Remove guard page mechanism from promotion queue.

src/heap/heap.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/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 1347 matching lines @@
 void PromotionQueue::Initialize() {
   // Assumes that a NewSpacePage exactly fits a number of promotion queue
   // entries (where each is a pair of intptr_t). This allows us to simplify
   // the test fpr when to switch pages.
   DCHECK((Page::kPageSize - MemoryChunk::kBodyOffset) % (2 * kPointerSize) ==
          0);
   limit_ = reinterpret_cast<intptr_t*>(heap_->new_space()->ToSpaceStart());
   front_ = rear_ =
       reinterpret_cast<intptr_t*>(heap_->new_space()->ToSpaceEnd());
   emergency_stack_ = NULL;
-  guard_ = false;
 }
 
 
 void PromotionQueue::RelocateQueueHead() {
   DCHECK(emergency_stack_ == NULL);
 
   Page* p = Page::FromAllocationTop(reinterpret_cast<Address>(rear_));
   intptr_t* head_start = rear_;
   intptr_t* head_end = Min(front_, reinterpret_cast<intptr_t*>(p->area_end()));
 
@@ skipping 577 matching lines @@
       DCHECK(alignment == kDoubleAlignment);
       allocation_size += kPointerSize;
     }
 
     DCHECK(heap->AllowedToBeMigrated(object, NEW_SPACE));
     AllocationResult allocation =
         heap->new_space()->AllocateRaw(allocation_size);
 
     HeapObject* target = NULL;  // Initialization to please compiler.
     if (allocation.To(&target)) {
+      // Order is important here: Set the promotion limit before storing a
+      // filler for double alignment or migrating the object. Otherwise we
+      // may end up overwriting promotion queue entries when we migrate the
+      // object.
+      heap->promotion_queue()->SetNewLimit(heap->new_space()->top());
+
       if (alignment != kObjectAlignment) {
         target = EnsureDoubleAligned(heap, target, allocation_size);
       }
 
-      // Order is important here: Set the promotion limit before migrating
-      // the object. Otherwise we may end up overwriting promotion queue
-      // entries when we migrate the object.
-      heap->promotion_queue()->SetNewLimit(heap->new_space()->top());
-
       // Order is important: slot might be inside of the target if target
       // was allocated over a dead object and slot comes from the store
       // buffer.
       *slot = target;
       MigrateObject(heap, object, target, object_size);
 
       heap->IncrementSemiSpaceCopiedObjectSize(object_size);
       return true;
     }
     return false;
@@ skipping 4141 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal