cmake/modules/CheckAtomic.cmake

   1 # atomic builtins are required for threading support.
   2
   3 INCLUDE(CheckCXXSourceCompiles)
   4
   5 check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
   6 if (HAVE_LIBATOMIC)
   7   list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
   8 endif()
   9
  10 CHECK_CXX_SOURCE_COMPILES("
  11 #ifdef _MSC_VER
  12 #include <windows.h>
  13 #endif
  14 int main() {
  15 #ifdef _MSC_VER
  16         volatile LONG val = 1;
  17         MemoryBarrier();
  18         InterlockedCompareExchange(&val, 0, 1);
  19         InterlockedIncrement(&val);
  20         InterlockedDecrement(&val);
  21 #else
  22         volatile unsigned long val = 1;
  23         __sync_synchronize();
  24         __sync_val_compare_and_swap(&val, 1, 0);
  25         __sync_add_and_fetch(&val, 1);
  26         __sync_sub_and_fetch(&val, 1);
  27 #endif
  28         return 0;
  29       }
  30 " LLVM_HAS_ATOMICS)
  31
  32 if( NOT LLVM_HAS_ATOMICS )
  33   message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
  34 endif()