Check for cached transition to ExternalArray elements kind.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "v8.h"
 
 #include "accessors.h"
 #include "allocation-site-scopes.h"
 #include "api.h"
 #include "arguments.h"
@@ skipping 3361 matching lines @@
 }
 
 
 static Map* FindClosestElementsTransition(Map* map, ElementsKind to_kind) {
   Map* current_map = map;
   int target_kind =
       IsFastElementsKind(to_kind) || IsExternalArrayElementsKind(to_kind)
       ? to_kind
       : TERMINAL_FAST_ELEMENTS_KIND;
 
-  // Support for legacy API.
+  // Support for legacy API: SetIndexedPropertiesTo{External,Pixel}Data
+  // allows to change elements from arbitrary kind to any

[Igor Sheludko, 2014/05/23 12:24:14]

nit: please reformat comment

+  // ExternalArray elements kind. Satisfy its requirements, checking whether
+  // we already have the cached transition.
   if (IsExternalArrayElementsKind(to_kind) &&
       !IsFixedTypedArrayElementsKind(map->elements_kind())) {
+    if (map->HasElementsTransition()) {
+        Map* next_map = map->elements_transition_map();
+        if (next_map->elements_kind() == to_kind) return next_map;
+    }
     return map;
   }
 
   ElementsKind kind = map->elements_kind();
   while (kind != target_kind) {
     kind = GetNextTransitionElementsKind(kind);
     if (!current_map->HasElementsTransition()) return current_map;
     current_map = current_map->elements_transition_map();
   }
 
@@ skipping 13860 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal