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 mkUnfolding, mkCoreUnfolding,
23 mkTopUnfolding, mkSimpleUnfolding,
24 mkInlineUnfolding, mkInlinableUnfolding, mkWwInlineRule,
25 mkCompulsoryUnfolding, mkDFunUnfolding,
27 interestingArg, ArgSummary(..),
29 couldBeSmallEnoughToInline, inlineBoringOk,
30 certainlyWillInline, smallEnoughToInline,
32 callSiteInline, CallCtxt(..),
38 #include "HsVersions.h"
43 import PprCore () -- Instances
44 import TcType ( tcSplitSigmaTy, tcSplitDFunHead )
46 import CoreSubst hiding( substTy )
47 import CoreFVs ( exprFreeVars )
48 import CoreArity ( manifestArity, exprBotStrictness_maybe )
56 import BasicTypes ( Arity )
57 import TcType ( tcSplitDFunTy )
61 import VarEnv ( mkInScopeSet )
71 %************************************************************************
73 \subsection{Making unfoldings}
75 %************************************************************************
78 mkTopUnfolding :: Bool -> CoreExpr -> Unfolding
79 mkTopUnfolding = mkUnfolding InlineRhs True {- Top level -}
81 mkImplicitUnfolding :: CoreExpr -> Unfolding
82 -- For implicit Ids, do a tiny bit of optimising first
83 mkImplicitUnfolding expr = mkTopUnfolding False (simpleOptExpr expr)
85 -- Note [Top-level flag on inline rules]
86 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
87 -- Slight hack: note that mk_inline_rules conservatively sets the
88 -- top-level flag to True. It gets set more accurately by the simplifier
89 -- Simplify.simplUnfolding.
91 mkSimpleUnfolding :: CoreExpr -> Unfolding
92 mkSimpleUnfolding = mkUnfolding InlineRhs False False
94 mkDFunUnfolding :: Type -> [DFunArg CoreExpr] -> Unfolding
95 mkDFunUnfolding dfun_ty ops
96 = DFunUnfolding dfun_nargs data_con ops
98 (tvs, theta, head_ty) = tcSplitSigmaTy dfun_ty
99 -- NB: tcSplitSigmaTy: do not look through a newtype
100 -- when the dictionary type is a newtype
101 (cls, _) = tcSplitDFunHead head_ty
102 dfun_nargs = length tvs + length theta
103 data_con = classDataCon cls
105 mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding
106 mkWwInlineRule id expr arity
107 = mkCoreUnfolding (InlineWrapper id) True
108 (simpleOptExpr expr) arity
109 (UnfWhen unSaturatedOk boringCxtNotOk)
111 mkCompulsoryUnfolding :: CoreExpr -> Unfolding
112 mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
113 = mkCoreUnfolding InlineCompulsory True
114 expr 0 -- Arity of unfolding doesn't matter
115 (UnfWhen unSaturatedOk boringCxtOk)
117 mkInlineUnfolding :: Maybe Arity -> CoreExpr -> Unfolding
118 mkInlineUnfolding mb_arity expr
119 = mkCoreUnfolding InlineStable
120 True -- Note [Top-level flag on inline rules]
122 (UnfWhen unsat_ok boring_ok)
124 expr' = simpleOptExpr expr
125 (unsat_ok, arity) = case mb_arity of
126 Nothing -> (unSaturatedOk, manifestArity expr')
127 Just ar -> (needSaturated, ar)
129 boring_ok = inlineBoringOk expr'
131 mkInlinableUnfolding :: CoreExpr -> Unfolding
132 mkInlinableUnfolding expr
133 = mkUnfolding InlineStable True is_bot expr'
135 expr' = simpleOptExpr expr
136 is_bot = isJust (exprBotStrictness_maybe expr')
142 mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
143 -> Arity -> UnfoldingGuidance -> Unfolding
144 -- Occurrence-analyses the expression before capturing it
145 mkCoreUnfolding src top_lvl expr arity guidance
146 = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
150 uf_is_value = exprIsHNF expr,
151 uf_is_conlike = exprIsConLike expr,
152 uf_is_cheap = exprIsCheap expr,
153 uf_expandable = exprIsExpandable expr,
154 uf_guidance = guidance }
156 mkUnfolding :: UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
157 -- Calculates unfolding guidance
158 -- Occurrence-analyses the expression before capturing it
159 mkUnfolding src top_lvl is_bottoming expr
160 | top_lvl && is_bottoming
161 , not (exprIsTrivial expr)
162 = NoUnfolding -- See Note [Do not inline top-level bottoming functions]
164 = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
168 uf_is_value = exprIsHNF expr,
169 uf_is_conlike = exprIsConLike expr,
170 uf_expandable = exprIsExpandable expr,
171 uf_is_cheap = is_cheap,
172 uf_guidance = guidance }
174 is_cheap = exprIsCheap expr
175 (arity, guidance) = calcUnfoldingGuidance is_cheap
176 opt_UF_CreationThreshold expr
177 -- Sometimes during simplification, there's a large let-bound thing
178 -- which has been substituted, and so is now dead; so 'expr' contains
179 -- two copies of the thing while the occurrence-analysed expression doesn't
180 -- Nevertheless, we *don't* occ-analyse before computing the size because the
181 -- size computation bales out after a while, whereas occurrence analysis does not.
183 -- This can occasionally mean that the guidance is very pessimistic;
184 -- it gets fixed up next round. And it should be rare, because large
185 -- let-bound things that are dead are usually caught by preInlineUnconditionally
188 %************************************************************************
190 \subsection{The UnfoldingGuidance type}
192 %************************************************************************
195 inlineBoringOk :: CoreExpr -> Bool
196 -- See Note [INLINE for small functions]
197 -- True => the result of inlining the expression is
198 -- no bigger than the expression itself
199 -- eg (\x y -> f y x)
200 -- This is a quick and dirty version. It doesn't attempt
201 -- to deal with (\x y z -> x (y z))
202 -- The really important one is (x `cast` c)
206 go :: Int -> CoreExpr -> Bool
207 go credit (Lam x e) | isId x = go (credit+1) e
208 | otherwise = go credit e
209 go credit (App f (Type {})) = go credit f
210 go credit (App f a) | credit > 0
211 , exprIsTrivial a = go (credit-1) f
212 go credit (Note _ e) = go credit e
213 go credit (Cast e _) = go credit e
214 go _ (Var {}) = boringCxtOk
215 go _ _ = boringCxtNotOk
217 calcUnfoldingGuidance
218 :: Bool -- True <=> the rhs is cheap, or we want to treat it
219 -- as cheap (INLINE things)
220 -> Int -- Bomb out if size gets bigger than this
221 -> CoreExpr -- Expression to look at
222 -> (Arity, UnfoldingGuidance)
223 calcUnfoldingGuidance expr_is_cheap bOMB_OUT_SIZE expr
224 = case collectBinders expr of { (bndrs, body) ->
226 val_bndrs = filter isId bndrs
227 n_val_bndrs = length val_bndrs
230 = case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_bndrs body) of
232 SizeIs size cased_bndrs scrut_discount
233 | uncondInline n_val_bndrs (iBox size)
235 -> UnfWhen unSaturatedOk boringCxtOk -- Note [INLINE for small functions]
237 -> UnfIfGoodArgs { ug_args = map (discount cased_bndrs) val_bndrs
238 , ug_size = iBox size
239 , ug_res = iBox scrut_discount }
242 = foldlBag (\acc (b',n) -> if bndr==b' then acc+n else acc)
245 (n_val_bndrs, guidance) }
248 Note [Computing the size of an expression]
249 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
250 The basic idea of sizeExpr is obvious enough: count nodes. But getting the
251 heuristics right has taken a long time. Here's the basic strategy:
253 * Variables, literals: 0
254 (Exception for string literals, see litSize.)
256 * Function applications (f e1 .. en): 1 + #value args
258 * Constructor applications: 1, regardless of #args
260 * Let(rec): 1 + size of components
275 Notice that 'x' counts 0, while (f x) counts 2. That's deliberate: there's
276 a function call to account for. Notice also that constructor applications
277 are very cheap, because exposing them to a caller is so valuable.
280 Note [Do not inline top-level bottoming functions]
281 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
282 The FloatOut pass has gone to some trouble to float out calls to 'error'
283 and similar friends. See Note [Bottoming floats] in SetLevels.
284 Do not re-inline them! But we *do* still inline if they are very small
285 (the uncondInline stuff).
288 Note [INLINE for small functions]
289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
290 Consider {-# INLINE f #-}
293 Then f's RHS is no larger than its LHS, so we should inline it into
294 even the most boring context. In general, f the function is
295 sufficiently small that its body is as small as the call itself, the
296 inline unconditionally, regardless of how boring the context is.
300 * We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
301 than the thing it's replacing. Notice that
302 (f x) --> (g 3) -- YES, unconditionally
303 (f x) --> x : [] -- YES, *even though* there are two
304 -- arguments to the cons
308 It's very important not to unconditionally replace a variable by
311 * We do this even if the thing isn't saturated, else we end up with the
315 doesn't inline. Even in a boring context, inlining without being
316 saturated will give a lambda instead of a PAP, and will be more
317 efficient at runtime.
319 * However, when the function's arity > 0, we do insist that it
320 has at least one value argument at the call site. Otherwise we find this:
323 If we inline f here we get
324 d = /\b. MkD (\x:b. x)
325 and then prepareRhs floats out the argument, abstracting the type
326 variables, so we end up with the original again!
330 uncondInline :: Arity -> Int -> Bool
331 -- Inline unconditionally if there no size increase
332 -- Size of call is arity (+1 for the function)
333 -- See Note [INLINE for small functions]
334 uncondInline arity size
335 | arity == 0 = size == 0
336 | otherwise = size <= arity + 1
341 sizeExpr :: FastInt -- Bomb out if it gets bigger than this
342 -> [Id] -- Arguments; we're interested in which of these
347 -- Note [Computing the size of an expression]
349 sizeExpr bOMB_OUT_SIZE top_args expr
352 size_up (Cast e _) = size_up e
353 size_up (Note _ e) = size_up e
354 size_up (Type _) = sizeZero -- Types cost nothing
355 size_up (Lit lit) = sizeN (litSize lit)
356 size_up (Var f) = size_up_call f [] -- Make sure we get constructor
357 -- discounts even on nullary constructors
359 size_up (App fun (Type _)) = size_up fun
360 size_up (App fun arg) = size_up arg `addSizeNSD`
361 size_up_app fun [arg]
363 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
364 | otherwise = size_up e
366 size_up (Let (NonRec binder rhs) body)
367 = size_up rhs `addSizeNSD`
368 size_up body `addSizeN`
369 (if isUnLiftedType (idType binder) then 0 else 1)
370 -- For the allocation
371 -- If the binder has an unlifted type there is no allocation
373 size_up (Let (Rec pairs) body)
374 = foldr (addSizeNSD . size_up . snd)
375 (size_up body `addSizeN` length pairs) -- (length pairs) for the allocation
378 size_up (Case (Var v) _ _ alts)
379 | v `elem` top_args -- We are scrutinising an argument variable
380 = alts_size (foldr1 addAltSize alt_sizes)
381 (foldr1 maxSize alt_sizes)
382 -- Good to inline if an arg is scrutinised, because
383 -- that may eliminate allocation in the caller
384 -- And it eliminates the case itself
386 alt_sizes = map size_up_alt alts
388 -- alts_size tries to compute a good discount for
389 -- the case when we are scrutinising an argument variable
390 alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
391 (SizeIs max _ _) -- Size of biggest alternative
392 = SizeIs tot (unitBag (v, iBox (_ILIT(2) +# tot -# max)) `unionBags` tot_disc) tot_scrut
393 -- If the variable is known, we produce a discount that
394 -- will take us back to 'max', the size of the largest alternative
395 -- The 1+ is a little discount for reduced allocation in the caller
397 -- Notice though, that we return tot_disc, the total discount from
398 -- all branches. I think that's right.
400 alts_size tot_size _ = tot_size
402 size_up (Case e _ _ alts) = size_up e `addSizeNSD`
403 foldr (addAltSize . size_up_alt) sizeZero alts
404 -- We don't charge for the case itself
405 -- It's a strict thing, and the price of the call
406 -- is paid by scrut. Also consider
407 -- case f x of DEFAULT -> e
408 -- This is just ';'! Don't charge for it.
410 -- Moreover, we charge one per alternative.
413 -- size_up_app is used when there's ONE OR MORE value args
414 size_up_app (App fun arg) args
415 | isTypeArg arg = size_up_app fun args
416 | otherwise = size_up arg `addSizeNSD`
417 size_up_app fun (arg:args)
418 size_up_app (Var fun) args = size_up_call fun args
419 size_up_app other args = size_up other `addSizeN` length args
422 size_up_call :: Id -> [CoreExpr] -> ExprSize
423 size_up_call fun val_args
424 = case idDetails fun of
425 FCallId _ -> sizeN opt_UF_DearOp
426 DataConWorkId dc -> conSize dc (length val_args)
427 PrimOpId op -> primOpSize op (length val_args)
428 ClassOpId _ -> classOpSize top_args val_args
429 _ -> funSize top_args fun (length val_args)
432 size_up_alt (_con, _bndrs, rhs) = size_up rhs `addSizeN` 1
433 -- Don't charge for args, so that wrappers look cheap
434 -- (See comments about wrappers with Case)
436 -- IMPORATANT: *do* charge 1 for the alternative, else we
437 -- find that giant case nests are treated as practically free
438 -- A good example is Foreign.C.Error.errrnoToIOError
441 -- These addSize things have to be here because
442 -- I don't want to give them bOMB_OUT_SIZE as an argument
443 addSizeN TooBig _ = TooBig
444 addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
446 -- addAltSize is used to add the sizes of case alternatives
447 addAltSize TooBig _ = TooBig
448 addAltSize _ TooBig = TooBig
449 addAltSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
450 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
452 (d1 +# d2) -- Note [addAltSize result discounts]
454 -- This variant ignores the result discount from its LEFT argument
455 -- It's used when the second argument isn't part of the result
456 addSizeNSD TooBig _ = TooBig
457 addSizeNSD _ TooBig = TooBig
458 addSizeNSD (SizeIs n1 xs _) (SizeIs n2 ys d2)
459 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
465 -- | Finds a nominal size of a string literal.
466 litSize :: Literal -> Int
467 -- Used by CoreUnfold.sizeExpr
468 litSize (MachStr str) = 1 + ((lengthFS str + 3) `div` 4)
469 -- If size could be 0 then @f "x"@ might be too small
470 -- [Sept03: make literal strings a bit bigger to avoid fruitless
471 -- duplication of little strings]
472 litSize _other = 0 -- Must match size of nullary constructors
473 -- Key point: if x |-> 4, then x must inline unconditionally
474 -- (eg via case binding)
476 classOpSize :: [Id] -> [CoreExpr] -> ExprSize
477 -- See Note [Conlike is interesting]
480 classOpSize top_args (arg1 : other_args)
481 = SizeIs (iUnbox size) arg_discount (_ILIT(0))
483 size = 2 + length other_args
484 -- If the class op is scrutinising a lambda bound dictionary then
485 -- give it a discount, to encourage the inlining of this function
486 -- The actual discount is rather arbitrarily chosen
487 arg_discount = case arg1 of
488 Var dict | dict `elem` top_args
489 -> unitBag (dict, opt_UF_DictDiscount)
492 funSize :: [Id] -> Id -> Int -> ExprSize
493 -- Size for functions that are not constructors or primops
494 -- Note [Function applications]
495 funSize top_args fun n_val_args
496 | fun `hasKey` buildIdKey = buildSize
497 | fun `hasKey` augmentIdKey = augmentSize
498 | otherwise = SizeIs (iUnbox size) arg_discount (iUnbox res_discount)
500 some_val_args = n_val_args > 0
502 arg_discount | some_val_args && fun `elem` top_args
503 = unitBag (fun, opt_UF_FunAppDiscount)
504 | otherwise = emptyBag
505 -- If the function is an argument and is applied
506 -- to some values, give it an arg-discount
508 res_discount | idArity fun > n_val_args = opt_UF_FunAppDiscount
510 -- If the function is partially applied, show a result discount
512 size | some_val_args = 1 + n_val_args
514 -- The 1+ is for the function itself
515 -- Add 1 for each non-trivial arg;
516 -- the allocation cost, as in let(rec)
519 conSize :: DataCon -> Int -> ExprSize
520 conSize dc n_val_args
521 | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables
523 -- See Note [Constructor size]
524 | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))
526 -- See Note [Unboxed tuple result discount]
527 -- | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
529 -- See Note [Constructor size]
530 | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
533 Note [Constructor size]
534 ~~~~~~~~~~~~~~~~~~~~~~~
535 Treat a constructors application as size 1, regardless of how many
536 arguments it has; we are keen to expose them (and we charge separately
537 for their args). We can't treat them as size zero, else we find that
538 (Just x) has size 0, which is the same as a lone variable; and hence
539 'v' will always be replaced by (Just x), where v is bound to Just x.
541 However, unboxed tuples count as size zero. I found occasions where we had
542 f x y z = case op# x y z of { s -> (# s, () #) }
543 and f wasn't getting inlined.
545 Note [Unboxed tuple result discount]
546 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
547 I tried giving unboxed tuples a *result discount* of zero (see the
548 commented-out line). Why? When returned as a result they do not
549 allocate, so maybe we don't want to charge so much for them If you
550 have a non-zero discount here, we find that workers often get inlined
551 back into wrappers, because it look like
552 f x = case $wf x of (# a,b #) -> (a,b)
553 and we are keener because of the case. However while this change
554 shrank binary sizes by 0.5% it also made spectral/boyer allocate 5%
555 more. All other changes were very small. So it's not a big deal but I
556 didn't adopt the idea.
559 primOpSize :: PrimOp -> Int -> ExprSize
560 primOpSize op n_val_args
561 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
562 | not (primOpOutOfLine op) = sizeN 1
563 -- Be very keen to inline simple primops.
564 -- We give a discount of 1 for each arg so that (op# x y z) costs 2.
565 -- We can't make it cost 1, else we'll inline let v = (op# x y z)
566 -- at every use of v, which is excessive.
568 -- A good example is:
569 -- let x = +# p q in C {x}
570 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
571 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
573 | otherwise = sizeN n_val_args
576 buildSize :: ExprSize
577 buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
578 -- We really want to inline applications of build
579 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
580 -- Indeed, we should add a result_discount becuause build is
581 -- very like a constructor. We don't bother to check that the
582 -- build is saturated (it usually is). The "-2" discounts for the \c n,
583 -- The "4" is rather arbitrary.
585 augmentSize :: ExprSize
586 augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
587 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
588 -- e plus ys. The -2 accounts for the \cn
590 -- When we return a lambda, give a discount if it's used (applied)
591 lamScrutDiscount :: ExprSize -> ExprSize
592 lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)
593 lamScrutDiscount TooBig = TooBig
596 Note [addAltSize result discounts]
597 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
598 When adding the size of alternatives, we *add* the result discounts
599 too, rather than take the *maximum*. For a multi-branch case, this
600 gives a discount for each branch that returns a constructor, making us
601 keener to inline. I did try using 'max' instead, but it makes nofib
602 'rewrite' and 'puzzle' allocate significantly more, and didn't make
603 binary sizes shrink significantly either.
605 Note [Discounts and thresholds]
606 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
607 Constants for discounts and thesholds are defined in main/StaticFlags,
608 all of form opt_UF_xxxx. They are:
610 opt_UF_CreationThreshold (45)
611 At a definition site, if the unfolding is bigger than this, we
612 may discard it altogether
614 opt_UF_UseThreshold (6)
615 At a call site, if the unfolding, less discounts, is smaller than
616 this, then it's small enough inline
618 opt_UF_KeennessFactor (1.5)
619 Factor by which the discounts are multiplied before
620 subtracting from size
622 opt_UF_DictDiscount (1)
623 The discount for each occurrence of a dictionary argument
624 as an argument of a class method. Should be pretty small
625 else big functions may get inlined
627 opt_UF_FunAppDiscount (6)
628 Discount for a function argument that is applied. Quite
629 large, because if we inline we avoid the higher-order call.
632 The size of a foreign call or not-dupable PrimOp
635 Note [Function applications]
636 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
637 In a function application (f a b)
639 - If 'f' is an argument to the function being analysed,
640 and there's at least one value arg, record a FunAppDiscount for f
642 - If the application if a PAP (arity > 2 in this example)
643 record a *result* discount (because inlining
644 with "extra" args in the call may mean that we now
645 get a saturated application)
647 Code for manipulating sizes
650 data ExprSize = TooBig
651 | SizeIs FastInt -- Size found
652 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
653 FastInt -- Size to subtract if result is scrutinised
654 -- by a case expression
656 instance Outputable ExprSize where
657 ppr TooBig = ptext (sLit "TooBig")
658 ppr (SizeIs a _ c) = brackets (int (iBox a) <+> int (iBox c))
660 -- subtract the discount before deciding whether to bale out. eg. we
661 -- want to inline a large constructor application into a selector:
662 -- tup = (a_1, ..., a_99)
663 -- x = case tup of ...
665 mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize
666 mkSizeIs max n xs d | (n -# d) ># max = TooBig
667 | otherwise = SizeIs n xs d
669 maxSize :: ExprSize -> ExprSize -> ExprSize
670 maxSize TooBig _ = TooBig
671 maxSize _ TooBig = TooBig
672 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
676 sizeN :: Int -> ExprSize
678 sizeZero = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
679 sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT(0))
683 %************************************************************************
685 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
687 %************************************************************************
689 We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that
690 we ``couldn't possibly use'' on the other side. Can be overridden w/
691 flaggery. Just the same as smallEnoughToInline, except that it has no
695 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
696 couldBeSmallEnoughToInline threshold rhs
697 = case sizeExpr (iUnbox threshold) [] body of
701 (_, body) = collectBinders rhs
704 smallEnoughToInline :: Unfolding -> Bool
705 smallEnoughToInline (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})
706 = size <= opt_UF_UseThreshold
707 smallEnoughToInline _
711 certainlyWillInline :: Unfolding -> Bool
712 -- Sees if the unfolding is pretty certain to inline
713 certainlyWillInline (CoreUnfolding { uf_is_cheap = is_cheap, uf_arity = n_vals, uf_guidance = guidance })
717 UnfIfGoodArgs { ug_size = size}
718 -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold
720 certainlyWillInline _
724 %************************************************************************
726 \subsection{callSiteInline}
728 %************************************************************************
730 This is the key function. It decides whether to inline a variable at a call site
732 callSiteInline is used at call sites, so it is a bit more generous.
733 It's a very important function that embodies lots of heuristics.
734 A non-WHNF can be inlined if it doesn't occur inside a lambda,
735 and occurs exactly once or
736 occurs once in each branch of a case and is small
738 If the thing is in WHNF, there's no danger of duplicating work,
739 so we can inline if it occurs once, or is small
741 NOTE: we don't want to inline top-level functions that always diverge.
742 It just makes the code bigger. Tt turns out that the convenient way to prevent
743 them inlining is to give them a NOINLINE pragma, which we do in
744 StrictAnal.addStrictnessInfoToTopId
747 callSiteInline :: DynFlags
749 -> Bool -- True <=> unfolding is active
750 -> Bool -- True if there are are no arguments at all (incl type args)
751 -> [ArgSummary] -- One for each value arg; True if it is interesting
752 -> CallCtxt -- True <=> continuation is interesting
753 -> Maybe CoreExpr -- Unfolding, if any
755 instance Outputable ArgSummary where
756 ppr TrivArg = ptext (sLit "TrivArg")
757 ppr NonTrivArg = ptext (sLit "NonTrivArg")
758 ppr ValueArg = ptext (sLit "ValueArg")
760 data CallCtxt = BoringCtxt
762 | ArgCtxt -- We are somewhere in the argument of a function
763 Bool -- True <=> we're somewhere in the RHS of function with rules
764 -- False <=> we *are* the argument of a function with non-zero
767 -- we *are* the RHS of a let Note [RHS of lets]
768 -- In both cases, be a little keener to inline
770 | ValAppCtxt -- We're applied to at least one value arg
771 -- This arises when we have ((f x |> co) y)
772 -- Then the (f x) has argument 'x' but in a ValAppCtxt
774 | CaseCtxt -- We're the scrutinee of a case
775 -- that decomposes its scrutinee
777 instance Outputable CallCtxt where
778 ppr BoringCtxt = ptext (sLit "BoringCtxt")
779 ppr (ArgCtxt rules) = ptext (sLit "ArgCtxt") <+> ppr rules
780 ppr CaseCtxt = ptext (sLit "CaseCtxt")
781 ppr ValAppCtxt = ptext (sLit "ValAppCtxt")
783 callSiteInline dflags id active_unfolding lone_variable arg_infos cont_info
784 = case idUnfolding id of
785 -- idUnfolding checks for loop-breakers, returning NoUnfolding
786 -- Things with an INLINE pragma may have an unfolding *and*
787 -- be a loop breaker (maybe the knot is not yet untied)
788 CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top
789 , uf_is_cheap = is_cheap, uf_arity = uf_arity
790 , uf_guidance = guidance }
791 | active_unfolding -> tryUnfolding dflags id lone_variable
792 arg_infos cont_info unf_template is_top
793 is_cheap uf_arity guidance
794 | otherwise -> Nothing
795 NoUnfolding -> Nothing
796 OtherCon {} -> Nothing
797 DFunUnfolding {} -> Nothing -- Never unfold a DFun
799 tryUnfolding :: DynFlags -> Id -> Bool -> [ArgSummary] -> CallCtxt
800 -> CoreExpr -> Bool -> Bool -> Arity -> UnfoldingGuidance
802 tryUnfolding dflags id lone_variable
803 arg_infos cont_info unf_template is_top
804 is_cheap uf_arity guidance
805 -- uf_arity will typically be equal to (idArity id),
806 -- but may be less for InlineRules
807 | dopt Opt_D_dump_inlinings dflags && dopt Opt_D_verbose_core2core dflags
808 = pprTrace ("Considering inlining: " ++ showSDoc (ppr id))
809 (vcat [text "arg infos" <+> ppr arg_infos,
810 text "uf arity" <+> ppr uf_arity,
811 text "interesting continuation" <+> ppr cont_info,
812 text "some_benefit" <+> ppr some_benefit,
813 text "is cheap:" <+> ppr is_cheap,
814 text "guidance" <+> ppr guidance,
816 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])
821 n_val_args = length arg_infos
822 saturated = n_val_args >= uf_arity
824 result | yes_or_no = Just unf_template
825 | otherwise = Nothing
827 interesting_args = any nonTriv arg_infos
828 -- NB: (any nonTriv arg_infos) looks at the
829 -- over-saturated args too which is "wrong";
830 -- but if over-saturated we inline anyway.
832 -- some_benefit is used when the RHS is small enough
833 -- and the call has enough (or too many) value
834 -- arguments (ie n_val_args >= arity). But there must
835 -- be *something* interesting about some argument, or the
836 -- result context, to make it worth inlining
838 | not saturated = interesting_args -- Under-saturated
839 -- Note [Unsaturated applications]
840 | n_val_args > uf_arity = True -- Over-saturated
841 | otherwise = interesting_args -- Saturated
842 || interesting_saturated_call
844 interesting_saturated_call
846 BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]
847 CaseCtxt -> not (lone_variable && is_cheap) -- Note [Lone variables]
848 ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt]
849 ValAppCtxt -> True -- Note [Cast then apply]
851 (yes_or_no, extra_doc)
853 UnfNever -> (False, empty)
855 UnfWhen unsat_ok boring_ok
856 -> (enough_args && (boring_ok || some_benefit), empty )
857 where -- See Note [INLINE for small functions]
858 enough_args = saturated || (unsat_ok && n_val_args > 0)
860 UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
861 -> ( is_cheap && some_benefit && small_enough
862 , (text "discounted size =" <+> int discounted_size) )
864 discounted_size = size - discount
865 small_enough = discounted_size <= opt_UF_UseThreshold
866 discount = computeDiscount uf_arity arg_discounts
867 res_discount arg_infos cont_info
872 Be a tiny bit keener to inline in the RHS of a let, because that might
873 lead to good thing later
875 g y = let x = f y in ...(case x of (a,b,c) -> ...) ...
876 We'd inline 'f' if the call was in a case context, and it kind-of-is,
877 only we can't see it. So we treat the RHS of a let as not-totally-boring.
879 Note [Unsaturated applications]
880 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
881 When a call is not saturated, we *still* inline if one of the
882 arguments has interesting structure. That's sometimes very important.
883 A good example is the Ord instance for Bool in Base:
886 $fOrdBool =GHC.Classes.D:Ord
891 $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool
892 $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool
895 But the defn of GHC.Classes.$dmmin is:
897 $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a
898 {- Arity: 3, HasNoCafRefs, Strictness: SLL,
899 Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a ->
900 case @ a GHC.Classes.<= @ a $dOrd x y of wild {
901 GHC.Types.False -> y GHC.Types.True -> x }) -}
903 We *really* want to inline $dmmin, even though it has arity 3, in
904 order to unravel the recursion.
907 Note [Things to watch]
908 ~~~~~~~~~~~~~~~~~~~~~~
909 * { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
910 Assume x is exported, so not inlined unconditionally.
911 Then we want x to inline unconditionally; no reason for it
912 not to, and doing so avoids an indirection.
914 * { x = I# 3; ....f x.... }
915 Make sure that x does not inline unconditionally!
916 Lest we get extra allocation.
918 Note [Inlining an InlineRule]
919 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
920 An InlineRules is used for
921 (a) programmer INLINE pragmas
922 (b) inlinings from worker/wrapper
924 For (a) the RHS may be large, and our contract is that we *only* inline
925 when the function is applied to all the arguments on the LHS of the
926 source-code defn. (The uf_arity in the rule.)
928 However for worker/wrapper it may be worth inlining even if the
929 arity is not satisfied (as we do in the CoreUnfolding case) so we don't
933 Note [Nested functions]
934 ~~~~~~~~~~~~~~~~~~~~~~~
935 If a function has a nested defn we also record some-benefit, on the
936 grounds that we are often able to eliminate the binding, and hence the
937 allocation, for the function altogether; this is good for join points.
938 But this only makes sense for *functions*; inlining a constructor
939 doesn't help allocation unless the result is scrutinised. UNLESS the
940 constructor occurs just once, albeit possibly in multiple case
941 branches. Then inlining it doesn't increase allocation, but it does
942 increase the chance that the constructor won't be allocated at all in
943 the branches that don't use it.
945 Note [Cast then apply]
946 ~~~~~~~~~~~~~~~~~~~~~~
948 myIndex = __inline_me ( (/\a. <blah>) |> co )
949 co :: (forall a. a -> a) ~ (forall a. T a)
950 ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ...
952 We need to inline myIndex to unravel this; but the actual call (myIndex a) has
953 no value arguments. The ValAppCtxt gives it enough incentive to inline.
955 Note [Inlining in ArgCtxt]
956 ~~~~~~~~~~~~~~~~~~~~~~~~~~
957 The condition (arity > 0) here is very important, because otherwise
958 we end up inlining top-level stuff into useless places; eg
961 This can make a very big difference: it adds 16% to nofib 'integer' allocs,
964 At one stage I replaced this condition by 'True' (leading to the above
965 slow-down). The motivation was test eyeball/inline1.hs; but that seems
968 NOTE: arguably, we should inline in ArgCtxt only if the result of the
969 call is at least CONLIKE. At least for the cases where we use ArgCtxt
970 for the RHS of a 'let', we only profit from the inlining if we get a
971 CONLIKE thing (modulo lets).
973 Note [Lone variables] See also Note [Interaction of exprIsCheap and lone variables]
974 ~~~~~~~~~~~~~~~~~~~~~ which appears below
975 The "lone-variable" case is important. I spent ages messing about
976 with unsatisfactory varaints, but this is nice. The idea is that if a
977 variable appears all alone
979 as an arg of lazy fn, or rhs BoringCtxt
980 as scrutinee of a case CaseCtxt
981 as arg of a fn ArgCtxt
983 it is bound to a cheap expression
985 then we should not inline it (unless there is some other reason,
986 e.g. is is the sole occurrence). That is what is happening at
987 the use of 'lone_variable' in 'interesting_saturated_call'.
989 Why? At least in the case-scrutinee situation, turning
990 let x = (a,b) in case x of y -> ...
992 let x = (a,b) in case (a,b) of y -> ...
994 let x = (a,b) in let y = (a,b) in ...
995 is bad if the binding for x will remain.
997 Another example: I discovered that strings
998 were getting inlined straight back into applications of 'error'
999 because the latter is strict.
1001 f = \x -> ...(error s)...
1003 Fundamentally such contexts should not encourage inlining because the
1004 context can ``see'' the unfolding of the variable (e.g. case or a
1005 RULE) so there's no gain. If the thing is bound to a value.
1010 foo = _inline_ (\n. [n])
1011 bar = _inline_ (foo 20)
1012 baz = \n. case bar of { (m:_) -> m + n }
1013 Here we really want to inline 'bar' so that we can inline 'foo'
1014 and the whole thing unravels as it should obviously do. This is
1015 important: in the NDP project, 'bar' generates a closure data
1016 structure rather than a list.
1018 So the non-inlining of lone_variables should only apply if the
1019 unfolding is regarded as cheap; because that is when exprIsConApp_maybe
1020 looks through the unfolding. Hence the "&& is_cheap" in the
1023 * Even a type application or coercion isn't a lone variable.
1025 case $fMonadST @ RealWorld of { :DMonad a b c -> c }
1026 We had better inline that sucker! The case won't see through it.
1028 For now, I'm treating treating a variable applied to types
1029 in a *lazy* context "lone". The motivating example was
1031 g = /\a. \y. h (f a)
1032 There's no advantage in inlining f here, and perhaps
1033 a significant disadvantage. Hence some_val_args in the Stop case
1035 Note [Interaction of exprIsCheap and lone variables]
1036 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1037 The lone-variable test says "don't inline if a case expression
1038 scrutines a lone variable whose unfolding is cheap". It's very
1039 important that, under these circumstances, exprIsConApp_maybe
1040 can spot a constructor application. So, for example, we don't
1043 to be cheap, and that's good because exprIsConApp_maybe doesn't
1044 think that expression is a constructor application.
1046 I used to test is_value rather than is_cheap, which was utterly
1047 wrong, because the above expression responds True to exprIsHNF.
1049 This kind of thing can occur if you have
1052 foo = let x = e in (x,x)
1057 computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
1058 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info
1059 -- We multiple the raw discounts (args_discount and result_discount)
1060 -- ty opt_UnfoldingKeenessFactor because the former have to do with
1061 -- *size* whereas the discounts imply that there's some extra
1062 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
1065 = 1 -- Discount of 1 because the result replaces the call
1066 -- so we count 1 for the function itself
1068 + length (take n_vals_wanted arg_infos)
1069 -- Discount of (un-scaled) 1 for each arg supplied,
1070 -- because the result replaces the call
1072 + round (opt_UF_KeenessFactor *
1073 fromIntegral (arg_discount + res_discount'))
1075 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
1077 mk_arg_discount _ TrivArg = 0
1078 mk_arg_discount _ NonTrivArg = 1
1079 mk_arg_discount discount ValueArg = discount
1081 res_discount' = case cont_info of
1083 CaseCtxt -> res_discount
1084 _other -> 4 `min` res_discount
1085 -- res_discount can be very large when a function returns
1086 -- constructors; but we only want to invoke that large discount
1087 -- when there's a case continuation.
1088 -- Otherwise we, rather arbitrarily, threshold it. Yuk.
1089 -- But we want to aovid inlining large functions that return
1090 -- constructors into contexts that are simply "interesting"
1093 %************************************************************************
1095 Interesting arguments
1097 %************************************************************************
1099 Note [Interesting arguments]
1100 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1101 An argument is interesting if it deserves a discount for unfoldings
1102 with a discount in that argument position. The idea is to avoid
1103 unfolding a function that is applied only to variables that have no
1104 unfolding (i.e. they are probably lambda bound): f x y z There is
1105 little point in inlining f here.
1107 Generally, *values* (like (C a b) and (\x.e)) deserve discounts. But
1108 we must look through lets, eg (let x = e in C a b), because the let will
1109 float, exposing the value, if we inline. That makes it different to
1112 Before 2009 we said it was interesting if the argument had *any* structure
1113 at all; i.e. (hasSomeUnfolding v). But does too much inlining; see Trac #3016.
1115 But we don't regard (f x y) as interesting, unless f is unsaturated.
1116 If it's saturated and f hasn't inlined, then it's probably not going
1119 Note [Conlike is interesting]
1120 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1122 f d = ...((*) d x y)...
1124 where df is con-like. Then we'd really like to inline 'f' so that the
1125 rule for (*) (df d) can fire. To do this
1126 a) we give a discount for being an argument of a class-op (eg (*) d)
1127 b) we say that a con-like argument (eg (df d)) is interesting
1130 data ArgSummary = TrivArg -- Nothing interesting
1131 | NonTrivArg -- Arg has structure
1132 | ValueArg -- Arg is a con-app or PAP
1133 -- ..or con-like. Note [Conlike is interesting]
1135 interestingArg :: CoreExpr -> ArgSummary
1136 -- See Note [Interesting arguments]
1137 interestingArg e = go e 0
1139 -- n is # value args to which the expression is applied
1140 go (Lit {}) _ = ValueArg
1142 | isConLikeId v = ValueArg -- Experimenting with 'conlike' rather that
1143 -- data constructors here
1144 | idArity v > n = ValueArg -- Catches (eg) primops with arity but no unfolding
1145 | n > 0 = NonTrivArg -- Saturated or unknown call
1146 | conlike_unfolding = ValueArg -- n==0; look for an interesting unfolding
1147 -- See Note [Conlike is interesting]
1148 | otherwise = TrivArg -- n==0, no useful unfolding
1150 conlike_unfolding = isConLikeUnfolding (idUnfolding v)
1152 go (Type _) _ = TrivArg
1153 go (App fn (Type _)) n = go fn n
1154 go (App fn _) n = go fn (n+1)
1155 go (Note _ a) n = go a n
1156 go (Cast e _) n = go e n
1158 | isTyCoVar v = go e n
1160 | otherwise = ValueArg
1161 go (Let _ e) n = case go e n of { ValueArg -> ValueArg; _ -> NonTrivArg }
1162 go (Case {}) _ = NonTrivArg
1164 nonTriv :: ArgSummary -> Bool
1165 nonTriv TrivArg = False
1169 %************************************************************************
1173 %************************************************************************
1175 Note [exprIsConApp_maybe]
1176 ~~~~~~~~~~~~~~~~~~~~~~~~~
1177 exprIsConApp_maybe is a very important function. There are two principal
1179 * case e of { .... }
1180 * cls_op e, where cls_op is a class operation
1182 In both cases you want to know if e is of form (C e1..en) where C is
1185 However e might not *look* as if
1188 -- | Returns @Just (dc, [t1..tk], [x1..xn])@ if the argument expression is
1189 -- a *saturated* constructor application of the form @dc t1..tk x1 .. xn@,
1190 -- where t1..tk are the *universally-qantified* type args of 'dc'
1191 exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])
1193 exprIsConApp_maybe id_unf (Note note expr)
1195 = exprIsConApp_maybe id_unf expr
1196 -- We ignore all notes except SCCs. For example,
1197 -- case _scc_ "foo" (C a b) of
1199 -- should not be optimised away, because we'll lose the
1200 -- entry count on 'foo'; see Trac #4414
1202 exprIsConApp_maybe id_unf (Cast expr co)
1203 = -- Here we do the KPush reduction rule as described in the FC paper
1204 -- The transformation applies iff we have
1205 -- (C e1 ... en) `cast` co
1206 -- where co :: (T t1 .. tn) ~ to_ty
1207 -- The left-hand one must be a T, because exprIsConApp returned True
1208 -- but the right-hand one might not be. (Though it usually will.)
1210 case exprIsConApp_maybe id_unf expr of {
1211 Nothing -> Nothing ;
1212 Just (dc, _dc_univ_args, dc_args) ->
1214 let (_from_ty, to_ty) = coercionKind co
1215 dc_tc = dataConTyCon dc
1217 case splitTyConApp_maybe to_ty of {
1218 Nothing -> Nothing ;
1219 Just (to_tc, to_tc_arg_tys)
1220 | dc_tc /= to_tc -> Nothing
1221 -- These two Nothing cases are possible; we might see
1222 -- (C x y) `cast` (g :: T a ~ S [a]),
1223 -- where S is a type function. In fact, exprIsConApp
1224 -- will probably not be called in such circumstances,
1225 -- but there't nothing wrong with it
1229 tc_arity = tyConArity dc_tc
1230 dc_univ_tyvars = dataConUnivTyVars dc
1231 dc_ex_tyvars = dataConExTyVars dc
1232 arg_tys = dataConRepArgTys dc
1234 dc_eqs :: [(Type,Type)] -- All equalities from the DataCon
1235 dc_eqs = [(mkTyVarTy tv, ty) | (tv,ty) <- dataConEqSpec dc] ++
1236 [getEqPredTys eq_pred | eq_pred <- dataConEqTheta dc]
1238 (ex_args, rest1) = splitAtList dc_ex_tyvars dc_args
1239 (co_args, val_args) = splitAtList dc_eqs rest1
1241 -- Make the "theta" from Fig 3 of the paper
1242 gammas = decomposeCo tc_arity co
1243 theta = zipOpenTvSubst (dc_univ_tyvars ++ dc_ex_tyvars)
1244 (gammas ++ stripTypeArgs ex_args)
1246 -- Cast the existential coercion arguments
1247 cast_co (ty1, ty2) (Type co)
1248 = Type $ mkSymCoercion (substTy theta ty1)
1249 `mkTransCoercion` co
1250 `mkTransCoercion` (substTy theta ty2)
1251 cast_co _ other_arg = pprPanic "cast_co" (ppr other_arg)
1252 new_co_args = zipWith cast_co dc_eqs co_args
1254 -- Cast the value arguments (which include dictionaries)
1255 new_val_args = zipWith cast_arg arg_tys val_args
1256 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
1259 let dump_doc = vcat [ppr dc, ppr dc_univ_tyvars, ppr dc_ex_tyvars,
1260 ppr arg_tys, ppr dc_args, ppr _dc_univ_args,
1261 ppr ex_args, ppr val_args]
1263 ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )
1264 ASSERT2( all isTypeArg (ex_args ++ co_args), dump_doc )
1265 ASSERT2( equalLength val_args arg_tys, dump_doc )
1268 Just (dc, to_tc_arg_tys, ex_args ++ new_co_args ++ new_val_args)
1271 exprIsConApp_maybe id_unf expr
1274 analyse (App fun arg) args = analyse fun (arg:args)
1275 analyse fun@(Lam {}) args = beta fun [] args
1277 analyse (Var fun) args
1278 | Just con <- isDataConWorkId_maybe fun
1279 , count isValArg args == idArity fun
1280 , let (univ_ty_args, rest_args) = splitAtList (dataConUnivTyVars con) args
1281 = Just (con, stripTypeArgs univ_ty_args, rest_args)
1283 -- Look through dictionary functions; see Note [Unfolding DFuns]
1284 | DFunUnfolding dfun_nargs con ops <- unfolding
1285 , let sat = length args == dfun_nargs -- See Note [DFun arity check]
1286 in if sat then True else
1287 pprTrace "Unsaturated dfun" (ppr fun <+> int dfun_nargs $$ ppr args) False
1288 , let (dfun_tvs, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)
1289 subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args))
1290 mk_arg (DFunConstArg e) = e
1291 mk_arg (DFunLamArg i) = args !! i
1292 mk_arg (DFunPolyArg e) = mkApps e args
1293 = Just (con, substTys subst dfun_res_tys, map mk_arg ops)
1295 -- Look through unfoldings, but only cheap ones, because
1296 -- we are effectively duplicating the unfolding
1297 | Just rhs <- expandUnfolding_maybe unfolding
1298 = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
1301 unfolding = id_unf fun
1303 analyse _ _ = Nothing
1306 beta (Lam v body) pairs (arg : args)
1308 = beta body ((v,arg):pairs) args
1310 beta (Lam {}) _ _ -- Un-saturated, or not a type lambda
1314 = analyse (substExpr (text "subst-expr-is-con-app") subst fun) args
1316 subst = mkOpenSubst (mkInScopeSet (exprFreeVars fun)) pairs
1317 -- doc = vcat [ppr fun, ppr expr, ppr pairs, ppr args]
1320 stripTypeArgs :: [CoreExpr] -> [Type]
1321 stripTypeArgs args = ASSERT2( all isTypeArg args, ppr args )
1322 [ty | Type ty <- args]
1325 Note [Unfolding DFuns]
1326 ~~~~~~~~~~~~~~~~~~~~~~
1329 df :: forall a b. (Eq a, Eq b) -> Eq (a,b)
1330 df a b d_a d_b = MkEqD (a,b) ($c1 a b d_a d_b)
1333 So to split it up we just need to apply the ops $c1, $c2 etc
1334 to the very same args as the dfun. It takes a little more work
1335 to compute the type arguments to the dictionary constructor.
1337 Note [DFun arity check]
1338 ~~~~~~~~~~~~~~~~~~~~~~~
1339 Here we check that the total number of supplied arguments (inclding
1340 type args) matches what the dfun is expecting. This may be *less*
1341 than the ordinary arity of the dfun: see Note [DFun unfoldings] in CoreSyn