[Mesa-dev] [PATCH 4/5] nir: Recognize mul(b2f(a), b2f(b)) as a logical AND.

[Connor Abbott]

On Wed, Mar 18, 2015 at 11:35 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>
> On Mar 18, 2015 8:32 PM, "Matt Turner" <mattst88 at gmail.com> wrote:
>>
>> On Wed, Mar 18, 2015 at 7:39 PM, Jason Ekstrand <jason at jlekstrand.net>
>> wrote:
>> > On Wed, Mar 18, 2015 at 11:37 AM, Matt Turner <mattst88 at gmail.com>
>> > wrote:
>> >> Transform this into b2f(and(a, b)).
>> >>
>> >> total instructions in shared programs: 6205448 -> 6204391 (-0.02%)
>> >> instructions in affected programs:     284030 -> 282973 (-0.37%)
>> >> helped:                                903
>> >> HURT:                                  6
>> >> ---
>> >>  src/glsl/nir/nir_opt_algebraic.py | 2 ++
>> >>  1 file changed, 2 insertions(+)
>> >>
>> >> diff --git a/src/glsl/nir/nir_opt_algebraic.py
>> >> b/src/glsl/nir/nir_opt_algebraic.py
>> >> index ef855aa..f956edf 100644
>> >> --- a/src/glsl/nir/nir_opt_algebraic.py
>> >> +++ b/src/glsl/nir/nir_opt_algebraic.py
>> >> @@ -95,6 +95,8 @@ optimizations = [
>> >>     (('fsat', a), ('fmin', ('fmax', a, 0.0), 1.0),
>> >> 'options->lower_fsat'),
>> >>     (('fsat', ('fsat', a)), ('fsat', a)),
>> >>     (('fmin', ('fmax', ('fmin', ('fmax', a, 0.0), 1.0), 0.0), 1.0),
>> >> ('fmin', ('fmax', a, 0.0), 1.0)),
>> >> +   # Emulating booleans
>> >> +   (('fmul', ('b2f', a), ('b2f', b)), ('b2f', ('iand', a, b))),
>> >
>> > Those are only equivalent if the sources are known booleans.
>> > Otherwise, no dice.
>>
>> Well... they're the source of a b2f. Are you saying that's not sufficient?
>
> No, that's not.  Fortunately, @bool should solve it for you in all of the
> cases you care about.

I think Matt has a point here. There's not much point in defining how
b2f should work for things that aren't bools, and I'm fine with
transforms that produce "bad"/undefined results when the input isn't 0
or ~0. We should never get into that situation anyways. This is
different from the issue that compare instructions always have to
produce 0 or ~0, although both do stem from the fact that NIR doesn't
have a bool type.

>
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