Re: [tree-ssa]: Dominator opts change LHS without changing VDEF's

[Daniel Berlin <dberlin at dberlin dot org>]

On Sun, 10 Aug 2003, Daniel Berlin wrote:

>
>
> On Sun, 10 Aug 2003, Diego Novillo wrote:
>
> > On Sun, 2003-08-10 at 17:17, Daniel Berlin wrote:
> >
> > > > > This causes the vdef's to changes, because the memory tag for elt isn't
> > > > > the same as elt.
> > > > >
> > > > They aren't?
> > > No.
> > >
> > But, why?  This only occurs with PTA,
>
> > why aren't those variables considered aliased?
> Because they aren't?
>
>
> > They do seem aliased to me.  If they are aliased,
> > they will get the same memory tag.  In this case they don't get the same
> > memory tag because alias analysis tells us that they aren't aliased, I
> > want to know why alias analysis doesn't consider them aliased.
> >
> > The very fact that we can copy propagate one into the other means that
> > they are aliased.  If alias analysis is saying that they can't alias,
> > then alias analysis is wrong.
> >
> >
> > bitmap_element_free (struct bitmap_element *elt)
> > {
> > ....
> >   {
> >      struct bitmap_element * elt;
> >      struct bitmap_head_def * head;
> >
> >      head = head;
> >      elt = elt;			<-- Here 'elt' points to 'elt'.
>
> No, this statement means elt (lhs) points to whatever elt (rhs) points to.
> elt doesn't point to elt.
> That would be *elt = elt
Sorry, I meant elt = &elt.
*elt = elt means whatever elt points to points to elt.


> In other words, it means that elt has to point to whatever elt points to.
> Not that elt points to elt.
> elt *doesn't* point to elt.
>
>
>