• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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
21function(check_working_cxx_atomics64 varname)
22  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
23  set(CMAKE_REQUIRED_FLAGS "-std=c++11 ${CMAKE_REQUIRED_FLAGS}")
24  CHECK_CXX_SOURCE_COMPILES("
25#include <atomic>
26#include <cstdint>
27std::atomic<uint64_t> x (0);
28int main() {
29  uint64_t i = x.load(std::memory_order_relaxed);
30  return 0;
31}
32" ${varname})
33  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
34endfunction(check_working_cxx_atomics64)
35
36
37# This isn't necessary on MSVC, so avoid command-line switch annoyance
38# by only running on GCC-like hosts.
39if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
40  # First check if atomics work without the library.
41  check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
42  # If not, check if the library exists, and atomics work with it.
43  if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
44    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
45    if( HAVE_LIBATOMIC )
46      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
47      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
48      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
49	message(FATAL_ERROR "Host compiler must support std::atomic!")
50      endif()
51    else()
52      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
53    endif()
54  endif()
55endif()
56
57# Check for 64 bit atomic operations.
58if(MSVC)
59  set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
60else()
61  check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
62endif()
63
64# If not, check if the library exists, and atomics work with it.
65if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
66  check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
67  if(HAVE_CXX_LIBATOMICS64)
68    list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
69    check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
70    if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
71      message(FATAL_ERROR "Host compiler must support std::atomic!")
72    endif()
73  else()
74    message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
75  endif()
76endif()
77
78## TODO: This define is only used for the legacy atomic operations in
79## llvm's Atomic.h, which should be replaced.  Other code simply
80## assumes C++11 <atomic> works.
81CHECK_CXX_SOURCE_COMPILES("
82#ifdef _MSC_VER
83#include <Intrin.h> /* Workaround for PR19898. */
84#include <windows.h>
85#endif
86int main() {
87#ifdef _MSC_VER
88        volatile LONG val = 1;
89        MemoryBarrier();
90        InterlockedCompareExchange(&val, 0, 1);
91        InterlockedIncrement(&val);
92        InterlockedDecrement(&val);
93#else
94        volatile unsigned long val = 1;
95        __sync_synchronize();
96        __sync_val_compare_and_swap(&val, 1, 0);
97        __sync_add_and_fetch(&val, 1);
98        __sync_sub_and_fetch(&val, 1);
99#endif
100        return 0;
101      }
102" LLVM_HAS_ATOMICS)
103
104if( NOT LLVM_HAS_ATOMICS )
105  message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
106endif()
107