Optimize isFinite and isNaN.

src/v8natives.js

 // Copyright 2011 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 22 matching lines @@
 // const $Number = global.Number;
 // const $Function = global.Function;
 // const $Array = global.Array;
 // const $NaN = 0/0;
 //
 // in math.js:
 // const $floor = MathFloor
 
 const $isNaN = GlobalIsNaN;
 const $isFinite = GlobalIsFinite;
 

[PhistucK, 2011/09/02 20:24:34]

I know this code was there already, but see http://crbug.com/80149 - should
"const" be used here (or anywhere in any run time code)?

[Lasse Reichstein, 2011/09/05 10:51:16]

We shouldn't use "const" at all.
The primary reason is that const isn't well-specified, and we might be forced to
change its semantics to match Safari. For that reason, we shouldn't be using it
for security (which is the reason it's used here - someone getting hold of the
builtins object shouldn't be able to change the behavior of internal builtin
functions.
It won't affect performance here, since global variables aren't as bad as local
const variables.
It will be changed, at some point, to not using const, but not for performance
reasons.

-
 // ----------------------------------------------------------------------------
 
 
 // Helper function used to install functions on objects.
 function InstallFunctions(object, attributes, functions) {
   if (functions.length >= 8) {
     %OptimizeObjectForAddingMultipleProperties(object, functions.length >> 1);
   }
   for (var i = 0; i < functions.length; i += 2) {
     var key = functions[i];
@@ skipping 24 matching lines @@
   %SetHiddenPrototype(object, hidden_prototype);
   InstallFunctions(hidden_prototype, attributes, functions);
 }
 
 
 // ----------------------------------------------------------------------------
 
 
 // ECMA 262 - 15.1.4
 function GlobalIsNaN(number) {
-  var n = ToNumber(number);
-  return NUMBER_IS_NAN(n);
+  if (!IS_NUMBER(number)) number = NonNumberToNumber(number);
+  return NUMBER_IS_NAN(number);
 }
 
 
 // ECMA 262 - 15.1.5
 function GlobalIsFinite(number) {
   if (!IS_NUMBER(number)) number = NonNumberToNumber(number);
-
-  // NaN - NaN == NaN, Infinity - Infinity == NaN, -Infinity - -Infinity == NaN.
-  return %_IsSmi(number) || number - number == 0;
+  return !NUMBER_IS_NAN(number) && number !== (1 / 0) && number !== (-1 / 0);

[Sven Panne, 2011/09/02 16:00:14]

!NUMBER_IS_NAN(number) is equivalent to %_IsSmi(%IS_VAR(number)) || (number ==
number), but the double-untag before the cmp-id-and-branch (the compiled
equality check) already does the smi check. Therefore I propose to replace
(every?) !NUMBER_IS_NAN(foo) with (foo === foo). This gains another 5% speed for
issue 1657.

[Lasse Reichstein, 2011/09/05 10:51:16]

That depends a lot on the test.
My, admittedly very artificial, benchmark gets a 20% performance reduction when
I remove the %_IsSmi from the macro.
We can try changing the NUMBER_IS_NAN and NUMBER_IS_FINITE macros and give it a
run at the some benchmarks, but I won't do that in this CL.

 }
 
 
 // ECMA-262 - 15.1.2.2
 function GlobalParseInt(string, radix) {
   if (IS_UNDEFINED(radix) || radix === 10 || radix === 0) {
     // Some people use parseInt instead of Math.floor.  This
     // optimization makes parseInt on a Smi 12 times faster (60ns
     // vs 800ns).  The following optimization makes parseInt on a
     // non-Smi number 9 times faster (230ns vs 2070ns).  Together
@@ skipping 1422 matching lines @@
 // ----------------------------------------------------------------------------
 
 function SetupFunction() {
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "bind", FunctionBind,
     "toString", FunctionToString
   ));
 }
 
 SetupFunction();