tree-diff: move all action-taking code out of compare_tree_entry()

- let it do only comparison.

This way the code is cleaner and more structured - cmp function only
compares, and the driver takes action based on comparison result.

There should be no change in performance, as effectively, we just move
if series from on place into another, and merge it to was-already-there
same switch/if, so the result is maybe a little bit faster.

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

tree-diff.c

@@ -9,8 +9,7 @@
 static void show_path(struct strbuf *base, struct diff_options *opt,
 		      struct tree_desc *t1, struct tree_desc *t2);
 
-static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2,
-			      struct strbuf *base, struct diff_options *opt)
+static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2)
 {
 	unsigned mode1, mode2;
 	const char *path1, *path2;
@@ -28,19 +27,7 @@ static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2,
 	 * even when having the same name.
 	 */
 	cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
-	if (cmp < 0) {
-		show_path(base, opt, t1, /*t2=*/NULL);
-		return -1;
-	}
-	if (cmp > 0) {
-		show_path(base, opt, /*t1=*/NULL, t2);
-		return 1;
-	}
-	if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER) && !hashcmp(sha1, sha2) && mode1 == mode2)
-		return 0;
-
-	show_path(base, opt, t1, t2);
-	return 0;
+	return cmp;
 }
 
 
@@ -160,6 +147,8 @@ int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
 	strbuf_add(&base, base_str, baselen);
 
 	for (;;) {
+		int cmp;
+
 		if (diff_can_quit_early(opt))
 			break;
 		if (opt->pathspec.nr) {
@@ -179,21 +168,28 @@ int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
 			continue;
 		}
 
-		cmp = compare_tree_entry(t1, t2, &base, opt);
+		cmp = compare_tree_entry(t1, t2);
 
 		/* t1 = t2 */
 		if (cmp == 0) {
+			if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER) ||
+			    hashcmp(t1->entry.sha1, t2->entry.sha1) ||
+			    (t1->entry.mode != t2->entry.mode))
+				show_path(&base, opt, t1, t2);
+
 			update_tree_entry(t1);
 			update_tree_entry(t2);
 		}
 
 		/* t1 < t2 */
 		else if (cmp < 0) {
+			show_path(&base, opt, t1, /*t2=*/NULL);
 			update_tree_entry(t1);
 		}
 
 		/* t1 > t2 */
 		else {
+			show_path(&base, opt, /*t1=*/NULL, t2);
 			update_tree_entry(t2);
 		}
 	}