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, idInlinePragma,
24 isDataConWorkId, isGlobalId, idArity,
26 idDemandInfo, idStrictness, idCprInfo, idName,
28 idNewStrictness, idNewStrictness_maybe,
29 setIdNewStrictness, idNewDemandInfo,
30 idNewDemandInfo_maybe,
34 import IdInfo ( newStrictnessFromOld, newDemand )
38 import TysWiredIn ( unboxedPairDataCon )
39 import TysPrim ( realWorldStatePrimTy )
40 import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
41 keysUFM, minusUFM, ufmToList, filterUFM )
42 import Type ( isUnLiftedType, eqType )
43 import CoreLint ( showPass, endPass )
44 import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs )
45 import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
47 import Maybes ( orElse, expectJust )
53 * set a noinline pragma on bottoming Ids
55 * Consider f x = x+1 `fatbar` error (show x)
56 We'd like to unbox x, even if that means reboxing it in the error case.
59 instance Outputable TopLevelFlag where
63 %************************************************************************
65 \subsection{Top level stuff}
67 %************************************************************************
70 dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
71 dmdAnalPgm dflags binds
73 showPass dflags "Demand analysis" ;
74 let { binds_plus_dmds = do_prog binds } ;
76 endPass dflags "Demand analysis"
77 Opt_D_dump_stranal binds_plus_dmds ;
79 -- Only if OLD_STRICTNESS is on, because only then is the old
80 -- strictness analyser run
81 let { dmd_changes = get_changes binds_plus_dmds } ;
82 printDump (text "Changes in demands" $$ dmd_changes) ;
84 return binds_plus_dmds
87 do_prog :: [CoreBind] -> [CoreBind]
88 do_prog binds = snd $ mapAccumL dmdAnalTopBind emptySigEnv binds
90 dmdAnalTopBind :: SigEnv
93 dmdAnalTopBind sigs (NonRec id rhs)
95 ( _, _, (_, rhs1)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs)
96 (sigs2, _, (id2, rhs2)) = dmdAnalRhs TopLevel NonRecursive sigs (id, rhs1)
97 -- Do two passes to improve CPR information
98 -- See comments with ignore_cpr_info in mk_sig_ty
99 -- and with extendSigsWithLam
101 (sigs2, NonRec id2 rhs2)
103 dmdAnalTopBind sigs (Rec pairs)
105 (sigs', _, pairs') = dmdFix TopLevel sigs pairs
106 -- We get two iterations automatically
107 -- c.f. the NonRec case above
113 dmdAnalTopRhs :: CoreExpr -> (StrictSig, CoreExpr)
114 -- Analyse the RHS and return
115 -- a) appropriate strictness info
116 -- b) the unfolding (decorated with stricntess info)
120 arity = exprArity rhs
121 (rhs_ty, rhs') = dmdAnal emptySigEnv (vanillaCall arity) rhs
122 sig = mkTopSigTy rhs rhs_ty
125 %************************************************************************
127 \subsection{The analyser itself}
129 %************************************************************************
132 dmdAnal :: SigEnv -> Demand -> CoreExpr -> (DmdType, CoreExpr)
134 dmdAnal sigs Abs e = (topDmdType, e)
137 | not (isStrictDmd dmd)
139 (res_ty, e') = dmdAnal sigs evalDmd e
141 (deferType res_ty, e')
142 -- It's important not to analyse e with a lazy demand because
143 -- a) When we encounter case s of (a,b) ->
144 -- we demand s with U(d1d2)... but if the overall demand is lazy
145 -- that is wrong, and we'd need to reduce the demand on s,
146 -- which is inconvenient
147 -- b) More important, consider
148 -- f (let x = R in x+x), where f is lazy
149 -- We still want to mark x as demanded, because it will be when we
150 -- enter the let. If we analyse f's arg with a Lazy demand, we'll
151 -- just mark x as Lazy
152 -- c) The application rule wouldn't be right either
153 -- Evaluating (f x) in a L demand does *not* cause
154 -- evaluation of f in a C(L) demand!
157 dmdAnal sigs dmd (Lit lit)
158 = (topDmdType, Lit lit)
160 dmdAnal sigs dmd (Var var)
161 = (dmdTransform sigs var dmd, Var var)
163 dmdAnal sigs dmd (Note n e)
164 = (dmd_ty, Note n e')
166 (dmd_ty, e') = dmdAnal sigs dmd' e
168 Coerce _ _ -> evalDmd -- This coerce usually arises from a recursive
169 other -> dmd -- newtype, and we don't want to look inside them
170 -- for exactly the same reason that we don't look
171 -- inside recursive products -- we might not reach
172 -- a fixpoint. So revert to a vanilla Eval demand
174 dmdAnal sigs dmd (App fun (Type ty))
175 = (fun_ty, App fun' (Type ty))
177 (fun_ty, fun') = dmdAnal sigs dmd fun
179 -- Lots of the other code is there to make this
180 -- beautiful, compositional, application rule :-)
181 dmdAnal sigs dmd e@(App fun arg) -- Non-type arguments
182 = let -- [Type arg handled above]
183 (fun_ty, fun') = dmdAnal sigs (Call dmd) fun
184 (arg_ty, arg') = dmdAnal sigs arg_dmd arg
185 (arg_dmd, res_ty) = splitDmdTy fun_ty
187 (res_ty `bothType` arg_ty, App fun' arg')
189 dmdAnal sigs dmd (Lam var body)
192 (body_ty, body') = dmdAnal sigs dmd body
194 (body_ty, Lam var body')
196 | Call body_dmd <- dmd -- A call demand: good!
198 sigs' = extendSigsWithLam sigs var
199 (body_ty, body') = dmdAnal sigs' body_dmd body
200 (lam_ty, var') = annotateLamIdBndr body_ty var
202 (lam_ty, Lam var' body')
204 | otherwise -- Not enough demand on the lambda; but do the body
205 = let -- anyway to annotate it and gather free var info
206 (body_ty, body') = dmdAnal sigs evalDmd body
207 (lam_ty, var') = annotateLamIdBndr body_ty var
209 (deferType lam_ty, Lam var' body')
211 dmdAnal sigs dmd (Case scrut case_bndr [alt@(DataAlt dc,bndrs,rhs)])
212 | let tycon = dataConTyCon dc,
213 isProductTyCon tycon,
214 not (isRecursiveTyCon tycon)
216 sigs_alt = extendSigEnv NotTopLevel sigs case_bndr case_bndr_sig
217 (alt_ty, alt') = dmdAnalAlt sigs_alt dmd alt
218 (alt_ty1, case_bndr') = annotateBndr alt_ty case_bndr
219 (_, bndrs', _) = alt'
220 case_bndr_sig = cprSig
221 -- Inside the alternative, the case binder has the CPR property.
222 -- Meaning that a case on it will successfully cancel.
224 -- f True x = case x of y { I# x' -> if x' ==# 3 then y else I# 8 }
227 -- We want f to have the CPR property:
228 -- f b x = case fw b x of { r -> I# r }
229 -- fw True x = case x of y { I# x' -> if x' ==# 3 then x' else 8 }
232 -- Figure out whether the demand on the case binder is used, and use
233 -- that to set the scrut_dmd. This is utterly essential.
234 -- Consider f x = case x of y { (a,b) -> k y a }
235 -- If we just take scrut_demand = U(L,A), then we won't pass x to the
236 -- worker, so the worker will rebuild
237 -- x = (a, absent-error)
238 -- and that'll crash.
239 -- So at one stage I had:
240 -- dead_case_bndr = isAbsentDmd (idNewDemandInfo case_bndr')
241 -- keepity | dead_case_bndr = Drop
242 -- | otherwise = Keep
245 -- case x of y { (a,b) -> h y + a }
246 -- where h : U(LL) -> T
247 -- The above code would compute a Keep for x, since y is not Abs, which is silly
248 -- The insight is, of course, that a demand on y is a demand on the
249 -- scrutinee, so we need to `both` it with the scrut demand
251 scrut_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
253 idNewDemandInfo case_bndr'
255 (scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
257 (alt_ty1 `bothType` scrut_ty, Case scrut' case_bndr' [alt'])
259 dmdAnal sigs dmd (Case scrut case_bndr alts)
261 (alt_tys, alts') = mapAndUnzip (dmdAnalAlt sigs dmd) alts
262 (scrut_ty, scrut') = dmdAnal sigs evalDmd scrut
263 (alt_ty, case_bndr') = annotateBndr (foldr1 lubType alt_tys) case_bndr
265 -- pprTrace "dmdAnal:Case" (ppr alts $$ ppr alt_tys)
266 (alt_ty `bothType` scrut_ty, Case scrut' case_bndr' alts')
268 dmdAnal sigs dmd (Let (NonRec id rhs) body)
270 (sigs', lazy_fv, (id1, rhs')) = dmdAnalRhs NotTopLevel NonRecursive sigs (id, rhs)
271 (body_ty, body') = dmdAnal sigs' dmd body
272 (body_ty1, id2) = annotateBndr body_ty id1
273 body_ty2 = addLazyFVs body_ty1 lazy_fv
275 -- If the actual demand is better than the vanilla call
276 -- demand, you might think that we might do better to re-analyse
277 -- the RHS with the stronger demand.
278 -- But (a) That seldom happens, because it means that *every* path in
279 -- the body of the let has to use that stronger demand
280 -- (b) It often happens temporarily in when fixpointing, because
281 -- the recursive function at first seems to place a massive demand.
282 -- But we don't want to go to extra work when the function will
283 -- probably iterate to something less demanding.
284 -- In practice, all the times the actual demand on id2 is more than
285 -- the vanilla call demand seem to be due to (b). So we don't
286 -- bother to re-analyse the RHS.
287 (body_ty2, Let (NonRec id2 rhs') body')
289 dmdAnal sigs dmd (Let (Rec pairs) body)
291 bndrs = map fst pairs
292 (sigs', lazy_fv, pairs') = dmdFix NotTopLevel sigs pairs
293 (body_ty, body') = dmdAnal sigs' dmd body
294 body_ty1 = addLazyFVs body_ty lazy_fv
296 sigs' `seq` body_ty `seq`
298 (body_ty2, _) = annotateBndrs body_ty1 bndrs
299 -- Don't bother to add demand info to recursive
300 -- binders as annotateBndr does;
301 -- being recursive, we can't treat them strictly.
302 -- But we do need to remove the binders from the result demand env
304 (body_ty2, Let (Rec pairs') body')
307 dmdAnalAlt sigs dmd (con,bndrs,rhs)
309 (rhs_ty, rhs') = dmdAnal sigs dmd rhs
310 (alt_ty, bndrs') = annotateBndrs rhs_ty bndrs
311 final_alt_ty | io_hack_reqd = alt_ty `lubType` topDmdType
314 -- There's a hack here for I/O operations. Consider
315 -- case foo x s of { (# s, r #) -> y }
316 -- Is this strict in 'y'. Normally yes, but what if 'foo' is an I/O
317 -- operation that simply terminates the program (not in an erroneous way)?
318 -- In that case we should not evaluate y before the call to 'foo'.
319 -- Hackish solution: spot the IO-like situation and add a virtual branch,
323 -- other -> return ()
324 -- So the 'y' isn't necessarily going to be evaluated
326 -- A more complete example where this shows up is:
327 -- do { let len = <expensive> ;
328 -- ; when (...) (exitWith ExitSuccess)
331 io_hack_reqd = con == DataAlt unboxedPairDataCon &&
332 idType (head bndrs) `eqType` realWorldStatePrimTy
334 (final_alt_ty, (con, bndrs', rhs'))
337 %************************************************************************
339 \subsection{Bindings}
341 %************************************************************************
344 dmdFix :: TopLevelFlag
345 -> SigEnv -- Does not include bindings for this binding
348 [(Id,CoreExpr)]) -- Binders annotated with stricness info
350 dmdFix top_lvl sigs orig_pairs
351 = loop 1 initial_sigs orig_pairs
353 bndrs = map fst orig_pairs
354 initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs]
357 -> SigEnv -- Already contains the current sigs
359 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
362 = (sigs', lazy_fv, pairs')
363 -- Note: use pairs', not pairs. pairs' is the result of
364 -- processing the RHSs with sigs (= sigs'), whereas pairs
365 -- is the result of processing the RHSs with the *previous*
366 -- iteration of sigs.
368 | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
369 [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
370 text "env:" <+> ppr (ufmToList sigs),
371 text "binds:" <+> pprCoreBinding (Rec pairs)]))
372 (emptySigEnv, lazy_fv, orig_pairs) -- Safe output
373 -- The lazy_fv part is really important! orig_pairs has no strictness
374 -- info, including nothing about free vars. But if we have
375 -- letrec f = ....y..... in ...f...
376 -- where 'y' is free in f, we must record that y is mentioned,
377 -- otherwise y will get recorded as absent altogether
379 | otherwise = loop (n+1) sigs' pairs'
381 found_fixpoint = all (same_sig sigs sigs') bndrs
382 -- Use the new signature to do the next pair
383 -- The occurrence analyser has arranged them in a good order
384 -- so this can significantly reduce the number of iterations needed
385 ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
387 my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
388 = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
390 -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
391 ((sigs', lazy_fv'), pair')
394 (sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive sigs (id,rhs)
395 lazy_fv' = plusUFM_C both lazy_fv lazy_fv1
396 -- old_sig = lookup sigs id
397 -- new_sig = lookup sigs' id
399 same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
400 lookup sigs var = case lookupVarEnv sigs var of
403 -- Get an initial strictness signature from the Id
404 -- itself. That way we make use of earlier iterations
405 -- of the fixpoint algorithm. (Cunning plan.)
406 -- Note that the cunning plan extends to the DmdEnv too,
407 -- since it is part of the strictness signature
408 initialSig id = idNewStrictness_maybe id `orElse` botSig
410 dmdAnalRhs :: TopLevelFlag -> RecFlag
411 -> SigEnv -> (Id, CoreExpr)
412 -> (SigEnv, DmdEnv, (Id, CoreExpr))
413 -- Process the RHS of the binding, add the strictness signature
414 -- to the Id, and augment the environment with the signature as well.
416 dmdAnalRhs top_lvl rec_flag sigs (id, rhs)
417 = (sigs', lazy_fv, (id', rhs'))
419 arity = idArity id -- The idArity should be up to date
420 -- The simplifier was run just beforehand
421 (rhs_dmd_ty, rhs') = dmdAnal sigs (vanillaCall arity) rhs
422 (lazy_fv, sig_ty) = WARN( arity /= dmdTypeDepth rhs_dmd_ty, ppr id )
423 mkSigTy top_lvl rec_flag id rhs rhs_dmd_ty
424 id' = id `setIdNewStrictness` sig_ty
425 sigs' = extendSigEnv top_lvl sigs id sig_ty
428 %************************************************************************
430 \subsection{Strictness signatures and types}
432 %************************************************************************
435 mkTopSigTy :: CoreExpr -> DmdType -> StrictSig
436 -- Take a DmdType and turn it into a StrictSig
437 -- NB: not used for never-inline things; hence False
438 mkTopSigTy rhs dmd_ty = snd (mk_sig_ty False False rhs dmd_ty)
440 mkSigTy :: TopLevelFlag -> RecFlag -> Id -> CoreExpr -> DmdType -> (DmdEnv, StrictSig)
441 mkSigTy top_lvl rec_flag id rhs dmd_ty
442 = mk_sig_ty never_inline thunk_cpr_ok rhs dmd_ty
444 never_inline = isNeverActive (idInlinePragma id)
445 maybe_id_dmd = idNewDemandInfo_maybe id
446 -- Is Nothing the first time round
449 | isTopLevel top_lvl = False -- Top level things don't get
450 -- their demandInfo set at all
451 | isRec rec_flag = False -- Ditto recursive things
452 | Just dmd <- maybe_id_dmd = isStrictDmd dmd
453 | otherwise = True -- Optimistic, first time round
457 The thunk_cpr_ok stuff [CPR-AND-STRICTNESS]
458 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
459 If the rhs is a thunk, we usually forget the CPR info, because
460 it is presumably shared (else it would have been inlined, and
461 so we'd lose sharing if w/w'd it into a function.
463 However, if the strictness analyser has figured out (in a previous
464 iteration) that it's strict, then we DON'T need to forget the CPR info.
465 Instead we can retain the CPR info and do the thunk-splitting transform
466 (see WorkWrap.splitThunk).
468 This made a big difference to PrelBase.modInt, which had something like
469 modInt = \ x -> let r = ... -> I# v in
470 ...body strict in r...
471 r's RHS isn't a value yet; but modInt returns r in various branches, so
472 if r doesn't have the CPR property then neither does modInt
473 Another case I found in practice (in Complex.magnitude), looks like this:
474 let k = if ... then I# a else I# b
475 in ... body strict in k ....
476 (For this example, it doesn't matter whether k is returned as part of
477 the overall result; but it does matter that k's RHS has the CPR property.)
478 Left to itself, the simplifier will make a join point thus:
479 let $j k = ...body strict in k...
480 if ... then $j (I# a) else $j (I# b)
481 With thunk-splitting, we get instead
482 let $j x = let k = I#x in ...body strict in k...
483 in if ... then $j a else $j b
484 This is much better; there's a good chance the I# won't get allocated.
486 The difficulty with this is that we need the strictness type to
487 look at the body... but we now need the body to calculate the demand
488 on the variable, so we can decide whether its strictness type should
489 have a CPR in it or not. Simple solution:
490 a) use strictness info from the previous iteration
491 b) make sure we do at least 2 iterations, by doing a second
492 round for top-level non-recs. Top level recs will get at
493 least 2 iterations except for totally-bottom functions
494 which aren't very interesting anyway.
496 NB: strictly_demanded is never true of a top-level Id, or of a recursive Id.
498 The Nothing case in thunk_cpr_ok [CPR-AND-STRICTNESS]
499 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
500 Demand info now has a 'Nothing' state, just like strictness info.
501 The analysis works from 'dangerous' towards a 'safe' state; so we
502 start with botSig for 'Nothing' strictness infos, and we start with
503 "yes, it's demanded" for 'Nothing' in the demand info. The
504 fixpoint iteration will sort it all out.
506 We can't start with 'not-demanded' because then consider
510 if ... then t else I# y else f x'
512 In the first iteration we'd have no demand info for x, so assume
513 not-demanded; then we'd get TopRes for f's CPR info. Next iteration
514 we'd see that t was demanded, and so give it the CPR property, but by
515 now f has TopRes, so it will stay TopRes. Instead, with the Nothing
516 setting the first time round, we say 'yes t is demanded' the first
519 However, this does mean that for non-recursive bindings we must
520 iterate twice to be sure of not getting over-optimistic CPR info,
521 in the case where t turns out to be not-demanded. This is handled
526 mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res)
527 | never_inline && not (isBotRes res)
529 -- Don't strictness-analyse NOINLINE things. Why not? Because
530 -- the NOINLINE says "don't expose any of the inner workings at the call
531 -- site" and the strictness is certainly an inner working.
533 -- More concretely, the demand analyser discovers the following strictness
534 -- for unsafePerformIO: C(U(AV))
536 -- unsafePerformIO (\s -> let r = f x in
537 -- case writeIORef v r s of (# s1, _ #) ->
539 -- The strictness analyser will find that the binding for r is strict,
540 -- (becuase of uPIO's strictness sig), and so it'll evaluate it before
541 -- doing the writeIORef. This actually makes tests/lib/should_run/memo002
544 -- Solution: don't expose the strictness of unsafePerformIO.
546 -- But we do want to expose the strictness of error functions,
547 -- which are also often marked NOINLINE
548 -- {-# NOINLINE foo #-}
549 -- foo x = error ("wubble buggle" ++ x)
550 -- So (hack, hack) we only drop the strictness for non-bottom things
551 -- This is all very unsatisfactory.
552 = (deferEnv fv, topSig)
555 = (lazy_fv, mkStrictSig dmd_ty)
557 dmd_ty = DmdType strict_fv final_dmds res'
559 lazy_fv = filterUFM (not . isStrictDmd) fv
560 strict_fv = filterUFM isStrictDmd fv
561 -- We put the strict FVs in the DmdType of the Id, so
562 -- that at its call sites we unleash demands on its strict fvs.
563 -- An example is 'roll' in imaginary/wheel-sieve2
564 -- Something like this:
566 -- go y = if ... then roll (x-1) else x+1
569 -- We want to see that roll is strict in x, which is because
570 -- go is called. So we put the DmdEnv for x in go's DmdType.
573 -- f :: Int -> Int -> Int
574 -- f x y = let t = x+1
575 -- h z = if z==0 then t else
576 -- if z==1 then x+1 else
580 -- Calling h does indeed evaluate x, but we can only see
581 -- that if we unleash a demand on x at the call site for t.
583 -- Incidentally, here's a place where lambda-lifting h would
584 -- lose the cigar --- we couldn't see the joint strictness in t/x
587 -- We don't want to put *all* the fv's from the RHS into the
588 -- DmdType, because that makes fixpointing very slow --- the
589 -- DmdType gets full of lazy demands that are slow to converge.
591 final_dmds = setUnpackStrategy dmds
592 -- Set the unpacking strategy
595 RetCPR | ignore_cpr_info -> TopRes
597 ignore_cpr_info = not (exprIsValue rhs || thunk_cpr_ok)
600 The unpack strategy determines whether we'll *really* unpack the argument,
601 or whether we'll just remember its strictness. If unpacking would give
602 rise to a *lot* of worker args, we may decide not to unpack after all.
605 setUnpackStrategy :: [Demand] -> [Demand]
607 = snd (go (opt_MaxWorkerArgs - nonAbsentArgs ds) ds)
609 go :: Int -- Max number of args available for sub-components of [Demand]
611 -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
613 go n (Eval (Prod cs) : ds)
614 | n' >= 0 = Eval (Prod cs') `cons` go n'' ds
615 | otherwise = Box (Eval (Prod cs)) `cons` go n ds
618 n' = n + 1 - non_abs_args
619 -- Add one to the budget 'cos we drop the top-level arg
620 non_abs_args = nonAbsentArgs cs
621 -- Delete # of non-absent args to which we'll now be committed
623 go n (d:ds) = d `cons` go n ds
626 cons d (n,ds) = (n, d:ds)
628 nonAbsentArgs :: [Demand] -> Int
630 nonAbsentArgs (Abs : ds) = nonAbsentArgs ds
631 nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
635 %************************************************************************
637 \subsection{Strictness signatures and types}
639 %************************************************************************
642 splitDmdTy :: DmdType -> (Demand, DmdType)
643 -- Split off one function argument
644 -- We already have a suitable demand on all
645 -- free vars, so no need to add more!
646 splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
647 splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty)
651 unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
653 addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
654 | isTopLevel top_lvl = dmd_ty -- Don't record top level things
655 | otherwise = DmdType (extendVarEnv fv var dmd) ds res
657 addLazyFVs (DmdType fv ds res) lazy_fvs
658 = DmdType both_fv1 ds res
660 both_fv = (plusUFM_C both fv lazy_fvs)
661 both_fv1 = modifyEnv (isBotRes res) (`both` Bot) lazy_fvs fv both_fv
662 -- This modifyEnv is vital. Consider
663 -- let f = \x -> (x,y)
665 -- Here, y is treated as a lazy-fv of f, but we must `both` that L
666 -- demand with the bottom coming up from 'error'
668 -- I got a loop in the fixpointer without this, due to an interaction
669 -- with the lazy_fv filtering in mkSigTy. Roughly, it was
671 -- = letrec g y = x `fatbar`
672 -- letrec h z = z + ...g...
675 -- In the initial iteration for f, f=Bot
676 -- Suppose h is found to be strict in z, but the occurrence of g in its RHS
677 -- is lazy. Now consider the fixpoint iteration for g, esp the demands it
678 -- places on its free variables. Suppose it places none. Then the
679 -- x `fatbar` ...call to h...
680 -- will give a x->V demand for x. That turns into a L demand for x,
681 -- which floats out of the defn for h. Without the modifyEnv, that
682 -- L demand doesn't get both'd with the Bot coming up from the inner
683 -- call to f. So we just get an L demand for x for g.
685 -- A better way to say this is that the lazy-fv filtering should give the
686 -- same answer as putting the lazy fv demands in the function's type.
688 annotateBndr :: DmdType -> Var -> (DmdType, Var)
689 -- The returned env has the var deleted
690 -- The returned var is annotated with demand info
691 -- No effect on the argument demands
692 annotateBndr dmd_ty@(DmdType fv ds res) var
693 | isTyVar var = (dmd_ty, var)
694 | otherwise = (DmdType fv' ds res, setIdNewDemandInfo var dmd)
696 (fv', dmd) = removeFV fv var res
698 annotateBndrs = mapAccumR annotateBndr
700 annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
701 -- For lambdas we add the demand to the argument demands
702 -- Only called for Ids
704 (DmdType fv' (hacked_dmd:ds) res, setIdNewDemandInfo id hacked_dmd)
706 (fv', dmd) = removeFV fv id res
707 hacked_dmd = argDemand dmd
708 -- This call to argDemand is vital, because otherwise we label
709 -- a lambda binder with demand 'B'. But in terms of calling
710 -- conventions that's Abs, because we don't pass it. But
711 -- when we do a w/w split we get
712 -- fw x = (\x y:B -> ...) x (error "oops")
713 -- And then the simplifier things the 'B' is a strict demand
714 -- and evaluates the (error "oops"). Sigh
716 removeFV fv id res = (fv', zapUnlifted id dmd)
718 fv' = fv `delVarEnv` id
719 dmd = lookupVarEnv fv id `orElse` deflt
720 deflt | isBotRes res = Bot
723 -- For unlifted-type variables, we are only
724 -- interested in Bot/Abs/Box Abs
725 zapUnlifted is Bot = Bot
726 zapUnlifted id Abs = Abs
727 zapUnlifted id dmd | isUnLiftedType (idType id) = lazyDmd
731 %************************************************************************
733 \subsection{Strictness signatures}
735 %************************************************************************
738 type SigEnv = VarEnv (StrictSig, TopLevelFlag)
739 -- We use the SigEnv to tell us whether to
740 -- record info about a variable in the DmdEnv
741 -- We do so if it's a LocalId, but not top-level
743 -- The DmdEnv gives the demand on the free vars of the function
744 -- when it is given enough args to satisfy the strictness signature
746 emptySigEnv = emptyVarEnv
748 extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
749 extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
751 extendSigEnvList = extendVarEnvList
753 extendSigsWithLam :: SigEnv -> Id -> SigEnv
754 -- Extend the SigEnv when we meet a lambda binder
755 -- If the binder is marked demanded with a product demand, then give it a CPR
756 -- signature, because in the likely event that this is a lambda on a fn defn
757 -- [we only use this when the lambda is being consumed with a call demand],
758 -- it'll be w/w'd and so it will be CPR-ish. E.g.
759 -- f = \x::(Int,Int). if ...strict in x... then
763 -- We want f to have the CPR property because x does, by the time f has been w/w'd
765 -- NOTE: see notes [CPR-AND-STRICTNESS]
767 -- Also note that we only want to do this for something that
768 -- definitely has product type, else we may get over-optimistic
769 -- CPR results (e.g. from \x -> x!).
771 extendSigsWithLam sigs id
772 = case idNewDemandInfo_maybe id of
773 Nothing -> extendVarEnv sigs id (cprSig, NotTopLevel)
774 Just (Eval (Prod ds)) -> extendVarEnv sigs id (cprSig, NotTopLevel)
778 dmdTransform :: SigEnv -- The strictness environment
779 -> Id -- The function
780 -> Demand -- The demand on the function
781 -> DmdType -- The demand type of the function in this context
782 -- Returned DmdEnv includes the demand on
783 -- this function plus demand on its free variables
785 dmdTransform sigs var dmd
787 ------ DATA CONSTRUCTOR
788 | isDataConWorkId var -- Data constructor
790 StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
791 DmdType _ _ con_res = dmd_ty
794 if arity == call_depth then -- Saturated, so unleash the demand
796 -- Important! If we Keep the constructor application, then
797 -- we need the demands the constructor places (always lazy)
798 -- If not, we don't need to. For example:
799 -- f p@(x,y) = (p,y) -- S(AL)
801 -- It's vital that we don't calculate Absent for a!
802 dmd_ds = case res_dmd of
803 Box (Eval ds) -> mapDmds box ds
807 -- ds can be empty, when we are just seq'ing the thing
808 -- If so we must make up a suitable bunch of demands
809 arg_ds = case dmd_ds of
810 Poly d -> replicate arity d
811 Prod ds -> ASSERT( ds `lengthIs` arity ) ds
814 mkDmdType emptyDmdEnv arg_ds con_res
815 -- Must remember whether it's a product, hence con_res, not TopRes
819 ------ IMPORTED FUNCTION
820 | isGlobalId var, -- Imported function
821 let StrictSig dmd_ty = idNewStrictness var
822 = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
827 ------ LOCAL LET/REC BOUND THING
828 | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
830 fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
831 | otherwise = deferType dmd_ty
832 -- NB: it's important to use deferType, and not just return topDmdType
833 -- Consider let { f x y = p + x } in f 1
834 -- The application isn't saturated, but we must nevertheless propagate
835 -- a lazy demand for p!
837 addVarDmd top_lvl fn_ty var dmd
839 ------ LOCAL NON-LET/REC BOUND THING
840 | otherwise -- Default case
844 (call_depth, res_dmd) = splitCallDmd dmd
848 %************************************************************************
852 %************************************************************************
855 splitCallDmd :: Demand -> (Int, Demand)
856 splitCallDmd (Call d) = case splitCallDmd d of
858 splitCallDmd d = (0, d)
860 vanillaCall :: Arity -> Demand
861 vanillaCall 0 = evalDmd
862 vanillaCall n = Call (vanillaCall (n-1))
864 deferType :: DmdType -> DmdType
865 deferType (DmdType fv _ _) = DmdType (deferEnv fv) [] TopRes
866 -- Notice that we throw away info about both arguments and results
867 -- For example, f = let ... in \x -> x
868 -- We don't want to get a stricness type V->T for f.
871 deferEnv :: DmdEnv -> DmdEnv
872 deferEnv fv = mapVarEnv defer fv
876 argDemand :: Demand -> Demand
877 -- The 'Defer' demands are just Lazy at function boundaries
878 -- Ugly! Ask John how to improve it.
879 argDemand Top = lazyDmd
880 argDemand (Defer d) = lazyDmd
881 argDemand (Eval ds) = Eval (mapDmds argDemand ds)
882 argDemand (Box Bot) = evalDmd
883 argDemand (Box d) = box (argDemand d)
884 argDemand Bot = Abs -- Don't pass args that are consumed (only) by bottom
889 betterStrictness :: StrictSig -> StrictSig -> Bool
890 betterStrictness (StrictSig t1) (StrictSig t2) = betterDmdType t1 t2
892 betterDmdType t1 t2 = (t1 `lubType` t2) == t2
894 betterDemand :: Demand -> Demand -> Bool
895 -- If d1 `better` d2, and d2 `better` d2, then d1==d2
896 betterDemand d1 d2 = (d1 `lub` d2) == d2
900 -------------------------
901 -- Consider (if x then y else []) with demand V
902 -- Then the first branch gives {y->V} and the second
903 -- *implicitly* has {y->A}. So we must put {y->(V `lub` A)}
904 -- in the result env.
905 lubType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
906 = DmdType lub_fv2 (lub_ds ds1 ds2) (r1 `lubRes` r2)
908 lub_fv = plusUFM_C lub fv1 fv2
909 lub_fv1 = modifyEnv (not (isBotRes r1)) absLub fv2 fv1 lub_fv
910 lub_fv2 = modifyEnv (not (isBotRes r2)) absLub fv1 fv2 lub_fv1
911 -- lub is the identity for Bot
913 -- Extend the shorter argument list to match the longer
914 lub_ds (d1:ds1) (d2:ds2) = lub d1 d2 : lub_ds ds1 ds2
916 lub_ds ds1 [] = map (`lub` resTypeArgDmd r2) ds1
917 lub_ds [] ds2 = map (resTypeArgDmd r1 `lub`) ds2
919 -----------------------------------
920 -- (t1 `bothType` t2) takes the argument/result info from t1,
921 -- using t2 just for its free-var info
922 -- NB: Don't forget about r2! It might be BotRes, which is
923 -- a bottom demand on all the in-scope variables.
924 -- Peter: can this be done more neatly?
925 bothType (DmdType fv1 ds1 r1) (DmdType fv2 ds2 r2)
926 = DmdType both_fv2 ds1 (r1 `bothRes` r2)
928 both_fv = plusUFM_C both fv1 fv2
929 both_fv1 = modifyEnv (isBotRes r1) (`both` Bot) fv2 fv1 both_fv
930 both_fv2 = modifyEnv (isBotRes r2) (`both` Bot) fv1 fv2 both_fv1
931 -- both is the identity for Abs
938 lubRes RetCPR RetCPR = RetCPR
939 lubRes r1 r2 = TopRes
941 -- If either diverges, the whole thing does
942 -- Otherwise take CPR info from the first
943 bothRes r1 BotRes = BotRes
948 modifyEnv :: Bool -- No-op if False
949 -> (Demand -> Demand) -- The zapper
950 -> DmdEnv -> DmdEnv -- Env1 and Env2
951 -> DmdEnv -> DmdEnv -- Transform this env
952 -- Zap anything in Env1 but not in Env2
953 -- Assume: dom(env) includes dom(Env1) and dom(Env2)
955 modifyEnv need_to_modify zapper env1 env2 env
956 | need_to_modify = foldr zap env (keysUFM (env1 `minusUFM` env2))
959 zap uniq env = addToUFM_Directly env uniq (zapper current_val)
961 current_val = expectJust "modifyEnv" (lookupUFM_Directly env uniq)
965 %************************************************************************
967 \subsection{LUB and BOTH}
969 %************************************************************************
972 lub :: Demand -> Demand -> Demand
975 lub Abs d2 = absLub d2
977 lub (Defer ds1) d2 = defer (Eval ds1 `lub` d2)
979 lub (Call d1) (Call d2) = Call (d1 `lub` d2)
980 lub d1@(Call _) (Box d2) = d1 `lub` d2 -- Just strip the box
981 lub d1@(Call _) d2@(Eval _) = d2 -- Presumably seq or vanilla eval
982 lub d1@(Call _) d2 = d2 `lub` d1 -- Bot, Abs, Top
984 -- For the Eval case, we use these approximation rules
985 -- Box Bot <= Eval (Box Bot ...)
986 -- Box Top <= Defer (Box Bot ...)
987 -- Box (Eval ds) <= Eval (map Box ds)
988 lub (Eval ds1) (Eval ds2) = Eval (ds1 `lubs` ds2)
989 lub (Eval ds1) (Box Bot) = Eval (mapDmds (`lub` Box Bot) ds1)
990 lub (Eval ds1) (Box (Eval ds2)) = Eval (ds1 `lubs` mapDmds box ds2)
991 lub (Eval ds1) (Box Abs) = deferEval (mapDmds (`lub` Box Bot) ds1)
992 lub d1@(Eval _) d2 = d2 `lub` d1 -- Bot,Abs,Top,Call,Defer
994 lub (Box d1) (Box d2) = box (d1 `lub` d2)
995 lub d1@(Box _) d2 = d2 `lub` d1
997 lubs = zipWithDmds lub
999 ---------------------
1000 -- box is the smart constructor for Box
1001 -- It computes <B,bot> & d
1002 -- INVARIANT: (Box d) => d = Bot, Abs, Eval
1003 -- Seems to be no point in allowing (Box (Call d))
1004 box (Call d) = Call d -- The odd man out. Why?
1006 box (Defer _) = lazyDmd
1007 box Top = lazyDmd -- Box Abs and Box Top
1008 box Abs = lazyDmd -- are the same <B,L>
1009 box d = Box d -- Bot, Eval
1012 defer :: Demand -> Demand
1014 -- defer is the smart constructor for Defer
1015 -- The idea is that (Defer ds) = <U(ds), L>
1017 -- It specifies what happens at a lazy function argument
1018 -- or a lambda; the L* operator
1019 -- Set the strictness part to L, but leave
1020 -- the boxity side unaffected
1021 -- It also ensures that Defer (Eval [LLLL]) = L
1026 defer (Call _) = lazyDmd -- Approximation here?
1027 defer (Box _) = lazyDmd
1028 defer (Defer ds) = Defer ds
1029 defer (Eval ds) = deferEval ds
1031 -- deferEval ds = defer (Eval ds)
1032 deferEval ds | allTop ds = Top
1033 | otherwise = Defer ds
1035 ---------------------
1036 absLub :: Demand -> Demand
1037 -- Computes (Abs `lub` d)
1038 -- For the Bot case consider
1039 -- f x y = if ... then x else error x
1040 -- Then for y we get Abs `lub` Bot, and we really
1045 absLub (Call _) = Top
1046 absLub (Box _) = Top
1047 absLub (Eval ds) = Defer (absLubs ds) -- Or (Defer ds)?
1048 absLub (Defer ds) = Defer (absLubs ds) -- Or (Defer ds)?
1050 absLubs = mapDmds absLub
1053 both :: Demand -> Demand -> Demand
1059 both Bot (Eval ds) = Eval (mapDmds (`both` Bot) ds)
1062 -- From 'error' itself we get demand Bot on x
1063 -- From the arg demand on x we get
1064 -- x :-> evalDmd = Box (Eval (Poly Abs))
1065 -- So we get Bot `both` Box (Eval (Poly Abs))
1066 -- = Seq Keep (Poly Bot)
1069 -- f x = if ... then error (fst x) else fst x
1070 -- Then we get (Eval (Box Bot, Bot) `lub` Eval (SA))
1072 -- which is what we want.
1075 both Top Bot = errDmd
1078 both Top (Box d) = Box d
1079 both Top (Call d) = Call d
1080 both Top (Eval ds) = Eval (mapDmds (`both` Top) ds)
1081 both Top (Defer ds) -- = defer (Top `both` Eval ds)
1082 -- = defer (Eval (mapDmds (`both` Top) ds))
1083 = deferEval (mapDmds (`both` Top) ds)
1086 both (Box d1) (Box d2) = box (d1 `both` d2)
1087 both (Box d1) d2@(Call _) = box (d1 `both` d2)
1088 both (Box d1) d2@(Eval _) = box (d1 `both` d2)
1089 both (Box d1) (Defer d2) = Box d1
1090 both d1@(Box _) d2 = d2 `both` d1
1092 both (Call d1) (Call d2) = Call (d1 `both` d2)
1093 both (Call d1) (Eval ds2) = Call d1 -- Could do better for (Poly Bot)?
1094 both (Call d1) (Defer ds2) = Call d1 -- Ditto
1095 both d1@(Call _) d2 = d1 `both` d1
1097 both (Eval ds1) (Eval ds2) = Eval (ds1 `boths` ds2)
1098 both (Eval ds1) (Defer ds2) = Eval (ds1 `boths` mapDmds defer ds2)
1099 both d1@(Eval ds1) d2 = d2 `both` d1
1101 both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2)
1102 both d1@(Defer ds1) d2 = d2 `both` d1
1104 boths = zipWithDmds both
1109 %************************************************************************
1111 \subsection{Miscellaneous
1113 %************************************************************************
1117 #ifdef OLD_STRICTNESS
1118 get_changes binds = vcat (map get_changes_bind binds)
1120 get_changes_bind (Rec pairs) = vcat (map get_changes_pr pairs)
1121 get_changes_bind (NonRec id rhs) = get_changes_pr (id,rhs)
1123 get_changes_pr (id,rhs)
1124 = get_changes_var id $$ get_changes_expr rhs
1127 | isId var = get_changes_str var $$ get_changes_dmd var
1130 get_changes_expr (Type t) = empty
1131 get_changes_expr (Var v) = empty
1132 get_changes_expr (Lit l) = empty
1133 get_changes_expr (Note n e) = get_changes_expr e
1134 get_changes_expr (App e1 e2) = get_changes_expr e1 $$ get_changes_expr e2
1135 get_changes_expr (Lam b e) = {- get_changes_var b $$ -} get_changes_expr e
1136 get_changes_expr (Let b e) = get_changes_bind b $$ get_changes_expr e
1137 get_changes_expr (Case e b a) = get_changes_expr e $$ {- get_changes_var b $$ -} vcat (map get_changes_alt a)
1139 get_changes_alt (con,bs,rhs) = {- vcat (map get_changes_var bs) $$ -} get_changes_expr rhs
1142 | new_better && old_better = empty
1143 | new_better = message "BETTER"
1144 | old_better = message "WORSE"
1145 | otherwise = message "INCOMPARABLE"
1147 message word = text word <+> text "strictness for" <+> ppr id <+> info
1148 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
1149 new = squashSig (idNewStrictness id) -- Don't report spurious diffs that the old
1150 -- strictness analyser can't track
1151 old = newStrictnessFromOld (idName id) (idArity id) (idStrictness id) (idCprInfo id)
1152 old_better = old `betterStrictness` new
1153 new_better = new `betterStrictness` old
1156 | isUnLiftedType (idType id) = empty -- Not useful
1157 | new_better && old_better = empty
1158 | new_better = message "BETTER"
1159 | old_better = message "WORSE"
1160 | otherwise = message "INCOMPARABLE"
1162 message word = text word <+> text "demand for" <+> ppr id <+> info
1163 info = (text "Old" <+> ppr old) $$ (text "New" <+> ppr new)
1164 new = squashDmd (argDemand (idNewDemandInfo id)) -- To avoid spurious improvements
1166 old = newDemand (idDemandInfo id)
1167 new_better = new `betterDemand` old
1168 old_better = old `betterDemand` new
1171 squashSig (StrictSig (DmdType fv ds res))
1172 = StrictSig (DmdType emptyDmdEnv (map squashDmd ds) res)
1174 -- squash just gets rid of call demands
1175 -- which the old analyser doesn't track
1176 squashDmd (Call d) = evalDmd
1177 squashDmd (Box d) = Box (squashDmd d)
1178 squashDmd (Eval ds) = Eval (mapDmds squashDmd ds)
1179 squashDmd (Defer ds) = Defer (mapDmds squashDmd ds)