diff --git a/llvm/cmake/modules/CheckAtomic.cmake b/llvm/cmake/modules/CheckAtomic.cmake
--- a/llvm/cmake/modules/CheckAtomic.cmake
+++ b/llvm/cmake/modules/CheckAtomic.cmake
@@ -39,46 +39,45 @@
 endfunction(check_working_cxx_atomics64)
 
 
-# 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 )
+    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!")
+        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()
-elseif(MSVC)
-  set(HAVE_CXX_ATOMICS_WITHOUT_LIB True)
 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 64-bit std::atomic!")
+  # 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()
-  else()
-    message(FATAL_ERROR "Host compiler appears to require libatomic for 64-bit operations, but cannot find it.")
   endif()
 endif()