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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/101223] New: wrong code at -Os and above on
 x86_64-linux-gnu
Date: Sat, 26 Jun 2021 12:44:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101223

            Bug ID: 101223
           Summary: wrong code at -Os and above 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: ---

It also affects GCC 11.*, but not GCC 10.*.=20

[516] % 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 20210626 (experimental) [master revision
2168bfb8144:f9d3bc42803:5b1ce655b25040048861af6c0264cb667b66fcd7] (GCC)=20
[517] %=20
[517] % gcctk -O1 small.c; ./a.out
[518] %=20
[518] % gcctk -Os small.c
[519] % ./a.out
Aborted
[520] %=20
[520] % cat small.c
struct {
  int a : 1;
} b;
int c =3D 1, d;
int main() {
  for (; d < 2; d++) {
    int e =3D ~c, f =3D 0, g;
    if (e) {
      f =3D c;
      g =3D b.a;
      b.a =3D f;
      if (b.a >=3D g)
        __builtin_abort();
    }
    c =3D f;
    b.a =3D g;
  }
  return 0;
}=