[llvm] [RFC][MC] Cache MCRegAliasIterator (PR #93510)

[Quentin Colombet via llvm-commits]

qcolombet wrote:

> > Maybe it's fine for a stopgap
> 
> It's what I think too, but as the saying goes, there's nothing as permanent as a temporary solution. I'm not comfortable landing this unless everyone is sure it'd beneficial even if we end up removing most uses of RegAlias iterator at some point.
> 
> I personally think it is beneficial anyway because:
> 
> * If we remove RegAlias iterator as a whole at some point, then this just goes away.
> * If we can't remove it and there are still some uses left in the hot path, caching is always a good thing.

Agree on everything that was discussed.

Just one comment on the caching (disclaimer I haven't looked at the implementation), how stable is it from run-to-run?

I want to make sure we do not create non-determinism.

https://github.com/llvm/llvm-project/pull/93510