Optimize String.prototype.includes

src/string.js

 // Copyright 2012 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.
 
 (function(global, utils) {
 
 %CheckIsBootstrapping();
 
 // -------------------------------------------------------------------
 // Imports
@@ skipping 1013 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(kFirstArgumentNotRegExp, "String.prototype.includes");
   }
 
-  var ss = TO_STRING_INLINE(searchString);
+  searchString = TO_STRING_INLINE(searchString);

[thefourtheye_, 2015/07/15 01:26:00]

Isn't this a DEOPT? Using the argument variable in both sides of an assignment
expression?

   var pos = 0;
   if (%_ArgumentsLength() > 1) {
     pos = %_Arguments(1);  // position
-    pos = $toInteger(pos);
+    pos = TO_INTEGER(pos);
   }
 
-  var s_len = s.length;
-  var start = MathMin(MathMax(pos, 0), s_len);
-  var ss_len = ss.length;
-  if (ss_len + start > s_len) {
+  var stringLength = string.length;
+  if (pos < 0) pos = 0;
+  if (pos > stringLength) pos = stringLength;
+  var searchStringLength = searchString.length;

[thefourtheye_, 2015/07/15 01:26:00]

Very minor optimization, but can we move this above and return true if it is
zero?

+
+  if (searchStringLength + pos > stringLength) {
     return false;
   }
 
-  return %StringIndexOf(s, ss, start) !== -1;
+  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 133 matching lines @@
   to.StringIndexOf = StringIndexOfJS;
   to.StringLastIndexOf = StringLastIndexOfJS;
   to.StringMatch = StringMatchJS;
   to.StringReplace = StringReplace;
   to.StringSplit = StringSplitJS;
   to.StringSubstr = StringSubstr;
   to.StringSubstring = StringSubstring;
 });
 
 })