[Mesa-dev] [PATCH] i965/fs: Remove try_replace_with_sel().

[Jason Ekstrand]

On Dec 4, 2014 11:22 PM, "Kenneth Graunke" <kenneth at whitecape.org> wrote:
>
> On Friday, November 21, 2014 10:23:43 AM Matt Turner wrote:
> > On Tue, Nov 11, 2014 at 9:41 AM, Matt Turner <mattst88 at gmail.com> wrote:
> > > The rest of our backend optimizations have replaced the need for this
> > > since it was written.
> > >
> > > instructions in affected programs:     30626 -> 30564 (-0.20%)
> > >
> > > Hurts a small number of CSGO shaders by one instruction, but helps
even
> > > more. Hurts two by a larger number because of something I noticed
when I
> > > first wrote the SEL peephole: try_replace_with_sel() operates on
> > > instructions before we've demoted uniforms to pull constants. So code
> > > like
> > >
> > >    var.x = ( -abs(r6.w) >= 0.0 ) ? pc[82].x : r9.x;
> > >    var.y = ( -abs(r6.w) >= 0.0 ) ? pc[82].y : r9.y;
> > >    var.z = ( -abs(r6.w) >= 0.0 ) ? pc[82].z : r9.z;
> > >    var.w = ( -abs(r6.w) >= 0.0 ) ? pc[82].w : r9.w;
> > >
> > > where pc[82] gets demoted to a pull constant, we end up emitting a
> > > send(4) instruction to load pc[82] each time, and since they're in
> > > different basic blocks because we mishandle the ternary operator in
this
> > > case we can't combine them. Once we handle this common ternary pattern
> > > better the problem will go away.
> > > ---
> >
> > Thoughts?
>
> I don't know...if I'm reading the above text correctly, this doesn't look
> compelling.  Your argument for deleting this is "it's not necessary
anymore",
> but you go on to undermine that by saying that it hurts a few shaders, and
> even quadrouples the number of pull loads in a few cases...
>
> Sure, it'll get fixed if we handle ternary operations better...but we
haven't
> yet...so...

First off, how is this different from the sel peephole?

Second, at the risk of sounding like a broken record, NIR should fix this
for us.  That said, I'm a little hesitant to delete whole passes until we
know what kind of code it will generate.

--Jason

>
> I'm pretty confused.  Maybe I'm misreading your justification...
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20141205/9c28489b/attachment.html>