Behavior of parallel and sequential:
Each function call (indirectly, can be inside a sequential block) within a parallel
block will update the end variable to the maximum now_mu in the block.
Each function call directly inside a parallel block will reset the timeline after
execution. A parallel block within a sequential block (or not within any block) will
set the timeline to the max now_mu within the block (and the outer max now_mu will also
be updated).
Implementation: We track the start and end separately.
- If there is a start variable, it indicates that we are directly inside a
parallel block and we have to reset the timeline after every function call.
- If there is a end variable, it indicates that we are (indirectly) inside a
parallel block, and we should update the max end value.
Note: requires testing, it is difficult to inspect the output IR
Previously, we have to copy types from one unification table to another,
and make the table sendable. This requires cloning (processing) the
whole table 3 times per function call which is not efficient and uses
more memory than required when the unification table is large.
We now use a concrete type table to only copy the type we need. This
reduces the overhead as we only need to process the unification table
for once (when we do the function codegen), and reduces memory usage by
a bit (but not noticeable when the unification table is small, i.e. the
types are simple).
