[PATCH] D32385: [libcxx] optional: Implement LWG 2900 and P0602

[Casey Carter via Phabricator via cfe-commits]

CaseyCarter added a comment.

In https://reviews.llvm.org/D32385#745771, @EricWF wrote:

> So Itanium ABI has this quirk where trivial types are passed using different conventions than non-trivial types. This means changing the triviality of `std::optional` for any instantiation is potentially ABI breaking. I'll need to do more investigation to find out how this will affect libc++, and if we can take this change.


libc++ committed to ABI stability for `optional`, a new feature of C++17, before the standard shipped?


https://reviews.llvm.org/D32385