swift

8d05d79f - AST: Cache substituted substitution maps inside the InFlightSubstitution

AST: Cache substituted substitution maps inside the InFlightSubstitution A substitution map contains conformances, and a conformance can contain a substitution map. This will always be a DAG, but not a tree, and to avoid exponential blowup in certain edge cases, let's cache the work to avoid visiting the same substitution map repeatedly, if multiple conformances refer to the same substitution map.