If the backend does not implement this too, or some other future transform
modifiess the phi so that this isn't the case (replace the phi with a
bcsel or replace undef with zero), then it will not actually be uniform.
This keeps it enabled to some degree for RADV/ACO.
fossil-db (navi31):
Totals from 76 (0.10% of 79395) affected shaders:
Instrs: 195008 -> 195282 (+0.14%)
CodeSize: 1012592 -> 1015884 (+0.33%)
Latency: 3892826 -> 3898843 (+0.15%); split: -0.00%, +0.15%
InvThroughput: 460681 -> 460964 (+0.06%)
Copies: 13508 -> 13516 (+0.06%)
Branches: 5244 -> 5412 (+3.20%)
PreVGPRs: 5092 -> 5096 (+0.08%)
VALU: 116177 -> 116197 (+0.02%)
SALU: 23449 -> 23785 (+1.43%)
fossil-db (navi21):
Totals from 76 (0.10% of 79395) affected shaders:
Instrs: 164471 -> 164981 (+0.31%)
CodeSize: 883988 -> 888420 (+0.50%)
Latency: 4074287 -> 4082043 (+0.19%)
InvThroughput: 783783 -> 784276 (+0.06%); split: -0.00%, +0.06%
Branches: 5262 -> 5430 (+3.19%)
PreVGPRs: 5100 -> 5104 (+0.08%)
VALU: 116375 -> 116381 (+0.01%)
SALU: 23589 -> 23925 (+1.42%)
Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30211>
Rhys Perry
67ad7359ff