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
14 deShadowBinds, substSpec, substRulesForImportedIds,
15 substTy, substExpr, substExprSC, substBind, substBindSC,
16 substUnfolding, substUnfoldingSC,
17 substUnfoldingSource, lookupIdSubst, lookupTvSubst, substIdOcc,
19 -- ** Operations on substitutions
20 emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst,
21 extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList,
22 extendSubst, extendSubstList, zapSubstEnv,
23 extendInScope, extendInScopeList, extendInScopeIds,
26 -- ** Substituting and cloning binders
27 substBndr, substBndrs, substRecBndrs,
28 cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs,
30 -- ** Simple expression optimiser
31 simpleOptPgm, simpleOptExpr, simpleOptExprWith
34 #include "HsVersions.h"
40 import OccurAnal( occurAnalyseExpr, occurAnalysePgm )
43 import Type ( Type, TvSubst(..), TvSubstEnv )
44 import Coercion ( isIdentityCoercion )
45 import OptCoercion ( optCoercion )
50 import Var ( Var, TyVar, setVarUnique )
56 import DynFlags ( DynFlags, DynFlag(..) )
57 import BasicTypes ( isAlwaysActive )
59 import PprCore () -- Instances
66 %************************************************************************
68 \subsection{Substitutions}
70 %************************************************************************
73 -- | A substitution environment, containing both 'Id' and 'TyVar' substitutions.
75 -- Some invariants apply to how you use the substitution:
77 -- 1. #in_scope_invariant# The in-scope set contains at least those 'Id's and 'TyVar's that will be in scope /after/
78 -- applying the substitution to a term. Precisely, the in-scope set must be a superset of the free vars of the
79 -- substitution range that might possibly clash with locally-bound variables in the thing being substituted in.
81 -- 2. #apply_once# You may apply the substitution only /once/
83 -- There are various ways of setting up the in-scope set such that the first of these invariants hold:
85 -- * Arrange that the in-scope set really is all the things in scope
87 -- * Arrange that it's the free vars of the range of the substitution
89 -- * Make it empty, if you know that all the free vars of the substitution are fresh, and hence can't possibly clash
91 = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) /after/
92 -- applying the substitution
93 IdSubstEnv -- Substitution for Ids
94 TvSubstEnv -- Substitution for TyVars
96 -- INVARIANT 1: See #in_scope_invariant#
97 -- This is what lets us deal with name capture properly
98 -- It's a hard invariant to check...
100 -- INVARIANT 2: The substitution is apply-once; see Note [Apply once] with
103 -- INVARIANT 3: See Note [Extending the Subst]
106 Note [Extending the Subst]
107 ~~~~~~~~~~~~~~~~~~~~~~~~~~
108 For a core Subst, which binds Ids as well, we make a different choice for Ids
109 than we do for TyVars.
111 For TyVars, see Note [Extending the TvSubst] with Type.TvSubstEnv
113 For Ids, we have a different invariant
114 The IdSubstEnv is extended *only* when the Unique on an Id changes
115 Otherwise, we just extend the InScopeSet
119 * If the TvSubstEnv and IdSubstEnv are both empty, substExpr would be a
120 no-op, so substExprSC ("short cut") does nothing.
122 However, substExpr still goes ahead and substitutes. Reason: we may
123 want to replace existing Ids with new ones from the in-scope set, to
126 * In substIdBndr, we extend the IdSubstEnv only when the unique changes
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.
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.
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.)
142 Why do we make a different choice for the IdSubstEnv than the TvSubstEnv?
144 * For Ids, we change the IdInfo all the time (e.g. deleting the
145 unfolding), and adding it back later, so using the TyVar convention
146 would entail extending the substitution almost all the time
148 * The simplifier wants to look up in the in-scope set anyway, in case it
149 can see a better unfolding from an enclosing case expression
151 * For TyVars, only coercion variables can possibly change, and they are
155 -- | An environment for substituting for 'Id's
156 type IdSubstEnv = IdEnv CoreExpr
158 ----------------------------
159 isEmptySubst :: Subst -> Bool
160 isEmptySubst (Subst _ id_env tv_env) = isEmptyVarEnv id_env && isEmptyVarEnv tv_env
163 emptySubst = Subst emptyInScopeSet emptyVarEnv emptyVarEnv
165 mkEmptySubst :: InScopeSet -> Subst
166 mkEmptySubst in_scope = Subst in_scope emptyVarEnv emptyVarEnv
168 mkSubst :: InScopeSet -> TvSubstEnv -> IdSubstEnv -> Subst
169 mkSubst in_scope tvs ids = Subst in_scope ids tvs
171 -- getTvSubst :: Subst -> TvSubst
172 -- getTvSubst (Subst in_scope _ tv_env) = TvSubst in_scope tv_env
174 -- getTvSubstEnv :: Subst -> TvSubstEnv
175 -- getTvSubstEnv (Subst _ _ tv_env) = tv_env
177 -- setTvSubstEnv :: Subst -> TvSubstEnv -> Subst
178 -- setTvSubstEnv (Subst in_scope ids _) tvs = Subst in_scope ids tvs
180 -- | Find the in-scope set: see "CoreSubst#in_scope_invariant"
181 substInScope :: Subst -> InScopeSet
182 substInScope (Subst in_scope _ _) = in_scope
184 -- | Remove all substitutions for 'Id's and 'Var's that might have been built up
185 -- while preserving the in-scope set
186 zapSubstEnv :: Subst -> Subst
187 zapSubstEnv (Subst in_scope _ _) = Subst in_scope emptyVarEnv emptyVarEnv
189 -- | Add a substitution for an 'Id' to the 'Subst': you must ensure that the in-scope set is
190 -- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this
191 extendIdSubst :: Subst -> Id -> CoreExpr -> Subst
192 -- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set
193 extendIdSubst (Subst in_scope ids tvs) v r = Subst in_scope (extendVarEnv ids v r) tvs
195 -- | Adds multiple 'Id' substitutions to the 'Subst': see also 'extendIdSubst'
196 extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst
197 extendIdSubstList (Subst in_scope ids tvs) prs = Subst in_scope (extendVarEnvList ids prs) tvs
199 -- | Add a substitution for a 'TyVar' to the 'Subst': you must ensure that the in-scope set is
200 -- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this
201 extendTvSubst :: Subst -> TyVar -> Type -> Subst
202 extendTvSubst (Subst in_scope ids tvs) v r = Subst in_scope ids (extendVarEnv tvs v r)
204 -- | Adds multiple 'TyVar' substitutions to the 'Subst': see also 'extendTvSubst'
205 extendTvSubstList :: Subst -> [(TyVar,Type)] -> Subst
206 extendTvSubstList (Subst in_scope ids tvs) prs = Subst in_scope ids (extendVarEnvList tvs prs)
208 -- | Add a substitution for a 'TyVar' or 'Id' as appropriate to the 'Var' being added. See also
209 -- 'extendIdSubst' and 'extendTvSubst'
210 extendSubst :: Subst -> Var -> CoreArg -> Subst
211 extendSubst (Subst in_scope ids tvs) tv (Type ty)
212 = ASSERT( isTyCoVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty)
213 extendSubst (Subst in_scope ids tvs) id expr
214 = ASSERT( isId id ) Subst in_scope (extendVarEnv ids id expr) tvs
216 -- | Add a substitution for a 'TyVar' or 'Id' as appropriate to all the 'Var's being added. See also 'extendSubst'
217 extendSubstList :: Subst -> [(Var,CoreArg)] -> Subst
218 extendSubstList subst [] = subst
219 extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs
221 -- | Find the substitution for an 'Id' in the 'Subst'
222 lookupIdSubst :: SDoc -> Subst -> Id -> CoreExpr
223 lookupIdSubst doc (Subst in_scope ids _) v
224 | not (isLocalId v) = Var v
225 | Just e <- lookupVarEnv ids v = e
226 | Just v' <- lookupInScope in_scope v = Var v'
227 -- Vital! See Note [Extending the Subst]
228 | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope $$ doc)
231 -- | Find the substitution for a 'TyVar' in the 'Subst'
232 lookupTvSubst :: Subst -> TyVar -> Type
233 lookupTvSubst (Subst _ _ tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v
235 -- | Simultaneously substitute for a bunch of variables
236 -- No left-right shadowing
237 -- ie the substitution for (\x \y. e) a1 a2
238 -- so neither x nor y scope over a1 a2
239 mkOpenSubst :: InScopeSet -> [(Var,CoreArg)] -> Subst
240 mkOpenSubst in_scope pairs = Subst in_scope
241 (mkVarEnv [(id,e) | (id, e) <- pairs, isId id])
242 (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
244 ------------------------------
245 isInScope :: Var -> Subst -> Bool
246 isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope
248 -- | Add the 'Var' to the in-scope set: as a side effect, removes any existing substitutions for it
249 extendInScope :: Subst -> Var -> Subst
250 extendInScope (Subst in_scope ids tvs) v
251 = Subst (in_scope `extendInScopeSet` v)
252 (ids `delVarEnv` v) (tvs `delVarEnv` v)
254 -- | Add the 'Var's to the in-scope set: see also 'extendInScope'
255 extendInScopeList :: Subst -> [Var] -> Subst
256 extendInScopeList (Subst in_scope ids tvs) vs
257 = Subst (in_scope `extendInScopeSetList` vs)
258 (ids `delVarEnvList` vs) (tvs `delVarEnvList` vs)
260 -- | Optimized version of 'extendInScopeList' that can be used if you are certain
261 -- all the things being added are 'Id's and hence none are 'TyVar's
262 extendInScopeIds :: Subst -> [Id] -> Subst
263 extendInScopeIds (Subst in_scope ids tvs) vs
264 = Subst (in_scope `extendInScopeSetList` vs)
265 (ids `delVarEnvList` vs) tvs
268 Pretty printing, for debugging only
271 instance Outputable Subst where
272 ppr (Subst in_scope ids tvs)
273 = ptext (sLit "<InScope =") <+> braces (fsep (map ppr (varEnvElts (getInScopeVars in_scope))))
274 $$ ptext (sLit " IdSubst =") <+> ppr ids
275 $$ ptext (sLit " TvSubst =") <+> ppr tvs
280 %************************************************************************
282 Substituting expressions
284 %************************************************************************
287 -- | Apply a substititon to an entire 'CoreExpr'. Rememeber, you may only
288 -- apply the substitution /once/: see "CoreSubst#apply_once"
290 -- Do *not* attempt to short-cut in the case of an empty substitution!
291 -- See Note [Extending the Subst]
292 substExprSC :: SDoc -> Subst -> CoreExpr -> CoreExpr
293 substExprSC _doc subst orig_expr
294 | isEmptySubst subst = orig_expr
295 | otherwise = -- pprTrace "enter subst-expr" (doc $$ ppr orig_expr) $
296 subst_expr subst orig_expr
298 substExpr :: SDoc -> Subst -> CoreExpr -> CoreExpr
299 substExpr _doc subst orig_expr = subst_expr subst orig_expr
301 subst_expr :: Subst -> CoreExpr -> CoreExpr
302 subst_expr subst expr
305 go (Var v) = lookupIdSubst (text "subst_expr") subst v
306 go (Type ty) = Type (substTy subst ty)
307 go (Lit lit) = Lit lit
308 go (App fun arg) = App (go fun) (go arg)
309 go (Note note e) = Note (go_note note) (go e)
310 go (Cast e co) = Cast (go e) (optCoercion (getTvSubst subst) co)
311 -- Do not optimise even identity coercions
312 -- Reason: substitution applies to the LHS of RULES, and
313 -- if you "optimise" an identity coercion, you may
314 -- lose a binder. We optimise the LHS of rules at
317 go (Lam bndr body) = Lam bndr' (subst_expr subst' body)
319 (subst', bndr') = substBndr subst bndr
321 go (Let bind body) = Let bind' (subst_expr subst' body)
323 (subst', bind') = substBind subst bind
325 go (Case scrut bndr ty alts) = Case (go scrut) bndr' (substTy subst ty) (map (go_alt subst') alts)
327 (subst', bndr') = substBndr subst bndr
329 go_alt subst (con, bndrs, rhs) = (con, bndrs', subst_expr subst' rhs)
331 (subst', bndrs') = substBndrs subst bndrs
335 -- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst'
336 -- that should be used by subsequent substitutons.
337 substBind, substBindSC :: Subst -> CoreBind -> (Subst, CoreBind)
339 substBindSC subst bind -- Short-cut if the substitution is empty
340 | not (isEmptySubst subst)
341 = substBind subst bind
344 NonRec bndr rhs -> (subst', NonRec bndr' rhs)
346 (subst', bndr') = substBndr subst bndr
347 Rec pairs -> (subst', Rec (bndrs' `zip` rhss'))
349 (bndrs, rhss) = unzip pairs
350 (subst', bndrs') = substRecBndrs subst bndrs
351 rhss' | isEmptySubst subst' = rhss
352 | otherwise = map (subst_expr subst') rhss
354 substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (subst_expr subst rhs))
356 (subst', bndr') = substBndr subst bndr
358 substBind subst (Rec pairs) = (subst', Rec (bndrs' `zip` rhss'))
360 (bndrs, rhss) = unzip pairs
361 (subst', bndrs') = substRecBndrs subst bndrs
362 rhss' = map (subst_expr subst') rhss
366 -- | De-shadowing the program is sometimes a useful pre-pass. It can be done simply
367 -- by running over the bindings with an empty substitution, becuase substitution
368 -- returns a result that has no-shadowing guaranteed.
370 -- (Actually, within a single /type/ there might still be shadowing, because
371 -- 'substTy' is a no-op for the empty substitution, but that's probably OK.)
373 -- [Aug 09] This function is not used in GHC at the moment, but seems so
374 -- short and simple that I'm going to leave it here
375 deShadowBinds :: [CoreBind] -> [CoreBind]
376 deShadowBinds binds = snd (mapAccumL substBind emptySubst binds)
380 %************************************************************************
384 %************************************************************************
386 Remember that substBndr and friends are used when doing expression
387 substitution only. Their only business is substitution, so they
388 preserve all IdInfo (suitably substituted). For example, we *want* to
389 preserve occ info in rules.
392 -- | Substitutes a 'Var' for another one according to the 'Subst' given, returning
393 -- the result and an updated 'Subst' that should be used by subsequent substitutons.
394 -- 'IdInfo' is preserved by this process, although it is substituted into appropriately.
395 substBndr :: Subst -> Var -> (Subst, Var)
397 | isTyCoVar bndr = substTyVarBndr subst bndr
398 | otherwise = substIdBndr (text "var-bndr") subst subst bndr
400 -- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right
401 substBndrs :: Subst -> [Var] -> (Subst, [Var])
402 substBndrs subst bndrs = mapAccumL substBndr subst bndrs
404 -- | Substitute in a mutually recursive group of 'Id's
405 substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
406 substRecBndrs subst bndrs
407 = (new_subst, new_bndrs)
408 where -- Here's the reason we need to pass rec_subst to subst_id
409 (new_subst, new_bndrs) = mapAccumL (substIdBndr (text "rec-bndr") new_subst) subst bndrs
415 -> Subst -- ^ Substitution to use for the IdInfo
416 -> Subst -> Id -- ^ Substitition and Id to transform
417 -> (Subst, Id) -- ^ Transformed pair
418 -- NB: unfolding may be zapped
420 substIdBndr _doc rec_subst subst@(Subst in_scope env tvs) old_id
421 = -- pprTrace "substIdBndr" (doc $$ ppr old_id $$ ppr in_scope) $
422 (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
424 id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
425 id2 | no_type_change = id1
426 | otherwise = setIdType id1 (substTy subst old_ty)
428 old_ty = idType old_id
429 no_type_change = isEmptyVarEnv tvs ||
430 isEmptyVarSet (Type.tyVarsOfType old_ty)
432 -- new_id has the right IdInfo
433 -- The lazy-set is because we're in a loop here, with
434 -- rec_subst, when dealing with a mutually-recursive group
435 new_id = maybeModifyIdInfo mb_new_info id2
436 mb_new_info = substIdInfo rec_subst id2 (idInfo id2)
437 -- NB: unfolding info may be zapped
439 -- Extend the substitution if the unique has changed
440 -- See the notes with substTyVarBndr for the delVarEnv
441 new_env | no_change = delVarEnv env old_id
442 | otherwise = extendVarEnv env old_id (Var new_id)
444 no_change = id1 == old_id
445 -- See Note [Extending the Subst]
446 -- it's /not/ necessary to check mb_new_info and no_type_change
449 Now a variant that unconditionally allocates a new unique.
450 It also unconditionally zaps the OccInfo.
453 -- | Very similar to 'substBndr', but it always allocates a new 'Unique' for
454 -- each variable in its output. It substitutes the IdInfo though.
455 cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
456 cloneIdBndr subst us old_id
457 = clone_id subst subst (old_id, uniqFromSupply us)
459 -- | Applies 'cloneIdBndr' to a number of 'Id's, accumulating a final
460 -- substitution from left to right
461 cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
462 cloneIdBndrs subst us ids
463 = mapAccumL (clone_id subst) subst (ids `zip` uniqsFromSupply us)
465 -- | Clone a mutually recursive group of 'Id's
466 cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
467 cloneRecIdBndrs subst us ids
470 (subst', ids') = mapAccumL (clone_id subst') subst
471 (ids `zip` uniqsFromSupply us)
473 -- Just like substIdBndr, except that it always makes a new unique
474 -- It is given the unique to use
475 clone_id :: Subst -- Substitution for the IdInfo
476 -> Subst -> (Id, Unique) -- Substitition and Id to transform
477 -> (Subst, Id) -- Transformed pair
479 clone_id rec_subst subst@(Subst in_scope env tvs) (old_id, uniq)
480 = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
482 id1 = setVarUnique old_id uniq
483 id2 = substIdType subst id1
484 new_id = maybeModifyIdInfo (substIdInfo rec_subst id2 (idInfo old_id)) id2
485 new_env = extendVarEnv env old_id (Var new_id)
489 %************************************************************************
493 %************************************************************************
495 For types we just call the corresponding function in Type, but we have
496 to repackage the substitution, from a Subst to a TvSubst
499 substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)
500 substTyVarBndr (Subst in_scope id_env tv_env) tv
501 = case Type.substTyVarBndr (TvSubst in_scope tv_env) tv of
502 (TvSubst in_scope' tv_env', tv')
503 -> (Subst in_scope' id_env tv_env', tv')
505 -- | See 'Type.substTy'
506 substTy :: Subst -> Type -> Type
507 substTy subst ty = Type.substTy (getTvSubst subst) ty
509 getTvSubst :: Subst -> TvSubst
510 getTvSubst (Subst in_scope _id_env tv_env) = TvSubst in_scope tv_env
514 %************************************************************************
516 \section{IdInfo substitution}
518 %************************************************************************
521 substIdType :: Subst -> Id -> Id
522 substIdType subst@(Subst _ _ tv_env) id
523 | isEmptyVarEnv tv_env || isEmptyVarSet (Type.tyVarsOfType old_ty) = id
524 | otherwise = setIdType id (substTy subst old_ty)
525 -- The tyVarsOfType is cheaper than it looks
526 -- because we cache the free tyvars of the type
527 -- in a Note in the id's type itself
532 -- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'.
533 substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo
534 substIdInfo subst new_id info
535 | nothing_to_do = Nothing
536 | otherwise = Just (info `setSpecInfo` substSpec subst new_id old_rules
537 `setUnfoldingInfo` substUnfolding subst old_unf)
539 old_rules = specInfo info
540 old_unf = unfoldingInfo info
541 nothing_to_do = isEmptySpecInfo old_rules && isClosedUnfolding old_unf
545 -- | Substitutes for the 'Id's within an unfolding
546 substUnfolding, substUnfoldingSC :: Subst -> Unfolding -> Unfolding
547 -- Seq'ing on the returned Unfolding is enough to cause
548 -- all the substitutions to happen completely
550 substUnfoldingSC subst unf -- Short-cut version
551 | isEmptySubst subst = unf
552 | otherwise = substUnfolding subst unf
554 substUnfolding subst (DFunUnfolding ar con args)
555 = DFunUnfolding ar con (map (substExpr (text "dfun-unf") subst) args)
557 substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_src = src })
558 -- Retain an InlineRule!
559 | not (isStableSource src) -- Zap an unstable unfolding, to save substitution work
561 | otherwise -- But keep a stable one!
562 = seqExpr new_tmpl `seq`
564 unf { uf_tmpl = new_tmpl, uf_src = new_src }
566 new_tmpl = substExpr (text "subst-unf") subst tmpl
567 new_src = substUnfoldingSource subst src
569 substUnfolding _ unf = unf -- NoUnfolding, OtherCon
572 substUnfoldingSource :: Subst -> UnfoldingSource -> UnfoldingSource
573 substUnfoldingSource (Subst in_scope ids _) (InlineWrapper wkr)
574 | Just wkr_expr <- lookupVarEnv ids wkr
576 Var w1 -> InlineWrapper w1
577 _other -> -- WARN( True, text "Interesting! CoreSubst.substWorker1:" <+> ppr wkr
578 -- <+> ifPprDebug (equals <+> ppr wkr_expr) )
579 -- Note [Worker inlining]
580 InlineStable -- It's not a wrapper any more, but still inline it!
582 | Just w1 <- lookupInScope in_scope wkr = InlineWrapper w1
583 | otherwise = -- WARN( True, text "Interesting! CoreSubst.substWorker2:" <+> ppr wkr )
584 -- This can legitimately happen. The worker has been inlined and
585 -- dropped as dead code, because we don't treat the UnfoldingSource
586 -- as an "occurrence".
587 -- Note [Worker inlining]
590 substUnfoldingSource _ src = src
593 substIdOcc :: Subst -> Id -> Id
594 -- These Ids should not be substituted to non-Ids
595 substIdOcc subst v = case lookupIdSubst (text "substIdOcc") subst v of
597 other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst])
600 -- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id'
601 substSpec :: Subst -> Id -> SpecInfo -> SpecInfo
602 substSpec subst new_id (SpecInfo rules rhs_fvs)
603 = seqSpecInfo new_spec `seq` new_spec
605 subst_ru_fn = const (idName new_id)
606 new_spec = SpecInfo (map (substRule subst subst_ru_fn) rules)
607 (substVarSet subst rhs_fvs)
610 substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule]
611 substRulesForImportedIds subst rules
612 = map (substRule subst not_needed) rules
614 not_needed name = pprPanic "substRulesForImportedIds" (ppr name)
617 substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule
619 -- The subst_ru_fn argument is applied to substitute the ru_fn field
621 -- - Rules for *imported* Ids never change ru_fn
622 -- - Rules for *local* Ids are in the IdInfo for that Id,
623 -- and the ru_fn field is simply replaced by the new name
626 substRule _ _ rule@(BuiltinRule {}) = rule
627 substRule subst subst_ru_fn rule@(Rule { ru_bndrs = bndrs, ru_args = args
628 , ru_fn = fn_name, ru_rhs = rhs
629 , ru_local = is_local })
630 = rule { ru_bndrs = bndrs',
632 then subst_ru_fn fn_name
634 ru_args = map (substExpr (text "subst-rule" <+> ppr fn_name) subst') args,
635 ru_rhs = simpleOptExprWith subst' rhs }
636 -- Do simple optimisation on RHS, in case substitution lets
637 -- you improve it. The real simplifier never gets to look at it.
639 (subst', bndrs') = substBndrs subst bndrs
642 substVarSet :: Subst -> VarSet -> VarSet
643 substVarSet subst fvs
644 = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
647 | isId fv = exprFreeVars (lookupIdSubst (text "substVarSet") subst fv)
648 | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)
651 Note [Worker inlining]
652 ~~~~~~~~~~~~~~~~~~~~~~
653 A worker can get sustituted away entirely.
654 - it might be trivial
655 - it might simply be very small
656 We do not treat an InlWrapper as an 'occurrence' in the occurence
657 analyser, so it's possible that the worker is not even in scope any more.
659 In all all these cases we simply drop the special case, returning to
660 InlVanilla. The WARN is just so I can see if it happens a lot.
663 %************************************************************************
665 The Very Simple Optimiser
667 %************************************************************************
670 simpleOptExpr :: CoreExpr -> CoreExpr
671 -- Do simple optimisation on an expression
672 -- The optimisation is very straightforward: just
673 -- inline non-recursive bindings that are used only once,
674 -- or where the RHS is trivial
676 -- The result is NOT guaranteed occurence-analysed, becuase
677 -- in (let x = y in ....) we substitute for x; so y's occ-info
678 -- may change radically
681 = -- pprTrace "simpleOptExpr" (ppr init_subst $$ ppr expr)
682 simpleOptExprWith init_subst expr
684 init_subst = mkEmptySubst (mkInScopeSet (exprFreeVars expr))
685 -- It's potentially important to make a proper in-scope set
686 -- Consider let x = ..y.. in \y. ...x...
687 -- Then we should remember to clone y before substituting
688 -- for x. It's very unlikely to occur, because we probably
689 -- won't *be* substituting for x if it occurs inside a
692 -- It's a bit painful to call exprFreeVars, because it makes
693 -- three passes instead of two (occ-anal, and go)
695 simpleOptExprWith :: Subst -> InExpr -> OutExpr
696 simpleOptExprWith subst expr = simple_opt_expr subst (occurAnalyseExpr expr)
698 ----------------------
699 simpleOptPgm :: DynFlags -> [CoreBind] -> [CoreRule] -> IO ([CoreBind], [CoreRule])
700 simpleOptPgm dflags binds rules
701 = do { dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
702 (pprCoreBindings occ_anald_binds);
704 ; return (reverse binds', substRulesForImportedIds subst' rules) }
706 occ_anald_binds = occurAnalysePgm Nothing {- No rules active -}
708 (subst', binds') = foldl do_one (emptySubst, []) occ_anald_binds
710 do_one (subst, binds') bind
711 = case simple_opt_bind subst bind of
712 (subst', Nothing) -> (subst', binds')
713 (subst', Just bind') -> (subst', bind':binds')
715 ----------------------
720 type InExpr = CoreExpr
721 type OutExpr = CoreExpr
723 -- In these functions the substitution maps InVar -> OutExpr
725 ----------------------
726 simple_opt_expr :: Subst -> InExpr -> OutExpr
727 simple_opt_expr subst expr
730 go (Var v) = lookupIdSubst (text "simpleOptExpr") subst v
731 go (App e1 e2) = simple_app subst e1 [go e2]
732 go (Type ty) = Type (substTy subst ty)
733 go (Lit lit) = Lit lit
734 go (Note note e) = Note note (go e)
735 go (Cast e co) | isIdentityCoercion co' = go e
736 | otherwise = Cast (go e) co'
738 co' = substTy subst co
740 go (Let bind body) = case simple_opt_bind subst bind of
741 (subst', Nothing) -> simple_opt_expr subst' body
742 (subst', Just bind) -> Let bind (simple_opt_expr subst' body)
744 go lam@(Lam {}) = go_lam [] subst lam
745 go (Case e b ty as) = Case (go e) b' (substTy subst ty)
746 (map (go_alt subst') as)
748 (subst', b') = subst_opt_bndr subst b
750 ----------------------
751 go_alt subst (con, bndrs, rhs)
752 = (con, bndrs', simple_opt_expr subst' rhs)
754 (subst', bndrs') = subst_opt_bndrs subst bndrs
756 ----------------------
757 -- go_lam tries eta reduction
758 go_lam bs' subst (Lam b e)
759 = go_lam (b':bs') subst' e
761 (subst', b') = subst_opt_bndr subst b
763 | Just etad_e <- tryEtaReduce bs e' = etad_e
764 | otherwise = mkLams bs e'
767 e' = simple_opt_expr subst e
769 ----------------------
770 -- simple_app collects arguments for beta reduction
771 simple_app :: Subst -> InExpr -> [OutExpr] -> CoreExpr
772 simple_app subst (App e1 e2) as
773 = simple_app subst e1 (simple_opt_expr subst e2 : as)
774 simple_app subst (Lam b e) (a:as)
775 = case maybe_substitute subst b a of
776 Just ext_subst -> simple_app ext_subst e as
777 Nothing -> Let (NonRec b2 a) (simple_app subst' e as)
779 (subst', b') = subst_opt_bndr subst b
780 b2 = add_info subst' b b'
781 simple_app subst e as
782 = foldl App (simple_opt_expr subst e) as
784 ----------------------
785 simple_opt_bind :: Subst -> CoreBind -> (Subst, Maybe CoreBind)
786 simple_opt_bind subst (Rec prs)
787 = (subst'', Just (Rec (reverse rev_prs')))
789 (subst', bndrs') = subst_opt_bndrs subst (map fst prs)
790 (subst'', rev_prs') = foldl do_pr (subst', []) (prs `zip` bndrs')
791 do_pr (subst, prs) ((b,r), b')
792 = case maybe_substitute subst b r2 of
793 Just subst' -> (subst', prs)
794 Nothing -> (subst, (b2,r2):prs)
796 b2 = add_info subst b b'
797 r2 = simple_opt_expr subst r
799 simple_opt_bind subst (NonRec b r)
800 = case maybe_substitute subst b r' of
801 Just ext_subst -> (ext_subst, Nothing)
802 Nothing -> (subst', Just (NonRec b2 r'))
804 r' = simple_opt_expr subst r
805 (subst', b') = subst_opt_bndr subst b
806 b2 = add_info subst' b b'
808 ----------------------
809 maybe_substitute :: Subst -> InVar -> OutExpr -> Maybe Subst
810 -- (maybe_substitute subst in_var out_rhs)
811 -- either extends subst with (in_var -> out_rhs)
812 -- or returns Nothing
813 maybe_substitute subst b r
814 | Type ty <- r -- let a::* = TYPE ty in <body>
815 = ASSERT( isTyCoVar b )
816 Just (extendTvSubst subst b ty)
818 | isId b -- let x = e in <body>
819 , safe_to_inline (idOccInfo b)
820 , isAlwaysActive (idInlineActivation b) -- Note [Inline prag in simplOpt]
821 , not (isStableUnfolding (idUnfolding b))
822 , not (isExportedId b)
823 = Just (extendIdSubst subst b r)
828 -- Unconditionally safe to inline
829 safe_to_inline :: OccInfo -> Bool
830 safe_to_inline (IAmALoopBreaker {}) = False
831 safe_to_inline IAmDead = True
832 safe_to_inline (OneOcc in_lam one_br _) = (not in_lam && one_br) || exprIsTrivial r
833 safe_to_inline NoOccInfo = exprIsTrivial r
835 ----------------------
836 subst_opt_bndr :: Subst -> InVar -> (Subst, OutVar)
837 subst_opt_bndr subst bndr
838 | isTyCoVar bndr = substTyVarBndr subst bndr
839 | otherwise = subst_opt_id_bndr subst bndr
841 subst_opt_id_bndr :: Subst -> InId -> (Subst, OutId)
842 -- Nuke all fragile IdInfo, unfolding, and RULES;
843 -- it gets added back later by add_info
844 -- Rather like SimplEnv.substIdBndr
846 -- It's important to zap fragile OccInfo (which CoreSubst.SubstIdBndr
847 -- carefully does not do) because simplOptExpr invalidates it
849 subst_opt_id_bndr subst@(Subst in_scope id_subst tv_subst) old_id
850 = (Subst new_in_scope new_id_subst tv_subst, new_id)
852 id1 = uniqAway in_scope old_id
853 id2 = setIdType id1 (substTy subst (idType old_id))
854 new_id = zapFragileIdInfo id2 -- Zaps rules, worker-info, unfolding
855 -- and fragile OccInfo
856 new_in_scope = in_scope `extendInScopeSet` new_id
858 -- Extend the substitution if the unique has changed,
859 -- or there's some useful occurrence information
860 -- See the notes with substTyVarBndr for the delSubstEnv
861 new_id_subst | new_id /= old_id
862 = extendVarEnv id_subst old_id (Var new_id)
864 = delVarEnv id_subst old_id
866 ----------------------
867 subst_opt_bndrs :: Subst -> [InVar] -> (Subst, [OutVar])
868 subst_opt_bndrs subst bndrs
869 = mapAccumL subst_opt_bndr subst bndrs
871 ----------------------
872 add_info :: Subst -> InVar -> OutVar -> OutVar
873 add_info subst old_bndr new_bndr
874 | isTyCoVar old_bndr = new_bndr
875 | otherwise = maybeModifyIdInfo mb_new_info new_bndr
877 mb_new_info = substIdInfo subst new_bndr (idInfo old_bndr)
880 Note [Inline prag in simplOpt]
881 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
882 If there's an INLINE/NOINLINE pragma that restricts the phase in
883 which the binder can be inlined, we don't inline here; after all,
884 we don't know what phase we're in. Here's an example
886 foo :: Int -> Int -> Int
890 {-# INLINE [1] inner #-}
896 When inlining 'foo' in 'bar' we want the let-binding for 'inner'
897 to remain visible until Phase 1