[Mesa-dev] [PATCH] ac/nir: use llvm fma intrinsic if nir instruction is exact.

[Dave Airlie]

On 6 October 2017 at 12:31, Marek Olšák <maraeo at gmail.com> wrote:
> On Fri, Oct 6, 2017 at 4:10 AM, Connor Abbott <cwabbott0 at gmail.com> wrote:
>> On Thu, Oct 5, 2017 at 10:08 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>> On Fri, Oct 6, 2017 at 3:50 AM, Connor Abbott <cwabbott0 at gmail.com> wrote:
>>>> Why? While it might technically be legal, always generating an unfused
>>>> mul+add when the user explicitly requested fma() seems harsh...
>>>
>>> It's slow on some chips. It doesn't need any other reason.
>>>
>>> Marek
>>
>> Presumably, if the developer asked for fma, then they don't care how
>> fast or slow it is...
>
> Feral asked for fma. They care. This debate is pointless. We just
> won't use fma by default. Period.

They didn't ask for it with precise precision. I'm assuming if someone wants
fma with precise precision we should give it to them. Like at least
the fma manpage states.

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/fma.xhtml

Dave.