X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fvectorise%2FVectUtils.hs;h=c7336efbc58514c01999e79115a88dc308a621a7;hb=724425265ded8958a719b3a62f43006674b506c8;hp=5b70bf4fdf2e8531d0cb0cdf99a30c419e6d982b;hpb=35380dd876960a2e88e8743545615040f08b4f27;p=ghc-hetmet.git

diff --git a/compiler/vectorise/VectUtils.hs b/compiler/vectorise/VectUtils.hs
index 5b70bf4..c7336ef 100644
--- a/compiler/vectorise/VectUtils.hs
+++ b/compiler/vectorise/VectUtils.hs
@@ -1,28 +1,49 @@
 module VectUtils (
   collectAnnTypeBinders, collectAnnTypeArgs, isAnnTypeArg,
+  collectAnnValBinders,
+  mkDataConTag,
   splitClosureTy,
-  mkPADictType, mkPArrayType,
-  paDictArgType, paDictOfType,
-  lookupPArrayFamInst,
-  hoistExpr
+
+  TyConRepr(..), mkTyConRepr,
+  mkToArrPRepr, mkFromPRepr, mkFromArrPRepr,
+  mkPADictType, mkPArrayType, mkPReprType,
+
+  parrayCoerce, parrayReprTyCon, parrayReprDataCon, mkVScrut,
+  prDictOfType, prCoerce,
+  paDictArgType, paDictOfType, paDFunType,
+  paMethod, lengthPA, replicatePA, emptyPA, liftPA,
+  polyAbstract, polyApply, polyVApply,
+  hoistBinding, hoistExpr, hoistPolyVExpr, takeHoisted,
+  buildClosure, buildClosures,
+  mkClosureApp
 ) where
 
 #include "HsVersions.h"
 
+import VectCore
 import VectMonad
 
+import DsUtils
 import CoreSyn
 import CoreUtils
+import Coercion
 import Type
 import TypeRep
 import TyCon
+import DataCon
 import Var
+import Id                 ( mkWildId )
+import MkId               ( unwrapFamInstScrut )
+import Name               ( Name )
 import PrelNames
+import TysWiredIn
+import BasicTypes         ( Boxity(..) )
 
 import Outputable
 import FastString
 
-import Control.Monad         ( liftM )
+import Data.List             ( zipWith4 )
+import Control.Monad         ( liftM, liftM2, zipWithM_ )
 
 collectAnnTypeArgs :: AnnExpr b ann -> (AnnExpr b ann, [Type])
 collectAnnTypeArgs expr = go expr []
@@ -36,32 +57,263 @@ collectAnnTypeBinders expr = go [] expr
     go bs (_, AnnLam b e) | isTyVar b = go (b:bs) e
     go bs e                           = (reverse bs, e)
 
+collectAnnValBinders :: AnnExpr Var ann -> ([Var], AnnExpr Var ann)
+collectAnnValBinders expr = go [] expr
+  where
+    go bs (_, AnnLam b e) | isId b = go (b:bs) e
+    go bs e                        = (reverse bs, e)
+
 isAnnTypeArg :: AnnExpr b ann -> Bool
 isAnnTypeArg (_, AnnType t) = True
 isAnnTypeArg _              = False
 
-isClosureTyCon :: TyCon -> Bool
-isClosureTyCon tc = tyConUnique tc == closureTyConKey
+mkDataConTag :: DataCon -> CoreExpr
+mkDataConTag dc = mkConApp intDataCon [mkIntLitInt $ dataConTag dc]
+
+splitUnTy :: String -> Name -> Type -> Type
+splitUnTy s name ty
+  | Just (tc, [ty']) <- splitTyConApp_maybe ty
+  , tyConName tc == name
+  = ty'
+
+  | otherwise = pprPanic s (ppr ty)
+
+splitBinTy :: String -> Name -> Type -> (Type, Type)
+splitBinTy s name ty
+  | Just (tc, [ty1, ty2]) <- splitTyConApp_maybe ty
+  , tyConName tc == name
+  = (ty1, ty2)
+
+  | otherwise = pprPanic s (ppr ty)
+
+splitFixedTyConApp :: TyCon -> Type -> [Type]
+splitFixedTyConApp tc ty
+  | Just (tc', tys) <- splitTyConApp_maybe ty
+  , tc == tc'
+  = tys
+
+  | otherwise = pprPanic "splitFixedTyConApp" (ppr tc <+> ppr ty)
 
 splitClosureTy :: Type -> (Type, Type)
-splitClosureTy ty
-  | Just (tc, [arg_ty, res_ty]) <- splitTyConApp_maybe ty
-  , isClosureTyCon tc
-  = (arg_ty, res_ty)
+splitClosureTy = splitBinTy "splitClosureTy" closureTyConName
 
-  | otherwise = pprPanic "splitClosureTy" (ppr ty)
+splitPArrayTy :: Type -> Type
+splitPArrayTy = splitUnTy "splitPArrayTy" parrayTyConName
 
-mkPADictType :: Type -> VM Type
-mkPADictType ty
+mkBuiltinTyConApp :: (Builtins -> TyCon) -> [Type] -> VM Type
+mkBuiltinTyConApp get_tc tys
+  = do
+      tc <- builtin get_tc
+      return $ mkTyConApp tc tys
+
+mkBuiltinTyConApps :: (Builtins -> TyCon) -> [Type] -> Type -> VM Type
+mkBuiltinTyConApps get_tc tys ty
+  = do
+      tc <- builtin get_tc
+      return $ foldr (mk tc) ty tys
+  where
+    mk tc ty1 ty2 = mkTyConApp tc [ty1,ty2]
+
+mkBuiltinTyConApps1 :: (Builtins -> TyCon) -> Type -> [Type] -> VM Type
+mkBuiltinTyConApps1 get_tc dft [] = return dft
+mkBuiltinTyConApps1 get_tc dft tys
+  = do
+      tc <- builtin get_tc
+      case tys of
+        [] -> pprPanic "mkBuiltinTyConApps1" (ppr tc)
+        _  -> return $ foldr1 (mk tc) tys
+  where
+    mk tc ty1 ty2 = mkTyConApp tc [ty1,ty2]
+
+data TyConRepr = TyConRepr {
+                   repr_tyvars      :: [TyVar]
+                 , repr_tys         :: [[Type]]
+
+                 , repr_prod_tycons :: [Maybe TyCon]
+                 , repr_prod_tys    :: [Type]
+                 , repr_sum_tycon   :: Maybe TyCon
+                 , repr_type        :: Type
+                 }
+
+mkTyConRepr :: TyCon -> VM TyConRepr
+mkTyConRepr vect_tc
   = do
-      tc <- builtin paDictTyCon
-      return $ TyConApp tc [ty]
+      prod_tycons <- mapM (mk_tycon prodTyCon) rep_tys
+      let prod_tys = zipWith mk_tc_app_maybe prod_tycons rep_tys
+      sum_tycon   <- mk_tycon sumTyCon prod_tys
+
+      return $ TyConRepr {
+                 repr_tyvars      = tyvars
+               , repr_tys         = rep_tys
+
+               , repr_prod_tycons = prod_tycons
+               , repr_prod_tys    = prod_tys
+               , repr_sum_tycon   = sum_tycon
+               , repr_type        = mk_tc_app_maybe sum_tycon prod_tys
+               }
+  where
+    tyvars = tyConTyVars vect_tc
+    data_cons = tyConDataCons vect_tc
+    rep_tys   = map dataConRepArgTys data_cons
+
+    mk_tycon get_tc tys
+      | n > 1     = builtin (Just . get_tc n)
+      | otherwise = return Nothing
+      where n = length tys
+
+    mk_tc_app_maybe Nothing   []   = unitTy
+    mk_tc_app_maybe Nothing   [ty] = ty
+    mk_tc_app_maybe (Just tc) tys  = mkTyConApp tc tys
+
+mkToArrPRepr :: CoreExpr -> CoreExpr -> [[CoreExpr]] -> VM CoreExpr
+mkToArrPRepr len sel ess
+  = do
+      let mk_sum [(expr, ty)] = return (expr, ty)
+          mk_sum es
+            = do
+                sum_tc <- builtin . sumTyCon $ length es
+                (sum_rtc, _) <- parrayReprTyCon (mkTyConApp sum_tc tys)
+                let [sum_rdc] = tyConDataCons sum_rtc
+
+                return (mkConApp sum_rdc (map Type tys ++ (len : sel : exprs)),
+                        mkTyConApp sum_tc tys)
+            where
+              (exprs, tys) = unzip es
+
+          mk_prod [expr] = return (expr, splitPArrayTy (exprType expr))
+          mk_prod exprs
+            = do
+                prod_tc <- builtin . prodTyCon $ length exprs
+                (prod_rtc, _) <- parrayReprTyCon (mkTyConApp prod_tc tys)
+                let [prod_rdc] = tyConDataCons prod_rtc
+
+                return (mkConApp prod_rdc (map Type tys ++ (len : exprs)),
+                        mkTyConApp prod_tc tys)
+            where
+              tys = map (splitPArrayTy . exprType) exprs
+
+      liftM fst (mk_sum =<< mapM mk_prod ess)
+
+mkFromPRepr :: CoreExpr -> Type -> [([Var], CoreExpr)] -> VM CoreExpr
+mkFromPRepr scrut res_ty alts
+  = do
+      sum_tcs  <- builtins sumTyCon
+      prod_tcs <- builtins prodTyCon
+
+      let un_sum expr ty [(vars, res)] = un_prod expr ty vars res
+          un_sum expr ty bs
+            = do
+                ps     <- mapM (newLocalVar FSLIT("p")) tys
+                bodies <- sequence
+                        $ zipWith4 un_prod (map Var ps) tys vars rs
+                return . Case expr (mkWildId ty) res_ty
+                       $ zipWith3 mk_alt sum_dcs ps bodies
+            where
+              (vars, rs) = unzip bs
+              tys        = splitFixedTyConApp sum_tc ty
+              sum_tc     = sum_tcs $ length bs
+              sum_dcs    = tyConDataCons sum_tc
+
+              mk_alt dc p body = (DataAlt dc, [p], body)
+
+          un_prod expr ty []    r = return r
+          un_prod expr ty [var] r = return $ Let (NonRec var expr) r
+          un_prod expr ty vars  r
+            = return $ Case expr (mkWildId ty) res_ty
+                       [(DataAlt prod_dc, vars, r)]
+            where
+              prod_tc   = prod_tcs $ length vars
+              [prod_dc] = tyConDataCons prod_tc
+
+      un_sum scrut (exprType scrut) alts
+
+mkFromArrPRepr :: CoreExpr -> Type -> Var -> Var -> [[Var]] -> CoreExpr
+               -> VM CoreExpr
+mkFromArrPRepr scrut res_ty len sel vars res
+  = return (Var unitDataConId)
+
+mkClosureType :: Type -> Type -> VM Type
+mkClosureType arg_ty res_ty = mkBuiltinTyConApp closureTyCon [arg_ty, res_ty]
+
+mkClosureTypes :: [Type] -> Type -> VM Type
+mkClosureTypes = mkBuiltinTyConApps closureTyCon
+
+mkPReprType :: Type -> VM Type
+mkPReprType ty = mkBuiltinTyConApp preprTyCon [ty]
+
+mkPADictType :: Type -> VM Type
+mkPADictType ty = mkBuiltinTyConApp paTyCon [ty]
 
 mkPArrayType :: Type -> VM Type
-mkPArrayType ty
+mkPArrayType ty = mkBuiltinTyConApp parrayTyCon [ty]
+
+parrayCoerce :: TyCon -> [Type] -> CoreExpr -> VM CoreExpr
+parrayCoerce repr_tc args expr
+  | Just arg_co <- tyConFamilyCoercion_maybe repr_tc
   = do
-      tc <- builtin parrayTyCon
-      return $ TyConApp tc [ty]
+      parray <- builtin parrayTyCon
+
+      let co = mkAppCoercion (mkTyConApp parray [])
+                             (mkSymCoercion (mkTyConApp arg_co args))
+
+      return $ mkCoerce co expr
+
+parrayReprTyCon :: Type -> VM (TyCon, [Type])
+parrayReprTyCon ty = builtin parrayTyCon >>= (`lookupFamInst` [ty])
+
+parrayReprDataCon :: Type -> VM (DataCon, [Type])
+parrayReprDataCon ty
+  = do
+      (tc, arg_tys) <- parrayReprTyCon ty
+      let [dc] = tyConDataCons tc
+      return (dc, arg_tys)
+
+mkVScrut :: VExpr -> VM (VExpr, TyCon, [Type])
+mkVScrut (ve, le)
+  = do
+      (tc, arg_tys) <- parrayReprTyCon (exprType ve)
+      return ((ve, unwrapFamInstScrut tc arg_tys le), tc, arg_tys)
+
+prDictOfType :: Type -> VM CoreExpr
+prDictOfType orig_ty
+  | Just (tycon, ty_args) <- splitTyConApp_maybe orig_ty
+  = do
+      dfun <- traceMaybeV "prDictOfType" (ppr tycon) (lookupTyConPR tycon)
+      prDFunApply (Var dfun) ty_args
+
+prDFunApply :: CoreExpr -> [Type] -> VM CoreExpr
+prDFunApply dfun tys
+  = do
+      args <- mapM mkDFunArg arg_tys
+      return $ mkApps mono_dfun args
+  where
+    mono_dfun    = mkTyApps dfun tys
+    (arg_tys, _) = splitFunTys (exprType mono_dfun)
+
+mkDFunArg :: Type -> VM CoreExpr
+mkDFunArg ty
+  | Just (tycon, [arg]) <- splitTyConApp_maybe ty
+
+  = let name = tyConName tycon
+
+        get_dict | name == paTyConName = paDictOfType
+                 | name == prTyConName = prDictOfType
+                 | otherwise           = pprPanic "mkDFunArg" (ppr ty)
+
+    in get_dict arg
+
+mkDFunArg ty = pprPanic "mkDFunArg" (ppr ty)
+
+prCoerce :: TyCon -> [Type] -> CoreExpr -> VM CoreExpr
+prCoerce repr_tc args expr
+  | Just arg_co <- tyConFamilyCoercion_maybe repr_tc
+  = do
+      pr_tc <- builtin prTyCon
+
+      let co = mkAppCoercion (mkTyConApp pr_tc [])
+                             (mkSymCoercion (mkTyConApp arg_co args))
+
+      return $ mkCoerce co expr
 
 paDictArgType :: TyVar -> VM (Maybe Type)
 paDictArgType tv = go (TyVarTy tv) (tyVarKind tv)
@@ -97,25 +349,234 @@ paDictOfTyApp (TyVarTy tv) ty_args
       paDFunApply dfun ty_args
 paDictOfTyApp (TyConApp tc _) ty_args
   = do
-      pa_class <- builtin paClass
-      (dfun, ty_args') <- lookupInst pa_class [TyConApp tc ty_args]
-      paDFunApply (Var dfun) ty_args'
+      dfun <- traceMaybeV "paDictOfTyApp" (ppr tc) (lookupTyConPA tc)
+      paDFunApply (Var dfun) ty_args
 paDictOfTyApp ty ty_args = pprPanic "paDictOfTyApp" (ppr ty)
 
+paDFunType :: TyCon -> VM Type
+paDFunType tc
+  = do
+      margs <- mapM paDictArgType tvs
+      res   <- mkPADictType (mkTyConApp tc arg_tys)
+      return . mkForAllTys tvs
+             $ mkFunTys [arg | Just arg <- margs] res
+  where
+    tvs = tyConTyVars tc
+    arg_tys = mkTyVarTys tvs
+
 paDFunApply :: CoreExpr -> [Type] -> VM CoreExpr
 paDFunApply dfun tys
   = do
       dicts <- mapM paDictOfType tys
       return $ mkApps (mkTyApps dfun tys) dicts
 
-lookupPArrayFamInst :: Type -> VM (TyCon, [Type])
-lookupPArrayFamInst ty = builtin parrayTyCon >>= (`lookupFamInst` [ty])
+paMethod :: (Builtins -> Var) -> Type -> VM CoreExpr
+paMethod method ty
+  = do
+      fn   <- builtin method
+      dict <- paDictOfType ty
+      return $ mkApps (Var fn) [Type ty, dict]
+
+mkPR :: Type -> VM CoreExpr
+mkPR = paMethod mkPRVar
+
+lengthPA :: CoreExpr -> VM CoreExpr
+lengthPA x = liftM (`App` x) (paMethod lengthPAVar ty)
+  where
+    ty = splitPArrayTy (exprType x)
+
+replicatePA :: CoreExpr -> CoreExpr -> VM CoreExpr
+replicatePA len x = liftM (`mkApps` [len,x])
+                          (paMethod replicatePAVar (exprType x))
+
+emptyPA :: Type -> VM CoreExpr
+emptyPA = paMethod emptyPAVar
+
+liftPA :: CoreExpr -> VM CoreExpr
+liftPA x
+  = do
+      lc <- builtin liftingContext
+      replicatePA (Var lc) x
+
+newLocalVVar :: FastString -> Type -> VM VVar
+newLocalVVar fs vty
+  = do
+      lty <- mkPArrayType vty
+      vv  <- newLocalVar fs vty
+      lv  <- newLocalVar fs lty
+      return (vv,lv)
+
+polyAbstract :: [TyVar] -> ((CoreExpr -> CoreExpr) -> VM a) -> VM a
+polyAbstract tvs p
+  = localV
+  $ do
+      mdicts <- mapM mk_dict_var tvs
+      zipWithM_ (\tv -> maybe (defLocalTyVar tv) (defLocalTyVarWithPA tv . Var)) tvs mdicts
+      p (mk_lams mdicts)
+  where
+    mk_dict_var tv = do
+                       r <- paDictArgType tv
+                       case r of
+                         Just ty -> liftM Just (newLocalVar FSLIT("dPA") ty)
+                         Nothing -> return Nothing
+
+    mk_lams mdicts = mkLams (tvs ++ [dict | Just dict <- mdicts])
+
+polyApply :: CoreExpr -> [Type] -> VM CoreExpr
+polyApply expr tys
+  = do
+      dicts <- mapM paDictOfType tys
+      return $ expr `mkTyApps` tys `mkApps` dicts
+
+polyVApply :: VExpr -> [Type] -> VM VExpr
+polyVApply expr tys
+  = do
+      dicts <- mapM paDictOfType tys
+      return $ mapVect (\e -> e `mkTyApps` tys `mkApps` dicts) expr
+
+hoistBinding :: Var -> CoreExpr -> VM ()
+hoistBinding v e = updGEnv $ \env ->
+  env { global_bindings = (v,e) : global_bindings env }
 
 hoistExpr :: FastString -> CoreExpr -> VM Var
 hoistExpr fs expr
   = do
       var <- newLocalVar fs (exprType expr)
-      updLEnv $ \env ->
-        env { local_bindings = (var, expr) : local_bindings env }
+      hoistBinding var expr
       return var
 
+hoistVExpr :: VExpr -> VM VVar
+hoistVExpr (ve, le)
+  = do
+      fs <- getBindName
+      vv <- hoistExpr ('v' `consFS` fs) ve
+      lv <- hoistExpr ('l' `consFS` fs) le
+      return (vv, lv)
+
+hoistPolyVExpr :: [TyVar] -> VM VExpr -> VM VExpr
+hoistPolyVExpr tvs p
+  = do
+      expr <- closedV . polyAbstract tvs $ \abstract ->
+              liftM (mapVect abstract) p
+      fn   <- hoistVExpr expr
+      polyVApply (vVar fn) (mkTyVarTys tvs)
+
+takeHoisted :: VM [(Var, CoreExpr)]
+takeHoisted
+  = do
+      env <- readGEnv id
+      setGEnv $ env { global_bindings = [] }
+      return $ global_bindings env
+
+mkClosure :: Type -> Type -> Type -> VExpr -> VExpr -> VM VExpr
+mkClosure arg_ty res_ty env_ty (vfn,lfn) (venv,lenv)
+  = do
+      dict <- paDictOfType env_ty
+      mkv  <- builtin mkClosureVar
+      mkl  <- builtin mkClosurePVar
+      return (Var mkv `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [dict, vfn, lfn, venv],
+              Var mkl `mkTyApps` [arg_ty, res_ty, env_ty] `mkApps` [dict, vfn, lfn, lenv])
+
+mkClosureApp :: VExpr -> VExpr -> VM VExpr
+mkClosureApp (vclo, lclo) (varg, larg)
+  = do
+      vapply <- builtin applyClosureVar
+      lapply <- builtin applyClosurePVar
+      return (Var vapply `mkTyApps` [arg_ty, res_ty] `mkApps` [vclo, varg],
+              Var lapply `mkTyApps` [arg_ty, res_ty] `mkApps` [lclo, larg])
+  where
+    (arg_ty, res_ty) = splitClosureTy (exprType vclo)
+
+buildClosures :: [TyVar] -> [VVar] -> [Type] -> Type -> VM VExpr -> VM VExpr
+buildClosures tvs vars [] res_ty mk_body
+  = mk_body
+buildClosures tvs vars [arg_ty] res_ty mk_body
+  = buildClosure tvs vars arg_ty res_ty mk_body
+buildClosures tvs vars (arg_ty : arg_tys) res_ty mk_body
+  = do
+      res_ty' <- mkClosureTypes arg_tys res_ty
+      arg <- newLocalVVar FSLIT("x") arg_ty
+      buildClosure tvs vars arg_ty res_ty'
+        . hoistPolyVExpr tvs
+        $ do
+            lc <- builtin liftingContext
+            clo <- buildClosures tvs (vars ++ [arg]) arg_tys res_ty mk_body
+            return $ vLams lc (vars ++ [arg]) clo
+
+-- (clo <x1,...,xn> <f,f^>, aclo (Arr lc xs1 ... xsn) <f,f^>)
+--   where
+--     f  = \env v -> case env of <x1,...,xn> -> e x1 ... xn v
+--     f^ = \env v -> case env of Arr l xs1 ... xsn -> e^ l x1 ... xn v
+--
+buildClosure :: [TyVar] -> [VVar] -> Type -> Type -> VM VExpr -> VM VExpr
+buildClosure tvs vars arg_ty res_ty mk_body
+  = do
+      (env_ty, env, bind) <- buildEnv vars
+      env_bndr <- newLocalVVar FSLIT("env") env_ty
+      arg_bndr <- newLocalVVar FSLIT("arg") arg_ty
+
+      fn <- hoistPolyVExpr tvs
+          $ do
+              lc    <- builtin liftingContext
+              body  <- mk_body
+              body' <- bind (vVar env_bndr)
+                            (vVarApps lc body (vars ++ [arg_bndr]))
+              return (vLamsWithoutLC [env_bndr, arg_bndr] body')
+
+      mkClosure arg_ty res_ty env_ty fn env
+
+buildEnv :: [VVar] -> VM (Type, VExpr, VExpr -> VExpr -> VM VExpr)
+buildEnv vvs
+  = do
+      lc <- builtin liftingContext
+      let (ty, venv, vbind) = mkVectEnv tys vs
+      (lenv, lbind) <- mkLiftEnv lc tys ls
+      return (ty, (venv, lenv),
+              \(venv,lenv) (vbody,lbody) ->
+              do
+                let vbody' = vbind venv vbody
+                lbody' <- lbind lenv lbody
+                return (vbody', lbody'))
+  where
+    (vs,ls) = unzip vvs
+    tys     = map idType vs
+
+mkVectEnv :: [Type] -> [Var] -> (Type, CoreExpr, CoreExpr -> CoreExpr -> CoreExpr)
+mkVectEnv []   []  = (unitTy, Var unitDataConId, \env body -> body)
+mkVectEnv [ty] [v] = (ty, Var v, \env body -> Let (NonRec v env) body)
+mkVectEnv tys  vs  = (ty, mkCoreTup (map Var vs),
+                        \env body -> Case env (mkWildId ty) (exprType body)
+                                       [(DataAlt (tupleCon Boxed (length vs)), vs, body)])
+  where
+    ty = mkCoreTupTy tys
+
+mkLiftEnv :: Var -> [Type] -> [Var] -> VM (CoreExpr, CoreExpr -> CoreExpr -> VM CoreExpr)
+mkLiftEnv lc [ty] [v]
+  = return (Var v, \env body ->
+                   do
+                     len <- lengthPA (Var v)
+                     return . Let (NonRec v env)
+                            $ Case len lc (exprType body) [(DEFAULT, [], body)])
+
+-- NOTE: this transparently deals with empty environments
+mkLiftEnv lc tys vs
+  = do
+      (env_tc, env_tyargs) <- parrayReprTyCon vty
+      let [env_con] = tyConDataCons env_tc
+          
+          env = Var (dataConWrapId env_con)
+                `mkTyApps`  env_tyargs
+                `mkVarApps` (lc : vs)
+
+          bind env body = let scrut = unwrapFamInstScrut env_tc env_tyargs env
+                          in
+                          return $ Case scrut (mkWildId (exprType scrut))
+                                        (exprType body)
+                                        [(DataAlt env_con, lc : bndrs, body)]
+      return (env, bind)
+  where
+    vty = mkCoreTupTy tys
+
+    bndrs | null vs   = [mkWildId unitTy]
+          | otherwise = vs
+