Drop the `MaterializeLoopScopes` pass after the re-design the loop
matching stage to work entirely on `clift`, without the need to insert a
`scope_closer` edge to guide the emission.
Simultaneously, drop the DAGify `Head` metadata insertion, since it will
not be checked anymore during the `MaterializeLoopScopes` pass.
We now ensure that even in case of blocks disconnected from the entry,
the `isDAG` function still search for loops in such parts of the graph.
This is achieved by instantiating multiple `scc_iterator` on the blocks
composing the underlying `Graph`.
During the `Head` election phase, we now introduce the following
additional criterion:
When processing a `GenericRegion` nested into an outer one (its
`ParentRegion`), if the inner `Region` contains the block that has been
elected as `Head` of the `ParentRegion`, we also force that block to be
the `Head` of the inner `GenericRegion`.
We add a unit test to check this behavior.
Perform the abnormal (late) entries normalization in the DAGify pass.
In this way, we are exploiting the information computed by
`GenericRegionInfo` as close as possible to where it is computed the
first time (in DAGify).
Actualize the unit tests to reflect these changes.
Implement the DAGify pass. This pass, using the results exposed by the
`GenericRegionInfo` analysis, transforms all the retreating edges of
each identified `GenericRegion`, processed in a bottom-up fashion, into
a `goto` edge on the `ScopeGraph`.
Alessandro Di Federico