More string-search optimisations

All-ASCII strings cannot have substrings with non-ASCII characters in
them; use this fact to avoid searching entirely.

* src/fns.c (Fstring_search): For multibyte non-ASCII needle and
unibyte haystack, don't check if the haystack is all-ASCII; it's a
waste of time. For multibyte non-ASCII needle and multibyte
all-ASCII haystack, fail immediately.
* test/src/fns-tests.el (string-search): Add more test cases.

1 files changed, 7 insertions, 0 deletions

diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index d3c22f966e6..86b8d655d26 100644
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -938,6 +938,13 @@
   (should (equal (string-search "\303" "aøb") nil))
   (should (equal (string-search "\270" "aøb") nil))
   (should (equal (string-search "ø" "\303\270") nil))
+  (should (equal (string-search "ø" (make-string 32 ?a)) nil))
+  (should (equal (string-search "ø" (string-to-multibyte (make-string 32 ?a)))
+                 nil))
+  (should (equal (string-search "o" (string-to-multibyte
+                                     (apply #'string
+                                            (number-sequence ?a ?z))))
+                 14))
 
   (should (equal (string-search "a\U00010f98z" "a\U00010f98a\U00010f98z") 2))