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.

1 files changed, 1 insertions, 1 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.  */