Introduce HTransitionElementsKind instruction.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index e0f507e1774bbd7c7d500994f40a07e74ae8f1e6..6f8fa2e548ba69a449c1d7f435a68302c7e6e0ca 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -4568,6 +4568,34 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_SetProperty) {
 }
 
 
+MaybeObject* TransitionElements(Handle<Object> object,
+                                ElementsKind to_kind,
+                                Isolate* isolate) {
+  HandleScope scope(isolate);
+  if (!object->IsJSObject()) return isolate->ThrowIllegalOperation();
+  Handle<Object> result =
+      TransitionElementsKind(Handle<JSObject>::cast(object), to_kind);
+  if (result.is_null()) return isolate->ThrowIllegalOperation();
+  return *result;
+}
+
+
+RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsSmiToDouble) {
+  NoHandleAllocation ha;
+  RUNTIME_ASSERT(args.length() == 1);
+  Handle<Object> object = args.at<Object>(0);
+  return TransitionElements(object, FAST_DOUBLE_ELEMENTS, isolate);
+}
+
+
+RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsDoubleToObject) {
+  NoHandleAllocation ha;
+  RUNTIME_ASSERT(args.length() == 1);
+  Handle<Object> object = args.at<Object>(0);
+  return TransitionElements(object, FAST_ELEMENTS, isolate);
+}
+
+
 // Set the native flag on the function.
 // This is used to decide if we should transform null and undefined
 // into the global object when doing call and apply.