[Mesa-dev] [PATCH] gallium: remove support for predicates from TGSI

[Eric Anholt]

Connor Abbott <cwabbott0 at gmail.com> writes:

> On Wed, Aug 6, 2014 at 6:29 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> What IR? A flatland GLSL IR? A replacement for Mesa IR? Something else?
>
> It's a flatland IR, similar to TGSI/Direct3D style with enough GLSL
> IR-like stuff to get existing things working now and enable us to
> eventually do linking in it (so we can use the same optimizations
> before linking and after). I was hoping to get a patch series out soon
> for discussion, and I've got an experimental i965 fs backend to try it
> out. It should be able to replace Mesa IR too, but that's not the
> primary goal - it's mostly to be able to do SSA-based optimizations in
> a backend-independent way. You can find a branch here:
>
> https://github.com/cwabbott0/mesa/tree/nir
>
> but I'd like to wait on discussing it until I put out some patches.
>
>>
>> It's more of a question of which gallium hardware drivers are going to
>> support it. I don't think there will be any eager candidates.
>
> AFAIK almost every HW out there supports predication in one form or
> another - why wouldn't it make sense for a higher level part of the
> compiler to do e.g. if-conversion based on cost estimates provided by
> the driver, similar to how LLVM handles vectorization? That way, it
> can take advantage of the fact that things are predicated by being
> more aggressive with optimizations like code motion, CSE, etc. -
> that's why I originally added support for predication to NIR. Also,
> I'm sure that drivers that don't support control flow (i.e. vc4) will
> like having the frontend do if-conversion for them and pass along the
> predicated code - Eric?

I'd be much more likely to eat whatever TGSI is generated, generate NIR,
and then do lowering to predicated moves in NIR.
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