2 % (c) The AQUA Project, Glasgow University, 1994-1996
4 \section[CoreUnfold]{Core-syntax unfoldings}
6 Unfoldings (which can travel across module boundaries) are in Core
7 syntax (namely @CoreExpr@s).
9 The type @Unfolding@ sits ``above'' simply-Core-expressions
10 unfoldings, capturing ``higher-level'' things we know about a binding,
11 usually things that the simplifier found out (e.g., ``it's a
12 literal''). In the corner of a @CoreUnfolding@ unfolding, you will
13 find, unsurprisingly, a Core expression.
17 Unfolding(..), UnfoldingGuidance(..), -- types
19 FormSummary(..), mkFormSummary, whnfOrBottom, exprSmallEnoughToDup,
22 noUnfolding, mkMagicUnfolding, mkUnfolding, getUnfoldingTemplate,
24 smallEnoughToInline, couldBeSmallEnoughToInline,
25 certainlySmallEnoughToInline, inlineUnconditionally,
27 calcUnfoldingGuidance,
29 PragmaInfo(..) -- Re-export
32 #include "HsVersions.h"
34 import {-# SOURCE #-} MagicUFs ( MagicUnfoldingFun, mkMagicUnfoldingFun )
36 import CmdLineOpts ( opt_UnfoldingCreationThreshold,
37 opt_UnfoldingUseThreshold,
38 opt_UnfoldingConDiscount,
39 opt_UnfoldingKeenessFactor
41 import Constants ( uNFOLDING_CHEAP_OP_COST,
42 uNFOLDING_DEAR_OP_COST,
43 uNFOLDING_NOREP_LIT_COST
45 import BinderInfo ( BinderInfo, isOneFunOcc, isOneSafeFunOcc
47 import PragmaInfo ( PragmaInfo(..) )
49 import Literal ( Literal )
50 import CoreUtils ( unTagBinders )
51 import OccurAnal ( occurAnalyseGlobalExpr )
52 import CoreUtils ( coreExprType )
53 import Id ( Id, idType, getIdArity, isBottomingId, isDataCon,
54 idWantsToBeINLINEd, idMustBeINLINEd, idMustNotBeINLINEd,
55 IdSet, GenId{-instances-} )
56 import PrimOp ( fragilePrimOp, primOpCanTriggerGC )
57 import IdInfo ( ArityInfo(..) )
58 import Literal ( isNoRepLit )
59 import TyCon ( tyConFamilySize )
60 import Type ( splitAlgTyConApp_maybe )
61 import Unique ( Unique )
62 import Util ( isIn, panic, assertPanic )
66 %************************************************************************
68 \subsection{@Unfolding@ and @UnfoldingGuidance@ types}
70 %************************************************************************
76 | OtherLit [Literal] -- It ain't one of these
77 | OtherCon [Id] -- It ain't one of these
79 | CoreUnfolding -- An unfolding with redundant cached information
80 FormSummary -- Tells whether the template is a WHNF or bottom
81 UnfoldingGuidance -- Tells about the *size* of the template.
82 SimplifiableCoreExpr -- Template
85 Unique -- Unique of the Id whose magic unfolding this is
90 noUnfolding = NoUnfolding
92 mkUnfolding inline_prag expr
94 -- strictness mangling (depends on there being no CSE)
95 ufg = calcUnfoldingGuidance inline_prag opt_UnfoldingCreationThreshold expr
96 occ = occurAnalyseGlobalExpr expr
97 cuf = CoreUnfolding (mkFormSummary expr) ufg occ
99 cont = case occ of { Var _ -> cuf; _ -> cuf }
101 case ufg of { UnfoldAlways -> cont; _ -> cont }
103 mkMagicUnfolding :: Unique -> Unfolding
104 mkMagicUnfolding tag = MagicUnfolding tag (mkMagicUnfoldingFun tag)
106 getUnfoldingTemplate :: Unfolding -> CoreExpr
107 getUnfoldingTemplate (CoreUnfolding _ _ expr)
109 getUnfoldingTemplate other = panic "getUnfoldingTemplate"
112 data UnfoldingGuidance
114 | UnfoldAlways -- There is no "original" definition,
115 -- so you'd better unfold. Or: something
116 -- so cheap to unfold (e.g., 1#) that
117 -- you should do it absolutely always.
119 | UnfoldIfGoodArgs Int -- if "m" type args
120 Int -- and "n" value args
122 [Int] -- Discount if the argument is evaluated.
123 -- (i.e., a simplification will definitely
124 -- be possible). One elt of the list per *value* arg.
126 Int -- The "size" of the unfolding; to be elaborated
129 Int -- Scrutinee discount: the discount to substract if the thing is in
130 -- a context (case (thing args) of ...),
131 -- (where there are the right number of arguments.)
135 instance Outputable UnfoldingGuidance where
136 ppr UnfoldAlways = ptext SLIT("_ALWAYS_")
137 ppr (UnfoldIfGoodArgs t v cs size discount)
138 = hsep [ptext SLIT("_IF_ARGS_"), int t, int v,
139 if null cs -- always print *something*
141 else hcat (map (text . show) cs),
147 %************************************************************************
149 \subsection{Figuring out things about expressions}
151 %************************************************************************
155 = VarForm -- Expression is a variable (or scc var, etc)
156 | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
157 | BottomForm -- Expression is guaranteed to be bottom. We're more gung
158 -- ho about inlining such things, because it can't waste work
159 | OtherForm -- Anything else
161 instance Outputable FormSummary where
162 ppr VarForm = ptext SLIT("Var")
163 ppr ValueForm = ptext SLIT("Value")
164 ppr BottomForm = ptext SLIT("Bot")
165 ppr OtherForm = ptext SLIT("Other")
167 mkFormSummary ::GenCoreExpr bndr Id flexi -> FormSummary
170 = go (0::Int) expr -- The "n" is the number of (value) arguments so far
172 go n (Lit _) = ASSERT(n==0) ValueForm
173 go n (Con _ _) = ASSERT(n==0) ValueForm
174 go n (Prim _ _) = OtherForm
175 go n (SCC _ e) = go n e
176 go n (Coerce _ _ e) = go n e
178 go n (Let (NonRec b r) e) | exprIsTrivial r = go n e -- let f = f' alpha in (f,g)
179 -- should be treated as a value
180 go n (Let _ e) = OtherForm
181 go n (Case _ _) = OtherForm
183 go 0 (Lam (ValBinder x) e) = ValueForm -- NB: \x.bottom /= bottom!
184 go n (Lam (ValBinder x) e) = go (n-1) e -- Applied lambda
185 go n (Lam other_binder e) = go n e
187 go n (App fun arg) | isValArg arg = go (n+1) fun
188 go n (App fun other_arg) = go n fun
190 go n (Var f) | isBottomingId f = BottomForm
191 | isDataCon f = ValueForm -- Can happen inside imported unfoldings
192 go 0 (Var f) = VarForm
193 go n (Var f) = case getIdArity f of
194 ArityExactly a | n < a -> ValueForm
195 ArityAtLeast a | n < a -> ValueForm
198 whnfOrBottom :: FormSummary -> Bool
199 whnfOrBottom VarForm = True
200 whnfOrBottom ValueForm = True
201 whnfOrBottom BottomForm = True
202 whnfOrBottom OtherForm = False
205 @exprIsTrivial@ is true of expressions we are unconditionally happy to duplicate;
206 simple variables and constants, and type applications.
209 exprIsTrivial (Var v) = True
210 exprIsTrivial (Lit lit) = not (isNoRepLit lit)
211 exprIsTrivial (App e (TyArg _)) = exprIsTrivial e
212 exprIsTrivial (Coerce _ _ e) = exprIsTrivial e
213 exprIsTrivial other = False
217 exprSmallEnoughToDup (Con _ _) = True -- Could check # of args
218 exprSmallEnoughToDup (Prim op _) = not (fragilePrimOp op) -- Could check # of args
219 exprSmallEnoughToDup (Lit lit) = not (isNoRepLit lit)
220 exprSmallEnoughToDup (Coerce _ _ e) = exprSmallEnoughToDup e
221 exprSmallEnoughToDup expr
222 = case (collectArgs expr) of { (fun, _, vargs) ->
224 Var v | length vargs <= 4 -> True
231 %************************************************************************
233 \subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
235 %************************************************************************
238 calcUnfoldingGuidance
239 :: PragmaInfo -- INLINE pragma stuff
240 -> Int -- bomb out if size gets bigger than this
241 -> CoreExpr -- expression to look at
244 calcUnfoldingGuidance IMustBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
245 calcUnfoldingGuidance IWantToBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
246 calcUnfoldingGuidance IMustNotBeINLINEd bOMB_OUT_SIZE expr = UnfoldNever -- ...and vice versa...
248 calcUnfoldingGuidance NoPragmaInfo bOMB_OUT_SIZE expr
249 = case collectBinders expr of { (ty_binders, val_binders, body) ->
250 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
252 TooBig -> UnfoldNever
254 SizeIs size cased_args scrut_discount
258 (map discount_for val_binders)
263 | is_data && b `is_elem` cased_args = tyConFamilySize tycon
267 = case (splitAlgTyConApp_maybe (idType b)) of
268 Nothing -> (False, panic "discount")
269 Just (tc,_,_) -> (True, tc)
271 is_elem = isIn "calcUnfoldingGuidance" }
275 sizeExpr :: Int -- Bomb out if it gets bigger than this
276 -> [Id] -- Arguments; we're interested in which of these
281 sizeExpr (I# bOMB_OUT_SIZE) args expr
284 size_up (Var v) = sizeZero
285 size_up (Lit lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
286 | otherwise = sizeZero
288 size_up (SCC lbl body) = size_up body -- SCCs cost nothing
289 size_up (Coerce _ _ body) = size_up body -- Coercions cost nothing
291 size_up (App fun arg) = size_up fun `addSize` size_up_arg arg
292 -- NB Zero cost for for type applications;
293 -- others cost 1 or more
295 size_up (Con con args) = conSizeN (numValArgs args)
296 -- We don't count 1 for the constructor because we're
297 -- quite keen to get constructors into the open
299 size_up (Prim op args) = sizeN op_cost -- NB: no charge for PrimOp args
301 op_cost = if primOpCanTriggerGC op
302 then uNFOLDING_DEAR_OP_COST
303 -- these *tend* to be more expensive;
304 -- number chosen to avoid unfolding (HACK)
305 else uNFOLDING_CHEAP_OP_COST
307 size_up expr@(Lam _ _)
309 (tyvars, args, body) = collectBinders expr
311 size_up body `addSizeN` length args
313 size_up (Let (NonRec binder rhs) body)
314 = nukeScrutDiscount (size_up rhs)
318 1 -- For the allocation
320 size_up (Let (Rec pairs) body)
321 = nukeScrutDiscount (foldr addSize sizeZero [size_up rhs | (_,rhs) <- pairs])
325 length pairs -- For the allocation
327 size_up (Case scrut alts)
328 = nukeScrutDiscount (size_up scrut)
332 size_up_alts (coreExprType scrut) alts
333 -- We charge for the "case" itself in "size_up_alts"
336 -- In an application we charge 0 for type application
337 -- 1 for most anything else
339 size_up_arg (LitArg lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
340 size_up_arg (TyArg _) = sizeZero
341 size_up_arg other = sizeOne
344 size_up_alts scrut_ty (AlgAlts alts deflt)
345 = (foldr (addSize . size_alg_alt) (size_up_deflt deflt) alts)
349 size_alg_alt (con,args,rhs) = size_up rhs
350 -- Don't charge for args, so that wrappers look cheap
352 -- NB: we charge N for an alg. "case", where N is
353 -- the number of constructors in the thing being eval'd.
354 -- (You'll eventually get a "discount" of N if you
355 -- think the "case" is likely to go away.)
356 -- It's important to charge for alternatives. If you don't then you
357 -- get size 1 for things like:
358 -- case x of { A -> 1#; B -> 2#; ... lots }
362 = case (splitAlgTyConApp_maybe scrut_ty) of
364 Just (tc,_,_) -> tyConFamilySize tc
366 size_up_alts _ (PrimAlts alts deflt)
367 = foldr (addSize . size_prim_alt) (size_up_deflt deflt) alts
368 -- *no charge* for a primitive "case"!
370 size_prim_alt (lit,rhs) = size_up rhs
373 size_up_deflt NoDefault = sizeZero
374 size_up_deflt (BindDefault binder rhs) = size_up rhs
377 -- We want to record if we're case'ing an argument
378 arg_discount (Var v) | v `is_elem` args = scrutArg v
379 arg_discount other = sizeZero
381 is_elem :: Id -> [Id] -> Bool
382 is_elem = isIn "size_up_scrut"
385 -- These addSize things have to be here because
386 -- I don't want to give them bOMB_OUT_SIZE as an argument
388 addSizeN TooBig _ = TooBig
389 addSizeN (SizeIs n xs d) (I# m)
390 | n_tot -# d <# bOMB_OUT_SIZE = SizeIs n_tot xs d
395 addSize TooBig _ = TooBig
396 addSize _ TooBig = TooBig
397 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
398 | (n_tot -# d_tot) <# bOMB_OUT_SIZE = SizeIs n_tot xys d_tot
408 Code for manipulating sizes
412 data ExprSize = TooBig
413 | SizeIs Int# -- Size found
414 [Id] -- Arguments cased herein
415 Int# -- Size to subtract if result is scrutinised
416 -- by a case expression
418 sizeZero = SizeIs 0# [] 0#
419 sizeOne = SizeIs 1# [] 0#
420 sizeN (I# n) = SizeIs n [] 0#
421 conSizeN (I# n) = SizeIs n [] n
422 scrutArg v = SizeIs 0# [v] 0#
424 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
425 nukeScrutDiscount TooBig = TooBig
428 %************************************************************************
430 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
432 %************************************************************************
434 We have very limited information about an unfolding expression: (1)~so
435 many type arguments and so many value arguments expected---for our
436 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
437 a single integer. (3)~An ``argument info'' vector. For this, what we
438 have at the moment is a Boolean per argument position that says, ``I
439 will look with great favour on an explicit constructor in this
440 position.'' (4)~The ``discount'' to subtract if the expression
441 is being scrutinised.
443 Assuming we have enough type- and value arguments (if not, we give up
444 immediately), then we see if the ``discounted size'' is below some
445 (semi-arbitrary) threshold. It works like this: for every argument
446 position where we're looking for a constructor AND WE HAVE ONE in our
447 hands, we get a (again, semi-arbitrary) discount [proportion to the
448 number of constructors in the type being scrutinized].
450 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
451 and the expression in question will evaluate to a constructor, we use
452 the computed discount size *for the result only* rather than
453 computing the argument discounts. Since we know the result of
454 the expression is going to be taken apart, discounting its size
455 is more accurate (see @sizeExpr@ above for how this discount size
459 smallEnoughToInline :: Id -- The function (for trace msg only)
460 -> [Bool] -- Evaluated-ness of value arguments
461 -> Bool -- Result is scrutinised
463 -> Bool -- True => unfold it
465 smallEnoughToInline _ _ _ UnfoldAlways = True
466 smallEnoughToInline _ _ _ UnfoldNever = False
467 smallEnoughToInline id arg_is_evald_s result_is_scruted
468 (UnfoldIfGoodArgs m_tys_wanted n_vals_wanted discount_vec size scrut_discount)
469 = if enough_args n_vals_wanted arg_is_evald_s &&
470 size - discount <= opt_UnfoldingUseThreshold
472 -- pprTrace "small enough" (ppr id <+> int size <+> int discount)
478 enough_args n [] | n > 0 = False -- A function with no value args => don't unfold
479 enough_args _ _ = True -- Otherwise it's ok to try
481 -- We multiple the raw discounts (args_discount and result_discount)
482 -- ty opt_UnfoldingKeenessFactor because the former have to do with
483 -- *size* whereas the discounts imply that there's some extra *efficiency*
484 -- to be gained (e.g. beta reductions, case reductions) by inlining.
487 opt_UnfoldingKeenessFactor *
488 fromInt (args_discount + result_discount)
491 args_discount = sum (zipWith arg_discount discount_vec arg_is_evald_s)
492 result_discount | result_is_scruted = scrut_discount
495 arg_discount no_of_constrs is_evald
496 | is_evald = no_of_constrs * opt_UnfoldingConDiscount
500 We use this one to avoid exporting inlinings that we ``couldn't possibly
501 use'' on the other side. Can be overridden w/ flaggery.
502 Just the same as smallEnoughToInline, except that it has no actual arguments.
505 couldBeSmallEnoughToInline :: Id -> UnfoldingGuidance -> Bool
506 couldBeSmallEnoughToInline id guidance = smallEnoughToInline id (repeat True) True guidance
508 certainlySmallEnoughToInline :: Id -> UnfoldingGuidance -> Bool
509 certainlySmallEnoughToInline id guidance = smallEnoughToInline id (repeat False) False guidance
515 @inlineUnconditionally@ decides whether a let-bound thing can
516 *definitely* be inlined at each of its call sites. If so, then
517 we can drop the binding right away. But remember, you have to be
518 certain that every use can be inlined. So, notably, any ArgOccs
519 rule this out. Since ManyOcc doesn't record FunOcc/ArgOcc
522 inlineUnconditionally :: Bool -> (Id,BinderInfo) -> Bool
524 inlineUnconditionally ok_to_dup (id, occ_info)
525 | idMustNotBeINLINEd id = False
527 | isOneFunOcc occ_info
528 && idMustBeINLINEd id = True
530 | isOneSafeFunOcc (ok_to_dup || idWantsToBeINLINEd id) occ_info