diff options
| -rw-r--r-- | ghc/compiler/basicTypes/Id.lhs | 15 | ||||
| -rw-r--r-- | ghc/compiler/basicTypes/IdInfo.lhs | 37 | ||||
| -rw-r--r-- | ghc/compiler/stranal/DmdAnal.lhs | 156 | ||||
| -rw-r--r-- | ghc/compiler/stranal/WorkWrap.lhs | 22 |
4 files changed, 154 insertions, 76 deletions
diff --git a/ghc/compiler/basicTypes/Id.lhs b/ghc/compiler/basicTypes/Id.lhs index b1a4a1a5d7..9f07786a3e 100644 --- a/ghc/compiler/basicTypes/Id.lhs +++ b/ghc/compiler/basicTypes/Id.lhs @@ -62,7 +62,7 @@ module Id ( #endif idArity, - idNewDemandInfo, + idNewDemandInfo, idNewDemandInfo_maybe, idNewStrictness, idNewStrictness_maybe, idTyGenInfo, idWorkerInfo, @@ -99,12 +99,12 @@ import Type ( Type, typePrimRep, addFreeTyVars, import IdInfo import qualified Demand ( Demand ) -import NewDemand ( Demand, StrictSig, topSig, isBottomingSig ) +import NewDemand ( Demand, StrictSig, topDmd, topSig, isBottomingSig ) import Name ( Name, OccName, mkSystemName, mkInternalName, getOccName, getSrcLoc ) -import OccName ( EncodedFS, UserFS, mkWorkerOcc ) +import OccName ( EncodedFS, mkWorkerOcc ) import PrimRep ( PrimRep ) import TysPrim ( statePrimTyCon ) import FieldLabel ( FieldLabel ) @@ -383,11 +383,14 @@ setIdDemandInfo :: Id -> Demand.Demand -> Id setIdDemandInfo id demand_info = modifyIdInfo (`setDemandInfo` demand_info) id #endif -idNewDemandInfo :: Id -> NewDemand.Demand -idNewDemandInfo id = newDemandInfo (idInfo id) +idNewDemandInfo_maybe :: Id -> Maybe NewDemand.Demand +idNewDemandInfo :: Id -> NewDemand.Demand + +idNewDemandInfo_maybe id = newDemandInfo (idInfo id) +idNewDemandInfo id = newDemandInfo (idInfo id) `orElse` NewDemand.topDmd setIdNewDemandInfo :: Id -> NewDemand.Demand -> Id -setIdNewDemandInfo id dmd = modifyIdInfo (`setNewDemandInfo` dmd) id +setIdNewDemandInfo id dmd = modifyIdInfo (`setNewDemandInfo` Just dmd) id --------------------------------- -- SPECIALISATION diff --git a/ghc/compiler/basicTypes/IdInfo.lhs b/ghc/compiler/basicTypes/IdInfo.lhs index 9910d1fed7..2dc8b42f27 100644 --- a/ghc/compiler/basicTypes/IdInfo.lhs +++ b/ghc/compiler/basicTypes/IdInfo.lhs @@ -105,6 +105,7 @@ import qualified Demand import NewDemand import Outputable import Util ( seqList, listLengthCmp ) +import Maybe ( isJust ) import List ( replicate ) -- infixl so you can say (id `set` a `set` b) @@ -215,6 +216,12 @@ oldDemand (Call _) = WwStrict \end{code} +\begin{code} +seqNewDemandInfo Nothing = () +seqNewDemandInfo (Just dmd) = seqDemand dmd +\end{code} + + %************************************************************************ %* * \subsection{GlobalIdDetails @@ -296,7 +303,10 @@ data IdInfo -- know whether whether this is the first visit, -- so it can assign botSig. Other customers want -- topSig. So Nothing is good. - newDemandInfo :: Demand + + newDemandInfo :: Maybe Demand -- Similarly we want to know if there's no + -- known demand yet, for when we are looking for + -- CPR info } seqIdInfo :: IdInfo -> () @@ -312,7 +322,7 @@ megaSeqIdInfo info -- some unfoldings are not calculated at all -- seqUnfolding (unfoldingInfo info) `seq` - seqDemand (newDemandInfo info) `seq` + seqNewDemandInfo (newDemandInfo info) `seq` seqNewStrictnessInfo (newStrictnessInfo info) `seq` #ifdef OLD_STRICTNESS @@ -352,7 +362,7 @@ setUnfoldingInfo info uf -- let x = (a,b) in h a b x -- and now x is not demanded (I'm assuming h is lazy) -- This really happens. The solution here is a bit ad hoc... - = info { unfoldingInfo = uf, newDemandInfo = Top } + = info { unfoldingInfo = uf, newDemandInfo = Nothing } | otherwise -- We do *not* seq on the unfolding info, For some reason, doing so @@ -392,7 +402,7 @@ vanillaIdInfo lbvarInfo = NoLBVarInfo, inlinePragInfo = AlwaysActive, occInfo = NoOccInfo, - newDemandInfo = topDmd, + newDemandInfo = Nothing, newStrictnessInfo = Nothing } @@ -765,28 +775,29 @@ part of an unsaturated lambda \begin{code} zapLamInfo :: IdInfo -> Maybe IdInfo zapLamInfo info@(IdInfo {occInfo = occ, newDemandInfo = demand}) - | is_safe_occ && not (isStrictDmd demand) + | is_safe_occ occ && is_safe_dmd demand = Nothing | otherwise - = Just (info {occInfo = safe_occ, - newDemandInfo = Top}) + = Just (info {occInfo = safe_occ, newDemandInfo = Nothing}) where -- The "unsafe" occ info is the ones that say I'm not in a lambda -- because that might not be true for an unsaturated lambda - is_safe_occ = case occ of - OneOcc in_lam once -> in_lam - other -> True + is_safe_occ (OneOcc in_lam once) = in_lam + is_safe_occ other = True safe_occ = case occ of OneOcc _ once -> OneOcc insideLam once other -> occ + + is_safe_dmd Nothing = True + is_safe_dmd (Just dmd) = not (isStrictDmd dmd) \end{code} \begin{code} zapDemandInfo :: IdInfo -> Maybe IdInfo -zapDemandInfo info@(IdInfo {newDemandInfo = demand}) - | not (isStrictDmd demand) = Nothing - | otherwise = Just (info {newDemandInfo = Top}) +zapDemandInfo info@(IdInfo {newDemandInfo = dmd}) + | isJust dmd = Just (info {newDemandInfo = Nothing}) + | otherwise = Nothing \end{code} diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs index 9e7a31c6b3..a55be50b8c 100644 --- a/ghc/compiler/stranal/DmdAnal.lhs +++ b/ghc/compiler/stranal/DmdAnal.lhs @@ -27,6 +27,7 @@ import Id ( Id, idType, idInlinePragma, #endif idNewStrictness, idNewStrictness_maybe, setIdNewStrictness, idNewDemandInfo, + idNewDemandInfo_maybe, setIdNewDemandInfo, idName ) #ifdef OLD_STRICTNESS @@ -68,6 +69,7 @@ dmdAnalPgm dflags binds = do { showPass dflags "Demand analysis" ; let { binds_plus_dmds = do_prog binds } ; + endPass dflags "Demand analysis" Opt_D_dump_stranal binds_plus_dmds ; #ifdef OLD_STRICTNESS @@ -90,7 +92,8 @@ dmdAnalTopBind sigs (NonRec id rhs) ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel sigs (id, rhs) (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel sigs (id, rhs1) -- Do two passes to improve CPR information - -- See the comments with mkSigTy.ignore_cpr_info below + -- See comments with ignore_cpr_info in mk_sig_ty + -- and with extendSigsWithLam in (sigs2, NonRec id2 rhs2) @@ -98,6 +101,7 @@ dmdAnalTopBind sigs (Rec pairs) = let (sigs', _, pairs') = dmdFix TopLevel sigs pairs -- We get two iterations automatically + -- c.f. the NonRec case above in (sigs', Rec pairs') \end{code} @@ -188,7 +192,8 @@ dmdAnal sigs dmd (Lam var body) | Call body_dmd <- dmd -- A call demand: good! = let - (body_ty, body') = dmdAnal sigs body_dmd body + sigs' = extendSigsWithLam sigs var + (body_ty, body') = dmdAnal sigs' body_dmd body (lam_ty, var') = annotateLamIdBndr body_ty var in (lam_ty, Lam var' body') @@ -209,7 +214,7 @@ dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)]) (alt_ty, alt') = dmdAnalAlt sigs_alt dmd alt (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr (_, bndrs', _) = alt' - case_bndr_sig = StrictSig (mkDmdType emptyVarEnv [] RetCPR) + case_bndr_sig = cprSig -- Inside the alternative, the case binder has the CPR property. -- Meaning that a case on it will successfully cancel. -- Example: @@ -321,7 +326,7 @@ dmdFix top_lvl sigs orig_pairs = loop 1 initial_sigs orig_pairs where bndrs = map fst orig_pairs - initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs] + initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs] loop :: Int -> SigEnv -- Already contains the current sigs @@ -358,16 +363,16 @@ dmdFix top_lvl sigs orig_pairs -- old_sig = lookup sigs id -- new_sig = lookup sigs' id + same_sig sigs sigs' var = lookup sigs var == lookup sigs' var + lookup sigs var = case lookupVarEnv sigs var of + Just (sig,_) -> sig + -- Get an initial strictness signature from the Id -- itself. That way we make use of earlier iterations -- of the fixpoint algorithm. (Cunning plan.) -- Note that the cunning plan extends to the DmdEnv too, -- since it is part of the strictness signature - initial_sig id = idNewStrictness_maybe id `orElse` botSig - - same_sig sigs sigs' var = lookup sigs var == lookup sigs' var - lookup sigs var = case lookupVarEnv sigs var of - Just (sig,_) -> sig +initialSig id = idNewStrictness_maybe id `orElse` botSig dmdAnalRhs :: TopLevelFlag -> SigEnv -> (Id, CoreExpr) @@ -401,10 +406,85 @@ mkTopSigTy rhs dmd_ty = snd (mk_sig_ty False False rhs dmd_ty) mkSigTy :: Id -> CoreExpr -> DmdType -> (DmdEnv, StrictSig) mkSigTy id rhs dmd_ty = mk_sig_ty (isNeverActive (idInlinePragma id)) - (isStrictDmd (idNewDemandInfo id)) + ok_to_keep_cpr_info rhs dmd_ty + where + ok_to_keep_cpr_info = case idNewDemandInfo_maybe id of + Nothing -> True -- Is the case the first time round + Just dmd -> isStrictDmd dmd +\end{code} + +The ok_to_keep_cpr_info stuff [CPR-AND-STRICTNESS] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If the rhs is a thunk, we usually forget the CPR info, because +it is presumably shared (else it would have been inlined, and +so we'd lose sharing if w/w'd it into a function. + +However, if the strictness analyser has figured out (in a previous +iteration) that it's strict, then we DON'T need to forget the CPR info. +Instead we can retain the CPR info and do the thunk-splitting transform +(see WorkWrap.splitThunk). + +This made a big difference to PrelBase.modInt, which had something like + modInt = \ x -> let r = ... -> I# v in + ...body strict in r... +r's RHS isn't a value yet; but modInt returns r in various branches, so +if r doesn't have the CPR property then neither does modInt +Another case I found in practice (in Complex.magnitude), looks like this: + let k = if ... then I# a else I# b + in ... body strict in k .... +(For this example, it doesn't matter whether k is returned as part of +the overall result; but it does matter that k's RHS has the CPR property.) +Left to itself, the simplifier will make a join point thus: + let $j k = ...body strict in k... + if ... then $j (I# a) else $j (I# b) +With thunk-splitting, we get instead + let $j x = let k = I#x in ...body strict in k... + in if ... then $j a else $j b +This is much better; there's a good chance the I# won't get allocated. + +The difficulty with this is that we need the strictness type to +look at the body... but we now need the body to calculate the demand +on the variable, so we can decide whether its strictness type should +have a CPR in it or not. Simple solution: + a) use strictness info from the previous iteration + b) make sure we do at least 2 iterations, by doing a second + round for top-level non-recs. Top level recs will get at + least 2 iterations except for totally-bottom functions + which aren't very interesting anyway. + +NB: strictly_demanded is never true of a top-level Id, or of a recursive Id. + +The Nothing case in ok_to_keep_cpr_info [CPR-AND-STRICTNESS] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Demand info now has a 'Nothing' state, just like strictness info. +The analysis works from 'dangerous' towards a 'safe' state; so we +start with botSig for 'Nothing' strictness infos, and we start with +"yes, it's demanded" for 'Nothing' in the demand info. The +fixpoint iteration will sort it all out. + +We can't start with 'not-demanded' because then consider + f x = let + t = ... I# x + in + if ... then t else I# y else f x' + +In the first iteration we'd have no demand info for x, so assume +not-demanded; then we'd get TopRes for f's CPR info. Next iteration +we'd see that t was demanded, and so give it the CPR property, but +by now f has TopRes, so it will stay TopRes. + +Instead, with the Nothing setting the first time round, we say +'yes t is demanded' the first time. + +However, this does mean that for non-recursive bindings we must +iterate twice to be sure of not getting over-optimistic CPR info, +in the case where t turns out to be not-demanded. This is handled +by dmdAnalTopBind. + -mk_sig_ty never_inline strictly_demanded rhs (DmdType fv dmds res) +\begin{code} +mk_sig_ty never_inline ok_to_keep_cpr_info rhs (DmdType fv dmds res) | never_inline && not (isBotRes res) -- HACK ALERT -- Don't strictness-analyse NOINLINE things. Why not? Because @@ -475,41 +555,7 @@ mk_sig_ty never_inline strictly_demanded rhs (DmdType fv dmds res) res' = case res of RetCPR | ignore_cpr_info -> TopRes other -> res - ignore_cpr_info = is_thunk && not strictly_demanded - is_thunk = not (exprIsValue rhs) - -- If the rhs is a thunk, we forget the CPR info, because - -- it is presumably shared (else it would have been inlined, and - -- so we'd lose sharing if w/w'd it into a function. - -- - -- Also, if the strictness analyser has figured out (in a previous iteration) - -- that it's strict, the let-to-case transformation will happen, so again - -- it's good. - -- This made a big difference to PrelBase.modInt, which had something like - -- modInt = \ x -> let r = ... -> I# v in - -- ...body strict in r... - -- r's RHS isn't a value yet; but modInt returns r in various branches, so - -- if r doesn't have the CPR property then neither does modInt - -- Another case I found in practice (in Complex.magnitude), looks like this: - -- let k = if ... then I# a else I# b - -- in ... body strict in k .... - -- (For this example, it doesn't matter whether k is returned as part of - -- the overall result.) Left to itself, the simplifier will make a join - -- point thus: - -- let $j k = ...body strict in k... - -- if ... then $j (I# a) else $j (I# b) - -- - -- - -- The difficulty with this is that we need the strictness type to - -- look at the body... but we now need the body to calculate the demand - -- on the variable, so we can decide whether its strictness type should - -- have a CPR in it or not. Simple solution: - -- a) use strictness info from the previous iteration - -- b) make sure we do at least 2 iterations, by doing a second - -- round for top-level non-recs. Top level recs will get at - -- least 2 iterations except for totally-bottom functions - -- which aren't very interesting anyway. - -- - -- NB: strictly_demanded is never true of a top-level Id, or of a recursive Id. + ignore_cpr_info = not (exprIsValue rhs || ok_to_keep_cpr_info) \end{code} The unpack strategy determines whether we'll *really* unpack the argument, @@ -665,6 +711,24 @@ extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl) extendSigEnvList = extendVarEnvList +extendSigsWithLam :: SigEnv -> Id -> SigEnv +-- Extend the SigEnv when we meet a lambda binder +-- If the binder is marked demanded with a product demand, +-- then give it a CPR signature, because in the likely event +-- that this is a lambda on a fn defn [we only use this when +-- the lambda is being consumed with a call demand], +-- it'll be w/w'd and so it will be CPR-ish +-- NOTE: see notes [CPR-AND-STRICTNESS] +extendSigsWithLam sigs id + = case idNewDemandInfo_maybe id of + Nothing -> pprTrace "Yes (bot)" (ppr id) $ extendVarEnv sigs id (cprSig, NotTopLevel) + Just (Eval ds) -> pprTrace "Yes" (ppr id) $ extendVarEnv sigs id (cprSig, NotTopLevel) + other -> pprTrace "No" (ppr id $$ ppr (idNewDemandInfo id)) $ sigs + +cprSig :: StrictSig +cprSig = StrictSig (mkDmdType emptyVarEnv [] RetCPR) + + dmdTransform :: SigEnv -- The strictness environment -> Id -- The function -> Demand -- The demand on the function diff --git a/ghc/compiler/stranal/WorkWrap.lhs b/ghc/compiler/stranal/WorkWrap.lhs index 6ceda4fffb..ab2b19e54c 100644 --- a/ghc/compiler/stranal/WorkWrap.lhs +++ b/ghc/compiler/stranal/WorkWrap.lhs @@ -204,7 +204,7 @@ tryWW is_rec fn_id rhs -- inside its __inline wrapper. Death! Disaster! = returnUs [ (fn_id', rhs) ] - | is_thunk && worthSplittingThunk fn_dmd res_info + | is_thunk && worthSplittingThunk maybe_fn_dmd res_info = ASSERT( isNonRec is_rec ) -- The thunk must be non-recursive splitThunk fn_id' rhs @@ -215,11 +215,11 @@ tryWW is_rec fn_id rhs = returnUs [ (fn_id', rhs) ] where - fn_info = idInfo fn_id - fn_dmd = newDemandInfo fn_info - unfolding = unfoldingInfo fn_info - inline_prag = inlinePragInfo fn_info - maybe_sig = newStrictnessInfo fn_info + fn_info = idInfo fn_id + maybe_fn_dmd = newDemandInfo fn_info + unfolding = unfoldingInfo fn_info + inline_prag = inlinePragInfo fn_info + maybe_sig = newStrictnessInfo fn_info -- In practice it always will have a strictness -- signature, even if it's a uninformative one @@ -360,15 +360,15 @@ worthSplittingFun ds res worth_it (Eval (Prod ds)) = True -- Product arg to evaluate worth_it other = False -worthSplittingThunk :: Demand -- Demand on the thunk +worthSplittingThunk :: Maybe Demand -- Demand on the thunk -> DmdResult -- CPR info for the thunk -> Bool -worthSplittingThunk dmd res - = worth_it dmd || returnsCPR res +worthSplittingThunk maybe_dmd res + = worth_it maybe_dmd || returnsCPR res where -- Split if the thing is unpacked - worth_it (Eval (Prod ds)) = not (all isAbsent ds) - worth_it other = False + worth_it (Just (Eval (Prod ds))) = not (all isAbsent ds) + worth_it other = False \end{code} |