2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
11 Subst, TvSubstEnv, IdSubstEnv, InScopeSet,
14 substTy, substExpr, substSpec, substWorker,
15 lookupIdSubst, lookupTvSubst,
17 emptySubst, mkEmptySubst, mkSubst, substInScope, isEmptySubst,
18 extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList,
19 extendSubstList, zapSubstEnv,
20 extendInScope, extendInScopeList, extendInScopeIds,
24 substBndr, substBndrs, substRecBndrs,
25 cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs
28 #include "HsVersions.h"
35 import Type ( Type, TvSubst(..), TvSubstEnv )
39 import Var ( Var, TyVar, setVarUnique )
45 import PprCore () -- Instances
51 %************************************************************************
53 \subsection{Substitutions}
55 %************************************************************************
59 = Subst InScopeSet -- Variables in in scope (both Ids and TyVars)
60 -- *after* applying the substitution
61 IdSubstEnv -- Substitution for Ids
62 TvSubstEnv -- Substitution for TyVars
64 -- INVARIANT 1: The (domain of the) in-scope set is a superset
65 -- of the free vars of the range of the substitution
66 -- that might possibly clash with locally-bound variables
67 -- in the thing being substituted in.
68 -- This is what lets us deal with name capture properly
69 -- It's a hard invariant to check...
70 -- There are various ways of causing it to happen:
71 -- - arrange that the in-scope set really is all the things in scope
72 -- - arrange that it's the free vars of the range of the substitution
73 -- - make it empty because all the free vars of the subst are fresh,
74 -- and hence can't possibly clash.a
76 -- INVARIANT 2: The substitution is apply-once; see Note [Apply once] with
79 -- INVARIANT 3: See Note [Extending the Subst]
82 Note [Extending the Subst]
83 ~~~~~~~~~~~~~~~~~~~~~~~~~~
84 For a core Subst, which binds Ids as well, we make a different choice for Ids
85 than we do for TyVars.
87 For TyVars, see Note [Extending the TvSubst] with Type.TvSubstEnv
89 For Ids, we have a different invariant
90 The IdSubstEnv is extended *only* when the Unique on an Id changes
91 Otherwise, we just extend the InScopeSet
95 * In substIdBndr, we extend the IdSubstEnv only when the unique changes
97 * If the TvSubstEnv and IdSubstEnv are both empty, substExpr does nothing
98 (Note that the above rule for substIdBndr maintains this property. If
99 the incoming envts are both empty, then substituting the type and
100 IdInfo can't change anything.)
102 * In lookupIdSubst, we *must* look up the Id in the in-scope set, because
103 it may contain non-trivial changes. Example:
104 (/\a. \x:a. ...x...) Int
105 We extend the TvSubstEnv with [a |-> Int]; but x's unique does not change
106 so we only extend the in-scope set. Then we must look up in the in-scope
107 set when we find the occurrence of x.
109 Why do we make a different choice for the IdSubstEnv than the TvSubstEnv?
111 * For Ids, we change the IdInfo all the time (e.g. deleting the
112 unfolding), and adding it back later, so using the TyVar convention
113 would entail extending the substitution almost all the time
115 * The simplifier wants to look up in the in-scope set anyway, in case it
116 can see a better unfolding from an enclosing case expression
118 * For TyVars, only coercion variables can possibly change, and they are
122 type IdSubstEnv = IdEnv CoreExpr
124 ----------------------------
125 isEmptySubst :: Subst -> Bool
126 isEmptySubst (Subst _ id_env tv_env) = isEmptyVarEnv id_env && isEmptyVarEnv tv_env
129 emptySubst = Subst emptyInScopeSet emptyVarEnv emptyVarEnv
131 mkEmptySubst :: InScopeSet -> Subst
132 mkEmptySubst in_scope = Subst in_scope emptyVarEnv emptyVarEnv
134 mkSubst :: InScopeSet -> TvSubstEnv -> IdSubstEnv -> Subst
135 mkSubst in_scope tvs ids = Subst in_scope ids tvs
137 -- getTvSubst :: Subst -> TvSubst
138 -- getTvSubst (Subst in_scope _ tv_env) = TvSubst in_scope tv_env
140 -- getTvSubstEnv :: Subst -> TvSubstEnv
141 -- getTvSubstEnv (Subst _ _ tv_env) = tv_env
143 -- setTvSubstEnv :: Subst -> TvSubstEnv -> Subst
144 -- setTvSubstEnv (Subst in_scope ids _) tvs = Subst in_scope ids tvs
146 substInScope :: Subst -> InScopeSet
147 substInScope (Subst in_scope _ _) = in_scope
149 zapSubstEnv :: Subst -> Subst
150 zapSubstEnv (Subst in_scope _ _) = Subst in_scope emptyVarEnv emptyVarEnv
152 -- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set
153 extendIdSubst :: Subst -> Id -> CoreExpr -> Subst
154 extendIdSubst (Subst in_scope ids tvs) v r = Subst in_scope (extendVarEnv ids v r) tvs
156 extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst
157 extendIdSubstList (Subst in_scope ids tvs) prs = Subst in_scope (extendVarEnvList ids prs) tvs
159 extendTvSubst :: Subst -> TyVar -> Type -> Subst
160 extendTvSubst (Subst in_scope ids tvs) v r = Subst in_scope ids (extendVarEnv tvs v r)
162 extendTvSubstList :: Subst -> [(TyVar,Type)] -> Subst
163 extendTvSubstList (Subst in_scope ids tvs) prs = Subst in_scope ids (extendVarEnvList tvs prs)
165 extendSubstList :: Subst -> [(Var,CoreArg)] -> Subst
166 extendSubstList subst []
168 extendSubstList (Subst in_scope ids tvs) ((tv,Type ty):prs)
169 = ASSERT( isTyVar tv ) extendSubstList (Subst in_scope ids (extendVarEnv tvs tv ty)) prs
170 extendSubstList (Subst in_scope ids tvs) ((id,expr):prs)
171 = ASSERT( isId id ) extendSubstList (Subst in_scope (extendVarEnv ids id expr) tvs) prs
173 lookupIdSubst :: Subst -> Id -> CoreExpr
174 lookupIdSubst (Subst in_scope ids tvs) v
175 | not (isLocalId v) = Var v
176 | Just e <- lookupVarEnv ids v = e
177 | Just v' <- lookupInScope in_scope v = Var v'
178 -- Vital! See Note [Extending the Subst]
179 | otherwise = WARN( True, ptext SLIT("CoreSubst.lookupIdSubst") <+> ppr v )
182 lookupTvSubst :: Subst -> TyVar -> Type
183 lookupTvSubst (Subst _ ids tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v
185 ------------------------------
186 isInScope :: Var -> Subst -> Bool
187 isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope
189 extendInScope :: Subst -> Var -> Subst
190 extendInScope (Subst in_scope ids tvs) v
191 = Subst (in_scope `extendInScopeSet` v)
192 (ids `delVarEnv` v) (tvs `delVarEnv` v)
194 extendInScopeList :: Subst -> [Var] -> Subst
195 extendInScopeList (Subst in_scope ids tvs) vs
196 = Subst (in_scope `extendInScopeSetList` vs)
197 (ids `delVarEnvList` vs) (tvs `delVarEnvList` vs)
199 extendInScopeIds :: Subst -> [Id] -> Subst
200 extendInScopeIds (Subst in_scope ids tvs) vs
201 = Subst (in_scope `extendInScopeSetList` vs)
202 (ids `delVarEnvList` vs) tvs
205 Pretty printing, for debugging only
208 instance Outputable Subst where
209 ppr (Subst in_scope ids tvs)
210 = ptext SLIT("<InScope =") <+> braces (fsep (map ppr (varEnvElts (getInScopeVars in_scope))))
211 $$ ptext SLIT(" IdSubst =") <+> ppr ids
212 $$ ptext SLIT(" TvSubst =") <+> ppr tvs
217 %************************************************************************
219 Substituting expressions
221 %************************************************************************
224 substExpr :: Subst -> CoreExpr -> CoreExpr
228 go (Var v) = lookupIdSubst subst v
229 go (Type ty) = Type (substTy subst ty)
230 go (Lit lit) = Lit lit
231 go (App fun arg) = App (go fun) (go arg)
232 go (Note note e) = Note (go_note note) (go e)
233 go (Cast e co) = Cast (go e) (substTy subst co)
234 go (Lam bndr body) = Lam bndr' (substExpr subst' body)
236 (subst', bndr') = substBndr subst bndr
238 go (Let bind body) = Let bind' (substExpr subst' body)
240 (subst', bind') = substBind subst bind
242 go (Case scrut bndr ty alts) = Case (go scrut) bndr' (substTy subst ty) (map (go_alt subst') alts)
244 (subst', bndr') = substBndr subst bndr
246 go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs)
248 (subst', bndrs') = substBndrs subst bndrs
252 substBind :: Subst -> CoreBind -> (Subst, CoreBind)
253 substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs))
255 (subst', bndr') = substBndr subst bndr
257 substBind subst (Rec pairs) = (subst', Rec pairs')
259 (subst', bndrs') = substRecBndrs subst (map fst pairs)
260 pairs' = bndrs' `zip` rhss'
261 rhss' = map (substExpr subst' . snd) pairs
264 De-shadowing the program is sometimes a useful pre-pass. It can be done simply
265 by running over the bindings with an empty substitution, becuase substitution
266 returns a result that has no-shadowing guaranteed.
268 (Actually, within a single *type* there might still be shadowing, because
269 substType is a no-op for the empty substitution, but that's OK.)
272 deShadowBinds :: [CoreBind] -> [CoreBind]
273 deShadowBinds binds = snd (mapAccumL substBind emptySubst binds)
277 %************************************************************************
281 %************************************************************************
283 Remember that substBndr and friends are used when doing expression
284 substitution only. Their only business is substitution, so they
285 preserve all IdInfo (suitably substituted). For example, we *want* to
286 preserve occ info in rules.
289 substBndr :: Subst -> Var -> (Subst, Var)
291 | isTyVar bndr = substTyVarBndr subst bndr
292 | otherwise = substIdBndr subst subst bndr
294 substBndrs :: Subst -> [Var] -> (Subst, [Var])
295 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
297 substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
298 -- Substitute a mutually recursive group
299 substRecBndrs subst bndrs
300 = (new_subst, new_bndrs)
301 where -- Here's the reason we need to pass rec_subst to subst_id
302 (new_subst, new_bndrs) = mapAccumL (substIdBndr new_subst) subst bndrs
307 substIdBndr :: Subst -- Substitution to use for the IdInfo
308 -> Subst -> Id -- Substitition and Id to transform
309 -> (Subst, Id) -- Transformed pair
311 substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id
312 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
314 id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
315 id2 | no_type_change = id1
316 | otherwise = setIdType id1 (substTy subst old_ty)
318 old_ty = idType old_id
319 no_type_change = isEmptyVarEnv tvs ||
320 isEmptyVarSet (Type.tyVarsOfType old_ty)
322 -- new_id has the right IdInfo
323 -- The lazy-set is because we're in a loop here, with
324 -- rec_subst, when dealing with a mutually-recursive group
325 new_id = maybeModifyIdInfo mb_new_info id2
326 mb_new_info = substIdInfo rec_subst (idInfo id2)
328 -- Extend the substitution if the unique has changed
329 -- See the notes with substTyVarBndr for the delVarEnv
330 new_env | no_change = delVarEnv env old_id
331 | otherwise = extendVarEnv env old_id (Var new_id)
333 no_change = id1 == old_id
334 -- See Note [Extending the Subst]
335 -- *not* necessary to check mb_new_info and no_type_change
338 Now a variant that unconditionally allocates a new unique.
339 It also unconditionally zaps the OccInfo.
342 cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
343 cloneIdBndr subst us old_id
344 = clone_id subst subst (old_id, uniqFromSupply us)
346 cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
347 cloneIdBndrs subst us ids
348 = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us)
350 cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
351 cloneRecIdBndrs subst us ids
354 (subst', ids') = mapAccumL (clone_id subst') subst
355 (ids `zip` uniqsFromSupply us)
357 -- Just like substIdBndr, except that it always makes a new unique
358 -- It is given the unique to use
359 clone_id :: Subst -- Substitution for the IdInfo
360 -> Subst -> (Id, Unique) -- Substitition and Id to transform
361 -> (Subst, Id) -- Transformed pair
363 clone_id rec_subst subst@(Subst in_scope env tvs) (old_id, uniq)
364 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
366 id1 = setVarUnique old_id uniq
367 id2 = substIdType subst id1
368 new_id = maybeModifyIdInfo (substIdInfo rec_subst (idInfo old_id)) id2
369 new_env = extendVarEnv env old_id (Var new_id)
373 %************************************************************************
377 %************************************************************************
379 For types we just call the corresponding function in Type, but we have
380 to repackage the substitution, from a Subst to a TvSubst
383 substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)
384 substTyVarBndr (Subst in_scope id_env tv_env) tv
385 = case Type.substTyVarBndr (TvSubst in_scope tv_env) tv of
386 (TvSubst in_scope' tv_env', tv')
387 -> (Subst in_scope' id_env tv_env', tv')
389 substTy :: Subst -> Type -> Type
390 substTy (Subst in_scope id_env tv_env) ty
391 = Type.substTy (TvSubst in_scope tv_env) ty
395 %************************************************************************
397 \section{IdInfo substitution}
399 %************************************************************************
402 substIdType :: Subst -> Id -> Id
403 substIdType subst@(Subst in_scope id_env tv_env) id
404 | isEmptyVarEnv tv_env || isEmptyVarSet (Type.tyVarsOfType old_ty) = id
405 | otherwise = setIdType id (substTy subst old_ty)
406 -- The tyVarsOfType is cheaper than it looks
407 -- because we cache the free tyvars of the type
408 -- in a Note in the id's type itself
413 substIdInfo :: Subst -> IdInfo -> Maybe IdInfo
414 -- Always zaps the unfolding, to save substitution work
415 substIdInfo subst info
416 | nothing_to_do = Nothing
417 | otherwise = Just (info `setSpecInfo` substSpec subst old_rules
418 `setWorkerInfo` substWorker subst old_wrkr
419 `setUnfoldingInfo` noUnfolding)
421 old_rules = specInfo info
422 old_wrkr = workerInfo info
423 nothing_to_do = isEmptySpecInfo old_rules &&
424 not (workerExists old_wrkr) &&
425 not (hasUnfolding (unfoldingInfo info))
429 substWorker :: Subst -> WorkerInfo -> WorkerInfo
430 -- Seq'ing on the returned WorkerInfo is enough to cause all the
431 -- substitutions to happen completely
433 substWorker subst NoWorker
435 substWorker subst (HasWorker w a)
436 = case lookupIdSubst subst w of
437 Var w1 -> HasWorker w1 a
438 other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr w )
439 NoWorker -- Worker has got substituted away altogether
440 -- (This can happen if it's trivial,
441 -- via postInlineUnconditionally, hence warning)
444 substSpec :: Subst -> SpecInfo -> SpecInfo
446 substSpec subst spec@(SpecInfo rules rhs_fvs)
450 = seqSpecInfo new_rules `seq` new_rules
452 new_rules = SpecInfo (map do_subst rules) (substVarSet subst rhs_fvs)
454 do_subst rule@(BuiltinRule {}) = rule
455 do_subst rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs })
456 = rule { ru_bndrs = bndrs',
457 ru_args = map (substExpr subst') args,
458 ru_rhs = substExpr subst' rhs }
460 (subst', bndrs') = substBndrs subst bndrs
463 substVarSet subst fvs
464 = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
467 | isId fv = exprFreeVars (lookupIdSubst subst fv)
468 | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)