regcomp.c: Move code into a function

[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_static.c"
#include "charclass_invlists.h"
#include "inline_invlist.c"
#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 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


struct RExC_state_t {
    U32         flags;                  /* RXf_* are we folding, multilining? */
    U32         pm_flags;               /* PMf_* stuff from the calling PMOP */
    char        *precomp;               /* 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. */
    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 parens we have moved
                                           through */
    U32         study_chunk_recursed_bytes;  /* bytes in bitmap */
    I32         in_lookbehind;
    I32         contains_locale;
    I32         contains_i;
    I32         override_recoding;
    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 */
#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 */
#define RExC_lastparse  (pRExC_state->lastparse)
#define RExC_lastnum    (pRExC_state->lastnum)
#define RExC_paren_name_list    (pRExC_state->paren_name_list)
#endif
};

#define RExC_flags      (pRExC_state->flags)
#define RExC_pm_flags   (pRExC_state->pm_flags)
#define RExC_precomp    (pRExC_state->precomp)
#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)
#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_naughty    (pRExC_state->naughty)
#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)
#define RExC_in_multi_char_class (pRExC_state->in_multi_char_class)


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

/*
 * 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_UTF8    0x20    /* Restart, 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    STMT_START {                                       \
                                     if (!UTF) {                           \
                                         *flagp = RESTART_UTF8;            \
                                         return NULL;                      \
                                     }                                     \
                        } 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;

/* The below is perhaps overboard, but this allows us to save a test at the
 * expense of a mask.  This is because on both EBCDIC and ASCII machines, 'A'
 * and 'a' differ by a single bit; the same with the upper and lower case of
 * all other ASCII-range alphabetics.  On ASCII platforms, they are 32 apart;
 * on EBCDIC, they are 64.  This uses an exclusive 'or' to find that bit and
 * then inverts it to form a mask, with just a single 0, in the bit position
 * where the upper- and lowercase differ.  XXX There are about 40 other
 * instances in the Perl core where this micro-optimization could be used.
 * Should decide if maintenance cost is worse, before changing those
 *
 * Returns a boolean as to whether or not 'v' is either a lowercase or
 * uppercase instance of 'c', where 'c' is in [A-Za-z].  If 'c' is a
 * compile-time constant, the generated code is better than some optimizing
 * compilers figure out, amounting to a mask and test.  The results are
 * meaningless if 'c' is not one of [A-Za-z] */
#define isARG2_lower_or_UPPER_ARG1(c, v) \
                              (((v) & ~('A' ^ 'a')) ==  ((c) & ~('A' ^ 'a')))

/*
 * 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 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"/"

#define REPORT_LOCATION_ARGS(offset)            \
                UTF8fARG(UTF, offset, RExC_precomp), \
                UTF8fARG(UTF, RExC_end - RExC_precomp - offset, RExC_precomp + offset)

/*
 * 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_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 {                                    \
    const IV offset = RExC_parse - RExC_precomp;                        \
    Perl_croak(aTHX_ "%s" REPORT_LOCATION,                              \
            m, REPORT_LOCATION_ARGS(offset));   \
} 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 {                        \
    const IV offset = RExC_parse - RExC_precomp;                        \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1,                      \
                      REPORT_LOCATION_ARGS(offset));    \
} 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 {                   \
    const IV offset = RExC_parse - RExC_precomp;                \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2,          \
            REPORT_LOCATION_ARGS(offset));      \
} 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 {               \
    const IV offset = RExC_parse - RExC_precomp;                \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2, a3,              \
            REPORT_LOCATION_ARGS(offset));      \
} 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 { \
    const IV offset = RExC_parse - RExC_precomp;   \
    if (!SIZE_ONLY)                                \
        SAVEFREESV(RExC_rx_sv);                    \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, \
            REPORT_LOCATION_ARGS(offset));         \
} STMT_END


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

#define ckWARNreg(loc,m) STMT_START {                                   \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,      \
            REPORT_LOCATION_ARGS(offset));              \
} STMT_END

#define vWARN_dep(loc, m) STMT_START {                                  \
    const IV offset = loc - RExC_precomp;                               \
    Perl_warner(aTHX_ packWARN(WARN_DEPRECATED), m REPORT_LOCATION,     \
            REPORT_LOCATION_ARGS(offset));              \
} STMT_END

#define ckWARNdep(loc,m) STMT_START {                                   \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner_d(aTHX_ packWARN(WARN_DEPRECATED),                   \
            m REPORT_LOCATION,                                          \
            REPORT_LOCATION_ARGS(offset));              \
} STMT_END

#define ckWARNregdep(loc,m) STMT_START {                                \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner_d(aTHX_ packWARN2(WARN_DEPRECATED, WARN_REGEXP),     \
            m REPORT_LOCATION,                                          \
            REPORT_LOCATION_ARGS(offset));              \
} STMT_END

#define ckWARN2reg_d(loc,m, a1) STMT_START {                            \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner_d(aTHX_ packWARN(WARN_REGEXP),                       \
            m REPORT_LOCATION,                                          \
            a1, REPORT_LOCATION_ARGS(offset));  \
} STMT_END

#define ckWARN2reg(loc, m, a1) STMT_START {                             \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,      \
            a1, REPORT_LOCATION_ARGS(offset));  \
} STMT_END

#define vWARN3(loc, m, a1, a2) STMT_START {                             \
    const IV offset = loc - RExC_precomp;                               \
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,         \
            a1, a2, REPORT_LOCATION_ARGS(offset));      \
} STMT_END

#define ckWARN3reg(loc, m, a1, a2) STMT_START {                         \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,      \
            a1, a2, REPORT_LOCATION_ARGS(offset));      \
} STMT_END

#define vWARN4(loc, m, a1, a2, a3) STMT_START {                         \
    const IV offset = loc - RExC_precomp;                               \
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,         \
            a1, a2, a3, REPORT_LOCATION_ARGS(offset)); \
} STMT_END

#define ckWARN4reg(loc, m, a1, a2, a3) STMT_START {                     \
    const IV offset = loc - RExC_precomp;                               \
    Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,      \
            a1, a2, a3, REPORT_LOCATION_ARGS(offset)); \
} STMT_END

#define vWARN5(loc, m, a1, a2, a3, a4) STMT_START {                     \
    const IV offset = loc - RExC_precomp;                               \
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,         \
            a1, a2, a3, a4, REPORT_LOCATION_ARGS(offset)); \
} STMT_END


/* Allow for side effects in s */
#define REGC(c,s) STMT_START {                  \
    if (!SIZE_ONLY) *(s) = (c); else (void)(s); \
} 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_CANY_SEEN)                                  \
                PerlIO_printf(Perl_debug_log,"REG_CANY_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_STUDYDATA(str,data,depth)                              \
DEBUG_OPTIMISE_MORE_r(if(data){                                      \
    PerlIO_printf(Perl_debug_log,                                    \
        "%*s" str "Pos:%"IVdf"/%"IVdf                                \
        " Flags: 0x%"UVXf" Whilem_c: %"IVdf" Lcp: %"IVdf" %s",       \
        (int)(depth)*2, "",                                          \
        (IV)((data)->pos_min),                                       \
        (IV)((data)->pos_delta),                                     \
        (UV)((data)->flags),                                         \
        (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");                              \
});

/* 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
                                         ? 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) |= ANYOF_EMPTY_STRING;    /* Plus match empty string */
}

STATIC int
S_ssc_is_anything(pTHX_ 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) & ANYOF_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_NONBITMAP_EMPTY);
    ssc_anything(ssc);

    /* If any portion of the regex is to operate under locale rules,
     * 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(pTHX_ 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 = sv_2mortal(_new_invlist(0));
    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_NONBITMAP_EMPTY) {
        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 */
            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) & ANYOF_LOC_FOLD)
            && ary[2] && ary[2] != &PL_sv_undef)
        {
            only_utf8_locale_invlist = ary[2];
        }
    }

    /* An ANYOF node contains a bitmap for the first 256 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 < 256; 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 */
    if (ANYOF_FLAGS(node) & ANYOF_NON_UTF8_NON_ASCII_ALL) {
        _invlist_union(invlist, PL_UpperLatin1, &invlist);
    }

    /* Similarly for these */
    if (ANYOF_FLAGS(node) & ANYOF_ABOVE_LATIN1_ALL) {
        invlist = _add_range_to_invlist(invlist, 256, UV_MAX);
    }

    if (ANYOF_FLAGS(node) & ANYOF_INVERT) {
        _invlist_invert(invlist);
    }
    else if (new_node_has_latin1 && ANYOF_FLAGS(node) & ANYOF_LOC_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_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_WARN_SUPER;
        }
    }
    else {
        anded_cp_list = get_ANYOF_cp_list_for_ssc(pRExC_state, and_with);
        anded_flags = ANYOF_FLAGS(and_with) & ANYOF_COMMON_FLAGS;
    }

    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_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_POSIXL) {
                    ANYOF_POSIXL_OR((regnode_charclass_posixl*) and_with, ssc);
                }
            }
        }
        else if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)
                 || (ANYOF_FLAGS(and_with) & ANYOF_POSIXL))
        {
            /* One or the other of P1, P2 is non-empty. */
            if (ANYOF_FLAGS(and_with) & ANYOF_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;
    }

    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_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(pTHX_ 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;
}

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 256 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 ANYOF_EMPTY_STRING, which should be cleared by the
     * time we reach here */
    assert(! (ANYOF_FLAGS(ssc) & ~ANYOF_COMMON_FLAGS));

    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_POSIXL;
    }

    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|Fl)/
  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 occured 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(7); /* XXX: optimize me */                   \
            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)
{
    dVAR;
    /* 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: break;
        case EXACTFA:
        case EXACTFU_SS:
        case EXACTFU: 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)
        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 void
S_make_trie_failtable(pTHX_ RExC_state_t *pRExC_state, regnode *source,  regnode *stclass, 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"));
    GET_RE_DEBUG_FLAGS_DECL;

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


    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;*/
}


#define DEBUG_PEEP(str,scan,depth) \
    DEBUG_OPTIMISE_r({if (scan){ \
       SV * const mysv=sv_newmortal(); \
       regnode *Next = regnext(scan); \
       regprop(RExC_rx, mysv, scan, NULL); \
       PerlIO_printf(Perl_debug_log, "%*s" str ">%3d: %s (%d)\n", \
       (int)depth*2, "", REG_NODE_NUM(scan), SvPV_nolen_const(mysv),\
       Next ? (REG_NODE_NUM(Next)) : 0 ); \
   }});


/* 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
 *
 * 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) {
        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 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) */
            while (s < s_end) {
                if (*s == LATIN_SMALL_LETTER_SHARP_S) {
                    OP(scan) = EXACTFA_NO_TRIE;
                    *unfolded_multi_char = TRUE;
                    break;
                }
                s++;
                continue;
            }
        }
        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
                    && isARG2_lower_or_UPPER_ARG1('s', *s)
                    && isARG2_lower_or_UPPER_ARG1('s', *(s+1)))
                {

                    /* 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;
            }
        }
    }

#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)

/* 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;  /* last node to process in this frame */
    regnode *next;  /* next node to process when last is reached */
    struct scan_frame *prev; /*previous frame*/
    U32 prev_recursed_depth;
    I32 stop; /* what stopparen do we use */
} scan_frame;


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 */
{
    dVAR;
    /* 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;

#ifdef DEBUGGING
    StructCopy(&zero_scan_data, &data_fake, scan_data_t);
#endif
    if ( depth == 0 ) {
        while (first_non_open && OP(first_non_open) == OPEN)
            first_non_open=regnext(first_non_open);
    }


  fake_study_recurse:
    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_OPTIMISE_MORE_r(
        {
            PerlIO_printf(Perl_debug_log,
                "%*sstudy_chunk stopparen=%ld depth=%lu recursed_depth=%lu ",
                ((int) depth*2), "", (long)stopparen,
                (unsigned long)depth, (unsigned long)recursed_depth);
            if (recursed_depth) {
                U32 i;
                U32 j;
                for ( j = 0 ; j < recursed_depth ; j++ ) {
                    PerlIO_printf(Perl_debug_log,"[");
                    for ( i = 0 ; i < (U32)RExC_npar ; i++ )
                        PerlIO_printf(Perl_debug_log,"%d",
                            PAREN_TEST(RExC_study_chunk_recursed +
                                       (j * RExC_study_chunk_recursed_bytes), i)
                            ? 1 : 0
                        );
                    PerlIO_printf(Perl_debug_log,"]");
                }
            }
            PerlIO_printf(Perl_debug_log,"\n");
        }
        );
        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) == BRANCH || OP(scan) == BRANCHJ
                   || OP(scan) == IFTHEN) {
            next = regnext(scan);
            code = OP(scan);
            /* demq: the op(next)==code check is to see if we have
             * "branch-branch" AFAICT */

            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;

                    num++;
                    data_fake.flags = 0;
                    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);
                    if (code != 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;

#ifdef DEBUGGING
                        SV * const mysv = sv_newmortal();   /* for dumping */
#endif
                        /* 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, mysv, tail, NULL);
                            PerlIO_printf( Perl_debug_log, "%*s%s%s\n",
                              (int)depth * 2 + 2, "",
                              "Looking for TRIE'able sequences. Tail node is: ",
                              SvPV_nolen_const( 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


                        */
#define TRIE_TYPE(X) ( ( NOTHING == (X) ) ? NOTHING :   \
                       ( EXACT == (X) )   ? EXACT :        \
                       ( EXACTFU == (X) || EXACTFU_SS == (X) ) ? EXACTFU :        \
                       ( EXACTFA == (X) ) ? EXACTFA :        \
                       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, mysv, cur, NULL);
                                PerlIO_printf( Perl_debug_log, "%*s- %s (%d)",
                                   (int)depth * 2 + 2,"", SvPV_nolen_const( mysv ), REG_NODE_NUM(cur) );

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

                                if ( noper_next ) {
                                  regprop(RExC_rx, mysv, noper_next, NULL);
                                  PerlIO_printf( Perl_debug_log,"\t=> %s\t",
                                    SvPV_nolen_const(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, mysv, cur, NULL);
                            PerlIO_printf( Perl_debug_log,
                              "%*s- %s (%d) <SCAN FINISHED>\n",
                              (int)depth * 2 + 2,
                              "", SvPV_nolen_const( 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, mysv, cur, NULL);
                                        PerlIO_printf( Perl_debug_log,
                                          "%*s- %s (%d) <NOTHING BRANCH SEQUENCE>\n", (int)depth * 2 + 2,
                                          "", SvPV_nolen_const( 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) {
            scan_frame *newframe = NULL;
            I32 paren;
            regnode *start;
            regnode *end;
            U32 my_recursed_depth= recursed_depth;

            if (OP(scan) != SUSPEND) {
                /* set the pointer */
                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 {
                    paren = 0;
                    start = RExC_rxi->program + 1;
                    end   = RExC_opend;
                }
                if (!recursed_depth
                    ||
                    !PAREN_TEST(RExC_study_chunk_recursed + ((recursed_depth-1) * RExC_study_chunk_recursed_bytes), paren)
                ) {
                    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;
                    Newx(newframe,1,scan_frame);
                } 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;
                }
            } else {
                Newx(newframe,1,scan_frame);
                paren = stopparen;
                start = scan+2;
                end = regnext(scan);
            }
            if (newframe) {
                assert(start);
                assert(end);
                SAVEFREEPV(newframe);
                newframe->next = regnext(scan);
                newframe->last = last;
                newframe->stop = stopparen;
                newframe->prev = frame;
                newframe->prev_recursed_depth = recursed_depth;

                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) {
            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) &= ~ANYOF_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) &= ~ANYOF_EMPTY_STRING;
            }
            flags &= ~SCF_DO_STCLASS;
        }
        else if (PL_regkind[OP(scan)] == EXACT) { /* But OP != EXACT! */
            SSize_t l = STR_LEN(scan);
            UV uc = *((U8*)STRING(scan));
            SV* EXACTF_invlist = _new_invlist(4); /* Start out big enough for 2
                                                     separate code points */

            /* Search for fixed substrings supports EXACT only. */
            if (flags & SCF_DO_SUBSTR) {
                assert(data);
                scan_commit(pRExC_state, data, minlenp, is_inf);
            }
            if (UTF) {
                const U8 * const s = (U8 *)STRING(scan);
                uc = utf8_to_uvchr_buf(s, s + l, NULL);
                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 (OP(scan) == EXACTFL) {

                /* We don't know what the folds are; it could be anything. XXX
                 * Actually, we only support UTF-8 encoding for code points
                 * above Latin1, so we could know what those folds are. */
                EXACTF_invlist = _add_range_to_invlist(EXACTF_invlist,
                                                       0,
                                                       UV_MAX);
            }
            else {  /* Non-locale EXACTFish */
                EXACTF_invlist = add_cp_to_invlist(EXACTF_invlist, uc);
                if (flags & SCF_DO_STCLASS_AND) {
                    ssc_clear_locale(data->start_class);
                }
                if (uc < 256) { /* We know what the Latin1 folds are ... */
                    if (IS_IN_SOME_FOLD_L1(uc)) {   /* For instance, we
                                                       know if anything folds
                                                       with this */
                        EXACTF_invlist = add_cp_to_invlist(EXACTF_invlist,
                                                           PL_fold_latin1[uc]);
                        if (OP(scan) != EXACTFA) { /* The folds below aren't
                                                      legal under /iaa */
                            if (isARG2_lower_or_UPPER_ARG1('s', uc)) {
                                EXACTF_invlist
                                    = add_cp_to_invlist(EXACTF_invlist,
                                                LATIN_SMALL_LETTER_SHARP_S);
                            }
                            else if (uc == LATIN_SMALL_LETTER_SHARP_S) {
                                EXACTF_invlist
                                    = add_cp_to_invlist(EXACTF_invlist, 's');
                                EXACTF_invlist
                                    = add_cp_to_invlist(EXACTF_invlist, 'S');
                            }
                        }

                        /* We also know if there are above-Latin1 code points
                         * that fold to this (none legal for ASCII and /iaa) */
                        if ((! isASCII(uc) || OP(scan) != EXACTFA)
                            && HAS_NONLATIN1_FOLD_CLOSURE(uc))
                        {
                            /* XXX We could know exactly what does fold to this
                             * if the reverse folds are loaded, as currently in
                             * S_regclass() */
                            _invlist_union(EXACTF_invlist,
                                           PL_AboveLatin1,
                                           &EXACTF_invlist);
                        }
                    }
                }
                else {  /* Non-locale, above Latin1.  XXX We don't currently
                           know what participates in folds with this, so have
                           to assume anything could */

                    /* XXX We could know exactly what does fold to this if the
                     * reverse folds are loaded, as currently in S_regclass().
                     * But we do know that under /iaa nothing in the ASCII
                     * range can participate */
                    if (OP(scan) == EXACTFA) {
                        _invlist_union_complement_2nd(EXACTF_invlist,
                                                      PL_XPosix_ptrs[_CC_ASCII],
                                                      &EXACTF_invlist);
                    }
                    else {
                        EXACTF_invlist = _add_range_to_invlist(EXACTF_invlist,
                                                               0, UV_MAX);
                    }
                }
            }
            if (flags & SCF_DO_STCLASS_AND) {
                ANYOF_FLAGS(data->start_class) &= ~ANYOF_EMPTY_STRING;
                ANYOF_POSIXL_ZERO(data->start_class);
                ssc_intersection(data->start_class, EXACTF_invlist, FALSE);
            }
            else if (flags & 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) &= ~ANYOF_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 || (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) |= ANYOF_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);
                    ckWARNreg(RExC_parse,
                            "Quantifier unexpected on zero-length expression");
                    (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
                                : (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=%"UVdf" deltanext=%"UVdf
                              " SSize_t_MAX=%"UVdf" minnext=%"UVdf
                              " maxcount=%"UVdf" mincount=%"UVdf"\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=%"UVdf" RHS=%"UVdf"\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) &= ~ANYOF_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) &= ~ANYOF_EMPTY_STRING;
                }
                flags &= ~SCF_DO_STCLASS;
            }
            min++;
            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 = sv_2mortal(_new_invlist(0));
                U8 namedclass;

                /* See commit msg 749e076fceedeb708a624933726e7989f2302f6a */
                ANYOF_FLAGS(data->start_class) &= ~ANYOF_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 CANY:
                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 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 = 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);
                    }
                }
                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 ( OP(scan) == UNLESSM &&
                 scan->flags == 0 &&
                 OP(NEXTOPER(NEXTOPER(scan))) == NOTHING &&
                 OP(regnext(NEXTOPER(NEXTOPER(scan)))) == SUCCEED
            ) {
                regnode *opt;
                regnode *upto= regnext(scan);
                DEBUG_PARSE_r({
                    SV * const mysv_val=sv_newmortal();
                    DEBUG_STUDYDATA("OPFAIL",data,depth);

                    /*DEBUG_PARSE_MSG("opfail");*/
                    regprop(RExC_rx, mysv_val, upto, NULL);
                    PerlIO_printf(Perl_debug_log,
                        "~ replace with OPFAIL pointed at %s (%"IVdf") offset %"IVdf"\n",
                        SvPV_nolen_const(mysv_val),
                        (IV)REG_NODE_NUM(upto),
                        (IV)(upto - scan)
                    );
                });
                OP(scan) = OPFAIL;
                NEXT_OFF(scan) = upto - scan;
                for (opt= scan + 1; opt < upto ; opt++)
                    OP(opt) = OPTIMIZED;
                scan= upto;
                continue;
            }
            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;

                data_fake.flags = 0;
                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 */
                        ssc_and(pRExC_state, data->start_class, (regnode_charclass *) &intrnl);
                    }
                }
            }
#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);
                }
                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;

                    data_fake.flags = 0;
                    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;
            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) {
        DEBUG_STUDYDATA("frame-end:",data,depth);
        DEBUG_PEEP("fend", scan, depth);
        /* restore previous context */
        last = frame->last;
        scan = frame->next;
        stopparen = frame->stop;
        recursed_depth = frame->prev_recursed_depth;
        depth = depth - 1;

        frame = frame->prev;
        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) && (RExC_maxlen < final_minlen + delta)) {
            RExC_maxlen = final_minlen + delta;
        }
        return final_minlen;
    }
    /* not-reached */
}

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 */
#ifndef PERL_IN_XSUB_RE
void
Perl_reginitcolors(pTHX)
{
    dVAR;
    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)
{
    dVAR;

    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)
{
    dVAR;
    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;
    int n=0;
    STRLEN s = 0, d = 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);

    while (s < *plen_p) {
        if (NATIVE_BYTE_IS_INVARIANT(src[s]))
            dst[d]   = src[s];
        else {
            dst[d++] = UTF8_EIGHT_BIT_HI(src[s]);
            dst[d]   = UTF8_EIGHT_BIT_LO(src[s]);
        }
        if (n < num_code_blocks) {
            if (!do_end && pRExC_state->code_blocks[n].start == s) {
                pRExC_state->code_blocks[n].start = d;
                assert(dst[d] == '(');
                do_end = 1;
            }
            else if (do_end && pRExC_state->code_blocks[n].end == s) {
                pRExC_state->code_blocks[n].end = d;
                assert(dst[d] == ')');
                do_end = 0;
                n++;
            }
        }
        s++;
        d++;
    }
    dst[d] = '\0';
    *plen_p = d;
    *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 = newSVpvn("", 0);
        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 = oplist->op_sibling;;
            }

            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 = oplist->op_sibling; /* skip CONST */
                assert(oplist);
            }
            oplist = oplist->op_sibling;;
        }

        /* 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;

    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)
{
    dVAR;
    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());

#ifndef PERL_IN_XSUB_RE
    /* Initialize these here instead of as-needed, as is quick and avoids
     * having to test them each time otherwise */
    if (! PL_AboveLatin1) {
        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);
    }
#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 = o->op_sibling)
            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 = o->op_sibling) {
                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 = o->op_sibling) {
                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 = expr->op_sibling;
    }

    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_contains_locale = 0;
    RExC_contains_i = 0;
    pRExC_state->runtime_code_qr = NULL;

    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 upgrade the pattern to utf8 and have to
     * recompile */

    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 (RExC_utf8 && initial_charset == REGEX_DEPENDS_CHARSET) {

        /* 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_flags = rx_flags;
    RExC_pm_flags = pm_flags;

    if (runtime_code) {
        if (TAINTING_get && 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;
    RExC_in_multi_char_class = 0;

    /* First pass: determine size, legality. */
    RExC_parse = exp;
    RExC_start = exp;
    RExC_end = exp + plen;
    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;

#if 0 /* REGC() is (currently) a NOP at the first pass.
       * Clever compilers notice this and complain. --jhi */
    REGC((U8)REG_MAGIC, (char*)RExC_emit);
#endif
    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_UTF8) {
            S_pat_upgrade_to_utf8(aTHX_ pRExC_state, &exp, &plen,
                                    pRExC_state->num_code_blocks);
            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);
        SAVEFREEPV(pRExC_state->code_blocks);
    }

    {
        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);
        U16 reganch = (U16)((r->extflags & RXf_PMf_STD_PMMOD)
                            >> RXf_PMf_STD_PMMOD_SHIFT);
        const char *fptr = STD_PAT_MODS;        /*"msix"*/
        char *p;
        /* Allocate for the worst case, which is all the std flags are turned
         * on.  If more precision is desired, we could do a population count of
         * the flags set.  This could be done with a small lookup table, or by
         * shifting, masking and adding, or even, when available, assembly
         * language for a machine-language population count.
         * 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 */

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

        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;

    REGC((U8)REG_MAGIC, (char*) RExC_emit++);
    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;
    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 >= 10)     /* 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)
                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)
        {
            regnode *trie_op;
            /* this can happen only on restudy */
            if ( OP(first) == TRIE ) {
                struct regnode_1 *trieop = (struct regnode_1 *)
                    PerlMemShared_calloc(1, sizeof(struct regnode_1));
                StructCopy(first,trieop,struct regnode_1);
                trie_op=(regnode *)trieop;
            } else {
                struct regnode_charclass *trieop = (struct regnode_charclass *)
                    PerlMemShared_calloc(1, sizeof(struct regnode_charclass));
                StructCopy(first,trieop,struct regnode_charclass);
                trie_op=(regnode *)trieop;
            }
            OP(trie_op)+=2;
            make_trie_failtable(pRExC_state, (regnode *)first, trie_op, 0);
            ri->regstclass = trie_op;
        }
#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
                           : (OP(first) == SBOL
                              ? PREGf_ANCH_SBOL
                              : PREGf_ANCH_BOL));
            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) &&
            (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) & ANYOF_EMPTY_STRING)
            && !ssc_is_anything(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);
                      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) & ANYOF_EMPTY_STRING)
            && ! ssc_is_anything(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);
                      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:%ld\n",
                      (IV)minlen, (IV)r->minlen, 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_CANY_SEEN)
        r->intflags |= PREGf_CANY_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 = NEXTOPER(first);
        U8 nop = OP(next);

        if (PL_regkind[fop] == NOTHING && nop == END)
            r->extflags |= RXf_NULL;
        else if (PL_regkind[fop] == BOL && nop == END)
            r->extflags |= RXf_START_ONLY;
        else if (fop == PLUS
                 && PL_regkind[nop] == POSIXD && FLAGS(next) == _CC_SPACE
                 && OP(regnext(first)) == END)
            r->extflags |= RXf_WHITE;
        else if ( r->extflags & RXf_SPLIT
                  && fop == EXACT
                  && STR_LEN(first) == 1
                  && *(STRING(first)) == ' '
                  && OP(regnext(first)) == 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_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 ( (rx->intflags & PREGf_CANY_SEEN)
            ? (RXp_MATCH_UTF8(rx)
                        && (!i || is_utf8_string((U8*)s, i)))
            : (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)) {
         /* 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);
        }
        assert(0); /* NOT REACHED */
    }
    return NULL;
}

#define DEBUG_PARSE_MSG(funcname)     DEBUG_PARSE_r({           \
    int rem=(int)(RExC_end - RExC_parse);                       \
    int cut;                                                    \
    int num;                                                    \
    int iscut=0;                                                \
    if (rem>10) {                                               \
        rem=10;                                                 \
        iscut=1;                                                \
    }                                                           \
    cut=10-rem;                                                 \
    if (RExC_lastparse!=RExC_parse)                             \
        PerlIO_printf(Perl_debug_log," >%.*s%-*s",              \
            rem, RExC_parse,                                    \
            cut + 4,                                            \
            iscut ? "..." : "<"                                 \
        );                                                      \
    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<inline_invlist.c> */

PERL_STATIC_INLINE UV*
S__invlist_array_init(pTHX_ 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 UV*
S_invlist_array(pTHX_ SV* const invlist)
{
    /* Returns the pointer to the inversion list's array.  Every time the
     * length changes, this needs to be called in case malloc or realloc moved
     * it */

    PERL_ARGS_ASSERT_INVLIST_ARRAY;

    /* Must not be empty.  If these fail, you probably didn't check for <len>
     * being non-zero before trying to get the array */
    assert(_invlist_len(invlist));

    /* The very first element always contains zero, The array begins either
     * there, or if the inversion list is offset, at the element after it.
     * The offset header field determines which; it contains 0 or 1 to indicate
     * how much additionally to add */
    assert(0 == *(SvPVX(invlist)));
    return ((UV *) SvPVX(invlist) + *get_invlist_offset_addr(invlist));
}

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_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));
}

PERL_STATIC_INLINE IV*
S_get_invlist_previous_index_addr(pTHX_ 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(pTHX_ 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(pTHX_ 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 UV
S_invlist_max(pTHX_ 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));
}

PERL_STATIC_INLINE void
S_invlist_trim(pTHX_ SV* const invlist)
{
    PERL_ARGS_ASSERT_INVLIST_TRIM;

    assert(SvTYPE(invlist) == SVt_INVLIST);

    /* Change the length of the inversion list to how many entries it currently
     * has */
    SvPV_shrink_to_cur((SV *) invlist);
}

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(pTHX_ 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> */

    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 && 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(pTHX_ 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 *output will be made correspondingly
     * mortal.  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);

    /* If either one is empty, the union is the other one */
    if (a == NULL || ((len_a = _invlist_len(a)) == 0)) {
        bool make_temp = FALSE; /* Should we mortalize the result? */

        if (*output == a) {
            if (a != NULL) {
                if (! (make_temp = cBOOL(SvTEMP(a)))) {
                    SvREFCNT_dec_NN(a);
                }
            }
        }
        if (*output != b) {
            *output = invlist_clone(b);
            if (complement_b) {
                _invlist_invert(*output);
            }
        } /* else *output already = b; */

        if (make_temp) {
            sv_2mortal(*output);
        }
        return;
    }
    else if ((len_b = _invlist_len(b)) == 0) {
        bool make_temp = FALSE;
        if (*output == b) {
            if (! (make_temp = cBOOL(SvTEMP(b)))) {
                SvREFCNT_dec_NN(b);
            }
        }

        /* The complement of an empty list is a list that has everything in it,
         * so the union with <a> includes everything too */
        if (complement_b) {
            if (a == *output) {
                if (! (make_temp = cBOOL(SvTEMP(a)))) {
                    SvREFCNT_dec_NN(a);
                }
            }
            *output = _new_invlist(1);
            _append_range_to_invlist(*output, 0, UV_MAX);
        }
        else if (*output != a) {
            *output = invlist_clone(a);
        }
        /* else *output already = a; */

        if (make_temp) {
            sv_2mortal(*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);
        }
    }

    /*  We may be removing a reference to one of the inputs.  If so, the output
     *  is made mortal if the input was.  (Mortal SVs shouldn't have their ref
     *  count decremented) */
    if (a == *output || b == *output) {
        assert(! invlist_is_iterating(*output));
        if ((SvTEMP(*output))) {
            sv_2mortal(u);
        }
        else {
            SvREFCNT_dec_NN(*output);
        }
    }

    *output = 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 *i will be made correspondingly mortal.
     * 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)) {
        bool make_temp = FALSE;

        if (len_a != 0 && complement_b) {

            /* Here, 'a' is not empty, therefore from the above '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) {
                if (*i == b) {
                    if (! (make_temp = cBOOL(SvTEMP(b)))) {
                        SvREFCNT_dec_NN(b);
                    }
                }

                *i = invlist_clone(a);
            }
            /* else *i is already 'a' */

            if (make_temp) {
                sv_2mortal(*i);
            }
            return;
        }

        /* Here, 'a' or 'b' is empty and not using the complement of 'b'.  The
         * intersection must be empty */
        if (*i == a) {
            if (! (make_temp = cBOOL(SvTEMP(a)))) {
                SvREFCNT_dec_NN(a);
            }
        }
        else if (*i == b) {
            if (! (make_temp = cBOOL(SvTEMP(b)))) {
                SvREFCNT_dec_NN(b);
            }
        }
        *i = _new_invlist(0);
        if (make_temp) {
            sv_2mortal(*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);
        }
    }

    /*  We may be removing a reference to one of the inputs.  If so, the output
     *  is made mortal if the input was.  (Mortal SVs shouldn't have their ref
     *  count decremented) */
    if (a == *i || b == *i) {
        assert(! invlist_is_iterating(*i));
        if (SvTEMP(*i)) {
            sv_2mortal(r);
        }
        else {
            SvREFCNT_dec_NN(*i);
        }
    }

    *i = 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 */
    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(pTHX_ 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(pTHX_ SV* invlist)   /* Initialize iterator for invlist */
{
    PERL_ARGS_ASSERT_INVLIST_ITERINIT;

    *get_invlist_iter_addr(invlist) = 0;
}

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

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

PERL_STATIC_INLINE UV
S_invlist_highest(pTHX_ 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;
}

#ifndef PERL_IN_XSUB_RE
SV *
Perl__invlist_contents(pTHX_ SV* const invlist)
{
    /* Get the contents of an inversion list into a string SV so that they can
     * be printed out.  It uses the format traditionally done for debug tracing
     */

    UV start, end;
    SV* output = newSVpvs("\n");

    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"\tINFINITY\n", start);
        }
        else if (end != start) {
            Perl_sv_catpvf(aTHX_ output, "%04"UVXf"\t%04"UVXf"\n",
                    start,       end);
        }
        else {
            Perl_sv_catpvf(aTHX_ output, "%04"UVXf"\n", start);
        }
    }

    return output;
}
#endif

#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

#ifdef PERL_ARGS_ASSERT__INVLISTEQ
bool
S__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

#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 '?' */

    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) {
        /* && strchr("iogcmsx", *RExC_parse) */
        /* (?g), (?gc) and (?o) are useless here
           and must be globally applied -- japhy */
        switch (*RExC_parse) {

            /* Code for the imsx flags */
            CASE_STD_PMMOD_FLAGS_PARSE_SET(flagsp);

            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));
                }
                /*NOTREACHED*/
            neg_modifier:
                RExC_parse++;
                vFAIL2("Regexp modifier \"%c\" may not appear after the \"-\"",
                                    *(RExC_parse - 1));
                /*NOTREACHED*/
            case ONCE_PAT_MOD: /* 'o' */
            case GLOBAL_PAT_MOD: /* 'g' */
                if (SIZE_ONLY && 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 (SIZE_ONLY && 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 (SIZE_ONLY)
                        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;
                }
                return;
                /*NOTREACHED*/
            default:
            fail_modifiers:
                RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                /* 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));
                /*NOTREACHED*/
        }

        ++RExC_parse;
    }
}

/*
 - 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

/* Returns NULL, setting *flagp to TRYAGAIN at the end of (?) that only sets
   flags. Returns NULL, setting *flagp to RESTART_UTF8 if the sizing scan
   needs to be restarted.
   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 */
{
    dVAR;
    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;

    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. */


    /* 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) != '(';

        if ( *RExC_parse == '*') { /* (*VERB:ARG) */
            char *start_verb = RExC_parse;
            STRLEN verb_len = 0;
            char *start_arg = NULL;
            unsigned char op = 0;
            int argok = 1;
            int internal_argval = 0; /* internal_argval is only useful if
                                        !argok */

            if (has_intervening_patws) {
                RExC_parse++;
                vFAIL("In '(*VERB...)', the '(' and '*' must be adjacent");
            }
            while ( *RExC_parse && *RExC_parse != ')' ) {
                if ( *RExC_parse == ':' ) {
                    start_arg = RExC_parse + 1;
                    break;
                }
                RExC_parse++;
            }
            ++start_verb;
            verb_len = RExC_parse - start_verb;
            if ( start_arg ) {
                RExC_parse++;
                while ( *RExC_parse && *RExC_parse != ')' )
                    RExC_parse++;
                if ( *RExC_parse != ')' )
                    vFAIL("Unterminated verb pattern argument");
                if ( RExC_parse == start_arg )
                    start_arg = NULL;
            } else {
                if ( *RExC_parse != ')' )
                    vFAIL("Unterminated verb pattern");
            }

            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;
                    argok = 0;
                }
                break;
            case ':':  /* (*:NAME) */
            case 'M':  /* (*MARK:NAME) */
                if ( verb_len==0 || memEQs(start_verb,verb_len,"MARK") ) {
                    op = MARKPOINT;
                    argok = -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 ( argok ) {
                if ( start_arg && internal_argval ) {
                    vFAIL3("Verb pattern '%.*s' may not have an argument",
                        verb_len, start_verb);
                } else if ( argok < 0 && !start_arg ) {
                    vFAIL3("Verb pattern '%.*s' has a mandatory argument",
                        verb_len, start_verb);
                } else {
                    ret = reganode(pRExC_state, op, internal_argval);
                    if ( ! internal_argval && ! 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 = 0;
                        } else {
                            ret->flags = 1;
                        }
                    }
                }
                if (!internal_argval)
                    RExC_seen |= REG_VERBARG_SEEN;
            } else if ( start_arg ) {
                vFAIL3("Verb pattern '%.*s' may not have an argument",
                        verb_len, start_verb);
            } else {
                ret = reg_node(pRExC_state, op);
            }
            nextchar(pRExC_state);
            return ret;
        }
        else if (*RExC_parse == '?') { /* (?...) */
            bool is_logical = 0;
            const char * const seqstart = RExC_parse;
            if (has_intervening_patws) {
                RExC_parse++;
                vFAIL("In '(?...)', the '(' and '?' must be adjacent");
            }

            RExC_parse++;
            paren = *RExC_parse++;
            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 */
                    goto named_capture;
                else if (paren == '>') {   /* (?P>name) named recursion */
                    goto named_recursion;
                }
                else if (paren == '=') {   /* (?P=...)  named backref */
                    /* this pretty much dupes the code for \k<NAME> in
                     * regatom(), if you change this make sure you change that
                     * */
                    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 != ')')
                        /* diag_listed_as: Sequence ?P=... 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;
                }
                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);
                /*NOTREACHED*/
            case '<':           /* (?<...) */
                if (*RExC_parse == '!')
                    paren = ',';
                else if (*RExC_parse != '=')
              named_capture:
                {               /* (?<...>) */
                    char *name_start;
                    SV *svname;
                    paren= '>';
            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 != 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++;
                /* FALLTHROUGH */
            case '=':           /* (?=...) */
                RExC_seen_zerolen++;
                break;
            case '!':           /* (?!...) */
                RExC_seen_zerolen++;
                if (*RExC_parse == ')') {
                    ret=reg_node(pRExC_state, OPFAIL);
                    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 */
                I32 num;
            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;
                assert(0); /* NOT REACHED */
            case '+':
                if (!(RExC_parse[0] >= '1' && RExC_parse[0] <= '9')) {
                    RExC_parse++;
                    vFAIL("Illegal pattern");
                }
                goto parse_recursion;
                /* NOT REACHED*/
            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--;
              parse_recursion:
                num = atoi(RExC_parse);
                parse_start = RExC_parse - 1; /* MJD */
                if (*RExC_parse == '-')
                    RExC_parse++;
                while (isDIGIT(*RExC_parse))
                        RExC_parse++;
                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 = reganode(pRExC_state, GOSUB, num);
                if (!SIZE_ONLY) {
                    if (num > (I32)RExC_rx->nparens) {
                        RExC_parse++;
                        vFAIL("Reference to nonexistent group");
                    }
                    ARG2L_SET( ret, RExC_recurse_count++);
                    RExC_emit++;
                    DEBUG_OPTIMISE_MORE_r(PerlIO_printf(Perl_debug_log,
                        "Recurse #%"UVuf" to %"IVdf"\n",
                              (UV)ARG(ret), (IV)ARG2L(ret)));
                } else {
                    RExC_size++;
                }
                    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;
            } /* named and numeric backreferences */
            assert(0); /* NOT REACHED */

            case '?':           /* (??...) */
                is_logical = 1;
                if (*RExC_parse != '{') {
                    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));
                    /*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 = reganode(pRExC_state, EVAL, n);
                    if (!SIZE_ONLY) {
                        ret->flags = 2;
                        /* for later propagation into (??{}) return value */
                        eval->flags = (U8) (RExC_flags & RXf_PMf_COMPILETIME);
                    }
                    REGTAIL(pRExC_state, ret, eval);
                    /* deal with the length of this later - MJD */
                    return ret;
                }
                ret = reganode(pRExC_state, EVAL, n);
                Set_Node_Length(ret, RExC_parse - parse_start + 1);
                Set_Node_Offset(ret, parse_start);
                return ret;
            }
            case '(':           /* (?(?{...})...) and (?(?=...)...) */
            {
                int is_define= 0;
                if (RExC_parse[0] == '?') {        /* (?(?...)) */
                    if (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_UTF8) {
                            *flagp = RESTART_UTF8;
                            return NULL;
                        }
                        REGTAIL(pRExC_state, ret, tail);
                        goto insert_if;
                    }
                }
                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 != 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_parse[0] == 'D' &&
                         RExC_parse[1] == 'E' &&
                         RExC_parse[2] == 'F' &&
                         RExC_parse[3] == 'I' &&
                         RExC_parse[4] == 'N' &&
                         RExC_parse[5] == 'E')
                {
                    ret = reganode(pRExC_state,DEFINEP,0);
                    RExC_parse +=6 ;
                    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' ) {
                        parno = atoi(RExC_parse++);
                        while (isDIGIT(*RExC_parse))
                            RExC_parse++;
                    } 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;
                    char *tmp;
                    parno = atoi(RExC_parse++);

                    while (isDIGIT(*RExC_parse))
                        RExC_parse++;
                    ret = reganode(pRExC_state, GROUPP, parno);

                 insert_if_check_paren:
                    if (*(tmp = nextchar(pRExC_state)) != ')') {
                        /* nextchar also skips comments, so undo its work
                         * and skip over the the next character.
                         */
                        RExC_parse = tmp;
                        RExC_parse += UTF ? UTF8SKIP(RExC_parse) : 1;
                        vFAIL("Switch condition not recognized");
                    }
                  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_UTF8) {
                            *flagp = RESTART_UTF8;
                            return NULL;
                        }
                        FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"",
                              (UV) flags);
                    } else
                        REGTAIL(pRExC_state, br, reganode(pRExC_state,
                                                          LONGJMP, 0));
                    c = *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_UTF8) {
                                *flagp = RESTART_UTF8;
                                return NULL;
                            }
                            FAIL2("panic: regbranch returned NULL, flags=%#"UVxf"",
                                  (UV) flags);
                        }
                        REGTAIL(pRExC_state, ret, lastbr);
                        if (flags&HASWIDTH)
                            *flagp |= HASWIDTH;
                        c = *nextchar(pRExC_state);
                    }
                    else
                        lastbr = NULL;
                    if (c != ')')
                        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;
                }
                else {
                    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:
                RExC_parse--; /* for vFAIL to print correctly */
                vFAIL("Sequence (? incomplete");
                break;
            default: /* e.g., (?i) */
                --RExC_parse;
              parse_flags:
                parse_lparen_question_flags(pRExC_state);
                if (UCHARAT(RExC_parse) != ':') {
                    nextchar(pRExC_state);
                    *flagp = TRYAGAIN;
                    return NULL;
                }
                paren = ':';
                nextchar(pRExC_state);
                ret = NULL;
                goto parse_rest;
            } /* end switch */
        }
        else {                  /* (...) */
          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,
                        "Setting open paren #%"IVdf" to %d\n",
                        (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                        /* ! 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_UTF8) {
            *flagp = RESTART_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_UTF8) {
                *flagp = RESTART_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,
                        "Setting close paren #%"IVdf" to %d\n",
                        (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) {
            SV * const mysv_val1=sv_newmortal();
            SV * const mysv_val2=sv_newmortal();
            DEBUG_PARSE_MSG("lsbr");
            regprop(RExC_rx, mysv_val1, lastbr, NULL);
            regprop(RExC_rx, mysv_val2, ender, NULL);
            PerlIO_printf(Perl_debug_log, "~ tying lastbr %s (%"IVdf") to ender %s (%"IVdf") offset %"IVdf"\n",
                          SvPV_nolen_const(mysv_val1),
                          (IV)REG_NODE_NUM(lastbr),
                          SvPV_nolen_const(mysv_val2),
                          (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) {
                    SV * const mysv_val1=sv_newmortal();
                    SV * const mysv_val2=sv_newmortal();
                    DEBUG_PARSE_MSG("NADA");
                    regprop(RExC_rx, mysv_val1, ret, NULL);
                    regprop(RExC_rx, mysv_val2, ender, NULL);
                    PerlIO_printf(Perl_debug_log, "~ converting ret %s (%"IVdf") to ender %s (%"IVdf") offset %"IVdf"\n",
                                  SvPV_nolen_const(mysv_val1),
                                  (IV)REG_NODE_NUM(ret),
                                  SvPV_nolen_const(mysv_val2),
                                  (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) */
        RExC_flags = oregflags | (RExC_flags & RXf_PMf_KEEPCOPY);
        if (RExC_parse >= RExC_end || *nextchar(pRExC_state) != ')') {
            RExC_parse = oregcomp_parse;
            vFAIL("Unmatched (");
        }
    }
    else if (!paren && RExC_parse < RExC_end) {
        if (*RExC_parse == ')') {
            RExC_parse++;
            vFAIL("Unmatched )");
        }
        else
            FAIL("Junk on end of regexp");      /* "Can't happen". */
        assert(0); /* 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_UTF8 if the sizing scan needs to be
 * restarted.
 */
STATIC regnode *
S_regbranch(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, I32 first, U32 depth)
{
    dVAR;
    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. */

    RExC_parse--;
    nextchar(pRExC_state);
    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_UTF8) {
                *flagp = RESTART_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 {
            RExC_naughty++;
            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_UTF8 if the sizing scan needs to be
 * restarted.
 */
STATIC regnode *
S_regpiece(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
{
    dVAR;
    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;

    /* 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_UTF8))
            *flagp |= flags & (TRYAGAIN|RESTART_UTF8);
        else
            FAIL2("panic: regatom returned NULL, flags=%#"UVxf"", (UV) flags);
        return(NULL);
    }

    op = *RExC_parse;

    if (op == '{' && regcurly(RExC_parse, FALSE)) {
        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 */
            if (!maxpos)
                maxpos = next;
            RExC_parse++;
            min = atoi(RExC_parse);
            if (*maxpos == ',')
                maxpos++;
            else
                maxpos = RExC_parse;
            max = atoi(maxpos);
            if (!max && *maxpos != '0')
                max = REG_INFTY;                /* meaning "infinity" */
            else if (max >= REG_INFTY)
                vFAIL2("Quantifier in {,} bigger than %d", REG_INFTY - 1);
            RExC_parse = next;
            nextchar(pRExC_state);
            if (max < min) {    /* If can't match, warn and optimize to fail
                                   unconditionally */
                if (SIZE_ONLY) {
                    ckWARNreg(RExC_parse, "Quantifier {n,m} with n > m can't match");

                    /* 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 ammount we are about
                     * to re-use here */
                    RExC_size = PREVOPER(RExC_size) - regarglen[(U8)OPFAIL];
                }
                else {
                    RExC_emit = orig_emit;
                }
                ret = reg_node(pRExC_state, OPFAIL);
                return ret;
            }
            else if (min == max
                     && RExC_parse < RExC_end
                     && (*RExC_parse == '?' || *RExC_parse == '+'))
            {
                if (SIZE_ONLY) {
                    ckWARN2reg(RExC_parse + 1,
                               "Useless use of greediness modifier '%c'",
                               *RExC_parse);
                }
                /* Absorb the modifier, so later code doesn't see nor use
                    * it */
                nextchar(pRExC_state);
            }

        do_curly:
            if ((flags&SIMPLE)) {
                RExC_naughty += 2 + RExC_naughty / 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;
                RExC_naughty += 4 + RExC_naughty;       /* 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 == '*' && (flags&SIMPLE)) {
        reginsert(pRExC_state, STAR, ret, depth+1);
        ret->flags = 0;
        RExC_naughty += 4;
        RExC_seen |= REG_UNBOUNDED_QUANTIFIER_SEEN;
    }
    else if (op == '*') {
        min = 0;
        goto do_curly;
    }
    else if (op == '+' && (flags&SIMPLE)) {
        reginsert(pRExC_state, PLUS, ret, depth+1);
        ret->flags = 0;
        RExC_naughty += 3;
        RExC_seen |= REG_UNBOUNDED_QUANTIFIER_SEEN;
    }
    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 < RExC_end && *RExC_parse == '?') {
        nextchar(pRExC_state);
        reginsert(pRExC_state, MINMOD, ret, depth+1);
        REGTAIL(pRExC_state, ret, ret + NODE_STEP_REGNODE);
    }
    else
    if (RExC_parse < RExC_end && *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 (RExC_parse < RExC_end && 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 *valuep, I32 *flagp, U32 depth, bool in_char_class,
                      const bool strict   /* Apply stricter parsing rules? */
    )
{

 /* This is expected to be called by a parser routine that has recognized '\N'
   and needs to handle the rest. RExC_parse is expected to point at the first
   char following the N at the time of the call.  On successful return,
   RExC_parse has been updated to point to just after the sequence identified
   by this routine, and <*flagp> has been updated.

   The \N may be inside (indicated by the boolean <in_char_class>) or outside a
   character class.

   \N may begin either a named sequence, or if outside a character class, mean
   to match a non-newline.  For non single-quoted regexes, the tokenizer has
   attempted to decide which, and in the case of a named sequence, converted it
   into one of the forms: \N{} (if the sequence is null), or \N{U+c1.c2...},
   where c1... are the characters in the sequence.  For single-quoted regexes,
   the tokenizer passes the \N sequence through unchanged; this code will not
   attempt to determine this nor expand those, instead raising a syntax error.
   The net effect is that if the beginning of the passed-in pattern isn't '{U+'
   or there is no '}', it signals that this \N occurrence means to match a
   non-newline.

   Only the \N{U+...} form should occur in a character class, for the same
   reason that '.' inside a character class means to just match a period: it
   just doesn't make sense.

   The function raises an error (via vFAIL), and doesn't return for various
   syntax errors.  Otherwise it returns TRUE and sets <node_p> or <valuep> on
   success; it returns FALSE otherwise. Returns FALSE, setting *flagp to
   RESTART_UTF8 if the sizing scan needs to be restarted. Such a restart is
   only possible if node_p is non-NULL.


   If <valuep> is non-null, it means the caller can accept an input sequence
   consisting of a just a single code point; <*valuep> is set to that value
   if the input is such.

   If <node_p> is non-null it signifies that the caller can accept any other
   legal sequence (i.e., one that isn't just a single code point).  <*node_p>
   is set as follows:
    1) \N means not-a-NL: points to a newly created REG_ANY node;
    2) \N{}:              points to a new NOTHING node;
    3) otherwise:         points to a new EXACT node containing the resolved
                          string.
   Note that FALSE is returned for single code point sequences if <valuep> is
   null.
 */

    char * endbrace;    /* '}' following the name */
    char* p;
    char *endchar;      /* Points to '.' or '}' ending cur char in the input
                           stream */
    bool has_multiple_chars; /* true if the input stream contains a sequence of
                                more than one character */

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_GROK_BSLASH_N;

    GET_RE_DEBUG_FLAGS;

    assert(cBOOL(node_p) ^ cBOOL(valuep));  /* Exactly one should be set */

    /* The [^\n] meaning of \N ignores spaces and comments under the /x
     * modifier.  The other meaning does not, so use a temporary until we find
     * out which we are being called with */
    p = (RExC_flags & RXf_PMf_EXTENDED)
        ? regpatws(pRExC_state, RExC_parse,
                                TRUE) /* means recognize comments */
        : RExC_parse;

    /* Disambiguate between \N meaning a named character versus \N meaning
     * [^\n].  The former is assumed when it can't be the latter. */
    if (*p != '{' || regcurly(p, FALSE)) {
        RExC_parse = p;
        if (! node_p) {
            /* no bare \N allowed in a charclass */
            if (in_char_class) {
                vFAIL("\\N in a character class must be a named character: \\N{...}");
            }
            return FALSE;
        }
        RExC_parse--;   /* Need to back off so nextchar() doesn't skip the
                           current char */
        nextchar(pRExC_state);
        *node_p = reg_node(pRExC_state, REG_ANY);
        *flagp |= HASWIDTH|SIMPLE;
        RExC_naughty++;
        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 below
                                                 */
                  && strnEQ(RExC_parse, "U+", 2)))) /* for a better error msg)
                                                     */
    {
        if (endbrace) RExC_parse = endbrace;    /* position msg's '<--HERE' */
        vFAIL("\\N{NAME} must be resolved by the lexer");
    }

    if (endbrace == RExC_parse) {   /* empty: \N{} */
        bool ret = TRUE;
        if (node_p) {
            *node_p = reg_node(pRExC_state,NOTHING);
        }
        else if (in_char_class) {
            if (SIZE_ONLY && in_char_class) {
                if (strict) {
                    RExC_parse++;   /* Position after the "}" */
                    vFAIL("Zero length \\N{}");
                }
                else {
                    ckWARNreg(RExC_parse,
                              "Ignoring zero length \\N{} in character class");
                }
            }
            ret = FALSE;
        }
        else {
            return FALSE;
        }
        nextchar(pRExC_state);
        return ret;
    }

    RExC_uni_semantics = 1; /* Unicode named chars imply Unicode semantics */
    RExC_parse += 2;    /* Skip past the 'U+' */

    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 */
    has_multiple_chars = (endchar < endbrace);

    if (valuep && (! has_multiple_chars || in_char_class)) {
        /* We only pay attention to the first char of
        multichar strings being returned in char classes. I kinda wonder
        if this makes sense as it does change the behaviour
        from earlier versions, OTOH that behaviour was broken
        as well. XXX Solution is to recharacterize as
        [rest-of-class]|multi1|multi2... */

        STRLEN length_of_hex = (STRLEN)(endchar - RExC_parse);
        I32 grok_hex_flags = PERL_SCAN_ALLOW_UNDERSCORES
            | PERL_SCAN_DISALLOW_PREFIX
            | (SIZE_ONLY ? PERL_SCAN_SILENT_ILLDIGIT : 0);

        *valuep = 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 */
        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+...}");
        }

        if (in_char_class && has_multiple_chars) {
            if (strict) {
                RExC_parse = endbrace;
                vFAIL("\\N{} in character class restricted to one character");
            }
            else {
                ckWARNreg(endchar, "Using just the first character returned by \\N{} in character class");
            }
        }

        RExC_parse = endbrace + 1;
    }
    else if (! node_p || ! has_multiple_chars) {

        /* Here, the input is legal, but not according to the caller's
         * options.  We fail without advancing the parse, so that the
         * caller can try again */
        RExC_parse = p;
        return FALSE;
    }
    else {

        /* What is done here is to convert this to a sub-pattern of the form
         * (?:\x{char1}\x{char2}...)
         * and then call reg recursively.  That way, it retains its atomicness,
         * while not having to worry about special handling that some code
         * points may have.  toke.c has converted the original Unicode values
         * to native, so that we can just pass on the hex values unchanged.  We
         * do have to set a flag to keep recoding from happening in the
         * recursion */

        SV * substitute_parse = newSVpvn_flags("?:", 2, SVf_UTF8|SVs_TEMP);
        STRLEN len;
        char *orig_end = RExC_end;
        I32 flags;

        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 = SvPV(substitute_parse, len);

        /* Don't allow empty number */
        if (len < 8) {
            vFAIL("Invalid hexadecimal number in \\N{U+...}");
        }
        RExC_end = RExC_parse + len;

        /* The values are Unicode, and therefore not subject to recoding */
        RExC_override_recoding = 1;

        if (!(*node_p = reg(pRExC_state, 1, &flags, depth+1))) {
            if (flags & RESTART_UTF8) {
                *flagp = RESTART_UTF8;
                return FALSE;
            }
            FAIL2("panic: reg returned NULL to grok_bslash_N, flags=%#"UVxf"",
                  (UV) flags);
        }
        *flagp |= flags&(HASWIDTH|SPSTART|SIMPLE|POSTPONED);

        RExC_parse = endbrace;
        RExC_end = orig_end;
        RExC_override_recoding = 0;

        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 char value, SV **encp)
{
    STRLEN numlen = 1;
    SV * const sv = newSVpvn_flags(&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(pTHX_ RExC_state_t *pRExC_state)
{
    U8 op;

    PERL_ARGS_ASSERT_COMPUTE_EXACTISH;

    if (! FOLD) {
        return 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 (UNI_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);
                    if (downgradable
                        && *character == code_point
                        && ! HAS_NONLATIN1_FOLD_CLOSURE(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
                    && ! _invlist_contains_cp(PL_utf8_foldable, code_point))
                {
                    OP(node) = 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 */
        else if (LIKELY(code_point != LATIN_SMALL_LETTER_SHARP_S)) {

            /* 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 == UNISKIP(code_point)))
        && (code_point != LATIN_SMALL_LETTER_SHARP_S
            || ! FOLD || ! DEPENDS_SEMANTICS))
    {
        *flagp |= SIMPLE;
    }

    /* The OP may not be well defined in PASS1 */
    if (PASS2 && OP(node) == EXACTFL) {
        RExC_contains_locale = 1;
    }
}


/* return atoi(p), 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)
{
    char *q = p;

    for (;isDIGIT(*q); q++) {} /* calculate length of num */
    if (q - p == 0 || q - p > 9)
        return I32_MAX;
    return atoi(p);
}


/*
 - 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_UTF8 if the sizing scan needs to be
   restarted.
   Otherwise does not return NULL.
*/

STATIC regnode *
S_regatom(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
{
    dVAR;
    regnode *ret = NULL;
    I32 flags = 0;
    char *parse_start = RExC_parse;
    U8 op;
    int invert = 0;

    GET_RE_DEBUG_FLAGS_DECL;

    *flagp = WORST;             /* Tentatively. */

    DEBUG_PARSE("atom");

    PERL_ARGS_ASSERT_REGATOM;

tryagain:
    switch ((U8)*RExC_parse) {
    case '^':
        RExC_seen_zerolen++;
        nextchar(pRExC_state);
        if (RExC_flags & RXf_PMf_MULTILINE)
            ret = reg_node(pRExC_state, MBOL);
        else if (RExC_flags & RXf_PMf_SINGLELINE)
            ret = reg_node(pRExC_state, SBOL);
        else
            ret = reg_node(pRExC_state, BOL);
        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 if (RExC_flags & RXf_PMf_SINGLELINE)
            ret = reg_node(pRExC_state, SEOL);
        else
            ret = reg_node(pRExC_state, EOL);
        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;
        RExC_naughty++;
        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. */
                       NULL);
        if (*RExC_parse != ']') {
            RExC_parse = oregcomp_parse;
            vFAIL("Unmatched [");
        }
        if (ret == NULL) {
            if (*flagp & RESTART_UTF8)
                return NULL;
            FAIL2("panic: regclass returned NULL to regatom, flags=%#"UVxf"",
                  (UV) *flagp);
        }
        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_UTF8) {
                    *flagp = RESTART_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 '{':
        if (!regcurly(RExC_parse, FALSE)) {
            RExC_parse++;
            goto defchar;
        }
        /* FALLTHROUGH */
    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.
        */
        switch ((U8)*++RExC_parse) {
            U8 arg;
        /* Special Escapes */
        case 'A':
            RExC_seen_zerolen++;
            ret = reg_node(pRExC_state, SBOL);
            *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':
            ret = reg_node(pRExC_state, CANY);
            RExC_seen |= REG_CANY_SEEN;
            *flagp |= HASWIDTH|SIMPLE;
            goto finish_meta_pat;
        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':
            RExC_seen_zerolen++;
            RExC_seen |= REG_LOOKBEHIND_SEEN;
            op = BOUND + get_regex_charset(RExC_flags);
            if (op > BOUNDA) {  /* /aa is same as /a */
                op = BOUNDA;
            }
            else if (op == BOUNDL) {
                RExC_contains_locale = 1;
            }
            ret = reg_node(pRExC_state, op);
            FLAGS(ret) = get_regex_charset(RExC_flags);
            *flagp |= SIMPLE;
            if (! SIZE_ONLY && (U8) *(RExC_parse + 1) == '{') {
                /* diag_listed_as: Use "%s" instead of "%s" */
                vFAIL("Use \"\\b\\{\" instead of \"\\b{\"");
            }
            goto finish_meta_pat;
        case 'B':
            RExC_seen_zerolen++;
            RExC_seen |= REG_LOOKBEHIND_SEEN;
            op = NBOUND + get_regex_charset(RExC_flags);
            if (op > NBOUNDA) { /* /aa is same as /a */
                op = NBOUNDA;
            }
            else if (op == NBOUNDL) {
                RExC_contains_locale = 1;
            }
            ret = reg_node(pRExC_state, op);
            FLAGS(ret) = get_regex_charset(RExC_flags);
            *flagp |= SIMPLE;
            if (! SIZE_ONLY && (U8) *(RExC_parse + 1) == '{') {
                /* diag_listed_as: Use "%s" instead of "%s" */
                vFAIL("Use \"\\B\\{\" instead of \"\\B{\"");
            }
            goto finish_meta_pat;

        case 'D':
            invert = 1;
            /* FALLTHROUGH */
        case 'd':
            arg = ANYOF_DIGIT;
            goto join_posix;

        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':
            {
#ifdef DEBUGGING
                char* parse_start = RExC_parse - 2;
#endif

                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 */
                               NULL);
                /* regclass() can only return RESTART_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 + 2);
                Set_Node_Cur_Length(ret, parse_start);
                nextchar(pRExC_state);
            }
            break;
        case 'N':
            /* Handle \N and \N{NAME} with multiple code points here and not
             * below because it can be multicharacter. join_exact() will join
             * them up later on.  Also this makes sure that things like
             * /\N{BLAH}+/ and \N{BLAH} being multi char Just Happen. dmq.
             * The options to the grok function call causes it to fail if the
             * sequence is just a single code point.  We then go treat it as
             * just another character in the current EXACT node, and hence it
             * gets uniform treatment with all the other characters.  The
             * special treatment for quantifiers is not needed for such single
             * character sequences */
            ++RExC_parse;
            if (! grok_bslash_N(pRExC_state, &ret, NULL, flagp, depth, FALSE,
                                FALSE /* not strict */ )) {
                if (*flagp & RESTART_UTF8)
                    return NULL;
                RExC_parse--;
                goto defchar;
            }
            break;
        case 'k':    /* Handle \k<NAME> and \k'NAME' */
        parse_named_seq:
        {
            char ch= RExC_parse[1];
            if (ch != '<' && 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 {
                /* this pretty much dupes the code for (?P=...) in reg(), if
                   you change this make sure you change that */
                char* name_start = (RExC_parse += 2);
                U32 num = 0;
                SV *sv_dat = reg_scan_name(pRExC_state,
                    SIZE_ONLY ? REG_RSN_RETURN_NULL : REG_RSN_RETURN_DATA);
                ch= (ch == '<') ? '>' : (ch == '{') ? '}' : '\'';
                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;

                /* override incorrect value set in reganode MJD */
                Set_Node_Offset(ret, parse_start+1);
                Set_Node_Cur_Length(ret, parse_start);
                nextchar(pRExC_state);

            }
            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;
                    }

                    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
                            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 and octal escape.
                     * Note RExC_npar is +1 from the actual number of parens*/
                    if (num == I32_MAX || (num > 9 && num >= RExC_npar
                            && *RExC_parse != '8' && *RExC_parse != '9'))
                    {
                        /* Probably a character specified in octal, e.g. \35 */
                        goto defchar;
                    }
                }

                /* at this point RExC_parse definitely points to a backref
                 * number */
                {
#ifdef RE_TRACK_PATTERN_OFFSETS
                    char * const parse_start = RExC_parse - 1; /* MJD */
#endif
                    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+1);
                    Set_Node_Cur_Length(ret, parse_start);
                    RExC_parse--;
                    nextchar(pRExC_state);
                }
            }
            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 */
            parse_start--;
            goto defchar;
        }
        break;

    case '#':
        if (RExC_flags & RXf_PMf_EXTENDED) {
            RExC_parse = reg_skipcomment( pRExC_state, RExC_parse );
            if (RExC_parse < RExC_end)
                goto tryagain;
        }
        /* FALLTHROUGH */

    default:

            parse_start = RExC_parse - 1;

            RExC_parse++;

        defchar: {
            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 EXACTFU 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 do the EXACTFish to EXACT node only if folding.  (And we
             * don't need to figure this out until pass 2) */
            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. */
            for (p = RExC_parse - 1;
                 len < upper_parse && p < RExC_end;
                 len++)
            {
                oldp = p;

                if (RExC_flags & RXf_PMf_EXTENDED)
                    p = regpatws(pRExC_state, p,
                                          TRUE); /* means recognize comments */
                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. */
                        /* The options cause it to fail if a multiple code
                         * point sequence.  Handle those in the switch() above
                         * */
                        RExC_parse = p + 1;
                        if (! grok_bslash_N(pRExC_state, NULL, &ender,
                                            flagp, depth, FALSE,
                                            FALSE /* not strict */ ))
                        {
                            if (*flagp & RESTART_UTF8)
                                FAIL("panic: grok_bslash_N set RESTART_UTF8");
                            RExC_parse = p = oldp;
                            goto loopdone;
                        }
                        p = RExC_parse;
                        if (ender > 0xff) {
                            REQUIRE_UTF8;
                        }
                        break;
                    case 'r':
                        ender = '\r';
                        p++;
                        break;
                    case 't':
                        ender = '\t';
                        p++;
                        break;
                    case 'f':
                        ender = '\f';
                        p++;
                        break;
                    case 'e':
                          ender = ASCII_TO_NATIVE('\033');
                        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,
                                                       TRUE, /* out warnings */
                                                       FALSE, /* not 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 (PL_encoding && ender < 0x100) {
                                goto recode_encoding;
                            }
                            if (ender > 0xff) {
                                REQUIRE_UTF8;
                            }
                            break;
                        }
                    case 'x':
                        {
                            UV result = UV_MAX; /* initialize to erroneous
                                                   value */
                            const char* error_msg;

                            bool valid = grok_bslash_x(&p,
                                                       &result,
                                                       &error_msg,
                                                       TRUE, /* out warnings */
                                                       FALSE, /* not 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 (PL_encoding && ender < 0x100) {
                                goto recode_encoding;
                            }
                            if (ender > 0xff) {
                                REQUIRE_UTF8;
                            }
                            break;
                        }
                    case 'c':
                        p++;
                        ender = grok_bslash_c(*p++, SIZE_ONLY);
                        break;
                    case '8': case '9': /* must be a backreference */
                        --p;
                        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 backslash. 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;
                            }
                            p += numlen;
                            if (SIZE_ONLY   /* like \08, \178 */
                                && numlen < 3
                                && p < RExC_end
                                && isDIGIT(*p) && ckWARN(WARN_REGEXP))
                            {
                                reg_warn_non_literal_string(
                                         p + 1,
                                         form_short_octal_warning(p, numlen));
                            }
                        }
                        if (PL_encoding && ender < 0x100)
                            goto recode_encoding;
                        break;
                    recode_encoding:
                        if (! RExC_override_recoding) {
                            SV* enc = PL_encoding;
                            ender = reg_recode((const char)(U8)ender, &enc);
                            if (!enc && SIZE_ONLY)
                                ckWARNreg(p, "Invalid escape in the specified encoding");
                            REQUIRE_UTF8;
                        }
                        break;
                    case '\0':
                        if (p >= RExC_end)
                            FAIL("Trailing \\");
                        /* FALLTHROUGH */
                    default:
                        if (!SIZE_ONLY&& isALPHANUMERIC(*p)) {
                            /* Include any { 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;
                default:    /* A literal character */

                  normal_default:
                    if (UTF8_IS_START(*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
                 */

                if ( RExC_flags & RXf_PMf_EXTENDED)
                    p = regpatws(pRExC_state, p,
                                          TRUE); /* means recognize comments */

                /* 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 = (p < RExC_end && ISMULT2(p))) && len)
                {
                    p = oldp;
                    goto loopdone;
                }

                if (! FOLD   /* The simple case, just append the literal */
                    || (LOC  /* Also don't fold for tricky chars under /l */
                        && is_PROBLEMATIC_LOCALE_FOLD_cp(ender)))
                {
                    if (UTF) {
                        const STRLEN unilen = reguni(pRExC_state, ender, s);
                        if (unilen > 0) {
                           s   += unilen;
                           len += unilen;
                        }

                        /* 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--;
                    }
                    else {
                        REGC((char)ender, s++);
                    }

                    /* Can get here if folding only if is one of the /l
                     * characters whose fold depends on the locale.  The
                     * occurrence of any of these indicate that we can't
                     * simplify things */
                    if (FOLD) {
                        maybe_exact = FALSE;
                        maybe_exactfu = FALSE;
                    }
                }
                else             /* FOLD */
                     if (! ( UTF
                        /* 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)))
                {
                    /* 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 (maybe_exactfu
                            && (PL_fold[ender] != PL_fold_latin1[ender]
                                || ender == LATIN_SMALL_LETTER_SHARP_S
                                || (len > 0
                                   && isARG2_lower_or_UPPER_ARG1('s', ender)
                                   && isARG2_lower_or_UPPER_ARG1('s',
                                                                 *(s-1)))))
                        {
                            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 */
                    /* 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.  (Hence we can't use REGC for
                     * the simple case just below.) */

                    UV folded;
                    if (isASCII(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(TWO_BYTE_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 && isARG2_lower_or_UPPER_ARG1('s', ender))
                    {
                        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) = EXACT;
                    }
                    else if (maybe_exactfu) {
                        OP(ret) = 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);
            nextchar(pRExC_state);
            {
                /* 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 char *
S_regpatws(pTHX_ RExC_state_t *pRExC_state, char *p , const bool recognize_comment )
{
    /* Returns the next non-pattern-white space, non-comment character (the
     * latter only if 'recognize_comment is true) in the string p, which is
     * ended by RExC_end.  See also reg_skipcomment */
    const char *e = RExC_end;

    PERL_ARGS_ASSERT_REGPATWS;

    while (p < e) {
        STRLEN len;
        if ((len = is_PATWS_safe(p, e, UTF))) {
            p += len;
        }
        else if (recognize_comment && *p == '#') {
            p = reg_skipcomment(pRExC_state, p);
        }
        else
            break;
    }
    return p;
}

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 <= 256) {
                ANYOF_FLAGS(node) |= ANYOF_ABOVE_LATIN1_ALL;
            }
            else if (end >= 256) {
                ANYOF_FLAGS(node) |= ANYOF_UTF8;
            }

            /* Quit if are above what we should change */
            if (start > 255) {
                break;
            }

            change_invlist = TRUE;

            /* Set all the bits in the range, up to the max that we are doing */
            high = (end < 255) ? end : 255;
            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 latin1 if we have a
         * flag to match all of them anyways */
        if (change_invlist) {
            _invlist_subtract(*invlist_ptr, PL_Latin1, invlist_ptr);
        }
        if (ANYOF_FLAGS(node) & ANYOF_ABOVE_LATIN1_ALL) {
            _invlist_intersection(*invlist_ptr, PL_Latin1, 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))

PERL_STATIC_INLINE I32
S_regpposixcc(pTHX_ RExC_state_t *pRExC_state, I32 value, const bool strict)
{
    dVAR;
    I32 namedclass = OOB_NAMEDCLASS;

    PERL_ARGS_ASSERT_REGPPOSIXCC;

    if (value == '[' && RExC_parse + 1 < RExC_end &&
        /* I smell either [: or [= or [. -- POSIX has been here, right? */
        POSIXCC(UCHARAT(RExC_parse)))
    {
        const char c = UCHARAT(RExC_parse);
        char* const s = RExC_parse++;

        while (RExC_parse < RExC_end && UCHARAT(RExC_parse) != c)
            RExC_parse++;
        if (RExC_parse == RExC_end) {
            if (strict) {

                /* Try to give a better location for the error (than the end of
                 * the string) by looking for the matching ']' */
                RExC_parse = s;
                while (RExC_parse < RExC_end && UCHARAT(RExC_parse) != ']') {
                    RExC_parse++;
                }
                vFAIL2("Unmatched '%c' in POSIX class", c);
            }
            /* Grandfather lone [:, [=, [. */
            RExC_parse = s;
        }
        else {
            const char* const t = RExC_parse++; /* skip over the c */
            assert(*t == c);

            if (UCHARAT(RExC_parse) == ']') {
                const char *posixcc = s + 1;
                RExC_parse++; /* skip over the ending ] */

                if (*s == ':') {
                    const I32 complement = *posixcc == '^' ? *posixcc++ : 0;
                    const I32 skip = t - posixcc;

                    /* Initially switch on the length of the name.  */
                    switch (skip) {
                    case 4:
                        if (memEQ(posixcc, "word", 4)) /* this is not POSIX,
                                                          this is the Perl \w
                                                        */
                            namedclass = 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 (posixcc[4]) {
                        case 'a':
                            if (memEQ(posixcc, "alph", 4)) /* alpha */
                                namedclass = ANYOF_ALPHA;
                            break;
                        case 'e':
                            if (memEQ(posixcc, "spac", 4)) /* space */
                                namedclass = ANYOF_PSXSPC;
                            break;
                        case 'h':
                            if (memEQ(posixcc, "grap", 4)) /* graph */
                                namedclass = ANYOF_GRAPH;
                            break;
                        case 'i':
                            if (memEQ(posixcc, "asci", 4)) /* ascii */
                                namedclass = ANYOF_ASCII;
                            break;
                        case 'k':
                            if (memEQ(posixcc, "blan", 4)) /* blank */
                                namedclass = ANYOF_BLANK;
                            break;
                        case 'l':
                            if (memEQ(posixcc, "cntr", 4)) /* cntrl */
                                namedclass = ANYOF_CNTRL;
                            break;
                        case 'm':
                            if (memEQ(posixcc, "alnu", 4)) /* alnum */
                                namedclass = ANYOF_ALPHANUMERIC;
                            break;
                        case 'r':
                            if (memEQ(posixcc, "lowe", 4)) /* lower */
                                namedclass = (FOLD) ? ANYOF_CASED : ANYOF_LOWER;
                            else if (memEQ(posixcc, "uppe", 4)) /* upper */
                                namedclass = (FOLD) ? ANYOF_CASED : ANYOF_UPPER;
                            break;
                        case 't':
                            if (memEQ(posixcc, "digi", 4)) /* digit */
                                namedclass = ANYOF_DIGIT;
                            else if (memEQ(posixcc, "prin", 4)) /* print */
                                namedclass = ANYOF_PRINT;
                            else if (memEQ(posixcc, "punc", 4)) /* punct */
                                namedclass = ANYOF_PUNCT;
                            break;
                        }
                        break;
                    case 6:
                        if (memEQ(posixcc, "xdigit", 6))
                            namedclass = ANYOF_XDIGIT;
                        break;
                    }

                    if (namedclass == OOB_NAMEDCLASS)
                        vFAIL2utf8f(
                            "POSIX class [:%"UTF8f":] unknown",
                            UTF8fARG(UTF, t - s - 1, s + 1));

                    /* The #defines are structured so each complement is +1 to
                     * the normal one */
                    if (complement) {
                        namedclass++;
                    }
                    assert (posixcc[skip] == ':');
                    assert (posixcc[skip+1] == ']');
                } else if (!SIZE_ONLY) {
                    /* [[=foo=]] and [[.foo.]] are still future. */

                    /* adjust RExC_parse so the warning shows after
                       the class closes */
                    while (UCHARAT(RExC_parse) && UCHARAT(RExC_parse) != ']')
                        RExC_parse++;
                    vFAIL3("POSIX syntax [%c %c] is reserved for future extensions", c, c);
                }
            } else {
                /* Maternal grandfather:
                 * "[:" ending in ":" but not in ":]" */
                if (strict) {
                    vFAIL("Unmatched '[' in POSIX class");
                }

                /* Grandfather lone [:, [=, [. */
                RExC_parse = s;
            }
        }
    }

    return namedclass;
}

STATIC bool
S_could_it_be_a_POSIX_class(pTHX_ RExC_state_t *pRExC_state)
{
    /* This applies some heuristics at the current parse position (which should
     * be at a '[') to see if what follows might be intended to be a [:posix:]
     * class.  It returns true if it really is a posix class, of course, but it
     * also can return true if it thinks that what was intended was a posix
     * class that didn't quite make it.
     *
     * It will return true for
     *      [:alphanumerics:
     *      [:alphanumerics]  (as long as the ] isn't followed immediately by a
     *                         ')' indicating the end of the (?[
     *      [:any garbage including %^&$ punctuation:]
     *
     * This is designed to be called only from S_handle_regex_sets; it could be
     * easily adapted to be called from the spot at the beginning of regclass()
     * that checks to see in a normal bracketed class if the surrounding []
     * have been omitted ([:word:] instead of [[:word:]]).  But doing so would
     * change long-standing behavior, so I (khw) didn't do that */
    char* p = RExC_parse + 1;
    char first_char = *p;

    PERL_ARGS_ASSERT_COULD_IT_BE_A_POSIX_CLASS;

    assert(*(p - 1) == '[');

    if (! POSIXCC(first_char)) {
        return FALSE;
    }

    p++;
    while (p < RExC_end && isWORDCHAR(*p)) p++;

    if (p >= RExC_end) {
        return FALSE;
    }

    if (p - RExC_parse > 2    /* Got at least 1 word character */
        && (*p == first_char
            || (*p == ']' && p + 1 < RExC_end && *(p + 1) != ')')))
    {
        return TRUE;
    }

    p = (char *) memchr(RExC_parse, ']', RExC_end - RExC_parse);

    return (p
            && p - RExC_parse > 2 /* [:] evaluates to colon;
                                      [::] is a bad posix class. */
            && first_char == *(p - 1));
}

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;
    UV start, end;      /* End points of code point ranges */
    SV* result_string;
    char *save_end, *save_parse;
    SV* final;
    STRLEN len;
    regnode* node;
    AV* stack;
    const bool save_fold = FOLD;

    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_HANDLE_REGEX_SETS;

    if (LOC) {
        vFAIL("(?[...]) not valid in locale");
    }
    RExC_uni_semantics = 1;

    /* 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 */

        Perl_ck_warner_d(aTHX_
            packWARN(WARN_EXPERIMENTAL__REGEX_SETS),
            "The regex_sets feature is experimental" REPORT_LOCATION,
                UTF8fARG(UTF, (RExC_parse - RExC_precomp), RExC_precomp),
                UTF8fARG(UTF,
                         RExC_end - RExC_start - (RExC_parse - RExC_precomp),
                         RExC_precomp + (RExC_parse - RExC_precomp)));

        while (RExC_parse < RExC_end) {
            SV* current = NULL;
            RExC_parse = regpatws(pRExC_state, RExC_parse,
                                          TRUE); /* means recognize comments */
            switch (*RExC_parse) {
                case '?':
                    if (RExC_parse[1] == '[') depth++, RExC_parse++;
                    /* FALLTHROUGH */
                default:
                    break;
                case '\\':
                    /* Skip the next byte (which could cause us to end up in
                     * the middle of a UTF-8 character, but since none of those
                     * are confusable with anything we currently handle in this
                     * switch (invariants all), it's safe.  We'll just hit the
                     * default: case next time and keep on incrementing until
                     * we find one of the invariants we do handle. */
                    RExC_parse++;
                    break;
                case '[':
                {
                    /* If this looks like it is a [:posix:] class, leave the
                     * parse pointer at the '[' to fool regclass() into
                     * thinking it is part of a '[[:posix:]]'.  That function
                     * will use strict checking to force a syntax error if it
                     * doesn't work out to a legitimate class */
                    bool is_posix_class
                                    = could_it_be_a_POSIX_class(pRExC_state);
                    if (! is_posix_class) {
                        RExC_parse++;
                    }

                    /* regclass() can only return RESTART_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. */
                                  &current))
                        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 < RExC_end
                        && *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 */
                        return node;
                    }
                    goto no_close;
            }
            RExC_parse++;
        }

        no_close:
        FAIL("Syntax error in (?[...])");
    }

    /* Pass 2 only after this.  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 the
     * '('; or else a pointer to an operand inversion list. */

#define IS_OPERAND(a)  (! SvIOK(a))

    /* The stack starts empty.  It is a syntax error if the first thing parsed
     * is a binary operator; everything else is pushed on the stack.  When an
     * operand is parsed, the top of the stack is examined.  If it is a binary
     * operator, the item before it should be an operand, and both are replaced
     * by the result of doing that operation on the new operand and the one on
     * the stack.   Thus a sequence of binary operands is reduced to a single
     * one before the next one is parsed.
     *
     * A unary operator may immediately follow a binary in the input, for
     * example
     *      [a] + ! [b]
     * When an operand is parsed and the top of the stack is a unary operator,
     * the operation is performed, and then the stack is rechecked to see if
     * this new operand is part of a binary operation; if so, it is handled as
     * above.
     *
     * A '(' is simply pushed on the stack; it is valid only if the stack is
     * empty, or the top element of the stack is an operator or another '('
     * (for which the parenthesized expression will become an operand).  By the
     * time the corresponding ')' is parsed everything in between should have
     * been parsed and evaluated to a single operand (or else is a syntax
     * error), and is handled as a regular operand */

    sv_2mortal((SV *)(stack = newAV()));

    while (RExC_parse < RExC_end) {
        I32 top_index = av_tindex(stack);
        SV** top_ptr;
        SV* current = NULL;

        /* Skip white space */
        RExC_parse = regpatws(pRExC_state, RExC_parse,
                                         TRUE /* means recognize comments */ );
        if (RExC_parse >= RExC_end) {
            Perl_croak(aTHX_ "panic: Read past end of '(?[ ])'");
        }
        if ((curchar = UCHARAT(RExC_parse)) == ']') {
            break;
        }

        switch (curchar) {

            case '?':
                if (av_tindex(stack) >= 0   /* This makes sure that we can
                                               safely subtract 1 from
                                               RExC_parse in the next clause.
                                               If we have something on the
                                               stack, we have parsed something
                                             */
                    && UCHARAT(RExC_parse - 1) == '('
                    && RExC_parse < RExC_end)
                {
                    /* 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 * const save_parse = ++RExC_parse;

                    parse_lparen_question_flags(pRExC_state);

                    if (RExC_parse == save_parse  /* Makes sure there was at
                                                     least one flag (or 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:(?[...'");
                    }
                    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 ')' which will be
                     * paired with the '(' that has been put on the stack, so
                     * the whole embedded expression reduces to '(operand)' */
                    RExC_parse++;

                    RExC_flags = save_flags;
                    goto handle_operand;
                }
                /* FALLTHROUGH */

            default:
                RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
                vFAIL("Unexpected character");

            case '\\':
                /* regclass() can only return RESTART_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.  */
                              &current))
                    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 */
            {
                bool is_posix_class = could_it_be_a_POSIX_class(pRExC_state);

                if (! is_posix_class) {
                    RExC_parse++;
                }

                /* regclass() can only return RESTART_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 */
                             FALSE, /* don't silence non-portable warnings.  */
                             &current))
                    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 '&':
            case '|':
            case '+':
            case '-':
            case '^':
                if (top_index < 0
                    || ( ! (top_ptr = av_fetch(stack, top_index, FALSE)))
                    || ! IS_OPERAND(*top_ptr))
                {
                    RExC_parse++;
                    vFAIL2("Unexpected binary operator '%c' with no preceding operand", curchar);
                }
                av_push(stack, newSVuv(curchar));
                break;

            case '!':
                av_push(stack, newSVuv(curchar));
                break;

            case '(':
                if (top_index >= 0) {
                    top_ptr = av_fetch(stack, top_index, FALSE);
                    assert(top_ptr);
                    if (IS_OPERAND(*top_ptr)) {
                        RExC_parse++;
                        vFAIL("Unexpected '(' with no preceding operator");
                    }
                }
                av_push(stack, newSVuv(curchar));
                break;

            case ')':
            {
                SV* lparen;
                if (top_index < 1
                    || ! (current = av_pop(stack))
                    || ! IS_OPERAND(current)
                    || ! (lparen = av_pop(stack))
                    || IS_OPERAND(lparen)
                    || SvUV(lparen) != '(')
                {
                    SvREFCNT_dec(current);
                    RExC_parse++;
                    vFAIL("Unexpected ')'");
                }
                top_index -= 2;
                SvREFCNT_dec_NN(lparen);

                /* FALLTHROUGH */
            }

              handle_operand:

                /* Here, we have an operand to process, in 'current' */

                if (top_index < 0) {    /* Just push if stack is empty */
                    av_push(stack, current);
                }
                else {
                    SV* top = av_pop(stack);
                    SV *prev = NULL;
                    char current_operator;

                    if (IS_OPERAND(top)) {
                        SvREFCNT_dec_NN(top);
                        SvREFCNT_dec_NN(current);
                        vFAIL("Operand with no preceding operator");
                    }
                    current_operator = (char) SvUV(top);
                    switch (current_operator) {
                        case '(':   /* Push the '(' back on followed by the new
                                       operand */
                            av_push(stack, top);
                            av_push(stack, current);
                            SvREFCNT_inc(top);  /* Counters the '_dec' done
                                                   just after the 'break', so
                                                   it doesn't get wrongly freed
                                                 */
                            break;

                        case '!':
                            _invlist_invert(current);

                            /* Unlike binary operators, the top of the stack,
                             * now that this unary one has been popped off, may
                             * legally be an operator, and we now have operand
                             * for it. */
                            top_index--;
                            SvREFCNT_dec_NN(top);
                            goto handle_operand;

                        case '&':
                            prev = av_pop(stack);
                            _invlist_intersection(prev,
                                                   current,
                                                   &current);
                            av_push(stack, current);
                            break;

                        case '|':
                        case '+':
                            prev = av_pop(stack);
                            _invlist_union(prev, current, &current);
                            av_push(stack, current);
                            break;

                        case '-':
                            prev = av_pop(stack);;
                            _invlist_subtract(prev, current, &current);
                            av_push(stack, current);
                            break;

                        case '^':   /* The union minus the intersection */
                        {
                            SV* i = NULL;
                            SV* u = NULL;
                            SV* element;

                            prev = av_pop(stack);
                            _invlist_union(prev, current, &u);
                            _invlist_intersection(prev, current, &i);
                            /* _invlist_subtract will overwrite current
                                without freeing what it already contains */
                            element = current;
                            _invlist_subtract(u, i, &current);
                            av_push(stack, current);
                            SvREFCNT_dec_NN(i);
                            SvREFCNT_dec_NN(u);
                            SvREFCNT_dec_NN(element);
                            break;
                        }

                        default:
                            Perl_croak(aTHX_ "panic: Unexpected item on '(?[ ])' stack");
                }
                SvREFCNT_dec_NN(top);
                SvREFCNT_dec(prev);
            }
        }

        RExC_parse += (UTF) ? UTF8SKIP(RExC_parse) : 1;
    }

    if (av_tindex(stack) < 0   /* Was empty */
        || ((final = av_pop(stack)) == NULL)
        || ! IS_OPERAND(final)
        || av_tindex(stack) >= 0)  /* More left on stack */
    {
        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);
        }
    }

    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_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 */
                    NULL);
    if (!node)
        FAIL2("panic: regclass returned NULL to handle_sets, flags=%#"UVxf,
                    PTR2UV(flagp));
    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_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 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;

    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;
        case LATIN_SMALL_LETTER_SHARP_S:
          *invlist = add_cp_to_invlist(*invlist, LATIN_CAPITAL_LETTER_SHARP_S);
            break;
        case 'F': case 'f':
        case 'I': case 'i':
        case 'L': case 'l':
        case 'T': case 't':
        case 'A': case 'a':
        case 'H': case 'h':
        case 'J': case 'j':
        case 'N': case 'n':
        case 'W': case 'w':
        case 'Y': case 'y':
            /* These all are targets of multi-character folds from code points
             * that require UTF8 to express, so they can't match unless the
             * target string is in UTF-8, so no action here is necessary, as
             * regexec.c properly handles the general case for UTF-8 matching
             * and multi-char folds */
            break;
        default:
            /* Use deprecated warning to increase the chances of this being
             * output */
            ckWARN2reg_d(RExC_parse, "Perl folding rules are not up-to-date for 0x%02X; please use the perlbug utility to report;", cp);
            break;
    }
}

/* 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)

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 */
                 SV** ret_invlist)  /* Return an inversion list, not a node */
{
    /* 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 256 characters, with the
     * corresponding bit set if that character is in the list.  For characters
     * above 255, 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_UTF8 if the sizing scan needs
     * to be restarted.  This can only happen if ret_invlist is non-NULL.
     */

    dVAR;
    UV prevvalue = OOB_UNICODE, save_prevvalue = OOB_UNICODE;
    IV range = 0;
    UV value = OOB_UNICODE, save_value = OOB_UNICODE;
    regnode *ret;
    STRLEN numlen;
    IV 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 */
    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? */
    const bool strict = cBOOL(ret_invlist); /* Apply strict parsing rules? */

    /* 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.  (Because is under /d) */
    SV* depends_list = 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;

#ifdef EBCDIC
    /* In a range, counts how many 0-2 of the ends of it came from literals,
     * not escapes.  Thus we can tell if 'A' was input vs \x{C1} */
    UV literal_endpoint = 0;
#endif
    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 ? */
    GET_RE_DEBUG_FLAGS_DECL;

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

    DEBUG_PARSE("clas");

    /* Assume we are going to generate an ANYOF node. */
    ret = reganode(pRExC_state, 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.  */
    }

    if (skip_white) {
        RExC_parse = regpatws(pRExC_state, RExC_parse,
                              FALSE /* means don't recognize comments */ );
    }

    if (UCHARAT(RExC_parse) == '^') {   /* Complement of range. */
        RExC_parse++;
        invert = TRUE;
        allow_multi_folds = FALSE;
        RExC_naughty++;
        if (skip_white) {
            RExC_parse = regpatws(pRExC_state, RExC_parse,
                                  FALSE /* means don't recognize comments */ );
        }
    }

    /* Check that they didn't say [:posix:] instead of [[:posix:]] */
    if (!SIZE_ONLY && RExC_parse < RExC_end && POSIXCC(UCHARAT(RExC_parse))) {
        const char *s = RExC_parse;
        const char  c = *s++;

        while (isWORDCHAR(*s))
            s++;
        if (*s && c == *s && s[1] == ']') {
            SAVEFREESV(RExC_rx_sv);
            ckWARN3reg(s+2,
                       "POSIX syntax [%c %c] belongs inside character classes",
                       c, c);
            (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;

parseit:
    while (1) {
        if  (RExC_parse >= stop_ptr) {
            break;
        }

        if (skip_white) {
            RExC_parse = regpatws(pRExC_state, RExC_parse,
                                  FALSE /* means don't recognize comments */ );
        }

        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++;
        }
        if (UTF) {
            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 == '['
            && RExC_parse < RExC_end
            && POSIXCC(UCHARAT(RExC_parse)))
        {
            namedclass = regpposixcc(pRExC_state, value, strict);
        }
        else if (value == '\\') {
            if (UTF) {
                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 || ! is_PATWS_cp(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 */
                {
                    /* We only pay attention to the first char of
                    multichar strings being returned. I kinda wonder
                    if this makes sense as it does change the behaviour
                    from earlier versions, OTOH that behaviour was broken
                    as well. */
                    if (! grok_bslash_N(pRExC_state, NULL, &value, flagp, depth,
                                      TRUE, /* => charclass */
                                      strict))
                    {
                        if (*flagp & RESTART_UTF8)
                            FAIL("panic: grok_bslash_N set RESTART_UTF8");
                        goto parseit;
                    }
                }
                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)
                        vFAIL2("Missing right brace on \\%c{}", c);
                    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--;
                }
                else {
                    e = RExC_parse;
                    n = 1;
                }
                if (!SIZE_ONLY) {
                    SV* invlist;
                    char* formatted;
                    char* name;

                    if (UCHARAT(RExC_parse) == '^') {
                         RExC_parse++;
                         n--;
                         /* toggle.  (The rhs xor gets the single bit that
                          * differs between P and p; the other xor inverts just
                          * that bit) */
                         value ^= 'P' ^ 'p';

                         while (isSPACE(*RExC_parse)) {
                              RExC_parse++;
                              n--;
                         }
                    }
                    /* 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 */
                    formatted = Perl_form(aTHX_
                                          "%s%.*s%s\n",
                                          (FOLD) ? "__" : "",
                                          (int)n,
                                          RExC_parse,
                                          (FOLD) ? "_i" : ""
                                );
                    name = savepvn(formatted, strlen(formatted));

                    /* Look up the property name, and get its swash and
                     * inversion list, if the property is found  */
                    if (swash) {
                        SvREFCNT_dec_NN(swash);
                    }
                    swash = _core_swash_init("utf8", name, &PL_sv_undef,
                                             1, /* binary */
                                             0, /* not tr/// */
                                             NULL, /* No inversion list */
                                             &swash_init_flags
                                            );
                    if (! swash || ! (invlist = _get_swash_invlist(swash))) {
                        if (swash) {
                            SvREFCNT_dec_NN(swash);
                            swash = NULL;
                        }

                        /* Here didn't find it.  It could be a user-defined
                         * property that will be available at run-time.  If we
                         * accept only compile-time properties, is an error;
                         * otherwise add it to the list for run-time look up */
                        if (ret_invlist) {
                            RExC_parse = e + 1;
                            vFAIL2utf8f(
                                "Property '%"UTF8f"' is unknown",
                                UTF8fARG(UTF, n, name));
                        }
                        Perl_sv_catpvf(aTHX_ listsv, "%cutf8::%"UTF8f"\n",
                                        (value == 'p' ? '+' : '!'),
                                        UTF8fARG(UTF, n, name));
                        has_user_defined_property = TRUE;

                        /* We don't know yet, so have to assume that the
                         * property could match something in the Latin1 range,
                         * hence something that isn't utf8.  Note that this
                         * would cause things in <depends_list> to match
                         * inappropriately, except that any \p{}, including
                         * this one forces Unicode semantics, which means there
                         * is no <depends_list> */
                        ANYOF_FLAGS(ret) |= ANYOF_NONBITMAP_NON_UTF8;
                    }
                    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 */
                RExC_uni_semantics = 1;
                }
                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 = ASCII_TO_NATIVE('\033');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,
                                               SIZE_ONLY,   /* warnings in pass
                                                               1 only */
                                               strict,
                                               silence_non_portable,
                                               UTF);
                    if (! valid) {
                        vFAIL(error_msg);
                    }
                }
                if (PL_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,
                                               TRUE, /* Output warnings */
                                               strict,
                                               silence_non_portable,
                                               UTF);
                    if (! valid) {
                        vFAIL(error_msg);
                    }
                }
                if (PL_encoding && value < 0x100)
                    goto recode_encoding;
                break;
            case 'c':
                value = grok_bslash_c(*RExC_parse++, SIZE_ONLY);
                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);
                        }
                    }
                    if (PL_encoding && value < 0x100)
                        goto recode_encoding;
                    break;
                }
            recode_encoding:
                if (! RExC_override_recoding) {
                    SV* enc = PL_encoding;
                    value = reg_recode((const char)(U8)value, &enc);
                    if (!enc) {
                        if (strict) {
                            vFAIL("Invalid escape in the specified encoding");
                        }
                        else if (SIZE_ONLY) {
                            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 */
#ifdef EBCDIC
        else
            literal_endpoint++;
#endif

        /* 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_POSIXL;
                    ANYOF_POSIXL_ZERO(ret);
                }

                /* See if it already matches the complement of this POSIX
                 * class */
                if ((ANYOF_FLAGS(ret) & ANYOF_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 {  /* Garden variety class.  If is NASCII, NDIGIT, ...
                           complement and use nposixes */
                    SV** posixes_ptr = namedclass % 2 == 0
                                       ? &posixes
                                       : &nposixes;
                    SV** source_ptr = &PL_XPosix_ptrs[classnum];
                    _invlist_union_maybe_complement_2nd(
                                                     *posixes_ptr,
                                                     *source_ptr,
                                                     namedclass % 2 != 0,
                                                     posixes_ptr);
                }
                continue;   /* Go get next character */
            }
        } /* end of namedclass \blah */

        /* Here, we have a single value.  If 'range' is set, it is the ending
         * of a range--check its validity.  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 (skip_white) {
            RExC_parse = regpatws(pRExC_state, RExC_parse,
                                FALSE /* means don't recognize comments */ );
        }

        if (range) {
            if (prevvalue > value) /* b-a */ {
                const int w = RExC_parse - rangebegin;
                vFAIL2utf8f(
                    "Invalid [] range \"%"UTF8f"\"",
                    UTF8fARG(UTF, w, rangebegin));
                range = 0; /* not a valid range */
            }
        }
        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;
                if (skip_white) {   /* Get the next real char after the '-' */
                    next_char_ptr = regpatws(pRExC_state,
                                             RExC_parse + 1,
                                             FALSE); /* means don't recognize
                                                        comments */
                }

                /* 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 || ckWARN(WARN_REGEXP)) {
                            const int w =
                                RExC_parse >= rangebegin ?
                                RExC_parse - rangebegin : 0;
                            if (strict) {
                                vFAIL4("False [] range \"%*.*s\"",
                                    w, w, rangebegin);
                            }
                            else {
                                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 */
                }
            }
        }

        /* Here, <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) {
            RExC_uni_semantics = 1;
        }

        /* 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) {
                        AV** this_array_ptr;
                        AV* this_array;
                        STRLEN cp_count = utf8_length(foldbuf,
                                                      foldbuf + foldlen);
                        SV* multi_fold = sv_2mortal(newSVpvn("", 0));

                        Perl_sv_catpvf(aTHX_ multi_fold, "\\x{%"UVXf"}", value);


                        if (! multi_char_matches) {
                            multi_char_matches = newAV();
                        }

                        /* <multi_char_matches> is actually an array of arrays.
                         * There will be one or two top-level elements: [2],
                         * and/or [3].  The [2] element is an array, each
                         * element thereof is a character which folds to TWO
                         * characters; [3] is for folds to THREE characters.
                         * (Unicode guarantees a maximum of 3 characters in any
                         * fold.)  When we rewrite the character class below,
                         * we will do so such that the longest folds 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
                         * programmer laziness.  Tom Christiansen has agreed
                         * that this is ok.  This makes the test for the
                         * ligature 'ffi' come before the test for 'ff' */
                        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_fold);
                    }

                    /* This element should not be processed further in this
                     * class */
                    element_count--;
                    value = save_value;
                    prevvalue = save_prevvalue;
                    continue;
                }
            }
        }

        /* 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
            SV* this_range = _new_invlist(1);
            _append_range_to_invlist(this_range, prevvalue, value);

            /* In EBCDIC, the ranges 'A-Z' and 'a-z' are each not contiguous.
             * If this range was specified using something like 'i-j', we want
             * to include only the 'i' and the 'j', and not anything in
             * between, so exclude non-ASCII, non-alphabetics from it.
             * However, if the range was specified with something like
             * [\x89-\x91] or [\x89-j], all code points within it should be
             * included.  literal_endpoint==2 means both ends of the range used
             * a literal character, not \x{foo} */
            if (literal_endpoint == 2
                && ((prevvalue >= 'a' && value <= 'z')
                    || (prevvalue >= 'A' && value <= 'Z')))
            {
                _invlist_intersection(this_range, PL_ASCII,
                                      &this_range);

                /* Since this above only contains ascii, the intersection of it
                 * with anything will still yield only ascii */
                _invlist_intersection(this_range, PL_XPosix_ptrs[_CC_ALPHA],
                                      &this_range);
            }
            _invlist_union(cp_foldable_list, this_range, &cp_foldable_list);
            literal_endpoint = 0;
#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;
        bool first_time = TRUE;     /* First multi-char occurrence doesn't get
                                       a "|" */
        I32 reg_flags;

        assert(! invert);
#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, "|[");
            sv_catpvn(substitute_parse, orig_parse, RExC_parse - orig_parse);
            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

        RExC_parse = SvPV(substitute_parse, len);
        RExC_end = RExC_parse + len;
        RExC_in_multi_char_class = 1;
        RExC_emit = (regnode *)orig_emit;

        ret = reg(pRExC_state, 1, &reg_flags, depth+1);

        *flagp |= reg_flags&(HASWIDTH|SIMPLE|SPSTART|POSTPONED|RESTART_UTF8);

        RExC_parse = save_parse;
        RExC_end = save_end;
        RExC_in_multi_char_class = 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 (! 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 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, locale */
                case ANYOF_ASCII:
                case ANYOF_NASCII:
#ifdef HAS_ISASCII
                    op = (LOC) ? POSIXL : POSIXA;
#else
                    op = POSIXA;
#endif
                    goto join_posix;

                case ANYOF_NCASED:
                case ANYOF_LOWER:
                case ANYOF_NLOWER:
                case ANYOF_UPPER:
                case ANYOF_NUPPER:
                    /* under /a could be alpha */
                    if (FOLD) {
                        if (ASCII_RESTRICTED) {
                            namedclass = ANYOF_ALPHA + (namedclass % 2);
                        }
                        else if (! LOC) {
                            break;
                        }
                    }
                    /* 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:
                    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;
                    RExC_naughty++;
                }
            }
            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 (prevvalue == 'A') {
                if (value == 'Z'
#ifdef EBCDIC
                    && literal_endpoint == 2
#endif
                ) {
                    arg = (FOLD) ? _CC_ALPHA : _CC_UPPER;
                    op = POSIXA;
                }
            }
            else if (prevvalue == 'a') {
                if (value == 'z'
#ifdef EBCDIC
                    && literal_endpoint == 2
#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(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 to 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 {
                                depends_list =
                                 add_cp_to_invlist(depends_list,
                                                   PL_fold_latin1[j]);
                            }
                        }

                        if (HAS_NONLATIN1_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;
                            if (c_p == NULL) {
                                Perl_croak(aTHX_ "panic: invalid PL_utf8_foldclosures structure");
                            }
                            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 */
                                depends_list = add_cp_to_invlist(depends_list,
                                                                 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 (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_NON_UTF8_NON_ASCII_ALL;
            }
            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 (depends_list) {
                _invlist_union(depends_list, nonascii_but_latin1_properties,
                               &depends_list);
                SvREFCNT_dec_NN(nonascii_but_latin1_properties);
            }
            else {
                depends_list = 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
     * <depends_list>, 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_WARN_SUPER;
        }
    }

    /* 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) {
        if (only_utf8_locale_list) {
            ANYOF_FLAGS(ret) |= ANYOF_LOC_FOLD;
        }
        else if (cp_list) { /* Look to see if there a 0-255 code point is in
                               the list */
            UV start, end;
            invlist_iterinit(cp_list);
            if (invlist_iternext(cp_list, &start, &end) && start < 256) {
                ANYOF_FLAGS(ret) |= ANYOF_LOC_FOLD;
            }
            invlist_iterfinish(cp_list);
        }
    }

    /* 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
        && ! (ANYOF_FLAGS(ret) & (ANYOF_LOCALE_FLAGS))
        && ! depends_list
        && ! 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) {
        *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.  I (khw) am not sure how much to look for here.  It would
     * be easy, but perhaps too slow, to check any candidates against all the
     * node types they could possibly match using _invlistEQ(). */

    if (cp_list
        && ! invert
        && ! depends_list
        && ! (ANYOF_FLAGS(ret) & (ANYOF_LOCALE_FLAGS))
        && ! HAS_NONLOCALE_RUNTIME_PROPERTY_DEFINITION

           /* We don't optimize if we are supposed to make sure all non-Unicode
            * code points raise a warning, as only ANYOF nodes have this check.
            * */
        && ! ((ANYOF_FLAGS(ret) & ANYOF_WARN_SUPER) && ALWAYS_WARN_SUPER))
    {
        UV start, end;
        U8 op = END;  /* The optimzation node-type */
        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 is the only thing in the character class, and
             * it doesn't match anything.  (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 = 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);
                    }
                }
            }
        }
        else if (start == 0) {
            if (end == UV_MAX) {
                op = SANY;
                *flagp |= HASWIDTH|SIMPLE;
                RExC_naughty++;
            }
            else if (end == '\n' - 1
                    && invlist_iternext(cp_list, &start, &end)
                    && start == '\n' + 1 && end == UV_MAX)
            {
                op = REG_ANY;
                *flagp |= HASWIDTH|SIMPLE;
                RExC_naughty++;
            }
        }
        invlist_iterfinish(cp_list);

        if (op != END) {
            RExC_parse = (char *)orig_parse;
            RExC_emit = (regnode *)orig_emit;

            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 */
                                          );
            }

            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 (<depends_list>). */
    if (depends_list) {
        if (cp_list) {
            _invlist_union(cp_list, depends_list, &cp_list);
            SvREFCNT_dec_NN(depends_list);
        }
        else {
            cp_list = depends_list;
        }
        ANYOF_FLAGS(ret) |= ANYOF_UTF8;
    }

    /* 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;
    }

    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_NONBITMAP_EMPTY.  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_UTF8|ANYOF_NONBITMAP_NON_UTF8)));
        ARG_SET(node, ANYOF_NONBITMAP_EMPTY);
    }
    else {
        AV * const av = newAV();
        SV *rv;

        assert(ANYOF_FLAGS(node)
                    & (ANYOF_UTF8|ANYOF_NONBITMAP_NON_UTF8|ANYOF_LOC_FOLD));

        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);
    }
}


/* 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(pTHX_ 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;
}

/* nextchar()

   Advances the parse position, and optionally absorbs
   "whitespace" from the inputstream.

   Without /x "whitespace" means (?#...) style comments only,
   with /x this means (?#...) and # comments and whitespace proper.

   Returns the RExC_parse point from BEFORE the scan occurs.

   This is the /x friendly way of saying RExC_parse++.
*/

STATIC char*
S_nextchar(pTHX_ RExC_state_t *pRExC_state)
{
    char* const retval = RExC_parse++;

    PERL_ARGS_ASSERT_NEXTCHAR;

    for (;;) {
        if (RExC_end - RExC_parse >= 3
            && *RExC_parse == '('
            && RExC_parse[1] == '?'
            && RExC_parse[2] == '#')
        {
            while (*RExC_parse != ')') {
                if (RExC_parse == RExC_end)
                    FAIL("Sequence (?#... not terminated");
                RExC_parse++;
            }
            RExC_parse++;
            continue;
        }
        if (RExC_flags & RXf_PMf_EXTENDED) {
            char * p = regpatws(pRExC_state, RExC_parse,
                                          TRUE); /* means recognize comments */
            if (p != RExC_parse) {
                RExC_parse = p;
                continue;
            }
        }
        return retval;
    }
}

/*
- reg_node - emit a node
*/
STATIC regnode *                        /* Location. */
S_reg_node(pTHX_ RExC_state_t *pRExC_state, U8 op)
{
    dVAR;
    regnode *ptr;
    regnode * const ret = RExC_emit;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REG_NODE;

    if (SIZE_ONLY) {
        SIZE_ALIGN(RExC_size);
        RExC_size += 1;
        return(ret);
    }
    if (RExC_emit >= RExC_emit_bound)
        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d, %p>=%p",
                   op, RExC_emit, RExC_emit_bound);

    NODE_ALIGN_FILL(ret);
    ptr = ret;
    FILL_ADVANCE_NODE(ptr, op);
#ifdef RE_TRACK_PATTERN_OFFSETS
    if (RExC_offsets) {         /* MJD */
        MJD_OFFSET_DEBUG(
              ("%s:%d: (op %s) %s %"UVuf" (len %"UVuf") (max %"UVuf").\n",
              "reg_node", __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
    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)
{
    dVAR;
    regnode *ptr;
    regnode * const ret = RExC_emit;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGANODE;

    if (SIZE_ONLY) {
        SIZE_ALIGN(RExC_size);
        RExC_size += 2;
        /*
           We can't do this:

           assert(2==regarglen[op]+1);

           Anything larger than this has to allocate the extra amount.
           If we changed this to be:

           RExC_size += (1 + regarglen[op]);

           then it wouldn't matter. Its not clear what side effect
           might come from that so its not done so far.
           -- dmq
        */
        return(ret);
    }
    if (RExC_emit >= RExC_emit_bound)
        Perl_croak(aTHX_ "panic: reg_node overrun trying to emit %d, %p>=%p",
                   op, RExC_emit, RExC_emit_bound);

    NODE_ALIGN_FILL(ret);
    ptr = ret;
    FILL_ADVANCE_NODE_ARG(ptr, op, arg);
#ifdef RE_TRACK_PATTERN_OFFSETS
    if (RExC_offsets) {         /* MJD */
        MJD_OFFSET_DEBUG(
              ("%s(%d): (op %s) %s %"UVuf" <- %"UVuf" (max %"UVuf").\n",
              "reganode",
              __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_Cur_Node_Offset;
    }
#endif
    RExC_emit = ptr;
    return(ret);
}

/*
- reguni - emit (if appropriate) a Unicode character
*/
PERL_STATIC_INLINE STRLEN
S_reguni(pTHX_ const RExC_state_t *pRExC_state, UV uv, char* s)
{
    dVAR;

    PERL_ARGS_ASSERT_REGUNI;

    return SIZE_ONLY ? UNISKIP(uv) : (uvchr_to_utf8((U8*)s, uv) - (U8*)s);
}

/*
- 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)
{
    dVAR;
    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_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
*/
/* TODO: All three parms should be const */
STATIC void
S_regtail(pTHX_ RExC_state_t *pRExC_state, regnode *p,
                const regnode *val,U32 depth)
{
    dVAR;
    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 = p;
    for (;;) {
        regnode * const temp = regnext(scan);
        DEBUG_PARSE_r({
            SV * const mysv=sv_newmortal();
            DEBUG_PARSE_MSG((scan==p ? "tail" : ""));
            regprop(RExC_rx, mysv, scan, NULL);
            PerlIO_printf(Perl_debug_log, "~ %s (%d) %s %s\n",
                SvPV_nolen_const(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)
{
    dVAR;
    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 EXACTF:
                case EXACTFA_NO_TRIE:
                case EXACTFA:
                case EXACTFU:
                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({
            SV * const mysv=sv_newmortal();
            DEBUG_PARSE_MSG((scan==p ? "tsdy" : ""));
            regprop(RExC_rx, mysv, scan, NULL);
            PerlIO_printf(Perl_debug_log, "~ %s (%d) -> %s\n",
                SvPV_nolen_const(mysv),
                REG_NODE_NUM(scan),
                PL_reg_name[exact]);
        });
        if (temp == NULL)
            break;
        scan = temp;
    }
    DEBUG_PARSE_r({
        SV * const mysv_val=sv_newmortal();
        DEBUG_PARSE_MSG("");
        regprop(RExC_rx, mysv_val, val, NULL);
        PerlIO_printf(Perl_debug_log,
                      "~ attach to %s (%"IVdf") offset to %"IVdf"\n",
                      SvPV_nolen_const(mysv_val),
                      (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
    dVAR;
    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);
        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_BOL)
            PerlIO_printf(Perl_debug_log, "(BOL)");
        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)");
        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 */
}

/*
- 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)
{
#ifdef DEBUGGING
    dVAR;
    int k;

    /* Should be synchronized with * ANYOF_ #xdefines in regcomp.h */
    static const char * const anyofs[] = {
#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_PSXSPC != 13 || _CC_CNTRL != 14 || _CC_ASCII != 15               \
    || _CC_VERTSPACE != 16
  #error Need to adjust order of anyofs[]
#endif
        "\\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:]",
        "[:space:]",
        "[:^space:]",
        "[:cntrl:]",
        "[:^cntrl:]",
        "[:ascii:]",
        "[:^ascii:]",
        "\\v",
        "\\V"
    };
    RXi_GET_DECL(prog,progi);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_REGPROP;

    sv_setpvs(sv, "");

    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_latin1_charclass_innards(sv, IS_ANYOF_TRIE(op)
                                                   ? ANYOF_BITMAP(o)
                                                   : TRIE_BITMAP(trie));
            sv_catpvs(sv, "]");
        }

    } else if (k == CURLY) {
        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, " {%d,%d}", ARG1(o), ARG2(o));
    }
    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)
    {
        Perl_sv_catpvf(aTHX_ sv, "%d", (int)ARG(o));    /* Parenth number */
        if ( RXp_PAREN_NAMES(prog) ) {
            if ( k != REF || (OP(o) < NREF)) {
                AV *list= MUTABLE_AV(progi->data->data[progi->name_list_idx]);
                SV **name= av_fetch(list, ARG(o), 0 );
                if (name)
                    Perl_sv_catpvf(aTHX_ sv, " '%"SVf"'", SVfARG(*name));
            }
            else {
                AV *list= MUTABLE_AV(progi->data->data[ progi->name_list_idx ]);
                SV *sv_dat= MUTABLE_SV(progi->data->data[ ARG( o ) ]);
                I32 *nums=(I32*)SvPVX(sv_dat);
                SV **name= av_fetch(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)
        /* Paren and offset */
        Perl_sv_catpvf(aTHX_ sv, "%d[%+d]", (int)ARG(o),(int)ARG2L(o));
    else if (k == VERB) {
        if (!o->flags)
            Perl_sv_catpvf(aTHX_ sv, ":%"SVf,
                           SVfARG((MUTABLE_SV(progi->data->data[ ARG( o ) ]))));
    } 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);
        int do_sep = 0;


        if (flags & ANYOF_LOCALE_FLAGS)
            sv_catpvs(sv, "{loc}");
        if (flags & ANYOF_LOC_FOLD)
            sv_catpvs(sv, "{i}");
        Perl_sv_catpvf(aTHX_ sv, "[%s", PL_colors[0]);
        if (flags & ANYOF_INVERT)
            sv_catpvs(sv, "^");

        /* output what the standard cp 0-255 bitmap matches */
        do_sep = put_latin1_charclass_innards(sv, ANYOF_BITMAP(o));

        /* output any special charclass tests (used entirely under use
         * locale) * */
        if (ANYOF_POSIXL_TEST_ANY_SET(o)) {
            int i;
            for (i = 0; i < ANYOF_POSIXL_MAX; i++) {
                if (ANYOF_POSIXL_TEST(o,i)) {
                    sv_catpv(sv, anyofs[i]);
                    do_sep = 1;
                }
            }
        }

        if ((flags & (ANYOF_ABOVE_LATIN1_ALL
                      |ANYOF_UTF8
                      |ANYOF_NONBITMAP_NON_UTF8
                      |ANYOF_LOC_FOLD)))
        {
            if (do_sep) {
                Perl_sv_catpvf(aTHX_ sv,"%s][%s",PL_colors[1],PL_colors[0]);
                if (flags & ANYOF_INVERT)
                    /*make sure the invert info is in each */
                    sv_catpvs(sv, "^");
            }

            if (flags & ANYOF_NON_UTF8_NON_ASCII_ALL) {
                sv_catpvs(sv, "{non-utf8-latin1-all}");
            }

            /* output information about the unicode matching */
            if (flags & ANYOF_ABOVE_LATIN1_ALL)
                sv_catpvs(sv, "{unicode_all}");
            else if (ARG(o) != ANYOF_NONBITMAP_EMPTY) {
                SV *lv; /* Set if there is something outside the bit map. */
                bool byte_output = FALSE;   /* If something in the bitmap has
                                               been output */
                SV *only_utf8_locale;

                /* Get the stuff that wasn't in the bitmap */
                (void) _get_regclass_nonbitmap_data(prog, o, FALSE,
                                                    &lv, &only_utf8_locale);
                if (lv && lv != &PL_sv_undef) {
                    char *s = savesvpv(lv);
                    char * const origs = s;

                    while (*s && *s != '\n')
                        s++;

                    if (*s == '\n') {
                        const char * const t = ++s;

                        if (flags & ANYOF_NONBITMAP_NON_UTF8) {
                            sv_catpvs(sv, "{outside bitmap}");
                        }
                        else {
                            sv_catpvs(sv, "{utf8}");
                        }

                        if (byte_output) {
                            sv_catpvs(sv, " ");
                        }

                        while (*s) {
                            if (*s == '\n') {

                                /* Truncate very long output */
                                if (s - origs > 256) {
                                    Perl_sv_catpvf(aTHX_ sv,
                                                "%.*s...",
                                                (int) (s - origs - 1),
                                                t);
                                    goto out_dump;
                                }
                                *s = ' ';
                            }
                            else if (*s == '\t') {
                                *s = '-';
                            }
                            s++;
                        }
                        if (s[-1] == ' ')
                            s[-1] = 0;

                        sv_catpv(sv, t);
                    }

                out_dump:

                    Safefree(origs);
                    SvREFCNT_dec_NN(lv);
                }

                if ((flags & ANYOF_LOC_FOLD)
                     && only_utf8_locale
                     && only_utf8_locale != &PL_sv_undef)
                {
                    UV start, end;
                    int max_entries = 256;

                    sv_catpvs(sv, "{utf8 locale}");
                    invlist_iterinit(only_utf8_locale);
                    while (invlist_iternext(only_utf8_locale,
                                            &start, &end)) {
                        put_range(sv, start, end);
                        max_entries --;
                        if (max_entries < 0) {
                            sv_catpvs(sv, "...");
                            break;
                        }
                    }
                    invlist_iterfinish(only_utf8_locale);
                }
            }
        }

        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 == BRANCHJ && (OP(o) == UNLESSM || OP(o) == IFMATCH))
        Perl_sv_catpvf(aTHX_ sv, "[%d]", -(o->flags));
#else
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(sv);
    PERL_UNUSED_ARG(o);
    PERL_UNUSED_ARG(prog);
    PERL_UNUSED_ARG(reginfo);
#endif  /* DEBUGGING */
}



SV *
Perl_re_intuit_string(pTHX_ REGEXP * const r)
{                               /* Assume that RE_INTUIT is set */
    dVAR;
    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(prog->check_substr
                      ? prog->check_substr : prog->check_utf8);

            if (!PL_colorset) reginitcolors();
            PerlIO_printf(Perl_debug_log,
                      "%sUsing REx %ssubstr:%s \"%s%.60s%s%s\"\n",
                      PL_colors[4],
                      prog->check_substr ? "" : "utf8 ",
                      PL_colors[5],PL_colors[0],
                      s,
                      PL_colors[1],
                      (strlen(s) > 60 ? "..." : ""));
        } );

    return prog->check_substr ? prog->check_substr : prog->check_utf8;
}

/*
   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)
{
    dVAR;
    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)
{
    dVAR;
    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];
                    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]);
                        PerlMemShared_free(ri->regstclass);
                    }
                }
                break;
            case 't':
                {
                    /* trie structure. */
                    U32 refcount;
                    reg_trie_data *trie=(reg_trie_data*)ri->data->data[n];
                    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)
{
    dVAR;
    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)
{
    dVAR;

    /* 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) {
            U32 i;
            for (i = 1; i <= RX_NPARENS(rx); 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_byte(pTHX_ SV *sv, int c)
{
    PERL_ARGS_ASSERT_PUT_BYTE;

    if (!isPRINT(c)) {
        switch (c) {
            case '\r': Perl_sv_catpvf(aTHX_ sv, "\\r"); break;
            case '\n': Perl_sv_catpvf(aTHX_ sv, "\\n"); break;
            case '\t': Perl_sv_catpvf(aTHX_ sv, "\\t"); break;
            case '\f': Perl_sv_catpvf(aTHX_ sv, "\\f"); break;
            case '\a': Perl_sv_catpvf(aTHX_ sv, "\\a"); break;

            default:
                Perl_sv_catpvf(aTHX_ sv, "\\x{%x}", c);
                break;
        }
    }
    else {
        const char string = c;
        if (c == '-' || c == ']' || c == '\\' || c == '^')
            sv_catpvs(sv, "\\");
        sv_catpvn(sv, &string, 1);
    }
}

STATIC void
S_put_range(pTHX_ SV *sv, UV start, UV end)
{

    /* Appends to 'sv' a displayable version of the range of code points from
     * 'start' to 'end' */

    assert(start <= end);

    PERL_ARGS_ASSERT_PUT_RANGE;

    if (end - start < 3) {  /* Individual chars in short ranges */
        for (; start <= end; start++)
            put_byte(sv, start);
    }
    else if (   end > 255
             || ! isALPHANUMERIC(start)
             || ! isALPHANUMERIC(end)
             || isDIGIT(start) != isDIGIT(end)
             || isUPPER(start) != isUPPER(end)
             || isLOWER(start) != isLOWER(end)

                /* This final test should get optimized out except on EBCDIC
                 * platforms, where it causes ranges that cross discontinuities
                 * like i/j to be shown as hex instead of the misleading,
                 * e.g. H-K (since that range includes more than H, I, J, K).
                 * */
             || (end - start) != NATIVE_TO_ASCII(end) - NATIVE_TO_ASCII(start))
    {
        Perl_sv_catpvf(aTHX_ sv, "\\x{%02" UVXf "}-\\x{%02" UVXf "}",
                       start,
                       (end < 256) ? end : 255);
    }
    else { /* Here, the ends of the range are both digits, or both uppercase,
              or both lowercase; and there's no discontinuity in the range
              (which could happen on EBCDIC platforms) */
        put_byte(sv, start);
        sv_catpvs(sv, "-");
        put_byte(sv, end);
    }
}

STATIC bool
S_put_latin1_charclass_innards(pTHX_ SV *sv, char *bitmap)
{
    /* Appends to 'sv' a displayable version of the innards of the bracketed
     * character class whose bitmap is 'bitmap';  Returns 'TRUE' if it actually
     * output anything */

    int i;
    bool has_output_anything = FALSE;

    PERL_ARGS_ASSERT_PUT_LATIN1_CHARCLASS_INNARDS;

    for (i = 0; i < 256; i++) {
        if (i < 256 && BITMAP_TEST((U8 *) bitmap,i)) {

            /* The character at index i should be output.  Find the next
             * character that should NOT be output */
            int j;
            for (j = i + 1; j <= 256; j++) {
                if (! BITMAP_TEST((U8 *) bitmap, j)) {
                    break;
                }
            }

            /* Everything between them is a single range that should be output
             * */
            put_range(sv, i, j - 1);
            has_output_anything = TRUE;
            i = j;
        }
    }

    return has_output_anything;
}

#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)
{
    dVAR;
    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);
        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_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 */

/*
 * Local variables:
 * c-indentation-style: bsd
 * c-basic-offset: 4
 * indent-tabs-mode: nil
 * End:
 *
 * ex: set ts=8 sts=4 sw=4 et:
 */