nir/opt_remove_phis: rematerialize equal alu

Foz-DB Navi31:
Totals from 399 (0.50% of 79395) affected shaders:
MaxWaves: 8508 -> 8558 (+0.59%)
Instrs: 1001209 -> 1004472 (+0.33%); split: -0.37%, +0.69%
CodeSize: 5238480 -> 5262936 (+0.47%); split: -0.25%, +0.71%
VGPRs: 32376 -> 32244 (-0.41%)
Latency: 14688638 -> 14616638 (-0.49%); split: -1.46%, +0.96%
InvThroughput: 2328270 -> 2318862 (-0.40%); split: -2.22%, +1.81%
VClause: 15999 -> 16022 (+0.14%); split: -0.76%, +0.90%
SClause: 22566 -> 22718 (+0.67%); split: -0.01%, +0.68%
Copies: 49705 -> 49834 (+0.26%); split: -0.71%, +0.97%
Branches: 21964 -> 22008 (+0.20%); split: -1.05%, +1.25%
PreSGPRs: 20806 -> 20971 (+0.79%); split: -0.11%, +0.90%
PreVGPRs: 28896 -> 28712 (-0.64%)
VALU: 607273 -> 608312 (+0.17%); split: -0.53%, +0.70%
SALU: 90800 -> 92294 (+1.65%); split: -0.26%, +1.90%
VMEM: 25944 -> 25963 (+0.07%); split: -0.72%, +0.80%
SMEM: 46270 -> 46498 (+0.49%)

Instruction count regressions are largly caused by additional loop unrolling.