X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FdeSugar%2FDsBinds.lhs;h=cc7ecfd38ee5c424ca4a0da9e225447c66a39b1a;hb=81e41fe31fb27b6330762d93ce90eb98899beb24;hp=add2c34a855cf2acd7f47ebb800b1260a6d54720;hpb=a25bbd11544e29225ebb260306fe00b7108a3024;p=ghc-hetmet.git diff --git a/compiler/deSugar/DsBinds.lhs b/compiler/deSugar/DsBinds.lhs index add2c34..cc7ecfd 100644 --- a/compiler/deSugar/DsBinds.lhs +++ b/compiler/deSugar/DsBinds.lhs @@ -17,7 +17,7 @@ module DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, #include "HsVersions.h" -import {-# SOURCE #-} DsExpr( dsLExpr, dsExpr ) +import {-# SOURCE #-} DsExpr( dsLExpr ) import {-# SOURCE #-} Match( matchWrapper ) import DsMonad @@ -29,19 +29,22 @@ import CoreSyn -- lots of things import CoreSubst import MkCore import CoreUtils +import CoreArity ( etaExpand ) import CoreUnfold import CoreFVs -import TcHsSyn ( mkArbitraryType ) -- Mis-placed? import TcType +import TysPrim ( anyTypeOfKind ) import CostCentre import Module import Id -import Var ( Var, TyVar ) +import Name ( localiseName ) +import MkId ( seqId ) +import Var ( Var, TyVar, tyVarKind ) +import IdInfo ( vanillaIdInfo ) import VarSet import Rules import VarEnv -import Type import Outputable import SrcLoc import Maybes @@ -49,10 +52,10 @@ import Bag import BasicTypes hiding ( TopLevel ) import FastString import StaticFlags ( opt_DsMultiTyVar ) -import Util ( count, mapAndUnzip, lengthExceeds ) +import Util ( count, lengthExceeds ) +import MonadUtils import Control.Monad -import Data.List \end{code} %************************************************************************ @@ -87,14 +90,14 @@ dsHsBind :: AutoScc -> HsBind Id -> DsM [(Id,CoreExpr)] -- Result -dsHsBind _ rest (VarBind var expr inline_regardless) +dsHsBind _ rest (VarBind { var_id = var, var_rhs = expr, var_inline = inline_regardless }) = do { core_expr <- dsLExpr expr -- Dictionary bindings are always VarBinds, -- so we only need do this here ; core_expr' <- addDictScc var core_expr ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr' - | otherwise = var + | otherwise = var ; return ((var', core_expr') : rest) } @@ -102,9 +105,9 @@ dsHsBind _ rest (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 - ; rhs <- dsCoercion co_fn (return (mkLams args body')) - ; return ((fun,rhs) : rest) } + ; body' <- mkOptTickBox tick body + ; wrap_fn' <- dsCoercion co_fn + ; return ((fun, wrap_fn' (mkLams args body')) : rest) } dsHsBind _ rest (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty }) @@ -112,127 +115,70 @@ dsHsBind _ rest ; sel_binds <- mkSelectorBinds pat body_expr ; return (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 - ar_env = mkArityEnv binds do_one (lcl_id, rhs) - | Just (_, gbl_id, _, prags) <- lookupVarEnv env lcl_id - = makeCorePair gbl_id (lookupArity ar_env lcl_id) prags $ - addAutoScc auto_scc gbl_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 = (lcl_id, rhs) + | otherwise = return [(lcl_id, rhs)] locals' = [(lcl_id, Var gbl_id) | (_, gbl_id, lcl_id, _) <- exports] -- Note [Rules and inlining] - ; return (map do_one core_prs ++ locals' ++ rest) } + ; 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 -{- Note [Abstracting over tyvars only] - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - When abstracting over type variable only (not dictionaries), we don't really need to - built a tuple and select from it, as we do in the general case. Instead we can take - - AbsBinds [a,b] [ ([a,b], fg, fl, _), - ([b], gg, gl, _) ] - { fl = e1 - gl = e2 - h = e3 } - - and desugar it to - - fg = /\ab. let B in e1 - gg = /\b. let a = () in let B in S(e2) - h = /\ab. let B in e3 - - where B is the *non-recursive* binding - fl = fg a b - gl = gg b - h = h a b -- See (b); note shadowing! - - Notice (a) g has a different number of type variables to f, so we must - use the mkArbitraryType thing to fill in the gaps. - We use a type-let to do that. - - (b) The local variable h isn't in the exports, and rather than - clone a fresh copy we simply replace h by (h a b), where - the two h's have different types! Shadowing happens here, - which looks confusing but works fine. - - (c) The result is *still* quadratic-sized if there are a lot of - small bindings. So if there are more than some small - number (10), we filter the binding set B by the free - variables of the particular RHS. Tiresome. - - Why got to this trouble? It's a common case, and it removes the - quadratic-sized tuple desugaring. Less clutter, hopefullly faster - compilation, especially in a case where there are a *lot* of - bindings. --} - - dsHsBind auto_scc rest (AbsBinds tyvars [] exports 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 = -- Note [Abstracting over tyvars only] do { core_prs <- ds_lhs_binds NoSccs binds - ; arby_env <- mkArbitraryTypeEnv tyvars exports - ; let (lg_binds, core_prs') = mapAndUnzip do_one core_prs + ; let arby_env = mkArbitraryTypeEnv tyvars exports bndrs = mkVarSet (map fst core_prs) add_lets | core_prs `lengthExceeds` 10 = add_some - | otherwise = mkLets lg_binds - add_some rhs = mkLets [ NonRec b r | NonRec b r <- lg_binds - , b `elemVarSet` fvs] rhs + | 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 - ar_env = mkArityEnv binds env = mkABEnv exports - - do_one (lcl_id, rhs) - | Just (id_tvs, gbl_id, _, prags) <- lookupVarEnv env lcl_id - = 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 rhs - in (NonRec lcl_id (mkTyApps (Var gbl_id) (mkTyVarTys id_tvs)), - makeCorePair gbl_id (lookupArity ar_env lcl_id) prags rhs') + 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 - = (NonRec lcl_id (mkTyApps (Var non_exp_gbl_id) (mkTyVarTys tyvars)), - (non_exp_gbl_id, mkLams tyvars (add_lets rhs))) - where - non_exp_gbl_id = setIdType lcl_id (mkForAllTys tyvars (idType lcl_id)) + = 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))]) } - ; return (core_prs' ++ rest) } + ; (_, core_prs') <- fixDs (\ ~(lg_binds, _) -> mapAndUnzipM (do_one lg_binds) core_prs) + ; return (concat core_prs' ++ rest) } -- Another common case: one exported variable -- Non-recursive bindings come through this way @@ -243,26 +189,23 @@ dsHsBind auto_scc rest = ASSERT( all (`elem` tyvars) all_tyvars ) do { core_prs <- ds_lhs_binds NoSccs binds - ; let -- Always treat the binds as recursive, because the typechecker - -- makes rather mixed-up dictionary bindings + ; let -- Always treat the binds as recursive, because the + -- typechecker makes rather mixed-up dictionary bindings core_bind = Rec core_prs - inl_arity = lookupArity (mkArityEnv binds) local - - ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global - local inl_arity core_bind) prags - - ; let (spec_binds, rules) = unzip (catMaybes mb_specs) - global' = addIdSpecialisations global rules rhs = addAutoScc auto_scc global $ mkLams tyvars $ mkLams dicts $ Let core_bind (Var local) - main_bind = makeCorePair global' (inl_arity + length dicts) prags rhs + + ; (spec_binds, rules) <- dsSpecs global rhs prags + + ; let global' = addIdSpecialisations global rules + main_bind = makeCorePair global' (isDefaultMethod prags) + (dictArity dicts) rhs ; return (main_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 - ar_env = mkArityEnv binds do_one (lcl_id,rhs) | Just (_, gbl_id, _, _prags) <- lookupVarEnv env lcl_id = (lcl_id, addAutoScc auto_scc gbl_id rhs) | otherwise = (lcl_id,rhs) @@ -270,175 +213,291 @@ dsHsBind auto_scc rest (AbsBinds all_tyvars dicts exports binds) -- Rec because of mixed-up dictionary bindings core_bind = Rec (map do_one core_prs) - tup_expr = mkBigCoreVarTup 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 - - inl_prags :: [(Id, SrcSpan)] - inl_prags = [(id, loc) | (_, id, _, prags) <- exports - , L loc (InlinePrag {}) <- prags ] + tup_expr = mkBigCoreVarTup locals + tup_ty = exprType tup_expr + poly_tup_rhs = mkLams all_tyvars $ mkLams dicts $ + Let core_bind tup_expr + locals = [local | (_, _, local, _) <- exports] + local_tys = map idType locals - ; mapM_ discardedInlineWarning inl_prags + ; poly_tup_id <- newSysLocalDs (exprType poly_tup_rhs) - ; 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 { ty_args <- mapM mk_ty_arg all_tyvars - ; let substitute = substTyWith all_tyvars ty_args + ; let mk_bind ((tyvars, global, _, spec_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 { let ty_args = map mk_ty_arg all_tyvars + substitute = substTyWith all_tyvars ty_args ; locals' <- newSysLocalsDs (map substitute local_tys) ; tup_id <- newSysLocalDs (substitute tup_ty) - ; mb_specs <- mapM (dsSpec all_tyvars dicts tyvars global local - (lookupArity ar_env local) core_bind) - prags - ; let (spec_binds, rules) = unzip (catMaybes mb_specs) - global' = addIdSpecialisations global rules - rhs = mkLams tyvars $ mkLams dicts $ + ; let rhs = mkLams tyvars $ mkLams dicts $ mkTupleSelector locals' (locals' !! n) tup_id $ - mkApps (mkTyApps (Var poly_tup_id) ty_args) dict_args + 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 + ; let global' = addIdSpecialisations global rules ; return ((global', rhs) : spec_binds) } where mk_ty_arg all_tyvar - | all_tyvar `elem` tyvars = return (mkTyVarTy all_tyvar) + | all_tyvar `elem` tyvars = mkTyVarTy all_tyvar | otherwise = dsMkArbitraryType all_tyvar ; export_binds_s <- mapM mk_bind (exports `zip` [0..]) -- Don't scc (auto-)annotate the tuple itself. - ; return ((poly_tup_id, poly_tup_expr) : + ; return ((poly_tup_id, poly_tup_rhs) : (concat export_binds_s ++ rest)) } ------------------------ -makeCorePair :: Id-> Arity -> [LPrag] -> CoreExpr -> (Id, CoreExpr) -makeCorePair gbl_id arity prags rhs - = (addInline gbl_id arity rhs prags, rhs) +makeCorePair :: Id -> Bool -> Arity -> CoreExpr -> (Id, CoreExpr) +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) + + | 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] + = (gbl_id `setIdUnfolding` mkInlineRule rhs (Just (dict_arity + arity)), + -- NB: The arity in the InlineRule takes account of the dictionaries + etaExpand arity 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 +dictArity dicts = count isId dicts ------------------------- -discardedInlineWarning :: (Id, SrcSpan) -> DsM () -discardedInlineWarning (id, loc) - = putSrcSpanDs loc $ - warnDs $ sep [ ptext (sLit "Discarding INLINE pragma for") <+> ppr id - , ptext (sLit "because it is bound by a pattern, or a mutual recursion") ] ------------------------ -type AbsBindEnv = VarEnv ([TyVar], Id, Id, [LPrag]) +type AbsBindEnv = VarEnv ([TyVar], Id, Id, TcSpecPrags) -- Maps the "lcl_id" for an AbsBind to -- its "gbl_id" and associated pragmas, if any -mkABEnv :: [([TyVar], Id, Id, [LPrag])] -> AbsBindEnv +mkABEnv :: [([TyVar], Id, Id, TcSpecPrags)] -> AbsBindEnv -- Takes the exports of a AbsBinds, and returns a mapping -- lcl_id -> (tyvars, gbl_id, lcl_id, prags) mkABEnv exports = mkVarEnv [ (lcl_id, export) | export@(_, _, lcl_id, _) <- exports] +\end{code} -mkArityEnv :: LHsBinds Id -> IdEnv Arity - -- Maps a local to the arity of its definition -mkArityEnv binds = mkVarEnv (mapCatMaybes get_arity (bagToList binds)) - where - get_arity (L _ (FunBind { fun_id = id, fun_matches = ms })) = Just (unLoc id, matchGroupArity ms) - get_arity _ = Nothing - -lookupArity :: IdEnv Arity -> Id -> Arity -lookupArity ar_env id = lookupVarEnv ar_env id `orElse` 0 - -addInline :: Id -> Arity -> CoreExpr -> [LPrag] -> Id -addInline id arity rhs prags - = case [inl | L _ (InlinePrag inl) <- prags] of - [] -> id - (inl_spec : _) -> addInlineToId id arity rhs inl_spec - -addInlineToId :: Id -> Arity -> CoreExpr -> InlineSpec -> Id -addInlineToId id inl_arity rhs (Inline phase is_inline) - = id `setInlinePragma` phase - `setIdUnfolding` inline_rule - where - inline_rule | is_inline = mkInlineRule rhs inl_arity - | otherwise = noUnfolding +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 -} + +Note [Specialising in no-dict case] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Even if there are no tyvars or dicts, we may have specialisation pragmas. +Class methods can generate + AbsBinds [] [] [( ... spec-prag] + { AbsBinds [tvs] [dicts] ...blah } +So the overloading is in the nested AbsBinds. A good example is in GHC.Float: + + class (Real a, Fractional a) => RealFrac a where + round :: (Integral b) => a -> b + + instance RealFrac Float where + {-# SPECIALIZE round :: Float -> Int #-} + +The top-level AbsBinds for $cround has no tyvars or dicts (because the +instance does not). But the method is locally overloaded! + +Note [Abstracting over tyvars only] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +When abstracting over type variable only (not dictionaries), we don't really need to +built a tuple and select from it, as we do in the general case. Instead we can take ------------------------- -dsSpec :: [TyVar] -> [DictId] -> [TyVar] - -> Id -> Id -> Arity -- Global, local, arity of 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 = let-nonrec f = /\fas\fds. let f_mono = in f_mono --- in f es --- and the RULE forall as, ds. 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 _ _ _ _ _ _ _ (L _ (InlinePrag {})) - = return Nothing - -dsSpec all_tvs dicts tvs poly_id mono_id inl_arity mono_bind - (L loc (SpecPrag spec_expr spec_ty inl)) - = putSrcSpanDs loc $ - do { let poly_name = idName poly_id - ; spec_name <- newLocalName poly_name - ; ds_spec_expr <- dsExpr spec_expr - ; case (decomposeRuleLhs ds_spec_expr) of { - Nothing -> do { warnDs decomp_msg; return Nothing } ; - - Just (bndrs, _fn, args) -> - - -- 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 -> do - - { f_body <- fix_up (Let mono_bind (Var mono_id)) - - ; let 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_id1 = addInlineToId spec_id (inl_arity + count isDictId bndrs) - spec_rhs inl - spec_rhs = Let (NonRec local_poly poly_f_body) ds_spec_expr - poly_f_body = mkLams (tvs ++ dicts) f_body - - extra_dict_bndrs = [localiseId d -- See Note [Constant rule dicts] - | d <- varSetElems (exprFreeVars ds_spec_expr) - , isDictId d] - -- Note [Const rule dicts] - - rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name))) - AlwaysActive poly_name - (extra_dict_bndrs ++ bndrs) args - (mkVarApps (Var spec_id) bndrs) - ; return (Just ((spec_id1, spec_rhs), rule)) - } } } } - where - -- Bind to Any any of all_ptvs that aren't - -- relevant for this particular function - fix_up body | null void_tvs = return body - | otherwise = do { void_tys <- mapM dsMkArbitraryType void_tvs - ; return (mkTyApps (mkLams void_tvs body) void_tys) } + AbsBinds [a,b] [ ([a,b], fg, fl, _), + ([b], gg, gl, _) ] + { fl = e1 + gl = e2 + h = e3 } + +and desugar it to + + fg = /\ab. let B in e1 + gg = /\b. let a = () in let B in S(e2) + h = /\ab. let B in e3 + +where B is the *non-recursive* binding + fl = fg a b + gl = gg b + h = h a b -- See (b); note shadowing! + +Notice (a) g has a different number of type variables to f, so we must + use the mkArbitraryType thing to fill in the gaps. + We use a type-let to do that. + + (b) The local variable h isn't in the exports, and rather than + clone a fresh copy we simply replace h by (h a b), where + the two h's have different types! Shadowing happens here, + which looks confusing but works fine. + + (c) The result is *still* quadratic-sized if there are a lot of + small bindings. So if there are more than some small + number (10), we filter the binding set B by the free + variables of the particular RHS. Tiresome. + +Why got to this trouble? It's a common case, and it removes the +quadratic-sized tuple desugaring. Less clutter, hopefullly faster +compilation, especially in a case where there are a *lot* of +bindings. + + +Note [Eta-expanding INLINE things] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + foo :: Eq a => a -> a + {-# INLINE foo #-} + foo x = ... + +If (foo d) ever gets floated out as a common sub-expression (which can +happen as a result of method sharing), there's a danger that we never +get to do the inlining, which is a Terribly Bad thing given that the +user said "inline"! + +To avoid this we pre-emptively eta-expand the definition, so that foo +has the arity with which it is declared in the source code. In this +example it has arity 2 (one for the Eq and one for x). Doing this +should mean that (foo d) is a PAP and we don't share it. + +Note [Nested arities] +~~~~~~~~~~~~~~~~~~~~~ +For reasons that are not entirely clear, method bindings come out looking like +this: + + AbsBinds [] [] [$cfromT <= [] fromT] + $cfromT [InlPrag=INLINE] :: T Bool -> Bool + { AbsBinds [] [] [fromT <= [] fromT_1] + fromT :: T Bool -> Bool + { fromT_1 ((TBool b)) = not b } } } + +Note the nested AbsBind. The arity for the InlineRule on $cfromT should be +gotten from the binding for fromT_1. + +It might be better to have just one level of AbsBinds, but that requires more +thought! + +Note [Implementing SPECIALISE pragmas] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Example: + f :: (Eq a, Ix b) => a -> b -> Bool + {-# SPECIALISE f :: (Ix p, Ix q) => Int -> (p,q) -> Bool #-} + f = + +From this the typechecker generates + + AbsBinds [ab] [d1,d2] [([ab], f, f_mono, prags)] binds + + SpecPrag (wrap_fn :: forall a b. (Eq a, Ix b) => XXX + -> forall p q. (Ix p, Ix q) => XXX[ Int/a, (p,q)/b ]) + +Note that wrap_fn can transform *any* function with the right type prefix + forall ab. (Eq a, Ix b) => XXX +regardless of XXX. It's sort of polymorphic in XXX. This is +useful: we use the same wrapper to transform each of the class ops, as +well as the dict. + +From these we generate: + + Rule: forall p, q, (dp:Ix p), (dq:Ix q). + f Int (p,q) dInt ($dfInPair dp dq) = f_spec p q dp dq - void_tvs = all_tvs \\ tvs + Spec bind: f_spec = wrap_fn + +Note that + + * The LHS of the rule may mention dictionary *expressions* (eg + $dfIxPair dp dq), and that is essential because the dp, dq are + needed on the RHS. + + * The RHS of f_spec, has a *copy* of 'binds', so that it + can fully specialise it. + +\begin{code} +------------------------ +dsSpecs :: Id -- The polymorphic Id + -> CoreExpr -- Its rhs + -> TcSpecPrags + -> DsM ( [(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 ([], []) + SpecPrags sps -> do { pairs <- mapMaybeM spec_one sps + ; let (spec_binds_s, rules) = unzip pairs + ; return (concat spec_binds_s, rules) } + where + spec_one :: Located TcSpecPrag -> DsM (Maybe ([(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 <- dsCoercion spec_co + ; let ds_spec_expr = wrap_fn (Var poly_id) + ; case decomposeRuleLhs ds_spec_expr of { + Nothing -> do { warnDs (decomp_msg spec_co) + ; return Nothing } ; + + Just (bndrs, _fn, args) -> + + -- 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 -> do + + { (spec_unf, unf_pairs) <- specUnfolding wrap_fn (realIdUnfolding poly_id) + + ; let spec_ty = exprType ds_spec_expr + 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 (exprFreeVars ds_spec_expr) + , 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 : unf_pairs, rule)) + } } } } dead_msg bs = vcat [ sep [ptext (sLit "Useless constraint") <> plural bs <+> ptext (sLit "in specialied type:"), @@ -446,31 +505,37 @@ dsSpec all_tvs dicts tvs poly_id mono_id inl_arity mono_bind , 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) + decomp_msg spec_co + = hang (ptext (sLit "Specialisation too complicated to desugar; ignored")) + 2 (pprHsWrapper (ppr poly_id) spec_co) -mkArbitraryTypeEnv :: [TyVar] -> [([TyVar], a, b, c)] -> DsM (TyVarEnv Type) +specUnfolding :: (CoreExpr -> CoreExpr) -> Unfolding -> DsM (Unfolding, [(Id,CoreExpr)]) +specUnfolding wrap_fn (DFunUnfolding con ops) + = do { let spec_rhss = map wrap_fn ops + ; spec_ids <- mapM (mkSysLocalM (fsLit "spec") . exprType) spec_rhss + ; return (DFunUnfolding con (map Var spec_ids), spec_ids `zip` spec_rhss) } +specUnfolding _ _ + = return (noUnfolding, []) + +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 [] = return env + go env [] = env go env ((ltvs, _, _, _) : exports) - = do { env' <- foldlM extend env [tv | tv <- tyvars - , not (tv `elem` ltvs) - , not (tv `elemVarEnv` env)] - ; go env' exports } + = go env' exports + where + env' = foldl extend env [tv | tv <- tyvars + , not (tv `elem` ltvs) + , not (tv `elemVarEnv` env)] - extend env tv = do { ty <- dsMkArbitraryType tv - ; return (extendVarEnv env tv ty) } + extend env tv = extendVarEnv env tv (dsMkArbitraryType tv) - -dsMkArbitraryType :: TcTyVar -> DsM Type -dsMkArbitraryType tv = mkArbitraryType warn tv - where - warn span msg = putSrcSpanDs span (warnDs msg) +dsMkArbitraryType :: TcTyVar -> Type +dsMkArbitraryType tv = anyTypeOfKind (tyVarKind tv) \end{code} Note [Unused spec binders] @@ -488,7 +553,7 @@ 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] +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 @@ -500,7 +565,7 @@ So for example when you have {-# SPECIALISE f :: Int -> Int #-} Then we get the SpecPrag - SpecPrag (f Int dInt) Int + SpecPrag (f Int dInt) And from that we want the rule @@ -509,8 +574,9 @@ And from that we want the rule 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. Hence the use of 'localiseId' to make it Internal. - +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. %************************************************************************ %* * @@ -528,7 +594,14 @@ decomposeRuleLhs :: CoreExpr -> Maybe ([Var], Id, [CoreExpr]) decomposeRuleLhs lhs = case collectArgs body of (Var fn, args) -> Just (bndrs, fn, args) - _other -> Nothing -- Unexpected shape + + (Case scrut bndr ty [(DEFAULT, _, body)], args) + | isDeadBinder bndr -- Note [Matching seqId] + -> Just (bndrs, seqId, args' ++ args) + where + args' = [Type (idType bndr), Type ty, scrut, body] + + _other -> Nothing -- Unexpected shape where (bndrs, body) = collectBinders (simpleOptExpr lhs) -- simpleOptExpr occurrence-analyses and simplifies the lhs @@ -543,6 +616,12 @@ decomposeRuleLhs lhs -- dictionary expressions that we might have to match \end{code} +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. + %************************************************************************ %* * @@ -595,23 +674,19 @@ addDictScc _ rhs = return rhs \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 (WpCast 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 v) thing_inside - | isTyVar v = do { expr <- thing_inside - {- Probably a coercion var -} ; return (App expr (Type (mkTyVarTy v))) } - | otherwise = do { expr <- thing_inside - {- An Id -} ; return (App expr (Var v)) } -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) } +dsCoercion :: HsWrapper -> DsM (CoreExpr -> CoreExpr) +dsCoercion WpHole = return (\e -> e) +dsCoercion (WpCompose c1 c2) = do { k1 <- dsCoercion c1 + ; k2 <- dsCoercion c2 + ; return (k1 . k2) } +dsCoercion (WpCast co) = return (\e -> Cast e co) +dsCoercion (WpLam id) = return (\e -> Lam id e) +dsCoercion (WpTyLam tv) = return (\e -> Lam tv e) +dsCoercion (WpApp v) | isTyVar v -- Probably a coercion var + = return (\e -> App e (Type (mkTyVarTy v))) + | otherwise + = return (\e -> App e (Var v)) +dsCoercion (WpTyApp ty) = return (\e -> App e (Type ty)) +dsCoercion (WpLet bs) = do { prs <- dsLHsBinds bs + ; return (\e -> Let (Rec prs) e) } \end{code}