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From: "zhendong.su at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102446] New: wrong code at -O3 on
 x86_64-linux-gnu
Date: Wed, 22 Sep 2021 09:00:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102446

            Bug ID: 102446
           Summary: wrong code at -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: zhendong.su at inf dot ethz.ch
  Target Milestone: ---

This seems to be a long-latent miscompilation, affecting GCC 5.1 and later.

[583] % gcctk -v
Using built-in specs.
COLLECT_GCC=3Dgcctk
COLLECT_LTO_WRAPPER=3D/local/suz-local/software/local/gcc-trunk/libexec/gcc=
/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--prefix=3D/local/suz-local/software/local/gcc-trunk --enable-languages=3Dc=
,c++
--disable-werror --enable-multilib --with-system-zlib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210922 (experimental) [master r12-3777-g578b7687338] (=
GCC)
[584] %
[584] % gcctk -O2 small.c; ./a.out
[585] %
[585] % gcctk -O3 small.c
[586] % ./a.out
Segmentation fault
[587] %
[587] % cat small.c
int a =3D 1, c, e, f, *j, k, o, *r =3D &f, s;
char b, l;
short d, *g;
unsigned h;
static void m(void);
static void n(int);
void p(int *q) {
  while (1) {
    if (*q)
      break;
    if (*g)
      o =3D c;
    while (l)
      ;
  }
}
void t() {
  for (; s < 8; s++)
    m();
}
void m() {
  int aa =3D 0, i =3D 0;
  for (; i < 3; i++)
    if (k < 0)
      aa |=3D *j;
  if (d)
    c =3D (h + *g + 2) & c;
  n(aa);
}
void n(int ac) {
  char *ad =3D &b, u =3D ac, *v =3D &b;
  int ae =3D *ad =3D a;
  u && (*v =3D e > 0);
  *r =3D c;
  p(&ae);
}
int main() {
  t();
  return 0;
}=