+{-# OPTIONS -fno-warn-missing-signatures #-}
module Vectorise( vectorise )
where
-import VectMonad
-import VectUtils
-import VectType
-import VectCore
+import Vectorise.Type.Env
+import Vectorise.Type.Type
+import Vectorise.Convert
+import Vectorise.Utils.Hoisting
+import Vectorise.Exp
+import Vectorise.Vect
+import Vectorise.Env
+import Vectorise.Monad
import HscTypes hiding ( MonadThings(..) )
-
import Module ( PackageId )
import CoreSyn
-import CoreUtils
-import CoreUnfold ( mkInlineRule )
-import MkCore ( mkWildCase )
+import CoreUnfold ( mkInlineUnfolding )
import CoreFVs
import CoreMonad ( CoreM, getHscEnv )
-import DataCon
-import TyCon
-import Type
import FamInstEnv ( extendFamInstEnvList )
import Var
-import VarEnv
-import VarSet
import Id
import OccName
import BasicTypes ( isLoopBreaker )
-
-import Literal ( Literal, mkMachInt )
-import TysWiredIn
-import TysPrim ( intPrimTy )
-
import Outputable
-import FastString
import Util ( zipLazy )
+import MonadUtils
+
import Control.Monad
-import Data.List ( sortBy, unzip4 )
+debug = False
+dtrace s x = if debug then pprTrace "Vectorise" s x else x
+
+-- | Vectorise a single module.
+-- Takes the package containing the DPH backend we're using. Eg either dph-par or dph-seq.
vectorise :: PackageId -> ModGuts -> CoreM ModGuts
-vectorise backend guts = do
- hsc_env <- getHscEnv
- liftIO $ vectoriseIO backend hsc_env guts
+vectorise backend guts
+ = do hsc_env <- getHscEnv
+ liftIO $ vectoriseIO backend hsc_env guts
+
+-- | Vectorise a single monad, given its HscEnv (code gen environment).
vectoriseIO :: PackageId -> HscEnv -> ModGuts -> IO ModGuts
vectoriseIO backend hsc_env guts
- = do
+ = do -- Get information about currently loaded external packages.
eps <- hscEPS hsc_env
+
+ -- Combine vectorisation info from the current module, and external ones.
let info = hptVectInfo hsc_env `plusVectInfo` eps_vect_info eps
+
+ -- Run the main VM computation.
Just (info', guts') <- initV backend hsc_env guts info (vectModule guts)
return (guts' { mg_vect_info = info' })
+
+-- | Vectorise a single module, in the VM monad.
vectModule :: ModGuts -> VM ModGuts
vectModule guts
- = do
+ = do -- Vectorise the type environment.
+ -- This may add new TyCons and DataCons.
+ -- TODO: What new binds do we get back here?
(types', fam_insts, tc_binds) <- vectTypeEnv (mg_types guts)
+ -- TODO: What is this?
let fam_inst_env' = extendFamInstEnvList (mg_fam_inst_env guts) fam_insts
updGEnv (setFamInstEnv fam_inst_env')
-- dicts <- mapM buildPADict pa_insts
-- workers <- mapM vectDataConWorkers pa_insts
+
+ -- Vectorise all the top level bindings.
binds' <- mapM vectTopBind (mg_binds guts)
+
return $ guts { mg_types = types'
, mg_binds = Rec tc_binds : binds'
, mg_fam_inst_env = fam_inst_env'
, mg_fam_insts = mg_fam_insts guts ++ fam_insts
}
+
+-- | Try to vectorise a top-level binding.
+-- If it doesn't vectorise then return it unharmed.
+--
+-- For example, for the binding
+--
+-- @
+-- foo :: Int -> Int
+-- foo = \x -> x + x
+-- @
+--
+-- we get
+-- @
+-- foo :: Int -> Int
+-- foo = \x -> vfoo $: x
+--
+-- v_foo :: Closure void vfoo lfoo
+-- v_foo = closure vfoo lfoo void
+--
+-- vfoo :: Void -> Int -> Int
+-- vfoo = ...
+--
+-- lfoo :: PData Void -> PData Int -> PData Int
+-- lfoo = ...
+-- @
+--
+-- @vfoo@ is the "vectorised", or scalar, version that does the same as the original
+-- function foo, but takes an explicit environment.
+--
+-- @lfoo@ is the "lifted" version that works on arrays.
+--
+-- @v_foo@ combines both of these into a `Closure` that also contains the
+-- environment.
+--
+-- The original binding @foo@ is rewritten to call the vectorised version
+-- present in the closure.
+--
vectTopBind :: CoreBind -> VM CoreBind
vectTopBind b@(NonRec var expr)
- = do
- (inline, expr') <- vectTopRhs var expr
- var' <- vectTopBinder var inline expr'
- hs <- takeHoisted
- cexpr <- tryConvert var var' expr
+ = do
+ (inline, expr') <- vectTopRhs var expr
+ var' <- vectTopBinder var inline expr'
+
+ -- Vectorising the body may create other top-level bindings.
+ hs <- takeHoisted
+
+ -- To get the same functionality as the original body we project
+ -- out its vectorised version from the closure.
+ cexpr <- tryConvert var var' expr
+
return . Rec $ (var, cexpr) : (var', expr') : hs
`orElseV`
return b
vectTopBind b@(Rec bs)
- = do
- (vars', _, exprs') <- fixV $ \ ~(_, inlines, rhss) ->
- do
- vars' <- sequence [vectTopBinder var inline rhs
- | (var, ~(inline, rhs))
- <- zipLazy vars (zip inlines rhss)]
- (inlines', exprs') <- mapAndUnzipM (uncurry vectTopRhs) bs
- return (vars', inlines', exprs')
+ = do
+ (vars', _, exprs')
+ <- fixV $ \ ~(_, inlines, rhss) ->
+ do vars' <- sequence [vectTopBinder var inline rhs
+ | (var, ~(inline, rhs)) <- zipLazy vars (zip inlines rhss)]
+ (inlines', exprs')
+ <- mapAndUnzipM (uncurry vectTopRhs) bs
+
+ return (vars', inlines', exprs')
+
hs <- takeHoisted
cexprs <- sequence $ zipWith3 tryConvert vars vars' exprs
return . Rec $ zip vars cexprs ++ zip vars' exprs' ++ hs
where
(vars, exprs) = unzip bs
--- NOTE: vectTopBinder *MUST* be lazy in inline and expr because of how it is
--- used inside of fixV in vectTopBind
-vectTopBinder :: Var -> Inline -> CoreExpr -> VM Var
+
+-- | Make the vectorised version of this top level binder, and add the mapping
+-- between it and the original to the state. For some binder @foo@ the vectorised
+-- version is @$v_foo@
+--
+-- NOTE: vectTopBinder *MUST* be lazy in inline and expr because of how it is
+-- used inside of fixV in vectTopBind
+vectTopBinder
+ :: Var -- ^ Name of the binding.
+ -> Inline -- ^ Whether it should be inlined, used to annotate it.
+ -> CoreExpr -- ^ RHS of the binding, used to set the `Unfolding` of the returned `Var`.
+ -> VM Var -- ^ Name of the vectorised binding.
+
vectTopBinder var inline expr
- = do
+ = do
+ -- Vectorise the type attached to the var.
vty <- vectType (idType var)
- var' <- liftM (`setIdUnfolding` unfolding) $ cloneId mkVectOcc var vty
+
+ -- Make the vectorised version of binding's name, and set the unfolding used for inlining.
+ var' <- liftM (`setIdUnfoldingLazily` unfolding)
+ $ cloneId mkVectOcc var vty
+
+ -- Add the mapping between the plain and vectorised name to the state.
defGlobalVar var var'
+
return var'
where
unfolding = case inline of
- Inline arity -> mkInlineRule needSaturated expr arity
+ Inline arity -> mkInlineUnfolding (Just arity) expr
DontInline -> noUnfolding
-vectTopRhs :: Var -> CoreExpr -> VM (Inline, CoreExpr)
+
+-- | Vectorise the RHS of a top-level binding, in an empty local environment.
+vectTopRhs
+ :: Var -- ^ Name of the binding.
+ -> CoreExpr -- ^ Body of the binding.
+ -> VM (Inline, CoreExpr)
+
vectTopRhs var expr
- = closedV
- $ do
- (inline, vexpr) <- inBind var
- $ vectPolyExpr (isLoopBreaker $ idOccInfo var)
+ = dtrace (vcat [text "vectTopRhs", ppr expr])
+ $ closedV
+ $ do (inline, vexpr) <- inBind var
+ $ vectPolyExpr (isLoopBreaker $ idOccInfo var)
(freeVars expr)
return (inline, vectorised vexpr)
-tryConvert :: Var -> Var -> CoreExpr -> VM CoreExpr
-tryConvert var vect_var rhs
- = fromVect (idType var) (Var vect_var) `orElseV` return rhs
-
--- ----------------------------------------------------------------------------
--- Bindings
-
-vectBndr :: Var -> VM VVar
-vectBndr v
- = do
- (vty, lty) <- vectAndLiftType (idType v)
- let vv = v `Id.setIdType` vty
- lv = v `Id.setIdType` lty
- updLEnv (mapTo vv lv)
- return (vv, lv)
- where
- mapTo vv lv env = env { local_vars = extendVarEnv (local_vars env) v (vv, lv) }
-
-vectBndrNew :: Var -> FastString -> VM VVar
-vectBndrNew v fs
- = do
- vty <- vectType (idType v)
- vv <- newLocalVVar fs vty
- updLEnv (upd vv)
- return vv
- where
- upd vv env = env { local_vars = extendVarEnv (local_vars env) v vv }
-
-vectBndrIn :: Var -> VM a -> VM (VVar, a)
-vectBndrIn v p
- = localV
- $ do
- vv <- vectBndr v
- x <- p
- return (vv, x)
-
-vectBndrNewIn :: Var -> FastString -> VM a -> VM (VVar, a)
-vectBndrNewIn v fs p
- = localV
- $ do
- vv <- vectBndrNew v fs
- x <- p
- return (vv, x)
-
-vectBndrsIn :: [Var] -> VM a -> VM ([VVar], a)
-vectBndrsIn vs p
- = localV
- $ do
- vvs <- mapM vectBndr vs
- x <- p
- return (vvs, x)
-
--- ----------------------------------------------------------------------------
--- Expressions
-
-vectVar :: Var -> VM VExpr
-vectVar v
- = do
- r <- lookupVar v
- case r of
- Local (vv,lv) -> return (Var vv, Var lv)
- Global vv -> do
- let vexpr = Var vv
- lexpr <- liftPD vexpr
- return (vexpr, lexpr)
-
-vectPolyVar :: Var -> [Type] -> VM VExpr
-vectPolyVar v tys
- = do
- vtys <- mapM vectType tys
- r <- lookupVar v
- case r of
- Local (vv, lv) -> liftM2 (,) (polyApply (Var vv) vtys)
- (polyApply (Var lv) vtys)
- Global poly -> do
- vexpr <- polyApply (Var poly) vtys
- lexpr <- liftPD vexpr
- return (vexpr, lexpr)
-
-vectLiteral :: Literal -> VM VExpr
-vectLiteral lit
- = do
- lexpr <- liftPD (Lit lit)
- return (Lit lit, lexpr)
-
-vectPolyExpr :: Bool -> CoreExprWithFVs -> VM (Inline, VExpr)
-vectPolyExpr loop_breaker (_, AnnNote note expr)
- = do
- (inline, expr') <- vectPolyExpr loop_breaker expr
- return (inline, vNote note expr')
-vectPolyExpr loop_breaker expr
- = do
- arity <- polyArity tvs
- polyAbstract tvs $ \args ->
- do
- (inline, mono') <- vectFnExpr False loop_breaker mono
- return (addInlineArity inline arity,
- mapVect (mkLams $ tvs ++ args) mono')
- where
- (tvs, mono) = collectAnnTypeBinders expr
-
-vectExpr :: CoreExprWithFVs -> VM VExpr
-vectExpr (_, AnnType ty)
- = liftM vType (vectType ty)
-
-vectExpr (_, AnnVar v) = vectVar v
-
-vectExpr (_, AnnLit lit) = vectLiteral lit
-
-vectExpr (_, AnnNote note expr)
- = liftM (vNote note) (vectExpr expr)
-vectExpr e@(_, AnnApp _ arg)
- | isAnnTypeArg arg
- = vectTyAppExpr fn tys
- where
- (fn, tys) = collectAnnTypeArgs e
-
-vectExpr (_, AnnApp (_, AnnVar v) (_, AnnLit lit))
- | Just con <- isDataConId_maybe v
- , is_special_con con
- = do
- let vexpr = App (Var v) (Lit lit)
- lexpr <- liftPD vexpr
- return (vexpr, lexpr)
- where
- is_special_con con = con `elem` [intDataCon, floatDataCon, doubleDataCon]
-
-
-vectExpr (_, AnnApp fn arg)
- = do
- arg_ty' <- vectType arg_ty
- res_ty' <- vectType res_ty
- fn' <- vectExpr fn
- arg' <- vectExpr arg
- mkClosureApp arg_ty' res_ty' fn' arg'
- where
- (arg_ty, res_ty) = splitFunTy . exprType $ deAnnotate fn
+-- | Project out the vectorised version of a binding from some closure,
+-- or return the original body if that doesn't work.
+tryConvert
+ :: Var -- ^ Name of the original binding (eg @foo@)
+ -> Var -- ^ Name of vectorised version of binding (eg @$vfoo@)
+ -> CoreExpr -- ^ The original body of the binding.
+ -> VM CoreExpr
-vectExpr (_, AnnCase scrut bndr ty alts)
- | Just (tycon, ty_args) <- splitTyConApp_maybe scrut_ty
- , isAlgTyCon tycon
- = vectAlgCase tycon ty_args scrut bndr ty alts
- where
- scrut_ty = exprType (deAnnotate scrut)
-
-vectExpr (_, AnnLet (AnnNonRec bndr rhs) body)
- = do
- vrhs <- localV . inBind bndr . liftM snd $ vectPolyExpr False rhs
- (vbndr, vbody) <- vectBndrIn bndr (vectExpr body)
- return $ vLet (vNonRec vbndr vrhs) vbody
-
-vectExpr (_, AnnLet (AnnRec bs) body)
- = do
- (vbndrs, (vrhss, vbody)) <- vectBndrsIn bndrs
- $ liftM2 (,)
- (zipWithM vect_rhs bndrs rhss)
- (vectExpr body)
- return $ vLet (vRec vbndrs vrhss) vbody
- where
- (bndrs, rhss) = unzip bs
-
- vect_rhs bndr rhs = localV
- . inBind bndr
- . liftM snd
- $ vectPolyExpr (isLoopBreaker $ idOccInfo bndr) rhs
-
-vectExpr e@(_, AnnLam bndr _)
- | isId bndr = liftM snd $ vectFnExpr True False e
-{-
-onlyIfV (isEmptyVarSet fvs) (vectScalarLam bs $ deAnnotate body)
- `orElseV` vectLam True fvs bs body
- where
- (bs,body) = collectAnnValBinders e
--}
-
-vectExpr e = cantVectorise "Can't vectorise expression" (ppr $ deAnnotate e)
-
-vectFnExpr :: Bool -> Bool -> CoreExprWithFVs -> VM (Inline, VExpr)
-vectFnExpr inline loop_breaker e@(fvs, AnnLam bndr _)
- | isId bndr = onlyIfV (isEmptyVarSet fvs)
- (mark DontInline . vectScalarLam bs $ deAnnotate body)
- `orElseV` mark inlineMe (vectLam inline loop_breaker fvs bs body)
- where
- (bs,body) = collectAnnValBinders e
-vectFnExpr _ _ e = mark DontInline $ vectExpr e
-
-mark :: Inline -> VM a -> VM (Inline, a)
-mark b p = do { x <- p; return (b,x) }
-
-vectScalarLam :: [Var] -> CoreExpr -> VM VExpr
-vectScalarLam args body
- = do
- scalars <- globalScalars
- onlyIfV (all is_scalar_ty arg_tys
- && is_scalar_ty res_ty
- && is_scalar (extendVarSetList scalars args) body)
- $ do
- fn_var <- hoistExpr (fsLit "fn") (mkLams args body) DontInline
- zipf <- zipScalars arg_tys res_ty
- clo <- scalarClosure arg_tys res_ty (Var fn_var)
- (zipf `App` Var fn_var)
- clo_var <- hoistExpr (fsLit "clo") clo DontInline
- lclo <- liftPD (Var clo_var)
- return (Var clo_var, lclo)
- where
- arg_tys = map idType args
- res_ty = exprType body
-
- is_scalar_ty ty | Just (tycon, []) <- splitTyConApp_maybe ty
- = tycon == intTyCon
- || tycon == floatTyCon
- || tycon == doubleTyCon
-
- | otherwise = False
-
- is_scalar vs (Var v) = v `elemVarSet` vs
- is_scalar _ e@(Lit _) = is_scalar_ty $ exprType e
- is_scalar vs (App e1 e2) = is_scalar vs e1 && is_scalar vs e2
- is_scalar _ _ = False
-
-vectLam :: Bool -> Bool -> VarSet -> [Var] -> CoreExprWithFVs -> VM VExpr
-vectLam inline loop_breaker fvs bs body
- = do
- tyvars <- localTyVars
- (vs, vvs) <- readLEnv $ \env ->
- unzip [(var, vv) | var <- varSetElems fvs
- , Just vv <- [lookupVarEnv (local_vars env) var]]
-
- arg_tys <- mapM (vectType . idType) bs
- res_ty <- vectType (exprType $ deAnnotate body)
-
- buildClosures tyvars vvs arg_tys res_ty
- . hoistPolyVExpr tyvars (maybe_inline (length vs + length bs))
- $ do
- lc <- builtin liftingContext
- (vbndrs, vbody) <- vectBndrsIn (vs ++ bs)
- (vectExpr body)
- vbody' <- break_loop lc res_ty vbody
- return $ vLams lc vbndrs vbody'
- where
- maybe_inline n | inline = Inline n
- | otherwise = DontInline
-
- break_loop lc ty (ve, le)
- | loop_breaker
- = do
- empty <- emptyPD ty
- lty <- mkPDataType ty
- return (ve, mkWildCase (Var lc) intPrimTy lty
- [(DEFAULT, [], le),
- (LitAlt (mkMachInt 0), [], empty)])
-
- | otherwise = return (ve, le)
-
-
-vectTyAppExpr :: CoreExprWithFVs -> [Type] -> VM VExpr
-vectTyAppExpr (_, AnnVar v) tys = vectPolyVar v tys
-vectTyAppExpr e tys = cantVectorise "Can't vectorise expression"
- (ppr $ deAnnotate e `mkTyApps` tys)
-
--- We convert
---
--- case e :: t of v { ... }
---
--- to
---
--- V: let v' = e in case v' of _ { ... }
--- L: let v' = e in case v' `cast` ... of _ { ... }
---
--- When lifting, we have to do it this way because v must have the type
--- [:V(T):] but the scrutinee must be cast to the representation type. We also
--- have to handle the case where v is a wild var correctly.
---
-
--- FIXME: this is too lazy
-vectAlgCase :: TyCon -> [Type] -> CoreExprWithFVs -> Var -> Type
- -> [(AltCon, [Var], CoreExprWithFVs)]
- -> VM VExpr
-vectAlgCase _tycon _ty_args scrut bndr ty [(DEFAULT, [], body)]
- = do
- vscrut <- vectExpr scrut
- (vty, lty) <- vectAndLiftType ty
- (vbndr, vbody) <- vectBndrIn bndr (vectExpr body)
- return $ vCaseDEFAULT vscrut vbndr vty lty vbody
-
-vectAlgCase _tycon _ty_args scrut bndr ty [(DataAlt _, [], body)]
- = do
- vscrut <- vectExpr scrut
- (vty, lty) <- vectAndLiftType ty
- (vbndr, vbody) <- vectBndrIn bndr (vectExpr body)
- return $ vCaseDEFAULT vscrut vbndr vty lty vbody
-
-vectAlgCase _tycon _ty_args scrut bndr ty [(DataAlt dc, bndrs, body)]
- = do
- (vty, lty) <- vectAndLiftType ty
- vexpr <- vectExpr scrut
- (vbndr, (vbndrs, (vect_body, lift_body)))
- <- vect_scrut_bndr
- . vectBndrsIn bndrs
- $ vectExpr body
- let (vect_bndrs, lift_bndrs) = unzip vbndrs
- (vscrut, lscrut, pdata_tc, _arg_tys) <- mkVScrut (vVar vbndr)
- vect_dc <- maybeV (lookupDataCon dc)
- let [pdata_dc] = tyConDataCons pdata_tc
-
- let vcase = mk_wild_case vscrut vty vect_dc vect_bndrs vect_body
- lcase = mk_wild_case lscrut lty pdata_dc lift_bndrs lift_body
-
- return $ vLet (vNonRec vbndr vexpr) (vcase, lcase)
- where
- vect_scrut_bndr | isDeadBinder bndr = vectBndrNewIn bndr (fsLit "scrut")
- | otherwise = vectBndrIn bndr
-
- mk_wild_case expr ty dc bndrs body
- = mkWildCase expr (exprType expr) ty [(DataAlt dc, bndrs, body)]
-
-vectAlgCase tycon _ty_args scrut bndr ty alts
- = do
- vect_tc <- maybeV (lookupTyCon tycon)
- (vty, lty) <- vectAndLiftType ty
-
- let arity = length (tyConDataCons vect_tc)
- sel_ty <- builtin (selTy arity)
- sel_bndr <- newLocalVar (fsLit "sel") sel_ty
- let sel = Var sel_bndr
-
- (vbndr, valts) <- vect_scrut_bndr
- $ mapM (proc_alt arity sel vty lty) alts'
- let (vect_dcs, vect_bndrss, lift_bndrss, vbodies) = unzip4 valts
-
- vexpr <- vectExpr scrut
- (vect_scrut, lift_scrut, pdata_tc, _arg_tys) <- mkVScrut (vVar vbndr)
- let [pdata_dc] = tyConDataCons pdata_tc
-
- let (vect_bodies, lift_bodies) = unzip vbodies
-
- vdummy <- newDummyVar (exprType vect_scrut)
- ldummy <- newDummyVar (exprType lift_scrut)
- let vect_case = Case vect_scrut vdummy vty
- (zipWith3 mk_vect_alt vect_dcs vect_bndrss vect_bodies)
-
- lc <- builtin liftingContext
- lbody <- combinePD vty (Var lc) sel lift_bodies
- let lift_case = Case lift_scrut ldummy lty
- [(DataAlt pdata_dc, sel_bndr : concat lift_bndrss,
- lbody)]
-
- return . vLet (vNonRec vbndr vexpr)
- $ (vect_case, lift_case)
- where
- vect_scrut_bndr | isDeadBinder bndr = vectBndrNewIn bndr (fsLit "scrut")
- | otherwise = vectBndrIn bndr
-
- alts' = sortBy (\(alt1, _, _) (alt2, _, _) -> cmp alt1 alt2) alts
-
- cmp (DataAlt dc1) (DataAlt dc2) = dataConTag dc1 `compare` dataConTag dc2
- cmp DEFAULT DEFAULT = EQ
- cmp DEFAULT _ = LT
- cmp _ DEFAULT = GT
- cmp _ _ = panic "vectAlgCase/cmp"
-
- proc_alt arity sel _ lty (DataAlt dc, bndrs, body)
- = do
- vect_dc <- maybeV (lookupDataCon dc)
- let ntag = dataConTagZ vect_dc
- tag = mkDataConTag vect_dc
- fvs = freeVarsOf body `delVarSetList` bndrs
-
- sel_tags <- liftM (`App` sel) (builtin (selTags arity))
- lc <- builtin liftingContext
- elems <- builtin (selElements arity ntag)
-
- (vbndrs, vbody)
- <- vectBndrsIn bndrs
- . localV
- $ do
- binds <- mapM (pack_var (Var lc) sel_tags tag)
- . filter isLocalId
- $ varSetElems fvs
- (ve, le) <- vectExpr body
- return (ve, Case (elems `App` sel) lc lty
- [(DEFAULT, [], (mkLets (concat binds) le))])
- -- empty <- emptyPD vty
- -- return (ve, Case (elems `App` sel) lc lty
- -- [(DEFAULT, [], Let (NonRec flags_var flags_expr)
- -- $ mkLets (concat binds) le),
- -- (LitAlt (mkMachInt 0), [], empty)])
- let (vect_bndrs, lift_bndrs) = unzip vbndrs
- return (vect_dc, vect_bndrs, lift_bndrs, vbody)
-
- proc_alt _ _ _ _ _ = panic "vectAlgCase/proc_alt"
-
- mk_vect_alt vect_dc bndrs body = (DataAlt vect_dc, bndrs, body)
-
- pack_var len tags t v
- = do
- r <- lookupVar v
- case r of
- Local (vv, lv) ->
- do
- lv' <- cloneVar lv
- expr <- packByTagPD (idType vv) (Var lv) len tags t
- updLEnv (\env -> env { local_vars = extendVarEnv
- (local_vars env) v (vv, lv') })
- return [(NonRec lv' expr)]
-
- _ -> return []
+tryConvert var vect_var rhs
+ = fromVect (idType var) (Var vect_var) `orElseV` return rhs