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, idSpecialisation,
28 import IdInfo ( isEmptySpecInfo )
29 import BasicTypes ( OccInfo(..), isOneOcc, InterestingCxt )
34 import Type ( isFunTy, dropForAlls )
35 import Maybes ( orElse )
36 import Digraph ( stronglyConnCompR, SCC(..) )
37 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
38 import Unique ( Unique )
39 import UniqFM ( keysUFM )
40 import Util ( zipWithEqual, mapAndUnzip )
45 %************************************************************************
47 \subsection[OccurAnal-main]{Counting occurrences: main function}
49 %************************************************************************
51 Here's the externally-callable interface:
54 occurAnalysePgm :: [CoreBind] -> [CoreBind]
56 = snd (go initOccEnv binds)
58 go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind])
62 = (final_usage, bind' ++ binds')
64 (bs_usage, binds') = go env binds
65 (final_usage, bind') = occAnalBind env bind bs_usage
67 occurAnalyseExpr :: CoreExpr -> CoreExpr
68 -- Do occurrence analysis, and discard occurence info returned
69 occurAnalyseExpr expr = snd (occAnal initOccEnv expr)
73 %************************************************************************
75 \subsection[OccurAnal-main]{Counting occurrences: main function}
77 %************************************************************************
83 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
85 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
86 -- which is gotten from the Id.
87 type Details1 = (Id, UsageDetails, CoreExpr)
88 type Details2 = (IdWithOccInfo, CoreExpr)
93 -> UsageDetails -- Usage details of scope
94 -> (UsageDetails, -- Of the whole let(rec)
97 occAnalBind env (NonRec binder rhs) body_usage
98 | not (binder `usedIn` body_usage) -- It's not mentioned
101 | otherwise -- It's mentioned in the body
102 = (final_body_usage `combineUsageDetails` rhs_usage,
103 [NonRec tagged_binder rhs'])
106 (final_body_usage, tagged_binder) = tagBinder body_usage binder
107 (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
110 Dropping dead code for recursive bindings is done in a very simple way:
112 the entire set of bindings is dropped if none of its binders are
113 mentioned in its body; otherwise none are.
115 This seems to miss an obvious improvement.
130 Now @f@ is unused. But dependency analysis will sort this out into a
131 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
132 It isn't easy to do a perfect job in one blow. Consider
146 occAnalBind env (Rec pairs) body_usage
147 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
149 analysed_pairs :: [Details1]
150 analysed_pairs = [ (bndr, rhs_usage, rhs')
151 | (bndr, rhs) <- pairs,
152 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
155 sccs :: [SCC (Node Details1)]
156 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
159 ---- stuff for dependency analysis of binds -------------------------------
160 edges :: [Node Details1]
161 edges = _scc_ "occAnalBind.assoc"
162 [ (details, idUnique id, edges_from rhs_usage)
163 | details@(id, rhs_usage, rhs) <- analysed_pairs
166 -- (a -> b) means a mentions b
167 -- Given the usage details (a UFM that gives occ info for each free var of
168 -- the RHS) we can get the list of free vars -- or rather their Int keys --
169 -- by just extracting the keys from the finite map. Grimy, but fast.
170 -- Previously we had this:
171 -- [ bndr | bndr <- bndrs,
172 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
173 -- which has n**2 cost, and this meant that edges_from alone
174 -- consumed 10% of total runtime!
175 edges_from :: UsageDetails -> [Unique]
176 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
179 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
182 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
183 | not (bndr `usedIn` body_usage)
184 = (body_usage, binds_so_far) -- Dead code
186 = (combined_usage, new_bind : binds_so_far)
188 total_usage = combineUsageDetails body_usage rhs_usage
189 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
190 new_bind = NonRec tagged_bndr rhs'
193 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
194 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
195 = (body_usage, binds_so_far) -- Dead code
197 = (combined_usage, final_bind:binds_so_far)
199 details = [details | (details, _, _) <- cycle]
200 bndrs = [bndr | (bndr, _, _) <- details]
201 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
202 total_usage = foldr combineUsageDetails body_usage rhs_usages
203 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
204 final_bind = Rec (reOrderRec env new_cycle)
206 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
207 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
210 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
211 strongly connected component (there's guaranteed to be a cycle). It returns the
213 a) in a better order,
214 b) with some of the Ids having a IMustNotBeINLINEd pragma
216 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
217 that the simplifier can guarantee not to loop provided it never records an inlining
218 for these no-inline guys.
220 Furthermore, the order of the binds is such that if we neglect dependencies
221 on the no-inline Ids then the binds are topologically sorted. This means
222 that the simplifier will generally do a good job if it works from top bottom,
223 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
226 [June 98: I don't understand the following paragraphs, and I've
227 changed the a=b case again so that it isn't a special case any more.]
229 Here's a case that bit me:
237 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
239 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
240 Perhaps something cleverer would suffice.
243 You might think that you can prevent non-termination simply by making
244 sure that we simplify a recursive binding's RHS in an environment that
245 simply clones the recursive Id. But no. Consider
247 letrec f = \x -> let z = f x' in ...
254 We bind n to its *simplified* RHS, we then *re-simplify* it when
255 we inline n. Then we may well inline f; and then the same thing
258 I don't think it's possible to prevent non-termination by environment
259 manipulation in this way. Apart from anything else, successive
260 iterations of the simplifier may unroll recursive loops in cases like
261 that above. The idea of beaking every recursive loop with an
262 IMustNotBeINLINEd pragma is much much better.
268 -> SCC (Node Details2)
270 -- Sorted into a plausible order. Enough of the Ids have
271 -- dontINLINE pragmas that there are no loops left.
273 -- Non-recursive case
274 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
276 -- Common case of simple self-recursion
277 reOrderRec env (CyclicSCC [bind])
278 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
280 ((tagged_bndr, rhs), _, _) = bind
282 reOrderRec env (CyclicSCC (bind : binds))
283 = -- Choose a loop breaker, mark it no-inline,
284 -- do SCC analysis on the rest, and recursively sort them out
285 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
287 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
290 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
291 (tagged_bndr, rhs) = chosen_pair
293 -- This loop looks for the bind with the lowest score
294 -- to pick as the loop breaker. The rest accumulate in
295 choose_loop_breaker (details,_,_) loop_sc acc []
296 = (details, acc) -- Done
298 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
299 | sc < loop_sc -- Lower score so pick this new one
300 = choose_loop_breaker bind sc (loop_bind : acc) binds
302 | otherwise -- No lower so don't pick it
303 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
307 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
308 score ((bndr, rhs), _, _)
309 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
310 -- Used to have also: && not (isExportedId bndr)
311 -- But I found this sometimes cost an extra iteration when we have
312 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
313 -- where df is the exported dictionary. Then df makes a really
314 -- bad choice for loop breaker
316 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
317 -- This used to have a lower score than inlineCandidate, but
318 -- it's *really* helpful if dictionaries get inlined fast,
319 -- so I'm experimenting with giving higher priority to data-typed things
321 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
323 | not (isEmptySpecInfo (idSpecialisation bndr)) = 1
324 -- Avoid things with specialisations; we'd like
325 -- to take advantage of them in the subsequent bindings
329 inlineCandidate :: Id -> CoreExpr -> Bool
330 inlineCandidate id (Note InlineMe _) = True
331 inlineCandidate id rhs = isOneOcc (idOccInfo id)
333 -- Real example (the Enum Ordering instance from PrelBase):
334 -- rec f = \ x -> case d of (p,q,r) -> p x
335 -- g = \ x -> case d of (p,q,r) -> q x
338 -- Here, f and g occur just once; but we can't inline them into d.
339 -- On the other hand we *could* simplify those case expressions if
340 -- we didn't stupidly choose d as the loop breaker.
341 -- But we won't because constructor args are marked "Many".
343 not_fun_ty ty = not (isFunTy (dropForAlls ty))
346 @occAnalRhs@ deals with the question of bindings where the Id is marked
347 by an INLINE pragma. For these we record that anything which occurs
348 in its RHS occurs many times. This pessimistically assumes that ths
349 inlined binder also occurs many times in its scope, but if it doesn't
350 we'll catch it next time round. At worst this costs an extra simplifier pass.
351 ToDo: try using the occurrence info for the inline'd binder.
353 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
354 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
359 -> Id -> CoreExpr -- Binder and rhs
360 -- For non-recs the binder is alrady tagged
361 -- with occurrence info
362 -> (UsageDetails, CoreExpr)
364 occAnalRhs env id rhs
365 = (final_usage, rhs')
367 (rhs_usage, rhs') = occAnal ctxt rhs
368 ctxt | certainly_inline id = env
369 | otherwise = rhsCtxt
370 -- Note that we generally use an rhsCtxt. This tells the occ anal n
371 -- that it's looking at an RHS, which has an effect in occAnalApp
373 -- But there's a problem. Consider
378 -- First time round, it looks as if x1 and x2 occur as an arg of a
379 -- let-bound constructor ==> give them a many-occurrence.
380 -- But then x3 is inlined (unconditionally as it happens) and
381 -- next time round, x2 will be, and the next time round x1 will be
382 -- Result: multiple simplifier iterations. Sigh.
383 -- Crude solution: use rhsCtxt for things that occur just once...
385 certainly_inline id = case idOccInfo id of
386 OneOcc in_lam one_br _ -> not in_lam && one_br
389 -- [March 98] A new wrinkle is that if the binder has specialisations inside
390 -- it then we count the specialised Ids as "extra rhs's". That way
391 -- the "parent" keeps the specialised "children" alive. If the parent
392 -- dies (because it isn't referenced any more), then the children will
393 -- die too unless they are already referenced directly.
395 final_usage = addRuleUsage rhs_usage id
397 addRuleUsage :: UsageDetails -> Id -> UsageDetails
398 -- Add the usage from RULES in Id to the usage
399 addRuleUsage usage id
400 = foldVarSet add usage (idRuleVars id)
402 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
403 -- (i.e manyOcc) because many copies
404 -- of the specialised thing can appear
412 -> (UsageDetails, -- Gives info only about the "interesting" Ids
415 occAnal env (Type t) = (emptyDetails, Type t)
416 occAnal env (Var v) = (mkOneOcc env v False, Var v)
417 -- At one stage, I gathered the idRuleVars for v here too,
418 -- which in a way is the right thing to do.
419 -- Btu that went wrong right after specialisation, when
420 -- the *occurrences* of the overloaded function didn't have any
421 -- rules in them, so the *specialised* versions looked as if they
422 -- weren't used at all.
425 We regard variables that occur as constructor arguments as "dangerousToDup":
429 f x = let y = expensive x in
431 (case z of {(p,q)->q}, case z of {(p,q)->q})
434 We feel free to duplicate the WHNF (True,y), but that means
435 that y may be duplicated thereby.
437 If we aren't careful we duplicate the (expensive x) call!
438 Constructors are rather like lambdas in this way.
441 occAnal env expr@(Lit lit) = (emptyDetails, expr)
445 occAnal env (Note InlineMe body)
446 = case occAnal env body of { (usage, body') ->
447 (mapVarEnv markMany usage, Note InlineMe body')
450 occAnal env (Note note@(SCC cc) body)
451 = case occAnal env body of { (usage, body') ->
452 (mapVarEnv markInsideSCC usage, Note note body')
455 occAnal env (Note note body)
456 = case occAnal env body of { (usage, body') ->
457 (usage, Note note body')
462 occAnal env app@(App fun arg)
463 = occAnalApp env (collectArgs app) False
465 -- Ignore type variables altogether
466 -- (a) occurrences inside type lambdas only not marked as InsideLam
467 -- (b) type variables not in environment
469 occAnal env expr@(Lam x body) | isTyVar x
470 = case occAnal env body of { (body_usage, body') ->
471 (body_usage, Lam x body')
474 -- For value lambdas we do a special hack. Consider
476 -- If we did nothing, x is used inside the \y, so would be marked
477 -- as dangerous to dup. But in the common case where the abstraction
478 -- is applied to two arguments this is over-pessimistic.
479 -- So instead, we just mark each binder with its occurrence
480 -- info in the *body* of the multiple lambda.
481 -- Then, the simplifier is careful when partially applying lambdas.
483 occAnal env expr@(Lam _ _)
484 = case occAnal env_body body of { (body_usage, body') ->
486 (final_usage, tagged_binders) = tagBinders body_usage binders
487 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
488 -- we get linear-typed things in the resulting program that we can't handle yet.
489 -- (e.g. PrelShow) TODO
491 really_final_usage = if linear then
494 mapVarEnv markInsideLam final_usage
497 mkLams tagged_binders body') }
499 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
500 (binders, body) = collectBinders expr
501 binders' = oneShotGroup env binders
502 linear = all is_one_shot binders'
503 is_one_shot b = isId b && isOneShotBndr b
505 occAnal env (Case scrut bndr ty alts)
506 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
507 case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
509 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
510 alts_usage' = addCaseBndrUsage alts_usage
511 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
512 total_usage = scrut_usage `combineUsageDetails` alts_usage1
514 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
516 -- The case binder gets a usage of either "many" or "dead", never "one".
517 -- Reason: we like to inline single occurrences, to eliminate a binding,
518 -- but inlining a case binder *doesn't* eliminate a binding.
519 -- We *don't* want to transform
520 -- case x of w { (p,q) -> f w }
522 -- case x of w { (p,q) -> f (p,q) }
523 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
525 Just occ -> extendVarEnv usage bndr (markMany occ)
527 occ_anal_scrut (Var v) (alt1 : other_alts)
528 | not (null other_alts) || not (isDefaultAlt alt1)
529 = (mkOneOcc env v True, Var v)
530 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
531 -- No need for rhsCtxt
533 occAnal env (Let bind body)
534 = case occAnal env body of { (body_usage, body') ->
535 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
536 (final_usage, mkLets new_binds body') }}
539 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
540 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
542 arg_env = vanillaCtxt
545 Applications are dealt with specially because we want
546 the "build hack" to work.
549 -- Hack for build, fold, runST
550 occAnalApp env (Var fun, args) is_rhs
551 = case args_stuff of { (args_uds, args') ->
553 -- We mark the free vars of the argument of a constructor or PAP
554 -- as "many", if it is the RHS of a let(rec).
555 -- This means that nothing gets inlined into a constructor argument
556 -- position, which is what we want. Typically those constructor
557 -- arguments are just variables, or trivial expressions.
559 -- This is the *whole point* of the isRhsEnv predicate
562 isDataConWorkId fun || valArgCount args < idArity fun
563 = mapVarEnv markMany args_uds
564 | otherwise = args_uds
566 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
568 fun_uniq = idUnique fun
569 fun_uds = mkOneOcc env fun (valArgCount args > 0)
570 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
571 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
572 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
573 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
574 -- (foldr k z xs) may call k many times, but it never
575 -- shares a partial application of k; hence [False,True]
576 -- This means we can optimise
577 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
578 -- by floating in the v
580 | otherwise = occAnalArgs env args
583 occAnalApp env (fun, args) is_rhs
584 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
585 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
586 -- often leaves behind beta redexs like
588 -- Here we would like to mark x,y as one-shot, and treat the whole
589 -- thing much like a let. We do this by pushing some True items
590 -- onto the context stack.
592 case occAnalArgs env args of { (args_uds, args') ->
594 final_uds = fun_uds `combineUsageDetails` args_uds
596 (final_uds, mkApps fun' args') }}
599 -> Int -> CtxtTy -- Argument number, and context to use for it
601 -> (UsageDetails, [CoreExpr])
602 appSpecial env n ctxt args
605 arg_env = vanillaCtxt
607 go n [] = (emptyDetails, []) -- Too few args
609 go 1 (arg:args) -- The magic arg
610 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
611 case occAnalArgs env args of { (args_uds, args') ->
612 (combineUsageDetails arg_uds args_uds, arg':args') }}
615 = case occAnal arg_env arg of { (arg_uds, arg') ->
616 case go (n-1) args of { (args_uds, args') ->
617 (combineUsageDetails arg_uds args_uds, arg':args') }}
623 If the case binder occurs at all, the other binders effectively do too.
625 case e of x { (a,b) -> rhs }
628 If e turns out to be (e1,e2) we indeed get something like
629 let a = e1; b = e2; x = (a,b) in rhs
632 occAnalAlt env case_bndr (con, bndrs, rhs)
633 = case occAnal env rhs of { (rhs_usage, rhs') ->
635 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
636 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
637 | otherwise = tagged_bndrs
638 -- Leave the binders untagged if the case
639 -- binder occurs at all; see note above
641 (final_usage, (con, final_bndrs, rhs')) }
645 %************************************************************************
647 \subsection[OccurAnal-types]{OccEnv}
649 %************************************************************************
653 = OccEnv OccEncl -- Enclosing context information
654 CtxtTy -- Tells about linearity
656 -- OccEncl is used to control whether to inline into constructor arguments
658 -- x = (p,q) -- Don't inline p or q
659 -- y = /\a -> (p a, q a) -- Still don't inline p or q
660 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
661 -- So OccEncl tells enought about the context to know what to do when
662 -- we encounter a contructor application or PAP.
665 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
666 -- Don't inline into constructor args here
667 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
668 -- Do inline into constructor args here
673 -- True:ctxt Analysing a function-valued expression that will be
676 -- False:ctxt Analysing a function-valued expression that may
677 -- be applied many times; but when it is,
678 -- the CtxtTy inside applies
681 initOccEnv = OccEnv OccRhs []
683 vanillaCtxt = OccEnv OccVanilla []
684 rhsCtxt = OccEnv OccRhs []
686 isRhsEnv (OccEnv OccRhs _) = True
687 isRhsEnv (OccEnv OccVanilla _) = False
689 setCtxt :: OccEnv -> CtxtTy -> OccEnv
690 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
692 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
693 -- The result binders have one-shot-ness set that they might not have had originally.
694 -- This happens in (build (\cn -> e)). Here the occurrence analyser
695 -- linearity context knows that c,n are one-shot, and it records that fact in
696 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
698 oneShotGroup (OccEnv encl ctxt) bndrs
701 go ctxt [] rev_bndrs = reverse rev_bndrs
703 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
704 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
706 bndr' | lin_ctxt = setOneShotLambda bndr
709 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
711 addAppCtxt (OccEnv encl ctxt) args
712 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
715 %************************************************************************
717 \subsection[OccurAnal-types]{OccEnv}
719 %************************************************************************
722 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
724 combineUsageDetails, combineAltsUsageDetails
725 :: UsageDetails -> UsageDetails -> UsageDetails
727 combineUsageDetails usage1 usage2
728 = plusVarEnv_C addOccInfo usage1 usage2
730 combineAltsUsageDetails usage1 usage2
731 = plusVarEnv_C orOccInfo usage1 usage2
733 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
734 addOneOcc usage id info
735 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
736 -- ToDo: make this more efficient
738 emptyDetails = (emptyVarEnv :: UsageDetails)
740 usedIn :: Id -> UsageDetails -> Bool
741 v `usedIn` details = isExportedId v || v `elemVarEnv` details
743 tagBinders :: UsageDetails -- Of scope
745 -> (UsageDetails, -- Details with binders removed
746 [IdWithOccInfo]) -- Tagged binders
748 tagBinders usage binders
750 usage' = usage `delVarEnvList` binders
751 uss = map (setBinderOcc usage) binders
753 usage' `seq` (usage', uss)
755 tagBinder :: UsageDetails -- Of scope
757 -> (UsageDetails, -- Details with binders removed
758 IdWithOccInfo) -- Tagged binders
760 tagBinder usage binder
762 usage' = usage `delVarEnv` binder
763 binder' = setBinderOcc usage binder
765 usage' `seq` (usage', binder')
767 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
768 setBinderOcc usage bndr
769 | isTyVar bndr = bndr
770 | isExportedId bndr = case idOccInfo bndr of
772 other -> setIdOccInfo bndr NoOccInfo
773 -- Don't use local usage info for visible-elsewhere things
774 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
775 -- about to re-generate it and it shouldn't be "sticky"
777 | otherwise = setIdOccInfo bndr occ_info
779 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
783 %************************************************************************
785 \subsection{Operations over OccInfo}
787 %************************************************************************
790 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
791 mkOneOcc env id int_cxt
792 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
793 | otherwise = emptyDetails
795 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
797 markMany IAmDead = IAmDead
798 markMany other = NoOccInfo
800 markInsideSCC occ = markMany occ
802 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
803 markInsideLam occ = occ
805 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
807 addOccInfo IAmDead info2 = info2
808 addOccInfo info1 IAmDead = info1
809 addOccInfo info1 info2 = NoOccInfo
811 -- (orOccInfo orig new) is used
812 -- when combining occurrence info from branches of a case
814 orOccInfo IAmDead info2 = info2
815 orOccInfo info1 IAmDead = info1
816 orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1)
817 (OneOcc in_lam2 one_branch2 int_cxt2)
818 = OneOcc (in_lam1 || in_lam2)
819 False -- False, because it occurs in both branches
820 (int_cxt1 && int_cxt2)
822 orOccInfo info1 info2 = NoOccInfo