[llvm] [CodeGen] Simplify updateLiveIn in MachineSink (PR #79831)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > You mean the whole tablegen `Register` field `list<Register> Aliases = [];` mechanism is an abuse of the system? Maybe, but it seems like quite a lot of work to get rid of the existing in-tree uses.
> 
> I mean the part where they don’t actually share a regunit. And to be clear I’m not advocating for removing the aliases field.

I was not aware of any uses of `Aliases` when the registers already share some regunit. Wouldn't that be redundant? I thought every use of `Aliases` was deemed to be "ad hoc aliasing".

https://github.com/llvm/llvm-project/pull/79831