Add some alignment info where LLVM might otherwise be more pessimistic. In particular, %.nest_arg is always aligned even though it's bitcast from i8*. Pointers in vtables are also guaranteed to be stored at aligned addresses.

module bug4;

int func(int i)
{
    i += 2;
    i -= 3;
    return i;
}

void main()
{
    assert(func(4) == 3);
}