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From: "shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/110732] New: Wrong code at -Os on x86_64-linux-gnu (recent
 regression)
Date: Wed, 19 Jul 2023 07:36:30 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110732

            Bug ID: 110732
           Summary: Wrong code at -Os on x86_64-linux-gnu (recent
                    regression)
           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
  Target Milestone: ---

This looks like a recent regression. gcc at -Os produces the wrong code.

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

$ cat a.c
int printf(const char *, ...);
int a;
char c[] =3D {0, 0, -4L};
char d, e;
int main() {
  int f;
  int *g =3D &a;
  *g =3D 1;
  for (; e <=3D 2; e++)
    for (;;) {
      {
        {
          int b =3D c[e];
          f =3D b < 0 ? b : b >> 6;
        }
        d =3D f && a;
      }
      break;
    }
  printf("%d\n", d);
}
$
$ gcc-tk -O0 a.c && ./a.out
1
$ gcc-tk -Os a.c && ./a.out
-1
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=3Dgcc-tk
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-322d1=
7ae51ea0137167424e0018d7fa355948f9f/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/=
lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=3Dc,c++
--prefix=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-322d17ae51ea0137=
167424e0018d7fa355948f9f
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230711 (experimental) (GCC)=20
$=