From 3cfc62aa08c671c4f7fccd21e1ff1af2b07d34b6 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Thu, 18 Jun 2009 16:08:27 +0000
Subject: [PATCH] As pointed out by Duncan, I accidentally dropped the first
 MemoryFence of the double-checked locking pattern here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73701 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/VMCore/Pass.cpp | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/VMCore/Pass.cpp b/lib/VMCore/Pass.cpp
index 579f1029ac3..70ec108fa18 100644
--- a/lib/VMCore/Pass.cpp
+++ b/lib/VMCore/Pass.cpp
@@ -197,17 +197,21 @@ static PassRegistrar *getPassRegistrar() {
   
   // Use double-checked locking to safely initialize the registrar when
   // we're running in multithreaded mode.
-  if (!PassRegistrarObj) {
+  PassRegistrar* tmp = PassRegistrarObj;
+  sys::MemoryFence();
+  if (!tmp) {
     if (llvm_is_multithreaded()) {
       llvm_acquire_global_lock();
-      if (!PassRegistrarObj) {
-        PassRegistrar* tmp = new PassRegistrar();
+      tmp = PassRegistrarObj;
+      if (!tmp) {
+        tmp = new PassRegistrar();
         sys::MemoryFence();
         PassRegistrarObj = tmp;
       }
       llvm_release_global_lock();
-    } else
+    } else {
       PassRegistrarObj = new PassRegistrar();
+    }
   }
   return PassRegistrarObj;
 }
-- 
2.34.1