On Fri, Mar 11, 2016 at 10:21 AM, Ian Romanick <i...@freedesktop.org> wrote: > On 03/10/2016 01:24 PM, Patrick Baggett wrote: >> On Thu, Mar 10, 2016 at 3:08 PM, Patrick Baggett >> <baggett.patr...@gmail.com> wrote: >>> On Thu, Mar 10, 2016 at 12:25 PM, Ian Romanick <i...@freedesktop.org> wrote: >>>> From: Ian Romanick <ian.d.roman...@intel.com> >>>> >>>> Sandy Bridge / Ivy Bridge / Haswell >>>> total instructions in shared programs: 8462180 -> 8462174 (-0.00%) >>>> instructions in affected programs: 564 -> 558 (-1.06%) >>>> helped: 6 >>>> HURT: 0 >>>> >>>> total cycles in shared programs: 117542462 -> 117542276 (-0.00%) >>>> cycles in affected programs: 9768 -> 9582 (-1.90%) >>>> helped: 12 >>>> HURT: 0 >>>> >>>> Broadwell / Skylake >>>> total instructions in shared programs: 8980833 -> 8980826 (-0.00%) >>>> instructions in affected programs: 626 -> 619 (-1.12%) >>>> helped: 7 >>>> HURT: 0 >>>> >>>> total cycles in shared programs: 70077900 -> 70077714 (-0.00%) >>>> cycles in affected programs: 9378 -> 9192 (-1.98%) >>>> helped: 12 >>>> HURT: 0 >>>> >>>> G45 and Ironlake showed no change. >>>> >>>> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com> >>>> --- >>>> src/compiler/nir/nir_opt_algebraic.py | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/src/compiler/nir/nir_opt_algebraic.py >>>> b/src/compiler/nir/nir_opt_algebraic.py >>>> index 4db8f84..1442ce8 100644 >>>> --- a/src/compiler/nir/nir_opt_algebraic.py >>>> +++ b/src/compiler/nir/nir_opt_algebraic.py >>>> @@ -108,6 +108,11 @@ optimizations = [ >>>> # inot(a) >>>> (('fge', 0.0, ('b2f', a)), ('inot', a)), >>>> >>>> + # 0.0 < fabs(a) >>>> + # 0.0 != fabs(a) because fabs(a) must be >= 0 >>> I think this is wrong. Because >= 0.0 can mean that fabs(a) == 0.0 for >>> some a, you can't say then fabs(a) != 0.0. >>> >>> Then, the counter-example is when a = 0.0 >>> >>> 1) 0.0 != fabs(0.0) >>> 2) 0.0 != 0.0 >>> >> Rather, I mean the comment is wrong, but the conclusion that: >> 0 < fabs(a) <-> a != 0.0 >> is correct. You can just build a truth table or just observe that when >> a == 0, 0 < 0 is false, and >> when a != 0.0, fabs(a) will be > 0, so 0 < fabs(a) will be always true. > > How about if I change it to > > # 0.0 != fabs(a) Since fabs(a) >= 0, 0 <= fabs(a) must be true > > I think it's trivial to see how to get from "0 < fabs(a)" to "0 != > fabs(a)" based on that. Yeah, I think what gave me a pause when I read was "0.0 != fabs(a)", because that's not a general mathematical truth unless qualified by "a != 0.0". I don't have any particularly strong feelings about the wording. I personally didn't reason about it using (in)equalities at all. My logic was mostly based on domain analysis of the expression: let p(a) := 0 < fabs(a) p(0) <-> false p(a) <-> true, for any other value of a therefore p(a) <-> true when a != 0.0 therefore p(a) <-> a != 0
It's up to you. > >>>> + # 0.0 != a >>>> + (('flt', 0.0, ('fabs', a)), ('fne', a, 0.0)), >>>> + >>>> (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)), >>>> (('bcsel', ('flt', a, b), a, b), ('fmin', a, b)), >>>> (('bcsel', ('flt', a, b), b, a), ('fmax', a, b)), >>>> -- >>>> 2.5.0 >>>> >>>> _______________________________________________ >>>> mesa-dev mailing list >>>> mesa-dev@lists.freedesktop.org >>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev > _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev