[Sbcl-devel] compiler inconsistency

[Alexey D. <ade...@co...>]

Hello,

----- pack.lisp -----
(defun target-if-desirable (read write)
  (declare (type tn-ref read write))
  (setf (tn-ref-target read) write)
  (setf (tn-ref-target write) read))
-----

In the description of TN-REF it is said that linked TN-REFs must have
different WRITE-Ps. I tried to insert an AVER here:

(defun target-if-desirable (read write)
  (declare (type tn-ref read write))
  (aver (eq (tn-ref-write-p read)
            (not (tn-ref-write-p write))))
  (setf (tn-ref-target read) write)
  (setf (tn-ref-target write) read))

and it immediately caused errors. But the word DESIRABLE embarrasses
me. Should this function link if it is "wanted" (in this case the
AVER is right and there is a bug upstream) or "wanted and possible"?
In the latter case the present code is erroneous and should be
written as follows:

(defun target-if-desirable (read write)
  (declare (type tn-ref read write))
  (when (eq (tn-ref-write-p read)
            (not (tn-ref-write-p write)))
        (setf (tn-ref-target read) write)
        (setf (tn-ref-target write) read)))

--
Regards,
Alexey Dejneka