\begin{code}
module MkId (
- mkSpecPragmaId, mkWorkerId,
-
mkDictFunId, mkDefaultMethodId,
- mkMethodSelId, mkSuperDictSelId,
-
- mkDataConId,
- mkRecordSelId,
- mkNewTySelId,
- mkPrimitiveId
+ mkDictSelId,
+
+ mkDataConId, mkDataConWrapId,
+ mkRecordSelId, rebuildConArgs,
+ mkPrimOpId, mkFCallId,
+
+ -- And some particular Ids; see below for why they are wired in
+ wiredInIds,
+ unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId,
+ eRROR_ID, eRROR_CSTRING_ID, rEC_SEL_ERROR_ID, pAT_ERROR_ID, rEC_CON_ERROR_ID,
+ rEC_UPD_ERROR_ID, iRREFUT_PAT_ERROR_ID, nON_EXHAUSTIVE_GUARDS_ERROR_ID,
+ nO_METHOD_BINDING_ERROR_ID, aBSENT_ERROR_ID, pAR_ERROR_ID
) where
#include "HsVersions.h"
-import {-# SOURCE #-} CoreUnfold ( mkUnfolding )
-import TysWiredIn ( boolTy )
-import Type ( Type, ThetaType,
- mkDictTy, mkTyConApp, mkTyVarTys, mkFunTys, mkFunTy, mkSigmaTy,
- isUnLiftedType, substTopTheta,
- splitSigmaTy, splitFunTy_maybe, splitAlgTyConApp,
- splitFunTys, splitForAllTys
+import BasicTypes ( Arity, StrictnessMark(..), isMarkedUnboxed, isMarkedStrict )
+import TysPrim ( openAlphaTyVars, alphaTyVar, alphaTy, betaTyVar, betaTy,
+ intPrimTy, realWorldStatePrimTy, addrPrimTy
)
-import TyCon ( TyCon, isNewTyCon, tyConDataCons, isDataTyCon )
-import Class ( Class, classBigSig, classTyCon )
-import Var ( Id, TyVar, VarDetails(..), mkId )
-import VarEnv ( zipVarEnv )
-import Const ( Con(..) )
-import Name ( mkDerivedName, mkWiredInIdName,
- mkWorkerOcc, mkSuperDictSelOcc,
- Name, NamedThing(..),
+import TysWiredIn ( charTy, mkListTy )
+import PrelRules ( primOpRules )
+import Rules ( addRule )
+import TcType ( Type, ThetaType, mkDictTy, mkPredTys, mkTyConApp,
+ mkTyVarTys, mkClassPred, tcEqPred,
+ mkFunTys, mkFunTy, mkSigmaTy, tcSplitSigmaTy,
+ isUnLiftedType, mkForAllTys, mkTyVarTy, tyVarsOfType,
+ tcSplitFunTys, tcSplitForAllTys, mkPredTy
)
-import PrimOp ( PrimOp, primOpType, primOpOcc, primOpUniq )
-import DataCon ( DataCon, dataConStrictMarks, dataConFieldLabels,
- dataConArgTys, dataConSig, dataConRawArgTys
+import Module ( Module )
+import CoreUtils ( exprType )
+import CoreUnfold ( mkTopUnfolding, mkCompulsoryUnfolding, mkOtherCon )
+import Literal ( Literal(..), nullAddrLit )
+import TyCon ( TyCon, isNewTyCon, tyConTyVars, tyConDataCons,
+ tyConTheta, isProductTyCon, isDataTyCon, isRecursiveTyCon )
+import Class ( Class, classTyCon, classTyVars, classSelIds )
+import Var ( Id, TyVar )
+import VarSet ( isEmptyVarSet )
+import Name ( mkWiredInName, mkFCallName, Name )
+import OccName ( mkVarOcc )
+import PrimOp ( PrimOp(DataToTagOp), primOpSig, mkPrimOpIdName )
+import ForeignCall ( ForeignCall )
+import DataCon ( DataCon,
+ dataConFieldLabels, dataConRepArity, dataConTyCon,
+ dataConArgTys, dataConRepType,
+ dataConInstOrigArgTys,
+ dataConName, dataConTheta,
+ dataConSig, dataConStrictMarks, dataConId,
+ splitProductType
)
-import Id ( idType,
- mkUserLocal, mkVanillaId, mkTemplateLocals,
- mkTemplateLocal, setInlinePragma
+import Id ( idType, mkGlobalId, mkVanillaGlobal, mkSysLocal,
+ mkTemplateLocals, mkTemplateLocalsNum,
+ mkTemplateLocal, idNewStrictness, idName
)
-import IdInfo ( noIdInfo,
- exactArity, setUnfoldingInfo,
- setArityInfo, setInlinePragInfo,
- InlinePragInfo(..), IdInfo
+import IdInfo ( IdInfo, noCafNoTyGenIdInfo,
+ setUnfoldingInfo,
+ setArityInfo, setSpecInfo, setCafInfo,
+ newStrictnessFromOld, setAllStrictnessInfo,
+ GlobalIdDetails(..), CafInfo(..), CprInfo(..)
)
-import FieldLabel ( FieldLabel, FieldLabelTag, mkFieldLabel, fieldLabelName,
- firstFieldLabelTag, allFieldLabelTags
+import NewDemand ( mkStrictSig, strictSigResInfo, DmdResult(..),
+ mkTopDmdType, topDmd, evalDmd, lazyDmd,
+ Demand(..), Demands(..) )
+import FieldLabel ( mkFieldLabel, fieldLabelName,
+ firstFieldLabelTag, allFieldLabelTags, fieldLabelType
)
+import DmdAnal ( dmdAnalTopRhs )
import CoreSyn
-import PrelVals ( rEC_SEL_ERROR_ID )
-import PrelMods ( pREL_GHC )
+import Unique ( mkBuiltinUnique )
import Maybes
-import BasicTypes ( Arity, StrictnessMark(..) )
-import Unique ( Unique )
+import PrelNames
import Maybe ( isJust )
+import Util ( dropList, isSingleton )
import Outputable
-import Util ( assoc )
-import List ( nub )
+import ListSetOps ( assoc, assocMaybe )
+import UnicodeUtil ( stringToUtf8 )
+import Char ( ord )
\end{code}
-
%************************************************************************
%* *
-\subsection{Easy ones}
+\subsection{Wired in Ids}
%* *
%************************************************************************
\begin{code}
-mkSpecPragmaId occ uniq ty loc
- = mkUserLocal occ uniq ty loc `setInlinePragma` IAmASpecPragmaId
- -- Maybe a SysLocal? But then we'd lose the location
-
-mkDefaultMethodId dm_name rec_c ty
- = mkVanillaId dm_name ty
-
-mkWorkerId uniq unwrkr ty
- = mkVanillaId (mkDerivedName mkWorkerOcc (getName unwrkr) uniq) ty
+wiredInIds
+ = [ -- These error-y things are wired in because we don't yet have
+ -- a way to express in an interface file that the result type variable
+ -- is 'open'; that is can be unified with an unboxed type
+ --
+ -- [The interface file format now carry such information, but there's
+ -- no way yet of expressing at the definition site for these
+ -- error-reporting functions that they have an 'open'
+ -- result type. -- sof 1/99]
+
+ aBSENT_ERROR_ID
+ , eRROR_ID
+ , eRROR_CSTRING_ID
+ , iRREFUT_PAT_ERROR_ID
+ , nON_EXHAUSTIVE_GUARDS_ERROR_ID
+ , nO_METHOD_BINDING_ERROR_ID
+ , pAR_ERROR_ID
+ , pAT_ERROR_ID
+ , rEC_CON_ERROR_ID
+ , rEC_UPD_ERROR_ID
+
+ -- These can't be defined in Haskell, but they have
+ -- perfectly reasonable unfoldings in Core
+ , realWorldPrimId
+ , unsafeCoerceId
+ , nullAddrId
+ , getTagId
+ , seqId
+ ]
\end{code}
%************************************************************************
%************************************************************************
\begin{code}
-mkDataConId :: DataCon -> Id
-mkDataConId data_con
- = mkId (getName data_con)
- id_ty
- (ConstantId (DataCon data_con))
- (dataConInfo data_con)
+mkDataConId :: Name -> DataCon -> Id
+ -- Makes the *worker* for the data constructor; that is, the function
+ -- that takes the reprsentation arguments and builds the constructor.
+mkDataConId work_name data_con
+ = mkGlobalId (DataConId data_con) work_name (dataConRepType data_con) info
where
- (tyvars, theta, ex_tyvars, ex_theta, arg_tys, tycon) = dataConSig data_con
- id_ty = mkSigmaTy (tyvars ++ ex_tyvars)
- (theta ++ ex_theta)
- (mkFunTys arg_tys (mkTyConApp tycon (mkTyVarTys tyvars)))
+ info = noCafNoTyGenIdInfo
+ `setArityInfo` arity
+ `setAllStrictnessInfo` Just strict_sig
+
+ arity = dataConRepArity data_con
+
+ strict_sig = mkStrictSig (mkTopDmdType (replicate arity topDmd) cpr_info)
+ -- Notice that we do *not* say the worker is strict
+ -- even if the data constructor is declared strict
+ -- e.g. data T = MkT !(Int,Int)
+ -- Why? Because the *wrapper* is strict (and its unfolding has case
+ -- expresssions that do the evals) but the *worker* itself is not.
+ -- If we pretend it is strict then when we see
+ -- case x of y -> $wMkT y
+ -- the simplifier thinks that y is "sure to be evaluated" (because
+ -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
+ --
+ -- When the simplifer sees a pattern
+ -- case e of MkT x -> ...
+ -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
+ -- but that's fine... dataConRepStrictness comes from the data con
+ -- not from the worker Id.
+
+ tycon = dataConTyCon data_con
+ cpr_info | isProductTyCon tycon &&
+ isDataTyCon tycon &&
+ arity > 0 &&
+ arity <= mAX_CPR_SIZE = RetCPR
+ | otherwise = TopRes
+ -- RetCPR is only true for products that are real data types;
+ -- that is, not unboxed tuples or [non-recursive] newtypes
+
+mAX_CPR_SIZE :: Arity
+mAX_CPR_SIZE = 10
+-- We do not treat very big tuples as CPR-ish:
+-- a) for a start we get into trouble because there aren't
+-- "enough" unboxed tuple types (a tiresome restriction,
+-- but hard to fix),
+-- b) more importantly, big unboxed tuples get returned mainly
+-- on the stack, and are often then allocated in the heap
+-- by the caller. So doing CPR for them may in fact make
+-- things worse.
\end{code}
+The wrapper for a constructor is an ordinary top-level binding that evaluates
+any strict args, unboxes any args that are going to be flattened, and calls
+the worker.
+
We're going to build a constructor that looks like:
data (Data a, C b) => T a b = T1 !a !Int b
* We have to check that we can construct Data dictionaries for
the types a and Int. Once we've done that we can throw d1 away too.
-* We use (case p of ...) to evaluate p, rather than "seq" because
+* We use (case p of q -> ...) to evaluate p, rather than "seq" because
all that matters is that the arguments are evaluated. "seq" is
very careful to preserve evaluation order, which we don't need
to be here.
-\begin{code}
-dataConInfo :: DataCon -> IdInfo
+ You might think that we could simply give constructors some strictness
+ info, like PrimOps, and let CoreToStg do the let-to-case transformation.
+ But we don't do that because in the case of primops and functions strictness
+ is a *property* not a *requirement*. In the case of constructors we need to
+ do something active to evaluate the argument.
+
+ Making an explicit case expression allows the simplifier to eliminate
+ it in the (common) case where the constructor arg is already evaluated.
-dataConInfo data_con
- = setInlinePragInfo IMustBeINLINEd $ -- Always inline constructors
- setArityInfo (exactArity (n_dicts + n_ex_dicts + n_id_args)) $
- setUnfoldingInfo unfolding $
- noIdInfo
+\begin{code}
+mkDataConWrapId data_con
+ = mkGlobalId (DataConWrapId data_con) (dataConName data_con) wrap_ty info
where
- unfolding = mkUnfolding con_rhs
-
- (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon)
- = dataConSig data_con
- rep_arg_tys = dataConRawArgTys data_con
- all_tyvars = tyvars ++ ex_tyvars
-
- dict_tys = [mkDictTy clas tys | (clas,tys) <- theta]
- ex_dict_tys = [mkDictTy clas tys | (clas,tys) <- ex_theta]
-
- n_dicts = length dict_tys
- n_ex_dicts = length ex_dict_tys
- n_id_args = length orig_arg_tys
- n_rep_args = length rep_arg_tys
-
- result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
-
- mkLocals i n tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
- (dict_args, i1) = mkLocals 1 n_dicts dict_tys
- (ex_dict_args,i2) = mkLocals i1 n_ex_dicts ex_dict_tys
- (id_args,i3) = mkLocals i2 n_id_args orig_arg_tys
-
- (id_arg1:_) = id_args -- Used for newtype only
- strict_marks = dataConStrictMarks data_con
-
- con_app i rep_ids
- | isNewTyCon tycon
- = ASSERT( length orig_arg_tys == 1 )
- Note (Coerce result_ty (head orig_arg_tys)) (Var id_arg1)
- | otherwise
- = mkConApp data_con
- (map Type (mkTyVarTys all_tyvars) ++
- map Var (reverse rep_ids))
-
- con_rhs = mkLams all_tyvars $ mkLams dict_args $
- mkLams ex_dict_args $ mkLams id_args $
- foldr mk_case con_app (zip id_args strict_marks) i3 []
-
- mk_case
- :: (Id, StrictnessMark) -- arg, strictness
- -> (Int -> [Id] -> CoreExpr) -- body
- -> Int -- next rep arg id
- -> [Id] -- rep args so far
+ work_id = dataConId data_con
+
+ info = noCafNoTyGenIdInfo
+ `setUnfoldingInfo` wrap_unf
+ -- The NoCaf-ness is set by noCafNoTyGenIdInfo
+ `setArityInfo` arity
+ -- It's important to specify the arity, so that partial
+ -- applications are treated as values
+ `setAllStrictnessInfo` Just wrap_sig
+
+ wrap_ty = mkForAllTys all_tyvars (mkFunTys all_arg_tys result_ty)
+
+ wrap_sig = mkStrictSig (mkTopDmdType arg_dmds res_info)
+ res_info = strictSigResInfo (idNewStrictness work_id)
+ arg_dmds = [Abs | d <- dict_args] ++ map mk_dmd strict_marks
+ mk_dmd str | isMarkedStrict str = evalDmd
+ | otherwise = lazyDmd
+ -- The Cpr info can be important inside INLINE rhss, where the
+ -- wrapper constructor isn't inlined.
+ -- And the argument strictness can be important too; we
+ -- may not inline a contructor when it is partially applied.
+ -- For example:
+ -- data W = C !Int !Int !Int
+ -- ...(let w = C x in ...(w p q)...)...
+ -- we want to see that w is strict in its two arguments
+
+ wrap_unf | isNewTyCon tycon
+ = ASSERT( null ex_tyvars && null ex_dict_args && isSingleton orig_arg_tys )
+ -- No existentials on a newtype, but it can have a context
+ -- e.g. newtype Eq a => T a = MkT (...)
+ mkTopUnfolding $ Note InlineMe $
+ mkLams tyvars $ mkLams dict_args $ Lam id_arg1 $
+ mkNewTypeBody tycon result_ty (Var id_arg1)
+
+ | null dict_args && not (any isMarkedStrict strict_marks)
+ = mkCompulsoryUnfolding (Var work_id)
+ -- The common case. Not only is this efficient,
+ -- but it also ensures that the wrapper is replaced
+ -- by the worker even when there are no args.
+ -- f (:) x
+ -- becomes
+ -- f $w: x
+ -- This is really important in rule matching,
+ -- (We could match on the wrappers,
+ -- but that makes it less likely that rules will match
+ -- when we bring bits of unfoldings together.)
+ --
+ -- NB: because of this special case, (map (:) ys) turns into
+ -- (map $w: ys). The top-level defn for (:) is never used.
+ -- This is somewhat of a bore, but I'm currently leaving it
+ -- as is, so that there still is a top level curried (:) for
+ -- the interpreter to call.
+
+ | otherwise
+ = mkTopUnfolding $ Note InlineMe $
+ mkLams all_tyvars $ mkLams dict_args $
+ mkLams ex_dict_args $ mkLams id_args $
+ foldr mk_case con_app
+ (zip (ex_dict_args++id_args) strict_marks) i3 []
+
+ con_app i rep_ids = mkApps (Var work_id)
+ (map varToCoreExpr (all_tyvars ++ reverse rep_ids))
+
+ (tyvars, theta, ex_tyvars, ex_theta, orig_arg_tys, tycon) = dataConSig data_con
+ all_tyvars = tyvars ++ ex_tyvars
+
+ dict_tys = mkPredTys theta
+ ex_dict_tys = mkPredTys ex_theta
+ all_arg_tys = dict_tys ++ ex_dict_tys ++ orig_arg_tys
+ result_ty = mkTyConApp tycon (mkTyVarTys tyvars)
+
+ mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
+ where
+ n = length tys
+
+ (dict_args, i1) = mkLocals 1 dict_tys
+ (ex_dict_args,i2) = mkLocals i1 ex_dict_tys
+ (id_args,i3) = mkLocals i2 orig_arg_tys
+ arity = i3-1
+ (id_arg1:_) = id_args -- Used for newtype only
+
+ strict_marks = dataConStrictMarks data_con
+
+ mk_case
+ :: (Id, StrictnessMark) -- Arg, strictness
+ -> (Int -> [Id] -> CoreExpr) -- Body
+ -> Int -- Next rep arg id
+ -> [Id] -- Rep args so far, reversed
-> CoreExpr
- mk_case (arg,strict) body i rep_args
+ mk_case (arg,strict) body i rep_args
= case strict of
NotMarkedStrict -> body i (arg:rep_args)
MarkedStrict
| otherwise ->
Case (Var arg) arg [(DEFAULT,[], body i (arg:rep_args))]
- MarkedUnboxed con tys ->
- Case (Var arg) arg [(DataCon con, con_args,
- body i' (reverse con_args++rep_args))]
- where n_tys = length tys
- (con_args,i') = mkLocals i (length tys) tys
+ MarkedUnboxed
+ -> case splitProductType "do_unbox" (idType arg) of
+ (tycon, tycon_args, con, tys) ->
+ Case (Var arg) arg [(DataAlt con, con_args,
+ body i' (reverse con_args ++ rep_args))]
+ where
+ (con_args, i') = mkLocals i tys
\end{code}
T2 ... x ... -> x
other -> error "..."
-\begin{code}
-mkRecordSelId field_label selector_ty
- = ASSERT( null theta && isDataTyCon tycon )
- sel_id
- where
- sel_id = mkId (fieldLabelName field_label) selector_ty
- (RecordSelId field_label) info
-
- info = exactArity 1 `setArityInfo` (
- unfolding `setUnfoldingInfo`
- noIdInfo)
- -- ToDo: consider adding further IdInfo
+Similarly for newtypes
- unfolding = mkUnfolding sel_rhs
+ newtype N a = MkN { unN :: a->a }
- (tyvars, theta, tau) = splitSigmaTy selector_ty
- (data_ty,rhs_ty) = expectJust "StdIdInfoRec" (splitFunTy_maybe tau)
- -- tau is of form (T a b c -> field-type)
- (tycon, _, data_cons) = splitAlgTyConApp data_ty
- tyvar_tys = mkTyVarTys tyvars
+ unN :: N a -> a -> a
+ unN n = coerce (a->a) n
- [data_id] = mkTemplateLocals [data_ty]
- alts = map mk_maybe_alt data_cons
- the_alts = catMaybes alts
- default_alt | all isJust alts = [] -- No default needed
- | otherwise = [(DEFAULT, [], error_expr)]
+We need to take a little care if the field has a polymorphic type:
- sel_rhs = mkLams tyvars $ Lam data_id $
- Case (Var data_id) data_id (the_alts ++ default_alt)
+ data R = R { f :: forall a. a->a }
- mk_maybe_alt data_con
- = case maybe_the_arg_id of
- Nothing -> Nothing
- Just the_arg_id -> Just (DataCon data_con, arg_ids, Var the_arg_id)
- where
- arg_ids = mkTemplateLocals (dataConArgTys data_con tyvar_tys)
- -- The first one will shadow data_id, but who cares
- field_lbls = dataConFieldLabels data_con
- maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
-
- error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type rhs_ty, mkStringLit full_msg]
- full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
-\end{code}
+Then we want
+ f :: forall a. R -> a -> a
+ f = /\ a \ r = case r of
+ R f -> f a
-%************************************************************************
-%* *
-\subsection{Newtype field selectors}
-%* *
-%************************************************************************
+(not f :: R -> forall a. a->a, which gives the type inference mechanism
+problems at call sites)
-Possibly overkill to do it this way:
+Similarly for newtypes
+
+ newtype N = MkN { unN :: forall a. a->a }
+
+ unN :: forall a. N -> a -> a
+ unN = /\a -> \n:N -> coerce (a->a) n
\begin{code}
-mkNewTySelId field_label selector_ty = sel_id
+mkRecordSelId tycon field_label unpack_id unpackUtf8_id
+ -- Assumes that all fields with the same field label have the same type
+ --
+ -- Annoyingly, we have to pass in the unpackCString# Id, because
+ -- we can't conjure it up out of thin air
+ = sel_id
where
- sel_id = mkId (fieldLabelName field_label) selector_ty
- (RecordSelId field_label) info
+ sel_id = mkGlobalId (RecordSelId field_label) (fieldLabelName field_label) selector_ty info
+ field_ty = fieldLabelType field_label
+ data_cons = tyConDataCons tycon
+ tyvars = tyConTyVars tycon -- These scope over the types in
+ -- the FieldLabels of constructors of this type
+ data_ty = mkTyConApp tycon tyvar_tys
+ tyvar_tys = mkTyVarTys tyvars
+
+ tycon_theta = tyConTheta tycon -- The context on the data decl
+ -- eg data (Eq a, Ord b) => T a b = ...
+ dict_tys = [mkPredTy pred | pred <- tycon_theta,
+ needed_dict pred]
+ needed_dict pred = or [ tcEqPred pred p
+ | (DataAlt dc, _, _) <- the_alts, p <- dataConTheta dc]
+ n_dict_tys = length dict_tys
+
+ (field_tyvars,field_theta,field_tau) = tcSplitSigmaTy field_ty
+ field_dict_tys = map mkPredTy field_theta
+ n_field_dict_tys = length field_dict_tys
+ -- If the field has a universally quantified type we have to
+ -- be a bit careful. Suppose we have
+ -- data R = R { op :: forall a. Foo a => a -> a }
+ -- Then we can't give op the type
+ -- op :: R -> forall a. Foo a => a -> a
+ -- because the typechecker doesn't understand foralls to the
+ -- right of an arrow. The "right" type to give it is
+ -- op :: forall a. Foo a => R -> a -> a
+ -- But then we must generate the right unfolding too:
+ -- op = /\a -> \dfoo -> \ r ->
+ -- case r of
+ -- R op -> op a dfoo
+ -- Note that this is exactly the type we'd infer from a user defn
+ -- op (R op) = op
+
+ -- Very tiresomely, the selectors are (unnecessarily!) overloaded over
+ -- just the dictionaries in the types of the constructors that contain
+ -- the relevant field. Urgh.
+ -- NB: this code relies on the fact that DataCons are quantified over
+ -- the identical type variables as their parent TyCon
+
+ selector_ty :: Type
+ selector_ty = mkForAllTys tyvars $ mkForAllTys field_tyvars $
+ mkFunTys dict_tys $ mkFunTys field_dict_tys $
+ mkFunTy data_ty field_tau
+
+ arity = 1 + n_dict_tys + n_field_dict_tys
+
+ (strict_sig, rhs_w_str) = dmdAnalTopRhs sel_rhs
+ -- Use the demand analyser to work out strictness.
+ -- With all this unpackery it's not easy!
+
+ info = noCafNoTyGenIdInfo
+ `setCafInfo` caf_info
+ `setArityInfo` arity
+ `setUnfoldingInfo` mkTopUnfolding rhs_w_str
+ `setAllStrictnessInfo` Just strict_sig
+
+ -- Allocate Ids. We do it a funny way round because field_dict_tys is
+ -- almost always empty. Also note that we use length_tycon_theta
+ -- rather than n_dict_tys, because the latter gives an infinite loop:
+ -- n_dict tys depends on the_alts, which depens on arg_ids, which depends
+ -- on arity, which depends on n_dict tys. Sigh! Mega sigh!
+ field_dict_base = length tycon_theta + 1
+ dict_id_base = field_dict_base + n_field_dict_tys
+ field_base = dict_id_base + 1
+ dict_ids = mkTemplateLocalsNum 1 dict_tys
+ field_dict_ids = mkTemplateLocalsNum field_dict_base field_dict_tys
+ data_id = mkTemplateLocal dict_id_base data_ty
- info = exactArity 1 `setArityInfo` (
- unfolding `setUnfoldingInfo`
- noIdInfo)
- -- ToDo: consider adding further IdInfo
+ alts = map mk_maybe_alt data_cons
+ the_alts = catMaybes alts
- unfolding = mkUnfolding sel_rhs
+ no_default = all isJust alts -- No default needed
+ default_alt | no_default = []
+ | otherwise = [(DEFAULT, [], error_expr)]
- (tyvars, theta, tau) = splitSigmaTy selector_ty
- (data_ty,rhs_ty) = expectJust "StdIdInfoRec" (splitFunTy_maybe tau)
- -- tau is of form (T a b c -> field-type)
- (tycon, _, data_cons) = splitAlgTyConApp data_ty
- tyvar_tys = mkTyVarTys tyvars
-
- [data_id] = mkTemplateLocals [data_ty]
- sel_rhs = mkLams tyvars $ Lam data_id $
- Note (Coerce rhs_ty data_ty) (Var data_id)
+ -- the default branch may have CAF refs, because it calls recSelError etc.
+ caf_info | no_default = NoCafRefs
+ | otherwise = MayHaveCafRefs
+
+ sel_rhs = mkLams tyvars $ mkLams field_tyvars $
+ mkLams dict_ids $ mkLams field_dict_ids $
+ Lam data_id $ sel_body
+ sel_body | isNewTyCon tycon = mkNewTypeBody tycon field_tau (mk_result data_id)
+ | otherwise = Case (Var data_id) data_id (default_alt ++ the_alts)
+
+ mk_result result_id = mkVarApps (mkVarApps (Var result_id) field_tyvars) field_dict_ids
+ -- We pull the field lambdas to the top, so we need to
+ -- apply them in the body. For example:
+ -- data T = MkT { foo :: forall a. a->a }
+ --
+ -- foo :: forall a. T -> a -> a
+ -- foo = /\a. \t:T. case t of { MkT f -> f a }
+
+ mk_maybe_alt data_con
+ = case maybe_the_arg_id of
+ Nothing -> Nothing
+ Just the_arg_id -> Just (DataAlt data_con, real_args, mkLets binds body)
+ where
+ body = mk_result the_arg_id
+ strict_marks = dataConStrictMarks data_con
+ (binds, real_args) = rebuildConArgs arg_ids strict_marks
+ (map mkBuiltinUnique [unpack_base..])
+ where
+ arg_ids = mkTemplateLocalsNum field_base (dataConInstOrigArgTys data_con tyvar_tys)
+
+ unpack_base = field_base + length arg_ids
+
+ -- arity+1 avoids all shadowing
+ maybe_the_arg_id = assocMaybe (field_lbls `zip` arg_ids) field_label
+ field_lbls = dataConFieldLabels data_con
+
+ error_expr = mkApps (Var rEC_SEL_ERROR_ID) [Type field_tau, err_string]
+ err_string
+ | all safeChar full_msg
+ = App (Var unpack_id) (Lit (MachStr (_PK_ full_msg)))
+ | otherwise
+ = App (Var unpackUtf8_id) (Lit (MachStr (_PK_ (stringToUtf8 (map ord full_msg)))))
+ where
+ safeChar c = c >= '\1' && c <= '\xFF'
+ -- TODO: Putting this Unicode stuff here is ugly. Find a better
+ -- generic place to make string literals. This logic is repeated
+ -- in DsUtils.
+ full_msg = showSDoc (sep [text "No match in record selector", ppr sel_id])
+
+
+-- This rather ugly function converts the unpacked data con
+-- arguments back into their packed form.
+
+rebuildConArgs
+ :: [Id] -- Source-level args
+ -> [StrictnessMark] -- Strictness annotations (per-arg)
+ -> [Unique] -- Uniques for the new Ids
+ -> ([CoreBind], [Id]) -- A binding for each source-level arg, plus
+ -- a list of the representation-level arguments
+-- e.g. data T = MkT Int !Int
+--
+-- rebuild [x::Int, y::Int] [Not, Unbox]
+-- = ([ y = I# t ], [x,t])
+
+rebuildConArgs [] stricts us = ([], [])
+
+-- Type variable case
+rebuildConArgs (arg:args) stricts us
+ | isTyVar arg
+ = let (binds, args') = rebuildConArgs args stricts us
+ in (binds, arg:args')
+
+-- Term variable case
+rebuildConArgs (arg:args) (str:stricts) us
+ | isMarkedUnboxed str
+ = let
+ arg_ty = idType arg
+
+ (_, tycon_args, pack_con, con_arg_tys)
+ = splitProductType "rebuildConArgs" arg_ty
+
+ unpacked_args = zipWith (mkSysLocal SLIT("rb")) us con_arg_tys
+ (binds, args') = rebuildConArgs args stricts (dropList con_arg_tys us)
+ con_app = mkConApp pack_con (map Type tycon_args ++ map Var unpacked_args)
+ in
+ (NonRec arg con_app : binds, unpacked_args ++ args')
+
+ | otherwise
+ = let (binds, args') = rebuildConArgs args stricts us
+ in (binds, arg:args')
\end{code}
%* *
%************************************************************************
-\begin{code}
-mkSuperDictSelId :: Unique -> Class -> FieldLabelTag -> Type -> Id
- -- The FieldLabelTag says which superclass is selected
- -- So, for
- -- class (C a, C b) => Foo a b where ...
- -- we get superclass selectors
- -- Foo_sc1, Foo_sc2
-
-mkSuperDictSelId uniq clas index ty
- = mkDictSelId name clas ty
- where
- name = mkDerivedName (mkSuperDictSelOcc index) (getName clas) uniq
-
- -- For method selectors the clean thing to do is
- -- to give the method selector the same name as the class op itself.
-mkMethodSelId name clas ty
- = mkDictSelId name clas ty
-\end{code}
-
Selecting a field for a dictionary. If there is just one field, then
-there's nothing to do.
+there's nothing to do.
+
+ToDo: unify with mkRecordSelId.
\begin{code}
-mkDictSelId name clas ty
- = sel_id
+mkDictSelId :: Name -> Class -> Id
+mkDictSelId name clas
+ = mkGlobalId (RecordSelId field_lbl) name sel_ty info
where
- sel_id = mkId name ty (RecordSelId field_lbl) info
- field_lbl = mkFieldLabel name ty tag
- tag = assoc "MkId.mkDictSelId" ((sc_sel_ids ++ op_sel_ids) `zip` allFieldLabelTags) sel_id
-
- info = setInlinePragInfo IMustBeINLINEd $
- setUnfoldingInfo unfolding noIdInfo
- -- The always-inline thing means we don't need any other IdInfo
- -- We need "Must" inline because we don't create any bindigs for
- -- the selectors.
-
- unfolding = mkUnfolding rhs
-
- (tyvars, _, sc_sel_ids, op_sel_ids, defms) = classBigSig clas
+ sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
+ -- We can't just say (exprType rhs), because that would give a type
+ -- C a -> C a
+ -- for a single-op class (after all, the selector is the identity)
+ -- But it's type must expose the representation of the dictionary
+ -- to gat (say) C a -> (a -> a)
+
+ field_lbl = mkFieldLabel name tycon sel_ty tag
+ tag = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` allFieldLabelTags) name
+
+ info = noCafNoTyGenIdInfo
+ `setArityInfo` 1
+ `setUnfoldingInfo` mkTopUnfolding rhs
+ `setAllStrictnessInfo` Just strict_sig
+
+ -- We no longer use 'must-inline' on record selectors. They'll
+ -- inline like crazy if they scrutinise a constructor
+
+ -- The strictness signature is of the form U(AAAVAAAA) -> T
+ -- where the V depends on which item we are selecting
+ -- It's worth giving one, so that absence info etc is generated
+ -- even if the selector isn't inlined
+ strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
+ arg_dmd | isNewTyCon tycon = evalDmd
+ | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
+ | id <- arg_ids ])
+
+ tyvars = classTyVars clas
tycon = classTyCon clas
[data_con] = tyConDataCons tycon
arg_tys = dataConArgTys data_con tyvar_tys
the_arg_id = arg_ids !! (tag - firstFieldLabelTag)
- dict_ty = mkDictTy clas tyvar_tys
- (dict_id:arg_ids) = mkTemplateLocals (dict_ty : arg_tys)
+ pred = mkClassPred clas tyvar_tys
+ (dict_id:arg_ids) = mkTemplateLocals (mkPredTy pred : arg_tys)
- rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
- Note (Coerce (head arg_tys) dict_ty) (Var dict_id)
+ rhs | isNewTyCon tycon = mkLams tyvars $ Lam dict_id $
+ mkNewTypeBody tycon (head arg_tys) (Var dict_id)
| otherwise = mkLams tyvars $ Lam dict_id $
Case (Var dict_id) dict_id
- [(DataCon data_con, arg_ids, Var the_arg_id)]
+ [(DataAlt data_con, arg_ids, Var the_arg_id)]
+
+mkNewTypeBody tycon result_ty result_expr
+ -- Adds a coerce where necessary
+ -- Used for both wrapping and unwrapping
+ | isRecursiveTyCon tycon -- Recursive case; use a coerce
+ = Note (Coerce result_ty (exprType result_expr)) result_expr
+ | otherwise -- Normal case
+ = result_expr
\end{code}
%* *
%************************************************************************
-
\begin{code}
-mkPrimitiveId :: PrimOp -> Id
-mkPrimitiveId prim_op
+mkPrimOpId :: PrimOp -> Id
+mkPrimOpId prim_op
= id
where
- occ_name = primOpOcc prim_op
- key = primOpUniq prim_op
- ty = primOpType prim_op
- name = mkWiredInIdName key pREL_GHC occ_name id
- id = mkId name ty (ConstantId (PrimOp prim_op)) info
+ (tyvars,arg_tys,res_ty, arity, strict_info) = primOpSig prim_op
+ ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
+ name = mkPrimOpIdName prim_op
+ id = mkGlobalId (PrimOpId prim_op) name ty info
- info = setUnfoldingInfo unfolding $
- setInlinePragInfo IMustBeINLINEd $
- -- The pragma @IMustBeINLINEd@ says that this Id absolutely
- -- must be inlined. It's only used for primitives,
- -- because we don't want to make a closure for each of them.
- noIdInfo
-
- unfolding = mkUnfolding rhs
-
- (tyvars, tau) = splitForAllTys ty
- (arg_tys, _) = splitFunTys tau
+ info = noCafNoTyGenIdInfo
+ `setSpecInfo` rules
+ `setArityInfo` arity
+ `setAllStrictnessInfo` Just (newStrictnessFromOld name arity strict_info NoCPRInfo)
+ -- Until we modify the primop generation code
+
+ rules = foldl (addRule id) emptyCoreRules (primOpRules prim_op)
+
+
+-- For each ccall we manufacture a separate CCallOpId, giving it
+-- a fresh unique, a type that is correct for this particular ccall,
+-- and a CCall structure that gives the correct details about calling
+-- convention etc.
+--
+-- The *name* of this Id is a local name whose OccName gives the full
+-- details of the ccall, type and all. This means that the interface
+-- file reader can reconstruct a suitable Id
+
+mkFCallId :: Unique -> ForeignCall -> Type -> Id
+mkFCallId uniq fcall ty
+ = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
+ -- A CCallOpId should have no free type variables;
+ -- when doing substitutions won't substitute over it
+ mkGlobalId (FCallId fcall) name ty info
+ where
+ occ_str = showSDocIface (braces (ppr fcall <+> ppr ty))
+ -- The "occurrence name" of a ccall is the full info about the
+ -- ccall; it is encoded, but may have embedded spaces etc!
- args = mkTemplateLocals arg_tys
- rhs = mkLams tyvars $ mkLams args $
- mkPrimApp prim_op (map Type (mkTyVarTys tyvars) ++ map Var args)
-\end{code}
+ name = mkFCallName uniq occ_str
-\end{code}
+ info = noCafNoTyGenIdInfo
+ `setArityInfo` arity
+ `setAllStrictnessInfo` Just strict_sig
-\begin{code}
-dyadic_fun_ty ty = mkFunTys [ty, ty] ty
-monadic_fun_ty ty = ty `mkFunTy` ty
-compare_fun_ty ty = mkFunTys [ty, ty] boolTy
+ (_, tau) = tcSplitForAllTys ty
+ (arg_tys, _) = tcSplitFunTys tau
+ arity = length arg_tys
+ strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
\end{code}
%************************************************************************
%* *
-\subsection{DictFuns}
+\subsection{DictFuns and default methods}
%* *
%************************************************************************
+Important notes about dict funs and default methods
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Dict funs and default methods are *not* ImplicitIds. Their definition
+involves user-written code, so we can't figure out their strictness etc
+based on fixed info, as we can for constructors and record selectors (say).
+
+We build them as GlobalIds, but when in the module where they are
+bound, we turn the Id at the *binding site* into an exported LocalId.
+This ensures that they are taken to account by free-variable finding
+and dependency analysis (e.g. CoreFVs.exprFreeVars). The simplifier
+will propagate the LocalId to all occurrence sites.
+
+Why shouldn't they be bound as GlobalIds? Because, in particular, if
+they are globals, the specialiser floats dict uses above their defns,
+which prevents good simplifications happening. Also the strictness
+analyser treats a occurrence of a GlobalId as imported and assumes it
+contains strictness in its IdInfo, which isn't true if the thing is
+bound in the same module as the occurrence.
+
+It's OK for dfuns to be LocalIds, because we form the instance-env to
+pass on to the next module (md_insts) in CoreTidy, afer tidying
+and globalising the top-level Ids.
+
+BUT make sure they are *exported* LocalIds (setIdLocalExported) so
+that they aren't discarded by the occurrence analyser.
+
\begin{code}
+mkDefaultMethodId dm_name ty = mkVanillaGlobal dm_name ty noCafNoTyGenIdInfo
+
mkDictFunId :: Name -- Name to use for the dict fun;
-> Class
-> [TyVar]
-> ThetaType
-> Id
-mkDictFunId dfun_name clas inst_tyvars inst_tys inst_decl_theta
- = mkVanillaId dfun_name dfun_ty
+mkDictFunId dfun_name clas inst_tyvars inst_tys dfun_theta
+ = mkVanillaGlobal dfun_name dfun_ty noCafNoTyGenIdInfo
where
- (class_tyvars, sc_theta, _, _, _) = classBigSig clas
- sc_theta' = substTopTheta (zipVarEnv class_tyvars inst_tys) sc_theta
+ dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
+
+{- 1 dec 99: disable the Mark Jones optimisation for the sake
+ of compatibility with Hugs.
+ See `types/InstEnv' for a discussion related to this.
+ (class_tyvars, sc_theta, _, _) = classBigSig clas
+ not_const (clas, tys) = not (isEmptyVarSet (tyVarsOfTypes tys))
+ sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys) sc_theta
dfun_theta = case inst_decl_theta of
[] -> [] -- If inst_decl_theta is empty, then we don't
-- want to have any dict arguments, so that we can
-- expose the constant methods.
- other -> nub (inst_decl_theta ++ sc_theta')
+ other -> nub (inst_decl_theta ++ filter not_const sc_theta')
-- Otherwise we pass the superclass dictionaries to
-- the dictionary function; the Mark Jones optimisation.
--
-- instance Monad m => MonadT (EnvT env) m where ...
-- Here, the inst_decl_theta has (Monad m); but so
-- does the sc_theta'!
+ --
+ -- NOTE the "not_const". I got caught by this one too:
+ -- class Foo a => Baz a b where ...
+ -- instance Wob b => Baz T b where..
+ -- Now sc_theta' has Foo T
+-}
+\end{code}
- dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
+
+%************************************************************************
+%* *
+\subsection{Un-definable}
+%* *
+%************************************************************************
+
+These Ids can't be defined in Haskell. They could be defined in
+unfoldings in PrelGHC.hi-boot, but we'd have to ensure that they
+were definitely, definitely inlined, because there is no curried
+identifier for them. That's what mkCompulsoryUnfolding does.
+If we had a way to get a compulsory unfolding from an interface file,
+we could do that, but we don't right now.
+
+unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
+just gets expanded into a type coercion wherever it occurs. Hence we
+add it as a built-in Id with an unfolding here.
+
+The type variables we use here are "open" type variables: this means
+they can unify with both unlifted and lifted types. Hence we provide
+another gun with which to shoot yourself in the foot.
+
+\begin{code}
+-- unsafeCoerce# :: forall a b. a -> b
+unsafeCoerceId
+ = pcMiscPrelId unsafeCoerceIdKey pREL_GHC SLIT("unsafeCoerce#") ty info
+ where
+ info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
+
+
+ ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
+ (mkFunTy openAlphaTy openBetaTy)
+ [x] = mkTemplateLocals [openAlphaTy]
+ rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
+ Note (Coerce openBetaTy openAlphaTy) (Var x)
+
+-- nullAddr# :: Addr#
+-- The reason is is here is because we don't provide
+-- a way to write this literal in Haskell.
+nullAddrId
+ = pcMiscPrelId nullAddrIdKey pREL_GHC SLIT("nullAddr#") addrPrimTy info
+ where
+ info = noCafNoTyGenIdInfo `setUnfoldingInfo`
+ mkCompulsoryUnfolding (Lit nullAddrLit)
+
+seqId
+ = pcMiscPrelId seqIdKey pREL_GHC SLIT("seq") ty info
+ where
+ info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
+
+
+ ty = mkForAllTys [alphaTyVar,betaTyVar]
+ (mkFunTy alphaTy (mkFunTy betaTy betaTy))
+ [x,y] = mkTemplateLocals [alphaTy, betaTy]
+ rhs = mkLams [alphaTyVar,betaTyVar,x,y] (Case (Var x) x [(DEFAULT, [], Var y)])
+\end{code}
+
+@getTag#@ is another function which can't be defined in Haskell. It needs to
+evaluate its argument and call the dataToTag# primitive.
+
+\begin{code}
+getTagId
+ = pcMiscPrelId getTagIdKey pREL_GHC SLIT("getTag#") ty info
+ where
+ info = noCafNoTyGenIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
+ -- We don't provide a defn for this; you must inline it
+
+ ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy intPrimTy)
+ [x,y] = mkTemplateLocals [alphaTy,alphaTy]
+ rhs = mkLams [alphaTyVar,x] $
+ Case (Var x) y [ (DEFAULT, [], mkApps (Var dataToTagId) [Type alphaTy, Var y]) ]
+
+dataToTagId = mkPrimOpId DataToTagOp
\end{code}
+
+@realWorld#@ used to be a magic literal, \tr{void#}. If things get
+nasty as-is, change it back to a literal (@Literal@).
+
+voidArgId is a Local Id used simply as an argument in functions
+where we just want an arg to avoid having a thunk of unlifted type.
+E.g.
+ x = \ void :: State# RealWorld -> (# p, q #)
+
+This comes up in strictness analysis
+
+\begin{code}
+realWorldPrimId -- :: State# RealWorld
+ = pcMiscPrelId realWorldPrimIdKey pREL_GHC SLIT("realWorld#")
+ realWorldStatePrimTy
+ (noCafNoTyGenIdInfo `setUnfoldingInfo` mkOtherCon [])
+ -- The mkOtherCon makes it look that realWorld# is evaluated
+ -- which in turn makes Simplify.interestingArg return True,
+ -- which in turn makes INLINE things applied to realWorld# likely
+ -- to be inlined
+
+voidArgId -- :: State# RealWorld
+ = mkSysLocal SLIT("void") voidArgIdKey realWorldStatePrimTy
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection[PrelVals-error-related]{@error@ and friends; @trace@}
+%* *
+%************************************************************************
+
+GHC randomly injects these into the code.
+
+@patError@ is just a version of @error@ for pattern-matching
+failures. It knows various ``codes'' which expand to longer
+strings---this saves space!
+
+@absentErr@ is a thing we put in for ``absent'' arguments. They jolly
+well shouldn't be yanked on, but if one is, then you will get a
+friendly message from @absentErr@ (rather than a totally random
+crash).
+
+@parError@ is a special version of @error@ which the compiler does
+not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
+templates, but we don't ever expect to generate code for it.
+
+\begin{code}
+eRROR_ID
+ = pc_bottoming_Id errorIdKey pREL_ERR SLIT("error") errorTy
+eRROR_CSTRING_ID
+ = pc_bottoming_Id errorCStringIdKey pREL_ERR SLIT("errorCString")
+ (mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy))
+pAT_ERROR_ID
+ = generic_ERROR_ID patErrorIdKey SLIT("patError")
+rEC_SEL_ERROR_ID
+ = generic_ERROR_ID recSelErrIdKey SLIT("recSelError")
+rEC_CON_ERROR_ID
+ = generic_ERROR_ID recConErrorIdKey SLIT("recConError")
+rEC_UPD_ERROR_ID
+ = generic_ERROR_ID recUpdErrorIdKey SLIT("recUpdError")
+iRREFUT_PAT_ERROR_ID
+ = generic_ERROR_ID irrefutPatErrorIdKey SLIT("irrefutPatError")
+nON_EXHAUSTIVE_GUARDS_ERROR_ID
+ = generic_ERROR_ID nonExhaustiveGuardsErrorIdKey SLIT("nonExhaustiveGuardsError")
+nO_METHOD_BINDING_ERROR_ID
+ = generic_ERROR_ID noMethodBindingErrorIdKey SLIT("noMethodBindingError")
+
+aBSENT_ERROR_ID
+ = pc_bottoming_Id absentErrorIdKey pREL_ERR SLIT("absentErr")
+ (mkSigmaTy [openAlphaTyVar] [] openAlphaTy)
+
+pAR_ERROR_ID
+ = pcMiscPrelId parErrorIdKey pREL_ERR SLIT("parError")
+ (mkSigmaTy [openAlphaTyVar] [] openAlphaTy) noCafNoTyGenIdInfo
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Utilities}
+%* *
+%************************************************************************
+
+\begin{code}
+pcMiscPrelId :: Unique{-IdKey-} -> Module -> FAST_STRING -> Type -> IdInfo -> Id
+pcMiscPrelId key mod str ty info
+ = let
+ name = mkWiredInName mod (mkVarOcc str) key
+ imp = mkVanillaGlobal name ty info -- the usual case...
+ in
+ imp
+ -- We lie and say the thing is imported; otherwise, we get into
+ -- a mess with dependency analysis; e.g., core2stg may heave in
+ -- random calls to GHCbase.unpackPS__. If GHCbase is the module
+ -- being compiled, then it's just a matter of luck if the definition
+ -- will be in "the right place" to be in scope.
+
+pc_bottoming_Id key mod name ty
+ = pcMiscPrelId key mod name ty bottoming_info
+ where
+ strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
+ bottoming_info = noCafNoTyGenIdInfo `setAllStrictnessInfo` Just strict_sig
+ -- these "bottom" out, no matter what their arguments
+
+generic_ERROR_ID u n = pc_bottoming_Id u pREL_ERR n errorTy
+
+(openAlphaTyVar:openBetaTyVar:_) = openAlphaTyVars
+openAlphaTy = mkTyVarTy openAlphaTyVar
+openBetaTy = mkTyVarTy openBetaTyVar
+
+errorTy :: Type
+errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy]
+ openAlphaTy)
+ -- Notice the openAlphaTyVar. It says that "error" can be applied
+ -- to unboxed as well as boxed types. This is OK because it never
+ -- returns, so the return type is irrelevant.
+\end{code}
+
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