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      1 # atomic builtins are required for threading support.
      2 
      3 INCLUDE(CheckCXXSourceCompiles)
      4 
      5 # Sometimes linking against libatomic is required for atomic ops, if
      6 # the platform doesn't support lock-free atomics.
      7 
      8 function(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>
     13 std::atomic<int> x;
     14 int main() {
     15   return x;
     16 }
     17 " ${varname})
     18   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
     19 endfunction(check_working_cxx_atomics)
     20 
     21 function(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>
     27 std::atomic<uint64_t> x (0);
     28 int 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})
     34 endfunction(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.
     39 if (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()
     55 endif()
     56 
     57 # Check for 64 bit atomic operations.
     58 if(MSVC)
     59   set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
     60 else()
     61   check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
     62 endif()
     63 
     64 # If not, check if the library exists, and atomics work with it.
     65 if(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()
     76 endif()
     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.
     81 CHECK_CXX_SOURCE_COMPILES("
     82 #ifdef _MSC_VER
     83 #include <Intrin.h> /* Workaround for PR19898. */
     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