SBCL:

* (load "/tmp/setf-test-1.lisp")
STYLE-WARNING: defining setf macro for FOO-VAL when (SETF FOO-VAL) is fbound

T
* *foo*

(0)
* (foo-val *foo*)

0
* (test)

1
* (foo-val *foo*)

1
* (setf (foo-val *foo*) 2)

2