A change in the way we place TransitionElementKinds in the tree.

src/elements-kind.cc

Index: src/elements-kind.cc
diff --git a/src/elements-kind.cc b/src/elements-kind.cc
index 7b1651a953fc8120f4c1a29fcb9bef77c330e62c..5866f7ec6f33174c53d417a99e2ddc947005c5c4 100644
--- a/src/elements-kind.cc
+++ b/src/elements-kind.cc
@@ -136,4 +136,23 @@ bool IsMoreGeneralElementsKindTransition(ElementsKind from_kind,
 }
 
 
+ElementsKind GetUnifiedFastElementsKind(ElementsKind kind1,
+                                        ElementsKind kind2) {
+  ASSERT(IsFastElementsKind(kind1));
+  ASSERT(IsFastElementsKind(kind2));
+  if (kind1 == kind2) {
+    return kind1;
+  }
+
+  int i1 = GetSequenceIndexFromFastElementsKind(kind1);
+  int i2 = GetSequenceIndexFromFastElementsKind(kind2);
+  ASSERT(i1 != i2);
+  ElementsKind result = GetFastElementsKindFromSequenceIndex(
+      i1 > i2 ? i1 : i2);
+  return (IsFastHoleyElementsKind(kind1) != IsFastHoleyElementsKind(kind2))
+      ? GetHoleyElementsKind(result)
+      : result;
+}
+
+
 } }  // namespace v8::internal