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

[Connor Abbott]

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'm not sure how predication in Gallium works - if it's old and crufty
compared to how drivers do things, then that's OK but I still think
it's useful to do some things with predication outside the driver.

>
> The D3D9 state tracker already converts predicates to IFs.
>
> Marek
>
> On Thu, Aug 7, 2014 at 2:25 AM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Wed, Aug 6, 2014 at 5:10 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>> From: Marek Olšák <marek.olsak at amd.com>
>>>
>>> Neved used.
>>> ---
>>
>> Connor's new IR has predication. You may not want to remove this quite yet.
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