[heap] Finish sweeping in safepoint

Refactor Heap::FinalizeSweeping such that EnsureSweepingCompleted
is executed in a safepoint.

Bug: v8:10315
Change-Id: Iee09765ba5fd35e3e696b018bd616954d609ef72
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2204098Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67827}

src/heap/incremental-marking.cc

@@ -958,24 +958,21 @@ StepResult IncrementalMarking::AdvanceWithDeadline(
 
 void IncrementalMarking::FinalizeSweeping() {
   DCHECK(state_ == SWEEPING);
-#ifdef DEBUG
-  // Enforce safepoint here such that background threads cannot allocate between
-  // completing sweeping and VerifyCountersAfterSweeping().
+  if (ContinueConcurrentSweeping()) return;
+
   SafepointScope scope(heap());
-#endif
-  if (collector_->sweeping_in_progress() &&
-      (!FLAG_concurrent_sweeping ||
-       !collector_->sweeper()->AreSweeperTasksRunning())) {
-    collector_->EnsureSweepingCompleted();
-  }
-  if (!collector_->sweeping_in_progress()) {
+  collector_->EnsureSweepingCompleted();
+  DCHECK(!collector_->sweeping_in_progress());
 #ifdef DEBUG
-    heap_->VerifyCountersAfterSweeping();
-#else
-    SafepointScope scope(heap());
+  heap_->VerifyCountersAfterSweeping();
 #endif
-    StartMarking();
-  }
+  StartMarking();
+}
+
+bool IncrementalMarking::ContinueConcurrentSweeping() {
+  if (!collector_->sweeping_in_progress()) return false;
+  return FLAG_concurrent_sweeping &&
+         collector_->sweeper()->AreSweeperTasksRunning();
 }
 
 size_t IncrementalMarking::StepSizeToKeepUpWithAllocations() {

src/heap/incremental-marking.h

@@ -168,6 +168,7 @@ class V8_EXPORT_PRIVATE IncrementalMarking final {
                                  StepOrigin step_origin);
 
   void FinalizeSweeping();
+  bool ContinueConcurrentSweeping();
 
   StepResult Step(double max_step_size_in_ms, CompletionAction action,
                   StepOrigin step_origin);