0.9.10.22:

0.9.10.22:
        Remove spurious VOPs for translating %INSTANCE-{REF,SET}.
        ... These VOPs were based on SLOT-{REF,SET} and in all ports
            there were also translations based on DEFINE-FULL-REFFER or
            WORD-INDEX-REF.  However, at the very least, the
            %INSTANCE-SET VOP based on SLOT-SET was bogus, as it did not
            return a value, thereby generating incorrect code.
            Therefore, this VOP was either disabled (#+nil) or the
            alternative via DEFINE-FULL-REFFER was carefully defined
            with a lower :GENERATOR cost so that the VOP based on
            SLOT-SET would never be called.  This patch eliminates such
            magic and eliminates the corresponding %INSTANCE-REF VOP as
            well, since it does not appear to have any advantages over
            the one created via DEFINE-FULL-REFFER.
        ... See also sbcl-devel, 2002-02-11, "Dubious VOPs".  This patch
            does not implement the DEFINE-VOP magic discussed in the
            email.