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Re: [RFA] optimizing predictable branches on x86
I hope so too. For the kernel we have some parts where
__builtin_expect is used quite a lot and noticably helps, and could
help even more if we cut down the use of cmov too. I guess on
architectures with even more predictated instructions it could be
even more useful too.
Looking at kernel's __builtin_expect usage, I think we ought to do a lot
better on taking the hints than we do now. In particular we should
be able to derrive more from
likely (test1||test2) and likely (test1&&test2)
and similar cases. I will try to prepare patch for this later too.
Right now it does
1. __b_e (a && b, 1) => __b_e (a, 1) && __b_e (b, 1)
2. __b_e (a && b, 0) => a && __b_e (b, 0)
3. __b_e (a || b, 1) => a || __b_e (b, 1)
4. __b_e (a || b, 0) => __b_e (a, 0) || __b_e (b, 0)
See http://gcc.gnu.org/ml/gcc-patches/2007-07/msg00410.html
Paolo