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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205831 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/User.h

@@ -55,7 +55,7 @@ protected:
   Use *allocHungoffUses(unsigned) const;
   void dropHungoffUses() {
     Use::zap(OperandList, OperandList + NumOperands, true);
-    OperandList = 0;
+    OperandList = nullptr;
     // Reset NumOperands so User::operator delete() does the right thing.
     NumOperands = 0;
   }
@@ -179,7 +179,7 @@ public:
   //
   void dropAllReferences() {
     for (Use &U : operands())
-      U.set(0);
+      U.set(nullptr);
   }
 
   /// replaceUsesOfWith - Replaces all references to the "From" definition with