#154336 causes performance regressions in a few of our graphics benchmarks. From staring at some large before-and-after shader dumps it seems that the slower shaders simply have more computational instructions in them (v_mul_f32, v_fme_f32 and similar). I tried automatically reducing a test case and came up with: r.txt

$ opt -S -p=instcombine,scalarizer,instcombine < r.txt

Before #154336, all the math is removed and the function just returns poison. After #154336, none of the math is removed.