git diff: Don't test submodule dirtiness with --ignore-submodules

The diff family suppresses the output of submodule changes when
requested but checks them nonetheless. But since recently submodules
get examined for their dirtiness, which is rather expensive. There is
no need to do that when the --ignore-submodules option is used, as
the gathered information is never used anyway.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -179,6 +179,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 		}
 		changed = ce_match_stat(ce, &st, ce_option);
 		if (S_ISGITLINK(ce->ce_mode)
+		    && !DIFF_OPT_TST(&revs->diffopt, IGNORE_SUBMODULES)
 		    && (!changed || (revs->diffopt.output_format & DIFF_FORMAT_PATCH))
 		    && is_submodule_modified(ce->name)) {
 			changed = 1;
@@ -220,7 +221,7 @@ static int get_stat_data(struct cache_entry *ce,
 			 const unsigned char **sha1p,
 			 unsigned int *modep,
 			 int cached, int match_missing,
-			 unsigned *dirty_submodule, int output_format)
+			 unsigned *dirty_submodule, struct diff_options *diffopt)
 {
 	const unsigned char *sha1 = ce->sha1;
 	unsigned int mode = ce->ce_mode;
@@ -241,7 +242,8 @@ static int get_stat_data(struct cache_entry *ce,
 		}
 		changed = ce_match_stat(ce, &st, 0);
 		if (S_ISGITLINK(ce->ce_mode)
-		    && (!changed || (output_format & DIFF_FORMAT_PATCH))
+		    && !DIFF_OPT_TST(diffopt, IGNORE_SUBMODULES)
+		    && (!changed || (diffopt->output_format & DIFF_FORMAT_PATCH))
 		    && is_submodule_modified(ce->name)) {
 			changed = 1;
 			*dirty_submodule = 1;
@@ -270,7 +272,7 @@ static void show_new_file(struct rev_info *revs,
 	 * the working copy.
 	 */
 	if (get_stat_data(new, &sha1, &mode, cached, match_missing,
-	    &dirty_submodule, revs->diffopt.output_format) < 0)
+	    &dirty_submodule, &revs->diffopt) < 0)
 		return;
 
 	diff_index_show_file(revs, "+", new, sha1, mode, dirty_submodule);
@@ -287,7 +289,7 @@ static int show_modified(struct rev_info *revs,
 	unsigned dirty_submodule = 0;
 
 	if (get_stat_data(new, &sha1, &mode, cached, match_missing,
-			  &dirty_submodule, revs->diffopt.output_format) < 0) {
+			  &dirty_submodule, &revs->diffopt) < 0) {
 		if (report_missing)
 			diff_index_show_file(revs, "-", old,
 					     old->sha1, old->ce_mode, 0);