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 `setInlinePragInfo` alwaysInlinePragma
274 `setUnfoldingInfo` newtype_unf
275 id_arg1 = mkTemplateLocal 1 (head orig_arg_tys)
276 newtype_unf = ASSERT2( isVanillaDataCon data_con &&
277 isSingleton orig_arg_tys, ppr data_con )
278 -- Note [Newtype datacons]
279 mkCompulsoryUnfolding $
280 mkLams wrap_tvs $ Lam id_arg1 $
281 wrapNewTypeBody tycon res_ty_args (Var id_arg1)
284 ----------- Wrapper --------------
285 -- We used to include the stupid theta in the wrapper's args
286 -- but now we don't. Instead the type checker just injects these
287 -- extra constraints where necessary.
288 wrap_tvs = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
289 res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
290 eq_tys = mkPredTys eq_theta
291 dict_tys = mkPredTys dict_theta
292 wrap_ty = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
293 mkFunTys orig_arg_tys $ res_ty
294 -- NB: watch out here if you allow user-written equality
295 -- constraints in data constructor signatures
297 ----------- Wrappers for algebraic data types --------------
298 alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
299 alg_wrap_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
300 `setArityInfo` wrap_arity
301 -- It's important to specify the arity, so that partial
302 -- applications are treated as values
303 `setInlinePragInfo` alwaysInlinePragma
304 `setUnfoldingInfo` wrap_unf
305 `setStrictnessInfo` Just wrap_sig
307 all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
308 wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
309 arg_dmds = map mk_dmd all_strict_marks
310 mk_dmd str | isBanged str = evalDmd
311 | otherwise = lazyDmd
312 -- The Cpr info can be important inside INLINE rhss, where the
313 -- wrapper constructor isn't inlined.
314 -- And the argument strictness can be important too; we
315 -- may not inline a contructor when it is partially applied.
317 -- data W = C !Int !Int !Int
318 -- ...(let w = C x in ...(w p q)...)...
319 -- we want to see that w is strict in its two arguments
321 wrap_unf = mkInlineUnfolding (Just (length dict_args + length id_args)) wrap_rhs
322 wrap_rhs = mkLams wrap_tvs $
324 mkLams dict_args $ mkLams id_args $
325 foldr mk_case con_app
326 (zip (dict_args ++ id_args) all_strict_marks)
329 con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
330 Var wrk_id `mkTyApps` res_ty_args
332 -- Equality evidence:
333 `mkTyApps` map snd eq_spec
335 `mkVarApps` reverse rep_ids
337 (dict_args,i2) = mkLocals 1 dict_tys
338 (id_args,i3) = mkLocals i2 orig_arg_tys
340 (eq_args,_) = mkCoVarLocals i3 eq_tys
342 mkCoVarLocals i [] = ([],i)
343 mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
344 y = mkCoVar (mkSysTvName (mkBuiltinUnique i)
349 :: (Id, HsBang) -- Arg, strictness
350 -> (Int -> [Id] -> CoreExpr) -- Body
351 -> Int -- Next rep arg id
352 -> [Id] -- Rep args so far, reversed
354 mk_case (arg,strict) body i rep_args
356 HsNoBang -> body i (arg:rep_args)
357 HsUnpack -> unboxProduct i (Var arg) (idType arg) the_body
359 the_body i con_args = body i (reverse con_args ++ rep_args)
360 _other -- HsUnpackFailed and HsStrict
361 | isUnLiftedType (idType arg) -> body i (arg:rep_args)
362 | otherwise -> Case (Var arg) arg res_ty
363 [(DEFAULT,[], body i (arg:rep_args))]
365 mAX_CPR_SIZE :: Arity
367 -- We do not treat very big tuples as CPR-ish:
368 -- a) for a start we get into trouble because there aren't
369 -- "enough" unboxed tuple types (a tiresome restriction,
371 -- b) more importantly, big unboxed tuples get returned mainly
372 -- on the stack, and are often then allocated in the heap
373 -- by the caller. So doing CPR for them may in fact make
376 mkLocals :: Int -> [Type] -> ([Id], Int)
377 mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
382 Note [Newtype datacons]
383 ~~~~~~~~~~~~~~~~~~~~~~~
384 The "data constructor" for a newtype should always be vanilla. At one
385 point this wasn't true, because the newtype arising from
388 newtype T:D a = D:D (C a)
389 so the data constructor for T:C had a single argument, namely the
390 predicate (C a). But now we treat that as an ordinary argument, not
391 part of the theta-type, so all is well.
394 %************************************************************************
396 \subsection{Dictionary selectors}
398 %************************************************************************
400 Selecting a field for a dictionary. If there is just one field, then
401 there's nothing to do.
403 Dictionary selectors may get nested forall-types. Thus:
406 op :: forall b. Ord b => a -> b -> b
408 Then the top-level type for op is
410 op :: forall a. Foo a =>
414 This is unlike ordinary record selectors, which have all the for-alls
415 at the outside. When dealing with classes it's very convenient to
416 recover the original type signature from the class op selector.
419 mkDictSelId :: Bool -- True <=> don't include the unfolding
420 -- Little point on imports without -O, because the
421 -- dictionary itself won't be visible
422 -> Name -- Name of one of the *value* selectors
423 -- (dictionary superclass or method)
425 mkDictSelId no_unf name clas
426 = mkGlobalId (ClassOpId clas) name sel_ty info
428 sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
429 -- We can't just say (exprType rhs), because that would give a type
431 -- for a single-op class (after all, the selector is the identity)
432 -- But it's type must expose the representation of the dictionary
433 -- to get (say) C a -> (a -> a)
435 base_info = noCafIdInfo
437 `setStrictnessInfo` Just strict_sig
438 `setUnfoldingInfo` (if no_unf then noUnfolding
439 else mkImplicitUnfolding rhs)
440 -- In module where class op is defined, we must add
441 -- the unfolding, even though it'll never be inlined
442 -- becuase we use that to generate a top-level binding
445 info | new_tycon = base_info `setInlinePragInfo` alwaysInlinePragma
446 -- See Note [Single-method classes] for why alwaysInlinePragma
447 | otherwise = base_info `setSpecInfo` mkSpecInfo [rule]
448 `setInlinePragInfo` neverInlinePragma
449 -- Add a magic BuiltinRule, and never inline it
450 -- so that the rule is always available to fire.
451 -- See Note [ClassOp/DFun selection] in TcInstDcls
453 n_ty_args = length tyvars
455 -- This is the built-in rule that goes
456 -- op (dfT d1 d2) ---> opT d1 d2
457 rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
458 occNameFS (getOccName name)
460 , ru_nargs = n_ty_args + 1
461 , ru_try = dictSelRule val_index n_ty_args n_eq_args }
463 -- The strictness signature is of the form U(AAAVAAAA) -> T
464 -- where the V depends on which item we are selecting
465 -- It's worth giving one, so that absence info etc is generated
466 -- even if the selector isn't inlined
467 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
468 arg_dmd | new_tycon = evalDmd
469 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
472 tycon = classTyCon clas
473 new_tycon = isNewTyCon tycon
474 [data_con] = tyConDataCons tycon
475 tyvars = dataConUnivTyVars data_con
476 arg_tys = dataConRepArgTys data_con -- Includes the dictionary superclasses
477 eq_theta = dataConEqTheta data_con
478 n_eq_args = length eq_theta
480 -- 'index' is a 0-index into the *value* arguments of the dictionary
481 val_index = assoc "MkId.mkDictSelId" sel_index_prs name
482 sel_index_prs = map idName (classAllSelIds clas) `zip` [0..]
484 the_arg_id = arg_ids !! val_index
485 pred = mkClassPred clas (mkTyVarTys tyvars)
486 dict_id = mkTemplateLocal 1 $ mkPredTy pred
487 arg_ids = mkTemplateLocalsNum 2 arg_tys
488 eq_ids = map mkWildEvBinder eq_theta
490 rhs = mkLams tyvars (Lam dict_id rhs_body)
491 rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
492 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
493 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
495 dictSelRule :: Int -> Arity -> Arity
496 -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
497 -- Tries to persuade the argument to look like a constructor
498 -- application, using exprIsConApp_maybe, and then selects
500 -- sel_i t1..tk (D t1..tk op1 ... opm) = opi
502 dictSelRule val_index n_ty_args n_eq_args id_unf args
503 | (dict_arg : _) <- drop n_ty_args args
504 , Just (_, _, con_args) <- exprIsConApp_maybe id_unf dict_arg
505 , let val_args = drop n_eq_args con_args
506 = Just (val_args !! val_index)
512 %************************************************************************
516 %************************************************************************
519 -- unbox a product type...
520 -- we will recurse into newtypes, casting along the way, and unbox at the
521 -- first product data constructor we find. e.g.
523 -- data PairInt = PairInt Int Int
524 -- newtype S = MkS PairInt
527 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
528 -- ids, we get (modulo int passing)
530 -- case (e `cast` CoT) `cast` CoS of
531 -- PairInt a b -> body [a,b]
533 -- The Ints passed around are just for creating fresh locals
534 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
535 unboxProduct i arg arg_ty body
538 result = mkUnpackCase the_id arg con_args boxing_con rhs
539 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
540 ([the_id], i') = mkLocals i [arg_ty]
541 (con_args, i'') = mkLocals i' tys
542 rhs = body i'' con_args
544 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
545 -- (mkUnpackCase x e args Con body)
547 -- case (e `cast` ...) of bndr { Con args -> body }
549 -- the type of the bndr passed in is irrelevent
550 mkUnpackCase bndr arg unpk_args boxing_con body
551 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
553 (cast_arg, bndr_ty) = go (idType bndr) arg
555 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
556 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
557 = go (newTyConInstRhs tycon tycon_args)
558 (unwrapNewTypeBody tycon tycon_args arg)
559 | otherwise = (arg, ty)
562 reboxProduct :: [Unique] -- uniques to create new local binders
563 -> Type -- type of product to box
564 -> ([Unique], -- remaining uniques
565 CoreExpr, -- boxed product
566 [Id]) -- Ids being boxed into product
569 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
571 us' = dropList con_arg_tys us
573 arg_ids = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys
575 bind_rhs = mkProductBox arg_ids ty
578 (us', bind_rhs, arg_ids)
580 mkProductBox :: [Id] -> Type -> CoreExpr
581 mkProductBox arg_ids ty
584 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
587 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
588 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
589 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
591 wrap expr = wrapNewTypeBody tycon tycon_args expr
594 -- (mkReboxingAlt us con xs rhs) basically constructs the case
595 -- alternative (con, xs, rhs)
596 -- but it does the reboxing necessary to construct the *source*
597 -- arguments, xs, from the representation arguments ys.
599 -- data T = MkT !(Int,Int) Bool
601 -- mkReboxingAlt MkT [x,b] r
602 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
604 -- mkDataAlt should really be in DataCon, but it can't because
605 -- it manipulates CoreSyn.
608 :: [Unique] -- Uniques for the new Ids
610 -> [Var] -- Source-level args, including existential dicts
614 mkReboxingAlt us con args rhs
615 | not (any isMarkedUnboxed stricts)
616 = (DataAlt con, args, rhs)
620 (binds, args') = go args stricts us
622 (DataAlt con, args', mkLets binds rhs)
625 stricts = dataConExStricts con ++ dataConStrictMarks con
627 go [] _stricts _us = ([], [])
629 -- Type variable case
630 go (arg:args) stricts us
632 = let (binds, args') = go args stricts us
633 in (binds, arg:args')
635 -- Term variable case
636 go (arg:args) (str:stricts) us
637 | isMarkedUnboxed str
639 let (binds, unpacked_args') = go args stricts us'
640 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
642 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
644 = let (binds, args') = go args stricts us
645 in (binds, arg:args')
646 go (_ : _) [] _ = panic "mkReboxingAlt"
650 %************************************************************************
652 Wrapping and unwrapping newtypes and type families
654 %************************************************************************
657 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
658 -- The wrapper for the data constructor for a newtype looks like this:
659 -- newtype T a = MkT (a,Int)
660 -- MkT :: forall a. (a,Int) -> T a
661 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
662 -- where CoT is the coercion TyCon assoicated with the newtype
664 -- The call (wrapNewTypeBody T [a] e) returns the
665 -- body of the wrapper, namely
666 -- e `cast` (CoT [a])
668 -- If a coercion constructor is provided in the newtype, then we use
669 -- it, otherwise the wrap/unwrap are both no-ops
671 -- If the we are dealing with a newtype *instance*, we have a second coercion
672 -- identifying the family instance with the constructor of the newtype
673 -- instance. This coercion is applied in any case (ie, composed with the
674 -- coercion constructor of the newtype or applied by itself).
676 wrapNewTypeBody tycon args result_expr
677 = wrapFamInstBody tycon args inner
680 | Just co_con <- newTyConCo_maybe tycon
681 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
685 -- When unwrapping, we do *not* apply any family coercion, because this will
686 -- be done via a CoPat by the type checker. We have to do it this way as
687 -- computing the right type arguments for the coercion requires more than just
688 -- a spliting operation (cf, TcPat.tcConPat).
690 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
691 unwrapNewTypeBody tycon args result_expr
692 | Just co_con <- newTyConCo_maybe tycon
693 = mkCoerce (mkTyConApp co_con args) result_expr
697 -- If the type constructor is a representation type of a data instance, wrap
698 -- the expression into a cast adjusting the expression type, which is an
699 -- instance of the representation type, to the corresponding instance of the
700 -- family instance type.
701 -- See Note [Wrappers for data instance tycons]
702 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
703 wrapFamInstBody tycon args body
704 | Just co_con <- tyConFamilyCoercion_maybe tycon
705 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
709 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
710 unwrapFamInstScrut tycon args scrut
711 | Just co_con <- tyConFamilyCoercion_maybe tycon
712 = mkCoerce (mkTyConApp co_con args) scrut
718 %************************************************************************
720 \subsection{Primitive operations}
722 %************************************************************************
725 mkPrimOpId :: PrimOp -> Id
729 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
730 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
731 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
732 (mkPrimOpIdUnique (primOpTag prim_op))
734 id = mkGlobalId (PrimOpId prim_op) name ty info
737 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
739 `setStrictnessInfo` Just strict_sig
741 -- For each ccall we manufacture a separate CCallOpId, giving it
742 -- a fresh unique, a type that is correct for this particular ccall,
743 -- and a CCall structure that gives the correct details about calling
746 -- The *name* of this Id is a local name whose OccName gives the full
747 -- details of the ccall, type and all. This means that the interface
748 -- file reader can reconstruct a suitable Id
750 mkFCallId :: Unique -> ForeignCall -> Type -> Id
751 mkFCallId uniq fcall ty
752 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
753 -- A CCallOpId should have no free type variables;
754 -- when doing substitutions won't substitute over it
755 mkGlobalId (FCallId fcall) name ty info
757 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
758 -- The "occurrence name" of a ccall is the full info about the
759 -- ccall; it is encoded, but may have embedded spaces etc!
761 name = mkFCallName uniq occ_str
765 `setStrictnessInfo` Just strict_sig
767 (_, tau) = tcSplitForAllTys ty
768 (arg_tys, _) = tcSplitFunTys tau
769 arity = length arg_tys
770 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
772 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
773 -- except for the type:
775 -- a plain HPC tick box has type (State# RealWorld)
776 -- a breakpoint Id has type forall a.a
778 -- The breakpoint Id will be applied to a list of arbitrary free variables,
779 -- which is why it needs a polymorphic type.
781 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
782 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
784 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
785 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
786 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
788 mkTickBox' :: Unique -> Module -> TickBoxId -> Type -> Id
789 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
791 tickbox = TickBox mod ix
792 occ_str = showSDoc (braces (ppr tickbox))
793 name = mkTickBoxOpName uniq occ_str
798 %************************************************************************
800 \subsection{DictFuns and default methods}
802 %************************************************************************
804 Important notes about dict funs and default methods
805 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
806 Dict funs and default methods are *not* ImplicitIds. Their definition
807 involves user-written code, so we can't figure out their strictness etc
808 based on fixed info, as we can for constructors and record selectors (say).
810 We build them as LocalIds, but with External Names. This ensures that
811 they are taken to account by free-variable finding and dependency
812 analysis (e.g. CoreFVs.exprFreeVars).
814 Why shouldn't they be bound as GlobalIds? Because, in particular, if
815 they are globals, the specialiser floats dict uses above their defns,
816 which prevents good simplifications happening. Also the strictness
817 analyser treats a occurrence of a GlobalId as imported and assumes it
818 contains strictness in its IdInfo, which isn't true if the thing is
819 bound in the same module as the occurrence.
821 It's OK for dfuns to be LocalIds, because we form the instance-env to
822 pass on to the next module (md_insts) in CoreTidy, afer tidying
823 and globalising the top-level Ids.
825 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
826 that they aren't discarded by the occurrence analyser.
829 mkDefaultMethodId :: Id -- Selector Id
830 -> Name -- Default method name
831 -> Id -- Default method Id
832 mkDefaultMethodId sel_id dm_name = mkExportedLocalId dm_name (idType sel_id)
834 mkDictFunId :: Name -- Name to use for the dict fun;
840 -- Implements the DFun Superclass Invariant (see TcInstDcls)
842 mkDictFunId dfun_name tvs theta clas tys
843 = mkExportedLocalVar (DFunId n_silent is_nt)
848 is_nt = isNewTyCon (classTyCon clas)
849 (n_silent, dfun_ty) = mkDictFunTy tvs theta clas tys
851 mkDictFunTy :: [TyVar] -> ThetaType -> Class -> [Type] -> (Int, Type)
852 mkDictFunTy tvs theta clas tys
853 = (length silent_theta, dfun_ty)
855 dfun_ty = mkSigmaTy tvs (silent_theta ++ theta) (mkDictTy clas tys)
856 silent_theta = filterOut discard $
857 substTheta (zipTopTvSubst (classTyVars clas) tys)
859 -- See Note [Silent Superclass Arguments]
860 discard pred = isEmptyVarSet (tyVarsOfPred pred)
861 || any (`tcEqPred` pred) theta
862 -- See the DFun Superclass Invariant in TcInstDcls
866 %************************************************************************
868 \subsection{Un-definable}
870 %************************************************************************
872 These Ids can't be defined in Haskell. They could be defined in
873 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
874 ensure that they were definitely, definitely inlined, because there is
875 no curried identifier for them. That's what mkCompulsoryUnfolding
876 does. If we had a way to get a compulsory unfolding from an interface
877 file, we could do that, but we don't right now.
879 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
880 just gets expanded into a type coercion wherever it occurs. Hence we
881 add it as a built-in Id with an unfolding here.
883 The type variables we use here are "open" type variables: this means
884 they can unify with both unlifted and lifted types. Hence we provide
885 another gun with which to shoot yourself in the foot.
888 lazyIdName, unsafeCoerceName, nullAddrName, seqName, realWorldName :: Name
889 unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
890 nullAddrName = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#") nullAddrIdKey nullAddrId
891 seqName = mkWiredInIdName gHC_PRIM (fsLit "seq") seqIdKey seqId
892 realWorldName = mkWiredInIdName gHC_PRIM (fsLit "realWorld#") realWorldPrimIdKey realWorldPrimId
893 lazyIdName = mkWiredInIdName gHC_BASE (fsLit "lazy") lazyIdKey lazyId
897 ------------------------------------------------
898 -- unsafeCoerce# :: forall a b. a -> b
901 = pcMiscPrelId unsafeCoerceName ty info
903 info = noCafIdInfo `setInlinePragInfo` alwaysInlinePragma
904 `setUnfoldingInfo` mkCompulsoryUnfolding rhs
907 ty = mkForAllTys [argAlphaTyVar,openBetaTyVar]
908 (mkFunTy argAlphaTy openBetaTy)
909 [x] = mkTemplateLocals [argAlphaTy]
910 rhs = mkLams [argAlphaTyVar,openBetaTyVar,x] $
911 Cast (Var x) (mkUnsafeCoercion argAlphaTy openBetaTy)
913 ------------------------------------------------
915 -- nullAddr# :: Addr#
916 -- The reason is is here is because we don't provide
917 -- a way to write this literal in Haskell.
918 nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
920 info = noCafIdInfo `setInlinePragInfo` alwaysInlinePragma
921 `setUnfoldingInfo` mkCompulsoryUnfolding (Lit nullAddrLit)
923 ------------------------------------------------
924 seqId :: Id -- See Note [seqId magic]
925 seqId = pcMiscPrelId seqName ty info
927 info = noCafIdInfo `setInlinePragInfo` alwaysInlinePragma
928 `setUnfoldingInfo` mkCompulsoryUnfolding rhs
929 `setSpecInfo` mkSpecInfo [seq_cast_rule]
932 ty = mkForAllTys [alphaTyVar,argBetaTyVar]
933 (mkFunTy alphaTy (mkFunTy argBetaTy argBetaTy))
934 [x,y] = mkTemplateLocals [alphaTy, argBetaTy]
935 rhs = mkLams [alphaTyVar,argBetaTyVar,x,y] (Case (Var x) x argBetaTy [(DEFAULT, [], Var y)])
937 -- See Note [Built-in RULES for seq]
938 seq_cast_rule = BuiltinRule { ru_name = fsLit "seq of cast"
941 , ru_try = match_seq_of_cast
944 match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
945 -- See Note [Built-in RULES for seq]
946 match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
947 = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
949 match_seq_of_cast _ _ = Nothing
951 ------------------------------------------------
952 lazyId :: Id -- See Note [lazyId magic]
953 lazyId = pcMiscPrelId lazyIdName ty info
956 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
961 'GHC.Prim.seq' is special in several ways.
963 a) Its second arg can have an unboxed type
966 b) Its fixity is set in LoadIface.ghcPrimIface
968 c) It has quite a bit of desugaring magic.
969 See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3)
971 d) There is some special rule handing: Note [User-defined RULES for seq]
973 e) See Note [Typing rule for seq] in TcExpr.
975 Note [User-defined RULES for seq]
976 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
977 Roman found situations where he had
979 where he knew that f (which was strict in n) would terminate if n did.
980 Notice that the result of (f n) is discarded. So it makes sense to
984 Rather than attempt some general analysis to support this, I've added
985 enough support that you can do this using a rewrite rule:
987 RULE "f/seq" forall n. seq (f n) e = seq n e
989 You write that rule. When GHC sees a case expression that discards
990 its result, it mentally transforms it to a call to 'seq' and looks for
991 a RULE. (This is done in Simplify.rebuildCase.) As usual, the
992 correctness of the rule is up to you.
994 To make this work, we need to be careful that the magical desugaring
995 done in Note [seqId magic] item (c) is *not* done on the LHS of a rule.
996 Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs.
998 Note [Built-in RULES for seq]
999 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1000 We also have the following built-in rule for seq
1002 seq (x `cast` co) y = seq x y
1004 This eliminates unnecessary casts and also allows other seq rules to
1005 match more often. Notably,
1007 seq (f x `cast` co) y --> seq (f x) y
1009 and now a user-defined rule for seq (see Note [User-defined RULES for seq])
1015 lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1017 Used to lazify pseq: pseq a b = a `seq` lazy b
1019 Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1020 not from GHC.Base.hi. This is important, because the strictness
1021 analyser will spot it as strict!
1023 Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep.
1024 It's very important to do this inlining *after* unfoldings are exposed
1025 in the interface file. Otherwise, the unfolding for (say) pseq in the
1026 interface file will not mention 'lazy', so if we inline 'pseq' we'll totally
1027 miss the very thing that 'lazy' was there for in the first place.
1028 See Trac #3259 for a real world example.
1030 lazyId is defined in GHC.Base, so we don't *have* to inline it. If it
1031 appears un-applied, we'll end up just calling it.
1033 -------------------------------------------------------------
1034 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1035 nasty as-is, change it back to a literal (@Literal@).
1037 voidArgId is a Local Id used simply as an argument in functions
1038 where we just want an arg to avoid having a thunk of unlifted type.
1040 x = \ void :: State# RealWorld -> (# p, q #)
1042 This comes up in strictness analysis
1045 realWorldPrimId :: Id
1046 realWorldPrimId -- :: State# RealWorld
1047 = pcMiscPrelId realWorldName realWorldStatePrimTy
1048 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1049 -- The evaldUnfolding makes it look that realWorld# is evaluated
1050 -- which in turn makes Simplify.interestingArg return True,
1051 -- which in turn makes INLINE things applied to realWorld# likely
1055 voidArgId -- :: State# RealWorld
1056 = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy
1061 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1062 pcMiscPrelId name ty info
1063 = mkVanillaGlobalWithInfo name ty info
1064 -- We lie and say the thing is imported; otherwise, we get into
1065 -- a mess with dependency analysis; e.g., core2stg may heave in
1066 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1067 -- being compiled, then it's just a matter of luck if the definition
1068 -- will be in "the right place" to be in scope.