grep: use grep matcher for grep -Fw when unibyte

In single byte locales with grep -Fw, prefer the grep matcher to the
kwset matcher, as the former uses KWset and a DFA, whereas the latter
calls kwsexec many times until it matches a word.
* src/grep.c (main): Change pattern for fgrep into grep for grep -Fw in
single byte locales.

1 files changed, 6 insertions, 3 deletions

diff --git a/src/grep.c b/src/grep.c
index d8ea70fc..0ca0d9ad 100644
--- a/src/grep.c
+++ b/src/grep.c
@@ -2563,9 +2563,12 @@ main (int argc, char **argv)
 
   /* If fgrep in a multibyte locale, then use grep if either
      (1) case is ignored (where grep is typically faster), or
-     (2) the pattern has an encoding error (where fgrep might not work).  */
-  if (compile == Fcompile && MB_CUR_MAX > 1
-      && (match_icase || contains_encoding_error (keys, keycc)))
+     (2) the pattern matches words (where grep is typically faster), or
+     (3) the pattern has an encoding error (where fgrep might not work).  */
+  if (compile == Fcompile
+      && (MB_CUR_MAX > 1 && (match_icase
+                             || contains_encoding_error (keys, keycc)))
+          || (MB_CUR_MAX == 1 && match_words))
     {
       size_t new_keycc;
       char *new_keys;