regcomp.c: calculate variants instead of assuming worst case

[perl5.git] / regcomp.c

/*    regcomp.c
 */

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

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

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

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

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

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

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

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

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

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

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

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

#ifndef STATIC
#define STATIC  static
#endif

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

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

/* Certain characters are output as a sequence with the first being a
 * backslash. */
#define isBACKSLASHED_PUNCT(c)  strchr("-[]\\^", c)


struct RExC_state_t {
    U32         flags;                  /* RXf_* are we folding, multilining? */
    U32         pm_flags;               /* PMf_* stuff from the calling PMOP */
    char        *precomp;               /* uncompiled string. */
    char        *precomp_end;           /* pointer to end of uncompiled string. */
    REGEXP      *rx_sv;                 /* The SV that is the regexp. */
    regexp      *rx;                    /* perl core regexp structure */
    regexp_internal     *rxi;           /* internal data for regexp object
                                           pprivate field */
    char        *start;                 /* Start of input for compile */
    char        *end;                   /* End of input for compile */
    char        *parse;                 /* Input-scan pointer. */
    char        *copy_start;            /* start of copy of input within
                                           constructed parse string */
    char        *copy_start_in_input;   /* Position in input string
                                           corresponding to copy_start */
    SSize_t     whilem_seen;            /* number of WHILEM in this expr */
    regnode     *emit_start;            /* Start of emitted-code area */
    regnode_offset emit;                /* Code-emit pointer */
    I32         naughty;                /* How bad is this pattern? */
    I32         sawback;                /* Did we see \1, ...? */
    U32         seen;
    SSize_t     size;                   /* Number of regnode equivalents in
                                           pattern */

    /* position beyond 'precomp' of the warning message furthest away from
     * 'precomp'.  During the parse, no warnings are raised for any problems
     * earlier in the parse than this position.  This works if warnings are
     * raised the first time a given spot is parsed, and if only one
     * independent warning is raised for any given spot */
    Size_t      latest_warn_offset;

    I32         npar;                   /* Capture buffer count so far in the
                                           parse, (OPEN) plus one. ("par" 0 is
                                           the whole pattern)*/
    I32         total_par;              /* During initial parse, is either 0,
                                           or -1; the latter indicating a
                                           reparse is needed.  After that pass,
                                           it is what 'npar' became after the
                                           pass.  Hence, it being > 0 indicates
                                           we are in a reparse situation */
    I32         nestroot;               /* root parens we are in - used by
                                           accept */
    I32         seen_zerolen;
    regnode_offset *open_parens;        /* offsets to open parens */
    regnode_offset *close_parens;       /* offsets to close parens */
    regnode     *end_op;                /* 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 we have generated */
    U8          *study_chunk_recursed;  /* bitmap of which subs we have moved
                                           through */
    U32         study_chunk_recursed_bytes;  /* bytes in bitmap */
    I32         in_lookbehind;
    I32         contains_locale;
    I32         override_recoding;
#ifdef EBCDIC
    I32         recode_x_to_native;
#endif
    I32         in_multi_char_class;
    struct reg_code_blocks *code_blocks;/* positions of literal (?{})
                                            within pattern */
    int         code_index;             /* next code_blocks[] slot */
    SSize_t     maxlen;                        /* mininum possible number of chars in string to match */
    scan_frame *frame_head;
    scan_frame *frame_last;
    U32         frame_count;
    AV         *warn_text;
#ifdef ADD_TO_REGEXEC
    char        *starttry;              /* -Dr: where regtry was called. */
#define RExC_starttry   (pRExC_state->starttry)
#endif
    SV          *runtime_code_qr;       /* qr with the runtime code blocks */
#ifdef DEBUGGING
    const char  *lastparse;
    I32         lastnum;
    AV          *paren_name_list;       /* idx -> name */
    U32         study_chunk_recursed_count;
    SV          *mysv1;
    SV          *mysv2;

#define RExC_lastparse  (pRExC_state->lastparse)
#define RExC_lastnum    (pRExC_state->lastnum)
#define RExC_paren_name_list    (pRExC_state->paren_name_list)
#define RExC_study_chunk_recursed_count    (pRExC_state->study_chunk_recursed_count)
#define RExC_mysv       (pRExC_state->mysv1)
#define RExC_mysv1      (pRExC_state->mysv1)
#define RExC_mysv2      (pRExC_state->mysv2)

#endif
    bool        seen_unfolded_sharp_s;
    bool        strict;
    bool        study_started;
    bool        in_script_run;
    bool        use_BRANCHJ;
};

#define RExC_flags      (pRExC_state->flags)
#define RExC_pm_flags   (pRExC_state->pm_flags)
#define RExC_precomp    (pRExC_state->precomp)
#define RExC_copy_start_in_input (pRExC_state->copy_start_in_input)
#define RExC_copy_start_in_constructed  (pRExC_state->copy_start)
#define RExC_precomp_end (pRExC_state->precomp_end)
#define RExC_rx_sv      (pRExC_state->rx_sv)
#define RExC_rx         (pRExC_state->rx)
#define RExC_rxi        (pRExC_state->rxi)
#define RExC_start      (pRExC_state->start)
#define RExC_end        (pRExC_state->end)
#define RExC_parse      (pRExC_state->parse)
#define RExC_latest_warn_offset (pRExC_state->latest_warn_offset )
#define RExC_whilem_seen        (pRExC_state->whilem_seen)

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

#ifdef RE_TRACK_PATTERN_OFFSETS
#  define RExC_offsets  (RExC_rxi->u.offsets) /* I am not like the
                                                         others */
#endif
#define RExC_emit       (pRExC_state->emit)
#define RExC_emit_start (pRExC_state->emit_start)
#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_total_parens       (pRExC_state->total_par)
#define RExC_nestroot   (pRExC_state->nestroot)
#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_end_op     (pRExC_state->end_op)
#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)
#ifdef EBCDIC
#   define RExC_recode_x_to_native (pRExC_state->recode_x_to_native)
#endif
#define RExC_in_multi_char_class (pRExC_state->in_multi_char_class)
#define RExC_frame_head (pRExC_state->frame_head)
#define RExC_frame_last (pRExC_state->frame_last)
#define RExC_frame_count (pRExC_state->frame_count)
#define RExC_strict (pRExC_state->strict)
#define RExC_study_started      (pRExC_state->study_started)
#define RExC_warn_text (pRExC_state->warn_text)
#define RExC_in_script_run      (pRExC_state->in_script_run)
#define RExC_use_BRANCHJ        (pRExC_state->use_BRANCHJ)

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

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

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

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

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

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



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

#define REQUIRE_UTF8(flagp) STMT_START {                                   \
                                     if (!UTF) {                           \
                                         *flagp = RESTART_PARSE|NEED_UTF8; \
                                         return 0;                         \
                                     }                                     \
                             } STMT_END

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

#define BRANCH_MAX_OFFSET   U16_MAX
#define REQUIRE_BRANCHJ(flagp, restart_retval)                              \
    STMT_START {                                                            \
                RExC_use_BRANCHJ = 1;                                       \
                *flagp |= RESTART_PARSE;                                    \
                return restart_retval;                                      \
    } STMT_END

#define REQUIRE_PARENS_PASS                                                 \
    STMT_START {                                                            \
                    if (RExC_total_parens == 0) RExC_total_parens = -1;     \
    } STMT_END

/* Executes a return statement with the value 'X', if 'flags' contains any of
 * 'RESTART_PARSE', 'NEED_UTF8', or 'extra'.  If so, *flagp is set to those
 * flags */
#define RETURN_X_ON_RESTART_OR_FLAGS(X, flags, flagp, extra)                \
    STMT_START {                                                            \
            if ((flags) & (RESTART_PARSE|NEED_UTF8|(extra))) {              \
                *(flagp) = (flags) & (RESTART_PARSE|NEED_UTF8|(extra));     \
                return X;                                                   \
            }                                                               \
    } STMT_END

#define RETURN_FAIL_ON_RESTART_OR_FLAGS(flags,flagp,extra)                  \
                    RETURN_X_ON_RESTART_OR_FLAGS(0,flags,flagp,extra)

#define RETURN_X_ON_RESTART(X, flags,flagp)                                 \
                        RETURN_X_ON_RESTART_OR_FLAGS( X, flags, flagp, 0)


#define RETURN_FAIL_ON_RESTART_FLAGP_OR_FLAGS(flagp,extra)                  \
            if (*(flagp) & (RESTART_PARSE|(extra))) return 0

#define MUST_RESTART(flags) ((flags) & (RESTART_PARSE))

#define RETURN_FAIL_ON_RESTART(flags,flagp)                                 \
                                    RETURN_X_ON_RESTART(0, flags,flagp)
#define RETURN_FAIL_ON_RESTART_FLAGP(flagp)                                 \
                            RETURN_FAIL_ON_RESTART_FLAGP_OR_FLAGS(flagp, 0)

/* 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:

  - 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.
    For fixed strings, it is equal to min_offset.

  - 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.

*/

struct scan_data_substrs {
    SV      *str;       /* longest substring found in pattern */
    SSize_t min_offset; /* earliest point in string it can appear */
    SSize_t max_offset; /* latest point in string it can appear */
    SSize_t *minlenp;   /* pointer to the minlen relevant to the string */
    SSize_t lookbehind; /* is the pos of the string modified by LB */
    I32 flags;          /* per substring SF_* and SCF_* flags */
};

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;
    U8      cur_is_floating; /* whether the last_* values should be set as
                              * the next fixed (0) or floating (1)
                              * substring */

    /* [0] is longest fixed substring so far, [1] is longest float so far */
    struct scan_data_substrs  substrs[2];

    I32 flags;             /* common SF_* and SCF_* flags */
    I32 whilem_c;
    SSize_t *last_closep;
    regnode_ssc *start_class;
} scan_data_t;

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

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

/* study flags */

#define SF_BEFORE_SEOL          0x0001
#define SF_BEFORE_MEOL          0x0002
#define SF_BEFORE_EOL           (SF_BEFORE_SEOL|SF_BEFORE_MEOL)

#define SF_IS_INF               0x0040
#define SF_HAS_PAR              0x0080
#define SF_IN_PAR               0x0100
#define SF_HAS_EVAL             0x0200


/* SCF_DO_SUBSTR is the flag that tells the regexp analyzer to track the
 * longest substring in the pattern. When it is not set the optimiser keeps
 * track of position, but does not keep track of the actual strings seen,
 *
 * So for instance /foo/ will be parsed with SCF_DO_SUBSTR being true, but
 * /foo/i will not.
 *
 * Similarly, /foo.*(blah|erm|huh).*fnorble/ will have "foo" and "fnorble"
 * parsed with SCF_DO_SUBSTR on, but while processing the (...) it will be
 * turned off because of the alternation (BRANCH). */
#define SCF_DO_SUBSTR           0x0400

#define SCF_DO_STCLASS_AND      0x0800
#define SCF_DO_STCLASS_OR       0x1000
#define SCF_DO_STCLASS          (SCF_DO_STCLASS_AND|SCF_DO_STCLASS_OR)
#define SCF_WHILEM_VISITED_POS  0x2000

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




#define UTF cBOOL(RExC_utf8)

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

#define FOLD cBOOL(RExC_flags & RXf_PMf_FOLD)

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

#define OOB_NAMEDCLASS          -1

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

#define CHR_SVLEN(sv) (UTF ? sv_len_utf8(sv) : SvCUR(sv))


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

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

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

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

#define sI              RExC_precomp
#define eI              RExC_precomp_end
#define sC              RExC_start
#define eC              RExC_end
#define tI              RExC_copy_start_in_input
#define tC              RExC_copy_start_in_constructed
#define xI(xC)          (tI + (xC - tC))
#define xI_offset(xC)   (xI(xC) - sI)

#define REPORT_LOCATION_ARGS(xC)                                            \
    UTF8fARG(UTF,                                                           \
             (xI(xC) > eI) /* Don't run off end */                          \
              ? eI - sI   /* Length before the <--HERE */                   \
              : ((xI_offset(xC) >= 0)                                       \
                 ? xI_offset(xC)                                            \
                 : (Perl_croak(aTHX_ "panic: %s: %d: negative offset: %"    \
                                    IVdf " trying to output message for "   \
                                    " pattern %.*s",                        \
                                    __FILE__, __LINE__, (IV) xI_offset(xC), \
                                    ((int) (eC - sC)), sC), 0)),            \
             sI),         /* The input pattern printed up to the <--HERE */ \
    UTF8fARG(UTF,                                                           \
             (xI(xC) > eI) ? 0 : eI - xI(xC), /* Length after <--HERE */    \
             (xI(xC) > eI) ? eI : xI(xC))     /* pattern after <--HERE */

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

/* Set up to clean up after our imminent demise */
#define PREPARE_TO_DIE                                                      \
    STMT_START {                                                            \
        if (RExC_rx_sv)                                                     \
            SAVEFREESV(RExC_rx_sv);                                         \
        if (RExC_open_parens)                                               \
            SAVEFREEPV(RExC_open_parens);                                   \
        if (RExC_close_parens)                                              \
            SAVEFREEPV(RExC_close_parens);                                  \
    } STMT_END

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

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

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

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

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

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

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


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

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

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

#define vFAIL4(m,a1,a2,a3) STMT_START {                 \
    PREPARE_TO_DIE;                                     \
    Simple_vFAIL4(m, a1, a2, a3);                       \
} STMT_END

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

#define vFAIL3utf8f(m, a1, a2) STMT_START {             \
    PREPARE_TO_DIE;                                     \
    S_re_croak2(aTHX_ UTF, m, REPORT_LOCATION, a1, a2,  \
            REPORT_LOCATION_ARGS(RExC_parse));          \
} STMT_END

/* Setting this to NULL is a signal to not output warnings */
#define TURN_OFF_WARNINGS_IN_SUBSTITUTE_PARSE RExC_copy_start_in_constructed = NULL
#define RESTORE_WARNINGS RExC_copy_start_in_constructed = RExC_precomp

/* Since a warning can be generated multiple times as the input is reparsed, we
 * output it the first time we come to that point in the parse, but suppress it
 * otherwise.  'RExC_copy_start_in_constructed' being NULL is a flag to not
 * generate any warnings */
#define TO_OUTPUT_WARNINGS(loc)                                         \
  (   RExC_copy_start_in_constructed                                    \
   && ((xI(loc)) - RExC_precomp) > (Ptrdiff_t) RExC_latest_warn_offset)

/* After we've emitted a warning, we save the position in the input so we don't
 * output it again */
#define UPDATE_WARNINGS_LOC(loc)                                        \
    STMT_START {                                                        \
        if (TO_OUTPUT_WARNINGS(loc)) {                                  \
            RExC_latest_warn_offset = (xI(loc)) - RExC_precomp;         \
        }                                                               \
    } STMT_END

/* 'warns' is the output of the packWARNx macro used in 'code' */
#define _WARN_HELPER(loc, warns, code)                                  \
    STMT_START {                                                        \
        if (! RExC_copy_start_in_constructed) {                         \
            Perl_croak( aTHX_ "panic! %s: %d: Tried to warn when none"  \
                              " expected at '%s'",                      \
                              __FILE__, __LINE__, loc);                 \
        }                                                               \
        if (TO_OUTPUT_WARNINGS(loc)) {                                  \
            if (ckDEAD(warns))                                          \
                PREPARE_TO_DIE;                                         \
            code;                                                       \
            UPDATE_WARNINGS_LOC(loc);                                   \
        }                                                               \
    } STMT_END

/* m is not necessarily a "literal string", in this macro */
#define reg_warn_non_literal_string(loc, m)                             \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_warner(aTHX_ packWARN(WARN_REGEXP),          \
                                       "%s" REPORT_LOCATION,            \
                                  m, REPORT_LOCATION_ARGS(loc)))

#define ckWARNreg(loc,m)                                                \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),       \
                                          m REPORT_LOCATION,            \
                                          REPORT_LOCATION_ARGS(loc)))

#define vWARN(loc, m)                                                   \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_warner(aTHX_ packWARN(WARN_REGEXP),          \
                                       m REPORT_LOCATION,               \
                                       REPORT_LOCATION_ARGS(loc)))      \

#define vWARN_dep(loc, m)                                               \
    _WARN_HELPER(loc, packWARN(WARN_DEPRECATED),                        \
                      Perl_warner(aTHX_ packWARN(WARN_DEPRECATED),      \
                                       m REPORT_LOCATION,               \
                                       REPORT_LOCATION_ARGS(loc)))

#define ckWARNdep(loc,m)                                                \
    _WARN_HELPER(loc, packWARN(WARN_DEPRECATED),                        \
                      Perl_ck_warner_d(aTHX_ packWARN(WARN_DEPRECATED), \
                                            m REPORT_LOCATION,          \
                                            REPORT_LOCATION_ARGS(loc)))

#define ckWARNregdep(loc,m)                                                 \
    _WARN_HELPER(loc, packWARN2(WARN_DEPRECATED, WARN_REGEXP),              \
                      Perl_ck_warner_d(aTHX_ packWARN2(WARN_DEPRECATED,     \
                                                      WARN_REGEXP),         \
                                             m REPORT_LOCATION,             \
                                             REPORT_LOCATION_ARGS(loc)))

#define ckWARN2reg_d(loc,m, a1)                                             \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                                \
                      Perl_ck_warner_d(aTHX_ packWARN(WARN_REGEXP),         \
                                            m REPORT_LOCATION,              \
                                            a1, REPORT_LOCATION_ARGS(loc)))

#define ckWARN2reg(loc, m, a1)                                              \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                                \
                      Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                          m REPORT_LOCATION,                \
                                          a1, REPORT_LOCATION_ARGS(loc)))

#define vWARN3(loc, m, a1, a2)                                              \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                                \
                      Perl_warner(aTHX_ packWARN(WARN_REGEXP),              \
                                       m REPORT_LOCATION,                   \
                                       a1, a2, REPORT_LOCATION_ARGS(loc)))

#define ckWARN3reg(loc, m, a1, a2)                                          \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                                \
                      Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),           \
                                          m REPORT_LOCATION,                \
                                          a1, a2,                           \
                                          REPORT_LOCATION_ARGS(loc)))

#define vWARN4(loc, m, a1, a2, a3)                                      \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_warner(aTHX_ packWARN(WARN_REGEXP),          \
                                       m REPORT_LOCATION,               \
                                       a1, a2, a3,                      \
                                       REPORT_LOCATION_ARGS(loc)))

#define ckWARN4reg(loc, m, a1, a2, a3)                                  \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_ck_warner(aTHX_ packWARN(WARN_REGEXP),       \
                                          m REPORT_LOCATION,            \
                                          a1, a2, a3,                   \
                                          REPORT_LOCATION_ARGS(loc)))

#define vWARN5(loc, m, a1, a2, a3, a4)                                  \
    _WARN_HELPER(loc, packWARN(WARN_REGEXP),                            \
                      Perl_warner(aTHX_ packWARN(WARN_REGEXP),          \
                                       m REPORT_LOCATION,               \
                                       a1, a2, a3, a4,                  \
                                       REPORT_LOCATION_ARGS(loc)))

#define ckWARNexperimental(loc, class, m)                               \
    _WARN_HELPER(loc, packWARN(class),                                  \
                      Perl_ck_warner_d(aTHX_ packWARN(class),           \
                                            m REPORT_LOCATION,          \
                                            REPORT_LOCATION_ARGS(loc)))

/* Convert between a pointer to a node and its offset from the beginning of the
 * program */
#define REGNODE_p(offset)    (RExC_emit_start + (offset))
#define REGNODE_OFFSET(node) ((node) - RExC_emit_start)

/* 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(offset,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
#define Track_Code(code)
#else
#define ProgLen(ri) ri->u.offsets[0]
#define SetProgLen(ri,x) ri->u.offsets[0] = x
#define Set_Node_Offset_To_R(offset,byte) STMT_START {                  \
        MJD_OFFSET_DEBUG(("** (%d) offset of node %d is %d.\n",         \
                    __LINE__, (int)(offset), (int)(byte)));             \
        if((offset) < 0) {                                              \
            Perl_croak(aTHX_ "value of node is %d in Offset macro",     \
                                         (int)(offset));                \
        } else {                                                        \
            RExC_offsets[2*(offset)-1] = (byte);                        \
        }                                                               \
} STMT_END

#define Set_Node_Offset(node,byte)                                      \
    Set_Node_Offset_To_R(REGNODE_OFFSET(node), (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 {                     \
        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(REGNODE_OFFSET(node), 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*(REGNODE_OFFSET(n))-1])
#define Node_Length(n) (RExC_offsets[2*(REGNODE_OFFSET(n))])

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

#define Track_Code(code) STMT_START { code } STMT_END
#endif

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

#ifdef DEBUGGING
int
Perl_re_printf(pTHX_ const char *fmt, ...)
{
    va_list ap;
    int result;
    PerlIO *f= Perl_debug_log;
    PERL_ARGS_ASSERT_RE_PRINTF;
    va_start(ap, fmt);
    result = PerlIO_vprintf(f, fmt, ap);
    va_end(ap);
    return result;
}

int
Perl_re_indentf(pTHX_ const char *fmt, U32 depth, ...)
{
    va_list ap;
    int result;
    PerlIO *f= Perl_debug_log;
    PERL_ARGS_ASSERT_RE_INDENTF;
    va_start(ap, depth);
    PerlIO_printf(f, "%*s", ( (int)depth % 20 ) * 2, "");
    result = PerlIO_vprintf(f, fmt, ap);
    va_end(ap);
    return result;
}
#endif /* DEBUGGING */

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

#define DEBUG_SHOW_STUDY_FLAG(flags,flag) \
  if ((flags) & flag) Perl_re_printf( aTHX_  "%s ", #flag)


#ifdef DEBUGGING
static void
S_debug_show_study_flags(pTHX_ U32 flags, const char *open_str,
                                    const char *close_str)
{
    if (!flags)
        return;

    Perl_re_printf( aTHX_  "%s", open_str);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_BEFORE_SEOL);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_BEFORE_MEOL);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_IS_INF);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_HAS_PAR);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_IN_PAR);
    DEBUG_SHOW_STUDY_FLAG(flags, SF_HAS_EVAL);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_DO_SUBSTR);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_DO_STCLASS_AND);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_DO_STCLASS_OR);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_DO_STCLASS);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_WHILEM_VISITED_POS);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_TRIE_RESTUDY);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_SEEN_ACCEPT);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_TRIE_DOING_RESTUDY);
    DEBUG_SHOW_STUDY_FLAG(flags, SCF_IN_DEFINE);
    Perl_re_printf( aTHX_  "%s", close_str);
}


static void
S_debug_studydata(pTHX_ const char *where, scan_data_t *data,
                    U32 depth, int is_inf)
{
    GET_RE_DEBUG_FLAGS_DECL;

    DEBUG_OPTIMISE_MORE_r({
        if (!data)
            return;
        Perl_re_indentf(aTHX_  "%s: Pos:%" IVdf "/%" IVdf " Flags: 0x%" UVXf,
            depth,
            where,
            (IV)data->pos_min,
            (IV)data->pos_delta,
            (UV)data->flags
        );

        S_debug_show_study_flags(aTHX_ data->flags," [","]");

        Perl_re_printf( aTHX_
            " Whilem_c: %" IVdf " Lcp: %" IVdf " %s",
            (IV)data->whilem_c,
            (IV)(data->last_closep ? *((data)->last_closep) : -1),
            is_inf ? "INF " : ""
        );

        if (data->last_found) {
            int i;
            Perl_re_printf(aTHX_
                "Last:'%s' %" IVdf ":%" IVdf "/%" IVdf,
                    SvPVX_const(data->last_found),
                    (IV)data->last_end,
                    (IV)data->last_start_min,
                    (IV)data->last_start_max
            );

            for (i = 0; i < 2; i++) {
                Perl_re_printf(aTHX_
                    " %s%s: '%s' @ %" IVdf "/%" IVdf,
                    data->cur_is_floating == i ? "*" : "",
                    i ? "Float" : "Fixed",
                    SvPVX_const(data->substrs[i].str),
                    (IV)data->substrs[i].min_offset,
                    (IV)data->substrs[i].max_offset
                );
                S_debug_show_study_flags(aTHX_ data->substrs[i].flags," [","]");
            }
        }

        Perl_re_printf( aTHX_ "\n");
    });
}


static void
S_debug_peep(pTHX_ const char *str, const RExC_state_t *pRExC_state,
                regnode *scan, U32 depth, U32 flags)
{
    GET_RE_DEBUG_FLAGS_DECL;

    DEBUG_OPTIMISE_r({
        regnode *Next;

        if (!scan)
            return;
        Next = regnext(scan);
        regprop(RExC_rx, RExC_mysv, scan, NULL, pRExC_state);
        Perl_re_indentf( aTHX_   "%s>%3d: %s (%d)",
            depth,
            str,
            REG_NODE_NUM(scan), SvPV_nolen_const(RExC_mysv),
            Next ? (REG_NODE_NUM(Next)) : 0 );
        S_debug_show_study_flags(aTHX_ flags," [ ","]");
        Perl_re_printf( aTHX_  "\n");
   });
}


#  define DEBUG_STUDYDATA(where, data, depth, is_inf) \
                    S_debug_studydata(aTHX_ where, data, depth, is_inf)

#  define DEBUG_PEEP(str, scan, depth, flags)   \
                    S_debug_peep(aTHX_ str, pRExC_state, scan, depth, flags)

#else
#  define DEBUG_STUDYDATA(where, data, depth, is_inf) NOOP
#  define DEBUG_PEEP(str, scan, depth, flags)         NOOP
#endif


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

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

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


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


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

    return NULL;
}

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

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

    return push(key, head);
}

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

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

    head = NULL;
}

/* End of Dictionary Stuff */

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

    PERL_ARGS_ASSERT_EDIT_DISTANCE;

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

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

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

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

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

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

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

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

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

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

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

    return NULL;
}

/* Mark that we cannot extend a found fixed substring at this point.
   Update the longest found anchored substring or 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);
    SV * const longest_sv = data->substrs[data->cur_is_floating].str;
    const STRLEN old_l = CHR_SVLEN(longest_sv);
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_SCAN_COMMIT;

    if ((l >= old_l) && ((l > old_l) || (data->flags & SF_BEFORE_EOL))) {
        const U8 i = data->cur_is_floating;
        SvSetMagicSV(longest_sv, data->last_found);
        data->substrs[i].min_offset = l ? data->last_start_min : data->pos_min;

        if (!i) /* fixed */
            data->substrs[0].max_offset = data->substrs[0].min_offset;
        else { /* float */
            data->substrs[1].max_offset = (l
                          ? data->last_start_max
                          : (data->pos_delta > SSize_t_MAX - data->pos_min
                                         ? SSize_t_MAX
                                         : data->pos_min + data->pos_delta));
            if (is_inf
                 || (STRLEN)data->substrs[1].max_offset > (STRLEN)SSize_t_MAX)
                data->substrs[1].max_offset = SSize_t_MAX;
        }

        if (data->flags & SF_BEFORE_EOL)
            data->substrs[i].flags |= (data->flags & SF_BEFORE_EOL);
        else
            data->substrs[i].flags &= ~SF_BEFORE_EOL;
        data->substrs[i].minlenp = minlenp;
        data->substrs[i].lookbehind = 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, is_inf);
}

/* 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));

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

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

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_ANYTHING;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    invlist_iterfinish(ssc->invlist);

    if (ret) {
        return TRUE;
    }

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

    return FALSE;
}

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

    PERL_ARGS_ASSERT_SSC_INIT;

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

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

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

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_CP_POSIXL_INIT;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

    invlist_iterfinish(ssc->invlist);

    if (! ret) {
        return FALSE;
    }

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

    return TRUE;
}

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

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

    PERL_ARGS_ASSERT_GET_ANYOF_CP_LIST_FOR_SSC;

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

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

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

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

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

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

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

    /* Add in the points from the bit map */
    for (i = 0; i < NUM_ANYOF_CODE_POINTS; i++) {
        if (ANYOF_BITMAP_TEST(node, i)) {
            unsigned int start = i++;

            for (; i < NUM_ANYOF_CODE_POINTS && ANYOF_BITMAP_TEST(node, i); ++i) {
                /* empty */
            }
            invlist = _add_range_to_invlist(invlist, start, i-1);
            new_node_has_latin1 = TRUE;
        }
    }

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

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

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

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

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

    return invlist;
}

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

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

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

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

    SV* anded_cp_list;
    U8  anded_flags;

    PERL_ARGS_ASSERT_SSC_AND;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    ANYOF_FLAGS(ssc) &= anded_flags;

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

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

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

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

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

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

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

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

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

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

    SV* ored_cp_list;
    U8 ored_flags;

    PERL_ARGS_ASSERT_SSC_OR;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

    ANYOF_FLAGS(ssc) |= ored_flags;

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

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

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

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

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    SV* cp_list = _new_invlist(2);

    PERL_ARGS_ASSERT_SSC_CP_AND;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

    assert(is_ANYOF_SYNTHETIC(ssc));

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

#define NON_OTHER_COUNT   NON_OTHER_COUNT_FOR_USE_ONLY_BY_REGCOMP_DOT_C

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

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

    PERL_ARGS_ASSERT_IS_SSC_WORTH_IT;

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

    return TRUE;
}


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

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

    PERL_ARGS_ASSERT_SSC_FINALIZE;

    assert(is_ANYOF_SYNTHETIC(ssc));

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

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

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

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

    if (ANYOF_POSIXL_SSC_TEST_ANY_SET(ssc)) {
        ANYOF_FLAGS(ssc) |= ANYOF_MATCHES_POSIXL;
        OP(ssc) = ANYOFPOSIXL;
    }
    else if (RExC_contains_locale) {
        OP(ssc) = ANYOFL;
    }

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

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


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

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

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

*/

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

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

    PERL_ARGS_ASSERT_DUMP_TRIE;

    Perl_re_indentf( aTHX_  "Char : %-6s%-6s%-4s ",
        depth+1, "Match","Base","Ofs" );

    for( state = 0 ; state < trie->uniquecharcount ; state++ ) {
        SV ** const tmp = av_fetch( revcharmap, state, 0);
        if ( tmp ) {
            Perl_re_printf( aTHX_  "%*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
                )
            );
        }
    }
    Perl_re_printf( aTHX_  "\n");
    Perl_re_indentf( aTHX_ "State|-----------------------", depth+1);

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

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

        Perl_re_indentf( aTHX_  "#%4" UVXf "|", depth+1, (UV)state);

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

        Perl_re_printf( aTHX_  " @%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++;

            Perl_re_printf( aTHX_  "+%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 )
                {
                   Perl_re_printf( aTHX_  "%*" UVXf, colwidth,
                    (UV)trie->trans[ base + ofs - trie->uniquecharcount ].next
                   );
                } else {
                    Perl_re_printf( aTHX_  "%*s", colwidth,"   ." );
                }
            }

            Perl_re_printf( aTHX_  "]");

        }
        Perl_re_printf( aTHX_  "\n" );
    }
    Perl_re_indentf( aTHX_  "word_info N:(prev,len)=",
                                depth);
    for (word=1; word <= trie->wordcount; word++) {
        Perl_re_printf( aTHX_  " %d:(%d,%d)",
            (int)word, (int)(trie->wordinfo[word].prev),
            (int)(trie->wordinfo[word].len));
    }
    Perl_re_printf( aTHX_  "\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.  */
    Perl_re_indentf( aTHX_  "State :Word | Transition Data\n",
            depth+1 );
    Perl_re_indentf( aTHX_  "%s",
            depth+1, "------:-----+-----------------\n" );

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

        Perl_re_indentf( aTHX_  " %4" UVXf " :",
            depth+1, (UV)state  );
        if ( ! trie->states[ state ].wordnum ) {
            Perl_re_printf( aTHX_  "%5s| ","");
        } else {
            Perl_re_printf( aTHX_  "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 ) {
                Perl_re_printf( aTHX_  "%*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))
                    Perl_re_printf( aTHX_  "\n%*s| ",
                        (int)((depth * 2) + 14), "");
            }
        }
        Perl_re_printf( aTHX_  "\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.
     */

    Perl_re_indentf( aTHX_  "Char : ", depth+1 );

    for( charid = 0 ; charid < trie->uniquecharcount ; charid++ ) {
        SV ** const tmp = av_fetch( revcharmap, charid, 0);
        if ( tmp ) {
            Perl_re_printf( aTHX_  "%*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
                )
            );
        }
    }

    Perl_re_printf( aTHX_ "\n");
    Perl_re_indentf( aTHX_  "State+-", depth+1 );

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

    Perl_re_printf( aTHX_  "\n" );

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

        Perl_re_indentf( aTHX_  "%4" UVXf " : ",
            depth+1,
            (UV)TRIE_NODENUM( state ) );

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

#endif


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

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

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

  /he|she|his|hers/

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

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

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

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

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

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

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

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

which prints out 'word' three times, but

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

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

Example of what happens on a structural level:

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

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

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

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

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

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

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

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

    d = uvchr_to_utf8_flags(d, uv, 0);

is the recommended Unicode-aware way of saying

    *(d++) = uv;
*/

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

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



#define TRIE_LIST_PUSH(state,fid,ns) STMT_START {               \
    if ( TRIE_LIST_CUR( state ) >=TRIE_LIST_LEN( state ) ) {    \
        U32 ging = TRIE_LIST_LEN( state ) * 2;                  \
        Renew( trie->states[ state ].trans.list, ging, reg_trie_trans_le ); \
        TRIE_LIST_LEN( state ) = ging;                          \
    }                                                           \
    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 {                       \
    Newx( 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 TRIE_BITMAP_SET_FOLDED(trie, uvc, folder)           \
STMT_START {                                                \
    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));   \
        }                                                   \
    }                                                       \
} STMT_END
#define MADE_TRIE       1
#define MADE_JUMP_TRIE  2
#define MADE_EXACT_TRIE 4

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

    /* in the below add_data call we are storing either 'tu' or 'tuaa'
     * which stands for one trie structure, one hash, optionally followed
     * by two arrays */
#ifdef DEBUGGING
    const U32 data_slot = add_data( pRExC_state, STR_WITH_LEN("tuaa"));
    AV *trie_words = NULL;
    /* along with revcharmap, this only used during construction but both are
     * useful during debugging so we store them in the struct when debugging.
     */
#else
    const U32 data_slot = add_data( pRExC_state, STR_WITH_LEN("tu"));
    STRLEN trie_charcount=0;
#endif
    SV *re_trie_maxbuff;
    GET_RE_DEBUG_FLAGS_DECL;

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

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

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

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

    re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
    assert(re_trie_maxbuff);
    if (!SvIOK(re_trie_maxbuff)) {
        sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
    }
    DEBUG_TRIE_COMPILE_r({
        Perl_re_indentf( aTHX_
          "make_trie start==%d, first==%d, last==%d, tail==%d depth=%d\n",
          depth+1,
          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;
        const U8 *e;
        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) {
            /* skip past a NOTHING at the start of an alternation
             * eg, /(?:)a|(?:b)/ should be the same as /a|b/
             */
            regnode *noper_next= regnext(noper);
            if (noper_next < tail)
                noper= noper_next;
        }

        if ( noper < tail &&
                (
                    OP(noper) == flags ||
                    (
                        flags == EXACTFU &&
                        OP(noper) == EXACTFU_SS
                    )
                )
        ) {
            uc= (U8*)STRING(noper);
            e= uc + 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_FOLDED(trie, uvc, folder);
                    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(
        Perl_re_indentf( aTHX_
                "TRIE(%s): W:%d C:%d Uq:%d Min:%d Max:%d\n",
                depth+1,
                ( 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( Perl_re_indentf( aTHX_  "Compiling trie using list compiler\n",
            depth+1));

        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 );
            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)
                    noper= noper_next;
            }

            if ( noper < tail && ( OP(noper) == flags || ( flags == EXACTFU && OP(noper) == EXACTFU_SS ) ) ) {
                const U8 *uc= (U8*)STRING(noper);
                const U8 *e= uc + STR_LEN(noper);

                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(
                    Perl_re_printf( aTHX_  "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(
                    Perl_re_printf( aTHX_  " 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( Perl_re_indentf( aTHX_  "Compiling trie using table compiler\n",
            depth+1));

        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 );

            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)
                    noper= noper_next;
            }

            if ( noper < tail && ( OP(noper) == flags || ( flags == EXACTFU && OP(noper) == EXACTFU_SS ) ) ) {
                const U8 *uc= (U8*)STRING(noper);
                const U8 *e= uc + STR_LEN(noper);

                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(
            Perl_re_indentf( aTHX_  "Alloc: %d Orig: %" IVdf " elements, Final:%" IVdf ". Savings of %%%5.2f\n",
                depth+1,
                (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(
            Perl_re_indentf( aTHX_  "Statecount:%" UVxf " Lasttrans:%" UVxf "\n",
                depth+1,
                (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(
            Perl_re_indentf( aTHX_  "MJD offset:%" UVuf " MJD length:%" UVuf "\n",
                depth+1,
                (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  ) {
            /* we want to find the first state that has more than
             * one transition, if that state is not the first state
             * then we have a common prefix which we can remove.
             */
            U32 state;
            for ( state = 1 ; state < trie->statecount-1 ; state++ ) {
                U32 ofs = 0;
                I32 first_ofs = -1; /* keeps track of the ofs of the first
                                       transition, -1 means none */
                U32 count = 0;
                const U32 base = trie->states[ state ].trans.base;

                /* does this state terminate an alternation? */
                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 ) {
                            /* we have more than one transition */
                            SV **tmp;
                            U8 *ch;
                            /* if this is the first state there is no common prefix
                             * to extract, so we can exit */
                            if ( state == 1 ) break;
                            tmp = av_fetch( revcharmap, ofs, 0);
                            ch = (U8*)SvPV_nolen_const( *tmp );

                            /* if we are on count 2 then we need to initialize the
                             * bitmap, and store the previous char if there was one
                             * in it*/
                            if ( count == 2 ) {
                                /* clear the bitmap */
                                Zero(trie->bitmap, ANYOF_BITMAP_SIZE, char);
                                DEBUG_OPTIMISE_r(
                                    Perl_re_indentf( aTHX_  "New Start State=%" UVuf " Class: [",
                                        depth+1,
                                        (UV)state));
                                if (first_ofs >= 0) {
                                    SV ** const tmp = av_fetch( revcharmap, first_ofs, 0);
                                    const U8 * const ch = (U8*)SvPV_nolen_const( *tmp );

                                    TRIE_BITMAP_SET_FOLDED(trie,*ch, folder);
                                    DEBUG_OPTIMISE_r(
                                        Perl_re_printf( aTHX_  "%s", (char*)ch)
                                    );
                                }
                            }
                            /* store the current firstchar in the bitmap */
                            TRIE_BITMAP_SET_FOLDED(trie,*ch, folder);
                            DEBUG_OPTIMISE_r(Perl_re_printf( aTHX_ "%s", ch));
                        }
                        first_ofs = ofs;
                    }
                }
                if ( count == 1 ) {
                    /* This state has only one transition, its transition is part
                     * of a common prefix - we need to concatenate the char it
                     * represents to what we have so far. */
                    SV **tmp = av_fetch( revcharmap, first_ofs, 0);
                    STRLEN len;
                    char *ch = SvPV( *tmp, len );
                    DEBUG_OPTIMISE_r({
                        SV *sv=sv_newmortal();
                        Perl_re_indentf( aTHX_  "Prefix State: %" UVuf " Ofs:%" UVuf " Char='%s'\n",
                            depth+1,
                            (UV)state, (UV)first_ofs,
                            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(Perl_re_printf( aTHX_ "]\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;
#ifdef RE_TRACK_PATTERN_OFFSETS
                   mjd_nodelen++;
#endif
                   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 ) {
                Track_Code( mjd_nodelen += Node_Length((optimize)); );
                OP( optimize ) = OPTIMIZED;
                Set_Node_Offset_Length(optimize, 0, 0);
                optimize++;
            }
            Set_Node_Offset_Length(convert, mjd_offset, mjd_nodelen);
        });
    } /* end node insert */

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

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


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

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

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

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

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

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

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

    ARG_SET( stclass, data_slot );
    aho = (reg_ac_data *) PerlMemShared_calloc( 1, sizeof(reg_ac_data) );
    RExC_rxi->data->data[ data_slot ] = (void*)aho;
    aho->trie=trie_offset;
    aho->states=(reg_trie_state *)PerlMemShared_malloc( numstates * sizeof(reg_trie_state) );
    Copy( trie->states, aho->states, numstates, reg_trie_state );
    Newx( 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({
        Perl_re_indentf( aTHX_  "Stclass Failtable (%" UVuf " states): 0",
                      depth, (UV)numstates
        );
        for( q_read=1; q_read<numstates; q_read++ ) {
            Perl_re_printf( aTHX_  ", %" UVuf, (UV)fail[q_read]);
        }
        Perl_re_printf( aTHX_  "\n");
    });
    Safefree(q);
    /*RExC_seen |= REG_TRIEDFA_SEEN;*/
    return stclass;
}


/* The below joins as many adjacent EXACTish nodes as possible into a single
 * one.  The regop may be changed if the node(s) contain certain sequences that
 * require special handling.  The joining is only done if:
 * 1) there is room in the current conglomerated node to entirely contain the
 *    next one.
 * 2) they are the exact same node type
 *
 * The adjacent nodes actually may be separated by NOTHING-kind nodes, and
 * these get optimized out
 *
 * XXX khw thinks this should be enhanced to fill EXACT (at least) nodes as full
 * as possible, even if that means splitting an existing node so that its first
 * part is moved to the preceeding node.  This would maximise the efficiency of
 * memEQ during matching.
 *
 * 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 it won't be known until
 * runtime whether the fold is valid or not; namely
 *  1) 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; or
 *  2) 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 EXACTFAA
 *      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 EXACTFAA
 *      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 EXACTFAA 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 EXACTFAA 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 EXACTFAA where it never does.  In an EXACTFAA 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 EXACTFAA nodes with the sharp s
 *      doesn't work.  Instead, such an EXACTFAA is turned into a new regnode,
 *      EXACTFAA_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, 0);

    /* 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, 0);
            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, 0);
            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, 0);
            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