On Tue, Jan 17, 2017 at 6:15 PM, anubhav <anubhav@xxxxxxxxxxxxxx> wrote:
> Hello,
>
> The following code prints different results when run with different
> optimization levels (O0 vs O2).
>
> int main() {
> int i = INT_MAX - 5;
> int j = 0;
> for (; i <= INT_MAX - 2; i += 3) {
> if (i <= 1) {
> j = 1;
> }
> }
> printf("%d",j);
> return 0;
> }
>
> Commands used :
> gcc -O0 -fno-strict-overflow bug.c -o bug # Output is 1
> gcc -O2 -fno-strict-overflow bug.c -o bug # Output is 0
>
> GCC version :
> gcc version 6.2.0 20160901 (Ubuntu 6.2.0-3ubuntu11~16.04)
>
> The expected output is 1 since the value of i overflows once.
In C, integer overflow is an undefined behavior.
Regards,
lee
> Is this an
> optimization bug?
>
> Thanks and regards,
> Anubhav
>
