diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 5a44b609aa..6c5cf35964 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -666,7 +666,7 @@ DEFINE_BOOL(age_code, true,
 DEFINE_BOOL(incremental_marking, true, "use incremental marking")
 DEFINE_BOOL(incremental_marking_wrappers, true,
             "use incremental marking for marking wrappers")
-DEFINE_BOOL(concurrent_marking, V8_CONCURRENT_MARKING, "use concurrent marking")
+DEFINE_BOOL(concurrent_marking, false, "use concurrent marking")
 DEFINE_BOOL(trace_concurrent_marking, false, "trace concurrent marking")
 DEFINE_INT(min_progress_during_incremental_marking_finalization, 32,
            "keep finalizing incremental marking as long as we discover at "
diff --git a/src/heap/concurrent-marking.cc b/src/heap/concurrent-marking.cc
index 2e91ae368f..618cb1139b 100644
--- a/src/heap/concurrent-marking.cc
+++ b/src/heap/concurrent-marking.cc
@@ -30,11 +30,6 @@ class ConcurrentMarkingVisitor final
   explicit ConcurrentMarkingVisitor(ConcurrentMarkingDeque* deque)
       : deque_(deque) {}
 
-  bool ShouldVisit(HeapObject* object) override {
-    return ObjectMarking::GreyToBlack<MarkBit::AccessMode::ATOMIC>(
-        object, marking_state(object));
-  }
-
   void VisitPointers(HeapObject* host, Object** start, Object** end) override {
     for (Object** p = start; p < end; p++) {
       if (!(*p)->IsHeapObject()) continue;
@@ -73,7 +68,7 @@ class ConcurrentMarkingVisitor final
   // ===========================================================================
 
   int VisitCode(Map* map, Code* object) override {
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): push the object to the bail-out deque.
     return 0;
   }
 
@@ -82,65 +77,58 @@ class ConcurrentMarkingVisitor final
   // ===========================================================================
 
   int VisitBytecodeArray(Map* map, BytecodeArray* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitJSFunction(Map* map, JSFunction* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitMap(Map* map, Map* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitNativeContext(Map* map, Context* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitSharedFunctionInfo(Map* map, SharedFunctionInfo* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitTransitionArray(Map* map, TransitionArray* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitWeakCell(Map* map, WeakCell* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
   int VisitJSWeakCollection(Map* map, JSWeakCollection* object) override {
-    // TODO(ulan): implement iteration of strong fields.
-    deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kBailout);
+    // TODO(ulan): implement iteration of strong fields and push the object to
+    // the bailout deque.
     return 0;
   }
 
-  void MarkObject(HeapObject* object) {
-    if (ObjectMarking::WhiteToGrey<MarkBit::AccessMode::ATOMIC>(
-            object, marking_state(object))) {
-      deque_->Push(object, MarkingThread::kConcurrent, TargetDeque::kShared);
-    }
+  void MarkObject(HeapObject* obj) {
+    deque_->Push(obj, MarkingThread::kConcurrent, TargetDeque::kShared);
   }
 
  private:
-  MarkingState marking_state(HeapObject* object) const {
-    return MarkingState::Internal(object);
-  }
-
   ConcurrentMarkingDeque* deque_;
 };
 
@@ -187,7 +175,7 @@ void ConcurrentMarking::Run() {
     TimedScope scope(&time_ms);
     HeapObject* object;
     while ((object = deque_->Pop(MarkingThread::kConcurrent)) != nullptr) {
-      bytes_marked += visitor_->Visit(object);
+      bytes_marked += visitor_->IterateBody(object);
     }
   }
   if (FLAG_trace_concurrent_marking) {
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 30e55ca974..0c33fcee03 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -4270,7 +4270,7 @@ void Heap::RegisterReservationsForBlackAllocation(Reservation* reservations) {
 void Heap::NotifyObjectLayoutChange(HeapObject* object,
                                     const DisallowHeapAllocation&) {
   if (FLAG_incremental_marking && incremental_marking()->IsMarking()) {
-    incremental_marking()->WhiteToGreyAndPush(object);
+    incremental_marking()->MarkGrey(object);
   }
 #ifdef VERIFY_HEAP
   DCHECK(pending_layout_change_object_ == nullptr);
@@ -4834,7 +4834,7 @@ class IterateAndScavengePromotedObjectsVisitor final : public ObjectVisitor {
     // promoted objects.
     if (heap_->incremental_marking()->black_allocation()) {
       Code* code = Code::cast(Code::GetObjectFromEntryAddress(code_entry_slot));
-      heap_->incremental_marking()->WhiteToGreyAndPush(code);
+      heap_->incremental_marking()->MarkGrey(code);
     }
   }
 
@@ -5628,7 +5628,7 @@ void Heap::RegisterExternallyReferencedObject(Object** object) {
   HeapObject* heap_object = HeapObject::cast(*object);
   DCHECK(Contains(heap_object));
   if (FLAG_incremental_marking_wrappers && incremental_marking()->IsMarking()) {
-    incremental_marking()->WhiteToGreyAndPush(heap_object);
+    incremental_marking()->MarkGrey(heap_object);
   } else {
     DCHECK(mark_compact_collector()->in_use());
     mark_compact_collector()->MarkObject(heap_object);
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index d9d42988f5..a9a71cfb63 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -52,13 +52,14 @@ IncrementalMarking::IncrementalMarking(Heap* heap)
 
 bool IncrementalMarking::BaseRecordWrite(HeapObject* obj, Object* value) {
   HeapObject* value_heap_obj = HeapObject::cast(value);
-  DCHECK(!ObjectMarking::IsImpossible<kAtomicity>(
-      value_heap_obj, marking_state(value_heap_obj)));
-  DCHECK(!ObjectMarking::IsImpossible<kAtomicity>(obj, marking_state(obj)));
-  const bool is_black =
-      ObjectMarking::IsBlack<kAtomicity>(obj, marking_state(obj));
+  DCHECK(!ObjectMarking::IsImpossible(value_heap_obj,
+                                      marking_state(value_heap_obj)));
+  DCHECK(!ObjectMarking::IsImpossible(obj, marking_state(obj)));
+  const bool is_black = ObjectMarking::IsBlack(obj, marking_state(obj));
 
-  if (is_black && WhiteToGreyAndPush(value_heap_obj)) {
+  if (is_black &&
+      ObjectMarking::IsWhite(value_heap_obj, marking_state(value_heap_obj))) {
+    WhiteToGreyAndPush(value_heap_obj);
     RestartIfNotMarking();
   }
   return is_compacting_ && is_black;
@@ -129,12 +130,9 @@ void IncrementalMarking::RecordWriteIntoCodeSlow(Code* host, RelocInfo* rinfo,
   }
 }
 
-bool IncrementalMarking::WhiteToGreyAndPush(HeapObject* obj) {
-  if (ObjectMarking::WhiteToGrey<kAtomicity>(obj, marking_state(obj))) {
-    marking_deque()->Push(obj);
-    return true;
-  }
-  return false;
+void IncrementalMarking::WhiteToGreyAndPush(HeapObject* obj) {
+  ObjectMarking::WhiteToGrey(obj, marking_state(obj));
+  marking_deque()->Push(obj);
 }
 
 void IncrementalMarking::TransferMark(Heap* heap, HeapObject* from,
@@ -154,32 +152,12 @@ void IncrementalMarking::TransferMark(Heap* heap, HeapObject* from,
   MarkBit new_mark_bit = ObjectMarking::MarkBitFrom(to, marking_state(to));
   MarkBit old_mark_bit = ObjectMarking::MarkBitFrom(from, marking_state(from));
 
-  if (Marking::IsBlack<kAtomicity>(old_mark_bit)) {
-    if (from->address() + kPointerSize == to->address()) {
-      // The old and the new markbits overlap. The |to| object has the
-      // grey color. To make it black, we need to set second bit.
-      DCHECK(new_mark_bit.Get<kAtomicity>());
-      new_mark_bit.Next().Set<kAtomicity>();
-    } else {
-      bool success = Marking::WhiteToBlack<kAtomicity>(new_mark_bit);
-      DCHECK(success);
-      USE(success);
-    }
-  } else if (Marking::IsGrey<kAtomicity>(old_mark_bit)) {
-    if (from->address() + kPointerSize == to->address()) {
-      // The old and the new markbits overlap. The |to| object has the
-      // white color. To make it black, we need to set both bits.
-      // Note that Marking::WhiteToGrey does not work here because
-      // old_mark_bit.Next() can be set by the concurrent marker at any time.
-      new_mark_bit.Set<kAtomicity>();
-      new_mark_bit.Next().Set<kAtomicity>();
-    } else {
-      bool success = Marking::WhiteToGrey<kAtomicity>(new_mark_bit);
-      DCHECK(success);
-      USE(success);
-      marking_deque()->Push(to);
-      RestartIfNotMarking();
-    }
+  if (Marking::IsBlack(old_mark_bit)) {
+    Marking::MarkBlack(new_mark_bit);
+  } else if (Marking::IsGrey(old_mark_bit)) {
+    Marking::WhiteToGrey(new_mark_bit);
+    marking_deque()->Push(to);
+    RestartIfNotMarking();
   }
 }
 
@@ -220,11 +198,11 @@ class IncrementalMarkingMarkingVisitor
       } while (scan_until_end && start_offset < object_size);
       chunk->set_progress_bar(start_offset);
       if (start_offset < object_size) {
-        if (ObjectMarking::IsGrey<IncrementalMarking::kAtomicity>(
+        if (ObjectMarking::IsGrey(
                 object, heap->incremental_marking()->marking_state(object))) {
           heap->incremental_marking()->marking_deque()->Unshift(object);
         } else {
-          DCHECK(ObjectMarking::IsBlack<IncrementalMarking::kAtomicity>(
+          DCHECK(ObjectMarking::IsBlack(
               object, heap->incremental_marking()->marking_state(object)));
           heap->mark_compact_collector()->UnshiftBlack(object);
         }
@@ -249,10 +227,12 @@ class IncrementalMarkingMarkingVisitor
         // Mark the object grey if it is white, do not enque it into the marking
         // deque.
         Heap* heap = map->GetHeap();
-        bool ignored =
-            ObjectMarking::WhiteToGrey<IncrementalMarking::kAtomicity>(
-                heap_obj, heap->incremental_marking()->marking_state(heap_obj));
-        USE(ignored);
+        if (ObjectMarking::IsWhite(
+                heap_obj,
+                heap->incremental_marking()->marking_state(heap_obj))) {
+          ObjectMarking::WhiteToGrey(
+              heap_obj, heap->incremental_marking()->marking_state(heap_obj));
+        }
       }
     }
     VisitNativeContext(map, context);
@@ -279,28 +259,33 @@ class IncrementalMarkingMarkingVisitor
 
   // Marks the object grey and pushes it on the marking stack.
   INLINE(static void MarkObject(Heap* heap, Object* obj)) {
-    heap->incremental_marking()->WhiteToGreyAndPush(HeapObject::cast(obj));
+    heap->incremental_marking()->MarkGrey(HeapObject::cast(obj));
   }
 
   // Marks the object black without pushing it on the marking stack.
   // Returns true if object needed marking and false otherwise.
   INLINE(static bool MarkObjectWithoutPush(Heap* heap, Object* obj)) {
     HeapObject* heap_object = HeapObject::cast(obj);
-    return ObjectMarking::WhiteToBlack<IncrementalMarking::kAtomicity>(
-        heap_object, heap->incremental_marking()->marking_state(heap_object));
+    if (ObjectMarking::IsWhite(
+            heap_object,
+            heap->incremental_marking()->marking_state(heap_object))) {
+      ObjectMarking::WhiteToBlack(
+          heap_object, heap->incremental_marking()->marking_state(heap_object));
+      return true;
+    }
+    return false;
   }
 };
 
 void IncrementalMarking::IterateBlackObject(HeapObject* object) {
-  if (IsMarking() &&
-      ObjectMarking::IsBlack<kAtomicity>(object, marking_state(object))) {
+  if (IsMarking() && ObjectMarking::IsBlack(object, marking_state(object))) {
     Page* page = Page::FromAddress(object->address());
     if ((page->owner() != nullptr) && (page->owner()->identity() == LO_SPACE)) {
       // IterateBlackObject requires us to visit the whole object.
       page->ResetProgressBar();
     }
     Map* map = object->map();
-    WhiteToGreyAndPush(map);
+    MarkGrey(map);
     IncrementalMarkingMarkingVisitor::IterateBody(map, object);
   }
 }
@@ -324,7 +309,7 @@ class IncrementalMarkingRootMarkingVisitor : public RootVisitor {
     Object* obj = *p;
     if (!obj->IsHeapObject()) return;
 
-    heap_->incremental_marking()->WhiteToGreyAndPush(HeapObject::cast(obj));
+    heap_->incremental_marking()->MarkGrey(HeapObject::cast(obj));
   }
 
   Heap* heap_;
@@ -650,7 +635,7 @@ void IncrementalMarking::ProcessWeakCells() {
     HeapObject* value = HeapObject::cast(weak_cell->value());
     // Remove weak cells with live objects from the list, they do not need
     // clearing.
-    if (ObjectMarking::IsBlackOrGrey<kAtomicity>(value, marking_state(value))) {
+    if (ObjectMarking::IsBlackOrGrey(value, marking_state(value))) {
       // Record slot, if value is pointing to an evacuation candidate.
       Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
       heap_->mark_compact_collector()->RecordSlot(weak_cell, slot, *slot);
@@ -681,10 +666,9 @@ bool ShouldRetainMap(Map* map, int age) {
   Object* constructor = map->GetConstructor();
   Heap* heap = map->GetHeap();
   if (!constructor->IsHeapObject() ||
-      ObjectMarking::IsWhite<IncrementalMarking::kAtomicity>(
-          HeapObject::cast(constructor),
-          heap->incremental_marking()->marking_state(
-              HeapObject::cast(constructor)))) {
+      ObjectMarking::IsWhite(HeapObject::cast(constructor),
+                             heap->incremental_marking()->marking_state(
+                                 HeapObject::cast(constructor)))) {
     // The constructor is dead, no new objects with this map can
     // be created. Do not retain this map.
     return false;
@@ -714,15 +698,14 @@ void IncrementalMarking::RetainMaps() {
     int new_age;
     Map* map = Map::cast(cell->value());
     if (i >= number_of_disposed_maps && !map_retaining_is_disabled &&
-        ObjectMarking::IsWhite<kAtomicity>(map, marking_state(map))) {
+        ObjectMarking::IsWhite(map, marking_state(map))) {
       if (ShouldRetainMap(map, age)) {
-        WhiteToGreyAndPush(map);
+        MarkGrey(map);
       }
       Object* prototype = map->prototype();
       if (age > 0 && prototype->IsHeapObject() &&
-          ObjectMarking::IsWhite<kAtomicity>(
-              HeapObject::cast(prototype),
-              marking_state(HeapObject::cast(prototype)))) {
+          ObjectMarking::IsWhite(HeapObject::cast(prototype),
+                                 marking_state(HeapObject::cast(prototype)))) {
         // The prototype is not marked, age the map.
         new_age = age - 1;
       } else {
@@ -813,21 +796,21 @@ void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
         return nullptr;
       }
       HeapObject* dest = map_word.ToForwardingAddress();
-      if (ObjectMarking::IsBlack<kAtomicity>(dest, marking_state(dest))) {
+      if (ObjectMarking::IsBlack(dest, marking_state(dest))) {
         // The object is already processed by the marker.
         return nullptr;
       }
-      DCHECK(ObjectMarking::IsGrey<kAtomicity>(obj, marking_state(obj)) ||
-             (obj->IsFiller() &&
-              ObjectMarking::IsWhite<kAtomicity>(obj, marking_state(obj))));
+      DCHECK(
+          ObjectMarking::IsGrey(obj, marking_state(obj)) ||
+          (obj->IsFiller() && ObjectMarking::IsWhite(obj, marking_state(obj))));
       return dest;
     } else {
-      DCHECK(ObjectMarking::IsGrey<kAtomicity>(obj, marking_state(obj)) ||
+      DCHECK(ObjectMarking::IsGrey(obj, marking_state(obj)) ||
              (obj->IsFiller() &&
-              ObjectMarking::IsWhite<kAtomicity>(obj, marking_state(obj))) ||
+              ObjectMarking::IsWhite(obj, marking_state(obj))) ||
              (MemoryChunk::FromAddress(obj->address())
                   ->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
-              ObjectMarking::IsBlack<kAtomicity>(obj, marking_state(obj))));
+              ObjectMarking::IsBlack(obj, marking_state(obj))));
       // Skip one word filler objects that appear on the
       // stack when we perform in place array shift.
       return (obj->map() == filler_map) ? nullptr : obj;
@@ -835,29 +818,33 @@ void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
   });
 }
 
-bool IncrementalMarking::IsFixedArrayWithProgressBar(HeapObject* obj) {
-  if (!obj->IsFixedArray()) return false;
-  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
-  return chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR);
-}
 
 void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {
+  MarkGrey(map);
+
+  IncrementalMarkingMarkingVisitor::IterateBody(map, obj);
+
 #if ENABLE_SLOW_DCHECKS
   MarkBit mark_bit = ObjectMarking::MarkBitFrom(obj, marking_state(obj));
   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
-  SLOW_DCHECK(Marking::IsGrey<kAtomicity>(mark_bit) ||
+  SLOW_DCHECK(Marking::IsGrey(mark_bit) ||
               (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
-               Marking::IsBlack<kAtomicity>(mark_bit)));
+               Marking::IsBlack(mark_bit)));
 #endif
-  if (ObjectMarking::GreyToBlack<kAtomicity>(obj, marking_state(obj))) {
-    WhiteToGreyAndPush(map);
-    IncrementalMarkingMarkingVisitor::IterateBody(map, obj);
-  } else if (IsFixedArrayWithProgressBar(obj)) {
-    DCHECK(ObjectMarking::IsBlack<kAtomicity>(obj, marking_state(obj)));
-    IncrementalMarkingMarkingVisitor::VisitFixedArrayIncremental(map, obj);
+  MarkBlack(obj, size);
+}
+
+void IncrementalMarking::MarkGrey(HeapObject* object) {
+  if (ObjectMarking::IsWhite(object, marking_state(object))) {
+    WhiteToGreyAndPush(object);
   }
 }
 
+void IncrementalMarking::MarkBlack(HeapObject* obj, int size) {
+  if (ObjectMarking::IsBlack(obj, marking_state(obj))) return;
+  ObjectMarking::GreyToBlack(obj, marking_state(obj));
+}
+
 intptr_t IncrementalMarking::ProcessMarkingDeque(
     intptr_t bytes_to_process, ForceCompletionAction completion) {
   intptr_t bytes_processed = 0;
@@ -868,7 +855,7 @@ intptr_t IncrementalMarking::ProcessMarkingDeque(
     // Left trimming may result in white, grey, or black filler objects on the
     // marking deque. Ignore these objects.
     if (obj->IsFiller()) {
-      DCHECK(!ObjectMarking::IsImpossible<kAtomicity>(obj, marking_state(obj)));
+      DCHECK(!ObjectMarking::IsImpossible(obj, marking_state(obj)));
       continue;
     }
 
@@ -923,10 +910,9 @@ void IncrementalMarking::Hurry() {
     HeapObject* cache = HeapObject::cast(
         Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));
     if (!cache->IsUndefined(heap_->isolate())) {
-      // Mark the cache black if it is grey.
-      bool ignored =
-          ObjectMarking::GreyToBlack<kAtomicity>(cache, marking_state(cache));
-      USE(ignored);
+      if (ObjectMarking::IsGrey(cache, marking_state(cache))) {
+        ObjectMarking::GreyToBlack(cache, marking_state(cache));
+      }
     }
     context = Context::cast(context)->next_context_link();
   }
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 0eaae2c699..35978f3f8e 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -65,6 +65,9 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
     return MarkingState::Internal(chunk);
   }
 
+  void MarkBlack(HeapObject* object, int size);
+  void MarkGrey(HeapObject* object);
+
   // Transfers mark bits without requiring proper object headers.
   void TransferMark(Heap* heap, HeapObject* from, HeapObject* to);
 
@@ -79,15 +82,9 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
 
     DCHECK(ObjectMarking::IsWhite<access_mode>(to, marking_state(to)));
     if (ObjectMarking::IsGrey<access_mode>(from, marking_state(from))) {
-      bool success =
-          ObjectMarking::WhiteToGrey<access_mode>(to, marking_state(to));
-      DCHECK(success);
-      USE(success);
+      ObjectMarking::WhiteToGrey<access_mode>(to, marking_state(to));
     } else if (ObjectMarking::IsBlack<access_mode>(from, marking_state(from))) {
-      bool success =
-          ObjectMarking::WhiteToBlack<access_mode>(to, marking_state(to));
-      DCHECK(success);
-      USE(success);
+      ObjectMarking::WhiteToBlack<access_mode>(to, marking_state(to));
     }
   }
 
@@ -182,12 +179,6 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
   static const intptr_t kActivationThreshold = 0;
 #endif
 
-#ifdef V8_CONCURRENT_MARKING
-  static const MarkBit::AccessMode kAtomicity = MarkBit::AccessMode::ATOMIC;
-#else
-  static const MarkBit::AccessMode kAtomicity = MarkBit::AccessMode::NON_ATOMIC;
-#endif
-
   void FinalizeSweeping();
 
   size_t Step(size_t bytes_to_process, CompletionAction action,
@@ -219,9 +210,7 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
   void RecordCodeTargetPatch(Code* host, Address pc, HeapObject* value);
   void RecordCodeTargetPatch(Address pc, HeapObject* value);
 
-  // Returns true if the function succeeds in transitioning the object
-  // from white to grey.
-  bool WhiteToGreyAndPush(HeapObject* obj);
+  void WhiteToGreyAndPush(HeapObject* obj);
 
   inline void SetOldSpacePageFlags(MemoryChunk* chunk) {
     SetOldSpacePageFlags(chunk, IsMarking(), IsCompacting());
@@ -312,7 +301,6 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
       intptr_t bytes_to_process,
       ForceCompletionAction completion = DO_NOT_FORCE_COMPLETION));
 
-  INLINE(bool IsFixedArrayWithProgressBar(HeapObject* object));
   INLINE(void VisitObject(Map* map, HeapObject* obj, int size));
 
   void IncrementIdleMarkingDelayCounter();
diff --git a/src/heap/mark-compact-inl.h b/src/heap/mark-compact-inl.h
index 584f86dc88..cb280e2bbb 100644
--- a/src/heap/mark-compact-inl.h
+++ b/src/heap/mark-compact-inl.h
@@ -38,15 +38,19 @@ void MarkCompactCollector::UnshiftBlack(HeapObject* obj) {
 }
 
 void MarkCompactCollector::MarkObject(HeapObject* obj) {
-  if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+  if (ObjectMarking::IsWhite<MarkBit::NON_ATOMIC>(
           obj, MarkingState::Internal(obj))) {
+    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+        obj, MarkingState::Internal(obj));
     PushBlack(obj);
   }
 }
 
 void MinorMarkCompactCollector::MarkObject(HeapObject* obj) {
-  if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+  if (ObjectMarking::IsWhite<MarkBit::NON_ATOMIC>(
           obj, MarkingState::External(obj))) {
+    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+        obj, MarkingState::External(obj));
     PushBlack(obj);
   }
 }
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index cd9f548f53..8e1be75877 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -1196,10 +1196,12 @@ class StaticYoungGenerationMarkingVisitor
     StackLimitCheck check(heap->isolate());
     if (check.HasOverflowed()) return false;
 
-    if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-            object, MarkingState::External(object))) {
-      IterateBody(object->map(), object);
-    }
+    if (ObjectMarking::IsBlackOrGrey<MarkBit::NON_ATOMIC>(
+            object, MarkingState::External(object)))
+      return true;
+    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+        object, MarkingState::External(object));
+    IterateBody(object->map(), object);
     return true;
   }
 };
@@ -1235,7 +1237,11 @@ class MarkCompactMarkingVisitor
   // Marks the object black without pushing it on the marking stack.
   // Returns true if object needed marking and false otherwise.
   INLINE(static bool MarkObjectWithoutPush(Heap* heap, HeapObject* object)) {
-    return ObjectMarking::WhiteToBlack(object, MarkingState::Internal(object));
+    if (ObjectMarking::IsWhite(object, MarkingState::Internal(object))) {
+      ObjectMarking::WhiteToBlack(object, MarkingState::Internal(object));
+      return true;
+    }
+    return false;
   }
 
   // Mark object pointed to by p.
@@ -1253,15 +1259,14 @@ class MarkCompactMarkingVisitor
                                          HeapObject* obj)) {
 #ifdef DEBUG
     DCHECK(collector->heap()->Contains(obj));
+    DCHECK(ObjectMarking::IsWhite(obj, MarkingState::Internal(obj)));
 #endif
-    if (ObjectMarking::WhiteToBlack(obj, MarkingState::Internal(obj))) {
-      Map* map = obj->map();
-      Heap* heap = obj->GetHeap();
-      ObjectMarking::WhiteToBlack(obj, MarkingState::Internal(obj));
-      // Mark the map pointer and the body.
-      heap->mark_compact_collector()->MarkObject(map);
-      IterateBody(map, obj);
-    }
+    Map* map = obj->map();
+    Heap* heap = obj->GetHeap();
+    ObjectMarking::WhiteToBlack(obj, MarkingState::Internal(obj));
+    // Mark the map pointer and the body.
+    heap->mark_compact_collector()->MarkObject(map);
+    IterateBody(map, obj);
   }
 
   // Visit all unmarked objects pointed to by [start, end).
@@ -1279,6 +1284,8 @@ class MarkCompactMarkingVisitor
       if (!o->IsHeapObject()) continue;
       collector->RecordSlot(object, p, o);
       HeapObject* obj = HeapObject::cast(o);
+      if (ObjectMarking::IsBlackOrGrey(obj, MarkingState::Internal(obj)))
+        continue;
       VisitUnmarkedObject(collector, obj);
     }
     return true;
@@ -1475,12 +1482,16 @@ class MinorMarkCompactCollector::RootMarkingVisitor : public RootVisitor {
 
     if (!collector_->heap()->InNewSpace(object)) return;
 
-    if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-            object, MarkingState::External(object))) {
-      Map* map = object->map();
-      StaticYoungGenerationMarkingVisitor::IterateBody(map, object);
-      collector_->EmptyMarkingDeque();
-    }
+    if (ObjectMarking::IsBlackOrGrey<MarkBit::NON_ATOMIC>(
+            object, MarkingState::External(object)))
+      return;
+
+    Map* map = object->map();
+    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+        object, MarkingState::External(object));
+    StaticYoungGenerationMarkingVisitor::IterateBody(map, object);
+
+    collector_->EmptyMarkingDeque();
   }
 
   MinorMarkCompactCollector* collector_;
@@ -1521,16 +1532,22 @@ class MarkCompactCollector::RootMarkingVisitor : public ObjectVisitor,
 
     HeapObject* object = HeapObject::cast(*p);
 
-    if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-            object, MarkingState::Internal(object))) {
-      Map* map = object->map();
-      // Mark the map pointer and body, and push them on the marking stack.
-      collector_->MarkObject(map);
-      MarkCompactMarkingVisitor::IterateBody(map, object);
-      // Mark all the objects reachable from the map and body.  May leave
-      // overflowed objects in the heap.
-      collector_->EmptyMarkingDeque();
-    }
+    if (ObjectMarking::IsBlackOrGrey<MarkBit::NON_ATOMIC>(
+            object, MarkingState::Internal(object)))
+      return;
+
+    Map* map = object->map();
+    // Mark the object.
+    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
+        object, MarkingState::Internal(object));
+
+    // Mark the map pointer and body, and push them on the marking stack.
+    collector_->MarkObject(map);
+    MarkCompactMarkingVisitor::IterateBody(map, object);
+
+    // Mark all the objects reachable from the map and body.  May leave
+    // overflowed objects in the heap.
+    collector_->EmptyMarkingDeque();
   }
 
   MarkCompactCollector* collector_;
@@ -1701,7 +1718,8 @@ void MarkCompactCollector::DiscoverGreyObjectsWithIterator(T* it) {
   Map* filler_map = heap()->one_pointer_filler_map();
   for (HeapObject* object = it->Next(); object != NULL; object = it->Next()) {
     if ((object->map() != filler_map) &&
-        ObjectMarking::GreyToBlack(object, MarkingState::Internal(object))) {
+        ObjectMarking::IsGrey(object, MarkingState::Internal(object))) {
+      ObjectMarking::GreyToBlack(object, MarkingState::Internal(object));
       PushBlack(object);
       if (marking_deque()->IsFull()) return;
     }
@@ -1713,10 +1731,8 @@ void MarkCompactCollector::DiscoverGreyObjectsOnPage(MemoryChunk* p) {
   LiveObjectIterator<kGreyObjects> it(p, MarkingState::Internal(p));
   HeapObject* object = NULL;
   while ((object = it.Next()) != NULL) {
-    bool success =
-        ObjectMarking::GreyToBlack(object, MarkingState::Internal(object));
-    DCHECK(success);
-    USE(success);
+    DCHECK(ObjectMarking::IsGrey(object, MarkingState::Internal(object)));
+    ObjectMarking::GreyToBlack(object, MarkingState::Internal(object));
     PushBlack(object);
     if (marking_deque()->IsFull()) return;
   }
@@ -2279,12 +2295,15 @@ bool MarkCompactCollector::IsUnmarkedHeapObject(Object** p) {
 void MarkCompactCollector::MarkStringTable(RootMarkingVisitor* visitor) {
   StringTable* string_table = heap()->string_table();
   // Mark the string table itself.
-  if (ObjectMarking::WhiteToBlack(string_table,
-                                  MarkingState::Internal(string_table))) {
-    // Explicitly mark the prefix.
-    string_table->IteratePrefix(visitor);
-    ProcessMarkingDeque();
+  if (ObjectMarking::IsWhite(string_table,
+                             MarkingState::Internal(string_table))) {
+    // String table could have already been marked by visiting the handles list.
+    ObjectMarking::WhiteToBlack(string_table,
+                                MarkingState::Internal(string_table));
   }
+  // Explicitly mark the prefix.
+  string_table->IteratePrefix(visitor);
+  ProcessMarkingDeque();
 }
 
 void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index b727124b9c..2f7801098f 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -82,6 +82,8 @@ class ObjectMarking : public AllStatic {
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool BlackToGrey(HeapObject* obj,
                                     const MarkingState& state) {
+    DCHECK(
+        (access_mode == MarkBit::ATOMIC || IsBlack<access_mode>(obj, state)));
     MarkBit markbit = MarkBitFrom(obj, state);
     if (!Marking::BlackToGrey<access_mode>(markbit)) return false;
     state.IncrementLiveBytes<access_mode>(-obj->Size());
@@ -91,19 +93,24 @@ class ObjectMarking : public AllStatic {
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool WhiteToGrey(HeapObject* obj,
                                     const MarkingState& state) {
+    DCHECK(
+        (access_mode == MarkBit::ATOMIC || IsWhite<access_mode>(obj, state)));
     return Marking::WhiteToGrey<access_mode>(MarkBitFrom(obj, state));
   }
 
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool WhiteToBlack(HeapObject* obj,
                                      const MarkingState& state) {
-    return ObjectMarking::WhiteToGrey<access_mode>(obj, state) &&
-           ObjectMarking::GreyToBlack<access_mode>(obj, state);
+    DCHECK(
+        (access_mode == MarkBit::ATOMIC || IsWhite<access_mode>(obj, state)));
+    if (!ObjectMarking::WhiteToGrey<access_mode>(obj, state)) return false;
+    return ObjectMarking::GreyToBlack<access_mode>(obj, state);
   }
 
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool GreyToBlack(HeapObject* obj,
                                     const MarkingState& state) {
+    DCHECK((access_mode == MarkBit::ATOMIC || IsGrey<access_mode>(obj, state)));
     MarkBit markbit = MarkBitFrom(obj, state);
     if (!Marking::GreyToBlack<access_mode>(markbit)) return false;
     state.IncrementLiveBytes<access_mode>(obj->Size());
diff --git a/src/heap/marking.h b/src/heap/marking.h
index ab98a124bc..b20a4d86f1 100644
--- a/src/heap/marking.h
+++ b/src/heap/marking.h
@@ -38,16 +38,12 @@ class MarkBit {
     }
   }
 
-  // The function returns true if it succeeded to
-  // transition the bit from 0 to 1.
   template <AccessMode mode = NON_ATOMIC>
   inline bool Set();
 
   template <AccessMode mode = NON_ATOMIC>
   inline bool Get();
 
-  // The function returns true if it succeeded to
-  // transition the bit from 1 to 0.
   template <AccessMode mode = NON_ATOMIC>
   inline bool Clear();
 
@@ -61,9 +57,8 @@ class MarkBit {
 
 template <>
 inline bool MarkBit::Set<MarkBit::NON_ATOMIC>() {
-  base::Atomic32 old_value = *cell_;
-  *cell_ = old_value | mask_;
-  return (old_value & mask_) == 0;
+  *cell_ |= mask_;
+  return true;
 }
 
 template <>
@@ -91,9 +86,8 @@ inline bool MarkBit::Get<MarkBit::ATOMIC>() {
 
 template <>
 inline bool MarkBit::Clear<MarkBit::NON_ATOMIC>() {
-  base::Atomic32 old_value = *cell_;
-  *cell_ = old_value & ~mask_;
-  return (old_value & mask_) == mask_;
+  *cell_ &= ~mask_;
+  return true;
 }
 
 template <>
@@ -418,17 +412,24 @@ class Marking : public AllStatic {
 
   template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
   INLINE(static bool WhiteToGrey(MarkBit markbit)) {
+    DCHECK(mode == MarkBit::ATOMIC || IsWhite(markbit));
     return markbit.Set<mode>();
   }
 
+  // Warning: this method is not safe in general in concurrent scenarios.
+  // If you know that nobody else will change the bits on the given location
+  // then you may use it.
   template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
-  INLINE(static bool WhiteToBlack(MarkBit markbit)) {
-    return markbit.Set<mode>() && markbit.Next().Set<mode>();
+  INLINE(static void WhiteToBlack(MarkBit markbit)) {
+    DCHECK(mode == MarkBit::ATOMIC || IsWhite(markbit));
+    markbit.Set<mode>();
+    markbit.Next().Set<mode>();
   }
 
   template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
   INLINE(static bool GreyToBlack(MarkBit markbit)) {
-    return markbit.Get<mode>() && markbit.Next().Set<mode>();
+    DCHECK(mode == MarkBit::ATOMIC || IsGrey(markbit));
+    return markbit.Next().Set<mode>();
   }
 
   enum ObjectColor {
diff --git a/src/heap/objects-visiting-inl.h b/src/heap/objects-visiting-inl.h
index 11bf679ec4..df3bab76a1 100644
--- a/src/heap/objects-visiting-inl.h
+++ b/src/heap/objects-visiting-inl.h
@@ -637,7 +637,8 @@ void StaticMarkingVisitor<StaticVisitor>::VisitJSFunctionWeakCode(
 }
 
 template <typename ResultType, typename ConcreteVisitor>
-ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit(HeapObject* object) {
+ResultType HeapVisitor<ResultType, ConcreteVisitor>::IterateBody(
+    HeapObject* object) {
   Map* map = object->map();
   ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
   switch (static_cast<VisitorId>(map->visitor_id())) {
@@ -668,28 +669,14 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit(HeapObject* object) {
   return ResultType();
 }
 
-template <typename ResultType, typename ConcreteVisitor>
-void HeapVisitor<ResultType, ConcreteVisitor>::VisitMapPointer(
-    HeapObject* host, HeapObject** map) {
-  static_cast<ConcreteVisitor*>(this)->VisitPointer(
-      host, reinterpret_cast<Object**>(map));
-}
-
-template <typename ResultType, typename ConcreteVisitor>
-bool HeapVisitor<ResultType, ConcreteVisitor>::ShouldVisit(HeapObject* object) {
-  return true;
-}
-
-#define VISIT(type)                                                 \
-  template <typename ResultType, typename ConcreteVisitor>          \
-  ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit##type( \
-      Map* map, type* object) {                                     \
-    ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this); \
-    if (!visitor->ShouldVisit(object)) return ResultType();         \
-    int size = type::BodyDescriptor::SizeOf(map, object);           \
-    visitor->VisitMapPointer(object, object->map_slot());           \
-    type::BodyDescriptor::IterateBody(object, size, visitor);       \
-    return static_cast<ResultType>(size);                           \
+#define VISIT(type)                                                         \
+  template <typename ResultType, typename ConcreteVisitor>                  \
+  ResultType HeapVisitor<ResultType, ConcreteVisitor>::Visit##type(         \
+      Map* map, type* object) {                                             \
+    int size = type::BodyDescriptor::SizeOf(map, object);                   \
+    type::BodyDescriptor::IterateBody(object, size,                         \
+                                      static_cast<ConcreteVisitor*>(this)); \
+    return static_cast<ResultType>(size);                                   \
   }
 TYPED_VISITOR_ID_LIST(VISIT)
 #undef VISIT
@@ -697,10 +684,7 @@ TYPED_VISITOR_ID_LIST(VISIT)
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitShortcutCandidate(
     Map* map, ConsString* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = ConsString::BodyDescriptor::SizeOf(map, object);
-  visitor->VisitMapPointer(object, object->map_slot());
   ConsString::BodyDescriptor::IterateBody(object, size,
                                           static_cast<ConcreteVisitor*>(this));
   return static_cast<ResultType>(size);
@@ -709,10 +693,7 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitShortcutCandidate(
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitNativeContext(
     Map* map, Context* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = Context::BodyDescriptor::SizeOf(map, object);
-  visitor->VisitMapPointer(object, object->map_slot());
   Context::BodyDescriptor::IterateBody(object, size,
                                        static_cast<ConcreteVisitor*>(this));
   return static_cast<ResultType>(size);
@@ -721,20 +702,14 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitNativeContext(
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitDataObject(
     Map* map, HeapObject* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = map->instance_size();
-  visitor->VisitMapPointer(object, object->map_slot());
   return static_cast<ResultType>(size);
 }
 
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitJSObjectFast(
     Map* map, JSObject* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = JSObject::FastBodyDescriptor::SizeOf(map, object);
-  visitor->VisitMapPointer(object, object->map_slot());
   JSObject::FastBodyDescriptor::IterateBody(
       object, size, static_cast<ConcreteVisitor*>(this));
   return static_cast<ResultType>(size);
@@ -742,10 +717,7 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitJSObjectFast(
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitJSApiObject(
     Map* map, JSObject* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = JSObject::BodyDescriptor::SizeOf(map, object);
-  visitor->VisitMapPointer(object, object->map_slot());
   JSObject::BodyDescriptor::IterateBody(object, size,
                                         static_cast<ConcreteVisitor*>(this));
   return static_cast<ResultType>(size);
@@ -753,10 +725,7 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitJSApiObject(
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitStruct(
     Map* map, HeapObject* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
   int size = map->instance_size();
-  visitor->VisitMapPointer(object, object->map_slot());
   StructBodyDescriptor::IterateBody(object, size,
                                     static_cast<ConcreteVisitor*>(this));
   return static_cast<ResultType>(size);
@@ -764,9 +733,6 @@ ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitStruct(
 template <typename ResultType, typename ConcreteVisitor>
 ResultType HeapVisitor<ResultType, ConcreteVisitor>::VisitFreeSpace(
     Map* map, FreeSpace* object) {
-  ConcreteVisitor* visitor = static_cast<ConcreteVisitor*>(this);
-  if (!visitor->ShouldVisit(object)) return ResultType();
-  visitor->VisitMapPointer(object, object->map_slot());
   return static_cast<ResultType>(FreeSpace::cast(object)->size());
 }
 
diff --git a/src/heap/objects-visiting.h b/src/heap/objects-visiting.h
index c578a42d64..c9d1c05c93 100644
--- a/src/heap/objects-visiting.h
+++ b/src/heap/objects-visiting.h
@@ -395,16 +395,9 @@ VisitorDispatchTable<typename StaticMarkingVisitor<StaticVisitor>::Callback>
 template <typename ResultType, typename ConcreteVisitor>
 class HeapVisitor : public ObjectVisitor {
  public:
-  ResultType Visit(HeapObject* object);
+  ResultType IterateBody(HeapObject* object);
 
  protected:
-  // A guard predicate for visiting the object.
-  // If it returns false then the default implementations of the Visit*
-  // functions bailout from iterating the object pointers.
-  virtual bool ShouldVisit(HeapObject* object);
-  // A callback for visiting the map pointer in the object header.
-  virtual void VisitMapPointer(HeapObject* host, HeapObject** map);
-
 #define VISIT(type) virtual ResultType Visit##type(Map* map, type* object);
   TYPED_VISITOR_ID_LIST(VISIT)
 #undef VISIT
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 9e91da2cdc..a3f87c4b24 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1525,9 +1525,6 @@ void HeapObject::set_map_no_write_barrier(Map* value) {
   set_map_word(MapWord::FromMap(value));
 }
 
-HeapObject** HeapObject::map_slot() {
-  return reinterpret_cast<HeapObject**>(FIELD_ADDR(this, kMapOffset));
-}
 
 MapWord HeapObject::map_word() const {
   return MapWord(
diff --git a/src/objects.h b/src/objects.h
index c73f28da5e..4c72ad5b2d 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1669,9 +1669,6 @@ class HeapObject: public Object {
   // information.
   inline Map* map() const;
   inline void set_map(Map* value);
-
-  inline HeapObject** map_slot();
-
   // The no-write-barrier version.  This is OK if the object is white and in
   // new space, or if the value is an immortal immutable object, like the maps
   // of primitive (non-JS) objects like strings, heap numbers etc.