Does mtree_lookup_walk need to use ma_data_end?

[Omar Sandoval]

Hi,

I'm reading some of the maple tree code in order to write drgn helpers
for maple trees, and I was hoping for some clarification on one bit of
code. Specifically, in mtree_lookup_walk:

	end = ma_data_end(node, type, pivots, max);
	...
	do {
		if (pivots[offset] >= mas->index) {
			max = pivots[offset];
			break;
		}
	} while (++offset < end);

So this is looping until the first pivot greater than or equal to the
desired index, stopping after it has checked the last pivot.

But we're guaranteed that either the last pivot or the implied maximum
is greater than or equal to the index, so is it necessary to get the
actual end with ma_data_end? I.e., would the following be equivalent?

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index bb24d84a4922..18297c6ed06f 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3739,7 +3739,7 @@ static inline void *mtree_lookup_walk(struct ma_state *mas)
 		node = mte_to_node(next);
 		type = mte_node_type(next);
 		pivots = ma_pivots(node, type);
-		end = ma_data_end(node, type, pivots, max);
+		end = mt_pivots[type];
 		if (unlikely(ma_dead_node(node)))
 			goto dead_node;
 		do {

I have no idea whether this is any better or faster. I guess it does
avoid a few branches and loads in ma_data_end. I'm mainly wondering
whether there's something I'm missing in my understanding.

Thanks!
Omar