Always transition empty FAST_DOUBLE_ARRAYs on push

src/builtins.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 395 matching lines @@
 
 MUST_USE_RESULT
 static inline MaybeObject* EnsureJSArrayWithWritableFastElements(
     Heap* heap, Object* receiver, Arguments* args, int first_added_arg) {
   if (!receiver->IsJSArray()) return NULL;
   JSArray* array = JSArray::cast(receiver);
   HeapObject* elms = array->elements();
   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()) {
     MaybeObject* maybe_writable_result = array->EnsureWritableFastElements();
     if (args == NULL || array->HasFastElements() ||
         maybe_writable_result->IsFailure()) {
       return maybe_writable_result;
     }
   } else {
     return NULL;
@@ skipping 1247 matching lines @@
   return Handle<Code>(code_address);                        \
 }
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 } }  // namespace v8::internal