[Bug d/94424] New: [D] Alignment holes can in structs can still end up with non-zero data

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94424

            Bug ID: 94424
           Summary: [D] Alignment holes can in structs can still end up
                    with non-zero data
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: ibuclaw at gdcproject dot org
  Target Milestone: ---

Example is a test that passes with -O0, but fails at -O2.

@safe unittest
{
    struct C
    {
        ubyte i;
        this(ubyte i) { this.i = i; }
    }

    auto c1 = C(1);
    auto c2 = C(2);

    assert(__cmp([c1, c1][], [c2, c2][]) < 0);
    assert(__cmp([c2, c2], [c1, c1]) > 0);
    assert(__cmp([c2, c2], [c2, c1]) > 0);
}

This happens despite the front-end attempting to do a best effort to plug all
holes with zeroes.