Fix sequence of element access in array builtins.

src/array.js

 // Copyright 2010 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 1006 matching lines @@
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   var result = new $Array();
   var accumulator = new InternalArray();
   var accumulator_length = 0;
   for (var i = 0; i < length; i++) {
-    var current = array[i];
-    if (!IS_UNDEFINED(current) || i in array) {
-      if (%_CallFunction(receiver, current, i, array, f)) {
-        accumulator[accumulator_length++] = current;
+    if (i in array) {
+      var element = array[i];
+      if (%_CallFunction(receiver, element, i, array, f)) {
+        accumulator[accumulator_length++] = element;
       }
     }
   }
   %MoveArrayContents(accumulator, result);
   return result;
 }
 
 
 function ArrayForEach(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.forEach"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   for (var i = 0; i < length; i++) {
-    var current = array[i];
-    if (!IS_UNDEFINED(current) || i in array) {
-      %_CallFunction(receiver, current, i, array, f);
+    if (i in array) {
+      var element = array[i];
+      %_CallFunction(receiver, element, i, array, f);
     }
   }
 }
 
 
 // Executes the function once for each element present in the
 // array until it finds one where callback returns true.
 function ArraySome(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.some"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   for (var i = 0; i < length; i++) {
-    var current = array[i];
-    if (!IS_UNDEFINED(current) || i in array) {
-      if (%_CallFunction(receiver, current, i, array, f)) return true;
+    if (i in array) {
+      var element = array[i];
+      if (%_CallFunction(receiver, element, i, array, f)) return true;
     }
   }
   return false;
 }
 
 
 function ArrayEvery(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.every"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   for (var i = 0; i < length; i++) {
-    var current = array[i];
-    if (!IS_UNDEFINED(current) || i in array) {
-      if (!%_CallFunction(receiver, current, i, array, f)) return false;
+    if (i in array) {
+      var element = array[i];
+      if (!%_CallFunction(receiver, element, i, array, f)) return false;
     }
   }
   return true;
 }
 
 function ArrayMap(f, receiver) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.map"]);
   }
 
   // Pull out the length so that modifications to the length in the
   // loop will not affect the looping and side effects are visible.
   var array = ToObject(this);
   var length = TO_UINT32(array.length);
 
   if (!IS_SPEC_FUNCTION(f)) {
     throw MakeTypeError('called_non_callable', [ f ]);
   }
   if (IS_NULL_OR_UNDEFINED(receiver)) {
     receiver = %GetDefaultReceiver(f) || receiver;
   } else if (!IS_SPEC_OBJECT(receiver)) {
     receiver = ToObject(receiver);
   }
 
   var result = new $Array();
   var accumulator = new InternalArray(length);
   for (var i = 0; i < length; i++) {
-    var current = array[i];
-    if (!IS_UNDEFINED(current) || i in array) {
-      accumulator[i] = %_CallFunction(receiver, current, i, array, f);
+    if (i in array) {
+      var element = array[i];
+      accumulator[i] = %_CallFunction(receiver, element, i, array, f);
     }
   }
   %MoveArrayContents(accumulator, result);
   return result;
 }
 
 
 function ArrayIndexOf(element, index) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
@@ skipping 136 matching lines @@
       if (!IS_UNDEFINED(current) || i in array) {
         i++;
         break find_initial;
       }
     }
     throw MakeTypeError('reduce_no_initial', []);
   }
 
   var receiver = %GetDefaultReceiver(callback);
   for (; i < length; i++) {
-    var element = array[i];
-    if (!IS_UNDEFINED(element) || i in array) {
+    if (i in array) {
+      var element = array[i];
       current = %_CallFunction(receiver, current, element, i, array, callback);
     }
   }
   return current;
 }
 
 function ArrayReduceRight(callback, current) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["Array.prototype.reduceRight"]);
@@ skipping 15 matching lines @@
       if (!IS_UNDEFINED(current) || i in array) {
         i--;
         break find_initial;
       }
     }
     throw MakeTypeError('reduce_no_initial', []);
   }
 
   var receiver = %GetDefaultReceiver(callback);
   for (; i >= 0; i--) {
-    var element = array[i];
-    if (!IS_UNDEFINED(element) || i in array) {
+    if (i in array) {
+      var element = array[i];
       current = %_CallFunction(receiver, current, element, i, array, callback);
     }
   }
   return current;
 }
 
 // ES5, 15.4.3.2
 function ArrayIsArray(obj) {
   return IS_ARRAY(obj);
 }
@@ skipping 58 matching lines @@
   // exposed to user code.
   // Adding only the functions that are actually used.
   SetUpLockedPrototype(InternalArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();