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:
94 where exp is exported, and loc is not, then we replace it with this:
100 Without this we never get rid of the exp = loc thing.
101 This save a gratuitous jump
102 (from \tr{x_exported} to \tr{x_local}), and makes strictness
103 information propagate better.
104 This used to happen in 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
149 go env [] = (emptyDetails, emptyVarEnv, [])
151 go env (bind : binds)
153 new_env = env `addNewCands` (bindersOf bind)
154 (scope_usage, ind_env, binds') = go new_env binds
155 (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
156 -- NB: I zap before occur-analysing, so
157 -- I don't need to worry about getting the
158 -- occ info on the new bindings right.
161 NonRec exported_id (Var local_id)
162 | shortMeOut ind_env exported_id local_id
163 -- Special case for eliminating indirections
164 -- Note: it's a shortcoming that this only works for
165 -- non-recursive bindings. Elminating indirections
166 -- makes perfect sense for recursive bindings too, but
167 -- it's more complicated to implement, so I haven't done so
168 -> (scope_usage, ind_env', binds')
170 ind_env' = extendVarEnv ind_env local_id exported_id
172 other -> -- Ho ho! The normal case
173 (final_usage, ind_env, new_binds ++ binds')
175 initialTopEnv = OccEnv isLocallyDefined -- Anything local is interesting
180 -- Deal with any indirections
181 zapBind ind_env (NonRec bndr rhs)
182 | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
183 -- The Rec isn't strictly necessary, but it's convenient
184 zapBind ind_env (Rec pairs)
185 | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
187 zapBind ind_env bind = bind
189 zap ind_env pair@(bndr,rhs)
190 = case lookupVarEnv ind_env bndr of
192 Just exported_id -> [(bndr, Var exported_id),
193 (exported_id_w_info, rhs)]
195 exported_id_w_info = modifyIdInfo (copyIdInfo (idInfo bndr)) exported_id
196 -- See notes with copyIdInfo about propagating IdInfo from
199 shortMeOut ind_env exported_id local_id
200 = isExportedId exported_id && -- Only if this is exported
202 isLocallyDefined local_id && -- Only if this one is defined in this
203 -- module, so that we *can* change its
204 -- binding to be the exported thing!
206 not (isExportedId local_id) && -- Only if this one is not itself exported,
207 -- since the transformation will nuke it
209 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
213 %************************************************************************
215 \subsection[OccurAnal-main]{Counting occurrences: main function}
217 %************************************************************************
223 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
225 type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
226 -- which is gotten from the Id.
227 type Details1 = (Id, UsageDetails, CoreExpr)
228 type Details2 = (IdWithOccInfo, CoreExpr)
231 occAnalBind :: OccEnv
233 -> UsageDetails -- Usage details of scope
234 -> (UsageDetails, -- Of the whole let(rec)
237 occAnalBind env (NonRec binder rhs) body_usage
238 | not (binder `usedIn` body_usage) -- It's not mentioned
241 | otherwise -- It's mentioned in the body
242 = (final_body_usage `combineUsageDetails` rhs_usage,
243 [NonRec tagged_binder rhs'])
246 (final_body_usage, tagged_binder) = tagBinder body_usage binder
247 (rhs_usage, rhs') = occAnalRhs env binder rhs
250 Dropping dead code for recursive bindings is done in a very simple way:
252 the entire set of bindings is dropped if none of its binders are
253 mentioned in its body; otherwise none are.
255 This seems to miss an obvious improvement.
270 Now @f@ is unused. But dependency analysis will sort this out into a
271 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
272 It isn't easy to do a perfect job in one blow. Consider
286 occAnalBind env (Rec pairs) body_usage
287 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
289 binders = map fst pairs
290 rhs_env = env `addNewCands` binders
292 analysed_pairs :: [Details1]
293 analysed_pairs = [ (bndr, rhs_usage, rhs')
294 | (bndr, rhs) <- pairs,
295 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
298 sccs :: [SCC (Node Details1)]
299 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
302 ---- stuff for dependency analysis of binds -------------------------------
303 edges :: [Node Details1]
304 edges = _scc_ "occAnalBind.assoc"
305 [ (details, IBOX(u2i (idUnique id)), edges_from rhs_usage)
306 | details@(id, rhs_usage, rhs) <- analysed_pairs
309 -- (a -> b) means a mentions b
310 -- Given the usage details (a UFM that gives occ info for each free var of
311 -- the RHS) we can get the list of free vars -- or rather their Int keys --
312 -- by just extracting the keys from the finite map. Grimy, but fast.
313 -- Previously we had this:
314 -- [ bndr | bndr <- bndrs,
315 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
316 -- which has n**2 cost, and this meant that edges_from alone
317 -- consumed 10% of total runtime!
318 edges_from :: UsageDetails -> [Int]
319 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
322 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
325 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
326 | not (bndr `usedIn` body_usage)
327 = (body_usage, binds_so_far) -- Dead code
329 = (combined_usage, new_bind : binds_so_far)
331 total_usage = combineUsageDetails body_usage rhs_usage
332 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
333 new_bind = NonRec tagged_bndr rhs'
336 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
337 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
338 = (body_usage, binds_so_far) -- Dead code
340 = (combined_usage, final_bind:binds_so_far)
342 details = [details | (details, _, _) <- cycle]
343 bndrs = [bndr | (bndr, _, _) <- details]
344 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
345 total_usage = foldr combineUsageDetails body_usage rhs_usages
346 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
347 final_bind = Rec (reOrderRec env new_cycle)
349 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
350 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
353 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
354 strongly connected component (there's guaranteed to be a cycle). It returns the
356 a) in a better order,
357 b) with some of the Ids having a IMustNotBeINLINEd pragma
359 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
360 that the simplifier can guarantee not to loop provided it never records an inlining
361 for these no-inline guys.
363 Furthermore, the order of the binds is such that if we neglect dependencies
364 on the no-inline Ids then the binds are topologically sorted. This means
365 that the simplifier will generally do a good job if it works from top bottom,
366 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
369 [June 98: I don't understand the following paragraphs, and I've
370 changed the a=b case again so that it isn't a special case any more.]
372 Here's a case that bit me:
380 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
382 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
383 Perhaps something cleverer would suffice.
386 You might think that you can prevent non-termination simply by making
387 sure that we simplify a recursive binding's RHS in an environment that
388 simply clones the recursive Id. But no. Consider
390 letrec f = \x -> let z = f x' in ...
397 We bind n to its *simplified* RHS, we then *re-simplify* it when
398 we inline n. Then we may well inline f; and then the same thing
401 I don't think it's possible to prevent non-termination by environment
402 manipulation in this way. Apart from anything else, successive
403 iterations of the simplifier may unroll recursive loops in cases like
404 that above. The idea of beaking every recursive loop with an
405 IMustNotBeINLINEd pragma is much much better.
411 -> SCC (Node Details2)
413 -- Sorted into a plausible order. Enough of the Ids have
414 -- dontINLINE pragmas that there are no loops left.
416 -- Non-recursive case
417 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
419 -- Common case of simple self-recursion
420 reOrderRec env (CyclicSCC [bind])
421 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
423 ((tagged_bndr, rhs), _, _) = bind
425 reOrderRec env (CyclicSCC (bind : binds))
426 = -- Choose a loop breaker, mark it no-inline,
427 -- do SCC analysis on the rest, and recursively sort them out
428 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
430 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
433 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
434 (tagged_bndr, rhs) = chosen_pair
436 -- This loop looks for the bind with the lowest score
437 -- to pick as the loop breaker. The rest accumulate in
438 choose_loop_breaker (details,_,_) loop_sc acc []
439 = (details, acc) -- Done
441 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
442 | sc < loop_sc -- Lower score so pick this new one
443 = choose_loop_breaker bind sc (loop_bind : acc) binds
445 | otherwise -- No lower so don't pick it
446 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
450 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
451 score ((bndr, rhs), _, _)
452 | exprIsTrivial rhs &&
453 not (isExportedId bndr) = 3 -- Practically certain to be inlined
454 | inlineCandidate bndr rhs = 3 -- Likely to be inlined
455 | not_fun_ty (idType bndr) = 2 -- Data types help with cases
456 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
457 -- Avoid things with specialisations; we'd like
458 -- to take advantage of them in the subsequent bindings
461 inlineCandidate :: Id -> CoreExpr -> Bool
462 inlineCandidate id (Note InlineMe _) = True
463 inlineCandidate id rhs = case idOccInfo id of
467 -- Real example (the Enum Ordering instance from PrelBase):
468 -- rec f = \ x -> case d of (p,q,r) -> p x
469 -- g = \ x -> case d of (p,q,r) -> q x
472 -- Here, f and g occur just once; but we can't inline them into d.
473 -- On the other hand we *could* simplify those case expressions if
474 -- we didn't stupidly choose d as the loop breaker.
475 -- But we won't because constructor args are marked "Many".
477 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
479 (_, rho_ty) = splitForAllTys ty
482 @occAnalRhs@ deals with the question of bindings where the Id is marked
483 by an INLINE pragma. For these we record that anything which occurs
484 in its RHS occurs many times. This pessimistically assumes that ths
485 inlined binder also occurs many times in its scope, but if it doesn't
486 we'll catch it next time round. At worst this costs an extra simplifier pass.
487 ToDo: try using the occurrence info for the inline'd binder.
489 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
490 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
495 -> Id -> CoreExpr -- Binder and rhs
496 -> (UsageDetails, CoreExpr)
498 occAnalRhs env id rhs
499 = (final_usage, rhs')
501 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
503 -- [March 98] A new wrinkle is that if the binder has specialisations inside
504 -- it then we count the specialised Ids as "extra rhs's". That way
505 -- the "parent" keeps the specialised "children" alive. If the parent
506 -- dies (because it isn't referenced any more), then the children will
507 -- die too unless they are already referenced directly.
509 final_usage = foldVarSet add rhs_usage (idRuleVars id)
510 add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
511 -- (i.e manyOcc) because many copies
512 -- of the specialised thing can appear
520 -> (UsageDetails, -- Gives info only about the "interesting" Ids
523 occAnal env (Type t) = (emptyDetails, Type t)
528 var_uds | isCandidate env v = unitVarEnv v funOccZero
529 | otherwise = emptyDetails
531 -- At one stage, I gathered the idRuleVars for v here too,
532 -- which in a way is the right thing to do.
533 -- But that went wrong right after specialisation, when
534 -- the *occurrences* of the overloaded function didn't have any
535 -- rules in them, so the *specialised* versions looked as if they
536 -- weren't used at all.
540 We regard variables that occur as constructor arguments as "dangerousToDup":
544 f x = let y = expensive x in
546 (case z of {(p,q)->q}, case z of {(p,q)->q})
549 We feel free to duplicate the WHNF (True,y), but that means
550 that y may be duplicated thereby.
552 If we aren't careful we duplicate the (expensive x) call!
553 Constructors are rather like lambdas in this way.
556 occAnal env expr@(Lit lit) = (emptyDetails, expr)
560 occAnal env (Note InlineMe body)
561 = case occAnal env body of { (usage, body') ->
562 (mapVarEnv markMany usage, Note InlineMe body')
565 occAnal env (Note note@(SCC cc) body)
566 = case occAnal env body of { (usage, body') ->
567 (mapVarEnv markInsideSCC usage, Note note body')
570 occAnal env (Note note body)
571 = case occAnal env body of { (usage, body') ->
572 (usage, Note note body')
577 occAnal env app@(App fun arg)
578 = occAnalApp env (collectArgs app)
580 -- Ignore type variables altogether
581 -- (a) occurrences inside type lambdas only not marked as InsideLam
582 -- (b) type variables not in environment
584 occAnal env expr@(Lam x body) | isTyVar x
585 = case occAnal env body of { (body_usage, body') ->
586 (body_usage, Lam x body')
589 -- For value lambdas we do a special hack. Consider
591 -- If we did nothing, x is used inside the \y, so would be marked
592 -- as dangerous to dup. But in the common case where the abstraction
593 -- is applied to two arguments this is over-pessimistic.
594 -- So instead, we just mark each binder with its occurrence
595 -- info in the *body* of the multiple lambda.
596 -- Then, the simplifier is careful when partially applying lambdas.
598 occAnal env expr@(Lam _ _)
599 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
601 (final_usage, tagged_binders) = tagBinders body_usage binders
602 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
603 -- we get linear-typed things in the resulting program that we can't handle yet.
604 -- (e.g. PrelShow) TODO
606 really_final_usage = if linear then
609 mapVarEnv markInsideLam final_usage
612 mkLams tagged_binders body') }
614 (binders, body) = collectBinders expr
615 (linear, env_body, _) = oneShotGroup env binders
617 occAnal env (Case scrut bndr alts)
618 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
619 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
621 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
622 alts_usage' = addCaseBndrUsage alts_usage
623 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
624 total_usage = scrut_usage `combineUsageDetails` alts_usage1
626 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
628 alt_env = env `addNewCand` bndr
630 -- The case binder gets a usage of either "many" or "dead", never "one".
631 -- Reason: we like to inline single occurrences, to eliminate a binding,
632 -- but inlining a case binder *doesn't* eliminate a binding.
633 -- We *don't* want to transform
634 -- case x of w { (p,q) -> f w }
636 -- case x of w { (p,q) -> f (p,q) }
637 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
639 Just occ -> extendVarEnv usage bndr (markMany occ)
641 occAnal env (Let bind body)
642 = case occAnal new_env body of { (body_usage, body') ->
643 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
644 (final_usage, mkLets new_binds body') }}
646 new_env = env `addNewCands` (bindersOf bind)
649 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
650 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
652 arg_env = zapCtxt env
655 Applications are dealt with specially because we want
656 the "build hack" to work.
659 -- Hack for build, fold, runST
660 occAnalApp env (Var fun, args)
661 = case args_stuff of { (args_uds, args') ->
663 final_uds = fun_uds `combineUsageDetails` args_uds
665 (final_uds, mkApps (Var fun) args') }
667 fun_uniq = idUnique fun
669 fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
670 | otherwise = emptyDetails
672 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
673 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
674 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
675 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
677 | isDataConId fun = case occAnalArgs env args of
678 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
679 -- We mark the free vars of the argument of a constructor as "many"
680 -- This means that nothing gets inlined into a constructor argument
681 -- position, which is what we want. Typically those constructor
682 -- arguments are just variables, or trivial expressions.
684 | otherwise = occAnalArgs env args
687 occAnalApp env (fun, args)
688 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
689 case occAnalArgs env args of { (args_uds, args') ->
691 final_uds = fun_uds `combineUsageDetails` args_uds
693 (final_uds, mkApps fun' args') }}
695 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
696 appSpecial env n ctxt args
699 go n [] = (emptyDetails, []) -- Too few args
701 go 1 (arg:args) -- The magic arg
702 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
703 case occAnalArgs env args of { (args_uds, args') ->
704 (combineUsageDetails arg_uds args_uds, arg':args') }}
707 = case occAnal env arg of { (arg_uds, arg') ->
708 case go (n-1) args of { (args_uds, args') ->
709 (combineUsageDetails arg_uds args_uds, arg':args') }}
716 occAnalAlt env (con, bndrs, rhs)
717 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
719 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
721 (final_usage, (con, tagged_bndrs, rhs')) }
725 %************************************************************************
727 \subsection[OccurAnal-types]{Data types}
729 %************************************************************************
732 -- We gather inforamtion for variables that are either
737 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
738 IdSet -- In-scope Ids
739 CtxtTy -- Tells about linearity
744 -- True:ctxt Analysing a function-valued expression that will be
747 -- False:ctxt Analysing a function-valued expression that may
748 -- be applied many times; but when it is,
749 -- the CtxtTy inside applies
751 isCandidate :: OccEnv -> Id -> Bool
752 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
754 addNewCands :: OccEnv -> [Id] -> OccEnv
755 addNewCands (OccEnv ifun cands ctxt) ids
756 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
758 addNewCand :: OccEnv -> Id -> OccEnv
759 addNewCand (OccEnv ifun cands ctxt) id
760 = OccEnv ifun (extendVarSet cands id) ctxt
762 setCtxt :: OccEnv -> CtxtTy -> OccEnv
763 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
765 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
766 -- True <=> this is a one-shot linear lambda group
767 -- The [CoreBndr] are the binders.
769 -- The result binders have one-shot-ness set that they might not have had originally.
770 -- This happens in (build (\cn -> e)). Here the occurrence analyser
771 -- linearity context knows that c,n are one-shot, and it records that fact in
772 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
774 oneShotGroup (OccEnv ifun cands ctxt) bndrs
775 = case go ctxt bndrs [] of
776 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
778 is_one_shot b = isId b && isOneShotLambda b
780 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
782 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
783 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
785 bndr' | lin_ctxt = setOneShotLambda bndr
788 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
791 zapCtxt env@(OccEnv ifun cands []) = env
792 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
794 type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
796 combineUsageDetails, combineAltsUsageDetails
797 :: UsageDetails -> UsageDetails -> UsageDetails
799 combineUsageDetails usage1 usage2
800 = plusVarEnv_C addBinderInfo usage1 usage2
802 combineAltsUsageDetails usage1 usage2
803 = plusVarEnv_C orBinderInfo usage1 usage2
805 addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
806 addOneOcc usage id info
807 = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
808 -- ToDo: make this more efficient
810 emptyDetails = (emptyVarEnv :: UsageDetails)
812 unitDetails id info = (unitVarEnv id info :: UsageDetails)
814 usedIn :: Id -> UsageDetails -> Bool
815 v `usedIn` details = isExportedId v || v `elemVarEnv` details
817 tagBinders :: UsageDetails -- Of scope
819 -> (UsageDetails, -- Details with binders removed
820 [IdWithOccInfo]) -- Tagged binders
822 tagBinders usage binders
824 usage' = usage `delVarEnvList` binders
825 uss = map (setBinderOcc usage) binders
827 usage' `seq` (usage', uss)
829 tagBinder :: UsageDetails -- Of scope
831 -> (UsageDetails, -- Details with binders removed
832 IdWithOccInfo) -- Tagged binders
834 tagBinder usage binder
836 usage' = usage `delVarEnv` binder
837 binder' = setBinderOcc usage binder
839 usage' `seq` (usage', binder')
842 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
843 setBinderOcc usage bndr
844 | isTyVar bndr = bndr
846 = -- Don't use local usage info for visible-elsewhere things
847 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
848 -- about to re-generate it and it shouldn't be "sticky"
849 case idOccInfo bndr of
851 other -> setIdOccInfo bndr NoOccInfo
853 | otherwise = setIdOccInfo bndr occ_info
855 occ_info = case lookupVarEnv usage bndr of
857 Just info -> binderInfoToOccInfo info
859 funOccZero = funOccurrence 0