[InstCombine] use 'match' to simplify code

There's probably some vector-with-undef-element pattern
that shows an improvement, so this is probably not quite
'NFC'.

This is the last step towards removing the fake binop 
queries for not/neg. Ie, there are no more uses of those
functions in trunk. Fneg should follow.

llvm-svn: 345050

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -141,7 +141,7 @@ static inline Constant *SubOne(Constant *C) {
 /// uses of V and only keep uses of ~V.
 static inline bool IsFreeToInvert(Value *V, bool WillInvertAllUses) {
   // ~(~(X)) -> X.
-  if (BinaryOperator::isNot(V))
+  if (match(V, m_Not(m_Value())))
     return true;
 
   // Constants can be considered to be not'ed values.