--- /dev/null
+# atomic builtins are required for threading support.
+
+INCLUDE(CheckCXXSourceCompiles)
+
+CHECK_CXX_SOURCE_COMPILES("
+int main() {
+ volatile unsigned long val = 1;
+ __sync_synchronize();
+ __sync_val_compare_and_swap(&val, 1, 0);
+ __sync_add_and_fetch(&val, 1);
+ __sync_sub_and_fetch(&val, 1);
+ return 0;
+ }
+" LLVM_MULTITHREADED)
+
+if( NOT LLVM_MULTITHREADED )
+ message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
+endif()