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Re: [PATCH] Compile AVX libm functions with -mavx
On Tue, Oct 2, 2012 at 12:47 PM, OndÅej BÃlka <neleai@seznam.cz> wrote:
> On Tue, Oct 02, 2012 at 03:31:50PM -0400, Mike Frysinger wrote:
>> On Tuesday 02 October 2012 15:20:54 H.J. Lu wrote:
>> > On Tue, Oct 2, 2012 at 12:02 PM, Mike Frysinger <vapier@gentoo.org> wrote:
>> > > On Tuesday 02 October 2012 09:53:25 H.J. Lu wrote:
>> > >> This patch compiles AVX libm functions with -mavx. It reduces text size
>> > >
>> > >> of libm.so by about 1%:
>> > > looks like you're reverting 56f6f6a2403cfa7267cad722597113be35ecf70d.
>> > > shouldn't you revert all of it and not just change the CFLAGS back ?
>> >
>> > Doesn't this patch:
>> >
>> > http://sourceware.org/ml/libc-alpha/2012-10/msg00055.html
>> >
>> > do that?
>>
>> yes, i missed the follow up
>>
>> > > it'd be useful to know *why* Ulrich moved away from -mavx, but
>> > > unfortunately his commit message is useless.
>> >
>> > I can only guess:
>>
>> might be useful to put some notes (like referring to the older commit) into
>> the commit message when you do commit things
>> -mike
>
> could it be a 60 cycle penalty when switching between legagy sse and avx
> state?
This true. We can use -mprefer-avx128 to make sure that only 128bit AVX
instructions are used.
--
H.J.