Index: include/llvm/Support/Threading.h
===================================================================
--- include/llvm/Support/Threading.h
+++ include/llvm/Support/Threading.h
@@ -15,6 +15,15 @@
 #ifndef LLVM_SUPPORT_THREADING_H
 #define LLVM_SUPPORT_THREADING_H
 
+#include "llvm/Config/llvm-config.h"  // for LLVM_ON_UNIX
+
+#if defined(LLVM_ON_UNIX)
+#include <mutex>
+#else
+#include "llvm/Support/Atomic.h"
+#include "llvm/Support/Valgrind.h"
+#endif
+
 namespace llvm {
   /// Returns true if LLVM is compiled with support for multi-threading, and
   /// false otherwise.
@@ -33,6 +42,48 @@
   /// the thread stack.
   void llvm_execute_on_thread(void (*UserFn)(void*), void *UserData,
                               unsigned RequestedStackSize = 0);
+
+/// \brief Execute the function specified as a template parameter once.
+///
+/// Calls \p UserFn once ever. The call uniqueness is based on the address of
+/// the function passed in via the template arguement. This means no matter how
+/// many times you call llvm_call_once<foo>() in the same or different
+/// locations, foo will only be called once.
+///
+/// Typical usage:
+/// \code
+///   void foo() {...};
+///   ...
+///   llvm_call_once<foo>();
+/// \endcode
+///
+/// \tparam UserFn Function to call once.
+template <void (*UserFn)(void)> void llvm_call_once() {
+#if defined(LLVM_ON_UNIX)
+  static std::once_flag flag;
+  std::call_once(flag, UserFn);
+#else
+  // Due to a bug in Windows 7's C++ runtime std::call_once cannot be called
+	// during a static initializer. To workaround this the hand rolled solution
+	// below uses thread primitives to implement call_once semantics.
+	// Visual Studio bug id #811192.
+	static volatile sys::cas_flag initialized = 0;
+	sys::cas_flag old_val = sys::CompareAndSwap(&initialized, 1, 0);
+	if (old_val == 0) {
+		UserFn();
+		sys::MemoryFence();
+		initialized = 2;
+	}
+	else {
+		sys::cas_flag tmp = initialized;
+		sys::MemoryFence();
+		while (tmp != 2) {
+			tmp = initialized;
+			sys::MemoryFence();
+		}
+	}
+#endif
+}
 }
 
 #endif
Index: lib/Support/ManagedStatic.cpp
===================================================================
--- lib/Support/ManagedStatic.cpp
+++ lib/Support/ManagedStatic.cpp
@@ -16,16 +16,22 @@
 #include "llvm/Support/Atomic.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/MutexGuard.h"
+#include "llvm/Support/Threading.h"
 #include <cassert>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = nullptr;
+static sys::Mutex *ManagedStaticMutex = nullptr;
 
-static sys::Mutex& getManagedStaticMutex() {
+static void initializeMutex() {
+  ManagedStaticMutex = new sys::Mutex();
+}
+
+static sys::Mutex* getManagedStaticMutex() {
   // We need to use a function local static here, since this can get called
   // during a static constructor and we need to guarantee that it's initialized
   // correctly.
-  static sys::Mutex ManagedStaticMutex;
+  llvm_call_once<initializeMutex>();
   return ManagedStaticMutex;
 }
 
@@ -33,7 +39,7 @@
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    MutexGuard Lock(getManagedStaticMutex());
+    MutexGuard Lock(*getManagedStaticMutex());
 
     if (!Ptr) {
       void* tmp = Creator();
@@ -83,7 +89,7 @@
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
-  MutexGuard Lock(getManagedStaticMutex());
+  MutexGuard Lock(*getManagedStaticMutex());
 
   while (StaticList)
     StaticList->destroy();