[libcxx] Allow use of <atomic> in C++03. Try 3.
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
llvm-svn: 245463
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 749adeba3d655f27abec2a3589a612a15d8be21c
diff --git a/src/memory.cpp b/src/memory.cpp
index 369f97f..5b81f26 100644
--- a/src/memory.cpp
+++ b/src/memory.cpp
@@ -124,7 +124,7 @@
#endif // _LIBCPP_NO_RTTI
-#if __has_feature(cxx_atomic) && !defined(_LIBCPP_HAS_NO_THREADS)
+#if defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
static const std::size_t __sp_mut_count = 16;
static pthread_mutex_t mut_back_imp[__sp_mut_count] =
@@ -177,7 +177,7 @@
return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
}
-#endif // __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
+#endif // defined(_LIBCPP_HAS_C_ATOMIC_IMP) && !defined(_LIBCPP_HAS_NO_THREADS)
void
declare_reachable(void*)