard adds new mappings, though that is not
     * really likely, and may be caught by the default: case of the switch
     * below. */

    PERL_ARGS_ASSERT_ADD_ABOVE_LATIN1_FOLDS;

    assert(HAS_NONLATIN1_SIMPLE_FOLD_CLOSURE(cp));

    switch (cp) {
        case 'k':
        case 'K':
          *invlist =
             add_cp_to_invlist(*invlist, KELVIN_SIGN);
            break;
        case 's':
        case 'S':
          *invlist = add_cp_to_invlist(*invlist, LATIN_SMALL_LETTER_LONG_S);
            break;
        case MICRO_SIGN:
          *invlist = add_cp_to_invlist(*invlist, GREEK_CAPITAL_LETTER_MU);
          *invlist = add_cp_to_invlist(*invlist, GREEK_SMALL_LETTER_MU);
            break;
        case LATIN_CAPITAL_LETTER_A_WITH_RING_ABOVE:
        case LATIN_SMALL_LETTER_A_WITH_RING_ABOVE:
          *invlist = add_cp_to_invlist(*invlist, ANGSTROM_SIGN);
            break;
        case LATIN_SMALL_LETTER_Y_WITH_DIAERESIS:
          *invlist = add_cp_to_invlist(*invlist,
                                        LATIN_CAPITAL_LETTER_Y_WITH_DIAERESIS);
            break;

#ifdef LATIN_CAPITAL_LETTER_SHARP_S /* not defined in early Unicode releases */

        case LATIN_SMALL_LETTER_SHARP_S:
          *invlist = add_cp_to_invlist(*invlist, LATIN_CAPITAL_LETTER_SHARP_S);
            break;

#endif

#if    UNICODE_MAJOR_VERSION < 3                                        \
   || (UNICODE_MAJOR_VERSION == 3 && UNICODE_DOT_VERSION == 0)

        /* In 3.0 and earlier, U+0130 folded simply to 'i'; and in 3.0.1 so did
         * U+0131.  */
        case 'i':
        case 'I':
          *invlist =
             add_cp_to_invlist(*invlist, LATIN_CAPITAL_LETTER_I_WITH_DOT_ABOVE);
#   if UNICODE_DOT_DOT_VERSION == 1
          *invlist = add_cp_to_invlist(*invlist, LATIN_SMALL_LETTER_DOTLESS_I);
#   endif
            break;
#endif

        default:
            /* Use deprecated warning to increase the chances of this being
             * output */
            if (PASS2) {
                ckWARN2reg_d(RExC_parse, "Perl folding rules are not up-to-date for 0x%02X; please use the perlbug utility to report;", cp);
            }
            break;
    }
}

STATIC AV *
S_add_multi_match(pTHX_ AV* multi_char_matches, SV* multi_string, const STRLEN cp_count)
{
    /* This adds the string scalar <multi_string> to the array
     * <multi_char_matches>.  <multi_string> is known to have exactly
     * <cp_count> code points in it.  This is used when constructing a
     * bracketed character class and we find something that needs to match more
     * than a single character.
     *
     * <multi_char_matches> is actually an array of arrays.  Each top-level
     * element is an array that contains all the strings known so far that are
     * the same length.  And that length (in number of code points) is the same
     * as the index of the top-level array.  Hence, the [2] element is an
     * array, each element thereof is a string containing TWO code points;
     * while element [3] is for strings of THREE characters, and so on.  Since
     * this is for multi-char strings there can never be a [0] nor [1] element.
     *
     * When we rewrite the character class below, we will do so such that the
     * longest strings are written first, so that it prefers the longest
     * matching strings first.  This is done even if it turns out that any
     * quantifier is non-greedy, out of this programmer's (khw) laziness.  Tom
     * Christiansen has agreed that this is ok.  This makes the test for the
     * ligature 'ffi' come before the test for 'ff', for example */

    AV* this_array;
    AV** this_array_ptr;

    PERL_ARGS_ASSERT_ADD_MULTI_MATCH;

    if (! multi_char_matches) {
        multi_char_matches = newAV();
    }

    if (av_exists(multi_char_matches, cp_count)) {
        this_array_ptr = (AV**) av_fetch(multi_char_matches, cp_count, FALSE);
        this_array = *this_array_ptr;
    }
    else {
        this_array = newAV();
        av_store(multi_char_matches, cp_count,
                 (SV*) this_array);
    }
    av_push(this_array, multi_string);

    return multi_char_matches;
}

/* The names of properties whose definitions are not known at compile time are
 * stored in this SV, after a constant heading.  So if the length has been
 * changed since initialization, then there is a run-time definition. */
#define HAS_NONLOCALE_RUNTIME_PROPERTY_DEFINITION                            \
                                        (SvCUR(listsv) != initial_listsv_len)

/* There is a restricted set of white space characters that are legal when
 * ignoring white space in a bracketed character class.  This generates the
 * code to skip them.
 *
 * There is a line below that uses the same white space criteria but is outside
 * this macro.  Both here and there must use the same definition */
#define SKIP_BRACKETED_WHITE_SPACE(do_skip, p)                          \
    STMT_START {                                                        \
        if (do_skip) {                                                  \
            while (isBLANK_A(UCHARAT(p)))                               \
            {                                                           \
                p++;                                                    \
            }                                                           \
        }                                                               \
    } STMT_END

STATIC regnode *
S_regclass(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth,
                 const bool stop_at_1,  /* Just parse the next thing, don't
                                           look for a full character class */
                 bool allow_multi_folds,
                 const bool silence_non_portable,   /* Don't output warnings
                                                       about too large
                                                       characters */
                 const bool strict,
                 bool optimizable,                  /* ? Allow a non-ANYOF return
                                                       node */
                 SV** ret_invlist, /* Return an inversion list, not a node */
                 AV** return_posix_warnings
          )
{
    /* parse a bracketed class specification.  Most of these will produce an
     * ANYOF node; but something like [a] will produce an EXACT node; [aA], an
     * EXACTFish node; [[:ascii:]], a POSIXA node; etc.  It is more complex
     * under /i with multi-character folds: it will be rewritten following the
     * paradigm of this example, where the <multi-fold>s are characters which
     * fold to multiple character sequences:
     *      /[abc\x{multi-fold1}def\x{multi-fold2}ghi]/i
     * gets effectively rewritten as:
     *      /(?:\x{multi-fold1}|\x{multi-fold2}|[abcdefghi]/i
     * reg() gets called (recursively) on the rewritten version, and this
     * function will return what it constructs.  (Actually the <multi-fold>s
     * aren't physically removed from the [abcdefghi], it's just that they are
     * ignored in the recursion by means of a flag:
     * <RExC_in_multi_char_class>.)
     *
     * ANYOF nodes contain a bit map for the first NUM_ANYOF_CODE_POINTS
     * characters, with the corresponding bit set if that character is in the
     * list.  For characters above this, a range list or swash is used.  There
     * are extra bits for \w, etc. in locale ANYOFs, as what these match is not
     * determinable at compile time
     *
     * Returns NULL, setting *flagp to RESTART_PASS1 if the sizing scan needs
     * to be restarted, or'd with NEED_UTF8 if the pattern needs to be upgraded
     * to UTF-8.  This can only happen if ret_invlist is non-NULL.
     */

    UV prevvalue = OOB_UNICODE, save_prevvalue = OOB_UNICODE;
    IV range = 0;
    UV value = OOB_UNICODE, save_value = OOB_UNICODE;
    regnode *ret;
    STRLEN numlen;
    int namedclass = OOB_NAMEDCLASS;
    char *rangebegin = NULL;
    bool need_class = 0;
    SV *listsv = NULL;
    STRLEN initial_listsv_len = 0; /* Kind of a kludge to see if it is more
                                      than just initialized.  */
    SV* properties = NULL;    /* Code points that match \p{} \P{} */
    SV* posixes = NULL;     /* Code points that match classes like [:word:],
                               extended beyond the Latin1 range.  These have to
                               be kept separate from other code points for much
                               of this function because their handling  is
                               different under /i, and for most classes under
                               /d as well */
    SV* nposixes = NULL;    /* Similarly for [:^word:].  These are kept
                               separate for a while from the non-complemented
                               versions because of complications with /d
                               matching */
    SV* simple_posixes = NULL; /* But under some conditions, the classes can be
                                  treated more simply than the general case,
                                  leading to less compilation and execution
                                  work */
    UV element_count = 0;   /* Number of distinct elements in the class.
                               Optimizations may be possible if this is tiny */
    AV * multi_char_matches = NULL; /* Code points that fold to more than one
                                       character; used under /i */
    UV n;
    char * stop_ptr = RExC_end;    /* where to stop parsing */
    const bool skip_white = cBOOL(ret_invlist); /* ignore unescaped white
                                                   space? */

    /* Unicode properties are stored in a swash; this holds the current one
     * being parsed.  If this swash is the only above-latin1 component of the
     * character class, an optimization is to pass it directly on to the
     * execution engine.  Otherwise, it is set to NULL to indicate that there
     * are other things in the class that have to be dealt with at execution
     * time */
    SV* swash = NULL;           /* Code points that match \p{} \P{} */

    /* Set if a component of this character class is user-defined; just passed
     * on to the engine */
    bool has_user_defined_property = FALSE;

    /* inversion list of code points this node matches only when the target
     * string is in UTF-8.  These are all non-ASCII, < 256.  (Because is under
     * /d) */
    SV* has_upper_latin1_only_utf8_matches = NULL;

    /* Inversion list of code points this node matches regardless of things
     * like locale, folding, utf8ness of the target string */
    SV* cp_list = NULL;

    /* Like cp_list, but code points on this list need to be checked for things
     * that fold to/from them under /i */
    SV* cp_foldable_list = NULL;

    /* Like cp_list, but code points on this list are valid only when the
     * runtime locale is UTF-8 */
    SV* only_utf8_locale_list = NULL;

    /* In a range, if one of the endpoints is non-character-set portable,
     * meaning that it hard-codes a code point that may mean a different
     * charactger in ASCII vs. EBCDIC, as opposed to, say, a literal 'A' or a
     * mnemonic '\t' which each mean the same character no matter which
     * character set the platform is on. */
    unsigned int non_portable_endpoint = 0;

    /* Is the range unicode? which means on a platform that isn't 1-1 native
     * to Unicode (i.e. non-ASCII), each code point in it should be considered
     * to be a Unicode value.  */
    bool unicode_range = FALSE;
    bool invert = FALSE;    /* Is this class to be complemented */

    bool warn_super = ALWAYS_WARN_SUPER;

    regnode * const orig_emit = RExC_emit; /* Save the original RExC_emit in
        case we need to change the emitted regop to an EXACT. */
    const char * orig_parse = RExC_parse;
    const SSize_t orig_size = RExC_size;
    bool posixl_matches_all = FALSE; /* Does /l class have both e.g. \W,\w ? */

    /* This variable is used to mark where in the input something that looks
     * like a POSIX construct ends.  During the parse, when something looks
     * like it could be such a construct is encountered, it is checked for
     * being one, but not if we've already checked this area of the input.
     * Only after this position is reached do we check again */
    char *not_posix_region_end = RExC_parse - 1;

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGCLASS;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif

    DEBUG_PARSE("clas");

#if UNICODE_MAJOR_VERSION < 3 /* no multifolds in early Unicode */      \
    || (UNICODE_MAJOR_VERSION == 3 && UNICODE_DOT_VERSION == 0          \
                                   && UNICODE_DOT_DOT_VERSION == 0)
    allow_multi_folds = FALSE;
#endif

    if (return_posix_warnings == NULL) {
        return_posix_warnings = (AV **) -1;
    }

    /* Assume we are going to generate an ANYOF node. */
    ret = reganode(pRExC_state,
                   (LOC)
                    ? ANYOFL
                    : ANYOF,
                   0);

    if (SIZE_ONLY) {
        RExC_size += ANYOF_SKIP;
        listsv = &PL_sv_undef; /* For code scanners: listsv always non-NULL. */
    }
    else {
        ANYOF_FLAGS(ret) = 0;

        RExC_emit += ANYOF_SKIP;
        listsv = newSVpvs_flags("# comment\n", SVs_TEMP);
        initial_listsv_len = SvCUR(listsv);
        SvTEMP_off(listsv); /* Grr, TEMPs and mortals are conflated.  */
    }

    SKIP_BRACKETED_WHITE_SPACE(skip_white, RExC_parse);

    assert(RExC_parse <= RExC_end);

    if (UCHARAT(RExC_parse) == '^') {   /* Complement the class */
        RExC_parse++;
        invert = TRUE;
        allow_multi_folds = FALSE;
        MARK_NAUGHTY(1);
        SKIP_BRACKETED_WHITE_SPACE(skip_white, RExC_parse);
    }

    /* Check that they didn't say [:posix:] instead of [[:posix:]] */
    if (! ret_invlist && MAYBE_POSIXCC(UCHARAT(RExC_parse))) {
        char *class_end;
        int maybe_class = handle_possible_posix(pRExC_state,
                                                RExC_parse,
                                                &class_end,
                                                NULL);
        if (maybe_class >= OOB_NAMEDCLASS) {
            not_posix_region_end = class_end;
            if (PASS2 && return_posix_warnings == (AV **) -1) {
                SAVEFREESV(RExC_rx_sv);
                ckWARN4reg(class_end,
                        "POSIX syntax [%c %c] belongs inside character classes%s",
                        *RExC_parse, *RExC_parse,
                        (maybe_class == OOB_NAMEDCLASS)
                        ? ((POSIXCC_NOTYET(*RExC_parse))
                            ? " (but this one isn't implemented)"
                            : " (but this one isn't fully valid)")
                        : ""
                        );
                (void)ReREFCNT_inc(RExC_rx_sv);
            }
        }
    }

    /* If the caller wants us to just parse a single element, accomplish this
     * by faking the loop ending condition */
    if (stop_at_1 && RExC_end > RExC_parse) {
        stop_ptr = RExC_parse + 1;
    }

    /* allow 1st char to be ']' (allowing it to be '-' is dealt with later) */
    if (UCHARAT(RExC_parse) == ']')
        goto charclassloop;

    while (1) {
        if  (RExC_parse >= stop_ptr) {
            break;
        }

        SKIP_BRACKETED_WHITE_SPACE(skip_white, RExC_parse);

        if  (UCHARAT(RExC_parse) == ']') {
            break;
        }

      charclassloop:

        namedclass = OOB_NAMEDCLASS; /* initialize as illegal */
        save_value = value;
        save_prevvalue = prevvalue;

        if (!range) {
            rangebegin = RExC_parse;
            element_count++;
            non_portable_endpoint = 0;
        }
        if (UTF && ! UTF8_IS_INVARIANT(* RExC_parse)) {
            value = utf8n_to_uvchr((U8*)RExC_parse,
                                   RExC_end - RExC_parse,
                                   &numlen, UTF8_ALLOW_DEFAULT);
            RExC_parse += numlen;
        }
        else
            value = UCHARAT(RExC_parse++);

        if (value == '[') {
            namedclass = handle_possible_posix(pRExC_state,
                                               RExC_parse,
                                               &not_posix_region_end,
                                               return_posix_warnings);
            if (namedclass > OOB_NAMEDCLASS) {
                RExC_parse = not_posix_region_end;
            }
            else {
                namedclass = OOB_NAMEDCLASS;
            }
        }
        else if (   RExC_parse - 1 > not_posix_region_end
                 && MAYBE_POSIXCC(value))
        {
            (void) handle_possible_posix(
                        pRExC_state,
                        RExC_parse - 1,  /* -1 because parse has already been
                                            advanced */
                        &not_posix_region_end,
                        return_posix_warnings);
        }
        else if (value == '\\') {
            /* Is a backslash; get the code point of the char after it */
            if (UTF && ! UTF8_IS_INVARIANT(UCHARAT(RExC_parse))) {
                value = utf8n_to_uvchr((U8*)RExC_parse,
                                   RExC_end - RExC_parse,
                                   &numlen, UTF8_ALLOW_DEFAULT);
                RExC_parse += numlen;
            }
            else
                value = UCHARAT(RExC_parse++);

            /* Some compilers cannot handle switching on 64-bit integer
             * values, therefore value cannot be an UV.  Yes, this will
             * be a problem later if we want switch on Unicode.
             * A similar issue a little bit later when switching on
             * namedclass. --jhi */

            /* If the \ is escaping white space when white space is being
             * skipped, it means that that white space is wanted literally, and
             * is already in 'value'.  Otherwise, need to translate the escape
             * into what it signifies. */
            if (! skip_white || ! isBLANK_A(value)) switch ((I32)value) {

            case 'w':   namedclass = ANYOF_WORDCHAR;    break;
            case 'W':   namedclass = ANYOF_NWORDCHAR;   break;
            case 's':   namedclass = ANYOF_SPACE;       break;
            case 'S':   namedclass = ANYOF_NSPACE;      break;
            case 'd':   namedclass = ANYOF_DIGIT;       break;
            case 'D':   namedclass = ANYOF_NDIGIT;      break;
            case 'v':   namedclass = ANYOF_VERTWS;      break;
            case 'V':   namedclass = ANYOF_NVERTWS;     break;
            case 'h':   namedclass = ANYOF_HORIZWS;     break;
            case 'H':   namedclass = ANYOF_NHORIZWS;    break;
            case 'N':  /* Handle \N{NAME} in class */
                {
                    const char * const backslash_N_beg = RExC_parse - 2;
                    int cp_count;

                    if (! grok_bslash_N(pRExC_state,
                                        NULL,      /* No regnode */
                                        &value,    /* Yes single value */
                                        &cp_count, /* Multiple code pt count */
                                        flagp,
                                        strict,
                                        depth)
                    ) {

                        if (*flagp & NEED_UTF8)
                            FAIL("panic: grok_bslash_N set NEED_UTF8");
                        if (*flagp & RESTART_PASS1)
                            return NULL;

                        if (cp_count < 0) {
                            vFAIL("\\N in a character class must be a named character: \\N{...}");
                        }
                        else if (cp_count == 0) {
                            if (PASS2) {
                                ckWARNreg(RExC_parse,
                                        "Ignoring zero length \\N{} in character class");
                            }
                        }
                        else { /* cp_count > 1 */
                            if (! RExC_in_multi_char_class) {
                                if (invert || range || *RExC_parse == '-') {
                                    if (strict) {
                                        RExC_parse--;
                                        vFAIL("\\N{} in inverted character class or as a range end-point is restricted to one character");
                                    }
                                    else if (PASS2) {
                                        ckWARNreg(RExC_parse, "Using just the first character returned by \\N{} in character class");
                                    }
                                    break; /* <value> contains the first code
                                              point. Drop out of the switch to
                                              process it */
                                }
                                else {
                                    SV * multi_char_N = newSVpvn(backslash_N_beg,
                                                 RExC_parse - backslash_N_beg);
                                    multi_char_matches
                                        = add_multi_match(multi_char_matches,
                                                          multi_char_N,
                                                          cp_count);
                                }
                            }
                        } /* End of cp_count != 1 */

                        /* This element should not be processed further in this
                         * class */
                        element_count--;
                        value = save_value;
                        prevvalue = save_prevvalue;
                        continue;   /* Back to top of loop to get next char */
                    }

                    /* Here, is a single code point, and <value> contains it */
                    unicode_range = TRUE;   /* \N{} are Unicode */
                }
                break;
            case 'p':
            case 'P':
                {
                char *e;

                /* We will handle any undefined properties ourselves */
                U8 swash_init_flags = _CORE_SWASH_INIT_RETURN_IF_UNDEF
                                       /* And we actually would prefer to get
                                        * the straight inversion list of the
                                        * swash, since we will be accessing it
                                        * anyway, to save a little time */
                                      |_CORE_SWASH_INIT_ACCEPT_INVLIST;

                if (RExC_parse >= RExC_end)
                    vFAIL2("Empty \\%c", (U8)value);
                if (*RExC_parse == '{') {
                    const U8 c = (U8)value;
                    e = strchr(RExC_parse, '}');
                    if (!e) {
                        RExC_parse++;
                        vFAIL2("Missing right brace on \\%c{}", c);
                    }

                    RExC_parse++;
                    while (isSPACE(*RExC_parse)) {
                         RExC_parse++;
                    }

                    if (UCHARAT(RExC_parse) == '^') {

                        /* toggle.  (The rhs xor gets the single bit that
                         * differs between P and p; the other xor inverts just
                         * that bit) */
                        value ^= 'P' ^ 'p';

                        RExC_parse++;
                        while (isSPACE(*RExC_parse)) {
                            RExC_parse++;
                        }
                    }

                    if (e == RExC_parse)
                        vFAIL2("Empty \\%c{}", c);

                    n = e - RExC_parse;
                    while (isSPACE(*(RExC_parse + n - 1)))
                        n--;
                }   /* The \p isn't immediately followed by a '{' */
                else if (! isALPHA(*RExC_parse)) {
                    RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
                    vFAIL2("Character following \\%c must be '{' or a "
                           "single-character Unicode property name",
                           (U8) value);
                }
                else {
                    e = RExC_parse;
                    n = 1;
                }
                if (!SIZE_ONLY) {
                    SV* invlist;
                    char* name;
                    char* base_name;    /* name after any packages are stripped */
                    char* lookup_name = NULL;
                    const char * const colon_colon = "::";

                    /* Try to get the definition of the property into
                     * <invlist>.  If /i is in effect, the effective property
                     * will have its name be <__NAME_i>.  The design is
                     * discussed in commit
                     * 2f833f5208e26b208886e51e09e2c072b5eabb46 */
                    name = savepv(Perl_form(aTHX_ "%.*s", (int)n, RExC_parse));
                    if (FOLD) {
                        lookup_name = savepv(Perl_form(aTHX_ "__%s_i", name));
                    }

                    /* Look up the property name, and get its swash and
                     * inversion list, if the property is found  */
                    SvREFCNT_dec(swash); /* Free any left-overs */
                    swash = _core_swash_init("utf8",
                                             (lookup_name)
                                              ? lookup_name
                                              : name,
                                             &PL_sv_undef,
                                             1, /* binary */
                                             0, /* not tr/// */
                                             NULL, /* No inversion list */
                                             &swash_init_flags
                                            );
                    if (lookup_name) {
                        Safefree(lookup_name);
                    }
                    if (! swash || ! (invlist = _get_swash_invlist(swash))) {
                        HV* curpkg = (IN_PERL_COMPILETIME)
                                      ? PL_curstash
                                      : CopSTASH(PL_curcop);
                        UV final_n = n;
                        bool has_pkg;

                        if (swash) {    /* Got a swash but no inversion list.
                                           Something is likely wrong that will
                                           be sorted-out later */
                            SvREFCNT_dec_NN(swash);
                            swash = NULL;
                        }

                        /* Here didn't find it.  It could be a an error (like a
                         * typo) in specifying a Unicode property, or it could
                         * be a user-defined property that will be available at
                         * run-time.  The names of these must begin with 'In'
                         * or 'Is' (after any packages are stripped off).  So
                         * if not one of those, or if we accept only
                         * compile-time properties, is an error; otherwise add
                         * it to the list for run-time look up. */
                        if ((base_name = rninstr(name, name + n,
                                                 colon_colon, colon_colon + 2)))
                        { /* Has ::.  We know this must be a user-defined
                             property */
                            base_name += 2;
                            final_n -= base_name - name;
                            has_pkg = TRUE;
                        }
                        else {
                            base_name = name;
                            has_pkg = FALSE;
                        }

                        if (   final_n < 3
                            || base_name[0] != 'I'
                            || (base_name[1] != 's' && base_name[1] != 'n')
                            || ret_invlist)
                        {
                            const char * const msg
                                = (has_pkg)
                                  ? "Illegal user-defined property name"
                                  : "Can't find Unicode property definition";
                            RExC_parse = e + 1;

                            /* diag_listed_as: Can't find Unicode property definition "%s" */
                            vFAIL3utf8f("%s \"%"UTF8f"\"",
                                msg, UTF8fARG(UTF, n, name));
                        }

                        /* If the property name doesn't already have a package
                         * name, add the current one to it so that it can be
                         * referred to outside it. [perl #121777] */
                        if (! has_pkg && curpkg) {
                            char* pkgname = HvNAME(curpkg);
                            if (strNE(pkgname, "main")) {
                                char* full_name = Perl_form(aTHX_
                                                            "%s::%s",
                                                            pkgname,
                                                            name);
                                n = strlen(full_name);
                                Safefree(name);
                                name = savepvn(full_name, n);
                            }
                        }
                        Perl_sv_catpvf(aTHX_ listsv, "%cutf8::%s%"UTF8f"%s\n",
                                        (value == 'p' ? '+' : '!'),
                                        (FOLD) ? "__" : "",
                                        UTF8fARG(UTF, n, name),
                                        (FOLD) ? "_i" : "");
                        has_user_defined_property = TRUE;
                        optimizable = FALSE;    /* Will have to leave this an
                                                   ANYOF node */

                        /* We don't know yet what this matches, so have to flag
                         * it */
                        ANYOF_FLAGS(ret) |= ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP;
                    }
                    else {

                        /* Here, did get the swash and its inversion list.  If
                         * the swash is from a user-defined property, then this
                         * whole character class should be regarded as such */
                        if (swash_init_flags
                            & _CORE_SWASH_INIT_USER_DEFINED_PROPERTY)
                        {
                            has_user_defined_property = TRUE;
                        }
                        else if
                            /* We warn on matching an above-Unicode code point
                             * if the match would return true, except don't
                             * warn for \p{All}, which has exactly one element
                             * = 0 */
                            (_invlist_contains_cp(invlist, 0x110000)
                                && (! (_invlist_len(invlist) == 1
                                       && *invlist_array(invlist) == 0)))
                        {
                            warn_super = TRUE;
                        }


                        /* Invert if asking for the complement */
                        if (value == 'P') {
                            _invlist_union_complement_2nd(properties,
                                                          invlist,
                                                          &properties);

                            /* The swash can't be used as-is, because we've
                             * inverted things; delay removing it to here after
                             * have copied its invlist above */
                            SvREFCNT_dec_NN(swash);
                            swash = NULL;
                        }
                        else {
                            _invlist_union(properties, invlist, &properties);
                        }
                    }
                    Safefree(name);
                }
                RExC_parse = e + 1;
                namedclass = ANYOF_UNIPROP;  /* no official name, but it's
                                                named */

                /* \p means they want Unicode semantics */
                REQUIRE_UNI_RULES(flagp, NULL);
                }
                break;
            case 'n':   value = '\n';                   break;
            case 'r':   value = '\r';                   break;
            case 't':   value = '\t';                   break;
            case 'f':   value = '\f';                   break;
            case 'b':   value = '\b';                   break;
            case 'e':   value = ESC_NATIVE;             break;
            case 'a':   value = '\a';                   break;
            case 'o':
                RExC_parse--;   /* function expects to be pointed at the 'o' */
                {
                    const char* error_msg;
                    bool valid = grok_bslash_o(&RExC_parse,
                                               &value,
                                               &error_msg,
                                               PASS2,   /* warnings only in
                                                           pass 2 */
                                               strict,
                                               silence_non_portable,
                                               UTF);
                    if (! valid) {
                        vFAIL(error_msg);
                    }
                }
                non_portable_endpoint++;
                if (IN_ENCODING && value < 0x100) {
                    goto recode_encoding;
                }
                break;
            case 'x':
                RExC_parse--;   /* function expects to be pointed at the 'x' */
                {
                    const char* error_msg;
                    bool valid = grok_bslash_x(&RExC_parse,
                                               &value,
                                               &error_msg,
                                               PASS2, /* Output warnings */
                                               strict,
                                               silence_non_portable,
                                               UTF);
                    if (! valid) {
                        vFAIL(error_msg);
                    }
                }
                non_portable_endpoint++;
                if (IN_ENCODING && value < 0x100)
                    goto recode_encoding;
                break;
            case 'c':
                value = grok_bslash_c(*RExC_parse++, PASS2);
                non_portable_endpoint++;
                break;
            case '0': case '1': case '2': case '3': case '4':
            case '5': case '6': case '7':
                {
                    /* Take 1-3 octal digits */
                    I32 flags = PERL_SCAN_SILENT_ILLDIGIT;
                    numlen = (strict) ? 4 : 3;
                    value = grok_oct(--RExC_parse, &numlen, &flags, NULL);
                    RExC_parse += numlen;
                    if (numlen != 3) {
                        if (strict) {
                            RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
                            vFAIL("Need exactly 3 octal digits");
                        }
                        else if (! SIZE_ONLY /* like \08, \178 */
                                 && numlen < 3
                                 && RExC_parse < RExC_end
                                 && isDIGIT(*RExC_parse)
                                 && ckWARN(WARN_REGEXP))
                        {
                            SAVEFREESV(RExC_rx_sv);
                            reg_warn_non_literal_string(
                                 RExC_parse + 1,
                                 form_short_octal_warning(RExC_parse, numlen));
                            (void)ReREFCNT_inc(RExC_rx_sv);
                        }
                    }
                    non_portable_endpoint++;
                    if (IN_ENCODING && value < 0x100)
                        goto recode_encoding;
                    break;
                }
              recode_encoding:
                if (! RExC_override_recoding) {
                    SV* enc = _get_encoding();
                    value = reg_recode((U8)value, &enc);
                    if (!enc) {
                        if (strict) {
                            vFAIL("Invalid escape in the specified encoding");
                        }
                        else if (PASS2) {
                            ckWARNreg(RExC_parse,
                                  "Invalid escape in the specified encoding");
                        }
                    }
                    break;
                }
            default:
                /* Allow \_ to not give an error */
                if (!SIZE_ONLY && isWORDCHAR(value) && value != '_') {
                    if (strict) {
                        vFAIL2("Unrecognized escape \\%c in character class",
                               (int)value);
                    }
                    else {
                        SAVEFREESV(RExC_rx_sv);
                        ckWARN2reg(RExC_parse,
                            "Unrecognized escape \\%c in character class passed through",
                            (int)value);
                        (void)ReREFCNT_inc(RExC_rx_sv);
                    }
                }
                break;
            }   /* End of switch on char following backslash */
        } /* end of handling backslash escape sequences */

        /* Here, we have the current token in 'value' */

        if (namedclass > OOB_NAMEDCLASS) { /* this is a named class \blah */
            U8 classnum;

            /* a bad range like a-\d, a-[:digit:].  The '-' is taken as a
             * literal, as is the character that began the false range, i.e.
             * the 'a' in the examples */
            if (range) {
                if (!SIZE_ONLY) {
                    const int w = (RExC_parse >= rangebegin)
                                  ? RExC_parse - rangebegin
                                  : 0;
                    if (strict) {
                        vFAIL2utf8f(
                            "False [] range \"%"UTF8f"\"",
                            UTF8fARG(UTF, w, rangebegin));
                    }
                    else {
                        SAVEFREESV(RExC_rx_sv); /* in case of fatal warnings */
                        ckWARN2reg(RExC_parse,
                            "False [] range \"%"UTF8f"\"",
                            UTF8fARG(UTF, w, rangebegin));
                        (void)ReREFCNT_inc(RExC_rx_sv);
                        cp_list = add_cp_to_invlist(cp_list, '-');
                        cp_foldable_list = add_cp_to_invlist(cp_foldable_list,
                                                             prevvalue);
                    }
                }

                range = 0; /* this was not a true range */
                element_count += 2; /* So counts for three values */
            }

            classnum = namedclass_to_classnum(namedclass);

            if (LOC && namedclass < ANYOF_POSIXL_MAX
#ifndef HAS_ISASCII
                && classnum != _CC_ASCII
#endif
            ) {
                /* What the Posix classes (like \w, [:space:]) match in locale
                 * isn't knowable under locale until actual match time.  Room
                 * must be reserved (one time per outer bracketed class) to
                 * store such classes.  The space will contain a bit for each
                 * named class that is to be matched against.  This isn't
                 * needed for \p{} and pseudo-classes, as they are not affected
                 * by locale, and hence are dealt with separately */
                if (! need_class) {
                    need_class = 1;
                    if (SIZE_ONLY) {
                        RExC_size += ANYOF_POSIXL_SKIP - ANYOF_SKIP;
                    }
                    else {
                        RExC_emit += ANYOF_POSIXL_SKIP - ANYOF_SKIP;
                    }
                    ANYOF_FLAGS(ret) |= ANYOF_MATCHES_POSIXL;
                    ANYOF_POSIXL_ZERO(ret);

                    /* We can't change this into some other type of node
                     * (unless this is the only element, in which case there
                     * are nodes that mean exactly this) as has runtime
                     * dependencies */
                    optimizable = FALSE;
                }

                /* Coverity thinks it is possible for this to be negative; both
                 * jhi and khw think it's not, but be safer */
                assert(! (ANYOF_FLAGS(ret) & ANYOF_MATCHES_POSIXL)
                       || (namedclass + ((namedclass % 2) ? -1 : 1)) >= 0);

                /* See if it already matches the complement of this POSIX
                 * class */
                if ((ANYOF_FLAGS(ret) & ANYOF_MATCHES_POSIXL)
                    && ANYOF_POSIXL_TEST(ret, namedclass + ((namedclass % 2)
                                                            ? -1
                                                            : 1)))
                {
                    posixl_matches_all = TRUE;
                    break;  /* No need to continue.  Since it matches both
                               e.g., \w and \W, it matches everything, and the
                               bracketed class can be optimized into qr/./s */
                }

                /* Add this class to those that should be checked at runtime */
                ANYOF_POSIXL_SET(ret, namedclass);

                /* The above-Latin1 characters are not subject to locale rules.
                 * Just add them, in the second pass, to the
                 * unconditionally-matched list */
                if (! SIZE_ONLY) {
                    SV* scratch_list = NULL;

                    /* Get the list of the above-Latin1 code points this
                     * matches */
                    _invlist_intersection_maybe_complement_2nd(PL_AboveLatin1,
                                          PL_XPosix_ptrs[classnum],

                                          /* Odd numbers are complements, like
                                           * NDIGIT, NASCII, ... */
                                          namedclass % 2 != 0,
                                          &scratch_list);
                    /* Checking if 'cp_list' is NULL first saves an extra
                     * clone.  Its reference count will be decremented at the
                     * next union, etc, or if this is the only instance, at the
                     * end of the routine */
                    if (! cp_list) {
                        cp_list = scratch_list;
                    }
                    else {
                        _invlist_union(cp_list, scratch_list, &cp_list);
                        SvREFCNT_dec_NN(scratch_list);
                    }
                    continue;   /* Go get next character */
                }
            }
            else if (! SIZE_ONLY) {

                /* Here, not in pass1 (in that pass we skip calculating the
                 * contents of this class), and is /l, or is a POSIX class for
                 * which /l doesn't matter (or is a Unicode property, which is
                 * skipped here). */
                if (namedclass >= ANYOF_POSIXL_MAX) {  /* If a special class */
                    if (namedclass != ANYOF_UNIPROP) { /* UNIPROP = \p and \P */

                        /* Here, should be \h, \H, \v, or \V.  None of /d, /i
                         * nor /l make a difference in what these match,
                         * therefore we just add what they match to cp_list. */
                        if (classnum != _CC_VERTSPACE) {
                            assert(   namedclass == ANYOF_HORIZWS
                                   || namedclass == ANYOF_NHORIZWS);

                            /* It turns out that \h is just a synonym for
                             * XPosixBlank */
                            classnum = _CC_BLANK;
                        }

                        _invlist_union_maybe_complement_2nd(
                                cp_list,
                                PL_XPosix_ptrs[classnum],
                                namedclass % 2 != 0,    /* Complement if odd
                                                          (NHORIZWS, NVERTWS)
                                                        */
                                &cp_list);
                    }
                }
                else if (UNI_SEMANTICS
                        || classnum == _CC_ASCII
                        || (DEPENDS_SEMANTICS && (classnum == _CC_DIGIT
                                                  || classnum == _CC_XDIGIT)))
                {
                    /* We usually have to worry about /d and /a affecting what
                     * POSIX classes match, with special code needed for /d
                     * because we won't know until runtime what all matches.
                     * But there is no extra work needed under /u, and
                     * [:ascii:] is unaffected by /a and /d; and :digit: and
                     * :xdigit: don't have runtime differences under /d.  So we
                     * can special case these, and avoid some extra work below,
                     * and at runtime. */
                    _invlist_union_maybe_complement_2nd(
                                                     simple_posixes,
                                                     PL_XPosix_ptrs[classnum],
                                                     namedclass % 2 != 0,
                                                     &simple_posixes);
                }
                else {  /* Garden variety class.  If is NUPPER, NALPHA, ...
                           complement and use nposixes */
                    SV** posixes_ptr = namedclass % 2 == 0
                                       ? &posixes
                                       : &nposixes;
                    _invlist_union_maybe_complement_2nd(
                                                     *posixes_ptr,
                                                     PL_XPosix_ptrs[classnum],
                                                     namedclass % 2 != 0,
                                                     posixes_ptr);
                }
            }
        } /* end of namedclass \blah */

        SKIP_BRACKETED_WHITE_SPACE(skip_white, RExC_parse);

        /* If 'range' is set, 'value' is the ending of a range--check its
         * validity.  (If value isn't a single code point in the case of a
         * range, we should have figured that out above in the code that
         * catches false ranges).  Later, we will handle each individual code
         * point in the range.  If 'range' isn't set, this could be the
         * beginning of a range, so check for that by looking ahead to see if
         * the next real character to be processed is the range indicator--the
         * minus sign */

        if (range) {
#ifdef EBCDIC
            /* For unicode ranges, we have to test that the Unicode as opposed
             * to the native values are not decreasing.  (Above 255, there is
             * no difference between native and Unicode) */
            if (unicode_range && prevvalue < 255 && value < 255) {
                if (NATIVE_TO_LATIN1(prevvalue) > NATIVE_TO_LATIN1(value)) {
                    goto backwards_range;
                }
            }
            else
#endif
            if (prevvalue > value) /* b-a */ {
                int w;
#ifdef EBCDIC
              backwards_range:
#endif
                w = RExC_parse - rangebegin;
                vFAIL2utf8f(
                    "Invalid [] range \"%"UTF8f"\"",
                    UTF8fARG(UTF, w, rangebegin));
                NOT_REACHED; /* NOTREACHED */
            }
        }
        else {
            prevvalue = value; /* save the beginning of the potential range */
            if (! stop_at_1     /* Can't be a range if parsing just one thing */
                && *RExC_parse == '-')
            {
                char* next_char_ptr = RExC_parse + 1;

                /* Get the next real char after the '-' */
                SKIP_BRACKETED_WHITE_SPACE(skip_white, next_char_ptr);

                /* If the '-' is at the end of the class (just before the ']',
                 * it is a literal minus; otherwise it is a range */
                if (next_char_ptr < RExC_end && *next_char_ptr != ']') {
                    RExC_parse = next_char_ptr;

                    /* a bad range like \w-, [:word:]- ? */
                    if (namedclass > OOB_NAMEDCLASS) {
                        if (strict || (PASS2 && ckWARN(WARN_REGEXP))) {
                            const int w = RExC_parse >= rangebegin
                                          ?  RExC_parse - rangebegin
                                          : 0;
                            if (strict) {
                                vFAIL4("False [] range \"%*.*s\"",
                                    w, w, rangebegin);
                            }
                            else if (PASS2) {
                                vWARN4(RExC_parse,
                                    "False [] range \"%*.*s\"",
                                    w, w, rangebegin);
                            }
                        }
                        if (!SIZE_ONLY) {
                            cp_list = add_cp_to_invlist(cp_list, '-');
                        }
                        element_count++;
                    } else
                        range = 1;      /* yeah, it's a range! */
                    continue;   /* but do it the next time */
                }
            }
        }

        if (namedclass > OOB_NAMEDCLASS) {
            continue;
        }

        /* Here, we have a single value this time through the loop, and
         * <prevvalue> is the beginning of the range, if any; or <value> if
         * not. */

        /* non-Latin1 code point implies unicode semantics.  Must be set in
         * pass1 so is there for the whole of pass 2 */
        if (value > 255) {
            REQUIRE_UNI_RULES(flagp, NULL);
        }

        /* Ready to process either the single value, or the completed range.
         * For single-valued non-inverted ranges, we consider the possibility
         * of multi-char folds.  (We made a conscious decision to not do this
         * for the other cases because it can often lead to non-intuitive
         * results.  For example, you have the peculiar case that:
         *  "s s" =~ /^[^\xDF]+$/i => Y
         *  "ss"  =~ /^[^\xDF]+$/i => N
         *
         * See [perl #89750] */
        if (FOLD && allow_multi_folds && value == prevvalue) {
            if (value == LATIN_SMALL_LETTER_SHARP_S
                || (value > 255 && _invlist_contains_cp(PL_HasMultiCharFold,
                                                        value)))
            {
                /* Here <value> is indeed a multi-char fold.  Get what it is */

                U8 foldbuf[UTF8_MAXBYTES_CASE];
                STRLEN foldlen;

                UV folded = _to_uni_fold_flags(
                                value,
                                foldbuf,
                                &foldlen,
                                FOLD_FLAGS_FULL | (ASCII_FOLD_RESTRICTED
                                                   ? FOLD_FLAGS_NOMIX_ASCII
                                                   : 0)
                                );

                /* Here, <folded> should be the first character of the
                 * multi-char fold of <value>, with <foldbuf> containing the
                 * whole thing.  But, if this fold is not allowed (because of
                 * the flags), <fold> will be the same as <value>, and should
                 * be processed like any other character, so skip the special
                 * handling */
                if (folded != value) {

                    /* Skip if we are recursed, currently parsing the class
                     * again.  Otherwise add this character to the list of
                     * multi-char folds. */
                    if (! RExC_in_multi_char_class) {
                        STRLEN cp_count = utf8_length(foldbuf,
                                                      foldbuf + foldlen);
                        SV* multi_fold = sv_2mortal(newSVpvs(""));

                        Perl_sv_catpvf(aTHX_ multi_fold, "\\x{%"UVXf"}", value);

                        multi_char_matches
                                        = add_multi_match(multi_char_matches,
                                                          multi_fold,
                                                          cp_count);

                    }

                    /* This element should not be processed further in this
                     * class */
                    element_count--;
                    value = save_value;
                    prevvalue = save_prevvalue;
                    continue;
                }
            }
        }

        if (strict && PASS2 && ckWARN(WARN_REGEXP)) {
            if (range) {

                /* If the range starts above 255, everything is portable and
                 * likely to be so for any forseeable character set, so don't
                 * warn. */
                if (unicode_range && non_portable_endpoint && prevvalue < 256) {
                    vWARN(RExC_parse, "Both or neither range ends should be Unicode");
                }
                else if (prevvalue != value) {

                    /* Under strict, ranges that stop and/or end in an ASCII
                     * printable should have each end point be a portable value
                     * for it (preferably like 'A', but we don't warn if it is
                     * a (portable) Unicode name or code point), and the range
                     * must be be all digits or all letters of the same case.
                     * Otherwise, the range is non-portable and unclear as to
                     * what it contains */
                    if ((isPRINT_A(prevvalue) || isPRINT_A(value))
                        && (non_portable_endpoint
                            || ! ((isDIGIT_A(prevvalue) && isDIGIT_A(value))
                                   || (isLOWER_A(prevvalue) && isLOWER_A(value))
                                   || (isUPPER_A(prevvalue) && isUPPER_A(value)))))
                    {
                        vWARN(RExC_parse, "Ranges of ASCII printables should be some subset of \"0-9\", \"A-Z\", or \"a-z\"");
                    }
                    else if (prevvalue >= 0x660) { /* ARABIC_INDIC_DIGIT_ZERO */

                        /* But the nature of Unicode and languages mean we
                         * can't do the same checks for above-ASCII ranges,
                         * except in the case of digit ones.  These should
                         * contain only digits from the same group of 10.  The
                         * ASCII case is handled just above.  0x660 is the
                         * first digit character beyond ASCII.  Hence here, the
                         * range could be a range of digits.  Find out.  */
                        IV index_start = _invlist_search(PL_XPosix_ptrs[_CC_DIGIT],
                                                         prevvalue);
                        IV index_final = _invlist_search(PL_XPosix_ptrs[_CC_DIGIT],
                                                         value);

                        /* If the range start and final points are in the same
                         * inversion list element, it means that either both
                         * are not digits, or both are digits in a consecutive
                         * sequence of digits.  (So far, Unicode has kept all
                         * such sequences as distinct groups of 10, but assert
                         * to make sure).  If the end points are not in the
                         * same element, neither should be a digit. */
                        if (index_start == index_final) {
                            assert(! ELEMENT_RANGE_MATCHES_INVLIST(index_start)
                            || (invlist_array(PL_XPosix_ptrs[_CC_DIGIT])[index_start+1]
                               - invlist_array(PL_XPosix_ptrs[_CC_DIGIT])[index_start]
                               == 10)
                               /* But actually Unicode did have one group of 11
                                * 'digits' in 5.2, so in case we are operating
                                * on that version, let that pass */
                            || (invlist_array(PL_XPosix_ptrs[_CC_DIGIT])[index_start+1]
                               - invlist_array(PL_XPosix_ptrs[_CC_DIGIT])[index_start]
                                == 11
                               && invlist_array(PL_XPosix_ptrs[_CC_DIGIT])[index_start]
                                == 0x19D0)
                            );
                        }
                        else if ((index_start >= 0
                                  && ELEMENT_RANGE_MATCHES_INVLIST(index_start))
                                 || (index_final >= 0
                                     && ELEMENT_RANGE_MATCHES_INVLIST(index_final)))
                        {
                            vWARN(RExC_parse, "Ranges of digits should be from the same group of 10");
                        }
                    }
                }
            }
            if ((! range || prevvalue == value) && non_portable_endpoint) {
                if (isPRINT_A(value)) {
                    char literal[3];
                    unsigned d = 0;
                    if (isBACKSLASHED_PUNCT(value)) {
                        literal[d++] = '\\';
                    }
                    literal[d++] = (char) value;
                    literal[d++] = '\0';

                    vWARN4(RExC_parse,
                           "\"%.*s\" is more clearly written simply as \"%s\"",
                           (int) (RExC_parse - rangebegin),
                           rangebegin,
                           literal
                        );
                }
                else if isMNEMONIC_CNTRL(value) {
                    vWARN4(RExC_parse,
                           "\"%.*s\" is more clearly written simply as \"%s\"",
                           (int) (RExC_parse - rangebegin),
                           rangebegin,
                           cntrl_to_mnemonic((U8) value)
                        );
                }
            }
        }

        /* Deal with this element of the class */
        if (! SIZE_ONLY) {

#ifndef EBCDIC
            cp_foldable_list = _add_range_to_invlist(cp_foldable_list,
                                                     prevvalue, value);
#else
            /* On non-ASCII platforms, for ranges that span all of 0..255, and
             * ones that don't require special handling, we can just add the
             * range like we do for ASCII platforms */
            if ((UNLIKELY(prevvalue == 0) && value >= 255)
                || ! (prevvalue < 256
                      && (unicode_range
                          || (! non_portable_endpoint
                              && ((isLOWER_A(prevvalue) && isLOWER_A(value))
                                  || (isUPPER_A(prevvalue)
                                      && isUPPER_A(value)))))))
            {
                cp_foldable_list = _add_range_to_invlist(cp_foldable_list,
                                                         prevvalue, value);
            }
            else {
                /* Here, requires special handling.  This can be because it is
                 * a range whose code points are considered to be Unicode, and
                 * so must be individually translated into native, or because
                 * its a subrange of 'A-Z' or 'a-z' which each aren't
                 * contiguous in EBCDIC, but we have defined them to include
                 * only the "expected" upper or lower case ASCII alphabetics.
                 * Subranges above 255 are the same in native and Unicode, so
                 * can be added as a range */
                U8 start = NATIVE_TO_LATIN1(prevvalue);
                unsigned j;
                U8 end = (value < 256) ? NATIVE_TO_LATIN1(value) : 255;
                for (j = start; j <= end; j++) {
                    cp_foldable_list = add_cp_to_invlist(cp_foldable_list, LATIN1_TO_NATIVE(j));
                }
                if (value > 255) {
                    cp_foldable_list = _add_range_to_invlist(cp_foldable_list,
                                                             256, value);
                }
            }
#endif
        }

        range = 0; /* this range (if it was one) is done now */
    } /* End of loop through all the text within the brackets */

    /* If anything in the class expands to more than one character, we have to
     * deal with them by building up a substitute parse string, and recursively
     * calling reg() on it, instead of proceeding */
    if (multi_char_matches) {
        SV * substitute_parse = newSVpvn_flags("?:", 2, SVs_TEMP);
        I32 cp_count;
        STRLEN len;
        char *save_end = RExC_end;
        char *save_parse = RExC_parse;
        char *save_start = RExC_start;
        STRLEN prefix_end = 0;      /* We copy the character class after a
                                       prefix supplied here.  This is the size
                                       + 1 of that prefix */
        bool first_time = TRUE;     /* First multi-char occurrence doesn't get
                                       a "|" */
        I32 reg_flags;

        assert(! invert);
        assert(RExC_precomp_adj == 0); /* Only one level of recursion allowed */

#if 0   /* Have decided not to deal with multi-char folds in inverted classes,
           because too confusing */
        if (invert) {
            sv_catpv(substitute_parse, "(?:");
        }
#endif

        /* Look at the longest folds first */
        for (cp_count = av_tindex(multi_char_matches); cp_count > 0; cp_count--) {

            if (av_exists(multi_char_matches, cp_count)) {
                AV** this_array_ptr;
                SV* this_sequence;

                this_array_ptr = (AV**) av_fetch(multi_char_matches,
                                                 cp_count, FALSE);
                while ((this_sequence = av_pop(*this_array_ptr)) !=
                                                                &PL_sv_undef)
                {
                    if (! first_time) {
                        sv_catpv(substitute_parse, "|");
                    }
                    first_time = FALSE;

                    sv_catpv(substitute_parse, SvPVX(this_sequence));
                }
            }
        }

        /* If the character class contains anything else besides these
         * multi-character folds, have to include it in recursive parsing */
        if (element_count) {
            sv_catpv(substitute_parse, "|[");
            prefix_end = SvCUR(substitute_parse);
            sv_catpvn(substitute_parse, orig_parse, RExC_parse - orig_parse);

            /* Put in a closing ']' only if not going off the end, as otherwise
             * we are adding something that really isn't there */
            if (RExC_parse < RExC_end) {
                sv_catpv(substitute_parse, "]");
            }
        }

        sv_catpv(substitute_parse, ")");
#if 0
        if (invert) {
            /* This is a way to get the parse to skip forward a whole named
             * sequence instead of matching the 2nd character when it fails the
             * first */
            sv_catpv(substitute_parse, "(*THEN)(*SKIP)(*FAIL)|.)");
        }
#endif

        /* Set up the data structure so that any errors will be properly
         * reported.  See the comments at the definition of
         * REPORT_LOCATION_ARGS for details */
        RExC_precomp_adj = orig_parse - RExC_precomp;
        RExC_start =  RExC_parse = SvPV(substitute_parse, len);
        RExC_adjusted_start = RExC_start + prefix_end;
        RExC_end = RExC_parse + len;
        RExC_in_multi_char_class = 1;
        RExC_override_recoding = 1;
        RExC_emit = (regnode *)orig_emit;

        ret = reg(pRExC_state, 1, &reg_flags, depth+1);

        *flagp |= reg_flags&(HASWIDTH|SIMPLE|SPSTART|POSTPONED|RESTART_PASS1|NEED_UTF8);

        /* And restore so can parse the rest of the pattern */
        RExC_parse = save_parse;
        RExC_start = RExC_adjusted_start = save_start;
        RExC_precomp_adj = 0;
        RExC_end = save_end;
        RExC_in_multi_char_class = 0;
        RExC_override_recoding = 0;
        SvREFCNT_dec_NN(multi_char_matches);
        return ret;
    }

    /* Here, we've gone through the entire class and dealt with multi-char
     * folds.  We are now in a position that we can do some checks to see if we
     * can optimize this ANYOF node into a simpler one, even in Pass 1.
     * Currently we only do two checks:
     * 1) is in the unlikely event that the user has specified both, eg. \w and
     *    \W under /l, then the class matches everything.  (This optimization
     *    is done only to make the optimizer code run later work.)
     * 2) if the character class contains only a single element (including a
     *    single range), we see if there is an equivalent node for it.
     * Other checks are possible */
    if (   optimizable
        && ! ret_invlist   /* Can't optimize if returning the constructed
                              inversion list */
        && (UNLIKELY(posixl_matches_all) || element_count == 1))
    {
        U8 op = END;
        U8 arg = 0;

        if (UNLIKELY(posixl_matches_all)) {
            op = SANY;
        }
        else if (namedclass > OOB_NAMEDCLASS) { /* this is a single named
                                                   class, like \w or [:digit:]
                                                   or \p{foo} */

            /* All named classes are mapped into POSIXish nodes, with its FLAG
             * argument giving which class it is */
            switch ((I32)namedclass) {
                case ANYOF_UNIPROP:
                    break;

                /* These don't depend on the charset modifiers.  They always
                 * match under /u rules */
                case ANYOF_NHORIZWS:
                case ANYOF_HORIZWS:
                    namedclass = ANYOF_BLANK + namedclass - ANYOF_HORIZWS;
                    /* FALLTHROUGH */

                case ANYOF_NVERTWS:
                case ANYOF_VERTWS:
                    op = POSIXU;
                    goto join_posix;

                /* The actual POSIXish node for all the rest depends on the
                 * charset modifier.  The ones in the first set depend only on
                 * ASCII or, if available on this platform, also locale */
                case ANYOF_ASCII:
                case ANYOF_NASCII:
#ifdef HAS_ISASCII
                    op = (LOC) ? POSIXL : POSIXA;
#else
                    op = POSIXA;
#endif
                    goto join_posix;

                /* The following don't have any matches in the upper Latin1
                 * range, hence /d is equivalent to /u for them.  Making it /u
                 * saves some branches at runtime */
                case ANYOF_DIGIT:
                case ANYOF_NDIGIT:
                case ANYOF_XDIGIT:
                case ANYOF_NXDIGIT:
                    if (! DEPENDS_SEMANTICS) {
                        goto treat_as_default;
                    }

                    op = POSIXU;
                    goto join_posix;

                /* The following change to CASED under /i */
                case ANYOF_LOWER:
                case ANYOF_NLOWER:
                case ANYOF_UPPER:
                case ANYOF_NUPPER:
                    if (FOLD) {
                        namedclass = ANYOF_CASED + (namedclass % 2);
                    }
                    /* FALLTHROUGH */

                /* The rest have more possibilities depending on the charset.
                 * We take advantage of the enum ordering of the charset
                 * modifiers to get the exact node type, */
                default:
                  treat_as_default:
                    op = POSIXD + get_regex_charset(RExC_flags);
                    if (op > POSIXA) { /* /aa is same as /a */
                        op = POSIXA;
                    }

                  join_posix:
                    /* The odd numbered ones are the complements of the
                     * next-lower even number one */
                    if (namedclass % 2 == 1) {
                        invert = ! invert;
                        namedclass--;
                    }
                    arg = namedclass_to_classnum(namedclass);
                    break;
            }
        }
        else if (value == prevvalue) {

            /* Here, the class consists of just a single code point */

            if (invert) {
                if (! LOC && value == '\n') {
                    op = REG_ANY; /* Optimize [^\n] */
                    *flagp |= HASWIDTH|SIMPLE;
                    MARK_NAUGHTY(1);
                }
            }
            else if (value < 256 || UTF) {

                /* Optimize a single value into an EXACTish node, but not if it
                 * would require converting the pattern to UTF-8. */
                op = compute_EXACTish(pRExC_state);
            }
        } /* Otherwise is a range */
        else if (! LOC) {   /* locale could vary these */
            if (prevvalue == '0') {
                if (value == '9') {
                    arg = _CC_DIGIT;
                    op = POSIXA;
                }
            }
            else if (! FOLD || ASCII_FOLD_RESTRICTED) {
                /* We can optimize A-Z or a-z, but not if they could match
                 * something like the KELVIN SIGN under /i. */
                if (prevvalue == 'A') {
                    if (value == 'Z'
#ifdef EBCDIC
                        && ! non_portable_endpoint
#endif
                    ) {
                        arg = (FOLD) ? _CC_ALPHA : _CC_UPPER;
                        op = POSIXA;
                    }
                }
                else if (prevvalue == 'a') {
                    if (value == 'z'
#ifdef EBCDIC
                        && ! non_portable_endpoint
#endif
                    ) {
                        arg = (FOLD) ? _CC_ALPHA : _CC_LOWER;
                        op = POSIXA;
                    }
                }
            }
        }

        /* Here, we have changed <op> away from its initial value iff we found
         * an optimization */
        if (op != END) {

            /* Throw away this ANYOF regnode, and emit the calculated one,
             * which should correspond to the beginning, not current, state of
             * the parse */
            const char * cur_parse = RExC_parse;
            RExC_parse = (char *)orig_parse;
            if ( SIZE_ONLY) {
                if (! LOC) {

                    /* To get locale nodes to not use the full ANYOF size would
                     * require moving the code above that writes the portions
                     * of it that aren't in other nodes to after this point.
                     * e.g.  ANYOF_POSIXL_SET */
                    RExC_size = orig_size;
                }
            }
            else {
                RExC_emit = (regnode *)orig_emit;
                if (PL_regkind[op] == POSIXD) {
                    if (op == POSIXL) {
                        RExC_contains_locale = 1;
                    }
                    if (invert) {
                        op += NPOSIXD - POSIXD;
                    }
                }
            }

            ret = reg_node(pRExC_state, op);

            if (PL_regkind[op] == POSIXD || PL_regkind[op] == NPOSIXD) {
                if (! SIZE_ONLY) {
                    FLAGS(ret) = arg;
                }
                *flagp |= HASWIDTH|SIMPLE;
            }
            else if (PL_regkind[op] == EXACT) {
                alloc_maybe_populate_EXACT(pRExC_state, ret, flagp, 0, value,
                                           TRUE /* downgradable to EXACT */
                                           );
            }

            RExC_parse = (char *) cur_parse;

            SvREFCNT_dec(posixes);
            SvREFCNT_dec(nposixes);
            SvREFCNT_dec(simple_posixes);
            SvREFCNT_dec(cp_list);
            SvREFCNT_dec(cp_foldable_list);
            return ret;
        }
    }

    if (SIZE_ONLY)
        return ret;
    /****** !SIZE_ONLY (Pass 2) AFTER HERE *********/

    /* If folding, we calculate all characters that could fold to or from the
     * ones already on the list */
    if (cp_foldable_list) {
        if (FOLD) {
            UV start, end;      /* End points of code point ranges */

            SV* fold_intersection = NULL;
            SV** use_list;

            /* Our calculated list will be for Unicode rules.  For locale
             * matching, we have to keep a separate list that is consulted at
             * runtime only when the locale indicates Unicode rules.  For
             * non-locale, we just use the general list */
            if (LOC) {
                use_list = &only_utf8_locale_list;
            }
            else {
                use_list = &cp_list;
            }

            /* Only the characters in this class that participate in folds need
             * be checked.  Get the intersection of this class and all the
             * possible characters that are foldable.  This can quickly narrow
             * down a large class */
            _invlist_intersection(PL_utf8_foldable, cp_foldable_list,
                                  &fold_intersection);

            /* The folds for all the Latin1 characters are hard-coded into this
             * program, but we have to go out to disk to get the others. */
            if (invlist_highest(cp_foldable_list) >= 256) {

                /* This is a hash that for a particular fold gives all
                 * characters that are involved in it */
                if (! PL_utf8_foldclosures) {
                    _load_PL_utf8_foldclosures();
                }
            }

            /* Now look at the foldable characters in this class individually */
            invlist_iterinit(fold_intersection);
            while (invlist_iternext(fold_intersection, &start, &end)) {
                UV j;

                /* Look at every character in the range */
                for (j = start; j <= end; j++) {
                    U8 foldbuf[UTF8_MAXBYTES_CASE+1];
                    STRLEN foldlen;
                    SV** listp;

                    if (j < 256) {

                        if (IS_IN_SOME_FOLD_L1(j)) {

                            /* ASCII is always matched; non-ASCII is matched
                             * only under Unicode rules (which could happen
                             * under /l if the locale is a UTF-8 one */
                            if (isASCII(j) || ! DEPENDS_SEMANTICS) {
                                *use_list = add_cp_to_invlist(*use_list,
                                                            PL_fold_latin1[j]);
                            }
                            else {
                                has_upper_latin1_only_utf8_matches
                                    = add_cp_to_invlist(
                                            has_upper_latin1_only_utf8_matches,
                                            PL_fold_latin1[j]);
                            }
                        }

                        if (HAS_NONLATIN1_SIMPLE_FOLD_CLOSURE(j)
                            && (! isASCII(j) || ! ASCII_FOLD_RESTRICTED))
                        {
                            add_above_Latin1_folds(pRExC_state,
                                                   (U8) j,
                                                   use_list);
                        }
                        continue;
                    }

                    /* Here is an above Latin1 character.  We don't have the
                     * rules hard-coded for it.  First, get its fold.  This is
                     * the simple fold, as the multi-character folds have been
                     * handled earlier and separated out */
                    _to_uni_fold_flags(j, foldbuf, &foldlen,
                                                        (ASCII_FOLD_RESTRICTED)
                                                        ? FOLD_FLAGS_NOMIX_ASCII
                                                        : 0);

                    /* Single character fold of above Latin1.  Add everything in
                    * its fold closure to the list that this node should match.
                    * The fold closures data structure is a hash with the keys
                    * being the UTF-8 of every character that is folded to, like
                    * 'k', and the values each an array of all code points that
                    * fold to its key.  e.g. [ 'k', 'K', KELVIN_SIGN ].
                    * Multi-character folds are not included */
                    if ((listp = hv_fetch(PL_utf8_foldclosures,
                                        (char *) foldbuf, foldlen, FALSE)))
                    {
                        AV* list = (AV*) *listp;
                        IV k;
                        for (k = 0; k <= av_tindex(list); k++) {
                            SV** c_p = av_fetch(list, k, FALSE);
                            UV c;
                            assert(c_p);

                            c = SvUV(*c_p);

                            /* /aa doesn't allow folds between ASCII and non- */
                            if ((ASCII_FOLD_RESTRICTED
                                && (isASCII(c) != isASCII(j))))
                            {
                                continue;
                            }

                            /* Folds under /l which cross the 255/256 boundary
                             * are added to a separate list.  (These are valid
                             * only when the locale is UTF-8.) */
                            if (c < 256 && LOC) {
                                *use_list = add_cp_to_invlist(*use_list, c);
                                continue;
                            }

                            if (isASCII(c) || c > 255 || AT_LEAST_UNI_SEMANTICS)
                            {
                                cp_list = add_cp_to_invlist(cp_list, c);
                            }
                            else {
                                /* Similarly folds involving non-ascii Latin1
                                * characters under /d are added to their list */
                                has_upper_latin1_only_utf8_matches
                                        = add_cp_to_invlist(
                                           has_upper_latin1_only_utf8_matches,
                                           c);
                            }
                        }
                    }
                }
            }
            SvREFCNT_dec_NN(fold_intersection);
        }

        /* Now that we have finished adding all the folds, there is no reason
         * to keep the foldable list separate */
        _invlist_union(cp_list, cp_foldable_list, &cp_list);
        SvREFCNT_dec_NN(cp_foldable_list);
    }

    /* And combine the result (if any) with any inversion list from posix
     * classes.  The lists are kept separate up to now because we don't want to
     * fold the classes (folding of those is automatically handled by the swash
     * fetching code) */
    if (simple_posixes) {
        _invlist_union(cp_list, simple_posixes, &cp_list);
        SvREFCNT_dec_NN(simple_posixes);
    }
    if (posixes || nposixes) {
        if (posixes && AT_LEAST_ASCII_RESTRICTED) {
            /* Under /a and /aa, nothing above ASCII matches these */
            _invlist_intersection(posixes,
                                  PL_XPosix_ptrs[_CC_ASCII],
                                  &posixes);
        }
        if (nposixes) {
            if (DEPENDS_SEMANTICS) {
                /* Under /d, everything in the upper half of the Latin1 range
                 * matches these complements */
                ANYOF_FLAGS(ret) |= ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER;
            }
            else if (AT_LEAST_ASCII_RESTRICTED) {
                /* Under /a and /aa, everything above ASCII matches these
                 * complements */
                _invlist_union_complement_2nd(nposixes,
                                              PL_XPosix_ptrs[_CC_ASCII],
                                              &nposixes);
            }
            if (posixes) {
                _invlist_union(posixes, nposixes, &posixes);
                SvREFCNT_dec_NN(nposixes);
            }
            else {
                posixes = nposixes;
            }
        }
        if (! DEPENDS_SEMANTICS) {
            if (cp_list) {
                _invlist_union(cp_list, posixes, &cp_list);
                SvREFCNT_dec_NN(posixes);
            }
            else {
                cp_list = posixes;
            }
        }
        else {
            /* Under /d, we put into a separate list the Latin1 things that
             * match only when the target string is utf8 */
            SV* nonascii_but_latin1_properties = NULL;
            _invlist_intersection(posixes, PL_UpperLatin1,
                                  &nonascii_but_latin1_properties);
            _invlist_subtract(posixes, nonascii_but_latin1_properties,
                              &posixes);
            if (cp_list) {
                _invlist_union(cp_list, posixes, &cp_list);
                SvREFCNT_dec_NN(posixes);
            }
            else {
                cp_list = posixes;
            }

            if (has_upper_latin1_only_utf8_matches) {
                _invlist_union(has_upper_latin1_only_utf8_matches,
                               nonascii_but_latin1_properties,
                               &has_upper_latin1_only_utf8_matches);
                SvREFCNT_dec_NN(nonascii_but_latin1_properties);
            }
            else {
                has_upper_latin1_only_utf8_matches
                                            = nonascii_but_latin1_properties;
            }
        }
    }

    /* And combine the result (if any) with any inversion list from properties.
     * The lists are kept separate up to now so that we can distinguish the two
     * in regards to matching above-Unicode.  A run-time warning is generated
     * if a Unicode property is matched against a non-Unicode code point. But,
     * we allow user-defined properties to match anything, without any warning,
     * and we also suppress the warning if there is a portion of the character
     * class that isn't a Unicode property, and which matches above Unicode, \W
     * or [\x{110000}] for example.
     * (Note that in this case, unlike the Posix one above, there is no
     * <has_upper_latin1_only_utf8_matches>, because having a Unicode property
     * forces Unicode semantics */
    if (properties) {
        if (cp_list) {

            /* If it matters to the final outcome, see if a non-property
             * component of the class matches above Unicode.  If so, the
             * warning gets suppressed.  This is true even if just a single
             * such code point is specified, as, though not strictly correct if
             * another such code point is matched against, the fact that they
             * are using above-Unicode code points indicates they should know
             * the issues involved */
            if (warn_super) {
                warn_super = ! (invert
                               ^ (invlist_highest(cp_list) > PERL_UNICODE_MAX));
            }

            _invlist_union(properties, cp_list, &cp_list);
            SvREFCNT_dec_NN(properties);
        }
        else {
            cp_list = properties;
        }

        if (warn_super) {
            ANYOF_FLAGS(ret)
             |= ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER;

            /* Because an ANYOF node is the only one that warns, this node
             * can't be optimized into something else */
            optimizable = FALSE;
        }
    }

    /* Here, we have calculated what code points should be in the character
     * class.
     *
     * Now we can see about various optimizations.  Fold calculation (which we
     * did above) needs to take place before inversion.  Otherwise /[^k]/i
     * would invert to include K, which under /i would match k, which it
     * shouldn't.  Therefore we can't invert folded locale now, as it won't be
     * folded until runtime */

    /* If we didn't do folding, it's because some information isn't available
     * until runtime; set the run-time fold flag for these.  (We don't have to
     * worry about properties folding, as that is taken care of by the swash
     * fetching).  We know to set the flag if we have a non-NULL list for UTF-8
     * locales, or the class matches at least one 0-255 range code point */
    if (LOC && FOLD) {

        /* Some things on the list might be unconditionally included because of
         * other components.  Remove them, and clean up the list if it goes to
         * 0 elements */
        if (only_utf8_locale_list && cp_list) {
            _invlist_subtract(only_utf8_locale_list, cp_list,
                              &only_utf8_locale_list);

            if (_invlist_len(only_utf8_locale_list) == 0) {
                SvREFCNT_dec_NN(only_utf8_locale_list);
                only_utf8_locale_list = NULL;
            }
        }
        if (only_utf8_locale_list) {
            ANYOF_FLAGS(ret)
                 |=  ANYOFL_FOLD
                    |ANYOFL_SHARED_UTF8_LOCALE_fold_HAS_MATCHES_nonfold_REQD;
        }
        else if (cp_list) { /* Look to see if a 0-255 code point is in list */
            UV start, end;
            invlist_iterinit(cp_list);
            if (invlist_iternext(cp_list, &start, &end) && start < 256) {
                ANYOF_FLAGS(ret) |= ANYOFL_FOLD;
            }
            invlist_iterfinish(cp_list);
        }
    }

#define MATCHES_ALL_NON_UTF8_NON_ASCII(ret)                                 \
    (   DEPENDS_SEMANTICS                                                   \
     && (ANYOF_FLAGS(ret)                                                   \
        & ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER))

    /* See if we can simplify things under /d */
    if (   has_upper_latin1_only_utf8_matches
        || MATCHES_ALL_NON_UTF8_NON_ASCII(ret))
    {
        /* But not if we are inverting, as that screws it up */
        if (! invert) {
            if (has_upper_latin1_only_utf8_matches) {
                if (MATCHES_ALL_NON_UTF8_NON_ASCII(ret)) {

                    /* Here, we have both the flag and inversion list.  Any
                     * character in 'has_upper_latin1_only_utf8_matches'
                     * matches when UTF-8 is in effect, but it also matches
                     * when UTF-8 is not in effect because of
                     * MATCHES_ALL_NON_UTF8_NON_ASCII.  Therefore it matches
                     * unconditionally, so can be added to the regular list,
                     * and 'has_upper_latin1_only_utf8_matches' cleared */
                    _invlist_union(cp_list,
                                   has_upper_latin1_only_utf8_matches,
                                   &cp_list);
                    SvREFCNT_dec_NN(has_upper_latin1_only_utf8_matches);
                    has_upper_latin1_only_utf8_matches = NULL;
                }
                else if (cp_list) {

                    /* Here, 'cp_list' gives chars that always match, and
                     * 'has_upper_latin1_only_utf8_matches' gives chars that
                     * were specified to match only if the target string is in
                     * UTF-8.  It may be that these overlap, so we can subtract
                     * the unconditionally matching from the conditional ones,
                     * to make the conditional list as small as possible,
                     * perhaps even clearing it, in which case more
                     * optimizations are possible later */
                    _invlist_subtract(has_upper_latin1_only_utf8_matches,
                                      cp_list,
                                      &has_upper_latin1_only_utf8_matches);
                    if (_invlist_len(has_upper_latin1_only_utf8_matches) == 0) {
                        SvREFCNT_dec_NN(has_upper_latin1_only_utf8_matches);
                        has_upper_latin1_only_utf8_matches = NULL;
                    }
                }
            }

            /* Similarly, if the unconditional matches include every upper
             * latin1 character, we can clear that flag to permit later
             * optimizations */
            if (cp_list && MATCHES_ALL_NON_UTF8_NON_ASCII(ret)) {
                SV* only_non_utf8_list = invlist_clone(PL_UpperLatin1);
                _invlist_subtract(only_non_utf8_list, cp_list,
                                  &only_non_utf8_list);
                if (_invlist_len(only_non_utf8_list) == 0) {
                    ANYOF_FLAGS(ret) &= ~ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER;
                }
                SvREFCNT_dec_NN(only_non_utf8_list);
                only_non_utf8_list = NULL;;
            }
        }

        /* If we haven't gotten rid of all conditional matching, we change the
         * regnode type to indicate that */
        if (   has_upper_latin1_only_utf8_matches
            || MATCHES_ALL_NON_UTF8_NON_ASCII(ret))
        {
            OP(ret) = ANYOFD;
            optimizable = FALSE;
        }
    }
#undef MATCHES_ALL_NON_UTF8_NON_ASCII

    /* Optimize inverted simple patterns (e.g. [^a-z]) when everything is known
     * at compile time.  Besides not inverting folded locale now, we can't
     * invert if there are things such as \w, which aren't known until runtime
     * */
    if (cp_list
        && invert
        && OP(ret) != ANYOFD
        && ! (ANYOF_FLAGS(ret) & (ANYOF_LOCALE_FLAGS))
        && ! HAS_NONLOCALE_RUNTIME_PROPERTY_DEFINITION)
    {
        _invlist_invert(cp_list);

        /* Any swash can't be used as-is, because we've inverted things */
        if (swash) {
            SvREFCNT_dec_NN(swash);
            swash = NULL;
        }

        /* Clear the invert flag since have just done it here */
        invert = FALSE;
    }

    if (ret_invlist) {
        assert(cp_list);

        *ret_invlist = cp_list;
        SvREFCNT_dec(swash);

        /* Discard the generated node */
        if (SIZE_ONLY) {
            RExC_size = orig_size;
        }
        else {
            RExC_emit = orig_emit;
        }
        return orig_emit;
    }

    /* Some character classes are equivalent to other nodes.  Such nodes take
     * up less room and generally fewer operations to execute than ANYOF nodes.
     * Above, we checked for and optimized into some such equivalents for
     * certain common classes that are easy to test.  Getting to this point in
     * the code means that the class didn't get optimized there.  Since this
     * code is only executed in Pass 2, it is too late to save space--it has
     * been allocated in Pass 1, and currently isn't given back.  But turning
     * things into an EXACTish node can allow the optimizer to join it to any
     * adjacent such nodes.  And if the class is equivalent to things like /./,
     * expensive run-time swashes can be avoided.  Now that we have more
     * complete information, we can find things necessarily missed by the
     * earlier code.  Another possible "optimization" that isn't done is that
     * something like [Ee] could be changed into an EXACTFU.  khw tried this
     * and found that the ANYOF is faster, including for code points not in the
     * bitmap.  This still might make sense to do, provided it got joined with
     * an adjacent node(s) to create a longer EXACTFU one.  This could be
     * accomplished by creating a pseudo ANYOF_EXACTFU node type that the join
     * routine would know is joinable.  If that didn't happen, the node type
     * could then be made a straight ANYOF */

    if (optimizable && cp_list && ! invert) {
        UV start, end;
        U8 op = END;  /* The optimzation node-type */
        int posix_class = -1;   /* Illegal value */
        const char * cur_parse= RExC_parse;

        invlist_iterinit(cp_list);
        if (! invlist_iternext(cp_list, &start, &end)) {

            /* Here, the list is empty.  This happens, for example, when a
             * Unicode property that doesn't match anything is the only element
             * in the character class (perluniprops.pod notes such properties).
             * */
            op = OPFAIL;
            *flagp |= HASWIDTH|SIMPLE;
        }
        else if (start == end) {    /* The range is a single code point */
            if (! invlist_iternext(cp_list, &start, &end)

                    /* Don't do this optimization if it would require changing
                     * the pattern to UTF-8 */
                && (start < 256 || UTF))
            {
                /* Here, the list contains a single code point.  Can optimize
                 * into an EXACTish node */

                value = start;

                if (! FOLD) {
                    op = (LOC)
                         ? EXACTL
                         : EXACT;
                }
                else if (LOC) {

                    /* A locale node under folding with one code point can be
                     * an EXACTFL, as its fold won't be calculated until
                     * runtime */
                    op = EXACTFL;
                }
                else {

                    /* Here, we are generally folding, but there is only one
                     * code point to match.  If we have to, we use an EXACT
                     * node, but it would be better for joining with adjacent
                     * nodes in the optimization pass if we used the same
                     * EXACTFish node that any such are likely to be.  We can
                     * do this iff the code point doesn't participate in any
                     * folds.  For example, an EXACTF of a colon is the same as
                     * an EXACT one, since nothing folds to or from a colon. */
                    if (value < 256) {
                        if (IS_IN_SOME_FOLD_L1(value)) {
                            op = EXACT;
                        }
                    }
                    else {
                        if (_invlist_contains_cp(PL_utf8_foldable, value)) {
                            op = EXACT;
                        }
                    }

                    /* If we haven't found the node type, above, it means we
                     * can use the prevailing one */
                    if (op == END) {
                        op = compute_EXACTish(pRExC_state);
                    }
                }
            }
        }   /* End of first range contains just a single code point */
        else if (start == 0) {
            if (end == UV_MAX) {
                op = SANY;
                *flagp |= HASWIDTH|SIMPLE;
                MARK_NAUGHTY(1);
            }
            else if (end == '\n' - 1
                    && invlist_iternext(cp_list, &start, &end)
                    && start == '\n' + 1 && end == UV_MAX)
            {
                op = REG_ANY;
                *flagp |= HASWIDTH|SIMPLE;
                MARK_NAUGHTY(1);
            }
        }
        invlist_iterfinish(cp_list);

        if (op == END) {
            const UV cp_list_len = _invlist_len(cp_list);
            const UV* cp_list_array = invlist_array(cp_list);

            /* Here, didn't find an optimization.  See if this matches any of
             * the POSIX classes.  These run slightly faster for above-Unicode
             * code points, so don't bother with POSIXA ones nor the 2 that
             * have no above-Unicode matches.  We can avoid these checks unless
             * the ANYOF matches at least as high as the lowest POSIX one
             * (which was manually found to be \v.  The actual code point may
             * increase in later Unicode releases, if a higher code point is
             * assigned to be \v, but this code will never break.  It would
             * just mean we could execute the checks for posix optimizations
             * unnecessarily) */

            if (cp_list_array[cp_list_len-1] > 0x2029) {
                for (posix_class = 0;
                     posix_class <= _HIGHEST_REGCOMP_DOT_H_SYNC;
                     posix_class++)
                {
                    int try_inverted;
                    if (posix_class == _CC_ASCII || posix_class == _CC_CNTRL) {
                        continue;
                    }
                    for (try_inverted = 0; try_inverted < 2; try_inverted++) {

                        /* Check if matches normal or inverted */
                        if (_invlistEQ(cp_list,
                                       PL_XPosix_ptrs[posix_class],
                                       try_inverted))
                        {
                            op = (try_inverted)
                                 ? NPOSIXU
                                 : POSIXU;
                            *flagp |= HASWIDTH|SIMPLE;
                            goto found_posix;
                        }
                    }
                }
              found_posix: ;
            }
        }

        if (op != END) {
            RExC_parse = (char *)orig_parse;
            RExC_emit = (regnode *)orig_emit;

            if (regarglen[op]) {
                ret = reganode(pRExC_state, op, 0);
            } else {
                ret = reg_node(pRExC_state, op);
            }

            RExC_parse = (char *)cur_parse;

            if (PL_regkind[op] == EXACT) {
                alloc_maybe_populate_EXACT(pRExC_state, ret, flagp, 0, value,
                                           TRUE /* downgradable to EXACT */
                                          );
            }
            else if (PL_regkind[op] == POSIXD || PL_regkind[op] == NPOSIXD) {
                FLAGS(ret) = posix_class;
            }

            SvREFCNT_dec_NN(cp_list);
            return ret;
        }
    }

    /* Here, <cp_list> contains all the code points we can determine at
     * compile time that match under all conditions.  Go through it, and
     * for things that belong in the bitmap, put them there, and delete from
     * <cp_list>.  While we are at it, see if everything above 255 is in the
     * list, and if so, set a flag to speed up execution */

    populate_ANYOF_from_invlist(ret, &cp_list);

    if (invert) {
        ANYOF_FLAGS(ret) |= ANYOF_INVERT;
    }

    /* Here, the bitmap has been populated with all the Latin1 code points that
     * always match.  Can now add to the overall list those that match only
     * when the target string is UTF-8 (<has_upper_latin1_only_utf8_matches>).
     * */
    if (has_upper_latin1_only_utf8_matches) {
        if (cp_list) {
            _invlist_union(cp_list,
                           has_upper_latin1_only_utf8_matches,
                           &cp_list);
            SvREFCNT_dec_NN(has_upper_latin1_only_utf8_matches);
        }
        else {
            cp_list = has_upper_latin1_only_utf8_matches;
        }
        ANYOF_FLAGS(ret) |= ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP;
    }

    /* If there is a swash and more than one element, we can't use the swash in
     * the optimization below. */
    if (swash && element_count > 1) {
        SvREFCNT_dec_NN(swash);
        swash = NULL;
    }

    /* Note that the optimization of using 'swash' if it is the only thing in
     * the class doesn't have us change swash at all, so it can include things
     * that are also in the bitmap; otherwise we have purposely deleted that
     * duplicate information */
    set_ANYOF_arg(pRExC_state, ret, cp_list,
                  (HAS_NONLOCALE_RUNTIME_PROPERTY_DEFINITION)
                   ? listsv : NULL,
                  only_utf8_locale_list,
                  swash, has_user_defined_property);

    *flagp |= HASWIDTH|SIMPLE;

    if (ANYOF_FLAGS(ret) & ANYOF_LOCALE_FLAGS) {
        RExC_contains_locale = 1;
    }

    return ret;
}

#undef HAS_NONLOCALE_RUNTIME_PROPERTY_DEFINITION

STATIC void
S_set_ANYOF_arg(pTHX_ RExC_state_t* const pRExC_state,
                regnode* const node,
                SV* const cp_list,
                SV* const runtime_defns,
                SV* const only_utf8_locale_list,
                SV* const swash,
                const bool has_user_defined_property)
{
    /* Sets the arg field of an ANYOF-type node 'node', using information about
     * the node passed-in.  If there is nothing outside the node's bitmap, the
     * arg is set to ANYOF_ONLY_HAS_BITMAP.  Otherwise, it sets the argument to
     * the count returned by add_data(), having allocated and stored an array,
     * av, that that count references, as follows:
     *  av[0] stores the character class description in its textual form.
     *        This is used later (regexec.c:Perl_regclass_swash()) to
     *        initialize the appropriate swash, and is also useful for dumping
     *        the regnode.  This is set to &PL_sv_undef if the textual
     *        description is not needed at run-time (as happens if the other
     *        elements completely define the class)
     *  av[1] if &PL_sv_undef, is a placeholder to later contain the swash
     *        computed from av[0].  But if no further computation need be done,
     *        the swash is stored here now (and av[0] is &PL_sv_undef).
     *  av[2] stores the inversion list of code points that match only if the
     *        current locale is UTF-8
     *  av[3] stores the cp_list inversion list for use in addition or instead
     *        of av[0]; used only if cp_list exists and av[1] is &PL_sv_undef.
     *        (Otherwise everything needed is already in av[0] and av[1])
     *  av[4] is set if any component of the class is from a user-defined
     *        property; used only if av[3] exists */

    UV n;

    PERL_ARGS_ASSERT_SET_ANYOF_ARG;

    if (! cp_list && ! runtime_defns && ! only_utf8_locale_list) {
        assert(! (ANYOF_FLAGS(node)
                & ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP));
        ARG_SET(node, ANYOF_ONLY_HAS_BITMAP);
    }
    else {
        AV * const av = newAV();
        SV *rv;

        av_store(av, 0, (runtime_defns)
                        ? SvREFCNT_inc(runtime_defns) : &PL_sv_undef);
        if (swash) {
            assert(cp_list);
            av_store(av, 1, swash);
            SvREFCNT_dec_NN(cp_list);
        }
        else {
            av_store(av, 1, &PL_sv_undef);
            if (cp_list) {
                av_store(av, 3, cp_list);
                av_store(av, 4, newSVuv(has_user_defined_property));
            }
        }

        if (only_utf8_locale_list) {
            av_store(av, 2, only_utf8_locale_list);
        }
        else {
            av_store(av, 2, &PL_sv_undef);
        }

        rv = newRV_noinc(MUTABLE_SV(av));
        n = add_data(pRExC_state, STR_WITH_LEN("s"));
        RExC_rxi->data->data[n] = (void*)rv;
        ARG_SET(node, n);
    }
}

#if !defined(PERL_IN_XSUB_RE) || defined(PLUGGABLE_RE_EXTENSION)
SV *
Perl__get_regclass_nonbitmap_data(pTHX_ const regexp *prog,
                                        const regnode* node,
                                        bool doinit,
                                        SV** listsvp,
                                        SV** only_utf8_locale_ptr,
                                        SV** output_invlist)

{
    /* For internal core use only.
     * Returns the swash for the input 'node' in the regex 'prog'.
     * If <doinit> is 'true', will attempt to create the swash if not already
     *    done.
     * If <listsvp> is non-null, will return the printable contents of the
     *    swash.  This can be used to get debugging information even before the
     *    swash exists, by calling this function with 'doinit' set to false, in
     *    which case the components that will be used to eventually create the
     *    swash are returned  (in a printable form).
     * If <only_utf8_locale_ptr> is not NULL, it is where this routine is to
     *    store an inversion list of code points that should match only if the
     *    execution-time locale is a UTF-8 one.
     * If <output_invlist> is not NULL, it is where this routine is to store an
     *    inversion list of the code points that would be instead returned in
     *    <listsvp> if this were NULL.  Thus, what gets output in <listsvp>
     *    when this parameter is used, is just the non-code point data that
     *    will go into creating the swash.  This currently should be just
     *    user-defined properties whose definitions were not known at compile
     *    time.  Using this parameter allows for easier manipulation of the
     *    swash's data by the caller.  It is illegal to call this function with
     *    this parameter set, but not <listsvp>
     *
     * Tied intimately to how S_set_ANYOF_arg sets up the data structure.  Note
     * that, in spite of this function's name, the swash it returns may include
     * the bitmap data as well */

    SV *sw  = NULL;
    SV *si  = NULL;         /* Input swash initialization string */
    SV* invlist = NULL;

    RXi_GET_DECL(prog,progi);
    const struct reg_data * const data = prog ? progi->data : NULL;

    PERL_ARGS_ASSERT__GET_REGCLASS_NONBITMAP_DATA;
    assert(! output_invlist || listsvp);

    if (data && data->count) {
        const U32 n = ARG(node);

        if (data->what[n] == 's') {
            SV * const rv = MUTABLE_SV(data->data[n]);
            AV * const av = MUTABLE_AV(SvRV(rv));
            SV **const ary = AvARRAY(av);
            U8 swash_init_flags = _CORE_SWASH_INIT_ACCEPT_INVLIST;

            si = *ary;  /* ary[0] = the string to initialize the swash with */

            if (av_tindex(av) >= 2) {
                if (only_utf8_locale_ptr
                    && ary[2]
                    && ary[2] != &PL_sv_undef)
                {
                    *only_utf8_locale_ptr = ary[2];
                }
                else {
                    assert(only_utf8_locale_ptr);
                    *only_utf8_locale_ptr = NULL;
                }

                /* Elements 3 and 4 are either both present or both absent. [3]
                 * is any inversion list generated at compile time; [4]
                 * indicates if that inversion list has any user-defined
                 * properties in it. */
                if (av_tindex(av) >= 3) {
                    invlist = ary[3];
                    if (SvUV(ary[4])) {
                        swash_init_flags |= _CORE_SWASH_INIT_USER_DEFINED_PROPERTY;
                    }
                }
                else {
                    invlist = NULL;
                }
            }

            /* Element [1] is reserved for the set-up swash.  If already there,
             * return it; if not, create it and store it there */
            if (ary[1] && SvROK(ary[1])) {
                sw = ary[1];
            }
            else if (doinit && ((si && si != &PL_sv_undef)
                                 || (invlist && invlist != &PL_sv_undef))) {
                assert(si);
                sw = _core_swash_init("utf8", /* the utf8 package */
                                      "", /* nameless */
                                      si,
                                      1, /* binary */
                                      0, /* not from tr/// */
                                      invlist,
                                      &swash_init_flags);
                (void)av_store(av, 1, sw);
            }
        }
    }

    /* If requested, return a printable version of what this swash matches */
    if (listsvp) {
        SV* matches_string = NULL;

        /* The swash should be used, if possible, to get the data, as it
         * contains the resolved data.  But this function can be called at
         * compile-time, before everything gets resolved, in which case we
         * return the currently best available information, which is the string
         * that will eventually be used to do that resolving, 'si' */
        if ((! sw || (invlist = _get_swash_invlist(sw)) == NULL)
            && (si && si != &PL_sv_undef))
        {
            /* Here, we only have 'si' (and possibly some passed-in data in
             * 'invlist', which is handled below)  If the caller only wants
             * 'si', use that.  */
            if (! output_invlist) {
                matches_string = newSVsv(si);
            }
            else {
                /* But if the caller wants an inversion list of the node, we
                 * need to parse 'si' and place as much as possible in the
                 * desired output inversion list, making 'matches_string' only
                 * contain the currently unresolvable things */
                const char *si_string = SvPVX(si);
                STRLEN remaining = SvCUR(si);
                UV prev_cp = 0;
                U8 count = 0;

                /* Ignore everything before the first new-line */
                while (*si_string != '\n' && remaining > 0) {
                    si_string++;
                    remaining--;
                }
                assert(remaining > 0);

                si_string++;
                remaining--;

                while (remaining > 0) {

                    /* The data consists of just strings defining user-defined
                     * property names, but in prior incarnations, and perhaps
                     * somehow from pluggable regex engines, it could still
                     * hold hex code point definitions.  Each component of a
                     * range would be separated by a tab, and each range by a
                     * new-line.  If these are found, instead add them to the
                     * inversion list */
                    I32 grok_flags =  PERL_SCAN_SILENT_ILLDIGIT
                                     |PERL_SCAN_SILENT_NON_PORTABLE;
                    STRLEN len = remaining;
                    UV cp = grok_hex(si_string, &len, &grok_flags, NULL);

                    /* If the hex decode routine found something, it should go
                     * up to the next \n */
                    if (   *(si_string + len) == '\n') {
                        if (count) {    /* 2nd code point on line */
                            *output_invlist = _add_range_to_invlist(*output_invlist, prev_cp, cp);
                        }
                        else {
                            *output_invlist = add_cp_to_invlist(*output_invlist, cp);
                        }
                        count = 0;
                        goto prepare_for_next_iteration;
                    }

                    /* If the hex decode was instead for the lower range limit,
                     * save it, and go parse the upper range limit */
                    if (*(si_string + len) == '\t') {
                        assert(count == 0);

                        prev_cp = cp;
                        count = 1;
                      prepare_for_next_iteration:
                        si_string += len + 1;
                        remaining -= len + 1;
                        continue;
                    }

                    /* Here, didn't find a legal hex number.  Just add it from
                     * here to the next \n */

                    remaining -= len;
                    while (*(si_string + len) != '\n' && remaining > 0) {
                        remaining--;
                        len++;
                    }
                    if (*(si_string + len) == '\n') {
                        len++;
                        remaining--;
                    }
                    if (matches_string) {
                        sv_catpvn(matches_string, si_string, len - 1);
                    }
                    else {
                        matches_string = newSVpvn(si_string, len - 1);
                    }
                    si_string += len;
                    sv_catpvs(matches_string, " ");
                } /* end of loop through the text */

                assert(matches_string);
                if (SvCUR(matches_string)) {  /* Get rid of trailing blank */
                    SvCUR_set(matches_string, SvCUR(matches_string) - 1);
                }
            } /* end of has an 'si' but no swash */
        }

        /* If we have a swash in place, its equivalent inversion list was above
         * placed into 'invlist'.  If not, this variable may contain a stored
         * inversion list which is information beyond what is in 'si' */
        if (invlist) {

            /* Again, if the caller doesn't want the output inversion list, put
             * everything in 'matches-string' */
            if (! output_invlist) {
                if ( ! matches_string) {
                    matches_string = newSVpvs("\n");
                }
                sv_catsv(matches_string, invlist_contents(invlist,
                                                  TRUE /* traditional style */
                                                  ));
            }
            else if (! *output_invlist) {
                *output_invlist = invlist_clone(invlist);
            }
            else {
                _invlist_union(*output_invlist, invlist, output_invlist);
            }
        }

        *listsvp = matches_string;
    }

    return sw;
}
#endif /* !defined(PERL_IN_XSUB_RE) || defined(PLUGGABLE_RE_EXTENSION) */

/* reg_skipcomment()

   Absorbs an /x style # comment from the input stream,
   returning a pointer to the first character beyond the comment, or if the
   comment terminates the pattern without anything following it, this returns
   one past the final character of the pattern (in other words, RExC_end) and
   sets the REG_RUN_ON_COMMENT_SEEN flag.

   Note it's the callers responsibility to ensure that we are
   actually in /x mode

*/

PERL_STATIC_INLINE char*
S_reg_skipcomment(RExC_state_t *pRExC_state, char* p)
{
    PERL_ARGS_ASSERT_REG_SKIPCOMMENT;

    assert(*p == '#');

    while (p < RExC_end) {
        if (*(++p) == '\n') {
            return p+1;
        }
    }

    /* we ran off the end of the pattern without ending the comment, so we have
     * to add an \n when wrapping */
    RExC_seen |= REG_RUN_ON_COMMENT_SEEN;
    return p;
}

STATIC void
S_skip_to_be_ignored_text(pTHX_ RExC_state_t *pRExC_state,
                                char ** p,
                                const bool force_to_xmod
                         )
{
    /* If the text at the current parse position '*p' is a '(?#...)' comment,
     * or if we are under /x or 'force_to_xmod' is TRUE, and the text at '*p'
     * is /x whitespace, advance '*p' so that on exit it points to the first
     * byte past all such white space and comments */

    const bool use_xmod = force_to_xmod || (RExC_flags & RXf_PMf_EXTENDED);

    PERL_ARGS_ASSERT_SKIP_TO_BE_IGNORED_TEXT;

    assert( ! UTF || UTF8_IS_INVARIANT(**p) || UTF8_IS_START(**p));

    for (;;) {
        if (RExC_end - (*p) >= 3
            && *(*p)     == '('
            && *(*p + 1) == '?'
            && *(*p + 2) == '#')
        {
            while (*(*p) != ')') {
                if ((*p) == RExC_end)
                    FAIL("Sequence (?#... not terminated");
                (*p)++;
            }
            (*p)++;
            continue;
        }

        if (use_xmod) {
            const char * save_p = *p;
            while ((*p) < RExC_end) {
                STRLEN len;
                if ((len = is_PATWS_safe((*p), RExC_end, UTF))) {
                    (*p) += len;
                }
                else if (*(*p) == '#') {
                    (*p) = reg_skipcomment(pRExC_state, (*p));
                }
                else {
                    break;
                }
            }
            if (*p != save_p) {
                continue;
            }
        }

        break;
    }

    return;
}

/* nextchar()

   Advances the parse position by one byte, unless that byte is the beginning
   of a '(?#...)' style comment, or is /x whitespace and /x is in effect.  In
   those two cases, the parse position is advanced beyond all such comments and
   white space.

   This is the UTF, (?#...), and /x friendly way of saying RExC_parse++.
*/

STATIC void
S_nextchar(pTHX_ RExC_state_t *pRExC_state)
{
    PERL_ARGS_ASSERT_NEXTCHAR;

    if (RExC_parse < RExC_end) {
        assert(   ! UTF
               || UTF8_IS_INVARIANT(*RExC_parse)
               || UTF8_IS_START(*RExC_parse));

        RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;

        skip_to_be_ignored_text(pRExC_state, &RExC_parse,
                                FALSE /* Don't assume /x */ );
    }
}

STATIC regnode *
S_regnode_guts(pTHX_ RExC_state_t *pRExC_state, const U8 op, const STRLEN extra_size, const char* const name)
{
    /* Allocate a regnode for 'op' and returns it, with 'extra_size' extra
     * space.  In pass1, it aligns and increments RExC_size; in pass2,
     * RExC_emit */

    regnode * const ret = RExC_emit;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGNODE_GUTS;

    assert(extra_size >= regarglen[op]);

    if (SIZE_ONLY) {
        SIZE_ALIGN(RExC_size);
        RExC_size += 1 + extra_size;
        return(ret);
    }
    if (RExC_emit >= RExC_emit_bound)
        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d, %p>=%p",
                   op, (void*)RExC_emit, (void*)RExC_emit_bound);

    NODE_ALIGN_FILL(ret);
#ifndef RE_TRACK_PATTERN_OFFSETS
    PERL_UNUSED_ARG(name);
#else
    if (RExC_offsets) {         /* MJD */
        MJD_OFFSET_DEBUG(
              ("%s:%d: (op %s) %s %"UVuf" (len %"UVuf") (max %"UVuf").\n",
              name, __LINE__,
              PL_reg_name[op],
              (UV)(RExC_emit - RExC_emit_start) > RExC_offsets[0]
                ? "Overwriting end of array!\n" : "OK",
              (UV)(RExC_emit - RExC_emit_start),
              (UV)(RExC_parse - RExC_start),
              (UV)RExC_offsets[0]));
        Set_Node_Offset(RExC_emit, RExC_parse + (op == END));
    }
#endif
    return(ret);
}

/*
- reg_node - emit a node
*/
STATIC regnode *                        /* Location. */
S_reg_node(pTHX_ RExC_state_t *pRExC_state, U8 op)
{
    regnode * const ret = regnode_guts(pRExC_state, op, regarglen[op], "reg_node");

    PERL_ARGS_ASSERT_REG_NODE;

    assert(regarglen[op] == 0);

    if (PASS2) {
        regnode *ptr = ret;
        FILL_ADVANCE_NODE(ptr, op);
        RExC_emit = ptr;
    }
    return(ret);
}

/*
- reganode - emit a node with an argument
*/
STATIC regnode *                        /* Location. */
S_reganode(pTHX_ RExC_state_t *pRExC_state, U8 op, U32 arg)
{
    regnode * const ret = regnode_guts(pRExC_state, op, regarglen[op], "reganode");

    PERL_ARGS_ASSERT_REGANODE;

    assert(regarglen[op] == 1);

    if (PASS2) {
        regnode *ptr = ret;
        FILL_ADVANCE_NODE_ARG(ptr, op, arg);
        RExC_emit = ptr;
    }
    return(ret);
}

STATIC regnode *
S_reg2Lanode(pTHX_ RExC_state_t *pRExC_state, const U8 op, const U32 arg1, const I32 arg2)
{
    /* emit a node with U32 and I32 arguments */

    regnode * const ret = regnode_guts(pRExC_state, op, regarglen[op], "reg2Lanode");

    PERL_ARGS_ASSERT_REG2LANODE;

    assert(regarglen[op] == 2);

    if (PASS2) {
        regnode *ptr = ret;
        FILL_ADVANCE_NODE_2L_ARG(ptr, op, arg1, arg2);
        RExC_emit = ptr;
    }
    return(ret);
}

/*
- reginsert - insert an operator in front of already-emitted operand
*
* Means relocating the operand.
*/
STATIC void
S_reginsert(pTHX_ RExC_state_t *pRExC_state, U8 op, regnode *opnd, U32 depth)
{
    regnode *src;
    regnode *dst;
    regnode *place;
    const int offset = regarglen[(U8)op];
    const int size = NODE_STEP_REGNODE + offset;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGINSERT;
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(depth);
/* (PL_regkind[(U8)op] == CURLY ? EXTRA_STEP_2ARGS : 0); */
    DEBUG_PARSE_FMT("inst"," - %s",PL_reg_name[op]);
    if (SIZE_ONLY) {
        RExC_size += size;
        return;
    }

    src = RExC_emit;
    RExC_emit += size;
    dst = RExC_emit;
    if (RExC_open_parens) {
        int paren;
        /*DEBUG_PARSE_FMT("inst"," - %"IVdf, (IV)RExC_npar);*/
        for ( paren=0 ; paren < RExC_npar ; paren++ ) {
            if ( RExC_open_parens[paren] >= opnd ) {
                /*DEBUG_PARSE_FMT("open"," - %d",size);*/
                RExC_open_parens[paren] += size;
            } else {
                /*DEBUG_PARSE_FMT("open"," - %s","ok");*/
            }
            if ( RExC_close_parens[paren] >= opnd ) {
                /*DEBUG_PARSE_FMT("close"," - %d",size);*/
                RExC_close_parens[paren] += size;
            } else {
                /*DEBUG_PARSE_FMT("close"," - %s","ok");*/
            }
        }
    }

    while (src > opnd) {
        StructCopy(--src, --dst, regnode);
#ifdef RE_TRACK_PATTERN_OFFSETS
        if (RExC_offsets) {     /* MJD 20010112 */
            MJD_OFFSET_DEBUG(
                 ("%s(%d): (op %s) %s copy %"UVuf" -> %"UVuf" (max %"UVuf").\n",
                  "reg_insert",
                  __LINE__,
                  PL_reg_name[op],
                  (UV)(dst - RExC_emit_start) > RExC_offsets[0]
                    ? "Overwriting end of array!\n" : "OK",
                  (UV)(src - RExC_emit_start),
                  (UV)(dst - RExC_emit_start),
                  (UV)RExC_offsets[0]));
            Set_Node_Offset_To_R(dst-RExC_emit_start, Node_Offset(src));
            Set_Node_Length_To_R(dst-RExC_emit_start, Node_Length(src));
        }
#endif
    }


    place = opnd;               /* Op node, where operand used to be. */
#ifdef RE_TRACK_PATTERN_OFFSETS
    if (RExC_offsets) {         /* MJD */
        MJD_OFFSET_DEBUG(
              ("%s(%d): (op %s) %s %"UVuf" <- %"UVuf" (max %"UVuf").\n",
              "reginsert",
              __LINE__,
              PL_reg_name[op],
              (UV)(place - RExC_emit_start) > RExC_offsets[0]
              ? "Overwriting end of array!\n" : "OK",
              (UV)(place - RExC_emit_start),
              (UV)(RExC_parse - RExC_start),
              (UV)RExC_offsets[0]));
        Set_Node_Offset(place, RExC_parse);
        Set_Node_Length(place, 1);
    }
#endif
    src = NEXTOPER(place);
    FILL_ADVANCE_NODE(place, op);
    Zero(src, offset, regnode);
}

/*
- regtail - set the next-pointer at the end of a node chain of p to val.
- SEE ALSO: regtail_study
*/
STATIC void
S_regtail(pTHX_ RExC_state_t * pRExC_state,
                const regnode * const p,
                const regnode * const val,
                const U32 depth)
{
    regnode *scan;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGTAIL;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif

    if (SIZE_ONLY)
        return;

    /* Find last node. */
    scan = (regnode *) p;
    for (;;) {
        regnode * const temp = regnext(scan);
        DEBUG_PARSE_r({
            DEBUG_PARSE_MSG((scan==p ? "tail" : ""));
            regprop(RExC_rx, RExC_mysv, scan, NULL, pRExC_state);
            PerlIO_printf(Perl_debug_log, "~ %s (%d) %s %s\n",
                SvPV_nolen_const(RExC_mysv), REG_NODE_NUM(scan),
                    (temp == NULL ? "->" : ""),
                    (temp == NULL ? PL_reg_name[OP(val)] : "")
            );
        });
        if (temp == NULL)
            break;
        scan = temp;
    }

    if (reg_off_by_arg[OP(scan)]) {
        ARG_SET(scan, val - scan);
    }
    else {
        NEXT_OFF(scan) = val - scan;
    }
}

#ifdef DEBUGGING
/*
- regtail_study - set the next-pointer at the end of a node chain of p to val.
- Look for optimizable sequences at the same time.
- currently only looks for EXACT chains.

This is experimental code. The idea is to use this routine to perform
in place optimizations on branches and groups as they are constructed,
with the long term intention of removing optimization from study_chunk so
that it is purely analytical.

Currently only used when in DEBUG mode. The macro REGTAIL_STUDY() is used
to control which is which.

*/
/* TODO: All four parms should be const */

STATIC U8
S_regtail_study(pTHX_ RExC_state_t *pRExC_state, regnode *p,
                      const regnode *val,U32 depth)
{
    regnode *scan;
    U8 exact = PSEUDO;
#ifdef EXPERIMENTAL_INPLACESCAN
    I32 min = 0;
#endif
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGTAIL_STUDY;


    if (SIZE_ONLY)
        return exact;

    /* Find last node. */

    scan = p;
    for (;;) {
        regnode * const temp = regnext(scan);
#ifdef EXPERIMENTAL_INPLACESCAN
        if (PL_regkind[OP(scan)] == EXACT) {
            bool unfolded_multi_char;   /* Unexamined in this routine */
            if (join_exact(pRExC_state, scan, &min,
                           &unfolded_multi_char, 1, val, depth+1))
                return EXACT;
        }
#endif
        if ( exact ) {
            switch (OP(scan)) {
                case EXACT:
                case EXACTL:
                case EXACTF:
                case EXACTFA_NO_TRIE:
                case EXACTFA:
                case EXACTFU:
                case EXACTFLU8:
                case EXACTFU_SS:
                case EXACTFL:
                        if( exact == PSEUDO )
                            exact= OP(scan);
                        else if ( exact != OP(scan) )
                            exact= 0;
                case NOTHING:
                    break;
                default:
                    exact= 0;
            }
        }
        DEBUG_PARSE_r({
            DEBUG_PARSE_MSG((scan==p ? "tsdy" : ""));
            regprop(RExC_rx, RExC_mysv, scan, NULL, pRExC_state);
            PerlIO_printf(Perl_debug_log, "~ %s (%d) -> %s\n",
                SvPV_nolen_const(RExC_mysv),
                REG_NODE_NUM(scan),
                PL_reg_name[exact]);
        });
        if (temp == NULL)
            break;
        scan = temp;
    }
    DEBUG_PARSE_r({
        DEBUG_PARSE_MSG("");
        regprop(RExC_rx, RExC_mysv, val, NULL, pRExC_state);
        PerlIO_printf(Perl_debug_log,
                      "~ attach to %s (%"IVdf") offset to %"IVdf"\n",
                      SvPV_nolen_const(RExC_mysv),
                      (IV)REG_NODE_NUM(val),
                      (IV)(val - scan)
        );
    });
    if (reg_off_by_arg[OP(scan)]) {
        ARG_SET(scan, val - scan);
    }
    else {
        NEXT_OFF(scan) = val - scan;
    }

    return exact;
}
#endif

/*
 - regdump - dump a regexp onto Perl_debug_log in vaguely comprehensible form
 */
#ifdef DEBUGGING

static void
S_regdump_intflags(pTHX_ const char *lead, const U32 flags)
{
    int bit;
    int set=0;

    ASSUME(REG_INTFLAGS_NAME_SIZE <= sizeof(flags)*8);

    for (bit=0; bit<REG_INTFLAGS_NAME_SIZE; bit++) {
        if (flags & (1<<bit)) {
            if (!set++ && lead)
                PerlIO_printf(Perl_debug_log, "%s",lead);
            PerlIO_printf(Perl_debug_log, "%s ",PL_reg_intflags_name[bit]);
        }
    }
    if (lead)  {
        if (set)
            PerlIO_printf(Perl_debug_log, "\n");
        else
            PerlIO_printf(Perl_debug_log, "%s[none-set]\n",lead);
    }
}

static void
S_regdump_extflags(pTHX_ const char *lead, const U32 flags)
{
    int bit;
    int set=0;
    regex_charset cs;

    ASSUME(REG_EXTFLAGS_NAME_SIZE <= sizeof(flags)*8);

    for (bit=0; bit<REG_EXTFLAGS_NAME_SIZE; bit++) {
        if (flags & (1<<bit)) {
            if ((1<<bit) & RXf_PMf_CHARSET) {   /* Output separately, below */
                continue;
            }
            if (!set++ && lead)
                PerlIO_printf(Perl_debug_log, "%s",lead);
            PerlIO_printf(Perl_debug_log, "%s ",PL_reg_extflags_name[bit]);
        }
    }
    if ((cs = get_regex_charset(flags)) != REGEX_DEPENDS_CHARSET) {
            if (!set++ && lead) {
                PerlIO_printf(Perl_debug_log, "%s",lead);
            }
            switch (cs) {
                case REGEX_UNICODE_CHARSET:
                    PerlIO_printf(Perl_debug_log, "UNICODE");
                    break;
                case REGEX_LOCALE_CHARSET:
                    PerlIO_printf(Perl_debug_log, "LOCALE");
                    break;
                case REGEX_ASCII_RESTRICTED_CHARSET:
                    PerlIO_printf(Perl_debug_log, "ASCII-RESTRICTED");
                    break;
                case REGEX_ASCII_MORE_RESTRICTED_CHARSET:
                    PerlIO_printf(Perl_debug_log, "ASCII-MORE_RESTRICTED");
                    break;
                default:
                    PerlIO_printf(Perl_debug_log, "UNKNOWN CHARACTER SET");
                    break;
            }
    }
    if (lead)  {
        if (set)
            PerlIO_printf(Perl_debug_log, "\n");
        else
            PerlIO_printf(Perl_debug_log, "%s[none-set]\n",lead);
    }
}
#endif

void
Perl_regdump(pTHX_ const regexp *r)
{
#ifdef DEBUGGING
    SV * const sv = sv_newmortal();
    SV *dsv= sv_newmortal();
    RXi_GET_DECL(r,ri);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGDUMP;

    (void)dumpuntil(r, ri->program, ri->program + 1, NULL, NULL, sv, 0, 0);

    /* Header fields of interest. */
    if (r->anchored_substr) {
        RE_PV_QUOTED_DECL(s, 0, dsv, SvPVX_const(r->anchored_substr),
            RE_SV_DUMPLEN(r->anchored_substr), 30);
        PerlIO_printf(Perl_debug_log,
                      "anchored %s%s at %"IVdf" ",
                      s, RE_SV_TAIL(r->anchored_substr),
                      (IV)r->anchored_offset);
    } else if (r->anchored_utf8) {
        RE_PV_QUOTED_DECL(s, 1, dsv, SvPVX_const(r->anchored_utf8),
            RE_SV_DUMPLEN(r->anchored_utf8), 30);
        PerlIO_printf(Perl_debug_log,
                      "anchored utf8 %s%s at %"IVdf" ",
                      s, RE_SV_TAIL(r->anchored_utf8),
                      (IV)r->anchored_offset);
    }
    if (r->float_substr) {
        RE_PV_QUOTED_DECL(s, 0, dsv, SvPVX_const(r->float_substr),
            RE_SV_DUMPLEN(r->float_substr), 30);
        PerlIO_printf(Perl_debug_log,
                      "floating %s%s at %"IVdf"..%"UVuf" ",
                      s, RE_SV_TAIL(r->float_substr),
                      (IV)r->float_min_offset, (UV)r->float_max_offset);
    } else if (r->float_utf8) {
        RE_PV_QUOTED_DECL(s, 1, dsv, SvPVX_const(r->float_utf8),
            RE_SV_DUMPLEN(r->float_utf8), 30);
        PerlIO_printf(Perl_debug_log,
                      "floating utf8 %s%s at %"IVdf"..%"UVuf" ",
                      s, RE_SV_TAIL(r->float_utf8),
                      (IV)r->float_min_offset, (UV)r->float_max_offset);
    }
    if (r->check_substr || r->check_utf8)
        PerlIO_printf(Perl_debug_log,
                      (const char *)
                      (r->check_substr == r->float_substr
                       && r->check_utf8 == r->float_utf8
                       ? "(checking floating" : "(checking anchored"));
    if (r->intflags & PREGf_NOSCAN)
        PerlIO_printf(Perl_debug_log, " noscan");
    if (r->extflags & RXf_CHECK_ALL)
        PerlIO_printf(Perl_debug_log, " isall");
    if (r->check_substr || r->check_utf8)
        PerlIO_printf(Perl_debug_log, ") ");

    if (ri->regstclass) {
        regprop(r, sv, ri->regstclass, NULL, NULL);
        PerlIO_printf(Perl_debug_log, "stclass %s ", SvPVX_const(sv));
    }
    if (r->intflags & PREGf_ANCH) {
        PerlIO_printf(Perl_debug_log, "anchored");
        if (r->intflags & PREGf_ANCH_MBOL)
            PerlIO_printf(Perl_debug_log, "(MBOL)");
        if (r->intflags & PREGf_ANCH_SBOL)
            PerlIO_printf(Perl_debug_log, "(SBOL)");
        if (r->intflags & PREGf_ANCH_GPOS)
            PerlIO_printf(Perl_debug_log, "(GPOS)");
        (void)PerlIO_putc(Perl_debug_log, ' ');
    }
    if (r->intflags & PREGf_GPOS_SEEN)
        PerlIO_printf(Perl_debug_log, "GPOS:%"UVuf" ", (UV)r->gofs);
    if (r->intflags & PREGf_SKIP)
        PerlIO_printf(Perl_debug_log, "plus ");
    if (r->intflags & PREGf_IMPLICIT)
        PerlIO_printf(Perl_debug_log, "implicit ");
    PerlIO_printf(Perl_debug_log, "minlen %"IVdf" ", (IV)r->minlen);
    if (r->extflags & RXf_EVAL_SEEN)
        PerlIO_printf(Perl_debug_log, "with eval ");
    PerlIO_printf(Perl_debug_log, "\n");
    DEBUG_FLAGS_r({
        regdump_extflags("r->extflags: ",r->extflags);
        regdump_intflags("r->intflags: ",r->intflags);
    });
#else
    PERL_ARGS_ASSERT_REGDUMP;
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(r);
#endif  /* DEBUGGING */
}

/* Should be synchronized with ANYOF_ #defines in regcomp.h */
#ifdef DEBUGGING

#  if   _CC_WORDCHAR != 0 || _CC_DIGIT != 1        || _CC_ALPHA != 2    \
     || _CC_LOWER != 3    || _CC_UPPER != 4        || _CC_PUNCT != 5    \
     || _CC_PRINT != 6    || _CC_ALPHANUMERIC != 7 || _CC_GRAPH != 8    \
     || _CC_CASED != 9    || _CC_SPACE != 10       || _CC_BLANK != 11   \
     || _CC_XDIGIT != 12  || _CC_CNTRL != 13       || _CC_ASCII != 14   \
     || _CC_VERTSPACE != 15
#   error Need to adjust order of anyofs[]
#  endif
static const char * const anyofs[] = {
    "\\w",
    "\\W",
    "\\d",
    "\\D",
    "[:alpha:]",
    "[:^alpha:]",
    "[:lower:]",
    "[:^lower:]",
    "[:upper:]",
    "[:^upper:]",
    "[:punct:]",
    "[:^punct:]",
    "[:print:]",
    "[:^print:]",
    "[:alnum:]",
    "[:^alnum:]",
    "[:graph:]",
    "[:^graph:]",
    "[:cased:]",
    "[:^cased:]",
    "\\s",
    "\\S",
    "[:blank:]",
    "[:^blank:]",
    "[:xdigit:]",
    "[:^xdigit:]",
    "[:cntrl:]",
    "[:^cntrl:]",
    "[:ascii:]",
    "[:^ascii:]",
    "\\v",
    "\\V"
};
#endif

/*
- regprop - printable representation of opcode, with run time support
*/

void
Perl_regprop(pTHX_ const regexp *prog, SV *sv, const regnode *o, const regmatch_info *reginfo, const RExC_state_t *pRExC_state)
{
#ifdef DEBUGGING
    int k;
    RXi_GET_DECL(prog,progi);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGPROP;

    sv_setpvn(sv, "", 0);

    if (OP(o) > REGNODE_MAX)            /* regnode.type is unsigned */
        /* It would be nice to FAIL() here, but this may be called from
           regexec.c, and it would be hard to supply pRExC_state. */
        Perl_croak(aTHX_ "Corrupted regexp opcode %d > %d",
                                              (int)OP(o), (int)REGNODE_MAX);
    sv_catpv(sv, PL_reg_name[OP(o)]); /* Take off const! */

    k = PL_regkind[OP(o)];

    if (k == EXACT) {
        sv_catpvs(sv, " ");
        /* Using is_utf8_string() (via PERL_PV_UNI_DETECT)
         * is a crude hack but it may be the best for now since
         * we have no flag "this EXACTish node was UTF-8"
         * --jhi */
        pv_pretty(sv, STRING(o), STR_LEN(o), 60, PL_colors[0], PL_colors[1],
                  PERL_PV_ESCAPE_UNI_DETECT |
                  PERL_PV_ESCAPE_NONASCII   |
                  PERL_PV_PRETTY_ELLIPSES   |
                  PERL_PV_PRETTY_LTGT       |
                  PERL_PV_PRETTY_NOCLEAR
                  );
    } else if (k == TRIE) {
        /* print the details of the trie in dumpuntil instead, as
         * progi->data isn't available here */
        const char op = OP(o);
        const U32 n = ARG(o);
        const reg_ac_data * const ac = IS_TRIE_AC(op) ?
               (reg_ac_data *)progi->data->data[n] :
               NULL;
        const reg_trie_data * const trie
            = (reg_trie_data*)progi->data->data[!IS_TRIE_AC(op) ? n : ac->trie];

        Perl_sv_catpvf(aTHX_ sv, "-%s",PL_reg_name[o->flags]);
        DEBUG_TRIE_COMPILE_r(
          Perl_sv_catpvf(aTHX_ sv,
            "<S:%"UVuf"/%"IVdf" W:%"UVuf" L:%"UVuf"/%"UVuf" C:%"UVuf"/%"UVuf">",
            (UV)trie->startstate,
            (IV)trie->statecount-1, /* -1 because of the unused 0 element */
            (UV)trie->wordcount,
            (UV)trie->minlen,
            (UV)trie->maxlen,
            (UV)TRIE_CHARCOUNT(trie),
            (UV)trie->uniquecharcount
          );
        );
        if ( IS_ANYOF_TRIE(op) || trie->bitmap ) {
            sv_catpvs(sv, "[");
            (void) put_charclass_bitmap_innards(sv,
                                                ((IS_ANYOF_TRIE(op))
                                                 ? ANYOF_BITMAP(o)
                                                 : TRIE_BITMAP(trie)),
                                                NULL,
                                                NULL,
                                                NULL
                                               );
            sv_catpvs(sv, "]");
        }

    } else if (k == CURLY) {
        U32 lo = ARG1(o), hi = ARG2(o);
        if (OP(o) == CURLYM || OP(o) == CURLYN || OP(o) == CURLYX)
            Perl_sv_catpvf(aTHX_ sv, "[%d]", o->flags); /* Parenth number */
        Perl_sv_catpvf(aTHX_ sv, "{%u,", (unsigned) lo);
        if (hi == REG_INFTY)
            sv_catpvs(sv, "INFTY");
        else
            Perl_sv_catpvf(aTHX_ sv, "%u", (unsigned) hi);
        sv_catpvs(sv, "}");
    }
    else if (k == WHILEM && o->flags)                   /* Ordinal/of */
        Perl_sv_catpvf(aTHX_ sv, "[%d/%d]", o->flags & 0xf, o->flags>>4);
    else if (k == REF || k == OPEN || k == CLOSE
             || k == GROUPP || OP(o)==ACCEPT)
    {
        AV *name_list= NULL;
        U32 parno= OP(o) == ACCEPT ? (U32)ARG2L(o) : ARG(o);
        Perl_sv_catpvf(aTHX_ sv, "%"UVuf, (UV)parno);        /* Parenth number */
        if ( RXp_PAREN_NAMES(prog) ) {
            name_list= MUTABLE_AV(progi->data->data[progi->name_list_idx]);
        } else if ( pRExC_state ) {
            name_list= RExC_paren_name_list;
        }
        if (name_list) {
            if ( k != REF || (OP(o) < NREF)) {
                SV **name= av_fetch(name_list, parno, 0 );
                if (name)
                    Perl_sv_catpvf(aTHX_ sv, " '%"SVf"'", SVfARG(*name));
            }
            else {
                SV *sv_dat= MUTABLE_SV(progi->data->data[ parno ]);
                I32 *nums=(I32*)SvPVX(sv_dat);
                SV **name= av_fetch(name_list, nums[0], 0 );
                I32 n;
                if (name) {
                    for ( n=0; n<SvIVX(sv_dat); n++ ) {
                        Perl_sv_catpvf(aTHX_ sv, "%s%"IVdf,
                                    (n ? "," : ""), (IV)nums[n]);
                    }
                    Perl_sv_catpvf(aTHX_ sv, " '%"SVf"'", SVfARG(*name));
                }
            }
        }
        if ( k == REF && reginfo) {
            U32 n = ARG(o);  /* which paren pair */
            I32 ln = prog->offs[n].start;
            if (prog->lastparen < n || ln == -1)
                Perl_sv_catpvf(aTHX_ sv, ": FAIL");
            else if (ln == prog->offs[n].end)
                Perl_sv_catpvf(aTHX_ sv, ": ACCEPT - EMPTY STRING");
            else {
                const char *s = reginfo->strbeg + ln;
                Perl_sv_catpvf(aTHX_ sv, ": ");
                Perl_pv_pretty( aTHX_ sv, s, prog->offs[n].end - prog->offs[n].start, 32, 0, 0,
                    PERL_PV_ESCAPE_UNI_DETECT|PERL_PV_PRETTY_NOCLEAR|PERL_PV_PRETTY_ELLIPSES|PERL_PV_PRETTY_QUOTE );
            }
        }
    } else if (k == GOSUB) {
        AV *name_list= NULL;
        if ( RXp_PAREN_NAMES(prog) ) {
            name_list= MUTABLE_AV(progi->data->data[progi->name_list_idx]);
        } else if ( pRExC_state ) {
            name_list= RExC_paren_name_list;
        }

        /* Paren and offset */
        Perl_sv_catpvf(aTHX_ sv, "%d[%+d]", (int)ARG(o),(int)ARG2L(o));
        if (name_list) {
            SV **name= av_fetch(name_list, ARG(o), 0 );
            if (name)
                Perl_sv_catpvf(aTHX_ sv, " '%"SVf"'", SVfARG(*name));
        }
    }
    else if (k == LOGICAL)
        /* 2: embedded, otherwise 1 */
        Perl_sv_catpvf(aTHX_ sv, "[%d]", o->flags);
    else if (k == ANYOF) {
        const U8 flags = ANYOF_FLAGS(o);
        bool do_sep = FALSE;    /* Do we need to separate various components of
                                   the output? */
        /* Set if there is still an unresolved user-defined property */
        SV *unresolved                = NULL;

        /* Things that are ignored except when the runtime locale is UTF-8 */
        SV *only_utf8_locale_invlist = NULL;

        /* Code points that don't fit in the bitmap */
        SV *nonbitmap_invlist = NULL;

        /* And things that aren't in the bitmap, but are small enough to be */
        SV* bitmap_range_not_in_bitmap = NULL;

        if (OP(o) == ANYOFL) {
            if (ANYOFL_UTF8_LOCALE_REQD(flags)) {
                sv_catpvs(sv, "{utf8-locale-reqd}");
            }
            if (flags & ANYOFL_FOLD) {
                sv_catpvs(sv, "{i}");
            }
        }

        /* If there is stuff outside the bitmap, get it */
        if (ARG(o) != ANYOF_ONLY_HAS_BITMAP) {
            (void) _get_regclass_nonbitmap_data(prog, o, FALSE,
                                                &unresolved,
                                                &only_utf8_locale_invlist,
                                                &nonbitmap_invlist);
            /* The non-bitmap data may contain stuff that could fit in the
             * bitmap.  This could come from a user-defined property being
             * finally resolved when this call was done; or much more likely
             * because there are matches that require UTF-8 to be valid, and so
             * aren't in the bitmap.  This is teased apart later */
            _invlist_intersection(nonbitmap_invlist,
                                  PL_InBitmap,
                                  &bitmap_range_not_in_bitmap);
            /* Leave just the things that don't fit into the bitmap */
            _invlist_subtract(nonbitmap_invlist,
                              PL_InBitmap,
                              &nonbitmap_invlist);
        }

        /* Obey this flag to add all above-the-bitmap code points */
        if (flags & ANYOF_MATCHES_ALL_ABOVE_BITMAP) {
            nonbitmap_invlist = _add_range_to_invlist(nonbitmap_invlist,
                                                      NUM_ANYOF_CODE_POINTS,
                                                      UV_MAX);
        }

        /* Ready to start outputting.  First, the initial left bracket */
        Perl_sv_catpvf(aTHX_ sv, "[%s", PL_colors[0]);

        /* Then all the things that could fit in the bitmap */
        do_sep = put_charclass_bitmap_innards(sv,
                                              ANYOF_BITMAP(o),
                                              bitmap_range_not_in_bitmap,
                                              only_utf8_locale_invlist,
                                              o);
        SvREFCNT_dec(bitmap_range_not_in_bitmap);

        /* If there are user-defined properties which haven't been defined yet,
         * output them, in a separate [] from the bitmap range stuff */
        if (unresolved) {
            if (do_sep) {
                Perl_sv_catpvf(aTHX_ sv,"%s][%s",PL_colors[1],PL_colors[0]);
            }
            if (flags & ANYOF_INVERT) {
                sv_catpvs(sv, "^");
            }
            sv_catsv(sv, unresolved);
            do_sep = TRUE;
            SvREFCNT_dec_NN(unresolved);
        }

        /* And, finally, add the above-the-bitmap stuff */
        if (nonbitmap_invlist) {
            SV* contents;

            /* See if truncation size is overridden */
            const STRLEN dump_len = (PL_dump_re_max_len)
                                    ? PL_dump_re_max_len
                                    : 256;

            /* This is output in a separate [] */
            if (do_sep) {
                Perl_sv_catpvf(aTHX_ sv,"%s][%s",PL_colors[1],PL_colors[0]);
            }

            /* And, for easy of understanding, it is always output not-shown as
             * complemented */
            if (flags & ANYOF_INVERT) {
                _invlist_invert(nonbitmap_invlist);
                _invlist_subtract(nonbitmap_invlist, PL_InBitmap, &nonbitmap_invlist);
            }

            contents = invlist_contents(nonbitmap_invlist,
                                        FALSE /* output suitable for catsv */
                                       );

            /* If the output is shorter than the permissible maximum, just do it. */
            if (SvCUR(contents) <= dump_len) {
                sv_catsv(sv, contents);
            }
            else {
                const char * contents_string = SvPVX(contents);
                STRLEN i = dump_len;

                /* Otherwise, start at the permissible max and work back to the
                 * first break possibility */
                while (i > 0 && contents_string[i] != ' ') {
                    i--;
                }
                if (i == 0) {       /* Fail-safe.  Use the max if we couldn't
                                       find a legal break */
                    i = dump_len;
                }

                sv_catpvn(sv, contents_string, i);
                sv_catpvs(sv, "...");
            }

            SvREFCNT_dec_NN(contents);
            SvREFCNT_dec_NN(nonbitmap_invlist);
        }

        /* And finally the matching, closing ']' */
        Perl_sv_catpvf(aTHX_ sv, "%s]", PL_colors[1]);
    }
    else if (k == POSIXD || k == NPOSIXD) {
        U8 index = FLAGS(o) * 2;
        if (index < C_ARRAY_LENGTH(anyofs)) {
            if (*anyofs[index] != '[')  {
                sv_catpv(sv, "[");
            }
            sv_catpv(sv, anyofs[index]);
            if (*anyofs[index] != '[')  {
                sv_catpv(sv, "]");
            }
        }
        else {
            Perl_sv_catpvf(aTHX_ sv, "[illegal type=%d])", index);
        }
    }
    else if (k == BOUND || k == NBOUND) {
        /* Must be synced with order of 'bound_type' in regcomp.h */
        const char * const bounds[] = {
            "",      /* Traditional */
            "{gcb}",
            "{lb}",
            "{sb}",
            "{wb}"
        };
        assert(FLAGS(o) < C_ARRAY_LENGTH(bounds));
        sv_catpv(sv, bounds[FLAGS(o)]);
    }
    else if (k == BRANCHJ && (OP(o) == UNLESSM || OP(o) == IFMATCH))
        Perl_sv_catpvf(aTHX_ sv, "[%d]", -(o->flags));
    else if (OP(o) == SBOL)
        Perl_sv_catpvf(aTHX_ sv, " /%s/", o->flags ? "\\A" : "^");

    /* add on the verb argument if there is one */
    if ( ( k == VERB || OP(o) == ACCEPT || OP(o) == OPFAIL ) && o->flags) {
        Perl_sv_catpvf(aTHX_ sv, ":%"SVf,
                       SVfARG((MUTABLE_SV(progi->data->data[ ARG( o ) ]))));
    }
#else
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(sv);
    PERL_UNUSED_ARG(o);
    PERL_UNUSED_ARG(prog);
    PERL_UNUSED_ARG(reginfo);
    PERL_UNUSED_ARG(pRExC_state);
#endif  /* DEBUGGING */
}



SV *
Perl_re_intuit_string(pTHX_ REGEXP * const r)
{                               /* Assume that RE_INTUIT is set */
    struct regexp *const prog = ReANY(r);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_RE_INTUIT_STRING;
    PERL_UNUSED_CONTEXT;

    DEBUG_COMPILE_r(
        {
            const char * const s = SvPV_nolen_const(RX_UTF8(r)
                      ? prog->check_utf8 : prog->check_substr);

            if (!PL_colorset) reginitcolors();
            PerlIO_printf(Perl_debug_log,
                      "%sUsing REx %ssubstr:%s \"%s%.60s%s%s\"\n",
                      PL_colors[4],
                      RX_UTF8(r) ? "utf8 " : "",
                      PL_colors[5],PL_colors[0],
                      s,
                      PL_colors[1],
                      (strlen(s) > 60 ? "..." : ""));
        } );

    /* use UTF8 check substring if regexp pattern itself is in UTF8 */
    return RX_UTF8(r) ? prog->check_utf8 : prog->check_substr;
}

/*
   pregfree()

   handles refcounting and freeing the perl core regexp structure. When
   it is necessary to actually free the structure the first thing it
   does is call the 'free' method of the regexp_engine associated to
   the regexp, allowing the handling of the void *pprivate; member
   first. (This routine is not overridable by extensions, which is why
   the extensions free is called first.)

   See regdupe and regdupe_internal if you change anything here.
*/
#ifndef PERL_IN_XSUB_RE
void
Perl_pregfree(pTHX_ REGEXP *r)
{
    SvREFCNT_dec(r);
}

void
Perl_pregfree2(pTHX_ REGEXP *rx)
{
    struct regexp *const r = ReANY(rx);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_PREGFREE2;

    if (r->mother_re) {
        ReREFCNT_dec(r->mother_re);
    } else {
        CALLREGFREE_PVT(rx); /* free the private data */
        SvREFCNT_dec(RXp_PAREN_NAMES(r));
        Safefree(r->xpv_len_u.xpvlenu_pv);
    }
    if (r->substrs) {
        SvREFCNT_dec(r->anchored_substr);
        SvREFCNT_dec(r->anchored_utf8);
        SvREFCNT_dec(r->float_substr);
        SvREFCNT_dec(r->float_utf8);
        Safefree(r->substrs);
    }
    RX_MATCH_COPY_FREE(rx);
#ifdef PERL_ANY_COW
    SvREFCNT_dec(r->saved_copy);
#endif
    Safefree(r->offs);
    SvREFCNT_dec(r->qr_anoncv);
    rx->sv_u.svu_rx = 0;
}

/*  reg_temp_copy()

    This is a hacky workaround to the structural issue of match results
    being stored in the regexp structure which is in turn stored in
    PL_curpm/PL_reg_curpm. The problem is that due to qr// the pattern
    could be PL_curpm in multiple contexts, and could require multiple
    result sets being associated with the pattern simultaneously, such
    as when doing a recursive match with (??{$qr})

    The solution is to make a lightweight copy of the regexp structure
    when a qr// is returned from the code executed by (??{$qr}) this
    lightweight copy doesn't actually own any of its data except for
    the starp/end and the actual regexp structure itself.

*/


REGEXP *
Perl_reg_temp_copy (pTHX_ REGEXP *ret_x, REGEXP *rx)
{
    struct regexp *ret;
    struct regexp *const r = ReANY(rx);
    const bool islv = ret_x && SvTYPE(ret_x) == SVt_PVLV;

    PERL_ARGS_ASSERT_REG_TEMP_COPY;

    if (!ret_x)
        ret_x = (REGEXP*) newSV_type(SVt_REGEXP);
    else {
        SvOK_off((SV *)ret_x);
        if (islv) {
            /* For PVLVs, SvANY points to the xpvlv body while sv_u points
               to the regexp.  (For SVt_REGEXPs, sv_upgrade has already
               made both spots point to the same regexp body.) */
            REGEXP *temp = (REGEXP *)newSV_type(SVt_REGEXP);
            assert(!SvPVX(ret_x));
            ret_x->sv_u.svu_rx = temp->sv_any;
            temp->sv_any = NULL;
            SvFLAGS(temp) = (SvFLAGS(temp) & ~SVTYPEMASK) | SVt_NULL;
            SvREFCNT_dec_NN(temp);
            /* SvCUR still resides in the xpvlv struct, so the regexp copy-
               ing below will not set it. */
            SvCUR_set(ret_x, SvCUR(rx));
        }
    }
    /* This ensures that SvTHINKFIRST(sv) is true, and hence that
       sv_force_normal(sv) is called.  */
    SvFAKE_on(ret_x);
    ret = ReANY(ret_x);

    SvFLAGS(ret_x) |= SvUTF8(rx);
    /* We share the same string buffer as the original regexp, on which we
       hold a reference count, incremented when mother_re is set below.
       The string pointer is copied here, being part of the regexp struct.
     */
    memcpy(&(ret->xpv_cur), &(r->xpv_cur),
           sizeof(regexp) - STRUCT_OFFSET(regexp, xpv_cur));
    if (r->offs) {
        const I32 npar = r->nparens+1;
        Newx(ret->offs, npar, regexp_paren_pair);
        Copy(r->offs, ret->offs, npar, regexp_paren_pair);
    }
    if (r->substrs) {
        Newx(ret->substrs, 1, struct reg_substr_data);
        StructCopy(r->substrs, ret->substrs, struct reg_substr_data);

        SvREFCNT_inc_void(ret->anchored_substr);
        SvREFCNT_inc_void(ret->anchored_utf8);
        SvREFCNT_inc_void(ret->float_substr);
        SvREFCNT_inc_void(ret->float_utf8);

        /* check_substr and check_utf8, if non-NULL, point to either their
           anchored or float namesakes, and don't hold a second reference.  */
    }
    RX_MATCH_COPIED_off(ret_x);
#ifdef PERL_ANY_COW
    ret->saved_copy = NULL;
#endif
    ret->mother_re = ReREFCNT_inc(r->mother_re ? r->mother_re : rx);
    SvREFCNT_inc_void(ret->qr_anoncv);

    return ret_x;
}
#endif

/* regfree_internal()

   Free the private data in a regexp. This is overloadable by
   extensions. Perl takes care of the regexp structure in pregfree(),
   this covers the *pprivate pointer which technically perl doesn't
   know about, however of course we have to handle the
   regexp_internal structure when no extension is in use.

   Note this is called before freeing anything in the regexp
   structure.
 */

void
Perl_regfree_internal(pTHX_ REGEXP * const rx)
{
    struct regexp *const r = ReANY(rx);
    RXi_GET_DECL(r,ri);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGFREE_INTERNAL;

    DEBUG_COMPILE_r({
        if (!PL_colorset)
            reginitcolors();
        {
            SV *dsv= sv_newmortal();
            RE_PV_QUOTED_DECL(s, RX_UTF8(rx),
                dsv, RX_PRECOMP(rx), RX_PRELEN(rx), 60);
            PerlIO_printf(Perl_debug_log,"%sFreeing REx:%s %s\n",
                PL_colors[4],PL_colors[5],s);
        }
    });
#ifdef RE_TRACK_PATTERN_OFFSETS
    if (ri->u.offsets)
        Safefree(ri->u.offsets);             /* 20010421 MJD */
#endif
    if (ri->code_blocks) {
        int n;
        for (n = 0; n < ri->num_code_blocks; n++)
            SvREFCNT_dec(ri->code_blocks[n].src_regex);
        Safefree(ri->code_blocks);
    }

    if (ri->data) {
        int n = ri->data->count;

        while (--n >= 0) {
          /* If you add a ->what type here, update the comment in regcomp.h */
            switch (ri->data->what[n]) {
            case 'a':
            case 'r':
            case 's':
            case 'S':
            case 'u':
                SvREFCNT_dec(MUTABLE_SV(ri->data->data[n]));
                break;
            case 'f':
                Safefree(ri->data->data[n]);
                break;
            case 'l':
            case 'L':
                break;
            case 'T':
                { /* Aho Corasick add-on structure for a trie node.
                     Used in stclass optimization only */
                    U32 refcount;
                    reg_ac_data *aho=(reg_ac_data*)ri->data->data[n];
#ifdef USE_ITHREADS
                    dVAR;
#endif
                    OP_REFCNT_LOCK;
                    refcount = --aho->refcount;
                    OP_REFCNT_UNLOCK;
                    if ( !refcount ) {
                        PerlMemShared_free(aho->states);
                        PerlMemShared_free(aho->fail);
                         /* do this last!!!! */
                        PerlMemShared_free(ri->data->data[n]);
                        /* we should only ever get called once, so
                         * assert as much, and also guard the free
                         * which /might/ happen twice. At the least
                         * it will make code anlyzers happy and it
                         * doesn't cost much. - Yves */
                        assert(ri->regstclass);
                        if (ri->regstclass) {
                            PerlMemShared_free(ri->regstclass);
                            ri->regstclass = 0;
                        }
                    }
                }
                break;
            case 't':
                {
                    /* trie structure. */
                    U32 refcount;
                    reg_trie_data *trie=(reg_trie_data*)ri->data->data[n];
#ifdef USE_ITHREADS
                    dVAR;
#endif
                    OP_REFCNT_LOCK;
                    refcount = --trie->refcount;
                    OP_REFCNT_UNLOCK;
                    if ( !refcount ) {
                        PerlMemShared_free(trie->charmap);
                        PerlMemShared_free(trie->states);
                        PerlMemShared_free(trie->trans);
                        if (trie->bitmap)
                            PerlMemShared_free(trie->bitmap);
                        if (trie->jump)
                            PerlMemShared_free(trie->jump);
                        PerlMemShared_free(trie->wordinfo);
                        /* do this last!!!! */
                        PerlMemShared_free(ri->data->data[n]);
                    }
                }
                break;
            default:
                Perl_croak(aTHX_ "panic: regfree data code '%c'",
                                                    ri->data->what[n]);
            }
        }
        Safefree(ri->data->what);
        Safefree(ri->data);
    }

    Safefree(ri);
}

#define av_dup_inc(s,t) MUTABLE_AV(sv_dup_inc((const SV *)s,t))
#define hv_dup_inc(s,t) MUTABLE_HV(sv_dup_inc((const SV *)s,t))
#define SAVEPVN(p,n)    ((p) ? savepvn(p,n) : NULL)

/*
   re_dup - duplicate a regexp.

   This routine is expected to clone a given regexp structure. It is only
   compiled under USE_ITHREADS.

   After all of the core data stored in struct regexp is duplicated
   the regexp_engine.dupe method is used to copy any private data
   stored in the *pprivate pointer. This allows extensions to handle
   any duplication it needs to do.

   See pregfree() and regfree_internal() if you change anything here.
*/
#if defined(USE_ITHREADS)
#ifndef PERL_IN_XSUB_RE
void
Perl_re_dup_guts(pTHX_ const REGEXP *sstr, REGEXP *dstr, CLONE_PARAMS *param)
{
    dVAR;
    I32 npar;
    const struct regexp *r = ReANY(sstr);
    struct regexp *ret = ReANY(dstr);

    PERL_ARGS_ASSERT_RE_DUP_GUTS;

    npar = r->nparens+1;
    Newx(ret->offs, npar, regexp_paren_pair);
    Copy(r->offs, ret->offs, npar, regexp_paren_pair);

    if (ret->substrs) {
        /* Do it this way to avoid reading from *r after the StructCopy().
           That way, if any of the sv_dup_inc()s dislodge *r from the L1
           cache, it doesn't matter.  */
        const bool anchored = r->check_substr
            ? r->check_substr == r->anchored_substr
            : r->check_utf8 == r->anchored_utf8;
        Newx(ret->substrs, 1, struct reg_substr_data);
        StructCopy(r->substrs, ret->substrs, struct reg_substr_data);

        ret->anchored_substr = sv_dup_inc(ret->anchored_substr, param);
        ret->anchored_utf8 = sv_dup_inc(ret->anchored_utf8, param);
        ret->float_substr = sv_dup_inc(ret->float_substr, param);
        ret->float_utf8 = sv_dup_inc(ret->float_utf8, param);

        /* check_substr and check_utf8, if non-NULL, point to either their
           anchored or float namesakes, and don't hold a second reference.  */

        if (ret->check_substr) {
            if (anchored) {
                assert(r->check_utf8 == r->anchored_utf8);
                ret->check_substr = ret->anchored_substr;
                ret->check_utf8 = ret->anchored_utf8;
            } else {
                assert(r->check_substr == r->float_substr);
                assert(r->check_utf8 == r->float_utf8);
                ret->check_substr = ret->float_substr;
                ret->check_utf8 = ret->float_utf8;
            }
        } else if (ret->check_utf8) {
            if (anchored) {
                ret->check_utf8 = ret->anchored_utf8;
            } else {
                ret->check_utf8 = ret->float_utf8;
            }
        }
    }

    RXp_PAREN_NAMES(ret) = hv_dup_inc(RXp_PAREN_NAMES(ret), param);
    ret->qr_anoncv = MUTABLE_CV(sv_dup_inc((const SV *)ret->qr_anoncv, param));

    if (ret->pprivate)
        RXi_SET(ret,CALLREGDUPE_PVT(dstr,param));

    if (RX_MATCH_COPIED(dstr))
        ret->subbeg  = SAVEPVN(ret->subbeg, ret->sublen);
    else
        ret->subbeg = NULL;
#ifdef PERL_ANY_COW
    ret->saved_copy = NULL;
#endif

    /* Whether mother_re be set or no, we need to copy the string.  We
       cannot refrain from copying it when the storage points directly to
       our mother regexp, because that's
               1: a buffer in a different thread
               2: something we no longer hold a reference on
               so we need to copy it locally.  */
    RX_WRAPPED(dstr) = SAVEPVN(RX_WRAPPED(sstr), SvCUR(sstr)+1);
    ret->mother_re   = NULL;
}
#endif /* PERL_IN_XSUB_RE */

/*
   regdupe_internal()

   This is the internal complement to regdupe() which is used to copy
   the structure pointed to by the *pprivate pointer in the regexp.
   This is the core version of the extension overridable cloning hook.
   The regexp structure being duplicated will be copied by perl prior
   to this and will be provided as the regexp *r argument, however
   with the /old/ structures pprivate pointer value. Thus this routine
   may override any copying normally done by perl.

   It returns a pointer to the new regexp_internal structure.
*/

void *
Perl_regdupe_internal(pTHX_ REGEXP * const rx, CLONE_PARAMS *param)
{
    dVAR;
    struct regexp *const r = ReANY(rx);
    regexp_internal *reti;
    int len;
    RXi_GET_DECL(r,ri);

    PERL_ARGS_ASSERT_REGDUPE_INTERNAL;

    len = ProgLen(ri);

    Newxc(reti, sizeof(regexp_internal) + len*sizeof(regnode),
          char, regexp_internal);
    Copy(ri->program, reti->program, len+1, regnode);

    reti->num_code_blocks = ri->num_code_blocks;
    if (ri->code_blocks) {
        int n;
        Newxc(reti->code_blocks, ri->num_code_blocks, struct reg_code_block,
                struct reg_code_block);
        Copy(ri->code_blocks, reti->code_blocks, ri->num_code_blocks,
                struct reg_code_block);
        for (n = 0; n < ri->num_code_blocks; n++)
             reti->code_blocks[n].src_regex = (REGEXP*)
                    sv_dup_inc((SV*)(ri->code_blocks[n].src_regex), param);
    }
    else
        reti->code_blocks = NULL;

    reti->regstclass = NULL;

    if (ri->data) {
        struct reg_data *d;
        const int count = ri->data->count;
        int i;

        Newxc(d, sizeof(struct reg_data) + count*sizeof(void *),
                char, struct reg_data);
        Newx(d->what, count, U8);

        d->count = count;
        for (i = 0; i < count; i++) {
            d->what[i] = ri->data->what[i];
            switch (d->what[i]) {
                /* see also regcomp.h and regfree_internal() */
            case 'a': /* actually an AV, but the dup function is identical.  */
            case 'r':
            case 's':
            case 'S':
            case 'u': /* actually an HV, but the dup function is identical.  */
                d->data[i] = sv_dup_inc((const SV *)ri->data->data[i], param);
                break;
            case 'f':
                /* This is cheating. */
                Newx(d->data[i], 1, regnode_ssc);
                StructCopy(ri->data->data[i], d->data[i], regnode_ssc);
                reti->regstclass = (regnode*)d->data[i];
                break;
            case 'T':
                /* Trie stclasses are readonly and can thus be shared
                 * without duplication. We free the stclass in pregfree
                 * when the corresponding reg_ac_data struct is freed.
                 */
                reti->regstclass= ri->regstclass;
                /* FALLTHROUGH */
            case 't':
                OP_REFCNT_LOCK;
                ((reg_trie_data*)ri->data->data[i])->refcount++;
                OP_REFCNT_UNLOCK;
                /* FALLTHROUGH */
            case 'l':
            case 'L':
                d->data[i] = ri->data->data[i];
                break;
            default:
                Perl_croak(aTHX_ "panic: re_dup unknown data code '%c'",
                                                           ri->data->what[i]);
            }
        }

        reti->data = d;
    }
    else
        reti->data = NULL;

    reti->name_list_idx = ri->name_list_idx;

#ifdef RE_TRACK_PATTERN_OFFSETS
    if (ri->u.offsets) {
        Newx(reti->u.offsets, 2*len+1, U32);
        Copy(ri->u.offsets, reti->u.offsets, 2*len+1, U32);
    }
#else
    SetProgLen(reti,len);
#endif

    return (void*)reti;
}

#endif    /* USE_ITHREADS */

#ifndef PERL_IN_XSUB_RE

/*
 - regnext - dig the "next" pointer out of a node
 */
regnode *
Perl_regnext(pTHX_ regnode *p)
{
    I32 offset;

    if (!p)
        return(NULL);

    if (OP(p) > REGNODE_MAX) {          /* regnode.type is unsigned */
        Perl_croak(aTHX_ "Corrupted regexp opcode %d > %d",
                                                (int)OP(p), (int)REGNODE_MAX);
    }

    offset = (reg_off_by_arg[OP(p)] ? ARG(p) : NEXT_OFF(p));
    if (offset == 0)
        return(NULL);

    return(p+offset);
}
#endif

STATIC void
S_re_croak2(pTHX_ bool utf8, const char* pat1,const char* pat2,...)
{
    va_list args;
    STRLEN l1 = strlen(pat1);
    STRLEN l2 = strlen(pat2);
    char buf[512];
    SV *msv;
    const char *message;

    PERL_ARGS_ASSERT_RE_CROAK2;

    if (l1 > 510)
        l1 = 510;
    if (l1 + l2 > 510)
        l2 = 510 - l1;
    Copy(pat1, buf, l1 , char);
    Copy(pat2, buf + l1, l2 , char);
    buf[l1 + l2] = '\n';
    buf[l1 + l2 + 1] = '\0';
    va_start(args, pat2);
    msv = vmess(buf, &args);
    va_end(args);
    message = SvPV_const(msv,l1);
    if (l1 > 512)
        l1 = 512;
    Copy(message, buf, l1 , char);
    /* l1-1 to avoid \n */
    Perl_croak(aTHX_ "%"UTF8f, UTF8fARG(utf8, l1-1, buf));
}

/* XXX Here's a total kludge.  But we need to re-enter for swash routines. */

#ifndef PERL_IN_XSUB_RE
void
Perl_save_re_context(pTHX)
{
    I32 nparens = -1;
    I32 i;

    /* Save $1..$n (#18107: UTF-8 s/(\w+)/uc($1)/e); AMS 20021106. */

    if (PL_curpm) {
        const REGEXP * const rx = PM_GETRE(PL_curpm);
        if (rx)
            nparens = RX_NPARENS(rx);
    }

    /* RT #124109. This is a complete hack; in the SWASHNEW case we know
     * that PL_curpm will be null, but that utf8.pm and the modules it
     * loads will only use $1..$3.
     * The t/porting/re_context.t test file checks this assumption.
     */
    if (nparens == -1)
        nparens = 3;

    for (i = 1; i <= nparens; i++) {
        char digits[TYPE_CHARS(long)];
        const STRLEN len = my_snprintf(digits, sizeof(digits),
                                       "%lu", (long)i);
        GV *const *const gvp
            = (GV**)hv_fetch(PL_defstash, digits, len, 0);

        if (gvp) {
            GV * const gv = *gvp;
            if (SvTYPE(gv) == SVt_PVGV && GvSV(gv))
                save_scalar(gv);
        }
    }
}
#endif

#ifdef DEBUGGING

STATIC void
S_put_code_point(pTHX_ SV *sv, UV c)
{
    PERL_ARGS_ASSERT_PUT_CODE_POINT;

    if (c > 255) {
        Perl_sv_catpvf(aTHX_ sv, "\\x{%04"UVXf"}", c);
    }
    else if (isPRINT(c)) {
        const char string = (char) c;

        /* We use {phrase} as metanotation in the class, so also escape literal
         * braces */
        if (isBACKSLASHED_PUNCT(c) || c == '{' || c == '}')
            sv_catpvs(sv, "\\");
        sv_catpvn(sv, &string, 1);
    }
    else if (isMNEMONIC_CNTRL(c)) {
        Perl_sv_catpvf(aTHX_ sv, "%s", cntrl_to_mnemonic((U8) c));
    }
    else {
        Perl_sv_catpvf(aTHX_ sv, "\\x%02X", (U8) c);
    }
}

#define MAX_PRINT_A MAX_PRINT_A_FOR_USE_ONLY_BY_REGCOMP_DOT_C

STATIC void
S_put_range(pTHX_ SV *sv, UV start, const UV end, const bool allow_literals)
{
    /* Appends to 'sv' a displayable version of the range of code points from
     * 'start' to 'end'.  Mnemonics (like '\r') are used for the few controls
     * that have them, when they occur at the beginning or end of the range.
     * It uses hex to output the remaining code points, unless 'allow_literals'
     * is true, in which case the printable ASCII ones are output as-is (though
     * some of these will be escaped by put_code_point()).
     *
     * NOTE:  This is designed only for printing ranges of code points that fit
     *        inside an ANYOF bitmap.  Higher code points are simply suppressed
     */

    const unsigned int min_range_count = 3;

    assert(start <= end);

    PERL_ARGS_ASSERT_PUT_RANGE;

    while (start <= end) {
        UV this_end;
        const char * format;

        if (end - start < min_range_count) {

            /* Output chars individually when they occur in short ranges */
            for (; start <= end; start++) {
                put_code_point(sv, start);
            }
            break;
        }

        /* If permitted by the input options, and there is a possibility that
         * this range contains a printable literal, look to see if there is
         * one. */
        if (allow_literals && start <= MAX_PRINT_A) {

            /* If the character at the beginning of the range isn't an ASCII
             * printable, effectively split the range into two parts:
             *  1) the portion before the first such printable,
             *  2) the rest
             * and output them separately. */
            if (! isPRINT_A(start)) {
                UV temp_end = start + 1;

                /* There is no point looking beyond the final possible
                 * printable, in MAX_PRINT_A */
                UV max = MIN(end, MAX_PRINT_A);

                while (temp_end <= max && ! isPRINT_A(temp_end)) {
                    temp_end++;
                }

                /* Here, temp_end points to one beyond the first printable if
                 * found, or to one beyond 'max' if not.  If none found, make
                 * sure that we use the entire range */
                if (temp_end > MAX_PRINT_A) {
                    temp_end = end + 1;
                }

                /* Output the first part of the split range: the part that
                 * doesn't have printables, with the parameter set to not look
                 * for literals (otherwise we would infinitely recurse) */
                put_range(sv, start, temp_end - 1, FALSE);

                /* The 2nd part of the range (if any) starts here. */
                start = temp_end;

                /* We do a continue, instead of dropping down, because even if
                 * the 2nd part is non-empty, it could be so short that we want
                 * to output it as individual characters, as tested for at the
                 * top of this loop.  */
                continue;
            }

            /* Here, 'start' is a printable ASCII.  If it is an alphanumeric,
             * output a sub-range of just the digits or letters, then process
             * the remaining portion as usual. */
            if (isALPHANUMERIC_A(start)) {
                UV mask = (isDIGIT_A(start))
                           ? _CC_DIGIT
                             : isUPPER_A(start)
                               ? _CC_UPPER
                               : _CC_LOWER;
                UV temp_end = start + 1;

                /* Find the end of the sub-range that includes just the
                 * characters in the same class as the first character in it */
                while (temp_end <= end && _generic_isCC_A(temp_end, mask)) {
                    temp_end++;
                }
                temp_end--;

                /* For short ranges, don't duplicate the code above to output
                 * them; just call recursively */
                if (temp_end - start < min_range_count) {
                    put_range(sv, start, temp_end, FALSE);
                }
                else {  /* Output as a range */
                    put_code_point(sv, start);
                    sv_catpvs(sv, "-");
                    put_code_point(sv, temp_end);
                }
                start = temp_end + 1;
                continue;
            }

            /* We output any other printables as individual characters */
            if (isPUNCT_A(start) || isSPACE_A(start)) {
                while (start <= end && (isPUNCT_A(start)
                                        || isSPACE_A(start)))
                {
                    put_code_point(sv, start);
                    start++;
                }
                continue;
            }
        } /* End of looking for literals */

        /* Here is not to output as a literal.  Some control characters have
         * mnemonic names.  Split off any of those at the beginning and end of
         * the range to print mnemonically.  It isn't possible for many of
         * these to be in a row, so this won't overwhelm with output */
        while (isMNEMONIC_CNTRL(start) && start <= end) {
            put_code_point(sv, start);
            start++;
        }
        if (start < end && isMNEMONIC_CNTRL(end)) {

            /* Here, the final character in the range has a mnemonic name.
             * Work backwards from the end to find the final non-mnemonic */
            UV temp_end = end - 1;
            while (isMNEMONIC_CNTRL(temp_end)) {
                temp_end--;
            }

            /* And separately output the interior range that doesn't start or
             * end with mnemonics */
            put_range(sv, start, temp_end, FALSE);

            /* Then output the mnemonic trailing controls */
            start = temp_end + 1;
            while (start <= end) {
                put_code_point(sv, start);
                start++;
            }
            break;
        }

        /* As a final resort, output the range or subrange as hex. */

        this_end = (end < NUM_ANYOF_CODE_POINTS)
                    ? end
                    : NUM_ANYOF_CODE_POINTS - 1;
#if NUM_ANYOF_CODE_POINTS > 256
        format = (this_end < 256)
                 ? "\\x%02"UVXf"-\\x%02"UVXf""
                 : "\\x{%04"UVXf"}-\\x{%04"UVXf"}";
#else
        format = "\\x%02"UVXf"-\\x%02"UVXf"";
#endif
        GCC_DIAG_IGNORE(-Wformat-nonliteral);
        Perl_sv_catpvf(aTHX_ sv, format, start, this_end);
        GCC_DIAG_RESTORE;
        break;
    }
}

STATIC void
S_put_charclass_bitmap_innards_invlist(pTHX_ SV *sv, SV* invlist)
{
    /* Concatenate onto the PV in 'sv' a displayable form of the inversion list
     * 'invlist' */

    UV start, end;
    bool allow_literals = TRUE;

    PERL_ARGS_ASSERT_PUT_CHARCLASS_BITMAP_INNARDS_INVLIST;

    /* Generally, it is more readable if printable characters are output as
     * literals, but if a range (nearly) spans all of them, it's best to output
     * it as a single range.  This code will use a single range if all but 2
     * ASCII printables are in it */
    invlist_iterinit(invlist);
    while (invlist_iternext(invlist, &start, &end)) {

        /* If the range starts beyond the final printable, it doesn't have any
         * in it */
        if (start > MAX_PRINT_A) {
            break;
        }

        /* In both ASCII and EBCDIC, a SPACE is the lowest printable.  To span
         * all but two, the range must start and end no later than 2 from
         * either end */
        if (start < ' ' + 2 && end > MAX_PRINT_A - 2) {
            if (end > MAX_PRINT_A) {
                end = MAX_PRINT_A;
            }
            if (start < ' ') {
                start = ' ';
            }
            if (end - start >= MAX_PRINT_A - ' ' - 2) {
                allow_literals = FALSE;
            }
            break;
        }
    }
    invlist_iterfinish(invlist);

    /* Here we have figured things out.  Output each range */
    invlist_iterinit(invlist);
    while (invlist_iternext(invlist, &start, &end)) {
        if (start >= NUM_ANYOF_CODE_POINTS) {
            break;
        }
        put_range(sv, start, end, allow_literals);
    }
    invlist_iterfinish(invlist);

    return;
}

STATIC SV*
S_put_charclass_bitmap_innards_common(pTHX_
        SV* invlist,            /* The bitmap */
        SV* posixes,            /* Under /l, things like [:word:], \S */
        SV* only_utf8,          /* Under /d, matches iff the target is UTF-8 */
        SV* not_utf8,           /* /d, matches iff the target isn't UTF-8 */
        SV* only_utf8_locale,   /* Under /l, matches if the locale is UTF-8 */
        const bool invert       /* Is the result to be inverted? */
)
{
    /* Create and return an SV containing a displayable version of the bitmap
     * and associated information determined by the input parameters. */

    SV * output;

    PERL_ARGS_ASSERT_PUT_CHARCLASS_BITMAP_INNARDS_COMMON;

    if (invert) {
        output = newSVpvs("^");
    }
    else {
        output = newSVpvs("");
    }

    /* First, the code points in the bitmap that are unconditionally there */
    put_charclass_bitmap_innards_invlist(output, invlist);

    /* Traditionally, these have been placed after the main code points */
    if (posixes) {
        sv_catsv(output, posixes);
    }

    if (only_utf8 && _invlist_len(only_utf8)) {
        Perl_sv_catpvf(aTHX_ output, "%s{utf8}%s", PL_colors[1], PL_colors[0]);
        put_charclass_bitmap_innards_invlist(output, only_utf8);
    }

    if (not_utf8 && _invlist_len(not_utf8)) {
        Perl_sv_catpvf(aTHX_ output, "%s{not utf8}%s", PL_colors[1], PL_colors[0]);
        put_charclass_bitmap_innards_invlist(output, not_utf8);
    }

    if (only_utf8_locale && _invlist_len(only_utf8_locale)) {
        Perl_sv_catpvf(aTHX_ output, "%s{utf8 locale}%s", PL_colors[1], PL_colors[0]);
        put_charclass_bitmap_innards_invlist(output, only_utf8_locale);

        /* This is the only list in this routine that can legally contain code
         * points outside the bitmap range.  The call just above to
         * 'put_charclass_bitmap_innards_invlist' will simply suppress them, so
         * output them here.  There's about a half-dozen possible, and none in
         * contiguous ranges longer than 2 */
        if (invlist_highest(only_utf8_locale) >= NUM_ANYOF_CODE_POINTS) {
            UV start, end;
            SV* above_bitmap = NULL;

            _invlist_subtract(only_utf8_locale, PL_InBitmap, &above_bitmap);

            invlist_iterinit(above_bitmap);
            while (invlist_iternext(above_bitmap, &start, &end)) {
                UV i;

                for (i = start; i <= end; i++) {
                    put_code_point(output, i);
                }
            }
            invlist_iterfinish(above_bitmap);
            SvREFCNT_dec_NN(above_bitmap);
        }
    }

    /* If the only thing we output is the '^', clear it */
    if (invert && SvCUR(output) == 1) {
        SvCUR_set(output, 0);
    }

    return output;
}

STATIC bool
S_put_charclass_bitmap_innards(pTHX_ SV *sv,
                                     char *bitmap,
                                     SV *nonbitmap_invlist,
                                     SV *only_utf8_locale_invlist,
                                     const regnode * const node)
{
    /* Appends to 'sv' a displayable version of the innards of the bracketed
     * character class defined by the other arguments:
     *  'bitmap' points to the bitmap.
     *  'nonbitmap_invlist' is an inversion list of the code points that are in
     *      the bitmap range, but for some reason aren't in the bitmap; NULL if
     *      none.  The reasons for this could be that they require some
     *      condition such as the target string being or not being in UTF-8
     *      (under /d), or because they came from a user-defined property that
     *      was not resolved at the time of the regex compilation (under /u)
     *  'only_utf8_locale_invlist' is an inversion list of the code points that
     *      are valid only if the runtime locale is a UTF-8 one; NULL if none
     *  'node' is the regex pattern node.  It is needed only when the above two
     *      parameters are not null, and is passed so that this routine can
     *      tease apart the various reasons for them.
     *
     * It returns TRUE if there was actually something output.  (It may be that
     * the bitmap, etc is empty.)
     *
     * When called for outputting the bitmap of a non-ANYOF node, just pass the
     * bitmap, with the succeeding parameters set to NULL.
     *
     */

    /* In general, it tries to display the 'cleanest' representation of the
     * innards, choosing whether to display them inverted or not, regardless of
     * whether the class itself is to be inverted.  However,  there are some
     * cases where it can't try inverting, as what actually matches isn't known
     * until runtime, and hence the inversion isn't either. */
    bool inverting_allowed = TRUE;

    int i;
    STRLEN orig_sv_cur = SvCUR(sv);

    SV* invlist;            /* Inversion list we accumulate of code points that
                               are unconditionally matched */
    SV* only_utf8 = NULL;   /* Under /d, list of matches iff the target is
                               UTF-8 */
    SV* not_utf8 =  NULL;   /* /d, list of matches iff the target isn't UTF-8
                             */
    SV* posixes = NULL;     /* Under /l, string of things like [:word:], \D */
    SV* only_utf8_locale = NULL;    /* Under /l, list of matches if the locale
                                       is UTF-8 */

    SV* as_is_display;      /* The output string when we take the inputs
                              literally */
    SV* inverted_display;   /* The output string when we invert the inputs */

    U8 flags = (node) ? ANYOF_FLAGS(node) : 0;

    bool invert = cBOOL(flags & ANYOF_INVERT);  /* Is the input to be inverted
                                                   to match? */
    /* We are biased in favor of displaying things without them being inverted,
     * as that is generally easier to understand */
    const int bias = 5;

    PERL_ARGS_ASSERT_PUT_CHARCLASS_BITMAP_INNARDS;

    /* Start off with whatever code points are passed in.  (We clone, so we
     * don't change the caller's list) */
    if (nonbitmap_invlist) {
        assert(invlist_highest(nonbitmap_invlist) < NUM_ANYOF_CODE_POINTS);
        invlist = invlist_clone(nonbitmap_invlist);
    }
    else {  /* Worst case size is every other code point is matched */
        invlist = _new_invlist(NUM_ANYOF_CODE_POINTS / 2);
    }

    if (flags) {
        if (OP(node) == ANYOFD) {

            /* This flag indicates that the code points below 0x100 in the
             * nonbitmap list are precisely the ones that match only when the
             * target is UTF-8 (they should all be non-ASCII). */
            if (flags & ANYOF_SHARED_d_UPPER_LATIN1_UTF8_STRING_MATCHES_non_d_RUNTIME_USER_PROP)
            {
                _invlist_intersection(invlist, PL_UpperLatin1, &only_utf8);
                _invlist_subtract(invlist, only_utf8, &invlist);
            }

            /* And this flag for matching all non-ASCII 0xFF and below */
            if (flags & ANYOF_SHARED_d_MATCHES_ALL_NON_UTF8_NON_ASCII_non_d_WARN_SUPER)
            {
                if (invert) {
                    not_utf8 = _new_invlist(0);
                }
                else {
                    not_utf8 = invlist_clone(PL_UpperLatin1);
                }
                inverting_allowed = FALSE;  /* XXX needs more work to be able
                                               to allow this */
            }
        }
        else if (OP(node) == ANYOFL) {

            /* If either of these flags are set, what matches isn't
             * determinable except during execution, so don't know enough here
             * to invert */
            if (flags & (ANYOFL_FOLD|ANYOF_MATCHES_POSIXL)) {
                inverting_allowed = FALSE;
            }

            /* What the posix classes match also varies at runtime, so these
             * will be output symbolically. */
            if (ANYOF_POSIXL_TEST_ANY_SET(node)) {
                int i;

                posixes = newSVpvs("");
                for (i = 0; i < ANYOF_POSIXL_MAX; i++) {
                    if (ANYOF_POSIXL_TEST(node,i)) {
                        sv_catpv(posixes, anyofs[i]);
                    }
                }
            }
        }
    }

    /* Accumulate the bit map into the unconditional match list */
    for (i = 0; i < NUM_ANYOF_CODE_POINTS; i++) {
        if (BITMAP_TEST(bitmap, i)) {
            invlist = add_cp_to_invlist(invlist, i);
        }
    }

    /* Make sure that the conditional match lists don't have anything in them
     * that match unconditionally; otherwise the output is quite confusing.
     * This could happen if the code that populates these misses some
     * duplication. */
    if (only_utf8) {
        _invlist_subtract(only_utf8, invlist, &only_utf8);
    }
    if (not_utf8) {
        _invlist_subtract(not_utf8, invlist, &not_utf8);
    }

    if (only_utf8_locale_invlist) {

        /* Since this list is passed in, we have to make a copy before
         * modifying it */
        only_utf8_locale = invlist_clone(only_utf8_locale_invlist);

        _invlist_subtract(only_utf8_locale, invlist, &only_utf8_locale);

        /* And, it can get really weird for us to try outputting an inverted
         * form of this list when it has things above the bitmap, so don't even
         * try */
        if (invlist_highest(only_utf8_locale) >= NUM_ANYOF_CODE_POINTS) {
            inverting_allowed = FALSE;
        }
    }

    /* Calculate what the output would be if we take the input as-is */
    as_is_display = put_charclass_bitmap_innards_common(invlist,
                                                    posixes,
                                                    only_utf8,
                                                    not_utf8,
                                                    only_utf8_locale,
                                                    invert);

    /* If have to take the output as-is, just do that */
    if (! inverting_allowed) {
        sv_catsv(sv, as_is_display);
    }
    else { /* But otherwise, create the output again on the inverted input, and
              use whichever version is shorter */

        int inverted_bias, as_is_bias;

        /* We will apply our bias to whichever of the the results doesn't have
         * the '^' */
        if (invert) {
            invert = FALSE;
            as_is_bias = bias;
            inverted_bias = 0;
        }
        else {
            invert = TRUE;
            as_is_bias = 0;
            inverted_bias = bias;
        }

        /* Now invert each of the lists that contribute to the output,
         * excluding from the result things outside the possible range */

        /* For the unconditional inversion list, we have to add in all the
         * conditional code points, so that when inverted, they will be gone
         * from it */
        _invlist_union(only_utf8, invlist, &invlist);
        _invlist_union(only_utf8_locale, invlist, &invlist);
        _invlist_invert(invlist);
        _invlist_intersection(invlist, PL_InBitmap, &invlist);

        if (only_utf8) {
            _invlist_invert(only_utf8);
            _invlist_intersection(only_utf8, PL_UpperLatin1, &only_utf8);
        }

        if (not_utf8) {
            _invlist_invert(not_utf8);
            _invlist_intersection(not_utf8, PL_UpperLatin1, &not_utf8);
        }

        if (only_utf8_locale) {
            _invlist_invert(only_utf8_locale);
            _invlist_intersection(only_utf8_locale,
                                  PL_InBitmap,
                                  &only_utf8_locale);
        }

        inverted_display = put_charclass_bitmap_innards_common(
                                            invlist,
                                            posixes,
                                            only_utf8,
                                            not_utf8,
                                            only_utf8_locale, invert);

        /* Use the shortest representation, taking into account our bias
         * against showing it inverted */
        if (SvCUR(inverted_display) + inverted_bias
            < SvCUR(as_is_display) + as_is_bias)
        {
            sv_catsv(sv, inverted_display);
        }
        else {
            sv_catsv(sv, as_is_display);
        }

        SvREFCNT_dec_NN(as_is_display);
        SvREFCNT_dec_NN(inverted_display);
    }

    SvREFCNT_dec_NN(invlist);
    SvREFCNT_dec(only_utf8);
    SvREFCNT_dec(not_utf8);
    SvREFCNT_dec(posixes);
    SvREFCNT_dec(only_utf8_locale);

    return SvCUR(sv) > orig_sv_cur;
}

#define CLEAR_OPTSTART \
    if (optstart) STMT_START {                                               \
        DEBUG_OPTIMISE_r(PerlIO_printf(Perl_debug_log,                       \
                              " (%"IVdf" nodes)\n", (IV)(node - optstart))); \
        optstart=NULL;                                                       \
    } STMT_END

#define DUMPUNTIL(b,e)                                                       \
                    CLEAR_OPTSTART;                                          \
                    node=dumpuntil(r,start,(b),(e),last,sv,indent+1,depth+1);

STATIC const regnode *
S_dumpuntil(pTHX_ const regexp *r, const regnode *start, const regnode *node,
            const regnode *last, const regnode *plast,
            SV* sv, I32 indent, U32 depth)
{
    U8 op = PSEUDO;     /* Arbitrary non-END op. */
    const regnode *next;
    const regnode *optstart= NULL;

    RXi_GET_DECL(r,ri);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_DUMPUNTIL;

#ifdef DEBUG_DUMPUNTIL
    PerlIO_printf(Perl_debug_log, "--- %d : %d - %d - %d\n",indent,node-start,
        last ? last-start : 0,plast ? plast-start : 0);
#endif

    if (plast && plast < last)
        last= plast;

    while (PL_regkind[op] != END && (!last || node < last)) {
        assert(node);
        /* While that wasn't END last time... */
        NODE_ALIGN(node);
        op = OP(node);
        if (op == CLOSE || op == WHILEM)
            indent--;
        next = regnext((regnode *)node);

        /* Where, what. */
        if (OP(node) == OPTIMIZED) {
            if (!optstart && RE_DEBUG_FLAG(RE_DEBUG_COMPILE_OPTIMISE))
                optstart = node;
            else
                goto after_print;
        } else
            CLEAR_OPTSTART;

        regprop(r, sv, node, NULL, NULL);
        PerlIO_printf(Perl_debug_log, "%4"IVdf":%*s%s", (IV)(node - start),
                      (int)(2*indent + 1), "", SvPVX_const(sv));

        if (OP(node) != OPTIMIZED) {
            if (next == NULL)           /* Next ptr. */
                PerlIO_printf(Perl_debug_log, " (0)");
            else if (PL_regkind[(U8)op] == BRANCH
                     && PL_regkind[OP(next)] != BRANCH )
                PerlIO_printf(Perl_debug_log, " (FAIL)");
            else
                PerlIO_printf(Perl_debug_log, " (%"IVdf")", (IV)(next - start));
            (void)PerlIO_putc(Perl_debug_log, '\n');
        }

      after_print:
        if (PL_regkind[(U8)op] == BRANCHJ) {
            assert(next);
            {
                const regnode *nnode = (OP(next) == LONGJMP
                                       ? regnext((regnode *)next)
                                       : next);
                if (last && nnode > last)
                    nnode = last;
                DUMPUNTIL(NEXTOPER(NEXTOPER(node)), nnode);
            }
        }
        else if (PL_regkind[(U8)op] == BRANCH) {
            assert(next);
            DUMPUNTIL(NEXTOPER(node), next);
        }
        else if ( PL_regkind[(U8)op]  == TRIE ) {
            const regnode *this_trie = node;
            const char op = OP(node);
            const U32 n = ARG(node);
            const reg_ac_data * const ac = op>=AHOCORASICK ?
               (reg_ac_data *)ri->data->data[n] :
               NULL;
            const reg_trie_data * const trie =
                (reg_trie_data*)ri->data->data[op<AHOCORASICK ? n : ac->trie];
#ifdef DEBUGGING
            AV *const trie_words
                           = MUTABLE_AV(ri->data->data[n + TRIE_WORDS_OFFSET]);
#endif
            const regnode *nextbranch= NULL;
            I32 word_idx;
            sv_setpvs(sv, "");
            for (word_idx= 0; word_idx < (I32)trie->wordcount; word_idx++) {
                SV ** const elem_ptr = av_fetch(trie_words,word_idx,0);

                PerlIO_printf(Perl_debug_log, "%*s%s ",
                   (int)(2*(indent+3)), "",
                    elem_ptr
                    ? pv_pretty(sv, SvPV_nolen_const(*elem_ptr),
                                SvCUR(*elem_ptr), 60,
                                PL_colors[0], PL_colors[1],
                                (SvUTF8(*elem_ptr)
                                 ? PERL_PV_ESCAPE_UNI
                                 : 0)
                                | PERL_PV_PRETTY_ELLIPSES
                                | PERL_PV_PRETTY_LTGT
                            )
                    : "???"
                );
                if (trie->jump) {
                    U16 dist= trie->jump[word_idx+1];
                    PerlIO_printf(Perl_debug_log, "(%"UVuf")\n",
                               (UV)((dist ? this_trie + dist : next) - start));
                    if (dist) {
                        if (!nextbranch)
                            nextbranch= this_trie + trie->jump[0];
                        DUMPUNTIL(this_trie + dist, nextbranch);
                    }
                    if (nextbranch && PL_regkind[OP(nextbranch)]==BRANCH)
                        nextbranch= regnext((regnode *)nextbranch);
                } else {
                    PerlIO_printf(Perl_debug_log, "\n");
                }
            }
            if (last && next > last)
                node= last;
            else
                node= next;
        }
        else if ( op == CURLY ) {   /* "next" might be very big: optimizer */
            DUMPUNTIL(NEXTOPER(node) + EXTRA_STEP_2ARGS,
                    NEXTOPER(node) + EXTRA_STEP_2ARGS + 1);
        }
        else if (PL_regkind[(U8)op] == CURLY && op != CURLYX) {
            assert(next);
            DUMPUNTIL(NEXTOPER(node) + EXTRA_STEP_2ARGS, next);
        }
        else if ( op == PLUS || op == STAR) {
            DUMPUNTIL(NEXTOPER(node), NEXTOPER(node) + 1);
        }
        else if (PL_regkind[(U8)op] == ANYOF) {
            /* arglen 1 + class block */
            node += 1 + ((ANYOF_FLAGS(node) & ANYOF_MATCHES_POSIXL)
                          ? ANYOF_POSIXL_SKIP
                          : ANYOF_SKIP);
            node = NEXTOPER(node);
        }
        else if (PL_regkind[(U8)op] == EXACT) {
            /* Literal string, where present. */
            node += NODE_SZ_STR(node) - 1;
            node = NEXTOPER(node);
        }
        else {
            node = NEXTOPER(node);
            node += regarglen[(U8)op];
        }
        if (op == CURLYX || op == OPEN)
            indent++;
    }
    CLEAR_OPTSTART;
#ifdef DEBUG_DUMPUNTIL
    PerlIO_printf(Perl_debug_log, "--- %d\n", (int)indent);
#endif
    return node;
}

#endif  /* DEBUGGING */

/*
 * ex: set ts=8 sts=4 sw=4 et:
 */