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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 {
+    CacheExists,   //< We know the file exists and its cached stat data.
+    CacheMissing   //< We know that the file doesn't exist.
+  };
+
+  /// FileSystemStatCache::get - Get the 'stat' information for the specified
+  /// path, using the cache to accellerate it if possible.  This returns true if
+  /// the path does not exist or false if it exists.
+  ///
+  /// If FileDescriptor is non-null, then this lookup should only return success
+  /// for files (not directories).  If it is null this lookup should only return
+  /// success for directories (not files).  On a successful file lookup, the
+  /// implementation can optionally fill in FileDescriptor with a valid
+  /// descriptor and the client guarantees that it will close it.
+  static bool get(const char *Path, struct stat &StatBuf, int *FileDescriptor,
+                  FileSystemStatCache *Cache);
+  
+  
+  /// \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:
+  virtual LookupResult getStat(const char *Path, struct stat &StatBuf,
+                               int *FileDescriptor) = 0;
+
+  LookupResult statChained(const char *Path, struct stat &StatBuf,
+                           int *FileDescriptor) {
+    if (FileSystemStatCache *Next = getNextStatCache())
+      return Next->getStat(Path, StatBuf, FileDescriptor);
+    
+    // If we hit the end of the list of stat caches to try, just compute and
+    // return it without a cache.
+    return get(Path, StatBuf, FileDescriptor, 0) ? CacheMissing : CacheExists;
+  }
+};
+
+/// \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 set of stat() calls that have been seen.
+  llvm::StringMap<struct stat, llvm::BumpPtrAllocator> StatCalls;
+  
+  typedef llvm::StringMap<struct stat, 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,
+                               int *FileDescriptor);
+};
+
+} // end namespace clang
+
+#endif