#11602: Exponential behaviour in typeKind, unifyTys etc -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In Trac #11371 Bartosz found some very suspicious performance behaviour. Specifically: * See comment 42 of #11371, which says that `liftCoMatch` and `promoteCoercion` is responsible for a significant fraction of all compiler allocation. Why so expensive? Especially since only used from `OptCoercion`. * There are two comments in `Unify` saying {{{ ty_co_match_app menv subst ty1a ty1b co2a co2b = do { -- TODO (RAE): Remove this exponential behavior. subst1 <- ty_co_match menv subst ki1a ki2a ki_ki_co ki_ki_co }}} and {{{ unify_ty_app ty1a ty1b ty2a ty2b = do { -- TODO (RAE): Remove this exponential behavior. let ki1a = typeKind ty1a ki2a = typeKind ty2a ; unify_ty ki1a ki2a (mkNomReflCo liftedTypeKind) }}} NB: `ty_co_match_app` is also called from `liftCoMatch`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11602 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler