X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=compiler%2FcoreSyn%2FCoreUnfold.lhs;h=258cd46cf26caf6e61fc54d3f3bd21fa992c1468;hb=d95ce839533391e7118257537044f01cbb1d6694;hp=b695c988c8874cdbcdd78483a7d77398a4701997;hpb=cac2aca1e1874e936f3ef15ca2a81a32c7863750;p=ghc-hetmet.git diff --git a/compiler/coreSyn/CoreUnfold.lhs b/compiler/coreSyn/CoreUnfold.lhs index b695c98..258cd46 100644 --- a/compiler/coreSyn/CoreUnfold.lhs +++ b/compiler/coreSyn/CoreUnfold.lhs @@ -18,38 +18,40 @@ find, unsurprisingly, a Core expression. 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 - ) where + callSiteInline, CallCtxt(..) -#include "HsVersions.h" + ) where import StaticFlags import DynFlags import CoreSyn import PprCore () -- Instances import OccurAnal +import CoreSubst ( emptySubst, substTy, extendIdSubst, extendTvSubst + , lookupIdSubst, substBndr, substBndrs, substRecBndrs ) 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 -import GHC.Exts ( Int# ) \end{code} @@ -60,19 +62,43 @@ import GHC.Exts ( Int# ) %************************************************************************ \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 @@ -82,14 +108,7 @@ 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} @@ -102,79 +121,31 @@ 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} -sizeExpr :: Int# -- Bomb out if it gets bigger than this +sizeExpr :: FastInt -- Bomb out if it gets bigger than this -> [Id] -- Arguments; we're interested in which of these -- get case'd -> CoreExpr @@ -183,22 +154,11 @@ sizeExpr :: Int# -- 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) @@ -234,7 +194,7 @@ sizeExpr bOMB_OUT_SIZE top_args expr case alts of - [alt] -> size_up_alt alt `addSize` SizeIs 0# (unitBag (v, 1)) 0# + [alt] -> size_up_alt alt `addSize` SizeIs (_ILIT(0)) (unitBag (v, 1)) (_ILIT(0)) -- We want to make wrapper-style evaluation look cheap, so that -- when we inline a wrapper it doesn't make call site (much) bigger -- Otherwise we get nasty phase ordering stuff: @@ -260,9 +220,9 @@ 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 - = SizeIs tot (unitBag (v, iBox (_ILIT 1 +# tot -# max)) `unionBags` max_disc) max_scrut + 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 -- The 1+ is a little discount for reduced allocation in the caller @@ -298,7 +258,7 @@ 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 @@ -308,7 +268,7 @@ 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; @@ -318,17 +278,17 @@ 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 0# (unitBag (v, opt_UF_FunAppDiscount)) 0# - fun_discount other = sizeZero + fun_discount v | v `elem` top_args = SizeIs (_ILIT(0)) (unitBag (v, opt_UF_FunAppDiscount)) (_ILIT(0)) + fun_discount _ = sizeZero ------------ -- These addSize things have to be here because @@ -357,20 +317,26 @@ 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 = SizeIs (_ILIT 0) emptyBag (_ILIT 0) -sizeOne = SizeIs (_ILIT 1) emptyBag (_ILIT 0) -sizeN n = SizeIs (iUnbox n) emptyBag (_ILIT 0) +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)) conSizeN dc n - | isUnboxedTupleCon dc = SizeIs (_ILIT 0) emptyBag (iUnbox n +# _ILIT 1) - | otherwise = SizeIs (_ILIT 1) emptyBag (iUnbox n +# _ILIT 1) + | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n +# _ILIT(1)) + | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n +# _ILIT(1)) -- Treat constructors as size 1; we are keen to expose them -- (and we charge separately for their args). We can't treat -- them as size zero, else we find that (iBox x) has size 1, @@ -382,6 +348,7 @@ 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) @@ -396,7 +363,8 @@ primOpSize op n_args -- and there's a good chance it'll get inlined back into C's RHS. Urgh! | otherwise = sizeOne -buildSize = SizeIs (-2#) emptyBag 4# +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) -- Indeed, we should add a result_discount becuause build is @@ -404,16 +372,19 @@ buildSize = SizeIs (-2#) emptyBag 4# -- build is saturated (it usually is). The "-2" discounts for the \c n, -- The "4" is rather arbitrary. -augmentSize = SizeIs (-2#) emptyBag 4# +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 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} @@ -454,20 +425,24 @@ 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} @@ -497,15 +472,40 @@ StrictAnal.addStrictnessInfoToTopId callSiteInline :: DynFlags -> Bool -- True <=> the Id can be inlined -> 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 - -> Bool -- True <=> continuation is interesting + -> CallCtxt -- True <=> continuation is interesting -> Maybe CoreExpr -- Unfolding, if any -callSiteInline dflags active_inline id arg_infos interesting_cont - = case idUnfolding id of { +data CallCtxt = BoringCtxt + + | 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 + = 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 @@ -514,17 +514,46 @@ callSiteInline dflags active_inline id arg_infos interesting_cont -- 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 - | not active_inline = False - | otherwise = is_cheap && consider_safe False + 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 -- caught by preInlineUnconditionally. In particular, @@ -533,71 +562,185 @@ callSiteInline dflags active_inline id arg_infos interesting_cont -- pre-inline will not have inlined it for fear of -- invalidating the occurrence info in the rhs. - consider_safe once + consider_safe -- consider_safe decides whether it's a good idea to -- inline something, given that there's no -- 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 - some_benefit = or arg_infos || really_interesting_cont || - (not is_top && ({- once || -} (n_vals_wanted > 0 && enough_args))) - -- [was (once && not in_lam)] - -- If it occurs more than once, there must be - -- something interesting about some argument, or the - -- result context, to make it worth inlining - -- - -- If a function has a nested defn we also record - -- some-benefit, on the grounds that we are often able - -- to eliminate the binding, and hence the allocation, - -- for the function altogether; this is good for join - -- points. But this only makes sense for *functions*; - -- inlining a constructor doesn't help allocation - -- unless the result is scrutinised. UNLESS the - -- constructor occurs just once, albeit possibly in - -- multiple case 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. - - enough_args = n_val_args >= n_vals_wanted - really_interesting_cont | n_val_args < n_vals_wanted = False -- Too few args - | n_val_args == n_vals_wanted = interesting_cont - | otherwise = True -- Extra args + enough_args = n_val_args >= n_vals_wanted + inline_enough_args = + not (dopt Opt_InlineIfEnoughArgs dflags) || enough_args + + + some_benefit = or arg_infos || really_interesting_cont + -- There must be something interesting + -- about some argument, or the result + -- context, to make it worth inlining + + really_interesting_cont + | n_val_args < n_vals_wanted = False -- Too few args + | n_val_args == n_vals_wanted = interesting_saturated_call + | otherwise = True -- Extra args -- really_interesting_cont tells if the result of the -- call is in an interesting context. + interesting_saturated_call + = case cont_info of + 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 really_interesting_cont + discount = computeDiscount n_vals_wanted arg_discounts + res_discount' arg_infos + res_discount' = case cont_info of + 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. + -- Otherwise we, rather arbitrarily, threshold it. Yuk. + -- But we want to aovid inlining large functions that return + -- constructors into contexts that are simply "interesting" 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 interesting_cont, - 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} -computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int -computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used +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. + + +Note [Nested functions] +~~~~~~~~~~~~~~~~~~~~~~~ +If a function has a nested defn we also record some-benefit, on the +grounds that we are often able to eliminate the binding, and hence the +allocation, for the function altogether; this is good for join points. +But this only makes sense for *functions*; inlining a constructor +doesn't help allocation unless the result is scrutinised. UNLESS the +constructor occurs just once, albeit possibly in multiple case +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 + as an arg of lazy fn, or rhs Stop + as scrutinee of a case Select + as arg of a strict fn ArgOf +AND + it is bound to a value +then we should not inline it (unless there is some other reason, +e.g. is is the sole occurrence). That is what is happening at +the use of 'lone_variable' in 'interesting_saturated_call'. + +Why? At least in the case-scrutinee situation, turning + let x = (a,b) in case x of y -> ... +into + let x = (a,b) in case (a,b) of y -> ... +and thence to + let x = (a,b) in let y = (a,b) in ... +is bad if the binding for x will remain. + +Another example: I discovered that strings +were getting inlined straight back into applications of 'error' +because the latter is strict. + s = "foo" + f = \x -> ...(error s)... + +Fundamentally such contexts should not encourage inlining because the +context can ``see'' the unfolding of the variable (e.g. case or a +RULE) so there's no gain. If the thing is bound to a value. + +However, watch out: + + * Consider this: + foo = _inline_ (\n. [n]) + bar = _inline_ (foo 20) + baz = \n. case bar of { (m:_) -> m + n } + Here we really want to inline 'bar' so that we can inline 'foo' + and the whole thing unravels as it should obviously do. This is + important: in the NDP project, 'bar' generates a closure data + structure rather than a list. + + * Even a type application or coercion isn't a lone variable. + Consider + case $fMonadST @ RealWorld of { :DMonad a b c -> c } + We had better inline that sucker! The case won't see through it. + + For now, I'm treating treating a variable applied to types + in a *lazy* context "lone". The motivating example was + f = /\a. \x. BIG + g = /\a. \y. h (f a) + There's no advantage in inlining f here, and perhaps + a significant disadvantage. Hence some_val_args in the Stop case + +\begin{code} +computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Int +computeDiscount n_vals_wanted arg_discounts result_discount arg_infos -- We multiple the raw discounts (args_discount and result_discount) -- ty opt_UnfoldingKeenessFactor because the former have to do with -- *size* whereas the discounts imply that there's some extra @@ -619,8 +762,76 @@ computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used mk_arg_discount discount is_evald | is_evald = discount | otherwise = 0 - - -- Don't give a result discount unless there are enough args - result_discount | result_used = res_discount -- Over-applied, or case scrut - | otherwise = 0 \end{code} + +%************************************************************************ +%* * + The Very Simple Optimiser +%* * +%************************************************************************ + + +\begin{code} +simpleOptExpr :: CoreExpr -> CoreExpr +-- Return an occur-analysed and slightly optimised expression +-- The optimisation is very straightforward: just +-- inline non-recursive bindings that are used only once, +-- or wheere the RHS is trivial + +simpleOptExpr expr + = go emptySubst (occurAnalyseExpr expr) + where + go subst (Var v) = lookupIdSubst subst v + go subst (App e1 e2) = App (go subst e1) (go subst e2) + go subst (Type ty) = Type (substTy subst ty) + go _ (Lit lit) = Lit lit + go subst (Note note e) = Note note (go subst e) + go subst (Cast e co) = Cast (go subst e) (substTy subst co) + go subst (Let bind body) = go_bind subst bind body + go subst (Lam bndr body) = Lam bndr' (go subst' body) + where + (subst', bndr') = substBndr subst bndr + + go subst (Case e b ty as) = Case (go subst e) b' + (substTy subst ty) + (map (go_alt subst') as) + where + (subst', b') = substBndr subst b + + + ---------------------- + go_alt subst (con, bndrs, rhs) = (con, bndrs', go subst' rhs) + where + (subst', bndrs') = substBndrs subst bndrs + + ---------------------- + go_bind subst (Rec prs) body = Let (Rec (bndrs' `zip` rhss')) + (go subst' body) + where + (bndrs, rhss) = unzip prs + (subst', bndrs') = substRecBndrs subst bndrs + rhss' = map (go subst') rhss + + go_bind subst (NonRec b r) body = go_nonrec subst b (go subst r) body + + ---------------------- + go_nonrec subst b (Type ty') body + | isTyVar b = go (extendTvSubst subst b ty') body + -- let a::* = TYPE ty in + go_nonrec subst b r' body + | isId b -- let x = e in + , exprIsTrivial r' || safe_to_inline (idOccInfo b) + = go (extendIdSubst subst b r') body + go_nonrec subst b r' body + = Let (NonRec b' r') (go subst' body) + where + (subst', b') = substBndr subst b + + ---------------------- + -- Unconditionally safe to inline + safe_to_inline :: OccInfo -> Bool + safe_to_inline IAmDead = True + safe_to_inline (OneOcc in_lam one_br _) = not in_lam && one_br + safe_to_inline (IAmALoopBreaker {}) = False + safe_to_inline NoOccInfo = False +\end{code} \ No newline at end of file