Avoid the KMP overhead for simple indexOf() operations.

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 314 matching lines @@
   }
   parameters[j] = index;
   parameters[j + 1] = subject;
   return ToString(replace.apply(null, parameters));
 }
 
 
 // ECMA-262 section 15.5.4.7
 %AddProperty($String.prototype, "indexOf", function(searchString /* position */) {  // length == 1
   var str = ToString(this);
+  var str_len = str.length;
   var searchStr = ToString(searchString);
   var index = 0;
   if (%_ArgumentsLength() > 1) {
     var arg1 = %_Arguments(1);  // position
     index = TO_INTEGER(arg1);
   }
   if (index < 0) index = 0;
-  if (index > str.length) index = str.length;
-  if (searchStr.length + index > str.length) return -1;
+  if (index > str_len) index = str_len;
+  if (searchStr.length + index > str_len) return -1;
   return %StringIndexOf(str, searchStr, index);
 }, DONT_ENUM);
 
 
 // ECMA-262 section 15.5.4.8
 %AddProperty($String.prototype, "lastIndexOf", function(searchString /* position */) {  // length == 1
   var sub = ToString(this);
   var pat = ToString(searchString);
   var index = (%_ArgumentsLength() > 1)
       ? ToNumber(%_Arguments(1) /* position */)
@@ skipping 408 matching lines @@
 
 
 StringBuilder.prototype.generate = function() {
   return %StringBuilderConcat(this.elements, "");
 }
 
 
 ReplaceResultBuilder.prototype.generate = function() {
   return %StringBuilderConcat(this.elements, this.special_string);
 }