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 mkOtherCon, otherCons,
21 unfoldingTemplate, maybeUnfoldingTemplate,
22 isEvaldUnfolding, isValueUnfolding, isCheapUnfolding, isCompulsoryUnfolding,
23 hasUnfolding, hasSomeUnfolding,
25 couldBeSmallEnoughToInline,
29 callSiteInline, blackListed
32 #include "HsVersions.h"
34 import CmdLineOpts ( opt_UF_CreationThreshold,
36 opt_UF_ScrutConDiscount,
37 opt_UF_FunAppDiscount,
38 opt_UF_PrimArgDiscount,
40 opt_UF_CheapOp, opt_UF_DearOp,
41 opt_UnfoldCasms, opt_PprStyle_Debug,
45 import PprCore ( pprCoreExpr )
46 import OccurAnal ( occurAnalyseGlobalExpr )
47 import CoreUtils ( exprIsValue, exprIsCheap, exprIsBottom, exprIsTrivial )
48 import Id ( Id, idType, idFlavour, isId, idWorkerInfo,
49 idSpecialisation, idInlinePragma, idUnfolding,
53 import Literal ( isLitLitLit )
54 import PrimOp ( PrimOp(..), primOpIsDupable, primOpOutOfLine, ccallIsCasm )
55 import IdInfo ( ArityInfo(..), InlinePragInfo(..), OccInfo(..), IdFlavour(..), CprInfo(..),
56 insideLam, workerExists, isNeverInlinePrag
58 import Type ( splitFunTy_maybe, isUnLiftedType )
59 import Unique ( Unique, buildIdKey, augmentIdKey, hasKey )
63 #if __GLASGOW_HASKELL__ >= 404
64 import GlaExts ( fromInt )
69 %************************************************************************
71 \subsection{Making unfoldings}
73 %************************************************************************
76 mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
78 mkUnfolding top_lvl expr
79 = CoreUnfolding (occurAnalyseGlobalExpr expr)
84 (calcUnfoldingGuidance opt_UF_CreationThreshold expr)
85 -- Sometimes during simplification, there's a large let-bound thing
86 -- which has been substituted, and so is now dead; so 'expr' contains
87 -- two copies of the thing while the occurrence-analysed expression doesn't
88 -- Nevertheless, we don't occ-analyse before computing the size because the
89 -- size computation bales out after a while, whereas occurrence analysis does not.
91 -- This can occasionally mean that the guidance is very pessimistic;
92 -- it gets fixed up next round
94 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
95 = CompulsoryUnfolding (occurAnalyseGlobalExpr expr)
99 %************************************************************************
101 \subsection{The UnfoldingGuidance type}
103 %************************************************************************
106 instance Outputable UnfoldingGuidance where
107 ppr UnfoldNever = ptext SLIT("NEVER")
108 ppr (UnfoldIfGoodArgs v cs size discount)
109 = hsep [ ptext SLIT("IF_ARGS"), int v,
110 brackets (hsep (map int cs)),
117 calcUnfoldingGuidance
118 :: Int -- bomb out if size gets bigger than this
119 -> CoreExpr -- expression to look at
121 calcUnfoldingGuidance bOMB_OUT_SIZE expr
122 = case collect_val_bndrs expr of { (inline, val_binders, body) ->
124 n_val_binders = length val_binders
126 max_inline_size = n_val_binders+2
127 -- The idea is that if there is an INLINE pragma (inline is True)
128 -- and there's a big body, we give a size of n_val_binders+2. This
129 -- This is just enough to fail the no-size-increase test in callSiteInline,
130 -- so that INLINE things don't get inlined into entirely boring contexts,
134 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
137 | not inline -> UnfoldNever
138 -- A big function with an INLINE pragma must
139 -- have an UnfoldIfGoodArgs guidance
140 | inline -> UnfoldIfGoodArgs n_val_binders
141 (map (const 0) val_binders)
144 SizeIs size cased_args scrut_discount
147 (map discount_for val_binders)
153 final_size | inline = boxed_size `min` max_inline_size
154 | otherwise = boxed_size
156 -- Sometimes an INLINE thing is smaller than n_val_binders+2.
157 -- A particular case in point is a constructor, which has size 1.
158 -- We want to inline this regardless, hence the `min`
160 discount_for b = foldlBag (\acc (b',n) -> if b==b' then acc+n else acc)
164 collect_val_bndrs e = go False [] e
165 -- We need to be a bit careful about how we collect the
166 -- value binders. In ptic, if we see
167 -- __inline_me (\x y -> e)
168 -- We want to say "2 value binders". Why? So that
169 -- we take account of information given for the arguments
171 go inline rev_vbs (Note InlineMe e) = go True rev_vbs e
172 go inline rev_vbs (Lam b e) | isId b = go inline (b:rev_vbs) e
173 | otherwise = go inline rev_vbs e
174 go inline rev_vbs e = (inline, reverse rev_vbs, e)
178 sizeExpr :: Int -- Bomb out if it gets bigger than this
179 -> [Id] -- Arguments; we're interested in which of these
184 sizeExpr (I# bOMB_OUT_SIZE) top_args expr
187 size_up (Type t) = sizeZero -- Types cost nothing
188 size_up (Var v) = sizeOne
190 size_up (Note _ body) = size_up body -- Notes cost nothing
192 size_up (App fun (Type t)) = size_up fun
193 size_up (App fun arg) = size_up_app fun [arg]
195 size_up (Lit lit) = sizeOne
197 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
198 | otherwise = size_up e
200 size_up (Let (NonRec binder rhs) body)
201 = nukeScrutDiscount (size_up rhs) `addSize`
202 size_up body `addSizeN`
203 (if isUnLiftedType (idType binder) then 0 else 1)
204 -- For the allocation
205 -- If the binder has an unlifted type there is no allocation
207 size_up (Let (Rec pairs) body)
208 = nukeScrutDiscount rhs_size `addSize`
209 size_up body `addSizeN`
210 length pairs -- For the allocation
212 rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
214 -- We want to make wrapper-style evaluation look cheap, so that
215 -- when we inline a wrapper it doesn't make call site (much) bigger
216 -- Otherwise we get nasty phase ordering stuff:
219 -- If we inline g's wrapper, f looks big, and doesn't get inlined
220 -- into h; if we inline f first, while it looks small, then g's
221 -- wrapper will get inlined later anyway. To avoid this nasty
222 -- ordering difference, we make (case a of (x,y) -> ...) look free.
223 size_up (Case (Var v) _ [alt])
225 = size_up_alt alt `addSize` SizeIs 0# (unitBag (v, 1)) 0#
226 -- Good to inline if an arg is scrutinised, because
227 -- that may eliminate allocation in the caller
228 -- And it eliminates the case itself
232 -- Scrutinising one of the argument variables,
233 -- with more than one alternative
234 size_up (Case (Var v) _ alts)
236 = alts_size (foldr addSize sizeOne alt_sizes) -- The 1 is for the scrutinee
237 (foldr1 maxSize alt_sizes)
239 alt_sizes = map size_up_alt alts
241 alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
242 (SizeIs max max_disc max_scrut) -- Size of biggest alternative
243 = SizeIs tot (unitBag (v, I# (1# +# tot -# max)) `unionBags` max_disc) max_scrut
244 -- If the variable is known, we produce a discount that
245 -- will take us back to 'max', the size of rh largest alternative
246 -- The 1+ is a little discount for reduced allocation in the caller
248 alts_size tot_size _ = tot_size
251 size_up (Case e _ alts) = nukeScrutDiscount (size_up e) `addSize`
252 foldr (addSize . size_up_alt) sizeZero alts
253 -- We don't charge for the case itself
254 -- It's a strict thing, and the price of the call
255 -- is paid by scrut. Also consider
256 -- case f x of DEFAULT -> e
257 -- This is just ';'! Don't charge for it.
260 size_up_app (App fun arg) args
261 | isTypeArg arg = size_up_app fun args
262 | otherwise = size_up_app fun (arg:args)
263 size_up_app fun args = foldr (addSize . nukeScrutDiscount . size_up)
264 (size_up_fun fun args)
267 -- A function application with at least one value argument
268 -- so if the function is an argument give it an arg-discount
270 -- Also behave specially if the function is a build
272 -- Also if the function is a constant Id (constr or primop)
273 -- compute discounts specially
274 size_up_fun (Var fun) args
275 | fun `hasKey` buildIdKey = buildSize
276 | fun `hasKey` augmentIdKey = augmentSize
278 = case idFlavour fun of
279 DataConId dc -> conSizeN (valArgCount args)
281 PrimOpId op -> primOpSize op (valArgCount args)
282 -- foldr addSize (primOpSize op) (map arg_discount args)
283 -- At one time I tried giving an arg-discount if a primop
284 -- is applied to one of the function's arguments, but it's
285 -- not good. At the moment, any unlifted-type arg gets a
286 -- 'True' for 'yes I'm evald', so we collect the discount even
287 -- if we know nothing about it. And just having it in a primop
288 -- doesn't help at all if we don't know something more.
290 other -> fun_discount fun `addSizeN`
291 (1 + length (filter (not . exprIsTrivial) args))
292 -- The 1+ is for the function itself
293 -- Add 1 for each non-trivial arg;
294 -- the allocation cost, as in let(rec)
295 -- Slight hack here: for constructors the args are almost always
296 -- trivial; and for primops they are almost always prim typed
297 -- We should really only count for non-prim-typed args in the
298 -- general case, but that seems too much like hard work
300 size_up_fun other args = size_up other
303 size_up_alt (con, bndrs, rhs) = size_up rhs
304 -- Don't charge for args, so that wrappers look cheap
307 -- We want to record if we're case'ing, or applying, an argument
308 fun_discount v | v `elem` top_args = SizeIs 0# (unitBag (v, opt_UF_FunAppDiscount)) 0#
309 fun_discount other = sizeZero
312 -- These addSize things have to be here because
313 -- I don't want to give them bOMB_OUT_SIZE as an argument
315 addSizeN TooBig _ = TooBig
316 addSizeN (SizeIs n xs d) (I# m)
317 | n_tot ># bOMB_OUT_SIZE = TooBig
318 | otherwise = SizeIs n_tot xs d
322 addSize TooBig _ = TooBig
323 addSize _ TooBig = TooBig
324 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
325 | n_tot ># bOMB_OUT_SIZE = TooBig
326 | otherwise = SizeIs n_tot xys d_tot
330 xys = xs `unionBags` ys
333 Code for manipulating sizes
337 data ExprSize = TooBig
338 | SizeIs Int# -- Size found
339 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
340 Int# -- Size to subtract if result is scrutinised
341 -- by a case expression
343 isTooBig TooBig = True
346 maxSize TooBig _ = TooBig
347 maxSize _ TooBig = TooBig
348 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
351 sizeZero = SizeIs 0# emptyBag 0#
352 sizeOne = SizeIs 1# emptyBag 0#
353 sizeTwo = SizeIs 2# emptyBag 0#
354 sizeN (I# n) = SizeIs n emptyBag 0#
355 conSizeN (I# n) = SizeIs 1# emptyBag (n +# 1#)
356 -- Treat constructors as size 1; we are keen to expose them
357 -- (and we charge separately for their args). We can't treat
358 -- them as size zero, else we find that (I# x) has size 1,
359 -- which is the same as a lone variable; and hence 'v' will
360 -- always be replaced by (I# x), where v is bound to I# x.
363 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
364 | not (primOpOutOfLine op) = sizeZero -- These are good to inline
365 | otherwise = sizeOne
367 buildSize = SizeIs (-2#) emptyBag 4#
368 -- We really want to inline applications of build
369 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
370 -- Indeed, we should add a result_discount becuause build is
371 -- very like a constructor. We don't bother to check that the
372 -- build is saturated (it usually is). The "-2" discounts for the \c n,
373 -- The "4" is rather arbitrary.
375 augmentSize = SizeIs (-2#) emptyBag 4#
376 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
377 -- e plus ys. The -2 accounts for the \cn
379 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
380 nukeScrutDiscount TooBig = TooBig
382 -- When we return a lambda, give a discount if it's used (applied)
383 lamScrutDiscount (SizeIs n vs d) = case opt_UF_FunAppDiscount of { I# d -> SizeIs n vs d }
384 lamScrutDiscount TooBig = TooBig
388 %************************************************************************
390 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
392 %************************************************************************
394 We have very limited information about an unfolding expression: (1)~so
395 many type arguments and so many value arguments expected---for our
396 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
397 a single integer. (3)~An ``argument info'' vector. For this, what we
398 have at the moment is a Boolean per argument position that says, ``I
399 will look with great favour on an explicit constructor in this
400 position.'' (4)~The ``discount'' to subtract if the expression
401 is being scrutinised.
403 Assuming we have enough type- and value arguments (if not, we give up
404 immediately), then we see if the ``discounted size'' is below some
405 (semi-arbitrary) threshold. It works like this: for every argument
406 position where we're looking for a constructor AND WE HAVE ONE in our
407 hands, we get a (again, semi-arbitrary) discount [proportion to the
408 number of constructors in the type being scrutinized].
410 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
411 and the expression in question will evaluate to a constructor, we use
412 the computed discount size *for the result only* rather than
413 computing the argument discounts. Since we know the result of
414 the expression is going to be taken apart, discounting its size
415 is more accurate (see @sizeExpr@ above for how this discount size
418 We use this one to avoid exporting inlinings that we ``couldn't possibly
419 use'' on the other side. Can be overridden w/ flaggery.
420 Just the same as smallEnoughToInline, except that it has no actual arguments.
423 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
424 couldBeSmallEnoughToInline threshold rhs = case calcUnfoldingGuidance threshold rhs of
428 certainlyWillInline :: Id -> Bool
429 -- Sees if the Id is pretty certain to inline
430 certainlyWillInline v
431 = case idUnfolding v of
433 CoreUnfolding _ _ _ is_value _ g@(UnfoldIfGoodArgs n_vals _ size _)
435 && size - (n_vals +1) <= opt_UF_UseThreshold
440 @okToUnfoldInHifile@ is used when emitting unfolding info into an interface
441 file to determine whether an unfolding candidate really should be unfolded.
442 The predicate is needed to prevent @_casm_@s (+ lit-lits) from being emitted
443 into interface files.
445 The reason for inlining expressions containing _casm_s into interface files
446 is that these fragments of C are likely to mention functions/#defines that
447 will be out-of-scope when inlined into another module. This is not an
448 unfixable problem for the user (just need to -#include the approp. header
449 file), but turning it off seems to the simplest thing to do.
452 okToUnfoldInHiFile :: CoreExpr -> Bool
453 okToUnfoldInHiFile e = opt_UnfoldCasms || go e
455 -- Race over an expression looking for CCalls..
456 go (Var v) = case isPrimOpId_maybe v of
457 Just op -> okToUnfoldPrimOp op
459 go (Lit lit) = not (isLitLitLit lit)
460 go (App fun arg) = go fun && go arg
461 go (Lam _ body) = go body
462 go (Let binds body) = and (map go (body :rhssOfBind binds))
463 go (Case scrut bndr alts) = and (map go (scrut:rhssOfAlts alts)) &&
464 not (any isLitLitLit [ lit | (LitAlt lit, _, _) <- alts ])
465 go (Note _ body) = go body
468 -- ok to unfold a PrimOp as long as it's not a _casm_
469 okToUnfoldPrimOp (CCallOp ccall) = not (ccallIsCasm ccall)
470 okToUnfoldPrimOp _ = True
474 %************************************************************************
476 \subsection{callSiteInline}
478 %************************************************************************
480 This is the key function. It decides whether to inline a variable at a call site
482 callSiteInline is used at call sites, so it is a bit more generous.
483 It's a very important function that embodies lots of heuristics.
484 A non-WHNF can be inlined if it doesn't occur inside a lambda,
485 and occurs exactly once or
486 occurs once in each branch of a case and is small
488 If the thing is in WHNF, there's no danger of duplicating work,
489 so we can inline if it occurs once, or is small
491 NOTE: we don't want to inline top-level functions that always diverge.
492 It just makes the code bigger. Tt turns out that the convenient way to prevent
493 them inlining is to give them a NOINLINE pragma, which we do in
494 StrictAnal.addStrictnessInfoToTopId
497 callSiteInline :: Bool -- True <=> the Id is black listed
498 -> Bool -- 'inline' note at call site
501 -> [Bool] -- One for each value arg; True if it is interesting
502 -> Bool -- True <=> continuation is interesting
503 -> Maybe CoreExpr -- Unfolding, if any
506 callSiteInline black_listed inline_call occ id arg_infos interesting_cont
507 = case idUnfolding id of {
508 NoUnfolding -> Nothing ;
509 OtherCon cs -> Nothing ;
510 CompulsoryUnfolding unf_template | black_listed -> Nothing
511 | otherwise -> Just unf_template ;
512 -- Constructors have compulsory unfoldings, but
513 -- may have rules, in which case they are
514 -- black listed till later
515 CoreUnfolding unf_template is_top is_cheap is_value is_bot guidance ->
518 result | yes_or_no = Just unf_template
519 | otherwise = Nothing
521 n_val_args = length arg_infos
523 ok_inside_lam = is_value || is_bot || (is_cheap && not is_top)
524 -- I'm experimenting with is_cheap && not is_top
527 | black_listed = False
528 | otherwise = case occ of
529 IAmDead -> pprTrace "callSiteInline: dead" (ppr id) False
530 IAmALoopBreaker -> False
531 OneOcc in_lam one_br -> (not in_lam || ok_inside_lam) && consider_safe in_lam True one_br
532 NoOccInfo -> ok_inside_lam && consider_safe True False False
534 consider_safe in_lam once once_in_one_branch
535 -- consider_safe decides whether it's a good idea to inline something,
536 -- given that there's no work-duplication issue (the caller checks that).
537 -- once_in_one_branch = True means there's a unique textual occurrence
541 -- Be very keen to inline something if this is its unique occurrence:
543 -- a) Inlining gives a good chance of eliminating the original
544 -- binding (and hence the allocation) for the thing.
545 -- (Provided it's not a top level binding, in which case the
546 -- allocation costs nothing.)
548 -- b) Inlining a function that is called only once exposes the
549 -- body function to the call site.
551 -- The only time we hold back is when substituting inside a lambda;
552 -- then if the context is totally uninteresting (not applied, not scrutinised)
553 -- there is no point in substituting because it might just increase allocation,
554 -- by allocating the function itself many times
556 -- Note: there used to be a '&& not top_level' in the guard above,
557 -- but that stopped us inlining top-level functions used only once,
559 = not in_lam || not (null arg_infos) || interesting_cont
563 UnfoldNever -> False ;
564 UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount
566 | enough_args && size <= (n_vals_wanted + 1)
568 -- Size of call is n_vals_wanted (+1 for the function)
572 -> some_benefit && small_enough
575 some_benefit = or arg_infos || really_interesting_cont ||
576 (not is_top && (once || (n_vals_wanted > 0 && enough_args)))
577 -- If it occurs more than once, there must be something interesting
578 -- about some argument, or the result context, to make it worth inlining
580 -- If a function has a nested defn we also record some-benefit,
581 -- on the grounds that we are often able to eliminate the binding,
582 -- and hence the allocation, for the function altogether; this is good
583 -- for join points. But this only makes sense for *functions*;
584 -- inlining a constructor doesn't help allocation unless the result is
585 -- scrutinised. UNLESS the constructor occurs just once, albeit possibly
586 -- in multiple case branches. Then inlining it doesn't increase allocation,
587 -- but it does increase the chance that the constructor won't be allocated at all
588 -- in the branches that don't use it.
590 enough_args = n_val_args >= n_vals_wanted
591 really_interesting_cont | n_val_args < n_vals_wanted = False -- Too few args
592 | n_val_args == n_vals_wanted = interesting_cont
593 | otherwise = True -- Extra args
594 -- really_interesting_cont tells if the result of the
595 -- call is in an interesting context.
597 small_enough = (size - discount) <= opt_UF_UseThreshold
598 discount = computeDiscount n_vals_wanted arg_discounts res_discount
599 arg_infos really_interesting_cont
603 if opt_D_dump_inlinings then
604 pprTrace "Considering inlining"
605 (ppr id <+> vcat [text "black listed" <+> ppr black_listed,
606 text "occ info:" <+> ppr occ,
607 text "arg infos" <+> ppr arg_infos,
608 text "interesting continuation" <+> ppr interesting_cont,
609 text "is value:" <+> ppr is_value,
610 text "is cheap:" <+> ppr is_cheap,
611 text "is bottom:" <+> ppr is_bot,
612 text "is top-level:" <+> ppr is_top,
613 text "guidance" <+> ppr guidance,
614 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO",
616 text "Unfolding =" <+> pprCoreExpr unf_template
624 computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int
625 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used
626 -- We multiple the raw discounts (args_discount and result_discount)
627 -- ty opt_UnfoldingKeenessFactor because the former have to do with
628 -- *size* whereas the discounts imply that there's some extra
629 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
632 -- we also discount 1 for each argument passed, because these will
633 -- reduce with the lambdas in the function (we count 1 for a lambda
635 = 1 + -- Discount of 1 because the result replaces the call
636 -- so we count 1 for the function itself
637 length (take n_vals_wanted arg_infos) +
638 -- Discount of 1 for each arg supplied, because the
639 -- result replaces the call
640 round (opt_UF_KeenessFactor *
641 fromInt (arg_discount + result_discount))
643 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
645 mk_arg_discount discount is_evald | is_evald = discount
648 -- Don't give a result discount unless there are enough args
649 result_discount | result_used = res_discount -- Over-applied, or case scrut
654 %************************************************************************
656 \subsection{Black-listing}
658 %************************************************************************
660 Inlining is controlled by the "Inline phase" number, which is set
661 by the per-simplification-pass '-finline-phase' flag.
663 For optimisation we use phase 1,2 and nothing (i.e. no -finline-phase flag)
664 in that order. The meanings of these are determined by the @blackListed@ function
667 The final simplification doesn't have a phase number.
673 (least black listing, most inlining)
674 INLINE n foo phase is Just p *and* p<n *and* foo appears on LHS of rule
675 INLINE foo phase is Just p *and* foo appears on LHS of rule
676 NOINLINE n foo phase is Just p *and* (p<n *or* foo appears on LHS of rule)
678 (most black listing, least inlining)
681 blackListed :: IdSet -- Used in transformation rules
682 -> Maybe Int -- Inline phase
683 -> Id -> Bool -- True <=> blacklisted
685 -- The blackListed function sees whether a variable should *not* be
686 -- inlined because of the inline phase we are in. This is the sole
687 -- place that the inline phase number is looked at.
689 blackListed rule_vars Nothing -- Last phase
690 = \v -> isNeverInlinePrag (idInlinePragma v)
692 blackListed rule_vars (Just phase)
693 = \v -> normal_case rule_vars phase v
695 normal_case rule_vars phase v
696 = case idInlinePragma v of
697 NoInlinePragInfo -> has_rules
699 IMustNotBeINLINEd from_INLINE Nothing
700 | from_INLINE -> has_rules -- Black list until final phase
701 | otherwise -> True -- Always blacklisted
703 IMustNotBeINLINEd from_inline (Just threshold)
704 | from_inline -> (phase < threshold && has_rules)
705 | otherwise -> (phase < threshold || has_rules)
707 has_rules = v `elemVarSet` rule_vars
708 || not (isEmptyCoreRules (idSpecialisation v))
712 SLPJ 95/04: Why @runST@ must be inlined very late:
716 (a, s') = newArray# 100 [] s
717 (_, s'') = fill_in_array_or_something a x s'
721 If we inline @runST@, we'll get:
724 (a, s') = newArray# 100 [] realWorld#{-NB-}
725 (_, s'') = fill_in_array_or_something a x s'
729 And now the @newArray#@ binding can be floated to become a CAF, which
730 is totally and utterly wrong:
733 (a, s') = newArray# 100 [] realWorld#{-NB-} -- YIKES!!!
736 let (_, s'') = fill_in_array_or_something a x s' in
739 All calls to @f@ will share a {\em single} array!
741 Yet we do want to inline runST sometime, so we can avoid
742 needless code. Solution: black list it until the last moment.