message: Rephrasing last statement invariant check in ReturnOp::verify() to be more
  elegant.
diff: @@ -438,8 +438,8 @@ void ReturnOp::print(OpAsmPrinter *p) const {
  const char *ReturnOp::verify() const {
  // ReturnOp must be part of an ML function.
  if (auto *stmt = dyn_cast<OperationStmt>(getOperation())) {
  - MLFunction *func = dyn_cast_or_null<MLFunction>(stmt->getBlock());
  - if (!func || &func->back() != stmt)
  + StmtBlock *block = stmt->getBlock();
  + if (!block || !isa<MLFunction>(block) || &block->back() != stmt)
  return "must be the last statement in the ML function";
  // Return success. Checking that operand types match those in the function
  