[Bug c/111472] New: Wrong code at -Os on x86_64-linux-gnu since

["shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111472

            Bug ID: 111472
           Summary: Wrong code at -Os on x86_64-linux-gnu since
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: amacleod at redhat dot com
  Target Milestone: ---

gcc at -Os produced the wrong code.

Bisected to r11-4563-gd0d8b5d836

Compiler explorer: https://godbolt.org/z/EPznGbaje

With -fwrapv the issue goes away.

$ cat a.c
int printf(const char *, ...);
int a, b, e, f;
short c = -1, i;
char g;
int h[4][1] = {8, 5, 8, 5};
int main() {
  int *j = &e, *k = &f;
  unsigned short d = c;
  i = d >> b;
  *j = i;
  g = 0;
  for (; g <= 3; g++)
    *k = h[(unsigned char)(1 + e) + g][0];
  printf("%d\n", f);
}
$
$ gcc -O0 a.c && ./a.out
5
$ gcc -Os a.c && ./a.out
Segmentation fault
$
$ gcc -fsanitize=undefined a.c && ./a.out
5
$