Skip invalidation entirely if the diff is empty

PiperOrigin-RevId: 205980620

2 files changed, 15 insertions, 9 deletions

diff --git a/src/main/java/com/google/devtools/build/skyframe/Differencer.java b/src/main/java/com/google/devtools/build/skyframe/Differencer.java
index ddcb34fe0d..35b42a3358 100644
--- a/src/main/java/com/google/devtools/build/skyframe/Differencer.java
+++ b/src/main/java/com/google/devtools/build/skyframe/Differencer.java
@@ -30,6 +30,10 @@ public interface Differencer {
    * Represents a set of changed values.
    */
   interface Diff {
+    default boolean isEmpty() {
+      return changedKeysWithoutNewValues().isEmpty() && changedKeysWithNewValues().isEmpty();
+    }
+
     /**
      * Returns the value keys whose values have changed, but for which we don't have the new values.
      */
diff --git a/src/main/java/com/google/devtools/build/skyframe/InMemoryMemoizingEvaluator.java b/src/main/java/com/google/devtools/build/skyframe/InMemoryMemoizingEvaluator.java
index a1f6461e50..ba3812689c 100644
--- a/src/main/java/com/google/devtools/build/skyframe/InMemoryMemoizingEvaluator.java
+++ b/src/main/java/com/google/devtools/build/skyframe/InMemoryMemoizingEvaluator.java
@@ -166,15 +166,17 @@ public final class InMemoryMemoizingEvaluator implements MemoizingEvaluator {
       // It clears the internal data structures after getDiff is called and will not return
       // diffs for historical versions. This makes the following code sensitive to interrupts.
       // Ideally we would simply not update lastGraphVersion if an interrupt occurs.
-      Diff diff = differencer.getDiff(new DelegatingWalkableGraph(graph), lastGraphVersion,
-          version);
-      valuesToInject.putAll(diff.changedKeysWithNewValues());
-      invalidate(diff.changedKeysWithoutNewValues());
-      pruneInjectedValues(valuesToInject);
-      invalidate(valuesToInject.keySet());
-
-      performInvalidation();
-      injectValues(intVersion);
+      Diff diff =
+          differencer.getDiff(new DelegatingWalkableGraph(graph), lastGraphVersion, version);
+      if (!diff.isEmpty() || !valuesToInject.isEmpty() || !valuesToDelete.isEmpty()) {
+        valuesToInject.putAll(diff.changedKeysWithNewValues());
+        invalidate(diff.changedKeysWithoutNewValues());
+        pruneInjectedValues(valuesToInject);
+        invalidate(valuesToInject.keySet());
+
+        performInvalidation();
+        injectValues(intVersion);
+      }
 
       ParallelEvaluator evaluator =
           new ParallelEvaluator(