X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreSubst.lhs;h=f63968e0fa132574c14e861875c0f1001fcb34fc;hp=addda3ad2b6612f9bc956b5467c61ff9e24986cb;hb=62eeda5aed31173b234b2965ccf4bd6979ffd9a4;hpb=2c969eccaa815888434143c9084b8ab855586dc6 diff --git a/compiler/coreSyn/CoreSubst.lhs b/compiler/coreSyn/CoreSubst.lhs index addda3a..f63968e 100644 --- a/compiler/coreSyn/CoreSubst.lhs +++ b/compiler/coreSyn/CoreSubst.lhs @@ -1,53 +1,53 @@ % +% (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % -\section[CoreUtils]{Utility functions on @Core@ syntax} + +Utility functions on @Core@ syntax \begin{code} module CoreSubst ( - -- Substitution stuff + -- * Main data types Subst, TvSubstEnv, IdSubstEnv, InScopeSet, + -- ** Substituting into expressions and related types deShadowBinds, - substTy, substExpr, substSpec, substWorker, + substTy, substExpr, substBind, substSpec, substWorker, lookupIdSubst, lookupTvSubst, + -- ** Operations on substitutions emptySubst, mkEmptySubst, mkSubst, substInScope, isEmptySubst, extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList, - extendInScope, extendInScopeIds, + extendSubst, extendSubstList, zapSubstEnv, + extendInScope, extendInScopeList, extendInScopeIds, isInScope, - -- Binders + -- ** Substituting and cloning binders substBndr, substBndrs, substRecBndrs, cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs ) where #include "HsVersions.h" -import CoreSyn ( Expr(..), Bind(..), Note(..), CoreExpr, CoreBind, - CoreRule(..), hasUnfolding, noUnfolding - ) -import CoreFVs ( exprFreeVars ) -import CoreUtils ( exprIsTrivial ) +import CoreSyn +import CoreFVs +import CoreUtils -import qualified Type ( substTy, substTyVarBndr ) -import Type ( Type, tyVarsOfType, TvSubstEnv, TvSubst(..), mkTyVarTy ) +import qualified Type +import Type ( Type, TvSubst(..), TvSubstEnv ) import VarSet import VarEnv -import Var ( setVarUnique, isId ) -import Id ( idType, setIdType, maybeModifyIdInfo, isLocalId ) -import IdInfo ( IdInfo, SpecInfo(..), specInfo, setSpecInfo, isEmptySpecInfo, - unfoldingInfo, setUnfoldingInfo, seqSpecInfo, - WorkerInfo(..), workerExists, workerInfo, setWorkerInfo - ) -import Unique ( Unique ) -import UniqSupply ( UniqSupply, uniqFromSupply, uniqsFromSupply ) -import Var ( Var, Id, TyVar, isTyVar ) -import Maybes ( orElse ) +import Id +import Var ( Var, TyVar, setVarUnique ) +import IdInfo +import Unique +import UniqSupply +import Maybes import Outputable import PprCore () -- Instances -import Util ( mapAccumL ) -import FastTypes +import FastString + +import Data.List \end{code} @@ -58,26 +58,87 @@ import FastTypes %************************************************************************ \begin{code} +-- | A substitution environment, containing both 'Id' and 'TyVar' substitutions. +-- +-- Some invariants apply to how you use the substitution: +-- +-- 1. #in_scope_invariant# The in-scope set contains at least those 'Id's and 'TyVar's that will be in scope /after/ +-- applying the substitution to a term. Precisely, the in-scope set must be a superset of the free vars of the +-- substitution range that might possibly clash with locally-bound variables in the thing being substituted in. +-- +-- 2. #apply_once# You may apply the substitution only /once/ +-- +-- There are various ways of setting up the in-scope set such that the first of these invariants hold: +-- +-- * Arrange that the in-scope set really is all the things in scope +-- +-- * Arrange that it's the free vars of the range of the substitution +-- +-- * Make it empty, if you know that all the free vars of the substitution are fresh, and hence can't possibly clash data Subst - = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) - IdSubstEnv -- Substitution for Ids - TvSubstEnv -- Substitution for TyVars - - -- INVARIANT 1: The (domain of the) in-scope set is a superset - -- of the free vars of the range of the substitution - -- that might possibly clash with locally-bound variables - -- in the thing being substituted in. + = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) /after/ + -- applying the substitution + IdSubstEnv -- Substitution for Ids + TvSubstEnv -- Substitution for TyVars + + -- INVARIANT 1: See #in_scope_invariant# -- This is what lets us deal with name capture properly -- It's a hard invariant to check... - -- There are various ways of causing it to happen: - -- - arrange that the in-scope set really is all the things in scope - -- - arrange that it's the free vars of the range of the substitution - -- - make it empty because all the free vars of the subst are fresh, - -- and hence can't possibly clash.a -- - -- INVARIANT 2: The substitution is apply-once; see notes with + -- INVARIANT 2: The substitution is apply-once; see Note [Apply once] with -- Types.TvSubstEnv + -- + -- INVARIANT 3: See Note [Extending the Subst] +\end{code} + +Note [Extending the Subst] +~~~~~~~~~~~~~~~~~~~~~~~~~~ +For a core Subst, which binds Ids as well, we make a different choice for Ids +than we do for TyVars. + +For TyVars, see Note [Extending the TvSubst] with Type.TvSubstEnv + +For Ids, we have a different invariant + The IdSubstEnv is extended *only* when the Unique on an Id changes + Otherwise, we just extend the InScopeSet + +In consequence: + +* In substIdBndr, we extend the IdSubstEnv only when the unique changes + +* If the TvSubstEnv and IdSubstEnv are both empty, substExpr does nothing + (Note that the above rule for substIdBndr maintains this property. If + the incoming envts are both empty, then substituting the type and + IdInfo can't change anything.) + +* In lookupIdSubst, we *must* look up the Id in the in-scope set, because + it may contain non-trivial changes. Example: + (/\a. \x:a. ...x...) Int + We extend the TvSubstEnv with [a |-> Int]; but x's unique does not change + so we only extend the in-scope set. Then we must look up in the in-scope + set when we find the occurrence of x. + +* The requirement to look up the Id in the in-scope set means that we + must NOT take no-op short cut in the case the substitution is empty. + We must still look up every Id in the in-scope set. + +* (However, we don't need to do so for expressions found in the IdSubst + itself, whose range is assumed to be correct wrt the in-scope set.) + +Why do we make a different choice for the IdSubstEnv than the TvSubstEnv? +* For Ids, we change the IdInfo all the time (e.g. deleting the + unfolding), and adding it back later, so using the TyVar convention + would entail extending the substitution almost all the time + +* The simplifier wants to look up in the in-scope set anyway, in case it + can see a better unfolding from an enclosing case expression + +* For TyVars, only coercion variables can possibly change, and they are + easy to spot + +\begin{code} +-- | An environment for substituting for 'Id's type IdSubstEnv = IdEnv CoreExpr ---------------------------- @@ -102,52 +163,79 @@ mkSubst in_scope tvs ids = Subst in_scope ids tvs -- setTvSubstEnv :: Subst -> TvSubstEnv -> Subst -- setTvSubstEnv (Subst in_scope ids _) tvs = Subst in_scope ids tvs +-- | Find the in-scope set: see "CoreSubst#in_scope_invariant" substInScope :: Subst -> InScopeSet substInScope (Subst in_scope _ _) = in_scope --- zapSubstEnv :: Subst -> Subst --- zapSubstEnv (Subst in_scope _ _) = Subst in_scope emptyVarEnv emptyVarEnv +-- | Remove all substitutions for 'Id's and 'Var's that might have been built up +-- while preserving the in-scope set +zapSubstEnv :: Subst -> Subst +zapSubstEnv (Subst in_scope _ _) = Subst in_scope emptyVarEnv emptyVarEnv --- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set +-- | Add a substitution for an 'Id' to the 'Subst': you must ensure that the in-scope set is +-- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this extendIdSubst :: Subst -> Id -> CoreExpr -> Subst +-- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set extendIdSubst (Subst in_scope ids tvs) v r = Subst in_scope (extendVarEnv ids v r) tvs +-- | Adds multiple 'Id' substitutions to the 'Subst': see also 'extendIdSubst' extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst extendIdSubstList (Subst in_scope ids tvs) prs = Subst in_scope (extendVarEnvList ids prs) tvs +-- | Add a substitution for a 'TyVar' to the 'Subst': you must ensure that the in-scope set is +-- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this extendTvSubst :: Subst -> TyVar -> Type -> Subst extendTvSubst (Subst in_scope ids tvs) v r = Subst in_scope ids (extendVarEnv tvs v r) +-- | Adds multiple 'TyVar' substitutions to the 'Subst': see also 'extendTvSubst' extendTvSubstList :: Subst -> [(TyVar,Type)] -> Subst extendTvSubstList (Subst in_scope ids tvs) prs = Subst in_scope ids (extendVarEnvList tvs prs) +-- | Add a substitution for a 'TyVar' or 'Id' as appropriate to the 'Var' being added. See also +-- 'extendIdSubst' and 'extendTvSubst' +extendSubst :: Subst -> Var -> CoreArg -> Subst +extendSubst (Subst in_scope ids tvs) tv (Type ty) + = ASSERT( isTyVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty) +extendSubst (Subst in_scope ids tvs) id expr + = ASSERT( isId id ) Subst in_scope (extendVarEnv ids id expr) tvs + +-- | Add a substitution for a 'TyVar' or 'Id' as appropriate to all the 'Var's being added. See also 'extendSubst' +extendSubstList :: Subst -> [(Var,CoreArg)] -> Subst +extendSubstList subst [] = subst +extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs + +-- | Find the substitution for an 'Id' in the 'Subst' lookupIdSubst :: Subst -> Id -> CoreExpr -lookupIdSubst (Subst in_scope ids tvs) v +lookupIdSubst (Subst in_scope ids _) v | not (isLocalId v) = Var v - | otherwise - = case lookupVarEnv ids v of { - Just e -> e ; - Nothing -> - case lookupInScope in_scope v of { - -- Watch out! Must get the Id from the in-scope set, - -- because its type there may differ - Just v -> Var v ; - Nothing -> WARN( True, ptext SLIT("CoreSubst.lookupIdSubst") <+> ppr v ) - Var v - }} + | Just e <- lookupVarEnv ids v = e + | Just v' <- lookupInScope in_scope v = Var v' + -- Vital! See Note [Extending the Subst] + | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v ) + Var v +-- | Find the substitution for a 'TyVar' in the 'Subst' lookupTvSubst :: Subst -> TyVar -> Type -lookupTvSubst (Subst _ ids tvs) v = lookupVarEnv tvs v `orElse` mkTyVarTy v +lookupTvSubst (Subst _ _ tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v ------------------------------ isInScope :: Var -> Subst -> Bool isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope +-- | Add the 'Var' to the in-scope set: as a side effect, removes any existing substitutions for it extendInScope :: Subst -> Var -> Subst extendInScope (Subst in_scope ids tvs) v = Subst (in_scope `extendInScopeSet` v) (ids `delVarEnv` v) (tvs `delVarEnv` v) +-- | Add the 'Var's to the in-scope set: see also 'extendInScope' +extendInScopeList :: Subst -> [Var] -> Subst +extendInScopeList (Subst in_scope ids tvs) vs + = Subst (in_scope `extendInScopeSetList` vs) + (ids `delVarEnvList` vs) (tvs `delVarEnvList` vs) + +-- | Optimized version of 'extendInScopeList' that can be used if you are certain +-- all the things being added are 'Id's and hence none are 'TyVar's extendInScopeIds :: Subst -> [Id] -> Subst extendInScopeIds (Subst in_scope ids tvs) vs = Subst (in_scope `extendInScopeSetList` vs) @@ -159,9 +247,9 @@ Pretty printing, for debugging only \begin{code} instance Outputable Subst where ppr (Subst in_scope ids tvs) - = ptext SLIT(" braces (fsep (map ppr (varEnvElts (getInScopeVars in_scope)))) - $$ ptext SLIT(" IdSubst =") <+> ppr ids - $$ ptext SLIT(" TvSubst =") <+> ppr tvs + = ptext (sLit " braces (fsep (map ppr (varEnvElts (getInScopeVars in_scope)))) + $$ ptext (sLit " IdSubst =") <+> ppr ids + $$ ptext (sLit " TvSubst =") <+> ppr tvs <> char '>' \end{code} @@ -173,6 +261,11 @@ instance Outputable Subst where %************************************************************************ \begin{code} +-- | Apply a substititon to an entire 'CoreExpr'. Rememeber, you may only +-- apply the substitution /once/: see "CoreSubst#apply_once" +-- +-- Do *not* attempt to short-cut in the case of an empty substitution! +-- See Note [Extending the Subst] substExpr :: Subst -> CoreExpr -> CoreExpr substExpr subst expr = go expr @@ -182,6 +275,7 @@ substExpr subst expr go (Lit lit) = Lit lit go (App fun arg) = App (go fun) (go arg) go (Note note e) = Note (go_note note) (go e) + go (Cast e co) = Cast (go e) (substTy subst co) go (Lam bndr body) = Lam bndr' (substExpr subst' body) where (subst', bndr') = substBndr subst bndr @@ -198,9 +292,10 @@ substExpr subst expr where (subst', bndrs') = substBndrs subst bndrs - go_note (Coerce ty1 ty2) = Coerce (substTy subst ty1) (substTy subst ty2) go_note note = note +-- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst' +-- that should be used by subsequent substitutons. substBind :: Subst -> CoreBind -> (Subst, CoreBind) substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs)) where @@ -213,14 +308,13 @@ substBind subst (Rec pairs) = (subst', Rec pairs') rhss' = map (substExpr subst' . snd) pairs \end{code} -De-shadowing the program is sometimes a useful pre-pass. It can be done simply -by running over the bindings with an empty substitution, becuase substitution -returns a result that has no-shadowing guaranteed. - -(Actually, within a single *type* there might still be shadowing, because -substType is a no-op for the empty substitution, but that's OK.) - \begin{code} +-- | De-shadowing the program is sometimes a useful pre-pass. It can be done simply +-- by running over the bindings with an empty substitution, becuase substitution +-- returns a result that has no-shadowing guaranteed. +-- +-- (Actually, within a single /type/ there might still be shadowing, because +-- 'substTy' is a no-op for the empty substitution, but that's probably OK.) deShadowBinds :: [CoreBind] -> [CoreBind] deShadowBinds binds = snd (mapAccumL substBind emptySubst binds) \end{code} @@ -238,16 +332,20 @@ preserve all IdInfo (suitably substituted). For example, we *want* to preserve occ info in rules. \begin{code} +-- | Substitutes a 'Var' for another one according to the 'Subst' given, returning +-- the result and an updated 'Subst' that should be used by subsequent substitutons. +-- 'IdInfo' is preserved by this process, although it is substituted into appropriately. substBndr :: Subst -> Var -> (Subst, Var) substBndr subst bndr | isTyVar bndr = substTyVarBndr subst bndr | otherwise = substIdBndr subst subst bndr +-- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right substBndrs :: Subst -> [Var] -> (Subst, [Var]) substBndrs subst bndrs = mapAccumL substBndr subst bndrs +-- | Substitute in a mutually recursive group of 'Id's substRecBndrs :: Subst -> [Id] -> (Subst, [Id]) --- Substitute a mutually recursive group substRecBndrs subst bndrs = (new_subst, new_bndrs) where -- Here's the reason we need to pass rec_subst to subst_id @@ -256,39 +354,56 @@ substRecBndrs subst bndrs \begin{code} -substIdBndr :: Subst -- Substitution to use for the IdInfo - -> Subst -> Id -- Substitition and Id to transform - -> (Subst, Id) -- Transformed pair +substIdBndr :: Subst -- ^ Substitution to use for the IdInfo + -> Subst -> Id -- ^ Substitition and Id to transform + -> (Subst, Id) -- ^ Transformed pair + -- NB: unfolding may be zapped substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id) where id1 = uniqAway in_scope old_id -- id1 is cloned if necessary - id2 = substIdType subst id1 -- id2 has its type zapped + id2 | no_type_change = id1 + | otherwise = setIdType id1 (substTy subst old_ty) + + old_ty = idType old_id + no_type_change = isEmptyVarEnv tvs || + isEmptyVarSet (Type.tyVarsOfType old_ty) -- new_id has the right IdInfo -- The lazy-set is because we're in a loop here, with -- rec_subst, when dealing with a mutually-recursive group - new_id = maybeModifyIdInfo (substIdInfo rec_subst) id2 + new_id = maybeModifyIdInfo mb_new_info id2 + mb_new_info = substIdInfo rec_subst id2 (idInfo id2) + -- NB: unfolding info may be zapped -- Extend the substitution if the unique has changed -- See the notes with substTyVarBndr for the delVarEnv - new_env | new_id /= old_id = extendVarEnv env old_id (Var new_id) - | otherwise = delVarEnv env old_id + new_env | no_change = delVarEnv env old_id + | otherwise = extendVarEnv env old_id (Var new_id) + + no_change = id1 == old_id + -- See Note [Extending the Subst] + -- it's /not/ necessary to check mb_new_info and no_type_change \end{code} Now a variant that unconditionally allocates a new unique. It also unconditionally zaps the OccInfo. \begin{code} +-- | Very similar to 'substBndr', but it always allocates a new 'Unique' for +-- each variable in its output and removes all 'IdInfo' cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id) cloneIdBndr subst us old_id = clone_id subst subst (old_id, uniqFromSupply us) +-- | Applies 'cloneIdBndr' to a number of 'Id's, accumulating a final +-- substitution from left to right cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id]) cloneIdBndrs subst us ids = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us) +-- | Clone a mutually recursive group of 'Id's cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id]) cloneRecIdBndrs subst us ids = (subst', ids') @@ -307,7 +422,7 @@ clone_id rec_subst subst@(Subst in_scope env tvs) (old_id, uniq) where id1 = setVarUnique old_id uniq id2 = substIdType subst id1 - new_id = maybeModifyIdInfo (substIdInfo rec_subst) id2 + new_id = maybeModifyIdInfo (substIdInfo rec_subst id2 (idInfo old_id)) id2 new_env = extendVarEnv env old_id (Var new_id) \end{code} @@ -328,8 +443,9 @@ substTyVarBndr (Subst in_scope id_env tv_env) tv (TvSubst in_scope' tv_env', tv') -> (Subst in_scope' id_env tv_env', tv') +-- | See 'Type.substTy' substTy :: Subst -> Type -> Type -substTy (Subst in_scope id_env tv_env) ty +substTy (Subst in_scope _id_env tv_env) ty = Type.substTy (TvSubst in_scope tv_env) ty \end{code} @@ -342,8 +458,8 @@ substTy (Subst in_scope id_env tv_env) ty \begin{code} substIdType :: Subst -> Id -> Id -substIdType subst@(Subst in_scope id_env tv_env) id - | isEmptyVarEnv tv_env || isEmptyVarSet (tyVarsOfType old_ty) = id +substIdType subst@(Subst _ _ tv_env) id + | isEmptyVarEnv tv_env || isEmptyVarSet (Type.tyVarsOfType old_ty) = id | otherwise = setIdType id (substTy subst old_ty) -- The tyVarsOfType is cheaper than it looks -- because we cache the free tyvars of the type @@ -352,11 +468,12 @@ substIdType subst@(Subst in_scope id_env tv_env) id old_ty = idType id ------------------ -substIdInfo :: Subst -> IdInfo -> Maybe IdInfo +-- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'. -- Always zaps the unfolding, to save substitution work -substIdInfo subst info +substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo +substIdInfo subst new_id info | nothing_to_do = Nothing - | otherwise = Just (info `setSpecInfo` substSpec subst old_rules + | otherwise = Just (info `setSpecInfo` substSpec subst new_id old_rules `setWorkerInfo` substWorker subst old_wrkr `setUnfoldingInfo` noUnfolding) where @@ -368,11 +485,12 @@ substIdInfo subst info ------------------ +-- | Substitutes for the 'Id's within the 'WorkerInfo' substWorker :: Subst -> WorkerInfo -> WorkerInfo -- Seq'ing on the returned WorkerInfo is enough to cause all the -- substitutions to happen completely -substWorker subst NoWorker +substWorker _ NoWorker = NoWorker substWorker subst (HasWorker w a) = case lookupIdSubst subst w of @@ -383,29 +501,29 @@ substWorker subst (HasWorker w a) -- via postInlineUnconditionally, hence warning) ------------------ -substSpec :: Subst -> SpecInfo -> SpecInfo - -substSpec subst spec@(SpecInfo rules rhs_fvs) - | isEmptySubst subst - = spec - | otherwise +-- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id' +substSpec :: Subst -> Id -> SpecInfo -> SpecInfo +substSpec subst new_fn (SpecInfo rules rhs_fvs) = seqSpecInfo new_rules `seq` new_rules where + new_name = idName new_fn new_rules = SpecInfo (map do_subst rules) (substVarSet subst rhs_fvs) do_subst rule@(BuiltinRule {}) = rule do_subst rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs }) - = rule { ru_bndrs = bndrs', + = rule { ru_bndrs = bndrs', + ru_fn = new_name, -- Important: the function may have changed its name! ru_args = map (substExpr subst') args, ru_rhs = substExpr subst' rhs } where (subst', bndrs') = substBndrs subst bndrs ------------------ +substVarSet :: Subst -> VarSet -> VarSet substVarSet subst fvs = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs where subst_fv subst fv | isId fv = exprFreeVars (lookupIdSubst subst fv) - | otherwise = tyVarsOfType (lookupTvSubst subst fv) + | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv) \end{code}