[Mesa-dev] [PATCH 15/22] nir: Use De Morgan's Law on logic compounded comparisons

[Ian Romanick]

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

The replacement of the comparison operators must happen during this
step.  If it does not, the next pass of nir_opt_algebraic will reapply
De Morgan's Law in the "opposite direction" before performing dead code
elimination.  The resulting infinite loop will eventually get OOM
killed.

Haswell, Broadwell, and Skylake had similar results. (Broadwell shown)
total instructions in shared programs: 14808185 -> 14808036 (<.01%)
instructions in affected programs: 13758 -> 13609 (-1.08%)
helped: 39
HURT: 0
helped stats (abs) min: 1 max: 10 x̄: 3.82 x̃: 3
helped stats (rel) min: 0.44% max: 1.55% x̄: 0.98% x̃: 1.01%
95% mean confidence interval for instructions value: -4.67 -2.97
95% mean confidence interval for instructions %-change: -1.09% -0.88%
Instructions are helped.

total cycles in shared programs: 559438333 -> 559435832 (<.01%)
cycles in affected programs: 199160 -> 196659 (-1.26%)
helped: 42
HURT: 3
helped stats (abs) min: 2 max: 184 x̄: 61.50 x̃: 51
helped stats (rel) min: 0.02% max: 6.94% x̄: 1.41% x̃: 1.40%
HURT stats (abs)   min: 2 max: 40 x̄: 27.33 x̃: 40
HURT stats (rel)   min: 0.05% max: 0.74% x̄: 0.51% x̃: 0.74%
95% mean confidence interval for cycles value: -71.47 -39.69
95% mean confidence interval for cycles %-change: -1.64% -0.93%
Cycles are helped.

Sandy Bridge and Ivy Bridge had similar results. (Ivy Bridge shown)
total instructions in shared programs: 11811776 -> 11811553 (<.01%)
instructions in affected programs: 15201 -> 14978 (-1.47%)
helped: 39
HURT: 0
helped stats (abs) min: 1 max: 20 x̄: 5.72 x̃: 6
helped stats (rel) min: 0.44% max: 2.53% x̄: 1.30% x̃: 1.26%
95% mean confidence interval for instructions value: -7.21 -4.23
95% mean confidence interval for instructions %-change: -1.48% -1.12%
Instructions are helped.

total cycles in shared programs: 257617270 -> 257614589 (<.01%)
cycles in affected programs: 212107 -> 209426 (-1.26%)
helped: 45
HURT: 0
helped stats (abs) min: 2 max: 180 x̄: 59.58 x̃: 54
helped stats (rel) min: 0.02% max: 6.02% x̄: 1.30% x̃: 1.32%
95% mean confidence interval for cycles value: -74.02 -45.14
95% mean confidence interval for cycles %-change: -1.59% -1.01%
Cycles are helped.

Iron Lake
total instructions in shared programs: 7886648 -> 7886515 (<.01%)
instructions in affected programs: 14106 -> 13973 (-0.94%)
helped: 29
HURT: 0
helped stats (abs) min: 1 max: 10 x̄: 4.59 x̃: 4
helped stats (rel) min: 0.35% max: 1.83% x̄: 0.90% x̃: 0.81%
95% mean confidence interval for instructions value: -5.65 -3.52
95% mean confidence interval for instructions %-change: -1.03% -0.76%
Instructions are helped.

total cycles in shared programs: 178100812 -> 178100396 (<.01%)
cycles in affected programs: 67970 -> 67554 (-0.61%)
helped: 29
HURT: 0
helped stats (abs) min: 2 max: 40 x̄: 14.34 x̃: 12
helped stats (rel) min: 0.15% max: 1.69% x̄: 0.58% x̃: 0.54%
95% mean confidence interval for cycles value: -18.30 -10.39
95% mean confidence interval for cycles %-change: -0.71% -0.45%
Cycles are helped.

GM45
total instructions in shared programs: 4857939 -> 4857872 (<.01%)
instructions in affected programs: 7426 -> 7359 (-0.90%)
helped: 15
HURT: 0
helped stats (abs) min: 1 max: 10 x̄: 4.47 x̃: 4
helped stats (rel) min: 0.33% max: 1.80% x̄: 0.87% x̃: 0.77%
95% mean confidence interval for instructions value: -6.06 -2.87
95% mean confidence interval for instructions %-change: -1.06% -0.67%
Instructions are helped.

total cycles in shared programs: 122167930 -> 122167654 (<.01%)
cycles in affected programs: 43118 -> 42842 (-0.64%)
helped: 15
HURT: 0
helped stats (abs) min: 4 max: 40 x̄: 18.40 x̃: 16
helped stats (rel) min: 0.15% max: 1.69% x̄: 0.62% x̃: 0.54%
95% mean confidence interval for cycles value: -25.03 -11.77
95% mean confidence interval for cycles %-change: -0.82% -0.41%
Cycles are helped.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/compiler/nir/nir_opt_algebraic.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 314b064..af3ad2c 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -24,6 +24,7 @@
 #    Jason Ekstrand (jason at jlekstrand.net)
 
 import nir_algebraic
+import itertools
 
 # Convenience variables
 a = 'a'
@@ -545,6 +546,14 @@ optimizations = [
      'options->lower_unpack_snorm_4x8'),
 ]
 
+invert = {'feq': 'fne', 'fne': 'feq', 'fge': 'flt', 'flt': 'fge' }
+
+for left, right in list(itertools.combinations(invert.keys(), 2)) + zip(invert.keys(), invert.keys()):
+   optimizations.append((('inot', ('ior(is_used_once)', (left, a, b), (right, c, d))),
+                         ('iand', (invert[left], a, b), (invert[right], c, d))))
+   optimizations.append((('inot', ('iand(is_used_once)', (left, a, b), (right, c, d))),
+                         ('ior', (invert[left], a, b), (invert[right], c, d))))
+
 def fexp2i(exp, bits):
    # We assume that exp is already in the right range.
    if bits == 32:
-- 
2.9.5