| otherwise
= case nameModule_maybe name of
Nothing -> pprTrace "mkUsageInfo: internal name?" (ppr name) mv_map
- Just mod -> extendModuleEnv_C (++) mv_map mod [occ]
+ Just mod -> -- We use this fiddly lambda function rather than
+ -- (++) as the argument to extendModuleEnv_C to
+ -- avoid quadratic behaviour (trac #2680)
+ extendModuleEnv_C (\xs _ -> occ:xs) mv_map mod [occ]
where occ = nameOccName name
-- We want to create a Usage for a home module if