[Bug tree-optimization/19626] New: Aliasing says stores to local memory do alias

[rguenth at tat dot physik dot uni-tuebingen dot de]

Given the attached testcase, for reference, the interesting function is
this:

int loc_test(void)
{
	const Loc<2> dX(1, 0);
	const Loc<2> k(0, 1);
	return k[0].first() + dX[0].first();
}

aliasing tells us that the initializations of dX and k alias each
other:

<bb 0>:
  D.2540 = (struct Loc<1> *) &dX.D.2210.D.2166.domain_m.buffer;
  #   dX_357 = V_MAY_DEF <dX_318>;
  #   k_358 = V_MAY_DEF <k_317>;
  *&(&D.2540->D.2094)->D.2057.domain_m = 1;
  #   dX_365 = V_MAY_DEF <dX_357>;
  #   k_364 = V_MAY_DEF <k_358>;
  *&(&(D.2540 + 4B)->D.2094)->D.2057.domain_m = 0;
  D.2682 = (struct Loc<1> *) &k.D.2210.D.2166.domain_m.buffer;
  #   dX_337 = V_MAY_DEF <dX_365>;
  #   k_338 = V_MAY_DEF <k_364>;
  *&(&D.2682->D.2094)->D.2057.domain_m = 0;
  #   dX_361 = V_MAY_DEF <dX_337>;
  #   k_63 = V_MAY_DEF <k_338>;
  *&(&(D.2682 + 4B)->D.2094)->D.2057.domain_m = 1;
  D.2769 = (struct Loc<1> *) &k.D.2210.D.2166.domain_m.buffer;
  D.2791 = (struct Loc<1> *) &dX.D.2210.D.2166.domain_m.buffer;
  return (&D.2769->D.2094)->D.2057.domain_m + (&D.2791->D.2094)->D.2057.domain_m;

which is of course (trivially) not true.  This may be obfuscated by
the actual implementation of the template class Loc (see attached
complete testcase).

At the RTL level we are able to optimize this to just return 1, as
expected.  This pessimizes tree loop optimizations if such constructs
are used inside a loop and as induction variable.

-- 
           Summary: Aliasing says stores to local memory do alias
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at tat dot physik dot uni-tuebingen dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19626