regex-emacs.c: Reduce the use of backtracking a bit further

bug#61514 exhibited some undesirable backtracking in a case where
it's easy to avoid it by making `mutually_exclusive_p` just a bit
more careful.

* src/regex-emacs.c (mutually_exclusive_p): Handle `on_failure_jump`s.

* test/src/regex-emacs-tests.el (regexp-tests-backtrack-optimization):
Add a few tests.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/regex-emacs.c b/src/regex-emacs.c
index 2dca0d16ad9..2571812cb39 100644
--- a/src/regex-emacs.c
+++ b/src/regex-emacs.c
@@ -3653,6 +3653,7 @@ mutually_exclusive_p (struct re_pattern_buffer *bufp, re_char *p1,
   re_opcode_t op2;
   bool multibyte = RE_MULTIBYTE_P (bufp);
   unsigned char *pend = bufp->buffer + bufp->used;
+  re_char *p2_orig = p2;
 
   eassert (p1 >= bufp->buffer && p1 < pend
            && p2 >= bufp->buffer && p2 <= pend);
@@ -3822,6 +3823,23 @@ mutually_exclusive_p (struct re_pattern_buffer *bufp, re_char *p1,
     case notcategoryspec:
       return ((re_opcode_t) *p1 == categoryspec && p1[1] == p2[1]);
 
+    case on_failure_jump_nastyloop:
+    case on_failure_jump_smart:
+    case on_failure_jump_loop:
+    case on_failure_keep_string_jump:
+    case on_failure_jump:
+      {
+        int mcnt;
+        p2++;
+        EXTRACT_NUMBER_AND_INCR (mcnt, p2);
+        /* Don't just test `mcnt > 0` because non-greedy loops have
+           their test at the end with an unconditional jump at the start.  */
+        if (p2 + mcnt > p2_orig) /* Ensure forward progress.  */
+          return (mutually_exclusive_p (bufp, p1, p2)
+                  && mutually_exclusive_p (bufp, p1, p2 + mcnt));
+        break;
+      }
+
     default:
       ;
     }