+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
-%
-
- -----------------
- A demand analysis
- -----------------
-
-\begin{code}
-module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs,
- both {- needed by WwLib -}
- ) where
-
-#include "HsVersions.h"
-
-import DynFlags ( DynFlags, DynFlag(..) )
-import StaticFlags ( opt_MaxWorkerArgs )
-import NewDemand -- All of it
-import CoreSyn
-import PprCore
-import CoreUtils ( exprIsHNF, exprIsTrivial, exprArity )
-import DataCon ( dataConTyCon )
-import TyCon ( isProductTyCon, isRecursiveTyCon )
-import Id ( Id, idType, idInlinePragma,
- isDataConWorkId, isGlobalId, idArity,
-#ifdef OLD_STRICTNESS
- idDemandInfo, idStrictness, idCprInfo, idName,
-#endif
- idNewStrictness, idNewStrictness_maybe,
- setIdNewStrictness, idNewDemandInfo,
- idNewDemandInfo_maybe,
- setIdNewDemandInfo
- )
-#ifdef OLD_STRICTNESS
-import IdInfo ( newStrictnessFromOld, newDemand )
-#endif
-import Var ( Var )
-import VarEnv
-import TysWiredIn ( unboxedPairDataCon )
-import TysPrim ( realWorldStatePrimTy )
-import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
- keysUFM, minusUFM, ufmToList, filterUFM )
-import Type ( isUnLiftedType, coreEqType )
-import CoreLint ( showPass, endPass )
-import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs )
-import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
- RecFlag(..), isRec )
-import Maybes ( orElse, expectJust )
-import Outputable
-\end{code}
-
-To think about
-
-* set a noinline pragma on bottoming Ids
-
-* Consider f x = x+1 `fatbar` error (show x)
- We'd like to unbox x, even if that means reboxing it in the error case.
-
-
-%************************************************************************
-%* *
-\subsection{Top level stuff}
-%* *
-%************************************************************************
-
-\begin{code}
-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
- let { dmd_changes = get_changes binds_plus_dmds } ;
- printDump (text "Changes in demands" $$ dmd_changes) ;
-#endif
- return binds_plus_dmds
- }
- where
- do_prog :: [CoreBind] -> [CoreBind]
- do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds
-
-dmdAnalTopBind :: SigEnv
- -> CoreBind
- -> (SigEnv, CoreBind)
-dmdAnalTopBind sigs (NonRec id rhs)
- = let
- ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs)
- (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs1)
- -- Do two passes to improve CPR information
- -- See comments with ignore_cpr_info in mk_sig_ty
- -- and with extendSigsWithLam
- in
- (sigs2, NonRec id2 rhs2)
-
-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}
-
-\begin{code}
-dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr)
--- Analyse the RHS and return
--- a) appropriate strictness info
--- b) the unfolding (decorated with stricntess info)
-dmdAnalTopRhs rhs
- = (sig, rhs2)
- where
- call_dmd = vanillaCall (exprArity rhs)
- (_, rhs1) = dmdAnal emptySigEnv call_dmd rhs
- (rhs_ty, rhs2) = dmdAnal emptySigEnv call_dmd rhs1
- sig = mkTopSigTy rhs rhs_ty
- -- Do two passes; see notes with extendSigsWithLam
- -- Otherwise we get bogus CPR info for constructors like
- -- newtype T a = MkT a
- -- The constructor looks like (\x::T a -> x), modulo the coerce
- -- extendSigsWithLam will optimistically give x a CPR tag the
- -- first time, which is wrong in the end.
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{The analyser itself}
-%* *
-%************************************************************************
-
-\begin{code}
-dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
-
-dmdAnal sigs Abs e = (topDmdType, e)
-
-dmdAnal sigs dmd e
- | not (isStrictDmd dmd)
- = let
- (res_ty, e') = dmdAnal sigs evalDmd e
- in
- (deferType res_ty, e')
- -- It's important not to analyse e with a lazy demand because
- -- a) When we encounter case s of (a,b) ->
- -- we demand s with U(d1d2)... but if the overall demand is lazy
- -- that is wrong, and we'd need to reduce the demand on s,
- -- which is inconvenient
- -- b) More important, consider
- -- f (let x = R in x+x), where f is lazy
- -- We still want to mark x as demanded, because it will be when we
- -- enter the let. If we analyse f's arg with a Lazy demand, we'll
- -- just mark x as Lazy
- -- c) The application rule wouldn't be right either
- -- Evaluating (f x) in a L demand does *not* cause
- -- evaluation of f in a C(L) demand!
-
-
-dmdAnal sigs dmd (Lit lit)
- = (topDmdType, Lit lit)
-
-dmdAnal sigs dmd (Var var)
- = (dmdTransform sigs var dmd, Var var)
-
-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
-
-dmdAnal sigs dmd (App fun (Type ty))
- = (fun_ty, App fun' (Type ty))
- where
- (fun_ty, fun') = dmdAnal sigs dmd fun
-
--- Lots of the other code is there to make this
--- beautiful, compositional, application rule :-)
-dmdAnal sigs dmd e@(App fun arg) -- Non-type arguments
- = let -- [Type arg handled above]
- (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
- (arg_ty, arg') = dmdAnal sigs arg_dmd arg
- (arg_dmd, res_ty) = splitDmdTy fun_ty
- in
- (res_ty `bothType` arg_ty, App fun' arg')
-
-dmdAnal sigs dmd (Lam var body)
- | isTyVar var
- = let
- (body_ty, body') = dmdAnal sigs dmd body
- in
- (body_ty, Lam var body')
-
- | Call body_dmd <- dmd -- A call demand: good!
- = let
- 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')
-
- | otherwise -- Not enough demand on the lambda; but do the body
- = let -- anyway to annotate it and gather free var info
- (body_ty, body') = dmdAnal sigs evalDmd body
- (lam_ty, var') = annotateLamIdBndr body_ty var
- in
- (deferType lam_ty, Lam var' body')
-
-dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)])
- | let tycon = dataConTyCon dc,
- isProductTyCon tycon,
- not (isRecursiveTyCon tycon)
- = let
- sigs_alt = extendSigEnv NotTopLevel sigs case_bndr case_bndr_sig
- (alt_ty, alt') = dmdAnalAlt sigs_alt dmd alt
- (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
- (_, bndrs', _) = alt'
- case_bndr_sig = cprSig
- -- Inside the alternative, the case binder has the CPR property.
- -- Meaning that a case on it will successfully cancel.
- -- Example:
- -- f True x = case x of y { I# x' -> if x' ==# 3 then y else I# 8 }
- -- f False x = I# 3
- --
- -- We want f to have the CPR property:
- -- f b x = case fw b x of { r -> I# r }
- -- fw True x = case x of y { I# x' -> if x' ==# 3 then x' else 8 }
- -- fw False x = 3
-
- -- Figure out whether the demand on the case binder is used, and use
- -- that to set the scrut_dmd. This is utterly essential.
- -- Consider f x = case x of y { (a,b) -> k y a }
- -- If we just take scrut_demand = U(L,A), then we won't pass x to the
- -- worker, so the worker will rebuild
- -- x = (a, absent-error)
- -- and that'll crash.
- -- So at one stage I had:
- -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
- -- keepity | dead_case_bndr = Drop
- -- | otherwise = Keep
- --
- -- But then consider
- -- case x of y { (a,b) -> h y + a }
- -- where h : U(LL) -> T
- -- The above code would compute a Keep for x, since y is not Abs, which is silly
- -- 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`
- idNewDemandInfo case_bndr'
-
- (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
- in
- (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' ty [alt'])
-
-dmdAnal sigs dmd (Case scrut case_bndr ty alts)
- = let
- (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
- (scrut_ty, scrut') = dmdAnal sigs evalDmd scrut
- (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
- in
--- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
- (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' ty alts')
-
-dmdAnal sigs dmd (Let (NonRec id rhs) body)
- = let
- (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel NonRecursive sigs (id, rhs)
- (body_ty, body') = dmdAnal sigs' dmd body
- (body_ty1, id2) = annotateBndr body_ty id1
- body_ty2 = addLazyFVs body_ty1 lazy_fv
- in
- -- If the actual demand is better than the vanilla call
- -- demand, you might think that we might do better to re-analyse
- -- the RHS with the stronger demand.
- -- But (a) That seldom happens, because it means that *every* path in
- -- the body of the let has to use that stronger demand
- -- (b) It often happens temporarily in when fixpointing, because
- -- the recursive function at first seems to place a massive demand.
- -- But we don't want to go to extra work when the function will
- -- probably iterate to something less demanding.
- -- In practice, all the times the actual demand on id2 is more than
- -- the vanilla call demand seem to be due to (b). So we don't
- -- bother to re-analyse the RHS.
- (body_ty2, Let (NonRec id2 rhs') body')
-
-dmdAnal sigs dmd (Let (Rec pairs) body)
- = let
- bndrs = map fst pairs
- (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
- (body_ty, body') = dmdAnal sigs' dmd body
- body_ty1 = addLazyFVs body_ty lazy_fv
- in
- sigs' `seq` body_ty `seq`
- let
- (body_ty2, _) = annotateBndrs body_ty1 bndrs
- -- Don't bother to add demand info to recursive
- -- binders as annotateBndr does;
- -- being recursive, we can't treat them strictly.
- -- But we do need to remove the binders from the result demand env
- in
- (body_ty2, Let (Rec pairs') body')
-
-
-dmdAnalAlt sigs dmd (con,bndrs,rhs)
- = let
- (rhs_ty, rhs') = dmdAnal sigs dmd rhs
- (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
- final_alt_ty | io_hack_reqd = alt_ty `lubType` topDmdType
- | otherwise = alt_ty
-
- -- There's a hack here for I/O operations. Consider
- -- case foo x s of { (# s, r #) -> y }
- -- Is this strict in 'y'. Normally yes, but what if 'foo' is an I/O
- -- operation that simply terminates the program (not in an erroneous way)?
- -- In that case we should not evaluate y before the call to 'foo'.
- -- Hackish solution: spot the IO-like situation and add a virtual branch,
- -- as if we had
- -- case foo x s of
- -- (# s, r #) -> y
- -- other -> return ()
- -- So the 'y' isn't necessarily going to be evaluated
- --
- -- A more complete example where this shows up is:
- -- do { let len = <expensive> ;
- -- ; when (...) (exitWith ExitSuccess)
- -- ; print len }
-
- io_hack_reqd = con == DataAlt unboxedPairDataCon &&
- idType (head bndrs) `coreEqType` realWorldStatePrimTy
- in
- (final_alt_ty, (con, bndrs', rhs'))
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Bindings}
-%* *
-%************************************************************************
-
-\begin{code}
-dmdFix :: TopLevelFlag
- -> SigEnv -- Does not include bindings for this binding
- -> [(Id,CoreExpr)]
- -> (SigEnv, DmdEnv,
- [(Id,CoreExpr)]) -- Binders annotated with stricness info
-
-dmdFix top_lvl sigs orig_pairs
- = loop 1 initial_sigs orig_pairs
- where
- bndrs = map fst orig_pairs
- initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs]
-
- loop :: Int
- -> SigEnv -- Already contains the current sigs
- -> [(Id,CoreExpr)]
- -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
- loop n sigs pairs
- | found_fixpoint
- = (sigs', lazy_fv, pairs')
- -- Note: use pairs', not pairs. pairs' is the result of
- -- processing the RHSs with sigs (= sigs'), whereas pairs
- -- is the result of processing the RHSs with the *previous*
- -- iteration of sigs.
-
- | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
- [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
- text "env:" <+> ppr (ufmToList sigs),
- text "binds:" <+> pprCoreBinding (Rec pairs)]))
- (emptySigEnv, lazy_fv, orig_pairs) -- Safe output
- -- The lazy_fv part is really important! orig_pairs has no strictness
- -- info, including nothing about free vars. But if we have
- -- letrec f = ....y..... in ...f...
- -- where 'y' is free in f, we must record that y is mentioned,
- -- otherwise y will get recorded as absent altogether
-
- | otherwise = loop (n+1) sigs' pairs'
- where
- found_fixpoint = all (same_sig sigs sigs') bndrs
- -- Use the new signature to do the next pair
- -- The occurrence analyser has arranged them in a good order
- -- so this can significantly reduce the number of iterations needed
- ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
-
- my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
- = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
- -- (new_sig `seq`
- -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
- ((sigs', lazy_fv'), pair')
- -- )
- where
- (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive sigs (id,rhs)
- lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
- -- 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
-initialSig id = idNewStrictness_maybe id `orElse` botSig
-
-dmdAnalRhs :: TopLevelFlag -> RecFlag
- -> SigEnv -> (Id, CoreExpr)
- -> (SigEnv, DmdEnv, (Id, CoreExpr))
--- Process the RHS of the binding, add the strictness signature
--- to the Id, and augment the environment with the signature as well.
-
-dmdAnalRhs top_lvl rec_flag sigs (id, rhs)
- = (sigs', lazy_fv, (id', rhs'))
- where
- arity = idArity id -- The idArity should be up to date
- -- The simplifier was run just beforehand
- (rhs_dmd_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
- (lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_dmd_ty && not (exprIsTrivial rhs), ppr id )
- -- The RHS can be eta-reduced to just a variable,
- -- in which case we should not complain.
- mkSigTy top_lvl rec_flag id rhs rhs_dmd_ty
- id' = id `setIdNewStrictness` sig_ty
- sigs' = extendSigEnv top_lvl sigs id sig_ty
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Strictness signatures and types}
-%* *
-%************************************************************************
-
-\begin{code}
-mkTopSigTy :: CoreExpr -> DmdType -> StrictSig
- -- Take a DmdType and turn it into a StrictSig
- -- NB: not used for never-inline things; hence False
-mkTopSigTy rhs dmd_ty = snd (mk_sig_ty False False rhs dmd_ty)
-
-mkSigTy :: TopLevelFlag -> RecFlag -> Id -> CoreExpr -> DmdType -> (DmdEnv, StrictSig)
-mkSigTy top_lvl rec_flag id rhs dmd_ty
- = mk_sig_ty never_inline thunk_cpr_ok rhs dmd_ty
- where
- never_inline = isNeverActive (idInlinePragma id)
- maybe_id_dmd = idNewDemandInfo_maybe id
- -- Is Nothing the first time round
-
- thunk_cpr_ok
- | isTopLevel top_lvl = False -- Top level things don't get
- -- their demandInfo set at all
- | isRec rec_flag = False -- Ditto recursive things
- | Just dmd <- maybe_id_dmd = isStrictDmd dmd
- | otherwise = True -- Optimistic, first time round
- -- See notes below
-\end{code}
-
-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.
-
-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 thunk_cpr_ok [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.
-
-
-\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)
- where
- dmd_ty = DmdType strict_fv final_dmds res'
-
- lazy_fv = filterUFM (not . isStrictDmd) fv
- strict_fv = filterUFM isStrictDmd fv
- -- We put the strict FVs in the DmdType of the Id, so
- -- that at its call sites we unleash demands on its strict fvs.
- -- An example is 'roll' in imaginary/wheel-sieve2
- -- Something like this:
- -- roll x = letrec
- -- go y = if ... then roll (x-1) else x+1
- -- in
- -- go ms
- -- We want to see that roll is strict in x, which is because
- -- go is called. So we put the DmdEnv for x in go's DmdType.
- --
- -- Another example:
- -- f :: Int -> Int -> Int
- -- f x y = let t = x+1
- -- h z = if z==0 then t else
- -- if z==1 then x+1 else
- -- x + h (z-1)
- -- in
- -- h y
- -- Calling h does indeed evaluate x, but we can only see
- -- that if we unleash a demand on x at the call site for t.
- --
- -- Incidentally, here's a place where lambda-lifting h would
- -- lose the cigar --- we couldn't see the joint strictness in t/x
- --
- -- ON THE OTHER HAND
- -- We don't want to put *all* the fv's from the RHS into the
- -- DmdType, because that makes fixpointing very slow --- the
- -- DmdType gets full of lazy demands that are slow to converge.
-
- final_dmds = setUnpackStrategy dmds
- -- Set the unpacking strategy
-
- res' = case res of
- RetCPR | ignore_cpr_info -> TopRes
- other -> res
- ignore_cpr_info = not (exprIsHNF rhs || thunk_cpr_ok)
-\end{code}
-
-The unpack strategy determines whether we'll *really* unpack the argument,
-or whether we'll just remember its strictness. If unpacking would give
-rise to a *lot* of worker args, we may decide not to unpack after all.
-
-\begin{code}
-setUnpackStrategy :: [Demand] -> [Demand]
-setUnpackStrategy ds
- = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
- where
- go :: Int -- Max number of args available for sub-components of [Demand]
- -> [Demand]
- -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
-
- go n (Eval (Prod cs) : ds)
- | n' >= 0 = Eval (Prod cs') `cons` go n'' ds
- | otherwise = Box (Eval (Prod cs)) `cons` go n ds
- where
- (n'',cs') = go n' cs
- n' = n + 1 - non_abs_args
- -- Add one to the budget 'cos we drop the top-level arg
- non_abs_args = nonAbsentArgs cs
- -- Delete # of non-absent args to which we'll now be committed
-
- go n (d:ds) = d `cons` go n ds
- go n [] = (n,[])
-
- cons d (n,ds) = (n, d:ds)
-
-nonAbsentArgs :: [Demand] -> Int
-nonAbsentArgs [] = 0
-nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
-nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Strictness signatures and types}
-%* *
-%************************************************************************
-
-\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
- | isTopLevel top_lvl = dmd_ty -- Don't record top level things
- | otherwise = DmdType (extendVarEnv fv var dmd) ds res
-
-addLazyFVs (DmdType fv ds res) lazy_fvs
- = DmdType both_fv1 ds res
- where
- both_fv = (plusUFM_C both fv lazy_fvs)
- both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv
- -- This modifyEnv is vital. Consider
- -- let f = \x -> (x,y)
- -- in error (f 3)
- -- Here, y is treated as a lazy-fv of f, but we must `both` that L
- -- demand with the bottom coming up from 'error'
- --
- -- I got a loop in the fixpointer without this, due to an interaction
- -- with the lazy_fv filtering in mkSigTy. Roughly, it was
- -- letrec f n x
- -- = letrec g y = x `fatbar`
- -- letrec h z = z + ...g...
- -- in h (f (n-1) x)
- -- in ...
- -- In the initial iteration for f, f=Bot
- -- Suppose h is found to be strict in z, but the occurrence of g in its RHS
- -- is lazy. Now consider the fixpoint iteration for g, esp the demands it
- -- places on its free variables. Suppose it places none. Then the
- -- x `fatbar` ...call to h...
- -- will give a x->V demand for x. That turns into a L demand for x,
- -- which floats out of the defn for h. Without the modifyEnv, that
- -- L demand doesn't get both'd with the Bot coming up from the inner
- -- call to f. So we just get an L demand for x for g.
- --
- -- A better way to say this is that the lazy-fv filtering should give the
- -- same answer as putting the lazy fv demands in the function's type.
-
-annotateBndr :: DmdType -> Var -> (DmdType, Var)
--- The returned env has the var deleted
--- The returned var is annotated with demand info
--- No effect on the argument demands
-annotateBndr dmd_ty@(DmdType fv ds res) var
- | isTyVar var = (dmd_ty, var)
- | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd)
- where
- (fv', dmd) = removeFV fv var res
-
-annotateBndrs = mapAccumR annotateBndr
-
-annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
--- For lambdas we add the demand to the argument demands
--- Only called for Ids
- = ASSERT( isId id )
- (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
- where
- (fv', dmd) = removeFV fv id res
- hacked_dmd = argDemand dmd
- -- This call to argDemand is vital, because otherwise we label
- -- a lambda binder with demand 'B'. But in terms of calling
- -- conventions that's Abs, because we don't pass it. But
- -- when we do a w/w split we get
- -- fw x = (\x y:B -> ...) x (error "oops")
- -- And then the simplifier things the 'B' is a strict demand
- -- and evaluates the (error "oops"). Sigh
-
-removeFV fv id res = (fv', zapUnlifted id dmd)
- where
- fv' = fv `delVarEnv` id
- dmd = lookupVarEnv fv id `orElse` deflt
- deflt | isBotRes res = Bot
- | otherwise = Abs
-
--- For unlifted-type variables, we are only
--- interested in Bot/Abs/Box Abs
-zapUnlifted is Bot = Bot
-zapUnlifted id Abs = Abs
-zapUnlifted id dmd | isUnLiftedType (idType id) = lazyDmd
- | otherwise = dmd
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Strictness signatures}
-%* *
-%************************************************************************
-
-\begin{code}
-type SigEnv = VarEnv (StrictSig, TopLevelFlag)
- -- We use the SigEnv to tell us whether to
- -- record info about a variable in the DmdEnv
- -- We do so if it's a LocalId, but not top-level
- --
- -- The DmdEnv gives the demand on the free vars of the function
- -- when it is given enough args to satisfy the strictness signature
-
-emptySigEnv = emptyVarEnv
-
-extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
-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. E.g.
--- f = \x::(Int,Int). if ...strict in x... then
--- x
--- else
--- (a,b)
--- We want f to have the CPR property because x does, by the time f has been w/w'd
---
--- Also note that we only want to do this for something that
--- definitely has product type, else we may get over-optimistic
--- CPR results (e.g. from \x -> x!).
-
-extendSigsWithLam sigs id
- = case idNewDemandInfo_maybe id of
- Nothing -> extendVarEnv sigs id (cprSig, NotTopLevel)
- -- Optimistic in the Nothing case;
- -- See notes [CPR-AND-STRICTNESS]
- Just (Eval (Prod ds)) -> extendVarEnv sigs id (cprSig, NotTopLevel)
- other -> sigs
-
-
-dmdTransform :: SigEnv -- The strictness environment
- -> Id -- The function
- -> Demand -- The demand on the function
- -> DmdType -- The demand type of the function in this context
- -- Returned DmdEnv includes the demand on
- -- this function plus demand on its free variables
-
-dmdTransform sigs var dmd
-
------- DATA CONSTRUCTOR
- | isDataConWorkId var -- Data constructor
- = let
- StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
- DmdType _ _ con_res = dmd_ty
- arity = idArity var
- in
- if arity == call_depth then -- Saturated, so unleash the demand
- let
- -- Important! If we Keep the constructor application, then
- -- we need the demands the constructor places (always lazy)
- -- If not, we don't need to. For example:
- -- f p@(x,y) = (p,y) -- S(AL)
- -- g a b = f (a,b)
- -- It's vital that we don't calculate Absent for a!
- dmd_ds = case res_dmd of
- Box (Eval ds) -> mapDmds box ds
- Eval ds -> ds
- other -> Poly Top
-
- -- ds can be empty, when we are just seq'ing the thing
- -- If so we must make up a suitable bunch of demands
- arg_ds = case dmd_ds of
- Poly d -> replicate arity d
- Prod ds -> ASSERT( ds `lengthIs` arity ) ds
-
- in
- mkDmdType emptyDmdEnv arg_ds con_res
- -- Must remember whether it's a product, hence con_res, not TopRes
- else
- topDmdType
-
------- IMPORTED FUNCTION
- | isGlobalId var, -- Imported function
- let StrictSig dmd_ty = idNewStrictness var
- = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
- dmd_ty
- else
- topDmdType
-
------- LOCAL LET/REC BOUND THING
- | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
- = let
- fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
- | otherwise = deferType dmd_ty
- -- NB: it's important to use deferType, and not just return topDmdType
- -- Consider let { f x y = p + x } in f 1
- -- The application isn't saturated, but we must nevertheless propagate
- -- a lazy demand for p!
- in
- addVarDmd top_lvl fn_ty var dmd
-
------- LOCAL NON-LET/REC BOUND THING
- | otherwise -- Default case
- = unitVarDmd var dmd
-
- where
- (call_depth, res_dmd) = splitCallDmd dmd
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Demands}
-%* *
-%************************************************************************
-
-\begin{code}
-splitCallDmd :: Demand -> (Int, Demand)
-splitCallDmd (Call d) = case splitCallDmd d of
- (n, r) -> (n+1, r)
-splitCallDmd d = (0, d)
-
-vanillaCall :: Arity -> Demand
-vanillaCall 0 = evalDmd
-vanillaCall n = Call (vanillaCall (n-1))
-
-deferType :: DmdType -> DmdType
-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
-
-
-----------------
-argDemand :: Demand -> Demand
--- The 'Defer' demands are just Lazy at function boundaries
--- Ugly! Ask John how to improve it.
-argDemand Top = lazyDmd
-argDemand (Defer d) = lazyDmd
-argDemand (Eval ds) = Eval (mapDmds argDemand ds)
-argDemand (Box Bot) = evalDmd
-argDemand (Box d) = box (argDemand d)
-argDemand Bot = Abs -- Don't pass args that are consumed (only) by bottom
-argDemand d = d
-\end{code}
-
-\begin{code}
--------------------------
--- Consider (if x then y else []) with demand V
--- Then the first branch gives {y->V} and the second
--- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
--- in the result env.
-lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
- = DmdType lub_fv2 (lub_ds ds1 ds2) (r1 `lubRes` r2)
- where
- lub_fv = plusUFM_C lub fv1 fv2
- lub_fv1 = modifyEnv (not (isBotRes r1)) absLub fv2 fv1 lub_fv
- lub_fv2 = modifyEnv (not (isBotRes r2)) absLub fv1 fv2 lub_fv1
- -- lub is the identity for Bot
-
- -- Extend the shorter argument list to match the longer
- lub_ds (d1:ds1) (d2:ds2) = lub d1 d2 : lub_ds ds1 ds2
- lub_ds [] [] = []
- lub_ds ds1 [] = map (`lub` resTypeArgDmd r2) ds1
- lub_ds [] ds2 = map (resTypeArgDmd r1 `lub`) ds2
-
------------------------------------
--- (t1 `bothType` t2) takes the argument/result info from t1,
--- using t2 just for its free-var info
--- NB: Don't forget about r2! It might be BotRes, which is
--- a bottom demand on all the in-scope variables.
--- Peter: can this be done more neatly?
-bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
- = DmdType both_fv2 ds1 (r1 `bothRes` r2)
- where
- both_fv = plusUFM_C both fv1 fv2
- both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
- both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
- -- both is the identity for Abs
-\end{code}
-
-
-\begin{code}
-lubRes BotRes r = r
-lubRes r BotRes = r
-lubRes RetCPR RetCPR = RetCPR
-lubRes r1 r2 = TopRes
-
--- If either diverges, the whole thing does
--- Otherwise take CPR info from the first
-bothRes r1 BotRes = BotRes
-bothRes r1 r2 = r1
-\end{code}
-
-\begin{code}
-modifyEnv :: Bool -- No-op if False
- -> (Demand -> Demand) -- The zapper
- -> DmdEnv -> DmdEnv -- Env1 and Env2
- -> DmdEnv -> DmdEnv -- Transform this env
- -- Zap anything in Env1 but not in Env2
- -- Assume: dom(env) includes dom(Env1) and dom(Env2)
-
-modifyEnv need_to_modify zapper env1 env2 env
- | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
- | otherwise = env
- where
- zap uniq env = addToUFM_Directly env uniq (zapper current_val)
- where
- current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq)
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{LUB and BOTH}
-%* *
-%************************************************************************
-
-\begin{code}
-lub :: Demand -> Demand -> Demand
-
-lub Bot d2 = d2
-lub Abs d2 = absLub d2
-lub Top d2 = Top
-lub (Defer ds1) d2 = defer (Eval ds1 `lub` d2)
-
-lub (Call d1) (Call d2) = Call (d1 `lub` d2)
-lub d1@(Call _) (Box d2) = d1 `lub` d2 -- Just strip the box
-lub d1@(Call _) d2@(Eval _) = d2 -- Presumably seq or vanilla eval
-lub d1@(Call _) d2 = d2 `lub` d1 -- Bot, Abs, Top
-
--- For the Eval case, we use these approximation rules
--- Box Bot <= Eval (Box Bot ...)
--- Box Top <= Defer (Box Bot ...)
--- Box (Eval ds) <= Eval (map Box ds)
-lub (Eval ds1) (Eval ds2) = Eval (ds1 `lubs` ds2)
-lub (Eval ds1) (Box Bot) = Eval (mapDmds (`lub` Box Bot) ds1)
-lub (Eval ds1) (Box (Eval ds2)) = Eval (ds1 `lubs` mapDmds box ds2)
-lub (Eval ds1) (Box Abs) = deferEval (mapDmds (`lub` Box Bot) ds1)
-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
-
----------------------
--- box is the smart constructor for Box
--- It computes <B,bot> & d
--- INVARIANT: (Box d) => d = Bot, Abs, Eval
--- Seems to be no point in allowing (Box (Call d))
-box (Call d) = Call d -- The odd man out. Why?
-box (Box d) = Box d
-box (Defer _) = lazyDmd
-box Top = lazyDmd -- Box Abs and Box Top
-box Abs = lazyDmd -- are the same <B,L>
-box d = Box d -- Bot, Eval
-
----------------
-defer :: Demand -> Demand
-
--- defer is the smart constructor for Defer
--- The idea is that (Defer ds) = <U(ds), L>
---
--- It specifies what happens at a lazy function argument
--- or a lambda; the L* operator
--- Set the strictness part to L, but leave
--- the boxity side unaffected
--- It also ensures that Defer (Eval [LLLL]) = L
-
-defer Bot = Abs
-defer Abs = Abs
-defer Top = Top
-defer (Call _) = lazyDmd -- Approximation here?
-defer (Box _) = lazyDmd
-defer (Defer ds) = Defer ds
-defer (Eval ds) = deferEval ds
-
--- deferEval ds = defer (Eval ds)
-deferEval ds | allTop ds = Top
- | otherwise = Defer ds
-
----------------------
-absLub :: Demand -> Demand
--- Computes (Abs `lub` d)
--- For the Bot case consider
--- f x y = if ... then x else error x
--- Then for y we get Abs `lub` Bot, and we really
--- want Abs overall
-absLub Bot = Abs
-absLub Abs = Abs
-absLub Top = Top
-absLub (Call _) = Top
-absLub (Box _) = Top
-absLub (Eval ds) = Defer (absLubs ds) -- Or (Defer ds)?
-absLub (Defer ds) = Defer (absLubs ds) -- Or (Defer ds)?
-
-absLubs = mapDmds absLub
-
----------------
-both :: Demand -> Demand -> Demand
-
-both Abs d2 = d2
-
-both Bot Bot = Bot
-both Bot Abs = Bot
-both Bot (Eval ds) = Eval (mapDmds (`both` Bot) ds)
- -- Consider
- -- f x = error x
- -- From 'error' itself we get demand Bot on x
- -- From the arg demand on x we get
- -- x :-> evalDmd = Box (Eval (Poly Abs))
- -- So we get Bot `both` Box (Eval (Poly Abs))
- -- = Seq Keep (Poly Bot)
- --
- -- Consider also
- -- f x = if ... then error (fst x) else fst x
- -- Then we get (Eval (Box Bot, Bot) `lub` Eval (SA))
- -- = Eval (SA)
- -- which is what we want.
-both Bot d = errDmd
-
-both Top Bot = errDmd
-both Top Abs = Top
-both Top Top = Top
-both Top (Box d) = Box d
-both Top (Call d) = Call d
-both Top (Eval ds) = Eval (mapDmds (`both` Top) ds)
-both Top (Defer ds) -- = defer (Top `both` Eval ds)
- -- = defer (Eval (mapDmds (`both` Top) ds))
- = deferEval (mapDmds (`both` Top) ds)
-
-
-both (Box d1) (Box d2) = box (d1 `both` d2)
-both (Box d1) d2@(Call _) = box (d1 `both` d2)
-both (Box d1) d2@(Eval _) = box (d1 `both` d2)
-both (Box d1) (Defer d2) = Box d1
-both d1@(Box _) d2 = d2 `both` d1
-
-both (Call d1) (Call d2) = Call (d1 `both` d2)
-both (Call d1) (Eval ds2) = Call d1 -- Could do better for (Poly Bot)?
-both (Call d1) (Defer ds2) = Call d1 -- Ditto
-both d1@(Call _) d2 = d1 `both` d1
-
-both (Eval ds1) (Eval ds2) = Eval (ds1 `boths` ds2)
-both (Eval ds1) (Defer ds2) = Eval (ds1 `boths` mapDmds defer ds2)
-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
-\end{code}
-
-
-
-%************************************************************************
-%* *
-\subsection{Miscellaneous
-%* *
-%************************************************************************
-
-
-\begin{code}
-#ifdef OLD_STRICTNESS
-get_changes binds = vcat (map get_changes_bind binds)
-
-get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
-get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
-
-get_changes_pr (id,rhs)
- = get_changes_var id $$ get_changes_expr rhs
-
-get_changes_var var
- | isId var = get_changes_str var $$ get_changes_dmd var
- | otherwise = empty
-
-get_changes_expr (Type t) = empty
-get_changes_expr (Var v) = empty
-get_changes_expr (Lit l) = empty
-get_changes_expr (Note n e) = get_changes_expr e
-get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
-get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
-get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
-get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
-
-get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
-
-get_changes_str id
- | new_better && old_better = empty
- | new_better = message "BETTER"
- | old_better = message "WORSE"
- | otherwise = message "INCOMPARABLE"
- where
- message word = text word <+> text "strictness for" <+> ppr id <+> info
- info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = squashSig (idNewStrictness id) -- Don't report spurious diffs that the old
- -- strictness analyser can't track
- old = newStrictnessFromOld (idName id) (idArity id) (idStrictness id) (idCprInfo id)
- old_better = old `betterStrictness` new
- new_better = new `betterStrictness` old
-
-get_changes_dmd id
- | isUnLiftedType (idType id) = empty -- Not useful
- | new_better && old_better = empty
- | new_better = message "BETTER"
- | old_better = message "WORSE"
- | otherwise = message "INCOMPARABLE"
- where
- message word = text word <+> text "demand for" <+> ppr id <+> info
- info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = squashDmd (argDemand (idNewDemandInfo id)) -- To avoid spurious improvements
- -- A bit of a hack
- old = newDemand (idDemandInfo id)
- new_better = new `betterDemand` old
- old_better = old `betterDemand` new
-
-betterStrictness :: StrictSig -> StrictSig -> Bool
-betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
-
-betterDmdType t1 t2 = (t1 `lubType` t2) == t2
-
-betterDemand :: Demand -> Demand -> Bool
--- If d1 `better` d2, and d2 `better` d2, then d1==d2
-betterDemand d1 d2 = (d1 `lub` d2) == d2
-
-squashSig (StrictSig (DmdType fv ds res))
- = StrictSig (DmdType emptyDmdEnv (map squashDmd ds) res)
- where
- -- squash just gets rid of call demands
- -- which the old analyser doesn't track
-squashDmd (Call d) = evalDmd
-squashDmd (Box d) = Box (squashDmd d)
-squashDmd (Eval ds) = Eval (mapDmds squashDmd ds)
-squashDmd (Defer ds) = Defer (mapDmds squashDmd ds)
-squashDmd d = d
-#endif
-\end{code}
projects / ghc-hetmet.git / blobdiff