[cfe-dev] Does libc++ really need both _LIBCPP_INLINE_VISIBILITY and _LIBCPP_ALWAYS_INLINE?

Hans Wennborg via cfe-dev cfe-dev at lists.llvm.org
Thu Dec 10 11:23:42 PST 2015


On Wed, Dec 9, 2015 at 4:44 PM, Eric Fiselier via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> Recently there has been a lot of work done on cleaning up libc++'s
> visibility annotations. To continue this work I would like to figure out why
> libc++ has two different macros, '_LIBCPP_INLINE_VISIBILITY` and
> `_LIBCPP_ALWAYS_INLINE`, for expressing function visibility. If there is no
> need for both macros I would like to remove one of them entirely.
>
> On every platform and configuration except for Clang on Windows these macros
> have identical definitions. The definition is
> `__attribute__((__visibility__("hidden"), __always_inline__))`. (Note:
> libc++ detects "Windows" using _WIN32, so this affects mingw and other
> enviroments)
>
> However the macros get different definitions when using Clang on Windows.
>
> #define _LIBCPP_INLINE_VISIBILITY __attribute__((__always_inline__))
> #define _LIBCPP_ALWAYS_INLINE  __attribute__((__visibility__("hidden"),
> __always_inline__))
>
> I'm almost certain this difference is unintentional. However before I remove
> one in favor of the other I would like to be sure this is the correct thing
> to do.
>
> I would like to find out if:
>
> 1.Do visibility attributes have any effect on windows? If not the two
> definitions are already functionally identical.

Maybe it could affect linkage? Rafael or Reid would probably know.

In any case it looks strange. And does libc++ even have Windows support?


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