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 ( isSpecPragmaId, isDataConId, isOneShotLambda, setOneShotLambda,
25 idOccInfo, setIdOccInfo,
26 isExportedId, modifyIdInfo, idInfo,
30 import IdInfo ( OccInfo(..), insideLam, copyIdInfo )
35 import Name ( isLocallyDefined )
36 import Type ( splitFunTy_maybe, splitForAllTys )
37 import Maybes ( maybeToBool )
38 import Digraph ( stronglyConnCompR, SCC(..) )
39 import Unique ( u2i, buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
40 import UniqFM ( keysUFM )
41 import Util ( zipWithEqual, mapAndUnzip )
46 %************************************************************************
48 \subsection[OccurAnal-main]{Counting occurrences: main function}
50 %************************************************************************
52 Here's the externally-callable interface:
55 occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
57 -> (IdEnv BinderInfo, -- Occ info for interesting free vars
60 occurAnalyseExpr interesting expr
61 = occAnal initial_env expr
63 initial_env = OccEnv interesting emptyVarSet []
65 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
66 occurAnalyseGlobalExpr expr
67 = -- Top level expr, so no interesting free vars, and
68 -- discard occurence info returned
69 snd (occurAnalyseExpr (\_ -> False) expr)
71 occurAnalyseRule :: CoreRule -> CoreRule
72 occurAnalyseRule rule@(BuiltinRule _) = rule
73 occurAnalyseRule (Rule str tpl_vars tpl_args rhs)
74 -- Add occ info to tpl_vars, rhs
75 = Rule str tpl_vars' tpl_args rhs'
77 (rhs_uds, rhs') = occurAnalyseExpr isLocallyDefined rhs
78 (_, tpl_vars') = tagBinders rhs_uds tpl_vars
82 %************************************************************************
84 \subsection{Top level stuff}
86 %************************************************************************
88 In @occAnalTop@ we do indirection-shorting. That is, if we have this:
90 x_local = <expression>
94 where exp is exported, and loc is not, then we replace it with this:
97 x_exported = <expression>
100 Without this we never get rid of the x_exported = x_local thing. This
101 save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
102 makes strictness information propagate better. This used to happen in
103 the final phase, but it's tidier to do it here.
105 If more than one exported thing is equal to a local thing (i.e., the
106 local thing really is shared), then we do one only:
109 x_exported1 = x_local
110 x_exported2 = x_local
114 x_exported2 = x_exported1
117 We rely on prior eta reduction to simplify things like
119 x_exported = /\ tyvars -> x_local tyvars
123 Hence,there's a possibility of leaving unchanged something like this:
126 x_exported1 = x_local Int
128 By the time we've thrown away the types in STG land this
129 could be eliminated. But I don't think it's very common
130 and it's dangerous to do this fiddling in STG land
131 because we might elminate a binding that's mentioned in the
132 unfolding for something.
135 occurAnalyseBinds :: [CoreBind] -> [CoreBind]
137 occurAnalyseBinds binds
140 (_, _, binds') = go initialTopEnv binds
142 go :: OccEnv -> [CoreBind]
143 -> (UsageDetails, -- Occurrence info
144 IdEnv Id, -- Indirection elimination info
145 -- Maps local-id -> exported-id, but it embodies
146 -- bindings of the form exported-id = local-id in
147 -- the argument to go
148 [CoreBind]) -- Occ-analysed bindings, less the exported-id=local-id ones
150 go env [] = (emptyDetails, emptyVarEnv, [])
152 go env (bind : binds)
154 new_env = env `addNewCands` (bindersOf bind)
155 (scope_usage, ind_env, binds') = go new_env binds
156 (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
157 -- NB: I zap before occur-analysing, so
158 -- I don't need to worry about getting the
159 -- occ info on the new bindings right.
162 NonRec exported_id (Var local_id)
163 | shortMeOut ind_env exported_id local_id
164 -- Special case for eliminating indirections
165 -- Note: it's a shortcoming that this only works for
166 -- non-recursive bindings. Elminating indirections
167 -- makes perfect sense for recursive bindings too, but
168 -- it's more complicated to implement, so I haven't done so
169 -> (scope_usage, ind_env', binds')
171 ind_env' = extendVarEnv ind_env local_id exported_id
173 other -> -- Ho ho! The normal case
174 (final_usage, ind_env, new_binds ++ binds')
176 initialTopEnv = OccEnv isLocallyDefined -- Anything local is interesting
181 -- Deal with any indirections
182 zapBind ind_env (NonRec bndr rhs)
183 | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
184 -- The Rec isn't strictly necessary, but it's convenient
185 zapBind ind_env (Rec pairs)
186 | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
188 zapBind ind_env bind = bind
190 zap ind_env pair@(bndr,rhs)
191 = case lookupVarEnv ind_env bndr of
193 Just exported_id -> [(bndr, Var exported_id),
194 (exported_id_w_info, rhs)]
196 exported_id_w_info = modifyIdInfo (copyIdInfo (idInfo bndr)) exported_id
197 -- See notes with copyIdInfo about propagating IdInfo from
200 shortMeOut ind_env exported_id local_id
201 = isExportedId exported_id && -- Only if this is exported
203 isLocallyDefined local_id && -- Only if this one is defined in this
204 -- module, so that we *can* change its
205 -- binding to be the exported thing!
207 not (isExportedId local_id) && -- Only if this one is not itself exported,
208 -- since the transformation will nuke it
210 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
214 %************************************************************************
216 \subsection[OccurAnal-main]{Counting occurrences: main function}
218 %************************************************************************
224 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
226 type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
227 -- which is gotten from the Id.
228 type Details1 = (Id, UsageDetails, CoreExpr)
229 type Details2 = (IdWithOccInfo, CoreExpr)
232 occAnalBind :: OccEnv
234 -> UsageDetails -- Usage details of scope
235 -> (UsageDetails, -- Of the whole let(rec)
238 occAnalBind env (NonRec binder rhs) body_usage
239 | not (binder `usedIn` body_usage) -- It's not mentioned
242 | otherwise -- It's mentioned in the body
243 = (final_body_usage `combineUsageDetails` rhs_usage,
244 [NonRec tagged_binder rhs'])
247 (final_body_usage, tagged_binder) = tagBinder body_usage binder
248 (rhs_usage, rhs') = occAnalRhs env binder rhs
251 Dropping dead code for recursive bindings is done in a very simple way:
253 the entire set of bindings is dropped if none of its binders are
254 mentioned in its body; otherwise none are.
256 This seems to miss an obvious improvement.
271 Now @f@ is unused. But dependency analysis will sort this out into a
272 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
273 It isn't easy to do a perfect job in one blow. Consider
287 occAnalBind env (Rec pairs) body_usage
288 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
290 binders = map fst pairs
291 rhs_env = env `addNewCands` binders
293 analysed_pairs :: [Details1]
294 analysed_pairs = [ (bndr, rhs_usage, rhs')
295 | (bndr, rhs) <- pairs,
296 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
299 sccs :: [SCC (Node Details1)]
300 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
303 ---- stuff for dependency analysis of binds -------------------------------
304 edges :: [Node Details1]
305 edges = _scc_ "occAnalBind.assoc"
306 [ (details, IBOX(u2i (idUnique id)), edges_from rhs_usage)
307 | details@(id, rhs_usage, rhs) <- analysed_pairs
310 -- (a -> b) means a mentions b
311 -- Given the usage details (a UFM that gives occ info for each free var of
312 -- the RHS) we can get the list of free vars -- or rather their Int keys --
313 -- by just extracting the keys from the finite map. Grimy, but fast.
314 -- Previously we had this:
315 -- [ bndr | bndr <- bndrs,
316 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
317 -- which has n**2 cost, and this meant that edges_from alone
318 -- consumed 10% of total runtime!
319 edges_from :: UsageDetails -> [Int]
320 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
323 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
326 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
327 | not (bndr `usedIn` body_usage)
328 = (body_usage, binds_so_far) -- Dead code
330 = (combined_usage, new_bind : binds_so_far)
332 total_usage = combineUsageDetails body_usage rhs_usage
333 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
334 new_bind = NonRec tagged_bndr rhs'
337 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
338 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
339 = (body_usage, binds_so_far) -- Dead code
341 = (combined_usage, final_bind:binds_so_far)
343 details = [details | (details, _, _) <- cycle]
344 bndrs = [bndr | (bndr, _, _) <- details]
345 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
346 total_usage = foldr combineUsageDetails body_usage rhs_usages
347 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
348 final_bind = Rec (reOrderRec env new_cycle)
350 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
351 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
354 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
355 strongly connected component (there's guaranteed to be a cycle). It returns the
357 a) in a better order,
358 b) with some of the Ids having a IMustNotBeINLINEd pragma
360 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
361 that the simplifier can guarantee not to loop provided it never records an inlining
362 for these no-inline guys.
364 Furthermore, the order of the binds is such that if we neglect dependencies
365 on the no-inline Ids then the binds are topologically sorted. This means
366 that the simplifier will generally do a good job if it works from top bottom,
367 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
370 [June 98: I don't understand the following paragraphs, and I've
371 changed the a=b case again so that it isn't a special case any more.]
373 Here's a case that bit me:
381 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
383 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
384 Perhaps something cleverer would suffice.
387 You might think that you can prevent non-termination simply by making
388 sure that we simplify a recursive binding's RHS in an environment that
389 simply clones the recursive Id. But no. Consider
391 letrec f = \x -> let z = f x' in ...
398 We bind n to its *simplified* RHS, we then *re-simplify* it when
399 we inline n. Then we may well inline f; and then the same thing
402 I don't think it's possible to prevent non-termination by environment
403 manipulation in this way. Apart from anything else, successive
404 iterations of the simplifier may unroll recursive loops in cases like
405 that above. The idea of beaking every recursive loop with an
406 IMustNotBeINLINEd pragma is much much better.
412 -> SCC (Node Details2)
414 -- Sorted into a plausible order. Enough of the Ids have
415 -- dontINLINE pragmas that there are no loops left.
417 -- Non-recursive case
418 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
420 -- Common case of simple self-recursion
421 reOrderRec env (CyclicSCC [bind])
422 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
424 ((tagged_bndr, rhs), _, _) = bind
426 reOrderRec env (CyclicSCC (bind : binds))
427 = -- Choose a loop breaker, mark it no-inline,
428 -- do SCC analysis on the rest, and recursively sort them out
429 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
431 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
434 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
435 (tagged_bndr, rhs) = chosen_pair
437 -- This loop looks for the bind with the lowest score
438 -- to pick as the loop breaker. The rest accumulate in
439 choose_loop_breaker (details,_,_) loop_sc acc []
440 = (details, acc) -- Done
442 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
443 | sc < loop_sc -- Lower score so pick this new one
444 = choose_loop_breaker bind sc (loop_bind : acc) binds
446 | otherwise -- No lower so don't pick it
447 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
451 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
452 score ((bndr, rhs), _, _)
453 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
454 -- Used to have also: && not (isExportedId bndr)
455 -- But I found this sometimes cost an extra iteration when we have
456 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
457 -- where df is the exported dictionary. Then df makes a really
458 -- bad choice for loop breaker
460 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
461 -- This used to have a lower score than inlineCandidate, but
462 -- it's *really* helpful if dictionaries get inlined fast,
463 -- so I'm experimenting with giving higher priority to data-typed things
465 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
467 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
468 -- Avoid things with specialisations; we'd like
469 -- to take advantage of them in the subsequent bindings
473 inlineCandidate :: Id -> CoreExpr -> Bool
474 inlineCandidate id (Note InlineMe _) = True
475 inlineCandidate id rhs = case idOccInfo id of
479 -- Real example (the Enum Ordering instance from PrelBase):
480 -- rec f = \ x -> case d of (p,q,r) -> p x
481 -- g = \ x -> case d of (p,q,r) -> q x
484 -- Here, f and g occur just once; but we can't inline them into d.
485 -- On the other hand we *could* simplify those case expressions if
486 -- we didn't stupidly choose d as the loop breaker.
487 -- But we won't because constructor args are marked "Many".
489 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
491 (_, rho_ty) = splitForAllTys ty
494 @occAnalRhs@ deals with the question of bindings where the Id is marked
495 by an INLINE pragma. For these we record that anything which occurs
496 in its RHS occurs many times. This pessimistically assumes that ths
497 inlined binder also occurs many times in its scope, but if it doesn't
498 we'll catch it next time round. At worst this costs an extra simplifier pass.
499 ToDo: try using the occurrence info for the inline'd binder.
501 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
502 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
507 -> Id -> CoreExpr -- Binder and rhs
508 -> (UsageDetails, CoreExpr)
510 occAnalRhs env id rhs
511 = (final_usage, rhs')
513 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
515 -- [March 98] A new wrinkle is that if the binder has specialisations inside
516 -- it then we count the specialised Ids as "extra rhs's". That way
517 -- the "parent" keeps the specialised "children" alive. If the parent
518 -- dies (because it isn't referenced any more), then the children will
519 -- die too unless they are already referenced directly.
521 final_usage = foldVarSet add rhs_usage (idRuleVars id)
522 add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
523 -- (i.e manyOcc) because many copies
524 -- of the specialised thing can appear
532 -> (UsageDetails, -- Gives info only about the "interesting" Ids
535 occAnal env (Type t) = (emptyDetails, Type t)
540 var_uds | isCandidate env v = unitVarEnv v funOccZero
541 | otherwise = emptyDetails
543 -- At one stage, I gathered the idRuleVars for v here too,
544 -- which in a way is the right thing to do.
545 -- But that went wrong right after specialisation, when
546 -- the *occurrences* of the overloaded function didn't have any
547 -- rules in them, so the *specialised* versions looked as if they
548 -- weren't used at all.
552 We regard variables that occur as constructor arguments as "dangerousToDup":
556 f x = let y = expensive x in
558 (case z of {(p,q)->q}, case z of {(p,q)->q})
561 We feel free to duplicate the WHNF (True,y), but that means
562 that y may be duplicated thereby.
564 If we aren't careful we duplicate the (expensive x) call!
565 Constructors are rather like lambdas in this way.
568 occAnal env expr@(Lit lit) = (emptyDetails, expr)
572 occAnal env (Note InlineMe body)
573 = case occAnal env body of { (usage, body') ->
574 (mapVarEnv markMany usage, Note InlineMe body')
577 occAnal env (Note note@(SCC cc) body)
578 = case occAnal env body of { (usage, body') ->
579 (mapVarEnv markInsideSCC usage, Note note body')
582 occAnal env (Note note body)
583 = case occAnal env body of { (usage, body') ->
584 (usage, Note note body')
589 occAnal env app@(App fun arg)
590 = occAnalApp env (collectArgs app)
592 -- Ignore type variables altogether
593 -- (a) occurrences inside type lambdas only not marked as InsideLam
594 -- (b) type variables not in environment
596 occAnal env expr@(Lam x body) | isTyVar x
597 = case occAnal env body of { (body_usage, body') ->
598 (body_usage, Lam x body')
601 -- For value lambdas we do a special hack. Consider
603 -- If we did nothing, x is used inside the \y, so would be marked
604 -- as dangerous to dup. But in the common case where the abstraction
605 -- is applied to two arguments this is over-pessimistic.
606 -- So instead, we just mark each binder with its occurrence
607 -- info in the *body* of the multiple lambda.
608 -- Then, the simplifier is careful when partially applying lambdas.
610 occAnal env expr@(Lam _ _)
611 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
613 (final_usage, tagged_binders) = tagBinders body_usage binders
614 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
615 -- we get linear-typed things in the resulting program that we can't handle yet.
616 -- (e.g. PrelShow) TODO
618 really_final_usage = if linear then
621 mapVarEnv markInsideLam final_usage
624 mkLams tagged_binders body') }
626 (binders, body) = collectBinders expr
627 (linear, env_body, _) = oneShotGroup env binders
629 occAnal env (Case scrut bndr alts)
630 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
631 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
633 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
634 alts_usage' = addCaseBndrUsage alts_usage
635 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
636 total_usage = scrut_usage `combineUsageDetails` alts_usage1
638 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
640 alt_env = env `addNewCand` bndr
642 -- The case binder gets a usage of either "many" or "dead", never "one".
643 -- Reason: we like to inline single occurrences, to eliminate a binding,
644 -- but inlining a case binder *doesn't* eliminate a binding.
645 -- We *don't* want to transform
646 -- case x of w { (p,q) -> f w }
648 -- case x of w { (p,q) -> f (p,q) }
649 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
651 Just occ -> extendVarEnv usage bndr (markMany occ)
653 occAnal env (Let bind body)
654 = case occAnal new_env body of { (body_usage, body') ->
655 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
656 (final_usage, mkLets new_binds body') }}
658 new_env = env `addNewCands` (bindersOf bind)
661 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
662 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
664 arg_env = zapCtxt env
667 Applications are dealt with specially because we want
668 the "build hack" to work.
671 -- Hack for build, fold, runST
672 occAnalApp env (Var fun, args)
673 = case args_stuff of { (args_uds, args') ->
675 final_uds = fun_uds `combineUsageDetails` args_uds
677 (final_uds, mkApps (Var fun) args') }
679 fun_uniq = idUnique fun
681 fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
682 | otherwise = emptyDetails
684 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
685 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
686 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
687 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
689 | isDataConId fun = case occAnalArgs env args of
690 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
691 -- We mark the free vars of the argument of a constructor as "many"
692 -- This means that nothing gets inlined into a constructor argument
693 -- position, which is what we want. Typically those constructor
694 -- arguments are just variables, or trivial expressions.
696 | otherwise = occAnalArgs env args
699 occAnalApp env (fun, args)
700 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
701 case occAnalArgs env args of { (args_uds, args') ->
703 final_uds = fun_uds `combineUsageDetails` args_uds
705 (final_uds, mkApps fun' args') }}
707 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
708 appSpecial env n ctxt args
711 go n [] = (emptyDetails, []) -- Too few args
713 go 1 (arg:args) -- The magic arg
714 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
715 case occAnalArgs env args of { (args_uds, args') ->
716 (combineUsageDetails arg_uds args_uds, arg':args') }}
719 = case occAnal env arg of { (arg_uds, arg') ->
720 case go (n-1) args of { (args_uds, args') ->
721 (combineUsageDetails arg_uds args_uds, arg':args') }}
728 occAnalAlt env (con, bndrs, rhs)
729 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
731 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
733 (final_usage, (con, tagged_bndrs, rhs')) }
737 %************************************************************************
739 \subsection[OccurAnal-types]{Data types}
741 %************************************************************************
744 -- We gather inforamtion for variables that are either
749 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
750 IdSet -- In-scope Ids
751 CtxtTy -- Tells about linearity
756 -- True:ctxt Analysing a function-valued expression that will be
759 -- False:ctxt Analysing a function-valued expression that may
760 -- be applied many times; but when it is,
761 -- the CtxtTy inside applies
763 isCandidate :: OccEnv -> Id -> Bool
764 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
766 addNewCands :: OccEnv -> [Id] -> OccEnv
767 addNewCands (OccEnv ifun cands ctxt) ids
768 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
770 addNewCand :: OccEnv -> Id -> OccEnv
771 addNewCand (OccEnv ifun cands ctxt) id
772 = OccEnv ifun (extendVarSet cands id) ctxt
774 setCtxt :: OccEnv -> CtxtTy -> OccEnv
775 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
777 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
778 -- True <=> this is a one-shot linear lambda group
779 -- The [CoreBndr] are the binders.
781 -- The result binders have one-shot-ness set that they might not have had originally.
782 -- This happens in (build (\cn -> e)). Here the occurrence analyser
783 -- linearity context knows that c,n are one-shot, and it records that fact in
784 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
786 oneShotGroup (OccEnv ifun cands ctxt) bndrs
787 = case go ctxt bndrs [] of
788 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
790 is_one_shot b = isId b && isOneShotLambda b
792 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
794 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
795 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
797 bndr' | lin_ctxt = setOneShotLambda bndr
800 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
803 zapCtxt env@(OccEnv ifun cands []) = env
804 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
806 type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
808 combineUsageDetails, combineAltsUsageDetails
809 :: UsageDetails -> UsageDetails -> UsageDetails
811 combineUsageDetails usage1 usage2
812 = plusVarEnv_C addBinderInfo usage1 usage2
814 combineAltsUsageDetails usage1 usage2
815 = plusVarEnv_C orBinderInfo usage1 usage2
817 addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
818 addOneOcc usage id info
819 = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
820 -- ToDo: make this more efficient
822 emptyDetails = (emptyVarEnv :: UsageDetails)
824 unitDetails id info = (unitVarEnv id info :: UsageDetails)
826 usedIn :: Id -> UsageDetails -> Bool
827 v `usedIn` details = isExportedId v || v `elemVarEnv` details
829 tagBinders :: UsageDetails -- Of scope
831 -> (UsageDetails, -- Details with binders removed
832 [IdWithOccInfo]) -- Tagged binders
834 tagBinders usage binders
836 usage' = usage `delVarEnvList` binders
837 uss = map (setBinderOcc usage) binders
839 usage' `seq` (usage', uss)
841 tagBinder :: UsageDetails -- Of scope
843 -> (UsageDetails, -- Details with binders removed
844 IdWithOccInfo) -- Tagged binders
846 tagBinder usage binder
848 usage' = usage `delVarEnv` binder
849 binder' = setBinderOcc usage binder
851 usage' `seq` (usage', binder')
854 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
855 setBinderOcc usage bndr
856 | isTyVar bndr = bndr
858 = -- Don't use local usage info for visible-elsewhere things
859 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
860 -- about to re-generate it and it shouldn't be "sticky"
861 case idOccInfo bndr of
863 other -> setIdOccInfo bndr NoOccInfo
865 | otherwise = setIdOccInfo bndr occ_info
867 occ_info = case lookupVarEnv usage bndr of
869 Just info -> binderInfoToOccInfo info
871 funOccZero = funOccurrence 0