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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/107293] New: Wrong code at -Os on x86_64-linux-gnu
Date: Mon, 17 Oct 2022 12:06:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107293

            Bug ID: 107293
           Summary: Wrong code at -Os on x86_64-linux-gnu
           Product: gcc
           Version: 13.0
            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: ---

% gcc-tk -v
Using built-in specs.
COLLECT_GCC=3Dgcc-tk
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-acdb2=
4166d13d87c374e578d2ad5d58249171930/libexec/gcc/x86_64-pc-linux-gnu/13.0.0/=
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-acdb24166d13d87c=
374e578d2ad5d58249171930
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20221017 (experimental) (GCC)
%
% gcc-tk -w -O0 a.c && ./a.out
1
% gcc-tk -w -Os a.c && ./a.out
0
% cat a.c
short a;
int b[1];

int c(int p) {
  return (p < 0) ? 0 : 10 + ((p / 100 - 16) / 4);
}

void f(int n) {
  while (1) {
    int m =3D n;
    while ((m ) )
      m /=3D 2;
    break;
  }
}

void g() {
  int h =3D a =3D 0;
  for (; h + a <=3D 0; a++) {
    if (b[c(a - 6)])
      break;
    f(a);
  }
}
int main() {
  g();
  __builtin_printf("%d\n", a);
}

%

Compiler explorer: https://godbolt.org/z/e7sssT7cq=