Aviod double checking IS_STRING when joining arrays.

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
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 //     * Redistributions in binary form must reproduce the above
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@@ skipping 49 matching lines @@
           keys.push(key);
         }
       }
     }
   }
   keys.sort(function(a, b) { return a - b; });
   return keys;
 }
 
 
 // Optimized for sparse arrays if separator is ''.

[Lasse Reichstein, 2011/01/07 13:13:43]

Make a comment saying that convert is only called on non-strings.

[sandholm, 2011/01/07 13:20:01]

Done.

 function SparseJoin(array, len, convert) {
   var keys = GetSortedArrayKeys(array, %GetArrayKeys(array, len));
   var last_key = -1;
   var keys_length = keys.length;
 
   var elements = new $Array(keys_length);
   var elements_length = 0;
 
   for (var i = 0; i < keys_length; i++) {
     var key = keys[i];
@@ skipping 33 matching lines @@
       return SparseJoin(array, length, convert);
     }
 
     // Fast case for one-element arrays.
     if (length == 1) {
       var e = array[0];
       if (!IS_UNDEFINED(e) || (0 in array)) {
         if (IS_STRING(e)) return e;
         return convert(e);
       }
+      return '';
     }
 
     // Construct an array for the elements.
     var elements;
     var elements_length = 0;
 
     // We pull the empty separator check outside the loop for speed!
     if (separator.length == 0) {
       elements = new $Array(length);
       for (var i = 0; i < length; i++) {
@@ skipping 19 matching lines @@
     if (!IS_UNDEFINED(result)) return result;
     return %StringBuilderConcat(elements, elements_length, '');
   } finally {
     // Make sure to pop the visited array no matter what happens.
     if (is_array) visited_arrays.pop();
   }
 }
 
 
 function ConvertToString(x) {
-  if (IS_STRING(x)) return x;
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   return (IS_NULL_OR_UNDEFINED(x)) ? '' : %ToString(%DefaultString(x));
 }
 
 
 function ConvertToLocaleString(e) {
   if (e == null) {
     return '';
   } else {
@@ skipping 1035 matching lines @@
     "lastIndexOf", getFunction("lastIndexOf", ArrayLastIndexOf, 1),
     "reduce", getFunction("reduce", ArrayReduce, 1),
     "reduceRight", getFunction("reduceRight", ArrayReduceRight, 1)
   ));
 
   %FinishArrayPrototypeSetup($Array.prototype);
 }
 
 
 SetupArray();