Retypechecking the loop in --make mode is super-linear when there are many .hs-boot modules
At time of writing master is at commit 14457cf6.
In GhcMake.hs, both upsweep and parUpsweep call getModLoop for each module. getModLoop is (at least) linear when called on a .hs-boot ModSummary. See comments in Phab:3646.
This isn't a big deal in practice, since .hs-boot modules are uncommon, but it does irk me, and it will be easy to fix. Fixing this would also be an opportunity to de-duplicate some logic in upsweep and parUpsweep.
ccing niteria as he has worked with this code recently.