Subject: [PATCH 2/2] sed: speed up matching by reguler expression with dfa matcher

From: Norihiro Tanaka <[email-masked]>
Date: Fri, 05 Aug 2016 23:03:26 +0900

Hi,

We can speeds up sed by using dfa matcher brought from grep.  gawk users
it, sed does not uses it yet.  It will speed up matching for typical
cases.

$ yes $(printf %040d 0) | head -1000000 >k

Before:

]$ time -p env LC_ALL=C sed/sed -ne /000000000k/p k
real 3.04
user 2.99
sys 0.03
$ time -p env LC_ALL=en_US.utf8 sed/sed -ne /000000000k/p k
real 3.04
user 2.90
sys 0.06
$ time -p env LC_ALL=ja_JP.eucjp sed/sed -ne /000000000k/p k
real 7.09
user 6.77
sys 0.31

After patching:

$ time -p env LC_ALL=C sed/sed -ne /000000000k/p k
real 0.29
user 0.15
sys 0.10
$ time -p env LC_ALL=en_US.utf8 sed/sed -ne /000000000k/p k
real 0.27
user 0.25
sys 0.02
$ time -p env LC_ALL=ja_JP.eucjp sed/sed -ne /000000000k/p k
real 0.33
user 0.29
sys 0.03

I believe that this patch can greatly improve performance of matching by
sed, however I worry about the maintenance as updates for dfa is always
done in grep.

Thanks,
Norihiro
From 8f6cef103e0ec05f00d09f514cb2cb1484f6fcdd Mon Sep 17 00:00:00 2001
From: Norihiro Tanaka <[email-masked]>
Date: Fri, 5 Aug 2016 08:50:32 +0900
Subject: [PATCH 2/2] sed: speed up matching by reguler expression with dfa matcher

Now sed uses dfa matcher for matching reguler expression, and it speeds
up 10x for typical case.

* sed/NEWS: Mention it.
* sed/local.mk (sed_sed_SOURCES): Add dfa.c.
(noinst_HEADERS): Add dfa.h.
* sed/regexp.c (dfaerror, dfawarn): New functions.
(compile_regex_1): Compile pattern with dfa.
(match_regex): Use dfa.
* sed/sed.h: Include dfa.h.
(struct regex): New member dfa.
* sed/dfa.c: New file derived from grep.
* sed/dfa.h: New file derived from grep.
---
 NEWS         |    2 +
 sed/dfa.c    | 4010 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 sed/dfa.h    |  103 ++
 sed/local.mk |    6 +-
 sed/regexp.c |   43 +
 sed/sed.h    |    2 +
 6 files changed, 4164 insertions(+), 2 deletions(-)
 create mode 100644 sed/dfa.c
 create mode 100644 sed/dfa.h

diff --git a/NEWS b/NEWS
index 6af8b9a..a86433b 100644
--- a/NEWS
+++ b/NEWS
@@ -76,6 +76,8 @@ GNU sed NEWS                                    -*- outline -*-
 
 ** Improvements
 
+  sed is now typicaly 10x fast for matching by regular expression.
+
   sed now uses unlocked-io where available, resulting in faster I/O
   operations.
 
diff --git a/sed/dfa.c b/sed/dfa.c
new file mode 100644
index 0000000..55d741c
--- /dev/null
+++ b/sed/dfa.c
@@ -0,0 +1,4010 @@
+/* dfa.c - deterministic extended regexp routines for GNU
+   Copyright (C) 1988, 1998, 2000, 2002, 2004-2005, 2007-2016 Free Software
+   Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc.,
+   51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA */
+
+/* Written June, 1988 by Mike Haertel
+   Modified July, 1988 by Arthur David Olson to assist BMG speedups  */
+
+#include <config.h>
+
+#include "dfa.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+#include <locale.h>
+
+#define STREQ(a, b) (strcmp (a, b) == 0)
+
+/* ISASCIIDIGIT differs from isdigit, as follows:
+   - Its arg may be any int or unsigned int; it need not be an unsigned char.
+   - It's guaranteed to evaluate its argument exactly once.
+   - It's typically faster.
+   Posix 1003.2-1992 section 2.5.2.1 page 50 lines 1556-1558 says that
+   only '0' through '9' are digits.  Prefer ISASCIIDIGIT to isdigit unless
+   it's important to use the locale's definition of "digit" even when the
+   host does not conform to Posix.  */
+#define ISASCIIDIGIT(c) ((unsigned) (c) - '0' <= 9)
+
+#include "gettext.h"
+#define _(str) gettext (str)
+
+#include <wchar.h>
+#include <wctype.h>
+
+/* HPUX defines these as macros in sys/param.h.  */
+#ifdef setbit
+# undef setbit
+#endif
+#ifdef clrbit
+# undef clrbit
+#endif
+
+/* First integer value that is greater than any character code.  */
+enum { NOTCHAR = 1 << CHAR_BIT };
+
+/* This represents part of a character class.  It must be unsigned and
+   at least CHARCLASS_WORD_BITS wide.  Any excess bits are zero.  */
+typedef unsigned int charclass_word;
+
+/* The number of bits used in a charclass word.  utf8_classes assumes
+   this is exactly 32.  */
+enum { CHARCLASS_WORD_BITS = 32 };
+
+/* The maximum useful value of a charclass_word; all used bits are 1.  */
+#define CHARCLASS_WORD_MASK \
+  (((charclass_word) 1 << (CHARCLASS_WORD_BITS - 1) << 1) - 1)
+
+/* Number of words required to hold a bit for every character.  */
+enum
+{
+  CHARCLASS_WORDS = (NOTCHAR + CHARCLASS_WORD_BITS - 1) / CHARCLASS_WORD_BITS
+};
+
+/* Sets of unsigned characters are stored as bit vectors in arrays of ints.  */
+typedef charclass_word charclass[CHARCLASS_WORDS];
+
+/* Convert a possibly-signed character to an unsigned character.  This is
+   a bit safer than casting to unsigned char, since it catches some type
+   errors that the cast doesn't.  */
+static unsigned char
+to_uchar (char ch)
+{
+  return ch;
+}
+
+/* Contexts tell us whether a character is a newline or a word constituent.
+   Word-constituent characters are those that satisfy iswalnum, plus '_'.
+   Each character has a single CTX_* value; bitmasks of CTX_* values denote
+   a particular character class.
+
+   A state also stores a context value, which is a bitmask of CTX_* values.
+   A state's context represents a set of characters that the state's
+   predecessors must match.  For example, a state whose context does not
+   include CTX_LETTER will never have transitions where the previous
+   character is a word constituent.  A state whose context is CTX_ANY
+   might have transitions from any character.  */
+
+#define CTX_NONE	1
+#define CTX_LETTER	2
+#define CTX_NEWLINE	4
+#define CTX_ANY		7
+
+/* Sometimes characters can only be matched depending on the surrounding
+   context.  Such context decisions depend on what the previous character
+   was, and the value of the current (lookahead) character.  Context
+   dependent constraints are encoded as 8 bit integers.  Each bit that
+   is set indicates that the constraint succeeds in the corresponding
+   context.
+
+   bit 8-11 - valid contexts when next character is CTX_NEWLINE
+   bit 4-7  - valid contexts when next character is CTX_LETTER
+   bit 0-3  - valid contexts when next character is CTX_NONE
+
+   The macro SUCCEEDS_IN_CONTEXT determines whether a given constraint
+   succeeds in a particular context.  Prev is a bitmask of possible
+   context values for the previous character, curr is the (single-bit)
+   context value for the lookahead character.  */
+#define NEWLINE_CONSTRAINT(constraint) (((constraint) >> 8) & 0xf)
+#define LETTER_CONSTRAINT(constraint)  (((constraint) >> 4) & 0xf)
+#define OTHER_CONSTRAINT(constraint)    ((constraint)       & 0xf)
+
+#define SUCCEEDS_IN_CONTEXT(constraint, prev, curr) \
+  ((((curr) & CTX_NONE      ? OTHER_CONSTRAINT (constraint) : 0) \
+    | ((curr) & CTX_LETTER  ? LETTER_CONSTRAINT (constraint) : 0) \
+    | ((curr) & CTX_NEWLINE ? NEWLINE_CONSTRAINT (constraint) : 0)) & (prev))
+
+/* The following macros describe what a constraint depends on.  */
+#define PREV_NEWLINE_CONSTRAINT(constraint) (((constraint) >> 2) & 0x111)
+#define PREV_LETTER_CONSTRAINT(constraint)  (((constraint) >> 1) & 0x111)
+#define PREV_OTHER_CONSTRAINT(constraint)    ((constraint)       & 0x111)
+
+#define PREV_NEWLINE_DEPENDENT(constraint) \
+  (PREV_NEWLINE_CONSTRAINT (constraint) != PREV_OTHER_CONSTRAINT (constraint))
+#define PREV_LETTER_DEPENDENT(constraint) \
+  (PREV_LETTER_CONSTRAINT (constraint) != PREV_OTHER_CONSTRAINT (constraint))
+
+/* Tokens that match the empty string subject to some constraint actually
+   work by applying that constraint to determine what may follow them,
+   taking into account what has gone before.  The following values are
+   the constraints corresponding to the special tokens previously defined.  */
+#define NO_CONSTRAINT         0x777
+#define BEGLINE_CONSTRAINT    0x444
+#define ENDLINE_CONSTRAINT    0x700
+#define BEGWORD_CONSTRAINT    0x050
+#define ENDWORD_CONSTRAINT    0x202
+#define LIMWORD_CONSTRAINT    0x252
+#define NOTLIMWORD_CONSTRAINT 0x525
+
+/* The regexp is parsed into an array of tokens in postfix form.  Some tokens
+   are operators and others are terminal symbols.  Most (but not all) of these
+   codes are returned by the lexical analyzer.  */
+
+typedef ptrdiff_t token;
+
+/* Predefined token values.  */
+enum
+{
+  END = -1,                     /* END is a terminal symbol that matches the
+                                   end of input; any value of END or less in
+                                   the parse tree is such a symbol.  Accepting
+                                   states of the DFA are those that would have
+                                   a transition on END.  */
+
+  /* Ordinary character values are terminal symbols that match themselves.  */
+
+  EMPTY = NOTCHAR,              /* EMPTY is a terminal symbol that matches
+                                   the empty string.  */
+
+  BACKREF,                      /* BACKREF is generated by \<digit>
+                                   or by any other construct that
+                                   is not completely handled.  If the scanner
+                                   detects a transition on backref, it returns
+                                   a kind of "semi-success" indicating that
+                                   the match will have to be verified with
+                                   a backtracking matcher.  */
+
+  BEGLINE,                      /* BEGLINE is a terminal symbol that matches
+                                   the empty string at the beginning of a
+                                   line.  */
+
+  ENDLINE,                      /* ENDLINE is a terminal symbol that matches
+                                   the empty string at the end of a line.  */
+
+  BEGWORD,                      /* BEGWORD is a terminal symbol that matches
+                                   the empty string at the beginning of a
+                                   word.  */
+
+  ENDWORD,                      /* ENDWORD is a terminal symbol that matches
+                                   the empty string at the end of a word.  */
+
+  LIMWORD,                      /* LIMWORD is a terminal symbol that matches
+                                   the empty string at the beginning or the
+                                   end of a word.  */
+
+  NOTLIMWORD,                   /* NOTLIMWORD is a terminal symbol that
+                                   matches the empty string not at
+                                   the beginning or end of a word.  */
+
+  QMARK,                        /* QMARK is an operator of one argument that
+                                   matches zero or one occurrences of its
+                                   argument.  */
+
+  STAR,                         /* STAR is an operator of one argument that
+                                   matches the Kleene closure (zero or more
+                                   occurrences) of its argument.  */
+
+  PLUS,                         /* PLUS is an operator of one argument that
+                                   matches the positive closure (one or more
+                                   occurrences) of its argument.  */
+
+  REPMN,                        /* REPMN is a lexical token corresponding
+                                   to the {m,n} construct.  REPMN never
+                                   appears in the compiled token vector.  */
+
+  CAT,                          /* CAT is an operator of two arguments that
+                                   matches the concatenation of its
+                                   arguments.  CAT is never returned by the
+                                   lexical analyzer.  */
+
+  OR,                           /* OR is an operator of two arguments that
+                                   matches either of its arguments.  */
+
+  LPAREN,                       /* LPAREN never appears in the parse tree,
+                                   it is only a lexeme.  */
+
+  RPAREN,                       /* RPAREN never appears in the parse tree.  */
+
+  ANYCHAR,                      /* ANYCHAR is a terminal symbol that matches
+                                   a valid multibyte (or single byte) character.
+                                   It is used only if MB_CUR_MAX > 1.  */
+
+  MBCSET,                       /* MBCSET is similar to CSET, but for
+                                   multibyte characters.  */
+
+  WCHAR,                        /* Only returned by lex.  wctok contains
+                                   the wide character representation.  */
+
+  CSET                          /* CSET and (and any value greater) is a
+                                   terminal symbol that matches any of a
+                                   class of characters.  */
+};
+
+
+/* States of the recognizer correspond to sets of positions in the parse
+   tree, together with the constraints under which they may be matched.
+   So a position is encoded as an index into the parse tree together with
+   a constraint.  */
+typedef struct
+{
+  size_t index;                 /* Index into the parse array.  */
+  unsigned int constraint;      /* Constraint for matching this position.  */
+} position;
+
+/* Sets of positions are stored as arrays.  */
+typedef struct
+{
+  position *elems;              /* Elements of this position set.  */
+  size_t nelem;                 /* Number of elements in this set.  */
+  size_t alloc;                 /* Number of elements allocated in ELEMS.  */
+} position_set;
+
+/* Sets of leaves are also stored as arrays.  */
+typedef struct
+{
+  size_t *elems;                /* Elements of this position set.  */
+  size_t nelem;                 /* Number of elements in this set.  */
+} leaf_set;
+
+/* A state of the dfa consists of a set of positions, some flags,
+   and the token value of the lowest-numbered position of the state that
+   contains an END token.  */
+typedef struct
+{
+  size_t hash;                  /* Hash of the positions of this state.  */
+  position_set elems;           /* Positions this state could match.  */
+  unsigned char context;        /* Context from previous state.  */
+  unsigned short constraint;    /* Constraint for this state to accept.  */
+  token first_end;              /* Token value of the first END in elems.  */
+  position_set mbps;            /* Positions which can match multibyte
+                                   characters, e.g., period.
+                                   Used only if MB_CUR_MAX > 1.  */
+} dfa_state;
+
+/* States are indexed by state_num values.  These are normally
+   nonnegative but -1 is used as a special value.  */
+typedef ptrdiff_t state_num;
+
+/* A bracket operator.
+   e.g., [a-c], [[:alpha:]], etc.  */
+struct mb_char_classes
+{
+  ptrdiff_t cset;
+  bool invert;
+  wchar_t *chars;               /* Normal characters.  */
+  size_t nchars;
+};
+
+/* A compiled regular expression.  */
+struct dfa
+{
+  /* Fields filled by the scanner.  */
+  charclass *charclasses;       /* Array of character sets for CSET tokens.  */
+  size_t cindex;                /* Index for adding new charclasses.  */
+  size_t calloc;                /* Number of charclasses allocated.  */
+
+  /* Fields filled by the parser.  */
+  token *tokens;                /* Postfix parse array.  */
+  size_t tindex;                /* Index for adding new tokens.  */
+  size_t talloc;                /* Number of tokens currently allocated.  */
+  size_t depth;                 /* Depth required of an evaluation stack
+                                   used for depth-first traversal of the
+                                   parse tree.  */
+  size_t nleaves;               /* Number of leaves on the parse tree.  */
+  size_t nregexps;              /* Count of parallel regexps being built
+                                   with dfaparse.  */
+  bool fast;			/* The DFA is fast.  */
+  bool multibyte;		/* MB_CUR_MAX > 1.  */
+  token utf8_anychar_classes[5]; /* To lower ANYCHAR in UTF-8 locales.  */
+  mbstate_t mbs;		/* Multibyte conversion state.  */
+
+  /* dfaexec implementation.  */
+  char *(*dfaexec) (struct dfa *, char const *, char *,
+                    bool, size_t *, bool *);
+
+  /* The following are valid only if MB_CUR_MAX > 1.  */
+
+  /* The value of multibyte_prop[i] is defined by following rule.
+     if tokens[i] < NOTCHAR
+     bit 0 : tokens[i] is the first byte of a character, including
+     single-byte characters.
+     bit 1 : tokens[i] is the last byte of a character, including
+     single-byte characters.
+
+     if tokens[i] = MBCSET
+     ("the index of mbcsets corresponding to this operator" << 2) + 3
+
+     e.g.
+     tokens
+     = 'single_byte_a', 'multi_byte_A', single_byte_b'
+     = 'sb_a', 'mb_A(1st byte)', 'mb_A(2nd byte)', 'mb_A(3rd byte)', 'sb_b'
+     multibyte_prop
+     = 3     , 1               ,  0              ,  2              , 3
+   */
+  int *multibyte_prop;
+
+  /* Array of the bracket expression in the DFA.  */
+  struct mb_char_classes *mbcsets;
+  size_t nmbcsets;
+  size_t mbcsets_alloc;
+
+  /* Fields filled by the superset.  */
+  struct dfa *superset;             /* Hint of the dfa.  */
+
+  /* Fields filled by the state builder.  */
+  dfa_state *states;            /* States of the dfa.  */
+  state_num sindex;             /* Index for adding new states.  */
+  size_t salloc;		/* Number of states currently allocated.  */
+
+  /* Fields filled by the parse tree->NFA conversion.  */
+  position_set *follows;        /* Array of follow sets, indexed by position
+                                   index.  The follow of a position is the set
+                                   of positions containing characters that
+                                   could conceivably follow a character
+                                   matching the given position in a string
+                                   matching the regexp.  Allocated to the
+                                   maximum possible position index.  */
+  bool searchflag;		/* We are supposed to build a searching
+                                   as opposed to an exact matcher.  A searching
+                                   matcher finds the first and shortest string
+                                   matching a regexp anywhere in the buffer,
+                                   whereas an exact matcher finds the longest
+                                   string matching, but anchored to the
+                                   beginning of the buffer.  */
+
+  /* Fields filled by dfaexec.  */
+  state_num tralloc;            /* Number of transition tables that have
+                                   slots so far, not counting trans[-1].  */
+  int trcount;                  /* Number of transition tables that have
+                                   actually been built.  */
+  int min_trcount;              /* Minimum of number of transition tables.
+                                   Always keep the number, even after freeing
+                                   the transition tables.  It is also the
+                                   number of initial states.  */
+  state_num **trans;            /* Transition tables for states that can
+                                   never accept.  If the transitions for a
+                                   state have not yet been computed, or the
+                                   state could possibly accept, its entry in
+                                   this table is NULL.  This points to one
+                                   past the start of the allocated array,
+                                   and trans[-1] is always NULL.  */
+  state_num **fails;            /* Transition tables after failing to accept
+                                   on a state that potentially could do so.  */
+  int *success;                 /* Table of acceptance conditions used in
+                                   dfaexec and computed in build_state.  */
+  state_num *newlines;          /* Transitions on newlines.  The entry for a
+                                   newline in any transition table is always
+                                   -1 so we can count lines without wasting
+                                   too many cycles.  The transition for a
+                                   newline is stored separately and handled
+                                   as a special case.  Newline is also used
+                                   as a sentinel at the end of the buffer.  */
+  state_num initstate_notbol;   /* Initial state for CTX_LETTER and CTX_NONE
+                                   context in multibyte locales, in which we
+                                   do not distinguish between their contexts,
+                                   as not supported word.  */
+  position_set mb_follows;      /* Follow set added by ANYCHAR and/or MBCSET
+                                   on demand.  */
+};
+
+/* Some macros for user access to dfa internals.  */
+
+/* S could possibly be an accepting state of R.  */
+#define ACCEPTING(s, r) ((r).states[s].constraint)
+
+/* STATE accepts in the specified context.  */
+#define ACCEPTS_IN_CONTEXT(prev, curr, state, dfa) \
+  SUCCEEDS_IN_CONTEXT ((dfa).states[state].constraint, prev, curr)
+
+static void regexp (void);
+
+/* A table indexed by byte values that contains the corresponding wide
+   character (if any) for that byte.  WEOF means the byte is not a
+   valid single-byte character.  */
+static wint_t mbrtowc_cache[NOTCHAR];
+
+/* Store into *PWC the result of converting the leading bytes of the
+   multibyte buffer S of length N bytes, using the mbrtowc_cache in *D
+   and updating the conversion state in *D.  On conversion error,
+   convert just a single byte, to WEOF.  Return the number of bytes
+   converted.
+
+   This differs from mbrtowc (PWC, S, N, &D->mbs) as follows:
+
+   * PWC points to wint_t, not to wchar_t.
+   * The last arg is a dfa *D instead of merely a multibyte conversion
+     state D->mbs.  D also contains an mbrtowc_cache for speed.
+   * N must be at least 1.
+   * S[N - 1] must be a sentinel byte.
+   * Shift encodings are not supported.
+   * The return value is always in the range 1..N.
+   * D->mbs is always valid afterwards.
+   * *PWC is always set to something.  */
+static size_t
+mbs_to_wchar (wint_t *pwc, char const *s, size_t n, struct dfa *d)
+{
+  unsigned char uc = s[0];
+  wint_t wc = mbrtowc_cache[uc];
+
+  if (wc == WEOF)
+    {
+      wchar_t wch;
+      size_t nbytes = mbrtowc (&wch, s, n, &d->mbs);
+      if (0 < nbytes && nbytes < (size_t) -2)
+        {
+          *pwc = wch;
+          return nbytes;
+        }
+      memset (&d->mbs, 0, sizeof d->mbs);
+    }
+
+  *pwc = wc;
+  return 1;
+}
+
+#ifdef DEBUG
+
+static void
+prtok (token t)
+{
+  char const *s;
+
+  if (t < 0)
+    fprintf (stderr, "END");
+  else if (t < NOTCHAR)
+    {
+      unsigned int ch = t;
+      fprintf (stderr, "0x%02x", ch);
+    }
+  else
+    {
+      switch (t)
+        {
+        case EMPTY:
+          s = "EMPTY";
+          break;
+        case BACKREF:
+          s = "BACKREF";
+          break;
+        case BEGLINE:
+          s = "BEGLINE";
+          break;
+        case ENDLINE:
+          s = "ENDLINE";
+          break;
+        case BEGWORD:
+          s = "BEGWORD";
+          break;
+        case ENDWORD:
+          s = "ENDWORD";
+          break;
+        case LIMWORD:
+          s = "LIMWORD";
+          break;
+        case NOTLIMWORD:
+          s = "NOTLIMWORD";
+          break;
+        case QMARK:
+          s = "QMARK";
+          break;
+        case STAR:
+          s = "STAR";
+          break;
+        case PLUS:
+          s = "PLUS";
+          break;
+        case CAT:
+          s = "CAT";
+          break;
+        case OR:
+          s = "OR";
+          break;
+        case LPAREN:
+          s = "LPAREN";
+          break;
+        case RPAREN:
+          s = "RPAREN";
+          break;
+        case ANYCHAR:
+          s = "ANYCHAR";
+          break;
+        case MBCSET:
+          s = "MBCSET";
+          break;
+        default:
+          s = "CSET";
+          break;
+        }
+      fprintf (stderr, "%s", s);
+    }
+}
+#endif /* DEBUG */
+
+/* Stuff pertaining to charclasses.  */
+
+static bool
+tstbit (unsigned int b, charclass const c)
+{
+  return c[b / CHARCLASS_WORD_BITS] >> b % CHARCLASS_WORD_BITS & 1;
+}
+
+static void
+setbit (unsigned int b, charclass c)
+{
+  c[b / CHARCLASS_WORD_BITS] |= (charclass_word) 1 << b % CHARCLASS_WORD_BITS;
+}
+
+static void
+clrbit (unsigned int b, charclass c)
+{
+  c[b / CHARCLASS_WORD_BITS] &= ~((charclass_word) 1
+                                  << b % CHARCLASS_WORD_BITS);
+}
+
+static void
+copyset (charclass const src, charclass dst)
+{
+  memcpy (dst, src, sizeof (charclass));
+}
+
+static void
+zeroset (charclass s)
+{
+  memset (s, 0, sizeof (charclass));
+}
+
+static void
+notset (charclass s)
+{
+  int i;
+
+  for (i = 0; i < CHARCLASS_WORDS; ++i)
+    s[i] = CHARCLASS_WORD_MASK & ~s[i];
+}
+
+static bool
+equal (charclass const s1, charclass const s2)
+{
+  return memcmp (s1, s2, sizeof (charclass)) == 0;
+}
+
+/* Ensure that the array addressed by PTR holds at least NITEMS +
+   (PTR || !NITEMS) items.  Either return PTR, or reallocate the array
+   and return its new address.  Although PTR may be null, the returned
+   value is never null.
+
+   The array holds *NALLOC items; *NALLOC is updated on reallocation.
+   ITEMSIZE is the size of one item.  Avoid O(N**2) behavior on arrays
+   growing linearly.  */
+static void *
+maybe_realloc (void *ptr, size_t nitems, size_t *nalloc, size_t itemsize)
+{
+  if (nitems < *nalloc)
+    return ptr;
+  *nalloc = nitems;
+  return x2nrealloc (ptr, nalloc, itemsize);
+}
+
+/* In DFA D, find the index of charclass S, or allocate a new one.  */
+static size_t
+dfa_charclass_index (struct dfa *d, charclass const s)
+{
+  size_t i;
+
+  for (i = 0; i < d->cindex; ++i)
+    if (equal (s, d->charclasses[i]))
+      return i;
+  d->charclasses = maybe_realloc (d->charclasses, d->cindex, &d->calloc,
+                                  sizeof *d->charclasses);
+  ++d->cindex;
+  copyset (s, d->charclasses[i]);
+  return i;
+}
+
+/* A pointer to the current dfa is kept here during parsing.  */
+static struct dfa *dfa;
+
+/* Find the index of charclass S in the current DFA, or allocate a new one.  */
+static size_t
+charclass_index (charclass const s)
+{
+  return dfa_charclass_index (dfa, s);
+}
+
+/* Syntax bits controlling the behavior of the lexical analyzer.  */
+static reg_syntax_t syntax_bits;
+static bool syntax_bits_set;
+
+/* Flag for case-folding letters into sets.  */
+static bool case_fold;
+
+/* End-of-line byte in data.  */
+static unsigned char eolbyte;
+
+/* Cache of char-context values.  */
+static int sbit[NOTCHAR];
+
+/* If never_trail[B], the byte B cannot be a non-initial byte in a
+   multibyte character.  */
+static bool never_trail[NOTCHAR];
+
+/* Set of characters considered letters.  */
+static charclass letters;
+
+/* Set of characters that are newline.  */
+static charclass newline;
+
+static bool
+unibyte_word_constituent (unsigned char c)
+{
+  return mbrtowc_cache[c] != WEOF && (isalnum (c) || (c) == '_');
+}
+
+static int
+char_context (unsigned char c)
+{
+  if (c == eolbyte)
+    return CTX_NEWLINE;
+  if (unibyte_word_constituent (c))
+    return CTX_LETTER;
+  return CTX_NONE;
+}
+
+/* Entry point to set syntax options.  */
+void
+dfasyntax (reg_syntax_t bits, bool fold, unsigned char eol)
+{
+  int i;
+  syntax_bits_set = true;
+  syntax_bits = bits;
+  case_fold = fold;
+  eolbyte = eol;
+
+  for (i = CHAR_MIN; i <= CHAR_MAX; ++i)
+    {
+      char c = i;
+      unsigned char uc = i;
+      mbstate_t s = { 0 };
+      wchar_t wc;
+      mbrtowc_cache[uc] = mbrtowc (&wc, &c, 1, &s) <= 1 ? wc : WEOF;
+
+      /* Now that mbrtowc_cache[uc] is set, use it to calculate sbit.  */
+      sbit[uc] = char_context (uc);
+      switch (sbit[uc])
+        {
+        case CTX_LETTER:
+          setbit (uc, letters);
+          break;
+        case CTX_NEWLINE:
+          setbit (uc, newline);
+          break;
+        }
+
+      /* POSIX requires that the five bytes in "\n\r./" (including the
+         terminating NUL) cannot occur inside a multibyte character.  */
+      never_trail[uc] = (using_utf8 () ? (uc & 0xc0) != 0x80
+                         : strchr ("\n\r./", uc) != NULL);
+    }
+}
+
+/* Set a bit in the charclass for the given wchar_t.  Do nothing if WC
+   is represented by a multi-byte sequence.  Even for MB_CUR_MAX == 1,
+   this may happen when folding case in weird Turkish locales where
+   dotless i/dotted I are not included in the chosen character set.
+   Return whether a bit was set in the charclass.  */
+static bool
+setbit_wc (wint_t wc, charclass c)
+{
+  int b = wctob (wc);
+  if (b == EOF)
+    return false;
+
+  setbit (b, c);
+  return true;
+}
+
+/* Set a bit for B and its case variants in the charclass C.
+   MB_CUR_MAX must be 1.  */
+static void
+setbit_case_fold_c (int b, charclass c)
+{
+  int ub = toupper (b);
+  int i;
+  for (i = 0; i < NOTCHAR; i++)
+    if (toupper (i) == ub)
+      setbit (i, c);
+}
+
+
+
+/* UTF-8 encoding allows some optimizations that we can't otherwise
+   assume in a multibyte encoding.  */
+bool
+using_utf8 (void)
+{
+  static int utf8 = -1;
+  if (utf8 < 0)
+    {
+      wchar_t wc;
+      mbstate_t mbs = { 0 };
+      utf8 = mbrtowc (&wc, "\xc4\x80", 2, &mbs) == 2 && wc == 0x100;
+    }
+  return utf8;
+}
+
+/* The current locale is known to be a unibyte locale
+   without multicharacter collating sequences and where range
+   comparisons simply use the native encoding.  These locales can be
+   processed more efficiently.  */
+
+static bool
+using_simple_locale (void)
+{
+  /* The native character set is known to be compatible with
+     the C locale.  The following test isn't perfect, but it's good
+     enough in practice, as only ASCII and EBCDIC are in common use
+     and this test correctly accepts ASCII and rejects EBCDIC.  */
+  enum { native_c_charset =
+    ('\b' == 8 && '\t' == 9 && '\n' == 10 && '\v' == 11 && '\f' == 12
+     && '\r' == 13 && ' ' == 32 && '!' == 33 && '"' == 34 && '#' == 35
+     && '%' == 37 && '&' == 38 && '\'' == 39 && '(' == 40 && ')' == 41
+     && '*' == 42 && '+' == 43 && ',' == 44 && '-' == 45 && '.' == 46
+     && '/' == 47 && '0' == 48 && '9' == 57 && ':' == 58 && ';' == 59
+     && '<' == 60 && '=' == 61 && '>' == 62 && '?' == 63 && 'A' == 65
+     && 'Z' == 90 && '[' == 91 && '\\' == 92 && ']' == 93 && '^' == 94
+     && '_' == 95 && 'a' == 97 && 'z' == 122 && '{' == 123 && '|' == 124
+     && '}' == 125 && '~' == 126)
+  };
+
+  if (! native_c_charset || dfa->multibyte)
+    return false;
+  else
+    {
+      static int unibyte_c = -1;
+      if (unibyte_c < 0)
+        {
+          char const *locale = setlocale (LC_ALL, NULL);
+          unibyte_c = (!locale
+                       || STREQ (locale, "C")
+                       || STREQ (locale, "POSIX"));
+        }
+      return unibyte_c;
+    }
+}
+
+/* Lexical analyzer.  All the dross that deals with the obnoxious
+   GNU Regex syntax bits is located here.  The poor, suffering
+   reader is referred to the GNU Regex documentation for the
+   meaning of the @#%!@#%^!@ syntax bits.  */
+
+static char const *lexptr;      /* Pointer to next input character.  */
+static size_t lexleft;          /* Number of characters remaining.  */
+static token lasttok;           /* Previous token returned; initially END.  */
+static bool laststart;		/* We're separated from beginning or (,
+                                   | only by zero-width characters.  */
+static size_t parens;           /* Count of outstanding left parens.  */
+static int minrep, maxrep;      /* Repeat counts for {m,n}.  */
+
+static int cur_mb_len = 1;      /* Length of the multibyte representation of
+                                   wctok.  */
+
+static wint_t wctok;		/* Wide character representation of the current
+                                   multibyte character, or WEOF if there was
+                                   an encoding error.  Used only if
+                                   MB_CUR_MAX > 1.  */
+
+
+/* Fetch the next lexical input character.  Set C (of type int) to the
+   next input byte, except set C to EOF if the input is a multibyte
+   character of length greater than 1.  Set WC (of type wint_t) to the
+   value of the input if it is a valid multibyte character (possibly
+   of length 1); otherwise set WC to WEOF.  If there is no more input,
+   report EOFERR if EOFERR is not null, and return lasttok = END
+   otherwise.  */
+# define FETCH_WC(c, wc, eoferr)		\
+  do {						\
+    if (! lexleft)				\
+      {						\
+        if ((eoferr) != 0)			\
+          dfaerror (eoferr);			\
+        else					\
+          return lasttok = END;			\
+      }						\
+    else					\
+      {						\
+        wint_t _wc;				\
+        size_t nbytes = mbs_to_wchar (&_wc, lexptr, lexleft, dfa); \
+        cur_mb_len = nbytes;			\
+        (wc) = _wc;				\
+        (c) = nbytes == 1 ? to_uchar (*lexptr) : EOF;    \
+        lexptr += nbytes;			\
+        lexleft -= nbytes;			\
+      }						\
+  } while (false)
+
+#ifndef MIN
+# define MIN(a,b) ((a) < (b) ? (a) : (b))
+#endif
+
+/* The set of wchar_t values C such that there's a useful locale
+   somewhere where C != towupper (C) && C != towlower (towupper (C)).
+   For example, 0x00B5 (U+00B5 MICRO SIGN) is in this table, because
+   towupper (0x00B5) == 0x039C (U+039C GREEK CAPITAL LETTER MU), and
+   towlower (0x039C) == 0x03BC (U+03BC GREEK SMALL LETTER MU).  */
+static short const lonesome_lower[] =
+  {
+    0x00B5, 0x0131, 0x017F, 0x01C5, 0x01C8, 0x01CB, 0x01F2, 0x0345,
+    0x03C2, 0x03D0, 0x03D1, 0x03D5, 0x03D6, 0x03F0, 0x03F1,
+
+    /* U+03F2 GREEK LUNATE SIGMA SYMBOL lacks a specific uppercase
+       counterpart in locales predating Unicode 4.0.0 (April 2003).  */
+    0x03F2,
+
+    0x03F5, 0x1E9B, 0x1FBE,
+  };
+
+/* Maximum number of characters that can be the case-folded
+   counterparts of a single character, not counting the character
+   itself.  This is 1 for towupper, 1 for towlower, and 1 for each
+   entry in LONESOME_LOWER.  */
+enum
+{ CASE_FOLDED_BUFSIZE = 2 + sizeof lonesome_lower / sizeof *lonesome_lower };
+
+/* Find the characters equal to C after case-folding, other than C
+   itself, and store them into FOLDED.  Return the number of characters
+   stored.  */
+static unsigned int
+case_folded_counterparts (wchar_t c, wchar_t folded[CASE_FOLDED_BUFSIZE])
+{
+  unsigned int i;
+  unsigned int n = 0;
+  wint_t uc = towupper (c);
+  wint_t lc = towlower (uc);
+  if (uc != c)
+    folded[n++] = uc;
+  if (lc != uc && lc != c && towupper (lc) == uc)
+    folded[n++] = lc;
+  for (i = 0; i < sizeof lonesome_lower / sizeof *lonesome_lower; i++)
+    {
+      wint_t li = lonesome_lower[i];
+      if (li != lc && li != uc && li != c && towupper (li) == uc)
+        folded[n++] = li;
+    }
+  return n;
+}
+
+typedef int predicate (int);
+
+/* The following list maps the names of the Posix named character classes
+   to predicate functions that determine whether a given character is in
+   the class.  The leading [ has already been eaten by the lexical
+   analyzer.  */
+struct dfa_ctype
+{
+  const char *name;
+  predicate *func;
+  bool single_byte_only;
+};
+
+static const struct dfa_ctype prednames[] = {
+  {"alpha", isalpha, false},
+  {"upper", isupper, false},
+  {"lower", islower, false},
+  {"digit", isdigit, true},
+  {"xdigit", isxdigit, false},
+  {"space", isspace, false},
+  {"punct", ispunct, false},
+  {"alnum", isalnum, false},
+  {"print", isprint, false},
+  {"graph", isgraph, false},
+  {"cntrl", iscntrl, false},
+  {"blank", isblank, false},
+  {NULL, NULL, false}
+};
+
+static const struct dfa_ctype *_GL_ATTRIBUTE_PURE
+find_pred (const char *str)
+{
+  unsigned int i;
+  for (i = 0; prednames[i].name; ++i)
+    if (STREQ (str, prednames[i].name))
+      return &prednames[i];
+  return NULL;
+}
+
+/* Multibyte character handling sub-routine for lex.
+   Parse a bracket expression and build a struct mb_char_classes.  */
+static token
+parse_bracket_exp (void)
+{
+  bool invert;
+  int c, c1, c2;
+  charclass ccl;
+
+  /* This is a bracket expression that dfaexec is known to
+     process correctly.  */
+  bool known_bracket_exp = true;
+
+  /* Used to warn about [:space:].
+     Bit 0 = first character is a colon.
+     Bit 1 = last character is a colon.
+     Bit 2 = includes any other character but a colon.
+     Bit 3 = includes ranges, char/equiv classes or collation elements.  */
+  int colon_warning_state;
+
+  wint_t wc;
+  wint_t wc2;
+  wint_t wc1 = 0;
+
+  /* Work area to build a mb_char_classes.  */
+  struct mb_char_classes *work_mbc;
+  size_t chars_al;
+
+  chars_al = 0;
+  if (dfa->multibyte)
+    {
+      dfa->mbcsets = maybe_realloc (dfa->mbcsets, dfa->nmbcsets,
+                                    &dfa->mbcsets_alloc,
+                                    sizeof *dfa->mbcsets);
+
+      /* dfa->multibyte_prop[] hold the index of dfa->mbcsets.
+         We will update dfa->multibyte_prop[] in addtok, because we can't
+         decide the index in dfa->tokens[].  */
+
+      /* Initialize work area.  */
+      work_mbc = &(dfa->mbcsets[dfa->nmbcsets++]);
+      memset (work_mbc, 0, sizeof *work_mbc);
+    }
+  else
+    work_mbc = NULL;
+
+  memset (ccl, 0, sizeof ccl);
+  FETCH_WC (c, wc, _("unbalanced ["));
+  if (c == '^')
+    {
+      FETCH_WC (c, wc, _("unbalanced ["));
+      invert = true;
+      known_bracket_exp = using_simple_locale ();
+    }
+  else
+    invert = false;
+
+  colon_warning_state = (c == ':');
+  do
+    {
+      c1 = NOTCHAR;	/* Mark c1 as not initialized.  */
+      colon_warning_state &= ~2;
+
+      /* Note that if we're looking at some other [:...:] construct,
+         we just treat it as a bunch of ordinary characters.  We can do
+         this because we assume regex has checked for syntax errors before
+         dfa is ever called.  */
+      if (c == '[')
+        {
+          FETCH_WC (c1, wc1, _("unbalanced ["));
+
+          if ((c1 == ':' && (syntax_bits & RE_CHAR_CLASSES))
+              || c1 == '.' || c1 == '=')
+            {
+              enum { MAX_BRACKET_STRING_LEN = 32 };
+              char str[MAX_BRACKET_STRING_LEN + 1];
+              size_t len = 0;
+              for (;;)
+                {
+                  FETCH_WC (c, wc, _("unbalanced ["));
+                  if ((c == c1 && *lexptr == ']') || lexleft == 0)
+                    break;
+                  if (len < MAX_BRACKET_STRING_LEN)
+                    str[len++] = c;
+                  else
+                    /* This is in any case an invalid class name.  */
+                    str[0] = '\0';
+                }
+              str[len] = '\0';
+
+              /* Fetch bracket.  */
+              FETCH_WC (c, wc, _("unbalanced ["));
+              if (c1 == ':')
+                /* Build character class.  POSIX allows character
+                   classes to match multicharacter collating elements,
+                   but the regex code does not support that, so do not
+                   worry about that possibility.  */
+                {
+                  char const *class
+                    = (case_fold && (STREQ (str, "upper")
+                                     || STREQ (str, "lower")) ? "alpha" : str);
+                  const struct dfa_ctype *pred = find_pred (class);
+                  if (!pred)
+                    dfaerror (_("invalid character class"));
+
+                  if (dfa->multibyte && !pred->single_byte_only)
+                    known_bracket_exp = false;
+                  else
+                    for (c2 = 0; c2 < NOTCHAR; ++c2)
+                      if (pred->func (c2))
+                        setbit (c2, ccl);
+                }
+              else
+                known_bracket_exp = false;
+
+              colon_warning_state |= 8;
+
+              /* Fetch new lookahead character.  */
+              FETCH_WC (c1, wc1, _("unbalanced ["));
+              continue;
+            }
+
+          /* We treat '[' as a normal character here.  c/c1/wc/wc1
+             are already set up.  */
+        }
+
+      if (c == '\\' && (syntax_bits & RE_BACKSLASH_ESCAPE_IN_LISTS))
+        FETCH_WC (c, wc, _("unbalanced ["));
+
+      if (c1 == NOTCHAR)
+        FETCH_WC (c1, wc1, _("unbalanced ["));
+
+      if (c1 == '-')
+        /* build range characters.  */
+        {
+          FETCH_WC (c2, wc2, _("unbalanced ["));
+
+          /* A bracket expression like [a-[.aa.]] matches an unknown set.
+             Treat it like [-a[.aa.]] while parsing it, and
+             remember that the set is unknown.  */
+          if (c2 == '[' && *lexptr == '.')
+            {
+              known_bracket_exp = false;
+              c2 = ']';
+            }
+
+          if (c2 == ']')
+            {
+              /* In the case [x-], the - is an ordinary hyphen,
+                 which is left in c1, the lookahead character.  */
+              lexptr -= cur_mb_len;
+              lexleft += cur_mb_len;
+            }
+          else
+            {
+              if (c2 == '\\' && (syntax_bits & RE_BACKSLASH_ESCAPE_IN_LISTS))
+                FETCH_WC (c2, wc2, _("unbalanced ["));
+
+              colon_warning_state |= 8;
+              FETCH_WC (c1, wc1, _("unbalanced ["));
+
+              /* Treat [x-y] as a range if x != y.  */
+              if (wc != wc2 || wc == WEOF)
+                {
+                  if (dfa->multibyte)
+                    known_bracket_exp = false;
+                  else if (using_simple_locale ())
+                    {
+                      int ci;
+                      for (ci = c; ci <= c2; ci++)
+                        setbit (ci, ccl);
+                      if (case_fold)
+                        {
+                          int uc = toupper (c);
+                          int uc2 = toupper (c2);
+                          for (ci = 0; ci < NOTCHAR; ci++)
+                            {
+                              int uci = toupper (ci);
+                              if (uc <= uci && uci <= uc2)
+                                setbit (ci, ccl);
+                            }
+                        }
+                    }
+                  else
+                    known_bracket_exp = false;
+
+                  continue;
+                }
+            }
+        }
+
+      colon_warning_state |= (c == ':') ? 2 : 4;
+
+      if (!dfa->multibyte)
+        {
+          if (case_fold)
+            setbit_case_fold_c (c, ccl);
+          else
+            setbit (c, ccl);
+          continue;
+        }
+
+      if (wc == WEOF)
+        known_bracket_exp = false;
+      else
+        {
+          wchar_t folded[CASE_FOLDED_BUFSIZE + 1];
+          unsigned int i;
+          unsigned int n = (case_fold
+                            ? case_folded_counterparts (wc, folded + 1) + 1
+                            : 1);
+          folded[0] = wc;
+          for (i = 0; i < n; i++)
+            if (!setbit_wc (folded[i], ccl))
+              {
+                work_mbc->chars
+                  = maybe_realloc (work_mbc->chars, work_mbc->nchars,
+                                   &chars_al, sizeof *work_mbc->chars);
+                work_mbc->chars[work_mbc->nchars++] = folded[i];
+              }
+        }
+    }
+  while ((wc = wc1, (c = c1) != ']'));
+
+  if (colon_warning_state == 7)
+    dfawarn (_("character class syntax is [[:space:]], not [:space:]"));
+
+  if (! known_bracket_exp)
+    return BACKREF;
+
+  if (dfa->multibyte)
+    {
+      static charclass const zeroclass;
+      work_mbc->invert = invert;
+      work_mbc->cset = equal (ccl, zeroclass) ? -1 : charclass_index (ccl);
+      return MBCSET;
+    }
+
+  if (invert)
+    {
+      assert (!dfa->multibyte);
+      notset (ccl);
+      if (syntax_bits & RE_HAT_LISTS_NOT_NEWLINE)
+        clrbit ('\n', ccl);
+    }
+
+  return CSET + charclass_index (ccl);
+}
+
+#define PUSH_LEX_STATE(s)			\
+  do						\
+    {						\
+      char const *lexptr_saved = lexptr;	\
+      size_t lexleft_saved = lexleft;		\
+      lexptr = (s);				\
+      lexleft = strlen (lexptr)
+
+#define POP_LEX_STATE()				\
+      lexptr = lexptr_saved;			\
+      lexleft = lexleft_saved;			\
+    }						\
+  while (false)
+
+static token
+lex (void)
+{
+  int c, c2;
+  bool backslash = false;
+  charclass ccl;
+  int i;
+
+  /* Basic plan: We fetch a character.  If it's a backslash,
+     we set the backslash flag and go through the loop again.
+     On the plus side, this avoids having a duplicate of the
+     main switch inside the backslash case.  On the minus side,
+     it means that just about every case begins with
+     "if (backslash) ...".  */
+  for (i = 0; i < 2; ++i)
+    {
+      FETCH_WC (c, wctok, NULL);
+
+      switch (c)
+        {
+        case '\\':
+          if (backslash)
+            goto normal_char;
+          if (lexleft == 0)
+            dfaerror (_("unfinished \\ escape"));
+          backslash = true;
+          break;
+
+        case '^':
+          if (backslash)
+            goto normal_char;
+          if (syntax_bits & RE_CONTEXT_INDEP_ANCHORS
+              || lasttok == END || lasttok == LPAREN || lasttok == OR)
+            return lasttok = BEGLINE;
+          goto normal_char;
+
+        case '$':
+          if (backslash)
+            goto normal_char;
+          if (syntax_bits & RE_CONTEXT_INDEP_ANCHORS
+              || lexleft == 0
+              || (syntax_bits & RE_NO_BK_PARENS
+                  ? lexleft > 0 && *lexptr == ')'
+                  : lexleft > 1 && lexptr[0] == '\\' && lexptr[1] == ')')
+              || (syntax_bits & RE_NO_BK_VBAR
+                  ? lexleft > 0 && *lexptr == '|'
+                  : lexleft > 1 && lexptr[0] == '\\' && lexptr[1] == '|')
+              || ((syntax_bits & RE_NEWLINE_ALT)
+                  && lexleft > 0 && *lexptr == '\n'))
+            return lasttok = ENDLINE;
+          goto normal_char;
+
+        case '1':
+        case '2':
+        case '3':
+        case '4':
+        case '5':
+        case '6':
+        case '7':
+        case '8':
+        case '9':
+          if (backslash && !(syntax_bits & RE_NO_BK_REFS))
+            {
+              laststart = false;
+              return lasttok = BACKREF;
+            }
+          goto normal_char;
+
+        case '`':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = BEGLINE; /* FIXME: should be beginning of string */
+          goto normal_char;
+
+        case '\'':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = ENDLINE;   /* FIXME: should be end of string */
+          goto normal_char;
+
+        case '<':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = BEGWORD;
+          goto normal_char;
+
+        case '>':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = ENDWORD;
+          goto normal_char;
+
+        case 'b':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = LIMWORD;
+          goto normal_char;
+
+        case 'B':
+          if (backslash && !(syntax_bits & RE_NO_GNU_OPS))
+            return lasttok = NOTLIMWORD;
+          goto normal_char;
+
+        case '?':
+          if (syntax_bits & RE_LIMITED_OPS)
+            goto normal_char;
+          if (backslash != ((syntax_bits & RE_BK_PLUS_QM) != 0))
+            goto normal_char;
+          if (!(syntax_bits & RE_CONTEXT_INDEP_OPS) && laststart)
+            goto normal_char;
+          return lasttok = QMARK;
+
+        case '*':
+          if (backslash)
+            goto normal_char;
+          if (!(syntax_bits & RE_CONTEXT_INDEP_OPS) && laststart)
+            goto normal_char;
+          return lasttok = STAR;
+
+        case '+':
+          if (syntax_bits & RE_LIMITED_OPS)
+            goto normal_char;
+          if (backslash != ((syntax_bits & RE_BK_PLUS_QM) != 0))
+            goto normal_char;
+          if (!(syntax_bits & RE_CONTEXT_INDEP_OPS) && laststart)
+            goto normal_char;
+          return lasttok = PLUS;
+
+        case '{':
+          if (!(syntax_bits & RE_INTERVALS))
+            goto normal_char;
+          if (backslash != ((syntax_bits & RE_NO_BK_BRACES) == 0))
+            goto normal_char;
+          if (!(syntax_bits & RE_CONTEXT_INDEP_OPS) && laststart)
+            goto normal_char;
+
+          /* Cases:
+             {M} - exact count
+             {M,} - minimum count, maximum is infinity
+             {,N} - 0 through N
+             {,} - 0 to infinity (same as '*')
+             {M,N} - M through N */
+          {
+            char const *p = lexptr;
+            char const *lim = p + lexleft;
+            minrep = maxrep = -1;
+            for (; p != lim && ISASCIIDIGIT (*p); p++)
+              {
+                if (minrep < 0)
+                  minrep = *p - '0';
+                else
+                  minrep = MIN (RE_DUP_MAX + 1, minrep * 10 + *p - '0');
+              }
+            if (p != lim)
+              {
+                if (*p != ',')
+                  maxrep = minrep;
+                else
+                  {
+                    if (minrep < 0)
+                      minrep = 0;
+                    while (++p != lim && ISASCIIDIGIT (*p))
+                      {
+                        if (maxrep < 0)
+                          maxrep = *p - '0';
+                        else
+                          maxrep = MIN (RE_DUP_MAX + 1, maxrep * 10 + *p - '0');
+                      }
+                  }
+              }
+            if (! ((! backslash || (p != lim && *p++ == '\\'))
+                   && p != lim && *p++ == '}'
+                   && 0 <= minrep && (maxrep < 0 || minrep <= maxrep)))
+              {
+                if (syntax_bits & RE_INVALID_INTERVAL_ORD)
+                  goto normal_char;
+                dfaerror (_("invalid content of \\{\\}"));
+              }
+            if (RE_DUP_MAX < maxrep)
+              dfaerror (_("regular expression too big"));
+            lexptr = p;
+            lexleft = lim - p;
+          }
+          laststart = false;
+          return lasttok = REPMN;
+
+        case '|':
+          if (syntax_bits & RE_LIMITED_OPS)
+            goto normal_char;
+          if (backslash != ((syntax_bits & RE_NO_BK_VBAR) == 0))
+            goto normal_char;
+          laststart = true;
+          return lasttok = OR;
+
+        case '\n':
+          if (syntax_bits & RE_LIMITED_OPS
+              || backslash || !(syntax_bits & RE_NEWLINE_ALT))
+            goto normal_char;
+          laststart = true;
+          return lasttok = OR;
+
+        case '(':
+          if (backslash != ((syntax_bits & RE_NO_BK_PARENS) == 0))
+            goto normal_char;
+          ++parens;
+          laststart = true;
+          return lasttok = LPAREN;
+
+        case ')':
+          if (backslash != ((syntax_bits & RE_NO_BK_PARENS) == 0))
+            goto normal_char;
+          if (parens == 0 && syntax_bits & RE_UNMATCHED_RIGHT_PAREN_ORD)
+            goto normal_char;
+          --parens;
+          laststart = false;
+          return lasttok = RPAREN;
+
+        case '.':
+          if (backslash)
+            goto normal_char;
+          if (dfa->multibyte)
+            {
+              /* In multibyte environment period must match with a single
+                 character not a byte.  So we use ANYCHAR.  */
+              laststart = false;
+              return lasttok = ANYCHAR;
+            }
+          zeroset (ccl);
+          notset (ccl);
+          if (!(syntax_bits & RE_DOT_NEWLINE))
+            clrbit ('\n', ccl);
+          if (syntax_bits & RE_DOT_NOT_NULL)
+            clrbit ('\0', ccl);
+          laststart = false;
+          return lasttok = CSET + charclass_index (ccl);
+
+        case 's':
+        case 'S':
+          if (!backslash || (syntax_bits & RE_NO_GNU_OPS))
+            goto normal_char;
+          if (!dfa->multibyte)
+            {
+              zeroset (ccl);
+              for (c2 = 0; c2 < NOTCHAR; ++c2)
+                if (isspace (c2))
+                  setbit (c2, ccl);
+              if (c == 'S')
+                notset (ccl);
+              laststart = false;
+              return lasttok = CSET + charclass_index (ccl);
+            }
+
+          /* FIXME: see if optimizing this, as is done with ANYCHAR and
+             add_utf8_anychar, makes sense.  */
+
+          /* \s and \S are documented to be equivalent to [[:space:]] and
+             [^[:space:]] respectively, so tell the lexer to process those
+             strings, each minus its "already processed" '['.  */
+          PUSH_LEX_STATE (c == 's' ? "[:space:]]" : "^[:space:]]");
+
+          lasttok = parse_bracket_exp ();
+
+          POP_LEX_STATE ();
+
+          laststart = false;
+          return lasttok;
+
+        case 'w':
+        case 'W':
+          if (!backslash || (syntax_bits & RE_NO_GNU_OPS))
+            goto normal_char;
+
+          if (!dfa->multibyte)
+            {
+              zeroset (ccl);
+              for (c2 = 0; c2 < NOTCHAR; ++c2)
+                if (unibyte_word_constituent (c2))
+                  setbit (c2, ccl);
+              if (c == 'W')
+                notset (ccl);
+              laststart = false;
+              return lasttok = CSET + charclass_index (ccl);
+            }
+
+          /* FIXME: see if optimizing this, as is done with ANYCHAR and
+             add_utf8_anychar, makes sense.  */
+
+          /* \w and \W are documented to be equivalent to [_[:alnum:]] and
+             [^_[:alnum:]] respectively, so tell the lexer to process those
+             strings, each minus its "already processed" '['.  */
+          PUSH_LEX_STATE (c == 'w' ? "_[:alnum:]]" : "^_[:alnum:]]");
+
+          lasttok = parse_bracket_exp ();
+
+          POP_LEX_STATE ();
+
+          laststart = false;
+          return lasttok;
+
+        case '[':
+          if (backslash)
+            goto normal_char;
+          laststart = false;
+          return lasttok = parse_bracket_exp ();
+
+        default:
+        normal_char:
+          laststart = false;
+          /* For multibyte character sets, folding is done in atom.  Always
+             return WCHAR.  */
+          if (dfa->multibyte)
+            return lasttok = WCHAR;
+
+          if (case_fold && isalpha (c))
+            {
+              zeroset (ccl);
+              setbit_case_fold_c (c, ccl);
+              return lasttok = CSET + charclass_index (ccl);
+            }
+
+          return lasttok = c;
+        }
+    }
+
+  /* The above loop should consume at most a backslash
+     and some other character.  */
+  abort ();
+  return END;                   /* keeps pedantic compilers happy.  */
+}
+
+/* Recursive descent parser for regular expressions.  */
+
+static token tok;               /* Lookahead token.  */
+static size_t depth;            /* Current depth of a hypothetical stack
+                                   holding deferred productions.  This is
+                                   used to determine the depth that will be
+                                   required of the real stack later on in
+                                   dfaanalyze.  */
+
+static void
+addtok_mb (token t, int mbprop)
+{
+  if (dfa->talloc == dfa->tindex)
+    {
+      dfa->tokens = x2nrealloc (dfa->tokens, &dfa->talloc,
+                                sizeof *dfa->tokens);
+      if (dfa->multibyte)
+        dfa->multibyte_prop = xnrealloc (dfa->multibyte_prop, dfa->talloc,
+                                         sizeof *dfa->multibyte_prop);
+    }
+  if (dfa->multibyte)
+    dfa->multibyte_prop[dfa->tindex] = mbprop;
+  dfa->tokens[dfa->tindex++] = t;
+
+  switch (t)
+    {
+    case QMARK:
+    case STAR:
+    case PLUS:
+      break;
+
+    case CAT:
+    case OR:
+      --depth;
+      break;
+
+    case BACKREF:
+      dfa->fast = false;
+      /* fallthrough */
+    default:
+      ++dfa->nleaves;
+      /* fallthrough */
+    case EMPTY:
+      ++depth;
+      break;
+    }
+  if (depth > dfa->depth)
+    dfa->depth = depth;
+}
+
+static void addtok_wc (wint_t wc);
+
+/* Add the given token to the parse tree, maintaining the depth count and
+   updating the maximum depth if necessary.  */
+static void
+addtok (token t)
+{
+  if (dfa->multibyte && t == MBCSET)
+    {
+      bool need_or = false;
+      struct mb_char_classes *work_mbc = &dfa->mbcsets[dfa->nmbcsets - 1];
+      size_t i;
+
+      /* Extract wide characters into alternations for better performance.
+         This does not require UTF-8.  */
+      for (i = 0; i < work_mbc->nchars; i++)
+        {
+          addtok_wc (work_mbc->chars[i]);
+          if (need_or)
+            addtok (OR);
+          need_or = true;
+        }
+      work_mbc->nchars = 0;
+
+      /* Characters have been handled above, so it is possible
+         that the mbcset is empty now.  Do nothing in that case.  */
+      if (work_mbc->cset != -1)
+        {
+          addtok (CSET + work_mbc->cset);
+          if (need_or)
+            addtok (OR);
+        }
+    }
+  else
+    {
+      addtok_mb (t, 3);
+    }
+}
+
+/* We treat a multibyte character as a single atom, so that DFA
+   can treat a multibyte character as a single expression.
+
+   e.g., we construct the following tree from "<mb1><mb2>".
+   <mb1(1st-byte)><mb1(2nd-byte)><CAT><mb1(3rd-byte)><CAT>
+   <mb2(1st-byte)><mb2(2nd-byte)><CAT><mb2(3rd-byte)><CAT><CAT> */
+static void
+addtok_wc (wint_t wc)
+{
+  unsigned char buf[MB_LEN_MAX];
+  mbstate_t s = { 0 };
+  int i;
+  size_t stored_bytes = wcrtomb ((char *) buf, wc, &s);
+
+  if (stored_bytes != (size_t) -1)
+    cur_mb_len = stored_bytes;
+  else
+    {
+      /* This is merely stop-gap.  buf[0] is undefined, yet skipping
+         the addtok_mb call altogether can corrupt the heap.  */
+      cur_mb_len = 1;
+      buf[0] = 0;
+    }
+
+  addtok_mb (buf[0], cur_mb_len == 1 ? 3 : 1);
+  for (i = 1; i < cur_mb_len; i++)
+    {
+      addtok_mb (buf[i], i == cur_mb_len - 1 ? 2 : 0);
+      addtok (CAT);
+    }
+}
+
+static void
+add_utf8_anychar (void)
+{
+  static charclass const utf8_classes[5] = {
+    /* 80-bf: non-leading bytes.  */
+    {0, 0, 0, 0, CHARCLASS_WORD_MASK, CHARCLASS_WORD_MASK, 0, 0},
+
+    /* 00-7f: 1-byte sequence.  */
+    {CHARCLASS_WORD_MASK, CHARCLASS_WORD_MASK, CHARCLASS_WORD_MASK,
+     CHARCLASS_WORD_MASK, 0, 0, 0, 0},
+
+    /* c2-df: 2-byte sequence.  */
+    {0, 0, 0, 0, 0, 0, ~3 & CHARCLASS_WORD_MASK, 0},
+
+    /* e0-ef: 3-byte sequence.  */
+    {0, 0, 0, 0, 0, 0, 0, 0xffff},
+
+    /* f0-f7: 4-byte sequence.  */
+    {0, 0, 0, 0, 0, 0, 0, 0xff0000}
+  };
+  const unsigned int n = sizeof (utf8_classes) / sizeof (utf8_classes[0]);
+  unsigned int i;
+
+  /* Define the five character classes that are needed below.  */
+  if (dfa->utf8_anychar_classes[0] == 0)
+    for (i = 0; i < n; i++)
+      {
+        charclass c;
+        copyset (utf8_classes[i], c);
+        if (i == 1)
+          {
+            if (!(syntax_bits & RE_DOT_NEWLINE))
+              clrbit ('\n', c);
+            if (syntax_bits & RE_DOT_NOT_NULL)
+              clrbit ('\0', c);
+          }
+        dfa->utf8_anychar_classes[i] = CSET + charclass_index (c);
+      }
+
+  /* A valid UTF-8 character is
+
+     ([0x00-0x7f]
+     |[0xc2-0xdf][0x80-0xbf]
+     |[0xe0-0xef[0x80-0xbf][0x80-0xbf]
+     |[0xf0-f7][0x80-0xbf][0x80-0xbf][0x80-0xbf])
+
+     which I'll write more concisely "B|CA|DAA|EAAA".  Factor the [0x00-0x7f]
+     and you get "B|(C|(D|EA)A)A".  And since the token buffer is in reverse
+     Polish notation, you get "B C D E A CAT OR A CAT OR A CAT OR".  */
+  for (i = 1; i < n; i++)
+    addtok (dfa->utf8_anychar_classes[i]);
+  while (--i > 1)
+    {
+      addtok (dfa->utf8_anychar_classes[0]);
+      addtok (CAT);
+      addtok (OR);
+    }
+}
+
+/* The grammar understood by the parser is as follows.
+
+   regexp:
+     regexp OR branch
+     branch
+
+   branch:
+     branch closure
+     closure
+
+   closure:
+     closure QMARK
+     closure STAR
+     closure PLUS
+     closure REPMN
+     atom
+
+   atom:
+     <normal character>
+     <multibyte character>
+     ANYCHAR
+     MBCSET
+     CSET
+     BACKREF
+     BEGLINE
+     ENDLINE
+     BEGWORD
+     ENDWORD
+     LIMWORD
+     NOTLIMWORD
+     LPAREN regexp RPAREN
+     <empty>
+
+   The parser builds a parse tree in postfix form in an array of tokens.  */
+
+static void
+atom (void)
+{
+  if (tok == WCHAR)
+    {
+      if (wctok == WEOF)
+        addtok (BACKREF);
+      else
+        {
+          addtok_wc (wctok);
+
+          if (case_fold)
+            {
+              wchar_t folded[CASE_FOLDED_BUFSIZE];
+              unsigned int i, n = case_folded_counterparts (wctok, folded);
+              for (i = 0; i < n; i++)
+                {
+                  addtok_wc (folded[i]);
+                  addtok (OR);
+                }
+            }
+        }
+
+      tok = lex ();
+    }
+  else if (tok == ANYCHAR && using_utf8 ())
+    {
+      /* For UTF-8 expand the period to a series of CSETs that define a valid
+         UTF-8 character.  This avoids using the slow multibyte path.  I'm
+         pretty sure it would be both profitable and correct to do it for
+         any encoding; however, the optimization must be done manually as
+         it is done above in add_utf8_anychar.  So, let's start with
+         UTF-8: it is the most used, and the structure of the encoding
+         makes the correctness more obvious.  */
+      add_utf8_anychar ();
+      tok = lex ();
+    }
+  else if ((tok >= 0 && tok < NOTCHAR) || tok >= CSET || tok == BACKREF
+           || tok == BEGLINE || tok == ENDLINE || tok == BEGWORD
+           || tok == ANYCHAR || tok == MBCSET
+           || tok == ENDWORD || tok == LIMWORD || tok == NOTLIMWORD)
+    {
+      addtok (tok);
+      tok = lex ();
+    }
+  else if (tok == LPAREN)
+    {
+      tok = lex ();
+      regexp ();
+      if (tok != RPAREN)
+        dfaerror (_("unbalanced ("));
+      tok = lex ();
+    }
+  else
+    addtok (EMPTY);
+}
+
+/* Return the number of tokens in the given subexpression.  */
+static size_t _GL_ATTRIBUTE_PURE
+nsubtoks (size_t tindex)
+{
+  size_t ntoks1;
+
+  switch (dfa->tokens[tindex - 1])
+    {
+    default:
+      return 1;
+    case QMARK:
+    case STAR:
+    case PLUS:
+      return 1 + nsubtoks (tindex - 1);
+    case CAT:
+    case OR:
+      ntoks1 = nsubtoks (tindex - 1);
+      return 1 + ntoks1 + nsubtoks (tindex - 1 - ntoks1);
+    }
+}
+
+/* Copy the given subexpression to the top of the tree.  */
+static void
+copytoks (size_t tindex, size_t ntokens)
+{
+  size_t i;
+
+  if (dfa->multibyte)
+    for (i = 0; i < ntokens; ++i)
+      addtok_mb (dfa->tokens[tindex + i], dfa->multibyte_prop[tindex + i]);
+  else
+    for (i = 0; i < ntokens; ++i)
+      addtok_mb (dfa->tokens[tindex + i], 3);
+}
+
+static void
+closure (void)
+{
+  int i;
+  size_t tindex, ntokens;
+
+  atom ();
+  while (tok == QMARK || tok == STAR || tok == PLUS || tok == REPMN)
+    if (tok == REPMN && (minrep || maxrep))
+      {
+        ntokens = nsubtoks (dfa->tindex);
+        tindex = dfa->tindex - ntokens;
+        if (maxrep < 0)
+          addtok (PLUS);
+        if (minrep == 0)
+          addtok (QMARK);
+        for (i = 1; i < minrep; ++i)
+          {
+            copytoks (tindex, ntokens);
+            addtok (CAT);
+          }
+        for (; i < maxrep; ++i)
+          {
+            copytoks (tindex, ntokens);
+            addtok (QMARK);
+            addtok (CAT);
+          }
+        tok = lex ();
+      }
+    else if (tok == REPMN)
+      {
+        dfa->tindex -= nsubtoks (dfa->tindex);
+        tok = lex ();
+        closure ();
+      }
+    else
+      {
+        addtok (tok);
+        tok = lex ();
+      }
+}
+
+static void
+branch (void)
+{
+  closure ();
+  while (tok != RPAREN && tok != OR && tok >= 0)
+    {
+      closure ();
+      addtok (CAT);
+    }
+}
+
+static void
+regexp (void)
+{
+  branch ();
+  while (tok == OR)
+    {
+      tok = lex ();
+      branch ();
+      addtok (OR);
+    }
+}
+
+/* Main entry point for the parser.  S is a string to be parsed, len is the
+   length of the string, so s can include NUL characters.  D is a pointer to
+   the struct dfa to parse into.  */
+static void
+dfaparse (char const *s, size_t len, struct dfa *d)
+{
+  dfa = d;
+  lexptr = s;
+  lexleft = len;
+  lasttok = END;
+  laststart = true;
+  parens = 0;
+  if (dfa->multibyte)
+    {
+      cur_mb_len = 0;
+      memset (&d->mbs, 0, sizeof d->mbs);
+    }
+
+  if (!syntax_bits_set)
+    dfaerror (_("no syntax specified"));
+
+  tok = lex ();
+  depth = d->depth;
+
+  regexp ();
+
+  if (tok != END)
+    dfaerror (_("unbalanced )"));
+
+  addtok (END - d->nregexps);
+  addtok (CAT);
+
+  if (d->nregexps)
+    addtok (OR);
+
+  ++d->nregexps;
+}
+
+/* Some primitives for operating on sets of positions.  */
+
+/* Copy one set to another.  */
+static void
+copy (position_set const *src, position_set *dst)
+{
+  if (dst->alloc < src->nelem)
+    {
+      free (dst->elems);
+      dst->alloc = src->nelem;
+      dst->elems = x2nrealloc (NULL, &dst->alloc, sizeof *dst->elems);
+    }
+  memcpy (dst->elems, src->elems, src->nelem * sizeof *dst->elems);
+  dst->nelem = src->nelem;
+}
+
+static void
+alloc_position_set (position_set *s, size_t size)
+{
+  s->elems = xnmalloc (size, sizeof *s->elems);
+  s->alloc = size;
+  s->nelem = 0;
+}
+
+/* Insert position P in set S.  S is maintained in sorted order on
+   decreasing index.  If there is already an entry in S with P.index
+   then merge (logically-OR) P's constraints into the one in S.
+   S->elems must point to an array large enough to hold the resulting set.  */
+static void
+insert (position p, position_set *s)
+{
+  size_t count = s->nelem;
+  size_t lo = 0, hi = count;
+  size_t i;
+  while (lo < hi)
+    {
+      size_t mid = (lo + hi) >> 1;
+      if (s->elems[mid].index > p.index)
+        lo = mid + 1;
+      else
+        hi = mid;
+    }
+
+  if (lo < count && p.index == s->elems[lo].index)
+    {
+      s->elems[lo].constraint |= p.constraint;
+      return;
+    }
+
+  s->elems = maybe_realloc (s->elems, count, &s->alloc, sizeof *s->elems);
+  for (i = count; i > lo; i--)
+    s->elems[i] = s->elems[i - 1];
+  s->elems[lo] = p;
+  ++s->nelem;
+}
+
+/* Merge two sets of positions into a third.  The result is exactly as if
+   the positions of both sets were inserted into an initially empty set.  */
+static void
+merge (position_set const *s1, position_set const *s2, position_set *m)
+{
+  size_t i = 0, j = 0;
+
+  if (m->alloc < s1->nelem + s2->nelem)
+    {
+      free (m->elems);
+      m->elems = maybe_realloc (NULL, s1->nelem + s2->nelem, &m->alloc,
+                                sizeof *m->elems);
+    }
+  m->nelem = 0;
+  while (i < s1->nelem && j < s2->nelem)
+    if (s1->elems[i].index > s2->elems[j].index)
+      m->elems[m->nelem++] = s1->elems[i++];
+    else if (s1->elems[i].index < s2->elems[j].index)
+      m->elems[m->nelem++] = s2->elems[j++];
+    else
+      {
+        m->elems[m->nelem] = s1->elems[i++];
+        m->elems[m->nelem++].constraint |= s2->elems[j++].constraint;
+      }
+  while (i < s1->nelem)
+    m->elems[m->nelem++] = s1->elems[i++];
+  while (j < s2->nelem)
+    m->elems[m->nelem++] = s2->elems[j++];
+}
+
+/* Delete a position from a set.  */
+static void
+delete (position p, position_set *s)
+{
+  size_t i;
+
+  for (i = 0; i < s->nelem; ++i)
+    if (p.index == s->elems[i].index)
+      break;
+  if (i < s->nelem)
+    for (--s->nelem; i < s->nelem; ++i)
+      s->elems[i] = s->elems[i + 1];
+}
+
+/* Find the index of the state corresponding to the given position set with
+   the given preceding context, or create a new state if there is no such
+   state.  Context tells whether we got here on a newline or letter.  */
+static state_num
+state_index (struct dfa *d, position_set const *s, int context)
+{
+  size_t hash = 0;
+  int constraint;
+  state_num i, j;
+
+  for (i = 0; i < s->nelem; ++i)
+    hash ^= s->elems[i].index + s->elems[i].constraint;
+
+  /* Try to find a state that exactly matches the proposed one.  */
+  for (i = 0; i < d->sindex; ++i)
+    {
+      if (hash != d->states[i].hash || s->nelem != d->states[i].elems.nelem
+          || context != d->states[i].context)
+        continue;
+      for (j = 0; j < s->nelem; ++j)
+        if (s->elems[j].constraint
+            != d->states[i].elems.elems[j].constraint
+            || s->elems[j].index != d->states[i].elems.elems[j].index)
+          break;
+      if (j == s->nelem)
+        return i;
+    }
+
+#ifdef DEBUG
+  fprintf (stderr, "new state %zd\n nextpos:", i);
+  for (j = 0; j < s->nelem; ++j)
+    {
+      fprintf (stderr, " %zu:", s->elems[j].index);
+      prtok (d->tokens[s->elems[j].index]);
+    }
+  fprintf (stderr, "\n context:");
+  if (context ^ CTX_ANY)
+    {
+      if (context & CTX_NONE)
+        fprintf (stderr, " CTX_NONE");
+      if (context & CTX_LETTER)
+        fprintf (stderr, " CTX_LETTER");
+      if (context & CTX_NEWLINE)
+        fprintf (stderr, " CTX_NEWLINE");
+    }
+  else
+    fprintf (stderr, " CTX_ANY");
+  fprintf (stderr, "\n");
+#endif
+
+  /* We'll have to create a new state.  */
+  d->states = maybe_realloc (d->states, d->sindex, &d->salloc,
+                             sizeof *d->states);
+  d->states[i].hash = hash;
+  alloc_position_set (&d->states[i].elems, s->nelem);
+  copy (s, &d->states[i].elems);
+  d->states[i].context = context;
+  d->states[i].constraint = 0;
+  d->states[i].first_end = 0;
+  d->states[i].mbps.nelem = 0;
+  d->states[i].mbps.elems = NULL;
+
+  for (j = 0; j < s->nelem; ++j)
+    if (d->tokens[s->elems[j].index] < 0)
+      {
+        constraint = s->elems[j].constraint;
+        if (SUCCEEDS_IN_CONTEXT (constraint, context, CTX_ANY))
+          d->states[i].constraint |= constraint;
+        if (!d->states[i].first_end)
+          d->states[i].first_end = d->tokens[s->elems[j].index];
+      }
+    else if (d->tokens[s->elems[j].index] == BACKREF)
+      d->states[i].constraint = NO_CONSTRAINT;
+
+  ++d->sindex;
+
+  return i;
+}
+
+/* Find the epsilon closure of a set of positions.  If any position of the set
+   contains a symbol that matches the empty string in some context, replace
+   that position with the elements of its follow labeled with an appropriate
+   constraint.  Repeat exhaustively until no funny positions are left.
+   S->elems must be large enough to hold the result.  */
+static void
+epsclosure (position_set *s, struct dfa const *d, char *visited)
+{
+  size_t i, j;
+  position p, old;
+  bool initialized = false;
+
+  for (i = 0; i < s->nelem; ++i)
+    if (d->tokens[s->elems[i].index] >= NOTCHAR
+        && d->tokens[s->elems[i].index] != BACKREF
+        && d->tokens[s->elems[i].index] != ANYCHAR
+        && d->tokens[s->elems[i].index] != MBCSET
+        && d->tokens[s->elems[i].index] < CSET)
+      {
+        if (!initialized)
+          {
+            memset (visited, 0, d->tindex * sizeof (*visited));
+            initialized = true;
+          }
+        old = s->elems[i];
+        p.constraint = old.constraint;
+        delete (s->elems[i], s);
+        if (visited[old.index])
+          {
+            --i;
+            continue;
+          }
+        visited[old.index] = 1;
+        switch (d->tokens[old.index])
+          {
+          case BEGLINE:
+            p.constraint &= BEGLINE_CONSTRAINT;
+            break;
+          case ENDLINE:
+            p.constraint &= ENDLINE_CONSTRAINT;
+            break;
+          case BEGWORD:
+            p.constraint &= BEGWORD_CONSTRAINT;
+            break;
+          case ENDWORD:
+            p.constraint &= ENDWORD_CONSTRAINT;
+            break;
+          case LIMWORD:
+            p.constraint &= LIMWORD_CONSTRAINT;
+            break;
+          case NOTLIMWORD:
+            p.constraint &= NOTLIMWORD_CONSTRAINT;
+            break;
+          default:
+            break;
+          }
+        for (j = 0; j < d->follows[old.index].nelem; ++j)
+          {
+            p.index = d->follows[old.index].elems[j].index;
+            insert (p, s);
+          }
+        /* Force rescan to start at the beginning.  */
+        i = -1;
+      }
+}
+
+/* Returns the set of contexts for which there is at least one
+   character included in C.  */
+
+static int
+charclass_context (charclass c)
+{
+  int context = 0;
+  unsigned int j;
+
+  if (tstbit (eolbyte, c))
+    context |= CTX_NEWLINE;
+
+  for (j = 0; j < CHARCLASS_WORDS; ++j)
+    {
+      if (c[j] & letters[j])
+        context |= CTX_LETTER;
+      if (c[j] & ~(letters[j] | newline[j]))
+        context |= CTX_NONE;
+    }
+
+  return context;
+}
+
+/* Returns the contexts on which the position set S depends.  Each context
+   in the set of returned contexts (let's call it SC) may have a different
+   follow set than other contexts in SC, and also different from the
+   follow set of the complement set (sc ^ CTX_ANY).  However, all contexts
+   in the complement set will have the same follow set.  */
+
+static int _GL_ATTRIBUTE_PURE
+state_separate_contexts (position_set const *s)
+{
+  int separate_contexts = 0;
+  size_t j;
+
+  for (j = 0; j < s->nelem; ++j)
+    {
+      if (PREV_NEWLINE_DEPENDENT (s->elems[j].constraint))
+        separate_contexts |= CTX_NEWLINE;
+      if (PREV_LETTER_DEPENDENT (s->elems[j].constraint))
+        separate_contexts |= CTX_LETTER;
+    }
+
+  return separate_contexts;
+}
+
+
+/* Perform bottom-up analysis on the parse tree, computing various functions.
+   Note that at this point, we're pretending constructs like \< are real
+   characters rather than constraints on what can follow them.
+
+   Nullable:  A node is nullable if it is at the root of a regexp that can
+   match the empty string.
+   *  EMPTY leaves are nullable.
+   * No other leaf is nullable.
+   * A QMARK or STAR node is nullable.
+   * A PLUS node is nullable if its argument is nullable.
+   * A CAT node is nullable if both its arguments are nullable.
+   * An OR node is nullable if either argument is nullable.
+
+   Firstpos:  The firstpos of a node is the set of positions (nonempty leaves)
+   that could correspond to the first character of a string matching the
+   regexp rooted at the given node.
+   * EMPTY leaves have empty firstpos.
+   * The firstpos of a nonempty leaf is that leaf itself.
+   * The firstpos of a QMARK, STAR, or PLUS node is the firstpos of its
+     argument.
+   * The firstpos of a CAT node is the firstpos of the left argument, union
+     the firstpos of the right if the left argument is nullable.
+   * The firstpos of an OR node is the union of firstpos of each argument.
+
+   Lastpos:  The lastpos of a node is the set of positions that could
+   correspond to the last character of a string matching the regexp at
+   the given node.
+   * EMPTY leaves have empty lastpos.
+   * The lastpos of a nonempty leaf is that leaf itself.
+   * The lastpos of a QMARK, STAR, or PLUS node is the lastpos of its
+     argument.
+   * The lastpos of a CAT node is the lastpos of its right argument, union
+     the lastpos of the left if the right argument is nullable.
+   * The lastpos of an OR node is the union of the lastpos of each argument.
+
+   Follow:  The follow of a position is the set of positions that could
+   correspond to the character following a character matching the node in
+   a string matching the regexp.  At this point we consider special symbols
+   that match the empty string in some context to be just normal characters.
+   Later, if we find that a special symbol is in a follow set, we will
+   replace it with the elements of its follow, labeled with an appropriate
+   constraint.
+   * Every node in the firstpos of the argument of a STAR or PLUS node is in
+     the follow of every node in the lastpos.
+   * Every node in the firstpos of the second argument of a CAT node is in
+     the follow of every node in the lastpos of the first argument.
+
+   Because of the postfix representation of the parse tree, the depth-first
+   analysis is conveniently done by a linear scan with the aid of a stack.
+   Sets are stored as arrays of the elements, obeying a stack-like allocation
+   scheme; the number of elements in each set deeper in the stack can be
+   used to determine the address of a particular set's array.  */
+static void
+dfaanalyze (struct dfa *d, bool searchflag)
+{
+  /* Array allocated to hold position sets.  */
+  position *posalloc = xnmalloc (d->nleaves, 2 * sizeof *posalloc);
+  /* Firstpos and lastpos elements.  */
+  position *firstpos = posalloc + d->nleaves;
+  position *lastpos = firstpos + d->nleaves;
+
+  /* Stack for element counts and nullable flags.  */
+  struct
+  {
+    /* Whether the entry is nullable.  */
+    bool nullable;
+
+    /* Counts of firstpos and lastpos sets.  */
+    size_t nfirstpos;
+    size_t nlastpos;
+  } *stkalloc = xnmalloc (d->depth, sizeof *stkalloc), *stk = stkalloc;
+
+  position_set tmp;             /* Temporary set for merging sets.  */
+  position_set merged;          /* Result of merging sets.  */
+  int separate_contexts;        /* Context wanted by some position.  */
+  size_t i, j;
+  position *pos;
+  char *visited = xnmalloc (d->tindex, sizeof *visited);
+
+#ifdef DEBUG
+  fprintf (stderr, "dfaanalyze:\n");
+  for (i = 0; i < d->tindex; ++i)
+    {
+      fprintf (stderr, " %zu:", i);
+      prtok (d->tokens[i]);
+    }
+  putc ('\n', stderr);
+#endif
+
+  d->searchflag = searchflag;
+  alloc_position_set (&merged, d->nleaves);
+  d->follows = xcalloc (d->tindex, sizeof *d->follows);
+
+  for (i = 0; i < d->tindex; ++i)
+    {
+      switch (d->tokens[i])
+        {
+        case EMPTY:
+          /* The empty set is nullable.  */
+          stk->nullable = true;
+
+          /* The firstpos and lastpos of the empty leaf are both empty.  */
+          stk->nfirstpos = stk->nlastpos = 0;
+          stk++;
+          break;
+
+        case STAR:
+        case PLUS:
+          /* Every element in the firstpos of the argument is in the follow
+             of every element in the lastpos.  */
+          tmp.nelem = stk[-1].nfirstpos;
+          tmp.elems = firstpos;
+          pos = lastpos;
+          for (j = 0; j < stk[-1].nlastpos; ++j)
+            {
+              merge (&tmp, &d->follows[pos[j].index], &merged);
+              copy (&merged, &d->follows[pos[j].index]);
+            }
+          /* fallthrough */
+
+        case QMARK:
+          /* A QMARK or STAR node is automatically nullable.  */
+          if (d->tokens[i] != PLUS)
+            stk[-1].nullable = true;
+          break;
+
+        case CAT:
+          /* Every element in the firstpos of the second argument is in the
+             follow of every element in the lastpos of the first argument.  */
+          tmp.nelem = stk[-1].nfirstpos;
+          tmp.elems = firstpos;
+          pos = lastpos + stk[-1].nlastpos;
+          for (j = 0; j < stk[-2].nlastpos; ++j)
+            {
+              merge (&tmp, &d->follows[pos[j].index], &merged);
+              copy (&merged, &d->follows[pos[j].index]);
+            }
+
+          /* The firstpos of a CAT node is the firstpos of the first argument,
+             union that of the second argument if the first is nullable.  */
+          if (stk[-2].nullable)
+            stk[-2].nfirstpos += stk[-1].nfirstpos;
+          else
+            firstpos += stk[-1].nfirstpos;
+
+          /* The lastpos of a CAT node is the lastpos of the second argument,
+             union that of the first argument if the second is nullable.  */
+          if (stk[-1].nullable)
+            stk[-2].nlastpos += stk[-1].nlastpos;
+          else
+            {
+              pos = lastpos + stk[-2].nlastpos;
+              for (j = stk[-1].nlastpos; j-- > 0;)
+                pos[j] = lastpos[j];
+              lastpos += stk[-2].nlastpos;
+              stk[-2].nlastpos = stk[-1].nlastpos;
+            }
+
+          /* A CAT node is nullable if both arguments are nullable.  */
+          stk[-2].nullable &= stk[-1].nullable;
+          stk--;
+          break;
+
+        case OR:
+          /* The firstpos is the union of the firstpos of each argument.  */
+          stk[-2].nfirstpos += stk[-1].nfirstpos;
+
+          /* The lastpos is the union of the lastpos of each argument.  */
+          stk[-2].nlastpos += stk[-1].nlastpos;
+
+          /* An OR node is nullable if either argument is nullable.  */
+          stk[-2].nullable |= stk[-1].nullable;
+          stk--;
+          break;
+
+        default:
+          /* Anything else is a nonempty position.  (Note that special
+             constructs like \< are treated as nonempty strings here;
+             an "epsilon closure" effectively makes them nullable later.
+             Backreferences have to get a real position so we can detect
+             transitions on them later.  But they are nullable.  */
+          stk->nullable = d->tokens[i] == BACKREF;
+
+          /* This position is in its own firstpos and lastpos.  */
+          stk->nfirstpos = stk->nlastpos = 1;
+          stk++;
+
+          --firstpos, --lastpos;
+          firstpos->index = lastpos->index = i;
+          firstpos->constraint = lastpos->constraint = NO_CONSTRAINT;
+
+          /* Allocate the follow set for this position.  */
+          alloc_position_set (&d->follows[i], 1);
+          break;
+        }
+#ifdef DEBUG
+      /* ... balance the above nonsyntactic #ifdef goo...  */
+      fprintf (stderr, "node %zu:", i);
+      prtok (d->tokens[i]);
+      putc ('\n', stderr);
+      fprintf (stderr,
+               stk[-1].nullable ? " nullable: yes\n" : " nullable: no\n");
+      fprintf (stderr, " firstpos:");
+      for (j = stk[-1].nfirstpos; j-- > 0;)
+        {
+          fprintf (stderr, " %zu:", firstpos[j].index);
+          prtok (d->tokens[firstpos[j].index]);
+        }
+      fprintf (stderr, "\n lastpos:");
+      for (j = stk[-1].nlastpos; j-- > 0;)
+        {
+          fprintf (stderr, " %zu:", lastpos[j].index);
+          prtok (d->tokens[lastpos[j].index]);
+        }
+      putc ('\n', stderr);
+#endif
+    }
+
+  /* For each follow set that is the follow set of a real position, replace
+     it with its epsilon closure.  */
+  for (i = 0; i < d->tindex; ++i)
+    if (d->tokens[i] < NOTCHAR || d->tokens[i] == BACKREF
+        || d->tokens[i] == ANYCHAR || d->tokens[i] == MBCSET
+        || d->tokens[i] >= CSET)
+      {
+#ifdef DEBUG
+        fprintf (stderr, "follows(%zu:", i);
+        prtok (d->tokens[i]);
+        fprintf (stderr, "):");
+        for (j = d->follows[i].nelem; j-- > 0;)
+          {
+            fprintf (stderr, " %zu:", d->follows[i].elems[j].index);
+            prtok (d->tokens[d->follows[i].elems[j].index]);
+          }
+        putc ('\n', stderr);
+#endif
+        copy (&d->follows[i], &merged);
+        epsclosure (&merged, d, visited);
+        copy (&merged, &d->follows[i]);
+      }
+
+  /* Get the epsilon closure of the firstpos of the regexp.  The result will
+     be the set of positions of state 0.  */
+  merged.nelem = 0;
+  for (i = 0; i < stk[-1].nfirstpos; ++i)
+    insert (firstpos[i], &merged);
+  epsclosure (&merged, d, visited);
+
+  /* Build the initial state.  */
+  separate_contexts = state_separate_contexts (&merged);
+  if (separate_contexts & CTX_NEWLINE)
+    state_index (d, &merged, CTX_NEWLINE);
+  d->initstate_notbol = d->min_trcount
+    = state_index (d, &merged, separate_contexts ^ CTX_ANY);
+  if (separate_contexts & CTX_LETTER)
+    d->min_trcount = state_index (d, &merged, CTX_LETTER);
+  d->min_trcount++;
+
+  free (posalloc);
+  free (stkalloc);
+  free (merged.elems);
+  free (visited);
+}
+
+
+/* Find, for each character, the transition out of state s of d, and store
+   it in the appropriate slot of trans.
+
+   We divide the positions of s into groups (positions can appear in more
+   than one group).  Each group is labeled with a set of characters that
+   every position in the group matches (taking into account, if necessary,
+   preceding context information of s).  For each group, find the union
+   of the its elements' follows.  This set is the set of positions of the
+   new state.  For each character in the group's label, set the transition
+   on this character to be to a state corresponding to the set's positions,
+   and its associated backward context information, if necessary.
+
+   If we are building a searching matcher, we include the positions of state
+   0 in every state.
+
+   The collection of groups is constructed by building an equivalence-class
+   partition of the positions of s.
+
+   For each position, find the set of characters C that it matches.  Eliminate
+   any characters from C that fail on grounds of backward context.
+
+   Search through the groups, looking for a group whose label L has nonempty
+   intersection with C.  If L - C is nonempty, create a new group labeled
+   L - C and having the same positions as the current group, and set L to
+   the intersection of L and C.  Insert the position in this group, set
+   C = C - L, and resume scanning.
+
+   If after comparing with every group there are characters remaining in C,
+   create a new group labeled with the characters of C and insert this
+   position in that group.  */
+static void
+dfastate (state_num s, struct dfa *d, state_num trans[])
+{
+  leaf_set grps[NOTCHAR];       /* As many as will ever be needed.  */
+  charclass labels[NOTCHAR];    /* Labels corresponding to the groups.  */
+  size_t ngrps = 0;             /* Number of groups actually used.  */
+  position pos;                 /* Current position being considered.  */
+  charclass matches;            /* Set of matching characters.  */
+  charclass_word matchesf;	/* Nonzero if matches is nonempty.  */
+  charclass intersect;          /* Intersection with some label set.  */
+  charclass_word intersectf;	/* Nonzero if intersect is nonempty.  */
+  charclass leftovers;          /* Stuff in the label that didn't match.  */
+  charclass_word leftoversf;	/* Nonzero if leftovers is nonempty.  */
+  position_set follows;         /* Union of the follows of some group.  */
+  position_set tmp;             /* Temporary space for merging sets.  */
+  int possible_contexts;        /* Contexts that this group can match.  */
+  int separate_contexts;        /* Context that new state wants to know.  */
+  state_num state;              /* New state.  */
+  state_num state_newline;      /* New state on a newline transition.  */
+  state_num state_letter;       /* New state on a letter transition.  */
+  bool next_isnt_1st_byte = false; /* We can't add state0.  */
+  size_t i, j, k;
+
+#ifdef DEBUG
+  fprintf (stderr, "build state %td\n", s);
+#endif
+
+  zeroset (matches);
+
+  for (i = 0; i < d->states[s].elems.nelem; ++i)
+    {
+      pos = d->states[s].elems.elems[i];
+      if (d->tokens[pos.index] >= 0 && d->tokens[pos.index] < NOTCHAR)
+        setbit (d->tokens[pos.index], matches);
+      else if (d->tokens[pos.index] >= CSET)
+        copyset (d->charclasses[d->tokens[pos.index] - CSET], matches);
+      else
+        {
+          if (d->tokens[pos.index] == MBCSET
+              || d->tokens[pos.index] == ANYCHAR)
+            {
+              /* ANYCHAR and MBCSET must match with a single character, so we
+                 must put it to d->states[s].mbps, which contains the positions
+                 which can match with a single character not a byte.  */
+              if (d->states[s].mbps.nelem == 0)
+                alloc_position_set (&d->states[s].mbps, 1);
+              insert (pos, &(d->states[s].mbps));
+            }
+          continue;
+        }
+
+      /* Some characters may need to be eliminated from matches because
+         they fail in the current context.  */
+      if (pos.constraint != NO_CONSTRAINT)
+        {
+          if (!SUCCEEDS_IN_CONTEXT (pos.constraint,
+                                    d->states[s].context, CTX_NEWLINE))
+            for (j = 0; j < CHARCLASS_WORDS; ++j)
+              matches[j] &= ~newline[j];
+          if (!SUCCEEDS_IN_CONTEXT (pos.constraint,
+                                    d->states[s].context, CTX_LETTER))
+            for (j = 0; j < CHARCLASS_WORDS; ++j)
+              matches[j] &= ~letters[j];
+          if (!SUCCEEDS_IN_CONTEXT (pos.constraint,
+                                    d->states[s].context, CTX_NONE))
+            for (j = 0; j < CHARCLASS_WORDS; ++j)
+              matches[j] &= letters[j] | newline[j];
+
+          /* If there are no characters left, there's no point in going on.  */
+          for (j = 0; j < CHARCLASS_WORDS && !matches[j]; ++j)
+            continue;
+          if (j == CHARCLASS_WORDS)
+            continue;
+        }
+
+#ifdef DEBUG
+      fprintf (stderr, " nextpos %zu:", pos.index);
+      prtok (d->tokens[pos.index]);
+      fprintf (stderr, " of");
+      for (j = 0; j < NOTCHAR; j++)
+        if (tstbit (j, matches))
+          fprintf (stderr, " 0x%02zx", j);
+      fprintf (stderr, "\n");
+#endif
+
+      for (j = 0; j < ngrps; ++j)
+        {
+          /* If matches contains a single character only, and the current
+             group's label doesn't contain that character, go on to the
+             next group.  */
+          if (d->tokens[pos.index] >= 0 && d->tokens[pos.index] < NOTCHAR
+              && !tstbit (d->tokens[pos.index], labels[j]))
+            continue;
+
+          /* Check if this group's label has a nonempty intersection with
+             matches.  */
+          intersectf = 0;
+          for (k = 0; k < CHARCLASS_WORDS; ++k)
+            intersectf |= intersect[k] = matches[k] & labels[j][k];
+          if (!intersectf)
+            continue;
+
+          /* It does; now find the set differences both ways.  */
+          leftoversf = matchesf = 0;
+          for (k = 0; k < CHARCLASS_WORDS; ++k)
+            {
+              /* Even an optimizing compiler can't know this for sure.  */
+              charclass_word match = matches[k], label = labels[j][k];
+
+              leftoversf |= leftovers[k] = ~match & label;
+              matchesf |= matches[k] = match & ~label;
+            }
+
+          /* If there were leftovers, create a new group labeled with them.  */
+          if (leftoversf)
+            {
+              copyset (leftovers, labels[ngrps]);
+              copyset (intersect, labels[j]);
+              grps[ngrps].elems = xnmalloc (d->nleaves,
+                                            sizeof *grps[ngrps].elems);
+              memcpy (grps[ngrps].elems, grps[j].elems,
+                      sizeof (grps[j].elems[0]) * grps[j].nelem);
+              grps[ngrps].nelem = grps[j].nelem;
+              ++ngrps;
+            }
+
+          /* Put the position in the current group.  The constraint is
+             irrelevant here.  */
+          grps[j].elems[grps[j].nelem++] = pos.index;
+
+          /* If every character matching the current position has been
+             accounted for, we're done.  */
+          if (!matchesf)
+            break;
+        }
+
+      /* If we've passed the last group, and there are still characters
+         unaccounted for, then we'll have to create a new group.  */
+      if (j == ngrps)
+        {
+          copyset (matches, labels[ngrps]);
+          zeroset (matches);
+          grps[ngrps].elems = xnmalloc (d->nleaves, sizeof *grps[ngrps].elems);
+          grps[ngrps].nelem = 1;
+          grps[ngrps].elems[0] = pos.index;
+          ++ngrps;
+        }
+    }
+
+  alloc_position_set (&follows, d->nleaves);
+  alloc_position_set (&tmp, d->nleaves);
+
+  /* If we are a searching matcher, the default transition is to a state
+     containing the positions of state 0, otherwise the default transition
+     is to fail miserably.  */
+  if (d->searchflag)
+    {
+      /* Find the state(s) corresponding to the positions of state 0.  */
+      copy (&d->states[0].elems, &follows);
+      separate_contexts = state_separate_contexts (&follows);
+      state = state_index (d, &follows, separate_contexts ^ CTX_ANY);
+      if (separate_contexts & CTX_NEWLINE)
+        state_newline = state_index (d, &follows, CTX_NEWLINE);
+      else
+        state_newline = state;
+      if (separate_contexts & CTX_LETTER)
+        state_letter = state_index (d, &follows, CTX_LETTER);
+      else
+        state_letter = state;
+
+      for (i = 0; i < NOTCHAR; ++i)
+        trans[i] = unibyte_word_constituent (i) ? state_letter : state;
+      trans[eolbyte] = state_newline;
+    }
+  else
+    for (i = 0; i < NOTCHAR; ++i)
+      trans[i] = -1;
+
+  for (i = 0; i < ngrps; ++i)
+    {
+      follows.nelem = 0;
+
+      /* Find the union of the follows of the positions of the group.
+         This is a hideously inefficient loop.  Fix it someday.  */
+      for (j = 0; j < grps[i].nelem; ++j)
+        for (k = 0; k < d->follows[grps[i].elems[j]].nelem; ++k)
+          insert (d->follows[grps[i].elems[j]].elems[k], &follows);
+
+      if (d->multibyte)
+        {
+          /* If a token in follows.elems is not 1st byte of a multibyte
+             character, or the states of follows must accept the bytes
+             which are not 1st byte of the multibyte character.
+             Then, if a state of follows encounter a byte, it must not be
+             a 1st byte of a multibyte character nor single byte character.
+             We cansel to add state[0].follows to next state, because
+             state[0] must accept 1st-byte
+
+             For example, we assume <sb a> is a certain single byte
+             character, <mb A> is a certain multibyte character, and the
+             codepoint of <sb a> equals the 2nd byte of the codepoint of
+             <mb A>.
+             When state[0] accepts <sb a>, state[i] transit to state[i+1]
+             by accepting accepts 1st byte of <mb A>, and state[i+1]
+             accepts 2nd byte of <mb A>, if state[i+1] encounter the
+             codepoint of <sb a>, it must not be <sb a> but 2nd byte of
+             <mb A>, so we cannot add state[0].  */
+
+          next_isnt_1st_byte = false;
+          for (j = 0; j < follows.nelem; ++j)
+            {
+              if (!(d->multibyte_prop[follows.elems[j].index] & 1))
+                {
+                  next_isnt_1st_byte = true;
+                  break;
+                }
+            }
+        }
+
+      /* If we are building a searching matcher, throw in the positions
+         of state 0 as well.  */
+      if (d->searchflag && (!d->multibyte || !next_isnt_1st_byte))
+        {
+          merge (&d->states[0].elems, &follows, &tmp);
+          copy (&tmp, &follows);
+        }
+
+      /* Find out if the new state will want any context information.  */
+      possible_contexts = charclass_context (labels[i]);
+      separate_contexts = state_separate_contexts (&follows);
+
+      /* Find the state(s) corresponding to the union of the follows.  */
+      if ((separate_contexts & possible_contexts) != possible_contexts)
+        state = state_index (d, &follows, separate_contexts ^ CTX_ANY);
+      else
+        state = -1;
+      if (separate_contexts & possible_contexts & CTX_NEWLINE)
+        state_newline = state_index (d, &follows, CTX_NEWLINE);
+      else
+        state_newline = state;
+      if (separate_contexts & possible_contexts & CTX_LETTER)
+        state_letter = state_index (d, &follows, CTX_LETTER);
+      else
+        state_letter = state;
+
+#ifdef DEBUG
+      fprintf (stderr, "group %zu\n nextpos:", i);
+      for (j = 0; j < grps[i].nelem; ++j)
+        {
+          fprintf (stderr, " %zu:", grps[i].elems[j]);
+          prtok (d->tokens[grps[i].elems[j]]);
+        }
+      fprintf (stderr, "\n follows:");
+      for (j = 0; j < follows.nelem; ++j)
+        {
+          fprintf (stderr, " %zu:", follows.elems[j].index);
+          prtok (d->tokens[follows.elems[j].index]);
+        }
+      fprintf (stderr, "\n states:");
+      if (possible_contexts & CTX_NEWLINE)
+        fprintf (stderr, " CTX_NEWLINE:%td", state_newline);
+      if (possible_contexts & CTX_LETTER)
+        fprintf (stderr, " CTX_LETTER:%td", state_letter);
+      if (possible_contexts & CTX_NONE)
+        fprintf (stderr, " CTX_NONE:%td", state);
+      fprintf (stderr, "\n");
+#endif
+
+      /* Set the transitions for each character in the current label.  */
+      for (j = 0; j < CHARCLASS_WORDS; ++j)
+        for (k = 0; k < CHARCLASS_WORD_BITS; ++k)
+          if (labels[i][j] >> k & 1)
+            {
+              int c = j * CHARCLASS_WORD_BITS + k;
+
+              if (c == eolbyte)
+                trans[c] = state_newline;
+              else if (unibyte_word_constituent (c))
+                trans[c] = state_letter;
+              else if (c < NOTCHAR)
+                trans[c] = state;
+            }
+    }
+
+#ifdef DEBUG
+  fprintf (stderr, "trans table %td", s);
+  for (i = 0; i < NOTCHAR; ++i)
+    {
+      if (!(i & 0xf))
+        fprintf (stderr, "\n");
+      fprintf (stderr, " %2td", trans[i]);
+    }
+  fprintf (stderr, "\n");
+#endif
+
+  for (i = 0; i < ngrps; ++i)
+    free (grps[i].elems);
+  free (follows.elems);
+  free (tmp.elems);
+}
+
+/* Make sure D's state arrays are large enough to hold NEW_STATE.  */
+static void
+realloc_trans_if_necessary (struct dfa *d, state_num new_state)
+{
+  state_num oldalloc = d->tralloc;
+  if (oldalloc <= new_state)
+    {
+      state_num **realtrans = d->trans ? d->trans - 1 : NULL;
+      size_t newalloc, newalloc1;
+      newalloc1 = new_state + 1;
+      realtrans = x2nrealloc (realtrans, &newalloc1, sizeof *realtrans);
+      realtrans[0] = NULL;
+      d->trans = realtrans + 1;
+      d->tralloc = newalloc = newalloc1 - 1;
+      d->fails = xnrealloc (d->fails, newalloc, sizeof *d->fails);
+      d->success = xnrealloc (d->success, newalloc, sizeof *d->success);
+      d->newlines = xnrealloc (d->newlines, newalloc, sizeof *d->newlines);
+      for (; oldalloc < newalloc; oldalloc++)
+        {
+          d->trans[oldalloc] = NULL;
+          d->fails[oldalloc] = NULL;
+        }
+    }
+}
+
+/* Some routines for manipulating a compiled dfa's transition tables.
+   Each state may or may not have a transition table; if it does, and it
+   is a non-accepting state, then d->trans[state] points to its table.
+   If it is an accepting state then d->fails[state] points to its table.
+   If it has no table at all, then d->trans[state] is NULL.
+   TODO: Improve this comment, get rid of the unnecessary redundancy.  */
+
+static void
+build_state (state_num s, struct dfa *d)
+{
+  state_num *trans;             /* The new transition table.  */
+  state_num i, maxstate;
+
+  /* Set an upper limit on the number of transition tables that will ever
+     exist at once.  1024 is arbitrary.  The idea is that the frequently
+     used transition tables will be quickly rebuilt, whereas the ones that
+     were only needed once or twice will be cleared away.  However, do not
+     clear the initial D->min_trcount states, since they are always used.  */
+  if (d->trcount >= 1024)
+    {
+      for (i = d->min_trcount; i < d->tralloc; ++i)
+        {
+          free (d->trans[i]);
+          free (d->fails[i]);
+          d->trans[i] = d->fails[i] = NULL;
+        }
+      d->trcount = d->min_trcount;
+    }
+
+  ++d->trcount;
+
+  /* Set up the success bits for this state.  */
+  d->success[s] = 0;
+  if (ACCEPTS_IN_CONTEXT (d->states[s].context, CTX_NEWLINE, s, *d))
+    d->success[s] |= CTX_NEWLINE;
+  if (ACCEPTS_IN_CONTEXT (d->states[s].context, CTX_LETTER, s, *d))
+    d->success[s] |= CTX_LETTER;
+  if (ACCEPTS_IN_CONTEXT (d->states[s].context, CTX_NONE, s, *d))
+    d->success[s] |= CTX_NONE;
+
+  trans = xmalloc (NOTCHAR * sizeof *trans);
+  dfastate (s, d, trans);
+
+  /* Now go through the new transition table, and make sure that the trans
+     and fail arrays are allocated large enough to hold a pointer for the
+     largest state mentioned in the table.  */
+  maxstate = -1;
+  for (i = 0; i < NOTCHAR; ++i)
+    if (maxstate < trans[i])
+      maxstate = trans[i];
+  realloc_trans_if_necessary (d, maxstate);
+
+  /* Keep the newline transition in a special place so we can use it as
+     a sentinel.  */
+  d->newlines[s] = trans[eolbyte];
+  trans[eolbyte] = -1;
+
+  if (ACCEPTING (s, *d))
+    d->fails[s] = trans;
+  else
+    d->trans[s] = trans;
+}
+
+/* Multibyte character handling sub-routines for dfaexec.  */
+
+/* Consume a single byte and transit state from 's' to '*next_state'.
+   This function is almost same as the state transition routin in dfaexec.
+   But state transition is done just once, otherwise matching succeed or
+   reach the end of the buffer.  */
+static state_num
+transit_state_singlebyte (struct dfa *d, state_num s, unsigned char const **pp)
+{
+  state_num *t;
+
+  if (**pp == eolbyte)
+    {
+      /* S is always an initial state in transit_state, so the
+         transition table for the state must have been built already.  */
+      assert (d->trans[s] || d->fails[s]);
+
+      ++*pp;
+      return d->newlines[s];
+    }
+
+  if (d->trans[s])
+    t = d->trans[s];
+  else if (d->fails[s])
+    t = d->fails[s];
+  else
+    {
+      build_state (s, d);
+      if (d->trans[s])
+        t = d->trans[s];
+      else
+        {
+          t = d->fails[s];
+          assert (t);
+        }
+    }
+
+  return t[*(*pp)++];
+}
+
+/* Transit state from s, then return new state and update the pointer of
+   the buffer.  This function is for a period operator which can match a
+   multi-byte character.  */
+static state_num
+transit_state (struct dfa *d, state_num s, unsigned char const **pp,
+               unsigned char const *end)
+{
+  state_num s1, s2;
+  wint_t wc;
+  size_t i, j;
+  int k;
+  int separate_contexts;
+
+  int mbclen = mbs_to_wchar (&wc, (char const *) *pp, end - *pp, d);
+  int context = wc == eolbyte ? CTX_NEWLINE : CTX_NONE;
+
+  /* This state has some operators which can match a multibyte character.  */
+  d->mb_follows.nelem = 0;
+
+  /* Calculate the state which can be reached from the state 's' by
+     consuming 'mbclen' single bytes from the buffer.  */
+  s1 = s;
+  for (k = 0; k < mbclen; k++)
+    {
+      s2 = s1;
+      s1 = transit_state_singlebyte (d, s2, pp);
+    }
+  copy (&d->states[s1].elems, &d->mb_follows);
+
+  /* Add all of the positions which can be reached from 's' by consuming
+     a single character.  */
+  for (i = 0; i < d->states[s].mbps.nelem; i++)
+    {
+      if (!SUCCEEDS_IN_CONTEXT (d->states[s].mbps.elems[i].constraint,
+                                d->states[s].context, context))
+        continue;
+      for (j = 0; j < d->follows[d->states[s].mbps.elems[i].index].nelem; j++)
+        insert (d->follows[d->states[s].mbps.elems[i].index].elems[j],
+                &d->mb_follows);
+    }
+
+  separate_contexts = state_separate_contexts (&d->mb_follows);
+  if (! (context == CTX_NEWLINE || separate_contexts & CTX_NEWLINE))
+    context = separate_contexts ^ CTX_ANY;
+  s1 = state_index (d, &d->mb_follows, context);
+  realloc_trans_if_necessary (d, s1);
+
+  return s1;
+}
+
+/* The initial state may encounter a byte which is not a single byte character
+   nor the first byte of a multibyte character.  But it is incorrect for the
+   initial state to accept such a byte.  For example, in Shift JIS the regular
+   expression "\\" accepts the codepoint 0x5c, but should not accept the second
+   byte of the codepoint 0x815c.  Then the initial state must skip the bytes
+   that are not a single byte character nor the first byte of a multibyte
+   character.
+
+   Given DFA state d, use mbs_to_wchar to advance MBP until it reaches
+   or exceeds P, and return the advanced MBP.  If WCP is non-NULL and
+   the result is greater than P, set *WCP to the final wide character
+   processed, or to WEOF if no wide character is processed.  Otherwise,
+   if WCP is non-NULL, *WCP may or may not be updated.
+
+   Both P and MBP must be no larger than END.  */
+static unsigned char const *
+skip_remains_mb (struct dfa *d, unsigned char const *p,
+                 unsigned char const *mbp, char const *end, wint_t *wcp)
+{
+  wint_t wc = WEOF;
+  if (never_trail[*p])
+    return p;
+  while (mbp < p)
+    mbp += mbs_to_wchar (&wc, (char const *) mbp,
+                         end - (char const *) mbp, d);
+  if (wcp != NULL)
+    *wcp = wc;
+  return mbp;
+}
+
+/* Search through a buffer looking for a match to the struct dfa *D.
+   Find the first occurrence of a string matching the regexp in the
+   buffer, and the shortest possible version thereof.  Return a pointer to
+   the first character after the match, or NULL if none is found.  BEGIN
+   points to the beginning of the buffer, and END points to the first byte
+   after its end.  Note however that we store a sentinel byte (usually
+   newline) in *END, so the actual buffer must be one byte longer.
+   When ALLOW_NL, newlines may appear in the matching string.
+   If COUNT is non-NULL, increment *COUNT once for each newline processed.
+   If MULTIBYTE, the input consists of multibyte characters and/or
+   encoding-error bytes.  Otherwise, it consists of single-byte characters.
+   Here is the list of features that make this DFA matcher punt:
+    - [M-N] range in non-simple locale: regex is up to 25% faster on [a-z]
+    - [^...] in non-simple locale
+    - [[=foo=]] or [[.foo.]]
+    - [[:alpha:]] etc. in multibyte locale (except [[:digit:]] works OK)
+    - back-reference: (.)\1
+    - word-delimiter in multibyte locale: \<, \>, \b, \B
+   See using_simple_locale for the definition of "simple locale".  */
+
+static inline char *
+dfaexec_main (struct dfa *d, char const *begin, char *end, bool allow_nl,
+              size_t *count, bool multibyte)
+{
+  state_num s, s1;              /* Current state.  */
+  unsigned char const *p, *mbp; /* Current input character.  */
+  state_num **trans, *t;        /* Copy of d->trans so it can be optimized
+                                   into a register.  */
+  unsigned char eol = eolbyte;  /* Likewise for eolbyte.  */
+  unsigned char saved_end;
+  size_t nlcount = 0;
+
+  if (!d->tralloc)
+    {
+      realloc_trans_if_necessary (d, 1);
+      build_state (0, d);
+    }
+
+  s = s1 = 0;
+  p = mbp = (unsigned char const *) begin;
+  trans = d->trans;
+  saved_end = *(unsigned char *) end;
+  *end = eol;
+
+  if (multibyte)
+    {
+      memset (&d->mbs, 0, sizeof d->mbs);
+      if (d->mb_follows.alloc == 0)
+        alloc_position_set (&d->mb_follows, d->nleaves);
+    }
+
+  for (;;)
+    {
+      if (multibyte)
+        {
+          while ((t = trans[s]) != NULL)
+            {
+              s1 = s;
+
+              if (s < d->min_trcount)
+                {
+                  if (d->min_trcount == 1)
+                    {
+                      if (d->states[s].mbps.nelem == 0)
+                        {
+                          do
+                            {
+                              while (t[*p] == 0)
+                                p++;
+                              p = mbp = skip_remains_mb (d, p, mbp, end, NULL);
+                            }
+                          while (t[*p] == 0);
+                        }
+                      else
+                        p = mbp = skip_remains_mb (d, p, mbp, end, NULL);
+                    }
+                  else
+                    {
+                      wint_t wc;
+                      mbp = skip_remains_mb (d, p, mbp, end, &wc);
+
+                      /* If d->min_trcount is greater than 1, maybe
+                         transit to another initial state after skip.  */
+                      if (p < mbp)
+                        {
+                          /* It's CTX_LETTER or CTX_NONE.  CTX_NEWLINE
+                             cannot happen, as we assume that a newline
+                             is always a single byte character.  */
+                          s1 = s = d->initstate_notbol;
+                          p = mbp;
+                        }
+                    }
+                }
+
+              if (d->states[s].mbps.nelem == 0 || (*p == eol && !allow_nl)
+                  || (*p == '\n' && !(syntax_bits & RE_DOT_NEWLINE))
+                  || (*p == '\0' && (syntax_bits & RE_DOT_NOT_NULL))
+                  || (char *) p >= end)
+                {
+                  /* If an input character does not match ANYCHAR, do it
+                     like a single-byte character.  */
+                  s = t[*p++];
+                }
+              else
+                {
+                  s = transit_state (d, s, &p, (unsigned char *) end);
+                  if (s >= 0 && p[-1] == eol)
+                    nlcount++;
+                  mbp = p;
+                  trans = d->trans;
+                }
+            }
+        }
+      else
+        {
+          if (s == 0 && (t = trans[s]) != NULL)
+            {
+              while (t[*p] == 0)
+                p++;
+              s1 = 0;
+              s = t[*p++];
+            }
+
+          while ((t = trans[s]) != NULL)
+            {
+              s1 = t[*p++];
+              if ((t = trans[s1]) == NULL)
+                {
+                  state_num tmp = s;
+                  s = s1;
+                  s1 = tmp;     /* swap */
+                  break;
+                }
+              s = t[*p++];
+            }
+        }
+
+      if (s < 0)
+        {
+          if ((char *) p > end || p[-1] != eol || d->newlines[s1] < 0)
+            {
+              p = NULL;
+              goto done;
+            }
+
+          /* The previous character was a newline, count it, and skip
+             checking of multibyte character boundary until here.  */
+          nlcount++;
+          mbp = p;
+
+          s = allow_nl ? d->newlines[s1] : 0;
+        }
+      else if (d->fails[s])
+        {
+          if (d->success[s] & sbit[*p])
+            goto done;
+
+          s1 = s;
+          if (!multibyte || d->states[s].mbps.nelem == 0
+              || (*p == eol && !allow_nl)
+              || (*p == '\n' && !(syntax_bits & RE_DOT_NEWLINE))
+              || (*p == '\0' && (syntax_bits & RE_DOT_NOT_NULL))
+              || (char *) p >= end)
+            {
+              /* If a input character does not match ANYCHAR, do it
+                 like a single-byte character.  */
+              s = d->fails[s][*p++];
+            }
+          else
+            {
+              s = transit_state (d, s, &p, (unsigned char *) end);
+              if (s >= 0 && p[-1] == eol)
+                nlcount++;
+              mbp = p;
+              trans = d->trans;
+            }
+        }
+      else
+        {
+          build_state (s, d);
+          trans = d->trans;
+        }
+    }
+
+ done:
+  if (count)
+    *count += nlcount;
+  *end = saved_end;
+  return (char *) p;
+}
+
+/* Specialized versions of dfaexec for multibyte and single-byte cases.
+   This is for performance, as dfaexec_main is an inline function.  */
+
+static char *
+dfaexec_mb (struct dfa *d, char const *begin, char *end,
+            bool allow_nl, size_t *count, bool *backref)
+{
+  return dfaexec_main (d, begin, end, allow_nl, count, true);
+}
+
+static char *
+dfaexec_sb (struct dfa *d, char const *begin, char *end,
+            bool allow_nl, size_t *count, bool *backref)
+{
+  return dfaexec_main (d, begin, end, allow_nl, count, false);
+}
+
+/* Always set *BACKREF and return BEGIN.  Use this wrapper for
+   any regexp that uses a construct not supported by this code.  */
+static char *
+dfaexec_noop (struct dfa *d, char const *begin, char *end,
+              bool allow_nl, size_t *count, bool *backref)
+{
+  *backref = true;
+  return (char *) begin;
+}
+
+/* Like dfaexec_main (D, BEGIN, END, ALLOW_NL, COUNT, D->multibyte),
+   but faster and set *BACKREF if the DFA code does not support this
+   regexp usage.  */
+
+char *
+dfaexec (struct dfa *d, char const *begin, char *end,
+         bool allow_nl, size_t *count, bool *backref)
+{
+  return d->dfaexec (d, begin, end, allow_nl, count, backref);
+}
+
+struct dfa *
+dfasuperset (struct dfa const *d)
+{
+  return d->superset;
+}
+
+bool
+dfaisfast (struct dfa const *d)
+{
+  return d->fast;
+}
+
+static void
+free_mbdata (struct dfa *d)
+{
+  size_t i;
+
+  free (d->multibyte_prop);
+
+  for (i = 0; i < d->nmbcsets; ++i)
+    {
+      struct mb_char_classes *p = &(d->mbcsets[i]);
+      free (p->chars);
+    }
+
+  free (d->mbcsets);
+  free (d->mb_follows.elems);
+}
+
+/* Initialize the components of a dfa that the other routines don't
+   initialize for themselves.  */
+static void
+dfainit (struct dfa *d)
+{
+  memset (d, 0, sizeof *d);
+  d->multibyte = MB_CUR_MAX > 1;
+  d->dfaexec = d->multibyte ? dfaexec_mb : dfaexec_sb;
+  d->fast = !d->multibyte;
+}
+
+/* Return true if every construct in D is supported by this DFA matcher.  */
+static bool _GL_ATTRIBUTE_PURE
+dfa_supported (struct dfa const *d)
+{
+  for (size_t i = 0; i < d->tindex; i++)
+    {
+      switch (d->tokens[i])
+        {
+        case BEGWORD:
+        case ENDWORD:
+        case LIMWORD:
+        case NOTLIMWORD:
+          if (!d->multibyte)
+            continue;
+          /* fallthrough */
+
+        case BACKREF:
+        case MBCSET:
+          return false;
+        }
+    }
+  return true;
+}
+
+static void
+dfaoptimize (struct dfa *d)
+{
+  size_t i;
+  bool have_backref = false;
+
+  if (!using_utf8 ())
+    return;
+
+  for (i = 0; i < d->tindex; ++i)
+    {
+      switch (d->tokens[i])
+        {
+        case ANYCHAR:
+          /* Lowered.  */
+          abort ();
+        case BACKREF:
+          have_backref = true;
+          break;
+        case MBCSET:
+          /* Requires multi-byte algorithm.  */
+          return;
+        default:
+          break;
+        }
+    }
+
+  if (!have_backref && d->superset)
+    {
+      /* The superset DFA is not likely to be much faster, so remove it.  */
+      dfafree (d->superset);
+      free (d->superset);
+      d->superset = NULL;
+    }
+
+  free_mbdata (d);
+  d->multibyte = false;
+  d->dfaexec = dfaexec_sb;
+  d->fast = true;
+}
+
+static void
+dfassbuild (struct dfa *d)
+{
+  size_t i, j;
+  charclass ccl;
+  bool have_achar = false;
+  bool have_nchar = false;
+  struct dfa *sup = dfaalloc ();
+
+  *sup = *d;
+  sup->multibyte = false;
+  sup->dfaexec = dfaexec_sb;
+  sup->multibyte_prop = NULL;
+  sup->mbcsets = NULL;
+  sup->superset = NULL;
+  sup->states = NULL;
+  sup->sindex = 0;
+  sup->follows = NULL;
+  sup->tralloc = 0;
+  sup->trans = NULL;
+  sup->fails = NULL;
+  sup->success = NULL;
+  sup->newlines = NULL;
+
+  sup->charclasses = xnmalloc (sup->calloc, sizeof *sup->charclasses);
+  if (d->cindex)
+    {
+      memcpy (sup->charclasses, d->charclasses,
+              d->cindex * sizeof *sup->charclasses);
+    }
+
+  sup->tokens = xnmalloc (d->tindex, 2 * sizeof *sup->tokens);
+  sup->talloc = d->tindex * 2;
+
+  for (i = j = 0; i < d->tindex; i++)
+    {
+      switch (d->tokens[i])
+        {
+        case ANYCHAR:
+        case MBCSET:
+        case BACKREF:
+          zeroset (ccl);
+          notset (ccl);
+          sup->tokens[j++] = CSET + dfa_charclass_index (sup, ccl);
+          sup->tokens[j++] = STAR;
+          if (d->tokens[i + 1] == QMARK || d->tokens[i + 1] == STAR
+              || d->tokens[i + 1] == PLUS)
+            i++;
+          have_achar = true;
+          break;
+        case BEGWORD:
+        case ENDWORD:
+        case LIMWORD:
+        case NOTLIMWORD:
+          if (d->multibyte)
+            {
+              /* These constraints aren't supported in a multibyte locale.
+                 Ignore them in the superset DFA.  */
+              sup->tokens[j++] = EMPTY;
+              break;
+            }
+        default:
+          sup->tokens[j++] = d->tokens[i];
+          if ((0 <= d->tokens[i] && d->tokens[i] < NOTCHAR)
+              || d->tokens[i] >= CSET)
+            have_nchar = true;
+          break;
+        }
+    }
+  sup->tindex = j;
+
+  if (have_nchar && (have_achar || d->multibyte))
+    d->superset = sup;
+  else
+    {
+      dfafree (sup);
+      free (sup);
+    }
+}
+
+/* Parse and analyze a single string of the given length.  */
+void
+dfacomp (char const *s, size_t len, struct dfa *d, bool searchflag)
+{
+  dfainit (d);
+  dfaparse (s, len, d);
+  dfassbuild (d);
+
+  if (dfa_supported (d))
+    {
+      dfaoptimize (d);
+      dfaanalyze (d, searchflag);
+    }
+  else
+    {
+      d->dfaexec = dfaexec_noop;
+    }
+
+  if (d->superset)
+    {
+      d->fast = true;
+      dfaanalyze (d->superset, searchflag);
+    }
+}
+
+/* Free the storage held by the components of a dfa.  */
+void
+dfafree (struct dfa *d)
+{
+  size_t i;
+
+  free (d->charclasses);
+  free (d->tokens);
+
+  if (d->multibyte)
+    free_mbdata (d);
+
+  for (i = 0; i < d->sindex; ++i)
+    {
+      free (d->states[i].elems.elems);
+      free (d->states[i].mbps.elems);
+    }
+  free (d->states);
+
+  if (d->follows)
+    {
+      for (i = 0; i < d->tindex; ++i)
+        free (d->follows[i].elems);
+      free (d->follows);
+    }
+
+  if (d->trans)
+    {
+      for (i = 0; i < d->tralloc; ++i)
+        {
+          free (d->trans[i]);
+          free (d->fails[i]);
+        }
+
+      free (d->trans - 1);
+      free (d->fails);
+      free (d->newlines);
+      free (d->success);
+    }
+
+  if (d->superset)
+    dfafree (d->superset);
+}
+
+/* Having found the postfix representation of the regular expression,
+   try to find a long sequence of characters that must appear in any line
+   containing the r.e.
+   Finding a "longest" sequence is beyond the scope here;
+   we take an easy way out and hope for the best.
+   (Take "(ab|a)b"--please.)
+
+   We do a bottom-up calculation of sequences of characters that must appear
+   in matches of r.e.'s represented by trees rooted at the nodes of the postfix
+   representation:
+        sequences that must appear at the left of the match ("left")
+        sequences that must appear at the right of the match ("right")
+        lists of sequences that must appear somewhere in the match ("in")
+        sequences that must constitute the match ("is")
+
+   When we get to the root of the tree, we use one of the longest of its
+   calculated "in" sequences as our answer.
+
+   The sequences calculated for the various types of node (in pseudo ANSI c)
+   are shown below.  "p" is the operand of unary operators (and the left-hand
+   operand of binary operators); "q" is the right-hand operand of binary
+   operators.
+
+   "ZERO" means "a zero-length sequence" below.
+
+        Type	left		right		is		in
+        ----	----		-----		--		--
+        char c	# c		# c		# c		# c
+
+        ANYCHAR	ZERO		ZERO		ZERO		ZERO
+
+        MBCSET	ZERO		ZERO		ZERO		ZERO
+
+        CSET	ZERO		ZERO		ZERO		ZERO
+
+        STAR	ZERO		ZERO		ZERO		ZERO
+
+        QMARK	ZERO		ZERO		ZERO		ZERO
+
+        PLUS	p->left		p->right	ZERO		p->in
+
+        CAT	(p->is==ZERO)?	(q->is==ZERO)?	(p->is!=ZERO &&	p->in plus
+                p->left :	q->right :	q->is!=ZERO) ?	q->in plus
+                p->is##q->left	p->right##q->is	p->is##q->is : p->right##q->left
+                                                ZERO
+
+        OR	longest common	longest common	(do p->is and substrings common
+                leading		trailing	to q->is have same p->in and
+                (sub)sequence	(sub)sequence	q->in length and content) ?
+                of p->left	of p->right
+                and q->left	and q->right	p->is : NULL
+
+   If there's anything else we recognize in the tree, all four sequences get set
+   to zero-length sequences.  If there's something we don't recognize in the
+   tree, we just return a zero-length sequence.
+
+   Break ties in favor of infrequent letters (choosing 'zzz' in preference to
+   'aaa')?
+
+   And ... is it here or someplace that we might ponder "optimizations" such as
+        egrep 'psi|epsilon'	->	egrep 'psi'
+        egrep 'pepsi|epsilon'	->	egrep 'epsi'
+                                        (Yes, we now find "epsi" as a "string
+                                        that must occur", but we might also
+                                        simplify the *entire* r.e. being sought)
+        grep '[c]'		->	grep 'c'
+        grep '(ab|a)b'		->	grep 'ab'
+        grep 'ab*'		->	grep 'a'
+        grep 'a*b'		->	grep 'b'
+
+   There are several issues:
+
+   Is optimization easy (enough)?
+
+   Does optimization actually accomplish anything,
+   or is the automaton you get from "psi|epsilon" (for example)
+   the same as the one you get from "psi" (for example)?
+
+   Are optimizable r.e.'s likely to be used in real-life situations
+   (something like 'ab*' is probably unlikely; something like is
+   'psi|epsilon' is likelier)?  */
+
+static char *
+icatalloc (char *old, char const *new)
+{
+  char *result;
+  size_t oldsize;
+  size_t newsize = strlen (new);
+  if (newsize == 0)
+    return old;
+  oldsize = strlen (old);
+  result = xrealloc (old, oldsize + newsize + 1);
+  memcpy (result + oldsize, new, newsize + 1);
+  return result;
+}
+
+static void
+freelist (char **cpp)
+{
+  while (*cpp)
+    free (*cpp++);
+}
+
+static char **
+enlist (char **cpp, char *new, size_t len)
+{
+  size_t i, j;
+  new = memcpy (xmalloc (len + 1), new, len);
+  new[len] = '\0';
+  /* Is there already something in the list that's new (or longer)?  */
+  for (i = 0; cpp[i] != NULL; ++i)
+    if (strstr (cpp[i], new) != NULL)
+      {
+        free (new);
+        return cpp;
+      }
+  /* Eliminate any obsoleted strings.  */
+  j = 0;
+  while (cpp[j] != NULL)
+    if (strstr (new, cpp[j]) == NULL)
+      ++j;
+    else
+      {
+        free (cpp[j]);
+        if (--i == j)
+          break;
+        cpp[j] = cpp[i];
+        cpp[i] = NULL;
+      }
+  /* Add the new string.  */
+  cpp = xnrealloc (cpp, i + 2, sizeof *cpp);
+  cpp[i] = new;
+  cpp[i + 1] = NULL;
+  return cpp;
+}
+
+/* Given pointers to two strings, return a pointer to an allocated
+   list of their distinct common substrings.  */
+static char **
+comsubs (char *left, char const *right)
+{
+  char **cpp = xzalloc (sizeof *cpp);
+  char *lcp;
+
+  for (lcp = left; *lcp != '\0'; ++lcp)
+    {
+      size_t len = 0;
+      char *rcp = strchr (right, *lcp);
+      while (rcp != NULL)
+        {
+          size_t i;
+          for (i = 1; lcp[i] != '\0' && lcp[i] == rcp[i]; ++i)
+            continue;
+          if (i > len)
+            len = i;
+          rcp = strchr (rcp + 1, *lcp);
+        }
+      if (len != 0)
+        cpp = enlist (cpp, lcp, len);
+    }
+  return cpp;
+}
+
+static char **
+addlists (char **old, char **new)
+{
+  for (; *new; new++)
+    old = enlist (old, *new, strlen (*new));
+  return old;
+}
+
+/* Given two lists of substrings, return a new list giving substrings
+   common to both.  */
+static char **
+inboth (char **left, char **right)
+{
+  char **both = xzalloc (sizeof *both);
+  size_t lnum, rnum;
+
+  for (lnum = 0; left[lnum] != NULL; ++lnum)
+    {
+      for (rnum = 0; right[rnum] != NULL; ++rnum)
+        {
+          char **temp = comsubs (left[lnum], right[rnum]);
+          both = addlists (both, temp);
+          freelist (temp);
+          free (temp);
+        }
+    }
+  return both;
+}
+
+typedef struct must must;
+
+struct must
+{
+  char **in;
+  char *left;
+  char *right;
+  char *is;
+  bool begline;
+  bool endline;
+  must *prev;
+};
+
+static must *
+allocmust (must *mp, size_t size)
+{
+  must *new_mp = xmalloc (sizeof *new_mp);
+  new_mp->in = xzalloc (sizeof *new_mp->in);
+  new_mp->left = xzalloc (size);
+  new_mp->right = xzalloc (size);
+  new_mp->is = xzalloc (size);
+  new_mp->begline = false;
+  new_mp->endline = false;
+  new_mp->prev = mp;
+  return new_mp;
+}
+
+static void
+resetmust (must *mp)
+{
+  freelist (mp->in);
+  mp->in[0] = NULL;
+  mp->left[0] = mp->right[0] = mp->is[0] = '\0';
+  mp->begline = false;
+  mp->endline = false;
+}
+
+static void
+freemust (must *mp)
+{
+  freelist (mp->in);
+  free (mp->in);
+  free (mp->left);
+  free (mp->right);
+  free (mp->is);
+  free (mp);
+}
+
+struct dfamust *
+dfamust (struct dfa const *d)
+{
+  must *mp = NULL;
+  char const *result = "";
+  size_t i;
+  bool exact = false;
+  bool begline = false;
+  bool endline = false;
+  bool need_begline = false;
+  bool need_endline = false;
+  bool case_fold_unibyte = case_fold && MB_CUR_MAX == 1;
+
+  for (size_t ri = 0; ri < d->tindex; ++ri)
+    {
+      token t = d->tokens[ri];
+      switch (t)
+        {
+        case BEGLINE:
+          mp = allocmust (mp, 2);
+          mp->begline = true;
+          need_begline = true;
+          break;
+        case ENDLINE:
+          mp = allocmust (mp, 2);
+          mp->endline = true;
+          need_endline = true;
+          break;
+        case LPAREN:
+        case RPAREN:
+          assert (!"neither LPAREN nor RPAREN may appear here");
+
+        case EMPTY:
+        case BEGWORD:
+        case ENDWORD:
+        case LIMWORD:
+        case NOTLIMWORD:
+        case BACKREF:
+        case ANYCHAR:
+        case MBCSET:
+          mp = allocmust (mp, 2);
+          break;
+
+        case STAR:
+        case QMARK:
+          resetmust (mp);
+          break;
+
+        case OR:
+          {
+            char **new;
+            must *rmp = mp;
+            must *lmp = mp = mp->prev;
+            size_t j, ln, rn, n;
+
+            /* Guaranteed to be.  Unlikely, but ...  */
+            if (STREQ (lmp->is, rmp->is))
+              {
+                lmp->begline &= rmp->begline;
+                lmp->endline &= rmp->endline;
+              }
+            else
+              {
+                lmp->is[0] = '\0';
+                lmp->begline = false;
+                lmp->endline = false;
+              }
+            /* Left side--easy */
+            i = 0;
+            while (lmp->left[i] != '\0' && lmp->left[i] == rmp->left[i])
+              ++i;
+            lmp->left[i] = '\0';
+            /* Right side */
+            ln = strlen (lmp->right);
+            rn = strlen (rmp->right);
+            n = ln;
+            if (n > rn)
+              n = rn;
+            for (i = 0; i < n; ++i)
+              if (lmp->right[ln - i - 1] != rmp->right[rn - i - 1])
+                break;
+            for (j = 0; j < i; ++j)
+              lmp->right[j] = lmp->right[(ln - i) + j];
+            lmp->right[j] = '\0';
+            new = inboth (lmp->in, rmp->in);
+            freelist (lmp->in);
+            free (lmp->in);
+            lmp->in = new;
+            freemust (rmp);
+          }
+          break;
+
+        case PLUS:
+          mp->is[0] = '\0';
+          break;
+
+        case END:
+          assert (!mp->prev);
+          for (i = 0; mp->in[i] != NULL; ++i)
+            if (strlen (mp->in[i]) > strlen (result))
+              result = mp->in[i];
+          if (STREQ (result, mp->is))
+            {
+              if ((!need_begline || mp->begline) && (!need_endline
+                                                     || mp->endline))
+                exact = true;
+              begline = mp->begline;
+              endline = mp->endline;
+            }
+          goto done;
+
+        case CAT:
+          {
+            must *rmp = mp;
+            must *lmp = mp = mp->prev;
+
+            /* In.  Everything in left, plus everything in
+               right, plus concatenation of
+               left's right and right's left.  */
+            lmp->in = addlists (lmp->in, rmp->in);
+            if (lmp->right[0] != '\0' && rmp->left[0] != '\0')
+              {
+                size_t lrlen = strlen (lmp->right);
+                size_t rllen = strlen (rmp->left);
+                char *tp = xmalloc (lrlen + rllen);
+                memcpy (tp, lmp->right, lrlen);
+                memcpy (tp + lrlen, rmp->left, rllen);
+                lmp->in = enlist (lmp->in, tp, lrlen + rllen);
+                free (tp);
+              }
+            /* Left-hand */
+            if (lmp->is[0] != '\0')
+              lmp->left = icatalloc (lmp->left, rmp->left);
+            /* Right-hand */
+            if (rmp->is[0] == '\0')
+              lmp->right[0] = '\0';
+            lmp->right = icatalloc (lmp->right, rmp->right);
+            /* Guaranteed to be */
+            if ((lmp->is[0] != '\0' || lmp->begline)
+                && (rmp->is[0] != '\0' || rmp->endline))
+              {
+                lmp->is = icatalloc (lmp->is, rmp->is);
+                lmp->endline = rmp->endline;
+              }
+            else
+              {
+                lmp->is[0] = '\0';
+                lmp->begline = false;
+                lmp->endline = false;
+              }
+            freemust (rmp);
+          }
+          break;
+
+        case '\0':
+          /* Not on *my* shift.  */
+          goto done;
+
+        default:
+          if (CSET <= t)
+            {
+              /* If T is a singleton, or if case-folding in a unibyte
+                 locale and T's members all case-fold to the same char,
+                 convert T to one of its members.  Otherwise, do
+                 nothing further with T.  */
+              charclass *ccl = &d->charclasses[t - CSET];
+              int j;
+              for (j = 0; j < NOTCHAR; j++)
+                if (tstbit (j, *ccl))
+                  break;
+              if (! (j < NOTCHAR))
+                {
+                  mp = allocmust (mp, 2);
+                  break;
+                }
+              t = j;
+              while (++j < NOTCHAR)
+                if (tstbit (j, *ccl)
+                    && ! (case_fold_unibyte
+                          && toupper (j) == toupper (t)))
+                  break;
+              if (j < NOTCHAR)
+                {
+                  mp = allocmust (mp, 2);
+                  break;
+                }
+            }
+
+          size_t rj = ri + 2;
+          if (d->tokens[ri + 1] == CAT)
+            {
+              for (; rj < d->tindex - 1; rj += 2)
+                {
+                  if ((rj != ri && (d->tokens[rj] <= 0
+                                    || NOTCHAR <= d->tokens[rj]))
+                      || d->tokens[rj + 1] != CAT)
+                    break;
+                }
+            }
+          mp = allocmust (mp, ((rj - ri) >> 1) + 1);
+          mp->is[0] = mp->left[0] = mp->right[0]
+            = case_fold_unibyte ? toupper (t) : t;
+
+          for (i = 1; ri + 2 < rj; i++)
+            {
+              ri += 2;
+              t = d->tokens[ri];
+              mp->is[i] = mp->left[i] = mp->right[i]
+                = case_fold_unibyte ? toupper (t) : t;
+            }
+          mp->is[i] = mp->left[i] = mp->right[i] = '\0';
+          mp->in = enlist (mp->in, mp->is, i);
+          break;
+        }
+    }
+ done:;
+
+  struct dfamust *dm = NULL;
+  if (*result)
+    {
+      dm = xmalloc (sizeof *dm);
+      dm->exact = exact;
+      dm->begline = begline;
+      dm->endline = endline;
+      dm->must = xstrdup (result);
+    }
+
+  while (mp)
+    {
+      must *prev = mp->prev;
+      freemust (mp);
+      mp = prev;
+    }
+
+  return dm;
+}
+
+void
+dfamustfree (struct dfamust *dm)
+{
+  free (dm->must);
+  free (dm);
+}
+
+struct dfa *
+dfaalloc (void)
+{
+  return xmalloc (sizeof (struct dfa));
+}
+
+/* vim:set shiftwidth=2: */
diff --git a/sed/dfa.h b/sed/dfa.h
new file mode 100644
index 0000000..60da0e4
--- /dev/null
+++ b/sed/dfa.h
@@ -0,0 +1,103 @@
+/* dfa.h - declarations for GNU deterministic regexp compiler
+   Copyright (C) 1988, 1998, 2007, 2009-2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc.,
+   51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA */
+
+/* Written June, 1988 by Mike Haertel */
+
+#include <regex.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+#include "xalloc.h" /* for _GL_ATTRIBUTE_MALLOC */
+
+/* Element of a list of strings, at least one of which is known to
+   appear in any R.E. matching the DFA. */
+struct dfamust
+{
+  bool exact;
+  bool begline;
+  bool endline;
+  char *must;
+};
+
+/* The dfa structure. It is completely opaque. */
+struct dfa;
+
+/* Entry points. */
+
+/* Allocate a struct dfa.  The struct dfa is completely opaque.
+   The returned pointer should be passed directly to free() after
+   calling dfafree() on it. */
+extern struct dfa *dfaalloc (void) _GL_ATTRIBUTE_MALLOC;
+
+/* Build and return the struct dfamust from the given struct dfa. */
+extern struct dfamust *dfamust (struct dfa const *);
+
+/* Free the storage held by the components of a struct dfamust. */
+extern void dfamustfree (struct dfamust *);
+
+/* dfasyntax() takes three arguments; the first sets the syntax bits described
+   earlier in this file, the second sets the case-folding flag, and the
+   third specifies the line terminator. */
+extern void dfasyntax (reg_syntax_t, bool, unsigned char);
+
+/* Compile the given string of the given length into the given struct dfa.
+   Final argument is a flag specifying whether to build a searching or an
+   exact matcher. */
+extern void dfacomp (char const *, size_t, struct dfa *, bool);
+
+/* Search through a buffer looking for a match to the given struct dfa.
+   Find the first occurrence of a string matching the regexp in the
+   buffer, and the shortest possible version thereof.  Return a pointer to
+   the first character after the match, or NULL if none is found.  BEGIN
+   points to the beginning of the buffer, and END points to the first byte
+   after its end.  Note however that we store a sentinel byte (usually
+   newline) in *END, so the actual buffer must be one byte longer.
+   When ALLOW_NL is true, newlines may appear in the matching string.
+   If COUNT is non-NULL, increment *COUNT once for each newline processed.
+   Finally, if BACKREF is non-NULL set *BACKREF to indicate whether we
+   encountered a back-reference.  The caller can use this to decide
+   whether to fall back on a backtracking matcher.  */
+extern char *dfaexec (struct dfa *d, char const *begin, char *end,
+                      bool allow_nl, size_t *count, bool *backref);
+
+/* Return a superset for D.  The superset matches everything that D
+   matches, along with some other strings (though the latter should be
+   rare, for efficiency reasons).  Return a null pointer if no useful
+   superset is available.  */
+extern struct dfa *dfasuperset (struct dfa const *d) _GL_ATTRIBUTE_PURE;
+
+/* The DFA is likely to be fast.  */
+extern bool dfaisfast (struct dfa const *) _GL_ATTRIBUTE_PURE;
+
+/* Free the storage held by the components of a struct dfa. */
+extern void dfafree (struct dfa *);
+
+/* Error handling. */
+
+/* dfawarn() is called by the regexp routines whenever a regex is compiled
+   that likely doesn't do what the user wanted.  It takes a single
+   argument, a NUL-terminated string describing the situation.  The user
+   must supply a dfawarn.  */
+extern void dfawarn (const char *);
+
+/* dfaerror() is called by the regexp routines whenever an error occurs.  It
+   takes a single argument, a NUL-terminated string describing the error.
+   The user must supply a dfaerror.  */
+extern _Noreturn void dfaerror (const char *);
+
+extern bool using_utf8 (void);
diff --git a/sed/local.mk b/sed/local.mk
index 7f88fa8..1a187d4 100644
--- a/sed/local.mk
+++ b/sed/local.mk
@@ -22,10 +22,12 @@ sed_sed_SOURCES = sed/sed.c \
                   sed/execute.c \
                   sed/regexp.c \
                   sed/mbcs.c \
-                  sed/utils.c
+                  sed/utils.c \
+                  sed/dfa.c
 
 noinst_HEADERS += sed/sed.h \
-                  sed/utils.h
+                  sed/utils.h \
+                  sed/dfa.h
 
 sed_sed_CPPFLAGS = $(AM_CPPFLAGS)  -DLOCALEDIR=\"$(localedir)\"
 sed_sed_CFLAGS = $(AM_CFLAGS) $(WARN_CFLAGS) $(WERROR_CFLAGS)
diff --git a/sed/regexp.c b/sed/regexp.c
index 98f9e61..13d4c5f 100644
--- a/sed/regexp.c
+++ b/sed/regexp.c
@@ -39,6 +39,25 @@ static const char errors[] =
 
 
 
+void
+dfaerror (char const *mesg)
+{
+  panic ("%s", mesg);
+
+  /* notreached */
+  /* Tell static analyzers that this function does not return.  */
+  abort ();
+}
+
+void
+dfawarn (char const *mesg)
+{
+  if (!getenv ("POSIXLY_CORRECT"))
+    dfaerror (mesg);
+}
+
+
+
 static void
 compile_regex_1 (struct regex *new_regex, int needed_sub)
 {
@@ -126,6 +145,10 @@ compile_regex_1 (struct regex *new_regex, int needed_sub)
               needed_sub - 1);
       bad_prog(buf);
     }
+
+  dfasyntax (syntax, (new_regex->flags & REG_ICASE) != 0, '\n');
+  new_regex->dfa = dfaalloc ();
+  dfacomp (new_regex->re, new_regex->sz, new_regex->dfa, 1);
 }
 
 struct regex *
@@ -236,6 +259,26 @@ match_regex(struct regex *regex, char *buf, size_t buflen,
 
   regex->pattern.regs_allocated = REGS_REALLOCATE;
 
+  if (buf_start_offset == 0)
+    {
+      struct dfa *superset = dfasuperset (regex->dfa);
+
+      if (superset && !dfaexec(superset, buf, buf + buflen, true, NULL, NULL))
+        return 0;
+
+      if ((!regsize && regex->pattern.newline_anchor)
+          || (!superset && dfaisfast (regex->dfa)))
+        {
+          bool backref = false;
+
+          if (!dfaexec(regex->dfa, buf, buf + buflen, true, NULL, &backref))
+            return 0;
+
+          if (!regsize && regex->pattern.newline_anchor && !backref)
+            return 1;
+        }
+    }
+
   ret = re_search (&regex->pattern, buf, buflen, buf_start_offset,
                    buflen - buf_start_offset,
                    regsize ? regarray : NULL);
diff --git a/sed/sed.h b/sed/sed.h
index 3716bcb..065a672 100644
--- a/sed/sed.h
+++ b/sed/sed.h
@@ -18,6 +18,7 @@
 #include <config.h>
 #include "basicdefs.h"
 #include "regex.h"
+#include "dfa.h"
 #include <stdio.h>
 #include <limits.h>
 #include "unlocked-io.h"
@@ -51,6 +52,7 @@ struct regex {
   regex_t pattern;
   int flags;
   size_t sz;
+  struct dfa *dfa;
   char re[1];
 };
 
-- 
1.7.1