nir/algebraic: Simplify comparison with sequential integers starting with 0

All of the affected shaders are Unreal4 demos.

All Gen6+ platforms had similar results. (Skylake shown)
total instructions in shared programs: 15437170 -> 15437001 (<.01%)
instructions in affected programs: 21536 -> 21367 (-0.78%)
helped: 43
HURT: 0
helped stats (abs) min: 1 max: 4 x̄: 3.93 x̃: 4
helped stats (rel) min: 0.68% max: 1.01% x̄: 0.80% x̃: 0.80%
95% mean confidence interval for instructions value: -4.07 -3.79
95% mean confidence interval for instructions %-change: -0.83% -0.77%
Instructions are helped.

total cycles in shared programs: 383007896 -> 383007378 (<.01%)
cycles in affected programs: 158640 -> 158122 (-0.33%)
helped: 38
HURT: 4
helped stats (abs) min: 1 max: 48 x̄: 13.89 x̃: 6
helped stats (rel) min: 0.03% max: 1.01% x̄: 0.33% x̃: 0.19%
HURT stats (abs)   min: 2 max: 3 x̄: 2.50 x̃: 2
HURT stats (rel)   min: 0.06% max: 0.09% x̄: 0.08% x̃: 0.08%
95% mean confidence interval for cycles value: -16.90 -7.77
95% mean confidence interval for cycles %-change: -0.39% -0.19%
Cycles are helped.

Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 8213746 -> 8213745 (<.01%)
instructions in affected programs: 127 -> 126 (-0.79%)
helped: 1
HURT: 0

total cycles in shared programs: 187734146 -> 187734144 (<.01%)
cycles in affected programs: 2132 -> 2130 (-0.09%)
helped: 1
HURT: 0

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
24 jobs for review/bug-109404 in 40 minutes and 4 seconds (queued for 10 seconds)
latest
Status Job ID Name Coverage
  Build+Test
passed #117724
build:make-gallium-drivers-other

00:09:38

passed #117723
build:make-gallium-drivers-radeonsi

00:07:21

passed #117722
build:make-gallium-drivers-swr

00:09:54

passed #117725
build:make-gallium-st-clover-llvm-39

00:07:36

passed #117726
build:make-gallium-st-clover-llvm-4

00:06:31

passed #117727
build:make-gallium-st-clover-llvm-5

00:06:26

passed #117728
build:make-gallium-st-clover-llvm-6

00:07:30

passed #117729
build:make-gallium-st-clover-llvm-7

00:08:14

passed #117730
build:make-gallium-st-other

00:08:31

passed #117721
build:make-loader-classic-dri

00:10:22

passed #117720
build:make-vulkan

00:06:14

passed #117716
build:meson-gallium-clover-llvm5

00:03:33

passed #117717
build:meson-gallium-clover-llvm6

00:03:28

passed #117718
build:meson-gallium-clover-llvm7

00:04:28

passed #117715
build:meson-gallium-drivers-other

00:04:02

passed #117714
build:meson-gallium-radeonsi

00:04:53

passed #117719
build:meson-gallium-st-other

00:04:08

passed #117713
build:meson-gallium-swr

00:09:54

passed #117712
build:meson-glvnd

00:03:28

passed #117711
build:meson-loader-classic-dri

00:07:22

passed #117710
build:meson-vulkan

00:01:47

passed #117732
build:scons-llvm

00:04:10

passed #117731
build:scons-nollvm

00:03:38

passed #117733
build:scons-swr

00:06:26