[cfe-commits] [PATCH] PR13824 warn if reinterpret_cast used for up/downcast

[Alexander Zinenko]

On 24 January 2013 04:33, Jordan Rose <jordan_rose at apple.com> wrote:

>
> On Jan 23, 2013, at 14:53 , Dmitri Gribenko <gribozavr at gmail.com> wrote:
>
> > On Thu, Jan 24, 2013 at 12:40 AM, Alexander Zinenko <ftynse at gmail.com>
> wrote:
> >> On 23 January 2013 23:52, Dmitri Gribenko <gribozavr at gmail.com> wrote:
> >>> I think it is sensible to leave the warning on by default.  The
> >>> purpose of a separate flag is to turn off the (possibly) noisy case
> >>> separately.
> >>
> >> Having it on by default, clang fails to pass these tests:
> >>    Clang :: Analysis/inlining/dyn-dispatch-bifurcate.cpp
> >>    Clang :: SemaCXX/address-space-conversion.cpp
> >> That's why the noisy version was disabled by default even in the first
> >> version.
> >
> > Well, compiler tests do weird things, so this is not representative.
>
> dyn-dispatch-bifurcate is actually what encouraged me to file that PR in
> the first place. You can go ahead and add it as an expected warning there.


> For address-space-conversion, you could disable the warning in the RUN
> line.
>

Thanks, I was not sure changing anyone else's test is OK.  Updated patch
modifies these tests.

On Jan 23, 2013, at 14:53 , Dmitri Gribenko <gribozavr at gmail.com> wrote:

> > I think the only reasonable false positive source for zero adjustment
> > case is templates:
> >
> > template<typename T, typename U>
> > void foo(T *t) {
> >  ... reinterpret_cast<U*>(t);
> > }
> >
> > Where T and U have some subtyping relationship.
>

Warning could be disabled for dependent types.
Trivial case warning adds an extra note where the template was
instantiated, though. As for me it's worth still having it enabled.

template.cpp:15:10: warning: 'reinterpret_cast' is used as an upcast from
type 'B *' to its base type 'A *' [-Wreinterpret-updown-zero-adjustment]
  (void)*reinterpret_cast<U *>(t);
         ^~~~~~~~~~~~~~~~~~~~~~~~
template.cpp:20:3: note: in instantiation of function template
specialization 'foo<B, A>' requested here
  foo<B, A>(&b);
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