[Bug tree-optimization/126942] New: Wrong code at -O1/s on x86_64-pc-linux-gnu

[xintong.zhou1 at uwaterloo dot ca via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126942

            Bug ID: 126942
           Summary: Wrong code at -O1/s on x86_64-pc-linux-gnu
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xintong.zhou1 at uwaterloo dot ca
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/Tn8aaEr5z

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=/data/x27zhou/compiler-nightly/install/gcc/bin/gcc
COLLECT_LTO_WRAPPER=/data/x27zhou/compiler-nightly/install/gcc/libexec/gcc/x86_64-pc-linux-gnu/17.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /data/x27zhou/compiler-nightly/src/gcc/configure CC='ccache
clang' CXX='ccache clang++' --enable-checking=yes --disable-bootstrap
--disable-multilib --enable-languages=c,c++
--prefix=/data/x27zhou/compiler-nightly/install/gcc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 17.0.0 20260818 (experimental) (GCC)
$
$ gcc-trunk -O0 small.c && ./a.out
0
$ gcc-trunk -O1 small.c && ./a.out
1
$ gcc-trunk -Os small.c && ./a.out
1
$
$ cat small.c
#include <stdio.h>
char a;
int b, c;
short d[1];
short e(short *f, short g) {
  int m = 0, i = 0, j, l;
  long n = 1;
  unsigned k = 0;
  for (; m < a; m++)
    for (; i <= m; i++)
      n = i;
  for (; k < g; k++) {
    l = 0;
    do
      if (f)
        j = l + a;
    while (++l <= k);
  }
  n ^= j;
  for (; a;)
    n ^= b;
  return n;
}
int main() {
  c = e(d, 2);
  printf("%d\n", c);
}