[heap] Do not clear mark bits of left trimmed old object start.

src/heap/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 120 matching lines @@
   if (!heap->incremental_marking()->IsMarking()) return;
 
   // If the mark doesn't move, we don't check the color of the object.
   // It doesn't matter whether the object is black, since it hasn't changed
   // size, so the adjustment to the live data count will be zero anyway.
   if (from == to) return;
 
   MarkBit new_mark_bit = ObjectMarking::MarkBitFrom(to);
   MarkBit old_mark_bit = ObjectMarking::MarkBitFrom(from);
 
-#ifdef DEBUG
-  Marking::ObjectColor old_color = Marking::Color(old_mark_bit);
-#endif
-
   if (Marking::IsBlack(old_mark_bit)) {
-    Marking::MarkWhite(old_mark_bit);
-    Marking::WhiteToBlack(new_mark_bit);
-    return;
+    Marking::MarkBlack(new_mark_bit);
   } else if (Marking::IsGrey(old_mark_bit)) {
-    Marking::MarkWhite(old_mark_bit);
-    Marking::WhiteToGrey(new_mark_bit);
+    Marking::MarkGrey(new_mark_bit);
     heap->mark_compact_collector()->marking_deque()->Push(to);
     heap->incremental_marking()->RestartIfNotMarking();
   }
-
-#ifdef DEBUG
-  Marking::ObjectColor new_color = Marking::Color(new_mark_bit);
-  DCHECK(new_color == old_color);
-#endif
 }
 
 class IncrementalMarkingMarkingVisitor
     : public StaticMarkingVisitor<IncrementalMarkingMarkingVisitor> {
  public:
   static void Initialize() {
     StaticMarkingVisitor<IncrementalMarkingMarkingVisitor>::Initialize();
     table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);
     table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);
   }
@@ skipping 658 matching lines @@
 
 intptr_t IncrementalMarking::ProcessMarkingDeque(
     intptr_t bytes_to_process, ForceCompletionAction completion) {
   intptr_t bytes_processed = 0;
   MarkingDeque* marking_deque =
       heap_->mark_compact_collector()->marking_deque();
   while (!marking_deque->IsEmpty() && (bytes_processed < bytes_to_process ||
                                        completion == FORCE_COMPLETION)) {
     HeapObject* obj = marking_deque->Pop();
 
-    // Left trimming may result in white filler objects on the marking deque.
-    // Ignore these objects.
+    // Left trimming may result in white, grey, or black filler objects on the
+    // marking deque. Ignore these objects.
     if (obj->IsFiller()) {
-      DCHECK(ObjectMarking::IsImpossible(obj) || ObjectMarking::IsWhite(obj));
+      DCHECK(!ObjectMarking::IsImpossible(obj));
       continue;
     }
 
     Map* map = obj->map();
     int size = obj->SizeFromMap(map);
     unscanned_bytes_of_large_object_ = 0;
     VisitObject(map, obj, size);
     bytes_processed += size - unscanned_bytes_of_large_object_;
   }
   // Report all found wrappers to the embedder. This is necessary as the
@@ skipping 316 matching lines @@
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 
 }  // namespace internal
 }  // namespace v8