PATCH: [perl #120041] regcomp.c missing parens and broken STCLASS

[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 const struct regexp_engine my_reg_engine;
#else
#  include "regcomp.h"
#endif

#include "dquote_static.c"
#include "charclass_invlists.h"
#include "inline_invlist.c"
#include "unicode_constants.h"

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

#ifndef STATIC
#define	STATIC	static
#endif


struct RExC_state_t {
    U32		flags;			/* RXf_* are we folding, multilining? */
    U32		pm_flags;		/* PMf_* stuff from the calling PMOP */
    char	*precomp;		/* uncompiled string. */
    REGEXP	*rx_sv;			/* The SV that is the regexp. */
    regexp	*rx;                    /* perl core regexp structure */
    regexp_internal	*rxi;           /* internal data for regexp object pprivate field */        
    char	*start;			/* Start of input for compile */
    char	*end;			/* End of input for compile */
    char	*parse;			/* Input-scan pointer. */
    SSize_t	whilem_seen;		/* number of WHILEM in this expr */
    regnode	*emit_start;		/* Start of emitted-code area */
    regnode	*emit_bound;		/* First regnode outside of the allocated space */
    regnode	*emit;			/* Code-emit pointer; if = &emit_dummy,
                                           implies compiling, so don't emit */
    regnode_ssc	emit_dummy;		/* placeholder for emit to point to;
                                           large enough for the largest
                                           non-EXACTish node, so can use it as
                                           scratch in pass1 */
    I32		naughty;		/* How bad is this pattern? */
    I32		sawback;		/* Did we see \1, ...? */
    U32		seen;
    SSize_t	size;			/* Code size. */
    I32		npar;			/* Capture buffer count, (OPEN). */
    I32		cpar;			/* Capture buffer count, (CLOSE). */
    I32		nestroot;		/* root parens we are in - used by accept */
    I32		extralen;
    I32		seen_zerolen;
    regnode	**open_parens;		/* pointers to open parens */
    regnode	**close_parens;		/* pointers to close parens */
    regnode	*opend;			/* END node in program */
    I32		utf8;		/* whether the pattern is utf8 or not */
    I32		orig_utf8;	/* whether the pattern was originally in utf8 */
				/* XXX use this for future optimisation of case
				 * where pattern must be upgraded to utf8. */
    I32		uni_semantics;	/* If a d charset modifier should use unicode
				   rules, even if the pattern is not in
				   utf8 */
    HV		*paren_names;		/* Paren names */
    
    regnode	**recurse;		/* Recurse regops */
    I32		recurse_count;		/* Number of recurse regops */
    I32		in_lookbehind;
    I32		contains_locale;
    I32		contains_i;
    I32		override_recoding;
    I32		in_multi_char_class;
    struct reg_code_block *code_blocks;	/* positions of literal (?{})
					    within pattern */
    int		num_code_blocks;	/* size of code_blocks[] */
    int		code_index;		/* next code_blocks[] slot */
#if ADD_TO_REGEXEC
    char 	*starttry;		/* -Dr: where regtry was called. */
#define RExC_starttry	(pRExC_state->starttry)
#endif
    SV		*runtime_code_qr;	/* qr with the runtime code blocks */
#ifdef DEBUGGING
    const char  *lastparse;
    I32         lastnum;
    AV          *paren_name_list;       /* idx -> name */
#define RExC_lastparse	(pRExC_state->lastparse)
#define RExC_lastnum	(pRExC_state->lastnum)
#define RExC_paren_name_list    (pRExC_state->paren_name_list)
#endif
};

#define RExC_flags	(pRExC_state->flags)
#define RExC_pm_flags	(pRExC_state->pm_flags)
#define RExC_precomp	(pRExC_state->precomp)
#define RExC_rx_sv	(pRExC_state->rx_sv)
#define RExC_rx		(pRExC_state->rx)
#define RExC_rxi	(pRExC_state->rxi)
#define RExC_start	(pRExC_state->start)
#define RExC_end	(pRExC_state->end)
#define RExC_parse	(pRExC_state->parse)
#define RExC_whilem_seen	(pRExC_state->whilem_seen)
#ifdef RE_TRACK_PATTERN_OFFSETS
#define RExC_offsets	(pRExC_state->rxi->u.offsets) /* I am not like the others */
#endif
#define RExC_emit	(pRExC_state->emit)
#define RExC_emit_dummy	(pRExC_state->emit_dummy)
#define RExC_emit_start	(pRExC_state->emit_start)
#define RExC_emit_bound	(pRExC_state->emit_bound)
#define RExC_naughty	(pRExC_state->naughty)
#define RExC_sawback	(pRExC_state->sawback)
#define RExC_seen	(pRExC_state->seen)
#define RExC_size	(pRExC_state->size)
#define RExC_npar	(pRExC_state->npar)
#define RExC_nestroot   (pRExC_state->nestroot)
#define RExC_extralen	(pRExC_state->extralen)
#define RExC_seen_zerolen	(pRExC_state->seen_zerolen)
#define RExC_utf8	(pRExC_state->utf8)
#define RExC_uni_semantics	(pRExC_state->uni_semantics)
#define RExC_orig_utf8	(pRExC_state->orig_utf8)
#define RExC_open_parens	(pRExC_state->open_parens)
#define RExC_close_parens	(pRExC_state->close_parens)
#define RExC_opend	(pRExC_state->opend)
#define RExC_paren_names	(pRExC_state->paren_names)
#define RExC_recurse	(pRExC_state->recurse)
#define RExC_recurse_count	(pRExC_state->recurse_count)
#define RExC_in_lookbehind	(pRExC_state->in_lookbehind)
#define RExC_contains_locale	(pRExC_state->contains_locale)
#define RExC_contains_i (pRExC_state->contains_i)
#define RExC_override_recoding (pRExC_state->override_recoding)
#define RExC_in_multi_char_class (pRExC_state->in_multi_char_class)


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

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

/* Simple enough to be STAR/PLUS operand; in an EXACTish node must be a single
 * character.  (There needs to be a case: in the switch statement in regexec.c
 * for any node marked SIMPLE.)  Note that this is not the same thing as
 * REGNODE_SIMPLE */
#define	SIMPLE		0x02
#define	SPSTART		0x04	/* Starts with * or + */
#define POSTPONED	0x08    /* (?1),(?&name), (??{...}) or similar */
#define TRYAGAIN	0x10	/* Weeded out a declaration. */
#define RESTART_UTF8    0x20    /* Restart, need to calcuate sizes as UTF-8 */

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

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



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

#define REQUIRE_UTF8	STMT_START {                                       \
                                     if (!UTF) {                           \
                                         *flagp = RESTART_UTF8;            \
                                         return NULL;                      \
                                     }                                     \
                        } STMT_END

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

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

/* About scan_data_t.

  During optimisation we recurse through the regexp program performing
  various inplace (keyhole style) optimisations. In addition study_chunk
  and scan_commit populate this data structure with information about
  what strings MUST appear in the pattern. We look for the longest 
  string that must appear at a fixed location, and we look for the
  longest string that may appear at a floating location. So for instance
  in the pattern:
  
    /FOO[xX]A.*B[xX]BAR/
    
  Both 'FOO' and 'A' are fixed strings. Both 'B' and 'BAR' are floating
  strings (because they follow a .* construct). study_chunk will identify
  both FOO and BAR as being the longest fixed and floating strings respectively.
  
  The strings can be composites, for instance
  
     /(f)(o)(o)/
     
  will result in a composite fixed substring 'foo'.
  
  For each string some basic information is maintained:
  
  - offset or min_offset
    This is the position the string must appear at, or not before.
    It also implicitly (when combined with minlenp) tells us how many
    characters must match before the string we are searching for.
    Likewise when combined with minlenp and the length of the string it
    tells us how many characters must appear after the string we have 
    found.
  
  - max_offset
    Only used for floating strings. This is the rightmost point that
    the string can appear at. If set to SSize_t_MAX it indicates that the
    string can occur infinitely far to the right.
  
  - minlenp
    A pointer to the minimum number of characters of the pattern that the
    string was found inside. This is important as in the case of positive
    lookahead or positive lookbehind we can have multiple patterns 
    involved. Consider
    
    /(?=FOO).*F/
    
    The minimum length of the pattern overall is 3, the minimum length
    of the lookahead part is 3, but the minimum length of the part that
    will actually match is 1. So 'FOO's minimum length is 3, but the 
    minimum length for the F is 1. This is important as the minimum length
    is used to determine offsets in front of and behind the string being 
    looked for.  Since strings can be composites this is the length of the
    pattern at the time it was committed with a scan_commit. Note that
    the length is calculated by study_chunk, so that the minimum lengths
    are not known until the full pattern has been compiled, thus the 
    pointer to the value.
  
  - lookbehind
  
    In the case of lookbehind the string being searched for can be
    offset past the start point of the final matching string. 
    If this value was just blithely removed from the min_offset it would
    invalidate some of the calculations for how many chars must match
    before or after (as they are derived from min_offset and minlen and
    the length of the string being searched for). 
    When the final pattern is compiled and the data is moved from the
    scan_data_t structure into the regexp structure the information
    about lookbehind is factored in, with the information that would 
    have been lost precalculated in the end_shift field for the 
    associated string.

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

*/

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

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

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

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

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

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

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

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

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

#define UTF cBOOL(RExC_utf8)

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

#define FOLD cBOOL(RExC_flags & RXf_PMf_FOLD)

#define OOB_NAMEDCLASS		-1

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

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


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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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


/* Allow for side effects in s */
#define REGC(c,s) STMT_START {			\
    if (!SIZE_ONLY) *(s) = (c); else (void)(s);	\
} STMT_END

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

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

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

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

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

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

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

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

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

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

    PERL_ARGS_ASSERT_SCAN_COMMIT;

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

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

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

    PERL_ARGS_ASSERT_SSC_ANYTHING;

    assert(OP(ssc) == ANYOF_SYNTHETIC);

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

STATIC int
S_ssc_is_anything(pTHX_ const regnode_ssc *ssc)
{
    /* Returns TRUE if the SSC 'ssc' can match the empty string or any code
     * point */

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_ANYTHING;

    assert(OP(ssc) == ANYOF_SYNTHETIC);

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

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

    invlist_iterfinish(ssc->invlist);

    if (ret) {
        return TRUE;
    }

    /* If e.g., both \w and \W are set, matches everything */
    if (ANYOF_FLAGS(ssc) & ANYOF_POSIXL) {
        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);
    OP(ssc) = ANYOF_SYNTHETIC;
    ARG_SET(ssc, ANYOF_NONBITMAP_EMPTY);
    ssc_anything(ssc);

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

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

    UV start, end;
    bool ret;

    PERL_ARGS_ASSERT_SSC_IS_CP_POSIXL_INIT;

    assert(OP(ssc) == ANYOF_SYNTHETIC);

    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) {
        if (! (ANYOF_FLAGS(ssc) & ANYOF_LOCALE)
            || ! (ANYOF_FLAGS(ssc) & ANYOF_POSIXL)
            || ! ANYOF_POSIXL_TEST_ALL_SET(ssc))
        {
            return FALSE;
        }
        if (RExC_contains_i && ! (ANYOF_FLAGS(ssc) & ANYOF_LOC_FOLD)) {
            return FALSE;
        }
    }

    return TRUE;
}

STATIC SV*
S_get_ANYOF_cp_list_for_ssc(pTHX_ const RExC_state_t *pRExC_state,
                                  const regnode_charclass_posixl* 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 possible code point. */

    SV* invlist = sv_2mortal(_new_invlist(0));
    unsigned int i;
    const U32 n = ARG(node);

    PERL_ARGS_ASSERT_GET_ANYOF_CP_LIST_FOR_SSC;

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

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

            /* Here, no compile-time swash, and there are things that won't be
             * known until runtime -- we have to assume it could be anything */
            return _add_range_to_invlist(invlist, 0, UV_MAX);
        }
        else {

            /* Here no compile-time swash, and no run-time only data.  Use the
             * node's inversion list */
            invlist = sv_2mortal(invlist_clone(ary[2]));
        }
    }

    /* An ANYOF node contains a bitmap for the first 256 code points, and an
     * inversion list for the others, but if there are code points that should
     * match only conditionally on the target string being UTF-8, those are
     * placed in the inversion list, and not the bitmap.  Since there are
     * circumstances under which they could match, they are included in the
     * SSC.  But if the ANYOF node is to be inverted, we have to exclude them
     * here, so that when we invert below, the end result actually does include
     * them.  (Think about "\xe0" =~ /[^\xc0]/di;).  We have to do this here
     * before we add the unconditionally matched code points */
    if (ANYOF_FLAGS(node) & ANYOF_INVERT) {
        _invlist_intersection_complement_2nd(invlist,
                                             PL_UpperLatin1,
                                             &invlist);
    }

    /* Add in the points from the bit map */
    for (i = 0; i < 256; i++) {
        if (ANYOF_BITMAP_TEST(node, i)) {
            invlist = add_cp_to_invlist(invlist, i);
        }
    }

    /* If this can match all upper Latin1 code points, have to add them
     * as well */
    if (ANYOF_FLAGS(node) & ANYOF_NON_UTF8_LATIN1_ALL) {
        _invlist_union(invlist, PL_UpperLatin1, &invlist);
    }

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

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

    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)

STATIC void
S_ssc_flags_and(regnode_ssc *ssc, const U8 and_with)
{
    /* Take the flags 'and_with' and accumulate them anded into the flags for
     * the SSC 'ssc'.  The non-SSC related flags in 'and_with' are ignored.
     * The flags 'and_with' should not come from another SSC (otherwise the
     * EMPTY_STRING flag won't work) */

    const U8 ssc_only_flags = ANYOF_FLAGS(ssc) & ~ANYOF_LOCALE_FLAGS;

    PERL_ARGS_ASSERT_SSC_FLAGS_AND;

    /* Use just the SSC-related flags from 'and_with' */
    ANYOF_FLAGS(ssc) &= (and_with & ANYOF_LOCALE_FLAGS);
    ANYOF_FLAGS(ssc) |= ssc_only_flags;
}

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

STATIC void
S_ssc_and(pTHX_ const RExC_state_t *pRExC_state, regnode_ssc *ssc,
                const regnode_ssc *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(OP(ssc) == ANYOF_SYNTHETIC);

    /* '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 (OP(and_with) == ANYOF_SYNTHETIC) {
        anded_cp_list = and_with->invlist;
        anded_flags = ANYOF_FLAGS(and_with);
    }
    else {
        anded_cp_list = get_ANYOF_cp_list_for_ssc(pRExC_state,
                                        (regnode_charclass_posixl*) and_with);
        anded_flags = ANYOF_FLAGS(and_with) & ANYOF_LOCALE_FLAGS;
    }

    ANYOF_FLAGS(ssc) &= anded_flags;

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

    if ((ANYOF_FLAGS(and_with) & ANYOF_INVERT)
        && OP(and_with) != ANYOF_SYNTHETIC)
    {
        unsigned int i;

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

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

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

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

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

                if (ANYOF_POSIXL_TEST(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 (OP(and_with) != ANYOF_SYNTHETIC
             || ! ssc_is_cp_posixl_init(pRExC_state, 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 (OP(and_with) == ANYOF_SYNTHETIC) {
                StructCopy(and_with, ssc, regnode_ssc);
            }
            else {
                ssc->invlist = anded_cp_list;
                ANYOF_POSIXL_ZERO(ssc);
                if (ANYOF_FLAGS(and_with) & ANYOF_POSIXL) {
                    ANYOF_POSIXL_OR(and_with, ssc);
                }
            }
        }
        else if ((ANYOF_FLAGS(ssc) & ANYOF_POSIXL)
                    || (ANYOF_FLAGS(and_with) & ANYOF_POSIXL))
        {
            /* One or the other of P1, P2 is non-empty. */
            ANYOF_POSIXL_AND(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_ssc *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(OP(ssc) == ANYOF_SYNTHETIC);

    /* '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 (OP(or_with) == ANYOF_SYNTHETIC) {
        ored_cp_list = or_with->invlist;
        ored_flags = ANYOF_FLAGS(or_with);
    }
    else {
        ored_cp_list = get_ANYOF_cp_list_for_ssc(pRExC_state,
                                        (regnode_charclass_posixl*) or_with);
        ored_flags = ANYOF_FLAGS(or_with) & ANYOF_LOCALE_FLAGS;
    }

    ANYOF_FLAGS(ssc) |= ored_flags;

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

    if ((ANYOF_FLAGS(or_with) & ANYOF_INVERT)
        && OP(or_with) != ANYOF_SYNTHETIC)
    {
        /* We ignore P2, leaving P1 going forward */
    }
    else {  /* Not inverted */
        ANYOF_POSIXL_OR(or_with, ssc);
        if (ANYOF_POSIXL_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);
                    if (! ANYOF_POSIXL_TEST_ANY_SET(ssc)) {
                        ANYOF_FLAGS(ssc) &= ~ANYOF_POSIXL;
                    }
                }
            }
        }
    }

    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(OP(ssc) == ANYOF_SYNTHETIC);

    _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(OP(ssc) == ANYOF_SYNTHETIC);

    _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(OP(ssc) == ANYOF_SYNTHETIC);

    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(OP(ssc) == ANYOF_SYNTHETIC);

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

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

    PERL_ARGS_ASSERT_SSC_CLEAR_LOCALE;

    assert(OP(ssc) == ANYOF_SYNTHETIC);

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

STATIC void
S_ssc_finalize(pTHX_ RExC_state_t *pRExC_state, regnode_ssc *ssc)
{
    /* The inversion list in the SSC is marked mortal; now we need a more
     * permanent copy, which is stored the same way that is done in a regular
     * ANYOF node, with the first 256 code points in a bit map */

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

    PERL_ARGS_ASSERT_SSC_FINALIZE;

    assert(OP(ssc) == ANYOF_SYNTHETIC);

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

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

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

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

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


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

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

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

*/

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

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

    PERL_ARGS_ASSERT_DUMP_TRIE;

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

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

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

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

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

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

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

        if ( base ) {
            U32 ofs = 0;

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

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

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

            PerlIO_printf( Perl_debug_log, "]");

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

    PERL_ARGS_ASSERT_DUMP_TRIE_INTERIM_LIST;

    /* print out the table precompression.  */
    PerlIO_printf( Perl_debug_log, "%*sState :Word | Transition Data\n%*s%s",
        (int)depth * 2 + 2,"", (int)depth * 2 + 2,"",
        "------:-----+-----------------\n" );
    
    for( state=1 ; state < next_alloc ; state ++ ) {
        U16 charid;
    
        PerlIO_printf( Perl_debug_log, "%*s %4"UVXf" :",
            (int)depth * 2 + 2,"", (UV)state  );
        if ( ! trie->states[ state ].wordnum ) {
            PerlIO_printf( Perl_debug_log, "%5s| ","");
        } else {
            PerlIO_printf( Perl_debug_log, "W%4x| ",
                trie->states[ state ].wordnum
            );
        }
        for( charid = 1 ; charid <= TRIE_LIST_USED( state ) ; charid++ ) {
	    SV ** const tmp = av_fetch( revcharmap, TRIE_LIST_ITEM(state,charid).forid, 0);
	    if ( tmp ) {
                PerlIO_printf( Perl_debug_log, "%*s:%3X=%4"UVXf" | ",
                    colwidth,
                    pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth, 
	                    PL_colors[0], PL_colors[1],
	                    (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
	                    PERL_PV_ESCAPE_FIRSTCHAR 
                    ) ,
                    TRIE_LIST_ITEM(state,charid).forid,
                    (UV)TRIE_LIST_ITEM(state,charid).newstate
                );
                if (!(charid % 10)) 
                    PerlIO_printf(Perl_debug_log, "\n%*s| ",
                        (int)((depth * 2) + 14), "");
            }
        }
        PerlIO_printf( Perl_debug_log, "\n");
    }
}    

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

    PERL_ARGS_ASSERT_DUMP_TRIE_INTERIM_TABLE;
    
    /*
       print out the table precompression so that we can do a visual check
       that they are identical.
     */
    
    PerlIO_printf( Perl_debug_log, "%*sChar : ",(int)depth * 2 + 2,"" );

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

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

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

    PerlIO_printf( Perl_debug_log, "\n" );

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

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

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

#endif


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

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

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

  /he|she|his|hers/

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

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

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

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

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

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

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

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

which prints out 'word' three times, but

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

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

Example of what happens on a structural level:

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

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

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

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

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

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

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

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

    d = uvchr_to_utf8_flags(d, uv, 0);

is the recommended Unicode-aware way of saying

    *(d++) = uv;
*/

#define TRIE_STORE_REVCHAR(val)                                            \
    STMT_START {                                                           \
	if (UTF) {							   \
            SV *zlopp = newSV(7); /* XXX: optimize me */                   \
	    unsigned char *flrbbbbb = (unsigned char *) SvPVX(zlopp);	   \
            unsigned const char *const kapow = uvchr_to_utf8(flrbbbbb, val); \
	    SvCUR_set(zlopp, kapow - flrbbbbb);				   \
	    SvPOK_on(zlopp);						   \
	    SvUTF8_on(zlopp);						   \
	    av_push(revcharmap, zlopp);					   \
	} else {							   \
            char ooooff = (char)val;                                           \
	    av_push(revcharmap, newSVpvn(&ooooff, 1));			   \
	}								   \
        } STMT_END

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



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

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

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


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

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

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

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

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

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

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

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

    re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
    if (!SvIOK(re_trie_maxbuff)) {
        sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
    }
    DEBUG_TRIE_COMPILE_r({
                PerlIO_printf( Perl_debug_log,
                  "%*smake_trie start==%d, first==%d, last==%d, tail==%d depth=%d\n",
                  (int)depth * 2 + 2, "", 
                  REG_NODE_NUM(startbranch),REG_NODE_NUM(first), 
                  REG_NODE_NUM(last), REG_NODE_NUM(tail),
                  (int)depth);
    });
   
   /* Find the node we are going to overwrite */
    if ( first == startbranch && OP( last ) != BRANCH ) {
        /* whole branch chain */
        convert = first;
    } else {
        /* branch sub-chain */
        convert = NEXTOPER( first );
    }
        
    /*  -- First loop and Setup --

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

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

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

     */

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

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

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

            /* Acummulate to the current values, the range in the number of
             * bytes that this character could match.  The max is presumed to
             * be the same as the folded input (which TRIE_READ_CHAR returns),
             * except that when this is not in UTF-8, it could be matched
             * against a string which is UTF-8, and the variant characters
             * could be 2 bytes instead of the 1 here.  Likewise, for the
             * minimum number of bytes when not folded.  When folding, the min
             * is assumed to be 1 byte could fold to match the single character
             * here, or in the case of a multi-char fold, 1 byte can fold to
             * the whole sequence.  'foldlen' is used to denote whether we are
             * in such a sequence, skipping the min setting if so.  XXX TODO
             * Use the exact list of what folds to each character, from
             * PL_utf8_foldclosures */
            if (UTF) {
                maxbytes += UTF8SKIP(uc);
                if (! folder) {
                    /* A non-UTF-8 string could be 1 byte to match our 2 */
                    minbytes += (UTF8_IS_DOWNGRADEABLE_START(*uc))
                                ? 1
                                : UTF8SKIP(uc);
                }
                else {
                    if (foldlen) {
                        foldlen -= UTF8SKIP(uc);
                    }
                    else {
                        foldlen = is_MULTI_CHAR_FOLD_utf8_safe(uc, e);
                        minbytes++;
                    }
                }
            }
            else {
                maxbytes += (UNI_IS_INVARIANT(*uc))
                             ? 1
                             : 2;
                if (! folder) {
                    minbytes++;
                }
                else {
                    if (foldlen) {
                        foldlen--;
                    }
                    else {
                        foldlen = is_MULTI_CHAR_FOLD_latin1_safe(uc, e);
                        minbytes++;
                    }
                }
            }
            if ( uvc < 256 ) {
                if ( folder ) {
                    U8 folded= folder[ (U8) uvc ];
                    if ( !trie->charmap[ folded ] ) {
                        trie->charmap[ folded ]=( ++trie->uniquecharcount );
                        TRIE_STORE_REVCHAR( folded );
                    }
                }
                if ( !trie->charmap[ uvc ] ) {
                    trie->charmap[ uvc ]=( ++trie->uniquecharcount );
                    TRIE_STORE_REVCHAR( uvc );
                }
                if ( set_bit ) {
		    /* store the codepoint in the bitmap, and its folded
		     * equivalent. */
                    TRIE_BITMAP_SET(trie, uvc);

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

		    if ( !UTF ) {
			/* store first byte of utf8 representation of
			   variant codepoints */
			if (! UVCHR_IS_INVARIANT(uvc)) {
			    TRIE_BITMAP_SET(trie, UTF8_TWO_BYTE_HI(uvc));
			}
		    }
                    set_bit = 0; /* We've done our bit :-) */
                }
            } else {
                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);
                }
            }
        }
        if( cur == first ) {
            trie->minlen = minbytes;
            trie->maxlen = maxbytes;
        } else if (minbytes < trie->minlen) {
            trie->minlen = minbytes;
        } else if (maxbytes > trie->maxlen) {
            trie->maxlen = maxbytes;
        }
    } /* end first pass */
    DEBUG_TRIE_COMPILE_r(
        PerlIO_printf( Perl_debug_log, "%*sTRIE(%s): W:%d C:%d Uq:%d Min:%d Max:%d\n",
                (int)depth * 2 + 2,"",
                ( widecharmap ? "UTF8" : "NATIVE" ), (int)word_count,
		(int)TRIE_CHARCOUNT(trie), trie->uniquecharcount,
		(int)trie->minlen, (int)trie->maxlen )
    );

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

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

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

    */


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

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

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

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

        STRLEN transcount = 1;

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

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

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

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

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

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

                    TRIE_READ_CHAR;

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

                        U16 check;
                        U32 newstate = 0;

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

        } /* end second pass */

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

            U32 state        = 1;         /* required init */

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

            U32 wordlen      = 0;         /* required init */

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

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

                    TRIE_READ_CHAR;

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

        } /* end second pass */

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

        {
        /*
           * Inplace compress the table.*

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                                    TRIE_BITMAP_SET(trie,*ch);
                                    if ( folder )
                                        TRIE_BITMAP_SET(trie, folder[ *ch ]);
                                    DEBUG_OPTIMISE_r(
                                        PerlIO_printf(Perl_debug_log, "%s", (char*)ch)
                                    );
				}
			    }
			    TRIE_BITMAP_SET(trie,*ch);
			    if ( folder )
				TRIE_BITMAP_SET(trie,folder[ *ch ]);
			    DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"%s", ch));
			}
                        idx = ofs;
		    }
                }
                if ( count == 1 ) {
                    SV **tmp = av_fetch( revcharmap, idx, 0);
                    STRLEN len;
                    char *ch = SvPV( *tmp, len );
                    DEBUG_OPTIMISE_r({
                        SV *sv=sv_newmortal();
                        PerlIO_printf( Perl_debug_log,
			    "%*sPrefix State: %"UVuf" Idx:%"UVuf" Char='%s'\n",
                            (int)depth * 2 + 2, "",
                            (UV)state, (UV)idx, 
                            pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), 6, 
	                        PL_colors[0], PL_colors[1],
	                        (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
	                        PERL_PV_ESCAPE_FIRSTCHAR 
                            )
                        );
                    });
                    if ( state==1 ) {
                        OP( convert ) = nodetype;
                        str=STRING(convert);
                        STR_LEN(convert)=0;
                    }
                    STR_LEN(convert) += len;
                    while (len--)
                        *str++ = *ch++;
		} else {
#ifdef DEBUGGING	    
		    if (state>1)
			DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"]\n"));
#endif
		    break;
		}
	    }
	    trie->prefixlen = (state-1);
            if (str) {
                regnode *n = convert+NODE_SZ_STR(convert);
                NEXT_OFF(convert) = NODE_SZ_STR(convert);
                trie->startstate = state;
                trie->minlen -= (state - 1);
                trie->maxlen -= (state - 1);
#ifdef DEBUGGING
               /* At least the UNICOS C compiler choked on this
                * being argument to DEBUG_r(), so let's just have
                * it right here. */
               if (
#ifdef PERL_EXT_RE_BUILD
                   1
#else
                   DEBUG_r_TEST
#endif
                   ) {
                   regnode *fix = convert;
                   U32 word = trie->wordcount;
                   mjd_nodelen++;
                   Set_Node_Offset_Length(convert, mjd_offset, state - 1);
                   while( ++fix < n ) {
                       Set_Node_Offset_Length(fix, 0, 0);
                   }
                   while (word--) {
                       SV ** const tmp = av_fetch( trie_words, word, 0 );
                       if (tmp) {
                           if ( STR_LEN(convert) <= SvCUR(*tmp) )
                               sv_chop(*tmp, SvPV_nolen(*tmp) + STR_LEN(convert));
                           else
                               sv_chop(*tmp, SvPV_nolen(*tmp) + SvCUR(*tmp));
                       }
                   }
               }
#endif
                if (trie->maxlen) {
                    convert = n;
		} else {
                    NEXT_OFF(convert) = (U16)(tail - convert);
                    DEBUG_r(optimize= n);
                }
            }
        }
        if (!jumper) 
            jumper = last; 
        if ( trie->maxlen ) {
	    NEXT_OFF( convert ) = (U16)(tail - convert);
	    ARG_SET( convert, data_slot );
	    /* Store the offset to the first unabsorbed branch in 
	       jump[0], which is otherwise unused by the jump logic. 
	       We use this when dumping a trie and during optimisation. */
	    if (trie->jump) 
	        trie->jump[0] = (U16)(nextbranch - convert);
            
            /* If the start state is not accepting (meaning there is no empty string/NOTHING)
	     *   and there is a bitmap
	     *   and the first "jump target" node we found leaves enough room
	     * then convert the TRIE node into a TRIEC node, with the bitmap
	     * embedded inline in the opcode - this is hypothetically faster.
	     */
            if ( !trie->states[trie->startstate].wordnum
		 && trie->bitmap
		 && ( (char *)jumper - (char *)convert) >= (int)sizeof(struct regnode_charclass) )
            {
                OP( convert ) = TRIEC;
                Copy(trie->bitmap, ((struct regnode_charclass *)convert)->bitmap, ANYOF_BITMAP_SIZE, char);
                PerlMemShared_free(trie->bitmap);
                trie->bitmap= NULL;
            } else 
                OP( convert ) = TRIE;

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

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

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

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


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

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

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

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

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

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


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

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

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

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


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


/* The below joins as many adjacent EXACTish nodes as possible into a single
 * one.  The regop may be changed if the node(s) contain certain sequences that
 * require special handling.  The joining is only done if:
 * 1) there is room in the current conglomerated node to entirely contain the
 *    next one.
 * 2) they are the exact same node type
 *
 * The adjacent nodes actually may be separated by NOTHING-kind nodes, and
 * these get optimized out
 *
 * If a node is to match under /i (folded), the number of characters it matches
 * can be different than its character length if it contains a multi-character
 * fold.  *min_subtract is set to the total delta of the input nodes.
 *
 * And *has_exactf_sharp_s is set to indicate whether or not the node is EXACTF
 * and contains LATIN SMALL LETTER SHARP S
 *
 * 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 work, as evidenced by this example:
 *      "\xDFs" =~ /s\xDF/ui    # Used to fail before these patches
 * Both these 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".
 *
 * 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 fold sequences.  It returns in *min_subtract how much 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 folds.  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.  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 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 the sharp s in EXACTF and EXACTFA nodes when the
 *      pattern isn't in UTF-8. (BTW, there cannot be an EXACTF node with a
 *      UTF-8 pattern.)  An assumption that the optimizer part of regexec.c
 *      (probably unwittingly, in Perl_regexec_flags()) makes is 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 nodes can match the
 *      two character string 'ss'; in EXACTFA nodes it can match
 *      "\x{17F}\x{17F}".  These 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 (when the pattern
 *      isn't UTF-8) EXACTF and EXACTFA nodes for the sharp s, and returns a
 *      boolean indicating whether or not the node contains a sharp s.  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
 *      non-UTF8-pattern EXACTF and EXACTFA nodes that contain the sharp s.
 *      (The reason the assumption is wrong only in these two 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.  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.  It will match iff the target string is
 *      in UTF-8, unlike the EXACTFU nodes, where it always matches; and
 *      EXACTFA and EXACTFL where it never does.  In an EXACTFA node in a UTF-8
 *      pattern, sharp s is folded to "\x{17F}\x{17F}, avoiding the problem;
 *      but in a non-UTF8 pattern, folding it to that above-Latin1 string would
 *      require the pattern to be forced into UTF-8, the overhead of which we
 *      want to avoid.)
 *
 *      Similarly, the code that generates tries doesn't currently handle
 *      not-already-folded multi-char folds, and it looks like a pain to change
 *      that.  Therefore, trie generation of EXACTFA nodes with the sharp s
 *      doesn't work.  Instead, such an EXACTFA is turned into a new regnode,
 *      EXACTFA_NO_TRIE, which the trie code knows not to handle.  Most people
 *      using /iaa matching will be doing so almost entirely with ASCII
 *      strings, so this should rarely be encountered in practice */

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

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

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

    /* Look through the subsequent nodes in the chain.  Skip NOTHING, merge
     * EXACT ones that are mergeable to the current one. */
    while (n
           && (PL_regkind[OP(n)] == NOTHING
               || (stringok && OP(n) == OP(scan)))
           && NEXT_OFF(n)
           && NEXT_OFF(scan) + NEXT_OFF(n) < I16_MAX)
    {
        
        if (OP(n) == TAIL || n > next)
            stringok = 0;
        if (PL_regkind[OP(n)] == NOTHING) {
            DEBUG_PEEP("skip:",n,depth);
            NEXT_OFF(scan) += NEXT_OFF(n);
            next = n + NODE_STEP_REGNODE;
#ifdef DEBUGGING
            if (stringok)
                stop = n;
#endif
            n = regnext(n);
        }
        else if (stringok) {
            const unsigned int oldl = STR_LEN(scan);
            regnode * const nnext = regnext(n);

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

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

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

    *min_subtract = 0;
    *has_exactf_sharp_s = FALSE;

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

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

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

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

                    /* Count how many characters in it.  In the case of /l and
                     * /aa, no folds which contain ASCII code points are
                     * allowed, so check for those, and skip if found.  (In
                     * EXACTFL, no folds are allowed to any Latin1 code point,
                     * not just ASCII.  But there aren't any of these
                     * currently, nor ever likely, so don't take the time to
                     * test for them.  The code that generates the
                     * is_MULTI_foo() macros croaks should one actually get put
                     * into Unicode .) */
                    if (OP(scan) != EXACTFL
                        && OP(scan) != EXACTFA
                        && OP(scan) != EXACTFA_NO_TRIE)
                    {
                        count = utf8_length(s, multi_end);
                        s = multi_end;
                    }
                    else {
                        while (s < multi_end) {
                            if (isASCII(*s)) {
                                s++;
                                goto next_iteration;
                            }
                            else {
                                s += UTF8SKIP(s);
                            }
                            count++;
                        }
                    }
                }

                /* The delta is how long the sequence is minus 1 (1 is how long
                 * the character that folds to the sequence is) */
                *min_subtract += count - 1;
            next_iteration: ;
	    }
	}
	else if (OP(scan) == EXACTFA) {

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

            /* Non-UTF-8 pattern, not EXACTFA nor EXACTFL node.  Look for the
             * multi-char folds that are all Latin1.  (This code knows that
             * there are no current multi-char folds possible with EXACTFL,
             * relying on fold_grind.t to catch any errors if the very unlikely
             * event happens that some get added in future Unicode versions.)
             * As explained in the comments preceding this function, we look
             * also for the sharp s in EXACTF nodes; it can be in the final
             * position.  Otherwise we can stop looking 1 byte earlier because
             * have to find at least two characters for a multi-fold */
	    const U8* upper = (OP(scan) == EXACTF) ? s_end : s_end -1;

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

                if (len == 2
                    && isARG2_lower_or_UPPER_ARG1('s', *s)
                    && isARG2_lower_or_UPPER_ARG1('s', *(s+1)))
                {

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

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

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

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

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

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

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


#define SCAN_COMMIT(s, data, m) scan_commit(s, data, m, is_inf)

STATIC SSize_t
S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp,
                        SSize_t *minlenp, SSize_t *deltap,
			regnode *last,
			scan_data_t *data,
			I32 stopparen,
			U8* recursed,
			regnode_ssc *and_withp,
			U32 flags, U32 depth)
			/* scanp: Start here (read-write). */
			/* deltap: Write maxlen-minlen here. */
			/* last: Stop before this one. */
			/* data: string data about the pattern */
			/* stopparen: treat close N as END */
			/* recursed: which subroutines have we recursed into */
			/* and_withp: Valid if flags & SCF_DO_STCLASS_OR */
{
    dVAR;
    /* There must be at least this number of characters to match */
    SSize_t min = 0;
    I32 pars = 0, code;
    regnode *scan = *scanp, *next;
    SSize_t delta = 0;
    int is_inf = (flags & SCF_DO_SUBSTR) && (data->flags & SF_IS_INF);
    int is_inf_internal = 0;		/* The studied chunk is infinite */
    I32 is_par = OP(scan) == OPEN ? ARG(scan) : 0;
    scan_data_t data_fake;
    SV *re_trie_maxbuff = NULL;
    regnode *first_non_open = scan;
    SSize_t stopmin = SSize_t_MAX;
    scan_frame *frame = NULL;
    GET_RE_DEBUG_FLAGS_DECL;

    PERL_ARGS_ASSERT_STUDY_CHUNK;

#ifdef DEBUGGING
    StructCopy(&zero_scan_data, &data_fake, scan_data_t);
#endif

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


  fake_study_recurse:
    while ( scan && OP(scan) != END && scan < last ){
        UV min_subtract = 0;    /* How mmany chars to subtract from the minimum
                                   node length to get a real minimum (because
                                   the folded version may be shorter) */
	bool has_exactf_sharp_s = FALSE;
	/* Peephole optimizer: */
	DEBUG_STUDYDATA("Peep:", data,depth);
	DEBUG_PEEP("Peep",scan,depth);

        /* Its not clear to khw or hv why this is done here, and not in the
         * clauses that deal with EXACT nodes.  khw's guess is that it's
         * because of a previous design */
        JOIN_EXACT(scan,&min_subtract, &has_exactf_sharp_s, 0);

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

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



	/* The principal pseudo-switch.  Cannot be a switch, since we
	   look into several different things.  */
	if (OP(scan) == BRANCH || OP(scan) == BRANCHJ
		   || OP(scan) == IFTHEN) {
	    next = regnext(scan);
	    code = OP(scan);
	    /* demq: the op(next)==code check is to see if we have "branch-branch" AFAICT */

	    if (OP(next) == code || code == IFTHEN) {
                /* NOTE - There is similar code to this block below for
                 * handling TRIE nodes on a re-study.  If you change stuff here
                 * check there too. */
		SSize_t max1 = 0, min1 = SSize_t_MAX, num = 0;
		regnode_ssc accum;
		regnode * const startbranch=scan;

		if (flags & SCF_DO_SUBSTR)
		    SCAN_COMMIT(pRExC_state, data, minlenp); /* Cannot merge strings after this. */
		if (flags & SCF_DO_STCLASS)
		    ssc_init_zero(pRExC_state, &accum);

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

		    num++;
		    data_fake.flags = 0;
		    if (data) {
			data_fake.whilem_c = data->whilem_c;
			data_fake.last_closep = data->last_closep;
		    }
		    else
			data_fake.last_closep = &fake;

		    data_fake.pos_delta = delta;
		    next = regnext(scan);
		    scan = NEXTOPER(scan);
		    if (code != BRANCH)
			scan = NEXTOPER(scan);
		    if (flags & SCF_DO_STCLASS) {
			ssc_init(pRExC_state, &this_class);
			data_fake.start_class = &this_class;
			f = SCF_DO_STCLASS_AND;
		    }
		    if (flags & SCF_WHILEM_VISITED_POS)
			f |= SCF_WHILEM_VISITED_POS;

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

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

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

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

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

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

		   We have two cases

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

		     2. patterns where only a subset can be converted.

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

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

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

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

		*/

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

#ifdef DEBUGGING
                        SV * const mysv = sv_newmortal();       /* for dumping */
#endif
                        /* var tail is used because there may be a TAIL
                           regop in the way. Ie, the exacts will point to the
                           thing following the TAIL, but the last branch will
                           point at the TAIL. So we advance tail. If we
                           have nested (?:) we may have to move through several
                           tails.
                         */

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

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

                            Step through the branches
                                cur represents each branch,