regex.c (mutually_exclusive_aux) <wordbound>: Remove optimization

Another case that was too optimistic.  Better use \> or \< rather
than \b if you want your regexp to be handled efficiently.

* src/regex-emacs.c (mutually_exclusive_aux) <wordbound>: Cancel optimization.
* test/src/regex-emacs-tests.el (regexp-tests-backtrack-optimization):
New test.

1 files changed, 15 insertions, 2 deletions

diff --git a/src/regex-emacs.c b/src/regex-emacs.c
index ae82dd63917..ad140908609 100644
--- a/src/regex-emacs.c
+++ b/src/regex-emacs.c
@@ -3874,9 +3874,22 @@ mutually_exclusive_aux (struct re_pattern_buffer *bufp, re_char *p1,
       return ((re_opcode_t) *p1 == notsyntaxspec && p1[1] == p2[1]);
 
     case wordbound:
+      /* FIXME: This optimization seems correct after the first iteration
+         of the loop, but not for the very first :-(
+         IOW we'd need to pull out the first iteration and do:
+
+            syntaxspec w
+            on_failure_keep_string_jump end
+          loop:
+            syntaxspec w
+            goto loop
+          end:
+            wordbound
+
       return (((re_opcode_t) *p1 == notsyntaxspec
-               || (re_opcode_t) *p1 == syntaxspec)
-              && p1[1] == Sword);
+               || (re_opcode_t) *p1 == syntaxspec)
+              && p1[1] == Sword);  */
+      return false;
 
     case categoryspec:
       return ((re_opcode_t) *p1 == notcategoryspec && p1[1] == p2[1]);