Index: include/llvm/Support/COM.h
===================================================================
--- /dev/null
+++ include/llvm/Support/COM.h
@@ -0,0 +1,35 @@
+//===- llvm/Support/COM.h ---------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// Provides a library for accessing COM functionality of the Host OS.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_COM_H
+#define LLVM_SUPPORT_COM_H
+
+namespace llvm {
+namespace sys {
+
+enum class COMThreadingMode { ApartmentThreaded, FreeThreaded };
+
+class COMInitializer {
+public:
+  COMInitializer(COMThreadingMode Threading, bool SpeedOverMemory = false);
+  ~COMInitializer();
+
+private:
+  COMInitializer(const COMInitializer &) = delete;
+  void operator=(const COMInitializer &) = delete;
+};
+}
+}
+
+#endif
Index: lib/Support/CMakeLists.txt
===================================================================
--- lib/Support/CMakeLists.txt
+++ lib/Support/CMakeLists.txt
@@ -37,6 +37,7 @@
   BlockFrequency.cpp
   BranchProbability.cpp
   circular_raw_ostream.cpp
+  COM.cpp
   CommandLine.cpp
   Compression.cpp
   ConvertUTF.c
Index: lib/Support/COM.cpp
===================================================================
--- /dev/null
+++ lib/Support/COM.cpp
@@ -0,0 +1,24 @@
+//===-- COM.cpp - Implement COM utility classes -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements utility classes related to COM.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/COM.h"
+
+#include "llvm/Config/config.h"
+
+// Include the platform-specific parts of this class.
+#ifdef LLVM_ON_UNIX
+#include "Unix/COM.inc"
+#endif
+#ifdef LLVM_ON_WIN32
+#include "Windows/COM.inc"
+#endif
Index: lib/Support/Unix/COM.inc
===================================================================
--- /dev/null
+++ lib/Support/Unix/COM.inc
@@ -0,0 +1,27 @@
+//===- llvm/Support/Unix/COM.inc - Unix COM Implementation -----*- C++ -*-===//
+//
+//                     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 Unix portion of COM support.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only generic UNIX code that
+//===          is guaranteed to work on *all* UNIX variants.
+//===----------------------------------------------------------------------===//
+
+namespace llvm {
+namespace sys {
+
+COMInitializer::COMInitializer(COMThreadingMode Threading,
+                               bool SpeedOverMemory) {}
+
+COMInitializer::~COMInitializer() {}
+}
+}
Index: lib/Support/Windows/COM.inc
===================================================================
--- /dev/null
+++ lib/Support/Windows/COM.inc
@@ -0,0 +1,41 @@
+//===- llvm/Support/Windows/COM.inc - Windows COM Implementation *- C++ -*-===//
+//
+//                     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 Windows portion of COM support.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only generic UNIX code that
+//===          is guaranteed to work on *all* UNIX variants.
+//===----------------------------------------------------------------------===//
+
+// We need to #include <windows.h> directly, and not WindowsSupport.h, because
+// WindowsSupport.h #defines WIN32_LEAN_AND_MEAN, which will prevent COM headers
+// from getting included.
+#include <windows.h>
+
+namespace llvm {
+namespace sys {
+
+COMInitializer::COMInitializer(COMThreadingMode Threading,
+                               bool SpeedOverMemory) {
+  DWORD Coinit = 0;
+  if (Threading == COMThreadingMode::ApartmentThreaded)
+    Coinit |= COINIT_APARTMENTTHREADED;
+  else
+    Coinit |= COINIT_MULTITHREADED;
+  if (SpeedOverMemory)
+    Coinit |= COINIT_SPEED_OVER_MEMORY;
+  ::CoInitializeEx(nullptr, Coinit);
+}
+
+COMInitializer::~COMInitializer() { ::CoUninitialize(); }
+}
+}