% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % Pattern-matching bindings (HsBinds and MonoBinds) Handles @HsBinds@; those at the top level require different handling, 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, dsCoercion, AutoScc(..) ) where #include "HsVersions.h" import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr ) import {-# SOURCE #-} Match( matchWrapper ) import DsMonad import DsGRHSs import DsUtils import HsSyn -- lots of things import CoreSyn -- lots of things import CoreUtils import TcHsSyn ( mkArbitraryType ) -- Mis-placed? import TcType import OccurAnal import CostCentre import Module import Id import Var ( TyVar ) import Rules import VarEnv import Type import Outputable import SrcLoc import Maybes import Bag import BasicTypes hiding ( TopLevel ) import FastString import Util ( mapSnd ) import Control.Monad import Data.List \end{code} %************************************************************************ %* * \subsection[dsMonoBinds]{Desugaring a @MonoBinds@} %* * %************************************************************************ \begin{code} dsTopLHsBinds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)] dsTopLHsBinds auto_scc binds = ds_lhs_binds auto_scc binds dsLHsBinds :: LHsBinds Id -> DsM [(Id,CoreExpr)] dsLHsBinds binds = ds_lhs_binds NoSccs binds ------------------------ ds_lhs_binds :: AutoScc -> LHsBinds Id -> DsM [(Id,CoreExpr)] -- scc annotation policy (see below) ds_lhs_binds auto_scc binds = foldM (dsLHsBind auto_scc) [] (bagToList binds) dsLHsBind :: AutoScc -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append) -> LHsBind Id -> DsM [(Id,CoreExpr)] -- Result dsLHsBind auto_scc rest (L loc bind) = putSrcSpanDs loc $ dsHsBind auto_scc rest bind dsHsBind :: AutoScc -> [(Id,CoreExpr)] -- Put this on the end (avoid quadratic append) -> HsBind Id -> DsM [(Id,CoreExpr)] -- Result dsHsBind auto_scc rest (VarBind var expr) = dsLExpr expr `thenDs` \ core_expr -> -- Dictionary bindings are always VarMonoBinds, so -- we only need do this here addDictScc var core_expr `thenDs` \ core_expr' -> returnDs ((var, core_expr') : rest) dsHsBind auto_scc rest (FunBind { fun_id = L _ fun, fun_matches = matches, fun_co_fn = co_fn, fun_tick = tick }) = matchWrapper (FunRhs (idName fun)) matches `thenDs` \ (args, body) -> mkOptTickBox tick body `thenDs` \ body' -> dsCoercion co_fn (return (mkLams args body')) `thenDs` \ rhs -> returnDs ((fun,rhs) : rest) dsHsBind auto_scc rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }) = dsGuarded grhss ty `thenDs` \ body_expr -> mkSelectorBinds pat body_expr `thenDs` \ sel_binds -> returnDs (sel_binds ++ rest) -- Note [Rules and inlining] -- Common special case: no type or dictionary abstraction -- This is a bit less trivial than you might suppose -- The naive way woudl be to desguar to something like -- f_lcl = ...f_lcl... -- The "binds" from AbsBinds -- M.f = f_lcl -- Generated from "exports" -- But we don't want that, because if M.f isn't exported, -- it'll be inlined unconditionally at every call site (its rhs is -- trivial). That would be ok unless it has RULES, which would -- thereby be completely lost. Bad, bad, bad. -- -- Instead we want to generate -- M.f = ...f_lcl... -- f_lcl = M.f -- Now all is cool. The RULES are attached to M.f (by SimplCore), -- and f_lcl is rapidly inlined away. -- -- 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 dsHsBind auto_scc rest (AbsBinds [] [] exports binds) = do { core_prs <- ds_lhs_binds NoSccs binds ; let env = mkABEnv exports do_one (lcl_id, rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id = addInlinePrags prags gbl_id $ addAutoScc auto_scc gbl_id rhs | otherwise = (lcl_id, rhs) locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports] ; return (map do_one core_prs ++ locals' ++ rest) } -- No Rec needed here (contrast the other AbsBinds cases) -- because we can rely on the enclosing dsBind to wrap in Rec -- Another common case: one exported variable -- Non-recursive bindings come through this way dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports@[(tyvars, global, local, prags)] binds) = ASSERT( all (`elem` tyvars) all_tyvars ) ds_lhs_binds NoSccs binds `thenDs` \ core_prs -> let -- Always treat the binds as recursive, because the typechecker -- makes rather mixed-up dictionary bindings core_bind = Rec core_prs in mappM (dsSpec all_tyvars dicts tyvars global local core_bind) prags `thenDs` \ mb_specs -> let (spec_binds, rules) = unzip (catMaybes mb_specs) global' = addIdSpecialisations global rules rhs' = mkLams tyvars $ mkLams dicts $ Let core_bind (Var local) bind = addInlinePrags prags global' $ addAutoScc auto_scc global' rhs' in returnDs (bind : spec_binds ++ rest) dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds) = do { core_prs <- ds_lhs_binds NoSccs binds ; let env = mkABEnv exports do_one (lcl_id,rhs) | Just (gbl_id, prags) <- lookupVarEnv env lcl_id = addInlinePrags prags lcl_id $ addAutoScc auto_scc gbl_id rhs | otherwise = (lcl_id,rhs) -- Rec because of mixed-up dictionary bindings core_bind = Rec (map do_one core_prs) tup_expr = mkTupleExpr locals tup_ty = exprType tup_expr poly_tup_expr = mkLams all_tyvars $ mkLams dicts $ Let core_bind tup_expr locals = [local | (_, _, local, _) <- exports] local_tys = map idType locals ; poly_tup_id <- newSysLocalDs (exprType poly_tup_expr) ; let dict_args = map Var dicts mk_bind ((tyvars, global, local, prags), n) -- locals !! n == local = -- Need to make fresh locals to bind in the selector, because -- some of the tyvars will be bound to 'Any' do { locals' <- newSysLocalsDs (map substitute local_tys) ; tup_id <- newSysLocalDs (substitute tup_ty) ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local core_bind) prags ; let (spec_binds, rules) = unzip (catMaybes mb_specs) global' = addIdSpecialisations global rules rhs = mkLams tyvars $ mkLams dicts $ mkTupleSelector locals' (locals' !! n) tup_id $ mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args ; returnDs ((global', rhs) : spec_binds) } where mk_ty_arg all_tyvar | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar | otherwise = mkArbitraryType all_tyvar ty_args = map mk_ty_arg all_tyvars substitute = substTyWith all_tyvars ty_args ; export_binds_s <- mappM mk_bind (exports `zip` [0..]) -- don't scc (auto-)annotate the tuple itself. ; returnDs ((poly_tup_id, poly_tup_expr) : (concat export_binds_s ++ rest)) } mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> VarEnv (Id, [LPrag]) -- Takes the exports of a AbsBinds, and returns a mapping -- lcl_id -> (gbl_id, prags) mkABEnv exports = mkVarEnv [ (lcl_id, (gbl_id, prags)) | (_, gbl_id, lcl_id, prags) <- exports] dsSpec :: [TyVar] -> [DictId] -> [TyVar] -> Id -> Id -- Global, local -> CoreBind -> LPrag -> DsM (Maybe ((Id,CoreExpr), -- Binding for specialised Id CoreRule)) -- Rule for the Global Id -- Example: -- f :: (Eq a, Ix b) => a -> b -> b -- {-# SPECIALISE f :: Ix b => Int -> b -> b #-} -- -- AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds -- -- SpecPrag (/\b.\(d:Ix b). f Int b dInt d) -- (forall b. Ix b => Int -> b -> b) -- -- Rule: forall b,(d:Ix b). f Int b dInt d = f_spec b d -- -- Spec bind: f_spec = Let f = /\ab \(d1:Eq a)(d2:Ix b). let binds in f_mono -- /\b.\(d:Ix b). in f Int b dInt d -- The idea is that f occurs just once, so it'll be -- inlined and specialised -- -- Given SpecPrag (/\as.\ds. f es) t, we have -- the defn f_spec as ds = f es -- and the RULE f es = f_spec as ds -- -- It is *possible* that 'es' does not mention all of the dictionaries 'ds' -- (a bit silly, because then the dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (L _ (InlinePrag {})) = return Nothing dsSpec all_tvs dicts tvs poly_id mono_id mono_bind (L loc (SpecPrag spec_expr spec_ty _const_dicts inl)) -- See Note [Const rule dicts] = putSrcSpanDs loc $ do { let poly_name = idName poly_id ; spec_name <- newLocalName poly_name ; ds_spec_expr <- dsExpr spec_expr ; let (bndrs, body) = collectBinders (occurAnalyseExpr ds_spec_expr) -- The occurrence-analysis does two things -- (a) identifies unused binders: Note [Unused spec binders] -- (b) sorts dict bindings into NonRecs -- so they can be inlined by decomposeRuleLhs mb_lhs = decomposeRuleLhs body -- Check for dead binders: Note [Unused spec binders] ; case filter isDeadBinder bndrs of { bs | not (null bs) -> do { warnDs (dead_msg bs); return Nothing } | otherwise -> case mb_lhs of Nothing -> do { warnDs decomp_msg; return Nothing } Just (var, args) -> return (Just (addInlineInfo inl spec_id spec_rhs, rule)) where local_poly = setIdNotExported poly_id -- Very important to make the 'f' non-exported, -- else it won't be inlined! spec_id = mkLocalId spec_name spec_ty spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr poly_f_body = mkLams (tvs ++ dicts) $ fix_up (Let mono_bind (Var mono_id)) rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name))) AlwaysActive poly_name bndrs args (mkVarApps (Var spec_id) bndrs) } } where -- Bind to Any any of all_ptvs that aren't -- relevant for this particular function fix_up body | null void_tvs = body | otherwise = mkTyApps (mkLams void_tvs body) (map mkArbitraryType void_tvs) void_tvs = all_tvs \\ tvs 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 = hang (ptext SLIT("Specialisation too complicated to desugar; ignored")) 2 (ppr spec_expr) \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 [Const rule dicts] ~~~~~~~~~~~~~~~~~~~~~~~ A SpecPrag has a field for "constant dicts" in the RULE, but I think it's pretty useless. See the place where it's generated in TcBinds. TcSimplify will discharge a constraint by binding it to, say, GHC.Base.$f2 :: Eq Int, withour putting anything in the LIE, so this dict won't show up in the const-dicts field. It probably doesn't matter, because the rule will end up being something like f Int GHC.Base.$f2 = ... rather than forall d. f Int d = ... The latter is more general, but in practice I think it won't make any difference. %************************************************************************ %* * \subsection{Adding inline pragmas} %* * %************************************************************************ \begin{code} decomposeRuleLhs :: CoreExpr -> Maybe (Id, [CoreExpr]) -- Returns Nothing if the LHS isn't of the expected shape decomposeRuleLhs lhs = go emptyVarEnv (occurAnalyseExpr lhs) -- Occurrence analysis sorts out the dict -- bindings so we know if they are recursive where -- Substitute dicts in the LHS args, so that there -- aren't any lets getting in the way -- Note that we substitute the function too; we might have this as -- a LHS: let f71 = M.f Int in f71 go env (Let (NonRec dict rhs) body) = go (extendVarEnv env dict (simpleSubst env rhs)) body go env body = case collectArgs (simpleSubst env body) of (Var fn, args) -> Just (fn, args) other -> Nothing simpleSubst :: IdEnv CoreExpr -> CoreExpr -> CoreExpr -- Similar to CoreSubst.substExpr, except that -- (a) takes no account of capture; dictionary bindings use new names -- (b) can have a GlobalId (imported) in its domain -- (c) Ids only; no types are substituted -- -- (b) is the reason we can't use CoreSubst... and it's no longer relevant -- so really we should replace simpleSubst simpleSubst subst expr = go expr where go (Var v) = lookupVarEnv subst v `orElse` Var v go (Cast e co) = Cast (go e) co go (Type ty) = Type ty go (Lit lit) = Lit lit go (App fun arg) = App (go fun) (go arg) go (Note note e) = Note note (go e) go (Lam bndr body) = Lam bndr (go body) go (Let (NonRec bndr rhs) body) = Let (NonRec bndr (go rhs)) (go body) go (Let (Rec pairs) body) = Let (Rec (mapSnd go pairs)) (go body) go (Case scrut bndr ty alts) = Case (go scrut) bndr ty [(c,bs,go r) | (c,bs,r) <- alts] addInlinePrags :: [LPrag] -> Id -> CoreExpr -> (Id,CoreExpr) addInlinePrags prags bndr rhs = case [inl | L _ (InlinePrag inl) <- prags] of [] -> (bndr, rhs) (inl:_) -> addInlineInfo inl bndr rhs addInlineInfo :: InlineSpec -> Id -> CoreExpr -> (Id,CoreExpr) addInlineInfo (Inline phase is_inline) bndr rhs = (attach_phase bndr phase, wrap_inline is_inline rhs) where attach_phase bndr phase | isAlwaysActive phase = bndr -- Default phase | otherwise = bndr `setInlinePragma` phase wrap_inline True body = mkInlineMe body wrap_inline False body = body \end{code} %************************************************************************ %* * \subsection[addAutoScc]{Adding automatic sccs} %* * %************************************************************************ \begin{code} data AutoScc = NoSccs | AddSccs Module (Id -> Bool) -- The (Id->Bool) says which Ids to add SCCs to addAutoScc :: AutoScc -> Id -- Binder -> CoreExpr -- Rhs -> CoreExpr -- Scc'd Rhs addAutoScc NoSccs _ rhs = rhs addAutoScc (AddSccs mod add_scc) id rhs | add_scc id = mkSCC (mkAutoCC id mod NotCafCC) rhs | otherwise = rhs \end{code} If profiling and dealing with a dict binding, wrap the dict in @_scc_ DICT @: \begin{code} addDictScc var rhs = returnDs rhs {- DISABLED for now (need to somehow make up a name for the scc) -- SDM | not ( opt_SccProfilingOn && opt_AutoSccsOnDicts) || not (isDictId var) = returnDs rhs -- That's easy: do nothing | otherwise = getModuleAndGroupDs `thenDs` \ (mod, grp) -> -- ToDo: do -dicts-all flag (mark dict things with individual CCs) returnDs (Note (SCC (mkAllDictsCC mod grp False)) rhs) -} \end{code} %************************************************************************ %* * Desugaring coercions %* * %************************************************************************ \begin{code} dsCoercion :: HsWrapper -> DsM CoreExpr -> DsM CoreExpr dsCoercion WpHole thing_inside = thing_inside dsCoercion (WpCompose c1 c2) thing_inside = dsCoercion c1 (dsCoercion c2 thing_inside) dsCoercion (WpCo co) thing_inside = do { expr <- thing_inside ; return (Cast expr co) } dsCoercion (WpLam id) thing_inside = do { expr <- thing_inside ; return (Lam id expr) } dsCoercion (WpTyLam tv) thing_inside = do { expr <- thing_inside ; return (Lam tv expr) } dsCoercion (WpApp id) thing_inside = do { expr <- thing_inside ; return (App expr (Var id)) } dsCoercion (WpTyApp ty) thing_inside = do { expr <- thing_inside ; return (App expr (Type ty)) } dsCoercion (WpLet bs) thing_inside = do { prs <- dsLHsBinds bs ; expr <- thing_inside ; return (Let (Rec prs) expr) } \end{code}