bazel nestedset: don't allocate empty CompactHashSet in addAll
commit 565c199f51cf8b9898342c47c07666c1a8159375 recently changed the depset constructor to use
NestedSetBuilder.addAll, which should be more efficient than a loop
around add, but it was not, resulting in a measurable memory regression:
addAll causes the allocation of a CompactHashSet even when there are no elements.
This change fixes the bug. Thanks to brandjon for spotting the problem.
PiperOrigin-RevId: 283537882
diff --git a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetBuilder.java b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetBuilder.java
index d8bb68e..e84180f 100644
--- a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetBuilder.java
@@ -100,7 +100,11 @@
throw new IllegalArgumentException("NestedSet should be added as a transitive member");
}
if (items == null) {
- items = CompactHashSet.createWithExpectedSize(Iterables.size(elements));
+ int n = Iterables.size(elements);
+ if (n == 0) {
+ return this; // avoid allocating an empty set
+ }
+ items = CompactHashSet.createWithExpectedSize(n);
}
Iterables.addAll(items, elements);
return this;
