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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206252 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Instruction.cpp

@@ -53,7 +53,7 @@ Instruction::Instruction(Type *ty, unsigned it, Use *Ops, unsigned NumOps,
 
 // Out of line virtual method, so the vtable, etc has a home.
 Instruction::~Instruction() {
-  assert(Parent == 0 && "Instruction still linked in the program!");
+  assert(!Parent && "Instruction still linked in the program!");
   if (hasMetadataHashEntry())
     clearMetadataHashEntries();
 }