Optimize String.prototype.includes

src/harmony-string.js

Index: src/harmony-string.js
diff --git a/src/harmony-string.js b/src/harmony-string.js
index 6bbe139e87a3a2e96227799fea537261e9f87b51..073ecb14d7975e1dcc4cd8fb82ca619b167dc925 100644
--- a/src/harmony-string.js
+++ b/src/harmony-string.js
@@ -98,28 +98,25 @@ function StringEndsWith(searchString /* position */) {  // length == 1
 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;
+
+  if (pos < 0) pos = 0;
+  else if (pos > len) pos = len;
+
+  if (searchLength + pos > len) return false;
 
-  return %StringIndexOf(s, ss, start) !== -1;
+  return %StringIndexOf(string, searchString, pos) !== -1;
 }