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

[Jan Kokemüller via libcxx-commits]

jiixyj wrote:


> > All `std::construct_at`/`std::destroy_at` calls are funneled through helper functions that save/restore just the minimum amount of bytes that might be overwritten by the constructor/destructor, including the `__has_value_` flag.
> > Could that be a way out of this?
> 
> But I guess it won't work in constant expression and it does not work in multithreading cases as the memory is changed then changed it back later

Ah yes, the multithreading issues might be a deal breaker for this approach :/

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