diff --git a/include/llvm/Support/Threading.h b/include/llvm/Support/Threading.h
index 74fe745f3bb..7e8758407c7 100644
--- a/include/llvm/Support/Threading.h
+++ b/include/llvm/Support/Threading.h
@@ -15,14 +15,6 @@
 #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"
-#endif
-
 namespace llvm {
   /// Returns true if LLVM is compiled with support for multi-threading, and
   /// false otherwise.
@@ -41,34 +33,6 @@ namespace llvm {
   /// the thread stack.
   void llvm_execute_on_thread(void (*UserFn)(void*), void *UserData,
                               unsigned RequestedStackSize = 0);
-
-#if defined(LLVM_ON_UNIX)
-typedef std::once_flag once_flag;
-#define LLVM_DEFINE_ONCE_FLAG(flag) static once_flag flag
-#else
-enum InitStatus {
-  Done = -1,
-  Uninitialized = 0,
-  Wait = 1
-};
-typedef volatile sys::cas_flag once_flag;
-
-#define LLVM_DEFINE_ONCE_FLAG(flag) static once_flag flag = Uninitialized
-#endif
-
-/// \brief Execute the function specified as a parameter once.
-///
-/// Typical usage:
-/// \code
-///   void foo() {...};
-///   ...
-///   LLVM_DEFINE_ONCE_FLAG(flag);
-///   call_once(flag, foo);
-/// \endcode
-///
-/// \param flag Flag used for tracking whether or not this has run.
-/// \param UserFn Function to call once.
-void call_once(once_flag &flag, void (*UserFn)(void));
 }
 
 #endif
diff --git a/lib/Support/CMakeLists.txt b/lib/Support/CMakeLists.txt
index 24a115e0157..a751d62ebb8 100644
--- a/lib/Support/CMakeLists.txt
+++ b/lib/Support/CMakeLists.txt
@@ -102,7 +102,6 @@ add_llvm_library(LLVMSupport
   Unix/Program.inc
   Unix/RWMutex.inc
   Unix/Signals.inc
-  Unix/Threading.inc
   Unix/ThreadLocal.inc
   Unix/TimeValue.inc
   Unix/Watchdog.inc
@@ -115,7 +114,6 @@ add_llvm_library(LLVMSupport
   Windows/Program.inc
   Windows/RWMutex.inc
   Windows/Signals.inc
-  Windows/Threading.inc
   Windows/ThreadLocal.inc
   Windows/TimeValue.inc
   Windows/Watchdog.inc
diff --git a/lib/Support/ManagedStatic.cpp b/lib/Support/ManagedStatic.cpp
index b1feddc09ec..b8fb2841e52 100644
--- a/lib/Support/ManagedStatic.cpp
+++ b/lib/Support/ManagedStatic.cpp
@@ -16,23 +16,16 @@
 #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;
-LLVM_DEFINE_ONCE_FLAG(mutex_init_flag);
 
-static void initializeMutex() {
-  ManagedStaticMutex = new sys::Mutex();
-}
-
-static sys::Mutex* getManagedStaticMutex() {
+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.
-  call_once(mutex_init_flag, initializeMutex);
+  static sys::Mutex ManagedStaticMutex;
   return ManagedStaticMutex;
 }
 
@@ -40,7 +33,7 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    MutexGuard Lock(*getManagedStaticMutex());
+    MutexGuard Lock(getManagedStaticMutex());
 
     if (!Ptr) {
       void* tmp = Creator();
@@ -90,7 +83,7 @@ void ManagedStaticBase::destroy() const {
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
-  MutexGuard Lock(*getManagedStaticMutex());
+  MutexGuard Lock(getManagedStaticMutex());
 
   while (StaticList)
     StaticList->destroy();
diff --git a/lib/Support/Threading.cpp b/lib/Support/Threading.cpp
index 59b937d9842..ca7f3f64aa3 100644
--- a/lib/Support/Threading.cpp
+++ b/lib/Support/Threading.cpp
@@ -110,10 +110,3 @@ void llvm::llvm_execute_on_thread(void (*Fn)(void*), void *UserData,
 }
 
 #endif
-
-#if defined(LLVM_ON_UNIX)
-#include "Unix/Threading.inc"
-#else
-#include "Windows/Threading.inc"
-#endif
-
diff --git a/lib/Support/Unix/Threading.inc b/lib/Support/Unix/Threading.inc
deleted file mode 100644
index 35ec876904a..00000000000
--- a/lib/Support/Unix/Threading.inc
+++ /dev/null
@@ -1,5 +0,0 @@
-#include <thread>
-
-void llvm::call_once(once_flag& flag, void (*fptr)(void)) {
-  std::call_once(flag, fptr);
-}
diff --git a/lib/Support/Windows/Threading.inc b/lib/Support/Windows/Threading.inc
deleted file mode 100644
index 196be890dbf..00000000000
--- a/lib/Support/Windows/Threading.inc
+++ /dev/null
@@ -1,24 +0,0 @@
- #include <windows.h>
-
-#ifdef MemoryFence
-// WinNT.h seems to define a MemoryFence macro.
-#undef MemoryFence
-#endif
-
-void llvm::call_once(once_flag &flag, void (*fptr)(void)) {
-  while (flag != Done) {
-    if (flag == Wait) {
-      ::Sleep(1);
-      continue;
-    }
-
-    sys::cas_flag old_val = sys::CompareAndSwap(&flag, Wait, Uninitialized);
-    if (old_val == Uninitialized) {
-      fptr();
-      sys::MemoryFence();
-      flag = Done;
-      return;
-    }
-  }
-  sys::MemoryFence();
-}