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

[Alexander Richardson via llvm-commits]

arichardson wrote:

> 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.

Thanks, that's a good suggestion. How about only doing it for assertions builds or EXPENSIVE_CHECKS? I haven't measured the performance impact here but since it's only for assembly inputs it shouldn't be on the critical path for most projects.

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