set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
endfunction(check_working_cxx_atomics)
+function(check_working_cxx_atomics64 varname)
+ set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+ set(CMAKE_REQUIRED_FLAGS "-std=c++11 ${CMAKE_REQUIRED_FLAGS}")
+ CHECK_CXX_SOURCE_COMPILES("
+#include <atomic>
+#include <cstdint>
+std::atomic<uint64_t> x (0);
+int main() {
+ uint64_t i = x.load(std::memory_order_relaxed);
+ return 0;
+}
+" ${varname})
+ set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+endfunction(check_working_cxx_atomics64)
+
+
# This isn't necessary on MSVC, so avoid command-line switch annoyance
# by only running on GCC-like hosts.
if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
endif()
endif()
+# Check for 64 bit atomic operations.
+if(MSVC)
+ set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
+else()
+ check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+endif()
+
+# If not, check if the library exists, and atomics work with it.
+if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+ check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
+ if(HAVE_CXX_LIBATOMICS64)
+ list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+ check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
+ if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
+ message(FATAL_ERROR "Host compiler must support std::atomic!")
+ endif()
+ else()
+ message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
+ endif()
+endif()
+
## TODO: This define is only used for the legacy atomic operations in
## llvm's Atomic.h, which should be replaced. Other code simply
## assumes C++11 <atomic> works.