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

[Matt Turner]

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?