Don't use SmartSlice just because the receiver is an array.

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 613 matching lines @@
     end_i += len;
     if (end_i < 0) end_i = 0;
   } else {
     if (end_i > len) end_i = len;
   }
 
   var result = [];
 
   if (end_i < start_i) return result;
 
-  if (IS_ARRAY(this)) {
+  if (IS_ARRAY(this) &&
+      (end_i > 1000) &&
+      (%EstimateNumberOfElements(this) < end_i)) {
     SmartSlice(this, start_i, end_i - start_i, len, result);
   } else {
     SimpleSlice(this, start_i, end_i - start_i, len, result);
   }
 
   result.length = end_i - start_i;
 
   return result;
 }
 
@@ skipping 712 matching lines @@
   InternalArray.prototype.join = getFunction("join", ArrayJoin);
   InternalArray.prototype.pop = getFunction("pop", ArrayPop);
   InternalArray.prototype.push = getFunction("push", ArrayPush);
   InternalArray.prototype.toString = function() {
     return "Internal Array, length " + this.length;
   };
 }
 
 
 SetupArray();