{- (c) The AQUA Project, Glasgow University, 1993-1998 \section[SimplMonad]{The simplifier Monad} -} {-# LANGUAGE CPP #-} module SimplEnv ( InId, InBind, InExpr, InAlt, InArg, InType, InBndr, InVar, OutId, OutTyVar, OutBind, OutExpr, OutAlt, OutArg, OutType, OutBndr, OutVar, InCoercion, OutCoercion, -- The simplifier mode setMode, getMode, updMode, -- Environments SimplEnv(..), StaticEnv, pprSimplEnv, -- Temp not abstract mkSimplEnv, extendIdSubst, SimplEnv.extendTvSubst, SimplEnv.extendCvSubst, zapSubstEnv, setSubstEnv, getInScope, setInScope, setInScopeSet, modifyInScope, addNewInScopeIds, getSimplRules, SimplSR(..), mkContEx, substId, lookupRecBndr, refineFromInScope, substExpr, simplNonRecBndr, simplRecBndrs, simplBinder, simplBinders, substTy, substTyVar, getTvSubst, getCvSubst, substCo, substCoVar, -- Floats Floats, emptyFloats, isEmptyFloats, addNonRec, addFloats, extendFloats, wrapFloats, setFloats, zapFloats, addRecFloats, mapFloats, doFloatFromRhs, getFloatBinds ) where #include "HsVersions.h" import SimplMonad import CoreMonad ( SimplifierMode(..) ) import CoreSyn import CoreUtils import Var import VarEnv import VarSet import OrdList import Id import qualified CoreSubst import MkCore ( mkWildValBinder ) import TysWiredIn import qualified Type import Type hiding ( substTy, substTyVarBndr, substTyVar ) import qualified Coercion import Coercion hiding ( substCo, substTy, substCoVar, substCoVarBndr, substTyVarBndr ) import BasicTypes import MonadUtils import Outputable import FastString import Util import Data.List {- ************************************************************************ * * \subsection[Simplify-types]{Type declarations} * * ************************************************************************ -} type InBndr = CoreBndr type InVar = Var -- Not yet cloned type InId = Id -- Not yet cloned type InType = Type -- Ditto type InBind = CoreBind type InExpr = CoreExpr type InAlt = CoreAlt type InArg = CoreArg type InCoercion = Coercion type OutBndr = CoreBndr type OutVar = Var -- Cloned type OutId = Id -- Cloned type OutTyVar = TyVar -- Cloned type OutType = Type -- Cloned type OutCoercion = Coercion type OutBind = CoreBind type OutExpr = CoreExpr type OutAlt = CoreAlt type OutArg = CoreArg {- ************************************************************************ * * \subsubsection{The @SimplEnv@ type} * * ************************************************************************ -} data SimplEnv = SimplEnv { ----------- Static part of the environment ----------- -- Static in the sense of lexically scoped, -- wrt the original expression seMode :: SimplifierMode, -- The current substitution seTvSubst :: TvSubstEnv, -- InTyVar |--> OutType seCvSubst :: CvSubstEnv, -- InCoVar |--> OutCoercion seIdSubst :: SimplIdSubst, -- InId |--> OutExpr ----------- Dynamic part of the environment ----------- -- Dynamic in the sense of describing the setup where -- the expression finally ends up -- The current set of in-scope variables -- They are all OutVars, and all bound in this module seInScope :: InScopeSet, -- OutVars only -- Includes all variables bound by seFloats seFloats :: Floats -- See Note [Simplifier floats] } type StaticEnv = SimplEnv -- Just the static part is relevant pprSimplEnv :: SimplEnv -> SDoc -- Used for debugging; selective pprSimplEnv env = vcat [ptext (sLit "TvSubst:") <+> ppr (seTvSubst env), ptext (sLit "IdSubst:") <+> ppr (seIdSubst env), ptext (sLit "InScope:") <+> vcat (map ppr_one in_scope_vars) ] where in_scope_vars = varEnvElts (getInScopeVars (seInScope env)) ppr_one v | isId v = ppr v <+> ppr (idUnfolding v) | otherwise = ppr v type SimplIdSubst = IdEnv SimplSR -- IdId |--> OutExpr -- See Note [Extending the Subst] in CoreSubst data SimplSR = DoneEx OutExpr -- Completed term | DoneId OutId -- Completed term variable | ContEx TvSubstEnv -- A suspended substitution CvSubstEnv SimplIdSubst InExpr instance Outputable SimplSR where ppr (DoneEx e) = ptext (sLit "DoneEx") <+> ppr e ppr (DoneId v) = ptext (sLit "DoneId") <+> ppr v ppr (ContEx _tv _cv _id e) = vcat [ptext (sLit "ContEx") <+> ppr e {-, ppr (filter_env tv), ppr (filter_env id) -}] -- where -- fvs = exprFreeVars e -- filter_env env = filterVarEnv_Directly keep env -- keep uniq _ = uniq `elemUFM_Directly` fvs {- Note [SimplEnv invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~ seInScope: The in-scope part of Subst includes *all* in-scope TyVars and Ids The elements of the set may have better IdInfo than the occurrences of in-scope Ids, and (more important) they will have a correctly-substituted type. So we use a lookup in this set to replace occurrences The Ids in the InScopeSet are replete with their Rules, and as we gather info about the unfolding of an Id, we replace it in the in-scope set. The in-scope set is actually a mapping OutVar -> OutVar, and in case expressions we sometimes bind seIdSubst: The substitution is *apply-once* only, because InIds and OutIds can overlap. For example, we generally omit mappings a77 -> a77 from the substitution, when we decide not to clone a77, but it's quite legitimate to put the mapping in the substitution anyway. Furthermore, consider let x = case k of I# x77 -> ... in let y = case k of I# x77 -> ... in ... and suppose the body is strict in both x and y. Then the simplifier will pull the first (case k) to the top; so the second (case k) will cancel out, mapping x77 to, well, x77! But one is an in-Id and the other is an out-Id. Of course, the substitution *must* applied! Things in its domain simply aren't necessarily bound in the result. * substId adds a binding (DoneId new_id) to the substitution if the Id's unique has changed Note, though that the substitution isn't necessarily extended if the type of the Id changes. Why not? Because of the next point: * We *always, always* finish by looking up in the in-scope set any variable that doesn't get a DoneEx or DoneVar hit in the substitution. Reason: so that we never finish up with a "old" Id in the result. An old Id might point to an old unfolding and so on... which gives a space leak. [The DoneEx and DoneVar hits map to "new" stuff.] * It follows that substExpr must not do a no-op if the substitution is empty. substType is free to do so, however. * When we come to a let-binding (say) we generate new IdInfo, including an unfolding, attach it to the binder, and add this newly adorned binder to the in-scope set. So all subsequent occurrences of the binder will get mapped to the full-adorned binder, which is also the one put in the binding site. * The in-scope "set" usually maps x->x; we use it simply for its domain. But sometimes we have two in-scope Ids that are synomyms, and should map to the same target: x->x, y->x. Notably: case y of x { ... } That's why the "set" is actually a VarEnv Var -} mkSimplEnv :: SimplifierMode -> SimplEnv mkSimplEnv mode = SimplEnv { seMode = mode , seInScope = init_in_scope , seFloats = emptyFloats , seTvSubst = emptyVarEnv , seCvSubst = emptyVarEnv , seIdSubst = emptyVarEnv } -- The top level "enclosing CC" is "SUBSUMED". init_in_scope :: InScopeSet init_in_scope = mkInScopeSet (unitVarSet (mkWildValBinder unitTy)) -- See Note [WildCard binders] {- Note [WildCard binders] ~~~~~~~~~~~~~~~~~~~~~~~ The program to be simplified may have wild binders case e of wild { p -> ... } We want to *rename* them away, so that there are no occurrences of 'wild-id' (with wildCardKey). The easy way to do that is to start of with a representative Id in the in-scope set There can be be *occurrences* of wild-id. For example, MkCore.mkCoreApp transforms e (a /# b) --> case (a /# b) of wild { DEFAULT -> e wild } This is ok provided 'wild' isn't free in 'e', and that's the delicate thing. Generally, you want to run the simplifier to get rid of the wild-ids before doing much else. It's a very dark corner of GHC. Maybe it should be cleaned up. -} getMode :: SimplEnv -> SimplifierMode getMode env = seMode env setMode :: SimplifierMode -> SimplEnv -> SimplEnv setMode mode env = env { seMode = mode } updMode :: (SimplifierMode -> SimplifierMode) -> SimplEnv -> SimplEnv updMode upd env = env { seMode = upd (seMode env) } --------------------- extendIdSubst :: SimplEnv -> Id -> SimplSR -> SimplEnv extendIdSubst env@(SimplEnv {seIdSubst = subst}) var res = ASSERT2( isId var && not (isCoVar var), ppr var ) env {seIdSubst = extendVarEnv subst var res} extendTvSubst :: SimplEnv -> TyVar -> Type -> SimplEnv extendTvSubst env@(SimplEnv {seTvSubst = subst}) var res = env {seTvSubst = extendVarEnv subst var res} extendCvSubst :: SimplEnv -> CoVar -> Coercion -> SimplEnv extendCvSubst env@(SimplEnv {seCvSubst = subst}) var res = env {seCvSubst = extendVarEnv subst var res} --------------------- getInScope :: SimplEnv -> InScopeSet getInScope env = seInScope env setInScopeSet :: SimplEnv -> InScopeSet -> SimplEnv setInScopeSet env in_scope = env {seInScope = in_scope} setInScope :: SimplEnv -> SimplEnv -> SimplEnv -- Set the in-scope set, and *zap* the floats setInScope env env_with_scope = env { seInScope = seInScope env_with_scope, seFloats = emptyFloats } setFloats :: SimplEnv -> SimplEnv -> SimplEnv -- Set the in-scope set *and* the floats setFloats env env_with_floats = env { seInScope = seInScope env_with_floats, seFloats = seFloats env_with_floats } addNewInScopeIds :: SimplEnv -> [CoreBndr] -> SimplEnv -- The new Ids are guaranteed to be freshly allocated addNewInScopeIds env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) vs = env { seInScope = in_scope `extendInScopeSetList` vs, seIdSubst = id_subst `delVarEnvList` vs } -- Why delete? Consider -- let x = a*b in (x, \x -> x+3) -- We add [x |-> a*b] to the substitution, but we must -- _delete_ it from the substitution when going inside -- the (\x -> ...)! modifyInScope :: SimplEnv -> CoreBndr -> SimplEnv -- The variable should already be in scope, but -- replace the existing version with this new one -- which has more information modifyInScope env@(SimplEnv {seInScope = in_scope}) v = env {seInScope = extendInScopeSet in_scope v} --------------------- zapSubstEnv :: SimplEnv -> SimplEnv zapSubstEnv env = env {seTvSubst = emptyVarEnv, seCvSubst = emptyVarEnv, seIdSubst = emptyVarEnv} setSubstEnv :: SimplEnv -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> SimplEnv setSubstEnv env tvs cvs ids = env { seTvSubst = tvs, seCvSubst = cvs, seIdSubst = ids } mkContEx :: SimplEnv -> InExpr -> SimplSR mkContEx (SimplEnv { seTvSubst = tvs, seCvSubst = cvs, seIdSubst = ids }) e = ContEx tvs cvs ids e {- ************************************************************************ * * \subsection{Floats} * * ************************************************************************ Note [Simplifier floats] ~~~~~~~~~~~~~~~~~~~~~~~~~ The Floats is a bunch of bindings, classified by a FloatFlag. * All of them satisfy the let/app invariant Examples NonRec x (y:ys) FltLifted Rec [(x,rhs)] FltLifted NonRec x* (p:q) FltOKSpec -- RHS is WHNF. Question: why not FltLifted? NonRec x# (y +# 3) FltOkSpec -- Unboxed, but ok-for-spec'n NonRec x* (f y) FltCareful -- Strict binding; might fail or diverge Can't happen: NonRec x# (a /# b) -- Might fail; does not satisfy let/app NonRec x# (f y) -- Might diverge; does not satisfy let/app -} data Floats = Floats (OrdList OutBind) FloatFlag -- See Note [Simplifier floats] data FloatFlag = FltLifted -- All bindings are lifted and lazy -- Hence ok to float to top level, or recursive | FltOkSpec -- All bindings are FltLifted *or* -- strict (perhaps because unlifted, -- perhaps because of a strict binder), -- *and* ok-for-speculation -- Hence ok to float out of the RHS -- of a lazy non-recursive let binding -- (but not to top level, or into a rec group) | FltCareful -- At least one binding is strict (or unlifted) -- and not guaranteed cheap -- Do not float these bindings out of a lazy let instance Outputable Floats where ppr (Floats binds ff) = ppr ff $$ ppr (fromOL binds) instance Outputable FloatFlag where ppr FltLifted = ptext (sLit "FltLifted") ppr FltOkSpec = ptext (sLit "FltOkSpec") ppr FltCareful = ptext (sLit "FltCareful") andFF :: FloatFlag -> FloatFlag -> FloatFlag andFF FltCareful _ = FltCareful andFF FltOkSpec FltCareful = FltCareful andFF FltOkSpec _ = FltOkSpec andFF FltLifted flt = flt doFloatFromRhs :: TopLevelFlag -> RecFlag -> Bool -> OutExpr -> SimplEnv -> Bool -- If you change this function look also at FloatIn.noFloatFromRhs doFloatFromRhs lvl rec str rhs (SimplEnv {seFloats = Floats fs ff}) = not (isNilOL fs) && want_to_float && can_float where want_to_float = isTopLevel lvl || exprIsCheap rhs || exprIsExpandable rhs -- See Note [Float when cheap or expandable] can_float = case ff of FltLifted -> True FltOkSpec -> isNotTopLevel lvl && isNonRec rec FltCareful -> isNotTopLevel lvl && isNonRec rec && str {- Note [Float when cheap or expandable] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to float a let from a let if the residual RHS is a) cheap, such as (\x. blah) b) expandable, such as (f b) if f is CONLIKE But there are - cheap things that are not expandable (eg \x. expensive) - expandable things that are not cheap (eg (f b) where b is CONLIKE) so we must take the 'or' of the two. -} emptyFloats :: Floats emptyFloats = Floats nilOL FltLifted unitFloat :: OutBind -> Floats -- This key function constructs a singleton float with the right form unitFloat bind = Floats (unitOL bind) (flag bind) where flag (Rec {}) = FltLifted flag (NonRec bndr rhs) | not (isStrictId bndr) = FltLifted | exprOkForSpeculation rhs = FltOkSpec -- Unlifted, and lifted but ok-for-spec (eg HNF) | otherwise = ASSERT2( not (isUnLiftedType (idType bndr)), ppr bndr ) FltCareful -- Unlifted binders can only be let-bound if exprOkForSpeculation holds addNonRec :: SimplEnv -> OutId -> OutExpr -> SimplEnv -- Add a non-recursive binding and extend the in-scope set -- The latter is important; the binder may already be in the -- in-scope set (although it might also have been created with newId) -- but it may now have more IdInfo addNonRec env id rhs = id `seq` -- This seq forces the Id, and hence its IdInfo, -- and hence any inner substitutions env { seFloats = seFloats env `addFlts` unitFloat (NonRec id rhs), seInScope = extendInScopeSet (seInScope env) id } extendFloats :: SimplEnv -> OutBind -> SimplEnv -- Add these bindings to the floats, and extend the in-scope env too extendFloats env bind = env { seFloats = seFloats env `addFlts` unitFloat bind, seInScope = extendInScopeSetList (seInScope env) bndrs } where bndrs = bindersOf bind addFloats :: SimplEnv -> SimplEnv -> SimplEnv -- Add the floats for env2 to env1; -- *plus* the in-scope set for env2, which is bigger -- than that for env1 addFloats env1 env2 = env1 {seFloats = seFloats env1 `addFlts` seFloats env2, seInScope = seInScope env2 } addFlts :: Floats -> Floats -> Floats addFlts (Floats bs1 l1) (Floats bs2 l2) = Floats (bs1 `appOL` bs2) (l1 `andFF` l2) zapFloats :: SimplEnv -> SimplEnv zapFloats env = env { seFloats = emptyFloats } addRecFloats :: SimplEnv -> SimplEnv -> SimplEnv -- Flattens the floats from env2 into a single Rec group, -- prepends the floats from env1, and puts the result back in env2 -- This is all very specific to the way recursive bindings are -- handled; see Simplify.simplRecBind addRecFloats env1 env2@(SimplEnv {seFloats = Floats bs ff}) = ASSERT2( case ff of { FltLifted -> True; _ -> False }, ppr (fromOL bs) ) env2 {seFloats = seFloats env1 `addFlts` unitFloat (Rec (flattenBinds (fromOL bs)))} wrapFloats :: SimplEnv -> OutExpr -> OutExpr -- Wrap the floats around the expression; they should all -- satisfy the let/app invariant, so mkLets should do the job just fine wrapFloats (SimplEnv {seFloats = Floats bs _}) body = foldrOL Let body bs getFloatBinds :: SimplEnv -> [CoreBind] getFloatBinds (SimplEnv {seFloats = Floats bs _}) = fromOL bs isEmptyFloats :: SimplEnv -> Bool isEmptyFloats (SimplEnv {seFloats = Floats bs _}) = isNilOL bs mapFloats :: SimplEnv -> ((Id,CoreExpr) -> (Id,CoreExpr)) -> SimplEnv mapFloats env@SimplEnv { seFloats = Floats fs ff } fun = env { seFloats = Floats (mapOL app fs) ff } where app (NonRec b e) = case fun (b,e) of (b',e') -> NonRec b' e' app (Rec bs) = Rec (map fun bs) {- ************************************************************************ * * Substitution of Vars * * ************************************************************************ Note [Global Ids in the substitution] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We look up even a global (eg imported) Id in the substitution. Consider case X.g_34 of b { (a,b) -> ... case X.g_34 of { (p,q) -> ...} ... } The binder-swap in the occurrence analyser will add a binding for a LocalId version of g (with the same unique though): case X.g_34 of b { (a,b) -> let g_34 = b in ... case X.g_34 of { (p,q) -> ...} ... } So we want to look up the inner X.g_34 in the substitution, where we'll find that it has been substituted by b. (Or conceivably cloned.) -} substId :: SimplEnv -> InId -> SimplSR -- Returns DoneEx only on a non-Var expression substId (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v = case lookupVarEnv ids v of -- Note [Global Ids in the substitution] Nothing -> DoneId (refineFromInScope in_scope v) Just (DoneId v) -> DoneId (refineFromInScope in_scope v) Just (DoneEx (Var v)) -> DoneId (refineFromInScope in_scope v) Just res -> res -- DoneEx non-var, or ContEx -- Get the most up-to-date thing from the in-scope set -- Even though it isn't in the substitution, it may be in -- the in-scope set with better IdInfo refineFromInScope :: InScopeSet -> Var -> Var refineFromInScope in_scope v | isLocalId v = case lookupInScope in_scope v of Just v' -> v' Nothing -> WARN( True, ppr v ) v -- This is an error! | otherwise = v lookupRecBndr :: SimplEnv -> InId -> OutId -- Look up an Id which has been put into the envt by simplRecBndrs, -- but where we have not yet done its RHS lookupRecBndr (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v = case lookupVarEnv ids v of Just (DoneId v) -> v Just _ -> pprPanic "lookupRecBndr" (ppr v) Nothing -> refineFromInScope in_scope v {- ************************************************************************ * * \section{Substituting an Id binder} * * ************************************************************************ * sinplBndr, simplBndrs: monadic version, only so that they can be made strict via seq. -} ------------- simplBinders :: SimplEnv -> [InBndr] -> SimplM (SimplEnv, [OutBndr]) simplBinders env bndrs = mapAccumLM simplBinder env bndrs simplBinder :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr) -- Used for lambda and case-bound variables -- Clone Id if necessary, substitute type -- Return with IdInfo already substituted, but (fragile) occurrence info zapped -- The substitution is extended only if the variable is cloned, because -- we *don't* need to use it to track occurrence info. simplBinder env bndr | isTyVar bndr = do { let (env', tv) = substTyVarBndr env bndr ; seqTyVar tv `seq` return (env', tv) } | otherwise = do { let (env', id) = substIdBndr env bndr ; seqId id `seq` return (env', id) } simplNonRecBndr :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr) -- A non-recursive let binder simplNonRecBndr env id = do { let (env1, id1) = substIdBndr env id ; seqId id1 `seq` return (env1, id1) } simplRecBndrs :: SimplEnv -> [InBndr] -> SimplM SimplEnv -- Recursive let binders simplRecBndrs env@(SimplEnv {}) ids = do { let (env1, ids1) = mapAccumL substIdBndr env ids ; seqIds ids1 `seq` return env1 } substIdBndr :: SimplEnv -> InBndr -> (SimplEnv, OutBndr) -- Might be a coercion variable substIdBndr env bndr | isCoVar bndr = substCoVarBndr env bndr | otherwise = substNonCoVarIdBndr env bndr --------------- substNonCoVarIdBndr :: SimplEnv -> InBndr -- Env and binder to transform -> (SimplEnv, OutBndr) -- Clone Id if necessary, substitute its type -- Return an Id with its -- * Type substituted -- * UnfoldingInfo, Rules, WorkerInfo zapped -- * Fragile OccInfo (only) zapped: Note [Robust OccInfo] -- * Robust info, retained especially arity and demand info, -- so that they are available to occurrences that occur in an -- earlier binding of a letrec -- -- For the robust info, see Note [Arity robustness] -- -- Augment the substitution if the unique changed -- Extend the in-scope set with the new Id -- -- Similar to CoreSubst.substIdBndr, except that -- the type of id_subst differs -- all fragile info is zapped substNonCoVarIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) old_id = ASSERT2( not (isCoVar old_id), ppr old_id ) (env { seInScope = in_scope `extendInScopeSet` new_id, seIdSubst = new_subst }, new_id) where id1 = uniqAway in_scope old_id id2 = substIdType env id1 new_id = zapFragileIdInfo id2 -- Zaps rules, worker-info, unfolding -- and fragile OccInfo -- Extend the substitution if the unique has changed, -- or there's some useful occurrence information -- See the notes with substTyVarBndr for the delSubstEnv new_subst | new_id /= old_id = extendVarEnv id_subst old_id (DoneId new_id) | otherwise = delVarEnv id_subst old_id ------------------------------------ seqTyVar :: TyVar -> () seqTyVar b = b `seq` () seqId :: Id -> () seqId id = seqType (idType id) `seq` idInfo id `seq` () seqIds :: [Id] -> () seqIds [] = () seqIds (id:ids) = seqId id `seq` seqIds ids {- Note [Arity robustness] ~~~~~~~~~~~~~~~~~~~~~~~ We *do* transfer the arity from from the in_id of a let binding to the out_id. This is important, so that the arity of an Id is visible in its own RHS. For example: f = \x. ....g (\y. f y).... We can eta-reduce the arg to g, because f is a value. But that needs to be visible. This interacts with the 'state hack' too: f :: Bool -> IO Int f = \x. case x of True -> f y False -> \s -> ... Can we eta-expand f? Only if we see that f has arity 1, and then we take advantage of the 'state hack' on the result of (f y) :: State# -> (State#, Int) to expand the arity one more. There is a disadvantage though. Making the arity visible in the RHS allows us to eta-reduce f = \x -> f x to f = f which technically is not sound. This is very much a corner case, so I'm not worried about it. Another idea is to ensure that f's arity never decreases; its arity started as 1, and we should never eta-reduce below that. Note [Robust OccInfo] ~~~~~~~~~~~~~~~~~~~~~ It's important that we *do* retain the loop-breaker OccInfo, because that's what stops the Id getting inlined infinitely, in the body of the letrec. -} {- ************************************************************************ * * Impedence matching to type substitution * * ************************************************************************ -} getTvSubst :: SimplEnv -> TvSubst getTvSubst (SimplEnv { seInScope = in_scope, seTvSubst = tv_env }) = mkTvSubst in_scope tv_env getCvSubst :: SimplEnv -> CvSubst getCvSubst (SimplEnv { seInScope = in_scope, seTvSubst = tv_env, seCvSubst = cv_env }) = CvSubst in_scope tv_env cv_env substTy :: SimplEnv -> Type -> Type substTy env ty = Type.substTy (getTvSubst env) ty substTyVar :: SimplEnv -> TyVar -> Type substTyVar env tv = Type.substTyVar (getTvSubst env) tv substTyVarBndr :: SimplEnv -> TyVar -> (SimplEnv, TyVar) substTyVarBndr env tv = case Type.substTyVarBndr (getTvSubst env) tv of (TvSubst in_scope' tv_env', tv') -> (env { seInScope = in_scope', seTvSubst = tv_env' }, tv') substCoVar :: SimplEnv -> CoVar -> Coercion substCoVar env tv = Coercion.substCoVar (getCvSubst env) tv substCoVarBndr :: SimplEnv -> CoVar -> (SimplEnv, CoVar) substCoVarBndr env cv = case Coercion.substCoVarBndr (getCvSubst env) cv of (CvSubst in_scope' tv_env' cv_env', cv') -> (env { seInScope = in_scope', seTvSubst = tv_env', seCvSubst = cv_env' }, cv') substCo :: SimplEnv -> Coercion -> Coercion substCo env co = Coercion.substCo (getCvSubst env) co ------------------ substIdType :: SimplEnv -> Id -> Id substIdType (SimplEnv { seInScope = in_scope, seTvSubst = tv_env }) id | isEmptyVarEnv tv_env || isEmptyVarSet (tyVarsOfType old_ty) = id | otherwise = Id.setIdType id (Type.substTy (TvSubst in_scope tv_env) old_ty) -- The tyVarsOfType is cheaper than it looks -- because we cache the free tyvars of the type -- in a Note in the id's type itself where old_ty = idType id substExpr :: SimplEnv -> CoreExpr -> CoreExpr -- See Note [Substitution in the simplifier] substExpr (SimplEnv { seInScope = in_scope , seTvSubst = tv_env , seCvSubst = cv_env , seIdSubst = id_env }) = subst_expr in_scope tv_env cv_env id_env where subst_expr :: InScopeSet -> TvSubstEnv -> CvSubstEnv -> SimplIdSubst -> CoreExpr -> CoreExpr subst_expr is tvs cvs id_env = CoreSubst.substExpr (text "SimplEnv.substExpr") (CoreSubst.mkGblSubst is tvs cvs lookup_id) where lookup_id in_scope v = case lookupVarEnv id_env v of Nothing -> Nothing Just (DoneEx e) -> Just e Just (DoneId v) -> Just (Var v) Just (ContEx tv cv id e) -> Just (subst_expr in_scope tv cv id e) {- Note [Substitution in the simplifier] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In just one place (sigh) we need to lazily substitute over a CoreExpr. For that we need CoreSubst.substExpr. But there is a difficulty: SimplEnv has a SimplIdSubst, whose range is SimplSR, not just CoreExpr. So SimplEnv.substExpr has to perform impedence-matching, via the ambient substitution provided by mkGblSubst. It seems like a lot of work for a small thing. Previously we attempted to construct a (VarEnv CoreExpr) from the SimplIdSubst, but that had absolutely terrible performance (Trac #10370 comment:12). Then I tried to write a complete new substExpr that used SimplIdSubst insead of (VarEnv CoreExpr), but that got out of hand because we need to substitute over rules and unfoldings too (Trac #5113, comment:7 and following). -}