Optimize Object.seal and Object.preventExtensions

src/v8natives.js

 // Copyright 2012 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.
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Boolean = global.Boolean;
 // var $Number = global.Number;
 // var $Function = global.Function;
@@ skipping 1224 matching lines @@
     %FunctionSetPrototype(obj, prototype);
     obj.length = 0;
   } else {
     %Fix(obj);
   }
   ObjectDefineProperties(obj, props);
 }
 
 
 // ES5 section 15.2.3.8.
-function ObjectSeal(obj) {
+function ObjectSealJS(obj) {
   if (!IS_SPEC_OBJECT(obj)) {
     throw MakeTypeError("called_on_non_object", ["Object.seal"]);
   }
-  if (%_IsJSProxy(obj)) {
-    ProxyFix(obj);
+  var isProxy = %_IsJSProxy(obj);
+  if (isProxy || %HasSloppyArgumentsElements(obj) || %IsObserved(obj)) {
+    if (isProxy) {
+      ProxyFix(obj);
+    }
+    var names = ObjectGetOwnPropertyNames(obj);
+    for (var i = 0; i < names.length; i++) {
+      var name = names[i];
+      var desc = GetOwnPropertyJS(obj, name);
+      if (desc.isConfigurable()) {
+        desc.setConfigurable(false);
+        DefineOwnProperty(obj, name, desc, true);
+      }
+    }
+    %PreventExtensions(obj);
+  } else {
+    // TODO(adamk): Is it worth going to this fast path if the
+    // object's properties are already in dictionary mode?
+    %ObjectSeal(obj);
   }
-  var names = ObjectGetOwnPropertyNames(obj);
-  for (var i = 0; i < names.length; i++) {
-    var name = names[i];
-    var desc = GetOwnPropertyJS(obj, name);
-    if (desc.isConfigurable()) {
-      desc.setConfigurable(false);
-      DefineOwnProperty(obj, name, desc, true);
-    }
-  }
-  %PreventExtensions(obj);
   return obj;
 }
 
 
 // ES5 section 15.2.3.9.
 function ObjectFreezeJS(obj) {
   if (!IS_SPEC_OBJECT(obj)) {
     throw MakeTypeError("called_on_non_object", ["Object.freeze"]);
   }
   var isProxy = %_IsJSProxy(obj);
@@ skipping 161 matching lines @@
     "getPrototypeOf", ObjectGetPrototypeOf,
     "setPrototypeOf", ObjectSetPrototypeOf,
     "getOwnPropertyDescriptor", ObjectGetOwnPropertyDescriptor,
     "getOwnPropertyNames", ObjectGetOwnPropertyNames,
     // getOwnPropertySymbols is added in symbol.js.
     "is", ObjectIs,
     "isExtensible", ObjectIsExtensible,
     "isFrozen", ObjectIsFrozen,
     "isSealed", ObjectIsSealed,
     "preventExtensions", ObjectPreventExtension,
-    "seal", ObjectSeal
+    "seal", ObjectSealJS
     // deliverChangeRecords, getNotifier, observe and unobserve are added
     // in object-observe.js.
   ));
 }
 
 SetUpObject();
 
 
 // ----------------------------------------------------------------------------
 // Boolean
@@ skipping 446 matching lines @@
   }
   if (!IS_SPEC_FUNCTION(method)) {
     throw MakeTypeError('not_iterable', [obj]);
   }
   var iterator = %_CallFunction(obj, method);
   if (!IS_SPEC_OBJECT(iterator)) {
     throw MakeTypeError('not_an_iterator', [iterator]);
   }
   return iterator;
 }