make S_regmatch() iterative rather than recursive.
authorDave Mitchell <davem@fdisolutions.com>
Fri, 24 Mar 2006 23:05:11 +0000 (23:05 +0000)
committerDave Mitchell <davem@fdisolutions.com>
Fri, 24 Mar 2006 23:05:11 +0000 (23:05 +0000)
Goodbye stack-bustng regexes!

p4raw-id: //depot/perl@27598

regexec.c

index 2190878..79254eb 100644 (file)
--- a/regexec.c
+++ b/regexec.c
@@ -296,7 +296,7 @@ typedef struct re_cc_state
 
 #define regcpblow(cp) LEAVE_SCOPE(cp)  /* Ignores regcppush()ed data. */
 
-#define TRYPAREN(paren, n, input) {                            \
+#define TRYPAREN(paren, n, input, where) {                     \
     if (paren) {                                               \
        if (n) {                                                \
            PL_regstartp[paren] = HOPc(input, -1) - PL_bostr;   \
@@ -305,7 +305,8 @@ typedef struct re_cc_state
        else                                                    \
            PL_regendp[paren] = -1;                             \
     }                                                          \
-    if (regmatch(next))                                                \
+    REGMATCH(next, where);                                     \
+    if (result)                                                        \
        sayYES;                                                 \
     if (paren && n)                                            \
        PL_regendp[paren] = -1;                                 \
@@ -1646,8 +1647,6 @@ Perl_regexec_flags(pTHX_ register regexp *prog, char *stringarg, register char *
     PERL_UNUSED_ARG(data);
     RX_MATCH_UTF8_set(prog,do_utf8);
 
-    PL_regcc = 0;
-
     cache_re(prog);
 #ifdef DEBUGGING
     PL_regnarrate = DEBUG_r_TEST;
@@ -2313,6 +2312,69 @@ typedef union re_unwind_t {
 #define TRIE_INITAL_ACCEPT_BUFFLEN 4;
 
 
+/* simulate a recursive call to regmatch */
+
+#define REGMATCH(ns, where) \
+    new_scan = (ns); \
+    resume_state = resume_##where; \
+    goto start_recurse; \
+    resume_point_##where:
+
+typedef enum {
+    resume_TRIE1,
+    resume_TRIE2,
+    resume_CURLYX,
+    resume_WHILEM1,
+    resume_WHILEM2,
+    resume_WHILEM3,
+    resume_WHILEM4,
+    resume_WHILEM5,
+    resume_WHILEM6,
+    resume_CURLYM1,
+    resume_CURLYM2,
+    resume_CURLYM3,
+    resume_CURLYM4,
+    resume_IFMATCH,
+    resume_PLUS1,
+    resume_PLUS2,
+    resume_PLUS3,
+    resume_PLUS4,
+    resume_END
+} resume_states;
+
+
+struct regmatch_state {
+    struct regmatch_state *prev_state;
+    resume_states resume_state;
+    regnode *scan;
+    regnode *next;
+    bool minmod;
+    bool sw;
+    int logical;
+    I32 unwind;
+    CURCUR *cc;
+    char *locinput;
+
+    I32 n;
+    I32 ln;
+    I32 c1, c2, paren;
+    CHECKPOINT cp, lastcp;
+    CURCUR *oldcc;
+    char *lastloc;
+    I32 cache_offset, cache_bit;
+    I32 curlym_l;
+    I32 matches;
+    I32 maxwanted;
+    char *e; 
+    char *old;
+    int count;
+    re_cc_state *cur_call_cc;
+    regexp *end_re;
+    reg_trie_accepted *accept_buff;
+    U32 accepted;
+
+    re_cc_state *reg_call_cc;  /* saved value of PL_reg_call_cc */
+};
 
 /*
  - regmatch - main matching routine
@@ -2327,44 +2389,154 @@ typedef union re_unwind_t {
 /* [lwall] I've hoisted the register declarations to the outer block in order to
  * maybe save a little bit of pushing and popping on the stack.  It also takes
  * advantage of machines that use a register save mask on subroutine entry.
+ *
+ * This function used to be heavily recursive, but since this had the
+ * effect of blowing the CPU stack on complex regexes, it has been
+ * restructured to be iterative, and to save state onto the heap rather
+ * than the stack. Essentially whereever regmatch() used to be called, it
+ * pushes the current state, notes where to return, then jumps back into
+ * the main loop.
+ *
+ * Originally the structure of this function used to look something like
+
+    S_regmatch() {
+       int a = 1, b = 2;
+       ...
+       while (scan != NULL) {
+           ...
+           switch (OP(scan)) {
+               case FOO: {
+                   int local = 3;
+                   ...
+                   if (regmatch(...))  // recurse
+                       goto yes;
+               }
+               ...
+           }
+       }
+       yes:
+       return 1;
+    }
+
+ * Now it looks something like this:
+
+    struct regmatch_state {
+       int a, b, local;
+       int resume_state;
+    };
+
+    S_regmatch() {
+       int a = 1, b = 2;
+       int local;
+       ...
+       while (scan != NULL) {
+           ...
+           switch (OP(scan)) {
+               case FOO: {
+                   local = 3;
+                   ...
+                   resume_state = resume_FOO;
+                   new_scan = ...;
+                   goto start_recurse;
+                   resume_point_FOO:
+
+                   if (result)  // recurse
+                       goto yes;
+               }
+               ...
+           }
+           start_recurse:
+           ...push a, b, local onto the heap
+           a = 1; b = 2;
+           scan = new_scan;
+       }
+       yes:
+       result = 1;
+       if (states pushed on heap) {
+           ... restore a, b, local from heap
+           switch (resume_state) {
+           case resume_FOO:
+               goto resume_point_FOO;
+           ...
+           }
+       }
+       return result
+    }
+           
+ * WARNING: this means that any line in this function that contains a
+ * REGMATCH() or TRYPAREN() is actually simulating a recursive call to
+ * regmatch() using gotos instead. Thus the values of any local variables
+ * not saved in the regmatch_state structure will have been lost when
+ * execution resumes on the next line .
  */
+
 STATIC I32                     /* 0 failure, 1 success */
 S_regmatch(pTHX_ regnode *prog)
 {
     dVAR;
+    register const bool do_utf8 = PL_reg_match_utf8;
+    const U32 uniflags = ckWARN(WARN_UTF8) ? 0 : UTF8_ALLOW_ANY;
+
+    /************************************************************
+     * the following variabes are saved and restored on each fake
+     * recursive call to regmatch:
+     *
+     * The first ones contain state that needs to be maintained
+     * across the main while loop: */
+
+    struct regmatch_state *prev_state = NULL; /* stack of pushed states */
+    resume_states resume_state; /* where to jump to on return */
     register regnode *scan;    /* Current node. */
     regnode *next;             /* Next node. */
-    regnode *inner;            /* Next node in internal branch. */
-    register I32 nextchr;      /* renamed nextchr - nextchar colides with
-                                  function of same name */
-    register I32 n;            /* no or next */
-    register I32 ln = 0;       /* len or last */
-    register char *s = NULL;   /* operand or save */
+    bool minmod = 0;           /* the next {n.m} is a {n,m}? */
+    bool sw = 0;               /* the condition value in (?(cond)a|b) */
+    int logical = 0;
+    I32 unwind = 0;            /* savestack index of current unwind block */
+    CURCUR *cc = NULL;         /* current innermost curly struct */
     register char *locinput = PL_reginput;
-    register I32 c1 = 0, c2 = 0, paren;        /* case fold search, parenth */
-    int minmod = 0, sw = 0, logical = 0;
-    I32 unwind = 0;
 
-#if 0
-    I32 firstcp = PL_savestack_ix;
-#endif
-    register const bool do_utf8 = PL_reg_match_utf8;
-#ifdef DEBUGGING
-    SV * const dsv0 = PERL_DEBUG_PAD_ZERO(0);
-    SV * const dsv1 = PERL_DEBUG_PAD_ZERO(1);
-    SV * const dsv2 = PERL_DEBUG_PAD_ZERO(2);
+    /* while the rest of these are local to an individual branch, and
+     * have only been hoisted into this outer scope to allow for saving and
+     * restoration - thus they can be safely reused in other branches.
+     * Note that they are only initialized here to silence compiler
+     * warnings :-( */
 
+    register I32 n = 0;                /* no or next */
+    register I32 ln = 0;       /* len or last */
+    register I32 c1 = 0, c2 = 0, paren = 0; /* case fold search, parenth */
+    CHECKPOINT cp = 0;         /* remember current savestack indexes */
+    CHECKPOINT lastcp = 0;
+    CURCUR *oldcc = NULL;      /* tmp copy of cc */
+    char *lastloc = NULL;      /* Detection of 0-len. */
+    I32 cache_offset = 0;
+    I32 cache_bit = 0;
+    I32 curlym_l = 0;
+    I32 matches = 0;
+    I32 maxwanted = 0;
+    char *e = NULL;
+    char *old = NULL;
+    int count = 0;
+    re_cc_state *cur_call_cc = NULL;
+    regexp *end_re = NULL;
+    reg_trie_accepted *accept_buff = NULL;
+    U32 accepted = 0; /* how many accepting states we have seen */
+
+    /************************************************************
+     * these variables are NOT saved: */
+
+    register I32 nextchr;   /* is always set to UCHARAT(locinput) */
+    regnode *new_scan; /* node to begin exedcution at when recursing */
+    bool result;       /* return value of S_regmatch */
+
+    regnode *inner;    /* Next node in internal branch. */
+    
+#ifdef DEBUGGING
     SV *re_debug_flags = NULL;
-#endif
-    U32 uniflags = ckWARN(WARN_UTF8) ? 0 : UTF8_ALLOW_ANY;
-
     GET_RE_DEBUG_FLAGS;
-
-#ifdef DEBUGGING
     PL_regindent++;
 #endif
 
-
     /* Note that nextchr is a byte even in UTF */
     nextchr = UCHARAT(locinput);
     scan = prog;
@@ -2401,17 +2573,18 @@ S_regmatch(pTHX_ regnode *prog)
            {
              const char * const s0 =
                do_utf8 && OP(scan) != CANY ?
-               pv_uni_display(dsv0, (U8*)(locinput - pref_len),
+               pv_uni_display(PERL_DEBUG_PAD(0), (U8*)(locinput - pref_len),
                               pref0_len, 60, UNI_DISPLAY_REGEX) :
                locinput - pref_len;
              const int len0 = do_utf8 ? strlen(s0) : pref0_len;
              const char * const s1 = do_utf8 && OP(scan) != CANY ?
-               pv_uni_display(dsv1, (U8*)(locinput - pref_len + pref0_len),
+               pv_uni_display(PERL_DEBUG_PAD(1),
+                              (U8*)(locinput - pref_len + pref0_len),
                               pref_len - pref0_len, 60, UNI_DISPLAY_REGEX) :
                locinput - pref_len + pref0_len;
              const int len1 = do_utf8 ? strlen(s1) : pref_len - pref0_len;
              const char * const s2 = do_utf8 && OP(scan) != CANY ?
-               pv_uni_display(dsv2, (U8*)locinput,
+               pv_uni_display(PERL_DEBUG_PAD(2), (U8*)locinput,
                               PL_regeol - locinput, 60, UNI_DISPLAY_REGEX) :
                locinput;
              const int len2 = do_utf8 ? strlen(s2) : l;
@@ -2530,18 +2703,16 @@ S_regmatch(pTHX_ regnode *prog)
                STRLEN foldlen = 0;
                U8 *uscan = (U8*)NULL;
                STRLEN bufflen=0;
+               SV *sv_accept_buff = NULL;
                const enum { trie_plain, trie_utf8, trie_uft8_fold }
                    trie_type = do_utf8 ?
                          (OP(scan) == TRIE ? trie_utf8 : trie_uft8_fold)
                        : trie_plain;
 
-               int gotit = 0;
-               /* accepting states we have traversed */
-               SV *sv_accept_buff = NULL;
-               reg_trie_accepted  *accept_buff = NULL;
                reg_trie_data *trie; /* what trie are we using right now */
-               U32 accepted = 0; /* how many accepting states we have seen */
 
+               accepted = 0; /* how many accepting states we have seen */
+               result = 0;
                trie = (reg_trie_data*)PL_regdata->data[ ARG( scan ) ];
 
                while ( state && uc <= (U8*)PL_regeol ) {
@@ -2679,14 +2850,15 @@ S_regmatch(pTHX_ regnode *prog)
                       as we wont be using accept_buff again. */
                    FREETMPS;
                    LEAVE;
-                   gotit = regmatch( scan + NEXT_OFF( scan ) );
+                   REGMATCH(scan + NEXT_OFF(scan), TRIE1);
+                   /*** all unsaved local vars undefined at this point */
                } else {
                     DEBUG_EXECUTE_r(
                         PerlIO_printf( Perl_debug_log,"%*s  %sgot %"IVdf" possible matches%s\n",
                             REPORT_CODE_OFF + PL_regindent * 2, "", PL_colors[4], (IV)accepted,
                             PL_colors[5] );
                     );
-                   while ( !gotit && accepted-- ) {
+                   while ( !result && accepted-- ) {
                        U32 best = 0;
                        U32 cur;
                        for( cur = 1 ; cur <= accepted ; cur++ ) {
@@ -2723,22 +2895,23 @@ S_regmatch(pTHX_ regnode *prog)
                            all until I can be sure.
                          */
                        SAVETMPS;
-                       gotit = regmatch( scan + NEXT_OFF( scan ) ) ;
+                       REGMATCH(scan + NEXT_OFF(scan), TRIE2);
+                       /*** all unsaved local vars undefined at this point */
                        FREETMPS;
                    }
                    FREETMPS;
                    LEAVE;
                }
                
-               if ( gotit ) {
+               if (result) {
                    sayYES;
                } else {
                    sayNO;
                }
            }
            /* unreached codepoint */
-       case EXACT:
-           s = STRING(scan);
+       case EXACT: {
+           char *s = STRING(scan);
            ln = STR_LEN(scan);
            if (do_utf8 != UTF) {
                /* The target and the pattern have differing utf8ness. */
@@ -2788,11 +2961,12 @@ S_regmatch(pTHX_ regnode *prog)
            locinput += ln;
            nextchr = UCHARAT(locinput);
            break;
+           }
        case EXACTFL:
            PL_reg_flags |= RF_tainted;
            /* FALL THROUGH */
-       case EXACTF:
-           s = STRING(scan);
+       case EXACTF: {
+           char *s = STRING(scan);
            ln = STR_LEN(scan);
 
            if (do_utf8 || UTF) {
@@ -2836,6 +3010,7 @@ S_regmatch(pTHX_ regnode *prog)
            locinput += ln;
            nextchr = UCHARAT(locinput);
            break;
+           }
        case ANYOF:
            if (do_utf8) {
                STRLEN inclasslen = PL_regeol - locinput;
@@ -3078,7 +3253,8 @@ S_regmatch(pTHX_ regnode *prog)
            PL_reg_flags |= RF_tainted;
            /* FALL THROUGH */
         case REF:
-       case REFF:
+       case REFF: {
+           char *s;
            n = ARG(scan);  /* which paren pair */
            ln = PL_regstartp[n];
            PL_reg_leftiter = PL_reg_maxiter;           /* Void cache */
@@ -3135,6 +3311,7 @@ S_regmatch(pTHX_ regnode *prog)
            locinput += ln;
            nextchr = UCHARAT(locinput);
            break;
+           }
 
        case NOTHING:
        case TAIL:
@@ -3176,7 +3353,6 @@ S_regmatch(pTHX_ regnode *prog)
                    regexp *re;
                    MAGIC *mg = NULL;
                    re_cc_state state;
-                   CHECKPOINT cp, lastcp;
                     int toggleutf;
                    register SV *sv;
 
@@ -3223,10 +3399,10 @@ S_regmatch(pTHX_ regnode *prog)
                        );
                    state.node = next;
                    state.prev = PL_reg_call_cc;
-                   state.cc = PL_regcc;
+                   state.cc = cc;
                    state.re = PL_reg_re;
 
-                   PL_regcc = 0;
+                   cc = 0;
                
                    cp = regcppush(0);  /* Save *all* the positions. */
                    REGCP_SET(lastcp);
@@ -3243,6 +3419,7 @@ S_regmatch(pTHX_ regnode *prog)
                    /* XXXX This is too dramatic a measure... */
                    PL_reg_maxiter = 0;
 
+                   /* XXX the only recursion left in regmatch() */
                    if (regmatch(re->program + 1)) {
                        /* Even though we succeeded, we need to restore
                           global variables, since we may be wrapped inside
@@ -3250,7 +3427,7 @@ S_regmatch(pTHX_ regnode *prog)
 
                        /* XXXX Do this only if SUSPENDed? */
                        PL_reg_call_cc = state.prev;
-                       PL_regcc = state.cc;
+                       cc = state.cc;
                        PL_reg_re = state.re;
                        cache_re(PL_reg_re);
                        if (toggleutf) PL_reg_flags ^= RF_utf8;
@@ -3267,7 +3444,7 @@ S_regmatch(pTHX_ regnode *prog)
                    REGCP_UNWIND(lastcp);
                    regcppop();
                    PL_reg_call_cc = state.prev;
-                   PL_regcc = state.cc;
+                   cc = state.cc;
                    PL_reg_re = state.re;
                    cache_re(PL_reg_re);
                    if (toggleutf) PL_reg_flags ^= RF_utf8;
@@ -3319,15 +3496,15 @@ S_regmatch(pTHX_ regnode *prog)
            logical = scan->flags;
            break;
 /*******************************************************************
- PL_regcc contains infoblock about the innermost (...)* loop, and
+ cc contains infoblock about the innermost (...)* loop, and
  a pointer to the next outer infoblock.
 
  Here is how Y(A)*Z is processed (if it is compiled into CURLYX/WHILEM):
 
-   1) After matching X, regnode for CURLYX is processed;
+   1) After matching Y, regnode for CURLYX is processed;
 
-   2) This regnode creates infoblock on the stack, and calls
-      regmatch() recursively with the starting point at WHILEM node;
+   2) This regnode mallocs an infoblock, and calls regmatch() recursively
+      with the starting point at WHILEM node;
 
    3) Each hit of WHILEM node tries to match A and Z (in the order
       depending on the current iteration, min/max of {min,max} and
@@ -3337,9 +3514,9 @@ S_regmatch(pTHX_ regnode *prog)
 
    4) After A matches, the same WHILEM node is hit again.
 
-   5) Each time WHILEM is hit, PL_regcc is the infoblock created by CURLYX
+   5) Each time WHILEM is hit, cc is the infoblock created by CURLYX
       of the same pair.  Thus when WHILEM tries to match Z, it temporarily
-      resets PL_regcc, since this Y(A)*Z can be a part of some other loop:
+      resets cc, since this Y(A)*Z can be a part of some other loop:
       as in (Y(A)*Z)*.  If Z matches, the automaton will hit the WHILEM node
       of the external loop.
 
@@ -3347,7 +3524,7 @@ S_regmatch(pTHX_ regnode *prog)
  and whatever it mentions via ->next, and additional attached trees
  corresponding to temporarily unset infoblocks as in "5" above.
 
- In the following picture infoblocks for outer loop of
+ In the following picture, infoblocks for outer loop of
  (Y(A)*?Z)*?T are denoted O, for inner I.  NULL starting block
  is denoted by x.  The matched string is YAAZYAZT.  Temporarily postponed
  infoblocks are drawn below the "reset" infoblock.
@@ -3393,33 +3570,40 @@ S_regmatch(pTHX_ regnode *prog)
                                O
                                I,I
  *******************************************************************/
+
        case CURLYX: {
-               CURCUR cc;
-               CHECKPOINT cp = PL_savestack_ix;
                /* No need to save/restore up to this paren */
                I32 parenfloor = scan->flags;
 
+               {
+                   CURCUR *newcc;
+                   Newx(newcc, 1, CURCUR);
+                   oldcc = cc;
+                   newcc->oldcc = cc;
+                   cc = newcc;
+               }
+               cp = PL_savestack_ix;
                if (OP(PREVOPER(next)) == NOTHING) /* LONGJMP */
                    next += ARG(next);
-               cc.oldcc = PL_regcc;
-               PL_regcc = &cc;
                /* XXXX Probably it is better to teach regpush to support
                   parenfloor > PL_regsize... */
                if (parenfloor > (I32)*PL_reglastparen)
                    parenfloor = *PL_reglastparen; /* Pessimization... */
-               cc.parenfloor = parenfloor;
-               cc.cur = -1;
-               cc.min = ARG1(scan);
-               cc.max  = ARG2(scan);
-               cc.scan = NEXTOPER(scan) + EXTRA_STEP_2ARGS;
-               cc.next = next;
-               cc.minmod = minmod;
-               cc.lastloc = 0;
+               cc->parenfloor = parenfloor;
+               cc->cur = -1;
+               cc->min = ARG1(scan);
+               cc->max  = ARG2(scan);
+               cc->scan = NEXTOPER(scan) + EXTRA_STEP_2ARGS;
+               cc->next = next;
+               cc->minmod = minmod;
+               cc->lastloc = 0;
                PL_reginput = locinput;
-               n = regmatch(PREVOPER(next));   /* start on the WHILEM */
+               REGMATCH(PREVOPER(next), CURLYX); /* start on the WHILEM */
+               /*** all unsaved local vars undefined at this point */
                regcpblow(cp);
-               PL_regcc = cc.oldcc;
-               saySAME(n);
+               Safefree(cc);
+               cc = oldcc;
+               saySAME(result);
            }
            /* NOTREACHED */
        case WHILEM: {
@@ -3432,10 +3616,9 @@ S_regmatch(pTHX_ regnode *prog)
                 * that we can try again after backing off.
                 */
 
-               CHECKPOINT cp, lastcp;
-               CURCUR* cc = PL_regcc;
-               char * const lastloc = cc->lastloc; /* Detection of 0-len. */
-               I32 cache_offset = 0, cache_bit = 0;
+               lastloc = cc->lastloc; /* Detection of 0-len. */
+               cache_offset = 0;
+               cache_bit = 0;
                
                n = cc->cur + 1;        /* how many we know we matched */
                PL_reginput = locinput;
@@ -3451,19 +3634,22 @@ S_regmatch(pTHX_ regnode *prog)
                /* If degenerate scan matches "", assume scan done. */
 
                if (locinput == cc->lastloc && n >= cc->min) {
-                   PL_regcc = cc->oldcc;
-                   if (PL_regcc)
-                       ln = PL_regcc->cur;
+                   oldcc = cc;
+                   cc = cc->oldcc;
+                   if (cc)
+                       ln = cc->cur;
                    DEBUG_EXECUTE_r(
                        PerlIO_printf(Perl_debug_log,
                           "%*s  empty match detected, try continuation...\n",
                           REPORT_CODE_OFF+PL_regindent*2, "")
                        );
-                   if (regmatch(cc->next))
+                   REGMATCH(oldcc->next, WHILEM1);
+                   /*** all unsaved local vars undefined at this point */
+                   cc = oldcc;
+                   if (result)
                        sayYES;
-                   if (PL_regcc)
-                       PL_regcc->cur = ln;
-                   PL_regcc = cc;
+                   if (cc->oldcc)
+                       cc->oldcc->cur = ln;
                    sayNO;
                }
 
@@ -3472,7 +3658,9 @@ S_regmatch(pTHX_ regnode *prog)
                if (n < cc->min) {
                    cc->cur = n;
                    cc->lastloc = locinput;
-                   if (regmatch(cc->scan))
+                   REGMATCH(cc->scan, WHILEM2);
+                   /*** all unsaved local vars undefined at this point */
+                   if (result)
                        sayYES;
                    cc->cur = n - 1;
                    cc->lastloc = lastloc;
@@ -3533,20 +3721,23 @@ S_regmatch(pTHX_ regnode *prog)
                /* Prefer next over scan for minimal matching. */
 
                if (cc->minmod) {
-                   PL_regcc = cc->oldcc;
-                   if (PL_regcc)
-                       ln = PL_regcc->cur;
-                   cp = regcppush(cc->parenfloor);
+                   oldcc = cc;
+                   cc = cc->oldcc;
+                   if (cc)
+                       ln = cc->cur;
+                   cp = regcppush(oldcc->parenfloor);
                    REGCP_SET(lastcp);
-                   if (regmatch(cc->next)) {
+                   REGMATCH(oldcc->next, WHILEM3);
+                   /*** all unsaved local vars undefined at this point */
+                   cc = oldcc;
+                   if (result) {
                        regcpblow(cp);
                        CACHEsayYES;    /* All done. */
                    }
                    REGCP_UNWIND(lastcp);
                    regcppop();
-                   if (PL_regcc)
-                       PL_regcc->cur = ln;
-                   PL_regcc = cc;
+                   if (cc->oldcc)
+                       cc->oldcc->cur = ln;
 
                    if (n >= cc->max) { /* Maximum greed exceeded? */
                        if (ckWARN(WARN_REGEXP) && n >= REG_INFTY
@@ -3570,7 +3761,9 @@ S_regmatch(pTHX_ regnode *prog)
                    cc->lastloc = locinput;
                    cp = regcppush(cc->parenfloor);
                    REGCP_SET(lastcp);
-                   if (regmatch(cc->scan)) {
+                   REGMATCH(cc->scan, WHILEM4);
+                   /*** all unsaved local vars undefined at this point */
+                   if (result) {
                        regcpblow(cp);
                        CACHEsayYES;
                    }
@@ -3588,7 +3781,9 @@ S_regmatch(pTHX_ regnode *prog)
                    cc->cur = n;
                    cc->lastloc = locinput;
                    REGCP_SET(lastcp);
-                   if (regmatch(cc->scan)) {
+                   REGMATCH(cc->scan, WHILEM5);
+                   /*** all unsaved local vars undefined at this point */
+                   if (result) {
                        regcpblow(cp);
                        CACHEsayYES;
                    }
@@ -3610,14 +3805,17 @@ S_regmatch(pTHX_ regnode *prog)
                }
 
                /* Failed deeper matches of scan, so see if this one works. */
-               PL_regcc = cc->oldcc;
-               if (PL_regcc)
-                   ln = PL_regcc->cur;
-               if (regmatch(cc->next))
+               oldcc = cc;
+               cc = cc->oldcc;
+               if (cc)
+                   ln = cc->cur;
+               REGMATCH(oldcc->next, WHILEM6);
+               /*** all unsaved local vars undefined at this point */
+               cc = oldcc;
+               if (result)
                    CACHEsayYES;
-               if (PL_regcc)
-                   PL_regcc->cur = ln;
-               PL_regcc = cc;
+               if (cc->oldcc)
+                   cc->oldcc->cur = ln;
                cc->cur = n - 1;
                cc->lastloc = lastloc;
                CACHEsayNO;
@@ -3667,10 +3865,7 @@ S_regmatch(pTHX_ regnode *prog)
            break;
        case CURLYM:
        {
-           I32 l = 0;
-           I32 matches = 0;
-           CHECKPOINT lastcp;
-           I32 maxwanted;
+           curlym_l = matches = 0;
        
            /* We suppose that the next guy does not need
               backtracking: in particular, it is of constant non-zero length,
@@ -3691,21 +3886,23 @@ S_regmatch(pTHX_ regnode *prog)
            maxwanted = minmod ? ln : n;
            if (maxwanted) {
                while (PL_reginput < PL_regeol && matches < maxwanted) {
-                   if (!regmatch(scan))
+                   REGMATCH(scan, CURLYM1);
+                   /*** all unsaved local vars undefined at this point */
+                   if (!result)
                        break;
-                   /* on first match, determine length, l */
+                   /* on first match, determine length, curlym_l */
                    if (!matches++) {
                        if (PL_reg_match_utf8) {
                            char *s = locinput;
                            while (s < PL_reginput) {
-                               l++;
+                               curlym_l++;
                                s += UTF8SKIP(s);
                            }
                        }
                        else {
-                           l = PL_reginput - locinput;
+                           curlym_l = PL_reginput - locinput;
                        }
-                       if (l == 0) {
+                       if (curlym_l == 0) {
                            matches = maxwanted;
                            break;
                        }
@@ -3753,19 +3950,23 @@ S_regmatch(pTHX_ regnode *prog)
                        if (paren) {
                            if (ln) {
                                PL_regstartp[paren] =
-                                   HOPc(PL_reginput, -l) - PL_bostr;
+                                   HOPc(PL_reginput, -curlym_l) - PL_bostr;
                                PL_regendp[paren] = PL_reginput - PL_bostr;
                            }
                            else
                                PL_regendp[paren] = -1;
                        }
-                       if (regmatch(next))
+                       REGMATCH(next, CURLYM2);
+                       /*** all unsaved local vars undefined at this point */
+                       if (result)
                            sayYES;
                        REGCP_UNWIND(lastcp);
                    }
                    /* Couldn't or didn't -- move forward. */
                    PL_reginput = locinput;
-                   if (regmatch(scan)) {
+                   REGMATCH(scan, CURLYM3);
+                   /*** all unsaved local vars undefined at this point */
+                   if (result) {
                        ln++;
                        locinput = PL_reginput;
                    }
@@ -3776,9 +3977,9 @@ S_regmatch(pTHX_ regnode *prog)
            else {
                DEBUG_EXECUTE_r(
                    PerlIO_printf(Perl_debug_log,
-                                 "%*s  matched %"IVdf" times, len=%"IVdf"...\n",
-                                 (int)(REPORT_CODE_OFF+PL_regindent*2), "",
-                                 (IV) matches, (IV)l)
+                             "%*s  matched %"IVdf" times, len=%"IVdf"...\n",
+                             (int)(REPORT_CODE_OFF+PL_regindent*2), "",
+                             (IV) matches, (IV)curlym_l)
                    );
                if (matches >= ln) {
                    if (HAS_TEXT(next) || JUMPABLE(next)) {
@@ -3821,19 +4022,22 @@ S_regmatch(pTHX_ regnode *prog)
                            );
                        if (paren) {
                            if (matches) {
-                               PL_regstartp[paren] = HOPc(PL_reginput, -l) - PL_bostr;
+                               PL_regstartp[paren]
+                                   = HOPc(PL_reginput, -curlym_l) - PL_bostr;
                                PL_regendp[paren] = PL_reginput - PL_bostr;
                            }
                            else
                                PL_regendp[paren] = -1;
                        }
-                       if (regmatch(next))
+                       REGMATCH(next, CURLYM4);
+                       /*** all unsaved local vars undefined at this point */
+                       if (result)
                            sayYES;
                        REGCP_UNWIND(lastcp);
                    }
                    /* Couldn't or didn't -- back up. */
                    matches--;
-                   locinput = HOPc(locinput, -l);
+                   locinput = HOPc(locinput, -curlym_l);
                    PL_reginput = locinput;
                }
            }
@@ -3927,16 +4131,14 @@ S_regmatch(pTHX_ regnode *prog)
        assume_ok_easy:
            PL_reginput = locinput;
            if (minmod) {
-               CHECKPOINT lastcp;
                minmod = 0;
                if (ln && regrepeat(scan, ln) < ln)
                    sayNO;
                locinput = PL_reginput;
                REGCP_SET(lastcp);
                if (c1 != -1000) {
-                   char *e; /* Should not check after this */
-                   char *old = locinput;
-                   int count = 0;
+                   old = locinput;
+                   count = 0;
 
                    if  (n == REG_INFTY) {
                        e = PL_regeol - 1;
@@ -4006,7 +4208,8 @@ S_regmatch(pTHX_ regnode *prog)
                                sayNO;
                        }
                        /* PL_reginput == locinput now */
-                       TRYPAREN(paren, ln, locinput);
+                       TRYPAREN(paren, ln, locinput, PLUS1);
+                       /*** all unsaved local vars undefined at this point */
                        PL_reginput = locinput; /* Could be reset... */
                        REGCP_UNWIND(lastcp);
                        /* Couldn't or didn't -- move forward. */
@@ -4031,14 +4234,16 @@ S_regmatch(pTHX_ regnode *prog)
                        /* If it could work, try it. */
                        if (c == (UV)c1 || c == (UV)c2)
                        {
-                           TRYPAREN(paren, ln, PL_reginput);
+                           TRYPAREN(paren, ln, PL_reginput, PLUS2);
+                           /*** all unsaved local vars undefined at this point */
                            REGCP_UNWIND(lastcp);
                        }
                    }
                    /* If it could work, try it. */
                    else if (c1 == -1000)
                    {
-                       TRYPAREN(paren, ln, PL_reginput);
+                       TRYPAREN(paren, ln, PL_reginput, PLUS3);
+                       /*** all unsaved local vars undefined at this point */
                        REGCP_UNWIND(lastcp);
                    }
                    /* Couldn't or didn't -- move forward. */
@@ -4052,7 +4257,6 @@ S_regmatch(pTHX_ regnode *prog)
                }
            }
            else {
-               CHECKPOINT lastcp;
                n = regrepeat(scan, n);
                locinput = PL_reginput;
                if (ln < n && PL_regkind[(U8)OP(next)] == EOL &&
@@ -4081,7 +4285,8 @@ S_regmatch(pTHX_ regnode *prog)
                        /* If it could work, try it. */
                        if (c1 == -1000 || c == (UV)c1 || c == (UV)c2)
                            {
-                               TRYPAREN(paren, n, PL_reginput);
+                               TRYPAREN(paren, n, PL_reginput, PLUS4);
+                               /*** all unsaved local vars undefined at this point */
                                REGCP_UNWIND(lastcp);
                            }
                        /* Couldn't or didn't -- back up. */
@@ -4094,29 +4299,31 @@ S_regmatch(pTHX_ regnode *prog)
            break;
        case END:
            if (PL_reg_call_cc) {
-               re_cc_state *cur_call_cc = PL_reg_call_cc;
-               CURCUR *cctmp = PL_regcc;
-               regexp *re = PL_reg_re;
-               CHECKPOINT lastcp;
-               I32 tmp;
+               cur_call_cc = PL_reg_call_cc;
+               end_re = PL_reg_re;
 
                /* Save *all* the positions. */
-               const CHECKPOINT cp = regcppush(0);
+               cp = regcppush(0);
                REGCP_SET(lastcp);
 
                /* Restore parens of the caller. */
-               tmp = PL_savestack_ix;
-               PL_savestack_ix = PL_reg_call_cc->ss;
-               regcppop();
-               PL_savestack_ix = tmp;
+               {
+                   I32 tmp = PL_savestack_ix;
+                   PL_savestack_ix = PL_reg_call_cc->ss;
+                   regcppop();
+                   PL_savestack_ix = tmp;
+               }
 
                /* Make position available to the callcc. */
                PL_reginput = locinput;
 
                cache_re(PL_reg_call_cc->re);
-               PL_regcc = PL_reg_call_cc->cc;
+               oldcc = cc;
+               cc = PL_reg_call_cc->cc;
                PL_reg_call_cc = PL_reg_call_cc->prev;
-               if (regmatch(cur_call_cc->node)) {
+               REGMATCH(cur_call_cc->node, END);
+               /*** all unsaved local vars undefined at this point */
+               if (result) {
                    PL_reg_call_cc = cur_call_cc;
                    regcpblow(cp);
                    sayYES;
@@ -4124,9 +4331,9 @@ S_regmatch(pTHX_ regnode *prog)
                REGCP_UNWIND(lastcp);
                regcppop();
                PL_reg_call_cc = cur_call_cc;
-               PL_regcc = cctmp;
-               PL_reg_re = re;
-               cache_re(re);
+               cc = oldcc;
+               PL_reg_re = end_re;
+               cache_re(end_re);
 
                DEBUG_EXECUTE_r(
                    PerlIO_printf(Perl_debug_log,
@@ -4156,7 +4363,7 @@ S_regmatch(pTHX_ regnode *prog)
        case UNLESSM:
            n = 0;
            if (scan->flags) {
-               s = HOPBACKc(locinput, scan->flags);
+               char *s = HOPBACKc(locinput, scan->flags);
                if (!s)
                    goto say_yes;
                PL_reginput = s;
@@ -4167,7 +4374,7 @@ S_regmatch(pTHX_ regnode *prog)
        case IFMATCH:
            n = 1;
            if (scan->flags) {
-               s = HOPBACKc(locinput, scan->flags);
+               char *s = HOPBACKc(locinput, scan->flags);
                if (!s)
                    goto say_no;
                PL_reginput = s;
@@ -4176,8 +4383,9 @@ S_regmatch(pTHX_ regnode *prog)
                PL_reginput = locinput;
 
          do_ifmatch:
-           inner = NEXTOPER(NEXTOPER(scan));
-           if (regmatch(inner) != n) {
+           REGMATCH(NEXTOPER(NEXTOPER(scan)), IFMATCH);
+           /*** all unsaved local vars undefined at this point */
+           if (result != n) {
              say_no:
                if (logical) {
                    logical = 0;
@@ -4208,8 +4416,68 @@ S_regmatch(pTHX_ regnode *prog)
                          PTR2UV(scan), OP(scan));
            Perl_croak(aTHX_ "regexp memory corruption");
        }
+
       reenter:
        scan = next;
+       continue;
+       /* NOTREACHED */
+
+       /* simulate recursively calling regmatch(), but without actually
+        * recursing - ie save the current state on the heap rather than on
+        * the stack, then re-enter the loop. This avoids complex regexes
+        * blowing the processor stack */
+
+      start_recurse:
+       {
+           /* save existing local variables */
+           struct regmatch_state *p;
+
+           Newx(p, 1, struct regmatch_state);
+           p->prev_state = prev_state;
+           prev_state = p;
+           p->resume_state = resume_state;
+           p->scan = scan;
+           p->next = next;
+           p->minmod = minmod;
+           p->sw = sw;
+           p->logical = logical;
+           p->unwind = unwind;
+           p->cc = cc;
+           p->locinput = locinput;
+           p->n = n;
+           p->ln = ln;
+           p->c1 = c1;
+           p->c2 = c2;
+           p->paren = paren;
+           p->cp = cp;
+           p->lastcp = lastcp;
+           p->oldcc = oldcc;
+           p->lastloc = lastloc;
+           p->cache_offset = cache_offset;
+           p->cache_bit = cache_bit;
+           p->curlym_l = curlym_l;
+           p->matches = matches;
+           p->maxwanted = maxwanted;
+           p->e = e;
+           p->old = old;
+           p->count = count;
+           p->cur_call_cc = cur_call_cc;
+           p->end_re = end_re;
+           p->accept_buff = accept_buff;
+           p->accepted = accepted;
+           p->reg_call_cc = PL_reg_call_cc;
+
+           scan = new_scan;
+           locinput = PL_reginput;
+           nextchr = UCHARAT(locinput);
+           minmod = 0;
+           sw = 0;
+           logical = 0;
+           unwind = 0;
+#ifdef DEBUGGING
+           PL_regindent++;
+#endif
+       }
     }
 
     /*
@@ -4235,11 +4503,8 @@ yes:
     PL_regindent--;
 #endif
 
-#if 0                                  /* Breaks $^R */
-    if (unwind)
-       regcpblow(firstcp);
-#endif
-    return 1;
+    result = 1;
+    goto exit_level;
 
 no:
     DEBUG_EXECUTE_r(
@@ -4301,7 +4566,92 @@ do_no:
 #ifdef DEBUGGING
     PL_regindent--;
 #endif
-    return 0;
+    result = 0;
+exit_level:
+    if (prev_state) {
+       /* restore previous state and re-enter */
+
+       struct regmatch_state *p = prev_state;
+       resume_state = p->resume_state;
+       scan = p->scan;
+       next = p->next;
+       minmod = p->minmod;
+       sw = p->sw;
+       logical = p->logical;
+       unwind = p->unwind;
+       cc = p->cc;
+       locinput = p->locinput;
+       nextchr = UCHARAT(locinput);
+       n = p->n;
+       ln = p->ln;
+       c1 = p->c1;
+       c2 = p->c2;
+       paren = p->paren;
+       cp = p->cp;
+       lastcp = p->lastcp;
+       oldcc = p->oldcc;
+       lastloc = p->lastloc;
+       cache_offset = p->cache_offset;
+       cache_bit = p->cache_bit;
+       curlym_l = p->curlym_l;
+       matches = p->matches;
+       maxwanted = p->maxwanted;
+       e = p->e;
+       old = p->old;
+       count = p->count;
+       cur_call_cc = p->cur_call_cc;
+       end_re = p->end_re;
+       accept_buff = p->accept_buff;
+       accepted = p->accepted;
+       PL_reg_call_cc = p->reg_call_cc;
+       prev_state = p->prev_state;
+
+       switch (resume_state) {
+       case resume_TRIE1:
+           goto resume_point_TRIE1;
+       case resume_TRIE2:
+           goto resume_point_TRIE2;
+       case resume_CURLYX:
+           goto resume_point_CURLYX;
+       case resume_WHILEM1:
+           goto resume_point_WHILEM1;
+       case resume_WHILEM2:
+           goto resume_point_WHILEM2;
+       case resume_WHILEM3:
+           goto resume_point_WHILEM3;
+       case resume_WHILEM4:
+           goto resume_point_WHILEM4;
+       case resume_WHILEM5:
+           goto resume_point_WHILEM5;
+       case resume_WHILEM6:
+           goto resume_point_WHILEM6;
+       case resume_CURLYM1:
+           goto resume_point_CURLYM1;
+       case resume_CURLYM2:
+           goto resume_point_CURLYM2;
+       case resume_CURLYM3:
+           goto resume_point_CURLYM3;
+       case resume_CURLYM4:
+           goto resume_point_CURLYM4;
+       case resume_IFMATCH:
+           goto resume_point_IFMATCH;
+       case resume_PLUS1:
+           goto resume_point_PLUS1;
+       case resume_PLUS2:
+           goto resume_point_PLUS2;
+       case resume_PLUS3:
+           goto resume_point_PLUS3;
+       case resume_PLUS4:
+           goto resume_point_PLUS4;
+       case resume_END:
+           goto resume_point_END;
+       default:
+           Perl_croak(aTHX_ "regexp resume memory corruption");
+       }
+       /* NOTREACHED */
+    }
+    return result;
+
 }
 
 /*