%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section{SetLevels}
***************************
Overview
***************************
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,
Level(..), tOP_LEVEL,
LevelledBind, LevelledExpr, LevelledBndr,
FloatSpec(..), floatSpecLevel,
incMinorLvl, ltMajLvl, ltLvl, isTopLvl
) where
#include "HsVersions.h"
import CoreSyn
import CoreMonad ( FloatOutSwitches(..) )
import CoreUtils ( exprType, exprOkForSpeculation, exprIsBottom )
import CoreArity ( exprBotStrictness_maybe )
import CoreFVs
import Coercion ( isCoVar )
import CoreSubst ( Subst, emptySubst, substBndrs, substRecBndrs,
extendIdSubst, extendSubstWithVar, cloneBndrs,
cloneRecIdBndrs, substTy, substCo, substVarSet )
import MkCore ( sortQuantVars )
import Id
import IdInfo
import Var
import VarSet
import VarEnv
import Literal ( litIsTrivial )
import Demand ( StrictSig )
import Name ( getOccName, mkSystemVarName )
import OccName ( occNameString )
import Type ( isUnLiftedType, Type, mkPiTypes )
import BasicTypes ( Arity, RecFlag(..) )
import UniqSupply
import Util
import Outputable
import FastString
\end{code}
%************************************************************************
%* *
\subsection{Level numbers}
%* *
%************************************************************************
\begin{code}
type LevelledExpr = TaggedExpr FloatSpec
type LevelledBind = TaggedBind FloatSpec
type LevelledBndr = TaggedBndr FloatSpec
data Level = Level Int
Int
data FloatSpec
= FloatMe Level
| StayPut Level
floatSpecLevel :: FloatSpec -> Level
floatSpecLevel (FloatMe l) = l
floatSpecLevel (StayPut l) = l
\end{code}
The {\em level number} on a (type-)lambda-bound variable is the
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
as ``subscripts'')...
\begin{verbatim}
a_0 = let b_? = ... in
x_1 = ... b ... in ...
\end{verbatim}
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.
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@.
Note [FloatOut inside INLINE]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@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}
instance Outputable FloatSpec where
ppr (FloatMe l) = char 'F' <> ppr l
ppr (StayPut l) = ppr l
tOP_LEVEL :: Level
tOP_LEVEL = Level 0 0
incMajorLvl :: Level -> Level
incMajorLvl (Level major _) = Level (major + 1) 0
incMinorLvl :: Level -> Level
incMinorLvl (Level major minor) = Level major (minor+1)
maxLvl :: Level -> Level -> Level
maxLvl l1@(Level maj1 min1) l2@(Level maj2 min2)
| (maj1 > maj2) || (maj1 == maj2 && min1 > min2) = l1
| otherwise = l2
ltLvl :: Level -> Level -> Bool
ltLvl (Level maj1 min1) (Level maj2 min2)
= (maj1 < maj2) || (maj1 == maj2 && min1 < min2)
ltMajLvl :: Level -> Level -> Bool
ltMajLvl (Level maj1 _) (Level maj2 _) = maj1 < maj2
isTopLvl :: Level -> Bool
isTopLvl (Level 0 0) = True
isTopLvl _ = False
instance Outputable Level where
ppr (Level maj min) = hcat [ char '<', int maj, char ',', int min, char '>' ]
instance Eq Level where
(Level maj1 min1) == (Level maj2 min2) = maj1 == maj2 && min1 == min2
\end{code}
%************************************************************************
%* *
\subsection{Main level-setting code}
%* *
%************************************************************************
\begin{code}
setLevels :: FloatOutSwitches
-> CoreProgram
-> UniqSupply
-> [LevelledBind]
setLevels float_lams binds us
= initLvl us (do_them init_env binds)
where
init_env = initialEnv float_lams
do_them :: LevelEnv -> [CoreBind] -> LvlM [LevelledBind]
do_them _ [] = return []
do_them env (b:bs)
= do { (lvld_bind, env') <- lvlTopBind env b
; lvld_binds <- do_them env' bs
; return (lvld_bind : lvld_binds) }
lvlTopBind :: LevelEnv -> Bind Id -> LvlM (LevelledBind, LevelEnv)
lvlTopBind env (NonRec bndr rhs)
= do { rhs' <- lvlExpr env (freeVars rhs)
; let (env', [bndr']) = substAndLvlBndrs NonRecursive env tOP_LEVEL [bndr]
; return (NonRec bndr' rhs', env') }
lvlTopBind env (Rec pairs)
= do let (bndrs,rhss) = unzip pairs
(env', bndrs') = substAndLvlBndrs Recursive env tOP_LEVEL bndrs
rhss' <- mapM (lvlExpr env' . freeVars) rhss
return (Rec (bndrs' `zip` rhss'), env')
\end{code}
%************************************************************************
%* *
\subsection{Setting expression levels}
%* *
%************************************************************************
\begin{code}
lvlExpr :: LevelEnv
-> CoreExprWithFVs
-> LvlM LevelledExpr
\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 env (_, AnnType ty) = return (Type (substTy (le_subst env) ty))
lvlExpr env (_, AnnCoercion co) = return (Coercion (substCo (le_subst env) co))
lvlExpr env (_, AnnVar v) = return (lookupVar env v)
lvlExpr _ (_, AnnLit lit) = return (Lit lit)
lvlExpr env (_, AnnCast expr (_, co)) = do
expr' <- lvlExpr env expr
return (Cast expr' (substCo (le_subst env) co))
lvlExpr env (_, AnnTick tickish expr) = do
expr' <- lvlExpr env expr
return (Tick tickish expr')
lvlExpr env expr@(_, AnnApp _ _) = do
let
(fun, args) = collectAnnArgs expr
case fun of
(_, AnnVar f) | floatPAPs env &&
arity > 0 && arity < n_val_args ->
do
let (lapp, rargs) = left (n_val_args arity) expr []
rargs' <- mapM (lvlMFE False env) rargs
lapp' <- lvlMFE False env lapp
return (foldl App lapp' rargs')
where
n_val_args = count (isValArg . deAnnotate) args
arity = idArity f
left 0 e rargs = (e, rargs)
left n (_, AnnApp f a) rargs
| isValArg (deAnnotate a) = left (n1) f (a:rargs)
| otherwise = left n f (a:rargs)
left _ _ _ = panic "SetLevels.lvlExpr.left"
_otherwise -> do
args' <- mapM (lvlMFE False env) args
fun' <- lvlExpr env fun
return (foldl App fun' args')
lvlExpr env expr@(_, AnnLam {})
= do { new_body <- lvlMFE True new_env body
; return (mkLams new_bndrs new_body) }
where
(bndrs, body) = collectAnnBndrs expr
(env1, bndrs1) = substBndrsSL NonRecursive env bndrs
(new_env, new_bndrs) = lvlLamBndrs env1 (le_ctxt_lvl env) bndrs1
lvlExpr env (_, AnnLet bind body)
= do { (bind', new_env) <- lvlBind env bind
; body' <- lvlExpr new_env body
; return (Let bind' body') }
lvlExpr env (_, AnnCase scrut@(scrut_fvs,_) case_bndr ty alts)
= do { scrut' <- lvlMFE True env scrut
; lvlCase env scrut_fvs scrut' case_bndr ty alts }
lvlCase :: LevelEnv
-> VarSet
-> LevelledExpr
-> Id -> Type
-> [AnnAlt Id VarSet]
-> LvlM LevelledExpr
lvlCase env scrut_fvs scrut' case_bndr ty alts
| [(con@(DataAlt {}), bs, body)] <- alts
, exprOkForSpeculation scrut'
, not (isTopLvl dest_lvl)
=
do { (rhs_env, (case_bndr':bs')) <- cloneVars NonRecursive env dest_lvl (case_bndr:bs)
; body' <- lvlMFE True rhs_env body
; let alt' = (con, [TB b (StayPut dest_lvl) | b <- bs'], body')
; return (Case scrut' (TB case_bndr' (FloatMe dest_lvl)) ty [alt']) }
| otherwise
= do { let (alts_env1, [case_bndr']) = substAndLvlBndrs NonRecursive env incd_lvl [case_bndr]
alts_env = extendCaseBndrEnv alts_env1 case_bndr scrut'
; alts' <- mapM (lvl_alt alts_env) alts
; return (Case scrut' case_bndr' ty alts') }
where
incd_lvl = incMinorLvl (le_ctxt_lvl env)
dest_lvl = maxFvLevel (const True) env scrut_fvs
lvl_alt alts_env (con, bs, rhs)
= do { rhs' <- lvlMFE True new_env rhs
; return (con, bs', rhs') }
where
(new_env, bs') = substAndLvlBndrs NonRecursive alts_env incd_lvl bs
\end{code}
Note [Floating cases]
~~~~~~~~~~~~~~~~~~~~~
Consider this:
data T a = MkT !a
f :: T Int -> blah
f x vs = case x of { MkT y ->
let f vs = ...(case y of I# w -> e)...f..
in f vs
Here we can float the (case y ...) out , because y is sure
to be evaluated, to give
f x vs = case x of { MkT y ->
caes y of I# w ->
let f vs = ...(e)...f..
in f vs
That saves unboxing it every time round the loop. It's important in
some DPH stuff where we really want to avoid that repeated unboxing in
the inner loop.
Things to note
* We can't float a case to top level
* It's worth doing this float even if we don't float
the case outside a value lambda. Example
case x of {
MkT y -> (case y of I# w2 -> ..., case y of I# w2 -> ...)
If we floated the cases out we could eliminate one of them.
* We only do this with a single-alternative case
Note [Check the output scrutinee for okForSpec]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
case x of y {
A -> ....(case y of alts)....
}
Because of the binder-swap, the inner case will get substituted to
(case x of ..). So when testing whether the scrutinee is
okForSpecuation we must be careful to test the *result* scrutinee ('x'
in this case), not the *input* one 'y'. The latter *is* ok for
speculation here, but the former is not -- and indeed we can't float
the inner case out, at least not unless x is also evaluated at its
binding site.
That's why we apply exprOkForSpeculation to scrut' and not to scrut.
\begin{code}
lvlMFE :: Bool
-> LevelEnv
-> CoreExprWithFVs
-> LvlM LevelledExpr
lvlMFE _ env (_, AnnType ty)
= return (Type (substTy (le_subst env) ty))
lvlMFE strict_ctxt env (_, AnnTick t e)
= do { e' <- lvlMFE strict_ctxt env e
; return (Tick t e') }
lvlMFE strict_ctxt env (_, AnnCast e (_, co))
= do { e' <- lvlMFE strict_ctxt env e
; return (Cast e' (substCo (le_subst env) co)) }
lvlMFE True env e@(_, AnnCase {})
= lvlExpr env e
lvlMFE strict_ctxt env ann_expr@(fvs, _)
| isUnLiftedType (exprType expr)
|| notWorthFloating ann_expr abs_vars
|| not float_me
=
lvlExpr env ann_expr
| otherwise
= do { expr' <- lvlFloatRhs abs_vars dest_lvl env ann_expr
; var <- newLvlVar expr' is_bot
; return (Let (NonRec (TB var (FloatMe dest_lvl)) expr')
(mkVarApps (Var var) abs_vars)) }
where
expr = deAnnotate ann_expr
is_bot = exprIsBottom expr
dest_lvl = destLevel env fvs (isFunction ann_expr) is_bot
abs_vars = abstractVars dest_lvl env fvs
float_me = dest_lvl `ltMajLvl` (le_ctxt_lvl env)
|| (isTopLvl dest_lvl
&& floatConsts env
&& not strict_ctxt)
\end{code}
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.
Note [Bottoming floats]
~~~~~~~~~~~~~~~~~~~~~~~
If we see
f = \x. g (error "urk")
we'd like to float the call to error, to get
lvl = error "urk"
f = \x. g lvl
Furthermore, we want to float a bottoming expression even if it has free
variables:
f = \x. g (let v = h x in error ("urk" ++ v))
Then we'd like to abstact over 'x' can float the whole arg of g:
lvl = \x. let v = h x in error ("urk" ++ v)
f = \x. g (lvl x)
See Maessen's paper 1999 "Bottom extraction: factoring error handling out
of functional programs" (unpublished I think).
When we do this, we set the strictness and arity of the new bottoming
Id, *immediately*, for two reasons:
* To prevent the abstracted thing being immediately inlined back in again
via preInlineUnconditionally. The latter has a test for bottoming Ids
to stop inlining them, so we'd better make sure it *is* a bottoming Id!
* So that it's properly exposed as such in the interface file, even if
this is all happening after strictness analysis.
Note [Bottoming floats: eta expansion] c.f Note [Bottoming floats]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tiresomely, though, the simplifier has an invariant that the manifest
arity of the RHS should be the same as the arity; but we can't call
etaExpand during SetLevels because it works over a decorated form of
CoreExpr. So we do the eta expansion later, in FloatOut.
Note [Case MFEs]
~~~~~~~~~~~~~~~~
We don't float a case expression as an MFE from a strict context. Why not?
Because in doing so we share a tiny bit of computation (the switch) but
in exchange we build a thunk, which is bad. This case reduces allocation
by 7% in spectral/puzzle (a rather strange benchmark) and 1.2% in real/fem.
Doesn't change any other allocation at all.
\begin{code}
annotateBotStr :: Id -> Maybe (Arity, StrictSig) -> Id
annotateBotStr id Nothing = id
annotateBotStr id (Just (arity, sig)) = id `setIdArity` arity
`setIdStrictness` sig
notWorthFloating :: CoreExprWithFVs -> [Var] -> Bool
notWorthFloating e abs_vars
= go e (count isId abs_vars)
where
go (_, AnnVar {}) n = n >= 0
go (_, AnnLit lit) n = ASSERT( n==0 )
litIsTrivial lit
go (_, AnnCast e _) n = go e n
go (_, AnnApp e arg) n
| (_, AnnType {}) <- arg = go e n
| (_, AnnCoercion {}) <- arg = go e n
| n==0 = False
| is_triv arg = go e (n1)
| otherwise = False
go _ _ = False
is_triv (_, AnnLit {}) = True
is_triv (_, AnnVar {}) = True
is_triv (_, AnnCast e _) = is_triv e
is_triv (_, AnnApp e (_, AnnType {})) = is_triv e
is_triv (_, AnnApp e (_, AnnCoercion {})) = is_triv e
is_triv _ = False
\end{code}
Note [Floating literals]
~~~~~~~~~~~~~~~~~~~~~~~~
It's important to float Integer literals, so that they get shared,
rather than being allocated every time round the loop.
Hence the litIsTrivial.
We'd *like* to share MachStr literal strings too, mainly so we could
CSE them, but alas can't do so directly because they are unlifted.
Note [Escaping a value lambda]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We want to float even cheap expressions out of value lambdas,
because that saves allocation. Consider
f = \x. .. (\y.e) ...
Then we'd like to avoid allocating the (\y.e) every time we call f,
(assuming e does not mention x).
An example where this really makes a difference is simplrun009.
Another reason it's good is because it makes SpecContr fire on functions.
Consider
f = \x. ....(f (\y.e))....
After floating we get
lvl = \y.e
f = \x. ....(f lvl)...
and that is much easier for SpecConstr to generate a robust specialisation for.
The OLD CODE (given where this Note is referred to) prevents floating
of the example above, so I just don't understand the old code. I
don't understand the old comment either (which appears below). I
measured the effect on nofib of changing OLD CODE to 'True', and got
zeros everywhere, but a 4% win for 'puzzle'. Very small 0.5% loss for
'cse'; turns out to be because our arity analysis isn't good enough
yet (mentioned in Simon-nofib-notes).
OLD comment was:
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.
%************************************************************************
%* *
\subsection{Bindings}
%* *
%************************************************************************
The binding stuff works for top level too.
\begin{code}
lvlBind :: LevelEnv
-> CoreBindWithFVs
-> LvlM (LevelledBind, LevelEnv)
lvlBind env (AnnNonRec bndr rhs@(rhs_fvs,_))
| isTyVar bndr
|| isCoVar bndr
|| not (profitableFloat env dest_lvl)
|| (isTopLvl dest_lvl && isUnLiftedType (idType bndr))
=
do { rhs' <- lvlExpr env rhs
; let bind_lvl = incMinorLvl (le_ctxt_lvl env)
(env', [bndr']) = substAndLvlBndrs NonRecursive env bind_lvl [bndr]
; return (NonRec bndr' rhs', env') }
| null abs_vars
= do {
rhs' <- lvlExpr (setCtxtLvl env dest_lvl) rhs
; (env', [bndr']) <- cloneVars NonRecursive env dest_lvl [bndr]
; return (NonRec (TB bndr' (FloatMe dest_lvl)) rhs', env') }
| otherwise
= do {
rhs' <- lvlFloatRhs abs_vars dest_lvl env rhs
; (env', [bndr']) <- newPolyBndrs dest_lvl env abs_vars [bndr]
; return (NonRec (TB bndr' (FloatMe dest_lvl)) rhs', env') }
where
bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
abs_vars = abstractVars dest_lvl env bind_fvs
dest_lvl = destLevel env bind_fvs (isFunction rhs) is_bot
is_bot = exprIsBottom (deAnnotate rhs)
lvlBind env (AnnRec pairs)
| not (profitableFloat env dest_lvl)
= do { let bind_lvl = incMinorLvl (le_ctxt_lvl env)
(env', bndrs') = substAndLvlBndrs Recursive env bind_lvl bndrs
; rhss' <- mapM (lvlExpr env') rhss
; return (Rec (bndrs' `zip` rhss'), env') }
| null abs_vars
= do { (new_env, new_bndrs) <- cloneVars Recursive env dest_lvl bndrs
; new_rhss <- mapM (lvlExpr (setCtxtLvl new_env dest_lvl)) rhss
; return ( Rec ([TB b (FloatMe dest_lvl) | b <- new_bndrs] `zip` new_rhss)
, new_env) }
| [(bndr,rhs)] <- pairs
, count isId abs_vars > 1
= do
let (rhs_env, abs_vars_w_lvls) = lvlLamBndrs env dest_lvl abs_vars
rhs_lvl = le_ctxt_lvl rhs_env
(rhs_env', [new_bndr]) <- cloneVars Recursive rhs_env rhs_lvl [bndr]
let
(lam_bndrs, rhs_body) = collectAnnBndrs rhs
(body_env1, lam_bndrs1) = substBndrsSL NonRecursive rhs_env' lam_bndrs
(body_env2, lam_bndrs2) = lvlLamBndrs body_env1 rhs_lvl lam_bndrs1
new_rhs_body <- lvlExpr body_env2 rhs_body
(poly_env, [poly_bndr]) <- newPolyBndrs dest_lvl env abs_vars [bndr]
return (Rec [(TB poly_bndr (FloatMe dest_lvl)
, mkLams abs_vars_w_lvls $
mkLams lam_bndrs2 $
Let (Rec [( TB new_bndr (StayPut rhs_lvl)
, mkLams lam_bndrs2 new_rhs_body)])
(mkVarApps (Var new_bndr) lam_bndrs1))]
, poly_env)
| otherwise
= do { (new_env, new_bndrs) <- newPolyBndrs dest_lvl env abs_vars bndrs
; new_rhss <- mapM (lvlFloatRhs abs_vars dest_lvl new_env) rhss
; return ( Rec ([TB b (FloatMe dest_lvl) | b <- new_bndrs] `zip` new_rhss)
, new_env) }
where
(bndrs,rhss) = unzip pairs
bind_fvs = (unionVarSets [ idFreeVars bndr `unionVarSet` rhs_fvs
| (bndr, (rhs_fvs,_)) <- pairs])
`minusVarSet`
mkVarSet bndrs
dest_lvl = destLevel env bind_fvs (all isFunction rhss) False
abs_vars = abstractVars dest_lvl env bind_fvs
profitableFloat :: LevelEnv -> Level -> Bool
profitableFloat env dest_lvl
= (dest_lvl `ltMajLvl` le_ctxt_lvl env)
|| isTopLvl dest_lvl
lvlFloatRhs :: [OutVar] -> Level -> LevelEnv -> CoreExprWithFVs
-> UniqSM (Expr LevelledBndr)
lvlFloatRhs abs_vars dest_lvl env rhs
= do { rhs' <- lvlExpr rhs_env rhs
; return (mkLams abs_vars_w_lvls rhs') }
where
(rhs_env, abs_vars_w_lvls) = lvlLamBndrs env dest_lvl abs_vars
\end{code}
%************************************************************************
%* *
\subsection{Deciding floatability}
%* *
%************************************************************************
\begin{code}
substAndLvlBndrs :: RecFlag -> LevelEnv -> Level -> [InVar] -> (LevelEnv, [LevelledBndr])
substAndLvlBndrs is_rec env lvl bndrs
= lvlBndrs subst_env lvl subst_bndrs
where
(subst_env, subst_bndrs) = substBndrsSL is_rec env bndrs
substBndrsSL :: RecFlag -> LevelEnv -> [InVar] -> (LevelEnv, [OutVar])
substBndrsSL is_rec env@(LE { le_subst = subst, le_env = id_env }) bndrs
= ( env { le_subst = subst'
, le_env = foldl add_id id_env (bndrs `zip` bndrs') }
, bndrs')
where
(subst', bndrs') = case is_rec of
NonRecursive -> substBndrs subst bndrs
Recursive -> substRecBndrs subst bndrs
lvlLamBndrs :: LevelEnv -> Level -> [OutVar] -> (LevelEnv, [LevelledBndr])
lvlLamBndrs env lvl bndrs
= lvlBndrs env new_lvl bndrs
where
new_lvl | any is_major bndrs = incMajorLvl lvl
| otherwise = incMinorLvl lvl
is_major bndr = isId bndr && not (isProbablyOneShotLambda bndr)
lvlBndrs :: LevelEnv -> Level -> [CoreBndr] -> (LevelEnv, [LevelledBndr])
lvlBndrs env@(LE { le_lvl_env = lvl_env }) new_lvl bndrs
= ( env { le_ctxt_lvl = new_lvl
, le_lvl_env = foldl add_lvl lvl_env bndrs }
, lvld_bndrs)
where
lvld_bndrs = [TB bndr (StayPut new_lvl) | bndr <- bndrs]
add_lvl env v = extendVarEnv env v new_lvl
\end{code}
\begin{code}
destLevel :: LevelEnv -> VarSet
-> Bool
-> Bool
-> Level
destLevel env fvs is_function is_bot
| is_bot = tOP_LEVEL
| Just n_args <- floatLams env
, n_args > 0
, is_function
, countFreeIds fvs <= n_args
= tOP_LEVEL
| otherwise = maxFvLevel isId env fvs
isFunction :: CoreExprWithFVs -> Bool
isFunction (_, AnnLam b e) | isId b = True
| otherwise = isFunction e
isFunction _ = False
countFreeIds :: VarSet -> Int
countFreeIds = foldVarSet add 0
where
add :: Var -> Int -> Int
add v n | isId v = n+1
| otherwise = n
\end{code}
%************************************************************************
%* *
\subsection{Free-To-Level Monad}
%* *
%************************************************************************
\begin{code}
type InVar = Var
type InId = Id
type OutVar = Var
type OutId = Id
data LevelEnv
= LE { le_switches :: FloatOutSwitches
, le_ctxt_lvl :: Level
, le_lvl_env :: VarEnv Level
, le_subst :: Subst
, le_env :: IdEnv ([OutVar], LevelledExpr)
}
initialEnv :: FloatOutSwitches -> LevelEnv
initialEnv float_lams
= LE { le_switches = float_lams
, le_ctxt_lvl = tOP_LEVEL
, le_lvl_env = emptyVarEnv
, le_subst = emptySubst
, le_env = emptyVarEnv }
floatLams :: LevelEnv -> Maybe Int
floatLams le = floatOutLambdas (le_switches le)
floatConsts :: LevelEnv -> Bool
floatConsts le = floatOutConstants (le_switches le)
floatPAPs :: LevelEnv -> Bool
floatPAPs le = floatOutPartialApplications (le_switches le)
setCtxtLvl :: LevelEnv -> Level -> LevelEnv
setCtxtLvl env lvl = env { le_ctxt_lvl = lvl }
extendCaseBndrEnv :: LevelEnv
-> Id
-> Expr LevelledBndr
-> LevelEnv
extendCaseBndrEnv le@(LE { le_subst = subst, le_env = id_env })
case_bndr (Var scrut_var)
= le { le_subst = extendSubstWithVar subst case_bndr scrut_var
, le_env = add_id id_env (case_bndr, scrut_var) }
extendCaseBndrEnv env _ _ = env
maxFvLevel :: (Var -> Bool) -> LevelEnv -> VarSet -> Level
maxFvLevel max_me (LE { le_lvl_env = lvl_env, le_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
| max_me out_var = case lookupVarEnv lvl_env out_var of
Just lvl' -> maxLvl lvl' lvl
Nothing -> lvl
| otherwise = lvl
lookupVar :: LevelEnv -> Id -> LevelledExpr
lookupVar le v = case lookupVarEnv (le_env le) v of
Just (_, expr) -> expr
_ -> Var v
abstractVars :: Level -> LevelEnv -> VarSet -> [OutVar]
abstractVars dest_lvl (LE { le_subst = subst, le_lvl_env = lvl_env }) in_fvs
= map zap $ uniq $ sortQuantVars
[out_var | out_fv <- varSetElems (substVarSet subst in_fvs)
, out_var <- varSetElems (close out_fv)
, abstract_me out_var ]
where
uniq :: [Var] -> [Var]
uniq (v1:v2:vs) | v1 == v2 = uniq (v2:vs)
| otherwise = v1 : uniq (v2:vs)
uniq vs = vs
abstract_me v = case lookupVarEnv lvl_env v of
Just lvl -> dest_lvl `ltLvl` lvl
Nothing -> False
zap v | isId v = WARN( isStableUnfolding (idUnfolding v) ||
not (isEmptySpecInfo (idSpecialisation v)),
text "absVarsOf: discarding info on" <+> ppr v )
setIdInfo v vanillaIdInfo
| otherwise = v
close :: Var -> VarSet
close v = foldVarSet (unionVarSet . close)
(unitVarSet v)
(varTypeTyVars v)
\end{code}
\begin{code}
type LvlM result = UniqSM result
initLvl :: UniqSupply -> UniqSM a -> a
initLvl = initUs_
\end{code}
\begin{code}
newPolyBndrs :: Level -> LevelEnv -> [OutVar] -> [InId] -> UniqSM (LevelEnv, [OutId])
newPolyBndrs dest_lvl
env@(LE { le_lvl_env = lvl_env, le_subst = subst, le_env = id_env })
abs_vars bndrs
= ASSERT( all (not . isCoVar) bndrs )
do { uniqs <- getUniquesM
; let new_bndrs = zipWith mk_poly_bndr bndrs uniqs
bndr_prs = bndrs `zip` new_bndrs
env' = env { le_lvl_env = foldl add_lvl lvl_env new_bndrs
, le_subst = foldl add_subst subst bndr_prs
, le_env = foldl add_id id_env bndr_prs }
; return (env', new_bndrs) }
where
add_lvl env 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)
mk_poly_bndr bndr uniq = transferPolyIdInfo bndr abs_vars $
mkSysLocal (mkFastString str) uniq poly_ty
where
str = "poly_" ++ occNameString (getOccName bndr)
poly_ty = mkPiTypes abs_vars (substTy subst (idType bndr))
newLvlVar :: LevelledExpr
-> Bool
-> LvlM Id
newLvlVar lvld_rhs is_bot
= do { uniq <- getUniqueM
; return (add_bot_info (mkLocalId (mk_name uniq) rhs_ty)) }
where
add_bot_info var
| is_bot = annotateBotStr var (exprBotStrictness_maybe de_tagged_rhs)
| otherwise = var
de_tagged_rhs = deTagExpr lvld_rhs
rhs_ty = exprType de_tagged_rhs
mk_name uniq = mkSystemVarName uniq (mkFastString "lvl")
cloneVars :: RecFlag -> LevelEnv -> Level -> [Var] -> LvlM (LevelEnv, [Var])
cloneVars is_rec
env@(LE { le_subst = subst, le_lvl_env = lvl_env, le_env = id_env })
dest_lvl vs
= do { us <- getUniqueSupplyM
; let (subst', vs1) = case is_rec of
NonRecursive -> cloneBndrs subst us vs
Recursive -> cloneRecIdBndrs subst us vs
vs2 = map zap_demand_info vs1
prs = vs `zip` vs2
env' = env { le_lvl_env = foldl add_lvl lvl_env vs2
, le_subst = subst'
, le_env = foldl add_id id_env prs }
; return (env', vs2) }
where
add_lvl env v_cloned = extendVarEnv env v_cloned dest_lvl
add_id :: IdEnv ([Var], LevelledExpr) -> (Var, Var) -> IdEnv ([Var], LevelledExpr)
add_id id_env (v, v1)
| isTyVar v = delVarEnv id_env v
| otherwise = extendVarEnv id_env v ([v1], ASSERT(not (isCoVar v1)) Var v1)
zap_demand_info :: Var -> Var
zap_demand_info v
| isId v = zapDemandIdInfo v
| otherwise = v
\end{code}
Note [Zapping the demand info]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
VERY IMPORTANT: we must zap the demand info if the thing is going to
float out, becuause it may be less demanded than at its original
binding site. Eg
f :: Int -> Int
f x = let v = 3*4 in v+x
Here v is strict; but if we float v to top level, it isn't any more.