On Fri, Oct 27, 2017 at 02:30:39PM -0400, Nathan Sidwell wrote:
> On 10/27/2017 02:18 PM, Jakub Jelinek wrote:
> > On Fri, Oct 27, 2017 at 02:10:10PM -0400, Jason Merrill wrote:
>
> > > If the point is to clear the vptr, why are you also clearing the rest
> > > of the object?
> >
> > Can there be multiple vptr pointers in the object or is there just one?
> > Even if there can be multiple, perhaps earlier destructors would
> > have cleared those other vptr pointers though.
>
> There can be multiple vptrs in an object (multiple polymorphic bases).
> However, each such case will have its own base dtor invoked, as you
> postulated. In fact, there may be a base dtor invoked that maps onto the
> single vptr, in the cases when we're singly inheriting a polymorphic base.
But when singly inheriting a polymorphic base and thus mapped to the same
vptr all but the last dtor will not be in charge, right?
So, if using build_clobber_this for this, instead of clobbering what we
clobber we'd just clear the single vptr (couldn't clobber the rest, even
if before the store, because that would make the earlier other vptr stores
dead).
Jakub
