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
61 showPass dflags "Demand analysis" ;
62 let { binds_plus_dmds = do_prog binds ;
63 dmd_changes = get_changes binds_plus_dmds } ;
64 endPass dflags "Demand analysis"
65 Opt_D_dump_stranal binds_plus_dmds ;
67 -- Only if DEBUG is on, because only then is the old strictness analyser run
68 printDump (text "Changes in demands" $$ dmd_changes) ;
70 return binds_plus_dmds
73 do_prog :: [CoreBind] -> [CoreBind]
74 do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds
76 dmdAnalTopBind :: SigEnv
79 dmdAnalTopBind sigs (NonRec id rhs)
80 | isImplicitId id -- Don't touch the info on constructors, selectors etc
81 = (sigs, NonRec id rhs) -- It's pre-computed in MkId.lhs
84 (sigs', _, (id', rhs')) = downRhs TopLevel sigs (id, rhs)
86 (sigs', NonRec id' rhs')
88 dmdAnalTopBind sigs (Rec pairs)
90 (sigs', _, pairs') = dmdFix TopLevel sigs pairs
96 %************************************************************************
98 \subsection{The analyser itself}
100 %************************************************************************
103 dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
105 dmdAnal sigs Abs e = (topDmdType, e)
107 dmdAnal sigs Lazy e = let
108 (res_ty, e') = dmdAnal sigs Eval e
110 (deferType res_ty, e')
111 -- It's important not to analyse e with a lazy demand because
112 -- a) When we encounter case s of (a,b) ->
113 -- we demand s with U(d1d2)... but if the overall demand is lazy
114 -- that is wrong, and we'd need to reduce the demand on s,
115 -- which is inconvenient
116 -- b) More important, consider
117 -- f (let x = R in x+x), where f is lazy
118 -- We still want to mark x as demanded, because it will be when we
119 -- enter the let. If we analyse f's arg with a Lazy demand, we'll
120 -- just mark x as Lazy
123 dmdAnal sigs dmd (Lit lit)
124 = (topDmdType, Lit lit)
126 dmdAnal sigs dmd (Var var)
127 = (dmdTransform sigs var dmd, Var var)
129 dmdAnal sigs dmd (Note n e)
130 = (dmd_ty, Note n e')
132 (dmd_ty, e') = dmdAnal sigs dmd' e
134 Coerce _ _ -> Eval -- This coerce usually arises from a recursive
135 other -> dmd -- newtype, and we don't want to look inside them
136 -- for exactly the same reason that we don't look
137 -- inside recursive products -- we might not reach
138 -- a fixpoint. So revert to a vanilla Eval demand
140 dmdAnal sigs dmd (App fun (Type ty))
141 = (fun_ty, App fun' (Type ty))
143 (fun_ty, fun') = dmdAnal sigs dmd fun
145 dmdAnal sigs dmd (App fun arg) -- Non-type arguments
146 = let -- [Type arg handled above]
147 (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
148 (arg_ty, arg') = dmdAnal sigs arg_dmd arg
149 (arg_dmd, res_ty) = splitDmdTy fun_ty
151 (res_ty `bothType` arg_ty, App fun' arg')
153 dmdAnal sigs dmd (Lam var body)
156 (body_ty, body') = dmdAnal sigs dmd body
158 (body_ty, Lam var body')
160 | Call body_dmd <- dmd -- A call demand: good!
162 (body_ty, body') = dmdAnal sigs body_dmd body
163 (lam_ty, var') = annotateLamIdBndr body_ty var
165 (lam_ty, Lam var' body')
167 | otherwise -- Not enough demand on the lambda; but do the body
168 = let -- anyway to annotate it and gather free var info
169 (body_ty, body') = dmdAnal sigs Eval body
170 (lam_ty, var') = annotateLamIdBndr body_ty var
172 (deferType lam_ty, Lam var' body')
174 dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)])
175 | let tycon = dataConTyCon dc,
176 isProductTyCon tycon,
177 not (isRecursiveTyCon tycon)
179 bndr_ids = filter isId bndrs
180 (alt_ty, alt') = dmdAnalAlt sigs dmd alt
181 (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
182 (_, bndrs', _) = alt'
184 -- Figure out whether the case binder is used, and use
185 -- that to set the keepity of the demand. This is utterly essential.
186 -- Consider f x = case x of y { (a,b) -> k y a }
187 -- If we just take scrut_demand = U(L,A), then we won't pass x to the
188 -- worker, so the worker will rebuild
189 -- x = (a, absent-error)
190 -- and that'll crash.
191 dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
192 keepity | dead_case_bndr = Drop
195 scrut_dmd = Seq keepity Now [idNewDemandInfo b | b <- bndrs', isId b]
196 (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
198 (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt'])
200 dmdAnal sigs dmd (Case scrut case_bndr alts)
202 (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
203 (scrut_ty, scrut') = dmdAnal sigs Eval scrut
204 (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
206 -- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
207 (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts')
209 dmdAnal sigs dmd (Let (NonRec id rhs) body)
211 (sigs', lazy_fv, (id1, rhs')) = downRhs NotTopLevel sigs (id, rhs)
212 (body_ty, body') = dmdAnal sigs' dmd body
213 (body_ty1, id2) = annotateBndr body_ty id1
214 body_ty2 = addLazyFVs body_ty1 lazy_fv
216 -- pprTrace "dmdLet" (ppr id <+> ppr (sig,rhs_env))
217 (body_ty2, Let (NonRec id2 rhs') body')
219 dmdAnal sigs dmd (Let (Rec pairs) body)
221 bndrs = map fst pairs
222 (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
223 (body_ty, body') = dmdAnal sigs' dmd body
224 body_ty1 = addLazyFVs body_ty lazy_fv
226 sigs' `seq` body_ty `seq`
228 (body_ty2, _) = annotateBndrs body_ty1 bndrs
229 -- Don't bother to add demand info to recursive
230 -- binders as annotateBndr does;
231 -- being recursive, we can't treat them strictly.
232 -- But we do need to remove the binders from the result demand env
234 (body_ty2, Let (Rec pairs') body')
237 dmdAnalAlt sigs dmd (con,bndrs,rhs)
239 (rhs_ty, rhs') = dmdAnal sigs dmd rhs
240 (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
242 (alt_ty, (con, bndrs', rhs'))
245 %************************************************************************
247 \subsection{Bindings}
249 %************************************************************************
252 dmdFix :: TopLevelFlag
253 -> SigEnv -- Does not include bindings for this binding
256 [(Id,CoreExpr)]) -- Binders annotated with stricness info
258 dmdFix top_lvl sigs pairs
259 = loop 1 initial_sigs pairs
261 bndrs = map fst pairs
262 initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs]
265 -> SigEnv -- Already contains the current sigs
267 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
269 | all (same_sig sigs sigs') bndrs = (sigs', lazy_fv, pairs')
270 -- Note: use pairs', not pairs. pairs' is the result of
271 -- processing the RHSs with sigs (= sigs'), whereas pairs
272 -- is the result of processing the RHSs with the *previous*
273 -- iteration of sigs.
274 | n >= 5 = pprTrace "dmdFix" (ppr n <+> (vcat
275 [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
276 text "env:" <+> ppr (ufmToList sigs),
277 text "binds:" <+> ppr pairs]))
278 (loop (n+1) sigs' pairs')
279 | otherwise = {- pprTrace "dmdFixLoop" (ppr id_sigs) -} (loop (n+1) sigs' pairs')
281 -- Use the new signature to do the next pair
282 -- The occurrence analyser has arranged them in a good order
283 -- so this can significantly reduce the number of iterations needed
284 ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
286 my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
287 = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
289 -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
290 ((sigs', lazy_fv'), pair')
293 (sigs', lazy_fv1, pair') = downRhs top_lvl sigs (id,rhs)
294 lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
295 old_sig = lookup sigs id
296 new_sig = lookup sigs' id
298 -- Get an initial strictness signature from the Id
299 -- itself. That way we make use of earlier iterations
300 -- of the fixpoint algorithm. (Cunning plan.)
301 -- Note that the cunning plan extends to the DmdEnv too,
302 -- since it is part of the strictness signature
303 initial_sig id = idNewStrictness_maybe id `orElse` botSig
305 same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
306 lookup sigs var = case lookupVarEnv sigs var of
309 downRhs :: TopLevelFlag
310 -> SigEnv -> (Id, CoreExpr)
311 -> (SigEnv, DmdEnv, (Id, CoreExpr))
312 -- Process the RHS of the binding, add the strictness signature
313 -- to the Id, and augment the environment with the signature as well.
315 downRhs top_lvl sigs (id, rhs)
316 = (sigs', lazy_fv, (id', rhs'))
318 arity = exprArity rhs -- The idArity may not be up to date
319 (rhs_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
320 (lazy_fv, sig_ty) = mkSigTy id arity rhs rhs_ty
321 id' = id `setIdNewStrictness` sig_ty
322 sigs' = extendSigEnv top_lvl sigs id sig_ty
325 %************************************************************************
327 \subsection{Strictness signatures and types}
329 %************************************************************************
332 mkSigTy :: Id -> Arity -> CoreExpr -> DmdType -> (DmdEnv, StrictSig)
333 -- Take a DmdType and turn it into a StrictSig
334 mkSigTy id arity rhs (DmdType fv dmds res)
335 = (lazy_fv, mkStrictSig id arity dmd_ty)
337 dmd_ty = DmdType strict_fv lazified_dmds res'
339 lazy_fv = filterUFM (not . isStrictDmd) fv
340 strict_fv = filterUFM isStrictDmd fv
341 -- We put the strict FVs in the DmdType of the Id, so
342 -- that at its call sites we unleash demands on its strict fvs.
343 -- An example is 'roll' in imaginary/wheel-sieve2
344 -- Something like this:
346 -- go y = if ... then roll (x-1) else x+1
349 -- We want to see that roll is strict in x, which is because
350 -- go is called. So we put the DmdEnv for x in go's DmdType.
353 -- f :: Int -> Int -> Int
354 -- f x y = let t = x+1
355 -- h z = if z==0 then t else
356 -- if z==1 then x+1 else
360 -- Calling h does indeed evaluate x, but we can only see
361 -- that if we unleash a demand on x at the call site for t.
363 -- Incidentally, here's a place where lambda-lifting h would
364 -- lose the cigar --- we couldn't see the joint strictness in t/x
367 -- We don't want to put *all* the fv's from the RHS into the
368 -- DmdType, because that makes fixpointing very slow --- the
369 -- DmdType gets full of lazy demands that are slow to converge.
371 lazified_dmds = map lazify dmds
372 -- Get rid of defers in the arguments
373 final_dmds = setUnpackStrategy lazified_dmds
374 -- Set the unpacking strategy
376 res' = case (dmds, res) of
377 ([], RetCPR) | not (exprIsValue rhs) -> TopRes
379 -- If the rhs is a thunk, we forget the CPR info, because
380 -- it is presumably shared (else it would have been inlined, and
381 -- so we'd lose sharing if w/w'd it into a function.
383 -- DONE IN OLD CPR ANALYSER, BUT NOT YET HERE
384 -- Also, if the strictness analyser has figured out that it's strict,
385 -- the let-to-case transformation will happen, so again it's good.
386 -- (CPR analysis runs before the simplifier has had a chance to do
387 -- the let-to-case transform.)
388 -- This made a big difference to PrelBase.modInt, which had something like
389 -- modInt = \ x -> let r = ... -> I# v in
390 -- ...body strict in r...
391 -- r's RHS isn't a value yet; but modInt returns r in various branches, so
392 -- if r doesn't have the CPR property then neither does modInt
395 The unpack strategy determines whether we'll *really* unpack the argument,
396 or whether we'll just remember its strictness. If unpacking would give
397 rise to a *lot* of worker args, we may decide not to unpack after all.
400 setUnpackStrategy :: [Demand] -> [Demand]
402 = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
404 go :: Int -- Max number of args available for sub-components of [Demand]
406 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
408 go n (Seq keep _ cs : ds)
409 | n' >= 0 = Seq keep Now cs' `cons` go n'' ds
410 | otherwise = Eval `cons` go n ds
413 n' = n + box - non_abs_args
416 Drop -> 1 -- Add one to the budget if we drop the top-level arg
417 non_abs_args = nonAbsentArgs cs
418 -- Delete # of non-absent args to which we'll now be committed
420 go n (d:ds) = d `cons` go n ds
423 cons d (n,ds) = (n, d:ds)
425 nonAbsentArgs :: [Demand] -> Int
427 nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
428 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
432 %************************************************************************
434 \subsection{Strictness signatures and types}
436 %************************************************************************
439 splitDmdTy :: DmdType -> (Demand, DmdType)
440 -- Split off one function argument
441 splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
442 splitDmdTy ty@(DmdType fv [] TopRes) = (topDmd, ty)
443 splitDmdTy ty@(DmdType fv [] BotRes) = (Abs, ty)
444 -- We already have a suitable demand on all
445 -- free vars, so no need to add more!
446 splitDmdTy (DmdType fv [] RetCPR) = panic "splitDmdTy"
450 unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
452 addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
453 | isTopLevel top_lvl = dmd_ty -- Don't record top level things
454 | otherwise = DmdType (extendVarEnv fv var dmd) ds res
456 addLazyFVs (DmdType fv ds res) lazy_fvs
457 = DmdType (plusUFM_C both fv lazy_fvs) ds res
459 annotateBndr :: DmdType -> Var -> (DmdType, Var)
460 -- The returned env has the var deleted
461 -- The returned var is annotated with demand info
462 -- No effect on the argument demands
463 annotateBndr dmd_ty@(DmdType fv ds res) var
464 | isTyVar var = (dmd_ty, var)
465 | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd)
467 (fv', dmd) = removeFV fv var res
469 annotateBndrs = mapAccumR annotateBndr
471 annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
472 -- For lambdas we add the demand to the argument demands
473 -- Only called for Ids
475 (DmdType fv' (dmd:ds) res, setIdNewDemandInfo id dmd)
477 (fv', dmd) = removeFV fv id res
479 removeFV fv var res = (fv', dmd)
481 fv' = fv `delVarEnv` var
482 dmd = lookupVarEnv fv var `orElse` deflt
483 deflt | isBotRes res = Bot
487 %************************************************************************
489 \subsection{Strictness signatures}
491 %************************************************************************
494 type SigEnv = VarEnv (StrictSig, TopLevelFlag)
495 -- We use the SigEnv to tell us whether to
496 -- record info about a variable in the DmdEnv
497 -- We do so if it's a LocalId, but not top-level
499 -- The DmdEnv gives the demand on the free vars of the function
500 -- when it is given enough args to satisfy the strictness signature
502 emptySigEnv = emptyVarEnv
504 extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
505 extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
507 extendSigEnvList = extendVarEnvList
509 dmdTransform :: SigEnv -- The strictness environment
510 -> Id -- The function
511 -> Demand -- The demand on the function
512 -> DmdType -- The demand type of the function in this context
513 -- Returned DmdEnv includes the demand on
514 -- this function plus demand on its free variables
516 dmdTransform sigs var dmd
518 ------ DATA CONSTRUCTOR
519 | isDataConId var, -- Data constructor
520 Seq k Now ds <- res_dmd, -- and the demand looks inside its fields
521 let StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
522 = if dmdTypeDepth dmd_ty == length ds then -- Saturated, so unleash the demand
523 -- ds can be empty, when we are just seq'ing the thing
524 mkDmdType emptyDmdEnv ds (dmdTypeRes dmd_ty)
525 -- Need to extract whether it's a product, hence dmdTypeRes
529 ------ IMPORTED FUNCTION
530 | isGlobalId var, -- Imported function
531 let StrictSig dmd_ty = getNewStrictness var
532 = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
537 ------ LOCAL LET/REC BOUND THING
538 | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
540 fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
541 | otherwise = deferType dmd_ty
542 -- NB: it's important to use deferType, and not just return topDmdType
543 -- Consider let { f x y = p + x } in f 1
544 -- The application isn't saturated, but we must nevertheless propagate
545 -- a lazy demand for p!
547 addVarDmd top_lvl fn_ty var dmd
549 ------ LOCAL NON-LET/REC BOUND THING
550 | otherwise -- Default case
554 (call_depth, res_dmd) = splitCallDmd dmd
558 %************************************************************************
562 %************************************************************************
565 splitCallDmd :: Demand -> (Int, Demand)
566 splitCallDmd (Call d) = case splitCallDmd d of
568 splitCallDmd d = (0, d)
570 vanillaCall :: Arity -> Demand
572 vanillaCall n = Call (vanillaCall (n-1))
574 deferType :: DmdType -> DmdType
575 deferType (DmdType fv _ _) = DmdType (mapVarEnv defer fv) [] TopRes
576 -- Notice that we throw away info about both arguments and results
577 -- For example, f = let ... in \x -> x
578 -- We don't want to get a stricness type V->T for f.
580 defer :: Demand -> Demand
583 defer (Seq k _ ds) = Seq k Defer ds
586 lazify :: Demand -> Demand
587 -- The 'Defer' demands are just Lazy at function boundaries
588 lazify (Seq k Defer ds) = Lazy
589 lazify (Seq k Now ds) = Seq k Now (map lazify ds)
590 lazify Bot = Abs -- Don't pass args that are consumed by bottom
595 betterStrictness :: StrictSig -> StrictSig -> Bool
596 betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
598 betterDmdType t1 t2 = (t1 `lubType` t2) == t2
600 betterDemand :: Demand -> Demand -> Bool
601 -- If d1 `better` d2, and d2 `better` d2, then d1==d2
602 betterDemand d1 d2 = (d1 `lub` d2) == d2
604 squashDmdEnv (StrictSig (DmdType fv ds res)) = StrictSig (DmdType emptyDmdEnv ds res)
608 %************************************************************************
610 \subsection{LUB and BOTH}
612 %************************************************************************
615 lub :: Demand -> Demand -> Demand
627 lub Abs (Seq k _ ds) = Seq k Defer ds -- Very important ('radicals' example)
632 lub Eval (Seq k Now ds) = Seq Keep Now ds
633 lub Eval (Seq k Defer ds) = Lazy
636 lub (Call d1) (Call d2) = Call (lub d1 d2)
638 lub (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) (l1 `or_defer` l2) (lubs ds1 ds2)
640 -- The last clauses deal with the remaining cases for Call and Seq
641 lub d1@(Call _) d2@(Seq _ _ _) = pprPanic "lub" (ppr d1 $$ ppr d2)
642 lub d1 d2 = lub d2 d1
644 -- A Seq can have an empty list of demands, in the polymorphic case.
647 lubs ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith lub ds1 ds2
649 or_defer Now Now = Now
652 -------------------------
653 -- Consider (if x then y else []) with demand V
654 -- Then the first branch gives {y->V} and the second
655 -- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
656 -- in the result env.
657 lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
658 = DmdType lub_fv2 (zipWith lub ds1 ds2) (r1 `lubRes` r2)
660 lub_fv = plusUFM_C lub fv1 fv2
661 lub_fv1 = modifyEnv (not (isBotRes r1)) (Abs `lub`) fv2 fv1 lub_fv
662 lub_fv2 = modifyEnv (not (isBotRes r2)) (Abs `lub`) fv1 fv2 lub_fv1
663 -- lub is the identity for Bot
665 -------------------------
668 lubRes RetCPR RetCPR = RetCPR
669 lubRes r1 r2 = TopRes
671 -----------------------------------
672 vee :: Keepity -> Keepity -> Keepity
676 -----------------------------------
677 both :: Demand -> Demand -> Demand
682 -- The experimental one
683 -- The idea is that (error x) places on x
684 -- both demand Bot (like on all free vars)
685 -- and demand Eval (for the arg to error)
686 -- and we want the result to be Eval.
700 both Lazy (Seq k l ds) = Seq Keep l ds
702 -- Notice that the Seq case ensures that we have the
703 -- boxed value. The equation originally said
704 -- both (Seq k Now ds) = Seq Keep Now ds
705 -- but it's important that the Keep is switched on even
706 -- for a deferred demand. Otherwise a (Seq Drop Now [])
707 -- might both'd with the result, and then we won't pass
708 -- the boxed value. Here's an example:
709 -- (x-1) `seq` (x+1, x)
710 -- From the (x+1, x) we get (U*(V) `both` L), which must give S*(V)
711 -- From (x-1) we get U(V). Combining, we must get S(V).
712 -- If we got U*(V) from the pair, we'd end up with U(V), and that
713 -- can be a disaster if a component of the data structure is absent.
714 -- [Disaster = enter an absent argument.]
716 both Eval (Seq k l ds) = Seq Keep Now ds
717 both Eval (Call d) = Call d
720 both (Seq k1 Defer ds1) (Seq k2 Defer ds2) = Seq (k1 `vee` k2) Defer (boths ds1 ds2)
721 both (Seq k1 l1 ds1) (Seq k2 l2 ds2) = Seq (k1 `vee` k2) Now (boths ds1' ds2')
723 ds1' = case l1 of { Now -> ds1; Defer -> map defer ds1 }
724 ds2' = case l2 of { Now -> ds2; Defer -> map defer ds2 }
726 both (Call d1) (Call d2) = Call (d1 `both` d2)
728 -- The last clauses deal with the remaining cases for Call and Seq
729 both d1@(Call _) d2@(Seq _ _ _) = pprPanic "both" (ppr d1 $$ ppr d2)
730 both d1 d2 = both d2 d1
732 -----------------------------------
733 -- A Seq can have an empty list of demands, in the polymorphic case.
736 boths ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith both ds1 ds2
738 -----------------------------------
739 bothRes :: DmdResult -> DmdResult -> DmdResult
740 -- Left-biased for CPR info
741 bothRes BotRes _ = BotRes
742 bothRes _ BotRes = BotRes
745 -----------------------------------
746 -- (t1 `bothType` t2) takes the argument/result info from t1,
747 -- using t2 just for its free-var info
748 bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
749 = DmdType both_fv2 ds1 r1
751 both_fv = plusUFM_C both fv1 fv2
752 both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
753 both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
754 -- both is the identity for Abs
758 modifyEnv :: Bool -- No-op if False
759 -> (Demand -> Demand) -- The zapper
760 -> DmdEnv -> DmdEnv -- Env1 and Env2
761 -> DmdEnv -> DmdEnv -- Transform this env
762 -- Zap anything in Env1 but not in Env2
763 -- Assume: dom(env) includes dom(Env1) and dom(Env2)
765 modifyEnv need_to_modify zapper env1 env2 env
766 | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
769 zap uniq env = addToUFM_Directly env uniq (zapper current_val)
771 current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq)
775 %************************************************************************
777 \subsection{Miscellaneous
779 %************************************************************************
783 get_changes binds = vcat (map get_changes_bind binds)
785 get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
786 get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
788 get_changes_pr (id,rhs)
789 | isImplicitId id = empty -- We don't look inside these
790 | otherwise = get_changes_var id $$ get_changes_expr rhs
793 | isId var = get_changes_str var $$ get_changes_dmd var
796 get_changes_expr (Type t) = empty
797 get_changes_expr (Var v) = empty
798 get_changes_expr (Lit l) = empty
799 get_changes_expr (Note n e) = get_changes_expr e
800 get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
801 get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
802 get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
803 get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
805 get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
808 | new_better && old_better = empty
809 | new_better = message "BETTER"
810 | old_better = message "WORSE"
811 | otherwise = message "INCOMPARABLE"
813 message word = text word <+> text "strictness for" <+> ppr id <+> info
814 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
815 new = squashDmdEnv (idNewStrictness id) -- Don't report diffs in the env
816 old = newStrictnessFromOld id
817 old_better = old `betterStrictness` new
818 new_better = new `betterStrictness` old
821 | isUnLiftedType (idType id) = empty -- Not useful
822 | new_better && old_better = empty
823 | new_better = message "BETTER"
824 | old_better = message "WORSE"
825 | otherwise = message "INCOMPARABLE"
827 message word = text word <+> text "demand for" <+> ppr id <+> info
828 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
829 new = lazify (idNewDemandInfo id) -- Lazify to avoid spurious improvements
830 old = newDemand (idDemandInfo id)
831 new_better = new `betterDemand` old
832 old_better = old `betterDemand` new