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diff --git a/include/clang/Basic/MemoryBufferCache.h b/include/clang/Basic/MemoryBufferCache.h
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+++ b/include/clang/Basic/MemoryBufferCache.h
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+//===- MemoryBufferCache.h - Cache for loaded memory buffers ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
+#define LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
+
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/StringMap.h"
+#include <memory>
+
+namespace llvm {
+class MemoryBuffer;
+} // end namespace llvm
+
+namespace clang {
+
+/// Manage memory buffers across multiple users.
+///
+/// Ensures that multiple users have a consistent view of each buffer.  This is
+/// used by \a CompilerInstance when building PCMs to ensure that each \a
+/// ModuleManager sees the same files.
+///
+/// \a finalizeCurrentBuffers() should be called before creating a new user.
+/// This locks in the current buffers, ensuring that no buffer that has already
+/// been accessed can be purged, preventing use-after-frees.
+class MemoryBufferCache : public llvm::RefCountedBase<MemoryBufferCache> {
+  struct BufferEntry {
+    std::unique_ptr<llvm::MemoryBuffer> Buffer;
+
+    /// Track the timeline of when this was added to the cache.
+    unsigned Index;
+  };
+
+  /// Cache of buffers.
+  llvm::StringMap<BufferEntry> Buffers;
+
+  /// Monotonically increasing index.
+  unsigned NextIndex = 0;
+
+  /// Bumped to prevent "older" buffers from being removed.
+  unsigned FirstRemovableIndex = 0;
+
+public:
+  /// Store the Buffer under the Filename.
+  ///
+  /// \pre There is not already buffer is not already in the cache.
+  /// \return a reference to the buffer as a convenience.
+  llvm::MemoryBuffer &addBuffer(llvm::StringRef Filename,
+                                std::unique_ptr<llvm::MemoryBuffer> Buffer);
+
+  /// Try to remove a buffer from the cache.
+  ///
+  /// \return false on success, iff \c !isBufferFinal().
+  bool tryToRemoveBuffer(llvm::StringRef Filename);
+
+  /// Get a pointer to the buffer if it exists; else nullptr.
+  llvm::MemoryBuffer *lookupBuffer(llvm::StringRef Filename);
+
+  /// Check whether the buffer is final.
+  ///
+  /// \return true iff \a finalizeCurrentBuffers() has been called since the
+  /// buffer was added.  This prevents buffers from being removed.
+  bool isBufferFinal(llvm::StringRef Filename);
+
+  /// Finalize the current buffers in the cache.
+  ///
+  /// Should be called when creating a new user to ensure previous uses aren't
+  /// invalidated.
+  void finalizeCurrentBuffers();
+};
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H