nir/opt_algebraic: optimize patterns from Skia

shaders/skia/1567.shader_test relies on algebraic + constant folding, subtle
changes in the input compiling flow can cause it to baloon. these patterns fix
that. annoying!

shader-db results aren't amazing, but they avert a major stats regression for
that one Skia shader.

total instructions in shared programs: 2751399 -> 2751295 (<.01%)
instructions in affected programs: 6509 -> 6405 (-1.60%)
helped: 21
HURT: 1
helped stats (abs) min: 1 max: 14 x̄: 5.62 x̃: 6
helped stats (rel) min: 0.53% max: 13.73% x̄: 3.57% x̃: 1.62%
HURT stats (abs)   min: 14 max: 14 x̄: 14.00 x̃: 14
HURT stats (rel)   min: 2.45% max: 2.45% x̄: 2.45% x̃: 2.45%
95% mean confidence interval for instructions value: -7.09 -2.36
95% mean confidence interval for instructions %-change: -5.14% -1.45%
Instructions are helped.

total alu in shared programs: 2274577 -> 2274468 (<.01%)
alu in affected programs: 6178 -> 6069 (-1.76%)
helped: 21
HURT: 1
helped stats (abs) min: 1 max: 14 x̄: 5.86 x̃: 7
helped stats (rel) min: 0.55% max: 16.47% x̄: 3.93% x̃: 1.72%
HURT stats (abs)   min: 14 max: 14 x̄: 14.00 x̃: 14
HURT stats (rel)   min: 2.83% max: 2.83% x̄: 2.83% x̃: 2.83%
95% mean confidence interval for alu value: -7.35 -2.56
95% mean confidence interval for alu %-change: -5.67% -1.57%
Alu are helped.

total fscib in shared programs: 2272894 -> 2272785 (<.01%)
fscib in affected programs: 6178 -> 6069 (-1.76%)
helped: 21
HURT: 1
helped stats (abs) min: 1 max: 14 x̄: 5.86 x̃: 7
helped stats (rel) min: 0.55% max: 16.47% x̄: 3.93% x̃: 1.72%
HURT stats (abs)   min: 14 max: 14 x̄: 14.00 x̃: 14
HURT stats (rel)   min: 2.83% max: 2.83% x̄: 2.83% x̃: 2.83%
95% mean confidence interval for fscib value: -7.35 -2.56
95% mean confidence interval for fscib %-change: -5.67% -1.57%
Fscib are helped.

total bytes in shared programs: 21489352 -> 21488668 (<.01%)
bytes in affected programs: 53362 -> 52678 (-1.28%)
helped: 21
HURT: 2
helped stats (abs) min: 6 max: 98 x̄: 35.52 x̃: 40
helped stats (rel) min: 0.39% max: 10.63% x̄: 2.27% x̃: 1.27%
HURT stats (abs)   min: 2 max: 60 x̄: 31.00 x̃: 31
HURT stats (rel)   min: 0.08% max: 1.40% x̄: 0.74% x̃: 0.74%
95% mean confidence interval for bytes value: -42.73 -16.74
95% mean confidence interval for bytes %-change: -3.13% -0.89%
Bytes are helped.

total regs in shared programs: 865162 -> 865148 (<.01%)
regs in affected programs: 509 -> 495 (-2.75%)
helped: 4
HURT: 5
helped stats (abs) min: 2 max: 14 x̄: 6.00 x̃: 4
helped stats (rel) min: 3.17% max: 35.90% x̄: 14.01% x̃: 8.48%
HURT stats (abs)   min: 2 max: 2 x̄: 2.00 x̃: 2
HURT stats (rel)   min: 3.17% max: 3.17% x̄: 3.17% x̃: 3.17%
95% mean confidence interval for regs value: -5.75 2.64
95% mean confidence interval for regs %-change: -14.31% 5.39%
Inconclusive result (value mean confidence interval includes 0).

total uniforms in shared programs: 2120731 -> 2120735 (<.01%)
uniforms in affected programs: 358 -> 362 (1.12%)
helped: 1
HURT: 2
helped stats (abs) min: 2 max: 2 x̄: 2.00 x̃: 2
helped stats (rel) min: 2.94% max: 2.94% x̄: 2.94% x̃: 2.94%
HURT stats (abs)   min: 2 max: 4 x̄: 3.00 x̃: 3
HURT stats (rel)   min: 1.05% max: 4.00% x̄: 2.53% x̃: 2.53%

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31964>

src/compiler/nir/nir_opt_algebraic.py

@@ -946,6 +946,12 @@ optimizations.extend([
    # fmin(0.0, b)) while the right one is "b", so this optimization is inexact.
    (('~fmin', ('fsat', a), '#b(is_zero_to_one)'), ('fsat', ('fmin', a, b))),
 
+   # If a >= 0 ... 1 + a >= 1 ... so fsat(1 + a) = 1
+   (('fsat', ('fadd', 1.0, 'a(is_ge_zero)')), 1.0),
+
+   # Let constant folding do its job. This can have emergent behaviour.
+   (('fneg', ('bcsel(is_used_once)', a, '#b', '#c')), ('bcsel', a, ('fneg', b), ('fneg', c))),
+
    # max(-min(b, a), b) -> max(abs(b), -a)
    # min(-max(b, a), b) -> min(-abs(b), -a)
    (('fmax', ('fneg', ('fmin', b, a)), b), ('fmax', ('fabs', b), ('fneg', a))),