I'm not sure how to test this. The AMDGPU use
case registers aren't CSRs.
ARM is the only other user, and mostly uses it for
CPSR which also isn't a CSR.
The use in getImplicitSPRUseForDPRUse seems like
it may be possible to use a CSR here, but so far
I don't know enough about ARM to come up with an
example where this matters.