Add a hasPoisonGeneratingFlags proxy wrapper to Instruction [NFC]

This just cuts down on casts to Operator.

llvm/include/llvm/IR/Instruction.h

@@ -387,6 +387,10 @@ public:
   /// Determine whether the no signed wrap flag is set.
   bool hasNoSignedWrap() const;
 
+  /// Return true if this operator has flags which may cause this instruction
+  /// to evaluate to poison despite having non-poison inputs.
+  bool hasPoisonGeneratingFlags() const;
+
   /// Drops flags that may cause this instruction to evaluate to poison despite
   /// having non-poison inputs.
   void dropPoisonGeneratingFlags();

llvm/lib/IR/Instruction.cpp

@@ -141,6 +141,10 @@ bool Instruction::hasNoSignedWrap() const {
   return cast<OverflowingBinaryOperator>(this)->hasNoSignedWrap();
 }
 
+bool Instruction::hasPoisonGeneratingFlags() const {
+  return cast<Operator>(this)->hasPoisonGeneratingFlags();
+}
+
 void Instruction::dropPoisonGeneratingFlags() {
   switch (getOpcode()) {
   case Instruction::Add:
@@ -164,8 +168,7 @@ void Instruction::dropPoisonGeneratingFlags() {
   }
   // TODO: FastMathFlags!
 
-  assert(!cast<Operator>(this)->hasPoisonGeneratingFlags() &&
-         "must be kept in sync");
+  assert(!hasPoisonGeneratingFlags() && "must be kept in sync");
 }
 
 void Instruction::dropUndefImplyingAttrsAndUnknownMetadata(