[llvm] [RISCV] Add a PseudoVSETVLIX0X0 pseudo for the x0, x0 vsetvli. NFC (PR #141875)

[Luke Lau via llvm-commits]

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lukel97 wrote:

I think there's an assertion that MI isn't x0,x0 in getInfoForVSETVLI that needs updated

https://github.com/llvm/llvm-project/pull/141875