[Bug d/92309] New: Assignment to anonymous union member corrupts sibling members in struct

[sahmi.soulaimane at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92309

            Bug ID: 92309
           Summary: Assignment to anonymous union member corrupts sibling
                    members in struct
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: sahmi.soulaimane at gmail dot com
  Target Milestone: ---

Test case

```
union U
{
    struct
    {
        size_t a;
        size_t b;
        union
        {
            size_t c;
            size_t d;
        }
    }
}

void main()
{
    U u;
    assert(u.a == 0); // ok
    u.d = 1;
    assert(u.a == 0); // error
}
```