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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107699] [12/13 Regression] False positive
 -Warray-bounds, non-existent offset reported by GCC
Date: Tue, 29 Nov 2022 13:22:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107699

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
At the point of the diagnostic we see

<bb 2> [local count: 1073741824]:
data._M_elems[0] =3D 3;
data._M_elems[1] =3D 2;
data._M_elems[2] =3D 1;
_8 =3D getCount ();
_1 =3D _8 * 4;
_2 =3D &data._M_elems + _1;
if (&data._M_elems !=3D _2)
  goto <bb 3>; [53.47%]
else
  goto <bb 12>; [46.53%]

that should possibly be optimized to

if (_1 !=3D 0)

but we cannot statically decide this jump.  There's a later dynamic jump
based on the very same _1, a check whether that's > 16, guarded by that
we diagnose

# .MEM_35 =3D VDEF <.MEM_34>
std::__insertion_sort.isra (&data._M_elems, &MEM <int[3]> [(void *)&data +
64B]);

where we complain about forming the (void *)&data + 64 address.

I can't see a way to suppress the diagnostic completely but it should
be possible to re-word it.

Note using a global getCount without a conditional that this bound
is inside 'data' bounds is not good programming practice.=