[Mesa-dev] [PATCH] nir: Copy-propagate vecN operations that are actually moves

[Matt Turner]

On Fri, Feb 20, 2015 at 9:23 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>
>
> On Thu, Feb 19, 2015 at 11:03 PM, Matt Turner <mattst88 at gmail.com> wrote:
>>
>> On Thu, Feb 19, 2015 at 11:01 PM, Connor Abbott <cwabbott0 at gmail.com>
>> wrote:
>> > I agree with Ken that the regressions are small enough, and it seems
>> > they're mostly stuff we can prevent by being smarter when doing the
>> > sel peephole, so it seems like the cleanup that will probably help
>> > other passes is worth it.
>>
>> So, usually we do that as a preparatory patch. Why aren't we doing that
>> here?
>
>
> Do what in a preparatory patch?  Fix up the sel peephole to be able to
> handle "if (foo) bar = baz;"?  Sure, I can put that patch together.

I thought that this would get turned into a conditional select as a
side-effect of going out of SSA anyway (assuming baz was
unconditionally set before the if)? Are these shaders not setting baz
unconditionally?

>>
>> NIR instruction counts is not the metric we care about.
>
>
> No, but cleaning things up means that we can do other optimizations better.
> Also, in each of those cases, the non-ssa NIR code was better it was just
> less cleanable by the backend.  We need to work on that, but I don't think
> it's an indicator of a problem.
> --Jason

Okay, that seems fine. I wouldn't bother updating the SEL peephole. It
sounds like a number of the regressions we have are related to it not
handling something so we might need to do a larger evaluation.