X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FdeSugar%2FDsBinds.lhs;h=65cb8157daaef65e72e26a0e92b9ac83f1628106;hp=c886c8ef6bae478161b78a4138af630395c0f4fd;hb=b2524b3960999fffdb3767900f58825903f6560f;hpb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516 diff --git a/compiler/deSugar/DsBinds.lhs b/compiler/deSugar/DsBinds.lhs index c886c8e..65cb815 100644 --- a/compiler/deSugar/DsBinds.lhs +++ b/compiler/deSugar/DsBinds.lhs @@ -10,7 +10,7 @@ in that the @Rec@/@NonRec@/etc structure is thrown away (whereas at lower levels it is preserved with @let@/@letrec@s). \begin{code} -module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, +module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, dsSpec, dsHsWrapper, dsTcEvBinds, dsEvBinds, wrapDsEvBinds, DsEvBind(..), AutoScc(..) ) where @@ -36,6 +36,7 @@ import Digraph import TcType import Type +import Coercion import TysPrim ( anyTypeOfKind ) import CostCentre import Module @@ -56,7 +57,6 @@ import OrdList import Bag import BasicTypes hiding ( TopLevel ) import FastString --- import StaticFlags ( opt_DsMultiTyVar ) import Util import MonadUtils @@ -69,9 +69,8 @@ import MonadUtils %************************************************************************ \begin{code} -dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)] -dsTopLHsBinds auto_scc binds = do { binds' <- ds_lhs_binds auto_scc binds - ; return (fromOL binds') } +dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM (OrdList (Id,CoreExpr)) +dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)] dsLHsBinds binds = do { binds' <- ds_lhs_binds NoSccs binds @@ -91,7 +90,7 @@ dsLHsBind auto_scc (L loc bind) dsHsBind :: AutoScc -> HsBind Id -> DsM (OrdList (Id,CoreExpr)) dsHsBind _ (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless }) - = do { core_expr <- dsLExpr expr + = do { core_expr <- dsLExpr expr -- Dictionary bindings are always VarBinds, -- so we only need do this here @@ -99,98 +98,25 @@ dsHsBind _ (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardle ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr' | otherwise = var - ; return (unitOL (var', core_expr')) } + ; return (unitOL (makeCorePair var' False 0 core_expr')) } -dsHsBind _ (FunBind { fun_id = L _ fun, fun_matches = matches +dsHsBind auto_scc (FunBind { fun_id = L _ fun, fun_matches = matches , fun_co_fn = co_fn, fun_tick = tick , fun_infix = inf }) = do { (args, body) <- matchWrapper (FunRhs (idName fun) inf) matches ; body' <- mkOptTickBox tick body ; wrap_fn' <- dsHsWrapper co_fn - ; return (unitOL (fun, wrap_fn' (mkLams args body'))) } + ; let rhs = addAutoScc auto_scc fun $ wrap_fn' (mkLams args body') + ; return (unitOL (makeCorePair fun False 0 rhs)) } -dsHsBind _ (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }) +dsHsBind auto_scc (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }) = do { body_expr <- dsGuarded grhss ty ; sel_binds <- mkSelectorBinds pat body_expr - ; return (toOL sel_binds) } - -{- -dsHsBind auto_scc (AbsBinds { abs_tvs = [], abs_ev_vars = [] - , abs_exports = exports, abs_ev_binds = ev_binds - , abs_binds = binds }) - = do { bind_prs <- ds_lhs_binds NoSccs binds - ; ds_ev_binds <- dsTcEvBinds ev_binds - - ; let core_prs = addEvPairs ds_ev_binds bind_prs - env = mkABEnv exports - do_one (lcl_id, rhs) - | Just (_, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id - = do { let rhs' = addAutoScc auto_scc gbl_id rhs - ; (spec_binds, rules) <- dsSpecs gbl_id (Let (Rec core_prs) rhs') spec_prags - -- See Note [Specialising in no-dict case] - ; let gbl_id' = addIdSpecialisations gbl_id rules - main_bind = makeCorePair gbl_id' False 0 rhs' - ; return (main_bind : spec_binds) } - - | otherwise = return [(lcl_id, rhs)] - - locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports] - -- Note [Rules and inlining] - ; export_binds <- mapM do_one core_prs - ; return (concat export_binds ++ locals' ++ rest) } - -- No Rec needed here (contrast the other AbsBinds cases) - -- because we can rely on the enclosing dsBind to wrap in Rec - - -dsHsBind auto_scc rest (AbsBinds { abs_tvs = tyvars, abs_ev_vars = [] - , abs_exports = exports, abs_ev_binds = ev_binds - , abs_binds = binds }) - | opt_DsMultiTyVar -- This (static) debug flag just lets us - -- switch on and off this optimisation to - -- see if it has any impact; it is on by default - , allOL isLazyEvBind ev_binds - = -- Note [Abstracting over tyvars only] - do { bind_prs <- ds_lhs_binds NoSccs binds - ; ds_ev_binds <- dsTcEvBinds ev_binds - - ; let core_prs = addEvPairs ds_ev_binds bind_prs - arby_env = mkArbitraryTypeEnv tyvars exports - bndrs = mkVarSet (map fst core_prs) - - add_lets | core_prs `lengthExceeds` 10 = add_some - | otherwise = mkLets - add_some lg_binds rhs = mkLets [ NonRec b r | NonRec b r <- lg_binds - , b `elemVarSet` fvs] rhs - where - fvs = exprSomeFreeVars (`elemVarSet` bndrs) rhs - - env = mkABEnv exports - mk_lg_bind lcl_id gbl_id tyvars - = NonRec (setIdInfo lcl_id vanillaIdInfo) - -- Nuke the IdInfo so that no old unfoldings - -- confuse use (it might mention something not - -- even in scope at the new site - (mkTyApps (Var gbl_id) (mkTyVarTys tyvars)) - - do_one lg_binds (lcl_id, rhs) - | Just (id_tvs, gbl_id, _, spec_prags) <- lookupVarEnv env lcl_id - = do { let rhs' = addAutoScc auto_scc gbl_id $ - mkLams id_tvs $ - mkLets [ NonRec tv (Type (lookupVarEnv_NF arby_env tv)) - | tv <- tyvars, not (tv `elem` id_tvs)] $ - add_lets lg_binds rhs - ; (spec_binds, rules) <- dsSpecs gbl_id rhs' spec_prags - ; let gbl_id' = addIdSpecialisations gbl_id rules - main_bind = makeCorePair gbl_id' False 0 rhs' - ; return (mk_lg_bind lcl_id gbl_id' id_tvs, main_bind : spec_binds) } - | otherwise - = do { non_exp_gbl_id <- newUniqueId lcl_id (mkForAllTys tyvars (idType lcl_id)) - ; return (mk_lg_bind lcl_id non_exp_gbl_id tyvars, - [(non_exp_gbl_id, mkLams tyvars (add_lets lg_binds rhs))]) } - - ; (_, core_prs') <- fixDs (\ ~(lg_binds, _) -> mapAndUnzipM (do_one lg_binds) core_prs) - ; return (concat core_prs' ++ rest) } --} + -- We silently ignore inline pragmas; no makeCorePair + -- Not so cool, but really doesn't matter + ; let sel_binds' = [ (v, addAutoScc auto_scc v expr) + | (v, expr) <- sel_binds ] + ; return (toOL sel_binds') } -- A common case: one exported variable -- Non-recursive bindings come through this way @@ -210,7 +136,7 @@ dsHsBind auto_scc (AbsBinds { abs_tvs = all_tyvars, abs_ev_vars = dicts Let core_bind $ Var local - ; (spec_binds, rules) <- dsSpecs global rhs prags + ; (spec_binds, rules) <- dsSpecs rhs prags ; let global' = addIdSpecialisations global rules main_bind = makeCorePair global' (isDefaultMethod prags) @@ -253,9 +179,9 @@ dsHsBind auto_scc (AbsBinds { abs_tvs = all_tyvars, abs_ev_vars = dicts mkTupleSelector locals' (locals' !! n) tup_id $ mkVarApps (mkTyApps (Var poly_tup_id) ty_args) dicts - ; (spec_binds, rules) <- dsSpecs global - (Let (NonRec poly_tup_id poly_tup_rhs) rhs) - spec_prags + full_rhs = Let (NonRec poly_tup_id poly_tup_rhs) rhs + ; (spec_binds, rules) <- dsSpecs full_rhs spec_prags + ; let global' = addIdSpecialisations global rules ; return ((global', rhs) `consOL` spec_binds) } where @@ -305,8 +231,8 @@ dsEvBinds bs = return (map dsEvGroup sccs) free_vars_of :: EvTerm -> [EvVar] free_vars_of (EvId v) = [v] - free_vars_of (EvCast v co) = v : varSetElems (tyVarsOfType co) - free_vars_of (EvCoercion co) = varSetElems (tyVarsOfType co) + free_vars_of (EvCast v co) = v : varSetElems (tyCoVarsOfCo co) + free_vars_of (EvCoercion co) = varSetElems (tyCoVarsOfCo co) free_vars_of (EvDFunApp _ _ vs) = vs free_vars_of (EvSuperClass d _) = [d] @@ -322,7 +248,7 @@ dsEvGroup (AcyclicSCC (EvBind co_var (EvSuperClass dict n))) (arg_tys, _) = splitFunTys rho bndrs = ex_tvs ++ map mk_wild_pred (theta `zip` [0..]) ++ map mkWildValBinder arg_tys - mk_wild_pred (p, i) | i==n = ASSERT( p `tcEqPred` (coVarPred co_var)) + mk_wild_pred (p, i) | i==n = ASSERT( p `eqPred` (coVarPred co_var)) co_var | otherwise = mkWildEvBinder p @@ -335,10 +261,10 @@ dsEvGroup (CyclicSCC bs) ds_pair (EvBind v r) = (v, dsEvTerm r) dsEvTerm :: EvTerm -> CoreExpr -dsEvTerm (EvId v) = Var v -dsEvTerm (EvCast v co) = Cast (Var v) co +dsEvTerm (EvId v) = Var v +dsEvTerm (EvCast v co) = Cast (Var v) co dsEvTerm (EvDFunApp df tys vars) = Var df `mkTyApps` tys `mkVarApps` vars -dsEvTerm (EvCoercion co) = Type co +dsEvTerm (EvCoercion co) = Coercion co dsEvTerm (EvSuperClass d n) = ASSERT( isClassPred (classSCTheta cls !! n) ) -- We can only select *dictionary* superclasses @@ -355,21 +281,29 @@ makeCorePair gbl_id is_default_method dict_arity rhs | is_default_method -- Default methods are *always* inlined = (gbl_id `setIdUnfolding` mkCompulsoryUnfolding rhs, rhs) - | not (isInlinePragma inline_prag) - = (gbl_id, rhs) + | otherwise + = case inlinePragmaSpec inline_prag of + EmptyInlineSpec -> (gbl_id, rhs) + NoInline -> (gbl_id, rhs) + Inlinable -> (gbl_id `setIdUnfolding` inlinable_unf, rhs) + Inline -> inline_pair - | Just arity <- inlinePragmaSat inline_prag + where + inline_prag = idInlinePragma gbl_id + inlinable_unf = mkInlinableUnfolding rhs + inline_pair + | Just arity <- inlinePragmaSat inline_prag -- Add an Unfolding for an INLINE (but not for NOINLINE) -- And eta-expand the RHS; see Note [Eta-expanding INLINE things] - , let real_arity = dict_arity + arity + , let real_arity = dict_arity + arity -- NB: The arity in the InlineRule takes account of the dictionaries - = (gbl_id `setIdUnfolding` mkInlineRule rhs (Just real_arity), - etaExpand real_arity rhs) + = ( gbl_id `setIdUnfolding` mkInlineUnfolding (Just real_arity) rhs + , etaExpand real_arity rhs) + + | otherwise + = pprTrace "makeCorePair: arity missing" (ppr gbl_id) $ + (gbl_id `setIdUnfolding` mkInlineUnfolding Nothing rhs, rhs) - | otherwise - = (gbl_id `setIdUnfolding` mkInlineRule rhs Nothing, rhs) - where - inline_prag = idInlinePragma gbl_id dictArity :: [Var] -> Arity -- Don't count coercion variables in arity @@ -409,7 +343,7 @@ This does not happen in the same way to polymorphic binds, because they desugar to M.f = /\a. let f_lcl = ...f_lcl... in f_lcl Although I'm a bit worried about whether full laziness might -float the f_lcl binding out and then inline M.f at its call site -} +float the f_lcl binding out and then inline M.f at its call site Note [Specialising in no-dict case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -542,148 +476,83 @@ Note that \begin{code} ------------------------ -dsSpecs :: Id -- The polymorphic Id - -> CoreExpr -- Its rhs +dsSpecs :: CoreExpr -- Its rhs -> TcSpecPrags -> DsM ( OrdList (Id,CoreExpr) -- Binding for specialised Ids , [CoreRule] ) -- Rules for the Global Ids -- See Note [Implementing SPECIALISE pragmas] -dsSpecs poly_id poly_rhs prags - = case prags of - IsDefaultMethod -> return (nilOL, []) - SpecPrags sps -> do { pairs <- mapMaybeM spec_one sps - ; let (spec_binds_s, rules) = unzip pairs - ; return (concatOL spec_binds_s, rules) } - where - spec_one :: Located TcSpecPrag -> DsM (Maybe (OrdList (Id,CoreExpr), CoreRule)) - spec_one (L loc (SpecPrag spec_co spec_inl)) - = putSrcSpanDs loc $ - do { let poly_name = idName poly_id - ; spec_name <- newLocalName poly_name - ; wrap_fn <- dsHsWrapper spec_co - ; let (bndrs, ds_lhs) = collectBinders (wrap_fn (Var poly_id)) - spec_ty = mkPiTypes bndrs (exprType ds_lhs) - ; case decomposeRuleLhs ds_lhs of { - Nothing -> do { warnDs (decomp_msg spec_co) - ; return Nothing } ; - - Just (_fn, args) -> - - -- Check for dead binders: Note [Unused spec binders] - let arg_fvs = exprsFreeVars args - bad_bndrs = filterOut (`elemVarSet` arg_fvs) bndrs - in if not (null bad_bndrs) - then do { warnDs (dead_msg bad_bndrs); return Nothing } - else do - - { (spec_unf, unf_pairs) <- specUnfolding wrap_fn spec_ty (realIdUnfolding poly_id) - - ; let spec_id = mkLocalId spec_name spec_ty - `setInlinePragma` inl_prag - `setIdUnfolding` spec_unf - inl_prag | isDefaultInlinePragma spec_inl = idInlinePragma poly_id - | otherwise = spec_inl - -- Get the INLINE pragma from SPECIALISE declaration, or, - -- failing that, from the original Id - - extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d) - -- See Note [Constant rule dicts] - | d <- varSetElems (arg_fvs `delVarSetList` bndrs) - , isDictId d] - - rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name))) - AlwaysActive poly_name - (extra_dict_bndrs ++ bndrs) args - (mkVarApps (Var spec_id) bndrs) - - spec_rhs = wrap_fn poly_rhs - spec_pair = makeCorePair spec_id False (dictArity bndrs) spec_rhs - - ; return (Just (spec_pair `consOL` unf_pairs, rule)) - } } } - - dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs - <+> ptext (sLit "in specialied type:"), - nest 2 (pprTheta (map get_pred bs))] - , ptext (sLit "SPECIALISE pragma ignored")] - get_pred b = ASSERT( isId b ) expectJust "dsSpec" (tcSplitPredTy_maybe (idType b)) - - decomp_msg spec_co - = hang (ptext (sLit "Specialisation too complicated to desugar; ignored")) - 2 (pprHsWrapper (ppr poly_id) spec_co) - +dsSpecs _ IsDefaultMethod = return (nilOL, []) +dsSpecs poly_rhs (SpecPrags sps) + = do { pairs <- mapMaybeM (dsSpec (Just poly_rhs)) sps + ; let (spec_binds_s, rules) = unzip pairs + ; return (concatOL spec_binds_s, rules) } + +dsSpec :: Maybe CoreExpr -- Just rhs => RULE is for a local binding + -- Nothing => RULE is for an imported Id + -- rhs is in the Id's unfolding + -> Located TcSpecPrag + -> DsM (Maybe (OrdList (Id,CoreExpr), CoreRule)) +dsSpec mb_poly_rhs (L loc (SpecPrag poly_id spec_co spec_inl)) + = putSrcSpanDs loc $ + do { let poly_name = idName poly_id + ; spec_name <- newLocalName poly_name + ; wrap_fn <- dsHsWrapper spec_co + ; let (bndrs, ds_lhs) = collectBinders (wrap_fn (Var poly_id)) + spec_ty = mkPiTypes bndrs (exprType ds_lhs) + ; case decomposeRuleLhs bndrs ds_lhs of { + Left msg -> do { warnDs msg; return Nothing } ; + Right (final_bndrs, _fn, args) -> do + + { (spec_unf, unf_pairs) <- specUnfolding wrap_fn spec_ty (realIdUnfolding poly_id) + + ; let spec_id = mkLocalId spec_name spec_ty + `setInlinePragma` inl_prag + `setIdUnfolding` spec_unf + inl_prag | isDefaultInlinePragma spec_inl = idInlinePragma poly_id + | otherwise = spec_inl + -- Get the INLINE pragma from SPECIALISE declaration, or, + -- failing that, from the original Id + + rule = mkRule False {- Not auto -} is_local_id + (mkFastString ("SPEC " ++ showSDoc (ppr poly_name))) + AlwaysActive poly_name + final_bndrs args + (mkVarApps (Var spec_id) bndrs) + + spec_rhs = wrap_fn poly_rhs + spec_pair = makeCorePair spec_id False (dictArity bndrs) spec_rhs + + ; return (Just (spec_pair `consOL` unf_pairs, rule)) + } } } + where + is_local_id = isJust mb_poly_rhs + poly_rhs | Just rhs <- mb_poly_rhs + = rhs -- Local Id; this is its rhs + | Just unfolding <- maybeUnfoldingTemplate (realIdUnfolding poly_id) + = unfolding -- Imported Id; this is its unfolding + -- Use realIdUnfolding so we get the unfolding + -- even when it is a loop breaker. + -- We want to specialise recursive functions! + | otherwise = pprPanic "dsImpSpecs" (ppr poly_id) + -- The type checker has checked that it *has* an unfolding specUnfolding :: (CoreExpr -> CoreExpr) -> Type -> Unfolding -> DsM (Unfolding, OrdList (Id,CoreExpr)) +{- [Dec 10: TEMPORARILY commented out, until we can straighten out how to + generate unfoldings for specialised DFuns + specUnfolding wrap_fn spec_ty (DFunUnfolding _ _ ops) = do { let spec_rhss = map wrap_fn ops ; spec_ids <- mapM (mkSysLocalM (fsLit "spec") . exprType) spec_rhss ; return (mkDFunUnfolding spec_ty (map Var spec_ids), toOL (spec_ids `zip` spec_rhss)) } +-} specUnfolding _ _ _ = return (noUnfolding, nilOL) -{- -mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> TyVarEnv Type --- If any of the tyvars is missing from any of the lists in --- the second arg, return a binding in the result -mkArbitraryTypeEnv tyvars exports - = go emptyVarEnv exports - where - go env [] = env - go env ((ltvs, _, _, _) : exports) - = go env' exports - where - env' = foldl extend env [tv | tv <- tyvars - , not (tv `elem` ltvs) - , not (tv `elemVarEnv` env)] - - extend env tv = extendVarEnv env tv (dsMkArbitraryType tv) --} - dsMkArbitraryType :: TcTyVar -> Type dsMkArbitraryType tv = anyTypeOfKind (tyVarKind tv) \end{code} -Note [Unused spec binders] -~~~~~~~~~~~~~~~~~~~~~~~~~~ -Consider - f :: a -> a - {-# SPECIALISE f :: Eq a => a -> a #-} -It's true that this *is* a more specialised type, but the rule -we get is something like this: - f_spec d = f - RULE: f = f_spec d -Note that the rule is bogus, becuase it mentions a 'd' that is -not bound on the LHS! But it's a silly specialisation anyway, becuase -the constraint is unused. We could bind 'd' to (error "unused") -but it seems better to reject the program because it's almost certainly -a mistake. That's what the isDeadBinder call detects. - -Note [Constant rule dicts] -~~~~~~~~~~~~~~~~~~~~~~~ -When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict, -which is presumably in scope at the function definition site, we can quantify -over it too. *Any* dict with that type will do. - -So for example when you have - f :: Eq a => a -> a - f = - {-# SPECIALISE f :: Int -> Int #-} - -Then we get the SpecPrag - SpecPrag (f Int dInt) - -And from that we want the rule - - RULE forall dInt. f Int dInt = f_spec - f_spec = let f = in f Int dInt - -But be careful! That dInt might be GHC.Base.$fOrdInt, which is an External -Name, and you can't bind them in a lambda or forall without getting things -confused. Likewise it might have an InlineRule or something, which would be -utterly bogus. So we really make a fresh Id, with the same unique and type -as the old one, but with an Internal name and no IdInfo. - %************************************************************************ %* * \subsection{Adding inline pragmas} @@ -691,24 +560,51 @@ as the old one, but with an Internal name and no IdInfo. %************************************************************************ \begin{code} -decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr]) +decomposeRuleLhs :: [Var] -> CoreExpr -> Either SDoc ([Var], Id, [CoreExpr]) -- Take apart the LHS of a RULE. It's suuposed to look like -- /\a. f a Int dOrdInt -- or /\a.\d:Ord a. let { dl::Ord [a] = dOrdList a d } in f [a] dl -- That is, the RULE binders are lambda-bound -- Returns Nothing if the LHS isn't of the expected shape -decomposeRuleLhs lhs +decomposeRuleLhs bndrs lhs = -- Note [Simplifying the left-hand side of a RULE] - case collectArgs (simpleOptExpr lhs) of - (Var fn, args) -> Just (fn, args) + case collectArgs opt_lhs of + (Var fn, args) -> check_bndrs fn args (Case scrut bndr ty [(DEFAULT, _, body)], args) | isDeadBinder bndr -- Note [Matching seqId] - -> Just (seqId, args' ++ args) + -> check_bndrs seqId (args' ++ args) where args' = [Type (idType bndr), Type ty, scrut, body] - _other -> Nothing -- Unexpected shape + _other -> Left bad_shape_msg + where + opt_lhs = simpleOptExpr lhs + + check_bndrs fn args + | null (dead_bndrs) = Right (extra_dict_bndrs ++ bndrs, fn, args) + | otherwise = Left (vcat (map dead_msg dead_bndrs)) + where + arg_fvs = exprsFreeVars args + + -- Check for dead binders: Note [Unused spec binders] + dead_bndrs = filterOut (`elemVarSet` arg_fvs) bndrs + + -- Add extra dict binders: Note [Constant rule dicts] + extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d) + | d <- varSetElems (arg_fvs `delVarSetList` bndrs) + , isDictId d] + + + bad_shape_msg = hang (ptext (sLit "RULE left-hand side too complicated to desugar")) + 2 (ppr opt_lhs) + dead_msg bndr = hang (sep [ ptext (sLit "Forall'd") <+> pp_bndr bndr + , ptext (sLit "is not bound in RULE lhs")]) + 2 (ppr opt_lhs) + pp_bndr bndr + | isTyVar bndr = ptext (sLit "type variable") <+> quotes (ppr bndr) + | isEvVar bndr = ptext (sLit "constraint") <+> quotes (ppr (evVarPred bndr)) + | otherwise = ptext (sLit "variable") <+> quotes (ppr bndr) \end{code} Note [Simplifying the left-hand side of a RULE] @@ -735,13 +631,52 @@ otherwise we don't match when given an argument like NB: tcSimplifyRuleLhs is very careful not to generate complicated dictionary expressions that we might have to match - Note [Matching seqId] ~~~~~~~~~~~~~~~~~~~ The desugarer turns (seq e r) into (case e of _ -> r), via a special-case hack and this code turns it back into an application of seq! See Note [Rules for seq] in MkId for the details. +Note [Unused spec binders] +~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + f :: a -> a + {-# SPECIALISE f :: Eq a => a -> a #-} +It's true that this *is* a more specialised type, but the rule +we get is something like this: + f_spec d = f + RULE: f = f_spec d +Note that the rule is bogus, becuase it mentions a 'd' that is +not bound on the LHS! But it's a silly specialisation anyway, becuase +the constraint is unused. We could bind 'd' to (error "unused") +but it seems better to reject the program because it's almost certainly +a mistake. That's what the isDeadBinder call detects. + +Note [Constant rule dicts] +~~~~~~~~~~~~~~~~~~~~~~~ +When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict, +which is presumably in scope at the function definition site, we can quantify +over it too. *Any* dict with that type will do. + +So for example when you have + f :: Eq a => a -> a + f = + {-# SPECIALISE f :: Int -> Int #-} + +Then we get the SpecPrag + SpecPrag (f Int dInt) + +And from that we want the rule + + RULE forall dInt. f Int dInt = f_spec + f_spec = let f = in f Int dInt + +But be careful! That dInt might be GHC.Base.$fOrdInt, which is an External +Name, and you can't bind them in a lambda or forall without getting things +confused. Likewise it might have an InlineRule or something, which would be +utterly bogus. So we really make a fresh Id, with the same unique and type +as the old one, but with an Internal name and no IdInfo. + %************************************************************************ %* *