X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplUtils.lhs;h=a1a7c1473eba9b34c52280f89b684610b160eaf8;hp=1ff6f8fbceebcd46c434d48aeb4f2d4258bd3176;hb=ab676aa34302b346cc05181100b46d8490023971;hpb=e9f23b4cc3df781f2fc84b48716a7779ecc8ab06 diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs index 1ff6f8f..a1a7c14 100644 --- a/compiler/simplCore/SimplUtils.lhs +++ b/compiler/simplCore/SimplUtils.lhs @@ -15,11 +15,13 @@ module SimplUtils ( -- The continuation type SimplCont(..), DupFlag(..), LetRhsFlag(..), contIsDupable, contResultType, contIsTrivial, contArgs, dropArgs, - countValArgs, countArgs, + countValArgs, countArgs, splitInlineCont, mkBoringStop, mkLazyArgStop, mkRhsStop, contIsRhsOrArg, interestingCallContext, interestingArgContext, - interestingArg, mkArgInfo + interestingArg, mkArgInfo, + + abstractFloats ) where #include "HsVersions.h" @@ -28,19 +30,23 @@ import SimplEnv import DynFlags import StaticFlags import CoreSyn +import qualified CoreSubst import PprCore import CoreFVs import CoreUtils import Literal import CoreUnfold import MkId +import Name import Id +import Var ( isCoVar ) import NewDemand import SimplMonad -import Type +import Type ( Type, funArgTy, mkForAllTys, mkTyVarTys, + splitTyConApp_maybe, tyConAppArgs ) import TyCon import DataCon -import TcGadt ( dataConCanMatch ) +import Unify ( dataConCannotMatch ) import VarSet import BasicTypes import Util @@ -123,12 +129,12 @@ instance Outputable LetRhsFlag where instance Outputable SimplCont where ppr (Stop ty is_rhs _) = ptext SLIT("Stop") <> brackets (ppr is_rhs) <+> ppr ty - ppr (ApplyTo dup arg se cont) = ((ptext SLIT("ApplyTo") <+> ppr dup <+> pprParendExpr arg) $$ - nest 2 (pprSimplEnv se)) $$ ppr cont + ppr (ApplyTo dup arg se cont) = ((ptext SLIT("ApplyTo") <+> ppr dup <+> pprParendExpr arg) + {- $$ nest 2 (pprSimplEnv se) -}) $$ ppr cont ppr (StrictBind b _ _ _ cont) = (ptext SLIT("StrictBind") <+> ppr b) $$ ppr cont ppr (StrictArg f _ _ cont) = (ptext SLIT("StrictArg") <+> ppr f) $$ ppr cont ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$ - (nest 4 (ppr alts $$ pprSimplEnv se)) $$ ppr cont + (nest 4 (ppr alts)) $$ ppr cont ppr (CoerceIt co cont) = (ptext SLIT("CoerceIt") <+> ppr co) $$ ppr cont data DupFlag = OkToDup | NoDup @@ -149,14 +155,15 @@ mkLazyArgStop ty has_rules = Stop ty AnArg (canUpdateInPlace ty || has_rules) mkRhsStop :: OutType -> SimplCont mkRhsStop ty = Stop ty AnRhs (canUpdateInPlace ty) -contIsRhsOrArg (Stop _ _ _) = True -contIsRhsOrArg (StrictBind {}) = True -contIsRhsOrArg (StrictArg {}) = True -contIsRhsOrArg other = False +------------------- +contIsRhsOrArg (Stop {}) = True +contIsRhsOrArg (StrictBind {}) = True +contIsRhsOrArg (StrictArg {}) = True +contIsRhsOrArg other = False ------------------- contIsDupable :: SimplCont -> Bool -contIsDupable (Stop _ _ _) = True +contIsDupable (Stop {}) = True contIsDupable (ApplyTo OkToDup _ _ _) = True contIsDupable (Select OkToDup _ _ _ _) = True contIsDupable (CoerceIt _ cont) = contIsDupable cont @@ -164,7 +171,7 @@ contIsDupable other = False ------------------- contIsTrivial :: SimplCont -> Bool -contIsTrivial (Stop _ _ _) = True +contIsTrivial (Stop {}) = True contIsTrivial (ApplyTo _ (Type _) _ cont) = contIsTrivial cont contIsTrivial (CoerceIt _ cont) = contIsTrivial cont contIsTrivial other = False @@ -199,6 +206,26 @@ dropArgs :: Int -> SimplCont -> SimplCont dropArgs 0 cont = cont dropArgs n (ApplyTo _ _ _ cont) = dropArgs (n-1) cont dropArgs n other = pprPanic "dropArgs" (ppr n <+> ppr other) + +-------------------- +splitInlineCont :: SimplCont -> Maybe (SimplCont, SimplCont) +-- Returns Nothing if the continuation should dissolve an InlineMe Note +-- Return Just (c1,c2) otherwise, +-- where c1 is the continuation to put inside the InlineMe +-- and c2 outside + +-- Example: (__inline_me__ (/\a. e)) ty +-- Here we want to do the beta-redex without dissolving the InlineMe +-- See test simpl017 (and Trac #1627) for a good example of why this is important + +splitInlineCont (ApplyTo dup (Type ty) se c) + | Just (c1, c2) <- splitInlineCont c = Just (ApplyTo dup (Type ty) se c1, c2) +splitInlineCont cont@(Stop ty _ _) = Just (mkBoringStop ty, cont) +splitInlineCont cont@(StrictBind bndr _ _ se _) = Just (mkBoringStop (substTy se (idType bndr)), cont) +splitInlineCont cont@(StrictArg _ fun_ty _ _) = Just (mkBoringStop (funArgTy fun_ty), cont) +splitInlineCont other = Nothing + -- NB: the calculation of the type for mkBoringStop is an annoying + -- duplication of the same calucation in mkDupableCont \end{code} @@ -774,10 +801,11 @@ activeInline env id where prag = idInlinePragma id -activeRule :: SimplEnv -> Maybe (Activation -> Bool) +activeRule :: DynFlags -> SimplEnv -> Maybe (Activation -> Bool) -- Nothing => No rules at all -activeRule env - | opt_RulesOff = Nothing +activeRule dflags env + | not (dopt Opt_RewriteRules dflags) + = Nothing -- Rewriting is off | otherwise = case getMode env of SimplGently -> Just isAlwaysActive @@ -802,6 +830,8 @@ mkLam :: [OutBndr] -> OutExpr -> SimplM OutExpr -- a) eta reduction, if that gives a trivial expression -- b) eta expansion [only if there are some value lambdas] +mkLam [] body + = return body mkLam bndrs body = do { dflags <- getDOptsSmpl ; mkLam' dflags bndrs body } @@ -940,8 +970,35 @@ tryEtaExpansion dflags body %* * %************************************************************************ -tryRhsTyLam tries this transformation, when the big lambda appears as -the RHS of a let(rec) binding: +Note [Floating and type abstraction] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this: + x = /\a. C e1 e2 +We'd like to float this to + y1 = /\a. e1 + y2 = /\a. e2 + x = /\a. C (y1 a) (y2 a) +for the usual reasons: we want to inline x rather vigorously. + +You may think that this kind of thing is rare. But in some programs it is +common. For example, if you do closure conversion you might get: + + data a :-> b = forall e. (e -> a -> b) :$ e + + f_cc :: forall a. a :-> a + f_cc = /\a. (\e. id a) :$ () + +Now we really want to inline that f_cc thing so that the +construction of the closure goes away. + +So I have elaborated simplLazyBind to understand right-hand sides that look +like + /\ a1..an. body + +and treat them specially. The real work is done in SimplUtils.abstractFloats, +but there is quite a bit of plumbing in simplLazyBind as well. + +The same transformation is good when there are lets in the body: /\abc -> let(rec) x = e in b ==> @@ -963,25 +1020,6 @@ let-floating. This optimisation is CRUCIAL in eliminating the junk introduced by desugaring mutually recursive definitions. Don't eliminate it lightly! -So far as the implementation is concerned: - - Invariant: go F e = /\tvs -> F e - - Equalities: - go F (Let x=e in b) - = Let x' = /\tvs -> F e - in - go G b - where - G = F . Let x = x' tvs - - go F (Letrec xi=ei in b) - = Letrec {xi' = /\tvs -> G ei} - in - go G b - where - G = F . Let {xi = xi' tvs} - [May 1999] If we do this transformation *regardless* then we can end up with some pretty silly stuff. For example, @@ -1003,43 +1041,34 @@ and is of the form If we abstract this wrt the tyvar we then can't do the case inline as we would normally do. +That's why the whole transformation is part of the same process that +floats let-bindings and constructor arguments out of RHSs. In particular, +it is guarded by the doFloatFromRhs call in simplLazyBind. -\begin{code} -{- Trying to do this in full laziness - -tryRhsTyLam :: SimplEnv -> [OutTyVar] -> OutExpr -> SimplM FloatsWithExpr --- Call ensures that all the binders are type variables - -tryRhsTyLam env tyvars body -- Only does something if there's a let - | not (all isTyVar tyvars) - || not (worth_it body) -- inside a type lambda, - = returnSmpl (emptyFloats env, body) -- and a WHNF inside that - - | otherwise - = go env (\x -> x) body +\begin{code} +abstractFloats :: [OutTyVar] -> SimplEnv -> OutExpr -> SimplM ([OutBind], OutExpr) +abstractFloats main_tvs body_env body + = ASSERT( notNull body_floats ) + do { (subst, float_binds) <- mapAccumLSmpl abstract empty_subst body_floats + ; return (float_binds, CoreSubst.substExpr subst body) } where - worth_it e@(Let _ _) = whnf_in_middle e - worth_it e = False - - whnf_in_middle (Let (NonRec x rhs) e) | isUnLiftedType (idType x) = False - whnf_in_middle (Let _ e) = whnf_in_middle e - whnf_in_middle e = exprIsCheap e - - main_tyvar_set = mkVarSet tyvars - - go env fn (Let bind@(NonRec var rhs) body) - | exprIsTrivial rhs - = go env (fn . Let bind) body - - go env fn (Let (NonRec var rhs) body) - = mk_poly tyvars_here var `thenSmpl` \ (var', rhs') -> - addAuxiliaryBind env (NonRec var' (mkLams tyvars_here (fn rhs))) $ \ env -> - go env (fn . Let (mk_silly_bind var rhs')) body - + main_tv_set = mkVarSet main_tvs + body_floats = getFloats body_env + empty_subst = CoreSubst.mkEmptySubst (seInScope body_env) + + abstract :: CoreSubst.Subst -> OutBind -> SimplM (CoreSubst.Subst, OutBind) + abstract subst (NonRec id rhs) + = do { (poly_id, poly_app) <- mk_poly tvs_here id + ; let poly_rhs = mkLams tvs_here rhs' + subst' = CoreSubst.extendIdSubst subst id poly_app + ; return (subst', (NonRec poly_id poly_rhs)) } where - - tyvars_here = varSetElems (main_tyvar_set `intersectVarSet` exprSomeFreeVars isTyVar rhs) + rhs' = CoreSubst.substExpr subst rhs + tvs_here | any isCoVar main_tvs = main_tvs -- Note [Abstract over coercions] + | otherwise + = varSetElems (main_tv_set `intersectVarSet` exprSomeFreeVars isTyVar rhs') + -- Abstract only over the type variables free in the rhs -- wrt which the new binding is abstracted. But the naive -- approach of abstract wrt the tyvars free in the Id's type @@ -1056,28 +1085,34 @@ tryRhsTyLam env tyvars body -- Only does something if there's a let -- abstracting wrt *all* the tyvars. We'll see if that -- gives rise to problems. SLPJ June 98 - go env fn (Let (Rec prs) body) - = mapAndUnzipSmpl (mk_poly tyvars_here) vars `thenSmpl` \ (vars', rhss') -> - let - gn body = fn (foldr Let body (zipWith mk_silly_bind vars rhss')) - pairs = vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss] - in - addAuxiliaryBind env (Rec pairs) $ \ env -> - go env gn body + abstract subst (Rec prs) + = do { (poly_ids, poly_apps) <- mapAndUnzipSmpl (mk_poly tvs_here) ids + ; let subst' = CoreSubst.extendSubstList subst (ids `zip` poly_apps) + poly_rhss = [mkLams tvs_here (CoreSubst.substExpr subst' rhs) | rhs <- rhss] + ; return (subst', Rec (poly_ids `zip` poly_rhss)) } where - (vars,rhss) = unzip prs - tyvars_here = varSetElems (main_tyvar_set `intersectVarSet` exprsSomeFreeVars isTyVar (map snd prs)) - -- See notes with tyvars_here above - - go env fn body = returnSmpl (emptyFloats env, fn body) - - mk_poly tyvars_here var - = getUniqueSmpl `thenSmpl` \ uniq -> - let - poly_name = setNameUnique (idName var) uniq -- Keep same name - poly_ty = mkForAllTys tyvars_here (idType var) -- But new type of course - poly_id = mkLocalId poly_name poly_ty - + (ids,rhss) = unzip prs + -- For a recursive group, it's a bit of a pain to work out the minimal + -- set of tyvars over which to abstract: + -- /\ a b c. let x = ...a... in + -- letrec { p = ...x...q... + -- q = .....p...b... } in + -- ... + -- Since 'x' is abstracted over 'a', the {p,q} group must be abstracted + -- over 'a' (because x is replaced by (poly_x a)) as well as 'b'. + -- Since it's a pain, we just use the whole set, which is always safe + -- + -- If you ever want to be more selective, remember this bizarre case too: + -- x::a = x + -- Here, we must abstract 'x' over 'a'. + tvs_here = main_tvs + + mk_poly tvs_here var + = do { uniq <- getUniqueSmpl + ; let poly_name = setNameUnique (idName var) uniq -- Keep same name + poly_ty = mkForAllTys tvs_here (idType var) -- But new type of course + poly_id = mkLocalId poly_name poly_ty + ; return (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tvs_here)) } -- In the olden days, it was crucial to copy the occInfo of the original var, -- because we were looking at occurrence-analysed but as yet unsimplified code! -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking @@ -1090,10 +1125,17 @@ tryRhsTyLam env tyvars body -- Only does something if there's a let -- where x* has an INLINE prag on it. Now, once x* is inlined, -- the occurrences of x' will be just the occurrences originally -- pinned on x. - in - returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here)) +\end{code} + +Note [Abstract over coercions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If a coercion variable (g :: a ~ Int) is free in the RHS, then so is the +type variable a. Rather than sort this mess out, we simply bale out and abstract +wrt all the type variables if any of them are coercion variables. + + +Historical note: if you use let-bindings instead of a substitution, beware of this: - mk_silly_bind var rhs = NonRec var (Note InlineMe rhs) -- Suppose we start with: -- -- x = /\ a -> let g = G in E @@ -1113,8 +1155,6 @@ tryRhsTyLam env tyvars body -- Only does something if there's a let -- Solution: put an INLINE note on g's RHS, so that poly_g seems -- to appear many times. (NB: mkInlineMe eliminates -- such notes on trivial RHSs, so do it manually.) --} -\end{code} %************************************************************************ %* * @@ -1192,20 +1232,19 @@ prepareAlts scrut case_bndr' alts ; let (alts_wo_default, maybe_deflt) = findDefault alts alt_cons = [con | (con,_,_) <- alts_wo_default] imposs_deflt_cons = nub (imposs_cons ++ alt_cons) - -- "imposs_deflt_cons" are handled either by the context, - -- OR by a branch in this case expression. - -- Don't include DEFAULT!! + -- "imposs_deflt_cons" are handled + -- EITHER by the context, + -- OR by a non-DEFAULT branch in this case expression. ; default_alts <- prepareDefault dflags scrut case_bndr' mb_tc_app imposs_deflt_cons maybe_deflt - ; let trimmed_alts = filter possible_alt alts_wo_default - merged_alts = mergeAlts default_alts trimmed_alts + ; let trimmed_alts = filterOut impossible_alt alts_wo_default + merged_alts = mergeAlts trimmed_alts default_alts -- We need the mergeAlts in case the new default_alt -- has turned into a constructor alternative. -- The merge keeps the inner DEFAULT at the front, if there is one - -- and eliminates any inner_alts that are shadowed by the outer_alts - + -- and interleaves the alternatives in the right order ; return (imposs_deflt_cons, merged_alts) } where @@ -1216,10 +1255,10 @@ prepareAlts scrut case_bndr' alts Var v -> otherCons (idUnfolding v) other -> [] - possible_alt :: CoreAlt -> Bool - possible_alt (con, _, _) | con `elem` imposs_cons = False - possible_alt (DataAlt con, _, _) = dataConCanMatch inst_tys con - possible_alt alt = True + impossible_alt :: CoreAlt -> Bool + impossible_alt (con, _, _) | con `elem` imposs_cons = True + impossible_alt (DataAlt con, _, _) = dataConCannotMatch inst_tys con + impossible_alt alt = False -------------------------------------------------- @@ -1262,7 +1301,17 @@ prepareDefault dflags scrut outer_bndr bndr_ty imposs_cons (Just deflt_rhs) = do { tick (CaseMerge outer_bndr) ; let munge_rhs rhs = bindCaseBndr inner_bndr (Var outer_bndr) rhs - ; return [(con, args, munge_rhs rhs) | (con, args, rhs) <- inner_alts] } + ; return [(con, args, munge_rhs rhs) | (con, args, rhs) <- inner_alts, + not (con `elem` imposs_cons) ] + -- NB: filter out any imposs_cons. Example: + -- case x of + -- A -> e1 + -- DEFAULT -> case x of + -- A -> e2 + -- B -> e3 + -- When we merge, we must ensure that e1 takes + -- precedence over e2 as the value for A! + } -- Warning: don't call prepareAlts recursively! -- Firstly, there's no point, because inner alts have already had -- mkCase applied to them, so they won't have a case in their default @@ -1297,9 +1346,8 @@ prepareDefault dflags scrut case_bndr (Just (tycon, inst_tys)) imposs_cons (Just -- which would be quite legitmate. But it's a really obscure corner, and -- not worth wasting code on. , let imposs_data_cons = [con | DataAlt con <- imposs_cons] -- We now know it's a data type - is_possible con = not (con `elem` imposs_data_cons) - && dataConCanMatch inst_tys con - = case filter is_possible all_cons of + impossible con = con `elem` imposs_data_cons || dataConCannotMatch inst_tys con + = case filterOut impossible all_cons of [] -> return [] -- Eliminate the default alternative -- altogether if it can't match @@ -1352,7 +1400,7 @@ mkCase :: OutExpr -> OutId -> OutType -- put an error case here insteadd mkCase scrut case_bndr ty [] = pprTrace "mkCase: null alts" (ppr case_bndr <+> ppr scrut) $ - return (mkApps (Var eRROR_ID) + return (mkApps (Var rUNTIME_ERROR_ID) [Type ty, Lit (mkStringLit "Impossible alternative")])