Moved one check outside of the loop and moved another one under an if stateme...

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 369 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 {
-      var startOfMatch = matchInfo[CAPTURE0];
-      result.addSpecialSlice(previous, startOfMatch);
-      previous = matchInfo[CAPTURE1];
-      if (numberOfCaptures == 1) {
+    var startOfMatch;
+    if (NUMBER_OF_CAPTURES(matchInfo) == 2) {
+      // Both branches contain essentially the same loop except for the call
+      // to the replace function. The branch is put outside of the loop for
+      // speed
+      do {
+        startOfMatch = matchInfo[CAPTURE0];
+        result.addSpecialSlice(previous, startOfMatch);
+        previous = matchInfo[CAPTURE1];
         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 {
+        // 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);
+          }
+          previous++;
+          // Per ECMA-262 15.10.6.2, if the previous index is greater than the
+          // string length, there is no match
+          if (previous > subject.length) {
+            return result.generate();
+          }
+        }
+        matchInfo = DoRegExpExec(regexp, subject, previous);
+      } while (!IS_NULL(matchInfo));
+    } else {
+      do {
+        startOfMatch = matchInfo[CAPTURE0];
+        result.addSpecialSlice(previous, startOfMatch);
+        previous = matchInfo[CAPTURE1];
         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);
+        // 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);
+          }
+          previous++;
+          // Per ECMA-262 15.10.6.2, if the previous index is greater than the
+          // string length, there is no match
+          if (previous > subject.length) {
+            return result.generate();
+          }
         }
-        previous++;
-      }
+        matchInfo = DoRegExpExec(regexp, subject, previous);
+      } while (!IS_NULL(matchInfo));
+    }
 
-      // Per ECMA-262 15.10.6.2, if the previous index is greater than the
-      // string length, there is no match
-      matchInfo = (previous > subject.length)
-          ? null
-          : DoRegExpExec(regexp, subject, previous);
-    } while (!IS_NULL(matchInfo));
+    // Tack on the final right substring after the last match.
+    result.addSpecialSlice(previous, subject.length);
 
-    // Tack on the final right substring after the last match, if necessary.
-    if (previous < subject.length) {
-      result.addSpecialSlice(previous, subject.length);
-    }
   } else { // Not a global regexp, no need to loop.
     result.addSpecialSlice(0, matchInfo[CAPTURE0]);
     var endOfMatch = matchInfo[CAPTURE1];
     result.add(ApplyReplacementFunction(replace, matchInfo, subject));
     // Can't use matchInfo any more from here, since the function could
     // overwrite it.
     result.addSpecialSlice(endOfMatch, subject.length);
   }
 
   return result.generate();
@@ skipping 473 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();