diff options
| -rw-r--r-- | compiler/coreSyn/CoreUtils.hs | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/compiler/coreSyn/CoreUtils.hs b/compiler/coreSyn/CoreUtils.hs index fbe7ebd9a6..5e32dc6093 100644 --- a/compiler/coreSyn/CoreUtils.hs +++ b/compiler/coreSyn/CoreUtils.hs @@ -94,6 +94,8 @@ import Data.Function ( on ) import Data.List import Data.Ord ( comparing ) import OrdList +import qualified Data.Set as Set +import UniqSet {- ************************************************************************ @@ -629,13 +631,15 @@ filterAlts _tycon inst_tys imposs_cons alts trimmed_alts = filterOut (impossible_alt inst_tys) alts_wo_default - imposs_deflt_cons = nub (imposs_cons ++ alt_cons) + imposs_cons_set = Set.fromList imposs_cons + imposs_deflt_cons = + imposs_cons ++ filterOut (`Set.member` imposs_cons_set) alt_cons -- "imposs_deflt_cons" are handled -- EITHER by the context, -- OR by a non-DEFAULT branch in this case expression. impossible_alt :: [Type] -> (AltCon, a, b) -> Bool - impossible_alt _ (con, _, _) | con `elem` imposs_cons = True + impossible_alt _ (con, _, _) | con `Set.member` imposs_cons_set = True impossible_alt inst_tys (DataAlt con, _, _) = dataConCannotMatch inst_tys con impossible_alt _ _ = False @@ -652,8 +656,11 @@ refineDefaultAlt us tycon tys imposs_deflt_cons all_alts -- case x of { DEFAULT -> e } -- and we don't want to fill in a default for them! , Just all_cons <- tyConDataCons_maybe tycon - , let imposs_data_cons = [con | DataAlt con <- imposs_deflt_cons] -- We now know it's a data type - impossible con = con `elem` imposs_data_cons || dataConCannotMatch tys con + , let imposs_data_cons = mkUniqSet [con | DataAlt con <- imposs_deflt_cons] + -- We now know it's a data type, so we can use + -- UniqSet rather than Set (more efficient) + impossible con = con `elementOfUniqSet` imposs_data_cons + || dataConCannotMatch tys con = case filterOut impossible all_cons of -- Eliminate the default alternative -- altogether if it can't match: |