Another dynamic extent bug (failed AVER)

[Paul F. Dietz]

(defun f52 (x)
  (let ((*s*
         (list (list x)
               (catch 'ct1
                 (block b2
                   (multiple-value-prog1
                       -259440630174253438
                     (throw 'ct8 30)))))
          ))
    (declare (special *s*) (dynamic-extent *s*))))

==>

failed AVER: (SUBSETP SB-C::END SB-C::END-STACK)

Note: this is not a malformed code bug.

[Alastair Bridgewater (alastair-bridgewater)]

Two variants, both exemplifying the same bug:

(defun f52a (x)
  (let ((*s*
         (multiple-value-prog1 (list x)
           (catch 'ct1
             (throw 'ct8 30)))))
    (declare (special *s*) (dynamic-extent *s*))))

(defun f52b (x y)
  (let ((s
         (multiple-value-prog1 (list x)
           (catch 'ct1
             (throw 'ct8 30)))))
    (declare (dynamic-extent s))
    (funcall (truly-the function y) s)))

The THROW doesn't return, but the CATCH entry is still live (yes, it is possible to set up a context where control leaves via the THROW and ends up at the CATCH), and is the only path back from the "entry DX" for S or *S*. BACK-PROPAGATE-DX-LVARS can't see through the entry to its allocator, though, so it finds no path to (LIST X), and thus the LVAR doesn't get back-propagated anywhere.

[Alastair Bridgewater (alastair-bridgewater)]

Fixed in 6eb755deadbfd2df3e1f54c891e8ef331f176076.