SimpleMove now calls [[Has]] before [[Get]] when moving elements

src/array.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.
 
 "use strict";
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 284 matching lines @@
 
 
 function SimpleMove(array, start_i, del_count, len, num_additional_args) {
   if (num_additional_args !== del_count) {
     // Move the existing elements after the elements to be deleted
     // to the right position in the resulting array.
     if (num_additional_args > del_count) {
       for (var i = len - del_count; i > start_i; i--) {
         var from_index = i + del_count - 1;
         var to_index = i + num_additional_args - 1;
-        // The spec could also be interpreted such that
-        // %HasOwnProperty would be the appropriate test.  We follow
-        // KJS in consulting the prototype.
-        var current = array[from_index];
-        if (!IS_UNDEFINED(current) || from_index in array) {
-          array[to_index] = current;
+        if (from_index in array) {
+          array[to_index] = array[from_index];
         } else {
           delete array[to_index];
         }
       }
     } else {
       for (var i = start_i; i < len - del_count; i++) {
         var from_index = i + del_count;
         var to_index = i + num_additional_args;
-        // The spec could also be interpreted such that
-        // %HasOwnProperty would be the appropriate test.  We follow
-        // KJS in consulting the prototype.
-        var current = array[from_index];
-        if (!IS_UNDEFINED(current) || from_index in array) {
-          array[to_index] = current;
+        if (from_index in array) {
+          array[to_index] = array[from_index];
         } else {
           delete array[to_index];
         }
       }
       for (var i = len; i > len - del_count + num_additional_args; i--) {
         delete array[i - 1];
       }
     }
   }
 }
@@ skipping 1229 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();