On 9/24/21 11:38 AM, Andrew Pinski wrote:
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.
Well, *that* was embarrassing.
Thanks, and sorry for the noise.
Aldy
