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,
13 -- ** Substituting into expressions and related types
15 substTy, substExpr, substSpec, substWorker,
16 lookupIdSubst, lookupTvSubst,
18 -- ** Operations on substitutions
19 emptySubst, mkEmptySubst, mkSubst, substInScope, isEmptySubst,
20 extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList,
21 extendSubst, extendSubstList, zapSubstEnv,
22 extendInScope, extendInScopeList, extendInScopeIds,
25 -- ** Substituting and cloning binders
26 substBndr, substBndrs, substRecBndrs,
27 cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs
30 #include "HsVersions.h"
37 import Type ( Type, TvSubst(..), TvSubstEnv )
41 import Var ( Var, TyVar, setVarUnique )
47 import PprCore () -- Instances
54 %************************************************************************
56 \subsection{Substitutions}
58 %************************************************************************
61 -- | A substitution environment, containing both 'Id' and 'TyVar' substitutions.
63 -- Some invariants apply to how you use the substitution:
65 -- 1. #in_scope_invariant# The in-scope set contains at least those 'Id's and 'TyVar's that will be in scope /after/
66 -- applying the substitution to a term. Precisely, the in-scope set must be a superset of the free vars of the
67 -- substitution range that might possibly clash with locally-bound variables in the thing being substituted in.
69 -- 2. #apply_once# You may apply the substitution only /once/
71 -- There are various ways of setting up the in-scope set such that the first of these invariants hold:
73 -- * Arrange that the in-scope set really is all the things in scope
75 -- * Arrange that it's the free vars of the range of the substitution
77 -- * Make it empty, if you know that all the free vars of the substitution are fresh, and hence can't possibly clash
79 = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) /after/
80 -- applying the substitution
81 IdSubstEnv -- Substitution for Ids
82 TvSubstEnv -- Substitution for TyVars
84 -- INVARIANT 1: See #in_scope_invariant#
85 -- This is what lets us deal with name capture properly
86 -- It's a hard invariant to check...
88 -- INVARIANT 2: The substitution is apply-once; see Note [Apply once] with
91 -- INVARIANT 3: See Note [Extending the Subst]
94 Note [Extending the Subst]
95 ~~~~~~~~~~~~~~~~~~~~~~~~~~
96 For a core Subst, which binds Ids as well, we make a different choice for Ids
97 than we do for TyVars.
99 For TyVars, see Note [Extending the TvSubst] with Type.TvSubstEnv
101 For Ids, we have a different invariant
102 The IdSubstEnv is extended *only* when the Unique on an Id changes
103 Otherwise, we just extend the InScopeSet
107 * In substIdBndr, we extend the IdSubstEnv only when the unique changes
109 * If the TvSubstEnv and IdSubstEnv are both empty, substExpr does nothing
110 (Note that the above rule for substIdBndr maintains this property. If
111 the incoming envts are both empty, then substituting the type and
112 IdInfo can't change anything.)
114 * In lookupIdSubst, we *must* look up the Id in the in-scope set, because
115 it may contain non-trivial changes. Example:
116 (/\a. \x:a. ...x...) Int
117 We extend the TvSubstEnv with [a |-> Int]; but x's unique does not change
118 so we only extend the in-scope set. Then we must look up in the in-scope
119 set when we find the occurrence of x.
121 Why do we make a different choice for the IdSubstEnv than the TvSubstEnv?
123 * For Ids, we change the IdInfo all the time (e.g. deleting the
124 unfolding), and adding it back later, so using the TyVar convention
125 would entail extending the substitution almost all the time
127 * The simplifier wants to look up in the in-scope set anyway, in case it
128 can see a better unfolding from an enclosing case expression
130 * For TyVars, only coercion variables can possibly change, and they are
134 -- | An environment for substituting for 'Id's
135 type IdSubstEnv = IdEnv CoreExpr
137 ----------------------------
138 isEmptySubst :: Subst -> Bool
139 isEmptySubst (Subst _ id_env tv_env) = isEmptyVarEnv id_env && isEmptyVarEnv tv_env
142 emptySubst = Subst emptyInScopeSet emptyVarEnv emptyVarEnv
144 mkEmptySubst :: InScopeSet -> Subst
145 mkEmptySubst in_scope = Subst in_scope emptyVarEnv emptyVarEnv
147 mkSubst :: InScopeSet -> TvSubstEnv -> IdSubstEnv -> Subst
148 mkSubst in_scope tvs ids = Subst in_scope ids tvs
150 -- getTvSubst :: Subst -> TvSubst
151 -- getTvSubst (Subst in_scope _ tv_env) = TvSubst in_scope tv_env
153 -- getTvSubstEnv :: Subst -> TvSubstEnv
154 -- getTvSubstEnv (Subst _ _ tv_env) = tv_env
156 -- setTvSubstEnv :: Subst -> TvSubstEnv -> Subst
157 -- setTvSubstEnv (Subst in_scope ids _) tvs = Subst in_scope ids tvs
159 -- | Find the in-scope set: see "CoreSubst#in_scope_invariant"
160 substInScope :: Subst -> InScopeSet
161 substInScope (Subst in_scope _ _) = in_scope
163 -- | Remove all substitutions for 'Id's and 'Var's that might have been built up
164 -- while preserving the in-scope set
165 zapSubstEnv :: Subst -> Subst
166 zapSubstEnv (Subst in_scope _ _) = Subst in_scope emptyVarEnv emptyVarEnv
168 -- | Add a substitution for an 'Id' to the 'Subst': you must ensure that the in-scope set is
169 -- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this
170 extendIdSubst :: Subst -> Id -> CoreExpr -> Subst
171 -- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set
172 extendIdSubst (Subst in_scope ids tvs) v r = Subst in_scope (extendVarEnv ids v r) tvs
174 -- | Adds multiple 'Id' substitutions to the 'Subst': see also 'extendIdSubst'
175 extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst
176 extendIdSubstList (Subst in_scope ids tvs) prs = Subst in_scope (extendVarEnvList ids prs) tvs
178 -- | Add a substitution for a 'TyVar' to the 'Subst': you must ensure that the in-scope set is
179 -- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this
180 extendTvSubst :: Subst -> TyVar -> Type -> Subst
181 extendTvSubst (Subst in_scope ids tvs) v r = Subst in_scope ids (extendVarEnv tvs v r)
183 -- | Adds multiple 'TyVar' substitutions to the 'Subst': see also 'extendTvSubst'
184 extendTvSubstList :: Subst -> [(TyVar,Type)] -> Subst
185 extendTvSubstList (Subst in_scope ids tvs) prs = Subst in_scope ids (extendVarEnvList tvs prs)
187 -- | Add a substitution for a 'TyVar' or 'Id' as appropriate to the 'Var' being added. See also
188 -- 'extendIdSubst' and 'extendTvSubst'
189 extendSubst :: Subst -> Var -> CoreArg -> Subst
190 extendSubst (Subst in_scope ids tvs) tv (Type ty)
191 = ASSERT( isTyVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty)
192 extendSubst (Subst in_scope ids tvs) id expr
193 = ASSERT( isId id ) Subst in_scope (extendVarEnv ids id expr) tvs
195 -- | Add a substitution for a 'TyVar' or 'Id' as appropriate to all the 'Var's being added. See also 'extendSubst'
196 extendSubstList :: Subst -> [(Var,CoreArg)] -> Subst
197 extendSubstList subst [] = subst
198 extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs
200 -- | Find the substitution for an 'Id' in the 'Subst'
201 lookupIdSubst :: Subst -> Id -> CoreExpr
202 lookupIdSubst (Subst in_scope ids _) v
203 | not (isLocalId v) = Var v
204 | Just e <- lookupVarEnv ids v = e
205 | Just v' <- lookupInScope in_scope v = Var v'
206 -- Vital! See Note [Extending the Subst]
207 | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v )
210 -- | Find the substitution for a 'TyVar' in the 'Subst'
211 lookupTvSubst :: Subst -> TyVar -> Type
212 lookupTvSubst (Subst _ _ tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v
214 ------------------------------
215 isInScope :: Var -> Subst -> Bool
216 isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope
218 -- | Add the 'Var' to the in-scope set: as a side effect, removes any existing substitutions for it
219 extendInScope :: Subst -> Var -> Subst
220 extendInScope (Subst in_scope ids tvs) v
221 = Subst (in_scope `extendInScopeSet` v)
222 (ids `delVarEnv` v) (tvs `delVarEnv` v)
224 -- | Add the 'Var's to the in-scope set: see also 'extendInScope'
225 extendInScopeList :: Subst -> [Var] -> Subst
226 extendInScopeList (Subst in_scope ids tvs) vs
227 = Subst (in_scope `extendInScopeSetList` vs)
228 (ids `delVarEnvList` vs) (tvs `delVarEnvList` vs)
230 -- | Optimized version of 'extendInScopeList' that can be used if you are certain
231 -- all the things being added are 'Id's and hence none are 'TyVar's
232 extendInScopeIds :: Subst -> [Id] -> Subst
233 extendInScopeIds (Subst in_scope ids tvs) vs
234 = Subst (in_scope `extendInScopeSetList` vs)
235 (ids `delVarEnvList` vs) tvs
238 Pretty printing, for debugging only
241 instance Outputable Subst where
242 ppr (Subst in_scope ids tvs)
243 = ptext (sLit "<InScope =") <+> braces (fsep (map ppr (varEnvElts (getInScopeVars in_scope))))
244 $$ ptext (sLit " IdSubst =") <+> ppr ids
245 $$ ptext (sLit " TvSubst =") <+> ppr tvs
250 %************************************************************************
252 Substituting expressions
254 %************************************************************************
257 -- | Apply a substititon to an entire 'CoreExpr'. Rememeber, you may only
258 -- apply the substitution /once/: see "CoreSubst#apply_once"
259 substExpr :: Subst -> CoreExpr -> CoreExpr
263 go (Var v) = lookupIdSubst subst v
264 go (Type ty) = Type (substTy subst ty)
265 go (Lit lit) = Lit lit
266 go (App fun arg) = App (go fun) (go arg)
267 go (Note note e) = Note (go_note note) (go e)
268 go (Cast e co) = Cast (go e) (substTy subst co)
269 go (Lam bndr body) = Lam bndr' (substExpr subst' body)
271 (subst', bndr') = substBndr subst bndr
273 go (Let bind body) = Let bind' (substExpr subst' body)
275 (subst', bind') = substBind subst bind
277 go (Case scrut bndr ty alts) = Case (go scrut) bndr' (substTy subst ty) (map (go_alt subst') alts)
279 (subst', bndr') = substBndr subst bndr
281 go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs)
283 (subst', bndrs') = substBndrs subst bndrs
287 -- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst'
288 -- that should be used by subsequent substitutons.
289 substBind :: Subst -> CoreBind -> (Subst, CoreBind)
290 substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs))
292 (subst', bndr') = substBndr subst bndr
294 substBind subst (Rec pairs) = (subst', Rec pairs')
296 (subst', bndrs') = substRecBndrs subst (map fst pairs)
297 pairs' = bndrs' `zip` rhss'
298 rhss' = map (substExpr subst' . snd) pairs
302 -- | De-shadowing the program is sometimes a useful pre-pass. It can be done simply
303 -- by running over the bindings with an empty substitution, becuase substitution
304 -- returns a result that has no-shadowing guaranteed.
306 -- (Actually, within a single /type/ there might still be shadowing, because
307 -- 'substTy' is a no-op for the empty substitution, but that's probably OK.)
308 deShadowBinds :: [CoreBind] -> [CoreBind]
309 deShadowBinds binds = snd (mapAccumL substBind emptySubst binds)
313 %************************************************************************
317 %************************************************************************
319 Remember that substBndr and friends are used when doing expression
320 substitution only. Their only business is substitution, so they
321 preserve all IdInfo (suitably substituted). For example, we *want* to
322 preserve occ info in rules.
325 -- | Substitutes a 'Var' for another one according to the 'Subst' given, returning
326 -- the result and an updated 'Subst' that should be used by subsequent substitutons.
327 -- 'IdInfo' is preserved by this process, although it is substituted into appropriately.
328 substBndr :: Subst -> Var -> (Subst, Var)
330 | isTyVar bndr = substTyVarBndr subst bndr
331 | otherwise = substIdBndr subst subst bndr
333 -- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right
334 substBndrs :: Subst -> [Var] -> (Subst, [Var])
335 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
337 -- | Substitute in a mutually recursive group of 'Id's
338 substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
339 substRecBndrs subst bndrs
340 = (new_subst, new_bndrs)
341 where -- Here's the reason we need to pass rec_subst to subst_id
342 (new_subst, new_bndrs) = mapAccumL (substIdBndr new_subst) subst bndrs
347 substIdBndr :: Subst -- ^ Substitution to use for the IdInfo
348 -> Subst -> Id -- ^ Substitition and Id to transform
349 -> (Subst, Id) -- ^ Transformed pair
350 -- NB: unfolding may be zapped
352 substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id
353 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
355 id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
356 id2 | no_type_change = id1
357 | otherwise = setIdType id1 (substTy subst old_ty)
359 old_ty = idType old_id
360 no_type_change = isEmptyVarEnv tvs ||
361 isEmptyVarSet (Type.tyVarsOfType old_ty)
363 -- new_id has the right IdInfo
364 -- The lazy-set is because we're in a loop here, with
365 -- rec_subst, when dealing with a mutually-recursive group
366 new_id = maybeModifyIdInfo mb_new_info id2
367 mb_new_info = substIdInfo rec_subst id2 (idInfo id2)
368 -- NB: unfolding info may be zapped
370 -- Extend the substitution if the unique has changed
371 -- See the notes with substTyVarBndr for the delVarEnv
372 new_env | no_change = delVarEnv env old_id
373 | otherwise = extendVarEnv env old_id (Var new_id)
375 no_change = id1 == old_id
376 -- See Note [Extending the Subst]
377 -- it's /not/ necessary to check mb_new_info and no_type_change
380 Now a variant that unconditionally allocates a new unique.
381 It also unconditionally zaps the OccInfo.
384 -- | Very similar to 'substBndr', but it always allocates a new 'Unique' for
385 -- each variable in its output and removes all 'IdInfo'
386 cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
387 cloneIdBndr subst us old_id
388 = clone_id subst subst (old_id, uniqFromSupply us)
390 -- | Applies 'cloneIdBndr' to a number of 'Id's, accumulating a final
391 -- substitution from left to right
392 cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
393 cloneIdBndrs subst us ids
394 = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us)
396 -- | Clone a mutually recursive group of 'Id's
397 cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
398 cloneRecIdBndrs subst us ids
401 (subst', ids') = mapAccumL (clone_id subst') subst
402 (ids `zip` uniqsFromSupply us)
404 -- Just like substIdBndr, except that it always makes a new unique
405 -- It is given the unique to use
406 clone_id :: Subst -- Substitution for the IdInfo
407 -> Subst -> (Id, Unique) -- Substitition and Id to transform
408 -> (Subst, Id) -- Transformed pair
410 clone_id rec_subst subst@(Subst in_scope env tvs) (old_id, uniq)
411 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
413 id1 = setVarUnique old_id uniq
414 id2 = substIdType subst id1
415 new_id = maybeModifyIdInfo (substIdInfo rec_subst id2 (idInfo old_id)) id2
416 new_env = extendVarEnv env old_id (Var new_id)
420 %************************************************************************
424 %************************************************************************
426 For types we just call the corresponding function in Type, but we have
427 to repackage the substitution, from a Subst to a TvSubst
430 substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)
431 substTyVarBndr (Subst in_scope id_env tv_env) tv
432 = case Type.substTyVarBndr (TvSubst in_scope tv_env) tv of
433 (TvSubst in_scope' tv_env', tv')
434 -> (Subst in_scope' id_env tv_env', tv')
436 -- | See 'Type.substTy'
437 substTy :: Subst -> Type -> Type
438 substTy (Subst in_scope _id_env tv_env) ty
439 = Type.substTy (TvSubst in_scope tv_env) ty
443 %************************************************************************
445 \section{IdInfo substitution}
447 %************************************************************************
450 substIdType :: Subst -> Id -> Id
451 substIdType subst@(Subst _ _ tv_env) id
452 | isEmptyVarEnv tv_env || isEmptyVarSet (Type.tyVarsOfType old_ty) = id
453 | otherwise = setIdType id (substTy subst old_ty)
454 -- The tyVarsOfType is cheaper than it looks
455 -- because we cache the free tyvars of the type
456 -- in a Note in the id's type itself
461 -- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'.
462 -- Always zaps the unfolding, to save substitution work
463 substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo
464 substIdInfo subst new_id info
465 | nothing_to_do = Nothing
466 | otherwise = Just (info `setSpecInfo` substSpec subst new_id old_rules
467 `setWorkerInfo` substWorker subst old_wrkr
468 `setUnfoldingInfo` noUnfolding)
470 old_rules = specInfo info
471 old_wrkr = workerInfo info
472 nothing_to_do = isEmptySpecInfo old_rules &&
473 not (workerExists old_wrkr) &&
474 not (hasUnfolding (unfoldingInfo info))
478 -- | Substitutes for the 'Id's within the 'WorkerInfo'
479 substWorker :: Subst -> WorkerInfo -> WorkerInfo
480 -- Seq'ing on the returned WorkerInfo is enough to cause all the
481 -- substitutions to happen completely
483 substWorker _ NoWorker
485 substWorker subst (HasWorker w a)
486 = case lookupIdSubst subst w of
487 Var w1 -> HasWorker w1 a
488 other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr w )
489 NoWorker -- Worker has got substituted away altogether
490 -- (This can happen if it's trivial,
491 -- via postInlineUnconditionally, hence warning)
494 -- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id'
495 substSpec :: Subst -> Id -> SpecInfo -> SpecInfo
497 substSpec subst new_fn spec@(SpecInfo rules rhs_fvs)
501 = seqSpecInfo new_rules `seq` new_rules
503 new_name = idName new_fn
504 new_rules = SpecInfo (map do_subst rules) (substVarSet subst rhs_fvs)
506 do_subst rule@(BuiltinRule {}) = rule
507 do_subst rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs })
508 = rule { ru_bndrs = bndrs',
509 ru_fn = new_name, -- Important: the function may have changed its name!
510 ru_args = map (substExpr subst') args,
511 ru_rhs = substExpr subst' rhs }
513 (subst', bndrs') = substBndrs subst bndrs
516 substVarSet :: Subst -> VarSet -> VarSet
517 substVarSet subst fvs
518 = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
521 | isId fv = exprFreeVars (lookupIdSubst subst fv)
522 | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)