Remove %_SwapElements. This inlined runtime contained an optimization that was dangerous in the pr…

src/array.js

 // Copyright 2012 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 809 matching lines @@
     var high_start = to - 1;  // Lower bound of elements greater than pivot.
     a[middle_index] = a[low_end];
     a[low_end] = pivot;
 
     // From low_end to i are elements equal to pivot.
     // From i to high_start are elements that haven't been compared yet.
     partition: for (var i = low_end + 1; i < high_start; i++) {
       var element = a[i];
       var order = %_CallFunction(receiver, element, pivot, comparefn);
       if (order < 0) {
-        %_SwapElements(a, i, low_end);
+        a[i] = a[low_end];
+        a[low_end] = element;
         low_end++;
       } else if (order > 0) {
         do {
           high_start--;
           if (high_start == i) break partition;
           var top_elem = a[high_start];
           order = %_CallFunction(receiver, top_elem, pivot, comparefn);
         } while (order > 0);
-        %_SwapElements(a, i, high_start);
+        a[i] = a[high_start];
+        a[high_start] = element;
         if (order < 0) {
-          %_SwapElements(a, i, low_end);
+          element = a[i];
+          a[i] = a[low_end];
+          a[low_end] = element;
           low_end++;
         }
       }
     }
     QuickSort(a, from, low_end);
     QuickSort(a, high_start, to);
   };
 
   // Copy elements in the range 0..length from obj's prototype chain
   // to obj itself, if obj has holes. Return one more than the maximal index
@@ skipping 668 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();