Github Use AnonConst for asm! constants by Amanieu · Pull Request #83916 · rust-...

RalfJung commented 21 days ago

Considering these limitations, is this still something that we want to move forward with?

Well, what are the alternatives? With array repeat expressions not being promotion points any more, and stdarch switching away from rustc_args_required_const, we are close to cutting down promotion to be just about lifetime extension (making &expr have 'static lifetime), as it was originally intended. I still think that is a worthwhile goal, so we should make sure that anything we do here is forward-compatible with such a future.

We lose the ability to use expressions derived from generics.

Note that this affects other situations as well, such as array repeat expressions. We certainly want to fix this in the future. If this is for now "good enough" elsewhere, then why not for asm!?

IMO we should just do the same kind of post-monomorphization evaluation that we do for associated consts and promoteds (AFAIK that would be rather easy to implement, we already have those codepaths for associated consts and promoteds), but @lcnr has plans to ensure that there are no post-monomorphization failures which (to my knowledge) needs a lot of design still.