Revert "Revert 220932.": "Removing the static initializer in ManagedStatic.cpp by using llvm_call_once to initialize the ManagedStatic mutex"

This reverts commit r221331 and reinstate r220932 as discussed in D19271.
Original commit message was:

This patch adds an llvm_call_once which is a wrapper around
std::call_once on platforms where it is available and devoid
of bugs. The patch also migrates the ManagedStatic mutex to
be allocated using llvm_call_once.

These changes are philosophically equivalent to the changes
added in r219638, which were reverted due to a hang on Win32
which was the result of a bug in the Windows implementation
of std::call_once.

Differential Revision: http://reviews.llvm.org/D5922

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 269577

1 files changed, 11 insertions, 4 deletions

diff --git a/llvm/lib/Support/ManagedStatic.cpp b/llvm/lib/Support/ManagedStatic.cpp
index b8fb2841e52..b1feddc09ec 100644
--- a/llvm/lib/Support/ManagedStatic.cpp
+++ b/llvm/lib/Support/ManagedStatic.cpp
@@ -16,16 +16,23 @@
 #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 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;
+  call_once(mutex_init_flag, initializeMutex);
   return ManagedStaticMutex;
 }
 
@@ -33,7 +40,7 @@ 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();
@@ -83,7 +90,7 @@ 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();