Revert https://codereview.chromium.org/2857713002 and dependencies

Revert "[heap] Make non-atomic markbit operations consistent with atomic ones."

This reverts commit dd37366f

Revert "[heap] Use atomic marking operations in incremental marking if"

This reverts commit 1f2c3596

Revert "[heap] Prepare IncrementalMarking::VisitObject for concurrent marking."

This reverts commit 00d1e2cf

Revert "[heap] Use shared markbits in the concurrent marker."

This reverts commit b0db0541

https://codereview.chromium.org/2857713002 blocks the current roll:
https://codereview.chromium.org/2857423002/

Doesn't revert cleanly.

NOTRY=true
TBR=ulan@chromium.org

Bug: chromium:694255
Change-Id: Iada35af5c2529cd9e604802700604b16cc30aa2d
Reviewed-on: https://chromium-review.googlesource.com/497387Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45118}

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 "

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) {

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);

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);
     } else if (ObjectMarking::IsBlack<access_mode>(from, marking_state(from))) {
-      bool success =
       ObjectMarking::WhiteToBlack<access_mode>(to, marking_state(to));
-      DCHECK(success);
-      USE(success);
     }
   }
 
@@ -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();

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);
   }
 }

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))) {
+    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.
@@ -1253,8 +1259,8 @@ 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));
@@ -1262,7 +1268,6 @@ class MarkCompactMarkingVisitor
     heap->mark_compact_collector()->MarkObject(map);
     IterateBody(map, obj);
   }
-  }
 
   // Visit all unmarked objects pointed to by [start, end).
   // Returns false if the operation fails (lack of stack space).
@@ -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;
@@ -1475,13 +1482,17 @@ class MinorMarkCompactCollector::RootMarkingVisitor : public RootVisitor {
 
     if (!collector_->heap()->InNewSpace(object)) return;
 
-    if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-            object, MarkingState::External(object))) {
+    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_;
 };
@@ -1521,17 +1532,23 @@ class MarkCompactCollector::RootMarkingVisitor : public ObjectVisitor,
 
     HeapObject* object = HeapObject::cast(*p);
 
-    if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-            object, MarkingState::Internal(object))) {
+    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 =
+    DCHECK(ObjectMarking::IsGrey(object, MarkingState::Internal(object)));
     ObjectMarking::GreyToBlack(object, MarkingState::Internal(object));
-    DCHECK(success);
-    USE(success);
     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,
+  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) {

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());

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 {

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())) {
@@ -668,27 +669,13 @@ 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);       \
+    type::BodyDescriptor::IterateBody(object, size,                         \
+                                      static_cast<ConcreteVisitor*>(this)); \
     return static_cast<ResultType>(size);                                   \
   }
 TYPED_VISITOR_ID_LIST(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());
 }
 

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

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(

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.