%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[Demand]{@Demand@: A decoupled implementation of a demand domain}
\begin{code}
module Demand (
StrDmd, UseDmd(..), Count(..),
countOnce, countMany,
Demand, CleanDemand,
mkProdDmd, mkOnceUsedDmd, mkManyUsedDmd, mkHeadStrict, oneifyDmd,
getUsage, toCleanDmd,
absDmd, topDmd, botDmd, seqDmd,
lubDmd, bothDmd, apply1Dmd, apply2Dmd,
isTopDmd, isBotDmd, isAbsDmd, isSeqDmd,
peelUseCall, cleanUseDmd_maybe, strictenDmd, bothCleanDmd,
DmdType(..), dmdTypeDepth, lubDmdType, bothDmdType,
nopDmdType, botDmdType, mkDmdType,
addDemand, removeDmdTyArgs,
BothDmdArg, mkBothDmdArg, toBothDmdArg,
DmdEnv, emptyDmdEnv,
peelFV,
DmdResult, CPRResult,
isBotRes, isTopRes,
topRes, botRes, cprProdRes, vanillaCprProdRes, cprSumRes,
appIsBottom, isBottomingSig, pprIfaceStrictSig,
trimCPRInfo, returnsCPR_maybe,
StrictSig(..), mkStrictSig, mkClosedStrictSig, nopSig, botSig, cprProdSig,
isNopSig, splitStrictSig, increaseStrictSigArity,
seqDemand, seqDemandList, seqDmdType, seqStrictSig,
evalDmd, cleanEvalDmd, cleanEvalProdDmd, isStrictDmd,
splitDmdTy, splitFVs,
deferAfterIO,
postProcessUnsat, postProcessDmdTypeM,
splitProdDmd, splitProdDmd_maybe, peelCallDmd, mkCallDmd,
dmdTransformSig, dmdTransformDataConSig, dmdTransformDictSelSig,
argOneShots, argsOneShots,
isSingleUsed, reuseEnv, zapDemand, zapStrictSig,
strictifyDictDmd
) where
#include "HsVersions.h"
import StaticFlags
import DynFlags
import Outputable
import Var ( Var )
import VarEnv
import UniqFM
import Util
import BasicTypes
import Binary
import Maybes ( orElse )
import Type ( Type )
import TyCon ( isNewTyCon, isClassTyCon )
import DataCon ( splitDataProductType_maybe )
\end{code}
%************************************************************************
%* *
\subsection{Strictness domain}
%* *
%************************************************************************
Lazy
|
HeadStr
/ \
SCall SProd
\ /
HyperStr
\begin{code}
data StrDmd
= HyperStr
| SCall StrDmd
| SProd [MaybeStr]
| HeadStr
deriving ( Eq, Show )
data MaybeStr = Lazy
| Str StrDmd
deriving ( Eq, Show )
strBot, strTop :: MaybeStr
strBot = Str HyperStr
strTop = Lazy
mkSCall :: StrDmd -> StrDmd
mkSCall HyperStr = HyperStr
mkSCall s = SCall s
mkSProd :: [MaybeStr] -> StrDmd
mkSProd sx
| any isHyperStr sx = HyperStr
| all isLazy sx = HeadStr
| otherwise = SProd sx
isLazy :: MaybeStr -> Bool
isLazy Lazy = True
isLazy (Str _) = False
isHyperStr :: MaybeStr -> Bool
isHyperStr (Str HyperStr) = True
isHyperStr _ = False
instance Outputable StrDmd where
ppr HyperStr = char 'B'
ppr (SCall s) = char 'C' <> parens (ppr s)
ppr HeadStr = char 'S'
ppr (SProd sx) = char 'S' <> parens (hcat (map ppr sx))
instance Outputable MaybeStr where
ppr (Str s) = ppr s
ppr Lazy = char 'L'
lubMaybeStr :: MaybeStr -> MaybeStr -> MaybeStr
lubMaybeStr Lazy _ = Lazy
lubMaybeStr _ Lazy = Lazy
lubMaybeStr (Str s1) (Str s2) = Str (s1 `lubStr` s2)
lubStr :: StrDmd -> StrDmd -> StrDmd
lubStr HyperStr s = s
lubStr (SCall s1) HyperStr = SCall s1
lubStr (SCall _) HeadStr = HeadStr
lubStr (SCall s1) (SCall s2) = SCall (s1 `lubStr` s2)
lubStr (SCall _) (SProd _) = HeadStr
lubStr (SProd sx) HyperStr = SProd sx
lubStr (SProd _) HeadStr = HeadStr
lubStr (SProd s1) (SProd s2)
| length s1 == length s2 = mkSProd (zipWith lubMaybeStr s1 s2)
| otherwise = HeadStr
lubStr (SProd _) (SCall _) = HeadStr
lubStr HeadStr _ = HeadStr
bothMaybeStr :: MaybeStr -> MaybeStr -> MaybeStr
bothMaybeStr Lazy s = s
bothMaybeStr s Lazy = s
bothMaybeStr (Str s1) (Str s2) = Str (s1 `bothStr` s2)
bothStr :: StrDmd -> StrDmd -> StrDmd
bothStr HyperStr _ = HyperStr
bothStr HeadStr s = s
bothStr (SCall _) HyperStr = HyperStr
bothStr (SCall s1) HeadStr = SCall s1
bothStr (SCall s1) (SCall s2) = SCall (s1 `bothStr` s2)
bothStr (SCall _) (SProd _) = HyperStr
bothStr (SProd _) HyperStr = HyperStr
bothStr (SProd s1) HeadStr = SProd s1
bothStr (SProd s1) (SProd s2)
| length s1 == length s2 = mkSProd (zipWith bothMaybeStr s1 s2)
| otherwise = HyperStr
bothStr (SProd _) (SCall _) = HyperStr
seqStrDmd :: StrDmd -> ()
seqStrDmd (SProd ds) = seqStrDmdList ds
seqStrDmd (SCall s) = s `seq` ()
seqStrDmd _ = ()
seqStrDmdList :: [MaybeStr] -> ()
seqStrDmdList [] = ()
seqStrDmdList (d:ds) = seqMaybeStr d `seq` seqStrDmdList ds
seqMaybeStr :: MaybeStr -> ()
seqMaybeStr Lazy = ()
seqMaybeStr (Str s) = seqStrDmd s
splitStrProdDmd :: Int -> StrDmd -> [MaybeStr]
splitStrProdDmd n HyperStr = replicate n strBot
splitStrProdDmd n HeadStr = replicate n strTop
splitStrProdDmd n (SProd ds) = ASSERT( ds `lengthIs` n) ds
splitStrProdDmd _ d@(SCall {}) = pprPanic "attempt to prod-split strictness call demand" (ppr d)
\end{code}
%************************************************************************
%* *
\subsection{Absence domain}
%* *
%************************************************************************
Used
/ \
UCall UProd
\ /
UHead
|
Abs
\begin{code}
data UseDmd
= UCall Count UseDmd
| UProd [MaybeUsed]
| UHead
| Used
deriving ( Eq, Show )
data MaybeUsed
= Abs
| Use Count UseDmd
deriving ( Eq, Show )
data Count = One | Many
deriving ( Eq, Show )
instance Outputable MaybeUsed where
ppr Abs = char 'A'
ppr (Use Many a) = ppr a
ppr (Use One a) = char '1' <> char '*' <> ppr a
instance Outputable UseDmd where
ppr Used = char 'U'
ppr (UCall c a) = char 'C' <> ppr c <> parens (ppr a)
ppr UHead = char 'H'
ppr (UProd as) = char 'U' <> parens (hcat (punctuate (char ',') (map ppr as)))
instance Outputable Count where
ppr One = char '1'
ppr Many = text ""
countOnce, countMany :: Count
countOnce = One
countMany = Many
useBot, useTop :: MaybeUsed
useBot = Abs
useTop = Use Many Used
mkUCall :: Count -> UseDmd -> UseDmd
mkUCall c a = UCall c a
mkUProd :: [MaybeUsed] -> UseDmd
mkUProd ux
| all (== Abs) ux = UHead
| otherwise = UProd ux
lubCount :: Count -> Count -> Count
lubCount _ Many = Many
lubCount Many _ = Many
lubCount x _ = x
lubMaybeUsed :: MaybeUsed -> MaybeUsed -> MaybeUsed
lubMaybeUsed Abs x = x
lubMaybeUsed x Abs = x
lubMaybeUsed (Use c1 a1) (Use c2 a2) = Use (lubCount c1 c2) (lubUse a1 a2)
lubUse :: UseDmd -> UseDmd -> UseDmd
lubUse UHead u = u
lubUse (UCall c u) UHead = UCall c u
lubUse (UCall c1 u1) (UCall c2 u2) = UCall (lubCount c1 c2) (lubUse u1 u2)
lubUse (UCall _ _) _ = Used
lubUse (UProd ux) UHead = UProd ux
lubUse (UProd ux1) (UProd ux2)
| length ux1 == length ux2 = UProd $ zipWith lubMaybeUsed ux1 ux2
| otherwise = Used
lubUse (UProd {}) (UCall {}) = Used
lubUse (UProd ux) Used = UProd (map (`lubMaybeUsed` useTop) ux)
lubUse Used (UProd ux) = UProd (map (`lubMaybeUsed` useTop) ux)
lubUse Used _ = Used
bothMaybeUsed :: MaybeUsed -> MaybeUsed -> MaybeUsed
bothMaybeUsed Abs x = x
bothMaybeUsed x Abs = x
bothMaybeUsed (Use _ a1) (Use _ a2) = Use Many (bothUse a1 a2)
bothUse :: UseDmd -> UseDmd -> UseDmd
bothUse UHead u = u
bothUse (UCall c u) UHead = UCall c u
bothUse (UCall _ u1) (UCall _ u2) = UCall Many (u1 `lubUse` u2)
bothUse (UCall {}) _ = Used
bothUse (UProd ux) UHead = UProd ux
bothUse (UProd ux1) (UProd ux2)
| length ux1 == length ux2 = UProd $ zipWith bothMaybeUsed ux1 ux2
| otherwise = Used
bothUse (UProd {}) (UCall {}) = Used
bothUse Used (UProd ux) = UProd (map (`bothMaybeUsed` useTop) ux)
bothUse (UProd ux) Used = UProd (map (`bothMaybeUsed` useTop) ux)
bothUse Used _ = Used
peelUseCall :: UseDmd -> Maybe (Count, UseDmd)
peelUseCall (UCall c u) = Just (c,u)
peelUseCall _ = Nothing
\end{code}
Note [Don't optimise UProd(Used) to Used]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These two UseDmds:
UProd [Used, Used] and Used
are semantically equivalent, but we do not turn the former into
the latter, for a regrettable-subtle reason. Suppose we did.
then
f (x,y) = (y,x)
would get
StrDmd = Str = SProd [Lazy, Lazy]
UseDmd = Used = UProd [Used, Used]
But with the joint demand of doesn't convey any clue
that there is a product involved, and so the worthSplittingFun
will not fire. (We'd need to use the type as well to make it fire.)
Moreover, consider
g h p@(_,_) = h p
This too would get , but this time there really isn't any
point in w/w since the components of the pair are not used at all.
So the solution is: don't aggressively collapse UProd [Used,Used] to
Used; intead leave it as-is. In effect we are using the UseDmd to do a
little bit of boxity analysis. Not very nice.
Note [Used should win]
~~~~~~~~~~~~~~~~~~~~~~
Both in lubUse and bothUse we want (Used `both` UProd us) to be Used.
Why? Because Used carries the implication the whole thing is used,
box and all, so we don't want to w/w it. If we use it both boxed and
unboxed, then we are definitely using the box, and so we are quite
likely to pay a reboxing cost. So we make Used win here.
Example is in the Buffer argument of GHC.IO.Handle.Internals.writeCharBuffer
Baseline: (A) Not making Used win (UProd wins)
Compare with: (B) making Used win for lub and both
Min -0.3% -5.6% -10.7% -11.0% -33.3%
Max +0.3% +45.6% +11.5% +11.5% +6.9%
Geometric Mean -0.0% +0.5% +0.3% +0.2% -0.8%
Baseline: (B) Making Used win for both lub and both
Compare with: (C) making Used win for both, but UProd win for lub
Min -0.1% -0.3% -7.9% -8.0% -6.5%
Max +0.1% +1.0% +21.0% +21.0% +0.5%
Geometric Mean +0.0% +0.0% -0.0% -0.1% -0.1%
\begin{code}
markReusedDmd :: MaybeUsed -> MaybeUsed
markReusedDmd Abs = Abs
markReusedDmd (Use _ a) = Use Many (markReused a)
markReused :: UseDmd -> UseDmd
markReused (UCall _ u) = UCall Many u
markReused (UProd ux) = UProd (map markReusedDmd ux)
markReused u = u
isUsedMU :: MaybeUsed -> Bool
isUsedMU Abs = True
isUsedMU (Use One _) = False
isUsedMU (Use Many u) = isUsedU u
isUsedU :: UseDmd -> Bool
isUsedU Used = True
isUsedU UHead = True
isUsedU (UProd us) = all isUsedMU us
isUsedU (UCall One _) = False
isUsedU (UCall Many _) = True
seqUseDmd :: UseDmd -> ()
seqUseDmd (UProd ds) = seqMaybeUsedList ds
seqUseDmd (UCall c d) = c `seq` seqUseDmd d
seqUseDmd _ = ()
seqMaybeUsedList :: [MaybeUsed] -> ()
seqMaybeUsedList [] = ()
seqMaybeUsedList (d:ds) = seqMaybeUsed d `seq` seqMaybeUsedList ds
seqMaybeUsed :: MaybeUsed -> ()
seqMaybeUsed (Use c u) = c `seq` seqUseDmd u
seqMaybeUsed _ = ()
splitUseProdDmd :: Int -> UseDmd -> [MaybeUsed]
splitUseProdDmd n Used = replicate n useTop
splitUseProdDmd n UHead = replicate n Abs
splitUseProdDmd n (UProd ds) = ASSERT2( ds `lengthIs` n, ppr n $$ ppr ds ) ds
splitUseProdDmd _ d@(UCall _ _) = pprPanic "attempt to prod-split usage call demand" (ppr d)
\end{code}
%************************************************************************
%* *
\subsection{Joint domain for Strictness and Absence}
%* *
%************************************************************************
\begin{code}
data JointDmd = JD { strd :: MaybeStr, absd :: MaybeUsed }
deriving ( Eq, Show )
instance Outputable JointDmd where
ppr (JD {strd = s, absd = a}) = angleBrackets (ppr s <> char ',' <> ppr a)
mkJointDmd :: MaybeStr -> MaybeUsed -> JointDmd
mkJointDmd s a = JD { strd = s, absd = a }
mkJointDmds :: [MaybeStr] -> [MaybeUsed] -> [JointDmd]
mkJointDmds ss as = zipWithEqual "mkJointDmds" mkJointDmd ss as
absDmd :: JointDmd
absDmd = mkJointDmd Lazy Abs
apply1Dmd, apply2Dmd :: Demand
apply1Dmd = JD { strd = Lazy, absd = Use Many (UCall One Used) }
apply2Dmd = JD { strd = Lazy, absd = Use Many (UCall One (UCall One Used)) }
topDmd :: JointDmd
topDmd = mkJointDmd Lazy useTop
seqDmd :: JointDmd
seqDmd = mkJointDmd (Str HeadStr) (Use One UHead)
botDmd :: JointDmd
botDmd = mkJointDmd strBot useBot
lubDmd :: JointDmd -> JointDmd -> JointDmd
lubDmd (JD {strd = s1, absd = a1})
(JD {strd = s2, absd = a2}) = mkJointDmd (s1 `lubMaybeStr` s2) (a1 `lubMaybeUsed` a2)
bothDmd :: JointDmd -> JointDmd -> JointDmd
bothDmd (JD {strd = s1, absd = a1})
(JD {strd = s2, absd = a2}) = mkJointDmd (s1 `bothMaybeStr` s2) (a1 `bothMaybeUsed` a2)
isTopDmd :: JointDmd -> Bool
isTopDmd (JD {strd = Lazy, absd = Use Many Used}) = True
isTopDmd _ = False
isBotDmd :: JointDmd -> Bool
isBotDmd (JD {strd = Str HyperStr, absd = Abs}) = True
isBotDmd _ = False
isAbsDmd :: JointDmd -> Bool
isAbsDmd (JD {absd = Abs}) = True
isAbsDmd _ = False
isSeqDmd :: JointDmd -> Bool
isSeqDmd (JD {strd=Str HeadStr, absd=Use _ UHead}) = True
isSeqDmd _ = False
seqDemand :: JointDmd -> ()
seqDemand (JD {strd = x, absd = y}) = seqMaybeStr x `seq` seqMaybeUsed y `seq` ()
seqDemandList :: [JointDmd] -> ()
seqDemandList [] = ()
seqDemandList (d:ds) = seqDemand d `seq` seqDemandList ds
isStrictDmd :: Demand -> Bool
isStrictDmd (JD {absd = Abs}) = False
isStrictDmd (JD {strd = Lazy}) = False
isStrictDmd _ = True
isWeakDmd :: Demand -> Bool
isWeakDmd (JD {strd = s, absd = a}) = isLazy s && isUsedMU a
cleanUseDmd_maybe :: JointDmd -> Maybe UseDmd
cleanUseDmd_maybe (JD { absd = Use _ ud }) = Just ud
cleanUseDmd_maybe _ = Nothing
splitFVs :: Bool
-> DmdEnv -> (DmdEnv, DmdEnv)
splitFVs is_thunk rhs_fvs
| is_thunk = foldUFM_Directly add (emptyVarEnv, emptyVarEnv) rhs_fvs
| otherwise = partitionVarEnv isWeakDmd rhs_fvs
where
add uniq dmd@(JD { strd = s, absd = u }) (lazy_fv, sig_fv)
| Lazy <- s = (addToUFM_Directly lazy_fv uniq dmd, sig_fv)
| otherwise = ( addToUFM_Directly lazy_fv uniq (JD { strd = Lazy, absd = u })
, addToUFM_Directly sig_fv uniq (JD { strd = s, absd = Abs }) )
\end{code}
%************************************************************************
%* *
\subsection{Clean demand for Strictness and Usage}
%* *
%************************************************************************
This domain differst from JointDemand in the sence that pure absence
is taken away, i.e., we deal *only* with non-absent demands.
Note [Strict demands]
~~~~~~~~~~~~~~~~~~~~~
isStrictDmd returns true only of demands that are
both strict
and used
In particular, it is False for , which can and does
arise in, say (Trac #7319)
f x = raise#
Then 'x' is not used, so f gets strictness -> .
Now the w/w generates
fx = let x = absentError "unused"
in raise
At this point we really don't want to convert to
fx = case absentError "unused" of x -> raise
Since the program is going to diverge, this swaps one error for another,
but it's really a bad idea to *ever* evaluate an absent argument.
In Trac #7319 we get
T7319.exe: Oops! Entered absent arg w_s1Hd{v} [lid] [base:GHC.Base.String{tc 36u}]
Note [Dealing with call demands]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Call demands are constructed and deconstructed coherently for
strictness and absence. For instance, the strictness signature for the
following function
f :: (Int -> (Int, Int)) -> (Int, Bool)
f g = (snd (g 3), True)
should be: m
\begin{code}
data CleanDemand = CD { sd :: StrDmd, ud :: UseDmd }
deriving ( Eq, Show )
instance Outputable CleanDemand where
ppr (CD {sd = s, ud = a}) = angleBrackets (ppr s <> comma <> ppr a)
mkCleanDmd :: StrDmd -> UseDmd -> CleanDemand
mkCleanDmd s a = CD { sd = s, ud = a }
bothCleanDmd :: CleanDemand -> CleanDemand -> CleanDemand
bothCleanDmd (CD { sd = s1, ud = a1}) (CD { sd = s2, ud = a2})
= CD { sd = s1 `bothStr` s2, ud = a1 `bothUse` a2 }
mkHeadStrict :: CleanDemand -> CleanDemand
mkHeadStrict (CD { ud = a }) = mkCleanDmd HeadStr a
oneifyDmd :: JointDmd -> JointDmd
oneifyDmd (JD { strd = s, absd = Use _ a }) = JD { strd = s, absd = Use One a }
oneifyDmd jd = jd
mkOnceUsedDmd, mkManyUsedDmd :: CleanDemand -> JointDmd
mkOnceUsedDmd (CD {sd = s,ud = a}) = mkJointDmd (Str s) (Use One a)
mkManyUsedDmd (CD {sd = s,ud = a}) = mkJointDmd (Str s) (Use Many a)
getUsage :: CleanDemand -> UseDmd
getUsage = ud
evalDmd :: JointDmd
evalDmd = mkJointDmd (Str HeadStr) useTop
mkProdDmd :: [JointDmd] -> CleanDemand
mkProdDmd dx
= mkCleanDmd sp up
where
sp = mkSProd $ map strd dx
up = mkUProd $ map absd dx
mkCallDmd :: CleanDemand -> CleanDemand
mkCallDmd (CD {sd = d, ud = u})
= mkCleanDmd (mkSCall d) (mkUCall One u)
cleanEvalDmd :: CleanDemand
cleanEvalDmd = mkCleanDmd HeadStr Used
cleanEvalProdDmd :: Arity -> CleanDemand
cleanEvalProdDmd n = mkCleanDmd HeadStr (UProd (replicate n useTop))
isSingleUsed :: JointDmd -> Bool
isSingleUsed (JD {absd=a}) = is_used_once a
where
is_used_once Abs = True
is_used_once (Use One _) = True
is_used_once _ = False
\end{code}
Note [Threshold demands]
~~~~~~~~~~~~~~~~~~~~~~~~
Threshold usage demand is generated to figure out if
cardinality-instrumented demands of a binding's free variables should
be unleashed. See also [Aggregated demand for cardinality].
Note [Replicating polymorphic demands]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some demands can be considered as polymorphic. Generally, it is
applicable to such beasts as tops, bottoms as well as Head-Used adn
Head-stricts demands. For instance,
S ~ S(L, ..., L)
Also, when top or bottom is occurred as a result demand, it in fact
can be expanded to saturate a callee's arity.
\begin{code}
splitProdDmd :: Arity -> JointDmd -> [JointDmd]
splitProdDmd n (JD {strd = s, absd = u})
= mkJointDmds (split_str s) (split_abs u)
where
split_str Lazy = replicate n Lazy
split_str (Str s) = splitStrProdDmd n s
split_abs Abs = replicate n Abs
split_abs (Use _ u) = splitUseProdDmd n u
splitProdDmd_maybe :: JointDmd -> Maybe [JointDmd]
splitProdDmd_maybe (JD {strd = s, absd = u})
= case (s,u) of
(Str (SProd sx), Use _ u) -> Just (mkJointDmds sx (splitUseProdDmd (length sx) u))
(Str s, Use _ (UProd ux)) -> Just (mkJointDmds (splitStrProdDmd (length ux) s) ux)
(Lazy, Use _ (UProd ux)) -> Just (mkJointDmds (replicate (length ux) Lazy) ux)
_ -> Nothing
\end{code}
%************************************************************************
%* *
Demand results
%* *
%************************************************************************
DmdResult: Dunno CPRResult
/
Diverges
CPRResult: NoCPR
/ \
RetProd RetSum ConTag
Product contructors return (Dunno (RetProd rs))
In a fixpoint iteration, start from Diverges
We have lubs, but not glbs; but that is ok.
\begin{code}
data Termination r = Diverges
| Dunno r
deriving( Eq, Show )
type DmdResult = Termination CPRResult
data CPRResult = NoCPR
| RetProd
| RetSum ConTag
deriving( Eq, Show )
lubCPR :: CPRResult -> CPRResult -> CPRResult
lubCPR (RetSum t1) (RetSum t2)
| t1 == t2 = RetSum t1
lubCPR RetProd RetProd = RetProd
lubCPR _ _ = NoCPR
lubDmdResult :: DmdResult -> DmdResult -> DmdResult
lubDmdResult Diverges r = r
lubDmdResult (Dunno c1) Diverges = Dunno c1
lubDmdResult (Dunno c1) (Dunno c2) = Dunno (c1 `lubCPR` c2)
bothDmdResult :: DmdResult -> Termination () -> DmdResult
bothDmdResult _ Diverges = Diverges
bothDmdResult r _ = r
instance Outputable DmdResult where
ppr Diverges = char 'b'
ppr (Dunno c) = ppr c
instance Outputable CPRResult where
ppr NoCPR = empty
ppr (RetSum n) = char 'm' <> int n
ppr RetProd = char 'm'
seqDmdResult :: DmdResult -> ()
seqDmdResult Diverges = ()
seqDmdResult (Dunno c) = seqCPRResult c
seqCPRResult :: CPRResult -> ()
seqCPRResult NoCPR = ()
seqCPRResult (RetSum n) = n `seq` ()
seqCPRResult RetProd = ()
topRes, botRes :: DmdResult
topRes = Dunno NoCPR
botRes = Diverges
cprSumRes :: ConTag -> DmdResult
cprSumRes tag | opt_CprOff = topRes
| otherwise = Dunno $ RetSum tag
cprProdRes :: [DmdType] -> DmdResult
cprProdRes _arg_tys
| opt_CprOff = topRes
| otherwise = Dunno $ RetProd
vanillaCprProdRes :: Arity -> DmdResult
vanillaCprProdRes _arity
| opt_CprOff = topRes
| otherwise = Dunno $ RetProd
isTopRes :: DmdResult -> Bool
isTopRes (Dunno NoCPR) = True
isTopRes _ = False
isBotRes :: DmdResult -> Bool
isBotRes Diverges = True
isBotRes _ = False
trimCPRInfo :: Bool -> Bool -> DmdResult -> DmdResult
trimCPRInfo trim_all trim_sums res
= trimR res
where
trimR (Dunno c) = Dunno (trimC c)
trimR Diverges = Diverges
trimC (RetSum n) | trim_all || trim_sums = NoCPR
| otherwise = RetSum n
trimC RetProd | trim_all = NoCPR
| otherwise = RetProd
trimC NoCPR = NoCPR
returnsCPR_maybe :: DmdResult -> Maybe ConTag
returnsCPR_maybe (Dunno c) = retCPR_maybe c
returnsCPR_maybe Diverges = Nothing
retCPR_maybe :: CPRResult -> Maybe ConTag
retCPR_maybe (RetSum t) = Just t
retCPR_maybe RetProd = Just fIRST_TAG
retCPR_maybe NoCPR = Nothing
defaultDmd :: Termination r -> JointDmd
defaultDmd Diverges = botDmd
defaultDmd _ = absDmd
resTypeArgDmd :: DmdResult -> JointDmd
resTypeArgDmd r | isBotRes r = botDmd
resTypeArgDmd _ = topDmd
\end{code}
Note [defaultDmd and resTypeArgDmd]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These functions are similar: They express the demand on something not
explicitly mentioned in the environment resp. the argument list. Yet they are
different:
* Variables not mentioned in the free variables environment are definitely
unused, so we can use absDmd there.
* Further arguments *can* be used, of course. Hence topDmd is used.
Note [Worthy functions for Worker-Wrapper split]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For non-bottoming functions a worker-wrapper transformation takes into
account several possibilities to decide if the function is worthy for
splitting:
1. The result is of product type and the function is strict in some
(or even all) of its arguments. The check that the argument is used is
more of sanity nature, since strictness implies usage. Example:
f :: (Int, Int) -> Int
f p = (case p of (a,b) -> a) + 1
should be splitted to
f :: (Int, Int) -> Int
f p = case p of (a,b) -> $wf a
$wf :: Int -> Int
$wf a = a + 1
2. Sometimes it also makes sense to perform a WW split if the
strictness analysis cannot say for sure if the function is strict in
components of its argument. Then we reason according to the inferred
usage information: if the function uses its product argument's
components, the WW split can be beneficial. Example:
g :: Bool -> (Int, Int) -> Int
g c p = case p of (a,b) ->
if c then a else b
The function g is strict in is argument p and lazy in its
components. However, both components are used in the RHS. The idea is
since some of the components (both in this case) are used in the
right-hand side, the product must presumable be taken apart.
Therefore, the WW transform splits the function g to
g :: Bool -> (Int, Int) -> Int
g c p = case p of (a,b) -> $wg c a b
$wg :: Bool -> Int -> Int -> Int
$wg c a b = if c then a else b
3. If an argument is absent, it would be silly to pass it to a
function, hence the worker with reduced arity is generated.
Note [Worker-wrapper for bottoming functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We used not to split if the result is bottom.
[Justification: there's no efficiency to be gained.]
But it's sometimes bad not to make a wrapper. Consider
fw = \x# -> let x = I# x# in case e of
p1 -> error_fn x
p2 -> error_fn x
p3 -> the real stuff
The re-boxing code won't go away unless error_fn gets a wrapper too.
[We don't do reboxing now, but in general it's better to pass an
unboxed thing to f, and have it reboxed in the error cases....]
However we *don't* want to do this when the argument is not actually
taken apart in the function at all. Otherwise we risk decomposing a
masssive tuple which is barely used. Example:
f :: ((Int,Int) -> String) -> (Int,Int) -> a
f g pr = error (g pr)
main = print (f fst (1, error "no"))
Here, f does not take 'pr' apart, and it's stupid to do so.
Imagine that it had millions of fields. This actually happened
in GHC itself where the tuple was DynFlags
%************************************************************************
%* *
\subsection{Demand environments and types}
%* *
%************************************************************************
\begin{code}
type Demand = JointDmd
type DmdEnv = VarEnv Demand
data DmdType = DmdType
DmdEnv
[Demand]
DmdResult
\end{code}
Note [Nature of result demand]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A DmdResult contains information about termination (currently distinguishing
definite divergence and no information; it is possible to include definite
convergence here), and CPR information about the result.
The semantics of this depends on whether we are looking at a DmdType, i.e. the
demand put on by an expression _under a specific incoming demand_ on its
environment, or at a StrictSig describing a demand transformer.
For a
* DmdType, the termination information is true given the demand it was
generated with, while for
* a StrictSig it is olds after applying enough arguments.
The CPR information, though, is valid after the number of arguments mentioned
in the type is given. Therefore, when forgetting the demand on arguments, as in
dmdAnalRhs, this needs to be considere (via removeDmdTyArgs).
Consider
b2 x y = x `seq` y `seq` error (show x)
this has a strictness signature of
b
meaning that "b2 `seq` ()" and "b2 1 `seq` ()" might well terminate, but
for "b2 1 2 `seq` ()" we get definite divergence.
For comparision,
b1 x = x `seq` error (show x)
has a strictness signature of
b
and "b1 1 `seq` ()" is known to terminate.
Now consider a function h with signature "", and the expression
e1 = h b1
now h puts a demand of onto its argument, and the demand transformer
turns it into
b
Now the DmdResult "b" does apply to us, even though "b1 `seq` ()" does not
diverge, and we do not anything being passed to b.
Note [Asymmetry of 'both' for DmdType and DmdResult]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'both' for DmdTypes is *assymetrical*, because there is only one
result! For example, given (e1 e2), we get a DmdType dt1 for e1, use
its arg demand to analyse e2 giving dt2, and then do (dt1 `bothType` dt2).
Similarly with
case e of { p -> rhs }
we get dt_scrut from the scrutinee and dt_rhs from the RHS, and then
compute (dt_rhs `bothType` dt_scrut).
We
1. combine the information on the free variables,
2. take the demand on arguments from the first argument
3. combine the termination results, but
4. take CPR info from the first argument.
3 and 4 are implementd in bothDmdResult.
\begin{code}
instance Eq DmdType where
(==) (DmdType fv1 ds1 res1)
(DmdType fv2 ds2 res2) = ufmToList fv1 == ufmToList fv2
&& ds1 == ds2 && res1 == res2
lubDmdType :: DmdType -> DmdType -> DmdType
lubDmdType d1 d2
= DmdType lub_fv lub_ds lub_res
where
n = max (dmdTypeDepth d1) (dmdTypeDepth d2)
(DmdType fv1 ds1 r1) = ensureArgs n d1
(DmdType fv2 ds2 r2) = ensureArgs n d2
lub_fv = plusVarEnv_CD lubDmd fv1 (defaultDmd r1) fv2 (defaultDmd r2)
lub_ds = zipWithEqual "lubDmdType" lubDmd ds1 ds2
lub_res = lubDmdResult r1 r2
\end{code}
Note [The need for BothDmdArg]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Previously, the right argument to bothDmdType, as well as the return value of
dmdAnalStar via postProcessDmdTypeM, was a DmdType. But bothDmdType only needs
to know about the free variables and termination information, but nothing about
the demand put on arguments, nor cpr information. So we make that explicit by
only passing the relevant information.
\begin{code}
type BothDmdArg = (DmdEnv, Termination ())
mkBothDmdArg :: DmdEnv -> BothDmdArg
mkBothDmdArg env = (env, Dunno ())
toBothDmdArg :: DmdType -> BothDmdArg
toBothDmdArg (DmdType fv _ r) = (fv, go r)
where
go (Dunno {}) = Dunno ()
go Diverges = Diverges
bothDmdType :: DmdType -> BothDmdArg -> DmdType
bothDmdType (DmdType fv1 ds1 r1) (fv2, t2)
= DmdType both_fv ds1 (r1 `bothDmdResult` t2)
where both_fv = plusVarEnv_CD bothDmd fv1 (defaultDmd r1) fv2 (defaultDmd t2)
instance Outputable DmdType where
ppr (DmdType fv ds res)
= hsep [text "DmdType",
hcat (map ppr ds) <> ppr res,
if null fv_elts then empty
else braces (fsep (map pp_elt fv_elts))]
where
pp_elt (uniq, dmd) = ppr uniq <> text "->" <> ppr dmd
fv_elts = ufmToList fv
emptyDmdEnv :: VarEnv Demand
emptyDmdEnv = emptyVarEnv
nopDmdType, botDmdType :: DmdType
nopDmdType = DmdType emptyDmdEnv [] topRes
botDmdType = DmdType emptyDmdEnv [] botRes
cprProdDmdType :: Arity -> DmdType
cprProdDmdType _arity
= DmdType emptyDmdEnv [] (Dunno RetProd)
isNopDmdType :: DmdType -> Bool
isNopDmdType (DmdType env [] res)
| isTopRes res && isEmptyVarEnv env = True
isNopDmdType _ = False
mkDmdType :: DmdEnv -> [Demand] -> DmdResult -> DmdType
mkDmdType fv ds res = DmdType fv ds res
dmdTypeDepth :: DmdType -> Arity
dmdTypeDepth (DmdType _ ds _) = length ds
removeDmdTyArgs :: DmdType -> DmdType
removeDmdTyArgs = ensureArgs 0
ensureArgs :: Arity -> DmdType -> DmdType
ensureArgs n d | n == depth = d
| otherwise = DmdType fv ds' r'
where depth = dmdTypeDepth d
DmdType fv ds r = d
ds' = take n (ds ++ repeat (resTypeArgDmd r))
r' | Diverges <- r = r
| otherwise = topRes
seqDmdType :: DmdType -> ()
seqDmdType (DmdType _env ds res) =
seqDemandList ds `seq` seqDmdResult res `seq` ()
splitDmdTy :: DmdType -> (Demand, DmdType)
splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
splitDmdTy ty@(DmdType _ [] res_ty) = (resTypeArgDmd res_ty, ty)
deferAfterIO :: DmdType -> DmdType
deferAfterIO d@(DmdType _ _ res) =
case d `lubDmdType` nopDmdType of
DmdType fv ds _ -> DmdType fv ds (defer_res res)
where
defer_res Diverges = topRes
defer_res r = r
strictenDmd :: JointDmd -> CleanDemand
strictenDmd (JD {strd = s, absd = u})
= CD { sd = poke_s s, ud = poke_u u }
where
poke_s Lazy = HeadStr
poke_s (Str s) = s
poke_u Abs = UHead
poke_u (Use _ u) = u
\end{code}
Deferring and peeeling
\begin{code}
type DeferAndUse
=( Bool
, Count)
type DeferAndUseM = Maybe DeferAndUse
toCleanDmd :: Demand -> (CleanDemand, DeferAndUseM)
toCleanDmd (JD { strd = s, absd = u })
= case (s,u) of
(Str s', Use c u') -> (CD { sd = s', ud = u' }, Just (False, c))
(Lazy, Use c u') -> (CD { sd = HeadStr, ud = u' }, Just (True, c))
(_, Abs) -> (CD { sd = HeadStr, ud = Used }, Nothing)
postProcessDmdTypeM :: DeferAndUseM -> DmdType -> BothDmdArg
postProcessDmdTypeM Nothing _ = (emptyDmdEnv, Dunno ())
postProcessDmdTypeM (Just du) (DmdType fv _ res_ty)
= (postProcessDmdEnv du fv, postProcessDmdResult du res_ty)
postProcessDmdResult :: DeferAndUse -> DmdResult -> Termination ()
postProcessDmdResult (True,_) _ = Dunno ()
postProcessDmdResult (False,_) (Dunno {}) = Dunno ()
postProcessDmdResult (False,_) Diverges = Diverges
postProcessDmdEnv :: DeferAndUse -> DmdEnv -> DmdEnv
postProcessDmdEnv (True, Many) env = deferReuseEnv env
postProcessDmdEnv (False, Many) env = reuseEnv env
postProcessDmdEnv (True, One) env = deferEnv env
postProcessDmdEnv (False, One) env = env
postProcessUnsat :: DeferAndUse -> DmdType -> DmdType
postProcessUnsat (True, Many) ty = deferReuse ty
postProcessUnsat (False, Many) ty = reuseType ty
postProcessUnsat (True, One) ty = deferType ty
postProcessUnsat (False, One) ty = ty
deferType, reuseType, deferReuse :: DmdType -> DmdType
deferType (DmdType fv ds _) = DmdType (deferEnv fv) (map deferDmd ds) topRes
reuseType (DmdType fv ds res_ty) = DmdType (reuseEnv fv) (map reuseDmd ds) res_ty
deferReuse (DmdType fv ds _) = DmdType (deferReuseEnv fv) (map deferReuseDmd ds) topRes
deferEnv, reuseEnv, deferReuseEnv :: DmdEnv -> DmdEnv
deferEnv fv = mapVarEnv deferDmd fv
reuseEnv fv = mapVarEnv reuseDmd fv
deferReuseEnv fv = mapVarEnv deferReuseDmd fv
deferDmd, reuseDmd, deferReuseDmd :: JointDmd -> JointDmd
deferDmd (JD {strd=_, absd=a}) = mkJointDmd Lazy a
reuseDmd (JD {strd=d, absd=a}) = mkJointDmd d (markReusedDmd a)
deferReuseDmd (JD {strd=_, absd=a}) = mkJointDmd Lazy (markReusedDmd a)
peelCallDmd :: CleanDemand -> (CleanDemand, DeferAndUse)
peelCallDmd (CD {sd = s, ud = u})
= case (s, u) of
(SCall s', UCall c u') -> (CD { sd = s', ud = u' }, (False, c))
(SCall s', _) -> (CD { sd = s', ud = Used }, (False, Many))
(HyperStr, UCall c u') -> (CD { sd = HyperStr, ud = u' }, (False, c))
(HyperStr, _) -> (CD { sd = HyperStr, ud = Used }, (False, Many))
(_, UCall c u') -> (CD { sd = HeadStr, ud = u' }, (True, c))
(_, _) -> (CD { sd = HeadStr, ud = Used }, (True, Many))
peelManyCalls :: Int -> CleanDemand -> DeferAndUse
peelManyCalls n (CD { sd = str, ud = abs })
= (go_str n str, go_abs n abs)
where
go_str :: Int -> StrDmd -> Bool
go_str 0 _ = False
go_str _ HyperStr = False
go_str n (SCall d') = go_str (n1) d'
go_str _ _ = True
go_abs :: Int -> UseDmd -> Count
go_abs 0 _ = One
go_abs n (UCall One d') = go_abs (n1) d'
go_abs _ _ = Many
\end{code}
Note [Demands from unsaturated function calls]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider a demand transformer d1 -> d2 -> r for f.
If a sufficiently detailed demand is fed into this transformer,
e.g arising from "f x1 x2" in a strict, use-once context,
then d1 and d2 is precisely the demand unleashed onto x1 and x2 (similar for
the free variable environment) and furthermore the result information r is the
one we want to use.
An anonymous lambda is also an unsaturated function all (needs one argument,
none given), so this applies to that case as well.
But the demand fed into f might be less than . There are a few cases:
* Not enough demand on the strictness side:
- In that case, we need to zap all strictness in the demand on arguments and
free variables.
- Furthermore, we remove CPR information. It could be left, but given the incoming
demand is not enough to evaluate so far we just do not bother.
- And finally termination information: If r says that f diverges for sure,
then this holds when the demand guarantees that two arguments are going to
be passed. If the demand is lower, we may just as well converge.
If we were tracking definite convegence, than that would still hold under
a weaker demand than expected by the demand transformer.
* Not enough demand from the usage side: The missing usage can be expanded
using UCall Many, therefore this is subsumed by the third case:
* At least one of the uses has a cardinality of Many.
- Even if f puts a One demand on any of its argument or free variables, if
we call f multiple times, we may evaluate this argument or free variable
multiple times. So forget about any occurrence of "One" in the demand.
In dmdTransformSig, we call peelManyCalls to find out if we are in any of these
cases, and then call postProcessUnsat to reduce the demand appropriately.
Similarly, dmdTransformDictSelSig and dmdAnal, when analyzing a Lambda, use
peelCallDmd, which peels only one level, but also returns the demand put on the
body of the function.
\begin{code}
peelFV :: DmdType -> Var -> (DmdType, Demand)
peelFV (DmdType fv ds res) id =
(DmdType fv' ds res, dmd)
where
fv' = fv `delVarEnv` id
dmd = lookupVarEnv fv id `orElse` defaultDmd res
addDemand :: Demand -> DmdType -> DmdType
addDemand dmd (DmdType fv ds res) = DmdType fv (dmd:ds) res
\end{code}
Note [Default demand on free variables]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the variable is not mentioned in the environment of a demand type,
its demand is taken to be a result demand of the type.
For the stricness component,
if the result demand is a Diverges, then we use HyperStr
else we use Lazy
For the usage component, we use Absent.
So we use either absDmd or botDmd.
Also note the equations for lubDmdResult (resp. bothDmdResult) noted there.
Note [Always analyse in virgin pass]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tricky point: make sure that we analyse in the 'virgin' pass. Consider
rec { f acc x True = f (...rec { g y = ...g... }...)
f acc x False = acc }
In the virgin pass for 'f' we'll give 'f' a very strict (bottom) type.
That might mean that we analyse the sub-expression containing the
E = "...rec g..." stuff in a bottom demand. Suppose we *didn't analyse*
E, but just retuned botType.
Then in the *next* (non-virgin) iteration for 'f', we might analyse E
in a weaker demand, and that will trigger doing a fixpoint iteration
for g. But *because it's not the virgin pass* we won't start g's
iteration at bottom. Disaster. (This happened in $sfibToList' of
nofib/spectral/fibheaps.)
So in the virgin pass we make sure that we do analyse the expression
at least once, to initialise its signatures.
Note [Analyzing with lazy demand and lambdas]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The insight for analyzing lambdas follows from the fact that for
strictness S = C(L). This polymorphic expansion is critical for
cardinality analysis of the following example:
{-# NOINLINE build #-}
build g = (g (:) [], g (:) [])
h c z = build (\x ->
let z1 = z ++ z
in if c
then \y -> x (y ++ z1)
else \y -> x (z1 ++ y))
One can see that `build` assigns to `g` demand .
Therefore, when analyzing the lambda `(\x -> ...)`, we
expect each lambda \y -> ... to be annotated as "one-shot"
one. Therefore (\x -> \y -> x (y ++ z)) should be analyzed with a
demand .
This is achieved by, first, converting the lazy demand L into the
strict S by the second clause of the analysis.
%************************************************************************
%* *
Demand signatures
%* *
%************************************************************************
In a let-bound Id we record its strictness info.
In principle, this strictness info is a demand transformer, mapping
a demand on the Id into a DmdType, which gives
a) the free vars of the Id's value
b) the Id's arguments
c) an indication of the result of applying
the Id to its arguments
However, in fact we store in the Id an extremely emascuated demand
transfomer, namely
a single DmdType
(Nevertheless we dignify StrictSig as a distinct type.)
This DmdType gives the demands unleashed by the Id when it is applied
to as many arguments as are given in by the arg demands in the DmdType.
Also see Note [Nature of result demand] for the meaning of a DmdResult in a
strictness signature.
If an Id is applied to less arguments than its arity, it means that
the demand on the function at a call site is weaker than the vanilla
call demand, used for signature inference. Therefore we place a top
demand on all arguments. Otherwise, the demand is specified by Id's
signature.
For example, the demand transformer described by the demand signature
StrictSig (DmdType {x -> } m)
says that when the function is applied to two arguments, it
unleashes demand on the free var x, on the first arg,
and on the second, then returning a constructor.
If this same function is applied to one arg, all we can say is that it
uses x with , and its arg with demand .
\begin{code}
newtype StrictSig = StrictSig DmdType
deriving( Eq )
instance Outputable StrictSig where
ppr (StrictSig ty) = ppr ty
mkStrictSig :: DmdType -> StrictSig
mkStrictSig dmd_ty = StrictSig dmd_ty
mkClosedStrictSig :: [Demand] -> DmdResult -> StrictSig
mkClosedStrictSig ds res = mkStrictSig (DmdType emptyDmdEnv ds res)
splitStrictSig :: StrictSig -> ([Demand], DmdResult)
splitStrictSig (StrictSig (DmdType _ dmds res)) = (dmds, res)
increaseStrictSigArity :: Int -> StrictSig -> StrictSig
increaseStrictSigArity arity_increase (StrictSig (DmdType env dmds res))
= StrictSig (DmdType env (replicate arity_increase topDmd ++ dmds) res)
isNopSig :: StrictSig -> Bool
isNopSig (StrictSig ty) = isNopDmdType ty
isBottomingSig :: StrictSig -> Bool
isBottomingSig (StrictSig (DmdType _ _ res)) = isBotRes res
nopSig, botSig :: StrictSig
nopSig = StrictSig nopDmdType
botSig = StrictSig botDmdType
cprProdSig :: Arity -> StrictSig
cprProdSig arity = StrictSig (cprProdDmdType arity)
argsOneShots :: StrictSig -> Arity -> [[OneShotInfo]]
argsOneShots (StrictSig (DmdType _ arg_ds _)) n_val_args
= go arg_ds
where
good_one_shot
| arg_ds `lengthExceeds` n_val_args = ProbOneShot
| otherwise = OneShotLam
go [] = []
go (arg_d : arg_ds) = argOneShots good_one_shot arg_d `cons` go arg_ds
cons [] [] = []
cons a as = a:as
argOneShots :: OneShotInfo -> JointDmd -> [OneShotInfo]
argOneShots one_shot_info (JD { absd = usg })
= case usg of
Use _ arg_usg -> go arg_usg
_ -> []
where
go (UCall One u) = one_shot_info : go u
go (UCall Many u) = NoOneShotInfo : go u
go _ = []
dmdTransformSig :: StrictSig -> CleanDemand -> DmdType
dmdTransformSig (StrictSig dmd_ty@(DmdType _ arg_ds _)) cd
= postProcessUnsat (peelManyCalls (length arg_ds) cd) dmd_ty
dmdTransformDataConSig :: Arity -> StrictSig -> CleanDemand -> DmdType
dmdTransformDataConSig arity (StrictSig (DmdType _ _ con_res))
(CD { sd = str, ud = abs })
| Just str_dmds <- go_str arity str
, Just abs_dmds <- go_abs arity abs
= DmdType emptyDmdEnv (mkJointDmds str_dmds abs_dmds) con_res
| otherwise
= nopDmdType
where
go_str 0 dmd = Just (splitStrProdDmd arity dmd)
go_str n (SCall s') = go_str (n1) s'
go_str n HyperStr = go_str (n1) HyperStr
go_str _ _ = Nothing
go_abs 0 dmd = Just (splitUseProdDmd arity dmd)
go_abs n (UCall One u') = go_abs (n1) u'
go_abs _ _ = Nothing
dmdTransformDictSelSig :: StrictSig -> CleanDemand -> DmdType
dmdTransformDictSelSig (StrictSig (DmdType _ [dict_dmd] _)) cd
| (cd',defer_use) <- peelCallDmd cd
, Just jds <- splitProdDmd_maybe dict_dmd
= postProcessUnsat defer_use $
DmdType emptyDmdEnv [mkOnceUsedDmd $ mkProdDmd $ map (enhance cd') jds] topRes
| otherwise
= nopDmdType
where
enhance cd old | isAbsDmd old = old
| otherwise = mkOnceUsedDmd cd
dmdTransformDictSelSig _ _ = panic "dmdTransformDictSelSig: no args"
\end{code}
Note [Demand transformer for a dictionary selector]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If we evaluate (op dict-expr) under demand 'd', then we can push the demand 'd'
into the appropriate field of the dictionary. What *is* the appropriate field?
We just look at the strictness signature of the class op, which will be
something like: U(AAASAAAAA). Then replace the 'S' by the demand 'd'.
For single-method classes, which are represented by newtypes the signature
of 'op' won't look like U(...), so the splitProdDmd_maybe will fail.
That's fine: if we are doing strictness analysis we are also doing inling,
so we'll have inlined 'op' into a cast. So we can bale out in a conservative
way, returning nopDmdType.
It is (just.. Trac #8329) possible to be running strictness analysis *without*
having inlined class ops from single-method classes. Suppose you are using
ghc --make; and the first module has a local -O0 flag. So you may load a class
without interface pragmas, ie (currently) without an unfolding for the class
ops. Now if a subsequent module in the --make sweep has a local -O flag
you might do strictness analysis, but there is no inlining for the class op.
This is weird, so I'm not worried about whether this optimises brilliantly; but
it should not fall over.
Note [Non-full application]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
If a function having bottom as its demand result is applied to a less
number of arguments than its syntactic arity, we cannot say for sure
that it is going to diverge. This is the reason why we use the
function appIsBottom, which, given a strictness signature and a number
of arguments, says conservatively if the function is going to diverge
or not.
\begin{code}
appIsBottom :: StrictSig -> Int -> Bool
appIsBottom (StrictSig (DmdType _ ds res)) n
| isBotRes res = not $ lengthExceeds ds n
appIsBottom _ _ = False
seqStrictSig :: StrictSig -> ()
seqStrictSig (StrictSig ty) = seqDmdType ty
pprIfaceStrictSig :: StrictSig -> SDoc
pprIfaceStrictSig (StrictSig (DmdType _ dmds res))
= hcat (map ppr dmds) <> ppr res
\end{code}
Zap absence or one-shot information, under control of flags
\begin{code}
zapDemand :: DynFlags -> Demand -> Demand
zapDemand dflags dmd
| Just kfs <- killFlags dflags = zap_dmd kfs dmd
| otherwise = dmd
zapStrictSig :: DynFlags -> StrictSig -> StrictSig
zapStrictSig dflags sig@(StrictSig (DmdType env ds r))
| Just kfs <- killFlags dflags = StrictSig (DmdType env (map (zap_dmd kfs) ds) r)
| otherwise = sig
type KillFlags = (Bool, Bool)
killFlags :: DynFlags -> Maybe KillFlags
killFlags dflags
| not kill_abs && not kill_one_shot = Nothing
| otherwise = Just (kill_abs, kill_one_shot)
where
kill_abs = gopt Opt_KillAbsence dflags
kill_one_shot = gopt Opt_KillOneShot dflags
zap_dmd :: KillFlags -> Demand -> Demand
zap_dmd kfs (JD {strd = s, absd = u}) = JD {strd = s, absd = zap_musg kfs u}
zap_musg :: KillFlags -> MaybeUsed -> MaybeUsed
zap_musg (kill_abs, _) Abs
| kill_abs = useTop
| otherwise = Abs
zap_musg kfs (Use c u) = Use (zap_count kfs c) (zap_usg kfs u)
zap_count :: KillFlags -> Count -> Count
zap_count (_, kill_one_shot) c
| kill_one_shot = Many
| otherwise = c
zap_usg :: KillFlags -> UseDmd -> UseDmd
zap_usg kfs (UCall c u) = UCall (zap_count kfs c) (zap_usg kfs u)
zap_usg kfs (UProd us) = UProd (map (zap_musg kfs) us)
zap_usg _ u = u
\end{code}
\begin{code}
strictifyDictDmd :: Type -> Demand -> Demand
strictifyDictDmd ty dmd = case absd dmd of
Use n _ |
Just (tycon, _arg_tys, _data_con, inst_con_arg_tys)
<- splitDataProductType_maybe ty,
not (isNewTyCon tycon), isClassTyCon tycon
-> seqDmd `bothDmd`
case splitProdDmd_maybe dmd of
Nothing -> dmd
Just dmds
| all (not . isAbsDmd) dmds -> evalDmd
| otherwise -> case mkProdDmd $ zipWith strictifyDictDmd inst_con_arg_tys dmds of
CD {sd = s,ud = a} -> JD (Str s) (Use n a)
_ -> dmd
\end{code}
Note [HyperStr and Use demands]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The information "HyperStr" needs to be in the strictness signature, and not in
the demand signature, because we still want to know about the demand on things. Consider
f (x,y) True = error (show x)
f (x,y) False = x+1
The signature of f should be m. If we were not
distinguishing the uses on x and y in the True case, we could either not figure
out how deeply we can unpack x, or that we do not have to pass y.
%************************************************************************
%* *
Serialisation
%* *
%************************************************************************
\begin{code}
instance Binary StrDmd where
put_ bh HyperStr = do putByte bh 0
put_ bh HeadStr = do putByte bh 1
put_ bh (SCall s) = do putByte bh 2
put_ bh s
put_ bh (SProd sx) = do putByte bh 3
put_ bh sx
get bh = do
h <- getByte bh
case h of
0 -> do return HyperStr
1 -> do return HeadStr
2 -> do s <- get bh
return (SCall s)
_ -> do sx <- get bh
return (SProd sx)
instance Binary MaybeStr where
put_ bh Lazy = do
putByte bh 0
put_ bh (Str s) = do
putByte bh 1
put_ bh s
get bh = do
h <- getByte bh
case h of
0 -> return Lazy
_ -> do s <- get bh
return $ Str s
instance Binary Count where
put_ bh One = do putByte bh 0
put_ bh Many = do putByte bh 1
get bh = do h <- getByte bh
case h of
0 -> return One
_ -> return Many
instance Binary MaybeUsed where
put_ bh Abs = do
putByte bh 0
put_ bh (Use c u) = do
putByte bh 1
put_ bh c
put_ bh u
get bh = do
h <- getByte bh
case h of
0 -> return Abs
_ -> do c <- get bh
u <- get bh
return $ Use c u
instance Binary UseDmd where
put_ bh Used = do
putByte bh 0
put_ bh UHead = do
putByte bh 1
put_ bh (UCall c u) = do
putByte bh 2
put_ bh c
put_ bh u
put_ bh (UProd ux) = do
putByte bh 3
put_ bh ux
get bh = do
h <- getByte bh
case h of
0 -> return $ Used
1 -> return $ UHead
2 -> do c <- get bh
u <- get bh
return (UCall c u)
_ -> do ux <- get bh
return (UProd ux)
instance Binary JointDmd where
put_ bh (JD {strd = x, absd = y}) = do put_ bh x; put_ bh y
get bh = do
x <- get bh
y <- get bh
return $ mkJointDmd x y
instance Binary StrictSig where
put_ bh (StrictSig aa) = do
put_ bh aa
get bh = do
aa <- get bh
return (StrictSig aa)
instance Binary DmdType where
put_ bh (DmdType _ ds dr)
= do put_ bh ds
put_ bh dr
get bh
= do ds <- get bh
dr <- get bh
return (DmdType emptyDmdEnv ds dr)
instance Binary DmdResult where
put_ bh (Dunno c) = do { putByte bh 0; put_ bh c }
put_ bh Diverges = putByte bh 2
get bh = do { h <- getByte bh
; case h of
0 -> do { c <- get bh; return (Dunno c) }
_ -> return Diverges }
instance Binary CPRResult where
put_ bh (RetSum n) = do { putByte bh 0; put_ bh n }
put_ bh RetProd = putByte bh 1
put_ bh NoCPR = putByte bh 2
get bh = do
h <- getByte bh
case h of
0 -> do { n <- get bh; return (RetSum n) }
1 -> return RetProd
_ -> return NoCPR
\end{code}