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[libc++] Use exclude_from_explicit_instantiation instead of always_inline 

Summary:
This commit adopts the exclude_from_explicit_instantiation attribute discussed
at [1] and reviewed in [2] in libc++ to supplant the use of __always_inline__
for visibility purposes.

This change means that users wanting to link together translation units built
with different versions of libc++'s headers into the same final linked image
MUST define the _LIBCPP_HIDE_FROM_ABI_PER_TU macro to 1 when building those
TUs. Doing otherwise will lead to ODR violations and ABI issues.

[1]: http://lists.llvm.org/pipermail/cfe-dev/2018-August/059024.html
[2]: https://reviews.llvm.org/D51789

Reviewers: rsmith, EricWF

Subscribers: dexonsmith, libcxx-commits

Differential Revision: https://reviews.llvm.org/D52405

llvm-svn: 345516
This commit is contained in:
Louis Dionne 2018-10-29 17:30:04 +00:00
parent bfd32d4377
commit e9d85264ac
2 changed files with 17 additions and 1 deletions
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7
libcxx/docs/ReleaseNotes.rst
View File

@ -41,3 +41,10 @@ New Features
API Changes
-----------
- Building libc++ for Mac OSX 10.6 is not supported anymore.
- Starting with LLVM 8.0.0, users that wish to link together translation units
built with different versions of libc++'s headers into the same final linked
image MUST define the _LIBCPP_HIDE_FROM_ABI_PER_TU macro to 1 when building
those translation units. Not defining _LIBCPP_HIDE_FROM_ABI_PER_TU to 1 and
linking translation units built with different versions of libc++'s headers
together may lead to ODR violations and ABI issues. On the flipside, code
size improvements should be expected for everyone not defining the macro.

11
libcxx/include/__config
View File

@ -787,6 +787,15 @@ _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_END_NAMESPACE_STD
# define _LIBCPP_INTERNAL_LINKAGE _LIBCPP_ALWAYS_INLINE
#endif
#if __has_attribute(exclude_from_explicit_instantiation)
# define _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION __attribute__ ((__exclude_from_explicit_instantiation__))
#else
// Try to approximate the effect of exclude_from_explicit_instantiation
// (which is that entities are not assumed to be provided by explicit
// template instantitations in the dylib) by always inlining those entities.
# define _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION _LIBCPP_ALWAYS_INLINE
#endif
#ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU
# ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT
# define _LIBCPP_HIDE_FROM_ABI_PER_TU 0
@ -799,7 +808,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_END_NAMESPACE_STD
# if _LIBCPP_HIDE_FROM_ABI_PER_TU
# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_INTERNAL_LINKAGE
# else
# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_ALWAYS_INLINE
# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION
# endif
#endif