On Wednesday, August 10, 2016 10:02:12 AM PDT Erik Faye-Lund wrote: > On Wed, Aug 10, 2016 at 4:30 AM, Kenneth Graunke <kenn...@whitecape.org> > wrote: > > On Haswell (GL 3.3): > > > > total instructions in shared programs: 6208759 -> 6203860 (-0.08%) > > instructions in affected programs: 856541 -> 851642 (-0.57%) > > helped: 3157 > > HURT: 113 > > LOST: 7 > > GAINED: 15 > > > > On Broadwell (GL 4.4): > > > > total instructions in shared programs: 11637854 -> 11632016 (-0.05%) > > instructions in affected programs: 1055693 -> 1049855 (-0.55%) > > helped: 3900 > > HURT: 176 > > LOST: 1 > > GAINED: 18 > > > > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> > > --- > > src/compiler/nir/nir_opt_algebraic.py | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/src/compiler/nir/nir_opt_algebraic.py > > b/src/compiler/nir/nir_opt_algebraic.py > > index 1cf614c..4e9896f 100644 > > --- a/src/compiler/nir/nir_opt_algebraic.py > > +++ b/src/compiler/nir/nir_opt_algebraic.py > > @@ -251,6 +251,10 @@ optimizations = [ > > (('ieq', 'a@bool', False), ('inot', 'a')), > > (('bcsel', a, True, False), ('ine', a, 0)), > > (('bcsel', a, False, True), ('ieq', a, 0)), > > + (('bcsel@32', a, 1.0, 0.0), ('b2f', ('ine', a, 0))), > > + (('bcsel@32', a, 0.0, 1.0), ('b2f', ('ieq', a, 0))), > > + (('bcsel@32', a, -1.0, -0.0), ('fneg', ('b2f', ('ine', a, 0)))), > > + (('bcsel@32', a, -0.0, -1.0), ('fneg', ('b2f', ('ieq', a, 0)))), > > (('bcsel', True, b, c), b), > > (('bcsel', False, b, c), c), > > # The result of this should be hit by constant propagation and, in the > > Same as the previous patch, this smells like intel-isms. Hardware that > has native bcsel with support for two inline immediates will do better > without.
It definitely feels a little strange replacing a single bcsel with a fneg/b2f/ine, as that's three operations instead of one. I expect the ine to go away - assuming 'a' is a properly formatted boolean (0 or 0xFFFFFFFF), "ine a 0" will just become 'a'. ieq would turn into inot. If the boolean was a comparison, the inot could be folded in - i.e. inot(flt(a,b)) -> fge(a,b). Or, some GPUs can handle boolean negation as a source modifier, so it might be free there too. Floating point negation can usually be done as a source modifier. For reference, here's a shader snippet from Goat Simulator which prompted me to write this optimization: const vec4 LocalConst1 = vec4(0.250000, -0.250000, 0.000000, 1.000000); void main() { ... InstrHelpTemp.r = ( ( Temporary1.r >= 0.0 ) ? LocalConst1.b : LocalConst1.a ); ... } which could be turned into InstrHelpTemp.r = float(Temporary1.r < 0.0); which seems arguably better, regardless of hardware.
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