On 12/22/2016 01:14 PM, Jason Ekstrand wrote: > On Thu, Dec 22, 2016 at 1:13 PM, Ian Romanick <i...@freedesktop.org > <mailto:i...@freedesktop.org>> wrote: > > On 12/19/2016 09:32 PM, Jason Ekstrand wrote: > > This sequence shows up The Talos Principal, at least under Vulkan, > > and prevents loop analysis from properly computing trip counts in a > > few loops. > > --- > > src/compiler/nir/nir_opt_algebraic.py | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/src/compiler/nir/nir_opt_algebraic.py > b/src/compiler/nir/nir_opt_algebraic.py > > index 698ac67..cc70ad5 100644 > > --- a/src/compiler/nir/nir_opt_algebraic.py > > +++ b/src/compiler/nir/nir_opt_algebraic.py > > @@ -464,6 +464,14 @@ def bitfield_reverse(u): > > > > optimizations += [(bitfield_reverse('x@32'), ('bitfield_reverse', > 'x'))] > > > > +# For any comparison operation, "cmp", if you have "a != a && a cmp b" > then > > +# the "a != a" is redundant because it's equivalent to "a is not NaN" > and, if > > +# a is a NaN then the second comparison will fail anyway. > > +for op in ['flt', 'fge', 'feq', 'fne']: > > + optimizations += [ > > + (('iand', ('feq', a, a), (op, a, b)), (op, a, b)), > > + (('iand', ('feq', a, a), (op, b, a)), (op, b, a)), > > + ] > > I don't think this is right. That will change (NaN == NaN) && (NaN != > 7) from false to true. Right? You should just drop fne from the > list... I think. Math is hard. > > Don't all comparisons with NaN return false? Wouldn't NaN != 7 be > false? Maybe I don't understand NaN!
As far as I'm aware, (!(a == b)) is always the same as (a !== b). According to https://en.wikipedia.org/wiki/IEEE_754-1985#Recommended_functions_and_predicates, a != a is how you can implement isnan(). > --Jason > > > # Add optimizations to handle the case where the result of a > ternary is > > # compared to a constant. This way we can take things like _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev