[Bug tree-optimization/128054] New: wrong code at -O2 and above: program traps on a valid path before a call that exits

[kyuwoncho18 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128054

            Bug ID: 128054
           Summary: wrong code at -O2 and above: program traps on a valid
                    path before a call that exits
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kyuwoncho18 at gmail dot com
  Target Milestone: ---
            Target: x86_64-pc-linux-gnu

#include <stdlib.h>

volatile int sel = 1;
int x = 5, y = 42;

__attribute__((noipa)) void maybe_exit(int c) {
  if (c == 42)
    exit(0);
}

int main(void) {
  int *p1, *p2;
  if (sel) {
    p1 = 0;
    p2 = &y;
  } else {
    p1 = &x;
    p2 = 0;
  }
  int v = *p2;
  maybe_exit(v);
  return *p1;
}

godbolt: https://godbolt.org/z/zMPd9Yxr7

With -O0, -O1 or -O2 -fno-isolate-erroneous-paths-dereference, maybe_exit (42)
calls exit (0) before the null *p1 is reached, so the program exits with status
0, which is correct. With -O2, -O3 or -Os it dies with SIGILL (ud2) without
calling maybe_exit.