1# atomic builtins are required for threading support.
2
3INCLUDE(CheckCXXSourceCompiles)
4
5# Sometimes linking against libatomic is required for atomic ops, if
6# the platform doesn't support lock-free atomics.
7
8function(check_working_cxx_atomics varname)
9  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
10  set(CMAKE_REQUIRED_FLAGS "-std=c++11")
11  CHECK_CXX_SOURCE_COMPILES("
12#include <atomic>
13std::atomic<int> x;
14int main() {
15  return x;
16}
17" ${varname})
18  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
19endfunction(check_working_cxx_atomics)
20
21# This isn't necessary on MSVC, so avoid command-line switch annoyance
22# by only running on GCC-like hosts.
23if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
24  # First check if atomics work without the library.
25  check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
26  # If not, check if the library exists, and atomics work with it.
27  if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
28    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
29    if( HAVE_LIBATOMIC )
30      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
31      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
32      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
33	message(FATAL_ERROR "Host compiler must support std::atomic!")
34      endif()
35    else()
36      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
37    endif()
38  endif()
39endif()
40
41## TODO: This define is only used for the legacy atomic operations in
42## llvm's Atomic.h, which should be replaced.  Other code simply
43## assumes C++11 <atomic> works.
44CHECK_CXX_SOURCE_COMPILES("
45#ifdef _MSC_VER
46#include <Intrin.h> /* Workaround for PR19898. */
47#include <windows.h>
48#endif
49int main() {
50#ifdef _MSC_VER
51        volatile LONG val = 1;
52        MemoryBarrier();
53        InterlockedCompareExchange(&val, 0, 1);
54        InterlockedIncrement(&val);
55        InterlockedDecrement(&val);
56#else
57        volatile unsigned long val = 1;
58        __sync_synchronize();
59        __sync_val_compare_and_swap(&val, 1, 0);
60        __sync_add_and_fetch(&val, 1);
61        __sync_sub_and_fetch(&val, 1);
62#endif
63        return 0;
64      }
65" LLVM_HAS_ATOMICS)
66
67if( NOT LLVM_HAS_ATOMICS )
68  message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
69endif()
70