Don't UnshiftGrey any black objects

src/heap/incremental-marking.cc

 // 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.
 
 #include "src/v8.h"
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 169 matching lines @@
       do {
         VisitPointersWithAnchor(heap, HeapObject::RawField(object, 0),
                                 HeapObject::RawField(object, start_offset),
                                 HeapObject::RawField(object, end_offset));
         start_offset = end_offset;
         end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);
         scan_until_end =
             heap->mark_compact_collector()->marking_deque()->IsFull();
       } while (scan_until_end && start_offset < object_size);
       chunk->set_progress_bar(start_offset);
       if (start_offset < object_size) {

[Hannes Payer (out of office), 2015/05/15 15:26:06]

As discussed offline, let's figure out the reason first why the invariant *here
should be just grey object* does not hold.

-        heap->mark_compact_collector()->marking_deque()->UnshiftGrey(object);
+        if (Marking::IsGrey(Marking::MarkBitFrom(object))) {
+          heap->mark_compact_collector()->marking_deque()->UnshiftGrey(object);
+        } else {
+          DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
+          heap->mark_compact_collector()->marking_deque()->UnshiftBlack(object);
+        }
         heap->incremental_marking()->NotifyIncompleteScanOfObject(
             object_size - (start_offset - already_scanned_offset));
       }
     } else {
       FixedArrayVisitor::Visit(map, object);
     }
   }
 
   static void VisitNativeContextIncremental(Map* map, HeapObject* object) {
     Context* context = Context::cast(object);
@@ skipping 826 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }
 }  // namespace v8::internal