Always transition empty FAST_DOUBLE_ARRAYs on push

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 6d1c6a978599a96720b6e259469681ddf3c70f7e..5d4b2b410190ba375e7db8ae394d8f3b5b55394c 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -413,13 +413,13 @@ static inline MaybeObject* EnsureJSArrayWithWritableFastElements(
   Map* map = elms->map();
   if (map == heap->fixed_array_map()) {
     if (array->HasFastElements()) return elms;
+    if (array->HasFastDoubleElements()) {
+      ASSERT(elms == heap->empty_fixed_array());
+      MaybeObject* maybe_transition =
+          array->TransitionElementsKind(FAST_ELEMENTS);
+      if (maybe_transition->IsFailure()) return maybe_transition;

[Michael Starzinger, 2012/05/15 15:38:13]

At this point we know that the array has FAST_ELEMENTS, so we could early return
with array->elements() as result.

+    }
     if (args == NULL) {

[Michael Starzinger, 2012/05/15 15:38:13]

Can we merge that into line 415 like the following? That would make behavior
consistent between FAST_DOUBLE_ELEMENTS and other FAST_FOOBAR_ELEMENTS. And it
would also be consistent with the copy-on-write case below.

if (args == NULL || array->HasFastElements()) return elms;

-      if (array->HasFastDoubleElements()) {
-        ASSERT(elms == heap->empty_fixed_array());
-        MaybeObject* maybe_transition =
-            array->TransitionElementsKind(FAST_ELEMENTS);
-        if (maybe_transition->IsFailure()) return maybe_transition;
-      }
       return elms;
     }
   } else if (map == heap->fixed_cow_array_map()) {