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 `mkTyApps` map snd eq_spec -- Equality evidence
348 `mkVarApps` reverse rep_ids
350 (dict_args,i2) = mkLocals 1 dict_tys
351 (id_args,i3) = mkLocals i2 orig_arg_tys
353 (eq_args,_) = mkCoVarLocals i3 eq_tys
355 mkCoVarLocals i [] = ([],i)
356 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
357 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
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 res_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)
396 %************************************************************************
398 \subsection{Record selectors}
400 %************************************************************************
402 We're going to build a record selector unfolding that looks like this:
404 data T a b c = T1 { ..., op :: a, ...}
405 | T2 { ..., op :: a, ...}
408 sel = /\ a b c -> \ d -> case d of
413 Similarly for newtypes
415 newtype N a = MkN { unN :: a->a }
418 unN n = coerce (a->a) n
420 We need to take a little care if the field has a polymorphic type:
422 data R = R { f :: forall a. a->a }
426 f :: forall a. R -> a -> a
427 f = /\ a \ r = case r of
430 (not f :: R -> forall a. a->a, which gives the type inference mechanism
431 problems at call sites)
433 Similarly for (recursive) newtypes
435 newtype N = MkN { unN :: forall a. a->a }
437 unN :: forall b. N -> b -> b
438 unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
441 Note [Naughty record selectors]
442 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
443 A "naughty" field is one for which we can't define a record
444 selector, because an existential type variable would escape. For example:
445 data T = forall a. MkT { x,y::a }
446 We obviously can't define
448 Nevertheless we *do* put a RecordSelId into the type environment
449 so that if the user tries to use 'x' as a selector we can bleat
450 helpfully, rather than saying unhelpfully that 'x' is not in scope.
451 Hence the sel_naughty flag, to identify record selectors that don't really exist.
453 In general, a field is naughty if its type mentions a type variable that
454 isn't in the result type of the constructor.
456 Note [GADT record selectors]
457 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
458 For GADTs, we require that all constructors with a common field 'f' have the same
459 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
462 T1 { f :: a } :: T [a]
463 T2 { f :: a, y :: b } :: T [a]
464 and now the selector takes that type as its argument:
465 f :: forall a. T [a] -> a
469 Note the forall'd tyvars of the selector are just the free tyvars
470 of the result type; there may be other tyvars in the constructor's
471 type (e.g. 'b' in T2).
473 Note [Selector running example]
474 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
475 It's OK to combine GADTs and type families. Here's a running example:
477 data instance T [a] where
478 T1 { fld :: b } :: T [Maybe b]
480 The representation type looks like this
482 T1 { fld :: b } :: :R7T (Maybe b)
484 and there's coercion from the family type to the representation type
485 :CoR7T a :: T [a] ~ :R7T a
487 The selector we want for fld looks like this:
489 fld :: forall b. T [Maybe b] -> b
490 fld = /\b. \(d::T [Maybe b]).
491 case d `cast` :CoR7T (Maybe b) of
494 The scrutinee of the case has type :R7T (Maybe b), which can be
495 gotten by appying the eq_spec to the univ_tvs of the data con.
498 mkRecordSelId :: TyCon -> FieldLabel -> Id
499 mkRecordSelId tycon field_label
500 -- Assumes that all fields with the same field label have the same type
503 -- Because this function gets called by implicitTyThings, we need to
504 -- produce the OccName of the Id without doing any suspend type checks.
505 -- (see the note [Tricky iface loop]).
506 -- A suspended type-check is sometimes necessary to compute field_ty,
507 -- so we need to make sure that we suspend anything that depends on field_ty.
509 -- the overall result
510 sel_id = mkGlobalId sel_id_details field_label theType theInfo
512 -- check whether the type is naughty: this thunk does not get forced
513 -- until the type is actually needed
514 field_ty = dataConFieldType con1 field_label
515 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tv_set)
517 -- it's important that this doesn't force the if
518 (theType, theInfo) = if is_naughty
519 -- Escapist case here for naughty constructors
520 -- We give it no IdInfo, and a type of forall a.a (never looked at)
521 then (forall_a_a, noCafIdInfo)
522 -- otherwise do the real case
523 else (selector_ty, info)
525 sel_id_details = RecordSelId { sel_tycon = tycon, sel_label = field_label, sel_naughty = is_naughty }
526 -- For a data type family, the tycon is the *instance* TyCon
529 forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar)
531 -- real case starts here:
532 data_cons = tyConDataCons tycon
533 data_cons_w_field = filter has_field data_cons -- Can't be empty!
534 has_field con = field_label `elem` dataConFieldLabels con
536 con1 = ASSERT( not (null data_cons_w_field) ) head data_cons_w_field
537 (univ_tvs, _, eq_spec, _, _, _, data_ty) = dataConFullSig con1
538 -- For a data type family, the data_ty (and hence selector_ty) mentions
539 -- only the family TyCon, not the instance TyCon
540 data_tv_set = tyVarsOfType data_ty
541 data_tvs = varSetElems data_tv_set
543 -- *Very* tiresomely, the selectors are (unnecessarily!) overloaded over
544 -- just the dictionaries in the types of the constructors that contain
545 -- the relevant field. [The Report says that pattern matching on a
546 -- constructor gives the same constraints as applying it.] Urgh.
548 -- However, not all data cons have all constraints (because of
549 -- BuildTyCl.mkDataConStupidTheta). So we need to find all the data cons
550 -- involved in the pattern match and take the union of their constraints.
551 stupid_dict_tys = mkPredTys (dataConsStupidTheta data_cons_w_field)
552 n_stupid_dicts = length stupid_dict_tys
554 (field_tyvars,pre_field_theta,field_tau) = tcSplitSigmaTy field_ty
555 field_theta = filter (not . isEqPred) pre_field_theta
556 field_dict_tys = mkPredTys field_theta
557 n_field_dict_tys = length field_dict_tys
558 -- If the field has a universally quantified type we have to
559 -- be a bit careful. Suppose we have
560 -- data R = R { op :: forall a. Foo a => a -> a }
561 -- Then we can't give op the type
562 -- op :: R -> forall a. Foo a => a -> a
563 -- because the typechecker doesn't understand foralls to the
564 -- right of an arrow. The "right" type to give it is
565 -- op :: forall a. Foo a => R -> a -> a
566 -- But then we must generate the right unfolding too:
567 -- op = /\a -> \dfoo -> \ r ->
570 -- Note that this is exactly the type we'd infer from a user defn
574 selector_ty = mkForAllTys data_tvs $ mkForAllTys field_tyvars $
575 mkFunTys stupid_dict_tys $ mkFunTys field_dict_tys $
576 mkFunTy data_ty field_tau
578 arity = 1 + n_stupid_dicts + n_field_dict_tys
580 (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
581 -- Use the demand analyser to work out strictness.
582 -- With all this unpackery it's not easy!
585 `setCafInfo` caf_info
587 `setUnfoldingInfo` mkTopUnfolding rhs_w_str
588 `setAllStrictnessInfo` Just strict_sig
590 -- Allocate Ids. We do it a funny way round because field_dict_tys is
591 -- almost always empty. Also note that we use max_dict_tys
592 -- rather than n_dict_tys, because the latter gives an infinite loop:
593 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
594 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
595 stupid_dict_ids = mkTemplateLocalsNum 1 stupid_dict_tys
596 max_stupid_dicts = length (tyConStupidTheta tycon)
597 field_dict_base = max_stupid_dicts + 1
598 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
599 dict_id_base = field_dict_base + n_field_dict_tys
600 data_id = mkTemplateLocal dict_id_base data_ty
601 scrut_id = mkTemplateLocal (dict_id_base+1) scrut_ty
602 arg_base = dict_id_base + 2
604 the_alts :: [CoreAlt]
605 the_alts = map mk_alt data_cons_w_field -- Already sorted by data-con
606 no_default = length data_cons == length data_cons_w_field -- No default needed
608 default_alt | no_default = []
609 | otherwise = [(DEFAULT, [], error_expr)]
611 -- The default branch may have CAF refs, because it calls recSelError etc.
612 caf_info | no_default = NoCafRefs
613 | otherwise = MayHaveCafRefs
615 sel_rhs = mkLams data_tvs $ mkLams field_tyvars $
616 mkLams stupid_dict_ids $ mkLams field_dict_ids $
617 Lam data_id $ mk_result sel_body
619 scrut_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
620 scrut_ty = mkTyConApp tycon scrut_ty_args
621 scrut = unwrapFamInstScrut tycon scrut_ty_args (Var data_id)
622 -- First coerce from the type family to the representation type
624 -- NB: A newtype always has a vanilla DataCon; no existentials etc
625 -- data_tys will simply be the dataConUnivTyVars
626 sel_body | isNewTyCon tycon = unwrapNewTypeBody tycon scrut_ty_args scrut
627 | otherwise = Case scrut scrut_id field_ty (default_alt ++ the_alts)
629 mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
630 -- We pull the field lambdas to the top, so we need to
631 -- apply them in the body. For example:
632 -- data T = MkT { foo :: forall a. a->a }
634 -- foo :: forall a. T -> a -> a
635 -- foo = /\a. \t:T. case t of { MkT f -> f a }
638 = ASSERT2( data_ty `tcEqType` field_ty, ppr data_con $$ ppr data_ty $$ ppr field_ty )
639 mkReboxingAlt rebox_uniqs data_con (ex_tvs ++ co_tvs ++ arg_vs) rhs
641 -- get pattern binders with types appropriately instantiated
642 arg_uniqs = map mkBuiltinUnique [arg_base..]
643 (ex_tvs, co_tvs, arg_vs) = dataConOrigInstPat arg_uniqs data_con scrut_ty_args
645 rebox_base = arg_base + length ex_tvs + length co_tvs + length arg_vs
646 rebox_uniqs = map mkBuiltinUnique [rebox_base..]
648 -- data T :: *->* where T1 { fld :: Maybe b } -> T [b]
649 -- Hence T1 :: forall a b. (a=[b]) => b -> T a
650 -- fld :: forall b. T [b] -> Maybe b
651 -- fld = /\b.\(t:T[b]). case t of
652 -- T1 b' (c : [b]=[b']) (x:Maybe b')
653 -- -> x `cast` Maybe (sym (right c))
656 -- Generate the refinement for b'=b,
657 -- and apply to (Maybe b'), to get (Maybe b)
658 Succeeded refinement = gadtRefine emptyRefinement ex_tvs co_tvs
659 the_arg_id_ty = idType the_arg_id
660 (rhs, data_ty) = case refineType refinement the_arg_id_ty of
661 Just (co, data_ty) -> (Cast (Var the_arg_id) co, data_ty)
662 Nothing -> (Var the_arg_id, the_arg_id_ty)
664 field_vs = filter (not . isPredTy . idType) arg_vs
665 the_arg_id = assoc "mkRecordSelId:mk_alt" (field_lbls `zip` field_vs) field_label
666 field_lbls = dataConFieldLabels data_con
668 error_expr = mkRuntimeErrorApp rEC_SEL_ERROR_ID field_ty full_msg
669 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
671 -- unbox a product type...
672 -- we will recurse into newtypes, casting along the way, and unbox at the
673 -- first product data constructor we find. e.g.
675 -- data PairInt = PairInt Int Int
676 -- newtype S = MkS PairInt
679 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
680 -- ids, we get (modulo int passing)
682 -- case (e `cast` CoT) `cast` CoS of
683 -- PairInt a b -> body [a,b]
685 -- The Ints passed around are just for creating fresh locals
686 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
687 unboxProduct i arg arg_ty body
690 result = mkUnpackCase the_id arg con_args boxing_con rhs
691 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
692 ([the_id], i') = mkLocals i [arg_ty]
693 (con_args, i'') = mkLocals i' tys
694 rhs = body i'' con_args
696 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
697 -- (mkUnpackCase x e args Con body)
699 -- case (e `cast` ...) of bndr { Con args -> body }
701 -- the type of the bndr passed in is irrelevent
702 mkUnpackCase bndr arg unpk_args boxing_con body
703 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
705 (cast_arg, bndr_ty) = go (idType bndr) arg
707 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
708 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
709 = go (newTyConInstRhs tycon tycon_args)
710 (unwrapNewTypeBody tycon tycon_args arg)
711 | otherwise = (arg, ty)
714 reboxProduct :: [Unique] -- uniques to create new local binders
715 -> Type -- type of product to box
716 -> ([Unique], -- remaining uniques
717 CoreExpr, -- boxed product
718 [Id]) -- Ids being boxed into product
721 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
723 us' = dropList con_arg_tys us
725 arg_ids = zipWith (mkSysLocal FSLIT("rb")) us con_arg_tys
727 bind_rhs = mkProductBox arg_ids ty
730 (us', bind_rhs, arg_ids)
732 mkProductBox :: [Id] -> Type -> CoreExpr
733 mkProductBox arg_ids ty
736 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
739 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
740 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
741 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
743 wrap expr = wrapNewTypeBody tycon tycon_args expr
746 -- (mkReboxingAlt us con xs rhs) basically constructs the case
747 -- alternative (con, xs, rhs)
748 -- but it does the reboxing necessary to construct the *source*
749 -- arguments, xs, from the representation arguments ys.
751 -- data T = MkT !(Int,Int) Bool
753 -- mkReboxingAlt MkT [x,b] r
754 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
756 -- mkDataAlt should really be in DataCon, but it can't because
757 -- it manipulates CoreSyn.
760 :: [Unique] -- Uniques for the new Ids
762 -> [Var] -- Source-level args, including existential dicts
766 mkReboxingAlt us con args rhs
767 | not (any isMarkedUnboxed stricts)
768 = (DataAlt con, args, rhs)
772 (binds, args') = go args stricts us
774 (DataAlt con, args', mkLets binds rhs)
777 stricts = dataConExStricts con ++ dataConStrictMarks con
779 go [] _stricts _us = ([], [])
781 -- Type variable case
782 go (arg:args) stricts us
784 = let (binds, args') = go args stricts us
785 in (binds, arg:args')
787 -- Term variable case
788 go (arg:args) (str:stricts) us
789 | isMarkedUnboxed str
791 let (binds, unpacked_args') = go args stricts us'
792 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
794 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
796 = let (binds, args') = go args stricts us
797 in (binds, arg:args')
801 %************************************************************************
803 \subsection{Dictionary selectors}
805 %************************************************************************
807 Selecting a field for a dictionary. If there is just one field, then
808 there's nothing to do.
810 Dictionary selectors may get nested forall-types. Thus:
813 op :: forall b. Ord b => a -> b -> b
815 Then the top-level type for op is
817 op :: forall a. Foo a =>
821 This is unlike ordinary record selectors, which have all the for-alls
822 at the outside. When dealing with classes it's very convenient to
823 recover the original type signature from the class op selector.
826 mkDictSelId :: Name -> Class -> Id
827 mkDictSelId name clas
828 = mkGlobalId (ClassOpId clas) name sel_ty info
830 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
831 -- We can't just say (exprType rhs), because that would give a type
833 -- for a single-op class (after all, the selector is the identity)
834 -- But it's type must expose the representation of the dictionary
835 -- to get (say) C a -> (a -> a)
839 `setUnfoldingInfo` mkTopUnfolding rhs
840 `setAllStrictnessInfo` Just strict_sig
842 -- We no longer use 'must-inline' on record selectors. They'll
843 -- inline like crazy if they scrutinise a constructor
845 -- The strictness signature is of the form U(AAAVAAAA) -> T
846 -- where the V depends on which item we are selecting
847 -- It's worth giving one, so that absence info etc is generated
848 -- even if the selector isn't inlined
849 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
850 arg_dmd | isNewTyCon tycon = evalDmd
851 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
854 tycon = classTyCon clas
855 [data_con] = tyConDataCons tycon
856 tyvars = dataConUnivTyVars data_con
857 arg_tys = {- ASSERT( isVanillaDataCon data_con ) -} dataConRepArgTys data_con
858 eq_theta = dataConEqTheta data_con
859 the_arg_id = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` arg_ids) name
861 pred = mkClassPred clas (mkTyVarTys tyvars)
862 dict_id = mkTemplateLocal 1 $ mkPredTy pred
863 (eq_ids,n) = mkCoVarLocals 2 $ mkPredTys eq_theta
864 arg_ids = mkTemplateLocalsNum n arg_tys
866 mkCoVarLocals i [] = ([],i)
867 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
868 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) FSLIT("dc_co")) x
871 rhs = mkLams tyvars (Lam dict_id rhs_body)
872 rhs_body | isNewTyCon tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
873 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
874 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
878 %************************************************************************
880 Wrapping and unwrapping newtypes and type families
882 %************************************************************************
885 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
886 -- The wrapper for the data constructor for a newtype looks like this:
887 -- newtype T a = MkT (a,Int)
888 -- MkT :: forall a. (a,Int) -> T a
889 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
890 -- where CoT is the coercion TyCon assoicated with the newtype
892 -- The call (wrapNewTypeBody T [a] e) returns the
893 -- body of the wrapper, namely
894 -- e `cast` (CoT [a])
896 -- If a coercion constructor is provided in the newtype, then we use
897 -- it, otherwise the wrap/unwrap are both no-ops
899 -- If the we are dealing with a newtype *instance*, we have a second coercion
900 -- identifying the family instance with the constructor of the newtype
901 -- instance. This coercion is applied in any case (ie, composed with the
902 -- coercion constructor of the newtype or applied by itself).
904 wrapNewTypeBody tycon args result_expr
905 = wrapFamInstBody tycon args inner
908 | Just co_con <- newTyConCo_maybe tycon
909 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
913 -- When unwrapping, we do *not* apply any family coercion, because this will
914 -- be done via a CoPat by the type checker. We have to do it this way as
915 -- computing the right type arguments for the coercion requires more than just
916 -- a spliting operation (cf, TcPat.tcConPat).
918 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
919 unwrapNewTypeBody tycon args result_expr
920 | Just co_con <- newTyConCo_maybe tycon
921 = mkCoerce (mkTyConApp co_con args) result_expr
925 -- If the type constructor is a representation type of a data instance, wrap
926 -- the expression into a cast adjusting the expression type, which is an
927 -- instance of the representation type, to the corresponding instance of the
928 -- family instance type.
929 -- See Note [Wrappers for data instance tycons]
930 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
931 wrapFamInstBody tycon args body
932 | Just co_con <- tyConFamilyCoercion_maybe tycon
933 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
937 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
938 unwrapFamInstScrut tycon args scrut
939 | Just co_con <- tyConFamilyCoercion_maybe tycon
940 = mkCoerce (mkTyConApp co_con args) scrut
946 %************************************************************************
948 \subsection{Primitive operations
950 %************************************************************************
953 mkPrimOpId :: PrimOp -> Id
957 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
958 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
959 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
960 (mkPrimOpIdUnique (primOpTag prim_op))
962 id = mkGlobalId (PrimOpId prim_op) name ty info
965 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
967 `setAllStrictnessInfo` Just strict_sig
969 -- For each ccall we manufacture a separate CCallOpId, giving it
970 -- a fresh unique, a type that is correct for this particular ccall,
971 -- and a CCall structure that gives the correct details about calling
974 -- The *name* of this Id is a local name whose OccName gives the full
975 -- details of the ccall, type and all. This means that the interface
976 -- file reader can reconstruct a suitable Id
978 mkFCallId :: Unique -> ForeignCall -> Type -> Id
979 mkFCallId uniq fcall ty
980 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
981 -- A CCallOpId should have no free type variables;
982 -- when doing substitutions won't substitute over it
983 mkGlobalId (FCallId fcall) name ty info
985 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
986 -- The "occurrence name" of a ccall is the full info about the
987 -- ccall; it is encoded, but may have embedded spaces etc!
989 name = mkFCallName uniq occ_str
993 `setAllStrictnessInfo` Just strict_sig
995 (_, tau) = tcSplitForAllTys ty
996 (arg_tys, _) = tcSplitFunTys tau
997 arity = length arg_tys
998 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
1000 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
1001 -- except for the type:
1003 -- a plain HPC tick box has type (State# RealWorld)
1004 -- a breakpoint Id has type forall a.a
1006 -- The breakpoint Id will be applied to a list of arbitrary free variables,
1007 -- which is why it needs a polymorphic type.
1009 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
1010 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
1012 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
1013 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
1014 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
1016 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
1018 tickbox = TickBox mod ix
1019 occ_str = showSDoc (braces (ppr tickbox))
1020 name = mkTickBoxOpName uniq occ_str
1025 %************************************************************************
1027 \subsection{DictFuns and default methods}
1029 %************************************************************************
1031 Important notes about dict funs and default methods
1032 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1033 Dict funs and default methods are *not* ImplicitIds. Their definition
1034 involves user-written code, so we can't figure out their strictness etc
1035 based on fixed info, as we can for constructors and record selectors (say).
1037 We build them as LocalIds, but with External Names. This ensures that
1038 they are taken to account by free-variable finding and dependency
1039 analysis (e.g. CoreFVs.exprFreeVars).
1041 Why shouldn't they be bound as GlobalIds? Because, in particular, if
1042 they are globals, the specialiser floats dict uses above their defns,
1043 which prevents good simplifications happening. Also the strictness
1044 analyser treats a occurrence of a GlobalId as imported and assumes it
1045 contains strictness in its IdInfo, which isn't true if the thing is
1046 bound in the same module as the occurrence.
1048 It's OK for dfuns to be LocalIds, because we form the instance-env to
1049 pass on to the next module (md_insts) in CoreTidy, afer tidying
1050 and globalising the top-level Ids.
1052 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
1053 that they aren't discarded by the occurrence analyser.
1056 mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
1058 mkDictFunId :: Name -- Name to use for the dict fun;
1065 mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
1066 = mkExportedLocalId dfun_name dfun_ty
1068 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
1070 {- 1 dec 99: disable the Mark Jones optimisation for the sake
1071 of compatibility with Hugs.
1072 See `types/InstEnv' for a discussion related to this.
1074 (class_tyvars, sc_theta, _, _) = classBigSig clas
1075 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
1076 sc_theta' = substClasses (zipTopTvSubst class_tyvars inst_tys) sc_theta
1077 dfun_theta = case inst_decl_theta of
1078 [] -> [] -- If inst_decl_theta is empty, then we don't
1079 -- want to have any dict arguments, so that we can
1080 -- expose the constant methods.
1082 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
1083 -- Otherwise we pass the superclass dictionaries to
1084 -- the dictionary function; the Mark Jones optimisation.
1086 -- NOTE the "nub". I got caught by this one:
1087 -- class Monad m => MonadT t m where ...
1088 -- instance Monad m => MonadT (EnvT env) m where ...
1089 -- Here, the inst_decl_theta has (Monad m); but so
1090 -- does the sc_theta'!
1092 -- NOTE the "not_const". I got caught by this one too:
1093 -- class Foo a => Baz a b where ...
1094 -- instance Wob b => Baz T b where..
1095 -- Now sc_theta' has Foo T
1100 %************************************************************************
1102 \subsection{Un-definable}
1104 %************************************************************************
1106 These Ids can't be defined in Haskell. They could be defined in
1107 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
1108 ensure that they were definitely, definitely inlined, because there is
1109 no curried identifier for them. That's what mkCompulsoryUnfolding
1110 does. If we had a way to get a compulsory unfolding from an interface
1111 file, we could do that, but we don't right now.
1113 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
1114 just gets expanded into a type coercion wherever it occurs. Hence we
1115 add it as a built-in Id with an unfolding here.
1117 The type variables we use here are "open" type variables: this means
1118 they can unify with both unlifted and lifted types. Hence we provide
1119 another gun with which to shoot yourself in the foot.
1122 mkWiredInIdName mod fs uniq id
1123 = mkWiredInName mod (mkOccNameFS varName fs) uniq (AnId id) UserSyntax
1125 unsafeCoerceName = mkWiredInIdName gHC_PRIM FSLIT("unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
1126 nullAddrName = mkWiredInIdName gHC_PRIM FSLIT("nullAddr#") nullAddrIdKey nullAddrId
1127 seqName = mkWiredInIdName gHC_PRIM FSLIT("seq") seqIdKey seqId
1128 realWorldName = mkWiredInIdName gHC_PRIM FSLIT("realWorld#") realWorldPrimIdKey realWorldPrimId
1129 lazyIdName = mkWiredInIdName gHC_BASE FSLIT("lazy") lazyIdKey lazyId
1131 errorName = mkWiredInIdName gHC_ERR FSLIT("error") errorIdKey eRROR_ID
1132 recSelErrorName = mkWiredInIdName gHC_ERR FSLIT("recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
1133 runtimeErrorName = mkWiredInIdName gHC_ERR FSLIT("runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
1134 irrefutPatErrorName = mkWiredInIdName gHC_ERR FSLIT("irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
1135 recConErrorName = mkWiredInIdName gHC_ERR FSLIT("recConError") recConErrorIdKey rEC_CON_ERROR_ID
1136 patErrorName = mkWiredInIdName gHC_ERR FSLIT("patError") patErrorIdKey pAT_ERROR_ID
1137 noMethodBindingErrorName = mkWiredInIdName gHC_ERR FSLIT("noMethodBindingError")
1138 noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
1139 nonExhaustiveGuardsErrorName
1140 = mkWiredInIdName gHC_ERR FSLIT("nonExhaustiveGuardsError")
1141 nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
1145 -- unsafeCoerce# :: forall a b. a -> b
1147 = pcMiscPrelId unsafeCoerceName ty info
1149 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1152 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
1153 (mkFunTy openAlphaTy openBetaTy)
1154 [x] = mkTemplateLocals [openAlphaTy]
1155 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
1156 Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
1158 -- nullAddr# :: Addr#
1159 -- The reason is is here is because we don't provide
1160 -- a way to write this literal in Haskell.
1162 = pcMiscPrelId nullAddrName addrPrimTy info
1164 info = noCafIdInfo `setUnfoldingInfo`
1165 mkCompulsoryUnfolding (Lit nullAddrLit)
1168 = pcMiscPrelId seqName ty info
1170 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
1173 ty = mkForAllTys [alphaTyVar,openBetaTyVar]
1174 (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
1175 [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
1176 rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
1178 -- lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1179 -- Used to lazify pseq: pseq a b = a `seq` lazy b
1181 -- Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1182 -- not from GHC.Base.hi. This is important, because the strictness
1183 -- analyser will spot it as strict!
1185 -- Also no unfolding in lazyId: it gets "inlined" by a HACK in the worker/wrapperpass
1186 -- (see WorkWrap.wwExpr)
1187 -- We could use inline phases to do this, but that would be vulnerable to changes in
1188 -- phase numbering....we must inline precisely after strictness analysis.
1190 = pcMiscPrelId lazyIdName ty info
1193 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
1195 lazyIdUnfolding :: CoreExpr -- Used to expand 'lazyId' after strictness anal
1196 lazyIdUnfolding = mkLams [openAlphaTyVar,x] (Var x)
1198 [x] = mkTemplateLocals [openAlphaTy]
1201 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1202 nasty as-is, change it back to a literal (@Literal@).
1204 voidArgId is a Local Id used simply as an argument in functions
1205 where we just want an arg to avoid having a thunk of unlifted type.
1207 x = \ void :: State# RealWorld -> (# p, q #)
1209 This comes up in strictness analysis
1212 realWorldPrimId -- :: State# RealWorld
1213 = pcMiscPrelId realWorldName realWorldStatePrimTy
1214 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1215 -- The evaldUnfolding makes it look that realWorld# is evaluated
1216 -- which in turn makes Simplify.interestingArg return True,
1217 -- which in turn makes INLINE things applied to realWorld# likely
1220 voidArgId -- :: State# RealWorld
1221 = mkSysLocal FSLIT("void") voidArgIdKey realWorldStatePrimTy
1225 %************************************************************************
1227 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
1229 %************************************************************************
1231 GHC randomly injects these into the code.
1233 @patError@ is just a version of @error@ for pattern-matching
1234 failures. It knows various ``codes'' which expand to longer
1235 strings---this saves space!
1237 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
1238 well shouldn't be yanked on, but if one is, then you will get a
1239 friendly message from @absentErr@ (rather than a totally random
1242 @parError@ is a special version of @error@ which the compiler does
1243 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
1244 templates, but we don't ever expect to generate code for it.
1248 :: Id -- Should be of type (forall a. Addr# -> a)
1249 -- where Addr# points to a UTF8 encoded string
1250 -> Type -- The type to instantiate 'a'
1251 -> String -- The string to print
1254 mkRuntimeErrorApp err_id res_ty err_msg
1255 = mkApps (Var err_id) [Type res_ty, err_string]
1257 err_string = Lit (mkStringLit err_msg)
1259 rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
1260 rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
1261 iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
1262 rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
1263 pAT_ERROR_ID = mkRuntimeErrorId patErrorName
1264 nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
1265 nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
1267 -- The runtime error Ids take a UTF8-encoded string as argument
1268 mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
1269 runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
1273 eRROR_ID = pc_bottoming_Id errorName errorTy
1276 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
1277 -- Notice the openAlphaTyVar. It says that "error" can be applied
1278 -- to unboxed as well as boxed types. This is OK because it never
1279 -- returns, so the return type is irrelevant.
1283 %************************************************************************
1285 \subsection{Utilities}
1287 %************************************************************************
1290 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1291 pcMiscPrelId name ty info
1292 = mkVanillaGlobal name ty info
1293 -- We lie and say the thing is imported; otherwise, we get into
1294 -- a mess with dependency analysis; e.g., core2stg may heave in
1295 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1296 -- being compiled, then it's just a matter of luck if the definition
1297 -- will be in "the right place" to be in scope.
1299 pc_bottoming_Id name ty
1300 = pcMiscPrelId name ty bottoming_info
1302 bottoming_info = vanillaIdInfo `setAllStrictnessInfo` Just strict_sig
1303 -- Do *not* mark them as NoCafRefs, because they can indeed have
1304 -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
1305 -- which has some CAFs
1306 -- In due course we may arrange that these error-y things are
1307 -- regarded by the GC as permanently live, in which case we
1308 -- can give them NoCaf info. As it is, any function that calls
1309 -- any pc_bottoming_Id will itself have CafRefs, which bloats
1312 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
1313 -- These "bottom" out, no matter what their arguments