Eliminate recursion in setting/clearing marks in commit list

Recursion in a DAG is generally a bad idea because it could be very
deep. Be defensive and avoid recursion in mark_parents_uninteresting()
and clear_commit_marks().

mark_parents_uninteresting() learns a trick from clear_commit_marks()
to avoid malloc() in (dominant) single-parent case.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.c

@@ -421,7 +421,8 @@ struct commit *pop_most_recent_commit(struct commit_list **list,
 	return ret;
 }
 
-void clear_commit_marks(struct commit *commit, unsigned int mark)
+static void clear_commit_marks_1(struct commit_list **plist,
+				 struct commit *commit, unsigned int mark)
 {
 	while (commit) {
 		struct commit_list *parents;
@@ -436,12 +437,20 @@ void clear_commit_marks(struct commit *commit, unsigned int mark)
 			return;
 
 		while ((parents = parents->next))
-			clear_commit_marks(parents->item, mark);
+			commit_list_insert(parents->item, plist);
 
 		commit = commit->parents->item;
 	}
 }
 
+void clear_commit_marks(struct commit *commit, unsigned int mark)
+{
+	struct commit_list *list = NULL;
+	commit_list_insert(commit, &list);
+	while (list)
+		clear_commit_marks_1(&list, pop_commit(&list), mark);
+}
+
 void clear_commit_marks_for_object_array(struct object_array *a, unsigned mark)
 {
 	struct object *object;

revision.c

@@ -139,25 +139,18 @@ void mark_tree_uninteresting(struct tree *tree)
 
 void mark_parents_uninteresting(struct commit *commit)
 {
-	struct commit_list *parents = commit->parents;
+	struct commit_list *parents = NULL, *l;
+
+	for (l = commit->parents; l; l = l->next)
+		commit_list_insert(l->item, &parents);
 
 	while (parents) {
 		struct commit *commit = parents->item;
-		if (!(commit->object.flags & UNINTERESTING)) {
-			commit->object.flags |= UNINTERESTING;
-
-			/*
-			 * Normally we haven't parsed the parent
-			 * yet, so we won't have a parent of a parent
-			 * here. However, it may turn out that we've
-			 * reached this commit some other way (where it
-			 * wasn't uninteresting), in which case we need
-			 * to mark its parents recursively too..
-			 */
-			if (commit->parents)
-				mark_parents_uninteresting(commit);
-		}
+		l = parents;
+		parents = parents->next;
+		free(l);
 
+		while (commit) {
 			/*
 			 * A missing commit is ok iff its parent is marked
 			 * uninteresting.
@@ -168,7 +161,27 @@ void mark_parents_uninteresting(struct commit *commit)
 			 */
 			if (!has_sha1_file(commit->object.sha1))
 				commit->object.parsed = 1;
-		parents = parents->next;
+
+			if (commit->object.flags & UNINTERESTING)
+				break;
+
+			commit->object.flags |= UNINTERESTING;
+
+			/*
+			 * Normally we haven't parsed the parent
+			 * yet, so we won't have a parent of a parent
+			 * here. However, it may turn out that we've
+			 * reached this commit some other way (where it
+			 * wasn't uninteresting), in which case we need
+			 * to mark its parents recursively too..
+			 */
+			if (!commit->parents)
+				break;
+
+			for (l = commit->parents->next; l; l = l->next)
+				commit_list_insert(l->item, &parents);
+			commit = commit->parents->item;
+		}
 	}
 }