[Bug c/26719] New: Computed (integer) table changes with -O

[Bug c/26719] New: Computed (integer) table changes with -O

[kmshanah at disenchant dot net]

System info: Debian Unstable, x86 (Transmeta Crusoe TM5800)

The following program produces different output when compiled with and without
optimisations. This didn't occur with gcc 4.0.3, it seems to be new with 4.1.0.

#include <stdio.h>

int table[32][256];

int main(void)
{
    int i, j;

    for (i = 0; i < 32; i++)
        for (j = 0; j < 256; j++)
            table[i][j] = ((signed char)j) * i;

    for (i = 0; i < 10; i++)
        printf("%10i %10i\n", table[i][5], table[i][132]);

    return 0;
}

Compiling without optimisations, the output is as desired. With -O1 the output
changes. Here's how I can reproduce the problem:

$ gcc-4.1 -o example.O0 example.c
$ gcc-4.1 -O1 -o example.O1 example.c
$ ./example.O0 
         0          0
         5       -124
        10       -248
        15       -372
        20       -496
        25       -620
        30       -744
        35       -868
        40       -992
        45      -1116
$ ./example.O1 
         0          0
         5        132
        10        264
        15        396
        20        528
        25        660
        30        792
        35        924
        40       1056
        45       1188
$ gcc-4.1 -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,java,fortran,objc,obj-c++,ada,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.1-1.4.2.0/jre --enable-mpfr
--with-tune=i686 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.0 (Debian 4.1.0-0)


-- 
           Summary: Computed (integer) table changes with -O
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kmshanah at disenchant dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-03-16 18:24 -------
Confirmed, ivopts is causing this one.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |critical
             Status|UNCONFIRMED                 |NEW
          Component|c                           |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
   Last reconfirmed|0000-00-00 00:00:00         |2006-03-16 18:24:54
               date|                            |
            Summary|Computed (integer) table    |[4.1/4.2 Regression]
                   |changes with -O             |Computed (integer) table
                   |                            |changes with -O
   Target Milestone|---                         |4.1.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rakdver at gcc dot gnu dot org]

------- Comment #2 from rakdver at gcc dot gnu dot org  2006-03-16 18:50 -------
This is a scev analysis problem; on code

  D.2160_17 = (signed char) j_15;
  D.2161_18 = (int) D.2160_17;

it says D.2161_18 = {0, +, 1};  however, since it wraps at 128 to -127, this is
not correct -- (int) {0, +, 1}  (where the type of the chrec is char) would be.


-- 

rakdver at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sebastian dot pop at cri dot
                   |                            |ensmp dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rakdver at gcc dot gnu dot org]

------- Comment #3 from rakdver at gcc dot gnu dot org  2006-03-16 18:51 -------
More precisely, the correct chrec would be

(int) (char) {0,+,1}

since we assume signed chrecs do not overflow.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[sebastian dot pop at cri dot ensmp dot fr]

------- Comment #4 from sebastian dot pop at cri dot ensmp dot fr  2006-03-28 22:44 -------
Created an attachment (id=11146)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11146&action=view)
first step

with this patch scev returns (int) (char) {0,+,1} but then 
chrec_convert_aggressive is removing the casts and the result
is just {0,+,1}.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2006-04-27 11:23 -------
Still happens.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
   Last reconfirmed|2006-03-16 18:24:54         |2006-04-27 11:23:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[steven at gcc dot gnu dot org]

------- Comment #6 from steven at gcc dot gnu dot org  2006-05-14 14:25 -------
Seb, wrong code regression in your code.  Are you working on this??


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rakdver at gcc dot gnu dot org]

------- Comment #7 from rakdver at gcc dot gnu dot org  2006-05-14 14:49 -------
(In reply to comment #4)
> Created an attachment (id=11146)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11146&action=view) [edit]
> first step
> 
> with this patch scev returns (int) (char) {0,+,1} but then 
> chrec_convert_aggressive is removing the casts and the result
> is just {0,+,1}.

This sounds suspicious, the result after chrec_convert_aggressive
should be (int) [0,+,1] (where the type of 0 and 1 is char).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rakdver at gcc dot gnu dot org]

------- Comment #8 from rakdver at gcc dot gnu dot org  2006-05-20 19:27 -------
Patch: http://gcc.gnu.org/ml/gcc-patches/2006-05/msg01032.html


-- 

rakdver at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2006-
                   |                            |05/msg01032.html


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[rakdver at gcc dot gnu dot org]

------- Comment #9 from rakdver at gcc dot gnu dot org  2006-05-24 22:55 -------
Subject: Bug 26719

Author: rakdver
Date: Wed May 24 22:55:15 2006
New Revision: 114057

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=114057
Log:
        PR tree-optimization/27639
        PR tree-optimization/26719
        * tree-vrp.c (adjust_range_with_scev): Use scev_direction and adjust
        call to scev_probably_wraps_p.
        * tree-ssa-loop-niter.c (compare_trees, convert_step_widening,
        used_in_pointer_arithmetic_p, convert_step): Removed.
        (nowrap_type_p): New function.
        (scev_probably_wraps_p): Rewritten.
        * tree-scalar-evolution.c (instantiate_parameters_1): Do not call
        chrec_convert if chrec_convert_aggressive might have been used.
        * tree-chrec.c (convert_affine_scev, chrec_convert_1,
        scev_direction): New functions.
        (chrec_convert): Changed to a wrapper over chrec_convert_1.
        * tree-ssa-loop-ivopts.c (idx_find_step): Use convert_affine_scev
        instead of convert_step.
        * tree-flow.h (scev_probably_wraps_p): Declaration changed.
        (convert_step): Declaration removed.
        (convert_affine_scev, nowrap_type_p, scev_direction): Declare.

        * gcc.dg/pr27639.c: New test.
        * gcc.dg/pr26719.c: New test.
        * gcc.dg/tree-ssa/scev-cast.c: New test.


Added:
    trunk/gcc/testsuite/gcc.dg/pr26719.c
    trunk/gcc/testsuite/gcc.dg/pr27639.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/scev-cast.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-chrec.c
    trunk/gcc/tree-flow.h
    trunk/gcc/tree-scalar-evolution.c
    trunk/gcc/tree-ssa-loop-ivopts.c
    trunk/gcc/tree-ssa-loop-niter.c
    trunk/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1/4.2 Regression] Computed (integer) table changes with -O

[mmitchel at gcc dot gnu dot org]

------- Comment #10 from mmitchel at gcc dot gnu dot org  2006-05-25 02:31 -------
Will not be fixed in 4.1.1; adjust target milestone to 4.1.2.


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.1                       |4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[pinskia at gcc dot gnu dot org]

------- Comment #11 from pinskia at gcc dot gnu dot org  2006-05-25 17:09 -------
Fixed on the mainline at least.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.1.0 4.1.1
      Known to work|                            |4.0.3 4.2.0
            Summary|[4.1/4.2 Regression]        |[4.1 Regression] Computed
                   |Computed (integer) table    |(integer) table changes with
                   |changes with -O             |-O


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2006-07-24 08:26 -------
Subject: Bug 26719

Author: rguenth
Date: Mon Jul 24 08:25:57 2006
New Revision: 115709

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=115709
Log:
2006-07-21  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27795
        PR tree-optimization/27639
        PR tree-optimization/26719
        Backport from mainline
        2006-05-24  Zdenek Dvorak <dvorakz@suse.cz>

        * tree-vrp.c (adjust_range_with_scev): Use scev_direction and adjust
        call to scev_probably_wraps_p.
        * tree-ssa-loop-niter.c (compare_trees, convert_step_widening,
        used_in_pointer_arithmetic_p, convert_step): Removed.
        (nowrap_type_p): New function.
        (scev_probably_wraps_p): Rewritten.
        * tree-scalar-evolution.c (instantiate_parameters_1): Do not call
        chrec_convert if chrec_convert_aggressive might have been used.
        * tree-chrec.c (convert_affine_scev, chrec_convert_1,
        scev_direction): New functions.
        (chrec_convert): Changed to a wrapper over chrec_convert_1.
        * tree-ssa-loop-ivopts.c (idx_find_step): Use convert_affine_scev
        instead of convert_step.
        * tree-flow.h (scev_probably_wraps_p): Declaration changed.
        (convert_step): Declaration removed.
        (convert_affine_scev, nowrap_type_p, scev_direction): Declare.

        * gcc.dg/pr27639.c: New test.
        * gcc.dg/pr26719.c: New test.
        * gcc.dg/tree-ssa/scev-cast.c: New test.

Added:
    branches/gcc-4_1-branch/gcc/testsuite/gcc.dg/pr26719.c
      - copied unchanged from r114057, trunk/gcc/testsuite/gcc.dg/pr26719.c
    branches/gcc-4_1-branch/gcc/testsuite/gcc.dg/pr27639.c
      - copied unchanged from r114057, trunk/gcc/testsuite/gcc.dg/pr27639.c
    branches/gcc-4_1-branch/gcc/testsuite/gcc.dg/tree-ssa/scev-cast.c
      - copied unchanged from r114057,
trunk/gcc/testsuite/gcc.dg/tree-ssa/scev-cast.c
Modified:
    branches/gcc-4_1-branch/gcc/ChangeLog
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_1-branch/gcc/tree-chrec.c
    branches/gcc-4_1-branch/gcc/tree-flow.h
    branches/gcc-4_1-branch/gcc/tree-scalar-evolution.c
    branches/gcc-4_1-branch/gcc/tree-ssa-loop-ivopts.c
    branches/gcc-4_1-branch/gcc/tree-ssa-loop-niter.c
    branches/gcc-4_1-branch/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2006-07-24 08:29 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[pinskia at gcc dot gnu dot org]

------- Comment #14 from pinskia at gcc dot gnu dot org  2007-03-23 15:37 -------
*** Bug 31327 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |thutt at vmware dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[thutt at vmware dot com]

------- Comment #15 from thutt at vmware dot com  2007-03-23 15:51 -------
In regards to comment #13: In what tarball is this defect fixed?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719

[Bug tree-optimization/26719] [4.1 Regression] Computed (integer) table changes with -O

[pinskia at gcc dot gnu dot org]

------- Comment #16 from pinskia at gcc dot gnu dot org  2007-03-23 15:54 -------
> In regards to comment #13: In what tarball is this defect fixed?

The 4.1.2 release as indicated by the target milestone and the known to work
field.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|4.0.3 4.2.0                 |4.0.3 4.2.0 4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26719