[Bug c/111233] New: Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[Bug c/111233] New: Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

            Bug ID: 111233
           Summary: Wrong code at -O3 on x86_64-linux-gnu since
                    r14-2852-gf5fb9ff2396
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: hubicka at gcc dot gnu.org, jh at suse dot cz
  Target Milestone: ---

gcc at -O3 produces the wrong code.

Bisected to r14-2852-gf5fb9ff2396

Compiler explorer: https://godbolt.org/z/vrEMjKr9f

$ cat a.c
int printf(const char *, ...);
int a, c, f;
char b, g;
int *d = &c;
long e;
int main() {
  for (; e != 25; e++) {
    f = -17;
    for (; f <= 0; f = f + 7) {
      g = f ? 0 : b;
      a = *d;
    }
  }
  printf("%d\n", a);g
}
$
$ gcc -O2 a.c && ./a.out
0
$ gcc -O3 a.c
$ ./a.out
(Timeout)
$

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
            Summary|Wrong code at -O3 on        |[14 Regression] Wrong code
                   |x86_64-linux-gnu since      |at -O3 on x86_64-linux-gnu
                   |r14-2852-gf5fb9ff2396       |since r14-2852-gf5fb9ff2396

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #1 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Shaohua Li from comment #0)

>   printf("%d\n", a);g

I assume the "g" is a typo？

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

--- Comment #2 from Shaohua Li <shaohua.li at inf dot ethz.ch> ---
(In reply to Xi Ruoyao from comment #1)
> (In reply to Shaohua Li from comment #0)
> 
> >   printf("%d\n", a);g
> 
> I assume the "g" is a typo？

Oh, that's indeed a typo. Sorry for that.

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-08-30
           Priority|P3                          |P1
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Also miscompiled with -O2 -fsplit-loops.  Note enabling
-fsplit-loops yields

t.c: In function 'main':
t.c:9:26: warning: iteration 3 invokes undefined behavior
[-Waggressive-loop-optimizations]
    9 |     for (; f <= 0; f = f + 7) {
      |                        ~~^~~
t.c:9:14: note: within this loop
    9 |     for (; f <= 0; f = f + 7) {
      |            ~~^~~~

when this happens we usually end up with an endless loop.

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:2066c29bf8dea87c9810eb261e342d941a6b2059

commit r14-5446-g2066c29bf8dea87c9810eb261e342d941a6b2059
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Nov 14 14:26:17 2023 +0100

    tree-optimization/111233 - loop splitting miscompile

    The change in r14-2852-gf5fb9ff2396fd4 failed to update patch_loop_exit
    to compensate for rewriting of a NE/EQ_EXPR to a new code.  Fixed
    with the following.

            PR tree-optimization/111233
            PR tree-optimization/111652
            PR tree-optimization/111727
            PR tree-optimization/111838
            PR tree-optimization/112113
            * tree-ssa-loop-split.cc (patch_loop_exit): Get the new
            guard code instead of the old guard stmt.
            (split_loop): Adjust.

            * gcc.dg/torture/pr111233.c: New testcase.
            * gcc.dg/torture/pr111652.c: Likewise.
            * gcc.dg/torture/pr111727.c: Likewise.
            * gcc.dg/torture/pr111838.c: Likewise.
            * gcc.dg/torture/pr112113.c: Likewise.

[Bug tree-optimization/111233] [14 Regression] Wrong code at -O3 on x86_64-linux-gnu since r14-2852-gf5fb9ff2396

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111233

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

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

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.