https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752
--- Comment #30 from mail at robbertkrebbers dot nl --- Hi Gil, Nice example! I am a bit occupied lately, and thus have not read all comments at the bug report in detail. I will be away for the weekend, but will read those quickly after. Robbert On 05/22/2015 04:12 AM, gil.hur at sf dot snu.ac.kr wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752 > > --- Comment #29 from Chung-Kil Hur <gil.hur at sf dot snu.ac.kr> --- > Dear Richard, > > This time, I think I constructed a real bug. > Please have a look and correct me if I am wrong. > > ===================== > #include <stdio.h> > > int main() { > int x = 0; > uintptr_t xp = (uintptr_t) &x; > uintptr_t i; > > for (i = 0; i < xp; i++) { } > > *(int*)xp = 15; > > printf("%d\n", x); > } > ===================== > > This program prints "15" and I do not think this raises UB. > > Now I add an if-statement to the program. > > ===================== > #include <stdio.h> > > int main() { > int x = 0; > uintptr_t xp = (uintptr_t) &x; > uintptr_t i; > > for (i = 0; i < xp; i++) { } > > /*** begin ***/ > if (xp != i) { > printf("hello\n"); > xp = i; > } > /*** end ***/ > > *(int*)xp = 15; > > printf("%d\n", x); > } > ===================== > > This program just prints "0". > > Since "hello" is not printed, the if-statement is not executed. > However, it prints a different result than before, which I think is a bug. >
