[AMDGPU][True16][CodeGen] stop emitting spgr_lo16 from isel (#144819)
When true16 is enabled, isel start to emit sgpr_lo16 register when a
trunc/sext i16/i32 is generated, or a salu32 is used by vgpr16 or vice
versa. And this causes a problem as sgpr_lo16 is not fully supported in
the pipeline.
True16 mode works fine in -O3 mode since folding pass remove sgpr_lo16
from the pipeline. However it hit a problem in -O0 mode as folding pass
is skipped.
This patch did:
1. stop emitting sgpr_lo16 from isel
2. update codegen pattern to split uniformed/divergent pattern for
i16/i32 conversion
3. update fix-sgpr-copy pass to address legalization requirement in
true16 mode, update fix-sgpr-copies-f16-true16.mir
test to include all possible combinations
This patch is tested with cts and downstream repo with -O0 testing