% % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998 % \section[CoreToStg]{Converts Core to STG Syntax} And, as we have the info in hand, we may convert some lets to let-no-escapes. \begin{code}

    module CoreToStg ( coreToStg, coreExprToStg ) where

    #include "HsVersions.h"

    import CoreSyn
    import CoreUtils        ( exprType, findDefault )
    import CoreArity        ( manifestArity )
    import StgSyn

    import Type
    import TyCon
    import Id
    import Var              ( Var )
    import IdInfo
    import DataCon
    import CostCentre       ( noCCS )
    import VarSet
    import VarEnv
    import Maybes           ( maybeToBool )
    import Name             ( getOccName, isExternalName, nameOccName )
    import OccName          ( occNameString, occNameFS )
    import BasicTypes       ( Arity )
    import Module
    import Outputable
    import MonadUtils
    import FastString
    import Util
    import ForeignCall
    import PrimOp           ( PrimCall(..) )

\end{code} %************************************************************************ %* * \subsection[live-vs-free-doc]{Documentation} %* * %************************************************************************ (There is other relevant documentation in codeGen/CgLetNoEscape.) The actual Stg datatype is decorated with {\em live variable} information, as well as {\em free variable} information. The two are {\em not} the same. Liveness is an operational property rather than a semantic one. A variable is live at a particular execution point if it can be referred to {\em directly} again. In particular, a dead variable's stack slot (if it has one): \begin{enumerate} \item should be stubbed to avoid space leaks, and \item may be reused for something else. \end{enumerate} There ought to be a better way to say this. Here are some examples: \begin{verbatim} let v = [q] \[x] -> e in ...v... (but no q's) \end{verbatim} Just after the `in', v is live, but q is dead. If the whole of that let expression was enclosed in a case expression, thus: \begin{verbatim} case (let v = [q] \[x] -> e in ...v...) of alts[...q...] \end{verbatim} (ie @alts@ mention @q@), then @q@ is live even after the `in'; because we'll return later to the @alts@ and need it. Let-no-escapes make this a bit more interesting: \begin{verbatim} let-no-escape v = [q] \ [x] -> e in ...v... \end{verbatim} Here, @q@ is still live at the `in', because @v@ is represented not by a closure but by the current stack state. In other words, if @v@ is live then so is @q@. Furthermore, if @e@ mentions an enclosing let-no-escaped variable, then {\em its} free variables are also live if @v@ is. %************************************************************************ %* * \subsection[caf-info]{Collecting live CAF info} %* * %************************************************************************ In this pass we also collect information on which CAFs are live for constructing SRTs (see SRT.lhs). A top-level Id has CafInfo, which is - MayHaveCafRefs, if it may refer indirectly to one or more CAFs, or - NoCafRefs if it definitely doesn't The CafInfo has already been calculated during the CoreTidy pass. During CoreToStg, we then pin onto each binding and case expression, a list of Ids which represents the "live" CAFs at that point. The meaning of "live" here is the same as for live variables, see above (which is why it's convenient to collect CAF information here rather than elsewhere). The later SRT pass takes these lists of Ids and uses them to construct the actual nested SRTs, and replaces the lists of Ids with (offset,length) pairs. Interaction of let-no-escape with SRTs [Sept 01] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider let-no-escape x = ...caf1...caf2... in ...x...x...x... where caf1,caf2 are CAFs. Since x doesn't have a closure, we build SRTs just as if x's defn was inlined at each call site, and that means that x's CAF refs get duplicated in the overall SRT. This is unlike ordinary lets, in which the CAF refs are not duplicated. We could fix this loss of (static) sharing by making a sort of pseudo-closure for x, solely to put in the SRTs lower down. %************************************************************************ %* * \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs} %* * %************************************************************************ \begin{code}

    coreToStg :: PackageId -> [CoreBind] -> IO [StgBinding]
    coreToStg this_pkg pgm
      = return pgm'
      where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm

    coreExprToStg :: CoreExpr -> StgExpr
    coreExprToStg expr
      = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)

    coreTopBindsToStg
        :: PackageId
        -> IdEnv HowBound           -- environment for the bindings
        -> [CoreBind]
        -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])

    coreTopBindsToStg _        env [] = (env, emptyFVInfo, [])
    coreTopBindsToStg this_pkg env (b:bs)
      = (env2, fvs2, b':bs')
      where
            -- Notice the mutually-recursive "knot" here:
            --   env accumulates down the list of binds,
            --   fvs accumulates upwards
            (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
            (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs

    coreTopBindToStg
            :: PackageId
            -> IdEnv HowBound
            -> FreeVarsInfo         -- Info about the body
            -> CoreBind
            -> (IdEnv HowBound, FreeVarsInfo, StgBinding)

    coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
      = let
            env'      = extendVarEnv env id how_bound
            how_bound = LetBound TopLet $! manifestArity rhs

            (stg_rhs, fvs') =
                initLne env $ do
                  (stg_rhs, fvs') <- coreToTopStgRhs this_pkg body_fvs (id,rhs)
                  return (stg_rhs, fvs')

            bind = StgNonRec id stg_rhs
        in
        ASSERT2(consistentCafInfo id bind, ppr id )
          -- NB: previously the assertion printed 'rhs' and 'bind'
          --     as well as 'id', but that led to a black hole
          --     where printing the assertion error tripped the
          --     assertion again!
        (env', fvs' `unionFVInfo` body_fvs, bind)

    coreTopBindToStg this_pkg env body_fvs (Rec pairs)
      = ASSERT( not (null pairs) )
        let
            binders = map fst pairs

            extra_env' = [ (b, LetBound TopLet $! manifestArity rhs)
                         | (b, rhs) <- pairs ]
            env' = extendVarEnvList env extra_env'

            (stg_rhss, fvs')
              = initLne env' $ do
                   (stg_rhss, fvss') <- mapAndUnzipM (coreToTopStgRhs this_pkg body_fvs) pairs
                   let fvs' = unionFVInfos fvss'
                   return (stg_rhss, fvs')

            bind = StgRec (zip binders stg_rhss)
        in
        ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
        (env', fvs' `unionFVInfo` body_fvs, bind)

    -- Assertion helper: this checks that the CafInfo on the Id matches
    -- what CoreToStg has figured out about the binding's SRT.  The
    -- CafInfo will be exact in all cases except when CorePrep has
    -- floated out a binding, in which case it will be approximate.
    consistentCafInfo :: Id -> GenStgBinding Var Id -> Bool
    consistentCafInfo id bind
      = WARN( not (exact || is_sat_thing) , ppr id )
        safe
      where
        safe  = id_marked_caffy || not binding_is_caffy
        exact = id_marked_caffy == binding_is_caffy
        id_marked_caffy  = mayHaveCafRefs (idCafInfo id)
        binding_is_caffy = stgBindHasCafRefs bind
        is_sat_thing = occNameFS (nameOccName (idName id)) == fsLit "sat"

\end{code} \begin{code}

    coreToTopStgRhs
            :: PackageId
            -> FreeVarsInfo         -- Free var info for the scope of the binding
            -> (Id,CoreExpr)
            -> LneM (StgRhs, FreeVarsInfo)

    coreToTopStgRhs this_pkg scope_fv_info (bndr, rhs)
      = do { (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs
           ; lv_info <- freeVarsToLiveVars rhs_fvs

           ; let stg_rhs   = mkTopStgRhs this_pkg rhs_fvs (mkSRT lv_info) bndr_info new_rhs
                 stg_arity = stgRhsArity stg_rhs
           ; return (ASSERT2( arity_ok stg_arity, mk_arity_msg stg_arity) stg_rhs,
                     rhs_fvs) }
      where
        bndr_info = lookupFVInfo scope_fv_info bndr

            -- It's vital that the arity on a top-level Id matches
            -- the arity of the generated STG binding, else an importing
            -- module will use the wrong calling convention
            --      (Trac #2844 was an example where this happened)
            -- NB1: we can't move the assertion further out without
            --      blocking the "knot" tied in coreTopBindsToStg
            -- NB2: the arity check is only needed for Ids with External
            --      Names, because they are externally visible.  The CorePrep
            --      pass introduces "sat" things with Local Names and does
            --      not bother to set their Arity info, so don't fail for those
        arity_ok stg_arity
           | isExternalName (idName bndr) = id_arity == stg_arity
           | otherwise                    = True
        id_arity  = idArity bndr
        mk_arity_msg stg_arity
            = vcat [ppr bndr,
                    ptext (sLit "Id arity:") <+> ppr id_arity,
                    ptext (sLit "STG arity:") <+> ppr stg_arity]

    mkTopStgRhs :: PackageId -> FreeVarsInfo
                -> SRT -> StgBinderInfo -> StgExpr
                -> StgRhs

    mkTopStgRhs _ rhs_fvs srt binder_info (StgLam _ bndrs body)
      = StgRhsClosure noCCS binder_info
                      (getFVs rhs_fvs)
                      ReEntrant
                      srt
                      bndrs body

    mkTopStgRhs this_pkg _ _ _ (StgConApp con args)
      | not (isDllConApp this_pkg con args)  -- Dynamic StgConApps are updatable
      = StgRhsCon noCCS con args

    mkTopStgRhs _ rhs_fvs srt binder_info rhs
      = StgRhsClosure noCCS binder_info
                      (getFVs rhs_fvs)
                      Updatable
                      srt
                      [] rhs

\end{code} -- --------------------------------------------------------------------------- -- Expressions -- --------------------------------------------------------------------------- \begin{code}

    coreToStgExpr
            :: CoreExpr
            -> LneM (StgExpr,       -- Decorated STG expr
                     FreeVarsInfo,  -- Its free vars (NB free, not live)
                     EscVarsSet)    -- Its escapees, a subset of its free vars;
                                    -- also a subset of the domain of the envt
                                    -- because we are only interested in the escapees
                                    -- for vars which might be turned into
                                    -- let-no-escaped ones.

\end{code} The second and third components can be derived in a simple bottom up pass, not dependent on any decisions about which variables will be let-no-escaped or not. The first component, that is, the decorated expression, may then depend on these components, but it in turn is not scrutinised as the basis for any decisions. Hence no black holes. \begin{code}

    coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet)
    coreToStgExpr (Var v) = coreToStgApp Nothing v []

    coreToStgExpr expr@(App _ _)
      = coreToStgApp Nothing f args
      where
        (f, args) = myCollectArgs expr

    coreToStgExpr expr@(Lam _ _)
      = let
            (args, body) = myCollectBinders expr
            args'        = filterStgBinders args
        in
        extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
        (body, body_fvs, body_escs) <- coreToStgExpr body
        let
            fvs             = args' `minusFVBinders` body_fvs
            escs            = body_escs `delVarSetList` args'
            result_expr | null args' = body
                        | otherwise  = StgLam (exprType expr) args' body

        return (result_expr, fvs, escs)

    coreToStgExpr (Note (SCC cc) expr) = do
        (expr2, fvs, escs) <- coreToStgExpr expr
        return (StgSCC cc expr2, fvs, escs)

    coreToStgExpr (Case (Var id) _bndr _ty [(DEFAULT,[],expr)])
      | Just (TickBox m n) <- isTickBoxOp_maybe id = do
        (expr2, fvs, escs) <- coreToStgExpr expr
        return (StgTick m n expr2, fvs, escs)

    coreToStgExpr (Note _ expr)
      = coreToStgExpr expr

    coreToStgExpr (Cast expr _)
      = coreToStgExpr expr

    -- Cases require a little more real work.

    coreToStgExpr (Case scrut bndr _ alts) = do
        (alts2, alts_fvs, alts_escs)
           <- extendVarEnvLne [(bndr, LambdaBound)] $ do
                (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
                return ( alts2,
                         unionFVInfos fvs_s,
                         unionVarSets escs_s )
        let
            -- Determine whether the default binder is dead or not
            -- This helps the code generator to avoid generating an assignment
            -- for the case binder (is extremely rare cases) ToDo: remove.
            bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
                  | otherwise                       = bndr `setIdOccInfo` IAmDead

            -- Don't consider the default binder as being 'live in alts',
            -- since this is from the point of view of the case expr, where
            -- the default binder is not free.
            alts_fvs_wo_bndr  = bndr `minusFVBinder` alts_fvs
            alts_escs_wo_bndr = alts_escs `delVarSet` bndr

        alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr

            -- We tell the scrutinee that everything
            -- live in the alts is live in it, too.
        (scrut2, scrut_fvs, _scrut_escs, scrut_lv_info)
           <- setVarsLiveInCont alts_lv_info $ do
                (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
                scrut_lv_info <- freeVarsToLiveVars scrut_fvs
                return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)

        return (
          StgCase scrut2 (getLiveVars scrut_lv_info)
                         (getLiveVars alts_lv_info)
                         bndr'
                         (mkSRT alts_lv_info)
                         (mkStgAltType bndr alts)
                         alts2,
          scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
          alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
                    -- You might think we should have scrut_escs, not
                    -- (getFVSet scrut_fvs), but actually we can't call, and
                    -- then return from, a let-no-escape thing.
          )
      where
        vars_alt (con, binders, rhs)
          = let     -- Remove type variables
                binders' = filterStgBinders binders
            in
            extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
            (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
            let
                    -- Records whether each param is used in the RHS
                good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]

            return ( (con, binders', good_use_mask, rhs2),
                     binders' `minusFVBinders` rhs_fvs,
                     rhs_escs `delVarSetList` binders' )
                    -- ToDo: remove the delVarSet;
                    -- since escs won't include any of these binders

\end{code} Lets not only take quite a bit of work, but this is where we convert then to let-no-escapes, if we wish. (Meanwhile, we don't expect to see let-no-escapes...) \begin{code}

    coreToStgExpr (Let bind body) = do
        (new_let, fvs, escs, _)
           <- mfix (\ ~(_, _, _, no_binder_escapes) ->
                 coreToStgLet no_binder_escapes bind body
              )

        return (new_let, fvs, escs)

    coreToStgExpr e = pprPanic "coreToStgExpr" (ppr e)

\end{code} \begin{code}

    mkStgAltType :: Id -> [CoreAlt] -> AltType
    mkStgAltType bndr alts
      = case splitTyConApp_maybe (repType (idType bndr)) of
            Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
                        | isUnLiftedTyCon tc     -> PrimAlt tc
                        | isHiBootTyCon tc       -> look_for_better_tycon
                        | isAlgTyCon tc          -> AlgAlt tc
                        | otherwise              -> ASSERT2( _is_poly_alt_tycon tc, ppr tc )
                                                    PolyAlt
            Nothing                              -> PolyAlt

      where
       _is_poly_alt_tycon tc
            =  isFunTyCon tc
            || isPrimTyCon tc   -- "Any" is lifted but primitive
            || isFamilyTyCon tc   -- Type family; e.g. arising from strict
                                -- function application where argument has a
                                -- type-family type

       -- Sometimes, the TyCon is a HiBootTyCon which may not have any
       -- constructors inside it.  Then we can get a better TyCon by
       -- grabbing the one from a constructor alternative
       -- if one exists.
       look_for_better_tycon
            | ((DataAlt con, _, _) : _) <- data_alts =
                    AlgAlt (dataConTyCon con)
            | otherwise =
                    ASSERT(null data_alts)
                    PolyAlt
            where
                    (data_alts, _deflt) = findDefault alts

\end{code} -- --------------------------------------------------------------------------- -- Applications -- --------------------------------------------------------------------------- \begin{code}

    coreToStgApp
             :: Maybe UpdateFlag            -- Just upd <=> this application is
                                            -- the rhs of a thunk binding
                                            --      x = [...] \upd [] -> the_app
                                            -- with specified update flag
            -> Id                           -- Function
            -> [CoreArg]                    -- Arguments
            -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)

    coreToStgApp _ f args = do
        (args', args_fvs) <- coreToStgArgs args
        how_bound <- lookupVarLne f

        let
            n_val_args       = valArgCount args
            not_letrec_bound = not (isLetBound how_bound)
            fun_fvs = singletonFVInfo f how_bound fun_occ
                -- e.g. (f :: a -> int) (x :: a)
                -- Here the free variables are "f", "x" AND the type variable "a"
                -- coreToStgArgs will deal with the arguments recursively

            -- Mostly, the arity info of a function is in the fn's IdInfo
            -- But new bindings introduced by CoreSat may not have no
            -- arity info; it would do us no good anyway.  For example:
            --      let f = \ab -> e in f
            -- No point in having correct arity info for f!
            -- Hence the hasArity stuff below.
            -- NB: f_arity is only consulted for LetBound things
            f_arity   = stgArity f how_bound
            saturated = f_arity <= n_val_args

            fun_occ
             | not_letrec_bound         = noBinderInfo      -- Uninteresting variable
             | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
             | otherwise                = stgUnsatOcc       -- Unsaturated function or thunk

            fun_escs
             | not_letrec_bound      = emptyVarSet  -- Only letrec-bound escapees are interesting
             | f_arity == n_val_args = emptyVarSet  -- A function *or thunk* with an exactly
                                                    -- saturated call doesn't escape
                                                    -- (let-no-escape applies to 'thunks' too)

             | otherwise         = unitVarSet f     -- Inexact application; it does escape

            -- At the moment of the call:

            --  either the function is *not* let-no-escaped, in which case
            --         nothing is live except live_in_cont
            --      or the function *is* let-no-escaped in which case the
            --         variables it uses are live, but still the function
            --         itself is not.  PS.  In this case, the function's
            --         live vars should already include those of the
            --         continuation, but it does no harm to just union the
            --         two regardless.

            res_ty = exprType (mkApps (Var f) args)
            app = case idDetails f of
                    DataConWorkId dc | saturated -> StgConApp dc args'

                    -- Some primitive operator that might be implemented as a library call.
                    PrimOpId op      -> ASSERT( saturated )
                                        StgOpApp (StgPrimOp op) args' res_ty

                    -- A call to some primitive Cmm function.
                    FCallId (CCall (CCallSpec (StaticTarget lbl (Just pkgId)) PrimCallConv _))
                                     -> ASSERT( saturated )
                                        StgOpApp (StgPrimCallOp (PrimCall lbl pkgId)) args' res_ty

                    -- A regular foreign call.
                    FCallId call     -> ASSERT( saturated )
                                        StgOpApp (StgFCallOp call (idUnique f)) args' res_ty

                    TickBoxOpId {}   -> pprPanic "coreToStg TickBox" $ ppr (f,args')
                    _other           -> StgApp f args'
            fvs = fun_fvs  `unionFVInfo` args_fvs
            vars = fun_escs `unionVarSet` (getFVSet args_fvs)
                                    -- All the free vars of the args are disqualified
                                    -- from being let-no-escaped.

        -- Forcing these fixes a leak in the code generator, noticed while
        -- profiling for trac #4367
        app `seq` fvs `seq` seqVarSet vars `seq` return (
            app,
            fvs,
            vars
         )

    -- ---------------------------------------------------------------------------
    -- Argument lists
    -- This is the guy that turns applications into A-normal form
    -- ---------------------------------------------------------------------------

    coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
    coreToStgArgs []
      = return ([], emptyFVInfo)

    coreToStgArgs (Type _ : args) = do     -- Type argument
        (args', fvs) <- coreToStgArgs args
        return (args', fvs)

    coreToStgArgs (arg : args) = do         -- Non-type argument
        (stg_args, args_fvs) <- coreToStgArgs args
        (arg', arg_fvs, _escs) <- coreToStgExpr arg
        let
            fvs = args_fvs `unionFVInfo` arg_fvs
            stg_arg = case arg' of
                           StgApp v []      -> StgVarArg v
                           StgConApp con [] -> StgVarArg (dataConWorkId con)
                           StgLit lit       -> StgLitArg lit
                           _                -> pprPanic "coreToStgArgs" (ppr arg)

            -- WARNING: what if we have an argument like (v `cast` co)
            --          where 'co' changes the representation type?
            --          (This really only happens if co is unsafe.)
            -- Then all the getArgAmode stuff in CgBindery will set the
            -- cg_rep of the CgIdInfo based on the type of v, rather
            -- than the type of 'co'.
            -- This matters particularly when the function is a primop
            -- or foreign call.
            -- Wanted: a better solution than this hacky warning
        let
            arg_ty = exprType arg
            stg_arg_ty = stgArgType stg_arg
            bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
                    || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
            -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
            -- and pass it to a function expecting an HValue (arg_ty).  This is ok because
            -- we can treat an unlifted value as lifted.  But the other way round
            -- we complain.
            -- We also want to check if a pointer is cast to a non-ptr etc

        WARN( bad_args, ptext (sLit "Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
         return (stg_arg : stg_args, fvs)

    -- ---------------------------------------------------------------------------
    -- The magic for lets:
    -- ---------------------------------------------------------------------------

    coreToStgLet
             :: Bool        -- True <=> yes, we are let-no-escaping this let
             -> CoreBind    -- bindings
             -> CoreExpr    -- body
             -> LneM (StgExpr,      -- new let
                      FreeVarsInfo, -- variables free in the whole let
                      EscVarsSet,   -- variables that escape from the whole let
                      Bool)         -- True <=> none of the binders in the bindings
                                    -- is among the escaping vars

    coreToStgLet let_no_escape bind body = do
        (bind2, bind_fvs, bind_escs, bind_lvs,
         body2, body_fvs, body_escs, body_lvs)
           <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do

              -- Do the bindings, setting live_in_cont to empty if
              -- we ain't in a let-no-escape world
              live_in_cont <- getVarsLiveInCont
              ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
                    <- setVarsLiveInCont (if let_no_escape
                                              then live_in_cont
                                              else emptyLiveInfo)
                                         (vars_bind rec_body_fvs bind)

              -- Do the body
              extendVarEnvLne env_ext $ do
                 (body2, body_fvs, body_escs) <- coreToStgExpr body
                 body_lv_info <- freeVarsToLiveVars body_fvs

                 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
                         body2, body_fvs, body_escs, getLiveVars body_lv_info)

            -- Compute the new let-expression
        let
            new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
                    | otherwise     = StgLet bind2 body2

            free_in_whole_let
              = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)

            live_in_whole_let
              = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)

            real_bind_escs = if let_no_escape then
                                bind_escs
                             else
                                getFVSet bind_fvs
                                -- Everything escapes which is free in the bindings

            let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders

            all_escs = bind_escs `unionVarSet` body_escs    -- Still includes binders of
                                                            -- this let(rec)

            no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)

            -- Debugging code as requested by Andrew Kennedy
            checked_no_binder_escapes
                    | debugIsOn && not no_binder_escapes && any is_join_var binders
                    = pprTrace "Interesting!  A join var that isn't let-no-escaped" (ppr binders)
                      False
                    | otherwise = no_binder_escapes

                    -- Mustn't depend on the passed-in let_no_escape flag, since
                    -- no_binder_escapes is used by the caller to derive the flag!
        return (
            new_let,
            free_in_whole_let,
            let_escs,
            checked_no_binder_escapes
          )
      where
        set_of_binders = mkVarSet binders
        binders        = bindersOf bind

        mk_binding bind_lv_info binder rhs
            = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
            where
               live_vars | let_no_escape = addLiveVar bind_lv_info binder
                         | otherwise     = unitLiveVar binder
                    -- c.f. the invariant on NestedLet

        vars_bind :: FreeVarsInfo           -- Free var info for body of binding
                  -> CoreBind
                  -> LneM (StgBinding,
                           FreeVarsInfo,
                           EscVarsSet,        -- free vars; escapee vars
                           LiveInfo,          -- Vars and CAFs live in binding
                           [(Id, HowBound)])  -- extension to environment

        vars_bind body_fvs (NonRec binder rhs) = do
            (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
            let
                env_ext_item = mk_binding bind_lv_info binder rhs

            return (StgNonRec binder rhs2,
                    bind_fvs, escs, bind_lv_info, [env_ext_item])

        vars_bind body_fvs (Rec pairs)
          = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
               let
                    rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
                    binders = map fst pairs
                    env_ext = [ mk_binding bind_lv_info b rhs
                              | (b,rhs) <- pairs ]
               in
               extendVarEnvLne env_ext $ do
                  (rhss2, fvss, lv_infos, escss)
                         <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
                  let
                            bind_fvs = unionFVInfos fvss
                            bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
                            escs     = unionVarSets escss

                  return (StgRec (binders `zip` rhss2),
                          bind_fvs, escs, bind_lv_info, env_ext)

    is_join_var :: Id -> Bool
    -- A hack (used only for compiler debuggging) to tell if
    -- a variable started life as a join point ($j)
    is_join_var j = occNameString (getOccName j) == "$j"

\end{code} \begin{code}

    coreToStgRhs :: FreeVarsInfo            -- Free var info for the scope of the binding
                 -> [Id]
                 -> (Id,CoreExpr)
                 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)

    coreToStgRhs scope_fv_info binders (bndr, rhs) = do
        (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
        lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
        return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
                rhs_fvs, lv_info, rhs_escs)
      where
        bndr_info = lookupFVInfo scope_fv_info bndr

    mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs

    mkStgRhs _ _ _ (StgConApp con args) = StgRhsCon noCCS con args

    mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
      = StgRhsClosure noCCS binder_info
                      (getFVs rhs_fvs)
                      ReEntrant
                      srt bndrs body

    mkStgRhs rhs_fvs srt binder_info rhs
      = StgRhsClosure noCCS binder_info
                      (getFVs rhs_fvs)
                      upd_flag srt [] rhs
      where
       upd_flag = Updatable
      {-
        SDM: disabled.  Eval/Apply can't handle functions with arity zero very
        well; and making these into simple non-updatable thunks breaks other
        assumptions (namely that they will be entered only once).

        upd_flag | isPAP env rhs  = ReEntrant
    	     | otherwise      = Updatable
      -}

    {- ToDo:
              upd = if isOnceDem dem
                        then (if isNotTop toplev
                                then SingleEntry    -- HA!  Paydirt for "dem"
                                else
    #ifdef DEBUG
                         trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
    #endif
                         Updatable)
                    else Updatable
            -- For now we forbid SingleEntry CAFs; they tickle the
            -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
            -- and I don't understand why.  There's only one SE_CAF (well,
            -- only one that tickled a great gaping bug in an earlier attempt
            -- at ClosureInfo.getEntryConvention) in the whole of nofib,
            -- specifically Main.lvl6 in spectral/cryptarithm2.
            -- So no great loss.  KSW 2000-07.
    -}

\end{code} Detect thunks which will reduce immediately to PAPs, and make them non-updatable. This has several advantages: - the non-updatable thunk behaves exactly like the PAP, - the thunk is more efficient to enter, because it is specialised to the task. - we save one update frame, one stg_update_PAP, one update and lots of PAP_enters. - in the case where the thunk is top-level, we save building a black hole and futhermore the thunk isn't considered to be a CAF any more, so it doesn't appear in any SRTs. We do it here, because the arity information is accurate, and we need to do it before the SRT pass to save the SRT entries associated with any top-level PAPs. isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args where arity = stgArity f (lookupBinding env f) isPAP env _ = False %************************************************************************ %* * \subsection[LNE-monad]{A little monad for this let-no-escaping pass} %* * %************************************************************************ There's a lot of stuff to pass around, so we use this @LneM@ monad to help. All the stuff here is only passed *down*. \begin{code}

    newtype LneM a = LneM
        { unLneM :: IdEnv HowBound
                 -> LiveInfo                -- Vars and CAFs live in continuation
                 -> a
        }

    type LiveInfo = (StgLiveVars,   -- Dynamic live variables;
                                    -- i.e. ones with a nested (non-top-level) binding
                     CafSet)        -- Static live variables;
                                    -- i.e. top-level variables that are CAFs or refer to them

    type EscVarsSet = IdSet
    type CafSet     = IdSet

    data HowBound
      = ImportBound         -- Used only as a response to lookupBinding; never
                            -- exists in the range of the (IdEnv HowBound)

      | LetBound            -- A let(rec) in this module
            LetInfo         -- Whether top level or nested
            Arity           -- Its arity (local Ids don't have arity info at this point)

      | LambdaBound         -- Used for both lambda and case

    data LetInfo
      = TopLet              -- top level things
      | NestedLet LiveInfo  -- For nested things, what is live if this
                            -- thing is live?  Invariant: the binder
                            -- itself is always a member of
                            -- the dynamic set of its own LiveInfo

    isLetBound :: HowBound -> Bool
    isLetBound (LetBound _ _) = True
    isLetBound _              = False

    topLevelBound :: HowBound -> Bool
    topLevelBound ImportBound         = True
    topLevelBound (LetBound TopLet _) = True
    topLevelBound _                   = False

\end{code} For a let(rec)-bound variable, x, we record LiveInfo, the set of variables that are live if x is live. This LiveInfo comprises (a) dynamic live variables (ones with a non-top-level binding) (b) static live variabes (CAFs or things that refer to CAFs) For "normal" variables (a) is just x alone. If x is a let-no-escaped variable then x is represented by a code pointer and a stack pointer (well, one for each stack). So all of the variables needed in the execution of x are live if x is, and are therefore recorded in the LetBound constructor; x itself *is* included. The set of dynamic live variables is guaranteed ot have no further let-no-escaped variables in it. \begin{code}

    emptyLiveInfo :: LiveInfo
    emptyLiveInfo = (emptyVarSet,emptyVarSet)

    unitLiveVar :: Id -> LiveInfo
    unitLiveVar lv = (unitVarSet lv, emptyVarSet)

    unitLiveCaf :: Id -> LiveInfo
    unitLiveCaf caf = (emptyVarSet, unitVarSet caf)

    addLiveVar :: LiveInfo -> Id -> LiveInfo
    addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)

    unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
    unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)

    mkSRT :: LiveInfo -> SRT
    mkSRT (_, cafs) = SRTEntries cafs

    getLiveVars :: LiveInfo -> StgLiveVars
    getLiveVars (lvs, _) = lvs

\end{code} The std monad functions: \begin{code}

    initLne :: IdEnv HowBound -> LneM a -> a
    initLne env m = unLneM m env emptyLiveInfo

    {-# INLINE thenLne #-}
    {-# INLINE returnLne #-}

    returnLne :: a -> LneM a
    returnLne e = LneM $ \_ _ -> e

    thenLne :: LneM a -> (a -> LneM b) -> LneM b
    thenLne m k = LneM $ \env lvs_cont
      -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont

    instance Monad LneM where
        return = returnLne
        (>>=)  = thenLne

    instance MonadFix LneM where
        mfix expr = LneM $ \env lvs_cont ->
                           let result = unLneM (expr result) env lvs_cont
                           in  result

\end{code} Functions specific to this monad: \begin{code}

    getVarsLiveInCont :: LneM LiveInfo
    getVarsLiveInCont = LneM $ \_env lvs_cont -> lvs_cont

    setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
    setVarsLiveInCont new_lvs_cont expr
       =    LneM $   \env _lvs_cont
       -> unLneM expr env new_lvs_cont

    extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
    extendVarEnvLne ids_w_howbound expr
       =    LneM $   \env lvs_cont
       -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont

    lookupVarLne :: Id -> LneM HowBound
    lookupVarLne v = LneM $ \env _lvs_cont -> lookupBinding env v

    lookupBinding :: IdEnv HowBound -> Id -> HowBound
    lookupBinding env v = case lookupVarEnv env v of
                            Just xx -> xx
                            Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound

    -- The result of lookupLiveVarsForSet, a set of live variables, is
    -- only ever tacked onto a decorated expression. It is never used as
    -- the basis of a control decision, which might give a black hole.

    freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
    freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
     where
      freeVarsToLiveVars' _env live_in_cont = live_info
       where
        live_info    = foldr unionLiveInfo live_in_cont lvs_from_fvs
        lvs_from_fvs = map do_one (allFreeIds fvs)

        do_one (v, how_bound)
          = case how_bound of
              ImportBound                     -> unitLiveCaf v      -- Only CAF imports are
                                                                    -- recorded in fvs
              LetBound TopLet _
                    | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
                    | otherwise                    -> emptyLiveInfo

              LetBound (NestedLet lvs) _      -> lvs        -- lvs already contains v
                                                            -- (see the invariant on NestedLet)

              _lambda_or_case_binding         -> unitLiveVar v      -- Bound by lambda or case

\end{code} %************************************************************************ %* * \subsection[Free-var info]{Free variable information} %* * %************************************************************************ \begin{code}

    type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
            -- The Var is so we can gather up the free variables
            -- as a set.
            --
            -- The HowBound info just saves repeated lookups;
            -- we look up just once when we encounter the occurrence.
            -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
            --            Imported Ids without CAF refs are simply
            --            not put in the FreeVarsInfo for an expression.
            --            See singletonFVInfo and freeVarsToLiveVars
            --
            -- StgBinderInfo records how it occurs; notably, we
            -- are interested in whether it only occurs in saturated
            -- applications, because then we don't need to build a
            -- curried version.
            -- If f is mapped to noBinderInfo, that means
            -- that f *is* mentioned (else it wouldn't be in the
            -- IdEnv at all), but perhaps in an unsaturated applications.
            --
            -- All case/lambda-bound things are also mapped to
            -- noBinderInfo, since we aren't interested in their
            -- occurence info.
            --
            -- For ILX we track free var info for type variables too;
            -- hence VarEnv not IdEnv

\end{code} \begin{code}

    emptyFVInfo :: FreeVarsInfo
    emptyFVInfo = emptyVarEnv

    singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
    -- Don't record non-CAF imports at all, to keep free-var sets small
    singletonFVInfo id ImportBound info
       | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
       | otherwise                     = emptyVarEnv
    singletonFVInfo id how_bound info  = unitVarEnv id (id, how_bound, info)

    unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
    unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2

    unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
    unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs

    minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
    minusFVBinders vs fv = foldr minusFVBinder fv vs

    minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
    minusFVBinder v fv = fv `delVarEnv` v
            -- When removing a binder, remember to add its type variables
            -- c.f. CoreFVs.delBinderFV

    elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
    elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)

    lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
    -- Find how the given Id is used.
    -- Externally visible things may be used any old how
    lookupFVInfo fvs id
      | isExternalName (idName id) = noBinderInfo
      | otherwise = case lookupVarEnv fvs id of
                            Nothing         -> noBinderInfo
                            Just (_,_,info) -> info

    allFreeIds :: FreeVarsInfo -> [(Id,HowBound)]   -- Both top level and non-top-level Ids
    allFreeIds fvs = ASSERT( all (isId . fst) ids ) ids
          where
            ids = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs]

    -- Non-top-level things only, both type variables and ids
    getFVs :: FreeVarsInfo -> [Var]
    getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
                        not (topLevelBound how_bound) ]

    getFVSet :: FreeVarsInfo -> VarSet
    getFVSet fvs = mkVarSet (getFVs fvs)

    plusFVInfo :: (Var, HowBound, StgBinderInfo)
               -> (Var, HowBound, StgBinderInfo)
               -> (Var, HowBound, StgBinderInfo)
    plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
      = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
        (id1, hb1, combineStgBinderInfo info1 info2)

    -- The HowBound info for a variable in the FVInfo should be consistent
    check_eq_how_bound :: HowBound -> HowBound -> Bool
    check_eq_how_bound ImportBound        ImportBound        = True
    check_eq_how_bound LambdaBound        LambdaBound        = True
    check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
    check_eq_how_bound _                  _                  = False

    check_eq_li :: LetInfo -> LetInfo -> Bool
    check_eq_li (NestedLet _) (NestedLet _) = True
    check_eq_li TopLet        TopLet        = True
    check_eq_li _             _             = False

\end{code} Misc. \begin{code}

    filterStgBinders :: [Var] -> [Var]
    filterStgBinders bndrs = filter isId bndrs

\end{code} \begin{code}

            -- Ignore all notes except SCC
    myCollectBinders :: Expr Var -> ([Var], Expr Var)
    myCollectBinders expr
      = go [] expr
      where
        go bs (Lam b e)          = go (b:bs) e
        go bs e@(Note (SCC _) _) = (reverse bs, e)
        go bs (Cast e _)         = go bs e
        go bs (Note _ e)         = go bs e
        go bs e                  = (reverse bs, e)

    myCollectArgs :: CoreExpr -> (Id, [CoreArg])
            -- We assume that we only have variables
            -- in the function position by now
    myCollectArgs expr
      = go expr []
      where
        go (Var v)          as = (v, as)
        go (App f a) as        = go f (a:as)
        go (Note (SCC _) _) _  = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
        go (Cast e _)       as = go e as
        go (Note _ e)       as = go e as
        go (Lam b e)        as
           | isTyCoVar b         = go e as  -- Note [Collect args]
        go _                _  = pprPanic "CoreToStg.myCollectArgs" (ppr expr)

\end{code} Note [Collect args] ~~~~~~~~~~~~~~~~~~~ This big-lambda case occurred following a rather obscure eta expansion. It all seems a bit yukky to me. \begin{code}

    stgArity :: Id -> HowBound -> Arity
    stgArity _ (LetBound _ arity) = arity
    stgArity f ImportBound        = idArity f
    stgArity _ LambdaBound        = 0

\end{code}