[libcxx-commits] [libcxx] [libc++] Fix UB in <expected> related to "has value" flag (#68552) (PR #68733)

[A. Jiang via libcxx-commits]

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frederick-vs-ja wrote:

> Separately, I think it'd be a good idea to explore a language extension to allow constructing over the top of a `[[no_unique_address]]` subobject without clobbering fields in its tail padding.

It seems to me that bad things only need to happen when the subobject is "actually overlapping" (or is a base class subobject whose type has a virtual function or virtual base class). But the current standard wording only says potentially-overlapping, without caring about whether the subobject is actually overlapping.

https://github.com/llvm/llvm-project/pull/68733