Perf: Make dep_finsts a map from type family Name to Module
Today, when we do a family consistency check, we always do a pairwise comparison of every module, even though most of the time, the modules don't even define instances of the same family (making the check futile.)
A far better strategy is to say, for any family, which modules transitively below us define instances for it, and only check THOSE pairwise. All we have to do is turn dep_finsts from a list of modules into a mapping from type family names to modules; then we can union the maps and do pairwise comparisons as before.
Note that we want to RECORD the map from Name to Module, because we expect any family to have instances defined in many modules (Module to Name is better if a single module defines instances for many families, but clearly this is rare.)
This is related to #9717, in that the proposed map here is a more coarse version of what was proposed in that ticket. This may strike a happy compromise between keeping interface files small and speeding things up.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.1 |
| Type | Task |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |