2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 %************************************************************************
6 \section[OccurAnal]{Occurrence analysis pass}
8 %************************************************************************
10 The occurrence analyser re-typechecks a core expression, returning a new
11 core expression with (hopefully) improved usage information.
15 occurAnalyseBinds, occurAnalyseGlobalExpr, occurAnalyseRule
18 #include "HsVersions.h"
22 import CoreFVs ( idRuleVars )
23 import CoreUtils ( exprIsTrivial )
24 import Id ( isDataConId, isOneShotLambda, setOneShotLambda,
25 idOccInfo, setIdOccInfo,
26 isExportedId, modifyIdInfo, idInfo,
30 import IdInfo ( OccInfo(..), shortableIdInfo, copyIdInfo )
35 import Name ( isLocallyDefined )
36 import Type ( splitFunTy_maybe, splitForAllTys )
37 import Maybes ( maybeToBool )
38 import Digraph ( stronglyConnCompR, SCC(..) )
39 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
41 import UniqFM ( keysUFM )
42 import Util ( zipWithEqual, mapAndUnzip )
48 %************************************************************************
50 \subsection[OccurAnal-main]{Counting occurrences: main function}
52 %************************************************************************
54 Here's the externally-callable interface:
57 occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
59 -> (IdEnv BinderInfo, -- Occ info for interesting free vars
62 occurAnalyseExpr interesting expr
63 = occAnal initial_env expr
65 initial_env = OccEnv interesting emptyVarSet []
67 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
68 occurAnalyseGlobalExpr expr
69 = -- Top level expr, so no interesting free vars, and
70 -- discard occurence info returned
71 snd (occurAnalyseExpr (\_ -> False) expr)
73 occurAnalyseRule :: CoreRule -> CoreRule
74 occurAnalyseRule rule@(BuiltinRule _) = rule
75 occurAnalyseRule (Rule str tpl_vars tpl_args rhs)
76 -- Add occ info to tpl_vars, rhs
77 = Rule str tpl_vars' tpl_args rhs'
79 (rhs_uds, rhs') = occurAnalyseExpr isLocallyDefined rhs
80 (_, tpl_vars') = tagBinders rhs_uds tpl_vars
84 %************************************************************************
86 \subsection{Top level stuff}
88 %************************************************************************
90 In @occAnalTop@ we do indirection-shorting. That is, if we have this:
92 x_local = <expression>
96 where exp is exported, and loc is not, then we replace it with this:
99 x_exported = <expression>
102 Without this we never get rid of the x_exported = x_local thing. This
103 save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
104 makes strictness information propagate better. This used to happen in
105 the final phase, but it's tidier to do it here.
107 If more than one exported thing is equal to a local thing (i.e., the
108 local thing really is shared), then we do one only:
111 x_exported1 = x_local
112 x_exported2 = x_local
116 x_exported2 = x_exported1
119 We rely on prior eta reduction to simplify things like
121 x_exported = /\ tyvars -> x_local tyvars
125 Hence,there's a possibility of leaving unchanged something like this:
128 x_exported1 = x_local Int
130 By the time we've thrown away the types in STG land this
131 could be eliminated. But I don't think it's very common
132 and it's dangerous to do this fiddling in STG land
133 because we might elminate a binding that's mentioned in the
134 unfolding for something.
137 occurAnalyseBinds :: [CoreBind] -> [CoreBind]
139 occurAnalyseBinds binds
142 (_, _, binds') = go initialTopEnv binds
144 go :: OccEnv -> [CoreBind]
145 -> (UsageDetails, -- Occurrence info
146 IdEnv Id, -- Indirection elimination info
147 -- Maps local-id -> exported-id, but it embodies
148 -- bindings of the form exported-id = local-id in
149 -- the argument to go
150 [CoreBind]) -- Occ-analysed bindings, less the exported-id=local-id ones
152 go env [] = (emptyDetails, emptyVarEnv, [])
154 go env (bind : binds)
156 new_env = env `addNewCands` (bindersOf bind)
157 (scope_usage, ind_env, binds') = go new_env binds
158 (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
159 -- NB: I zap before occur-analysing, so
160 -- I don't need to worry about getting the
161 -- occ info on the new bindings right.
164 NonRec exported_id (Var local_id)
165 | shortMeOut ind_env exported_id local_id
166 -- Special case for eliminating indirections
167 -- Note: it's a shortcoming that this only works for
168 -- non-recursive bindings. Elminating indirections
169 -- makes perfect sense for recursive bindings too, but
170 -- it's more complicated to implement, so I haven't done so
171 -> (scope_usage, ind_env', binds')
173 ind_env' = extendVarEnv ind_env local_id exported_id
175 other -> -- Ho ho! The normal case
176 (final_usage, ind_env, new_binds ++ binds')
178 initialTopEnv = OccEnv isLocallyDefined -- Anything local is interesting
183 -- Deal with any indirections
184 zapBind ind_env (NonRec bndr rhs)
185 | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
186 -- The Rec isn't strictly necessary, but it's convenient
187 zapBind ind_env (Rec pairs)
188 | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
190 zapBind ind_env bind = bind
192 zap ind_env pair@(local_id,rhs)
193 = case lookupVarEnv ind_env local_id of
195 Just exported_id -> [(local_id, Var exported_id),
198 exported_id' = modifyIdInfo (copyIdInfo (idInfo local_id)) exported_id
200 shortMeOut ind_env exported_id local_id
201 -- The if-then-else stuff is just so I can get a pprTrace to see
202 -- how often I don't get shorting out becuase of IdInfo stuff
203 = if isExportedId exported_id && -- Only if this is exported
205 isLocallyDefined local_id && -- Only if this one is defined in this
206 -- module, so that we *can* change its
207 -- binding to be the exported thing!
209 not (isExportedId local_id) && -- Only if this one is not itself exported,
210 -- since the transformation will nuke it
212 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
214 if shortableIdInfo (idInfo exported_id) -- Only if its IdInfo is 'shortable'
215 -- (see the defn of IdInfo.shortableIdInfo
217 else pprTrace "shortMeOut:" (ppr exported_id) False
223 %************************************************************************
225 \subsection[OccurAnal-main]{Counting occurrences: main function}
227 %************************************************************************
233 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
235 type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
236 -- which is gotten from the Id.
237 type Details1 = (Id, UsageDetails, CoreExpr)
238 type Details2 = (IdWithOccInfo, CoreExpr)
241 occAnalBind :: OccEnv
243 -> UsageDetails -- Usage details of scope
244 -> (UsageDetails, -- Of the whole let(rec)
247 occAnalBind env (NonRec binder rhs) body_usage
248 | not (binder `usedIn` body_usage) -- It's not mentioned
251 | otherwise -- It's mentioned in the body
252 = (final_body_usage `combineUsageDetails` rhs_usage,
253 [NonRec tagged_binder rhs'])
256 (final_body_usage, tagged_binder) = tagBinder body_usage binder
257 (rhs_usage, rhs') = occAnalRhs env binder rhs
260 Dropping dead code for recursive bindings is done in a very simple way:
262 the entire set of bindings is dropped if none of its binders are
263 mentioned in its body; otherwise none are.
265 This seems to miss an obvious improvement.
280 Now @f@ is unused. But dependency analysis will sort this out into a
281 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
282 It isn't easy to do a perfect job in one blow. Consider
296 occAnalBind env (Rec pairs) body_usage
297 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
299 binders = map fst pairs
300 rhs_env = env `addNewCands` binders
302 analysed_pairs :: [Details1]
303 analysed_pairs = [ (bndr, rhs_usage, rhs')
304 | (bndr, rhs) <- pairs,
305 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
308 sccs :: [SCC (Node Details1)]
309 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
312 ---- stuff for dependency analysis of binds -------------------------------
313 edges :: [Node Details1]
314 edges = _scc_ "occAnalBind.assoc"
315 [ (details, iBox (u2i (idUnique id)), edges_from rhs_usage)
316 | details@(id, rhs_usage, rhs) <- analysed_pairs
319 -- (a -> b) means a mentions b
320 -- Given the usage details (a UFM that gives occ info for each free var of
321 -- the RHS) we can get the list of free vars -- or rather their Int keys --
322 -- by just extracting the keys from the finite map. Grimy, but fast.
323 -- Previously we had this:
324 -- [ bndr | bndr <- bndrs,
325 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
326 -- which has n**2 cost, and this meant that edges_from alone
327 -- consumed 10% of total runtime!
328 edges_from :: UsageDetails -> [Int]
329 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
332 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
335 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
336 | not (bndr `usedIn` body_usage)
337 = (body_usage, binds_so_far) -- Dead code
339 = (combined_usage, new_bind : binds_so_far)
341 total_usage = combineUsageDetails body_usage rhs_usage
342 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
343 new_bind = NonRec tagged_bndr rhs'
346 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
347 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
348 = (body_usage, binds_so_far) -- Dead code
350 = (combined_usage, final_bind:binds_so_far)
352 details = [details | (details, _, _) <- cycle]
353 bndrs = [bndr | (bndr, _, _) <- details]
354 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
355 total_usage = foldr combineUsageDetails body_usage rhs_usages
356 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
357 final_bind = Rec (reOrderRec env new_cycle)
359 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
360 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
363 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
364 strongly connected component (there's guaranteed to be a cycle). It returns the
366 a) in a better order,
367 b) with some of the Ids having a IMustNotBeINLINEd pragma
369 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
370 that the simplifier can guarantee not to loop provided it never records an inlining
371 for these no-inline guys.
373 Furthermore, the order of the binds is such that if we neglect dependencies
374 on the no-inline Ids then the binds are topologically sorted. This means
375 that the simplifier will generally do a good job if it works from top bottom,
376 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
379 [June 98: I don't understand the following paragraphs, and I've
380 changed the a=b case again so that it isn't a special case any more.]
382 Here's a case that bit me:
390 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
392 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
393 Perhaps something cleverer would suffice.
396 You might think that you can prevent non-termination simply by making
397 sure that we simplify a recursive binding's RHS in an environment that
398 simply clones the recursive Id. But no. Consider
400 letrec f = \x -> let z = f x' in ...
407 We bind n to its *simplified* RHS, we then *re-simplify* it when
408 we inline n. Then we may well inline f; and then the same thing
411 I don't think it's possible to prevent non-termination by environment
412 manipulation in this way. Apart from anything else, successive
413 iterations of the simplifier may unroll recursive loops in cases like
414 that above. The idea of beaking every recursive loop with an
415 IMustNotBeINLINEd pragma is much much better.
421 -> SCC (Node Details2)
423 -- Sorted into a plausible order. Enough of the Ids have
424 -- dontINLINE pragmas that there are no loops left.
426 -- Non-recursive case
427 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
429 -- Common case of simple self-recursion
430 reOrderRec env (CyclicSCC [bind])
431 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
433 ((tagged_bndr, rhs), _, _) = bind
435 reOrderRec env (CyclicSCC (bind : binds))
436 = -- Choose a loop breaker, mark it no-inline,
437 -- do SCC analysis on the rest, and recursively sort them out
438 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
440 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
443 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
444 (tagged_bndr, rhs) = chosen_pair
446 -- This loop looks for the bind with the lowest score
447 -- to pick as the loop breaker. The rest accumulate in
448 choose_loop_breaker (details,_,_) loop_sc acc []
449 = (details, acc) -- Done
451 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
452 | sc < loop_sc -- Lower score so pick this new one
453 = choose_loop_breaker bind sc (loop_bind : acc) binds
455 | otherwise -- No lower so don't pick it
456 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
460 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
461 score ((bndr, rhs), _, _)
462 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
463 -- Used to have also: && not (isExportedId bndr)
464 -- But I found this sometimes cost an extra iteration when we have
465 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
466 -- where df is the exported dictionary. Then df makes a really
467 -- bad choice for loop breaker
469 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
470 -- This used to have a lower score than inlineCandidate, but
471 -- it's *really* helpful if dictionaries get inlined fast,
472 -- so I'm experimenting with giving higher priority to data-typed things
474 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
476 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
477 -- Avoid things with specialisations; we'd like
478 -- to take advantage of them in the subsequent bindings
482 inlineCandidate :: Id -> CoreExpr -> Bool
483 inlineCandidate id (Note InlineMe _) = True
484 inlineCandidate id rhs = case idOccInfo id of
488 -- Real example (the Enum Ordering instance from PrelBase):
489 -- rec f = \ x -> case d of (p,q,r) -> p x
490 -- g = \ x -> case d of (p,q,r) -> q x
493 -- Here, f and g occur just once; but we can't inline them into d.
494 -- On the other hand we *could* simplify those case expressions if
495 -- we didn't stupidly choose d as the loop breaker.
496 -- But we won't because constructor args are marked "Many".
498 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
500 (_, rho_ty) = splitForAllTys ty
503 @occAnalRhs@ deals with the question of bindings where the Id is marked
504 by an INLINE pragma. For these we record that anything which occurs
505 in its RHS occurs many times. This pessimistically assumes that ths
506 inlined binder also occurs many times in its scope, but if it doesn't
507 we'll catch it next time round. At worst this costs an extra simplifier pass.
508 ToDo: try using the occurrence info for the inline'd binder.
510 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
511 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
516 -> Id -> CoreExpr -- Binder and rhs
517 -> (UsageDetails, CoreExpr)
519 occAnalRhs env id rhs
520 = (final_usage, rhs')
522 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
524 -- [March 98] A new wrinkle is that if the binder has specialisations inside
525 -- it then we count the specialised Ids as "extra rhs's". That way
526 -- the "parent" keeps the specialised "children" alive. If the parent
527 -- dies (because it isn't referenced any more), then the children will
528 -- die too unless they are already referenced directly.
530 final_usage = foldVarSet add rhs_usage (idRuleVars id)
531 add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
532 -- (i.e manyOcc) because many copies
533 -- of the specialised thing can appear
541 -> (UsageDetails, -- Gives info only about the "interesting" Ids
544 occAnal env (Type t) = (emptyDetails, Type t)
549 var_uds | isCandidate env v = unitVarEnv v funOccZero
550 | otherwise = emptyDetails
552 -- At one stage, I gathered the idRuleVars for v here too,
553 -- which in a way is the right thing to do.
554 -- But that went wrong right after specialisation, when
555 -- the *occurrences* of the overloaded function didn't have any
556 -- rules in them, so the *specialised* versions looked as if they
557 -- weren't used at all.
561 We regard variables that occur as constructor arguments as "dangerousToDup":
565 f x = let y = expensive x in
567 (case z of {(p,q)->q}, case z of {(p,q)->q})
570 We feel free to duplicate the WHNF (True,y), but that means
571 that y may be duplicated thereby.
573 If we aren't careful we duplicate the (expensive x) call!
574 Constructors are rather like lambdas in this way.
577 occAnal env expr@(Lit lit) = (emptyDetails, expr)
581 occAnal env (Note InlineMe body)
582 = case occAnal env body of { (usage, body') ->
583 (mapVarEnv markMany usage, Note InlineMe body')
586 occAnal env (Note note@(SCC cc) body)
587 = case occAnal env body of { (usage, body') ->
588 (mapVarEnv markInsideSCC usage, Note note body')
591 occAnal env (Note note body)
592 = case occAnal env body of { (usage, body') ->
593 (usage, Note note body')
598 occAnal env app@(App fun arg)
599 = occAnalApp env (collectArgs app)
601 -- Ignore type variables altogether
602 -- (a) occurrences inside type lambdas only not marked as InsideLam
603 -- (b) type variables not in environment
605 occAnal env expr@(Lam x body) | isTyVar x
606 = case occAnal env body of { (body_usage, body') ->
607 (body_usage, Lam x body')
610 -- For value lambdas we do a special hack. Consider
612 -- If we did nothing, x is used inside the \y, so would be marked
613 -- as dangerous to dup. But in the common case where the abstraction
614 -- is applied to two arguments this is over-pessimistic.
615 -- So instead, we just mark each binder with its occurrence
616 -- info in the *body* of the multiple lambda.
617 -- Then, the simplifier is careful when partially applying lambdas.
619 occAnal env expr@(Lam _ _)
620 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
622 (final_usage, tagged_binders) = tagBinders body_usage binders
623 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
624 -- we get linear-typed things in the resulting program that we can't handle yet.
625 -- (e.g. PrelShow) TODO
627 really_final_usage = if linear then
630 mapVarEnv markInsideLam final_usage
633 mkLams tagged_binders body') }
635 (binders, body) = collectBinders expr
636 (linear, env_body, _) = oneShotGroup env binders
638 occAnal env (Case scrut bndr alts)
639 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
640 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
642 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
643 alts_usage' = addCaseBndrUsage alts_usage
644 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
645 total_usage = scrut_usage `combineUsageDetails` alts_usage1
647 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
649 alt_env = env `addNewCand` bndr
651 -- The case binder gets a usage of either "many" or "dead", never "one".
652 -- Reason: we like to inline single occurrences, to eliminate a binding,
653 -- but inlining a case binder *doesn't* eliminate a binding.
654 -- We *don't* want to transform
655 -- case x of w { (p,q) -> f w }
657 -- case x of w { (p,q) -> f (p,q) }
658 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
660 Just occ -> extendVarEnv usage bndr (markMany occ)
662 occAnal env (Let bind body)
663 = case occAnal new_env body of { (body_usage, body') ->
664 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
665 (final_usage, mkLets new_binds body') }}
667 new_env = env `addNewCands` (bindersOf bind)
670 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
671 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
673 arg_env = zapCtxt env
676 Applications are dealt with specially because we want
677 the "build hack" to work.
680 -- Hack for build, fold, runST
681 occAnalApp env (Var fun, args)
682 = case args_stuff of { (args_uds, args') ->
684 final_uds = fun_uds `combineUsageDetails` args_uds
686 (final_uds, mkApps (Var fun) args') }
688 fun_uniq = idUnique fun
690 fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
691 | otherwise = emptyDetails
693 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
694 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
695 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
696 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
698 | isDataConId fun = case occAnalArgs env args of
699 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
700 -- We mark the free vars of the argument of a constructor as "many"
701 -- This means that nothing gets inlined into a constructor argument
702 -- position, which is what we want. Typically those constructor
703 -- arguments are just variables, or trivial expressions.
705 | otherwise = occAnalArgs env args
708 occAnalApp env (fun, args)
709 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
710 case occAnalArgs env args of { (args_uds, args') ->
712 final_uds = fun_uds `combineUsageDetails` args_uds
714 (final_uds, mkApps fun' args') }}
716 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
717 appSpecial env n ctxt args
720 go n [] = (emptyDetails, []) -- Too few args
722 go 1 (arg:args) -- The magic arg
723 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
724 case occAnalArgs env args of { (args_uds, args') ->
725 (combineUsageDetails arg_uds args_uds, arg':args') }}
728 = case occAnal env arg of { (arg_uds, arg') ->
729 case go (n-1) args of { (args_uds, args') ->
730 (combineUsageDetails arg_uds args_uds, arg':args') }}
737 occAnalAlt env (con, bndrs, rhs)
738 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
740 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
742 (final_usage, (con, tagged_bndrs, rhs')) }
746 %************************************************************************
748 \subsection[OccurAnal-types]{Data types}
750 %************************************************************************
753 -- We gather inforamtion for variables that are either
758 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
759 IdSet -- In-scope Ids
760 CtxtTy -- Tells about linearity
765 -- True:ctxt Analysing a function-valued expression that will be
768 -- False:ctxt Analysing a function-valued expression that may
769 -- be applied many times; but when it is,
770 -- the CtxtTy inside applies
772 isCandidate :: OccEnv -> Id -> Bool
773 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
775 addNewCands :: OccEnv -> [Id] -> OccEnv
776 addNewCands (OccEnv ifun cands ctxt) ids
777 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
779 addNewCand :: OccEnv -> Id -> OccEnv
780 addNewCand (OccEnv ifun cands ctxt) id
781 = OccEnv ifun (extendVarSet cands id) ctxt
783 setCtxt :: OccEnv -> CtxtTy -> OccEnv
784 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
786 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
787 -- True <=> this is a one-shot linear lambda group
788 -- The [CoreBndr] are the binders.
790 -- The result binders have one-shot-ness set that they might not have had originally.
791 -- This happens in (build (\cn -> e)). Here the occurrence analyser
792 -- linearity context knows that c,n are one-shot, and it records that fact in
793 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
795 oneShotGroup (OccEnv ifun cands ctxt) bndrs
796 = case go ctxt bndrs [] of
797 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
799 is_one_shot b = isId b && isOneShotLambda b
801 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
803 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
804 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
806 bndr' | lin_ctxt = setOneShotLambda bndr
809 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
812 zapCtxt env@(OccEnv ifun cands []) = env
813 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
815 type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
817 combineUsageDetails, combineAltsUsageDetails
818 :: UsageDetails -> UsageDetails -> UsageDetails
820 combineUsageDetails usage1 usage2
821 = plusVarEnv_C addBinderInfo usage1 usage2
823 combineAltsUsageDetails usage1 usage2
824 = plusVarEnv_C orBinderInfo usage1 usage2
826 addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
827 addOneOcc usage id info
828 = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
829 -- ToDo: make this more efficient
831 emptyDetails = (emptyVarEnv :: UsageDetails)
833 unitDetails id info = (unitVarEnv id info :: UsageDetails)
835 usedIn :: Id -> UsageDetails -> Bool
836 v `usedIn` details = isExportedId v || v `elemVarEnv` details
838 tagBinders :: UsageDetails -- Of scope
840 -> (UsageDetails, -- Details with binders removed
841 [IdWithOccInfo]) -- Tagged binders
843 tagBinders usage binders
845 usage' = usage `delVarEnvList` binders
846 uss = map (setBinderOcc usage) binders
848 usage' `seq` (usage', uss)
850 tagBinder :: UsageDetails -- Of scope
852 -> (UsageDetails, -- Details with binders removed
853 IdWithOccInfo) -- Tagged binders
855 tagBinder usage binder
857 usage' = usage `delVarEnv` binder
858 binder' = setBinderOcc usage binder
860 usage' `seq` (usage', binder')
863 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
864 setBinderOcc usage bndr
865 | isTyVar bndr = bndr
867 = -- Don't use local usage info for visible-elsewhere things
868 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
869 -- about to re-generate it and it shouldn't be "sticky"
870 case idOccInfo bndr of
872 other -> setIdOccInfo bndr NoOccInfo
874 | otherwise = setIdOccInfo bndr occ_info
876 occ_info = case lookupVarEnv usage bndr of
878 Just info -> binderInfoToOccInfo info
880 funOccZero = funOccurrence 0