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, occurAnalyseGlobalExpr
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 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
68 occurAnalyseGlobalExpr expr
69 = -- Top level expr, so no interesting free vars, and
70 -- discard occurence info returned
71 snd (occAnal initOccEnv expr)
75 %************************************************************************
77 \subsection[OccurAnal-main]{Counting occurrences: main function}
79 %************************************************************************
85 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
87 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
88 -- which is gotten from the Id.
89 type Details1 = (Id, UsageDetails, CoreExpr)
90 type Details2 = (IdWithOccInfo, CoreExpr)
95 -> UsageDetails -- Usage details of scope
96 -> (UsageDetails, -- Of the whole let(rec)
99 occAnalBind env (NonRec binder rhs) body_usage
100 | not (binder `usedIn` body_usage) -- It's not mentioned
103 | otherwise -- It's mentioned in the body
104 = (final_body_usage `combineUsageDetails` rhs_usage,
105 [NonRec tagged_binder rhs'])
108 (final_body_usage, tagged_binder) = tagBinder body_usage binder
109 (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
112 Dropping dead code for recursive bindings is done in a very simple way:
114 the entire set of bindings is dropped if none of its binders are
115 mentioned in its body; otherwise none are.
117 This seems to miss an obvious improvement.
132 Now @f@ is unused. But dependency analysis will sort this out into a
133 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
134 It isn't easy to do a perfect job in one blow. Consider
148 occAnalBind env (Rec pairs) body_usage
149 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
151 binders = map fst pairs
153 analysed_pairs :: [Details1]
154 analysed_pairs = [ (bndr, rhs_usage, rhs')
155 | (bndr, rhs) <- pairs,
156 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
159 sccs :: [SCC (Node Details1)]
160 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
163 ---- stuff for dependency analysis of binds -------------------------------
164 edges :: [Node Details1]
165 edges = _scc_ "occAnalBind.assoc"
166 [ (details, idUnique id, edges_from rhs_usage)
167 | details@(id, rhs_usage, rhs) <- analysed_pairs
170 -- (a -> b) means a mentions b
171 -- Given the usage details (a UFM that gives occ info for each free var of
172 -- the RHS) we can get the list of free vars -- or rather their Int keys --
173 -- by just extracting the keys from the finite map. Grimy, but fast.
174 -- Previously we had this:
175 -- [ bndr | bndr <- bndrs,
176 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
177 -- which has n**2 cost, and this meant that edges_from alone
178 -- consumed 10% of total runtime!
179 edges_from :: UsageDetails -> [Unique]
180 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
183 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
186 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
187 | not (bndr `usedIn` body_usage)
188 = (body_usage, binds_so_far) -- Dead code
190 = (combined_usage, new_bind : binds_so_far)
192 total_usage = combineUsageDetails body_usage rhs_usage
193 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
194 new_bind = NonRec tagged_bndr rhs'
197 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
198 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
199 = (body_usage, binds_so_far) -- Dead code
201 = (combined_usage, final_bind:binds_so_far)
203 details = [details | (details, _, _) <- cycle]
204 bndrs = [bndr | (bndr, _, _) <- details]
205 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
206 total_usage = foldr combineUsageDetails body_usage rhs_usages
207 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
208 final_bind = Rec (reOrderRec env new_cycle)
210 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
211 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
214 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
215 strongly connected component (there's guaranteed to be a cycle). It returns the
217 a) in a better order,
218 b) with some of the Ids having a IMustNotBeINLINEd pragma
220 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
221 that the simplifier can guarantee not to loop provided it never records an inlining
222 for these no-inline guys.
224 Furthermore, the order of the binds is such that if we neglect dependencies
225 on the no-inline Ids then the binds are topologically sorted. This means
226 that the simplifier will generally do a good job if it works from top bottom,
227 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
230 [June 98: I don't understand the following paragraphs, and I've
231 changed the a=b case again so that it isn't a special case any more.]
233 Here's a case that bit me:
241 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
243 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
244 Perhaps something cleverer would suffice.
247 You might think that you can prevent non-termination simply by making
248 sure that we simplify a recursive binding's RHS in an environment that
249 simply clones the recursive Id. But no. Consider
251 letrec f = \x -> let z = f x' in ...
258 We bind n to its *simplified* RHS, we then *re-simplify* it when
259 we inline n. Then we may well inline f; and then the same thing
262 I don't think it's possible to prevent non-termination by environment
263 manipulation in this way. Apart from anything else, successive
264 iterations of the simplifier may unroll recursive loops in cases like
265 that above. The idea of beaking every recursive loop with an
266 IMustNotBeINLINEd pragma is much much better.
272 -> SCC (Node Details2)
274 -- Sorted into a plausible order. Enough of the Ids have
275 -- dontINLINE pragmas that there are no loops left.
277 -- Non-recursive case
278 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
280 -- Common case of simple self-recursion
281 reOrderRec env (CyclicSCC [bind])
282 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
284 ((tagged_bndr, rhs), _, _) = bind
286 reOrderRec env (CyclicSCC (bind : binds))
287 = -- Choose a loop breaker, mark it no-inline,
288 -- do SCC analysis on the rest, and recursively sort them out
289 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
291 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
294 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
295 (tagged_bndr, rhs) = chosen_pair
297 -- This loop looks for the bind with the lowest score
298 -- to pick as the loop breaker. The rest accumulate in
299 choose_loop_breaker (details,_,_) loop_sc acc []
300 = (details, acc) -- Done
302 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
303 | sc < loop_sc -- Lower score so pick this new one
304 = choose_loop_breaker bind sc (loop_bind : acc) binds
306 | otherwise -- No lower so don't pick it
307 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
311 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
312 score ((bndr, rhs), _, _)
313 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
314 -- Used to have also: && not (isExportedId bndr)
315 -- But I found this sometimes cost an extra iteration when we have
316 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
317 -- where df is the exported dictionary. Then df makes a really
318 -- bad choice for loop breaker
320 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
321 -- This used to have a lower score than inlineCandidate, but
322 -- it's *really* helpful if dictionaries get inlined fast,
323 -- so I'm experimenting with giving higher priority to data-typed things
325 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
327 | not (isEmptySpecInfo (idSpecialisation bndr)) = 1
328 -- Avoid things with specialisations; we'd like
329 -- to take advantage of them in the subsequent bindings
333 inlineCandidate :: Id -> CoreExpr -> Bool
334 inlineCandidate id (Note InlineMe _) = True
335 inlineCandidate id rhs = isOneOcc (idOccInfo id)
337 -- Real example (the Enum Ordering instance from PrelBase):
338 -- rec f = \ x -> case d of (p,q,r) -> p x
339 -- g = \ x -> case d of (p,q,r) -> q x
342 -- Here, f and g occur just once; but we can't inline them into d.
343 -- On the other hand we *could* simplify those case expressions if
344 -- we didn't stupidly choose d as the loop breaker.
345 -- But we won't because constructor args are marked "Many".
347 not_fun_ty ty = not (isFunTy (dropForAlls ty))
350 @occAnalRhs@ deals with the question of bindings where the Id is marked
351 by an INLINE pragma. For these we record that anything which occurs
352 in its RHS occurs many times. This pessimistically assumes that ths
353 inlined binder also occurs many times in its scope, but if it doesn't
354 we'll catch it next time round. At worst this costs an extra simplifier pass.
355 ToDo: try using the occurrence info for the inline'd binder.
357 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
358 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
363 -> Id -> CoreExpr -- Binder and rhs
364 -- For non-recs the binder is alrady tagged
365 -- with occurrence info
366 -> (UsageDetails, CoreExpr)
368 occAnalRhs env id rhs
369 = (final_usage, rhs')
371 (rhs_usage, rhs') = occAnal ctxt rhs
372 ctxt | certainly_inline id = env
373 | otherwise = rhsCtxt
374 -- Note that we generally use an rhsCtxt. This tells the occ anal n
375 -- that it's looking at an RHS, which has an effect in occAnalApp
377 -- But there's a problem. Consider
382 -- First time round, it looks as if x1 and x2 occur as an arg of a
383 -- let-bound constructor ==> give them a many-occurrence.
384 -- But then x3 is inlined (unconditionally as it happens) and
385 -- next time round, x2 will be, and the next time round x1 will be
386 -- Result: multiple simplifier iterations. Sigh.
387 -- Crude solution: use rhsCtxt for things that occur just once...
389 certainly_inline id = case idOccInfo id of
390 OneOcc in_lam one_br -> not in_lam && one_br
393 -- [March 98] A new wrinkle is that if the binder has specialisations inside
394 -- it then we count the specialised Ids as "extra rhs's". That way
395 -- the "parent" keeps the specialised "children" alive. If the parent
396 -- dies (because it isn't referenced any more), then the children will
397 -- die too unless they are already referenced directly.
399 final_usage = addRuleUsage rhs_usage id
401 addRuleUsage :: UsageDetails -> Id -> UsageDetails
402 -- Add the usage from RULES in Id to the usage
403 addRuleUsage usage id
404 = foldVarSet add usage (idRuleVars id)
406 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
407 -- (i.e manyOcc) because many copies
408 -- of the specialised thing can appear
416 -> (UsageDetails, -- Gives info only about the "interesting" Ids
419 occAnal env (Type t) = (emptyDetails, Type t)
424 var_uds | isLocalId v = unitVarEnv v oneOcc
425 | otherwise = emptyDetails
427 -- At one stage, I gathered the idRuleVars for v here too,
428 -- which in a way is the right thing to do.
429 -- Btu that went wrong right after specialisation, when
430 -- the *occurrences* of the overloaded function didn't have any
431 -- rules in them, so the *specialised* versions looked as if they
432 -- weren't used at all.
435 We regard variables that occur as constructor arguments as "dangerousToDup":
439 f x = let y = expensive x in
441 (case z of {(p,q)->q}, case z of {(p,q)->q})
444 We feel free to duplicate the WHNF (True,y), but that means
445 that y may be duplicated thereby.
447 If we aren't careful we duplicate the (expensive x) call!
448 Constructors are rather like lambdas in this way.
451 occAnal env expr@(Lit lit) = (emptyDetails, expr)
455 occAnal env (Note InlineMe body)
456 = case occAnal env body of { (usage, body') ->
457 (mapVarEnv markMany usage, Note InlineMe body')
460 occAnal env (Note note@(SCC cc) body)
461 = case occAnal env body of { (usage, body') ->
462 (mapVarEnv markInsideSCC usage, Note note body')
465 occAnal env (Note note body)
466 = case occAnal env body of { (usage, body') ->
467 (usage, Note note body')
472 occAnal env app@(App fun arg)
473 = occAnalApp env (collectArgs app) False
475 -- Ignore type variables altogether
476 -- (a) occurrences inside type lambdas only not marked as InsideLam
477 -- (b) type variables not in environment
479 occAnal env expr@(Lam x body) | isTyVar x
480 = case occAnal env body of { (body_usage, body') ->
481 (body_usage, Lam x body')
484 -- For value lambdas we do a special hack. Consider
486 -- If we did nothing, x is used inside the \y, so would be marked
487 -- as dangerous to dup. But in the common case where the abstraction
488 -- is applied to two arguments this is over-pessimistic.
489 -- So instead, we just mark each binder with its occurrence
490 -- info in the *body* of the multiple lambda.
491 -- Then, the simplifier is careful when partially applying lambdas.
493 occAnal env expr@(Lam _ _)
494 = case occAnal env_body body of { (body_usage, body') ->
496 (final_usage, tagged_binders) = tagBinders body_usage binders
497 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
498 -- we get linear-typed things in the resulting program that we can't handle yet.
499 -- (e.g. PrelShow) TODO
501 really_final_usage = if linear then
504 mapVarEnv markInsideLam final_usage
507 mkLams tagged_binders body') }
509 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
510 (binders, body) = collectBinders expr
511 binders' = oneShotGroup env binders
512 linear = all is_one_shot binders'
513 is_one_shot b = isId b && isOneShotBndr b
515 occAnal env (Case scrut bndr ty alts)
516 = case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
517 case occAnal vanillaCtxt scrut of { (scrut_usage, scrut') ->
518 -- No need for rhsCtxt
520 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
521 alts_usage' = addCaseBndrUsage alts_usage
522 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
523 total_usage = scrut_usage `combineUsageDetails` alts_usage1
525 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
527 -- The case binder gets a usage of either "many" or "dead", never "one".
528 -- Reason: we like to inline single occurrences, to eliminate a binding,
529 -- but inlining a case binder *doesn't* eliminate a binding.
530 -- We *don't* want to transform
531 -- case x of w { (p,q) -> f w }
533 -- case x of w { (p,q) -> f (p,q) }
534 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
536 Just occ -> extendVarEnv usage bndr (markMany occ)
538 occAnal env (Let bind body)
539 = case occAnal env body of { (body_usage, body') ->
540 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
541 (final_usage, mkLets new_binds body') }}
544 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
545 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
547 arg_env = vanillaCtxt
550 Applications are dealt with specially because we want
551 the "build hack" to work.
554 -- Hack for build, fold, runST
555 occAnalApp env (Var fun, args) is_rhs
556 = case args_stuff of { (args_uds, args') ->
558 -- We mark the free vars of the argument of a constructor or PAP
559 -- as "many", if it is the RHS of a let(rec).
560 -- This means that nothing gets inlined into a constructor argument
561 -- position, which is what we want. Typically those constructor
562 -- arguments are just variables, or trivial expressions.
564 -- This is the *whole point* of the isRhsEnv predicate
567 isDataConWorkId fun || valArgCount args < idArity fun
568 = mapVarEnv markMany args_uds
569 | otherwise = args_uds
571 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
573 fun_uniq = idUnique fun
575 fun_uds | isLocalId fun = unitVarEnv fun oneOcc
576 | otherwise = emptyDetails
578 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
579 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
580 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
581 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
582 -- (foldr k z xs) may call k many times, but it never
583 -- shares a partial application of k; hence [False,True]
584 -- This means we can optimise
585 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
586 -- by floating in the v
588 | otherwise = occAnalArgs env args
591 occAnalApp env (fun, args) is_rhs
592 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
593 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
594 -- often leaves behind beta redexs like
596 -- Here we would like to mark x,y as one-shot, and treat the whole
597 -- thing much like a let. We do this by pushing some True items
598 -- onto the context stack.
600 case occAnalArgs env args of { (args_uds, args') ->
602 final_uds = fun_uds `combineUsageDetails` args_uds
604 (final_uds, mkApps fun' args') }}
607 -> Int -> CtxtTy -- Argument number, and context to use for it
609 -> (UsageDetails, [CoreExpr])
610 appSpecial env n ctxt args
613 arg_env = vanillaCtxt
615 go n [] = (emptyDetails, []) -- Too few args
617 go 1 (arg:args) -- The magic arg
618 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
619 case occAnalArgs env args of { (args_uds, args') ->
620 (combineUsageDetails arg_uds args_uds, arg':args') }}
623 = case occAnal arg_env arg of { (arg_uds, arg') ->
624 case go (n-1) args of { (args_uds, args') ->
625 (combineUsageDetails arg_uds args_uds, arg':args') }}
631 If the case binder occurs at all, the other binders effectively do too.
633 case e of x { (a,b) -> rhs }
636 If e turns out to be (e1,e2) we indeed get something like
637 let a = e1; b = e2; x = (a,b) in rhs
640 occAnalAlt env case_bndr (con, bndrs, rhs)
641 = case occAnal env rhs of { (rhs_usage, rhs') ->
643 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
644 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
645 | otherwise = tagged_bndrs
646 -- Leave the binders untagged if the case
647 -- binder occurs at all; see note above
649 (final_usage, (con, final_bndrs, rhs')) }
653 %************************************************************************
655 \subsection[OccurAnal-types]{OccEnv}
657 %************************************************************************
661 = OccEnv OccEncl -- Enclosing context information
662 CtxtTy -- Tells about linearity
664 -- OccEncl is used to control whether to inline into constructor arguments
666 -- x = (p,q) -- Don't inline p or q
667 -- y = /\a -> (p a, q a) -- Still don't inline p or q
668 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
669 -- So OccEncl tells enought about the context to know what to do when
670 -- we encounter a contructor application or PAP.
673 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
674 -- Don't inline into constructor args here
675 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
676 -- Do inline into constructor args here
681 -- True:ctxt Analysing a function-valued expression that will be
684 -- False:ctxt Analysing a function-valued expression that may
685 -- be applied many times; but when it is,
686 -- the CtxtTy inside applies
689 initOccEnv = OccEnv OccRhs []
691 vanillaCtxt = OccEnv OccVanilla []
692 rhsCtxt = OccEnv OccRhs []
694 isRhsEnv (OccEnv OccRhs _) = True
695 isRhsEnv (OccEnv OccVanilla _) = False
697 setCtxt :: OccEnv -> CtxtTy -> OccEnv
698 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
700 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
701 -- The result binders have one-shot-ness set that they might not have had originally.
702 -- This happens in (build (\cn -> e)). Here the occurrence analyser
703 -- linearity context knows that c,n are one-shot, and it records that fact in
704 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
706 oneShotGroup (OccEnv encl ctxt) bndrs
709 go ctxt [] rev_bndrs = reverse rev_bndrs
711 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
712 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
714 bndr' | lin_ctxt = setOneShotLambda bndr
717 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
719 addAppCtxt (OccEnv encl ctxt) args
720 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
723 %************************************************************************
725 \subsection[OccurAnal-types]{OccEnv}
727 %************************************************************************
730 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
732 combineUsageDetails, combineAltsUsageDetails
733 :: UsageDetails -> UsageDetails -> UsageDetails
735 combineUsageDetails usage1 usage2
736 = plusVarEnv_C addOccInfo usage1 usage2
738 combineAltsUsageDetails usage1 usage2
739 = plusVarEnv_C orOccInfo usage1 usage2
741 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
742 addOneOcc usage id info
743 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
744 -- ToDo: make this more efficient
746 emptyDetails = (emptyVarEnv :: UsageDetails)
748 usedIn :: Id -> UsageDetails -> Bool
749 v `usedIn` details = isExportedId v || v `elemVarEnv` details
751 tagBinders :: UsageDetails -- Of scope
753 -> (UsageDetails, -- Details with binders removed
754 [IdWithOccInfo]) -- Tagged binders
756 tagBinders usage binders
758 usage' = usage `delVarEnvList` binders
759 uss = map (setBinderOcc usage) binders
761 usage' `seq` (usage', uss)
763 tagBinder :: UsageDetails -- Of scope
765 -> (UsageDetails, -- Details with binders removed
766 IdWithOccInfo) -- Tagged binders
768 tagBinder usage binder
770 usage' = usage `delVarEnv` binder
771 binder' = setBinderOcc usage binder
773 usage' `seq` (usage', binder')
775 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
776 setBinderOcc usage bndr
777 | isTyVar bndr = bndr
778 | isExportedId bndr = case idOccInfo bndr of
780 other -> setIdOccInfo bndr NoOccInfo
781 -- Don't use local usage info for visible-elsewhere things
782 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
783 -- about to re-generate it and it shouldn't be "sticky"
785 | otherwise = setIdOccInfo bndr occ_info
787 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
791 %************************************************************************
793 \subsection{Operations over OccInfo}
795 %************************************************************************
799 oneOcc = OneOcc False True
801 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
803 markMany IAmDead = IAmDead
804 markMany other = NoOccInfo
806 markInsideSCC occ = markMany occ
808 markInsideLam (OneOcc _ one_br) = OneOcc True one_br
809 markInsideLam occ = occ
811 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
813 addOccInfo IAmDead info2 = info2
814 addOccInfo info1 IAmDead = info1
815 addOccInfo info1 info2 = NoOccInfo
817 -- (orOccInfo orig new) is used
818 -- when combining occurrence info from branches of a case
820 orOccInfo IAmDead info2 = info2
821 orOccInfo info1 IAmDead = info1
822 orOccInfo (OneOcc in_lam1 one_branch1)
823 (OneOcc in_lam2 one_branch2)
824 = OneOcc (in_lam1 || in_lam2)
825 False -- False, because it occurs in both branches
827 orOccInfo info1 info2 = NoOccInfo