[heap] Simplify MarkingDeque implementation.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 6168436ee06d684986d9ad208aece45e8ebf4547..51a117d43d69ac22a9fb8d0a6c37bc77dc92ea76 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -205,18 +205,17 @@ class MarkingDeque {
 
   void SetOverflowed() { overflowed_ = true; }
 
-  // Push the (marked) object on the marking stack if there is room,
-  // otherwise mark the object as overflowed and wait for a rescan of the
-  // heap.
-  INLINE(void PushBlack(HeapObject* object)) {
+  // Push the (marked) object on the marking stack if there is room, otherwise
+  // mark the deque as overflowed and wait for a rescan of the heap.
+  INLINE(bool PushBlack(HeapObject* object)) {

[Michael Starzinger, 2015/08/14 12:08:23]

Note that {PushBlack} and {PushGrey} can now be unified into one single {Push}
method. Let me know if you want me to do that in this CL or in a separate CL.

[Hannes Payer (out of office), 2015/08/17 09:39:10]

I like it, you can do it in a separate cl.

     DCHECK(object->IsHeapObject());
     if (IsFull()) {
-      Marking::BlackToGrey(object);
-      MemoryChunk::IncrementLiveBytesFromGC(object, -object->Size());
       SetOverflowed();
+      return false;
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
+      return true;
     }
   }
 
@@ -248,16 +247,16 @@ class MarkingDeque {
     }
   }
 
-  INLINE(void UnshiftBlack(HeapObject* object)) {
+  INLINE(bool UnshiftBlack(HeapObject* object)) {
     DCHECK(object->IsHeapObject());
     DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
     if (IsFull()) {
-      Marking::BlackToGrey(object);
-      MemoryChunk::IncrementLiveBytesFromGC(object, -object->Size());
       SetOverflowed();
+      return false;
     } else {
       bottom_ = ((bottom_ - 1) & mask_);
       array_[bottom_] = object;
+      return true;
     }
   }
 
@@ -778,6 +777,9 @@ class MarkCompactCollector {
 
   void AfterMarking();
 
+  // Pushes a black object onto the marking stack and accounts for live bytes.
+  INLINE(void PushBlack(HeapObject* obj));
+
   // Marks the object black and pushes it on the marking stack.
   // This is for non-incremental marking only.
   INLINE(void MarkObject(HeapObject* obj, MarkBit mark_bit));
@@ -826,6 +828,14 @@ class MarkCompactCollector {
   // flag on the marking stack.
   void RefillMarkingDeque();
 
+  // Helper methods for refilling the marking stack by discovering grey objects
+  // on various pages of the heap. Used by {RefillMarkingDeque} only.
+  template <class T>
+  void DiscoverGreyObjectsWithIterator(T* it);
+  void DiscoverGreyObjectsOnPage(MemoryChunk* p);
+  void DiscoverGreyObjectsInSpace(PagedSpace* space);
+  void DiscoverGreyObjectsInNewSpace();
+
   // Callback function for telling whether the object *p is an unmarked
   // heap object.
   static bool IsUnmarkedHeapObject(Object** p);