Re: Control flow hints

On Thu, 22 Sep 2005 11:48:01 +0200, "Piotr Wyderski"
<wyderskiREMOVE@xxxxxxxxxxxxxx> wrote:

>Hello,
>
>in GCC it is possible to give the compiler a hint about expected
>control flow probabilities using the "__builtin_expect" extension.
>One can define two macros:
>
> #define SELDOM(expr) __builtin_expect((expr),(1==0))
> #define OFTEN(expr) __builtin_expect((expr),(1==1))
>
>and use them like below:
>
> if (SELDOM(p == null)) {
>
> // this situation seldom happens, so the compiler can generate
> // this branch using worse translation method, i.e. prefer the
> // quality of the complementary control flow path
> }
>
> if (OFTEN(p != null)) {
>
> // The body of this branch should be generated as good as possible
> }
>
>This is very helpful when the probability of branch selection is known
>to the programmer. Is it possible to implement the same behaviour using
>VC++ extensions?

I'm not aware of anything like the above, but some other things that come
to mind include:

__declspec(noreturn)
__declspec(nothrow)
__assume

--
Doug Harrison
VC++ MVP
.

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