[libcxx-commits] [PATCH] D103357: [libc++][format] Add __format_arg_store.

[Mark de Wever via Phabricator via libcxx-commits]

Mordante added a comment.

In D103357#2975190 <https://reviews.llvm.org/D103357#2975190>, @ldionne wrote:

> I read the comments and while I am not a big fan of reimplementing `std::variant`, I understand why it's needed (unless we want to break `std::variant`'s ABI, which we don't). Also, this needs to make progress so I'm approving it -- worst case I can request some post-commit changes.

Thanks!

A note on the `std::variant`; breaking the ABI won't help. The tags and unions should be stored separately, something like:

  std::array<tag, 4> tags;
  std::array<unions, 4> unions;

And the note mentions packing the unions, so something like:

  std::array<tag, 4> tags;
  std::tuple<t0, t1, t2, t3> packed_unions;

(This is an example, I haven't investigated the solution I want to use.)


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D103357/new/

https://reviews.llvm.org/D103357