[heap] Don't clear black areas when deserializing, they will be marked black later anyway.

BUG=chromium:630386

Review-Url: https://codereview.chromium.org/2264493002
Cr-Commit-Position: refs/heads/master@{#38737}

src/heap/heap.cc

@@ -1162,7 +1162,7 @@ bool Heap::ReserveSpace(Reservation* reservations, List<Address>* maps) {
             // deserializing.
             Address free_space_address = free_space->address();
             CreateFillerObjectAt(free_space_address, Map::kSize,
-                                 ClearRecordedSlots::kNo);
+                                 ClearRecordedSlots::kNo, ClearBlackArea::kNo);
             maps->Add(free_space_address);
           } else {
             perform_gc = true;
@@ -1192,7 +1192,7 @@ bool Heap::ReserveSpace(Reservation* reservations, List<Address>* maps) {
             // deserializing.
             Address free_space_address = free_space->address();
             CreateFillerObjectAt(free_space_address, size,
-                                 ClearRecordedSlots::kNo);
+                                 ClearRecordedSlots::kNo, ClearBlackArea::kNo);
             DCHECK(space < SerializerDeserializer::kNumberOfPreallocatedSpaces);
             chunk.start = free_space_address;
             chunk.end = free_space_address + size;
@@ -3081,8 +3081,8 @@ AllocationResult Heap::AllocateBytecodeArray(int length,
   return result;
 }
 
-void Heap::CreateFillerObjectAt(Address addr, int size,
-                                ClearRecordedSlots mode) {
+void Heap::CreateFillerObjectAt(Address addr, int size, ClearRecordedSlots mode,
+                                ClearBlackArea black_area_mode) {
   if (size == 0) return;
   HeapObject* filler = HeapObject::FromAddress(addr);
   if (size == kPointerSize) {
@@ -3103,7 +3103,8 @@ void Heap::CreateFillerObjectAt(Address addr, int size,
 
   // If the location where the filler is created is within a black area we have
   // to clear the mark bits of the filler space.
-  if (incremental_marking()->black_allocation() &&
+  if (black_area_mode == ClearBlackArea::kYes &&
+      incremental_marking()->black_allocation() &&
       Marking::IsBlackOrGrey(ObjectMarking::MarkBitFrom(addr))) {
     Page* page = Page::FromAddress(addr);
     page->markbits()->ClearRange(page->AddressToMarkbitIndex(addr),

src/heap/heap.h

@@ -450,6 +450,8 @@ enum ArrayStorageAllocationMode {
 
 enum class ClearRecordedSlots { kYes, kNo };
 
+enum class ClearBlackArea { kYes, kNo };
+
 class Heap {
  public:
   // Declare all the root indices.  This defines the root list order.
@@ -673,8 +675,12 @@ class Heap {
   // Initialize a filler object to keep the ability to iterate over the heap
   // when introducing gaps within pages. If slots could have been recorded in
   // the freed area, then pass ClearRecordedSlots::kYes as the mode. Otherwise,
-  // pass ClearRecordedSlots::kNo.
-  void CreateFillerObjectAt(Address addr, int size, ClearRecordedSlots mode);
+  // pass ClearRecordedSlots::kNo. If the filler was created in a black area
+  // we may want to clear the corresponding mark bits with ClearBlackArea::kYes,
+  // which is the default. ClearBlackArea::kNo does not clear the mark bits.
+  void CreateFillerObjectAt(
+      Address addr, int size, ClearRecordedSlots mode,
+      ClearBlackArea black_area_mode = ClearBlackArea::kYes);
 
   bool CanMoveObjectStart(HeapObject* object);