Periods are the central "clock" of the compiler. A period consists of a run id and a phase id. run ids represent compiler runs phase ids represent compiler phases
op at given period
op at given phase id
Are all base types in the current period guaranteed to be the same as in period
The current phase identifier
The current run identifier
The period containing the current period where denotations do not change. We compute this by taking as first phase the first phase less or equal to the current phase that has the same "nextTransformerId". As last phase we take the next transformer id following the current phase.