https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105277
Bug ID: 105277
Summary: Pointer to member UB in constant expression is not
checked.
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: malorubi at outlook dot com
Target Milestone: ---
The standard says
[expr.mptr.oper] bullet 4 https://eel.is/c++draft/expr#mptr.oper-4
...
If the dynamic type of E1 does not contain the member to which E2 refers, the
behavior is undefined.
...
This is currently not checked, it is possible to invoke a function pointer
using an expression of invalid dynamic type in a constant expression, without
such call being diagnosed as UB.
Example on compiler explorer: https://godbolt.org/z/s4G8ovs7n
Example verbatim:
=== BEGIN EXAMPLE
struct Base {};
struct Derived1 : Base
{
int x;
constexpr int fn() const
{ return 0; }
};
struct Derived2 : Base
{
int x;
constexpr int fn() const
{ return 1; }
};
inline void test()
{
using common_fn = int (Base::*)() const;
constexpr Derived1 instance1 {};
constexpr Derived2 instance2 {};
constexpr auto ptr1 = (common_fn) &Derived1::fn;
constexpr auto ptr2 = (common_fn) &Derived2::fn;
static_assert ((instance1.*ptr1)() == 0);
static_assert ((instance2.*ptr2)() == 1);
static_assert ((instance1.*ptr2) () == 1); // ?
static_assert ((instance2.*ptr1) () == 0); // ?
}
=== END EXAMPLE
