[Bug tree-optimization/67955] tree-dse does not use pointer info

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67955

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |alias, missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-10-14
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to vries from comment #2)
> (In reply to Richard Biener from comment #1)
> > The same points-to set results from
> > 
> > int *p = (int *)((char *)&a + 2);
> > 
> > or even
> > 
> > int *p = &a + 1;
> > 
> 
> I see, I didn't realize that. But AFAICT, in both these cases, storing to *p
> is illegal (if 'a' is a scalar int).
> 
> > so you can't use points-to info that way (to derive a must-alias).
> 
> I see your point related to an array object, there pointers to different
> array elements would have identical points-to sets.
> 
> I wonder though: if we have a store '*p = 0', and the size of the store is
> the same as the size of the pointed-to object of pointer p, can't we
> conclude that  pointer p points to the start of the object?

Yes, for that special case we indeed can do that.  I wonder if it's worth
doing though ;)  Care to adjust stmt_kills_ref_p accordingly and instrument it
to see how many times during bootstrap this triggers?