Optimize isFinite and isNaN.

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 2039fea2766316f7bfa9f4038b115df734d11ac4..6e8d5bbad33ccf1c92ffa0bb6bc83ab456534a4a 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -41,7 +41,6 @@
 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.

-
 // ----------------------------------------------------------------------------
 
 
@@ -86,17 +85,15 @@ function InstallFunctionsOnHiddenPrototype(object, 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.

 }