[Bug sanitizer/108060] UBsan missed an out-of-bound bug at -O0 since r7-1900-g8a1b7b7fd75a3847

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108060

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-12-12
                 CC|                            |jason at gcc dot gnu.org
            Summary|UBsan missed an             |UBsan missed an
                   |out-of-bound bug at -O0     |out-of-bound bug at -O0
                   |                            |since
                   |                            |r7-1900-g8a1b7b7fd75a3847
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed. So it started with r7-1900-g8a1b7b7fd75a3847 where the array is
accessed before UBSAN check:

gcc pr108060.c -fsanitize=undefined -fdump-tree-gimple=/dev/stdout
int main ()
{
  int D.2422;
  int D.2423;

  {
    b = -32768;
    b.0_1 = b;
    _2 = (int) b.0_1;
    _3 = a[_2]; <--- load happens here
    c.1_4 = c;
    _5 = (int) c.1_4;
    b.2_6 = b;
    D.2422 = (int) b.2_6;
    .UBSAN_BOUNDS (0B, D.2422, 7);
    _7 = _3 | _5;
    a[D.2422] = _7;
  }
  D.2423 = 0;
  return D.2423;
}

thus we crashes before the .UBSAN_BOUNDS happens. Before the revision we
emitted:

   {
    b = -4169;
    b.0_1 = b;
    D.2074 = (int) b.0_1;
    UBSAN_BOUNDS (0B, D.2074, 7);
    b.1_2 = b;
    _3 = (int) b.1_2;
    _4 = a[_3];
    _5 = _4 | 1;
    a[D.2074] = _5;
  }