2 % (c) The AQUA Project, Glasgow University, 1998
4 \section[StdIdInfo]{Standard unfoldings}
6 This module contains definitions for the IdInfo for things that
7 have a standard form, namely:
11 * method and superclass selectors
12 * primitive operations
16 mkDictFunId, mkDefaultMethodId,
21 mkPrimOpId, mkFCallId,
23 mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
24 mkUnpackCase, mkProductBox,
26 -- And some particular Ids; see below for why they are wired in
27 wiredInIds, ghcPrimIds,
28 unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId,
29 lazyId, lazyIdUnfolding, lazyIdKey,
32 rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
33 nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
34 pAT_ERROR_ID, eRROR_ID,
39 #include "HsVersions.h"
42 import BasicTypes ( Arity, StrictnessMark(..), isMarkedUnboxed, isMarkedStrict )
43 import Rules ( mkSpecInfo )
44 import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy,
45 realWorldStatePrimTy, addrPrimTy
47 import TysWiredIn ( charTy, mkListTy )
48 import PrelRules ( primOpRules )
49 import Type ( TyThing(..), mkForAllTy, tyVarsOfTypes,
50 newTyConInstRhs, mkTopTvSubst, substTyVar,
51 substTys, zipTopTvSubst )
52 import TcGadt ( gadtRefine, refineType, emptyRefinement )
53 import HsBinds ( HsWrapper(..), isIdHsWrapper )
54 import Coercion ( mkSymCoercion, mkUnsafeCoercion, isEqPred )
55 import TcType ( Type, ThetaType, mkDictTy, mkPredTys, mkPredTy,
56 mkTyConApp, mkTyVarTys, mkClassPred, isPredTy,
57 mkFunTys, mkFunTy, mkSigmaTy, tcSplitSigmaTy, tcEqType,
58 isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType,
59 tcSplitFunTys, tcSplitForAllTys, dataConsStupidTheta
61 import CoreUtils ( exprType, dataConOrigInstPat, mkCoerce )
62 import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding )
63 import Literal ( nullAddrLit, mkStringLit )
64 import TyCon ( TyCon, isNewTyCon, tyConTyVars, tyConDataCons,
66 tyConStupidTheta, isProductTyCon, isDataTyCon,
67 isRecursiveTyCon, isFamInstTyCon,
68 tyConFamInst_maybe, tyConFamilyCoercion_maybe,
70 import Class ( Class, classTyCon, classSelIds )
71 import Var ( Id, TyVar, Var, setIdType )
72 import VarSet ( isEmptyVarSet, subVarSet, varSetElems )
73 import Name ( mkFCallName, mkWiredInName, Name, BuiltInSyntax(..))
74 import OccName ( mkOccNameFS, varName )
75 import PrimOp ( PrimOp, primOpSig, primOpOcc, primOpTag )
76 import ForeignCall ( ForeignCall )
77 import DataCon ( DataCon, DataConIds(..), dataConTyCon,
79 dataConFieldLabels, dataConRepArity, dataConResTys,
80 dataConRepArgTys, dataConRepType, dataConFullSig,
81 dataConStrictMarks, dataConExStricts,
82 splitProductType, isVanillaDataCon, dataConFieldType,
85 import Id ( idType, mkGlobalId, mkVanillaGlobal, mkSysLocal,
86 mkTemplateLocals, mkTemplateLocalsNum, mkExportedLocalId,
87 mkTemplateLocal, idName
89 import IdInfo ( IdInfo, noCafIdInfo, setUnfoldingInfo,
90 setArityInfo, setSpecInfo, setCafInfo,
91 setAllStrictnessInfo, vanillaIdInfo,
92 GlobalIdDetails(..), CafInfo(..)
94 import NewDemand ( mkStrictSig, DmdResult(..),
95 mkTopDmdType, topDmd, evalDmd, lazyDmd, retCPR,
96 Demand(..), Demands(..) )
97 import DmdAnal ( dmdAnalTopRhs )
99 import Unique ( mkBuiltinUnique, mkPrimOpIdUnique )
102 import Util ( dropList, isSingleton )
105 import ListSetOps ( assoc, minusList )
108 %************************************************************************
110 \subsection{Wired in Ids}
112 %************************************************************************
116 = [ -- These error-y things are wired in because we don't yet have
117 -- a way to express in an interface file that the result type variable
118 -- is 'open'; that is can be unified with an unboxed type
120 -- [The interface file format now carry such information, but there's
121 -- no way yet of expressing at the definition site for these
122 -- error-reporting functions that they have an 'open'
123 -- result type. -- sof 1/99]
125 eRROR_ID, -- This one isn't used anywhere else in the compiler
126 -- But we still need it in wiredInIds so that when GHC
127 -- compiles a program that mentions 'error' we don't
128 -- import its type from the interface file; we just get
129 -- the Id defined here. Which has an 'open-tyvar' type.
132 iRREFUT_PAT_ERROR_ID,
133 nON_EXHAUSTIVE_GUARDS_ERROR_ID,
134 nO_METHOD_BINDING_ERROR_ID,
141 -- These Ids are exported from GHC.Prim
143 = [ -- These can't be defined in Haskell, but they have
144 -- perfectly reasonable unfoldings in Core
152 %************************************************************************
154 \subsection{Data constructors}
156 %************************************************************************
158 The wrapper for a constructor is an ordinary top-level binding that evaluates
159 any strict args, unboxes any args that are going to be flattened, and calls
162 We're going to build a constructor that looks like:
164 data (Data a, C b) => T a b = T1 !a !Int b
167 \d1::Data a, d2::C b ->
168 \p q r -> case p of { p ->
170 Con T1 [a,b] [p,q,r]}}
174 * d2 is thrown away --- a context in a data decl is used to make sure
175 one *could* construct dictionaries at the site the constructor
176 is used, but the dictionary isn't actually used.
178 * We have to check that we can construct Data dictionaries for
179 the types a and Int. Once we've done that we can throw d1 away too.
181 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
182 all that matters is that the arguments are evaluated. "seq" is
183 very careful to preserve evaluation order, which we don't need
186 You might think that we could simply give constructors some strictness
187 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
188 But we don't do that because in the case of primops and functions strictness
189 is a *property* not a *requirement*. In the case of constructors we need to
190 do something active to evaluate the argument.
192 Making an explicit case expression allows the simplifier to eliminate
193 it in the (common) case where the constructor arg is already evaluated.
195 [Wrappers for data instance tycons]
196 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
197 In the case of data instances, the wrapper also applies the coercion turning
198 the representation type into the family instance type to cast the result of
199 the wrapper. For example, consider the declarations
201 data family Map k :: * -> *
202 data instance Map (a, b) v = MapPair (Map a (Pair b v))
204 The tycon to which the datacon MapPair belongs gets a unique internal name of
205 the form :R123Map, and we call it the representation tycon. In contrast, Map
206 is the family tycon (accessible via tyConFamInst_maybe). The wrapper and work
207 of MapPair get the types
209 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
210 $wMapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
212 which implies that the wrapper code will have to apply the coercion moving
213 between representation and family type. It is accessible via
214 tyConFamilyCoercion_maybe and has kind
216 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
218 This coercion is conditionally applied by wrapFamInstBody.
221 mkDataConIds :: Name -> Name -> DataCon -> DataConIds
222 mkDataConIds wrap_name wkr_name data_con
224 = DCIds Nothing nt_work_id -- Newtype, only has a worker
226 | any isMarkedStrict all_strict_marks -- Algebraic, needs wrapper
227 || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
228 || isFamInstTyCon tycon -- depends on this test
229 = DCIds (Just alg_wrap_id) wrk_id
231 | otherwise -- Algebraic, no wrapper
232 = DCIds Nothing wrk_id
234 (univ_tvs, ex_tvs, eq_spec,
235 theta, orig_arg_tys) = dataConFullSig data_con
236 tycon = dataConTyCon data_con
238 ----------- Wrapper --------------
239 -- We used to include the stupid theta in the wrapper's args
240 -- but now we don't. Instead the type checker just injects these
241 -- extra constraints where necessary.
242 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
243 subst = mkTopTvSubst eq_spec
244 famSubst = ASSERT( length (tyConTyVars tycon ) ==
245 length (mkTyVarTys univ_tvs) )
246 zipTopTvSubst (tyConTyVars tycon) (mkTyVarTys univ_tvs)
247 -- substitution mapping the type constructor's type
248 -- arguments to the universals of the data constructor
249 -- (crucial when type checking interfaces)
250 dict_tys = mkPredTys theta
251 result_ty_args = map (substTyVar subst) univ_tvs
252 result_ty = case tyConFamInst_maybe tycon of
253 -- ordinary constructor
254 Nothing -> mkTyConApp tycon result_ty_args
255 -- family instance constructor
258 mkTyConApp familyTyCon ( substTys subst
261 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys dict_tys $
262 mkFunTys orig_arg_tys $ result_ty
263 -- NB: watch out here if you allow user-written equality
264 -- constraints in data constructor signatures
266 ----------- Worker (algebraic data types only) --------------
267 -- The *worker* for the data constructor is the function that
268 -- takes the representation arguments and builds the constructor.
269 wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
270 (dataConRepType data_con) wkr_info
272 wkr_arity = dataConRepArity data_con
273 wkr_info = noCafIdInfo
274 `setArityInfo` wkr_arity
275 `setAllStrictnessInfo` Just wkr_sig
276 `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
279 wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
280 -- Notice that we do *not* say the worker is strict
281 -- even if the data constructor is declared strict
282 -- e.g. data T = MkT !(Int,Int)
283 -- Why? Because the *wrapper* is strict (and its unfolding has case
284 -- expresssions that do the evals) but the *worker* itself is not.
285 -- If we pretend it is strict then when we see
286 -- case x of y -> $wMkT y
287 -- the simplifier thinks that y is "sure to be evaluated" (because
288 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
290 -- When the simplifer sees a pattern
291 -- case e of MkT x -> ...
292 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
293 -- but that's fine... dataConRepStrictness comes from the data con
294 -- not from the worker Id.
296 cpr_info | isProductTyCon tycon &&
299 wkr_arity <= mAX_CPR_SIZE = retCPR
301 -- RetCPR is only true for products that are real data types;
302 -- that is, not unboxed tuples or [non-recursive] newtypes
304 ----------- Workers for newtypes --------------
305 nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
306 nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
307 `setArityInfo` 1 -- Arity 1
308 `setUnfoldingInfo` newtype_unf
309 newtype_unf = ASSERT( isVanillaDataCon data_con &&
310 isSingleton orig_arg_tys )
311 -- No existentials on a newtype, but it can have a context
312 -- e.g. newtype Eq a => T a = MkT (...)
313 mkCompulsoryUnfolding $
314 mkLams wrap_tvs $ Lam id_arg1 $
315 wrapNewTypeBody tycon result_ty_args
318 id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
320 ----------- Wrappers for algebraic data types --------------
321 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
322 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
323 `setArityInfo` alg_arity
324 -- It's important to specify the arity, so that partial
325 -- applications are treated as values
326 `setUnfoldingInfo` alg_unf
327 `setAllStrictnessInfo` Just wrap_sig
329 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
330 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
331 arg_dmds = map mk_dmd all_strict_marks
332 mk_dmd str | isMarkedStrict str = evalDmd
333 | otherwise = lazyDmd
334 -- The Cpr info can be important inside INLINE rhss, where the
335 -- wrapper constructor isn't inlined.
336 -- And the argument strictness can be important too; we
337 -- may not inline a contructor when it is partially applied.
339 -- data W = C !Int !Int !Int
340 -- ...(let w = C x in ...(w p q)...)...
341 -- we want to see that w is strict in its two arguments
343 alg_unf = mkTopUnfolding $ Note InlineMe $
345 mkLams dict_args $ mkLams id_args $
346 foldr mk_case con_app
347 (zip (dict_args ++ id_args) all_strict_marks)
350 con_app _ rep_ids = wrapFamInstBody tycon result_ty_args $
351 Var wrk_id `mkTyApps` result_ty_args
353 `mkTyApps` map snd eq_spec
354 `mkVarApps` reverse rep_ids
356 (dict_args,i2) = mkLocals 1 dict_tys
357 (id_args,i3) = mkLocals i2 orig_arg_tys
361 :: (Id, StrictnessMark) -- Arg, strictness
362 -> (Int -> [Id] -> CoreExpr) -- Body
363 -> Int -- Next rep arg id
364 -> [Id] -- Rep args so far, reversed
366 mk_case (arg,strict) body i rep_args
368 NotMarkedStrict -> body i (arg:rep_args)
370 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
372 Case (Var arg) arg result_ty [(DEFAULT,[], body i (arg:rep_args))]
375 -> unboxProduct i (Var arg) (idType arg) the_body
377 the_body i con_args = body i (reverse con_args ++ rep_args)
379 mAX_CPR_SIZE :: Arity
381 -- We do not treat very big tuples as CPR-ish:
382 -- a) for a start we get into trouble because there aren't
383 -- "enough" unboxed tuple types (a tiresome restriction,
385 -- b) more importantly, big unboxed tuples get returned mainly
386 -- on the stack, and are often then allocated in the heap
387 -- by the caller. So doing CPR for them may in fact make
390 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
394 -- If the type constructor is a representation type of a data instance, wrap
395 -- the expression into a cast adjusting the expression type, which is an
396 -- instance of the representation type, to the corresponding instance of the
397 -- family instance type.
399 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
400 wrapFamInstBody tycon args result_expr
401 | Just co_con <- tyConFamilyCoercion_maybe tycon
402 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
408 %************************************************************************
410 \subsection{Record selectors}
412 %************************************************************************
414 We're going to build a record selector unfolding that looks like this:
416 data T a b c = T1 { ..., op :: a, ...}
417 | T2 { ..., op :: a, ...}
420 sel = /\ a b c -> \ d -> case d of
425 Similarly for newtypes
427 newtype N a = MkN { unN :: a->a }
430 unN n = coerce (a->a) n
432 We need to take a little care if the field has a polymorphic type:
434 data R = R { f :: forall a. a->a }
438 f :: forall a. R -> a -> a
439 f = /\ a \ r = case r of
442 (not f :: R -> forall a. a->a, which gives the type inference mechanism
443 problems at call sites)
445 Similarly for (recursive) newtypes
447 newtype N = MkN { unN :: forall a. a->a }
449 unN :: forall b. N -> b -> b
450 unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
453 Note [Naughty record selectors]
454 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
455 A "naughty" field is one for which we can't define a record
456 selector, because an existential type variable would escape. For example:
457 data T = forall a. MkT { x,y::a }
458 We obviously can't define
460 Nevertheless we *do* put a RecordSelId into the type environment
461 so that if the user tries to use 'x' as a selector we can bleat
462 helpfully, rather than saying unhelpfully that 'x' is not in scope.
463 Hence the sel_naughty flag, to identify record selectors that don't really exist.
465 In general, a field is naughty if its type mentions a type variable that
466 isn't in the result type of the constructor.
468 Note [GADT record selectors]
469 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
470 For GADTs, we require that all constructors with a common field 'f' have the same
471 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
474 T1 { f :: a } :: T [a]
475 T2 { f :: a, y :: b } :: T [a]
476 and now the selector takes that type as its argument:
477 f :: forall a. T [a] -> a
481 Note the forall'd tyvars of the selector are just the free tyvars
482 of the result type; there may be other tyvars in the constructor's
483 type (e.g. 'b' in T2).
487 -- Steps for handling "naughty" vs "non-naughty" selectors:
488 -- 1. Determine naughtiness by comparing field type vs result type
489 -- 2. Install naughty ones with selector_ty of type _|_ and fill in mzero for info
490 -- 3. If it's not naughty, do the normal plan.
492 mkRecordSelId :: TyCon -> FieldLabel -> Id
493 mkRecordSelId tycon field_label
494 -- Assumes that all fields with the same field label have the same type
495 | is_naughty = naughty_id
498 is_naughty = not (tyVarsOfType field_ty `subVarSet` res_tv_set)
499 sel_id_details = RecordSelId tycon field_label is_naughty
501 -- Escapist case here for naughty construcotrs
502 -- We give it no IdInfo, and a type of forall a.a (never looked at)
503 naughty_id = mkGlobalId sel_id_details field_label forall_a_a noCafIdInfo
504 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
506 -- Normal case starts here
507 sel_id = mkGlobalId sel_id_details field_label selector_ty info
508 data_cons = tyConDataCons tycon
509 data_cons_w_field = filter has_field data_cons -- Can't be empty!
510 has_field con = field_label `elem` dataConFieldLabels con
512 con1 = head data_cons_w_field
513 res_tys = dataConResTys con1
514 res_tv_set = tyVarsOfTypes res_tys
515 res_tvs = varSetElems res_tv_set
516 data_ty = mkTyConApp tycon res_tys
517 field_ty = dataConFieldType con1 field_label
519 -- *Very* tiresomely, the selectors are (unnecessarily!) overloaded over
520 -- just the dictionaries in the types of the constructors that contain
521 -- the relevant field. [The Report says that pattern matching on a
522 -- constructor gives the same constraints as applying it.] Urgh.
524 -- However, not all data cons have all constraints (because of
525 -- BuildTyCl.mkDataConStupidTheta). So we need to find all the data cons
526 -- involved in the pattern match and take the union of their constraints.
527 stupid_dict_tys = mkPredTys (dataConsStupidTheta data_cons_w_field)
528 n_stupid_dicts = length stupid_dict_tys
530 (field_tyvars,pre_field_theta,field_tau) = tcSplitSigmaTy field_ty
532 field_theta = filter (not . isEqPred) pre_field_theta
533 field_dict_tys = mkPredTys field_theta
534 n_field_dict_tys = length field_dict_tys
535 -- If the field has a universally quantified type we have to
536 -- be a bit careful. Suppose we have
537 -- data R = R { op :: forall a. Foo a => a -> a }
538 -- Then we can't give op the type
539 -- op :: R -> forall a. Foo a => a -> a
540 -- because the typechecker doesn't understand foralls to the
541 -- right of an arrow. The "right" type to give it is
542 -- op :: forall a. Foo a => R -> a -> a
543 -- But then we must generate the right unfolding too:
544 -- op = /\a -> \dfoo -> \ r ->
547 -- Note that this is exactly the type we'd infer from a user defn
551 selector_ty = mkForAllTys res_tvs $ mkForAllTys field_tyvars $
552 mkFunTys stupid_dict_tys $ mkFunTys field_dict_tys $
553 mkFunTy data_ty field_tau
555 arity = 1 + n_stupid_dicts + n_field_dict_tys
557 (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
558 -- Use the demand analyser to work out strictness.
559 -- With all this unpackery it's not easy!
562 `setCafInfo` caf_info
564 `setUnfoldingInfo` mkTopUnfolding rhs_w_str
565 `setAllStrictnessInfo` Just strict_sig
567 -- Allocate Ids. We do it a funny way round because field_dict_tys is
568 -- almost always empty. Also note that we use max_dict_tys
569 -- rather than n_dict_tys, because the latter gives an infinite loop:
570 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
571 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
572 stupid_dict_ids = mkTemplateLocalsNum 1 stupid_dict_tys
573 max_stupid_dicts = length (tyConStupidTheta tycon)
574 field_dict_base = max_stupid_dicts + 1
575 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
576 dict_id_base = field_dict_base + n_field_dict_tys
577 data_id = mkTemplateLocal dict_id_base data_ty
578 arg_base = dict_id_base + 1
580 the_alts :: [CoreAlt]
581 the_alts = map mk_alt data_cons_w_field -- Already sorted by data-con
582 no_default = length data_cons == length data_cons_w_field -- No default needed
584 default_alt | no_default = []
585 | otherwise = [(DEFAULT, [], error_expr)]
587 -- The default branch may have CAF refs, because it calls recSelError etc.
588 caf_info | no_default = NoCafRefs
589 | otherwise = MayHaveCafRefs
591 sel_rhs = mkLams res_tvs $ mkLams field_tyvars $
592 mkLams stupid_dict_ids $ mkLams field_dict_ids $
593 Lam data_id $ mk_result sel_body
595 -- NB: A newtype always has a vanilla DataCon; no existentials etc
596 -- res_tys will simply be the dataConUnivTyVars
597 sel_body | isNewTyCon tycon = unwrapNewTypeBody tycon res_tys (Var data_id)
598 | otherwise = Case (Var data_id) data_id field_ty (default_alt ++ the_alts)
600 mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
601 -- We pull the field lambdas to the top, so we need to
602 -- apply them in the body. For example:
603 -- data T = MkT { foo :: forall a. a->a }
605 -- foo :: forall a. T -> a -> a
606 -- foo = /\a. \t:T. case t of { MkT f -> f a }
609 = ASSERT2( res_ty `tcEqType` field_ty, ppr data_con $$ ppr res_ty $$ ppr field_ty )
610 mkReboxingAlt rebox_uniqs data_con (ex_tvs ++ co_tvs ++ arg_vs) rhs
612 -- get pattern binders with types appropriately instantiated
613 arg_uniqs = map mkBuiltinUnique [arg_base..]
614 (ex_tvs, co_tvs, arg_vs) = dataConOrigInstPat arg_uniqs data_con res_tys
616 rebox_base = arg_base + length ex_tvs + length co_tvs + length arg_vs
617 rebox_uniqs = map mkBuiltinUnique [rebox_base..]
619 -- data T :: *->* where T1 { fld :: Maybe b } -> T [b]
620 -- Hence T1 :: forall a b. (a=[b]) => b -> T a
621 -- fld :: forall b. T [b] -> Maybe b
622 -- fld = /\b.\(t:T[b]). case t of
623 -- T1 b' (c : [b]=[b']) (x:Maybe b')
624 -- -> x `cast` Maybe (sym (right c))
626 Succeeded refinement = gadtRefine emptyRefinement ex_tvs co_tvs
627 (co_fn, res_ty) = refineType refinement (idType the_arg_id)
628 -- Generate the refinement for b'=b,
629 -- and apply to (Maybe b'), to get (Maybe b)
632 WpCo co -> Cast (Var the_arg_id) co
633 id_co -> ASSERT(isIdHsWrapper id_co) Var the_arg_id
635 field_vs = filter (not . isPredTy . idType) arg_vs
636 the_arg_id = assoc "mkRecordSelId:mk_alt" (field_lbls `zip` field_vs) field_label
637 field_lbls = dataConFieldLabels data_con
639 error_expr = mkRuntimeErrorApp rEC_SEL_ERROR_ID field_ty full_msg
640 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
642 -- unbox a product type...
643 -- we will recurse into newtypes, casting along the way, and unbox at the
644 -- first product data constructor we find. e.g.
646 -- data PairInt = PairInt Int Int
647 -- newtype S = MkS PairInt
650 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
651 -- ids, we get (modulo int passing)
653 -- case (e `cast` CoT) `cast` CoS of
654 -- PairInt a b -> body [a,b]
656 -- The Ints passed around are just for creating fresh locals
657 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
658 unboxProduct i arg arg_ty body
661 result = mkUnpackCase the_id arg con_args boxing_con rhs
662 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
663 ([the_id], i') = mkLocals i [arg_ty]
664 (con_args, i'') = mkLocals i' tys
665 rhs = body i'' con_args
667 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
668 -- (mkUnpackCase x e args Con body)
670 -- case (e `cast` ...) of bndr { Con args -> body }
672 -- the type of the bndr passed in is irrelevent
673 mkUnpackCase bndr arg unpk_args boxing_con body
674 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
676 (cast_arg, bndr_ty) = go (idType bndr) arg
678 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
679 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
680 = go (newTyConInstRhs tycon tycon_args)
681 (unwrapNewTypeBody tycon tycon_args arg)
682 | otherwise = (arg, ty)
685 reboxProduct :: [Unique] -- uniques to create new local binders
686 -> Type -- type of product to box
687 -> ([Unique], -- remaining uniques
688 CoreExpr, -- boxed product
689 [Id]) -- Ids being boxed into product
692 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
694 us' = dropList con_arg_tys us
696 arg_ids = zipWith (mkSysLocal FSLIT("rb")) us con_arg_tys
698 bind_rhs = mkProductBox arg_ids ty
701 (us', bind_rhs, arg_ids)
703 mkProductBox :: [Id] -> Type -> CoreExpr
704 mkProductBox arg_ids ty
707 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
710 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
711 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
712 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
714 wrap expr = wrapNewTypeBody tycon tycon_args expr
717 -- (mkReboxingAlt us con xs rhs) basically constructs the case
718 -- alternative (con, xs, rhs)
719 -- but it does the reboxing necessary to construct the *source*
720 -- arguments, xs, from the representation arguments ys.
722 -- data T = MkT !(Int,Int) Bool
724 -- mkReboxingAlt MkT [x,b] r
725 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
727 -- mkDataAlt should really be in DataCon, but it can't because
728 -- it manipulates CoreSyn.
731 :: [Unique] -- Uniques for the new Ids
733 -> [Var] -- Source-level args, including existential dicts
737 mkReboxingAlt us con args rhs
738 | not (any isMarkedUnboxed stricts)
739 = (DataAlt con, args, rhs)
743 (binds, args') = go args stricts us
745 (DataAlt con, args', mkLets binds rhs)
748 stricts = dataConExStricts con ++ dataConStrictMarks con
750 go [] _stricts _us = ([], [])
752 -- Type variable case
753 go (arg:args) stricts us
755 = let (binds, args') = go args stricts us
756 in (binds, arg:args')
758 -- Term variable case
759 go (arg:args) (str:stricts) us
760 | isMarkedUnboxed str
762 let (binds, unpacked_args') = go args stricts us'
763 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
765 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
767 = let (binds, args') = go args stricts us
768 in (binds, arg:args')
772 %************************************************************************
774 \subsection{Dictionary selectors}
776 %************************************************************************
778 Selecting a field for a dictionary. If there is just one field, then
779 there's nothing to do.
781 Dictionary selectors may get nested forall-types. Thus:
784 op :: forall b. Ord b => a -> b -> b
786 Then the top-level type for op is
788 op :: forall a. Foo a =>
792 This is unlike ordinary record selectors, which have all the for-alls
793 at the outside. When dealing with classes it's very convenient to
794 recover the original type signature from the class op selector.
797 mkDictSelId :: Name -> Class -> Id
798 mkDictSelId name clas
799 = mkGlobalId (ClassOpId clas) name sel_ty info
801 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
802 -- We can't just say (exprType rhs), because that would give a type
804 -- for a single-op class (after all, the selector is the identity)
805 -- But it's type must expose the representation of the dictionary
806 -- to gat (say) C a -> (a -> a)
810 `setUnfoldingInfo` mkTopUnfolding rhs
811 `setAllStrictnessInfo` Just strict_sig
813 -- We no longer use 'must-inline' on record selectors. They'll
814 -- inline like crazy if they scrutinise a constructor
816 -- The strictness signature is of the form U(AAAVAAAA) -> T
817 -- where the V depends on which item we are selecting
818 -- It's worth giving one, so that absence info etc is generated
819 -- even if the selector isn't inlined
820 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
821 arg_dmd | isNewTyCon tycon = evalDmd
822 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
825 tycon = classTyCon clas
826 [data_con] = tyConDataCons tycon
827 tyvars = dataConUnivTyVars data_con
828 arg_tys = ASSERT( isVanillaDataCon data_con ) dataConRepArgTys data_con
829 the_arg_id = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` arg_ids) name
831 pred = mkClassPred clas (mkTyVarTys tyvars)
832 (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
834 rhs = mkLams tyvars (Lam dict_id rhs_body)
835 rhs_body | isNewTyCon tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
836 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
837 [(DataAlt data_con, arg_ids, Var the_arg_id)]
839 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
840 -- The wrapper for the data constructor for a newtype looks like this:
841 -- newtype T a = MkT (a,Int)
842 -- MkT :: forall a. (a,Int) -> T a
843 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
844 -- where CoT is the coercion TyCon assoicated with the newtype
846 -- The call (wrapNewTypeBody T [a] e) returns the
847 -- body of the wrapper, namely
848 -- e `cast` (CoT [a])
850 -- If a coercion constructor is prodivided in the newtype, then we use
851 -- it, otherwise the wrap/unwrap are both no-ops
853 -- If the we are dealing with a newtype instance, we have a second coercion
854 -- identifying the family instance with the constructor of the newtype
855 -- instance. This coercion is applied in any case (ie, composed with the
856 -- coercion constructor of the newtype or applied by itself).
858 wrapNewTypeBody tycon args result_expr
859 = wrapFamInstBody tycon args inner
862 | Just co_con <- newTyConCo_maybe tycon
863 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
867 -- When unwrapping, we do *not* apply any family coercion, because this will
868 -- be done via a CoPat by the type checker. We have to do it this way as
869 -- computing the right type arguments for the coercion requires more than just
870 -- a spliting operation (cf, TcPat.tcConPat).
872 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
873 unwrapNewTypeBody tycon args result_expr
874 | Just co_con <- newTyConCo_maybe tycon
875 = mkCoerce (mkTyConApp co_con args) result_expr
883 %************************************************************************
885 \subsection{Primitive operations
887 %************************************************************************
890 mkPrimOpId :: PrimOp -> Id
894 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
895 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
896 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
897 (mkPrimOpIdUnique (primOpTag prim_op))
898 Nothing (AnId id) UserSyntax
899 id = mkGlobalId (PrimOpId prim_op) name ty info
902 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
904 `setAllStrictnessInfo` Just strict_sig
906 -- For each ccall we manufacture a separate CCallOpId, giving it
907 -- a fresh unique, a type that is correct for this particular ccall,
908 -- and a CCall structure that gives the correct details about calling
911 -- The *name* of this Id is a local name whose OccName gives the full
912 -- details of the ccall, type and all. This means that the interface
913 -- file reader can reconstruct a suitable Id
915 mkFCallId :: Unique -> ForeignCall -> Type -> Id
916 mkFCallId uniq fcall ty
917 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
918 -- A CCallOpId should have no free type variables;
919 -- when doing substitutions won't substitute over it
920 mkGlobalId (FCallId fcall) name ty info
922 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
923 -- The "occurrence name" of a ccall is the full info about the
924 -- ccall; it is encoded, but may have embedded spaces etc!
926 name = mkFCallName uniq occ_str
930 `setAllStrictnessInfo` Just strict_sig
932 (_, tau) = tcSplitForAllTys ty
933 (arg_tys, _) = tcSplitFunTys tau
934 arity = length arg_tys
935 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
939 %************************************************************************
941 \subsection{DictFuns and default methods}
943 %************************************************************************
945 Important notes about dict funs and default methods
946 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
947 Dict funs and default methods are *not* ImplicitIds. Their definition
948 involves user-written code, so we can't figure out their strictness etc
949 based on fixed info, as we can for constructors and record selectors (say).
951 We build them as LocalIds, but with External Names. This ensures that
952 they are taken to account by free-variable finding and dependency
953 analysis (e.g. CoreFVs.exprFreeVars).
955 Why shouldn't they be bound as GlobalIds? Because, in particular, if
956 they are globals, the specialiser floats dict uses above their defns,
957 which prevents good simplifications happening. Also the strictness
958 analyser treats a occurrence of a GlobalId as imported and assumes it
959 contains strictness in its IdInfo, which isn't true if the thing is
960 bound in the same module as the occurrence.
962 It's OK for dfuns to be LocalIds, because we form the instance-env to
963 pass on to the next module (md_insts) in CoreTidy, afer tidying
964 and globalising the top-level Ids.
966 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
967 that they aren't discarded by the occurrence analyser.
970 mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
972 mkDictFunId :: Name -- Name to use for the dict fun;
979 mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
980 = mkExportedLocalId dfun_name dfun_ty
982 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
984 {- 1 dec 99: disable the Mark Jones optimisation for the sake
985 of compatibility with Hugs.
986 See `types/InstEnv' for a discussion related to this.
988 (class_tyvars, sc_theta, _, _) = classBigSig clas
989 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
990 sc_theta' = substClasses (zipTopTvSubst class_tyvars inst_tys) sc_theta
991 dfun_theta = case inst_decl_theta of
992 [] -> [] -- If inst_decl_theta is empty, then we don't
993 -- want to have any dict arguments, so that we can
994 -- expose the constant methods.
996 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
997 -- Otherwise we pass the superclass dictionaries to
998 -- the dictionary function; the Mark Jones optimisation.
1000 -- NOTE the "nub". I got caught by this one:
1001 -- class Monad m => MonadT t m where ...
1002 -- instance Monad m => MonadT (EnvT env) m where ...
1003 -- Here, the inst_decl_theta has (Monad m); but so
1004 -- does the sc_theta'!
1006 -- NOTE the "not_const". I got caught by this one too:
1007 -- class Foo a => Baz a b where ...
1008 -- instance Wob b => Baz T b where..
1009 -- Now sc_theta' has Foo T
1014 %************************************************************************
1016 \subsection{Un-definable}
1018 %************************************************************************
1020 These Ids can't be defined in Haskell. They could be defined in
1021 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
1022 ensure that they were definitely, definitely inlined, because there is
1023 no curried identifier for them. That's what mkCompulsoryUnfolding
1024 does. If we had a way to get a compulsory unfolding from an interface
1025 file, we could do that, but we don't right now.
1027 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
1028 just gets expanded into a type coercion wherever it occurs. Hence we
1029 add it as a built-in Id with an unfolding here.
1031 The type variables we use here are "open" type variables: this means
1032 they can unify with both unlifted and lifted types. Hence we provide
1033 another gun with which to shoot yourself in the foot.
1036 mkWiredInIdName mod fs uniq id
1037 = mkWiredInName mod (mkOccNameFS varName fs) uniq Nothing (AnId id) UserSyntax
1039 unsafeCoerceName = mkWiredInIdName gHC_PRIM FSLIT("unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
1040 nullAddrName = mkWiredInIdName gHC_PRIM FSLIT("nullAddr#") nullAddrIdKey nullAddrId
1041 seqName = mkWiredInIdName gHC_PRIM FSLIT("seq") seqIdKey seqId
1042 realWorldName = mkWiredInIdName gHC_PRIM FSLIT("realWorld#") realWorldPrimIdKey realWorldPrimId
1043 lazyIdName = mkWiredInIdName gHC_BASE FSLIT("lazy") lazyIdKey lazyId
1045 errorName = mkWiredInIdName gHC_ERR FSLIT("error") errorIdKey eRROR_ID
1046 recSelErrorName = mkWiredInIdName gHC_ERR FSLIT("recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
1047 runtimeErrorName = mkWiredInIdName gHC_ERR FSLIT("runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
1048 irrefutPatErrorName = mkWiredInIdName gHC_ERR FSLIT("irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
1049 recConErrorName = mkWiredInIdName gHC_ERR FSLIT("recConError") recConErrorIdKey rEC_CON_ERROR_ID
1050 patErrorName = mkWiredInIdName gHC_ERR FSLIT("patError") patErrorIdKey pAT_ERROR_ID
1051 noMethodBindingErrorName = mkWiredInIdName gHC_ERR FSLIT("noMethodBindingError")
1052 noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
1053 nonExhaustiveGuardsErrorName
1054 = mkWiredInIdName gHC_ERR FSLIT("nonExhaustiveGuardsError")
1055 nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
1059 -- unsafeCoerce# :: forall a b. a -> b
1061 = pcMiscPrelId unsafeCoerceName ty info
1063 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1066 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
1067 (mkFunTy openAlphaTy openBetaTy)
1068 [x] = mkTemplateLocals [openAlphaTy]
1069 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
1070 -- Note (Coerce openBetaTy openAlphaTy) (Var x)
1071 Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
1073 -- nullAddr# :: Addr#
1074 -- The reason is is here is because we don't provide
1075 -- a way to write this literal in Haskell.
1077 = pcMiscPrelId nullAddrName addrPrimTy info
1079 info = noCafIdInfo `setUnfoldingInfo`
1080 mkCompulsoryUnfolding (Lit nullAddrLit)
1083 = pcMiscPrelId seqName ty info
1085 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1088 ty = mkForAllTys [alphaTyVar,openBetaTyVar]
1089 (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
1090 [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
1091 rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
1093 -- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1094 -- Used to lazify pseq: pseq a b = a `seq` lazy b
1096 -- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1097 -- not from GHC.Base.hi. This is important, because the strictness
1098 -- analyser will spot it as strict!
1100 -- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapper pass
1101 -- (see WorkWrap.wwExpr)
1102 -- We could use inline phases to do this, but that would be vulnerable to changes in
1103 -- phase numbering....we must inline precisely after strictness analysis.
1105 = pcMiscPrelId lazyIdName ty info
1108 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
1110 lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal
1111 lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
1113 [x] = mkTemplateLocals [openAlphaTy]
1116 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1117 nasty as-is, change it back to a literal (@Literal@).
1119 voidArgId is a Local Id used simply as an argument in functions
1120 where we just want an arg to avoid having a thunk of unlifted type.
1122 x = \ void :: State# RealWorld -> (# p, q #)
1124 This comes up in strictness analysis
1127 realWorldPrimId -- :: State# RealWorld
1128 = pcMiscPrelId realWorldName realWorldStatePrimTy
1129 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1130 -- The evaldUnfolding makes it look that realWorld# is evaluated
1131 -- which in turn makes Simplify.interestingArg return True,
1132 -- which in turn makes INLINE things applied to realWorld# likely
1135 voidArgId -- :: State# RealWorld
1136 = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
1140 %************************************************************************
1142 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
1144 %************************************************************************
1146 GHC randomly injects these into the code.
1148 @patError@ is just a version of @error@ for pattern-matching
1149 failures. It knows various ``codes'' which expand to longer
1150 strings---this saves space!
1152 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
1153 well shouldn't be yanked on, but if one is, then you will get a
1154 friendly message from @absentErr@ (rather than a totally random
1157 @parError@ is a special version of @error@ which the compiler does
1158 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
1159 templates, but we don't ever expect to generate code for it.
1163 :: Id -- Should be of type (forall a. Addr# -> a)
1164 -- where Addr# points to a UTF8 encoded string
1165 -> Type -- The type to instantiate 'a'
1166 -> String -- The string to print
1169 mkRuntimeErrorApp err_id res_ty err_msg
1170 = mkApps (Var err_id) [Type res_ty, err_string]
1172 err_string = Lit (mkStringLit err_msg)
1174 rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
1175 rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
1176 iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
1177 rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
1178 pAT_ERROR_ID = mkRuntimeErrorId patErrorName
1179 nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
1180 nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
1182 -- The runtime error Ids take a UTF8-encoded string as argument
1183 mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
1184 runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
1188 eRROR_ID = pc_bottoming_Id errorName errorTy
1191 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
1192 -- Notice the openAlphaTyVar. It says that "error" can be applied
1193 -- to unboxed as well as boxed types. This is OK because it never
1194 -- returns, so the return type is irrelevant.
1198 %************************************************************************
1200 \subsection{Utilities}
1202 %************************************************************************
1205 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1206 pcMiscPrelId name ty info
1207 = mkVanillaGlobal name ty info
1208 -- We lie and say the thing is imported; otherwise, we get into
1209 -- a mess with dependency analysis; e.g., core2stg may heave in
1210 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1211 -- being compiled, then it's just a matter of luck if the definition
1212 -- will be in "the right place" to be in scope.
1214 pc_bottoming_Id name ty
1215 = pcMiscPrelId name ty bottoming_info
1217 bottoming_info = vanillaIdInfo `setAllStrictnessInfo` Just strict_sig
1218 -- Do *not* mark them as NoCafRefs, because they can indeed have
1219 -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
1220 -- which has some CAFs
1221 -- In due course we may arrange that these error-y things are
1222 -- regarded by the GC as permanently live, in which case we
1223 -- can give them NoCaf info. As it is, any function that calls
1224 -- any pc_bottoming_Id will itself have CafRefs, which bloats
1227 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
1228 -- These "bottom" out, no matter what their arguments
1230 (openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
1231 openAlphaTy = mkTyVarTy openAlphaTyVar
1232 openBetaTy = mkTyVarTy openBetaTyVar