Index: llvm/include/llvm/Support/Compiler.h
===================================================================
--- llvm/include/llvm/Support/Compiler.h
+++ llvm/include/llvm/Support/Compiler.h
@@ -122,6 +122,11 @@
 /// LLVM_NODISCARD - Warn if a type or return value is discarded.
 #if __cplusplus > 201402L && __has_cpp_attribute(nodiscard)
 #define LLVM_NODISCARD [[nodiscard]]
+// Detect MSVC directly, since __cplusplus still defaults to old version
+#elif _MSVC_LANG >= 201703L
+#define LLVM_NODISCARD [[nodiscard]]
+#elif _MSC_VER
+#define LLVM_NODISCARD
 #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.
@@ -242,6 +247,11 @@
 /// LLVM_FALLTHROUGH - Mark fallthrough cases in switch statements.
 #if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
 #define LLVM_FALLTHROUGH [[fallthrough]]
+// Detect MSVC directly, since __cplusplus still defaults to old version
+#elif _MSVC_LANG >= 201703L
+#define LLVM_FALLTHROUGH [[fallthrough]]
+#elif _MSC_VER
+#define LLVM_FALLTHROUGH
 #elif __has_cpp_attribute(gnu::fallthrough)
 #define LLVM_FALLTHROUGH [[gnu::fallthrough]]
 #elif !__cplusplus