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 apply the substitution /once/: see "CoreSubst#apply_once"
258 substExpr :: Subst -> CoreExpr -> CoreExpr
262 go (Var v) = lookupIdSubst subst v
263 go (Type ty) = Type (substTy subst ty)
264 go (Lit lit) = Lit lit
265 go (App fun arg) = App (go fun) (go arg)
266 go (Note note e) = Note (go_note note) (go e)
267 go (Cast e co) = Cast (go e) (substTy subst co)
268 go (Lam bndr body) = Lam bndr' (substExpr subst' body)
270 (subst', bndr') = substBndr subst bndr
272 go (Let bind body) = Let bind' (substExpr subst' body)
274 (subst', bind') = substBind subst bind
276 go (Case scrut bndr ty alts) = Case (go scrut) bndr' (substTy subst ty) (map (go_alt subst') alts)
278 (subst', bndr') = substBndr subst bndr
280 go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs)
282 (subst', bndrs') = substBndrs subst bndrs
286 -- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst'
287 -- that should be used by subsequent substitutons.
288 substBind :: Subst -> CoreBind -> (Subst, CoreBind)
289 substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs))
291 (subst', bndr') = substBndr subst bndr
293 substBind subst (Rec pairs) = (subst', Rec pairs')
295 (subst', bndrs') = substRecBndrs subst (map fst pairs)
296 pairs' = bndrs' `zip` rhss'
297 rhss' = map (substExpr subst' . snd) pairs
301 -- | De-shadowing the program is sometimes a useful pre-pass. It can be done simply
302 -- by running over the bindings with an empty substitution, becuase substitution
303 -- returns a result that has no-shadowing guaranteed.
305 -- (Actually, within a single /type/ there might still be shadowing, because
306 -- 'substTy' is a no-op for the empty substitution, but that's probably OK.)
307 deShadowBinds :: [CoreBind] -> [CoreBind]
308 deShadowBinds binds = snd (mapAccumL substBind emptySubst binds)
312 %************************************************************************
316 %************************************************************************
318 Remember that substBndr and friends are used when doing expression
319 substitution only. Their only business is substitution, so they
320 preserve all IdInfo (suitably substituted). For example, we *want* to
321 preserve occ info in rules.
324 -- | Substitutes a 'Var' for another one according to the 'Subst' given, returning
325 -- the result and an updated 'Subst' that should be used by subsequent substitutons.
326 -- 'IdInfo' is preserved by this process, although it is substituted into appropriately.
327 substBndr :: Subst -> Var -> (Subst, Var)
329 | isTyVar bndr = substTyVarBndr subst bndr
330 | otherwise = substIdBndr subst subst bndr
332 -- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right
333 substBndrs :: Subst -> [Var] -> (Subst, [Var])
334 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
336 -- | Substitute in a mutually recursive group of 'Id's
337 substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
338 substRecBndrs subst bndrs
339 = (new_subst, new_bndrs)
340 where -- Here's the reason we need to pass rec_subst to subst_id
341 (new_subst, new_bndrs) = mapAccumL (substIdBndr new_subst) subst bndrs
346 substIdBndr :: Subst -- ^ Substitution to use for the IdInfo
347 -> Subst -> Id -- ^ Substitition and Id to transform
348 -> (Subst, Id) -- ^ Transformed pair
349 -- NB: unfolding may be zapped
351 substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id
352 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
354 id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
355 id2 | no_type_change = id1
356 | otherwise = setIdType id1 (substTy subst old_ty)
358 old_ty = idType old_id
359 no_type_change = isEmptyVarEnv tvs ||
360 isEmptyVarSet (Type.tyVarsOfType old_ty)
362 -- new_id has the right IdInfo
363 -- The lazy-set is because we're in a loop here, with
364 -- rec_subst, when dealing with a mutually-recursive group
365 new_id = maybeModifyIdInfo mb_new_info id2
366 mb_new_info = substIdInfo rec_subst id2 (idInfo id2)
367 -- NB: unfolding info may be zapped
369 -- Extend the substitution if the unique has changed
370 -- See the notes with substTyVarBndr for the delVarEnv
371 new_env | no_change = delVarEnv env old_id
372 | otherwise = extendVarEnv env old_id (Var new_id)
374 no_change = id1 == old_id
375 -- See Note [Extending the Subst]
376 -- it's /not/ necessary to check mb_new_info and no_type_change
379 Now a variant that unconditionally allocates a new unique.
380 It also unconditionally zaps the OccInfo.
383 -- | Very similar to 'substBndr', but it always allocates a new 'Unique' for
384 -- each variable in its output and removes all 'IdInfo'
385 cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
386 cloneIdBndr subst us old_id
387 = clone_id subst subst (old_id, uniqFromSupply us)
389 -- | Applies 'cloneIdBndr' to a number of 'Id's, accumulating a final
390 -- substitution from left to right
391 cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
392 cloneIdBndrs subst us ids
393 = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us)
395 -- | Clone a mutually recursive group of 'Id's
396 cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
397 cloneRecIdBndrs subst us ids
400 (subst', ids') = mapAccumL (clone_id subst') subst
401 (ids `zip` uniqsFromSupply us)
403 -- Just like substIdBndr, except that it always makes a new unique
404 -- It is given the unique to use
405 clone_id :: Subst -- Substitution for the IdInfo
406 -> Subst -> (Id, Unique) -- Substitition and Id to transform
407 -> (Subst, Id) -- Transformed pair
409 clone_id rec_subst subst@(Subst in_scope env tvs) (old_id, uniq)
410 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
412 id1 = setVarUnique old_id uniq
413 id2 = substIdType subst id1
414 new_id = maybeModifyIdInfo (substIdInfo rec_subst id2 (idInfo old_id)) id2
415 new_env = extendVarEnv env old_id (Var new_id)
419 %************************************************************************
423 %************************************************************************
425 For types we just call the corresponding function in Type, but we have
426 to repackage the substitution, from a Subst to a TvSubst
429 substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)
430 substTyVarBndr (Subst in_scope id_env tv_env) tv
431 = case Type.substTyVarBndr (TvSubst in_scope tv_env) tv of
432 (TvSubst in_scope' tv_env', tv')
433 -> (Subst in_scope' id_env tv_env', tv')
435 -- | See 'Type.substTy'
436 substTy :: Subst -> Type -> Type
437 substTy (Subst in_scope _id_env tv_env) ty
438 = Type.substTy (TvSubst in_scope tv_env) ty
442 %************************************************************************
444 \section{IdInfo substitution}
446 %************************************************************************
449 substIdType :: Subst -> Id -> Id
450 substIdType subst@(Subst _ _ tv_env) id
451 | isEmptyVarEnv tv_env || isEmptyVarSet (Type.tyVarsOfType old_ty) = id
452 | otherwise = setIdType id (substTy subst old_ty)
453 -- The tyVarsOfType is cheaper than it looks
454 -- because we cache the free tyvars of the type
455 -- in a Note in the id's type itself
460 -- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'.
461 -- Always zaps the unfolding, to save substitution work
462 substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo
463 substIdInfo subst new_id info
464 | nothing_to_do = Nothing
465 | otherwise = Just (info `setSpecInfo` substSpec subst new_id old_rules
466 `setWorkerInfo` substWorker subst old_wrkr
467 `setUnfoldingInfo` noUnfolding)
469 old_rules = specInfo info
470 old_wrkr = workerInfo info
471 nothing_to_do = isEmptySpecInfo old_rules &&
472 not (workerExists old_wrkr) &&
473 not (hasUnfolding (unfoldingInfo info))
477 -- | Substitutes for the 'Id's within the 'WorkerInfo'
478 substWorker :: Subst -> WorkerInfo -> WorkerInfo
479 -- Seq'ing on the returned WorkerInfo is enough to cause all the
480 -- substitutions to happen completely
482 substWorker _ NoWorker
484 substWorker subst (HasWorker w a)
485 = case lookupIdSubst subst w of
486 Var w1 -> HasWorker w1 a
487 other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr w )
488 NoWorker -- Worker has got substituted away altogether
489 -- (This can happen if it's trivial,
490 -- via postInlineUnconditionally, hence warning)
493 -- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id'
494 substSpec :: Subst -> Id -> SpecInfo -> SpecInfo
496 substSpec subst new_fn spec@(SpecInfo rules rhs_fvs)
500 = seqSpecInfo new_rules `seq` new_rules
502 new_name = idName new_fn
503 new_rules = SpecInfo (map do_subst rules) (substVarSet subst rhs_fvs)
505 do_subst rule@(BuiltinRule {}) = rule
506 do_subst rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs })
507 = rule { ru_bndrs = bndrs',
508 ru_fn = new_name, -- Important: the function may have changed its name!
509 ru_args = map (substExpr subst') args,
510 ru_rhs = substExpr subst' rhs }
512 (subst', bndrs') = substBndrs subst bndrs
515 substVarSet :: Subst -> VarSet -> VarSet
516 substVarSet subst fvs
517 = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
520 | isId fv = exprFreeVars (lookupIdSubst subst fv)
521 | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)