X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreUnfold.lhs;h=4cbe04a27178b360ba20afecc48ea3d83969c9c2;hb=4f51ac1246f9a9b2bd172e2d6957d95942d12d23;hp=d8e0cb054de73d97650316063bba8fa0e3c46940;hpb=d8c0a66c1e5d357eae882963ee6834f485868d22;p=ghc-hetmet.git diff --git a/compiler/coreSyn/CoreUnfold.lhs b/compiler/coreSyn/CoreUnfold.lhs index d8e0cb0..4cbe04a 100644 --- a/compiler/coreSyn/CoreUnfold.lhs +++ b/compiler/coreSyn/CoreUnfold.lhs @@ -15,46 +15,40 @@ literal''). In the corner of a @CoreUnfolding@ unfolding, you will find, unsurprisingly, a Core expression. \begin{code} -{-# OPTIONS -w #-} --- The above warning supression flag is a temporary kludge. --- While working on this module you are encouraged to remove it and fix --- any warnings in the module. See --- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings --- for details - module CoreUnfold ( Unfolding, UnfoldingGuidance, -- Abstract types - noUnfolding, mkTopUnfolding, mkUnfolding, mkCompulsoryUnfolding, seqUnfolding, - evaldUnfolding, mkOtherCon, otherCons, - unfoldingTemplate, maybeUnfoldingTemplate, - isEvaldUnfolding, isValueUnfolding, isCheapUnfolding, isCompulsoryUnfolding, - hasUnfolding, hasSomeUnfolding, neverUnfold, + noUnfolding, mkImplicitUnfolding, + mkTopUnfolding, mkUnfolding, + mkInlineRule, mkWwInlineRule, + mkCompulsoryUnfolding, couldBeSmallEnoughToInline, certainlyWillInline, smallEnoughToInline, - callSiteInline, CallContInfo(..) + callSiteInline, CallCtxt(..) ) where -#include "HsVersions.h" - import StaticFlags import DynFlags import CoreSyn import PprCore () -- Instances import OccurAnal +import CoreSubst import CoreUtils import Id import DataCon import Literal import PrimOp import IdInfo -import Type +import BasicTypes ( Arity ) +import Type hiding( substTy, extendTvSubst ) +import Maybes import PrelNames import Bag import FastTypes +import FastString import Outputable \end{code} @@ -67,19 +61,43 @@ import Outputable %************************************************************************ \begin{code} +mkTopUnfolding :: CoreExpr -> Unfolding mkTopUnfolding expr = mkUnfolding True {- Top level -} expr -mkUnfolding top_lvl expr - = CoreUnfolding (occurAnalyseExpr expr) - top_lvl - +mkImplicitUnfolding :: CoreExpr -> Unfolding +-- For implicit Ids, do a tiny bit of optimising first +mkImplicitUnfolding expr + = CoreUnfolding (simpleOptExpr expr) + True (exprIsHNF expr) - -- Already evaluated - (exprIsCheap expr) - -- OK to inline inside a lambda - (calcUnfoldingGuidance opt_UF_CreationThreshold expr) + +mkInlineRule :: CoreExpr -> Arity -> Unfolding +mkInlineRule expr arity + = InlineRule { uf_tmpl = simpleOptExpr expr, + uf_is_top = True, -- Conservative; this gets set more + -- accuately by the simplifier (slight hack) + -- in SimplEnv.substUnfolding + uf_arity = arity, + uf_is_value = exprIsHNF expr, + uf_worker = Nothing } + +mkWwInlineRule :: CoreExpr -> Arity -> Id -> Unfolding +mkWwInlineRule expr arity wkr + = InlineRule { uf_tmpl = simpleOptExpr expr, + uf_is_top = True, -- Conservative; see mkInlineRule + uf_arity = arity, + uf_is_value = exprIsHNF expr, + uf_worker = Just wkr } + +mkUnfolding :: Bool -> CoreExpr -> Unfolding +mkUnfolding top_lvl expr + = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr, + uf_is_top = top_lvl, + uf_is_value = exprIsHNF expr, + uf_is_cheap = exprIsCheap expr, + uf_guidance = calcUnfoldingGuidance opt_UF_CreationThreshold expr } -- Sometimes during simplification, there's a large let-bound thing -- which has been substituted, and so is now dead; so 'expr' contains -- two copies of the thing while the occurrence-analysed expression doesn't @@ -89,14 +107,7 @@ mkUnfolding top_lvl expr -- This can occasionally mean that the guidance is very pessimistic; -- it gets fixed up next round -instance Outputable Unfolding where - ppr NoUnfolding = ptext SLIT("No unfolding") - ppr (OtherCon cs) = ptext SLIT("OtherCon") <+> ppr cs - ppr (CompulsoryUnfolding e) = ptext SLIT("Compulsory") <+> ppr e - ppr (CoreUnfolding e top hnf cheap g) - = ptext SLIT("Unf") <+> sep [ppr top <+> ppr hnf <+> ppr cheap <+> ppr g, - ppr e] - +mkCompulsoryUnfolding :: CoreExpr -> Unfolding mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded = CompulsoryUnfolding (occurAnalyseExpr expr) \end{code} @@ -109,75 +120,27 @@ mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded %************************************************************************ \begin{code} -instance Outputable UnfoldingGuidance where - ppr UnfoldNever = ptext SLIT("NEVER") - ppr (UnfoldIfGoodArgs v cs size discount) - = hsep [ ptext SLIT("IF_ARGS"), int v, - brackets (hsep (map int cs)), - int size, - int discount ] -\end{code} - - -\begin{code} calcUnfoldingGuidance :: Int -- bomb out if size gets bigger than this -> CoreExpr -- expression to look at -> UnfoldingGuidance calcUnfoldingGuidance bOMB_OUT_SIZE expr - = case collect_val_bndrs expr of { (inline, val_binders, body) -> + = case collectBinders expr of { (binders, body) -> let + val_binders = filter isId binders n_val_binders = length val_binders - - max_inline_size = n_val_binders+2 - -- The idea is that if there is an INLINE pragma (inline is True) - -- and there's a big body, we give a size of n_val_binders+2. This - -- This is just enough to fail the no-size-increase test in callSiteInline, - -- so that INLINE things don't get inlined into entirely boring contexts, - -- but no more. - in case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_binders body) of - - TooBig - | not inline -> UnfoldNever - -- A big function with an INLINE pragma must - -- have an UnfoldIfGoodArgs guidance - | otherwise -> UnfoldIfGoodArgs n_val_binders - (map (const 0) val_binders) - max_inline_size 0 - + TooBig -> UnfoldNever SizeIs size cased_args scrut_discount - -> UnfoldIfGoodArgs - n_val_binders - (map discount_for val_binders) - final_size - (iBox scrut_discount) + -> UnfoldIfGoodArgs { ug_arity = n_val_binders + , ug_args = map discount_for val_binders + , ug_size = iBox size + , ug_res = iBox scrut_discount } where - boxed_size = iBox size - - final_size | inline = boxed_size `min` max_inline_size - | otherwise = boxed_size - - -- Sometimes an INLINE thing is smaller than n_val_binders+2. - -- A particular case in point is a constructor, which has size 1. - -- We want to inline this regardless, hence the `min` - discount_for b = foldlBag (\acc (b',n) -> if b==b' then acc+n else acc) 0 cased_args } - where - collect_val_bndrs e = go False [] e - -- We need to be a bit careful about how we collect the - -- value binders. In ptic, if we see - -- __inline_me (\x y -> e) - -- We want to say "2 value binders". Why? So that - -- we take account of information given for the arguments - - go inline rev_vbs (Note InlineMe e) = go True rev_vbs e - go inline rev_vbs (Lam b e) | isId b = go inline (b:rev_vbs) e - | otherwise = go inline rev_vbs e - go inline rev_vbs e = (inline, reverse rev_vbs, e) \end{code} \begin{code} @@ -190,22 +153,11 @@ sizeExpr :: FastInt -- Bomb out if it gets bigger than this sizeExpr bOMB_OUT_SIZE top_args expr = size_up expr where - size_up (Type t) = sizeZero -- Types cost nothing - size_up (Var v) = sizeOne - - size_up (Note InlineMe body) = sizeOne -- Inline notes make it look very small - -- This can be important. If you have an instance decl like this: - -- instance Foo a => Foo [a] where - -- {-# INLINE op1, op2 #-} - -- op1 = ... - -- op2 = ... - -- then we'll get a dfun which is a pair of two INLINE lambdas - - size_up (Note _ body) = size_up body -- Other notes cost nothing - - size_up (Cast e _) = size_up e - - size_up (App fun (Type t)) = size_up fun + size_up (Type _) = sizeZero -- Types cost nothing + size_up (Var _) = sizeOne + size_up (Note _ body) = size_up body -- Notes cost nothing + size_up (Cast e _) = size_up e + size_up (App fun (Type _)) = size_up fun size_up (App fun arg) = size_up_app fun [arg] size_up (Lit lit) = sizeN (litSize lit) @@ -267,8 +219,8 @@ sizeExpr bOMB_OUT_SIZE top_args expr -- alts_size tries to compute a good discount for -- the case when we are scrutinising an argument variable - alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives - (SizeIs max max_disc max_scrut) -- Size of biggest alternative + alts_size (SizeIs tot _tot_disc _tot_scrut) -- Size of all alternatives + (SizeIs max max_disc max_scrut) -- Size of biggest alternative = SizeIs tot (unitBag (v, iBox (_ILIT(1) +# tot -# max)) `unionBags` max_disc) max_scrut -- If the variable is known, we produce a discount that -- will take us back to 'max', the size of rh largest alternative @@ -305,7 +257,7 @@ sizeExpr bOMB_OUT_SIZE top_args expr = case globalIdDetails fun of DataConWorkId dc -> conSizeN dc (valArgCount args) - FCallId fc -> sizeN opt_UF_DearOp + FCallId _ -> sizeN opt_UF_DearOp PrimOpId op -> primOpSize op (valArgCount args) -- foldr addSize (primOpSize op) (map arg_discount args) -- At one time I tried giving an arg-discount if a primop @@ -315,7 +267,7 @@ sizeExpr bOMB_OUT_SIZE top_args expr -- if we know nothing about it. And just having it in a primop -- doesn't help at all if we don't know something more. - other -> fun_discount fun `addSizeN` + _ -> fun_discount fun `addSizeN` (1 + length (filter (not . exprIsTrivial) args)) -- The 1+ is for the function itself -- Add 1 for each non-trivial arg; @@ -325,17 +277,17 @@ sizeExpr bOMB_OUT_SIZE top_args expr -- We should really only count for non-prim-typed args in the -- general case, but that seems too much like hard work - size_up_fun other args = size_up other + size_up_fun other _ = size_up other ------------ - size_up_alt (con, bndrs, rhs) = size_up rhs + size_up_alt (_con, _bndrs, rhs) = size_up rhs -- Don't charge for args, so that wrappers look cheap -- (See comments about wrappers with Case) ------------ -- We want to record if we're case'ing, or applying, an argument fun_discount v | v `elem` top_args = SizeIs (_ILIT(0)) (unitBag (v, opt_UF_FunAppDiscount)) (_ILIT(0)) - fun_discount other = sizeZero + fun_discount _ = sizeZero ------------ -- These addSize things have to be here because @@ -364,14 +316,20 @@ data ExprSize = TooBig -- tup = (a_1, ..., a_99) -- x = case tup of ... -- +mkSizeIs :: FastInt -> FastInt -> Bag (Id, Int) -> FastInt -> ExprSize mkSizeIs max n xs d | (n -# d) ># max = TooBig | otherwise = SizeIs n xs d +maxSize :: ExprSize -> ExprSize -> ExprSize maxSize TooBig _ = TooBig maxSize _ TooBig = TooBig maxSize s1@(SizeIs n1 _ _) s2@(SizeIs n2 _ _) | n1 ># n2 = s1 | otherwise = s2 +sizeZero, sizeOne :: ExprSize +sizeN :: Int -> ExprSize +conSizeN :: DataCon ->Int -> ExprSize + sizeZero = SizeIs (_ILIT(0)) emptyBag (_ILIT(0)) sizeOne = SizeIs (_ILIT(1)) emptyBag (_ILIT(0)) sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT(0)) @@ -389,6 +347,7 @@ conSizeN dc n -- f x y z = case op# x y z of { s -> (# s, () #) } -- and f wasn't getting inlined +primOpSize :: PrimOp -> Int -> ExprSize primOpSize op n_args | not (primOpIsDupable op) = sizeN opt_UF_DearOp | not (primOpOutOfLine op) = sizeN (2 - n_args) @@ -403,6 +362,7 @@ primOpSize op n_args -- and there's a good chance it'll get inlined back into C's RHS. Urgh! | otherwise = sizeOne +buildSize :: ExprSize buildSize = SizeIs (_ILIT(-2)) emptyBag (_ILIT(4)) -- We really want to inline applications of build -- build t (\cn -> e) should cost only the cost of e (because build will be inlined later) @@ -411,16 +371,19 @@ buildSize = SizeIs (_ILIT(-2)) emptyBag (_ILIT(4)) -- build is saturated (it usually is). The "-2" discounts for the \c n, -- The "4" is rather arbitrary. +augmentSize :: ExprSize augmentSize = SizeIs (_ILIT(-2)) emptyBag (_ILIT(4)) -- Ditto (augment t (\cn -> e) ys) should cost only the cost of -- e plus ys. The -2 accounts for the \cn - -nukeScrutDiscount (SizeIs n vs d) = SizeIs n vs (_ILIT(0)) -nukeScrutDiscount TooBig = TooBig + +nukeScrutDiscount :: ExprSize -> ExprSize +nukeScrutDiscount (SizeIs n vs _) = SizeIs n vs (_ILIT(0)) +nukeScrutDiscount TooBig = TooBig -- When we return a lambda, give a discount if it's used (applied) -lamScrutDiscount (SizeIs n vs d) = case opt_UF_FunAppDiscount of { d -> SizeIs n vs (iUnbox d) } -lamScrutDiscount TooBig = TooBig +lamScrutDiscount :: ExprSize -> ExprSize +lamScrutDiscount (SizeIs n vs _) = case opt_UF_FunAppDiscount of { d -> SizeIs n vs (iUnbox d) } +lamScrutDiscount TooBig = TooBig \end{code} @@ -461,20 +424,24 @@ Just the same as smallEnoughToInline, except that it has no actual arguments. \begin{code} couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool couldBeSmallEnoughToInline threshold rhs = case calcUnfoldingGuidance threshold rhs of - UnfoldNever -> False - other -> True + UnfoldNever -> False + _ -> True certainlyWillInline :: Unfolding -> Bool -- Sees if the unfolding is pretty certain to inline -certainlyWillInline (CoreUnfolding _ _ _ is_cheap (UnfoldIfGoodArgs n_vals _ size _)) +certainlyWillInline (CompulsoryUnfolding {}) = True +certainlyWillInline (InlineRule {}) = True +certainlyWillInline (CoreUnfolding + { uf_is_cheap = is_cheap + , uf_guidance = UnfoldIfGoodArgs {ug_arity = n_vals, ug_size = size}}) = is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold -certainlyWillInline other +certainlyWillInline _ = False smallEnoughToInline :: Unfolding -> Bool -smallEnoughToInline (CoreUnfolding _ _ _ _ (UnfoldIfGoodArgs _ _ size _)) +smallEnoughToInline (CoreUnfolding {uf_guidance = UnfoldIfGoodArgs {ug_size = size}}) = size <= opt_UF_UseThreshold -smallEnoughToInline other +smallEnoughToInline _ = False \end{code} @@ -496,7 +463,7 @@ If the thing is in WHNF, there's no danger of duplicating work, so we can inline if it occurs once, or is small NOTE: we don't want to inline top-level functions that always diverge. -It just makes the code bigger. It turns out that the convenient way to prevent +It just makes the code bigger. Tt turns out that the convenient way to prevent them inlining is to give them a NOINLINE pragma, which we do in StrictAnal.addStrictnessInfoToTopId @@ -506,24 +473,38 @@ callSiteInline :: DynFlags -> Id -- The Id -> Bool -- True if there are are no arguments at all (incl type args) -> [Bool] -- One for each value arg; True if it is interesting - -> CallContInfo -- True <=> continuation is interesting + -> CallCtxt -- True <=> continuation is interesting -> Maybe CoreExpr -- Unfolding, if any -data CallContInfo = BoringCont - | InterestingCont -- Somewhat interesting - | CaseCont -- Very interesting; the argument of a case - -- that decomposes its scrutinee +data CallCtxt = BoringCtxt -instance Outputable CallContInfo where - ppr BoringCont = ptext SLIT("BoringCont") - ppr InterestingCont = ptext SLIT("InterestingCont") - ppr CaseCont = ptext SLIT("CaseCont") + | ArgCtxt Bool -- We're somewhere in the RHS of function with rules + -- => be keener to inline + Int -- We *are* the argument of a function with this arg discount + -- => be keener to inline + -- INVARIANT: ArgCtxt False 0 ==> BoringCtxt + + | ValAppCtxt -- We're applied to at least one value arg + -- This arises when we have ((f x |> co) y) + -- Then the (f x) has argument 'x' but in a ValAppCtxt + + | CaseCtxt -- We're the scrutinee of a case + -- that decomposes its scrutinee + +instance Outputable CallCtxt where + ppr BoringCtxt = ptext (sLit "BoringCtxt") + ppr (ArgCtxt _ _) = ptext (sLit "ArgCtxt") + ppr CaseCtxt = ptext (sLit "CaseCtxt") + ppr ValAppCtxt = ptext (sLit "ValAppCtxt") callSiteInline dflags active_inline id lone_variable arg_infos cont_info - = case idUnfolding id of { + = let + n_val_args = length arg_infos + in + case idUnfolding id of { NoUnfolding -> Nothing ; - OtherCon cs -> Nothing ; + OtherCon _ -> Nothing ; CompulsoryUnfolding unf_template -> Just unf_template ; -- CompulsoryUnfolding => there is no top-level binding @@ -532,14 +513,45 @@ callSiteInline dflags active_inline id lone_variable arg_infos cont_info -- compulsory unfoldings (see MkId.lhs). -- We don't allow them to be inactive - CoreUnfolding unf_template is_top is_value is_cheap guidance -> + InlineRule { uf_tmpl = unf_template, uf_arity = arity, uf_is_top = is_top + , uf_is_value = is_value, uf_worker = mb_worker } + -> let yes_or_no | not active_inline = False + | n_val_args < arity = yes_unsat -- Not enough value args + | n_val_args == arity = yes_exact -- Exactly saturated + | otherwise = True -- Over-saturated + result | yes_or_no = Just unf_template + | otherwise = Nothing + + -- See Note [Inlining an InlineRule] + is_wrapper = isJust mb_worker + yes_unsat | is_wrapper = or arg_infos + | otherwise = False + + yes_exact = or arg_infos || interesting_saturated_call + interesting_saturated_call + = case cont_info of + BoringCtxt -> not is_top -- Note [Nested functions] + CaseCtxt -> not lone_variable || not is_value -- Note [Lone variables] + ArgCtxt {} -> arity > 0 -- Note [Inlining in ArgCtxt] + ValAppCtxt -> True -- Note [Cast then apply] + in + if dopt Opt_D_dump_inlinings dflags then + pprTrace ("Considering InlineRule for: " ++ showSDoc (ppr id)) + (vcat [text "active:" <+> ppr active_inline, + text "arg infos" <+> ppr arg_infos, + text "interesting call" <+> ppr interesting_saturated_call, + text "is value:" <+> ppr is_value, + text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"]) + result + else result ; + + CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top, uf_is_value = is_value, + uf_is_cheap = is_cheap, uf_guidance = guidance } -> let result | yes_or_no = Just unf_template | otherwise = Nothing - n_val_args = length arg_infos - yes_or_no = active_inline && is_cheap && consider_safe -- We consider even the once-in-one-branch -- occurrences, because they won't all have been @@ -555,17 +567,21 @@ callSiteInline dflags active_inline id lone_variable arg_infos cont_info -- work-duplication issue (the caller checks that). = case guidance of UnfoldNever -> False - UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount + UnfoldIfGoodArgs { ug_arity = n_vals_wanted, ug_args = arg_discounts + , ug_res = res_discount, ug_size = size } | enough_args && size <= (n_vals_wanted + 1) -- Inline unconditionally if there no size increase -- Size of call is n_vals_wanted (+1 for the function) -> True | otherwise - -> some_benefit && small_enough + -> some_benefit && small_enough && inline_enough_args + where enough_args = n_val_args >= n_vals_wanted - -- Note [Enough args] + inline_enough_args = + not (dopt Opt_InlineIfEnoughArgs dflags) || enough_args + some_benefit = or arg_infos || really_interesting_cont -- There must be something interesting @@ -581,17 +597,18 @@ callSiteInline dflags active_inline id lone_variable arg_infos cont_info interesting_saturated_call = case cont_info of - BoringCont -> not is_top && n_vals_wanted > 0 -- Note [Nested functions] - CaseCont -> not lone_variable || not is_value -- Note [Lone variables] - InterestingCont -> True -- Something else interesting about continuation + BoringCtxt -> not is_top && n_vals_wanted > 0 -- Note [Nested functions] + CaseCtxt -> not lone_variable || not is_value -- Note [Lone variables] + ArgCtxt {} -> n_vals_wanted > 0 -- Note [Inlining in ArgCtxt] + ValAppCtxt -> True -- Note [Cast then apply] small_enough = (size - discount) <= opt_UF_UseThreshold discount = computeDiscount n_vals_wanted arg_discounts res_discount' arg_infos res_discount' = case cont_info of - BoringCont -> 0 - CaseCont -> res_discount - InterestingCont -> 4 `min` res_discount + BoringCtxt -> 0 + CaseCtxt -> res_discount + _other -> 4 `min` res_discount -- res_discount can be very large when a function returns -- construtors; but we only want to invoke that large discount -- when there's a case continuation. @@ -601,30 +618,34 @@ callSiteInline dflags active_inline id lone_variable arg_infos cont_info in if dopt Opt_D_dump_inlinings dflags then - pprTrace "Considering inlining" - (ppr id <+> vcat [text "active:" <+> ppr active_inline, - text "arg infos" <+> ppr arg_infos, - text "interesting continuation" <+> ppr cont_info <+> - ppr n_val_args, - text "is value:" <+> ppr is_value, - text "is cheap:" <+> ppr is_cheap, - text "guidance" <+> ppr guidance, - text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"]) + pprTrace ("Considering inlining: " ++ showSDoc (ppr id)) + (vcat [text "active:" <+> ppr active_inline, + text "arg infos" <+> ppr arg_infos, + text "interesting continuation" <+> ppr cont_info, + text "is value:" <+> ppr is_value, + text "is cheap:" <+> ppr is_cheap, + text "guidance" <+> ppr guidance, + text "ANSWER =" <+> if yes_or_no then text "YES" else text "NO"]) result else result } \end{code} -Note [Enough args] -~~~~~~~~~~~~~~~~~~ -At one stage we considered only inlining a function that has enough -arguments to saturate its arity. But we can lose from this. For -example (f . g) might not be a saturated application of (.), but -nevertheless f and g might usefully optimise with each other if we -inlined (.) and f and g. +Note [Inlining an InlineRule] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +An InlineRules is used for + (a) pogrammer INLINE pragmas + (b) inlinings from worker/wrapper + +For (a) the RHS may be large, and our contract is that we *only* inline +when the function is applied to all the arguments on the LHS of the +source-code defn. (The uf_arity in the rule.) + +However for worker/wrapper it may be worth inlining even if the +arity is not satisfied (as we do in the CoreUnfolding case) so we don't +require saturation. -Current story (Jan08): inline even if not saturated. Note [Nested functions] ~~~~~~~~~~~~~~~~~~~~~~~ @@ -638,8 +659,31 @@ branches. Then inlining it doesn't increase allocation, but it does increase the chance that the constructor won't be allocated at all in the branches that don't use it. +Note [Cast then apply] +~~~~~~~~~~~~~~~~~~~~~~ +Consider + myIndex = __inline_me ( (/\a. ) |> co ) + co :: (forall a. a -> a) ~ (forall a. T a) + ... /\a.\x. case ((myIndex a) |> sym co) x of { ... } ... + +We need to inline myIndex to unravel this; but the actual call (myIndex a) has +no value arguments. The ValAppCtxt gives it enough incentive to inline. + +Note [Inlining in ArgCtxt] +~~~~~~~~~~~~~~~~~~~~~~~~~~ +The condition (n_vals_wanted > 0) here is very important, because otherwise +we end up inlining top-level stuff into useless places; eg + x = I# 3# + f = \y. g x +This can make a very big difference: it adds 16% to nofib 'integer' allocs, +and 20% to 'power'. + +At one stage I replaced this condition by 'True' (leading to the above +slow-down). The motivation was test eyeball/inline1.hs; but that seems +to work ok now. + Note [Lone variables] -~~~~~~~~~~~~~~~~~~~~~ +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The "lone-variable" case is important. I spent ages messing about with unsatisfactory varaints, but this is nice. The idea is that if a variable appears all alone @@ -718,3 +762,4 @@ computeDiscount n_vals_wanted arg_discounts result_discount arg_infos mk_arg_discount discount is_evald | is_evald = discount | otherwise = 0 \end{code} +