Revert r229082 for a bit, it caused PR22577.

llvm-svn: 229123
diff --git a/clang/lib/CodeGen/CGStmtOpenMP.cpp b/clang/lib/CodeGen/CGStmtOpenMP.cpp
index 6b3faa1..b4dcadc 100644
--- a/clang/lib/CodeGen/CGStmtOpenMP.cpp
+++ b/clang/lib/CodeGen/CGStmtOpenMP.cpp
@@ -829,11 +829,8 @@
   assert(X->isLValue() && "X of 'omp atomic read' is not lvalue");
   LValue XLValue = CGF.EmitLValue(X);
   LValue VLValue = CGF.EmitLValue(V);
-  RValue Res = XLValue.isGlobalReg()
-                   ? CGF.EmitLoadOfLValue(XLValue, Loc)
-                   : CGF.EmitAtomicLoad(XLValue, Loc,
-                                        IsSeqCst ? llvm::SequentiallyConsistent
-                                                 : llvm::Monotonic);
+  RValue Res = XLValue.isGlobalReg() ? CGF.EmitLoadOfLValue(XLValue, Loc)
+                                     : CGF.EmitAtomicLoad(XLValue, Loc);
   // OpenMP, 2.12.6, atomic Construct
   // Any atomic construct with a seq_cst clause forces the atomically
   // performed operation to include an implicit flush operation without a