From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-402541-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 15162 invoked by alias); 3 Oct 2012 15:30:06 -0000
Received: (qmail 14902 invoked by uid 48); 3 Oct 2012 15:29:40 -0000
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/54796] New: [4.8 Regression] Non-addressable stack parameter debug quality regression
Date: Wed, 03 Oct 2012 15:30:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: debug
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-54796-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
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
X-SW-Source: 2012-10/txt/msg00217.txt.bz2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54796

             Bug #: 54796
           Summary: [4.8 Regression] Non-addressable stack parameter debug
                    quality regression
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: aoliva@gcc.gnu.org
            Target: i686-linux


/* PR debug/NNNNN */
/* { dg-do run } */
/* { dg-options "-g" } */

__attribute__((noinline, noclone)) void
bar (char *a, int b)
{
  __asm volatile ("" : "+r" (a), "+r" (b) : : "memory");
}

__attribute__((noinline, noclone)) void
foo (int a, int b)
{
  int c = a;
  char d[b];/* { dg-final { gdb-test 17 "a" "5" } } */
  bar (d, 2);/* { dg-final { gdb-test 17 "b" "6" } } */
  bar (d, 4);/* { dg-final { gdb-test 17 "c" "5" } } */
}

int
main ()
{
  foo (5, 6);
  return 0;
}

(line 17 is the second call to bar) regressed for -m32 -Os -g on
{i686,x86_64}-linux supposedly with the
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=188871
change.  I've mentioned this already in
http://gcc.gnu.org/ml/gcc-patches/2012-10/msg00262.html
but filing it now on a testcase that is not dependent on any GCC patches.

The problem is that vt_canon_true_dep/canon_true_dependence doesn't figure out
that the stack stores (after prologue where hard fp is initialized) can't alias
argp.  Without the VLA or other reasons forcing use of frame pointer
var-tracking replaces sp accesses with argp + offset accesses and
canon_true_dependence then disambiguates it using the offsets.