Inline common case of one capture when using replace with a regexp and...

src/string.js

 // Copyright 2006-2009 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 362 matching lines @@
   var matchInfo = DoRegExpExec(regexp, subject, 0);
   if (IS_NULL(matchInfo)) return subject;
 
   var result = new ReplaceResultBuilder(subject);
   // There's at least one match.  If the regexp is global, we have to loop
   // over all matches.  The loop is not in C++ code here like the one in
   // RegExp.prototype.exec, because of the interleaved function application.
   // Unfortunately, that means this code is nearly duplicated, here and in
   // jsregexp.cc.
   if (regexp.global) {
+    var numberOfCaptures = NUMBER_OF_CAPTURES(matchInfo) >> 1;
     var previous = 0;
     do {
-      result.addSpecialSlice(previous, matchInfo[CAPTURE0]);
       var startOfMatch = matchInfo[CAPTURE0];
+      result.addSpecialSlice(previous, startOfMatch);
       previous = matchInfo[CAPTURE1];
-      result.add(ApplyReplacementFunction(replace, matchInfo, subject));
+      if (numberOfCaptures == 1) {
+        var match = SubString(subject, startOfMatch, previous);
+        // Don't call directly to avoid exposing the built-in global object.
+        result.add(replace.call(null, match, startOfMatch, subject));
+      } else {
+        result.add(ApplyReplacementFunction(replace, matchInfo, subject));
+      }
       // Can't use matchInfo any more from here, since the function could
       // overwrite it.
       // Continue with the next match.
       // Increment previous if we matched an empty string, as per ECMA-262
       // 15.5.4.10.
       if (previous == startOfMatch) {
         // Add the skipped character to the output, if any.
         if (previous < subject.length) {
           result.addSpecialSlice(previous, previous + 1);
         }
@@ skipping 486 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();