[Bug tree-optimization/63602] New: Wrong code w/ -O2 -ftree-loop-linear

[Bug tree-optimization/63602] New: Wrong code w/ -O2 -ftree-loop-linear

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63602

            Bug ID: 63602
           Summary: Wrong code w/ -O2 -ftree-loop-linear
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com

gcc produces wrong code w/ -ftree-loop-linear -O2 (and above) for the following
reduced case:

int sx;
int bn;
int vz = 1;
int *volatile n6 = &bn;

int
main(void)
{
  for (int i = 0; i < 3; ++i) {
    sx = vz;
    vz = bn;
  }
  return sx;
}

It struck me first w/ gcc-4.10.0-alpha20140810, but today I've reproduced it w/
4.8.3, 4.9.1 and 5-alpha20141019, so I'm not marking it as a regression.

Expected results:
% gcc-5.0_alpha20141019 -O2 -o good 963b8772.c
% ./good
% echo $?
0

Actual results:
% gcc-5.0_alpha20141019 -O2 -ftree-loop-linear -o bad 963b8772.c
% ./bad
% echo $?
1

[Bug tree-optimization/63602] Wrong code w/ -O2 -ftree-loop-linear

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63602

--- Comment #1 from Arseny Solokha <asolokha at gmx dot com> ---
It seems I've reduced the snippet too hard. However, are global variables
declared static or not, it doesn't change anything.

[Bug tree-optimization/63602] [5/6 Regression] Wrong code w/ -O2 -ftree-loop-linear

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63602

Arseny Solokha <asolokha at gmx dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.2
            Summary|Wrong code w/ -O2           |[5/6 Regression] Wrong code
                   |-ftree-loop-linear          |w/ -O2 -ftree-loop-linear
      Known to fail|4.8.3, 4.9.1, 5.0           |5.1.0, 6.0

--- Comment #2 from Arseny Solokha <asolokha at gmx dot com> ---
I've just checked it and found that gcc 4.9.2 compiles it correctly. So,
relabelling as a regression.

[Bug tree-optimization/63602] [5/6 Regression] Wrong code w/ -O2 -ftree-loop-linear

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63602

Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bernd.edlinger at hotmail dot de

--- Comment #3 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
BTW: same results for gcc-5.1.0 with isl-0.12.2:

gcc -floop-block -O2 pr63602.c
gcc -floop-interchange -O2 pr63602.c
gcc -floop-parallelize-all -O2 pr63602.c
gcc -floop-strip-mine -O2 pr63602.c

even worse:

gcc -floop-unroll-and-jam -O2 pr63602.c
../../gcc-5.1.0/isl/isl_ctx.c:172: isl_ctx freed, but some objects still
reference it
pr63602.c: In function 'main':
pr63602.c:7:1: internal compiler error: Aborted
 main(void)
 ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

[Bug tree-optimization/63602] [5/6 Regression] Wrong code w/ -O2 -ftree-loop-linear

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63602

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |5.3