This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Fix PR47594: Sign extend constants while translating to Graphite
On Tue, 26 Jul 2011, Sebastian Pop wrote:
> On Tue, Jul 26, 2011 at 09:07, Richard Guenther <rguenther@suse.de> wrote:
> >> > Randomly sign-extending stuff looks bogus to me.
> >> > Does graphite operate on infinite precision signed integers? ?Or
> >> > does it operate on twos-complement fixed precision integers?
> >>
> >> Graphite represents constants using mpz_t.
> >
> > Not exactly an answer but I guess all mpz_t do have a sign and are
> > of arbitrary precision. ?Thus it's wrong to change unsigned + -1U
> > to mpz_t + -1 unless you truncate to unsigneds precision after
> > doing that operation. ?Do we properly handle this?
>
> Graphite is not truncating after conversion of an unsigned expression to mpz_t.
>
> I still don't see how truncating -1U to its precision changes anything,
> could you explain?
Truncating -1 doesn't matter - it matters that if you perform any
unsigned arithmetic in arbitrary precision signed arithmetic that
you properly truncate after each operation to simulate unsigned
twos-complement wrapping semantic. And if you did that you wouldn't
need to sign-extend -1U either.
Richard.