--- a/include/llvm/Support/FileOutputBuffer.h	Sun Dec 23 19:23:36 2018 +0900
+++ b/include/llvm/Support/FileOutputBuffer.h	Wed Aug 14 19:46:37 2019 +0900
@@ -1,9 +1,8 @@
 //=== FileOutputBuffer.h - File Output Buffer -------------------*- 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
 //
 //===----------------------------------------------------------------------===//
 //
@@ -30,13 +29,20 @@
 /// not committed, the file will be deleted in the FileOutputBuffer destructor.
 class FileOutputBuffer {
 public:
-  enum  {
-    F_executable = 1  /// set the 'x' bit on the resulting file
+  enum {
+    /// set the 'x' bit on the resulting file
+    F_executable = 1,
   };
 
   /// Factory method to create an OutputBuffer object which manages a read/write
   /// buffer of the specified size. When committed, the buffer will be written
   /// to the file at the specified path.
+  ///
+  /// When F_modify is specified and \p FilePath refers to an existing on-disk
+  /// file \p Size may be set to -1, in which case the entire file is used.
+  /// Otherwise, the file shrinks or grows as necessary based on the value of
+  /// \p Size.  It is an error to specify F_modify and Size=-1 if \p FilePath
+  /// does not exist.
   static Expected<std::unique_ptr<FileOutputBuffer>>
   create(StringRef FilePath, size_t Size, unsigned Flags = 0);
 
@@ -64,6 +70,10 @@
   /// deallocates the buffer and the target file is never written.
   virtual ~FileOutputBuffer() {}
 
+  /// This removes the temporary file (unless it already was committed)
+  /// but keeps the memory mapping alive.
+  virtual void discard() {}
+
 protected:
   FileOutputBuffer(StringRef Path) : FinalPath(Path) {}