ExtendStorageStub added, it is aimed for extending objects backing store when it runs out of space.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index e5a93a7bd5b1f4ec513e0427d54f033b0fdf5dce..2c38d8059ee21a3d410ade1d0d3d99867646efc4 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -2789,12 +2789,6 @@ void HGraphBuilder::BuildFillElementsWithValue(HValue* elements,
     }
   }
 
-  // Since we're about to store a hole value, the store instruction below must
-  // assume an elements kind that supports heap object values.
-  if (IsFastSmiOrObjectElementsKind(elements_kind)) {
-    elements_kind = FAST_HOLEY_ELEMENTS;
-  }
-
   if (initial_capacity >= 0) {
     for (int i = 0; i < initial_capacity; i++) {
       HInstruction* key = Add<HConstant>(i);
@@ -2832,10 +2826,41 @@ void HGraphBuilder::BuildFillElementsWithHole(HValue* elements,
       ? Add<HConstant>(factory->the_hole_value())
       : Add<HConstant>(nan_double);
 
+  // Since we're about to store a hole value, the store instruction below must
+  // assume an elements kind that supports heap object values.
+  if (IsFastSmiOrObjectElementsKind(elements_kind)) {
+    elements_kind = FAST_HOLEY_ELEMENTS;
+  }
+
   BuildFillElementsWithValue(elements, elements_kind, from, to, hole);
 }
 
 
+void HGraphBuilder::BuildCopyProperties(HValue* from_properties,
+                                        HValue* to_properties, HValue* length,
+                                        HValue* capacity) {
+  ElementsKind kind = FAST_ELEMENTS;
+
+  BuildFillElementsWithValue(to_properties, kind, length, capacity,
+                             graph()->GetConstantUndefined());
+
+  LoopBuilder builder(this, context(), LoopBuilder::kPostDecrement);
+
+  HValue* key = builder.BeginBody(length, graph()->GetConstant0(), Token::GT);
+
+  key = AddUncasted<HSub>(key, graph()->GetConstant1());
+  key->ClearFlag(HValue::kCanOverflow);
+
+  HValue* element =
+      Add<HLoadKeyed>(from_properties, key, static_cast<HValue*>(NULL), kind);
+
+  HStoreKeyed* store = Add<HStoreKeyed>(to_properties, key, element, kind);
+  store->SetFlag(HValue::kAllowUndefinedAsNaN);

[Toon Verwaest, 2014/09/22 08:55:29]

I don't think this flag has any meaning for FAST_ELEMENTS.

[Igor Sheludko, 2014/09/23 07:38:47]

Done.

+
+  builder.EndBody();
+}
+
+
 void HGraphBuilder::BuildCopyElements(HValue* from_elements,
                                       ElementsKind from_elements_kind,
                                       HValue* to_elements,