> (declaim (optimize (safety 3)))
((OPTIMIZE (SAFETY 3)))

> (compile nil (lambda () (let ((x most-positive-fixnum)) (declare (fixnum x)) (locally (declare (ext:assume-right-type)) (setq x (1+ x))))))
;;; OPTIMIZE levels: Safety=3, Space=0, Speed=3, Debug=0
;;;
;;; End of Pass 1.
#<compiled-function 0x555ccc118c40>
NIL
NIL

> (funcall *)
-2305843009213693952