[heap] Remove Marking::MarkBlack and some minor cleanups.

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 <deque>
 
 #include "src/base/bits.h"
@@ skipping 48 matching lines @@
   }
 
   V8_INLINE static bool IsGrey(HeapObject* obj) {
     return Marking::IsGrey(MarkBitFrom(obj));
   }
 
   V8_INLINE static bool IsBlackOrGrey(HeapObject* obj) {
     return Marking::IsBlackOrGrey(MarkBitFrom(obj));
   }
 
   V8_INLINE static void ClearMarkBit(HeapObject* obj) {

[ulan, 2017/02/28 15:43:47]

If object is black at the callsites, can we just used BlackToWhite(obj) directly
and remove this function?

It is not clear from the name that the object must be black.

[Hannes Payer (out of office), 2017/03/01 13:49:18]

No we cannot, since the object can also be grey (when marking aborts).

-    Marking::MarkWhite(MarkBitFrom(obj));
+    DCHECK(IsBlack(obj));
+    Marking::BlackToWhite(MarkBitFrom(obj));
   }
 
   V8_INLINE static void BlackToWhite(HeapObject* obj) {
     DCHECK(IsBlack(obj));
     MarkBit markbit = MarkBitFrom(obj);
     Marking::BlackToWhite(markbit);
     MemoryChunk::IncrementLiveBytes(obj, -obj->Size());
   }
 
   V8_INLINE static void GreyToWhite(HeapObject* obj) {
@@ skipping 762 matching lines @@
 
  private:
   MarkCompactCollector* collector_;
 };
 
 V8_EXPORT_PRIVATE const char* AllocationSpaceName(AllocationSpace space);
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_H_