\section[SimplMonad]{The simplifier Monad}
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
+-- for details
+
module SimplEnv (
- InId, InBind, InExpr, InAlt, InArg, InType, InBinder,
- OutId, OutTyVar, OutBind, OutExpr, OutAlt, OutArg, OutType, OutBinder,
+ InId, InBind, InExpr, InAlt, InArg, InType, InBndr,
+ OutId, OutTyVar, OutBind, OutExpr, OutAlt, OutArg, OutType, OutBndr,
InCoercion, OutCoercion,
-- The simplifier mode
setEnclosingCC, getEnclosingCC,
-- Environments
- SimplEnv, mkSimplEnv, extendIdSubst, extendTvSubst,
+ SimplEnv(..), pprSimplEnv, -- Temp not abstract
+ mkSimplEnv, extendIdSubst, SimplEnv.extendTvSubst,
zapSubstEnv, setSubstEnv,
getInScope, setInScope, setInScopeSet, modifyInScope, addNewInScopeIds,
getRules,
- SimplSR(..), mkContEx, substId,
+ SimplSR(..), mkContEx, substId, lookupRecBndr,
simplNonRecBndr, simplRecBndrs, simplLamBndr, simplLamBndrs,
simplBinder, simplBinders, addLetIdInfo,
- substExpr, substTy,
+ substExpr, substTy,
-- Floats
- FloatsWith, FloatsWithExpr,
- Floats, emptyFloats, isEmptyFloats, unitFloat, addFloats, flattenFloats,
- allLifted, wrapFloats, floatBinds,
- addAuxiliaryBind,
+ Floats, emptyFloats, isEmptyFloats, addNonRec, addFloats, extendFloats,
+ wrapFloats, floatBinds, setFloats, zapFloats, addRecFloats,
+ doFloatFromRhs, getFloats
) where
#include "HsVersions.h"
import SimplMonad
-import Id ( Id, idType, idOccInfo, idUnfolding, setIdUnfolding )
-import IdInfo ( IdInfo, vanillaIdInfo, occInfo, setOccInfo, specInfo, setSpecInfo,
- arityInfo, workerInfo, setWorkerInfo,
- unfoldingInfo, setUnfoldingInfo, isEmptySpecInfo,
- workerExists
- )
+import IdInfo
import CoreSyn
-import Rules ( RuleBase )
-import CoreUtils ( needsCaseBinding )
-import CostCentre ( CostCentreStack, subsumedCCS )
-import Var
+import Rules
+import CoreUtils
+import CostCentre
+import Var
import VarEnv
-import VarSet ( isEmptyVarSet )
+import VarSet
import OrdList
-
+import Id
import qualified CoreSubst ( Subst, mkSubst, substExpr, substSpec, substWorker )
import qualified Type ( substTy, substTyVarBndr )
-
-import Type ( Type, TvSubst(..), TvSubstEnv,
- isUnLiftedType, seqType, tyVarsOfType )
-import Coercion ( Coercion )
-import BasicTypes ( OccInfo(..), isFragileOcc )
-import DynFlags ( SimplifierMode(..) )
-import Util ( mapAccumL )
+import Type hiding ( substTy, substTyVarBndr )
+import Coercion
+import BasicTypes
+import DynFlags
+import Util
import Outputable
+
+import Data.List
\end{code}
%************************************************************************
%************************************************************************
\begin{code}
-type InBinder = CoreBndr
+type InBndr = CoreBndr
type InId = Id -- Not yet cloned
type InType = Type -- Ditto
type InBind = CoreBind
type InArg = CoreArg
type InCoercion = Coercion
-type OutBinder = CoreBndr
+type OutBndr = CoreBndr
type OutId = Id -- Cloned
type OutTyVar = TyVar -- Cloned
type OutType = Type -- Cloned
seChkr :: SwitchChecker,
seCC :: CostCentreStack, -- The enclosing CCS (when profiling)
- -- Rules from other modules
- seExtRules :: RuleBase,
-
-- The current set of in-scope variables
-- They are all OutVars, and all bound in this module
seInScope :: InScopeSet, -- OutVars only
+ -- Includes all variables bound by seFloats
+ seFloats :: Floats,
+ -- See Note [Simplifier floats]
-- The current substitution
seTvSubst :: TvSubstEnv, -- InTyVar |--> OutType
seIdSubst :: SimplIdSubst -- InId |--> OutExpr
+
}
+pprSimplEnv :: SimplEnv -> SDoc
+-- Used for debugging; selective
+pprSimplEnv env
+ = vcat [ptext SLIT("TvSubst:") <+> ppr (seTvSubst env),
+ ptext SLIT("IdSubst:") <+> ppr (seIdSubst env) ]
+
type SimplIdSubst = IdEnv SimplSR -- IdId |--> OutExpr
+ -- See Note [Extending the Subst] in CoreSubst
data SimplSR
= DoneEx OutExpr -- Completed term
| ContEx TvSubstEnv -- A suspended substitution
SimplIdSubst
InExpr
+
+instance Outputable SimplSR where
+ ppr (DoneEx e) = ptext SLIT("DoneEx") <+> ppr e
+ ppr (DoneId v) = ptext SLIT("DoneId") <+> ppr v
+ ppr (ContEx tv id e) = vcat [ptext SLIT("ContEx") <+> ppr e {-,
+ ppr (filter_env tv), ppr (filter_env id) -}]
+ -- where
+ -- fvs = exprFreeVars e
+ -- filter_env env = filterVarEnv_Directly keep env
+ -- keep uniq _ = uniq `elemUFM_Directly` fvs
\end{code}
\begin{code}
-mkSimplEnv :: SimplifierMode -> SwitchChecker -> RuleBase -> SimplEnv
-mkSimplEnv mode switches rules
+mkSimplEnv :: SimplifierMode -> SwitchChecker -> SimplEnv
+mkSimplEnv mode switches
= SimplEnv { seChkr = switches, seCC = subsumedCCS,
seMode = mode, seInScope = emptyInScopeSet,
- seExtRules = rules,
+ seFloats = emptyFloats,
seTvSubst = emptyVarEnv, seIdSubst = emptyVarEnv }
-- The top level "enclosing CC" is "SUBSUMED".
setInScopeSet env in_scope = env {seInScope = in_scope}
setInScope :: SimplEnv -> SimplEnv -> SimplEnv
-setInScope env env_with_in_scope = setInScopeSet env (getInScope env_with_in_scope)
+-- Set the in-scope set, and *zap* the floats
+setInScope env env_with_scope
+ = env { seInScope = seInScope env_with_scope,
+ seFloats = emptyFloats }
+
+setFloats :: SimplEnv -> SimplEnv -> SimplEnv
+-- Set the in-scope set *and* the floats
+setFloats env env_with_floats
+ = env { seInScope = seInScope env_with_floats,
+ seFloats = seFloats env_with_floats }
addNewInScopeIds :: SimplEnv -> [CoreBndr] -> SimplEnv
-- The new Ids are guaranteed to be freshly allocated
isEmptySimplSubst :: SimplEnv -> Bool
isEmptySimplSubst (SimplEnv { seTvSubst = tvs, seIdSubst = ids })
= isEmptyVarEnv tvs && isEmptyVarEnv ids
+\end{code}
----------------------
-getRules :: SimplEnv -> RuleBase
-getRules = seExtRules
+
+
+%************************************************************************
+%* *
+\subsection{Floats}
+%* *
+%************************************************************************
+
+Note [Simplifier floats]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+The Floats is a bunch of bindings, classified by a FloatFlag.
+
+ NonRec x (y:ys) FltLifted
+ Rec [(x,rhs)] FltLifted
+
+ NonRec x# (y +# 3) FltOkSpec -- Unboxed, but ok-for-spec'n
+
+ NonRec x# (a /# b) FltCareful
+ NonRec x* (f y) FltCareful -- Strict binding; might fail or diverge
+ NonRec x# (f y) FltCareful -- Unboxed binding: might fail or diverge
+ -- (where f :: Int -> Int#)
+
+\begin{code}
+data Floats = Floats (OrdList OutBind) FloatFlag
+ -- See Note [Simplifier floats]
+
+data FloatFlag
+ = FltLifted -- All bindings are lifted and lazy
+ -- Hence ok to float to top level, or recursive
+
+ | FltOkSpec -- All bindings are FltLifted *or*
+ -- strict (perhaps because unlifted,
+ -- perhaps because of a strict binder),
+ -- *and* ok-for-speculation
+ -- Hence ok to float out of the RHS
+ -- of a lazy non-recursive let binding
+ -- (but not to top level, or into a rec group)
+
+ | FltCareful -- At least one binding is strict (or unlifted)
+ -- and not guaranteed cheap
+ -- Do not float these bindings out of a lazy let
+
+instance Outputable Floats where
+ ppr (Floats binds ff) = ppr ff $$ ppr (fromOL binds)
+
+instance Outputable FloatFlag where
+ ppr FltLifted = ptext SLIT("FltLifted")
+ ppr FltOkSpec = ptext SLIT("FltOkSpec")
+ ppr FltCareful = ptext SLIT("FltCareful")
+
+andFF :: FloatFlag -> FloatFlag -> FloatFlag
+andFF FltCareful _ = FltCareful
+andFF FltOkSpec FltCareful = FltCareful
+andFF FltOkSpec flt = FltOkSpec
+andFF FltLifted flt = flt
+
+classifyFF :: CoreBind -> FloatFlag
+classifyFF (Rec _) = FltLifted
+classifyFF (NonRec bndr rhs)
+ | not (isStrictId bndr) = FltLifted
+ | exprOkForSpeculation rhs = FltOkSpec
+ | otherwise = FltCareful
+
+doFloatFromRhs :: TopLevelFlag -> RecFlag -> Bool -> OutExpr -> SimplEnv -> Bool
+doFloatFromRhs lvl rec str rhs (SimplEnv {seFloats = Floats fs ff})
+ = not (isNilOL fs) && want_to_float && can_float
+ where
+ want_to_float = isTopLevel lvl || exprIsCheap rhs
+ can_float = case ff of
+ FltLifted -> True
+ FltOkSpec -> isNotTopLevel lvl && isNonRec rec
+ FltCareful -> isNotTopLevel lvl && isNonRec rec && str
+\end{code}
+
+
+\begin{code}
+emptyFloats :: Floats
+emptyFloats = Floats nilOL FltLifted
+
+unitFloat :: OutBind -> Floats
+-- A single-binding float
+unitFloat bind = Floats (unitOL bind) (classifyFF bind)
+
+addNonRec :: SimplEnv -> OutId -> OutExpr -> SimplEnv
+-- Add a non-recursive binding and extend the in-scope set
+-- The latter is important; the binder may already be in the
+-- in-scope set (although it might also have been created with newId)
+-- but it may now have more IdInfo
+addNonRec env id rhs
+ = env { seFloats = seFloats env `addFlts` unitFloat (NonRec id rhs),
+ seInScope = extendInScopeSet (seInScope env) id }
+
+extendFloats :: SimplEnv -> [OutBind] -> SimplEnv
+-- Add these bindings to the floats, and extend the in-scope env too
+extendFloats env binds
+ = env { seFloats = seFloats env `addFlts` new_floats,
+ seInScope = extendInScopeSetList (seInScope env) bndrs }
+ where
+ bndrs = bindersOfBinds binds
+ new_floats = Floats (toOL binds)
+ (foldr (andFF . classifyFF) FltLifted binds)
+
+addFloats :: SimplEnv -> SimplEnv -> SimplEnv
+-- Add the floats for env2 to env1;
+-- *plus* the in-scope set for env2, which is bigger
+-- than that for env1
+addFloats env1 env2
+ = env1 {seFloats = seFloats env1 `addFlts` seFloats env2,
+ seInScope = seInScope env2 }
+
+addFlts :: Floats -> Floats -> Floats
+addFlts (Floats bs1 l1) (Floats bs2 l2)
+ = Floats (bs1 `appOL` bs2) (l1 `andFF` l2)
+
+zapFloats :: SimplEnv -> SimplEnv
+zapFloats env = env { seFloats = emptyFloats }
+
+addRecFloats :: SimplEnv -> SimplEnv -> SimplEnv
+-- Flattens the floats from env2 into a single Rec group,
+-- prepends the floats from env1, and puts the result back in env2
+-- This is all very specific to the way recursive bindings are
+-- handled; see Simplify.simplRecBind
+addRecFloats env1 env2@(SimplEnv {seFloats = Floats bs ff})
+ = ASSERT2( case ff of { FltLifted -> True; other -> False }, ppr (fromOL bs) )
+ env2 {seFloats = seFloats env1 `addFlts` unitFloat (Rec (flattenBinds (fromOL bs)))}
+
+wrapFloats :: SimplEnv -> OutExpr -> OutExpr
+wrapFloats env expr = wrapFlts (seFloats env) expr
+
+wrapFlts :: Floats -> OutExpr -> OutExpr
+-- Wrap the floats around the expression, using case-binding where necessary
+wrapFlts (Floats bs _) body = foldrOL wrap body bs
+ where
+ wrap (Rec prs) body = Let (Rec prs) body
+ wrap (NonRec b r) body = bindNonRec b r body
+
+getFloats :: SimplEnv -> [CoreBind]
+getFloats (SimplEnv {seFloats = Floats bs _}) = fromOL bs
+
+isEmptyFloats :: SimplEnv -> Bool
+isEmptyFloats env = isEmptyFlts (seFloats env)
+
+isEmptyFlts :: Floats -> Bool
+isEmptyFlts (Floats bs _) = isNilOL bs
+
+floatBinds :: Floats -> [OutBind]
+floatBinds (Floats bs _) = fromOL bs
\end{code}
= DoneId v
| otherwise -- A local Id
= case lookupVarEnv ids v of
- Just (DoneId v) -> DoneId (refine v)
+ Just (DoneId v) -> DoneId (refine in_scope v)
Just res -> res
- Nothing -> DoneId (refine v)
+ Nothing -> DoneId (refine in_scope v)
where
+
-- Get the most up-to-date thing from the in-scope set
-- Even though it isn't in the substitution, it may be in
-- the in-scope set with better IdInfo
- refine v = case lookupInScope in_scope v of
- Just v' -> v'
- Nothing -> WARN( True, ppr v ) v -- This is an error!
+refine in_scope v = case lookupInScope in_scope v of
+ Just v' -> v'
+ Nothing -> WARN( True, ppr v ) v -- This is an error!
+
+lookupRecBndr :: SimplEnv -> Id -> Id
+-- Look up an Id which has been put into the envt by simplRecBndrs,
+-- but where we have not yet done its RHS
+lookupRecBndr (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v
+ = case lookupVarEnv ids v of
+ Just (DoneId v) -> v
+ Just res -> pprPanic "lookupRecBndr" (ppr v)
+ Nothing -> refine in_scope v
\end{code}
\begin{code}
simplBinders, simplLamBndrs
- :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder])
+ :: SimplEnv -> [InBndr] -> SimplM (SimplEnv, [OutBndr])
simplBinders env bndrs = mapAccumLSmpl simplBinder env bndrs
simplLamBndrs env bndrs = mapAccumLSmpl simplLamBndr env bndrs
-------------
-simplBinder :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder)
+simplBinder :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr)
-- Used for lambda and case-bound variables
-- Clone Id if necessary, substitute type
-- Return with IdInfo already substituted, but (fragile) occurrence info zapped
-- * The substitution extended with a DoneId if unique changed
-- In this case, the var in the DoneId is the same as the
-- var returned
+--
+-- Exactly like CoreSubst.substIdBndr, except that the type of id_subst differs
substIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst})
old_id
-- Extend the substitution if the unique has changed
-- See the notes with substTyVarBndr for the delSubstEnv
+ -- Also see Note [Extending the Subst] in CoreSubst
new_subst | new_id /= old_id
= extendVarEnv id_subst old_id (DoneId new_id)
| otherwise
= delVarEnv id_subst old_id
\end{code}
-
\begin{code}
+------------------------------------
seqTyVar :: TyVar -> ()
seqTyVar b = b `seq` ()
seqIds (id:ids) = seqId id `seq` seqIds ids
\end{code}
-
%************************************************************************
%* *
Let bindings
Rename the binders if necessary,
\begin{code}
-simplNonRecBndr :: SimplEnv -> InBinder -> SimplM (SimplEnv, OutBinder)
+simplNonRecBndr :: SimplEnv -> InBndr -> SimplM (SimplEnv, OutBndr)
simplNonRecBndr env id
= do { let (env1, id1) = substLetIdBndr env id
; seqId id1 `seq` return (env1, id1) }
---------------
-simplRecBndrs :: SimplEnv -> [InBinder] -> SimplM (SimplEnv, [OutBinder])
+simplRecBndrs :: SimplEnv -> [InBndr] -> SimplM SimplEnv
simplRecBndrs env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) ids
= do { let (env1, ids1) = mapAccumL substLetIdBndr env ids
- ; seqIds ids1 `seq` return (env1, ids1) }
+ ; seqIds ids1 `seq` return env1 }
---------------
-substLetIdBndr :: SimplEnv -> InBinder -- Env and binder to transform
- -> (SimplEnv, OutBinder)
--- C.f. CoreSubst.substIdBndr
+substLetIdBndr :: SimplEnv -> InBndr -- Env and binder to transform
+ -> (SimplEnv, OutBndr)
+-- C.f. substIdBndr above
-- Clone Id if necessary, substitute its type
--- Return an Id with completely zapped IdInfo
+-- Return an Id with its fragile info zapped
+-- namely, any info that depends on free variables
-- [addLetIdInfo, below, will restore its IdInfo]
+-- We want to retain robust info, especially arity and demand info,
+-- so that they are available to occurrences that occur in an
+-- earlier binding of a letrec
-- Augment the subtitution
-- if the unique changed, *or*
-- if there's interesting occurrence info
where
id1 = uniqAway in_scope old_id
id2 = substIdType env id1
- new_id = setIdInfo id2 vanillaIdInfo
+
+ -- We want to get rid of any info that's dependent on free variables,
+ -- but keep other info (like the arity).
+ new_id = zapFragileIdInfo id2
-- Extend the substitution if the unique has changed,
-- or there's some useful occurrence information
-- See the notes with substTyVarBndr for the delSubstEnv
- occ_info = occInfo (idInfo old_id)
new_subst | new_id /= old_id
= extendVarEnv id_subst old_id (DoneId new_id)
| otherwise
= delVarEnv id_subst old_id
\end{code}
-Add IdInfo back onto a let-bound Id
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Note [Add IdInfo back onto a let-bound Id]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We must transfer the IdInfo of the original binder to the new binder.
This is crucial, to preserve
strictness
when substituting in h's RULE.
\begin{code}
-addLetIdInfo :: SimplEnv -> InBinder -> OutBinder -> (SimplEnv, OutBinder)
+addLetIdInfo :: SimplEnv -> InBndr -> OutBndr -> (SimplEnv, OutBndr)
addLetIdInfo env in_id out_id
= (modifyInScope env out_id final_id, final_id)
where
substIdType :: SimplEnv -> Id -> Id
substIdType env@(SimplEnv { seInScope = in_scope, seTvSubst = tv_env}) id
| isEmptyVarEnv tv_env || isEmptyVarSet (tyVarsOfType old_ty) = id
- | otherwise = setIdType id (Type.substTy (TvSubst in_scope tv_env) old_ty)
+ | otherwise = Id.setIdType id (Type.substTy (TvSubst in_scope tv_env) old_ty)
-- The tyVarsOfType is cheaper than it looks
-- because we cache the free tyvars of the type
-- in a Note in the id's type itself
| otherwise = CoreSubst.substExpr (mkCoreSubst env) expr
\end{code}
-
-%************************************************************************
-%* *
-\subsection{Floats}
-%* *
-%************************************************************************
-
-\begin{code}
-type FloatsWithExpr = FloatsWith OutExpr
-type FloatsWith a = (Floats, a)
- -- We return something equivalent to (let b in e), but
- -- in pieces to avoid the quadratic blowup when floating
- -- incrementally. Comments just before simplExprB in Simplify.lhs
-
-data Floats = Floats (OrdList OutBind)
- InScopeSet -- Environment "inside" all the floats
- Bool -- True <=> All bindings are lifted
-
-allLifted :: Floats -> Bool
-allLifted (Floats _ _ is_lifted) = is_lifted
-
-wrapFloats :: Floats -> OutExpr -> OutExpr
-wrapFloats (Floats bs _ _) body = foldrOL Let body bs
-
-isEmptyFloats :: Floats -> Bool
-isEmptyFloats (Floats bs _ _) = isNilOL bs
-
-floatBinds :: Floats -> [OutBind]
-floatBinds (Floats bs _ _) = fromOL bs
-
-flattenFloats :: Floats -> Floats
--- Flattens into a single Rec group
-flattenFloats (Floats bs is is_lifted)
- = ASSERT2( is_lifted, ppr (fromOL bs) )
- Floats (unitOL (Rec (flattenBinds (fromOL bs)))) is is_lifted
-\end{code}
-
-\begin{code}
-emptyFloats :: SimplEnv -> Floats
-emptyFloats env = Floats nilOL (getInScope env) True
-
-unitFloat :: SimplEnv -> OutId -> OutExpr -> Floats
--- A single non-rec float; extend the in-scope set
-unitFloat env var rhs = Floats (unitOL (NonRec var rhs))
- (extendInScopeSet (getInScope env) var)
- (not (isUnLiftedType (idType var)))
-
-addFloats :: SimplEnv -> Floats
- -> (SimplEnv -> SimplM (FloatsWith a))
- -> SimplM (FloatsWith a)
-addFloats env (Floats b1 is1 l1) thing_inside
- | isNilOL b1
- = thing_inside env
- | otherwise
- = thing_inside (setInScopeSet env is1) `thenSmpl` \ (Floats b2 is2 l2, res) ->
- returnSmpl (Floats (b1 `appOL` b2) is2 (l1 && l2), res)
-
-addLetBind :: OutBind -> Floats -> Floats
-addLetBind bind (Floats binds in_scope lifted)
- = Floats (bind `consOL` binds) in_scope (lifted && is_lifted_bind bind)
-
-is_lifted_bind (Rec _) = True
-is_lifted_bind (NonRec b r) = not (isUnLiftedType (idType b))
-
--- addAuxiliaryBind * takes already-simplified things (bndr and rhs)
--- * extends the in-scope env
--- * assumes it's a let-bindable thing
-addAuxiliaryBind :: SimplEnv -> OutBind
- -> (SimplEnv -> SimplM (FloatsWith a))
- -> SimplM (FloatsWith a)
- -- Extends the in-scope environment as well as wrapping the bindings
-addAuxiliaryBind env bind thing_inside
- = ASSERT( case bind of { NonRec b r -> not (needsCaseBinding (idType b) r) ; Rec _ -> True } )
- thing_inside (addNewInScopeIds env (bindersOf bind)) `thenSmpl` \ (floats, x) ->
- returnSmpl (addLetBind bind floats, x)
-\end{code}
-
-
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