[clang] [llvm] [RISCV] Add MC layer support for XSfmm*. (PR #133031)

[Craig Topper via llvm-commits]

topperc wrote:

> > SiFive's AME proposal locates in OP-V/OP-VE category
> 
> Yes, this is a good point. I do think we should also remove other vendor instruction sets which abused the standard op fields.

The RISC-V specification does not take a hard stance on non-conforming extensions. It should not be consider "abusing". Whether a non-concforming extensions is allowed is up to indvidual platform requirements. We have discussed in the past about taking patches for the T-Head 0.7 vector extension. I think we were willing to take it if there was a promise of continued maintenance.

https://github.com/llvm/llvm-project/pull/133031