Optimize String.prototype.includes

src/harmony-string.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 "use strict";
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $String = global.String;
 // var $Array = global.Array;
@@ skipping 80 matching lines @@
   }
 
   return %StringLastIndexOf(s, ss, start) === start;
 }
 
 
 // ES6 draft 04-05-14, section 21.1.3.6
 function StringIncludes(searchString /* position */) {  // length == 1
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.includes");
 
-  var s = TO_STRING_INLINE(this);
+  var string = TO_STRING_INLINE(this);
 
   if (IS_REGEXP(searchString)) {
     throw MakeTypeError("first_argument_not_regexp",
                         ["String.prototype.includes"]);
   }
 
-  var ss = TO_STRING_INLINE(searchString);
-  var pos = 0;
-  if (%_ArgumentsLength() > 1) {
-    pos = %_Arguments(1);  // position
-    pos = ToInteger(pos);
-  }
+  searchString = TO_STRING_INLINE(searchString);
 
-  var s_len = s.length;
-  var start = MathMin(MathMax(pos, 0), s_len);
-  var ss_len = ss.length;
-  if (ss_len + start > s_len) {
-    return false;
-  }
+  var pos = ToInteger(%_Arguments(1));
+  var len = string.length;
+  var searchLength = searchString.length;
 
-  return %StringIndexOf(s, ss, start) !== -1;
+  if (pos < 0) pos = 0;
+  else if (pos > len) pos = len;
+
+  if (searchLength + pos > len) return false;
+
+  return %StringIndexOf(string, searchString, pos) !== -1;
 }
 
 
 // ES6 Draft 05-22-2014, section 21.1.3.3
 function StringCodePointAt(pos) {
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.codePointAt");
 
   var string = TO_STRING_INLINE(this);
   var size = string.length;
   pos = TO_INTEGER(pos);
@@ skipping 52 matching lines @@
   InstallFunctions($String.prototype, DONT_ENUM, $Array(
     "codePointAt", StringCodePointAt,
     "includes", StringIncludes,
     "endsWith", StringEndsWith,
     "repeat", StringRepeat,
     "startsWith", StringStartsWith
   ));
 }
 
 ExtendStringPrototype();