Messages in this thread | | | Date | Tue, 20 Jan 2009 05:20:48 +0100 | From | Andi Kleen <> | Subject | Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning |
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> The problem with 'restrict' is that almost nobody uses it, and it does
Also gcc traditionally didn't do a very good job using it (this might be better in the very latest versions). At least some of the 3.x often discarded this information.
> automatically. But it should work well as a way to get Fortran-like > performance from HPC workloads written in C - which is where most of the > people are who really want the alias analysis.
It's more than just HPC -- a lot of code has critical loops.
> > it seems like a nice opt-in thing that can be used where the aliases are > > verified and the code is particularly performance critical... > > Yes. I think we could use it in the kernel, although I'm not sure how many > cases we would ever find where we really care.
Very little I suspect. Also the optimizations that gcc does with this often increase the code size. While that can be a win, with people judging gcc's output apparently *ONLY* on the code size as seen in this thread[1] it would obviously not compete well.
-Andi
[1] although there are compilers around that generate smaller code than gcc at its best.
-- ak@linux.intel.com -- Speaking for myself only.
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