[llvm] [AMDGPU] Remove unnecessary predicates from aliases. NFC. (PR #91602)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > I think that since Requires is the last defined class in def _gfx12 ..., only the predicates in Requires will apply to the whole instruction definition.
> 
> Oh, good point. I had not noticed that the instruction and alias used the same def. I am tempted to split the alias into its own anonymous def.

Or if you are close to merging #89288 then I'll wait for you to merge that one first.

https://github.com/llvm/llvm-project/pull/91602