Re: operator new returns nonzero

[Marc Glisse <marc dot glisse at inria dot fr>]

On Sat, 7 Sep 2013, Basile Starynkevitch wrote:

> On Sat, 2013-09-07 at 12:33 +0200, Marc Glisse wrote:
> > Hello,
> >
> > this patch teaches the compiler that operator new, when it can throw,
> > isn't allowed to return a null pointer. Note that it doesn't work for
> > placement new (that one may have to be handled in the front-end or the
> > inliner), and it will not work on user-defined operator new if they are
> > inlined. I guess it would be possible to teach the inliner to insert an
> > assert_expr or something when inlining such a function, but that's not for
> > now. The code I removed from vrp_visit_stmt was duplicated in
> > stmt_interesting_for_vrp and thus useless.
>
>
> Interesting patch. However, I feel that we should give advanced users
> the ability to say that their new operator is never returning null...

Easy, don't specify noexcept on it and that's what the patch already does, 
as long as the function is not inlined.

> In particular, if I define my own new operator which never returns nil,
> I find strange that it would be less optimized than the system's
> operator new.
>
> Perhaps we need an attribute `nonnullresult'  which whould means that.
> (we already the nonnull attribute for function arguments)

There is already a PR about that, linked from this PR. But even if we 
create this attribute, we will still want to be able to guess that new 
should have it even if it isn't written.

--
Marc Glisse