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 @SimpleUnfolding@ unfolding, you will
13 find, unsurprisingly, a Core expression.
16 #include "HsVersions.h"
19 SimpleUnfolding(..), Unfolding(..), UnfoldingGuidance(..), -- types
20 UfExpr, RdrName, -- For closure (delete in 1.3)
22 FormSummary(..), mkFormSummary, whnfOrBottom, exprSmallEnoughToDup, exprIsTrivial,
24 noUnfolding, mkMagicUnfolding, mkUnfolding, getUnfoldingTemplate,
26 smallEnoughToInline, couldBeSmallEnoughToInline, certainlySmallEnoughToInline,
29 calcUnfoldingGuidance,
31 PragmaInfo(..) -- Re-export
35 IMPORT_DELOOPER(IdLoop) -- for paranoia checking;
36 -- and also to get mkMagicUnfoldingFun
37 IMPORT_DELOOPER(PrelLoop) -- for paranoia checking
38 IMPORT_DELOOPER(SmplLoop)
40 import Bag ( emptyBag, unitBag, unionBags, Bag )
42 import CmdLineOpts ( opt_UnfoldingCreationThreshold,
43 opt_UnfoldingUseThreshold,
44 opt_UnfoldingConDiscount
46 import Constants ( uNFOLDING_CHEAP_OP_COST,
47 uNFOLDING_DEAR_OP_COST,
48 uNFOLDING_NOREP_LIT_COST
50 import BinderInfo ( BinderInfo(..), FunOrArg, DuplicationDanger, InsideSCC, isDupDanger )
51 import PragmaInfo ( PragmaInfo(..) )
53 import CoreUtils ( unTagBinders )
54 import HsCore ( UfExpr )
55 import RdrHsSyn ( RdrName )
56 import OccurAnal ( occurAnalyseGlobalExpr )
57 import CoreUtils ( coreExprType )
58 --import CostCentre ( ccMentionsId )
59 import Id ( idType, getIdArity, isBottomingId, isDataCon, isPrimitiveId_maybe,
60 SYN_IE(IdSet), GenId{-instances-} )
61 import PrimOp ( primOpCanTriggerGC, fragilePrimOp, PrimOp(..) )
62 import IdInfo ( ArityInfo(..), bottomIsGuaranteed )
63 import Literal ( isNoRepLit, isLitLitLit )
65 import TyCon ( tyConFamilySize )
66 import Type ( maybeAppDataTyConExpandingDicts )
67 import Unique ( Unique )
68 import UniqSet ( emptyUniqSet, unitUniqSet, mkUniqSet,
69 addOneToUniqSet, unionUniqSets
71 import Usage ( SYN_IE(UVar) )
72 import Maybes ( maybeToBool )
73 import Util ( isIn, panic, assertPanic )
74 #if __GLASGOW_HASKELL__ >= 202
80 %************************************************************************
82 \subsection{@Unfolding@ and @UnfoldingGuidance@ types}
84 %************************************************************************
90 | CoreUnfolding SimpleUnfolding
93 Unique -- Unique of the Id whose magic unfolding this is
98 = SimpleUnfolding -- An unfolding with redundant cached information
99 FormSummary -- Tells whether the template is a WHNF or bottom
100 UnfoldingGuidance -- Tells about the *size* of the template.
101 SimplifiableCoreExpr -- Template
104 noUnfolding = NoUnfolding
106 mkUnfolding inline_prag expr
108 -- strictness mangling (depends on there being no CSE)
109 ufg = calcUnfoldingGuidance inline_prag opt_UnfoldingCreationThreshold expr
110 occ = occurAnalyseGlobalExpr expr
111 cuf = CoreUnfolding (SimpleUnfolding (mkFormSummary expr) ufg occ)
113 cont = case occ of { Var _ -> cuf; _ -> cuf }
115 case ufg of { UnfoldAlways -> cont; _ -> cont }
117 mkMagicUnfolding :: Unique -> Unfolding
118 mkMagicUnfolding tag = MagicUnfolding tag (mkMagicUnfoldingFun tag)
120 getUnfoldingTemplate :: Unfolding -> CoreExpr
121 getUnfoldingTemplate (CoreUnfolding (SimpleUnfolding _ _ expr))
123 getUnfoldingTemplate other = panic "getUnfoldingTemplate"
126 data UnfoldingGuidance
128 | UnfoldAlways -- There is no "original" definition,
129 -- so you'd better unfold. Or: something
130 -- so cheap to unfold (e.g., 1#) that
131 -- you should do it absolutely always.
133 | UnfoldIfGoodArgs Int -- if "m" type args
134 Int -- and "n" value args
136 [Int] -- Discount if the argument is evaluated.
137 -- (i.e., a simplification will definitely
138 -- be possible). One elt of the list per *value* arg.
140 Int -- The "size" of the unfolding; to be elaborated
143 Int -- Scrutinee discount: the discount to substract if the thing is in
144 -- a context (case (thing args) of ...),
145 -- (where there are the right number of arguments.)
149 instance Outputable UnfoldingGuidance where
150 ppr sty UnfoldAlways = ptext SLIT("_ALWAYS_")
151 ppr sty (UnfoldIfGoodArgs t v cs size discount)
152 = hsep [ptext SLIT("_IF_ARGS_"), int t, int v,
153 if null cs -- always print *something*
155 else hcat (map (text . show) cs),
161 %************************************************************************
163 \subsection{Figuring out things about expressions}
165 %************************************************************************
169 = VarForm -- Expression is a variable (or scc var, etc)
170 | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
171 | BottomForm -- Expression is guaranteed to be bottom. We're more gung
172 -- ho about inlining such things, because it can't waste work
173 | OtherForm -- Anything else
175 instance Outputable FormSummary where
176 ppr sty VarForm = ptext SLIT("Var")
177 ppr sty ValueForm = ptext SLIT("Value")
178 ppr sty BottomForm = ptext SLIT("Bot")
179 ppr sty OtherForm = ptext SLIT("Other")
181 mkFormSummary ::GenCoreExpr bndr Id tyvar uvar -> FormSummary
184 = go (0::Int) expr -- The "n" is the number of (value) arguments so far
186 go n (Lit _) = ASSERT(n==0) ValueForm
187 go n (Con _ _) = ASSERT(n==0) ValueForm
188 go n (Prim _ _) = OtherForm
189 go n (SCC _ e) = go n e
190 go n (Coerce _ _ e) = go n e
192 go n (Let (NonRec b r) e) | exprIsTrivial r = go n e -- let f = f' alpha in (f,g)
193 -- should be treated as a value
194 go n (Let _ e) = OtherForm
195 go n (Case _ _) = OtherForm
197 go 0 (Lam (ValBinder x) e) = ValueForm -- NB: \x.bottom /= bottom!
198 go n (Lam (ValBinder x) e) = go (n-1) e -- Applied lambda
199 go n (Lam other_binder e) = go n e
201 go n (App fun arg) | isValArg arg = go (n+1) fun
202 go n (App fun other_arg) = go n fun
204 go n (Var f) | isBottomingId f = BottomForm
205 | isDataCon f = ValueForm -- Can happen inside imported unfoldings
206 go 0 (Var f) = VarForm
207 go n (Var f) = case getIdArity f of
208 ArityExactly a | n < a -> ValueForm
209 ArityAtLeast a | n < a -> ValueForm
212 whnfOrBottom :: GenCoreExpr bndr Id tyvar uvar -> Bool
213 whnfOrBottom e = case mkFormSummary e of
220 @exprIsTrivial@ is true of expressions we are unconditionally happy to duplicate;
221 simple variables and constants, and type applications.
224 exprIsTrivial (Var v) = True
225 exprIsTrivial (Lit lit) = not (isNoRepLit lit)
226 exprIsTrivial (App e (TyArg _)) = exprIsTrivial e
227 exprIsTrivial other = False
231 exprSmallEnoughToDup (Con _ _) = True -- Could check # of args
232 exprSmallEnoughToDup (Prim op _) = not (fragilePrimOp op) -- Could check # of args
233 exprSmallEnoughToDup (Lit lit) = not (isNoRepLit lit)
234 exprSmallEnoughToDup expr
235 = case (collectArgs expr) of { (fun, _, _, vargs) ->
237 Var v | length vargs <= 4 -> True
244 %************************************************************************
246 \subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
248 %************************************************************************
251 calcUnfoldingGuidance
252 :: PragmaInfo -- INLINE pragma stuff
253 -> Int -- bomb out if size gets bigger than this
254 -> CoreExpr -- expression to look at
257 calcUnfoldingGuidance IMustBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
258 calcUnfoldingGuidance IWantToBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
259 calcUnfoldingGuidance IMustNotBeINLINEd bOMB_OUT_SIZE expr = UnfoldNever -- ...and vice versa...
261 calcUnfoldingGuidance NoPragmaInfo bOMB_OUT_SIZE expr
262 = case collectBinders expr of { (use_binders, ty_binders, val_binders, body) ->
263 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
265 TooBig -> UnfoldNever
267 SizeIs size cased_args scrut_discount
271 (map discount_for val_binders)
276 | is_data && b `is_elem` cased_args = tyConFamilySize tycon
280 = case (maybeAppDataTyConExpandingDicts (idType b)) of
281 Nothing -> (False, panic "discount")
282 Just (tc,_,_) -> (True, tc)
284 is_elem = isIn "calcUnfoldingGuidance" }
288 sizeExpr :: Int -- Bomb out if it gets bigger than this
289 -> [Id] -- Arguments; we're interested in which of these
294 sizeExpr (I# bOMB_OUT_SIZE) args expr
297 size_up (Var v) = sizeZero
298 size_up (Lit lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
299 | otherwise = sizeZero
301 size_up (SCC lbl body) = size_up body -- SCCs cost nothing
302 size_up (Coerce _ _ body) = size_up body -- Coercions cost nothing
304 size_up (App fun arg) = size_up fun `addSize` size_up_arg arg
305 -- NB Zero cost for for type applications;
306 -- others cost 1 or more
308 size_up (Con con args) = conSizeN (numValArgs args)
309 -- We don't count 1 for the constructor because we're
310 -- quite keen to get constructors into the open
312 size_up (Prim op args) = sizeN op_cost -- NB: no charge for PrimOp args
314 op_cost = if primOpCanTriggerGC op
315 then uNFOLDING_DEAR_OP_COST
316 -- these *tend* to be more expensive;
317 -- number chosen to avoid unfolding (HACK)
318 else uNFOLDING_CHEAP_OP_COST
320 size_up expr@(Lam _ _)
322 (uvars, tyvars, args, body) = collectBinders expr
324 size_up body `addSizeN` length args
326 size_up (Let (NonRec binder rhs) body)
327 = nukeScrutDiscount (size_up rhs)
331 size_up (Let (Rec pairs) body)
332 = nukeScrutDiscount (foldr addSize sizeZero [size_up rhs | (_,rhs) <- pairs])
336 size_up (Case scrut alts)
337 = nukeScrutDiscount (size_up scrut)
341 size_up_alts (coreExprType scrut) alts
342 -- We charge for the "case" itself in "size_up_alts"
345 -- In an application we charge 0 for type application
346 -- 1 for most anything else
348 size_up_arg (LitArg lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
349 size_up_arg (TyArg _) = sizeZero
350 size_up_arg other = sizeOne
353 size_up_alts scrut_ty (AlgAlts alts deflt)
354 = (foldr (addSize . size_alg_alt) (size_up_deflt deflt) alts)
358 size_alg_alt (con,args,rhs) = size_up rhs
359 -- Don't charge for args, so that wrappers look cheap
361 -- NB: we charge N for an alg. "case", where N is
362 -- the number of constructors in the thing being eval'd.
363 -- (You'll eventually get a "discount" of N if you
364 -- think the "case" is likely to go away.)
365 -- It's important to charge for alternatives. If you don't then you
366 -- get size 1 for things like:
367 -- case x of { A -> 1#; B -> 2#; ... lots }
371 = case (maybeAppDataTyConExpandingDicts scrut_ty) of
373 Just (tc,_,_) -> tyConFamilySize tc
375 size_up_alts _ (PrimAlts alts deflt)
376 = foldr (addSize . size_prim_alt) (size_up_deflt deflt) alts
377 -- *no charge* for a primitive "case"!
379 size_prim_alt (lit,rhs) = size_up rhs
382 size_up_deflt NoDefault = sizeZero
383 size_up_deflt (BindDefault binder rhs) = size_up rhs
386 -- We want to record if we're case'ing an argument
387 arg_discount (Var v) | v `is_elem` args = scrutArg v
388 arg_discount other = sizeZero
390 is_elem :: Id -> [Id] -> Bool
391 is_elem = isIn "size_up_scrut"
394 -- These addSize things have to be here because
395 -- I don't want to give them bOMB_OUT_SIZE as an argument
397 addSizeN TooBig _ = TooBig
398 addSizeN (SizeIs n xs d) (I# m)
399 | n_tot -# d <# bOMB_OUT_SIZE = SizeIs n_tot xs d
404 addSize TooBig _ = TooBig
405 addSize _ TooBig = TooBig
406 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
407 | (n_tot -# d_tot) <# bOMB_OUT_SIZE = SizeIs n_tot xys d_tot
417 Code for manipulating sizes
421 data ExprSize = TooBig
422 | SizeIs Int# -- Size found
423 [Id] -- Arguments cased herein
424 Int# -- Size to subtract if result is scrutinised
425 -- by a case expression
427 sizeZero = SizeIs 0# [] 0#
428 sizeOne = SizeIs 1# [] 0#
429 sizeN (I# n) = SizeIs n [] 0#
430 conSizeN (I# n) = SizeIs n [] n
431 scrutArg v = SizeIs 0# [v] 0#
433 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
434 nukeScrutDiscount TooBig = TooBig
437 %************************************************************************
439 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
441 %************************************************************************
443 We have very limited information about an unfolding expression: (1)~so
444 many type arguments and so many value arguments expected---for our
445 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
446 a single integer. (3)~An ``argument info'' vector. For this, what we
447 have at the moment is a Boolean per argument position that says, ``I
448 will look with great favour on an explicit constructor in this
449 position.'' (4)~The ``discount'' to subtract if the expression
450 is being scrutinised.
452 Assuming we have enough type- and value arguments (if not, we give up
453 immediately), then we see if the ``discounted size'' is below some
454 (semi-arbitrary) threshold. It works like this: for every argument
455 position where we're looking for a constructor AND WE HAVE ONE in our
456 hands, we get a (again, semi-arbitrary) discount [proportion to the
457 number of constructors in the type being scrutinized].
459 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
460 and the expression in question will evaluate to a constructor, we use
461 the computed discount size *for the result only* rather than
462 computing the argument discounts. Since we know the result of
463 the expression is going to be taken apart, discounting its size
464 is more accurate (see @sizeExpr@ above for how this discount size
468 smallEnoughToInline :: [Bool] -- Evaluated-ness of value arguments
469 -> Bool -- Result is scrutinised
471 -> Bool -- True => unfold it
473 smallEnoughToInline _ _ UnfoldAlways = True
474 smallEnoughToInline _ _ UnfoldNever = False
475 smallEnoughToInline arg_is_evald_s result_is_scruted
476 (UnfoldIfGoodArgs m_tys_wanted n_vals_wanted discount_vec size scrut_discount)
477 = enough_args n_vals_wanted arg_is_evald_s &&
478 discounted_size <= opt_UnfoldingUseThreshold
481 enough_args n [] | n > 0 = False -- A function with no value args => don't unfold
482 enough_args _ _ = True -- Otherwise it's ok to try
484 {- OLD: require saturated args
485 enough_args 0 evals = True
486 enough_args n [] = False
487 enough_args n (e:es) = enough_args (n-1) es
488 -- NB: don't take the length of arg_is_evald_s because when
489 -- called from couldBeSmallEnoughToInline it is infinite!
492 discounted_size = size - args_discount - result_discount
494 args_discount = sum (zipWith arg_discount discount_vec arg_is_evald_s)
495 result_discount | result_is_scruted = scrut_discount
498 arg_discount no_of_constrs is_evald
499 | is_evald = 1 + no_of_constrs * opt_UnfoldingConDiscount
503 We use this one to avoid exporting inlinings that we ``couldn't possibly
504 use'' on the other side. Can be overridden w/ flaggery.
505 Just the same as smallEnoughToInline, except that it has no actual arguments.
509 couldBeSmallEnoughToInline :: UnfoldingGuidance -> Bool
510 couldBeSmallEnoughToInline guidance = smallEnoughToInline (repeat True) True guidance
512 certainlySmallEnoughToInline :: UnfoldingGuidance -> Bool
513 certainlySmallEnoughToInline guidance = smallEnoughToInline (repeat False) False guidance
521 :: FormSummary -- What the thing to be inlined is like
522 -> BinderInfo -- How the thing to be inlined occurs
523 -> Bool -- True => it's small enough to inline
524 -> Bool -- True => yes, inline it
526 -- If there's no danger of duplicating work, we can inline if it occurs once, or is small
527 okToInline form occ_info small_enough
529 = small_enough || one_occ
531 one_occ = case occ_info of
532 OneOcc _ _ _ n_alts _ -> n_alts <= 1
535 no_dup_danger VarForm = True
536 no_dup_danger ValueForm = True
537 no_dup_danger BottomForm = True
538 no_dup_danger other = False
540 -- A non-WHNF can be inlined if it doesn't occur inside a lambda,
541 -- and occurs exactly once or
542 -- occurs once in each branch of a case and is small
543 okToInline OtherForm (OneOcc _ dup_danger _ n_alts _) small_enough
544 = not (isDupDanger dup_danger) && (n_alts <= 1 || small_enough)
546 okToInline form any_occ small_enough = False