Question w.r.t. `'class Foo' has virtual functions but non-virtualdestructor` warning.

[Mark Mitchell]

Chris Lattner wrote:

> I've run into this warning with C++ code as well, and it is quite 
> annoying.  There are lots of possible reasons to want to do this sort of 
> thing, and adding a virtual dtor increases the size of the vtable for 
> the class.

Yeah, there goes one whole pointer per class in your program image. :-) 
   Seriously, you'd have to have a lot of classes and not very many 
objects before that got to be *too* big a deal.  But, we do have 
customers who count every byte, so I'm not totally discounting this 
objection.

> It seems that the warning could be improved to be emitted when the 
> *delete* is seen of a class without a virtual dtor (but that does have 
> virtual methods).  If you never actually do the questionable behavior, 
> you'd never get the warning.  It seems like a bug to emit it for the 
> class definition.

Age-old debate: better to warn early about possibly broken interfaces, 
or late about definitely broken usage?  I think that warning early, 
together with what DJ is calling fine-grained warning control is the 
best solution.

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304