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, 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(..) )
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 three can't be defined in Haskell
132 %************************************************************************
134 \subsection{Data constructors}
136 %************************************************************************
139 mkDataConId :: Name -> DataCon -> Id
140 -- Makes the *worker* for the data constructor; that is, the function
141 -- that takes the reprsentation arguments and builds the constructor.
142 mkDataConId work_name data_con
143 = mkGlobalId (DataConId data_con) work_name (dataConRepType data_con) info
145 info = noCafNoTyGenIdInfo
148 `setNewStrictnessInfo` Just strict_sig
150 arity = dataConRepArity data_con
152 strict_sig = mkStrictSig (mkTopDmdType (replicate arity topDmd) cpr_info)
153 -- Notice that we do *not* say the worker is strict
154 -- even if the data constructor is declared strict
155 -- e.g. data T = MkT !(Int,Int)
156 -- Why? Because the *wrapper* is strict (and its unfolding has case
157 -- expresssions that do the evals) but the *worker* itself is not.
158 -- If we pretend it is strict then when we see
159 -- case x of y -> $wMkT y
160 -- the simplifier thinks that y is "sure to be evaluated" (because
161 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
163 -- When the simplifer sees a pattern
164 -- case e of MkT x -> ...
165 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
166 -- but that's fine... dataConRepStrictness comes from the data con
167 -- not from the worker Id.
169 tycon = dataConTyCon data_con
170 cpr_info | isProductTyCon tycon &&
173 arity <= mAX_CPR_SIZE = RetCPR
175 -- RetCPR is only true for products that are real data types;
176 -- that is, not unboxed tuples or [non-recursive] newtypes
178 mAX_CPR_SIZE :: Arity
180 -- We do not treat very big tuples as CPR-ish:
181 -- a) for a start we get into trouble because there aren't
182 -- "enough" unboxed tuple types (a tiresome restriction,
184 -- b) more importantly, big unboxed tuples get returned mainly
185 -- on the stack, and are often then allocated in the heap
186 -- by the caller. So doing CPR for them may in fact make
190 The wrapper for a constructor is an ordinary top-level binding that evaluates
191 any strict args, unboxes any args that are going to be flattened, and calls
194 We're going to build a constructor that looks like:
196 data (Data a, C b) => T a b = T1 !a !Int b
199 \d1::Data a, d2::C b ->
200 \p q r -> case p of { p ->
202 Con T1 [a,b] [p,q,r]}}
206 * d2 is thrown away --- a context in a data decl is used to make sure
207 one *could* construct dictionaries at the site the constructor
208 is used, but the dictionary isn't actually used.
210 * We have to check that we can construct Data dictionaries for
211 the types a and Int. Once we've done that we can throw d1 away too.
213 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
214 all that matters is that the arguments are evaluated. "seq" is
215 very careful to preserve evaluation order, which we don't need
218 You might think that we could simply give constructors some strictness
219 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
220 But we don't do that because in the case of primops and functions strictness
221 is a *property* not a *requirement*. In the case of constructors we need to
222 do something active to evaluate the argument.
224 Making an explicit case expression allows the simplifier to eliminate
225 it in the (common) case where the constructor arg is already evaluated.
228 mkDataConWrapId data_con
229 = mkGlobalId (DataConWrapId data_con) (dataConName data_con) wrap_ty info
231 work_id = dataConId data_con
233 info = noCafNoTyGenIdInfo
234 `setUnfoldingInfo` mkTopUnfolding (mkInlineMe wrap_rhs)
236 -- The NoCaf-ness is set by noCafNoTyGenIdInfo
238 -- It's important to specify the arity, so that partial
239 -- applications are treated as values
240 `setNewStrictnessInfo` Just wrap_sig
242 wrap_ty = mkForAllTys all_tyvars (mkFunTys all_arg_tys result_ty)
244 res_info = strictSigResInfo (idNewStrictness work_id)
245 wrap_sig = mkStrictSig (mkTopDmdType (replicate arity topDmd) res_info)
246 -- The Cpr info can be important inside INLINE rhss, where the
247 -- wrapper constructor isn't inlined
248 -- But we are sloppy about the argument demands, because we expect
249 -- to inline the constructor very vigorously.
251 wrap_rhs | isNewTyCon tycon
252 = ASSERT( null ex_tyvars && null ex_dict_args && length orig_arg_tys == 1 )
253 -- No existentials on a newtype, but it can have a context
254 -- e.g. newtype Eq a => T a = MkT (...)
255 mkLams tyvars $ mkLams dict_args $ Lam id_arg1 $
256 mkNewTypeBody tycon result_ty id_arg1
258 | null dict_args && not (any isMarkedStrict strict_marks)
259 = Var work_id -- The common case. Not only is this efficient,
260 -- but it also ensures that the wrapper is replaced
261 -- by the worker even when there are no args.
265 -- This is really important in rule matching,
266 -- (We could match on the wrappers,
267 -- but that makes it less likely that rules will match
268 -- when we bring bits of unfoldings together.)
270 -- NB: because of this special case, (map (:) ys) turns into
271 -- (map $w: ys), and thence into (map (\x xs. $w: x xs) ys)
272 -- in core-to-stg. The top-level defn for (:) is never used.
273 -- This is somewhat of a bore, but I'm currently leaving it
274 -- as is, so that there still is a top level curried (:) for
275 -- the interpreter to call.
278 = mkLams all_tyvars $ mkLams dict_args $
279 mkLams ex_dict_args $ mkLams id_args $
280 foldr mk_case con_app
281 (zip (ex_dict_args++id_args) strict_marks) i3 []
283 con_app i rep_ids = mkApps (Var work_id)
284 (map varToCoreExpr (all_tyvars ++ reverse rep_ids))
286 (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon) = dataConSig data_con
287 all_tyvars = tyvars ++ ex_tyvars
289 dict_tys = mkPredTys theta
290 ex_dict_tys = mkPredTys ex_theta
291 all_arg_tys = dict_tys ++ ex_dict_tys ++ orig_arg_tys
292 result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
294 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
298 (dict_args, i1) = mkLocals 1 dict_tys
299 (ex_dict_args,i2) = mkLocals i1 ex_dict_tys
300 (id_args,i3) = mkLocals i2 orig_arg_tys
302 (id_arg1:_) = id_args -- Used for newtype only
304 strict_marks = dataConStrictMarks data_con
307 :: (Id, StrictnessMark) -- Arg, strictness
308 -> (Int -> [Id] -> CoreExpr) -- Body
309 -> Int -- Next rep arg id
310 -> [Id] -- Rep args so far, reversed
312 mk_case (arg,strict) body i rep_args
314 NotMarkedStrict -> body i (arg:rep_args)
316 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
318 Case (Var arg) arg [(DEFAULT,[], body i (arg:rep_args))]
321 -> case splitProductType "do_unbox" (idType arg) of
322 (tycon, tycon_args, con, tys) ->
323 Case (Var arg) arg [(DataAlt con, con_args,
324 body i' (reverse con_args ++ rep_args))]
326 (con_args, i') = mkLocals i tys
330 %************************************************************************
332 \subsection{Record selectors}
334 %************************************************************************
336 We're going to build a record selector unfolding that looks like this:
338 data T a b c = T1 { ..., op :: a, ...}
339 | T2 { ..., op :: a, ...}
342 sel = /\ a b c -> \ d -> case d of
347 Similarly for newtypes
349 newtype N a = MkN { unN :: a->a }
352 unN n = coerce (a->a) n
354 We need to take a little care if the field has a polymorphic type:
356 data R = R { f :: forall a. a->a }
360 f :: forall a. R -> a -> a
361 f = /\ a \ r = case r of
364 (not f :: R -> forall a. a->a, which gives the type inference mechanism
365 problems at call sites)
367 Similarly for newtypes
369 newtype N = MkN { unN :: forall a. a->a }
371 unN :: forall a. N -> a -> a
372 unN = /\a -> \n:N -> coerce (a->a) n
375 mkRecordSelId tycon field_label unpack_id unpackUtf8_id
376 -- Assumes that all fields with the same field label have the same type
378 -- Annoyingly, we have to pass in the unpackCString# Id, because
379 -- we can't conjure it up out of thin air
382 sel_id = mkGlobalId (RecordSelId field_label) (fieldLabelName field_label) selector_ty info
383 field_ty = fieldLabelType field_label
384 data_cons = tyConDataCons tycon
385 tyvars = tyConTyVars tycon -- These scope over the types in
386 -- the FieldLabels of constructors of this type
387 data_ty = mkTyConApp tycon tyvar_tys
388 tyvar_tys = mkTyVarTys tyvars
390 tycon_theta = tyConTheta tycon -- The context on the data decl
391 -- eg data (Eq a, Ord b) => T a b = ...
392 dict_tys = [mkPredTy pred | pred <- tycon_theta,
394 needed_dict pred = or [ tcEqPred pred p
395 | (DataAlt dc, _, _) <- the_alts, p <- dataConTheta dc]
396 n_dict_tys = length dict_tys
398 (field_tyvars,field_theta,field_tau) = tcSplitSigmaTy field_ty
399 field_dict_tys = map mkPredTy field_theta
400 n_field_dict_tys = length field_dict_tys
401 -- If the field has a universally quantified type we have to
402 -- be a bit careful. Suppose we have
403 -- data R = R { op :: forall a. Foo a => a -> a }
404 -- Then we can't give op the type
405 -- op :: R -> forall a. Foo a => a -> a
406 -- because the typechecker doesn't understand foralls to the
407 -- right of an arrow. The "right" type to give it is
408 -- op :: forall a. Foo a => R -> a -> a
409 -- But then we must generate the right unfolding too:
410 -- op = /\a -> \dfoo -> \ r ->
413 -- Note that this is exactly the type we'd infer from a user defn
416 -- Very tiresomely, the selectors are (unnecessarily!) overloaded over
417 -- just the dictionaries in the types of the constructors that contain
418 -- the relevant field. Urgh.
419 -- NB: this code relies on the fact that DataCons are quantified over
420 -- the identical type variables as their parent TyCon
423 selector_ty = mkForAllTys tyvars $ mkForAllTys field_tyvars $
424 mkFunTys dict_tys $ mkFunTys field_dict_tys $
425 mkFunTy data_ty field_tau
427 arity = 1 + n_dict_tys + n_field_dict_tys
429 (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
430 -- Use the demand analyser to work out strictness.
431 -- With all this unpackery it's not easy!
433 info = noCafNoTyGenIdInfo
434 `setCgInfo` CgInfo arity caf_info
436 `setUnfoldingInfo` mkTopUnfolding rhs_w_str
437 `setNewStrictnessInfo` Just strict_sig
439 -- Allocate Ids. We do it a funny way round because field_dict_tys is
440 -- almost always empty. Also note that we use length_tycon_theta
441 -- rather than n_dict_tys, because the latter gives an infinite loop:
442 -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
443 -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
444 field_dict_base = length tycon_theta + 1
445 dict_id_base = field_dict_base + n_field_dict_tys
446 field_base = dict_id_base + 1
447 dict_ids = mkTemplateLocalsNum 1 dict_tys
448 field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
449 data_id = mkTemplateLocal dict_id_base data_ty
451 alts = map mk_maybe_alt data_cons
452 the_alts = catMaybes alts
454 no_default = all isJust alts -- No default needed
455 default_alt | no_default = []
456 | otherwise = [(DEFAULT, [], error_expr)]
458 -- the default branch may have CAF refs, because it calls recSelError etc.
459 caf_info | no_default = NoCafRefs
460 | otherwise = MayHaveCafRefs
462 sel_rhs = mkLams tyvars $ mkLams field_tyvars $
463 mkLams dict_ids $ mkLams field_dict_ids $
464 Lam data_id $ sel_body
466 sel_body | isNewTyCon tycon = mkNewTypeBody tycon field_tau data_id
467 | otherwise = Case (Var data_id) data_id (default_alt ++ the_alts)
469 mk_maybe_alt data_con
470 = case maybe_the_arg_id of
472 Just the_arg_id -> Just (DataAlt data_con, real_args, mkLets binds body)
474 body = mkVarApps (mkVarApps (Var the_arg_id) field_tyvars) field_dict_ids
475 strict_marks = dataConStrictMarks data_con
476 (binds, real_args) = rebuildConArgs arg_ids strict_marks
477 (map mkBuiltinUnique [unpack_base..])
479 arg_ids = mkTemplateLocalsNum field_base (dataConInstOrigArgTys data_con tyvar_tys)
481 unpack_base = field_base + length arg_ids
483 -- arity+1 avoids all shadowing
484 maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
485 field_lbls = dataConFieldLabels data_con
487 error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type field_tau, err_string]
489 | all safeChar full_msg
490 = App (Var unpack_id) (Lit (MachStr (_PK_ full_msg)))
492 = App (Var unpackUtf8_id) (Lit (MachStr (_PK_ (stringToUtf8 (map ord full_msg)))))
494 safeChar c = c >= '\1' && c <= '\xFF'
495 -- TODO: Putting this Unicode stuff here is ugly. Find a better
496 -- generic place to make string literals. This logic is repeated
498 full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
501 -- This rather ugly function converts the unpacked data con
502 -- arguments back into their packed form.
505 :: [Id] -- Source-level args
506 -> [StrictnessMark] -- Strictness annotations (per-arg)
507 -> [Unique] -- Uniques for the new Ids
508 -> ([CoreBind], [Id]) -- A binding for each source-level arg, plus
509 -- a list of the representation-level arguments
510 -- e.g. data T = MkT Int !Int
512 -- rebuild [x::Int, y::Int] [Not, Unbox]
513 -- = ([ y = I# t ], [x,t])
515 rebuildConArgs [] stricts us = ([], [])
517 -- Type variable case
518 rebuildConArgs (arg:args) stricts us
520 = let (binds, args') = rebuildConArgs args stricts us
521 in (binds, arg:args')
523 -- Term variable case
524 rebuildConArgs (arg:args) (str:stricts) us
525 | isMarkedUnboxed str
529 (_, tycon_args, pack_con, con_arg_tys)
530 = splitProductType "rebuildConArgs" arg_ty
532 unpacked_args = zipWith (mkSysLocal SLIT("rb")) us con_arg_tys
533 (binds, args') = rebuildConArgs args stricts (drop (length con_arg_tys) us)
534 con_app = mkConApp pack_con (map Type tycon_args ++ map Var unpacked_args)
536 (NonRec arg con_app : binds, unpacked_args ++ args')
539 = let (binds, args') = rebuildConArgs args stricts us
540 in (binds, arg:args')
544 %************************************************************************
546 \subsection{Dictionary selectors}
548 %************************************************************************
550 Selecting a field for a dictionary. If there is just one field, then
551 there's nothing to do.
553 ToDo: unify with mkRecordSelId.
556 mkDictSelId :: Name -> Class -> Id
557 mkDictSelId name clas
558 = mkGlobalId (RecordSelId field_lbl) name sel_ty info
560 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
561 -- We can't just say (exprType rhs), because that would give a type
563 -- for a single-op class (after all, the selector is the identity)
564 -- But it's type must expose the representation of the dictionary
565 -- to gat (say) C a -> (a -> a)
567 field_lbl = mkFieldLabel name tycon sel_ty tag
568 tag = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` allFieldLabelTags) name
570 info = noCafNoTyGenIdInfo
573 `setUnfoldingInfo` mkTopUnfolding rhs
574 `setNewStrictnessInfo` Just strict_sig
576 -- We no longer use 'must-inline' on record selectors. They'll
577 -- inline like crazy if they scrutinise a constructor
579 -- The strictness signature is of the form U(AAAVAAAA) -> T
580 -- where the V depends on which item we are selecting
581 -- It's worth giving one, so that absence info etc is generated
582 -- even if the selector isn't inlined
583 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
584 arg_dmd | isNewTyCon tycon = Eval
585 | otherwise = Seq Drop [ if the_arg_id == id then Eval else Abs
588 tyvars = classTyVars clas
590 tycon = classTyCon clas
591 [data_con] = tyConDataCons tycon
592 tyvar_tys = mkTyVarTys tyvars
593 arg_tys = dataConArgTys data_con tyvar_tys
594 the_arg_id = arg_ids !! (tag - firstFieldLabelTag)
596 pred = mkClassPred clas tyvar_tys
597 (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
599 rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
600 mkNewTypeBody tycon (head arg_tys) dict_id
601 | otherwise = mkLams tyvars $ Lam dict_id $
602 Case (Var dict_id) dict_id
603 [(DataAlt data_con, arg_ids, Var the_arg_id)]
605 mkNewTypeBody tycon result_ty result_id
606 | isRecursiveTyCon tycon -- Recursive case; use a coerce
607 = Note (Coerce result_ty (idType result_id)) (Var result_id)
608 | otherwise -- Normal case
613 %************************************************************************
615 \subsection{Primitive operations
617 %************************************************************************
620 mkPrimOpId :: PrimOp -> Id
624 (tyvars,arg_tys,res_ty, arity, strict_info) = primOpSig prim_op
625 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
626 name = mkPrimOpIdName prim_op
627 id = mkGlobalId (PrimOpId prim_op) name ty info
629 info = noCafNoTyGenIdInfo
633 `setNewStrictnessInfo` Just (mkNewStrictnessInfo id arity strict_info NoCPRInfo)
634 -- Until we modify the primop generation code
636 rules = foldl (addRule id) emptyCoreRules (primOpRules prim_op)
639 -- For each ccall we manufacture a separate CCallOpId, giving it
640 -- a fresh unique, a type that is correct for this particular ccall,
641 -- and a CCall structure that gives the correct details about calling
644 -- The *name* of this Id is a local name whose OccName gives the full
645 -- details of the ccall, type and all. This means that the interface
646 -- file reader can reconstruct a suitable Id
648 mkFCallId :: Unique -> ForeignCall -> Type -> Id
649 mkFCallId uniq fcall ty
650 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
651 -- A CCallOpId should have no free type variables;
652 -- when doing substitutions won't substitute over it
653 mkGlobalId (FCallId fcall) name ty info
655 occ_str = showSDocIface (braces (ppr fcall <+> ppr ty))
656 -- The "occurrence name" of a ccall is the full info about the
657 -- ccall; it is encoded, but may have embedded spaces etc!
659 name = mkFCallName uniq occ_str
661 info = noCafNoTyGenIdInfo
664 `setNewStrictnessInfo` Just strict_sig
666 (_, tau) = tcSplitForAllTys ty
667 (arg_tys, _) = tcSplitFunTys tau
668 arity = length arg_tys
669 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
673 %************************************************************************
675 \subsection{DictFuns and default methods}
677 %************************************************************************
679 Important notes about dict funs and default methods
680 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
681 Dict funs and default methods are *not* ImplicitIds. Their definition
682 involves user-written code, so we can't figure out their strictness etc
683 based on fixed info, as we can for constructors and record selectors (say).
685 We build them as GlobalIds, but when in the module where they are
686 bound, we turn the Id at the *binding site* into an exported LocalId.
687 This ensures that they are taken to account by free-variable finding
688 and dependency analysis (e.g. CoreFVs.exprFreeVars). The simplifier
689 will propagate the LocalId to all occurrence sites.
691 Why shouldn't they be bound as GlobalIds? Because, in particular, if
692 they are globals, the specialiser floats dict uses above their defns,
693 which prevents good simplifications happening. Also the strictness
694 analyser treats a occurrence of a GlobalId as imported and assumes it
695 contains strictness in its IdInfo, which isn't true if the thing is
696 bound in the same module as the occurrence.
698 It's OK for dfuns to be LocalIds, because we form the instance-env to
699 pass on to the next module (md_insts) in CoreTidy, afer tidying
700 and globalising the top-level Ids.
702 BUT make sure they are *exported* LocalIds (setIdLocalExported) so
703 that they aren't discarded by the occurrence analyser.
706 mkDefaultMethodId dm_name ty = mkVanillaGlobal dm_name ty noCafNoTyGenIdInfo
708 mkDictFunId :: Name -- Name to use for the dict fun;
715 mkDictFunId dfun_name clas inst_tyvars inst_tys dfun_theta
716 = mkVanillaGlobal dfun_name dfun_ty noCafNoTyGenIdInfo
718 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
720 {- 1 dec 99: disable the Mark Jones optimisation for the sake
721 of compatibility with Hugs.
722 See `types/InstEnv' for a discussion related to this.
724 (class_tyvars, sc_theta, _, _) = classBigSig clas
725 not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
726 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys) sc_theta
727 dfun_theta = case inst_decl_theta of
728 [] -> [] -- If inst_decl_theta is empty, then we don't
729 -- want to have any dict arguments, so that we can
730 -- expose the constant methods.
732 other -> nub (inst_decl_theta ++ filter not_const sc_theta')
733 -- Otherwise we pass the superclass dictionaries to
734 -- the dictionary function; the Mark Jones optimisation.
736 -- NOTE the "nub". I got caught by this one:
737 -- class Monad m => MonadT t m where ...
738 -- instance Monad m => MonadT (EnvT env) m where ...
739 -- Here, the inst_decl_theta has (Monad m); but so
740 -- does the sc_theta'!
742 -- NOTE the "not_const". I got caught by this one too:
743 -- class Foo a => Baz a b where ...
744 -- instance Wob b => Baz T b where..
745 -- Now sc_theta' has Foo T
750 %************************************************************************
752 \subsection{Un-definable}
754 %************************************************************************
756 These Ids can't be defined in Haskell. They could be defined in
757 unfoldings in PrelGHC.hi-boot, but we'd have to ensure that they
758 were definitely, definitely inlined, because there is no curried
759 identifier for them. Thats what mkCompulsoryUnfolding does.
760 If we had a way to get a compulsory unfolding from an interface file,
761 we could do that, but we don't right now.
763 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
764 just gets expanded into a type coercion wherever it occurs. Hence we
765 add it as a built-in Id with an unfolding here.
767 The type variables we use here are "open" type variables: this means
768 they can unify with both unlifted and lifted types. Hence we provide
769 another gun with which to shoot yourself in the foot.
772 -- unsafeCoerce# :: forall a b. a -> b
774 = pcMiscPrelId unsafeCoerceIdKey pREL_GHC SLIT("unsafeCoerce#") ty info
776 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
779 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
780 (mkFunTy openAlphaTy openBetaTy)
781 [x] = mkTemplateLocals [openAlphaTy]
782 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
783 Note (Coerce openBetaTy openAlphaTy) (Var x)
786 = pcMiscPrelId seqIdKey pREL_GHC SLIT("seq") ty info
788 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
791 ty = mkForAllTys [alphaTyVar,betaTyVar]
792 (mkFunTy alphaTy (mkFunTy betaTy betaTy))
793 [x,y] = mkTemplateLocals [alphaTy, betaTy]
794 rhs = mkLams [alphaTyVar,betaTyVar,x,y] (Case (Var x) x [(DEFAULT, [], Var y)])
797 @getTag#@ is another function which can't be defined in Haskell. It needs to
798 evaluate its argument and call the dataToTag# primitive.
802 = pcMiscPrelId getTagIdKey pREL_GHC SLIT("getTag#") ty info
804 info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
805 -- We don't provide a defn for this; you must inline it
807 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy intPrimTy)
808 [x,y] = mkTemplateLocals [alphaTy,alphaTy]
809 rhs = mkLams [alphaTyVar,x] $
810 Case (Var x) y [ (DEFAULT, [], mkApps (Var dataToTagId) [Type alphaTy, Var y]) ]
812 dataToTagId = mkPrimOpId DataToTagOp
815 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
816 nasty as-is, change it back to a literal (@Literal@).
819 realWorldPrimId -- :: State# RealWorld
820 = pcMiscPrelId realWorldPrimIdKey pREL_GHC SLIT("realWorld#")
822 (noCafNoTyGenIdInfo `setUnfoldingInfo` mkOtherCon [])
823 -- The mkOtherCon makes it look that realWorld# is evaluated
824 -- which in turn makes Simplify.interestingArg return True,
825 -- which in turn makes INLINE things applied to realWorld# likely
830 %************************************************************************
832 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
834 %************************************************************************
836 GHC randomly injects these into the code.
838 @patError@ is just a version of @error@ for pattern-matching
839 failures. It knows various ``codes'' which expand to longer
840 strings---this saves space!
842 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
843 well shouldn't be yanked on, but if one is, then you will get a
844 friendly message from @absentErr@ (rather than a totally random
847 @parError@ is a special version of @error@ which the compiler does
848 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
849 templates, but we don't ever expect to generate code for it.
853 = pc_bottoming_Id errorIdKey pREL_ERR SLIT("error") errorTy
855 = pc_bottoming_Id errorCStringIdKey pREL_ERR SLIT("errorCString")
856 (mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy))
858 = generic_ERROR_ID patErrorIdKey SLIT("patError")
860 = generic_ERROR_ID recSelErrIdKey SLIT("recSelError")
862 = generic_ERROR_ID recConErrorIdKey SLIT("recConError")
864 = generic_ERROR_ID recUpdErrorIdKey SLIT("recUpdError")
866 = generic_ERROR_ID irrefutPatErrorIdKey SLIT("irrefutPatError")
867 nON_EXHAUSTIVE_GUARDS_ERROR_ID
868 = generic_ERROR_ID nonExhaustiveGuardsErrorIdKey SLIT("nonExhaustiveGuardsError")
869 nO_METHOD_BINDING_ERROR_ID
870 = generic_ERROR_ID noMethodBindingErrorIdKey SLIT("noMethodBindingError")
873 = pc_bottoming_Id absentErrorIdKey pREL_ERR SLIT("absentErr")
874 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy)
877 = pcMiscPrelId parErrorIdKey pREL_ERR SLIT("parError")
878 (mkSigmaTy [openAlphaTyVar] [] openAlphaTy) noCafNoTyGenIdInfo
882 %************************************************************************
884 \subsection{Utilities}
886 %************************************************************************
889 pcMiscPrelId :: Unique{-IdKey-} -> Module -> FAST_STRING -> Type -> IdInfo -> Id
890 pcMiscPrelId key mod str ty info
892 name = mkWiredInName mod (mkVarOcc str) key
893 imp = mkVanillaGlobal name ty info -- the usual case...
896 -- We lie and say the thing is imported; otherwise, we get into
897 -- a mess with dependency analysis; e.g., core2stg may heave in
898 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
899 -- being compiled, then it's just a matter of luck if the definition
900 -- will be in "the right place" to be in scope.
902 pc_bottoming_Id key mod name ty
903 = pcMiscPrelId key mod name ty bottoming_info
905 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
906 bottoming_info = noCafNoTyGenIdInfo `setNewStrictnessInfo` Just strict_sig
907 -- these "bottom" out, no matter what their arguments
909 generic_ERROR_ID u n = pc_bottoming_Id u pREL_ERR n errorTy
911 (openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
912 openAlphaTy = mkTyVarTy openAlphaTyVar
913 openBetaTy = mkTyVarTy openBetaTyVar
916 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy]
918 -- Notice the openAlphaTyVar. It says that "error" can be applied
919 -- to unboxed as well as boxed types. This is OK because it never
920 -- returns, so the return type is irrelevant.