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, nullAddrId,
26 eRROR_ID, eRROR_CSTRING_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, StrictnessMark(..), isMarkedUnboxed, isMarkedStrict )
35 import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy, betaTyVar, betaTy,
36 intPrimTy, realWorldStatePrimTy, addrPrimTy
38 import TysWiredIn ( charTy, mkListTy )
39 import PrelRules ( primOpRules )
40 import Rules ( addRule )
41 import TcType ( Type, ThetaType, mkDictTy, mkPredTys, mkTyConApp,
42 mkTyVarTys, mkClassPred, tcEqPred,
43 mkFunTys, mkFunTy, mkSigmaTy, tcSplitSigmaTy,
44 isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType,
45 tcSplitFunTys, tcSplitForAllTys, mkPredTy
47 import Module ( Module )
48 import CoreUtils ( mkInlineMe )
49 import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding, mkOtherCon )
50 import Literal ( Literal(..), nullAddrLit )
51 import TyCon ( TyCon, isNewTyCon, tyConTyVars, tyConDataCons,
52 tyConTheta, isProductTyCon, isDataTyCon, isRecursiveTyCon )
53 import Class ( Class, classTyCon, classTyVars, classSelIds )
54 import Var ( Id, TyVar )
55 import VarSet ( isEmptyVarSet )
56 import Name ( mkWiredInName, mkFCallName, Name )
57 import OccName ( mkVarOcc )
58 import PrimOp ( PrimOp(DataToTagOp), primOpSig, mkPrimOpIdName )
59 import ForeignCall ( ForeignCall )
60 import DataCon ( DataCon,
61 dataConFieldLabels, dataConRepArity, dataConTyCon,
62 dataConArgTys, dataConRepType,
63 dataConInstOrigArgTys,
64 dataConName, dataConTheta,
65 dataConSig, dataConStrictMarks, dataConId,
68 import Id ( idType, mkGlobalId, mkVanillaGlobal, mkSysLocal,
69 mkTemplateLocals, mkTemplateLocalsNum,
70 mkTemplateLocal, idNewStrictness, idName
72 import IdInfo ( IdInfo, noCafNoTyGenIdInfo,
74 setArityInfo, setSpecInfo, setCgInfo,
75 mkNewStrictnessInfo, setNewStrictnessInfo,
76 GlobalIdDetails(..), CafInfo(..), CprInfo(..),
77 CgInfo(..), setCgArity
79 import NewDemand ( mkStrictSig, strictSigResInfo, DmdResult(..),
80 mkTopDmdType, topDmd, evalDmd, Demand(..), Keepity(..) )
81 import FieldLabel ( mkFieldLabel, fieldLabelName,
82 firstFieldLabelTag, allFieldLabelTags, fieldLabelType
84 import DmdAnal ( dmdAnalTopRhs )
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]
116 , iRREFUT_PAT_ERROR_ID
117 , nON_EXHAUSTIVE_GUARDS_ERROR_ID
118 , nO_METHOD_BINDING_ERROR_ID
124 -- These can't be defined in Haskell, but they have
125 -- perfectly reasonable unfoldings in Core
134 %************************************************************************
136 \subsection{Data constructors}
138 %************************************************************************
141 mkDataConId :: Name -> DataCon -> Id
142 -- Makes the *worker* for the data constructor; that is, the function
143 -- that takes the reprsentation arguments and builds the constructor.
144 mkDataConId work_name data_con
145 = mkGlobalId (DataConId data_con) work_name (dataConRepType data_con) info
147 info = noCafNoTyGenIdInfo
150 `setNewStrictnessInfo` Just strict_sig
152 arity = dataConRepArity data_con
154 strict_sig = mkStrictSig (mkTopDmdType (replicate arity topDmd) cpr_info)
155 -- Notice that we do *not* say the worker is strict
156 -- even if the data constructor is declared strict
157 -- e.g. data T = MkT !(Int,Int)
158 -- Why? Because the *wrapper* is strict (and its unfolding has case
159 -- expresssions that do the evals) but the *worker* itself is not.
160 -- If we pretend it is strict then when we see
161 -- case x of y -> $wMkT y
162 -- the simplifier thinks that y is "sure to be evaluated" (because
163 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
165 -- When the simplifer sees a pattern
166 -- case e of MkT x -> ...
167 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
168 -- but that's fine... dataConRepStrictness comes from the data con
169 -- not from the worker Id.
171 tycon = dataConTyCon data_con
172 cpr_info | isProductTyCon tycon &&
175 arity <= mAX_CPR_SIZE = RetCPR
177 -- RetCPR is only true for products that are real data types;
178 -- that is, not unboxed tuples or [non-recursive] newtypes
180 mAX_CPR_SIZE :: Arity
182 -- We do not treat very big tuples as CPR-ish:
183 -- a) for a start we get into trouble because there aren't
184 -- "enough" unboxed tuple types (a tiresome restriction,
186 -- b) more importantly, big unboxed tuples get returned mainly
187 -- on the stack, and are often then allocated in the heap
188 -- by the caller. So doing CPR for them may in fact make
192 The wrapper for a constructor is an ordinary top-level binding that evaluates
193 any strict args, unboxes any args that are going to be flattened, and calls
196 We're going to build a constructor that looks like:
198 data (Data a, C b) => T a b = T1 !a !Int b
201 \d1::Data a, d2::C b ->
202 \p q r -> case p of { p ->
204 Con T1 [a,b] [p,q,r]}}
208 * d2 is thrown away --- a context in a data decl is used to make sure
209 one *could* construct dictionaries at the site the constructor
210 is used, but the dictionary isn't actually used.
212 * We have to check that we can construct Data dictionaries for
213 the types a and Int. Once we've done that we can throw d1 away too.
215 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
216 all that matters is that the arguments are evaluated. "seq" is
217 very careful to preserve evaluation order, which we don't need
220 You might think that we could simply give constructors some strictness
221 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
222 But we don't do that because in the case of primops and functions strictness
223 is a *property* not a *requirement*. In the case of constructors we need to
224 do something active to evaluate the argument.
226 Making an explicit case expression allows the simplifier to eliminate
227 it in the (common) case where the constructor arg is already evaluated.
230 mkDataConWrapId data_con
231 = mkGlobalId (DataConWrapId data_con) (dataConName data_con) wrap_ty info
233 work_id = dataConId data_con
235 info = noCafNoTyGenIdInfo
236 `setUnfoldingInfo` mkTopUnfolding (mkInlineMe wrap_rhs)
238 -- The NoCaf-ness is set by noCafNoTyGenIdInfo
240 -- It's important to specify the arity, so that partial
241 -- applications are treated as values
242 `setNewStrictnessInfo` Just wrap_sig
244 wrap_ty = mkForAllTys all_tyvars (mkFunTys all_arg_tys result_ty)
246 res_info = strictSigResInfo (idNewStrictness work_id)
247 wrap_sig = mkStrictSig (mkTopDmdType (replicate arity topDmd) res_info)
248 -- The Cpr info can be important inside INLINE rhss, where the
249 -- wrapper constructor isn't inlined
250 -- But we are sloppy about the argument demands, because we expect
251 -- to inline the constructor very vigorously.
253 wrap_rhs | isNewTyCon tycon
254 = ASSERT( null ex_tyvars && null ex_dict_args && length orig_arg_tys == 1 )
255 -- No existentials on a newtype, but it can have a context
256 -- e.g. newtype Eq a => T a = MkT (...)
257 mkLams tyvars $ mkLams dict_args $ Lam id_arg1 $
258 mkNewTypeBody tycon result_ty id_arg1
260 | null dict_args && not (any isMarkedStrict strict_marks)
261 = Var work_id -- The common case. Not only is this efficient,
262 -- but it also ensures that the wrapper is replaced
263 -- by the worker even when there are no args.
267 -- This is really important in rule matching,
268 -- (We could match on the wrappers,
269 -- but that makes it less likely that rules will match
270 -- when we bring bits of unfoldings together.)
272 -- NB: because of this special case, (map (:) ys) turns into
273 -- (map $w: ys), and thence into (map (\x xs. $w: x xs) ys)
274 -- in core-to-stg. The top-level defn for (:) is never used.
275 -- This is somewhat of a bore, but I'm currently leaving it
276 -- as is, so that there still is a top level curried (:) for
277 -- the interpreter to call.
280 = mkLams all_tyvars $ mkLams dict_args $
281 mkLams ex_dict_args $ mkLams id_args $
282 foldr mk_case con_app
283 (zip (ex_dict_args++id_args) strict_marks) i3 []
285 con_app i rep_ids = mkApps (Var work_id)
286 (map varToCoreExpr (all_tyvars ++ reverse rep_ids))
288 (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon) = dataConSig data_con
289 all_tyvars = tyvars ++ ex_tyvars
291 dict_tys = mkPredTys theta
292 ex_dict_tys = mkPredTys ex_theta
293 all_arg_tys = dict_tys ++ ex_dict_tys ++ orig_arg_tys
294 result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
296 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
300 (dict_args, i1) = mkLocals 1 dict_tys
301 (ex_dict_args,i2) = mkLocals i1 ex_dict_tys
302 (id_args,i3) = mkLocals i2 orig_arg_tys
304 (id_arg1:_) = id_args -- Used for newtype only
306 strict_marks = dataConStrictMarks data_con
309 :: (Id, StrictnessMark) -- Arg, strictness
310 -> (Int -> [Id] -> CoreExpr) -- Body
311 -> Int -- Next rep arg id
312 -> [Id] -- Rep args so far, reversed
314 mk_case (arg,strict) body i rep_args
316 NotMarkedStrict -> body i (arg:rep_args)
318 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
320 Case (Var arg) arg [(DEFAULT,[], body i (arg:rep_args))]
323 -> case splitProductType "do_unbox" (idType arg) of
324 (tycon, tycon_args, con, tys) ->
325 Case (Var arg) arg [(DataAlt con, con_args,
326 body i' (reverse con_args ++ rep_args))]
328 (con_args, i') = mkLocals i tys
332 %************************************************************************
334 \subsection{Record selectors}
336 %************************************************************************
338 We're going to build a record selector unfolding that looks like this:
340 data T a b c = T1 { ..., op :: a, ...}
341 | T2 { ..., op :: a, ...}
344 sel = /\ a b c -> \ d -> case d of
349 Similarly for newtypes
351 newtype N a = MkN { unN :: a->a }
354 unN n = coerce (a->a) n
356 We need to take a little care if the field has a polymorphic type:
358 data R = R { f :: forall a. a->a }
362 f :: forall a. R -> a -> a
363 f = /\ a \ r = case r of
366 (not f :: R -> forall a. a->a, which gives the type inference mechanism
367 problems at call sites)
369 Similarly for newtypes
371 newtype N = MkN { unN :: forall a. a->a }
373 unN :: forall a. N -> a -> a
374 unN = /\a -> \n:N -> coerce (a->a) n
377 mkRecordSelId tycon field_label unpack_id unpackUtf8_id
378 -- Assumes that all fields with the same field label have the same type
380 -- Annoyingly, we have to pass in the unpackCString# Id, because
381 -- we can't conjure it up out of thin air
384 sel_id = mkGlobalId (RecordSelId field_label) (fieldLabelName field_label) selector_ty info
385 field_ty = fieldLabelType field_label
386 data_cons = tyConDataCons tycon
387 tyvars = tyConTyVars tycon -- These scope over the types in
388 -- the FieldLabels of constructors of this type
389 data_ty = mkTyConApp tycon tyvar_tys
390 tyvar_tys = mkTyVarTys tyvars
392 tycon_theta = tyConTheta tycon -- The context on the data decl
393 -- eg data (Eq a, Ord b) => T a b = ...
394 dict_tys = [mkPredTy pred | pred <- tycon_theta,
396 needed_dict pred = or [ tcEqPred pred p
397 | (DataAlt dc, _, _) <- the_alts, p <- dataConTheta dc]
398 n_dict_tys = length dict_tys
400 (field_tyvars,field_theta,field_tau) = tcSplitSigmaTy field_ty
401 field_dict_tys = map mkPredTy field_theta
402 n_field_dict_tys = length field_dict_tys
403 -- If the field has a universally quantified type we have to
404 -- be a bit careful. Suppose we have
405 -- data R = R { op :: forall a. Foo a => a -> a }
406 -- Then we can't give op the type
407 -- op :: R -> forall a. Foo a => a -> a
408 -- because the typechecker doesn't understand foralls to the
409 -- right of an arrow. The "right" type to give it is
410 -- op :: forall a. Foo a => R -> a -> a
411 -- But then we must generate the right unfolding too:
412 -- op = /\a -> \dfoo -> \ r ->
415 -- Note that this is exactly the type we'd infer from a user defn
418 -- Very tiresomely, the selectors are (unnecessarily!) overloaded over
419 -- just the dictionaries in the types of the constructors that contain
420 -- the relevant field. Urgh.
421 -- NB: this code relies on the fact that DataCons are quantified over
422 -- the identical type variables as their parent TyCon
425 selector_ty = mkForAllTys tyvars $ mkForAllTys field_tyvars $
426 mkFunTys dict_tys $ mkFunTys field_dict_tys $
427 mkFunTy data_ty field_tau
429 arity = 1 + n_dict_tys + n_field_dict_tys
431 (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
432 -- Use the demand analyser to work out strictness.
433 -- With all this unpackery it's not easy!
435 info = noCafNoTyGenIdInfo
436 `setCgInfo` CgInfo arity caf_info
438 `setUnfoldingInfo` mkTopUnfolding rhs_w_str
439 `setNewStrictnessInfo` Just strict_sig
441 -- Allocate Ids. We do it a funny way round because field_dict_tys is
442 -- almost always empty. Also note that we use length_tycon_theta
443 -- rather than n_dict_tys, because the latter gives an infinite loop:
444 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
445 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
446 field_dict_base = length tycon_theta + 1
447 dict_id_base = field_dict_base + n_field_dict_tys
448 field_base = dict_id_base + 1
449 dict_ids = mkTemplateLocalsNum 1 dict_tys
450 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
451 data_id = mkTemplateLocal dict_id_base data_ty
453 alts = map mk_maybe_alt data_cons
454 the_alts = catMaybes alts
456 no_default = all isJust alts -- No default needed
457 default_alt | no_default = []
458 | otherwise = [(DEFAULT, [], error_expr)]
460 -- the default branch may have CAF refs, because it calls recSelError etc.
461 caf_info | no_default = NoCafRefs
462 | otherwise = MayHaveCafRefs
464 sel_rhs = mkLams tyvars $ mkLams field_tyvars $
465 mkLams dict_ids $ mkLams field_dict_ids $
466 Lam data_id $ sel_body
468 sel_body | isNewTyCon tycon = mkNewTypeBody tycon field_tau data_id
469 | otherwise = Case (Var data_id) data_id (default_alt ++ the_alts)
471 mk_maybe_alt data_con
472 = case maybe_the_arg_id of
474 Just the_arg_id -> Just (DataAlt data_con, real_args, mkLets binds body)
476 body = mkVarApps (mkVarApps (Var the_arg_id) field_tyvars) field_dict_ids
477 strict_marks = dataConStrictMarks data_con
478 (binds, real_args) = rebuildConArgs arg_ids strict_marks
479 (map mkBuiltinUnique [unpack_base..])
481 arg_ids = mkTemplateLocalsNum field_base (dataConInstOrigArgTys data_con tyvar_tys)
483 unpack_base = field_base + length arg_ids
485 -- arity+1 avoids all shadowing
486 maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
487 field_lbls = dataConFieldLabels data_con
489 error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type field_tau, err_string]
491 | all safeChar full_msg
492 = App (Var unpack_id) (Lit (MachStr (_PK_ full_msg)))
494 = App (Var unpackUtf8_id) (Lit (MachStr (_PK_ (stringToUtf8 (map ord full_msg)))))
496 safeChar c = c >= '\1' && c <= '\xFF'
497 -- TODO: Putting this Unicode stuff here is ugly. Find a better
498 -- generic place to make string literals. This logic is repeated
500 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
503 -- This rather ugly function converts the unpacked data con
504 -- arguments back into their packed form.
507 :: [Id] -- Source-level args
508 -> [StrictnessMark] -- Strictness annotations (per-arg)
509 -> [Unique] -- Uniques for the new Ids
510 -> ([CoreBind], [Id]) -- A binding for each source-level arg, plus
511 -- a list of the representation-level arguments
512 -- e.g. data T = MkT Int !Int
514 -- rebuild [x::Int, y::Int] [Not, Unbox]
515 -- = ([ y = I# t ], [x,t])
517 rebuildConArgs [] stricts us = ([], [])
519 -- Type variable case
520 rebuildConArgs (arg:args) stricts us
522 = let (binds, args') = rebuildConArgs args stricts us
523 in (binds, arg:args')
525 -- Term variable case
526 rebuildConArgs (arg:args) (str:stricts) us
527 | isMarkedUnboxed str
531 (_, tycon_args, pack_con, con_arg_tys)
532 = splitProductType "rebuildConArgs" arg_ty
534 unpacked_args = zipWith (mkSysLocal SLIT("rb")) us con_arg_tys
535 (binds, args') = rebuildConArgs args stricts (drop (length con_arg_tys) us)
536 con_app = mkConApp pack_con (map Type tycon_args ++ map Var unpacked_args)
538 (NonRec arg con_app : binds, unpacked_args ++ args')
541 = let (binds, args') = rebuildConArgs args stricts us
542 in (binds, arg:args')
546 %************************************************************************
548 \subsection{Dictionary selectors}
550 %************************************************************************
552 Selecting a field for a dictionary. If there is just one field, then
553 there's nothing to do.
555 ToDo: unify with mkRecordSelId.
558 mkDictSelId :: Name -> Class -> Id
559 mkDictSelId name clas
560 = mkGlobalId (RecordSelId field_lbl) name sel_ty info
562 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
563 -- We can't just say (exprType rhs), because that would give a type
565 -- for a single-op class (after all, the selector is the identity)
566 -- But it's type must expose the representation of the dictionary
567 -- to gat (say) C a -> (a -> a)
569 field_lbl = mkFieldLabel name tycon sel_ty tag
570 tag = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` allFieldLabelTags) name
572 info = noCafNoTyGenIdInfo
575 `setUnfoldingInfo` mkTopUnfolding rhs
576 `setNewStrictnessInfo` Just strict_sig
578 -- We no longer use 'must-inline' on record selectors. They'll
579 -- inline like crazy if they scrutinise a constructor
581 -- The strictness signature is of the form U(AAAVAAAA) -> T
582 -- where the V depends on which item we are selecting
583 -- It's worth giving one, so that absence info etc is generated
584 -- even if the selector isn't inlined
585 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
586 arg_dmd | isNewTyCon tycon = Eval
587 | otherwise = Seq Drop [ if the_arg_id == id then Eval else Abs
590 tyvars = classTyVars clas
592 tycon = classTyCon clas
593 [data_con] = tyConDataCons tycon
594 tyvar_tys = mkTyVarTys tyvars
595 arg_tys = dataConArgTys data_con tyvar_tys
596 the_arg_id = arg_ids !! (tag - firstFieldLabelTag)
598 pred = mkClassPred clas tyvar_tys
599 (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
601 rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
602 mkNewTypeBody tycon (head arg_tys) dict_id
603 | otherwise = mkLams tyvars $ Lam dict_id $
604 Case (Var dict_id) dict_id
605 [(DataAlt data_con, arg_ids, Var the_arg_id)]
607 mkNewTypeBody tycon result_ty result_id
608 | isRecursiveTyCon tycon -- Recursive case; use a coerce
609 = Note (Coerce result_ty (idType result_id)) (Var result_id)
610 | otherwise -- Normal case
615 %************************************************************************
617 \subsection{Primitive operations
619 %************************************************************************
622 mkPrimOpId :: PrimOp -> Id
626 (tyvars,arg_tys,res_ty, arity, strict_info) = primOpSig prim_op
627 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
628 name = mkPrimOpIdName prim_op
629 id = mkGlobalId (PrimOpId prim_op) name ty info
631 info = noCafNoTyGenIdInfo
635 `setNewStrictnessInfo` Just (mkNewStrictnessInfo id arity strict_info NoCPRInfo)
636 -- Until we modify the primop generation code
638 rules = foldl (addRule id) emptyCoreRules (primOpRules prim_op)
641 -- For each ccall we manufacture a separate CCallOpId, giving it
642 -- a fresh unique, a type that is correct for this particular ccall,
643 -- and a CCall structure that gives the correct details about calling
646 -- The *name* of this Id is a local name whose OccName gives the full
647 -- details of the ccall, type and all. This means that the interface
648 -- file reader can reconstruct a suitable Id
650 mkFCallId :: Unique -> ForeignCall -> Type -> Id
651 mkFCallId uniq fcall ty
652 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
653 -- A CCallOpId should have no free type variables;
654 -- when doing substitutions won't substitute over it
655 mkGlobalId (FCallId fcall) name ty info
657 occ_str = showSDocIface (braces (ppr fcall <+> ppr ty))
658 -- The "occurrence name" of a ccall is the full info about the
659 -- ccall; it is encoded, but may have embedded spaces etc!
661 name = mkFCallName uniq occ_str
663 info = noCafNoTyGenIdInfo
666 `setNewStrictnessInfo` Just strict_sig
668 (_, tau) = tcSplitForAllTys ty
669 (arg_tys, _) = tcSplitFunTys tau
670 arity = length arg_tys
671 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
675 %************************************************************************
677 \subsection{DictFuns and default methods}
679 %************************************************************************
681 Important notes about dict funs and default methods
682 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
683 Dict funs and default methods are *not* ImplicitIds. Their definition
684 involves user-written code, so we can't figure out their strictness etc
685 based on fixed info, as we can for constructors and record selectors (say).
687 We build them as GlobalIds, but when in the module where they are
688 bound, we turn the Id at the *binding site* into an exported LocalId.
689 This ensures that they are taken to account by free-variable finding
690 and dependency analysis (e.g. CoreFVs.exprFreeVars). The simplifier
691 will propagate the LocalId to all occurrence sites.
693 Why shouldn't they be bound as GlobalIds? Because, in particular, if
694 they are globals, the specialiser floats dict uses above their defns,
695 which prevents good simplifications happening. Also the strictness
696 analyser treats a occurrence of a GlobalId as imported and assumes it
697 contains strictness in its IdInfo, which isn't true if the thing is
698 bound in the same module as the occurrence.
700 It's OK for dfuns to be LocalIds, because we form the instance-env to
701 pass on to the next module (md_insts) in CoreTidy, afer tidying
702 and globalising the top-level Ids.
704 BUT make sure they are *exported* LocalIds (setIdLocalExported) so
705 that they aren't discarded by the occurrence analyser.
708 mkDefaultMethodId dm_name ty = mkVanillaGlobal dm_name ty noCafNoTyGenIdInfo
710 mkDictFunId :: Name -- Name to use for the dict fun;
717 mkDictFunId dfun_name clas inst_tyvars inst_tys dfun_theta
718 = mkVanillaGlobal dfun_name dfun_ty noCafNoTyGenIdInfo
720 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
722 {- 1 dec 99: disable the Mark Jones optimisation for the sake
723 of compatibility with Hugs.
724 See `types/InstEnv' for a discussion related to this.
726 (class_tyvars, sc_theta, _, _) = classBigSig clas
727 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
728 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys) sc_theta
729 dfun_theta = case inst_decl_theta of
730 [] -> [] -- If inst_decl_theta is empty, then we don't
731 -- want to have any dict arguments, so that we can
732 -- expose the constant methods.
734 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
735 -- Otherwise we pass the superclass dictionaries to
736 -- the dictionary function; the Mark Jones optimisation.
738 -- NOTE the "nub". I got caught by this one:
739 -- class Monad m => MonadT t m where ...
740 -- instance Monad m => MonadT (EnvT env) m where ...
741 -- Here, the inst_decl_theta has (Monad m); but so
742 -- does the sc_theta'!
744 -- NOTE the "not_const". I got caught by this one too:
745 -- class Foo a => Baz a b where ...
746 -- instance Wob b => Baz T b where..
747 -- Now sc_theta' has Foo T
752 %************************************************************************
754 \subsection{Un-definable}
756 %************************************************************************
758 These Ids can't be defined in Haskell. They could be defined in
759 unfoldings in PrelGHC.hi-boot, but we'd have to ensure that they
760 were definitely, definitely inlined, because there is no curried
761 identifier for them. That's what mkCompulsoryUnfolding does.
762 If we had a way to get a compulsory unfolding from an interface file,
763 we could do that, but we don't right now.
765 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
766 just gets expanded into a type coercion wherever it occurs. Hence we
767 add it as a built-in Id with an unfolding here.
769 The type variables we use here are "open" type variables: this means
770 they can unify with both unlifted and lifted types. Hence we provide
771 another gun with which to shoot yourself in the foot.
774 -- unsafeCoerce# :: forall a b. a -> b
776 = pcMiscPrelId unsafeCoerceIdKey pREL_GHC SLIT("unsafeCoerce#") ty info
778 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
781 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
782 (mkFunTy openAlphaTy openBetaTy)
783 [x] = mkTemplateLocals [openAlphaTy]
784 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
785 Note (Coerce openBetaTy openAlphaTy) (Var x)
787 -- nullAddr# :: Addr#
788 -- The reason is is here is because we don't provide
789 -- a way to write this literal in Haskell.
791 = pcMiscPrelId nullAddrIdKey pREL_GHC SLIT("nullAddr#") addrPrimTy info
793 info = noCafNoTyGenIdInfo `setUnfoldingInfo`
794 mkCompulsoryUnfolding (Lit nullAddrLit)
797 = pcMiscPrelId seqIdKey pREL_GHC SLIT("seq") ty info
799 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
802 ty = mkForAllTys [alphaTyVar,betaTyVar]
803 (mkFunTy alphaTy (mkFunTy betaTy betaTy))
804 [x,y] = mkTemplateLocals [alphaTy, betaTy]
805 rhs = mkLams [alphaTyVar,betaTyVar,x,y] (Case (Var x) x [(DEFAULT, [], Var y)])
808 @getTag#@ is another function which can't be defined in Haskell. It needs to
809 evaluate its argument and call the dataToTag# primitive.
813 = pcMiscPrelId getTagIdKey pREL_GHC SLIT("getTag#") ty info
815 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
816 -- We don't provide a defn for this; you must inline it
818 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy intPrimTy)
819 [x,y] = mkTemplateLocals [alphaTy,alphaTy]
820 rhs = mkLams [alphaTyVar,x] $
821 Case (Var x) y [ (DEFAULT, [], mkApps (Var dataToTagId) [Type alphaTy, Var y]) ]
823 dataToTagId = mkPrimOpId DataToTagOp
826 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
827 nasty as-is, change it back to a literal (@Literal@).
830 realWorldPrimId -- :: State# RealWorld
831 = pcMiscPrelId realWorldPrimIdKey pREL_GHC SLIT("realWorld#")
833 (noCafNoTyGenIdInfo `setUnfoldingInfo` mkOtherCon [])
834 -- The mkOtherCon makes it look that realWorld# is evaluated
835 -- which in turn makes Simplify.interestingArg return True,
836 -- which in turn makes INLINE things applied to realWorld# likely
841 %************************************************************************
843 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
845 %************************************************************************
847 GHC randomly injects these into the code.
849 @patError@ is just a version of @error@ for pattern-matching
850 failures. It knows various ``codes'' which expand to longer
851 strings---this saves space!
853 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
854 well shouldn't be yanked on, but if one is, then you will get a
855 friendly message from @absentErr@ (rather than a totally random
858 @parError@ is a special version of @error@ which the compiler does
859 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
860 templates, but we don't ever expect to generate code for it.
864 = pc_bottoming_Id errorIdKey pREL_ERR SLIT("error") errorTy
866 = pc_bottoming_Id errorCStringIdKey pREL_ERR SLIT("errorCString")
867 (mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy))
869 = generic_ERROR_ID patErrorIdKey SLIT("patError")
871 = generic_ERROR_ID recSelErrIdKey SLIT("recSelError")
873 = generic_ERROR_ID recConErrorIdKey SLIT("recConError")
875 = generic_ERROR_ID recUpdErrorIdKey SLIT("recUpdError")
877 = generic_ERROR_ID irrefutPatErrorIdKey SLIT("irrefutPatError")
878 nON_EXHAUSTIVE_GUARDS_ERROR_ID
879 = generic_ERROR_ID nonExhaustiveGuardsErrorIdKey SLIT("nonExhaustiveGuardsError")
880 nO_METHOD_BINDING_ERROR_ID
881 = generic_ERROR_ID noMethodBindingErrorIdKey SLIT("noMethodBindingError")
884 = pc_bottoming_Id absentErrorIdKey pREL_ERR SLIT("absentErr")
885 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy)
888 = pcMiscPrelId parErrorIdKey pREL_ERR SLIT("parError")
889 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy) noCafNoTyGenIdInfo
893 %************************************************************************
895 \subsection{Utilities}
897 %************************************************************************
900 pcMiscPrelId :: Unique{-IdKey-} -> Module -> FAST_STRING -> Type -> IdInfo -> Id
901 pcMiscPrelId key mod str ty info
903 name = mkWiredInName mod (mkVarOcc str) key
904 imp = mkVanillaGlobal name ty info -- the usual case...
907 -- We lie and say the thing is imported; otherwise, we get into
908 -- a mess with dependency analysis; e.g., core2stg may heave in
909 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
910 -- being compiled, then it's just a matter of luck if the definition
911 -- will be in "the right place" to be in scope.
913 pc_bottoming_Id key mod name ty
914 = pcMiscPrelId key mod name ty bottoming_info
916 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
917 bottoming_info = noCafNoTyGenIdInfo `setNewStrictnessInfo` Just strict_sig
918 -- these "bottom" out, no matter what their arguments
920 generic_ERROR_ID u n = pc_bottoming_Id u pREL_ERR n errorTy
922 (openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
923 openAlphaTy = mkTyVarTy openAlphaTyVar
924 openBetaTy = mkTyVarTy openBetaTyVar
927 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy]
929 -- Notice the openAlphaTyVar. It says that "error" can be applied
930 -- to unboxed as well as boxed types. This is OK because it never
931 -- returns, so the return type is irrelevant.