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diff --git a/third_party/llvm-project/include/llvm/Support/FileOutputBuffer.h b/third_party/llvm-project/include/llvm/Support/FileOutputBuffer.h
new file mode 100644
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+++ b/third_party/llvm-project/include/llvm/Support/FileOutputBuffer.h
@@ -0,0 +1,88 @@
+//=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Utility for creating a in-memory buffer that will be written to a file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H
+#define LLVM_SUPPORT_FILEOUTPUTBUFFER_H
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
+
+namespace llvm {
+/// FileOutputBuffer - This interface provides simple way to create an in-memory
+/// buffer which will be written to a file. During the lifetime of these
+/// objects, the content or existence of the specified file is undefined. That
+/// is, creating an OutputBuffer for a file may immediately remove the file.
+/// If the FileOutputBuffer is committed, the target file's content will become
+/// the buffer content at the time of the commit.  If the FileOutputBuffer is
+/// not committed, the file will be deleted in the FileOutputBuffer destructor.
+class FileOutputBuffer {
+public:
+  enum {
+    /// set the 'x' bit on the resulting file
+    F_executable = 1,
+
+    /// Don't use mmap and instead write an in-memory buffer to a file when this
+    /// buffer is closed.
+    F_no_mmap = 2,
+  };
+
+  /// 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);
+
+  /// Returns a pointer to the start of the buffer.
+  virtual uint8_t *getBufferStart() const = 0;
+
+  /// Returns a pointer to the end of the buffer.
+  virtual uint8_t *getBufferEnd() const = 0;
+
+  /// Returns size of the buffer.
+  virtual size_t getBufferSize() const = 0;
+
+  /// Returns path where file will show up if buffer is committed.
+  StringRef getPath() const { return FinalPath; }
+
+  /// Flushes the content of the buffer to its file and deallocates the
+  /// buffer.  If commit() is not called before this object's destructor
+  /// is called, the file is deleted in the destructor. The optional parameter
+  /// is used if it turns out you want the file size to be smaller than
+  /// initially requested.
+  virtual Error commit() = 0;
+
+  /// If this object was previously committed, the destructor just deletes
+  /// this object.  If this object was not committed, the destructor
+  /// 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) {}
+
+  std::string FinalPath;
+};
+} // end namespace llvm
+
+#endif