Optimize clearing of map transitions.

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/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 631 matching lines @@
       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
   heap_->isolate()->global_handles()->RemoveObjectGroups();
 }
 
 
 void IncrementalMarking::ProcessWeakCells() {
   DCHECK(!finalize_marking_completed_);
   DCHECK(IsMarking());
 
+  Object* the_hole_value = heap()->the_hole_value();
   Object* weak_cell_obj = heap()->encountered_weak_cells();
   Object* weak_cell_head = Smi::FromInt(0);
   WeakCell* prev_weak_cell_obj = NULL;
   while (weak_cell_obj != Smi::FromInt(0)) {
     WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
     // We do not insert cleared weak cells into the list, so the value
     // cannot be a Smi here.
     HeapObject* value = HeapObject::cast(weak_cell->value());
     // Remove weak cells with live objects from the list, they do not need
     // clearing.
     if (MarkCompactCollector::IsMarked(value)) {
       // Record slot, if value is pointing to an evacuation candidate.
       Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
       heap_->mark_compact_collector()->RecordSlot(weak_cell, slot, *slot);
       // Remove entry somewhere after top.
       if (prev_weak_cell_obj != NULL) {
         prev_weak_cell_obj->set_next(weak_cell->next());
       }
       weak_cell_obj = weak_cell->next();
-      weak_cell->clear_next(heap());
+      weak_cell->clear_next(the_hole_value);
     } else {
       if (weak_cell_head == Smi::FromInt(0)) {
         weak_cell_head = weak_cell;
       }
       prev_weak_cell_obj = weak_cell;
       weak_cell_obj = weak_cell->next();
     }
   }
   // Top may have changed.
   heap()->set_encountered_weak_cells(weak_cell_head);
@@ skipping 521 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }  // namespace internal
 }  // namespace v8