[llvm] [RISCV] Add Zilsd to RISCVMergeBaseOffset. (PR #140157)

[Sam Elliott via llvm-commits]

lenary wrote:

@topperc i guess if this pass is early enough we'd have an insert_subreg. You're right that the check you pointed out is the one that I wondered if it needed generalising to some kind of "do these two alias". My main thought is that if this was a problem, we'd have already seen it with rv32Zdinx loads and stores, which i think are already supported.

https://github.com/llvm/llvm-project/pull/140157