Home | History | Annotate | Download | only in modules 
      1 # atomic builtins are required for threading support.
      2 
      3 INCLUDE(CheckCXXSourceCompiles)
      4 INCLUDE(CheckLibraryExists)
      5 
      6 # Sometimes linking against libatomic is required for atomic ops, if
      7 # the platform doesn't support lock-free atomics.
      8 
      9 function(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>
     14 std::atomic<int> x;
     15 int main() {
     16   return x;
     17 }
     18 " ${varname})
     19   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
     20 endfunction(check_working_cxx_atomics)
     21 
     22 function(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>
     28 std::atomic<uint64_t> x (0);
     29 int 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})
     35 endfunction(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.
     40 if (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()
     56 endif()
     57 
     58 # Check for 64 bit atomic operations.
     59 if(MSVC)
     60   set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
     61 else()
     62   check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
     63 endif()
     64 
     65 # If not, check if the library exists, and atomics work with it.
     66 if(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()
     77 endif()
     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.
     82 CHECK_CXX_SOURCE_COMPILES("
     83 #ifdef _MSC_VER
     84 #include <windows.h>
     85 #endif
     86 int 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 
    104 if( NOT LLVM_HAS_ATOMICS )
    105   message(STATUS "Warning: LLVM will be built thread-unsafe because atomic builtins are missing")
    106 endif()
    107