Short-circuit visitation of empty nested sets, reinstating the spirit of commit 7c991c333999f3027d31da6af700f575924066cd.

--
MOS_MIGRATED_REVID=125969403

1 files changed, 5 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetVisitor.java b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetVisitor.java
index 705653f063..686991cfab 100644
--- a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetVisitor.java
+++ b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSetVisitor.java
@@ -58,7 +58,11 @@ public final class NestedSetVisitor<E> {
    */
   public void visit(NestedSet<E> nestedSet) {
     Preconditions.checkArgument(nestedSet.getOrder() == Order.STABLE_ORDER);
-    visitRaw(nestedSet.rawChildren());
+    // We can short-circuit empty nested set visitation here, avoiding load on the shared map
+    // VisitedState#seenNodes.
+    if (!nestedSet.isEmpty()) {
+      visitRaw(nestedSet.rawChildren());
+    }
   }
 
   @SuppressWarnings("unchecked")