[Bug c++/13118] [ABI] Missed covariant return thunk

["grigory at stl dot sarov dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From grigory at stl dot sarov dot ru  2003-11-22 14:46 -------
There is another example illustrating the same problem.

In the hierarchy listed below, c3 shares virtual table both with c2 and c1
bases. That is c3 v-table introduces 3 slots for covariant return type function
"foo". First and second slots contain pointer to adjustment thunks and third one
contains pointer to non-adjusting entry.
        [0] c1-in-c2-in-c3::foo, returning r1-in-r3
        [1] c2-in-c3::foo,       returning r2-in-r3
        [2] c3::foo,             returning r3-in-r3

However the actually generated vtable for c3 contains pointer to wrong thunk in
the first slot:
        [skip]
        16    c3::_ZTcv0_n12_v0_n12_N2c33fooEv
        20    c3::_ZTcv0_n12_v0_n12_N2c33fooEv
        24    c3::foo

Basing on thunk encoding "v0_n12_v0_n12_", contents of c3's and r3's virtual
tables we can say that "this" value will be incorrectly adjusted to c2-in-c3 and
the return value will be adjusted to r2 instead of r1 in the r3's hierarchy.
I.e. actually used thunk appears to be:
        c1-in-c2::foo, returning r1-in-r2

It looks like g++ 3.4 compiler just inherits this slot value from the vtable of
base class c2 introduced as complete object.
        Vtable for c2
        [skip]
        16    c2::_ZTcv0_n12_v0_n12_N2c23fooEv
        20    c2::foo


Class hierarchy
---------------

struct r1 {
    int j;
    virtual ~r1();
};

struct r2 : virtual r1 {
    int j;
    virtual ~r2();
};

struct r3 : virtual r2, virtual r1 {
    int i;
};

struct c1 {
    virtual r1& foo() {};
};

struct c2 : virtual c1 {
    virtual r2& foo() {};
};

struct c3 : c2 {
    virtual r3& foo() {};
};


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13118