[Bug c++/51331] New: bad code generated when explicitly calling auto-generated constructor of virtual base

["zhezherun at yandex dot ru" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51331

             Bug #: 51331
           Summary: bad code generated when explicitly calling
                    auto-generated constructor of virtual base
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zhezherun@yandex.ru


If a virtual base class has an auto-generated default constructor, explicitly
calling it from the derived class' constructor can result in bad code. The
following stripped-down example reproduces the issue:


#include <iostream>

struct A {
    A(): x(10) {}
    virtual ~A() {}

    int x;
};

struct B: public virtual A {
};

struct C: public virtual A {
};

struct D: public B, virtual public C {
    D(): B(), C() {}  // note an explicit call to C() which is auto-generated
};

int main() {
    D* d = new D();
    std::cout << d->x << std::endl;

    // Crashes here with the following message:
    // *** glibc detected *** ./test: free(): invalid next size (fast)
    delete d;
}


This code used to work correctly in gcc 4.1.2 but crashes in gcc 4.6.2 on i386
(both -m32 and -m64).