1 INCLUDE(CheckCXXSourceCompiles) 2 3 # Sometimes linking against libatomic is required for atomic ops, if 4 # the platform doesn't support lock-free atomics. 5 # 6 # We could modify LLVM's CheckAtomic module and have it check for 64-bit 7 # atomics instead. However, we would like to avoid careless uses of 64-bit 8 # atomics inside LLVM over time on 32-bit platforms. 9 10 function(check_cxx_atomics varname) 11 set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS}) 12 set(CMAKE_REQUIRED_FLAGS "-std=c++11 -nostdinc++ -isystem ${LIBCXX_SOURCE_DIR}/include") 13 if (${LIBCXX_GCC_TOOLCHAIN}) 14 set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}") 15 endif() 16 check_cxx_source_compiles(" 17 #include <cstdint> 18 #include <atomic> 19 std::atomic<uintptr_t> x; 20 std::atomic<uintmax_t> y; 21 int main() { 22 return x + y; 23 } 24 " ${varname}) 25 set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS}) 26 endfunction(check_cxx_atomics) 27 28 check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB) 29 # If not, check if the library exists, and atomics work with it. 30 if(NOT LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB) 31 check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB) 32 if(LIBCXX_HAS_ATOMIC_LIB) 33 list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic") 34 check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB) 35 if (NOT LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB) 36 message(WARNING "Host compiler must support std::atomic!") 37 endif() 38 else() 39 message(WARNING "Host compiler appears to require libatomic, but cannot find it.") 40 endif() 41 endif() 42
