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,
24 noUnfolding, mkMagicUnfolding, mkUnfolding, getUnfoldingTemplate,
26 smallEnoughToInline, couldBeSmallEnoughToInline, certainlySmallEnoughToInline,
33 IMPORT_DELOOPER(IdLoop) -- for paranoia checking;
34 -- and also to get mkMagicUnfoldingFun
35 IMPORT_DELOOPER(PrelLoop) -- for paranoia checking
37 import Bag ( emptyBag, unitBag, unionBags, Bag )
39 import CmdLineOpts ( opt_UnfoldingCreationThreshold,
40 opt_UnfoldingUseThreshold,
41 opt_UnfoldingConDiscount
43 import Constants ( uNFOLDING_CHEAP_OP_COST,
44 uNFOLDING_DEAR_OP_COST,
45 uNFOLDING_NOREP_LIT_COST
47 import BinderInfo ( BinderInfo(..), FunOrArg, DuplicationDanger, InsideSCC, isDupDanger )
49 import CoreUtils ( unTagBinders )
50 import HsCore ( UfExpr )
51 import RdrHsSyn ( RdrName )
52 import OccurAnal ( occurAnalyseGlobalExpr )
53 import CoreUtils ( coreExprType )
54 import CostCentre ( ccMentionsId )
55 import Id ( idType, getIdArity, isBottomingId, isDataCon, isPrimitiveId_maybe,
56 SYN_IE(IdSet), GenId{-instances-} )
57 import PrimOp ( primOpCanTriggerGC, fragilePrimOp, PrimOp(..) )
58 import IdInfo ( ArityInfo(..), bottomIsGuaranteed )
59 import Literal ( isNoRepLit, isLitLitLit )
61 import TyCon ( tyConFamilySize )
62 import Type ( maybeAppDataTyConExpandingDicts )
63 import UniqSet ( emptyUniqSet, unitUniqSet, mkUniqSet,
64 addOneToUniqSet, unionUniqSets
66 import Usage ( SYN_IE(UVar) )
67 import Maybes ( maybeToBool )
68 import Util ( isIn, panic, assertPanic )
72 %************************************************************************
74 \subsection{@Unfolding@ and @UnfoldingGuidance@ types}
76 %************************************************************************
82 | CoreUnfolding SimpleUnfolding
85 Unique -- Unique of the Id whose magic unfolding this is
90 = SimpleUnfolding -- An unfolding with redundant cached information
91 FormSummary -- Tells whether the template is a WHNF or bottom
92 UnfoldingGuidance -- Tells about the *size* of the template.
93 SimplifiableCoreExpr -- Template
96 noUnfolding = NoUnfolding
98 mkUnfolding inline_me expr
99 = CoreUnfolding (SimpleUnfolding
101 (calcUnfoldingGuidance inline_me opt_UnfoldingCreationThreshold expr)
102 (occurAnalyseGlobalExpr expr))
104 mkMagicUnfolding :: Unique -> Unfolding
105 mkMagicUnfolding tag = MagicUnfolding tag (mkMagicUnfoldingFun tag)
107 getUnfoldingTemplate :: Unfolding -> CoreExpr
108 getUnfoldingTemplate (CoreUnfolding (SimpleUnfolding _ _ expr))
110 getUnfoldingTemplate other = panic "getUnfoldingTemplate"
113 data UnfoldingGuidance
115 | UnfoldAlways -- There is no "original" definition,
116 -- so you'd better unfold. Or: something
117 -- so cheap to unfold (e.g., 1#) that
118 -- you should do it absolutely always.
120 | UnfoldIfGoodArgs Int -- if "m" type args
121 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.
125 Int -- The "size" of the unfolding; to be elaborated
130 instance Outputable UnfoldingGuidance where
131 ppr sty UnfoldAlways = ppStr "_ALWAYS_"
132 -- ppr sty EssentialUnfolding = ppStr "_ESSENTIAL_" -- shouldn't appear in an iface
133 ppr sty (UnfoldIfGoodArgs t v cs size)
134 = ppCat [ppStr "_IF_ARGS_", ppInt t, ppInt v,
135 if null cs -- always print *something*
137 else ppBesides (map (ppStr . show) cs),
142 %************************************************************************
144 \subsection{Figuring out things about expressions}
146 %************************************************************************
150 = VarForm -- Expression is a variable (or scc var, etc)
151 | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
152 | BottomForm -- Expression is guaranteed to be bottom. We're more gung
153 -- ho about inlining such things, because it can't waste work
154 | OtherForm -- Anything else
156 instance Outputable FormSummary where
157 ppr sty VarForm = ppStr "Var"
158 ppr sty ValueForm = ppStr "Value"
159 ppr sty BottomForm = ppStr "Bot"
160 ppr sty OtherForm = ppStr "Other"
162 mkFormSummary ::GenCoreExpr bndr Id tyvar uvar -> FormSummary
165 = go (0::Int) expr -- The "n" is the number of (value) arguments so far
167 go n (Lit _) = ASSERT(n==0) ValueForm
168 go n (Con _ _) = ASSERT(n==0) ValueForm
169 go n (Prim _ _) = OtherForm
170 go n (SCC _ e) = go n e
171 go n (Coerce _ _ e) = go n e
172 go n (Let _ e) = OtherForm
173 go n (Case _ _) = OtherForm
175 go 0 (Lam (ValBinder x) e) = ValueForm -- NB: \x.bottom /= bottom!
176 go n (Lam (ValBinder x) e) = go (n-1) e -- Applied lambda
177 go n (Lam other_binder e) = go n e
179 go n (App fun arg) | isValArg arg = go (n+1) fun
180 go n (App fun other_arg) = go n fun
182 go n (Var f) | isBottomingId f = BottomForm
183 | isDataCon f = ValueForm -- Can happen inside imported unfoldings
184 go 0 (Var f) = VarForm
185 go n (Var f) = case getIdArity f of
186 ArityExactly a | n < a -> ValueForm
187 ArityAtLeast a | n < a -> ValueForm
190 whnfOrBottom :: GenCoreExpr bndr Id tyvar uvar -> Bool
191 whnfOrBottom e = case mkFormSummary e of
200 exprSmallEnoughToDup (Con _ _) = True -- Could check # of args
201 exprSmallEnoughToDup (Prim op _) = not (fragilePrimOp op) -- Could check # of args
202 exprSmallEnoughToDup (Lit lit) = not (isNoRepLit lit)
203 exprSmallEnoughToDup expr
204 = case (collectArgs expr) of { (fun, _, _, vargs) ->
206 Var v | length vargs == 0 -> True
212 exprSmallEnoughToDup expr -- for now, just: <var> applied to <args>
213 = case (collectArgs expr) of { (fun, _, _, vargs) ->
215 Var v -> v /= buildId
217 && length vargs <= 6 -- or 10 or 1 or 4 or anything smallish.
222 Question (ADR): What is the above used for? Is a _ccall_ really small
225 %************************************************************************
227 \subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
229 %************************************************************************
232 calcUnfoldingGuidance
233 :: Bool -- True <=> there's an INLINE pragma on this thing
234 -> Int -- bomb out if size gets bigger than this
235 -> CoreExpr -- expression to look at
238 calcUnfoldingGuidance True bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
240 calcUnfoldingGuidance False bOMB_OUT_SIZE expr
242 (use_binders, ty_binders, val_binders, body) = collectBinders expr
244 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
246 Nothing -> UnfoldNever
248 Just (size, cased_args)
252 (map discount_for val_binders)
256 | is_data && b `is_elem` cased_args = tyConFamilySize tycon
260 = case (maybeAppDataTyConExpandingDicts (idType b)) of
261 Nothing -> (False, panic "discount")
262 Just (tc,_,_) -> (True, tc)
264 is_elem = isIn "calcUnfoldingGuidance"
268 sizeExpr :: Int -- Bomb out if it gets bigger than this
269 -> [Id] -- Arguments; we're interested in which of these
272 -> Maybe (Int, -- Size
273 [Id] -- Subset of args which are cased
276 sizeExpr bOMB_OUT_SIZE args expr
279 -- We are very keen to inline literals, constructors, or primitives
280 -- including their slightly-disguised forms as applications (the latter
281 -- can show up in the bodies of things imported from interfaces).
287 (fun, _) = splitCoreApps expr
288 data_or_prim (Var v) = maybeToBool (isPrimitiveId_maybe v) ||
290 data_or_prim (Con _ _) = True
291 data_or_prim (Prim _ _) = True
292 data_or_prim (Lit _) = True
293 data_or_prim other = False
295 size_up (Var v) = sizeZero
296 size_up (App fun arg) = size_up fun `addSize` size_up_arg arg `addSizeN` 1
297 -- 1 for application node
299 size_up (Lit lit) = if isNoRepLit lit
300 then sizeN uNFOLDING_NOREP_LIT_COST
303 -- I don't understand this hack so I'm removing it! SLPJ Nov 96
304 -- size_up (SCC _ (Con _ _)) = Nothing -- **** HACK *****
306 size_up (SCC lbl body) = size_up body -- SCCs cost nothing
307 size_up (Coerce _ _ body) = size_up body -- Coercions cost nothing
309 size_up (Con con args) = sizeN (numValArgs args)
310 -- We don't count 1 for the constructor because we're
311 -- quite keen to get constructors into the open
313 size_up (Prim op args) = sizeN op_cost -- NB: no charge for PrimOp args
315 op_cost = if primOpCanTriggerGC op
316 then uNFOLDING_DEAR_OP_COST
317 -- these *tend* to be more expensive;
318 -- number chosen to avoid unfolding (HACK)
319 else uNFOLDING_CHEAP_OP_COST
321 size_up expr@(Lam _ _)
323 (uvars, tyvars, args, body) = collectBinders expr
325 size_up body `addSizeN` length args
327 size_up (Let (NonRec binder rhs) body)
334 size_up (Let (Rec pairs) body)
335 = foldr addSize sizeZero [size_up rhs | (_,rhs) <- pairs]
341 size_up (Case scrut alts)
342 = size_up_scrut scrut
344 size_up_alts (coreExprType scrut) alts
345 -- We charge for the "case" itself in "size_up_alts"
348 size_up_arg (LitArg lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
349 size_up_arg other = sizeZero
352 size_up_alts scrut_ty (AlgAlts alts deflt)
353 = foldr (addSize . size_alg_alt) (size_up_deflt deflt) alts `addSizeN` 1
354 -- "1" for the case itself
356 -- `addSizeN` (if is_data then tyConFamilySize tycon else 1)
358 -- OLD COMMENT: looks unfair to me! So I've nuked this extra charge
360 -- NB: we charge N for an alg. "case", where N is
361 -- the number of constructors in the thing being eval'd.
362 -- (You'll eventually get a "discount" of N if you
363 -- think the "case" is likely to go away.)
366 size_alg_alt (con,args,rhs) = size_up rhs
367 -- Don't charge for args, so that wrappers look cheap
370 = --trace "CoreUnfold.getAppDataTyConExpandingDicts:2" $
371 case (maybeAppDataTyConExpandingDicts scrut_ty) of
372 Nothing -> (False, panic "size_up_alts")
373 Just (tc,_,_) -> (True, 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 -- Scrutinees. There are two things going on here.
387 -- First, we want to record if we're case'ing an argument
388 -- Second, we want to charge nothing for the srutinee if it's just
389 -- a variable. That way wrapper-like things look cheap.
390 size_up_scrut (Var v) | v `is_elem` args = Just (0, [v])
391 | otherwise = Just (0, [])
392 size_up_scrut other = size_up other
394 is_elem :: Id -> [Id] -> Bool
395 is_elem = isIn "size_up_scrut"
398 sizeZero = Just (0, [])
399 sizeOne = Just (1, [])
400 sizeN n = Just (n, [])
402 addSizeN Nothing _ = Nothing
403 addSizeN (Just (n, xs)) m
404 | tot < bOMB_OUT_SIZE = Just (tot, xs)
405 | otherwise = Nothing
409 addSize Nothing _ = Nothing
410 addSize _ Nothing = Nothing
411 addSize (Just (n, xs)) (Just (m, ys))
412 | tot < bOMB_OUT_SIZE = Just (tot, xys)
413 | otherwise = Nothing
421 go (App fun arg) args = go fun (arg:args)
422 go fun args = (fun,args)
425 %************************************************************************
427 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
429 %************************************************************************
431 We have very limited information about an unfolding expression: (1)~so
432 many type arguments and so many value arguments expected---for our
433 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
434 a single integer. (3)~An ``argument info'' vector. For this, what we
435 have at the moment is a Boolean per argument position that says, ``I
436 will look with great favour on an explicit constructor in this
439 Assuming we have enough type- and value arguments (if not, we give up
440 immediately), then we see if the ``discounted size'' is below some
441 (semi-arbitrary) threshold. It works like this: for every argument
442 position where we're looking for a constructor AND WE HAVE ONE in our
443 hands, we get a (again, semi-arbitrary) discount [proportion to the
444 number of constructors in the type being scrutinized].
447 smallEnoughToInline :: [Bool] -- Evaluated-ness of value arguments
449 -> Bool -- True => unfold it
451 smallEnoughToInline _ UnfoldAlways = True
452 smallEnoughToInline _ UnfoldNever = False
453 smallEnoughToInline arg_is_evald_s
454 (UnfoldIfGoodArgs m_tys_wanted n_vals_wanted discount_vec size)
455 = enough_args n_vals_wanted arg_is_evald_s &&
456 discounted_size <= opt_UnfoldingUseThreshold
458 enough_args 0 evals = True
459 enough_args n [] = False
460 enough_args n (e:es) = enough_args (n-1) es
461 -- NB: don't take the length of arg_is_evald_s because when
462 -- called from couldBeSmallEnoughToInline it is infinite!
464 discounted_size = size - sum (zipWith arg_discount discount_vec arg_is_evald_s)
466 arg_discount no_of_constrs is_evald
467 | is_evald = 1 + no_of_constrs * opt_UnfoldingConDiscount
471 We use this one to avoid exporting inlinings that we ``couldn't possibly
472 use'' on the other side. Can be overridden w/ flaggery.
473 Just the same as smallEnoughToInline, except that it has no actual arguments.
476 couldBeSmallEnoughToInline :: UnfoldingGuidance -> Bool
477 couldBeSmallEnoughToInline guidance = smallEnoughToInline (repeat True) guidance
479 certainlySmallEnoughToInline :: UnfoldingGuidance -> Bool
480 certainlySmallEnoughToInline guidance = smallEnoughToInline (repeat False) guidance
488 :: FormSummary -- What the thing to be inlined is like
489 -> BinderInfo -- How the thing to be inlined occurs
490 -> Bool -- True => it's small enough to inline
491 -> Bool -- True => yes, inline it
493 -- If there's no danger of duplicating work, we can inline if it occurs once, or is small
494 okToInline form occ_info small_enough
496 = small_enough || one_occ
498 one_occ = case occ_info of
499 OneOcc _ _ _ n_alts _ -> n_alts <= 1
502 no_dup_danger VarForm = True
503 no_dup_danger ValueForm = True
504 no_dup_danger BottomForm = True
505 no_dup_danger other = False
507 -- A non-WHNF can be inlined if it doesn't occur inside a lambda,
508 -- and occurs exactly once or
509 -- occurs once in each branch of a case and is small
510 okToInline OtherForm (OneOcc _ dup_danger _ n_alts _) small_enough
511 = not (isDupDanger dup_danger) && (n_alts <= 1 || small_enough)
513 okToInline form any_occ small_enough = False