2 % (c) The AQUA Project, Glasgow University, 1998
4 \section[StdIdInfo]{Standard unfoldings}
6 This module contains definitions for the IdInfo for things that
7 have a standard form, namely:
11 * method and superclass selectors
12 * primitive operations
16 mkDictFunId, mkDefaultMethodId,
19 mkDataConId, mkDataConWrapId,
20 mkRecordSelId, rebuildConArgs,
21 mkPrimOpId, mkFCallId,
23 -- And some particular Ids; see below for why they are wired in
25 unsafeCoerceId, realWorldPrimId,
26 eRROR_ID, rEC_SEL_ERROR_ID, pAT_ERROR_ID, rEC_CON_ERROR_ID,
27 rEC_UPD_ERROR_ID, iRREFUT_PAT_ERROR_ID, nON_EXHAUSTIVE_GUARDS_ERROR_ID,
28 nO_METHOD_BINDING_ERROR_ID, aBSENT_ERROR_ID, pAR_ERROR_ID
31 #include "HsVersions.h"
34 import BasicTypes ( Arity )
35 import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy,
36 intPrimTy, realWorldStatePrimTy
38 import TysWiredIn ( charTy, mkListTy )
39 import PrelNames ( pREL_ERR, pREL_GHC )
40 import PrelRules ( primOpRule )
41 import Rules ( addRule )
42 import TcType ( Type, ThetaType, mkDictTy, mkPredTys, mkTyConApp,
43 mkTyVarTys, mkClassPred, tcEqPred,
44 mkFunTys, mkFunTy, mkSigmaTy, tcSplitSigmaTy,
45 isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType,
46 tcSplitFunTys, tcSplitForAllTys, mkPredTy
48 import Module ( Module )
49 import CoreUtils ( exprType, mkInlineMe )
50 import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding, mkOtherCon )
51 import Literal ( Literal(..) )
52 import TyCon ( TyCon, isNewTyCon, tyConTyVars, tyConDataCons,
53 tyConTheta, isProductTyCon, isDataTyCon, isRecursiveTyCon )
54 import Class ( Class, classTyCon, classTyVars, classSelIds )
55 import Var ( Id, TyVar )
56 import VarSet ( isEmptyVarSet )
57 import Name ( mkWiredInName, mkFCallName, Name )
58 import OccName ( mkVarOcc )
59 import PrimOp ( PrimOp(DataToTagOp), primOpSig, mkPrimOpIdName )
60 import ForeignCall ( ForeignCall )
61 import Demand ( wwStrict, wwPrim, mkStrictnessInfo,
62 StrictnessMark(..), isMarkedUnboxed, isMarkedStrict )
63 import DataCon ( DataCon,
64 dataConFieldLabels, dataConRepArity, dataConTyCon,
65 dataConArgTys, dataConRepType, dataConRepStrictness,
66 dataConInstOrigArgTys,
67 dataConName, dataConTheta,
68 dataConSig, dataConStrictMarks, dataConId,
71 import Id ( idType, mkGlobalId, mkVanillaGlobal, mkSysLocal,
72 mkTemplateLocals, mkTemplateLocalsNum,
73 mkTemplateLocal, idCprInfo, idName
75 import IdInfo ( IdInfo, noCafNoTyGenIdInfo,
76 exactArity, setUnfoldingInfo, setCprInfo,
77 setArityInfo, setSpecInfo, setCgInfo,
78 mkStrictnessInfo, setStrictnessInfo,
79 GlobalIdDetails(..), CafInfo(..), CprInfo(..),
80 CgInfo(..), setCgArity
82 import FieldLabel ( mkFieldLabel, fieldLabelName,
83 firstFieldLabelTag, allFieldLabelTags, fieldLabelType
86 import Unique ( mkBuiltinUnique )
89 import Maybe ( isJust )
91 import ListSetOps ( assoc, assocMaybe )
92 import UnicodeUtil ( stringToUtf8 )
96 %************************************************************************
98 \subsection{Wired in Ids}
100 %************************************************************************
104 = [ -- These error-y things are wired in because we don't yet have
105 -- a way to express in an interface file that the result type variable
106 -- is 'open'; that is can be unified with an unboxed type
108 -- [The interface file format now carry such information, but there's
109 -- no way yet of expressing at the definition site for these
111 -- functions that they have an 'open' result type. -- sof 1/99]
115 , iRREFUT_PAT_ERROR_ID
116 , nON_EXHAUSTIVE_GUARDS_ERROR_ID
117 , nO_METHOD_BINDING_ERROR_ID
123 -- These three can't be defined in Haskell
130 %************************************************************************
132 \subsection{Data constructors}
134 %************************************************************************
137 mkDataConId :: Name -> DataCon -> Id
138 -- Makes the *worker* for the data constructor; that is, the function
139 -- that takes the reprsentation arguments and builds the constructor.
140 mkDataConId work_name data_con
141 = mkGlobalId (DataConId data_con) work_name (dataConRepType data_con) info
143 info = noCafNoTyGenIdInfo
145 `setArityInfo` exactArity arity
146 `setStrictnessInfo` strict_info
147 `setCprInfo` cpr_info
149 arity = dataConRepArity data_con
151 strict_info = mkStrictnessInfo (dataConRepStrictness data_con, False)
153 tycon = dataConTyCon data_con
154 cpr_info | isProductTyCon tycon &&
157 arity <= mAX_CPR_SIZE = ReturnsCPR
158 | otherwise = NoCPRInfo
159 -- ReturnsCPR is only true for products that are real data types;
160 -- that is, not unboxed tuples or [non-recursive] newtypes
162 mAX_CPR_SIZE :: Arity
164 -- We do not treat very big tuples as CPR-ish:
165 -- a) for a start we get into trouble because there aren't
166 -- "enough" unboxed tuple types (a tiresome restriction,
168 -- b) more importantly, big unboxed tuples get returned mainly
169 -- on the stack, and are often then allocated in the heap
170 -- by the caller. So doing CPR for them may in fact make
174 The wrapper for a constructor is an ordinary top-level binding that evaluates
175 any strict args, unboxes any args that are going to be flattened, and calls
178 We're going to build a constructor that looks like:
180 data (Data a, C b) => T a b = T1 !a !Int b
183 \d1::Data a, d2::C b ->
184 \p q r -> case p of { p ->
186 Con T1 [a,b] [p,q,r]}}
190 * d2 is thrown away --- a context in a data decl is used to make sure
191 one *could* construct dictionaries at the site the constructor
192 is used, but the dictionary isn't actually used.
194 * We have to check that we can construct Data dictionaries for
195 the types a and Int. Once we've done that we can throw d1 away too.
197 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
198 all that matters is that the arguments are evaluated. "seq" is
199 very careful to preserve evaluation order, which we don't need
202 You might think that we could simply give constructors some strictness
203 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
204 But we don't do that because in the case of primops and functions strictness
205 is a *property* not a *requirement*. In the case of constructors we need to
206 do something active to evaluate the argument.
208 Making an explicit case expression allows the simplifier to eliminate
209 it in the (common) case where the constructor arg is already evaluated.
212 mkDataConWrapId data_con
215 wrap_id = mkGlobalId (DataConWrapId data_con) (dataConName data_con) wrap_ty info
216 work_id = dataConId data_con
218 info = noCafNoTyGenIdInfo
219 `setUnfoldingInfo` mkTopUnfolding (mkInlineMe wrap_rhs)
220 `setCprInfo` cpr_info
221 -- The Cpr info can be important inside INLINE rhss, where the
222 -- wrapper constructor isn't inlined
224 -- The NoCaf-ness is set by noCafNoTyGenIdInfo
225 `setArityInfo` exactArity arity
226 -- It's important to specify the arity, so that partial
227 -- applications are treated as values
229 wrap_ty = mkForAllTys all_tyvars $
233 cpr_info = idCprInfo work_id
235 wrap_rhs | isNewTyCon tycon
236 = ASSERT( null ex_tyvars && null ex_dict_args && length orig_arg_tys == 1 )
237 -- No existentials on a newtype, but it can have a context
238 -- e.g. newtype Eq a => T a = MkT (...)
239 mkLams tyvars $ mkLams dict_args $ Lam id_arg1 $
240 mkNewTypeBody tycon result_ty id_arg1
242 | null dict_args && not (any isMarkedStrict strict_marks)
243 = Var work_id -- The common case. Not only is this efficient,
244 -- but it also ensures that the wrapper is replaced
245 -- by the worker even when there are no args.
249 -- This is really important in rule matching,
250 -- (We could match on the wrappers,
251 -- but that makes it less likely that rules will match
252 -- when we bring bits of unfoldings together.)
254 -- NB: because of this special case, (map (:) ys) turns into
255 -- (map $w: ys), and thence into (map (\x xs. $w: x xs) ys)
256 -- in core-to-stg. The top-level defn for (:) is never used.
257 -- This is somewhat of a bore, but I'm currently leaving it
258 -- as is, so that there still is a top level curried (:) for
259 -- the interpreter to call.
262 = mkLams all_tyvars $ mkLams dict_args $
263 mkLams ex_dict_args $ mkLams id_args $
264 foldr mk_case con_app
265 (zip (ex_dict_args++id_args) strict_marks) i3 []
267 con_app i rep_ids = mkApps (Var work_id)
268 (map varToCoreExpr (all_tyvars ++ reverse rep_ids))
270 (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon) = dataConSig data_con
271 all_tyvars = tyvars ++ ex_tyvars
273 dict_tys = mkPredTys theta
274 ex_dict_tys = mkPredTys ex_theta
275 all_arg_tys = dict_tys ++ ex_dict_tys ++ orig_arg_tys
276 result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
278 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
282 (dict_args, i1) = mkLocals 1 dict_tys
283 (ex_dict_args,i2) = mkLocals i1 ex_dict_tys
284 (id_args,i3) = mkLocals i2 orig_arg_tys
286 (id_arg1:_) = id_args -- Used for newtype only
288 strict_marks = dataConStrictMarks data_con
291 :: (Id, StrictnessMark) -- Arg, strictness
292 -> (Int -> [Id] -> CoreExpr) -- Body
293 -> Int -- Next rep arg id
294 -> [Id] -- Rep args so far, reversed
296 mk_case (arg,strict) body i rep_args
298 NotMarkedStrict -> body i (arg:rep_args)
300 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
302 Case (Var arg) arg [(DEFAULT,[], body i (arg:rep_args))]
305 -> case splitProductType "do_unbox" (idType arg) of
306 (tycon, tycon_args, con, tys) ->
307 Case (Var arg) arg [(DataAlt con, con_args,
308 body i' (reverse con_args ++ rep_args))]
310 (con_args, i') = mkLocals i tys
314 %************************************************************************
316 \subsection{Record selectors}
318 %************************************************************************
320 We're going to build a record selector unfolding that looks like this:
322 data T a b c = T1 { ..., op :: a, ...}
323 | T2 { ..., op :: a, ...}
326 sel = /\ a b c -> \ d -> case d of
331 Similarly for newtypes
333 newtype N a = MkN { unN :: a->a }
336 unN n = coerce (a->a) n
338 We need to take a little care if the field has a polymorphic type:
340 data R = R { f :: forall a. a->a }
344 f :: forall a. R -> a -> a
345 f = /\ a \ r = case r of
348 (not f :: R -> forall a. a->a, which gives the type inference mechanism
349 problems at call sites)
351 Similarly for newtypes
353 newtype N = MkN { unN :: forall a. a->a }
355 unN :: forall a. N -> a -> a
356 unN = /\a -> \n:N -> coerce (a->a) n
359 mkRecordSelId tycon field_label unpack_id unpackUtf8_id
360 -- Assumes that all fields with the same field label have the same type
362 -- Annoyingly, we have to pass in the unpackCString# Id, because
363 -- we can't conjure it up out of thin air
366 sel_id = mkGlobalId (RecordSelId field_label) (fieldLabelName field_label) selector_ty info
367 field_ty = fieldLabelType field_label
368 data_cons = tyConDataCons tycon
369 tyvars = tyConTyVars tycon -- These scope over the types in
370 -- the FieldLabels of constructors of this type
371 data_ty = mkTyConApp tycon tyvar_tys
372 tyvar_tys = mkTyVarTys tyvars
374 tycon_theta = tyConTheta tycon -- The context on the data decl
375 -- eg data (Eq a, Ord b) => T a b = ...
376 dict_tys = [mkPredTy pred | pred <- tycon_theta,
378 needed_dict pred = or [ tcEqPred pred p
379 | (DataAlt dc, _, _) <- the_alts, p <- dataConTheta dc]
380 n_dict_tys = length dict_tys
382 (field_tyvars,field_theta,field_tau) = tcSplitSigmaTy field_ty
383 field_dict_tys = map mkPredTy field_theta
384 n_field_dict_tys = length field_dict_tys
385 -- If the field has a universally quantified type we have to
386 -- be a bit careful. Suppose we have
387 -- data R = R { op :: forall a. Foo a => a -> a }
388 -- Then we can't give op the type
389 -- op :: R -> forall a. Foo a => a -> a
390 -- because the typechecker doesn't understand foralls to the
391 -- right of an arrow. The "right" type to give it is
392 -- op :: forall a. Foo a => R -> a -> a
393 -- But then we must generate the right unfolding too:
394 -- op = /\a -> \dfoo -> \ r ->
397 -- Note that this is exactly the type we'd infer from a user defn
400 -- Very tiresomely, the selectors are (unnecessarily!) overloaded over
401 -- just the dictionaries in the types of the constructors that contain
402 -- the relevant field. Urgh.
403 -- NB: this code relies on the fact that DataCons are quantified over
404 -- the identical type variables as their parent TyCon
407 selector_ty = mkForAllTys tyvars $ mkForAllTys field_tyvars $
408 mkFunTys dict_tys $ mkFunTys field_dict_tys $
409 mkFunTy data_ty field_tau
411 arity = 1 + n_dict_tys + n_field_dict_tys
412 info = noCafNoTyGenIdInfo
413 `setCgInfo` (CgInfo arity caf_info)
414 `setArityInfo` exactArity arity
415 `setUnfoldingInfo` unfolding
416 -- ToDo: consider adding further IdInfo
418 unfolding = mkTopUnfolding sel_rhs
420 -- Allocate Ids. We do it a funny way round because field_dict_tys is
421 -- almost always empty. Also note that we use length_tycon_theta
422 -- rather than n_dict_tys, because the latter gives an infinite loop:
423 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
424 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
425 field_dict_base = length tycon_theta + 1
426 dict_id_base = field_dict_base + n_field_dict_tys
427 field_base = dict_id_base + 1
428 dict_ids = mkTemplateLocalsNum 1 dict_tys
429 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
430 data_id = mkTemplateLocal dict_id_base data_ty
432 alts = map mk_maybe_alt data_cons
433 the_alts = catMaybes alts
435 no_default = all isJust alts -- No default needed
436 default_alt | no_default = []
437 | otherwise = [(DEFAULT, [], error_expr)]
439 -- the default branch may have CAF refs, because it calls recSelError etc.
440 caf_info | no_default = NoCafRefs
441 | otherwise = MayHaveCafRefs
443 sel_rhs = mkLams tyvars $ mkLams field_tyvars $
444 mkLams dict_ids $ mkLams field_dict_ids $
445 Lam data_id $ sel_body
447 sel_body | isNewTyCon tycon = mkNewTypeBody tycon field_tau data_id
448 | otherwise = Case (Var data_id) data_id (default_alt ++ the_alts)
450 mk_maybe_alt data_con
451 = case maybe_the_arg_id of
453 Just the_arg_id -> Just (DataAlt data_con, real_args, mkLets binds body)
455 body = mkVarApps (mkVarApps (Var the_arg_id) field_tyvars) field_dict_ids
456 strict_marks = dataConStrictMarks data_con
457 (binds, real_args) = rebuildConArgs arg_ids strict_marks
458 (map mkBuiltinUnique [unpack_base..])
460 arg_ids = mkTemplateLocalsNum field_base (dataConInstOrigArgTys data_con tyvar_tys)
462 unpack_base = field_base + length arg_ids
464 -- arity+1 avoids all shadowing
465 maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
466 field_lbls = dataConFieldLabels data_con
468 error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type field_tau, err_string]
470 | all safeChar full_msg
471 = App (Var unpack_id) (Lit (MachStr (_PK_ full_msg)))
473 = App (Var unpackUtf8_id) (Lit (MachStr (_PK_ (stringToUtf8 (map ord full_msg)))))
475 safeChar c = c >= '\1' && c <= '\xFF'
476 -- TODO: Putting this Unicode stuff here is ugly. Find a better
477 -- generic place to make string literals. This logic is repeated
479 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
482 -- This rather ugly function converts the unpacked data con
483 -- arguments back into their packed form.
486 :: [Id] -- Source-level args
487 -> [StrictnessMark] -- Strictness annotations (per-arg)
488 -> [Unique] -- Uniques for the new Ids
489 -> ([CoreBind], [Id]) -- A binding for each source-level arg, plus
490 -- a list of the representation-level arguments
491 -- e.g. data T = MkT Int !Int
493 -- rebuild [x::Int, y::Int] [Not, Unbox]
494 -- = ([ y = I# t ], [x,t])
496 rebuildConArgs [] stricts us = ([], [])
498 -- Type variable case
499 rebuildConArgs (arg:args) stricts us
501 = let (binds, args') = rebuildConArgs args stricts us
502 in (binds, arg:args')
504 -- Term variable case
505 rebuildConArgs (arg:args) (str:stricts) us
506 | isMarkedUnboxed str
510 (_, tycon_args, pack_con, con_arg_tys)
511 = splitProductType "rebuildConArgs" arg_ty
513 unpacked_args = zipWith (mkSysLocal SLIT("rb")) us con_arg_tys
514 (binds, args') = rebuildConArgs args stricts (drop (length con_arg_tys) us)
515 con_app = mkConApp pack_con (map Type tycon_args ++ map Var unpacked_args)
517 (NonRec arg con_app : binds, unpacked_args ++ args')
520 = let (binds, args') = rebuildConArgs args stricts us
521 in (binds, arg:args')
525 %************************************************************************
527 \subsection{Dictionary selectors}
529 %************************************************************************
531 Selecting a field for a dictionary. If there is just one field, then
532 there's nothing to do.
534 ToDo: unify with mkRecordSelId.
537 mkDictSelId :: Name -> Class -> Id
538 mkDictSelId name clas
539 = mkGlobalId (RecordSelId field_lbl) name sel_ty info
541 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
542 -- We can't just say (exprType rhs), because that would give a type
544 -- for a single-op class (after all, the selector is the identity)
545 -- But it's type must expose the representation of the dictionary
546 -- to gat (say) C a -> (a -> a)
548 field_lbl = mkFieldLabel name tycon sel_ty tag
549 tag = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` allFieldLabelTags) name
551 info = noCafNoTyGenIdInfo
553 `setArityInfo` exactArity 1
554 `setUnfoldingInfo` unfolding
556 -- We no longer use 'must-inline' on record selectors. They'll
557 -- inline like crazy if they scrutinise a constructor
559 unfolding = mkTopUnfolding rhs
561 tyvars = classTyVars clas
563 tycon = classTyCon clas
564 [data_con] = tyConDataCons tycon
565 tyvar_tys = mkTyVarTys tyvars
566 arg_tys = dataConArgTys data_con tyvar_tys
567 the_arg_id = arg_ids !! (tag - firstFieldLabelTag)
569 pred = mkClassPred clas tyvar_tys
570 (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
572 rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
573 mkNewTypeBody tycon (head arg_tys) dict_id
574 | otherwise = mkLams tyvars $ Lam dict_id $
575 Case (Var dict_id) dict_id
576 [(DataAlt data_con, arg_ids, Var the_arg_id)]
578 mkNewTypeBody tycon result_ty result_id
579 | isRecursiveTyCon tycon -- Recursive case; use a coerce
580 = Note (Coerce result_ty (idType result_id)) (Var result_id)
581 | otherwise -- Normal case
586 %************************************************************************
588 \subsection{Primitive operations
590 %************************************************************************
593 mkPrimOpId :: PrimOp -> Id
597 (tyvars,arg_tys,res_ty, arity, strict_info) = primOpSig prim_op
598 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
599 name = mkPrimOpIdName prim_op
600 id = mkGlobalId (PrimOpId prim_op) name ty info
602 info = noCafNoTyGenIdInfo
605 `setArityInfo` exactArity arity
606 `setStrictnessInfo` strict_info
608 rules = maybe emptyCoreRules (addRule emptyCoreRules id)
612 -- For each ccall we manufacture a separate CCallOpId, giving it
613 -- a fresh unique, a type that is correct for this particular ccall,
614 -- and a CCall structure that gives the correct details about calling
617 -- The *name* of this Id is a local name whose OccName gives the full
618 -- details of the ccall, type and all. This means that the interface
619 -- file reader can reconstruct a suitable Id
621 mkFCallId :: Unique -> ForeignCall -> Type -> Id
622 mkFCallId uniq fcall ty
623 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
624 -- A CCallOpId should have no free type variables;
625 -- when doing substitutions won't substitute over it
626 mkGlobalId (FCallId fcall) name ty info
628 occ_str = showSDocIface (braces (ppr fcall <+> ppr ty))
629 -- The "occurrence name" of a ccall is the full info about the
630 -- ccall; it is encoded, but may have embedded spaces etc!
632 name = mkFCallName uniq occ_str
634 info = noCafNoTyGenIdInfo
636 `setArityInfo` exactArity arity
637 `setStrictnessInfo` strict_info
639 (_, tau) = tcSplitForAllTys ty
640 (arg_tys, _) = tcSplitFunTys tau
641 arity = length arg_tys
642 strict_info = mkStrictnessInfo (take arity (repeat wwPrim), False)
646 %************************************************************************
648 \subsection{DictFuns and default methods}
650 %************************************************************************
653 mkDefaultMethodId dm_name ty
654 = mkVanillaGlobal dm_name ty noCafNoTyGenIdInfo
656 mkDictFunId :: Name -- Name to use for the dict fun;
663 mkDictFunId dfun_name clas inst_tyvars inst_tys dfun_theta
664 = mkVanillaGlobal dfun_name dfun_ty noCafNoTyGenIdInfo
666 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
668 {- 1 dec 99: disable the Mark Jones optimisation for the sake
669 of compatibility with Hugs.
670 See `types/InstEnv' for a discussion related to this.
672 (class_tyvars, sc_theta, _, _) = classBigSig clas
673 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
674 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys) sc_theta
675 dfun_theta = case inst_decl_theta of
676 [] -> [] -- If inst_decl_theta is empty, then we don't
677 -- want to have any dict arguments, so that we can
678 -- expose the constant methods.
680 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
681 -- Otherwise we pass the superclass dictionaries to
682 -- the dictionary function; the Mark Jones optimisation.
684 -- NOTE the "nub". I got caught by this one:
685 -- class Monad m => MonadT t m where ...
686 -- instance Monad m => MonadT (EnvT env) m where ...
687 -- Here, the inst_decl_theta has (Monad m); but so
688 -- does the sc_theta'!
690 -- NOTE the "not_const". I got caught by this one too:
691 -- class Foo a => Baz a b where ...
692 -- instance Wob b => Baz T b where..
693 -- Now sc_theta' has Foo T
698 %************************************************************************
700 \subsection{Un-definable}
702 %************************************************************************
704 These two can't be defined in Haskell.
706 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
707 just gets expanded into a type coercion wherever it occurs. Hence we
708 add it as a built-in Id with an unfolding here.
710 The type variables we use here are "open" type variables: this means
711 they can unify with both unlifted and lifted types. Hence we provide
712 another gun with which to shoot yourself in the foot.
716 = pcMiscPrelId unsafeCoerceIdKey pREL_GHC SLIT("unsafeCoerce#") ty info
718 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
721 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
722 (mkFunTy openAlphaTy openBetaTy)
723 [x] = mkTemplateLocals [openAlphaTy]
724 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
725 Note (Coerce openBetaTy openAlphaTy) (Var x)
729 @getTag#@ is another function which can't be defined in Haskell. It needs to
730 evaluate its argument and call the dataToTag# primitive.
734 = pcMiscPrelId getTagIdKey pREL_GHC SLIT("getTag#") ty info
736 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
737 -- We don't provide a defn for this; you must inline it
739 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy intPrimTy)
740 [x,y] = mkTemplateLocals [alphaTy,alphaTy]
741 rhs = mkLams [alphaTyVar,x] $
742 Case (Var x) y [ (DEFAULT, [], mkApps (Var dataToTagId) [Type alphaTy, Var y]) ]
744 dataToTagId = mkPrimOpId DataToTagOp
747 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
748 nasty as-is, change it back to a literal (@Literal@).
751 realWorldPrimId -- :: State# RealWorld
752 = pcMiscPrelId realWorldPrimIdKey pREL_GHC SLIT("realWorld#")
754 (noCafNoTyGenIdInfo `setUnfoldingInfo` mkOtherCon [])
755 -- The mkOtherCon makes it look that realWorld# is evaluated
756 -- which in turn makes Simplify.interestingArg return True,
757 -- which in turn makes INLINE things applied to realWorld# likely
762 %************************************************************************
764 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
766 %************************************************************************
768 GHC randomly injects these into the code.
770 @patError@ is just a version of @error@ for pattern-matching
771 failures. It knows various ``codes'' which expand to longer
772 strings---this saves space!
774 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
775 well shouldn't be yanked on, but if one is, then you will get a
776 friendly message from @absentErr@ (rather than a totally random
779 @parError@ is a special version of @error@ which the compiler does
780 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
781 templates, but we don't ever expect to generate code for it.
785 = pc_bottoming_Id errorIdKey pREL_ERR SLIT("error") errorTy
787 = generic_ERROR_ID patErrorIdKey SLIT("patError")
789 = generic_ERROR_ID recSelErrIdKey SLIT("recSelError")
791 = generic_ERROR_ID recConErrorIdKey SLIT("recConError")
793 = generic_ERROR_ID recUpdErrorIdKey SLIT("recUpdError")
795 = generic_ERROR_ID irrefutPatErrorIdKey SLIT("irrefutPatError")
796 nON_EXHAUSTIVE_GUARDS_ERROR_ID
797 = generic_ERROR_ID nonExhaustiveGuardsErrorIdKey SLIT("nonExhaustiveGuardsError")
798 nO_METHOD_BINDING_ERROR_ID
799 = generic_ERROR_ID noMethodBindingErrorIdKey SLIT("noMethodBindingError")
802 = pc_bottoming_Id absentErrorIdKey pREL_ERR SLIT("absentErr")
803 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy)
806 = pcMiscPrelId parErrorIdKey pREL_ERR SLIT("parError")
807 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy) noCafNoTyGenIdInfo
811 %************************************************************************
813 \subsection{Utilities}
815 %************************************************************************
818 pcMiscPrelId :: Unique{-IdKey-} -> Module -> FAST_STRING -> Type -> IdInfo -> Id
819 pcMiscPrelId key mod str ty info
821 name = mkWiredInName mod (mkVarOcc str) key
822 imp = mkVanillaGlobal name ty info -- the usual case...
825 -- We lie and say the thing is imported; otherwise, we get into
826 -- a mess with dependency analysis; e.g., core2stg may heave in
827 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
828 -- being compiled, then it's just a matter of luck if the definition
829 -- will be in "the right place" to be in scope.
831 pc_bottoming_Id key mod name ty
832 = pcMiscPrelId key mod name ty bottoming_info
834 bottoming_info = noCafNoTyGenIdInfo
835 `setStrictnessInfo` mkStrictnessInfo ([wwStrict], True)
837 -- these "bottom" out, no matter what their arguments
839 generic_ERROR_ID u n = pc_bottoming_Id u pREL_ERR n errorTy
841 (openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
842 openAlphaTy = mkTyVarTy openAlphaTyVar
843 openBetaTy = mkTyVarTy openBetaTyVar
846 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy]
848 -- Notice the openAlphaTyVar. It says that "error" can be applied
849 -- to unboxed as well as boxed types. This is OK because it never
850 -- returns, so the return type is irrelevant.