re_intuit_start(): introduce rx_origin var

re_intuit_start() is a bit of mess. It uses two general function-scope
vars, s and t, to point at string offsets while processing. These vars
mean different things at different times. Introduce a new var, rx_origin,
which indicates the current minimum position that the regex could begin
matching at. It starts off at strpos, and gradually moves up as various
constraints are rejected. It will be the value eventually returned.

For the moment, s and/or t will continue serving that function at various
points in the code; this commit just makes rx_origin valid at the entry to
the 'restart:' block.

diff --git a/regexec.c b/regexec.c
index 26907d3..2c75916 100644 (file)
--- a/regexec.c
+++ b/regexec.c
@@ -639,6 +639,8 @@ Perl_re_intuit_start(pTHX_
     /* Should be nonnegative! */
     SSize_t end_shift   = 0;
     char *s;
+    /* current lowest pos in string where the regex can start matching */
+    char *rx_origin = strpos;
     SV *check;
     char *t;
     const bool utf8_target = (sv && SvUTF8(sv)) ? 1 : 0; /* if no sv we have to assume bytes */
@@ -794,7 +796,7 @@ Perl_re_intuit_start(pTHX_
            }
        }
     }
-    s = strpos;
+
     start_shift = prog->check_offset_min;  /* okay to underestimate on CC */
     end_shift = prog->check_end_shift;
 
@@ -805,8 +807,10 @@ Perl_re_intuit_start(pTHX_
 #endif
 
   restart:
-    /* Find a possible match in the region s..strend by looking for
-       the "check" substring in the region corrected by start/end_shift. */
+    /* 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.
+     */
     
     {
         U8* start_point;
@@ -817,7 +821,7 @@ Perl_re_intuit_start(pTHX_
                 "  At restart: s=%"IVdf" Check offset min: %"IVdf
                 " Start shift: %"IVdf" End shift %"IVdf
                 " Real End Shift: %"IVdf"\n",
-                (IV)(s - i_strpos),
+                (IV)(rx_origin - i_strpos),
                 (IV)prog->check_offset_min,
                 (IV)start_shift,
                 (IV)end_shift,
@@ -825,10 +829,10 @@ Perl_re_intuit_start(pTHX_
         });
         
         if (prog->intflags & PREGf_CANY_SEEN) {
-            start_point= (U8*)(s + start_shift);
+            start_point= (U8*)(rx_origin + start_shift);
             end_point= (U8*)(strend - end_shift);
         } else {
-           start_point= HOP3(s, start_shift, strend);
+           start_point= HOP3(rx_origin, start_shift, strend);
             end_point= HOP3(strend, -end_shift, strbeg);
        }
 
@@ -970,7 +974,7 @@ Perl_re_intuit_start(pTHX_
                        ", trying floating at offset %ld...\n",
                        (long)(HOP3c(saved_s, 1, strend) - i_strpos)));
                    other_last = HOP3c(last1, 1, strend);
-                   s = HOP4c(last, 1 - prog->anchored_offset, strbeg, strend);
+                   rx_origin = HOP4c(last, 1 - prog->anchored_offset, strbeg, strend);
                    goto restart;
                }
                else {
@@ -1069,7 +1073,7 @@ Perl_re_intuit_start(pTHX_
                    ", trying anchored starting at offset %ld...\n",
                    (long)(saved_s + 1 - i_strpos)));
                other_last = last; /* highest failure */
-               s = HOP3c(t, 1, strend);
+               rx_origin = HOP3c(t, 1, strend);
                goto restart;
            }
            else {
@@ -1148,7 +1152,7 @@ Perl_re_intuit_start(pTHX_
                       than for "\n", so one should lower the limit for t? */
                    DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log, "  Found /%s^%s/m, restarting lookup for check-string at offset %ld...\n",
                        PL_colors[0], PL_colors[1], (long)(t + 1 - i_strpos)));
-                   other_last = strpos = s = t + 1;
+                   other_last = strpos = rx_origin = t + 1;
                    goto restart;
                }
                t++;
@@ -1296,9 +1300,10 @@ Perl_re_intuit_start(pTHX_
                    }
                    if (!check)
                        goto giveup;
+                    rx_origin = s;
                    DEBUG_EXECUTE_r( PerlIO_printf(Perl_debug_log,
                                "  Looking for %s substr starting at offset %ld...\n",
-                                what, (long)(s + start_shift - i_strpos)) );
+                                what, (long)(rx_origin + start_shift - i_strpos)) );
                    goto restart;
                }
                /* Have both, check_string is floating */