From e729b5e31950be6938ea0bbbd12a83a5808a61df Mon Sep 17 00:00:00 2001
From: Hannes Verschore <hv1989@gmail.com>
Date: Thu, 4 Sep 2014 11:08:00 +0200
Subject: [PATCH] Bug 1061764 - Atomic<bool, Relaxed> should mean no
 synchronization on windows x86, r=froydnj

---
 mfbt/Atomics.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mfbt/Atomics.h b/mfbt/Atomics.h
index 71d95c61bac7..495a9d3f595e 100644
--- a/mfbt/Atomics.h
+++ b/mfbt/Atomics.h
@@ -40,7 +40,14 @@
 #  elif MOZ_USING_LIBCXX
 #    define MOZ_HAVE_CXX11_ATOMICS
 #  endif
-#elif defined(_MSC_VER) && _MSC_VER >= 1700
+/*
+ * Although Visual Studio 2012's CRT supports <atomic>, its atomic load
+ * implementation unnecessarily uses an atomic intrinsic for the less
+ * restrictive memory orderings, which can be prohibitively expensive.
+ * Therefore, we require at least Visual Studio 2013 for using the CRT
+ * (bug 1061764).
+ */
+#elif defined(_MSC_VER) && _MSC_VER >= 1800
 #  if defined(DEBUG)
      /*
       * Provide our own failure code since we're having trouble linking to