[llvm] [RISC-V][MC] Validate instructions prior to emission in AsmParser (PR #171739)

[Sam Elliott via llvm-commits]

https://github.com/lenary commented:

IMO this should be behind a developer-oriented flag, like `-verify-machineinstrs` is for llc today.

The logic looks right, and yes sharing between targets would be good but can come later.

https://github.com/llvm/llvm-project/pull/171739