[llvm] [RISCV] Fold vmand of mask comparisons into a masked comparison (PR #216264)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> > Only LMUL <= 1 is folded: for larger LMUL the masked comparison's dest
> > is earlyclobbered into vrnov0 and cannot share v0 with the mask, which
> > would introduce extra vmv1r.v moves and regress.
> 
> Is that earlyclobber a real restriction required by the ISA?

Yes I think so:
https://github.com/llvm/llvm-project/blob/3cc0457eb8f91ec655fbc0910a4852fbb3c0310f/llvm/lib/Target/RISCV/RISCVInstrInfoVPseudos.td#L2602-L2629

https://github.com/llvm/llvm-project/pull/216264