S_CMP_LG_U64 was added in gfx8 and is guarded by hasScalarCompareEq64().
Rewrite S_CMP_LG_U64 to S_OR_B32 + S_CMP_LG_U32 for targets that
do not support 64-bit scalar compare.
Differential Revision: https://reviews.llvm.org/D89536
This was resulting in a missing vreg def in the use select
instruction.
The output of the pseudo doesn't make sense, since it really shouldn't
have the vreg output in the first place, and instead an implicit scc
def to match the real scalar behavior.
We could have easier to understand tests if we selected scalar
versions of the [us]{add|sub}.with.overflow intrinsics.
This does still end up producing vector code in the end, since it gets
moved later.
Piotr Sobczak