[llvm] AMDGPU: Use OtherPredicates for v_dot2_bf16_bf16(f16_f16) pseudo (PR #84354)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

> > > LGTM, but this is really unfortunate. Can we try to address dpp predicates?
> > 
> > 
> > let SubtargetPredicate = HasDPP8;
> > I am thinking whether we can put hasDPP8 into OtherPredicates (using concat). But we need to be very careful of the ordering this assignment with copy from pseudo to real of OtherPredicates.
> 
> let SubtargetPredicate = HasDPP8; // do we really need? let AssemblerPredicate = HasDPP8;
> 
> Actually why do we need to set both SubtargetPredicate and AssemblerPredicate? One of them enough? "AssemblerPredicate = HasDPP8" may also have "overriden" issue on the path.

Imagine you have the same instruction in different targets, so you are using 'SubtargetPredicate = HasFeature' on the pseudo. But the encoding is different, so you this HasFeature is not sufficient, you need to use AssemblerPredicate to distinguish between targets for real instructions.

https://github.com/llvm/llvm-project/pull/84354