Optimizing BuildResultFromMatchInfo, StringReplace and StringSplit.

src/regexp.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 102 matching lines @@
 
 function DoRegExpExec(regexp, string, index) {
   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 result = %_RegExpConstructResult(numResults, lastMatchInfo[CAPTURE0], s);
-  if (numResults === 1) {
-    var matchStart = lastMatchInfo[CAPTURE(0)];
-    var matchEnd = lastMatchInfo[CAPTURE(1)];
-    result[0] = SubString(s, matchStart, matchEnd);
+  var start = lastMatchInfo[CAPTURE0];
+  var end = lastMatchInfo[CAPTURE1];
+  var result = %_RegExpConstructResult(numResults, start, s);
+  if (start + 1 == end) {

[Lasse Reichstein, 2010/12/13 09:29:13]

Why not just lop from match 0/j = 3 instead of special-casting the first result?
You always perform the loop test anyway.

[sandholm, 2010/12/13 12:03:35]

The array lookup for start is re-used in the RegExpConstructResult call and the
'end != -1' check is not needed.

+    result[0] = %_StringCharAt(s, start);
   } else {
-    for (var i = 0; i < numResults; i++) {
-      var matchStart = lastMatchInfo[CAPTURE(i << 1)];
-      var matchEnd = lastMatchInfo[CAPTURE((i << 1) + 1)];
-      if (matchStart != -1 && matchEnd != -1) {
-        result[i] = SubString(s, matchStart, matchEnd);
+    result[0] = %_SubString(s, start, end);
+  }
+  var j = 5;

[Lasse Reichstein, 2010/12/13 09:29:13]

var j = REGEXP_FIRST_CAPTURE + 2;

[sandholm, 2010/12/13 12:03:35]

Done.

+  for (var i = 1; i < numResults; i++) {
+    start = lastMatchInfo[j++];
+    end = lastMatchInfo[j++];
+    if (end != -1) {
+      if (start + 1 == end) {
+        result[i] = %_StringCharAt(s, start);
       } else {
-        // Make sure the element is present. Avoid reading the undefined
-        // property from the global object since this may change.
-        result[i] = void 0;
+        result[i] = %_SubString(s, start, end);
       }
+    } else {
+      // Make sure the element is present. Avoid reading the undefined
+      // property from the global object since this may change.
+      result[i] = void 0;
     }
   }
   return result;
 }
 
 
 function RegExpExecNoTests(regexp, string, start) {
   // Must be called with RegExp, string and positive integer as arguments.
   var matchInfo = DoRegExpExec(regexp, string, start);
   var result = null;
@@ skipping 326 matching lines @@
   %DefineAccessor($RegExp, "$'", SETTER, NoOpSetter, DONT_ENUM | DONT_DELETE);
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessor($RegExp, '$' + i, GETTER, RegExpMakeCaptureGetter(i), DONT_DELETE);
     %DefineAccessor($RegExp, '$' + i, SETTER, NoOpSetter, DONT_DELETE);
   }
 }
 
 
 SetupRegExp();