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 -- The above warning supression flag is a temporary kludge.
17 -- While working on this module you are encouraged to remove it and fix
18 -- any warnings in the module. See
19 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
23 mkDictFunId, mkDefaultMethodId,
28 mkPrimOpId, mkFCallId, mkTickBoxOpId, mkBreakPointOpId,
30 mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
31 wrapFamInstBody, unwrapFamInstScrut,
32 mkUnpackCase, mkProductBox,
34 -- And some particular Ids; see below for why they are wired in
35 wiredInIds, ghcPrimIds,
36 unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId,
37 lazyId, lazyIdUnfolding, lazyIdKey,
40 rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
41 nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
42 pAT_ERROR_ID, eRROR_ID,
47 #include "HsVersions.h"
70 import Var ( Var, TyVar, mkCoVar)
78 import BasicTypes hiding ( SuccessFlag(..) )
86 %************************************************************************
88 \subsection{Wired in Ids}
90 %************************************************************************
94 = [ -- These error-y things are wired in because we don't yet have
95 -- a way to express in an interface file that the result type variable
96 -- is 'open'; that is can be unified with an unboxed type
98 -- [The interface file format now carry such information, but there's
99 -- no way yet of expressing at the definition site for these
100 -- error-reporting functions that they have an 'open'
101 -- result type. -- sof 1/99]
103 eRROR_ID, -- This one isn't used anywhere else in the compiler
104 -- But we still need it in wiredInIds so that when GHC
105 -- compiles a program that mentions 'error' we don't
106 -- import its type from the interface file; we just get
107 -- the Id defined here. Which has an 'open-tyvar' type.
110 iRREFUT_PAT_ERROR_ID,
111 nON_EXHAUSTIVE_GUARDS_ERROR_ID,
112 nO_METHOD_BINDING_ERROR_ID,
119 -- These Ids are exported from GHC.Prim
121 = [ -- These can't be defined in Haskell, but they have
122 -- perfectly reasonable unfoldings in Core
130 %************************************************************************
132 \subsection{Data constructors}
134 %************************************************************************
136 The wrapper for a constructor is an ordinary top-level binding that evaluates
137 any strict args, unboxes any args that are going to be flattened, and calls
140 We're going to build a constructor that looks like:
142 data (Data a, C b) => T a b = T1 !a !Int b
145 \d1::Data a, d2::C b ->
146 \p q r -> case p of { p ->
148 Con T1 [a,b] [p,q,r]}}
152 * d2 is thrown away --- a context in a data decl is used to make sure
153 one *could* construct dictionaries at the site the constructor
154 is used, but the dictionary isn't actually used.
156 * We have to check that we can construct Data dictionaries for
157 the types a and Int. Once we've done that we can throw d1 away too.
159 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
160 all that matters is that the arguments are evaluated. "seq" is
161 very careful to preserve evaluation order, which we don't need
164 You might think that we could simply give constructors some strictness
165 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
166 But we don't do that because in the case of primops and functions strictness
167 is a *property* not a *requirement*. In the case of constructors we need to
168 do something active to evaluate the argument.
170 Making an explicit case expression allows the simplifier to eliminate
171 it in the (common) case where the constructor arg is already evaluated.
173 Note [Wrappers for data instance tycons]
174 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
175 In the case of data instances, the wrapper also applies the coercion turning
176 the representation type into the family instance type to cast the result of
177 the wrapper. For example, consider the declarations
179 data family Map k :: * -> *
180 data instance Map (a, b) v = MapPair (Map a (Pair b v))
182 The tycon to which the datacon MapPair belongs gets a unique internal
183 name of the form :R123Map, and we call it the representation tycon.
184 In contrast, Map is the family tycon (accessible via
185 tyConFamInst_maybe). A coercion allows you to move between
186 representation and family type. It is accessible from :R123Map via
187 tyConFamilyCoercion_maybe and has kind
189 Co123Map a b v :: {Map (a, b) v :=: :R123Map a b v}
191 The wrapper and worker of MapPair get the types
194 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
195 $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v)
198 MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
200 This coercion is conditionally applied by wrapFamInstBody.
202 It's a bit more complicated if the data instance is a GADT as well!
204 data instance T [a] where
205 T1 :: forall b. b -> T [Maybe b]
207 Co7T a :: T [a] ~ :R7T a
212 $WT1 :: forall b. b -> T [Maybe b]
213 $WT1 b v = T1 (Maybe b) b (Maybe b) v
214 `cast` sym (Co7T (Maybe b))
217 T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c
220 mkDataConIds :: Name -> Name -> DataCon -> DataConIds
221 mkDataConIds wrap_name wkr_name data_con
222 | isNewTyCon tycon -- Newtype, only has a worker
223 = DCIds Nothing nt_work_id
225 | any isMarkedStrict all_strict_marks -- Algebraic, needs wrapper
226 || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
227 || isFamInstTyCon tycon -- depends on this test
228 = DCIds (Just alg_wrap_id) wrk_id
230 | otherwise -- Algebraic, no wrapper
231 = DCIds Nothing wrk_id
233 (univ_tvs, ex_tvs, eq_spec,
234 eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
235 tycon = dataConTyCon data_con -- The representation TyCon (not family)
237 ----------- Worker (algebraic data types only) --------------
238 -- The *worker* for the data constructor is the function that
239 -- takes the representation arguments and builds the constructor.
240 wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
241 (dataConRepType data_con) wkr_info
243 wkr_arity = dataConRepArity data_con
244 wkr_info = noCafIdInfo
245 `setArityInfo` wkr_arity
246 `setAllStrictnessInfo` Just wkr_sig
247 `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
250 wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
251 -- Note [Data-con worker strictness]
252 -- Notice that we do *not* say the worker is strict
253 -- even if the data constructor is declared strict
254 -- e.g. data T = MkT !(Int,Int)
255 -- Why? Because the *wrapper* is strict (and its unfolding has case
256 -- expresssions that do the evals) but the *worker* itself is not.
257 -- If we pretend it is strict then when we see
258 -- case x of y -> $wMkT y
259 -- the simplifier thinks that y is "sure to be evaluated" (because
260 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
262 -- When the simplifer sees a pattern
263 -- case e of MkT x -> ...
264 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
265 -- but that's fine... dataConRepStrictness comes from the data con
266 -- not from the worker Id.
268 cpr_info | isProductTyCon tycon &&
271 wkr_arity <= mAX_CPR_SIZE = retCPR
273 -- RetCPR is only true for products that are real data types;
274 -- that is, not unboxed tuples or [non-recursive] newtypes
276 ----------- Workers for newtypes --------------
277 nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
278 nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
279 `setArityInfo` 1 -- Arity 1
280 `setUnfoldingInfo` newtype_unf
281 newtype_unf = -- The assertion below is no longer correct:
282 -- there may be a dict theta rather than a singleton orig_arg_ty
283 -- ASSERT( isVanillaDataCon data_con &&
284 -- isSingleton orig_arg_tys )
286 -- No existentials on a newtype, but it can have a context
287 -- e.g. newtype Eq a => T a = MkT (...)
288 mkCompulsoryUnfolding $
289 mkLams wrap_tvs $ Lam id_arg1 $
290 wrapNewTypeBody tycon res_ty_args
293 id_arg1 = mkTemplateLocal 1
294 (if null orig_arg_tys
295 then ASSERT(not (null $ dataConDictTheta data_con)) mkPredTy $ head (dataConDictTheta data_con)
296 else head orig_arg_tys
299 ----------- Wrapper --------------
300 -- We used to include the stupid theta in the wrapper's args
301 -- but now we don't. Instead the type checker just injects these
302 -- extra constraints where necessary.
303 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
304 res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
305 eq_tys = mkPredTys eq_theta
306 dict_tys = mkPredTys dict_theta
307 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
308 mkFunTys orig_arg_tys $ res_ty
309 -- NB: watch out here if you allow user-written equality
310 -- constraints in data constructor signatures
312 ----------- Wrappers for algebraic data types --------------
313 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
314 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
315 `setArityInfo` wrap_arity
316 -- It's important to specify the arity, so that partial
317 -- applications are treated as values
318 `setUnfoldingInfo` wrap_unf
319 `setAllStrictnessInfo` Just wrap_sig
321 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
322 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
323 arg_dmds = map mk_dmd all_strict_marks
324 mk_dmd str | isMarkedStrict str = evalDmd
325 | otherwise = lazyDmd
326 -- The Cpr info can be important inside INLINE rhss, where the
327 -- wrapper constructor isn't inlined.
328 -- And the argument strictness can be important too; we
329 -- may not inline a contructor when it is partially applied.
331 -- data W = C !Int !Int !Int
332 -- ...(let w = C x in ...(w p q)...)...
333 -- we want to see that w is strict in its two arguments
335 wrap_unf = mkTopUnfolding $ Note InlineMe $
338 mkLams dict_args $ mkLams id_args $
339 foldr mk_case con_app
340 (zip (dict_args ++ id_args) all_strict_marks)
343 con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
344 Var wrk_id `mkTyApps` res_ty_args
346 -- Equality evidence:
347 `mkTyApps` map snd eq_spec
349 `mkVarApps` reverse rep_ids
351 (dict_args,i2) = mkLocals 1 dict_tys
352 (id_args,i3) = mkLocals i2 orig_arg_tys
354 (eq_args,_) = mkCoVarLocals i3 eq_tys
356 mkCoVarLocals i [] = ([],i)
357 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
358 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
362 :: (Id, StrictnessMark) -- Arg, strictness
363 -> (Int -> [Id] -> CoreExpr) -- Body
364 -> Int -- Next rep arg id
365 -> [Id] -- Rep args so far, reversed
367 mk_case (arg,strict) body i rep_args
369 NotMarkedStrict -> body i (arg:rep_args)
371 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
373 Case (Var arg) arg res_ty [(DEFAULT,[], body i (arg:rep_args))]
376 -> unboxProduct i (Var arg) (idType arg) the_body
378 the_body i con_args = body i (reverse con_args ++ rep_args)
380 mAX_CPR_SIZE :: Arity
382 -- We do not treat very big tuples as CPR-ish:
383 -- a) for a start we get into trouble because there aren't
384 -- "enough" unboxed tuple types (a tiresome restriction,
386 -- b) more importantly, big unboxed tuples get returned mainly
387 -- on the stack, and are often then allocated in the heap
388 -- by the caller. So doing CPR for them may in fact make
391 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
397 %************************************************************************
399 \subsection{Record selectors}
401 %************************************************************************
403 We're going to build a record selector unfolding that looks like this:
405 data T a b c = T1 { ..., op :: a, ...}
406 | T2 { ..., op :: a, ...}
409 sel = /\ a b c -> \ d -> case d of
414 Similarly for newtypes
416 newtype N a = MkN { unN :: a->a }
419 unN n = coerce (a->a) n
421 We need to take a little care if the field has a polymorphic type:
423 data R = R { f :: forall a. a->a }
427 f :: forall a. R -> a -> a
428 f = /\ a \ r = case r of
431 (not f :: R -> forall a. a->a, which gives the type inference mechanism
432 problems at call sites)
434 Similarly for (recursive) newtypes
436 newtype N = MkN { unN :: forall a. a->a }
438 unN :: forall b. N -> b -> b
439 unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
442 Note [Naughty record selectors]
443 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
444 A "naughty" field is one for which we can't define a record
445 selector, because an existential type variable would escape. For example:
446 data T = forall a. MkT { x,y::a }
447 We obviously can't define
449 Nevertheless we *do* put a RecordSelId into the type environment
450 so that if the user tries to use 'x' as a selector we can bleat
451 helpfully, rather than saying unhelpfully that 'x' is not in scope.
452 Hence the sel_naughty flag, to identify record selectors that don't really exist.
454 In general, a field is naughty if its type mentions a type variable that
455 isn't in the result type of the constructor.
457 Note [GADT record selectors]
458 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
459 For GADTs, we require that all constructors with a common field 'f' have the same
460 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
463 T1 { f :: a } :: T [a]
464 T2 { f :: a, y :: b } :: T [a]
465 and now the selector takes that type as its argument:
466 f :: forall a. T [a] -> a
470 Note the forall'd tyvars of the selector are just the free tyvars
471 of the result type; there may be other tyvars in the constructor's
472 type (e.g. 'b' in T2).
474 Note [Selector running example]
475 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
476 It's OK to combine GADTs and type families. Here's a running example:
478 data instance T [a] where
479 T1 { fld :: b } :: T [Maybe b]
481 The representation type looks like this
483 T1 { fld :: b } :: :R7T (Maybe b)
485 and there's coercion from the family type to the representation type
486 :CoR7T a :: T [a] ~ :R7T a
488 The selector we want for fld looks like this:
490 fld :: forall b. T [Maybe b] -> b
491 fld = /\b. \(d::T [Maybe b]).
492 case d `cast` :CoR7T (Maybe b) of
495 The scrutinee of the case has type :R7T (Maybe b), which can be
496 gotten by appying the eq_spec to the univ_tvs of the data con.
499 mkRecordSelId :: TyCon -> FieldLabel -> Id
500 mkRecordSelId tycon field_label
501 -- Assumes that all fields with the same field label have the same type
504 -- Because this function gets called by implicitTyThings, we need to
505 -- produce the OccName of the Id without doing any suspend type checks.
506 -- (see the note [Tricky iface loop]).
507 -- A suspended type-check is sometimes necessary to compute field_ty,
508 -- so we need to make sure that we suspend anything that depends on field_ty.
510 -- the overall result
511 sel_id = mkGlobalId sel_id_details field_label theType theInfo
513 -- check whether the type is naughty: this thunk does not get forced
514 -- until the type is actually needed
515 field_ty = dataConFieldType con1 field_label
516 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tv_set)
518 -- it's important that this doesn't force the if
519 (theType, theInfo) = if is_naughty
520 -- Escapist case here for naughty constructors
521 -- We give it no IdInfo, and a type of
522 -- forall a.a (never looked at)
523 then (forall_a_a, noCafIdInfo)
524 -- otherwise do the real case
525 else (selector_ty, info)
527 sel_id_details = RecordSelId { sel_tycon = tycon,
528 sel_label = field_label,
529 sel_naughty = is_naughty }
530 -- For a data type family, the tycon is the *instance* TyCon
533 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
535 -- real case starts here:
536 data_cons = tyConDataCons tycon
537 data_cons_w_field = filter has_field data_cons -- Can't be empty!
538 has_field con = field_label `elem` dataConFieldLabels con
540 con1 = ASSERT( not (null data_cons_w_field) ) head data_cons_w_field
541 (univ_tvs, _, eq_spec, _, _, _, data_ty) = dataConFullSig con1
542 -- For a data type family, the data_ty (and hence selector_ty) mentions
543 -- only the family TyCon, not the instance TyCon
544 data_tv_set = tyVarsOfType data_ty
545 data_tvs = varSetElems data_tv_set
547 -- *Very* tiresomely, the selectors are (unnecessarily!) overloaded over
548 -- just the dictionaries in the types of the constructors that contain
549 -- the relevant field. [The Report says that pattern matching on a
550 -- constructor gives the same constraints as applying it.] Urgh.
552 -- However, not all data cons have all constraints (because of
553 -- BuildTyCl.mkDataConStupidTheta). So we need to find all the data cons
554 -- involved in the pattern match and take the union of their constraints.
555 stupid_dict_tys = mkPredTys (dataConsStupidTheta data_cons_w_field)
556 n_stupid_dicts = length stupid_dict_tys
558 (field_tyvars,pre_field_theta,field_tau) = tcSplitSigmaTy field_ty
559 field_theta = filter (not . isEqPred) pre_field_theta
560 field_dict_tys = mkPredTys field_theta
561 n_field_dict_tys = length field_dict_tys
562 -- If the field has a universally quantified type we have to
563 -- be a bit careful. Suppose we have
564 -- data R = R { op :: forall a. Foo a => a -> a }
565 -- Then we can't give op the type
566 -- op :: R -> forall a. Foo a => a -> a
567 -- because the typechecker doesn't understand foralls to the
568 -- right of an arrow. The "right" type to give it is
569 -- op :: forall a. Foo a => R -> a -> a
570 -- But then we must generate the right unfolding too:
571 -- op = /\a -> \dfoo -> \ r ->
574 -- Note that this is exactly the type we'd infer from a user defn
578 selector_ty = mkForAllTys data_tvs $ mkForAllTys field_tyvars $
579 mkFunTys stupid_dict_tys $ mkFunTys field_dict_tys $
580 mkFunTy data_ty field_tau
582 arity = 1 + n_stupid_dicts + n_field_dict_tys
584 (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
585 -- Use the demand analyser to work out strictness.
586 -- With all this unpackery it's not easy!
589 `setCafInfo` caf_info
591 `setUnfoldingInfo` mkTopUnfolding rhs_w_str
592 `setAllStrictnessInfo` Just strict_sig
594 -- Allocate Ids. We do it a funny way round because field_dict_tys is
595 -- almost always empty. Also note that we use max_dict_tys
596 -- rather than n_dict_tys, because the latter gives an infinite loop:
597 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
598 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
599 stupid_dict_ids = mkTemplateLocalsNum 1 stupid_dict_tys
600 max_stupid_dicts = length (tyConStupidTheta tycon)
601 field_dict_base = max_stupid_dicts + 1
602 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
603 dict_id_base = field_dict_base + n_field_dict_tys
604 data_id = mkTemplateLocal dict_id_base data_ty
605 scrut_id = mkTemplateLocal (dict_id_base+1) scrut_ty
606 arg_base = dict_id_base + 2
608 the_alts :: [CoreAlt]
609 the_alts = map mk_alt data_cons_w_field -- Already sorted by data-con
610 no_default = length data_cons == length data_cons_w_field -- No default needed
612 default_alt | no_default = []
613 | otherwise = [(DEFAULT, [], error_expr)]
615 -- The default branch may have CAF refs, because it calls recSelError etc.
616 caf_info | no_default = NoCafRefs
617 | otherwise = MayHaveCafRefs
619 sel_rhs = mkLams data_tvs $ mkLams field_tyvars $
620 mkLams stupid_dict_ids $ mkLams field_dict_ids $
621 Lam data_id $ mk_result sel_body
623 scrut_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
624 scrut_ty = mkTyConApp tycon scrut_ty_args
625 scrut = unwrapFamInstScrut tycon scrut_ty_args (Var data_id)
626 -- First coerce from the type family to the representation type
628 -- NB: A newtype always has a vanilla DataCon; no existentials etc
629 -- data_tys will simply be the dataConUnivTyVars
630 sel_body | isNewTyCon tycon = unwrapNewTypeBody tycon scrut_ty_args scrut
631 | otherwise = Case scrut scrut_id field_ty (default_alt ++ the_alts)
633 mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
634 -- We pull the field lambdas to the top, so we need to
635 -- apply them in the body. For example:
636 -- data T = MkT { foo :: forall a. a->a }
638 -- foo :: forall a. T -> a -> a
639 -- foo = /\a. \t:T. case t of { MkT f -> f a }
642 = ASSERT2( data_ty `tcEqType` field_ty, ppr data_con $$ ppr data_ty $$ ppr field_ty )
643 mkReboxingAlt rebox_uniqs data_con (ex_tvs ++ co_tvs ++ arg_vs) rhs
645 -- get pattern binders with types appropriately instantiated
646 arg_uniqs = map mkBuiltinUnique [arg_base..]
647 (ex_tvs, co_tvs, arg_vs) = dataConOrigInstPat arg_uniqs data_con scrut_ty_args
649 rebox_base = arg_base + length ex_tvs + length co_tvs + length arg_vs
650 rebox_uniqs = map mkBuiltinUnique [rebox_base..]
652 -- data T :: *->* where T1 { fld :: Maybe b } -> T [b]
653 -- Hence T1 :: forall a b. (a=[b]) => b -> T a
654 -- fld :: forall b. T [b] -> Maybe b
655 -- fld = /\b.\(t:T[b]). case t of
656 -- T1 b' (c : [b]=[b']) (x:Maybe b')
657 -- -> x `cast` Maybe (sym (right c))
660 -- Generate the refinement for b'=b,
661 -- and apply to (Maybe b'), to get (Maybe b)
662 Succeeded refinement = gadtRefine emptyRefinement ex_tvs co_tvs
663 the_arg_id_ty = idType the_arg_id
664 (rhs, data_ty) = case refineType refinement the_arg_id_ty of
665 Just (co, data_ty) -> (Cast (Var the_arg_id) co, data_ty)
666 Nothing -> (Var the_arg_id, the_arg_id_ty)
668 field_vs = filter (not . isPredTy . idType) arg_vs
669 the_arg_id = assoc "mkRecordSelId:mk_alt" (field_lbls `zip` field_vs) field_label
670 field_lbls = dataConFieldLabels data_con
672 error_expr = mkRuntimeErrorApp rEC_SEL_ERROR_ID field_ty full_msg
673 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
675 -- unbox a product type...
676 -- we will recurse into newtypes, casting along the way, and unbox at the
677 -- first product data constructor we find. e.g.
679 -- data PairInt = PairInt Int Int
680 -- newtype S = MkS PairInt
683 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
684 -- ids, we get (modulo int passing)
686 -- case (e `cast` CoT) `cast` CoS of
687 -- PairInt a b -> body [a,b]
689 -- The Ints passed around are just for creating fresh locals
690 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
691 unboxProduct i arg arg_ty body
694 result = mkUnpackCase the_id arg con_args boxing_con rhs
695 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
696 ([the_id], i') = mkLocals i [arg_ty]
697 (con_args, i'') = mkLocals i' tys
698 rhs = body i'' con_args
700 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
701 -- (mkUnpackCase x e args Con body)
703 -- case (e `cast` ...) of bndr { Con args -> body }
705 -- the type of the bndr passed in is irrelevent
706 mkUnpackCase bndr arg unpk_args boxing_con body
707 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
709 (cast_arg, bndr_ty) = go (idType bndr) arg
711 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
712 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
713 = go (newTyConInstRhs tycon tycon_args)
714 (unwrapNewTypeBody tycon tycon_args arg)
715 | otherwise = (arg, ty)
718 reboxProduct :: [Unique] -- uniques to create new local binders
719 -> Type -- type of product to box
720 -> ([Unique], -- remaining uniques
721 CoreExpr, -- boxed product
722 [Id]) -- Ids being boxed into product
725 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
727 us' = dropList con_arg_tys us
729 arg_ids = zipWith (mkSysLocal FSLIT("rb")) us con_arg_tys
731 bind_rhs = mkProductBox arg_ids ty
734 (us', bind_rhs, arg_ids)
736 mkProductBox :: [Id] -> Type -> CoreExpr
737 mkProductBox arg_ids ty
740 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
743 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
744 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
745 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
747 wrap expr = wrapNewTypeBody tycon tycon_args expr
750 -- (mkReboxingAlt us con xs rhs) basically constructs the case
751 -- alternative (con, xs, rhs)
752 -- but it does the reboxing necessary to construct the *source*
753 -- arguments, xs, from the representation arguments ys.
755 -- data T = MkT !(Int,Int) Bool
757 -- mkReboxingAlt MkT [x,b] r
758 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
760 -- mkDataAlt should really be in DataCon, but it can't because
761 -- it manipulates CoreSyn.
764 :: [Unique] -- Uniques for the new Ids
766 -> [Var] -- Source-level args, including existential dicts
770 mkReboxingAlt us con args rhs
771 | not (any isMarkedUnboxed stricts)
772 = (DataAlt con, args, rhs)
776 (binds, args') = go args stricts us
778 (DataAlt con, args', mkLets binds rhs)
781 stricts = dataConExStricts con ++ dataConStrictMarks con
783 go [] _stricts _us = ([], [])
785 -- Type variable case
786 go (arg:args) stricts us
788 = let (binds, args') = go args stricts us
789 in (binds, arg:args')
791 -- Term variable case
792 go (arg:args) (str:stricts) us
793 | isMarkedUnboxed str
795 let (binds, unpacked_args') = go args stricts us'
796 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
798 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
800 = let (binds, args') = go args stricts us
801 in (binds, arg:args')
805 %************************************************************************
807 \subsection{Dictionary selectors}
809 %************************************************************************
811 Selecting a field for a dictionary. If there is just one field, then
812 there's nothing to do.
814 Dictionary selectors may get nested forall-types. Thus:
817 op :: forall b. Ord b => a -> b -> b
819 Then the top-level type for op is
821 op :: forall a. Foo a =>
825 This is unlike ordinary record selectors, which have all the for-alls
826 at the outside. When dealing with classes it's very convenient to
827 recover the original type signature from the class op selector.
830 mkDictSelId :: Name -> Class -> Id
831 mkDictSelId name clas
832 = mkGlobalId (ClassOpId clas) name sel_ty info
834 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
835 -- We can't just say (exprType rhs), because that would give a type
837 -- for a single-op class (after all, the selector is the identity)
838 -- But it's type must expose the representation of the dictionary
839 -- to get (say) C a -> (a -> a)
843 `setUnfoldingInfo` mkTopUnfolding rhs
844 `setAllStrictnessInfo` Just strict_sig
846 -- We no longer use 'must-inline' on record selectors. They'll
847 -- inline like crazy if they scrutinise a constructor
849 -- The strictness signature is of the form U(AAAVAAAA) -> T
850 -- where the V depends on which item we are selecting
851 -- It's worth giving one, so that absence info etc is generated
852 -- even if the selector isn't inlined
853 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
854 arg_dmd | isNewTyCon tycon = evalDmd
855 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
858 tycon = classTyCon clas
859 [data_con] = tyConDataCons tycon
860 tyvars = dataConUnivTyVars data_con
861 arg_tys = {- ASSERT( isVanillaDataCon data_con ) -} dataConRepArgTys data_con
862 eq_theta = dataConEqTheta data_con
863 the_arg_id = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` arg_ids) name
865 pred = mkClassPred clas (mkTyVarTys tyvars)
866 dict_id = mkTemplateLocal 1 $ mkPredTy pred
867 (eq_ids,n) = mkCoVarLocals 2 $ mkPredTys eq_theta
868 arg_ids = mkTemplateLocalsNum n arg_tys
870 mkCoVarLocals i [] = ([],i)
871 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
872 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
875 rhs = mkLams tyvars (Lam dict_id rhs_body)
876 rhs_body | isNewTyCon tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
877 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
878 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
882 %************************************************************************
884 Wrapping and unwrapping newtypes and type families
886 %************************************************************************
889 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
890 -- The wrapper for the data constructor for a newtype looks like this:
891 -- newtype T a = MkT (a,Int)
892 -- MkT :: forall a. (a,Int) -> T a
893 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
894 -- where CoT is the coercion TyCon assoicated with the newtype
896 -- The call (wrapNewTypeBody T [a] e) returns the
897 -- body of the wrapper, namely
898 -- e `cast` (CoT [a])
900 -- If a coercion constructor is provided in the newtype, then we use
901 -- it, otherwise the wrap/unwrap are both no-ops
903 -- If the we are dealing with a newtype *instance*, we have a second coercion
904 -- identifying the family instance with the constructor of the newtype
905 -- instance. This coercion is applied in any case (ie, composed with the
906 -- coercion constructor of the newtype or applied by itself).
908 wrapNewTypeBody tycon args result_expr
909 = wrapFamInstBody tycon args inner
912 | Just co_con <- newTyConCo_maybe tycon
913 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
917 -- When unwrapping, we do *not* apply any family coercion, because this will
918 -- be done via a CoPat by the type checker. We have to do it this way as
919 -- computing the right type arguments for the coercion requires more than just
920 -- a spliting operation (cf, TcPat.tcConPat).
922 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
923 unwrapNewTypeBody tycon args result_expr
924 | Just co_con <- newTyConCo_maybe tycon
925 = mkCoerce (mkTyConApp co_con args) result_expr
929 -- If the type constructor is a representation type of a data instance, wrap
930 -- the expression into a cast adjusting the expression type, which is an
931 -- instance of the representation type, to the corresponding instance of the
932 -- family instance type.
933 -- See Note [Wrappers for data instance tycons]
934 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
935 wrapFamInstBody tycon args body
936 | Just co_con <- tyConFamilyCoercion_maybe tycon
937 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
941 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
942 unwrapFamInstScrut tycon args scrut
943 | Just co_con <- tyConFamilyCoercion_maybe tycon
944 = mkCoerce (mkTyConApp co_con args) scrut
950 %************************************************************************
952 \subsection{Primitive operations
954 %************************************************************************
957 mkPrimOpId :: PrimOp -> Id
961 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
962 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
963 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
964 (mkPrimOpIdUnique (primOpTag prim_op))
966 id = mkGlobalId (PrimOpId prim_op) name ty info
969 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
971 `setAllStrictnessInfo` Just strict_sig
973 -- For each ccall we manufacture a separate CCallOpId, giving it
974 -- a fresh unique, a type that is correct for this particular ccall,
975 -- and a CCall structure that gives the correct details about calling
978 -- The *name* of this Id is a local name whose OccName gives the full
979 -- details of the ccall, type and all. This means that the interface
980 -- file reader can reconstruct a suitable Id
982 mkFCallId :: Unique -> ForeignCall -> Type -> Id
983 mkFCallId uniq fcall ty
984 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
985 -- A CCallOpId should have no free type variables;
986 -- when doing substitutions won't substitute over it
987 mkGlobalId (FCallId fcall) name ty info
989 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
990 -- The "occurrence name" of a ccall is the full info about the
991 -- ccall; it is encoded, but may have embedded spaces etc!
993 name = mkFCallName uniq occ_str
997 `setAllStrictnessInfo` Just strict_sig
999 (_, tau) = tcSplitForAllTys ty
1000 (arg_tys, _) = tcSplitFunTys tau
1001 arity = length arg_tys
1002 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
1004 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
1005 -- except for the type:
1007 -- a plain HPC tick box has type (State# RealWorld)
1008 -- a breakpoint Id has type forall a.a
1010 -- The breakpoint Id will be applied to a list of arbitrary free variables,
1011 -- which is why it needs a polymorphic type.
1013 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
1014 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
1016 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
1017 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
1018 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
1020 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
1022 tickbox = TickBox mod ix
1023 occ_str = showSDoc (braces (ppr tickbox))
1024 name = mkTickBoxOpName uniq occ_str
1029 %************************************************************************
1031 \subsection{DictFuns and default methods}
1033 %************************************************************************
1035 Important notes about dict funs and default methods
1036 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1037 Dict funs and default methods are *not* ImplicitIds. Their definition
1038 involves user-written code, so we can't figure out their strictness etc
1039 based on fixed info, as we can for constructors and record selectors (say).
1041 We build them as LocalIds, but with External Names. This ensures that
1042 they are taken to account by free-variable finding and dependency
1043 analysis (e.g. CoreFVs.exprFreeVars).
1045 Why shouldn't they be bound as GlobalIds? Because, in particular, if
1046 they are globals, the specialiser floats dict uses above their defns,
1047 which prevents good simplifications happening. Also the strictness
1048 analyser treats a occurrence of a GlobalId as imported and assumes it
1049 contains strictness in its IdInfo, which isn't true if the thing is
1050 bound in the same module as the occurrence.
1052 It's OK for dfuns to be LocalIds, because we form the instance-env to
1053 pass on to the next module (md_insts) in CoreTidy, afer tidying
1054 and globalising the top-level Ids.
1056 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
1057 that they aren't discarded by the occurrence analyser.
1060 mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
1062 mkDictFunId :: Name -- Name to use for the dict fun;
1069 mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
1070 = mkExportedLocalId dfun_name dfun_ty
1072 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
1074 {- 1 dec 99: disable the Mark Jones optimisation for the sake
1075 of compatibility with Hugs.
1076 See `types/InstEnv' for a discussion related to this.
1078 (class_tyvars, sc_theta, _, _) = classBigSig clas
1079 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
1080 sc_theta' = substClasses (zipTopTvSubst class_tyvars inst_tys) sc_theta
1081 dfun_theta = case inst_decl_theta of
1082 [] -> [] -- If inst_decl_theta is empty, then we don't
1083 -- want to have any dict arguments, so that we can
1084 -- expose the constant methods.
1086 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
1087 -- Otherwise we pass the superclass dictionaries to
1088 -- the dictionary function; the Mark Jones optimisation.
1090 -- NOTE the "nub". I got caught by this one:
1091 -- class Monad m => MonadT t m where ...
1092 -- instance Monad m => MonadT (EnvT env) m where ...
1093 -- Here, the inst_decl_theta has (Monad m); but so
1094 -- does the sc_theta'!
1096 -- NOTE the "not_const". I got caught by this one too:
1097 -- class Foo a => Baz a b where ...
1098 -- instance Wob b => Baz T b where..
1099 -- Now sc_theta' has Foo T
1104 %************************************************************************
1106 \subsection{Un-definable}
1108 %************************************************************************
1110 These Ids can't be defined in Haskell. They could be defined in
1111 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
1112 ensure that they were definitely, definitely inlined, because there is
1113 no curried identifier for them. That's what mkCompulsoryUnfolding
1114 does. If we had a way to get a compulsory unfolding from an interface
1115 file, we could do that, but we don't right now.
1117 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
1118 just gets expanded into a type coercion wherever it occurs. Hence we
1119 add it as a built-in Id with an unfolding here.
1121 The type variables we use here are "open" type variables: this means
1122 they can unify with both unlifted and lifted types. Hence we provide
1123 another gun with which to shoot yourself in the foot.
1126 mkWiredInIdName mod fs uniq id
1127 = mkWiredInName mod (mkOccNameFS varName fs) uniq (AnId id) UserSyntax
1129 unsafeCoerceName = mkWiredInIdName gHC_PRIM FSLIT("unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
1130 nullAddrName = mkWiredInIdName gHC_PRIM FSLIT("nullAddr#") nullAddrIdKey nullAddrId
1131 seqName = mkWiredInIdName gHC_PRIM FSLIT("seq") seqIdKey seqId
1132 realWorldName = mkWiredInIdName gHC_PRIM FSLIT("realWorld#") realWorldPrimIdKey realWorldPrimId
1133 lazyIdName = mkWiredInIdName gHC_BASE FSLIT("lazy") lazyIdKey lazyId
1135 errorName = mkWiredInIdName gHC_ERR FSLIT("error") errorIdKey eRROR_ID
1136 recSelErrorName = mkWiredInIdName gHC_ERR FSLIT("recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
1137 runtimeErrorName = mkWiredInIdName gHC_ERR FSLIT("runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
1138 irrefutPatErrorName = mkWiredInIdName gHC_ERR FSLIT("irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
1139 recConErrorName = mkWiredInIdName gHC_ERR FSLIT("recConError") recConErrorIdKey rEC_CON_ERROR_ID
1140 patErrorName = mkWiredInIdName gHC_ERR FSLIT("patError") patErrorIdKey pAT_ERROR_ID
1141 noMethodBindingErrorName = mkWiredInIdName gHC_ERR FSLIT("noMethodBindingError")
1142 noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
1143 nonExhaustiveGuardsErrorName
1144 = mkWiredInIdName gHC_ERR FSLIT("nonExhaustiveGuardsError")
1145 nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
1149 -- unsafeCoerce# :: forall a b. a -> b
1151 = pcMiscPrelId unsafeCoerceName ty info
1153 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1156 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
1157 (mkFunTy openAlphaTy openBetaTy)
1158 [x] = mkTemplateLocals [openAlphaTy]
1159 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
1160 Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
1162 -- nullAddr# :: Addr#
1163 -- The reason is is here is because we don't provide
1164 -- a way to write this literal in Haskell.
1166 = pcMiscPrelId nullAddrName addrPrimTy info
1168 info = noCafIdInfo `setUnfoldingInfo`
1169 mkCompulsoryUnfolding (Lit nullAddrLit)
1172 = pcMiscPrelId seqName ty info
1174 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1177 ty = mkForAllTys [alphaTyVar,openBetaTyVar]
1178 (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
1179 [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
1180 rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
1182 -- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1183 -- Used to lazify pseq: pseq a b = a `seq` lazy b
1185 -- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1186 -- not from GHC.Base.hi. This is important, because the strictness
1187 -- analyser will spot it as strict!
1189 -- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapperpass
1190 -- (see WorkWrap.wwExpr)
1191 -- We could use inline phases to do this, but that would be vulnerable to changes in
1192 -- phase numbering....we must inline precisely after strictness analysis.
1194 = pcMiscPrelId lazyIdName ty info
1197 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
1199 lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal
1200 lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
1202 [x] = mkTemplateLocals [openAlphaTy]
1205 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1206 nasty as-is, change it back to a literal (@Literal@).
1208 voidArgId is a Local Id used simply as an argument in functions
1209 where we just want an arg to avoid having a thunk of unlifted type.
1211 x = \ void :: State# RealWorld -> (# p, q #)
1213 This comes up in strictness analysis
1216 realWorldPrimId -- :: State# RealWorld
1217 = pcMiscPrelId realWorldName realWorldStatePrimTy
1218 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1219 -- The evaldUnfolding makes it look that realWorld# is evaluated
1220 -- which in turn makes Simplify.interestingArg return True,
1221 -- which in turn makes INLINE things applied to realWorld# likely
1224 voidArgId -- :: State# RealWorld
1225 = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
1229 %************************************************************************
1231 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
1233 %************************************************************************
1235 GHC randomly injects these into the code.
1237 @patError@ is just a version of @error@ for pattern-matching
1238 failures. It knows various ``codes'' which expand to longer
1239 strings---this saves space!
1241 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
1242 well shouldn't be yanked on, but if one is, then you will get a
1243 friendly message from @absentErr@ (rather than a totally random
1246 @parError@ is a special version of @error@ which the compiler does
1247 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
1248 templates, but we don't ever expect to generate code for it.
1252 :: Id -- Should be of type (forall a. Addr# -> a)
1253 -- where Addr# points to a UTF8 encoded string
1254 -> Type -- The type to instantiate 'a'
1255 -> String -- The string to print
1258 mkRuntimeErrorApp err_id res_ty err_msg
1259 = mkApps (Var err_id) [Type res_ty, err_string]
1261 err_string = Lit (mkStringLit err_msg)
1263 rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
1264 rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
1265 iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
1266 rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
1267 pAT_ERROR_ID = mkRuntimeErrorId patErrorName
1268 nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
1269 nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
1271 -- The runtime error Ids take a UTF8-encoded string as argument
1272 mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
1273 runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
1277 eRROR_ID = pc_bottoming_Id errorName errorTy
1280 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
1281 -- Notice the openAlphaTyVar. It says that "error" can be applied
1282 -- to unboxed as well as boxed types. This is OK because it never
1283 -- returns, so the return type is irrelevant.
1287 %************************************************************************
1289 \subsection{Utilities}
1291 %************************************************************************
1294 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1295 pcMiscPrelId name ty info
1296 = mkVanillaGlobal name ty info
1297 -- We lie and say the thing is imported; otherwise, we get into
1298 -- a mess with dependency analysis; e.g., core2stg may heave in
1299 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1300 -- being compiled, then it's just a matter of luck if the definition
1301 -- will be in "the right place" to be in scope.
1303 pc_bottoming_Id name ty
1304 = pcMiscPrelId name ty bottoming_info
1306 bottoming_info = vanillaIdInfo `setAllStrictnessInfo` Just strict_sig
1307 -- Do *not* mark them as NoCafRefs, because they can indeed have
1308 -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
1309 -- which has some CAFs
1310 -- In due course we may arrange that these error-y things are
1311 -- regarded by the GC as permanently live, in which case we
1312 -- can give them NoCaf info. As it is, any function that calls
1313 -- any pc_bottoming_Id will itself have CafRefs, which bloats
1316 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
1317 -- These "bottom" out, no matter what their arguments