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From: "larsbj at gullik dot net" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104017] unexpeted -Warray-bounds popping a
 fixed number of std::deque elements
Date: Tue, 18 Jan 2022 11:12:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104017

Lars Gullik Bj=C3=B8nnes <larsbj at gullik dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |larsbj at gullik dot net

--- Comment #2 from Lars Gullik Bj=C3=B8nnes <larsbj at gullik dot net> ---
(In reply to Martin Sebor from comment #1)

...
> #include <deque>
>=20
> struct Node { Node const * parent =3D nullptr; };
>=20
> void func(Node const * n)
> {
>     std::deque<Node const *> p;
>=20
>     Node const * e =3D n;
>=20
>     while (e !=3D nullptr) {
>         p.push_front(e);
>         e =3D e->parent;
>     }
>=20
>     if (p.size ())
>       p.pop_front();
>     if (p.size ())
>       p.pop_front();
>     if (p.size ())
>       p.pop_back();
> }
>=20
>=20
> This test case also triggers a warning, for the same reason: GCC can't
> determine the relationship between a deque's internal node pointers and t=
he
> result of std::deque::size() (which is a function of the node pointers).

This is also the case amended with a check that the std::deque::size is lar=
ge
enough (for the same reason). In that case the crash can never happen, still
GCC12 warns/errors.

I agree that the first test case, and the warning from it, is helpful. Howe=
ver
this second one not so much.=