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 Gen7+ platforms had similar results. (Skylake shown)
total instructions in shared programs: 14276886 -> 14276838 (<.01%)
instructions in affected programs: 312 -> 264 (-15.38%)
helped: 2
HURT: 0

total cycles in shared programs: 532578395 -> 532570985 (<.01%)
cycles in affected programs: 682562 -> 675152 (-1.09%)
helped: 374
HURT: 4
helped stats (abs) min: 2 max: 200 x̄: 20.39 x̃: 18
helped stats (rel) min: 0.07% max: 11.64% x̄: 1.25% x̃: 1.28%
HURT stats (abs)   min: 2 max: 114 x̄: 53.50 x̃: 49
HURT stats (rel)   min: 0.06% max: 11.70% x̄: 5.02% x̃: 4.15%
95% mean confidence interval for cycles value: -21.30 -17.91
95% mean confidence interval for cycles %-change: -1.30% -1.06%
Cycles are helped.

Sandy Bridge
total instructions in shared programs: 10488123 -> 10488075 (<.01%)
instructions in affected programs: 336 -> 288 (-14.29%)
helped: 2
HURT: 0

total cycles in shared programs: 150260379 -> 150260439 (<.01%)
cycles in affected programs: 4726 -> 4786 (1.27%)
helped: 0
HURT: 2

No changes on Iron Lake or GM45.

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