[Bug tree-optimization/127762] New: Wrong code at -O1/2/3/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=127762

            Bug ID: 127762
           Summary: Wrong code at -O1/2/3/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/bvdavTY9G

Note:
 - fail: trunk, 15, 16
 - work: 14 or earlier

$ 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 20261007 (experimental) (GCC)
$
$ gcc-trunk -O0 small.c && ./a.out
2
$ gcc-trunk -O1 small.c && ./a.out
3
$
$ cat small.c
#include <stdio.h>
#define a() 0
int b, c, d;
int fn1() {
  unsigned long e = b = 7;
  for (; b; b--) {
    c = ~e;
    c >>= 10;
  }
  e = c & 8 ? c & ~0x3fc00 : a();
  if (e != 18446744073709290495UL)
    return 3;
  return 2;
}
int main() {
  d = fn1();
  printf("%d\n", d);
}