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,
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 -- NOT NEEDED ANY MORE [Feb06]
323 -- We make all rules available in all bindings, by substituting
324 -- the IdInfo before looking at any RHSs. I'm just leaving this
325 -- snippet in as a commment so we can find it again if necessary.
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)
420 occAnal env (Var v) = (mkOneOcc env v False, Var v)
421 -- At one stage, I gathered the idRuleVars for v here too,
422 -- which in a way is the right thing to do.
423 -- Btu that went wrong right after specialisation, when
424 -- the *occurrences* of the overloaded function didn't have any
425 -- rules in them, so the *specialised* versions looked as if they
426 -- weren't used at all.
429 We regard variables that occur as constructor arguments as "dangerousToDup":
433 f x = let y = expensive x in
435 (case z of {(p,q)->q}, case z of {(p,q)->q})
438 We feel free to duplicate the WHNF (True,y), but that means
439 that y may be duplicated thereby.
441 If we aren't careful we duplicate the (expensive x) call!
442 Constructors are rather like lambdas in this way.
445 occAnal env expr@(Lit lit) = (emptyDetails, expr)
449 occAnal env (Note InlineMe body)
450 = case occAnal env body of { (usage, body') ->
451 (mapVarEnv markMany usage, Note InlineMe body')
454 occAnal env (Note note@(SCC cc) body)
455 = case occAnal env body of { (usage, body') ->
456 (mapVarEnv markInsideSCC usage, Note note body')
459 occAnal env (Note note body)
460 = case occAnal env body of { (usage, body') ->
461 (usage, Note note body')
466 occAnal env app@(App fun arg)
467 = occAnalApp env (collectArgs app) False
469 -- Ignore type variables altogether
470 -- (a) occurrences inside type lambdas only not marked as InsideLam
471 -- (b) type variables not in environment
473 occAnal env expr@(Lam x body) | isTyVar x
474 = case occAnal env body of { (body_usage, body') ->
475 (body_usage, Lam x body')
478 -- For value lambdas we do a special hack. Consider
480 -- If we did nothing, x is used inside the \y, so would be marked
481 -- as dangerous to dup. But in the common case where the abstraction
482 -- is applied to two arguments this is over-pessimistic.
483 -- So instead, we just mark each binder with its occurrence
484 -- info in the *body* of the multiple lambda.
485 -- Then, the simplifier is careful when partially applying lambdas.
487 occAnal env expr@(Lam _ _)
488 = case occAnal env_body body of { (body_usage, body') ->
490 (final_usage, tagged_binders) = tagBinders body_usage binders
491 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
492 -- we get linear-typed things in the resulting program that we can't handle yet.
493 -- (e.g. PrelShow) TODO
495 really_final_usage = if linear then
498 mapVarEnv markInsideLam final_usage
501 mkLams tagged_binders body') }
503 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
504 (binders, body) = collectBinders expr
505 binders' = oneShotGroup env binders
506 linear = all is_one_shot binders'
507 is_one_shot b = isId b && isOneShotBndr b
509 occAnal env (Case scrut bndr ty alts)
510 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
511 case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') ->
513 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
514 alts_usage' = addCaseBndrUsage alts_usage
515 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
516 total_usage = scrut_usage `combineUsageDetails` alts_usage1
518 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
520 -- The case binder gets a usage of either "many" or "dead", never "one".
521 -- Reason: we like to inline single occurrences, to eliminate a binding,
522 -- but inlining a case binder *doesn't* eliminate a binding.
523 -- We *don't* want to transform
524 -- case x of w { (p,q) -> f w }
526 -- case x of w { (p,q) -> f (p,q) }
527 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
529 Just occ -> extendVarEnv usage bndr (markMany occ)
531 occ_anal_scrut (Var v) (alt1 : other_alts)
532 | not (null other_alts) || not (isDefaultAlt alt1)
533 = (mkOneOcc env v True, Var v)
534 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
535 -- No need for rhsCtxt
537 occAnal env (Let bind body)
538 = case occAnal env body of { (body_usage, body') ->
539 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
540 (final_usage, mkLets new_binds body') }}
543 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
544 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
546 arg_env = vanillaCtxt
549 Applications are dealt with specially because we want
550 the "build hack" to work.
553 -- Hack for build, fold, runST
554 occAnalApp env (Var fun, args) is_rhs
555 = case args_stuff of { (args_uds, args') ->
557 -- We mark the free vars of the argument of a constructor or PAP
558 -- as "many", if it is the RHS of a let(rec).
559 -- This means that nothing gets inlined into a constructor argument
560 -- position, which is what we want. Typically those constructor
561 -- arguments are just variables, or trivial expressions.
563 -- This is the *whole point* of the isRhsEnv predicate
566 isDataConWorkId fun || valArgCount args < idArity fun
567 = mapVarEnv markMany args_uds
568 | otherwise = args_uds
570 (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
572 fun_uniq = idUnique fun
573 fun_uds = mkOneOcc env fun (valArgCount args > 0)
574 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
575 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
576 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
577 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
578 -- (foldr k z xs) may call k many times, but it never
579 -- shares a partial application of k; hence [False,True]
580 -- This means we can optimise
581 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
582 -- by floating in the v
584 | otherwise = occAnalArgs env args
587 occAnalApp env (fun, args) is_rhs
588 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
589 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
590 -- often leaves behind beta redexs like
592 -- Here we would like to mark x,y as one-shot, and treat the whole
593 -- thing much like a let. We do this by pushing some True items
594 -- onto the context stack.
596 case occAnalArgs env args of { (args_uds, args') ->
598 final_uds = fun_uds `combineUsageDetails` args_uds
600 (final_uds, mkApps fun' args') }}
603 -> Int -> CtxtTy -- Argument number, and context to use for it
605 -> (UsageDetails, [CoreExpr])
606 appSpecial env n ctxt args
609 arg_env = vanillaCtxt
611 go n [] = (emptyDetails, []) -- Too few args
613 go 1 (arg:args) -- The magic arg
614 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
615 case occAnalArgs env args of { (args_uds, args') ->
616 (combineUsageDetails arg_uds args_uds, arg':args') }}
619 = case occAnal arg_env arg of { (arg_uds, arg') ->
620 case go (n-1) args of { (args_uds, args') ->
621 (combineUsageDetails arg_uds args_uds, arg':args') }}
627 If the case binder occurs at all, the other binders effectively do too.
629 case e of x { (a,b) -> rhs }
632 If e turns out to be (e1,e2) we indeed get something like
633 let a = e1; b = e2; x = (a,b) in rhs
636 occAnalAlt env case_bndr (con, bndrs, rhs)
637 = case occAnal env rhs of { (rhs_usage, rhs') ->
639 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
640 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
641 | otherwise = tagged_bndrs
642 -- Leave the binders untagged if the case
643 -- binder occurs at all; see note above
645 (final_usage, (con, final_bndrs, rhs')) }
649 %************************************************************************
651 \subsection[OccurAnal-types]{OccEnv}
653 %************************************************************************
657 = OccEnv OccEncl -- Enclosing context information
658 CtxtTy -- Tells about linearity
660 -- OccEncl is used to control whether to inline into constructor arguments
662 -- x = (p,q) -- Don't inline p or q
663 -- y = /\a -> (p a, q a) -- Still don't inline p or q
664 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
665 -- So OccEncl tells enought about the context to know what to do when
666 -- we encounter a contructor application or PAP.
669 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
670 -- Don't inline into constructor args here
671 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
672 -- Do inline into constructor args here
677 -- True:ctxt Analysing a function-valued expression that will be
680 -- False:ctxt Analysing a function-valued expression that may
681 -- be applied many times; but when it is,
682 -- the CtxtTy inside applies
685 initOccEnv = OccEnv OccRhs []
687 vanillaCtxt = OccEnv OccVanilla []
688 rhsCtxt = OccEnv OccRhs []
690 isRhsEnv (OccEnv OccRhs _) = True
691 isRhsEnv (OccEnv OccVanilla _) = False
693 setCtxt :: OccEnv -> CtxtTy -> OccEnv
694 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
696 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
697 -- The result binders have one-shot-ness set that they might not have had originally.
698 -- This happens in (build (\cn -> e)). Here the occurrence analyser
699 -- linearity context knows that c,n are one-shot, and it records that fact in
700 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
702 oneShotGroup (OccEnv encl ctxt) bndrs
705 go ctxt [] rev_bndrs = reverse rev_bndrs
707 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
708 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
710 bndr' | lin_ctxt = setOneShotLambda bndr
713 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
715 addAppCtxt (OccEnv encl ctxt) args
716 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
719 %************************************************************************
721 \subsection[OccurAnal-types]{OccEnv}
723 %************************************************************************
726 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
728 combineUsageDetails, combineAltsUsageDetails
729 :: UsageDetails -> UsageDetails -> UsageDetails
731 combineUsageDetails usage1 usage2
732 = plusVarEnv_C addOccInfo usage1 usage2
734 combineAltsUsageDetails usage1 usage2
735 = plusVarEnv_C orOccInfo usage1 usage2
737 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
738 addOneOcc usage id info
739 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
740 -- ToDo: make this more efficient
742 emptyDetails = (emptyVarEnv :: UsageDetails)
744 usedIn :: Id -> UsageDetails -> Bool
745 v `usedIn` details = isExportedId v || v `elemVarEnv` details
747 tagBinders :: UsageDetails -- Of scope
749 -> (UsageDetails, -- Details with binders removed
750 [IdWithOccInfo]) -- Tagged binders
752 tagBinders usage binders
754 usage' = usage `delVarEnvList` binders
755 uss = map (setBinderOcc usage) binders
757 usage' `seq` (usage', uss)
759 tagBinder :: UsageDetails -- Of scope
761 -> (UsageDetails, -- Details with binders removed
762 IdWithOccInfo) -- Tagged binders
764 tagBinder usage binder
766 usage' = usage `delVarEnv` binder
767 binder' = setBinderOcc usage binder
769 usage' `seq` (usage', binder')
771 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
772 setBinderOcc usage bndr
773 | isTyVar bndr = bndr
774 | isExportedId bndr = case idOccInfo bndr of
776 other -> setIdOccInfo bndr NoOccInfo
777 -- Don't use local usage info for visible-elsewhere things
778 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
779 -- about to re-generate it and it shouldn't be "sticky"
781 | otherwise = setIdOccInfo bndr occ_info
783 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
787 %************************************************************************
789 \subsection{Operations over OccInfo}
791 %************************************************************************
794 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
795 mkOneOcc env id int_cxt
796 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
797 | otherwise = emptyDetails
799 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
801 markMany IAmDead = IAmDead
802 markMany other = NoOccInfo
804 markInsideSCC occ = markMany occ
806 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
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 int_cxt1)
821 (OneOcc in_lam2 one_branch2 int_cxt2)
822 = OneOcc (in_lam1 || in_lam2)
823 False -- False, because it occurs in both branches
824 (int_cxt1 && int_cxt2)
826 orOccInfo info1 info2 = NoOccInfo