From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-183841-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 26747 invoked by alias); 24 Apr 2006 15:33:13 -0000
Received: (qmail 26696 invoked by uid 48); 24 Apr 2006 15:33:05 -0000
Date: Mon, 24 Apr 2006 15:33:00 -0000
Subject: [Bug tree-optimization/27285]  New: [4.1 regression] ivopts postgresql miscompilation
X-Bugzilla-Reason: CC
Message-ID: <bug-27285-87@http.gcc.gnu.org/bugzilla/>
Reply-To: gcc-bugzilla@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org
From: "jakub at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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
X-SW-Source: 2006-04/txt/msg02081.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

extern void abort (void);

struct S { unsigned char a, b, c, d[16]; };

void __attribute__ ((noinline))
foo (struct S *x, struct S *y)
{
  int a, b;
  unsigned char c, *d, *e;

  b = x->b;
  d = x->d;
  e = y->d;
  a = 0;
  while (b)
    {
      if (b >= 8)
        {
          c = 0xff;
          b -= 8;
        }
      else
        {
          c = 0xff << (8 - b);
          b = 0;
        }

      e[a] = d[a] & c;
      a++;
    }
}

int
main (void)
{
  struct S x = { 0, 25, 0, { 0xaa, 0xbb, 0xcc, 0xdd }};
  struct S y = { 0, 0, 0, { 0 }};

  foo (&x, &y);
  if (x.d[0] != y.d[0] || x.d[1] != y.d[1]
      || x.d[2] != y.d[2] || (x.d[3] & 0x80) != y.d[3])
    abort ();
   return 0;
}

On i686-linux with -O2 -m32 the loop is miscompiled, it copies over just
first 24 bits and not the 25th bit.  From quick skimming of the tree dumps,
this looks messed up by ivopts pass.  Seems to be a recent regression,
at least 20060304 GCC 4.1.x worked fine, while 20060420 does not.


-- 
           Summary: [4.1 regression] ivopts postgresql miscompilation
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27285