[Bug tree-optimization/89720] [9 Regression] Spurious -Warray-bounds warning

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89720

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-03-14
          Component|c++                         |tree-optimization
      Known to work|                            |8.3.0
     Ever confirmed|0                           |1
      Known to fail|                            |9.0

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed.  It was introduced in r262893:

Author: msebor <msebor@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Thu Jul 19 23:36:34 2018 +0000

    PR tree-optimization/84047 - missing -Warray-bounds on an out-of-bounds
index into an array
    PR tree-optimization/83776 - missing -Warray-bounds indexing past the end
of a string literal

    gcc/ChangeLog:

            PR tree-optimization/84047
            PR tree-optimization/83776
            * tree-vrp.c (vrp_prop::check_mem_ref): New function.
            (check_array_bounds): Call it.


I think it's another instance of incorrectly dealing with unsigned pointer
offsets (similar to bug 89350).  The range of the offset is [0, -3221225473]
which the code misinterprets as [-3221225473, 0]:

(gdb) p min
$10 = {<fixed_wide_int_storage<128>> = {val = {0, 10836215197923, 36503164},
len = 1}, static is_sign_extended = true}
(gdb) p max
$11 = {<fixed_wide_int_storage<128>> = {val = {-3221225473, 140737128894544,
140737488345360}, len = 1}, static is_sign_extended = true}

      if (vr->kind () == VR_RANGE)
        {
          if (tree_int_cst_lt (vr->min (), vr->max ()))
            {
              offset_int min
                = wi::to_offset (fold_convert (ptrdiff_type_node, vr->min ()));
              offset_int max
                = wi::to_offset (fold_convert (ptrdiff_type_node, vr->max ()));
              if (min < max)
                {
                  offrange[0] += min;
                  offrange[1] += max;
                }
              else
                {
                  offrange[0] += max;
                  offrange[1] += min;
                }