[Bug other/78678] possibly missing -Warray-bounds warning

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78678

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-05-02
                 CC|                            |marxin at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, very nice example :) I'm attaching reduced test-case.

Problem is that without -fsanitize=object-size, we fold lt_lcd_regs[20] in
einline here in fold_array_ctor_reference:


  6152    /* When memory is not explicitely mentioned in constructor,
  6153       it is 0 (or out of range).  */
  6154    return build_zero_cst (type);

Using the sanitizer preserves following statement:

  UBSAN_OBJECT_SIZE (&lt_lcd_regs[20], _7, 36, 0);

which is identified by VRP as the warning. The code that folds to zero was
written by Richi, I'm CCing for ideas. Maybe we can be more conservative is
some situations?