{- (c) The University of Glasgow 2006 (c) The AQUA Project, Glasgow University, 1994-1998 Core-syntax unfoldings Unfoldings (which can travel across module boundaries) are in Core syntax (namely @CoreExpr@s). The type @Unfolding@ sits ``above'' simply-Core-expressions unfoldings, capturing ``higher-level'' things we know about a binding, usually things that the simplifier found out (e.g., ``it's a literal''). In the corner of a @CoreUnfolding@ unfolding, you will find, unsurprisingly, a Core expression. -} {-# LANGUAGE BangPatterns #-} module GHC.Core.Unfold ( Unfolding, UnfoldingGuidance, -- Abstract types UnfoldingOpts (..), defaultUnfoldingOpts, updateCreationThreshold, updateUseThreshold, updateFunAppDiscount, updateDictDiscount, updateVeryAggressive, updateCaseScaling, updateCaseThreshold, updateReportPrefix, ArgSummary(..), couldBeSmallEnoughToInline, inlineBoringOk, smallEnoughToInline, callSiteInline, CallCtxt(..), calcUnfoldingGuidance ) where import GHC.Prelude import GHC.Driver.Flags import GHC.Core import GHC.Core.Utils import GHC.Types.Id import GHC.Core.DataCon import GHC.Types.Literal import GHC.Builtin.PrimOps import GHC.Types.Id.Info import GHC.Types.RepType ( isZeroBitTy ) import GHC.Types.Basic ( Arity, RecFlag(..) ) import GHC.Core.Type import GHC.Builtin.Names import GHC.Data.Bag import GHC.Utils.Logger import GHC.Utils.Misc import GHC.Utils.Outputable import GHC.Types.ForeignCall import GHC.Types.Name import GHC.Types.Tickish import qualified Data.ByteString as BS import Data.List (isPrefixOf) -- | Unfolding options data UnfoldingOpts = UnfoldingOpts { UnfoldingOpts -> Int unfoldingCreationThreshold :: !Int -- ^ Threshold above which unfoldings are not *created* , UnfoldingOpts -> Int unfoldingUseThreshold :: !Int -- ^ Threshold above which unfoldings are not *inlined* , UnfoldingOpts -> Int unfoldingFunAppDiscount :: !Int -- ^ Discount for lambdas that are used (applied) , UnfoldingOpts -> Int unfoldingDictDiscount :: !Int -- ^ Discount for dictionaries , UnfoldingOpts -> Bool unfoldingVeryAggressive :: !Bool -- ^ Force inlining in many more cases , UnfoldingOpts -> Int unfoldingCaseThreshold :: !Int -- ^ Don't consider depth up to x , UnfoldingOpts -> Int unfoldingCaseScaling :: !Int -- ^ Penalize depth with 1/x , UnfoldingOpts -> Maybe String unfoldingReportPrefix :: !(Maybe String) -- ^ Only report inlining decisions for names with this prefix } defaultUnfoldingOpts :: UnfoldingOpts defaultUnfoldingOpts :: UnfoldingOpts defaultUnfoldingOpts = UnfoldingOpts { unfoldingCreationThreshold :: Int unfoldingCreationThreshold = Int 750 -- The unfoldingCreationThreshold threshold must be reasonably high -- to take account of possible discounts. -- E.g. 450 is not enough in 'fulsom' for Interval.sqr to -- inline into Csg.calc (The unfolding for sqr never makes it -- into the interface file.) , unfoldingUseThreshold :: Int unfoldingUseThreshold = Int 90 -- Last adjusted upwards in #18282, when I reduced -- the result discount for constructors. , unfoldingFunAppDiscount :: Int unfoldingFunAppDiscount = Int 60 -- Be fairly keen to inline a function if that means -- we'll be able to pick the right method from a dictionary , unfoldingDictDiscount :: Int unfoldingDictDiscount = Int 30 -- Be fairly keen to inline a function if that means -- we'll be able to pick the right method from a dictionary , unfoldingVeryAggressive :: Bool unfoldingVeryAggressive = Bool False -- Only apply scaling once we are deeper than threshold cases -- in an RHS. , unfoldingCaseThreshold :: Int unfoldingCaseThreshold = Int 2 -- Penalize depth with (size*depth)/scaling , unfoldingCaseScaling :: Int unfoldingCaseScaling = Int 30 -- Don't filter inlining decision reports , unfoldingReportPrefix :: Maybe String unfoldingReportPrefix = Maybe String forall a. Maybe a Nothing } -- Helpers for "GHC.Driver.Session" updateCreationThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateCreationThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateCreationThreshold Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingCreationThreshold = n } updateUseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateUseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateUseThreshold Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingUseThreshold = n } updateFunAppDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts updateFunAppDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts updateFunAppDiscount Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingFunAppDiscount = n } updateDictDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts updateDictDiscount :: Int -> UnfoldingOpts -> UnfoldingOpts updateDictDiscount Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingDictDiscount = n } updateVeryAggressive :: Bool -> UnfoldingOpts -> UnfoldingOpts updateVeryAggressive :: Bool -> UnfoldingOpts -> UnfoldingOpts updateVeryAggressive Bool n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingVeryAggressive = n } updateCaseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateCaseThreshold :: Int -> UnfoldingOpts -> UnfoldingOpts updateCaseThreshold Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingCaseThreshold = n } updateCaseScaling :: Int -> UnfoldingOpts -> UnfoldingOpts updateCaseScaling :: Int -> UnfoldingOpts -> UnfoldingOpts updateCaseScaling Int n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingCaseScaling = n } updateReportPrefix :: Maybe String -> UnfoldingOpts -> UnfoldingOpts updateReportPrefix :: Maybe String -> UnfoldingOpts -> UnfoldingOpts updateReportPrefix Maybe String n UnfoldingOpts opts = UnfoldingOpts opts { unfoldingReportPrefix = n } {- Note [Occurrence analysis of unfoldings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We do occurrence-analysis of unfoldings once and for all, when the unfolding is built, rather than each time we inline them. But given this decision it's vital that we do *always* do it. Consider this unfolding \x -> letrec { f = ...g...; g* = f } in body where g* is (for some strange reason) the loop breaker. If we don't occ-anal it when reading it in, we won't mark g as a loop breaker, and we may inline g entirely in body, dropping its binding, and leaving the occurrence in f out of scope. This happened in #8892, where the unfolding in question was a DFun unfolding. But more generally, the simplifier is designed on the basis that it is looking at occurrence-analysed expressions, so better ensure that they actually are. Note [Calculate unfolding guidance on the non-occ-anal'd expression] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Notice that we give the non-occur-analysed expression to calcUnfoldingGuidance. In some ways it'd be better to occur-analyse first; for example, 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. Nevertheless, we *don't* and *must not* occ-analyse before computing the size because a) The size computation bales out after a while, whereas occurrence analysis does not. b) Residency increases sharply if you occ-anal first. I'm not 100% sure why, but it's a large effect. Compiling Cabal went from residency of 534M to over 800M with this one change. This can occasionally mean that the guidance is very pessimistic; it gets fixed up next round. And it should be rare, because large let-bound things that are dead are usually caught by preInlineUnconditionally ************************************************************************ * * \subsection{The UnfoldingGuidance type} * * ************************************************************************ -} inlineBoringOk :: CoreExpr -> Bool -- See Note [INLINE for small functions] -- True => the result of inlining the expression is -- no bigger than the expression itself -- eg (\x y -> f y x) -- This is a quick and dirty version. It doesn't attempt -- to deal with (\x y z -> x (y z)) -- The really important one is (x `cast` c) inlineBoringOk :: CoreExpr -> Bool inlineBoringOk CoreExpr e = Int -> CoreExpr -> Bool go Int 0 CoreExpr e where go :: Int -> CoreExpr -> Bool go :: Int -> CoreExpr -> Bool go Int credit (Lam Id x CoreExpr e) | Id -> Bool isId Id x = Int -> CoreExpr -> Bool go (Int creditInt -> Int -> Int forall a. Num a => a -> a -> a +Int 1) CoreExpr e | Bool otherwise = Int -> CoreExpr -> Bool go Int credit CoreExpr e -- See Note [Count coercion arguments in boring contexts] go Int credit (App CoreExpr f (Type {})) = Int -> CoreExpr -> Bool go Int credit CoreExpr f go Int credit (App CoreExpr f CoreExpr a) | Int credit Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 , CoreExpr -> Bool exprIsTrivial CoreExpr a = Int -> CoreExpr -> Bool go (Int creditInt -> Int -> Int forall a. Num a => a -> a -> a -Int 1) CoreExpr f go Int credit (Tick CoreTickish _ CoreExpr e) = Int -> CoreExpr -> Bool go Int credit CoreExpr e -- dubious go Int credit (Cast CoreExpr e CoercionR _) = Int -> CoreExpr -> Bool go Int credit CoreExpr e go Int credit (Case CoreExpr scrut Id _ Type _ [Alt AltCon _ [Id] _ CoreExpr rhs]) -- See Note [Inline unsafeCoerce] | CoreExpr -> Bool isUnsafeEqualityProof CoreExpr scrut = Int -> CoreExpr -> Bool go Int credit CoreExpr rhs go Int _ (Var {}) = Bool boringCxtOk go Int _ CoreExpr _ = Bool boringCxtNotOk calcUnfoldingGuidance :: UnfoldingOpts -> Bool -- Definitely a top-level, bottoming binding -> CoreExpr -- Expression to look at -> UnfoldingGuidance calcUnfoldingGuidance :: UnfoldingOpts -> Bool -> CoreExpr -> UnfoldingGuidance calcUnfoldingGuidance UnfoldingOpts opts Bool is_top_bottoming (Tick CoreTickish t CoreExpr expr) | Bool -> Bool not (CoreTickish -> Bool forall (pass :: TickishPass). GenTickish pass -> Bool tickishIsCode CoreTickish t) -- non-code ticks don't matter for unfolding = UnfoldingOpts -> Bool -> CoreExpr -> UnfoldingGuidance calcUnfoldingGuidance UnfoldingOpts opts Bool is_top_bottoming CoreExpr expr calcUnfoldingGuidance UnfoldingOpts opts Bool is_top_bottoming CoreExpr expr = case UnfoldingOpts -> Int -> [Id] -> CoreExpr -> ExprSize sizeExpr UnfoldingOpts opts Int bOMB_OUT_SIZE [Id] val_bndrs CoreExpr body of ExprSize TooBig -> UnfoldingGuidance UnfNever SizeIs Int size Bag (Id, Int) cased_bndrs Int scrut_discount | CoreExpr -> Int -> Int -> Bool uncondInline CoreExpr expr Int n_val_bndrs Int size -> UnfWhen { ug_unsat_ok :: Bool ug_unsat_ok = Bool unSaturatedOk , ug_boring_ok :: Bool ug_boring_ok = Bool boringCxtOk , ug_arity :: Int ug_arity = Int n_val_bndrs } -- Note [INLINE for small functions] | Bool is_top_bottoming -> UnfoldingGuidance UnfNever -- See Note [Do not inline top-level bottoming functions] | Bool otherwise -> UnfIfGoodArgs { ug_args :: [Int] ug_args = (Id -> Int) -> [Id] -> [Int] forall a b. (a -> b) -> [a] -> [b] map (Bag (Id, Int) -> Id -> Int mk_discount Bag (Id, Int) cased_bndrs) [Id] val_bndrs , ug_size :: Int ug_size = Int size , ug_res :: Int ug_res = Int scrut_discount } where ([Id] bndrs, CoreExpr body) = CoreExpr -> ([Id], CoreExpr) forall b. Expr b -> ([b], Expr b) collectBinders CoreExpr expr bOMB_OUT_SIZE :: Int bOMB_OUT_SIZE = UnfoldingOpts -> Int unfoldingCreationThreshold UnfoldingOpts opts -- Bomb out if size gets bigger than this val_bndrs :: [Id] val_bndrs = (Id -> Bool) -> [Id] -> [Id] forall a. (a -> Bool) -> [a] -> [a] filter Id -> Bool isId [Id] bndrs n_val_bndrs :: Int n_val_bndrs = [Id] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [Id] val_bndrs mk_discount :: Bag (Id,Int) -> Id -> Int mk_discount :: Bag (Id, Int) -> Id -> Int mk_discount Bag (Id, Int) cbs Id bndr = (Int -> (Id, Int) -> Int) -> Int -> Bag (Id, Int) -> Int forall b a. (b -> a -> b) -> b -> Bag a -> b forall (t :: * -> *) b a. Foldable t => (b -> a -> b) -> b -> t a -> b foldl' Int -> (Id, Int) -> Int combine Int 0 Bag (Id, Int) cbs where combine :: Int -> (Id, Int) -> Int combine Int acc (Id bndr', Int disc) | Id bndr Id -> Id -> Bool forall a. Eq a => a -> a -> Bool == Id bndr' = Int acc Int -> Int -> Int `plus_disc` Int disc | Bool otherwise = Int acc plus_disc :: Int -> Int -> Int plus_disc :: Int -> Int -> Int plus_disc | Type -> Bool isFunTy (Id -> Type idType Id bndr) = Int -> Int -> Int forall a. Ord a => a -> a -> a max | Bool otherwise = Int -> Int -> Int forall a. Num a => a -> a -> a (+) -- See Note [Function and non-function discounts] {- Note [Inline unsafeCoerce] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We really want to inline unsafeCoerce, even when applied to boring arguments. It doesn't look as if its RHS is smaller than the call unsafeCoerce x = case unsafeEqualityProof @a @b of UnsafeRefl -> x but that case is discarded -- see Note [Implementing unsafeCoerce] in base:Unsafe.Coerce. Moreover, if we /don't/ inline it, we may be left with f (unsafeCoerce x) which will build a thunk -- bad, bad, bad. Conclusion: we really want inlineBoringOk to be True of the RHS of unsafeCoerce. This is (U4) in Note [Implementing unsafeCoerce]. Note [Computing the size of an expression] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The basic idea of sizeExpr is obvious enough: count nodes. But getting the heuristics right has taken a long time. Here's the basic strategy: * Variables, literals: 0 (Exception for string literals, see litSize.) * Function applications (f e1 .. en): 1 + #value args * Constructor applications: 1, regardless of #args * Let(rec): 1 + size of components * Note, cast: 0 Examples Size Term -------------- 0 42# 0 x 0 True 2 f x 1 Just x 4 f (g x) Notice that 'x' counts 0, while (f x) counts 2. That's deliberate: there's a function call to account for. Notice also that constructor applications are very cheap, because exposing them to a caller is so valuable. [25/5/11] All sizes are now multiplied by 10, except for primops (which have sizes like 1 or 4. This makes primops look fantastically cheap, and seems to be almost universally beneficial. Done partly as a result of #4978. Note [Do not inline top-level bottoming functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The FloatOut pass has gone to some trouble to float out calls to 'error' and similar friends. See Note [Bottoming floats] in GHC.Core.Opt.SetLevels. Do not re-inline them! But we *do* still inline if they are very small (the uncondInline stuff). Note [INLINE for small functions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider {-# INLINE f #-} f x = Just x g y = f y Then f's RHS is no larger than its LHS, so we should inline it into even the most boring context. In general, f the function is sufficiently small that its body is as small as the call itself, the inline unconditionally, regardless of how boring the context is. Things to note: (1) We inline *unconditionally* if inlined thing is smaller (using sizeExpr) than the thing it's replacing. Notice that (f x) --> (g 3) -- YES, unconditionally (f x) --> x : [] -- YES, *even though* there are two -- arguments to the cons x --> g 3 -- NO x --> Just v -- NO It's very important not to unconditionally replace a variable by a non-atomic term. (2) We do this even if the thing isn't saturated, else we end up with the silly situation that f x y = x ...map (f 3)... doesn't inline. Even in a boring context, inlining without being saturated will give a lambda instead of a PAP, and will be more efficient at runtime. (3) However, when the function's arity > 0, we do insist that it has at least one value argument at the call site. (This check is made in the UnfWhen case of callSiteInline.) Otherwise we find this: f = /\a \x:a. x d = /\b. MkD (f b) If we inline f here we get d = /\b. MkD (\x:b. x) and then prepareRhs floats out the argument, abstracting the type variables, so we end up with the original again! (4) We must be much more cautious about arity-zero things. Consider let x = y +# z in ... In *size* terms primops look very small, because the generate a single instruction, but we do not want to unconditionally replace every occurrence of x with (y +# z). So we only do the unconditional-inline thing for *trivial* expressions. NB: you might think that PostInlineUnconditionally would do this but it doesn't fire for top-level things; see GHC.Core.Opt.Simplify.Utils Note [Top level and postInlineUnconditionally] Note [Count coercion arguments in boring contexts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In inlineBoringOK, we ignore type arguments when deciding whether an expression is okay to inline into boring contexts. This is good, since if we have a definition like let y = x @Int in f y y there’s no reason not to inline y at both use sites — no work is actually duplicated. It may seem like the same reasoning applies to coercion arguments, and indeed, in #17182 we changed inlineBoringOK to treat coercions the same way. However, this isn’t a good idea: unlike type arguments, which have no runtime representation, coercion arguments *do* have a runtime representation (albeit the zero-width VoidRep, see Note [Coercion tokens] in "GHC.CoreToStg"). This caused trouble in #17787 for DataCon wrappers for nullary GADT constructors: the wrappers would be inlined and each use of the constructor would lead to a separate allocation instead of just sharing the wrapper closure. The solution: don’t ignore coercion arguments after all. -} uncondInline :: CoreExpr -> Arity -> Int -> Bool -- Inline unconditionally if there no size increase -- Size of call is arity (+1 for the function) -- See Note [INLINE for small functions] uncondInline :: CoreExpr -> Int -> Int -> Bool uncondInline CoreExpr rhs Int arity Int size | Int arity Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 = Int size Int -> Int -> Bool forall a. Ord a => a -> a -> Bool <= Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a * (Int arity Int -> Int -> Int forall a. Num a => a -> a -> a + Int 1) -- See Note [INLINE for small functions] (1) | Bool otherwise = CoreExpr -> Bool exprIsTrivial CoreExpr rhs -- See Note [INLINE for small functions] (4) sizeExpr :: UnfoldingOpts -> Int -- Bomb out if it gets bigger than this -> [Id] -- Arguments; we're interested in which of these -- get case'd -> CoreExpr -> ExprSize -- Note [Computing the size of an expression] -- Forcing bOMB_OUT_SIZE early prevents repeated -- unboxing of the Int argument. sizeExpr :: UnfoldingOpts -> Int -> [Id] -> CoreExpr -> ExprSize sizeExpr UnfoldingOpts opts !Int bOMB_OUT_SIZE [Id] top_args CoreExpr expr = CoreExpr -> ExprSize size_up CoreExpr expr where size_up :: CoreExpr -> ExprSize size_up (Cast CoreExpr e CoercionR _) = CoreExpr -> ExprSize size_up CoreExpr e size_up (Tick CoreTickish _ CoreExpr e) = CoreExpr -> ExprSize size_up CoreExpr e size_up (Type Type _) = ExprSize sizeZero -- Types cost nothing size_up (Coercion CoercionR _) = ExprSize sizeZero size_up (Lit Literal lit) = Int -> ExprSize sizeN (Literal -> Int litSize Literal lit) size_up (Var Id f) | Id -> Bool isZeroBitId Id f = ExprSize sizeZero -- Make sure we get constructor discounts even -- on nullary constructors | Bool otherwise = Id -> [CoreExpr] -> Int -> ExprSize size_up_call Id f [] Int 0 size_up (App CoreExpr fun CoreExpr arg) | CoreExpr -> Bool forall b. Expr b -> Bool isTyCoArg CoreExpr arg = CoreExpr -> ExprSize size_up CoreExpr fun | Bool otherwise = CoreExpr -> ExprSize size_up CoreExpr arg ExprSize -> ExprSize -> ExprSize `addSizeNSD` CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr fun [CoreExpr arg] (if CoreExpr -> Bool forall b. Expr b -> Bool isZeroBitExpr CoreExpr arg then Int 1 else Int 0) size_up (Lam Id b CoreExpr e) | Id -> Bool isId Id b Bool -> Bool -> Bool && Bool -> Bool not (Id -> Bool isZeroBitId Id b) = UnfoldingOpts -> ExprSize -> ExprSize lamScrutDiscount UnfoldingOpts opts (CoreExpr -> ExprSize size_up CoreExpr e ExprSize -> Int -> ExprSize `addSizeN` Int 10) | Bool otherwise = CoreExpr -> ExprSize size_up CoreExpr e size_up (Let (NonRec Id binder CoreExpr rhs) CoreExpr body) = (Id, CoreExpr) -> ExprSize size_up_rhs (Id binder, CoreExpr rhs) ExprSize -> ExprSize -> ExprSize `addSizeNSD` CoreExpr -> ExprSize size_up CoreExpr body ExprSize -> Int -> ExprSize `addSizeN` Id -> Int forall {a}. Num a => Id -> a size_up_alloc Id binder size_up (Let (Rec [(Id, CoreExpr)] pairs) CoreExpr body) = ((Id, CoreExpr) -> ExprSize -> ExprSize) -> ExprSize -> [(Id, CoreExpr)] -> ExprSize forall a b. (a -> b -> b) -> b -> [a] -> b forall (t :: * -> *) a b. Foldable t => (a -> b -> b) -> b -> t a -> b foldr (ExprSize -> ExprSize -> ExprSize addSizeNSD (ExprSize -> ExprSize -> ExprSize) -> ((Id, CoreExpr) -> ExprSize) -> (Id, CoreExpr) -> ExprSize -> ExprSize forall b c a. (b -> c) -> (a -> b) -> a -> c . (Id, CoreExpr) -> ExprSize size_up_rhs) (CoreExpr -> ExprSize size_up CoreExpr body ExprSize -> Int -> ExprSize `addSizeN` [Int] -> Int forall a. Num a => [a] -> a forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a sum (((Id, CoreExpr) -> Int) -> [(Id, CoreExpr)] -> [Int] forall a b. (a -> b) -> [a] -> [b] map (Id -> Int forall {a}. Num a => Id -> a size_up_alloc (Id -> Int) -> ((Id, CoreExpr) -> Id) -> (Id, CoreExpr) -> Int forall b c a. (b -> c) -> (a -> b) -> a -> c . (Id, CoreExpr) -> Id forall a b. (a, b) -> a fst) [(Id, CoreExpr)] pairs)) [(Id, CoreExpr)] pairs size_up (Case CoreExpr e Id _ Type _ [Alt Id] alts) | [Alt Id] -> Bool forall a. [a] -> Bool forall (t :: * -> *) a. Foldable t => t a -> Bool null [Alt Id] alts = CoreExpr -> ExprSize size_up CoreExpr e -- case e of {} never returns, so take size of scrutinee size_up (Case CoreExpr e Id _ Type _ [Alt Id] alts) -- Now alts is non-empty | Just Id v <- CoreExpr -> Maybe Id is_top_arg CoreExpr e -- We are scrutinising an argument variable = let alt_sizes :: [ExprSize] alt_sizes = (Alt Id -> ExprSize) -> [Alt Id] -> [ExprSize] forall a b. (a -> b) -> [a] -> [b] map Alt Id -> ExprSize size_up_alt [Alt Id] alts -- alts_size tries to compute a good discount for -- the case when we are scrutinising an argument variable alts_size :: ExprSize -> ExprSize -> ExprSize alts_size (SizeIs Int tot Bag (Id, Int) tot_disc Int tot_scrut) -- Size of all alternatives (SizeIs Int max Bag (Id, Int) _ Int _) -- Size of biggest alternative = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int tot ((Id, Int) -> Bag (Id, Int) forall a. a -> Bag a unitBag (Id v, Int 20 Int -> Int -> Int forall a. Num a => a -> a -> a + Int tot Int -> Int -> Int forall a. Num a => a -> a -> a - Int max) Bag (Id, Int) -> Bag (Id, Int) -> Bag (Id, Int) forall a. Bag a -> Bag a -> Bag a `unionBags` Bag (Id, Int) tot_disc) Int tot_scrut -- If the variable is known, we produce a -- discount that will take us back to 'max', -- the size of the largest alternative The -- 1+ is a little discount for reduced -- allocation in the caller -- -- Notice though, that we return tot_disc, -- the total discount from all branches. I -- think that's right. alts_size ExprSize tot_size ExprSize _ = ExprSize tot_size in ExprSize -> ExprSize -> ExprSize alts_size ((ExprSize -> ExprSize -> ExprSize) -> [ExprSize] -> ExprSize forall a. (a -> a -> a) -> [a] -> a forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a foldr1 ExprSize -> ExprSize -> ExprSize addAltSize [ExprSize] alt_sizes) -- alts is non-empty ((ExprSize -> ExprSize -> ExprSize) -> [ExprSize] -> ExprSize forall a. (a -> a -> a) -> [a] -> a forall (t :: * -> *) a. Foldable t => (a -> a -> a) -> t a -> a foldr1 ExprSize -> ExprSize -> ExprSize maxSize [ExprSize] alt_sizes) -- Good to inline if an arg is scrutinised, because -- that may eliminate allocation in the caller -- And it eliminates the case itself where is_top_arg :: CoreExpr -> Maybe Id is_top_arg (Var Id v) | Id v Id -> [Id] -> Bool forall a. Eq a => a -> [a] -> Bool forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool `elem` [Id] top_args = Id -> Maybe Id forall a. a -> Maybe a Just Id v is_top_arg (Cast CoreExpr e CoercionR _) = CoreExpr -> Maybe Id is_top_arg CoreExpr e is_top_arg CoreExpr _ = Maybe Id forall a. Maybe a Nothing size_up (Case CoreExpr e Id _ Type _ [Alt Id] alts) = CoreExpr -> ExprSize size_up CoreExpr e ExprSize -> ExprSize -> ExprSize `addSizeNSD` (Alt Id -> ExprSize -> ExprSize) -> ExprSize -> [Alt Id] -> ExprSize forall a b. (a -> b -> b) -> b -> [a] -> b forall (t :: * -> *) a b. Foldable t => (a -> b -> b) -> b -> t a -> b foldr (ExprSize -> ExprSize -> ExprSize addAltSize (ExprSize -> ExprSize -> ExprSize) -> (Alt Id -> ExprSize) -> Alt Id -> ExprSize -> ExprSize forall b c a. (b -> c) -> (a -> b) -> a -> c . Alt Id -> ExprSize size_up_alt) ExprSize case_size [Alt Id] alts where case_size :: ExprSize case_size | CoreExpr -> Bool forall b. Expr b -> Bool is_inline_scrut CoreExpr e, [Alt Id] -> Int -> Bool forall a. [a] -> Int -> Bool lengthAtMost [Alt Id] alts Int 1 = Int -> ExprSize sizeN (-Int 10) | Bool otherwise = ExprSize sizeZero -- Normally we don't charge for the case itself, but -- we charge one per alternative (see size_up_alt, -- below) to account for the cost of the info table -- and comparisons. -- -- However, in certain cases (see is_inline_scrut -- below), no code is generated for the case unless -- there are multiple alts. In these cases we -- subtract one, making the first alt free. -- e.g. case x# +# y# of _ -> ... should cost 1 -- case touch# x# of _ -> ... should cost 0 -- (see #4978) -- -- I would like to not have the "lengthAtMost alts 1" -- condition above, but without that some programs got worse -- (spectral/hartel/event and spectral/para). I don't fully -- understand why. (SDM 24/5/11) -- unboxed variables, inline primops and unsafe foreign calls -- are all "inline" things: is_inline_scrut :: Expr b -> Bool is_inline_scrut (Var Id v) = (() :: Constraint) => Type -> Bool Type -> Bool isUnliftedType (Id -> Type idType Id v) -- isUnliftedType is OK here: scrutinees have a fixed RuntimeRep (search for FRRCase) is_inline_scrut Expr b scrut | (Var Id f, [Expr b] _) <- Expr b -> (Expr b, [Expr b]) forall b. Expr b -> (Expr b, [Expr b]) collectArgs Expr b scrut = case Id -> IdDetails idDetails Id f of FCallId ForeignCall fc -> Bool -> Bool not (ForeignCall -> Bool isSafeForeignCall ForeignCall fc) PrimOpId PrimOp op Bool _ -> Bool -> Bool not (PrimOp -> Bool primOpOutOfLine PrimOp op) IdDetails _other -> Bool False | Bool otherwise = Bool False size_up_rhs :: (Id, CoreExpr) -> ExprSize size_up_rhs (Id bndr, CoreExpr rhs) | Just Int join_arity <- Id -> Maybe Int isJoinId_maybe Id bndr -- Skip arguments to join point , ([Id] _bndrs, CoreExpr body) <- Int -> CoreExpr -> ([Id], CoreExpr) forall b. Int -> Expr b -> ([b], Expr b) collectNBinders Int join_arity CoreExpr rhs = CoreExpr -> ExprSize size_up CoreExpr body | Bool otherwise = CoreExpr -> ExprSize size_up CoreExpr rhs ------------ -- size_up_app is used when there's ONE OR MORE value args size_up_app :: CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app (App CoreExpr fun CoreExpr arg) [CoreExpr] args Int voids | CoreExpr -> Bool forall b. Expr b -> Bool isTyCoArg CoreExpr arg = CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr fun [CoreExpr] args Int voids | CoreExpr -> Bool forall b. Expr b -> Bool isZeroBitExpr CoreExpr arg = CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr fun (CoreExpr argCoreExpr -> [CoreExpr] -> [CoreExpr] forall a. a -> [a] -> [a] :[CoreExpr] args) (Int voids Int -> Int -> Int forall a. Num a => a -> a -> a + Int 1) | Bool otherwise = CoreExpr -> ExprSize size_up CoreExpr arg ExprSize -> ExprSize -> ExprSize `addSizeNSD` CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr fun (CoreExpr argCoreExpr -> [CoreExpr] -> [CoreExpr] forall a. a -> [a] -> [a] :[CoreExpr] args) Int voids size_up_app (Var Id fun) [CoreExpr] args Int voids = Id -> [CoreExpr] -> Int -> ExprSize size_up_call Id fun [CoreExpr] args Int voids size_up_app (Tick CoreTickish _ CoreExpr expr) [CoreExpr] args Int voids = CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr expr [CoreExpr] args Int voids size_up_app (Cast CoreExpr expr CoercionR _) [CoreExpr] args Int voids = CoreExpr -> [CoreExpr] -> Int -> ExprSize size_up_app CoreExpr expr [CoreExpr] args Int voids size_up_app CoreExpr other [CoreExpr] args Int voids = CoreExpr -> ExprSize size_up CoreExpr other ExprSize -> Int -> ExprSize `addSizeN` Int -> Int -> Int callSize ([CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] args) Int voids -- if the lhs is not an App or a Var, or an invisible thing like a -- Tick or Cast, then we should charge for a complete call plus the -- size of the lhs itself. ------------ size_up_call :: Id -> [CoreExpr] -> Int -> ExprSize size_up_call :: Id -> [CoreExpr] -> Int -> ExprSize size_up_call Id fun [CoreExpr] val_args Int voids = case Id -> IdDetails idDetails Id fun of FCallId ForeignCall _ -> Int -> ExprSize sizeN (Int -> Int -> Int callSize ([CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] val_args) Int voids) DataConWorkId DataCon dc -> DataCon -> Int -> ExprSize conSize DataCon dc ([CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] val_args) PrimOpId PrimOp op Bool _ -> PrimOp -> Int -> ExprSize primOpSize PrimOp op ([CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] val_args) ClassOpId Class _ -> UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize classOpSize UnfoldingOpts opts [Id] top_args [CoreExpr] val_args IdDetails _ -> UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize funSize UnfoldingOpts opts [Id] top_args Id fun ([CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] val_args) Int voids ------------ size_up_alt :: Alt Id -> ExprSize size_up_alt (Alt AltCon _con [Id] _bndrs CoreExpr rhs) = CoreExpr -> ExprSize size_up CoreExpr rhs ExprSize -> Int -> ExprSize `addSizeN` Int 10 -- Don't charge for args, so that wrappers look cheap -- (See comments about wrappers with Case) -- -- IMPORTANT: *do* charge 1 for the alternative, else we -- find that giant case nests are treated as practically free -- A good example is Foreign.C.Error.errnoToIOError ------------ -- Cost to allocate binding with given binder size_up_alloc :: Id -> a size_up_alloc Id bndr | Id -> Bool isTyVar Id bndr -- Doesn't exist at runtime Bool -> Bool -> Bool || Id -> Bool isJoinId Id bndr -- Not allocated at all Bool -> Bool -> Bool || Bool -> Bool not (Type -> Bool isBoxedType (Id -> Type idType Id bndr)) -- Doesn't live in heap = a 0 | Bool otherwise = a 10 ------------ -- These addSize things have to be here because -- I don't want to give them bOMB_OUT_SIZE as an argument addSizeN :: ExprSize -> Int -> ExprSize addSizeN ExprSize TooBig Int _ = ExprSize TooBig addSizeN (SizeIs Int n Bag (Id, Int) xs Int d) Int m = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize mkSizeIs Int bOMB_OUT_SIZE (Int n Int -> Int -> Int forall a. Num a => a -> a -> a + Int m) Bag (Id, Int) xs Int d -- addAltSize is used to add the sizes of case alternatives addAltSize :: ExprSize -> ExprSize -> ExprSize addAltSize ExprSize TooBig ExprSize _ = ExprSize TooBig addAltSize ExprSize _ ExprSize TooBig = ExprSize TooBig addAltSize (SizeIs Int n1 Bag (Id, Int) xs Int d1) (SizeIs Int n2 Bag (Id, Int) ys Int d2) = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize mkSizeIs Int bOMB_OUT_SIZE (Int n1 Int -> Int -> Int forall a. Num a => a -> a -> a + Int n2) (Bag (Id, Int) xs Bag (Id, Int) -> Bag (Id, Int) -> Bag (Id, Int) forall a. Bag a -> Bag a -> Bag a `unionBags` Bag (Id, Int) ys) (Int d1 Int -> Int -> Int forall a. Num a => a -> a -> a + Int d2) -- Note [addAltSize result discounts] -- This variant ignores the result discount from its LEFT argument -- It's used when the second argument isn't part of the result addSizeNSD :: ExprSize -> ExprSize -> ExprSize addSizeNSD ExprSize TooBig ExprSize _ = ExprSize TooBig addSizeNSD ExprSize _ ExprSize TooBig = ExprSize TooBig addSizeNSD (SizeIs Int n1 Bag (Id, Int) xs Int _) (SizeIs Int n2 Bag (Id, Int) ys Int d2) = Int -> Int -> Bag (Id, Int) -> Int -> ExprSize mkSizeIs Int bOMB_OUT_SIZE (Int n1 Int -> Int -> Int forall a. Num a => a -> a -> a + Int n2) (Bag (Id, Int) xs Bag (Id, Int) -> Bag (Id, Int) -> Bag (Id, Int) forall a. Bag a -> Bag a -> Bag a `unionBags` Bag (Id, Int) ys) Int d2 -- Ignore d1 -- don't count expressions such as State# RealWorld -- exclude join points, because they can be rep-polymorphic -- and typePrimRep will crash isZeroBitId :: Id -> Bool isZeroBitId Id id = Bool -> Bool not (Id -> Bool isJoinId Id id) Bool -> Bool -> Bool && (() :: Constraint) => Type -> Bool Type -> Bool isZeroBitTy (Id -> Type idType Id id) isZeroBitExpr :: Expr b -> Bool isZeroBitExpr (Var Id id) = Id -> Bool isZeroBitId Id id isZeroBitExpr (Tick CoreTickish _ Expr b e) = Expr b -> Bool isZeroBitExpr Expr b e isZeroBitExpr Expr b _ = Bool False -- | Finds a nominal size of a string literal. litSize :: Literal -> Int -- Used by GHC.Core.Unfold.sizeExpr litSize :: Literal -> Int litSize (LitNumber LitNumType LitNumBigNat Integer _) = Int 100 litSize (LitString ByteString str) = Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a + Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a * ((ByteString -> Int BS.length ByteString str Int -> Int -> Int forall a. Num a => a -> a -> a + Int 3) Int -> Int -> Int forall a. Integral a => a -> a -> a `div` Int 4) -- If size could be 0 then @f "x"@ might be too small -- [Sept03: make literal strings a bit bigger to avoid fruitless -- duplication of little strings] litSize Literal _other = Int 0 -- Must match size of nullary constructors -- Key point: if x |-> 4, then x must inline unconditionally -- (eg via case binding) classOpSize :: UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize -- See Note [Conlike is interesting] classOpSize :: UnfoldingOpts -> [Id] -> [CoreExpr] -> ExprSize classOpSize UnfoldingOpts _ [Id] _ [] = ExprSize sizeZero classOpSize UnfoldingOpts opts [Id] top_args (CoreExpr arg1 : [CoreExpr] other_args) = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int size Bag (Id, Int) arg_discount Int 0 where size :: Int size = Int 20 Int -> Int -> Int forall a. Num a => a -> a -> a + (Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a * [CoreExpr] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [CoreExpr] other_args) -- If the class op is scrutinising a lambda bound dictionary then -- give it a discount, to encourage the inlining of this function -- The actual discount is rather arbitrarily chosen arg_discount :: Bag (Id, Int) arg_discount = case CoreExpr arg1 of Var Id dict | Id dict Id -> [Id] -> Bool forall a. Eq a => a -> [a] -> Bool forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool `elem` [Id] top_args -> (Id, Int) -> Bag (Id, Int) forall a. a -> Bag a unitBag (Id dict, UnfoldingOpts -> Int unfoldingDictDiscount UnfoldingOpts opts) CoreExpr _other -> Bag (Id, Int) forall a. Bag a emptyBag -- | The size of a function call callSize :: Int -- ^ number of value args -> Int -- ^ number of value args that are void -> Int callSize :: Int -> Int -> Int callSize Int n_val_args Int voids = Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a * (Int 1 Int -> Int -> Int forall a. Num a => a -> a -> a + Int n_val_args Int -> Int -> Int forall a. Num a => a -> a -> a - Int voids) -- The 1+ is for the function itself -- Add 1 for each non-trivial arg; -- the allocation cost, as in let(rec) -- | The size of a jump to a join point jumpSize :: Int -- ^ number of value args -> Int -- ^ number of value args that are void -> Int jumpSize :: Int -> Int -> Int jumpSize Int n_val_args Int voids = Int 2 Int -> Int -> Int forall a. Num a => a -> a -> a * (Int 1 Int -> Int -> Int forall a. Num a => a -> a -> a + Int n_val_args Int -> Int -> Int forall a. Num a => a -> a -> a - Int voids) -- A jump is 20% the size of a function call. Making jumps free reopens -- bug #6048, but making them any more expensive loses a 21% improvement in -- spectral/puzzle. TODO Perhaps adjusting the default threshold would be a -- better solution? funSize :: UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize -- Size for functions that are not constructors or primops -- Note [Function applications] funSize :: UnfoldingOpts -> [Id] -> Id -> Int -> Int -> ExprSize funSize UnfoldingOpts opts [Id] top_args Id fun Int n_val_args Int voids | Id fun Id -> Unique -> Bool forall a. Uniquable a => a -> Unique -> Bool `hasKey` Unique buildIdKey = ExprSize buildSize | Id fun Id -> Unique -> Bool forall a. Uniquable a => a -> Unique -> Bool `hasKey` Unique augmentIdKey = ExprSize augmentSize | Bool otherwise = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int size Bag (Id, Int) arg_discount Int res_discount where some_val_args :: Bool some_val_args = Int n_val_args Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 is_join :: Bool is_join = Id -> Bool isJoinId Id fun size :: Int size | Bool is_join = Int -> Int -> Int jumpSize Int n_val_args Int voids | Bool -> Bool not Bool some_val_args = Int 0 | Bool otherwise = Int -> Int -> Int callSize Int n_val_args Int voids -- DISCOUNTS -- See Note [Function and non-function discounts] arg_discount :: Bag (Id, Int) arg_discount | Bool some_val_args Bool -> Bool -> Bool && Id fun Id -> [Id] -> Bool forall a. Eq a => a -> [a] -> Bool forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool `elem` [Id] top_args = (Id, Int) -> Bag (Id, Int) forall a. a -> Bag a unitBag (Id fun, UnfoldingOpts -> Int unfoldingFunAppDiscount UnfoldingOpts opts) | Bool otherwise = Bag (Id, Int) forall a. Bag a emptyBag -- If the function is an argument and is applied -- to some values, give it an arg-discount res_discount :: Int res_discount | Id -> Int idArity Id fun Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int n_val_args = UnfoldingOpts -> Int unfoldingFunAppDiscount UnfoldingOpts opts | Bool otherwise = Int 0 -- If the function is partially applied, show a result discount -- XXX maybe behave like ConSize for eval'd variable conSize :: DataCon -> Int -> ExprSize conSize :: DataCon -> Int -> ExprSize conSize DataCon dc Int n_val_args | Int n_val_args Int -> Int -> Bool forall a. Eq a => a -> a -> Bool == Int 0 = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 0 Bag (Id, Int) forall a. Bag a emptyBag Int 10 -- Like variables -- See Note [Unboxed tuple size and result discount] | DataCon -> Bool isUnboxedTupleDataCon DataCon dc = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 0 Bag (Id, Int) forall a. Bag a emptyBag Int 10 -- See Note [Constructor size and result discount] | Bool otherwise = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 10 Bag (Id, Int) forall a. Bag a emptyBag Int 10 {- Note [Constructor size and result discount] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Treat a constructors application as size 10, regardless of how many arguments it has; 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 (Just x) has size 0, which is the same as a lone variable; and hence 'v' will always be replaced by (Just x), where v is bound to Just x. The "result discount" is applied if the result of the call is scrutinised (say by a case). For a constructor application that will mean the constructor application will disappear, so we don't need to charge it to the function. So the discount should at least match the cost of the constructor application, namely 10. Historical note 1: Until Jun 2020 we gave it a "bit of extra incentive" via a discount of 10*(1 + n_val_args), but that was FAR too much (#18282). In particular, consider a huge case tree like let r = case y1 of Nothing -> B1 a b c Just v1 -> case y2 of Nothing -> B1 c b a Just v2 -> ... If conSize gives a cost of 10 (regardless of n_val_args) and a discount of 10, that'll make each alternative RHS cost zero. We charge 10 for each case alternative (see size_up_alt). If we give a bigger discount (say 20) in conSize, we'll make the case expression cost *nothing*, and that can make a huge case tree cost nothing. This leads to massive, sometimes exponential inlinings (#18282). In short, don't give a discount that give a negative size to a sub-expression! Historical note 2: Much longer ago, Simon M tried a MUCH bigger discount: (10 * (10 + n_val_args)), and said it was an "unambiguous win", but its terribly dangerous because a function with many many case branches, each finishing with a constructor, can have an arbitrarily large discount. This led to terrible code bloat: see #6099. Note [Unboxed tuple size and result discount] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ However, unboxed tuples count as size zero. I found occasions where we had f x y z = case op# x y z of { s -> (# s, () #) } and f wasn't getting inlined. I tried giving unboxed tuples a *result discount* of zero (see the commented-out line). Why? When returned as a result they do not allocate, so maybe we don't want to charge so much for them. If you have a non-zero discount here, we find that workers often get inlined back into wrappers, because it look like f x = case $wf x of (# a,b #) -> (a,b) and we are keener because of the case. However while this change shrank binary sizes by 0.5% it also made spectral/boyer allocate 5% more. All other changes were very small. So it's not a big deal but I didn't adopt the idea. When fixing #18282 (see Note [Constructor size and result discount]) I changed the result discount to be just 10, not 10*(1+n_val_args). Note [Function and non-function discounts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We want a discount if the function is applied. A good example is monadic combinators with continuation arguments, where inlining is quite important. But we don't want a big discount when a function is called many times (see the detailed comments with #6048) because if the function is big it won't be inlined at its many call sites and no benefit results. Indeed, we can get exponentially big inlinings this way; that is what #6048 is about. On the other hand, for data-valued arguments, if there are lots of case expressions in the body, each one will get smaller if we apply the function to a constructor application, so we *want* a big discount if the argument is scrutinised by many case expressions. Conclusion: - For functions, take the max of the discounts - For data values, take the sum of the discounts Note [Literal integer size] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Literal integers *can* be big (mkInteger [...coefficients...]), but need not be (IS n). We just use an arbitrary big-ish constant here so that, in particular, we don't inline top-level defns like n = IS 5 There's no point in doing so -- any optimisations will see the IS through n's unfolding. Nor will a big size inhibit unfoldings functions that mention a literal Integer, because the float-out pass will float all those constants to top level. -} primOpSize :: PrimOp -> Int -> ExprSize primOpSize :: PrimOp -> Int -> ExprSize primOpSize PrimOp op Int n_val_args = if PrimOp -> Bool primOpOutOfLine PrimOp op then Int -> ExprSize sizeN (Int op_size Int -> Int -> Int forall a. Num a => a -> a -> a + Int n_val_args) else Int -> ExprSize sizeN Int op_size where op_size :: Int op_size = PrimOp -> Int primOpCodeSize PrimOp op buildSize :: ExprSize buildSize :: ExprSize buildSize = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 0 Bag (Id, Int) forall a. Bag a emptyBag Int 40 -- 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 because build is -- very like a constructor. We don't bother to check that the -- build is saturated (it usually is). The "-2" discounts for the \c n, -- The "4" is rather arbitrary. augmentSize :: ExprSize augmentSize :: ExprSize augmentSize = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 0 Bag (Id, Int) forall a. Bag a emptyBag Int 40 -- Ditto (augment t (\cn -> e) ys) should cost only the cost of -- e plus ys. The -2 accounts for the \cn -- When we return a lambda, give a discount if it's used (applied) lamScrutDiscount :: UnfoldingOpts -> ExprSize -> ExprSize lamScrutDiscount :: UnfoldingOpts -> ExprSize -> ExprSize lamScrutDiscount UnfoldingOpts opts (SizeIs Int n Bag (Id, Int) vs Int _) = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int n Bag (Id, Int) vs (UnfoldingOpts -> Int unfoldingFunAppDiscount UnfoldingOpts opts) lamScrutDiscount UnfoldingOpts _ ExprSize TooBig = ExprSize TooBig {- Note [addAltSize result discounts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When adding the size of alternatives, we *add* the result discounts too, rather than take the *maximum*. For a multi-branch case, this gives a discount for each branch that returns a constructor, making us keener to inline. I did try using 'max' instead, but it makes nofib 'rewrite' and 'puzzle' allocate significantly more, and didn't make binary sizes shrink significantly either. Note [Discounts and thresholds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Constants for discounts and thresholds are defined in 'UnfoldingOpts'. They are: unfoldingCreationThreshold At a definition site, if the unfolding is bigger than this, we may discard it altogether unfoldingUseThreshold At a call site, if the unfolding, less discounts, is smaller than this, then it's small enough inline unfoldingDictDiscount The discount for each occurrence of a dictionary argument as an argument of a class method. Should be pretty small else big functions may get inlined unfoldingFunAppDiscount Discount for a function argument that is applied. Quite large, because if we inline we avoid the higher-order call. unfoldingVeryAggressive If True, the compiler ignores all the thresholds and inlines very aggressively. It still adheres to arity, simplifier phase control and loop breakers. Historical Note: Before April 2020 we had another factor, ufKeenessFactor, which would scale the discounts before they were subtracted from the size. This was justified with the following comment: -- We multiply 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 -- *efficiency* to be gained (e.g. beta reductions, case reductions) -- by inlining. However, this is highly suspect since it means that we subtract a *scaled* size from an absolute size, resulting in crazy (e.g. negative) scores in some cases (#15304). We consequently killed off ufKeenessFactor and bumped up the ufUseThreshold to compensate. Note [Function applications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In a function application (f a b) - If 'f' is an argument to the function being analysed, and there's at least one value arg, record a FunAppDiscount for f - If the application if a PAP (arity > 2 in this example) record a *result* discount (because inlining with "extra" args in the call may mean that we now get a saturated application) Code for manipulating sizes -} -- | The size of a candidate expression for unfolding data ExprSize = TooBig | SizeIs { ExprSize -> Int _es_size_is :: {-# UNPACK #-} !Int -- ^ Size found , ExprSize -> Bag (Id, Int) _es_args :: !(Bag (Id,Int)) -- ^ Arguments cased herein, and discount for each such , ExprSize -> Int _es_discount :: {-# UNPACK #-} !Int -- ^ Size to subtract if result is scrutinised by a case -- expression } instance Outputable ExprSize where ppr :: ExprSize -> SDoc ppr ExprSize TooBig = String -> SDoc forall doc. IsLine doc => String -> doc text String "TooBig" ppr (SizeIs Int a Bag (Id, Int) _ Int c) = SDoc -> SDoc forall doc. IsLine doc => doc -> doc brackets (Int -> SDoc forall doc. IsLine doc => Int -> doc int Int a SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Int -> SDoc forall doc. IsLine doc => Int -> doc int Int c) -- subtract the discount before deciding whether to bale out. eg. we -- want to inline a large constructor application into a selector: -- tup = (a_1, ..., a_99) -- x = case tup of ... -- mkSizeIs :: Int -> Int -> Bag (Id, Int) -> Int -> ExprSize mkSizeIs :: Int -> Int -> Bag (Id, Int) -> Int -> ExprSize mkSizeIs Int max Int n Bag (Id, Int) xs Int d | (Int n Int -> Int -> Int forall a. Num a => a -> a -> a - Int d) Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int max = ExprSize TooBig | Bool otherwise = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int n Bag (Id, Int) xs Int d maxSize :: ExprSize -> ExprSize -> ExprSize maxSize :: ExprSize -> ExprSize -> ExprSize maxSize ExprSize TooBig ExprSize _ = ExprSize TooBig maxSize ExprSize _ ExprSize TooBig = ExprSize TooBig maxSize s1 :: ExprSize s1@(SizeIs Int n1 Bag (Id, Int) _ Int _) s2 :: ExprSize s2@(SizeIs Int n2 Bag (Id, Int) _ Int _) | Int n1 Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int n2 = ExprSize s1 | Bool otherwise = ExprSize s2 sizeZero :: ExprSize sizeN :: Int -> ExprSize sizeZero :: ExprSize sizeZero = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int 0 Bag (Id, Int) forall a. Bag a emptyBag Int 0 sizeN :: Int -> ExprSize sizeN Int n = Int -> Bag (Id, Int) -> Int -> ExprSize SizeIs Int n Bag (Id, Int) forall a. Bag a emptyBag Int 0 {- ************************************************************************ * * \subsection[considerUnfolding]{Given all the info, do (not) do the unfolding} * * ************************************************************************ We use 'couldBeSmallEnoughToInline' to avoid exporting inlinings that we ``couldn't possibly use'' on the other side. Can be overridden w/ flaggery. Just the same as smallEnoughToInline, except that it has no actual arguments. -} couldBeSmallEnoughToInline :: UnfoldingOpts -> Int -> CoreExpr -> Bool couldBeSmallEnoughToInline :: UnfoldingOpts -> Int -> CoreExpr -> Bool couldBeSmallEnoughToInline UnfoldingOpts opts Int threshold CoreExpr rhs = case UnfoldingOpts -> Int -> [Id] -> CoreExpr -> ExprSize sizeExpr UnfoldingOpts opts Int threshold [] CoreExpr body of ExprSize TooBig -> Bool False ExprSize _ -> Bool True where ([Id] _, CoreExpr body) = CoreExpr -> ([Id], CoreExpr) forall b. Expr b -> ([b], Expr b) collectBinders CoreExpr rhs ---------------- smallEnoughToInline :: UnfoldingOpts -> Unfolding -> Bool smallEnoughToInline :: UnfoldingOpts -> Unfolding -> Bool smallEnoughToInline UnfoldingOpts opts (CoreUnfolding {uf_guidance :: Unfolding -> UnfoldingGuidance uf_guidance = UnfoldingGuidance guidance}) = case UnfoldingGuidance guidance of UnfIfGoodArgs {ug_size :: UnfoldingGuidance -> Int ug_size = Int size} -> Int size Int -> Int -> Bool forall a. Ord a => a -> a -> Bool <= UnfoldingOpts -> Int unfoldingUseThreshold UnfoldingOpts opts UnfWhen {} -> Bool True UnfoldingGuidance UnfNever -> Bool False smallEnoughToInline UnfoldingOpts _ Unfolding _ = Bool False {- ************************************************************************ * * \subsection{callSiteInline} * * ************************************************************************ This is the key function. It decides whether to inline a variable at a call site callSiteInline is used at call sites, so it is a bit more generous. It's a very important function that embodies lots of heuristics. A non-WHNF can be inlined if it doesn't occur inside a lambda, and occurs exactly once or occurs once in each branch of a case and is small 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. Tt turns out that the convenient way to prevent them inlining is to give them a NOINLINE pragma, which we do in StrictAnal.addStrictnessInfoToTopId -} data ArgSummary = TrivArg -- Nothing interesting | NonTrivArg -- Arg has structure | ValueArg -- Arg is a con-app or PAP -- ..or con-like. Note [Conlike is interesting] instance Outputable ArgSummary where ppr :: ArgSummary -> SDoc ppr ArgSummary TrivArg = String -> SDoc forall doc. IsLine doc => String -> doc text String "TrivArg" ppr ArgSummary NonTrivArg = String -> SDoc forall doc. IsLine doc => String -> doc text String "NonTrivArg" ppr ArgSummary ValueArg = String -> SDoc forall doc. IsLine doc => String -> doc text String "ValueArg" nonTriv :: ArgSummary -> Bool nonTriv :: ArgSummary -> Bool nonTriv ArgSummary TrivArg = Bool False nonTriv ArgSummary _ = Bool True data CallCtxt = BoringCtxt | RhsCtxt RecFlag -- Rhs of a let-binding; see Note [RHS of lets] | DiscArgCtxt -- Argument of a function with non-zero arg discount | RuleArgCtxt -- We are somewhere in the argument of a function with rules | 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 :: CallCtxt -> SDoc ppr CallCtxt CaseCtxt = String -> SDoc forall doc. IsLine doc => String -> doc text String "CaseCtxt" ppr CallCtxt ValAppCtxt = String -> SDoc forall doc. IsLine doc => String -> doc text String "ValAppCtxt" ppr CallCtxt BoringCtxt = String -> SDoc forall doc. IsLine doc => String -> doc text String "BoringCtxt" ppr (RhsCtxt RecFlag ir)= String -> SDoc forall doc. IsLine doc => String -> doc text String "RhsCtxt" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <> SDoc -> SDoc forall doc. IsLine doc => doc -> doc parens (RecFlag -> SDoc forall a. Outputable a => a -> SDoc ppr RecFlag ir) ppr CallCtxt DiscArgCtxt = String -> SDoc forall doc. IsLine doc => String -> doc text String "DiscArgCtxt" ppr CallCtxt RuleArgCtxt = String -> SDoc forall doc. IsLine doc => String -> doc text String "RuleArgCtxt" callSiteInline :: Logger -> UnfoldingOpts -> Int -- Case depth -> Id -- The Id -> Bool -- True <=> unfolding is active -> Bool -- True if there are no arguments at all (incl type args) -> [ArgSummary] -- One for each value arg; True if it is interesting -> CallCtxt -- True <=> continuation is interesting -> Maybe CoreExpr -- Unfolding, if any callSiteInline :: Logger -> UnfoldingOpts -> Int -> Id -> Bool -> Bool -> [ArgSummary] -> CallCtxt -> Maybe CoreExpr callSiteInline Logger logger UnfoldingOpts opts !Int case_depth Id id Bool active_unfolding Bool lone_variable [ArgSummary] arg_infos CallCtxt cont_info = case IdUnfoldingFun idUnfolding Id id of -- idUnfolding checks for loop-breakers, returning NoUnfolding -- Things with an INLINE pragma may have an unfolding *and* -- be a loop breaker (maybe the knot is not yet untied) CoreUnfolding { uf_tmpl :: Unfolding -> CoreExpr uf_tmpl = CoreExpr unf_template , uf_cache :: Unfolding -> UnfoldingCache uf_cache = UnfoldingCache unf_cache , uf_guidance :: Unfolding -> UnfoldingGuidance uf_guidance = UnfoldingGuidance guidance } | Bool active_unfolding -> Logger -> UnfoldingOpts -> Int -> Id -> Bool -> [ArgSummary] -> CallCtxt -> CoreExpr -> UnfoldingCache -> UnfoldingGuidance -> Maybe CoreExpr tryUnfolding Logger logger UnfoldingOpts opts Int case_depth Id id Bool lone_variable [ArgSummary] arg_infos CallCtxt cont_info CoreExpr unf_template UnfoldingCache unf_cache UnfoldingGuidance guidance | Bool otherwise -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String "Inactive unfolding:" (Id -> SDoc forall a. Outputable a => a -> SDoc ppr Id id) Maybe CoreExpr forall a. Maybe a Nothing Unfolding NoUnfolding -> Maybe CoreExpr forall a. Maybe a Nothing Unfolding BootUnfolding -> Maybe CoreExpr forall a. Maybe a Nothing OtherCon {} -> Maybe CoreExpr forall a. Maybe a Nothing DFunUnfolding {} -> Maybe CoreExpr forall a. Maybe a Nothing -- Never unfold a DFun -- | Report the inlining of an identifier's RHS to the user, if requested. traceInline :: Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline :: forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id inline_id String str SDoc doc a result -- We take care to ensure that doc is used in only one branch, ensuring that -- the simplifier can push its allocation into the branch. See Note [INLINE -- conditional tracing utilities]. | Bool enable = Logger -> String -> SDoc -> a -> a forall a. Logger -> String -> SDoc -> a -> a logTraceMsg Logger logger String str SDoc doc a result | Bool otherwise = a result where enable :: Bool enable | Logger -> DumpFlag -> Bool logHasDumpFlag Logger logger DumpFlag Opt_D_dump_verbose_inlinings = Bool True | Just String prefix <- UnfoldingOpts -> Maybe String unfoldingReportPrefix UnfoldingOpts opts = String prefix String -> String -> Bool forall a. Eq a => [a] -> [a] -> Bool `isPrefixOf` OccName -> String occNameString (Id -> OccName forall a. NamedThing a => a -> OccName getOccName Id inline_id) | Bool otherwise = Bool False {-# INLINE traceInline #-} -- see Note [INLINE conditional tracing utilities] {- Note [Avoid inlining into deeply nested cases] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a function f like this: f arg1 arg2 = case ... ... -> g arg1 ... -> g arg2 This function is small. So should be safe to inline. However sometimes this doesn't quite work out like that. Consider this code: f1 arg1 arg2 ... = ... case _foo of alt1 -> ... f2 arg1 ... alt2 -> ... f2 arg2 ... f2 arg1 arg2 ... = ... case _foo of alt1 -> ... f3 arg1 ... alt2 -> ... f3 arg2 ... f3 arg1 arg2 ... = ... ... repeats up to n times. And then f1 is applied to some arguments: foo = ... f1 <interestingArgs> ... Initially f2..fn are not interesting to inline so we don't. However we see that f1 is applied to interesting args. So it's an obvious choice to inline those: foo = ... case _foo of alt1 -> ... f2 <interestingArg> ... alt2 -> ... f2 <interestingArg> ... As a result we go and inline f2 both mentions of f2 in turn are now applied to interesting arguments and f2 is small: foo = ... case _foo of alt1 -> ... case _foo of alt1 -> ... f3 <interestingArg> ... alt2 -> ... f3 <interestingArg> ... alt2 -> ... case _foo of alt1 -> ... f3 <interestingArg> ... alt2 -> ... f3 <interestingArg> ... The same thing happens for each binding up to f_n, duplicating the amount of inlining done in each step. Until at some point we are either done or run out of simplifier ticks/RAM. This pattern happened #18730. To combat this we introduce one more heuristic when weighing inlining decision. We keep track of a "case-depth". Which increases each time we look inside a case expression with more than one alternative. We then apply a penalty to inlinings based on the case-depth at which they would be inlined. Bounding the number of inlinings in such a scenario. The heuristic can be tuned in two ways: * We can ignore the first n levels of case nestings for inlining decisions using -funfolding-case-threshold. * The penalty grows linear with the depth. It's computed as size*(depth-threshold)/scaling. Scaling can be set with -funfolding-case-scaling. Some guidance on setting these defaults: * A low treshold (<= 2) is needed to prevent exponential cases from spiraling out of control. We picked 2 for no particular reason. * Scaling the penalty by any more than 30 means the reproducer from T18730 won't compile even with reasonably small values of n. Instead it will run out of runs/ticks. This means to positively affect the reproducer a scaling <= 30 is required. * A scaling of >= 15 still causes a few very large regressions on some nofib benchmarks. (+80% for gc/fulsom, +90% for real/ben-raytrace, +20% for spectral/fibheaps) * A scaling of >= 25 showed no regressions on nofib. However it showed a number of (small) regression for compiler perf benchmarks. The end result is that we are settling for a scaling of 30, with a threshold of 2. This gives us minimal compiler perf regressions. No nofib runtime regressions and will still avoid this pattern sometimes. This is a "safe" default, where we err on the side of compiler blowup instead of risking runtime regressions. For cases where the default falls short the flag can be changed to allow more/less inlining as needed on a per-module basis. -} tryUnfolding :: Logger -> UnfoldingOpts -> Int -> Id -> Bool -> [ArgSummary] -> CallCtxt -> CoreExpr -> UnfoldingCache -> UnfoldingGuidance -> Maybe CoreExpr tryUnfolding :: Logger -> UnfoldingOpts -> Int -> Id -> Bool -> [ArgSummary] -> CallCtxt -> CoreExpr -> UnfoldingCache -> UnfoldingGuidance -> Maybe CoreExpr tryUnfolding Logger logger UnfoldingOpts opts !Int case_depth Id id Bool lone_variable [ArgSummary] arg_infos CallCtxt cont_info CoreExpr unf_template UnfoldingCache unf_cache UnfoldingGuidance guidance = case UnfoldingGuidance guidance of UnfoldingGuidance UnfNever -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (String -> SDoc forall doc. IsLine doc => String -> doc text String "UnfNever") Maybe CoreExpr forall a. Maybe a Nothing UnfWhen { ug_arity :: UnfoldingGuidance -> Int ug_arity = Int uf_arity, ug_unsat_ok :: UnfoldingGuidance -> Bool ug_unsat_ok = Bool unsat_ok, ug_boring_ok :: UnfoldingGuidance -> Bool ug_boring_ok = Bool boring_ok } | Bool enough_args Bool -> Bool -> Bool && (Bool boring_ok Bool -> Bool -> Bool || Bool some_benefit Bool -> Bool -> Bool || UnfoldingOpts -> Bool unfoldingVeryAggressive UnfoldingOpts opts) -- See Note [INLINE for small functions] (3) -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc forall doc. IsOutput doc => doc empty Bool True) (CoreExpr -> Maybe CoreExpr forall a. a -> Maybe a Just CoreExpr unf_template) | Bool otherwise -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc forall doc. IsOutput doc => doc empty Bool False) Maybe CoreExpr forall a. Maybe a Nothing where some_benefit :: Bool some_benefit = Int -> Bool calc_some_benefit Int uf_arity enough_args :: Bool enough_args = (Int n_val_args Int -> Int -> Bool forall a. Ord a => a -> a -> Bool >= Int uf_arity) Bool -> Bool -> Bool || (Bool unsat_ok Bool -> Bool -> Bool && Int n_val_args Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0) UnfIfGoodArgs { ug_args :: UnfoldingGuidance -> [Int] ug_args = [Int] arg_discounts, ug_res :: UnfoldingGuidance -> Int ug_res = Int res_discount, ug_size :: UnfoldingGuidance -> Int ug_size = Int size } | UnfoldingOpts -> Bool unfoldingVeryAggressive UnfoldingOpts opts -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc extra_doc Bool True) (CoreExpr -> Maybe CoreExpr forall a. a -> Maybe a Just CoreExpr unf_template) | Bool is_wf Bool -> Bool -> Bool && Bool some_benefit Bool -> Bool -> Bool && Bool small_enough -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc extra_doc Bool True) (CoreExpr -> Maybe CoreExpr forall a. a -> Maybe a Just CoreExpr unf_template) | Bool otherwise -> Logger -> UnfoldingOpts -> Id -> String -> SDoc -> Maybe CoreExpr -> Maybe CoreExpr forall a. Logger -> UnfoldingOpts -> Id -> String -> SDoc -> a -> a traceInline Logger logger UnfoldingOpts opts Id id String str (Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc extra_doc Bool False) Maybe CoreExpr forall a. Maybe a Nothing where some_benefit :: Bool some_benefit = Int -> Bool calc_some_benefit ([Int] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [Int] arg_discounts) -- See Note [Avoid inlining into deeply nested cases] depth_treshold :: Int depth_treshold = UnfoldingOpts -> Int unfoldingCaseThreshold UnfoldingOpts opts depth_scaling :: Int depth_scaling = UnfoldingOpts -> Int unfoldingCaseScaling UnfoldingOpts opts depth_penalty :: Int depth_penalty | Int case_depth Int -> Int -> Bool forall a. Ord a => a -> a -> Bool <= Int depth_treshold = Int 0 | Bool otherwise = (Int size Int -> Int -> Int forall a. Num a => a -> a -> a * (Int case_depth Int -> Int -> Int forall a. Num a => a -> a -> a - Int depth_treshold)) Int -> Int -> Int forall a. Integral a => a -> a -> a `div` Int depth_scaling adjusted_size :: Int adjusted_size = Int size Int -> Int -> Int forall a. Num a => a -> a -> a + Int depth_penalty Int -> Int -> Int forall a. Num a => a -> a -> a - Int discount small_enough :: Bool small_enough = Int adjusted_size Int -> Int -> Bool forall a. Ord a => a -> a -> Bool <= UnfoldingOpts -> Int unfoldingUseThreshold UnfoldingOpts opts discount :: Int discount = [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int computeDiscount [Int] arg_discounts Int res_discount [ArgSummary] arg_infos CallCtxt cont_info extra_doc :: SDoc extra_doc = [SDoc] -> SDoc forall doc. IsDoc doc => [doc] -> doc vcat [ String -> SDoc forall doc. IsLine doc => String -> doc text String "case depth =" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Int -> SDoc forall doc. IsLine doc => Int -> doc int Int case_depth , String -> SDoc forall doc. IsLine doc => String -> doc text String "depth based penalty =" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Int -> SDoc forall doc. IsLine doc => Int -> doc int Int depth_penalty , String -> SDoc forall doc. IsLine doc => String -> doc text String "discounted size =" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Int -> SDoc forall doc. IsLine doc => Int -> doc int Int adjusted_size ] where -- Unpack the UnfoldingCache lazily because it may not be needed, and all -- its fields are strict; so evaluating unf_cache at all forces all the -- isWorkFree etc computations to take place. That risks wasting effort for -- Ids that are never going to inline anyway. -- See Note [UnfoldingCache] in GHC.Core UnfoldingCache{ uf_is_work_free :: UnfoldingCache -> Bool uf_is_work_free = Bool is_wf, uf_expandable :: UnfoldingCache -> Bool uf_expandable = Bool is_exp } = UnfoldingCache unf_cache mk_doc :: Bool -> SDoc -> Bool -> SDoc mk_doc Bool some_benefit SDoc extra_doc Bool yes_or_no = [SDoc] -> SDoc forall doc. IsDoc doc => [doc] -> doc vcat [ String -> SDoc forall doc. IsLine doc => String -> doc text String "arg infos" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> [ArgSummary] -> SDoc forall a. Outputable a => a -> SDoc ppr [ArgSummary] arg_infos , String -> SDoc forall doc. IsLine doc => String -> doc text String "interesting continuation" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> CallCtxt -> SDoc forall a. Outputable a => a -> SDoc ppr CallCtxt cont_info , String -> SDoc forall doc. IsLine doc => String -> doc text String "some_benefit" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Bool -> SDoc forall a. Outputable a => a -> SDoc ppr Bool some_benefit , String -> SDoc forall doc. IsLine doc => String -> doc text String "is exp:" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Bool -> SDoc forall a. Outputable a => a -> SDoc ppr Bool is_exp , String -> SDoc forall doc. IsLine doc => String -> doc text String "is work-free:" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> Bool -> SDoc forall a. Outputable a => a -> SDoc ppr Bool is_wf , String -> SDoc forall doc. IsLine doc => String -> doc text String "guidance" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> UnfoldingGuidance -> SDoc forall a. Outputable a => a -> SDoc ppr UnfoldingGuidance guidance , SDoc extra_doc , String -> SDoc forall doc. IsLine doc => String -> doc text String "ANSWER =" SDoc -> SDoc -> SDoc forall doc. IsLine doc => doc -> doc -> doc <+> if Bool yes_or_no then String -> SDoc forall doc. IsLine doc => String -> doc text String "YES" else String -> SDoc forall doc. IsLine doc => String -> doc text String "NO"] ctx :: SDocContext ctx = LogFlags -> SDocContext log_default_dump_context (Logger -> LogFlags logFlags Logger logger) str :: String str = String "Considering inlining: " String -> String -> String forall a. [a] -> [a] -> [a] ++ SDocContext -> SDoc -> String showSDocOneLine SDocContext ctx (Id -> SDoc forall a. Outputable a => a -> SDoc ppr Id id) n_val_args :: Int n_val_args = [ArgSummary] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [ArgSummary] arg_infos -- some_benefit is used when the RHS is small enough -- and the call has enough (or too many) value -- arguments (ie n_val_args >= arity). But there must -- be *something* interesting about some argument, or the -- result context, to make it worth inlining calc_some_benefit :: Arity -> Bool -- The Arity is the number of args -- expected by the unfolding calc_some_benefit :: Int -> Bool calc_some_benefit Int uf_arity | Bool -> Bool not Bool saturated = Bool interesting_args -- Under-saturated -- Note [Unsaturated applications] | Bool otherwise = Bool interesting_args -- Saturated or over-saturated Bool -> Bool -> Bool || Bool interesting_call where saturated :: Bool saturated = Int n_val_args Int -> Int -> Bool forall a. Ord a => a -> a -> Bool >= Int uf_arity over_saturated :: Bool over_saturated = Int n_val_args Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int uf_arity interesting_args :: Bool interesting_args = (ArgSummary -> Bool) -> [ArgSummary] -> Bool forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool any ArgSummary -> Bool nonTriv [ArgSummary] arg_infos -- NB: (any nonTriv arg_infos) looks at the -- over-saturated args too which is "wrong"; -- but if over-saturated we inline anyway. interesting_call :: Bool interesting_call | Bool over_saturated = Bool True | Bool otherwise = case CallCtxt cont_info of CallCtxt CaseCtxt -> Bool -> Bool not (Bool lone_variable Bool -> Bool -> Bool && Bool is_exp) -- Note [Lone variables] CallCtxt ValAppCtxt -> Bool True -- Note [Cast then apply] CallCtxt RuleArgCtxt -> Int uf_arity Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 -- See Note [RHS of lets] CallCtxt DiscArgCtxt -> Int uf_arity Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 -- Note [Inlining in ArgCtxt] RhsCtxt RecFlag NonRecursive -> Int uf_arity Int -> Int -> Bool forall a. Ord a => a -> a -> Bool > Int 0 -- See Note [RHS of lets] CallCtxt _other -> Bool False -- See Note [Nested functions] {- Note [RHS of lets] ~~~~~~~~~~~~~~~~~~~~~ When the call is the argument of a function with a RULE, or the RHS of a let, we are a little bit keener to inline (in tryUnfolding). For example f y = (y,y,y) g y = let x = f y in ...(case x of (a,b,c) -> ...) ... We'd inline 'f' if the call was in a case context, and it kind-of-is, only we can't see it. Also x = f v could be expensive whereas x = case v of (a,b) -> a is patently cheap and may allow more eta expansion. So, in `interesting_call` in `tryUnfolding`, we treat the RHS of a /non-recursive/ let as not-totally-boring. A /recursive/ let isn't going be inlined so there is much less point. Hence the (only reason for the) RecFlag in RhsCtxt Note [Unsaturated applications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When a call is not saturated, we *still* inline if one of the arguments has interesting structure. That's sometimes very important. A good example is the Ord instance for Bool in Base: Rec { $fOrdBool =GHC.Classes.D:Ord @ Bool ... $cmin_ajX $cmin_ajX [Occ=LoopBreaker] :: Bool -> Bool -> Bool $cmin_ajX = GHC.Classes.$dmmin @ Bool $fOrdBool } But the defn of GHC.Classes.$dmmin is: $dmmin :: forall a. GHC.Classes.Ord a => a -> a -> a {- Arity: 3, HasNoCafRefs, Strictness: SLL, Unfolding: (\ @ a $dOrd :: GHC.Classes.Ord a x :: a y :: a -> case @ a GHC.Classes.<= @ a $dOrd x y of wild { GHC.Types.False -> y GHC.Types.True -> x }) -} We *really* want to inline $dmmin, even though it has arity 3, in order to unravel the recursion. Note [Things to watch] ~~~~~~~~~~~~~~~~~~~~~~ * { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... } Assume x is exported, so not inlined unconditionally. Then we want x to inline unconditionally; no reason for it not to, and doing so avoids an indirection. * { x = I# 3; ....f x.... } Make sure that x does not inline unconditionally! Lest we get extra allocation. Note [Nested functions] ~~~~~~~~~~~~~~~~~~~~~~~ At one time we treated a call of a non-top-level function as "interesting" (regardless of how boring the context) in the hope that inlining it would eliminate the binding, and its allocation. Specifically, in the default case of interesting_call we had _other -> not is_top && uf_arity > 0 But actually postInlineUnconditionally does some of this and overall it makes virtually no difference to nofib. So I simplified away this special case Note [Cast then apply] ~~~~~~~~~~~~~~~~~~~~~~ Consider myIndex = __inline_me ( (/\a. <blah>) |> 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 (arity > 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: arguably, we should inline in ArgCtxt only if the result of the call is at least CONLIKE. At least for the cases where we use ArgCtxt for the RHS of a 'let', we only profit from the inlining if we get a CONLIKE thing (modulo lets). Note [Lone variables] ~~~~~~~~~~~~~~~~~~~~~ See also Note [Interaction of exprIsWorkFree and lone variables] which appears below The "lone-variable" case is important. I spent ages messing about with unsatisfactory variants, but this is nice. The idea is that if a variable appears all alone as an arg of lazy fn, or rhs BoringCtxt as scrutinee of a case CaseCtxt as arg of a fn ArgCtxt AND it is bound to a cheap expression then we should not inline it (unless there is some other reason, e.g. it is the sole occurrence). That is what is happening at the use of 'lone_variable' in 'interesting_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, provided the RHS is "expandable" (see Note [exprIsExpandable] in GHC.Core.Utils) the context can ``see'' the unfolding of the variable (e.g. case or a RULE) so there's no gain. However, watch out: * Consider this: foo = \n. [n]) {-# INLINE foo #-} bar = foo 20 {-# INLINE bar #-} 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. So the non-inlining of lone_variables should only apply if the unfolding is regarded as expandable; because that is when exprIsConApp_maybe looks through the unfolding. Hence the "&& is_exp" in the CaseCtxt branch of interesting_call * 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 Note [Interaction of exprIsWorkFree and lone variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The lone-variable test says "don't inline if a case expression scrutinises a lone variable whose unfolding is cheap". It's very important that, under these circumstances, exprIsConApp_maybe can spot a constructor application. So, for example, we don't consider let x = e in (x,x) to be cheap, and that's good because exprIsConApp_maybe doesn't think that expression is a constructor application. In the 'not (lone_variable && is_wf)' test, I used to test is_value rather than is_wf, which was utterly wrong, because the above expression responds True to exprIsHNF, which is what sets is_value. This kind of thing can occur if you have {-# INLINE foo #-} foo = let x = e in (x,x) which Roman did. -} computeDiscount :: [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int computeDiscount :: [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int computeDiscount [Int] arg_discounts Int res_discount [ArgSummary] arg_infos CallCtxt cont_info = Int 10 -- Discount of 10 because the result replaces the call -- so we count 10 for the function itself Int -> Int -> Int forall a. Num a => a -> a -> a + Int 10 Int -> Int -> Int forall a. Num a => a -> a -> a * [Int] -> Int forall a. [a] -> Int forall (t :: * -> *) a. Foldable t => t a -> Int length [Int] actual_arg_discounts -- Discount of 10 for each arg supplied, -- because the result replaces the call Int -> Int -> Int forall a. Num a => a -> a -> a + Int total_arg_discount Int -> Int -> Int forall a. Num a => a -> a -> a + Int res_discount' where actual_arg_discounts :: [Int] actual_arg_discounts = (Int -> ArgSummary -> Int) -> [Int] -> [ArgSummary] -> [Int] forall a b c. (a -> b -> c) -> [a] -> [b] -> [c] zipWith Int -> ArgSummary -> Int forall {a}. Num a => a -> ArgSummary -> a mk_arg_discount [Int] arg_discounts [ArgSummary] arg_infos total_arg_discount :: Int total_arg_discount = [Int] -> Int forall a. Num a => [a] -> a forall (t :: * -> *) a. (Foldable t, Num a) => t a -> a sum [Int] actual_arg_discounts mk_arg_discount :: a -> ArgSummary -> a mk_arg_discount a _ ArgSummary TrivArg = a 0 mk_arg_discount a _ ArgSummary NonTrivArg = a 10 mk_arg_discount a discount ArgSummary ValueArg = a discount res_discount' :: Int res_discount' | Ordering LT <- [Int] arg_discounts [Int] -> [ArgSummary] -> Ordering forall a b. [a] -> [b] -> Ordering `compareLength` [ArgSummary] arg_infos = Int res_discount -- Over-saturated | Bool otherwise = case CallCtxt cont_info of CallCtxt BoringCtxt -> Int 0 CallCtxt CaseCtxt -> Int res_discount -- Presumably a constructor CallCtxt ValAppCtxt -> Int res_discount -- Presumably a function CallCtxt _ -> Int 40 Int -> Int -> Int forall a. Ord a => a -> a -> a `min` Int res_discount -- ToDo: this 40 `min` res_discount doesn't seem right -- for DiscArgCtxt it shouldn't matter because the function will -- get the arg discount for any non-triv arg -- for RuleArgCtxt we do want to be keener to inline; but not only -- constructor results -- for RhsCtxt I suppose that exposing a data con is good in general -- And 40 seems very arbitrary -- -- res_discount can be very large when a function returns -- constructors; 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 avoid inlining large functions that return -- constructors into contexts that are simply "interesting"