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From: "thomas at thomaslabs dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/106890] New: virtual inheritance triggers compiler error
 when instatiating derived class with in-class initialization
Date: Thu, 08 Sep 2022 10:06:59 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106890

            Bug ID: 106890
           Summary: virtual inheritance triggers compiler error when
                    instatiating derived class with in-class
                    initialization
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thomas at thomaslabs dot org
  Target Milestone: ---

Created attachment 53549
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53549&action=3Dedit
The exact source code used to trigger the error

The following code sample triggers an internal compiler error. This happends
when using the virtual keyword in the definition of B and is related to the
function call to f inside the class definition. When later attempting to
instantiate the class B the compiler fails.

I'm working with GCC version 12.2.0 but this bug seems to be present as ear=
ly
as version 8.5.0. Version 7.5.0 managed to compile without a problem.

* Command line=20

g++ bug.cpp

* Compiler output:

during RTL pass: expand
bug.cpp: In constructor =E2=80=98B<T>::B(int) [with T =3D int]=E2=80=99:
bug.cpp:26:5: internal compiler error: in expand_expr_real_1, at expr.cc:10=
586
   26 |     B(int a) {
      |     ^
0x1b286a6 internal_error(char const*, ...)
        ???:0
0x6ccc1e fancy_abort(char const*, int, char const*)
        ???:0

* Compiler version:

GNU C++17 (GCC) version 12.2.0 (x86_64-unknown-linux-gnu)
        compiled by GNU C version 12.2.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.23-GMP

* System

GNU/Guix x86_64

* Source code

class O
{
public:
    int f() {
        return 1;
    }
};

template<typename T>
class A
{
public:
    A();
    A(int a);

protected:
    O p =3D O();
};

template<typename T>
class B : virtual public A<T>
{
public:
    B() {
    }
    B(int a) {
    }

protected:
    using A<T>::p;
    unsigned int k =3D p.f();
};

template class B<int>;

int main()
{
    return 0;
}=