2 files changed, 17 insertions, 40 deletions

diff --git a/llvm/include/llvm/Support/ManagedStatic.h b/llvm/include/llvm/Support/ManagedStatic.h
index 3a34bdbd01f..ec8154b828e 100644
--- a/llvm/include/llvm/Support/ManagedStatic.h
+++ b/llvm/include/llvm/Support/ManagedStatic.h
@@ -14,9 +14,9 @@
 #ifndef LLVM_SUPPORT_MANAGEDSTATIC_H
 #define LLVM_SUPPORT_MANAGEDSTATIC_H
 
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Compiler.h"
-#include "llvm/Support/Threading.h"
+#include <atomic>
+#include <cstddef>
 
 namespace llvm {
 
@@ -41,7 +41,7 @@ class ManagedStaticBase {
 protected:
   // This should only be used as a static variable, which guarantees that this
   // will be zero initialized.
-  mutable void *Ptr;
+  mutable std::atomic<void *> Ptr;
   mutable void (*DeleterFn)(void*);
   mutable const ManagedStaticBase *Next;
 
@@ -61,40 +61,26 @@ public:
 template<class C>
 class ManagedStatic : public ManagedStaticBase {
 public:
-
   // Accessors.
   C &operator*() {
-    void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
-    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
-    TsanHappensAfter(this);
+    void *Tmp = Ptr.load(std::memory_order_acquire);
+    if (!Tmp)
+      RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
 
-    return *static_cast<C*>(Ptr);
+    return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
   }
-  C *operator->() {
-    void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
-    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
-    TsanHappensAfter(this);
 
-    return static_cast<C*>(Ptr);
-  }
+  C *operator->() { return &**this; }
+
   const C &operator*() const {
-    void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
-    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
-    TsanHappensAfter(this);
+    void *Tmp = Ptr.load(std::memory_order_acquire);
+    if (!Tmp)
+      RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
 
-    return *static_cast<C*>(Ptr);
+    return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
   }
-  const C *operator->() const {
-    void* tmp = Ptr;
-    if (llvm_is_multithreaded()) sys::MemoryFence();
-    if (!tmp) RegisterManagedStatic(object_creator<C>, object_deleter<C>::call);
-    TsanHappensAfter(this);
 
-    return static_cast<C*>(Ptr);
-  }
+  const C *operator->() const { return &**this; }
 };
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
diff --git a/llvm/lib/Support/ManagedStatic.cpp b/llvm/lib/Support/ManagedStatic.cpp
index bc4fe954e22..7dd31315f90 100644
--- a/llvm/lib/Support/ManagedStatic.cpp
+++ b/llvm/lib/Support/ManagedStatic.cpp
@@ -13,7 +13,6 @@
 
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Config/config.h"
-#include "llvm/Support/Atomic.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/MutexGuard.h"
 #include "llvm/Support/Threading.h"
@@ -42,18 +41,10 @@ void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
   if (llvm_is_multithreaded()) {
     MutexGuard Lock(*getManagedStaticMutex());
 
-    if (!Ptr) {
-      void* tmp = Creator();
+    if (!Ptr.load(std::memory_order_relaxed)) {
+      void *Tmp = Creator();
 
-      TsanHappensBefore(this);
-      sys::MemoryFence();
-
-      // This write is racy against the first read in the ManagedStatic
-      // accessors. The race is benign because it does a second read after a
-      // memory fence, at which point it isn't possible to get a partial value.
-      TsanIgnoreWritesBegin();
-      Ptr = tmp;
-      TsanIgnoreWritesEnd();
+      Ptr.store(Tmp, std::memory_order_release);
       DeleterFn = Deleter;
       
       // Add to list of managed statics.