Restructure RegExp exec cache code.

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 593 matching lines @@
 
     return result;
   }
 
   var cache = regExpCache;
   var saveAnswer = false;
 
   if (%_ObjectEquals(cache.type, 'split') &&
       %_IsRegExpEquivalent(cache.regExp, separator) &&
       %_ObjectEquals(cache.subject, subject) &&
-      %_ObjectEquals(cache.lastIndex, limit)) {
+      %_ObjectEquals(cache.splitLimit, limit)) {
     if (cache.answerSaved) {
       return CloneDenseArray(cache.answer);
     } else {
       saveAnswer = true;
     }
   }
 
   cache.type = 'split';
   cache.regExp = separator;
   cache.subject = subject;
-  // Reuse lastIndex field for split limit when type is "split".
-  cache.lastIndex = limit;
+  cache.splitLimit = limit;
 
   %_Log('regexp', 'regexp-split,%0S,%1r', [subject, separator]);
 
   if (length === 0) {
     cache.answerSaved = true;
     if (splitMatch(separator, subject, 0, 0) != null) {
       cache.answer = [];
       return [];
     }
     cache.answer = [subject];
@@ skipping 363 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();