Faster moving FixedArray elements around.

test/mjsunit/undeletable-functions.js

 // Copyright 2009 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 21 matching lines @@
 // version back by deleting the new definition.
 
 var array;
 
 array = [
   "toString", "toLocaleString", "join", "pop", "push", "concat", "reverse",
   "shift", "unshift", "slice", "splice", "sort", "filter", "forEach", "some",
   "every", "map", "indexOf", "lastIndexOf", "reduce", "reduceRight"];
 CheckJSCSemantics(Array.prototype, array, "Array prototype");
 
+var old_Array_prototype = Array.prototype;
+var new_Array_prototype = {};
+for (var i = 0; i < 7; i++) {
+  Array.prototype = new_Array_prototype;
+  assertEquals(old_Array_prototype, Array.prototype);
+}
+
 array = [
   "toString", "toDateString", "toTimeString", "toLocaleString",
   "toLocaleDateString", "toLocaleTimeString", "valueOf", "getTime",
   "getFullYear", "getUTCFullYear", "getMonth", "getUTCMonth", "getDate",
   "getUTCDate", "getDay", "getUTCDay", "getHours", "getUTCHours", "getMinutes",
   "getUTCMinutes", "getSeconds", "getUTCSeconds", "getMilliseconds",
   "getUTCMilliseconds", "getTimezoneOffset", "setTime", "setMilliseconds",
   "setUTCMilliseconds", "setSeconds", "setUTCSeconds", "setMinutes",
   "setUTCMinutes", "setHours", "setUTCHours", "setDate", "setUTCDate",
   "setMonth", "setUTCMonth", "setFullYear", "setUTCFullYear", "toGMTString",
@@ skipping 20 matching lines @@
 
 array = ["exec", "test", "toString", "compile"];
 CheckEcmaSemantics(RegExp.prototype, array, "RegExp prototype");
 
 array = [
   "toString", "toLocaleString", "valueOf", "hasOwnProperty",
   "isPrototypeOf", "propertyIsEnumerable", "__defineGetter__",
   "__lookupGetter__", "__defineSetter__", "__lookupSetter__"];
 CheckEcmaSemantics(Object.prototype, array, "Object prototype");
 
+var old_Object_prototype = Object.prototype;
+var new_Object_prototype = {};
+for (var i = 0; i < 7; i++) {
+  Object.prototype = new_Object_prototype;
+  assertEquals(old_Object_prototype, Object.prototype);
+}
+
 array = [
   "toString", "valueOf", "toJSON"];
 CheckEcmaSemantics(Boolean.prototype, array, "Boolean prototype");
 
 array = [
   "toString", "toLocaleString", "valueOf", "toFixed", "toExponential",
   "toPrecision", "toJSON"];
 CheckEcmaSemantics(Number.prototype, array, "Number prototype");
 
 CheckEcmaSemantics(Function.prototype, ["toString"], "Function prototype");
@@ skipping 80 matching lines @@
   if (!type[prop]) return;
   assertTrue(type.hasOwnProperty(prop), "inherited: " + prop);
   var deleted = delete type[prop];
   assertFalse(deleted, "delete operator returned true: " + prop);
   assertTrue(type.hasOwnProperty(prop), "not there after delete: " + prop);
   type[prop] = "foo";
   assertEquals("foo", type[prop], "overwritable: " + prop);
 }
 
 print("OK");