2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1998
6 This module contains definitions for the IdInfo for things that
7 have a standard form, namely:
11 - method and superclass selectors
12 - primitive operations
15 {-# OPTIONS -fno-warn-missing-signatures #-}
16 -- The above warning supression flag is a temporary kludge.
17 -- While working on this module you are encouraged to remove it and fix
18 -- any warnings in the module. See
19 -- <http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings>
23 mkDictFunId, mkDefaultMethodId,
27 mkPrimOpId, mkFCallId, mkTickBoxOpId, mkBreakPointOpId,
29 mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
30 wrapFamInstBody, unwrapFamInstScrut,
31 mkUnpackCase, mkProductBox,
33 -- And some particular Ids; see below for why they are wired in
34 wiredInIds, ghcPrimIds,
35 unsafeCoerceId, realWorldPrimId, voidArgId, nullAddrId, seqId,
38 mkRuntimeErrorApp, mkImpossibleExpr,
39 rEC_CON_ERROR_ID, iRREFUT_PAT_ERROR_ID, rUNTIME_ERROR_ID,
40 nON_EXHAUSTIVE_GUARDS_ERROR_ID, nO_METHOD_BINDING_ERROR_ID,
41 pAT_ERROR_ID, eRROR_ID, rEC_SEL_ERROR_ID,
46 #include "HsVersions.h"
55 import CoreUtils ( exprType, mkCoerce )
66 import Var ( Var, TyVar, mkCoVar, mkExportedLocalVar )
72 import BasicTypes hiding ( SuccessFlag(..) )
80 %************************************************************************
82 \subsection{Wired in Ids}
84 %************************************************************************
88 There are several reasons why an Id might appear in the wiredInIds:
90 (1) The ghcPrimIds are wired in because they can't be defined in
91 Haskell at all, although the can be defined in Core. They have
92 compulsory unfoldings, so they are always inlined and they have
93 no definition site. Their home module is GHC.Prim, so they
94 also have a description in primops.txt.pp, where they are called
97 (2) The 'error' function, eRROR_ID, is wired in because we don't yet have
98 a way to express in an interface file that the result type variable
99 is 'open'; that is can be unified with an unboxed type
101 [The interface file format now carry such information, but there's
102 no way yet of expressing at the definition site for these
103 error-reporting functions that they have an 'open'
104 result type. -- sof 1/99]
106 (3) Other error functions (rUNTIME_ERROR_ID) are wired in (a) because
107 the desugarer generates code that mentiones them directly, and
108 (b) for the same reason as eRROR_ID
110 (4) lazyId is wired in because the wired-in version overrides the
111 strictness of the version defined in GHC.Base
113 In cases (2-4), the function has a definition in a library module, and
114 can be called; but the wired-in version means that the details are
115 never read from that module's interface file; instead, the full definition
123 eRROR_ID, -- This one isn't used anywhere else in the compiler
124 -- But we still need it in wiredInIds so that when GHC
125 -- compiles a program that mentions 'error' we don't
126 -- import its type from the interface file; we just get
127 -- the Id defined here. Which has an 'open-tyvar' type.
130 iRREFUT_PAT_ERROR_ID,
131 nON_EXHAUSTIVE_GUARDS_ERROR_ID,
132 nO_METHOD_BINDING_ERROR_ID,
140 -- These Ids are exported from GHC.Prim
143 = [ -- These can't be defined in Haskell, but they have
144 -- perfectly reasonable unfoldings in Core
152 %************************************************************************
154 \subsection{Data constructors}
156 %************************************************************************
158 The wrapper for a constructor is an ordinary top-level binding that evaluates
159 any strict args, unboxes any args that are going to be flattened, and calls
162 We're going to build a constructor that looks like:
164 data (Data a, C b) => T a b = T1 !a !Int b
167 \d1::Data a, d2::C b ->
168 \p q r -> case p of { p ->
170 Con T1 [a,b] [p,q,r]}}
174 * d2 is thrown away --- a context in a data decl is used to make sure
175 one *could* construct dictionaries at the site the constructor
176 is used, but the dictionary isn't actually used.
178 * We have to check that we can construct Data dictionaries for
179 the types a and Int. Once we've done that we can throw d1 away too.
181 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
182 all that matters is that the arguments are evaluated. "seq" is
183 very careful to preserve evaluation order, which we don't need
186 You might think that we could simply give constructors some strictness
187 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
188 But we don't do that because in the case of primops and functions strictness
189 is a *property* not a *requirement*. In the case of constructors we need to
190 do something active to evaluate the argument.
192 Making an explicit case expression allows the simplifier to eliminate
193 it in the (common) case where the constructor arg is already evaluated.
195 Note [Wrappers for data instance tycons]
196 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
197 In the case of data instances, the wrapper also applies the coercion turning
198 the representation type into the family instance type to cast the result of
199 the wrapper. For example, consider the declarations
201 data family Map k :: * -> *
202 data instance Map (a, b) v = MapPair (Map a (Pair b v))
204 The tycon to which the datacon MapPair belongs gets a unique internal
205 name of the form :R123Map, and we call it the representation tycon.
206 In contrast, Map is the family tycon (accessible via
207 tyConFamInst_maybe). A coercion allows you to move between
208 representation and family type. It is accessible from :R123Map via
209 tyConFamilyCoercion_maybe and has kind
211 Co123Map a b v :: {Map (a, b) v ~ :R123Map a b v}
213 The wrapper and worker of MapPair get the types
216 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
217 $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v)
220 MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
222 This coercion is conditionally applied by wrapFamInstBody.
224 It's a bit more complicated if the data instance is a GADT as well!
226 data instance T [a] where
227 T1 :: forall b. b -> T [Maybe b]
229 Co7T a :: T [a] ~ :R7T a
234 $WT1 :: forall b. b -> T [Maybe b]
235 $WT1 b v = T1 (Maybe b) b (Maybe b) v
236 `cast` sym (Co7T (Maybe b))
239 T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c
242 mkDataConIds :: Name -> Name -> DataCon -> DataConIds
243 mkDataConIds wrap_name wkr_name data_con
244 | isNewTyCon tycon -- Newtype, only has a worker
245 = DCIds Nothing nt_work_id
247 | any isMarkedStrict all_strict_marks -- Algebraic, needs wrapper
248 || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
249 || isFamInstTyCon tycon -- depends on this test
250 = DCIds (Just alg_wrap_id) wrk_id
252 | otherwise -- Algebraic, no wrapper
253 = DCIds Nothing wrk_id
255 (univ_tvs, ex_tvs, eq_spec,
256 eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
257 tycon = dataConTyCon data_con -- The representation TyCon (not family)
259 ----------- Worker (algebraic data types only) --------------
260 -- The *worker* for the data constructor is the function that
261 -- takes the representation arguments and builds the constructor.
262 wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
263 (dataConRepType data_con) wkr_info
265 wkr_arity = dataConRepArity data_con
266 wkr_info = noCafIdInfo
267 `setArityInfo` wkr_arity
268 `setStrictnessInfo` Just wkr_sig
269 `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
272 wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
273 -- Note [Data-con worker strictness]
274 -- Notice that we do *not* say the worker is strict
275 -- even if the data constructor is declared strict
276 -- e.g. data T = MkT !(Int,Int)
277 -- Why? Because the *wrapper* is strict (and its unfolding has case
278 -- expresssions that do the evals) but the *worker* itself is not.
279 -- If we pretend it is strict then when we see
280 -- case x of y -> $wMkT y
281 -- the simplifier thinks that y is "sure to be evaluated" (because
282 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
284 -- When the simplifer sees a pattern
285 -- case e of MkT x -> ...
286 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
287 -- but that's fine... dataConRepStrictness comes from the data con
288 -- not from the worker Id.
290 cpr_info | isProductTyCon tycon &&
293 wkr_arity <= mAX_CPR_SIZE = retCPR
295 -- RetCPR is only true for products that are real data types;
296 -- that is, not unboxed tuples or [non-recursive] newtypes
298 ----------- Workers for newtypes --------------
299 nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
300 nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
301 `setArityInfo` 1 -- Arity 1
302 `setUnfoldingInfo` newtype_unf
303 id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
304 newtype_unf = ASSERT2( isVanillaDataCon data_con &&
305 isSingleton orig_arg_tys, ppr data_con )
306 -- Note [Newtype datacons]
307 mkCompulsoryUnfolding $
308 mkLams wrap_tvs $ Lam id_arg1 $
309 wrapNewTypeBody tycon res_ty_args (Var id_arg1)
312 ----------- Wrapper --------------
313 -- We used to include the stupid theta in the wrapper's args
314 -- but now we don't. Instead the type checker just injects these
315 -- extra constraints where necessary.
316 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
317 res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
318 eq_tys = mkPredTys eq_theta
319 dict_tys = mkPredTys dict_theta
320 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
321 mkFunTys orig_arg_tys $ res_ty
322 -- NB: watch out here if you allow user-written equality
323 -- constraints in data constructor signatures
325 ----------- Wrappers for algebraic data types --------------
326 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
327 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
328 `setArityInfo` wrap_arity
329 -- It's important to specify the arity, so that partial
330 -- applications are treated as values
331 `setUnfoldingInfo` wrap_unf
332 `setStrictnessInfo` Just wrap_sig
334 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
335 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
336 arg_dmds = map mk_dmd all_strict_marks
337 mk_dmd str | isMarkedStrict str = evalDmd
338 | otherwise = lazyDmd
339 -- The Cpr info can be important inside INLINE rhss, where the
340 -- wrapper constructor isn't inlined.
341 -- And the argument strictness can be important too; we
342 -- may not inline a contructor when it is partially applied.
344 -- data W = C !Int !Int !Int
345 -- ...(let w = C x in ...(w p q)...)...
346 -- we want to see that w is strict in its two arguments
348 wrap_unf = mkInlineRule wrap_rhs (Just (length dict_args + length id_args))
349 wrap_rhs = mkLams wrap_tvs $
351 mkLams dict_args $ mkLams id_args $
352 foldr mk_case con_app
353 (zip (dict_args ++ id_args) all_strict_marks)
356 con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
357 Var wrk_id `mkTyApps` res_ty_args
359 -- Equality evidence:
360 `mkTyApps` map snd eq_spec
362 `mkVarApps` reverse rep_ids
364 (dict_args,i2) = mkLocals 1 dict_tys
365 (id_args,i3) = mkLocals i2 orig_arg_tys
367 (eq_args,_) = mkCoVarLocals i3 eq_tys
369 mkCoVarLocals i [] = ([],i)
370 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
371 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) (fsLit "dc_co")) x
375 :: (Id, StrictnessMark) -- Arg, strictness
376 -> (Int -> [Id] -> CoreExpr) -- Body
377 -> Int -- Next rep arg id
378 -> [Id] -- Rep args so far, reversed
380 mk_case (arg,strict) body i rep_args
382 NotMarkedStrict -> body i (arg:rep_args)
384 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
386 Case (Var arg) arg res_ty [(DEFAULT,[], body i (arg:rep_args))]
389 -> unboxProduct i (Var arg) (idType arg) the_body
391 the_body i con_args = body i (reverse con_args ++ rep_args)
393 mAX_CPR_SIZE :: Arity
395 -- We do not treat very big tuples as CPR-ish:
396 -- a) for a start we get into trouble because there aren't
397 -- "enough" unboxed tuple types (a tiresome restriction,
399 -- b) more importantly, big unboxed tuples get returned mainly
400 -- on the stack, and are often then allocated in the heap
401 -- by the caller. So doing CPR for them may in fact make
404 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
409 Note [Newtype datacons]
410 ~~~~~~~~~~~~~~~~~~~~~~~
411 The "data constructor" for a newtype should always be vanilla. At one
412 point this wasn't true, because the newtype arising from
415 newtype T:D a = D:D (C a)
416 so the data constructor for T:C had a single argument, namely the
417 predicate (C a). But now we treat that as an ordinary argument, not
418 part of the theta-type, so all is well.
421 %************************************************************************
423 \subsection{Dictionary selectors}
425 %************************************************************************
427 Selecting a field for a dictionary. If there is just one field, then
428 there's nothing to do.
430 Dictionary selectors may get nested forall-types. Thus:
433 op :: forall b. Ord b => a -> b -> b
435 Then the top-level type for op is
437 op :: forall a. Foo a =>
441 This is unlike ordinary record selectors, which have all the for-alls
442 at the outside. When dealing with classes it's very convenient to
443 recover the original type signature from the class op selector.
446 mkDictSelId :: Bool -- True <=> don't include the unfolding
447 -- Little point on imports without -O, because the
448 -- dictionary itself won't be visible
449 -> Name -> Class -> Id
450 mkDictSelId no_unf name clas
451 = mkGlobalId (ClassOpId clas) name sel_ty info
453 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
454 -- We can't just say (exprType rhs), because that would give a type
456 -- for a single-op class (after all, the selector is the identity)
457 -- But it's type must expose the representation of the dictionary
458 -- to get (say) C a -> (a -> a)
460 base_info = noCafIdInfo
462 `setStrictnessInfo` Just strict_sig
463 `setUnfoldingInfo` (if no_unf then noUnfolding
464 else mkImplicitUnfolding rhs)
465 -- In module where class op is defined, we must add
466 -- the unfolding, even though it'll never be inlined
467 -- becuase we use that to generate a top-level binding
470 info = base_info `setSpecInfo` mkSpecInfo [rule]
471 `setInlinePragInfo` neverInlinePragma
472 -- Add a magic BuiltinRule, and never inline it
473 -- so that the rule is always available to fire.
474 -- See Note [ClassOp/DFun selection] in TcInstDcls
476 n_ty_args = length tyvars
478 -- This is the built-in rule that goes
479 -- op (dfT d1 d2) ---> opT d1 d2
480 rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
481 occNameFS (getOccName name)
483 , ru_nargs = n_ty_args + 1
484 , ru_try = dictSelRule index n_ty_args }
486 -- The strictness signature is of the form U(AAAVAAAA) -> T
487 -- where the V depends on which item we are selecting
488 -- It's worth giving one, so that absence info etc is generated
489 -- even if the selector isn't inlined
490 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
491 arg_dmd | new_tycon = evalDmd
492 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
495 tycon = classTyCon clas
496 new_tycon = isNewTyCon tycon
497 [data_con] = tyConDataCons tycon
498 tyvars = dataConUnivTyVars data_con
499 arg_tys = {- ASSERT( isVanillaDataCon data_con ) -} dataConRepArgTys data_con
500 eq_theta = dataConEqTheta data_con
501 index = assoc "MkId.mkDictSelId" (map idName (classSelIds clas) `zip` [0..]) name
502 the_arg_id = arg_ids !! index
504 pred = mkClassPred clas (mkTyVarTys tyvars)
505 dict_id = mkTemplateLocal 1 $ mkPredTy pred
506 (eq_ids,n) = mkCoVarLocals 2 $ mkPredTys eq_theta
507 arg_ids = mkTemplateLocalsNum n arg_tys
509 mkCoVarLocals i [] = ([],i)
510 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
511 y = mkCoVar (mkSysTvName (mkBuiltinUnique i) (fsLit "dc_co")) x
514 rhs = mkLams tyvars (Lam dict_id rhs_body)
515 rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
516 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
517 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
519 dictSelRule :: Int -> Arity -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
521 -- op_i t1..tk (df s1..sn d1..dm) = op_i_helper s1..sn d1..dm
522 -- op_i t1..tk (D t1..tk op1 ... opm) = opi
524 -- NB: the data constructor has the same number of type args as the class op
526 dictSelRule index n_ty_args id_unf args
527 | (dict_arg : _) <- drop n_ty_args args
528 , Just (_, _, val_args) <- exprIsConApp_maybe id_unf dict_arg
529 = Just (val_args !! index)
535 %************************************************************************
539 %************************************************************************
542 -- unbox a product type...
543 -- we will recurse into newtypes, casting along the way, and unbox at the
544 -- first product data constructor we find. e.g.
546 -- data PairInt = PairInt Int Int
547 -- newtype S = MkS PairInt
550 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
551 -- ids, we get (modulo int passing)
553 -- case (e `cast` CoT) `cast` CoS of
554 -- PairInt a b -> body [a,b]
556 -- The Ints passed around are just for creating fresh locals
557 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
558 unboxProduct i arg arg_ty body
561 result = mkUnpackCase the_id arg con_args boxing_con rhs
562 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
563 ([the_id], i') = mkLocals i [arg_ty]
564 (con_args, i'') = mkLocals i' tys
565 rhs = body i'' con_args
567 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
568 -- (mkUnpackCase x e args Con body)
570 -- case (e `cast` ...) of bndr { Con args -> body }
572 -- the type of the bndr passed in is irrelevent
573 mkUnpackCase bndr arg unpk_args boxing_con body
574 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
576 (cast_arg, bndr_ty) = go (idType bndr) arg
578 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
579 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
580 = go (newTyConInstRhs tycon tycon_args)
581 (unwrapNewTypeBody tycon tycon_args arg)
582 | otherwise = (arg, ty)
585 reboxProduct :: [Unique] -- uniques to create new local binders
586 -> Type -- type of product to box
587 -> ([Unique], -- remaining uniques
588 CoreExpr, -- boxed product
589 [Id]) -- Ids being boxed into product
592 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
594 us' = dropList con_arg_tys us
596 arg_ids = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys
598 bind_rhs = mkProductBox arg_ids ty
601 (us', bind_rhs, arg_ids)
603 mkProductBox :: [Id] -> Type -> CoreExpr
604 mkProductBox arg_ids ty
607 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
610 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
611 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
612 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
614 wrap expr = wrapNewTypeBody tycon tycon_args expr
617 -- (mkReboxingAlt us con xs rhs) basically constructs the case
618 -- alternative (con, xs, rhs)
619 -- but it does the reboxing necessary to construct the *source*
620 -- arguments, xs, from the representation arguments ys.
622 -- data T = MkT !(Int,Int) Bool
624 -- mkReboxingAlt MkT [x,b] r
625 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
627 -- mkDataAlt should really be in DataCon, but it can't because
628 -- it manipulates CoreSyn.
631 :: [Unique] -- Uniques for the new Ids
633 -> [Var] -- Source-level args, including existential dicts
637 mkReboxingAlt us con args rhs
638 | not (any isMarkedUnboxed stricts)
639 = (DataAlt con, args, rhs)
643 (binds, args') = go args stricts us
645 (DataAlt con, args', mkLets binds rhs)
648 stricts = dataConExStricts con ++ dataConStrictMarks con
650 go [] _stricts _us = ([], [])
652 -- Type variable case
653 go (arg:args) stricts us
655 = let (binds, args') = go args stricts us
656 in (binds, arg:args')
658 -- Term variable case
659 go (arg:args) (str:stricts) us
660 | isMarkedUnboxed str
662 let (binds, unpacked_args') = go args stricts us'
663 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
665 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
667 = let (binds, args') = go args stricts us
668 in (binds, arg:args')
669 go (_ : _) [] _ = panic "mkReboxingAlt"
673 %************************************************************************
675 Wrapping and unwrapping newtypes and type families
677 %************************************************************************
680 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
681 -- The wrapper for the data constructor for a newtype looks like this:
682 -- newtype T a = MkT (a,Int)
683 -- MkT :: forall a. (a,Int) -> T a
684 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
685 -- where CoT is the coercion TyCon assoicated with the newtype
687 -- The call (wrapNewTypeBody T [a] e) returns the
688 -- body of the wrapper, namely
689 -- e `cast` (CoT [a])
691 -- If a coercion constructor is provided in the newtype, then we use
692 -- it, otherwise the wrap/unwrap are both no-ops
694 -- If the we are dealing with a newtype *instance*, we have a second coercion
695 -- identifying the family instance with the constructor of the newtype
696 -- instance. This coercion is applied in any case (ie, composed with the
697 -- coercion constructor of the newtype or applied by itself).
699 wrapNewTypeBody tycon args result_expr
700 = wrapFamInstBody tycon args inner
703 | Just co_con <- newTyConCo_maybe tycon
704 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
708 -- When unwrapping, we do *not* apply any family coercion, because this will
709 -- be done via a CoPat by the type checker. We have to do it this way as
710 -- computing the right type arguments for the coercion requires more than just
711 -- a spliting operation (cf, TcPat.tcConPat).
713 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
714 unwrapNewTypeBody tycon args result_expr
715 | Just co_con <- newTyConCo_maybe tycon
716 = mkCoerce (mkTyConApp co_con args) result_expr
720 -- If the type constructor is a representation type of a data instance, wrap
721 -- the expression into a cast adjusting the expression type, which is an
722 -- instance of the representation type, to the corresponding instance of the
723 -- family instance type.
724 -- See Note [Wrappers for data instance tycons]
725 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
726 wrapFamInstBody tycon args body
727 | Just co_con <- tyConFamilyCoercion_maybe tycon
728 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
732 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
733 unwrapFamInstScrut tycon args scrut
734 | Just co_con <- tyConFamilyCoercion_maybe tycon
735 = mkCoerce (mkTyConApp co_con args) scrut
741 %************************************************************************
743 \subsection{Primitive operations}
745 %************************************************************************
748 mkPrimOpId :: PrimOp -> Id
752 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
753 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
754 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
755 (mkPrimOpIdUnique (primOpTag prim_op))
757 id = mkGlobalId (PrimOpId prim_op) name ty info
760 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
762 `setStrictnessInfo` Just strict_sig
764 -- For each ccall we manufacture a separate CCallOpId, giving it
765 -- a fresh unique, a type that is correct for this particular ccall,
766 -- and a CCall structure that gives the correct details about calling
769 -- The *name* of this Id is a local name whose OccName gives the full
770 -- details of the ccall, type and all. This means that the interface
771 -- file reader can reconstruct a suitable Id
773 mkFCallId :: Unique -> ForeignCall -> Type -> Id
774 mkFCallId uniq fcall ty
775 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
776 -- A CCallOpId should have no free type variables;
777 -- when doing substitutions won't substitute over it
778 mkGlobalId (FCallId fcall) name ty info
780 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
781 -- The "occurrence name" of a ccall is the full info about the
782 -- ccall; it is encoded, but may have embedded spaces etc!
784 name = mkFCallName uniq occ_str
788 `setStrictnessInfo` Just strict_sig
790 (_, tau) = tcSplitForAllTys ty
791 (arg_tys, _) = tcSplitFunTys tau
792 arity = length arg_tys
793 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
795 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
796 -- except for the type:
798 -- a plain HPC tick box has type (State# RealWorld)
799 -- a breakpoint Id has type forall a.a
801 -- The breakpoint Id will be applied to a list of arbitrary free variables,
802 -- which is why it needs a polymorphic type.
804 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
805 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
807 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
808 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
809 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
811 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
813 tickbox = TickBox mod ix
814 occ_str = showSDoc (braces (ppr tickbox))
815 name = mkTickBoxOpName uniq occ_str
820 %************************************************************************
822 \subsection{DictFuns and default methods}
824 %************************************************************************
826 Important notes about dict funs and default methods
827 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
828 Dict funs and default methods are *not* ImplicitIds. Their definition
829 involves user-written code, so we can't figure out their strictness etc
830 based on fixed info, as we can for constructors and record selectors (say).
832 We build them as LocalIds, but with External Names. This ensures that
833 they are taken to account by free-variable finding and dependency
834 analysis (e.g. CoreFVs.exprFreeVars).
836 Why shouldn't they be bound as GlobalIds? Because, in particular, if
837 they are globals, the specialiser floats dict uses above their defns,
838 which prevents good simplifications happening. Also the strictness
839 analyser treats a occurrence of a GlobalId as imported and assumes it
840 contains strictness in its IdInfo, which isn't true if the thing is
841 bound in the same module as the occurrence.
843 It's OK for dfuns to be LocalIds, because we form the instance-env to
844 pass on to the next module (md_insts) in CoreTidy, afer tidying
845 and globalising the top-level Ids.
847 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
848 that they aren't discarded by the occurrence analyser.
851 mkDefaultMethodId dm_name ty = mkExportedLocalId dm_name ty
853 mkDictFunId :: Name -- Name to use for the dict fun;
860 mkDictFunId dfun_name inst_tyvars dfun_theta clas inst_tys
861 = mkExportedLocalVar (DFunId is_nt) dfun_name dfun_ty vanillaIdInfo
863 is_nt = isNewTyCon (classTyCon clas)
864 dfun_ty = mkSigmaTy inst_tyvars dfun_theta (mkDictTy clas inst_tys)
868 %************************************************************************
870 \subsection{Un-definable}
872 %************************************************************************
874 These Ids can't be defined in Haskell. They could be defined in
875 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
876 ensure that they were definitely, definitely inlined, because there is
877 no curried identifier for them. That's what mkCompulsoryUnfolding
878 does. If we had a way to get a compulsory unfolding from an interface
879 file, we could do that, but we don't right now.
881 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
882 just gets expanded into a type coercion wherever it occurs. Hence we
883 add it as a built-in Id with an unfolding here.
885 The type variables we use here are "open" type variables: this means
886 they can unify with both unlifted and lifted types. Hence we provide
887 another gun with which to shoot yourself in the foot.
890 mkWiredInIdName mod fs uniq id
891 = mkWiredInName mod (mkOccNameFS varName fs) uniq (AnId id) UserSyntax
893 unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
894 nullAddrName = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#") nullAddrIdKey nullAddrId
895 seqName = mkWiredInIdName gHC_PRIM (fsLit "seq") seqIdKey seqId
896 realWorldName = mkWiredInIdName gHC_PRIM (fsLit "realWorld#") realWorldPrimIdKey realWorldPrimId
897 lazyIdName = mkWiredInIdName gHC_BASE (fsLit "lazy") lazyIdKey lazyId
899 errorName = mkWiredInIdName gHC_ERR (fsLit "error") errorIdKey eRROR_ID
900 recSelErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "recSelError") recSelErrorIdKey rEC_SEL_ERROR_ID
901 runtimeErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "runtimeError") runtimeErrorIdKey rUNTIME_ERROR_ID
902 irrefutPatErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "irrefutPatError") irrefutPatErrorIdKey iRREFUT_PAT_ERROR_ID
903 recConErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "recConError") recConErrorIdKey rEC_CON_ERROR_ID
904 patErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "patError") patErrorIdKey pAT_ERROR_ID
905 noMethodBindingErrorName = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "noMethodBindingError")
906 noMethodBindingErrorIdKey nO_METHOD_BINDING_ERROR_ID
907 nonExhaustiveGuardsErrorName
908 = mkWiredInIdName cONTROL_EXCEPTION_BASE (fsLit "nonExhaustiveGuardsError")
909 nonExhaustiveGuardsErrorIdKey nON_EXHAUSTIVE_GUARDS_ERROR_ID
913 ------------------------------------------------
914 -- unsafeCoerce# :: forall a b. a -> b
916 = pcMiscPrelId unsafeCoerceName ty info
918 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
921 ty = mkForAllTys [openAlphaTyVar,openBetaTyVar]
922 (mkFunTy openAlphaTy openBetaTy)
923 [x] = mkTemplateLocals [openAlphaTy]
924 rhs = mkLams [openAlphaTyVar,openBetaTyVar,x] $
925 Cast (Var x) (mkUnsafeCoercion openAlphaTy openBetaTy)
927 ------------------------------------------------
929 -- nullAddr# :: Addr#
930 -- The reason is is here is because we don't provide
931 -- a way to write this literal in Haskell.
932 nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
934 info = noCafIdInfo `setUnfoldingInfo`
935 mkCompulsoryUnfolding (Lit nullAddrLit)
937 ------------------------------------------------
938 seqId :: Id -- See Note [seqId magic]
939 seqId = pcMiscPrelId seqName ty info
941 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
942 `setSpecInfo` mkSpecInfo [seq_cast_rule]
945 ty = mkForAllTys [alphaTyVar,openBetaTyVar]
946 (mkFunTy alphaTy (mkFunTy openBetaTy openBetaTy))
947 [x,y] = mkTemplateLocals [alphaTy, openBetaTy]
948 rhs = mkLams [alphaTyVar,openBetaTyVar,x,y] (Case (Var x) x openBetaTy [(DEFAULT, [], Var y)])
950 -- See Note [Built-in RULES for seq]
951 seq_cast_rule = BuiltinRule { ru_name = fsLit "seq of cast"
954 , ru_try = match_seq_of_cast
957 match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
958 -- See Note [Built-in RULES for seq]
959 match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
960 = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
962 match_seq_of_cast _ _ = Nothing
964 ------------------------------------------------
965 lazyId :: Id -- See Note [lazyId magic]
966 lazyId = pcMiscPrelId lazyIdName ty info
969 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
974 'GHC.Prim.seq' is special in several ways.
976 a) Its second arg can have an unboxed type
979 b) Its fixity is set in LoadIface.ghcPrimIface
981 c) It has quite a bit of desugaring magic.
982 See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3)
984 d) There is some special rule handing: Note [User-defined RULES for seq]
986 Note [User-defined RULES for seq]
987 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
988 Roman found situations where he had
990 where he knew that f (which was strict in n) would terminate if n did.
991 Notice that the result of (f n) is discarded. So it makes sense to
995 Rather than attempt some general analysis to support this, I've added
996 enough support that you can do this using a rewrite rule:
998 RULE "f/seq" forall n. seq (f n) e = seq n e
1000 You write that rule. When GHC sees a case expression that discards
1001 its result, it mentally transforms it to a call to 'seq' and looks for
1002 a RULE. (This is done in Simplify.rebuildCase.) As usual, the
1003 correctness of the rule is up to you.
1005 To make this work, we need to be careful that the magical desugaring
1006 done in Note [seqId magic] item (c) is *not* done on the LHS of a rule.
1007 Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs.
1009 Note [Built-in RULES for seq]
1010 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1011 We also have the following built-in rule for seq
1013 seq (x `cast` co) y = seq x y
1015 This eliminates unnecessary casts and also allows other seq rules to
1016 match more often. Notably,
1018 seq (f x `cast` co) y --> seq (f x) y
1020 and now a user-defined rule for seq (see Note [User-defined RULES for seq])
1026 lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1028 Used to lazify pseq: pseq a b = a `seq` lazy b
1030 Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1031 not from GHC.Base.hi. This is important, because the strictness
1032 analyser will spot it as strict!
1034 Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep.
1035 It's very important to do this inlining *after* unfoldings are exposed
1036 in the interface file. Otherwise, the unfolding for (say) pseq in the
1037 interface file will not mention 'lazy', so if we inline 'pseq' we'll totally
1038 miss the very thing that 'lazy' was there for in the first place.
1039 See Trac #3259 for a real world example.
1041 lazyId is defined in GHC.Base, so we don't *have* to inline it. If it
1042 appears un-applied, we'll end up just calling it.
1044 -------------------------------------------------------------
1045 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1046 nasty as-is, change it back to a literal (@Literal@).
1048 voidArgId is a Local Id used simply as an argument in functions
1049 where we just want an arg to avoid having a thunk of unlifted type.
1051 x = \ void :: State# RealWorld -> (# p, q #)
1053 This comes up in strictness analysis
1056 realWorldPrimId -- :: State# RealWorld
1057 = pcMiscPrelId realWorldName realWorldStatePrimTy
1058 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1059 -- The evaldUnfolding makes it look that realWorld# is evaluated
1060 -- which in turn makes Simplify.interestingArg return True,
1061 -- which in turn makes INLINE things applied to realWorld# likely
1065 voidArgId -- :: State# RealWorld
1066 = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy
1070 %************************************************************************
1072 \subsection[PrelVals-error-related]{@error@ and friends; @trace@}
1074 %************************************************************************
1076 GHC randomly injects these into the code.
1078 @patError@ is just a version of @error@ for pattern-matching
1079 failures. It knows various ``codes'' which expand to longer
1080 strings---this saves space!
1082 @absentErr@ is a thing we put in for ``absent'' arguments. They jolly
1083 well shouldn't be yanked on, but if one is, then you will get a
1084 friendly message from @absentErr@ (rather than a totally random
1087 @parError@ is a special version of @error@ which the compiler does
1088 not know to be a bottoming Id. It is used in the @_par_@ and @_seq_@
1089 templates, but we don't ever expect to generate code for it.
1093 :: Id -- Should be of type (forall a. Addr# -> a)
1094 -- where Addr# points to a UTF8 encoded string
1095 -> Type -- The type to instantiate 'a'
1096 -> String -- The string to print
1099 mkRuntimeErrorApp err_id res_ty err_msg
1100 = mkApps (Var err_id) [Type res_ty, err_string]
1102 err_string = Lit (mkMachString err_msg)
1104 mkImpossibleExpr :: Type -> CoreExpr
1105 mkImpossibleExpr res_ty
1106 = mkRuntimeErrorApp rUNTIME_ERROR_ID res_ty "Impossible case alternative"
1108 rEC_SEL_ERROR_ID = mkRuntimeErrorId recSelErrorName
1109 rUNTIME_ERROR_ID = mkRuntimeErrorId runtimeErrorName
1110 iRREFUT_PAT_ERROR_ID = mkRuntimeErrorId irrefutPatErrorName
1111 rEC_CON_ERROR_ID = mkRuntimeErrorId recConErrorName
1112 pAT_ERROR_ID = mkRuntimeErrorId patErrorName
1113 nO_METHOD_BINDING_ERROR_ID = mkRuntimeErrorId noMethodBindingErrorName
1114 nON_EXHAUSTIVE_GUARDS_ERROR_ID = mkRuntimeErrorId nonExhaustiveGuardsErrorName
1116 -- The runtime error Ids take a UTF8-encoded string as argument
1118 mkRuntimeErrorId :: Name -> Id
1119 mkRuntimeErrorId name = pc_bottoming_Id name runtimeErrorTy
1121 runtimeErrorTy :: Type
1122 runtimeErrorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTy addrPrimTy openAlphaTy)
1126 eRROR_ID = pc_bottoming_Id errorName errorTy
1129 errorTy = mkSigmaTy [openAlphaTyVar] [] (mkFunTys [mkListTy charTy] openAlphaTy)
1130 -- Notice the openAlphaTyVar. It says that "error" can be applied
1131 -- to unboxed as well as boxed types. This is OK because it never
1132 -- returns, so the return type is irrelevant.
1136 %************************************************************************
1138 \subsection{Utilities}
1140 %************************************************************************
1143 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1144 pcMiscPrelId name ty info
1145 = mkVanillaGlobalWithInfo name ty info
1146 -- We lie and say the thing is imported; otherwise, we get into
1147 -- a mess with dependency analysis; e.g., core2stg may heave in
1148 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1149 -- being compiled, then it's just a matter of luck if the definition
1150 -- will be in "the right place" to be in scope.
1152 pc_bottoming_Id :: Name -> Type -> Id
1153 -- Function of arity 1, which diverges after being given one argument
1154 pc_bottoming_Id name ty
1155 = pcMiscPrelId name ty bottoming_info
1157 bottoming_info = vanillaIdInfo `setStrictnessInfo` Just strict_sig
1159 -- Make arity and strictness agree
1161 -- Do *not* mark them as NoCafRefs, because they can indeed have
1162 -- CAF refs. For example, pAT_ERROR_ID calls GHC.Err.untangle,
1163 -- which has some CAFs
1164 -- In due course we may arrange that these error-y things are
1165 -- regarded by the GC as permanently live, in which case we
1166 -- can give them NoCaf info. As it is, any function that calls
1167 -- any pc_bottoming_Id will itself have CafRefs, which bloats
1170 strict_sig = mkStrictSig (mkTopDmdType [evalDmd] BotRes)
1171 -- These "bottom" out, no matter what their arguments