[Bug tree-optimization/97821] [9/10/11/12 Regression] wrong code with -ftree-vectorize at -O1 on x86_64-pc-linux-gnu by r6-3608

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97821

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|ASSIGNED                    |RESOLVED

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, cvise reduced it to the following for me - clearly invalid in this case
since 'av' is no longer live at h = *n.

res[];
pos, h;
*n;
**aq_ay = &n;
main() {
  { int av = *aq_ay = &av; }
  h = *n;
  res[pos] = h;
  __builtin_puts(res);
}

OK, so the original testcase has

  for (; m <= 1; m++) {
    int av = 0, k, aw = e && u, ax = aw || ag;
    int **ay = &n;
...
    for (; t <= 1; t++)
      *ay = an(&au, &av);
    e++;
  }

which effectively does

     n = &av;

and in the loop following that

  for (; r >= 0;)
    for (; ag <= 5;) {
...
      h = *n; 
    }

that's invalid since 'av' is no longer live here.

-fsanitize=address shows this:

=================================================================
==24252==ERROR: AddressSanitizer: stack-use-after-scope on address
0x7fffffffdd20 at pc 0x000000401827 bp 0x7fffffffdca0 sp 0x7fffffffdc98
READ of size 4 at 0x7fffffffdd20 thread T0
    #0 0x401826 in aq /tmp/t.c:173
    #1 0x401ba3 in main /tmp/t.c:200
    #2 0x7ffff6e4029c in __libc_start_main (/lib64/libc.so.6+0x3529c)
    #3 0x400859 in _start (/tmp/a.out+0x400859)

meh, I only tried -fsanitize=undefined sofar :/

The symptom (bad stack slot sharing) is exactly what you'd expect from such
an error.