[Bug tree-optimization/57359] wrong code for union access at -O3 on x86_64-linux

["ch3root at openwall dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57359

Alexander Cherepanov <ch3root at openwall dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |ch3root at openwall dot com

--- Comment #12 from Alexander Cherepanov <ch3root at openwall dot com> ---
Still reproducible if the number of iterations is changed to 3.

I've also converted the testcase to allocated memory:

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#include <stdlib.h>
#include <stdio.h>

__attribute__((__noinline__,__noclone__))
void test(int *pi, long *pl, int k, int *pa)
{
  for (int i = 0; i < 3; i++) {
    pl[k] = // something that doesn't change but have to be calculated
    *pa; // something that potentially can be changed by assignment to *pi
    *pi = 0;
  }
}

int main(void)
{
  int *pi = malloc(10);
  int a = 1;

  test(pi, (void *)pi, 0, &a);

  printf("%d\n", *pi);
}
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Results:

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$ gcc -std=c11 -pedantic -Wall -Wextra test.c && ./a.out
0
$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
1
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gcc version: gcc (GCC) 8.0.0 20171024 (experimental)