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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;
15int main() {
16  return x;
17}
18" ${varname})
19  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
20endfunction(check_working_cxx_atomics)
21
22function(check_working_cxx_atomics64 varname)
23  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
24  set(CMAKE_REQUIRED_FLAGS "-std=c++11 ${CMAKE_REQUIRED_FLAGS}")
25  CHECK_CXX_SOURCE_COMPILES("
26#include <atomic>
27#include <cstdint>
28std::atomic<uint64_t> x (0);
29int main() {
30  uint64_t i = x.load(std::memory_order_relaxed);
31  return 0;
32}
33" ${varname})
34  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
35endfunction(check_working_cxx_atomics64)
36
37
38# This isn't necessary on MSVC, so avoid command-line switch annoyance
39# by only running on GCC-like hosts.
40if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
41  # First check if atomics work without the library.
42  check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
43  # If not, check if the library exists, and atomics work with it.
44  if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
45    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
46    if( HAVE_LIBATOMIC )
47      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
48      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
49      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
50	message(FATAL_ERROR "Host compiler must support std::atomic!")
51      endif()
52    else()
53      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
54    endif()
55  endif()
56endif()
57
58# Check for 64 bit atomic operations.
59if(MSVC)
60  set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
61else()
62  check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
63endif()
64
65# If not, check if the library exists, and atomics work with it.
66if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
67  check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
68  if(HAVE_CXX_LIBATOMICS64)
69    list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
70    check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
71    if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
72      message(FATAL_ERROR "Host compiler must support std::atomic!")
73    endif()
74  else()
75    message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
76  endif()
77endif()
78
79## TODO: This define is only used for the legacy atomic operations in
80## llvm's Atomic.h, which should be replaced.  Other code simply
81## assumes C++11 <atomic> works.
82CHECK_CXX_SOURCE_COMPILES("
83#ifdef _MSC_VER
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