X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSetLevels.lhs;h=2acdc9dcaad277db278373dc573b92ae662d0a59;hb=f016a43fcbcca53a284e8d6206705ed468a97736;hp=d1b50a5f837c9b8fdf1cae1ccb4bde6561362f8b;hpb=5cf27e8f1731c52fe63a5b9615f927484164c61b;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/SetLevels.lhs b/ghc/compiler/simplCore/SetLevels.lhs index d1b50a5..2acdc9d 100644 --- a/ghc/compiler/simplCore/SetLevels.lhs +++ b/ghc/compiler/simplCore/SetLevels.lhs @@ -1,53 +1,50 @@ % -% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996 +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section{SetLevels} -We attach binding levels to Core bindings, in preparation for floating -outwards (@FloatOut@). + *************************** + Overview + *************************** + +* We attach binding levels to Core bindings, in preparation for floating + outwards (@FloatOut@). + +* We also let-ify many expressions (notably case scrutinees), so they + will have a fighting chance of being floated sensible. + +* We clone the binders of any floatable let-binding, so that when it is + floated out it will be unique. (This used to be done by the simplifier + but the latter now only ensures that there's no shadowing.) -We also let-ify many applications (notably case scrutinees), so they -will have a fighting chance of being floated sensible. -\begin{code} -#include "HsVersions.h" +\begin{code} module SetLevels ( setLevels, Level(..), tOP_LEVEL, incMinorLvl, ltMajLvl, ltLvl, isTopLvl --- not exported: , incMajorLvl, isTopMajLvl, unTopify ) where -import Ubiq{-uitous-} +#include "HsVersions.h" -import AnnCoreSyn import CoreSyn -import CoreUtils ( coreExprType, manifestlyWHNF, manifestlyBottom ) -import FreeVars -- all of it -import Id ( idType, mkSysLocal, toplevelishId, - nullIdEnv, addOneToIdEnv, growIdEnvList, - unionManyIdSets, minusIdSet, mkIdSet, - idSetToList, - lookupIdEnv, IdEnv(..) - ) -import Pretty ( ppStr, ppBesides, ppChar, ppInt ) -import SrcLoc ( mkUnknownSrcLoc ) -import Type ( isPrimType, mkTyVarTys, mkForAllTys ) -import TyVar ( nullTyVarEnv, addOneToTyVarEnv, - growTyVarEnvList, lookupTyVarEnv, - tyVarSetToList, - TyVarEnv(..), - unionManyTyVarSets - ) -import UniqSupply ( thenUs, returnUs, mapUs, mapAndUnzipUs, - mapAndUnzip3Us, getUnique, UniqSM(..) - ) -import Usage ( UVar(..) ) -import Util ( mapAccumL, zipWithEqual, zipEqual, panic, assertPanic ) +import CoreUtils ( coreExprType, exprIsTrivial, exprIsBottom ) +import CoreFVs -- all of it +import Id ( Id, idType, mkSysLocal, isOneShotLambda ) +import Var ( IdOrTyVar, Var, setVarUnique ) +import VarEnv +import VarSet +import Type ( isUnLiftedType, mkTyVarTys, mkForAllTys, Type ) +import VarSet +import VarEnv +import UniqSupply +import Maybes ( maybeToBool ) +import Util ( zipWithEqual, zipEqual ) +import Outputable isLeakFreeType x y = False -- safe option; ToDo \end{code} @@ -60,17 +57,19 @@ isLeakFreeType x y = False -- safe option; ToDo \begin{code} data Level - = Top -- Means *really* the top level. + = Top -- Means *really* the top level; short for (Level 0 0). | Level Int -- Level number of enclosing lambdas Int -- Number of big-lambda and/or case expressions between -- here and the nearest enclosing lambda \end{code} The {\em level number} on a (type-)lambda-bound variable is the -nesting depth of the (type-)lambda which binds it. On an expression, -it's the maximum level number of its free (type-)variables. On a -let(rec)-bound variable, it's the level of its RHS. On a case-bound -variable, it's the number of enclosing lambdas. +nesting depth of the (type-)lambda which binds it. The outermost lambda +has level 1, so (Level 0 0) means that the variable is bound outside any lambda. + +On an expression, it's the maximum level number of its free +(type-)variables. On a let(rec)-bound variable, it's the level of its +RHS. On a case-bound variable, it's the number of enclosing lambdas. Top-level variables: level~0. Those bound on the RHS of a top-level definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown @@ -91,12 +90,9 @@ sub-expression so that it will indeed float. This context level starts at @Level 0 0@; it is never @Top@. \begin{code} -type LevelledExpr = GenCoreExpr (Id, Level) Id TyVar UVar -type LevelledArg = GenCoreArg Id TyVar UVar -type LevelledBind = GenCoreBinding (Id, Level) Id TyVar UVar - -type LevelEnvs = (IdEnv Level, -- bind Ids to levels - TyVarEnv Level) -- bind type variables to levels +type LevelledExpr = TaggedExpr Level +type LevelledArg = TaggedArg Level +type LevelledBind = TaggedBind Level tOP_LEVEL = Top @@ -108,6 +104,13 @@ incMinorLvl :: Level -> Level incMinorLvl Top = Level 0 1 incMinorLvl (Level major minor) = Level major (minor+1) +unTopify :: Type -> Level -> Level +unTopify ty lvl + | isUnLiftedType ty = case lvl of + Top -> Level 0 0 -- Unboxed floats can't go right + other -> lvl -- to the top + | otherwise = lvl + maxLvl :: Level -> Level -> Level maxLvl Top l2 = l2 maxLvl l1 Top = l1 @@ -136,13 +139,39 @@ isTopMajLvl :: Level -> Bool -- Tells if it's the top *lambda* level isTopMajLvl Top = True isTopMajLvl (Level maj _) = maj == 0 -unTopify :: Level -> Level -unTopify Top = Level 0 0 -unTopify lvl = lvl - instance Outputable Level where - ppr sty Top = ppStr "" - ppr sty (Level maj min) = ppBesides [ ppChar '<', ppInt maj, ppChar ',', ppInt min, ppChar '>' ] + ppr Top = ptext SLIT("") + ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ] +\end{code} + +\begin{code} +type LevelEnv = VarEnv (Var, Level) + -- We clone let-bound variables so that they are still + -- distinct when floated out; hence the Var in the range + +extendLvlEnv :: LevelEnv -> [(Var,Level)] -> LevelEnv + -- Used when *not* cloning +extendLvlEnv env prs = foldl add env prs + where + add env (v,l) = extendVarEnv env v (v,l) + +varLevel :: LevelEnv -> IdOrTyVar -> Level +varLevel env v + = case lookupVarEnv env v of + Just (_,level) -> level + Nothing -> tOP_LEVEL + +maxIdLvl :: LevelEnv -> IdOrTyVar -> Level -> Level +maxIdLvl env var lvl | isTyVar var = lvl + | otherwise = case lookupVarEnv env var of + Just (_,lvl') -> maxLvl lvl' lvl + Nothing -> lvl + +maxTyVarLvl :: LevelEnv -> IdOrTyVar -> Level -> Level +maxTyVarLvl env var lvl | isId var = lvl + | otherwise = case lookupVarEnv env var of + Just (_,lvl') -> maxLvl lvl' lvl + Nothing -> lvl \end{code} %************************************************************************ @@ -152,32 +181,32 @@ instance Outputable Level where %************************************************************************ \begin{code} -setLevels :: [CoreBinding] +setLevels :: [CoreBind] -> UniqSupply -> [LevelledBind] setLevels binds us - = do_them binds us + = initLvl us (do_them binds) where -- "do_them"'s main business is to thread the monad along -- It gives each top binding the same empty envt, because -- things unbound in the envt have level number zero implicitly - do_them :: [CoreBinding] -> LvlM [LevelledBind] + do_them :: [CoreBind] -> LvlM [LevelledBind] do_them [] = returnLvl [] do_them (b:bs) = lvlTopBind b `thenLvl` \ (lvld_bind, _) -> - do_them bs `thenLvl` \ lvld_binds -> + do_them bs `thenLvl` \ lvld_binds -> returnLvl (lvld_bind ++ lvld_binds) -initial_envs = (nullIdEnv, nullTyVarEnv) +initialEnv = emptyVarEnv lvlTopBind (NonRec binder rhs) - = lvlBind (Level 0 0) initial_envs (AnnNonRec binder (freeVars rhs)) + = lvlBind Top initialEnv (AnnNonRec binder (freeVars rhs)) -- Rhs can have no free vars! lvlTopBind (Rec pairs) - = lvlBind (Level 0 0) initial_envs (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs]) + = lvlBind Top initialEnv (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs]) \end{code} %************************************************************************ @@ -189,34 +218,23 @@ lvlTopBind (Rec pairs) The binding stuff works for top level too. \begin{code} -type CoreBindingWithFVs = AnnCoreBinding Id Id TyVar UVar FVInfo - lvlBind :: Level - -> LevelEnvs - -> CoreBindingWithFVs - -> LvlM ([LevelledBind], LevelEnvs) + -> LevelEnv + -> CoreBindWithFVs + -> LvlM ([LevelledBind], LevelEnv) -lvlBind ctxt_lvl envs@(venv, tenv) (AnnNonRec name rhs) - = setFloatLevel True {- Already let-bound -} - ctxt_lvl envs rhs ty `thenLvl` \ (final_lvl, rhs') -> +lvlBind ctxt_lvl env (AnnNonRec bndr rhs) + = setFloatLevel (Just bndr) ctxt_lvl env rhs ty `thenLvl` \ (final_lvl, rhs') -> + cloneVar ctxt_lvl bndr `thenLvl` \ new_bndr -> let - new_envs = (addOneToIdEnv venv name final_lvl, tenv) + new_env = extendVarEnv env bndr (new_bndr,final_lvl) in - returnLvl ([NonRec (name, final_lvl) rhs'], new_envs) + returnLvl ([NonRec (new_bndr, final_lvl) rhs'], new_env) where - ty = idType name + ty = idType bndr -lvlBind ctxt_lvl envs@(venv, tenv) (AnnRec pairs) - = decideRecFloatLevel ctxt_lvl envs binders rhss - `thenLvl` \ (final_lvl, extra_binds, rhss') -> - let - binders_w_lvls = binders `zip` repeat final_lvl - new_envs = (growIdEnvList venv binders_w_lvls, tenv) - in - returnLvl (extra_binds ++ [Rec (zipEqual "lvlBind" binders_w_lvls rhss')], new_envs) - where - (binders,rhss) = unzip pairs +lvlBind ctxt_lvl env (AnnRec pairs) = lvlRecBind ctxt_lvl env pairs \end{code} %************************************************************************ @@ -227,7 +245,7 @@ lvlBind ctxt_lvl envs@(venv, tenv) (AnnRec pairs) \begin{code} lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression - -> LevelEnvs -- Level of in-scope names/tyvars + -> LevelEnv -- Level of in-scope names/tyvars -> CoreExprWithFVs -- input expression -> LvlM LevelledExpr -- Result expression \end{code} @@ -250,83 +268,73 @@ don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE If there were another lambda in @r@'s rhs, it would get level-2 as well. \begin{code} -lvlExpr _ _ (_, AnnVar v) = returnLvl (Var v) -lvlExpr _ _ (_, AnnLit l) = returnLvl (Lit l) -lvlExpr _ _ (_, AnnCon con args) = returnLvl (Con con args) -lvlExpr _ _ (_, AnnPrim op args) = returnLvl (Prim op args) - -lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnApp fun arg) - = lvlExpr ctxt_lvl envs fun `thenLvl` \ fun' -> - returnLvl (App fun' arg) - -lvlExpr ctxt_lvl envs (_, AnnSCC cc expr) - = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' -> - returnLvl (SCC cc expr') - -lvlExpr ctxt_lvl envs (_, AnnCoerce c ty expr) - = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' -> - returnLvl (Coerce c ty expr') - -lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnLam (ValBinder arg) rhs) - = lvlMFE incd_lvl (new_venv, tenv) rhs `thenLvl` \ rhs' -> - returnLvl (Lam (ValBinder (arg,incd_lvl)) rhs') +lvlExpr _ _ (_, AnnType ty) = returnLvl (Type ty) +lvlExpr _ env (_, AnnVar v) = case lookupVarEnv env v of + Just (v',_) -> returnLvl (Var v') + Nothing -> returnLvl (Var v) + +lvlExpr ctxt_lvl env (_, AnnCon con args) + = mapLvl (lvlExpr ctxt_lvl env) args `thenLvl` \ args' -> + returnLvl (Con con args') + +lvlExpr ctxt_lvl env (_, AnnApp fun arg) + = lvlExpr ctxt_lvl env fun `thenLvl` \ fun' -> + lvlMFE ctxt_lvl env arg `thenLvl` \ arg' -> + returnLvl (App fun' arg') + +lvlExpr ctxt_lvl env (_, AnnNote note expr) + = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' -> + returnLvl (Note note expr') + +-- We don't split adjacent lambdas. That is, given +-- \x y -> (x+1,y) +-- we don't float to give +-- \x -> let v = x+y in \y -> (v,y) +-- Why not? Because partial applications are fairly rare, and splitting +-- lambdas makes them more expensive. + +lvlExpr ctxt_lvl env (_, AnnLam bndr rhs) + = lvlMFE incd_lvl new_env body `thenLvl` \ body' -> + returnLvl (mkLams lvld_bndrs body') where - incd_lvl = incMajorLvl ctxt_lvl - new_venv = growIdEnvList venv [(arg,incd_lvl)] - -lvlExpr ctxt_lvl (venv, tenv) (_, AnnLam (TyBinder tyvar) e) - = lvlExpr incd_lvl (venv, new_tenv) e `thenLvl` \ e' -> - returnLvl (Lam (TyBinder tyvar) e') + bndr_is_id = isId bndr + bndr_is_tyvar = isTyVar bndr + (bndrs, body) = go rhs + + incd_lvl | bndr_is_id && not (all isOneShotLambda bndrs) = incMajorLvl ctxt_lvl + | otherwise = incMinorLvl ctxt_lvl + -- Only bump the major level number if the binders include + -- at least one more-than-one-shot lambda + + lvld_bndrs = [(b,incd_lvl) | b <- (bndr:bndrs)] + new_env = extendLvlEnv env lvld_bndrs + + go (_, AnnLam bndr rhs) | bndr_is_id && isId bndr + || bndr_is_tyvar && isTyVar bndr + = case go rhs of { (bndrs, body) -> (bndr:bndrs, body) } + go body = ([], body) + +lvlExpr ctxt_lvl env (_, AnnLet bind body) + = lvlBind ctxt_lvl env bind `thenLvl` \ (binds', new_env) -> + lvlExpr ctxt_lvl new_env body `thenLvl` \ body' -> + returnLvl (mkLets binds' body') + +lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr alts) + = lvlMFE ctxt_lvl env expr `thenLvl` \ expr' -> + mapLvl lvl_alt alts `thenLvl` \ alts' -> + returnLvl (Case expr' (case_bndr, incd_lvl) alts') where - incd_lvl = incMinorLvl ctxt_lvl - new_tenv = addOneToTyVarEnv tenv tyvar incd_lvl - -lvlExpr ctxt_lvl (venv, tenv) (_, AnnLam (UsageBinder u) e) - = panic "SetLevels.lvlExpr:AnnLam UsageBinder" - -lvlExpr ctxt_lvl envs (_, AnnLet bind body) - = lvlBind ctxt_lvl envs bind `thenLvl` \ (binds', new_envs) -> - lvlExpr ctxt_lvl new_envs body `thenLvl` \ body' -> - returnLvl (foldr Let body' binds') -- mkCoLet* requires Core... - -lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnCase expr alts) - = lvlMFE ctxt_lvl envs expr `thenLvl` \ expr' -> - lvl_alts alts `thenLvl` \ alts' -> - returnLvl (Case expr' alts') - where expr_type = coreExprType (deAnnotate expr) incd_lvl = incMinorLvl ctxt_lvl - - lvl_alts (AnnAlgAlts alts deflt) - = mapLvl lvl_alt alts `thenLvl` \ alts' -> - lvl_deflt deflt `thenLvl` \ deflt' -> - returnLvl (AlgAlts alts' deflt') - where - lvl_alt (con, bs, e) - = let - bs' = [ (b, incd_lvl) | b <- bs ] - new_envs = (growIdEnvList venv bs', tenv) - in - lvlMFE incd_lvl new_envs e `thenLvl` \ e' -> - returnLvl (con, bs', e') - - lvl_alts (AnnPrimAlts alts deflt) - = mapLvl lvl_alt alts `thenLvl` \ alts' -> - lvl_deflt deflt `thenLvl` \ deflt' -> - returnLvl (PrimAlts alts' deflt') - where - lvl_alt (lit, e) - = lvlMFE incd_lvl envs e `thenLvl` \ e' -> - returnLvl (lit, e') - - lvl_deflt AnnNoDefault = returnLvl NoDefault - - lvl_deflt (AnnBindDefault b expr) - = let - new_envs = (addOneToIdEnv venv b incd_lvl, tenv) - in - lvlMFE incd_lvl new_envs expr `thenLvl` \ expr' -> - returnLvl (BindDefault (b, incd_lvl) expr') + alts_env = extendVarEnv env case_bndr (case_bndr,incd_lvl) + + lvl_alt (con, bs, rhs) + = let + bs' = [ (b, incd_lvl) | b <- bs ] + new_env = extendLvlEnv alts_env bs' + in + lvlMFE incd_lvl new_env rhs `thenLvl` \ rhs' -> + returnLvl (con, bs', rhs') \end{code} @lvlMFE@ is just like @lvlExpr@, except that it might let-bind @@ -334,17 +342,20 @@ the expression, so that it can itself be floated. \begin{code} lvlMFE :: Level -- Level of innermost enclosing lambda/tylam - -> LevelEnvs -- Level of in-scope names/tyvars + -> LevelEnv -- Level of in-scope names/tyvars -> CoreExprWithFVs -- input expression -> LvlM LevelledExpr -- Result expression -lvlMFE ctxt_lvl envs@(venv,_) ann_expr - | isPrimType ty -- Can't let-bind it - = lvlExpr ctxt_lvl envs ann_expr +lvlMFE ctxt_lvl env (_, AnnType ty) + = returnLvl (Type ty) + +lvlMFE ctxt_lvl env ann_expr + | isUnLiftedType ty -- Can't let-bind it + = lvlExpr ctxt_lvl env ann_expr | otherwise -- Not primitive type so could be let-bound - = setFloatLevel False {- Not already let-bound -} - ctxt_lvl envs ann_expr ty `thenLvl` \ (final_lvl, expr') -> + = setFloatLevel Nothing {- Not already let-bound -} + ctxt_lvl env ann_expr ty `thenLvl` \ (final_lvl, expr') -> returnLvl expr' where ty = coreExprType (deAnnotate ann_expr) @@ -384,21 +395,18 @@ Let Bound? Pin (leave) expression here. \begin{code} -setFloatLevel :: Bool -- True <=> the expression is already let-bound - -- False <=> it's a possible MFE +setFloatLevel :: Maybe Id -- Just id <=> the expression is already let-bound to id + -- Nothing <=> it's a possible MFE -> Level -- of context - -> LevelEnvs + -> LevelEnv -> CoreExprWithFVs -- Original rhs - -> Type -- Type of rhs + -> Type -- Type of rhs -> LvlM (Level, -- Level to attribute to this let-binding LevelledExpr) -- Final rhs -setFloatLevel alreadyLetBound ctxt_lvl envs@(venv, tenv) - expr@(FVInfo fvs tfvs might_leak, _) ty --- Invariant: ctxt_lvl is never = Top --- Beautiful ASSERT, dudes (WDP 95/04)... +setFloatLevel maybe_let_bound ctxt_lvl env expr@(expr_fvs, _) ty -- Now deal with (by not floating) trivial non-let-bound expressions -- which just aren't worth let-binding in order to float. We always @@ -406,7 +414,7 @@ setFloatLevel alreadyLetBound ctxt_lvl envs@(venv, tenv) -- any harm, and not floating it may pin something important. For -- example -- --- x = let v = Nil +-- x = let v = [] -- w = 1:v -- in ... -- @@ -415,85 +423,65 @@ setFloatLevel alreadyLetBound ctxt_lvl envs@(venv, tenv) -- for top level. | not alreadyLetBound - && (manifestly_whnf || not will_float_past_lambda) - = -- Pin whnf non-let-bound expressions, + && (expr_is_trivial || expr_is_bottom || not will_float_past_lambda) + + = -- Pin trivial non-let-bound expressions, -- or ones which aren't going anywhere useful - lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' -> - returnLvl (ctxt_lvl, expr') + lvlExpr ctxt_lvl env expr `thenLvl` \ expr' -> + returnLvl (safe_ctxt_lvl, expr') + +{- SDM 7/98 +The above case used to read (whnf_or_bottom || not will_float_past_lambda). +It was changed because we really do want to float out constructors if possible: +this can save a great deal of needless allocation inside a loop. On the other +hand, there's no point floating out nullary constructors and literals, hence +the expr_is_trivial condition. +-} | alreadyLetBound && not worth_type_abstraction = -- Process the expression with a new ctxt_lvl, obtained from -- the free vars of the expression itself - lvlExpr (unTopify expr_lvl) envs expr `thenLvl` \ expr' -> - returnLvl (maybe_unTopify expr_lvl, expr') + lvlExpr expr_lvl env expr `thenLvl` \ expr' -> + returnLvl (safe_expr_lvl, expr') | otherwise -- This will create a let anyway, even if there is no -- type variable to abstract, so we try to abstract anyway - = abstractWrtTyVars offending_tyvars ty envs lvl_after_ty_abstr expr + = abstractWrtTyVars offending_tyvars ty env lvl_after_ty_abstr expr `thenLvl` \ final_expr -> - returnLvl (expr_lvl, final_expr) + returnLvl (safe_expr_lvl, final_expr) -- OLD LIE: The body of the let, just a type application, isn't worth floating -- so pin it with ctxt_lvl -- The truth: better to give it expr_lvl in case it is pinning -- something non-trivial which depends on it. where - fv_list = idSetToList fvs - tv_list = tyVarSetToList tfvs - expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl - ids_only_lvl = foldr (maxLvl . idLevel venv) tOP_LEVEL fv_list - tyvars_only_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL tv_list + alreadyLetBound = maybeToBool maybe_let_bound + + safe_ctxt_lvl = unTopify ty ctxt_lvl + safe_expr_lvl = unTopify ty expr_lvl + + fvs = case maybe_let_bound of + Nothing -> expr_fvs + Just id -> expr_fvs `unionVarSet` idFreeVars id + + ids_only_lvl = foldVarSet (maxIdLvl env) tOP_LEVEL fvs + tyvars_only_lvl = foldVarSet (maxTyVarLvl env) tOP_LEVEL fvs + expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl lvl_after_ty_abstr = ids_only_lvl --`maxLvl` non_offending_tyvars_lvl - will_float_past_lambda = -- Will escape lambda if let-bound - ids_only_lvl `ltMajLvl` ctxt_lvl - - worth_type_abstraction = -- Will escape (more) lambda(s)/type lambda(s) - -- if type abstracted - (ids_only_lvl `ltLvl` tyvars_only_lvl) - && not (is_trivial de_ann_expr) -- avoids abstracting trivial type applications - - de_ann_expr = deAnnotate expr - - is_trivial (App e a) - | notValArg a = is_trivial e - is_trivial (Var _) = True - is_trivial _ = False - - offending_tyvars = filter offending tv_list - --non_offending_tyvars = filter (not . offending) tv_list - --non_offending_tyvars_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL non_offending_tyvars - - offending tyvar = ids_only_lvl `ltLvl` tyvarLevel tenv tyvar - - manifestly_whnf = manifestlyWHNF de_ann_expr || manifestlyBottom de_ann_expr - - maybe_unTopify Top | not (canFloatToTop (ty, expr)) = Level 0 0 - maybe_unTopify lvl = lvl - {- ToDo [Andre]: the line above (maybe) should be Level 1 0, - -- so that the let will not go past the *last* lambda if it can - -- generate a space leak. If it is already in major level 0 - -- It won't do any harm to give it a Level 1 0. - -- we should do the same test not only for things with level Top, - -- but also for anything that gets a major level 0. - the problem is that - f = \a -> let x = [1..1000] - in zip a x - ==> - f = let x = [1..1000] - in \a -> zip a x - is just as bad as floating x to the top level. - Notice it would be OK in cases like - f = \a -> let x = [1..1000] - y = length x - in a + y - ==> - f = let x = [1..1000] - y = length x - in \a -> a + y - as x will be gc'd after y is updated. - [We did not hit any problems with the above (Level 0 0) code - in nofib benchmark] - -} + -- Will escape lambda if let-bound + will_float_past_lambda = ids_only_lvl `ltMajLvl` ctxt_lvl + + -- Will escape (more) lambda(s)/type lambda(s) if type abstracted + worth_type_abstraction = (ids_only_lvl `ltLvl` tyvars_only_lvl) + && not expr_is_trivial -- Avoids abstracting trivial type applications + + offending_tyvars = filter offending_tv (varSetElems fvs) + offending_tv var | isId var = False + | otherwise = ids_only_lvl `ltLvl` varLevel env var + + expr_is_trivial = exprIsTrivial de_ann_expr + expr_is_bottom = exprIsBottom de_ann_expr + de_ann_expr = deAnnotate expr \end{code} Abstract wrt tyvars, by making it just as if we had seen @@ -506,13 +494,13 @@ has no free type variables. Of course, if E has no free type variables, then we just return E. \begin{code} -abstractWrtTyVars offending_tyvars ty (venv,tenv) lvl expr - = lvlExpr incd_lvl new_envs expr `thenLvl` \ expr' -> +abstractWrtTyVars offending_tyvars ty env lvl expr + = lvlExpr incd_lvl new_env expr `thenLvl` \ expr' -> newLvlVar poly_ty `thenLvl` \ poly_var -> let - poly_var_rhs = mkTyLam offending_tyvars expr' + poly_var_rhs = mkLams tyvar_lvls expr' poly_var_binding = NonRec (poly_var, lvl) poly_var_rhs - poly_var_app = mkTyApp (Var poly_var) (mkTyVarTys offending_tyvars) + poly_var_app = mkTyApps (Var poly_var) (mkTyVarTys offending_tyvars) final_expr = Let poly_var_binding poly_var_app -- mkCoLet* requires Core in returnLvl final_expr @@ -520,13 +508,9 @@ abstractWrtTyVars offending_tyvars ty (venv,tenv) lvl expr poly_ty = mkForAllTys offending_tyvars ty -- These defns are just like those in the TyLam case of lvlExpr - (incd_lvl, tyvar_lvls) = mapAccumL next (unTopify lvl) offending_tyvars - - next lvl tyvar = (lvl1, (tyvar,lvl1)) - where lvl1 = incMinorLvl lvl - - new_tenv = growTyVarEnvList tenv tyvar_lvls - new_envs = (venv, new_tenv) + incd_lvl = incMinorLvl lvl + tyvar_lvls = [(tv,incd_lvl) | tv <- offending_tyvars] + new_env = extendLvlEnv env tyvar_lvls \end{code} Recursive definitions. We want to transform @@ -548,7 +532,7 @@ to let D in body where ab are the tyvars pinning the defn further in than it -need be, and D is a bunch of simple type applications: +need be, and D is a bunch of simple type applications: x1_cl = x1' ab ... @@ -566,153 +550,74 @@ but differ in their level numbers; here the ab are the newly-introduced type lambdas. \begin{code} -decideRecFloatLevel ctxt_lvl envs@(venv, tenv) ids rhss - | isTopMajLvl ids_only_lvl && -- Destination = top - not (all canFloatToTop (zipEqual "decideRec" tys rhss)) -- Some can't float to top - = -- Pin it here - let - ids_w_lvls = ids `zip` repeat ctxt_lvl - new_envs = (growIdEnvList venv ids_w_lvls, tenv) - in - mapLvl (lvlExpr ctxt_lvl new_envs) rhss `thenLvl` \ rhss' -> - returnLvl (ctxt_lvl, [], rhss') - -{- OMITTED; see comments above near isWorthFloatingExpr - - | not (any (isWorthFloating True . deAnnotate) rhss) - = -- Pin it here - mapLvl (lvlExpr ctxt_lvl envs) rhss `thenLvl` \ rhss' -> - returnLvl (ctxt_lvl, [], rhss') - --} - +lvlRecBind ctxt_lvl env pairs | ids_only_lvl `ltLvl` tyvars_only_lvl = -- Abstract wrt tyvars; -- offending_tyvars is definitely non-empty -- (I love the ASSERT to check this... WDP 95/02) let - -- These defns are just like those in the TyLam case of lvlExpr - (incd_lvl, tyvar_lvls) = mapAccumL next (unTopify ids_only_lvl) offending_tyvars - - next lvl tyvar = (lvl1, (tyvar,lvl1)) - where lvl1 = incMinorLvl lvl - - ids_w_incd_lvl = [(id,incd_lvl) | id <- ids] - new_tenv = growTyVarEnvList tenv tyvar_lvls - new_venv = growIdEnvList venv ids_w_incd_lvl - new_envs = (new_venv, new_tenv) + incd_lvl = incMinorLvl ids_only_lvl + tyvars_w_rhs_lvl = [(var,incd_lvl) | var <- offending_tyvars] + bndrs_w_rhs_lvl = [(var,incd_lvl) | var <- bndrs] + rhs_env = extendLvlEnv env (tyvars_w_rhs_lvl ++ bndrs_w_rhs_lvl) in - mapLvl (lvlExpr incd_lvl new_envs) rhss `thenLvl` \ rhss' -> + mapLvl (lvlExpr incd_lvl rhs_env) rhss `thenLvl` \ rhss' -> mapLvl newLvlVar poly_tys `thenLvl` \ poly_vars -> + mapLvl (cloneVar ctxt_lvl) bndrs `thenLvl` \ new_bndrs -> let - ids_w_poly_vars = zipEqual "decideRec2" ids poly_vars - -- The "d_rhss" are the right-hand sides of "D" and "D'" -- in the documentation above - d_rhss = [ mkTyApp (Var poly_var) offending_tyvar_tys | poly_var <- poly_vars] + d_rhss = [ mkTyApps (Var poly_var) offending_tyvar_tys | poly_var <- poly_vars] -- "local_binds" are "D'" in the documentation above - local_binds = zipWithEqual "SetLevels" NonRec ids_w_incd_lvl d_rhss + local_binds = zipWithEqual "SetLevels" NonRec bndrs_w_rhs_lvl d_rhss - poly_var_rhss = [ mkTyLam offending_tyvars (foldr Let rhs' local_binds) - | rhs' <- rhss' -- mkCoLet* requires Core... + poly_var_rhss = [ mkLams tyvars_w_rhs_lvl (mkLets local_binds rhs') + | rhs' <- rhss' ] - poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars] poly_var_rhss + poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars] + poly_var_rhss + + -- The new right-hand sides, just a type application, + -- aren't worth floating so pin it with ctxt_lvl + bndrs_w_lvl = new_bndrs `zip` repeat ctxt_lvl + new_env = extendVarEnvList env (bndrs `zip` bndrs_w_lvl) + -- "d_binds" are the "D" in the documentation above + d_binds = zipWithEqual "SetLevels" NonRec bndrs_w_lvl d_rhss in - returnLvl (ctxt_lvl, [Rec poly_binds], d_rhss) - -- The new right-hand sides, just a type application, aren't worth floating - -- so pin it with ctxt_lvl + returnLvl (Rec poly_binds : d_binds, new_env) | otherwise = -- Let it float freely + mapLvl (cloneVar ctxt_lvl) bndrs `thenLvl` \ new_bndrs -> let - ids_w_lvls = ids `zip` repeat expr_lvl - new_envs = (growIdEnvList venv ids_w_lvls, tenv) + bndrs_w_lvls = new_bndrs `zip` repeat expr_lvl + new_env = extendVarEnvList env (bndrs `zip` bndrs_w_lvls) in - mapLvl (lvlExpr (unTopify expr_lvl) new_envs) rhss `thenLvl` \ rhss' -> - returnLvl (expr_lvl, [], rhss') + mapLvl (lvlExpr expr_lvl new_env) rhss `thenLvl` \ rhss' -> + returnLvl ([Rec (bndrs_w_lvls `zip` rhss')], new_env) where - tys = map idType ids + (bndrs,rhss) = unzip pairs - fvs = unionManyIdSets [freeVarsOf rhs | rhs <- rhss] `minusIdSet` mkIdSet ids - tfvs = unionManyTyVarSets [freeTyVarsOf rhs | rhs <- rhss] - fv_list = idSetToList fvs - tv_list = tyVarSetToList tfvs + -- Finding the free vars of the binding group is annoying + bind_fvs = (unionVarSets (map fst rhss) `unionVarSet` unionVarSets (map idFreeVars bndrs)) + `minusVarSet` + mkVarSet bndrs - ids_only_lvl = foldr (maxLvl . idLevel venv) tOP_LEVEL fv_list - tyvars_only_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL tv_list + ids_only_lvl = foldVarSet (maxIdLvl env) tOP_LEVEL bind_fvs + tyvars_only_lvl = foldVarSet (maxTyVarLvl env) tOP_LEVEL bind_fvs expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl - offending_tyvars - | ids_only_lvl `ltLvl` tyvars_only_lvl = filter offending tv_list - | otherwise = [] - + offending_tyvars = filter offending_tv (varSetElems bind_fvs) + offending_tv var | isId var = False + | otherwise = ids_only_lvl `ltLvl` varLevel env var offending_tyvar_tys = mkTyVarTys offending_tyvars - poly_tys = map (mkForAllTys offending_tyvars) tys - - offending tyvar = ids_only_lvl `ltLvl` tyvarLevel tenv tyvar -\end{code} - - -\begin{code} -{- ******** OMITTED NOW - -isWorthFloating :: Bool -- True <=> already let-bound - -> CoreExpr -- The expression - -> Bool - -isWorthFloating alreadyLetBound expr - - | alreadyLetBound = isWorthFloatingExpr expr - | otherwise = -- No point in adding a fresh let-binding for a WHNF, because - -- floating it isn't beneficial enough. - isWorthFloatingExpr expr && - not (manifestlyWHNF expr || manifestlyBottom expr) -********** -} - -isWorthFloatingExpr :: CoreExpr -> Bool - -isWorthFloatingExpr (Var v) = False -isWorthFloatingExpr (Lit lit) = False -isWorthFloatingExpr (App e arg) - | notValArg arg = isWorthFloatingExpr e -isWorthFloatingExpr (Con con as) - | all notValArg as = False -- Just a type application -isWorthFloatingExpr _ = True - -canFloatToTop :: (Type, CoreExprWithFVs) -> Bool - -canFloatToTop (ty, (FVInfo _ _ (LeakFree _), expr)) = True -canFloatToTop (ty, (FVInfo _ _ MightLeak, expr)) = isLeakFreeType [] ty - -valSuggestsLeakFree expr = manifestlyWHNF expr || manifestlyBottom expr -\end{code} - - - -%************************************************************************ -%* * -\subsection{Help functions} -%* * -%************************************************************************ - -\begin{code} -idLevel :: IdEnv Level -> Id -> Level -idLevel venv v - = case lookupIdEnv venv v of - Just level -> level - Nothing -> ASSERT(toplevelishId v) - tOP_LEVEL - -tyvarLevel :: TyVarEnv Level -> TyVar -> Level -tyvarLevel tenv tyvar - = case lookupTyVarEnv tenv tyvar of - Just level -> level - Nothing -> tOP_LEVEL + tys = map idType bndrs + poly_tys = map (mkForAllTys offending_tyvars) tys \end{code} %************************************************************************ @@ -724,19 +629,19 @@ tyvarLevel tenv tyvar \begin{code} type LvlM result = UniqSM result +initLvl = initUs_ thenLvl = thenUs returnLvl = returnUs mapLvl = mapUs -mapAndUnzipLvl = mapAndUnzipUs -mapAndUnzip3Lvl = mapAndUnzip3Us \end{code} -We create a let-binding for `interesting' (non-utterly-trivial) -applications, to give them a fighting chance of being floated. - \begin{code} newLvlVar :: Type -> LvlM Id +newLvlVar ty = getUniqueUs `thenLvl` \ uniq -> + returnUs (mkSysLocal SLIT("lvl") uniq ty) -newLvlVar ty us - = mkSysLocal SLIT("lvl") (getUnique us) ty mkUnknownSrcLoc +cloneVar :: Level -> Id -> LvlM Id +cloneVar Top v = returnUs v -- Don't clone top level things +cloneVar _ v = getUniqueUs `thenLvl` \ uniq -> + returnUs (setVarUnique v uniq) \end{code}