2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[SimplMonad]{The simplifier Monad}
8 InId, InBind, InExpr, InAlt, InArg, InType, InBndr, InVar,
9 OutId, OutTyVar, OutBind, OutExpr, OutAlt, OutArg, OutType, OutBndr, OutVar,
10 InCoercion, OutCoercion,
12 -- The simplifier mode
13 setMode, getMode, updMode,
16 SwitchChecker, SwitchResult(..), getSwitchChecker, getSimplIntSwitch,
17 isAmongSimpl, intSwitchSet, switchIsOn,
19 setEnclosingCC, getEnclosingCC,
22 SimplEnv(..), StaticEnv, pprSimplEnv, -- Temp not abstract
23 mkSimplEnv, extendIdSubst, SimplEnv.extendTvSubst,
24 zapSubstEnv, setSubstEnv,
25 getInScope, setInScope, setInScopeSet, modifyInScope, addNewInScopeIds,
26 getSimplRules, inGentleMode,
28 SimplSR(..), mkContEx, substId, lookupRecBndr,
30 simplNonRecBndr, simplRecBndrs, simplLamBndr, simplLamBndrs,
31 simplBinder, simplBinders, addBndrRules,
32 substExpr, substTy, substTyVar, getTvSubst, mkCoreSubst,
35 Floats, emptyFloats, isEmptyFloats, addNonRec, addFloats, extendFloats,
36 wrapFloats, floatBinds, setFloats, zapFloats, addRecFloats,
37 doFloatFromRhs, getFloats
40 #include "HsVersions.h"
43 import CoreMonad ( SimplifierMode(..) )
53 import qualified CoreSubst
54 import qualified Type ( substTy, substTyVarBndr, substTyVar )
55 import Type hiding ( substTy, substTyVarBndr, substTyVar )
65 %************************************************************************
67 \subsection[Simplify-types]{Type declarations}
69 %************************************************************************
72 type InBndr = CoreBndr
73 type InVar = Var -- Not yet cloned
74 type InId = Id -- Not yet cloned
75 type InType = Type -- Ditto
76 type InBind = CoreBind
77 type InExpr = CoreExpr
80 type InCoercion = Coercion
82 type OutBndr = CoreBndr
83 type OutVar = Var -- Cloned
84 type OutId = Id -- Cloned
85 type OutTyVar = TyVar -- Cloned
86 type OutType = Type -- Cloned
87 type OutCoercion = Coercion
88 type OutBind = CoreBind
89 type OutExpr = CoreExpr
94 %************************************************************************
96 \subsubsection{The @SimplEnv@ type}
98 %************************************************************************
104 ----------- Static part of the environment -----------
105 -- Static in the sense of lexically scoped,
106 -- wrt the original expression
108 seMode :: SimplifierMode,
109 seChkr :: SwitchChecker,
110 seCC :: CostCentreStack, -- The enclosing CCS (when profiling)
112 -- The current substitution
113 seTvSubst :: TvSubstEnv, -- InTyVar |--> OutType
114 seIdSubst :: SimplIdSubst, -- InId |--> OutExpr
116 ----------- Dynamic part of the environment -----------
117 -- Dynamic in the sense of describing the setup where
118 -- the expression finally ends up
120 -- The current set of in-scope variables
121 -- They are all OutVars, and all bound in this module
122 seInScope :: InScopeSet, -- OutVars only
123 -- Includes all variables bound by seFloats
125 -- See Note [Simplifier floats]
128 type StaticEnv = SimplEnv -- Just the static part is relevant
130 pprSimplEnv :: SimplEnv -> SDoc
131 -- Used for debugging; selective
133 = vcat [ptext (sLit "TvSubst:") <+> ppr (seTvSubst env),
134 ptext (sLit "IdSubst:") <+> ppr (seIdSubst env),
135 ptext (sLit "InScope:") <+> vcat (map ppr_one in_scope_vars)
138 in_scope_vars = varEnvElts (getInScopeVars (seInScope env))
139 ppr_one v | isId v = ppr v <+> ppr (idUnfolding v)
142 type SimplIdSubst = IdEnv SimplSR -- IdId |--> OutExpr
143 -- See Note [Extending the Subst] in CoreSubst
146 = DoneEx OutExpr -- Completed term
147 | DoneId OutId -- Completed term variable
148 | ContEx TvSubstEnv -- A suspended substitution
152 instance Outputable SimplSR where
153 ppr (DoneEx e) = ptext (sLit "DoneEx") <+> ppr e
154 ppr (DoneId v) = ptext (sLit "DoneId") <+> ppr v
155 ppr (ContEx _tv _id e) = vcat [ptext (sLit "ContEx") <+> ppr e {-,
156 ppr (filter_env tv), ppr (filter_env id) -}]
158 -- fvs = exprFreeVars e
159 -- filter_env env = filterVarEnv_Directly keep env
160 -- keep uniq _ = uniq `elemUFM_Directly` fvs
163 Note [SimplEnv invariants]
164 ~~~~~~~~~~~~~~~~~~~~~~~~~~
166 The in-scope part of Subst includes *all* in-scope TyVars and Ids
167 The elements of the set may have better IdInfo than the
168 occurrences of in-scope Ids, and (more important) they will
169 have a correctly-substituted type. So we use a lookup in this
170 set to replace occurrences
172 The Ids in the InScopeSet are replete with their Rules,
173 and as we gather info about the unfolding of an Id, we replace
174 it in the in-scope set.
176 The in-scope set is actually a mapping OutVar -> OutVar, and
177 in case expressions we sometimes bind
180 The substitution is *apply-once* only, because InIds and OutIds can overlap.
181 For example, we generally omit mappings
183 from the substitution, when we decide not to clone a77, but it's quite
184 legitimate to put the mapping in the substitution anyway.
186 Furthermore, consider
187 let x = case k of I# x77 -> ... in
188 let y = case k of I# x77 -> ... in ...
189 and suppose the body is strict in both x and y. Then the simplifier
190 will pull the first (case k) to the top; so the second (case k) will
191 cancel out, mapping x77 to, well, x77! But one is an in-Id and the
194 Of course, the substitution *must* applied! Things in its domain
195 simply aren't necessarily bound in the result.
197 * substId adds a binding (DoneId new_id) to the substitution if
198 the Id's unique has changed
200 Note, though that the substitution isn't necessarily extended
201 if the type of the Id changes. Why not? Because of the next point:
203 * We *always, always* finish by looking up in the in-scope set
204 any variable that doesn't get a DoneEx or DoneVar hit in the substitution.
205 Reason: so that we never finish up with a "old" Id in the result.
206 An old Id might point to an old unfolding and so on... which gives a space leak.
208 [The DoneEx and DoneVar hits map to "new" stuff.]
210 * It follows that substExpr must not do a no-op if the substitution is empty.
211 substType is free to do so, however.
213 * When we come to a let-binding (say) we generate new IdInfo, including an
214 unfolding, attach it to the binder, and add this newly adorned binder to
215 the in-scope set. So all subsequent occurrences of the binder will get mapped
216 to the full-adorned binder, which is also the one put in the binding site.
218 * The in-scope "set" usually maps x->x; we use it simply for its domain.
219 But sometimes we have two in-scope Ids that are synomyms, and should
220 map to the same target: x->x, y->x. Notably:
222 That's why the "set" is actually a VarEnv Var
226 mkSimplEnv :: SwitchChecker -> SimplifierMode -> SimplEnv
227 mkSimplEnv switches mode
228 = SimplEnv { seChkr = switches, seCC = subsumedCCS,
229 seMode = mode, seInScope = emptyInScopeSet,
230 seFloats = emptyFloats,
231 seTvSubst = emptyVarEnv, seIdSubst = emptyVarEnv }
232 -- The top level "enclosing CC" is "SUBSUMED".
234 ---------------------
235 getSwitchChecker :: SimplEnv -> SwitchChecker
236 getSwitchChecker env = seChkr env
238 ---------------------
239 getMode :: SimplEnv -> SimplifierMode
240 getMode env = seMode env
242 setMode :: SimplifierMode -> SimplEnv -> SimplEnv
243 setMode mode env = env { seMode = mode }
245 updMode :: (SimplifierMode -> SimplifierMode) -> SimplEnv -> SimplEnv
246 updMode upd env = env { seMode = upd (seMode env) }
248 inGentleMode :: SimplEnv -> Bool
249 inGentleMode env = case seMode env of
250 SimplGently {} -> True
253 ---------------------
254 getEnclosingCC :: SimplEnv -> CostCentreStack
255 getEnclosingCC env = seCC env
257 setEnclosingCC :: SimplEnv -> CostCentreStack -> SimplEnv
258 setEnclosingCC env cc = env {seCC = cc}
260 ---------------------
261 extendIdSubst :: SimplEnv -> Id -> SimplSR -> SimplEnv
262 extendIdSubst env@(SimplEnv {seIdSubst = subst}) var res
263 = env {seIdSubst = extendVarEnv subst var res}
265 extendTvSubst :: SimplEnv -> TyVar -> Type -> SimplEnv
266 extendTvSubst env@(SimplEnv {seTvSubst = subst}) var res
267 = env {seTvSubst = extendVarEnv subst var res}
269 ---------------------
270 getInScope :: SimplEnv -> InScopeSet
271 getInScope env = seInScope env
273 setInScopeSet :: SimplEnv -> InScopeSet -> SimplEnv
274 setInScopeSet env in_scope = env {seInScope = in_scope}
276 setInScope :: SimplEnv -> SimplEnv -> SimplEnv
277 -- Set the in-scope set, and *zap* the floats
278 setInScope env env_with_scope
279 = env { seInScope = seInScope env_with_scope,
280 seFloats = emptyFloats }
282 setFloats :: SimplEnv -> SimplEnv -> SimplEnv
283 -- Set the in-scope set *and* the floats
284 setFloats env env_with_floats
285 = env { seInScope = seInScope env_with_floats,
286 seFloats = seFloats env_with_floats }
288 addNewInScopeIds :: SimplEnv -> [CoreBndr] -> SimplEnv
289 -- The new Ids are guaranteed to be freshly allocated
290 addNewInScopeIds env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) vs
291 = env { seInScope = in_scope `extendInScopeSetList` vs,
292 seIdSubst = id_subst `delVarEnvList` vs }
293 -- Why delete? Consider
294 -- let x = a*b in (x, \x -> x+3)
295 -- We add [x |-> a*b] to the substitution, but we must
296 -- _delete_ it from the substitution when going inside
299 modifyInScope :: SimplEnv -> CoreBndr -> SimplEnv
300 -- The variable should already be in scope, but
301 -- replace the existing version with this new one
302 -- which has more information
303 modifyInScope env@(SimplEnv {seInScope = in_scope}) v
304 = env {seInScope = extendInScopeSet in_scope v}
306 ---------------------
307 zapSubstEnv :: SimplEnv -> SimplEnv
308 zapSubstEnv env = env {seTvSubst = emptyVarEnv, seIdSubst = emptyVarEnv}
310 setSubstEnv :: SimplEnv -> TvSubstEnv -> SimplIdSubst -> SimplEnv
311 setSubstEnv env tvs ids = env { seTvSubst = tvs, seIdSubst = ids }
313 mkContEx :: SimplEnv -> InExpr -> SimplSR
314 mkContEx (SimplEnv { seTvSubst = tvs, seIdSubst = ids }) e = ContEx tvs ids e
319 %************************************************************************
323 %************************************************************************
325 Note [Simplifier floats]
326 ~~~~~~~~~~~~~~~~~~~~~~~~~
327 The Floats is a bunch of bindings, classified by a FloatFlag.
329 NonRec x (y:ys) FltLifted
330 Rec [(x,rhs)] FltLifted
332 NonRec x# (y +# 3) FltOkSpec -- Unboxed, but ok-for-spec'n
334 NonRec x# (a /# b) FltCareful
335 NonRec x* (f y) FltCareful -- Strict binding; might fail or diverge
336 NonRec x# (f y) FltCareful -- Unboxed binding: might fail or diverge
337 -- (where f :: Int -> Int#)
340 data Floats = Floats (OrdList OutBind) FloatFlag
341 -- See Note [Simplifier floats]
344 = FltLifted -- All bindings are lifted and lazy
345 -- Hence ok to float to top level, or recursive
347 | FltOkSpec -- All bindings are FltLifted *or*
348 -- strict (perhaps because unlifted,
349 -- perhaps because of a strict binder),
350 -- *and* ok-for-speculation
351 -- Hence ok to float out of the RHS
352 -- of a lazy non-recursive let binding
353 -- (but not to top level, or into a rec group)
355 | FltCareful -- At least one binding is strict (or unlifted)
356 -- and not guaranteed cheap
357 -- Do not float these bindings out of a lazy let
359 instance Outputable Floats where
360 ppr (Floats binds ff) = ppr ff $$ ppr (fromOL binds)
362 instance Outputable FloatFlag where
363 ppr FltLifted = ptext (sLit "FltLifted")
364 ppr FltOkSpec = ptext (sLit "FltOkSpec")
365 ppr FltCareful = ptext (sLit "FltCareful")
367 andFF :: FloatFlag -> FloatFlag -> FloatFlag
368 andFF FltCareful _ = FltCareful
369 andFF FltOkSpec FltCareful = FltCareful
370 andFF FltOkSpec _ = FltOkSpec
371 andFF FltLifted flt = flt
373 classifyFF :: CoreBind -> FloatFlag
374 classifyFF (Rec _) = FltLifted
375 classifyFF (NonRec bndr rhs)
376 | not (isStrictId bndr) = FltLifted
377 | exprOkForSpeculation rhs = FltOkSpec
378 | otherwise = FltCareful
380 doFloatFromRhs :: TopLevelFlag -> RecFlag -> Bool -> OutExpr -> SimplEnv -> Bool
381 doFloatFromRhs lvl rec str rhs (SimplEnv {seFloats = Floats fs ff})
382 = not (isNilOL fs) && want_to_float && can_float
384 want_to_float = isTopLevel lvl || exprIsExpandable rhs
385 can_float = case ff of
387 FltOkSpec -> isNotTopLevel lvl && isNonRec rec
388 FltCareful -> isNotTopLevel lvl && isNonRec rec && str
393 emptyFloats :: Floats
394 emptyFloats = Floats nilOL FltLifted
396 unitFloat :: OutBind -> Floats
397 -- A single-binding float
398 unitFloat bind = Floats (unitOL bind) (classifyFF bind)
400 addNonRec :: SimplEnv -> OutId -> OutExpr -> SimplEnv
401 -- Add a non-recursive binding and extend the in-scope set
402 -- The latter is important; the binder may already be in the
403 -- in-scope set (although it might also have been created with newId)
404 -- but it may now have more IdInfo
406 = env { seFloats = seFloats env `addFlts` unitFloat (NonRec id rhs),
407 seInScope = extendInScopeSet (seInScope env) id }
409 extendFloats :: SimplEnv -> OutBind -> SimplEnv
410 -- Add these bindings to the floats, and extend the in-scope env too
411 extendFloats env bind
412 = env { seFloats = seFloats env `addFlts` unitFloat bind,
413 seInScope = extendInScopeSetList (seInScope env) bndrs }
415 bndrs = bindersOf bind
417 addFloats :: SimplEnv -> SimplEnv -> SimplEnv
418 -- Add the floats for env2 to env1;
419 -- *plus* the in-scope set for env2, which is bigger
420 -- than that for env1
422 = env1 {seFloats = seFloats env1 `addFlts` seFloats env2,
423 seInScope = seInScope env2 }
425 addFlts :: Floats -> Floats -> Floats
426 addFlts (Floats bs1 l1) (Floats bs2 l2)
427 = Floats (bs1 `appOL` bs2) (l1 `andFF` l2)
429 zapFloats :: SimplEnv -> SimplEnv
430 zapFloats env = env { seFloats = emptyFloats }
432 addRecFloats :: SimplEnv -> SimplEnv -> SimplEnv
433 -- Flattens the floats from env2 into a single Rec group,
434 -- prepends the floats from env1, and puts the result back in env2
435 -- This is all very specific to the way recursive bindings are
436 -- handled; see Simplify.simplRecBind
437 addRecFloats env1 env2@(SimplEnv {seFloats = Floats bs ff})
438 = ASSERT2( case ff of { FltLifted -> True; _ -> False }, ppr (fromOL bs) )
439 env2 {seFloats = seFloats env1 `addFlts` unitFloat (Rec (flattenBinds (fromOL bs)))}
441 wrapFloats :: SimplEnv -> OutExpr -> OutExpr
442 wrapFloats env expr = wrapFlts (seFloats env) expr
444 wrapFlts :: Floats -> OutExpr -> OutExpr
445 -- Wrap the floats around the expression, using case-binding where necessary
446 wrapFlts (Floats bs _) body = foldrOL wrap body bs
448 wrap (Rec prs) body = Let (Rec prs) body
449 wrap (NonRec b r) body = bindNonRec b r body
451 getFloats :: SimplEnv -> [CoreBind]
452 getFloats (SimplEnv {seFloats = Floats bs _}) = fromOL bs
454 isEmptyFloats :: SimplEnv -> Bool
455 isEmptyFloats env = isEmptyFlts (seFloats env)
457 isEmptyFlts :: Floats -> Bool
458 isEmptyFlts (Floats bs _) = isNilOL bs
460 floatBinds :: Floats -> [OutBind]
461 floatBinds (Floats bs _) = fromOL bs
465 %************************************************************************
469 %************************************************************************
471 Note [Global Ids in the substitution]
472 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
473 We look up even a global (eg imported) Id in the substitution. Consider
474 case X.g_34 of b { (a,b) -> ... case X.g_34 of { (p,q) -> ...} ... }
475 The binder-swap in the occurence analyser will add a binding
476 for a LocalId version of g (with the same unique though):
477 case X.g_34 of b { (a,b) -> let g_34 = b in
478 ... case X.g_34 of { (p,q) -> ...} ... }
479 So we want to look up the inner X.g_34 in the substitution, where we'll
480 find that it has been substituted by b. (Or conceivably cloned.)
483 substId :: SimplEnv -> InId -> SimplSR
484 -- Returns DoneEx only on a non-Var expression
485 substId (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v
486 = case lookupVarEnv ids v of -- Note [Global Ids in the substitution]
487 Nothing -> DoneId (refine in_scope v)
488 Just (DoneId v) -> DoneId (refine in_scope v)
489 Just (DoneEx (Var v)) -> DoneId (refine in_scope v)
490 Just res -> res -- DoneEx non-var, or ContEx
493 -- Get the most up-to-date thing from the in-scope set
494 -- Even though it isn't in the substitution, it may be in
495 -- the in-scope set with better IdInfo
496 refine :: InScopeSet -> Var -> Var
498 | isLocalId v = case lookupInScope in_scope v of
500 Nothing -> WARN( True, ppr v ) v -- This is an error!
503 lookupRecBndr :: SimplEnv -> InId -> OutId
504 -- Look up an Id which has been put into the envt by simplRecBndrs,
505 -- but where we have not yet done its RHS
506 lookupRecBndr (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v
507 = case lookupVarEnv ids v of
509 Just _ -> pprPanic "lookupRecBndr" (ppr v)
510 Nothing -> refine in_scope v
514 %************************************************************************
516 \section{Substituting an Id binder}
518 %************************************************************************
521 These functions are in the monad only so that they can be made strict via seq.
524 simplBinders, simplLamBndrs
525 :: SimplEnv -> [InBndr] -> SimplM (SimplEnv, [OutBndr])
526 simplBinders env bndrs = mapAccumLM simplBinder env bndrs
527 simplLamBndrs env bndrs = mapAccumLM simplLamBndr env bndrs
530 simplBinder :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr)
531 -- Used for lambda and case-bound variables
532 -- Clone Id if necessary, substitute type
533 -- Return with IdInfo already substituted, but (fragile) occurrence info zapped
534 -- The substitution is extended only if the variable is cloned, because
535 -- we *don't* need to use it to track occurrence info.
537 | isTyCoVar bndr = do { let (env', tv) = substTyVarBndr env bndr
538 ; seqTyVar tv `seq` return (env', tv) }
539 | otherwise = do { let (env', id) = substIdBndr env bndr
540 ; seqId id `seq` return (env', id) }
543 simplLamBndr :: SimplEnv -> Var -> SimplM (SimplEnv, Var)
544 -- Used for lambda binders. These sometimes have unfoldings added by
545 -- the worker/wrapper pass that must be preserved, because they can't
546 -- be reconstructed from context. For example:
547 -- f x = case x of (a,b) -> fw a b x
548 -- fw a b x{=(a,b)} = ...
549 -- The "{=(a,b)}" is an unfolding we can't reconstruct otherwise.
550 simplLamBndr env bndr
551 | isId bndr && hasSomeUnfolding old_unf = seqId id2 `seq` return (env2, id2) -- Special case
552 | otherwise = simplBinder env bndr -- Normal case
554 old_unf = idUnfolding bndr
555 (env1, id1) = substIdBndr env bndr
556 id2 = id1 `setIdUnfolding` substUnfolding env old_unf
557 env2 = modifyInScope env1 id2
560 simplNonRecBndr :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr)
561 -- A non-recursive let binder
562 simplNonRecBndr env id
563 = do { let (env1, id1) = substIdBndr env id
564 ; seqId id1 `seq` return (env1, id1) }
567 simplRecBndrs :: SimplEnv -> [InBndr] -> SimplM SimplEnv
568 -- Recursive let binders
569 simplRecBndrs env@(SimplEnv {}) ids
570 = do { let (env1, ids1) = mapAccumL substIdBndr env ids
571 ; seqIds ids1 `seq` return env1 }
574 substIdBndr :: SimplEnv
575 -> InBndr -- Env and binder to transform
576 -> (SimplEnv, OutBndr)
577 -- Clone Id if necessary, substitute its type
578 -- Return an Id with its
579 -- * Type substituted
580 -- * UnfoldingInfo, Rules, WorkerInfo zapped
581 -- * Fragile OccInfo (only) zapped: Note [Robust OccInfo]
582 -- * Robust info, retained especially arity and demand info,
583 -- so that they are available to occurrences that occur in an
584 -- earlier binding of a letrec
586 -- For the robust info, see Note [Arity robustness]
588 -- Augment the substitution if the unique changed
589 -- Extend the in-scope set with the new Id
591 -- Similar to CoreSubst.substIdBndr, except that
592 -- the type of id_subst differs
593 -- all fragile info is zapped
595 substIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst })
597 = (env { seInScope = in_scope `extendInScopeSet` new_id,
598 seIdSubst = new_subst }, new_id)
600 id1 = uniqAway in_scope old_id
601 id2 = substIdType env id1
602 new_id = zapFragileIdInfo id2 -- Zaps rules, worker-info, unfolding
603 -- and fragile OccInfo
605 -- Extend the substitution if the unique has changed,
606 -- or there's some useful occurrence information
607 -- See the notes with substTyVarBndr for the delSubstEnv
608 new_subst | new_id /= old_id
609 = extendVarEnv id_subst old_id (DoneId new_id)
611 = delVarEnv id_subst old_id
615 ------------------------------------
616 seqTyVar :: TyVar -> ()
617 seqTyVar b = b `seq` ()
620 seqId id = seqType (idType id) `seq`
626 seqIds (id:ids) = seqId id `seq` seqIds ids
630 Note [Arity robustness]
631 ~~~~~~~~~~~~~~~~~~~~~~~
632 We *do* transfer the arity from from the in_id of a let binding to the
633 out_id. This is important, so that the arity of an Id is visible in
634 its own RHS. For example:
635 f = \x. ....g (\y. f y)....
636 We can eta-reduce the arg to g, becuase f is a value. But that
639 This interacts with the 'state hack' too:
644 Can we eta-expand f? Only if we see that f has arity 1, and then we
645 take advantage of the 'state hack' on the result of
646 (f y) :: State# -> (State#, Int) to expand the arity one more.
648 There is a disadvantage though. Making the arity visible in the RHS
649 allows us to eta-reduce
653 which technically is not sound. This is very much a corner case, so
654 I'm not worried about it. Another idea is to ensure that f's arity
655 never decreases; its arity started as 1, and we should never eta-reduce
659 Note [Robust OccInfo]
660 ~~~~~~~~~~~~~~~~~~~~~
661 It's important that we *do* retain the loop-breaker OccInfo, because
662 that's what stops the Id getting inlined infinitely, in the body of
666 Note [Rules in a letrec]
667 ~~~~~~~~~~~~~~~~~~~~~~~~
668 After creating fresh binders for the binders of a letrec, we
669 substitute the RULES and add them back onto the binders; this is done
670 *before* processing any of the RHSs. This is important. Manuel found
671 cases where he really, really wanted a RULE for a recursive function
672 to apply in that function's own right-hand side.
674 See Note [Loop breaking and RULES] in OccAnal.
678 addBndrRules :: SimplEnv -> InBndr -> OutBndr -> (SimplEnv, OutBndr)
679 -- Rules are added back in to to the bin
680 addBndrRules env in_id out_id
681 | isEmptySpecInfo old_rules = (env, out_id)
682 | otherwise = (modifyInScope env final_id, final_id)
684 subst = mkCoreSubst (text "local rules") env
685 old_rules = idSpecialisation in_id
686 new_rules = CoreSubst.substSpec subst out_id old_rules
687 final_id = out_id `setIdSpecialisation` new_rules
691 %************************************************************************
693 Impedence matching to type substitution
695 %************************************************************************
698 getTvSubst :: SimplEnv -> TvSubst
699 getTvSubst (SimplEnv { seInScope = in_scope, seTvSubst = tv_env })
700 = mkTvSubst in_scope tv_env
702 substTy :: SimplEnv -> Type -> Type
703 substTy env ty = Type.substTy (getTvSubst env) ty
705 substTyVar :: SimplEnv -> TyVar -> Type
706 substTyVar env tv = Type.substTyVar (getTvSubst env) tv
708 substTyVarBndr :: SimplEnv -> TyVar -> (SimplEnv, TyVar)
709 substTyVarBndr env tv
710 = case Type.substTyVarBndr (getTvSubst env) tv of
711 (TvSubst in_scope' tv_env', tv')
712 -> (env { seInScope = in_scope', seTvSubst = tv_env'}, tv')
714 -- When substituting in rules etc we can get CoreSubst to do the work
715 -- But CoreSubst uses a simpler form of IdSubstEnv, so we must impedence-match
716 -- here. I think the this will not usually result in a lot of work;
717 -- the substitutions are typically small, and laziness will avoid work in many cases.
719 mkCoreSubst :: SDoc -> SimplEnv -> CoreSubst.Subst
720 mkCoreSubst doc (SimplEnv { seInScope = in_scope, seTvSubst = tv_env, seIdSubst = id_env })
721 = mk_subst tv_env id_env
723 mk_subst tv_env id_env = CoreSubst.mkSubst in_scope tv_env (mapVarEnv fiddle id_env)
725 fiddle (DoneEx e) = e
726 fiddle (DoneId v) = Var v
727 fiddle (ContEx tv id e) = CoreSubst.substExpr (text "mkCoreSubst" <+> doc) (mk_subst tv id) e
728 -- Don't shortcut here
731 substIdType :: SimplEnv -> Id -> Id
732 substIdType (SimplEnv { seInScope = in_scope, seTvSubst = tv_env}) id
733 | isEmptyVarEnv tv_env || isEmptyVarSet (tyVarsOfType old_ty) = id
734 | otherwise = Id.setIdType id (Type.substTy (TvSubst in_scope tv_env) old_ty)
735 -- The tyVarsOfType is cheaper than it looks
736 -- because we cache the free tyvars of the type
737 -- in a Note in the id's type itself
742 substExpr :: SDoc -> SimplEnv -> CoreExpr -> CoreExpr
744 = CoreSubst.substExpr (text "SimplEnv.substExpr1" <+> doc)
745 (mkCoreSubst (text "SimplEnv.substExpr2" <+> doc) env)
746 -- Do *not* short-cut in the case of an empty substitution
747 -- See Note [SimplEnv invariants]
749 substUnfolding :: SimplEnv -> Unfolding -> Unfolding
750 substUnfolding env unf = CoreSubst.substUnfolding (mkCoreSubst (text "subst-unfolding") env) unf
751 -- Do *not* short-cut in the case of an empty substitution
752 -- See Note [SimplEnv invariants]