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,
27 idSpecialisation, isLocalId,
30 import IdInfo ( OccInfo(..), shortableIdInfo, copyIdInfo )
35 import Type ( splitFunTy_maybe, splitForAllTys )
36 import Maybes ( maybeToBool )
37 import Digraph ( stronglyConnCompR, SCC(..) )
38 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
40 import UniqFM ( keysUFM )
41 import Util ( zipWithEqual, mapAndUnzip )
47 %************************************************************************
49 \subsection[OccurAnal-main]{Counting occurrences: main function}
51 %************************************************************************
53 Here's the externally-callable interface:
56 occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
58 -> (IdEnv BinderInfo, -- Occ info for interesting free vars
61 occurAnalyseExpr interesting expr
62 = occAnal initial_env expr
64 initial_env = OccEnv interesting emptyVarSet []
66 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
67 occurAnalyseGlobalExpr expr
68 = -- Top level expr, so no interesting free vars, and
69 -- discard occurence info returned
70 snd (occurAnalyseExpr (\_ -> False) expr)
72 occurAnalyseRule :: CoreRule -> CoreRule
73 occurAnalyseRule rule@(BuiltinRule _) = rule
74 occurAnalyseRule (Rule str tpl_vars tpl_args rhs)
75 -- Add occ info to tpl_vars, rhs
76 = Rule str tpl_vars' tpl_args rhs'
78 (rhs_uds, rhs') = occurAnalyseExpr isLocalId rhs
79 (_, tpl_vars') = tagBinders rhs_uds tpl_vars
83 %************************************************************************
85 \subsection{Top level stuff}
87 %************************************************************************
89 In @occAnalTop@ we do indirection-shorting. That is, if we have this:
91 x_local = <expression>
95 where exp is exported, and loc is not, then we replace it with this:
98 x_exported = <expression>
101 Without this we never get rid of the x_exported = x_local thing. This
102 save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
103 makes strictness information propagate better. This used to happen in
104 the final phase, but it's tidier to do it here.
106 If more than one exported thing is equal to a local thing (i.e., the
107 local thing really is shared), then we do one only:
110 x_exported1 = x_local
111 x_exported2 = x_local
115 x_exported2 = x_exported1
118 We rely on prior eta reduction to simplify things like
120 x_exported = /\ tyvars -> x_local tyvars
124 Hence,there's a possibility of leaving unchanged something like this:
127 x_exported1 = x_local Int
129 By the time we've thrown away the types in STG land this
130 could be eliminated. But I don't think it's very common
131 and it's dangerous to do this fiddling in STG land
132 because we might elminate a binding that's mentioned in the
133 unfolding for something.
136 occurAnalyseBinds :: [CoreBind] -> [CoreBind]
138 occurAnalyseBinds binds
141 (_, _, binds') = go initialTopEnv binds
143 go :: OccEnv -> [CoreBind]
144 -> (UsageDetails, -- Occurrence info
145 IdEnv Id, -- Indirection elimination info
146 -- Maps local-id -> exported-id, but it embodies
147 -- bindings of the form exported-id = local-id in
148 -- the argument to go
149 [CoreBind]) -- Occ-analysed bindings, less the exported-id=local-id ones
151 go env [] = (emptyDetails, emptyVarEnv, [])
153 go env (bind : binds)
155 new_env = env `addNewCands` (bindersOf bind)
156 (scope_usage, ind_env, binds') = go new_env binds
157 (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
158 -- NB: I zap before occur-analysing, so
159 -- I don't need to worry about getting the
160 -- occ info on the new bindings right.
163 NonRec exported_id (Var local_id)
164 | shortMeOut ind_env exported_id local_id
165 -- Special case for eliminating indirections
166 -- Note: it's a shortcoming that this only works for
167 -- non-recursive bindings. Elminating indirections
168 -- makes perfect sense for recursive bindings too, but
169 -- it's more complicated to implement, so I haven't done so
170 -> (scope_usage, ind_env', binds')
172 ind_env' = extendVarEnv ind_env local_id exported_id
174 other -> -- Ho ho! The normal case
175 (final_usage, ind_env, new_binds ++ binds')
177 initialTopEnv = OccEnv isLocalId -- Anything local is interesting
182 -- Deal with any indirections
183 zapBind ind_env (NonRec bndr rhs)
184 | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
185 -- The Rec isn't strictly necessary, but it's convenient
186 zapBind ind_env (Rec pairs)
187 | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
189 zapBind ind_env bind = bind
191 zap ind_env pair@(local_id,rhs)
192 = case lookupVarEnv ind_env local_id of
194 Just exported_id -> [(local_id, Var exported_id),
197 exported_id' = modifyIdInfo (copyIdInfo (idInfo local_id)) exported_id
199 shortMeOut ind_env exported_id local_id
200 -- The if-then-else stuff is just so I can get a pprTrace to see
201 -- how often I don't get shorting out becuase of IdInfo stuff
202 = if isExportedId exported_id && -- Only if this is exported
204 isLocalId local_id && -- Only if this one is defined in this
205 -- module, so that we *can* change its
206 -- binding to be the exported thing!
208 not (isExportedId local_id) && -- Only if this one is not itself exported,
209 -- since the transformation will nuke it
211 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
213 if shortableIdInfo (idInfo exported_id) -- Only if its IdInfo is 'shortable'
214 -- (see the defn of IdInfo.shortableIdInfo
216 else pprTrace "shortMeOut:" (ppr exported_id) False
222 %************************************************************************
224 \subsection[OccurAnal-main]{Counting occurrences: main function}
226 %************************************************************************
232 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
234 type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
235 -- which is gotten from the Id.
236 type Details1 = (Id, UsageDetails, CoreExpr)
237 type Details2 = (IdWithOccInfo, CoreExpr)
240 occAnalBind :: OccEnv
242 -> UsageDetails -- Usage details of scope
243 -> (UsageDetails, -- Of the whole let(rec)
246 occAnalBind env (NonRec binder rhs) body_usage
247 | not (binder `usedIn` body_usage) -- It's not mentioned
250 | otherwise -- It's mentioned in the body
251 = (final_body_usage `combineUsageDetails` rhs_usage,
252 [NonRec tagged_binder rhs'])
255 (final_body_usage, tagged_binder) = tagBinder body_usage binder
256 (rhs_usage, rhs') = occAnalRhs env binder rhs
259 Dropping dead code for recursive bindings is done in a very simple way:
261 the entire set of bindings is dropped if none of its binders are
262 mentioned in its body; otherwise none are.
264 This seems to miss an obvious improvement.
279 Now @f@ is unused. But dependency analysis will sort this out into a
280 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
281 It isn't easy to do a perfect job in one blow. Consider
295 occAnalBind env (Rec pairs) body_usage
296 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
298 binders = map fst pairs
299 rhs_env = env `addNewCands` binders
301 analysed_pairs :: [Details1]
302 analysed_pairs = [ (bndr, rhs_usage, rhs')
303 | (bndr, rhs) <- pairs,
304 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
307 sccs :: [SCC (Node Details1)]
308 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
311 ---- stuff for dependency analysis of binds -------------------------------
312 edges :: [Node Details1]
313 edges = _scc_ "occAnalBind.assoc"
314 [ (details, iBox (u2i (idUnique id)), edges_from rhs_usage)
315 | details@(id, rhs_usage, rhs) <- analysed_pairs
318 -- (a -> b) means a mentions b
319 -- Given the usage details (a UFM that gives occ info for each free var of
320 -- the RHS) we can get the list of free vars -- or rather their Int keys --
321 -- by just extracting the keys from the finite map. Grimy, but fast.
322 -- Previously we had this:
323 -- [ bndr | bndr <- bndrs,
324 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
325 -- which has n**2 cost, and this meant that edges_from alone
326 -- consumed 10% of total runtime!
327 edges_from :: UsageDetails -> [Int]
328 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
331 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
334 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
335 | not (bndr `usedIn` body_usage)
336 = (body_usage, binds_so_far) -- Dead code
338 = (combined_usage, new_bind : binds_so_far)
340 total_usage = combineUsageDetails body_usage rhs_usage
341 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
342 new_bind = NonRec tagged_bndr rhs'
345 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
346 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
347 = (body_usage, binds_so_far) -- Dead code
349 = (combined_usage, final_bind:binds_so_far)
351 details = [details | (details, _, _) <- cycle]
352 bndrs = [bndr | (bndr, _, _) <- details]
353 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
354 total_usage = foldr combineUsageDetails body_usage rhs_usages
355 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
356 final_bind = Rec (reOrderRec env new_cycle)
358 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
359 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
362 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
363 strongly connected component (there's guaranteed to be a cycle). It returns the
365 a) in a better order,
366 b) with some of the Ids having a IMustNotBeINLINEd pragma
368 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
369 that the simplifier can guarantee not to loop provided it never records an inlining
370 for these no-inline guys.
372 Furthermore, the order of the binds is such that if we neglect dependencies
373 on the no-inline Ids then the binds are topologically sorted. This means
374 that the simplifier will generally do a good job if it works from top bottom,
375 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
378 [June 98: I don't understand the following paragraphs, and I've
379 changed the a=b case again so that it isn't a special case any more.]
381 Here's a case that bit me:
389 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
391 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
392 Perhaps something cleverer would suffice.
395 You might think that you can prevent non-termination simply by making
396 sure that we simplify a recursive binding's RHS in an environment that
397 simply clones the recursive Id. But no. Consider
399 letrec f = \x -> let z = f x' in ...
406 We bind n to its *simplified* RHS, we then *re-simplify* it when
407 we inline n. Then we may well inline f; and then the same thing
410 I don't think it's possible to prevent non-termination by environment
411 manipulation in this way. Apart from anything else, successive
412 iterations of the simplifier may unroll recursive loops in cases like
413 that above. The idea of beaking every recursive loop with an
414 IMustNotBeINLINEd pragma is much much better.
420 -> SCC (Node Details2)
422 -- Sorted into a plausible order. Enough of the Ids have
423 -- dontINLINE pragmas that there are no loops left.
425 -- Non-recursive case
426 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
428 -- Common case of simple self-recursion
429 reOrderRec env (CyclicSCC [bind])
430 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
432 ((tagged_bndr, rhs), _, _) = bind
434 reOrderRec env (CyclicSCC (bind : binds))
435 = -- Choose a loop breaker, mark it no-inline,
436 -- do SCC analysis on the rest, and recursively sort them out
437 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
439 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
442 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
443 (tagged_bndr, rhs) = chosen_pair
445 -- This loop looks for the bind with the lowest score
446 -- to pick as the loop breaker. The rest accumulate in
447 choose_loop_breaker (details,_,_) loop_sc acc []
448 = (details, acc) -- Done
450 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
451 | sc < loop_sc -- Lower score so pick this new one
452 = choose_loop_breaker bind sc (loop_bind : acc) binds
454 | otherwise -- No lower so don't pick it
455 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
459 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
460 score ((bndr, rhs), _, _)
461 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
462 -- Used to have also: && not (isExportedId bndr)
463 -- But I found this sometimes cost an extra iteration when we have
464 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
465 -- where df is the exported dictionary. Then df makes a really
466 -- bad choice for loop breaker
468 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
469 -- This used to have a lower score than inlineCandidate, but
470 -- it's *really* helpful if dictionaries get inlined fast,
471 -- so I'm experimenting with giving higher priority to data-typed things
473 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
475 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
476 -- Avoid things with specialisations; we'd like
477 -- to take advantage of them in the subsequent bindings
481 inlineCandidate :: Id -> CoreExpr -> Bool
482 inlineCandidate id (Note InlineMe _) = True
483 inlineCandidate id rhs = case idOccInfo id of
487 -- Real example (the Enum Ordering instance from PrelBase):
488 -- rec f = \ x -> case d of (p,q,r) -> p x
489 -- g = \ x -> case d of (p,q,r) -> q x
492 -- Here, f and g occur just once; but we can't inline them into d.
493 -- On the other hand we *could* simplify those case expressions if
494 -- we didn't stupidly choose d as the loop breaker.
495 -- But we won't because constructor args are marked "Many".
497 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
499 (_, rho_ty) = splitForAllTys ty
502 @occAnalRhs@ deals with the question of bindings where the Id is marked
503 by an INLINE pragma. For these we record that anything which occurs
504 in its RHS occurs many times. This pessimistically assumes that ths
505 inlined binder also occurs many times in its scope, but if it doesn't
506 we'll catch it next time round. At worst this costs an extra simplifier pass.
507 ToDo: try using the occurrence info for the inline'd binder.
509 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
510 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
515 -> Id -> CoreExpr -- Binder and rhs
516 -> (UsageDetails, CoreExpr)
518 occAnalRhs env id rhs
519 = (final_usage, rhs')
521 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
523 -- [March 98] A new wrinkle is that if the binder has specialisations inside
524 -- it then we count the specialised Ids as "extra rhs's". That way
525 -- the "parent" keeps the specialised "children" alive. If the parent
526 -- dies (because it isn't referenced any more), then the children will
527 -- die too unless they are already referenced directly.
529 final_usage = foldVarSet add rhs_usage (idRuleVars id)
530 add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
531 -- (i.e manyOcc) because many copies
532 -- of the specialised thing can appear
540 -> (UsageDetails, -- Gives info only about the "interesting" Ids
543 occAnal env (Type t) = (emptyDetails, Type t)
548 var_uds | isCandidate env v = unitVarEnv v funOccZero
549 | otherwise = emptyDetails
551 -- At one stage, I gathered the idRuleVars for v here too,
552 -- which in a way is the right thing to do.
553 -- But that went wrong right after specialisation, when
554 -- the *occurrences* of the overloaded function didn't have any
555 -- rules in them, so the *specialised* versions looked as if they
556 -- weren't used at all.
560 We regard variables that occur as constructor arguments as "dangerousToDup":
564 f x = let y = expensive x in
566 (case z of {(p,q)->q}, case z of {(p,q)->q})
569 We feel free to duplicate the WHNF (True,y), but that means
570 that y may be duplicated thereby.
572 If we aren't careful we duplicate the (expensive x) call!
573 Constructors are rather like lambdas in this way.
576 occAnal env expr@(Lit lit) = (emptyDetails, expr)
580 occAnal env (Note InlineMe body)
581 = case occAnal env body of { (usage, body') ->
582 (mapVarEnv markMany usage, Note InlineMe body')
585 occAnal env (Note note@(SCC cc) body)
586 = case occAnal env body of { (usage, body') ->
587 (mapVarEnv markInsideSCC usage, Note note body')
590 occAnal env (Note note body)
591 = case occAnal env body of { (usage, body') ->
592 (usage, Note note body')
597 occAnal env app@(App fun arg)
598 = occAnalApp env (collectArgs app)
600 -- Ignore type variables altogether
601 -- (a) occurrences inside type lambdas only not marked as InsideLam
602 -- (b) type variables not in environment
604 occAnal env expr@(Lam x body) | isTyVar x
605 = case occAnal env body of { (body_usage, body') ->
606 (body_usage, Lam x body')
609 -- For value lambdas we do a special hack. Consider
611 -- If we did nothing, x is used inside the \y, so would be marked
612 -- as dangerous to dup. But in the common case where the abstraction
613 -- is applied to two arguments this is over-pessimistic.
614 -- So instead, we just mark each binder with its occurrence
615 -- info in the *body* of the multiple lambda.
616 -- Then, the simplifier is careful when partially applying lambdas.
618 occAnal env expr@(Lam _ _)
619 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
621 (final_usage, tagged_binders) = tagBinders body_usage binders
622 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
623 -- we get linear-typed things in the resulting program that we can't handle yet.
624 -- (e.g. PrelShow) TODO
626 really_final_usage = if linear then
629 mapVarEnv markInsideLam final_usage
632 mkLams tagged_binders body') }
634 (binders, body) = collectBinders expr
635 (linear, env_body, _) = oneShotGroup env binders
637 occAnal env (Case scrut bndr alts)
638 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
639 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
641 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
642 alts_usage' = addCaseBndrUsage alts_usage
643 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
644 total_usage = scrut_usage `combineUsageDetails` alts_usage1
646 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
648 alt_env = env `addNewCand` bndr
650 -- The case binder gets a usage of either "many" or "dead", never "one".
651 -- Reason: we like to inline single occurrences, to eliminate a binding,
652 -- but inlining a case binder *doesn't* eliminate a binding.
653 -- We *don't* want to transform
654 -- case x of w { (p,q) -> f w }
656 -- case x of w { (p,q) -> f (p,q) }
657 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
659 Just occ -> extendVarEnv usage bndr (markMany occ)
661 occAnal env (Let bind body)
662 = case occAnal new_env body of { (body_usage, body') ->
663 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
664 (final_usage, mkLets new_binds body') }}
666 new_env = env `addNewCands` (bindersOf bind)
669 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
670 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
672 arg_env = zapCtxt env
675 Applications are dealt with specially because we want
676 the "build hack" to work.
679 -- Hack for build, fold, runST
680 occAnalApp env (Var fun, args)
681 = case args_stuff of { (args_uds, args') ->
683 final_uds = fun_uds `combineUsageDetails` args_uds
685 (final_uds, mkApps (Var fun) args') }
687 fun_uniq = idUnique fun
689 fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
690 | otherwise = emptyDetails
692 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
693 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
694 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
695 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
697 | isDataConId fun = case occAnalArgs env args of
698 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
699 -- We mark the free vars of the argument of a constructor as "many"
700 -- This means that nothing gets inlined into a constructor argument
701 -- position, which is what we want. Typically those constructor
702 -- arguments are just variables, or trivial expressions.
704 | otherwise = occAnalArgs env args
707 occAnalApp env (fun, args)
708 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
709 case occAnalArgs env args of { (args_uds, args') ->
711 final_uds = fun_uds `combineUsageDetails` args_uds
713 (final_uds, mkApps fun' args') }}
715 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
716 appSpecial env n ctxt args
719 go n [] = (emptyDetails, []) -- Too few args
721 go 1 (arg:args) -- The magic arg
722 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
723 case occAnalArgs env args of { (args_uds, args') ->
724 (combineUsageDetails arg_uds args_uds, arg':args') }}
727 = case occAnal env arg of { (arg_uds, arg') ->
728 case go (n-1) args of { (args_uds, args') ->
729 (combineUsageDetails arg_uds args_uds, arg':args') }}
736 occAnalAlt env (con, bndrs, rhs)
737 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
739 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
741 (final_usage, (con, tagged_bndrs, rhs')) }
745 %************************************************************************
747 \subsection[OccurAnal-types]{Data types}
749 %************************************************************************
752 -- We gather inforamtion for variables that are either
757 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
758 IdSet -- In-scope Ids
759 CtxtTy -- Tells about linearity
764 -- True:ctxt Analysing a function-valued expression that will be
767 -- False:ctxt Analysing a function-valued expression that may
768 -- be applied many times; but when it is,
769 -- the CtxtTy inside applies
771 isCandidate :: OccEnv -> Id -> Bool
772 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
774 addNewCands :: OccEnv -> [Id] -> OccEnv
775 addNewCands (OccEnv ifun cands ctxt) ids
776 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
778 addNewCand :: OccEnv -> Id -> OccEnv
779 addNewCand (OccEnv ifun cands ctxt) id
780 = OccEnv ifun (extendVarSet cands id) ctxt
782 setCtxt :: OccEnv -> CtxtTy -> OccEnv
783 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
785 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
786 -- True <=> this is a one-shot linear lambda group
787 -- The [CoreBndr] are the binders.
789 -- The result binders have one-shot-ness set that they might not have had originally.
790 -- This happens in (build (\cn -> e)). Here the occurrence analyser
791 -- linearity context knows that c,n are one-shot, and it records that fact in
792 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
794 oneShotGroup (OccEnv ifun cands ctxt) bndrs
795 = case go ctxt bndrs [] of
796 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
798 is_one_shot b = isId b && isOneShotLambda b
800 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
802 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
803 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
805 bndr' | lin_ctxt = setOneShotLambda bndr
808 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
811 zapCtxt env@(OccEnv ifun cands []) = env
812 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
814 type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
816 combineUsageDetails, combineAltsUsageDetails
817 :: UsageDetails -> UsageDetails -> UsageDetails
819 combineUsageDetails usage1 usage2
820 = plusVarEnv_C addBinderInfo usage1 usage2
822 combineAltsUsageDetails usage1 usage2
823 = plusVarEnv_C orBinderInfo usage1 usage2
825 addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
826 addOneOcc usage id info
827 = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
828 -- ToDo: make this more efficient
830 emptyDetails = (emptyVarEnv :: UsageDetails)
832 usedIn :: Id -> UsageDetails -> Bool
833 v `usedIn` details = isExportedId v || v `elemVarEnv` details
835 tagBinders :: UsageDetails -- Of scope
837 -> (UsageDetails, -- Details with binders removed
838 [IdWithOccInfo]) -- Tagged binders
840 tagBinders usage binders
842 usage' = usage `delVarEnvList` binders
843 uss = map (setBinderOcc usage) binders
845 usage' `seq` (usage', uss)
847 tagBinder :: UsageDetails -- Of scope
849 -> (UsageDetails, -- Details with binders removed
850 IdWithOccInfo) -- Tagged binders
852 tagBinder usage binder
854 usage' = usage `delVarEnv` binder
855 binder' = setBinderOcc usage binder
857 usage' `seq` (usage', binder')
860 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
861 setBinderOcc usage bndr
862 | isTyVar bndr = bndr
864 = -- Don't use local usage info for visible-elsewhere things
865 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
866 -- about to re-generate it and it shouldn't be "sticky"
867 case idOccInfo bndr of
869 other -> setIdOccInfo bndr NoOccInfo
871 | otherwise = setIdOccInfo bndr occ_info
873 occ_info = case lookupVarEnv usage bndr of
875 Just info -> binderInfoToOccInfo info
877 funOccZero = funOccurrence 0