[GSB] Flatten list of same-type requirements. #12592
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When computing connected components for the graph of derived same-type constraints within an equivalence, replace the depth-first search with union-find. The latter does not require us to have an out-edges list for each node in the graph.
Equivalence classes stored their same-type constraints in a MapVector keyed on the source potential archetype, which allowed traversal along the paths of the graph. However, this capability isn't required, because we end up walking all of the edges each time. Flatten the list of same-type constraints to a single vector, eliminating constraint duplication between the source and the target out-edge lists. This cuts down on the number of same-type constraints we record by 50%, but performance gains are limited (6% of stdlib type-checking time) because most of the time these same-type constraints were skipped anyway.
Centralizes the logic for short-circuiting based on same-type constraints.
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@swift-ci please smoke test and merge |
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Equivalence classes stored their same-type constraints in a MapVector
keyed on the source potential archetype, which allowed traversal along the
paths of the graph. This was used in a depth-first search to compute connected
components in the graph, so switch over to a union-find based algorithm.
Then, flatten the list of same-type constraints to a single vector, eliminating
constraint duplication between the source and the target out-edge lists.
This cuts down on the number of same-type constraints we record by 50%,
but performance gains are limited (6% of stdlib type-checking time)
because most of the time these same-type constraints were skipped
anyway.