nir/algebraic: Replace i2b used by bcsel or if-statement with comparison

nir/algebraic: Replace i2b used by bcsel or if-statement with comparison

All of the helped shaders are in Deus Ex.  I looked at a couple shaders,
and they have a pattern like:

    vec1 32 ssa_373 = i2b32 ssa_345.w
    vec1 32 ssa_374 = bcsel ssa_373, ssa_20, ssa_0
    ...
    vec1 32 ssa_377 = ine ssa_345.w, ssa_0
    if ssa_377 {
        ...
        vec1 32 ssa_416 = i2b32 ssa_385.w
        vec1 32 ssa_417 = bcsel ssa_416, ssa_386, ssa_374
        ...
    }

The massive help occurs because the i2b32 is removed, then other passes
determine that ssa_374 must be ssa_20 inside the if-statement allowing
the first bcsel to also be deleted.

v2: Rebase on 1-bit Boolean changes.

v3: Fix i2b32 vs ine problem in if-statement replacement.  Noticed by
Bas.

Skylake
total instructions in shared programs: 15241394 -> 15186287 (-0.36%)
instructions in affected programs: 890583 -> 835476 (-6.19%)
helped: 355
HURT: 0
helped stats (abs) min: 1 max: 497 x̄: 155.23 x̃: 149
helped stats (rel) min: 0.09% max: 16.49% x̄: 6.10% x̃: 6.59%
95% mean confidence interval for instructions value: -165.07 -145.39
95% mean confidence interval for instructions %-change: -6.42% -5.77%
Instructions are helped.

total cycles in shared programs: 373846583 -> 371023357 (-0.76%)
cycles in affected programs: 118972102 -> 116148876 (-2.37%)
helped: 343
HURT: 14
helped stats (abs) min: 45 max: 118284 x̄: 8332.32 x̃: 6089
helped stats (rel) min: 0.03% max: 38.19% x̄: 2.48% x̃: 1.77%
HURT stats (abs)   min: 120 max: 4126 x̄: 2482.79 x̃: 3019
HURT stats (rel)   min: 0.16% max: 17.37% x̄: 2.13% x̃: 1.11%
95% mean confidence interval for cycles value: -8723.28 -7093.12
95% mean confidence interval for cycles %-change: -2.57% -2.02%
Cycles are helped.

total spills in shared programs: 32401 -> 23465 (-27.58%)
spills in affected programs: 24457 -> 15521 (-36.54%)
helped: 343
HURT: 0

total fills in shared programs: 37866 -> 31765 (-16.11%)
fills in affected programs: 18889 -> 12788 (-32.30%)
helped: 343
HURT: 0

Broadwell and Haswell had similar results. (Haswell shown)
Haswell
total instructions in shared programs: 13764783 -> 13750679 (-0.10%)
instructions in affected programs: 1176256 -> 1162152 (-1.20%)
helped: 334
HURT: 21
helped stats (abs) min: 1 max: 358 x̄: 42.59 x̃: 47
helped stats (rel) min: 0.09% max: 11.81% x̄: 1.30% x̃: 1.37%
HURT stats (abs)   min: 1 max: 61 x̄: 5.76 x̃: 1
HURT stats (rel)   min: 0.03% max: 1.84% x̄: 0.17% x̃: 0.03%
95% mean confidence interval for instructions value: -43.99 -35.47
95% mean confidence interval for instructions %-change: -1.35% -1.08%
Instructions are helped.

total cycles in shared programs: 386511910 -> 385402528 (-0.29%)
cycles in affected programs: 143831110 -> 142721728 (-0.77%)
helped: 327
HURT: 39
helped stats (abs) min: 16 max: 25219 x̄: 3519.74 x̃: 3570
helped stats (rel) min: <.01% max: 10.26% x̄: 0.95% x̃: 0.96%
HURT stats (abs)   min: 16 max: 4881 x̄: 1065.95 x̃: 997
HURT stats (rel)   min: <.01% max: 16.67% x̄: 0.70% x̃: 0.24%
95% mean confidence interval for cycles value: -3375.59 -2686.60
95% mean confidence interval for cycles %-change: -0.92% -0.64%
Cycles are helped.

total spills in shared programs: 100480 -> 97846 (-2.62%)
spills in affected programs: 84702 -> 82068 (-3.11%)
helped: 316
HURT: 21

total fills in shared programs: 96877 -> 94369 (-2.59%)
fills in affected programs: 69167 -> 66659 (-3.63%)
helped: 316
HURT: 9

No changes on Ivy Bridge or earlier platforms.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>