pan/bi: Clear reg in squeeze_index

pan/bi: Clear reg in squeeze_index

SSA is broken at this point. Let's not pretend otherwise. The numbering produced
by squeeze_index already disambiguates what-used-to-be SSA variables and
registers. A few shader-db changes because this shuffles the register allocation
around because LCRA is stupid.

total instructions in shared programs: 2658849 -> 2650196 (-0.33%)
instructions in affected programs: 463733 -> 455080 (-1.87%)
helped: 1089
HURT: 135
helped stats (abs) min: 1.0 max: 43.0 x̄: 8.20 x̃: 5
helped stats (rel) min: 0.11% max: 17.05% x̄: 2.28% x̃: 1.52%
HURT stats (abs)   min: 1.0 max: 7.0 x̄: 2.07 x̃: 2
HURT stats (rel)   min: 0.10% max: 2.97% x̄: 1.03% x̃: 0.83%
95% mean confidence interval for instructions value: -7.52 -6.62
95% mean confidence interval for instructions %-change: -2.04% -1.78%
Instructions are helped.

total cycles in shared programs: 140617.52 -> 140613.14 (<.01%)
cycles in affected programs: 227.45 -> 223.08 (-1.92%)
helped: 45
HURT: 1
helped stats (abs) min: 0.015625 max: 0.4375 x̄: 0.10 x̃: 0
helped stats (rel) min: 0.43% max: 17.72% x̄: 2.79% x̃: 1.29%
HURT stats (abs)   min: 0.015625 max: 0.015625 x̄: 0.02 x̃: 0
HURT stats (rel)   min: 1.47% max: 1.47% x̄: 1.47% x̃: 1.47%
95% mean confidence interval for cycles value: -0.12 -0.07
95% mean confidence interval for cycles %-change: -3.76% -1.64%
Cycles are helped.

total cvt in shared programs: 13877.61 -> 13742.41 (-0.97%)
cvt in affected programs: 3432 -> 3296.80 (-3.94%)
helped: 1089
HURT: 135
helped stats (abs) min: 0.015625 max: 0.671875 x̄: 0.13 x̃: 0
helped stats (rel) min: 0.18% max: 28.36% x̄: 5.05% x̃: 3.38%
HURT stats (abs)   min: 0.015625 max: 0.109375 x̄: 0.03 x̃: 0
HURT stats (rel)   min: 0.15% max: 8.33% x̄: 2.87% x̃: 2.27%
95% mean confidence interval for cvt value: -0.12 -0.10
95% mean confidence interval for cvt %-change: -4.46% -3.88%
Cvt are helped.

total quadwords in shared programs: 1442328 -> 1437776 (-0.32%)
quadwords in affected programs: 106240 -> 101688 (-4.28%)
helped: 478
HURT: 17
helped stats (abs) min: 8.0 max: 24.0 x̄: 9.81 x̃: 8
helped stats (rel) min: 1.54% max: 20.00% x̄: 5.27% x̃: 3.70%
HURT stats (abs)   min: 8.0 max: 8.0 x̄: 8.00 x̃: 8
HURT stats (rel)   min: 1.61% max: 14.29% x̄: 6.42% x̃: 6.25%
95% mean confidence interval for quadwords value: -9.61 -8.78
95% mean confidence interval for quadwords %-change: -5.20% -4.54%
Quadwords are helped.

total threads in shared programs: 53557 -> 53550 (-0.01%)
threads in affected programs: 14 -> 7 (-50.00%)
helped: 0
HURT: 7
HURT stats (abs)   min: 1.0 max: 1.0 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 50.00% max: 50.00% x̄: 50.00% x̃: 50.00%
95% mean confidence interval for threads value: -1.00 -1.00
95% mean confidence interval for threads %-change: -50.00% -50.00%
Threads are HURT.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17794>