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,
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 -> [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 = case calcUnfoldingGuidance True -- Treat as cheap
130 False -- But not bottoming
132 (_, UnfWhen _ boring_ok) -> boring_ok
133 _other -> boringCxtNotOk
134 -- See Note [INLINE for small functions]
136 mkInlinableUnfolding :: CoreExpr -> Unfolding
137 mkInlinableUnfolding expr
138 = mkUnfolding InlineStable True is_bot expr'
140 expr' = simpleOptExpr expr
141 is_bot = isJust (exprBotStrictness_maybe expr')
147 mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
148 -> Arity -> UnfoldingGuidance -> Unfolding
149 -- Occurrence-analyses the expression before capturing it
150 mkCoreUnfolding src top_lvl expr arity guidance
151 = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
155 uf_is_value = exprIsHNF expr,
156 uf_is_conlike = exprIsConLike expr,
157 uf_is_cheap = exprIsCheap expr,
158 uf_expandable = exprIsExpandable expr,
159 uf_guidance = guidance }
161 mkUnfolding :: UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
162 -- Calculates unfolding guidance
163 -- Occurrence-analyses the expression before capturing it
164 mkUnfolding src top_lvl is_bottoming expr
165 = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
169 uf_is_value = exprIsHNF expr,
170 uf_is_conlike = exprIsConLike expr,
171 uf_expandable = exprIsExpandable expr,
172 uf_is_cheap = is_cheap,
173 uf_guidance = guidance }
175 is_cheap = exprIsCheap expr
176 (arity, guidance) = calcUnfoldingGuidance is_cheap (top_lvl && is_bottoming)
177 opt_UF_CreationThreshold expr
178 -- Sometimes during simplification, there's a large let-bound thing
179 -- which has been substituted, and so is now dead; so 'expr' contains
180 -- two copies of the thing while the occurrence-analysed expression doesn't
181 -- Nevertheless, we *don't* occ-analyse before computing the size because the
182 -- size computation bales out after a while, whereas occurrence analysis does not.
184 -- This can occasionally mean that the guidance is very pessimistic;
185 -- it gets fixed up next round. And it should be rare, because large
186 -- let-bound things that are dead are usually caught by preInlineUnconditionally
189 %************************************************************************
191 \subsection{The UnfoldingGuidance type}
193 %************************************************************************
196 calcUnfoldingGuidance
197 :: Bool -- True <=> the rhs is cheap, or we want to treat it
198 -- as cheap (INLINE things)
199 -> Bool -- True <=> this is a top-level unfolding for a
200 -- diverging function; don't inline this
201 -> Int -- Bomb out if size gets bigger than this
202 -> CoreExpr -- Expression to look at
203 -> (Arity, UnfoldingGuidance)
204 calcUnfoldingGuidance expr_is_cheap top_bot bOMB_OUT_SIZE expr
205 = case collectBinders expr of { (bndrs, body) ->
207 val_bndrs = filter isId bndrs
208 n_val_bndrs = length val_bndrs
211 = case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_bndrs body) of
213 SizeIs size cased_bndrs scrut_discount
214 | uncondInline n_val_bndrs (iBox size)
216 -> UnfWhen unSaturatedOk boringCxtOk -- Note [INLINE for small functions]
217 | top_bot -- See Note [Do not inline top-level bottoming functions]
221 -> UnfIfGoodArgs { ug_args = map (discount cased_bndrs) val_bndrs
222 , ug_size = iBox size
223 , ug_res = iBox scrut_discount }
226 = foldlBag (\acc (b',n) -> if bndr==b' then acc+n else acc)
229 (n_val_bndrs, guidance) }
232 Note [Computing the size of an expression]
233 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
234 The basic idea of sizeExpr is obvious enough: count nodes. But getting the
235 heuristics right has taken a long time. Here's the basic strategy:
237 * Variables, literals: 0
238 (Exception for string literals, see litSize.)
240 * Function applications (f e1 .. en): 1 + #value args
242 * Constructor applications: 1, regardless of #args
244 * Let(rec): 1 + size of components
259 Notice that 'x' counts 0, while (f x) counts 2. That's deliberate: there's
260 a function call to account for. Notice also that constructor applications
261 are very cheap, because exposing them to a caller is so valuable.
264 Note [Do not inline top-level bottoming functions]
265 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
266 The FloatOut pass has gone to some trouble to float out calls to 'error'
267 and similar friends. See Note [Bottoming floats] in SetLevels.
268 Do not re-inline them! But we *do* still inline if they are very small
269 (the uncondInline stuff).
272 Note [INLINE for small functions]
273 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
274 Consider {-# INLINE f #-}
277 Then f's RHS is no larger than its LHS, so we should inline it into
278 even the most boring context. In general, f the function is
279 sufficiently small that its body is as small as the call itself, the
280 inline unconditionally, regardless of how boring the context is.
284 * We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
285 than the thing it's replacing. Notice that
286 (f x) --> (g 3) -- YES, unconditionally
287 (f x) --> x : [] -- YES, *even though* there are two
288 -- arguments to the cons
292 It's very important not to unconditionally replace a variable by
295 * We do this even if the thing isn't saturated, else we end up with the
299 doesn't inline. Even in a boring context, inlining without being
300 saturated will give a lambda instead of a PAP, and will be more
301 efficient at runtime.
303 * However, when the function's arity > 0, we do insist that it
304 has at least one value argument at the call site. Otherwise we find this:
307 If we inline f here we get
308 d = /\b. MkD (\x:b. x)
309 and then prepareRhs floats out the argument, abstracting the type
310 variables, so we end up with the original again!
314 uncondInline :: Arity -> Int -> Bool
315 -- Inline unconditionally if there no size increase
316 -- Size of call is arity (+1 for the function)
317 -- See Note [INLINE for small functions]
318 uncondInline arity size
319 | arity == 0 = size == 0
320 | otherwise = size <= arity + 1
325 sizeExpr :: FastInt -- Bomb out if it gets bigger than this
326 -> [Id] -- Arguments; we're interested in which of these
331 -- Note [Computing the size of an expression]
333 sizeExpr bOMB_OUT_SIZE top_args expr
336 size_up (Cast e _) = size_up e
337 size_up (Note _ e) = size_up e
338 size_up (Type _) = sizeZero -- Types cost nothing
339 size_up (Lit lit) = sizeN (litSize lit)
340 size_up (Var f) = size_up_call f [] -- Make sure we get constructor
341 -- discounts even on nullary constructors
343 size_up (App fun (Type _)) = size_up fun
344 size_up (App fun arg) = size_up arg `addSizeNSD`
345 size_up_app fun [arg]
347 size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
348 | otherwise = size_up e
350 size_up (Let (NonRec binder rhs) body)
351 = size_up rhs `addSizeNSD`
352 size_up body `addSizeN`
353 (if isUnLiftedType (idType binder) then 0 else 1)
354 -- For the allocation
355 -- If the binder has an unlifted type there is no allocation
357 size_up (Let (Rec pairs) body)
358 = foldr (addSizeNSD . size_up . snd)
359 (size_up body `addSizeN` length pairs) -- (length pairs) for the allocation
362 size_up (Case (Var v) _ _ alts)
363 | v `elem` top_args -- We are scrutinising an argument variable
364 = alts_size (foldr1 addAltSize alt_sizes)
365 (foldr1 maxSize alt_sizes)
366 -- Good to inline if an arg is scrutinised, because
367 -- that may eliminate allocation in the caller
368 -- And it eliminates the case itself
370 alt_sizes = map size_up_alt alts
372 -- alts_size tries to compute a good discount for
373 -- the case when we are scrutinising an argument variable
374 alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
375 (SizeIs max _ _) -- Size of biggest alternative
376 = SizeIs tot (unitBag (v, iBox (_ILIT(2) +# tot -# max)) `unionBags` tot_disc) tot_scrut
377 -- If the variable is known, we produce a discount that
378 -- will take us back to 'max', the size of the largest alternative
379 -- The 1+ is a little discount for reduced allocation in the caller
381 -- Notice though, that we return tot_disc, the total discount from
382 -- all branches. I think that's right.
384 alts_size tot_size _ = tot_size
386 size_up (Case e _ _ alts) = size_up e `addSizeNSD`
387 foldr (addAltSize . size_up_alt) sizeZero alts
388 -- We don't charge for the case itself
389 -- It's a strict thing, and the price of the call
390 -- is paid by scrut. Also consider
391 -- case f x of DEFAULT -> e
392 -- This is just ';'! Don't charge for it.
394 -- Moreover, we charge one per alternative.
397 -- size_up_app is used when there's ONE OR MORE value args
398 size_up_app (App fun arg) args
399 | isTypeArg arg = size_up_app fun args
400 | otherwise = size_up arg `addSizeNSD`
401 size_up_app fun (arg:args)
402 size_up_app (Var fun) args = size_up_call fun args
403 size_up_app other args = size_up other `addSizeN` length args
406 size_up_call :: Id -> [CoreExpr] -> ExprSize
407 size_up_call fun val_args
408 = case idDetails fun of
409 FCallId _ -> sizeN opt_UF_DearOp
410 DataConWorkId dc -> conSize dc (length val_args)
411 PrimOpId op -> primOpSize op (length val_args)
412 ClassOpId _ -> classOpSize top_args val_args
413 _ -> funSize top_args fun (length val_args)
416 size_up_alt (_con, _bndrs, rhs) = size_up rhs `addSizeN` 1
417 -- Don't charge for args, so that wrappers look cheap
418 -- (See comments about wrappers with Case)
420 -- IMPORATANT: *do* charge 1 for the alternative, else we
421 -- find that giant case nests are treated as practically free
422 -- A good example is Foreign.C.Error.errrnoToIOError
425 -- These addSize things have to be here because
426 -- I don't want to give them bOMB_OUT_SIZE as an argument
427 addSizeN TooBig _ = TooBig
428 addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
430 -- addAltSize is used to add the sizes of case alternatives
431 addAltSize TooBig _ = TooBig
432 addAltSize _ TooBig = TooBig
433 addAltSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
434 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
436 (d1 +# d2) -- Note [addAltSize result discounts]
438 -- This variant ignores the result discount from its LEFT argument
439 -- It's used when the second argument isn't part of the result
440 addSizeNSD TooBig _ = TooBig
441 addSizeNSD _ TooBig = TooBig
442 addSizeNSD (SizeIs n1 xs _) (SizeIs n2 ys d2)
443 = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
449 -- | Finds a nominal size of a string literal.
450 litSize :: Literal -> Int
451 -- Used by CoreUnfold.sizeExpr
452 litSize (MachStr str) = 1 + ((lengthFS str + 3) `div` 4)
453 -- If size could be 0 then @f "x"@ might be too small
454 -- [Sept03: make literal strings a bit bigger to avoid fruitless
455 -- duplication of little strings]
456 litSize _other = 0 -- Must match size of nullary constructors
457 -- Key point: if x |-> 4, then x must inline unconditionally
458 -- (eg via case binding)
460 classOpSize :: [Id] -> [CoreExpr] -> ExprSize
461 -- See Note [Conlike is interesting]
464 classOpSize top_args (arg1 : other_args)
465 = SizeIs (iUnbox size) arg_discount (_ILIT(0))
467 size = 2 + length other_args
468 -- If the class op is scrutinising a lambda bound dictionary then
469 -- give it a discount, to encourage the inlining of this function
470 -- The actual discount is rather arbitrarily chosen
471 arg_discount = case arg1 of
472 Var dict | dict `elem` top_args
473 -> unitBag (dict, opt_UF_DictDiscount)
476 funSize :: [Id] -> Id -> Int -> ExprSize
477 -- Size for functions that are not constructors or primops
478 -- Note [Function applications]
479 funSize top_args fun n_val_args
480 | fun `hasKey` buildIdKey = buildSize
481 | fun `hasKey` augmentIdKey = augmentSize
482 | otherwise = SizeIs (iUnbox size) arg_discount (iUnbox res_discount)
484 some_val_args = n_val_args > 0
486 arg_discount | some_val_args && fun `elem` top_args
487 = unitBag (fun, opt_UF_FunAppDiscount)
488 | otherwise = emptyBag
489 -- If the function is an argument and is applied
490 -- to some values, give it an arg-discount
492 res_discount | idArity fun > n_val_args = opt_UF_FunAppDiscount
494 -- If the function is partially applied, show a result discount
496 size | some_val_args = 1 + n_val_args
498 -- The 1+ is for the function itself
499 -- Add 1 for each non-trivial arg;
500 -- the allocation cost, as in let(rec)
503 conSize :: DataCon -> Int -> ExprSize
504 conSize dc n_val_args
505 | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables
507 -- See Note [Constructor size]
508 | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))
510 -- See Note [Unboxed tuple result discount]
511 -- | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
513 -- See Note [Constructor size]
514 | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
517 Note [Constructor size]
518 ~~~~~~~~~~~~~~~~~~~~~~~
519 Treat a constructors application as size 1, regardless of how many
520 arguments it has; we are keen to expose them (and we charge separately
521 for their args). We can't treat them as size zero, else we find that
522 (Just x) has size 0, which is the same as a lone variable; and hence
523 'v' will always be replaced by (Just x), where v is bound to Just x.
525 However, unboxed tuples count as size zero. I found occasions where we had
526 f x y z = case op# x y z of { s -> (# s, () #) }
527 and f wasn't getting inlined.
529 Note [Unboxed tuple result discount]
530 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
531 I tried giving unboxed tuples a *result discount* of zero (see the
532 commented-out line). Why? When returned as a result they do not
533 allocate, so maybe we don't want to charge so much for them If you
534 have a non-zero discount here, we find that workers often get inlined
535 back into wrappers, because it look like
536 f x = case $wf x of (# a,b #) -> (a,b)
537 and we are keener because of the case. However while this change
538 shrank binary sizes by 0.5% it also made spectral/boyer allocate 5%
539 more. All other changes were very small. So it's not a big deal but I
540 didn't adopt the idea.
543 primOpSize :: PrimOp -> Int -> ExprSize
544 primOpSize op n_val_args
545 | not (primOpIsDupable op) = sizeN opt_UF_DearOp
546 | not (primOpOutOfLine op) = sizeN 1
547 -- Be very keen to inline simple primops.
548 -- We give a discount of 1 for each arg so that (op# x y z) costs 2.
549 -- We can't make it cost 1, else we'll inline let v = (op# x y z)
550 -- at every use of v, which is excessive.
552 -- A good example is:
553 -- let x = +# p q in C {x}
554 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
555 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
557 | otherwise = sizeN n_val_args
560 buildSize :: ExprSize
561 buildSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
562 -- We really want to inline applications of build
563 -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later)
564 -- Indeed, we should add a result_discount becuause build is
565 -- very like a constructor. We don't bother to check that the
566 -- build is saturated (it usually is). The "-2" discounts for the \c n,
567 -- The "4" is rather arbitrary.
569 augmentSize :: ExprSize
570 augmentSize = SizeIs (_ILIT(0)) emptyBag (_ILIT(4))
571 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of
572 -- e plus ys. The -2 accounts for the \cn
574 -- When we return a lambda, give a discount if it's used (applied)
575 lamScrutDiscount :: ExprSize -> ExprSize
576 lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)
577 lamScrutDiscount TooBig = TooBig
580 Note [addAltSize result discounts]
581 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
582 When adding the size of alternatives, we *add* the result discounts
583 too, rather than take the *maximum*. For a multi-branch case, this
584 gives a discount for each branch that returns a constructor, making us
585 keener to inline. I did try using 'max' instead, but it makes nofib
586 'rewrite' and 'puzzle' allocate significantly more, and didn't make
587 binary sizes shrink significantly either.
589 Note [Discounts and thresholds]
590 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
591 Constants for discounts and thesholds are defined in main/StaticFlags,
592 all of form opt_UF_xxxx. They are:
594 opt_UF_CreationThreshold (45)
595 At a definition site, if the unfolding is bigger than this, we
596 may discard it altogether
598 opt_UF_UseThreshold (6)
599 At a call site, if the unfolding, less discounts, is smaller than
600 this, then it's small enough inline
602 opt_UF_KeennessFactor (1.5)
603 Factor by which the discounts are multiplied before
604 subtracting from size
606 opt_UF_DictDiscount (1)
607 The discount for each occurrence of a dictionary argument
608 as an argument of a class method. Should be pretty small
609 else big functions may get inlined
611 opt_UF_FunAppDiscount (6)
612 Discount for a function argument that is applied. Quite
613 large, because if we inline we avoid the higher-order call.
616 The size of a foreign call or not-dupable PrimOp
619 Note [Function applications]
620 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
621 In a function application (f a b)
623 - If 'f' is an argument to the function being analysed,
624 and there's at least one value arg, record a FunAppDiscount for f
626 - If the application if a PAP (arity > 2 in this example)
627 record a *result* discount (because inlining
628 with "extra" args in the call may mean that we now
629 get a saturated application)
631 Code for manipulating sizes
634 data ExprSize = TooBig
635 | SizeIs FastInt -- Size found
636 (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
637 FastInt -- Size to subtract if result is scrutinised
638 -- by a case expression
640 instance Outputable ExprSize where
641 ppr TooBig = ptext (sLit "TooBig")
642 ppr (SizeIs a _ c) = brackets (int (iBox a) <+> int (iBox c))
644 -- subtract the discount before deciding whether to bale out. eg. we
645 -- want to inline a large constructor application into a selector:
646 -- tup = (a_1, ..., a_99)
647 -- x = case tup of ...
649 mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize
650 mkSizeIs max n xs d | (n -# d) ># max = TooBig
651 | otherwise = SizeIs n xs d
653 maxSize :: ExprSize -> ExprSize -> ExprSize
654 maxSize TooBig _ = TooBig
655 maxSize _ TooBig = TooBig
656 maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1
660 sizeN :: Int -> ExprSize
662 sizeZero = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
663 sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT(0))
667 %************************************************************************
669 \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
671 %************************************************************************
673 We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that
674 we ``couldn't possibly use'' on the other side. Can be overridden w/
675 flaggery. Just the same as smallEnoughToInline, except that it has no
679 couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
680 couldBeSmallEnoughToInline threshold rhs
681 = case sizeExpr (iUnbox threshold) [] body of
685 (_, body) = collectBinders rhs
688 smallEnoughToInline :: Unfolding -> Bool
689 smallEnoughToInline (CoreUnfolding {uf_guidance = UnfIfGoodArgs {ug_size = size}})
690 = size <= opt_UF_UseThreshold
691 smallEnoughToInline _
695 certainlyWillInline :: Unfolding -> Bool
696 -- Sees if the unfolding is pretty certain to inline
697 certainlyWillInline (CoreUnfolding { uf_is_cheap = is_cheap, uf_arity = n_vals, uf_guidance = guidance })
701 UnfIfGoodArgs { ug_size = size}
702 -> is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold
704 certainlyWillInline _
708 %************************************************************************
710 \subsection{callSiteInline}
712 %************************************************************************
714 This is the key function. It decides whether to inline a variable at a call site
716 callSiteInline is used at call sites, so it is a bit more generous.
717 It's a very important function that embodies lots of heuristics.
718 A non-WHNF can be inlined if it doesn't occur inside a lambda,
719 and occurs exactly once or
720 occurs once in each branch of a case and is small
722 If the thing is in WHNF, there's no danger of duplicating work,
723 so we can inline if it occurs once, or is small
725 NOTE: we don't want to inline top-level functions that always diverge.
726 It just makes the code bigger. Tt turns out that the convenient way to prevent
727 them inlining is to give them a NOINLINE pragma, which we do in
728 StrictAnal.addStrictnessInfoToTopId
731 callSiteInline :: DynFlags
733 -> Bool -- True <=> unfolding is active
734 -> Bool -- True if there are are no arguments at all (incl type args)
735 -> [ArgSummary] -- One for each value arg; True if it is interesting
736 -> CallCtxt -- True <=> continuation is interesting
737 -> Maybe CoreExpr -- Unfolding, if any
739 instance Outputable ArgSummary where
740 ppr TrivArg = ptext (sLit "TrivArg")
741 ppr NonTrivArg = ptext (sLit "NonTrivArg")
742 ppr ValueArg = ptext (sLit "ValueArg")
744 data CallCtxt = BoringCtxt
746 | ArgCtxt -- We are somewhere in the argument of a function
747 Bool -- True <=> we're somewhere in the RHS of function with rules
748 -- False <=> we *are* the argument of a function with non-zero
751 -- we *are* the RHS of a let Note [RHS of lets]
752 -- In both cases, be a little keener to inline
754 | ValAppCtxt -- We're applied to at least one value arg
755 -- This arises when we have ((f x |> co) y)
756 -- Then the (f x) has argument 'x' but in a ValAppCtxt
758 | CaseCtxt -- We're the scrutinee of a case
759 -- that decomposes its scrutinee
761 instance Outputable CallCtxt where
762 ppr BoringCtxt = ptext (sLit "BoringCtxt")
763 ppr (ArgCtxt rules) = ptext (sLit "ArgCtxt") <+> ppr rules
764 ppr CaseCtxt = ptext (sLit "CaseCtxt")
765 ppr ValAppCtxt = ptext (sLit "ValAppCtxt")
767 callSiteInline dflags id active_unfolding lone_variable arg_infos cont_info
768 = case idUnfolding id of
769 -- idUnfolding checks for loop-breakers, returning NoUnfolding
770 -- Things with an INLINE pragma may have an unfolding *and*
771 -- be a loop breaker (maybe the knot is not yet untied)
772 CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top
773 , uf_is_cheap = is_cheap, uf_arity = uf_arity
774 , uf_guidance = guidance }
775 | active_unfolding -> tryUnfolding dflags id lone_variable
776 arg_infos cont_info unf_template is_top
777 is_cheap uf_arity guidance
778 | otherwise -> Nothing
779 NoUnfolding -> Nothing
780 OtherCon {} -> Nothing
781 DFunUnfolding {} -> Nothing -- Never unfold a DFun
783 tryUnfolding :: DynFlags -> Id -> Bool -> [ArgSummary] -> CallCtxt
784 -> CoreExpr -> Bool -> Bool -> Arity -> UnfoldingGuidance
786 tryUnfolding dflags id lone_variable
787 arg_infos cont_info unf_template is_top
788 is_cheap uf_arity guidance
789 -- uf_arity will typically be equal to (idArity id),
790 -- but may be less for InlineRules
791 | dopt Opt_D_dump_inlinings dflags && dopt Opt_D_verbose_core2core dflags
792 = pprTrace ("Considering inlining: " ++ showSDoc (ppr id))
793 (vcat [text "arg infos" <+> ppr arg_infos,
794 text "uf arity" <+> ppr uf_arity,
795 text "interesting continuation" <+> ppr cont_info,
796 text "some_benefit" <+> ppr some_benefit,
797 text "is cheap:" <+> ppr is_cheap,
798 text "guidance" <+> ppr guidance,
800 text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"])
805 n_val_args = length arg_infos
806 saturated = n_val_args >= uf_arity
808 result | yes_or_no = Just unf_template
809 | otherwise = Nothing
811 interesting_args = any nonTriv arg_infos
812 -- NB: (any nonTriv arg_infos) looks at the
813 -- over-saturated args too which is "wrong";
814 -- but if over-saturated we inline anyway.
816 -- some_benefit is used when the RHS is small enough
817 -- and the call has enough (or too many) value
818 -- arguments (ie n_val_args >= arity). But there must
819 -- be *something* interesting about some argument, or the
820 -- result context, to make it worth inlining
822 | not saturated = interesting_args -- Under-saturated
823 -- Note [Unsaturated applications]
824 | n_val_args > uf_arity = True -- Over-saturated
825 | otherwise = interesting_args -- Saturated
826 || interesting_saturated_call
828 interesting_saturated_call
830 BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]
831 CaseCtxt -> not (lone_variable && is_cheap) -- Note [Lone variables]
832 ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt]
833 ValAppCtxt -> True -- Note [Cast then apply]
835 (yes_or_no, extra_doc)
837 UnfNever -> (False, empty)
839 UnfWhen unsat_ok boring_ok
840 -> (enough_args && (boring_ok || some_benefit), empty )
841 where -- See Note [INLINE for small functions]
842 enough_args = saturated || (unsat_ok && n_val_args > 0)
844 UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
845 -> ( is_cheap && some_benefit && small_enough
846 , (text "discounted size =" <+> int discounted_size) )
848 discounted_size = size - discount
849 small_enough = discounted_size <= opt_UF_UseThreshold
850 discount = computeDiscount uf_arity arg_discounts
851 res_discount arg_infos cont_info
856 Be a tiny bit keener to inline in the RHS of a let, because that might
857 lead to good thing later
859 g y = let x = f y in ...(case x of (a,b,c) -> ...) ...
860 We'd inline 'f' if the call was in a case context, and it kind-of-is,
861 only we can't see it. So we treat the RHS of a let as not-totally-boring.
863 Note [Unsaturated applications]
864 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
865 When a call is not saturated, we *still* inline if one of the
866 arguments has interesting structure. That's sometimes very important.
867 A good example is the Ord instance for Bool in Base:
870 $fOrdBool =GHC.Classes.D:Ord
875 $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool
876 $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool
879 But the defn of GHC.Classes.$dmmin is:
881 $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a
882 {- Arity: 3, HasNoCafRefs, Strictness: SLL,
883 Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a ->
884 case @ a GHC.Classes.<= @ a $dOrd x y of wild {
885 GHC.Types.False -> y GHC.Types.True -> x }) -}
887 We *really* want to inline $dmmin, even though it has arity 3, in
888 order to unravel the recursion.
891 Note [Things to watch]
892 ~~~~~~~~~~~~~~~~~~~~~~
893 * { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
894 Assume x is exported, so not inlined unconditionally.
895 Then we want x to inline unconditionally; no reason for it
896 not to, and doing so avoids an indirection.
898 * { x = I# 3; ....f x.... }
899 Make sure that x does not inline unconditionally!
900 Lest we get extra allocation.
902 Note [Inlining an InlineRule]
903 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
904 An InlineRules is used for
905 (a) programmer INLINE pragmas
906 (b) inlinings from worker/wrapper
908 For (a) the RHS may be large, and our contract is that we *only* inline
909 when the function is applied to all the arguments on the LHS of the
910 source-code defn. (The uf_arity in the rule.)
912 However for worker/wrapper it may be worth inlining even if the
913 arity is not satisfied (as we do in the CoreUnfolding case) so we don't
917 Note [Nested functions]
918 ~~~~~~~~~~~~~~~~~~~~~~~
919 If a function has a nested defn we also record some-benefit, on the
920 grounds that we are often able to eliminate the binding, and hence the
921 allocation, for the function altogether; this is good for join points.
922 But this only makes sense for *functions*; inlining a constructor
923 doesn't help allocation unless the result is scrutinised. UNLESS the
924 constructor occurs just once, albeit possibly in multiple case
925 branches. Then inlining it doesn't increase allocation, but it does
926 increase the chance that the constructor won't be allocated at all in
927 the branches that don't use it.
929 Note [Cast then apply]
930 ~~~~~~~~~~~~~~~~~~~~~~
932 myIndex = __inline_me ( (/\a. <blah>) |> co )
933 co :: (forall a. a -> a) ~ (forall a. T a)
934 ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ...
936 We need to inline myIndex to unravel this; but the actual call (myIndex a) has
937 no value arguments. The ValAppCtxt gives it enough incentive to inline.
939 Note [Inlining in ArgCtxt]
940 ~~~~~~~~~~~~~~~~~~~~~~~~~~
941 The condition (arity > 0) here is very important, because otherwise
942 we end up inlining top-level stuff into useless places; eg
945 This can make a very big difference: it adds 16% to nofib 'integer' allocs,
948 At one stage I replaced this condition by 'True' (leading to the above
949 slow-down). The motivation was test eyeball/inline1.hs; but that seems
952 NOTE: arguably, we should inline in ArgCtxt only if the result of the
953 call is at least CONLIKE. At least for the cases where we use ArgCtxt
954 for the RHS of a 'let', we only profit from the inlining if we get a
955 CONLIKE thing (modulo lets).
957 Note [Lone variables] See also Note [Interaction of exprIsCheap and lone variables]
958 ~~~~~~~~~~~~~~~~~~~~~ which appears below
959 The "lone-variable" case is important. I spent ages messing about
960 with unsatisfactory varaints, but this is nice. The idea is that if a
961 variable appears all alone
963 as an arg of lazy fn, or rhs BoringCtxt
964 as scrutinee of a case CaseCtxt
965 as arg of a fn ArgCtxt
967 it is bound to a cheap expression
969 then we should not inline it (unless there is some other reason,
970 e.g. is is the sole occurrence). That is what is happening at
971 the use of 'lone_variable' in 'interesting_saturated_call'.
973 Why? At least in the case-scrutinee situation, turning
974 let x = (a,b) in case x of y -> ...
976 let x = (a,b) in case (a,b) of y -> ...
978 let x = (a,b) in let y = (a,b) in ...
979 is bad if the binding for x will remain.
981 Another example: I discovered that strings
982 were getting inlined straight back into applications of 'error'
983 because the latter is strict.
985 f = \x -> ...(error s)...
987 Fundamentally such contexts should not encourage inlining because the
988 context can ``see'' the unfolding of the variable (e.g. case or a
989 RULE) so there's no gain. If the thing is bound to a value.
994 foo = _inline_ (\n. [n])
995 bar = _inline_ (foo 20)
996 baz = \n. case bar of { (m:_) -> m + n }
997 Here we really want to inline 'bar' so that we can inline 'foo'
998 and the whole thing unravels as it should obviously do. This is
999 important: in the NDP project, 'bar' generates a closure data
1000 structure rather than a list.
1002 So the non-inlining of lone_variables should only apply if the
1003 unfolding is regarded as cheap; because that is when exprIsConApp_maybe
1004 looks through the unfolding. Hence the "&& is_cheap" in the
1007 * Even a type application or coercion isn't a lone variable.
1009 case $fMonadST @ RealWorld of { :DMonad a b c -> c }
1010 We had better inline that sucker! The case won't see through it.
1012 For now, I'm treating treating a variable applied to types
1013 in a *lazy* context "lone". The motivating example was
1015 g = /\a. \y. h (f a)
1016 There's no advantage in inlining f here, and perhaps
1017 a significant disadvantage. Hence some_val_args in the Stop case
1019 Note [Interaction of exprIsCheap and lone variables]
1020 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1021 The lone-variable test says "don't inline if a case expression
1022 scrutines a lone variable whose unfolding is cheap". It's very
1023 important that, under these circumstances, exprIsConApp_maybe
1024 can spot a constructor application. So, for example, we don't
1027 to be cheap, and that's good because exprIsConApp_maybe doesn't
1028 think that expression is a constructor application.
1030 I used to test is_value rather than is_cheap, which was utterly
1031 wrong, because the above expression responds True to exprIsHNF.
1033 This kind of thing can occur if you have
1036 foo = let x = e in (x,x)
1041 computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
1042 computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info
1043 -- We multiple the raw discounts (args_discount and result_discount)
1044 -- ty opt_UnfoldingKeenessFactor because the former have to do with
1045 -- *size* whereas the discounts imply that there's some extra
1046 -- *efficiency* to be gained (e.g. beta reductions, case reductions)
1049 = 1 -- Discount of 1 because the result replaces the call
1050 -- so we count 1 for the function itself
1052 + length (take n_vals_wanted arg_infos)
1053 -- Discount of (un-scaled) 1 for each arg supplied,
1054 -- because the result replaces the call
1056 + round (opt_UF_KeenessFactor *
1057 fromIntegral (arg_discount + res_discount'))
1059 arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
1061 mk_arg_discount _ TrivArg = 0
1062 mk_arg_discount _ NonTrivArg = 1
1063 mk_arg_discount discount ValueArg = discount
1065 res_discount' = case cont_info of
1067 CaseCtxt -> res_discount
1068 _other -> 4 `min` res_discount
1069 -- res_discount can be very large when a function returns
1070 -- constructors; but we only want to invoke that large discount
1071 -- when there's a case continuation.
1072 -- Otherwise we, rather arbitrarily, threshold it. Yuk.
1073 -- But we want to aovid inlining large functions that return
1074 -- constructors into contexts that are simply "interesting"
1077 %************************************************************************
1079 Interesting arguments
1081 %************************************************************************
1083 Note [Interesting arguments]
1084 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1085 An argument is interesting if it deserves a discount for unfoldings
1086 with a discount in that argument position. The idea is to avoid
1087 unfolding a function that is applied only to variables that have no
1088 unfolding (i.e. they are probably lambda bound): f x y z There is
1089 little point in inlining f here.
1091 Generally, *values* (like (C a b) and (\x.e)) deserve discounts. But
1092 we must look through lets, eg (let x = e in C a b), because the let will
1093 float, exposing the value, if we inline. That makes it different to
1096 Before 2009 we said it was interesting if the argument had *any* structure
1097 at all; i.e. (hasSomeUnfolding v). But does too much inlining; see Trac #3016.
1099 But we don't regard (f x y) as interesting, unless f is unsaturated.
1100 If it's saturated and f hasn't inlined, then it's probably not going
1103 Note [Conlike is interesting]
1104 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1106 f d = ...((*) d x y)...
1108 where df is con-like. Then we'd really like to inline 'f' so that the
1109 rule for (*) (df d) can fire. To do this
1110 a) we give a discount for being an argument of a class-op (eg (*) d)
1111 b) we say that a con-like argument (eg (df d)) is interesting
1114 data ArgSummary = TrivArg -- Nothing interesting
1115 | NonTrivArg -- Arg has structure
1116 | ValueArg -- Arg is a con-app or PAP
1117 -- ..or con-like. Note [Conlike is interesting]
1119 interestingArg :: CoreExpr -> ArgSummary
1120 -- See Note [Interesting arguments]
1121 interestingArg e = go e 0
1123 -- n is # value args to which the expression is applied
1124 go (Lit {}) _ = ValueArg
1126 | isConLikeId v = ValueArg -- Experimenting with 'conlike' rather that
1127 -- data constructors here
1128 | idArity v > n = ValueArg -- Catches (eg) primops with arity but no unfolding
1129 | n > 0 = NonTrivArg -- Saturated or unknown call
1130 | conlike_unfolding = ValueArg -- n==0; look for an interesting unfolding
1131 -- See Note [Conlike is interesting]
1132 | otherwise = TrivArg -- n==0, no useful unfolding
1134 conlike_unfolding = isConLikeUnfolding (idUnfolding v)
1136 go (Type _) _ = TrivArg
1137 go (App fn (Type _)) n = go fn n
1138 go (App fn _) n = go fn (n+1)
1139 go (Note _ a) n = go a n
1140 go (Cast e _) n = go e n
1142 | isTyCoVar v = go e n
1144 | otherwise = ValueArg
1145 go (Let _ e) n = case go e n of { ValueArg -> ValueArg; _ -> NonTrivArg }
1146 go (Case {}) _ = NonTrivArg
1148 nonTriv :: ArgSummary -> Bool
1149 nonTriv TrivArg = False
1153 %************************************************************************
1157 %************************************************************************
1159 Note [exprIsConApp_maybe]
1160 ~~~~~~~~~~~~~~~~~~~~~~~~~
1161 exprIsConApp_maybe is a very important function. There are two principal
1163 * case e of { .... }
1164 * cls_op e, where cls_op is a class operation
1166 In both cases you want to know if e is of form (C e1..en) where C is
1169 However e might not *look* as if
1172 -- | Returns @Just (dc, [t1..tk], [x1..xn])@ if the argument expression is
1173 -- a *saturated* constructor application of the form @dc t1..tk x1 .. xn@,
1174 -- where t1..tk are the *universally-qantified* type args of 'dc'
1175 exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])
1177 exprIsConApp_maybe id_unf (Note note expr)
1179 = exprIsConApp_maybe id_unf expr
1180 -- We ignore all notes except SCCs. For example,
1181 -- case _scc_ "foo" (C a b) of
1183 -- should not be optimised away, because we'll lose the
1184 -- entry count on 'foo'; see Trac #4414
1186 exprIsConApp_maybe id_unf (Cast expr co)
1187 = -- Here we do the KPush reduction rule as described in the FC paper
1188 -- The transformation applies iff we have
1189 -- (C e1 ... en) `cast` co
1190 -- where co :: (T t1 .. tn) ~ to_ty
1191 -- The left-hand one must be a T, because exprIsConApp returned True
1192 -- but the right-hand one might not be. (Though it usually will.)
1194 case exprIsConApp_maybe id_unf expr of {
1195 Nothing -> Nothing ;
1196 Just (dc, _dc_univ_args, dc_args) ->
1198 let (_from_ty, to_ty) = coercionKind co
1199 dc_tc = dataConTyCon dc
1201 case splitTyConApp_maybe to_ty of {
1202 Nothing -> Nothing ;
1203 Just (to_tc, to_tc_arg_tys)
1204 | dc_tc /= to_tc -> Nothing
1205 -- These two Nothing cases are possible; we might see
1206 -- (C x y) `cast` (g :: T a ~ S [a]),
1207 -- where S is a type function. In fact, exprIsConApp
1208 -- will probably not be called in such circumstances,
1209 -- but there't nothing wrong with it
1213 tc_arity = tyConArity dc_tc
1214 dc_univ_tyvars = dataConUnivTyVars dc
1215 dc_ex_tyvars = dataConExTyVars dc
1216 arg_tys = dataConRepArgTys dc
1218 dc_eqs :: [(Type,Type)] -- All equalities from the DataCon
1219 dc_eqs = [(mkTyVarTy tv, ty) | (tv,ty) <- dataConEqSpec dc] ++
1220 [getEqPredTys eq_pred | eq_pred <- dataConEqTheta dc]
1222 (ex_args, rest1) = splitAtList dc_ex_tyvars dc_args
1223 (co_args, val_args) = splitAtList dc_eqs rest1
1225 -- Make the "theta" from Fig 3 of the paper
1226 gammas = decomposeCo tc_arity co
1227 theta = zipOpenTvSubst (dc_univ_tyvars ++ dc_ex_tyvars)
1228 (gammas ++ stripTypeArgs ex_args)
1230 -- Cast the existential coercion arguments
1231 cast_co (ty1, ty2) (Type co)
1232 = Type $ mkSymCoercion (substTy theta ty1)
1233 `mkTransCoercion` co
1234 `mkTransCoercion` (substTy theta ty2)
1235 cast_co _ other_arg = pprPanic "cast_co" (ppr other_arg)
1236 new_co_args = zipWith cast_co dc_eqs co_args
1238 -- Cast the value arguments (which include dictionaries)
1239 new_val_args = zipWith cast_arg arg_tys val_args
1240 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
1243 let dump_doc = vcat [ppr dc, ppr dc_univ_tyvars, ppr dc_ex_tyvars,
1244 ppr arg_tys, ppr dc_args, ppr _dc_univ_args,
1245 ppr ex_args, ppr val_args]
1247 ASSERT2( coreEqType _from_ty (mkTyConApp dc_tc _dc_univ_args), dump_doc )
1248 ASSERT2( all isTypeArg (ex_args ++ co_args), dump_doc )
1249 ASSERT2( equalLength val_args arg_tys, dump_doc )
1252 Just (dc, to_tc_arg_tys, ex_args ++ new_co_args ++ new_val_args)
1255 exprIsConApp_maybe id_unf expr
1258 analyse (App fun arg) args = analyse fun (arg:args)
1259 analyse fun@(Lam {}) args = beta fun [] args
1261 analyse (Var fun) args
1262 | Just con <- isDataConWorkId_maybe fun
1263 , count isValArg args == idArity fun
1264 , let (univ_ty_args, rest_args) = splitAtList (dataConUnivTyVars con) args
1265 = Just (con, stripTypeArgs univ_ty_args, rest_args)
1267 -- Look through dictionary functions; see Note [Unfolding DFuns]
1268 | DFunUnfolding dfun_nargs con ops <- unfolding
1269 , let sat = length args == dfun_nargs -- See Note [DFun arity check]
1270 in if sat then True else
1271 pprTrace "Unsaturated dfun" (ppr fun <+> int dfun_nargs $$ ppr args) False
1272 , let (dfun_tvs, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)
1273 subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args))
1274 = Just (con, substTys subst dfun_res_tys,
1275 [mkApps op args | op <- ops])
1277 -- Look through unfoldings, but only cheap ones, because
1278 -- we are effectively duplicating the unfolding
1279 | Just rhs <- expandUnfolding_maybe unfolding
1280 = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
1283 unfolding = id_unf fun
1285 analyse _ _ = Nothing
1288 beta (Lam v body) pairs (arg : args)
1290 = beta body ((v,arg):pairs) args
1292 beta (Lam {}) _ _ -- Un-saturated, or not a type lambda
1296 = analyse (substExpr (text "subst-expr-is-con-app") subst fun) args
1298 subst = mkOpenSubst (mkInScopeSet (exprFreeVars fun)) pairs
1299 -- doc = vcat [ppr fun, ppr expr, ppr pairs, ppr args]
1302 stripTypeArgs :: [CoreExpr] -> [Type]
1303 stripTypeArgs args = ASSERT2( all isTypeArg args, ppr args )
1304 [ty | Type ty <- args]
1307 Note [Unfolding DFuns]
1308 ~~~~~~~~~~~~~~~~~~~~~~
1311 df :: forall a b. (Eq a, Eq b) -> Eq (a,b)
1312 df a b d_a d_b = MkEqD (a,b) ($c1 a b d_a d_b)
1315 So to split it up we just need to apply the ops $c1, $c2 etc
1316 to the very same args as the dfun. It takes a little more work
1317 to compute the type arguments to the dictionary constructor.
1319 Note [DFun arity check]
1320 ~~~~~~~~~~~~~~~~~~~~~~~
1321 Here we check that the total number of supplied arguments (inclding
1322 type args) matches what the dfun is expecting. This may be *less*
1323 than the ordinary arity of the dfun: see Note [DFun unfoldings] in CoreSyn