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diff --git a/include/clang/Basic/FileSystemStatCache.h b/include/clang/Basic/FileSystemStatCache.h
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+++ b/include/clang/Basic/FileSystemStatCache.h
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+//===--- FileSystemStatCache.h - Caching for 'stat' calls -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the FileSystemStatCache interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_FILESYSTEMSTATCACHE_H
+#define LLVM_CLANG_FILESYSTEMSTATCACHE_H
+
+#include "llvm/ADT/OwningPtr.h"
+#include "llvm/ADT/StringMap.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+
+namespace clang {
+
+/// \brief Abstract interface for introducing a FileManager cache for 'stat'
+/// system calls, which is used by precompiled and pretokenized headers to
+/// improve performance.
+class FileSystemStatCache {
+protected:
+  llvm::OwningPtr<FileSystemStatCache> NextStatCache;
+  
+public:
+  virtual ~FileSystemStatCache() {}
+  
+  enum LookupResult {
+    CacheHitExists,   //< We know the file exists and its cached stat data.
+    CacheHitMissing,  //< We know that the file doesn't exist.
+    CacheMiss         //< We don't know anything about the file.
+  };
+  
+  virtual LookupResult getStat(const char *Path, struct stat &StatBuf) = 0;
+  
+  /// \brief Sets the next stat call cache in the chain of stat caches.
+  /// Takes ownership of the given stat cache.
+  void setNextStatCache(FileSystemStatCache *Cache) {
+    NextStatCache.reset(Cache);
+  }
+  
+  /// \brief Retrieve the next stat call cache in the chain.
+  FileSystemStatCache *getNextStatCache() { return NextStatCache.get(); }
+  
+  /// \brief Retrieve the next stat call cache in the chain, transferring
+  /// ownership of this cache (and, transitively, all of the remaining caches)
+  /// to the caller.
+  FileSystemStatCache *takeNextStatCache() { return NextStatCache.take(); }
+  
+protected:
+  LookupResult statChained(const char *Path, struct stat &StatBuf) {
+    if (FileSystemStatCache *Next = getNextStatCache())
+      return Next->getStat(Path, StatBuf);
+    
+    return CacheMiss;
+  }
+};
+
+/// \brief A stat "cache" that can be used by FileManager to keep
+/// track of the results of stat() calls that occur throughout the
+/// execution of the front end.
+class MemorizeStatCalls : public FileSystemStatCache {
+public:
+  /// \brief The result of a stat() call.
+  ///
+  /// The first member is the result of calling stat(). If stat()
+  /// found something, the second member is a copy of the stat
+  /// structure.
+  typedef std::pair<int, struct stat> StatResult;
+  
+  /// \brief The set of stat() calls that have been
+  llvm::StringMap<StatResult, llvm::BumpPtrAllocator> StatCalls;
+  
+  typedef llvm::StringMap<StatResult, llvm::BumpPtrAllocator>::const_iterator
+  iterator;
+  
+  iterator begin() const { return StatCalls.begin(); }
+  iterator end() const { return StatCalls.end(); }
+  
+  virtual LookupResult getStat(const char *Path, struct stat &StatBuf);
+};
+
+} // end namespace clang
+
+#endif