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
335 is_con_app (Var v) = isDataConWorkId v
336 is_con_app (App f _) = is_con_app f
337 is_con_app (Lam b e) | isTyVar b = is_con_app e
338 is_con_app (Note _ e) = is_con_app e
339 is_con_app other = False
341 makeLoopBreaker :: VarSet -- Binders of this group
342 -> UsageDetails -- Usage of this rhs (neglecting rules)
344 -- Set the loop-breaker flag, recording whether the thing occurs only in
345 -- the RHS of a RULE (in this recursive group)
346 makeLoopBreaker bndrs rhs_usg bndr
347 = setIdOccInfo bndr (IAmALoopBreaker rules_only)
349 rules_only = bndrs `intersectsUFM` rhs_usg
352 @occAnalRhs@ deals with the question of bindings where the Id is marked
353 by an INLINE pragma. For these we record that anything which occurs
354 in its RHS occurs many times. This pessimistically assumes that ths
355 inlined binder also occurs many times in its scope, but if it doesn't
356 we'll catch it next time round. At worst this costs an extra simplifier pass.
357 ToDo: try using the occurrence info for the inline'd binder.
359 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
360 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
365 -> Id -> CoreExpr -- Binder and rhs
366 -- For non-recs the binder is alrady tagged
367 -- with occurrence info
368 -> (UsageDetails, CoreExpr)
370 occAnalRhs env id rhs
373 ctxt | certainly_inline id = env
374 | otherwise = rhsCtxt
375 -- Note that we generally use an rhsCtxt. This tells the occ anal n
376 -- that it's looking at an RHS, which has an effect in occAnalApp
378 -- But there's a problem. Consider
383 -- First time round, it looks as if x1 and x2 occur as an arg of a
384 -- let-bound constructor ==> give them a many-occurrence.
385 -- But then x3 is inlined (unconditionally as it happens) and
386 -- next time round, x2 will be, and the next time round x1 will be
387 -- Result: multiple simplifier iterations. Sigh.
388 -- Crude solution: use rhsCtxt for things that occur just once...
390 certainly_inline id = case idOccInfo id of
391 OneOcc in_lam one_br _ -> not in_lam && one_br
397 If the binder has RULES inside it then we count the specialised Ids as
398 "extra rhs's". That way the "parent" keeps the specialised "children"
399 alive. If the parent dies (because it isn't referenced any more),
400 then the children will die too unless they are already referenced
403 That's the basic idea. However in a recursive situation we want to be a bit
404 cleverer. Example (from GHC.Enum):
406 eftInt :: Int# -> Int# -> [Int]
407 eftInt x y = ...(non-recursive)...
409 {-# INLINE [0] eftIntFB #-}
410 eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
411 eftIntFB c n x y = ...(non-recursive)...
414 "eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
415 "eftIntList" [1] eftIntFB (:) [] = eftInt
418 The two look mutually recursive only because of their RULES; we don't want
419 that to inhibit inlining!
421 So when we identify a LoopBreaker, we mark it to say whether it only mentions
422 the other binders in its recursive group in a RULE. If so, we can inline it,
423 because doing so will not expose new occurrences of binders in its group.
428 addRuleUsage :: UsageDetails -> Id -> UsageDetails
429 -- Add the usage from RULES in Id to the usage
430 addRuleUsage usage id
431 = foldVarSet add usage (idRuleVars id)
433 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
434 -- (i.e manyOcc) because many copies
435 -- of the specialised thing can appear
443 -> (UsageDetails, -- Gives info only about the "interesting" Ids
446 occAnal env (Type t) = (emptyDetails, Type t)
447 occAnal env (Var v) = (mkOneOcc env v False, Var v)
448 -- At one stage, I gathered the idRuleVars for v here too,
449 -- which in a way is the right thing to do.
450 -- Btu that went wrong right after specialisation, when
451 -- the *occurrences* of the overloaded function didn't have any
452 -- rules in them, so the *specialised* versions looked as if they
453 -- weren't used at all.
456 We regard variables that occur as constructor arguments as "dangerousToDup":
460 f x = let y = expensive x in
462 (case z of {(p,q)->q}, case z of {(p,q)->q})
465 We feel free to duplicate the WHNF (True,y), but that means
466 that y may be duplicated thereby.
468 If we aren't careful we duplicate the (expensive x) call!
469 Constructors are rather like lambdas in this way.
472 occAnal env expr@(Lit lit) = (emptyDetails, expr)
476 occAnal env (Note InlineMe body)
477 = case occAnal env body of { (usage, body') ->
478 (mapVarEnv markMany usage, Note InlineMe body')
481 occAnal env (Note note@(SCC cc) body)
482 = case occAnal env body of { (usage, body') ->
483 (mapVarEnv markInsideSCC usage, Note note body')
486 occAnal env (Note note body)
487 = case occAnal env body of { (usage, body') ->
488 (usage, Note note body')
491 occAnal env (Cast expr co)
492 = case occAnal env expr of { (usage, expr') ->
493 (markRhsUds env True usage, Cast expr' co)
494 -- If we see let x = y `cast` co
495 -- then mark y as 'Many' so that we don't
496 -- immediately inline y again.
501 occAnal env app@(App fun arg)
502 = occAnalApp env (collectArgs app) False
504 -- Ignore type variables altogether
505 -- (a) occurrences inside type lambdas only not marked as InsideLam
506 -- (b) type variables not in environment
508 occAnal env expr@(Lam x body) | isTyVar x
509 = case occAnal env body of { (body_usage, body') ->
510 (body_usage, Lam x body')
513 -- For value lambdas we do a special hack. Consider
515 -- If we did nothing, x is used inside the \y, so would be marked
516 -- as dangerous to dup. But in the common case where the abstraction
517 -- is applied to two arguments this is over-pessimistic.
518 -- So instead, we just mark each binder with its occurrence
519 -- info in the *body* of the multiple lambda.
520 -- Then, the simplifier is careful when partially applying lambdas.
522 occAnal env expr@(Lam _ _)
523 = case occAnal env_body body of { (body_usage, body') ->
525 (final_usage, tagged_binders) = tagBinders body_usage binders
526 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
527 -- we get linear-typed things in the resulting program that we can't handle yet.
528 -- (e.g. PrelShow) TODO
530 really_final_usage = if linear then
533 mapVarEnv markInsideLam final_usage
536 mkLams tagged_binders body') }
538 env_body = vanillaCtxt -- Body is (no longer) an RhsContext
539 (binders, body) = collectBinders expr
540 binders' = oneShotGroup env binders
541 linear = all is_one_shot binders'
542 is_one_shot b = isId b && isOneShotBndr b
544 occAnal env (Case scrut bndr ty alts)
545 = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') ->
546 case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts') ->
548 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
549 alts_usage' = addCaseBndrUsage alts_usage
550 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
551 total_usage = scrut_usage +++ alts_usage1
553 total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }}
555 -- The case binder gets a usage of either "many" or "dead", never "one".
556 -- Reason: we like to inline single occurrences, to eliminate a binding,
557 -- but inlining a case binder *doesn't* eliminate a binding.
558 -- We *don't* want to transform
559 -- case x of w { (p,q) -> f w }
561 -- case x of w { (p,q) -> f (p,q) }
562 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
564 Just occ -> extendVarEnv usage bndr (markMany occ)
566 alt_env = setVanillaCtxt env
567 -- Consider x = case v of { True -> (p,q); ... }
568 -- Then it's fine to inline p and q
570 occ_anal_scrut (Var v) (alt1 : other_alts)
571 | not (null other_alts) || not (isDefaultAlt alt1)
572 = (mkOneOcc env v True, Var v)
573 occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut
574 -- No need for rhsCtxt
576 occAnal env (Let bind body)
577 = case occAnal env body of { (body_usage, body') ->
578 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
579 (final_usage, mkLets new_binds body') }}
582 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
583 (foldr (+++) emptyDetails arg_uds_s, args')}
585 arg_env = vanillaCtxt
588 Applications are dealt with specially because we want
589 the "build hack" to work.
592 occAnalApp env (Var fun, args) is_rhs
593 = case args_stuff of { (args_uds, args') ->
595 final_args_uds = markRhsUds env is_pap args_uds
597 (fun_uds +++ final_args_uds, mkApps (Var fun) args') }
599 fun_uniq = idUnique fun
600 fun_uds = mkOneOcc env fun (valArgCount args > 0)
601 is_pap = isDataConWorkId fun || valArgCount args < idArity fun
603 -- Hack for build, fold, runST
604 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
605 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
606 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
607 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
608 -- (foldr k z xs) may call k many times, but it never
609 -- shares a partial application of k; hence [False,True]
610 -- This means we can optimise
611 -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
612 -- by floating in the v
614 | otherwise = occAnalArgs env args
617 occAnalApp env (fun, args) is_rhs
618 = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
619 -- The addAppCtxt is a bit cunning. One iteration of the simplifier
620 -- often leaves behind beta redexs like
622 -- Here we would like to mark x,y as one-shot, and treat the whole
623 -- thing much like a let. We do this by pushing some True items
624 -- onto the context stack.
626 case occAnalArgs env args of { (args_uds, args') ->
628 final_uds = fun_uds +++ args_uds
630 (final_uds, mkApps fun' args') }}
633 markRhsUds :: OccEnv -- Check if this is a RhsEnv
634 -> Bool -- and this is true
635 -> UsageDetails -- The do markMany on this
637 -- We mark the free vars of the argument of a constructor or PAP
638 -- as "many", if it is the RHS of a let(rec).
639 -- This means that nothing gets inlined into a constructor argument
640 -- position, which is what we want. Typically those constructor
641 -- arguments are just variables, or trivial expressions.
643 -- This is the *whole point* of the isRhsEnv predicate
644 markRhsUds env is_pap arg_uds
645 | isRhsEnv env && is_pap = mapVarEnv markMany arg_uds
646 | otherwise = arg_uds
650 -> Int -> CtxtTy -- Argument number, and context to use for it
652 -> (UsageDetails, [CoreExpr])
653 appSpecial env n ctxt args
656 arg_env = vanillaCtxt
658 go n [] = (emptyDetails, []) -- Too few args
660 go 1 (arg:args) -- The magic arg
661 = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') ->
662 case occAnalArgs env args of { (args_uds, args') ->
663 (arg_uds +++ args_uds, arg':args') }}
666 = case occAnal arg_env arg of { (arg_uds, arg') ->
667 case go (n-1) args of { (args_uds, args') ->
668 (arg_uds +++ args_uds, arg':args') }}
674 If the case binder occurs at all, the other binders effectively do too.
676 case e of x { (a,b) -> rhs }
679 If e turns out to be (e1,e2) we indeed get something like
680 let a = e1; b = e2; x = (a,b) in rhs
682 Note [Aug 06]: I don't think this is necessary any more, and it helpe
683 to know when binders are unused. See esp the call to
684 isDeadBinder in Simplify.mkDupableAlt
687 occAnalAlt env case_bndr (con, bndrs, rhs)
688 = case occAnal env rhs of { (rhs_usage, rhs') ->
690 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
691 final_bndrs = tagged_bndrs -- See Note [Aug06] above
693 final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
694 | otherwise = tagged_bndrs
695 -- Leave the binders untagged if the case
696 -- binder occurs at all; see note above
699 (final_usage, (con, final_bndrs, rhs')) }
703 %************************************************************************
705 \subsection[OccurAnal-types]{OccEnv}
707 %************************************************************************
711 = OccEnv OccEncl -- Enclosing context information
712 CtxtTy -- Tells about linearity
714 -- OccEncl is used to control whether to inline into constructor arguments
716 -- x = (p,q) -- Don't inline p or q
717 -- y = /\a -> (p a, q a) -- Still don't inline p or q
718 -- z = f (p,q) -- Do inline p,q; it may make a rule fire
719 -- So OccEncl tells enought about the context to know what to do when
720 -- we encounter a contructor application or PAP.
723 = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
724 -- Don't inline into constructor args here
725 | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
726 -- Do inline into constructor args here
731 -- True:ctxt Analysing a function-valued expression that will be
734 -- False:ctxt Analysing a function-valued expression that may
735 -- be applied many times; but when it is,
736 -- the CtxtTy inside applies
739 initOccEnv = OccEnv OccRhs []
741 vanillaCtxt = OccEnv OccVanilla []
742 rhsCtxt = OccEnv OccRhs []
744 isRhsEnv (OccEnv OccRhs _) = True
745 isRhsEnv (OccEnv OccVanilla _) = False
747 setVanillaCtxt :: OccEnv -> OccEnv
748 setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty
749 setVanillaCtxt other_env = other_env
751 setCtxt :: OccEnv -> CtxtTy -> OccEnv
752 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt
754 oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr]
755 -- The result binders have one-shot-ness set that they might not have had originally.
756 -- This happens in (build (\cn -> e)). Here the occurrence analyser
757 -- linearity context knows that c,n are one-shot, and it records that fact in
758 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
760 oneShotGroup (OccEnv encl ctxt) bndrs
763 go ctxt [] rev_bndrs = reverse rev_bndrs
765 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
766 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
768 bndr' | lin_ctxt = setOneShotLambda bndr
771 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
773 addAppCtxt (OccEnv encl ctxt) args
774 = OccEnv encl (replicate (valArgCount args) True ++ ctxt)
777 %************************************************************************
779 \subsection[OccurAnal-types]{OccEnv}
781 %************************************************************************
784 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
786 (+++), combineAltsUsageDetails
787 :: UsageDetails -> UsageDetails -> UsageDetails
790 = plusVarEnv_C addOccInfo usage1 usage2
792 combineAltsUsageDetails usage1 usage2
793 = plusVarEnv_C orOccInfo usage1 usage2
795 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
796 addOneOcc usage id info
797 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
798 -- ToDo: make this more efficient
800 emptyDetails = (emptyVarEnv :: UsageDetails)
802 usedIn :: Id -> UsageDetails -> Bool
803 v `usedIn` details = isExportedId v || v `elemVarEnv` details
805 type IdWithOccInfo = Id
807 tagBinders :: UsageDetails -- Of scope
809 -> (UsageDetails, -- Details with binders removed
810 [IdWithOccInfo]) -- Tagged binders
812 tagBinders usage binders
814 usage' = usage `delVarEnvList` binders
815 uss = map (setBinderOcc usage) binders
817 usage' `seq` (usage', uss)
819 tagBinder :: UsageDetails -- Of scope
821 -> (UsageDetails, -- Details with binders removed
822 IdWithOccInfo) -- Tagged binders
824 tagBinder usage binder
826 usage' = usage `delVarEnv` binder
827 binder' = setBinderOcc usage binder
829 usage' `seq` (usage', binder')
831 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
832 setBinderOcc usage bndr
833 | isTyVar bndr = bndr
834 | isExportedId bndr = case idOccInfo bndr of
836 other -> setIdOccInfo bndr NoOccInfo
837 -- Don't use local usage info for visible-elsewhere things
838 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
839 -- about to re-generate it and it shouldn't be "sticky"
841 | otherwise = setIdOccInfo bndr occ_info
843 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
847 %************************************************************************
849 \subsection{Operations over OccInfo}
851 %************************************************************************
854 mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails
855 mkOneOcc env id int_cxt
856 | isLocalId id = unitVarEnv id (OneOcc False True int_cxt)
857 | otherwise = emptyDetails
859 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
861 markMany IAmDead = IAmDead
862 markMany other = NoOccInfo
864 markInsideSCC occ = markMany occ
866 markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt
867 markInsideLam occ = occ
869 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
871 addOccInfo IAmDead info2 = info2
872 addOccInfo info1 IAmDead = info1
873 addOccInfo info1 info2 = NoOccInfo
875 -- (orOccInfo orig new) is used
876 -- when combining occurrence info from branches of a case
878 orOccInfo IAmDead info2 = info2
879 orOccInfo info1 IAmDead = info1
880 orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1)
881 (OneOcc in_lam2 one_branch2 int_cxt2)
882 = OneOcc (in_lam1 || in_lam2)
883 False -- False, because it occurs in both branches
884 (int_cxt1 && int_cxt2)
885 orOccInfo info1 info2 = NoOccInfo