Kill the LLVM global lock.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211069 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/ManagedStatic.cpp

@@ -16,16 +16,34 @@
 #include "llvm/Support/Atomic.h"
 #include "llvm/Support/MutexGuard.h"
 #include <cassert>
+#include <mutex>
 using namespace llvm;
 
 static const ManagedStaticBase *StaticList = nullptr;
 
+// ManagedStatics can get created during execution of static constructors.  As a
+// result, we cannot use a global static std::mutex object for the lock since it
+// may not have been constructed.  Instead, we do a call-once initialization of
+// a pointer to a mutex.  This also means that we must not "initialize" the
+// mutex with nullptr, otherwise it might get reset to nullptr after being
+// initialized by std::call_once.
+static std::once_flag MutexInitializationFlag;
+static std::recursive_mutex *ManagedStaticMutex;
+
+namespace {
+  void InitializeManagedStaticMutex() {
+    std::call_once(MutexInitializationFlag,
+        []() { ManagedStaticMutex = new std::recursive_mutex(); });
+  }
+}
+
 void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);
   if (llvm_is_multithreaded()) {
-    llvm::MutexGuard Lock(llvm::llvm_get_global_lock());
+    InitializeManagedStaticMutex();
 
+    std::lock_guard<std::recursive_mutex> Lock(*ManagedStaticMutex);
     if (!Ptr) {
       void* tmp = Creator();
 
@@ -74,6 +92,9 @@ void ManagedStaticBase::destroy() const {
 
 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
 void llvm::llvm_shutdown() {
+  InitializeManagedStaticMutex();
+  std::lock_guard<std::recursive_mutex> Lock(*ManagedStaticMutex);
+
   while (StaticList)
     StaticList->destroy();
 }