[Bug c/71452] New: Wrong optimization of stores to _Bool via char*

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71452

            Bug ID: 71452
           Summary: Wrong optimization of stores to _Bool via char*
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ch3root at openwall dot com
  Target Milestone: ---

Source code:

----------------------------------------------------------------------
#include <stdio.h>

int main()
{
  _Bool b;
  *(char *)&b = 123;
  printf("%d\n", *(char *)&b);
}
----------------------------------------------------------------------

Results:

----------------------------------------------------------------------
$ gcc -std=c11 -pedantic -Wall -Wextra test.c && ./a.out
123

$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
1
----------------------------------------------------------------------

gcc version: gcc (GCC) 7.0.0 20160604 (experimental)

This is somewhat counterintuitive behavior and it's a bug according to
https://gcc.gnu.org/ml/gcc/2016-06/msg00046.html .

According to https://gcc.godbolt.org/ such optimization is observed with gcc
4.6.4 but not in gcc 4.5.3.