2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1998
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, mkTickBoxOpId, mkBreakPointOpId,
23 mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
24 wrapFamInstBody, unwrapFamInstScrut,
25 mkUnpackCase, mkProductBox,
27 -- And some particular Ids; see below for why they are wired in
28 wiredInIds, ghcPrimIds,
29 unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId,
30 lazyId, lazyIdUnfolding, lazyIdKey,
33 rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
34 nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
35 pAT_ERROR_ID, eRROR_ID,
40 #include "HsVersions.h"
63 import Var ( Var, TyVar, mkCoVar)
71 import BasicTypes hiding ( SuccessFlag(..) )
79 %************************************************************************
81 \subsection{Wired in Ids}
83 %************************************************************************
87 = [ -- These error-y things are wired in because we don't yet have
88 -- a way to express in an interface file that the result type variable
89 -- is 'open'; that is can be unified with an unboxed type
91 -- [The interface file format now carry such information, but there's
92 -- no way yet of expressing at the definition site for these
93 -- error-reporting functions that they have an 'open'
94 -- result type. -- sof 1/99]
96 eRROR_ID, -- This one isn't used anywhere else in the compiler
97 -- But we still need it in wiredInIds so that when GHC
98 -- compiles a program that mentions 'error' we don't
99 -- import its type from the interface file; we just get
100 -- the Id defined here. Which has an 'open-tyvar' type.
103 iRREFUT_PAT_ERROR_ID,
104 nON_EXHAUSTIVE_GUARDS_ERROR_ID,
105 nO_METHOD_BINDING_ERROR_ID,
112 -- These Ids are exported from GHC.Prim
114 = [ -- These can't be defined in Haskell, but they have
115 -- perfectly reasonable unfoldings in Core
123 %************************************************************************
125 \subsection{Data constructors}
127 %************************************************************************
129 The wrapper for a constructor is an ordinary top-level binding that evaluates
130 any strict args, unboxes any args that are going to be flattened, and calls
133 We're going to build a constructor that looks like:
135 data (Data a, C b) => T a b = T1 !a !Int b
138 \d1::Data a, d2::C b ->
139 \p q r -> case p of { p ->
141 Con T1 [a,b] [p,q,r]}}
145 * d2 is thrown away --- a context in a data decl is used to make sure
146 one *could* construct dictionaries at the site the constructor
147 is used, but the dictionary isn't actually used.
149 * We have to check that we can construct Data dictionaries for
150 the types a and Int. Once we've done that we can throw d1 away too.
152 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
153 all that matters is that the arguments are evaluated. "seq" is
154 very careful to preserve evaluation order, which we don't need
157 You might think that we could simply give constructors some strictness
158 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
159 But we don't do that because in the case of primops and functions strictness
160 is a *property* not a *requirement*. In the case of constructors we need to
161 do something active to evaluate the argument.
163 Making an explicit case expression allows the simplifier to eliminate
164 it in the (common) case where the constructor arg is already evaluated.
166 Note [Wrappers for data instance tycons]
167 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
168 In the case of data instances, the wrapper also applies the coercion turning
169 the representation type into the family instance type to cast the result of
170 the wrapper. For example, consider the declarations
172 data family Map k :: * -> *
173 data instance Map (a, b) v = MapPair (Map a (Pair b v))
175 The tycon to which the datacon MapPair belongs gets a unique internal
176 name of the form :R123Map, and we call it the representation tycon.
177 In contrast, Map is the family tycon (accessible via
178 tyConFamInst_maybe). A coercion allows you to move between
179 representation and family type. It is accessible from :R123Map via
180 tyConFamilyCoercion_maybe and has kind
182 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
184 The wrapper and worker of MapPair get the types
187 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
188 $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v)
191 MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
193 This coercion is conditionally applied by wrapFamInstBody.
195 It's a bit more complicated if the data instance is a GADT as well!
197 data instance T [a] where
198 T1 :: forall b. b -> T [Maybe b]
200 Co7T a :: T [a] ~ :R7T a
205 $WT1 :: forall b. b -> T [Maybe b]
206 $WT1 b v = T1 (Maybe b) b (Maybe b) v
207 `cast` sym (Co7T (Maybe b))
210 T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c
213 mkDataConIds :: Name -> Name -> DataCon -> DataConIds
214 mkDataConIds wrap_name wkr_name data_con
215 | isNewTyCon tycon -- Newtype, only has a worker
216 = DCIds Nothing nt_work_id
218 | any isMarkedStrict all_strict_marks -- Algebraic, needs wrapper
219 || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
220 || isFamInstTyCon tycon -- depends on this test
221 = DCIds (Just alg_wrap_id) wrk_id
223 | otherwise -- Algebraic, no wrapper
224 = DCIds Nothing wrk_id
226 (univ_tvs, ex_tvs, eq_spec,
227 eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
228 tycon = dataConTyCon data_con -- The representation TyCon (not family)
230 ----------- Worker (algebraic data types only) --------------
231 -- The *worker* for the data constructor is the function that
232 -- takes the representation arguments and builds the constructor.
233 wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
234 (dataConRepType data_con) wkr_info
236 wkr_arity = dataConRepArity data_con
237 wkr_info = noCafIdInfo
238 `setArityInfo` wkr_arity
239 `setAllStrictnessInfo` Just wkr_sig
240 `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
243 wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
244 -- Note [Data-con worker strictness]
245 -- Notice that we do *not* say the worker is strict
246 -- even if the data constructor is declared strict
247 -- e.g. data T = MkT !(Int,Int)
248 -- Why? Because the *wrapper* is strict (and its unfolding has case
249 -- expresssions that do the evals) but the *worker* itself is not.
250 -- If we pretend it is strict then when we see
251 -- case x of y -> $wMkT y
252 -- the simplifier thinks that y is "sure to be evaluated" (because
253 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
255 -- When the simplifer sees a pattern
256 -- case e of MkT x -> ...
257 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
258 -- but that's fine... dataConRepStrictness comes from the data con
259 -- not from the worker Id.
261 cpr_info | isProductTyCon tycon &&
264 wkr_arity <= mAX_CPR_SIZE = retCPR
266 -- RetCPR is only true for products that are real data types;
267 -- that is, not unboxed tuples or [non-recursive] newtypes
269 ----------- Workers for newtypes --------------
270 nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
271 nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
272 `setArityInfo` 1 -- Arity 1
273 `setUnfoldingInfo` newtype_unf
274 newtype_unf = -- The assertion below is no longer correct:
275 -- there may be a dict theta rather than a singleton orig_arg_ty
276 -- ASSERT( isVanillaDataCon data_con &&
277 -- isSingleton orig_arg_tys )
279 -- No existentials on a newtype, but it can have a context
280 -- e.g. newtype Eq a => T a = MkT (...)
281 mkCompulsoryUnfolding $
282 mkLams wrap_tvs $ Lam id_arg1 $
283 wrapNewTypeBody tycon res_ty_args
286 id_arg1 = mkTemplateLocal 1
287 (if null orig_arg_tys
288 then ASSERT(not (null $ dataConDictTheta data_con)) mkPredTy $ head (dataConDictTheta data_con)
289 else head orig_arg_tys
292 ----------- Wrapper --------------
293 -- We used to include the stupid theta in the wrapper's args
294 -- but now we don't. Instead the type checker just injects these
295 -- extra constraints where necessary.
296 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
297 res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
298 eq_tys = mkPredTys eq_theta
299 dict_tys = mkPredTys dict_theta
300 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
301 mkFunTys orig_arg_tys $ res_ty
302 -- NB: watch out here if you allow user-written equality
303 -- constraints in data constructor signatures
305 ----------- Wrappers for algebraic data types --------------
306 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
307 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
308 `setArityInfo` wrap_arity
309 -- It's important to specify the arity, so that partial
310 -- applications are treated as values
311 `setUnfoldingInfo` wrap_unf
312 `setAllStrictnessInfo` Just wrap_sig
314 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
315 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
316 arg_dmds = map mk_dmd all_strict_marks
317 mk_dmd str | isMarkedStrict str = evalDmd
318 | otherwise = lazyDmd
319 -- The Cpr info can be important inside INLINE rhss, where the
320 -- wrapper constructor isn't inlined.
321 -- And the argument strictness can be important too; we
322 -- may not inline a contructor when it is partially applied.
324 -- data W = C !Int !Int !Int
325 -- ...(let w = C x in ...(w p q)...)...
326 -- we want to see that w is strict in its two arguments
328 wrap_unf = mkTopUnfolding $ Note InlineMe $
331 mkLams dict_args $ mkLams id_args $
332 foldr mk_case con_app
333 (zip (dict_args ++ id_args) all_strict_marks)
336 con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
337 Var wrk_id `mkTyApps` res_ty_args
339 `mkTyApps` map snd eq_spec -- Equality evidence
341 `mkVarApps` reverse rep_ids
343 (dict_args,i2) = mkLocals 1 dict_tys
344 (id_args,i3) = mkLocals i2 orig_arg_tys
346 (eq_args,_) = mkCoVarLocals i3 eq_tys
348 mkCoVarLocals i [] = ([],i)
349 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
350 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
354 :: (Id, StrictnessMark) -- Arg, strictness
355 -> (Int -> [Id] -> CoreExpr) -- Body
356 -> Int -- Next rep arg id
357 -> [Id] -- Rep args so far, reversed
359 mk_case (arg,strict) body i rep_args
361 NotMarkedStrict -> body i (arg:rep_args)
363 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
365 Case (Var arg) arg res_ty [(DEFAULT,[], body i (arg:rep_args))]
368 -> unboxProduct i (Var arg) (idType arg) the_body
370 the_body i con_args = body i (reverse con_args ++ rep_args)
372 mAX_CPR_SIZE :: Arity
374 -- We do not treat very big tuples as CPR-ish:
375 -- a) for a start we get into trouble because there aren't
376 -- "enough" unboxed tuple types (a tiresome restriction,
378 -- b) more importantly, big unboxed tuples get returned mainly
379 -- on the stack, and are often then allocated in the heap
380 -- by the caller. So doing CPR for them may in fact make
383 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
389 %************************************************************************
391 \subsection{Record selectors}
393 %************************************************************************
395 We're going to build a record selector unfolding that looks like this:
397 data T a b c = T1 { ..., op :: a, ...}
398 | T2 { ..., op :: a, ...}
401 sel = /\ a b c -> \ d -> case d of
406 Similarly for newtypes
408 newtype N a = MkN { unN :: a->a }
411 unN n = coerce (a->a) n
413 We need to take a little care if the field has a polymorphic type:
415 data R = R { f :: forall a. a->a }
419 f :: forall a. R -> a -> a
420 f = /\ a \ r = case r of
423 (not f :: R -> forall a. a->a, which gives the type inference mechanism
424 problems at call sites)
426 Similarly for (recursive) newtypes
428 newtype N = MkN { unN :: forall a. a->a }
430 unN :: forall b. N -> b -> b
431 unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
434 Note [Naughty record selectors]
435 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
436 A "naughty" field is one for which we can't define a record
437 selector, because an existential type variable would escape. For example:
438 data T = forall a. MkT { x,y::a }
439 We obviously can't define
441 Nevertheless we *do* put a RecordSelId into the type environment
442 so that if the user tries to use 'x' as a selector we can bleat
443 helpfully, rather than saying unhelpfully that 'x' is not in scope.
444 Hence the sel_naughty flag, to identify record selectors that don't really exist.
446 In general, a field is naughty if its type mentions a type variable that
447 isn't in the result type of the constructor.
449 Note [GADT record selectors]
450 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
451 For GADTs, we require that all constructors with a common field 'f' have the same
452 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
455 T1 { f :: a } :: T [a]
456 T2 { f :: a, y :: b } :: T [a]
457 and now the selector takes that type as its argument:
458 f :: forall a. T [a] -> a
462 Note the forall'd tyvars of the selector are just the free tyvars
463 of the result type; there may be other tyvars in the constructor's
464 type (e.g. 'b' in T2).
466 Note [Selector running example]
467 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
468 It's OK to combine GADTs and type families. Here's a running example:
470 data instance T [a] where
471 T1 { fld :: b } :: T [Maybe b]
473 The representation type looks like this
475 T1 { fld :: b } :: :R7T (Maybe b)
477 and there's coercion from the family type to the representation type
478 :CoR7T a :: T [a] ~ :R7T a
480 The selector we want for fld looks like this:
482 fld :: forall b. T [Maybe b] -> b
483 fld = /\b. \(d::T [Maybe b]).
484 case d `cast` :CoR7T (Maybe b) of
487 The scrutinee of the case has type :R7T (Maybe b), which can be
488 gotten by appying the eq_spec to the univ_tvs of the data con.
491 mkRecordSelId :: TyCon -> FieldLabel -> Id
492 mkRecordSelId tycon field_label
493 -- Assumes that all fields with the same field label have the same type
494 | is_naughty = naughty_id
497 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tv_set)
498 sel_id_details = RecordSelId { sel_tycon = tycon, sel_label = field_label, sel_naughty = is_naughty }
499 -- For a data type family, the tycon is the *instance* TyCon
501 -- Escapist case here for naughty constructors
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 = ASSERT( not (null data_cons_w_field) ) head data_cons_w_field
513 (univ_tvs, _, eq_spec, _, _, _, data_ty) = dataConFullSig con1
514 -- For a data type family, the data_ty (and hence selector_ty) mentions
515 -- only the family TyCon, not the instance TyCon
516 data_tv_set = tyVarsOfType data_ty
517 data_tvs = varSetElems data_tv_set
518 field_ty = dataConFieldType con1 field_label
520 -- *Very* tiresomely, the selectors are (unnecessarily!) overloaded over
521 -- just the dictionaries in the types of the constructors that contain
522 -- the relevant field. [The Report says that pattern matching on a
523 -- constructor gives the same constraints as applying it.] Urgh.
525 -- However, not all data cons have all constraints (because of
526 -- BuildTyCl.mkDataConStupidTheta). So we need to find all the data cons
527 -- involved in the pattern match and take the union of their constraints.
528 stupid_dict_tys = mkPredTys (dataConsStupidTheta data_cons_w_field)
529 n_stupid_dicts = length stupid_dict_tys
531 (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 data_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 scrut_id = mkTemplateLocal (dict_id_base+1) scrut_ty
579 arg_base = dict_id_base + 2
581 the_alts :: [CoreAlt]
582 the_alts = map mk_alt data_cons_w_field -- Already sorted by data-con
583 no_default = length data_cons == length data_cons_w_field -- No default needed
585 default_alt | no_default = []
586 | otherwise = [(DEFAULT, [], error_expr)]
588 -- The default branch may have CAF refs, because it calls recSelError etc.
589 caf_info | no_default = NoCafRefs
590 | otherwise = MayHaveCafRefs
592 sel_rhs = mkLams data_tvs $ mkLams field_tyvars $
593 mkLams stupid_dict_ids $ mkLams field_dict_ids $
594 Lam data_id $ mk_result sel_body
596 scrut_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
597 scrut_ty = mkTyConApp tycon scrut_ty_args
598 scrut = unwrapFamInstScrut tycon scrut_ty_args (Var data_id)
599 -- First coerce from the type family to the representation type
601 -- NB: A newtype always has a vanilla DataCon; no existentials etc
602 -- data_tys will simply be the dataConUnivTyVars
603 sel_body | isNewTyCon tycon = unwrapNewTypeBody tycon scrut_ty_args scrut
604 | otherwise = Case scrut scrut_id field_ty (default_alt ++ the_alts)
606 mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
607 -- We pull the field lambdas to the top, so we need to
608 -- apply them in the body. For example:
609 -- data T = MkT { foo :: forall a. a->a }
611 -- foo :: forall a. T -> a -> a
612 -- foo = /\a. \t:T. case t of { MkT f -> f a }
615 = ASSERT2( data_ty `tcEqType` field_ty, ppr data_con $$ ppr data_ty $$ ppr field_ty )
616 mkReboxingAlt rebox_uniqs data_con (ex_tvs ++ co_tvs ++ arg_vs) rhs
618 -- get pattern binders with types appropriately instantiated
619 arg_uniqs = map mkBuiltinUnique [arg_base..]
620 (ex_tvs, co_tvs, arg_vs) = dataConOrigInstPat arg_uniqs data_con scrut_ty_args
622 rebox_base = arg_base + length ex_tvs + length co_tvs + length arg_vs
623 rebox_uniqs = map mkBuiltinUnique [rebox_base..]
625 -- data T :: *->* where T1 { fld :: Maybe b } -> T [b]
626 -- Hence T1 :: forall a b. (a=[b]) => b -> T a
627 -- fld :: forall b. T [b] -> Maybe b
628 -- fld = /\b.\(t:T[b]). case t of
629 -- T1 b' (c : [b]=[b']) (x:Maybe b')
630 -- -> x `cast` Maybe (sym (right c))
633 -- Generate the refinement for b'=b,
634 -- and apply to (Maybe b'), to get (Maybe b)
635 Succeeded refinement = gadtRefine emptyRefinement ex_tvs co_tvs
636 the_arg_id_ty = idType the_arg_id
637 (rhs, data_ty) = case refineType refinement the_arg_id_ty of
638 Just (co, data_ty) -> (Cast (Var the_arg_id) co, data_ty)
639 Nothing -> (Var the_arg_id, the_arg_id_ty)
641 field_vs = filter (not . isPredTy . idType) arg_vs
642 the_arg_id = assoc "mkRecordSelId:mk_alt" (field_lbls `zip` field_vs) field_label
643 field_lbls = dataConFieldLabels data_con
645 error_expr = mkRuntimeErrorApp rEC_SEL_ERROR_ID field_ty full_msg
646 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
648 -- unbox a product type...
649 -- we will recurse into newtypes, casting along the way, and unbox at the
650 -- first product data constructor we find. e.g.
652 -- data PairInt = PairInt Int Int
653 -- newtype S = MkS PairInt
656 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
657 -- ids, we get (modulo int passing)
659 -- case (e `cast` CoT) `cast` CoS of
660 -- PairInt a b -> body [a,b]
662 -- The Ints passed around are just for creating fresh locals
663 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
664 unboxProduct i arg arg_ty body
667 result = mkUnpackCase the_id arg con_args boxing_con rhs
668 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
669 ([the_id], i') = mkLocals i [arg_ty]
670 (con_args, i'') = mkLocals i' tys
671 rhs = body i'' con_args
673 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
674 -- (mkUnpackCase x e args Con body)
676 -- case (e `cast` ...) of bndr { Con args -> body }
678 -- the type of the bndr passed in is irrelevent
679 mkUnpackCase bndr arg unpk_args boxing_con body
680 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
682 (cast_arg, bndr_ty) = go (idType bndr) arg
684 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
685 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
686 = go (newTyConInstRhs tycon tycon_args)
687 (unwrapNewTypeBody tycon tycon_args arg)
688 | otherwise = (arg, ty)
691 reboxProduct :: [Unique] -- uniques to create new local binders
692 -> Type -- type of product to box
693 -> ([Unique], -- remaining uniques
694 CoreExpr, -- boxed product
695 [Id]) -- Ids being boxed into product
698 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
700 us' = dropList con_arg_tys us
702 arg_ids = zipWith (mkSysLocal FSLIT("rb")) us con_arg_tys
704 bind_rhs = mkProductBox arg_ids ty
707 (us', bind_rhs, arg_ids)
709 mkProductBox :: [Id] -> Type -> CoreExpr
710 mkProductBox arg_ids ty
713 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
716 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
717 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
718 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
720 wrap expr = wrapNewTypeBody tycon tycon_args expr
723 -- (mkReboxingAlt us con xs rhs) basically constructs the case
724 -- alternative (con, xs, rhs)
725 -- but it does the reboxing necessary to construct the *source*
726 -- arguments, xs, from the representation arguments ys.
728 -- data T = MkT !(Int,Int) Bool
730 -- mkReboxingAlt MkT [x,b] r
731 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
733 -- mkDataAlt should really be in DataCon, but it can't because
734 -- it manipulates CoreSyn.
737 :: [Unique] -- Uniques for the new Ids
739 -> [Var] -- Source-level args, including existential dicts
743 mkReboxingAlt us con args rhs
744 | not (any isMarkedUnboxed stricts)
745 = (DataAlt con, args, rhs)
749 (binds, args') = go args stricts us
751 (DataAlt con, args', mkLets binds rhs)
754 stricts = dataConExStricts con ++ dataConStrictMarks con
756 go [] _stricts _us = ([], [])
758 -- Type variable case
759 go (arg:args) stricts us
761 = let (binds, args') = go args stricts us
762 in (binds, arg:args')
764 -- Term variable case
765 go (arg:args) (str:stricts) us
766 | isMarkedUnboxed str
768 let (binds, unpacked_args') = go args stricts us'
769 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
771 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
773 = let (binds, args') = go args stricts us
774 in (binds, arg:args')
778 %************************************************************************
780 \subsection{Dictionary selectors}
782 %************************************************************************
784 Selecting a field for a dictionary. If there is just one field, then
785 there's nothing to do.
787 Dictionary selectors may get nested forall-types. Thus:
790 op :: forall b. Ord b => a -> b -> b
792 Then the top-level type for op is
794 op :: forall a. Foo a =>
798 This is unlike ordinary record selectors, which have all the for-alls
799 at the outside. When dealing with classes it's very convenient to
800 recover the original type signature from the class op selector.
803 mkDictSelId :: Name -> Class -> Id
804 mkDictSelId name clas
805 = mkGlobalId (ClassOpId clas) name sel_ty info
807 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
808 -- We can't just say (exprType rhs), because that would give a type
810 -- for a single-op class (after all, the selector is the identity)
811 -- But it's type must expose the representation of the dictionary
812 -- to get (say) C a -> (a -> a)
816 `setUnfoldingInfo` mkTopUnfolding rhs
817 `setAllStrictnessInfo` Just strict_sig
819 -- We no longer use 'must-inline' on record selectors. They'll
820 -- inline like crazy if they scrutinise a constructor
822 -- The strictness signature is of the form U(AAAVAAAA) -> T
823 -- where the V depends on which item we are selecting
824 -- It's worth giving one, so that absence info etc is generated
825 -- even if the selector isn't inlined
826 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
827 arg_dmd | isNewTyCon tycon = evalDmd
828 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
831 tycon = classTyCon clas
832 [data_con] = tyConDataCons tycon
833 tyvars = dataConUnivTyVars data_con
834 arg_tys = {- ASSERT( isVanillaDataCon data_con ) -} dataConRepArgTys data_con
835 eq_theta = dataConEqTheta data_con
836 the_arg_id = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` arg_ids) name
838 pred = mkClassPred clas (mkTyVarTys tyvars)
839 dict_id = mkTemplateLocal 1 $ mkPredTy pred
840 (eq_ids,n) = mkCoVarLocals 2 $ mkPredTys eq_theta
841 arg_ids = mkTemplateLocalsNum n arg_tys
843 mkCoVarLocals i [] = ([],i)
844 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
845 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
848 rhs = mkLams tyvars (Lam dict_id rhs_body)
849 rhs_body | isNewTyCon tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
850 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
851 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
855 %************************************************************************
857 Wrapping and unwrapping newtypes and type families
859 %************************************************************************
862 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
863 -- The wrapper for the data constructor for a newtype looks like this:
864 -- newtype T a = MkT (a,Int)
865 -- MkT :: forall a. (a,Int) -> T a
866 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
867 -- where CoT is the coercion TyCon assoicated with the newtype
869 -- The call (wrapNewTypeBody T [a] e) returns the
870 -- body of the wrapper, namely
871 -- e `cast` (CoT [a])
873 -- If a coercion constructor is provided in the newtype, then we use
874 -- it, otherwise the wrap/unwrap are both no-ops
876 -- If the we are dealing with a newtype *instance*, we have a second coercion
877 -- identifying the family instance with the constructor of the newtype
878 -- instance. This coercion is applied in any case (ie, composed with the
879 -- coercion constructor of the newtype or applied by itself).
881 wrapNewTypeBody tycon args result_expr
882 = wrapFamInstBody tycon args inner
885 | Just co_con <- newTyConCo_maybe tycon
886 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
890 -- When unwrapping, we do *not* apply any family coercion, because this will
891 -- be done via a CoPat by the type checker. We have to do it this way as
892 -- computing the right type arguments for the coercion requires more than just
893 -- a spliting operation (cf, TcPat.tcConPat).
895 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
896 unwrapNewTypeBody tycon args result_expr
897 | Just co_con <- newTyConCo_maybe tycon
898 = mkCoerce (mkTyConApp co_con args) result_expr
902 -- If the type constructor is a representation type of a data instance, wrap
903 -- the expression into a cast adjusting the expression type, which is an
904 -- instance of the representation type, to the corresponding instance of the
905 -- family instance type.
906 -- See Note [Wrappers for data instance tycons]
907 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
908 wrapFamInstBody tycon args body
909 | Just co_con <- tyConFamilyCoercion_maybe tycon
910 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
914 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
915 unwrapFamInstScrut tycon args scrut
916 | Just co_con <- tyConFamilyCoercion_maybe tycon
917 = mkCoerce (mkTyConApp co_con args) scrut
923 %************************************************************************
925 \subsection{Primitive operations
927 %************************************************************************
930 mkPrimOpId :: PrimOp -> Id
934 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
935 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
936 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
937 (mkPrimOpIdUnique (primOpTag prim_op))
939 id = mkGlobalId (PrimOpId prim_op) name ty info
942 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
944 `setAllStrictnessInfo` Just strict_sig
946 -- For each ccall we manufacture a separate CCallOpId, giving it
947 -- a fresh unique, a type that is correct for this particular ccall,
948 -- and a CCall structure that gives the correct details about calling
951 -- The *name* of this Id is a local name whose OccName gives the full
952 -- details of the ccall, type and all. This means that the interface
953 -- file reader can reconstruct a suitable Id
955 mkFCallId :: Unique -> ForeignCall -> Type -> Id
956 mkFCallId uniq fcall ty
957 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
958 -- A CCallOpId should have no free type variables;
959 -- when doing substitutions won't substitute over it
960 mkGlobalId (FCallId fcall) name ty info
962 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
963 -- The "occurrence name" of a ccall is the full info about the
964 -- ccall; it is encoded, but may have embedded spaces etc!
966 name = mkFCallName uniq occ_str
970 `setAllStrictnessInfo` Just strict_sig
972 (_, tau) = tcSplitForAllTys ty
973 (arg_tys, _) = tcSplitFunTys tau
974 arity = length arg_tys
975 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
977 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
978 -- except for the type:
980 -- a plain HPC tick box has type (State# RealWorld)
981 -- a breakpoint Id has type forall a.a
983 -- The breakpoint Id will be applied to a list of arbitrary free variables,
984 -- which is why it needs a polymorphic type.
986 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
987 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
989 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
990 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
991 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
993 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
995 tickbox = TickBox mod ix
996 occ_str = showSDoc (braces (ppr tickbox))
997 name = mkTickBoxOpName uniq occ_str
1002 %************************************************************************
1004 \subsection{DictFuns and default methods}
1006 %************************************************************************
1008 Important notes about dict funs and default methods
1009 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1010 Dict funs and default methods are *not* ImplicitIds. Their definition
1011 involves user-written code, so we can't figure out their strictness etc
1012 based on fixed info, as we can for constructors and record selectors (say).
1014 We build them as LocalIds, but with External Names. This ensures that
1015 they are taken to account by free-variable finding and dependency
1016 analysis (e.g. CoreFVs.exprFreeVars).
1018 Why shouldn't they be bound as GlobalIds? Because, in particular, if
1019 they are globals, the specialiser floats dict uses above their defns,
1020 which prevents good simplifications happening. Also the strictness
1021 analyser treats a occurrence of a GlobalId as imported and assumes it
1022 contains strictness in its IdInfo, which isn't true if the thing is
1023 bound in the same module as the occurrence.
1025 It's OK for dfuns to be LocalIds, because we form the instance-env to
1026 pass on to the next module (md_insts) in CoreTidy, afer tidying
1027 and globalising the top-level Ids.
1029 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
1030 that they aren't discarded by the occurrence analyser.
1033 mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
1035 mkDictFunId :: Name -- Name to use for the dict fun;
1042 mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
1043 = mkExportedLocalId dfun_name dfun_ty
1045 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
1047 {- 1 dec 99: disable the Mark Jones optimisation for the sake
1048 of compatibility with Hugs.
1049 See `types/InstEnv' for a discussion related to this.
1051 (class_tyvars, sc_theta, _, _) = classBigSig clas
1052 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
1053 sc_theta' = substClasses (zipTopTvSubst class_tyvars inst_tys) sc_theta
1054 dfun_theta = case inst_decl_theta of
1055 [] -> [] -- If inst_decl_theta is empty, then we don't
1056 -- want to have any dict arguments, so that we can
1057 -- expose the constant methods.
1059 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
1060 -- Otherwise we pass the superclass dictionaries to
1061 -- the dictionary function; the Mark Jones optimisation.
1063 -- NOTE the "nub". I got caught by this one:
1064 -- class Monad m => MonadT t m where ...
1065 -- instance Monad m => MonadT (EnvT env) m where ...
1066 -- Here, the inst_decl_theta has (Monad m); but so
1067 -- does the sc_theta'!
1069 -- NOTE the "not_const". I got caught by this one too:
1070 -- class Foo a => Baz a b where ...
1071 -- instance Wob b => Baz T b where..
1072 -- Now sc_theta' has Foo T
1077 %************************************************************************
1079 \subsection{Un-definable}
1081 %************************************************************************
1083 These Ids can't be defined in Haskell. They could be defined in
1084 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
1085 ensure that they were definitely, definitely inlined, because there is
1086 no curried identifier for them. That's what mkCompulsoryUnfolding
1087 does. If we had a way to get a compulsory unfolding from an interface
1088 file, we could do that, but we don't right now.
1090 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
1091 just gets expanded into a type coercion wherever it occurs. Hence we
1092 add it as a built-in Id with an unfolding here.
1094 The type variables we use here are "open" type variables: this means
1095 they can unify with both unlifted and lifted types. Hence we provide
1096 another gun with which to shoot yourself in the foot.
1099 mkWiredInIdName mod fs uniq id
1100 = mkWiredInName mod (mkOccNameFS varName fs) uniq (AnId id) UserSyntax
1102 unsafeCoerceName = mkWiredInIdName gHC_PRIM FSLIT("unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
1103 nullAddrName = mkWiredInIdName gHC_PRIM FSLIT("nullAddr#") nullAddrIdKey nullAddrId
1104 seqName = mkWiredInIdName gHC_PRIM FSLIT("seq") seqIdKey seqId
1105 realWorldName = mkWiredInIdName gHC_PRIM FSLIT("realWorld#") realWorldPrimIdKey realWorldPrimId
1106 lazyIdName = mkWiredInIdName gHC_BASE FSLIT("lazy") lazyIdKey lazyId
1108 errorName = mkWiredInIdName gHC_ERR FSLIT("error") errorIdKey eRROR_ID
1109 recSelErrorName = mkWiredInIdName gHC_ERR FSLIT("recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
1110 runtimeErrorName = mkWiredInIdName gHC_ERR FSLIT("runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
1111 irrefutPatErrorName = mkWiredInIdName gHC_ERR FSLIT("irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
1112 recConErrorName = mkWiredInIdName gHC_ERR FSLIT("recConError") recConErrorIdKey rEC_CON_ERROR_ID
1113 patErrorName = mkWiredInIdName gHC_ERR FSLIT("patError") patErrorIdKey pAT_ERROR_ID
1114 noMethodBindingErrorName = mkWiredInIdName gHC_ERR FSLIT("noMethodBindingError")
1115 noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
1116 nonExhaustiveGuardsErrorName
1117 = mkWiredInIdName gHC_ERR FSLIT("nonExhaustiveGuardsError")
1118 nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
1122 -- unsafeCoerce# :: forall a b. a -> b
1124 = pcMiscPrelId unsafeCoerceName ty info
1126 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1129 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
1130 (mkFunTy openAlphaTy openBetaTy)
1131 [x] = mkTemplateLocals [openAlphaTy]
1132 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
1133 Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
1135 -- nullAddr# :: Addr#
1136 -- The reason is is here is because we don't provide
1137 -- a way to write this literal in Haskell.
1139 = pcMiscPrelId nullAddrName addrPrimTy info
1141 info = noCafIdInfo `setUnfoldingInfo`
1142 mkCompulsoryUnfolding (Lit nullAddrLit)
1145 = pcMiscPrelId seqName ty info
1147 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1150 ty = mkForAllTys [alphaTyVar,openBetaTyVar]
1151 (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
1152 [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
1153 rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
1155 -- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1156 -- Used to lazify pseq: pseq a b = a `seq` lazy b
1158 -- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1159 -- not from GHC.Base.hi. This is important, because the strictness
1160 -- analyser will spot it as strict!
1162 -- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapperpass
1163 -- (see WorkWrap.wwExpr)
1164 -- We could use inline phases to do this, but that would be vulnerable to changes in
1165 -- phase numbering....we must inline precisely after strictness analysis.
1167 = pcMiscPrelId lazyIdName ty info
1170 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
1172 lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal
1173 lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
1175 [x] = mkTemplateLocals [openAlphaTy]
1178 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1179 nasty as-is, change it back to a literal (@Literal@).
1181 voidArgId is a Local Id used simply as an argument in functions
1182 where we just want an arg to avoid having a thunk of unlifted type.
1184 x = \ void :: State# RealWorld -> (# p, q #)
1186 This comes up in strictness analysis
1189 realWorldPrimId -- :: State# RealWorld
1190 = pcMiscPrelId realWorldName realWorldStatePrimTy
1191 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1192 -- The evaldUnfolding makes it look that realWorld# is evaluated
1193 -- which in turn makes Simplify.interestingArg return True,
1194 -- which in turn makes INLINE things applied to realWorld# likely
1197 voidArgId -- :: State# RealWorld
1198 = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
1202 %************************************************************************
1204 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
1206 %************************************************************************
1208 GHC randomly injects these into the code.
1210 @patError@ is just a version of @error@ for pattern-matching
1211 failures. It knows various ``codes'' which expand to longer
1212 strings---this saves space!
1214 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
1215 well shouldn't be yanked on, but if one is, then you will get a
1216 friendly message from @absentErr@ (rather than a totally random
1219 @parError@ is a special version of @error@ which the compiler does
1220 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
1221 templates, but we don't ever expect to generate code for it.
1225 :: Id -- Should be of type (forall a. Addr# -> a)
1226 -- where Addr# points to a UTF8 encoded string
1227 -> Type -- The type to instantiate 'a'
1228 -> String -- The string to print
1231 mkRuntimeErrorApp err_id res_ty err_msg
1232 = mkApps (Var err_id) [Type res_ty, err_string]
1234 err_string = Lit (mkStringLit err_msg)
1236 rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
1237 rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
1238 iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
1239 rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
1240 pAT_ERROR_ID = mkRuntimeErrorId patErrorName
1241 nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
1242 nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
1244 -- The runtime error Ids take a UTF8-encoded string as argument
1245 mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
1246 runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
1250 eRROR_ID = pc_bottoming_Id errorName errorTy
1253 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
1254 -- Notice the openAlphaTyVar. It says that "error" can be applied
1255 -- to unboxed as well as boxed types. This is OK because it never
1256 -- returns, so the return type is irrelevant.
1260 %************************************************************************
1262 \subsection{Utilities}
1264 %************************************************************************
1267 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1268 pcMiscPrelId name ty info
1269 = mkVanillaGlobal name ty info
1270 -- We lie and say the thing is imported; otherwise, we get into
1271 -- a mess with dependency analysis; e.g., core2stg may heave in
1272 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1273 -- being compiled, then it's just a matter of luck if the definition
1274 -- will be in "the right place" to be in scope.
1276 pc_bottoming_Id name ty
1277 = pcMiscPrelId name ty bottoming_info
1279 bottoming_info = vanillaIdInfo `setAllStrictnessInfo` Just strict_sig
1280 -- Do *not* mark them as NoCafRefs, because they can indeed have
1281 -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
1282 -- which has some CAFs
1283 -- In due course we may arrange that these error-y things are
1284 -- regarded by the GC as permanently live, in which case we
1285 -- can give them NoCaf info. As it is, any function that calls
1286 -- any pc_bottoming_Id will itself have CafRefs, which bloats
1289 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
1290 -- These "bottom" out, no matter what their arguments