2 % (c) The AQUA Project, Glasgow University, 1994-1998
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, -- Abstract types
19 noUnfolding, mkTopUnfolding, mkUnfolding, mkCompulsoryUnfolding, seqUnfolding,
20 evaldUnfolding, mkOtherCon, otherCons,
21 unfoldingTemplate, maybeUnfoldingTemplate,
22 isEvaldUnfolding, isValueUnfolding, isCheapUnfolding, isCompulsoryUnfolding,
23 hasUnfolding, hasSomeUnfolding, neverUnfold,
25 couldBeSmallEnoughToInline,
26 certainlyWillInline, smallEnoughToInline,
31 #include "HsVersions.h"
33 import StaticFlags ( opt_UF_CreationThreshold, opt_UF_UseThreshold,
34 opt_UF_FunAppDiscount, opt_UF_KeenessFactor,
37 import DynFlags ( DynFlags, DynFlag(..), dopt )
39 import PprCore () -- Instances
40 import OccurAnal ( occurAnalyseExpr )
41 import CoreUtils ( exprIsHNF, exprIsCheap, exprIsTrivial )
42 import Id ( Id, idType, isId,
43 idUnfolding, globalIdDetails
45 import DataCon ( isUnboxedTupleCon )
46 import Literal ( litSize )
47 import PrimOp ( primOpIsDupable, primOpOutOfLine )
48 import IdInfo ( OccInfo(..), GlobalIdDetails(..) )
49 import Type ( isUnLiftedType )
50 import PrelNames ( hasKey, buildIdKey, augmentIdKey )
55 #if __GLASGOW_HASKELL__ >= 404
56 import GLAEXTS ( Int# )
61 %************************************************************************
63 \subsection{Making unfoldings}
65 %************************************************************************
68 mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
70 mkUnfolding top_lvl expr
71 = CoreUnfolding (occurAnalyseExpr expr)
78 -- OK to inline inside a lambda
80 (calcUnfoldingGuidance opt_UF_CreationThreshold expr)
81 -- Sometimes during simplification, there's a large let-bound thing
82 -- which has been substituted, and so is now dead; so 'expr' contains
83 -- two copies of the thing while the occurrence-analysed expression doesn't
84 -- Nevertheless, we don't occ-analyse before computing the size because the
85 -- size computation bales out after a while, whereas occurrence analysis does not.
87 -- This can occasionally mean that the guidance is very pessimistic;
88 -- it gets fixed up next round
90 instance Outputable Unfolding where
91 ppr NoUnfolding = ptext SLIT("No unfolding")
92 ppr (OtherCon cs) = ptext SLIT("OtherCon") <+> ppr cs
93 ppr (CompulsoryUnfolding e) = ptext SLIT("Compulsory") <+> ppr e
94 ppr (CoreUnfolding e top hnf cheap g)
95 = ptext SLIT("Unf") <+> sep [ppr top <+> ppr hnf <+> ppr cheap <+> ppr g,
98 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
99 = CompulsoryUnfolding (occurAnalyseExpr expr)
103 %************************************************************************
105 \subsection{The UnfoldingGuidance type}
107 %************************************************************************
110 instance Outputable UnfoldingGuidance where
111 ppr UnfoldNever = ptext SLIT("NEVER")
112 ppr (UnfoldIfGoodArgs v cs size discount)
113 = hsep [ ptext SLIT("IF_ARGS"), int v,
114 brackets (hsep (map int cs)),
121 calcUnfoldingGuidance
122 :: Int -- bomb out if size gets bigger than this
123 -> CoreExpr -- expression to look at
125 calcUnfoldingGuidance bOMB_OUT_SIZE expr
126 = case collect_val_bndrs expr of { (inline, val_binders, body) ->
128 n_val_binders = length val_binders
130 max_inline_size = n_val_binders+2
131 -- The idea is that if there is an INLINE pragma (inline is True)
132 -- and there's a big body, we give a size of n_val_binders+2. This
133 -- This is just enough to fail the no-size-increase test in callSiteInline,
134 -- so that INLINE things don't get inlined into entirely boring contexts,
138 case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_binders body) of
141 | not inline -> UnfoldNever
142 -- A big function with an INLINE pragma must
143 -- have an UnfoldIfGoodArgs guidance
144 | otherwise -> UnfoldIfGoodArgs n_val_binders
145 (map (const 0) val_binders)
148 SizeIs size cased_args scrut_discount
151 (map discount_for val_binders)
153 (iBox scrut_discount)
155 boxed_size = iBox size
157 final_size | inline = boxed_size `min` max_inline_size
158 | otherwise = boxed_size
160 -- Sometimes an INLINE thing is smaller than n_val_binders+2.
161 -- A particular case in point is a constructor, which has size 1.
162 -- We want to inline this regardless, hence the `min`
164 discount_for b = foldlBag (\acc (b',n) -> if b==b' then acc+n else acc)
168 collect_val_bndrs e = go False [] e
169 -- We need to be a bit careful about how we collect the
170 -- value binders. In ptic, if we see
171 -- __inline_me (\x y -> e)
172 -- We want to say "2 value binders". Why? So that
173 -- we take account of information given for the arguments
175 go inline rev_vbs (Note InlineMe e) = go True rev_vbs e
176 go inline rev_vbs (Lam b e) | isId b = go inline (b:rev_vbs) e
177 | otherwise = go inline rev_vbs e
178 go inline rev_vbs e = (inline, reverse rev_vbs, e)
182 sizeExpr :: Int# -- Bomb out if it gets bigger than this
183 -> [Id] -- Arguments; we're interested in which of these
188 sizeExpr bOMB_OUT_SIZE top_args expr
191 size_up (Type t) = sizeZero -- Types cost nothing
192 size_up (Var v) = sizeOne
194 size_up (Note InlineMe body) = sizeOne -- Inline notes make it look very small
195 -- This can be important. If you have an instance decl like this:
196 -- instance Foo a => Foo [a] where
197 -- {-# INLINE op1, op2 #-}
200 -- then we'll get a dfun which is a pair of two INLINE lambdas
202 size_up (Note _ body) = size_up body -- Other notes cost nothing
204 size_up (Cast e _) = size_up e
206 size_up (App fun (Type t)) = size_up fun
207 size_up (App fun arg) = size_up_app fun [arg]
209 size_up (Lit lit) = sizeN (litSize lit)
211 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
212 | otherwise = size_up e
214 size_up (Let (NonRec binder rhs) body)
215 = nukeScrutDiscount (size_up rhs) `addSize`
216 size_up body `addSizeN`
217 (if isUnLiftedType (idType binder) then 0 else 1)
218 -- For the allocation
219 -- If the binder has an unlifted type there is no allocation
221 size_up (Let (Rec pairs) body)
222 = nukeScrutDiscount rhs_size `addSize`
223 size_up body `addSizeN`
224 length pairs -- For the allocation
226 rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
228 size_up (Case (Var v) _ _ alts)
229 | v `elem` top_args -- We are scrutinising an argument variable
231 {- I'm nuking this special case; BUT see the comment with case alternatives.
233 (a) It's too eager. We don't want to inline a wrapper into a
234 context with no benefit.
235 E.g. \ x. f (x+x) no point in inlining (+) here!
237 (b) It's ineffective. Once g's wrapper is inlined, its case-expressions
238 aren't scrutinising arguments any more
242 [alt] -> size_up_alt alt `addSize` SizeIs 0# (unitBag (v, 1)) 0#
243 -- We want to make wrapper-style evaluation look cheap, so that
244 -- when we inline a wrapper it doesn't make call site (much) bigger
245 -- Otherwise we get nasty phase ordering stuff:
248 -- If we inline g's wrapper, f looks big, and doesn't get inlined
249 -- into h; if we inline f first, while it looks small, then g's
250 -- wrapper will get inlined later anyway. To avoid this nasty
251 -- ordering difference, we make (case a of (x,y) -> ...),
252 -- *where a is one of the arguments* look free.
256 alts_size (foldr addSize sizeOne alt_sizes) -- The 1 is for the scrutinee
257 (foldr1 maxSize alt_sizes)
259 -- Good to inline if an arg is scrutinised, because
260 -- that may eliminate allocation in the caller
261 -- And it eliminates the case itself
264 alt_sizes = map size_up_alt alts
266 -- alts_size tries to compute a good discount for
267 -- the case when we are scrutinising an argument variable
268 alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
269 (SizeIs max max_disc max_scrut) -- Size of biggest alternative
270 = SizeIs tot (unitBag (v, iBox (_ILIT 1 +# tot -# max)) `unionBags` max_disc) max_scrut
271 -- If the variable is known, we produce a discount that
272 -- will take us back to 'max', the size of rh largest alternative
273 -- The 1+ is a little discount for reduced allocation in the caller
274 alts_size tot_size _ = tot_size
277 size_up (Case e _ _ alts) = nukeScrutDiscount (size_up e) `addSize`
278 foldr (addSize . size_up_alt) sizeZero alts
279 -- We don't charge for the case itself
280 -- It's a strict thing, and the price of the call
281 -- is paid by scrut. Also consider
282 -- case f x of DEFAULT -> e
283 -- This is just ';'! Don't charge for it.
286 size_up_app (App fun arg) args
287 | isTypeArg arg = size_up_app fun args
288 | otherwise = size_up_app fun (arg:args)
289 size_up_app fun args = foldr (addSize . nukeScrutDiscount . size_up)
290 (size_up_fun fun args)
293 -- A function application with at least one value argument
294 -- so if the function is an argument give it an arg-discount
296 -- Also behave specially if the function is a build
298 -- Also if the function is a constant Id (constr or primop)
299 -- compute discounts specially
300 size_up_fun (Var fun) args
301 | fun `hasKey` buildIdKey = buildSize
302 | fun `hasKey` augmentIdKey = augmentSize
304 = case globalIdDetails fun of
305 DataConWorkId dc -> conSizeN dc (valArgCount args)
307 FCallId fc -> sizeN opt_UF_DearOp
308 PrimOpId op -> primOpSize op (valArgCount args)
309 -- foldr addSize (primOpSize op) (map arg_discount args)
310 -- At one time I tried giving an arg-discount if a primop
311 -- is applied to one of the function's arguments, but it's
312 -- not good. At the moment, any unlifted-type arg gets a
313 -- 'True' for 'yes I'm evald', so we collect the discount even
314 -- if we know nothing about it. And just having it in a primop
315 -- doesn't help at all if we don't know something more.
317 other -> fun_discount fun `addSizeN`
318 (1 + length (filter (not . exprIsTrivial) args))
319 -- The 1+ is for the function itself
320 -- Add 1 for each non-trivial arg;
321 -- the allocation cost, as in let(rec)
322 -- Slight hack here: for constructors the args are almost always
323 -- trivial; and for primops they are almost always prim typed
324 -- We should really only count for non-prim-typed args in the
325 -- general case, but that seems too much like hard work
327 size_up_fun other args = size_up other
330 size_up_alt (con, bndrs, rhs) = size_up rhs
331 -- Don't charge for args, so that wrappers look cheap
332 -- (See comments about wrappers with Case)
335 -- We want to record if we're case'ing, or applying, an argument
336 fun_discount v | v `elem` top_args = SizeIs 0# (unitBag (v, opt_UF_FunAppDiscount)) 0#
337 fun_discount other = sizeZero
340 -- These addSize things have to be here because
341 -- I don't want to give them bOMB_OUT_SIZE as an argument
343 addSizeN TooBig _ = TooBig
344 addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
346 addSize TooBig _ = TooBig
347 addSize _ TooBig = TooBig
348 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
349 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2) (xs `unionBags` ys) (d1 +# d2)
352 Code for manipulating sizes
355 data ExprSize = TooBig
356 | SizeIs FastInt -- Size found
357 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
358 FastInt -- Size to subtract if result is scrutinised
359 -- by a case expression
361 -- subtract the discount before deciding whether to bale out. eg. we
362 -- want to inline a large constructor application into a selector:
363 -- tup = (a_1, ..., a_99)
364 -- x = case tup of ...
366 mkSizeIs max n xs d | (n -# d) ># max = TooBig
367 | otherwise = SizeIs n xs d
369 maxSize TooBig _ = TooBig
370 maxSize _ TooBig = TooBig
371 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
374 sizeZero = SizeIs (_ILIT 0) emptyBag (_ILIT 0)
375 sizeOne = SizeIs (_ILIT 1) emptyBag (_ILIT 0)
376 sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT 0)
378 | isUnboxedTupleCon dc = SizeIs (_ILIT 0) emptyBag (iUnbox n +# _ILIT 1)
379 | otherwise = SizeIs (_ILIT 1) emptyBag (iUnbox n +# _ILIT 1)
380 -- Treat constructors as size 1; we are keen to expose them
381 -- (and we charge separately for their args). We can't treat
382 -- them as size zero, else we find that (iBox x) has size 1,
383 -- which is the same as a lone variable; and hence 'v' will
384 -- always be replaced by (iBox x), where v is bound to iBox x.
386 -- However, unboxed tuples count as size zero
387 -- I found occasions where we had
388 -- f x y z = case op# x y z of { s -> (# s, () #) }
389 -- and f wasn't getting inlined
392 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
393 | not (primOpOutOfLine op) = sizeN (2 - n_args)
394 -- Be very keen to inline simple primops.
395 -- We give a discount of 1 for each arg so that (op# x y z) costs 2.
396 -- We can't make it cost 1, else we'll inline let v = (op# x y z)
397 -- at every use of v, which is excessive.
399 -- A good example is:
400 -- let x = +# p q in C {x}
401 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
402 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
403 | otherwise = sizeOne
405 buildSize = SizeIs (-2#) emptyBag 4#
406 -- We really want to inline applications of build
407 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
408 -- Indeed, we should add a result_discount becuause build is
409 -- very like a constructor. We don't bother to check that the
410 -- build is saturated (it usually is). The "-2" discounts for the \c n,
411 -- The "4" is rather arbitrary.
413 augmentSize = SizeIs (-2#) emptyBag 4#
414 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
415 -- e plus ys. The -2 accounts for the \cn
417 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
418 nukeScrutDiscount TooBig = TooBig
420 -- When we return a lambda, give a discount if it's used (applied)
421 lamScrutDiscount (SizeIs n vs d) = case opt_UF_FunAppDiscount of { d -> SizeIs n vs (iUnbox d) }
422 lamScrutDiscount TooBig = TooBig
426 %************************************************************************
428 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
430 %************************************************************************
432 We have very limited information about an unfolding expression: (1)~so
433 many type arguments and so many value arguments expected---for our
434 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
435 a single integer. (3)~An ``argument info'' vector. For this, what we
436 have at the moment is a Boolean per argument position that says, ``I
437 will look with great favour on an explicit constructor in this
438 position.'' (4)~The ``discount'' to subtract if the expression
439 is being scrutinised.
441 Assuming we have enough type- and value arguments (if not, we give up
442 immediately), then we see if the ``discounted size'' is below some
443 (semi-arbitrary) threshold. It works like this: for every argument
444 position where we're looking for a constructor AND WE HAVE ONE in our
445 hands, we get a (again, semi-arbitrary) discount [proportion to the
446 number of constructors in the type being scrutinized].
448 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
449 and the expression in question will evaluate to a constructor, we use
450 the computed discount size *for the result only* rather than
451 computing the argument discounts. Since we know the result of
452 the expression is going to be taken apart, discounting its size
453 is more accurate (see @sizeExpr@ above for how this discount size
456 We use this one to avoid exporting inlinings that we ``couldn't possibly
457 use'' on the other side. Can be overridden w/ flaggery.
458 Just the same as smallEnoughToInline, except that it has no actual arguments.
461 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
462 couldBeSmallEnoughToInline threshold rhs = case calcUnfoldingGuidance threshold rhs of
466 certainlyWillInline :: Unfolding -> Bool
467 -- Sees if the unfolding is pretty certain to inline
468 certainlyWillInline (CoreUnfolding _ _ _ is_cheap (UnfoldIfGoodArgs n_vals _ size _))
469 = is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold
470 certainlyWillInline other
473 smallEnoughToInline :: Unfolding -> Bool
474 smallEnoughToInline (CoreUnfolding _ _ _ _ (UnfoldIfGoodArgs _ _ size _))
475 = size <= opt_UF_UseThreshold
476 smallEnoughToInline other
480 %************************************************************************
482 \subsection{callSiteInline}
484 %************************************************************************
486 This is the key function. It decides whether to inline a variable at a call site
488 callSiteInline is used at call sites, so it is a bit more generous.
489 It's a very important function that embodies lots of heuristics.
490 A non-WHNF can be inlined if it doesn't occur inside a lambda,
491 and occurs exactly once or
492 occurs once in each branch of a case and is small
494 If the thing is in WHNF, there's no danger of duplicating work,
495 so we can inline if it occurs once, or is small
497 NOTE: we don't want to inline top-level functions that always diverge.
498 It just makes the code bigger. Tt turns out that the convenient way to prevent
499 them inlining is to give them a NOINLINE pragma, which we do in
500 StrictAnal.addStrictnessInfoToTopId
503 callSiteInline :: DynFlags
504 -> Bool -- True <=> the Id can be inlined
507 -> [Bool] -- One for each value arg; True if it is interesting
508 -> Bool -- True <=> continuation is interesting
509 -> Maybe CoreExpr -- Unfolding, if any
512 callSiteInline dflags active_inline occ id arg_infos interesting_cont
513 = case idUnfolding id of {
514 NoUnfolding -> Nothing ;
515 OtherCon cs -> Nothing ;
517 CompulsoryUnfolding unf_template -> Just unf_template ;
518 -- CompulsoryUnfolding => there is no top-level binding
519 -- for these things, so we must inline it.
520 -- Only a couple of primop-like things have
521 -- compulsory unfoldings (see MkId.lhs).
522 -- We don't allow them to be inactive
524 CoreUnfolding unf_template is_top is_value is_cheap guidance ->
527 result | yes_or_no = Just unf_template
528 | otherwise = Nothing
530 n_val_args = length arg_infos
533 | not active_inline = False
534 | otherwise = case occ of
535 IAmDead -> pprTrace "callSiteInline: dead" (ppr id) False
536 IAmALoopBreaker -> False
537 --OneOcc in_lam _ _ -> (not in_lam || is_cheap) && consider_safe True
538 other -> is_cheap && consider_safe False
539 -- we consider even the once-in-one-branch
540 -- occurrences, because they won't all have been
541 -- caught by preInlineUnconditionally. In particular,
542 -- if the occurrence is once inside a lambda, and the
543 -- rhs is cheap but not a manifest lambda, then
544 -- pre-inline will not have inlined it for fear of
545 -- invalidating the occurrence info in the rhs.
548 -- consider_safe decides whether it's a good idea to
549 -- inline something, given that there's no
550 -- work-duplication issue (the caller checks that).
553 UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount
555 | enough_args && size <= (n_vals_wanted + 1)
556 -- Inline unconditionally if there no size increase
557 -- Size of call is n_vals_wanted (+1 for the function)
561 -> some_benefit && small_enough
564 some_benefit = or arg_infos || really_interesting_cont ||
565 (not is_top && ({- once || -} (n_vals_wanted > 0 && enough_args)))
566 -- [was (once && not in_lam)]
567 -- If it occurs more than once, there must be
568 -- something interesting about some argument, or the
569 -- result context, to make it worth inlining
571 -- If a function has a nested defn we also record
572 -- some-benefit, on the grounds that we are often able
573 -- to eliminate the binding, and hence the allocation,
574 -- for the function altogether; this is good for join
575 -- points. But this only makes sense for *functions*;
576 -- inlining a constructor doesn't help allocation
577 -- unless the result is scrutinised. UNLESS the
578 -- constructor occurs just once, albeit possibly in
579 -- multiple case branches. Then inlining it doesn't
580 -- increase allocation, but it does increase the
581 -- chance that the constructor won't be allocated at
582 -- all in the branches that don't use it.
584 enough_args = n_val_args >= n_vals_wanted
585 really_interesting_cont | n_val_args < n_vals_wanted = False -- Too few args
586 | n_val_args == n_vals_wanted = interesting_cont
587 | otherwise = True -- Extra args
588 -- really_interesting_cont tells if the result of the
589 -- call is in an interesting context.
591 small_enough = (size - discount) <= opt_UF_UseThreshold
592 discount = computeDiscount n_vals_wanted arg_discounts res_discount
593 arg_infos really_interesting_cont
596 if dopt Opt_D_dump_inlinings dflags then
597 pprTrace "Considering inlining"
598 (ppr id <+> vcat [text "active:" <+> ppr active_inline,
599 text "occ info:" <+> ppr occ,
600 text "arg infos" <+> ppr arg_infos,
601 text "interesting continuation" <+> ppr interesting_cont,
602 text "is value:" <+> ppr is_value,
603 text "is cheap:" <+> ppr is_cheap,
604 text "guidance" <+> ppr guidance,
605 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])
611 computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int
612 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used
613 -- We multiple the raw discounts (args_discount and result_discount)
614 -- ty opt_UnfoldingKeenessFactor because the former have to do with
615 -- *size* whereas the discounts imply that there's some extra
616 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
619 -- we also discount 1 for each argument passed, because these will
620 -- reduce with the lambdas in the function (we count 1 for a lambda
622 = 1 + -- Discount of 1 because the result replaces the call
623 -- so we count 1 for the function itself
624 length (take n_vals_wanted arg_infos) +
625 -- Discount of 1 for each arg supplied, because the
626 -- result replaces the call
627 round (opt_UF_KeenessFactor *
628 fromIntegral (arg_discount + result_discount))
630 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
632 mk_arg_discount discount is_evald | is_evald = discount
635 -- Don't give a result discount unless there are enough args
636 result_discount | result_used = res_discount -- Over-applied, or case scrut