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, occurAnalyseRule,
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 BasicTypes ( OccInfo(..), isOneOcc )
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 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
67 occurAnalyseGlobalExpr expr
68 = -- Top level expr, so no interesting free vars, and
69 -- discard occurence info returned
70 snd (occAnal initOccEnv expr)
72 occurAnalyseRule :: CoreRule -> CoreRule
73 occurAnalyseRule rule@(BuiltinRule _ _) = rule
74 occurAnalyseRule (Rule str act tpl_vars tpl_args rhs)
75 -- Add occ info to tpl_vars, rhs
76 = Rule str act tpl_vars' tpl_args rhs'
78 (rhs_uds, rhs') = occAnal initOccEnv rhs
79 (_, tpl_vars') = tagBinders rhs_uds tpl_vars
83 %************************************************************************
85 \subsection[OccurAnal-main]{Counting occurrences: main function}
87 %************************************************************************
93 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
95 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
96 -- which is gotten from the Id.
97 type Details1 = (Id, UsageDetails, CoreExpr)
98 type Details2 = (IdWithOccInfo, CoreExpr)
101 occAnalBind :: OccEnv
103 -> UsageDetails -- Usage details of scope
104 -> (UsageDetails, -- Of the whole let(rec)
107 occAnalBind env (NonRec binder rhs) body_usage
108 | not (binder `usedIn` body_usage) -- It's not mentioned
111 | otherwise -- It's mentioned in the body
112 = (final_body_usage `combineUsageDetails` rhs_usage,
113 [NonRec tagged_binder rhs'])
116 (final_body_usage, tagged_binder) = tagBinder body_usage binder
117 (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
120 Dropping dead code for recursive bindings is done in a very simple way:
122 the entire set of bindings is dropped if none of its binders are
123 mentioned in its body; otherwise none are.
125 This seems to miss an obvious improvement.
140 Now @f@ is unused. But dependency analysis will sort this out into a
141 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
142 It isn't easy to do a perfect job in one blow. Consider
156 occAnalBind env (Rec pairs) body_usage
157 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
159 binders = map fst pairs
161 analysed_pairs :: [Details1]
162 analysed_pairs = [ (bndr, rhs_usage, rhs')
163 | (bndr, rhs) <- pairs,
164 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
167 sccs :: [SCC (Node Details1)]
168 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
171 ---- stuff for dependency analysis of binds -------------------------------
172 edges :: [Node Details1]
173 edges = _scc_ "occAnalBind.assoc"
174 [ (details, idUnique id, edges_from rhs_usage)
175 | details@(id, rhs_usage, rhs) <- analysed_pairs
178 -- (a -> b) means a mentions b
179 -- Given the usage details (a UFM that gives occ info for each free var of
180 -- the RHS) we can get the list of free vars -- or rather their Int keys --
181 -- by just extracting the keys from the finite map. Grimy, but fast.
182 -- Previously we had this:
183 -- [ bndr | bndr <- bndrs,
184 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
185 -- which has n**2 cost, and this meant that edges_from alone
186 -- consumed 10% of total runtime!
187 edges_from :: UsageDetails -> [Unique]
188 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
191 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
194 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
195 | not (bndr `usedIn` body_usage)
196 = (body_usage, binds_so_far) -- Dead code
198 = (combined_usage, new_bind : binds_so_far)
200 total_usage = combineUsageDetails body_usage rhs_usage
201 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
202 new_bind = NonRec tagged_bndr rhs'
205 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
206 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
207 = (body_usage, binds_so_far) -- Dead code
209 = (combined_usage, final_bind:binds_so_far)
211 details = [details | (details, _, _) <- cycle]
212 bndrs = [bndr | (bndr, _, _) <- details]
213 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
214 total_usage = foldr combineUsageDetails body_usage rhs_usages
215 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
216 final_bind = Rec (reOrderRec env new_cycle)
218 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
219 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
222 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
223 strongly connected component (there's guaranteed to be a cycle). It returns the
225 a) in a better order,
226 b) with some of the Ids having a IMustNotBeINLINEd pragma
228 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
229 that the simplifier can guarantee not to loop provided it never records an inlining
230 for these no-inline guys.
232 Furthermore, the order of the binds is such that if we neglect dependencies
233 on the no-inline Ids then the binds are topologically sorted. This means
234 that the simplifier will generally do a good job if it works from top bottom,
235 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
238 [June 98: I don't understand the following paragraphs, and I've
239 changed the a=b case again so that it isn't a special case any more.]
241 Here's a case that bit me:
249 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
251 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
252 Perhaps something cleverer would suffice.
255 You might think that you can prevent non-termination simply by making
256 sure that we simplify a recursive binding's RHS in an environment that
257 simply clones the recursive Id. But no. Consider
259 letrec f = \x -> let z = f x' in ...
266 We bind n to its *simplified* RHS, we then *re-simplify* it when
267 we inline n. Then we may well inline f; and then the same thing
270 I don't think it's possible to prevent non-termination by environment
271 manipulation in this way. Apart from anything else, successive
272 iterations of the simplifier may unroll recursive loops in cases like
273 that above. The idea of beaking every recursive loop with an
274 IMustNotBeINLINEd pragma is much much better.
280 -> SCC (Node Details2)
282 -- Sorted into a plausible order. Enough of the Ids have
283 -- dontINLINE pragmas that there are no loops left.
285 -- Non-recursive case
286 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
288 -- Common case of simple self-recursion
289 reOrderRec env (CyclicSCC [bind])
290 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
292 ((tagged_bndr, rhs), _, _) = bind
294 reOrderRec env (CyclicSCC (bind : binds))
295 = -- Choose a loop breaker, mark it no-inline,
296 -- do SCC analysis on the rest, and recursively sort them out
297 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
299 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
302 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
303 (tagged_bndr, rhs) = chosen_pair
305 -- This loop looks for the bind with the lowest score
306 -- to pick as the loop breaker. The rest accumulate in
307 choose_loop_breaker (details,_,_) loop_sc acc []
308 = (details, acc) -- Done
310 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
311 | sc < loop_sc -- Lower score so pick this new one
312 = choose_loop_breaker bind sc (loop_bind : acc) binds
314 | otherwise -- No lower so don't pick it
315 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
319 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
320 score ((bndr, rhs), _, _)
321 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
322 -- Used to have also: && not (isExportedId bndr)
323 -- But I found this sometimes cost an extra iteration when we have
324 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
325 -- where df is the exported dictionary. Then df makes a really
326 -- bad choice for loop breaker
328 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
329 -- This used to have a lower score than inlineCandidate, but
330 -- it's *really* helpful if dictionaries get inlined fast,
331 -- so I'm experimenting with giving higher priority to data-typed things
333 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
335 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
336 -- Avoid things with specialisations; we'd like
337 -- to take advantage of them in the subsequent bindings
341 inlineCandidate :: Id -> CoreExpr -> Bool
342 inlineCandidate id (Note InlineMe _) = True
343 inlineCandidate id rhs = isOneOcc (idOccInfo id)
345 -- Real example (the Enum Ordering instance from PrelBase):
346 -- rec f = \ x -> case d of (p,q,r) -> p x
347 -- g = \ x -> case d of (p,q,r) -> q x
350 -- Here, f and g occur just once; but we can't inline them into d.
351 -- On the other hand we *could* simplify those case expressions if
352 -- we didn't stupidly choose d as the loop breaker.
353 -- But we won't because constructor args are marked "Many".
355 not_fun_ty ty = not (isFunTy (dropForAlls ty))
358 @occAnalRhs@ deals with the question of bindings where the Id is marked
359 by an INLINE pragma. For these we record that anything which occurs
360 in its RHS occurs many times. This pessimistically assumes that ths
361 inlined binder also occurs many times in its scope, but if it doesn't
362 we'll catch it next time round. At worst this costs an extra simplifier pass.
363 ToDo: try using the occurrence info for the inline'd binder.
365 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
366 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
371 -> Id -> CoreExpr -- Binder and rhs
372 -- For non-recs the binder is alrady tagged
373 -- with occurrence info
374 -> (UsageDetails, CoreExpr)
376 occAnalRhs env id rhs
377 = (final_usage, rhs')
379 (rhs_usage, rhs') = occAnal ctxt rhs
380 ctxt | certainly_inline id = env
381 | otherwise = rhsCtxt
382 -- Note that we generally use an rhsCtxt. This tells the occ anal n
383 -- that it's looking at an RHS, which has an effect in occAnalApp
385 -- But there's a problem. Consider
390 -- First time round, it looks as if x1 and x2 occur as an arg of a
391 -- let-bound constructor ==> give them a many-occurrence.
392 -- But then x3 is inlined (unconditionally as it happens) and
393 -- next time round, x2 will be, and the next time round x1 will be
394 -- Result: multiple simplifier iterations. Sigh.
395 -- Crude solution: use rhsCtxt for things that occur just once...
397 certainly_inline id = case idOccInfo id of
398 OneOcc in_lam one_br -> not in_lam && one_br
401 -- [March 98] A new wrinkle is that if the binder has specialisations inside
402 -- it then we count the specialised Ids as "extra rhs's". That way
403 -- the "parent" keeps the specialised "children" alive. If the parent
404 -- dies (because it isn't referenced any more), then the children will
405 -- die too unless they are already referenced directly.
407 final_usage = addRuleUsage rhs_usage id
409 addRuleUsage :: UsageDetails -> Id -> UsageDetails
410 -- Add the usage from RULES in Id to the usage
411 addRuleUsage usage id
412 = foldVarSet add usage (idRuleVars id)
414 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
415 -- (i.e manyOcc) because many copies
416 -- of the specialised thing can appear
424 -> (UsageDetails, -- Gives info only about the "interesting" Ids
427 occAnal env (Type t) = (emptyDetails, Type t)
432 var_uds | isLocalId v = unitVarEnv v oneOcc
433 | otherwise = emptyDetails
435 -- At one stage, I gathered the idRuleVars for v here too,
436 -- which in a way is the right thing to do.
437 -- But that went wrong right after specialisation, when
438 -- the *occurrences* of the overloaded function didn't have any
439 -- rules in them, so the *specialised* versions looked as if they
440 -- weren't used at all.
443 We regard variables that occur as constructor arguments as "dangerousToDup":
447 f x = let y = expensive x in
449 (case z of {(p,q)->q}, case z of {(p,q)->q})
452 We feel free to duplicate the WHNF (True,y), but that means
453 that y may be duplicated thereby.
455 If we aren't careful we duplicate the (expensive x) call!
456 Constructors are rather like lambdas in this way.
459 occAnal env expr@(Lit lit) = (emptyDetails, expr)
463 occAnal env (Note InlineMe body)
464 = case occAnal env body of { (usage, body') ->
465 (mapVarEnv markMany usage, Note InlineMe body')
468 occAnal env (Note note@(SCC cc) body)
469 = case occAnal env body of { (usage, body') ->
470 (mapVarEnv markInsideSCC usage, Note note body')
473 occAnal env (Note note body)
474 = case occAnal env body of { (usage, body') ->
475 (usage, Note note body')
480 occAnal env app@(App fun arg)
481 = occAnalApp env (collectArgs app) False
483 -- Ignore type variables altogether
484 -- (a) occurrences inside type lambdas only not marked as InsideLam
485 -- (b) type variables not in environment
487 occAnal env expr@(Lam x body) | isTyVar x
488 = case occAnal env body of { (body_usage, body') ->
489 (body_usage, Lam x body')
492 -- For value lambdas we do a special hack. Consider
494 -- If we did nothing, x is used inside the \y, so would be marked
495 -- as dangerous to dup. But in the common case where the abstraction
496 -- is applied to two arguments this is over-pessimistic.
497 -- So instead, we just mark each binder with its occurrence
498 -- info in the *body* of the multiple lambda.
499 -- Then, the simplifier is careful when partially applying lambdas.
501 occAnal env expr@(Lam _ _)
502 = case occAnal env_body body of { (body_usage, body') ->
504 (final_usage, tagged_binders) = tagBinders body_usage binders
505 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
506 -- we get linear-typed things in the resulting program that we can't handle yet.
507 -- (e.g. PrelShow) TODO
509 really_final_usage = if linear then
512 mapVarEnv markInsideLam final_usage
515 mkLams tagged_binders body') }
517 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
518 (binders, body) = collectBinders expr
519 binders' = oneShotGroup env binders
520 linear = all is_one_shot binders'
521 is_one_shot b = isId b && isOneShotBndr b
523 occAnal env (Case scrut bndr ty alts)
524 = case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
525 case occAnal vanillaCtxt scrut of { (scrut_usage, scrut') ->
526 -- No need for rhsCtxt
528 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
529 alts_usage' = addCaseBndrUsage alts_usage
530 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
531 total_usage = scrut_usage `combineUsageDetails` alts_usage1
533 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
535 -- The case binder gets a usage of either "many" or "dead", never "one".
536 -- Reason: we like to inline single occurrences, to eliminate a binding,
537 -- but inlining a case binder *doesn't* eliminate a binding.
538 -- We *don't* want to transform
539 -- case x of w { (p,q) -> f w }
541 -- case x of w { (p,q) -> f (p,q) }
542 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
544 Just occ -> extendVarEnv usage bndr (markMany occ)
546 occAnal env (Let bind body)
547 = case occAnal env body of { (body_usage, body') ->
548 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
549 (final_usage, mkLets new_binds body') }}
552 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
553 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
555 arg_env = vanillaCtxt
558 Applications are dealt with specially because we want
559 the "build hack" to work.
562 -- Hack for build, fold, runST
563 occAnalApp env (Var fun, args) is_rhs
564 = case args_stuff of { (args_uds, args') ->
566 -- We mark the free vars of the argument of a constructor or PAP
567 -- as "many", if it is the RHS of a let(rec).
568 -- This means that nothing gets inlined into a constructor argument
569 -- position, which is what we want. Typically those constructor
570 -- arguments are just variables, or trivial expressions.
572 -- This is the *whole point* of the isRhsEnv predicate
575 isDataConWorkId fun || valArgCount args < idArity fun
576 = mapVarEnv markMany args_uds
577 | otherwise = args_uds
579 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
581 fun_uniq = idUnique fun
583 fun_uds | isLocalId fun = unitVarEnv fun oneOcc
584 | otherwise = emptyDetails
586 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
587 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
588 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
589 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
590 -- (foldr k z xs) may call k many times, but it never
591 -- shares a partial application of k; hence [False,True]
592 -- This means we can optimise
593 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
594 -- by floating in the v
596 | otherwise = occAnalArgs env args
599 occAnalApp env (fun, args) is_rhs
600 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
601 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
602 -- often leaves behind beta redexs like
604 -- Here we would like to mark x,y as one-shot, and treat the whole
605 -- thing much like a let. We do this by pushing some True items
606 -- onto the context stack.
608 case occAnalArgs env args of { (args_uds, args') ->
610 final_uds = fun_uds `combineUsageDetails` args_uds
612 (final_uds, mkApps fun' args') }}
615 -> Int -> CtxtTy -- Argument number, and context to use for it
617 -> (UsageDetails, [CoreExpr])
618 appSpecial env n ctxt args
621 arg_env = vanillaCtxt
623 go n [] = (emptyDetails, []) -- Too few args
625 go 1 (arg:args) -- The magic arg
626 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
627 case occAnalArgs env args of { (args_uds, args') ->
628 (combineUsageDetails arg_uds args_uds, arg':args') }}
631 = case occAnal arg_env arg of { (arg_uds, arg') ->
632 case go (n-1) args of { (args_uds, args') ->
633 (combineUsageDetails arg_uds args_uds, arg':args') }}
639 If the case binder occurs at all, the other binders effectively do too.
641 case e of x { (a,b) -> rhs }
644 If e turns out to be (e1,e2) we indeed get something like
645 let a = e1; b = e2; x = (a,b) in rhs
648 occAnalAlt env case_bndr (con, bndrs, rhs)
649 = case occAnal env rhs of { (rhs_usage, rhs') ->
651 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
652 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
653 | otherwise = tagged_bndrs
654 -- Leave the binders untagged if the case
655 -- binder occurs at all; see note above
657 (final_usage, (con, final_bndrs, rhs')) }
661 %************************************************************************
663 \subsection[OccurAnal-types]{OccEnv}
665 %************************************************************************
669 = OccEnv OccEncl -- Enclosing context information
670 CtxtTy -- Tells about linearity
672 -- OccEncl is used to control whether to inline into constructor arguments
674 -- x = (p,q) -- Don't inline p or q
675 -- y = /\a -> (p a, q a) -- Still don't inline p or q
676 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
677 -- So OccEncl tells enought about the context to know what to do when
678 -- we encounter a contructor application or PAP.
681 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
682 -- Don't inline into constructor args here
683 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
684 -- Do inline into constructor args here
689 -- True:ctxt Analysing a function-valued expression that will be
692 -- False:ctxt Analysing a function-valued expression that may
693 -- be applied many times; but when it is,
694 -- the CtxtTy inside applies
697 initOccEnv = OccEnv OccRhs []
699 vanillaCtxt = OccEnv OccVanilla []
700 rhsCtxt = OccEnv OccRhs []
702 isRhsEnv (OccEnv OccRhs _) = True
703 isRhsEnv (OccEnv OccVanilla _) = False
705 setCtxt :: OccEnv -> CtxtTy -> OccEnv
706 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
708 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
709 -- The result binders have one-shot-ness set that they might not have had originally.
710 -- This happens in (build (\cn -> e)). Here the occurrence analyser
711 -- linearity context knows that c,n are one-shot, and it records that fact in
712 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
714 oneShotGroup (OccEnv encl ctxt) bndrs
717 go ctxt [] rev_bndrs = reverse rev_bndrs
719 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
720 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
722 bndr' | lin_ctxt = setOneShotLambda bndr
725 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
727 addAppCtxt (OccEnv encl ctxt) args
728 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
731 %************************************************************************
733 \subsection[OccurAnal-types]{OccEnv}
735 %************************************************************************
738 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
740 combineUsageDetails, combineAltsUsageDetails
741 :: UsageDetails -> UsageDetails -> UsageDetails
743 combineUsageDetails usage1 usage2
744 = plusVarEnv_C addOccInfo usage1 usage2
746 combineAltsUsageDetails usage1 usage2
747 = plusVarEnv_C orOccInfo usage1 usage2
749 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
750 addOneOcc usage id info
751 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
752 -- ToDo: make this more efficient
754 emptyDetails = (emptyVarEnv :: UsageDetails)
756 usedIn :: Id -> UsageDetails -> Bool
757 v `usedIn` details = isExportedId v || v `elemVarEnv` details
759 tagBinders :: UsageDetails -- Of scope
761 -> (UsageDetails, -- Details with binders removed
762 [IdWithOccInfo]) -- Tagged binders
764 tagBinders usage binders
766 usage' = usage `delVarEnvList` binders
767 uss = map (setBinderOcc usage) binders
769 usage' `seq` (usage', uss)
771 tagBinder :: UsageDetails -- Of scope
773 -> (UsageDetails, -- Details with binders removed
774 IdWithOccInfo) -- Tagged binders
776 tagBinder usage binder
778 usage' = usage `delVarEnv` binder
779 binder' = setBinderOcc usage binder
781 usage' `seq` (usage', binder')
783 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
784 setBinderOcc usage bndr
785 | isTyVar bndr = bndr
786 | isExportedId bndr = case idOccInfo bndr of
788 other -> setIdOccInfo bndr NoOccInfo
789 -- Don't use local usage info for visible-elsewhere things
790 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
791 -- about to re-generate it and it shouldn't be "sticky"
793 | otherwise = setIdOccInfo bndr occ_info
795 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
799 %************************************************************************
801 \subsection{Operations over OccInfo}
803 %************************************************************************
807 oneOcc = OneOcc False True
809 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
811 markMany IAmDead = IAmDead
812 markMany other = NoOccInfo
814 markInsideSCC occ = markMany occ
816 markInsideLam (OneOcc _ one_br) = OneOcc True one_br
817 markInsideLam occ = occ
819 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
821 addOccInfo IAmDead info2 = info2
822 addOccInfo info1 IAmDead = info1
823 addOccInfo info1 info2 = NoOccInfo
825 -- (orOccInfo orig new) is used
826 -- when combining occurrence info from branches of a case
828 orOccInfo IAmDead info2 = info2
829 orOccInfo info1 IAmDead = info1
830 orOccInfo (OneOcc in_lam1 one_branch1)
831 (OneOcc in_lam2 one_branch2)
832 = OneOcc (in_lam1 || in_lam2)
833 False -- False, because it occurs in both branches
835 orOccInfo info1 info2 = NoOccInfo