mark_parents_uninteresting(): replace list with stack
The mark_parents_uninteresting() function uses two loops: an outer one to process our queue of pending parents, and an inner one to process first-parent chains. This is a clever optimization from 941ba8db57 (Eliminate recursion in setting/clearing marks in commit list, 2012-01-14) to limit the number of linked-list allocations when following single-parent chains. Unfortunately, this makes the result a little hard to read. Let's replace the list with a stack. Then we don't have to worry about doing this double-loop optimization, as we'll just reuse the top element of the stack as we pop/push. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jeff King committed
May 11, 2018 at 14:02 UTC
43fc643b75af91363eb1246528c706c1654ddc2e
1 file changed
+43
-24
revision.c
+43
-24
@@ -91,38 +91,57 @@ void mark_tree_uninteresting(struct tree *tree)
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mark_tree_contents_uninteresting(tree);
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}
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-void mark_parents_uninteresting(struct commit *commit)
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+struct commit_stack {
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+ struct commit **items;
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+ size_t nr, alloc;
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+};
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+#define COMMIT_STACK_INIT { NULL, 0, 0 }
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+
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+static void commit_stack_push(struct commit_stack *stack, struct commit *commit)
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{
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- struct commit_list *parents = NULL, *l;
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+ ALLOC_GROW(stack->items, stack->nr + 1, stack->alloc);
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+ stack->items[stack->nr++] = commit;
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+}
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- for (l = commit->parents; l; l = l->next)
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- commit_list_insert(l->item, &parents);
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+static struct commit *commit_stack_pop(struct commit_stack *stack)
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+{
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+ return stack->nr ? stack->items[--stack->nr] : NULL;
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+}
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- while (parents) {
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- struct commit *commit = pop_commit(&parents);
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+static void commit_stack_clear(struct commit_stack *stack)
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+{
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+ FREE_AND_NULL(stack->items);
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+ stack->nr = stack->alloc = 0;
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+}
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- while (commit) {
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- if (commit->object.flags & UNINTERESTING)
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- break;
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+void mark_parents_uninteresting(struct commit *commit)
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+{
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+ struct commit_stack pending = COMMIT_STACK_INIT;
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+ struct commit_list *l;
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- commit->object.flags |= UNINTERESTING;
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+ for (l = commit->parents; l; l = l->next)
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+ commit_stack_push(&pending, l->item);
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- /*
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- * Normally we haven't parsed the parent
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- * yet, so we won't have a parent of a parent
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- * here. However, it may turn out that we've
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- * reached this commit some other way (where it
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- * wasn't uninteresting), in which case we need
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- * to mark its parents recursively too..
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- */
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- if (!commit->parents)
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- break;
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+ while (pending.nr > 0) {
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+ struct commit *commit = commit_stack_pop(&pending);
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- for (l = commit->parents->next; l; l = l->next)
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- commit_list_insert(l->item, &parents);
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- commit = commit->parents->item;
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- }
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+ if (commit->object.flags & UNINTERESTING)
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+ return;
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+ commit->object.flags |= UNINTERESTING;
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+
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+ /*
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+ * Normally we haven't parsed the parent
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+ * yet, so we won't have a parent of a parent
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+ * here. However, it may turn out that we've
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+ * reached this commit some other way (where it
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+ * wasn't uninteresting), in which case we need
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+ * to mark its parents recursively too..
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+ */
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+ for (l = commit->parents; l; l = l->next)
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+ commit_stack_push(&pending, l->item);
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}
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+
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+ commit_stack_clear(&pending);
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}
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static void add_pending_object_with_path(struct rev_info *revs,