nir/algebraic: Rearrange 1-((1-a) * (1-b)) into flrp-friendly form

No shader-db changes Ice Lake, Iron Lake, or GM45 as these platforms
lack a LRP instruction.

v2: Convert the pattern directly to flrp.  There were negligible
improvements on Gen4 and Gen5, and Gen11 was actually hurt.  I believe
the problem is this optimization conflicts with the (1-x)*y =>
ffma(-x, y, y) optimization on Gen11.

Skylake
total instructions in shared programs: 15046487 -> 15041996 (-0.03%)
instructions in affected programs: 194681 -> 190190 (-2.31%)
helped: 880
HURT: 20
helped stats (abs) min: 1 max: 19 x̄: 5.13 x̃: 4
helped stats (rel) min: 0.19% max: 36.36% x̄: 4.85% x̃: 3.33%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.11% max: 1.06% x̄: 0.28% x̃: 0.17%
95% mean confidence interval for instructions value: -5.25 -4.73
95% mean confidence interval for instructions %-change: -5.11% -4.36%
Instructions are helped.

total cycles in shared programs: 354340839 -> 354303333 (-0.01%)
cycles in affected programs: 1753622 -> 1716116 (-2.14%)
helped: 786
HURT: 182
helped stats (abs) min: 1 max: 1842 x̄: 56.52 x̃: 22
helped stats (rel) min: 0.03% max: 43.17% x̄: 3.90% x̃: 2.84%
HURT stats (abs)   min: 1 max: 440 x̄: 37.99 x̃: 9
HURT stats (rel)   min: 0.03% max: 29.37% x̄: 1.96% x̃: 0.32%
95% mean confidence interval for cycles value: -45.90 -31.59
95% mean confidence interval for cycles %-change: -3.09% -2.50%
Cycles are helped.

All Gen6-Gen8 platforms had similar results. (Broadwell shown)
total instructions in shared programs: 15055907 -> 15051466 (-0.03%)
instructions in affected programs: 196370 -> 191929 (-2.26%)
helped: 871
HURT: 26
helped stats (abs) min: 1 max: 19 x̄: 5.13 x̃: 4
helped stats (rel) min: 0.19% max: 36.36% x̄: 4.76% x̃: 3.27%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.11% max: 1.06% x̄: 0.24% x̃: 0.12%
95% mean confidence interval for instructions value: -5.21 -4.69
95% mean confidence interval for instructions %-change: -4.99% -4.24%
Instructions are helped.

total cycles in shared programs: 387729170 -> 387699745 (<.01%)
cycles in affected programs: 1816409 -> 1786984 (-1.62%)
helped: 788
HURT: 172
helped stats (abs) min: 1 max: 662 x̄: 47.29 x̃: 22
helped stats (rel) min: 0.03% max: 31.26% x̄: 3.55% x̃: 2.76%
HURT stats (abs)   min: 1 max: 404 x̄: 45.59 x̃: 14
HURT stats (rel)   min: 0.03% max: 22.92% x̄: 1.53% x̃: 0.43%
95% mean confidence interval for cycles value: -35.69 -25.61
95% mean confidence interval for cycles %-change: -2.88% -2.40%
Cycles are helped.

total fills in shared programs: 34712 -> 34710 (<.01%)
fills in affected programs: 7 -> 5 (-28.57%)
helped: 1
HURT: 0

LOST:   0
GAINED: 2

Reviewed-by: Matt Turner <mattst88@gmail.com>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 09eaeaf3f23a8bfe9323591fe13b87bf2a9e4fb9..8fcf0a1cbffe697765331a6ca20925229a597892 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -186,6 +186,16 @@ optimizations = [
    # If x > 1: 1 - fsat(x) => 1 - 1 => 0 and fsat(1 - x) => fsat(< 0) => 0
    (('~fadd', ('fneg(is_used_once)', ('fsat(is_used_once)', 'a(is_not_fmul)')), 1.0), ('fsat', ('fadd', 1.0, ('fneg', a)))),
 
+   # 1 - ((1 - a) * (1 - b))
+   # 1 - (1 - a - b + a*b)
+   # 1 - 1 + a + b - a*b
+   # a + b - a*b
+   # a + b*(1 - a)
+   # b*(1 - a) + 1*a
+   # flrp(b, 1, a)
+   (('~fadd@32', 1.0, ('fneg', ('fmul', ('fadd', 1.0, ('fneg', a)), ('fadd', 1.0, ('fneg', b))))),
+    ('flrp', b, 1.0, a), '!options->lower_flrp32'),
+
    # (a * #b + #c) << #d
    # ((a * #b) << #d) + (#c << #d)
    # (a * (#b << #d)) + (#c << #d)