[Bug c/23282] New: wrong results at -O on x86

[Bug c/23282] New: wrong results at -O on x86

[jv244 at cam dot ac dot uk]

Using gcc 4.0.1 :

Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /data1/vondele/gcc-401/gcc/configure --
prefix=/data1/vondele/gcc-401/result --with-gmp-dir=/data1/vondele/gmp-4.1.4/ -
-with-mpfr=/home/vondele/ --enable-languages=c,f95
Thread model: posix
gcc version 4.0.1

The following program generates wrong results (-1 instead of 4 for the second 
number printed out) if compiled with -O. It works fine with gcc 3.3.4 and the 
portland group c compiler:

#include <stdio.h>

void sub(int *m) {
  int index, l, count;

  l = 2;

  for(count=2; count>0; count--, l++) {
    index = l*l+1;

    printf("%d\n", m[index-2*l]);

    m[index+1] = -1;
  }
}


int main(void) {
  int i, m[20];

  for(i=0; i<20; i++)
    m[i] = i;

  sub(m);

  for(i=0; i<20; i++)
    printf("%d ", m[i]);

  putchar('\n');
}

vondele> gcc test.c
vondele> ./a.out
1
4
0 1 2 3 4 5 -1 7 8 9 10 -1 12 13 14 15 16 17 18 19

vondele> gcc -O test.c
vondele> ./a.out
1
-1
0 1 2 3 4 5 -1 7 8 9 10 -1 12 13 14 15 16 17 18 19

-- 
           Summary: wrong results at -O on x86
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-08 06:38 -------
This might already be fixed in 4.0.2.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |tree-optimization
           Keywords|                            |wrong-code
      Known to fail|                            |4.0.0
      Known to work|                            |4.1.0 3.4.0
            Summary|wrong results at -O on x86  |[4.0 Regression] wrong
                   |                            |results at -O on x86
   Target Milestone|---                         |4.0.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[belyshev at depni dot sinp dot msu dot ru]

------- Additional Comments From belyshev at depni dot sinp dot msu dot ru  2005-08-08 08:00 -------
Confirmed, smaller testcase:

void abort (void);

int main (void)
{
  int j, a, b;
  
  for (j = 0; j < 2; j++)
    {
      a = j * j;
      b = a - 2 * j;
    }
  if (b != -1)
    abort ();
  return 0;
}

This bug fixed (or masked) on mainline by this patch:

2005-05-06  Zdenek Dvorak  <dvorakz@suse.cz>

	PR tree-optimization/19401
	* tree-flow.h (tree_unroll_loops_completely): Declaration changed.
	* tree-ssa-loop-ivcanon.c (enum unroll_level): New.
        ...


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
      Known to fail|4.0.0                       |4.0.0 4.0.1 4.0.2
   Last reconfirmed|0000-00-00 00:00:00         |2005-08-08 08:00:14
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[rguenth at gcc dot gnu dot org]

------- Additional Comments From rguenth at gcc dot gnu dot org  2005-08-08 08:25 -------
Mainline seems to be really fixed, even with complete loop unrolling disabled.
4.0.2 as of 20050728 is still affected by the bug (you can hide it there, too,
with specifying -fpeel-loops, which enables complete unrolling).

Must be a IVOPTs or scalar evolution problem (the latter got some fixes on
the mainline).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-08-08 08:44 -------
GCC 4.0.2 (CVS) does this:  
  
ivcanon dump:  
  
  # b_9 = PHI <b_3(1)>;  
<L2>:;  
  if (b_9 != -1) goto <L3>; else goto <L4>;  
  
<L3>:;  
  printf (&"%d\n"[0], b_9);  
  abort ();  
  
  
.ivopts dump:  
  # b_9 = PHI <b_3(1)>;  
<L2>:;  
  if (b_9 != -1) goto <L3>; else goto <L4>;  
  
<L3>:;  
  printf (&"%d\n"[0], b_9);  
  abort ();  
  
  
Looks like final value replacement screws up.  
  

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-08-08 09:08 -------
Definitely IVopts. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P2                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[rakdver at gcc dot gnu dot org]

------- Additional Comments From rakdver at gcc dot gnu dot org  2005-08-16 08:03 -------
Seems like a duplicate of PR22442 to me.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[belyshev at depni dot sinp dot msu dot ru]

------- Additional Comments From belyshev at depni dot sinp dot msu dot ru  2005-08-16 10:17 -------
(In reply to comment #6)
> Seems like a duplicate of PR22442 to me.

Even if this is a dup, tescase from that bug does not fail on 4.0 and vice versa ;)
Testcase from this bug still fails on 4.0 branch.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[rakdver at atrey dot karlin dot mff dot cuni dot cz]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2005-08-16 10:21 -------
Subject: Re:  [4.0 Regression] wrong results at -O on x86

> > Seems like a duplicate of PR22442 to me.
> 
> Even if this is a dup, tescase from that bug does not fail on 4.0 and
> vice versa ;)
> Testcase from this bug still fails on 4.0 branch.

The patch for PR22442 should fix the problem.  The underlying problem
seems to be the same, it just shows up in a different optimizer this
time.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[jv244 at cam dot ac dot uk]

------- Additional Comments From jv244 at cam dot ac dot uk  2005-09-09 08:54 -------

> The patch for PR22442 should fix the problem.  

has anybody updated this patch so far or can it be applied as is ?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[mmitchel at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.0.2                       |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[pinskia at gcc dot gnu dot org]

------- Comment #16 from pinskia at gcc dot gnu dot org  2006-01-19 00:55 -------
Fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[rakdver at gcc dot gnu dot org]

------- Comment #15 from rakdver at gcc dot gnu dot org  2006-01-18 23:31 -------
Subject: Bug 23282

Author: rakdver
Date: Wed Jan 18 23:31:16 2006
New Revision: 109920

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=109920
Log:
        PR tree-optimization/23282
        * tree-chrec.c (chrec_fold_multiply_poly_poly): Associate chrecs
        correctly.

        PR tree-optimization/23282
        * gcc.c-torture/execute/pr23282.c: New test.


Added:
    branches/gcc-4_0-branch/gcc/testsuite/gcc.c-torture/execute/pr23282.c
Modified:
    branches/gcc-4_0-branch/gcc/ChangeLog
    branches/gcc-4_0-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_0-branch/gcc/tree-chrec.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[belyshev at depni dot sinp dot msu dot ru]

------- Comment #14 from belyshev at depni dot sinp dot msu dot ru  2006-01-15 21:22 -------
PING!!!


-- 

belyshev at depni dot sinp dot msu dot ru changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2005-12-21 15:58:03         |2006-01-15 21:22:01
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[jv244 at cam dot ac dot uk]

------- Comment #13 from jv244 at cam dot ac dot uk  2006-01-03 09:36 -------
Still causing trouble with gcc version 4.0.3 20060103 (prerelease)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[belyshev at depni dot sinp dot msu dot ru]

------- Comment #12 from belyshev at depni dot sinp dot msu dot ru  2005-12-21 15:58 -------
Zdenek, ping!

Please apply patch for this bug to gcc-4_0-branch.


-- 

belyshev at depni dot sinp dot msu dot ru changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2005-08-08 08:00:14         |2005-12-21 15:58:03
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[jv244 at cam dot ac dot uk]

------- Comment #11 from jv244 at cam dot ac dot uk  2005-12-01 10:21 -------
> 
> svn merge -r 101961:101962 svn://gcc.gnu.org/svn/gcc/trunk/gcc/tree-chrec.c
> gcc/tree-chrec.c
> 

Yes, this fixes the problem for me (tested on _4_0_1_release). This really
should be applied to the branch I think.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282

[Bug tree-optimization/23282] [4.0 Regression] wrong results at -O on x86

[belyshev at depni dot sinp dot msu dot ru]

------- Comment #10 from belyshev at depni dot sinp dot msu dot ru  2005-11-03 10:39 -------
Created an attachment (id=10121)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10121&action=view)
patch for gcc-4_0-branch (same as in
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22442#c5)

(In reply to comment #9)
> > The patch for PR22442 should fix the problem.  
> 
> has anybody updated this patch so far or can it be applied as is ?

just do:

svn merge -r 101961:101962 svn://gcc.gnu.org/svn/gcc/trunk/gcc/tree-chrec.c
gcc/tree-chrec.c

in your working copy of gcc-4_0-branch (see detailed instructions how to use
subversion here: http://gcc.gnu.org/wiki/SvnHelp )

Zdenek, please apply this patch to gcc-4_0-branch too.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23282