-----------------
\begin{code}
-module DmdAnal ( dmdAnalPgm ) where
+module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs,
+ both {- needed by WwLib -}
+ ) where
#include "HsVersions.h"
-import CmdLineOpts ( DynFlags, DynFlag(..), opt_MaxWorkerArgs )
+import DynFlags ( DynFlags, DynFlag(..) )
+import StaticFlags ( opt_MaxWorkerArgs )
import NewDemand -- All of it
import CoreSyn
-import CoreUtils ( exprIsValue, exprArity )
+import PprCore
+import CoreUtils ( exprIsHNF, exprIsTrivial, exprArity )
import DataCon ( dataConTyCon )
import TyCon ( isProductTyCon, isRecursiveTyCon )
-import Id ( Id, idType, idInfo, idArity, idCprInfo, idDemandInfo,
- modifyIdInfo, isDataConId, isImplicitId, isGlobalId,
- idNewStrictness, idNewStrictness_maybe, getNewStrictness, setIdNewStrictness,
- idNewDemandInfo, setIdNewDemandInfo, newStrictnessFromOld )
-import IdInfo ( newDemand )
+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 )
+import Type ( isUnLiftedType, coreEqType )
import CoreLint ( showPass, endPass )
-import ErrUtils ( dumpIfSet_dyn )
-import Util ( mapAndUnzip, mapAccumL, mapAccumR, zipWithEqual )
-import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel )
+import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs )
+import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
+ RecFlag(..), isRec )
import Maybes ( orElse, expectJust )
import Outputable
-import FastTypes
\end{code}
To think about
* 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.
-\begin{code}
-instance Outputable TopLevelFlag where
- ppr flag = empty
-\end{code}
%************************************************************************
%* *
dmdAnalPgm dflags binds
= do {
showPass dflags "Demand analysis" ;
- let { binds_plus_dmds = do_prog binds ;
- dmd_changes = get_changes binds_plus_dmds } ;
+ let { binds_plus_dmds = do_prog binds } ;
+
endPass dflags "Demand analysis"
Opt_D_dump_stranal binds_plus_dmds ;
-#ifdef DEBUG
- -- Only if DEBUG is on, because only then is the old strictness analyser run
+#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
-> CoreBind
-> (SigEnv, CoreBind)
dmdAnalTopBind sigs (NonRec id rhs)
- | isImplicitId id -- Don't touch the info on constructors, selectors etc
- = (sigs, NonRec id rhs) -- It's pre-computed in MkId.lhs
- | otherwise
= let
- (sigs', _, (id', rhs')) = downRhs TopLevel sigs (id, rhs)
+ ( _, _, (_, 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
- (sigs', NonRec id' rhs')
+ (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}
%************************************************************************
%* *
dmdAnal sigs Abs e = (topDmdType, e)
-dmdAnal sigs Lazy e = let
- (res_ty, e') = dmdAnal sigs Eval e
- in
- (deferType res_ty, 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
-- 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)
where
(dmd_ty, e') = dmdAnal sigs dmd' e
dmd' = case n of
- Coerce _ _ -> Eval -- 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
+ 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
-dmdAnal sigs dmd (App fun arg) -- Non-type arguments
+-- 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
| 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')
| 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 Eval body
+ (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 [alt@(DataAlt dc,bndrs,rhs)])
+dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)])
| let tycon = dataConTyCon dc,
isProductTyCon tycon,
not (isRecursiveTyCon tycon)
= let
- bndr_ids = filter isId bndrs
- (alt_ty, alt') = dmdAnalAlt sigs dmd alt
- (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
- (_, bndrs', _) = alt'
-
- -- Figure out whether the case binder is used, and use
- -- that to set the keepity of the demand. This is utterly essential.
+ 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.
- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
- keepity | dead_case_bndr = Drop
- | otherwise = Keep
-
- scrut_dmd = Seq keepity Now [idNewDemandInfo b | b <- bndrs', isId b]
- (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
+ -- 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' [alt'])
+ (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' ty [alt'])
-dmdAnal sigs dmd (Case scrut case_bndr alts)
+dmdAnal sigs dmd (Case scrut case_bndr ty alts)
= let
(alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
- (scrut_ty, scrut') = dmdAnal sigs Eval scrut
+ (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' alts')
+ (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')) = downRhs NotTopLevel sigs (id, rhs)
+ (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
--- pprTrace "dmdLet" (ppr id <+> ppr (sig,rhs_env))
+ -- 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
(rhs_ty, rhs') = dmdAnal sigs dmd rhs
(alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
- in
- (alt_ty, (con, bndrs', rhs'))
+ 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}
%************************************************************************
-> (SigEnv, DmdEnv,
[(Id,CoreExpr)]) -- Binders annotated with stricness info
-dmdFix top_lvl sigs pairs
- = loop 1 initial_sigs pairs
+dmdFix top_lvl sigs orig_pairs
+ = loop 1 initial_sigs orig_pairs
where
- bndrs = map fst pairs
- initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs]
+ 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
- | all (same_sig sigs sigs') bndrs = (sigs', lazy_fv, 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 >= 5 = pprTrace "dmdFix" (ppr n <+> (vcat
+
+ | 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:" <+> ppr pairs]))
- (loop (n+1) sigs' pairs')
- | otherwise = {- pprTrace "dmdFixLoop" (ppr id_sigs) -} (loop (n+1) sigs' pairs')
+ 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'), pair')
-- )
where
- (sigs', lazy_fv1, pair') = downRhs top_lvl sigs (id,rhs)
+ (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
+ -- 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
-downRhs :: TopLevelFlag
+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.
-downRhs top_lvl sigs (id, rhs)
+dmdAnalRhs top_lvl rec_flag sigs (id, rhs)
= (sigs', lazy_fv, (id', rhs'))
where
- arity = exprArity rhs -- The idArity may not be up to date
- (rhs_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
- (lazy_fv, sig_ty) = mkSigTy id arity rhs rhs_ty
- id' = id `setIdNewStrictness` sig_ty
- sigs' = extendSigEnv top_lvl sigs id sig_ty
+ 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}
%************************************************************************
%************************************************************************
\begin{code}
-mkSigTy :: Id -> Arity -> CoreExpr -> DmdType -> (DmdEnv, StrictSig)
--- Take a DmdType and turn it into a StrictSig
-mkSigTy id arity rhs (DmdType fv dmds res)
- = (lazy_fv, mkStrictSig id arity dmd_ty)
+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 lazified_dmds res'
+ dmd_ty = DmdType strict_fv final_dmds res'
lazy_fv = filterUFM (not . isStrictDmd) fv
strict_fv = filterUFM isStrictDmd fv
-- DmdType, because that makes fixpointing very slow --- the
-- DmdType gets full of lazy demands that are slow to converge.
- lazified_dmds = map lazify dmds
- -- Get rid of defers in the arguments
- final_dmds = setUnpackStrategy lazified_dmds
+ final_dmds = setUnpackStrategy dmds
-- Set the unpacking strategy
- res' = case (dmds, res) of
- ([], RetCPR) | not (exprIsValue rhs) -> TopRes
- other -> res
- -- 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.
- --
- -- DONE IN OLD CPR ANALYSER, BUT NOT YET HERE
- -- Also, if the strictness analyser has figured out that it's strict,
- -- the let-to-case transformation will happen, so again it's good.
- -- (CPR analysis runs before the simplifier has had a chance to do
- -- the let-to-case transform.)
- -- 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
+ 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,
-> [Demand]
-> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
- go n (Seq keep _ cs : ds)
- | n' >= 0 = Seq keep Now cs' `cons` go n'' ds
- | otherwise = Eval `cons` go n ds
+ 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 + box - non_abs_args
- box = case keep of
- Keep -> 0
- Drop -> 1 -- Add one to the budget if we drop the top-level arg
+ 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
\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 [] TopRes) = (topDmd, ty)
-splitDmdTy ty@(DmdType fv [] BotRes) = (Abs, ty)
- -- We already have a suitable demand on all
- -- free vars, so no need to add more!
-splitDmdTy (DmdType fv [] RetCPR) = panic "splitDmdTy"
+splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty)
\end{code}
\begin{code}
| otherwise = DmdType (extendVarEnv fv var dmd) ds res
addLazyFVs (DmdType fv ds res) lazy_fvs
- = DmdType (plusUFM_C both fv lazy_fvs) ds res
+ = 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
-- For lambdas we add the demand to the argument demands
-- Only called for Ids
= ASSERT( isId id )
- (DmdType fv' (dmd:ds) res, setIdNewDemandInfo id dmd)
+ (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
where
(fv', dmd) = removeFV fv id res
-
-removeFV fv var res = (fv', dmd)
+ 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` var
- dmd = lookupVarEnv fv var `orElse` deflt
+ 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}
%************************************************************************
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
dmdTransform sigs var dmd
------ DATA CONSTRUCTOR
- | isDataConId var, -- Data constructor
- Seq k Now ds <- res_dmd, -- and the demand looks inside its fields
- let StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
- = if dmdTypeDepth dmd_ty == length ds then -- Saturated, so unleash the demand
- -- ds can be empty, when we are just seq'ing the thing
- mkDmdType emptyDmdEnv ds (dmdTypeRes dmd_ty)
- -- Need to extract whether it's a product, hence dmdTypeRes
+ | 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 = getNewStrictness var
+ let StrictSig dmd_ty = idNewStrictness var
= if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
dmd_ty
else
splitCallDmd d = (0, d)
vanillaCall :: Arity -> Demand
-vanillaCall 0 = Eval
+vanillaCall 0 = evalDmd
vanillaCall n = Call (vanillaCall (n-1))
deferType :: DmdType -> DmdType
-deferType (DmdType fv _ _) = DmdType (mapVarEnv defer fv) [] TopRes
+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??
-defer :: Demand -> Demand
--- c.f. `lub` Abs
-defer Abs = Abs
-defer (Seq k _ ds) = Seq k Defer ds
-defer other = Lazy
+deferEnv :: DmdEnv -> DmdEnv
+deferEnv fv = mapVarEnv defer fv
-lazify :: Demand -> Demand
--- The 'Defer' demands are just Lazy at function boundaries
-lazify (Seq k Defer ds) = Lazy
-lazify (Seq k Now ds) = Seq k Now (map lazify ds)
-lazify Bot = Abs -- Don't pass args that are consumed by bottom
-lazify d = d
-\end{code}
-\begin{code}
-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
-
-squashDmdEnv (StrictSig (DmdType fv ds res)) = StrictSig (DmdType emptyDmdEnv ds res)
+----------------
+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}
-
-%************************************************************************
-%* *
-\subsection{LUB and BOTH}
-%* *
-%************************************************************************
-
\begin{code}
-lub :: Demand -> Demand -> Demand
-
-lub Bot d = d
-
-lub Lazy d = Lazy
-
-lub Err Bot = Err
-lub Err d = d
-
-lub Abs Bot = Abs
-lub Abs Err = Abs
-lub Abs Abs = Abs
-lub Abs (Seq k _ ds) = Seq k Defer ds -- Very important ('radicals' example)
-lub Abs d = Lazy
-
-lub Eval Abs = Lazy
-lub Eval Lazy = Lazy
-lub Eval (Seq k Now ds) = Eval -- Was (incorrectly): Seq Keep Now ds
-lub Eval (Seq k Defer ds) = Lazy
-lub Eval d = Eval
-
-lub (Call d1) (Call d2) = Call (lub d1 d2)
-
-lub (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) (l1 `or_defer` l2) (lubs ds1 ds2)
-
--- The last clauses deal with the remaining cases for Call and Seq
-lub d1@(Call _) d2@(Seq _ _ _) = pprPanic "lub" (ppr d1 $$ ppr d2)
-lub d1 d2 = lub d2 d1
-
--- A Seq can have an empty list of demands, in the polymorphic case.
-lubs [] ds2 = ds2
-lubs ds1 [] = ds1
-lubs ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith lub ds1 ds2
-
-or_defer Now Now = Now
-or_defer _ _ = Defer
-
-------------------------
-- 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)}
+-- *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 (zipWith lub ds1 ds2) (r1 `lubRes` 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)) (Abs `lub`) fv2 fv1 lub_fv
- lub_fv2 = modifyEnv (not (isBotRes r2)) (Abs `lub`) fv1 fv2 lub_fv1
+ 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
--------------------------
-lubRes BotRes r = r
-lubRes r BotRes = r
-lubRes RetCPR RetCPR = RetCPR
-lubRes r1 r2 = TopRes
-
------------------------------------
-vee :: Keepity -> Keepity -> Keepity
-vee Drop Drop = Drop
-vee k1 k2 = Keep
-
------------------------------------
-both :: Demand -> Demand -> Demand
-
--- The normal one
--- both Bot d = Bot
-
--- The experimental one
--- The idea is that (error x) places on x
--- both demand Bot (like on all free vars)
--- and demand Eval (for the arg to error)
--- and we want the result to be Eval.
-both Bot Bot = Bot
-both Bot Abs = Bot
-both Bot d = d
-
-both Abs d = d
-
-both Err Bot = Err
-both Err Abs = Err
-both Err d = d
-
-both Lazy Bot = Lazy
-both Lazy Abs = Lazy
-both Lazy Err = Lazy
-both Lazy (Seq k l ds) = Seq Keep l ds
-both Lazy d = d
- -- Notice that the Seq case ensures that we have the
- -- boxed value. The equation originally said
- -- both (Seq k Now ds) = Seq Keep Now ds
- -- but it's important that the Keep is switched on even
- -- for a deferred demand. Otherwise a (Seq Drop Now [])
- -- might both'd with the result, and then we won't pass
- -- the boxed value. Here's an example:
- -- (x-1) `seq` (x+1, x)
- -- From the (x+1, x) we get (U*(V) `both` L), which must give S*(V)
- -- From (x-1) we get U(V). Combining, we must get S(V).
- -- If we got U*(V) from the pair, we'd end up with U(V), and that
- -- can be a disaster if a component of the data structure is absent.
- -- [Disaster = enter an absent argument.]
-
-both Eval (Seq k l ds) = Seq Keep Now ds
-both Eval (Call d) = Call d
-both Eval d = Eval
-
-both (Seq k1 Defer ds1) (Seq k2 Defer ds2) = Seq (k1 `vee` k2) Defer (boths ds1 ds2)
-both (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) Now (boths ds1' ds2')
- where
- ds1' = case l1 of { Now -> ds1; Defer -> map defer ds1 }
- ds2' = case l2 of { Now -> ds2; Defer -> map defer ds2 }
-
-both (Call d1) (Call d2) = Call (d1 `both` d2)
-
--- The last clauses deal with the remaining cases for Call and Seq
-both d1@(Call _) d2@(Seq _ _ _) = pprPanic "both" (ppr d1 $$ ppr d2)
-both d1 d2 = both d2 d1
-
------------------------------------
--- A Seq can have an empty list of demands, in the polymorphic case.
-boths [] ds2 = ds2
-boths ds1 [] = ds1
-boths ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith both ds1 ds2
-
------------------------------------
-bothRes :: DmdResult -> DmdResult -> DmdResult
--- Left-biased for CPR info
-bothRes BotRes _ = BotRes
-bothRes _ BotRes = BotRes
-bothRes r1 _ = r1
+ -- 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
+ = 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 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
%************************************************************************
%* *
+\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)
- | isImplicitId id = empty -- We don't look inside these
- | otherwise = get_changes_var id $$ get_changes_expr rhs
+ = get_changes_var id $$ get_changes_expr rhs
get_changes_var var
| isId var = get_changes_str var $$ get_changes_dmd var
where
message word = text word <+> text "strictness for" <+> ppr id <+> info
info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = squashDmdEnv (idNewStrictness id) -- Don't report diffs in the env
- old = newStrictnessFromOld id
+ 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
where
message word = text word <+> text "demand for" <+> ppr id <+> info
info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
- new = lazify (idNewDemandInfo id) -- Lazify to avoid spurious improvements
+ 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