Index: llvm/include/llvm/Support/FileSystem.h
===================================================================
--- llvm/include/llvm/Support/FileSystem.h
+++ llvm/include/llvm/Support/FileSystem.h
@@ -1262,10 +1262,18 @@
 
   std::error_code init(sys::fs::file_t FD, uint64_t Offset, mapmode Mode);
 
+  void moveFrom(mapped_file_region &MovedFrom);
+
 public:
   mapped_file_region() = delete;
-  mapped_file_region(mapped_file_region&) = delete;
-  mapped_file_region &operator =(mapped_file_region&) = delete;
+  mapped_file_region(const mapped_file_region &) = delete;
+  mapped_file_region &operator=(const mapped_file_region &) = delete;
+
+  mapped_file_region(mapped_file_region &&MovedFrom) { moveFrom(MovedFrom); }
+  mapped_file_region &operator=(mapped_file_region &&MovedFrom) {
+    moveFrom(MovedFrom);
+    return *this;
+  }
 
   /// \param fd An open file descriptor to map. Does not take ownership of fd.
   mapped_file_region(sys::fs::file_t fd, mapmode mode, size_t length, uint64_t offset,
Index: llvm/lib/Support/FileOutputBuffer.cpp
===================================================================
--- llvm/lib/Support/FileOutputBuffer.cpp
+++ llvm/lib/Support/FileOutputBuffer.cpp
@@ -33,8 +33,7 @@
 // with the temporary file on commit().
 class OnDiskBuffer : public FileOutputBuffer {
 public:
-  OnDiskBuffer(StringRef Path, fs::TempFile Temp,
-               std::unique_ptr<fs::mapped_file_region> Buf)
+  OnDiskBuffer(StringRef Path, fs::TempFile Temp, fs::mapped_file_region Buf)
       : FileOutputBuffer(Path), Buffer(std::move(Buf)), Temp(std::move(Temp)) {}
 
   uint8_t *getBufferStart() const override { return (uint8_t *)Buffer->data(); }
@@ -47,7 +46,7 @@
 
   Error commit() override {
     // Unmap buffer, letting OS flush dirty pages to file on disk.
-    Buffer.reset();
+    Buffer = None;
 
     // Atomically replace the existing file with the new one.
     return Temp.keep(FinalPath);
@@ -56,7 +55,7 @@
   ~OnDiskBuffer() override {
     // Close the mapping before deleting the temp file, so that the removal
     // succeeds.
-    Buffer.reset();
+    Buffer = None;
     consumeError(Temp.discard());
   }
 
@@ -67,7 +66,7 @@
   }
 
 private:
-  std::unique_ptr<fs::mapped_file_region> Buffer;
+  Optional<fs::mapped_file_region> Buffer;
   fs::TempFile Temp;
 };
 
@@ -139,9 +138,9 @@
 
   // Mmap it.
   std::error_code EC;
-  auto MappedFile = std::make_unique<fs::mapped_file_region>(
-      fs::convertFDToNativeFile(File.FD), fs::mapped_file_region::readwrite,
-      Size, 0, EC);
+  fs::mapped_file_region MappedFile =
+      fs::mapped_file_region(fs::convertFDToNativeFile(File.FD),
+                             fs::mapped_file_region::readwrite, Size, 0, EC);
 
   // mmap(2) can fail if the underlying filesystem does not support it.
   // If that happens, we fall back to in-memory buffer as the last resort.
Index: llvm/lib/Support/Path.cpp
===================================================================
--- llvm/lib/Support/Path.cpp
+++ llvm/lib/Support/Path.cpp
@@ -1152,6 +1152,21 @@
   return Status.permissions();
 }
 
+void mapped_file_region::moveFrom(mapped_file_region &MovedFrom) {
+  Size = MovedFrom.Size;
+  Mapping = MovedFrom.Mapping;
+  Mode = MovedFrom.Mode;
+
+  MovedFrom.Size = 0;
+  MovedFrom.Mapping = 0;
+  MovedFrom.Mode = mapmode();
+
+#ifdef _WIN32
+  FileHandle = MovedFrom.FileHandle;
+  MovedFrom.FileHandle = nullptr;
+#endif
+}
+
 } // end namespace fs
 } // end namespace sys
 } // end namespace llvm
Index: llvm/unittests/Support/Path.cpp
===================================================================
--- llvm/unittests/Support/Path.cpp
+++ llvm/unittests/Support/Path.cpp
@@ -1341,6 +1341,7 @@
   // Map in temp file and add some content
   std::error_code EC;
   StringRef Val("hello there");
+  Optional<fs::mapped_file_region> MaybeMFR;
   {
     fs::mapped_file_region mfr(fs::convertFDToNativeFile(FileDescriptor),
                                fs::mapped_file_region::readwrite, Size, 0, EC);
@@ -1348,8 +1349,22 @@
     std::copy(Val.begin(), Val.end(), mfr.data());
     // Explicitly add a 0.
     mfr.data()[Val.size()] = 0;
-    // Unmap temp file
+
+    // Move it out of the scope and confirm mfr is reset.
+    MaybeMFR.emplace(std::move(mfr));
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+    EXPECT_DEATH(mfr.data(), "Mapping failed but used anyway!");
+    EXPECT_DEATH(mfr.size(), "Mapping failed but used anyway!");
+#endif
   }
+
+  // Check that the moved-to region is still valid.
+  EXPECT_EQ(Val, StringRef(MaybeMFR->data()));
+  EXPECT_EQ(Size, MaybeMFR->size());
+
+  // Unmap temp file.
+  MaybeMFR = None;
+
   ASSERT_EQ(close(FileDescriptor), 0);
 
   // Map it back in read-only