%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section{SetLevels}
-We attach binding levels to Core bindings, in preparation for floating
-outwards (@FloatOut@).
+ ***************************
+ Overview
+ ***************************
-We also let-ify many applications (notably case scrutinees), so they
-will have a fighting chance of being floated sensible.
+* We attach binding levels to Core bindings, in preparation for floating
+ outwards (@FloatOut@).
+
+* We also let-ify many expressions (notably case scrutinees), so they
+ will have a fighting chance of being floated sensible.
+
+* We clone the binders of any floatable let-binding, so that when it is
+ floated out it will be unique. (This used to be done by the simplifier
+ but the latter now only ensures that there's no shadowing.)
+ 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
+
+* 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.
\begin{code}
module SetLevels (
#include "HsVersions.h"
-import AnnCoreSyn
import CoreSyn
-import CoreUtils ( coreExprType )
-import CoreUnfold ( FormSummary, whnfOrBottom, mkFormSummary )
-import FreeVars -- all of it
-import Id ( idType, mkSysLocal,
- nullIdEnv, addOneToIdEnv, growIdEnvList,
- unionManyIdSets, minusIdSet, mkIdSet,
- idSetToList, Id,
- lookupIdEnv, IdEnv
+import CoreUtils ( coreExprType, exprIsTrivial, exprIsBottom )
+import CoreFVs -- all of it
+import Id ( Id, idType, mkSysLocal, isOneShotLambda, modifyIdInfo,
+ getIdSpecialisation, getIdWorkerInfo
)
-import SrcLoc ( noSrcLoc )
-import Type ( isUnpointedType, mkTyVarTys, mkForAllTys, tyVarsOfTypes, Type )
-import TyVar ( emptyTyVarEnv, addToTyVarEnv,
- growTyVarEnvList, lookupTyVarEnv,
- tyVarSetToList,
- TyVarEnv, TyVar,
- unionManyTyVarSets, unionTyVarSets
- )
-import UniqSupply ( thenUs, returnUs, mapUs, mapAndUnzipUs,
- mapAndUnzip3Us, getUnique, UniqSM,
- UniqSupply
- )
-import BasicTypes ( Unused )
-import Util ( mapAccumL, zipWithEqual, zipEqual, panic, assertPanic )
+import IdInfo ( workerExists )
+import Var ( IdOrTyVar, Var, TyVar, setVarUnique )
+import VarEnv
+import Subst
+import VarSet
+import Name ( getOccName )
+import OccName ( occNameUserString )
+import Type ( isUnLiftedType, mkTyVarTy, mkForAllTys, Type )
+import BasicTypes ( TopLevelFlag(..) )
+import VarSet
+import VarEnv
+import UniqSupply
+import Maybes ( maybeToBool )
+import Util ( zipWithEqual, zipEqual )
import Outputable
-
-isLeakFreeType x y = False -- safe option; ToDo
+import List ( nub )
\end{code}
%************************************************************************
%************************************************************************
\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
+data 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.
+nesting depth of the (type-)lambda which binds it. The outermost lambda
+has level 1, so (Level 0 0) means that the variable is bound outside any lambda.
+
+On an expression, it's the maximum level number of its free
+(type-)variables. On a let(rec)-bound variable, it's the level of its
+RHS. On a case-bound variable, it's the number of enclosing lambdas.
Top-level variables: level~0. Those bound on the RHS of a top-level
definition but ``before'' a lambda; e.g., the \tr{x} in (levels shown
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@.
+at @Level 0 0@.
\begin{code}
-type LevelledExpr = GenCoreExpr (Id, Level) Id Unused
-type LevelledArg = GenCoreArg Id Unused
-type LevelledBind = GenCoreBinding (Id, Level) Id Unused
-
-type LevelEnvs = (IdEnv Level, -- bind Ids to levels
- TyVarEnv Level) -- bind type variables to levels
+type LevelledExpr = TaggedExpr Level
+type LevelledArg = TaggedArg Level
+type LevelledBind = TaggedBind Level
-tOP_LEVEL = Top
+tOP_LEVEL = Level 0 0
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
+isTopLvl (Level 0 0) = True
+isTopLvl other = False
instance Outputable Level where
- ppr Top = ptext SLIT("<Top>")
ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
\end{code}
%************************************************************************
\begin{code}
-setLevels :: [CoreBinding]
+setLevels :: [CoreBind]
-> UniqSupply
-> [LevelledBind]
setLevels binds us
- = do_them binds us
+ = initLvl us (do_them binds)
where
-- "do_them"'s main business is to thread the monad along
-- It gives each top binding the same empty envt, because
-- things unbound in the envt have level number zero implicitly
- do_them :: [CoreBinding] -> LvlM [LevelledBind]
+ do_them :: [CoreBind] -> LvlM [LevelledBind]
do_them [] = returnLvl []
do_them (b:bs)
= lvlTopBind b `thenLvl` \ (lvld_bind, _) ->
- do_them bs `thenLvl` \ lvld_binds ->
- returnLvl (lvld_bind ++ lvld_binds)
-
-initial_envs = (nullIdEnv, emptyTyVarEnv)
+ do_them bs `thenLvl` \ lvld_binds ->
+ returnLvl (lvld_bind : lvld_binds)
lvlTopBind (NonRec binder rhs)
- = lvlBind (Level 0 0) initial_envs (AnnNonRec binder (freeVars rhs))
+ = lvlBind TopLevel tOP_LEVEL initialEnv (AnnNonRec binder (freeVars rhs))
-- Rhs can have no free vars!
lvlTopBind (Rec pairs)
- = lvlBind (Level 0 0) initial_envs (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Bindings}
-%* *
-%************************************************************************
-
-The binding stuff works for top level too.
-
-\begin{code}
-type CoreBindingWithFVs = AnnCoreBinding Id Id Unused 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
+ = lvlBind TopLevel tOP_LEVEL initialEnv (AnnRec [(b,freeVars rhs) | (b,rhs) <- pairs])
\end{code}
%************************************************************************
\begin{code}
lvlExpr :: Level -- ctxt_lvl: Level of enclosing expression
- -> LevelEnvs -- Level of in-scope names/tyvars
+ -> LevelEnv -- Level of in-scope names/tyvars
-> CoreExprWithFVs -- input expression
-> LvlM LevelledExpr -- Result expression
\end{code}
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..
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 _ _ (_, AnnType ty) = returnLvl (Type ty)
+lvlExpr _ env (_, AnnVar v) = returnLvl (lookupVar env v)
-lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnApp fun arg)
- = lvlExpr ctxt_lvl envs fun `thenLvl` \ fun' ->
- returnLvl (App fun' arg)
+lvlExpr ctxt_lvl env (_, AnnCon con args)
+ = mapLvl (lvlExpr ctxt_lvl env) args `thenLvl` \ args' ->
+ returnLvl (Con con args')
-lvlExpr ctxt_lvl envs (_, AnnSCC cc expr)
- = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
- returnLvl (SCC cc expr')
+lvlExpr ctxt_lvl env (_, AnnApp fun arg)
+ = lvlExpr ctxt_lvl env fun `thenLvl` \ fun' ->
+ lvlMFE False ctxt_lvl env arg `thenLvl` \ arg' ->
+ returnLvl (App fun' arg')
-lvlExpr ctxt_lvl envs (_, AnnCoerce c ty expr)
- = lvlExpr ctxt_lvl envs expr `thenLvl` \ expr' ->
- returnLvl (Coerce c ty expr')
+lvlExpr ctxt_lvl env (_, AnnNote InlineMe expr)
+ -- Don't float anything out of an InlineMe
+ = lvlExpr tOP_LEVEL env expr `thenLvl` \ expr' ->
+ returnLvl (Note InlineMe expr')
+
+lvlExpr ctxt_lvl env (_, AnnNote note expr)
+ = lvlExpr ctxt_lvl env expr `thenLvl` \ expr' ->
+ returnLvl (Note note expr')
-- We don't split adjacent lambdas. That is, given
-- \x y -> (x+1,y)
-- Why not? Because partial applications are fairly rare, and splitting
-- lambdas makes them more expensive.
-lvlExpr ctxt_lvl envs@(venv, tenv) (_, AnnLam (ValBinder arg) rhs)
- = lvlMFE incd_lvl (new_venv, tenv) body `thenLvl` \ body' ->
- returnLvl (foldr (Lam . ValBinder) body' lvld_args)
- where
- incd_lvl = incMajorLvl ctxt_lvl
- (args, body) = annCollectValBinders rhs
- lvld_args = [(a,incd_lvl) | a <- (arg:args)]
- new_venv = growIdEnvList venv lvld_args
-
--- We don't need to play such tricks for type lambdas, because
--- they don't get annotated
-
-lvlExpr ctxt_lvl (venv, tenv) (_, AnnLam (TyBinder tyvar) body)
- = lvlExpr incd_lvl (venv, new_tenv) body `thenLvl` \ body' ->
- returnLvl (Lam (TyBinder tyvar) body')
+lvlExpr ctxt_lvl env expr@(_, AnnLam bndr rhs)
+ = go (incMinorLvl ctxt_lvl) env False {- Havn't bumped major level in this group -} expr
+ where
+ go lvl env bumped_major (_, AnnLam bndr body)
+ = go new_lvl new_env new_bumped_major body `thenLvl` \ new_body ->
+ returnLvl (Lam lvld_bndr new_body)
+ where
+ -- Go to the next major level if this is a value binder,
+ -- and we havn't already gone to the next level (one jump per group)
+ -- and it isn't a one-shot lambda
+ (new_lvl, new_bumped_major)
+ | isId bndr &&
+ not bumped_major &&
+ not (isOneShotLambda bndr) = (incMajorLvl ctxt_lvl, True)
+ | otherwise = (lvl, bumped_major)
+ new_env = extendLvlEnv env [lvld_bndr]
+ lvld_bndr = (bndr, new_lvl)
+
+ -- Ignore notes, because we don't want to split
+ -- a lambda like this (\x -> coerce t (\s -> ...))
+ -- This happens quite a bit in state-transformer programs
+ go lvl env bumped_major (_, AnnNote note body)
+ = go lvl env bumped_major body `thenLvl` \ new_body ->
+ returnLvl (Note note new_body)
+
+ go lvl env bumped_major body
+ = lvlMFE True lvl env body
+
+
+lvlExpr ctxt_lvl env (_, AnnLet bind body)
+ = 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 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' (case_bndr, incd_lvl) alts')
where
- incd_lvl = incMinorLvl ctxt_lvl
- new_tenv = addToTyVarEnv tenv tyvar incd_lvl
-
-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')
+ lvl_alt alts_env (con, bs, rhs)
+ = lvlMFE True incd_lvl new_env rhs `thenLvl` \ rhs' ->
+ returnLvl (con, bs', rhs')
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')
+ bs' = [ (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.
\begin{code}
-lvlMFE :: Level -- Level of innermost enclosing lambda/tylam
- -> LevelEnvs -- Level of in-scope names/tyvars
+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 envs@(venv,_) ann_expr
- | isUnpointedType 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'
+lvlMFE strict_ctxt ctxt_lvl env (_, AnnType ty)
+ = returnLvl (Type ty)
+
+lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
+ | isUnLiftedType ty -- Can't let-bind it
+ || not (dest_lvl `ltMajLvl` ctxt_lvl) -- Does not escape a value lambda
+ -- A decision to float entails let-binding this thing, and we only do
+ -- that if we'll escape a value lambda. I considered doing it if it
+ -- would make the thing go to top level, but I found things like
+ -- concat = /\ a -> foldr ..a.. (++) []
+ -- was getting turned into
+ -- concat = /\ a -> lvl a
+ -- lvl = /\ a -> foldr ..a.. (++) []
+ -- which is pretty stupid. So for now at least, I don't let-bind things
+ -- simply because they could go to top level.
+ || exprIsTrivial expr -- Is trivial
+ || (strict_ctxt && exprIsBottom expr) -- Strict context and is bottom
+ = -- Don't float it out
+ lvlExpr ctxt_lvl env ann_expr
+
+ | otherwise -- Float it out!
+ = lvlExpr expr_lvl expr_env ann_expr `thenLvl` \ expr' ->
+ newLvlVar "lvl" (mkForAllTys tyvars ty) `thenLvl` \ var ->
+ returnLvl (Let (NonRec (var,dest_lvl) (mkLams tyvars_w_lvls expr'))
+ (mkTyVarApps var tyvars))
where
- ty = coreExprType (deAnnotate ann_expr)
+ expr = deAnnotate ann_expr
+ ty = coreExprType expr
+ dest_lvl = destLevel env fvs
+ (tyvars, tyvars_w_lvls, expr_lvl) = abstractTyVars dest_lvl env fvs
+ expr_env = extendLvlEnv env tyvars_w_lvls
\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 :: 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 = []
--- 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 = whnfOrBottom (mkFormSummary 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.
+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)
+
+lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
+ | null tyvars
+ = -- No type abstraction; clone existing binder
+ lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->
+ cloneVar top_lvl env bndr dest_lvl `thenLvl` \ (env', bndr') ->
+ returnLvl (NonRec (bndr', dest_lvl) rhs', env')
-\begin{code}
-abstractWrtTyVars offending_tyvars ty (venv,tenv) lvl expr
- = lvlExpr incd_lvl new_envs expr `thenLvl` \ expr' ->
- newLvlVar poly_ty `thenLvl` \ poly_var ->
+ | otherwise
+ = -- Yes, type abstraction; create a new binder, extend substitution, etc
+ WARN( workerExists (getIdWorkerInfo bndr)
+ || not (isEmptyCoreRules (getIdSpecialisation bndr)),
+ text "lvlBind: discarding info on" <+> ppr bndr )
+
+ lvl_poly_rhs tyvars_w_lvls rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->
+ new_poly_bndr tyvars bndr `thenLvl` \ bndr' ->
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
+ env' = extendPolyLvlEnv env dest_lvl tyvars [(bndr, bndr')]
in
- returnLvl final_expr
- where
- poly_ty = mkForAllTys offending_tyvars ty
+ returnLvl (NonRec (bndr', dest_lvl) rhs', env')
- -- These defns are just like those in the TyLam case of lvlExpr
- (incd_lvl, tyvar_lvls) = mapAccumL next (unTopify lvl) offending_tyvars
+ where
+ bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
- next lvl tyvar = (lvl1, (tyvar,lvl1))
- where lvl1 = incMinorLvl lvl
+ dest_lvl | isUnLiftedType (idType bndr) = destLevel env bind_fvs `maxLvl` Level 1 0
+ | otherwise = destLevel env bind_fvs
+ -- Hack alert! We do have some unlifted bindings, for cheap primops, and
+ -- it is ok to float them out; but not to the top level. If they would otherwise
+ -- go to the top level, we pin them inside the topmost lambda
- new_tenv = growTyVarEnvList tenv tyvar_lvls
- new_envs = (venv, new_tenv)
+ (tyvars, tyvars_w_lvls, rhs_lvl) = abstractTyVars dest_lvl env bind_fvs
+ rhs_env = extendLvlEnv env tyvars_w_lvls
\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
+lvlBind top_lvl ctxt_lvl env (AnnRec pairs)
+ | null tyvars
+ = cloneVars top_lvl env bndrs dest_lvl `thenLvl` \ (new_env, new_bndrs) ->
+ mapLvl (lvlExpr rhs_lvl new_env) rhss `thenLvl` \ new_rhss ->
+ returnLvl (Rec ((new_bndrs `zip` repeat dest_lvl) `zip` new_rhss), new_env)
- 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 ->
+ | otherwise
+ = mapLvl (new_poly_bndr tyvars) bndrs `thenLvl` \ new_bndrs ->
let
- ids_w_poly_vars = zipEqual "decideRec2" ids poly_vars
+ new_env = extendPolyLvlEnv env dest_lvl tyvars (bndrs `zip` new_bndrs)
+ rhs_env = extendLvlEnv new_env tyvars_w_lvls
+ in
+ mapLvl (lvl_poly_rhs tyvars_w_lvls rhs_lvl rhs_env) rhss `thenLvl` \ new_rhss ->
+ returnLvl (Rec ((new_bndrs `zip` repeat dest_lvl) `zip` new_rhss), new_env)
- -- 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]
+ where
+ (bndrs,rhss) = unzip pairs
- -- "local_binds" are "D'" in the documentation above
- local_binds = zipWithEqual "SetLevels" NonRec ids_w_incd_lvl d_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
- poly_var_rhss = [ mkTyLam offending_tyvars (foldr Let rhs' local_binds)
- | rhs' <- rhss' -- mkCoLet* requires Core...
- ]
+ dest_lvl = destLevel env bind_fvs
- poly_binds = zipEqual "poly_binds" [(poly_var, ids_only_lvl) | poly_var <- poly_vars]
- poly_var_rhss
+ (tyvars, tyvars_w_lvls, rhs_lvl) = abstractTyVars dest_lvl env bind_fvs
- 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
+----------------------------------------------------
+-- Three help functons Stuff for the type-abstraction case
- | 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')
+new_poly_bndr tyvars bndr
+ = newLvlVar ("poly_" ++ occNameUserString (getOccName bndr))
+ (mkForAllTys tyvars (idType bndr))
- where
- tys = map idType ids
-
- fvs = unionManyIdSets [freeVarsOf rhs | rhs <- rhss] `minusIdSet` mkIdSet ids
- tfvs = unionManyTyVarSets [freeTyVarsOf rhs | rhs <- rhss]
- `unionTyVarSets`
- tyVarsOfTypes tys
- -- Why the "tyVarsOfTypes" part? Consider this:
- -- /\a -> letrec x::a = x in E
- -- Now, there are no explicit free type variables in the RHS of x,
- -- but nevertheless "a" is free in its definition. So we add in
- -- the free tyvars of the types of the binders.
- -- This actually happened in the defn of errorIO in IOBase.lhs:
- -- errorIO (ST io) = case (errorIO# io) of
- -- _ -> bottom
- -- where
- -- bottom = bottom -- Never evaluated
- -- I don't think this can every happen for non-recursive bindings.
-
- 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
+lvl_poly_rhs tyvars_w_lvls rhs_lvl rhs_env rhs
+ = lvlExpr rhs_lvl rhs_env rhs `thenLvl` \ rhs' ->
+ returnLvl (mkLams tyvars_w_lvls rhs')
\end{code}
-\begin{code}
-{- ******** OMITTED NOW
-
-isWorthFloating :: Bool -- True <=> already let-bound
- -> CoreExpr -- The expression
- -> Bool
+%************************************************************************
+%* *
+\subsection{Deciding floatability}
+%* *
+%************************************************************************
-isWorthFloating alreadyLetBound expr
+\begin{code}
+abstractTyVars :: Level -> LevelEnv -> VarSet
+ -> ([TyVar], [(TyVar,Level)], Level)
+ -- Find the tyvars whose level is higher than the supplied level
+ -- There should be no Ids with this property
+abstractTyVars lvl env fvs
+ | null tyvars = ([], [], lvl) -- Don't increment level
- | alreadyLetBound = isWorthFloatingExpr expr
+ | otherwise
+ = ASSERT( not (any bad fv_list) )
+ (tyvars, tyvars_w_lvls, incd_lvl)
+ where
+ bad v = isId v && lvl `ltLvl` varLevel env v
+ fv_list = varSetElems fvs
+ tyvars = nub [tv | v <- fv_list, tv <- tvs_of v, abstract_tv tv]
- | otherwise = -- No point in adding a fresh let-binding for a WHNF, because
- -- floating it isn't beneficial enough.
- isWorthFloatingExpr expr &&
- not (whnfOrBottom expr)
-********** -}
+ -- If f is free in the exression, and f maps to poly_f a b c in the
+ -- current substitution, then we must report a b c as candidate type
+ -- variables
+ tvs_of v | isId v = lookupTyVars env v
+ | otherwise = [v]
-isWorthFloatingExpr :: CoreExpr -> Bool
+ abstract_tv var | isId var = False
+ | otherwise = lvl `ltLvl` varLevel env var
-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
+ -- These defns are just like those in the TyLam case of lvlExpr
+ incd_lvl = incMinorLvl lvl
+ tyvars_w_lvls = [(tv,incd_lvl) | tv <- tyvars]
-canFloatToTop :: (Type, CoreExprWithFVs) -> Bool
-canFloatToTop (ty, (FVInfo _ _ (LeakFree _), expr)) = True
-canFloatToTop (ty, (FVInfo _ _ MightLeak, expr)) = isLeakFreeType [] ty
+ -- Destintion level is the max Id level of the expression
+ -- (We'll abstract the type variables, if any.)
+destLevel :: LevelEnv -> VarSet -> Level
+destLevel env fvs = foldVarSet (maxIdLvl env) tOP_LEVEL fvs
-valSuggestsLeakFree expr = whnfOrBottom expr
+maxIdLvl :: LevelEnv -> IdOrTyVar -> Level -> Level
+maxIdLvl (lvl_env,_,_) var lvl | isTyVar var = lvl
+ | otherwise = case lookupVarEnv lvl_env var of
+ Just lvl' -> maxLvl lvl' lvl
+ Nothing -> lvl
\end{code}
-
%************************************************************************
%* *
-\subsection{Help functions}
+\subsection{Free-To-Level Monad}
%* *
%************************************************************************
\begin{code}
-idLevel :: IdEnv Level -> Id -> Level
-idLevel venv v
- = case lookupIdEnv venv v of
- Just level -> level
- Nothing -> tOP_LEVEL
+type LevelEnv = (VarEnv Level, SubstEnv, IdEnv ([TyVar], LevelledExpr))
+ -- We clone let-bound variables so that they are still
+ -- distinct when floated out; hence the SubstEnv/IdEnv.
+ -- We also use these envs when making a variable polymorphic
+ -- because we want to float it out past a big lambda.
+ --
+ -- The two Envs 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
+
+initialEnv :: LevelEnv
+initialEnv = (emptyVarEnv, emptySubstEnv, emptyVarEnv)
+
+extendLvlEnv :: LevelEnv -> [(Var,Level)] -> LevelEnv
+ -- Used when *not* cloning
+extendLvlEnv (lvl_env, subst_env, id_env) prs
+ = (foldl add lvl_env prs, subst_env, id_env)
+ where
+ add env (v,l) = extendVarEnv env v l
+
+-- extendCaseBndrLvlEnv adds the mapping case-bndr->scrut-var if it can
+extendCaseBndrLvlEnv (lvl_env, subst_env, id_env) scrut case_bndr lvl
+ = case scrut of
+ Var v -> (new_lvl_env, extendSubstEnv subst_env case_bndr (DoneEx (Var v)),
+ extendVarEnv id_env case_bndr ([], scrut))
+ other -> (new_lvl_env, subst_env, id_env)
+ where
+ new_lvl_env = extendVarEnv lvl_env case_bndr lvl
-tyvarLevel :: TyVarEnv Level -> TyVar -> Level
-tyvarLevel tenv tyvar
- = case lookupTyVarEnv tenv tyvar of
+extendPolyLvlEnv (lvl_env, subst_env, id_env) dest_lvl tyvars bndr_pairs
+ = (foldl add_lvl lvl_env bndr_pairs,
+ foldl add_subst subst_env bndr_pairs,
+ foldl add_id id_env bndr_pairs)
+ where
+ add_lvl env (v,_ ) = extendVarEnv env v dest_lvl
+ add_subst env (v,v') = extendSubstEnv env v (DoneEx (mkTyVarApps v' tyvars))
+ add_id env (v,v') = extendVarEnv env v (tyvars, mkTyVarApps v' tyvars)
+
+varLevel :: LevelEnv -> IdOrTyVar -> Level
+varLevel (lvl_env, _, _) v
+ = case lookupVarEnv lvl_env v of
Just level -> level
Nothing -> tOP_LEVEL
-\end{code}
-\begin{code}
-annCollectValBinders (_, (AnnLam (ValBinder arg) rhs))
- = (arg:args, body)
- where
- (args, body) = annCollectValBinders rhs
+lookupVar :: LevelEnv -> Id -> LevelledExpr
+lookupVar (_, _, id_env) v = case lookupVarEnv id_env v of
+ Just (_, expr) -> expr
+ other -> Var v
-annCollectValBinders body
- = ([], body)
+lookupTyVars :: LevelEnv -> Id -> [TyVar]
+lookupTyVars (_, _, id_env) v = case lookupVarEnv id_env v of
+ Just (tyvars, _) -> tyvars
+ Nothing -> []
\end{code}
-%************************************************************************
-%* *
-\subsection{Free-To-Level Monad}
-%* *
-%************************************************************************
-
\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 :: String -> Type -> LvlM Id
+newLvlVar str ty = getUniqueUs `thenLvl` \ uniq ->
+ returnUs (mkSysLocal (_PK_ str) uniq 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 -> LvlM (LevelEnv, Id)
+cloneVar TopLevel env v lvl
+ = returnUs (env, v) -- Don't clone top level things
+cloneVar NotTopLevel (lvl_env, subst_env, id_env) v lvl
+ = getUniqueUs `thenLvl` \ uniq ->
+ let
+ subst = mkSubst emptyVarSet subst_env
+ v' = setVarUnique v uniq
+ v'' = modifyIdInfo (\info -> substIdInfo subst info info) v'
+ subst_env' = extendSubstEnv subst_env v (DoneEx (Var v''))
+ id_env' = extendVarEnv id_env v ([], Var v'')
+ lvl_env' = extendVarEnv lvl_env v lvl
+ in
+ returnUs ((lvl_env', subst_env', id_env'), v'')
+
+cloneVars :: TopLevelFlag -> LevelEnv -> [Id] -> Level -> LvlM (LevelEnv, [Id])
+cloneVars TopLevel env vs lvl
+ = returnUs (env, vs) -- Don't clone top level things
+cloneVars NotTopLevel (lvl_env, subst_env, id_env) vs lvl
+ = getUniquesUs (length vs) `thenLvl` \ uniqs ->
+ let
+ subst = mkSubst emptyVarSet subst_env'
+ vs' = zipWith setVarUnique vs uniqs
+ vs'' = map (modifyIdInfo (\info -> substIdInfo subst info info)) vs'
+ subst_env' = extendSubstEnvList subst_env vs [DoneEx (Var v'') | v'' <- vs'']
+ id_env' = extendVarEnvList id_env (vs `zip` [([], Var v') | v' <- vs''])
+ lvl_env' = extendVarEnvList lvl_env (vs `zip` repeat lvl)
+ in
+ returnUs ((lvl_env', subst_env', id_env'), vs'')
-newLvlVar ty us
- = mkSysLocal SLIT("lvl") (getUnique us) ty noSrcLoc
+mkTyVarApps var tyvars = foldl (\e tv -> App e (Type (mkTyVarTy tv)))
+ (Var var) tyvars
\end{code}
projects / ghc-hetmet.git / blobdiff