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SubjectRe: [PATCH] 2.4.22pre10: {,un}likely_p() macros for pointers
On Sat, Aug 09, 2003 at 01:21:17AM +0100, Jamie Lokier wrote:
> Albert Cahalan wrote:
> > // tell gcc what to expect: if(unlikely(err)) die(err);
> > #define likely(x) __builtin_expect(!!(x),1)
> > #define unlikely(x) __builtin_expect(!!(x),0)
> > #define expected(x,y) __builtin_expect((x),(y))
>
> You may want to check that GCC generates the same code as for
>
> #define likely(x) __builtin_expect((x),1)
> #define unlikely(x) __builtin_expect((x),0)
>
> I tried this once, and I don't recall the precise result but I do
> recall it generating different code (i.e. not optimal for one of the
> definitions).

anyway, in __builtin_expect(!!(x),0) there is a useless conversion, because
it's totally equivalent to __builtin_expect((x),0) (how could !!x be 0 if x
isn't ?), but I'm pretty sure that the compiler will add the test.

Willy

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