Remove unnecessary checks and runtime calls from ToLength

src/runtime.js

 // Copyright 2006-2008 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.
 
 // This files contains runtime support implemented in JavaScript.
 
 // CAUTION: Some of the functions specified in this file are called
 // directly from compiled code. These are the functions with names in
 // ALL CAPS. The compiled code passes the first argument in 'this'.
 
@@ skipping 714 matching lines @@
 }
 
 
 // ECMA-262, section 9.4, page 34.
 function ToInteger(x) {
   if (%_IsSmi(x)) return x;
   return %NumberToInteger(ToNumber(x));
 }
 
 
-// ES6, draft 08-24-14, section 7.1.15
+// ES6, section 7.1.15
 function ToLength(arg) {
-  arg = ToInteger(arg);
-  if (arg < 0) return 0;
-  return arg < GlobalNumber.MAX_SAFE_INTEGER ? arg
-                                             : GlobalNumber.MAX_SAFE_INTEGER;
+  arg = TO_NUMBER_INLINE(arg);

[adamk, 2015/08/24 22:42:17]

Not sure what the state of the art is...should this be "arg = +arg"? (or should
we add a TO_NUMBER macro that does +(arg)?)

+  if (arg <= 0) return 0;
+  arg = %_MathFloor(arg);
+  return arg < kMaxSafeInteger ? arg : kMaxSafeInteger;
 }
 
 
 // ES5, section 9.12
 function SameValue(x, y) {
   if (typeof x != typeof y) return false;
   if (IS_NUMBER(x)) {
     if (NUMBER_IS_NAN(x) && NUMBER_IS_NAN(y)) return true;
     // x is +0 and y is -0 or vice versa.
     if (x === 0 && y === 0 && %_IsMinusZero(x) != %_IsMinusZero(y)) {
@@ skipping 170 matching lines @@
   to["to_string_fun"] = ToString;
 });
 
 utils.Export(function(to) {
   to.ToBoolean = ToBoolean;
   to.ToNumber = ToNumber;
   to.ToString = ToString;
 })
 
 })