% % (c) The University of Glasgow, 1994-2006 % Core pass to saturate constructors and PrimOps \begin{code}

    module CorePrep (
          corePrepPgm, corePrepExpr
      ) where

    #include "HsVersions.h"

    import PrelNames	( lazyIdKey, hasKey )
    import CoreUtils
    import CoreArity
    import CoreFVs
    import CoreMonad	( endPass, CoreToDo(..) )
    import CoreSyn
    import CoreSubst
    import Type
    import Coercion
    import TyCon
    import Demand
    import Var
    import VarSet
    import VarEnv
    import Id
    import IdInfo
    import DataCon
    import PrimOp
    import BasicTypes
    import UniqSupply
    import Maybes
    import OrdList
    import ErrUtils
    import DynFlags
    import Util
    import Outputable
    import MonadUtils
    import FastString
    import Data.List	( mapAccumL )
    import Control.Monad

\end{code} -- --------------------------------------------------------------------------- -- Overview -- --------------------------------------------------------------------------- The goal of this pass is to prepare for code generation. 1. Saturate constructor and primop applications. 2. Convert to A-normal form; that is, function arguments are always variables. * Use case for strict arguments: f E ==> case E of x -> f x (where f is strict) * Use let for non-trivial lazy arguments f E ==> let x = E in f x (were f is lazy and x is non-trivial) 3. Similarly, convert any unboxed lets into cases. [I'm experimenting with leaving 'ok-for-speculation' rhss in let-form right up to this point.] 4. Ensure that *value* lambdas only occur as the RHS of a binding (The code generator can't deal with anything else.) Type lambdas are ok, however, because the code gen discards them. 5. [Not any more; nuked Jun 2002] Do the seq/par munging. 6. Clone all local Ids. This means that all such Ids are unique, rather than the weaker guarantee of no clashes which the simplifier provides. And that is what the code generator needs. We don't clone TyVars. The code gen doesn't need that, and doing so would be tiresome because then we'd need to substitute in types. 7. Give each dynamic CCall occurrence a fresh unique; this is rather like the cloning step above. 8. Inject bindings for the "implicit" Ids: * Constructor wrappers * Constructor workers We want curried definitions for all of these in case they aren't inlined by some caller. 9. Replace (lazy e) by e. See Note [lazyId magic] in MkId.lhs This is all done modulo type applications and abstractions, so that when type erasure is done for conversion to STG, we don't end up with any trivial or useless bindings. Invariants ~~~~~~~~~~ Here is the syntax of the Core produced by CorePrep: Trivial expressions triv ::= lit | var | triv ty | /\a. triv | triv |> co Applications app ::= lit | var | app triv | app ty | app |> co Expressions body ::= app | let(rec) x = rhs in body -- Boxed only | case body of pat -> body | /\a. body | body |> co Right hand sides (only place where lambdas can occur) rhs ::= /\a.rhs | \x.rhs | body We define a synonym for each of these non-terminals. Functions with the corresponding name produce a result in that syntax. \begin{code}

    type CpeTriv = CoreExpr	   -- Non-terminal 'triv'
    type CpeApp  = CoreExpr	   -- Non-terminal 'app'
    type CpeBody = CoreExpr	   -- Non-terminal 'body'
    type CpeRhs  = CoreExpr	   -- Non-terminal 'rhs'

\end{code} %************************************************************************ %* * Top level stuff %* * %************************************************************************ \begin{code}

    corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]
    corePrepPgm dflags binds data_tycons = do
        showPass dflags "CorePrep"
        us <- mkSplitUniqSupply 's'

        let implicit_binds = mkDataConWorkers data_tycons
                -- NB: we must feed mkImplicitBinds through corePrep too
                -- so that they are suitably cloned and eta-expanded

            binds_out = initUs_ us $ do
                          floats1 <- corePrepTopBinds binds
                          floats2 <- corePrepTopBinds implicit_binds
                          return (deFloatTop (floats1 `appendFloats` floats2))

        endPass dflags CorePrep binds_out []
        return binds_out

    corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
    corePrepExpr dflags expr = do
        showPass dflags "CorePrep"
        us <- mkSplitUniqSupply 's'
        let new_expr = initUs_ us (cpeBodyNF emptyCorePrepEnv expr)
        dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr)
        return new_expr

    corePrepTopBinds :: [CoreBind] -> UniqSM Floats
    -- Note [Floating out of top level bindings]
    corePrepTopBinds binds
      = go emptyCorePrepEnv binds
      where
        go _   []             = return emptyFloats
        go env (bind : binds) = do (env', bind') <- cpeBind TopLevel env bind
                                   binds' <- go env' binds
                                   return (bind' `appendFloats` binds')

    mkDataConWorkers :: [TyCon] -> [CoreBind]
    -- See Note [Data constructor workers]
    mkDataConWorkers data_tycons
      = [ NonRec id (Var id)	-- The ice is thin here, but it works
        | tycon <- data_tycons, 	-- CorePrep will eta-expand it
          data_con <- tyConDataCons tycon,
          let id = dataConWorkId data_con ]

\end{code} Note [Floating out of top level bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NB: we do need to float out of top-level bindings Consider x = length [True,False] We want to get s1 = False : [] s2 = True : s1 x = length s2 We return a *list* of bindings, because we may start with x* = f (g y) where x is demanded, in which case we want to finish with a = g y x* = f a And then x will actually end up case-bound Note [CafInfo and floating] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ What happens when we try to float bindings to the top level? At this point all the CafInfo is supposed to be correct, and we must make certain that is true of the new top-level bindings. There are two cases to consider a) The top-level binding is marked asCafRefs. In that case we are basically fine. The floated bindings had better all be lazy lets, so they can float to top level, but they'll all have HasCafRefs (the default) which is safe. b) The top-level binding is marked NoCafRefs. This really happens Example. CoreTidy produces $fApplicativeSTM [NoCafRefs] = D:Alternative retry# ...blah... Now CorePrep has to eta-expand to $fApplicativeSTM = let sat = \xy. retry x y in D:Alternative sat ...blah... So what we *want* is sat [NoCafRefs] = \xy. retry x y $fApplicativeSTM [NoCafRefs] = D:Alternative sat ...blah... So, gruesomely, we must set the NoCafRefs flag on the sat bindings, *and* substutite the modified 'sat' into the old RHS. It should be the case that 'sat' is itself [NoCafRefs] (a value, no cafs) else the original top-level binding would not itself have been marked [NoCafRefs]. The DEBUG check in CoreToStg for consistentCafInfo will find this. This is all very gruesome and horrible. It would be better to figure out CafInfo later, after CorePrep. We'll do that in due course. Meanwhile this horrible hack works. Note [Data constructor workers] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Create any necessary "implicit" bindings for data con workers. We create the rather strange (non-recursive!) binding $wC = \x y -> $wC x y i.e. a curried constructor that allocates. This means that we can treat the worker for a constructor like any other function in the rest of the compiler. The point here is that CoreToStg will generate a StgConApp for the RHS, rather than a call to the worker (which would give a loop). As Lennart says: the ice is thin here, but it works. Hmm. Should we create bindings for dictionary constructors? They are always fully applied, and the bindings are just there to support partial applications. But it's easier to let them through. %************************************************************************ %* * The main code %* * %************************************************************************ \begin{code}

    cpeBind :: TopLevelFlag
    	-> CorePrepEnv -> CoreBind
    	-> UniqSM (CorePrepEnv, Floats)
    cpeBind top_lvl env (NonRec bndr rhs)
      = do { (_, bndr1) <- cloneBndr env bndr
           ; let is_strict   = isStrictDmd (idDemandInfo bndr)
                 is_unlifted = isUnLiftedType (idType bndr)
           ; (floats, bndr2, rhs2) <- cpePair top_lvl NonRecursive
           	 	  	       	  	  (is_strict || is_unlifted)
    					  env bndr1 rhs
           ; let new_float = mkFloat is_strict is_unlifted bndr2 rhs2

            -- We want bndr'' in the envt, because it records
            -- the evaluated-ness of the binder
           ; return (extendCorePrepEnv env bndr bndr2,
           	         addFloat floats new_float) }

    cpeBind top_lvl env (Rec pairs)
      = do { let (bndrs,rhss) = unzip pairs
           ; (env', bndrs1) <- cloneBndrs env (map fst pairs)
           ; stuff <- zipWithM (cpePair top_lvl Recursive False env') bndrs1 rhss

           ; let (floats_s, bndrs2, rhss2) = unzip3 stuff
                 all_pairs = foldrOL add_float (bndrs2 `zip` rhss2)
    	     	       	 	 	   (concatFloats floats_s)
           ; return (extendCorePrepEnvList env (bndrs `zip` bndrs2),
           	 	 unitFloat (FloatLet (Rec all_pairs))) }
      where
    	-- Flatten all the floats, and the currrent
    	-- group into a single giant Rec
        add_float (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
        add_float (FloatLet (Rec prs1))   prs2 = prs1 ++ prs2
        add_float b                       _    = pprPanic "cpeBind" (ppr b)

    ---------------
    cpePair :: TopLevelFlag -> RecFlag -> RhsDemand
    	-> CorePrepEnv -> Id -> CoreExpr
    	-> UniqSM (Floats, Id, CpeRhs)
    -- Used for all bindings
    cpePair top_lvl is_rec is_strict_or_unlifted env bndr rhs
      = do { (floats1, rhs1) <- cpeRhsE env rhs

           -- See if we are allowed to float this stuff out of the RHS
           ; (floats2, rhs2) <- float_from_rhs floats1 rhs1

           -- Make the arity match up
           ; (floats3, rhs')
                <- if manifestArity rhs1 <= arity
    	       then return (floats2, cpeEtaExpand arity rhs2)
    	       else WARN(True, text "CorePrep: silly extra arguments:" <+> ppr bndr)
    	       	    	       -- Note [Silly extra arguments]
    	       	    (do { v <- newVar (idType bndr)
    		        ; let float = mkFloat False False v rhs2
    		        ; return (addFloat floats2 float, cpeEtaExpand arity (Var v)) })

         	-- Record if the binder is evaluated
    	-- and otherwise trim off the unfolding altogether
    	-- It's not used by the code generator; getting rid of it reduces
    	-- heap usage and, since we may be changing uniques, we'd have
    	-- to substitute to keep it right
           ; let bndr' | exprIsHNF rhs' = bndr `setIdUnfolding` evaldUnfolding
           	     	   | otherwise      = bndr `setIdUnfolding` noUnfolding

           ; return (floats3, bndr', rhs') }
      where
        arity = idArity bndr	-- We must match this arity

        ---------------------
        float_from_rhs floats rhs
          | isEmptyFloats floats = return (emptyFloats, rhs)
          | isTopLevel top_lvl    = float_top    floats rhs
          | otherwise             = float_nested floats rhs

        ---------------------
        float_nested floats rhs
          | wantFloatNested is_rec is_strict_or_unlifted floats rhs
                      = return (floats, rhs)
          | otherwise = dont_float floats rhs

        ---------------------
        float_top floats rhs	-- Urhgh!  See Note [CafInfo and floating]
          | mayHaveCafRefs (idCafInfo bndr)
          , allLazyTop floats
          = return (floats, rhs)

          -- So the top-level binding is marked NoCafRefs
          | Just (floats', rhs') <- canFloatFromNoCaf floats rhs
          = return (floats', rhs')

          | otherwise
          = dont_float floats rhs

        ---------------------
        dont_float floats rhs
          -- Non-empty floats, but do not want to float from rhs
          -- So wrap the rhs in the floats
          -- But: rhs1 might have lambdas, and we can't
          --      put them inside a wrapBinds
          = do { body <- rhsToBodyNF rhs
      	   ; return (emptyFloats, wrapBinds floats body) }

    {- Note [Silly extra arguments]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Suppose we had this
    	f{arity=1} = \x\y. e
    We *must* match the arity on the Id, so we have to generate
            f' = \x\y. e
     	f  = \x. f' x

    It's a bizarre case: why is the arity on the Id wrong?  Reason
    (in the days of __inline_me__):
            f{arity=0} = __inline_me__ (let v = expensive in \xy. e)
    When InlineMe notes go away this won't happen any more.  But
    it seems good for CorePrep to be robust.
    -}

    -- ---------------------------------------------------------------------------
    --		CpeRhs: produces a result satisfying CpeRhs
    -- ---------------------------------------------------------------------------

    cpeRhsE :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)
    -- If
    --	e  ===>  (bs, e')
    -- then
    --	e = let bs in e'	(semantically, that is!)
    --
    -- For example
    --	f (g x)	  ===>   ([v = g x], f v)

    cpeRhsE _env expr@(Type _) = return (emptyFloats, expr)
    cpeRhsE _env expr@(Lit _)  = return (emptyFloats, expr)
    cpeRhsE env expr@(Var {})  = cpeApp env expr

    cpeRhsE env (Var f `App` _ `App` arg)
      | f `hasKey` lazyIdKey  	  -- Replace (lazy a) by a
      = cpeRhsE env arg		  -- See Note [lazyId magic] in MkId

    cpeRhsE env expr@(App {}) = cpeApp env expr

    cpeRhsE env (Let bind expr)
      = do { (env', new_binds) <- cpeBind NotTopLevel env bind
           ; (floats, body) <- cpeRhsE env' expr
           ; return (new_binds `appendFloats` floats, body) }

    cpeRhsE env (Note note expr)
      | ignoreNote note
      = cpeRhsE env expr
      | otherwise	      -- Just SCCs actually
      = do { body <- cpeBodyNF env expr
           ; return (emptyFloats, Note note body) }

    cpeRhsE env (Cast expr co)
       = do { (floats, expr') <- cpeRhsE env expr
            ; return (floats, Cast expr' co) }

    cpeRhsE env expr@(Lam {})
       = do { let (bndrs,body) = collectBinders expr
            ; (env', bndrs') <- cloneBndrs env bndrs
    	; body' <- cpeBodyNF env' body
    	; return (emptyFloats, mkLams bndrs' body') }

    cpeRhsE env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
      | Just (TickBox {}) <- isTickBoxOp_maybe id
      = do { body <- cpeBodyNF env expr
           ; return (emptyFloats, Case (Var id) bndr ty [(DEFAULT,[],body)]) }

    cpeRhsE env (Case scrut bndr ty alts)
      = do { (floats, scrut') <- cpeBody env scrut
           ; let bndr1 = bndr `setIdUnfolding` evaldUnfolding
                -- Record that the case binder is evaluated in the alternatives
           ; (env', bndr2) <- cloneBndr env bndr1
           ; alts' <- mapM (sat_alt env') alts
           ; return (floats, Case scrut' bndr2 ty alts') }
      where
        sat_alt env (con, bs, rhs)
           = do { (env2, bs') <- cloneBndrs env bs
                ; rhs' <- cpeBodyNF env2 rhs
                ; return (con, bs', rhs') }

    -- ---------------------------------------------------------------------------
    --		CpeBody: produces a result satisfying CpeBody
    -- ---------------------------------------------------------------------------

    cpeBodyNF :: CorePrepEnv -> CoreExpr -> UniqSM CpeBody
    cpeBodyNF env expr
      = do { (floats, body) <- cpeBody env expr
           ; return (wrapBinds floats body) }

    --------
    cpeBody :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeBody)
    cpeBody env expr
      = do { (floats1, rhs) <- cpeRhsE env expr
           ; (floats2, body) <- rhsToBody rhs
           ; return (floats1 `appendFloats` floats2, body) }

    --------
    rhsToBodyNF :: CpeRhs -> UniqSM CpeBody
    rhsToBodyNF rhs = do { (floats,body) <- rhsToBody rhs
    	    	     ; return (wrapBinds floats body) }

    --------
    rhsToBody :: CpeRhs -> UniqSM (Floats, CpeBody)
    -- Remove top level lambdas by let-binding

    rhsToBody (Note n expr)
            -- You can get things like
            --      case e of { p -> coerce t (\s -> ...) }
      = do { (floats, expr') <- rhsToBody expr
           ; return (floats, Note n expr') }

    rhsToBody (Cast e co)
      = do { (floats, e') <- rhsToBody e
           ; return (floats, Cast e' co) }

    rhsToBody expr@(Lam {})
      | Just no_lam_result <- tryEtaReducePrep bndrs body
      = return (emptyFloats, no_lam_result)
      | all isTyCoVar bndrs		-- Type lambdas are ok
      = return (emptyFloats, expr)
      | otherwise			-- Some value lambdas
      = do { fn <- newVar (exprType expr)
           ; let rhs   = cpeEtaExpand (exprArity expr) expr
           	     float = FloatLet (NonRec fn rhs)
           ; return (unitFloat float, Var fn) }
      where
        (bndrs,body) = collectBinders expr

    rhsToBody expr = return (emptyFloats, expr)

    -- ---------------------------------------------------------------------------
    --		CpeApp: produces a result satisfying CpeApp
    -- ---------------------------------------------------------------------------

    cpeApp :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)
    -- May return a CpeRhs because of saturating primops
    cpeApp env expr
      = do { (app, (head,depth), _, floats, ss) <- collect_args expr 0
           ; MASSERT(null ss)	-- make sure we used all the strictness info

    	-- Now deal with the function
           ; case head of
               Var fn_id -> do { sat_app <- maybeSaturate fn_id app depth
    	       	     	   ; return (floats, sat_app) }
               _other    -> return (floats, app) }

      where
        -- Deconstruct and rebuild the application, floating any non-atomic
        -- arguments to the outside.  We collect the type of the expression,
        -- the head of the application, and the number of actual value arguments,
        -- all of which are used to possibly saturate this application if it
        -- has a constructor or primop at the head.

        collect_args
    	:: CoreExpr
    	-> Int			   -- Current app depth
    	-> UniqSM (CpeApp,	   -- The rebuilt expression
    		   (CoreExpr,Int), -- The head of the application,
    				   -- and no. of args it was applied to
    		   Type,	   -- Type of the whole expr
    		   Floats, 	   -- Any floats we pulled out
    		   [Demand])	   -- Remaining argument demands

        collect_args (App fun arg@(Type arg_ty)) depth
          = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun depth
               ; return (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss) }

        collect_args (App fun arg) depth
          = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
          	   ; let
                  (ss1, ss_rest)   = case ss of
                                       (ss1:ss_rest) -> (ss1,     ss_rest)
                                       []            -> (lazyDmd, [])
                  (arg_ty, res_ty) = expectJust "cpeBody:collect_args" $
                                     splitFunTy_maybe fun_ty

               ; (fs, arg') <- cpeArg env (isStrictDmd ss1) arg arg_ty
               ; return (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest) }

        collect_args (Var v) depth
          = do { v1 <- fiddleCCall v
               ; let v2 = lookupCorePrepEnv env v1
               ; return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts) }
    	where
    	  stricts = case idStrictness v of
    			StrictSig (DmdType _ demands _)
    			    | listLengthCmp demands depth /= GT -> demands
    			            -- length demands <= depth
    			    | otherwise                         -> []
    		-- If depth < length demands, then we have too few args to
    		-- satisfy strictness  info so we have to  ignore all the
    		-- strictness info, e.g. + (error "urk")
    		-- Here, we can't evaluate the arg strictly, because this
    		-- partial application might be seq'd

        collect_args (Cast fun co) depth
          = do { let (_ty1,ty2) = coercionKind co
               ; (fun', hd, _, floats, ss) <- collect_args fun depth
               ; return (Cast fun' co, hd, ty2, floats, ss) }

        collect_args (Note note fun) depth
          | ignoreNote note         -- Drop these notes altogether
          = collect_args fun depth  -- They aren't used by the code generator

    	-- N-variable fun, better let-bind it
        collect_args fun depth
          = do { (fun_floats, fun') <- cpeArg env True fun ty
          	     		  -- The True says that it's sure to be evaluated,
    			  -- so we'll end up case-binding it
               ; return (fun', (fun', depth), ty, fun_floats, []) }
            where
    	  ty = exprType fun

    -- ---------------------------------------------------------------------------
    --	CpeArg: produces a result satisfying CpeArg
    -- ---------------------------------------------------------------------------

    -- This is where we arrange that a non-trivial argument is let-bound
    cpeArg :: CorePrepEnv -> RhsDemand -> CoreArg -> Type
           -> UniqSM (Floats, CpeTriv)
    cpeArg env is_strict arg arg_ty
      | cpe_ExprIsTrivial arg   -- Do not eta expand etc a trivial argument
      = cpeBody env arg	    -- Must still do substitution though
      | otherwise
      = do { (floats1, arg1) <- cpeRhsE env arg	-- arg1 can be a lambda
           ; (floats2, arg2) <- if want_float floats1 arg1
           	 	   	    then return (floats1, arg1)
           	 	   	    else do { body1 <- rhsToBodyNF arg1
      			            ; return (emptyFloats, wrapBinds floats1 body1) }
    	 	-- Else case: arg1 might have lambdas, and we can't
    		--            put them inside a wrapBinds

           ; v <- newVar arg_ty
           ; let arg3      = cpeEtaExpand (exprArity arg2) arg2
           	     arg_float = mkFloat is_strict is_unlifted v arg3
           ; return (addFloat floats2 arg_float, Var v) }
      where
        is_unlifted = isUnLiftedType arg_ty
        want_float = wantFloatNested NonRecursive (is_strict || is_unlifted)

\end{code} Note [Floating unlifted arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider C (let v* = expensive in v) where the "*" indicates "will be demanded". Usually v will have been inlined by now, but let's suppose it hasn't (see Trac #2756). Then we do *not* want to get let v* = expensive in C v because that has different strictness. Hence the use of 'allLazy'. (NB: the let v* turns into a FloatCase, in mkLocalNonRec.) ------------------------------------------------------------------------------ -- Building the saturated syntax -- --------------------------------------------------------------------------- maybeSaturate deals with saturating primops and constructors The type is the type of the entire application \begin{code}

    maybeSaturate :: Id -> CpeApp -> Int -> UniqSM CpeRhs
    maybeSaturate fn expr n_args
      | Just DataToTagOp <- isPrimOpId_maybe fn     -- DataToTag must have an evaluated arg
                                                    -- A gruesome special case
      = saturateDataToTag sat_expr

      | hasNoBinding fn 	   -- There's no binding
      = return sat_expr

      | otherwise
      = return expr
      where
        fn_arity	 = idArity fn
        excess_arity = fn_arity - n_args
        sat_expr     = cpeEtaExpand excess_arity expr

    -------------
    saturateDataToTag :: CpeApp -> UniqSM CpeApp
    -- Horrid: ensure that the arg of data2TagOp is evaluated
    --   (data2tag x) -->  (case x of y -> data2tag y)
    -- (yuk yuk) take into account the lambdas we've now introduced
    saturateDataToTag sat_expr
      = do { let (eta_bndrs, eta_body) = collectBinders sat_expr
           ; eta_body' <- eval_data2tag_arg eta_body
           ; return (mkLams eta_bndrs eta_body') }
      where
        eval_data2tag_arg :: CpeApp -> UniqSM CpeBody
        eval_data2tag_arg app@(fun `App` arg)
            | exprIsHNF arg         -- Includes nullary constructors
            = return app		-- The arg is evaluated
            | otherwise                     -- Arg not evaluated, so evaluate it
            = do { arg_id <- newVar (exprType arg)
                 ; let arg_id1 = setIdUnfolding arg_id evaldUnfolding
                 ; return (Case arg arg_id1 (exprType app)
                                [(DEFAULT, [], fun `App` Var arg_id1)]) }

        eval_data2tag_arg (Note note app)	-- Scc notes can appear
            = do { app' <- eval_data2tag_arg app
                 ; return (Note note app') }

        eval_data2tag_arg other	-- Should not happen
    	= pprPanic "eval_data2tag" (ppr other)

\end{code} %************************************************************************ %* * Simple CoreSyn operations %* * %************************************************************************ \begin{code}

    	-- We don't ignore SCCs, since they require some code generation
    ignoreNote :: Note -> Bool
    -- Tells which notes to drop altogether; they are ignored by code generation
    -- Do not ignore SCCs!
    -- It's important that we do drop InlineMe notes; for example
    --    unzip = __inline_me__ (/\ab. foldr (..) (..))
    -- Here unzip gets arity 1 so we'll eta-expand it. But we don't
    -- want to get this:
    --     unzip = /\ab \xs. (__inline_me__ ...) a b xs
    ignoreNote (CoreNote _) = True
    ignoreNote _other       = False

    cpe_ExprIsTrivial :: CoreExpr -> Bool
    -- Version that doesn't consider an scc annotation to be trivial.
    cpe_ExprIsTrivial (Var _)                  = True
    cpe_ExprIsTrivial (Type _)                 = True
    cpe_ExprIsTrivial (Lit _)                  = True
    cpe_ExprIsTrivial (App e arg)              = isTypeArg arg && cpe_ExprIsTrivial e
    cpe_ExprIsTrivial (Note n e)               = notSccNote n  && cpe_ExprIsTrivial e
    cpe_ExprIsTrivial (Cast e _)               = cpe_ExprIsTrivial e
    cpe_ExprIsTrivial (Lam b body) | isTyCoVar b = cpe_ExprIsTrivial body
    cpe_ExprIsTrivial _                        = False

\end{code} -- ----------------------------------------------------------------------------- -- Eta reduction -- ----------------------------------------------------------------------------- Note [Eta expansion] ~~~~~~~~~~~~~~~~~~~~~ Eta expand to match the arity claimed by the binder Remember, CorePrep must not change arity Eta expansion might not have happened already, because it is done by the simplifier only when there at least one lambda already. NB1:we could refrain when the RHS is trivial (which can happen for exported things). This would reduce the amount of code generated (a little) and make things a little words for code compiled without -O. The case in point is data constructor wrappers. NB2: we have to be careful that the result of etaExpand doesn't invalidate any of the assumptions that CorePrep is attempting to establish. One possible cause is eta expanding inside of an SCC note - we're now careful in etaExpand to make sure the SCC is pushed inside any new lambdas that are generated. Note [Eta expansion and the CorePrep invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It turns out to be much much easier to do eta expansion *after* the main CorePrep stuff. But that places constraints on the eta expander: given a CpeRhs, it must return a CpeRhs. For example here is what we do not want: f = /\a -> g (h 3) -- h has arity 2 After ANFing we get f = /\a -> let s = h 3 in g s and now we do NOT want eta expansion to give f = /\a -> \ y -> (let s = h 3 in g s) y Instead CoreArity.etaExpand gives f = /\a -> \y -> let s = h 3 in g s y \begin{code}

    cpeEtaExpand :: Arity -> CpeRhs -> CpeRhs
    cpeEtaExpand arity expr
      | arity == 0 = expr
      | otherwise  = etaExpand arity expr

\end{code} -- ----------------------------------------------------------------------------- -- Eta reduction -- ----------------------------------------------------------------------------- Why try eta reduction? Hasn't the simplifier already done eta? But the simplifier only eta reduces if that leaves something trivial (like f, or f Int). But for deLam it would be enough to get to a partial application: case x of { p -> \xs. map f xs } ==> case x of { p -> map f } \begin{code}

    tryEtaReducePrep :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr
    tryEtaReducePrep bndrs expr@(App _ _)
      | ok_to_eta_reduce f &&
        n_remaining >= 0 &&
        and (zipWith ok bndrs last_args) &&
        not (any (`elemVarSet` fvs_remaining) bndrs)
      = Just remaining_expr
      where
        (f, args) = collectArgs expr
        remaining_expr = mkApps f remaining_args
        fvs_remaining = exprFreeVars remaining_expr
        (remaining_args, last_args) = splitAt n_remaining args
        n_remaining = length args - length bndrs

        ok bndr (Var arg) = bndr == arg
        ok _    _         = False

    	  -- we can't eta reduce something which must be saturated.
        ok_to_eta_reduce (Var f) = not (hasNoBinding f)
        ok_to_eta_reduce _       = False --safe. ToDo: generalise

    tryEtaReducePrep bndrs (Let bind@(NonRec _ r) body)
      | not (any (`elemVarSet` fvs) bndrs)
      = case tryEtaReducePrep bndrs body of
    	Just e -> Just (Let bind e)
    	Nothing -> Nothing
      where
        fvs = exprFreeVars r

    tryEtaReducePrep _ _ = Nothing

\end{code} -- ----------------------------------------------------------------------------- -- Demands -- ----------------------------------------------------------------------------- \begin{code}

    type RhsDemand = Bool  -- True => used strictly; hence not top-level, non-recursive

\end{code} %************************************************************************ %* * Floats %* * %************************************************************************ \begin{code}

    data FloatingBind
      = FloatLet CoreBind	 -- Rhs of bindings are CpeRhss
        	     		 -- They are always of lifted type;
     			 -- unlifted ones are done with FloatCase

     | FloatCase
          Id CpeBody
          Bool		-- The bool indicates "ok-for-speculation"

    data Floats = Floats OkToSpec (OrdList FloatingBind)

    instance Outputable FloatingBind where
      ppr (FloatLet b) = ppr b
      ppr (FloatCase b r ok) = brackets (ppr ok) <+> ppr b <+> equals <+> ppr r

    instance Outputable Floats where
      ppr (Floats flag fs) = ptext (sLit "Floats") <> brackets (ppr flag) <+>
                             braces (vcat (map ppr (fromOL fs)))

    instance Outputable OkToSpec where
      ppr OkToSpec    = ptext (sLit "OkToSpec")
      ppr IfUnboxedOk = ptext (sLit "IfUnboxedOk")
      ppr NotOkToSpec = ptext (sLit "NotOkToSpec")

    -- Can we float these binds out of the rhs of a let?  We cache this decision
    -- to avoid having to recompute it in a non-linear way when there are
    -- deeply nested lets.
    data OkToSpec
       = OkToSpec		-- Lazy bindings of lifted type
       | IfUnboxedOk	-- A mixture of lazy lifted bindings and n
         			-- ok-to-speculate unlifted bindings
       | NotOkToSpec 	-- Some not-ok-to-speculate unlifted bindings

    mkFloat :: Bool -> Bool -> Id -> CpeRhs -> FloatingBind
    mkFloat is_strict is_unlifted bndr rhs
      | use_case  = FloatCase bndr rhs (exprOkForSpeculation rhs)
      | otherwise = FloatLet (NonRec bndr rhs)
      where
        use_case = is_unlifted || is_strict && not (exprIsHNF rhs)
         	      	-- Don't make a case for a value binding,
    		-- even if it's strict.  Otherwise we get
    		-- 	case (\x -> e) of ...!

    emptyFloats :: Floats
    emptyFloats = Floats OkToSpec nilOL

    isEmptyFloats :: Floats -> Bool
    isEmptyFloats (Floats _ bs) = isNilOL bs

    wrapBinds :: Floats -> CpeBody -> CpeBody
    wrapBinds (Floats _ binds) body
      = foldrOL mk_bind body binds
      where
        mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
        mk_bind (FloatLet bind)        body = Let bind body

    addFloat :: Floats -> FloatingBind -> Floats
    addFloat (Floats ok_to_spec floats) new_float
      = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
      where
        check (FloatLet _) = OkToSpec
        check (FloatCase _ _ ok_for_spec)
    	| ok_for_spec  =  IfUnboxedOk
    	| otherwise    =  NotOkToSpec
    	-- The ok-for-speculation flag says that it's safe to
    	-- float this Case out of a let, and thereby do it more eagerly
    	-- We need the top-level flag because it's never ok to float
    	-- an unboxed binding to the top level

    unitFloat :: FloatingBind -> Floats
    unitFloat = addFloat emptyFloats

    appendFloats :: Floats -> Floats -> Floats
    appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
      = Floats (combine spec1 spec2) (floats1 `appOL` floats2)

    concatFloats :: [Floats] -> OrdList FloatingBind
    concatFloats = foldr (\ (Floats _ bs1) bs2 -> appOL bs1 bs2) nilOL

    combine :: OkToSpec -> OkToSpec -> OkToSpec
    combine NotOkToSpec _ = NotOkToSpec
    combine _ NotOkToSpec = NotOkToSpec
    combine IfUnboxedOk _ = IfUnboxedOk
    combine _ IfUnboxedOk = IfUnboxedOk
    combine _ _           = OkToSpec

    deFloatTop :: Floats -> [CoreBind]
    -- For top level only; we don't expect any FloatCases
    deFloatTop (Floats _ floats)
      = foldrOL get [] floats
      where
        get (FloatLet b) bs = b:bs
        get b            _  = pprPanic "corePrepPgm" (ppr b)

    -------------------------------------------
    canFloatFromNoCaf ::  Floats -> CpeRhs -> Maybe (Floats, CpeRhs)
           -- Note [CafInfo and floating]
    canFloatFromNoCaf (Floats ok_to_spec fs) rhs
      | OkToSpec <- ok_to_spec 	     -- Worth trying
      , Just (subst, fs') <- go (emptySubst, nilOL) (fromOL fs)
      = Just (Floats OkToSpec fs', subst_expr subst rhs)
      | otherwise
      = Nothing
      where
        subst_expr = substExpr (text "CorePrep")

        go :: (Subst, OrdList FloatingBind) -> [FloatingBind]
           -> Maybe (Subst, OrdList FloatingBind)

        go (subst, fbs_out) [] = Just (subst, fbs_out)

        go (subst, fbs_out) (FloatLet (NonRec b r) : fbs_in)
          | rhs_ok r
          = go (subst', fbs_out `snocOL` new_fb) fbs_in
          where
            (subst', b') = set_nocaf_bndr subst b
            new_fb = FloatLet (NonRec b' (subst_expr subst r))

        go (subst, fbs_out) (FloatLet (Rec prs) : fbs_in)
          | all rhs_ok rs
          = go (subst', fbs_out `snocOL` new_fb) fbs_in
          where
            (bs,rs) = unzip prs
            (subst', bs') = mapAccumL set_nocaf_bndr subst bs
            rs' = map (subst_expr subst') rs
            new_fb = FloatLet (Rec (bs' `zip` rs'))

        go _ _ = Nothing	  -- Encountered a caffy binding

        ------------
        set_nocaf_bndr subst bndr
          = (extendIdSubst subst bndr (Var bndr'), bndr')
          where
            bndr' = bndr `setIdCafInfo` NoCafRefs

        ------------
        rhs_ok :: CoreExpr -> Bool
        -- We can only float to top level from a NoCaf thing if
        -- the new binding is static. However it can't mention
        -- any non-static things or it would *already* be Caffy
        rhs_ok = rhsIsStatic (\_ -> False)

    wantFloatNested :: RecFlag -> Bool -> Floats -> CpeRhs -> Bool
    wantFloatNested is_rec strict_or_unlifted floats rhs
      =  isEmptyFloats floats
      || strict_or_unlifted
      || (allLazyNested is_rec floats && exprIsHNF rhs)
       	-- Why the test for allLazyNested?
    	--	v = f (x `divInt#` y)
    	-- we don't want to float the case, even if f has arity 2,
    	-- because floating the case would make it evaluated too early

    allLazyTop :: Floats -> Bool
    allLazyTop (Floats OkToSpec _) = True
    allLazyTop _ 	   	       = False

    allLazyNested :: RecFlag -> Floats -> Bool
    allLazyNested _      (Floats OkToSpec    _) = True
    allLazyNested _      (Floats NotOkToSpec _) = False
    allLazyNested is_rec (Floats IfUnboxedOk _) = isNonRec is_rec

\end{code} %************************************************************************ %* * Cloning %* * %************************************************************************ \begin{code}

    -- ---------------------------------------------------------------------------
    -- 			The environment
    -- ---------------------------------------------------------------------------

    data CorePrepEnv = CPE (IdEnv Id)	-- Clone local Ids

    emptyCorePrepEnv :: CorePrepEnv
    emptyCorePrepEnv = CPE emptyVarEnv

    extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
    extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')

    extendCorePrepEnvList :: CorePrepEnv -> [(Id,Id)] -> CorePrepEnv
    extendCorePrepEnvList (CPE env) prs = CPE (extendVarEnvList env prs)

    lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
    lookupCorePrepEnv (CPE env) id
      = case lookupVarEnv env id of
    	Nothing	 -> id
    	Just id' -> id'

    ------------------------------------------------------------------------------
    -- Cloning binders
    -- ---------------------------------------------------------------------------

    cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
    cloneBndrs env bs = mapAccumLM cloneBndr env bs

    cloneBndr  :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
    cloneBndr env bndr
      | isLocalId bndr
      = do bndr' <- setVarUnique bndr <$> getUniqueM
           return (extendCorePrepEnv env bndr bndr', bndr')

      | otherwise	-- Top level things, which we don't want
    		-- to clone, have become GlobalIds by now
    		-- And we don't clone tyvars
      = return (env, bndr)

    ------------------------------------------------------------------------------
    -- Cloning ccall Ids; each must have a unique name,
    -- to give the code generator a handle to hang it on
    -- ---------------------------------------------------------------------------

    fiddleCCall :: Id -> UniqSM Id
    fiddleCCall id
      | isFCallId id = (id `setVarUnique`) <$> getUniqueM
      | otherwise    = return id

    ------------------------------------------------------------------------------
    -- Generating new binders
    -- ---------------------------------------------------------------------------

    newVar :: Type -> UniqSM Id
    newVar ty
     = seqType ty `seq` do
         uniq <- getUniqueM
         return (mkSysLocal (fsLit "sat") uniq ty)

\end{code}