nir: Transform expressions of b2f(a) and b2f(b) to a || b

nir: Transform expressions of b2f(a) and b2f(b) to a || b

All Gen6+ platforms had pretty similar results. (Skylake shown)
total instructions in shared programs: 14277184 -> 14276964 (<.01%)
instructions in affected programs: 10082 -> 9862 (-2.18%)
helped: 37
HURT: 1
helped stats (abs) min: 1 max: 30 x̄: 5.97 x̃: 4
helped stats (rel) min: 0.14% max: 16.00% x̄: 5.23% x̃: 2.04%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.70% max: 0.70% x̄: 0.70% x̃: 0.70%
95% mean confidence interval for instructions value: -7.87 -3.71
95% mean confidence interval for instructions %-change: -6.98% -3.16%
Instructions are helped.

total cycles in shared programs: 532577990 -> 532577062 (<.01%)
cycles in affected programs: 170959 -> 170031 (-0.54%)
helped: 33
HURT: 9
helped stats (abs) min: 2 max: 120 x̄: 30.91 x̃: 30
helped stats (rel) min: 0.02% max: 7.65% x̄: 2.66% x̃: 1.13%
HURT stats (abs)   min: 2 max: 24 x̄: 10.22 x̃: 8
HURT stats (rel)   min: 0.09% max: 1.79% x̄: 0.61% x̃: 0.22%
95% mean confidence interval for cycles value: -31.23 -12.96
95% mean confidence interval for cycles %-change: -2.90% -1.02%
Cycles are helped.

Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 7781539 -> 7781301 (<.01%)
instructions in affected programs: 10169 -> 9931 (-2.34%)
helped: 32
HURT: 0
helped stats (abs) min: 2 max: 20 x̄: 7.44 x̃: 6
helped stats (rel) min: 0.47% max: 17.02% x̄: 4.03% x̃: 1.88%
95% mean confidence interval for instructions value: -9.53 -5.34
95% mean confidence interval for instructions %-change: -5.94% -2.12%
Instructions are helped.

total cycles in shared programs: 177878590 -> 177878932 (<.01%)
cycles in affected programs: 78706 -> 79048 (0.43%)
helped: 7
HURT: 21
helped stats (abs) min: 6 max: 34 x̄: 24.57 x̃: 28
helped stats (rel) min: 0.15% max: 8.33% x̄: 4.66% x̃: 6.37%
HURT stats (abs)   min: 2 max: 86 x̄: 24.48 x̃: 22
HURT stats (rel)   min: 0.01% max: 4.28% x̄: 1.21% x̃: 0.70%
95% mean confidence interval for cycles value: 0.30 24.13
95% mean confidence interval for cycles %-change: -1.52% 1.01%
Inconclusive result (%-change mean confidence interval includes 0).

v2: s/fmin/fmax/.  Noticed by Thomas Helland.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>