nir/algebraic: Strip double negatives from comparison sources

nir/algebraic: Strip double negatives from comparison sources

All Intel platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 17224623 -> 17224337 (<.01%)
instructions in affected programs: 32648 -> 32362 (-0.88%)
helped: 148
HURT: 0
helped stats (abs) min: 1 max: 2 x̄: 1.93 x̃: 2
helped stats (rel) min: 0.16% max: 2.74% x̄: 1.07% x̃: 1.08%
95% mean confidence interval for instructions value: -1.97 -1.89
95% mean confidence interval for instructions %-change: -1.15% -1.00%
Instructions are helped.

total cycles in shared programs: 360828714 -> 360826090 (<.01%)
cycles in affected programs: 347416 -> 344792 (-0.76%)
helped: 148
HURT: 26
helped stats (abs) min: 1 max: 426 x̄: 26.33 x̃: 18
helped stats (rel) min: 0.03% max: 15.10% x̄: 1.78% x̃: 1.41%
HURT stats (abs)   min: 2 max: 337 x̄: 48.96 x̃: 6
HURT stats (rel)   min: 0.04% max: 18.82% x̄: 2.15% x̃: 0.27%
95% mean confidence interval for cycles value: -23.78 -6.38
95% mean confidence interval for cycles %-change: -1.59% -0.79%
Cycles are helped.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>