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From: "zhendong.su at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/112281] New: wrong code at -O3 on
 x86_64-linux-gnu
Date: Sun, 29 Oct 2023 20:51:13 +0000
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X-Bugzilla-Component: tree-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112281

            Bug ID: 112281
           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 is a regression from 11.*, and affects 12.* and later. It should be
distinct from those couple of open issues with loop splitting.=20

Compiler Explorer: https://godbolt.org/z/1anT983Td

[573] % 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/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=3Dyes --prefix=3D/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=3Dc,c++ --disable-werror --enable-mu=
ltilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20231029 (experimental) (GCC)=20
[574] %=20
[574] % gcctk -O2 small.c; ./a.out
[575] %=20
[575] % gcctk -O3 small.c; ./a.out
Aborted
[576] % gcctk -O3 -fno-split-loops small.c; ./a.out
Aborted
[577] %=20
[577] % cat small.c
struct {
  int : 8;
  int a;
} b, d[4] =3D {{0}, {0}, {0}, {5}};
int c, e;
int main() {
  for (c =3D 2; c; c--)
    for (e =3D 0; e < 2; e++) {
      d[c] =3D b =3D d[c + 1];
      d[c + 1].a =3D 0;
    }
  if (b.a !=3D 0)
    __builtin_abort();
  return 0;
}=