master e88be844bf7: regex.c (mutually_exclusive_p): Fix initial value of `loop_beg`

[Stefan Monnier]

branch: master
commit e88be844bf774b336ab67995e435416328b53776
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    regex.c (mutually_exclusive_p): Fix initial value of `loop_beg`
    
    * src/regex-emacs.c (mutually_exclusive_p): Don't pretend that pattern
    position 0 has been checked already.
    
    * test/src/regex-emacs-tests.el (regexp-tests-backtrack-optimization):
    Add a corresponding regression test plus some other related tests
    I had around.
---
 src/regex-emacs.c             |  2 +-
 test/src/regex-emacs-tests.el | 20 +++++++++++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/regex-emacs.c b/src/regex-emacs.c
index cf7b704ee95..338323cf79e 100644
--- a/src/regex-emacs.c
+++ b/src/regex-emacs.c
@@ -3941,7 +3941,7 @@ static bool
 mutually_exclusive_p (struct re_pattern_buffer *bufp, re_char *p1,
                      re_char *p2)
 {
-  return mutually_exclusive_aux (bufp, p1, p2, bufp->buffer, NULL);
+  return mutually_exclusive_aux (bufp, p1, p2, bufp->buffer - 1, NULL);
 }
 
 /* Matching routines.  */
diff --git a/test/src/regex-emacs-tests.el b/test/src/regex-emacs-tests.el
index f2bee713864..c84998e1184 100644
--- a/test/src/regex-emacs-tests.el
+++ b/test/src/regex-emacs-tests.el
@@ -878,10 +878,28 @@ This evaluates the TESTS test cases from glibc."
     (erase-buffer)
     (insert (make-string 1000000 ?x) "=")
     (goto-char (point-min))
+    ;; Make sure we do perform the optimization (if we don't, the
+    ;; below will burp with regexp-stack-overflow).
     (should (looking-at "x*=*"))
     (should (looking-at "x*\\(=\\|:\\)"))
     (should (looking-at "x*\\(=\\|:\\)*"))
-    (should (looking-at "x*=*?"))))
+    (should (looking-at "x*=*?"))
+    (should (looking-at "x*\\(=*\\|h\\)*?"))
+    (should (looking-at "x*\\(=*\\|h\\)*"))
+    (should (looking-at "x*\\(=*?\\|h\\)*"))
+    (should (looking-at "x*\\(=*?\\|h\\)*?"))
+    (should (looking-at "x*\\(=*\\|h\\)+?"))
+    (should (looking-at "x*\\(=*\\|h\\)+"))
+    (should (looking-at "x*\\(=*?\\|h\\)+"))
+    (should (looking-at "x*\\(=*?\\|h\\)+?"))
+    (should (looking-at "x*\\(=+\\|h\\)+?"))
+    (should (looking-at "x*\\(=+\\|h\\)+"))
+    (should (looking-at "x*\\(=+?\\|h\\)+"))
+    (should (looking-at "x*\\(=+?\\|h\\)+?"))
+    ;; Regression check for overly optimistic optimization.
+    (should (eq 0 (string-match "\\(ca*\\|ab\\)+d" "cabd")))
+    (should (string-match "\\(aa*\\|b\\)*c" "ababc"))
+    ))
 
 (ert-deftest regexp-tests-zero-width-assertion-repetition ()
   ;; Check compatibility behaviour with repetition operators after