[C++ PATCH] ctor vtable vcall offsets
Mark Mitchell
mark@codesourcery.com
Tue Feb 27 10:16:00 GMT 2001
>>>>> "Jason" == Jason Merrill <jason@redhat.com> writes:
Jason> Actually, I don't see why we ever need to emit thunks with
Jason> the vtable. The example in the ABI document is
Jason> struct A { virtual void f(); }; struct B : virtual public
Jason> A { int i; }; struct C : virtual public A { int j; };
Jason> struct D : public B, public C {};
Jason> But here, calling A::f() means converting to A* then
Jason> calling through the A vtable, so the entry in the C vtable
Jason> is never used.
Jason> What am I missing?
I thought the intent was to avoid having to do that conversion.
At the time you do the conversion, you don't know where the override
will be; in many cases it will be wasted work.
So, I thought the intent was to make sure that the entry in C's vtable
(which contains an entry for `f' since A is the primary base) is
valid.
--
Mark Mitchell mark@codesourcery.com
CodeSourcery, LLC http://www.codesourcery.com
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