diff_tree(): Skip skip_uninteresting() when all remaining paths interesting

In 1d848f6 (tree_entry_interesting(): allow it to say "everything is
interesting" 2007-03-21), both show_tree() and skip_uninteresting() were
modified to determine if all remaining tree entries were interesting.
However, the latter returns as soon as it finds the first interesting path,
without any way to signal to its caller (namely, diff_tree()) that all
remaining paths are interesting, making these extra checks useless.

Pass whether all remaining entries are interesting back to diff_tree(), and
whenever they are, have diff_tree() skip subsequent calls to
skip_uninteresting().

With this change, I measure speedups of 3-4% for the commands

  $ git rev-list --quiet HEAD -- Documentation/
  $ git rev-list --quiet HEAD -- t/

in git.git.

Signed-off-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: newren

tree-diff.c

@@ -259,19 +259,12 @@ static void show_entry(struct diff_options *opt, const char *prefix, struct tree
 	}
 }
 
-static void skip_uninteresting(struct tree_desc *t, const char *base, int baselen, struct diff_options *opt)
+static void skip_uninteresting(struct tree_desc *t, const char *base, int baselen, struct diff_options *opt, int *all_interesting)
 {
-	int all_interesting = 0;
 	while (t->size) {
-		int show;
-
-		if (all_interesting)
-			show = 1;
-		else {
-			show = tree_entry_interesting(t, base, baselen, opt);
-			if (show == 2)
-				all_interesting = 1;
-		}
+		int show = tree_entry_interesting(t, base, baselen, opt);
+		if (show == 2)
+			*all_interesting = 1;
 		if (!show) {
 			update_tree_entry(t);
 			continue;
@@ -286,14 +279,20 @@ static void skip_uninteresting(struct tree_desc *t, const char *base, int basele
 int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
 {
 	int baselen = strlen(base);
+	int all_t1_interesting = 0;
+	int all_t2_interesting = 0;
 
 	for (;;) {
 		if (DIFF_OPT_TST(opt, QUICK) &&
 		    DIFF_OPT_TST(opt, HAS_CHANGES))
 			break;
 		if (opt->nr_paths) {
-			skip_uninteresting(t1, base, baselen, opt);
-			skip_uninteresting(t2, base, baselen, opt);
+			if (!all_t1_interesting)
+				skip_uninteresting(t1, base, baselen, opt,
+						   &all_t1_interesting);
+			if (!all_t2_interesting)
+				skip_uninteresting(t2, base, baselen, opt,
+						   &all_t2_interesting);
 		}
 		if (!t1->size) {
 			if (!t2->size)