From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-128235-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 15928 invoked by alias); 25 Jan 2005 16:56:38 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 15902 invoked by uid 48); 25 Jan 2005 16:56:32 -0000
Date: Tue, 25 Jan 2005 16:56:00 -0000
From: "rguenth at tat dot physik dot uni-tuebingen dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050125165629.19626.rguenth@tat.physik.uni-tuebingen.de>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug tree-optimization/19626] New: Aliasing says stores to local memory do alias
X-Bugzilla-Reason: CC
X-SW-Source: 2005-01/txt/msg03716.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

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