Index: include/clang/Basic/FileManager.h
===================================================================
--- include/clang/Basic/FileManager.h
+++ include/clang/Basic/FileManager.h
@@ -19,7 +19,6 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/VirtualFileSystem.h"
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
@@ -113,7 +112,7 @@
 /// as a single file.
 ///
 class FileManager : public RefCountedBase<FileManager> {
-  IntrusiveRefCntPtr<vfs::FileSystem> FS;
+  std::shared_ptr<vfs::FileSystem> FS;
   FileSystemOptions FileSystemOpts;
 
   /// \brief Cache for existing real directories.
@@ -172,7 +171,7 @@
 
 public:
   FileManager(const FileSystemOptions &FileSystemOpts,
-              IntrusiveRefCntPtr<vfs::FileSystem> FS = nullptr);
+              std::shared_ptr<vfs::FileSystem> FS = nullptr);
   ~FileManager();
 
   /// \brief Installs the provided FileSystemStatCache object within
@@ -221,7 +220,7 @@
   FileSystemOptions &getFileSystemOpts() { return FileSystemOpts; }
   const FileSystemOptions &getFileSystemOpts() const { return FileSystemOpts; }
 
-  IntrusiveRefCntPtr<vfs::FileSystem> getVirtualFileSystem() const {
+  std::shared_ptr<vfs::FileSystem> getVirtualFileSystem() const {
     return FS;
   }
 
Index: include/clang/Basic/VirtualFileSystem.h
===================================================================
--- include/clang/Basic/VirtualFileSystem.h
+++ include/clang/Basic/VirtualFileSystem.h
@@ -14,7 +14,6 @@
 #define LLVM_CLANG_BASIC_VIRTUALFILESYSTEM_H
 
 #include "clang/Basic/LLVM.h"
-#include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/FileSystem.h"
@@ -179,7 +178,7 @@
 };
 
 /// \brief The virtual file system interface.
-class FileSystem : public llvm::ThreadSafeRefCountedBase<FileSystem> {
+class FileSystem {
 public:
   virtual ~FileSystem();
 
@@ -225,7 +224,7 @@
 
 /// \brief Gets an \p vfs::FileSystem for the 'real' file system, as seen by
 /// the operating system.
-IntrusiveRefCntPtr<FileSystem> getRealFileSystem();
+std::shared_ptr<FileSystem> getRealFileSystem();
 
 /// \brief A file system that allows overlaying one \p AbstractFileSystem on top
 /// of another.
@@ -238,15 +237,15 @@
 /// that exists in more than one file system, the file in the top-most file
 /// system overrides the other(s).
 class OverlayFileSystem : public FileSystem {
-  typedef SmallVector<IntrusiveRefCntPtr<FileSystem>, 1> FileSystemList;
+  typedef SmallVector<std::shared_ptr<FileSystem>, 1> FileSystemList;
   /// \brief The stack of file systems, implemented as a list in order of
   /// their addition.
   FileSystemList FSList;
 
 public:
-  OverlayFileSystem(IntrusiveRefCntPtr<FileSystem> Base);
+  OverlayFileSystem(std::shared_ptr<FileSystem> Base);
   /// \brief Pushes a file system on top of the stack.
-  void pushOverlay(IntrusiveRefCntPtr<FileSystem> FS);
+  void pushOverlay(std::shared_ptr<FileSystem> FS);
 
   llvm::ErrorOr<Status> status(const Twine &Path) override;
   llvm::ErrorOr<std::unique_ptr<File>>
@@ -307,11 +306,11 @@
 
 /// \brief Gets a \p FileSystem for a virtual file system described in YAML
 /// format.
-IntrusiveRefCntPtr<FileSystem>
+std::shared_ptr<FileSystem>
 getVFSFromYAML(std::unique_ptr<llvm::MemoryBuffer> Buffer,
                llvm::SourceMgr::DiagHandlerTy DiagHandler,
                void *DiagContext = nullptr,
-               IntrusiveRefCntPtr<FileSystem> ExternalFS = getRealFileSystem());
+               std::shared_ptr<FileSystem> ExternalFS = getRealFileSystem());
 
 struct YAMLVFSEntry {
   template <typename T1, typename T2> YAMLVFSEntry(T1 &&VPath, T2 &&RPath)
Index: include/clang/Driver/Driver.h
===================================================================
--- include/clang/Driver/Driver.h
+++ include/clang/Driver/Driver.h
@@ -67,7 +67,7 @@
 
   DiagnosticsEngine &Diags;
 
-  IntrusiveRefCntPtr<vfs::FileSystem> VFS;
+  std::shared_ptr<vfs::FileSystem> VFS;
 
   enum DriverMode {
     GCCMode,
@@ -221,7 +221,7 @@
 public:
   Driver(StringRef ClangExecutable, StringRef DefaultTargetTriple,
          DiagnosticsEngine &Diags,
-         IntrusiveRefCntPtr<vfs::FileSystem> VFS = nullptr);
+         std::shared_ptr<vfs::FileSystem> VFS = nullptr);
   ~Driver();
 
   /// @name Accessors
Index: include/clang/Frontend/CompilerInstance.h
===================================================================
--- include/clang/Frontend/CompilerInstance.h
+++ include/clang/Frontend/CompilerInstance.h
@@ -82,7 +82,7 @@
   IntrusiveRefCntPtr<TargetInfo> AuxTarget;
 
   /// The virtual file system.
-  IntrusiveRefCntPtr<vfs::FileSystem> VirtualFileSystem;
+  std::shared_ptr<vfs::FileSystem> VirtualFileSystem;
 
   /// The file manager.
   IntrusiveRefCntPtr<FileManager> FileMgr;
@@ -369,17 +369,17 @@
 
   bool hasVirtualFileSystem() const { return VirtualFileSystem != nullptr; }
 
-  vfs::FileSystem &getVirtualFileSystem() const {
+  std::shared_ptr<vfs::FileSystem> getVirtualFileSystem() const {
     assert(hasVirtualFileSystem() &&
            "Compiler instance has no virtual file system");
-    return *VirtualFileSystem;
+    return VirtualFileSystem;
   }
 
   /// \brief Replace the current virtual file system.
   ///
   /// \note Most clients should use setFileManager, which will implicitly reset
   /// the virtual file system to the one contained in the file manager.
-  void setVirtualFileSystem(IntrusiveRefCntPtr<vfs::FileSystem> FS) {
+  void setVirtualFileSystem(std::shared_ptr<vfs::FileSystem> FS) {
     VirtualFileSystem = FS;
   }
 
Index: include/clang/Frontend/CompilerInvocation.h
===================================================================
--- include/clang/Frontend/CompilerInvocation.h
+++ include/clang/Frontend/CompilerInvocation.h
@@ -210,7 +210,7 @@
   class FileSystem;
 }
 
-IntrusiveRefCntPtr<vfs::FileSystem>
+std::shared_ptr<vfs::FileSystem>
 createVFSFromCompilerInvocation(const CompilerInvocation &CI,
                                 DiagnosticsEngine &Diags);
 
Index: include/clang/Tooling/Tooling.h
===================================================================
--- include/clang/Tooling/Tooling.h
+++ include/clang/Tooling/Tooling.h
@@ -332,8 +332,8 @@
   std::vector<std::string> SourcePaths;
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
 
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem;
-  llvm::IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem;
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem;
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem;
   llvm::IntrusiveRefCntPtr<FileManager> Files;
   // Contains a list of pairs (<file name>, <file content>).
   std::vector< std::pair<StringRef, StringRef> > MappedFileContents;
Index: lib/Basic/FileManager.cpp
===================================================================
--- lib/Basic/FileManager.cpp
+++ lib/Basic/FileManager.cpp
@@ -47,7 +47,7 @@
 //===----------------------------------------------------------------------===//
 
 FileManager::FileManager(const FileSystemOptions &FSO,
-                         IntrusiveRefCntPtr<vfs::FileSystem> FS)
+                         std::shared_ptr<vfs::FileSystem> FS)
   : FS(FS), FileSystemOpts(FSO),
     SeenDirEntries(64), SeenFileEntries(64), NextFileUID(0) {
   NumDirLookups = NumFileLookups = 0;
Index: lib/Basic/VirtualFileSystem.cpp
===================================================================
--- lib/Basic/VirtualFileSystem.cpp
+++ lib/Basic/VirtualFileSystem.cpp
@@ -225,8 +225,8 @@
   return std::error_code();
 }
 
-IntrusiveRefCntPtr<FileSystem> vfs::getRealFileSystem() {
-  static IntrusiveRefCntPtr<FileSystem> FS = new RealFileSystem();
+std::shared_ptr<FileSystem> vfs::getRealFileSystem() {
+  static std::shared_ptr<FileSystem> FS(new RealFileSystem());
   return FS;
 }
 
@@ -270,11 +270,11 @@
 //===-----------------------------------------------------------------------===/
 // OverlayFileSystem implementation
 //===-----------------------------------------------------------------------===/
-OverlayFileSystem::OverlayFileSystem(IntrusiveRefCntPtr<FileSystem> BaseFS) {
+OverlayFileSystem::OverlayFileSystem(std::shared_ptr<FileSystem> BaseFS) {
   FSList.push_back(BaseFS);
 }
 
-void OverlayFileSystem::pushOverlay(IntrusiveRefCntPtr<FileSystem> FS) {
+void OverlayFileSystem::pushOverlay(std::shared_ptr<FileSystem> FS) {
   FSList.push_back(FS);
   // Synchronize added file systems by duplicating the working directory from
   // the first one in the list.
@@ -814,7 +814,7 @@
   /// The root(s) of the virtual file system.
   std::vector<std::unique_ptr<Entry>> Roots;
   /// \brief The file system to use for external references.
-  IntrusiveRefCntPtr<FileSystem> ExternalFS;
+  std::shared_ptr<FileSystem> ExternalFS;
 
   /// @name Configuration
   /// @{
@@ -832,7 +832,7 @@
   friend class RedirectingFileSystemParser;
 
 private:
-  RedirectingFileSystem(IntrusiveRefCntPtr<FileSystem> ExternalFS)
+  RedirectingFileSystem(std::shared_ptr<FileSystem> ExternalFS)
       : ExternalFS(ExternalFS), CaseSensitive(true), UseExternalNames(true) {}
 
   /// \brief Looks up \p Path in \c Roots.
@@ -852,7 +852,7 @@
   static RedirectingFileSystem *
   create(std::unique_ptr<MemoryBuffer> Buffer,
          SourceMgr::DiagHandlerTy DiagHandler, void *DiagContext,
-         IntrusiveRefCntPtr<FileSystem> ExternalFS);
+         std::shared_ptr<FileSystem> ExternalFS);
 
   ErrorOr<Status> status(const Twine &Path) override;
   ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override;
@@ -1207,7 +1207,7 @@
 
 RedirectingFileSystem *RedirectingFileSystem::create(
     std::unique_ptr<MemoryBuffer> Buffer, SourceMgr::DiagHandlerTy DiagHandler,
-    void *DiagContext, IntrusiveRefCntPtr<FileSystem> ExternalFS) {
+    void *DiagContext, std::shared_ptr<FileSystem> ExternalFS) {
 
   SourceMgr SM;
   yaml::Stream Stream(Buffer->getMemBufferRef(), SM);
@@ -1360,12 +1360,14 @@
       llvm::make_unique<FileWithFixedStatus>(std::move(*Result), S));
 }
 
-IntrusiveRefCntPtr<FileSystem>
+std::shared_ptr<FileSystem>
 vfs::getVFSFromYAML(std::unique_ptr<MemoryBuffer> Buffer,
                     SourceMgr::DiagHandlerTy DiagHandler, void *DiagContext,
-                    IntrusiveRefCntPtr<FileSystem> ExternalFS) {
-  return RedirectingFileSystem::create(std::move(Buffer), DiagHandler,
-                                       DiagContext, ExternalFS);
+                    std::shared_ptr<FileSystem> ExternalFS) {
+  std::shared_ptr<FileSystem> FS(
+    RedirectingFileSystem::create(std::move(Buffer), DiagHandler,
+                                  DiagContext, ExternalFS));
+  return FS;
 }
 
 UniqueID vfs::getNextVirtualUniqueID() {
Index: lib/Driver/Driver.cpp
===================================================================
--- lib/Driver/Driver.cpp
+++ lib/Driver/Driver.cpp
@@ -48,7 +48,7 @@
 
 Driver::Driver(StringRef ClangExecutable, StringRef DefaultTargetTriple,
                DiagnosticsEngine &Diags,
-               IntrusiveRefCntPtr<vfs::FileSystem> VFS)
+               std::shared_ptr<vfs::FileSystem> VFS)
     : Opts(createDriverOptTable()), Diags(Diags), VFS(VFS), Mode(GCCMode),
       SaveTemps(SaveTempsNone), LTOMode(LTOK_None),
       ClangExecutable(ClangExecutable),
Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp
+++ lib/Format/Format.cpp
@@ -1897,7 +1897,7 @@
   if (Style.DisableFormat)
     return tooling::Replacements();
 
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   FileManager Files(FileSystemOptions(), InMemoryFileSystem);
   DiagnosticsEngine Diagnostics(
Index: lib/Frontend/ASTUnit.cpp
===================================================================
--- lib/Frontend/ASTUnit.cpp
+++ lib/Frontend/ASTUnit.cpp
@@ -670,7 +670,7 @@
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->CaptureDiagnostics = CaptureDiagnostics;
   AST->Diagnostics = Diags;
-  IntrusiveRefCntPtr<vfs::FileSystem> VFS = vfs::getRealFileSystem();
+  std::shared_ptr<vfs::FileSystem> VFS = vfs::getRealFileSystem();
   AST->FileMgr = new FileManager(FileSystemOpts, VFS);
   AST->UserFilesAreVolatile = UserFilesAreVolatile;
   AST->SourceMgr = new SourceManager(AST->getDiagnostics(),
@@ -1550,7 +1550,7 @@
   TopLevelDeclsInPreamble.clear();
   PreambleDiagnostics.clear();
 
-  IntrusiveRefCntPtr<vfs::FileSystem> VFS =
+  std::shared_ptr<vfs::FileSystem> VFS =
       createVFSFromCompilerInvocation(Clang->getInvocation(), getDiagnostics());
   if (!VFS)
     return nullptr;
@@ -1708,7 +1708,7 @@
   AST->Diagnostics = Diags;
   AST->Invocation = CI;
   AST->FileSystemOpts = CI->getFileSystemOpts();
-  IntrusiveRefCntPtr<vfs::FileSystem> VFS =
+  std::shared_ptr<vfs::FileSystem> VFS =
       createVFSFromCompilerInvocation(*CI, *Diags);
   if (!VFS)
     return nullptr;
@@ -1979,7 +1979,7 @@
   ConfigureDiags(Diags, *AST, CaptureDiagnostics);
   AST->Diagnostics = Diags;
   AST->FileSystemOpts = CI->getFileSystemOpts();
-  IntrusiveRefCntPtr<vfs::FileSystem> VFS =
+  std::shared_ptr<vfs::FileSystem> VFS =
       createVFSFromCompilerInvocation(*CI, *Diags);
   if (!VFS)
     return nullptr;
Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -953,7 +953,7 @@
                                    ImportingInstance.getDiagnosticClient()),
                              /*ShouldOwnClient=*/true);
 
-  Instance.setVirtualFileSystem(&ImportingInstance.getVirtualFileSystem());
+  Instance.setVirtualFileSystem(ImportingInstance.getVirtualFileSystem());
 
   // Note that this module is part of the module build stack, so that we
   // can detect cycles in the module graph.
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -2289,13 +2289,13 @@
   GraveYard[Idx] = Ptr;
 }
 
-IntrusiveRefCntPtr<vfs::FileSystem>
+std::shared_ptr<vfs::FileSystem>
 createVFSFromCompilerInvocation(const CompilerInvocation &CI,
                                 DiagnosticsEngine &Diags) {
   if (CI.getHeaderSearchOpts().VFSOverlayFiles.empty())
     return vfs::getRealFileSystem();
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem>
+  std::shared_ptr<vfs::OverlayFileSystem>
     Overlay(new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
   // earlier vfs files are on the bottom
   for (const std::string &File : CI.getHeaderSearchOpts().VFSOverlayFiles) {
@@ -2303,14 +2303,14 @@
         llvm::MemoryBuffer::getFile(File);
     if (!Buffer) {
       Diags.Report(diag::err_missing_vfs_overlay_file) << File;
-      return IntrusiveRefCntPtr<vfs::FileSystem>();
+      return std::shared_ptr<vfs::FileSystem>();
     }
 
-    IntrusiveRefCntPtr<vfs::FileSystem> FS =
+    std::shared_ptr<vfs::FileSystem> FS =
         vfs::getVFSFromYAML(std::move(Buffer.get()), /*DiagHandler*/ nullptr);
     if (!FS.get()) {
       Diags.Report(diag::err_invalid_vfs_overlay) << File;
-      return IntrusiveRefCntPtr<vfs::FileSystem>();
+      return std::shared_ptr<vfs::FileSystem>();
     }
     Overlay->pushOverlay(FS);
   }
Index: lib/Frontend/FrontendAction.cpp
===================================================================
--- lib/Frontend/FrontendAction.cpp
+++ lib/Frontend/FrontendAction.cpp
@@ -223,7 +223,7 @@
   }
 
   if (!CI.hasVirtualFileSystem()) {
-    if (IntrusiveRefCntPtr<vfs::FileSystem> VFS =
+    if (std::shared_ptr<vfs::FileSystem> VFS =
           createVFSFromCompilerInvocation(CI.getInvocation(),
                                           CI.getDiagnostics()))
       CI.setVirtualFileSystem(VFS);
Index: lib/Index/SimpleFormatContext.h
===================================================================
--- lib/Index/SimpleFormatContext.h
+++ lib/Index/SimpleFormatContext.h
@@ -63,7 +63,7 @@
 
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts;
   IntrusiveRefCntPtr<DiagnosticsEngine> Diagnostics;
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem;
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem;
   FileManager Files;
   SourceManager Sources;
   Rewriter Rewrite;
Index: lib/StaticAnalyzer/Frontend/ModelInjector.cpp
===================================================================
--- lib/StaticAnalyzer/Frontend/ModelInjector.cpp
+++ lib/StaticAnalyzer/Frontend/ModelInjector.cpp
@@ -84,7 +84,7 @@
 
   Instance.getDiagnostics().setSourceManager(&SM);
 
-  Instance.setVirtualFileSystem(&CI.getVirtualFileSystem());
+  Instance.setVirtualFileSystem(CI.getVirtualFileSystem());
 
   // The instance wants to take ownership, however DisableFree frontend option
   // is set to true to avoid double free issues
Index: lib/Tooling/Core/Replacement.cpp
===================================================================
--- lib/Tooling/Core/Replacement.cpp
+++ lib/Tooling/Core/Replacement.cpp
@@ -255,7 +255,7 @@
 }
 
 std::string applyAllReplacements(StringRef Code, const Replacements &Replaces) {
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   FileManager Files(FileSystemOptions(), InMemoryFileSystem);
   DiagnosticsEngine Diagnostics(
Index: lib/Tooling/Tooling.cpp
===================================================================
--- lib/Tooling/Tooling.cpp
+++ lib/Tooling/Tooling.cpp
@@ -48,7 +48,7 @@
 /// \brief Builds a clang driver initialized for running clang tools.
 static clang::driver::Driver *newDriver(
     clang::DiagnosticsEngine *Diagnostics, const char *BinaryName,
-    IntrusiveRefCntPtr<vfs::FileSystem> VFS) {
+    std::shared_ptr<vfs::FileSystem> VFS) {
   clang::driver::Driver *CompilerDriver = new clang::driver::Driver(
       BinaryName, llvm::sys::getDefaultTargetTriple(), *Diagnostics, VFS);
   CompilerDriver->setTitle("clang_based_tool");
@@ -125,9 +125,9 @@
 
   SmallString<16> FileNameStorage;
   StringRef FileNameRef = FileName.toNullTerminatedStringRef(FileNameStorage);
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem(
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem(
       new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
-  llvm::IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   OverlayFileSystem->pushOverlay(InMemoryFileSystem);
   llvm::IntrusiveRefCntPtr<FileManager> Files(
@@ -482,9 +482,9 @@
 
   std::vector<std::unique_ptr<ASTUnit>> ASTs;
   ASTBuilderAction Action(ASTs);
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem(
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem(
       new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
-  llvm::IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   OverlayFileSystem->pushOverlay(InMemoryFileSystem);
   llvm::IntrusiveRefCntPtr<FileManager> Files(
Index: tools/clang-format/ClangFormat.cpp
===================================================================
--- tools/clang-format/ClangFormat.cpp
+++ tools/clang-format/ClangFormat.cpp
@@ -129,7 +129,7 @@
 
 static bool fillRanges(MemoryBuffer *Code,
                        std::vector<tooling::Range> &Ranges) {
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   FileManager Files(FileSystemOptions(), InMemoryFileSystem);
   DiagnosticsEngine Diagnostics(
@@ -278,7 +278,7 @@
     outputReplacementsXML(Replaces); 
     outs() << "</replacements>\n";
   } else {
-    IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+    std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
         new vfs::InMemoryFileSystem);
     FileManager Files(FileSystemOptions(), InMemoryFileSystem);
     DiagnosticsEngine Diagnostics(
Index: unittests/Basic/VirtualFileSystemTest.cpp
===================================================================
--- unittests/Basic/VirtualFileSystemTest.cpp
+++ unittests/Basic/VirtualFileSystemTest.cpp
@@ -134,7 +134,7 @@
 } // end anonymous namespace
 
 TEST(VirtualFileSystemTest, StatusQueries) {
-  IntrusiveRefCntPtr<DummyFileSystem> D(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> D(new DummyFileSystem());
   ErrorOr<vfs::Status> Status((std::error_code()));
 
   D->addRegularFile("/foo");
@@ -174,11 +174,11 @@
 }
 
 TEST(VirtualFileSystemTest, BaseOnlyOverlay) {
-  IntrusiveRefCntPtr<DummyFileSystem> D(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> D(new DummyFileSystem());
   ErrorOr<vfs::Status> Status((std::error_code()));
   EXPECT_FALSE(Status = D->status("/foo"));
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(new vfs::OverlayFileSystem(D));
+  std::shared_ptr<vfs::OverlayFileSystem> O(new vfs::OverlayFileSystem(D));
   EXPECT_FALSE(Status = O->status("/foo"));
 
   D->addRegularFile("/foo");
@@ -192,10 +192,10 @@
 }
 
 TEST(VirtualFileSystemTest, OverlayFiles) {
-  IntrusiveRefCntPtr<DummyFileSystem> Base(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Middle(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Top(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Base(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Middle(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Top(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Base));
   O->pushOverlay(Middle);
   O->pushOverlay(Top);
@@ -231,9 +231,9 @@
 }
 
 TEST(VirtualFileSystemTest, OverlayDirsNonMerged) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Upper);
 
@@ -256,9 +256,9 @@
 
 TEST(VirtualFileSystemTest, MergedDirPermissions) {
   // merged directories get the permissions of the upper dir
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Upper);
 
@@ -305,7 +305,7 @@
 
 TEST(VirtualFileSystemTest, BasicRealFSIteration) {
   ScopedDir TestDirectory("virtual-file-system-test", /*Unique*/true);
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = vfs::getRealFileSystem();
+  std::shared_ptr<vfs::FileSystem> FS = vfs::getRealFileSystem();
 
   std::error_code EC;
   vfs::directory_iterator I = FS->dir_begin(Twine(TestDirectory), EC);
@@ -332,7 +332,7 @@
 
 TEST(VirtualFileSystemTest, BasicRealFSRecursiveIteration) {
   ScopedDir TestDirectory("virtual-file-system-test", /*Unique*/true);
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = vfs::getRealFileSystem();
+  std::shared_ptr<vfs::FileSystem> FS = vfs::getRealFileSystem();
 
   std::error_code EC;
   auto I = vfs::recursive_directory_iterator(*FS, Twine(TestDirectory), EC);
@@ -384,9 +384,9 @@
 }
 
 TEST(VirtualFileSystemTest, OverlayIteration) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Upper);
 
@@ -408,10 +408,10 @@
 }
 
 TEST(VirtualFileSystemTest, OverlayRecursiveIteration) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Middle(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Middle(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Middle);
   O->pushOverlay(Upper);
@@ -450,10 +450,10 @@
 }
 
 TEST(VirtualFileSystemTest, ThreeLevelIteration) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Middle(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Middle(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Middle);
   O->pushOverlay(Upper);
@@ -470,10 +470,10 @@
 }
 
 TEST(VirtualFileSystemTest, HiddenInIteration) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Middle(new DummyFileSystem());
-  IntrusiveRefCntPtr<DummyFileSystem> Upper(new DummyFileSystem());
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Middle(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Upper(new DummyFileSystem());
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(Middle);
   O->pushOverlay(Upper);
@@ -659,17 +659,18 @@
     ++Test->NumDiagnostics;
   }
 
-  IntrusiveRefCntPtr<vfs::FileSystem>
+  std::shared_ptr<vfs::FileSystem>
   getFromYAMLRawString(StringRef Content,
-                       IntrusiveRefCntPtr<vfs::FileSystem> ExternalFS) {
+                       std::shared_ptr<vfs::FileSystem> ExternalFS) {
     std::unique_ptr<MemoryBuffer> Buffer = MemoryBuffer::getMemBuffer(Content);
     return getVFSFromYAML(std::move(Buffer), CountingDiagHandler, this,
                           ExternalFS);
   }
 
-  IntrusiveRefCntPtr<vfs::FileSystem> getFromYAMLString(
+  std::shared_ptr<vfs::FileSystem> getFromYAMLString(
       StringRef Content,
-      IntrusiveRefCntPtr<vfs::FileSystem> ExternalFS = new DummyFileSystem()) {
+      std::shared_ptr<vfs::FileSystem> ExternalFS =
+        std::make_shared<DummyFileSystem>()) {
     std::string VersionPlusContent("{\n  'version':0,\n");
     VersionPlusContent += Content.slice(Content.find('{') + 1, StringRef::npos);
     return getFromYAMLRawString(VersionPlusContent, ExternalFS);
@@ -677,7 +678,7 @@
 };
 
 TEST_F(VFSFromYAMLTest, BasicVFSFromYAML) {
-  IntrusiveRefCntPtr<vfs::FileSystem> FS;
+  std::shared_ptr<vfs::FileSystem> FS;
   FS = getFromYAMLString("");
   EXPECT_EQ(nullptr, FS.get());
   FS = getFromYAMLString("[]");
@@ -688,9 +689,9 @@
 }
 
 TEST_F(VFSFromYAMLTest, MappedFiles) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/foo/bar/a");
-  IntrusiveRefCntPtr<vfs::FileSystem> FS =
+  std::shared_ptr<vfs::FileSystem> FS =
       getFromYAMLString("{ 'roots': [\n"
                         "{\n"
                         "  'type': 'directory',\n"
@@ -712,7 +713,7 @@
                         Lower);
   ASSERT_TRUE(FS.get() != nullptr);
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(FS);
 
@@ -748,9 +749,9 @@
 }
 
 TEST_F(VFSFromYAMLTest, CaseInsensitive) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/foo/bar/a");
-  IntrusiveRefCntPtr<vfs::FileSystem> FS =
+  std::shared_ptr<vfs::FileSystem> FS =
       getFromYAMLString("{ 'case-sensitive': 'false',\n"
                         "  'roots': [\n"
                         "{\n"
@@ -766,7 +767,7 @@
                         Lower);
   ASSERT_TRUE(FS.get() != nullptr);
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(FS);
 
@@ -784,9 +785,9 @@
 }
 
 TEST_F(VFSFromYAMLTest, CaseSensitive) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/foo/bar/a");
-  IntrusiveRefCntPtr<vfs::FileSystem> FS =
+  std::shared_ptr<vfs::FileSystem> FS =
       getFromYAMLString("{ 'case-sensitive': 'true',\n"
                         "  'roots': [\n"
                         "{\n"
@@ -802,7 +803,7 @@
                         Lower);
   ASSERT_TRUE(FS.get() != nullptr);
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(FS);
 
@@ -816,10 +817,10 @@
 }
 
 TEST_F(VFSFromYAMLTest, IllegalVFSFile) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
 
   // invalid YAML at top-level
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = getFromYAMLString("{]", Lower);
+  std::shared_ptr<vfs::FileSystem> FS = getFromYAMLString("{]", Lower);
   EXPECT_EQ(nullptr, FS.get());
   // invalid YAML in roots
   FS = getFromYAMLString("{ 'roots':[}", Lower);
@@ -907,10 +908,10 @@
 }
 
 TEST_F(VFSFromYAMLTest, UseExternalName) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/external/file");
 
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = getFromYAMLString(
+  std::shared_ptr<vfs::FileSystem> FS = getFromYAMLString(
       "{ 'roots': [\n"
       "  { 'type': 'file', 'name': '//root/A',\n"
       "    'external-contents': '//root/external/file'\n"
@@ -958,11 +959,11 @@
 }
 
 TEST_F(VFSFromYAMLTest, MultiComponentPath) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/other");
 
   // file in roots
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = getFromYAMLString(
+  std::shared_ptr<vfs::FileSystem> FS = getFromYAMLString(
       "{ 'roots': [\n"
       "  { 'type': 'file', 'name': '//root/path/to/file',\n"
       "    'external-contents': '//root/other' }]\n"
@@ -1001,11 +1002,11 @@
 }
 
 TEST_F(VFSFromYAMLTest, TrailingSlashes) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addRegularFile("//root/other");
 
   // file in roots
-  IntrusiveRefCntPtr<vfs::FileSystem> FS = getFromYAMLString(
+  std::shared_ptr<vfs::FileSystem> FS = getFromYAMLString(
       "{ 'roots': [\n"
       "  { 'type': 'directory', 'name': '//root/path/to////',\n"
       "    'contents': [ { 'type': 'file', 'name': 'file',\n"
@@ -1019,14 +1020,14 @@
 }
 
 TEST_F(VFSFromYAMLTest, DirectoryIteration) {
-  IntrusiveRefCntPtr<DummyFileSystem> Lower(new DummyFileSystem());
+  std::shared_ptr<DummyFileSystem> Lower(new DummyFileSystem());
   Lower->addDirectory("//root/");
   Lower->addDirectory("//root/foo");
   Lower->addDirectory("//root/foo/bar");
   Lower->addRegularFile("//root/foo/bar/a");
   Lower->addRegularFile("//root/foo/bar/b");
   Lower->addRegularFile("//root/file3");
-  IntrusiveRefCntPtr<vfs::FileSystem> FS =
+  std::shared_ptr<vfs::FileSystem> FS =
   getFromYAMLString("{ 'use-external-names': false,\n"
                     "  'roots': [\n"
                     "{\n"
@@ -1049,7 +1050,7 @@
                     Lower);
   ASSERT_TRUE(FS.get() != nullptr);
 
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> O(
+  std::shared_ptr<vfs::OverlayFileSystem> O(
       new vfs::OverlayFileSystem(Lower));
   O->pushOverlay(FS);
 
Index: unittests/Driver/ToolChainTest.cpp
===================================================================
--- unittests/Driver/ToolChainTest.cpp
+++ unittests/Driver/ToolChainTest.cpp
@@ -31,7 +31,7 @@
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
   struct TestDiagnosticConsumer : public DiagnosticConsumer {};
   DiagnosticsEngine Diags(DiagID, &*DiagOpts, new TestDiagnosticConsumer);
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   Driver TheDriver("/bin/clang", "arm-linux-gnueabihf", Diags,
                    InMemoryFileSystem);
@@ -84,7 +84,7 @@
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
   struct TestDiagnosticConsumer : public DiagnosticConsumer {};
   DiagnosticsEngine Diags(DiagID, &*DiagOpts, new TestDiagnosticConsumer);
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   Driver TheDriver("/home/test/bin/clang", "arm-linux-gnueabi", Diags,
                    InMemoryFileSystem);
Index: unittests/Lex/PPCallbacksTest.cpp
===================================================================
--- unittests/Lex/PPCallbacksTest.cpp
+++ unittests/Lex/PPCallbacksTest.cpp
@@ -119,7 +119,7 @@
     Target = TargetInfo::CreateTargetInfo(Diags, TargetOpts);
   }
 
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem;
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem;
   FileManager FileMgr;
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID;
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts;
Index: unittests/Tooling/RewriterTestContext.h
===================================================================
--- unittests/Tooling/RewriterTestContext.h
+++ unittests/Tooling/RewriterTestContext.h
@@ -114,8 +114,8 @@
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts;
   DiagnosticsEngine Diagnostics;
   TextDiagnosticPrinter DiagnosticPrinter;
-  IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem;
-  IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem;
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem;
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem;
   FileManager Files;
   SourceManager Sources;
   LangOptions Options;
Index: unittests/Tooling/ToolingTest.cpp
===================================================================
--- unittests/Tooling/ToolingTest.cpp
+++ unittests/Tooling/ToolingTest.cpp
@@ -149,9 +149,9 @@
 }
 
 TEST(ToolInvocation, TestMapVirtualFile) {
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem(
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem(
       new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
-  llvm::IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   OverlayFileSystem->pushOverlay(InMemoryFileSystem);
   llvm::IntrusiveRefCntPtr<FileManager> Files(
@@ -175,9 +175,9 @@
   // mapped module.map is found on the include path. In the future, expand this
   // test to run a full modules enabled compilation, so we make sure we can
   // rerun modules compilations with a virtual file system.
-  llvm::IntrusiveRefCntPtr<vfs::OverlayFileSystem> OverlayFileSystem(
+  std::shared_ptr<vfs::OverlayFileSystem> OverlayFileSystem(
       new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
-  llvm::IntrusiveRefCntPtr<vfs::InMemoryFileSystem> InMemoryFileSystem(
+  std::shared_ptr<vfs::InMemoryFileSystem> InMemoryFileSystem(
       new vfs::InMemoryFileSystem);
   OverlayFileSystem->pushOverlay(InMemoryFileSystem);
   llvm::IntrusiveRefCntPtr<FileManager> Files(