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
16 mkDictFunId, mkDictFunTy, mkDefaultMethodId, mkDictSelId,
19 mkPrimOpId, mkFCallId, mkTickBoxOpId, mkBreakPointOpId,
21 mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
22 wrapFamInstBody, unwrapFamInstScrut,
23 mkUnpackCase, mkProductBox,
25 -- And some particular Ids; see below for why they are wired in
26 wiredInIds, ghcPrimIds,
27 unsafeCoerceName, unsafeCoerceId, realWorldPrimId,
28 voidArgId, nullAddrId, seqId, lazyId, lazyIdKey
31 #include "HsVersions.h"
40 import CoreUtils ( exprType, mkCoerce )
51 import Var ( Var, TyVar, mkCoVar, mkExportedLocalVar )
57 import BasicTypes hiding ( SuccessFlag(..) )
65 %************************************************************************
67 \subsection{Wired in Ids}
69 %************************************************************************
73 There are several reasons why an Id might appear in the wiredInIds:
75 (1) The ghcPrimIds are wired in because they can't be defined in
76 Haskell at all, although the can be defined in Core. They have
77 compulsory unfoldings, so they are always inlined and they have
78 no definition site. Their home module is GHC.Prim, so they
79 also have a description in primops.txt.pp, where they are called
82 (2) The 'error' function, eRROR_ID, is wired in because we don't yet have
83 a way to express in an interface file that the result type variable
84 is 'open'; that is can be unified with an unboxed type
86 [The interface file format now carry such information, but there's
87 no way yet of expressing at the definition site for these
88 error-reporting functions that they have an 'open'
89 result type. -- sof 1/99]
91 (3) Other error functions (rUNTIME_ERROR_ID) are wired in (a) because
92 the desugarer generates code that mentiones them directly, and
93 (b) for the same reason as eRROR_ID
95 (4) lazyId is wired in because the wired-in version overrides the
96 strictness of the version defined in GHC.Base
98 In cases (2-4), the function has a definition in a library module, and
99 can be called; but the wired-in version means that the details are
100 never read from that module's interface file; instead, the full definition
107 ++ errorIds -- Defined in MkCore
110 -- These Ids are exported from GHC.Prim
113 = [ -- These can't be defined in Haskell, but they have
114 -- perfectly reasonable unfoldings in Core
122 %************************************************************************
124 \subsection{Data constructors}
126 %************************************************************************
128 The wrapper for a constructor is an ordinary top-level binding that evaluates
129 any strict args, unboxes any args that are going to be flattened, and calls
132 We're going to build a constructor that looks like:
134 data (Data a, C b) => T a b = T1 !a !Int b
137 \d1::Data a, d2::C b ->
138 \p q r -> case p of { p ->
140 Con T1 [a,b] [p,q,r]}}
144 * d2 is thrown away --- a context in a data decl is used to make sure
145 one *could* construct dictionaries at the site the constructor
146 is used, but the dictionary isn't actually used.
148 * We have to check that we can construct Data dictionaries for
149 the types a and Int. Once we've done that we can throw d1 away too.
151 * We use (case p of q -> ...) to evaluate p, rather than "seq" because
152 all that matters is that the arguments are evaluated. "seq" is
153 very careful to preserve evaluation order, which we don't need
156 You might think that we could simply give constructors some strictness
157 info, like PrimOps, and let CoreToStg do the let-to-case transformation.
158 But we don't do that because in the case of primops and functions strictness
159 is a *property* not a *requirement*. In the case of constructors we need to
160 do something active to evaluate the argument.
162 Making an explicit case expression allows the simplifier to eliminate
163 it in the (common) case where the constructor arg is already evaluated.
165 Note [Wrappers for data instance tycons]
166 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
167 In the case of data instances, the wrapper also applies the coercion turning
168 the representation type into the family instance type to cast the result of
169 the wrapper. For example, consider the declarations
171 data family Map k :: * -> *
172 data instance Map (a, b) v = MapPair (Map a (Pair b v))
174 The tycon to which the datacon MapPair belongs gets a unique internal
175 name of the form :R123Map, and we call it the representation tycon.
176 In contrast, Map is the family tycon (accessible via
177 tyConFamInst_maybe). A coercion allows you to move between
178 representation and family type. It is accessible from :R123Map via
179 tyConFamilyCoercion_maybe and has kind
181 Co123Map a b v :: {Map (a, b) v ~ :R123Map a b v}
183 The wrapper and worker of MapPair get the types
186 $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v
187 $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v)
190 MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v
192 This coercion is conditionally applied by wrapFamInstBody.
194 It's a bit more complicated if the data instance is a GADT as well!
196 data instance T [a] where
197 T1 :: forall b. b -> T [Maybe b]
199 Hence we translate to
202 $WT1 :: forall b. b -> T [Maybe b]
203 $WT1 b v = T1 (Maybe b) b (Maybe b) v
204 `cast` sym (Co7T (Maybe b))
207 T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c
209 -- Coercion from family type to representation type
210 Co7T a :: T [a] ~ :R7T a
213 mkDataConIds :: Name -> Name -> DataCon -> DataConIds
214 mkDataConIds wrap_name wkr_name data_con
215 | isNewTyCon tycon -- Newtype, only has a worker
216 = DCIds Nothing nt_work_id
218 | any isBanged all_strict_marks -- Algebraic, needs wrapper
219 || not (null eq_spec) -- NB: LoadIface.ifaceDeclSubBndrs
220 || isFamInstTyCon tycon -- depends on this test
221 = DCIds (Just alg_wrap_id) wrk_id
223 | otherwise -- Algebraic, no wrapper
224 = DCIds Nothing wrk_id
226 (univ_tvs, ex_tvs, eq_spec,
227 eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
228 tycon = dataConTyCon data_con -- The representation TyCon (not family)
230 ----------- Worker (algebraic data types only) --------------
231 -- The *worker* for the data constructor is the function that
232 -- takes the representation arguments and builds the constructor.
233 wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
234 (dataConRepType data_con) wkr_info
236 wkr_arity = dataConRepArity data_con
237 wkr_info = noCafIdInfo
238 `setArityInfo` wkr_arity
239 `setStrictnessInfo` Just wkr_sig
240 `setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
243 wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
244 -- Note [Data-con worker strictness]
245 -- Notice that we do *not* say the worker is strict
246 -- even if the data constructor is declared strict
247 -- e.g. data T = MkT !(Int,Int)
248 -- Why? Because the *wrapper* is strict (and its unfolding has case
249 -- expresssions that do the evals) but the *worker* itself is not.
250 -- If we pretend it is strict then when we see
251 -- case x of y -> $wMkT y
252 -- the simplifier thinks that y is "sure to be evaluated" (because
253 -- $wMkT is strict) and drops the case. No, $wMkT is not strict.
255 -- When the simplifer sees a pattern
256 -- case e of MkT x -> ...
257 -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
258 -- but that's fine... dataConRepStrictness comes from the data con
259 -- not from the worker Id.
261 cpr_info | isProductTyCon tycon &&
264 wkr_arity <= mAX_CPR_SIZE = retCPR
266 -- RetCPR is only true for products that are real data types;
267 -- that is, not unboxed tuples or [non-recursive] newtypes
269 ----------- Workers for newtypes --------------
270 nt_work_id = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
271 nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
272 `setArityInfo` 1 -- Arity 1
273 `setUnfoldingInfo` newtype_unf
274 id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
275 newtype_unf = ASSERT2( isVanillaDataCon data_con &&
276 isSingleton orig_arg_tys, ppr data_con )
277 -- Note [Newtype datacons]
278 mkCompulsoryUnfolding $
279 mkLams wrap_tvs $ Lam id_arg1 $
280 wrapNewTypeBody tycon res_ty_args (Var id_arg1)
283 ----------- Wrapper --------------
284 -- We used to include the stupid theta in the wrapper's args
285 -- but now we don't. Instead the type checker just injects these
286 -- extra constraints where necessary.
287 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
288 res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
289 eq_tys = mkPredTys eq_theta
290 dict_tys = mkPredTys dict_theta
291 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
292 mkFunTys orig_arg_tys $ res_ty
293 -- NB: watch out here if you allow user-written equality
294 -- constraints in data constructor signatures
296 ----------- Wrappers for algebraic data types --------------
297 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
298 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
299 `setArityInfo` wrap_arity
300 -- It's important to specify the arity, so that partial
301 -- applications are treated as values
302 `setInlinePragInfo` alwaysInlinePragma
303 `setUnfoldingInfo` wrap_unf
304 `setStrictnessInfo` Just wrap_sig
306 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
307 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
308 arg_dmds = map mk_dmd all_strict_marks
309 mk_dmd str | isBanged str = evalDmd
310 | otherwise = lazyDmd
311 -- The Cpr info can be important inside INLINE rhss, where the
312 -- wrapper constructor isn't inlined.
313 -- And the argument strictness can be important too; we
314 -- may not inline a contructor when it is partially applied.
316 -- data W = C !Int !Int !Int
317 -- ...(let w = C x in ...(w p q)...)...
318 -- we want to see that w is strict in its two arguments
320 wrap_unf = mkInlineUnfolding (Just (length dict_args + length id_args)) wrap_rhs
321 wrap_rhs = mkLams wrap_tvs $
323 mkLams dict_args $ mkLams id_args $
324 foldr mk_case con_app
325 (zip (dict_args ++ id_args) all_strict_marks)
328 con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
329 Var wrk_id `mkTyApps` res_ty_args
331 -- Equality evidence:
332 `mkTyApps` map snd eq_spec
334 `mkVarApps` reverse rep_ids
336 (dict_args,i2) = mkLocals 1 dict_tys
337 (id_args,i3) = mkLocals i2 orig_arg_tys
339 (eq_args,_) = mkCoVarLocals i3 eq_tys
341 mkCoVarLocals i [] = ([],i)
342 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
343 y = mkCoVar (mkSysTvName (mkBuiltinUnique i)
348 :: (Id, HsBang) -- Arg, strictness
349 -> (Int -> [Id] -> CoreExpr) -- Body
350 -> Int -- Next rep arg id
351 -> [Id] -- Rep args so far, reversed
353 mk_case (arg,strict) body i rep_args
355 HsNoBang -> body i (arg:rep_args)
356 HsUnpack -> unboxProduct i (Var arg) (idType arg) the_body
358 the_body i con_args = body i (reverse con_args ++ rep_args)
359 _other -- HsUnpackFailed and HsStrict
360 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
361 | otherwise -> Case (Var arg) arg res_ty
362 [(DEFAULT,[], body i (arg:rep_args))]
364 mAX_CPR_SIZE :: Arity
366 -- We do not treat very big tuples as CPR-ish:
367 -- a) for a start we get into trouble because there aren't
368 -- "enough" unboxed tuple types (a tiresome restriction,
370 -- b) more importantly, big unboxed tuples get returned mainly
371 -- on the stack, and are often then allocated in the heap
372 -- by the caller. So doing CPR for them may in fact make
375 mkLocals :: Int -> [Type] -> ([Id], Int)
376 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
381 Note [Newtype datacons]
382 ~~~~~~~~~~~~~~~~~~~~~~~
383 The "data constructor" for a newtype should always be vanilla. At one
384 point this wasn't true, because the newtype arising from
387 newtype T:D a = D:D (C a)
388 so the data constructor for T:C had a single argument, namely the
389 predicate (C a). But now we treat that as an ordinary argument, not
390 part of the theta-type, so all is well.
393 %************************************************************************
395 \subsection{Dictionary selectors}
397 %************************************************************************
399 Selecting a field for a dictionary. If there is just one field, then
400 there's nothing to do.
402 Dictionary selectors may get nested forall-types. Thus:
405 op :: forall b. Ord b => a -> b -> b
407 Then the top-level type for op is
409 op :: forall a. Foo a =>
413 This is unlike ordinary record selectors, which have all the for-alls
414 at the outside. When dealing with classes it's very convenient to
415 recover the original type signature from the class op selector.
418 mkDictSelId :: Bool -- True <=> don't include the unfolding
419 -- Little point on imports without -O, because the
420 -- dictionary itself won't be visible
421 -> Name -- Name of one of the *value* selectors
422 -- (dictionary superclass or method)
424 mkDictSelId no_unf name clas
425 = mkGlobalId (ClassOpId clas) name sel_ty info
427 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
428 -- We can't just say (exprType rhs), because that would give a type
430 -- for a single-op class (after all, the selector is the identity)
431 -- But it's type must expose the representation of the dictionary
432 -- to get (say) C a -> (a -> a)
434 base_info = noCafIdInfo
436 `setStrictnessInfo` Just strict_sig
437 `setUnfoldingInfo` (if no_unf then noUnfolding
438 else mkImplicitUnfolding rhs)
439 -- In module where class op is defined, we must add
440 -- the unfolding, even though it'll never be inlined
441 -- becuase we use that to generate a top-level binding
444 info | new_tycon = base_info `setInlinePragInfo` alwaysInlinePragma
445 -- See Note [Single-method classes] for why alwaysInlinePragma
446 | otherwise = base_info `setSpecInfo` mkSpecInfo [rule]
447 `setInlinePragInfo` neverInlinePragma
448 -- Add a magic BuiltinRule, and never inline it
449 -- so that the rule is always available to fire.
450 -- See Note [ClassOp/DFun selection] in TcInstDcls
452 n_ty_args = length tyvars
454 -- This is the built-in rule that goes
455 -- op (dfT d1 d2) ---> opT d1 d2
456 rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
457 occNameFS (getOccName name)
459 , ru_nargs = n_ty_args + 1
460 , ru_try = dictSelRule val_index n_ty_args n_eq_args }
462 -- The strictness signature is of the form U(AAAVAAAA) -> T
463 -- where the V depends on which item we are selecting
464 -- It's worth giving one, so that absence info etc is generated
465 -- even if the selector isn't inlined
466 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
467 arg_dmd | new_tycon = evalDmd
468 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
471 tycon = classTyCon clas
472 new_tycon = isNewTyCon tycon
473 [data_con] = tyConDataCons tycon
474 tyvars = dataConUnivTyVars data_con
475 arg_tys = dataConRepArgTys data_con -- Includes the dictionary superclasses
476 eq_theta = dataConEqTheta data_con
477 n_eq_args = length eq_theta
479 -- 'index' is a 0-index into the *value* arguments of the dictionary
480 val_index = assoc "MkId.mkDictSelId" sel_index_prs name
481 sel_index_prs = map idName (classAllSelIds clas) `zip` [0..]
483 the_arg_id = arg_ids !! val_index
484 pred = mkClassPred clas (mkTyVarTys tyvars)
485 dict_id = mkTemplateLocal 1 $ mkPredTy pred
486 arg_ids = mkTemplateLocalsNum 2 arg_tys
487 eq_ids = map mkWildEvBinder eq_theta
489 rhs = mkLams tyvars (Lam dict_id rhs_body)
490 rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
491 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
492 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
494 dictSelRule :: Int -> Arity -> Arity
495 -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
496 -- Tries to persuade the argument to look like a constructor
497 -- application, using exprIsConApp_maybe, and then selects
499 -- sel_i t1..tk (D t1..tk op1 ... opm) = opi
501 dictSelRule val_index n_ty_args n_eq_args id_unf args
502 | (dict_arg : _) <- drop n_ty_args args
503 , Just (_, _, con_args) <- exprIsConApp_maybe id_unf dict_arg
504 , let val_args = drop n_eq_args con_args
505 = Just (val_args !! val_index)
511 %************************************************************************
515 %************************************************************************
518 -- unbox a product type...
519 -- we will recurse into newtypes, casting along the way, and unbox at the
520 -- first product data constructor we find. e.g.
522 -- data PairInt = PairInt Int Int
523 -- newtype S = MkS PairInt
526 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
527 -- ids, we get (modulo int passing)
529 -- case (e `cast` CoT) `cast` CoS of
530 -- PairInt a b -> body [a,b]
532 -- The Ints passed around are just for creating fresh locals
533 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
534 unboxProduct i arg arg_ty body
537 result = mkUnpackCase the_id arg con_args boxing_con rhs
538 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
539 ([the_id], i') = mkLocals i [arg_ty]
540 (con_args, i'') = mkLocals i' tys
541 rhs = body i'' con_args
543 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
544 -- (mkUnpackCase x e args Con body)
546 -- case (e `cast` ...) of bndr { Con args -> body }
548 -- the type of the bndr passed in is irrelevent
549 mkUnpackCase bndr arg unpk_args boxing_con body
550 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
552 (cast_arg, bndr_ty) = go (idType bndr) arg
554 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
555 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
556 = go (newTyConInstRhs tycon tycon_args)
557 (unwrapNewTypeBody tycon tycon_args arg)
558 | otherwise = (arg, ty)
561 reboxProduct :: [Unique] -- uniques to create new local binders
562 -> Type -- type of product to box
563 -> ([Unique], -- remaining uniques
564 CoreExpr, -- boxed product
565 [Id]) -- Ids being boxed into product
568 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
570 us' = dropList con_arg_tys us
572 arg_ids = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys
574 bind_rhs = mkProductBox arg_ids ty
577 (us', bind_rhs, arg_ids)
579 mkProductBox :: [Id] -> Type -> CoreExpr
580 mkProductBox arg_ids ty
583 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
586 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
587 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
588 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
590 wrap expr = wrapNewTypeBody tycon tycon_args expr
593 -- (mkReboxingAlt us con xs rhs) basically constructs the case
594 -- alternative (con, xs, rhs)
595 -- but it does the reboxing necessary to construct the *source*
596 -- arguments, xs, from the representation arguments ys.
598 -- data T = MkT !(Int,Int) Bool
600 -- mkReboxingAlt MkT [x,b] r
601 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
603 -- mkDataAlt should really be in DataCon, but it can't because
604 -- it manipulates CoreSyn.
607 :: [Unique] -- Uniques for the new Ids
609 -> [Var] -- Source-level args, including existential dicts
613 mkReboxingAlt us con args rhs
614 | not (any isMarkedUnboxed stricts)
615 = (DataAlt con, args, rhs)
619 (binds, args') = go args stricts us
621 (DataAlt con, args', mkLets binds rhs)
624 stricts = dataConExStricts con ++ dataConStrictMarks con
626 go [] _stricts _us = ([], [])
628 -- Type variable case
629 go (arg:args) stricts us
631 = let (binds, args') = go args stricts us
632 in (binds, arg:args')
634 -- Term variable case
635 go (arg:args) (str:stricts) us
636 | isMarkedUnboxed str
638 let (binds, unpacked_args') = go args stricts us'
639 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
641 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
643 = let (binds, args') = go args stricts us
644 in (binds, arg:args')
645 go (_ : _) [] _ = panic "mkReboxingAlt"
649 %************************************************************************
651 Wrapping and unwrapping newtypes and type families
653 %************************************************************************
656 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
657 -- The wrapper for the data constructor for a newtype looks like this:
658 -- newtype T a = MkT (a,Int)
659 -- MkT :: forall a. (a,Int) -> T a
660 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
661 -- where CoT is the coercion TyCon assoicated with the newtype
663 -- The call (wrapNewTypeBody T [a] e) returns the
664 -- body of the wrapper, namely
665 -- e `cast` (CoT [a])
667 -- If a coercion constructor is provided in the newtype, then we use
668 -- it, otherwise the wrap/unwrap are both no-ops
670 -- If the we are dealing with a newtype *instance*, we have a second coercion
671 -- identifying the family instance with the constructor of the newtype
672 -- instance. This coercion is applied in any case (ie, composed with the
673 -- coercion constructor of the newtype or applied by itself).
675 wrapNewTypeBody tycon args result_expr
676 = wrapFamInstBody tycon args inner
679 | Just co_con <- newTyConCo_maybe tycon
680 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
684 -- When unwrapping, we do *not* apply any family coercion, because this will
685 -- be done via a CoPat by the type checker. We have to do it this way as
686 -- computing the right type arguments for the coercion requires more than just
687 -- a spliting operation (cf, TcPat.tcConPat).
689 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
690 unwrapNewTypeBody tycon args result_expr
691 | Just co_con <- newTyConCo_maybe tycon
692 = mkCoerce (mkTyConApp co_con args) result_expr
696 -- If the type constructor is a representation type of a data instance, wrap
697 -- the expression into a cast adjusting the expression type, which is an
698 -- instance of the representation type, to the corresponding instance of the
699 -- family instance type.
700 -- See Note [Wrappers for data instance tycons]
701 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
702 wrapFamInstBody tycon args body
703 | Just co_con <- tyConFamilyCoercion_maybe tycon
704 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
708 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
709 unwrapFamInstScrut tycon args scrut
710 | Just co_con <- tyConFamilyCoercion_maybe tycon
711 = mkCoerce (mkTyConApp co_con args) scrut
717 %************************************************************************
719 \subsection{Primitive operations}
721 %************************************************************************
724 mkPrimOpId :: PrimOp -> Id
728 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
729 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
730 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
731 (mkPrimOpIdUnique (primOpTag prim_op))
733 id = mkGlobalId (PrimOpId prim_op) name ty info
736 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
738 `setStrictnessInfo` Just strict_sig
740 -- For each ccall we manufacture a separate CCallOpId, giving it
741 -- a fresh unique, a type that is correct for this particular ccall,
742 -- and a CCall structure that gives the correct details about calling
745 -- The *name* of this Id is a local name whose OccName gives the full
746 -- details of the ccall, type and all. This means that the interface
747 -- file reader can reconstruct a suitable Id
749 mkFCallId :: Unique -> ForeignCall -> Type -> Id
750 mkFCallId uniq fcall ty
751 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
752 -- A CCallOpId should have no free type variables;
753 -- when doing substitutions won't substitute over it
754 mkGlobalId (FCallId fcall) name ty info
756 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
757 -- The "occurrence name" of a ccall is the full info about the
758 -- ccall; it is encoded, but may have embedded spaces etc!
760 name = mkFCallName uniq occ_str
764 `setStrictnessInfo` Just strict_sig
766 (_, tau) = tcSplitForAllTys ty
767 (arg_tys, _) = tcSplitFunTys tau
768 arity = length arg_tys
769 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
771 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
772 -- except for the type:
774 -- a plain HPC tick box has type (State# RealWorld)
775 -- a breakpoint Id has type forall a.a
777 -- The breakpoint Id will be applied to a list of arbitrary free variables,
778 -- which is why it needs a polymorphic type.
780 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
781 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
783 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
784 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
785 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
787 mkTickBox' :: Unique -> Module -> TickBoxId -> Type -> Id
788 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
790 tickbox = TickBox mod ix
791 occ_str = showSDoc (braces (ppr tickbox))
792 name = mkTickBoxOpName uniq occ_str
797 %************************************************************************
799 \subsection{DictFuns and default methods}
801 %************************************************************************
803 Important notes about dict funs and default methods
804 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
805 Dict funs and default methods are *not* ImplicitIds. Their definition
806 involves user-written code, so we can't figure out their strictness etc
807 based on fixed info, as we can for constructors and record selectors (say).
809 We build them as LocalIds, but with External Names. This ensures that
810 they are taken to account by free-variable finding and dependency
811 analysis (e.g. CoreFVs.exprFreeVars).
813 Why shouldn't they be bound as GlobalIds? Because, in particular, if
814 they are globals, the specialiser floats dict uses above their defns,
815 which prevents good simplifications happening. Also the strictness
816 analyser treats a occurrence of a GlobalId as imported and assumes it
817 contains strictness in its IdInfo, which isn't true if the thing is
818 bound in the same module as the occurrence.
820 It's OK for dfuns to be LocalIds, because we form the instance-env to
821 pass on to the next module (md_insts) in CoreTidy, afer tidying
822 and globalising the top-level Ids.
824 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
825 that they aren't discarded by the occurrence analyser.
828 mkDefaultMethodId :: Id -- Selector Id
829 -> Name -- Default method name
830 -> Id -- Default method Id
831 mkDefaultMethodId sel_id dm_name = mkExportedLocalId dm_name (idType sel_id)
833 mkDictFunId :: Name -- Name to use for the dict fun;
839 -- Implements the DFun Superclass Invariant (see TcInstDcls)
841 mkDictFunId dfun_name tvs theta clas tys
842 = mkExportedLocalVar (DFunId n_silent is_nt)
847 is_nt = isNewTyCon (classTyCon clas)
848 (n_silent, dfun_ty) = mkDictFunTy tvs theta clas tys
850 mkDictFunTy :: [TyVar] -> ThetaType -> Class -> [Type] -> (Int, Type)
851 mkDictFunTy tvs theta clas tys
852 = (length silent_theta, dfun_ty)
854 dfun_ty = mkSigmaTy tvs (silent_theta ++ theta) (mkDictTy clas tys)
855 silent_theta = filterOut discard $
856 substTheta (zipTopTvSubst (classTyVars clas) tys)
858 -- See Note [Silent Superclass Arguments]
859 discard pred = isEmptyVarSet (tyVarsOfPred pred)
860 || any (`tcEqPred` pred) theta
861 -- See the DFun Superclass Invariant in TcInstDcls
865 %************************************************************************
867 \subsection{Un-definable}
869 %************************************************************************
871 These Ids can't be defined in Haskell. They could be defined in
872 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
873 ensure that they were definitely, definitely inlined, because there is
874 no curried identifier for them. That's what mkCompulsoryUnfolding
875 does. If we had a way to get a compulsory unfolding from an interface
876 file, we could do that, but we don't right now.
878 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
879 just gets expanded into a type coercion wherever it occurs. Hence we
880 add it as a built-in Id with an unfolding here.
882 The type variables we use here are "open" type variables: this means
883 they can unify with both unlifted and lifted types. Hence we provide
884 another gun with which to shoot yourself in the foot.
887 lazyIdName, unsafeCoerceName, nullAddrName, seqName, realWorldName :: Name
888 unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
889 nullAddrName = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#") nullAddrIdKey nullAddrId
890 seqName = mkWiredInIdName gHC_PRIM (fsLit "seq") seqIdKey seqId
891 realWorldName = mkWiredInIdName gHC_PRIM (fsLit "realWorld#") realWorldPrimIdKey realWorldPrimId
892 lazyIdName = mkWiredInIdName gHC_BASE (fsLit "lazy") lazyIdKey lazyId
896 ------------------------------------------------
897 -- unsafeCoerce# :: forall a b. a -> b
900 = pcMiscPrelId unsafeCoerceName ty info
902 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
905 ty = mkForAllTys [argAlphaTyVar,openBetaTyVar]
906 (mkFunTy argAlphaTy openBetaTy)
907 [x] = mkTemplateLocals [argAlphaTy]
908 rhs = mkLams [argAlphaTyVar,openBetaTyVar,x] $
909 Cast (Var x) (mkUnsafeCoercion argAlphaTy openBetaTy)
911 ------------------------------------------------
913 -- nullAddr# :: Addr#
914 -- The reason is is here is because we don't provide
915 -- a way to write this literal in Haskell.
916 nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
918 info = noCafIdInfo `setUnfoldingInfo`
919 mkCompulsoryUnfolding (Lit nullAddrLit)
921 ------------------------------------------------
922 seqId :: Id -- See Note [seqId magic]
923 seqId = pcMiscPrelId seqName ty info
925 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
926 `setSpecInfo` mkSpecInfo [seq_cast_rule]
929 ty = mkForAllTys [alphaTyVar,argBetaTyVar]
930 (mkFunTy alphaTy (mkFunTy argBetaTy argBetaTy))
931 [x,y] = mkTemplateLocals [alphaTy, argBetaTy]
932 rhs = mkLams [alphaTyVar,argBetaTyVar,x,y] (Case (Var x) x argBetaTy [(DEFAULT, [], Var y)])
934 -- See Note [Built-in RULES for seq]
935 seq_cast_rule = BuiltinRule { ru_name = fsLit "seq of cast"
938 , ru_try = match_seq_of_cast
941 match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
942 -- See Note [Built-in RULES for seq]
943 match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
944 = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
946 match_seq_of_cast _ _ = Nothing
948 ------------------------------------------------
949 lazyId :: Id -- See Note [lazyId magic]
950 lazyId = pcMiscPrelId lazyIdName ty info
953 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
958 'GHC.Prim.seq' is special in several ways.
960 a) Its second arg can have an unboxed type
963 b) Its fixity is set in LoadIface.ghcPrimIface
965 c) It has quite a bit of desugaring magic.
966 See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3)
968 d) There is some special rule handing: Note [User-defined RULES for seq]
970 e) See Note [Typing rule for seq] in TcExpr.
972 Note [User-defined RULES for seq]
973 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
974 Roman found situations where he had
976 where he knew that f (which was strict in n) would terminate if n did.
977 Notice that the result of (f n) is discarded. So it makes sense to
981 Rather than attempt some general analysis to support this, I've added
982 enough support that you can do this using a rewrite rule:
984 RULE "f/seq" forall n. seq (f n) e = seq n e
986 You write that rule. When GHC sees a case expression that discards
987 its result, it mentally transforms it to a call to 'seq' and looks for
988 a RULE. (This is done in Simplify.rebuildCase.) As usual, the
989 correctness of the rule is up to you.
991 To make this work, we need to be careful that the magical desugaring
992 done in Note [seqId magic] item (c) is *not* done on the LHS of a rule.
993 Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs.
995 Note [Built-in RULES for seq]
996 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
997 We also have the following built-in rule for seq
999 seq (x `cast` co) y = seq x y
1001 This eliminates unnecessary casts and also allows other seq rules to
1002 match more often. Notably,
1004 seq (f x `cast` co) y --> seq (f x) y
1006 and now a user-defined rule for seq (see Note [User-defined RULES for seq])
1012 lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1014 Used to lazify pseq: pseq a b = a `seq` lazy b
1016 Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1017 not from GHC.Base.hi. This is important, because the strictness
1018 analyser will spot it as strict!
1020 Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep.
1021 It's very important to do this inlining *after* unfoldings are exposed
1022 in the interface file. Otherwise, the unfolding for (say) pseq in the
1023 interface file will not mention 'lazy', so if we inline 'pseq' we'll totally
1024 miss the very thing that 'lazy' was there for in the first place.
1025 See Trac #3259 for a real world example.
1027 lazyId is defined in GHC.Base, so we don't *have* to inline it. If it
1028 appears un-applied, we'll end up just calling it.
1030 -------------------------------------------------------------
1031 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1032 nasty as-is, change it back to a literal (@Literal@).
1034 voidArgId is a Local Id used simply as an argument in functions
1035 where we just want an arg to avoid having a thunk of unlifted type.
1037 x = \ void :: State# RealWorld -> (# p, q #)
1039 This comes up in strictness analysis
1042 realWorldPrimId :: Id
1043 realWorldPrimId -- :: State# RealWorld
1044 = pcMiscPrelId realWorldName realWorldStatePrimTy
1045 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1046 -- The evaldUnfolding makes it look that realWorld# is evaluated
1047 -- which in turn makes Simplify.interestingArg return True,
1048 -- which in turn makes INLINE things applied to realWorld# likely
1052 voidArgId -- :: State# RealWorld
1053 = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy
1058 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1059 pcMiscPrelId name ty info
1060 = mkVanillaGlobalWithInfo name ty info
1061 -- We lie and say the thing is imported; otherwise, we get into
1062 -- a mess with dependency analysis; e.g., core2stg may heave in
1063 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1064 -- being compiled, then it's just a matter of luck if the definition
1065 -- will be in "the right place" to be in scope.