Unify mechanism to find trailing AllocationMementos

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index ea7dcda3b0acd8aee62f2507a5ab5852bd7196d1..ae10b3a121a30d4f064eea7091e4b2f384309290 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -490,33 +490,51 @@ void Heap::ScavengePointer(HeapObject** p) {
 }
 
 
-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;
-
+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
-  // 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.
+  // 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;
+    return NULL;
   }
 
   HeapObject* candidate = HeapObject::FromAddress(memento_address);
-  if (candidate->map() != heap->allocation_memento_map()) return;
+  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;
+  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;
+
+  AllocationMemento* memento = heap->FindAllocationMemento(object);
+  if (memento == NULL) return;
 
   if (memento->GetAllocationSite()->IncrementMementoFoundCount()) {
     heap->AddAllocationSiteToScratchpad(memento->GetAllocationSite(), mode);