X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSetLevels.lhs;h=f8ab29dcd593189f77eb18929143305d51ae4b5a;hb=9d7da331989abcd1844e9d03b8d1e4163796fa85;hp=10c6de626cd9534fa82aef201db449e24a092b75;hpb=d133b73a4d4717892ced072d05e039a54ede0ceb;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/SetLevels.lhs b/ghc/compiler/simplCore/SetLevels.lhs index 10c6de6..f8ab29d 100644 --- a/ghc/compiler/simplCore/SetLevels.lhs +++ b/ghc/compiler/simplCore/SetLevels.lhs @@ -3,42 +3,79 @@ % \section{SetLevels} -We attach binding levels to Core bindings, in preparation for floating -outwards (@FloatOut@). + *************************** + Overview + *************************** -We also let-ify many applications (notably case scrutinees), so they -will have a fighting chance of being floated sensible. +1. We attach binding levels to Core bindings, in preparation for floating + outwards (@FloatOut@). + +2. We also let-ify many expressions (notably case scrutinees), so they + will have a fighting chance of being floated sensible. + +3. 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; indeed, even + that may not be true.) + + NOTE: this can't be done using the uniqAway idea, because the variable + must be unique in the whole program, not just its current scope, + because two variables in different scopes may float out to the + same top level place + + NOTE: Very tiresomely, we must apply this substitution to + the rules stored inside a variable too. + + We do *not* clone top-level bindings, because some of them must not change, + but we *do* clone bindings that are heading for the top level + +4. In the expression + case x of wild { p -> ...wild... } + we substitute x for wild in the RHS of the case alternatives: + case x of wild { p -> ...x... } + This means that a sub-expression involving x is not "trapped" inside the RHS. + And it's not inconvenient because we already have a substitution. + + Note that this is EXACTLY BACKWARDS from the what the simplifier does. + The simplifier tries to get rid of occurrences of x, in favour of wild, + in the hope that there will only be one remaining occurrence of x, namely + the scrutinee of the case, and we can inline it. \begin{code} module SetLevels ( - setLevels, + setLevels, Level(..), tOP_LEVEL, + LevelledBind, LevelledExpr, - incMinorLvl, ltMajLvl, ltLvl, isTopLvl + incMinorLvl, ltMajLvl, ltLvl, isTopLvl, isInlineCtxt ) where #include "HsVersions.h" import CoreSyn -import CoreUtils ( coreExprType, exprIsTrivial, idFreeVars, exprIsBottom +import DynFlags ( FloatOutSwitches(..) ) +import CoreUtils ( exprType, exprIsTrivial, exprIsCheap, mkPiTypes ) +import CoreFVs -- all of it +import CoreSubst ( Subst, emptySubst, extendInScope, extendIdSubst, + cloneIdBndr, cloneRecIdBndrs ) +import Id ( Id, idType, mkSysLocal, isOneShotLambda, + zapDemandIdInfo, + idSpecialisation, idWorkerInfo, setIdInfo ) -import FreeVars -- all of it -import Id ( Id, idType, mkSysLocal ) -import Var ( IdOrTyVar ) -import VarEnv -import VarSet -import Type ( isUnLiftedType, mkTyVarTys, mkForAllTys, Type ) +import IdInfo ( workerExists, vanillaIdInfo, isEmptySpecInfo ) +import Var ( Var ) import VarSet import VarEnv -import UniqSupply ( initUs_, thenUs, returnUs, mapUs, mapAndUnzipUs, getUniqueUs, - mapAndUnzip3Us, UniqSM, UniqSupply ) -import Maybes ( maybeToBool ) -import Util ( zipWithEqual, zipEqual ) +import Name ( getOccName ) +import OccName ( occNameString ) +import Type ( isUnLiftedType, Type ) +import BasicTypes ( TopLevelFlag(..) ) +import UniqSupply +import Util ( sortLe, isSingleton, count ) import Outputable - -isLeakFreeType x y = False -- safe option; ToDo +import FastString \end{code} %************************************************************************ @@ -48,11 +85,11 @@ isLeakFreeType x y = False -- safe option; ToDo %************************************************************************ \begin{code} -data 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 +data Level = InlineCtxt -- A level that's used only for + -- the context parameter ctxt_lvl + | 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 @@ -71,86 +108,99 @@ a_0 = let b_? = ... in x_1 = ... b ... in ... \end{verbatim} -Level 0 0 will make something get floated to a top-level "equals", -@Top@ makes it go right to the top. - The main function @lvlExpr@ carries a ``context level'' (@ctxt_lvl@). That's meant to be the level number of the enclosing binder in the final (floated) program. If the level number of a sub-expression is less than that of the context, then it might be worth let-binding the -sub-expression so that it will indeed float. This context level starts -at @Level 0 0@; it is never @Top@. +sub-expression so that it will indeed float. + +If you can float to level @Level 0 0@ worth doing so because then your +allocation becomes static instead of dynamic. We always start with +context @Level 0 0@. + + +InlineCtxt +~~~~~~~~~~ +@InlineCtxt@ very similar to @Level 0 0@, but is used for one purpose: +to say "don't float anything out of here". That's exactly what we +want for the body of an INLINE, where we don't want to float anything +out at all. See notes with lvlMFE below. + +But, check this out: + +-- At one time I tried the effect of not float anything out of an InlineMe, +-- but it sometimes works badly. For example, consider PrelArr.done. It +-- has the form __inline (\d. e) +-- where e doesn't mention d. If we float this to +-- __inline (let x = e in \d. x) +-- things are bad. The inliner doesn't even inline it because it doesn't look +-- like a head-normal form. So it seems a lesser evil to let things float. +-- In SetLevels we do set the context to (Level 0 0) when we get to an InlineMe +-- which discourages floating out. + +So the conclusion is: don't do any floating at all inside an InlineMe. +(In the above example, don't float the {x=e} out of the \d.) + +One particular case is that of workers: we don't want to float the +call to the worker outside the wrapper, otherwise the worker might get +inlined into the floated expression, and an importing module won't see +the worker at all. \begin{code} type LevelledExpr = TaggedExpr Level -type LevelledArg = TaggedArg Level type LevelledBind = TaggedBind Level -tOP_LEVEL = Top +tOP_LEVEL = Level 0 0 +iNLINE_CTXT = InlineCtxt incMajorLvl :: Level -> Level -incMajorLvl Top = Level 1 0 +-- For InlineCtxt we ignore any inc's; we don't want +-- to do any floating at all; see notes above +incMajorLvl InlineCtxt = InlineCtxt incMajorLvl (Level major minor) = Level (major+1) 0 incMinorLvl :: Level -> Level -incMinorLvl Top = Level 0 1 +incMinorLvl InlineCtxt = InlineCtxt incMinorLvl (Level major minor) = Level major (minor+1) maxLvl :: Level -> Level -> Level -maxLvl Top l2 = l2 -maxLvl l1 Top = l1 +maxLvl InlineCtxt l2 = l2 +maxLvl l1 InlineCtxt = l1 maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2) | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1 | otherwise = l2 ltLvl :: Level -> Level -> Bool -ltLvl l1 Top = False -ltLvl Top (Level _ _) = True +ltLvl any_lvl InlineCtxt = False +ltLvl InlineCtxt (Level _ _) = True ltLvl (Level maj1 min1) (Level maj2 min2) = (maj1 < maj2) || (maj1 == maj2 && min1 < min2) ltMajLvl :: Level -> Level -> Bool -- Tells if one level belongs to a difft *lambda* level to another -ltMajLvl l1 Top = False -ltMajLvl Top (Level 0 _) = False -ltMajLvl Top (Level _ _) = True +ltMajLvl any_lvl InlineCtxt = False +ltMajLvl InlineCtxt (Level maj2 _) = 0 < maj2 ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2 isTopLvl :: Level -> Bool -isTopLvl Top = True -isTopLvl other = False +isTopLvl (Level 0 0) = True +isTopLvl other = False -isTopMajLvl :: Level -> Bool -- Tells if it's the top *lambda* level -isTopMajLvl Top = True -isTopMajLvl (Level maj _) = maj == 0 +isInlineCtxt :: Level -> Bool +isInlineCtxt InlineCtxt = True +isInlineCtxt other = False instance Outputable Level where - ppr Top = ptext SLIT("") + ppr InlineCtxt = text "" ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ] -\end{code} -\begin{code} -type LevelEnv = VarEnv Level - -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 +instance Eq Level where + InlineCtxt == InlineCtxt = True + (Level maj1 min1) == (Level maj2 min2) = maj1==maj2 && min1==min2 + l1 == l2 = False \end{code} + %************************************************************************ %* * \subsection{Main level-setting code} @@ -158,11 +208,12 @@ maxTyVarLvl env var lvl | isId var = lvl %************************************************************************ \begin{code} -setLevels :: [CoreBind] +setLevels :: FloatOutSwitches + -> [CoreBind] -> UniqSupply -> [LevelledBind] -setLevels binds us +setLevels float_lams binds us = initLvl us (do_them binds) where -- "do_them"'s main business is to thread the monad along @@ -172,53 +223,18 @@ setLevels binds us do_them [] = returnLvl [] do_them (b:bs) - = lvlTopBind b `thenLvl` \ (lvld_bind, _) -> - do_them bs `thenLvl` \ lvld_binds -> - returnLvl (lvld_bind ++ lvld_binds) + = lvlTopBind init_env b `thenLvl` \ (lvld_bind, _) -> + do_them bs `thenLvl` \ lvld_binds -> + returnLvl (lvld_bind : lvld_binds) -initialEnv = emptyVarEnv + init_env = initialEnv float_lams -lvlTopBind (NonRec binder rhs) - = lvlBind Top initialEnv (AnnNonRec binder (freeVars rhs)) +lvlTopBind env (NonRec binder rhs) + = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs)) -- Rhs can have no free vars! -lvlTopBind (Rec pairs) - = lvlBind Top initialEnv (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs]) -\end{code} - -%************************************************************************ -%* * -\subsection{Bindings} -%* * -%************************************************************************ - -The binding stuff works for top level too. - -\begin{code} -lvlBind :: Level - -> LevelEnv - -> CoreBindWithFVs - -> LvlM ([LevelledBind], LevelEnv) - -lvlBind ctxt_lvl env (AnnNonRec name rhs) - = setFloatLevel (Just name) ctxt_lvl env rhs ty `thenLvl` \ (final_lvl, rhs') -> - let - new_env = extendVarEnv env name final_lvl - in - returnLvl ([NonRec (name, final_lvl) rhs'], new_env) - where - ty = idType name - - -lvlBind ctxt_lvl env (AnnRec pairs) - = decideRecFloatLevel ctxt_lvl env binders rhss `thenLvl` \ (final_lvl, extra_binds, rhss') -> - let - binders_w_lvls = binders `zip` repeat final_lvl - new_env = extendVarEnvList env binders_w_lvls - in - returnLvl (extra_binds ++ [Rec (zipEqual "lvlBind" binders_w_lvls rhss')], new_env) - where - (binders,rhss) = unzip pairs +lvlTopBind env (Rec pairs) + = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs]) \end{code} %************************************************************************ @@ -235,9 +251,7 @@ lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression \end{code} The @ctxt_lvl@ is, roughly, the level of the innermost enclosing -binder. - -Here's an example +binder. Here's an example v = \x -> ...\y -> let r = case (..x..) of ..x.. @@ -252,17 +266,25 @@ 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 _ _ (_, AnnType ty) = returnLvl (Type ty) -lvlExpr _ _ (_, AnnVar v) = returnLvl (Var v) - -lvlExpr ctxt_lvl env (_, AnnCon con args) - = mapLvl (lvlExpr ctxt_lvl env) args `thenLvl` \ args' -> - returnLvl (Con con args') +lvlExpr _ _ (_, AnnType ty) = returnLvl (Type ty) +lvlExpr _ env (_, AnnVar v) = returnLvl (lookupVar env v) +lvlExpr _ env (_, AnnLit lit) = returnLvl (Lit lit) lvlExpr ctxt_lvl env (_, AnnApp fun arg) - = lvlExpr ctxt_lvl env fun `thenLvl` \ fun' -> - lvlMFE ctxt_lvl env arg `thenLvl` \ arg' -> + = lvl_fun fun `thenLvl` \ fun' -> + lvlMFE False ctxt_lvl env arg `thenLvl` \ arg' -> returnLvl (App fun' arg') + where +-- gaw 2004 + lvl_fun (_, AnnCase _ _ _ _) = lvlMFE True ctxt_lvl env fun + lvl_fun other = lvlExpr ctxt_lvl env fun + -- We don't do MFE on partial applications generally, + -- but we do if the function is big and hairy, like a case + +lvlExpr ctxt_lvl env (_, AnnNote InlineMe expr) +-- Don't float anything out of an InlineMe; hence the iNLINE_CTXT + = lvlExpr iNLINE_CTXT env expr `thenLvl` \ expr' -> + returnLvl (Note InlineMe expr') lvlExpr ctxt_lvl env (_, AnnNote note expr) = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' -> @@ -275,319 +297,319 @@ lvlExpr ctxt_lvl env (_, AnnNote note expr) -- 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') +lvlExpr ctxt_lvl env expr@(_, AnnLam bndr rhs) + = lvlMFE True new_lvl new_env body `thenLvl` \ new_body -> + returnLvl (mkLams new_bndrs new_body) + where + (bndrs, body) = collectAnnBndrs expr + (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs + new_env = extendLvlEnv env new_bndrs + -- At one time we called a special verion of collectBinders, + -- which ignored coercions, because we don't want to split + -- a lambda like this (\x -> coerce t (\s -> ...)) + -- This used to happen quite a bit in state-transformer programs, + -- but not nearly so much now non-recursive newtypes are transparent. + -- [See SetLevels rev 1.50 for a version with this approach.] + +lvlExpr ctxt_lvl env (_, AnnLet (AnnNonRec bndr rhs) body) + | isUnLiftedType (idType bndr) + -- Treat unlifted let-bindings (let x = b in e) just like (case b of x -> e) + -- That is, leave it exactly where it is + -- We used to float unlifted bindings too (e.g. to get a cheap primop + -- outside a lambda (to see how, look at lvlBind in rev 1.58) + -- but an unrelated change meant that these unlifed bindings + -- could get to the top level which is bad. And there's not much point; + -- unlifted bindings are always cheap, and so hardly worth floating. + = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' -> + lvlExpr incd_lvl env' body `thenLvl` \ body' -> + returnLvl (Let (NonRec bndr' rhs') body') where - bndr_is_id = isId bndr - bndr_is_tyvar = isTyVar bndr - (bndrs, body) = go rhs - - incd_lvl | bndr_is_id = incMajorLvl ctxt_lvl - | otherwise = incMinorLvl ctxt_lvl - lvld_bndrs = [(b,incd_lvl) | b <- (bndr:bndrs)] - new_env = extendVarEnvList 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) + incd_lvl = incMinorLvl ctxt_lvl + bndr' = TB bndr incd_lvl + env' = extendLvlEnv env [bndr'] 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') + = lvlBind NotTopLevel ctxt_lvl env bind `thenLvl` \ (bind', new_env) -> + lvlExpr ctxt_lvl new_env body `thenLvl` \ body' -> + returnLvl (Let bind' body') + +lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr ty alts) + = lvlMFE True ctxt_lvl env expr `thenLvl` \ expr' -> + let + alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl + in + mapLvl (lvl_alt alts_env) alts `thenLvl` \ alts' -> + returnLvl (Case expr' (TB case_bndr incd_lvl) ty alts') where - expr_type = coreExprType (deAnnotate expr) incd_lvl = incMinorLvl ctxt_lvl - alts_env = extendVarEnv env case_bndr incd_lvl - - lvl_alt (con, bs, rhs) - = let - bs' = [ (b, incd_lvl) | b <- bs ] - new_env = extendVarEnvList alts_env bs' - in - lvlMFE incd_lvl new_env rhs `thenLvl` \ rhs' -> + + lvl_alt alts_env (con, bs, rhs) + = lvlMFE True incd_lvl new_env rhs `thenLvl` \ rhs' -> returnLvl (con, bs', rhs') + where + bs' = [ TB b incd_lvl | b <- bs ] + new_env = extendLvlEnv alts_env bs' \end{code} @lvlMFE@ is just like @lvlExpr@, except that it might let-bind the expression, so that it can itself be floated. +[NOTE: unlifted MFEs] +We don't float unlifted MFEs, which potentially loses big opportunites. +For example: + \x -> f (h y) +where h :: Int -> Int# is expensive. We'd like to float the (h y) outside +the \x, but we don't because it's unboxed. Possible solution: box it. + \begin{code} -lvlMFE :: Level -- Level of innermost enclosing lambda/tylam +lvlMFE :: Bool -- True <=> strict context [body of case or let] + -> Level -- Level of innermost enclosing lambda/tylam -> LevelEnv -- Level of in-scope names/tyvars -> CoreExprWithFVs -- input expression -> LvlM LevelledExpr -- Result expression -lvlMFE ctxt_lvl env (_, AnnType ty) +lvlMFE strict_ctxt 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 Nothing {- Not already let-bound -} - ctxt_lvl env ann_expr ty `thenLvl` \ (final_lvl, expr') -> - returnLvl expr' +lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _) + | isUnLiftedType ty -- Can't let-bind it; see [NOTE: unlifted MFEs] + || isInlineCtxt ctxt_lvl -- Don't float out of an __inline__ context + || exprIsTrivial expr -- Never float if it's trivial + || not good_destination + = -- Don't float it out + lvlExpr ctxt_lvl env ann_expr + + | otherwise -- Float it out! + = lvlFloatRhs abs_vars dest_lvl env ann_expr `thenLvl` \ expr' -> + newLvlVar "lvl" abs_vars ty `thenLvl` \ var -> + returnLvl (Let (NonRec (TB var dest_lvl) expr') + (mkVarApps (Var var) abs_vars)) where - ty = coreExprType (deAnnotate ann_expr) + expr = deAnnotate ann_expr + ty = exprType expr + dest_lvl = destLevel env fvs (isFunction ann_expr) + abs_vars = abstractVars dest_lvl env fvs + + -- A decision to float entails let-binding this thing, and we only do + -- that if we'll escape a value lambda, or will go to the top level. + good_destination + | dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda + = not (exprIsCheap expr) || isTopLvl dest_lvl + -- Even if it escapes a value lambda, we only + -- float if it's not cheap (unless it'll get all the + -- way to the top). I've seen cases where we + -- float dozens of tiny free expressions, which cost + -- more to allocate than to evaluate. + -- NB: exprIsCheap is also true of bottom expressions, which + -- is good; we don't want to share them + -- + -- It's only Really Bad to float a cheap expression out of a + -- strict context, because that builds a thunk that otherwise + -- would never be built. So another alternative would be to + -- add + -- || (strict_ctxt && not (exprIsBottom expr)) + -- to the condition above. We should really try this out. + + | otherwise -- Does not escape a value lambda + = isTopLvl dest_lvl -- Only float if we are going to the top level + && floatConsts env -- and the floatConsts flag is on + && not strict_ctxt -- Don't float from a strict context + -- We are keen to float something to the top level, even if it does not + -- escape a lambda, because then it needs no allocation. But it's controlled + -- by a flag, because doing this too early loses opportunities for RULES + -- which (needless to say) are important in some nofib programs + -- (gcd is an example). + -- + -- Beware: + -- concat = /\ a -> foldr ..a.. (++) [] + -- was getting turned into + -- concat = /\ a -> lvl a + -- lvl = /\ a -> foldr ..a.. (++) [] + -- which is pretty stupid. Hence the strict_ctxt test \end{code} %************************************************************************ %* * -\subsection{Deciding floatability} +\subsection{Bindings} %* * %************************************************************************ -@setFloatLevel@ is used for let-bound right-hand-sides, or for MFEs which -are being created as let-bindings - -Decision tree: -Let Bound? - YES. -> (a) try abstracting type variables. - If we abstract type variables it will go further, that is, past more - lambdas. same as asking if the level number given by the free - variables is less than the level number given by free variables - and type variables together. - Abstract offending type variables, e.g. - change f ty a b - to let v = /\ty' -> f ty' a b - in v ty - so that v' is not stopped by the level number of ty - tag the original let with its level number - (from its variables and type variables) - NO. is a WHNF? - YES. -> No point in let binding to float a WHNF. - Pin (leave) expression here. - NO. -> Will float past a lambda? - (check using free variables only, not type variables) - YES. -> do the same as (a) above. - NO. -> No point in let binding if it is not going anywhere - Pin (leave) expression here. +The binding stuff works for top level too. \begin{code} -setFloatLevel :: Maybe Id -- Just id <=> the expression is already let-bound to id - -- Nothing <=> it's a possible MFE - -> Level -- of context - -> LevelEnv - - -> CoreExprWithFVs -- Original rhs - -> Type -- Type of rhs - - -> LvlM (Level, -- Level to attribute to this let-binding - LevelledExpr) -- Final rhs - -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 --- choose to float even trivial let-bound things because it doesn't do --- any harm, and not floating it may pin something important. For --- example --- --- x = let v = [] --- w = 1:v --- in ... --- --- Here, if we don't float v we won't float w, which is Bad News. --- If this gives any problems we could restrict the idea to things destined --- for top level. - - | not alreadyLetBound - && (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 env expr `thenLvl` \ expr' -> - returnLvl (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 expr_lvl env expr `thenLvl` \ expr' -> - returnLvl (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 env lvl_after_ty_abstr expr - `thenLvl` \ final_expr -> - returnLvl (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 - alreadyLetBound = maybeToBool maybe_let_bound - - 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 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} +lvlBind :: TopLevelFlag -- Used solely to decide whether to clone + -> Level -- Context level; might be Top even for bindings nested in the RHS + -- of a top level binding + -> LevelEnv + -> CoreBindWithFVs + -> LvlM (LevelledBind, LevelEnv) -Abstract wrt tyvars, by making it just as if we had seen +lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_)) + | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe + = lvlExpr ctxt_lvl env rhs `thenLvl` \ rhs' -> + returnLvl (NonRec (TB bndr ctxt_lvl) rhs', env) - let v = /\a1..an. E - in v a1 ... an + | null abs_vars + = -- No type abstraction; clone existing binder + lvlExpr dest_lvl env rhs `thenLvl` \ rhs' -> + cloneVar top_lvl env bndr ctxt_lvl dest_lvl `thenLvl` \ (env', bndr') -> + returnLvl (NonRec (TB bndr' dest_lvl) rhs', env') -instead of simply E. The idea is that v can be freely floated, since it -has no free type variables. Of course, if E has no free type -variables, then we just return E. + | otherwise + = -- Yes, type abstraction; create a new binder, extend substitution, etc + lvlFloatRhs abs_vars dest_lvl env rhs `thenLvl` \ rhs' -> + newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (env', [bndr']) -> + returnLvl (NonRec (TB bndr' dest_lvl) rhs', env') -\begin{code} -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 = mkLams tyvar_lvls expr' - poly_var_binding = NonRec (poly_var, lvl) poly_var_rhs - 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 where - poly_ty = mkForAllTys offending_tyvars ty - - -- These defns are just like those in the TyLam case of lvlExpr - incd_lvl = incMinorLvl lvl - tyvar_lvls = [(tv,incd_lvl) | tv <- offending_tyvars] - new_env = extendVarEnvList env tyvar_lvls + bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr + abs_vars = abstractVars dest_lvl env bind_fvs + dest_lvl = destLevel env bind_fvs (isFunction rhs) \end{code} -Recursive definitions. We want to transform - - letrec - x1 = e1 - ... - xn = en - in - body - -to - - letrec - x1' = /\ ab -> let D' in e1 - ... - xn' = /\ ab -> let D' in en - in - 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: - - x1_cl = x1' ab - ... - xn_cl = xn' ab - -The "_cl" indicates that in D, the level numbers on the xi are the context level -number; type applications aren't worth floating. The D' decls are -similar: - - x1_ll = x1' ab - ... - xn_ll = xn' ab - -but differ in their level numbers; here the ab are the newly-introduced -type lambdas. \begin{code} -decideRecFloatLevel ctxt_lvl env ids rhss - | 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) +lvlBind top_lvl ctxt_lvl env (AnnRec pairs) + | isInlineCtxt ctxt_lvl -- Don't do anything inside InlineMe + = mapLvl (lvlExpr ctxt_lvl env) rhss `thenLvl` \ rhss' -> + returnLvl (Rec ([TB b ctxt_lvl | b <- bndrs] `zip` rhss'), env) + + | null abs_vars + = cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl `thenLvl` \ (new_env, new_bndrs) -> + mapLvl (lvlExpr ctxt_lvl new_env) rhss `thenLvl` \ new_rhss -> + returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env) + + | isSingleton pairs && count isId abs_vars > 1 + = -- Special case for self recursion where there are + -- several variables carried around: build a local loop: + -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars + -- This just makes the closures a bit smaller. If we don't do + -- this, allocation rises significantly on some programs + -- + -- We could elaborate it for the case where there are several + -- mutually functions, but it's quite a bit more complicated + -- + -- This all seems a bit ad hoc -- sigh let - incd_lvl = incMinorLvl ids_only_lvl - tyvars_w_lvl = [(var,incd_lvl) | var <- offending_tyvars] - ids_w_lvl = [(var,incd_lvl) | var <- ids] - new_env = extendVarEnvList env (tyvars_w_lvl ++ ids_w_lvl) + (bndr,rhs) = head pairs + (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars + rhs_env = extendLvlEnv env abs_vars_w_lvls in - mapLvl (lvlExpr incd_lvl new_env) rhss `thenLvl` \ rhss' -> - mapLvl newLvlVar poly_tys `thenLvl` \ poly_vars -> + cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl `thenLvl` \ (rhs_env', new_bndr) -> 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 = [ 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_lvl d_rhss + (lam_bndrs, rhs_body) = collectAnnBndrs rhs + (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs + body_env = extendLvlEnv rhs_env' new_lam_bndrs + in + lvlExpr body_lvl body_env rhs_body `thenLvl` \ new_rhs_body -> + newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (poly_env, [poly_bndr]) -> + returnLvl (Rec [(TB poly_bndr dest_lvl, + mkLams abs_vars_w_lvls $ + mkLams new_lam_bndrs $ + Let (Rec [(TB new_bndr rhs_lvl, mkLams new_lam_bndrs new_rhs_body)]) + (mkVarApps (Var new_bndr) lam_bndrs))], + poly_env) + + | otherwise -- Non-null abs_vars + = newPolyBndrs dest_lvl env abs_vars bndrs `thenLvl` \ (new_env, new_bndrs) -> + mapLvl (lvlFloatRhs abs_vars dest_lvl new_env) rhss `thenLvl` \ new_rhss -> + returnLvl (Rec ([TB b dest_lvl | b <- new_bndrs] `zip` new_rhss), new_env) - poly_var_rhss = [ mkLams tyvars_w_lvl (mkLets local_binds rhs') - | rhs' <- rhss' - ] + where + (bndrs,rhss) = unzip pairs - poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars] - poly_var_rhss + -- Finding the free vars of the binding group is annoying + bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs + | (bndr, (rhs_fvs,_)) <- pairs]) + `minusVarSet` + mkVarSet bndrs - 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 + dest_lvl = destLevel env bind_fvs (all isFunction rhss) + abs_vars = abstractVars dest_lvl env bind_fvs - | otherwise - = -- Let it float freely - let - ids_w_lvls = ids `zip` repeat expr_lvl - new_env = extendVarEnvList env ids_w_lvls - in - mapLvl (lvlExpr expr_lvl new_env) rhss `thenLvl` \ rhss' -> - returnLvl (expr_lvl, [], rhss') +---------------------------------------------------- +-- Three help functons for the type-abstraction case +lvlFloatRhs abs_vars dest_lvl env rhs + = lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' -> + returnLvl (mkLams abs_vars_w_lvls rhs') where - -- Finding the free vars of the binding group is annoying - bind_fvs = (unionVarSets (map fst rhss) `unionVarSet` unionVarSets (map idFreeVars ids)) - `minusVarSet` - mkVarSet ids + (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars + rhs_env = extendLvlEnv env abs_vars_w_lvls +\end{code} - 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 = 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 +%************************************************************************ +%* * +\subsection{Deciding floatability} +%* * +%************************************************************************ + +\begin{code} +lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [TaggedBndr Level]) +-- Compute the levels for the binders of a lambda group +-- The binders returned are exactly the same as the ones passed, +-- but they are now paired with a level +lvlLamBndrs lvl [] + = (lvl, []) + +lvlLamBndrs lvl bndrs + = go (incMinorLvl lvl) + False -- Havn't bumped major level in this group + [] bndrs + where + go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs) + | isId bndr && -- Go to the next major level if this is a value binder, + not bumped_major && -- and we havn't already gone to the next level (one jump per group) + not (isOneShotLambda bndr) -- and it isn't a one-shot lambda + = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs + + | otherwise + = go old_lvl bumped_major (TB bndr old_lvl : rev_lvld_bndrs) bndrs + + where + new_lvl = incMajorLvl old_lvl + + go old_lvl _ rev_lvld_bndrs [] + = (old_lvl, reverse rev_lvld_bndrs) + -- a lambda like this (\x -> coerce t (\s -> ...)) + -- This happens quite a bit in state-transformer programs +\end{code} - tys = map idType ids - poly_tys = map (mkForAllTys offending_tyvars) tys +\begin{code} + -- Destintion level is the max Id level of the expression + -- (We'll abstract the type variables, if any.) +destLevel :: LevelEnv -> VarSet -> Bool -> Level +destLevel env fvs is_function + | floatLams env + && is_function = tOP_LEVEL -- Send functions to top level; see + -- the comments with isFunction + | otherwise = maxIdLevel env fvs + +isFunction :: CoreExprWithFVs -> Bool +-- The idea here is that we want to float *functions* to +-- the top level. This saves no work, but +-- (a) it can make the host function body a lot smaller, +-- and hence inlinable. +-- (b) it can also save allocation when the function is recursive: +-- h = \x -> letrec f = \y -> ...f...y...x... +-- in f x +-- becomes +-- f = \x y -> ...(f x)...y...x... +-- h = \x -> f x x +-- No allocation for f now. +-- We may only want to do this if there are sufficiently few free +-- variables. We certainly only want to do it for values, and not for +-- constructors. So the simple thing is just to look for lambdas +isFunction (_, AnnLam b e) | isId b = True + | otherwise = isFunction e +isFunction (_, AnnNote n e) = isFunction e +isFunction other = False \end{code} + %************************************************************************ %* * \subsection{Free-To-Level Monad} @@ -595,21 +617,231 @@ decideRecFloatLevel ctxt_lvl env ids rhss %************************************************************************ \begin{code} +type LevelEnv = (FloatOutSwitches, + VarEnv Level, -- Domain is *post-cloned* TyVars and Ids + Subst, -- Domain is pre-cloned Ids; tracks the in-scope set + -- so that subtitution is capture-avoiding + IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids + -- We clone let-bound variables so that they are still + -- distinct when floated out; hence the SubstEnv/IdEnv. + -- (see point 3 of the module overview comment). + -- We also use these envs when making a variable polymorphic + -- because we want to float it out past a big lambda. + -- + -- The SubstEnv and IdEnv always implement the same mapping, but the + -- SubstEnv maps to CoreExpr and the IdEnv to LevelledExpr + -- Since the range is always a variable or type application, + -- there is never any difference between the two, but sadly + -- the types differ. The SubstEnv is used when substituting in + -- a variable's IdInfo; the IdEnv when we find a Var. + -- + -- In addition the IdEnv records a list of tyvars free in the + -- type application, just so we don't have to call freeVars on + -- the type application repeatedly. + -- + -- The domain of the both envs is *pre-cloned* Ids, though + -- + -- The domain of the VarEnv Level is the *post-cloned* Ids + +initialEnv :: FloatOutSwitches -> LevelEnv +initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv) + +floatLams :: LevelEnv -> Bool +floatLams (FloatOutSw float_lams _, _, _, _) = float_lams + +floatConsts :: LevelEnv -> Bool +floatConsts (FloatOutSw _ float_consts, _, _, _) = float_consts + +extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv +-- Used when *not* cloning +extendLvlEnv (float_lams, lvl_env, subst, id_env) prs + = (float_lams, + foldl add_lvl lvl_env prs, + foldl del_subst subst prs, + foldl del_id id_env prs) + where + add_lvl env (TB v l) = extendVarEnv env v l + del_subst env (TB v _) = extendInScope env v + del_id env (TB v _) = delVarEnv env v + -- We must remove any clone for this variable name in case of + -- shadowing. This bit me in the following case + -- (in nofib/real/gg/Spark.hs): + -- + -- case ds of wild { + -- ... -> case e of wild { + -- ... -> ... wild ... + -- } + -- } + -- + -- The inside occurrence of @wild@ was being replaced with @ds@, + -- incorrectly, because the SubstEnv was still lying around. Ouch! + -- KSW 2000-07. + +-- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can +-- (see point 4 of the module overview comment) +extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl + = (float_lams, + extendVarEnv lvl_env case_bndr lvl, + extendIdSubst subst case_bndr (Var scrut_var), + extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var)) + +extendCaseBndrLvlEnv env scrut case_bndr lvl + = extendLvlEnv env [TB case_bndr lvl] + +extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs + = (float_lams, + foldl add_lvl lvl_env bndr_pairs, + foldl add_subst subst bndr_pairs, + foldl add_id id_env bndr_pairs) + where + add_lvl env (v,v') = extendVarEnv env v' dest_lvl + add_subst env (v,v') = extendIdSubst env v (mkVarApps (Var v') abs_vars) + add_id env (v,v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars) + +extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs + = (float_lams, + foldl add_lvl lvl_env bndr_pairs, + new_subst, + foldl add_id id_env bndr_pairs) + where + add_lvl env (v,v') = extendVarEnv env v' lvl + add_id env (v,v') = extendVarEnv env v ([v'], Var v') + + +maxIdLevel :: LevelEnv -> VarSet -> Level +maxIdLevel (_, lvl_env,_,id_env) var_set + = foldVarSet max_in tOP_LEVEL var_set + where + max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of + Just (abs_vars, _) -> abs_vars + Nothing -> [in_var]) + + max_out out_var lvl + | isId out_var = case lookupVarEnv lvl_env out_var of + Just lvl' -> maxLvl lvl' lvl + Nothing -> lvl + | otherwise = lvl -- Ignore tyvars in *maxIdLevel* + +lookupVar :: LevelEnv -> Id -> LevelledExpr +lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of + Just (_, expr) -> expr + other -> Var v + +abstractVars :: Level -> LevelEnv -> VarSet -> [Var] + -- Find the variables in fvs, free vars of the target expresion, + -- whose level is greater than the destination level + -- These are the ones we are going to abstract out +abstractVars dest_lvl env fvs + = uniq (sortLe le [var | fv <- varSetElems fvs, var <- absVarsOf dest_lvl env fv]) + where + -- Sort the variables so we don't get + -- mixed-up tyvars and Ids; it's just messy + v1 `le` v2 = case (isId v1, isId v2) of + (True, False) -> False + (False, True) -> True + other -> v1 <= v2 -- Same family + + uniq :: [Var] -> [Var] + -- Remove adjacent duplicates; the sort will have brought them together + uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs) + | otherwise = v1 : uniq (v2:vs) + uniq vs = vs + +absVarsOf :: Level -> LevelEnv -> Var -> [Var] + -- If f is free in the expression, and f maps to poly_f a b c in the + -- current substitution, then we must report a b c as candidate type + -- variables +absVarsOf dest_lvl (_, lvl_env, _, id_env) v + | isId v + = [zap av2 | av1 <- lookup_avs v, av2 <- add_tyvars av1, abstract_me av2] + + | otherwise + = if abstract_me v then [v] else [] + + where + abstract_me v = case lookupVarEnv lvl_env v of + Just lvl -> dest_lvl `ltLvl` lvl + Nothing -> False + + lookup_avs v = case lookupVarEnv id_env v of + Just (abs_vars, _) -> abs_vars + Nothing -> [v] + + add_tyvars v | isId v = v : varSetElems (idFreeTyVars v) + | otherwise = [v] + + -- We are going to lambda-abstract, so nuke any IdInfo, + -- and add the tyvars of the Id (if necessary) + zap v | isId v = WARN( workerExists (idWorkerInfo v) || + not (isEmptySpecInfo (idSpecialisation v)), + text "absVarsOf: discarding info on" <+> ppr v ) + setIdInfo v vanillaIdInfo + | otherwise = v +\end{code} + +\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) +newPolyBndrs dest_lvl env abs_vars bndrs + = getUniquesUs `thenLvl` \ uniqs -> + let + new_bndrs = zipWith mk_poly_bndr bndrs uniqs + in + returnLvl (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs) + where + mk_poly_bndr bndr uniq = mkSysLocal (mkFastString str) uniq poly_ty + where + str = "poly_" ++ occNameString (getOccName bndr) + poly_ty = mkPiTypes abs_vars (idType bndr) + + +newLvlVar :: String + -> [CoreBndr] -> Type -- Abstract wrt these bndrs + -> LvlM Id +newLvlVar str vars body_ty + = getUniqueUs `thenLvl` \ uniq -> + returnUs (mkSysLocal (mkFastString str) uniq (mkPiTypes vars body_ty)) + +-- The deeply tiresome thing is that we have to apply the substitution +-- to the rules inside each Id. Grr. But it matters. + +cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id) +cloneVar TopLevel env v ctxt_lvl dest_lvl + = returnUs (env, v) -- Don't clone top level things +cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl + = ASSERT( isId v ) + getUs `thenLvl` \ us -> + let + (subst', v1) = cloneIdBndr subst us v + v2 = zap_demand ctxt_lvl dest_lvl v1 + env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)] + in + returnUs (env', v2) + +cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id]) +cloneRecVars TopLevel env vs ctxt_lvl dest_lvl + = returnUs (env, vs) -- Don't clone top level things +cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl + = ASSERT( all isId vs ) + getUs `thenLvl` \ us -> + let + (subst', vs1) = cloneRecIdBndrs subst us vs + vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1 + env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2) + in + returnUs (env', vs2) + + -- VERY IMPORTANT: we must zap the demand info + -- if the thing is going to float out past a lambda +zap_demand dest_lvl ctxt_lvl id + | ctxt_lvl == dest_lvl = id -- Stays put + | otherwise = zapDemandIdInfo id -- Floats out \end{code} +