X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fstranal%2FDmdAnal.lhs;h=917c624280355905dce3cc77afefe51254c59827;hp=c5cfb7b4bdedde682e5b88669b8305dfef7c07ab;hb=9ffadf219cbc4f8ec57264786df936a3cee88aec;hpb=0065d5ab628975892cea1ec7303f968c3338cbe1 diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs index c5cfb7b..917c624 100644 --- a/compiler/stranal/DmdAnal.lhs +++ b/compiler/stranal/DmdAnal.lhs @@ -7,6 +7,13 @@ ----------------- \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/Commentary/CodingStyle#Warnings +-- for details + module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs, both {- needed by WwLib -} ) where @@ -40,13 +47,16 @@ import TysWiredIn ( unboxedPairDataCon ) import TysPrim ( realWorldStatePrimTy ) import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly, keysUFM, minusUFM, ufmToList, filterUFM ) -import Type ( isUnLiftedType, coreEqType ) +import Type ( isUnLiftedType, coreEqType, splitTyConApp_maybe ) +import Coercion ( coercionKind ) import CoreLint ( showPass, endPass ) -import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs ) +import Util ( mapAndUnzip, lengthIs ) import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive, RecFlag(..), isRec ) import Maybes ( orElse, expectJust ) import Outputable + +import Data.List \end{code} To think about @@ -67,11 +77,7 @@ To think about dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind] 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 -- Only if OLD_STRICTNESS is on, because only then is the old -- strictness analyser run @@ -164,16 +170,25 @@ dmdAnal sigs dmd (Lit lit) dmdAnal sigs dmd (Var var) = (dmdTransform sigs var dmd, Var var) +dmdAnal sigs dmd (Cast e co) + = (dmd_ty, Cast e' co) + where + (dmd_ty, e') = dmdAnal sigs dmd' e + to_co = snd (coercionKind co) + dmd' + | Just (tc, args) <- splitTyConApp_maybe to_co + , isRecursiveTyCon tc = evalDmd + | otherwise = dmd + -- This coerce usually arises from a recursive + -- newtype, and we don't want to look inside them + -- for exactly the same reason that we don't look + -- inside recursive products -- we might not reach + -- a fixpoint. So revert to a vanilla Eval demand + dmdAnal sigs dmd (Note n e) = (dmd_ty, Note n e') where - (dmd_ty, e') = dmdAnal sigs dmd' e - dmd' = case n of - Coerce _ _ -> evalDmd -- This coerce usually arises from a recursive - other -> dmd -- newtype, and we don't want to look inside them - -- for exactly the same reason that we don't look - -- inside recursive products -- we might not reach - -- a fixpoint. So revert to a vanilla Eval demand + (dmd_ty, e') = dmdAnal sigs dmd e dmdAnal sigs dmd (App fun (Type ty)) = (fun_ty, App fun' (Type ty)) @@ -252,8 +267,8 @@ dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)]) -- The insight is, of course, that a demand on y is a demand on the -- scrutinee, so we need to `both` it with the scrut demand - scrut_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b]) - `both` + alt_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b]) + scrut_dmd = alt_dmd `both` idNewDemandInfo case_bndr' (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut @@ -464,7 +479,27 @@ The thunk_cpr_ok 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. +so we'd lose sharing if w/w'd it into a function). E.g. + + let r = case expensive of + (a,b) -> (b,a) + in ... + +If we marked r as having the CPR property, then we'd w/w into + + let $wr = \() -> case expensive of + (a,b) -> (# b, a #) + r = case $wr () of + (# b,a #) -> (b,a) + in ... + +But now r is a thunk, which won't be inlined, so we are no further ahead. +But consider + + f x = let r = case expensive of (a,b) -> (b,a) + in if foo r then r else (x,x) + +Does f have the CPR property? Well, no. 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. @@ -528,37 +563,47 @@ in the case where t turns out to be not-demanded. This is handled by dmdAnalTopBind. +Note [NOINLINE and strictness] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The strictness analyser used to have a HACK which ensured that NOINLNE +things were not strictness-analysed. The reason was unsafePerformIO. +Left to itself, the strictness analyser would discover this strictness +for unsafePerformIO: + unsafePerformIO: C(U(AV)) +But then consider this sub-expression + unsafePerformIO (\s -> let r = f x in + case writeIORef v r s of (# s1, _ #) -> + (# s1, r #) +The strictness analyser will now find that r is sure to be eval'd, +and may then hoist it out. This makes tests/lib/should_run/memo002 +deadlock. + +Solving this by making all NOINLINE things have no strictness info is overkill. +In particular, it's overkill for runST, which is perfectly respectable. +Consider + f x = runST (return x) +This should be strict in x. + +So the new plan is to define unsafePerformIO using the 'lazy' combinator: + + unsafePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r) + +Remember, 'lazy' is a wired-in identity-function Id, of type a->a, which is +magically NON-STRICT, and is inlined after strictness analysis. So +unsafePerformIO will look non-strict, and that's what we want. + +Now we don't need the hack in the strictness analyser. HOWEVER, this +decision does mean that even a NOINLINE function is not entirely +opaque: some aspect of its implementation leaks out, notably its +strictness. For example, if you have a function implemented by an +error stub, but which has RULES, you may want it not to be eliminated +in favour of error! + + \begin{code} mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res) - | never_inline && not (isBotRes res) - -- HACK ALERT - -- Don't strictness-analyse NOINLINE things. Why not? Because - -- the NOINLINE says "don't expose any of the inner workings at the call - -- site" and the strictness is certainly an inner working. - -- - -- More concretely, the demand analyser discovers the following strictness - -- for unsafePerformIO: C(U(AV)) - -- But then consider - -- unsafePerformIO (\s -> let r = f x in - -- case writeIORef v r s of (# s1, _ #) -> - -- (# s1, r #) - -- The strictness analyser will find that the binding for r is strict, - -- (becuase of uPIO's strictness sig), and so it'll evaluate it before - -- doing the writeIORef. This actually makes tests/lib/should_run/memo002 - -- get a deadlock! - -- - -- Solution: don't expose the strictness of unsafePerformIO. - -- - -- But we do want to expose the strictness of error functions, - -- which are also often marked NOINLINE - -- {-# NOINLINE foo #-} - -- foo x = error ("wubble buggle" ++ x) - -- So (hack, hack) we only drop the strictness for non-bottom things - -- This is all very unsatisfactory. - = (deferEnv fv, topSig) - - | otherwise = (lazy_fv, mkStrictSig dmd_ty) + -- Re unused never_inline, see Note [NOINLINE and strictness] where dmd_ty = DmdType strict_fv final_dmds res' @@ -645,15 +690,6 @@ nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds %************************************************************************ \begin{code} -splitDmdTy :: DmdType -> (Demand, DmdType) --- Split off one function argument --- We already have a suitable demand on all --- free vars, so no need to add more! -splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty) -splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty) -\end{code} - -\begin{code} unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd @@ -703,6 +739,11 @@ annotateBndr dmd_ty@(DmdType fv ds res) var annotateBndrs = mapAccumR annotateBndr +annotateLamIdBndr :: DmdType -- Demand type of body + -> Id -- Lambda binder + -> (DmdType, -- Demand type of lambda + Id) -- and binder annotated with demand + annotateLamIdBndr dmd_ty@(DmdType fv ds res) id -- For lambdas we add the demand to the argument demands -- Only called for Ids @@ -858,6 +899,13 @@ dmdTransform sigs var dmd %************************************************************************ \begin{code} +splitDmdTy :: DmdType -> (Demand, DmdType) +-- Split off one function argument +-- We already have a suitable demand on all +-- free vars, so no need to add more! +splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty) +splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty) + splitCallDmd :: Demand -> (Int, Demand) splitCallDmd (Call d) = case splitCallDmd d of (n, r) -> (n+1, r) @@ -872,7 +920,6 @@ deferType (DmdType fv _ _) = DmdType (deferEnv fv) [] TopRes -- Notice that we throw away info about both arguments and results -- For example, f = let ... in \x -> x -- We don't want to get a stricness type V->T for f. - -- Peter?? deferEnv :: DmdEnv -> DmdEnv deferEnv fv = mapVarEnv defer fv @@ -989,7 +1036,7 @@ lub d1@(Eval _) d2 = d2 `lub` d1 -- Bot,Abs,Top,Call,Defer lub (Box d1) (Box d2) = box (d1 `lub` d2) lub d1@(Box _) d2 = d2 `lub` d1 -lubs = zipWithDmds lub +lubs ds1 ds2 = zipWithDmds lub ds1 ds2 --------------------- -- box is the smart constructor for Box @@ -1096,7 +1143,7 @@ both d1@(Eval ds1) d2 = d2 `both` d1 both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2) both d1@(Defer ds1) d2 = d2 `both` d1 -boths = zipWithDmds both +boths ds1 ds2 = zipWithDmds both ds1 ds2 \end{code}