Update CheckAtomic.cmake from llvm.

As CheckAtomic.cmake is a copy and we need to keep sync.

a348de480d34257ffe394ab51b880c9aef243d80
Date: 04/18/2020
repo: https://github.com/llvm/llvm-project
file: /llvm/cmake/modules/CheckAtomic.cmake

1 files changed, 34 insertions, 30 deletions

diff --git a/modules/CheckAtomic.cmake b/modules/CheckAtomic.cmake
index 900ae7e0..41cff207 100644
--- a/modules/CheckAtomic.cmake
+++ b/modules/CheckAtomic.cmake
@@ -27,8 +27,12 @@ function(check_working_cxx_atomics varname)
   check_cxx_source_compiles("
   #include <atomic>
   std::atomic<int> x;
+  std::atomic<short> y;
+  std::atomic<char> z;
   int main() {
-    return std::atomic_is_lock_free(&x);
+    ++z;
+    ++y;
+    return ++x;
   }
   " ${varname})
   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
@@ -43,50 +47,50 @@ function(check_working_cxx_atomics64 varname)
   std::atomic<uint64_t> x (0);
   int main() {
     uint64_t i = x.load(std::memory_order_relaxed);
-    return std::atomic_is_lock_free(&x);
+    return 0;
   }
   " ${varname})
   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
 endfunction()
 
-
-# This isn't necessary on MSVC, so avoid command-line switch annoyance
-# by only running on GCC-like hosts.
-if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
+# Check for (non-64-bit) atomic operations.
+if(MSVC)
+  set(HAVE_CXX_ATOMICS_WITHOUT_LIB True)
+elseif(LLVM_COMPILER_IS_GCC_COMPATIBLE)
   # First check if atomics work without the library.
   check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB)
   # If not, check if the library exists, and atomics work with it.
   if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
-     check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
-     if(HAVE_LIBATOMIC)
-        list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
-        check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
-        if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
-           message(FATAL_ERROR "Host compiler must support std::atomic!")
-        endif()
-     else()
-        message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
-     endif()
+    check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_LIBATOMIC)
+    if(HAVE_LIBATOMIC)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+      check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB)
+      if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
+        message(FATAL_ERROR "Host compiler must support std::atomic!")
+      endif()
+    else()
+      message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
+    endif()
   endif()
 endif()
 
 # Check for 64 bit atomic operations.
 if(MSVC)
   set(HAVE_CXX_ATOMICS64_WITHOUT_LIB True)
-else()
+elseif(LLVM_COMPILER_IS_GCC_COMPATIBLE)
+  # First check if atomics work without the library.
   check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITHOUT_LIB)
-endif()
-
-# If not, check if the library exists, and atomics work with it.
-if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
-  check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
-  if(HAVE_CXX_LIBATOMICS64)
-     list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
-     check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
-     if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
-        message(FATAL_ERROR "Host compiler must support std::atomic!")
-     endif()
-  else()
-     message(FATAL_ERROR "Host compiler appears to require libatomic, but cannot find it.")
+  # If not, check if the library exists, and atomics work with it.
+  if(NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+    check_library_exists(atomic __atomic_load_8 "" HAVE_CXX_LIBATOMICS64)
+    if(HAVE_CXX_LIBATOMICS64)
+      list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+      check_working_cxx_atomics64(HAVE_CXX_ATOMICS64_WITH_LIB)
+      if (NOT HAVE_CXX_ATOMICS64_WITH_LIB)
+        message(FATAL_ERROR "Host compiler must support 64-bit std::atomic!")
+      endif()
+    else()
+      message(FATAL_ERROR "Host compiler appears to require libatomic for 64-bit operations, but cannot find it.")
+    endif()
   endif()
 endif()