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| -rw-r--r-- | modules/CheckAtomic.cmake | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/modules/CheckAtomic.cmake b/modules/CheckAtomic.cmake new file mode 100644 index 00000000..900ae7e0 --- /dev/null +++ b/modules/CheckAtomic.cmake @@ -0,0 +1,92 @@ +#.rst: +# CheckAtomic +# ----------- +# +# Check if the compiler supports std:atomic out of the box or if libatomic is +# needed for atomic support. If it is needed libatomicis added to +# CMAKE_REQUIRED_LIBRARIES. So after running CheckAtomic you can use +# std:atomic. +# +# Since 5.XX.0. + +#============================================================================= +# SPDX-FileCopyrightText: 2003-2018 University of Illinois at Urbana-Champaign. +# +# SPDX-License-Identifier: BSD-3-Clause +#============================================================================= + +include(CheckCXXSourceCompiles) +include(CheckLibraryExists) + +# Sometimes linking against libatomic is required for atomic ops, if +# the platform doesn't support lock-free atomics. + +function(check_working_cxx_atomics varname) + set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS}) + set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -std=c++11") + check_cxx_source_compiles(" + #include <atomic> + std::atomic<int> x; + int main() { + return std::atomic_is_lock_free(&x); + } + " ${varname}) + set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS}) +endfunction() + +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 std::atomic_is_lock_free(&x); + } + " ${varname}) + set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS}) +endfunction() + + +# 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) + # First check if atomics work without the library. + check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB) + # If not, check if the library exists, and atomics work with it. + if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB) + check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC) + if(HAVE_LIBATOMIC) + list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic") + check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB) + if (NOT HAVE_CXX_ATOMICS_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() +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() |