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[libcxx] Allow use of <atomic> in C++03. Try 3.

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Summary:
After putting this question up on cfe-dev I have decided that it would be best to allow the use of `<atomic>` in C++03. Although static initialization is a concern the syntax required to get it is C++11 only. Meaning that C++11 constant static initialization cannot silently break in C++03, it will always cause a syntax error. Furthermore `ATOMIC_VAR_INIT` and `ATOMIC_FLAG_INIT` remain defined in C++03 even though they cannot be used because C++03 usages will cause better error messages.

The main change in this patch is to replace `__has_feature(cxx_atomic)`, which only returns true when C++ >= 11, to `__has_extension(c_atomic)` which returns true whenever clang supports the required atomic builtins.


This patch adds the following macros:
* `_LIBCPP_HAS_C_ATOMIC_IMP`      - Defined on clang versions which provide the C `_Atomic` keyword.
* `_LIBCPP_HAS_GCC_ATOMIC_IMP` - Defined on GCC > 4.7. We must use the fallback atomic implementation.
* `_LIBCPP_HAS_NO_ATOMIC_HEADER` - Defined when it is not safe to include `<atomic>`.

`_LIBCPP_HAS_C_ATOMIC_IMP` and `_LIBCPP_HAS_GCC_ATOMIC_IMP` are mutually exclusive, only one should be defined. If neither is defined then `<atomic>` is not implemented and including `<atomic>` will issue an error.

Reviewers: chandlerc, jroelofs, mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D11555

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245463 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2015-08-19 17:21:46 +00:00
parent 8966350d61
commit 00f4a49b0b
37 changed files with 363 additions and 757 deletions
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16
include/__config
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@@ -37,6 +37,9 @@
#ifndef __has_builtin
#define __has_builtin(__x) 0
#endif
#ifndef __has_extension
#define __has_extension(__x) 0
#endif
#ifndef __has_feature
#define __has_feature(__x) 0
#endif
@@ -773,4 +776,15 @@ extern "C" void __sanitizer_annotate_contiguous_container(
#define _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
#endif
#endif // _LIBCPP_CONFIG
#if __has_extension(c_atomic)
#define _LIBCPP_HAS_C_ATOMIC_IMP
#elif _GNUC_VER > 407
#define _LIBCPP_HAS_GCC_ATOMIC_IMP
#endif
#if (!defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_GCC_ATOMIC_IMP)) \
|| defined(_LIBCPP_HAS_NO_THREADS)
#define _LIBCPP_HAS_NO_ATOMIC_HEADER
#endif
#endif // _LIBCPP_CONFIG