[Mesa-dev] mesa/st: support lowering user-clip-planes automatically

[Marek Olšák]

Oh BTW, drivers that want to implement pipe_screen::finalize_nir to improve
cached shader compilation can't use any of those lowering passes, because
then things blow up. The only _optional_ lowering you can do in st/mesa is
clamp_color and force_persample_in_shader, which covers iris at least
(radeonsi doesn't need any). If you need more, you either need to invest a
significant amount of time to make driver-specific NIR work with the
lowering passes, or give up on good shader cache efficiency.

Marek

On Fri, Oct 18, 2019 at 4:17 PM Marek Olšák <maraeo at gmail.com> wrote:

> Note that none of the lowering passes work if I enable them on radeonsi.
> So if you think about enabling them for your driver, I guess you have some
> work to do in the driver as well.
>
> On the other hand, having multiple shader variants in st/mesa is a
> performance disadvantage. The lowering should be done at the machine-level
> assembly code, so that you don't have to completely recompile from a
> higher-level IR.
>
> Marek
>
> On Fri, Oct 18, 2019 at 4:08 PM Marek Olšák <maraeo at gmail.com> wrote:
>
>> On Fri, Oct 18, 2019 at 9:07 AM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>
>>> On Fri, Oct 18, 2019 at 9:04 AM Erik Faye-Lund
>>> <erik.faye-lund at collabora.com> wrote:
>>> >
>>> > On Fri, 2019-10-18 at 08:57 -0400, Ilia Mirkin wrote:
>>> > > On Fri, Oct 18, 2019 at 8:51 AM Erik Faye-Lund
>>> > > <erik.faye-lund at collabora.com> wrote:
>>> > > > On Thu, 2019-10-17 at 22:24 -0400, Ilia Mirkin wrote:
>>> > > > > In the meanwhile (unless you plan on taking up Jason's
>>> > > > > suggestion),
>>> > > > > might I recommend some assert's for the unhandled cases so that
>>> > > > > there
>>> > > > > are no surprises?
>>> > > >
>>> > > > Good idea. I sent a MR for it here:
>>> > > >
>>> > > > https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2380
>>> > >
>>> > > Not sure that approach works, esp with SSO.
>>> >
>>> > If so, wouldn't that already be a problem with the existing
>>> > lower_depth_clamp-stuff, then? I mean, I just lifted the logic from
>>> > there...
>>>
>>> Yeah, that looks bogus. I'm moderately sure that checking
>>> "st->vp/gp/tep" at LinkShader time is wrong. Marek can probably
>>> confirm.
>>>
>>
>> Don't read any context states at link time. It's wrong.
>>
>> Marek
>>
>
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