Re: PATCH RFA: PR 29286: Handle placement new aliasing issues

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 6/10/07, Eric Botcazou <ebotcazou@adacore.com> wrote:
> > Also we won't see (int*alias) except as a cast in the generated C++ IR
> > because the type that is returned from placement new is void* and the other
> > pointer types that people use will never have TYPE_REF_CAN_ALIAS_ALL
> > set on them and it is hard to know what variable would like a type
> > which has TYPE_REF_CAN_ALIAS_ALL set on it.
>
> OK, it's true that you need a pointer object to put TYPE_REF_CAN_ALIAS_ALL on
> its type, a mere cast somewhere in the IR won't do it.  From your description
> I gather that the C++ compiler doesn't generate one for a placement new, in
> which case the TYPE_REF_CAN_ALIAS_ALL approach indeed won't work.

It's also that for most uses of placement new the underlying type doesn't change
(but is just set for the first time, or just re-initializes an
object).  In these cases
it is important to "strip" the optimization barrier away again.

Richard.