[PATCH] BZ #14649: Add multiarch FMA support to x86-64 libm

[H.J. Lu]

On Mon, Oct 1, 2012 at 10:56 AM, Andreas Jaeger <aj@suse.com> wrote:
> On 10/01/2012 05:14 PM, H.J. Lu wrote:
>>
>> Hi,
>>
>> This patch adds multiarch FMA support to x86-64 libm.  Tested on
>> FMA machine.  OK for master?
>
>
> What kind of performance benefits does it bring us? Are you sure that all

I don't have any performance numbers.  My patch just
enables FMA optimization, similar to FMA4 optimization.

> the functions you enhance are really using fma and thus benefit from the
> change?

Not all FMA/FMA4 functions have FMA/FMA4 instructions.  We should
take a look and use AVX functions instead.

> Btw. are there any processors that have both fma variants in hardware - or
> is it at most one of them?
>

I think some AMD processors support both FMA and FMA4.  But Intel
processors only support FMA.   My patch follows s_fma.c which prefers
FMA over FMA4.

-- 
H.J.