Simon Jakobi pushed to branch wip/sjakobi/tweak-mk_mod_usage_info at Glasgow Haskell Compiler / GHC Commits: f595622f by Simon Jakobi at 2026-04-22T02:52:00+02:00 Tweak mk_mod_usage_info * Use O(log n) `elemModuleEnv` instead of O(n) `elem` to filter the direct imports. * Use `nonDetModuleEnvKeys` to avoid sorting the ent_map keys twice. * Prepend the presumably shorter list when creating all_mods with `(++)`. Actually this eliminates the `(++)` entirely, as it seems to fuse with the `filter` expression. * As the above changes change the demand on ent_map, we force it to ensure it's only computed once. As a result there is a tiny speed-up when generating the .hi-files for modules with many imports. None of the changes affect compilation determinism as the module list is explicitly sorted to ensure a canonical order. - - - - - 2 changed files: - compiler/GHC/HsToCore/Usage.hs - compiler/GHC/Unit/Module/Env.hs Changes: ===================================== compiler/GHC/HsToCore/Usage.hs ===================================== @@ -219,15 +219,20 @@ mk_mod_usage_info :: UsageConfig -> NameSet -> IfG [Usage] mk_mod_usage_info uc home_unit home_unit_ids this_mod direct_imports imp_decls used_names - = mapMaybeM mkUsageM usage_mods + = ent_map `seq` mapMaybeM mkUsageM usage_mods + -- ent_map is required _lazily_ for several sub-computations, so we force + -- it here to ensure it's built only once. where safe_implicit_imps_req = uc_safe_implicit_imps_req uc - used_mods = moduleEnvKeys ent_map - dir_imp_mods = Map.keys direct_imports - all_mods = used_mods ++ filter (`notElem` used_mods) dir_imp_mods - usage_mods = sortBy stableModuleCmp all_mods - -- canonical order is imported, to avoid interface-file + used_mods = nonDetModuleEnvKeys ent_map + -- nonDetModuleEnvKeys is OK here, because the + -- resulting usage_mods are sorted explicitly. + is_used_mod m = m `elemModuleEnv` ent_map + dir_imp_mods = Map.keys direct_imports + all_mods = filter (not . is_used_mod) dir_imp_mods ++ used_mods + usage_mods = sortBy stableModuleCmp all_mods + -- canonical order is important, to avoid interface-file -- wobblage. -- ent_map groups together all the things imported and used ===================================== compiler/GHC/Unit/Module/Env.hs ===================================== @@ -8,7 +8,7 @@ module GHC.Unit.Module.Env , lookupWithDefaultModuleEnv, mapModuleEnv, mkModuleEnv, emptyModuleEnv , alterModuleEnv , partitionModuleEnv - , moduleEnvKeys, moduleEnvElts, moduleEnvToList + , moduleEnvKeys, nonDetModuleEnvKeys, moduleEnvElts, moduleEnvToList , unitModuleEnv, isEmptyModuleEnv , extendModuleEnvWith, filterModuleEnv, mapMaybeModuleEnv @@ -157,8 +157,15 @@ mkModuleEnv xs = ModuleEnv (Map.fromList [(NDModule k, v) | (k,v) <- xs]) emptyModuleEnv :: ModuleEnv a emptyModuleEnv = ModuleEnv Map.empty +-- | See Note [ModuleEnv performance and determinism]. +-- +-- If you use this, please provide a justification why it doesn't introduce +-- nondeterminism. +nonDetModuleEnvKeys :: ModuleEnv a -> [Module] +nonDetModuleEnvKeys (ModuleEnv e) = map unNDModule $ Map.keys e + moduleEnvKeys :: ModuleEnv a -> [Module] -moduleEnvKeys (ModuleEnv e) = sort $ map unNDModule $ Map.keys e +moduleEnvKeys = sort . nonDetModuleEnvKeys -- See Note [ModuleEnv performance and determinism] moduleEnvElts :: ModuleEnv a -> [a] View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f595622f28c7d8fec5cd5227b2e48049... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f595622f28c7d8fec5cd5227b2e48049... You're receiving this email because of your account on gitlab.haskell.org.