On Fri, Sep 24, 2021 at 2:35 AM Aldy Hernandez <al...@redhat.com> wrote:
>
>
>
> On 9/24/21 11:29 AM, Andrew Pinski wrote:
> > On Fri, Sep 24, 2021 at 1:05 AM Aldy Hernandez via Gcc <gcc@gcc.gnu.org>
> > wrote:
> >>
> >> Hi folks.
> >>
> >> My upcoming threading improvements turn the test below into an infinite
> >> runtime loop:
> >>
> >> int a, b;
> >> short c;
> >>
> >> int
> >> main ()
> >> {
> >> int j, d = 1;
> >> for (; c >= 0; c++)
> >> {
> >> BODY:
> >> a = d;
> >> d = 0;
> >> if (b)
> >> {
> >> xprintf (0);
> >> if (j)
> >> xprintf (0);
> >> }
> >> }
> >> xprintf (d);
> >> exit (0);
> >> }
> >>
> >> On the false edge out of if(b) we thread directly to BODY, eliding the
> >> loop conditional, because we know that c>=0 because it could never
> >> overflow.
> >
> > Huh about c>=0 being always true? the expression, "c++" is really c=
> > (short)(((int)c)+1). So it will definitely wrap over when c is
> > SHRT_MAX.
>
> I see.
>
> Is this only for C++ or does it affect C as well?
This is standard C code; promotion rules; that is if a type is less
than int, it will be promoted to int if all of the values fit into
int; otherwise it will be promoted to unsigned int.
Thanks,
Andrew Pinski
>
> Aldy
>
