This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: [tree-ssa]: Dominator opts change LHS without changing VDEF's
On Sun, 10 Aug 2003, Diego Novillo wrote:
> On Sun, 2003-08-10 at 17:31, Daniel Berlin wrote:
>
> > > 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.
> >
> Ah, yes. I see the distinction now. To fix this, you need to change
> the query we do in tree-dfa.c:get_memory_tag_for. Currently, we only
> ask whether the pointer may point to the variable. Is there a query
> that we can do to ask 'whether this pointer points to the same memory
> pointed by this other pointer?'. That's the query we are missing.
>
> Both LHS elt and RHS elt *must* have the same memory tag.
I'm curious why. The copy propagation was perfectly valid, and should
have been performed, actually.