[Bug tree-optimization/61383] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[Bug tree-optimization/61383] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

            Bug ID: 61383
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk (as well as gcc 4.8 and 4.9) miscompiles the following
code on x86_64-linux at -O2 and -O3 in both 32-bit and 64-bit modes.

This is a regression from 4.7.x. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.10.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.10.0 20140601 (experimental) [trunk revision 211110] (GCC) 
$ 
$ gcc-trunk -Os small.c; a.out
$ gcc-4.7.3 -O2 small.c; a.out
$ 
$ gcc-trunk -O2 small.c; a.out
Floating point exception (core dumped)
$ gcc-4.8.2 -O2 small.c; a.out
Floating point exception (core dumped)
$ 


------------------------------


int a, b = 1, c, d, e, f, g;

int
fn1 ()
{
  int h;
  for (;;)
    {
      g = b;
      g = g ? 0 : 1 % g;
      e = a + 1;
      for (; d < 1; d = e)
    {
      h = f == 0 ? 0 : 1 % f;
      if (f < 1)
        c = 0;
      else if (h)
        break;
    }
      if (b)
    return 0;
    }
}

int
main ()
{
  fn1 ();
  return 0;
}

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-06-02
      Known to work|                            |4.7.3
   Target Milestone|---                         |4.8.4
            Summary|wrong code at -O2 and -O3   |[4.8/4.9/4.10 Regression]
                   |on x86_64-linux-gnu         |wrong code at -O2 and -O3
                   |                            |on x86_64-linux-gnu
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |glisse at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r190184.

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
This very minor variant also misbehaves with 4.7 and 4.6, so before my patch.
An unsafe instruction (1%f) is taken out of a branch in ifcombine.

int a, b = 1, c, d, e, f, g;

int
fn1 ()
{
  int h;
  for (;;)
    {
      g = b;
      g = g ? 0 : 1 % g;
      e = a + 1;
      for (; d < 1; d = e)
        {
          if (f == 0)
            h = 0;
          else
            h = 1 % f;
          if (f < 1)
            c = 0;
          else if (h)
            break;
        }
      if (b)
        return 0;
    }
}

int
main ()
{
  fn1 ();
  return 0;
}

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
There is similar issue in RTL PRE GCSE [1], PR45223.
>From gcc-bugs-return-452995-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Jun 02 14:02:13 2014
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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu
Date: Mon, 02 Jun 2014 14:02:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida383

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #3)
> This very minor variant also misbehaves with 4.7 and 4.6, so before my
> patch. An unsafe instruction (1%f) is taken out of a branch in ifcombine.
>
> int a, b = 1, c, d, e, f, g;
>
> int
> fn1 ()
> {
>   int h;
>   for (;;)
>     {
>       g = b;
>       g = g ? 0 : 1 % g;
>       e = a + 1;
>       for (; d < 1; d = e)
>         {
>           if (f == 0)
>             h = 0;
>           else
>             h = 1 % f;
>           if (f < 1)
>             c = 0;
>           else if (h)
>             break;
>         }
>       if (b)
>         return 0;
>     }
> }
>
> int
> main ()
> {
>   fn1 ();
>   return 0;
> }

I have a patch in testing.  (and fixed the tree PRE issue in the past...)

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu.org

--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> There is similar issue in RTL PRE GCSE [1], PR45223.

Right, there are various similar old issues in the RTL optimizers, but we must
be extra careful because we really don't want to pessimize the common case to
fix some artificial testcases.

Note that we have some backup here: the (green) Dragon Book gives a code motion
algorithm that is subject to this kind of issues and the authors elegantly
write "For this reason, it is wise to use the following algorithm for code
motion only if optimization may be inhibited by the programmer". :-)

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Tue Jun  3 08:48:28 2014
New Revision: 211163

URL: http://gcc.gnu.org/viewcvs?rev=211163&root=gcc&view=rev
Log:
2014-06-03  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/61383
    * tree-ssa-ifcombine.c (bb_no_side_effects_p): Make sure
    stmts can't trap.

    * gcc.dg/torture/pr61383-1.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr61383-1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-ifcombine.c

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Wed Jun  4 13:41:09 2014
New Revision: 211232

URL: http://gcc.gnu.org/viewcvs?rev=211232&root=gcc&view=rev
Log:
2014-06-04  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/61383
    * tree-ssa-ifcombine.c (bb_no_side_effects_p): Make sure
    stmts can't trap.

    * gcc.dg/torture/pr61383-1.c: New testcase.

Added:
    branches/gcc-4_8-branch/gcc/testsuite/gcc.dg/torture/pr61383-1.c
Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_8-branch/gcc/tree-ssa-ifcombine.c

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |4.10.0, 4.8.4, 4.9.1
         Resolution|---                         |FIXED
      Known to fail|                            |4.8.3, 4.9.0

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/61383] [4.8/4.9/4.10 Regression] wrong code at -O2 and -O3 on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61383

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Wed Jun  4 13:40:33 2014
New Revision: 211231

URL: http://gcc.gnu.org/viewcvs?rev=211231&root=gcc&view=rev
Log:
2014-06-04  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/61383
    * tree-ssa-ifcombine.c (bb_no_side_effects_p): Make sure
    stmts can't trap.

    * gcc.dg/torture/pr61383-1.c: New testcase.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/gcc.dg/torture/pr61383-1.c
Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_9-branch/gcc/tree-ssa-ifcombine.c