Narrow cases where Sparse/Smart versions of Array methods are used

test/mjsunit/array-natives-elements.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 262 matching lines @@
   assertTrue(%HasFastSmiElements(a4));
   assertEquals([1,1,2,3], a4);
   a4 = [1,2,3];
   a4.unshift(1.1);
   // TODO(verwaest): We'll want to support double unshifting as well.
   // assertTrue(%HasFastDoubleElements(a4));
   assertTrue(%HasFastObjectElements(a4));
   assertEquals([1.1,1,2,3], a4);
   a4 = [1.1,2,3];
   a4.unshift(1);
-  // assertTrue(%HasFastDoubleElements(a4));
-  assertTrue(%HasFastObjectElements(a4));
+  assertTrue(%HasFastDoubleElements(a4));
   assertEquals([1,1.1,2,3], a4);
   a4 = [{},2,3];
   a4.unshift(1);
   assertTrue(%HasFastObjectElements(a4));
   assertEquals([1,{},2,3], a4);
   a4 = [{},2,3];
   a4.unshift(1.1);
   assertTrue(%HasFastObjectElements(a4));
   assertEquals([1.1,{},2,3], a4);
 }
 
 for (var i = 0; i < 3; i++) {
   array_natives_test();
 }
 %OptimizeFunctionOnNextCall(array_natives_test);
 array_natives_test();