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Re: Speed impact of virtual inheritance
On Mon, Oct 10, 2005 at 09:25:15PM +0000, Frans Englich wrote:
> Followup question: what is the increased cost of calling a non-virtual,
> inlined function('inline' keyword) on a virtual base?
If the function is successfully inlined, then the question really refers
to the cost of the code inside the function.
If this code accesses a member of a virtual base object, from a pointer
or reference to the derived object, this involves an extra level of
dereferencing that would not be present for a non-virtual base. The
derived part of the object has a pointer to the virtual base, so this
pointer must be dereferenced to find the base object, then the actual
member is found using a constant offset from the beginning of the base.
If nonvirtual inheritance were used, the member could be found directly,
at an offset from the address of the object as a whole.