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, -- types
19 noUnfolding, mkUnfolding,
20 mkOtherCon, otherCons,
21 unfoldingTemplate, maybeUnfoldingTemplate,
22 isEvaldUnfolding, isCheapUnfolding,
23 hasUnfolding, hasSomeUnfolding,
25 couldBeSmallEnoughToInline,
26 certainlySmallEnoughToInline,
29 calcUnfoldingGuidance,
31 callSiteInline, blackListed
34 #include "HsVersions.h"
36 import CmdLineOpts ( opt_UF_CreationThreshold,
38 opt_UF_ScrutConDiscount,
39 opt_UF_FunAppDiscount,
40 opt_UF_PrimArgDiscount,
42 opt_UF_CheapOp, opt_UF_DearOp, opt_UF_NoRepLit,
43 opt_UnfoldCasms, opt_PprStyle_Debug,
47 import PprCore ( pprCoreExpr )
48 import OccurAnal ( occurAnalyseGlobalExpr )
50 import CoreUtils ( coreExprType, exprIsTrivial, exprIsValue, exprIsCheap )
51 import Id ( Id, idType, idUnique, isId,
52 getIdSpecialisation, getInlinePragma, getIdUnfolding
55 import Name ( isLocallyDefined )
56 import Const ( Con(..), isLitLitLit, isWHNFCon )
57 import PrimOp ( PrimOp(..), primOpIsDupable )
58 import IdInfo ( ArityInfo(..), InlinePragInfo(..), OccInfo(..) )
59 import TyCon ( tyConFamilySize )
60 import Type ( splitAlgTyConApp_maybe, splitFunTy_maybe, isUnLiftedType )
61 import Const ( isNoRepLit )
62 import Unique ( Unique, buildIdKey, augmentIdKey, runSTRepIdKey )
63 import Maybes ( maybeToBool )
65 import Util ( isIn, lengthExceeds )
69 %************************************************************************
71 \subsection{@Unfolding@ and @UnfoldingGuidance@ types}
73 %************************************************************************
79 | OtherCon [Con] -- It ain't one of these
80 -- (OtherCon xs) also indicates that something has been evaluated
81 -- and hence there's no point in re-evaluating it.
82 -- OtherCon [] is used even for non-data-type values
83 -- to indicated evaluated-ness. Notably:
84 -- data C = C !(Int -> Int)
85 -- case x of { C f -> ... }
86 -- Here, f gets an OtherCon [] unfolding.
88 | CoreUnfolding -- An unfolding with redundant cached information
89 CoreExpr -- Template; binder-info is correct
90 Bool -- exprIsCheap template (cached); it won't duplicate (much) work
91 -- if you inline this in more than one place
92 Bool -- exprIsValue template (cached); it is ok to discard a `seq` on
94 UnfoldingGuidance -- Tells about the *size* of the template.
98 noUnfolding = NoUnfolding
102 = CoreUnfolding (occurAnalyseGlobalExpr expr)
105 (calcUnfoldingGuidance opt_UF_CreationThreshold expr)
107 unfoldingTemplate :: Unfolding -> CoreExpr
108 unfoldingTemplate (CoreUnfolding expr _ _ _) = expr
109 unfoldingTemplate other = panic "getUnfoldingTemplate"
111 maybeUnfoldingTemplate :: Unfolding -> Maybe CoreExpr
112 maybeUnfoldingTemplate (CoreUnfolding expr _ _ _) = Just expr
113 maybeUnfoldingTemplate other = Nothing
115 otherCons (OtherCon cons) = cons
118 isEvaldUnfolding :: Unfolding -> Bool
119 isEvaldUnfolding (OtherCon _) = True
120 isEvaldUnfolding (CoreUnfolding _ _ is_evald _) = is_evald
121 isEvaldUnfolding other = False
123 isCheapUnfolding :: Unfolding -> Bool
124 isCheapUnfolding (CoreUnfolding _ is_cheap _ _) = is_cheap
125 isCheapUnfolding other = False
127 hasUnfolding :: Unfolding -> Bool
128 hasUnfolding (CoreUnfolding _ _ _ _) = True
129 hasUnfolding other = False
131 hasSomeUnfolding :: Unfolding -> Bool
132 hasSomeUnfolding NoUnfolding = False
133 hasSomeUnfolding other = True
135 data UnfoldingGuidance
137 | UnfoldAlways -- There is no "original" definition,
138 -- so you'd better unfold. Or: something
139 -- so cheap to unfold (e.g., 1#) that
140 -- you should do it absolutely always.
142 | UnfoldIfGoodArgs Int -- and "n" value args
144 [Int] -- Discount if the argument is evaluated.
145 -- (i.e., a simplification will definitely
146 -- be possible). One elt of the list per *value* arg.
148 Int -- The "size" of the unfolding; to be elaborated
151 Int -- Scrutinee discount: the discount to substract if the thing is in
152 -- a context (case (thing args) of ...),
153 -- (where there are the right number of arguments.)
157 instance Outputable UnfoldingGuidance where
158 ppr UnfoldAlways = ptext SLIT("ALWAYS")
159 ppr UnfoldNever = ptext SLIT("NEVER")
160 ppr (UnfoldIfGoodArgs v cs size discount)
161 = hsep [ptext SLIT("IF_ARGS"), int v,
162 if null cs -- always print *something*
164 else hcat (map (text . show) cs),
170 %************************************************************************
172 \subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
174 %************************************************************************
177 calcUnfoldingGuidance
178 :: Int -- bomb out if size gets bigger than this
179 -> CoreExpr -- expression to look at
181 calcUnfoldingGuidance bOMB_OUT_SIZE expr
182 | exprIsTrivial expr -- Often trivial expressions are never bound
183 -- to an expression, but it can happen. For
184 -- example, the Id for a nullary constructor has
185 -- a trivial expression as its unfolding, and
186 -- we want to make sure that we always unfold it.
190 = case collectBinders expr of { (binders, body) ->
192 val_binders = filter isId binders
194 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
196 TooBig -> UnfoldNever
198 SizeIs size cased_args scrut_discount
201 (map discount_for val_binders)
207 | is_fun_ty = num_cases * opt_UF_FunAppDiscount
208 | is_data_ty = num_cases * opt_UF_ScrutConDiscount
209 | otherwise = num_cases * opt_UF_PrimArgDiscount
211 num_cases = foldlBag (\n b' -> if b==b' then n+1 else n) 0 cased_args
212 -- Count occurrences of b in cased_args
214 is_fun_ty = maybeToBool (splitFunTy_maybe arg_ty)
215 (is_data_ty, tycon) = case (splitAlgTyConApp_maybe (idType b)) of
216 Nothing -> (False, panic "discount")
217 Just (tc,_,_) -> (True, tc)
222 sizeExpr :: Int -- Bomb out if it gets bigger than this
223 -> [Id] -- Arguments; we're interested in which of these
228 sizeExpr (I# bOMB_OUT_SIZE) args expr
231 size_up (Type t) = sizeZero -- Types cost nothing
232 size_up (Var v) = sizeOne
234 size_up (Note InlineMe _) = sizeTwo -- The idea is that this is one more
235 -- than the size of the "call" (i.e. 1)
236 -- We want to reply "no" to noSizeIncrease
237 -- for a bare reference (i.e. applied to no args)
238 -- to an INLINE thing
240 size_up (Note _ body) = size_up body -- Notes cost nothing
242 size_up (App fun (Type t)) = size_up fun
243 size_up (App fun arg) = size_up_app fun [arg]
245 size_up (Con con args) = foldr (addSize . size_up)
246 (size_up_con con args)
249 size_up (Lam b e) | isId b = size_up e `addSizeN` 1
250 | otherwise = size_up e
252 size_up (Let (NonRec binder rhs) body)
253 = nukeScrutDiscount (size_up rhs) `addSize`
254 size_up body `addSizeN`
255 (if isUnLiftedType (idType binder) then 0 else 1)
256 -- For the allocation
257 -- If the binder has an unlifted type there is no allocation
259 size_up (Let (Rec pairs) body)
260 = nukeScrutDiscount rhs_size `addSize`
261 size_up body `addSizeN`
262 length pairs -- For the allocation
264 rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
266 size_up (Case scrut _ alts)
267 = nukeScrutDiscount (size_up scrut) `addSize`
268 arg_discount scrut `addSize`
269 foldr (addSize . size_up_alt) sizeZero alts
270 `addSizeN` 1 -- charge one for the case itself.
272 -- Just charge for the alts that exist, not the ones that might exist
274 -- case (splitAlgTyConApp_maybe (coreExprType scrut)) of
276 -- Just (tc,_,_) -> tyConFamilySize tc
279 size_up_app (App fun arg) args = size_up_app fun (arg:args)
280 size_up_app fun args = foldr (addSize . size_up) (fun_discount fun) args
282 -- A function application with at least one value argument
283 -- so if the function is an argument give it an arg-discount
284 -- Also behave specially if the function is a build
285 fun_discount (Var fun) | idUnique fun == buildIdKey = buildSize
286 | idUnique fun == augmentIdKey = augmentSize
287 | fun `is_elem` args = scrutArg fun
288 fun_discount other = sizeZero
291 size_up_alt (con, bndrs, rhs) = size_up rhs
292 -- Don't charge for args, so that wrappers look cheap
295 size_up_con (Literal lit) args | isNoRepLit lit = sizeN opt_UF_NoRepLit
296 | otherwise = sizeOne
298 size_up_con (DataCon dc) args = conSizeN (valArgCount args)
300 size_up_con (PrimOp op) args = foldr addSize (sizeN op_cost) (map arg_discount args)
301 -- Give an arg-discount if a primop is applies to
302 -- one of the function's arguments
304 op_cost | primOpIsDupable op = opt_UF_CheapOp
305 | otherwise = opt_UF_DearOp
307 -- We want to record if we're case'ing, or applying, an argument
308 arg_discount (Var v) | v `is_elem` args = scrutArg v
309 arg_discount other = sizeZero
312 is_elem :: Id -> [Id] -> Bool
313 is_elem = isIn "size_up_scrut"
316 -- These addSize things have to be here because
317 -- I don't want to give them bOMB_OUT_SIZE as an argument
319 addSizeN TooBig _ = TooBig
320 addSizeN (SizeIs n xs d) (I# m)
321 | n_tot -# d <# bOMB_OUT_SIZE = SizeIs n_tot xs d
326 addSize TooBig _ = TooBig
327 addSize _ TooBig = TooBig
328 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
329 | (n_tot -# d_tot) <# bOMB_OUT_SIZE = SizeIs n_tot xys d_tot
334 xys = xs `unionBags` ys
337 Code for manipulating sizes
341 data ExprSize = TooBig
342 | SizeIs Int# -- Size found
343 (Bag Id) -- Arguments cased herein
344 Int# -- Size to subtract if result is scrutinised
345 -- by a case expression
347 sizeZero = SizeIs 0# emptyBag 0#
348 sizeOne = SizeIs 1# emptyBag 0#
349 sizeTwo = SizeIs 2# emptyBag 0#
350 sizeN (I# n) = SizeIs n emptyBag 0#
351 conSizeN (I# n) = SizeIs 1# emptyBag (n +# 1#)
352 -- Treat constructors as size 1, that unfoldAlways responsds 'False'
353 -- when asked about 'x' when x is bound to (C 3#).
354 -- This avoids gratuitous 'ticks' when x itself appears as an
355 -- atomic constructor argument.
357 buildSize = SizeIs (-2#) emptyBag 4#
358 -- We really want to inline applications of build
359 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
360 -- Indeed, we should add a result_discount becuause build is
361 -- very like a constructor. We don't bother to check that the
362 -- build is saturated (it usually is). The "-2" discounts for the \c n,
363 -- The "4" is rather arbitrary.
365 augmentSize = SizeIs (-2#) emptyBag 4#
366 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
367 -- e plus ys. The -2 accounts for the \cn
369 scrutArg v = SizeIs 0# (unitBag v) 0#
371 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
372 nukeScrutDiscount TooBig = TooBig
376 %************************************************************************
378 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
380 %************************************************************************
382 We have very limited information about an unfolding expression: (1)~so
383 many type arguments and so many value arguments expected---for our
384 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
385 a single integer. (3)~An ``argument info'' vector. For this, what we
386 have at the moment is a Boolean per argument position that says, ``I
387 will look with great favour on an explicit constructor in this
388 position.'' (4)~The ``discount'' to subtract if the expression
389 is being scrutinised.
391 Assuming we have enough type- and value arguments (if not, we give up
392 immediately), then we see if the ``discounted size'' is below some
393 (semi-arbitrary) threshold. It works like this: for every argument
394 position where we're looking for a constructor AND WE HAVE ONE in our
395 hands, we get a (again, semi-arbitrary) discount [proportion to the
396 number of constructors in the type being scrutinized].
398 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
399 and the expression in question will evaluate to a constructor, we use
400 the computed discount size *for the result only* rather than
401 computing the argument discounts. Since we know the result of
402 the expression is going to be taken apart, discounting its size
403 is more accurate (see @sizeExpr@ above for how this discount size
406 We use this one to avoid exporting inlinings that we ``couldn't possibly
407 use'' on the other side. Can be overridden w/ flaggery.
408 Just the same as smallEnoughToInline, except that it has no actual arguments.
411 couldBeSmallEnoughToInline :: UnfoldingGuidance -> Bool
412 couldBeSmallEnoughToInline UnfoldNever = False
413 couldBeSmallEnoughToInline other = True
415 certainlySmallEnoughToInline :: UnfoldingGuidance -> Bool
416 certainlySmallEnoughToInline UnfoldNever = False
417 certainlySmallEnoughToInline UnfoldAlways = True
418 certainlySmallEnoughToInline (UnfoldIfGoodArgs _ _ size _) = size <= opt_UF_UseThreshold
421 @okToUnfoldInHifile@ is used when emitting unfolding info into an interface
422 file to determine whether an unfolding candidate really should be unfolded.
423 The predicate is needed to prevent @_casm_@s (+ lit-lits) from being emitted
424 into interface files.
426 The reason for inlining expressions containing _casm_s into interface files
427 is that these fragments of C are likely to mention functions/#defines that
428 will be out-of-scope when inlined into another module. This is not an
429 unfixable problem for the user (just need to -#include the approp. header
430 file), but turning it off seems to the simplest thing to do.
433 okToUnfoldInHiFile :: CoreExpr -> Bool
434 okToUnfoldInHiFile e = opt_UnfoldCasms || go e
436 -- Race over an expression looking for CCalls..
438 go (Con (Literal lit) _) = not (isLitLitLit lit)
439 go (Con (PrimOp op) args) = okToUnfoldPrimOp op && all go args
440 go (Con con args) = True -- con args are always atomic
441 go (App fun arg) = go fun && go arg
442 go (Lam _ body) = go body
443 go (Let binds body) = and (map go (body :rhssOfBind binds))
444 go (Case scrut bndr alts) = and (map go (scrut:rhssOfAlts alts))
445 go (Note _ body) = go body
448 -- ok to unfold a PrimOp as long as it's not a _casm_
449 okToUnfoldPrimOp (CCallOp _ is_casm _ _) = not is_casm
450 okToUnfoldPrimOp _ = True
454 %************************************************************************
456 \subsection{callSiteInline}
458 %************************************************************************
460 This is the key function. It decides whether to inline a variable at a call site
462 callSiteInline is used at call sites, so it is a bit more generous.
463 It's a very important function that embodies lots of heuristics.
464 A non-WHNF can be inlined if it doesn't occur inside a lambda,
465 and occurs exactly once or
466 occurs once in each branch of a case and is small
468 If the thing is in WHNF, there's no danger of duplicating work,
469 so we can inline if it occurs once, or is small
472 callSiteInline :: Bool -- True <=> the Id is black listed
473 -> Bool -- 'inline' note at call site
475 -> [Bool] -- One for each value arg; True if it is interesting
476 -> Bool -- True <=> continuation is interesting
477 -> Maybe CoreExpr -- Unfolding, if any
480 callSiteInline black_listed inline_call id arg_infos interesting_cont
481 = case getIdUnfolding id of {
482 NoUnfolding -> Nothing ;
483 OtherCon _ -> Nothing ;
484 CoreUnfolding unf_template is_cheap _ guidance ->
487 result | yes_or_no = Just unf_template
488 | otherwise = Nothing
490 inline_prag = getInlinePragma id
491 n_val_args = length arg_infos
495 IAmDead -> pprTrace "callSiteInline: dead" (ppr id) False
496 IMustNotBeINLINEd -> False
497 IAmALoopBreaker -> False
498 IMustBeINLINEd -> True -- Overrides absolutely everything, including the black list
499 ICanSafelyBeINLINEd in_lam one_br -> consider in_lam True one_br
500 NoInlinePragInfo -> consider InsideLam False False
502 consider in_lam once once_in_one_branch
503 | black_listed = False
505 | once_in_one_branch -- Be very keen to inline something if this is its unique occurrence; that
506 -- gives a good chance of eliminating the original binding for the thing.
507 -- The only time we hold back is when substituting inside a lambda;
508 -- then if the context is totally uninteresting (not applied, not scrutinised)
509 -- there is no point in substituting because it might just increase allocation.
510 = WARN( case in_lam of { NotInsideLam -> True; other -> False },
511 text "callSiteInline:oneOcc" <+> ppr id )
512 -- If it has one occurrence, not inside a lambda, PreInlineUnconditionally
513 -- should have zapped it already
514 is_cheap && (not (null arg_infos) || interesting_cont)
516 | otherwise -- Occurs (textually) more than once, so look at its size
520 UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount
521 | enough_args && size <= (n_vals_wanted + 1)
523 -- Size of call is n_vals_wanted (+1 for the function)
526 InsideLam -> is_cheap
528 | not (or arg_infos || really_interesting_cont || once)
529 -- If it occurs more than once, there must be something interesting
530 -- about some argument, or the result, to make it worth inlining
531 -- We also drop this case if the thing occurs once, although perhaps in
532 -- several branches. In this case we are keener about inlining in the hope
533 -- that we'll be able to drop the allocation for the function altogether.
538 NotInsideLam -> small_enough
539 InsideLam -> is_cheap && small_enough
542 enough_args = n_val_args >= n_vals_wanted
543 really_interesting_cont | n_val_args < n_vals_wanted = False -- Too few args
544 | n_val_args == n_vals_wanted = interesting_cont
545 | otherwise = True -- Extra args
546 -- This rather elaborate defn for really_interesting_cont is important
547 -- Consider an I# = INLINE (\x -> I# {x})
548 -- The unfolding guidance deems it to have size 2, and no arguments.
549 -- So in an application (I# y) we must take the extra arg 'y' as
550 -- evidence of an interesting context!
552 small_enough = (size - discount) <= opt_UF_UseThreshold
553 discount = computeDiscount n_vals_wanted arg_discounts res_discount
554 arg_infos really_interesting_cont
559 if opt_D_dump_inlinings then
560 pprTrace "Considering inlining"
561 (ppr id <+> vcat [text "black listed" <+> ppr black_listed,
562 text "inline prag:" <+> ppr inline_prag,
563 text "arg infos" <+> ppr arg_infos,
564 text "interesting continuation" <+> ppr interesting_cont,
565 text "is cheap" <+> ppr is_cheap,
566 text "guidance" <+> ppr guidance,
567 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO",
569 text "Unfolding =" <+> pprCoreExpr unf_template
577 computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int
578 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used
579 -- We multiple the raw discounts (args_discount and result_discount)
580 -- ty opt_UnfoldingKeenessFactor because the former have to do with
581 -- *size* whereas the discounts imply that there's some extra
582 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
585 -- we also discount 1 for each argument passed, because these will
586 -- reduce with the lambdas in the function (we count 1 for a lambda
588 = length (take n_vals_wanted arg_infos) +
589 -- Discount of 1 for each arg supplied, because the
590 -- result replaces the call
591 round (opt_UF_KeenessFactor *
592 fromInt (arg_discount + result_discount))
594 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
596 mk_arg_discount discount is_evald | is_evald = discount
599 -- Don't give a result discount unless there are enough args
600 result_discount | result_used = res_discount -- Over-applied, or case scrut
605 %************************************************************************
607 \subsection{Black-listing}
609 %************************************************************************
611 Inlining is controlled by the "Inline phase" number, which is set
612 by the per-simplification-pass '-finline-phase' flag.
614 For optimisation we use phase 1,2 and nothing (i.e. no -finline-phase flag)
615 in that order. The meanings of these are determined by the @blackListed@ function
619 blackListed :: IdSet -- Used in transformation rules
620 -> Maybe Int -- Inline phase
621 -> Id -> Bool -- True <=> blacklisted
623 -- The blackListed function sees whether a variable should *not* be
624 -- inlined because of the inline phase we are in. This is the sole
625 -- place that the inline phase number is looked at.
627 -- Phase 0: used for 'no imported inlinings please'
628 -- This prevents wrappers getting inlined which in turn is bad for full laziness
629 blackListed rule_vars (Just 0)
630 = \v -> not (isLocallyDefined v)
632 -- Phase 1: don't inline any rule-y things or things with specialisations
633 blackListed rule_vars (Just 1)
634 = \v -> let v_uniq = idUnique v
635 in v `elemVarSet` rule_vars
636 || not (isEmptyCoreRules (getIdSpecialisation v))
637 || v_uniq == runSTRepIdKey
639 -- Phase 2: allow build/augment to inline, and specialisations
640 blackListed rule_vars (Just 2)
641 = \v -> let v_uniq = idUnique v
642 in (v `elemVarSet` rule_vars && not (v_uniq == buildIdKey ||
643 v_uniq == augmentIdKey))
644 || v_uniq == runSTRepIdKey
646 -- Otherwise just go for it
647 blackListed rule_vars phase
652 SLPJ 95/04: Why @runST@ must be inlined very late:
656 (a, s') = newArray# 100 [] s
657 (_, s'') = fill_in_array_or_something a x s'
661 If we inline @runST@, we'll get:
664 (a, s') = newArray# 100 [] realWorld#{-NB-}
665 (_, s'') = fill_in_array_or_something a x s'
669 And now the @newArray#@ binding can be floated to become a CAF, which
670 is totally and utterly wrong:
673 (a, s') = newArray# 100 [] realWorld#{-NB-} -- YIKES!!!
676 let (_, s'') = fill_in_array_or_something a x s' in
679 All calls to @f@ will share a {\em single} array!
681 Yet we do want to inline runST sometime, so we can avoid
682 needless code. Solution: black list it until the last moment.