https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93310
Bug ID: 93310
Summary: Incorrect constexpr virtual evaluation inside a
constructor
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ppalka at gcc dot gnu.org
Target Milestone: ---
The following testcase gets miscompiled on GCC 9 and on GCC 10 with
-DUSE_CONSTEXPR due to (I believe) the constexpr virtual evaluation incorrectly
resolving the dynamic type of ((A *)this) to C rather than B inside B's
constructor.
$ cat virtual-2.cc
#if defined USE_CONSTEXPR
# define CONSTEXPR constexpr
#else
# define CONSTEXPR
#endif
struct A
{
virtual CONSTEXPR char f () const
{ return 'A'; }
};
struct B : A
{
char x;
constexpr B () : x (0)
{ x = ((A *)this)->f(); }
virtual CONSTEXPR char f () const
{ return 'B'; }
};
struct C : B
{
virtual CONSTEXPR char f () const
{ return 'C'; }
};
int main ()
{
CONSTEXPR C c;
if (c.x != 'B')
__builtin_abort ();
}
$ g++ -std=c++2a virtual-2.cc
$ ./a.out
$ g++ -std=c++2a virtual-2.cc -DUSE_CONSTEXPR
$ ./a.out
zsh: abort ./a.out
