> > On 07/02/2014 01:18 PM, Jan Hubicka wrote: > > >We propagate types from places we know instances are created across > > >pointers > > >passed to functions. Once non-POD type is created at a given memory > > >location, > > >one can not change its type by placement_new into something else. > > > > Hmm. If the memory location is untyped (i.e. from malloc) or a > > character array, or a union, you can indeed destroy an object of one > > type and create an object of a different type in that location. > > > > >Jason, this assumes that one can not destroy the type and re-construct same > > >type at the same spot. > > > > That is an invalid assumption; you can destroy one object and > > construct a new one in the same location. Doing it within a method > > would be unusual, but I don't think there's a rule against it. > > The types get currently are one comming from declarations of variables > and parameters passed by reference. > Can I really destroy it/allocate new type/destroy new type/allocate back the > original > type (or terminate the program) so the destruction at the end of the > lifetimate of the > variable apsses? > > I suppose we should keep track if memory location is comming from declaration > or > it is dynamically typed (i.e. type seen from calling constructor)? Currently > we don't > deal with dynamic types, but I have patches for that.
But this is one of things that was not quite clear to me. I know that polymorphic type A was created at a give memory location. THis means that accesses to that location in one alias class has been made. Now I destroy A and turn it into B, construct B and make memory accesses in different alias set. I see this has chance to work if one is base of another, but if B is completely different type, I think strick aliasin should just make those accesses to not alias and in turn make whole thing undefined? honza
