[cfe-dev] Adding a new attribute: no_extern_template

[Reid Kleckner via cfe-dev]

On Wed, Aug 22, 2018 at 3:02 PM Louis Dionne <ldionne at apple.com> wrote:

> The problem here is that there's no function in the dylib that we can call
> that would itself have access to
> __vector_base_common<true>::__vector_base_common(), which has hidden
> visibility.
>
> Also, even disregarding this issue, it turns out that preventing inlining
> of all methods that are part of the ABI is kind of a big deal -- I'm quite
> concerned about the performance impact this could have. I’d much rather
> pursue a path that does not require telling the compiler whether to inline
> something or not, as this is an orthogonal decision IMO. Does that make
> sense?
>

True, if the dylib does not provide the symbols that are being called
directly from user code, then neither of my suggestions will help. You
really do need to emit the functions with linkonce_odr linkage, because
they are not actually available, and the extern template declaration is a
bit of a lie.

At this point, you might want to consider finding a way to make
libc++.dylib expose the symbols so that at some point in the future so that
these functions can be emitted as avaiable_externally instead of
linkonce_odr.
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