On 11 Sep 2007 18:14:21 -0700, Ian Lance Taylor <[EMAIL PROTECTED]> wrote:
> "Richard Guenther" <[EMAIL PROTECTED]> writes:
>
> > On 9/9/07, Richard Guenther <[EMAIL PROTECTED]> wrote:
> > >
> > > Which brings back the fact that you cannot implement malloc in C
> > > (you certainly remember the discussions about C++ placement new
> > > handling wrt aliasing). To re-use the machinery we invented there
> > > we would need to place a CHANGE_DYNAMIC_TYPE_EXPR for
> > > the pointer assignment resulting from inlining a function with
> > > attribute malloc set. As you say, unless we are inlining such functions
> > > we are safe in practice.
> >
> > Actually this looks nice in general. We could implement placement
> > new in C this way:
> >
> > extern inline T * __attribute__((malloc)) placement_new (void *p)
> > { return p; }
> >
> > if we can somehow encode the target type here. Note that only
> > type-based aliasing is a problem with this discussion - PTA will
> > be obviously fine if new is inlined as it will see that both pointers
> > are related and we loose the 'malloc' attribution on the target pointer
> > during inlining.
>
> CHANGE_DYNAMIC_TYPE_EXPR has the target type, of course. So perhaps
> we need __attribute__ ((change_dynamic_type))?
>
> Or actually of course __attribute__ ((malloc)) is fine but we could
> throw in a CHANGE_DYNAMIC_TYPE_EXPR after any call to such a
> function. That ought to do the right thing for C malloc
> implementations as well, I think.
We should need this only if inlining malloc functions in C.
Richard.
