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 occurAnalysePgm, occurAnalyseExpr
18 #include "HsVersions.h"
21 import CoreFVs ( idRuleVars )
22 import CoreUtils ( exprIsTrivial, isDefaultAlt )
23 import Id ( isDataConWorkId, isOneShotBndr, setOneShotLambda,
24 idOccInfo, setIdOccInfo, isLocalId,
25 isExportedId, idArity, idHasRules,
28 import BasicTypes ( OccInfo(..), isOneOcc, InterestingCxt )
33 import Type ( isFunTy, dropForAlls )
34 import Maybes ( orElse )
35 import Digraph ( stronglyConnCompR, SCC(..) )
36 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
37 import Unique ( Unique )
38 import UniqFM ( keysUFM, lookupUFM_Directly )
39 import Util ( zipWithEqual, mapAndUnzip )
44 %************************************************************************
46 \subsection[OccurAnal-main]{Counting occurrences: main function}
48 %************************************************************************
50 Here's the externally-callable interface:
53 occurAnalysePgm :: [CoreBind] -> [CoreBind]
55 = snd (go initOccEnv binds)
57 go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind])
61 = (final_usage, bind' ++ binds')
63 (bs_usage, binds') = go env binds
64 (final_usage, bind') = occAnalBind env bind bs_usage
66 occurAnalyseExpr :: CoreExpr -> CoreExpr
67 -- Do occurrence analysis, and discard occurence info returned
68 occurAnalyseExpr expr = snd (occAnal initOccEnv expr)
72 %************************************************************************
74 \subsection[OccurAnal-main]{Counting occurrences: main function}
76 %************************************************************************
82 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
84 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
85 -- which is gotten from the Id.
86 type Details1 = (Id, UsageDetails, CoreExpr)
87 type Details2 = (IdWithOccInfo, CoreExpr)
92 -> UsageDetails -- Usage details of scope
93 -> (UsageDetails, -- Of the whole let(rec)
96 occAnalBind env (NonRec binder rhs) body_usage
97 | not (binder `usedIn` body_usage) -- It's not mentioned
100 | otherwise -- It's mentioned in the body
101 = (final_body_usage `combineUsageDetails` rhs_usage,
102 [NonRec tagged_binder rhs'])
105 (final_body_usage, tagged_binder) = tagBinder body_usage binder
106 (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
109 Dropping dead code for recursive bindings is done in a very simple way:
111 the entire set of bindings is dropped if none of its binders are
112 mentioned in its body; otherwise none are.
114 This seems to miss an obvious improvement.
129 Now @f@ is unused. But dependency analysis will sort this out into a
130 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
131 It isn't easy to do a perfect job in one blow. Consider
145 occAnalBind env (Rec pairs) body_usage
146 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
148 analysed_pairs :: [Details1]
149 analysed_pairs = [ (bndr, rhs_usage, rhs')
150 | (bndr, rhs) <- pairs,
151 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
154 sccs :: [SCC (Node Details1)]
155 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
158 ---- stuff for dependency analysis of binds -------------------------------
159 edges :: [Node Details1]
160 edges = _scc_ "occAnalBind.assoc"
161 [ (details, idUnique id, edges_from rhs_usage)
162 | details@(id, rhs_usage, rhs) <- analysed_pairs
165 -- (a -> b) means a mentions b
166 -- Given the usage details (a UFM that gives occ info for each free var of
167 -- the RHS) we can get the list of free vars -- or rather their Int keys --
168 -- by just extracting the keys from the finite map. Grimy, but fast.
169 -- Previously we had this:
170 -- [ bndr | bndr <- bndrs,
171 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
172 -- which has n**2 cost, and this meant that edges_from alone
173 -- consumed 10% of total runtime!
174 edges_from :: UsageDetails -> [Unique]
175 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
178 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
181 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
182 | not (bndr `usedIn` body_usage)
183 = (body_usage, binds_so_far) -- Dead code
185 = (combined_usage, new_bind : binds_so_far)
187 total_usage = combineUsageDetails body_usage rhs_usage
188 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
189 new_bind = NonRec tagged_bndr rhs'
192 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
193 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
194 = (body_usage, binds_so_far) -- Dead code
196 = (combined_usage, final_bind:binds_so_far)
198 details = [details | (details, _, _) <- cycle]
199 bndrs = [bndr | (bndr, _, _) <- details]
200 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
201 total_usage = foldr combineUsageDetails body_usage rhs_usages
202 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
203 final_bind = Rec (doReorder edges)
205 -- Hopefully 'bndrs' is a relatively small group now
206 -- Now get ready for the loop-breaking phase, this time ignoring RulesOnly references
207 -- We've done dead-code elimination already, so no worries about un-referenced binders
208 edges :: [Node Details2]
209 edges = zipWithEqual "reorder" mk_edge tagged_bndrs details
210 keys = map idUnique bndrs
211 mk_edge tagged_bndr (_, rhs_usage, rhs')
212 = ((tagged_bndr, rhs'), idUnique tagged_bndr, used)
214 used = [key | key <- keys, used_outside_rule rhs_usage key ]
216 used_outside_rule usage uniq = case lookupUFM_Directly usage uniq of
218 Just RulesOnly -> False -- Ignore rules
222 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
223 strongly connected component (there's guaranteed to be a cycle). It returns the
225 a) in a better order,
226 b) with some of the Ids having a IMustNotBeINLINEd pragma
228 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
229 that the simplifier can guarantee not to loop provided it never records an inlining
230 for these no-inline guys.
232 Furthermore, the order of the binds is such that if we neglect dependencies
233 on the no-inline Ids then the binds are topologically sorted. This means
234 that the simplifier will generally do a good job if it works from top bottom,
235 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
238 [June 98: I don't understand the following paragraphs, and I've
239 changed the a=b case again so that it isn't a special case any more.]
241 Here's a case that bit me:
249 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
251 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
252 Perhaps something cleverer would suffice.
255 You might think that you can prevent non-termination simply by making
256 sure that we simplify a recursive binding's RHS in an environment that
257 simply clones the recursive Id. But no. Consider
259 letrec f = \x -> let z = f x' in ...
266 We bind n to its *simplified* RHS, we then *re-simplify* it when
267 we inline n. Then we may well inline f; and then the same thing
270 I don't think it's possible to prevent non-termination by environment
271 manipulation in this way. Apart from anything else, successive
272 iterations of the simplifier may unroll recursive loops in cases like
273 that above. The idea of beaking every recursive loop with an
274 IMustNotBeINLINEd pragma is much much better.
278 doReorder :: [Node Details2] -> [Details2]
279 -- Sorted into a plausible order. Enough of the Ids have
280 -- dontINLINE pragmas that there are no loops left.
281 doReorder nodes = concatMap reOrderRec (stronglyConnCompR nodes)
283 reOrderRec :: SCC (Node Details2) -> [Details2]
285 -- Non-recursive case
286 reOrderRec (AcyclicSCC (bind, _, _)) = [bind]
288 -- Common case of simple self-recursion
289 reOrderRec (CyclicSCC [])
292 reOrderRec (CyclicSCC [bind])
293 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
295 ((tagged_bndr, rhs), _, _) = bind
297 reOrderRec (CyclicSCC (bind : binds))
298 = -- Choose a loop breaker, mark it no-inline,
299 -- do SCC analysis on the rest, and recursively sort them out
300 doReorder unchosen ++
301 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
304 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
305 (tagged_bndr, rhs) = chosen_pair
307 -- This loop looks for the bind with the lowest score
308 -- to pick as the loop breaker. The rest accumulate in
309 choose_loop_breaker (details,_,_) loop_sc acc []
310 = (details, acc) -- Done
312 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
313 | sc < loop_sc -- Lower score so pick this new one
314 = choose_loop_breaker bind sc (loop_bind : acc) binds
316 | otherwise -- No lower so don't pick it
317 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
321 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
322 score ((bndr, rhs), _, _)
323 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
324 -- Used to have also: && not (isExportedId bndr)
325 -- But I found this sometimes cost an extra iteration when we have
326 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
327 -- where df is the exported dictionary. Then df makes a really
328 -- bad choice for loop breaker
330 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
331 -- This used to have a lower score than inlineCandidate, but
332 -- it's *really* helpful if dictionaries get inlined fast,
333 -- so I'm experimenting with giving higher priority to data-typed things
335 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
337 | idHasRules bndr = 1
338 -- Avoid things with specialisations; we'd like
339 -- to take advantage of them in the subsequent bindings
343 inlineCandidate :: Id -> CoreExpr -> Bool
344 inlineCandidate id (Note InlineMe _) = True
345 inlineCandidate id rhs = isOneOcc (idOccInfo id)
347 -- Real example (the Enum Ordering instance from PrelBase):
348 -- rec f = \ x -> case d of (p,q,r) -> p x
349 -- g = \ x -> case d of (p,q,r) -> q x
352 -- Here, f and g occur just once; but we can't inline them into d.
353 -- On the other hand we *could* simplify those case expressions if
354 -- we didn't stupidly choose d as the loop breaker.
355 -- But we won't because constructor args are marked "Many".
357 not_fun_ty ty = not (isFunTy (dropForAlls ty))
360 @occAnalRhs@ deals with the question of bindings where the Id is marked
361 by an INLINE pragma. For these we record that anything which occurs
362 in its RHS occurs many times. This pessimistically assumes that ths
363 inlined binder also occurs many times in its scope, but if it doesn't
364 we'll catch it next time round. At worst this costs an extra simplifier pass.
365 ToDo: try using the occurrence info for the inline'd binder.
367 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
368 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
373 -> Id -> CoreExpr -- Binder and rhs
374 -- For non-recs the binder is alrady tagged
375 -- with occurrence info
376 -> (UsageDetails, CoreExpr)
378 occAnalRhs env id rhs
379 = (final_usage, rhs')
381 (rhs_usage, rhs') = occAnal ctxt rhs
382 ctxt | certainly_inline id = env
383 | otherwise = rhsCtxt
384 -- Note that we generally use an rhsCtxt. This tells the occ anal n
385 -- that it's looking at an RHS, which has an effect in occAnalApp
387 -- But there's a problem. Consider
392 -- First time round, it looks as if x1 and x2 occur as an arg of a
393 -- let-bound constructor ==> give them a many-occurrence.
394 -- But then x3 is inlined (unconditionally as it happens) and
395 -- next time round, x2 will be, and the next time round x1 will be
396 -- Result: multiple simplifier iterations. Sigh.
397 -- Crude solution: use rhsCtxt for things that occur just once...
399 certainly_inline id = case idOccInfo id of
400 OneOcc in_lam one_br _ -> not in_lam && one_br
403 -- [March 98] A new wrinkle is that if the binder has specialisations inside
404 -- it then we count the specialised Ids as "extra rhs's". That way
405 -- the "parent" keeps the specialised "children" alive. If the parent
406 -- dies (because it isn't referenced any more), then the children will
407 -- die too unless they are already referenced directly.
409 final_usage = addRuleUsage rhs_usage id
411 addRuleUsage :: UsageDetails -> Id -> UsageDetails
412 -- Add the usage from RULES in Id to the usage
413 addRuleUsage usage id
414 = foldVarSet add usage (idRuleVars id)
416 add v u = addOneOcc u v RulesOnly -- Give a non-committal binder info
417 -- (i.e manyOcc) because many copies
418 -- of the specialised thing can appear
426 -> (UsageDetails, -- Gives info only about the "interesting" Ids
429 occAnal env (Type t) = (emptyDetails, Type t)
430 occAnal env (Var v) = (mkOneOcc env v False, Var v)
431 -- At one stage, I gathered the idRuleVars for v here too,
432 -- which in a way is the right thing to do.
433 -- Btu that went wrong right after specialisation, when
434 -- the *occurrences* of the overloaded function didn't have any
435 -- rules in them, so the *specialised* versions looked as if they
436 -- weren't used at all.
439 We regard variables that occur as constructor arguments as "dangerousToDup":
443 f x = let y = expensive x in
445 (case z of {(p,q)->q}, case z of {(p,q)->q})
448 We feel free to duplicate the WHNF (True,y), but that means
449 that y may be duplicated thereby.
451 If we aren't careful we duplicate the (expensive x) call!
452 Constructors are rather like lambdas in this way.
455 occAnal env expr@(Lit lit) = (emptyDetails, expr)
459 occAnal env (Note InlineMe body)
460 = case occAnal env body of { (usage, body') ->
461 (mapVarEnv markMany usage, Note InlineMe body')
464 occAnal env (Note note@(SCC cc) body)
465 = case occAnal env body of { (usage, body') ->
466 (mapVarEnv markInsideSCC usage, Note note body')
469 occAnal env (Note note body)
470 = case occAnal env body of { (usage, body') ->
471 (usage, Note note body')
474 occAnal env (Cast expr co)
475 = case occAnal env expr of { (usage, expr') ->
476 (usage, Cast expr' co)
481 occAnal env app@(App fun arg)
482 = occAnalApp env (collectArgs app) False
484 -- Ignore type variables altogether
485 -- (a) occurrences inside type lambdas only not marked as InsideLam
486 -- (b) type variables not in environment
488 occAnal env expr@(Lam x body) | isTyVar x
489 = case occAnal env body of { (body_usage, body') ->
490 (body_usage, Lam x body')
493 -- For value lambdas we do a special hack. Consider
495 -- If we did nothing, x is used inside the \y, so would be marked
496 -- as dangerous to dup. But in the common case where the abstraction
497 -- is applied to two arguments this is over-pessimistic.
498 -- So instead, we just mark each binder with its occurrence
499 -- info in the *body* of the multiple lambda.
500 -- Then, the simplifier is careful when partially applying lambdas.
502 occAnal env expr@(Lam _ _)
503 = case occAnal env_body body of { (body_usage, body') ->
505 (final_usage, tagged_binders) = tagBinders body_usage binders
506 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
507 -- we get linear-typed things in the resulting program that we can't handle yet.
508 -- (e.g. PrelShow) TODO
510 really_final_usage = if linear then
513 mapVarEnv markInsideLam final_usage
516 mkLams tagged_binders body') }
518 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
519 (binders, body) = collectBinders expr
520 binders' = oneShotGroup env binders
521 linear = all is_one_shot binders'
522 is_one_shot b = isId b && isOneShotBndr b
524 occAnal env (Case scrut bndr ty alts)
525 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
526 case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts') ->
528 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
529 alts_usage' = addCaseBndrUsage alts_usage
530 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
531 total_usage = scrut_usage `combineUsageDetails` alts_usage1
533 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
535 -- The case binder gets a usage of either "many" or "dead", never "one".
536 -- Reason: we like to inline single occurrences, to eliminate a binding,
537 -- but inlining a case binder *doesn't* eliminate a binding.
538 -- We *don't* want to transform
539 -- case x of w { (p,q) -> f w }
541 -- case x of w { (p,q) -> f (p,q) }
542 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
544 Just occ -> extendVarEnv usage bndr (markMany occ)
546 alt_env = setVanillaCtxt env
547 -- Consider x = case v of { True -> (p,q); ... }
548 -- Then it's fine to inline p and q
550 occ_anal_scrut (Var v) (alt1 : other_alts)
551 | not (null other_alts) || not (isDefaultAlt alt1)
552 = (mkOneOcc env v True, Var v)
553 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
554 -- No need for rhsCtxt
556 occAnal env (Let bind body)
557 = case occAnal env body of { (body_usage, body') ->
558 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
559 (final_usage, mkLets new_binds body') }}
562 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
563 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
565 arg_env = vanillaCtxt
568 Applications are dealt with specially because we want
569 the "build hack" to work.
572 occAnalApp env (Var fun, args) is_rhs
573 = case args_stuff of { (args_uds, args') ->
575 -- We mark the free vars of the argument of a constructor or PAP
576 -- as "many", if it is the RHS of a let(rec).
577 -- This means that nothing gets inlined into a constructor argument
578 -- position, which is what we want. Typically those constructor
579 -- arguments are just variables, or trivial expressions.
581 -- This is the *whole point* of the isRhsEnv predicate
584 isDataConWorkId fun || valArgCount args < idArity fun
585 = mapVarEnv markMany args_uds
586 | otherwise = args_uds
588 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
590 fun_uniq = idUnique fun
591 fun_uds = mkOneOcc env fun (valArgCount args > 0)
593 -- Hack for build, fold, runST
594 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
595 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
596 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
597 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
598 -- (foldr k z xs) may call k many times, but it never
599 -- shares a partial application of k; hence [False,True]
600 -- This means we can optimise
601 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
602 -- by floating in the v
604 | otherwise = occAnalArgs env args
607 occAnalApp env (fun, args) is_rhs
608 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
609 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
610 -- often leaves behind beta redexs like
612 -- Here we would like to mark x,y as one-shot, and treat the whole
613 -- thing much like a let. We do this by pushing some True items
614 -- onto the context stack.
616 case occAnalArgs env args of { (args_uds, args') ->
618 final_uds = fun_uds `combineUsageDetails` args_uds
620 (final_uds, mkApps fun' args') }}
623 -> Int -> CtxtTy -- Argument number, and context to use for it
625 -> (UsageDetails, [CoreExpr])
626 appSpecial env n ctxt args
629 arg_env = vanillaCtxt
631 go n [] = (emptyDetails, []) -- Too few args
633 go 1 (arg:args) -- The magic arg
634 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
635 case occAnalArgs env args of { (args_uds, args') ->
636 (combineUsageDetails arg_uds args_uds, arg':args') }}
639 = case occAnal arg_env arg of { (arg_uds, arg') ->
640 case go (n-1) args of { (args_uds, args') ->
641 (combineUsageDetails arg_uds args_uds, arg':args') }}
647 If the case binder occurs at all, the other binders effectively do too.
649 case e of x { (a,b) -> rhs }
652 If e turns out to be (e1,e2) we indeed get something like
653 let a = e1; b = e2; x = (a,b) in rhs
655 Note [Aug 06]: I don't think this is necessary any more, and it helpe
656 to know when binders are unused. See esp the call to
657 isDeadBinder in Simplify.mkDupableAlt
660 occAnalAlt env case_bndr (con, bndrs, rhs)
661 = case occAnal env rhs of { (rhs_usage, rhs') ->
663 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
664 final_bndrs = tagged_bndrs -- See Note [Aug06] above
666 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
667 | otherwise = tagged_bndrs
668 -- Leave the binders untagged if the case
669 -- binder occurs at all; see note above
672 (final_usage, (con, final_bndrs, rhs')) }
676 %************************************************************************
678 \subsection[OccurAnal-types]{OccEnv}
680 %************************************************************************
684 = OccEnv OccEncl -- Enclosing context information
685 CtxtTy -- Tells about linearity
687 -- OccEncl is used to control whether to inline into constructor arguments
689 -- x = (p,q) -- Don't inline p or q
690 -- y = /\a -> (p a, q a) -- Still don't inline p or q
691 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
692 -- So OccEncl tells enought about the context to know what to do when
693 -- we encounter a contructor application or PAP.
696 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
697 -- Don't inline into constructor args here
698 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
699 -- Do inline into constructor args here
704 -- True:ctxt Analysing a function-valued expression that will be
707 -- False:ctxt Analysing a function-valued expression that may
708 -- be applied many times; but when it is,
709 -- the CtxtTy inside applies
712 initOccEnv = OccEnv OccRhs []
714 vanillaCtxt = OccEnv OccVanilla []
715 rhsCtxt = OccEnv OccRhs []
717 isRhsEnv (OccEnv OccRhs _) = True
718 isRhsEnv (OccEnv OccVanilla _) = False
720 setVanillaCtxt :: OccEnv -> OccEnv
721 setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty
722 setVanillaCtxt other_env = other_env
724 setCtxt :: OccEnv -> CtxtTy -> OccEnv
725 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
727 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
728 -- The result binders have one-shot-ness set that they might not have had originally.
729 -- This happens in (build (\cn -> e)). Here the occurrence analyser
730 -- linearity context knows that c,n are one-shot, and it records that fact in
731 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
733 oneShotGroup (OccEnv encl ctxt) bndrs
736 go ctxt [] rev_bndrs = reverse rev_bndrs
738 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
739 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
741 bndr' | lin_ctxt = setOneShotLambda bndr
744 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
746 addAppCtxt (OccEnv encl ctxt) args
747 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
750 %************************************************************************
752 \subsection[OccurAnal-types]{OccEnv}
754 %************************************************************************
757 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
759 combineUsageDetails, combineAltsUsageDetails
760 :: UsageDetails -> UsageDetails -> UsageDetails
762 combineUsageDetails usage1 usage2
763 = plusVarEnv_C addOccInfo usage1 usage2
765 combineAltsUsageDetails usage1 usage2
766 = plusVarEnv_C orOccInfo usage1 usage2
768 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
769 addOneOcc usage id info
770 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
771 -- ToDo: make this more efficient
773 emptyDetails = (emptyVarEnv :: UsageDetails)
775 usedIn :: Id -> UsageDetails -> Bool
776 v `usedIn` details = isExportedId v || v `elemVarEnv` details
778 tagBinders :: UsageDetails -- Of scope
780 -> (UsageDetails, -- Details with binders removed
781 [IdWithOccInfo]) -- Tagged binders
783 tagBinders usage binders
785 usage' = usage `delVarEnvList` binders
786 uss = map (setBinderOcc usage) binders
788 usage' `seq` (usage', uss)
790 tagBinder :: UsageDetails -- Of scope
792 -> (UsageDetails, -- Details with binders removed
793 IdWithOccInfo) -- Tagged binders
795 tagBinder usage binder
797 usage' = usage `delVarEnv` binder
798 binder' = setBinderOcc usage binder
800 usage' `seq` (usage', binder')
802 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
803 setBinderOcc usage bndr
804 | isTyVar bndr = bndr
805 | isExportedId bndr = case idOccInfo bndr of
807 other -> setIdOccInfo bndr NoOccInfo
808 -- Don't use local usage info for visible-elsewhere things
809 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
810 -- about to re-generate it and it shouldn't be "sticky"
812 | otherwise = setIdOccInfo bndr occ_info
814 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
818 %************************************************************************
820 \subsection{Operations over OccInfo}
822 %************************************************************************
825 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
826 mkOneOcc env id int_cxt
827 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
828 | otherwise = emptyDetails
830 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
832 markMany IAmDead = IAmDead
833 markMany other = NoOccInfo
835 markInsideSCC occ = markMany occ
837 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
838 markInsideLam occ = occ
840 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
842 addOccInfo IAmDead info2 = info2
843 addOccInfo info1 IAmDead = info1
844 addOccInfo RulesOnly RulesOnly = RulesOnly
845 addOccInfo info1 info2 = NoOccInfo
847 -- (orOccInfo orig new) is used
848 -- when combining occurrence info from branches of a case
850 orOccInfo IAmDead info2 = info2
851 orOccInfo info1 IAmDead = info1
852 orOccInfo RulesOnly RulesOnly = RulesOnly
853 orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1)
854 (OneOcc in_lam2 one_branch2 int_cxt2)
855 = OneOcc (in_lam1 || in_lam2)
856 False -- False, because it occurs in both branches
857 (int_cxt1 && int_cxt2)
858 orOccInfo info1 info2 = NoOccInfo