auto function = dyn_cast_or_null<mlir::func::FuncOp>(
      SymbolTable::lookupSymbolIn(module, op.getReducer()));
  if (!function) return op.emitOpError() << "No reducer";
  if (!function.getBody().hasOneBlock())
    return op.emitOpError() << "reducer has more than one block";

  return success();
}

//===----------------------------------------------------------------------===//
// XlaVariadicSortOp