Re: Linux 2.4.10-pre11 -- __builtin_expect

Andreas Schwab
2001-09-27T12:51:44Z

James Antill <james@and.org> writes:

|> Andi Kleen <ak@suse.de> writes:
|>
|> > Good point. I somehow assumed that __builtin_expect would just signify
|> > a boolean, but if I read gcc source correctly this was wrong.
|>
|> Yeh, it's a long so you'll get no cast warnings too.
|>
|> > Here is an updated patch.
|>
|> [snip ... ]
|>
|> > --- include/linux/kernel.h-LIKELY Tue Sep 18 11:12:20 2001
|> > +++ include/linux/kernel.h Tue Sep 18 14:35:17 2001
|> > @@ -171,4 +171,14 @@
|> > char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding: libc5 uses this.. */
|> > };
|> >
|> > +
|> > +/* This loses on a few early 2.96 snapshots, but hopefully nobody uses them anymore. */
|> > +#if __GNUC__ > 2 || (__GNUC__ == 2 && _GNUC_MINOR__ == 96)
|> > +#define likely(x) __builtin_expect(!!(x), 1)
|> > +#define unlikely(x) __builtin_expect((x), 0)
|>
|> unlikely() also needs to be...
|>
|> #define unlikely(x) __builtin_expect(!(x), 1)
|>
|> ...or...
|>
|> #define unlikely(x) __builtin_expect(!!(x), 0)

This is not needed, since only 0 is the likely value and !! does not
change that.

Andreas.

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