Unify mechanism to find trailing AllocationMementos

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/234703003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20675 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

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);

src/heap.h

@@ -1452,6 +1452,10 @@ class Heap {
     RECORD_SCRATCHPAD_SLOT
   };
 
+  // If an object has an AllocationMemento trailing it, return it, otherwise
+  // return NULL;
+  inline AllocationMemento* FindAllocationMemento(HeapObject* object);
+
   // An object may have an AllocationSite associated with it through a trailing
   // AllocationMemento. Its feedback should be updated when objects are found
   // in the heap.

src/objects.cc

@@ -12778,30 +12778,9 @@ void JSObject::UpdateAllocationSite(Handle<JSObject> object,
   Handle<AllocationSite> site;
   {
     DisallowHeapAllocation no_allocation;
-    // Check if there is potentially a memento behind the object. If
-    // the last word of the momento is on another page we return
-    // immediatelly.
-    Address object_address = object->address();
-    Address memento_address = object_address + JSArray::kSize;
-    Address last_memento_word_address = memento_address + kPointerSize;
-    if (!NewSpacePage::OnSamePage(object_address,
-                                  last_memento_word_address)) {
-      return;
-    }
-
-    // Either 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.
-    Address top = heap->NewSpaceTop();
-    ASSERT(memento_address == top ||
-           memento_address + HeapObject::kHeaderSize <= top);
-    if (memento_address == top) 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;
 
     // Walk through to the Allocation Site
     site = handle(memento->GetAllocationSite());