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regexec.c: Comments and white-space only
[perl5.git] / regexec.c
index 022b52b..f71c28a 100644 (file)
--- a/regexec.c
+++ b/regexec.c
@@ -288,7 +288,6 @@ static regmatch_state * S_push_slab(pTHX);
 STATIC CHECKPOINT
 S_regcppush(pTHX_ const regexp *rex, I32 parenfloor, U32 maxopenparen)
 {
-    dVAR;
     const int retval = PL_savestack_ix;
     const int paren_elems_to_push =
                 (maxopenparen - parenfloor) * REGCP_PAREN_ELEMS;
@@ -300,8 +299,9 @@ S_regcppush(pTHX_ const regexp *rex, I32 parenfloor, U32 maxopenparen)
     PERL_ARGS_ASSERT_REGCPPUSH;
 
     if (paren_elems_to_push < 0)
-        Perl_croak(aTHX_ "panic: paren_elems_to_push, %i < 0, maxopenparen: %i parenfloor: %i REGCP_PAREN_ELEMS: %i",
-                   paren_elems_to_push, maxopenparen, parenfloor, REGCP_PAREN_ELEMS);
+        Perl_croak(aTHX_ "panic: paren_elems_to_push, %i < 0, maxopenparen: %i parenfloor: %i REGCP_PAREN_ELEMS: %u",
+                   (int)paren_elems_to_push, (int)maxopenparen,
+                   (int)parenfloor, (unsigned)REGCP_PAREN_ELEMS);
 
     if ((elems_shifted >> SAVE_TIGHT_SHIFT) != total_elems)
        Perl_croak(aTHX_ "panic: paren_elems_to_push offset %"UVuf
@@ -368,7 +368,6 @@ S_regcppush(pTHX_ const regexp *rex, I32 parenfloor, U32 maxopenparen)
 STATIC void
 S_regcppop(pTHX_ regexp *rex, U32 *maxopenparen_p)
 {
-    dVAR;
     UV i;
     U32 paren;
     GET_RE_DEBUG_FLAGS_DECL;
@@ -572,64 +571,70 @@ Perl_pregexec(pTHX_ REGEXP * const prog, char* stringarg, char *strend,
 }
 #endif
 
-/*
- * Need to implement the following flags for reg_anch:
- *
- * USE_INTUIT_NOML             - Useful to call re_intuit_start() first
- * USE_INTUIT_ML
- * INTUIT_AUTORITATIVE_NOML    - Can trust a positive answer
- * INTUIT_AUTORITATIVE_ML
- * INTUIT_ONCE_NOML            - Intuit can match in one location only.
- * INTUIT_ONCE_ML
- *
- * Another flag for this function: SECOND_TIME (so that float substrs
- * with giant delta may be not rechecked).
- */
-
-/* If SCREAM, then SvPVX_const(sv) should be compatible with strpos and strend.
-   Otherwise, only SvCUR(sv) is used to get strbeg. */
-
-/* XXXX Some places assume that there is a fixed substring.
-       An update may be needed if optimizer marks as "INTUITable"
-       RExen without fixed substrings.  Similarly, it is assumed that
-       lengths of all the strings are no more than minlen, thus they
-       cannot come from lookahead.
-       (Or minlen should take into account lookahead.) 
-  NOTE: Some of this comment is not correct. minlen does now take account
-  of lookahead/behind. Further research is required. -- demerphq
 
-*/
-
-/* A failure to find a constant substring means that there is no need to make
-   an expensive call to REx engine, thus we celebrate a failure.  Similarly,
-   finding a substring too deep into the string means that fewer calls to
-   regtry() should be needed.
-
-   REx compiler's optimizer found 4 possible hints:
-       a) Anchored substring;
-       b) Fixed substring;
-       c) Whether we are anchored (beginning-of-line or \G);
-       d) First node (of those at offset 0) which may distinguish positions;
-   We use a)b)d) and multiline-part of c), and try to find a position in the
-   string which does not contradict any of them.
- */
 
-/* Most of decisions we do here should have been done at compile time.
-   The nodes of the REx which we used for the search should have been
-   deleted from the finite automaton. */
-
-/* args:
- * rx:     the regex to match against
- * sv:     the SV being matched: only used for utf8 flag; the string
- *         itself is accessed via the pointers below. Note that on
- *         something like an overloaded SV, SvPOK(sv) may be false
- *         and the string pointers may point to something unrelated to
- *         the SV itself.
- * strbeg: real beginning of string
- * strpos: the point in the string at which to begin matching
- * strend: pointer to the byte following the last char of the string
- * flags   currently unused; set to 0
- * data:   currently unused; set to NULL
+/* re_intuit_start():
+ *
+ * Based on some optimiser hints, try to find the earliest position in the
+ * string where the regex could match.
+ *
+ *   rx:     the regex to match against
+ *   sv:     the SV being matched: only used for utf8 flag; the string
+ *           itself is accessed via the pointers below. Note that on
+ *           something like an overloaded SV, SvPOK(sv) may be false
+ *           and the string pointers may point to something unrelated to
+ *           the SV itself.
+ *   strbeg: real beginning of string
+ *   strpos: the point in the string at which to begin matching
+ *   strend: pointer to the byte following the last char of the string
+ *   flags   currently unused; set to 0
+ *   data:   currently unused; set to NULL
+ *
+ * The basic idea of re_intuit_start() is to use some known information
+ * about the pattern, namely:
+ *
+ *   a) the longest known anchored substring (i.e. one that's at a
+ *      constant offset from the beginning of the pattern; but not
+ *      necessarily at a fixed offset from the beginning of the
+ *      string);
+ *   b) the longest floating substring (i.e. one that's not at a constant
+ *      offset from the beginning of the pattern);
+ *   c) Whether the pattern is anchored to the string; either
+ *      an absolute anchor: /^../, or anchored to \n: /^.../m,
+ *      or anchored to pos(): /\G/;
+ *   d) A start class: a real or synthetic character class which
+ *      represents which characters are legal at the start of the pattern;
+ *
+ * to either quickly reject the match, or to find the earliest position
+ * within the string at which the pattern might match, thus avoiding
+ * running the full NFA engine at those earlier locations, only to
+ * eventually fail and retry further along.
+ *
+ * Returns NULL if the pattern can't match, or returns the address within
+ * the string which is the earliest place the match could occur.
+ *
+ * The longest of the anchored and floating substrings is called 'check'
+ * and is checked first. The other is called 'other' and is checked
+ * second. The 'other' substring may not be present.  For example,
+ *
+ *    /(abc|xyz)ABC\d{0,3}DEFG/
+ *
+ * will have
+ *
+ *   check substr (float)    = "DEFG", offset 6..9 chars
+ *   other substr (anchored) = "ABC",  offset 3..3 chars
+ *   stclass = [ax]
+ *
+ * Be aware that during the course of this function, sometimes 'anchored'
+ * refers to a substring being anchored relative to the start of the
+ * pattern, and sometimes to the pattern itself being anchored relative to
+ * the string. For example:
+ *
+ *   /\dabc/:   "abc" is anchored to the pattern;
+ *   /^\dabc/:  "abc" is anchored to the pattern and the string;
+ *   /\d+abc/:  "abc" is anchored to neither the pattern nor the string;
+ *   /^\d+abc/: "abc" is anchored to neither the pattern nor the string,
+ *                    but the pattern is anchored to the string.
  */
 
 char *
@@ -642,7 +647,6 @@ Perl_re_intuit_start(pTHX_
                     const U32 flags,
                     re_scream_pos_data *data)
 {
-    dVAR;
     struct regexp *const prog = ReANY(rx);
     SSize_t start_shift = prog->check_offset_min;
     /* Should be nonnegative! */
@@ -692,7 +696,9 @@ Perl_re_intuit_start(pTHX_
               && (prog->float_utf8    || prog->float_substr))
            || (prog->float_min_offset >= prog->anchored_offset));
 
-    /* CHR_DIST() would be more correct here but it makes things slow. */
+    /* byte rather than char calculation for efficiency. It fails
+     * to quickly reject some cases that can't match, but will reject
+     * them later after doing full char arithmetic */
     if (prog->minlen > strend - strpos) {
        DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
                              "  String too short...\n"));
@@ -744,21 +750,31 @@ Perl_re_intuit_start(pTHX_
     });
 
     if (prog->intflags & PREGf_ANCH) { /* Match at \G, beg-of-str or after \n */
-        /* Check after \n? */
-       ml_anch = (     (prog->intflags & PREGf_ANCH_MBOL)
-                   || ((prog->intflags & PREGf_ANCH_BOL) && multiline));
 
-       if (!ml_anch) {
+        /* ml_anch: check after \n?
+         *
+         * A note about IMPLICIT: on an un-anchored pattern beginning
+         * with /.*.../, these flags will have been added by the
+         * compiler:
+         *   /.*abc/, /.*abc/m:  PREGf_IMPLICIT | PREGf_ANCH_MBOL
+         *   /.*abc/s:           PREGf_IMPLICIT | PREGf_ANCH_SBOL
+         */
+       ml_anch =      (prog->intflags & PREGf_ANCH_MBOL)
+                   && !(prog->intflags & PREGf_IMPLICIT);
+
+       if (!ml_anch && !(prog->intflags & PREGf_IMPLICIT)) {
             /* we are only allowed to match at BOS or \G */
 
             /* trivially reject if there's a BOS anchor and we're not at BOS.
-             * In the case of \G, we hope(!) that the caller has already
-             * set strpos to pos()-gofs, and will already have checked
-             * that this anchor position is legal. So we can skip it here.
+             *
+             * Note that we don't try to do a similar quick reject for
+             * \G, since generally the caller will have calculated strpos
+             * based on pos() and gofs, so the string is already correctly
+             * anchored by definition; and handling the exceptions would
+             * be too fiddly (e.g. REXEC_IGNOREPOS).
              */
-            if (   !(prog->intflags & PREGf_ANCH_GPOS)
-                && !(prog->intflags & PREGf_IMPLICIT) /* not a real BOL */
-               && (strpos != strbeg))
+            if (   strpos != strbeg
+                && (prog->intflags & (PREGf_ANCH_BOL|PREGf_ANCH_SBOL)))
             {
                DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
                                 "  Not at start...\n"));
@@ -767,30 +783,34 @@ Perl_re_intuit_start(pTHX_
 
             /* in the presence of an anchor, the anchored (relative to the
              * start of the regex) substr must also be anchored relative
-             * to strpos. So quickly reject if substr isn't found there */
+             * to strpos. So quickly reject if substr isn't found there.
+             * This works for \G too, because the caller will already have
+             * subtracted gofs from pos, and gofs is the offset from the
+             * \G to the start of the regex. For example, in /.abc\Gdef/,
+             * where substr="abcdef", pos()=3, gofs=4, offset_min=1:
+             * caller will have set strpos=pos()-4; we look for the substr
+             * at position pos()-4+1, which lines up with the "a" */
 
            if (prog->check_offset_min == prog->check_offset_max
-                && !(prog->intflags & PREGf_CANY_SEEN)
-                && ! multiline)   /* /m can cause \n's to match that aren't
-                                     accounted for in the string max length.
-                                     See [perl #115242] */
+                && !(prog->intflags & PREGf_CANY_SEEN))
             {
                /* Substring at constant offset from beg-of-str... */
                SSize_t slen = SvCUR(check);
-                char *s;
-
-               s = HOP3c(strpos, prog->check_offset_min, strend);
+                char *s = HOP3c(strpos, prog->check_offset_min, strend);
            
                 DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
                     "  Looking for check substr at fixed offset %"IVdf"...\n",
                     (IV)prog->check_offset_min));
 
                if (SvTAIL(check)) {
-                    /* In this case, the regex is anchored at the end too,
-                     * so the lengths must match exactly, give or take a \n.
-                    * NB: slen >= 1 since the last char of check is \n */
-                   if (   strend - s > slen || strend - s < slen - 1
-                      || (strend - s == slen && strend[-1] != '\n'))
+                    /* In this case, the regex is anchored at the end too.
+                     * Unless it's a multiline match, the lengths must match
+                     * exactly, give or take a \n.  NB: slen >= 1 since
+                     * the last char of check is \n */
+                   if (!multiline
+                        && (   strend - s > slen
+                            || strend - s < slen - 1
+                            || (strend - s == slen && strend[-1] != '\n')))
                     {
                         DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
                                             "  String too long...\n"));
@@ -822,11 +842,32 @@ Perl_re_intuit_start(pTHX_
 #endif
 
   restart:
-    /* Find a candidate regex origin in the region rx_origin..strend
-     * by looking for the "check" substring in that region, corrected by
-     * start/end_shift.
-     */
     
+    /* This is the (re)entry point of the main loop in this function.
+     * The goal of this loop is to:
+     * 1) find the "check" substring in the region rx_origin..strend
+     *    (adjusted by start_shift / end_shift). If not found, reject
+     *    immediately.
+     * 2) If it exists, look for the "other" substr too if defined; for
+     *    example, if the check substr maps to the anchored substr, then
+     *    check the floating substr, and vice-versa. If not found, go
+     *    back to (1) with rx_origin suitably incremented.
+     * 3) If we find an rx_origin position that doesn't contradict
+     *    either of the substrings, then check the possible additional
+     *    constraints on rx_origin of /^.../m or a known start class.
+     *    If these fail, then depending on which constraints fail, jump
+     *    back to here, or to various other re-entry points further along
+     *    that skip some of the first steps.
+     * 4) If we pass all those tests, update the BmUSEFUL() count on the
+     *    substring. If the start position was determined to be at the
+     *    beginning of the string  - so, not rejected, but not optimised,
+     *    since we have to run regmatch from position 0 - decrement the
+     *    BmUSEFUL() count. Otherwise increment it.
+     */
+
+
+    /* first, look for the 'check' substring */
+
     {
         U8* start_point;
         U8* end_point;
@@ -856,19 +897,32 @@ Perl_re_intuit_start(pTHX_
        }
 
 
-        /* if the regex is absolutely anchored to the start of the string,
-         * then check_offset_max represents an upper bound on the string
-         * where the substr could start */
+        /* If the regex is absolutely anchored to either the start of the
+         * string (BOL,SBOL) or to pos() (ANCH_GPOS), then
+         * check_offset_max represents an upper bound on the string where
+         * the substr could start. For the ANCH_GPOS case, we assume that
+         * the caller of intuit will have already set strpos to
+         * pos()-gofs, so in this case strpos + offset_max will still be
+         * an upper bound on the substr.
+         */
         if (!ml_anch
             && prog->intflags & PREGf_ANCH
-            && prog->check_offset_max != SSize_t_MAX
-            && start_shift < prog->check_offset_max)
+            && prog->check_offset_max != SSize_t_MAX)
         {
             SSize_t len = SvCUR(check) - !!SvTAIL(check);
-            end_point = HOP3lim(start_point,
-                            prog->check_offset_max - start_shift,
-                            end_point -len)
-                        + len;
+            const char * const anchor =
+                        (prog->intflags & PREGf_ANCH_GPOS ? strpos : strbeg);
+
+            /* do a bytes rather than chars comparison. It's conservative;
+             * so it skips doing the HOP if the result can't possibly end
+             * up earlier than the old value of end_point.
+             */
+            if ((char*)end_point - anchor > prog->check_offset_max) {
+                end_point = HOP3lim((U8*)anchor,
+                                prog->check_offset_max,
+                                end_point -len)
+                            + len;
+            }
         }
 
        DEBUG_OPTIMISE_MORE_r({
@@ -880,50 +934,38 @@ Perl_re_intuit_start(pTHX_
 
        check_at = fbm_instr( start_point, end_point,
                      check, multiline ? FBMrf_MULTILINE : 0);
-    }
 
-    /* Update the count-of-usability, remove useless subpatterns,
-       unshift s.  */
-
-    DEBUG_EXECUTE_r({
-        RE_PV_QUOTED_DECL(quoted, utf8_target, PERL_DEBUG_PAD_ZERO(0),
-            SvPVX_const(check), RE_SV_DUMPLEN(check), 30);
-        PerlIO_printf(Perl_debug_log, "  %s %s substr %s%s%s",
-                         (check_at ? "Found" : "Did not find"),
-           (check == (utf8_target ? prog->anchored_utf8 : prog->anchored_substr)
-               ? "anchored" : "floating"),
-           quoted,
-           RE_SV_TAIL(check),
-           (check_at ? " at offset " : "...\n") );
-    });
+        /* Update the count-of-usability, remove useless subpatterns,
+            unshift s.  */
 
-    if (!check_at)
-       goto fail_finish;
-    /* Finish the diagnostic message */
-    DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log, "%ld...\n", (long)(check_at - strpos)) );
+        DEBUG_EXECUTE_r({
+            RE_PV_QUOTED_DECL(quoted, utf8_target, PERL_DEBUG_PAD_ZERO(0),
+                SvPVX_const(check), RE_SV_DUMPLEN(check), 30);
+            PerlIO_printf(Perl_debug_log, "  %s %s substr %s%s%s",
+                              (check_at ? "Found" : "Did not find"),
+                (check == (utf8_target ? prog->anchored_utf8 : prog->anchored_substr)
+                    ? "anchored" : "floating"),
+                quoted,
+                RE_SV_TAIL(check),
+                (check_at ? " at offset " : "...\n") );
+        });
 
-    /* set rx_origin to the minimum position where the regex could start
-     * matching, given the constraint of the just-matched check substring.
-     * But don't set it lower than previously.
-     */
+        if (!check_at)
+            goto fail_finish;
+        /* Finish the diagnostic message */
+        DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log, "%ld...\n", (long)(check_at - strpos)) );
 
-    if (check_at - rx_origin > prog->check_offset_max)
-        rx_origin = HOP3c(check_at, -prog->check_offset_max, rx_origin);
+        /* set rx_origin to the minimum position where the regex could start
+         * matching, given the constraint of the just-matched check substring.
+         * But don't set it lower than previously.
+         */
 
+        if (check_at - rx_origin > prog->check_offset_max)
+            rx_origin = HOP3c(check_at, -prog->check_offset_max, rx_origin);
+    }
 
-    /* XXX dmq: first branch is for positive lookbehind...
-       Our check string is offset from the beginning of the pattern.
-       So we need to do any stclass tests offset forward from that 
-       point. I think. :-(
-     */
-    
-    /* Got a candidate.  Check MBOL anchoring, and the *other* substr.
-       Start with the other substr.
-       XXXX no SCREAM optimization yet - and a very coarse implementation
-       XXXX /ttx+/ results in anchored="ttx", floating="x".  floating will
-               *always* match.  Probably should be marked during compile...
-       Probably it is right to do no SCREAM here...
-     */
+
+    /* now look for the 'other' substring if defined */
 
     if (utf8_target ? prog->substrs->data[other_ix].utf8_substr
                     : prog->substrs->data[other_ix].substr)
@@ -1102,12 +1144,9 @@ Perl_re_intuit_start(pTHX_
 
   postprocess_substr_matches:
 
-    /* handle the extra constraint of /^/m  */
+    /* handle the extra constraint of /^.../m if present */
 
-    if (ml_anch && rx_origin != strbeg && rx_origin[-1] != '\n'
-        /* May be due to an implicit anchor of m{.*foo}  */
-        && !(prog->intflags & PREGf_IMPLICIT))
-    {
+    if (ml_anch && rx_origin != strbeg && rx_origin[-1] != '\n') {
         char *s;
 
         DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
@@ -1179,8 +1218,7 @@ Perl_re_intuit_start(pTHX_
     }
     else {
         DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
-            "  Starting position does not contradict /%s^%s/m...\n",
-            PL_colors[0], PL_colors[1]));
+            "  (multiline anchor test skipped)\n"));
     }
 
   success_at_start:
@@ -1253,7 +1291,8 @@ Perl_re_intuit_start(pTHX_
            }
            DEBUG_EXECUTE_r( PerlIO_printf(Perl_debug_log,
                                "  This position contradicts STCLASS...\n") );
-            if ((prog->intflags & PREGf_ANCH) && !ml_anch)
+            if ((prog->intflags & PREGf_ANCH) && !ml_anch
+                        && !(prog->intflags & PREGf_IMPLICIT))
                goto fail;
 
            /* Contradict one of substrings */
@@ -1371,19 +1410,10 @@ Perl_re_intuit_start(pTHX_
            prog->check_substr = prog->check_utf8 = NULL;       /* disable */
            prog->float_substr = prog->float_utf8 = NULL;       /* clear */
            check = NULL;                       /* abort */
-           /* XXXX If the check string was an implicit check MBOL, then we need to unset the relevant flag
-                   see http://bugs.activestate.com/show_bug.cgi?id=87173 */
-            if (prog->intflags & PREGf_IMPLICIT) {
-                prog->intflags &= ~PREGf_ANCH_MBOL;
-                /* maybe we have no anchors left after this... */
-                if (!(prog->intflags & PREGf_ANCH))
-                    prog->extflags &= ~RXf_IS_ANCHORED;
-            }
            /* XXXX This is a remnant of the old implementation.  It
                    looks wasteful, since now INTUIT can use many
                    other heuristics. */
            prog->extflags &= ~RXf_USE_INTUIT;
-           /* XXXX What other flags might need to be cleared in this branch? */
        }
     }
 
@@ -1419,7 +1449,7 @@ STMT_START {
     switch (trie_type) {                                                            \
     case trie_utf8_exactfa_fold:                                                    \
         flags |= FOLD_FLAGS_NOMIX_ASCII;                                            \
-        /* FALL THROUGH */                                                          \
+        /* FALLTHROUGH */                                                          \
     case trie_utf8_fold:                                                            \
         if ( foldlen>0 ) {                                                          \
             uvc = utf8n_to_uvchr( (const U8*) uscan, UTF8_MAXLEN, &len, uniflags ); \
@@ -1436,7 +1466,7 @@ STMT_START {
         break;                                                                      \
     case trie_latin_utf8_exactfa_fold:                                              \
         flags |= FOLD_FLAGS_NOMIX_ASCII;                                            \
-        /* FALL THROUGH */                                                          \
+        /* FALLTHROUGH */                                                          \
     case trie_latin_utf8_fold:                                                      \
         if ( foldlen>0 ) {                                                          \
             uvc = utf8n_to_uvchr( (const U8*) uscan, UTF8_MAXLEN, &len, uniflags ); \
@@ -1472,10 +1502,10 @@ STMT_START {
     }                                                                               \
 } STMT_END
 
-#define REXEC_FBC_EXACTISH_SCAN(CoNd)                     \
+#define REXEC_FBC_EXACTISH_SCAN(COND)                     \
 STMT_START {                                              \
     while (s <= e) {                                      \
-       if ( (CoNd)                                       \
+       if ( (COND)                                       \
             && (ln == 1 || folder(s, pat_string, ln))    \
             && (reginfo->intuit || regtry(reginfo, &s)) )\
            goto got_it;                                  \
@@ -1483,134 +1513,179 @@ STMT_START {                                              \
     }                                                     \
 } STMT_END
 
-#define REXEC_FBC_UTF8_SCAN(CoDe)                     \
+#define REXEC_FBC_UTF8_SCAN(CODE)                     \
 STMT_START {                                          \
     while (s < strend) {                              \
-       CoDe                                          \
+       CODE                                          \
        s += UTF8SKIP(s);                             \
     }                                                 \
 } STMT_END
 
-#define REXEC_FBC_SCAN(CoDe)                          \
+#define REXEC_FBC_SCAN(CODE)                          \
 STMT_START {                                          \
     while (s < strend) {                              \
-       CoDe                                          \
+       CODE                                          \
        s++;                                          \
     }                                                 \
 } STMT_END
 
-#define REXEC_FBC_UTF8_CLASS_SCAN(CoNd)               \
-REXEC_FBC_UTF8_SCAN(                                  \
-    if (CoNd) {                                       \
-       if (tmp && (reginfo->intuit || regtry(reginfo, &s))) \
-           goto got_it;                              \
-       else                                          \
-           tmp = doevery;                            \
-    }                                                 \
-    else                                              \
-       tmp = 1;                                      \
+#define REXEC_FBC_UTF8_CLASS_SCAN(COND)                        \
+REXEC_FBC_UTF8_SCAN( /* Loops while (s < strend) */            \
+    if (COND) {                                                \
+       if (tmp && (reginfo->intuit || regtry(reginfo, &s)))   \
+           goto got_it;                                       \
+       else                                                   \
+           tmp = doevery;                                     \
+    }                                                          \
+    else                                                       \
+       tmp = 1;                                               \
 )
 
-#define REXEC_FBC_CLASS_SCAN(CoNd)                    \
-REXEC_FBC_SCAN(                                       \
-    if (CoNd) {                                       \
-       if (tmp && (reginfo->intuit || regtry(reginfo, &s)))  \
-           goto got_it;                              \
-       else                                          \
-           tmp = doevery;                            \
-    }                                                 \
-    else                                              \
-       tmp = 1;                                      \
+#define REXEC_FBC_CLASS_SCAN(COND)                             \
+REXEC_FBC_SCAN( /* Loops while (s < strend) */                 \
+    if (COND) {                                                \
+       if (tmp && (reginfo->intuit || regtry(reginfo, &s)))   \
+           goto got_it;                                       \
+       else                                                   \
+           tmp = doevery;                                     \
+    }                                                          \
+    else                                                       \
+       tmp = 1;                                               \
 )
 
-#define REXEC_FBC_TRYIT                       \
-if ((reginfo->intuit || regtry(reginfo, &s))) \
-    goto got_it
+/* This is the macro to use when we want to see if something that looks like it
+ * could match, actually does, and if so exits the loop */
+#define REXEC_FBC_TRYIT                            \
+    if ((reginfo->intuit || regtry(reginfo, &s)))  \
+        goto got_it
 
-#define REXEC_FBC_CSCAN(CoNdUtF8,CoNd)                         \
+#define REXEC_FBC_CSCAN(CONDUTF8,COND)                         \
     if (utf8_target) {                                         \
-       REXEC_FBC_UTF8_CLASS_SCAN(CoNdUtF8);                   \
+       REXEC_FBC_UTF8_CLASS_SCAN(CONDUTF8);                   \
     }                                                          \
     else {                                                     \
-       REXEC_FBC_CLASS_SCAN(CoNd);                            \
+       REXEC_FBC_CLASS_SCAN(COND);                            \
     }
-    
+
 #define DUMP_EXEC_POS(li,s,doutf8)                          \
     dump_exec_pos(li,s,(reginfo->strend),(reginfo->strbeg), \
                 startpos, doutf8)
 
-
-#define UTF8_NOLOAD(TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)                        \
-       tmp = (s != reginfo->strbeg) ? UCHARAT(s - 1) : '\n';                  \
-       tmp = TEST_NON_UTF8(tmp);                                              \
-       REXEC_FBC_UTF8_SCAN(                                                   \
-           if (tmp == ! TEST_NON_UTF8((U8) *s)) {                             \
-               tmp = !tmp;                                                    \
-               IF_SUCCESS;                                                    \
-           }                                                                  \
-           else {                                                             \
-               IF_FAIL;                                                       \
-           }                                                                  \
-       );                                                                     \
-
-#define UTF8_LOAD(TeSt1_UtF8, TeSt2_UtF8, IF_SUCCESS, IF_FAIL)                 \
-       if (s == reginfo->strbeg) {                                            \
-           tmp = '\n';                                                        \
-       }                                                                      \
-       else {                                                                 \
-           U8 * const r = reghop3((U8*)s, -1, (U8*)reginfo->strbeg);          \
-           tmp = utf8n_to_uvchr(r, (U8*) reginfo->strend - r,                 \
+/* The three macros below are slightly different versions of the same logic.
+ *
+ * The first is for /a and /aa when the target string is UTF-8.  This can only
+ * match ascii, but it must advance based on UTF-8.   The other two handle the
+ * non-UTF-8 and the more generic UTF-8 cases.   In all three, we are looking
+ * for the boundary (or non-boundary) between a word and non-word character.
+ * The utf8 and non-utf8 cases have the same logic, but the details must be
+ * different.  Find the "wordness" of the character just prior to this one, and
+ * compare it with the wordness of this one.  If they differ, we have a
+ * boundary.  At the beginning of the string, pretend that the previous
+ * character was a new-line.
+ *
+ * All these macros uncleanly have side-effects with each other and outside
+ * variables.  So far it's been too much trouble to clean-up
+ *
+ * TEST_NON_UTF8 is the macro or function to call to test if its byte input is
+ *               a word character or not.
+ * IF_SUCCESS    is code to do if it finds that we are at a boundary between
+ *               word/non-word
+ * IF_FAIL       is code to do if we aren't at a boundary between word/non-word
+ *
+ * Exactly one of the two IF_FOO parameters is a no-op, depending on whether we
+ * are looking for a boundary or for a non-boundary.  If we are looking for a
+ * boundary, we want IF_FAIL to be the no-op, and for IF_SUCCESS to go out and
+ * see if this tentative match actually works, and if so, to quit the loop
+ * here.  And vice-versa if we are looking for a non-boundary.
+ *
+ * 'tmp' below in the next three macros in the REXEC_FBC_SCAN and
+ * REXEC_FBC_UTF8_SCAN loops is a loop invariant, a bool giving the return of
+ * TEST_NON_UTF8(s-1).  To see this, note that that's what it is defined to be
+ * at entry to the loop, and to get to the IF_FAIL branch, tmp must equal
+ * TEST_NON_UTF8(s), and in the opposite branch, IF_SUCCESS, tmp is that
+ * complement.  But in that branch we complement tmp, meaning that at the
+ * bottom of the loop tmp is always going to be equal to TEST_NON_UTF8(s),
+ * which means at the top of the loop in the next iteration, it is
+ * TEST_NON_UTF8(s-1) */
+#define FBC_UTF8_A(TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)                         \
+    tmp = (s != reginfo->strbeg) ? UCHARAT(s - 1) : '\n';                      \
+    tmp = TEST_NON_UTF8(tmp);                                                  \
+    REXEC_FBC_UTF8_SCAN( /* advances s while s < strend */                     \
+        if (tmp == ! TEST_NON_UTF8((U8) *s)) {                                 \
+            tmp = !tmp;                                                        \
+            IF_SUCCESS; /* Is a boundary if values for s-1 and s differ */     \
+        }                                                                      \
+        else {                                                                 \
+            IF_FAIL;                                                           \
+        }                                                                      \
+    );                                                                         \
+
+/* Like FBC_UTF8_A, but TEST_UV is a macro which takes a UV as its input, and
+ * TEST_UTF8 is a macro that for the same input code points returns identically
+ * to TEST_UV, but takes a pointer to a UTF-8 encoded string instead */
+#define FBC_UTF8(TEST_UV, TEST_UTF8, IF_SUCCESS, IF_FAIL)                      \
+    if (s == reginfo->strbeg) {                                                \
+        tmp = '\n';                                                            \
+    }                                                                          \
+    else { /* Back-up to the start of the previous character */                \
+        U8 * const r = reghop3((U8*)s, -1, (U8*)reginfo->strbeg);              \
+        tmp = utf8n_to_uvchr(r, (U8*) reginfo->strend - r,                     \
                                                        0, UTF8_ALLOW_DEFAULT); \
-       }                                                                      \
-       tmp = TeSt1_UtF8;                                                      \
-       LOAD_UTF8_CHARCLASS_ALNUM();                                           \
-       REXEC_FBC_UTF8_SCAN(                                                   \
-           if (tmp == ! (TeSt2_UtF8)) {                                       \
-               tmp = !tmp;                                                    \
-               IF_SUCCESS;                                                    \
-           }                                                                  \
-           else {                                                             \
-               IF_FAIL;                                                       \
-           }                                                                  \
-       );                                                                     \
+    }                                                                          \
+    tmp = TEST_UV(tmp);                                                        \
+    LOAD_UTF8_CHARCLASS_ALNUM();                                               \
+    REXEC_FBC_UTF8_SCAN( /* advances s while s < strend */                     \
+        if (tmp == ! (TEST_UTF8((U8 *) s))) {                                  \
+            tmp = !tmp;                                                        \
+            IF_SUCCESS;                                                        \
+        }                                                                      \
+        else {                                                                 \
+            IF_FAIL;                                                           \
+        }                                                                      \
+    );
 
 /* The only difference between the BOUND and NBOUND cases is that
  * REXEC_FBC_TRYIT is called when matched in BOUND, and when non-matched in
- * NBOUND.  This is accomplished by passing it in either the if or else clause,
- * with the other one being empty */
-#define FBC_BOUND(TEST_NON_UTF8, TEST1_UTF8, TEST2_UTF8) \
-    FBC_BOUND_COMMON(UTF8_LOAD(TEST1_UTF8, TEST2_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER), TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)
-
-#define FBC_BOUND_NOLOAD(TEST_NON_UTF8, TEST1_UTF8, TEST2_UTF8) \
-    FBC_BOUND_COMMON(UTF8_NOLOAD(TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER), TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)
-
-#define FBC_NBOUND(TEST_NON_UTF8, TEST1_UTF8, TEST2_UTF8) \
-    FBC_BOUND_COMMON(UTF8_LOAD(TEST1_UTF8, TEST2_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT), TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)
-
-#define FBC_NBOUND_NOLOAD(TEST_NON_UTF8, TEST1_UTF8, TEST2_UTF8) \
-    FBC_BOUND_COMMON(UTF8_NOLOAD(TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT), TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)
-
-
-/* Common to the BOUND and NBOUND cases.  Unfortunately the UTF8 tests need to
- * be passed in completely with the variable name being tested, which isn't
- * such a clean interface, but this is easier to read than it was before.  We
- * are looking for the boundary (or non-boundary between a word and non-word
- * character.  The utf8 and non-utf8 cases have the same logic, but the details
- * must be different.  Find the "wordness" of the character just prior to this
- * one, and compare it with the wordness of this one.  If they differ, we have
- * a boundary.  At the beginning of the string, pretend that the previous
- * character was a new-line */
+ * NBOUND.  This is accomplished by passing it as either the if or else clause,
+ * with the other one being empty (PLACEHOLDER is defined as empty).
+ *
+ * The TEST_FOO parameters are for operating on different forms of input, but
+ * all should be ones that return identically for the same underlying code
+ * points */
+#define FBC_BOUND(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                           \
+    FBC_BOUND_COMMON(                                                          \
+          FBC_UTF8(TEST_UV, TEST_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER),          \
+          TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)
+
+#define FBC_BOUND_A(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                         \
+    FBC_BOUND_COMMON(                                                          \
+            FBC_UTF8_A(TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER),           \
+            TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)
+
+#define FBC_NBOUND(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                          \
+    FBC_BOUND_COMMON(                                                          \
+          FBC_UTF8(TEST_UV, TEST_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT),          \
+          TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)
+
+#define FBC_NBOUND_A(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                        \
+    FBC_BOUND_COMMON(                                                          \
+            FBC_UTF8_A(TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT),           \
+            TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)
+
+/* Like the above two macros.  UTF8_CODE is the complete code for handling
+ * UTF-8.  Common to the BOUND and NBOUND cases, set-up by the FBC_BOUND, etc
+ * macros below */
 #define FBC_BOUND_COMMON(UTF8_CODE, TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)        \
     if (utf8_target) {                                                         \
-               UTF8_CODE                                                      \
+        UTF8_CODE                                                              \
     }                                                                          \
     else {  /* Not utf8 */                                                     \
        tmp = (s != reginfo->strbeg) ? UCHARAT(s - 1) : '\n';                  \
        tmp = TEST_NON_UTF8(tmp);                                              \
-       REXEC_FBC_SCAN(                                                        \
+       REXEC_FBC_SCAN( /* advances s while s < strend */                      \
            if (tmp == ! TEST_NON_UTF8((U8) *s)) {                             \
-               tmp = !tmp;                                                    \
                IF_SUCCESS;                                                    \
+               tmp = !tmp;                                                    \
            }                                                                  \
            else {                                                             \
                IF_FAIL;                                                       \
@@ -1620,11 +1695,11 @@ if ((reginfo->intuit || regtry(reginfo, &s))) \
     if ((!prog->minlen && tmp) && (reginfo->intuit || regtry(reginfo, &s)))    \
        goto got_it;
 
+
 /* We know what class REx starts with.  Try to find this position... */
 /* if reginfo->intuit, its a dryrun */
 /* annoyingly all the vars in this routine have different names from their counterparts
    in regmatch. /grrr */
-
 STATIC char *
 S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s, 
     const char *strend, regmatch_info *reginfo)
@@ -1675,7 +1750,7 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
 
     case EXACTFA_NO_TRIE:   /* This node only generated for non-utf8 patterns */
         assert(! is_utf8_pat);
-       /* FALL THROUGH */
+       /* FALLTHROUGH */
     case EXACTFA:
         if (is_utf8_pat || utf8_target) {
             utf8_fold_flags = FOLDEQ_UTF8_NOMIX_ASCII;
@@ -1722,7 +1797,7 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
         fold_array = PL_fold_latin1;
         folder = foldEQ_latin1;
 
-        /* FALL THROUGH */
+        /* FALLTHROUGH */
 
     do_exactf_non_utf8: /* Neither pattern nor string are UTF8, and there
                            are no glitches with fold-length differences
@@ -1813,45 +1888,30 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
         }
         break;
     }
+
     case BOUNDL:
-        FBC_BOUND(isWORDCHAR_LC,
-                  isWORDCHAR_LC_uvchr(tmp),
-                  isWORDCHAR_LC_utf8((U8*)s));
+        FBC_BOUND(isWORDCHAR_LC, isWORDCHAR_LC_uvchr, isWORDCHAR_LC_utf8);
         break;
     case NBOUNDL:
-        FBC_NBOUND(isWORDCHAR_LC,
-                   isWORDCHAR_LC_uvchr(tmp),
-                   isWORDCHAR_LC_utf8((U8*)s));
+        FBC_NBOUND(isWORDCHAR_LC, isWORDCHAR_LC_uvchr, isWORDCHAR_LC_utf8);
         break;
     case BOUND:
-        FBC_BOUND(isWORDCHAR,
-                  isWORDCHAR_uni(tmp),
-                  cBOOL(swash_fetch(PL_utf8_swash_ptrs[_CC_WORDCHAR], (U8*)s, utf8_target)));
+        FBC_BOUND(isWORDCHAR, isWORDCHAR_uni, isWORDCHAR_utf8);
         break;
     case BOUNDA:
-        FBC_BOUND_NOLOAD(isWORDCHAR_A,
-                         isWORDCHAR_A(tmp),
-                         isWORDCHAR_A((U8*)s));
+        FBC_BOUND_A(isWORDCHAR_A, isWORDCHAR_A, isWORDCHAR_A);
         break;
     case NBOUND:
-        FBC_NBOUND(isWORDCHAR,
-                   isWORDCHAR_uni(tmp),
-                   cBOOL(swash_fetch(PL_utf8_swash_ptrs[_CC_WORDCHAR], (U8*)s, utf8_target)));
+        FBC_NBOUND(isWORDCHAR, isWORDCHAR_uni, isWORDCHAR_utf8);
         break;
     case NBOUNDA:
-        FBC_NBOUND_NOLOAD(isWORDCHAR_A,
-                          isWORDCHAR_A(tmp),
-                          isWORDCHAR_A((U8*)s));
+        FBC_NBOUND_A(isWORDCHAR_A, isWORDCHAR_A, isWORDCHAR_A);
         break;
     case BOUNDU:
-        FBC_BOUND(isWORDCHAR_L1,
-                  isWORDCHAR_uni(tmp),
-                  cBOOL(swash_fetch(PL_utf8_swash_ptrs[_CC_WORDCHAR], (U8*)s, utf8_target)));
+        FBC_BOUND(isWORDCHAR_L1, isWORDCHAR_uni, isWORDCHAR_utf8);
         break;
     case NBOUNDU:
-        FBC_NBOUND(isWORDCHAR_L1,
-                   isWORDCHAR_uni(tmp),
-                   cBOOL(swash_fetch(PL_utf8_swash_ptrs[_CC_WORDCHAR], (U8*)s, utf8_target)));
+        FBC_NBOUND(isWORDCHAR_L1, isWORDCHAR_uni, isWORDCHAR_utf8);
         break;
     case LNBREAK:
         REXEC_FBC_CSCAN(is_LNBREAK_utf8_safe(s, strend),
@@ -1884,9 +1944,8 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
     case NPOSIXA:
         if (utf8_target) {
             /* The complement of something that matches only ASCII matches all
-             * UTF-8 variant code points, plus everything in ASCII that isn't
-             * in the class */
-            REXEC_FBC_UTF8_CLASS_SCAN(! UTF8_IS_INVARIANT(*s)
+             * non-ASCII, plus everything in ASCII that isn't in the class. */
+            REXEC_FBC_UTF8_CLASS_SCAN(! isASCII_utf8(s)
                                       || ! _generic_isCC_A(*s, FLAGS(c)));
             break;
         }
@@ -1950,7 +2009,7 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
                                            macros */
                 case _CC_ENUM_SPACE: /* XXX would require separate code if we
                                         revert the change of \v matching this */
-                    /* FALL THROUGH */
+                    /* FALLTHROUGH */
 
                 case _CC_ENUM_PSXSPC:
                     REXEC_FBC_UTF8_CLASS_SCAN(
@@ -2227,7 +2286,6 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
         break;
     default:
         Perl_croak(aTHX_ "panic: unknown regstclass %d", (int)OP(c));
-        break;
     }
     return 0;
   got_it:
@@ -2402,7 +2460,6 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
 /* flags:     For optimizations. See REXEC_* in regexp.h */
 
 {
-    dVAR;
     struct regexp *const prog = ReANY(rx);
     char *s;
     regnode *c;
@@ -2424,7 +2481,6 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
     /* Be paranoid... */
     if (prog == NULL || stringarg == NULL) {
        Perl_croak(aTHX_ "NULL regexp parameter");
-       return 0;
     }
 
     DEBUG_EXECUTE_r(
@@ -2552,6 +2608,8 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
        Perl_croak(aTHX_ "corrupted regexp program");
     }
 
+    RX_MATCH_TAINTED_off(rx);
+
     reginfo->prog = rx;         /* Yes, sorry that this is confusing.  */
     reginfo->intuit = 0;
     reginfo->is_utf8_target = cBOOL(utf8_target);
@@ -3122,7 +3180,6 @@ phooey:
 STATIC I32                     /* 0 failure, 1 success */
 S_regtry(pTHX_ regmatch_info *reginfo, char **startposp)
 {
-    dVAR;
     CHECKPOINT lastcp;
     REGEXP *const rx = reginfo->prog;
     regexp *const prog = ReANY(rx);
@@ -3493,7 +3550,7 @@ S_dump_exec_pos(pTHX_ const char *locinput,
  * or 0 if non of the buffers matched.
  */
 STATIC I32
-S_reg_check_named_buff_matched(pTHX_ const regexp *rex, const regnode *scan)
+S_reg_check_named_buff_matched(const regexp *rex, const regnode *scan)
 {
     I32 n;
     RXi_GET_DECL(rex,rexi);
@@ -3661,18 +3718,11 @@ S_setup_EXACTISH_ST_c1_c2(pTHX_ const regnode * const text_node, int *c1p,
         }
         else { /* an EXACTFish node which doesn't begin with a multi-char fold */
             c1 = is_utf8_pat ? valid_utf8_to_uvchr(pat, NULL) : *pat;
-            if (c1 > 256) {
+            if (c1 > 255) {
                 /* Load the folds hash, if not already done */
                 SV** listp;
                 if (! PL_utf8_foldclosures) {
-                    if (! PL_utf8_tofold) {
-                        U8 dummy[UTF8_MAXBYTES_CASE+1];
-
-                        /* Force loading this by folding an above-Latin1 char */
-                        to_utf8_fold((U8*) HYPHEN_UTF8, dummy, NULL);
-                        assert(PL_utf8_tofold); /* Verify that worked */
-                    }
-                    PL_utf8_foldclosures = _swash_inversion_hash(PL_utf8_tofold);
+                    _load_PL_utf8_foldclosures();
                 }
 
                 /* The fold closures data structure is a hash with the keys
@@ -3714,10 +3764,10 @@ S_setup_EXACTISH_ST_c1_c2(pTHX_ const regnode * const text_node, int *c1p,
                         /* Folds that cross the 255/256 boundary are forbidden
                          * if EXACTFL (and isnt a UTF8 locale), or EXACTFA and
                          * one is ASCIII.  Since the pattern character is above
-                         * 256, and its only other match is below 256, the only
+                         * 255, and its only other match is below 256, the only
                          * legal match will be to itself.  We have thrown away
                          * the original, so have to compute which is the one
-                         * above 255 */
+                         * above 255. */
                         if ((c1 < 256) != (c2 < 256)) {
                             if ((OP(text_node) == EXACTFL
                                  && ! IN_UTF8_CTYPE_LOCALE)
@@ -3736,7 +3786,7 @@ S_setup_EXACTISH_ST_c1_c2(pTHX_ const regnode * const text_node, int *c1p,
                     }
                 }
             }
-            else /* Here, c1 is < 255 */
+            else /* Here, c1 is <= 255 */
                 if (utf8_target
                     && HAS_NONLATIN1_FOLD_CLOSURE(c1)
                     && ( ! (OP(text_node) == EXACTFL && ! IN_UTF8_CTYPE_LOCALE))
@@ -3777,7 +3827,7 @@ S_setup_EXACTISH_ST_c1_c2(pTHX_ const regnode * const text_node, int *c1p,
                     case EXACTFA_NO_TRIE:   /* This node only generated for
                                             non-utf8 patterns */
                         assert(! is_utf8_pat);
-                        /* FALL THROUGH */
+                        /* FALLTHROUGH */
                     case EXACTFA:
                     case EXACTFU_SS:
                     case EXACTFU:
@@ -3992,7 +4042,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
            break;
 
        case EOL: /* /..$/  */
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
        case SEOL: /* /..$/s  */
            if (!NEXTCHR_IS_EOS && nextchr != '\n')
                sayNO;
@@ -4037,7 +4087,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                 sayNO_SILENT;
                 assert(0); /* NOTREACHED */
             }
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
        case TRIE:  /* (ab|cd)  */
            /* the basic plan of execution of the trie is:
             * At the beginning, run though all the states, and
@@ -4465,7 +4515,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
         case EXACTFA_NO_TRIE:   /* This node only generated for non-utf8
                                    patterns */
             assert(! is_utf8_pat);
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
        case EXACTFA:            /*  /abc/iaa     */
            folder = foldEQ_latin1;
            fold_array = PL_fold_latin1;
@@ -4592,7 +4642,6 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                        break;
                    default:
                        Perl_croak(aTHX_ "panic: Unexpected FLAGS %u in op %u", FLAGS(scan), OP(scan));
-                       break;
                }
            }
            /* Note requires that all BOUNDs be lower than all NBOUNDs in
@@ -5900,7 +5949,7 @@ NULL
            assert(0); /* NOTREACHED */
 
        case WHILEM_A_min_fail: /* just failed to match A in a minimal match */
-           /* FALL THROUGH */
+           /* FALLTHROUGH */
        case WHILEM_A_pre_fail: /* just failed to match even minimal A */
            REGCP_UNWIND(ST.lastcp);
            regcppop(rex, &maxopenparen);
@@ -5977,7 +6026,7 @@ NULL
            if (next == scan)
                next = NULL;
            scan = NEXTOPER(scan);
-           /* FALL THROUGH */
+           /* FALLTHROUGH */
 
        case BRANCH:        /*  /(...|A|...)/ */
            scan = NEXTOPER(scan); /* scan now points to inner node */
@@ -6532,7 +6581,7 @@ NULL
                    assert(0); /* NOTREACHED */
                }
            }
-           /* FALL THROUGH */
+           /* FALLTHROUGH */
 
        case CURLY_B_max_fail:
            /* failed to find B in a greedy match */
@@ -6653,7 +6702,7 @@ NULL
 
        case IFMATCH_A_fail: /* body of (?...A) failed */
            ST.wanted = !ST.wanted;
-           /* FALL THROUGH */
+           /* FALLTHROUGH */
 
        case IFMATCH_A: /* body of (?...A) succeeded */
            if (ST.logical) {
@@ -6817,7 +6866,7 @@ NULL
        /* push a state that backtracks on success */
        st->u.yes.prev_yes_state = yes_state;
        yes_state = st;
-       /* FALL THROUGH */
+       /* FALLTHROUGH */
       push_state:
        /* push a new regex state, then continue at scan  */
        {
@@ -6976,6 +7025,8 @@ no_silent:
                 sv_commit = &PL_sv_yes;
             sv_yes_mark = &PL_sv_no;
         }
+        assert(sv_err);
+        assert(sv_mrk);
         sv_setsv(sv_err, sv_commit);
         sv_setsv(sv_mrk, sv_yes_mark);
     }
@@ -7009,7 +7060,6 @@ STATIC I32
 S_regrepeat(pTHX_ regexp *prog, char **startposp, const regnode *p,
             regmatch_info *const reginfo, I32 max, int depth)
 {
-    dVAR;
     char *scan;     /* Pointer to current position in target string */
     I32 c;
     char *loceol = reginfo->strend;   /* local version */
@@ -7152,7 +7202,7 @@ S_regrepeat(pTHX_ regexp *prog, char **startposp, const regnode *p,
 
     case EXACTFA_NO_TRIE:   /* This node only generated for non-utf8 patterns */
         assert(! reginfo->is_utf8_pat);
-        /* FALL THROUGH */
+        /* FALLTHROUGH */
     case EXACTFA:
         utf8_flags = FOLDEQ_UTF8_NOMIX_ASCII;
        goto do_exactf;
@@ -7292,7 +7342,7 @@ S_regrepeat(pTHX_ regexp *prog, char **startposp, const regnode *p,
             to_complement = 1;
             goto utf8_posix;
         }
-        /* FALL THROUGH */
+        /* FALLTHROUGH */
 
     case NPOSIXA:
         if (! utf8_target) {
@@ -7303,10 +7353,9 @@ S_regrepeat(pTHX_ regexp *prog, char **startposp, const regnode *p,
         else {
 
             /* The complement of something that matches only ASCII matches all
-             * UTF-8 variant code points, plus everything in ASCII that isn't
-             * in the class. */
+             * non-ASCII, plus everything in ASCII that isn't in the class. */
            while (hardcount < max && scan < loceol
-                   && (! UTF8_IS_INVARIANT(*scan)
+                   && (! isASCII_utf8(scan)
                        || ! _generic_isCC_A((U8) *scan, FLAGS(p))))
             {
                 scan += UTF8SKIP(scan);
@@ -7374,7 +7423,7 @@ S_regrepeat(pTHX_ regexp *prog, char **startposp, const regnode *p,
                     case _CC_ENUM_SPACE:    /* XXX would require separate code
                                                if we revert the change of \v
                                                matching this */
-                        /* FALL THROUGH */
+                        /* FALLTHROUGH */
                     case _CC_ENUM_PSXSPC:
                         while (hardcount < max
                                && scan < loceol
@@ -7551,7 +7600,6 @@ Perl__get_regclass_nonbitmap_data(pTHX_ const regexp *prog,
      *    swash are returned  (in a printable form).
      * Tied intimately to how regcomp.c sets up the data structure */
 
-    dVAR;
     SV *sw  = NULL;
     SV *si  = NULL;         /* Input swash initialization string */
     SV*  invlist = NULL;
@@ -7586,6 +7634,7 @@ Perl__get_regclass_nonbitmap_data(pTHX_ const regexp *prog,
                     *only_utf8_locale_ptr = ary[2];
                 }
                 else {
+                    assert(only_utf8_locale_ptr);
                     *only_utf8_locale_ptr = NULL;
                 }
 
@@ -7607,7 +7656,7 @@ Perl__get_regclass_nonbitmap_data(pTHX_ const regexp *prog,
            }
            else if (doinit && ((si && si != &PL_sv_undef)
                                  || (invlist && invlist != &PL_sv_undef))) {
-
+               assert(si);
                sw = _core_swash_init("utf8", /* the utf8 package */
                                      "", /* nameless */
                                      si,
@@ -7622,7 +7671,7 @@ Perl__get_regclass_nonbitmap_data(pTHX_ const regexp *prog,
        
     /* If requested, return a printable version of what this swash matches */
     if (listsvp) {
-       SV* matches_string = newSVpvn("", 0);
+       SV* matches_string = newSVpvs("");
 
         /* The swash should be used, if possible, to get the data, as it
          * contains the resolved data.  But this function can be called at
@@ -7768,20 +7817,19 @@ S_reginclass(pTHX_ regexp * const prog, const regnode * const n, const U8* const
            SV * const sw = _get_regclass_nonbitmap_data(prog, n, TRUE, 0,
                                                             &only_utf8_locale);
            if (sw) {
+                U8 utf8_buffer[2];
                U8 * utf8_p;
                if (utf8_target) {
                    utf8_p = (U8 *) p;
                } else { /* Convert to utf8 */
-                   STRLEN len = 1;
-                   utf8_p = bytes_to_utf8(p, &len);
+                   utf8_p = utf8_buffer;
+                    append_utf8_from_native_byte(*p, &utf8_p);
+                   utf8_p = utf8_buffer;
                }
 
                if (swash_fetch(sw, utf8_p, TRUE)) {
                    match = TRUE;
                 }
-
-               /* If we allocated a string above, free it */
-               if (! utf8_target) Safefree(utf8_p);
            }
             if (! match && only_utf8_locale && IN_UTF8_CTYPE_LOCALE) {
                 match = _invlist_contains_cp(only_utf8_locale, c);
@@ -7814,8 +7862,6 @@ S_reghop3(U8 *s, SSize_t off, const U8* lim)
      * 'off' >= 0, backwards if negative.  But don't go outside of position
      * 'lim', which better be < s  if off < 0 */
 
-    dVAR;
-
     PERL_ARGS_ASSERT_REGHOP3;
 
     if (off >= 0) {
@@ -7840,8 +7886,6 @@ S_reghop3(U8 *s, SSize_t off, const U8* lim)
 STATIC U8 *
 S_reghop4(U8 *s, SSize_t off, const U8* llim, const U8* rlim)
 {
-    dVAR;
-
     PERL_ARGS_ASSERT_REGHOP4;
 
     if (off >= 0) {
@@ -7869,8 +7913,6 @@ S_reghop4(U8 *s, SSize_t off, const U8* llim, const U8* rlim)
 STATIC U8 *
 S_reghopmaybe3(U8* s, SSize_t off, const U8* lim)
 {
-    dVAR;
-
     PERL_ARGS_ASSERT_REGHOPMAYBE3;
 
     if (off >= 0) {
@@ -7987,7 +8029,6 @@ S_setup_eval_state(pTHX_ regmatch_info *const reginfo)
 static void
 S_cleanup_regmatch_info_aux(pTHX_ void *arg)
 {
-    dVAR;
     regmatch_info_aux *aux = (regmatch_info_aux *) arg;
     regmatch_info_aux_eval *eval_state =  aux->info_aux_eval;
     regmatch_slab *s;
@@ -8079,7 +8120,6 @@ S_to_byte_substr(pTHX_ regexp *prog)
     /* Converts substr fields in prog from UTF-8 to bytes, calling fbm_compile
      * on the converted value; returns FALSE if can't be converted. */
 
-    dVAR;
     int i = 1;
 
     PERL_ARGS_ASSERT_TO_BYTE_SUBSTR;