2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 %************************************************************************
6 \section[OccurAnal]{Occurrence analysis pass}
8 %************************************************************************
10 The occurrence analyser re-typechecks a core expression, returning a new
11 core expression with (hopefully) improved usage information.
15 occurAnalysePgm, occurAnalyseExpr
18 #include "HsVersions.h"
21 import CoreFVs ( idRuleVars )
22 import CoreUtils ( exprIsTrivial, isDefaultAlt )
23 import Id ( isDataConWorkId, isOneShotBndr, setOneShotLambda,
24 idOccInfo, setIdOccInfo, isLocalId,
25 isExportedId, idArity, idHasRules,
28 import BasicTypes ( OccInfo(..), isOneOcc, InterestingCxt )
33 import Maybes ( orElse )
34 import Digraph ( stronglyConnCompR, SCC(..) )
35 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
36 import Unique ( Unique )
37 import UniqFM ( keysUFM, intersectsUFM )
38 import Util ( mapAndUnzip, mapAccumL )
43 %************************************************************************
45 \subsection[OccurAnal-main]{Counting occurrences: main function}
47 %************************************************************************
49 Here's the externally-callable interface:
52 occurAnalysePgm :: [CoreBind] -> [CoreBind]
54 = snd (go initOccEnv binds)
56 go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind])
60 = (final_usage, bind' ++ binds')
62 (bs_usage, binds') = go env binds
63 (final_usage, bind') = occAnalBind env bind bs_usage
65 occurAnalyseExpr :: CoreExpr -> CoreExpr
66 -- Do occurrence analysis, and discard occurence info returned
67 occurAnalyseExpr expr = snd (occAnal initOccEnv expr)
71 %************************************************************************
73 \subsection[OccurAnal-main]{Counting occurrences: main function}
75 %************************************************************************
83 -> UsageDetails -- Usage details of scope
84 -> (UsageDetails, -- Of the whole let(rec)
87 occAnalBind env (NonRec binder rhs) body_usage
88 | not (binder `usedIn` body_usage) -- It's not mentioned
91 | otherwise -- It's mentioned in the body
92 = (body_usage' +++ addRuleUsage rhs_usage binder, -- Note [RulesOnly]
93 [NonRec tagged_binder rhs'])
95 (body_usage', tagged_binder) = tagBinder body_usage binder
96 (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
99 Dropping dead code for recursive bindings is done in a very simple way:
101 the entire set of bindings is dropped if none of its binders are
102 mentioned in its body; otherwise none are.
104 This seems to miss an obvious improvement.
119 Now @f@ is unused. But dependency analysis will sort this out into a
120 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
121 It isn't easy to do a perfect job in one blow. Consider
135 occAnalBind env (Rec pairs) body_usage
136 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
138 analysed_pairs :: [Details]
139 analysed_pairs = [ (bndr, rhs_usage, rhs')
140 | (bndr, rhs) <- pairs,
141 let (rhs_usage, rhs') = occAnalRhs env bndr rhs
144 sccs :: [SCC (Node Details)]
145 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
148 ---- stuff for dependency analysis of binds -------------------------------
149 edges :: [Node Details]
150 edges = _scc_ "occAnalBind.assoc"
151 [ (details, idUnique id, edges_from id rhs_usage)
152 | details@(id, rhs_usage, rhs) <- analysed_pairs
155 -- (a -> b) means a mentions b
156 -- Given the usage details (a UFM that gives occ info for each free var of
157 -- the RHS) we can get the list of free vars -- or rather their Int keys --
158 -- by just extracting the keys from the finite map. Grimy, but fast.
159 -- Previously we had this:
160 -- [ bndr | bndr <- bndrs,
161 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
162 -- which has n**2 cost, and this meant that edges_from alone
163 -- consumed 10% of total runtime!
164 edges_from :: Id -> UsageDetails -> [Unique]
165 edges_from bndr rhs_usage = _scc_ "occAnalBind.edges_from"
166 keysUFM (addRuleUsage rhs_usage bndr)
168 ---- Stuff to "re-constitute" bindings from dependency-analysis info ------
171 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
172 | not (bndr `usedIn` body_usage)
173 = (body_usage, binds_so_far) -- Dead code
175 = (body_usage' +++ addRuleUsage rhs_usage bndr, new_bind : binds_so_far)
177 (body_usage', tagged_bndr) = tagBinder body_usage bndr
178 new_bind = NonRec tagged_bndr rhs'
181 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
182 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
183 = (body_usage, binds_so_far) -- Dead code
184 | otherwise -- If any is used, they all are
185 = (final_usage, final_bind : binds_so_far)
187 details = [details | (details, _, _) <- cycle]
188 bndrs = [bndr | (bndr, _, _) <- details]
189 bndr_usages = [addRuleUsage rhs_usage bndr | (bndr, rhs_usage, _) <- details]
190 total_usage = foldr (+++) body_usage bndr_usages
191 (final_usage, tagged_cycle) = mapAccumL tag_bind total_usage cycle
192 tag_bind usg ((bndr,rhs_usg,rhs),k,ks) = (usg', ((bndr',rhs_usg,rhs),k,ks))
194 (usg', bndr') = tagBinder usg bndr
195 final_bind = Rec (reOrderCycle (mkVarSet bndrs) tagged_cycle)
197 {- An alternative; rebuild the edges. No semantic difference, but perf might change
199 -- Hopefully 'bndrs' is a relatively small group now
200 -- Now get ready for the loop-breaking phase
201 -- We've done dead-code elimination already, so no worries about un-referenced binders
202 keys = map idUnique bndrs
203 mk_node tagged_bndr (_, rhs_usage, rhs')
204 = ((tagged_bndr, rhs'), idUnique tagged_bndr, used)
206 used = [key | key <- keys, used_outside_rule rhs_usage key ]
208 used_outside_rule usage uniq = case lookupUFM_Directly usage uniq of
210 Just RulesOnly -> False -- Ignore rules
215 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
216 strongly connected component (there's guaranteed to be a cycle). It returns the
218 a) in a better order,
219 b) with some of the Ids having a IAmALoopBreaker pragma
221 The "loop-breaker" Ids are sufficient to break all cycles in the SCC. This means
222 that the simplifier can guarantee not to loop provided it never records an inlining
223 for these no-inline guys.
225 Furthermore, the order of the binds is such that if we neglect dependencies
226 on the no-inline Ids then the binds are topologically sorted. This means
227 that the simplifier will generally do a good job if it works from top bottom,
228 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
231 [June 98: I don't understand the following paragraphs, and I've
232 changed the a=b case again so that it isn't a special case any more.]
234 Here's a case that bit me:
242 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
244 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
245 Perhaps something cleverer would suffice.
250 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
251 -- which is gotten from the Id.
252 type Details = (Id, UsageDetails, CoreExpr)
254 reOrderRec :: IdSet -- Binders of this group
255 -> SCC (Node Details)
257 -- Sorted into a plausible order. Enough of the Ids have
258 -- IAmALoopBreaker pragmas that there are no loops left.
259 reOrderRec bndrs (AcyclicSCC ((bndr, _, rhs), _, _)) = [(bndr, rhs)]
260 reOrderRec bndrs (CyclicSCC cycle) = reOrderCycle bndrs cycle
262 reOrderCycle :: IdSet -> [Node Details] -> [(Id,CoreExpr)]
263 reOrderCycle bndrs []
264 = panic "reOrderCycle"
265 reOrderCycle bndrs [bind] -- Common case of simple self-recursion
266 = [(makeLoopBreaker bndrs rhs_usg bndr, rhs)]
268 ((bndr, rhs_usg, rhs), _, _) = bind
270 reOrderCycle bndrs (bind : binds)
271 = -- Choose a loop breaker, mark it no-inline,
272 -- do SCC analysis on the rest, and recursively sort them out
273 concatMap (reOrderRec bndrs) (stronglyConnCompR unchosen) ++
274 [(makeLoopBreaker bndrs rhs_usg bndr, rhs)]
277 (chosen_bind, unchosen) = choose_loop_breaker bind (score bind) [] binds
278 (bndr, rhs_usg, rhs) = chosen_bind
280 -- This loop looks for the bind with the lowest score
281 -- to pick as the loop breaker. The rest accumulate in
282 choose_loop_breaker (details,_,_) loop_sc acc []
283 = (details, acc) -- Done
285 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
286 | sc < loop_sc -- Lower score so pick this new one
287 = choose_loop_breaker bind sc (loop_bind : acc) binds
289 | otherwise -- No lower so don't pick it
290 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
294 score :: Node Details -> Int -- Higher score => less likely to be picked as loop breaker
295 score ((bndr, _, rhs), _, _)
296 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
297 -- Used to have also: && not (isExportedId bndr)
298 -- But I found this sometimes cost an extra iteration when we have
299 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
300 -- where df is the exported dictionary. Then df makes a really
301 -- bad choice for loop breaker
303 | is_con_app rhs = 3 -- Data types help with cases
304 -- This used to have a lower score than inlineCandidate, but
305 -- it's *really* helpful if dictionaries get inlined fast,
306 -- so I'm experimenting with giving higher priority to data-typed things
308 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
310 | idHasRules bndr = 1
311 -- Avoid things with specialisations; we'd like
312 -- to take advantage of them in the subsequent bindings
316 inlineCandidate :: Id -> CoreExpr -> Bool
317 inlineCandidate id (Note InlineMe _) = True
318 inlineCandidate id rhs = isOneOcc (idOccInfo id)
320 -- Real example (the Enum Ordering instance from PrelBase):
321 -- rec f = \ x -> case d of (p,q,r) -> p x
322 -- g = \ x -> case d of (p,q,r) -> q x
325 -- Here, f and g occur just once; but we can't inline them into d.
326 -- On the other hand we *could* simplify those case expressions if
327 -- we didn't stupidly choose d as the loop breaker.
328 -- But we won't because constructor args are marked "Many".
330 -- Cheap and cheerful; the simplifer moves casts out of the way
331 -- The lambda case is important to spot x = /\a. C (f a)
332 -- which comes up when C is a dictionary constructor and
333 -- f is a default method.
334 -- Example: the instance for Show (ST s a) in GHC.ST
336 -- However we *also* treat (\x. C p q) as a con-app-like thing,
337 -- Note [Closure conversion]
338 is_con_app (Var v) = isDataConWorkId v
339 is_con_app (App f _) = is_con_app f
340 is_con_app (Lam b e) = is_con_app e
341 is_con_app (Note _ e) = is_con_app e
342 is_con_app other = False
344 makeLoopBreaker :: VarSet -- Binders of this group
345 -> UsageDetails -- Usage of this rhs (neglecting rules)
347 -- Set the loop-breaker flag, recording whether the thing occurs only in
348 -- the RHS of a RULE (in this recursive group)
349 makeLoopBreaker bndrs rhs_usg bndr
350 = setIdOccInfo bndr (IAmALoopBreaker rules_only)
352 rules_only = bndrs `intersectsUFM` rhs_usg
355 Note [Closure conversion]
356 ~~~~~~~~~~~~~~~~~~~~~~~~~
357 We treat (\x. C p q) as a high-score candidate in the letrec scoring algorithm.
358 The immediate motivation came from the result of a closure-conversion transformation
359 which generated code like this:
361 data Clo a b = forall c. Clo (c -> a -> b) c
363 ($:) :: Clo a b -> a -> b
364 Clo f env $: x = f env x
366 rec { plus = Clo plus1 ()
368 ; plus1 _ n = Clo plus2 n
371 ; plus2 (Succ m) n = Succ (plus $: m $: n) }
373 If we inline 'plus' and 'plus1', everything unravels nicely. But if
374 we choose 'plus1' as the loop breaker (which is entirely possible
375 otherwise), the loop does not unravel nicely.
378 @occAnalRhs@ deals with the question of bindings where the Id is marked
379 by an INLINE pragma. For these we record that anything which occurs
380 in its RHS occurs many times. This pessimistically assumes that ths
381 inlined binder also occurs many times in its scope, but if it doesn't
382 we'll catch it next time round. At worst this costs an extra simplifier pass.
383 ToDo: try using the occurrence info for the inline'd binder.
385 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
386 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
391 -> Id -> CoreExpr -- Binder and rhs
392 -- For non-recs the binder is alrady tagged
393 -- with occurrence info
394 -> (UsageDetails, CoreExpr)
396 occAnalRhs env id rhs
399 ctxt | certainly_inline id = env
400 | otherwise = rhsCtxt
401 -- Note that we generally use an rhsCtxt. This tells the occ anal n
402 -- that it's looking at an RHS, which has an effect in occAnalApp
404 -- But there's a problem. Consider
409 -- First time round, it looks as if x1 and x2 occur as an arg of a
410 -- let-bound constructor ==> give them a many-occurrence.
411 -- But then x3 is inlined (unconditionally as it happens) and
412 -- next time round, x2 will be, and the next time round x1 will be
413 -- Result: multiple simplifier iterations. Sigh.
414 -- Crude solution: use rhsCtxt for things that occur just once...
416 certainly_inline id = case idOccInfo id of
417 OneOcc in_lam one_br _ -> not in_lam && one_br
423 If the binder has RULES inside it then we count the specialised Ids as
424 "extra rhs's". That way the "parent" keeps the specialised "children"
425 alive. If the parent dies (because it isn't referenced any more),
426 then the children will die too unless they are already referenced
429 That's the basic idea. However in a recursive situation we want to be a bit
430 cleverer. Example (from GHC.Enum):
432 eftInt :: Int# -> Int# -> [Int]
433 eftInt x y = ...(non-recursive)...
435 {-# INLINE [0] eftIntFB #-}
436 eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
437 eftIntFB c n x y = ...(non-recursive)...
440 "eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
441 "eftIntList" [1] eftIntFB (:) [] = eftInt
444 The two look mutually recursive only because of their RULES; we don't want
445 that to inhibit inlining!
447 So when we identify a LoopBreaker, we mark it to say whether it only mentions
448 the other binders in its recursive group in a RULE. If so, we can inline it,
449 because doing so will not expose new occurrences of binders in its group.
454 addRuleUsage :: UsageDetails -> Id -> UsageDetails
455 -- Add the usage from RULES in Id to the usage
456 addRuleUsage usage id
457 = foldVarSet add usage (idRuleVars id)
459 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
460 -- (i.e manyOcc) because many copies
461 -- of the specialised thing can appear
469 -> (UsageDetails, -- Gives info only about the "interesting" Ids
472 occAnal env (Type t) = (emptyDetails, Type t)
473 occAnal env (Var v) = (mkOneOcc env v False, Var v)
474 -- At one stage, I gathered the idRuleVars for v here too,
475 -- which in a way is the right thing to do.
476 -- Btu that went wrong right after specialisation, when
477 -- the *occurrences* of the overloaded function didn't have any
478 -- rules in them, so the *specialised* versions looked as if they
479 -- weren't used at all.
482 We regard variables that occur as constructor arguments as "dangerousToDup":
486 f x = let y = expensive x in
488 (case z of {(p,q)->q}, case z of {(p,q)->q})
491 We feel free to duplicate the WHNF (True,y), but that means
492 that y may be duplicated thereby.
494 If we aren't careful we duplicate the (expensive x) call!
495 Constructors are rather like lambdas in this way.
498 occAnal env expr@(Lit lit) = (emptyDetails, expr)
502 occAnal env (Note InlineMe body)
503 = case occAnal env body of { (usage, body') ->
504 (mapVarEnv markMany usage, Note InlineMe body')
507 occAnal env (Note note@(SCC cc) body)
508 = case occAnal env body of { (usage, body') ->
509 (mapVarEnv markInsideSCC usage, Note note body')
512 occAnal env (Note note body)
513 = case occAnal env body of { (usage, body') ->
514 (usage, Note note body')
517 occAnal env (Cast expr co)
518 = case occAnal env expr of { (usage, expr') ->
519 (markRhsUds env True usage, Cast expr' co)
520 -- If we see let x = y `cast` co
521 -- then mark y as 'Many' so that we don't
522 -- immediately inline y again.
527 occAnal env app@(App fun arg)
528 = occAnalApp env (collectArgs app) False
530 -- Ignore type variables altogether
531 -- (a) occurrences inside type lambdas only not marked as InsideLam
532 -- (b) type variables not in environment
534 occAnal env expr@(Lam x body) | isTyVar x
535 = case occAnal env body of { (body_usage, body') ->
536 (body_usage, Lam x body')
539 -- For value lambdas we do a special hack. Consider
541 -- If we did nothing, x is used inside the \y, so would be marked
542 -- as dangerous to dup. But in the common case where the abstraction
543 -- is applied to two arguments this is over-pessimistic.
544 -- So instead, we just mark each binder with its occurrence
545 -- info in the *body* of the multiple lambda.
546 -- Then, the simplifier is careful when partially applying lambdas.
548 occAnal env expr@(Lam _ _)
549 = case occAnal env_body body of { (body_usage, body') ->
551 (final_usage, tagged_binders) = tagBinders body_usage binders
552 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
553 -- we get linear-typed things in the resulting program that we can't handle yet.
554 -- (e.g. PrelShow) TODO
556 really_final_usage = if linear then
559 mapVarEnv markInsideLam final_usage
562 mkLams tagged_binders body') }
564 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
565 (binders, body) = collectBinders expr
566 binders' = oneShotGroup env binders
567 linear = all is_one_shot binders'
568 is_one_shot b = isId b && isOneShotBndr b
570 occAnal env (Case scrut bndr ty alts)
571 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
572 case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts') ->
574 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
575 alts_usage' = addCaseBndrUsage alts_usage
576 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
577 total_usage = scrut_usage +++ alts_usage1
579 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
581 -- The case binder gets a usage of either "many" or "dead", never "one".
582 -- Reason: we like to inline single occurrences, to eliminate a binding,
583 -- but inlining a case binder *doesn't* eliminate a binding.
584 -- We *don't* want to transform
585 -- case x of w { (p,q) -> f w }
587 -- case x of w { (p,q) -> f (p,q) }
588 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
590 Just occ -> extendVarEnv usage bndr (markMany occ)
592 alt_env = setVanillaCtxt env
593 -- Consider x = case v of { True -> (p,q); ... }
594 -- Then it's fine to inline p and q
596 occ_anal_scrut (Var v) (alt1 : other_alts)
597 | not (null other_alts) || not (isDefaultAlt alt1)
598 = (mkOneOcc env v True, Var v)
599 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
600 -- No need for rhsCtxt
602 occAnal env (Let bind body)
603 = case occAnal env body of { (body_usage, body') ->
604 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
605 (final_usage, mkLets new_binds body') }}
608 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
609 (foldr (+++) emptyDetails arg_uds_s, args')}
611 arg_env = vanillaCtxt
614 Applications are dealt with specially because we want
615 the "build hack" to work.
618 occAnalApp env (Var fun, args) is_rhs
619 = case args_stuff of { (args_uds, args') ->
621 final_args_uds = markRhsUds env is_pap args_uds
623 (fun_uds +++ final_args_uds, mkApps (Var fun) args') }
625 fun_uniq = idUnique fun
626 fun_uds = mkOneOcc env fun (valArgCount args > 0)
627 is_pap = isDataConWorkId fun || valArgCount args < idArity fun
629 -- Hack for build, fold, runST
630 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
631 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
632 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
633 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
634 -- (foldr k z xs) may call k many times, but it never
635 -- shares a partial application of k; hence [False,True]
636 -- This means we can optimise
637 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
638 -- by floating in the v
640 | otherwise = occAnalArgs env args
643 occAnalApp env (fun, args) is_rhs
644 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
645 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
646 -- often leaves behind beta redexs like
648 -- Here we would like to mark x,y as one-shot, and treat the whole
649 -- thing much like a let. We do this by pushing some True items
650 -- onto the context stack.
652 case occAnalArgs env args of { (args_uds, args') ->
654 final_uds = fun_uds +++ args_uds
656 (final_uds, mkApps fun' args') }}
659 markRhsUds :: OccEnv -- Check if this is a RhsEnv
660 -> Bool -- and this is true
661 -> UsageDetails -- The do markMany on this
663 -- We mark the free vars of the argument of a constructor or PAP
664 -- as "many", if it is the RHS of a let(rec).
665 -- This means that nothing gets inlined into a constructor argument
666 -- position, which is what we want. Typically those constructor
667 -- arguments are just variables, or trivial expressions.
669 -- This is the *whole point* of the isRhsEnv predicate
670 markRhsUds env is_pap arg_uds
671 | isRhsEnv env && is_pap = mapVarEnv markMany arg_uds
672 | otherwise = arg_uds
676 -> Int -> CtxtTy -- Argument number, and context to use for it
678 -> (UsageDetails, [CoreExpr])
679 appSpecial env n ctxt args
682 arg_env = vanillaCtxt
684 go n [] = (emptyDetails, []) -- Too few args
686 go 1 (arg:args) -- The magic arg
687 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
688 case occAnalArgs env args of { (args_uds, args') ->
689 (arg_uds +++ args_uds, arg':args') }}
692 = case occAnal arg_env arg of { (arg_uds, arg') ->
693 case go (n-1) args of { (args_uds, args') ->
694 (arg_uds +++ args_uds, arg':args') }}
700 If the case binder occurs at all, the other binders effectively do too.
702 case e of x { (a,b) -> rhs }
705 If e turns out to be (e1,e2) we indeed get something like
706 let a = e1; b = e2; x = (a,b) in rhs
708 Note [Aug 06]: I don't think this is necessary any more, and it helpe
709 to know when binders are unused. See esp the call to
710 isDeadBinder in Simplify.mkDupableAlt
713 occAnalAlt env case_bndr (con, bndrs, rhs)
714 = case occAnal env rhs of { (rhs_usage, rhs') ->
716 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
717 final_bndrs = tagged_bndrs -- See Note [Aug06] above
719 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
720 | otherwise = tagged_bndrs
721 -- Leave the binders untagged if the case
722 -- binder occurs at all; see note above
725 (final_usage, (con, final_bndrs, rhs')) }
729 %************************************************************************
731 \subsection[OccurAnal-types]{OccEnv}
733 %************************************************************************
737 = OccEnv OccEncl -- Enclosing context information
738 CtxtTy -- Tells about linearity
740 -- OccEncl is used to control whether to inline into constructor arguments
742 -- x = (p,q) -- Don't inline p or q
743 -- y = /\a -> (p a, q a) -- Still don't inline p or q
744 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
745 -- So OccEncl tells enought about the context to know what to do when
746 -- we encounter a contructor application or PAP.
749 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
750 -- Don't inline into constructor args here
751 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
752 -- Do inline into constructor args here
757 -- True:ctxt Analysing a function-valued expression that will be
760 -- False:ctxt Analysing a function-valued expression that may
761 -- be applied many times; but when it is,
762 -- the CtxtTy inside applies
765 initOccEnv = OccEnv OccRhs []
767 vanillaCtxt = OccEnv OccVanilla []
768 rhsCtxt = OccEnv OccRhs []
770 isRhsEnv (OccEnv OccRhs _) = True
771 isRhsEnv (OccEnv OccVanilla _) = False
773 setVanillaCtxt :: OccEnv -> OccEnv
774 setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty
775 setVanillaCtxt other_env = other_env
777 setCtxt :: OccEnv -> CtxtTy -> OccEnv
778 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
780 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
781 -- The result binders have one-shot-ness set that they might not have had originally.
782 -- This happens in (build (\cn -> e)). Here the occurrence analyser
783 -- linearity context knows that c,n are one-shot, and it records that fact in
784 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
786 oneShotGroup (OccEnv encl ctxt) bndrs
789 go ctxt [] rev_bndrs = reverse rev_bndrs
791 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
792 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
794 bndr' | lin_ctxt = setOneShotLambda bndr
797 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
799 addAppCtxt (OccEnv encl ctxt) args
800 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
803 %************************************************************************
805 \subsection[OccurAnal-types]{OccEnv}
807 %************************************************************************
810 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
812 (+++), combineAltsUsageDetails
813 :: UsageDetails -> UsageDetails -> UsageDetails
816 = plusVarEnv_C addOccInfo usage1 usage2
818 combineAltsUsageDetails usage1 usage2
819 = plusVarEnv_C orOccInfo usage1 usage2
821 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
822 addOneOcc usage id info
823 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
824 -- ToDo: make this more efficient
826 emptyDetails = (emptyVarEnv :: UsageDetails)
828 usedIn :: Id -> UsageDetails -> Bool
829 v `usedIn` details = isExportedId v || v `elemVarEnv` details
831 type IdWithOccInfo = Id
833 tagBinders :: UsageDetails -- Of scope
835 -> (UsageDetails, -- Details with binders removed
836 [IdWithOccInfo]) -- Tagged binders
838 tagBinders usage binders
840 usage' = usage `delVarEnvList` binders
841 uss = map (setBinderOcc usage) binders
843 usage' `seq` (usage', uss)
845 tagBinder :: UsageDetails -- Of scope
847 -> (UsageDetails, -- Details with binders removed
848 IdWithOccInfo) -- Tagged binders
850 tagBinder usage binder
852 usage' = usage `delVarEnv` binder
853 binder' = setBinderOcc usage binder
855 usage' `seq` (usage', binder')
857 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
858 setBinderOcc usage bndr
859 | isTyVar bndr = bndr
860 | isExportedId bndr = case idOccInfo bndr of
862 other -> setIdOccInfo bndr NoOccInfo
863 -- Don't use local usage info for visible-elsewhere things
864 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
865 -- about to re-generate it and it shouldn't be "sticky"
867 | otherwise = setIdOccInfo bndr occ_info
869 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
873 %************************************************************************
875 \subsection{Operations over OccInfo}
877 %************************************************************************
880 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
881 mkOneOcc env id int_cxt
882 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
883 | otherwise = emptyDetails
885 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
887 markMany IAmDead = IAmDead
888 markMany other = NoOccInfo
890 markInsideSCC occ = markMany occ
892 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
893 markInsideLam occ = occ
895 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
897 addOccInfo IAmDead info2 = info2
898 addOccInfo info1 IAmDead = info1
899 addOccInfo info1 info2 = NoOccInfo
901 -- (orOccInfo orig new) is used
902 -- when combining occurrence info from branches of a case
904 orOccInfo IAmDead info2 = info2
905 orOccInfo info1 IAmDead = info1
906 orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1)
907 (OneOcc in_lam2 one_branch2 int_cxt2)
908 = OneOcc (in_lam1 || in_lam2)
909 False -- False, because it occurs in both branches
910 (int_cxt1 && int_cxt2)
911 orOccInfo info1 info2 = NoOccInfo