[libcxx-commits] [PATCH] D150896: [libc++] Apply _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION only in classes that we have instantiated externally

[Nikolas Klauser via Phabricator via libcxx-commits]

philnik added a comment.

In D150896#4376959 <https://reviews.llvm.org/D150896#4376959>, @jwakely wrote:

> In D150896#4376904 <https://reviews.llvm.org/D150896#4376904>, @ldionne wrote:
>
>> - or we drop the guarantee that users can do explicit instantiations on GCC (or if they do, then we don't guarantee ABI stability for them)
>
> This seems acceptable to me.
>
>> This is a mess. @jwakely Do you think there's any chance we could get GCC to add this attribute? The attribute is pretty simple, it basically excludes the marked member functions from any explicit instantiation or explicit instantiation declaration.
>
> Dunno, file a bugzilla and find out :-)
>
> Why is this only a problem for explicit instantiations? If users have implicit instantiations of members of `std::vector`, isn't there also an ABI stability requirement there? If two translation units each have an implicit instantiation, but with different ABI semantics, the linker could pick either of the definitions. That could be incompatible with one of the TUs.

All the functions have `abi_tag`s which get bumped with every release, so if two TUs get compiled against different libc++ versions, the functions have different symbols names.


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https://reviews.llvm.org/D150896