AMDGPU: Fix inconsistent lowering of select of vectors

f32 vectors would use a sequence of BFI instructions instead
of unrolled cmp + select. This was better in the case of a VALU
select with SGPR inputs, but we don't have a way of dealing with that
in the DAG.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270731 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed