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, idArity,
24 isDataConId, isImplicitId, isGlobalId,
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)
81 | isImplicitId id -- Don't touch the info on constructors, selectors etc
82 = (sigs, NonRec id rhs) -- It's pre-computed in MkId.lhs
85 (sigs', _, (id', rhs')) = dmdAnalRhs TopLevel sigs (id, rhs)
87 (sigs', NonRec id' rhs')
89 dmdAnalTopBind sigs (Rec pairs)
91 (sigs', _, pairs') = dmdFix TopLevel sigs pairs
97 dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr)
98 -- Analyse the RHS and return
99 -- a) appropriate strictness info
100 -- b) the unfolding (decorated with stricntess info)
104 arity = exprArity rhs
105 (rhs_ty, rhs') = dmdAnal emptySigEnv (vanillaCall arity) rhs
106 (_, sig) = mkSigTy rhs rhs_ty
109 %************************************************************************
111 \subsection{The analyser itself}
113 %************************************************************************
116 dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
118 dmdAnal sigs Abs e = (topDmdType, e)
119 dmdAnal sigs Bot e = (botDmdType, e)
121 dmdAnal sigs Lazy e = let
122 (res_ty, e') = dmdAnal sigs Eval e
124 (deferType res_ty, e')
125 -- It's important not to analyse e with a lazy demand because
126 -- a) When we encounter case s of (a,b) ->
127 -- we demand s with U(d1d2)... but if the overall demand is lazy
128 -- that is wrong, and we'd need to reduce the demand on s,
129 -- which is inconvenient
130 -- b) More important, consider
131 -- f (let x = R in x+x), where f is lazy
132 -- We still want to mark x as demanded, because it will be when we
133 -- enter the let. If we analyse f's arg with a Lazy demand, we'll
134 -- just mark x as Lazy
135 -- c) The application rule wouldn't be right either
136 -- Evaluating (f x) in a L demand does *not* cause
137 -- evaluation of f in a C(L) demand!
140 dmdAnal sigs dmd (Lit lit)
141 = (topDmdType, Lit lit)
143 dmdAnal sigs dmd (Var var)
144 = (dmdTransform sigs var dmd, Var var)
146 dmdAnal sigs dmd (Note n e)
147 = (dmd_ty, Note n e')
149 (dmd_ty, e') = dmdAnal sigs dmd' e
151 Coerce _ _ -> Eval -- This coerce usually arises from a recursive
152 other -> dmd -- newtype, and we don't want to look inside them
153 -- for exactly the same reason that we don't look
154 -- inside recursive products -- we might not reach
155 -- a fixpoint. So revert to a vanilla Eval demand
157 dmdAnal sigs dmd (App fun (Type ty))
158 = (fun_ty, App fun' (Type ty))
160 (fun_ty, fun') = dmdAnal sigs dmd fun
162 -- Lots of the other code is there to make this
163 -- beautiful, compositional, application rule :-)
164 dmdAnal sigs dmd (App fun arg) -- Non-type arguments
165 = let -- [Type arg handled above]
166 (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
167 (arg_ty, arg') = dmdAnal sigs arg_dmd arg
168 (arg_dmd, res_ty) = splitDmdTy fun_ty
170 (res_ty `bothType` arg_ty, App fun' arg')
172 dmdAnal sigs dmd (Lam var body)
175 (body_ty, body') = dmdAnal sigs dmd body
177 (body_ty, Lam var body')
179 | Call body_dmd <- dmd -- A call demand: good!
181 (body_ty, body') = dmdAnal sigs body_dmd body
182 (lam_ty, var') = annotateLamIdBndr body_ty var
184 (lam_ty, Lam var' body')
186 | otherwise -- Not enough demand on the lambda; but do the body
187 = let -- anyway to annotate it and gather free var info
188 (body_ty, body') = dmdAnal sigs Eval body
189 (lam_ty, var') = annotateLamIdBndr body_ty var
191 (deferType lam_ty, Lam var' body')
193 dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)])
194 | let tycon = dataConTyCon dc,
195 isProductTyCon tycon,
196 not (isRecursiveTyCon tycon)
198 (alt_ty, alt') = dmdAnalAlt sigs dmd alt
199 (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
200 (_, bndrs', _) = alt'
202 -- Figure out whether the demand on the case binder is used, and use
203 -- that to set the scrut_dmd. This is utterly essential.
204 -- Consider f x = case x of y { (a,b) -> k y a }
205 -- If we just take scrut_demand = U(L,A), then we won't pass x to the
206 -- worker, so the worker will rebuild
207 -- x = (a, absent-error)
208 -- and that'll crash.
209 -- So at one stage I had:
210 -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
211 -- keepity | dead_case_bndr = Drop
212 -- | otherwise = Keep
215 -- case x of y { (a,b) -> h y + a }
216 -- where h : U(LL) -> T
217 -- The above code would compute a Keep for x, since y is not Abs, which is silly
218 -- The insight is, of course, that a demand on y is a demand on the
219 -- scrutinee, so we need to `both` it with the scrut demand
221 scrut_dmd = mkSeq Drop [idNewDemandInfo b | b <- bndrs', isId b]
223 idNewDemandInfo case_bndr'
225 (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
227 (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt'])
229 dmdAnal sigs dmd (Case scrut case_bndr alts)
231 (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
232 (scrut_ty, scrut') = dmdAnal sigs Eval scrut
233 (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
235 -- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
236 (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts')
238 dmdAnal sigs dmd (Let (NonRec id rhs) body)
240 (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel sigs (id, rhs)
241 (body_ty, body') = dmdAnal sigs' dmd body
242 (body_ty1, id2) = annotateBndr body_ty id1
243 body_ty2 = addLazyFVs body_ty1 lazy_fv
245 -- pprTrace "dmdLet" (ppr id <+> ppr (sig,rhs_env))
246 (body_ty2, Let (NonRec id2 rhs') body')
248 dmdAnal sigs dmd (Let (Rec pairs) body)
250 bndrs = map fst pairs
251 (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
252 (body_ty, body') = dmdAnal sigs' dmd body
253 body_ty1 = addLazyFVs body_ty lazy_fv
255 sigs' `seq` body_ty `seq`
257 (body_ty2, _) = annotateBndrs body_ty1 bndrs
258 -- Don't bother to add demand info to recursive
259 -- binders as annotateBndr does;
260 -- being recursive, we can't treat them strictly.
261 -- But we do need to remove the binders from the result demand env
263 (body_ty2, Let (Rec pairs') body')
266 dmdAnalAlt sigs dmd (con,bndrs,rhs)
268 (rhs_ty, rhs') = dmdAnal sigs dmd rhs
269 (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
271 (alt_ty, (con, bndrs', rhs'))
274 %************************************************************************
276 \subsection{Bindings}
278 %************************************************************************
281 dmdFix :: TopLevelFlag
282 -> SigEnv -- Does not include bindings for this binding
285 [(Id,CoreExpr)]) -- Binders annotated with stricness info
287 dmdFix top_lvl sigs orig_pairs
288 = loop 1 initial_sigs orig_pairs
290 bndrs = map fst orig_pairs
291 initial_sigs = extendSigEnvList sigs [(id, (initial_sig id, top_lvl)) | id <- bndrs]
294 -> SigEnv -- Already contains the current sigs
296 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
298 | all (same_sig sigs sigs') bndrs
299 = (sigs', lazy_fv, pairs')
300 -- Note: use pairs', not pairs. pairs' is the result of
301 -- processing the RHSs with sigs (= sigs'), whereas pairs
302 -- is the result of processing the RHSs with the *previous*
303 -- iteration of sigs.
304 | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
305 [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
306 text "env:" <+> ppr (ufmToList sigs),
307 text "binds:" <+> pprCoreBinding (Rec pairs)]))
308 (emptySigEnv, emptyDmdEnv, orig_pairs) -- Safe output
309 | otherwise = loop (n+1) sigs' pairs'
311 -- Use the new signature to do the next pair
312 -- The occurrence analyser has arranged them in a good order
313 -- so this can significantly reduce the number of iterations needed
314 ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
316 my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
317 = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
319 -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
320 ((sigs', lazy_fv'), pair')
323 (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl sigs (id,rhs)
324 lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
325 -- old_sig = lookup sigs id
326 -- new_sig = lookup sigs' id
328 -- Get an initial strictness signature from the Id
329 -- itself. That way we make use of earlier iterations
330 -- of the fixpoint algorithm. (Cunning plan.)
331 -- Note that the cunning plan extends to the DmdEnv too,
332 -- since it is part of the strictness signature
333 initial_sig id = idNewStrictness_maybe id `orElse` botSig
335 same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
336 lookup sigs var = case lookupVarEnv sigs var of
339 dmdAnalRhs :: TopLevelFlag
340 -> SigEnv -> (Id, CoreExpr)
341 -> (SigEnv, DmdEnv, (Id, CoreExpr))
342 -- Process the RHS of the binding, add the strictness signature
343 -- to the Id, and augment the environment with the signature as well.
345 dmdAnalRhs top_lvl sigs (id, rhs)
346 = (sigs', lazy_fv, (id', rhs'))
348 arity = exprArity rhs -- The idArity may not be up to date
349 (rhs_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
350 (lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_ty, ppr id )
352 id' = id `setIdNewStrictness` sig_ty
353 sigs' = extendSigEnv top_lvl sigs id sig_ty
356 %************************************************************************
358 \subsection{Strictness signatures and types}
360 %************************************************************************
363 mkSigTy :: CoreExpr -> DmdType -> (DmdEnv, StrictSig)
364 -- Take a DmdType and turn it into a StrictSig
365 mkSigTy rhs (DmdType fv dmds res)
366 = (lazy_fv, mkStrictSig dmd_ty)
368 dmd_ty = DmdType strict_fv final_dmds res'
370 lazy_fv = filterUFM (not . isStrictDmd) fv
371 strict_fv = filterUFM isStrictDmd fv
372 -- We put the strict FVs in the DmdType of the Id, so
373 -- that at its call sites we unleash demands on its strict fvs.
374 -- An example is 'roll' in imaginary/wheel-sieve2
375 -- Something like this:
377 -- go y = if ... then roll (x-1) else x+1
380 -- We want to see that roll is strict in x, which is because
381 -- go is called. So we put the DmdEnv for x in go's DmdType.
384 -- f :: Int -> Int -> Int
385 -- f x y = let t = x+1
386 -- h z = if z==0 then t else
387 -- if z==1 then x+1 else
391 -- Calling h does indeed evaluate x, but we can only see
392 -- that if we unleash a demand on x at the call site for t.
394 -- Incidentally, here's a place where lambda-lifting h would
395 -- lose the cigar --- we couldn't see the joint strictness in t/x
398 -- We don't want to put *all* the fv's from the RHS into the
399 -- DmdType, because that makes fixpointing very slow --- the
400 -- DmdType gets full of lazy demands that are slow to converge.
402 lazified_dmds = map funArgDemand dmds
403 -- Get rid of defers in the arguments
404 final_dmds = setUnpackStrategy lazified_dmds
405 -- Set the unpacking strategy
408 RetCPR | not (exprIsValue rhs) -> TopRes
410 -- If the rhs is a thunk, we forget the CPR info, because
411 -- it is presumably shared (else it would have been inlined, and
412 -- so we'd lose sharing if w/w'd it into a function.
414 -- DONE IN OLD CPR ANALYSER, BUT NOT YET HERE
415 -- Also, if the strictness analyser has figured out that it's strict,
416 -- the let-to-case transformation will happen, so again it's good.
417 -- (CPR analysis runs before the simplifier has had a chance to do
418 -- the let-to-case transform.)
419 -- This made a big difference to PrelBase.modInt, which had something like
420 -- modInt = \ x -> let r = ... -> I# v in
421 -- ...body strict in r...
422 -- r's RHS isn't a value yet; but modInt returns r in various branches, so
423 -- if r doesn't have the CPR property then neither does modInt
426 The unpack strategy determines whether we'll *really* unpack the argument,
427 or whether we'll just remember its strictness. If unpacking would give
428 rise to a *lot* of worker args, we may decide not to unpack after all.
431 setUnpackStrategy :: [Demand] -> [Demand]
433 = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
435 go :: Int -- Max number of args available for sub-components of [Demand]
437 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
439 go n (Seq keep cs : ds)
440 | n' >= 0 = Seq keep cs' `cons` go n'' ds
441 | otherwise = Eval `cons` go n ds
444 n' = n + box - non_abs_args
447 Drop -> 1 -- Add one to the budget if we drop the top-level arg
448 non_abs_args = nonAbsentArgs cs
449 -- Delete # of non-absent args to which we'll now be committed
451 go n (d:ds) = d `cons` go n ds
454 cons d (n,ds) = (n, d:ds)
456 nonAbsentArgs :: [Demand] -> Int
458 nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
459 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
463 %************************************************************************
465 \subsection{Strictness signatures and types}
467 %************************************************************************
470 splitDmdTy :: DmdType -> (Demand, DmdType)
471 -- Split off one function argument
472 -- We already have a suitable demand on all
473 -- free vars, so no need to add more!
474 splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
475 splitDmdTy ty@(DmdType fv [] TopRes) = (Lazy, ty)
476 splitDmdTy ty@(DmdType fv [] BotRes) = (Bot, ty)
478 splitDmdTy (DmdType fv [] RetCPR) = panic "splitDmdTy"
479 -- We should not be applying a product as a function!
483 unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
485 addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
486 | isTopLevel top_lvl = dmd_ty -- Don't record top level things
487 | otherwise = DmdType (extendVarEnv fv var dmd) ds res
489 addLazyFVs (DmdType fv ds res) lazy_fvs
490 = DmdType both_fv1 ds res
492 both_fv = (plusUFM_C both fv lazy_fvs)
493 both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv
494 -- This modifyEnv is vital. Consider
495 -- let f = \x -> (x,y)
497 -- Here, y is treated as a lazy-fv of f, but we must `both` that L
498 -- demand with the bottom coming up from 'error'
500 -- I got a loop in the fixpointer without this, due to an interaction
501 -- with the lazy_fv filtering in mkSigTy. Roughly, it was
503 -- = letrec g y = x `fatbar`
504 -- letrec h z = z + ...g...
507 -- In the initial iteration for f, f=Bot
508 -- Suppose h is found to be strict in z, but the occurrence of g in its RHS
509 -- is lazy. Now consider the fixpoint iteration for g, esp the demands it
510 -- places on its free variables. Suppose it places none. Then the
511 -- x `fatbar` ...call to h...
512 -- will give a x->V demand for x. That turns into a L demand for x,
513 -- which floats out of the defn for h. Without the modifyEnv, that
514 -- L demand doesn't get both'd with the Bot coming up from the inner
515 -- call to f. So we just get an L demand for x for g.
517 -- A better way to say this is that the lazy-fv filtering should give the
518 -- same answer as putting the lazy fv demands in the function's type.
520 annotateBndr :: DmdType -> Var -> (DmdType, Var)
521 -- The returned env has the var deleted
522 -- The returned var is annotated with demand info
523 -- No effect on the argument demands
524 annotateBndr dmd_ty@(DmdType fv ds res) var
525 | isTyVar var = (dmd_ty, var)
526 | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var hacked_dmd)
528 (fv', dmd) = removeFV fv var res
529 hacked_dmd | isUnLiftedType (idType var) = unliftedDemand dmd
532 annotateBndrs = mapAccumR annotateBndr
534 annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
535 -- For lambdas we add the demand to the argument demands
536 -- Only called for Ids
538 (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
540 (fv', dmd) = removeFV fv id res
541 hacked_dmd | isUnLiftedType (idType id) = unliftedDemand dmd
542 | otherwise = funArgDemand dmd
543 -- This call to funArgDemand is vital, because otherwise we label
544 -- a lambda binder with demand 'B'. But in terms of calling
545 -- conventions that's Abs, because we don't pass it. But
546 -- when we do a w/w split we get
547 -- fw x = (\x y:B -> ...) x (error "oops")
548 -- And then the simplifier things the 'B' is a strict demand
549 -- and evaluates the (error "oops"). Sigh
551 removeFV fv var res = (fv', dmd)
553 fv' = fv `delVarEnv` var
554 dmd = lookupVarEnv fv var `orElse` deflt
555 deflt | isBotRes res = Bot
559 %************************************************************************
561 \subsection{Strictness signatures}
563 %************************************************************************
566 type SigEnv = VarEnv (StrictSig, TopLevelFlag)
567 -- We use the SigEnv to tell us whether to
568 -- record info about a variable in the DmdEnv
569 -- We do so if it's a LocalId, but not top-level
571 -- The DmdEnv gives the demand on the free vars of the function
572 -- when it is given enough args to satisfy the strictness signature
574 emptySigEnv = emptyVarEnv
576 extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
577 extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
579 extendSigEnvList = extendVarEnvList
581 dmdTransform :: SigEnv -- The strictness environment
582 -> Id -- The function
583 -> Demand -- The demand on the function
584 -> DmdType -- The demand type of the function in this context
585 -- Returned DmdEnv includes the demand on
586 -- this function plus demand on its free variables
588 dmdTransform sigs var dmd
590 ------ DATA CONSTRUCTOR
591 | isDataConId var, -- Data constructor
592 Seq k ds <- res_dmd, -- and the demand looks inside its fields
593 let StrictSig dmd_ty = idNewStrictness var, -- It must have a strictness sig
594 let DmdType _ _ con_res = dmd_ty
595 = if idArity var == call_depth then -- Saturated, so unleash the demand
596 -- ds can be empty, when we are just seq'ing the thing
599 Keep -> bothLazy_s ds
601 Defer -> pprTrace "dmdTransform: surprising!" (ppr var)
602 -- I don't think this can happen
604 -- Important! If we Keep the constructor application, then
605 -- we need the demands the constructor places (always lazy)
606 -- If not, we don't need to. For example:
607 -- f p@(x,y) = (p,y) -- S(AL)
609 -- It's vital that we don't calculate Absent for a!
611 mkDmdType emptyDmdEnv arg_ds con_res
612 -- Must remember whether it's a product, hence con_res, not TopRes
616 ------ IMPORTED FUNCTION
617 | isGlobalId var, -- Imported function
618 let StrictSig dmd_ty = getNewStrictness var
619 = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
624 ------ LOCAL LET/REC BOUND THING
625 | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
627 fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
628 | otherwise = deferType dmd_ty
629 -- NB: it's important to use deferType, and not just return topDmdType
630 -- Consider let { f x y = p + x } in f 1
631 -- The application isn't saturated, but we must nevertheless propagate
632 -- a lazy demand for p!
634 addVarDmd top_lvl fn_ty var dmd
636 ------ LOCAL NON-LET/REC BOUND THING
637 | otherwise -- Default case
641 (call_depth, res_dmd) = splitCallDmd dmd
645 %************************************************************************
649 %************************************************************************
652 splitCallDmd :: Demand -> (Int, Demand)
653 splitCallDmd (Call d) = case splitCallDmd d of
655 splitCallDmd d = (0, d)
657 vanillaCall :: Arity -> Demand
659 vanillaCall n = Call (vanillaCall (n-1))
661 deferType :: DmdType -> DmdType
662 deferType (DmdType fv _ _) = DmdType (mapVarEnv defer fv) [] TopRes
663 -- Notice that we throw away info about both arguments and results
664 -- For example, f = let ... in \x -> x
665 -- We don't want to get a stricness type V->T for f.
669 bothLazy :: Demand -> Demand
671 bothLazy_s :: [Demand] -> [Demand]
672 bothLazy_s = map bothLazy
674 funArgDemand :: Demand -> Demand
675 -- The 'Defer' demands are just Lazy at function boundaries
676 -- Ugly! Ask John how to improve it.
677 funArgDemand (Seq Defer ds) = Lazy
678 funArgDemand (Seq k ds) = Seq k (map funArgDemand ds)
679 funArgDemand Err = Eval -- Args passed to a bottoming function
680 funArgDemand Bot = Abs -- Don't pass args that are consumed by bottom/err
683 unliftedDemand :: Demand -> Demand
684 -- Same idea, but for unlifted types the domain is much simpler:
685 -- Either we use it (Lazy) or we don't (Abs)
686 unliftedDemand Bot = Abs
687 unliftedDemand Abs = Abs
688 unliftedDemand other = Lazy
692 betterStrictness :: StrictSig -> StrictSig -> Bool
693 betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
695 betterDmdType t1 t2 = (t1 `lubType` t2) == t2
697 betterDemand :: Demand -> Demand -> Bool
698 -- If d1 `better` d2, and d2 `better` d2, then d1==d2
699 betterDemand d1 d2 = (d1 `lub` d2) == d2
701 squashDmdEnv (StrictSig (DmdType fv ds res)) = StrictSig (DmdType emptyDmdEnv ds res)
705 -------------------------
706 -- Consider (if x then y else []) with demand V
707 -- Then the first branch gives {y->V} and the second
708 -- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
709 -- in the result env.
710 lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
711 = DmdType lub_fv2 (zipWith lub ds1 ds2) (r1 `lubRes` r2)
713 lub_fv = plusUFM_C lub fv1 fv2
714 lub_fv1 = modifyEnv (not (isBotRes r1)) defer fv2 fv1 lub_fv
715 lub_fv2 = modifyEnv (not (isBotRes r2)) defer fv1 fv2 lub_fv1
716 -- lub is the identity for Bot
718 -----------------------------------
719 -- (t1 `bothType` t2) takes the argument/result info from t1,
720 -- using t2 just for its free-var info
721 -- NB: Don't forget about r2! It might be BotRes, which is
722 -- a bottom demand on all the in-scope variables.
723 -- Peter: can this be done more neatly?
724 bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
725 = DmdType both_fv2 ds1 (r1 `bothRes` r2)
727 both_fv = plusUFM_C both fv1 fv2
728 both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
729 both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
730 -- both is the identity for Abs
737 lubRes RetCPR RetCPR = RetCPR
738 lubRes r1 r2 = TopRes
740 -- If either diverges, the whole thing does
741 -- Otherwise take CPR info from the first
742 bothRes r1 BotRes = BotRes
747 -- A Seq can have an empty list of demands, in the polymorphic case.
750 lubs ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith lub ds1 ds2
752 -----------------------------------
753 -- A Seq can have an empty list of demands, in the polymorphic case.
756 boths ds1 ds2 = ASSERT( length ds1 == length ds2 ) zipWith both ds1 ds2
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{LUB and BOTH}
781 %************************************************************************
785 lub :: Demand -> Demand -> Demand
798 lub Eval (Seq Drop ds) | not (null ds) = Seq Drop [Lazy | d <- ds]
800 -- For the Seq case, consier
802 -- f n (x:xs) = f (n+x) xs
803 -- Here we want to do better than just V for n. It's
804 -- unboxed in the (x:xs) case, and we might be prepared to
805 -- rebox it in the [] case.
806 -- But if we don't use *any* of the components, give up
809 lub (Call d1) (Call d2) = Call (lub d1 d2)
810 lub d1@(Call _) d2 = d2 `lub` d1
812 lub (Seq k1 ds1) (Seq k2 ds2)
813 = Seq (k1 `lub_keep` k2) (lub_ds k1 ds1 k2 ds2)
816 lub_ds Keep ds1 Keep ds2 = ds1 `lubs` ds2
817 lub_ds Keep ds1 non_keep ds2 | null ds1 = [Lazy | d <- ds2]
818 | otherwise = bothLazy_s ds1 `lubs` ds2
820 lub_ds non_keep ds1 Keep ds2 | null ds2 = [Lazy | d <- ds1]
821 | otherwise = ds1 `lubs` bothLazy_s ds2
823 lub_ds k1 ds1 k2 ds2 = ds1 `lubs` ds2
828 lub_keep Drop Defer = Defer
829 lub_keep Drop k = Drop
831 lub_keep Defer k = Defer
833 lub d1@(Seq _ _) d2 = d2 `lub` d1
836 both :: Demand -> Demand -> Demand
848 both Lazy Eval = Eval
849 both Lazy (Call d) = Call d
850 both Lazy (Seq Defer ds) = Lazy
851 both Lazy (Seq k ds) = Seq Keep ds
854 -- For the (Eval `both` Bot) case, consider
856 -- From 'error' itself we get demand Bot on x
857 -- From the arg demand on x we get Eval
858 -- So we want Eval `both` Bot to be Err.
859 -- That's what Err is *for*
862 both Eval (Seq k ds) = Seq Keep ds
865 both (Call d1) (Call d2) = Call (d1 `both` d2)
866 both d1@(Call _) d2 = d2 `both` d1
868 both (Seq k1 ds1) (Seq k2 ds2)
869 = Seq (k1 `both_keep` k2) (both_ds k1 ds1 k2 ds2)
872 both_keep Keep k2 = Keep
874 both_keep Drop Keep = Keep
875 both_keep Drop k2 = Drop
877 both_keep Defer k2 = k2
880 both_ds Defer ds1 Defer ds2 = ds1 `boths` ds2
881 both_ds Defer ds1 non_defer ds2 = map defer ds1 `boths` ds2
883 both_ds non_defer ds1 Defer ds2 = ds1 `boths` map defer ds2
885 both_ds k1 ds1 k2 ds2 = ds1 `boths` ds2
887 both d1@(Seq _ _) d2 = d2 `both` d1
891 %************************************************************************
893 \subsection{Miscellaneous
895 %************************************************************************
899 get_changes binds = vcat (map get_changes_bind binds)
901 get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
902 get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
904 get_changes_pr (id,rhs)
905 | isImplicitId id = empty -- We don't look inside these
906 | otherwise = get_changes_var id $$ get_changes_expr rhs
909 | isId var = get_changes_str var $$ get_changes_dmd var
912 get_changes_expr (Type t) = empty
913 get_changes_expr (Var v) = empty
914 get_changes_expr (Lit l) = empty
915 get_changes_expr (Note n e) = get_changes_expr e
916 get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
917 get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
918 get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
919 get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
921 get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
924 | new_better && old_better = empty
925 | new_better = message "BETTER"
926 | old_better = message "WORSE"
927 | otherwise = message "INCOMPARABLE"
929 message word = text word <+> text "strictness for" <+> ppr id <+> info
930 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
931 new = squashDmdEnv (idNewStrictness id) -- Don't report diffs in the env
932 old = newStrictnessFromOld id
933 old_better = old `betterStrictness` new
934 new_better = new `betterStrictness` old
937 | isUnLiftedType (idType id) = empty -- Not useful
938 | new_better && old_better = empty
939 | new_better = message "BETTER"
940 | old_better = message "WORSE"
941 | otherwise = message "INCOMPARABLE"
943 message word = text word <+> text "demand for" <+> ppr id <+> info
944 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
945 new = funArgDemand (idNewDemandInfo id) -- FunArgDemand to avoid spurious improvements
946 old = newDemand (idDemandInfo id)
947 new_better = new `betterDemand` old
948 old_better = old `betterDemand` new