diff --git a/lib/Basic/FileManager.cpp b/lib/Basic/FileManager.cpp
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--- /dev/null
+++ b/lib/Basic/FileManager.cpp
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+///===--- FileManager.cpp - File System Probing and Caching ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements the FileManager interface.
+//
+//===----------------------------------------------------------------------===//
+//
+// TODO: This should index all interesting directories with dirent calls.
+//  getdirentries ?
+//  opendir/readdir_r/closedir ?
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/FileManager.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/System/Path.h"
+#include "llvm/Config/config.h"
+#include <map>
+#include <set>
+#include <string>
+using namespace clang;
+
+// FIXME: Enhance libsystem to support inode and other fields.
+#include <sys/stat.h>
+
+#if defined(_MSC_VER)
+#define S_ISDIR(s) (_S_IFDIR & s)
+#endif
+
+/// NON_EXISTENT_DIR - A special value distinct from null that is used to
+/// represent a dir name that doesn't exist on the disk.
+#define NON_EXISTENT_DIR reinterpret_cast<DirectoryEntry*>((intptr_t)-1)
+
+//===----------------------------------------------------------------------===//
+// Windows.
+//===----------------------------------------------------------------------===//
+
+#ifdef LLVM_ON_WIN32
+
+#define IS_DIR_SEPARATOR_CHAR(x) ((x) == '/' || (x) == '\\')
+
+namespace {
+  static std::string GetFullPath(const char *relPath) {
+    char *absPathStrPtr = _fullpath(NULL, relPath, 0);
+    assert(absPathStrPtr && "_fullpath() returned NULL!");
+
+    std::string absPath(absPathStrPtr);
+
+    free(absPathStrPtr);
+    return absPath;
+  }
+}
+
+class FileManager::UniqueDirContainer {
+  /// UniqueDirs - Cache from full path to existing directories/files.
+  ///
+  llvm::StringMap<DirectoryEntry> UniqueDirs;
+
+public:
+  DirectoryEntry &getDirectory(const char *Name, struct stat &StatBuf) {
+    std::string FullPath(GetFullPath(Name));
+    return UniqueDirs.GetOrCreateValue(
+                              FullPath.c_str(),
+                              FullPath.c_str() + FullPath.size()
+                                                                ).getValue();
+  }
+
+  size_t size() { return UniqueDirs.size(); }
+};
+
+class FileManager::UniqueFileContainer {
+  /// UniqueFiles - Cache from full path to existing directories/files.
+  ///
+  llvm::StringMap<FileEntry, llvm::BumpPtrAllocator> UniqueFiles;
+
+public:
+  FileEntry &getFile(const char *Name, struct stat &StatBuf) {
+    std::string FullPath(GetFullPath(Name));
+    return UniqueFiles.GetOrCreateValue(
+                               FullPath.c_str(),
+                               FullPath.c_str() + FullPath.size()
+                                                                 ).getValue();
+  }
+
+  size_t size() { return UniqueFiles.size(); }
+};
+
+//===----------------------------------------------------------------------===//
+// Unix-like Systems.
+//===----------------------------------------------------------------------===//
+
+#else
+
+#define IS_DIR_SEPARATOR_CHAR(x) ((x) == '/')
+
+class FileManager::UniqueDirContainer {
+  /// UniqueDirs - Cache from ID's to existing directories/files.
+  ///
+  std::map<std::pair<dev_t, ino_t>, DirectoryEntry> UniqueDirs;
+
+public:
+  DirectoryEntry &getDirectory(const char *Name, struct stat &StatBuf) {
+    return UniqueDirs[std::make_pair(StatBuf.st_dev, StatBuf.st_ino)];
+  }
+
+  size_t size() { return UniqueDirs.size(); }
+};
+
+class FileManager::UniqueFileContainer {
+  /// UniqueFiles - Cache from ID's to existing directories/files.
+  ///
+  std::set<FileEntry> UniqueFiles;
+
+public:
+  FileEntry &getFile(const char *Name, struct stat &StatBuf) {
+    return
+      const_cast<FileEntry&>(
+                    *UniqueFiles.insert(FileEntry(StatBuf.st_dev,
+                                                  StatBuf.st_ino,
+                                                  StatBuf.st_mode)).first);
+  }
+
+  size_t size() { return UniqueFiles.size(); }
+};
+
+#endif
+
+//===----------------------------------------------------------------------===//
+// Common logic.
+//===----------------------------------------------------------------------===//
+
+FileManager::FileManager()
+  : UniqueDirs(*new UniqueDirContainer),
+    UniqueFiles(*new UniqueFileContainer),
+    DirEntries(64), FileEntries(64), NextFileUID(0) {
+  NumDirLookups = NumFileLookups = 0;
+  NumDirCacheMisses = NumFileCacheMisses = 0;
+}
+
+FileManager::~FileManager() {
+  delete &UniqueDirs;
+  delete &UniqueFiles;
+  for (llvm::SmallVectorImpl<FileEntry *>::iterator
+         V = VirtualFileEntries.begin(),
+         VEnd = VirtualFileEntries.end();
+       V != VEnd; 
+       ++V)
+    delete *V;
+}
+
+void FileManager::addStatCache(StatSysCallCache *statCache, bool AtBeginning) {
+  assert(statCache && "No stat cache provided?");
+  if (AtBeginning || StatCache.get() == 0) {
+    statCache->setNextStatCache(StatCache.take());
+    StatCache.reset(statCache);
+    return;
+  }
+  
+  StatSysCallCache *LastCache = StatCache.get();
+  while (LastCache->getNextStatCache())
+    LastCache = LastCache->getNextStatCache();
+  
+  LastCache->setNextStatCache(statCache);
+}
+
+void FileManager::removeStatCache(StatSysCallCache *statCache) {
+  if (!statCache)
+    return;
+  
+  if (StatCache.get() == statCache) {
+    // This is the first stat cache.
+    StatCache.reset(StatCache->takeNextStatCache());
+    return;
+  }
+  
+  // Find the stat cache in the list.
+  StatSysCallCache *PrevCache = StatCache.get();
+  while (PrevCache && PrevCache->getNextStatCache() != statCache)
+    PrevCache = PrevCache->getNextStatCache();
+  if (PrevCache)
+    PrevCache->setNextStatCache(statCache->getNextStatCache());
+  else
+    assert(false && "Stat cache not found for removal");
+}
+
+/// \brief Retrieve the directory that the given file name resides in.
+static const DirectoryEntry *getDirectoryFromFile(FileManager &FileMgr,
+                                                  const char *NameStart,
+                                                  const char *NameEnd) {
+  // Figure out what directory it is in.   If the string contains a / in it,
+  // strip off everything after it.
+  // FIXME: this logic should be in sys::Path.
+  const char *SlashPos = NameEnd-1;
+  while (SlashPos >= NameStart && !IS_DIR_SEPARATOR_CHAR(SlashPos[0]))
+    --SlashPos;
+  // Ignore duplicate //'s.
+  while (SlashPos > NameStart && IS_DIR_SEPARATOR_CHAR(SlashPos[-1]))
+    --SlashPos;
+
+  if (SlashPos < NameStart) {
+    // Use the current directory if file has no path component.
+    const char *Name = ".";
+    return FileMgr.getDirectory(Name, Name+1);
+  } else if (SlashPos == NameEnd-1)
+    return 0;       // If filename ends with a /, it's a directory.
+  else
+    return FileMgr.getDirectory(NameStart, SlashPos);
+}
+
+/// getDirectory - Lookup, cache, and verify the specified directory.  This
+/// returns null if the directory doesn't exist.
+///
+const DirectoryEntry *FileManager::getDirectory(const char *NameStart,
+                                                const char *NameEnd) {
+  // stat doesn't like trailing separators (at least on Windows).
+  if (((NameEnd - NameStart) > 1) &&
+      ((*(NameEnd - 1) == '/') || (*(NameEnd - 1) == '\\')))
+    NameEnd--;
+
+  ++NumDirLookups;
+  llvm::StringMapEntry<DirectoryEntry *> &NamedDirEnt =
+    DirEntries.GetOrCreateValue(NameStart, NameEnd);
+
+  // See if there is already an entry in the map.
+  if (NamedDirEnt.getValue())
+    return NamedDirEnt.getValue() == NON_EXISTENT_DIR
+              ? 0 : NamedDirEnt.getValue();
+
+  ++NumDirCacheMisses;
+
+  // By default, initialize it to invalid.
+  NamedDirEnt.setValue(NON_EXISTENT_DIR);
+
+  // Get the null-terminated directory name as stored as the key of the
+  // DirEntries map.
+  const char *InterndDirName = NamedDirEnt.getKeyData();
+
+  // Check to see if the directory exists.
+  struct stat StatBuf;
+  if (stat_cached(InterndDirName, &StatBuf) ||   // Error stat'ing.
+      !S_ISDIR(StatBuf.st_mode))          // Not a directory?
+    return 0;
+
+  // It exists.  See if we have already opened a directory with the same inode.
+  // This occurs when one dir is symlinked to another, for example.
+  DirectoryEntry &UDE = UniqueDirs.getDirectory(InterndDirName, StatBuf);
+
+  NamedDirEnt.setValue(&UDE);
+  if (UDE.getName()) // Already have an entry with this inode, return it.
+    return &UDE;
+
+  // Otherwise, we don't have this directory yet, add it.  We use the string
+  // key from the DirEntries map as the string.
+  UDE.Name  = InterndDirName;
+  return &UDE;
+}
+
+/// NON_EXISTENT_FILE - A special value distinct from null that is used to
+/// represent a filename that doesn't exist on the disk.
+#define NON_EXISTENT_FILE reinterpret_cast<FileEntry*>((intptr_t)-1)
+
+/// getFile - Lookup, cache, and verify the specified file.  This returns null
+/// if the file doesn't exist.
+///
+const FileEntry *FileManager::getFile(const char *NameStart,
+                                      const char *NameEnd) {
+  ++NumFileLookups;
+
+  // See if there is already an entry in the map.
+  llvm::StringMapEntry<FileEntry *> &NamedFileEnt =
+    FileEntries.GetOrCreateValue(NameStart, NameEnd);
+
+  // See if there is already an entry in the map.
+  if (NamedFileEnt.getValue())
+    return NamedFileEnt.getValue() == NON_EXISTENT_FILE
+                 ? 0 : NamedFileEnt.getValue();
+
+  ++NumFileCacheMisses;
+
+  // By default, initialize it to invalid.
+  NamedFileEnt.setValue(NON_EXISTENT_FILE);
+
+
+  // Get the null-terminated file name as stored as the key of the
+  // FileEntries map.
+  const char *InterndFileName = NamedFileEnt.getKeyData();
+
+  const DirectoryEntry *DirInfo
+    = getDirectoryFromFile(*this, NameStart, NameEnd);
+  if (DirInfo == 0)  // Directory doesn't exist, file can't exist.
+    return 0;
+
+  // FIXME: Use the directory info to prune this, before doing the stat syscall.
+  // FIXME: This will reduce the # syscalls.
+
+  // Nope, there isn't.  Check to see if the file exists.
+  struct stat StatBuf;
+  //llvm::errs() << "STATING: " << Filename;
+  if (stat_cached(InterndFileName, &StatBuf) ||   // Error stat'ing.
+        S_ISDIR(StatBuf.st_mode)) {           // A directory?
+    // If this file doesn't exist, we leave a null in FileEntries for this path.
+    //llvm::errs() << ": Not existing\n";
+    return 0;
+  }
+  //llvm::errs() << ": exists\n";
+
+  // It exists.  See if we have already opened a file with the same inode.
+  // This occurs when one dir is symlinked to another, for example.
+  FileEntry &UFE = UniqueFiles.getFile(InterndFileName, StatBuf);
+
+  NamedFileEnt.setValue(&UFE);
+  if (UFE.getName())  // Already have an entry with this inode, return it.
+    return &UFE;
+
+  // Otherwise, we don't have this directory yet, add it.
+  // FIXME: Change the name to be a char* that points back to the 'FileEntries'
+  // key.
+  UFE.Name    = InterndFileName;
+  UFE.Size    = StatBuf.st_size;
+  UFE.ModTime = StatBuf.st_mtime;
+  UFE.Dir     = DirInfo;
+  UFE.UID     = NextFileUID++;
+  return &UFE;
+}
+
+const FileEntry *
+FileManager::getVirtualFile(const llvm::StringRef &Filename,
+                            off_t Size, time_t ModificationTime) {
+  const char *NameStart = Filename.begin(), *NameEnd = Filename.end();
+
+  ++NumFileLookups;
+
+  // See if there is already an entry in the map.
+  llvm::StringMapEntry<FileEntry *> &NamedFileEnt =
+    FileEntries.GetOrCreateValue(NameStart, NameEnd);
+
+  // See if there is already an entry in the map.
+  if (NamedFileEnt.getValue())
+    return NamedFileEnt.getValue() == NON_EXISTENT_FILE
+                 ? 0 : NamedFileEnt.getValue();
+
+  ++NumFileCacheMisses;
+
+  // By default, initialize it to invalid.
+  NamedFileEnt.setValue(NON_EXISTENT_FILE);
+
+  const DirectoryEntry *DirInfo
+    = getDirectoryFromFile(*this, NameStart, NameEnd);
+  if (DirInfo == 0)  // Directory doesn't exist, file can't exist.
+    return 0;
+
+  FileEntry *UFE = new FileEntry();
+  VirtualFileEntries.push_back(UFE);
+  NamedFileEnt.setValue(UFE);
+
+  UFE->Name    = NamedFileEnt.getKeyData();
+  UFE->Size    = Size;
+  UFE->ModTime = ModificationTime;
+  UFE->Dir     = DirInfo;
+  UFE->UID     = NextFileUID++;
+  return UFE;
+}
+
+void FileManager::PrintStats() const {
+  llvm::errs() << "\n*** File Manager Stats:\n";
+  llvm::errs() << UniqueFiles.size() << " files found, "
+               << UniqueDirs.size() << " dirs found.\n";
+  llvm::errs() << NumDirLookups << " dir lookups, "
+               << NumDirCacheMisses << " dir cache misses.\n";
+  llvm::errs() << NumFileLookups << " file lookups, "
+               << NumFileCacheMisses << " file cache misses.\n";
+
+  //llvm::errs() << PagesMapped << BytesOfPagesMapped << FSLookups;
+}
+
+int MemorizeStatCalls::stat(const char *path, struct stat *buf) {
+  int result = StatSysCallCache::stat(path, buf);
+  
+  // Do not cache failed stats, it is easy to construct common inconsistent
+  // situations if we do, and they are not important for PCH performance (which
+  // currently only needs the stats to construct the initial FileManager
+  // entries).
+  if (result != 0)
+    return result;
+
+  // Cache file 'stat' results and directories with absolutely paths.
+  if (!S_ISDIR(buf->st_mode) || llvm::sys::Path(path).isAbsolute())
+    StatCalls[path] = StatResult(result, *buf);
+
+  return result;
+}