This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
re_intuit_start(): rename some local vars
[perl5.git] / regexec.c
index 23b2d3f..0659724 100644 (file)
--- a/regexec.c
+++ b/regexec.c
@@ -119,7 +119,6 @@ static const char* const non_utf8_target_but_utf8_required
  */
 
 #define CHR_SVLEN(sv) (utf8_target ? sv_len_utf8(sv) : SvCUR(sv))
-#define CHR_DIST(a,b) (reginfo->is_utf8_target ? utf8_distance(a,b) : a - b)
 
 #define HOPc(pos,off) \
        (char *)(reginfo->is_utf8_target \
@@ -127,13 +126,16 @@ static const char* const non_utf8_target_but_utf8_required
                     (U8*)(off >= 0 ? reginfo->strend : reginfo->strbeg)) \
            : (U8*)(pos + off))
 
-#define HOPBACKc(pos, off) \
-       (char*)(reginfo->is_utf8_target \
-           ? reghopmaybe3((U8*)pos, (SSize_t)0-off, (U8*)(reginfo->strbeg)) \
-           : (pos - off >= reginfo->strbeg)    \
-               ? (U8*)pos - off                \
+/* like HOPMAYBE3 but backwards. lim must be +ve. Returns NULL on overshoot */
+#define HOPBACK3(pos, off, lim) \
+       (reginfo->is_utf8_target                          \
+           ? reghopmaybe3((U8*)pos, (SSize_t)0-off, (U8*)(lim)) \
+           : (pos - off >= lim)                                 \
+               ? (U8*)pos - off                                 \
                : NULL)
 
+#define HOPBACKc(pos, off) ((char*)HOPBACK3(pos, off, reginfo->strbeg))
+
 #define HOP3(pos,off,lim) (reginfo->is_utf8_target  ? reghop3((U8*)(pos), off, (U8*)(lim)) : (U8*)(pos + off))
 #define HOP3c(pos,off,lim) ((char*)HOP3(pos,off,lim))
 
@@ -150,6 +152,7 @@ static const char* const non_utf8_target_but_utf8_required
 #define HOP3lim(pos,off,lim) (reginfo->is_utf8_target \
     ? reghop3((U8*)(pos), off, (U8*)(lim)) \
     : (U8*)((pos + off) > lim ? lim : (pos + off)))
+#define HOP3clim(pos,off,lim) ((char*)HOP3lim(pos,off,lim))
 
 #define HOP4(pos,off,llim, rlim) (reginfo->is_utf8_target \
     ? reghop4((U8*)(pos), off, (U8*)(llim), (U8*)(rlim)) \
@@ -445,6 +448,8 @@ S_regcp_restore(pTHX_ regexp *rex, I32 ix, U32 *maxopenparen_p _pDEPTH)
 
 #define regcpblow(cp) LEAVE_SCOPE(cp)  /* Ignores regcppush()ed data. */
 
+#ifndef PERL_IN_XSUB_RE
+
 bool
 Perl_isFOO_lc(pTHX_ const U8 classnum, const U8 character)
 {
@@ -486,6 +491,8 @@ Perl_isFOO_lc(pTHX_ const U8 classnum, const U8 character)
     return FALSE;
 }
 
+#endif
+
 STATIC bool
 S_isFOO_utf8_lc(pTHX_ const U8 classnum, const U8* character)
 {
@@ -630,6 +637,9 @@ Perl_pregexec(pTHX_ REGEXP * const prog, char* stringarg, char *strend,
  *   /\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.
+ *
+ * Note the variables names suffixed with _c represent character counts
+ * while _b represent byte counts
  */
 
 char *
@@ -643,9 +653,16 @@ Perl_re_intuit_start(pTHX_
                     re_scream_pos_data *data)
 {
     struct regexp *const prog = ReANY(rx);
-    SSize_t start_shift = prog->check_offset_min;
-    /* Should be nonnegative! */
-    SSize_t end_shift   = 0;
+
+    /* Minimum number of chars which *must* precede the check substring to
+     * be capable of matching, e.g. 2 in /[ab]cd?substring/. */
+    SSize_t check_min_offset_c = prog->check_offset_min;
+
+    /* Minimum number of chars which *must* follow the check substring to
+     * be capable of matching, e.g. 2 in /substring[ab]cd?/.
+     * Should be nonnegative! */
+
+    SSize_t check_end_shift_c   = 0;
     /* current lowest pos in string where the regex can start matching */
     char *rx_origin = strpos;
     SV *check;
@@ -700,7 +717,7 @@ Perl_re_intuit_start(pTHX_
        goto fail;
     }
 
-    RX_MATCH_UTF8_set(rx,utf8_target);
+    RXp_MATCH_UTF8_set(prog, utf8_target);
     reginfo->is_utf8_target = cBOOL(utf8_target);
     reginfo->info_aux = NULL;
     reginfo->strbeg = strbeg;
@@ -790,7 +807,7 @@ Perl_re_intuit_start(pTHX_
 
            if (prog->check_offset_min == prog->check_offset_max) {
                /* Substring at constant offset from beg-of-str... */
-               SSize_t slen = SvCUR(check);
+               SSize_t slen_b = SvCUR(check);
                 char *s = HOP3c(strpos, prog->check_offset_min, strend);
            
                 DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
@@ -800,23 +817,23 @@ Perl_re_intuit_start(pTHX_
                if (SvTAIL(check)) {
                     /* 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
+                     * exactly, give or take a \n.  NB: slen_b >= 1 since
                      * the last char of check is \n */
                    if (!multiline
-                        && (   strend - s > slen
-                            || strend - s < slen - 1
-                            || (strend - s == slen && strend[-1] != '\n')))
+                        && (   strend - s > slen_b
+                            || strend - s < slen_b - 1
+                            || (strend - s == slen_b && strend[-1] != '\n')))
                     {
                         DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                             "  String too long...\n"));
                         goto fail_finish;
                     }
-                    /* Now should match s[0..slen-2] */
-                    slen--;
+                    /* Now should match s[0..slen_b-2] */
+                    slen_b--;
                 }
-                if (slen && (strend - s < slen
+                if (slen_b && (strend - s < slen_b
                     || *SvPVX_const(check) != *s
-                    || (slen > 1 && (memNE(SvPVX_const(check), s, slen)))))
+                    || (slen_b > 1 && (memNE(SvPVX_const(check), s, slen_b)))))
                 {
                     DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                     "  String not equal...\n"));
@@ -829,12 +846,12 @@ Perl_re_intuit_start(pTHX_
        }
     }
 
-    end_shift = prog->check_end_shift;
+    check_end_shift_c = prog->check_end_shift;
 
 #ifdef DEBUGGING       /* 7/99: reports of failure (with the older version) */
-    if (end_shift < 0)
+    if (check_end_shift_c < 0)
        Perl_croak(aTHX_ "panic: end_shift: %" IVdf " pattern:\n%s\n ",
-                  (IV)end_shift, RX_PRECOMP(prog));
+                  (IV)check_end_shift_c, RX_PRECOMP(rx));
 #endif
 
   restart:
@@ -842,7 +859,7 @@ Perl_re_intuit_start(pTHX_
     /* 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
+     *    (adjusted by check_min_offset_c / check_end_shift_c). 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
@@ -875,13 +892,15 @@ Perl_re_intuit_start(pTHX_
                 " Real end Shift: %" IVdf "\n",
                 (IV)(rx_origin - strbeg),
                 (IV)prog->check_offset_min,
-                (IV)start_shift,
-                (IV)end_shift,
+                (IV)check_min_offset_c,
+                (IV)check_end_shift_c,
                 (IV)prog->check_end_shift);
         });
         
-        end_point = HOP3(strend, -end_shift, strbeg);
-        start_point = HOPMAYBE3(rx_origin, start_shift, end_point);
+        end_point = HOPBACK3(strend, check_end_shift_c, rx_origin);
+        if (!end_point)
+            goto fail_finish;
+        start_point = HOPMAYBE3(rx_origin, check_min_offset_c, end_point);
         if (!start_point)
             goto fail_finish;
 
@@ -898,19 +917,28 @@ Perl_re_intuit_start(pTHX_
             && prog->intflags & PREGf_ANCH
             && prog->check_offset_max != SSize_t_MAX)
         {
-            SSize_t len = SvCUR(check) - !!SvTAIL(check);
+            SSize_t check_len_b = SvCUR(check) - !!SvTAIL(check);
             const char * const anchor =
                         (prog->intflags & PREGf_ANCH_GPOS ? strpos : strbeg);
+            SSize_t targ_len_b = (char*)end_point - anchor;
+
+            if (check_len_b > targ_len_b) {
+                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
+                             "Anchored string too short...\n"));
+                goto fail_finish;
+            }
 
             /* 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) {
+            assert(anchor + check_len_b <= (char *)end_point);
+            if (prog->check_offset_max + check_len_b < targ_len_b) {
                 end_point = HOP3lim((U8*)anchor,
                                 prog->check_offset_max,
-                                end_point -len)
-                            + len;
+                                end_point - check_len_b
+                            )
+                            + check_len_b;
             }
         }
 
@@ -1046,8 +1074,8 @@ Perl_re_intuit_start(pTHX_
                     : (char*)HOP3lim(rx_origin, other->max_offset, last1);
         }
         else {
-            assert(strpos + start_shift <= check_at);
-            last = HOP4c(check_at, other->min_offset - start_shift,
+            assert(strpos + check_min_offset_c <= check_at);
+            last = HOP4c(check_at, other->min_offset - check_min_offset_c,
                         strbeg, strend);
         }
 
@@ -1252,8 +1280,10 @@ Perl_re_intuit_start(pTHX_
     if (progi->regstclass && PL_regkind[OP(progi->regstclass)]!=TRIE) {
         const U8* const str = (U8*)STRING(progi->regstclass);
 
-        /* XXX this value could be pre-computed */
-        const int cl_l = (PL_regkind[OP(progi->regstclass)] == EXACT
+        /* The length (in chars) if the character class. This is almost
+         * always 1.
+         * XXX this value could be pre-computed */
+        const int class_len_c = (PL_regkind[OP(progi->regstclass)] == EXACT
                    ?  (reginfo->is_utf8_pat
                         ? utf8_distance(str + STR_LEN(progi->regstclass), str)
                         : STR_LEN(progi->regstclass))
@@ -1288,18 +1318,20 @@ Perl_re_intuit_start(pTHX_
          */
 
        if (prog->anchored_substr || prog->anchored_utf8 || ml_anch)
-            endpos= HOP3c(rx_origin, (prog->minlen ? cl_l : 0), strend);
+            endpos = HOP3clim(rx_origin,
+                              (prog->minlen ? class_len_c : 0),
+                              strend);
         else if (prog->float_substr || prog->float_utf8) {
-           rx_max_float = HOP3c(check_at, -start_shift, strbeg);
-           endpos= HOP3c(rx_max_float, cl_l, strend);
+           rx_max_float = HOP3c(check_at, -check_min_offset_c, strbeg);
+           endpos = HOP3clim(rx_max_float, class_len_c, strend);
         }
         else 
             endpos= strend;
                    
         DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
-            "  looking for class: start_shift: %" IVdf " check_at: %" IVdf
+            "  looking for class: check_min_offset: %" IVdf " check_at: %" IVdf
             " rx_origin: %" IVdf " endpos: %" IVdf "\n",
-              (IV)start_shift, (IV)(check_at - strbeg),
+              (IV)check_min_offset_c, (IV)(check_at - strbeg),
               (IV)(rx_origin - strbeg), (IV)(endpos - strbeg)));
 
         s = find_byclass(prog, progi->regstclass, rx_origin, endpos,
@@ -1320,8 +1352,8 @@ Perl_re_intuit_start(pTHX_
            if (prog->anchored_substr || prog->anchored_utf8) {
                 if (prog->substrs->check_ix == 1) { /* check is float */
                     /* Have both, check_string is floating */
-                    assert(rx_origin + start_shift <= check_at);
-                    if (rx_origin + start_shift != check_at) {
+                    assert(rx_origin + check_min_offset_c <= check_at);
+                    if (rx_origin + check_min_offset_c != check_at) {
                         /* not at latest position float substr could match:
                          * Recheck anchored substring, but not floating.
                          * The condition above is in bytes rather than
@@ -1375,7 +1407,7 @@ Perl_re_intuit_start(pTHX_
             /* uses bytes rather than char calculations for efficiency.
              * It's conservative: it errs on the side of doing 'goto restart',
              * where there is code that does a proper char-based test */
-            if (rx_origin + start_shift + end_shift > strend) {
+            if (rx_origin + check_min_offset_c + check_end_shift_c > strend) {
                 DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                                        "  Could not match STCLASS...\n") );
                 goto fail;
@@ -1383,7 +1415,7 @@ Perl_re_intuit_start(pTHX_
             DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                 "  about to look for %s substr starting at offset %ld (rx_origin now %" IVdf ")...\n",
                 (prog->substrs->check_ix ? "floating" : "anchored"),
-                (long)(rx_origin + start_shift - strbeg),
+                (long)(rx_origin + check_min_offset_c - strbeg),
                 (IV)(rx_origin - strbeg)
             ));
             goto restart;
@@ -1970,10 +2002,8 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
          * trying that it will fail; so don't start a match past the
          * required minimum number from the far end */
         e = HOP3c(strend, -((SSize_t)ln), s);
-
-        if (reginfo->intuit && e < s) {
-            e = s;                     /* Due to minlen logic of intuit() */
-        }
+        if (e < s)
+            break;
 
         c1 = *pat_string;
         c2 = fold_array[c1];
@@ -2017,10 +2047,6 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
          */
         e = HOP3c(strend, -((SSize_t)lnc), s);
 
-        if (reginfo->intuit && e < s) {
-            e = s;                     /* Due to minlen logic of intuit() */
-        }
-
         /* XXX Note that we could recalculate e to stop the loop earlier,
          * as the worst case expansion above will rarely be met, and as we
          * go along we would usually find that e moves further to the left.
@@ -2768,7 +2794,7 @@ S_reg_set_capture_string(pTHX_ REGEXP * const rx,
             }
             else {
                 /* create new COW SV to share string */
-                RX_MATCH_COPY_FREE(rx);
+                RXp_MATCH_COPY_FREE(prog);
                 prog->saved_copy = sv_setsv_cow(prog->saved_copy, sv);
             }
             prog->subbeg = (char *)SvPVX_const(prog->saved_copy);
@@ -2831,7 +2857,7 @@ S_reg_set_capture_string(pTHX_ REGEXP * const rx,
             assert(min >= 0 && min <= max && min <= strend - strbeg);
             sublen = max - min;
 
-            if (RX_MATCH_COPIED(rx)) {
+            if (RXp_MATCH_COPIED(prog)) {
                 if (sublen > prog->sublen)
                     prog->subbeg =
                             (char*)saferealloc(prog->subbeg, sublen+1);
@@ -2842,7 +2868,7 @@ S_reg_set_capture_string(pTHX_ REGEXP * const rx,
             prog->subbeg[sublen] = '\0';
             prog->suboffset = min;
             prog->sublen = sublen;
-            RX_MATCH_COPIED_on(rx);
+            RXp_MATCH_COPIED_on(prog);
         }
         prog->subcoffset = prog->suboffset;
         if (prog->suboffset && utf8_target) {
@@ -2869,7 +2895,7 @@ S_reg_set_capture_string(pTHX_ REGEXP * const rx,
         }
     }
     else {
-        RX_MATCH_COPY_FREE(rx);
+        RXp_MATCH_COPY_FREE(prog);
         prog->subbeg = strbeg;
         prog->suboffset = 0;
         prog->subcoffset = 0;
@@ -3026,7 +3052,7 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
             /* match via INTUIT shouldn't have any captures.
              * Let @-, @+, $^N know */
             prog->lastparen = prog->lastcloseparen = 0;
-            RX_MATCH_UTF8_set(rx, utf8_target);
+            RXp_MATCH_UTF8_set(prog, utf8_target);
             prog->offs[0].start = s - strbeg;
             prog->offs[0].end = utf8_target
                 ? (char*)utf8_hop((U8*)s, prog->minlenret) - strbeg
@@ -3053,8 +3079,8 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
        Perl_croak(aTHX_ "corrupted regexp program");
     }
 
-    RX_MATCH_TAINTED_off(rx);
-    RX_MATCH_UTF8_set(rx, utf8_target);
+    RXp_MATCH_TAINTED_off(prog);
+    RXp_MATCH_UTF8_set(prog, utf8_target);
 
     reginfo->prog = rx;         /* Yes, sorry that this is confusing.  */
     reginfo->intuit = 0;
@@ -3376,7 +3402,7 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
             regprop(prog, prop, c, reginfo, NULL);
            {
                RE_PV_QUOTED_DECL(quoted,utf8_target,PERL_DEBUG_PAD_ZERO(1),
-                   s,strend-s,60);
+                   s,strend-s,PL_dump_re_max_len);
                 Perl_re_printf( aTHX_
                    "Matching stclass %.*s against %s (%d bytes)\n",
                    (int)SvCUR(prop), SvPVX_const(prop),
@@ -3896,10 +3922,10 @@ S_debug_start_match(pTHX_ const REGEXP *prog, const bool utf8_target,
             reginitcolors();    
     {
         RE_PV_QUOTED_DECL(s0, utf8_pat, PERL_DEBUG_PAD_ZERO(0), 
-            RX_PRECOMP_const(prog), RX_PRELEN(prog), 60);   
+            RX_PRECOMP_const(prog), RX_PRELEN(prog), PL_dump_re_max_len);
         
         RE_PV_QUOTED_DECL(s1, utf8_target, PERL_DEBUG_PAD_ZERO(1),
-            start, end - start, 60); 
+            start, end - start, PL_dump_re_max_len);
         
         Perl_re_printf( aTHX_
             "%s%s REx%s %s against %s\n", 
@@ -3955,11 +3981,11 @@ S_dump_exec_pos(pTHX_ const char *locinput,
        const int is_uni = utf8_target ? 1 : 0;
 
        RE_PV_COLOR_DECL(s0,len0,is_uni,PERL_DEBUG_PAD(0),
-           (locinput - pref_len),pref0_len, 60, 4, 5);
+           (locinput - pref_len),pref0_len, PL_dump_re_max_len, 4, 5);
        
        RE_PV_COLOR_DECL(s1,len1,is_uni,PERL_DEBUG_PAD(1),
                    (locinput - pref_len + pref0_len),
-                   pref_len - pref0_len, 60, 2, 3);
+                   pref_len - pref0_len, PL_dump_re_max_len, 2, 3);
        
        RE_PV_COLOR_DECL(s2,len2,is_uni,PERL_DEBUG_PAD(2),
                    locinput, loc_regeol - locinput, 10, 0, 1);
@@ -4183,7 +4209,7 @@ S_setup_EXACTISH_ST_c1_c2(pTHX_ const regnode * const text_node, int *c1p,
                 }
                 else {  /* Does participate in folds */
                     AV* list = (AV*) *listp;
-                    if (av_tindex_nomg(list) != 1) {
+                    if (av_tindex_skip_len_mg(list) != 1) {
 
                         /* If there aren't exactly two folds to this, it is
                          * outside the scope of this function */
@@ -4342,7 +4368,7 @@ S_isGCB(pTHX_ const GCB_enum before, const GCB_enum after, const U8 * const strb
                 /* Do not break within emoji flag sequences. That is, do not
                  * break between regional indicator (RI) symbols if there is an
                  * odd number of RI characters before the break point.
-                 *  GB12     ^ (RI RI)* RI Ã— RI
+                 *  GB12   sot (RI RI)* RI Ã— RI
                  *  GB13 [^RI] (RI RI)* RI Ã— RI */
 
                 while (backup_one_GCB(strbeg,
@@ -4634,7 +4660,7 @@ S_isLB(pTHX_ LB_enum before,
                  * only if there are an even number of regional indicators
                  * preceding the position of the break.
                  *
-                 *  sot (RI RI)* RI Ã— RI
+                 *    sot (RI RI)* RI Ã— RI
                  *  [^RI] (RI RI)* RI Ã— RI */
 
                 while (backup_one_LB(strbeg,
@@ -5164,7 +5190,7 @@ S_isWB(pTHX_ WB_enum previous,
                  * odd number of RI characters before the potential break
                  * point.
                  *
-                 * WB15     ^ (RI RI)* RI Ã— RI
+                 * WB15   sot (RI RI)* RI Ã— RI
                  * WB16 [^RI] (RI RI)* RI Ã— RI */
 
                 while (backup_one_WB(&previous,
@@ -5345,6 +5371,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
     regnode *next;
     U32 n = 0; /* general value; init to avoid compiler warning */
     SSize_t ln = 0; /* len or last;  init to avoid compiler warning */
+    SSize_t endref = 0; /* offset of end of backref when ln is start */
     char *locinput = startpos;
     char *pushinput; /* where to continue after a PUSH */
     I32 nextchr;   /* is always set to UCHARAT(locinput), or -1 at EOS */
@@ -5371,7 +5398,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
     SV *sv_yes_mark = NULL; /* last mark name we have seen 
                                during a successful match */
     U32 lastopen = 0;       /* last open we saw */
-    bool has_cutgroup = RX_HAS_CUTGROUP(rex) ? 1 : 0;   
+    bool has_cutgroup = RXp_HAS_CUTGROUP(rex) ? 1 : 0;
     SV* const oreplsv = GvSVn(PL_replgv);
     /* these three flags are set by various ops to signal information to
      * the very next op. They have a useful lifetime of exactly one loop
@@ -5392,12 +5419,12 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
     U8 gimme = G_SCALAR;
     CV *caller_cv = NULL;      /* who called us */
     CV *last_pushed_cv = NULL; /* most recently called (?{}) CV */
-    CHECKPOINT runops_cp;      /* savestack position before executing EVAL */
     U32 maxopenparen = 0;       /* max '(' index seen so far */
     int to_complement;  /* Invert the result? */
     _char_class_number classnum;
     bool is_utf8_pat = reginfo->is_utf8_pat;
     bool match = FALSE;
+    I32 orig_savestack_ix = PL_savestack_ix;
 
 /* Solaris Studio 12.3 messes up fetching PL_charclass['\n'] */
 #if (defined(__SUNPRO_C) && (__SUNPRO_C == 0x5120) && defined(__x86_64) && defined(USE_64_BIT_ALL))
@@ -5594,6 +5621,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                 if (scan->flags == EXACTL || scan->flags == EXACTFLU8) {
                     _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
                     if (utf8_target
+                        && nextchr >= 0 /* guard against negative EOS value in nextchr */
                         && UTF8_IS_ABOVE_LATIN1(nextchr)
                         && scan->flags == EXACTL)
                     {
@@ -5737,6 +5765,11 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
         {
             U8 *uc;
             if ( ST.jump ) {
+                /* undo any captures done in the tail part of a branch,
+                 * e.g.
+                 *    /(?:X(.)(.)|Y(.)).../
+                 * where the trie just matches X then calls out to do the
+                 * rest of the branch */
                 REGCP_UNWIND(ST.cp);
                 UNWIND_PAREN(ST.lastparen, ST.lastcloseparen);
            }
@@ -6675,10 +6708,11 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
 
          do_nref_ref_common:
            ln = rex->offs[n].start;
+           endref = rex->offs[n].end;
            reginfo->poscache_iter = reginfo->poscache_maxiter; /* Void cache */
-           if (rex->lastparen < n || ln == -1)
+           if (rex->lastparen < n || ln == -1 || endref == -1)
                sayNO;                  /* Do not match unless seen CLOSEn. */
-           if (ln == rex->offs[n].end)
+           if (ln == endref)
                break;
 
            s = reginfo->strbeg + ln;
@@ -6692,7 +6726,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                     * not going off the end given by reginfo->strend, and
                     * returns in <limit> upon success, how much of the
                     * current input was matched */
-               if (! foldEQ_utf8_flags(s, NULL, rex->offs[n].end - ln, utf8_target,
+               if (! foldEQ_utf8_flags(s, NULL, endref - ln, utf8_target,
                                    locinput, &limit, 0, utf8_target, utf8_fold_flags))
                {
                    sayNO;
@@ -6707,7 +6741,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                (type == REF ||
                 UCHARAT(s) != fold_array[nextchr]))
                sayNO;
-           ln = rex->offs[n].end - ln;
+           ln = endref - ln;
            if (locinput + ln > reginfo->strend)
                sayNO;
            if (ln > 1 && (type == REF
@@ -6786,7 +6820,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
             goto eval_recurse_doit;
             /* NOTREACHED */
 
-        case EVAL:  /*   /(?{A})B/   /(??{A})B/  and /(?(?{A})X|Y)B/   */        
+        case EVAL:  /*   /(?{...})B/   /(??{A})B/  and  /(?(?{...})X|Y)B/   */
             if (cur_eval && cur_eval->locinput==locinput) {
                if ( ++nochange_depth > max_nochange_depth )
                     Perl_croak(aTHX_ "EVAL without pos change exceeded limit in regex");
@@ -6805,7 +6839,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
 
                /* save *all* paren positions */
                 regcppush(rex, 0, maxopenparen);
-               REGCP_SET(runops_cp);
+                REGCP_SET(ST.lastcp);
 
                if (!caller_cv)
                    caller_cv = find_runcv(NULL);
@@ -6830,30 +6864,67 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                    nop = (OP*)rexi->data->data[n];
                }
 
-               /* normally if we're about to execute code from the same
-                * CV that we used previously, we just use the existing
-                * CX stack entry. However, its possible that in the
-                * meantime we may have backtracked, popped from the save
-                * stack, and undone the SAVECOMPPAD(s) associated with
-                * PUSH_MULTICALL; in which case PL_comppad no longer
-                * points to newcv's pad. */
+                /* Some notes about MULTICALL and the context and save stacks.
+                 *
+                 * In something like
+                 *   /...(?{ my $x)}...(?{ my $y)}...(?{ my $z)}.../
+                 * since codeblocks don't introduce a new scope (so that
+                 * local() etc accumulate), at the end of a successful
+                 * match there will be a SAVEt_CLEARSV on the savestack
+                 * for each of $x, $y, $z. If the three code blocks above
+                 * happen to have come from different CVs (e.g. via
+                 * embedded qr//s), then we must ensure that during any
+                 * savestack unwinding, PL_comppad always points to the
+                 * right pad at each moment. We achieve this by
+                 * interleaving SAVEt_COMPPAD's on the savestack whenever
+                 * there is a change of pad.
+                 * In theory whenever we call a code block, we should
+                 * push a CXt_SUB context, then pop it on return from
+                 * that code block. This causes a bit of an issue in that
+                 * normally popping a context also clears the savestack
+                 * back to cx->blk_oldsaveix, but here we specifically
+                 * don't want to clear the save stack on exit from the
+                 * code block.
+                 * Also for efficiency we don't want to keep pushing and
+                 * popping the single SUB context as we backtrack etc.
+                 * So instead, we push a single context the first time
+                 * we need, it, then hang onto it until the end of this
+                 * function. Whenever we encounter a new code block, we
+                 * update the CV etc if that's changed. During the times
+                 * in this function where we're not executing a code
+                 * block, having the SUB context still there is a bit
+                 * naughty - but we hope that no-one notices.
+                 * When the SUB context is initially pushed, we fake up
+                 * cx->blk_oldsaveix to be as if we'd pushed this context
+                 * on first entry to S_regmatch rather than at some random
+                 * point during the regexe execution. That way if we
+                 * croak, popping the context stack will ensure that
+                 * *everything* SAVEd by this function is undone and then
+                 * the context popped, rather than e.g., popping the
+                 * context (and restoring the original PL_comppad) then
+                 * popping more of the savestack and restoring a bad
+                 * PL_comppad.
+                 */
+
+                /* If this is the first EVAL, push a MULTICALL. On
+                 * subsequent calls, if we're executing a different CV, or
+                 * if PL_comppad has got messed up from backtracking
+                 * through SAVECOMPPADs, then refresh the context.
+                 */
                if (newcv != last_pushed_cv || PL_comppad != last_pad)
                {
                     U8 flags = (CXp_SUB_RE |
                                 ((newcv == caller_cv) ? CXp_SUB_RE_FAKE : 0));
+                    SAVECOMPPAD();
                    if (last_pushed_cv) {
-                        /* PUSH/POP_MULTICALL save and restore the
-                         * caller's PL_comppad; if we call multiple subs
-                         * using the same CX block, we have to save and
-                         * unwind the varying PL_comppad's ourselves,
-                         * especially restoring the right PL_comppad on
-                         * backtrack - so save it on the save stack */
-                        SAVECOMPPAD();
                        CHANGE_MULTICALL_FLAGS(newcv, flags);
                    }
                    else {
                        PUSH_MULTICALL_FLAGS(newcv, flags);
                    }
+                    /* see notes above */
+                    CX_CUR()->blk_oldsaveix = orig_savestack_ix;
+
                    last_pushed_cv = newcv;
                }
                else {
@@ -6935,7 +7006,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                if (logical == 0)        /*   (?{})/   */
                    sv_setsv(save_scalar(PL_replgv), ret); /* $^R */
                else if (logical == 1) { /*   /(?(?{...})X|Y)/    */
-                   sw = cBOOL(SvTRUE(ret));
+                   sw = cBOOL(SvTRUE_NN(ret));
                    logical = 0;
                }
                else {                   /*  /(??{})  */
@@ -6970,12 +7041,14 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                 * in the regexp code uses the pad ! */
                PL_op = oop;
                PL_curcop = ocurcop;
-                regcp_restore(rex, runops_cp, &maxopenparen);
+                regcp_restore(rex, ST.lastcp, &maxopenparen);
                 PL_curpm_under = PL_curpm;
                 PL_curpm = PL_reg_curpm;
 
-               if (logical != 2)
-                   break;
+               if (logical != 2) {
+                    PUSH_STATE_GOTO(EVAL_B, next, locinput);
+                   /* NOTREACHED */
+                }
            }
 
                /* only /(??{})/  from now on */
@@ -7073,11 +7146,11 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
                ST.prev_eval = cur_eval;
                cur_eval = st;
                /* now continue from first node in postoned RE */
-               PUSH_YES_STATE_GOTO(EVAL_AB, startpoint, locinput);
+               PUSH_YES_STATE_GOTO(EVAL_postponed_AB, startpoint, locinput);
                NOT_REACHED; /* NOTREACHED */
        }
 
-       case EVAL_AB: /* cleanup after a successful (??{A})B */
+       case EVAL_postponed_AB: /* cleanup after a successful (??{A})B */
             /* note: this is called twice; first after popping B, then A */
             DEBUG_STACK_r({
                 Perl_re_exec_indentf( aTHX_  "EVAL_AB cur_eval=%p prev_eval=%p\n",
@@ -7123,7 +7196,11 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
            sayYES;
 
 
-       case EVAL_AB_fail: /* unsuccessfully ran A or B in (??{A})B */
+       case EVAL_B_fail: /* unsuccessful B in (?{...})B */
+           REGCP_UNWIND(ST.lastcp);
+            sayNO;
+
+       case EVAL_postponed_AB_fail: /* unsuccessfully ran A or B in (??{A})B */
            /* note: this is called twice; first after popping B, then A */
             DEBUG_STACK_r({
                 Perl_re_exec_indentf( aTHX_  "EVAL_AB_fail cur_eval=%p prev_eval=%p\n",
@@ -7523,9 +7600,6 @@ NULL
            if (cur_curlyx->u.curlyx.minmod) {
                ST.save_curlyx = cur_curlyx;
                cur_curlyx = cur_curlyx->u.curlyx.prev_curlyx;
-                ST.cp = regcppush(rex, ST.save_curlyx->u.curlyx.parenfloor,
-                            maxopenparen);
-               REGCP_SET(ST.lastcp);
                PUSH_YES_STATE_GOTO(WHILEM_B_min, ST.save_curlyx->u.curlyx.B,
                                     locinput);
                NOT_REACHED; /* NOTREACHED */
@@ -7558,11 +7632,11 @@ NULL
            CACHEsayNO;
            NOT_REACHED; /* NOTREACHED */
 
-       case WHILEM_A_min_fail: /* just failed to match A in a minimal match */
-           /* FALLTHROUGH */
        case WHILEM_A_pre_fail: /* just failed to match even minimal A */
            REGCP_UNWIND(ST.lastcp);
             regcppop(rex, &maxopenparen);
+           /* FALLTHROUGH */
+       case WHILEM_A_min_fail: /* just failed to match A in a minimal match */
            cur_curlyx->u.curlyx.lastloc = ST.save_lastloc;
            cur_curlyx->u.curlyx.count--;
            CACHEsayNO;
@@ -7595,8 +7669,6 @@ NULL
 
        case WHILEM_B_min_fail: /* just failed to match B in a minimal match */
            cur_curlyx = ST.save_curlyx;
-           REGCP_UNWIND(ST.lastcp);
-            regcppop(rex, &maxopenparen);
 
            if (cur_curlyx->u.curlyx.count >= /*max*/ARG2(cur_curlyx->u.curlyx.me)) {
                /* Maximum greed exceeded */
@@ -7618,9 +7690,6 @@ NULL
            );
            /* Try grabbing another A and see if it helps. */
            cur_curlyx->u.curlyx.lastloc = locinput;
-            ST.cp = regcppush(rex, cur_curlyx->u.curlyx.parenfloor,
-                            maxopenparen);
-           REGCP_SET(ST.lastcp);
            PUSH_STATE_GOTO(WHILEM_A_min,
                /*A*/ NEXTOPER(ST.save_curlyx->u.curlyx.me) + EXTRA_STEP_2ARGS,
                 locinput);
@@ -8225,7 +8294,7 @@ NULL
 
                 SET_RECURSE_LOCINPUT("FAKE-END[after]", cur_eval->locinput);
 
-                PUSH_YES_STATE_GOTO(EVAL_AB, st->u.eval.prev_eval->u.eval.B,
+                PUSH_YES_STATE_GOTO(EVAL_postponed_AB, st->u.eval.prev_eval->u.eval.B,
                                     locinput); /* match B */
            }
 
@@ -8453,7 +8522,8 @@ NULL
             assert(!NEXTCHR_IS_EOS);
             if (utf8_target) {
                 locinput += PL_utf8skip[nextchr];
-                /* locinput is allowed to go 1 char off the end, but not 2+ */
+                /* locinput is allowed to go 1 char off the end (signifying
+                 * EOS), but not 2+ */
                 if (locinput > reginfo->strend)
                     sayNO;
             }
@@ -8481,16 +8551,17 @@ NULL
            DEBUG_STACK_r({
                regmatch_state *cur = st;
                regmatch_state *curyes = yes_state;
-               int curd = depth;
+               U32 i;
                regmatch_slab *slab = PL_regmatch_slab;
-                for (;curd > -1 && (depth-curd < 3);cur--,curd--) {
+                for (i = 0; i < 3 && i <= depth; cur--,i++) {
                     if (cur < SLAB_FIRST(slab)) {
                        slab = slab->prev;
                        cur = SLAB_LAST(slab);
                     }
-                    Perl_re_exec_indentf( aTHX_ "#%-3d %-10s %s\n",
+                    Perl_re_exec_indentf( aTHX_ "%4s #%-3d %-10s %s\n",
                         depth,
-                        curd, PL_reg_name[cur->resume_state],
+                        i ? "    " : "push",
+                        depth - i, PL_reg_name[cur->resume_state],
                         (curyes == cur) ? "yes" : ""
                     );
                     if (curyes == cur)
@@ -8642,9 +8713,12 @@ NULL
 
     if (last_pushed_cv) {
        dSP;
+        /* see "Some notes about MULTICALL" above */
        POP_MULTICALL;
         PERL_UNUSED_VAR(SP);
     }
+    else
+        LEAVE_SCOPE(orig_savestack_ix);
 
     assert(!result ||  locinput - reginfo->strbeg >= 0);
     return result ?  locinput - reginfo->strbeg : -1;
@@ -9704,6 +9778,8 @@ S_to_byte_substr(pTHX_ regexp *prog)
     return TRUE;
 }
 
+#ifndef PERL_IN_XSUB_RE
+
 bool
 Perl__is_grapheme(pTHX_ const U8 * strbeg, const U8 * s, const U8 * strend, const UV cp)
 {
@@ -9759,6 +9835,7 @@ Perl__is_grapheme(pTHX_ const U8 * strbeg, const U8 * s, const U8 * strend, cons
     return isGCB(cp_gcb_val, next_cp_gcb_val, strbeg, s, TRUE);
 }
 
+#endif