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 )
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 (reOrderRec env new_cycle)
205 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
206 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
209 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
210 strongly connected component (there's guaranteed to be a cycle). It returns the
212 a) in a better order,
213 b) with some of the Ids having a IMustNotBeINLINEd pragma
215 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
216 that the simplifier can guarantee not to loop provided it never records an inlining
217 for these no-inline guys.
219 Furthermore, the order of the binds is such that if we neglect dependencies
220 on the no-inline Ids then the binds are topologically sorted. This means
221 that the simplifier will generally do a good job if it works from top bottom,
222 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
225 [June 98: I don't understand the following paragraphs, and I've
226 changed the a=b case again so that it isn't a special case any more.]
228 Here's a case that bit me:
236 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
238 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
239 Perhaps something cleverer would suffice.
242 You might think that you can prevent non-termination simply by making
243 sure that we simplify a recursive binding's RHS in an environment that
244 simply clones the recursive Id. But no. Consider
246 letrec f = \x -> let z = f x' in ...
253 We bind n to its *simplified* RHS, we then *re-simplify* it when
254 we inline n. Then we may well inline f; and then the same thing
257 I don't think it's possible to prevent non-termination by environment
258 manipulation in this way. Apart from anything else, successive
259 iterations of the simplifier may unroll recursive loops in cases like
260 that above. The idea of beaking every recursive loop with an
261 IMustNotBeINLINEd pragma is much much better.
267 -> SCC (Node Details2)
269 -- Sorted into a plausible order. Enough of the Ids have
270 -- dontINLINE pragmas that there are no loops left.
272 -- Non-recursive case
273 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
275 -- Common case of simple self-recursion
276 reOrderRec env (CyclicSCC [bind])
277 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
279 ((tagged_bndr, rhs), _, _) = bind
281 reOrderRec env (CyclicSCC (bind : binds))
282 = -- Choose a loop breaker, mark it no-inline,
283 -- do SCC analysis on the rest, and recursively sort them out
284 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
286 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
289 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
290 (tagged_bndr, rhs) = chosen_pair
292 -- This loop looks for the bind with the lowest score
293 -- to pick as the loop breaker. The rest accumulate in
294 choose_loop_breaker (details,_,_) loop_sc acc []
295 = (details, acc) -- Done
297 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
298 | sc < loop_sc -- Lower score so pick this new one
299 = choose_loop_breaker bind sc (loop_bind : acc) binds
301 | otherwise -- No lower so don't pick it
302 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
306 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
307 score ((bndr, rhs), _, _)
308 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
309 -- Used to have also: && not (isExportedId bndr)
310 -- But I found this sometimes cost an extra iteration when we have
311 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
312 -- where df is the exported dictionary. Then df makes a really
313 -- bad choice for loop breaker
315 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
316 -- This used to have a lower score than inlineCandidate, but
317 -- it's *really* helpful if dictionaries get inlined fast,
318 -- so I'm experimenting with giving higher priority to data-typed things
320 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
322 | idHasRules bndr = 1
323 -- Avoid things with specialisations; we'd like
324 -- to take advantage of them in the subsequent bindings
328 inlineCandidate :: Id -> CoreExpr -> Bool
329 inlineCandidate id (Note InlineMe _) = True
330 inlineCandidate id rhs = isOneOcc (idOccInfo id)
332 -- Real example (the Enum Ordering instance from PrelBase):
333 -- rec f = \ x -> case d of (p,q,r) -> p x
334 -- g = \ x -> case d of (p,q,r) -> q x
337 -- Here, f and g occur just once; but we can't inline them into d.
338 -- On the other hand we *could* simplify those case expressions if
339 -- we didn't stupidly choose d as the loop breaker.
340 -- But we won't because constructor args are marked "Many".
342 not_fun_ty ty = not (isFunTy (dropForAlls ty))
345 @occAnalRhs@ deals with the question of bindings where the Id is marked
346 by an INLINE pragma. For these we record that anything which occurs
347 in its RHS occurs many times. This pessimistically assumes that ths
348 inlined binder also occurs many times in its scope, but if it doesn't
349 we'll catch it next time round. At worst this costs an extra simplifier pass.
350 ToDo: try using the occurrence info for the inline'd binder.
352 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
353 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
358 -> Id -> CoreExpr -- Binder and rhs
359 -- For non-recs the binder is alrady tagged
360 -- with occurrence info
361 -> (UsageDetails, CoreExpr)
363 occAnalRhs env id rhs
364 = (final_usage, rhs')
366 (rhs_usage, rhs') = occAnal ctxt rhs
367 ctxt | certainly_inline id = env
368 | otherwise = rhsCtxt
369 -- Note that we generally use an rhsCtxt. This tells the occ anal n
370 -- that it's looking at an RHS, which has an effect in occAnalApp
372 -- But there's a problem. Consider
377 -- First time round, it looks as if x1 and x2 occur as an arg of a
378 -- let-bound constructor ==> give them a many-occurrence.
379 -- But then x3 is inlined (unconditionally as it happens) and
380 -- next time round, x2 will be, and the next time round x1 will be
381 -- Result: multiple simplifier iterations. Sigh.
382 -- Crude solution: use rhsCtxt for things that occur just once...
384 certainly_inline id = case idOccInfo id of
385 OneOcc in_lam one_br _ -> not in_lam && one_br
388 -- [March 98] A new wrinkle is that if the binder has specialisations inside
389 -- it then we count the specialised Ids as "extra rhs's". That way
390 -- the "parent" keeps the specialised "children" alive. If the parent
391 -- dies (because it isn't referenced any more), then the children will
392 -- die too unless they are already referenced directly.
394 final_usage = addRuleUsage rhs_usage id
396 addRuleUsage :: UsageDetails -> Id -> UsageDetails
397 -- Add the usage from RULES in Id to the usage
398 addRuleUsage usage id
399 = foldVarSet add usage (idRuleVars id)
401 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
402 -- (i.e manyOcc) because many copies
403 -- of the specialised thing can appear
411 -> (UsageDetails, -- Gives info only about the "interesting" Ids
414 occAnal env (Type t) = (emptyDetails, Type t)
415 occAnal env (Var v) = (mkOneOcc env v False, Var v)
416 -- At one stage, I gathered the idRuleVars for v here too,
417 -- which in a way is the right thing to do.
418 -- Btu that went wrong right after specialisation, when
419 -- the *occurrences* of the overloaded function didn't have any
420 -- rules in them, so the *specialised* versions looked as if they
421 -- weren't used at all.
424 We regard variables that occur as constructor arguments as "dangerousToDup":
428 f x = let y = expensive x in
430 (case z of {(p,q)->q}, case z of {(p,q)->q})
433 We feel free to duplicate the WHNF (True,y), but that means
434 that y may be duplicated thereby.
436 If we aren't careful we duplicate the (expensive x) call!
437 Constructors are rather like lambdas in this way.
440 occAnal env expr@(Lit lit) = (emptyDetails, expr)
444 occAnal env (Note InlineMe body)
445 = case occAnal env body of { (usage, body') ->
446 (mapVarEnv markMany usage, Note InlineMe body')
449 occAnal env (Note note@(SCC cc) body)
450 = case occAnal env body of { (usage, body') ->
451 (mapVarEnv markInsideSCC usage, Note note body')
454 occAnal env (Note note body)
455 = case occAnal env body of { (usage, body') ->
456 (usage, Note note body')
461 occAnal env app@(App fun arg)
462 = occAnalApp env (collectArgs app) False
464 -- Ignore type variables altogether
465 -- (a) occurrences inside type lambdas only not marked as InsideLam
466 -- (b) type variables not in environment
468 occAnal env expr@(Lam x body) | isTyVar x
469 = case occAnal env body of { (body_usage, body') ->
470 (body_usage, Lam x body')
473 -- For value lambdas we do a special hack. Consider
475 -- If we did nothing, x is used inside the \y, so would be marked
476 -- as dangerous to dup. But in the common case where the abstraction
477 -- is applied to two arguments this is over-pessimistic.
478 -- So instead, we just mark each binder with its occurrence
479 -- info in the *body* of the multiple lambda.
480 -- Then, the simplifier is careful when partially applying lambdas.
482 occAnal env expr@(Lam _ _)
483 = case occAnal env_body body of { (body_usage, body') ->
485 (final_usage, tagged_binders) = tagBinders body_usage binders
486 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
487 -- we get linear-typed things in the resulting program that we can't handle yet.
488 -- (e.g. PrelShow) TODO
490 really_final_usage = if linear then
493 mapVarEnv markInsideLam final_usage
496 mkLams tagged_binders body') }
498 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
499 (binders, body) = collectBinders expr
500 binders' = oneShotGroup env binders
501 linear = all is_one_shot binders'
502 is_one_shot b = isId b && isOneShotBndr b
504 occAnal env (Case scrut bndr ty alts)
505 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
506 case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
508 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
509 alts_usage' = addCaseBndrUsage alts_usage
510 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
511 total_usage = scrut_usage `combineUsageDetails` alts_usage1
513 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
515 -- The case binder gets a usage of either "many" or "dead", never "one".
516 -- Reason: we like to inline single occurrences, to eliminate a binding,
517 -- but inlining a case binder *doesn't* eliminate a binding.
518 -- We *don't* want to transform
519 -- case x of w { (p,q) -> f w }
521 -- case x of w { (p,q) -> f (p,q) }
522 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
524 Just occ -> extendVarEnv usage bndr (markMany occ)
526 occ_anal_scrut (Var v) (alt1 : other_alts)
527 | not (null other_alts) || not (isDefaultAlt alt1)
528 = (mkOneOcc env v True, Var v)
529 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
530 -- No need for rhsCtxt
532 occAnal env (Let bind body)
533 = case occAnal env body of { (body_usage, body') ->
534 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
535 (final_usage, mkLets new_binds body') }}
538 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
539 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
541 arg_env = vanillaCtxt
544 Applications are dealt with specially because we want
545 the "build hack" to work.
548 -- Hack for build, fold, runST
549 occAnalApp env (Var fun, args) is_rhs
550 = case args_stuff of { (args_uds, args') ->
552 -- We mark the free vars of the argument of a constructor or PAP
553 -- as "many", if it is the RHS of a let(rec).
554 -- This means that nothing gets inlined into a constructor argument
555 -- position, which is what we want. Typically those constructor
556 -- arguments are just variables, or trivial expressions.
558 -- This is the *whole point* of the isRhsEnv predicate
561 isDataConWorkId fun || valArgCount args < idArity fun
562 = mapVarEnv markMany args_uds
563 | otherwise = args_uds
565 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
567 fun_uniq = idUnique fun
568 fun_uds = mkOneOcc env fun (valArgCount args > 0)
569 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
570 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
571 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
572 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
573 -- (foldr k z xs) may call k many times, but it never
574 -- shares a partial application of k; hence [False,True]
575 -- This means we can optimise
576 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
577 -- by floating in the v
579 | otherwise = occAnalArgs env args
582 occAnalApp env (fun, args) is_rhs
583 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
584 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
585 -- often leaves behind beta redexs like
587 -- Here we would like to mark x,y as one-shot, and treat the whole
588 -- thing much like a let. We do this by pushing some True items
589 -- onto the context stack.
591 case occAnalArgs env args of { (args_uds, args') ->
593 final_uds = fun_uds `combineUsageDetails` args_uds
595 (final_uds, mkApps fun' args') }}
598 -> Int -> CtxtTy -- Argument number, and context to use for it
600 -> (UsageDetails, [CoreExpr])
601 appSpecial env n ctxt args
604 arg_env = vanillaCtxt
606 go n [] = (emptyDetails, []) -- Too few args
608 go 1 (arg:args) -- The magic arg
609 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
610 case occAnalArgs env args of { (args_uds, args') ->
611 (combineUsageDetails arg_uds args_uds, arg':args') }}
614 = case occAnal arg_env arg of { (arg_uds, arg') ->
615 case go (n-1) args of { (args_uds, args') ->
616 (combineUsageDetails arg_uds args_uds, arg':args') }}
622 If the case binder occurs at all, the other binders effectively do too.
624 case e of x { (a,b) -> rhs }
627 If e turns out to be (e1,e2) we indeed get something like
628 let a = e1; b = e2; x = (a,b) in rhs
631 occAnalAlt env case_bndr (con, bndrs, rhs)
632 = case occAnal env rhs of { (rhs_usage, rhs') ->
634 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
635 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
636 | otherwise = tagged_bndrs
637 -- Leave the binders untagged if the case
638 -- binder occurs at all; see note above
640 (final_usage, (con, final_bndrs, rhs')) }
644 %************************************************************************
646 \subsection[OccurAnal-types]{OccEnv}
648 %************************************************************************
652 = OccEnv OccEncl -- Enclosing context information
653 CtxtTy -- Tells about linearity
655 -- OccEncl is used to control whether to inline into constructor arguments
657 -- x = (p,q) -- Don't inline p or q
658 -- y = /\a -> (p a, q a) -- Still don't inline p or q
659 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
660 -- So OccEncl tells enought about the context to know what to do when
661 -- we encounter a contructor application or PAP.
664 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
665 -- Don't inline into constructor args here
666 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
667 -- Do inline into constructor args here
672 -- True:ctxt Analysing a function-valued expression that will be
675 -- False:ctxt Analysing a function-valued expression that may
676 -- be applied many times; but when it is,
677 -- the CtxtTy inside applies
680 initOccEnv = OccEnv OccRhs []
682 vanillaCtxt = OccEnv OccVanilla []
683 rhsCtxt = OccEnv OccRhs []
685 isRhsEnv (OccEnv OccRhs _) = True
686 isRhsEnv (OccEnv OccVanilla _) = False
688 setCtxt :: OccEnv -> CtxtTy -> OccEnv
689 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
691 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
692 -- The result binders have one-shot-ness set that they might not have had originally.
693 -- This happens in (build (\cn -> e)). Here the occurrence analyser
694 -- linearity context knows that c,n are one-shot, and it records that fact in
695 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
697 oneShotGroup (OccEnv encl ctxt) bndrs
700 go ctxt [] rev_bndrs = reverse rev_bndrs
702 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
703 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
705 bndr' | lin_ctxt = setOneShotLambda bndr
708 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
710 addAppCtxt (OccEnv encl ctxt) args
711 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
714 %************************************************************************
716 \subsection[OccurAnal-types]{OccEnv}
718 %************************************************************************
721 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
723 combineUsageDetails, combineAltsUsageDetails
724 :: UsageDetails -> UsageDetails -> UsageDetails
726 combineUsageDetails usage1 usage2
727 = plusVarEnv_C addOccInfo usage1 usage2
729 combineAltsUsageDetails usage1 usage2
730 = plusVarEnv_C orOccInfo usage1 usage2
732 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
733 addOneOcc usage id info
734 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
735 -- ToDo: make this more efficient
737 emptyDetails = (emptyVarEnv :: UsageDetails)
739 usedIn :: Id -> UsageDetails -> Bool
740 v `usedIn` details = isExportedId v || v `elemVarEnv` details
742 tagBinders :: UsageDetails -- Of scope
744 -> (UsageDetails, -- Details with binders removed
745 [IdWithOccInfo]) -- Tagged binders
747 tagBinders usage binders
749 usage' = usage `delVarEnvList` binders
750 uss = map (setBinderOcc usage) binders
752 usage' `seq` (usage', uss)
754 tagBinder :: UsageDetails -- Of scope
756 -> (UsageDetails, -- Details with binders removed
757 IdWithOccInfo) -- Tagged binders
759 tagBinder usage binder
761 usage' = usage `delVarEnv` binder
762 binder' = setBinderOcc usage binder
764 usage' `seq` (usage', binder')
766 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
767 setBinderOcc usage bndr
768 | isTyVar bndr = bndr
769 | isExportedId bndr = case idOccInfo bndr of
771 other -> setIdOccInfo bndr NoOccInfo
772 -- Don't use local usage info for visible-elsewhere things
773 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
774 -- about to re-generate it and it shouldn't be "sticky"
776 | otherwise = setIdOccInfo bndr occ_info
778 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
782 %************************************************************************
784 \subsection{Operations over OccInfo}
786 %************************************************************************
789 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
790 mkOneOcc env id int_cxt
791 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
792 | otherwise = emptyDetails
794 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
796 markMany IAmDead = IAmDead
797 markMany other = NoOccInfo
799 markInsideSCC occ = markMany occ
801 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
802 markInsideLam occ = occ
804 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
806 addOccInfo IAmDead info2 = info2
807 addOccInfo info1 IAmDead = info1
808 addOccInfo info1 info2 = NoOccInfo
810 -- (orOccInfo orig new) is used
811 -- when combining occurrence info from branches of a case
813 orOccInfo IAmDead info2 = info2
814 orOccInfo info1 IAmDead = info1
815 orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1)
816 (OneOcc in_lam2 one_branch2 int_cxt2)
817 = OneOcc (in_lam1 || in_lam2)
818 False -- False, because it occurs in both branches
819 (int_cxt1 && int_cxt2)
821 orOccInfo info1 info2 = NoOccInfo