2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
10 module DmdAnal ( dmdAnalPgm ) where
12 #include "HsVersions.h"
14 import CmdLineOpts ( DynFlags, DynFlag(..), opt_MaxWorkerArgs )
15 import NewDemand -- All of it
17 import CoreUtils ( exprIsValue, exprArity )
18 import DataCon ( dataConTyCon )
19 import TyCon ( isProductTyCon, isRecursiveTyCon )
20 import Id ( Id, idType, idInfo, idArity, idCprInfo, idDemandInfo,
21 modifyIdInfo, isDataConId, isImplicitId, isGlobalId,
22 idNewStrictness, idNewStrictness_maybe, getNewStrictness, setIdNewStrictness,
23 idNewDemandInfo, setIdNewDemandInfo, newStrictnessFromOld )
24 import IdInfo ( newDemand )
27 import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
28 keysUFM, minusUFM, ufmToList, filterUFM )
29 import Type ( isUnLiftedType )
30 import CoreLint ( showPass, endPass )
31 import ErrUtils ( dumpIfSet_dyn )
32 import Util ( mapAndUnzip, mapAccumL, mapAccumR, zipWithEqual )
33 import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel )
34 import Maybes ( orElse, expectJust )
41 * set a noinline pragma on bottoming Ids
43 * Consider f x = x+1 `fatbar` error (show x)
44 We'd like to unbox x, even if that means reboxing it in the error case.
47 instance Outputable TopLevelFlag where
51 %************************************************************************
53 \subsection{Top level stuff}
55 %************************************************************************
58 dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
59 dmdAnalPgm dflags binds
60 = panic "dmdAnalPgm called"
61 dmdAnalPgm dflags binds
63 showPass dflags "Demand analysis" ;
64 let { binds_plus_dmds = do_prog binds ;
65 dmd_changes = get_changes binds_plus_dmds } ;
66 endPass dflags "Demand analysis"
67 Opt_D_dump_stranal binds_plus_dmds ;
69 -- Only if DEBUG is on, because only then is the old strictness analyser run
70 printDump (text "Changes in demands" $$ dmd_changes) ;
72 return binds_plus_dmds
75 do_prog :: [CoreBind] -> [CoreBind]
76 do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds
78 dmdAnalTopBind :: SigEnv
81 dmdAnalTopBind sigs (NonRec id rhs)
82 | isImplicitId id -- Don't touch the info on constructors, selectors etc
83 = (sigs, NonRec id rhs) -- It's pre-computed in MkId.lhs
86 (sigs', _, (id', rhs')) = downRhs TopLevel sigs (id, rhs)
88 (sigs', NonRec id' rhs')
90 dmdAnalTopBind sigs (Rec pairs)
92 (sigs', _, pairs') = dmdFix TopLevel sigs pairs
98 %************************************************************************
100 \subsection{The analyser itself}
102 %************************************************************************
105 dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
107 dmdAnal sigs Abs e = (topDmdType, e)
109 dmdAnal sigs Lazy e = let
110 (res_ty, e') = dmdAnal sigs Eval e
112 (deferType res_ty, e')
113 -- It's important not to analyse e with a lazy demand because
114 -- a) When we encounter case s of (a,b) ->
115 -- we demand s with U(d1d2)... but if the overall demand is lazy
116 -- that is wrong, and we'd need to reduce the demand on s,
117 -- which is inconvenient
118 -- b) More important, consider
119 -- f (let x = R in x+x), where f is lazy
120 -- We still want to mark x as demanded, because it will be when we
121 -- enter the let. If we analyse f's arg with a Lazy demand, we'll
122 -- just mark x as Lazy
125 dmdAnal sigs dmd (Lit lit)
126 = (topDmdType, Lit lit)
128 dmdAnal sigs dmd (Var var)
129 = (dmdTransform sigs var dmd, Var var)
131 dmdAnal sigs dmd (Note n e)
132 = (dmd_ty, Note n e')
134 (dmd_ty, e') = dmdAnal sigs dmd' e
136 Coerce _ _ -> Eval -- This coerce usually arises from a recursive
137 other -> dmd -- newtype, and we don't want to look inside them
138 -- for exactly the same reason that we don't look
139 -- inside recursive products -- we might not reach
140 -- a fixpoint. So revert to a vanilla Eval demand
142 dmdAnal sigs dmd (App fun (Type ty))
143 = (fun_ty, App fun' (Type ty))
145 (fun_ty, fun') = dmdAnal sigs dmd fun
147 dmdAnal sigs dmd (App fun arg) -- Non-type arguments
148 = let -- [Type arg handled above]
149 (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
150 (arg_ty, arg') = dmdAnal sigs arg_dmd arg
151 (arg_dmd, res_ty) = splitDmdTy fun_ty
153 (res_ty `bothType` arg_ty, App fun' arg')
155 dmdAnal sigs dmd (Lam var body)
158 (body_ty, body') = dmdAnal sigs dmd body
160 (body_ty, Lam var body')
162 | Call body_dmd <- dmd -- A call demand: good!
164 (body_ty, body') = dmdAnal sigs body_dmd body
165 (lam_ty, var') = annotateLamIdBndr body_ty var
167 (lam_ty, Lam var' body')
169 | otherwise -- Not enough demand on the lambda; but do the body
170 = let -- anyway to annotate it and gather free var info
171 (body_ty, body') = dmdAnal sigs Eval body
172 (lam_ty, var') = annotateLamIdBndr body_ty var
174 (deferType lam_ty, Lam var' body')
176 dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)])
177 | let tycon = dataConTyCon dc,
178 isProductTyCon tycon,
179 not (isRecursiveTyCon tycon)
181 bndr_ids = filter isId bndrs
182 (alt_ty, alt') = dmdAnalAlt sigs dmd alt
183 (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
184 (_, bndrs', _) = alt'
186 -- Figure out whether the case binder is used, and use
187 -- that to set the keepity of the demand. This is utterly essential.
188 -- Consider f x = case x of y { (a,b) -> k y a }
189 -- If we just take scrut_demand = U(L,A), then we won't pass x to the
190 -- worker, so the worker will rebuild
191 -- x = (a, absent-error)
192 -- and that'll crash.
193 dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
194 keepity | dead_case_bndr = Drop
197 scrut_dmd = Seq keepity Now [idNewDemandInfo b | b <- bndrs', isId b]
198 (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
200 (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt'])
202 dmdAnal sigs dmd (Case scrut case_bndr alts)
204 (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
205 (scrut_ty, scrut') = dmdAnal sigs Eval scrut
206 (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
208 -- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
209 (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts')
211 dmdAnal sigs dmd (Let (NonRec id rhs) body)
213 (sigs', lazy_fv, (id1, rhs')) = downRhs NotTopLevel sigs (id, rhs)
214 (body_ty, body') = dmdAnal sigs' dmd body
215 (body_ty1, id2) = annotateBndr body_ty id1
216 body_ty2 = addLazyFVs body_ty1 lazy_fv
218 -- pprTrace "dmdLet" (ppr id <+> ppr (sig,rhs_env))
219 (body_ty2, Let (NonRec id2 rhs') body')
221 dmdAnal sigs dmd (Let (Rec pairs) body)
223 bndrs = map fst pairs
224 (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
225 (body_ty, body') = dmdAnal sigs' dmd body
226 body_ty1 = addLazyFVs body_ty lazy_fv
228 sigs' `seq` body_ty `seq`
230 (body_ty2, _) = annotateBndrs body_ty1 bndrs
231 -- Don't bother to add demand info to recursive
232 -- binders as annotateBndr does;
233 -- being recursive, we can't treat them strictly.
234 -- But we do need to remove the binders from the result demand env
236 (body_ty2, Let (Rec pairs') body')
239 dmdAnalAlt sigs dmd (con,bndrs,rhs)
241 (rhs_ty, rhs') = dmdAnal sigs dmd rhs
242 (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
244 (alt_ty, (con, bndrs', rhs'))
247 %************************************************************************
249 \subsection{Bindings}
251 %************************************************************************
254 dmdFix :: TopLevelFlag
255 -> SigEnv -- Does not include bindings for this binding
258 [(Id,CoreExpr)]) -- Binders annotated with stricness info
260 dmdFix top_lvl sigs pairs
261 = loop 1 initial_sigs pairs
263 bndrs = map fst pairs
264 initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs]
267 -> SigEnv -- Already contains the current sigs
269 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
271 | all (same_sig sigs sigs') bndrs = (sigs', lazy_fv, pairs')
272 -- Note: use pairs', not pairs. pairs' is the result of
273 -- processing the RHSs with sigs (= sigs'), whereas pairs
274 -- is the result of processing the RHSs with the *previous*
275 -- iteration of sigs.
276 | n >= 5 = pprTrace "dmdFix" (ppr n <+> (vcat
277 [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
278 text "env:" <+> ppr (ufmToList sigs),
279 text "binds:" <+> ppr pairs]))
280 (loop (n+1) sigs' pairs')
281 | otherwise = {- pprTrace "dmdFixLoop" (ppr id_sigs) -} (loop (n+1) sigs' pairs')
283 -- Use the new signature to do the next pair
284 -- The occurrence analyser has arranged them in a good order
285 -- so this can significantly reduce the number of iterations needed
286 ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
288 my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
289 = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
291 -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
292 ((sigs', lazy_fv'), pair')
295 (sigs', lazy_fv1, pair') = downRhs top_lvl sigs (id,rhs)
296 lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
297 old_sig = lookup sigs id
298 new_sig = lookup sigs' id
300 -- Get an initial strictness signature from the Id
301 -- itself. That way we make use of earlier iterations
302 -- of the fixpoint algorithm. (Cunning plan.)
303 -- Note that the cunning plan extends to the DmdEnv too,
304 -- since it is part of the strictness signature
305 initial_sig id = idNewStrictness_maybe id `orElse` botSig
307 same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
308 lookup sigs var = case lookupVarEnv sigs var of
311 downRhs :: TopLevelFlag
312 -> SigEnv -> (Id, CoreExpr)
313 -> (SigEnv, DmdEnv, (Id, CoreExpr))
314 -- Process the RHS of the binding, add the strictness signature
315 -- to the Id, and augment the environment with the signature as well.
317 downRhs top_lvl sigs (id, rhs)
318 = (sigs', lazy_fv, (id', rhs'))
320 arity = exprArity rhs -- The idArity may not be up to date
321 (rhs_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
322 (lazy_fv, sig_ty) = mkSigTy id arity rhs rhs_ty
323 id' = id `setIdNewStrictness` sig_ty
324 sigs' = extendSigEnv top_lvl sigs id sig_ty
327 %************************************************************************
329 \subsection{Strictness signatures and types}
331 %************************************************************************
334 mkSigTy :: Id -> Arity -> CoreExpr -> DmdType -> (DmdEnv, StrictSig)
335 -- Take a DmdType and turn it into a StrictSig
336 mkSigTy id arity rhs (DmdType fv dmds res)
337 = (lazy_fv, mkStrictSig id arity dmd_ty)
339 dmd_ty = DmdType strict_fv lazified_dmds res'
341 lazy_fv = filterUFM (not . isStrictDmd) fv
342 strict_fv = filterUFM isStrictDmd fv
343 -- We put the strict FVs in the DmdType of the Id, so
344 -- that at its call sites we unleash demands on its strict fvs.
345 -- An example is 'roll' in imaginary/wheel-sieve2
346 -- Something like this:
348 -- go y = if ... then roll (x-1) else x+1
351 -- We want to see that roll is strict in x, which is because
352 -- go is called. So we put the DmdEnv for x in go's DmdType.
355 -- f :: Int -> Int -> Int
356 -- f x y = let t = x+1
357 -- h z = if z==0 then t else
358 -- if z==1 then x+1 else
362 -- Calling h does indeed evaluate x, but we can only see
363 -- that if we unleash a demand on x at the call site for t.
365 -- Incidentally, here's a place where lambda-lifting h would
366 -- lose the cigar --- we couldn't see the joint strictness in t/x
369 -- We don't want to put *all* the fv's from the RHS into the
370 -- DmdType, because that makes fixpointing very slow --- the
371 -- DmdType gets full of lazy demands that are slow to converge.
373 lazified_dmds = map lazify dmds
374 -- Get rid of defers in the arguments
375 final_dmds = setUnpackStrategy lazified_dmds
376 -- Set the unpacking strategy
378 res' = case (dmds, res) of
379 ([], RetCPR) | not (exprIsValue rhs) -> TopRes
381 -- If the rhs is a thunk, we forget the CPR info, because
382 -- it is presumably shared (else it would have been inlined, and
383 -- so we'd lose sharing if w/w'd it into a function.
385 -- DONE IN OLD CPR ANALYSER, BUT NOT YET HERE
386 -- Also, if the strictness analyser has figured out that it's strict,
387 -- the let-to-case transformation will happen, so again it's good.
388 -- (CPR analysis runs before the simplifier has had a chance to do
389 -- the let-to-case transform.)
390 -- This made a big difference to PrelBase.modInt, which had something like
391 -- modInt = \ x -> let r = ... -> I# v in
392 -- ...body strict in r...
393 -- r's RHS isn't a value yet; but modInt returns r in various branches, so
394 -- if r doesn't have the CPR property then neither does modInt
397 The unpack strategy determines whether we'll *really* unpack the argument,
398 or whether we'll just remember its strictness. If unpacking would give
399 rise to a *lot* of worker args, we may decide not to unpack after all.
402 setUnpackStrategy :: [Demand] -> [Demand]
404 = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
406 go :: Int -- Max number of args available for sub-components of [Demand]
408 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
410 go n (Seq keep _ cs : ds)
411 | n' >= 0 = Seq keep Now cs' `cons` go n'' ds
412 | otherwise = Eval `cons` go n ds
415 n' = n + box - non_abs_args
418 Drop -> 1 -- Add one to the budget if we drop the top-level arg
419 non_abs_args = nonAbsentArgs cs
420 -- Delete # of non-absent args to which we'll now be committed
422 go n (d:ds) = d `cons` go n ds
425 cons d (n,ds) = (n, d:ds)
427 nonAbsentArgs :: [Demand] -> Int
429 nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
430 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
434 %************************************************************************
436 \subsection{Strictness signatures and types}
438 %************************************************************************
441 splitDmdTy :: DmdType -> (Demand, DmdType)
442 -- Split off one function argument
443 splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
444 splitDmdTy ty@(DmdType fv [] TopRes) = (topDmd, ty)
445 splitDmdTy ty@(DmdType fv [] BotRes) = (Abs, ty)
446 -- We already have a suitable demand on all
447 -- free vars, so no need to add more!
448 splitDmdTy (DmdType fv [] RetCPR) = panic "splitDmdTy"
452 unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
454 addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
455 | isTopLevel top_lvl = dmd_ty -- Don't record top level things
456 | otherwise = DmdType (extendVarEnv fv var dmd) ds res
458 addLazyFVs (DmdType fv ds res) lazy_fvs
459 = DmdType (plusUFM_C both fv lazy_fvs) ds res
461 annotateBndr :: DmdType -> Var -> (DmdType, Var)
462 -- The returned env has the var deleted
463 -- The returned var is annotated with demand info
464 -- No effect on the argument demands
465 annotateBndr dmd_ty@(DmdType fv ds res) var
466 | isTyVar var = (dmd_ty, var)
467 | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd)
469 (fv', dmd) = removeFV fv var res
471 annotateBndrs = mapAccumR annotateBndr
473 annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
474 -- For lambdas we add the demand to the argument demands
475 -- Only called for Ids
477 (DmdType fv' (dmd:ds) res, setIdNewDemandInfo id dmd)
479 (fv', dmd) = removeFV fv id res
481 removeFV fv var res = (fv', dmd)
483 fv' = fv `delVarEnv` var
484 dmd = lookupVarEnv fv var `orElse` deflt
485 deflt | isBotRes res = Bot
489 %************************************************************************
491 \subsection{Strictness signatures}
493 %************************************************************************
496 type SigEnv = VarEnv (StrictSig, TopLevelFlag)
497 -- We use the SigEnv to tell us whether to
498 -- record info about a variable in the DmdEnv
499 -- We do so if it's a LocalId, but not top-level
501 -- The DmdEnv gives the demand on the free vars of the function
502 -- when it is given enough args to satisfy the strictness signature
504 emptySigEnv = emptyVarEnv
506 extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
507 extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
509 extendSigEnvList = extendVarEnvList
511 dmdTransform :: SigEnv -- The strictness environment
512 -> Id -- The function
513 -> Demand -- The demand on the function
514 -> DmdType -- The demand type of the function in this context
515 -- Returned DmdEnv includes the demand on
516 -- this function plus demand on its free variables
518 dmdTransform sigs var dmd
520 ------ DATA CONSTRUCTOR
521 | isDataConId var, -- Data constructor
522 Seq k Now ds <- res_dmd, -- and the demand looks inside its fields
523 let StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
524 = if dmdTypeDepth dmd_ty == length ds then -- Saturated, so unleash the demand
525 -- ds can be empty, when we are just seq'ing the thing
526 mkDmdType emptyDmdEnv ds (dmdTypeRes dmd_ty)
527 -- Need to extract whether it's a product, hence dmdTypeRes
531 ------ IMPORTED FUNCTION
532 | isGlobalId var, -- Imported function
533 let StrictSig dmd_ty = getNewStrictness var
534 = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
539 ------ LOCAL LET/REC BOUND THING
540 | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
542 fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
543 | otherwise = deferType dmd_ty
544 -- NB: it's important to use deferType, and not just return topDmdType
545 -- Consider let { f x y = p + x } in f 1
546 -- The application isn't saturated, but we must nevertheless propagate
547 -- a lazy demand for p!
549 addVarDmd top_lvl fn_ty var dmd
551 ------ LOCAL NON-LET/REC BOUND THING
552 | otherwise -- Default case
556 (call_depth, res_dmd) = splitCallDmd dmd
560 %************************************************************************
564 %************************************************************************
567 splitCallDmd :: Demand -> (Int, Demand)
568 splitCallDmd (Call d) = case splitCallDmd d of
570 splitCallDmd d = (0, d)
572 vanillaCall :: Arity -> Demand
574 vanillaCall n = Call (vanillaCall (n-1))
576 deferType :: DmdType -> DmdType
577 deferType (DmdType fv _ _) = DmdType (mapVarEnv defer fv) [] TopRes
578 -- Notice that we throw away info about both arguments and results
579 -- For example, f = let ... in \x -> x
580 -- We don't want to get a stricness type V->T for f.
582 defer :: Demand -> Demand
585 defer (Seq k _ ds) = Seq k Defer ds
588 lazify :: Demand -> Demand
589 -- The 'Defer' demands are just Lazy at function boundaries
590 lazify (Seq k Defer ds) = Lazy
591 lazify (Seq k Now ds) = Seq k Now (map lazify ds)
592 lazify Bot = Abs -- Don't pass args that are consumed by bottom
597 betterStrictness :: StrictSig -> StrictSig -> Bool
598 betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
600 betterDmdType t1 t2 = (t1 `lubType` t2) == t2
602 betterDemand :: Demand -> Demand -> Bool
603 -- If d1 `better` d2, and d2 `better` d2, then d1==d2
604 betterDemand d1 d2 = (d1 `lub` d2) == d2
606 squashDmdEnv (StrictSig (DmdType fv ds res)) = StrictSig (DmdType emptyDmdEnv ds res)
610 %************************************************************************
612 \subsection{LUB and BOTH}
614 %************************************************************************
617 lub :: Demand -> Demand -> Demand
629 lub Abs (Seq k _ ds) = Seq k Defer ds -- Very important ('radicals' example)
634 lub Eval (Seq k Now ds) = Seq Keep Now ds
635 lub Eval (Seq k Defer ds) = Lazy
638 lub (Call d1) (Call d2) = Call (lub d1 d2)
640 lub (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) (l1 `or_defer` l2) (lubs ds1 ds2)
642 -- The last clauses deal with the remaining cases for Call and Seq
643 lub d1@(Call _) d2@(Seq _ _ _) = pprPanic "lub" (ppr d1 $$ ppr d2)
644 lub d1 d2 = lub d2 d1
646 -- A Seq can have an empty list of demands, in the polymorphic case.
649 lubs ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith lub ds1 ds2
651 or_defer Now Now = Now
654 -------------------------
655 -- Consider (if x then y else []) with demand V
656 -- Then the first branch gives {y->V} and the second
657 -- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
658 -- in the result env.
659 lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
660 = DmdType lub_fv2 (zipWith lub ds1 ds2) (r1 `lubRes` r2)
662 lub_fv = plusUFM_C lub fv1 fv2
663 lub_fv1 = modifyEnv (not (isBotRes r1)) (Abs `lub`) fv2 fv1 lub_fv
664 lub_fv2 = modifyEnv (not (isBotRes r2)) (Abs `lub`) fv1 fv2 lub_fv1
665 -- lub is the identity for Bot
667 -------------------------
670 lubRes RetCPR RetCPR = RetCPR
671 lubRes r1 r2 = TopRes
673 -----------------------------------
674 vee :: Keepity -> Keepity -> Keepity
678 -----------------------------------
679 both :: Demand -> Demand -> Demand
684 -- The experimental one
685 -- The idea is that (error x) places on x
686 -- both demand Bot (like on all free vars)
687 -- and demand Eval (for the arg to error)
688 -- and we want the result to be Eval.
702 both Lazy (Seq k l ds) = Seq Keep l ds
704 -- Notice that the Seq case ensures that we have the
705 -- boxed value. The equation originally said
706 -- both (Seq k Now ds) = Seq Keep Now ds
707 -- but it's important that the Keep is switched on even
708 -- for a deferred demand. Otherwise a (Seq Drop Now [])
709 -- might both'd with the result, and then we won't pass
710 -- the boxed value. Here's an example:
711 -- (x-1) `seq` (x+1, x)
712 -- From the (x+1, x) we get (U*(V) `both` L), which must give S*(V)
713 -- From (x-1) we get U(V). Combining, we must get S(V).
714 -- If we got U*(V) from the pair, we'd end up with U(V), and that
715 -- can be a disaster if a component of the data structure is absent.
716 -- [Disaster = enter an absent argument.]
718 both Eval (Seq k l ds) = Seq Keep Now ds
719 both Eval (Call d) = Call d
722 both (Seq k1 Defer ds1) (Seq k2 Defer ds2) = Seq (k1 `vee` k2) Defer (boths ds1 ds2)
723 both (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) Now (boths ds1' ds2')
725 ds1' = case l1 of { Now -> ds1; Defer -> map defer ds1 }
726 ds2' = case l2 of { Now -> ds2; Defer -> map defer ds2 }
728 both (Call d1) (Call d2) = Call (d1 `both` d2)
730 -- The last clauses deal with the remaining cases for Call and Seq
731 both d1@(Call _) d2@(Seq _ _ _) = pprPanic "both" (ppr d1 $$ ppr d2)
732 both d1 d2 = both d2 d1
734 -----------------------------------
735 -- A Seq can have an empty list of demands, in the polymorphic case.
738 boths ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith both ds1 ds2
740 -----------------------------------
741 bothRes :: DmdResult -> DmdResult -> DmdResult
742 -- Left-biased for CPR info
743 bothRes BotRes _ = BotRes
744 bothRes _ BotRes = BotRes
747 -----------------------------------
748 -- (t1 `bothType` t2) takes the argument/result info from t1,
749 -- using t2 just for its free-var info
750 bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
751 = DmdType both_fv2 ds1 r1
753 both_fv = plusUFM_C both fv1 fv2
754 both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
755 both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
756 -- both is the identity for Abs
760 modifyEnv :: Bool -- No-op if False
761 -> (Demand -> Demand) -- The zapper
762 -> DmdEnv -> DmdEnv -- Env1 and Env2
763 -> DmdEnv -> DmdEnv -- Transform this env
764 -- Zap anything in Env1 but not in Env2
765 -- Assume: dom(env) includes dom(Env1) and dom(Env2)
767 modifyEnv need_to_modify zapper env1 env2 env
768 | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
771 zap uniq env = addToUFM_Directly env uniq (zapper current_val)
773 current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq)
777 %************************************************************************
779 \subsection{Miscellaneous
781 %************************************************************************
785 get_changes binds = vcat (map get_changes_bind binds)
787 get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
788 get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
790 get_changes_pr (id,rhs)
791 | isImplicitId id = empty -- We don't look inside these
792 | otherwise = get_changes_var id $$ get_changes_expr rhs
795 | isId var = get_changes_str var $$ get_changes_dmd var
798 get_changes_expr (Type t) = empty
799 get_changes_expr (Var v) = empty
800 get_changes_expr (Lit l) = empty
801 get_changes_expr (Note n e) = get_changes_expr e
802 get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
803 get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
804 get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
805 get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
807 get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
810 | new_better && old_better = empty
811 | new_better = message "BETTER"
812 | old_better = message "WORSE"
813 | otherwise = message "INCOMPARABLE"
815 message word = text word <+> text "strictness for" <+> ppr id <+> info
816 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
817 new = squashDmdEnv (idNewStrictness id) -- Don't report diffs in the env
818 old = newStrictnessFromOld id
819 old_better = old `betterStrictness` new
820 new_better = new `betterStrictness` old
823 | isUnLiftedType (idType id) = empty -- Not useful
824 | new_better && old_better = empty
825 | new_better = message "BETTER"
826 | old_better = message "WORSE"
827 | otherwise = message "INCOMPARABLE"
829 message word = text word <+> text "demand for" <+> ppr id <+> info
830 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
831 new = lazify (idNewDemandInfo id) -- Lazify to avoid spurious improvements
832 old = newDemand (idDemandInfo id)
833 new_better = new `betterDemand` old
834 old_better = old `betterDemand` new