Refactored code a bit to improve StringReplace performance

src/string.js

 // Copyright 2012 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 166 matching lines @@
 
 // ECMA-262 section 15.5.4.10
 function StringMatch(regexp) {
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["String.prototype.match"]);
   }
   var subject = TO_STRING_INLINE(this);
   if (IS_REGEXP(regexp)) {
     // Emulate RegExp.prototype.exec's side effect in step 5, even though
-    // value is discarded.
-    ToInteger(regexp.lastIndex);
+    // value is discarded. Inline ToInteger() manually.
+    if (! %_IsSmi(regexp.lastIndex)) {
+      ToNumber(regexp.lastIndex);
+    }
     if (!regexp.global) return RegExpExecNoTests(regexp, subject, 0);
     %_Log('regexp', 'regexp-match,%0S,%1r', [subject, regexp]);
     // lastMatchInfo is defined in regexp.js.
     var result = %StringMatch(subject, regexp, lastMatchInfo);
     if (result !== null) lastMatchInfoOverride = null;
     regexp.lastIndex = 0;
     return result;
   }
   // Non-regexp argument.
   regexp = new $RegExp(regexp);
@@ skipping 29 matching lines @@
   // .... function replace
   // ...... global search
   // ...... non-global search
   // .. string search
   // .... special case that replaces with one single character
   // ...... function replace
   // ...... string replace (with $-expansion)
 
   if (IS_REGEXP(search)) {
     // Emulate RegExp.prototype.exec's side effect in step 5, even if
-    // value is discarded.
-    ToInteger(search.lastIndex);
+    // value is discarded. Inline ToInteger() manually.
+    if (! %_IsSmi(search.lastIndex)) {
+      ToNumber(search.lastIndex);
+    }
     %_Log('regexp', 'regexp-replace,%0r,%1S', [search, subject]);
 
     if (!IS_SPEC_FUNCTION(replace)) {
       replace = TO_STRING_INLINE(replace);
 
       if (!search.global) {
         // Non-global regexp search, string replace.
         var match = DoRegExpExec(search, subject, 0);
         if (match == null) {
           search.lastIndex = 0
@@ skipping 756 matching lines @@
     "fixed", StringFixed,
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup
   ));
 }
 
 SetUpString();