Index: include/llvm/Support/Compiler.h
===================================================================
--- include/llvm/Support/Compiler.h
+++ include/llvm/Support/Compiler.h
@@ -38,6 +38,13 @@
 
 #ifndef __has_cpp_attribute
 # define __has_cpp_attribute(x) 0
+# define __has_cpp_attribute_qualified(x) 0
+#elif defined(_MSC_VER)
+// MSVC only allows simple identifier in feature-test macros,
+// and reports IntelliSense error otherwise.
+# define __has_cpp_attribute_qualified(x) 0
+#else
+# define __has_cpp_attribute_qualified __has_cpp_attribute
 #endif
 
 #ifndef __has_builtin
@@ -127,7 +134,7 @@
 // Workaround for llvm.org/PR23435, since clang 3.6 and below emit a spurious
 // error when __has_cpp_attribute is given a scoped attribute in C mode.
 #define LLVM_NODISCARD
-#elif __has_cpp_attribute(clang::warn_unused_result)
+#elif __has_cpp_attribute_qualified(clang::warn_unused_result)
 #define LLVM_NODISCARD [[clang::warn_unused_result]]
 #else
 #define LLVM_NODISCARD
@@ -140,7 +147,7 @@
 // The clang-tidy check bugprone-use-after-move recognizes this attribute as a
 // marker that a moved-from object has left the indeterminate state and can be
 // reused.
-#if __has_cpp_attribute(clang::reinitializes)
+#if __has_cpp_attribute_qualified(clang::reinitializes)
 #define LLVM_ATTRIBUTE_REINITIALIZES [[clang::reinitializes]]
 #else
 #define LLVM_ATTRIBUTE_REINITIALIZES
@@ -243,13 +250,13 @@
 /// LLVM_FALLTHROUGH - Mark fallthrough cases in switch statements.
 #if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
 #define LLVM_FALLTHROUGH [[fallthrough]]
-#elif __has_cpp_attribute(gnu::fallthrough)
+#elif __has_cpp_attribute_qualified(gnu::fallthrough)
 #define LLVM_FALLTHROUGH [[gnu::fallthrough]]
 #elif !__cplusplus
 // Workaround for llvm.org/PR23435, since clang 3.6 and below emit a spurious
 // error when __has_cpp_attribute is given a scoped attribute in C mode.
 #define LLVM_FALLTHROUGH
-#elif __has_cpp_attribute(clang::fallthrough)
+#elif __has_cpp_attribute_qualified(clang::fallthrough)
 #define LLVM_FALLTHROUGH [[clang::fallthrough]]
 #else
 #define LLVM_FALLTHROUGH