The statement ids are now stable, so the life-time interval calculation
can re-use information calculated by the optimizer. This re-use will
be done in a separate patch.

It also allows for changes to the numbering in a non-intrusive way. This
will also come in a later patch.

Change-Id: Ie3a2e1d9e3537cc8070ff3e3007f3a5e8ca0579a
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>