This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: C provenance semantics proposal
Am Donnerstag, den 18.04.2019, 11:45 +0100 schrieb Peter Sewell:
> On Thu, 18 Apr 2019 at 10:32, Richard Biener <richard.guenther@gmail.com> wrote:
> An equality test of two pointers, on the other hand, doesn't necessarily
> mean that they are interchangeable. I don't see any good way to
> avoid that in a provenance semantics, where a one-past
> pointer might sometimes compare equal to a pointer to an
> adjacent object but be illegal for accessing it.
As I see it, there are essentially four options:
1.) Compilers do not use conditional equivalences for
optimizations of pointers (or only when additional
conditions apply which make it safe)
2.) We make pointer comparison between a pointer
and a one-after pointer of a different object
undefined behaviour.
3.) We make comparison have the side effect that
afterwards any of the two pointers could have any
of the two provenances. (with disambiguitation
similar to what we have for casts).
4.) Compilers make sure that exposed objects never
are allocated next to each other (as Jens proposed).
None of these options is great.
Best,
Martin