[llvm] [RISCV][LSR] Account for temporary register for base addition (PR #92296)

[Philip Reames via llvm-commits]

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preames wrote:

On both points, this wasn't a new test I added for this review.  As such, the fixme applies to something else entirely.  (I'm not clear from reading it what it even applies to.)

https://github.com/llvm/llvm-project/pull/92296