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 occurAnalyseBinds, occurAnalyseGlobalExpr, occurAnalyseRule
18 #include "HsVersions.h"
21 import CoreFVs ( idRuleVars )
22 import CoreUtils ( exprIsTrivial )
23 import Id ( isDataConId, isOneShotLambda, setOneShotLambda,
24 idOccInfo, setIdOccInfo,
25 isExportedId, modifyIdInfo, idInfo,
26 idSpecialisation, isLocalId,
29 import IdInfo ( OccInfo(..), shortableIdInfo, copyIdInfo )
34 import Type ( splitFunTy_maybe, splitForAllTys )
35 import Maybes ( maybeToBool, orElse )
36 import Digraph ( stronglyConnCompR, SCC(..) )
37 import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
38 import Unique ( Unique )
39 import UniqFM ( keysUFM )
40 import Util ( zipWithEqual, mapAndUnzip )
46 %************************************************************************
48 \subsection[OccurAnal-main]{Counting occurrences: main function}
50 %************************************************************************
52 Here's the externally-callable interface:
55 occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
57 -> (IdEnv OccInfo, -- Occ info for interesting free vars
60 occurAnalyseExpr interesting expr
61 = occAnal initial_env expr
63 initial_env = OccEnv interesting emptyVarSet []
65 occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
66 occurAnalyseGlobalExpr expr
67 = -- Top level expr, so no interesting free vars, and
68 -- discard occurence info returned
69 snd (occurAnalyseExpr (\_ -> False) expr)
71 occurAnalyseRule :: CoreRule -> CoreRule
72 occurAnalyseRule rule@(BuiltinRule _ _) = rule
73 occurAnalyseRule (Rule str tpl_vars tpl_args rhs)
74 -- Add occ info to tpl_vars, rhs
75 = Rule str tpl_vars' tpl_args rhs'
77 (rhs_uds, rhs') = occurAnalyseExpr isLocalId rhs
78 (_, tpl_vars') = tagBinders rhs_uds tpl_vars
82 %************************************************************************
84 \subsection{Top level stuff}
86 %************************************************************************
88 In @occAnalTop@ we do indirection-shorting. That is, if we have this:
90 x_local = <expression>
94 where exp is exported, and loc is not, then we replace it with this:
97 x_exported = <expression>
100 Without this we never get rid of the x_exported = x_local thing. This
101 save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
102 makes strictness information propagate better. This used to happen in
103 the final phase, but it's tidier to do it here.
105 If more than one exported thing is equal to a local thing (i.e., the
106 local thing really is shared), then we do one only:
109 x_exported1 = x_local
110 x_exported2 = x_local
114 x_exported2 = x_exported1
117 We rely on prior eta reduction to simplify things like
119 x_exported = /\ tyvars -> x_local tyvars
123 Hence,there's a possibility of leaving unchanged something like this:
126 x_exported1 = x_local Int
128 By the time we've thrown away the types in STG land this
129 could be eliminated. But I don't think it's very common
130 and it's dangerous to do this fiddling in STG land
131 because we might elminate a binding that's mentioned in the
132 unfolding for something.
135 occurAnalyseBinds :: [CoreBind] -> [CoreBind]
137 occurAnalyseBinds binds
140 (_, _, binds') = go initialTopEnv binds
142 go :: OccEnv -> [CoreBind]
143 -> (UsageDetails, -- Occurrence info
144 IdEnv Id, -- Indirection elimination info
145 -- Maps local-id -> exported-id, but it embodies
146 -- bindings of the form exported-id = local-id in
147 -- the argument to go
148 [CoreBind]) -- Occ-analysed bindings, less the exported-id=local-id ones
150 go env [] = (emptyDetails, emptyVarEnv, [])
152 go env (bind : binds)
154 new_env = env `addNewCands` (bindersOf bind)
155 (scope_usage, ind_env, binds') = go new_env binds
156 (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
157 -- NB: I zap before occur-analysing, so
158 -- I don't need to worry about getting the
159 -- occ info on the new bindings right.
162 NonRec exported_id (Var local_id)
163 | shortMeOut ind_env exported_id local_id
164 -- Special case for eliminating indirections
165 -- Note: it's a shortcoming that this only works for
166 -- non-recursive bindings. Elminating indirections
167 -- makes perfect sense for recursive bindings too, but
168 -- it's more complicated to implement, so I haven't done so
169 -> (scope_usage, ind_env', binds')
171 ind_env' = extendVarEnv ind_env local_id exported_id
173 other -> -- Ho ho! The normal case
174 (final_usage, ind_env, new_binds ++ binds')
176 initialTopEnv = OccEnv isLocalId -- Anything local is interesting
181 -- Deal with any indirections
182 zapBind ind_env (NonRec bndr rhs)
183 | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
184 -- The Rec isn't strictly necessary, but it's convenient
185 zapBind ind_env (Rec pairs)
186 | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
188 zapBind ind_env bind = bind
190 zap ind_env pair@(local_id,rhs)
191 = case lookupVarEnv ind_env local_id of
193 Just exported_id -> [(local_id, Var exported_id),
196 exported_id' = modifyIdInfo (copyIdInfo (idInfo local_id)) exported_id
198 shortMeOut ind_env exported_id local_id
199 -- The if-then-else stuff is just so I can get a pprTrace to see
200 -- how often I don't get shorting out becuase of IdInfo stuff
201 = if isExportedId exported_id && -- Only if this is exported
203 isLocalId local_id && -- Only if this one is defined in this
204 -- module, so that we *can* change its
205 -- binding to be the exported thing!
207 not (isExportedId local_id) && -- Only if this one is not itself exported,
208 -- since the transformation will nuke it
210 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
212 if shortableIdInfo (idInfo exported_id) -- Only if its IdInfo is 'shortable'
213 -- (see the defn of IdInfo.shortableIdInfo)
217 pprTrace "shortMeOut:" (ppr exported_id)
225 %************************************************************************
227 \subsection[OccurAnal-main]{Counting occurrences: main function}
229 %************************************************************************
235 type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
237 type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique,
238 -- which is gotten from the Id.
239 type Details1 = (Id, UsageDetails, CoreExpr)
240 type Details2 = (IdWithOccInfo, CoreExpr)
243 occAnalBind :: OccEnv
245 -> UsageDetails -- Usage details of scope
246 -> (UsageDetails, -- Of the whole let(rec)
249 occAnalBind env (NonRec binder rhs) body_usage
250 | not (binder `usedIn` body_usage) -- It's not mentioned
253 | otherwise -- It's mentioned in the body
254 = (final_body_usage `combineUsageDetails` rhs_usage,
255 [NonRec tagged_binder rhs'])
258 (final_body_usage, tagged_binder) = tagBinder body_usage binder
259 (rhs_usage, rhs') = occAnalRhs env binder rhs
262 Dropping dead code for recursive bindings is done in a very simple way:
264 the entire set of bindings is dropped if none of its binders are
265 mentioned in its body; otherwise none are.
267 This seems to miss an obvious improvement.
282 Now @f@ is unused. But dependency analysis will sort this out into a
283 @letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped.
284 It isn't easy to do a perfect job in one blow. Consider
298 occAnalBind env (Rec pairs) body_usage
299 = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
301 binders = map fst pairs
302 rhs_env = env `addNewCands` binders
304 analysed_pairs :: [Details1]
305 analysed_pairs = [ (bndr, rhs_usage, rhs')
306 | (bndr, rhs) <- pairs,
307 let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
310 sccs :: [SCC (Node Details1)]
311 sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
314 ---- stuff for dependency analysis of binds -------------------------------
315 edges :: [Node Details1]
316 edges = _scc_ "occAnalBind.assoc"
317 [ (details, idUnique id, edges_from rhs_usage)
318 | details@(id, rhs_usage, rhs) <- analysed_pairs
321 -- (a -> b) means a mentions b
322 -- Given the usage details (a UFM that gives occ info for each free var of
323 -- the RHS) we can get the list of free vars -- or rather their Int keys --
324 -- by just extracting the keys from the finite map. Grimy, but fast.
325 -- Previously we had this:
326 -- [ bndr | bndr <- bndrs,
327 -- maybeToBool (lookupVarEnv rhs_usage bndr)]
328 -- which has n**2 cost, and this meant that edges_from alone
329 -- consumed 10% of total runtime!
330 edges_from :: UsageDetails -> [Unique]
331 edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
334 ---- stuff to "re-constitute" bindings from dependency-analysis info ------
337 do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
338 | not (bndr `usedIn` body_usage)
339 = (body_usage, binds_so_far) -- Dead code
341 = (combined_usage, new_bind : binds_so_far)
343 total_usage = combineUsageDetails body_usage rhs_usage
344 (combined_usage, tagged_bndr) = tagBinder total_usage bndr
345 new_bind = NonRec tagged_bndr rhs'
348 do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
349 | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
350 = (body_usage, binds_so_far) -- Dead code
352 = (combined_usage, final_bind:binds_so_far)
354 details = [details | (details, _, _) <- cycle]
355 bndrs = [bndr | (bndr, _, _) <- details]
356 rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
357 total_usage = foldr combineUsageDetails body_usage rhs_usages
358 (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs
359 final_bind = Rec (reOrderRec env new_cycle)
361 new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
362 mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
365 @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
366 strongly connected component (there's guaranteed to be a cycle). It returns the
368 a) in a better order,
369 b) with some of the Ids having a IMustNotBeINLINEd pragma
371 The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
372 that the simplifier can guarantee not to loop provided it never records an inlining
373 for these no-inline guys.
375 Furthermore, the order of the binds is such that if we neglect dependencies
376 on the no-inline Ids then the binds are topologically sorted. This means
377 that the simplifier will generally do a good job if it works from top bottom,
378 recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
381 [June 98: I don't understand the following paragraphs, and I've
382 changed the a=b case again so that it isn't a special case any more.]
384 Here's a case that bit me:
392 Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
394 My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
395 Perhaps something cleverer would suffice.
398 You might think that you can prevent non-termination simply by making
399 sure that we simplify a recursive binding's RHS in an environment that
400 simply clones the recursive Id. But no. Consider
402 letrec f = \x -> let z = f x' in ...
409 We bind n to its *simplified* RHS, we then *re-simplify* it when
410 we inline n. Then we may well inline f; and then the same thing
413 I don't think it's possible to prevent non-termination by environment
414 manipulation in this way. Apart from anything else, successive
415 iterations of the simplifier may unroll recursive loops in cases like
416 that above. The idea of beaking every recursive loop with an
417 IMustNotBeINLINEd pragma is much much better.
423 -> SCC (Node Details2)
425 -- Sorted into a plausible order. Enough of the Ids have
426 -- dontINLINE pragmas that there are no loops left.
428 -- Non-recursive case
429 reOrderRec env (AcyclicSCC (bind, _, _)) = [bind]
431 -- Common case of simple self-recursion
432 reOrderRec env (CyclicSCC [bind])
433 = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
435 ((tagged_bndr, rhs), _, _) = bind
437 reOrderRec env (CyclicSCC (bind : binds))
438 = -- Choose a loop breaker, mark it no-inline,
439 -- do SCC analysis on the rest, and recursively sort them out
440 concat (map (reOrderRec env) (stronglyConnCompR unchosen))
442 [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
445 (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
446 (tagged_bndr, rhs) = chosen_pair
448 -- This loop looks for the bind with the lowest score
449 -- to pick as the loop breaker. The rest accumulate in
450 choose_loop_breaker (details,_,_) loop_sc acc []
451 = (details, acc) -- Done
453 choose_loop_breaker loop_bind loop_sc acc (bind : binds)
454 | sc < loop_sc -- Lower score so pick this new one
455 = choose_loop_breaker bind sc (loop_bind : acc) binds
457 | otherwise -- No lower so don't pick it
458 = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
462 score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
463 score ((bndr, rhs), _, _)
464 | exprIsTrivial rhs = 4 -- Practically certain to be inlined
465 -- Used to have also: && not (isExportedId bndr)
466 -- But I found this sometimes cost an extra iteration when we have
467 -- rec { d = (a,b); a = ...df...; b = ...df...; df = d }
468 -- where df is the exported dictionary. Then df makes a really
469 -- bad choice for loop breaker
471 | not_fun_ty (idType bndr) = 3 -- Data types help with cases
472 -- This used to have a lower score than inlineCandidate, but
473 -- it's *really* helpful if dictionaries get inlined fast,
474 -- so I'm experimenting with giving higher priority to data-typed things
476 | inlineCandidate bndr rhs = 2 -- Likely to be inlined
478 | not (isEmptyCoreRules (idSpecialisation bndr)) = 1
479 -- Avoid things with specialisations; we'd like
480 -- to take advantage of them in the subsequent bindings
484 inlineCandidate :: Id -> CoreExpr -> Bool
485 inlineCandidate id (Note InlineMe _) = True
486 inlineCandidate id rhs = case idOccInfo id of
490 -- Real example (the Enum Ordering instance from PrelBase):
491 -- rec f = \ x -> case d of (p,q,r) -> p x
492 -- g = \ x -> case d of (p,q,r) -> q x
495 -- Here, f and g occur just once; but we can't inline them into d.
496 -- On the other hand we *could* simplify those case expressions if
497 -- we didn't stupidly choose d as the loop breaker.
498 -- But we won't because constructor args are marked "Many".
500 not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
502 (_, rho_ty) = splitForAllTys ty
505 @occAnalRhs@ deals with the question of bindings where the Id is marked
506 by an INLINE pragma. For these we record that anything which occurs
507 in its RHS occurs many times. This pessimistically assumes that ths
508 inlined binder also occurs many times in its scope, but if it doesn't
509 we'll catch it next time round. At worst this costs an extra simplifier pass.
510 ToDo: try using the occurrence info for the inline'd binder.
512 [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
513 [June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
518 -> Id -> CoreExpr -- Binder and rhs
519 -> (UsageDetails, CoreExpr)
521 occAnalRhs env id rhs
522 = (final_usage, rhs')
524 (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
526 -- [March 98] A new wrinkle is that if the binder has specialisations inside
527 -- it then we count the specialised Ids as "extra rhs's". That way
528 -- the "parent" keeps the specialised "children" alive. If the parent
529 -- dies (because it isn't referenced any more), then the children will
530 -- die too unless they are already referenced directly.
532 final_usage = foldVarSet add rhs_usage (idRuleVars id)
533 add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
534 -- (i.e manyOcc) because many copies
535 -- of the specialised thing can appear
543 -> (UsageDetails, -- Gives info only about the "interesting" Ids
546 occAnal env (Type t) = (emptyDetails, Type t)
551 var_uds | isCandidate env v = unitVarEnv v oneOcc
552 | otherwise = emptyDetails
554 -- At one stage, I gathered the idRuleVars for v here too,
555 -- which in a way is the right thing to do.
556 -- But that went wrong right after specialisation, when
557 -- the *occurrences* of the overloaded function didn't have any
558 -- rules in them, so the *specialised* versions looked as if they
559 -- weren't used at all.
563 We regard variables that occur as constructor arguments as "dangerousToDup":
567 f x = let y = expensive x in
569 (case z of {(p,q)->q}, case z of {(p,q)->q})
572 We feel free to duplicate the WHNF (True,y), but that means
573 that y may be duplicated thereby.
575 If we aren't careful we duplicate the (expensive x) call!
576 Constructors are rather like lambdas in this way.
579 occAnal env expr@(Lit lit) = (emptyDetails, expr)
583 occAnal env (Note InlineMe body)
584 = case occAnal env body of { (usage, body') ->
585 (mapVarEnv markMany usage, Note InlineMe body')
588 occAnal env (Note note@(SCC cc) body)
589 = case occAnal env body of { (usage, body') ->
590 (mapVarEnv markInsideSCC usage, Note note body')
593 occAnal env (Note note body)
594 = case occAnal env body of { (usage, body') ->
595 (usage, Note note body')
600 occAnal env app@(App fun arg)
601 = occAnalApp env (collectArgs app)
603 -- Ignore type variables altogether
604 -- (a) occurrences inside type lambdas only not marked as InsideLam
605 -- (b) type variables not in environment
607 occAnal env expr@(Lam x body) | isTyVar x
608 = case occAnal env body of { (body_usage, body') ->
609 (body_usage, Lam x body')
612 -- For value lambdas we do a special hack. Consider
614 -- If we did nothing, x is used inside the \y, so would be marked
615 -- as dangerous to dup. But in the common case where the abstraction
616 -- is applied to two arguments this is over-pessimistic.
617 -- So instead, we just mark each binder with its occurrence
618 -- info in the *body* of the multiple lambda.
619 -- Then, the simplifier is careful when partially applying lambdas.
621 occAnal env expr@(Lam _ _)
622 = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
624 (final_usage, tagged_binders) = tagBinders body_usage binders
625 -- URGH! Sept 99: we don't seem to be able to use binders' here, because
626 -- we get linear-typed things in the resulting program that we can't handle yet.
627 -- (e.g. PrelShow) TODO
629 really_final_usage = if linear then
632 mapVarEnv markInsideLam final_usage
635 mkLams tagged_binders body') }
637 (binders, body) = collectBinders expr
638 (linear, env_body, _) = oneShotGroup env binders
640 occAnal env (Case scrut bndr alts)
641 = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
642 case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
644 alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
645 alts_usage' = addCaseBndrUsage alts_usage
646 (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
647 total_usage = scrut_usage `combineUsageDetails` alts_usage1
649 total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
651 alt_env = env `addNewCand` bndr
653 -- The case binder gets a usage of either "many" or "dead", never "one".
654 -- Reason: we like to inline single occurrences, to eliminate a binding,
655 -- but inlining a case binder *doesn't* eliminate a binding.
656 -- We *don't* want to transform
657 -- case x of w { (p,q) -> f w }
659 -- case x of w { (p,q) -> f (p,q) }
660 addCaseBndrUsage usage = case lookupVarEnv usage bndr of
662 Just occ -> extendVarEnv usage bndr (markMany occ)
664 occAnal env (Let bind body)
665 = case occAnal new_env body of { (body_usage, body') ->
666 case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
667 (final_usage, mkLets new_binds body') }}
669 new_env = env `addNewCands` (bindersOf bind)
672 = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
673 (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
675 arg_env = zapCtxt env
678 Applications are dealt with specially because we want
679 the "build hack" to work.
682 -- Hack for build, fold, runST
683 occAnalApp env (Var fun, args)
684 = case args_stuff of { (args_uds, args') ->
686 final_uds = fun_uds `combineUsageDetails` args_uds
688 (final_uds, mkApps (Var fun) args') }
690 fun_uniq = idUnique fun
692 fun_uds | isCandidate env fun = unitVarEnv fun oneOcc
693 | otherwise = emptyDetails
695 args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
696 | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
697 | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
698 | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
700 | isDataConId fun = case occAnalArgs env args of
701 (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
702 -- We mark the free vars of the argument of a constructor as "many"
703 -- This means that nothing gets inlined into a constructor argument
704 -- position, which is what we want. Typically those constructor
705 -- arguments are just variables, or trivial expressions.
707 | otherwise = occAnalArgs env args
710 occAnalApp env (fun, args)
711 = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
712 case occAnalArgs env args of { (args_uds, args') ->
714 final_uds = fun_uds `combineUsageDetails` args_uds
716 (final_uds, mkApps fun' args') }}
718 appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
719 appSpecial env n ctxt args
722 go n [] = (emptyDetails, []) -- Too few args
724 go 1 (arg:args) -- The magic arg
725 = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
726 case occAnalArgs env args of { (args_uds, args') ->
727 (combineUsageDetails arg_uds args_uds, arg':args') }}
730 = case occAnal env arg of { (arg_uds, arg') ->
731 case go (n-1) args of { (args_uds, args') ->
732 (combineUsageDetails arg_uds args_uds, arg':args') }}
739 occAnalAlt env (con, bndrs, rhs)
740 = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
742 (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
744 (final_usage, (con, tagged_bndrs, rhs')) }
748 %************************************************************************
750 \subsection[OccurAnal-types]{Data types}
752 %************************************************************************
755 -- We gather inforamtion for variables that are either
760 OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
761 IdSet -- In-scope Ids
762 CtxtTy -- Tells about linearity
767 -- True:ctxt Analysing a function-valued expression that will be
770 -- False:ctxt Analysing a function-valued expression that may
771 -- be applied many times; but when it is,
772 -- the CtxtTy inside applies
774 isCandidate :: OccEnv -> Id -> Bool
775 isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
777 addNewCands :: OccEnv -> [Id] -> OccEnv
778 addNewCands (OccEnv ifun cands ctxt) ids
779 = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
781 addNewCand :: OccEnv -> Id -> OccEnv
782 addNewCand (OccEnv ifun cands ctxt) id
783 = OccEnv ifun (extendVarSet cands id) ctxt
785 setCtxt :: OccEnv -> CtxtTy -> OccEnv
786 setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
788 oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
789 -- True <=> this is a one-shot linear lambda group
790 -- The [CoreBndr] are the binders.
792 -- The result binders have one-shot-ness set that they might not have had originally.
793 -- This happens in (build (\cn -> e)). Here the occurrence analyser
794 -- linearity context knows that c,n are one-shot, and it records that fact in
795 -- the binder. This is useful to guide subsequent float-in/float-out tranformations
797 oneShotGroup (OccEnv ifun cands ctxt) bndrs
798 = case go ctxt bndrs [] of
799 (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
801 is_one_shot b = isId b && isOneShotLambda b
803 go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
805 go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
806 | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
808 bndr' | lin_ctxt = setOneShotLambda bndr
811 go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
814 zapCtxt env@(OccEnv ifun cands []) = env
815 zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
817 type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
819 combineUsageDetails, combineAltsUsageDetails
820 :: UsageDetails -> UsageDetails -> UsageDetails
822 combineUsageDetails usage1 usage2
823 = plusVarEnv_C addOccInfo usage1 usage2
825 combineAltsUsageDetails usage1 usage2
826 = plusVarEnv_C orOccInfo usage1 usage2
828 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails
829 addOneOcc usage id info
830 = plusVarEnv_C addOccInfo usage (unitVarEnv id info)
831 -- ToDo: make this more efficient
833 emptyDetails = (emptyVarEnv :: UsageDetails)
835 usedIn :: Id -> UsageDetails -> Bool
836 v `usedIn` details = isExportedId v || v `elemVarEnv` details
838 tagBinders :: UsageDetails -- Of scope
840 -> (UsageDetails, -- Details with binders removed
841 [IdWithOccInfo]) -- Tagged binders
843 tagBinders usage binders
845 usage' = usage `delVarEnvList` binders
846 uss = map (setBinderOcc usage) binders
848 usage' `seq` (usage', uss)
850 tagBinder :: UsageDetails -- Of scope
852 -> (UsageDetails, -- Details with binders removed
853 IdWithOccInfo) -- Tagged binders
855 tagBinder usage binder
857 usage' = usage `delVarEnv` binder
858 binder' = setBinderOcc usage binder
860 usage' `seq` (usage', binder')
862 setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
863 setBinderOcc usage bndr
864 | isTyVar bndr = bndr
865 | isExportedId bndr = case idOccInfo bndr of
867 other -> setIdOccInfo bndr NoOccInfo
868 -- Don't use local usage info for visible-elsewhere things
869 -- BUT *do* erase any IAmALoopBreaker annotation, because we're
870 -- about to re-generate it and it shouldn't be "sticky"
872 | otherwise = setIdOccInfo bndr occ_info
874 occ_info = lookupVarEnv usage bndr `orElse` IAmDead
878 %************************************************************************
880 \subsection{Operations over OccInfo}
882 %************************************************************************
886 oneOcc = OneOcc False True
888 markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo
890 markMany IAmDead = IAmDead
891 markMany other = NoOccInfo
893 markInsideSCC occ = markMany occ
895 markInsideLam (OneOcc _ one_br) = OneOcc True one_br
896 markInsideLam occ = occ
898 addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo
900 addOccInfo IAmDead info2 = info2
901 addOccInfo info1 IAmDead = info1
902 addOccInfo info1 info2 = NoOccInfo
904 -- (orOccInfo orig new) is used
905 -- when combining occurrence info from branches of a case
907 orOccInfo IAmDead info2 = info2
908 orOccInfo info1 IAmDead = info1
909 orOccInfo (OneOcc in_lam1 one_branch1)
910 (OneOcc in_lam2 one_branch2)
911 = OneOcc (in_lam1 || in_lam2)
912 False -- False, because it occurs in both branches
914 orOccInfo info1 info2 = NoOccInfo