% % (c) The University of Glasgow 2006 % (c) The AQUA Project, Glasgow University, 1998 % This module contains definitions for the IdInfo for things that have a standard form, namely: - data constructors - record selectors - method and superclass selectors - primitive operations \begin{code}

    module MkId (
            mkDictFunId, mkDictFunTy, mkDefaultMethodId, mkDictSelId,

            mkDataConIds,
            mkPrimOpId, mkFCallId, mkTickBoxOpId, mkBreakPointOpId,

            mkReboxingAlt, wrapNewTypeBody, unwrapNewTypeBody,
            wrapFamInstBody, unwrapFamInstScrut,
            mkUnpackCase, mkProductBox,

            -- And some particular Ids; see below for why they are wired in
            wiredInIds, ghcPrimIds,
            unsafeCoerceName, unsafeCoerceId, realWorldPrimId,
            voidArgId, nullAddrId, seqId, lazyId, lazyIdKey
        ) where

    #include "HsVersions.h"

    import Rules
    import TysPrim
    import PrelRules
    import Type
    import Coercion
    import TcType
    import MkCore
    import CoreUtils	( exprType, mkCoerce )
    import CoreUnfold
    import Literal
    import TyCon
    import Class
    import VarSet
    import Name
    import PrimOp
    import ForeignCall
    import DataCon
    import Id
    import Var              ( Var, TyVar, mkCoVar, mkExportedLocalVar )
    import IdInfo
    import Demand
    import CoreSyn
    import Unique
    import PrelNames
    import BasicTypes       hiding ( SuccessFlag(..) )
    import Util
    import Outputable
    import FastString
    import ListSetOps
    import Module

\end{code} %************************************************************************ %* * \subsection{Wired in Ids} %* * %************************************************************************ Note [Wired-in Ids] ~~~~~~~~~~~~~~~~~~~ There are several reasons why an Id might appear in the wiredInIds: (1) The ghcPrimIds are wired in because they can't be defined in Haskell at all, although the can be defined in Core. They have compulsory unfoldings, so they are always inlined and they have no definition site. Their home module is GHC.Prim, so they also have a description in primops.txt.pp, where they are called 'pseudoops'. (2) The 'error' function, eRROR_ID, is wired in because we don't yet have a way to express in an interface file that the result type variable is 'open'; that is can be unified with an unboxed type [The interface file format now carry such information, but there's no way yet of expressing at the definition site for these error-reporting functions that they have an 'open' result type. -- sof 1/99] (3) Other error functions (rUNTIME_ERROR_ID) are wired in (a) because the desugarer generates code that mentiones them directly, and (b) for the same reason as eRROR_ID (4) lazyId is wired in because the wired-in version overrides the strictness of the version defined in GHC.Base In cases (2-4), the function has a definition in a library module, and can be called; but the wired-in version means that the details are never read from that module's interface file; instead, the full definition is right here. \begin{code}

    wiredInIds :: [Id]
    wiredInIds
      =  [lazyId]
      ++ errorIds		-- Defined in MkCore
      ++ ghcPrimIds

    -- These Ids are exported from GHC.Prim
    ghcPrimIds :: [Id]
    ghcPrimIds
      = [   -- These can't be defined in Haskell, but they have
            -- perfectly reasonable unfoldings in Core
        realWorldPrimId,
        unsafeCoerceId,
        nullAddrId,
        seqId
        ]

\end{code} %************************************************************************ %* * \subsection{Data constructors} %* * %************************************************************************ The wrapper for a constructor is an ordinary top-level binding that evaluates any strict args, unboxes any args that are going to be flattened, and calls the worker. We're going to build a constructor that looks like: data (Data a, C b) => T a b = T1 !a !Int b T1 = /\ a b -> \d1::Data a, d2::C b -> \p q r -> case p of { p -> case q of { q -> Con T1 [a,b] [p,q,r]}} Notice that * d2 is thrown away --- a context in a data decl is used to make sure one *could* construct dictionaries at the site the constructor is used, but the dictionary isn't actually used. * We have to check that we can construct Data dictionaries for the types a and Int. Once we've done that we can throw d1 away too. * We use (case p of q -> ...) to evaluate p, rather than "seq" because all that matters is that the arguments are evaluated. "seq" is very careful to preserve evaluation order, which we don't need to be here. You might think that we could simply give constructors some strictness info, like PrimOps, and let CoreToStg do the let-to-case transformation. But we don't do that because in the case of primops and functions strictness is a *property* not a *requirement*. In the case of constructors we need to do something active to evaluate the argument. Making an explicit case expression allows the simplifier to eliminate it in the (common) case where the constructor arg is already evaluated. Note [Wrappers for data instance tycons] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the case of data instances, the wrapper also applies the coercion turning the representation type into the family instance type to cast the result of the wrapper. For example, consider the declarations data family Map k :: * -> * data instance Map (a, b) v = MapPair (Map a (Pair b v)) The tycon to which the datacon MapPair belongs gets a unique internal name of the form :R123Map, and we call it the representation tycon. In contrast, Map is the family tycon (accessible via tyConFamInst_maybe). A coercion allows you to move between representation and family type. It is accessible from :R123Map via tyConFamilyCoercion_maybe and has kind Co123Map a b v :: {Map (a, b) v ~ :R123Map a b v} The wrapper and worker of MapPair get the types -- Wrapper $WMapPair :: forall a b v. Map a (Map a b v) -> Map (a, b) v $WMapPair a b v = MapPair a b v `cast` sym (Co123Map a b v) -- Worker MapPair :: forall a b v. Map a (Map a b v) -> :R123Map a b v This coercion is conditionally applied by wrapFamInstBody. It's a bit more complicated if the data instance is a GADT as well! data instance T [a] where T1 :: forall b. b -> T [Maybe b] Hence we translate to -- Wrapper $WT1 :: forall b. b -> T [Maybe b] $WT1 b v = T1 (Maybe b) b (Maybe b) v `cast` sym (Co7T (Maybe b)) -- Worker T1 :: forall c b. (c ~ Maybe b) => b -> :R7T c -- Coercion from family type to representation type Co7T a :: T [a] ~ :R7T a \begin{code}

    mkDataConIds :: Name -> Name -> DataCon -> DataConIds
    mkDataConIds wrap_name wkr_name data_con
      | isNewTyCon tycon                    -- Newtype, only has a worker
      = DCIds Nothing nt_work_id

      | any isBanged all_strict_marks      -- Algebraic, needs wrapper
        || not (null eq_spec)              -- NB: LoadIface.ifaceDeclSubBndrs
        || isFamInstTyCon tycon            --     depends on this test
      = DCIds (Just alg_wrap_id) wrk_id

      | otherwise                                -- Algebraic, no wrapper
      = DCIds Nothing wrk_id
      where
        (univ_tvs, ex_tvs, eq_spec,
         eq_theta, dict_theta, orig_arg_tys, res_ty) = dataConFullSig data_con
        tycon = dataConTyCon data_con       -- The representation TyCon (not family)

            ----------- Worker (algebraic data types only) --------------
            -- The *worker* for the data constructor is the function that
            -- takes the representation arguments and builds the constructor.
        wrk_id = mkGlobalId (DataConWorkId data_con) wkr_name
                            (dataConRepType data_con) wkr_info

        wkr_arity = dataConRepArity data_con
        wkr_info  = noCafIdInfo
                    `setArityInfo`          wkr_arity
                    `setStrictnessInfo`  Just wkr_sig
                    `setUnfoldingInfo`      evaldUnfolding  -- Record that it's evaluated,
                                                            -- even if arity = 0

        wkr_sig = mkStrictSig (mkTopDmdType (replicate wkr_arity topDmd) cpr_info)
            --      Note [Data-con worker strictness]
            -- Notice that we do *not* say the worker is strict
            -- even if the data constructor is declared strict
            --      e.g.    data T = MkT !(Int,Int)
            -- Why?  Because the *wrapper* is strict (and its unfolding has case
            -- expresssions that do the evals) but the *worker* itself is not.
            -- If we pretend it is strict then when we see
            --      case x of y -> $wMkT y
            -- the simplifier thinks that y is "sure to be evaluated" (because
            --  $wMkT is strict) and drops the case.  No, $wMkT is not strict.
            --
            -- When the simplifer sees a pattern
            --      case e of MkT x -> ...
            -- it uses the dataConRepStrictness of MkT to mark x as evaluated;
            -- but that's fine... dataConRepStrictness comes from the data con
            -- not from the worker Id.

        cpr_info | isProductTyCon tycon &&
                   isDataTyCon tycon    &&
                   wkr_arity > 0        &&
                   wkr_arity <= mAX_CPR_SIZE        = retCPR
                 | otherwise                        = TopRes
            -- RetCPR is only true for products that are real data types;
            -- that is, not unboxed tuples or [non-recursive] newtypes

            ----------- Workers for newtypes --------------
        nt_work_id   = mkGlobalId (DataConWrapId data_con) wkr_name wrap_ty nt_work_info
        nt_work_info = noCafIdInfo          -- The NoCaf-ness is set by noCafIdInfo
                      `setArityInfo` 1      -- Arity 1
                      `setUnfoldingInfo`     newtype_unf
        id_arg1      = mkTemplateLocal 1 (head orig_arg_tys)
        newtype_unf  = ASSERT2( isVanillaDataCon data_con &&
                                isSingleton orig_arg_tys, ppr data_con  )
    			      -- Note [Newtype datacons]
                       mkCompulsoryUnfolding $
                       mkLams wrap_tvs $ Lam id_arg1 $
                       wrapNewTypeBody tycon res_ty_args (Var id_arg1)

            ----------- Wrapper --------------
            -- We used to include the stupid theta in the wrapper's args
            -- but now we don't.  Instead the type checker just injects these
            -- extra constraints where necessary.
        wrap_tvs    = (univ_tvs `minusList` map fst eq_spec) ++ ex_tvs
        res_ty_args = substTyVars (mkTopTvSubst eq_spec) univ_tvs
        eq_tys   = mkPredTys eq_theta
        dict_tys = mkPredTys dict_theta
        wrap_ty  = mkForAllTys wrap_tvs $ mkFunTys eq_tys $ mkFunTys dict_tys $
                   mkFunTys orig_arg_tys $ res_ty
            -- NB: watch out here if you allow user-written equality
            --     constraints in data constructor signatures

            ----------- Wrappers for algebraic data types --------------
        alg_wrap_id = mkGlobalId (DataConWrapId data_con) wrap_name wrap_ty alg_wrap_info
        alg_wrap_info = noCafIdInfo         -- The NoCaf-ness is set by noCafIdInfo
                        `setArityInfo`         wrap_arity
                            -- It's important to specify the arity, so that partial
                            -- applications are treated as values
    		    `setInlinePragInfo`    alwaysInlinePragma
                        `setUnfoldingInfo`     wrap_unf
                        `setStrictnessInfo` Just wrap_sig

        all_strict_marks = dataConExStricts data_con ++ dataConStrictMarks data_con
        wrap_sig = mkStrictSig (mkTopDmdType arg_dmds cpr_info)
        arg_dmds = map mk_dmd all_strict_marks
        mk_dmd str | isBanged str = evalDmd
                   | otherwise    = lazyDmd
            -- The Cpr info can be important inside INLINE rhss, where the
            -- wrapper constructor isn't inlined.
            -- And the argument strictness can be important too; we
            -- may not inline a contructor when it is partially applied.
            -- For example:
            --      data W = C !Int !Int !Int
            --      ...(let w = C x in ...(w p q)...)...
            -- we want to see that w is strict in its two arguments

        wrap_unf = mkInlineUnfolding (Just (length dict_args + length id_args)) wrap_rhs
        wrap_rhs = mkLams wrap_tvs $
                   mkLams eq_args $
                   mkLams dict_args $ mkLams id_args $
                   foldr mk_case con_app
                         (zip (dict_args ++ id_args) all_strict_marks)
                         i3 []

        con_app _ rep_ids = wrapFamInstBody tycon res_ty_args $
                              Var wrk_id `mkTyApps`  res_ty_args
                                         `mkVarApps` ex_tvs
                                         -- Equality evidence:
                                         `mkTyApps`  map snd eq_spec
                                         `mkVarApps` eq_args
                                         `mkVarApps` reverse rep_ids

        (dict_args,i2) = mkLocals 1  dict_tys
        (id_args,i3)   = mkLocals i2 orig_arg_tys
        wrap_arity     = i3-1
        (eq_args,_)    = mkCoVarLocals i3 eq_tys

        mkCoVarLocals i []     = ([],i)
        mkCoVarLocals i (x:xs) = let (ys,j) = mkCoVarLocals (i+1) xs
                                     y      = mkCoVar (mkSysTvName (mkBuiltinUnique i)
                                                      (fsLit "dc_co")) x
                                 in (y:ys,j)

        mk_case
               :: (Id, HsBang)      -- Arg, strictness
               -> (Int -> [Id] -> CoreExpr) -- Body
               -> Int                       -- Next rep arg id
               -> [Id]                      -- Rep args so far, reversed
               -> CoreExpr
        mk_case (arg,strict) body i rep_args
              = case strict of
                    HsNoBang -> body i (arg:rep_args)
                    HsUnpack -> unboxProduct i (Var arg) (idType arg) the_body
                          where
                            the_body i con_args = body i (reverse con_args ++ rep_args)
                    _other  -- HsUnpackFailed and HsStrict
                       | isUnLiftedType (idType arg) -> body i (arg:rep_args)
                       | otherwise -> Case (Var arg) arg res_ty
                                           [(DEFAULT,[], body i (arg:rep_args))]

    mAX_CPR_SIZE :: Arity
    mAX_CPR_SIZE = 10
    -- We do not treat very big tuples as CPR-ish:
    --      a) for a start we get into trouble because there aren't
    --         "enough" unboxed tuple types (a tiresome restriction,
    --         but hard to fix),
    --      b) more importantly, big unboxed tuples get returned mainly
    --         on the stack, and are often then allocated in the heap
    --         by the caller.  So doing CPR for them may in fact make
    --         things worse.

    mkLocals :: Int -> [Type] -> ([Id], Int)
    mkLocals i tys = (zipWith mkTemplateLocal [i..i+n-1] tys, i+n)
                   where
                     n = length tys

\end{code} Note [Newtype datacons] ~~~~~~~~~~~~~~~~~~~~~~~ The "data constructor" for a newtype should always be vanilla. At one point this wasn't true, because the newtype arising from class C a => D a looked like newtype T:D a = D:D (C a) so the data constructor for T:C had a single argument, namely the predicate (C a). But now we treat that as an ordinary argument, not part of the theta-type, so all is well. %************************************************************************ %* * \subsection{Dictionary selectors} %* * %************************************************************************ Selecting a field for a dictionary. If there is just one field, then there's nothing to do. Dictionary selectors may get nested forall-types. Thus: class Foo a where op :: forall b. Ord b => a -> b -> b Then the top-level type for op is op :: forall a. Foo a => forall b. Ord b => a -> b -> b This is unlike ordinary record selectors, which have all the for-alls at the outside. When dealing with classes it's very convenient to recover the original type signature from the class op selector. \begin{code}

    mkDictSelId :: Bool	     -- True <=> don't include the unfolding
    			     -- Little point on imports without -O, because the
    			     -- dictionary itself won't be visible
     	    -> Name	     -- Name of one of the *value* selectors
    	       		     -- (dictionary superclass or method)
                -> Class -> Id
    mkDictSelId no_unf name clas
      = mkGlobalId (ClassOpId clas) name sel_ty info
      where
        sel_ty = mkForAllTys tyvars (mkFunTy (idType dict_id) (idType the_arg_id))
            -- We can't just say (exprType rhs), because that would give a type
            --      C a -> C a
            -- for a single-op class (after all, the selector is the identity)
            -- But it's type must expose the representation of the dictionary
            -- to get (say)         C a -> (a -> a)

        base_info = noCafIdInfo
                    `setArityInfo`      1
                    `setStrictnessInfo`  Just strict_sig
                    `setUnfoldingInfo`  (if no_unf then noUnfolding
    				     else mkImplicitUnfolding rhs)
    		   -- In module where class op is defined, we must add
    		   -- the unfolding, even though it'll never be inlined
    		   -- becuase we use that to generate a top-level binding
    		   -- for the ClassOp

        info = base_info    `setSpecInfo`       mkSpecInfo [rule]
    			`setInlinePragInfo` neverInlinePragma
    		-- Add a magic BuiltinRule, and never inline it
    		-- so that the rule is always available to fire.
    		-- See Note [ClassOp/DFun selection] in TcInstDcls

        n_ty_args = length tyvars

        -- This is the built-in rule that goes
        -- 	    op (dfT d1 d2) --->  opT d1 d2
        rule = BuiltinRule { ru_name = fsLit "Class op " `appendFS`
        	   	       	 	     occNameFS (getOccName name)
                           , ru_fn    = name
        	               , ru_nargs = n_ty_args + 1
                           , ru_try   = dictSelRule val_index n_ty_args n_eq_args }

            -- The strictness signature is of the form U(AAAVAAAA) -> T
            -- where the V depends on which item we are selecting
            -- It's worth giving one, so that absence info etc is generated
            -- even if the selector isn't inlined
        strict_sig = mkStrictSig (mkTopDmdType [arg_dmd] TopRes)
        arg_dmd | new_tycon = evalDmd
                | otherwise = Eval (Prod [ if the_arg_id == id then evalDmd else Abs
                                         | id <- arg_ids ])

        tycon      	   = classTyCon clas
        new_tycon  	   = isNewTyCon tycon
        [data_con] 	   = tyConDataCons tycon
        tyvars     	   = dataConUnivTyVars data_con
        arg_tys    	   = dataConRepArgTys data_con	-- Includes the dictionary superclasses
        eq_theta   	   = dataConEqTheta data_con
        n_eq_args      = length eq_theta

        -- 'index' is a 0-index into the *value* arguments of the dictionary
        val_index      = assoc "MkId.mkDictSelId" sel_index_prs name
        sel_index_prs  = map idName (classAllSelIds clas) `zip` [0..]

        the_arg_id     = arg_ids !! val_index
        pred       	   = mkClassPred clas (mkTyVarTys tyvars)
        dict_id    	   = mkTemplateLocal 1 $ mkPredTy pred
        arg_ids    	   = mkTemplateLocalsNum 2 arg_tys
        eq_ids     	   = map mkWildEvBinder eq_theta

        rhs = mkLams tyvars  (Lam dict_id   rhs_body)
        rhs_body | new_tycon = unwrapNewTypeBody tycon (map mkTyVarTy tyvars) (Var dict_id)
                 | otherwise = Case (Var dict_id) dict_id (idType the_arg_id)
                                    [(DataAlt data_con, eq_ids ++ arg_ids, Var the_arg_id)]

    dictSelRule :: Int -> Arity -> Arity
                -> IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
    -- Tries to persuade the argument to look like a constructor
    -- application, using exprIsConApp_maybe, and then selects
    -- from it
    --       sel_i t1..tk (D t1..tk op1 ... opm) = opi
    --
    dictSelRule val_index n_ty_args n_eq_args id_unf args
      | (dict_arg : _) <- drop n_ty_args args
      , Just (_, _, con_args) <- exprIsConApp_maybe id_unf dict_arg
      , let val_args = drop n_eq_args con_args
      = Just (val_args !! val_index)
      | otherwise
      = Nothing

\end{code} %************************************************************************ %* * Boxing and unboxing %* * %************************************************************************ \begin{code}

    -- unbox a product type...
    -- we will recurse into newtypes, casting along the way, and unbox at the
    -- first product data constructor we find. e.g.
    --
    --   data PairInt = PairInt Int Int
    --   newtype S = MkS PairInt
    --   newtype T = MkT S
    --
    -- If we have e = MkT (MkS (PairInt 0 1)) and some body expecting a list of
    -- ids, we get (modulo int passing)
    --
    --   case (e `cast` CoT) `cast` CoS of
    --     PairInt a b -> body [a,b]
    --
    -- The Ints passed around are just for creating fresh locals
    unboxProduct :: Int -> CoreExpr -> Type -> (Int -> [Id] -> CoreExpr) -> CoreExpr
    unboxProduct i arg arg_ty body
      = result
      where
        result = mkUnpackCase the_id arg con_args boxing_con rhs
        (_tycon, _tycon_args, boxing_con, tys) = deepSplitProductType "unboxProduct" arg_ty
        ([the_id], i') = mkLocals i [arg_ty]
        (con_args, i'') = mkLocals i' tys
        rhs = body i'' con_args

    mkUnpackCase ::  Id -> CoreExpr -> [Id] -> DataCon -> CoreExpr -> CoreExpr
    -- (mkUnpackCase x e args Con body)
    --      returns
    -- case (e `cast` ...) of bndr { Con args -> body }
    --
    -- the type of the bndr passed in is irrelevent
    mkUnpackCase bndr arg unpk_args boxing_con body
      = Case cast_arg (setIdType bndr bndr_ty) (exprType body) [(DataAlt boxing_con, unpk_args, body)]
      where
      (cast_arg, bndr_ty) = go (idType bndr) arg
      go ty arg
        | (tycon, tycon_args, _, _)  <- splitProductType "mkUnpackCase" ty
        , isNewTyCon tycon && not (isRecursiveTyCon tycon)
        = go (newTyConInstRhs tycon tycon_args)
             (unwrapNewTypeBody tycon tycon_args arg)
        | otherwise = (arg, ty)

    -- ...and the dual
    reboxProduct :: [Unique]     -- uniques to create new local binders
                 -> Type         -- type of product to box
                 -> ([Unique],   -- remaining uniques
                     CoreExpr,   -- boxed product
                     [Id])       -- Ids being boxed into product
    reboxProduct us ty
      = let
            (_tycon, _tycon_args, _pack_con, con_arg_tys) = deepSplitProductType "reboxProduct" ty

            us' = dropList con_arg_tys us

            arg_ids  = zipWith (mkSysLocal (fsLit "rb")) us con_arg_tys

            bind_rhs = mkProductBox arg_ids ty

        in
          (us', bind_rhs, arg_ids)

    mkProductBox :: [Id] -> Type -> CoreExpr
    mkProductBox arg_ids ty
      = result_expr
      where
        (tycon, tycon_args, pack_con, _con_arg_tys) = splitProductType "mkProductBox" ty

        result_expr
          | isNewTyCon tycon && not (isRecursiveTyCon tycon)
          = wrap (mkProductBox arg_ids (newTyConInstRhs tycon tycon_args))
          | otherwise = mkConApp pack_con (map Type tycon_args ++ map Var arg_ids)

        wrap expr = wrapNewTypeBody tycon tycon_args expr

    -- (mkReboxingAlt us con xs rhs) basically constructs the case
    -- alternative (con, xs, rhs)
    -- but it does the reboxing necessary to construct the *source*
    -- arguments, xs, from the representation arguments ys.
    -- For example:
    --      data T = MkT !(Int,Int) Bool
    --
    -- mkReboxingAlt MkT [x,b] r
    --      = (DataAlt MkT, [y::Int,z::Int,b], let x = (y,z) in r)
    --
    -- mkDataAlt should really be in DataCon, but it can't because
    -- it manipulates CoreSyn.

    mkReboxingAlt
      :: [Unique] -- Uniques for the new Ids
      -> DataCon
      -> [Var]    -- Source-level args, including existential dicts
      -> CoreExpr -- RHS
      -> CoreAlt

    mkReboxingAlt us con args rhs
      | not (any isMarkedUnboxed stricts)
      = (DataAlt con, args, rhs)

      | otherwise
      = let
            (binds, args') = go args stricts us
        in
        (DataAlt con, args', mkLets binds rhs)

      where
        stricts = dataConExStricts con ++ dataConStrictMarks con

        go [] _stricts _us = ([], [])

        -- Type variable case
        go (arg:args) stricts us
          | isTyCoVar arg
          = let (binds, args') = go args stricts us
            in  (binds, arg:args')

            -- Term variable case
        go (arg:args) (str:stricts) us
          | isMarkedUnboxed str
          =
            let (binds, unpacked_args')        = go args stricts us'
                (us', bind_rhs, unpacked_args) = reboxProduct us (idType arg)
            in
                (NonRec arg bind_rhs : binds, unpacked_args ++ unpacked_args')
          | otherwise
          = let (binds, args') = go args stricts us
            in  (binds, arg:args')
        go (_ : _) [] _ = panic "mkReboxingAlt"

\end{code} %************************************************************************ %* * Wrapping and unwrapping newtypes and type families %* * %************************************************************************ \begin{code}

    wrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
    -- The wrapper for the data constructor for a newtype looks like this:
    --      newtype T a = MkT (a,Int)
    --      MkT :: forall a. (a,Int) -> T a
    --      MkT = /\a. \(x:(a,Int)). x `cast` sym (CoT a)
    -- where CoT is the coercion TyCon assoicated with the newtype
    --
    -- The call (wrapNewTypeBody T [a] e) returns the
    -- body of the wrapper, namely
    --      e `cast` (CoT [a])
    --
    -- If a coercion constructor is provided in the newtype, then we use
    -- it, otherwise the wrap/unwrap are both no-ops
    --
    -- If the we are dealing with a newtype *instance*, we have a second coercion
    -- identifying the family instance with the constructor of the newtype
    -- instance.  This coercion is applied in any case (ie, composed with the
    -- coercion constructor of the newtype or applied by itself).

    wrapNewTypeBody tycon args result_expr
      = wrapFamInstBody tycon args inner
      where
        inner
          | Just co_con <- newTyConCo_maybe tycon
          = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) result_expr
          | otherwise
          = result_expr

    -- When unwrapping, we do *not* apply any family coercion, because this will
    -- be done via a CoPat by the type checker.  We have to do it this way as
    -- computing the right type arguments for the coercion requires more than just
    -- a spliting operation (cf, TcPat.tcConPat).

    unwrapNewTypeBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
    unwrapNewTypeBody tycon args result_expr
      | Just co_con <- newTyConCo_maybe tycon
      = mkCoerce (mkTyConApp co_con args) result_expr
      | otherwise
      = result_expr

    -- If the type constructor is a representation type of a data instance, wrap
    -- the expression into a cast adjusting the expression type, which is an
    -- instance of the representation type, to the corresponding instance of the
    -- family instance type.
    -- See Note [Wrappers for data instance tycons]
    wrapFamInstBody :: TyCon -> [Type] -> CoreExpr -> CoreExpr
    wrapFamInstBody tycon args body
      | Just co_con <- tyConFamilyCoercion_maybe tycon
      = mkCoerce (mkSymCoercion (mkTyConApp co_con args)) body
      | otherwise
      = body

    unwrapFamInstScrut :: TyCon -> [Type] -> CoreExpr -> CoreExpr
    unwrapFamInstScrut tycon args scrut
      | Just co_con <- tyConFamilyCoercion_maybe tycon
      = mkCoerce (mkTyConApp co_con args) scrut
      | otherwise
      = scrut

\end{code} %************************************************************************ %* * \subsection{Primitive operations} %* * %************************************************************************ \begin{code}

    mkPrimOpId :: PrimOp -> Id
    mkPrimOpId prim_op
      = id
      where
        (tyvars,arg_tys,res_ty, arity, strict_sig) = primOpSig prim_op
        ty   = mkForAllTys tyvars (mkFunTys arg_tys res_ty)
        name = mkWiredInName gHC_PRIM (primOpOcc prim_op)
                             (mkPrimOpIdUnique (primOpTag prim_op))
                             (AnId id) UserSyntax
        id   = mkGlobalId (PrimOpId prim_op) name ty info

        info = noCafIdInfo
               `setSpecInfo`          mkSpecInfo (primOpRules prim_op name)
               `setArityInfo`         arity
               `setStrictnessInfo` Just strict_sig

    -- For each ccall we manufacture a separate CCallOpId, giving it
    -- a fresh unique, a type that is correct for this particular ccall,
    -- and a CCall structure that gives the correct details about calling
    -- convention etc.
    --
    -- The *name* of this Id is a local name whose OccName gives the full
    -- details of the ccall, type and all.  This means that the interface
    -- file reader can reconstruct a suitable Id

    mkFCallId :: Unique -> ForeignCall -> Type -> Id
    mkFCallId uniq fcall ty
      = ASSERT( isEmptyVarSet (tyVarsOfType ty) )
        -- A CCallOpId should have no free type variables;
        -- when doing substitutions won't substitute over it
        mkGlobalId (FCallId fcall) name ty info
      where
        occ_str = showSDoc (braces (ppr fcall <+> ppr ty))
        -- The "occurrence name" of a ccall is the full info about the
        -- ccall; it is encoded, but may have embedded spaces etc!

        name = mkFCallName uniq occ_str

        info = noCafIdInfo
               `setArityInfo`         arity
               `setStrictnessInfo` Just strict_sig

        (_, tau)     = tcSplitForAllTys ty
        (arg_tys, _) = tcSplitFunTys tau
        arity        = length arg_tys
        strict_sig   = mkStrictSig (mkTopDmdType (replicate arity evalDmd) TopRes)

    -- Tick boxes and breakpoints are both represented as TickBoxOpIds,
    -- except for the type:
    --
    --    a plain HPC tick box has type (State# RealWorld)
    --    a breakpoint Id has type forall a.a
    --
    -- The breakpoint Id will be applied to a list of arbitrary free variables,
    -- which is why it needs a polymorphic type.

    mkTickBoxOpId :: Unique -> Module -> TickBoxId -> Id
    mkTickBoxOpId uniq mod ix = mkTickBox' uniq mod ix realWorldStatePrimTy

    mkBreakPointOpId :: Unique -> Module -> TickBoxId -> Id
    mkBreakPointOpId uniq mod ix = mkTickBox' uniq mod ix ty
     where ty = mkSigmaTy [openAlphaTyVar] [] openAlphaTy

    mkTickBox' :: Unique -> Module -> TickBoxId -> Type -> Id
    mkTickBox' uniq mod ix ty = mkGlobalId (TickBoxOpId tickbox) name ty info
      where
        tickbox = TickBox mod ix
        occ_str = showSDoc (braces (ppr tickbox))
        name    = mkTickBoxOpName uniq occ_str
        info    = noCafIdInfo

\end{code} %************************************************************************ %* * \subsection{DictFuns and default methods} %* * %************************************************************************ Important notes about dict funs and default methods ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dict funs and default methods are *not* ImplicitIds. Their definition involves user-written code, so we can't figure out their strictness etc based on fixed info, as we can for constructors and record selectors (say). We build them as LocalIds, but with External Names. This ensures that they are taken to account by free-variable finding and dependency analysis (e.g. CoreFVs.exprFreeVars). Why shouldn't they be bound as GlobalIds? Because, in particular, if they are globals, the specialiser floats dict uses above their defns, which prevents good simplifications happening. Also the strictness analyser treats a occurrence of a GlobalId as imported and assumes it contains strictness in its IdInfo, which isn't true if the thing is bound in the same module as the occurrence. It's OK for dfuns to be LocalIds, because we form the instance-env to pass on to the next module (md_insts) in CoreTidy, afer tidying and globalising the top-level Ids. BUT make sure they are *exported* LocalIds (mkExportedLocalId) so that they aren't discarded by the occurrence analyser. \begin{code}

    mkDefaultMethodId :: Id		-- Selector Id
    		  -> Name	-- Default method name
    		  -> Id		-- Default method Id
    mkDefaultMethodId sel_id dm_name = mkExportedLocalId dm_name (idType sel_id)

    mkDictFunId :: Name      -- Name to use for the dict fun;
                -> [TyVar]
                -> ThetaType
                -> Class
                -> [Type]
                -> Id
    -- Implements the DFun Superclass Invariant (see TcInstDcls)

    mkDictFunId dfun_name tvs theta clas tys
      = mkExportedLocalVar (DFunId n_silent is_nt)
                           dfun_name
                           dfun_ty
                           vanillaIdInfo
      where
        is_nt = isNewTyCon (classTyCon clas)
        (n_silent, dfun_ty) = mkDictFunTy tvs theta clas tys

    mkDictFunTy :: [TyVar] -> ThetaType -> Class -> [Type] -> (Int, Type)
    mkDictFunTy tvs theta clas tys
      = (length silent_theta, dfun_ty)
      where
        dfun_ty = mkSigmaTy tvs (silent_theta ++ theta) (mkDictTy clas tys)
        silent_theta = filterOut discard $
                       substTheta (zipTopTvSubst (classTyVars clas) tys)
                                  (classSCTheta clas)
                       -- See Note [Silent Superclass Arguments]
        discard pred = isEmptyVarSet (tyVarsOfPred pred)
                     || any (`tcEqPred` pred) theta
                     -- See the DFun Superclass Invariant in TcInstDcls

\end{code} %************************************************************************ %* * \subsection{Un-definable} %* * %************************************************************************ These Ids can't be defined in Haskell. They could be defined in unfoldings in the wired-in GHC.Prim interface file, but we'd have to ensure that they were definitely, definitely inlined, because there is no curried identifier for them. That's what mkCompulsoryUnfolding does. If we had a way to get a compulsory unfolding from an interface file, we could do that, but we don't right now. unsafeCoerce# isn't so much a PrimOp as a phantom identifier, that just gets expanded into a type coercion wherever it occurs. Hence we add it as a built-in Id with an unfolding here. The type variables we use here are "open" type variables: this means they can unify with both unlifted and lifted types. Hence we provide another gun with which to shoot yourself in the foot. \begin{code}

    lazyIdName, unsafeCoerceName, nullAddrName, seqName, realWorldName :: Name
    unsafeCoerceName = mkWiredInIdName gHC_PRIM (fsLit "unsafeCoerce#") unsafeCoerceIdKey  unsafeCoerceId
    nullAddrName     = mkWiredInIdName gHC_PRIM (fsLit "nullAddr#")     nullAddrIdKey      nullAddrId
    seqName          = mkWiredInIdName gHC_PRIM (fsLit "seq")           seqIdKey           seqId
    realWorldName    = mkWiredInIdName gHC_PRIM (fsLit "realWorld#")    realWorldPrimIdKey realWorldPrimId
    lazyIdName       = mkWiredInIdName gHC_BASE (fsLit "lazy")         lazyIdKey           lazyId

\end{code} \begin{code}

    ------------------------------------------------
    -- unsafeCoerce# :: forall a b. a -> b
    unsafeCoerceId :: Id
    unsafeCoerceId
      = pcMiscPrelId unsafeCoerceName ty info
      where
        info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs

        ty  = mkForAllTys [argAlphaTyVar,openBetaTyVar]
                          (mkFunTy argAlphaTy openBetaTy)
        [x] = mkTemplateLocals [argAlphaTy]
        rhs = mkLams [argAlphaTyVar,openBetaTyVar,x] $
              Cast (Var x) (mkUnsafeCoercion argAlphaTy openBetaTy)

    ------------------------------------------------
    nullAddrId :: Id
    -- nullAddr# :: Addr#
    -- The reason is is here is because we don't provide
    -- a way to write this literal in Haskell.
    nullAddrId = pcMiscPrelId nullAddrName addrPrimTy info
      where
        info = noCafIdInfo `setUnfoldingInfo`
               mkCompulsoryUnfolding (Lit nullAddrLit)

    ------------------------------------------------
    seqId :: Id	-- See Note [seqId magic]
    seqId = pcMiscPrelId seqName ty info
      where
        info = noCafIdInfo `setUnfoldingInfo` mkCompulsoryUnfolding rhs
                           `setSpecInfo` mkSpecInfo [seq_cast_rule]

        ty  = mkForAllTys [alphaTyVar,argBetaTyVar]
                          (mkFunTy alphaTy (mkFunTy argBetaTy argBetaTy))
        [x,y] = mkTemplateLocals [alphaTy, argBetaTy]
        rhs = mkLams [alphaTyVar,argBetaTyVar,x,y] (Case (Var x) x argBetaTy [(DEFAULT, [], Var y)])

        -- See Note [Built-in RULES for seq]
        seq_cast_rule = BuiltinRule { ru_name  = fsLit "seq of cast"
                                    , ru_fn    = seqName
                                    , ru_nargs = 4
                                    , ru_try   = match_seq_of_cast
                                    }

    match_seq_of_cast :: IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr
        -- See Note [Built-in RULES for seq]
    match_seq_of_cast _ [Type _, Type res_ty, Cast scrut co, expr]
      = Just (Var seqId `mkApps` [Type (fst (coercionKind co)), Type res_ty,
                                  scrut, expr])
    match_seq_of_cast _ _ = Nothing

    ------------------------------------------------
    lazyId :: Id	-- See Note [lazyId magic]
    lazyId = pcMiscPrelId lazyIdName ty info
      where
        info = noCafIdInfo
        ty  = mkForAllTys [alphaTyVar] (mkFunTy alphaTy alphaTy)

\end{code} Note [seqId magic] ~~~~~~~~~~~~~~~~~~ 'GHC.Prim.seq' is special in several ways. a) Its second arg can have an unboxed type x `seq` (v +# w) b) Its fixity is set in LoadIface.ghcPrimIface c) It has quite a bit of desugaring magic. See DsUtils.lhs Note [Desugaring seq (1)] and (2) and (3) d) There is some special rule handing: Note [User-defined RULES for seq] e) See Note [Typing rule for seq] in TcExpr. Note [User-defined RULES for seq] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Roman found situations where he had case (f n) of _ -> e where he knew that f (which was strict in n) would terminate if n did. Notice that the result of (f n) is discarded. So it makes sense to transform to case n of _ -> e Rather than attempt some general analysis to support this, I've added enough support that you can do this using a rewrite rule: RULE "f/seq" forall n. seq (f n) e = seq n e You write that rule. When GHC sees a case expression that discards its result, it mentally transforms it to a call to 'seq' and looks for a RULE. (This is done in Simplify.rebuildCase.) As usual, the correctness of the rule is up to you. To make this work, we need to be careful that the magical desugaring done in Note [seqId magic] item (c) is *not* done on the LHS of a rule. Or rather, we arrange to un-do it, in DsBinds.decomposeRuleLhs. Note [Built-in RULES for seq] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We also have the following built-in rule for seq seq (x `cast` co) y = seq x y This eliminates unnecessary casts and also allows other seq rules to match more often. Notably, seq (f x `cast` co) y --> seq (f x) y and now a user-defined rule for seq (see Note [User-defined RULES for seq]) may fire. Note [lazyId magic] ~~~~~~~~~~~~~~~~~~~ lazy :: forall a?. a? -> a? (i.e. works for unboxed types too) Used to lazify pseq: pseq a b = a `seq` lazy b Also, no strictness: by being a built-in Id, all the info about lazyId comes from here, not from GHC.Base.hi. This is important, because the strictness analyser will spot it as strict! Also no unfolding in lazyId: it gets "inlined" by a HACK in CorePrep. It's very important to do this inlining *after* unfoldings are exposed in the interface file. Otherwise, the unfolding for (say) pseq in the interface file will not mention 'lazy', so if we inline 'pseq' we'll totally miss the very thing that 'lazy' was there for in the first place. See Trac #3259 for a real world example. lazyId is defined in GHC.Base, so we don't *have* to inline it. If it appears un-applied, we'll end up just calling it. ------------------------------------------------------------- @realWorld#@ used to be a magic literal, \tr{void#}. If things get nasty as-is, change it back to a literal (@Literal@). voidArgId is a Local Id used simply as an argument in functions where we just want an arg to avoid having a thunk of unlifted type. E.g. x = \ void :: State# RealWorld -> (# p, q #) This comes up in strictness analysis \begin{code}

    realWorldPrimId :: Id
    realWorldPrimId -- :: State# RealWorld
      = pcMiscPrelId realWorldName realWorldStatePrimTy
                     (noCafIdInfo `setUnfoldingInfo` evaldUnfolding)
            -- The evaldUnfolding makes it look that realWorld# is evaluated
            -- which in turn makes Simplify.interestingArg return True,
            -- which in turn makes INLINE things applied to realWorld# likely
            -- to be inlined

    voidArgId :: Id
    voidArgId       -- :: State# RealWorld
      = mkSysLocal (fsLit "void") voidArgIdKey realWorldStatePrimTy

\end{code} \begin{code}

    pcMiscPrelId :: Name -> Type -> IdInfo -> Id
    pcMiscPrelId name ty info
      = mkVanillaGlobalWithInfo name ty info
        -- We lie and say the thing is imported; otherwise, we get into
        -- a mess with dependency analysis; e.g., core2stg may heave in
        -- random calls to GHCbase.unpackPS__.  If GHCbase is the module
        -- being compiled, then it's just a matter of luck if the definition
        -- will be in "the right place" to be in scope.

\end{code}