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INCLUDE(CheckCXXSourceCompiles)
# Sometimes linking against libatomic is required for atomic ops, if
# the platform doesn't support lock-free atomics.
#
# We could modify LLVM's CheckAtomic module and have it check for 64-bit
# atomics instead. However, we would like to avoid careless uses of 64-bit
# atomics inside LLVM over time on 32-bit platforms.
function(check_cxx_atomics varname)
set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
set(CMAKE_REQUIRED_FLAGS "-nodefaultlibs -std=c++11 -nostdinc++ -isystem ${LIBCXX_SOURCE_DIR}/include")
if (${LIBCXX_GCC_TOOLCHAIN})
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
endif()
if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
endif()
if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
endif()
check_cxx_source_compiles("
#include <cstdint>
#include <atomic>
std::atomic<uintptr_t> x;
std::atomic<uintmax_t> y;
int main() {
return x + y;
}
" ${varname})
set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
endfunction(check_cxx_atomics)
check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
# If not, check if the library exists, and atomics work with it.
if(NOT LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
if(LIBCXX_HAS_ATOMIC_LIB)
list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
if (NOT LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
message(WARNING "Host compiler must support std::atomic!")
endif()
else()
message(WARNING "Host compiler appears to require libatomic, but cannot find it.")
endif()
endif()
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