[cfe-dev] Microsoft vtordisp field support for clang.

[r4start]

On 15/02/2012 05:52, John McCall wrote:
> On Feb 14, 2012, at 3:40 AM, r4start wrote:
>> On 14/02/2012 15:34, r4start wrote:
>>> On 14/02/2012 05:06, John McCall wrote:
>>>> class A { virtual void foo(); } class B : public A { }; class C : public virtual B { C(); virtual void foo(); };
>>> For this test we will get next result:
>>>   class C    size(12):
>>>         +---
>>>   0    | {vbptr}
>>>         +---
>>>   4    | (vtordisp for vbase B)
>>>         +--- (virtual base B)
>>>         | +--- (base class A)
>>>   8    | | {vfptr}
>>>         | +---
>>>         +---
>>> If somewhere in inheritance path class has declare ctor or dtor and overload virtual method from virtual base,
>>> then before virtual base Microsoft compiler push vtordisp in layout.
>>>
>> Also for this test case:
>>
>> class A { virtual void foo(){} };
>> class B : public A { };
>> class C : public virtual B { C(){} virtual void foo(){} };
>> class D : public C { int qqq; };
>>
>>   class D    size(16):
>>          +---
>>          | +--- (base class C)
>>    0    | | {vbptr}
>>          | +---
>>    4    | qqq
>>          +---
>>    8    | (vtordisp for vbase B)
>>          +--- (virtual base B)
>>          | +--- (base class A)
>>   12   | | {vfptr}
>>          | +---
>>          +---
>> As you can see D also has vtordisp for B.
> Okay.  I don't think this fundamentally changes the algorithm.  I did think of
> a case that might matter, though:  a superclass might override a method
> from a non-virtual base that is *also* a virtual base in some derived class.
> That is to say, is there a vtordisp in 'C' in the following code?
>
> class A { virtual void foo(); };
> class B: public A { virtual void foo(); B(); };
> class C : public B, public virtual A { C(); };
>
Class C does not have vtordisp, because C does not override 'foo' and B 
inherit A non-virtual.

  - Dmitry.