[clang] [llvm] [RISCV] Update P extension to the 018 version of the spec. (PR #170399)

[Craig Topper via llvm-commits]

topperc wrote:

> > `Also, because extensions Zba and Zbb are now assumed to be required for Base P, this version removes these scalar instructions that exist in Zba and Zbb: SH1ADD SEXT.B SEXT.H MIN MINU MAX MAXU REV8 CLZ CLZW`
> > does is mean `P` implies `Zba` and `Zbb`?
> 
> This is not a nice wording, but to me it does mean P implies Zba_Zbb. It simply removes the overlap in anticipation that implementations will opt for Zba and Zbb when P is implemented.d Better to double check on the mailing list.

I agree we should ask on the mailing list. I don't think should block this PR.

https://github.com/llvm/llvm-project/pull/170399