[Bug tree-optimization/65752] Too strong optimizations int -> pointer casts

[mail at robbertkrebbers dot nl]

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.
>