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

llvm-svn: 206142
diff --git a/llvm/include/llvm/CodeGen/MachineTraceMetrics.h b/llvm/include/llvm/CodeGen/MachineTraceMetrics.h
index dc0bc1d..323b694 100644
--- a/llvm/include/llvm/CodeGen/MachineTraceMetrics.h
+++ b/llvm/include/llvm/CodeGen/MachineTraceMetrics.h
@@ -154,7 +154,7 @@
     unsigned InstrHeight;
 
     TraceBlockInfo() :
-      Pred(0), Succ(0),
+      Pred(nullptr), Succ(nullptr),
       InstrDepth(~0u), InstrHeight(~0u),
       HasValidInstrDepths(false), HasValidInstrHeights(false) {}