X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcInstDcls.lhs;h=55fc342e30911e9349b58fb1a7ae0b6a060ab756;hp=4d614e2c5ee844323c6c08e4bf33971450e2246c;hb=786932468faac49aafe20b65eabc8bdf465fbc9d;hpb=d7bc4e06c0b16d242f1f26100f4146f40f5de5a8 diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs index 4d614e2..55fc342 100644 --- a/compiler/typecheck/TcInstDcls.lhs +++ b/compiler/typecheck/TcInstDcls.lhs @@ -21,7 +21,6 @@ import FamInst import FamInstEnv import TcDeriv import TcEnv -import RnEnv ( lookupGlobalOccRn ) import RnSource ( addTcgDUs ) import TcHsType import TcUnify @@ -33,7 +32,6 @@ import DataCon import Class import Var import CoreUnfold ( mkDFunUnfolding ) -import PrelNames ( inlineIdName ) import Id import MkId import Name @@ -122,13 +120,8 @@ Running example: {-# RULE "op1@C[a]" forall a, d:C a. op1 [a] (df_i d) = op1_i a d #-} -* We want to inline the dictionary function itself as vigorously as we - possibly can, so that we expose that dictionary constructor to - selectors as much as poss. We don't actually inline it; rather, we - use a Builtin RULE for the ClassOps (see MkId.mkDictSelId) to short - circuit such applications. But the RULE only applies if it can "see" - the dfun's DFunUnfolding. - +Note [Instances and loop breakers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Note that df_i may be mutually recursive with both op1_i and op2_i. It's crucial that df_i is not chosen as the loop breaker, even though op1_i has a (user-specified) INLINE pragma. @@ -146,6 +139,91 @@ Running example: a RULE (the magic ClassOp rule above), and RULES work inside InlineRule unfoldings. See Note [RULEs enabled in SimplGently] in SimplUtils +Note [ClassOp/DFun selection] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +One thing we see a lot is stuff like + op2 (df d1 d2) +where 'op2' is a ClassOp and 'df' is DFun. Now, we could inline *both* +'op2' and 'df' to get + case (MkD ($cop1 d1 d2) ($cop2 d1 d2) ... of + MkD _ op2 _ _ _ -> op2 +And that will reduce to ($cop2 d1 d2) which is what we wanted. + +But it's tricky to make this work in practice, because it requires us to +inline both 'op2' and 'df'. But neither is keen to inline without having +seen the other's result; and it's very easy to get code bloat (from the +big intermediate) if you inline a bit too much. + +Instead we use a cunning trick. + * We arrange that 'df' and 'op2' NEVER inline. + + * We arrange that 'df' is ALWAYS defined in the sylised form + df d1 d2 = MkD ($cop1 d1 d2) ($cop2 d1 d2) ... + + * We give 'df' a magical unfolding (DFunUnfolding [$cop1, $cop2, ..]) + that lists its methods. + + * We make CoreUnfold.exprIsConApp_maybe spot a DFunUnfolding and return + a suitable constructor application -- inlining df "on the fly" as it + were. + + * We give the ClassOp 'op2' a BuiltinRule that extracts the right piece + iff its argument satisfies exprIsConApp_maybe. This is done in + MkId mkDictSelId + + * We make 'df' CONLIKE, so that shared uses stil match; eg + let d = df d1 d2 + in ...(op2 d)...(op1 d)... + +Note [Single-method classes] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If the class has just one method (or, more accurately, just one element +of {superclasses + methods}), then we still use the *same* strategy + + class C a where op :: a -> a + instance C a => C [a] where op = + +We translate the class decl into a newtype, which just gives +a top-level axiom: + + axiom Co:C a :: C a ~ (a->a) + + op :: forall a. C a -> (a -> a) + op a d = d |> (Co:C a) + + MkC :: forall a. (a->a) -> C a + MkC = /\a.\op. op |> (sym Co:C a) + + df :: forall a. C a => C [a] + {-# NOINLINE df DFun[ $cop_list ] #-} + df = /\a. \d. MkD ($cop_list a d) + + $cop_list :: forall a. C a => a -> a + $cop_list = + +The "constructor" MkD expands to a cast, as does the class-op selector. +The RULE works just like for multi-field dictionaries: + * (df a d) returns (Just (MkD,..,[$cop_list a d])) + to exprIsConApp_Maybe + + * The RULE for op picks the right result + +This is a bit of a hack, because (df a d) isn't *really* a constructor +application. But it works just fine in this case, exprIsConApp_maybe +is otherwise used only when we hit a case expression which will have +a real data constructor in it. + +The biggest reason for doing it this way, apart form uniformity, is +that we want to be very careful when we have + instance C a => C [a] where + {-# INLINE op #-} + op = ... +then we'll get an INLINE pragma on $cop_list. The danger is that +we'll get something like + foo = /\a.\d. $cop_list a d +and then we'll eta expand, and then we'll inline TOO EARLY. This happened in +Trac #3772 and I spent far too long fiddling arond trying to fix it. +Look at the test for Trac #3772. Note [Subtle interaction of recursion and overlap] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -208,93 +286,6 @@ which brings appropriate tyvars into scope. This happens for both and for , but that doesn't matter: the *renamer* will have complained if 'b' is mentioned in . -Note [Inline dfuns unconditionally] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The code above unconditionally inlines dict funs. Here's why. -Consider this program: - - test :: Int -> Int -> Bool - test x y = (x,y) == (y,x) || test y x - -- Recursive to avoid making it inline. - -This needs the (Eq (Int,Int)) instance. If we inline that dfun -the code we end up with is good: - - Test.$wtest = - \r -> case ==# [ww ww1] of wild { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> - case ==# [ww1 ww] of wild1 { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> PrelBase.True []; - }; - }; - Test.test = \r [w w1] - case w of w2 { - PrelBase.I# ww -> - case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; }; - }; - -If we don't inline the dfun, the code is not nearly as good: - - (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl { - PrelBase.:DEq tpl1 tpl2 -> tpl2; - }; - - Test.$wtest = - \r [ww ww1] - let { y = PrelBase.I#! [ww1]; } in - let { x = PrelBase.I#! [ww]; } in - let { sat_slx = PrelTup.(,)! [y x]; } in - let { sat_sly = PrelTup.(,)! [x y]; - } in - case == sat_sly sat_slx of wild { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> PrelBase.True []; - }; - - Test.test = - \r [w w1] - case w of w2 { - PrelBase.I# ww -> - case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; }; - }; - -Why didn't GHC inline $fEq in those days? Because it looked big: - - PrelTup.zdfEqZ1T{-rcX-} - = \ @ a{-reT-} :: * @ b{-reS-} :: * - zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}} - zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} -> - let { - zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-}) - zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in - let { - zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-}) - zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in - let { - zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-}) - zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-}) - ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) -> - case ds{-rf5-} - of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) -> - case ds1{-rf4-} - of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) -> - PrelBase.zaza{-r4e-} - (zeze1{-rf3-} a1{-rf2-} b1{-rf1-}) - (zeze{-rf0-} a2{-reZ-} b2{-reY-}) - } - } } in - let { - a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-}) - a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-}) - b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) -> - PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-}) - } in - PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-}) - -and it's not as bad as it seems, because it's further dramatically -simplified: only zeze2 is extracted and its body is simplified. %************************************************************************ @@ -418,8 +409,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) ; (tyvars, theta, tau) <- tcHsInstHead poly_ty -- Now, check the validity of the instance. - ; (clas, inst_tys) <- checkValidInstHead tau - ; checkValidInstance tyvars theta clas inst_tys + ; (clas, inst_tys) <- checkValidInstance poly_ty tyvars theta tau -- Next, process any associated types. ; idx_tycons <- recoverM (return []) $ @@ -607,7 +597,7 @@ tc_inst_decl2 :: Id -> InstBindings Name -> TcM (LHsBinds Id) -- If there are no superclasses, matters are simpler, because we don't need the case -- see Note [Newtype deriving superclasses] in TcDeriv.lhs -tc_inst_decl2 dfun_id (NewTypeDerived coi) +tc_inst_decl2 dfun_id (NewTypeDerived coi _) = do { let rigid_info = InstSkol origin = SigOrigin rigid_info inst_ty = idType dfun_id @@ -673,7 +663,7 @@ tc_inst_decl2 dfun_id (NewTypeDerived coi) ; return (unitBag $ noLoc $ AbsBinds inst_tvs' (map instToVar dfun_dicts) - [(inst_tvs', dfun_id, instToId this_dict, [])] + [(inst_tvs', dfun_id, instToId this_dict, noSpecPrags)] (dict_bind `consBag` sc_binds)) } where ----------------------- @@ -759,7 +749,7 @@ tc_inst_decl2 dfun_id (VanillaInst monobinds uprags standalone_deriv) ; spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) spec_inst_sigs -- Typecheck the methods - ; let prag_fn = mkPragFun uprags + ; let prag_fn = mkPragFun uprags monobinds tc_meth = tcInstanceMethod loc standalone_deriv clas inst_tyvars' dfun_dicts inst_tys' @@ -797,21 +787,78 @@ tc_inst_decl2 dfun_id (VanillaInst monobinds uprags standalone_deriv) mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id))) arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars') - dfun_id_w_fun = dfun_id - `setIdUnfolding` mkDFunUnfolding dict_constr (sc_ids ++ meth_ids) + -- Do not inline the dfun; instead give it a magic DFunFunfolding + -- See Note [ClassOp/DFun selection] + -- See also note [Single-method classes] + dfun_id_w_fun = dfun_id + `setIdUnfolding` mkDFunUnfolding dict_constr (sc_ids ++ meth_ids) `setInlinePragma` dfunInlinePragma - main_bind = noLoc $ AbsBinds - inst_tyvars' - dfun_lam_vars - [(inst_tyvars', dfun_id_w_fun, this_dict_id, spec_inst_prags)] - (unitBag dict_bind) + main_bind = AbsBinds + inst_tyvars' + dfun_lam_vars + [(inst_tyvars', dfun_id_w_fun, this_dict_id, SpecPrags spec_inst_prags)] + (unitBag dict_bind) ; showLIE (text "instance") - ; return (unitBag main_bind `unionBags` - listToBag meth_binds `unionBags` - listToBag sc_binds) } + ; return (unitBag (L loc main_bind) `unionBags` + listToBag meth_binds `unionBags` + listToBag sc_binds) + } + +{- + -- Create the result bindings + ; let this_dict_id = instToId this_dict + arg_ids = sc_ids ++ meth_ids + arg_binds = listToBag meth_binds `unionBags` + listToBag sc_binds + ; showLIE (text "instance") + ; case newTyConCo_maybe (classTyCon clas) of + Nothing -- A multi-method class + -> return (unitBag (L loc data_bind) `unionBags` arg_binds) + where + data_dfun_id = dfun_id -- Do not inline; instead give it a magic DFunFunfolding + -- See Note [ClassOp/DFun selection] + `setIdUnfolding` mkDFunUnfolding dict_constr arg_ids + `setInlinePragma` dfunInlinePragma + + data_bind = AbsBinds inst_tyvars' dfun_lam_vars + [(inst_tyvars', data_dfun_id, this_dict_id, spec_inst_prags)] + (unitBag dict_bind) + + dict_bind = mkVarBind this_dict_id dict_rhs + dict_rhs = foldl mk_app inst_constr arg_ids + dict_constr = classDataCon clas + inst_constr = L loc $ wrapId (mkWpTyApps inst_tys') + (dataConWrapId dict_constr) + -- We don't produce a binding for the dict_constr; instead we + -- rely on the simplifier to unfold this saturated application + -- We do this rather than generate an HsCon directly, because + -- it means that the special cases (e.g. dictionary with only one + -- member) are dealt with by the common MkId.mkDataConWrapId code rather + -- than needing to be repeated here. + + mk_app :: LHsExpr Id -> Id -> LHsExpr Id + mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id))) + arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars') + + Just the_nt_co -- (Just co) for a single-method class + -> return (unitBag (L loc nt_bind) `unionBags` arg_binds) + where + nt_dfun_id = dfun_id -- Just let the dfun inline; see Note [Single-method classes] + `setInlinePragma` alwaysInlinePragma + + local_nt_dfun = setIdType this_dict_id inst_ty -- A bit of a hack, but convenient + + nt_bind = AbsBinds [] [] + [([], nt_dfun_id, local_nt_dfun, spec_inst_prags)] + (unitBag (mkVarBind local_nt_dfun (L loc (wrapId nt_cast the_meth_id)))) + + the_meth_id = ASSERT( length arg_ids == 1 ) head arg_ids + nt_cast = WpCast $ mkPiTypes (inst_tyvars' ++ dfun_lam_vars) $ + mkSymCoercion (mkTyConApp the_nt_co inst_tys') +-} ------------------------------ tcSuperClass :: InstLoc -> [TyVar] -> [Inst] @@ -840,7 +887,7 @@ tcSuperClass inst_loc tyvars dicts (this_dict, this_bind) sc_id = instToVar sc_dict sc_op_bind = AbsBinds tyvars (map instToVar dicts) - [(tyvars, sc_op_id, sc_id, [])] + [(tyvars, sc_op_id, sc_id, noSpecPrags)] (this_bind `unionBags` sc_binds) ; return (sc_op_id, noLoc sc_op_bind) } @@ -897,7 +944,7 @@ SpecPrag which, as it turns out, can be used unchanged for each method. The "it turns out" bit is delicate, but it works fine! \begin{code} -tcSpecInst :: Id -> Sig Name -> TcM SpecPrag +tcSpecInst :: Id -> Sig Name -> TcM TcSpecPrag tcSpecInst dfun_id prag@(SpecInstSig hs_ty) = addErrCtxt (spec_ctxt prag) $ do { let name = idName dfun_id @@ -930,7 +977,7 @@ tcInstanceMethod :: SrcSpan -> Bool -> Class -> [TcTyVar] -> [Inst] -> [TcType] -> (Inst, LHsBinds Id) -- "This" and its binding -> TcPragFun -- Local prags - -> [LSpecPrag] -- Arising from 'SPECLALISE instance' + -> [Located TcSpecPrag] -- Arising from 'SPECLALISE instance' -> LHsBinds Name -> (Id, DefMeth) -> TcM (Id, LHsBind Id) @@ -955,13 +1002,13 @@ tcInstanceMethod loc standalone_deriv clas tyvars dfun_dicts inst_tys tc_body rn_bind = add_meth_ctxt rn_bind $ do { (meth_id1, spec_prags) <- tcPrags NonRecursive False True - meth_id (prag_fn sel_name) + meth_id (prag_fn sel_name) ; tcInstanceMethodBody (instLoc this_dict) tyvars dfun_dicts ([this_dict], this_dict_bind) meth_id1 local_meth_id meth_sig_fn - (spec_inst_prags ++ spec_prags) + (SpecPrags (spec_inst_prags ++ spec_prags)) rn_bind } -------------- @@ -978,7 +1025,7 @@ tcInstanceMethod loc standalone_deriv clas tyvars dfun_dicts inst_tys = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name ; tc_body meth_bind } - tc_default DefMeth -- An polymorphic default method + tc_default (DefMeth dm_name) -- An polymorphic default method = do { -- Build the typechecked version directly, -- without calling typecheck_method; -- see Note [Default methods in instances] @@ -986,17 +1033,11 @@ tcInstanceMethod loc standalone_deriv clas tyvars dfun_dicts inst_tys -- in $dm inst_tys this -- The 'let' is necessary only because HsSyn doesn't allow -- you to apply a function to a dictionary *expression*. - dm_name <- lookupGlobalOccRn (mkDefMethRdrName sel_name) - -- Might not be imported, but will be an OrigName + ; dm_id <- tcLookupId dm_name - ; inline_id <- tcLookupId inlineIdName ; let dm_inline_prag = idInlinePragma dm_id - dm_app = HsWrap (WpApp (instToId this_dict) <.> mkWpTyApps inst_tys) $ - HsVar dm_id - rhs | isInlinePragma dm_inline_prag -- See Note [INLINE and default methods] - = HsApp (L loc (HsWrap (WpTyApp local_meth_ty) (HsVar inline_id))) - (L loc dm_app) - | otherwise = dm_app + rhs = HsWrap (WpApp (instToId this_dict) <.> mkWpTyApps inst_tys) $ + HsVar dm_id meth_bind = L loc $ VarBind { var_id = local_meth_id , var_rhs = L loc rhs @@ -1006,8 +1047,8 @@ tcInstanceMethod loc standalone_deriv clas tyvars dfun_dicts inst_tys -- method to this version. Note [INLINE and default methods] bind = AbsBinds { abs_tvs = tyvars, abs_dicts = dfun_lam_vars - , abs_exports = [( tyvars, meth_id1 - , local_meth_id, spec_inst_prags)] + , abs_exports = [( tyvars, meth_id1, local_meth_id + , SpecPrags spec_inst_prags)] , abs_binds = this_dict_bind `unionBags` unitBag meth_bind } -- Default methods in an instance declaration can't have their own -- INLINE or SPECIALISE pragmas. It'd be possible to allow them, but @@ -1092,7 +1133,8 @@ From the class decl we get $dmfoo :: forall v x. Baz v x => x -> x $dmfoo y = -Notice that the type is ambiguous. That's fine, though. The instance decl generates +Notice that the type is ambiguous. That's fine, though. The instance +decl generates $dBazIntInt = MkBaz fooIntInt fooIntInt = $dmfoo Int Int $dBazIntInt @@ -1104,8 +1146,9 @@ less work to generate the translated version! Note [INLINE and default methods] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We *copy* any INLINE pragma from the default method to the instance. -Example: +Default methods need special case. They are supposed to behave rather like +macros. For exmample + class Foo a where op1, op2 :: Bool -> a -> a @@ -1113,31 +1156,57 @@ Example: op1 b x = op2 (not b) x instance Foo Int where + -- op1 via default method + op2 b x = + +The instance declaration should behave + + just as if 'op1' had been defined with the + code, and INLINE pragma, from its original + definition. + +That is, just as if you'd written + + instance Foo Int where op2 b x = -Then we generate: + {-# INLINE op1 #-} + op1 b x = op2 (not b) x + +So for the above example we generate: + {-# INLINE $dmop1 #-} + -- $dmop1 has an InlineCompulsory unfolding $dmop1 d b x = op2 d (not b) x $fFooInt = MkD $cop1 $cop2 {-# INLINE $cop1 #-} - $cop1 = inline $dmop1 $fFooInt + $cop1 = $dmop1 $fFooInt $cop2 = -Note carefully: - a) We copy $dmop1's inline pragma to $cop1. Otherwise - we'll just inline the former in the latter and stop, which - isn't what the user expected +Note carefullly: + +* We *copy* any INLINE pragma from the default method $dmop1 to the + instance $cop1. Otherwise we'll just inline the former in the + latter and stop, which isn't what the user expected + +* Regardless of its pragma, we give the default method an + unfolding with an InlineCompulsory source. That means + that it'll be inlined at every use site, notably in + each instance declaration, such as $cop1. This inlining + must happen even though + a) $dmop1 is not saturated in $cop1 + b) $cop1 itself has an INLINE pragma - b) We use the magic 'inline' Id to ensure that $dmop1 really is - inlined in $cop1, even though the latter itself has an INLINE pragma - That is important to allow the mutual recursion between $fooInt and - $cop1 to be broken + It's vital that $dmop1 *is* inlined in this way, to allow the mutual + recursion between $fooInt and $cop1 to be broken -This is all regrettably delicate. +* To communicate the need for an InlineCompulsory to the desugarer + (which makes the Unfoldings), we use the IsDefaultMethod constructor + in TcSpecPrags. %************************************************************************