2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1994-1998
8 Unfoldings (which can travel across module boundaries) are in Core
9 syntax (namely @CoreExpr@s).
11 The type @Unfolding@ sits ``above'' simply-Core-expressions
12 unfoldings, capturing ``higher-level'' things we know about a binding,
13 usually things that the simplifier found out (e.g., ``it's a
14 literal''). In the corner of a @CoreUnfolding@ unfolding, you will
15 find, unsurprisingly, a Core expression.
19 Unfolding, UnfoldingGuidance, -- Abstract types
21 noUnfolding, mkImplicitUnfolding,
22 mkTopUnfolding, mkUnfolding, mkCoreUnfolding,
23 mkInlineRule, mkWwInlineRule,
24 mkCompulsoryUnfolding, mkDFunUnfolding,
26 interestingArg, ArgSummary(..),
28 couldBeSmallEnoughToInline,
29 certainlyWillInline, smallEnoughToInline,
31 callSiteInline, CallCtxt(..),
37 #include "HsVersions.h"
42 import PprCore () -- Instances
44 import CoreSubst hiding( substTy )
45 import CoreFVs ( exprFreeVars )
53 import BasicTypes ( Arity )
54 import TcType ( tcSplitDFunTy )
58 import VarEnv ( mkInScopeSet )
68 %************************************************************************
70 \subsection{Making unfoldings}
72 %************************************************************************
75 mkTopUnfolding :: CoreExpr -> Unfolding
76 mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
78 mkImplicitUnfolding :: CoreExpr -> Unfolding
79 -- For implicit Ids, do a tiny bit of optimising first
80 mkImplicitUnfolding expr = mkTopUnfolding (simpleOptExpr expr)
82 -- Note [Top-level flag on inline rules]
83 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
84 -- Slight hack: note that mk_inline_rules conservatively sets the
85 -- top-level flag to True. It gets set more accurately by the simplifier
86 -- Simplify.simplUnfolding.
88 mkUnfolding :: Bool -> CoreExpr -> Unfolding
89 mkUnfolding top_lvl expr
90 = mkCoreUnfolding top_lvl expr arity guidance
92 (arity, guidance) = calcUnfoldingGuidance opt_UF_CreationThreshold expr
93 -- Sometimes during simplification, there's a large let-bound thing
94 -- which has been substituted, and so is now dead; so 'expr' contains
95 -- two copies of the thing while the occurrence-analysed expression doesn't
96 -- Nevertheless, we *don't* occ-analyse before computing the size because the
97 -- size computation bales out after a while, whereas occurrence analysis does not.
99 -- This can occasionally mean that the guidance is very pessimistic;
100 -- it gets fixed up next round. And it should be rare, because large
101 -- let-bound things that are dead are usually caught by preInlineUnconditionally
103 mkCoreUnfolding :: Bool -> CoreExpr -> Arity -> UnfoldingGuidance -> Unfolding
104 -- Occurrence-analyses the expression before capturing it
105 mkCoreUnfolding top_lvl expr arity guidance
106 = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
109 uf_is_value = exprIsHNF expr,
110 uf_is_conlike = exprIsConLike expr,
111 uf_is_cheap = exprIsCheap expr,
112 uf_expandable = exprIsExpandable expr,
113 uf_guidance = guidance }
115 mkDFunUnfolding :: DataCon -> [Id] -> Unfolding
116 mkDFunUnfolding con ops = DFunUnfolding con (map Var ops)
118 mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding
119 mkWwInlineRule id expr arity
120 = mkCoreUnfolding True (simpleOptExpr expr) arity
121 (InlineRule { ir_sat = InlUnSat, ir_info = InlWrapper id })
123 mkCompulsoryUnfolding :: CoreExpr -> Unfolding
124 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
125 = mkCoreUnfolding True expr
126 0 -- Arity of unfolding doesn't matter
127 (InlineRule { ir_info = InlAlways, ir_sat = InlUnSat })
129 mkInlineRule :: InlSatFlag -> CoreExpr -> Arity -> Unfolding
130 mkInlineRule sat expr arity
131 = mkCoreUnfolding True -- Note [Top-level flag on inline rules]
133 (InlineRule { ir_sat = sat, ir_info = info })
135 expr' = simpleOptExpr expr
136 info = if small then InlSmall else InlVanilla
137 small = case calcUnfoldingGuidance (arity+1) expr' of
138 (arity_e, UnfoldIfGoodArgs { ug_size = size_e })
139 -> uncondInline arity_e size_e
140 _other {- actually UnfoldNever -} -> False
144 %************************************************************************
146 \subsection{The UnfoldingGuidance type}
148 %************************************************************************
151 calcUnfoldingGuidance
152 :: Int -- bomb out if size gets bigger than this
153 -> CoreExpr -- expression to look at
154 -> (Arity, UnfoldingGuidance)
155 calcUnfoldingGuidance bOMB_OUT_SIZE expr
156 = case collectBinders expr of { (binders, body) ->
158 val_binders = filter isId binders
159 n_val_binders = length val_binders
161 case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_binders body) of
162 TooBig -> (n_val_binders, UnfoldNever)
163 SizeIs size cased_args scrut_discount
164 -> (n_val_binders, UnfoldIfGoodArgs { ug_args = map discount_for val_binders
165 , ug_size = iBox size
166 , ug_res = iBox scrut_discount })
168 discount_for b = foldlBag (\acc (b',n) -> if b==b' then acc+n else acc)
173 Note [Computing the size of an expression]
174 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
175 The basic idea of sizeExpr is obvious enough: count nodes. But getting the
176 heuristics right has taken a long time. Here's the basic strategy:
178 * Variables, literals: 0
179 (Exception for string literals, see litSize.)
181 * Function applications (f e1 .. en): 1 + #value args
183 * Constructor applications: 1, regardless of #args
185 * Let(rec): 1 + size of components
200 Notice that 'x' counts 0, while (f x) counts 2. That's deliberate: there's
201 a function call to account for. Notice also that constructor applications
202 are very cheap, because exposing them to a caller is so valuable.
204 Note [Unconditional inlining]
205 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
206 We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
207 than the thing it's replacing. Notice that
208 (f x) --> (g 3) -- YES, unconditionally
209 (f x) --> x : [] -- YES, *even though* there are two
210 -- arguments to the cons
214 It's very important not to unconditionally replace a variable by
218 uncondInline :: Arity -> Int -> Bool
219 -- Inline unconditionally if there no size increase
220 -- Size of call is arity (+1 for the function)
221 -- See Note [Unconditional inlining]
222 uncondInline arity size
223 | arity == 0 = size == 0
224 | otherwise = size <= arity + 1
229 sizeExpr :: FastInt -- Bomb out if it gets bigger than this
230 -> [Id] -- Arguments; we're interested in which of these
235 -- Note [Computing the size of an expression]
237 sizeExpr bOMB_OUT_SIZE top_args expr
240 size_up (Cast e _) = size_up e
241 size_up (Note _ e) = size_up e
242 size_up (Type _) = sizeZero -- Types cost nothing
243 size_up (Lit lit) = sizeN (litSize lit)
244 size_up (Var f) = size_up_call f [] -- Make sure we get constructor
245 -- discounts even on nullary constructors
247 size_up (App fun (Type _)) = size_up fun
248 size_up (App fun arg) = size_up_app fun [arg]
249 `addSize` nukeScrutDiscount (size_up arg)
251 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
252 | otherwise = size_up e
254 size_up (Let (NonRec binder rhs) body)
255 = nukeScrutDiscount (size_up rhs) `addSize`
256 size_up body `addSizeN`
257 (if isUnLiftedType (idType binder) then 0 else 1)
258 -- For the allocation
259 -- If the binder has an unlifted type there is no allocation
261 size_up (Let (Rec pairs) body)
262 = nukeScrutDiscount rhs_size `addSize`
263 size_up body `addSizeN`
264 length pairs -- For the allocation
266 rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
268 size_up (Case (Var v) _ _ alts)
269 | v `elem` top_args -- We are scrutinising an argument variable
270 = alts_size (foldr addSize sizeOne alt_sizes) -- The 1 is for the case itself
271 (foldr1 maxSize alt_sizes)
272 -- Good to inline if an arg is scrutinised, because
273 -- that may eliminate allocation in the caller
274 -- And it eliminates the case itself
276 alt_sizes = map size_up_alt alts
278 -- alts_size tries to compute a good discount for
279 -- the case when we are scrutinising an argument variable
280 alts_size (SizeIs tot tot_disc _tot_scrut) -- Size of all alternatives
281 (SizeIs max _max_disc max_scrut) -- Size of biggest alternative
282 = SizeIs tot (unitBag (v, iBox (_ILIT(1) +# tot -# max)) `unionBags` tot_disc) max_scrut
283 -- If the variable is known, we produce a discount that
284 -- will take us back to 'max', the size of the largest alternative
285 -- The 1+ is a little discount for reduced allocation in the caller
287 -- Notice though, that we return tot_disc, the total discount from
288 -- all branches. I think that's right.
290 alts_size tot_size _ = tot_size
292 size_up (Case e _ _ alts) = foldr (addSize . size_up_alt)
293 (nukeScrutDiscount (size_up e))
295 `addSizeN` 1 -- Add 1 for the case itself
296 -- We don't charge for the case itself
297 -- It's a strict thing, and the price of the call
298 -- is paid by scrut. Also consider
299 -- case f x of DEFAULT -> e
300 -- This is just ';'! Don't charge for it.
303 -- size_up_app is used when there's ONE OR MORE value args
304 size_up_app (App fun arg) args
305 | isTypeArg arg = size_up_app fun args
306 | otherwise = size_up_app fun (arg:args)
307 `addSize` nukeScrutDiscount (size_up arg)
308 size_up_app (Var fun) args = size_up_call fun args
309 size_up_app other args = size_up other `addSizeN` length args
312 size_up_call :: Id -> [CoreExpr] -> ExprSize
313 size_up_call fun val_args
314 = case idDetails fun of
315 FCallId _ -> sizeN opt_UF_DearOp
316 DataConWorkId dc -> conSize dc (length val_args)
317 PrimOpId op -> primOpSize op (length val_args)
318 ClassOpId _ -> classOpSize top_args val_args
319 _ -> funSize top_args fun (length val_args)
322 size_up_alt (_con, _bndrs, rhs) = size_up rhs
323 -- Don't charge for args, so that wrappers look cheap
324 -- (See comments about wrappers with Case)
327 -- These addSize things have to be here because
328 -- I don't want to give them bOMB_OUT_SIZE as an argument
329 addSizeN TooBig _ = TooBig
330 addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
332 addSize TooBig _ = TooBig
333 addSize _ TooBig = TooBig
334 addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
335 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2) (xs `unionBags` ys) (d1 +# d2)
339 -- | Finds a nominal size of a string literal.
340 litSize :: Literal -> Int
341 -- Used by CoreUnfold.sizeExpr
342 litSize (MachStr str) = 1 + ((lengthFS str + 3) `div` 4)
343 -- If size could be 0 then @f "x"@ might be too small
344 -- [Sept03: make literal strings a bit bigger to avoid fruitless
345 -- duplication of little strings]
346 litSize _other = 0 -- Must match size of nullary constructors
347 -- Key point: if x |-> 4, then x must inline unconditionally
348 -- (eg via case binding)
350 classOpSize :: [Id] -> [CoreExpr] -> ExprSize
351 -- See Note [Conlike is interesting]
354 classOpSize top_args (arg1 : other_args)
355 = SizeIs (iUnbox size) arg_discount (_ILIT(0))
357 size = 2 + length other_args
358 -- If the class op is scrutinising a lambda bound dictionary then
359 -- give it a discount, to encourage the inlining of this function
360 -- The actual discount is rather arbitrarily chosen
361 arg_discount = case arg1 of
362 Var dict | dict `elem` top_args
363 -> unitBag (dict, opt_UF_DictDiscount)
366 funSize :: [Id] -> Id -> Int -> ExprSize
367 -- Size for functions that are not constructors or primops
368 -- Note [Function applications]
369 funSize top_args fun n_val_args
370 | fun `hasKey` buildIdKey = buildSize
371 | fun `hasKey` augmentIdKey = augmentSize
372 | otherwise = SizeIs (iUnbox size) arg_discount (iUnbox res_discount)
374 some_val_args = n_val_args > 0
376 arg_discount | some_val_args && fun `elem` top_args
377 = unitBag (fun, opt_UF_FunAppDiscount)
378 | otherwise = emptyBag
379 -- If the function is an argument and is applied
380 -- to some values, give it an arg-discount
382 res_discount | idArity fun > n_val_args = opt_UF_FunAppDiscount
384 -- If the function is partially applied, show a result discount
386 size | some_val_args = 1 + n_val_args
388 -- The 1+ is for the function itself
389 -- Add 1 for each non-trivial arg;
390 -- the allocation cost, as in let(rec)
393 conSize :: DataCon -> Int -> ExprSize
394 conSize dc n_val_args
395 | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables
396 | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))
397 | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
398 -- Treat a constructors application as size 1, regardless of how
399 -- many arguments it has; we are keen to expose them
400 -- (and we charge separately for their args). We can't treat
401 -- them as size zero, else we find that (Just x) has size 0,
402 -- which is the same as a lone variable; and hence 'v' will
403 -- always be replaced by (Just x), where v is bound to Just x.
405 -- However, unboxed tuples count as size zero
406 -- I found occasions where we had
407 -- f x y z = case op# x y z of { s -> (# s, () #) }
408 -- and f wasn't getting inlined
410 primOpSize :: PrimOp -> Int -> ExprSize
411 primOpSize op n_val_args
412 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
413 | not (primOpOutOfLine op) = sizeN 1
414 -- Be very keen to inline simple primops.
415 -- We give a discount of 1 for each arg so that (op# x y z) costs 2.
416 -- We can't make it cost 1, else we'll inline let v = (op# x y z)
417 -- at every use of v, which is excessive.
419 -- A good example is:
420 -- let x = +# p q in C {x}
421 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
422 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
424 | otherwise = sizeN n_val_args
427 buildSize :: ExprSize
428 buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
429 -- We really want to inline applications of build
430 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
431 -- Indeed, we should add a result_discount becuause build is
432 -- very like a constructor. We don't bother to check that the
433 -- build is saturated (it usually is). The "-2" discounts for the \c n,
434 -- The "4" is rather arbitrary.
436 augmentSize :: ExprSize
437 augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
438 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
439 -- e plus ys. The -2 accounts for the \cn
441 nukeScrutDiscount :: ExprSize -> ExprSize
442 nukeScrutDiscount (SizeIs n vs _) = SizeIs n vs (_ILIT(0))
443 nukeScrutDiscount TooBig = TooBig
445 -- When we return a lambda, give a discount if it's used (applied)
446 lamScrutDiscount :: ExprSize -> ExprSize
447 lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)
448 lamScrutDiscount TooBig = TooBig
451 Note [Discounts and thresholds]
452 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
453 Constants for discounts and thesholds are defined in main/StaticFlags,
454 all of form opt_UF_xxxx. They are:
456 opt_UF_CreationThreshold (45)
457 At a definition site, if the unfolding is bigger than this, we
458 may discard it altogether
460 opt_UF_UseThreshold (6)
461 At a call site, if the unfolding, less discounts, is smaller than
462 this, then it's small enough inline
464 opt_UF_KeennessFactor (1.5)
465 Factor by which the discounts are multiplied before
466 subtracting from size
468 opt_UF_DictDiscount (1)
469 The discount for each occurrence of a dictionary argument
470 as an argument of a class method. Should be pretty small
471 else big functions may get inlined
473 opt_UF_FunAppDiscount (6)
474 Discount for a function argument that is applied. Quite
475 large, because if we inline we avoid the higher-order call.
478 The size of a foreign call or not-dupable PrimOp
481 Note [Function applications]
482 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
483 In a function application (f a b)
485 - If 'f' is an argument to the function being analysed,
486 and there's at least one value arg, record a FunAppDiscount for f
488 - If the application if a PAP (arity > 2 in this example)
489 record a *result* discount (because inlining
490 with "extra" args in the call may mean that we now
491 get a saturated application)
493 Code for manipulating sizes
496 data ExprSize = TooBig
497 | SizeIs FastInt -- Size found
498 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
499 FastInt -- Size to subtract if result is scrutinised
500 -- by a case expression
502 instance Outputable ExprSize where
503 ppr TooBig = ptext (sLit "TooBig")
504 ppr (SizeIs a _ c) = brackets (int (iBox a) <+> int (iBox c))
506 -- subtract the discount before deciding whether to bale out. eg. we
507 -- want to inline a large constructor application into a selector:
508 -- tup = (a_1, ..., a_99)
509 -- x = case tup of ...
511 mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize
512 mkSizeIs max n xs d | (n -# d) ># max = TooBig
513 | otherwise = SizeIs n xs d
515 maxSize :: ExprSize -> ExprSize -> ExprSize
516 maxSize TooBig _ = TooBig
517 maxSize _ TooBig = TooBig
518 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
521 sizeZero, sizeOne :: ExprSize
522 sizeN :: Int -> ExprSize
524 sizeZero = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
525 sizeOne = SizeIs (_ILIT(1)) emptyBag (_ILIT(0))
526 sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT(0))
532 %************************************************************************
534 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
536 %************************************************************************
538 We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that
539 we ``couldn't possibly use'' on the other side. Can be overridden w/
540 flaggery. Just the same as smallEnoughToInline, except that it has no
544 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
545 couldBeSmallEnoughToInline threshold rhs
546 = case calcUnfoldingGuidance threshold rhs of
547 (_, UnfoldNever) -> False
551 smallEnoughToInline :: Unfolding -> Bool
552 smallEnoughToInline (CoreUnfolding {uf_guidance = UnfoldIfGoodArgs {ug_size = size}})
553 = size <= opt_UF_UseThreshold
554 smallEnoughToInline _
558 certainlyWillInline :: Unfolding -> Bool
559 -- Sees if the unfolding is pretty certain to inline
560 certainlyWillInline (CoreUnfolding { uf_is_cheap = is_cheap, uf_arity = n_vals, uf_guidance = guidance })
563 InlineRule {} -> True
564 UnfoldIfGoodArgs { ug_size = size}
565 -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold
567 certainlyWillInline _
571 %************************************************************************
573 \subsection{callSiteInline}
575 %************************************************************************
577 This is the key function. It decides whether to inline a variable at a call site
579 callSiteInline is used at call sites, so it is a bit more generous.
580 It's a very important function that embodies lots of heuristics.
581 A non-WHNF can be inlined if it doesn't occur inside a lambda,
582 and occurs exactly once or
583 occurs once in each branch of a case and is small
585 If the thing is in WHNF, there's no danger of duplicating work,
586 so we can inline if it occurs once, or is small
588 NOTE: we don't want to inline top-level functions that always diverge.
589 It just makes the code bigger. Tt turns out that the convenient way to prevent
590 them inlining is to give them a NOINLINE pragma, which we do in
591 StrictAnal.addStrictnessInfoToTopId
594 callSiteInline :: DynFlags
595 -> Bool -- True <=> the Id can be inlined
597 -> Bool -- True if there are are no arguments at all (incl type args)
598 -> [ArgSummary] -- One for each value arg; True if it is interesting
599 -> CallCtxt -- True <=> continuation is interesting
600 -> Maybe CoreExpr -- Unfolding, if any
603 instance Outputable ArgSummary where
604 ppr TrivArg = ptext (sLit "TrivArg")
605 ppr NonTrivArg = ptext (sLit "NonTrivArg")
606 ppr ValueArg = ptext (sLit "ValueArg")
608 data CallCtxt = BoringCtxt
610 | ArgCtxt -- We are somewhere in the argument of a function
611 Bool -- True <=> we're somewhere in the RHS of function with rules
612 -- False <=> we *are* the argument of a function with non-zero
615 -- we *are* the RHS of a let Note [RHS of lets]
616 -- In both cases, be a little keener to inline
618 | ValAppCtxt -- We're applied to at least one value arg
619 -- This arises when we have ((f x |> co) y)
620 -- Then the (f x) has argument 'x' but in a ValAppCtxt
622 | CaseCtxt -- We're the scrutinee of a case
623 -- that decomposes its scrutinee
625 instance Outputable CallCtxt where
626 ppr BoringCtxt = ptext (sLit "BoringCtxt")
627 ppr (ArgCtxt rules) = ptext (sLit "ArgCtxt") <+> ppr rules
628 ppr CaseCtxt = ptext (sLit "CaseCtxt")
629 ppr ValAppCtxt = ptext (sLit "ValAppCtxt")
631 callSiteInline dflags active_inline id lone_variable arg_infos cont_info
633 n_val_args = length arg_infos
635 case idUnfolding id of {
636 NoUnfolding -> Nothing ;
637 OtherCon _ -> Nothing ;
638 DFunUnfolding {} -> Nothing ; -- Never unfold a DFun
639 CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top, uf_is_value = is_value,
640 uf_is_cheap = is_cheap, uf_arity = uf_arity, uf_guidance = guidance } ->
641 -- uf_arity will typically be equal to (idArity id),
642 -- but may be less for InlineRules
644 result | yes_or_no = Just unf_template
645 | otherwise = Nothing
647 interesting_args = any nonTriv arg_infos
648 -- NB: (any nonTriv arg_infos) looks at the
649 -- over-saturated args too which is "wrong";
650 -- but if over-saturated we inline anyway.
652 -- some_benefit is used when the RHS is small enough
653 -- and the call has enough (or too many) value
654 -- arguments (ie n_val_args >= arity). But there must
655 -- be *something* interesting about some argument, or the
656 -- result context, to make it worth inlining
657 some_benefit = interesting_args
658 || n_val_args > uf_arity -- Over-saturated
659 || interesting_saturated_call -- Exactly saturated
661 interesting_saturated_call
663 BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]
664 CaseCtxt -> not (lone_variable && is_value) -- Note [Lone variables]
665 ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt]
666 ValAppCtxt -> True -- Note [Cast then apply]
672 InlineRule { ir_info = inl_info, ir_sat = sat }
673 | InlAlways <- inl_info -> True -- No top-level binding, so inline!
674 -- Ignore is_active because we want to
675 -- inline even if SimplGently is on.
676 | not active_inline -> False
677 | n_val_args < uf_arity -> yes_unsat -- Not enough value args
678 | InlSmall <- inl_info -> True -- Note [INLINE for small functions]
679 | otherwise -> some_benefit -- Saturated or over-saturated
681 -- See Note [Inlining an InlineRule]
682 yes_unsat = case sat of
684 InlUnSat -> interesting_args
686 UnfoldIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
687 | not active_inline -> False
688 | not is_cheap -> False
689 | n_val_args < uf_arity -> interesting_args && small_enough
690 -- Note [Unsaturated applications]
691 | uncondInline uf_arity size -> True
692 | otherwise -> some_benefit && small_enough
695 small_enough = (size - discount) <= opt_UF_UseThreshold
696 discount = computeDiscount uf_arity arg_discounts
697 res_discount arg_infos cont_info
700 if dopt Opt_D_dump_inlinings dflags then
701 pprTrace ("Considering inlining: " ++ showSDoc (ppr id))
702 (vcat [text "active:" <+> ppr active_inline,
703 text "arg infos" <+> ppr arg_infos,
704 text "interesting continuation" <+> ppr cont_info,
705 text "is value:" <+> ppr is_value,
706 text "is cheap:" <+> ppr is_cheap,
707 text "guidance" <+> ppr guidance,
708 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])
717 Be a tiny bit keener to inline in the RHS of a let, because that might
718 lead to good thing later
720 g y = let x = f y in ...(case x of (a,b,c) -> ...) ...
721 We'd inline 'f' if the call was in a case context, and it kind-of-is,
722 only we can't see it. So we treat the RHS of a let as not-totally-boring.
724 Note [Unsaturated applications]
725 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
726 When a call is not saturated, we *still* inline if one of the
727 arguments has interesting structure. That's sometimes very important.
728 A good example is the Ord instance for Bool in Base:
731 $fOrdBool =GHC.Classes.D:Ord
736 $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool
737 $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool
740 But the defn of GHC.Classes.$dmmin is:
742 $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a
743 {- Arity: 3, HasNoCafRefs, Strictness: SLL,
744 Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a ->
745 case @ a GHC.Classes.<= @ a $dOrd x y of wild {
746 GHC.Bool.False -> y GHC.Bool.True -> x }) -}
748 We *really* want to inline $dmmin, even though it has arity 3, in
749 order to unravel the recursion.
752 Note [INLINE for small functions]
753 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
754 Consider {-# INLINE f #-}
757 Then f's RHS is no larger than its LHS, so we should inline it
758 into even the most boring context. (We do so if there is no INLINE
759 pragma!) That's the reason for the 'ug_small' flag on an InlineRule.
762 Note [Things to watch]
763 ~~~~~~~~~~~~~~~~~~~~~~
764 * { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
765 Assume x is exported, so not inlined unconditionally.
766 Then we want x to inline unconditionally; no reason for it
767 not to, and doing so avoids an indirection.
769 * { x = I# 3; ....f x.... }
770 Make sure that x does not inline unconditionally!
771 Lest we get extra allocation.
773 Note [Inlining an InlineRule]
774 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
775 An InlineRules is used for
776 (a) pogrammer INLINE pragmas
777 (b) inlinings from worker/wrapper
779 For (a) the RHS may be large, and our contract is that we *only* inline
780 when the function is applied to all the arguments on the LHS of the
781 source-code defn. (The uf_arity in the rule.)
783 However for worker/wrapper it may be worth inlining even if the
784 arity is not satisfied (as we do in the CoreUnfolding case) so we don't
788 Note [Nested functions]
789 ~~~~~~~~~~~~~~~~~~~~~~~
790 If a function has a nested defn we also record some-benefit, on the
791 grounds that we are often able to eliminate the binding, and hence the
792 allocation, for the function altogether; this is good for join points.
793 But this only makes sense for *functions*; inlining a constructor
794 doesn't help allocation unless the result is scrutinised. UNLESS the
795 constructor occurs just once, albeit possibly in multiple case
796 branches. Then inlining it doesn't increase allocation, but it does
797 increase the chance that the constructor won't be allocated at all in
798 the branches that don't use it.
800 Note [Cast then apply]
801 ~~~~~~~~~~~~~~~~~~~~~~
803 myIndex = __inline_me ( (/\a. <blah>) |> co )
804 co :: (forall a. a -> a) ~ (forall a. T a)
805 ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ...
807 We need to inline myIndex to unravel this; but the actual call (myIndex a) has
808 no value arguments. The ValAppCtxt gives it enough incentive to inline.
810 Note [Inlining in ArgCtxt]
811 ~~~~~~~~~~~~~~~~~~~~~~~~~~
812 The condition (arity > 0) here is very important, because otherwise
813 we end up inlining top-level stuff into useless places; eg
816 This can make a very big difference: it adds 16% to nofib 'integer' allocs,
819 At one stage I replaced this condition by 'True' (leading to the above
820 slow-down). The motivation was test eyeball/inline1.hs; but that seems
823 NOTE: arguably, we should inline in ArgCtxt only if the result of the
824 call is at least CONLIKE. At least for the cases where we use ArgCtxt
825 for the RHS of a 'let', we only profit from the inlining if we get a
826 CONLIKE thing (modulo lets).
828 Note [Lone variables]
829 ~~~~~~~~~~~~~~~~~~~~~
830 The "lone-variable" case is important. I spent ages messing about
831 with unsatisfactory varaints, but this is nice. The idea is that if a
832 variable appears all alone
834 as an arg of lazy fn, or rhs BoringCtxt
835 as scrutinee of a case CaseCtxt
836 as arg of a fn ArgCtxt
838 it is bound to a value
840 then we should not inline it (unless there is some other reason,
841 e.g. is is the sole occurrence). That is what is happening at
842 the use of 'lone_variable' in 'interesting_saturated_call'.
844 Why? At least in the case-scrutinee situation, turning
845 let x = (a,b) in case x of y -> ...
847 let x = (a,b) in case (a,b) of y -> ...
849 let x = (a,b) in let y = (a,b) in ...
850 is bad if the binding for x will remain.
852 Another example: I discovered that strings
853 were getting inlined straight back into applications of 'error'
854 because the latter is strict.
856 f = \x -> ...(error s)...
858 Fundamentally such contexts should not encourage inlining because the
859 context can ``see'' the unfolding of the variable (e.g. case or a
860 RULE) so there's no gain. If the thing is bound to a value.
865 foo = _inline_ (\n. [n])
866 bar = _inline_ (foo 20)
867 baz = \n. case bar of { (m:_) -> m + n }
868 Here we really want to inline 'bar' so that we can inline 'foo'
869 and the whole thing unravels as it should obviously do. This is
870 important: in the NDP project, 'bar' generates a closure data
871 structure rather than a list.
873 So the non-inlining of lone_variables should only apply if the
874 unfolding is regarded as cheap; because that is when exprIsConApp_maybe
875 looks through the unfolding. Hence the "&& is_cheap" in the
878 * Even a type application or coercion isn't a lone variable.
880 case $fMonadST @ RealWorld of { :DMonad a b c -> c }
881 We had better inline that sucker! The case won't see through it.
883 For now, I'm treating treating a variable applied to types
884 in a *lazy* context "lone". The motivating example was
887 There's no advantage in inlining f here, and perhaps
888 a significant disadvantage. Hence some_val_args in the Stop case
891 computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
892 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info
893 -- We multiple the raw discounts (args_discount and result_discount)
894 -- ty opt_UnfoldingKeenessFactor because the former have to do with
895 -- *size* whereas the discounts imply that there's some extra
896 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
899 = 1 -- Discount of 1 because the result replaces the call
900 -- so we count 1 for the function itself
902 + length (take n_vals_wanted arg_infos)
903 -- Discount of (un-scaled) 1 for each arg supplied,
904 -- because the result replaces the call
906 + round (opt_UF_KeenessFactor *
907 fromIntegral (arg_discount + res_discount'))
909 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
911 mk_arg_discount _ TrivArg = 0
912 mk_arg_discount _ NonTrivArg = 1
913 mk_arg_discount discount ValueArg = discount
915 res_discount' = case cont_info of
917 CaseCtxt -> res_discount
918 _other -> 4 `min` res_discount
919 -- res_discount can be very large when a function returns
920 -- constructors; but we only want to invoke that large discount
921 -- when there's a case continuation.
922 -- Otherwise we, rather arbitrarily, threshold it. Yuk.
923 -- But we want to aovid inlining large functions that return
924 -- constructors into contexts that are simply "interesting"
927 %************************************************************************
929 Interesting arguments
931 %************************************************************************
933 Note [Interesting arguments]
934 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
935 An argument is interesting if it deserves a discount for unfoldings
936 with a discount in that argument position. The idea is to avoid
937 unfolding a function that is applied only to variables that have no
938 unfolding (i.e. they are probably lambda bound): f x y z There is
939 little point in inlining f here.
941 Generally, *values* (like (C a b) and (\x.e)) deserve discounts. But
942 we must look through lets, eg (let x = e in C a b), because the let will
943 float, exposing the value, if we inline. That makes it different to
946 Before 2009 we said it was interesting if the argument had *any* structure
947 at all; i.e. (hasSomeUnfolding v). But does too much inlining; see Trac #3016.
949 But we don't regard (f x y) as interesting, unless f is unsaturated.
950 If it's saturated and f hasn't inlined, then it's probably not going
953 Note [Conlike is interesting]
954 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
956 f d = ...((*) d x y)...
958 where df is con-like. Then we'd really like to inline 'f' so that the
959 rule for (*) (df d) can fire. To do this
960 a) we give a discount for being an argument of a class-op (eg (*) d)
961 b) we say that a con-like argument (eg (df d)) is interesting
964 data ArgSummary = TrivArg -- Nothing interesting
965 | NonTrivArg -- Arg has structure
966 | ValueArg -- Arg is a con-app or PAP
967 -- ..or con-like. Note [Conlike is interesting]
969 interestingArg :: CoreExpr -> ArgSummary
970 -- See Note [Interesting arguments]
971 interestingArg e = go e 0
973 -- n is # value args to which the expression is applied
974 go (Lit {}) _ = ValueArg
976 | isConLikeId v = ValueArg -- Experimenting with 'conlike' rather that
977 -- data constructors here
978 | idArity v > n = ValueArg -- Catches (eg) primops with arity but no unfolding
979 | n > 0 = NonTrivArg -- Saturated or unknown call
980 | conlike_unfolding = ValueArg -- n==0; look for an interesting unfolding
981 -- See Note [Conlike is interesting]
982 | otherwise = TrivArg -- n==0, no useful unfolding
984 conlike_unfolding = isConLikeUnfolding (idUnfolding v)
986 go (Type _) _ = TrivArg
987 go (App fn (Type _)) n = go fn n
988 go (App fn _) n = go fn (n+1)
989 go (Note _ a) n = go a n
990 go (Cast e _) n = go e n
994 | otherwise = ValueArg
995 go (Let _ e) n = case go e n of { ValueArg -> ValueArg; _ -> NonTrivArg }
996 go (Case {}) _ = NonTrivArg
998 nonTriv :: ArgSummary -> Bool
999 nonTriv TrivArg = False
1003 %************************************************************************
1007 %************************************************************************
1009 Note [exprIsConApp_maybe]
1010 ~~~~~~~~~~~~~~~~~~~~~~~~~
1011 exprIsConApp_maybe is a very important function. There are two principal
1013 * case e of { .... }
1014 * cls_op e, where cls_op is a class operation
1016 In both cases you want to know if e is of form (C e1..en) where C is
1019 However e might not *look* as if
1022 -- | Returns @Just (dc, [t1..tk], [x1..xn])@ if the argument expression is
1023 -- a *saturated* constructor application of the form @dc t1..tk x1 .. xn@,
1024 -- where t1..tk are the *universally-qantified* type args of 'dc'
1025 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])
1027 exprIsConApp_maybe (Note _ expr)
1028 = exprIsConApp_maybe expr
1029 -- We ignore all notes. For example,
1030 -- case _scc_ "foo" (C a b) of
1032 -- should be optimised away, but it will be only if we look
1033 -- through the SCC note.
1035 exprIsConApp_maybe (Cast expr co)
1036 = -- Here we do the KPush reduction rule as described in the FC paper
1037 -- The transformation applies iff we have
1038 -- (C e1 ... en) `cast` co
1039 -- where co :: (T t1 .. tn) ~ to_ty
1040 -- The left-hand one must be a T, because exprIsConApp returned True
1041 -- but the right-hand one might not be. (Though it usually will.)
1043 case exprIsConApp_maybe expr of {
1044 Nothing -> Nothing ;
1045 Just (dc, _dc_univ_args, dc_args) ->
1047 let (_from_ty, to_ty) = coercionKind co
1048 dc_tc = dataConTyCon dc
1050 case splitTyConApp_maybe to_ty of {
1051 Nothing -> Nothing ;
1052 Just (to_tc, to_tc_arg_tys)
1053 | dc_tc /= to_tc -> Nothing
1054 -- These two Nothing cases are possible; we might see
1055 -- (C x y) `cast` (g :: T a ~ S [a]),
1056 -- where S is a type function. In fact, exprIsConApp
1057 -- will probably not be called in such circumstances,
1058 -- but there't nothing wrong with it
1062 tc_arity = tyConArity dc_tc
1063 dc_univ_tyvars = dataConUnivTyVars dc
1064 dc_ex_tyvars = dataConExTyVars dc
1065 arg_tys = dataConRepArgTys dc
1067 dc_eqs :: [(Type,Type)] -- All equalities from the DataCon
1068 dc_eqs = [(mkTyVarTy tv, ty) | (tv,ty) <- dataConEqSpec dc] ++
1069 [getEqPredTys eq_pred | eq_pred <- dataConEqTheta dc]
1071 (ex_args, rest1) = splitAtList dc_ex_tyvars dc_args
1072 (co_args, val_args) = splitAtList dc_eqs rest1
1074 -- Make the "theta" from Fig 3 of the paper
1075 gammas = decomposeCo tc_arity co
1076 theta = zipOpenTvSubst (dc_univ_tyvars ++ dc_ex_tyvars)
1077 (gammas ++ stripTypeArgs ex_args)
1079 -- Cast the existential coercion arguments
1080 cast_co (ty1, ty2) (Type co)
1081 = Type $ mkSymCoercion (substTy theta ty1)
1082 `mkTransCoercion` co
1083 `mkTransCoercion` (substTy theta ty2)
1084 cast_co _ other_arg = pprPanic "cast_co" (ppr other_arg)
1085 new_co_args = zipWith cast_co dc_eqs co_args
1087 -- Cast the value arguments (which include dictionaries)
1088 new_val_args = zipWith cast_arg arg_tys val_args
1089 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
1092 let dump_doc = vcat [ppr dc, ppr dc_univ_tyvars, ppr dc_ex_tyvars,
1093 ppr arg_tys, ppr dc_args, ppr _dc_univ_args,
1094 ppr ex_args, ppr val_args]
1096 ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )
1097 ASSERT2( all isTypeArg (ex_args ++ co_args), dump_doc )
1098 ASSERT2( equalLength val_args arg_tys, dump_doc )
1101 Just (dc, to_tc_arg_tys, ex_args ++ new_co_args ++ new_val_args)
1104 exprIsConApp_maybe expr
1107 analyse (App fun arg) args = analyse fun (arg:args)
1108 analyse fun@(Lam {}) args = beta fun [] args
1110 analyse (Var fun) args
1111 | Just con <- isDataConWorkId_maybe fun
1113 , let (univ_ty_args, rest_args) = splitAtList (dataConUnivTyVars con) args
1114 = Just (con, stripTypeArgs univ_ty_args, rest_args)
1116 -- Look through dictionary functions; see Note [Unfolding DFuns]
1117 | DFunUnfolding con ops <- unfolding
1119 , let (dfun_tvs, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)
1120 subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args))
1121 = Just (con, substTys subst dfun_res_tys,
1122 [mkApps op args | op <- ops])
1124 -- Look through unfoldings, but only cheap ones, because
1125 -- we are effectively duplicating the unfolding
1126 | CoreUnfolding { uf_expandable = expand_me, uf_tmpl = rhs } <- unfolding
1127 , expand_me = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
1130 is_saturated = count isValArg args == idArity fun
1131 unfolding = idUnfolding fun
1133 analyse _ _ = Nothing
1136 in_scope = mkInScopeSet (exprFreeVars expr)
1139 beta (Lam v body) pairs (arg : args)
1141 = beta body ((v,arg):pairs) args
1143 beta (Lam {}) _ _ -- Un-saturated, or not a type lambda
1147 = case analyse (substExpr subst fun) args of
1148 Nothing -> -- pprTrace "Bale out! exprIsConApp_maybe" doc $
1150 Just ans -> -- pprTrace "Woo-hoo! exprIsConApp_maybe" doc $
1153 subst = mkOpenSubst in_scope pairs
1154 -- doc = vcat [ppr fun, ppr expr, ppr pairs, ppr args]
1157 stripTypeArgs :: [CoreExpr] -> [Type]
1158 stripTypeArgs args = ASSERT2( all isTypeArg args, ppr args )
1159 [ty | Type ty <- args]
1162 Note [Unfolding DFuns]
1163 ~~~~~~~~~~~~~~~~~~~~~~
1166 df :: forall a b. (Eq a, Eq b) -> Eq (a,b)
1167 df a b d_a d_b = MkEqD (a,b) ($c1 a b d_a d_b)
1170 So to split it up we just need to apply the ops $c1, $c2 etc
1171 to the very same args as the dfun. It takes a little more work
1172 to compute the type arguments to the dictionary constructor.