[llvm] [AMDGPU][True16][MC][CodeGen] true16 mode for v_cvt_pk_bf8/fp8_f32 (PR #141881)

[Joe Nash via llvm-commits]

Sisyph wrote:

> > It seems like we can make better use of this instruction in true16 mode if it had a new intrinsic. Why should the caller have to decide whether to put the result in lo or hi? We should let RA do that. It also does not need the old operand then.
> > I understand we may need some version of support for backwards compatibility with the current intrinsic.
> 
> Discussed offline with Stanislav and he has explained the reason above. I guess we can have two pesudo for t16 version? We have a tied-version t16 and a regular version t16 pseudo, and then have separate intrinsics for them

I think 2 intrinsics and one t16 pseudo will work. 
Intrinsic1 : current
Intrinsic 2: no vdst in, no hi/lo select

t16 pseduo: no need for vdst_in. The the pat can use vdst_in from the intrinsic in a reg sequence, but no need to pass it into the pseduo inst.

https://github.com/llvm/llvm-project/pull/141881