Unify mechanism to find trailing AllocationMementos

src/heap-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 472 matching lines @@
     OS::MemMove(dst, src, static_cast<size_t>(byte_size));
   }
 }
 
 
 void Heap::ScavengePointer(HeapObject** p) {
   ScavengeObject(p, *p);
 }
 
 
+AllocationMemento* Heap::FindAllocationMemento(HeapObject* object) {
+  // Check if there is potentially a memento behind the object. If
+  // the last word of the momento is on another page we return
+  // immediately.
+  Address object_address = object->address();
+  Address memento_address = object_address + object->Size();
+  Address last_memento_word_address = memento_address + kPointerSize;
+  if (!NewSpacePage::OnSamePage(object_address,
+                                last_memento_word_address)) {
+    return NULL;
+  }
+
+  HeapObject* candidate = HeapObject::FromAddress(memento_address);
+  if (candidate->map() != allocation_memento_map()) return NULL;
+
+  // Either the object is the last object in the new space, or there is another
+  // object of at least word size (the header map word) following it, so
+  // suffices to compare ptr and top here. Note that technically we do not have
+  // to compare with the current top pointer of the from space page during GC,
+  // since we always install filler objects above the top pointer of a from
+  // space page when performing a garbage collection. However, always performing
+  // the test makes it possible to have a single, unified version of
+  // FindAllocationMemento that is used both by the GC and the mutator.
+  Address top = NewSpaceTop();
+  ASSERT(memento_address == top ||
+         memento_address + HeapObject::kHeaderSize <= top ||
+         !NewSpacePage::OnSamePage(memento_address, top));
+  if (memento_address == top) return NULL;
+
+  AllocationMemento* memento = AllocationMemento::cast(candidate);
+  if (!memento->IsValid()) return NULL;
+  return memento;
+}
+
+
 void Heap::UpdateAllocationSiteFeedback(HeapObject* object,
                                         ScratchpadSlotMode mode) {
   Heap* heap = object->GetHeap();
   ASSERT(heap->InFromSpace(object));
 
   if (!FLAG_allocation_site_pretenuring ||
       !AllocationSite::CanTrack(object->map()->instance_type())) return;
 
-  // Check if there is potentially a memento behind the object. If
-  // the last word of the momento is on another page we return
-  // immediatelly. Note that we do not have to compare with the current
-  // top pointer of the from space page, since we always install filler
-  // objects above the top pointer of a from space page when performing
-  // a garbage collection.
-  Address object_address = object->address();
-  Address memento_address = object_address + object->Size();
-  Address last_memento_word_address = memento_address + kPointerSize;
-  if (!NewSpacePage::OnSamePage(object_address,
-                                last_memento_word_address)) {
-    return;
-  }
-
-  HeapObject* candidate = HeapObject::FromAddress(memento_address);
-  if (candidate->map() != heap->allocation_memento_map()) return;
-
-  AllocationMemento* memento = AllocationMemento::cast(candidate);
-  if (!memento->IsValid()) return;
+  AllocationMemento* memento = heap->FindAllocationMemento(object);
+  if (memento == NULL) return;
 
   if (memento->GetAllocationSite()->IncrementMementoFoundCount()) {
     heap->AddAllocationSiteToScratchpad(memento->GetAllocationSite(), mode);
   }
 }
 
 
 void Heap::ScavengeObject(HeapObject** p, HeapObject* object) {
   ASSERT(object->GetIsolate()->heap()->InFromSpace(object));
 
@@ skipping 287 matching lines @@
 
 
 double GCTracer::SizeOfHeapObjects() {
   return (static_cast<double>(heap_->SizeOfObjects())) / MB;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_INL_H_