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,
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 Util ( isIn, panic, assertPanic )
71 %************************************************************************
73 \subsection{@Unfolding@ and @UnfoldingGuidance@ types}
75 %************************************************************************
81 | CoreUnfolding SimpleUnfolding
84 Unique -- Unique of the Id whose magic unfolding this is
89 = SimpleUnfolding -- An unfolding with redundant cached information
90 FormSummary -- Tells whether the template is a WHNF or bottom
91 UnfoldingGuidance -- Tells about the *size* of the template.
92 SimplifiableCoreExpr -- Template
95 noUnfolding = NoUnfolding
97 mkUnfolding inline_me expr
98 = CoreUnfolding (SimpleUnfolding
100 (calcUnfoldingGuidance inline_me opt_UnfoldingCreationThreshold expr)
101 (occurAnalyseGlobalExpr expr))
103 mkMagicUnfolding :: Unique -> Unfolding
104 mkMagicUnfolding tag = MagicUnfolding tag (mkMagicUnfoldingFun tag)
106 getUnfoldingTemplate :: Unfolding -> CoreExpr
107 getUnfoldingTemplate (CoreUnfolding (SimpleUnfolding _ _ 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
121 [Int] -- Discount if the argument is evaluated.
122 -- (i.e., a simplification will definitely
123 -- be possible). One elt of the list per *value* arg.
124 Int -- The "size" of the unfolding; to be elaborated
129 instance Outputable UnfoldingGuidance where
130 ppr sty UnfoldAlways = ppStr "_ALWAYS_"
131 -- ppr sty EssentialUnfolding = ppStr "_ESSENTIAL_" -- shouldn't appear in an iface
132 ppr sty (UnfoldIfGoodArgs t v cs size)
133 = ppCat [ppStr "_IF_ARGS_", ppInt t, ppInt v,
134 if null cs -- always print *something*
136 else ppBesides (map (ppStr . show) cs),
141 %************************************************************************
143 \subsection{Figuring out things about expressions}
145 %************************************************************************
149 = VarForm -- Expression is a variable (or scc var, etc)
150 | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
151 | BottomForm -- Expression is guaranteed to be bottom. We're more gung
152 -- ho about inlining such things, because it can't waste work
153 | OtherForm -- Anything else
155 instance Outputable FormSummary where
156 ppr sty VarForm = ppStr "Var"
157 ppr sty ValueForm = ppStr "Value"
158 ppr sty BottomForm = ppStr "Bot"
159 ppr sty OtherForm = ppStr "Other"
161 mkFormSummary ::GenCoreExpr bndr Id tyvar uvar -> FormSummary
164 = go (0::Int) expr -- The "n" is the number of (value) arguments so far
166 go n (Lit _) = ASSERT(n==0) ValueForm
167 go n (Con _ _) = ASSERT(n==0) ValueForm
168 go n (Prim _ _) = OtherForm
169 go n (SCC _ e) = go n e
170 go n (Coerce _ _ e) = go n e
171 go n (Let _ e) = OtherForm
172 go n (Case _ _) = OtherForm
174 go 0 (Lam (ValBinder x) e) = ValueForm -- NB: \x.bottom /= bottom!
175 go n (Lam (ValBinder x) e) = go (n-1) e -- Applied lambda
176 go n (Lam other_binder e) = go n e
178 go n (App fun arg) | isValArg arg = go (n+1) fun
179 go n (App fun other_arg) = go n fun
181 go n (Var f) | isBottomingId f = BottomForm
182 go 0 (Var f) = VarForm
183 go n (Var f) = case getIdArity f of
184 ArityExactly a | n < a -> ValueForm
185 ArityAtLeast a | n < a -> ValueForm
188 whnfOrBottom :: GenCoreExpr bndr Id tyvar uvar -> Bool
189 whnfOrBottom e = case mkFormSummary e of
198 exprSmallEnoughToDup (Con _ _) = True -- Could check # of args
199 exprSmallEnoughToDup (Prim op _) = not (fragilePrimOp op) -- Could check # of args
200 exprSmallEnoughToDup (Lit lit) = not (isNoRepLit lit)
201 exprSmallEnoughToDup expr
202 = case (collectArgs expr) of { (fun, _, _, vargs) ->
204 Var v | length vargs == 0 -> True
210 exprSmallEnoughToDup expr -- for now, just: <var> applied to <args>
211 = case (collectArgs expr) of { (fun, _, _, vargs) ->
213 Var v -> v /= buildId
215 && length vargs <= 6 -- or 10 or 1 or 4 or anything smallish.
220 Question (ADR): What is the above used for? Is a _ccall_ really small
223 %************************************************************************
225 \subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
227 %************************************************************************
230 calcUnfoldingGuidance
231 :: Bool -- True <=> there's an INLINE pragma on this thing
232 -> Int -- bomb out if size gets bigger than this
233 -> CoreExpr -- expression to look at
236 calcUnfoldingGuidance True bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
238 calcUnfoldingGuidance False any_size (Con _ _ ) = UnfoldAlways -- We are very gung ho about inlining
239 calcUnfoldingGuidance False any_size (Lit _) = UnfoldAlways -- constructors and literals
241 calcUnfoldingGuidance False bOMB_OUT_SIZE expr
243 (use_binders, ty_binders, val_binders, body) = collectBinders expr
245 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
247 Nothing -> UnfoldNever
249 Just (size, cased_args)
251 uf = UnfoldIfGoodArgs
254 (map discount_for val_binders)
258 | is_data && b `is_elem` cased_args = tyConFamilySize tycon
262 = --trace "CoreUnfold.getAppDataTyConExpandingDicts:1" $
263 case (maybeAppDataTyConExpandingDicts (idType b)) of
264 Nothing -> (False, panic "discount")
265 Just (tc,_,_) -> (True, tc)
267 -- pprTrace "calcUnfold:" (ppAbove (ppr PprDebug uf) (ppr PprDebug expr))
270 is_elem = isIn "calcUnfoldingGuidance"
274 sizeExpr :: Int -- Bomb out if it gets bigger than this
275 -> [Id] -- Arguments; we're interested in which of these
278 -> Maybe (Int, -- Size
279 [Id] -- Subset of args which are cased
282 sizeExpr bOMB_OUT_SIZE args expr
285 size_up (Var v) = sizeOne
286 size_up (App fun arg) = size_up fun `addSize` size_up_arg arg
287 size_up (Lit lit) = if isNoRepLit lit
288 then sizeN uNFOLDING_NOREP_LIT_COST
291 -- I don't understand this hack so I'm removing it! SLPJ Nov 96
292 -- size_up (SCC _ (Con _ _)) = Nothing -- **** HACK *****
294 size_up (SCC lbl body) = size_up body -- SCCs cost nothing
295 size_up (Coerce _ _ body) = size_up body -- Coercions cost nothing
297 size_up (Con con args) = -- 1 + # of val args
298 sizeN (1 + numValArgs args)
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 (uvars, tyvars, args, body) = collectBinders expr
311 size_up body `addSizeN` length args
313 size_up (Let (NonRec binder rhs) body)
320 size_up (Let (Rec pairs) body)
321 = foldr addSize sizeZero [size_up rhs | (_,rhs) <- pairs]
327 size_up (Case scrut alts)
328 = size_up_scrut scrut
330 size_up_alts (coreExprType scrut) alts
331 -- We charge for the "case" itself in "size_up_alts"
334 size_up_arg arg = if isValArg arg then sizeOne else sizeZero{-it's free-}
337 size_up_alts scrut_ty (AlgAlts alts deflt)
338 = foldr (addSize . size_alg_alt) (size_up_deflt deflt) alts
339 `addSizeN` (if is_data then tyConFamilySize tycon else 1{-??-})
340 -- NB: we charge N for an alg. "case", where N is
341 -- the number of constructors in the thing being eval'd.
342 -- (You'll eventually get a "discount" of N if you
343 -- think the "case" is likely to go away.)
345 size_alg_alt (con,args,rhs) = size_up rhs
346 -- Don't charge for args, so that wrappers look cheap
349 = --trace "CoreUnfold.getAppDataTyConExpandingDicts:2" $
350 case (maybeAppDataTyConExpandingDicts scrut_ty) of
351 Nothing -> (False, panic "size_up_alts")
352 Just (tc,_,_) -> (True, tc)
354 size_up_alts _ (PrimAlts alts deflt)
355 = foldr (addSize . size_prim_alt) (size_up_deflt deflt) alts
356 -- *no charge* for a primitive "case"!
358 size_prim_alt (lit,rhs) = size_up rhs
361 size_up_deflt NoDefault = sizeZero
362 size_up_deflt (BindDefault binder rhs) = size_up rhs
365 -- Scrutinees. There are two things going on here.
366 -- First, we want to record if we're case'ing an argument
367 -- Second, we want to charge nothing for the srutinee if it's just
368 -- a variable. That way wrapper-like things look cheap.
369 size_up_scrut (Var v) | v `is_elem` args = Just (0, [v])
370 | otherwise = Just (0, [])
371 size_up_scrut other = size_up other
373 is_elem :: Id -> [Id] -> Bool
374 is_elem = isIn "size_up_scrut"
377 sizeZero = Just (0, [])
378 sizeOne = Just (1, [])
379 sizeN n = Just (n, [])
381 addSizeN Nothing _ = Nothing
382 addSizeN (Just (n, xs)) m
383 | tot < bOMB_OUT_SIZE = Just (tot, xs)
384 | otherwise = Nothing
388 addSize Nothing _ = Nothing
389 addSize _ Nothing = Nothing
390 addSize (Just (n, xs)) (Just (m, ys))
391 | tot < bOMB_OUT_SIZE = Just (tot, xys)
392 | otherwise = Nothing
398 %************************************************************************
400 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
402 %************************************************************************
404 We have very limited information about an unfolding expression: (1)~so
405 many type arguments and so many value arguments expected---for our
406 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
407 a single integer. (3)~An ``argument info'' vector. For this, what we
408 have at the moment is a Boolean per argument position that says, ``I
409 will look with great favour on an explicit constructor in this
412 Assuming we have enough type- and value arguments (if not, we give up
413 immediately), then we see if the ``discounted size'' is below some
414 (semi-arbitrary) threshold. It works like this: for every argument
415 position where we're looking for a constructor AND WE HAVE ONE in our
416 hands, we get a (again, semi-arbitrary) discount [proportion to the
417 number of constructors in the type being scrutinized].
420 smallEnoughToInline :: [Bool] -- Evaluated-ness of value arguments
422 -> Bool -- True => unfold it
424 smallEnoughToInline _ UnfoldAlways = True
425 smallEnoughToInline _ UnfoldNever = False
426 smallEnoughToInline arg_is_evald_s
427 (UnfoldIfGoodArgs m_tys_wanted n_vals_wanted discount_vec size)
428 = enough_args n_vals_wanted arg_is_evald_s &&
429 discounted_size <= opt_UnfoldingUseThreshold
431 enough_args 0 evals = True
432 enough_args n [] = False
433 enough_args n (e:es) = enough_args (n-1) es
434 -- NB: don't take the length of arg_is_evald_s because when
435 -- called from couldBeSmallEnoughToInline it is infinite!
437 discounted_size = size - sum (zipWith arg_discount discount_vec arg_is_evald_s)
439 arg_discount no_of_constrs is_evald
440 | is_evald = 1 + no_of_constrs * opt_UnfoldingConDiscount
444 We use this one to avoid exporting inlinings that we ``couldn't possibly
445 use'' on the other side. Can be overridden w/ flaggery.
446 Just the same as smallEnoughToInline, except that it has no actual arguments.
449 couldBeSmallEnoughToInline :: UnfoldingGuidance -> Bool
450 couldBeSmallEnoughToInline guidance = smallEnoughToInline (repeat True) guidance
452 certainlySmallEnoughToInline :: UnfoldingGuidance -> Bool
453 certainlySmallEnoughToInline guidance = smallEnoughToInline (repeat False) guidance
461 :: FormSummary -- What the thing to be inlined is like
462 -> BinderInfo -- How the thing to be inlined occurs
463 -> Bool -- True => it's small enough to inline
464 -> Bool -- True => yes, inline it
466 -- If there's no danger of duplicating work, we can inline if it occurs once, or is small
467 okToInline form occ_info small_enough
469 = small_enough || one_occ
471 one_occ = case occ_info of
472 OneOcc _ _ _ n_alts _ -> n_alts <= 1
475 no_dup_danger VarForm = True
476 no_dup_danger ValueForm = True
477 no_dup_danger BottomForm = True
478 no_dup_danger other = False
480 -- A non-WHNF can be inlined if it doesn't occur inside a lambda,
481 -- and occurs exactly once or
482 -- occurs once in each branch of a case and is small
483 okToInline OtherForm (OneOcc _ dup_danger _ n_alts _) small_enough
484 = not (isDupDanger dup_danger) && (n_alts <= 1 || small_enough)
486 okToInline form any_occ small_enough = False