[heap] Simplify MarkingDeque implementation.

src/heap/mark-compact.h

 // 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
 #include "src/heap/spaces.h"
 
@@ skipping 187 matching lines @@
   inline bool IsEmpty() { return top_ == bottom_; }
 
   bool overflowed() const { return overflowed_; }
 
   bool in_use() const { return in_use_; }
 
   void ClearOverflowed() { overflowed_ = false; }
 
   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;
     }
   }
 
   INLINE(void PushGrey(HeapObject* object)) {
     DCHECK(object->IsHeapObject());
     if (IsFull()) {
       SetOverflowed();
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
     }
   }
 
   INLINE(HeapObject* Pop()) {
     DCHECK(!IsEmpty());
     top_ = ((top_ - 1) & mask_);
     HeapObject* object = array_[top_];
     DCHECK(object->IsHeapObject());
     return object;
   }
 
   INLINE(void UnshiftGrey(HeapObject* object)) {

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

Likewise for unification of {UnshiftGrey} and {UnshiftBlack}.

     DCHECK(object->IsHeapObject());
     if (IsFull()) {
       SetOverflowed();
     } else {
       bottom_ = ((bottom_ - 1) & mask_);
       array_[bottom_] = object;
     }
   }
 
-  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;
     }
   }
 
   HeapObject** array() { return array_; }
   int bottom() { return bottom_; }
   int top() { return top_; }
   int mask() { return mask_; }
   void set_top(int top) { top_ = top; }
 
  private:
@@ skipping 500 matching lines @@
   // from being flushed.
   void PrepareThreadForCodeFlushing(Isolate* isolate, ThreadLocalTop* top);
 
   void PrepareForCodeFlushing();
 
   // Marking operations for objects reachable from roots.
   void MarkLiveObjects();
 
   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));
 
   // Marks the object black assuming that it is not yet marked.
   // This is for non-incremental marking only.
   INLINE(void SetMark(HeapObject* obj, MarkBit mark_bit));
 
   // Mark the heap roots and all objects reachable from them.
   void MarkRoots(RootMarkingVisitor* visitor);
@@ skipping 28 matching lines @@
   // stack.  This function empties the marking stack, but may leave
   // overflowed objects in the heap, in which case the marking stack's
   // overflow flag will be set.
   void EmptyMarkingDeque();
 
   // Refill the marking stack with overflowed objects from the heap.  This
   // function either leaves the marking stack full or clears the overflow
   // 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);
 
   // Map transitions from a live map to a dead map must be killed.
   // We replace them with a null descriptor, with the same key.
   void ClearNonLiveReferences();
   void ClearNonLivePrototypeTransitions(Map* map);
   void ClearNonLiveMapTransitions(Map* map, MarkBit map_mark);
   void ClearMapTransitions(Map* map, Map* dead_transition);
@@ skipping 142 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_MARK_COMPACT_H_