[Bug tree-optimization/127391] New: Wrond code at -O3 on x86_64-pc-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127391

            Bug ID: 127391
           Summary: Wrond code at -O3 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/5TzT9corh

$ 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 20260914 (experimental) (GCC) 
$
$ gcc-trunk -O0 small.c && ./a.out
63
$ gcc-trunk -O3 small.c && ./a.out
120
$
$ cat small.c
#include <stdio.h>
long b;
int c;
int fn1(char e, long d) {
  for (int f = 0; f < 16; f++)
    switch (f % 3) {
    case 2:
      b += f;
      break;
    case 0:
      b |= f;
    case 1:
      b |= f;
    }
  return b;
}
int main() {
  c = fn1(0, 0);
  printf("%d\n", c);
}