Index: include/llvm/Support/DynamicLibrary.h
===================================================================
--- include/llvm/Support/DynamicLibrary.h
+++ include/llvm/Support/DynamicLibrary.h
@@ -14,6 +14,8 @@
 #ifndef LLVM_SUPPORT_DYNAMICLIBRARY_H
 #define LLVM_SUPPORT_DYNAMICLIBRARY_H
 
+#include "llvm/Support/Mutex.h"
+
 #include <string>
 
 namespace llvm {
@@ -43,6 +45,10 @@
     // Opaque data used to interface with OS-specific dynamic library handling.
     void *Data;
 
+    // Adds a opened library handle to the list of OpenedHandles.
+    static DynamicLibrary addPermanentLibraryWithLock(void *handle,
+                                                  sys::SmartScopedLock<true> &);
+
   public:
     explicit DynamicLibrary(void *data = &Invalid) : Data(data) {}
 
@@ -68,6 +74,14 @@
     static DynamicLibrary getPermanentLibrary(const char *filename,
                                               std::string *errMsg = nullptr);
 
+    /// Registers an externally loaded library. The library will be unloaded
+    /// when the program terminates.
+    ///
+    /// It is safe to call this function multiple times for the same library.
+    ///
+    /// \returns An empty \p DynamicLibrary on failure.
+    static DynamicLibrary addPermanentLibrary(void *handle);
+
     /// This function permanently loads the dynamic library at the given path.
     /// Use this instead of getPermanentLibrary() when you won't need to get
     /// symbols from the library itself.
Index: lib/Support/DynamicLibrary.cpp
===================================================================
--- lib/Support/DynamicLibrary.cpp
+++ lib/Support/DynamicLibrary.cpp
@@ -68,10 +68,28 @@
     handle = RTLD_DEFAULT;
 #endif
 
+  DynamicLibrary dyLib = addPermanentLibraryWithLock(handle, lock);
+
   // If we've already loaded this library, dlclose() the handle in order to
   // keep the internal refcount at +1.
-  if (!OpenedHandles->insert(handle).second)
+  if (!dyLib.isValid()) {
+    if (errMsg) *errMsg = std::string(filename) + ": Library already loaded";
     dlclose(handle);
+  }
+
+  return dyLib;
+}
+
+DynamicLibrary DynamicLibrary::addPermanentLibrary(void *handle) {
+  SmartScopedLock<true> lock(*SymbolsMutex);
+  return addPermanentLibraryWithLock(handle, lock);
+}
+
+DynamicLibrary DynamicLibrary::addPermanentLibraryWithLock(void *handle,
+                                                 sys::SmartScopedLock<true> &) {
+  // If we've already loaded this library, tell the caller.
+  if (!OpenedHandles->insert(handle).second)
+    return DynamicLibrary();
 
   return DynamicLibrary(handle);
 }
Index: lib/Support/Windows/DynamicLibrary.inc
===================================================================
--- lib/Support/Windows/DynamicLibrary.inc
+++ lib/Support/Windows/DynamicLibrary.inc
@@ -9,8 +9,6 @@
 //
 // This file provides the Win32 specific implementation of DynamicLibrary.
 //
-// FIXME: This file leaks OpenedHandles!
-//
 //===----------------------------------------------------------------------===//
 
 #include "WindowsSupport.h"
@@ -35,7 +33,7 @@
 
 typedef BOOL (WINAPI *fpEnumerateLoadedModules)(HANDLE,PENUMLOADED_MODULES_CALLBACK64,PVOID);
 static fpEnumerateLoadedModules fEnumerateLoadedModules;
-static DenseSet<HMODULE> *OpenedHandles;
+static llvm::ManagedStatic<DenseSet<HMODULE> > OpenedHandles;
 
 static bool loadDebugHelp(void) {
   HMODULE hLib = ::LoadLibraryW(L"Dbghelp.dll");
@@ -59,9 +57,6 @@
 
   if (!filename) {
     // When no file is specified, enumerate all DLLs and EXEs in the process.
-    if (OpenedHandles == 0)
-      OpenedHandles = new DenseSet<HMODULE>();
-
     if (!fEnumerateLoadedModules) {
       if (!loadDebugHelp()) {
         assert(false && "These APIs should always be available");
@@ -81,7 +76,7 @@
     MakeErrMsg(errMsg, std::string(filename) + ": Can't convert to UTF-16");
     return DynamicLibrary();
   }
-  
+
   HMODULE a_handle = LoadLibraryW(filenameUnicode.data());
 
   if (a_handle == 0) {
@@ -89,15 +84,29 @@
     return DynamicLibrary();
   }
 
-  if (OpenedHandles == 0)
-    OpenedHandles = new DenseSet<HMODULE>();
-
+  DynamicLibrary dyLib = addPermanentLibraryWithLock(a_handle, lock);
   // If we've already loaded this library, FreeLibrary() the handle in order to
   // keep the internal refcount at +1.
-  if (!OpenedHandles->insert(a_handle).second)
+  if (!dyLib.isValid()) {
+    MakeErrMsg(errMsg, std::string(filename) + ": Already loaded");
     FreeLibrary(a_handle);
+  }
+
+  return dyLib;
+}
+
+DynamicLibrary DynamicLibrary::addPermanentLibrary(void *handle) {
+  SmartScopedLock<true> lock(*SymbolsMutex);
+  return addPermanentLibraryWithLock(handle, lock);
+}
+
+DynamicLibrary DynamicLibrary::addPermanentLibraryWithLock(void *handle,
+                                                 sys::SmartScopedLock<true> &) {
+  // If we've already loaded this library, tell the caller.
+  if (!OpenedHandles->insert((const HMODULE)handle).second)
+    return DynamicLibrary();
 
-  return DynamicLibrary(a_handle);
+  return DynamicLibrary((HMODULE)handle);
 }
 
 // Stack probing routines are in the support library (e.g. libgcc), but we don't