[Mesa-dev] [PATCH] nir/algebraic: Replace a-fract(a) with floor(a)

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

I noticed this while looking at a shader that was affected by Tim's
"more loop unrolling" series.

All Gen6+ platforms had similar results. (Skylake shown)
total instructions in shared programs: 15437001 -> 15435259 (-0.01%)
instructions in affected programs: 213651 -> 211909 (-0.82%)
helped: 988
HURT: 0
helped stats (abs) min: 1 max: 27 x̄: 1.76 x̃: 1
helped stats (rel) min: 0.15% max: 11.54% x̄: 1.14% x̃: 0.59%
95% mean confidence interval for instructions value: -1.89 -1.63
95% mean confidence interval for instructions %-change: -1.23% -1.05%
Instructions are helped.

total cycles in shared programs: 383007378 -> 382997063 (<.01%)
cycles in affected programs: 1650825 -> 1640510 (-0.62%)
helped: 679
HURT: 302
helped stats (abs) min: 1 max: 348 x̄: 23.39 x̃: 14
helped stats (rel) min: 0.04% max: 28.77% x̄: 1.61% x̃: 0.98%
HURT stats (abs)   min: 1 max: 250 x̄: 18.43 x̃: 7
HURT stats (rel)   min: 0.04% max: 25.86% x̄: 1.41% x̃: 0.53%
95% mean confidence interval for cycles value: -13.05 -7.98
95% mean confidence interval for cycles %-change: -0.86% -0.50%
Cycles are helped.

Iron Lake and GM45 had similar results. (GM45 shown)
total instructions in shared programs: 5043616 -> 5043010 (-0.01%)
instructions in affected programs: 119691 -> 119085 (-0.51%)
helped: 432
HURT: 0
helped stats (abs) min: 1 max: 27 x̄: 1.40 x̃: 1
helped stats (rel) min: 0.10% max: 8.11% x̄: 0.66% x̃: 0.39%
95% mean confidence interval for instructions value: -1.58 -1.23
95% mean confidence interval for instructions %-change: -0.72% -0.59%
Instructions are helped.

total cycles in shared programs: 128139812 -> 128135762 (<.01%)
cycles in affected programs: 3829724 -> 3825674 (-0.11%)
helped: 602
HURT: 0
helped stats (abs) min: 2 max: 486 x̄: 6.73 x̃: 6
helped stats (rel) min: 0.02% max: 4.85% x̄: 0.19% x̃: 0.10%
95% mean confidence interval for cycles value: -8.40 -5.05
95% mean confidence interval for cycles %-change: -0.22% -0.16%
Cycles are helped.
---
 src/compiler/nir/nir_opt_algebraic.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index ba27d702b5d..c8fc938cc8f 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -127,6 +127,7 @@ optimizations = [
    (('flrp at 32', a, b, c), ('fadd', ('fmul', c, ('fsub', b, a)), a), 'options->lower_flrp32'),
    (('flrp at 64', a, b, c), ('fadd', ('fmul', c, ('fsub', b, a)), a), 'options->lower_flrp64'),
    (('ffloor', a), ('fsub', a, ('ffract', a)), 'options->lower_ffloor'),
+   (('fadd', a, ('fneg', ('ffract', a))), ('ffloor', a), '!options->lower_ffloor'),
    (('ffract', a), ('fsub', a, ('ffloor', a)), 'options->lower_ffract'),
    (('fceil', a), ('fneg', ('ffloor', ('fneg', a))), 'options->lower_fceil'),
    (('~fadd', ('fmul', a, ('fadd', 1.0, ('fneg', ('b2f', 'c at 1')))), ('fmul', b, ('b2f', c))), ('bcsel', c, b, a), 'options->lower_flrp32'),
-- 
2.14.4