base: Reintroduce fusion for scanr
[ghc.git] / compiler / coreSyn / CoreSubst.hs
1 {-
2 (c) The University of Glasgow 2006
3 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4
5
6 Utility functions on @Core@ syntax
7 -}
8
9 {-# LANGUAGE CPP #-}
10 module CoreSubst (
11 -- * Main data types
12 Subst(..), -- Implementation exported for supercompiler's Renaming.hs only
13 TvSubstEnv, IdSubstEnv, InScopeSet,
14
15 -- ** Substituting into expressions and related types
16 deShadowBinds, substSpec, substRulesForImportedIds,
17 substTy, substCo, substExpr, substExprSC, substBind, substBindSC,
18 substUnfolding, substUnfoldingSC,
19 lookupIdSubst, lookupTCvSubst, substIdOcc,
20 substTickish, substDVarSet, substIdInfo,
21
22 -- ** Operations on substitutions
23 emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst,
24 extendIdSubst, extendIdSubstList, extendTCvSubst, extendTvSubstList,
25 extendSubst, extendSubstList, extendSubstWithVar, zapSubstEnv,
26 addInScopeSet, extendInScope, extendInScopeList, extendInScopeIds,
27 isInScope, setInScope, getTCvSubst, extendTvSubst, extendCvSubst,
28 delBndr, delBndrs,
29
30 -- ** Substituting and cloning binders
31 substBndr, substBndrs, substRecBndrs, substTyVarBndr, substCoVarBndr,
32 cloneBndr, cloneBndrs, cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs,
33
34 ) where
35
36 #include "HsVersions.h"
37
38
39 import GhcPrelude
40
41 import CoreSyn
42 import CoreFVs
43 import CoreSeq
44 import CoreUtils
45 import qualified Type
46 import qualified Coercion
47
48 -- We are defining local versions
49 import Type hiding ( substTy, extendTvSubst, extendCvSubst, extendTvSubstList
50 , isInScope, substTyVarBndr, cloneTyVarBndr )
51 import Coercion hiding ( substCo, substCoVarBndr )
52
53 import PrelNames
54 import VarSet
55 import VarEnv
56 import Id
57 import Name ( Name )
58 import Var
59 import IdInfo
60 import UniqSupply
61 import Maybes
62 import Util
63 import Outputable
64 import Data.List
65
66
67
68 {-
69 ************************************************************************
70 * *
71 \subsection{Substitutions}
72 * *
73 ************************************************************************
74 -}
75
76 -- | A substitution environment, containing 'Id', 'TyVar', and 'CoVar'
77 -- substitutions.
78 --
79 -- Some invariants apply to how you use the substitution:
80 --
81 -- 1. Note [The substitution invariant] in TyCoSubst
82 --
83 -- 2. Note [Substitutions apply only once] in TyCoSubst
84 data Subst
85 = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) /after/
86 -- applying the substitution
87 IdSubstEnv -- Substitution from NcIds to CoreExprs
88 TvSubstEnv -- Substitution from TyVars to Types
89 CvSubstEnv -- Substitution from CoVars to Coercions
90
91 -- INVARIANT 1: See TyCoSubst Note [The substitution invariant]
92 -- This is what lets us deal with name capture properly
93 -- It's a hard invariant to check...
94 --
95 -- INVARIANT 2: The substitution is apply-once; see Note [Apply once] with
96 -- Types.TvSubstEnv
97 --
98 -- INVARIANT 3: See Note [Extending the Subst]
99
100 {-
101 Note [Extending the Subst]
102 ~~~~~~~~~~~~~~~~~~~~~~~~~~
103 For a core Subst, which binds Ids as well, we make a different choice for Ids
104 than we do for TyVars.
105
106 For TyVars, see Note [Extending the TCvSubst] in TyCoSubst.
107
108 For Ids, we have a different invariant
109 The IdSubstEnv is extended *only* when the Unique on an Id changes
110 Otherwise, we just extend the InScopeSet
111
112 In consequence:
113
114 * If all subst envs are empty, substExpr would be a
115 no-op, so substExprSC ("short cut") does nothing.
116
117 However, substExpr still goes ahead and substitutes. Reason: we may
118 want to replace existing Ids with new ones from the in-scope set, to
119 avoid space leaks.
120
121 * In substIdBndr, we extend the IdSubstEnv only when the unique changes
122
123 * If the CvSubstEnv, TvSubstEnv and IdSubstEnv are all empty,
124 substExpr does nothing (Note that the above rule for substIdBndr
125 maintains this property. If the incoming envts are both empty, then
126 substituting the type and IdInfo can't change anything.)
127
128 * In lookupIdSubst, we *must* look up the Id in the in-scope set, because
129 it may contain non-trivial changes. Example:
130 (/\a. \x:a. ...x...) Int
131 We extend the TvSubstEnv with [a |-> Int]; but x's unique does not change
132 so we only extend the in-scope set. Then we must look up in the in-scope
133 set when we find the occurrence of x.
134
135 * The requirement to look up the Id in the in-scope set means that we
136 must NOT take no-op short cut when the IdSubst is empty.
137 We must still look up every Id in the in-scope set.
138
139 * (However, we don't need to do so for expressions found in the IdSubst
140 itself, whose range is assumed to be correct wrt the in-scope set.)
141
142 Why do we make a different choice for the IdSubstEnv than the
143 TvSubstEnv and CvSubstEnv?
144
145 * For Ids, we change the IdInfo all the time (e.g. deleting the
146 unfolding), and adding it back later, so using the TyVar convention
147 would entail extending the substitution almost all the time
148
149 * The simplifier wants to look up in the in-scope set anyway, in case it
150 can see a better unfolding from an enclosing case expression
151
152 * For TyVars, only coercion variables can possibly change, and they are
153 easy to spot
154 -}
155
156 -- | An environment for substituting for 'Id's
157 type IdSubstEnv = IdEnv CoreExpr -- Domain is NcIds, i.e. not coercions
158
159 ----------------------------
160 isEmptySubst :: Subst -> Bool
161 isEmptySubst (Subst _ id_env tv_env cv_env)
162 = isEmptyVarEnv id_env && isEmptyVarEnv tv_env && isEmptyVarEnv cv_env
163
164 emptySubst :: Subst
165 emptySubst = Subst emptyInScopeSet emptyVarEnv emptyVarEnv emptyVarEnv
166
167 mkEmptySubst :: InScopeSet -> Subst
168 mkEmptySubst in_scope = Subst in_scope emptyVarEnv emptyVarEnv emptyVarEnv
169
170 mkSubst :: InScopeSet -> TvSubstEnv -> CvSubstEnv -> IdSubstEnv -> Subst
171 mkSubst in_scope tvs cvs ids = Subst in_scope ids tvs cvs
172
173 -- | Find the in-scope set: see TyCoSubst Note [The substitution invariant]
174 substInScope :: Subst -> InScopeSet
175 substInScope (Subst in_scope _ _ _) = in_scope
176
177 -- | Remove all substitutions for 'Id's and 'Var's that might have been built up
178 -- while preserving the in-scope set
179 zapSubstEnv :: Subst -> Subst
180 zapSubstEnv (Subst in_scope _ _ _) = Subst in_scope emptyVarEnv emptyVarEnv emptyVarEnv
181
182 -- | Add a substitution for an 'Id' to the 'Subst': you must ensure that the in-scope set is
183 -- such that TyCoSubst Note [The substitution invariant]
184 -- holds after extending the substitution like this
185 extendIdSubst :: Subst -> Id -> CoreExpr -> Subst
186 -- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set
187 extendIdSubst (Subst in_scope ids tvs cvs) v r
188 = ASSERT2( isNonCoVarId v, ppr v $$ ppr r )
189 Subst in_scope (extendVarEnv ids v r) tvs cvs
190
191 -- | Adds multiple 'Id' substitutions to the 'Subst': see also 'extendIdSubst'
192 extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst
193 extendIdSubstList (Subst in_scope ids tvs cvs) prs
194 = ASSERT( all (isNonCoVarId . fst) prs )
195 Subst in_scope (extendVarEnvList ids prs) tvs cvs
196
197 -- | Add a substitution for a 'TyVar' to the 'Subst'
198 -- The 'TyVar' *must* be a real TyVar, and not a CoVar
199 -- You must ensure that the in-scope set is such that
200 -- TyCoSubst Note [The substitution invariant] holds
201 -- after extending the substitution like this.
202 extendTvSubst :: Subst -> TyVar -> Type -> Subst
203 extendTvSubst (Subst in_scope ids tvs cvs) tv ty
204 = ASSERT( isTyVar tv )
205 Subst in_scope ids (extendVarEnv tvs tv ty) cvs
206
207 -- | Adds multiple 'TyVar' substitutions to the 'Subst': see also 'extendTvSubst'
208 extendTvSubstList :: Subst -> [(TyVar,Type)] -> Subst
209 extendTvSubstList subst vrs
210 = foldl' extend subst vrs
211 where
212 extend subst (v, r) = extendTvSubst subst v r
213
214 -- | Add a substitution from a 'CoVar' to a 'Coercion' to the 'Subst':
215 -- you must ensure that the in-scope set satisfies
216 -- TyCoSubst Note [The substitution invariant]
217 -- after extending the substitution like this
218 extendCvSubst :: Subst -> CoVar -> Coercion -> Subst
219 extendCvSubst (Subst in_scope ids tvs cvs) v r
220 = ASSERT( isCoVar v )
221 Subst in_scope ids tvs (extendVarEnv cvs v r)
222
223 -- | Add a substitution appropriate to the thing being substituted
224 -- (whether an expression, type, or coercion). See also
225 -- 'extendIdSubst', 'extendTvSubst', 'extendCvSubst'
226 extendSubst :: Subst -> Var -> CoreArg -> Subst
227 extendSubst subst var arg
228 = case arg of
229 Type ty -> ASSERT( isTyVar var ) extendTvSubst subst var ty
230 Coercion co -> ASSERT( isCoVar var ) extendCvSubst subst var co
231 _ -> ASSERT( isId var ) extendIdSubst subst var arg
232
233 extendSubstWithVar :: Subst -> Var -> Var -> Subst
234 extendSubstWithVar subst v1 v2
235 | isTyVar v1 = ASSERT( isTyVar v2 ) extendTvSubst subst v1 (mkTyVarTy v2)
236 | isCoVar v1 = ASSERT( isCoVar v2 ) extendCvSubst subst v1 (mkCoVarCo v2)
237 | otherwise = ASSERT( isId v2 ) extendIdSubst subst v1 (Var v2)
238
239 -- | Add a substitution as appropriate to each of the terms being
240 -- substituted (whether expressions, types, or coercions). See also
241 -- 'extendSubst'.
242 extendSubstList :: Subst -> [(Var,CoreArg)] -> Subst
243 extendSubstList subst [] = subst
244 extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs
245
246 -- | Find the substitution for an 'Id' in the 'Subst'
247 lookupIdSubst :: SDoc -> Subst -> Id -> CoreExpr
248 lookupIdSubst doc (Subst in_scope ids _ _) v
249 | not (isLocalId v) = Var v
250 | Just e <- lookupVarEnv ids v = e
251 | Just v' <- lookupInScope in_scope v = Var v'
252 -- Vital! See Note [Extending the Subst]
253 | otherwise = WARN( True, text "CoreSubst.lookupIdSubst" <+> doc <+> ppr v
254 $$ ppr in_scope)
255 Var v
256
257 -- | Find the substitution for a 'TyVar' in the 'Subst'
258 lookupTCvSubst :: Subst -> TyVar -> Type
259 lookupTCvSubst (Subst _ _ tvs cvs) v
260 | isTyVar v
261 = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v
262 | otherwise
263 = mkCoercionTy $ lookupVarEnv cvs v `orElse` mkCoVarCo v
264
265 delBndr :: Subst -> Var -> Subst
266 delBndr (Subst in_scope ids tvs cvs) v
267 | isCoVar v = Subst in_scope ids tvs (delVarEnv cvs v)
268 | isTyVar v = Subst in_scope ids (delVarEnv tvs v) cvs
269 | otherwise = Subst in_scope (delVarEnv ids v) tvs cvs
270
271 delBndrs :: Subst -> [Var] -> Subst
272 delBndrs (Subst in_scope ids tvs cvs) vs
273 = Subst in_scope (delVarEnvList ids vs) (delVarEnvList tvs vs) (delVarEnvList cvs vs)
274 -- Easiest thing is just delete all from all!
275
276 -- | Simultaneously substitute for a bunch of variables
277 -- No left-right shadowing
278 -- ie the substitution for (\x \y. e) a1 a2
279 -- so neither x nor y scope over a1 a2
280 mkOpenSubst :: InScopeSet -> [(Var,CoreArg)] -> Subst
281 mkOpenSubst in_scope pairs = Subst in_scope
282 (mkVarEnv [(id,e) | (id, e) <- pairs, isId id])
283 (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
284 (mkVarEnv [(v,co) | (v, Coercion co) <- pairs])
285
286 ------------------------------
287 isInScope :: Var -> Subst -> Bool
288 isInScope v (Subst in_scope _ _ _) = v `elemInScopeSet` in_scope
289
290 -- | Add the 'Var' to the in-scope set, but do not remove
291 -- any existing substitutions for it
292 addInScopeSet :: Subst -> VarSet -> Subst
293 addInScopeSet (Subst in_scope ids tvs cvs) vs
294 = Subst (in_scope `extendInScopeSetSet` vs) ids tvs cvs
295
296 -- | Add the 'Var' to the in-scope set: as a side effect,
297 -- and remove any existing substitutions for it
298 extendInScope :: Subst -> Var -> Subst
299 extendInScope (Subst in_scope ids tvs cvs) v
300 = Subst (in_scope `extendInScopeSet` v)
301 (ids `delVarEnv` v) (tvs `delVarEnv` v) (cvs `delVarEnv` v)
302
303 -- | Add the 'Var's to the in-scope set: see also 'extendInScope'
304 extendInScopeList :: Subst -> [Var] -> Subst
305 extendInScopeList (Subst in_scope ids tvs cvs) vs
306 = Subst (in_scope `extendInScopeSetList` vs)
307 (ids `delVarEnvList` vs) (tvs `delVarEnvList` vs) (cvs `delVarEnvList` vs)
308
309 -- | Optimized version of 'extendInScopeList' that can be used if you are certain
310 -- all the things being added are 'Id's and hence none are 'TyVar's or 'CoVar's
311 extendInScopeIds :: Subst -> [Id] -> Subst
312 extendInScopeIds (Subst in_scope ids tvs cvs) vs
313 = Subst (in_scope `extendInScopeSetList` vs)
314 (ids `delVarEnvList` vs) tvs cvs
315
316 setInScope :: Subst -> InScopeSet -> Subst
317 setInScope (Subst _ ids tvs cvs) in_scope = Subst in_scope ids tvs cvs
318
319 -- Pretty printing, for debugging only
320
321 instance Outputable Subst where
322 ppr (Subst in_scope ids tvs cvs)
323 = text "<InScope =" <+> in_scope_doc
324 $$ text " IdSubst =" <+> ppr ids
325 $$ text " TvSubst =" <+> ppr tvs
326 $$ text " CvSubst =" <+> ppr cvs
327 <> char '>'
328 where
329 in_scope_doc = pprVarSet (getInScopeVars in_scope) (braces . fsep . map ppr)
330
331 {-
332 ************************************************************************
333 * *
334 Substituting expressions
335 * *
336 ************************************************************************
337 -}
338
339 -- | Apply a substitution to an entire 'CoreExpr'. Remember, you may only
340 -- apply the substitution /once/:
341 -- See Note [Substitutions apply only once] in TyCoSubst
342 --
343 -- Do *not* attempt to short-cut in the case of an empty substitution!
344 -- See Note [Extending the Subst]
345 substExprSC :: SDoc -> Subst -> CoreExpr -> CoreExpr
346 substExprSC doc subst orig_expr
347 | isEmptySubst subst = orig_expr
348 | otherwise = -- pprTrace "enter subst-expr" (doc $$ ppr orig_expr) $
349 subst_expr doc subst orig_expr
350
351 substExpr :: SDoc -> Subst -> CoreExpr -> CoreExpr
352 substExpr doc subst orig_expr = subst_expr doc subst orig_expr
353
354 subst_expr :: SDoc -> Subst -> CoreExpr -> CoreExpr
355 subst_expr doc subst expr
356 = go expr
357 where
358 go (Var v) = lookupIdSubst (doc $$ text "subst_expr") subst v
359 go (Type ty) = Type (substTy subst ty)
360 go (Coercion co) = Coercion (substCo subst co)
361 go (Lit lit) = Lit lit
362 go (App fun arg) = App (go fun) (go arg)
363 go (Tick tickish e) = mkTick (substTickish subst tickish) (go e)
364 go (Cast e co) = Cast (go e) (substCo subst co)
365 -- Do not optimise even identity coercions
366 -- Reason: substitution applies to the LHS of RULES, and
367 -- if you "optimise" an identity coercion, you may
368 -- lose a binder. We optimise the LHS of rules at
369 -- construction time
370
371 go (Lam bndr body) = Lam bndr' (subst_expr doc subst' body)
372 where
373 (subst', bndr') = substBndr subst bndr
374
375 go (Let bind body) = Let bind' (subst_expr doc subst' body)
376 where
377 (subst', bind') = substBind subst bind
378
379 go (Case scrut bndr ty alts) = Case (go scrut) bndr' (substTy subst ty) (map (go_alt subst') alts)
380 where
381 (subst', bndr') = substBndr subst bndr
382
383 go_alt subst (con, bndrs, rhs) = (con, bndrs', subst_expr doc subst' rhs)
384 where
385 (subst', bndrs') = substBndrs subst bndrs
386
387 -- | Apply a substitution to an entire 'CoreBind', additionally returning an updated 'Subst'
388 -- that should be used by subsequent substitutions.
389 substBind, substBindSC :: Subst -> CoreBind -> (Subst, CoreBind)
390
391 substBindSC subst bind -- Short-cut if the substitution is empty
392 | not (isEmptySubst subst)
393 = substBind subst bind
394 | otherwise
395 = case bind of
396 NonRec bndr rhs -> (subst', NonRec bndr' rhs)
397 where
398 (subst', bndr') = substBndr subst bndr
399 Rec pairs -> (subst', Rec (bndrs' `zip` rhss'))
400 where
401 (bndrs, rhss) = unzip pairs
402 (subst', bndrs') = substRecBndrs subst bndrs
403 rhss' | isEmptySubst subst'
404 = rhss
405 | otherwise
406 = map (subst_expr (text "substBindSC") subst') rhss
407
408 substBind subst (NonRec bndr rhs)
409 = (subst', NonRec bndr' (subst_expr (text "substBind") subst rhs))
410 where
411 (subst', bndr') = substBndr subst bndr
412
413 substBind subst (Rec pairs)
414 = (subst', Rec (bndrs' `zip` rhss'))
415 where
416 (bndrs, rhss) = unzip pairs
417 (subst', bndrs') = substRecBndrs subst bndrs
418 rhss' = map (subst_expr (text "substBind") subst') rhss
419
420 -- | De-shadowing the program is sometimes a useful pre-pass. It can be done simply
421 -- by running over the bindings with an empty substitution, because substitution
422 -- returns a result that has no-shadowing guaranteed.
423 --
424 -- (Actually, within a single /type/ there might still be shadowing, because
425 -- 'substTy' is a no-op for the empty substitution, but that's probably OK.)
426 --
427 -- [Aug 09] This function is not used in GHC at the moment, but seems so
428 -- short and simple that I'm going to leave it here
429 deShadowBinds :: CoreProgram -> CoreProgram
430 deShadowBinds binds = snd (mapAccumL substBind emptySubst binds)
431
432 {-
433 ************************************************************************
434 * *
435 Substituting binders
436 * *
437 ************************************************************************
438
439 Remember that substBndr and friends are used when doing expression
440 substitution only. Their only business is substitution, so they
441 preserve all IdInfo (suitably substituted). For example, we *want* to
442 preserve occ info in rules.
443 -}
444
445 -- | Substitutes a 'Var' for another one according to the 'Subst' given, returning
446 -- the result and an updated 'Subst' that should be used by subsequent substitutions.
447 -- 'IdInfo' is preserved by this process, although it is substituted into appropriately.
448 substBndr :: Subst -> Var -> (Subst, Var)
449 substBndr subst bndr
450 | isTyVar bndr = substTyVarBndr subst bndr
451 | isCoVar bndr = substCoVarBndr subst bndr
452 | otherwise = substIdBndr (text "var-bndr") subst subst bndr
453
454 -- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right
455 substBndrs :: Subst -> [Var] -> (Subst, [Var])
456 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
457
458 -- | Substitute in a mutually recursive group of 'Id's
459 substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
460 substRecBndrs subst bndrs
461 = (new_subst, new_bndrs)
462 where -- Here's the reason we need to pass rec_subst to subst_id
463 (new_subst, new_bndrs) = mapAccumL (substIdBndr (text "rec-bndr") new_subst) subst bndrs
464
465 substIdBndr :: SDoc
466 -> Subst -- ^ Substitution to use for the IdInfo
467 -> Subst -> Id -- ^ Substitution and Id to transform
468 -> (Subst, Id) -- ^ Transformed pair
469 -- NB: unfolding may be zapped
470
471 substIdBndr _doc rec_subst subst@(Subst in_scope env tvs cvs) old_id
472 = -- pprTrace "substIdBndr" (doc $$ ppr old_id $$ ppr in_scope) $
473 (Subst (in_scope `extendInScopeSet` new_id) new_env tvs cvs, new_id)
474 where
475 id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
476 id2 | no_type_change = id1
477 | otherwise = setIdType id1 (substTy subst old_ty)
478
479 old_ty = idType old_id
480 no_type_change = (isEmptyVarEnv tvs && isEmptyVarEnv cvs) ||
481 noFreeVarsOfType old_ty
482
483 -- new_id has the right IdInfo
484 -- The lazy-set is because we're in a loop here, with
485 -- rec_subst, when dealing with a mutually-recursive group
486 new_id = maybeModifyIdInfo mb_new_info id2
487 mb_new_info = substIdInfo rec_subst id2 (idInfo id2)
488 -- NB: unfolding info may be zapped
489
490 -- Extend the substitution if the unique has changed
491 -- See the notes with substTyVarBndr for the delVarEnv
492 new_env | no_change = delVarEnv env old_id
493 | otherwise = extendVarEnv env old_id (Var new_id)
494
495 no_change = id1 == old_id
496 -- See Note [Extending the Subst]
497 -- it's /not/ necessary to check mb_new_info and no_type_change
498
499 {-
500 Now a variant that unconditionally allocates a new unique.
501 It also unconditionally zaps the OccInfo.
502 -}
503
504 -- | Very similar to 'substBndr', but it always allocates a new 'Unique' for
505 -- each variable in its output. It substitutes the IdInfo though.
506 cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
507 cloneIdBndr subst us old_id
508 = clone_id subst subst (old_id, uniqFromSupply us)
509
510 -- | Applies 'cloneIdBndr' to a number of 'Id's, accumulating a final
511 -- substitution from left to right
512 cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
513 cloneIdBndrs subst us ids
514 = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us)
515
516 cloneBndrs :: Subst -> UniqSupply -> [Var] -> (Subst, [Var])
517 -- Works for all kinds of variables (typically case binders)
518 -- not just Ids
519 cloneBndrs subst us vs
520 = mapAccumL (\subst (v, u) -> cloneBndr subst u v) subst (vs `zip` uniqsFromSupply us)
521
522 cloneBndr :: Subst -> Unique -> Var -> (Subst, Var)
523 cloneBndr subst uniq v
524 | isTyVar v = cloneTyVarBndr subst v uniq
525 | otherwise = clone_id subst subst (v,uniq) -- Works for coercion variables too
526
527 -- | Clone a mutually recursive group of 'Id's
528 cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
529 cloneRecIdBndrs subst us ids
530 = (subst', ids')
531 where
532 (subst', ids') = mapAccumL (clone_id subst') subst
533 (ids `zip` uniqsFromSupply us)
534
535 -- Just like substIdBndr, except that it always makes a new unique
536 -- It is given the unique to use
537 clone_id :: Subst -- Substitution for the IdInfo
538 -> Subst -> (Id, Unique) -- Substitution and Id to transform
539 -> (Subst, Id) -- Transformed pair
540
541 clone_id rec_subst subst@(Subst in_scope idvs tvs cvs) (old_id, uniq)
542 = (Subst (in_scope `extendInScopeSet` new_id) new_idvs tvs new_cvs, new_id)
543 where
544 id1 = setVarUnique old_id uniq
545 id2 = substIdType subst id1
546 new_id = maybeModifyIdInfo (substIdInfo rec_subst id2 (idInfo old_id)) id2
547 (new_idvs, new_cvs) | isCoVar old_id = (idvs, extendVarEnv cvs old_id (mkCoVarCo new_id))
548 | otherwise = (extendVarEnv idvs old_id (Var new_id), cvs)
549
550 {-
551 ************************************************************************
552 * *
553 Types and Coercions
554 * *
555 ************************************************************************
556
557 For types and coercions we just call the corresponding functions in
558 Type and Coercion, but we have to repackage the substitution, from a
559 Subst to a TCvSubst.
560 -}
561
562 substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)
563 substTyVarBndr (Subst in_scope id_env tv_env cv_env) tv
564 = case Type.substTyVarBndr (TCvSubst in_scope tv_env cv_env) tv of
565 (TCvSubst in_scope' tv_env' cv_env', tv')
566 -> (Subst in_scope' id_env tv_env' cv_env', tv')
567
568 cloneTyVarBndr :: Subst -> TyVar -> Unique -> (Subst, TyVar)
569 cloneTyVarBndr (Subst in_scope id_env tv_env cv_env) tv uniq
570 = case Type.cloneTyVarBndr (TCvSubst in_scope tv_env cv_env) tv uniq of
571 (TCvSubst in_scope' tv_env' cv_env', tv')
572 -> (Subst in_scope' id_env tv_env' cv_env', tv')
573
574 substCoVarBndr :: Subst -> TyVar -> (Subst, TyVar)
575 substCoVarBndr (Subst in_scope id_env tv_env cv_env) cv
576 = case Coercion.substCoVarBndr (TCvSubst in_scope tv_env cv_env) cv of
577 (TCvSubst in_scope' tv_env' cv_env', cv')
578 -> (Subst in_scope' id_env tv_env' cv_env', cv')
579
580 -- | See 'Type.substTy'
581 substTy :: Subst -> Type -> Type
582 substTy subst ty = Type.substTyUnchecked (getTCvSubst subst) ty
583
584 getTCvSubst :: Subst -> TCvSubst
585 getTCvSubst (Subst in_scope _ tenv cenv) = TCvSubst in_scope tenv cenv
586
587 -- | See 'Coercion.substCo'
588 substCo :: Subst -> Coercion -> Coercion
589 substCo subst co = Coercion.substCo (getTCvSubst subst) co
590
591 {-
592 ************************************************************************
593 * *
594 \section{IdInfo substitution}
595 * *
596 ************************************************************************
597 -}
598
599 substIdType :: Subst -> Id -> Id
600 substIdType subst@(Subst _ _ tv_env cv_env) id
601 | (isEmptyVarEnv tv_env && isEmptyVarEnv cv_env) || noFreeVarsOfType old_ty = id
602 | otherwise = setIdType id (substTy subst old_ty)
603 -- The tyCoVarsOfType is cheaper than it looks
604 -- because we cache the free tyvars of the type
605 -- in a Note in the id's type itself
606 where
607 old_ty = idType id
608
609 ------------------
610 -- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'.
611 substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo
612 substIdInfo subst new_id info
613 | nothing_to_do = Nothing
614 | otherwise = Just (info `setRuleInfo` substSpec subst new_id old_rules
615 `setUnfoldingInfo` substUnfolding subst old_unf)
616 where
617 old_rules = ruleInfo info
618 old_unf = unfoldingInfo info
619 nothing_to_do = isEmptyRuleInfo old_rules && not (isFragileUnfolding old_unf)
620
621 ------------------
622 -- | Substitutes for the 'Id's within an unfolding
623 substUnfolding, substUnfoldingSC :: Subst -> Unfolding -> Unfolding
624 -- Seq'ing on the returned Unfolding is enough to cause
625 -- all the substitutions to happen completely
626
627 substUnfoldingSC subst unf -- Short-cut version
628 | isEmptySubst subst = unf
629 | otherwise = substUnfolding subst unf
630
631 substUnfolding subst df@(DFunUnfolding { df_bndrs = bndrs, df_args = args })
632 = df { df_bndrs = bndrs', df_args = args' }
633 where
634 (subst',bndrs') = substBndrs subst bndrs
635 args' = map (substExpr (text "subst-unf:dfun") subst') args
636
637 substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_src = src })
638 -- Retain an InlineRule!
639 | not (isStableSource src) -- Zap an unstable unfolding, to save substitution work
640 = NoUnfolding
641 | otherwise -- But keep a stable one!
642 = seqExpr new_tmpl `seq`
643 unf { uf_tmpl = new_tmpl }
644 where
645 new_tmpl = substExpr (text "subst-unf") subst tmpl
646
647 substUnfolding _ unf = unf -- NoUnfolding, OtherCon
648
649 ------------------
650 substIdOcc :: Subst -> Id -> Id
651 -- These Ids should not be substituted to non-Ids
652 substIdOcc subst v = case lookupIdSubst (text "substIdOcc") subst v of
653 Var v' -> v'
654 other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst])
655
656 ------------------
657 -- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id'
658 substSpec :: Subst -> Id -> RuleInfo -> RuleInfo
659 substSpec subst new_id (RuleInfo rules rhs_fvs)
660 = seqRuleInfo new_spec `seq` new_spec
661 where
662 subst_ru_fn = const (idName new_id)
663 new_spec = RuleInfo (map (substRule subst subst_ru_fn) rules)
664 (substDVarSet subst rhs_fvs)
665
666 ------------------
667 substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule]
668 substRulesForImportedIds subst rules
669 = map (substRule subst not_needed) rules
670 where
671 not_needed name = pprPanic "substRulesForImportedIds" (ppr name)
672
673 ------------------
674 substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule
675
676 -- The subst_ru_fn argument is applied to substitute the ru_fn field
677 -- of the rule:
678 -- - Rules for *imported* Ids never change ru_fn
679 -- - Rules for *local* Ids are in the IdInfo for that Id,
680 -- and the ru_fn field is simply replaced by the new name
681 -- of the Id
682 substRule _ _ rule@(BuiltinRule {}) = rule
683 substRule subst subst_ru_fn rule@(Rule { ru_bndrs = bndrs, ru_args = args
684 , ru_fn = fn_name, ru_rhs = rhs
685 , ru_local = is_local })
686 = rule { ru_bndrs = bndrs'
687 , ru_fn = if is_local
688 then subst_ru_fn fn_name
689 else fn_name
690 , ru_args = map (substExpr doc subst') args
691 , ru_rhs = substExpr (text "foo") subst' rhs }
692 -- Do NOT optimise the RHS (previously we did simplOptExpr here)
693 -- See Note [Substitute lazily]
694 where
695 doc = text "subst-rule" <+> ppr fn_name
696 (subst', bndrs') = substBndrs subst bndrs
697
698 ------------------
699 substDVarSet :: Subst -> DVarSet -> DVarSet
700 substDVarSet subst fvs
701 = mkDVarSet $ fst $ foldr (subst_fv subst) ([], emptyVarSet) $ dVarSetElems fvs
702 where
703 subst_fv subst fv acc
704 | isId fv = expr_fvs (lookupIdSubst (text "substDVarSet") subst fv) isLocalVar emptyVarSet $! acc
705 | otherwise = tyCoFVsOfType (lookupTCvSubst subst fv) (const True) emptyVarSet $! acc
706
707 ------------------
708 substTickish :: Subst -> Tickish Id -> Tickish Id
709 substTickish subst (Breakpoint n ids)
710 = Breakpoint n (map do_one ids)
711 where
712 do_one = getIdFromTrivialExpr . lookupIdSubst (text "subst_tickish") subst
713 substTickish _subst other = other
714
715 {- Note [Substitute lazily]
716 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
717 The functions that substitute over IdInfo must be pretty lazy, because
718 they are knot-tied by substRecBndrs.
719
720 One case in point was #10627 in which a rule for a function 'f'
721 referred to 'f' (at a different type) on the RHS. But instead of just
722 substituting in the rhs of the rule, we were calling simpleOptExpr, which
723 looked at the idInfo for 'f'; result <<loop>>.
724
725 In any case we don't need to optimise the RHS of rules, or unfoldings,
726 because the simplifier will do that.
727
728
729 Note [substTickish]
730 ~~~~~~~~~~~~~~~~~~~~~~
731 A Breakpoint contains a list of Ids. What happens if we ever want to
732 substitute an expression for one of these Ids?
733
734 First, we ensure that we only ever substitute trivial expressions for
735 these Ids, by marking them as NoOccInfo in the occurrence analyser.
736 Then, when substituting for the Id, we unwrap any type applications
737 and abstractions to get back to an Id, with getIdFromTrivialExpr.
738
739 Second, we have to ensure that we never try to substitute a literal
740 for an Id in a breakpoint. We ensure this by never storing an Id with
741 an unlifted type in a Breakpoint - see Coverage.mkTickish.
742 Breakpoints can't handle free variables with unlifted types anyway.
743 -}
744
745 {-
746 Note [Worker inlining]
747 ~~~~~~~~~~~~~~~~~~~~~~
748 A worker can get sustituted away entirely.
749 - it might be trivial
750 - it might simply be very small
751 We do not treat an InlWrapper as an 'occurrence' in the occurrence
752 analyser, so it's possible that the worker is not even in scope any more.
753
754 In all all these cases we simply drop the special case, returning to
755 InlVanilla. The WARN is just so I can see if it happens a lot.
756 -}
757