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

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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.
This commit is contained in:
Stefan Monnier 2023-02-20 21:22:41 -05:00
parent e83c78b8c7
commit 5a864f23eb
2 changed files with 29 additions and 0 deletions
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18
src/regex-emacs.c
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@ -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:
;
}

11
test/src/regex-emacs-tests.el
View file

@ -872,4 +872,15 @@ This evaluates the TESTS test cases from glibc."
(should (equal (string-match "\\`\\(?:ab\\)*\\'" "a") nil))
(should (equal (string-match "\\`a\\{2\\}*\\'" "a") nil)))
(ert-deftest regexp-tests-backtrack-optimization () ;bug#61514
;; Make sure we don't use up the regexp stack needlessly.
(with-current-buffer (get-buffer-create "*bug*")
(erase-buffer)
(insert (make-string 1000000 ?x) "=")
(goto-char (point-min))
(should (looking-at "x*=*"))
(should (looking-at "x*\\(=\\|:\\)"))
(should (looking-at "x*\\(=\\|:\\)*"))
(should (looking-at "x*=*?"))))
;;; regex-emacs-tests.el ends here