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_FunAppDiscount,
38 opt_UF_DearOp, opt_UnfoldCasms,
39 DynFlags, DynFlag(..), dopt
42 import PprCore ( pprCoreExpr )
43 import OccurAnal ( occurAnalyseGlobalExpr )
44 import CoreUtils ( exprIsValue, exprIsCheap, exprIsTrivial )
45 import Id ( Id, idType, idFlavour, isId,
46 idSpecialisation, idInlinePragma, idUnfolding,
50 import Literal ( isLitLitLit, litIsDupable )
51 import PrimOp ( PrimOp(..), primOpIsDupable, primOpOutOfLine, ccallIsCasm )
52 import IdInfo ( InlinePragInfo(..), OccInfo(..), IdFlavour(..),
55 import Type ( isUnLiftedType )
56 import PrelNames ( hasKey, buildIdKey, augmentIdKey )
61 #if __GLASGOW_HASKELL__ >= 404
62 import GlaExts ( fromInt )
67 %************************************************************************
69 \subsection{Making unfoldings}
71 %************************************************************************
74 mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
76 mkUnfolding top_lvl expr
77 = CoreUnfolding (occurAnalyseGlobalExpr expr)
83 -- OK to inline inside a lambda
85 (calcUnfoldingGuidance opt_UF_CreationThreshold expr)
86 -- Sometimes during simplification, there's a large let-bound thing
87 -- which has been substituted, and so is now dead; so 'expr' contains
88 -- two copies of the thing while the occurrence-analysed expression doesn't
89 -- Nevertheless, we don't occ-analyse before computing the size because the
90 -- size computation bales out after a while, whereas occurrence analysis does not.
92 -- This can occasionally mean that the guidance is very pessimistic;
93 -- it gets fixed up next round
95 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
96 = CompulsoryUnfolding (occurAnalyseGlobalExpr expr)
100 %************************************************************************
102 \subsection{The UnfoldingGuidance type}
104 %************************************************************************
107 instance Outputable UnfoldingGuidance where
108 ppr UnfoldNever = ptext SLIT("NEVER")
109 ppr (UnfoldIfGoodArgs v cs size discount)
110 = hsep [ ptext SLIT("IF_ARGS"), int v,
111 brackets (hsep (map int cs)),
118 calcUnfoldingGuidance
119 :: Int -- bomb out if size gets bigger than this
120 -> CoreExpr -- expression to look at
122 calcUnfoldingGuidance bOMB_OUT_SIZE expr
123 = case collect_val_bndrs expr of { (inline, val_binders, body) ->
125 n_val_binders = length val_binders
127 max_inline_size = n_val_binders+2
128 -- The idea is that if there is an INLINE pragma (inline is True)
129 -- and there's a big body, we give a size of n_val_binders+2. This
130 -- This is just enough to fail the no-size-increase test in callSiteInline,
131 -- so that INLINE things don't get inlined into entirely boring contexts,
135 case (sizeExpr bOMB_OUT_SIZE val_binders body) of
138 | not inline -> UnfoldNever
139 -- A big function with an INLINE pragma must
140 -- have an UnfoldIfGoodArgs guidance
141 | inline -> UnfoldIfGoodArgs n_val_binders
142 (map (const 0) val_binders)
145 SizeIs size cased_args scrut_discount
148 (map discount_for val_binders)
150 (iBox scrut_discount)
152 boxed_size = iBox size
154 final_size | inline = boxed_size `min` max_inline_size
155 | otherwise = boxed_size
157 -- Sometimes an INLINE thing is smaller than n_val_binders+2.
158 -- A particular case in point is a constructor, which has size 1.
159 -- We want to inline this regardless, hence the `min`
161 discount_for b = foldlBag (\acc (b',n) -> if b==b' then acc+n else acc)
165 collect_val_bndrs e = go False [] e
166 -- We need to be a bit careful about how we collect the
167 -- value binders. In ptic, if we see
168 -- __inline_me (\x y -> e)
169 -- We want to say "2 value binders". Why? So that
170 -- we take account of information given for the arguments
172 go inline rev_vbs (Note InlineMe e) = go True rev_vbs e
173 go inline rev_vbs (Lam b e) | isId b = go inline (b:rev_vbs) e
174 | otherwise = go inline rev_vbs e
175 go inline rev_vbs e = (inline, reverse rev_vbs, e)
179 sizeExpr :: Int -- Bomb out if it gets bigger than this
180 -> [Id] -- Arguments; we're interested in which of these
185 sizeExpr bOMB_OUT_SIZE top_args expr
188 size_up (Type t) = sizeZero -- Types cost nothing
189 size_up (Var v) = sizeOne
191 size_up (Note _ body) = size_up body -- Notes cost nothing
193 size_up (App fun (Type t)) = size_up fun
194 size_up (App fun arg) = size_up_app fun [arg]
196 size_up (Lit lit) | litIsDupable lit = sizeOne
197 | otherwise = sizeN opt_UF_DearOp -- For lack of anything better
199 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
200 | otherwise = size_up e
202 size_up (Let (NonRec binder rhs) body)
203 = nukeScrutDiscount (size_up rhs) `addSize`
204 size_up body `addSizeN`
205 (if isUnLiftedType (idType binder) then 0 else 1)
206 -- For the allocation
207 -- If the binder has an unlifted type there is no allocation
209 size_up (Let (Rec pairs) body)
210 = nukeScrutDiscount rhs_size `addSize`
211 size_up body `addSizeN`
212 length pairs -- For the allocation
214 rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
216 size_up (Case (Var v) _ alts)
217 | v `elem` top_args -- We are scrutinising an argument variable
219 {- I'm nuking this special case; BUT see the comment with case alternatives.
221 (a) It's too eager. We don't want to inline a wrapper into a
222 context with no benefit.
223 E.g. \ x. f (x+x) o point in inlining (+) here!
225 (b) It's ineffective. Once g's wrapper is inlined, its case-expressions
226 aren't scrutinising arguments any more
230 [alt] -> size_up_alt alt `addSize` SizeIs 0# (unitBag (v, 1)) 0#
231 -- We want to make wrapper-style evaluation look cheap, so that
232 -- when we inline a wrapper it doesn't make call site (much) bigger
233 -- Otherwise we get nasty phase ordering stuff:
236 -- If we inline g's wrapper, f looks big, and doesn't get inlined
237 -- into h; if we inline f first, while it looks small, then g's
238 -- wrapper will get inlined later anyway. To avoid this nasty
239 -- ordering difference, we make (case a of (x,y) -> ...),
240 -- *where a is one of the arguments* look free.
244 alts_size (foldr addSize sizeOne alt_sizes) -- The 1 is for the scrutinee
245 (foldr1 maxSize alt_sizes)
247 -- Good to inline if an arg is scrutinised, because
248 -- that may eliminate allocation in the caller
249 -- And it eliminates the case itself
252 alt_sizes = map size_up_alt alts
254 -- alts_size tries to compute a good discount for
255 -- the case when we are scrutinising an argument variable
256 alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
257 (SizeIs max max_disc max_scrut) -- Size of biggest alternative
258 = SizeIs tot (unitBag (v, iBox (_ILIT 1 +# tot -# max)) `unionBags` max_disc) max_scrut
259 -- If the variable is known, we produce a discount that
260 -- will take us back to 'max', the size of rh largest alternative
261 -- The 1+ is a little discount for reduced allocation in the caller
262 alts_size tot_size _ = tot_size
265 size_up (Case e _ alts) = nukeScrutDiscount (size_up e) `addSize`
266 foldr (addSize . size_up_alt) sizeZero alts
267 -- We don't charge for the case itself
268 -- It's a strict thing, and the price of the call
269 -- is paid by scrut. Also consider
270 -- case f x of DEFAULT -> e
271 -- This is just ';'! Don't charge for it.
274 size_up_app (App fun arg) args
275 | isTypeArg arg = size_up_app fun args
276 | otherwise = size_up_app fun (arg:args)
277 size_up_app fun args = foldr (addSize . nukeScrutDiscount . size_up)
278 (size_up_fun fun args)
281 -- A function application with at least one value argument
282 -- so if the function is an argument give it an arg-discount
284 -- Also behave specially if the function is a build
286 -- Also if the function is a constant Id (constr or primop)
287 -- compute discounts specially
288 size_up_fun (Var fun) args
289 | fun `hasKey` buildIdKey = buildSize
290 | fun `hasKey` augmentIdKey = augmentSize
292 = case idFlavour fun of
293 DataConId dc -> conSizeN (valArgCount args)
295 PrimOpId op -> primOpSize op (valArgCount args)
296 -- foldr addSize (primOpSize op) (map arg_discount args)
297 -- At one time I tried giving an arg-discount if a primop
298 -- is applied to one of the function's arguments, but it's
299 -- not good. At the moment, any unlifted-type arg gets a
300 -- 'True' for 'yes I'm evald', so we collect the discount even
301 -- if we know nothing about it. And just having it in a primop
302 -- doesn't help at all if we don't know something more.
304 other -> fun_discount fun `addSizeN`
305 (1 + length (filter (not . exprIsTrivial) args))
306 -- The 1+ is for the function itself
307 -- Add 1 for each non-trivial arg;
308 -- the allocation cost, as in let(rec)
309 -- Slight hack here: for constructors the args are almost always
310 -- trivial; and for primops they are almost always prim typed
311 -- We should really only count for non-prim-typed args in the
312 -- general case, but that seems too much like hard work
314 size_up_fun other args = size_up other
317 size_up_alt (con, bndrs, rhs) = size_up rhs
318 -- Don't charge for args, so that wrappers look cheap
319 -- (See comments about wrappers with Case)
322 -- We want to record if we're case'ing, or applying, an argument
323 fun_discount v | v `elem` top_args = SizeIs 0# (unitBag (v, opt_UF_FunAppDiscount)) 0#
324 fun_discount other = sizeZero
327 -- These addSize things have to be here because
328 -- I don't want to give them bOMB_OUT_SIZE as an argument
330 addSizeN TooBig _ = TooBig
331 addSizeN (SizeIs n xs d) m
332 | n_tot ># (iUnbox bOMB_OUT_SIZE) = TooBig
333 | otherwise = SizeIs n_tot xs d
335 n_tot = n +# iUnbox m
337 addSize TooBig _ = TooBig
338 addSize _ TooBig = TooBig
339 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
340 | n_tot ># (iUnbox bOMB_OUT_SIZE) = TooBig
341 | otherwise = SizeIs n_tot xys d_tot
345 xys = xs `unionBags` ys
348 Code for manipulating sizes
352 data ExprSize = TooBig
353 | SizeIs FastInt -- Size found
354 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
355 FastInt -- Size to subtract if result is scrutinised
356 -- by a case expression
359 maxSize TooBig _ = TooBig
360 maxSize _ TooBig = TooBig
361 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
364 sizeZero = SizeIs (_ILIT 0) emptyBag (_ILIT 0)
365 sizeOne = SizeIs (_ILIT 1) emptyBag (_ILIT 0)
366 sizeTwo = SizeIs (_ILIT 2) emptyBag (_ILIT 0)
367 sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT 0)
368 conSizeN n = SizeIs (_ILIT 1) emptyBag (iUnbox n +# _ILIT 1)
369 -- Treat constructors as size 1; we are keen to expose them
370 -- (and we charge separately for their args). We can't treat
371 -- them as size zero, else we find that (iBox x) has size 1,
372 -- which is the same as a lone variable; and hence 'v' will
373 -- always be replaced by (iBox x), where v is bound to iBox x.
376 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
377 | not (primOpOutOfLine op) = sizeZero -- These are good to inline
378 | otherwise = sizeOne
380 buildSize = SizeIs (-2#) emptyBag 4#
381 -- We really want to inline applications of build
382 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
383 -- Indeed, we should add a result_discount becuause build is
384 -- very like a constructor. We don't bother to check that the
385 -- build is saturated (it usually is). The "-2" discounts for the \c n,
386 -- The "4" is rather arbitrary.
388 augmentSize = SizeIs (-2#) emptyBag 4#
389 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
390 -- e plus ys. The -2 accounts for the \cn
392 nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs 0#
393 nukeScrutDiscount TooBig = TooBig
395 -- When we return a lambda, give a discount if it's used (applied)
396 lamScrutDiscount (SizeIs n vs d) = case opt_UF_FunAppDiscount of { d -> SizeIs n vs (iUnbox d) }
397 lamScrutDiscount TooBig = TooBig
401 %************************************************************************
403 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
405 %************************************************************************
407 We have very limited information about an unfolding expression: (1)~so
408 many type arguments and so many value arguments expected---for our
409 purposes here, we assume we've got those. (2)~A ``size'' or ``cost,''
410 a single integer. (3)~An ``argument info'' vector. For this, what we
411 have at the moment is a Boolean per argument position that says, ``I
412 will look with great favour on an explicit constructor in this
413 position.'' (4)~The ``discount'' to subtract if the expression
414 is being scrutinised.
416 Assuming we have enough type- and value arguments (if not, we give up
417 immediately), then we see if the ``discounted size'' is below some
418 (semi-arbitrary) threshold. It works like this: for every argument
419 position where we're looking for a constructor AND WE HAVE ONE in our
420 hands, we get a (again, semi-arbitrary) discount [proportion to the
421 number of constructors in the type being scrutinized].
423 If we're in the context of a scrutinee ( \tr{(case <expr > of A .. -> ...;.. )})
424 and the expression in question will evaluate to a constructor, we use
425 the computed discount size *for the result only* rather than
426 computing the argument discounts. Since we know the result of
427 the expression is going to be taken apart, discounting its size
428 is more accurate (see @sizeExpr@ above for how this discount size
431 We use this one to avoid exporting inlinings that we ``couldn't possibly
432 use'' on the other side. Can be overridden w/ flaggery.
433 Just the same as smallEnoughToInline, except that it has no actual arguments.
436 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
437 couldBeSmallEnoughToInline threshold rhs = case calcUnfoldingGuidance threshold rhs of
441 certainlyWillInline :: Id -> Bool
442 -- Sees if the Id is pretty certain to inline
443 certainlyWillInline v
444 = case idUnfolding v of
446 CoreUnfolding _ _ is_value _ g@(UnfoldIfGoodArgs n_vals _ size _)
448 && size - (n_vals +1) <= opt_UF_UseThreshold
453 @okToUnfoldInHifile@ is used when emitting unfolding info into an interface
454 file to determine whether an unfolding candidate really should be unfolded.
455 The predicate is needed to prevent @_casm_@s (+ lit-lits) from being emitted
456 into interface files.
458 The reason for inlining expressions containing _casm_s into interface files
459 is that these fragments of C are likely to mention functions/#defines that
460 will be out-of-scope when inlined into another module. This is not an
461 unfixable problem for the user (just need to -#include the approp. header
462 file), but turning it off seems to the simplest thing to do.
465 okToUnfoldInHiFile :: CoreExpr -> Bool
466 okToUnfoldInHiFile e = opt_UnfoldCasms || go e
468 -- Race over an expression looking for CCalls..
469 go (Var v) = case isPrimOpId_maybe v of
470 Just op -> okToUnfoldPrimOp op
472 go (Lit lit) = not (isLitLitLit lit)
473 go (App fun arg) = go fun && go arg
474 go (Lam _ body) = go body
475 go (Let binds body) = and (map go (body :rhssOfBind binds))
476 go (Case scrut bndr alts) = and (map go (scrut:rhssOfAlts alts)) &&
477 not (any isLitLitLit [ lit | (LitAlt lit, _, _) <- alts ])
478 go (Note _ body) = go body
481 -- ok to unfold a PrimOp as long as it's not a _casm_
482 okToUnfoldPrimOp (CCallOp ccall) = not (ccallIsCasm ccall)
483 okToUnfoldPrimOp _ = True
487 %************************************************************************
489 \subsection{callSiteInline}
491 %************************************************************************
493 This is the key function. It decides whether to inline a variable at a call site
495 callSiteInline is used at call sites, so it is a bit more generous.
496 It's a very important function that embodies lots of heuristics.
497 A non-WHNF can be inlined if it doesn't occur inside a lambda,
498 and occurs exactly once or
499 occurs once in each branch of a case and is small
501 If the thing is in WHNF, there's no danger of duplicating work,
502 so we can inline if it occurs once, or is small
504 NOTE: we don't want to inline top-level functions that always diverge.
505 It just makes the code bigger. Tt turns out that the convenient way to prevent
506 them inlining is to give them a NOINLINE pragma, which we do in
507 StrictAnal.addStrictnessInfoToTopId
510 callSiteInline :: DynFlags
511 -> Bool -- True <=> the Id is black listed
512 -> Bool -- 'inline' note at call site
515 -> [Bool] -- One for each value arg; True if it is interesting
516 -> Bool -- True <=> continuation is interesting
517 -> Maybe CoreExpr -- Unfolding, if any
520 callSiteInline dflags black_listed inline_call occ id arg_infos interesting_cont
521 = case idUnfolding id of {
522 NoUnfolding -> Nothing ;
523 OtherCon cs -> Nothing ;
524 CompulsoryUnfolding unf_template | black_listed -> Nothing
525 | otherwise -> Just unf_template ;
526 -- Constructors have compulsory unfoldings, but
527 -- may have rules, in which case they are
528 -- black listed till later
529 CoreUnfolding unf_template is_top is_value is_cheap guidance ->
532 result | yes_or_no = Just unf_template
533 | otherwise = Nothing
535 n_val_args = length arg_infos
538 | black_listed = False
539 | otherwise = case occ of
540 IAmDead -> pprTrace "callSiteInline: dead" (ppr id) False
541 IAmALoopBreaker -> False
542 OneOcc in_lam one_br -> (not in_lam || is_cheap) && consider_safe in_lam True one_br
543 NoOccInfo -> is_cheap && consider_safe True False False
545 consider_safe in_lam once once_in_one_branch
546 -- consider_safe decides whether it's a good idea to inline something,
547 -- given that there's no work-duplication issue (the caller checks that).
548 -- once_in_one_branch = True means there's a unique textual occurrence
552 -- Be very keen to inline something if this is its unique occurrence:
554 -- a) Inlining gives a good chance of eliminating the original
555 -- binding (and hence the allocation) for the thing.
556 -- (Provided it's not a top level binding, in which case the
557 -- allocation costs nothing.)
559 -- b) Inlining a function that is called only once exposes the
560 -- body function to the call site.
562 -- The only time we hold back is when substituting inside a lambda;
563 -- then if the context is totally uninteresting (not applied, not scrutinised)
564 -- there is no point in substituting because it might just increase allocation,
565 -- by allocating the function itself many times
567 -- Note: there used to be a '&& not top_level' in the guard above,
568 -- but that stopped us inlining top-level functions used only once,
570 = not in_lam || not (null arg_infos) || interesting_cont
574 UnfoldNever -> False ;
575 UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount
577 | enough_args && size <= (n_vals_wanted + 1)
579 -- Size of call is n_vals_wanted (+1 for the function)
583 -> some_benefit && small_enough
586 some_benefit = or arg_infos || really_interesting_cont ||
587 (not is_top && (once || (n_vals_wanted > 0 && enough_args)))
588 -- If it occurs more than once, there must be something interesting
589 -- about some argument, or the result context, to make it worth inlining
591 -- If a function has a nested defn we also record some-benefit,
592 -- on the grounds that we are often able to eliminate the binding,
593 -- and hence the allocation, for the function altogether; this is good
594 -- for join points. But this only makes sense for *functions*;
595 -- inlining a constructor doesn't help allocation unless the result is
596 -- scrutinised. UNLESS the constructor occurs just once, albeit possibly
597 -- in multiple case branches. Then inlining it doesn't increase allocation,
598 -- but it does increase the chance that the constructor won't be allocated at all
599 -- in the branches that don't use it.
601 enough_args = n_val_args >= n_vals_wanted
602 really_interesting_cont | n_val_args < n_vals_wanted = False -- Too few args
603 | n_val_args == n_vals_wanted = interesting_cont
604 | otherwise = True -- Extra args
605 -- really_interesting_cont tells if the result of the
606 -- call is in an interesting context.
608 small_enough = (size - discount) <= opt_UF_UseThreshold
609 discount = computeDiscount n_vals_wanted arg_discounts res_discount
610 arg_infos really_interesting_cont
614 if dopt Opt_D_dump_inlinings dflags then
615 pprTrace "Considering inlining"
616 (ppr id <+> vcat [text "black listed:" <+> ppr black_listed,
617 text "occ info:" <+> ppr occ,
618 text "arg infos" <+> ppr arg_infos,
619 text "interesting continuation" <+> ppr interesting_cont,
620 text "is value:" <+> ppr is_value,
621 text "is cheap:" <+> ppr is_cheap,
622 text "guidance" <+> ppr guidance,
623 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO",
625 text "Unfolding =" <+> pprCoreExpr unf_template
633 computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int
634 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used
635 -- We multiple the raw discounts (args_discount and result_discount)
636 -- ty opt_UnfoldingKeenessFactor because the former have to do with
637 -- *size* whereas the discounts imply that there's some extra
638 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
641 -- we also discount 1 for each argument passed, because these will
642 -- reduce with the lambdas in the function (we count 1 for a lambda
644 = 1 + -- Discount of 1 because the result replaces the call
645 -- so we count 1 for the function itself
646 length (take n_vals_wanted arg_infos) +
647 -- Discount of 1 for each arg supplied, because the
648 -- result replaces the call
649 round (opt_UF_KeenessFactor *
650 fromInt (arg_discount + result_discount))
652 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
654 mk_arg_discount discount is_evald | is_evald = discount
657 -- Don't give a result discount unless there are enough args
658 result_discount | result_used = res_discount -- Over-applied, or case scrut
663 %************************************************************************
665 \subsection{Black-listing}
667 %************************************************************************
669 Inlining is controlled by the "Inline phase" number, which is set
670 by the per-simplification-pass '-finline-phase' flag.
672 For optimisation we use phase 1,2 and nothing (i.e. no -finline-phase flag)
673 in that order. The meanings of these are determined by the @blackListed@ function
676 The final simplification doesn't have a phase number.
682 (least black listing, most inlining)
683 INLINE n foo phase is Just p *and* p<n *and* foo appears on LHS of rule
684 INLINE foo phase is Just p *and* foo appears on LHS of rule
685 NOINLINE n foo phase is Just p *and* (p<n *or* foo appears on LHS of rule)
687 (most black listing, least inlining)
690 blackListed :: IdSet -- Used in transformation rules
691 -> Maybe Int -- Inline phase
692 -> Id -> Bool -- True <=> blacklisted
694 -- The blackListed function sees whether a variable should *not* be
695 -- inlined because of the inline phase we are in. This is the sole
696 -- place that the inline phase number is looked at.
698 blackListed rule_vars Nothing -- Last phase
699 = \v -> isNeverInlinePrag (idInlinePragma v)
701 blackListed rule_vars (Just phase)
702 = \v -> normal_case rule_vars phase v
704 normal_case rule_vars phase v
705 = case idInlinePragma v of
706 NoInlinePragInfo -> has_rules
708 IMustNotBeINLINEd from_INLINE Nothing
709 | from_INLINE -> has_rules -- Black list until final phase
710 | otherwise -> True -- Always blacklisted
712 IMustNotBeINLINEd from_INLINE (Just threshold)
713 | from_INLINE -> (phase < threshold && has_rules)
714 | otherwise -> (phase < threshold || has_rules)
716 has_rules = v `elemVarSet` rule_vars
717 || not (isEmptyCoreRules (idSpecialisation v))
721 SLPJ 95/04: Why @runST@ must be inlined very late:
725 (a, s') = newArray# 100 [] s
726 (_, s'') = fill_in_array_or_something a x s'
730 If we inline @runST@, we'll get:
733 (a, s') = newArray# 100 [] realWorld#{-NB-}
734 (_, s'') = fill_in_array_or_something a x s'
738 And now the @newArray#@ binding can be floated to become a CAF, which
739 is totally and utterly wrong:
742 (a, s') = newArray# 100 [] realWorld#{-NB-} -- YIKES!!!
745 let (_, s'') = fill_in_array_or_something a x s' in
748 All calls to @f@ will share a {\em single} array!
750 Yet we do want to inline runST sometime, so we can avoid
751 needless code. Solution: black list it until the last moment.