[C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.

llvm-svn: 206356
diff --git a/llvm/lib/CodeGen/RegAllocBase.h b/llvm/lib/CodeGen/RegAllocBase.h
index 68bd4b5..b333c36 100644
--- a/llvm/lib/CodeGen/RegAllocBase.h
+++ b/llvm/lib/CodeGen/RegAllocBase.h
@@ -65,7 +65,8 @@
   LiveRegMatrix *Matrix;
   RegisterClassInfo RegClassInfo;
 
-  RegAllocBase(): TRI(0), MRI(0), VRM(0), LIS(0), Matrix(0) {}
+  RegAllocBase()
+    : TRI(nullptr), MRI(nullptr), VRM(nullptr), LIS(nullptr), Matrix(nullptr) {}
 
   virtual ~RegAllocBase() {}