[heap] Replace compile time flag with runtime flag for parts of

concurrent marker.

Bug: chromium:694255
Change-Id: I973ba8df7a4afc5f58ede02f3f6d043cf7038784
Reviewed-on: https://chromium-review.googlesource.com/600970Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47153}

src/heap/heap.cc

@@ -5965,15 +5965,16 @@ bool Heap::SetUp() {
   mark_compact_collector_ = new MarkCompactCollector(this);
   incremental_marking_->set_marking_worklist(
       mark_compact_collector_->marking_worklist());
-#ifdef V8_CONCURRENT_MARKING
+  if (FLAG_concurrent_marking) {
     MarkCompactCollector::MarkingWorklist* marking_worklist =
         mark_compact_collector_->marking_worklist();
     concurrent_marking_ = new ConcurrentMarking(
         this, marking_worklist->shared(), marking_worklist->bailout(),
         mark_compact_collector_->weak_cells());
-#else
-  concurrent_marking_ = new ConcurrentMarking(this, nullptr, nullptr, nullptr);
-#endif
+  } else {
+    concurrent_marking_ =
+        new ConcurrentMarking(this, nullptr, nullptr, nullptr);
+  }
   minor_mark_compact_collector_ = new MinorMarkCompactCollector(this);
   gc_idle_time_handler_ = new GCIdleTimeHandler();
   memory_reducer_ = new MemoryReducer(this);

src/heap/incremental-marking.cc

@@ -123,13 +123,12 @@ void IncrementalMarking::MarkBlackAndPush(HeapObject* obj) {
   // Color the object black and push it into the bailout deque.
   ObjectMarking::WhiteToGrey<kAtomicity>(obj, marking_state(obj));
   if (ObjectMarking::GreyToBlack<kAtomicity>(obj, marking_state(obj))) {
-#ifdef V8_CONCURRENT_MARKING
+    if (FLAG_concurrent_marking) {
       marking_worklist()->PushBailout(obj);
-#else
-    if (!marking_worklist()->Push(obj)) {
-      ObjectMarking::BlackToGrey<kAtomicity>(obj, marking_state(obj));
+    } else if (!marking_worklist()->Push(obj)) {
+      ObjectMarking::BlackToGrey<AccessMode::NON_ATOMIC>(obj,
+                                                         marking_state(obj));
     }
-#endif
   }
 }
 
@@ -219,9 +218,9 @@ class IncrementalMarkingMarkingVisitor final
       int start_offset =
           Max(FixedArray::BodyDescriptor::kStartOffset, chunk->progress_bar());
       if (start_offset < object_size) {
-#ifdef V8_CONCURRENT_MARKING
+        if (FLAG_concurrent_marking) {
           incremental_marking_->marking_worklist()->PushBailout(object);
-#else
+        } else {
           if (ObjectMarking::IsGrey<IncrementalMarking::kAtomicity>(
                   object, incremental_marking_->marking_state(object))) {
             incremental_marking_->marking_worklist()->Push(object);
@@ -230,7 +229,7 @@ class IncrementalMarkingMarkingVisitor final
                 object, incremental_marking_->marking_state(object)));
             collector_->PushBlack(object);
           }
-#endif
+        }
         int end_offset =
             Min(object_size, start_offset + kProgressBarScanningChunk);
         int already_scanned_offset = start_offset;