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

llvm-svn: 206252
diff --git a/llvm/lib/IR/Instruction.cpp b/llvm/lib/IR/Instruction.cpp
index d2c47e7..e638540b 100644
--- a/llvm/lib/IR/Instruction.cpp
+++ b/llvm/lib/IR/Instruction.cpp
@@ -53,7 +53,7 @@
 
 // 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();
 }