--- a/include/llvm/Support/Casting.h	Sun Dec 23 19:23:36 2018 +0900
+++ b/include/llvm/Support/Casting.h	Wed Aug 14 19:46:37 2019 +0900
@@ -1,9 +1,8 @@
 //===- llvm/Support/Casting.h - Allow flexible, checked, casts --*- C++ -*-===//
 //
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
@@ -60,7 +59,7 @@
   }
 };
 
-/// \brief Always allow upcasts, and perform no dynamic check for them.
+/// Always allow upcasts, and perform no dynamic check for them.
 template <typename To, typename From>
 struct isa_impl<
     To, From, typename std::enable_if<std::is_base_of<To, From>::value>::type> {
@@ -144,6 +143,16 @@
                        typename simplify_type<const Y>::SimpleType>::doit(Val);
 }
 
+// isa_and_nonnull<X> - Functionally identical to isa, except that a null value
+// is accepted.
+//
+template <class X, class Y>
+LLVM_NODISCARD inline bool isa_and_nonnull(const Y &Val) {
+  if (!Val)
+    return false;
+  return isa<X>(Val);
+}
+
 //===----------------------------------------------------------------------===//
 //                          cast<x> Support Templates
 //===----------------------------------------------------------------------===//