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 = base_info `setSpecInfo` mkSpecInfo [rule]
445 `setInlinePragInfo` neverInlinePragma
446 -- Add a magic BuiltinRule, and never inline it
447 -- so that the rule is always available to fire.
448 -- See Note [ClassOp/DFun selection] in TcInstDcls
450 n_ty_args = length tyvars
452 -- This is the built-in rule that goes
453 -- op (dfT d1 d2) ---> opT d1 d2
454 rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
455 occNameFS (getOccName name)
457 , ru_nargs = n_ty_args + 1
458 , ru_try = dictSelRule val_index n_ty_args n_eq_args }
460 -- The strictness signature is of the form U(AAAVAAAA) -> T
461 -- where the V depends on which item we are selecting
462 -- It's worth giving one, so that absence info etc is generated
463 -- even if the selector isn't inlined
464 strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
465 arg_dmd | new_tycon = evalDmd
466 | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
469 tycon = classTyCon clas
470 new_tycon = isNewTyCon tycon
471 [data_con] = tyConDataCons tycon
472 tyvars = dataConUnivTyVars data_con
473 arg_tys = dataConRepArgTys data_con -- Includes the dictionary superclasses
474 eq_theta = dataConEqTheta data_con
475 n_eq_args = length eq_theta
477 -- 'index' is a 0-index into the *value* arguments of the dictionary
478 val_index = assoc "MkId.mkDictSelId" sel_index_prs name
479 sel_index_prs = map idName (classAllSelIds clas) `zip` [0..]
481 the_arg_id = arg_ids !! val_index
482 pred = mkClassPred clas (mkTyVarTys tyvars)
483 dict_id = mkTemplateLocal 1 $ mkPredTy pred
484 arg_ids = mkTemplateLocalsNum 2 arg_tys
485 eq_ids = map mkWildEvBinder eq_theta
487 rhs = mkLams tyvars (Lam dict_id rhs_body)
488 rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
489 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
490 [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]
492 dictSelRule :: Int -> Arity -> Arity
493 -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
494 -- Tries to persuade the argument to look like a constructor
495 -- application, using exprIsConApp_maybe, and then selects
497 -- sel_i t1..tk (D t1..tk op1 ... opm) = opi
499 dictSelRule val_index n_ty_args n_eq_args id_unf args
500 | (dict_arg : _) <- drop n_ty_args args
501 , Just (_, _, con_args) <- exprIsConApp_maybe id_unf dict_arg
502 , let val_args = drop n_eq_args con_args
503 = Just (val_args !! val_index)
509 %************************************************************************
513 %************************************************************************
516 -- unbox a product type...
517 -- we will recurse into newtypes, casting along the way, and unbox at the
518 -- first product data constructor we find. e.g.
520 -- data PairInt = PairInt Int Int
521 -- newtype S = MkS PairInt
524 -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
525 -- ids, we get (modulo int passing)
527 -- case (e `cast` CoT) `cast` CoS of
528 -- PairInt a b -> body [a,b]
530 -- The Ints passed around are just for creating fresh locals
531 unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
532 unboxProduct i arg arg_ty body
535 result = mkUnpackCase the_id arg con_args boxing_con rhs
536 (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
537 ([the_id], i') = mkLocals i [arg_ty]
538 (con_args, i'') = mkLocals i' tys
539 rhs = body i'' con_args
541 mkUnpackCase :: Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
542 -- (mkUnpackCase x e args Con body)
544 -- case (e `cast` ...) of bndr { Con args -> body }
546 -- the type of the bndr passed in is irrelevent
547 mkUnpackCase bndr arg unpk_args boxing_con body
548 = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
550 (cast_arg, bndr_ty) = go (idType bndr) arg
552 | (tycon, tycon_args, _, _) <- splitProductType "mkUnpackCase" ty
553 , isNewTyCon tycon && not (isRecursiveTyCon tycon)
554 = go (newTyConInstRhs tycon tycon_args)
555 (unwrapNewTypeBody tycon tycon_args arg)
556 | otherwise = (arg, ty)
559 reboxProduct :: [Unique] -- uniques to create new local binders
560 -> Type -- type of product to box
561 -> ([Unique], -- remaining uniques
562 CoreExpr, -- boxed product
563 [Id]) -- Ids being boxed into product
566 (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty
568 us' = dropList con_arg_tys us
570 arg_ids = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys
572 bind_rhs = mkProductBox arg_ids ty
575 (us', bind_rhs, arg_ids)
577 mkProductBox :: [Id] -> Type -> CoreExpr
578 mkProductBox arg_ids ty
581 (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty
584 | isNewTyCon tycon && not (isRecursiveTyCon tycon)
585 = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
586 | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)
588 wrap expr = wrapNewTypeBody tycon tycon_args expr
591 -- (mkReboxingAlt us con xs rhs) basically constructs the case
592 -- alternative (con, xs, rhs)
593 -- but it does the reboxing necessary to construct the *source*
594 -- arguments, xs, from the representation arguments ys.
596 -- data T = MkT !(Int,Int) Bool
598 -- mkReboxingAlt MkT [x,b] r
599 -- = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
601 -- mkDataAlt should really be in DataCon, but it can't because
602 -- it manipulates CoreSyn.
605 :: [Unique] -- Uniques for the new Ids
607 -> [Var] -- Source-level args, including existential dicts
611 mkReboxingAlt us con args rhs
612 | not (any isMarkedUnboxed stricts)
613 = (DataAlt con, args, rhs)
617 (binds, args') = go args stricts us
619 (DataAlt con, args', mkLets binds rhs)
622 stricts = dataConExStricts con ++ dataConStrictMarks con
624 go [] _stricts _us = ([], [])
626 -- Type variable case
627 go (arg:args) stricts us
629 = let (binds, args') = go args stricts us
630 in (binds, arg:args')
632 -- Term variable case
633 go (arg:args) (str:stricts) us
634 | isMarkedUnboxed str
636 let (binds, unpacked_args') = go args stricts us'
637 (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
639 (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
641 = let (binds, args') = go args stricts us
642 in (binds, arg:args')
643 go (_ : _) [] _ = panic "mkReboxingAlt"
647 %************************************************************************
649 Wrapping and unwrapping newtypes and type families
651 %************************************************************************
654 wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
655 -- The wrapper for the data constructor for a newtype looks like this:
656 -- newtype T a = MkT (a,Int)
657 -- MkT :: forall a. (a,Int) -> T a
658 -- MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
659 -- where CoT is the coercion TyCon assoicated with the newtype
661 -- The call (wrapNewTypeBody T [a] e) returns the
662 -- body of the wrapper, namely
663 -- e `cast` (CoT [a])
665 -- If a coercion constructor is provided in the newtype, then we use
666 -- it, otherwise the wrap/unwrap are both no-ops
668 -- If the we are dealing with a newtype *instance*, we have a second coercion
669 -- identifying the family instance with the constructor of the newtype
670 -- instance. This coercion is applied in any case (ie, composed with the
671 -- coercion constructor of the newtype or applied by itself).
673 wrapNewTypeBody tycon args result_expr
674 = wrapFamInstBody tycon args inner
677 | Just co_con <- newTyConCo_maybe tycon
678 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
682 -- When unwrapping, we do *not* apply any family coercion, because this will
683 -- be done via a CoPat by the type checker. We have to do it this way as
684 -- computing the right type arguments for the coercion requires more than just
685 -- a spliting operation (cf, TcPat.tcConPat).
687 unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
688 unwrapNewTypeBody tycon args result_expr
689 | Just co_con <- newTyConCo_maybe tycon
690 = mkCoerce (mkTyConApp co_con args) result_expr
694 -- If the type constructor is a representation type of a data instance, wrap
695 -- the expression into a cast adjusting the expression type, which is an
696 -- instance of the representation type, to the corresponding instance of the
697 -- family instance type.
698 -- See Note [Wrappers for data instance tycons]
699 wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
700 wrapFamInstBody tycon args body
701 | Just co_con <- tyConFamilyCoercion_maybe tycon
702 = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
706 unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
707 unwrapFamInstScrut tycon args scrut
708 | Just co_con <- tyConFamilyCoercion_maybe tycon
709 = mkCoerce (mkTyConApp co_con args) scrut
715 %************************************************************************
717 \subsection{Primitive operations}
719 %************************************************************************
722 mkPrimOpId :: PrimOp -> Id
726 (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
727 ty = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
728 name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
729 (mkPrimOpIdUnique (primOpTag prim_op))
731 id = mkGlobalId (PrimOpId prim_op) name ty info
734 `setSpecInfo` mkSpecInfo (primOpRules prim_op name)
736 `setStrictnessInfo` Just strict_sig
738 -- For each ccall we manufacture a separate CCallOpId, giving it
739 -- a fresh unique, a type that is correct for this particular ccall,
740 -- and a CCall structure that gives the correct details about calling
743 -- The *name* of this Id is a local name whose OccName gives the full
744 -- details of the ccall, type and all. This means that the interface
745 -- file reader can reconstruct a suitable Id
747 mkFCallId :: Unique -> ForeignCall -> Type -> Id
748 mkFCallId uniq fcall ty
749 = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
750 -- A CCallOpId should have no free type variables;
751 -- when doing substitutions won't substitute over it
752 mkGlobalId (FCallId fcall) name ty info
754 occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
755 -- The "occurrence name" of a ccall is the full info about the
756 -- ccall; it is encoded, but may have embedded spaces etc!
758 name = mkFCallName uniq occ_str
762 `setStrictnessInfo` Just strict_sig
764 (_, tau) = tcSplitForAllTys ty
765 (arg_tys, _) = tcSplitFunTys tau
766 arity = length arg_tys
767 strict_sig = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)
769 -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
770 -- except for the type:
772 -- a plain HPC tick box has type (State# RealWorld)
773 -- a breakpoint Id has type forall a.a
775 -- The breakpoint Id will be applied to a list of arbitrary free variables,
776 -- which is why it needs a polymorphic type.
778 mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
779 mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy
781 mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
782 mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
783 where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy
785 mkTickBox' :: Unique -> Module -> TickBoxId -> Type -> Id
786 mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
788 tickbox = TickBox mod ix
789 occ_str = showSDoc (braces (ppr tickbox))
790 name = mkTickBoxOpName uniq occ_str
795 %************************************************************************
797 \subsection{DictFuns and default methods}
799 %************************************************************************
801 Important notes about dict funs and default methods
802 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
803 Dict funs and default methods are *not* ImplicitIds. Their definition
804 involves user-written code, so we can't figure out their strictness etc
805 based on fixed info, as we can for constructors and record selectors (say).
807 We build them as LocalIds, but with External Names. This ensures that
808 they are taken to account by free-variable finding and dependency
809 analysis (e.g. CoreFVs.exprFreeVars).
811 Why shouldn't they be bound as GlobalIds? Because, in particular, if
812 they are globals, the specialiser floats dict uses above their defns,
813 which prevents good simplifications happening. Also the strictness
814 analyser treats a occurrence of a GlobalId as imported and assumes it
815 contains strictness in its IdInfo, which isn't true if the thing is
816 bound in the same module as the occurrence.
818 It's OK for dfuns to be LocalIds, because we form the instance-env to
819 pass on to the next module (md_insts) in CoreTidy, afer tidying
820 and globalising the top-level Ids.
822 BUT make sure they are *exported* LocalIds (mkExportedLocalId) so
823 that they aren't discarded by the occurrence analyser.
826 mkDefaultMethodId :: Id -- Selector Id
827 -> Name -- Default method name
828 -> Id -- Default method Id
829 mkDefaultMethodId sel_id dm_name = mkExportedLocalId dm_name (idType sel_id)
831 mkDictFunId :: Name -- Name to use for the dict fun;
837 -- Implements the DFun Superclass Invariant (see TcInstDcls)
839 mkDictFunId dfun_name tvs theta clas tys
840 = mkExportedLocalVar (DFunId n_silent is_nt)
845 is_nt = isNewTyCon (classTyCon clas)
846 (n_silent, dfun_ty) = mkDictFunTy tvs theta clas tys
848 mkDictFunTy :: [TyVar] -> ThetaType -> Class -> [Type] -> (Int, Type)
849 mkDictFunTy tvs theta clas tys
850 = (length silent_theta, dfun_ty)
852 dfun_ty = mkSigmaTy tvs (silent_theta ++ theta) (mkDictTy clas tys)
853 silent_theta = filterOut discard $
854 substTheta (zipTopTvSubst (classTyVars clas) tys)
856 -- See Note [Silent Superclass Arguments]
857 discard pred = isEmptyVarSet (tyVarsOfPred pred)
858 || any (`tcEqPred` pred) theta
859 -- See the DFun Superclass Invariant in TcInstDcls
863 %************************************************************************
865 \subsection{Un-definable}
867 %************************************************************************
869 These Ids can't be defined in Haskell. They could be defined in
870 unfoldings in the wired-in GHC.Prim interface file, but we'd have to
871 ensure that they were definitely, definitely inlined, because there is
872 no curried identifier for them. That's what mkCompulsoryUnfolding
873 does. If we had a way to get a compulsory unfolding from an interface
874 file, we could do that, but we don't right now.
876 unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that
877 just gets expanded into a type coercion wherever it occurs. Hence we
878 add it as a built-in Id with an unfolding here.
880 The type variables we use here are "open" type variables: this means
881 they can unify with both unlifted and lifted types. Hence we provide
882 another gun with which to shoot yourself in the foot.
885 lazyIdName, unsafeCoerceName, nullAddrName, seqName, realWorldName :: Name
886 unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey unsafeCoerceId
887 nullAddrName = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#") nullAddrIdKey nullAddrId
888 seqName = mkWiredInIdName gHC_PRIM (fsLit "seq") seqIdKey seqId
889 realWorldName = mkWiredInIdName gHC_PRIM (fsLit "realWorld#") realWorldPrimIdKey realWorldPrimId
890 lazyIdName = mkWiredInIdName gHC_BASE (fsLit "lazy") lazyIdKey lazyId
894 ------------------------------------------------
895 -- unsafeCoerce# :: forall a b. a -> b
898 = pcMiscPrelId unsafeCoerceName ty info
900 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
903 ty = mkForAllTys [argAlphaTyVar,openBetaTyVar]
904 (mkFunTy argAlphaTy openBetaTy)
905 [x] = mkTemplateLocals [argAlphaTy]
906 rhs = mkLams [argAlphaTyVar,openBetaTyVar,x] $
907 Cast (Var x) (mkUnsafeCoercion argAlphaTy openBetaTy)
909 ------------------------------------------------
911 -- nullAddr# :: Addr#
912 -- The reason is is here is because we don't provide
913 -- a way to write this literal in Haskell.
914 nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
916 info = noCafIdInfo `setUnfoldingInfo`
917 mkCompulsoryUnfolding (Lit nullAddrLit)
919 ------------------------------------------------
920 seqId :: Id -- See Note [seqId magic]
921 seqId = pcMiscPrelId seqName ty info
923 info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
924 `setSpecInfo` mkSpecInfo [seq_cast_rule]
927 ty = mkForAllTys [alphaTyVar,argBetaTyVar]
928 (mkFunTy alphaTy (mkFunTy argBetaTy argBetaTy))
929 [x,y] = mkTemplateLocals [alphaTy, argBetaTy]
930 rhs = mkLams [alphaTyVar,argBetaTyVar,x,y] (Case (Var x) x argBetaTy [(DEFAULT, [], Var y)])
932 -- See Note [Built-in RULES for seq]
933 seq_cast_rule = BuiltinRule { ru_name = fsLit "seq of cast"
936 , ru_try = match_seq_of_cast
939 match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
940 -- See Note [Built-in RULES for seq]
941 match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
942 = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
944 match_seq_of_cast _ _ = Nothing
946 ------------------------------------------------
947 lazyId :: Id -- See Note [lazyId magic]
948 lazyId = pcMiscPrelId lazyIdName ty info
951 ty = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)
956 'GHC.Prim.seq' is special in several ways.
958 a) Its second arg can have an unboxed type
961 b) Its fixity is set in LoadIface.ghcPrimIface
963 c) It has quite a bit of desugaring magic.
964 See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3)
966 d) There is some special rule handing: Note [User-defined RULES for seq]
968 e) See Note [Typing rule for seq] in TcExpr.
970 Note [User-defined RULES for seq]
971 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
972 Roman found situations where he had
974 where he knew that f (which was strict in n) would terminate if n did.
975 Notice that the result of (f n) is discarded. So it makes sense to
979 Rather than attempt some general analysis to support this, I've added
980 enough support that you can do this using a rewrite rule:
982 RULE "f/seq" forall n. seq (f n) e = seq n e
984 You write that rule. When GHC sees a case expression that discards
985 its result, it mentally transforms it to a call to 'seq' and looks for
986 a RULE. (This is done in Simplify.rebuildCase.) As usual, the
987 correctness of the rule is up to you.
989 To make this work, we need to be careful that the magical desugaring
990 done in Note [seqId magic] item (c) is *not* done on the LHS of a rule.
991 Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs.
993 Note [Built-in RULES for seq]
994 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
995 We also have the following built-in rule for seq
997 seq (x `cast` co) y = seq x y
999 This eliminates unnecessary casts and also allows other seq rules to
1000 match more often. Notably,
1002 seq (f x `cast` co) y --> seq (f x) y
1004 and now a user-defined rule for seq (see Note [User-defined RULES for seq])
1010 lazy :: forall a?. a? -> a? (i.e. works for unboxed types too)
1012 Used to lazify pseq: pseq a b = a `seq` lazy b
1014 Also, no strictness: by being a built-in Id, all the info about lazyId comes from here,
1015 not from GHC.Base.hi. This is important, because the strictness
1016 analyser will spot it as strict!
1018 Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep.
1019 It's very important to do this inlining *after* unfoldings are exposed
1020 in the interface file. Otherwise, the unfolding for (say) pseq in the
1021 interface file will not mention 'lazy', so if we inline 'pseq' we'll totally
1022 miss the very thing that 'lazy' was there for in the first place.
1023 See Trac #3259 for a real world example.
1025 lazyId is defined in GHC.Base, so we don't *have* to inline it. If it
1026 appears un-applied, we'll end up just calling it.
1028 -------------------------------------------------------------
1029 @realWorld#@ used to be a magic literal, \tr{void#}. If things get
1030 nasty as-is, change it back to a literal (@Literal@).
1032 voidArgId is a Local Id used simply as an argument in functions
1033 where we just want an arg to avoid having a thunk of unlifted type.
1035 x = \ void :: State# RealWorld -> (# p, q #)
1037 This comes up in strictness analysis
1040 realWorldPrimId :: Id
1041 realWorldPrimId -- :: State# RealWorld
1042 = pcMiscPrelId realWorldName realWorldStatePrimTy
1043 (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
1044 -- The evaldUnfolding makes it look that realWorld# is evaluated
1045 -- which in turn makes Simplify.interestingArg return True,
1046 -- which in turn makes INLINE things applied to realWorld# likely
1050 voidArgId -- :: State# RealWorld
1051 = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy
1056 pcMiscPrelId :: Name -> Type -> IdInfo -> Id
1057 pcMiscPrelId name ty info
1058 = mkVanillaGlobalWithInfo name ty info
1059 -- We lie and say the thing is imported; otherwise, we get into
1060 -- a mess with dependency analysis; e.g., core2stg may heave in
1061 -- random calls to GHCbase.unpackPS__. If GHCbase is the module
1062 -- being compiled, then it's just a matter of luck if the definition
1063 -- will be in "the right place" to be in scope.