intel/vec4: Try both sources as candidates for being immediates

intel/vec4: Try both sources as candidates for being immediates

For some reason, when I first wrote try_immediate_source, I thought the
sources had already been ordered so that the immediate value was the
second source.  That's rubbish.  The generator assumes *neither* source
is immediate, and it relies on later copy/constant propagation passes to
do the reordering.

For this reason, the changes to try_immediate_source have to go to some
efforts to reorder the operands and tell the caller when it reordered
them.  The generator for comparison instructions uses this to determine
when the comparison needs to change (e.g., from GT to LT).

No changes on any Gen8 or later platform because those platforms do not
use the vec4 backend.

Haswell
total instructions in shared programs: 13484431 -> 13480500 (-0.03%)
instructions in affected programs: 441138 -> 437207 (-0.89%)
helped: 1883
HURT: 0
helped stats (abs) min: 1 max: 49 x̄: 2.09 x̃: 1
helped stats (rel) min: 0.07% max: 8.91% x̄: 1.10% x̃: 0.90%
95% mean confidence interval for instructions value: -2.19 -1.98
95% mean confidence interval for instructions %-change: -1.14% -1.06%
Instructions are helped.

total cycles in shared programs: 376420286 -> 376406400 (<.01%)
cycles in affected programs: 15995668 -> 15981782 (-0.09%)
helped: 1692
HURT: 219
helped stats (abs) min: 2 max: 764 x̄: 13.78 x̃: 4
helped stats (rel) min: <.01% max: 9.69% x̄: 0.69% x̃: 0.35%
HURT stats (abs)   min: 2 max: 516 x̄: 43.09 x̃: 22
HURT stats (rel)   min: 0.02% max: 12.09% x̄: 2.30% x̃: 1.13%
95% mean confidence interval for cycles value: -9.70 -4.83
95% mean confidence interval for cycles %-change: -0.42% -0.28%
Cycles are helped.

total spills in shared programs: 23166 -> 23158 (-0.03%)
spills in affected programs: 66 -> 58 (-12.12%)
helped: 2
HURT: 0

total fills in shared programs: 34592 -> 34580 (-0.03%)
fills in affected programs: 75 -> 63 (-16.00%)
helped: 2
HURT: 0

Ivy Bridge
total instructions in shared programs: 12051590 -> 12048513 (-0.03%)
instructions in affected programs: 355911 -> 352834 (-0.86%)
helped: 1481
HURT: 0
helped stats (abs) min: 1 max: 12 x̄: 2.08 x̃: 1
helped stats (rel) min: 0.07% max: 4.92% x̄: 1.08% x̃: 0.90%
95% mean confidence interval for instructions value: -2.17 -1.98
95% mean confidence interval for instructions %-change: -1.12% -1.04%
Instructions are helped.

total cycles in shared programs: 180319624 -> 180307642 (<.01%)
cycles in affected programs: 15591028 -> 15579046 (-0.08%)
helped: 1340
HURT: 174
helped stats (abs) min: 2 max: 764 x̄: 14.19 x̃: 2
helped stats (rel) min: <.01% max: 8.68% x̄: 0.64% x̃: 0.32%
HURT stats (abs)   min: 2 max: 518 x̄: 40.41 x̃: 14
HURT stats (rel)   min: 0.02% max: 8.37% x̄: 1.59% x̃: 0.67%
95% mean confidence interval for cycles value: -10.85 -4.97
95% mean confidence interval for cycles %-change: -0.45% -0.31%
Cycles are helped.

All Gen6 and earlier platforms had simlar results. (Sandy Bridge shown)
total instructions in shared programs: 10863159 -> 10861462 (-0.02%)
instructions in affected programs: 157839 -> 156142 (-1.08%)
helped: 715
HURT: 0
helped stats (abs) min: 1 max: 12 x̄: 2.37 x̃: 2
helped stats (rel) min: 0.23% max: 4.33% x̄: 1.07% x̃: 0.85%
95% mean confidence interval for instructions value: -2.53 -2.21
95% mean confidence interval for instructions %-change: -1.13% -1.02%
Instructions are helped.

total cycles in shared programs: 153957782 -> 153948778 (<.01%)
cycles in affected programs: 3171648 -> 3162644 (-0.28%)
helped: 696
HURT: 62
helped stats (abs) min: 2 max: 390 x̄: 15.72 x̃: 4
helped stats (rel) min: 0.02% max: 10.57% x̄: 0.57% x̃: 0.12%
HURT stats (abs)   min: 2 max: 300 x̄: 31.29 x̃: 2
HURT stats (rel)   min: 0.11% max: 7.23% x̄: 0.83% x̃: 0.34%
95% mean confidence interval for cycles value: -15.65 -8.11
95% mean confidence interval for cycles %-change: -0.56% -0.36%
Cycles are helped.

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