1# atomic builtins are required for threading support.
2
3INCLUDE(CheckCXXSourceCompiles)
4INCLUDE(CheckLibraryExists)
5
6# Sometimes linking against libatomic is required for atomic ops, if
7# the platform doesn't support lock-free atomics.
8
9function(check_working_cxx_atomics varname)
10  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
11  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -std=c++11")
12  CHECK_CXX_SOURCE_COMPILES("
13#include <atomic>
14std::atomic<int> x;
15std::atomic<short> y;
16std::atomic<char> z;
17int main() {
18  ++z;
19  ++y;
20  return ++x;
21}
22" ${varname})
23  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
24endfunction(check_working_cxx_atomics)
25
26function(check_working_cxx_atomics64 varname)
27  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
28  set(CMAKE_REQUIRED_FLAGS "-std=c++11 ${CMAKE_REQUIRED_FLAGS}")
29  CHECK_CXX_SOURCE_COMPILES("
30#include <atomic>
31#include <cstdint>
32std::atomic<uint64_t> x (0);
33int main() {
34  uint64_t i = x.load(std::memory_order_relaxed);
35  return 0;
36}
37" ${varname})
38  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
39endfunction(check_working_cxx_atomics64)
40
41
42# Check for (non-64-bit) atomic operations.
43if(MSVC)
44  set(HAVE_CXX_ATOMICS_WITHOUT_LIB True)
45elseif(LLVM_COMPILER_IS_GCC_COMPATIBLE)
46  # First check if atomics work without the library.
47  check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
48  # If not, check if the library exists, and atomics work with it.
49  if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
50    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
51    if(HAVE_LIBATOMIC)
52      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
53      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
54      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
55        message(FATAL_ERROR "Host compiler must support std::atomic!")
56      endif()
57    else()
58      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
59    endif()
60  endif()
61endif()
62
63# Check for 64 bit atomic operations.
64if(MSVC)
65  set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
66elseif(LLVM_COMPILER_IS_GCC_COMPATIBLE)
67  # First check if atomics work without the library.
68  check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
69  # If not, check if the library exists, and atomics work with it.
70  if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
71    check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
72    if(HAVE_CXX_LIBATOMICS64)
73      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
74      check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
75      if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
76        message(FATAL_ERROR "Host compiler must support 64-bit std::atomic!")
77      endif()
78    else()
79      message(FATAL_ERROR "Host compiler appears to require libatomic for 64-bit operations, but cannot find it.")
80    endif()
81  endif()
82endif()
83
84## TODO: This define is only used for the legacy atomic operations in
85## llvm's Atomic.h, which should be replaced.  Other code simply
86## assumes C++11 <atomic> works.
87CHECK_CXX_SOURCE_COMPILES("
88#ifdef _MSC_VER
89#include <windows.h>
90#endif
91int main() {
92#ifdef _MSC_VER
93        volatile LONG val = 1;
94        MemoryBarrier();
95        InterlockedCompareExchange(&val, 0, 1);
96        InterlockedIncrement(&val);
97        InterlockedDecrement(&val);
98#else
99        volatile unsigned long val = 1;
100        __sync_synchronize();
101        __sync_val_compare_and_swap(&val, 1, 0);
102        __sync_add_and_fetch(&val, 1);
103        __sync_sub_and_fetch(&val, 1);
104#endif
105        return 0;
106      }
107" LLVM_HAS_ATOMICS)
108
109if( NOT LLVM_HAS_ATOMICS )
110  message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
111endif()
112