grep: avoid unnecessary regex compilation

Grep resorts to using the regex engine when the precision of either
-o or --color is required, or when the pattern is not supported by
our DFA engine (e.g., backref). Otherwise, grep would perform regex
compilation solely to check the syntax. This change makes grep skip
that compilation in the common case for which it is unnecessary.

The compilation we are avoiding is quite costly, consuming O(N^2)
RSS for N regular expressions.

* src/dfasearch.c (GEAcompile): Add new argument, and avoid unneeded
compilation of regex.
* src/grep.c (compile_fp_t): Update prototype.
(main): Update caller.
* src/kwsearch.c (Fcompile): Update caller and add new argument.
* src/pcresearch.c (Pcompile): Add new argument.
* src/search.h (GEAcompile, Fcompile, Pcompile): Update prototype.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/grep.c b/src/grep.c
index 3b40bbb7..1453b14a 100644
--- a/src/grep.c
+++ b/src/grep.c
@@ -635,7 +635,7 @@ static bool seek_failed;
 static bool seek_data_failed;
 
 /* Functions we'll use to search. */
-typedef void *(*compile_fp_t) (char *, size_t, reg_syntax_t);
+typedef void *(*compile_fp_t) (char *, size_t, reg_syntax_t, bool);
 typedef size_t (*execute_fp_t) (void *, char const *, size_t, size_t *,
                                 char const *);
 static execute_fp_t execute;
@@ -2973,8 +2973,9 @@ main (int argc, char **argv)
     matcher = try_fgrep_pattern (matcher, keys, &keycc);
 
   execute = matchers[matcher].execute;
-  compiled_pattern = matchers[matcher].compile (keys, keycc,
-                                                matchers[matcher].syntax);
+  compiled_pattern =
+    matchers[matcher].compile (keys, keycc, matchers[matcher].syntax,
+                               only_matching | color_option);
   /* We need one byte prior and one after.  */
   char eolbytes[3] = { 0, eolbyte, 0 };
   size_t match_size;