{- (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). -} {-# LANGUAGE CPP #-} module Language.Haskell.Liquid.Desugar.DsBinds ( dsTopLHsBinds, dsLHsBinds, decomposeRuleLhs, dsSpec, dsHsWrapper, dsTcEvBinds, dsTcEvBinds_s, dsEvBinds, dsMkUserRule ) where import {-# SOURCE #-} Language.Haskell.Liquid.Desugar.DsExpr( dsLExpr ) import {-# SOURCE #-} Language.Haskell.Liquid.Desugar.Match( matchWrapper ) import Language.Haskell.Liquid.Desugar.DsMonad import Language.Haskell.Liquid.Desugar.DsGRHSs import Language.Haskell.Liquid.Desugar.DsUtils import HsSyn -- lots of things import CoreSyn -- lots of things import Literal ( Literal(MachStr) ) import CoreSubst import OccurAnal ( occurAnalyseExpr ) import MkCore import CoreUtils import CoreArity ( etaExpand ) import CoreUnfold import CoreFVs import Digraph import PrelNames import TysPrim ( mkProxyPrimTy ) import TyCon import TcEvidence import TcType import Type import Coercion import TysWiredIn ( typeNatKind, typeSymbolKind ) import Id import MkId(proxyHashId) import Class import Name import VarSet import Rules import VarEnv import Outputable import Module import SrcLoc import Maybes import OrdList import Bag import BasicTypes hiding ( TopLevel ) import DynFlags import FastString import Util import MonadUtils import qualified GHC.LanguageExtensions as LangExt import Control.Monad {-********************************************************************** * * Desugaring a MonoBinds * * **********************************************************************-} -- | Desugar top level binds, strict binds are treated like normal -- binds since there is no good time to force before first usage. dsTopLHsBinds :: LHsBinds Id -> DsM (OrdList (Id,CoreExpr)) dsTopLHsBinds binds = fmap (toOL . snd) (ds_lhs_binds binds) -- | Desugar all other kind of bindings, Ids of strict binds are returned to -- later be forced in the binding gorup body, see Note [Desugar Strict binds] dsLHsBinds :: LHsBinds Id -> DsM ([Id], [(Id,CoreExpr)]) dsLHsBinds binds = do { (force_vars, binds') <- ds_lhs_binds binds ; return (force_vars, binds') } ------------------------ ds_lhs_binds :: LHsBinds Id -> DsM ([Id], [(Id,CoreExpr)]) ds_lhs_binds binds = do { ds_bs <- mapBagM dsLHsBind binds ; return (foldBag (\(a, a') (b, b') -> (a ++ b, a' ++ b')) id ([], []) ds_bs) } dsLHsBind :: LHsBind Id -> DsM ([Id], [(Id,CoreExpr)]) dsLHsBind (L loc bind) = do dflags <- getDynFlags putSrcSpanDs loc $ dsHsBind dflags bind -- | Desugar a single binding (or group of recursive binds). dsHsBind :: DynFlags -> HsBind Id -> DsM ([Id], [(Id,CoreExpr)]) -- ^ The Ids of strict binds, to be forced in the body of the -- binding group see Note [Desugar Strict binds] and all -- bindings and their desugared right hand sides. dsHsBind dflags (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 ; let var' | inline_regardless = var `setIdUnfolding` mkCompulsoryUnfolding core_expr | otherwise = var ; let core_bind@(id,_) = makeCorePair dflags var' False 0 core_expr force_var = if xopt LangExt.Strict dflags then [id] else [] ; return (force_var, [core_bind]) } dsHsBind dflags (FunBind { fun_id = L _ fun, fun_matches = matches , fun_co_fn = co_fn, fun_tick = tick }) = do { (args, body) <- matchWrapper (FunRhs (idName fun)) Nothing matches ; let body' = mkOptTickBox tick body ; rhs <- dsHsWrapper co_fn (mkLams args body') ; let core_binds@(id,_) = makeCorePair dflags fun False 0 rhs force_var = if xopt LangExt.Strict dflags && matchGroupArity matches == 0 -- no need to force lambdas then [id] else [] ; {- pprTrace "dsHsBind" (ppr fun <+> ppr (idInlinePragma fun)) $ -} return (force_var, [core_binds]) } dsHsBind dflags (PatBind { pat_lhs = pat, pat_rhs = grhss, pat_rhs_ty = ty , pat_ticks = (rhs_tick, var_ticks) }) = do { body_expr <- dsGuarded grhss ty ; let body' = mkOptTickBox rhs_tick body_expr pat' = decideBangHood dflags pat ; (force_var,sel_binds) <- mkSelectorBinds var_ticks pat body' -- We silently ignore inline pragmas; no makeCorePair -- Not so cool, but really doesn't matter ; let force_var' = if isBangedLPat pat' then [force_var] else [] ; return (force_var', sel_binds) } -- A common case: one exported variable, only non-strict binds -- Non-recursive bindings come through this way -- So do self-recursive bindings -- Bindings with complete signatures are AbsBindsSigs, below dsHsBind dflags (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts , abs_exports = [export] , abs_ev_binds = ev_binds, abs_binds = binds }) | ABE { abe_wrap = wrap, abe_poly = global , abe_mono = local, abe_prags = prags } <- export , not (xopt LangExt.Strict dflags) -- Handle strict binds , not (anyBag (isBangedPatBind . unLoc) binds) -- in the next case = -- See Note [AbsBinds wrappers] in HsBinds addDictsDs (toTcTypeBag (listToBag dicts)) $ -- addDictsDs: push type constraints deeper for pattern match check do { (_, bind_prs) <- ds_lhs_binds binds ; let core_bind = Rec bind_prs ; ds_binds <- dsTcEvBinds_s ev_binds ; rhs <- dsHsWrapper wrap $ -- Usually the identity mkLams tyvars $ mkLams dicts $ mkCoreLets ds_binds $ Let core_bind $ Var local ; (spec_binds, rules) <- dsSpecs rhs prags ; let global' = addIdSpecialisations global rules main_bind = makeCorePair dflags global' (isDefaultMethod prags) (dictArity dicts) rhs ; return ([], main_bind : fromOL spec_binds) } dsHsBind dflags (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts , abs_exports = exports, abs_ev_binds = ev_binds , abs_binds = binds }) -- See Note [Desugaring AbsBinds] = addDictsDs (toTcTypeBag (listToBag dicts)) $ -- addDictsDs: push type constraints deeper for pattern match check do { (local_force_vars, bind_prs) <- ds_lhs_binds binds ; let core_bind = Rec [ makeCorePair dflags (add_inline lcl_id) False 0 rhs | (lcl_id, rhs) <- bind_prs ] -- Monomorphic recursion possible, hence Rec new_force_vars = get_new_force_vars local_force_vars locals = map abe_mono exports all_locals = locals ++ new_force_vars tup_expr = mkBigCoreVarTup all_locals tup_ty = exprType tup_expr ; ds_binds <- dsTcEvBinds_s ev_binds ; let poly_tup_rhs = mkLams tyvars $ mkLams dicts $ mkCoreLets ds_binds $ Let core_bind $ tup_expr ; poly_tup_id <- newSysLocalDs (exprType poly_tup_rhs) -- Find corresponding global or make up a new one: sometimes -- we need to make new export to desugar strict binds, see -- Note [Desugar Strict binds] ; (exported_force_vars, extra_exports) <- get_exports local_force_vars ; let mk_bind (ABE { abe_wrap = wrap , abe_poly = global , abe_mono = local, abe_prags = spec_prags }) -- See Note [AbsBinds wrappers] in HsBinds = do { tup_id <- newSysLocalDs tup_ty ; rhs <- dsHsWrapper wrap $ mkLams tyvars $ mkLams dicts $ mkTupleSelector all_locals local tup_id $ mkVarApps (Var poly_tup_id) (tyvars ++ dicts) ; let rhs_for_spec = Let (NonRec poly_tup_id poly_tup_rhs) rhs ; (spec_binds, rules) <- dsSpecs rhs_for_spec spec_prags ; let global' = (global `setInlinePragma` defaultInlinePragma) `addIdSpecialisations` rules -- Kill the INLINE pragma because it applies to -- the user written (local) function. The global -- Id is just the selector. Hmm. ; return ((global', rhs) : fromOL spec_binds) } ; export_binds_s <- mapM mk_bind (exports ++ extra_exports) ; return (exported_force_vars ,(poly_tup_id, poly_tup_rhs) : concat export_binds_s) } where inline_env :: IdEnv Id -- Maps a monomorphic local Id to one with -- the inline pragma from the source -- The type checker put the inline pragma -- on the *global* Id, so we need to transfer it inline_env = mkVarEnv [ (lcl_id, setInlinePragma lcl_id prag) | ABE { abe_mono = lcl_id, abe_poly = gbl_id } <- exports , let prag = idInlinePragma gbl_id ] add_inline :: Id -> Id -- tran add_inline lcl_id = lookupVarEnv inline_env lcl_id `orElse` lcl_id global_env :: IdEnv Id -- Maps local Id to its global exported Id global_env = mkVarEnv [ (local, global) | ABE { abe_mono = local, abe_poly = global } <- exports ] -- find variables that are not exported get_new_force_vars lcls = foldr (\lcl acc -> case lookupVarEnv global_env lcl of Just _ -> acc Nothing -> lcl:acc) [] lcls -- find exports or make up new exports for force variables get_exports :: [Id] -> DsM ([Id], [ABExport Id]) get_exports lcls = foldM (\(glbls, exports) lcl -> case lookupVarEnv global_env lcl of Just glbl -> return (glbl:glbls, exports) Nothing -> do export <- mk_export lcl let glbl = abe_poly export return (glbl:glbls, export:exports)) ([],[]) lcls mk_export local = do global <- newSysLocalDs (exprType (mkLams tyvars (mkLams dicts (Var local)))) return (ABE {abe_poly = global ,abe_mono = local ,abe_wrap = WpHole ,abe_prags = SpecPrags []}) -- AbsBindsSig is a combination of AbsBinds and FunBind dsHsBind dflags (AbsBindsSig { abs_tvs = tyvars, abs_ev_vars = dicts , abs_sig_export = global , abs_sig_prags = prags , abs_sig_ev_bind = ev_bind , abs_sig_bind = bind }) | L bind_loc FunBind { fun_matches = matches , fun_co_fn = co_fn , fun_tick = tick } <- bind = putSrcSpanDs bind_loc $ addDictsDs (toTcTypeBag (listToBag dicts)) $ -- addDictsDs: push type constraints deeper for pattern match check do { (args, body) <- matchWrapper (FunRhs (idName global)) Nothing matches ; let body' = mkOptTickBox tick body ; fun_rhs <- dsHsWrapper co_fn $ mkLams args body' ; let force_vars | xopt LangExt.Strict dflags , matchGroupArity matches == 0 -- no need to force lambdas = [global] | otherwise = [] ; ds_binds <- dsTcEvBinds ev_bind ; let rhs = mkLams tyvars $ mkLams dicts $ mkCoreLets ds_binds $ fun_rhs ; (spec_binds, rules) <- dsSpecs rhs prags ; let global' = addIdSpecialisations global rules main_bind = makeCorePair dflags global' (isDefaultMethod prags) (dictArity dicts) rhs ; return (force_vars, main_bind : fromOL spec_binds) } | otherwise = pprPanic "dsHsBind: AbsBindsSig" (ppr bind) dsHsBind _ (PatSynBind{}) = panic "dsHsBind: PatSynBind" ------------------------ makeCorePair :: DynFlags -> Id -> Bool -> Arity -> CoreExpr -> (Id, CoreExpr) makeCorePair dflags gbl_id is_default_method dict_arity rhs | is_default_method -- Default methods are *always* inlined = (gbl_id `setIdUnfolding` mkCompulsoryUnfolding rhs, 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 where inline_prag = idInlinePragma gbl_id inlinable_unf = mkInlinableUnfolding dflags 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 -- NB: The arity in the InlineRule takes account of the dictionaries = ( 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) dictArity :: [Var] -> Arity -- Don't count coercion variables in arity dictArity dicts = count isId dicts {- Note [Desugaring AbsBinds] ~~~~~~~~~~~~~~~~~~~~~~~~~~ In the general AbsBinds case we desugar the binding to this: tup a (d:Num a) = let fm = ...gm... gm = ...fm... in (fm,gm) f a d = case tup a d of { (fm,gm) -> fm } g a d = case tup a d of { (fm,gm) -> fm } 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 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, hopefully 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 [Desugar Strict binds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Desugaring strict variable bindings looks as follows (core below ==>) let !x = rhs in body ==> let x = rhs in x `seq` body -- seq the variable and if it is a pattern binding the desugaring looks like let !pat = rhs in body ==> let x = rhs -- bind the rhs to a new variable pat = x in x `seq` body -- seq the new variable if there is no variable in the pattern desugaring looks like let False = rhs in body ==> let x = case rhs of {False -> (); _ -> error "Match failed"} in x `seq` body In order to force the Ids in the binding group they are passed around in the dsHsBind family of functions, and later seq'ed in DsExpr.ds_val_bind. Consider a recursive group like this letrec f : g = rhs[f,g] in <body> Without `Strict`, we get a translation like this: let t = /\a. letrec tm = rhs[fm,gm] fm = case t of fm:_ -> fm gm = case t of _:gm -> gm in (fm,gm) in let f = /\a. case t a of (fm,_) -> fm in let g = /\a. case t a of (_,gm) -> gm in <body> Here `tm` is the monomorphic binding for `rhs`. With `Strict`, we want to force `tm`, but NOT `fm` or `gm`. Alas, `tm` isn't in scope in the `in <body>` part. The simplest thing is to return it in the polymorphic tuple `t`, thus: let t = /\a. letrec tm = rhs[fm,gm] fm = case t of fm:_ -> fm gm = case t of _:gm -> gm in (tm, fm, gm) in let f = /\a. case t a of (_,fm,_) -> fm in let g = /\a. case t a of (_,_,gm) -> gm in let tm = /\a. case t a of (tm,_,_) -> tm in tm `seq` <body> See https://ghc.haskell.org/trac/ghc/wiki/StrictPragma for a more detailed explanation of the desugaring of strict bindings. -} ------------------------ dsSpecs :: CoreExpr -- Its rhs -> TcSpecPrags -> DsM ( OrdList (Id,CoreExpr) -- Binding for specialised Ids , [CoreRule] ) -- Rules for the Global Ids -- See Note [Handling SPECIALISE pragmas] in TcBinds 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)) | isJust (isClassOpId_maybe poly_id) = putSrcSpanDs loc $ do { warnDs NoReason (text "Ignoring useless SPECIALISE pragma for class method selector" <+> quotes (ppr poly_id)) ; return Nothing } -- There is no point in trying to specialise a class op -- Moreover, classops don't (currently) have an inl_sat arity set -- (it would be Just 0) and that in turn makes makeCorePair bleat | no_act_spec && isNeverActive rule_act = putSrcSpanDs loc $ do { warnDs NoReason (text "Ignoring useless SPECIALISE pragma for NOINLINE function:" <+> quotes (ppr poly_id)) ; return Nothing } -- Function is NOINLINE, and the specialiation inherits that -- See Note [Activation pragmas for SPECIALISE] | otherwise = putSrcSpanDs loc $ do { uniq <- newUnique ; let poly_name = idName poly_id spec_occ = mkSpecOcc (getOccName poly_name) spec_name = mkInternalName uniq spec_occ (getSrcSpan poly_name) ; (bndrs, ds_lhs) <- liftM collectBinders (dsHsWrapper spec_co (Var poly_id)) ; let spec_ty = mkPiTypes bndrs (exprType ds_lhs) ; -- pprTrace "dsRule" (vcat [ text "Id:" <+> ppr poly_id -- , text "spec_co:" <+> ppr spec_co -- , text "ds_rhs:" <+> ppr ds_lhs ]) $ case decomposeRuleLhs bndrs ds_lhs of { Left msg -> do { warnDs NoReason msg; return Nothing } ; Right (rule_bndrs, _fn, args) -> do { dflags <- getDynFlags ; this_mod <- getModule ; let fn_unf = realIdUnfolding poly_id unf_fvs = stableUnfoldingVars fn_unf `orElse` emptyVarSet in_scope = mkInScopeSet (unf_fvs `unionVarSet` exprsFreeVars args) spec_unf = specUnfolding dflags (mkEmptySubst in_scope) bndrs args fn_unf spec_id = mkLocalId spec_name spec_ty `setInlinePragma` inl_prag `setIdUnfolding` spec_unf ; rule <- dsMkUserRule this_mod is_local_id (mkFastString ("SPEC " ++ showPpr dflags poly_name)) rule_act poly_name rule_bndrs args (mkVarApps (Var spec_id) bndrs) ; spec_rhs <- dsHsWrapper spec_co poly_rhs -- Commented out: see Note [SPECIALISE on INLINE functions] -- ; when (isInlinePragma id_inl) -- (warnDs $ text "SPECIALISE pragma on INLINE function probably won't fire:" -- <+> quotes (ppr poly_name)) ; return (Just (unitOL (spec_id, spec_rhs), rule)) -- NB: do *not* use makeCorePair on (spec_id,spec_rhs), because -- makeCorePair overwrites the unfolding, which we have -- just created using specUnfolding } } } 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 id_inl = idInlinePragma poly_id -- See Note [Activation pragmas for SPECIALISE] inl_prag | not (isDefaultInlinePragma spec_inl) = spec_inl | not is_local_id -- See Note [Specialising imported functions] -- in OccurAnal , isStrongLoopBreaker (idOccInfo poly_id) = neverInlinePragma | otherwise = id_inl -- Get the INLINE pragma from SPECIALISE declaration, or, -- failing that, from the original Id spec_prag_act = inlinePragmaActivation spec_inl -- See Note [Activation pragmas for SPECIALISE] -- no_act_spec is True if the user didn't write an explicit -- phase specification in the SPECIALISE pragma no_act_spec = case inlinePragmaSpec spec_inl of NoInline -> isNeverActive spec_prag_act _ -> isAlwaysActive spec_prag_act rule_act | no_act_spec = inlinePragmaActivation id_inl -- Inherit | otherwise = spec_prag_act -- Specified by user dsMkUserRule :: Module -> Bool -> RuleName -> Activation -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> DsM CoreRule dsMkUserRule this_mod is_local name act fn bndrs args rhs = do let rule = mkRule this_mod False is_local name act fn bndrs args rhs dflags <- getDynFlags when (isOrphan (ru_orphan rule) && wopt Opt_WarnOrphans dflags) $ warnDs (Reason Opt_WarnOrphans) (ruleOrphWarn rule) return rule ruleOrphWarn :: CoreRule -> SDoc ruleOrphWarn rule = text "Orphan rule:" <+> ppr rule {- Note [SPECIALISE on INLINE functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used to warn that using SPECIALISE for a function marked INLINE would be a no-op; but it isn't! Especially with worker/wrapper split we might have {-# INLINE f #-} f :: Ord a => Int -> a -> ... f d x y = case x of I# x' -> $wf d x' y We might want to specialise 'f' so that we in turn specialise '$wf'. We can't even /name/ '$wf' in the source code, so we can't specialise it even if we wanted to. Trac #10721 is a case in point. Note [Activation pragmas for SPECIALISE] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ From a user SPECIALISE pragma for f, we generate a) A top-level binding spec_fn = rhs b) A RULE f dOrd = spec_fn We need two pragma-like things: * spec_fn's inline pragma: inherited from f's inline pragma (ignoring activation on SPEC), unless overriden by SPEC INLINE * Activation of RULE: from SPECIALISE pragma (if activation given) otherwise from f's inline pragma This is not obvious (see Trac #5237)! Examples Rule activation Inline prag on spec'd fn --------------------------------------------------------------------- SPEC [n] f :: ty [n] Always, or NOINLINE [n] copy f's prag NOINLINE f SPEC [n] f :: ty [n] NOINLINE copy f's prag NOINLINE [k] f SPEC [n] f :: ty [n] NOINLINE [k] copy f's prag INLINE [k] f SPEC [n] f :: ty [n] INLINE [k] copy f's prag SPEC INLINE [n] f :: ty [n] INLINE [n] (ignore INLINE prag on f, same activation for rule and spec'd fn) NOINLINE [k] f SPEC f :: ty [n] INLINE [k] ************************************************************************ * * \subsection{Adding inline pragmas} * * ************************************************************************ -} decomposeRuleLhs :: [Var] -> CoreExpr -> Either SDoc ([Var], Id, [CoreExpr]) -- (decomposeRuleLhs bndrs lhs) takes apart the LHS of a RULE, -- The 'bndrs' are the quantified binders of the rules, but decomposeRuleLhs -- may add some extra dictionary binders (see Note [Free dictionaries]) -- -- Returns Nothing if the LHS isn't of the expected shape -- Note [Decomposing the left-hand side of a RULE] decomposeRuleLhs orig_bndrs orig_lhs | not (null unbound) -- Check for things unbound on LHS -- See Note [Unused spec binders] = Left (vcat (map dead_msg unbound)) | Just (fn_id, args) <- decompose fun2 args2 , let extra_bndrs = mk_extra_bndrs fn_id args = -- pprTrace "decmposeRuleLhs" (vcat [ text "orig_bndrs:" <+> ppr orig_bndrs -- , text "orig_lhs:" <+> ppr orig_lhs -- , text "lhs1:" <+> ppr lhs1 -- , text "extra_dict_bndrs:" <+> ppr extra_dict_bndrs -- , text "fn_id:" <+> ppr fn_id -- , text "args:" <+> ppr args]) $ Right (orig_bndrs ++ extra_bndrs, fn_id, args) | otherwise = Left bad_shape_msg where lhs1 = drop_dicts orig_lhs lhs2 = simpleOptExpr lhs1 -- See Note [Simplify rule LHS] (fun2,args2) = collectArgs lhs2 lhs_fvs = exprFreeVars lhs2 unbound = filterOut (`elemVarSet` lhs_fvs) orig_bndrs orig_bndr_set = mkVarSet orig_bndrs -- Add extra tyvar binders: Note [Free tyvars in rule LHS] -- and extra dict binders: Note [Free dictionaries in rule LHS] mk_extra_bndrs fn_id args = toposortTyVars unbound_tvs ++ unbound_dicts where unbound_tvs = [ v | v <- unbound_vars, isTyVar v ] unbound_dicts = [ mkLocalId (localiseName (idName d)) (idType d) | d <- unbound_vars, isDictId d ] unbound_vars = [ v | v <- exprsFreeVarsList args , not (v `elemVarSet` orig_bndr_set) , not (v == fn_id) ] -- fn_id: do not quantify over the function itself, which may -- itself be a dictionary (in pathological cases, Trac #10251) decompose (Var fn_id) args | not (fn_id `elemVarSet` orig_bndr_set) = Just (fn_id, args) decompose _ _ = Nothing bad_shape_msg = hang (text "RULE left-hand side too complicated to desugar") 2 (vcat [ text "Optimised lhs:" <+> ppr lhs2 , text "Orig lhs:" <+> ppr orig_lhs]) dead_msg bndr = hang (sep [ text "Forall'd" <+> pp_bndr bndr , text "is not bound in RULE lhs"]) 2 (vcat [ text "Orig bndrs:" <+> ppr orig_bndrs , text "Orig lhs:" <+> ppr orig_lhs , text "optimised lhs:" <+> ppr lhs2 ]) pp_bndr bndr | isTyVar bndr = text "type variable" <+> quotes (ppr bndr) | Just pred <- evVarPred_maybe bndr = text "constraint" <+> quotes (ppr pred) | otherwise = text "variable" <+> quotes (ppr bndr) drop_dicts :: CoreExpr -> CoreExpr drop_dicts e = wrap_lets needed bnds body where needed = orig_bndr_set `minusVarSet` exprFreeVars body (bnds, body) = split_lets (occurAnalyseExpr e) -- The occurAnalyseExpr drops dead bindings which is -- crucial to ensure that every binding is used later; -- which in turn makes wrap_lets work right split_lets :: CoreExpr -> ([(DictId,CoreExpr)], CoreExpr) split_lets (Let (NonRec d r) body) | isDictId d = ((d,r):bs, body') where (bs, body') = split_lets body -- handle "unlifted lets" too, needed for "map/coerce" split_lets (Case r d _ [(DEFAULT, _, body)]) | isCoVar d = ((d,r):bs, body') where (bs, body') = split_lets body split_lets e = ([], e) wrap_lets :: VarSet -> [(DictId,CoreExpr)] -> CoreExpr -> CoreExpr wrap_lets _ [] body = body wrap_lets needed ((d, r) : bs) body | rhs_fvs `intersectsVarSet` needed = mkCoreLet (NonRec d r) (wrap_lets needed' bs body) | otherwise = wrap_lets needed bs body where rhs_fvs = exprFreeVars r needed' = (needed `minusVarSet` rhs_fvs) `extendVarSet` d {- Note [Decomposing the left-hand side of a RULE] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are several things going on here. * drop_dicts: see Note [Drop dictionary bindings on rule LHS] * simpleOptExpr: see Note [Simplify rule LHS] * extra_dict_bndrs: see Note [Free dictionaries] Note [Free tyvars on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T a = C foo :: T a -> Int foo C = 1 {-# RULES "myrule" foo C = 1 #-} After type checking the LHS becomes (foo alpha (C alpha)), where alpha is an unbound meta-tyvar. The zonker in TcHsSyn is careful not to turn the free alpha into Any (as it usually does). Instead it turns it into a skolem 'a'. See TcHsSyn Note [Zonking the LHS of a RULE]. Now we must quantify over that 'a'. It's /really/ inconvenient to do that in the zonker, because the HsExpr data type is very large. But it's /easy/ to do it here in the desugarer. Moreover, we have to do something rather similar for dictionaries; see Note [Free dictionaries on rule LHS]. So that's why we look for type variables free on the LHS, and quantify over them. Note [Free dictionaries on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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 = <rhs> ... 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 = <rhs> 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. Note [Drop dictionary bindings on rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drop_dicts drops dictionary bindings on the LHS where possible. E.g. let d:Eq [Int] = $fEqList $fEqInt in f d --> f d Reasoning here is that there is only one d:Eq [Int], and so we can quantify over it. That makes 'd' free in the LHS, but that is later picked up by extra_dict_bndrs (Note [Dead spec binders]). NB 1: We can only drop the binding if the RHS doesn't bind one of the orig_bndrs, which we assume occur on RHS. Example f :: (Eq a) => b -> a -> a {-# SPECIALISE f :: Eq a => b -> [a] -> [a] #-} Here we want to end up with RULE forall d:Eq a. f ($dfEqList d) = f_spec d Of course, the ($dfEqlist d) in the pattern makes it less likely to match, but there is no other way to get d:Eq a NB 2: We do drop_dicts *before* simplOptEpxr, so that we expect all the evidence bindings to be wrapped around the outside of the LHS. (After simplOptExpr they'll usually have been inlined.) dsHsWrapper does dependency analysis, so that civilised ones will be simple NonRec bindings. We don't handle recursive dictionaries! NB3: In the common case of a non-overloaded, but perhaps-polymorphic specialisation, we don't need to bind *any* dictionaries for use in the RHS. For example (Trac #8331) {-# SPECIALIZE INLINE useAbstractMonad :: ReaderST s Int #-} useAbstractMonad :: MonadAbstractIOST m => m Int Here, deriving (MonadAbstractIOST (ReaderST s)) is a lot of code but the RHS uses no dictionaries, so we want to end up with RULE forall s (d :: MonadAbstractIOST (ReaderT s)). useAbstractMonad (ReaderT s) d = $suseAbstractMonad s Trac #8848 is a good example of where there are some intersting dictionary bindings to discard. The drop_dicts algorithm is based on these observations: * Given (let d = rhs in e) where d is a DictId, matching 'e' will bind e's free variables. * So we want to keep the binding if one of the needed variables (for which we need a binding) is in fv(rhs) but not already in fv(e). * The "needed variables" are simply the orig_bndrs. Consider f :: (Eq a, Show b) => a -> b -> String ... SPECIALISE f :: (Show b) => Int -> b -> String ... Then orig_bndrs includes the *quantified* dictionaries of the type namely (dsb::Show b), but not the one for Eq Int So we work inside out, applying the above criterion at each step. Note [Simplify rule LHS] ~~~~~~~~~~~~~~~~~~~~~~~~ simplOptExpr occurrence-analyses and simplifies the LHS: (a) Inline any remaining dictionary bindings (which hopefully occur just once) (b) Substitute trivial lets so that they don't get in the way Note that we substitute the function too; we might have this as a LHS: let f71 = M.f Int in f71 (c) Do eta reduction. To see why, consider the fold/build rule, which without simplification looked like: fold k z (build (/\a. g a)) ==> ... This doesn't match unless you do eta reduction on the build argument. Similarly for a LHS like augment g (build h) we do not want to get augment (\a. g a) (build h) otherwise we don't match when given an argument like augment (\a. h a a) (build h) 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, because it mentions a 'd' that is not bound on the LHS! But it's a silly specialisation anyway, because 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. ************************************************************************ * * Desugaring evidence * * ************************************************************************ -} dsHsWrapper :: HsWrapper -> CoreExpr -> DsM CoreExpr dsHsWrapper WpHole e = return e dsHsWrapper (WpTyApp ty) e = return $ App e (Type ty) dsHsWrapper (WpLet ev_binds) e = do bs <- dsTcEvBinds ev_binds return (mkCoreLets bs e) dsHsWrapper (WpCompose c1 c2) e = do { e1 <- dsHsWrapper c2 e ; dsHsWrapper c1 e1 } dsHsWrapper (WpFun c1 c2 t1) e = do { x <- newSysLocalDs t1 ; e1 <- dsHsWrapper c1 (Var x) ; e2 <- dsHsWrapper c2 (mkCoreAppDs (text "dsHsWrapper") e e1) ; return (Lam x e2) } dsHsWrapper (WpCast co) e = return $ mkCastDs e co dsHsWrapper (WpEvLam ev) e = return $ Lam ev e dsHsWrapper (WpTyLam tv) e = return $ Lam tv e dsHsWrapper (WpEvApp tm) e = liftM (App e) (dsEvTerm tm) -------------------------------------- dsTcEvBinds_s :: [TcEvBinds] -> DsM [CoreBind] dsTcEvBinds_s [] = return [] dsTcEvBinds_s (b:_) = dsTcEvBinds b dsTcEvBinds :: TcEvBinds -> DsM [CoreBind] dsTcEvBinds (TcEvBinds {}) = panic "dsEvBinds" -- Zonker has got rid of this dsTcEvBinds (EvBinds bs) = dsEvBinds bs dsEvBinds :: Bag EvBind -> DsM [CoreBind] dsEvBinds bs = mapM ds_scc (sccEvBinds bs) where ds_scc (AcyclicSCC (EvBind { eb_lhs = v, eb_rhs = r})) = liftM (NonRec v) (dsEvTerm r) ds_scc (CyclicSCC bs) = liftM Rec (mapM dsEvBind bs) dsEvBind :: EvBind -> DsM (Id, CoreExpr) dsEvBind (EvBind { eb_lhs = v, eb_rhs = r}) = liftM ((,) v) (dsEvTerm r) {-********************************************************************** * * Desugaring EvTerms * * **********************************************************************-} dsEvTerm :: EvTerm -> DsM CoreExpr dsEvTerm (EvId v) = return (Var v) dsEvTerm (EvCallStack cs) = dsEvCallStack cs dsEvTerm (EvTypeable ty ev) = dsEvTypeable ty ev dsEvTerm (EvLit (EvNum n)) = mkIntegerExpr n dsEvTerm (EvLit (EvStr s)) = mkStringExprFS s dsEvTerm (EvCast tm co) = do { tm' <- dsEvTerm tm ; return $ mkCastDs tm' co } dsEvTerm (EvDFunApp df tys tms) = do { tms' <- mapM dsEvTerm tms ; return $ Var df `mkTyApps` tys `mkApps` tms' } dsEvTerm (EvCoercion co) = return (Coercion co) dsEvTerm (EvSuperClass d n) = do { d' <- dsEvTerm d ; let (cls, tys) = getClassPredTys (exprType d') sc_sel_id = classSCSelId cls n -- Zero-indexed ; return $ Var sc_sel_id `mkTyApps` tys `App` d' } dsEvTerm (EvDelayedError ty msg) = return $ dsEvDelayedError ty msg dsEvDelayedError :: Type -> FastString -> CoreExpr dsEvDelayedError ty msg = Var errorId `mkTyApps` [getRuntimeRep "dsEvTerm" ty, ty] `mkApps` [litMsg] where errorId = tYPE_ERROR_ID litMsg = Lit (MachStr (fastStringToByteString msg)) {-********************************************************************** * * Desugaring Typeable dictionaries * * **********************************************************************-} dsEvTypeable :: Type -> EvTypeable -> DsM CoreExpr -- Return a CoreExpr :: Typeable ty -- This code is tightly coupled to the representation -- of TypeRep, in base library Data.Typeable.Internals dsEvTypeable ty ev = do { tyCl <- dsLookupTyCon typeableClassName -- Typeable ; let kind = typeKind ty Just typeable_data_con = tyConSingleDataCon_maybe tyCl -- "Data constructor" -- for Typeable ; rep_expr <- ds_ev_typeable ty ev -- Build Core for (let r::TypeRep = rep in \proxy. rep) -- See Note [Memoising typeOf] ; repName <- newSysLocalDs (exprType rep_expr) ; let proxyT = mkProxyPrimTy kind ty method = bindNonRec repName rep_expr $ mkLams [mkWildValBinder proxyT] (Var repName) -- Package up the method as `Typeable` dictionary ; return $ mkConApp typeable_data_con [Type kind, Type ty, method] } ds_ev_typeable :: Type -> EvTypeable -> DsM CoreExpr -- Returns a CoreExpr :: TypeRep ty ds_ev_typeable ty (EvTypeableTyCon evs) | Just (tc, ks) <- splitTyConApp_maybe ty = do { ctr <- dsLookupGlobalId mkPolyTyConAppName -- mkPolyTyConApp :: TyCon -> [KindRep] -> [TypeRep] -> TypeRep ; tyRepTc <- dsLookupTyCon typeRepTyConName -- TypeRep (the TyCon) ; let tyRepType = mkTyConApp tyRepTc [] -- TypeRep (the Type) mkRep cRep kReps tReps = mkApps (Var ctr) [ cRep , mkListExpr tyRepType kReps , mkListExpr tyRepType tReps ] ; tcRep <- tyConRep tc ; kReps <- zipWithM getRep evs ks ; return (mkRep tcRep kReps []) } ds_ev_typeable ty (EvTypeableTyApp ev1 ev2) | Just (t1,t2) <- splitAppTy_maybe ty = do { e1 <- getRep ev1 t1 ; e2 <- getRep ev2 t2 ; ctr <- dsLookupGlobalId mkAppTyName ; return ( mkApps (Var ctr) [ e1, e2 ] ) } ds_ev_typeable ty (EvTypeableTyLit ev) = do { fun <- dsLookupGlobalId tr_fun ; dict <- dsEvTerm ev -- Of type KnownNat/KnownSym ; let proxy = mkTyApps (Var proxyHashId) [ty_kind, ty] ; return (mkApps (mkTyApps (Var fun) [ty]) [ dict, proxy ]) } where ty_kind = typeKind ty -- tr_fun is the Name of -- typeNatTypeRep :: KnownNat a => Proxy# a -> TypeRep -- of typeSymbolTypeRep :: KnownSymbol a => Proxy# a -> TypeRep tr_fun | ty_kind `eqType` typeNatKind = typeNatTypeRepName | ty_kind `eqType` typeSymbolKind = typeSymbolTypeRepName | otherwise = panic "dsEvTypeable: unknown type lit kind" ds_ev_typeable ty ev = pprPanic "dsEvTypeable" (ppr ty $$ ppr ev) getRep :: EvTerm -> Type -- EvTerm for Typeable ty, and ty -> DsM CoreExpr -- Return CoreExpr :: TypeRep (of ty) -- namely (typeRep# dict proxy) -- Remember that -- typeRep# :: forall k (a::k). Typeable k a -> Proxy k a -> TypeRep getRep ev ty = do { typeable_expr <- dsEvTerm ev ; typeRepId <- dsLookupGlobalId typeRepIdName ; let ty_args = [typeKind ty, ty] ; return (mkApps (mkTyApps (Var typeRepId) ty_args) [ typeable_expr , mkTyApps (Var proxyHashId) ty_args ]) } tyConRep :: TyCon -> DsM CoreExpr -- Returns CoreExpr :: TyCon tyConRep tc | Just tc_rep_nm <- tyConRepName_maybe tc = do { tc_rep_id <- dsLookupGlobalId tc_rep_nm ; return (Var tc_rep_id) } | otherwise = pprPanic "tyConRep" (ppr tc) {- Note [Memoising typeOf] ~~~~~~~~~~~~~~~~~~~~~~~~~~ See #3245, #9203 IMPORTANT: we don't want to recalculate the TypeRep once per call with the proxy argument. This is what went wrong in #3245 and #9203. So we help GHC by manually keeping the 'rep' *outside* the lambda. -} {-********************************************************************** * * Desugaring EvCallStack evidence * * **********************************************************************-} dsEvCallStack :: EvCallStack -> DsM CoreExpr -- See Note [Overview of implicit CallStacks] in TcEvidence.hs dsEvCallStack cs = do df <- getDynFlags m <- getModule srcLocDataCon <- dsLookupDataCon srcLocDataConName let mkSrcLoc l = liftM (mkCoreConApps srcLocDataCon) (sequence [ mkStringExprFS (unitIdFS $ moduleUnitId m) , mkStringExprFS (moduleNameFS $ moduleName m) , mkStringExprFS (srcSpanFile l) , return $ mkIntExprInt df (srcSpanStartLine l) , return $ mkIntExprInt df (srcSpanStartCol l) , return $ mkIntExprInt df (srcSpanEndLine l) , return $ mkIntExprInt df (srcSpanEndCol l) ]) emptyCS <- Var <$> dsLookupGlobalId emptyCallStackName pushCSVar <- dsLookupGlobalId pushCallStackName let pushCS name loc rest = mkCoreApps (Var pushCSVar) [mkCoreTup [name, loc], rest] let mkPush name loc tm = do nameExpr <- mkStringExprFS name locExpr <- mkSrcLoc loc case tm of EvCallStack EvCsEmpty -> return (pushCS nameExpr locExpr emptyCS) _ -> do tmExpr <- dsEvTerm tm -- at this point tmExpr :: IP sym CallStack -- but we need the actual CallStack to pass to pushCS, -- so we use unwrapIP to strip the dictionary wrapper -- See Note [Overview of implicit CallStacks] let ip_co = unwrapIP (exprType tmExpr) return (pushCS nameExpr locExpr (mkCastDs tmExpr ip_co)) case cs of EvCsPushCall name loc tm -> mkPush (occNameFS $ getOccName name) loc tm EvCsEmpty -> return emptyCS