diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ExecutionFinishedEvent.java b/src/main/java/com/google/devtools/build/lib/skyframe/ExecutionFinishedEvent.java
index 2853756..4c0b79a 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ExecutionFinishedEvent.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ExecutionFinishedEvent.java
@@ -13,47 +13,52 @@
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;
 
-import com.google.common.base.Preconditions;
+import com.google.auto.value.AutoValue;
 import java.time.Duration;
 
 /**
- * Event signaling the end of the execution phase. Contains statistics about the action cache,
- * the metadata cache and about last file save times.
+ * Event signaling the end of the execution phase. Contains statistics about the action cache, the
+ * metadata cache and about last file save times.
  */
-public class ExecutionFinishedEvent {
+@AutoValue
+public abstract class ExecutionFinishedEvent {
   public static final ExecutionFinishedEvent EMPTY =
-      new ExecutionFinishedEvent(0, 0, Duration.ZERO, Duration.ZERO);
+      builder()
+          .setOutputDirtyFiles(0)
+          .setOutputModifiedFilesDuringPreviousBuild(0)
+          .setSourceDiffCheckingDuration(Duration.ZERO)
+          .setNumSourceFilesCheckedBecauseOfMissingDiffs(0)
+          .setOutputTreeDiffCheckingDuration(Duration.ZERO)
+          .build();
 
-  private final int outputDirtyFiles;
-  private final int outputModifiedFilesDuringPreviousBuild;
-  private final Duration sourceDiffCheckingDuration;
-  private final Duration outputTreeDiffCheckingDuration;
+  public abstract int outputDirtyFiles();
 
-  ExecutionFinishedEvent(
-      int outputDirtyFiles,
-      int outputModifiedFilesDuringPreviousBuild,
-      Duration sourceDiffCheckingDuration,
-      Duration outputTreeDiffCheckingDuration) {
-    this.outputDirtyFiles = outputDirtyFiles;
-    this.outputModifiedFilesDuringPreviousBuild = outputModifiedFilesDuringPreviousBuild;
-    this.sourceDiffCheckingDuration = Preconditions.checkNotNull(sourceDiffCheckingDuration);
-    this.outputTreeDiffCheckingDuration =
-        Preconditions.checkNotNull(outputTreeDiffCheckingDuration);
+  public abstract int outputModifiedFilesDuringPreviousBuild();
+
+  public abstract Duration sourceDiffCheckingDuration();
+
+  public abstract int numSourceFilesCheckedBecauseOfMissingDiffs();
+
+  public abstract Duration outputTreeDiffCheckingDuration();
+
+  static Builder builder() {
+    return new AutoValue_ExecutionFinishedEvent.Builder();
   }
 
-  public int getOutputDirtyFiles() {
-    return outputDirtyFiles;
-  }
+  @AutoValue.Builder
+  abstract static class Builder {
+    abstract Builder setOutputDirtyFiles(int outputDirtyFiles);
 
-  public int getOutputModifiedFilesDuringPreviousBuild() {
-    return outputModifiedFilesDuringPreviousBuild;
-  }
+    abstract Builder setOutputModifiedFilesDuringPreviousBuild(
+        int outputModifiedFilesDuringPreviousBuild);
 
-  public Duration getSourceDiffCheckingDuration() {
-    return sourceDiffCheckingDuration;
-  }
+    abstract Builder setSourceDiffCheckingDuration(Duration sourceDiffCheckingDuration);
 
-  public Duration getOutputTreeDiffCheckingDuration() {
-    return outputTreeDiffCheckingDuration;
+    abstract Builder setNumSourceFilesCheckedBecauseOfMissingDiffs(
+        int numSourceFilesCheckedBecauseOfMissingDiffs);
+
+    abstract Builder setOutputTreeDiffCheckingDuration(Duration outputTreeDiffCheckingDuration);
+
+    abstract ExecutionFinishedEvent build();
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/FilesystemValueChecker.java b/src/main/java/com/google/devtools/build/lib/skyframe/FilesystemValueChecker.java
index 6c5342b..44665ee 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/FilesystemValueChecker.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/FilesystemValueChecker.java
@@ -45,6 +45,7 @@
 import com.google.devtools.build.lib.vfs.PathFragment;
 import com.google.devtools.build.lib.vfs.Symlinks;
 import com.google.devtools.build.skyframe.Differencer;
+import com.google.devtools.build.skyframe.Differencer.DiffWithDelta.Delta;
 import com.google.devtools.build.skyframe.FunctionHermeticity;
 import com.google.devtools.build.skyframe.SkyFunctionName;
 import com.google.devtools.build.skyframe.SkyKey;
@@ -99,8 +100,9 @@
    */
   // TODO(bazel-team): Refactor these methods so that FilesystemValueChecker only operates on a
   // WalkableGraph.
-  Differencer.DiffWithDelta getDirtyKeys(Map<SkyKey, SkyValue> valuesMap,
-      SkyValueDirtinessChecker dirtinessChecker) throws InterruptedException {
+  ImmutableBatchDirtyResult getDirtyKeys(
+      Map<SkyKey, SkyValue> valuesMap, SkyValueDirtinessChecker dirtinessChecker)
+      throws InterruptedException {
     return getDirtyValues(new MapBackedValueFetcher(valuesMap), valuesMap.keySet(),
         dirtinessChecker, /*checkMissingValues=*/false);
   }
@@ -109,9 +111,11 @@
    * Returns a {@link Differencer.DiffWithDelta} containing keys that are dirty according to the
    * passed-in {@code dirtinessChecker}.
    */
-  public Differencer.DiffWithDelta getNewAndOldValues(Map<SkyKey, SkyValue> valuesMap,
-      Iterable<SkyKey> keys, SkyValueDirtinessChecker dirtinessChecker)
-          throws InterruptedException {
+  public ImmutableBatchDirtyResult getNewAndOldValues(
+      Map<SkyKey, SkyValue> valuesMap,
+      Iterable<SkyKey> keys,
+      SkyValueDirtinessChecker dirtinessChecker)
+      throws InterruptedException {
     return getDirtyValues(new MapBackedValueFetcher(valuesMap), keys,
         dirtinessChecker, /*checkMissingValues=*/true);
   }
@@ -478,19 +482,22 @@
     return headPath != null && headPath.startsWith(artifactExecPath);
   }
 
-  private BatchDirtyResult getDirtyValues(ValueFetcher fetcher,
-      Iterable<SkyKey> keys, final SkyValueDirtinessChecker checker,
-      final boolean checkMissingValues) throws InterruptedException {
+  private ImmutableBatchDirtyResult getDirtyValues(
+      ValueFetcher fetcher,
+      Iterable<SkyKey> keys,
+      final SkyValueDirtinessChecker checker,
+      final boolean checkMissingValues)
+      throws InterruptedException {
     ExecutorService executor =
         Executors.newFixedThreadPool(
             DIRTINESS_CHECK_THREADS,
             new ThreadFactoryBuilder().setNameFormat("FileSystem Value Invalidator %d").build());
 
-    final BatchDirtyResult batchResult = new BatchDirtyResult();
     ThrowableRecordingRunnableWrapper wrapper =
         new ThrowableRecordingRunnableWrapper("FilesystemValueChecker#getDirtyValues");
     final AtomicInteger numKeysScanned = new AtomicInteger(0);
     final AtomicInteger numKeysChecked = new AtomicInteger(0);
+    MutableBatchDirtyResult batchResult = new MutableBatchDirtyResult(numKeysChecked);
     ElapsedTimeReceiver elapsedTimeReceiver =
         elapsedTimeNanos -> {
           if (elapsedTimeNanos > 0) {
@@ -540,19 +547,57 @@
         throw new InterruptedException();
       }
     }
-    return batchResult;
+    return batchResult.toImmutable();
+  }
+
+  static class ImmutableBatchDirtyResult implements Differencer.DiffWithDelta {
+    private final Collection<SkyKey> dirtyKeysWithoutNewValues;
+    private final Map<SkyKey, Delta> dirtyKeysWithNewAndOldValues;
+    private final int numKeysChecked;
+
+    private ImmutableBatchDirtyResult(
+        Collection<SkyKey> dirtyKeysWithoutNewValues,
+        Map<SkyKey, Delta> dirtyKeysWithNewAndOldValues,
+        int numKeysChecked) {
+      this.dirtyKeysWithoutNewValues = dirtyKeysWithoutNewValues;
+      this.dirtyKeysWithNewAndOldValues = dirtyKeysWithNewAndOldValues;
+      this.numKeysChecked = numKeysChecked;
+    }
+
+    @Override
+    public Collection<SkyKey> changedKeysWithoutNewValues() {
+      return dirtyKeysWithoutNewValues;
+    }
+
+    @Override
+    public Map<SkyKey, Delta> changedKeysWithNewAndOldValues() {
+      return dirtyKeysWithNewAndOldValues;
+    }
+
+    @Override
+    public Map<SkyKey, SkyValue> changedKeysWithNewValues() {
+      return Delta.newValues(dirtyKeysWithNewAndOldValues);
+    }
+
+    int getNumKeysChecked() {
+      return numKeysChecked;
+    }
   }
 
   /**
-   * Result of a batch call to {@link SkyValueDirtinessChecker#check}. Partitions the dirty
-   * values based on whether we have a new value available for them or not.
+   * Result of a batch call to {@link SkyValueDirtinessChecker#check}. Partitions the dirty values
+   * based on whether we have a new value available for them or not.
    */
-  private static class BatchDirtyResult implements Differencer.DiffWithDelta {
-
+  private static class MutableBatchDirtyResult {
     private final Set<SkyKey> concurrentDirtyKeysWithoutNewValues =
         Collections.newSetFromMap(new ConcurrentHashMap<SkyKey, Boolean>());
     private final ConcurrentHashMap<SkyKey, Delta> concurrentDirtyKeysWithNewAndOldValues =
         new ConcurrentHashMap<>();
+    private final AtomicInteger numChecked;
+
+    private MutableBatchDirtyResult(AtomicInteger numChecked) {
+      this.numChecked = numChecked;
+    }
 
     private void add(SkyKey key, @Nullable SkyValue oldValue, @Nullable SkyValue newValue) {
       if (newValue == null) {
@@ -566,19 +611,11 @@
       }
     }
 
-    @Override
-    public Collection<SkyKey> changedKeysWithoutNewValues() {
-      return concurrentDirtyKeysWithoutNewValues;
-    }
-
-    @Override
-    public Map<SkyKey, Delta> changedKeysWithNewAndOldValues() {
-      return concurrentDirtyKeysWithNewAndOldValues;
-    }
-
-    @Override
-    public Map<SkyKey, SkyValue> changedKeysWithNewValues() {
-      return Delta.newValues(concurrentDirtyKeysWithNewAndOldValues);
+    private ImmutableBatchDirtyResult toImmutable() {
+      return new ImmutableBatchDirtyResult(
+          concurrentDirtyKeysWithoutNewValues,
+          concurrentDirtyKeysWithNewAndOldValues,
+          numChecked.get());
     }
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
index 7f2df10..bea8cce 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
@@ -71,6 +71,7 @@
 import com.google.devtools.build.lib.skyframe.ExternalFilesHelper.ExternalFileAction;
 import com.google.devtools.build.lib.skyframe.ExternalFilesHelper.ExternalFilesKnowledge;
 import com.google.devtools.build.lib.skyframe.ExternalFilesHelper.FileType;
+import com.google.devtools.build.lib.skyframe.FilesystemValueChecker.ImmutableBatchDirtyResult;
 import com.google.devtools.build.lib.skyframe.PackageFunction.ActionOnIOExceptionReadingBuildFile;
 import com.google.devtools.build.lib.skyframe.PackageLookupFunction.CrossRepositoryLabelViolationStrategy;
 import com.google.devtools.build.lib.skyframe.actiongraph.ActionGraphDump;
@@ -86,7 +87,6 @@
 import com.google.devtools.build.lib.vfs.RootedPath;
 import com.google.devtools.build.skyframe.BuildDriver;
 import com.google.devtools.build.skyframe.Differencer;
-import com.google.devtools.build.skyframe.Differencer.Diff;
 import com.google.devtools.build.skyframe.EvaluationContext;
 import com.google.devtools.build.skyframe.GraphInconsistencyReceiver;
 import com.google.devtools.build.skyframe.InMemoryMemoizingEvaluator;
@@ -147,6 +147,7 @@
   private int outputDirtyFiles;
   private int modifiedFilesDuringPreviousBuild;
   private Duration sourceDiffCheckingDuration = Duration.ofSeconds(-1L);
+  private int numSourceFilesCheckedBecauseOfMissingDiffs;
   private Duration outputTreeDiffCheckingDuration = Duration.ofSeconds(-1L);
 
   // If this is null then workspace header pre-calculation won't happen.
@@ -331,6 +332,7 @@
       throws InterruptedException, AbruptExitException {
     TimestampGranularityMonitor tsgm = this.tsgm.get();
     modifiedFiles = 0;
+    numSourceFilesCheckedBecauseOfMissingDiffs = 0;
 
     boolean managedDirectoriesChanged =
         managedDirectoriesKnowledge != null && refreshWorkspaceHeader(eventHandler);
@@ -432,6 +434,7 @@
       handleChangedFiles(
           ImmutableList.of(pathEntry),
           getDiff(tsgm, modifiedFileSet.modifiedSourceFiles(), pathEntry),
+          /*numSourceFilesCheckedIfDiffWasMissing=*/ 0,
           managedDirectoriesChanged);
       processableModifiedFileSet.markProcessed();
     }
@@ -500,9 +503,9 @@
     logger.info(
         "About to scan skyframe graph checking for filesystem nodes of types "
             + Iterables.toString(fileTypesToCheck));
-    Differencer.Diff diff;
+    ImmutableBatchDirtyResult batchDirtyResult;
     try (SilentCloseable c = Profiler.instance().profile("fsvc.getDirtyKeys")) {
-      diff =
+      batchDirtyResult =
           fsvc.getDirtyKeys(
               memoizingEvaluator.getValues(),
               new UnionDirtinessChecker(
@@ -512,7 +515,11 @@
                           new ExternalDirtinessChecker(tmpExternalFilesHelper, fileTypesToCheck),
                           new MissingDiffDirtinessChecker(diffPackageRootsUnderWhichToCheck)))));
     }
-    handleChangedFiles(diffPackageRootsUnderWhichToCheck, diff, managedDirectoriesChanged);
+    handleChangedFiles(
+        diffPackageRootsUnderWhichToCheck,
+        batchDirtyResult,
+        /*numSourceFilesCheckedIfDiffWasMissing=*/ batchDirtyResult.getNumKeysChecked(),
+        managedDirectoriesChanged);
 
     for (Pair<Root, DiffAwarenessManager.ProcessableModifiedFileSet> pair :
         pathEntriesWithoutDiffInformation) {
@@ -527,7 +534,8 @@
 
   private void handleChangedFiles(
       Collection<Root> diffPackageRootsUnderWhichToCheck,
-      Diff diff,
+      Differencer.Diff diff,
+      int numSourceFilesCheckedIfDiffWasMissing,
       boolean managedDirectoriesChanged) {
     int numWithoutNewValues = diff.changedKeysWithoutNewValues().size();
     Iterable<SkyKey> keysToBeChangedLaterInThisBuild = diff.changedKeysWithoutNewValues();
@@ -552,6 +560,7 @@
     recordingDiffer.inject(changedKeysWithNewValues);
     modifiedFiles += getNumberOfModifiedFiles(keysToBeChangedLaterInThisBuild);
     modifiedFiles += getNumberOfModifiedFiles(changedKeysWithNewValues.keySet());
+    numSourceFilesCheckedBecauseOfMissingDiffs += numSourceFilesCheckedIfDiffWasMissing;
     incrementalBuildMonitor.accrue(keysToBeChangedLaterInThisBuild);
     incrementalBuildMonitor.accrue(changedKeysWithNewValues.keySet());
   }
@@ -855,11 +864,14 @@
   @Override
   public ExecutionFinishedEvent createExecutionFinishedEvent() {
     ExecutionFinishedEvent result =
-        new ExecutionFinishedEvent(
-            outputDirtyFiles,
-            modifiedFilesDuringPreviousBuild,
-            sourceDiffCheckingDuration,
-            outputTreeDiffCheckingDuration);
+        ExecutionFinishedEvent.builder()
+            .setOutputDirtyFiles(outputDirtyFiles)
+            .setOutputModifiedFilesDuringPreviousBuild(modifiedFilesDuringPreviousBuild)
+            .setSourceDiffCheckingDuration(sourceDiffCheckingDuration)
+            .setNumSourceFilesCheckedBecauseOfMissingDiffs(
+                numSourceFilesCheckedBecauseOfMissingDiffs)
+            .setOutputTreeDiffCheckingDuration(outputTreeDiffCheckingDuration)
+            .build();
     outputDirtyFiles = 0;
     modifiedFilesDuringPreviousBuild = 0;
     sourceDiffCheckingDuration = Duration.ZERO;