Compiler bug? Addition/subtraction code

[Era Scarecrow via D.gnu]

On Tuesday, 20 June 2017 at 03:31:24 UTC, Era Scarecrow wrote:
>  Apparently on GDC 6.3 this doesn't fail. So likely an old 
> compiler bug.

  Got a message not long ago, apparently the assertion still 
happens on GDC 6.3. So...