Re: How could I get alias set information from data_reference_p

[Tobias Grosser <grosser@fim.uni-passau.de>]

On Wed, 2009-07-15 at 22:48 +0200, Richard Guenther wrote:
> On Wed, Jul 15, 2009 at 10:46 PM, Richard
> Guenther<richard.guenther@gmail.com> wrote:
> > On Wed, Jul 15, 2009 at 9:15 PM, Tobias
> > Grosser<grosser@fim.uni-passau.de> wrote:
> >>> A note on Lis final graph algorithm.  I don't understand why you want
> >>> to allow data-references to be part of multiple alias-sets?  (Of course
> >>> I don't know how you are going to use the alias-sets ...)
> >>
> >> Just to pass more information to Graphite. The easiest example might be
> >> something like
> >>
> >> A -- B -- C
> >>
> >> if we have
> >>
> >> AS1 = {A,B}
> >> AS2 = {B,C}
> >>
> >> we know that A and C do not alias and therefore do not have any
> >
> > No, from the above you _don't_ know that.  How would you arrive
> > at that conclusion?
> 
> What I want to say is that, if  A -- B -- C is supposed to be the alias graph
> resulting from querying the alias oracle for the pairs (A, B), (A, C), (B, C)
> then this is a result that will never occur.  Because if (A, B) is true
> and (B, C) is true then (A, C) will be true as well.

What for example for this case:

void foo (*b) {
 int *a 
 int *c
 
 if (bar())
	a = b;
 else
	c = b;
}

I thought this may give us the example above, but it seems I am wrong.
If the alias oracle is transitive that would simplify the algorithm a
lot. Can we rely on the transitivity?

Tobi