Faster string.replace with regexp pattern.

src/string.js

 // Copyright 2006-2008 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 218 matching lines @@
 
   return builder.generate();
 }
 
 
 // This has the same size as the lastMatchInfo array, and can be used for
 // functions that expect that structure to be returned.  It is used when the
 // needle is a string rather than a regexp.  In this case we can't update
 // lastMatchArray without erroneously affecting the properties on the global
 // RegExp object.
 var reusableMatchInfo = [2, -1, -1, "", ""];

[Erik Corry, 2009/03/12 10:13:00]

Do we still need both of these?

[Lasse Reichstein, 2009/03/13 08:36:51]

No, well spotted, the reusabeMatchArray isn't used any more.

 var reusableMatchArray = [ void 0 ];
 
 
 // Helper function for regular expressions in String.prototype.replace.
 function StringReplaceRegExp(subject, regexp, replace) {
-  // Compute an array of matches; each match is really a list of
-  // captures - pairs of (start, end) indexes into the subject string.
-  var matches;
-  if (regexp.global) {
-    matches = DoRegExpExecGlobal(regexp, subject);
-    if (matches.length == 0) return subject;
-  } else {
-    var lastMatchInfo = DoRegExpExec(regexp, subject, 0);
-    if (IS_NULL(lastMatchInfo)) return subject;
-    reusableMatchArray[0] = lastMatchInfo;
-    matches = reusableMatchArray;
-  }
-
-  // Determine the number of matches.
-  var length = matches.length;
-
-  // Build the resulting string of subject slices and replacements.
-  var result = new ReplaceResultBuilder(subject);
-  var previous = 0;
-  // The caller of StringReplaceRegExp must ensure that replace is not a
-  // function.
   replace = ToString(replace);
-  if (%StringIndexOf(replace, "$", 0) < 0) {
-    for (var i = 0; i < length; i++) {
-      var matchInfo = matches[i];
-      result.addSpecialSlice(previous, matchInfo[CAPTURE0]);
-      result.add(replace);
-      previous = matchInfo[CAPTURE1];  // continue after match
-    }
-  } else {
-    for (var i = 0; i < length; i++) {
-      var matchInfo = matches[i];
-      result.addSpecialSlice(previous, matchInfo[CAPTURE0]);
-      ExpandReplacement(replace, subject, matchInfo, result);
-      previous = matchInfo[CAPTURE1];  // continue after match
-    }
-  }
-  result.addSpecialSlice(previous, subject.length);
-  return result.generate();
+  return %StringReplaceRegExpWithString(subject,
+                                        regexp,
+                                        replace,
+                                        lastMatchInfo);
 };
 
 
 // Expand the $-expressions in the string and return a new string with
 // the result.

[Erik Corry, 2009/03/12 10:13:00]

Do we still need this?

[Lasse Reichstein, 2009/03/13 08:36:51]

Sadly, yes. Replacing with a string pattern, instead of a RegExp, is still in
Javascript (using indexOf), and it uses this for replacement.

[Erik Corry, 2009/03/13 09:12:34]

But knowing that number of captures is always zero should permit simplifications
here.

[Lasse Reichstein, 2011/06/14 11:51:17]

True. I'll leave it as-is for now, expecting that we will want to move
string.replace(string,string) to C++ and remove it completely.

 function ExpandReplacement(string, subject, matchInfo, builder) {
   var next = %StringIndexOf(string, '$', 0);
   if (next < 0) {
     builder.add(string);
     return;
   }
 
   // Compute the number of captures; see ECMA-262, 15.5.4.11, p. 102.
   var m = NUMBER_OF_CAPTURES(matchInfo) >> 1;  // Includes the match.
 
@@ skipping 604 matching lines @@
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup
   ));
 }
 
 
 SetupString();