[PATCH] D114732: [clang] Mark `trivial_abi` types as "trivially relocatable".

[Devin Jeanpierre via Phabricator via cfe-commits]

devin.jeanpierre added a comment.

In D114732#3178312 <https://reviews.llvm.org/D114732#3178312>, @rjmccall wrote:

> Trivial relocation doesn't imply that types have to be safe against being suddenly relocated during the middle of operations while they're not in a safe internal state.  That is not a consideration.

In fact, I want to walk back that concern altogether. As a simple example, I think `swap()` is allowed to be defined as so:

  template <typename T>
  void swap(T& lhs, T& rhs) {
      ([&](T tmp) {lhs = std::move(rhs); rhs = std::move(tmp);})(std::move(lhs));
  }

It's really hard to argue that a type can sensibly call out to library code while in a state that is non-relocatable, despite self-labeling as `[[clang::trivial_abi]]`.  If the library is allowed to move the value, it's allowed to move it into a parameter, causing a relocation! So I actually regret pointing them out, or thinking that they might be a concern. :)

(Demonstration code: https://godbolt.org/z/j88Kqd49a)


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