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 )
23 import Id ( isDataConWorkId, isOneShotBndr, setOneShotLambda,
24 idOccInfo, setIdOccInfo, isLocalId,
25 isExportedId, idArity, idSpecialisation,
28 import IdInfo ( isEmptySpecInfo )
29 import BasicTypes ( OccInfo(..), isOneOcc )
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 binders = map fst pairs
151 analysed_pairs :: [Details1]
152 analysed_pairs = [ (bndr, rhs_usage, rhs')
153 | (bndr, rhs) <- pairs,
154 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
157 sccs :: [SCC (Node Details1)]
158 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
161 ---- stuff for dependency analysis of binds -------------------------------
162 edges :: [Node Details1]
163 edges = _scc_ "occAnalBind.assoc"
164 [ (details, idUnique id, edges_from rhs_usage)
165 | details@(id, rhs_usage, rhs) <- analysed_pairs
168 -- (a -> b) means a mentions b
169 -- Given the usage details (a UFM that gives occ info for each free var of
170 -- the RHS) we can get the list of free vars -- or rather their Int keys --
171 -- by just extracting the keys from the finite map. Grimy, but fast.
172 -- Previously we had this:
173 -- [ bndr | bndr <- bndrs,
174 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
175 -- which has n**2 cost, and this meant that edges_from alone
176 -- consumed 10% of total runtime!
177 edges_from :: UsageDetails -> [Unique]
178 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
181 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
184 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
185 | not (bndr `usedIn` body_usage)
186 = (body_usage, binds_so_far) -- Dead code
188 = (combined_usage, new_bind : binds_so_far)
190 total_usage = combineUsageDetails body_usage rhs_usage
191 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
192 new_bind = NonRec tagged_bndr rhs'
195 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
196 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
197 = (body_usage, binds_so_far) -- Dead code
199 = (combined_usage, final_bind:binds_so_far)
201 details = [details | (details, _, _) <- cycle]
202 bndrs = [bndr | (bndr, _, _) <- details]
203 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
204 total_usage = foldr combineUsageDetails body_usage rhs_usages
205 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
206 final_bind = Rec (reOrderRec env new_cycle)
208 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
209 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
212 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
213 strongly connected component (there's guaranteed to be a cycle). It returns the
215 a) in a better order,
216 b) with some of the Ids having a IMustNotBeINLINEd pragma
218 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
219 that the simplifier can guarantee not to loop provided it never records an inlining
220 for these no-inline guys.
222 Furthermore, the order of the binds is such that if we neglect dependencies
223 on the no-inline Ids then the binds are topologically sorted. This means
224 that the simplifier will generally do a good job if it works from top bottom,
225 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
228 [June 98: I don't understand the following paragraphs, and I've
229 changed the a=b case again so that it isn't a special case any more.]
231 Here's a case that bit me:
239 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
241 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
242 Perhaps something cleverer would suffice.
245 You might think that you can prevent non-termination simply by making
246 sure that we simplify a recursive binding's RHS in an environment that
247 simply clones the recursive Id. But no. Consider
249 letrec f = \x -> let z = f x' in ...
256 We bind n to its *simplified* RHS, we then *re-simplify* it when
257 we inline n. Then we may well inline f; and then the same thing
260 I don't think it's possible to prevent non-termination by environment
261 manipulation in this way. Apart from anything else, successive
262 iterations of the simplifier may unroll recursive loops in cases like
263 that above. The idea of beaking every recursive loop with an
264 IMustNotBeINLINEd pragma is much much better.
270 -> SCC (Node Details2)
272 -- Sorted into a plausible order. Enough of the Ids have
273 -- dontINLINE pragmas that there are no loops left.
275 -- Non-recursive case
276 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
278 -- Common case of simple self-recursion
279 reOrderRec env (CyclicSCC [bind])
280 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
282 ((tagged_bndr, rhs), _, _) = bind
284 reOrderRec env (CyclicSCC (bind : binds))
285 = -- Choose a loop breaker, mark it no-inline,
286 -- do SCC analysis on the rest, and recursively sort them out
287 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
289 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
292 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
293 (tagged_bndr, rhs) = chosen_pair
295 -- This loop looks for the bind with the lowest score
296 -- to pick as the loop breaker. The rest accumulate in
297 choose_loop_breaker (details,_,_) loop_sc acc []
298 = (details, acc) -- Done
300 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
301 | sc < loop_sc -- Lower score so pick this new one
302 = choose_loop_breaker bind sc (loop_bind : acc) binds
304 | otherwise -- No lower so don't pick it
305 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
309 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
310 score ((bndr, rhs), _, _)
311 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
312 -- Used to have also: && not (isExportedId bndr)
313 -- But I found this sometimes cost an extra iteration when we have
314 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
315 -- where df is the exported dictionary. Then df makes a really
316 -- bad choice for loop breaker
318 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
319 -- This used to have a lower score than inlineCandidate, but
320 -- it's *really* helpful if dictionaries get inlined fast,
321 -- so I'm experimenting with giving higher priority to data-typed things
323 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
325 | not (isEmptySpecInfo (idSpecialisation bndr)) = 1
326 -- Avoid things with specialisations; we'd like
327 -- to take advantage of them in the subsequent bindings
331 inlineCandidate :: Id -> CoreExpr -> Bool
332 inlineCandidate id (Note InlineMe _) = True
333 inlineCandidate id rhs = isOneOcc (idOccInfo id)
335 -- Real example (the Enum Ordering instance from PrelBase):
336 -- rec f = \ x -> case d of (p,q,r) -> p x
337 -- g = \ x -> case d of (p,q,r) -> q x
340 -- Here, f and g occur just once; but we can't inline them into d.
341 -- On the other hand we *could* simplify those case expressions if
342 -- we didn't stupidly choose d as the loop breaker.
343 -- But we won't because constructor args are marked "Many".
345 not_fun_ty ty = not (isFunTy (dropForAlls ty))
348 @occAnalRhs@ deals with the question of bindings where the Id is marked
349 by an INLINE pragma. For these we record that anything which occurs
350 in its RHS occurs many times. This pessimistically assumes that ths
351 inlined binder also occurs many times in its scope, but if it doesn't
352 we'll catch it next time round. At worst this costs an extra simplifier pass.
353 ToDo: try using the occurrence info for the inline'd binder.
355 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
356 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
361 -> Id -> CoreExpr -- Binder and rhs
362 -- For non-recs the binder is alrady tagged
363 -- with occurrence info
364 -> (UsageDetails, CoreExpr)
366 occAnalRhs env id rhs
367 = (final_usage, rhs')
369 (rhs_usage, rhs') = occAnal ctxt rhs
370 ctxt | certainly_inline id = env
371 | otherwise = rhsCtxt
372 -- Note that we generally use an rhsCtxt. This tells the occ anal n
373 -- that it's looking at an RHS, which has an effect in occAnalApp
375 -- But there's a problem. Consider
380 -- First time round, it looks as if x1 and x2 occur as an arg of a
381 -- let-bound constructor ==> give them a many-occurrence.
382 -- But then x3 is inlined (unconditionally as it happens) and
383 -- next time round, x2 will be, and the next time round x1 will be
384 -- Result: multiple simplifier iterations. Sigh.
385 -- Crude solution: use rhsCtxt for things that occur just once...
387 certainly_inline id = case idOccInfo id of
388 OneOcc in_lam one_br -> not in_lam && one_br
391 -- [March 98] A new wrinkle is that if the binder has specialisations inside
392 -- it then we count the specialised Ids as "extra rhs's". That way
393 -- the "parent" keeps the specialised "children" alive. If the parent
394 -- dies (because it isn't referenced any more), then the children will
395 -- die too unless they are already referenced directly.
397 final_usage = addRuleUsage rhs_usage id
399 addRuleUsage :: UsageDetails -> Id -> UsageDetails
400 -- Add the usage from RULES in Id to the usage
401 addRuleUsage usage id
402 = foldVarSet add usage (idRuleVars id)
404 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
405 -- (i.e manyOcc) because many copies
406 -- of the specialised thing can appear
414 -> (UsageDetails, -- Gives info only about the "interesting" Ids
417 occAnal env (Type t) = (emptyDetails, Type t)
422 var_uds | isLocalId v = unitVarEnv v oneOcc
423 | otherwise = emptyDetails
425 -- At one stage, I gathered the idRuleVars for v here too,
426 -- which in a way is the right thing to do.
427 -- Btu that went wrong right after specialisation, when
428 -- the *occurrences* of the overloaded function didn't have any
429 -- rules in them, so the *specialised* versions looked as if they
430 -- weren't used at all.
433 We regard variables that occur as constructor arguments as "dangerousToDup":
437 f x = let y = expensive x in
439 (case z of {(p,q)->q}, case z of {(p,q)->q})
442 We feel free to duplicate the WHNF (True,y), but that means
443 that y may be duplicated thereby.
445 If we aren't careful we duplicate the (expensive x) call!
446 Constructors are rather like lambdas in this way.
449 occAnal env expr@(Lit lit) = (emptyDetails, expr)
453 occAnal env (Note InlineMe body)
454 = case occAnal env body of { (usage, body') ->
455 (mapVarEnv markMany usage, Note InlineMe body')
458 occAnal env (Note note@(SCC cc) body)
459 = case occAnal env body of { (usage, body') ->
460 (mapVarEnv markInsideSCC usage, Note note body')
463 occAnal env (Note note body)
464 = case occAnal env body of { (usage, body') ->
465 (usage, Note note body')
470 occAnal env app@(App fun arg)
471 = occAnalApp env (collectArgs app) False
473 -- Ignore type variables altogether
474 -- (a) occurrences inside type lambdas only not marked as InsideLam
475 -- (b) type variables not in environment
477 occAnal env expr@(Lam x body) | isTyVar x
478 = case occAnal env body of { (body_usage, body') ->
479 (body_usage, Lam x body')
482 -- For value lambdas we do a special hack. Consider
484 -- If we did nothing, x is used inside the \y, so would be marked
485 -- as dangerous to dup. But in the common case where the abstraction
486 -- is applied to two arguments this is over-pessimistic.
487 -- So instead, we just mark each binder with its occurrence
488 -- info in the *body* of the multiple lambda.
489 -- Then, the simplifier is careful when partially applying lambdas.
491 occAnal env expr@(Lam _ _)
492 = case occAnal env_body body of { (body_usage, body') ->
494 (final_usage, tagged_binders) = tagBinders body_usage binders
495 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
496 -- we get linear-typed things in the resulting program that we can't handle yet.
497 -- (e.g. PrelShow) TODO
499 really_final_usage = if linear then
502 mapVarEnv markInsideLam final_usage
505 mkLams tagged_binders body') }
507 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
508 (binders, body) = collectBinders expr
509 binders' = oneShotGroup env binders
510 linear = all is_one_shot binders'
511 is_one_shot b = isId b && isOneShotBndr b
513 occAnal env (Case scrut bndr ty alts)
514 = case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
515 case occAnal vanillaCtxt scrut of { (scrut_usage, scrut') ->
516 -- No need for rhsCtxt
518 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
519 alts_usage' = addCaseBndrUsage alts_usage
520 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
521 total_usage = scrut_usage `combineUsageDetails` alts_usage1
523 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
525 -- The case binder gets a usage of either "many" or "dead", never "one".
526 -- Reason: we like to inline single occurrences, to eliminate a binding,
527 -- but inlining a case binder *doesn't* eliminate a binding.
528 -- We *don't* want to transform
529 -- case x of w { (p,q) -> f w }
531 -- case x of w { (p,q) -> f (p,q) }
532 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
534 Just occ -> extendVarEnv usage bndr (markMany occ)
536 occAnal env (Let bind body)
537 = case occAnal env body of { (body_usage, body') ->
538 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
539 (final_usage, mkLets new_binds body') }}
542 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
543 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
545 arg_env = vanillaCtxt
548 Applications are dealt with specially because we want
549 the "build hack" to work.
552 -- Hack for build, fold, runST
553 occAnalApp env (Var fun, args) is_rhs
554 = case args_stuff of { (args_uds, args') ->
556 -- We mark the free vars of the argument of a constructor or PAP
557 -- as "many", if it is the RHS of a let(rec).
558 -- This means that nothing gets inlined into a constructor argument
559 -- position, which is what we want. Typically those constructor
560 -- arguments are just variables, or trivial expressions.
562 -- This is the *whole point* of the isRhsEnv predicate
565 isDataConWorkId fun || valArgCount args < idArity fun
566 = mapVarEnv markMany args_uds
567 | otherwise = args_uds
569 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
571 fun_uniq = idUnique fun
573 fun_uds | isLocalId fun = unitVarEnv fun oneOcc
574 | otherwise = emptyDetails
576 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
577 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
578 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
579 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
580 -- (foldr k z xs) may call k many times, but it never
581 -- shares a partial application of k; hence [False,True]
582 -- This means we can optimise
583 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
584 -- by floating in the v
586 | otherwise = occAnalArgs env args
589 occAnalApp env (fun, args) is_rhs
590 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
591 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
592 -- often leaves behind beta redexs like
594 -- Here we would like to mark x,y as one-shot, and treat the whole
595 -- thing much like a let. We do this by pushing some True items
596 -- onto the context stack.
598 case occAnalArgs env args of { (args_uds, args') ->
600 final_uds = fun_uds `combineUsageDetails` args_uds
602 (final_uds, mkApps fun' args') }}
605 -> Int -> CtxtTy -- Argument number, and context to use for it
607 -> (UsageDetails, [CoreExpr])
608 appSpecial env n ctxt args
611 arg_env = vanillaCtxt
613 go n [] = (emptyDetails, []) -- Too few args
615 go 1 (arg:args) -- The magic arg
616 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
617 case occAnalArgs env args of { (args_uds, args') ->
618 (combineUsageDetails arg_uds args_uds, arg':args') }}
621 = case occAnal arg_env arg of { (arg_uds, arg') ->
622 case go (n-1) args of { (args_uds, args') ->
623 (combineUsageDetails arg_uds args_uds, arg':args') }}
629 If the case binder occurs at all, the other binders effectively do too.
631 case e of x { (a,b) -> rhs }
634 If e turns out to be (e1,e2) we indeed get something like
635 let a = e1; b = e2; x = (a,b) in rhs
638 occAnalAlt env case_bndr (con, bndrs, rhs)
639 = case occAnal env rhs of { (rhs_usage, rhs') ->
641 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
642 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
643 | otherwise = tagged_bndrs
644 -- Leave the binders untagged if the case
645 -- binder occurs at all; see note above
647 (final_usage, (con, final_bndrs, rhs')) }
651 %************************************************************************
653 \subsection[OccurAnal-types]{OccEnv}
655 %************************************************************************
659 = OccEnv OccEncl -- Enclosing context information
660 CtxtTy -- Tells about linearity
662 -- OccEncl is used to control whether to inline into constructor arguments
664 -- x = (p,q) -- Don't inline p or q
665 -- y = /\a -> (p a, q a) -- Still don't inline p or q
666 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
667 -- So OccEncl tells enought about the context to know what to do when
668 -- we encounter a contructor application or PAP.
671 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
672 -- Don't inline into constructor args here
673 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
674 -- Do inline into constructor args here
679 -- True:ctxt Analysing a function-valued expression that will be
682 -- False:ctxt Analysing a function-valued expression that may
683 -- be applied many times; but when it is,
684 -- the CtxtTy inside applies
687 initOccEnv = OccEnv OccRhs []
689 vanillaCtxt = OccEnv OccVanilla []
690 rhsCtxt = OccEnv OccRhs []
692 isRhsEnv (OccEnv OccRhs _) = True
693 isRhsEnv (OccEnv OccVanilla _) = False
695 setCtxt :: OccEnv -> CtxtTy -> OccEnv
696 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
698 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
699 -- The result binders have one-shot-ness set that they might not have had originally.
700 -- This happens in (build (\cn -> e)). Here the occurrence analyser
701 -- linearity context knows that c,n are one-shot, and it records that fact in
702 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
704 oneShotGroup (OccEnv encl ctxt) bndrs
707 go ctxt [] rev_bndrs = reverse rev_bndrs
709 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
710 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
712 bndr' | lin_ctxt = setOneShotLambda bndr
715 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
717 addAppCtxt (OccEnv encl ctxt) args
718 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
721 %************************************************************************
723 \subsection[OccurAnal-types]{OccEnv}
725 %************************************************************************
728 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
730 combineUsageDetails, combineAltsUsageDetails
731 :: UsageDetails -> UsageDetails -> UsageDetails
733 combineUsageDetails usage1 usage2
734 = plusVarEnv_C addOccInfo usage1 usage2
736 combineAltsUsageDetails usage1 usage2
737 = plusVarEnv_C orOccInfo usage1 usage2
739 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
740 addOneOcc usage id info
741 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
742 -- ToDo: make this more efficient
744 emptyDetails = (emptyVarEnv :: UsageDetails)
746 usedIn :: Id -> UsageDetails -> Bool
747 v `usedIn` details = isExportedId v || v `elemVarEnv` details
749 tagBinders :: UsageDetails -- Of scope
751 -> (UsageDetails, -- Details with binders removed
752 [IdWithOccInfo]) -- Tagged binders
754 tagBinders usage binders
756 usage' = usage `delVarEnvList` binders
757 uss = map (setBinderOcc usage) binders
759 usage' `seq` (usage', uss)
761 tagBinder :: UsageDetails -- Of scope
763 -> (UsageDetails, -- Details with binders removed
764 IdWithOccInfo) -- Tagged binders
766 tagBinder usage binder
768 usage' = usage `delVarEnv` binder
769 binder' = setBinderOcc usage binder
771 usage' `seq` (usage', binder')
773 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
774 setBinderOcc usage bndr
775 | isTyVar bndr = bndr
776 | isExportedId bndr = case idOccInfo bndr of
778 other -> setIdOccInfo bndr NoOccInfo
779 -- Don't use local usage info for visible-elsewhere things
780 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
781 -- about to re-generate it and it shouldn't be "sticky"
783 | otherwise = setIdOccInfo bndr occ_info
785 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
789 %************************************************************************
791 \subsection{Operations over OccInfo}
793 %************************************************************************
797 oneOcc = OneOcc False True
799 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
801 markMany IAmDead = IAmDead
802 markMany other = NoOccInfo
804 markInsideSCC occ = markMany occ
806 markInsideLam (OneOcc _ one_br) = OneOcc True one_br
807 markInsideLam occ = occ
809 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
811 addOccInfo IAmDead info2 = info2
812 addOccInfo info1 IAmDead = info1
813 addOccInfo info1 info2 = NoOccInfo
815 -- (orOccInfo orig new) is used
816 -- when combining occurrence info from branches of a case
818 orOccInfo IAmDead info2 = info2
819 orOccInfo info1 IAmDead = info1
820 orOccInfo (OneOcc in_lam1 one_branch1)
821 (OneOcc in_lam2 one_branch2)
822 = OneOcc (in_lam1 || in_lam2)
823 False -- False, because it occurs in both branches
825 orOccInfo info1 info2 = NoOccInfo