-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
-%
-\section{SetLevels}
-
-We attach binding levels to Core bindings, in preparation for floating
-outwards (@FloatOut@).
-
-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"
-
-module SetLevels (
- setLevels,
-
- Level(..), tOP_LEVEL,
-
- incMinorLvl, ltMajLvl, ltLvl, isTopLvl
--- not exported: , incMajorLvl, isTopMajLvl, unTopify
- ) where
-
-IMP_Ubiq(){-uitous-}
-
-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 )
-
-isLeakFreeType x y = False -- safe option; ToDo
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Level numbers}
-%* *
-%************************************************************************
-
-\begin{code}
-data Level
- = Top -- Means *really* the top level.
- | 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.
-
-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
-as ``subscripts'')...
-\begin{verbatim}
-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@.
-
-\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
-
-tOP_LEVEL = Top
-
-incMajorLvl :: Level -> Level
-incMajorLvl Top = Level 1 0
-incMajorLvl (Level major minor) = Level (major+1) 0
-
-incMinorLvl :: Level -> Level
-incMinorLvl Top = Level 0 1
-incMinorLvl (Level major minor) = Level major (minor+1)
-
-maxLvl :: Level -> Level -> Level
-maxLvl Top l2 = l2
-maxLvl l1 Top = 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 (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 (Level maj1 _) (Level maj2 _) = maj1 < maj2
-
-isTopLvl :: Level -> Bool
-isTopLvl Top = True
-isTopLvl other = False
-
-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 "<Top>"
- ppr sty (Level maj min) = ppBesides [ ppChar '<', ppInt maj, ppChar ',', ppInt min, ppChar '>' ]
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Main level-setting code}
-%* *
-%************************************************************************
-
-\begin{code}
-setLevels :: [CoreBinding]
- -> UniqSupply
- -> [LevelledBind]
-
-setLevels binds us
- = do_them binds us
- 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 [] = returnLvl []
- do_them (b:bs)
- = lvlTopBind b `thenLvl` \ (lvld_bind, _) ->
- do_them bs `thenLvl` \ lvld_binds ->
- returnLvl (lvld_bind ++ lvld_binds)
-
-initial_envs = (nullIdEnv, nullTyVarEnv)
-
-lvlTopBind (NonRec binder rhs)
- = lvlBind (Level 0 0) initial_envs (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])
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Bindings}
-%* *
-%************************************************************************
-
-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)
-
-lvlBind ctxt_lvl envs@(venv, tenv) (AnnNonRec name rhs)
- = setFloatLevel True {- Already let-bound -}
- ctxt_lvl envs rhs ty `thenLvl` \ (final_lvl, rhs') ->
- let
- new_envs = (addOneToIdEnv venv name final_lvl, tenv)
- in
- returnLvl ([NonRec (name, final_lvl) rhs'], new_envs)
- where
- ty = idType name
-
-
-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
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Setting expression levels}
-%* *
-%************************************************************************
-
-\begin{code}
-lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
- -> LevelEnvs -- Level of in-scope names/tyvars
- -> CoreExprWithFVs -- input expression
- -> LvlM LevelledExpr -- Result expression
-\end{code}
-
-The @ctxt_lvl@ is, roughly, the level of the innermost enclosing
-binder.
-
-Here's an example
-
- v = \x -> ...\y -> let r = case (..x..) of
- ..x..
- in ..
-
-When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's
-the level of @r@, even though it's inside a level-2 @\y@. It's
-important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we
-don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE
---- because it isn't a *maximal* free expression.
-
-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')
- 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')
- 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')
-\end{code}
-
-@lvlMFE@ is just like @lvlExpr@, except that it might let-bind
-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
- -> 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
-
- | 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') ->
- returnLvl expr'
- where
- ty = coreExprType (deAnnotate ann_expr)
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Deciding floatability}
-%* *
-%************************************************************************
-
-@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.
-
-\begin{code}
-setFloatLevel :: Bool -- True <=> the expression is already let-bound
- -- False <=> it's a possible MFE
- -> Level -- of context
- -> LevelEnvs
-
- -> CoreExprWithFVs -- Original 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)...
-
--- 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 = Nil
--- 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
- && (manifestly_whnf || not will_float_past_lambda)
- = -- Pin whnf non-let-bound expressions,
- -- or ones which aren't going anywhere useful
- lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
- returnLvl (ctxt_lvl, expr')
-
- | 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')
-
- | 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
- `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
- 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
- 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]
- -}
-\end{code}
-
-Abstract wrt tyvars, by making it just as if we had seen
-
- let v = /\a1..an. E
- in v a1 ... an
-
-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.
-
-\begin{code}
-abstractWrtTyVars offending_tyvars ty (venv,tenv) lvl expr
- = lvlExpr incd_lvl new_envs expr `thenLvl` \ expr' ->
- newLvlVar poly_ty `thenLvl` \ poly_var ->
- let
- poly_var_rhs = mkTyLam offending_tyvars expr'
- poly_var_binding = NonRec (poly_var, lvl) poly_var_rhs
- poly_var_app = mkTyApp (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, 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)
-\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 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')
-
--}
-
- | 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)
- in
- mapLvl (lvlExpr incd_lvl new_envs) rhss `thenLvl` \ rhss' ->
- mapLvl newLvlVar poly_tys `thenLvl` \ poly_vars ->
- 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]
-
- -- "local_binds" are "D'" in the documentation above
- local_binds = zipWithEqual "SetLevels" NonRec ids_w_incd_lvl d_rhss
-
- poly_var_rhss = [ mkTyLam offending_tyvars (foldr Let rhs' local_binds)
- | rhs' <- rhss' -- mkCoLet* requires Core...
- ]
-
- poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars] poly_var_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
-
- | otherwise
- = -- Let it float freely
- let
- ids_w_lvls = ids `zip` repeat expr_lvl
- new_envs = (growIdEnvList venv ids_w_lvls, tenv)
- in
- mapLvl (lvlExpr (unTopify expr_lvl) new_envs) rhss `thenLvl` \ rhss' ->
- returnLvl (expr_lvl, [], rhss')
-
- where
- tys = map idType ids
-
- fvs = unionManyIdSets [freeVarsOf rhs | rhs <- rhss] `minusIdSet` mkIdSet ids
- tfvs = unionManyTyVarSets [freeTyVarsOf rhs | rhs <- rhss]
- fv_list = idSetToList fvs
- tv_list = tyVarSetToList tfvs
-
- ids_only_lvl = foldr (maxLvl . idLevel venv) tOP_LEVEL fv_list
- tyvars_only_lvl = foldr (maxLvl . tyvarLevel tenv) tOP_LEVEL tv_list
- expr_lvl = ids_only_lvl `maxLvl` tyvars_only_lvl
-
- offending_tyvars
- | ids_only_lvl `ltLvl` tyvars_only_lvl = filter offending tv_list
- | otherwise = []
-
- 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
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Free-To-Level Monad}
-%* *
-%************************************************************************
-
-\begin{code}
-type LvlM result = UniqSM result
-
-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 us
- = mkSysLocal SLIT("lvl") (getUnique us) ty mkUnknownSrcLoc
-\end{code}
+%\r
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998\r
+%\r
+\section{SetLevels}\r
+\r
+ ***************************\r
+ Overview\r
+ ***************************\r
+\r
+1. We attach binding levels to Core bindings, in preparation for floating\r
+ outwards (@FloatOut@).\r
+\r
+2. We also let-ify many expressions (notably case scrutinees), so they\r
+ will have a fighting chance of being floated sensible.\r
+\r
+3. We clone the binders of any floatable let-binding, so that when it is\r
+ floated out it will be unique. (This used to be done by the simplifier\r
+ but the latter now only ensures that there's no shadowing; indeed, even \r
+ that may not be true.)\r
+\r
+ NOTE: this can't be done using the uniqAway idea, because the variable\r
+ must be unique in the whole program, not just its current scope,\r
+ because two variables in different scopes may float out to the\r
+ same top level place\r
+\r
+ NOTE: Very tiresomely, we must apply this substitution to\r
+ the rules stored inside a variable too.\r
+\r
+ We do *not* clone top-level bindings, because some of them must not change,\r
+ but we *do* clone bindings that are heading for the top level\r
+\r
+4. In the expression\r
+ case x of wild { p -> ...wild... }\r
+ we substitute x for wild in the RHS of the case alternatives:\r
+ case x of wild { p -> ...x... }\r
+ This means that a sub-expression involving x is not "trapped" inside the RHS.\r
+ And it's not inconvenient because we already have a substitution.\r
+\r
+ Note that this is EXACTLY BACKWARDS from the what the simplifier does.\r
+ The simplifier tries to get rid of occurrences of x, in favour of wild,\r
+ in the hope that there will only be one remaining occurrence of x, namely\r
+ the scrutinee of the case, and we can inline it. \r
+\r
+\begin{code}\r
+module SetLevels (\r
+ setLevels,\r
+\r
+ Level(..), tOP_LEVEL,\r
+\r
+ incMinorLvl, ltMajLvl, ltLvl, isTopLvl\r
+ ) where\r
+\r
+#include "HsVersions.h"\r
+\r
+import CoreSyn\r
+\r
+import CoreUtils ( exprType, exprIsTrivial, exprIsBottom, mkPiType )\r
+import CoreFVs -- all of it\r
+import Subst\r
+import Id ( Id, idType, mkSysLocal, isOneShotLambda, zapDemandIdInfo,\r
+ idSpecialisation, idWorkerInfo, setIdInfo\r
+ )\r
+import IdInfo ( workerExists, vanillaIdInfo, )\r
+import Var ( Var )\r
+import VarSet\r
+import VarEnv\r
+import Name ( getOccName )\r
+import OccName ( occNameUserString )\r
+import Type ( isUnLiftedType, Type )\r
+import BasicTypes ( TopLevelFlag(..) )\r
+import UniqSupply\r
+import Util ( sortLt, isSingleton, count )\r
+import Outputable\r
+\end{code}\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Level numbers}\r
+%* *\r
+%************************************************************************\r
+\r
+\begin{code}\r
+data Level = Level Int -- Level number of enclosing lambdas\r
+ Int -- Number of big-lambda and/or case expressions between\r
+ -- here and the nearest enclosing lambda\r
+\end{code}\r
+\r
+The {\em level number} on a (type-)lambda-bound variable is the\r
+nesting depth of the (type-)lambda which binds it. The outermost lambda\r
+has level 1, so (Level 0 0) means that the variable is bound outside any lambda.\r
+\r
+On an expression, it's the maximum level number of its free\r
+(type-)variables. On a let(rec)-bound variable, it's the level of its\r
+RHS. On a case-bound variable, it's the number of enclosing lambdas.\r
+\r
+Top-level variables: level~0. Those bound on the RHS of a top-level\r
+definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown\r
+as ``subscripts'')...\r
+\begin{verbatim}\r
+a_0 = let b_? = ... in\r
+ x_1 = ... b ... in ...\r
+\end{verbatim}\r
+\r
+The main function @lvlExpr@ carries a ``context level'' (@ctxt_lvl@).\r
+That's meant to be the level number of the enclosing binder in the\r
+final (floated) program. If the level number of a sub-expression is\r
+less than that of the context, then it might be worth let-binding the\r
+sub-expression so that it will indeed float. This context level starts\r
+at @Level 0 0@.\r
+\r
+\begin{code}\r
+type LevelledExpr = TaggedExpr Level\r
+type LevelledBind = TaggedBind Level\r
+\r
+tOP_LEVEL = Level 0 0\r
+\r
+incMajorLvl :: Level -> Level\r
+incMajorLvl (Level major minor) = Level (major+1) 0\r
+\r
+incMinorLvl :: Level -> Level\r
+incMinorLvl (Level major minor) = Level major (minor+1)\r
+\r
+maxLvl :: Level -> Level -> Level\r
+maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)\r
+ | (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1\r
+ | otherwise = l2\r
+\r
+ltLvl :: Level -> Level -> Bool\r
+ltLvl (Level maj1 min1) (Level maj2 min2)\r
+ = (maj1 < maj2) || (maj1 == maj2 && min1 < min2)\r
+\r
+ltMajLvl :: Level -> Level -> Bool\r
+ -- Tells if one level belongs to a difft *lambda* level to another\r
+ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2\r
+\r
+isTopLvl :: Level -> Bool\r
+isTopLvl (Level 0 0) = True\r
+isTopLvl other = False\r
+\r
+instance Outputable Level where\r
+ ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]\r
+\r
+instance Eq Level where\r
+ (Level maj1 min1) == (Level maj2 min2) = maj1==maj2 && min1==min2\r
+\end{code}\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Main level-setting code}\r
+%* *\r
+%************************************************************************\r
+\r
+\begin{code}\r
+setLevels :: Bool -- True <=> float lambdas to top level\r
+ -> [CoreBind]\r
+ -> UniqSupply\r
+ -> [LevelledBind]\r
+\r
+setLevels float_lams binds us\r
+ = initLvl us (do_them binds)\r
+ where\r
+ -- "do_them"'s main business is to thread the monad along\r
+ -- It gives each top binding the same empty envt, because\r
+ -- things unbound in the envt have level number zero implicitly\r
+ do_them :: [CoreBind] -> LvlM [LevelledBind]\r
+\r
+ do_them [] = returnLvl []\r
+ do_them (b:bs)\r
+ = lvlTopBind init_env b `thenLvl` \ (lvld_bind, _) ->\r
+ do_them bs `thenLvl` \ lvld_binds ->\r
+ returnLvl (lvld_bind : lvld_binds)\r
+\r
+ init_env = initialEnv float_lams\r
+\r
+lvlTopBind env (NonRec binder rhs)\r
+ = lvlBind TopLevel tOP_LEVEL env (AnnNonRec binder (freeVars rhs))\r
+ -- Rhs can have no free vars!\r
+\r
+lvlTopBind env (Rec pairs)\r
+ = lvlBind TopLevel tOP_LEVEL env (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])\r
+\end{code}\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Setting expression levels}\r
+%* *\r
+%************************************************************************\r
+\r
+\begin{code}\r
+lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression\r
+ -> LevelEnv -- Level of in-scope names/tyvars\r
+ -> CoreExprWithFVs -- input expression\r
+ -> LvlM LevelledExpr -- Result expression\r
+\end{code}\r
+\r
+The @ctxt_lvl@ is, roughly, the level of the innermost enclosing\r
+binder. Here's an example\r
+\r
+ v = \x -> ...\y -> let r = case (..x..) of\r
+ ..x..\r
+ in ..\r
+\r
+When looking at the rhs of @r@, @ctxt_lvl@ will be 1 because that's\r
+the level of @r@, even though it's inside a level-2 @\y@. It's\r
+important that @ctxt_lvl@ is 1 and not 2 in @r@'s rhs, because we\r
+don't want @lvlExpr@ to turn the scrutinee of the @case@ into an MFE\r
+--- because it isn't a *maximal* free expression.\r
+\r
+If there were another lambda in @r@'s rhs, it would get level-2 as well.\r
+\r
+\begin{code}\r
+lvlExpr _ _ (_, AnnType ty) = returnLvl (Type ty)\r
+lvlExpr _ env (_, AnnVar v) = returnLvl (lookupVar env v)\r
+lvlExpr _ env (_, AnnLit lit) = returnLvl (Lit lit)\r
+\r
+lvlExpr ctxt_lvl env (_, AnnApp fun arg)\r
+ = lvl_fun fun `thenLvl` \ fun' ->\r
+ lvlMFE False ctxt_lvl env arg `thenLvl` \ arg' ->\r
+ returnLvl (App fun' arg')\r
+ where\r
+ lvl_fun (_, AnnCase _ _ _) = lvlMFE True ctxt_lvl env fun\r
+ lvl_fun other = lvlExpr ctxt_lvl env fun\r
+ -- We don't do MFE on partial applications generally,\r
+ -- but we do if the function is big and hairy, like a case\r
+\r
+lvlExpr ctxt_lvl env (_, AnnNote InlineMe expr)\r
+-- Don't float anything out of an InlineMe; hence the tOP_LEVEL\r
+ = lvlExpr tOP_LEVEL env expr `thenLvl` \ expr' ->\r
+ returnLvl (Note InlineMe expr')\r
+\r
+lvlExpr ctxt_lvl env (_, AnnNote note expr)\r
+ = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' ->\r
+ returnLvl (Note note expr')\r
+\r
+-- We don't split adjacent lambdas. That is, given\r
+-- \x y -> (x+1,y)\r
+-- we don't float to give \r
+-- \x -> let v = x+y in \y -> (v,y)\r
+-- Why not? Because partial applications are fairly rare, and splitting\r
+-- lambdas makes them more expensive.\r
+\r
+lvlExpr ctxt_lvl env expr@(_, AnnLam bndr rhs)\r
+ = lvlMFE True new_lvl new_env body `thenLvl` \ new_body ->\r
+ returnLvl (glue_binders new_bndrs expr new_body)\r
+ where \r
+ (bndrs, body) = collect_binders expr\r
+ (new_lvl, new_bndrs) = lvlLamBndrs ctxt_lvl bndrs\r
+ new_env = extendLvlEnv env new_bndrs\r
+\r
+lvlExpr ctxt_lvl env (_, AnnLet bind body)\r
+ = lvlBind NotTopLevel ctxt_lvl env bind `thenLvl` \ (bind', new_env) ->\r
+ lvlExpr ctxt_lvl new_env body `thenLvl` \ body' ->\r
+ returnLvl (Let bind' body')\r
+\r
+lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr alts)\r
+ = lvlMFE True ctxt_lvl env expr `thenLvl` \ expr' ->\r
+ let\r
+ alts_env = extendCaseBndrLvlEnv env expr' case_bndr incd_lvl\r
+ in\r
+ mapLvl (lvl_alt alts_env) alts `thenLvl` \ alts' ->\r
+ returnLvl (Case expr' (case_bndr, incd_lvl) alts')\r
+ where\r
+ incd_lvl = incMinorLvl ctxt_lvl\r
+\r
+ lvl_alt alts_env (con, bs, rhs)\r
+ = lvlMFE True incd_lvl new_env rhs `thenLvl` \ rhs' ->\r
+ returnLvl (con, bs', rhs')\r
+ where\r
+ bs' = [ (b, incd_lvl) | b <- bs ]\r
+ new_env = extendLvlEnv alts_env bs'\r
+\r
+collect_binders lam\r
+ = go [] lam\r
+ where\r
+ go rev_bndrs (_, AnnLam b e) = go (b:rev_bndrs) e\r
+ go rev_bndrs (_, AnnNote n e) = go rev_bndrs e\r
+ go rev_bndrs rhs = (reverse rev_bndrs, rhs)\r
+ -- Ignore notes, because we don't want to split\r
+ -- a lambda like this (\x -> coerce t (\s -> ...))\r
+ -- This happens quite a bit in state-transformer programs\r
+\r
+ -- glue_binders puts the lambda back together\r
+glue_binders (b:bs) (_, AnnLam _ e) body = Lam b (glue_binders bs e body)\r
+glue_binders bs (_, AnnNote n e) body = Note n (glue_binders bs e body)\r
+glue_binders [] e body = body\r
+\end{code}\r
+\r
+@lvlMFE@ is just like @lvlExpr@, except that it might let-bind\r
+the expression, so that it can itself be floated.\r
+\r
+\begin{code}\r
+lvlMFE :: Bool -- True <=> strict context [body of case or let]\r
+ -> Level -- Level of innermost enclosing lambda/tylam\r
+ -> LevelEnv -- Level of in-scope names/tyvars\r
+ -> CoreExprWithFVs -- input expression\r
+ -> LvlM LevelledExpr -- Result expression\r
+\r
+lvlMFE strict_ctxt ctxt_lvl env (_, AnnType ty)\r
+ = returnLvl (Type ty)\r
+\r
+lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)\r
+ | isUnLiftedType ty -- Can't let-bind it\r
+ || not good_destination\r
+ || exprIsTrivial expr -- Is trivial\r
+ || (strict_ctxt && exprIsBottom expr) -- Strict context and is bottom\r
+ -- e.g. \x -> error "foo"\r
+ -- No gain from floating this\r
+ = -- Don't float it out\r
+ lvlExpr ctxt_lvl env ann_expr\r
+\r
+ | otherwise -- Float it out!\r
+ = lvlFloatRhs abs_vars dest_lvl env ann_expr `thenLvl` \ expr' ->\r
+ newLvlVar "lvl" abs_vars ty `thenLvl` \ var ->\r
+ returnLvl (Let (NonRec (var,dest_lvl) expr') \r
+ (mkVarApps (Var var) abs_vars))\r
+ where\r
+ expr = deAnnotate ann_expr\r
+ ty = exprType expr\r
+ dest_lvl = destLevel env fvs (isFunction ann_expr)\r
+ abs_vars = abstractVars dest_lvl env fvs\r
+\r
+ good_destination = dest_lvl `ltMajLvl` ctxt_lvl -- Escapes a value lambda\r
+ || (isTopLvl dest_lvl && not strict_ctxt) -- Goes to the top\r
+ -- A decision to float entails let-binding this thing, and we only do \r
+ -- that if we'll escape a value lambda, or will go to the top level.\r
+ -- But beware\r
+ -- concat = /\ a -> foldr ..a.. (++) []\r
+ -- was getting turned into\r
+ -- concat = /\ a -> lvl a\r
+ -- lvl = /\ a -> foldr ..a.. (++) []\r
+ -- which is pretty stupid. Hence the strict_ctxt test\r
+\end{code}\r
+\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Bindings}\r
+%* *\r
+%************************************************************************\r
+\r
+The binding stuff works for top level too.\r
+\r
+\begin{code}\r
+lvlBind :: TopLevelFlag -- Used solely to decide whether to clone\r
+ -> Level -- Context level; might be Top even for bindings nested in the RHS\r
+ -- of a top level binding\r
+ -> LevelEnv\r
+ -> CoreBindWithFVs\r
+ -> LvlM (LevelledBind, LevelEnv)\r
+\r
+lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))\r
+ | null abs_vars\r
+ = -- No type abstraction; clone existing binder\r
+ lvlExpr dest_lvl env rhs `thenLvl` \ rhs' ->\r
+ cloneVar top_lvl env bndr ctxt_lvl dest_lvl `thenLvl` \ (env', bndr') ->\r
+ returnLvl (NonRec (bndr', dest_lvl) rhs', env') \r
+\r
+ | otherwise\r
+ = -- Yes, type abstraction; create a new binder, extend substitution, etc\r
+ lvlFloatRhs abs_vars dest_lvl env rhs `thenLvl` \ rhs' ->\r
+ newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (env', [bndr']) ->\r
+ returnLvl (NonRec (bndr', dest_lvl) rhs', env')\r
+\r
+ where\r
+ bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr\r
+ abs_vars = abstractVars dest_lvl env bind_fvs\r
+\r
+ dest_lvl | isUnLiftedType (idType bndr) = destLevel env bind_fvs False `maxLvl` Level 1 0\r
+ | otherwise = destLevel env bind_fvs (isFunction rhs)\r
+ -- Hack alert! We do have some unlifted bindings, for cheap primops, and \r
+ -- it is ok to float them out; but not to the top level. If they would otherwise\r
+ -- go to the top level, we pin them inside the topmost lambda\r
+\end{code}\r
+\r
+\r
+\begin{code}\r
+lvlBind top_lvl ctxt_lvl env (AnnRec pairs)\r
+ | null abs_vars\r
+ = cloneRecVars top_lvl env bndrs ctxt_lvl dest_lvl `thenLvl` \ (new_env, new_bndrs) ->\r
+ mapLvl (lvlExpr ctxt_lvl new_env) rhss `thenLvl` \ new_rhss ->\r
+ returnLvl (Rec ((new_bndrs `zip` repeat dest_lvl) `zip` new_rhss), new_env)\r
+\r
+ | isSingleton pairs && count isId abs_vars > 1\r
+ = -- Special case for self recursion where there are\r
+ -- several variables carried around: build a local loop: \r
+ -- poly_f = \abs_vars. \lam_vars . letrec f = \lam_vars. rhs in f lam_vars\r
+ -- This just makes the closures a bit smaller. If we don't do\r
+ -- this, allocation rises significantly on some programs\r
+ --\r
+ -- We could elaborate it for the case where there are several\r
+ -- mutually functions, but it's quite a bit more complicated\r
+ -- \r
+ -- This all seems a bit ad hoc -- sigh\r
+ let\r
+ (bndr,rhs) = head pairs\r
+ (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars\r
+ rhs_env = extendLvlEnv env abs_vars_w_lvls\r
+ in\r
+ cloneVar NotTopLevel rhs_env bndr rhs_lvl rhs_lvl `thenLvl` \ (rhs_env', new_bndr) ->\r
+ let\r
+ (lam_bndrs, rhs_body) = collect_binders rhs\r
+ (body_lvl, new_lam_bndrs) = lvlLamBndrs rhs_lvl lam_bndrs\r
+ body_env = extendLvlEnv rhs_env' new_lam_bndrs\r
+ in\r
+ lvlExpr body_lvl body_env rhs_body `thenLvl` \ new_rhs_body ->\r
+ newPolyBndrs dest_lvl env abs_vars [bndr] `thenLvl` \ (poly_env, [poly_bndr]) ->\r
+ returnLvl (Rec [((poly_bndr,dest_lvl), mkLams abs_vars_w_lvls $\r
+ glue_binders new_lam_bndrs rhs $\r
+ Let (Rec [((new_bndr,rhs_lvl), mkLams new_lam_bndrs new_rhs_body)]) \r
+ (mkVarApps (Var new_bndr) lam_bndrs))],\r
+ poly_env)\r
+\r
+ | otherwise\r
+ = newPolyBndrs dest_lvl env abs_vars bndrs `thenLvl` \ (new_env, new_bndrs) ->\r
+ mapLvl (lvlFloatRhs abs_vars dest_lvl new_env) rhss `thenLvl` \ new_rhss ->\r
+ returnLvl (Rec ((new_bndrs `zip` repeat dest_lvl) `zip` new_rhss), new_env)\r
+\r
+ where\r
+ (bndrs,rhss) = unzip pairs\r
+\r
+ -- Finding the free vars of the binding group is annoying\r
+ bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs\r
+ | (bndr, (rhs_fvs,_)) <- pairs])\r
+ `minusVarSet`\r
+ mkVarSet bndrs\r
+\r
+ dest_lvl = destLevel env bind_fvs (all isFunction rhss)\r
+ abs_vars = abstractVars dest_lvl env bind_fvs\r
+\r
+----------------------------------------------------\r
+-- Three help functons for the type-abstraction case\r
+\r
+lvlFloatRhs abs_vars dest_lvl env rhs\r
+ = lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->\r
+ returnLvl (mkLams abs_vars_w_lvls rhs')\r
+ where\r
+ (rhs_lvl, abs_vars_w_lvls) = lvlLamBndrs dest_lvl abs_vars\r
+ rhs_env = extendLvlEnv env abs_vars_w_lvls\r
+\end{code}\r
+\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Deciding floatability}\r
+%* *\r
+%************************************************************************\r
+\r
+\begin{code}\r
+lvlLamBndrs :: Level -> [CoreBndr] -> (Level, [(CoreBndr, Level)])\r
+-- Compute the levels for the binders of a lambda group\r
+-- The binders returned are exactly the same as the ones passed,\r
+-- but they are now paired with a level\r
+lvlLamBndrs lvl [] \r
+ = (lvl, [])\r
+\r
+lvlLamBndrs lvl bndrs\r
+ = go (incMinorLvl lvl)\r
+ False -- Havn't bumped major level in this group\r
+ [] bndrs\r
+ where\r
+ go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)\r
+ | isId bndr && -- Go to the next major level if this is a value binder,\r
+ not bumped_major && -- and we havn't already gone to the next level (one jump per group)\r
+ not (isOneShotLambda bndr) -- and it isn't a one-shot lambda\r
+ = go new_lvl True ((bndr,new_lvl) : rev_lvld_bndrs) bndrs\r
+\r
+ | otherwise\r
+ = go old_lvl bumped_major ((bndr,old_lvl) : rev_lvld_bndrs) bndrs\r
+\r
+ where\r
+ new_lvl = incMajorLvl old_lvl\r
+\r
+ go old_lvl _ rev_lvld_bndrs []\r
+ = (old_lvl, reverse rev_lvld_bndrs)\r
+ -- a lambda like this (\x -> coerce t (\s -> ...))\r
+ -- This happens quite a bit in state-transformer programs\r
+\end{code}\r
+\r
+\begin{code}\r
+abstractVars :: Level -> LevelEnv -> VarSet -> [Var]\r
+ -- Find the variables in fvs, free vars of the target expresion,\r
+ -- whose level is less than than the supplied level\r
+ -- These are the ones we are going to abstract out\r
+abstractVars dest_lvl env fvs\r
+ = uniq (sortLt lt [var | fv <- varSetElems fvs, var <- absVarsOf dest_lvl env fv])\r
+ where\r
+ -- Sort the variables so we don't get \r
+ -- mixed-up tyvars and Ids; it's just messy\r
+ v1 `lt` v2 = case (isId v1, isId v2) of\r
+ (True, False) -> False\r
+ (False, True) -> True\r
+ other -> v1 < v2 -- Same family\r
+ uniq :: [Var] -> [Var]\r
+ -- Remove adjacent duplicates; the sort will have brought them together\r
+ uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)\r
+ | otherwise = v1 : uniq (v2:vs)\r
+ uniq vs = vs\r
+\r
+ -- Destintion level is the max Id level of the expression\r
+ -- (We'll abstract the type variables, if any.)\r
+destLevel :: LevelEnv -> VarSet -> Bool -> Level\r
+destLevel env fvs is_function\r
+ | floatLams env\r
+ && is_function = tOP_LEVEL -- Send functions to top level; see\r
+ -- the comments with isFunction\r
+ | otherwise = maxIdLevel env fvs\r
+\r
+isFunction :: CoreExprWithFVs -> Bool\r
+-- The idea here is that we want to float *functions* to\r
+-- the top level. This saves no work, but \r
+-- (a) it can make the host function body a lot smaller, \r
+-- and hence inlinable. \r
+-- (b) it can also save allocation when the function is recursive:\r
+-- h = \x -> letrec f = \y -> ...f...y...x...\r
+-- in f x\r
+-- becomes\r
+-- f = \x y -> ...(f x)...y...x...\r
+-- h = \x -> f x x\r
+-- No allocation for f now.\r
+-- We may only want to do this if there are sufficiently few free \r
+-- variables. We certainly only want to do it for values, and not for\r
+-- constructors. So the simple thing is just to look for lambdas\r
+isFunction (_, AnnLam b e) | isId b = True\r
+ | otherwise = isFunction e\r
+isFunction (_, AnnNote n e) = isFunction e\r
+isFunction other = False\r
+\end{code}\r
+\r
+\r
+%************************************************************************\r
+%* *\r
+\subsection{Free-To-Level Monad}\r
+%* *\r
+%************************************************************************\r
+\r
+\begin{code}\r
+type LevelEnv = (Bool, -- True <=> Float lambdas too\r
+ VarEnv Level, -- Domain is *post-cloned* TyVars and Ids\r
+ Subst, -- Domain is pre-cloned Ids; tracks the in-scope set\r
+ -- so that subtitution is capture-avoiding\r
+ IdEnv ([Var], LevelledExpr)) -- Domain is pre-cloned Ids\r
+ -- We clone let-bound variables so that they are still\r
+ -- distinct when floated out; hence the SubstEnv/IdEnv.\r
+ -- (see point 3 of the module overview comment).\r
+ -- We also use these envs when making a variable polymorphic\r
+ -- because we want to float it out past a big lambda.\r
+ --\r
+ -- The SubstEnv and IdEnv always implement the same mapping, but the\r
+ -- SubstEnv maps to CoreExpr and the IdEnv to LevelledExpr\r
+ -- Since the range is always a variable or type application,\r
+ -- there is never any difference between the two, but sadly\r
+ -- the types differ. The SubstEnv is used when substituting in\r
+ -- a variable's IdInfo; the IdEnv when we find a Var.\r
+ --\r
+ -- In addition the IdEnv records a list of tyvars free in the\r
+ -- type application, just so we don't have to call freeVars on\r
+ -- the type application repeatedly.\r
+ --\r
+ -- The domain of the both envs is *pre-cloned* Ids, though\r
+ --\r
+ -- The domain of the VarEnv Level is the *post-cloned* Ids\r
+\r
+initialEnv :: Bool -> LevelEnv\r
+initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)\r
+\r
+floatLams :: LevelEnv -> Bool\r
+floatLams (float_lams, _, _, _) = float_lams\r
+\r
+extendLvlEnv :: LevelEnv -> [(Var,Level)] -> LevelEnv\r
+-- Used when *not* cloning\r
+extendLvlEnv (float_lams, lvl_env, subst, id_env) prs\r
+ = (float_lams,\r
+ foldl add_lvl lvl_env prs,\r
+ foldl del_subst subst prs,\r
+ foldl del_id id_env prs)\r
+ where\r
+ add_lvl env (v,l) = extendVarEnv env v l\r
+ del_subst env (v,_) = extendInScope env v\r
+ del_id env (v,_) = delVarEnv env v\r
+ -- We must remove any clone for this variable name in case of\r
+ -- shadowing. This bit me in the following case\r
+ -- (in nofib/real/gg/Spark.hs):\r
+ -- \r
+ -- case ds of wild {\r
+ -- ... -> case e of wild {\r
+ -- ... -> ... wild ...\r
+ -- }\r
+ -- }\r
+ -- \r
+ -- The inside occurrence of @wild@ was being replaced with @ds@,\r
+ -- incorrectly, because the SubstEnv was still lying around. Ouch!\r
+ -- KSW 2000-07.\r
+\r
+-- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can\r
+-- (see point 4 of the module overview comment)\r
+extendCaseBndrLvlEnv (float_lams, lvl_env, subst, id_env) (Var scrut_var) case_bndr lvl\r
+ = (float_lams,\r
+ extendVarEnv lvl_env case_bndr lvl,\r
+ extendSubst subst case_bndr (DoneEx (Var scrut_var)),\r
+ extendVarEnv id_env case_bndr ([scrut_var], Var scrut_var))\r
+ \r
+extendCaseBndrLvlEnv env scrut case_bndr lvl\r
+ = extendLvlEnv env [(case_bndr,lvl)]\r
+\r
+extendPolyLvlEnv dest_lvl (float_lams, lvl_env, subst, id_env) abs_vars bndr_pairs\r
+ = (float_lams,\r
+ foldl add_lvl lvl_env bndr_pairs,\r
+ foldl add_subst subst bndr_pairs,\r
+ foldl add_id id_env bndr_pairs)\r
+ where\r
+ add_lvl env (v,v') = extendVarEnv env v' dest_lvl\r
+ add_subst env (v,v') = extendSubst env v (DoneEx (mkVarApps (Var v') abs_vars))\r
+ add_id env (v,v') = extendVarEnv env v ((v':abs_vars), mkVarApps (Var v') abs_vars)\r
+\r
+extendCloneLvlEnv lvl (float_lams, lvl_env, _, id_env) new_subst bndr_pairs\r
+ = (float_lams,\r
+ foldl add_lvl lvl_env bndr_pairs,\r
+ new_subst,\r
+ foldl add_id id_env bndr_pairs)\r
+ where\r
+ add_lvl env (v,v') = extendVarEnv env v' lvl\r
+ add_id env (v,v') = extendVarEnv env v ([v'], Var v')\r
+\r
+\r
+maxIdLevel :: LevelEnv -> VarSet -> Level\r
+maxIdLevel (_, lvl_env,_,id_env) var_set\r
+ = foldVarSet max_in tOP_LEVEL var_set\r
+ where\r
+ max_in in_var lvl = foldr max_out lvl (case lookupVarEnv id_env in_var of\r
+ Just (abs_vars, _) -> abs_vars\r
+ Nothing -> [in_var])\r
+\r
+ max_out out_var lvl \r
+ | isId out_var = case lookupVarEnv lvl_env out_var of\r
+ Just lvl' -> maxLvl lvl' lvl\r
+ Nothing -> lvl \r
+ | otherwise = lvl -- Ignore tyvars in *maxIdLevel*\r
+\r
+lookupVar :: LevelEnv -> Id -> LevelledExpr\r
+lookupVar (_, _, _, id_env) v = case lookupVarEnv id_env v of\r
+ Just (_, expr) -> expr\r
+ other -> Var v\r
+\r
+absVarsOf :: Level -> LevelEnv -> Var -> [Var]\r
+ -- If f is free in the exression, and f maps to poly_f a b c in the\r
+ -- current substitution, then we must report a b c as candidate type\r
+ -- variables\r
+absVarsOf dest_lvl (_, lvl_env, _, id_env) v \r
+ | isId v\r
+ = [final_av | av <- lookup_avs v, abstract_me av, final_av <- add_tyvars av]\r
+\r
+ | otherwise\r
+ = if abstract_me v then [v] else []\r
+\r
+ where\r
+ abstract_me v = case lookupVarEnv lvl_env v of\r
+ Just lvl -> dest_lvl `ltLvl` lvl\r
+ Nothing -> False\r
+\r
+ lookup_avs v = case lookupVarEnv id_env v of\r
+ Just (abs_vars, _) -> abs_vars\r
+ Nothing -> [v]\r
+\r
+ -- We are going to lambda-abstract, so nuke any IdInfo,\r
+ -- and add the tyvars of the Id\r
+ add_tyvars v | isId v = zap v : varSetElems (idFreeTyVars v)\r
+ | otherwise = [v]\r
+\r
+ zap v = WARN( workerExists (idWorkerInfo v)\r
+ || not (isEmptyCoreRules (idSpecialisation v)),\r
+ text "absVarsOf: discarding info on" <+> ppr v )\r
+ setIdInfo v vanillaIdInfo\r
+\end{code}\r
+\r
+\begin{code}\r
+type LvlM result = UniqSM result\r
+\r
+initLvl = initUs_\r
+thenLvl = thenUs\r
+returnLvl = returnUs\r
+mapLvl = mapUs\r
+\end{code}\r
+\r
+\begin{code}\r
+newPolyBndrs dest_lvl env abs_vars bndrs\r
+ = getUniquesUs (length bndrs) `thenLvl` \ uniqs ->\r
+ let\r
+ new_bndrs = zipWith mk_poly_bndr bndrs uniqs\r
+ in\r
+ returnLvl (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)\r
+ where\r
+ mk_poly_bndr bndr uniq = mkSysLocal (_PK_ str) uniq poly_ty\r
+ where\r
+ str = "poly_" ++ occNameUserString (getOccName bndr)\r
+ poly_ty = foldr mkPiType (idType bndr) abs_vars\r
+ \r
+\r
+newLvlVar :: String \r
+ -> [CoreBndr] -> Type -- Abstract wrt these bndrs\r
+ -> LvlM Id\r
+newLvlVar str vars body_ty \r
+ = getUniqueUs `thenLvl` \ uniq ->\r
+ returnUs (mkSysLocal (_PK_ str) uniq (foldr mkPiType body_ty vars))\r
+ \r
+-- The deeply tiresome thing is that we have to apply the substitution\r
+-- to the rules inside each Id. Grr. But it matters.\r
+\r
+cloneVar :: TopLevelFlag -> LevelEnv -> Id -> Level -> Level -> LvlM (LevelEnv, Id)\r
+cloneVar TopLevel env v ctxt_lvl dest_lvl\r
+ = returnUs (env, v) -- Don't clone top level things\r
+cloneVar NotTopLevel env@(_,_,subst,_) v ctxt_lvl dest_lvl\r
+ = ASSERT( isId v )\r
+ getUs `thenLvl` \ us ->\r
+ let\r
+ (subst', v1) = substAndCloneId subst us v\r
+ v2 = zap_demand ctxt_lvl dest_lvl v1\r
+ env' = extendCloneLvlEnv dest_lvl env subst' [(v,v2)]\r
+ in\r
+ returnUs (env', v2)\r
+\r
+cloneRecVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> Level -> LvlM (LevelEnv, [Id])\r
+cloneRecVars TopLevel env vs ctxt_lvl dest_lvl \r
+ = returnUs (env, vs) -- Don't clone top level things\r
+cloneRecVars NotTopLevel env@(_,_,subst,_) vs ctxt_lvl dest_lvl\r
+ = ASSERT( all isId vs )\r
+ getUs `thenLvl` \ us ->\r
+ let\r
+ (subst', vs1) = substAndCloneRecIds subst us vs\r
+ vs2 = map (zap_demand ctxt_lvl dest_lvl) vs1\r
+ env' = extendCloneLvlEnv dest_lvl env subst' (vs `zip` vs2)\r
+ in\r
+ returnUs (env', vs2)\r
+\r
+ -- VERY IMPORTANT: we must zap the demand info \r
+ -- if the thing is going to float out past a lambda\r
+zap_demand dest_lvl ctxt_lvl id\r
+ | ctxt_lvl == dest_lvl = id -- Stays put\r
+ | otherwise = zapDemandIdInfo id -- Floats out\r
+\end{code}\r
+ \r
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