Fix performance regression in regular expressions after Array.push() optimizations

src/regexp.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Array = global.Array;
 
 var $RegExp = global.RegExp;
@@ skipping 94 matching lines @@
   var result = %_RegExpExec(regexp, string, index, lastMatchInfo);
   if (result !== null) lastMatchInfoOverride = null;
   return result;
 }
 
 
 function BuildResultFromMatchInfo(lastMatchInfo, s) {
   var numResults = NUMBER_OF_CAPTURES(lastMatchInfo) >> 1;
   var start = lastMatchInfo[CAPTURE0];
   var end = lastMatchInfo[CAPTURE1];
+  var first_match = %_SubString(s, start, end);
   var result = %_RegExpConstructResult(numResults, start, s);
-  result[0] = %_SubString(s, start, end);
+  result[0] = first_match;

[Yang, 2014/05/14 13:25:23]

Is this change necessary?

+  if (numResults == 1) return result;
   var j = REGEXP_FIRST_CAPTURE + 2;
   for (var i = 1; i < numResults; i++) {
     start = lastMatchInfo[j++];
     if (start != -1) {
       end = lastMatchInfo[j];
       result[i] = %_SubString(s, start, end);
     }
     j++;
   }
   return result;
@@ skipping 323 matching lines @@
 
   for (var i = 1; i < 10; ++i) {
     %DefineOrRedefineAccessorProperty($RegExp, '$' + i,
                                       RegExpMakeCaptureGetter(i), NoOpSetter,
                                       DONT_DELETE);
   }
   %ToFastProperties($RegExp);
 }
 
 SetUpRegExp();