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, 11 insertions, 0 deletions

diff --git a/test/src/regex-emacs-tests.el b/test/src/regex-emacs-tests.el
index cd4924f9785..c8f161c9b24 100644
--- a/test/src/regex-emacs-tests.el
+++ b/test/src/regex-emacs-tests.el
@@ -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