2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section{Tidying up Core}
7 module TidyPgm( tidyCorePgm, tidyCoreExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( DynFlags, DynFlag(..), dopt )
13 import CoreUnfold ( noUnfolding, mkTopUnfolding )
14 import CoreFVs ( ruleLhsFreeIds, exprSomeFreeVars )
15 import CoreTidy ( tidyExpr, tidyVarOcc, tidyIdRules )
16 import PprCore ( pprIdRules )
17 import CoreLint ( showPass, endPass )
18 import CoreUtils ( exprArity, rhsIsStatic )
21 import Var ( Id, Var )
22 import Id ( idType, idInfo, idName, idCoreRules,
23 isExportedId, mkVanillaGlobal, isLocalId,
24 isImplicitId, idArity, setIdInfo, idCafInfo
26 import IdInfo {- loads of stuff -}
27 import NewDemand ( isBottomingSig, topSig )
28 import BasicTypes ( Arity, isNeverActive )
29 import Name ( Name, getOccName, nameOccName, mkInternalName,
30 localiseName, isExternalName, nameSrcLoc, nameParent_maybe
32 import IfaceEnv ( allocateGlobalBinder )
33 import NameEnv ( lookupNameEnv, filterNameEnv )
34 import OccName ( TidyOccEnv, initTidyOccEnv, tidyOccName )
35 import Type ( tidyTopType )
36 import Module ( Module )
37 import HscTypes ( HscEnv(..), NameCache( nsUniqs ),
38 TypeEnv, extendTypeEnvList, typeEnvIds,
39 ModGuts(..), ModGuts, TyThing(..)
41 import Maybes ( orElse )
42 import ErrUtils ( showPass, dumpIfSet_core )
43 import UniqSupply ( splitUniqSupply, uniqFromSupply )
44 import List ( partition )
45 import Maybe ( isJust )
47 import DATA_IOREF ( IORef, readIORef, writeIORef )
48 import FastTypes hiding ( fastOr )
52 %************************************************************************
54 \subsection{What goes on}
56 %************************************************************************
62 Step 1: Figure out external Ids
63 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
64 First we figure out which Ids are "external" Ids. An
65 "external" Id is one that is visible from outside the compilation
67 a) the user exported ones
68 b) ones mentioned in the unfoldings, workers,
69 or rules of externally-visible ones
70 This exercise takes a sweep of the bindings bottom to top. Actually,
71 in Step 2 we're also going to need to know which Ids should be
72 exported with their unfoldings, so we produce not an IdSet but an
76 Step 2: Tidy the program
77 ~~~~~~~~~~~~~~~~~~~~~~~~
78 Next we traverse the bindings top to bottom. For each *top-level*
81 1. Make it into a GlobalId
83 2. Give it a system-wide Unique.
84 [Even non-exported things need system-wide Uniques because the
85 byte-code generator builds a single Name->BCO symbol table.]
87 We use the NameCache kept in the HscEnv as the
88 source of such system-wide uniques.
90 For external Ids, use the original-name cache in the NameCache
91 to ensure that the unique assigned is the same as the Id had
92 in any previous compilation run.
94 3. If it's an external Id, make it have a global Name, otherwise
95 make it have a local Name.
96 This is used by the code generator to decide whether
97 to make the label externally visible
99 4. Give external Ids a "tidy" occurrence name. This means
100 we can print them in interface files without confusing
101 "x" (unique 5) with "x" (unique 10).
103 5. Give it its UTTERLY FINAL IdInfo; in ptic,
104 * Its IdDetails becomes VanillaGlobal, reflecting the fact that
105 from now on we regard it as a global, not local, Id
107 * its unfolding, if it should have one
109 * its arity, computed from the number of visible lambdas
111 * its CAF info, computed from what is free in its RHS
114 Finally, substitute these new top-level binders consistently
115 throughout, including in unfoldings. We also tidy binders in
116 RHSs, so that they print nicely in interfaces.
119 tidyCorePgm :: HscEnv -> ModGuts -> IO ModGuts
122 mod_impl@(ModGuts { mg_module = mod,
123 mg_types = env_tc, mg_insts = insts_tc,
124 mg_binds = binds_in, mg_rules = orphans_in })
125 = do { let { dflags = hsc_dflags hsc_env
126 ; nc_var = hsc_NC hsc_env }
127 ; showPass dflags "Tidy Core"
129 ; let omit_iface_prags = dopt Opt_OmitInterfacePragmas dflags
130 ; let ext_ids = findExternalSet omit_iface_prags binds_in
131 ; let ext_rules = findExternalRules omit_iface_prags binds_in orphans_in ext_ids
132 -- findExternalRules filters ext_rules to avoid binders that
133 -- aren't externally visible; but the externally-visible binders
134 -- are computed (by findExternalSet) assuming that all orphan
135 -- rules are exported (they get their Exported flag set in the desugarer)
136 -- So in fact we may export more than we need.
137 -- (It's a sort of mutual recursion.)
139 -- We also make sure to avoid any exported binders. Consider
140 -- f{-u1-} = 1 -- Local decl
142 -- f{-u2-} = 2 -- Exported decl
144 -- The second exported decl must 'get' the name 'f', so we
145 -- have to put 'f' in the avoids list before we get to the first
146 -- decl. tidyTopId then does a no-op on exported binders.
147 ; let init_env = (initTidyOccEnv avoids, emptyVarEnv)
148 avoids = [getOccName name | bndr <- typeEnvIds env_tc,
149 let name = idName bndr,
151 -- In computing our "avoids" list, we must include
153 -- all things with global names (assigned once and for
154 -- all by the renamer)
155 -- since their names are "taken".
156 -- The type environment is a convenient source of such things.
158 ; (final_env, tidy_binds)
159 <- tidyTopBinds dflags mod nc_var ext_ids init_env binds_in
161 ; let tidy_rules = tidyIdRules final_env ext_rules
163 ; let tidy_type_env = mkFinalTypeEnv omit_iface_prags env_tc tidy_binds
165 -- Dfuns are local Ids that might have
166 -- changed their unique during tidying. Remember
167 -- to lookup the id in the TypeEnv too, because
168 -- those Ids have had their IdInfo stripped if
170 ; let (_, subst_env ) = final_env
172 case lookupVarEnv subst_env id of
173 Nothing -> dfun_panic
175 case lookupNameEnv tidy_type_env (idName id) of
179 dfun_panic = pprPanic "lookup_dfun_id" (ppr id)
181 tidy_dfun_ids = map lookup_dfun_id insts_tc
183 ; let tidy_result = mod_impl { mg_types = tidy_type_env,
184 mg_rules = tidy_rules,
185 mg_insts = tidy_dfun_ids,
186 mg_binds = tidy_binds }
188 ; endPass dflags "Tidy Core" Opt_D_dump_simpl tidy_binds
189 ; dumpIfSet_core dflags Opt_D_dump_simpl
191 (pprIdRules tidy_rules)
196 tidyCoreExpr :: CoreExpr -> IO CoreExpr
197 tidyCoreExpr expr = return (tidyExpr emptyTidyEnv expr)
201 %************************************************************************
203 \subsection{Write a new interface file}
205 %************************************************************************
208 mkFinalTypeEnv :: Bool -- Omit interface pragmas
209 -> TypeEnv -- From typechecker
210 -> [CoreBind] -- Final Ids
213 -- The competed type environment is gotten from
214 -- a) keeping the types and classes
215 -- b) removing all Ids,
216 -- c) adding Ids with correct IdInfo, including unfoldings,
217 -- gotten from the bindings
218 -- From (c) we keep only those Ids with External names;
219 -- the CoreTidy pass makes sure these are all and only
220 -- the externally-accessible ones
221 -- This truncates the type environment to include only the
222 -- exported Ids and things needed from them, which saves space
224 -- However, we do keep things like constructors, which should not appear
225 -- in interface files, because they are needed by importing modules when
226 -- using the compilation manager
228 mkFinalTypeEnv omit_iface_prags type_env tidy_binds
229 = extendTypeEnvList (filterNameEnv keep_it type_env) final_ids
231 final_ids = [ AnId (strip_id_info id)
232 | bind <- tidy_binds,
233 id <- bindersOf bind,
234 isExternalName (idName id)]
237 | omit_iface_prags = id `setIdInfo` vanillaIdInfo
239 -- If the interface file has no pragma info then discard all
242 -- This is not so important for *this* module, but it's
243 -- vital for ghc --make:
244 -- subsequent compilations must not see (e.g.) the arity if
245 -- the interface file does not contain arity
246 -- If they do, they'll exploit the arity; then the arity might
247 -- change, but the iface file doesn't change => recompilation
248 -- does not happen => disaster
250 -- This IdInfo will live long-term in the Id => vanillaIdInfo makes
251 -- a conservative assumption about Caf-hood
253 -- We're not worried about occurrences of these Ids in unfoldings,
254 -- because in OmitInterfacePragmas mode we're stripping all the
255 -- unfoldings anyway.
257 -- We keep implicit Ids, because they won't appear
258 -- in the bindings from which final_ids are derived!
259 keep_it (AnId id) = isImplicitId id -- Remove all Ids except implicit ones
260 keep_it other = True -- Keep all TyCons and Classes
264 findExternalRules :: Bool -- Omit interface pragmas
266 -> [IdCoreRule] -- Orphan rules
267 -> IdEnv a -- Ids that are exported, so we need their rules
269 -- The complete rules are gotten by combining
270 -- a) the orphan rules
271 -- b) rules embedded in the top-level Ids
272 findExternalRules omit_iface_prags binds orphan_rules ext_ids
273 | omit_iface_prags = []
275 = filter (not . internal_rule) (orphan_rules ++ local_rules)
278 | id <- bindersOfBinds binds,
279 id `elemVarEnv` ext_ids,
280 rule <- idCoreRules id
282 internal_rule (IdCoreRule id is_orphan rule)
284 -- We can't print builtin rules in interface files
285 -- Since they are built in, an importing module
286 -- will have access to them anyway
288 || (not is_orphan && internal_id id)
289 -- Rule for an Id in this module; internal if the
290 -- Id is not exported
292 || any internal_id (varSetElems (ruleLhsFreeIds rule))
293 -- Don't export a rule whose LHS mentions an Id that
294 -- is completely internal (i.e. not visible to an
297 internal_id id = not (id `elemVarEnv` ext_ids)
300 %************************************************************************
302 \subsection{Step 1: finding externals}
304 %************************************************************************
307 findExternalSet :: Bool -- Omit interface pragmas
309 -> IdEnv Bool -- In domain => external
310 -- Range = True <=> show unfolding
311 -- Step 1 from the notes above
312 findExternalSet omit_iface_prags binds
313 = foldr find emptyVarEnv binds
315 find (NonRec id rhs) needed
316 | need_id needed id = addExternal omit_iface_prags (id,rhs) needed
318 find (Rec prs) needed = find_prs prs needed
320 -- For a recursive group we have to look for a fixed point
322 | null needed_prs = needed
323 | otherwise = find_prs other_prs new_needed
325 (needed_prs, other_prs) = partition (need_pr needed) prs
326 new_needed = foldr (addExternal omit_iface_prags) needed needed_prs
328 -- The 'needed' set contains the Ids that are needed by earlier
329 -- interface file emissions. If the Id isn't in this set, and isn't
330 -- exported, there's no need to emit anything
331 need_id needed_set id = id `elemVarEnv` needed_set || isExportedId id
332 need_pr needed_set (id,rhs) = need_id needed_set id
334 addExternal :: Bool -> (Id,CoreExpr) -> IdEnv Bool -> IdEnv Bool
335 -- The Id is needed; extend the needed set
336 -- with it and its dependents (free vars etc)
337 addExternal omit_iface_prags (id,rhs) needed
338 = extendVarEnv (foldVarSet add_occ needed new_needed_ids)
341 add_occ id needed = extendVarEnv needed id False
342 -- "False" because we don't know we need the Id's unfolding
343 -- We'll override it later when we find the binding site
345 new_needed_ids | omit_iface_prags = emptyVarSet
346 | otherwise = worker_ids `unionVarSet`
347 unfold_ids `unionVarSet`
351 dont_inline = isNeverActive (inlinePragInfo idinfo)
352 loop_breaker = isLoopBreaker (occInfo idinfo)
353 bottoming_fn = isBottomingSig (newStrictnessInfo idinfo `orElse` topSig)
354 spec_ids = rulesRhsFreeVars (specInfo idinfo)
355 worker_info = workerInfo idinfo
357 -- Stuff to do with the Id's unfolding
358 -- The simplifier has put an up-to-date unfolding
359 -- in the IdInfo, but the RHS will do just as well
360 unfolding = unfoldingInfo idinfo
361 rhs_is_small = not (neverUnfold unfolding)
363 -- We leave the unfolding there even if there is a worker
364 -- In GHCI the unfolding is used by importers
365 -- When writing an interface file, we omit the unfolding
366 -- if there is a worker
367 show_unfold = not bottoming_fn && -- Not necessary
370 rhs_is_small -- Small enough
372 unfold_ids | show_unfold = exprSomeFreeVars isLocalId rhs
373 | otherwise = emptyVarSet
375 worker_ids = case worker_info of
376 HasWorker work_id _ -> unitVarSet work_id
377 otherwise -> emptyVarSet
381 %************************************************************************
383 \subsection{Step 2: top-level tidying}
385 %************************************************************************
389 -- TopTidyEnv: when tidying we need to know
390 -- * nc_var: The NameCache, containing a unique supply and any pre-ordained Names.
391 -- These may have arisen because the
392 -- renamer read in an interface file mentioning M.$wf, say,
393 -- and assigned it unique r77. If, on this compilation, we've
394 -- invented an Id whose name is $wf (but with a different unique)
395 -- we want to rename it to have unique r77, so that we can do easy
396 -- comparisons with stuff from the interface file
398 -- * occ_env: The TidyOccEnv, which tells us which local occurrences
401 -- * subst_env: A Var->Var mapping that substitutes the new Var for the old
403 tidyTopBinds :: DynFlags
405 -> IORef NameCache -- For allocating new unique names
406 -> IdEnv Bool -- Domain = Ids that should be external
407 -- True <=> their unfolding is external too
408 -> TidyEnv -> [CoreBind]
409 -> IO (TidyEnv, [CoreBind])
410 tidyTopBinds dflags mod nc_var ext_ids tidy_env []
411 = return (tidy_env, [])
413 tidyTopBinds dflags mod nc_var ext_ids tidy_env (b:bs)
414 = do { (tidy_env1, b') <- tidyTopBind dflags mod nc_var ext_ids tidy_env b
415 ; (tidy_env2, bs') <- tidyTopBinds dflags mod nc_var ext_ids tidy_env1 bs
416 ; return (tidy_env2, b':bs') }
418 ------------------------
419 tidyTopBind :: DynFlags
421 -> IORef NameCache -- For allocating new unique names
422 -> IdEnv Bool -- Domain = Ids that should be external
423 -- True <=> their unfolding is external too
424 -> TidyEnv -> CoreBind
425 -> IO (TidyEnv, CoreBind)
427 tidyTopBind dflags mod nc_var ext_ids tidy_env1@(occ_env1,subst1) (NonRec bndr rhs)
428 = do { (occ_env2, name') <- tidyTopName mod nc_var ext_ids occ_env1 bndr
429 ; let { (bndr', rhs') = tidyTopPair ext_ids tidy_env2 caf_info name' (bndr, rhs)
430 ; subst2 = extendVarEnv subst1 bndr bndr'
431 ; tidy_env2 = (occ_env2, subst2) }
432 ; return (tidy_env2, NonRec bndr' rhs') }
434 caf_info = hasCafRefs dflags subst1 (idArity bndr) rhs
436 tidyTopBind dflags mod nc_var ext_ids tidy_env1@(occ_env1,subst1) (Rec prs)
437 = do { (occ_env2, names') <- tidyTopNames mod nc_var ext_ids occ_env1 bndrs
438 ; let { prs' = zipWith (tidyTopPair ext_ids tidy_env2 caf_info)
440 ; subst2 = extendVarEnvList subst1 (bndrs `zip` map fst prs')
441 ; tidy_env2 = (occ_env2, subst2) }
442 ; return (tidy_env2, Rec prs') }
446 -- the CafInfo for a recursive group says whether *any* rhs in
447 -- the group may refer indirectly to a CAF (because then, they all do).
449 | or [ mayHaveCafRefs (hasCafRefs dflags subst1 (idArity bndr) rhs)
450 | (bndr,rhs) <- prs ] = MayHaveCafRefs
451 | otherwise = NoCafRefs
453 --------------------------------------------------------------------
455 -- This is where we set names to local/global based on whether they really are
456 -- externally visible (see comment at the top of this module). If the name
457 -- was previously local, we have to give it a unique occurrence name if
458 -- we intend to externalise it.
459 tidyTopNames mod nc_var ext_ids occ_env [] = return (occ_env, [])
460 tidyTopNames mod nc_var ext_ids occ_env (id:ids)
461 = do { (occ_env1, name) <- tidyTopName mod nc_var ext_ids occ_env id
462 ; (occ_env2, names) <- tidyTopNames mod nc_var ext_ids occ_env1 ids
463 ; return (occ_env2, name:names) }
465 tidyTopName :: Module -> IORef NameCache -> VarEnv Bool -> TidyOccEnv
466 -> Id -> IO (TidyOccEnv, Name)
467 tidyTopName mod nc_var ext_ids occ_env id
468 | global && internal = return (occ_env, localiseName name)
470 | global && external = return (occ_env, name)
471 -- Global names are assumed to have been allocated by the renamer,
472 -- so they already have the "right" unique
473 -- And it's a system-wide unique too
475 -- Now we get to the real reason that all this is in the IO Monad:
476 -- we have to update the name cache in a nice atomic fashion
478 | local && internal = do { nc <- readIORef nc_var
479 ; let (nc', new_local_name) = mk_new_local nc
480 ; writeIORef nc_var nc'
481 ; return (occ_env', new_local_name) }
482 -- Even local, internal names must get a unique occurrence, because
483 -- if we do -split-objs we externalise the name later, in the code generator
485 -- Similarly, we must make sure it has a system-wide Unique, because
486 -- the byte-code generator builds a system-wide Name->BCO symbol table
488 | local && external = do { nc <- readIORef nc_var
489 ; let (nc', new_external_name) = mk_new_external nc
490 ; writeIORef nc_var nc'
491 ; return (occ_env', new_external_name) }
494 external = id `elemVarEnv` ext_ids
495 global = isExternalName name
497 internal = not external
498 mb_parent = nameParent_maybe name
499 loc = nameSrcLoc name
501 (occ_env', occ') = tidyOccName occ_env (nameOccName name)
503 mk_new_local nc = (nc { nsUniqs = us2 }, mkInternalName uniq occ' loc)
505 (us1, us2) = splitUniqSupply (nsUniqs nc)
506 uniq = uniqFromSupply us1
508 mk_new_external nc = allocateGlobalBinder nc mod occ' mb_parent loc
509 -- If we want to externalise a currently-local name, check
510 -- whether we have already assigned a unique for it.
511 -- If so, use it; if not, extend the table.
512 -- All this is done by allcoateGlobalBinder.
513 -- This is needed when *re*-compiling a module in GHCi; we want to
514 -- use the same name for externally-visible things as we did before.
517 -----------------------------------------------------------
518 tidyTopPair :: VarEnv Bool
519 -> TidyEnv -- The TidyEnv is used to tidy the IdInfo
520 -- It is knot-tied: don't look at it!
523 -> (Id, CoreExpr) -- Binder and RHS before tidying
525 -- This function is the heart of Step 2
526 -- The rec_tidy_env is the one to use for the IdInfo
527 -- It's necessary because when we are dealing with a recursive
528 -- group, a variable late in the group might be mentioned
529 -- in the IdInfo of one early in the group
531 tidyTopPair ext_ids rhs_tidy_env caf_info name' (bndr, rhs)
532 = ASSERT(isLocalId bndr) -- "all Ids defined in this module are local
533 -- until the CoreTidy phase" --GHC comentary
536 bndr' = mkVanillaGlobal name' ty' idinfo'
537 ty' = tidyTopType (idType bndr)
538 rhs' = tidyExpr rhs_tidy_env rhs
539 idinfo' = tidyTopIdInfo rhs_tidy_env (isJust maybe_external)
540 (idInfo bndr) unfold_info arity
543 -- Expose an unfolding if ext_ids tells us to
544 -- Remember that ext_ids maps an Id to a Bool:
545 -- True to show the unfolding, False to hide it
546 maybe_external = lookupVarEnv ext_ids bndr
547 show_unfold = maybe_external `orElse` False
548 unfold_info | show_unfold = mkTopUnfolding rhs'
549 | otherwise = noUnfolding
551 -- Usually the Id will have an accurate arity on it, because
552 -- the simplifier has just run, but not always.
553 -- One case I found was when the last thing the simplifier
554 -- did was to let-bind a non-atomic argument and then float
555 -- it to the top level. So it seems more robust just to
557 arity = exprArity rhs
560 -- tidyTopIdInfo creates the final IdInfo for top-level
561 -- binders. There are two delicate pieces:
563 -- * Arity. After CoreTidy, this arity must not change any more.
564 -- Indeed, CorePrep must eta expand where necessary to make
565 -- the manifest arity equal to the claimed arity.
567 -- * CAF info. This must also remain valid through to code generation.
568 -- We add the info here so that it propagates to all
569 -- occurrences of the binders in RHSs, and hence to occurrences in
570 -- unfoldings, which are inside Ids imported by GHCi. Ditto RULES.
571 -- CoreToStg makes use of this when constructing SRTs.
573 tidyTopIdInfo tidy_env is_external idinfo unfold_info arity caf_info
574 | not is_external -- For internal Ids (not externally visible)
575 = vanillaIdInfo -- we only need enough info for code generation
576 -- Arity and strictness info are enough;
577 -- c.f. CoreTidy.tidyLetBndr
578 `setCafInfo` caf_info
580 `setAllStrictnessInfo` newStrictnessInfo idinfo
582 | otherwise -- Externally-visible Ids get the whole lot
584 `setCafInfo` caf_info
586 `setAllStrictnessInfo` newStrictnessInfo idinfo
587 `setInlinePragInfo` inlinePragInfo idinfo
588 `setUnfoldingInfo` unfold_info
589 `setWorkerInfo` tidyWorker tidy_env (workerInfo idinfo)
590 -- NB: we throw away the Rules
591 -- They have already been extracted by findExternalRules
595 ------------ Worker --------------
596 tidyWorker tidy_env (HasWorker work_id wrap_arity)
597 = HasWorker (tidyVarOcc tidy_env work_id) wrap_arity
598 tidyWorker tidy_env other
602 %************************************************************************
604 \subsection{Figuring out CafInfo for an expression}
606 %************************************************************************
608 hasCafRefs decides whether a top-level closure can point into the dynamic heap.
609 We mark such things as `MayHaveCafRefs' because this information is
610 used to decide whether a particular closure needs to be referenced
613 There are two reasons for setting MayHaveCafRefs:
614 a) The RHS is a CAF: a top-level updatable thunk.
615 b) The RHS refers to something that MayHaveCafRefs
617 Possible improvement: In an effort to keep the number of CAFs (and
618 hence the size of the SRTs) down, we could also look at the expression and
619 decide whether it requires a small bounded amount of heap, so we can ignore
620 it as a CAF. In these cases however, we would need to use an additional
621 CAF list to keep track of non-collectable CAFs.
624 hasCafRefs :: DynFlags -> VarEnv Var -> Arity -> CoreExpr -> CafInfo
625 hasCafRefs dflags p arity expr
626 | is_caf || mentions_cafs = MayHaveCafRefs
627 | otherwise = NoCafRefs
629 mentions_cafs = isFastTrue (cafRefs p expr)
630 is_caf = not (arity > 0 || rhsIsStatic dflags expr)
631 -- NB. we pass in the arity of the expression, which is expected
632 -- to be calculated by exprArity. This is because exprArity
633 -- knows how much eta expansion is going to be done by
634 -- CorePrep later on, and we don't want to duplicate that
635 -- knowledge in rhsIsStatic below.
638 -- imported Ids first:
639 | not (isLocalId id) = fastBool (mayHaveCafRefs (idCafInfo id))
640 -- now Ids local to this module:
642 case lookupVarEnv p id of
643 Just id' -> fastBool (mayHaveCafRefs (idCafInfo id'))
644 Nothing -> fastBool False
646 cafRefs p (Lit l) = fastBool False
647 cafRefs p (App f a) = fastOr (cafRefs p f) (cafRefs p) a
648 cafRefs p (Lam x e) = cafRefs p e
649 cafRefs p (Let b e) = fastOr (cafRefss p (rhssOfBind b)) (cafRefs p) e
650 cafRefs p (Case e bndr _ alts) = fastOr (cafRefs p e) (cafRefss p) (rhssOfAlts alts)
651 cafRefs p (Note n e) = cafRefs p e
652 cafRefs p (Type t) = fastBool False
654 cafRefss p [] = fastBool False
655 cafRefss p (e:es) = fastOr (cafRefs p e) (cafRefss p) es
657 -- hack for lazy-or over FastBool.
658 fastOr a f x = fastBool (isFastTrue a || isFastTrue (f x))