[libcxx-commits] [PATCH] D146190: Fix EBO on std::optional and std::variant when targeting the MSVC ABI

[David Benjamin via Phabricator via libcxx-commits]

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Patch originally by Jan Dörrie in https://reviews.llvm.org/D120064. I've just updated it to include tests, and update documentation that MSVC ABI is not stable.

In the current implementation both `std::optional` and `std::variant` don't perform the EBO on MSVC's ABI. This is because both classes inherit from multiple empty base classes, which breaks the EBO for MSVC. This patch fixes this issue by applying the `empty_bases` declspec attribute, which is already used to fix a similar issue for `std::tuple`.

Fixes https://github.com/llvm/llvm-project/issues/61095.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146190

Files:
  libcxx/docs/index.rst
  libcxx/include/optional
  libcxx/include/variant
  libcxx/test/libcxx/utilities/optional/optional.object/optional_size.pass.cpp
  libcxx/test/libcxx/utilities/variant/variant.variant/variant_size.pass.cpp

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