aco/live_var_analysis: ignore dead phis
aco/live_var_analysis: ignore dead phis
Since we don't emit code for dead phis, we also don't
have to keep their operands around.
Totals from 44 (0.06% of 79395) affected shaders: (GFX11)
MaxWaves: 648 -> 650 (+0.31%)
Instrs: 449898 -> 449120 (-0.17%); split: -0.18%, +0.00%
CodeSize: 2395000 -> 2389300 (-0.24%); split: -0.24%, +0.00%
VGPRs: 5504 -> 5468 (-0.65%)
Latency: 9005058 -> 9000966 (-0.05%); split: -0.07%, +0.03%
InvThroughput: 2154567 -> 2139095 (-0.72%); split: -0.77%, +0.06%
VClause: 8362 -> 8354 (-0.10%)
SClause: 9135 -> 9134 (-0.01%)
Copies: 60678 -> 60118 (-0.92%); split: -0.93%, +0.01%
Branches: 14379 -> 14385 (+0.04%)
PreSGPRs: 3877 -> 3863 (-0.36%)
PreVGPRs: 6318 -> 6286 (-0.51%)
VALU: 266975 -> 266301 (-0.25%); split: -0.25%, +0.00%
SALU: 52741 -> 52667 (-0.14%); split: -0.15%, +0.01%
VMEM: 16140 -> 16132 (-0.05%)