| 12345678910111213141516171819202122232425262728293031323334353637 | # Inspired by CheckAtomic.cmake from LLVM project:# https://github.com/llvm/llvm-project/blob/master/llvm/cmake/modules/CheckAtomic.cmake## SPDX-License-Identifier: Apache-2.0 WITH LLVM-exceptioninclude(CheckCXXSourceCompiles)include(CheckLibraryExists)function(check_working_cxx_atomics varname)  check_cxx_source_compiles("#include <atomic>#include <cstdint>std::atomic<std::uint64_t> x(0);int main() {  std::uint64_t i = x.load(std::memory_order_relaxed);  return static_cast<int>(i);}" ${varname})endfunction()if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")  # 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_load_8 "" HAVE_CXX_LIBATOMIC)    if(HAVE_CXX_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 64-bit std::atomic!")      endif()    else()      message(FATAL_ERROR "Host compiler appears to require libatomic for 64-bit operations, but cannot find it.")    endif()  endif()endif()
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