nir: Mark fmin and fmax as commutative and associative

nir: Mark fmin and fmax as commutative and associative

Per the resolution of Khronos GLSL issue 80
(https://github.com/KhronosGroup/GLSL/issues/80).  Spec updates have not
landed yet, but I'll get to it soon. :)

The extra hurt shaders on Gen8+ are a handful of shaders that see things like

    bcsel(fmin(b - a, a - c) >= 0, x, y)

converted to

   bcsel(a >= b && c >= a, x, y)

The former can be generated as a CSEL instruction.  If either b - a or a
- c is used elsewhere in the shader, this saves an instruction.

All Haswell+ platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 14550188 -> 14550048 (<.01%)
instructions in affected programs: 12168 -> 12028 (-1.15%)
helped: 30
HURT: 3
helped stats (abs) min: 1 max: 17 x̄: 4.77 x̃: 2
helped stats (rel) min: 0.05% max: 3.85% x̄: 1.77% x̃: 1.80%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.50% max: 0.50% x̄: 0.50% x̃: 0.50%
95% mean confidence interval for instructions value: -6.15 -2.33
95% mean confidence interval for instructions %-change: -2.00% -1.12%
Instructions are helped.

total cycles in shared programs: 203770286 -> 203771464 (<.01%)
cycles in affected programs: 688466 -> 689644 (0.17%)
helped: 172
HURT: 220
helped stats (abs) min: 1 max: 286 x̄: 12.15 x̃: 6
helped stats (rel) min: 0.03% max: 5.97% x̄: 0.70% x̃: 0.35%
HURT stats (abs)   min: 1 max: 578 x̄: 14.85 x̃: 6
HURT stats (rel)   min: 0.03% max: 32.36% x̄: 1.21% x̃: 0.52%
95% mean confidence interval for cycles value: -0.74 6.75
95% mean confidence interval for cycles %-change: 0.15% 0.59%
Inconclusive result (value mean confidence interval includes 0).

total fills in shared programs: 4525 -> 4523 (-0.04%)
fills in affected programs: 48 -> 46 (-4.17%)
helped: 1
HURT: 0

Ivy Bridge
total instructions in shared programs: 11858995 -> 11858898 (<.01%)
instructions in affected programs: 10822 -> 10725 (-0.90%)
helped: 25
HURT: 13
helped stats (abs) min: 1 max: 17 x̄: 5.32 x̃: 2
helped stats (rel) min: 0.40% max: 5.00% x̄: 2.16% x̃: 1.85%
HURT stats (abs)   min: 1 max: 15 x̄: 2.77 x̃: 2
HURT stats (rel)   min: 0.47% max: 2.90% x̄: 1.83% x̃: 2.15%
95% mean confidence interval for instructions value: -4.66 -0.45
95% mean confidence interval for instructions %-change: -1.54% -0.05%
Instructions are helped.

total cycles in shared programs: 177947023 -> 177946880 (<.01%)
cycles in affected programs: 822075 -> 821932 (-0.02%)
helped: 157
HURT: 175
helped stats (abs) min: 1 max: 164 x̄: 13.17 x̃: 4
helped stats (rel) min: 0.03% max: 6.72% x̄: 0.64% x̃: 0.17%
HURT stats (abs)   min: 1 max: 308 x̄: 11.00 x̃: 4
HURT stats (rel)   min: 0.03% max: 9.76% x̄: 0.70% x̃: 0.18%
95% mean confidence interval for cycles value: -3.86 3.00
95% mean confidence interval for cycles %-change: -0.09% 0.22%
Inconclusive result (value mean confidence interval includes 0).

total spills in shared programs: 4185 -> 4188 (0.07%)
spills in affected programs: 146 -> 149 (2.05%)
helped: 0
HURT: 1

total fills in shared programs: 5248 -> 5249 (0.02%)
fills in affected programs: 347 -> 348 (0.29%)
helped: 0
HURT: 1

Sandy Bridge
total instructions in shared programs: 10680224 -> 10680144 (<.01%)
instructions in affected programs: 4702 -> 4622 (-1.70%)
helped: 15
HURT: 3
helped stats (abs) min: 1 max: 17 x̄: 5.53 x̃: 5
helped stats (rel) min: 0.39% max: 4.76% x̄: 2.17% x̃: 1.67%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.52% max: 0.52% x̄: 0.52% x̃: 0.52%
95% mean confidence interval for instructions value: -7.24 -1.65
95% mean confidence interval for instructions %-change: -2.55% -0.89%
Instructions are helped.

total cycles in shared programs: 152988780 -> 152985691 (<.01%)
cycles in affected programs: 1072850 -> 1069761 (-0.29%)
helped: 168
HURT: 145
helped stats (abs) min: 1 max: 592 x̄: 33.90 x̃: 12
helped stats (rel) min: 0.02% max: 10.73% x̄: 0.90% x̃: 0.31%
HURT stats (abs)   min: 1 max: 259 x̄: 17.98 x̃: 6
HURT stats (rel)   min: 0.02% max: 8.17% x̄: 0.77% x̃: 0.19%
95% mean confidence interval for cycles value: -17.95 -1.79
95% mean confidence interval for cycles %-change: -0.34% 0.08%
Inconclusive result (%-change mean confidence interval includes 0).

Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 8107033 -> 8107025 (<.01%)
instructions in affected programs: 696 -> 688 (-1.15%)
helped: 5
HURT: 0
helped stats (abs) min: 1 max: 2 x̄: 1.60 x̃: 2
helped stats (rel) min: 0.34% max: 7.14% x̄: 3.47% x̃: 4.65%
95% mean confidence interval for instructions value: -2.28 -0.92
95% mean confidence interval for instructions %-change: -7.22% 0.28%
Inconclusive result (%-change mean confidence interval includes 0).

total cycles in shared programs: 188348526 -> 188348404 (<.01%)
cycles in affected programs: 33618 -> 33496 (-0.36%)
helped: 23
HURT: 0
helped stats (abs) min: 2 max: 12 x̄: 5.30 x̃: 6
helped stats (rel) min: 0.05% max: 1.83% x̄: 0.47% x̃: 0.51%
95% mean confidence interval for cycles value: -6.70 -3.91
95% mean confidence interval for cycles %-change: -0.64% -0.30%
Cycles are helped.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/1359>