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"
21 import CmdLineOpts ( SimplifierSwitch(..) )
23 import CoreFVs ( idRuleVars )
24 import CoreUtils ( exprIsTrivial )
25 import Literal ( Literal(..) )
26 import Id ( isSpecPragmaId, isDataConId, isOneShotLambda, setOneShotLambda,
27 idOccInfo, setIdOccInfo,
28 isExportedId, modifyIdInfo, idInfo,
32 import IdInfo ( OccInfo(..), insideLam, copyIdInfo )
37 import Name ( isLocallyDefined )
38 import Type ( splitFunTy_maybe, splitForAllTys )
39 import Maybes ( maybeToBool )
40 import Digraph ( stronglyConnCompR, SCC(..) )
41 import Unique ( u2i, buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
42 import UniqFM ( keysUFM )
43 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 (rhs_uds1, 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:
96 where exp is exported, and loc is not, then we replace it with this:
102 Without this we never get rid of the exp = loc thing.
103 This save a gratuitous jump
104 (from \tr{x_exported} to \tr{x_local}), and makes strictness
105 information propagate better.
106 This used to happen in the final phase, but it's tidier to do it here.
109 If more than one exported thing is equal to a local thing (i.e., the
110 local thing really is shared), then we do one only:
113 x_exported1 = x_local
114 x_exported2 = x_local
118 x_exported2 = x_exported1
121 We rely on prior eta reduction to simplify things like
123 x_exported = /\ tyvars -> x_local tyvars
127 Hence,there's a possibility of leaving unchanged something like this:
130 x_exported1 = x_local Int
132 By the time we've thrown away the types in STG land this
133 could be eliminated. But I don't think it's very common
134 and it's dangerous to do this fiddling in STG land
135 because we might elminate a binding that's mentioned in the
136 unfolding for something.
139 occurAnalyseBinds :: [CoreBind] -> [CoreBind]
141 occurAnalyseBinds binds
144 (_, _, binds') = go initialTopEnv binds
146 go :: OccEnv -> [CoreBind]
147 -> (UsageDetails, -- Occurrence info
148 IdEnv Id, -- Indirection elimination info
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 isLocallyDefined -- 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@(bndr,rhs)
192 = case lookupVarEnv ind_env bndr of
194 Just exported_id -> [(bndr, Var exported_id),
195 (exported_id_w_info, rhs)]
197 exported_id_w_info = modifyIdInfo (copyIdInfo (idInfo bndr)) exported_id
198 -- See notes with copyIdInfo about propagating IdInfo from
201 shortMeOut ind_env exported_id local_id
202 = isExportedId exported_id && -- Only if this is exported
204 isLocallyDefined 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
215 %************************************************************************
217 \subsection[OccurAnal-main]{Counting occurrences: main function}
219 %************************************************************************
225 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
227 type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
228 -- which is gotten from the Id.
229 type Details1 = (Id, UsageDetails, CoreExpr)
230 type Details2 = (IdWithOccInfo, CoreExpr)
233 occAnalBind :: OccEnv
235 -> UsageDetails -- Usage details of scope
236 -> (UsageDetails, -- Of the whole let(rec)
239 occAnalBind env (NonRec binder rhs) body_usage
240 | not (binder `usedIn` body_usage) -- It's not mentioned
243 | otherwise -- It's mentioned in the body
244 = (final_body_usage `combineUsageDetails` rhs_usage,
245 [NonRec tagged_binder rhs'])
248 (final_body_usage, tagged_binder) = tagBinder body_usage binder
249 (rhs_usage, rhs') = occAnalRhs env binder rhs
252 Dropping dead code for recursive bindings is done in a very simple way:
254 the entire set of bindings is dropped if none of its binders are
255 mentioned in its body; otherwise none are.
257 This seems to miss an obvious improvement.
272 Now @f@ is unused. But dependency analysis will sort this out into a
273 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
274 It isn't easy to do a perfect job in one blow. Consider
288 occAnalBind env (Rec pairs) body_usage
289 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
291 pp_item (_, bndr, _) = ppr bndr
293 binders = map fst pairs
294 rhs_env = env `addNewCands` binders
296 analysed_pairs :: [Details1]
297 analysed_pairs = [ (bndr, rhs_usage, rhs')
298 | (bndr, rhs) <- pairs,
299 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
302 sccs :: [SCC (Node Details1)]
303 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
306 ---- stuff for dependency analysis of binds -------------------------------
307 edges :: [Node Details1]
308 edges = _scc_ "occAnalBind.assoc"
309 [ (details, IBOX(u2i (idUnique id)), edges_from rhs_usage)
310 | details@(id, rhs_usage, rhs) <- analysed_pairs
313 -- (a -> b) means a mentions b
314 -- Given the usage details (a UFM that gives occ info for each free var of
315 -- the RHS) we can get the list of free vars -- or rather their Int keys --
316 -- by just extracting the keys from the finite map. Grimy, but fast.
317 -- Previously we had this:
318 -- [ bndr | bndr <- bndrs,
319 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
320 -- which has n**2 cost, and this meant that edges_from alone
321 -- consumed 10% of total runtime!
322 edges_from :: UsageDetails -> [Int]
323 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
326 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
329 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
330 | not (bndr `usedIn` body_usage)
331 = (body_usage, binds_so_far) -- Dead code
333 = (combined_usage, new_bind : binds_so_far)
335 total_usage = combineUsageDetails body_usage rhs_usage
336 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
337 new_bind = NonRec tagged_bndr rhs'
340 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
341 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
342 = (body_usage, binds_so_far) -- Dead code
344 = (combined_usage, final_bind:binds_so_far)
346 details = [details | (details, _, _) <- cycle]
347 bndrs = [bndr | (bndr, _, _) <- details]
348 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
349 total_usage = foldr combineUsageDetails body_usage rhs_usages
350 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
351 final_bind = Rec (reOrderRec env new_cycle)
353 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
354 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
357 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
358 strongly connected component (there's guaranteed to be a cycle). It returns the
360 a) in a better order,
361 b) with some of the Ids having a IMustNotBeINLINEd pragma
363 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
364 that the simplifier can guarantee not to loop provided it never records an inlining
365 for these no-inline guys.
367 Furthermore, the order of the binds is such that if we neglect dependencies
368 on the no-inline Ids then the binds are topologically sorted. This means
369 that the simplifier will generally do a good job if it works from top bottom,
370 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
373 [June 98: I don't understand the following paragraphs, and I've
374 changed the a=b case again so that it isn't a special case any more.]
376 Here's a case that bit me:
384 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
386 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
387 Perhaps something cleverer would suffice.
390 You might think that you can prevent non-termination simply by making
391 sure that we simplify a recursive binding's RHS in an environment that
392 simply clones the recursive Id. But no. Consider
394 letrec f = \x -> let z = f x' in ...
401 We bind n to its *simplified* RHS, we then *re-simplify* it when
402 we inline n. Then we may well inline f; and then the same thing
405 I don't think it's possible to prevent non-termination by environment
406 manipulation in this way. Apart from anything else, successive
407 iterations of the simplifier may unroll recursive loops in cases like
408 that above. The idea of beaking every recursive loop with an
409 IMustNotBeINLINEd pragma is much much better.
415 -> SCC (Node Details2)
417 -- Sorted into a plausible order. Enough of the Ids have
418 -- dontINLINE pragmas that there are no loops left.
420 -- Non-recursive case
421 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
423 -- Common case of simple self-recursion
424 reOrderRec env (CyclicSCC [bind])
425 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
427 ((tagged_bndr, rhs), _, _) = bind
429 reOrderRec env (CyclicSCC (bind : binds))
430 = -- Choose a loop breaker, mark it no-inline,
431 -- do SCC analysis on the rest, and recursively sort them out
432 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
434 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
437 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
438 (tagged_bndr, rhs) = chosen_pair
440 -- This loop looks for the bind with the lowest score
441 -- to pick as the loop breaker. The rest accumulate in
442 choose_loop_breaker (details,_,_) loop_sc acc []
443 = (details, acc) -- Done
445 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
446 | sc < loop_sc -- Lower score so pick this new one
447 = choose_loop_breaker bind sc (loop_bind : acc) binds
449 | otherwise -- No lower so don't pick it
450 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
454 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
455 score ((bndr, rhs), _, _)
456 | exprIsTrivial rhs &&
457 not (isExportedId bndr) = 3 -- Practically certain to be inlined
458 | inlineCandidate bndr rhs = 3 -- Likely to be inlined
459 | not_fun_ty (idType bndr) = 2 -- Data types help with cases
460 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
461 -- Avoid things with specialisations; we'd like
462 -- to take advantage of them in the subsequent bindings
465 inlineCandidate :: Id -> CoreExpr -> Bool
466 inlineCandidate id (Note InlineMe _) = True
467 inlineCandidate id rhs = case idOccInfo id of
471 -- Real example (the Enum Ordering instance from PrelBase):
472 -- rec f = \ x -> case d of (p,q,r) -> p x
473 -- g = \ x -> case d of (p,q,r) -> q x
476 -- Here, f and g occur just once; but we can't inline them into d.
477 -- On the other hand we *could* simplify those case expressions if
478 -- we didn't stupidly choose d as the loop breaker.
479 -- But we won't because constructor args are marked "Many".
481 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
483 (_, rho_ty) = splitForAllTys ty
486 @occAnalRhs@ deals with the question of bindings where the Id is marked
487 by an INLINE pragma. For these we record that anything which occurs
488 in its RHS occurs many times. This pessimistically assumes that ths
489 inlined binder also occurs many times in its scope, but if it doesn't
490 we'll catch it next time round. At worst this costs an extra simplifier pass.
491 ToDo: try using the occurrence info for the inline'd binder.
493 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
494 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
499 -> Id -> CoreExpr -- Binder and rhs
500 -> (UsageDetails, CoreExpr)
502 occAnalRhs env id rhs
503 = (final_usage, rhs')
505 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
507 -- [March 98] A new wrinkle is that if the binder has specialisations inside
508 -- it then we count the specialised Ids as "extra rhs's". That way
509 -- the "parent" keeps the specialised "children" alive. If the parent
510 -- dies (because it isn't referenced any more), then the children will
511 -- die too unless they are already referenced directly.
513 final_usage = foldVarSet add rhs_usage (idRuleVars id)
514 add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
515 -- (i.e manyOcc) because many copies
516 -- of the specialised thing can appear
524 -> (UsageDetails, -- Gives info only about the "interesting" Ids
527 occAnal env (Type t) = (emptyDetails, Type t)
532 var_uds | isCandidate env v = unitVarEnv v funOccZero
533 | otherwise = emptyDetails
535 -- At one stage, I gathered the idRuleVars for v here too,
536 -- which in a way is the right thing to do.
537 -- But that went wrong right after specialisation, when
538 -- the *occurrences* of the overloaded function didn't have any
539 -- rules in them, so the *specialised* versions looked as if they
540 -- weren't used at all.
544 We regard variables that occur as constructor arguments as "dangerousToDup":
548 f x = let y = expensive x in
550 (case z of {(p,q)->q}, case z of {(p,q)->q})
553 We feel free to duplicate the WHNF (True,y), but that means
554 that y may be duplicated thereby.
556 If we aren't careful we duplicate the (expensive x) call!
557 Constructors are rather like lambdas in this way.
560 occAnal env expr@(Lit lit) = (emptyDetails, expr)
564 occAnal env (Note InlineMe body)
565 = case occAnal env body of { (usage, body') ->
566 (mapVarEnv markMany usage, Note InlineMe body')
569 occAnal env (Note note@(SCC cc) body)
570 = case occAnal env body of { (usage, body') ->
571 (mapVarEnv markInsideSCC usage, Note note body')
574 occAnal env (Note note body)
575 = case occAnal env body of { (usage, body') ->
576 (usage, Note note body')
581 occAnal env app@(App fun arg)
582 = occAnalApp env (collectArgs app)
584 -- Ignore type variables altogether
585 -- (a) occurrences inside type lambdas only not marked as InsideLam
586 -- (b) type variables not in environment
588 occAnal env expr@(Lam x body) | isTyVar x
589 = case occAnal env body of { (body_usage, body') ->
590 (body_usage, Lam x body')
593 -- For value lambdas we do a special hack. Consider
595 -- If we did nothing, x is used inside the \y, so would be marked
596 -- as dangerous to dup. But in the common case where the abstraction
597 -- is applied to two arguments this is over-pessimistic.
598 -- So instead, we just mark each binder with its occurrence
599 -- info in the *body* of the multiple lambda.
600 -- Then, the simplifier is careful when partially applying lambdas.
602 occAnal env expr@(Lam _ _)
603 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
605 (final_usage, tagged_binders) = tagBinders body_usage binders
606 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
607 -- we get linear-typed things in the resulting program that we can't handle yet.
608 -- (e.g. PrelShow) TODO
610 really_final_usage = if linear then
613 mapVarEnv markInsideLam final_usage
616 mkLams tagged_binders body') }
618 (binders, body) = collectBinders expr
619 (linear, env_body, binders') = oneShotGroup env binders
621 occAnal env (Case scrut bndr alts)
622 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
623 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
625 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
626 alts_usage' = addCaseBndrUsage alts_usage
627 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
628 total_usage = scrut_usage `combineUsageDetails` alts_usage1
630 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
632 alt_env = env `addNewCand` bndr
634 -- The case binder gets a usage of either "many" or "dead", never "one".
635 -- Reason: we like to inline single occurrences, to eliminate a binding,
636 -- but inlining a case binder *doesn't* eliminate a binding.
637 -- We *don't* want to transform
638 -- case x of w { (p,q) -> f w }
640 -- case x of w { (p,q) -> f (p,q) }
641 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
643 Just occ -> extendVarEnv usage bndr (markMany occ)
645 occAnal env (Let bind body)
646 = case occAnal new_env body of { (body_usage, body') ->
647 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
648 (final_usage, mkLets new_binds body') }}
650 new_env = env `addNewCands` (bindersOf bind)
653 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
654 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
656 arg_env = zapCtxt env
659 Applications are dealt with specially because we want
660 the "build hack" to work.
663 -- Hack for build, fold, runST
664 occAnalApp env (Var fun, args)
665 = case args_stuff of { (args_uds, args') ->
667 final_uds = fun_uds `combineUsageDetails` args_uds
669 (final_uds, mkApps (Var fun) args') }
671 fun_uniq = idUnique fun
673 fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
674 | otherwise = emptyDetails
676 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
677 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
678 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
679 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
681 | isDataConId fun = case occAnalArgs env args of
682 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
683 -- We mark the free vars of the argument of a constructor as "many"
684 -- This means that nothing gets inlined into a constructor argument
685 -- position, which is what we want. Typically those constructor
686 -- arguments are just variables, or trivial expressions.
688 | otherwise = occAnalArgs env args
691 occAnalApp env (fun, args)
692 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
693 case occAnalArgs env args of { (args_uds, args') ->
695 final_uds = fun_uds `combineUsageDetails` args_uds
697 (final_uds, mkApps fun' args') }}
699 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
700 appSpecial env n ctxt args
703 go n [] = (emptyDetails, []) -- Too few args
705 go 1 (arg:args) -- The magic arg
706 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
707 case occAnalArgs env args of { (args_uds, args') ->
708 (combineUsageDetails arg_uds args_uds, arg':args') }}
711 = case occAnal env arg of { (arg_uds, arg') ->
712 case go (n-1) args of { (args_uds, args') ->
713 (combineUsageDetails arg_uds args_uds, arg':args') }}
720 occAnalAlt env (con, bndrs, rhs)
721 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
723 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
725 (final_usage, (con, tagged_bndrs, rhs')) }
729 %************************************************************************
731 \subsection[OccurAnal-types]{Data types}
733 %************************************************************************
736 -- We gather inforamtion for variables that are either
741 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
742 IdSet -- In-scope Ids
743 CtxtTy -- Tells about linearity
748 -- True:ctxt Analysing a function-valued expression that will be
751 -- False:ctxt Analysing a function-valued expression that may
752 -- be applied many times; but when it is,
753 -- the CtxtTy inside applies
755 isCandidate :: OccEnv -> Id -> Bool
756 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
758 addNewCands :: OccEnv -> [Id] -> OccEnv
759 addNewCands (OccEnv ifun cands ctxt) ids
760 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
762 addNewCand :: OccEnv -> Id -> OccEnv
763 addNewCand (OccEnv ifun cands ctxt) id
764 = OccEnv ifun (extendVarSet cands id) ctxt
766 setCtxt :: OccEnv -> CtxtTy -> OccEnv
767 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
769 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
770 -- True <=> this is a one-shot linear lambda group
771 -- The [CoreBndr] are the binders.
773 -- The result binders have one-shot-ness set that they might not have had originally.
774 -- This happens in (build (\cn -> e)). Here the occurrence analyser
775 -- linearity context knows that c,n are one-shot, and it records that fact in
776 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
778 oneShotGroup (OccEnv ifun cands ctxt) bndrs
779 = case go ctxt bndrs [] of
780 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
782 is_one_shot b = isId b && isOneShotLambda b
784 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
786 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
787 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
789 bndr' | lin_ctxt = setOneShotLambda bndr
792 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
795 zapCtxt env@(OccEnv ifun cands []) = env
796 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
798 type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
800 combineUsageDetails, combineAltsUsageDetails
801 :: UsageDetails -> UsageDetails -> UsageDetails
803 combineUsageDetails usage1 usage2
804 = plusVarEnv_C addBinderInfo usage1 usage2
806 combineAltsUsageDetails usage1 usage2
807 = plusVarEnv_C orBinderInfo usage1 usage2
809 addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
810 addOneOcc usage id info
811 = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
812 -- ToDo: make this more efficient
814 emptyDetails = (emptyVarEnv :: UsageDetails)
816 unitDetails id info = (unitVarEnv id info :: UsageDetails)
818 usedIn :: Id -> UsageDetails -> Bool
819 v `usedIn` details = isExportedId v || v `elemVarEnv` details
821 tagBinders :: UsageDetails -- Of scope
823 -> (UsageDetails, -- Details with binders removed
824 [IdWithOccInfo]) -- Tagged binders
826 tagBinders usage binders
828 usage' = usage `delVarEnvList` binders
829 uss = map (setBinderOcc usage) binders
831 usage' `seq` (usage', uss)
833 tagBinder :: UsageDetails -- Of scope
835 -> (UsageDetails, -- Details with binders removed
836 IdWithOccInfo) -- Tagged binders
838 tagBinder usage binder
840 usage' = usage `delVarEnv` binder
841 binder' = setBinderOcc usage binder
843 usage' `seq` (usage', binder')
846 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
847 setBinderOcc usage bndr
848 | isTyVar bndr = bndr
850 = -- Don't use local usage info for visible-elsewhere things
851 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
852 -- about to re-generate it and it shouldn't be "sticky"
853 case idOccInfo bndr of
855 other -> setIdOccInfo bndr NoOccInfo
857 | otherwise = setIdOccInfo bndr occ_info
859 occ_info = case lookupVarEnv usage bndr of
861 Just info -> binderInfoToOccInfo info
863 funOccZero = funOccurrence 0