[Mesa-dev] [PATCH 07/13] nir: Transform expressions of b2f(a) and b2f(b) to a || b

Ian Romanick idr at freedesktop.org
Thu Aug 2 23:38:47 UTC 2018


On 08/02/2018 02:10 PM, Thomas Helland wrote:
> 2018-08-02 20:19 GMT+02:00 Ian Romanick <idr at freedesktop.org>:
>> From: Ian Romanick <ian.d.romanick at intel.com>
>>
>> All Gen6+ platforms had pretty similar results. (Skylake shown)
>> total instructions in shared programs: 14277184 -> 14276964 (<.01%)
>> instructions in affected programs: 10082 -> 9862 (-2.18%)
>> helped: 37
>> HURT: 1
>> helped stats (abs) min: 1 max: 30 x̄: 5.97 x̃: 4
>> helped stats (rel) min: 0.14% max: 16.00% x̄: 5.23% x̃: 2.04%
>> HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
>> HURT stats (rel)   min: 0.70% max: 0.70% x̄: 0.70% x̃: 0.70%
>> 95% mean confidence interval for instructions value: -7.87 -3.71
>> 95% mean confidence interval for instructions %-change: -6.98% -3.16%
>> Instructions are helped.
>>
>> total cycles in shared programs: 532577990 -> 532577062 (<.01%)
>> cycles in affected programs: 170959 -> 170031 (-0.54%)
>> helped: 33
>> HURT: 9
>> helped stats (abs) min: 2 max: 120 x̄: 30.91 x̃: 30
>> helped stats (rel) min: 0.02% max: 7.65% x̄: 2.66% x̃: 1.13%
>> HURT stats (abs)   min: 2 max: 24 x̄: 10.22 x̃: 8
>> HURT stats (rel)   min: 0.09% max: 1.79% x̄: 0.61% x̃: 0.22%
>> 95% mean confidence interval for cycles value: -31.23 -12.96
>> 95% mean confidence interval for cycles %-change: -2.90% -1.02%
>> Cycles are helped.
>>
>> Iron Lake and GM45 had similar results. (Iron Lake shown)
>> total instructions in shared programs: 7781539 -> 7781301 (<.01%)
>> instructions in affected programs: 10169 -> 9931 (-2.34%)
>> helped: 32
>> HURT: 0
>> helped stats (abs) min: 2 max: 20 x̄: 7.44 x̃: 6
>> helped stats (rel) min: 0.47% max: 17.02% x̄: 4.03% x̃: 1.88%
>> 95% mean confidence interval for instructions value: -9.53 -5.34
>> 95% mean confidence interval for instructions %-change: -5.94% -2.12%
>> Instructions are helped.
>>
>> total cycles in shared programs: 177878590 -> 177878932 (<.01%)
>> cycles in affected programs: 78706 -> 79048 (0.43%)
>> helped: 7
>> HURT: 21
>> helped stats (abs) min: 6 max: 34 x̄: 24.57 x̃: 28
>> helped stats (rel) min: 0.15% max: 8.33% x̄: 4.66% x̃: 6.37%
>> HURT stats (abs)   min: 2 max: 86 x̄: 24.48 x̃: 22
>> HURT stats (rel)   min: 0.01% max: 4.28% x̄: 1.21% x̃: 0.70%
>> 95% mean confidence interval for cycles value: 0.30 24.13
>> 95% mean confidence interval for cycles %-change: -1.52% 1.01%
>> Inconclusive result (%-change mean confidence interval includes 0).
>>
>> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
>> ---
>>  src/compiler/nir/nir_opt_algebraic.py | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
>> index 8300d6d01f5..4d60467fbac 100644
>> --- a/src/compiler/nir/nir_opt_algebraic.py
>> +++ b/src/compiler/nir/nir_opt_algebraic.py
>> @@ -166,6 +166,25 @@ optimizations = [
>>
>>     (('fge', ('fneg', ('b2f', a)), 0.0), ('inot', a)),
>>
>> +   (('fne', ('fadd', ('b2f', a), ('b2f', b)), 0.0), ('ior', a, b)),
>> +   (('fne', ('fmin', ('b2f', a), ('b2f', b)), 0.0), ('ior', a, b)),
> 
> Maybe I'm just too sleepy, but shouldn't this be either
> 
> (('fne', ('fmax', ('b2f', a), ('b2f', b)), 0.0), ('ior', a, b)),
> 
> or
> 
> (('fne', ('fmin', ('b2f', a), ('b2f', b)), 0.0), ('iand', a, b)),

Yes... which means that patch 10 is also incorrect.

>> +   (('fne', ('bcsel', a, 1.0, ('b2f', b))   , 0.0), ('ior', a, b)),
>> +   (('fne', ('b2f', a), ('fneg', ('b2f', b))),      ('ior', a, b)),
>> +
>> +   # -(b2f(a) + b2f(b)) < 0
>> +   # 0 < b2f(a) + b2f(b)
>> +   # 0 != b2f(a) + b2f(b)       b2f must be 0 or 1, so the sum is non-negative
>> +   # a || b
>> +   (('flt', ('fneg', ('fadd', ('b2f', a), ('b2f', b))), 0.0), ('ior', a, b)),
>> +   (('flt', 0.0, ('fadd', ('b2f', a), ('b2f', b))), ('ior', a, b)),
>> +
>> +   # Some optimizations (below) convert things like (a < b || c < b) into
>> +   # (min(a, c) < b).  However, this interfers with the previous optimizations
>> +   # that try to remove comparisons with negated sums of b2f.  This just
>> +   # breaks that apart.
>> +   (('flt', ('fmin', c, ('fneg', ('fadd', ('b2f', a), ('b2f', b)))), 0.0),
>> +    ('ior', ('flt', c, 0.0), ('ior', a, b))),
>> +
>>     (('~flt', ('fadd', a, b), a), ('flt', b, 0.0)),
>>     (('~fge', ('fadd', a, b), a), ('fge', b, 0.0)),
>>     (('~feq', ('fadd', a, b), a), ('feq', b, 0.0)),
>> --
>> 2.14.4
>>
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