)
import SimplMonad
import SimplEnv
-import SimplUtils ( mkCase, mkLam, prepareAlts,
+import SimplUtils ( mkCase, mkLam,
SimplCont(..), DupFlag(..), LetRhsFlag(..),
mkRhsStop, mkBoringStop, pushContArgs,
contResultType, countArgs, contIsDupable, contIsRhsOrArg,
inlineMode, activeInline, activeRule
)
import Id ( Id, idType, idInfo, idArity, isDataConWorkId,
- setIdUnfolding, isDeadBinder,
+ idUnfolding, setIdUnfolding, isDeadBinder,
idNewDemandInfo, setIdInfo,
setIdOccInfo, zapLamIdInfo, setOneShotLambda
)
occInfo
)
import NewDemand ( isStrictDmd )
-import Unify ( coreRefineTys )
-import DataCon ( dataConTyCon, dataConRepStrictness, isVanillaDataCon )
-import TyCon ( tyConArity )
+import Unify ( coreRefineTys, dataConCanMatch )
+import DataCon ( DataCon, dataConTyCon, dataConRepStrictness, isVanillaDataCon,
+ dataConInstArgTys, dataConTyVars )
+import TyCon ( tyConArity, isAlgTyCon, isNewTyCon, tyConDataCons_maybe )
import CoreSyn
import PprCore ( pprParendExpr, pprCoreExpr )
import CoreUnfold ( mkUnfolding, callSiteInline )
import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,
exprIsConApp_maybe, mkPiTypes, findAlt,
- exprType, exprIsHNF,
+ exprType, exprIsHNF, findDefault, mergeAlts,
exprOkForSpeculation, exprArity,
mkCoerce, mkCoerce2, mkSCC, mkInlineMe, applyTypeToArg
)
import BasicTypes ( isMarkedStrict )
import CostCentre ( currentCCS )
import Type ( TvSubstEnv, isUnLiftedType, seqType, tyConAppArgs, funArgTy,
- splitFunTy_maybe, splitFunTy, coreEqType
+ splitFunTy_maybe, splitFunTy, coreEqType, splitTyConApp_maybe,
+ isTyVarTy, mkTyVarTys
)
+import Var ( tyVarKind, mkTyVar )
import VarEnv ( elemVarEnv, emptyVarEnv )
import TysPrim ( realWorldStatePrimTy )
import PrelInfo ( realWorldPrimId )
import BasicTypes ( TopLevelFlag(..), isTopLevel,
RecFlag(..), isNonRec
)
+import Name ( mkSysTvName )
import StaticFlags ( opt_PprStyle_Debug )
import OrdList
+import List ( nub )
import Maybes ( orElse )
import Outputable
-import Util ( notNull )
+import Util ( notNull, filterOut )
\end{code}
= knownCon env (LitAlt lit) [] case_bndr alts cont
| otherwise
- = -- Prepare the alternatives.
- prepareAlts scrut case_bndr alts `thenSmpl` \ (better_alts, handled_cons) ->
-
- -- Prepare the continuation;
+ = -- Prepare the continuation;
-- The new subst_env is in place
- prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
- addFloats env floats $ \ env ->
+ prepareCaseCont env alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ addFloats env floats $ \ env ->
let
-- The case expression is annotated with the result type of the continuation
simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
-- Deal with the case alternatives
- simplAlts alt_env handled_cons
- case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
+ simplAlts alt_env scrut case_bndr' alts dup_cont `thenSmpl` \ alts' ->
-- Put the case back together
mkCase scrut case_bndr' res_ty' alts' `thenSmpl` \ case_expr ->
\end{code}
+simplAlts does two things:
+
+1. Eliminate alternatives that cannot match, including the
+ DEFAULT alternative.
+
+2. If the DEFAULT alternative can match only one possible constructor,
+ then make that constructor explicit.
+ e.g.
+ case e of x { DEFAULT -> rhs }
+ ===>
+ case e of x { (a,b) -> rhs }
+ where the type is a single constructor type. This gives better code
+ when rhs also scrutinises x or e.
+
+Here "cannot match" includes knowledge from GADTs
+
+It's a good idea do do this stuff before simplifying the alternatives, to
+avoid simplifying alternatives we know can't happen, and to come up with
+the list of constructors that are handled, to put into the IdInfo of the
+case binder, for use when simplifying the alternatives.
+
+Eliminating the default alternative in (1) isn't so obvious, but it can
+happen:
+
+data Colour = Red | Green | Blue
+
+f x = case x of
+ Red -> ..
+ Green -> ..
+ DEFAULT -> h x
+
+h y = case y of
+ Blue -> ..
+ DEFAULT -> [ case y of ... ]
+
+If we inline h into f, the default case of the inlined h can't happen.
+If we don't notice this, we may end up filtering out *all* the cases
+of the inner case y, which give us nowhere to go!
+
\begin{code}
simplAlts :: SimplEnv
- -> [AltCon] -- Alternatives the scrutinee can't be
- -- in the default case
+ -> OutExpr
-> OutId -- Case binder
-> [InAlt] -> SimplCont
-> SimplM [OutAlt] -- Includes the continuation
-simplAlts env handled_cons case_bndr' alts cont'
- = do { mb_alts <- mapSmpl simpl_alt alts
- ; return [alt' | Just (_, alt') <- mb_alts] }
- -- Filter out the alternatives that are inaccessible
+simplAlts env scrut case_bndr' alts cont'
+ = do { mb_alts <- mapSmpl (simplAlt env imposs_cons case_bndr' cont') alts_wo_default
+ ; default_alts <- simplDefault env case_bndr' imposs_deflt_cons cont' maybe_deflt
+ ; return (mergeAlts default_alts [alt' | Just (_, alt') <- mb_alts]) }
+ -- We need the mergeAlts in case the new default_alt
+ -- has turned into a constructor alternative.
where
- simpl_alt alt = simplAlt env handled_cons case_bndr' alt cont'
+ (alts_wo_default, maybe_deflt) = findDefault alts
+ imposs_cons = case scrut of
+ Var v -> otherCons (idUnfolding v)
+ other -> []
+
+ -- "imposs_deflt_cons" are handled either by the context,
+ -- OR by a branch in this case expression. (Don't include DEFAULT!!)
+ imposs_deflt_cons = nub (imposs_cons ++ [con | (con,_,_) <- alts_wo_default])
+
+simplDefault :: SimplEnv
+ -> OutId -- Case binder; need just for its type. Note that as an
+ -- OutId, it has maximum information; this is important.
+ -- Test simpl013 is an example
+ -> [AltCon] -- These cons can't happen when matching the default
+ -> SimplCont
+ -> Maybe InExpr
+ -> SimplM [OutAlt] -- One branch or none; we use a list because it's what
+ -- mergeAlts expects
+
+
+simplDefault env case_bndr' imposs_cons cont Nothing
+ = return [] -- No default branch
+simplDefault env case_bndr' imposs_cons cont (Just rhs)
+ | -- This branch handles the case where we are
+ -- scrutinisng an algebraic data type
+ Just (tycon, inst_tys) <- splitTyConApp_maybe (idType case_bndr'),
+ isAlgTyCon tycon, -- It's a data type, tuple, or unboxed tuples.
+ not (isNewTyCon tycon), -- We can have a newtype, if we are just doing an eval:
+ -- case x of { DEFAULT -> e }
+ -- and we don't want to fill in a default for them!
+ Just all_cons <- tyConDataCons_maybe tycon,
+ not (null all_cons), -- This is a tricky corner case. If the data type has no constructors,
+ -- which GHC allows, then the case expression will have at most a default
+ -- alternative. We don't want to eliminate that alternative, because the
+ -- invariant is that there's always one alternative. It's more convenient
+ -- to leave
+ -- case x of { DEFAULT -> e }
+ -- as it is, rather than transform it to
+ -- error "case cant match"
+ -- which would be quite legitmate. But it's a really obscure corner, and
+ -- not worth wasting code on.
+
+ let imposs_data_cons = [con | DataAlt con <- imposs_cons] -- We now know it's a data type
+ poss_data_cons = filterOut (`elem` imposs_data_cons) all_cons
+ gadt_imposs | all isTyVarTy inst_tys = []
+ | otherwise = filter (cant_match inst_tys) poss_data_cons
+ final_poss = filterOut (`elem` gadt_imposs) poss_data_cons
+
+ = case final_poss of
+ [] -> returnSmpl [] -- Eliminate the default alternative
+ -- altogether if it can't match
+
+ [con] -> -- It matches exactly one constructor, so fill it in
+ do { con_alt <- mkDataConAlt case_bndr' con inst_tys rhs
+ ; Just (_, alt') <- simplAlt env [] case_bndr' cont con_alt
+ -- The simplAlt must succeed with Just because we have
+ -- already filtered out construtors that can't match
+ ; return [alt'] }
-simplAlt :: SimplEnv -> [AltCon] -> OutId -> InAlt -> SimplCont
+ two_or_more -> simplify_default (map DataAlt gadt_imposs ++ imposs_cons)
+
+ | otherwise
+ = simplify_default imposs_cons
+ where
+ cant_match tys data_con = not (dataConCanMatch data_con tys)
+
+ simplify_default imposs_cons
+ = do { let env' = mk_rhs_env env case_bndr' (mkOtherCon imposs_cons)
+ -- Record the constructors that the case-binder *can't* be.
+ ; rhs' <- simplExprC env' rhs cont
+ ; return [(DEFAULT, [], rhs')] }
+
+mkDataConAlt :: Id -> DataCon -> [OutType] -> InExpr -> SimplM InAlt
+-- Make a data-constructor alternative to replace the DEFAULT case
+-- NB: there's something a bit bogus here, because we put OutTypes into an InAlt
+mkDataConAlt case_bndr con tys rhs
+ = do { tick (FillInCaseDefault case_bndr)
+ ; args <- mk_args con tys
+ ; return (DataAlt con, args, rhs) }
+ where
+ mk_args con inst_tys
+ = do { (tv_bndrs, inst_tys') <- mk_tv_bndrs con inst_tys
+ ; let arg_tys = dataConInstArgTys con inst_tys'
+ ; arg_ids <- mapM (newId FSLIT("a")) arg_tys
+ ; returnSmpl (tv_bndrs ++ arg_ids) }
+
+ mk_tv_bndrs con inst_tys
+ | isVanillaDataCon con
+ = return ([], inst_tys)
+ | otherwise
+ = do { tv_uniqs <- getUniquesSmpl
+ ; let new_tvs = zipWith mk tv_uniqs (dataConTyVars con)
+ mk uniq tv = mkTyVar (mkSysTvName uniq FSLIT("t")) (tyVarKind tv)
+ ; return (new_tvs, mkTyVarTys new_tvs) }
+
+simplAlt :: SimplEnv
+ -> [AltCon] -- These constructors can't be present when
+ -- matching this alternative
+ -> OutId -- The case binder
+ -> SimplCont
+ -> InAlt
-> SimplM (Maybe (TvSubstEnv, OutAlt))
+
-- Simplify an alternative, returning the type refinement for the
-- alternative, if the alternative does any refinement at all
-- Nothing => the alternative is inaccessible
-simplAlt env handled_cons case_bndr' (DEFAULT, bndrs, rhs) cont'
+simplAlt env imposs_cons case_bndr' cont' (con, bndrs, rhs)
+ | con `elem` imposs_cons -- This case can't match
+ = return Nothing
+
+simplAlt env handled_cons case_bndr' cont' (DEFAULT, bndrs, rhs)
+ -- TURGID DUPLICATION, needed only for the simplAlt call
+ -- in mkDupableAlt. Clean this up when moving to FC
= ASSERT( null bndrs )
simplExprC env' rhs cont' `thenSmpl` \ rhs' ->
returnSmpl (Just (emptyVarEnv, (DEFAULT, [], rhs')))
env' = mk_rhs_env env case_bndr' (mkOtherCon handled_cons)
-- Record the constructors that the case-binder *can't* be.
-simplAlt env handled_cons case_bndr' (LitAlt lit, bndrs, rhs) cont'
+simplAlt env handled_cons case_bndr' cont' (LitAlt lit, bndrs, rhs)
= ASSERT( null bndrs )
simplExprC env' rhs cont' `thenSmpl` \ rhs' ->
returnSmpl (Just (emptyVarEnv, (LitAlt lit, [], rhs')))
where
env' = mk_rhs_env env case_bndr' (mkUnfolding False (Lit lit))
-simplAlt env handled_cons case_bndr' (DataAlt con, vs, rhs) cont'
+simplAlt env handled_cons case_bndr' cont' (DataAlt con, vs, rhs)
| isVanillaDataCon con
= -- Deal with the pattern-bound variables
-- Mark the ones that are in ! positions in the data constructor
)}}
mkDupableAlt env case_bndr' cont alt
- = simplAlt env [] case_bndr' alt cont `thenSmpl` \ mb_stuff ->
+ = simplAlt env [] case_bndr' cont alt `thenSmpl` \ mb_stuff ->
case mb_stuff of {
Nothing -> returnSmpl (emptyFloats env, Nothing) ;
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