On Tue, Nov 11, 2014 at 9:41 AM, Matt Turner <matts...@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. > ---
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