On Thu, Jan 21, 2016 at 4:37 PM, Kenneth Graunke <kenn...@whitecape.org> wrote: > nir_lower_alu_to_scalar() and nir_lower_load_const_to_scalar() > handle most cases quite well. They also create nir_ssa_defs rather > than ir_variables, which are much less memory intensive. > > This can mean losing out on a few GLSL IR optimizations, however. > In most cases, this is fine. But a few cases still benefit: > > - add/mul/dot still benefit from opt_algebraic()'s constant > reassociation capabilities. > > - min/max still benefit from opt_minmax(). > > - comparisons seem to still benefit from opt_algebraic(), even > though we also do most of them in nir_opt_algebraic_late(). > > With this change, shader-db statistics on Skylake are: > > total instructions in shared programs: 9107924 -> 9107347 (-0.01%) > instructions in affected programs: 188830 -> 188253 (-0.31%) > helped: 572 > HURT: 154
I tried looking at the hurt programs. The first was guacamelee/368.shader_test, which went from 40 -> 43 instructions. It has a multiplication tree of (x * (y * 0.2) * 15.0), which we are able to convert into x * y * 3.0 after channel expressions. The shader looks like star_1 = (thing0 * 0.2) * thing1 star_1 = star_1 * 15.0 star_2 = (thing2 * 0.2) * thing3 star_2 = star_2 * 15.0 star_3 = (thing4 * 0.2) * thing5 star_3 = star_3 * 15.0 stars = sat(star_1) + sat(star_2) + sat(stars_3) Before linking and channel expressions, we don't have appropriate trees to see that we can reassociate constants. Tree grafting won't do its job on, for instance, star_1, because it sees that star_1 is assigned more than once -- even though it's just reassigning itself. Adding ir_unop_saturate back to channel_expressions solves the issue. I continued looking at the regressions and adding things back until I was down to 25 hurt programs (but also down to only 10 helped) after I'd readded sign, lrp, neg, f2i, i2f, exp2, log2, f2u, u2f. I think that by the time I was down to zero regressions, the only things I would have not readded would be opcodes unused in shader-db. I think I want to hold off on this patch. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
