2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
10 module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs,
11 both {- needed by WwLib -}
14 #include "HsVersions.h"
16 import CmdLineOpts ( DynFlags, DynFlag(..), opt_MaxWorkerArgs )
17 import NewDemand -- All of it
20 import CoreUtils ( exprIsValue, exprArity )
21 import DataCon ( dataConTyCon )
22 import TyCon ( isProductTyCon, isRecursiveTyCon )
23 import Id ( Id, idType, idDemandInfo,
24 isDataConId, isGlobalId, idArity,
25 idNewStrictness, idNewStrictness_maybe, getNewStrictness, setIdNewStrictness,
26 idNewDemandInfo, setIdNewDemandInfo, newStrictnessFromOld )
27 import IdInfo ( newDemand )
30 import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
31 keysUFM, minusUFM, ufmToList, filterUFM )
32 import Type ( isUnLiftedType )
33 import CoreLint ( showPass, endPass )
34 import Util ( mapAndUnzip, mapAccumL, mapAccumR )
35 import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel )
36 import Maybes ( orElse, expectJust )
42 * set a noinline pragma on bottoming Ids
44 * Consider f x = x+1 `fatbar` error (show x)
45 We'd like to unbox x, even if that means reboxing it in the error case.
48 instance Outputable TopLevelFlag where
52 %************************************************************************
54 \subsection{Top level stuff}
56 %************************************************************************
59 dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
60 dmdAnalPgm dflags binds
62 showPass dflags "Demand analysis" ;
63 let { binds_plus_dmds = do_prog binds ;
64 dmd_changes = get_changes binds_plus_dmds } ;
65 endPass dflags "Demand analysis"
66 Opt_D_dump_stranal binds_plus_dmds ;
68 -- Only if DEBUG is on, because only then is the old strictness analyser run
69 printDump (text "Changes in demands" $$ dmd_changes) ;
71 return binds_plus_dmds
74 do_prog :: [CoreBind] -> [CoreBind]
75 do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds
77 dmdAnalTopBind :: SigEnv
80 dmdAnalTopBind sigs (NonRec id rhs)
82 (sigs', _, (id', rhs')) = dmdAnalRhs TopLevel sigs (id, rhs)
84 (sigs', NonRec id' rhs')
86 dmdAnalTopBind sigs (Rec pairs)
88 (sigs', _, pairs') = dmdFix TopLevel sigs pairs
94 dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr)
95 -- Analyse the RHS and return
96 -- a) appropriate strictness info
97 -- b) the unfolding (decorated with stricntess info)
101 arity = exprArity rhs
102 (rhs_ty, rhs') = dmdAnal emptySigEnv (vanillaCall arity) rhs
103 (_, sig) = mkSigTy rhs rhs_ty
106 %************************************************************************
108 \subsection{The analyser itself}
110 %************************************************************************
113 dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
115 dmdAnal sigs Abs e = (topDmdType, e)
116 dmdAnal sigs Bot e = (botDmdType, e)
118 dmdAnal sigs Lazy e = let
119 (res_ty, e') = dmdAnal sigs Eval e
121 (deferType res_ty, e')
122 -- It's important not to analyse e with a lazy demand because
123 -- a) When we encounter case s of (a,b) ->
124 -- we demand s with U(d1d2)... but if the overall demand is lazy
125 -- that is wrong, and we'd need to reduce the demand on s,
126 -- which is inconvenient
127 -- b) More important, consider
128 -- f (let x = R in x+x), where f is lazy
129 -- We still want to mark x as demanded, because it will be when we
130 -- enter the let. If we analyse f's arg with a Lazy demand, we'll
131 -- just mark x as Lazy
132 -- c) The application rule wouldn't be right either
133 -- Evaluating (f x) in a L demand does *not* cause
134 -- evaluation of f in a C(L) demand!
137 dmdAnal sigs dmd (Lit lit)
138 = (topDmdType, Lit lit)
140 dmdAnal sigs dmd (Var var)
141 = (dmdTransform sigs var dmd, Var var)
143 dmdAnal sigs dmd (Note n e)
144 = (dmd_ty, Note n e')
146 (dmd_ty, e') = dmdAnal sigs dmd' e
148 Coerce _ _ -> Eval -- This coerce usually arises from a recursive
149 other -> dmd -- newtype, and we don't want to look inside them
150 -- for exactly the same reason that we don't look
151 -- inside recursive products -- we might not reach
152 -- a fixpoint. So revert to a vanilla Eval demand
154 dmdAnal sigs dmd (App fun (Type ty))
155 = (fun_ty, App fun' (Type ty))
157 (fun_ty, fun') = dmdAnal sigs dmd fun
159 -- Lots of the other code is there to make this
160 -- beautiful, compositional, application rule :-)
161 dmdAnal sigs dmd e@(App fun arg) -- Non-type arguments
162 = let -- [Type arg handled above]
163 (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
164 (arg_ty, arg') = dmdAnal sigs arg_dmd arg
165 (arg_dmd, res_ty) = splitDmdTy fun_ty
167 (res_ty `bothType` arg_ty, App fun' arg')
169 dmdAnal sigs dmd (Lam var body)
172 (body_ty, body') = dmdAnal sigs dmd body
174 (body_ty, Lam var body')
176 | Call body_dmd <- dmd -- A call demand: good!
178 (body_ty, body') = dmdAnal sigs body_dmd body
179 (lam_ty, var') = annotateLamIdBndr body_ty var
181 (lam_ty, Lam var' body')
183 | otherwise -- Not enough demand on the lambda; but do the body
184 = let -- anyway to annotate it and gather free var info
185 (body_ty, body') = dmdAnal sigs Eval body
186 (lam_ty, var') = annotateLamIdBndr body_ty var
188 (deferType lam_ty, Lam var' body')
190 dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)])
191 | let tycon = dataConTyCon dc,
192 isProductTyCon tycon,
193 not (isRecursiveTyCon tycon)
195 (alt_ty, alt') = dmdAnalAlt sigs dmd alt
196 (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
197 (_, bndrs', _) = alt'
199 -- Figure out whether the demand on the case binder is used, and use
200 -- that to set the scrut_dmd. This is utterly essential.
201 -- Consider f x = case x of y { (a,b) -> k y a }
202 -- If we just take scrut_demand = U(L,A), then we won't pass x to the
203 -- worker, so the worker will rebuild
204 -- x = (a, absent-error)
205 -- and that'll crash.
206 -- So at one stage I had:
207 -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
208 -- keepity | dead_case_bndr = Drop
209 -- | otherwise = Keep
212 -- case x of y { (a,b) -> h y + a }
213 -- where h : U(LL) -> T
214 -- The above code would compute a Keep for x, since y is not Abs, which is silly
215 -- The insight is, of course, that a demand on y is a demand on the
216 -- scrutinee, so we need to `both` it with the scrut demand
218 scrut_dmd = mkSeq Drop [idNewDemandInfo b | b <- bndrs', isId b]
220 idNewDemandInfo case_bndr'
222 (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
224 (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt'])
226 dmdAnal sigs dmd (Case scrut case_bndr alts)
228 (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
229 (scrut_ty, scrut') = dmdAnal sigs Eval scrut
230 (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
232 -- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
233 (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts')
235 dmdAnal sigs dmd (Let (NonRec id rhs) body)
237 (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel sigs (id, rhs)
238 (body_ty, body') = dmdAnal sigs' dmd body
239 (body_ty1, id2) = annotateBndr body_ty id1
240 body_ty2 = addLazyFVs body_ty1 lazy_fv
242 -- pprTrace "dmdLet" (ppr id <+> ppr (sig,rhs_env))
243 (body_ty2, Let (NonRec id2 rhs') body')
245 dmdAnal sigs dmd (Let (Rec pairs) body)
247 bndrs = map fst pairs
248 (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
249 (body_ty, body') = dmdAnal sigs' dmd body
250 body_ty1 = addLazyFVs body_ty lazy_fv
252 sigs' `seq` body_ty `seq`
254 (body_ty2, _) = annotateBndrs body_ty1 bndrs
255 -- Don't bother to add demand info to recursive
256 -- binders as annotateBndr does;
257 -- being recursive, we can't treat them strictly.
258 -- But we do need to remove the binders from the result demand env
260 (body_ty2, Let (Rec pairs') body')
263 dmdAnalAlt sigs dmd (con,bndrs,rhs)
265 (rhs_ty, rhs') = dmdAnal sigs dmd rhs
266 (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
268 (alt_ty, (con, bndrs', rhs'))
271 %************************************************************************
273 \subsection{Bindings}
275 %************************************************************************
278 dmdFix :: TopLevelFlag
279 -> SigEnv -- Does not include bindings for this binding
282 [(Id,CoreExpr)]) -- Binders annotated with stricness info
284 dmdFix top_lvl sigs orig_pairs
285 = loop 1 initial_sigs orig_pairs
287 bndrs = map fst orig_pairs
288 initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs]
291 -> SigEnv -- Already contains the current sigs
293 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
295 | all (same_sig sigs sigs') bndrs
296 = (sigs', lazy_fv, pairs')
297 -- Note: use pairs', not pairs. pairs' is the result of
298 -- processing the RHSs with sigs (= sigs'), whereas pairs
299 -- is the result of processing the RHSs with the *previous*
300 -- iteration of sigs.
301 | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
302 [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
303 text "env:" <+> ppr (ufmToList sigs),
304 text "binds:" <+> pprCoreBinding (Rec pairs)]))
305 (emptySigEnv, emptyDmdEnv, orig_pairs) -- Safe output
306 | otherwise = loop (n+1) sigs' pairs'
308 -- Use the new signature to do the next pair
309 -- The occurrence analyser has arranged them in a good order
310 -- so this can significantly reduce the number of iterations needed
311 ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
313 my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
314 = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
316 -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
317 ((sigs', lazy_fv'), pair')
320 (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl sigs (id,rhs)
321 lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
322 -- old_sig = lookup sigs id
323 -- new_sig = lookup sigs' id
325 -- Get an initial strictness signature from the Id
326 -- itself. That way we make use of earlier iterations
327 -- of the fixpoint algorithm. (Cunning plan.)
328 -- Note that the cunning plan extends to the DmdEnv too,
329 -- since it is part of the strictness signature
330 initial_sig id = idNewStrictness_maybe id `orElse` botSig
332 same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
333 lookup sigs var = case lookupVarEnv sigs var of
336 dmdAnalRhs :: TopLevelFlag
337 -> SigEnv -> (Id, CoreExpr)
338 -> (SigEnv, DmdEnv, (Id, CoreExpr))
339 -- Process the RHS of the binding, add the strictness signature
340 -- to the Id, and augment the environment with the signature as well.
342 dmdAnalRhs top_lvl sigs (id, rhs)
343 = (sigs', lazy_fv, (id', rhs'))
345 arity = exprArity rhs -- The idArity may not be up to date
346 (rhs_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
347 (lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_ty, ppr id )
349 id' = id `setIdNewStrictness` sig_ty
350 sigs' = extendSigEnv top_lvl sigs id sig_ty
353 %************************************************************************
355 \subsection{Strictness signatures and types}
357 %************************************************************************
360 mkSigTy :: CoreExpr -> DmdType -> (DmdEnv, StrictSig)
361 -- Take a DmdType and turn it into a StrictSig
362 mkSigTy rhs (DmdType fv dmds res)
363 = (lazy_fv, mkStrictSig dmd_ty)
365 dmd_ty = DmdType strict_fv final_dmds res'
367 lazy_fv = filterUFM (not . isStrictDmd) fv
368 strict_fv = filterUFM isStrictDmd fv
369 -- We put the strict FVs in the DmdType of the Id, so
370 -- that at its call sites we unleash demands on its strict fvs.
371 -- An example is 'roll' in imaginary/wheel-sieve2
372 -- Something like this:
374 -- go y = if ... then roll (x-1) else x+1
377 -- We want to see that roll is strict in x, which is because
378 -- go is called. So we put the DmdEnv for x in go's DmdType.
381 -- f :: Int -> Int -> Int
382 -- f x y = let t = x+1
383 -- h z = if z==0 then t else
384 -- if z==1 then x+1 else
388 -- Calling h does indeed evaluate x, but we can only see
389 -- that if we unleash a demand on x at the call site for t.
391 -- Incidentally, here's a place where lambda-lifting h would
392 -- lose the cigar --- we couldn't see the joint strictness in t/x
395 -- We don't want to put *all* the fv's from the RHS into the
396 -- DmdType, because that makes fixpointing very slow --- the
397 -- DmdType gets full of lazy demands that are slow to converge.
399 lazified_dmds = map funArgDemand dmds
400 -- Get rid of defers in the arguments
401 final_dmds = setUnpackStrategy lazified_dmds
402 -- Set the unpacking strategy
405 RetCPR | not (exprIsValue rhs) -> TopRes
407 -- If the rhs is a thunk, we forget the CPR info, because
408 -- it is presumably shared (else it would have been inlined, and
409 -- so we'd lose sharing if w/w'd it into a function.
411 -- DONE IN OLD CPR ANALYSER, BUT NOT YET HERE
412 -- Also, if the strictness analyser has figured out that it's strict,
413 -- the let-to-case transformation will happen, so again it's good.
414 -- (CPR analysis runs before the simplifier has had a chance to do
415 -- the let-to-case transform.)
416 -- This made a big difference to PrelBase.modInt, which had something like
417 -- modInt = \ x -> let r = ... -> I# v in
418 -- ...body strict in r...
419 -- r's RHS isn't a value yet; but modInt returns r in various branches, so
420 -- if r doesn't have the CPR property then neither does modInt
423 The unpack strategy determines whether we'll *really* unpack the argument,
424 or whether we'll just remember its strictness. If unpacking would give
425 rise to a *lot* of worker args, we may decide not to unpack after all.
428 setUnpackStrategy :: [Demand] -> [Demand]
430 = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
432 go :: Int -- Max number of args available for sub-components of [Demand]
434 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
436 go n (Seq keep cs : ds)
437 | n' >= 0 = Seq keep cs' `cons` go n'' ds
438 | otherwise = Eval `cons` go n ds
441 n' = n + box - non_abs_args
444 Drop -> 1 -- Add one to the budget if we drop the top-level arg
445 non_abs_args = nonAbsentArgs cs
446 -- Delete # of non-absent args to which we'll now be committed
448 go n (d:ds) = d `cons` go n ds
451 cons d (n,ds) = (n, d:ds)
453 nonAbsentArgs :: [Demand] -> Int
455 nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
456 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
460 %************************************************************************
462 \subsection{Strictness signatures and types}
464 %************************************************************************
467 splitDmdTy :: DmdType -> (Demand, DmdType)
468 -- Split off one function argument
469 -- We already have a suitable demand on all
470 -- free vars, so no need to add more!
471 splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
472 splitDmdTy ty@(DmdType fv [] TopRes) = (Lazy, ty)
473 splitDmdTy ty@(DmdType fv [] BotRes) = (Bot, ty)
475 splitDmdTy ty@(DmdType fv [] RetCPR) = panic "splitDmdTy"
476 -- We should not be applying a product as a function!
480 unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
482 addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
483 | isTopLevel top_lvl = dmd_ty -- Don't record top level things
484 | otherwise = DmdType (extendVarEnv fv var dmd) ds res
486 addLazyFVs (DmdType fv ds res) lazy_fvs
487 = DmdType both_fv1 ds res
489 both_fv = (plusUFM_C both fv lazy_fvs)
490 both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv
491 -- This modifyEnv is vital. Consider
492 -- let f = \x -> (x,y)
494 -- Here, y is treated as a lazy-fv of f, but we must `both` that L
495 -- demand with the bottom coming up from 'error'
497 -- I got a loop in the fixpointer without this, due to an interaction
498 -- with the lazy_fv filtering in mkSigTy. Roughly, it was
500 -- = letrec g y = x `fatbar`
501 -- letrec h z = z + ...g...
504 -- In the initial iteration for f, f=Bot
505 -- Suppose h is found to be strict in z, but the occurrence of g in its RHS
506 -- is lazy. Now consider the fixpoint iteration for g, esp the demands it
507 -- places on its free variables. Suppose it places none. Then the
508 -- x `fatbar` ...call to h...
509 -- will give a x->V demand for x. That turns into a L demand for x,
510 -- which floats out of the defn for h. Without the modifyEnv, that
511 -- L demand doesn't get both'd with the Bot coming up from the inner
512 -- call to f. So we just get an L demand for x for g.
514 -- A better way to say this is that the lazy-fv filtering should give the
515 -- same answer as putting the lazy fv demands in the function's type.
517 annotateBndr :: DmdType -> Var -> (DmdType, Var)
518 -- The returned env has the var deleted
519 -- The returned var is annotated with demand info
520 -- No effect on the argument demands
521 annotateBndr dmd_ty@(DmdType fv ds res) var
522 | isTyVar var = (dmd_ty, var)
523 | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var hacked_dmd)
525 (fv', dmd) = removeFV fv var res
526 hacked_dmd | isUnLiftedType (idType var) = unliftedDemand dmd
529 annotateBndrs = mapAccumR annotateBndr
531 annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
532 -- For lambdas we add the demand to the argument demands
533 -- Only called for Ids
535 (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
537 (fv', dmd) = removeFV fv id res
538 hacked_dmd | isUnLiftedType (idType id) = unliftedDemand dmd
539 | otherwise = funArgDemand dmd
540 -- This call to funArgDemand is vital, because otherwise we label
541 -- a lambda binder with demand 'B'. But in terms of calling
542 -- conventions that's Abs, because we don't pass it. But
543 -- when we do a w/w split we get
544 -- fw x = (\x y:B -> ...) x (error "oops")
545 -- And then the simplifier things the 'B' is a strict demand
546 -- and evaluates the (error "oops"). Sigh
548 removeFV fv var res = (fv', dmd)
550 fv' = fv `delVarEnv` var
551 dmd = lookupVarEnv fv var `orElse` deflt
552 deflt | isBotRes res = Bot
556 %************************************************************************
558 \subsection{Strictness signatures}
560 %************************************************************************
563 type SigEnv = VarEnv (StrictSig, TopLevelFlag)
564 -- We use the SigEnv to tell us whether to
565 -- record info about a variable in the DmdEnv
566 -- We do so if it's a LocalId, but not top-level
568 -- The DmdEnv gives the demand on the free vars of the function
569 -- when it is given enough args to satisfy the strictness signature
571 emptySigEnv = emptyVarEnv
573 extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
574 extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
576 extendSigEnvList = extendVarEnvList
578 dmdTransform :: SigEnv -- The strictness environment
579 -> Id -- The function
580 -> Demand -- The demand on the function
581 -> DmdType -- The demand type of the function in this context
582 -- Returned DmdEnv includes the demand on
583 -- this function plus demand on its free variables
585 dmdTransform sigs var dmd
587 ------ DATA CONSTRUCTOR
588 | isDataConId var, -- Data constructor
589 Seq k ds <- res_dmd -- and the demand looks inside its fields
591 StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
592 DmdType _ _ con_res = dmd_ty
595 if arity == call_depth then -- Saturated, so unleash the demand
597 -- ds can be empty, when we are just seq'ing the thing
598 -- If so we must make up a suitable bunch of demands
599 dmd_ds | null ds = replicate arity Abs
600 | otherwise = ASSERT( length ds == arity ) ds
603 Keep -> bothLazy_s dmd_ds
605 Defer -> pprTrace "dmdTransform: surprising!" (ppr var)
606 -- I don't think this can happen
608 -- Important! If we Keep the constructor application, then
609 -- we need the demands the constructor places (always lazy)
610 -- If not, we don't need to. For example:
611 -- f p@(x,y) = (p,y) -- S(AL)
613 -- It's vital that we don't calculate Absent for a!
615 mkDmdType emptyDmdEnv arg_ds con_res
616 -- Must remember whether it's a product, hence con_res, not TopRes
620 ------ IMPORTED FUNCTION
621 | isGlobalId var, -- Imported function
622 let StrictSig dmd_ty = getNewStrictness var
623 = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
628 ------ LOCAL LET/REC BOUND THING
629 | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
631 fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
632 | otherwise = deferType dmd_ty
633 -- NB: it's important to use deferType, and not just return topDmdType
634 -- Consider let { f x y = p + x } in f 1
635 -- The application isn't saturated, but we must nevertheless propagate
636 -- a lazy demand for p!
638 addVarDmd top_lvl fn_ty var dmd
640 ------ LOCAL NON-LET/REC BOUND THING
641 | otherwise -- Default case
645 (call_depth, res_dmd) = splitCallDmd dmd
649 %************************************************************************
653 %************************************************************************
656 splitCallDmd :: Demand -> (Int, Demand)
657 splitCallDmd (Call d) = case splitCallDmd d of
659 splitCallDmd d = (0, d)
661 vanillaCall :: Arity -> Demand
663 vanillaCall n = Call (vanillaCall (n-1))
665 deferType :: DmdType -> DmdType
666 deferType (DmdType fv _ _) = DmdType (mapVarEnv defer fv) [] TopRes
667 -- Notice that we throw away info about both arguments and results
668 -- For example, f = let ... in \x -> x
669 -- We don't want to get a stricness type V->T for f.
673 bothLazy :: Demand -> Demand
675 bothLazy_s :: [Demand] -> [Demand]
676 bothLazy_s = map bothLazy
678 funArgDemand :: Demand -> Demand
679 -- The 'Defer' demands are just Lazy at function boundaries
680 -- Ugly! Ask John how to improve it.
681 funArgDemand (Seq Defer ds) = Lazy
682 funArgDemand (Seq k ds) = Seq k (map funArgDemand ds)
683 funArgDemand Err = Eval -- Args passed to a bottoming function
684 funArgDemand Bot = Abs -- Don't pass args that are consumed by bottom/err
687 unliftedDemand :: Demand -> Demand
688 -- Same idea, but for unlifted types the domain is much simpler:
689 -- Either we use it (Lazy) or we don't (Abs)
690 unliftedDemand Bot = Abs
691 unliftedDemand Abs = Abs
692 unliftedDemand other = Lazy
696 betterStrictness :: StrictSig -> StrictSig -> Bool
697 betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
699 betterDmdType t1 t2 = (t1 `lubType` t2) == t2
701 betterDemand :: Demand -> Demand -> Bool
702 -- If d1 `better` d2, and d2 `better` d2, then d1==d2
703 betterDemand d1 d2 = (d1 `lub` d2) == d2
705 squashDmdEnv (StrictSig (DmdType fv ds res)) = StrictSig (DmdType emptyDmdEnv ds res)
709 -------------------------
710 -- Consider (if x then y else []) with demand V
711 -- Then the first branch gives {y->V} and the second
712 -- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
713 -- in the result env.
714 lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
715 = DmdType lub_fv2 (zipWith lub ds1 ds2) (r1 `lubRes` r2)
717 lub_fv = plusUFM_C lub fv1 fv2
718 lub_fv1 = modifyEnv (not (isBotRes r1)) defer fv2 fv1 lub_fv
719 lub_fv2 = modifyEnv (not (isBotRes r2)) defer fv1 fv2 lub_fv1
720 -- lub is the identity for Bot
722 -----------------------------------
723 -- (t1 `bothType` t2) takes the argument/result info from t1,
724 -- using t2 just for its free-var info
725 -- NB: Don't forget about r2! It might be BotRes, which is
726 -- a bottom demand on all the in-scope variables.
727 -- Peter: can this be done more neatly?
728 bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
729 = DmdType both_fv2 ds1 (r1 `bothRes` r2)
731 both_fv = plusUFM_C both fv1 fv2
732 both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
733 both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
734 -- both is the identity for Abs
741 lubRes RetCPR RetCPR = RetCPR
742 lubRes r1 r2 = TopRes
744 -- If either diverges, the whole thing does
745 -- Otherwise take CPR info from the first
746 bothRes r1 BotRes = BotRes
751 -- A Seq can have an empty list of demands, in the polymorphic case.
754 lubs ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith lub ds1 ds2
756 -----------------------------------
757 -- A Seq can have an empty list of demands, in the polymorphic case.
760 boths ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith both ds1 ds2
764 modifyEnv :: Bool -- No-op if False
765 -> (Demand -> Demand) -- The zapper
766 -> DmdEnv -> DmdEnv -- Env1 and Env2
767 -> DmdEnv -> DmdEnv -- Transform this env
768 -- Zap anything in Env1 but not in Env2
769 -- Assume: dom(env) includes dom(Env1) and dom(Env2)
771 modifyEnv need_to_modify zapper env1 env2 env
772 | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
775 zap uniq env = addToUFM_Directly env uniq (zapper current_val)
777 current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq)
781 %************************************************************************
783 \subsection{LUB and BOTH}
785 %************************************************************************
789 lub :: Demand -> Demand -> Demand
802 lub Eval (Seq Drop ds) | not (null ds) = Seq Drop [Lazy | d <- ds]
804 -- For the Seq case, consier
806 -- f n (x:xs) = f (n+x) xs
807 -- Here we want to do better than just V for n. It's
808 -- unboxed in the (x:xs) case, and we might be prepared to
809 -- rebox it in the [] case.
810 -- But if we don't use *any* of the components, give up
813 lub (Call d1) (Call d2) = Call (lub d1 d2)
814 lub d1@(Call _) d2 = d2 `lub` d1
816 lub (Seq k1 ds1) (Seq k2 ds2)
817 = Seq (k1 `lub_keep` k2) (lub_ds k1 ds1 k2 ds2)
820 lub_ds Keep ds1 Keep ds2 = ds1 `lubs` ds2
821 lub_ds Keep ds1 non_keep ds2 | null ds1 = [Lazy | d <- ds2]
822 | otherwise = bothLazy_s ds1 `lubs` ds2
824 lub_ds non_keep ds1 Keep ds2 | null ds2 = [Lazy | d <- ds1]
825 | otherwise = ds1 `lubs` bothLazy_s ds2
827 lub_ds k1 ds1 k2 ds2 = ds1 `lubs` ds2
832 lub_keep Drop Defer = Defer
833 lub_keep Drop k = Drop
835 lub_keep Defer k = Defer
837 lub d1@(Seq _ _) d2 = d2 `lub` d1
840 both :: Demand -> Demand -> Demand
852 both Lazy Eval = Eval
853 both Lazy (Call d) = Call d
854 both Lazy (Seq Defer ds) = Lazy
855 both Lazy (Seq k ds) = Seq Keep ds
858 -- For the (Eval `both` Bot) case, consider
860 -- From 'error' itself we get demand Bot on x
861 -- From the arg demand on x we get Eval
862 -- So we want Eval `both` Bot to be Err.
863 -- That's what Err is *for*
866 both Eval (Seq k ds) = Seq Keep ds
869 both (Call d1) (Call d2) = Call (d1 `both` d2)
870 both d1@(Call _) d2 = d2 `both` d1
872 both (Seq k1 ds1) (Seq k2 ds2)
873 = Seq (k1 `both_keep` k2) (both_ds k1 ds1 k2 ds2)
876 both_keep Keep k2 = Keep
878 both_keep Drop Keep = Keep
879 both_keep Drop k2 = Drop
881 both_keep Defer k2 = k2
884 both_ds Defer ds1 Defer ds2 = ds1 `boths` ds2
885 both_ds Defer ds1 non_defer ds2 = map defer ds1 `boths` ds2
887 both_ds non_defer ds1 Defer ds2 = ds1 `boths` map defer ds2
889 both_ds k1 ds1 k2 ds2 = ds1 `boths` ds2
891 both d1@(Seq _ _) d2 = d2 `both` d1
895 %************************************************************************
897 \subsection{Miscellaneous
899 %************************************************************************
903 get_changes binds = vcat (map get_changes_bind binds)
905 get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
906 get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
908 get_changes_pr (id,rhs)
909 = get_changes_var id $$ get_changes_expr rhs
912 | isId var = get_changes_str var $$ get_changes_dmd var
915 get_changes_expr (Type t) = empty
916 get_changes_expr (Var v) = empty
917 get_changes_expr (Lit l) = empty
918 get_changes_expr (Note n e) = get_changes_expr e
919 get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
920 get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
921 get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
922 get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
924 get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
927 | new_better && old_better = empty
928 | new_better = message "BETTER"
929 | old_better = message "WORSE"
930 | otherwise = message "INCOMPARABLE"
932 message word = text word <+> text "strictness for" <+> ppr id <+> info
933 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
934 new = squashDmdEnv (idNewStrictness id) -- Don't report diffs in the env
935 old = newStrictnessFromOld id
936 old_better = old `betterStrictness` new
937 new_better = new `betterStrictness` old
940 | isUnLiftedType (idType id) = empty -- Not useful
941 | new_better && old_better = empty
942 | new_better = message "BETTER"
943 | old_better = message "WORSE"
944 | otherwise = message "INCOMPARABLE"
946 message word = text word <+> text "demand for" <+> ppr id <+> info
947 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
948 new = funArgDemand (idNewDemandInfo id) -- FunArgDemand to avoid spurious improvements
949 old = newDemand (idDemandInfo id)
950 new_better = new `betterDemand` old
951 old_better = old `betterDemand` new