Add static flag -fsimple-list-literals

[ghc-hetmet.git] / compiler / deSugar / DsExpr.lhs

diff --git a/compiler/deSugar/DsExpr.lhs b/compiler/deSugar/DsExpr.lhs
index 6cbd538..6126b63 100644 (file)
--- a/compiler/deSugar/DsExpr.lhs
+++ b/compiler/deSugar/DsExpr.lhs
@@ -26,6 +26,7 @@ import DsUtils
 import DsArrows
 import DsMonad
 import Name
 import DsArrows
 import DsMonad
 import Name

+import NameEnv

 
 #ifdef GHCI
 import PrelNames
 
 #ifdef GHCI
 import PrelNames

@@ -40,11 +41,13 @@ import TcHsSyn
 --     needs to see source types
 import TcType
 import Type
 --     needs to see source types
 import TcType
 import Type

+import Coercion

 import CoreSyn
 import CoreUtils
 import MkCore
 
 import DynFlags
 import CoreSyn
 import CoreUtils
 import MkCore
 
 import DynFlags

+import StaticFlags

 import CostCentre
 import Id
 import PrelInfo
 import CostCentre
 import Id
 import PrelInfo

@@ -52,6 +55,7 @@ import DataCon
 import TysWiredIn
 import BasicTypes
 import PrelNames
 import TysWiredIn
 import BasicTypes
 import PrelNames

+import Maybes

 import SrcLoc
 import Util
 import Bag
 import SrcLoc
 import Util
 import Bag

@@ -426,52 +430,101 @@ RHSs, and do not generate a Core constructor application directly, because the c
 might do some argument-evaluation first; and may have to throw away some
 dictionaries.
 
 might do some argument-evaluation first; and may have to throw away some
 dictionaries.
 

+Note [Update for GADTs]
+~~~~~~~~~~~~~~~~~~~~~~~
+Consider 
+   data T a b where
+     T1 { f1 :: a } :: T a Int
+
+Then the wrapper function for T1 has type 
+   $WT1 :: a -> T a Int
+But if x::T a b, then
+   x { f1 = v } :: T a b   (not T a Int!)
+So we need to cast (T a Int) to (T a b).  Sigh.
+

 \begin{code}
 dsExpr expr@(RecordUpd record_expr (HsRecFields { rec_flds = fields })
                       cons_to_upd in_inst_tys out_inst_tys)
   | null fields
   = dsLExpr record_expr
   | otherwise
 \begin{code}
 dsExpr expr@(RecordUpd record_expr (HsRecFields { rec_flds = fields })
                       cons_to_upd in_inst_tys out_inst_tys)
   | null fields
   = dsLExpr record_expr
   | otherwise

-  =    -- Record stuff doesn't work for existentials
-       -- The type checker checks for this, but we need 
-       -- worry only about the constructors that are to be updated
-    ASSERT2( notNull cons_to_upd && all isVanillaDataCon cons_to_upd, ppr expr )
+  = ASSERT2( notNull cons_to_upd, ppr expr )

 
     do { record_expr' <- dsLExpr record_expr
 
     do { record_expr' <- dsLExpr record_expr

-       ; let   -- Awkwardly, for families, the match goes 
-               -- from instance type to family type
-               tycon     = dataConTyCon (head cons_to_upd)
-               in_ty     = mkTyConApp tycon in_inst_tys
-               in_out_ty = mkFunTy in_ty
-                                   (mkFamilyTyConApp tycon out_inst_tys)
-
-               mk_val_arg field old_arg_id 
-                 = case findField fields field  of
-                     (rhs:rest) -> ASSERT(null rest) rhs
-                     []         -> nlHsVar old_arg_id
-
-               mk_alt con
-                 = ASSERT( isVanillaDataCon con )
-                   do  { arg_ids <- newSysLocalsDs (dataConInstOrigArgTys con in_inst_tys)
-                       -- This call to dataConInstOrigArgTys won't work for existentials
-                       -- but existentials don't have record types anyway
-                       ; let val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
-                                               (dataConFieldLabels con) arg_ids
-                             rhs = foldl (\a b -> nlHsApp a b)
-                                         (nlHsTyApp (dataConWrapId con) out_inst_tys)
-                                         val_args
-                             pat = mkPrefixConPat con (map nlVarPat arg_ids) in_ty
-
-                       ; return (mkSimpleMatch [pat] rhs) }
+       ; field_binds' <- mapM ds_field fields
+       ; let upd_fld_env :: NameEnv Id -- Maps field name to the LocalId of the field binding
+             upd_fld_env = mkNameEnv [(f,l) | (f,l,_) <- field_binds']

 
        -- It's important to generate the match with matchWrapper,
        -- and the right hand sides with applications of the wrapper Id
        -- so that everything works when we are doing fancy unboxing on the
        -- constructor aguments.
 
        -- It's important to generate the match with matchWrapper,
        -- and the right hand sides with applications of the wrapper Id
        -- so that everything works when we are doing fancy unboxing on the
        -- constructor aguments.

-       ; alts <- mapM mk_alt cons_to_upd
-       ; ([discrim_var], matching_code) <- matchWrapper RecUpd (MatchGroup alts in_out_ty)
+       ; alts <- mapM (mk_alt upd_fld_env) cons_to_upd
+       ; ([discrim_var], matching_code) 
+               <- matchWrapper RecUpd (MatchGroup alts in_out_ty)
+
+       ; return (add_field_binds field_binds' $
+                 bindNonRec discrim_var record_expr' matching_code) }
+  where
+    ds_field :: HsRecField Id (LHsExpr Id) -> DsM (Name, Id, CoreExpr)
+      -- Clone the Id in the HsRecField, because its Name is that
+      -- of the record selector, and we must not make that a lcoal binder
+      -- else we shadow other uses of the record selector
+      -- Hence 'lcl_id'.  Cf Trac #2735
+    ds_field rec_field = do { rhs <- dsLExpr (hsRecFieldArg rec_field)
+                           ; let fld_id = unLoc (hsRecFieldId rec_field)
+                           ; lcl_id <- newSysLocalDs (idType fld_id)
+                           ; return (idName fld_id, lcl_id, rhs) }
+
+    add_field_binds [] expr = expr
+    add_field_binds ((_,b,r):bs) expr = bindNonRec b r (add_field_binds bs expr)
+
+       -- Awkwardly, for families, the match goes 
+       -- from instance type to family type
+    tycon     = dataConTyCon (head cons_to_upd)
+    in_ty     = mkTyConApp tycon in_inst_tys
+    in_out_ty = mkFunTy in_ty (mkFamilyTyConApp tycon out_inst_tys)
+
+    mk_alt upd_fld_env con
+      = do { let (univ_tvs, ex_tvs, eq_spec, 
+                 eq_theta, dict_theta, arg_tys, _) = dataConFullSig con
+                subst = mkTopTvSubst (univ_tvs `zip` in_inst_tys)
+
+               -- I'm not bothering to clone the ex_tvs
+          ; eqs_vars   <- mapM newPredVarDs (substTheta subst (eqSpecPreds eq_spec))
+          ; theta_vars <- mapM newPredVarDs (substTheta subst (eq_theta ++ dict_theta))
+          ; arg_ids    <- newSysLocalsDs (substTys subst arg_tys)
+          ; let val_args = zipWithEqual "dsExpr:RecordUpd" mk_val_arg
+                                        (dataConFieldLabels con) arg_ids
+                 mk_val_arg field_name pat_arg_id 
+                     = nlHsVar (lookupNameEnv upd_fld_env field_name `orElse` pat_arg_id)
+                inst_con = noLoc $ HsWrap wrap (HsVar (dataConWrapId con))
+                       -- Reconstruct with the WrapId so that unpacking happens
+                wrap = mkWpApps theta_vars `WpCompose` 
+                       mkWpTyApps (mkTyVarTys ex_tvs) `WpCompose`
+                       mkWpTyApps [ty | (tv, ty) <- univ_tvs `zip` out_inst_tys
+                                      , isNothing (lookupTyVar wrap_subst tv) ]
+                rhs = foldl (\a b -> nlHsApp a b) inst_con val_args
+
+                       -- Tediously wrap the application in a cast
+                       -- Note [Update for GADTs]
+                wrapped_rhs | null eq_spec = rhs
+                            | otherwise    = mkLHsWrap (WpCast wrap_co) rhs
+                wrap_co = mkTyConApp tycon [ lookup tv ty 
+                                           | (tv,ty) <- univ_tvs `zip` out_inst_tys]
+                lookup univ_tv ty = case lookupTyVar wrap_subst univ_tv of
+                                       Just ty' -> ty'
+                                       Nothing  -> ty
+                wrap_subst = mkTopTvSubst [ (tv,mkSymCoercion (mkTyVarTy co_var))
+                                          | ((tv,_),co_var) <- eq_spec `zip` eqs_vars ]
+                
+                pat = noLoc $ ConPatOut { pat_con = noLoc con, pat_tvs = ex_tvs
+                                        , pat_dicts = eqs_vars ++ theta_vars
+                                        , pat_binds = emptyLHsBinds 
+                                        , pat_args = PrefixCon $ map nlVarPat arg_ids
+                                        , pat_ty = in_ty }
+          ; return (mkSimpleMatch [pat] wrapped_rhs) }

 
 

-       ; return (bindNonRec discrim_var record_expr' matching_code) }

 \end{code}
 
 Here is where we desugar the Template Haskell brackets and escapes
 \end{code}
 
 Here is where we desugar the Template Haskell brackets and escapes

@@ -557,6 +610,23 @@ allocation in some nofib programs. Specifically
 
 Of course, if rules aren't turned on then there is pretty much no
 point doing this fancy stuff, and it may even be harmful.
 
 Of course, if rules aren't turned on then there is pretty much no
 point doing this fancy stuff, and it may even be harmful.

+
+=======>  Note by SLPJ Dec 08.
+
+I'm unconvinced that we should *ever* generate a build for an explicit
+list.  See the comments in GHC.Base about the foldr/cons rule, which 
+points out that (foldr k z [a,b,c]) may generate *much* less code than
+(a `k` b `k` c `k` z).
+
+Furthermore generating builds messes up the LHS of RULES. 
+Example: the foldr/single rule in GHC.Base
+   foldr k z [x] = ...
+We do not want to generate a build invocation on the LHS of this RULE!
+
+To test this I've added a (static) flag -fsimple-list-literals, which
+makes all list literals be generated via the simple route.  
+
+

 \begin{code}
 
 dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
 \begin{code}
 
 dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr

@@ -564,7 +634,7 @@ dsExplicitList :: PostTcType -> [LHsExpr Id] -> DsM CoreExpr
 dsExplicitList elt_ty xs = do
     dflags <- getDOptsDs
     xs' <- mapM dsLExpr xs
 dsExplicitList elt_ty xs = do
     dflags <- getDOptsDs
     xs' <- mapM dsLExpr xs

-    if not (dopt Opt_EnableRewriteRules dflags)
+    if  opt_SimpleListLiterals || not (dopt Opt_EnableRewriteRules dflags)

         then return $ mkListExpr elt_ty xs'
         else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
   where
         then return $ mkListExpr elt_ty xs'
         else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
   where