[C++] Use 'nullptr'.

llvm-svn: 207083
diff --git a/llvm/lib/CodeGen/AtomicExpandLoadLinkedPass.cpp b/llvm/lib/CodeGen/AtomicExpandLoadLinkedPass.cpp
index 2678b81..d995333 100644
--- a/llvm/lib/CodeGen/AtomicExpandLoadLinkedPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandLoadLinkedPass.cpp
@@ -30,8 +30,8 @@
     const TargetLowering *TLI;
   public:
     static char ID; // Pass identification, replacement for typeid
-    explicit AtomicExpandLoadLinked(const TargetMachine *TM = 0)
-      : FunctionPass(ID), TLI(TM ? TM->getTargetLowering() : 0) {
+    explicit AtomicExpandLoadLinked(const TargetMachine *TM = nullptr)
+      : FunctionPass(ID), TLI(TM ? TM->getTargetLowering() : nullptr) {
       initializeAtomicExpandLoadLinkedPass(*PassRegistry::getPassRegistry());
     }