From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-466087-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 31827 invoked by alias); 8 Nov 2014 20:52:33 -0000
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
Received: (qmail 31809 invoked by uid 48); 8 Nov 2014 20:52:29 -0000
From: "glaubitz at physik dot fu-berlin.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/63783] New: gcc-4.9: Miscompilation of boolean negation on SH4 using -O2
Date: Sat, 08 Nov 2014 20:52:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 4.9.1
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: glaubitz at physik dot fu-berlin.de
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter
Message-ID: <bug-63783-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2014-11/txt/msg00559.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63783

            Bug ID: 63783
           Summary: gcc-4.9: Miscompilation of boolean negation on SH4
                    using -O2
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glaubitz at physik dot fu-berlin.de

Hello!

Recently we ran into linker issues on our SH4 buildds in Debian [1]. We
initially blamed the linker for the problem, but after some more investigation,
Michael Karcher was eventually able to track down the problem being a
regression in gcc [2].

When compiling the following code snippet with optimization -O2 enabled, the
assertation will fail but succeed without:

#include <assert.h>

int decision_result;
int truecount = 0;
int val;

void buggy(int flag)
{
  int condition;
  if(flag == 0)
    condition = val != 0;
  else
    condition = !decision_result;
  if (condition)
  {
     truecount++;
  }
}

int main(void)
{
  decision_result = 1;
  buggy(1);
  assert(truecount == 0);
}

The issue did not arise with gcc-4.6, for example, so it appears to be a
regression with one of the later versions of gcc.

Cheers,
Adrian

> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=17553
> [2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=768574