%
-% (c) The AQUA Project, Glasgow University, 1994-1996
+% (c) The AQUA Project, Glasgow University, 1994-1998
%
\section[CoreUnfold]{Core-syntax unfoldings}
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 @SimpleUnfolding@ unfolding, you will
+literal''). In the corner of a @CoreUnfolding@ unfolding, you will
find, unsurprisingly, a Core expression.
\begin{code}
module CoreUnfold (
- SimpleUnfolding(..), Unfolding(..), UnfoldingGuidance(..), -- types
+ Unfolding, UnfoldingGuidance, -- Abstract types
- FormSummary(..), mkFormSummary, whnfOrBottom, exprSmallEnoughToDup,
- exprIsTrivial,
+ noUnfolding, mkTopUnfolding, mkUnfolding, mkCompulsoryUnfolding, seqUnfolding,
+ evaldUnfolding, mkOtherCon, otherCons,
+ unfoldingTemplate, maybeUnfoldingTemplate,
+ isEvaldUnfolding, isValueUnfolding, isCheapUnfolding, isCompulsoryUnfolding,
+ hasUnfolding, hasSomeUnfolding, neverUnfold,
- noUnfolding, mkMagicUnfolding, mkUnfolding, getUnfoldingTemplate,
+ couldBeSmallEnoughToInline,
+ certainlyWillInline,
- smallEnoughToInline, couldBeSmallEnoughToInline,
- certainlySmallEnoughToInline, inlineUnconditionally,
-
- calcUnfoldingGuidance,
-
- PragmaInfo(..) -- Re-export
+ callSiteInline
) where
#include "HsVersions.h"
-import {-# SOURCE #-} MagicUFs ( MagicUnfoldingFun, mkMagicUnfoldingFun )
-
-import CmdLineOpts ( opt_UnfoldingCreationThreshold,
- opt_UnfoldingUseThreshold,
- opt_UnfoldingConDiscount,
- opt_UnfoldingKeenessFactor
- )
-import Constants ( uNFOLDING_CHEAP_OP_COST,
- uNFOLDING_DEAR_OP_COST,
- uNFOLDING_NOREP_LIT_COST
+import StaticFlags ( opt_UF_CreationThreshold, opt_UF_UseThreshold,
+ opt_UF_FunAppDiscount, opt_UF_KeenessFactor,
+ opt_UF_DearOp,
)
-import BinderInfo ( BinderInfo, isOneFunOcc, isOneSafeFunOcc
- )
-import PragmaInfo ( PragmaInfo(..) )
+import DynFlags ( DynFlags, DynFlag(..), dopt )
import CoreSyn
-import CoreUtils ( unTagBinders )
-import OccurAnal ( occurAnalyseGlobalExpr )
-import CoreUtils ( coreExprType )
-import Id ( Id, idType, getIdArity, isBottomingId, isDataCon,
- idWantsToBeINLINEd, idMustBeINLINEd, idMustNotBeINLINEd,
- IdSet, GenId{-instances-} )
-import PrimOp ( fragilePrimOp, primOpCanTriggerGC )
-import IdInfo ( ArityInfo(..) )
-import Literal ( isNoRepLit )
-import TyCon ( tyConFamilySize )
-import Type ( splitAlgTyConApp_maybe )
-import Unique ( Unique )
-import Util ( isIn, panic, assertPanic )
+import PprCore ( pprCoreExpr )
+import OccurAnal ( occurAnalyseExpr )
+import CoreUtils ( exprIsValue, exprIsCheap, exprIsTrivial )
+import Id ( Id, idType, isId,
+ idUnfolding, globalIdDetails
+ )
+import DataCon ( isUnboxedTupleCon )
+import Literal ( litSize )
+import PrimOp ( primOpIsDupable, primOpOutOfLine )
+import IdInfo ( OccInfo(..), GlobalIdDetails(..) )
+import Type ( isUnLiftedType )
+import PrelNames ( hasKey, buildIdKey, augmentIdKey )
+import Bag
+import FastTypes
import Outputable
+import Util
+
+#if __GLASGOW_HASKELL__ >= 404
+import GLAEXTS ( Int# )
+#endif
\end{code}
+
%************************************************************************
%* *
-\subsection{@Unfolding@ and @UnfoldingGuidance@ types}
+\subsection{Making unfoldings}
%* *
%************************************************************************
\begin{code}
-data Unfolding
- = NoUnfolding
-
- | CoreUnfolding SimpleUnfolding
-
- | MagicUnfolding
- Unique -- Unique of the Id whose magic unfolding this is
- MagicUnfoldingFun
-
-
-data SimpleUnfolding
- = SimpleUnfolding -- An unfolding with redundant cached information
- FormSummary -- Tells whether the template is a WHNF or bottom
- UnfoldingGuidance -- Tells about the *size* of the template.
- SimplifiableCoreExpr -- Template
-
-
-noUnfolding = NoUnfolding
-
-mkUnfolding inline_prag expr
- = let
- -- strictness mangling (depends on there being no CSE)
- ufg = calcUnfoldingGuidance inline_prag opt_UnfoldingCreationThreshold expr
- occ = occurAnalyseGlobalExpr expr
- cuf = CoreUnfolding (SimpleUnfolding (mkFormSummary expr) ufg occ)
-
- cont = case occ of { Var _ -> cuf; _ -> cuf }
- in
- case ufg of { UnfoldAlways -> cont; _ -> cont }
-
-mkMagicUnfolding :: Unique -> Unfolding
-mkMagicUnfolding tag = MagicUnfolding tag (mkMagicUnfoldingFun tag)
-
-getUnfoldingTemplate :: Unfolding -> CoreExpr
-getUnfoldingTemplate (CoreUnfolding (SimpleUnfolding _ _ expr))
- = unTagBinders expr
-getUnfoldingTemplate other = panic "getUnfoldingTemplate"
-
-
-data UnfoldingGuidance
- = UnfoldNever
- | UnfoldAlways -- There is no "original" definition,
- -- so you'd better unfold. Or: something
- -- so cheap to unfold (e.g., 1#) that
- -- you should do it absolutely always.
-
- | UnfoldIfGoodArgs Int -- if "m" type args
- Int -- and "n" value args
-
- [Int] -- Discount if the argument is evaluated.
- -- (i.e., a simplification will definitely
- -- be possible). One elt of the list per *value* arg.
-
- Int -- The "size" of the unfolding; to be elaborated
- -- later. ToDo
-
- Int -- Scrutinee discount: the discount to substract if the thing is in
- -- a context (case (thing args) of ...),
- -- (where there are the right number of arguments.)
-\end{code}
-
-\begin{code}
-instance Outputable UnfoldingGuidance where
- ppr UnfoldAlways = ptext SLIT("_ALWAYS_")
- ppr (UnfoldIfGoodArgs t v cs size discount)
- = hsep [ptext SLIT("_IF_ARGS_"), int t, int v,
- if null cs -- always print *something*
- then char 'X'
- else hcat (map (text . show) cs),
- int size,
- int discount ]
+mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
+
+mkUnfolding top_lvl expr
+ = CoreUnfolding (occurAnalyseExpr expr)
+ top_lvl
+
+ (exprIsValue expr)
+ -- Already evaluated
+
+ (exprIsCheap expr)
+ -- OK to inline inside a lambda
+
+ (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
+ -- Nevertheless, we don't occ-analyse before computing the size because the
+ -- size computation bales out after a while, whereas occurrence analysis does not.
+ --
+ -- This can occasionally mean that the guidance is very pessimistic;
+ -- it gets fixed up next round
+
+mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
+ = CompulsoryUnfolding (occurAnalyseExpr expr)
\end{code}
%************************************************************************
%* *
-\subsection{Figuring out things about expressions}
+\subsection{The UnfoldingGuidance type}
%* *
%************************************************************************
\begin{code}
-data FormSummary
- = VarForm -- Expression is a variable (or scc var, etc)
- | ValueForm -- Expression is a value: i.e. a value-lambda,constructor, or literal
- | BottomForm -- Expression is guaranteed to be bottom. We're more gung
- -- ho about inlining such things, because it can't waste work
- | OtherForm -- Anything else
-
-instance Outputable FormSummary where
- ppr VarForm = ptext SLIT("Var")
- ppr ValueForm = ptext SLIT("Value")
- ppr BottomForm = ptext SLIT("Bot")
- ppr OtherForm = ptext SLIT("Other")
-
-mkFormSummary ::GenCoreExpr bndr Id flexi -> FormSummary
-
-mkFormSummary expr
- = go (0::Int) expr -- The "n" is the number of (value) arguments so far
- where
- go n (Lit _) = ASSERT(n==0) ValueForm
- go n (Con _ _) = ASSERT(n==0) ValueForm
- go n (Prim _ _) = OtherForm
- go n (SCC _ e) = go n e
- go n (Coerce _ _ e) = go n e
-
- go n (Let (NonRec b r) e) | exprIsTrivial r = go n e -- let f = f' alpha in (f,g)
- -- should be treated as a value
- go n (Let _ e) = OtherForm
- go n (Case _ _) = OtherForm
-
- go 0 (Lam (ValBinder x) e) = ValueForm -- NB: \x.bottom /= bottom!
- go n (Lam (ValBinder x) e) = go (n-1) e -- Applied lambda
- go n (Lam other_binder e) = go n e
-
- go n (App fun arg) | isValArg arg = go (n+1) fun
- go n (App fun other_arg) = go n fun
-
- go n (Var f) | isBottomingId f = BottomForm
- | isDataCon f = ValueForm -- Can happen inside imported unfoldings
- go 0 (Var f) = VarForm
- go n (Var f) = case getIdArity f of
- ArityExactly a | n < a -> ValueForm
- ArityAtLeast a | n < a -> ValueForm
- other -> OtherForm
-
-whnfOrBottom :: FormSummary -> Bool
-whnfOrBottom VarForm = True
-whnfOrBottom ValueForm = True
-whnfOrBottom BottomForm = True
-whnfOrBottom OtherForm = False
-\end{code}
-
-@exprIsTrivial@ is true of expressions we are unconditionally happy to duplicate;
-simple variables and constants, and type applications.
-
-\begin{code}
-exprIsTrivial (Var v) = True
-exprIsTrivial (Lit lit) = not (isNoRepLit lit)
-exprIsTrivial (App e (TyArg _)) = exprIsTrivial e
-exprIsTrivial (Coerce _ _ e) = exprIsTrivial e
-exprIsTrivial other = False
-\end{code}
-
-\begin{code}
-exprSmallEnoughToDup (Con _ _) = True -- Could check # of args
-exprSmallEnoughToDup (Prim op _) = not (fragilePrimOp op) -- Could check # of args
-exprSmallEnoughToDup (Lit lit) = not (isNoRepLit lit)
-exprSmallEnoughToDup (Coerce _ _ e) = exprSmallEnoughToDup e
-exprSmallEnoughToDup expr
- = case (collectArgs expr) of { (fun, _, vargs) ->
- case fun of
- Var v | length vargs <= 4 -> True
- _ -> False
- }
-
+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}
-%************************************************************************
-%* *
-\subsection[calcUnfoldingGuidance]{Calculate ``unfolding guidance'' for an expression}
-%* *
-%************************************************************************
-
\begin{code}
calcUnfoldingGuidance
- :: PragmaInfo -- INLINE pragma stuff
- -> Int -- bomb out if size gets bigger than this
+ :: 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) ->
+ let
+ 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.
-calcUnfoldingGuidance IMustBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
-calcUnfoldingGuidance IWantToBeINLINEd bOMB_OUT_SIZE expr = UnfoldAlways -- Always inline if the INLINE pragma says so
-calcUnfoldingGuidance IMustNotBeINLINEd bOMB_OUT_SIZE expr = UnfoldNever -- ...and vice versa...
-
-calcUnfoldingGuidance NoPragmaInfo bOMB_OUT_SIZE expr
- = case collectBinders expr of { (ty_binders, val_binders, body) ->
- case (sizeExpr bOMB_OUT_SIZE val_binders body) of
+ in
+ case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_binders body) of
- TooBig -> UnfoldNever
+ 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
SizeIs size cased_args scrut_discount
-> UnfoldIfGoodArgs
- (length ty_binders)
- (length val_binders)
+ n_val_binders
(map discount_for val_binders)
- (I# size)
- (I# scrut_discount)
+ final_size
+ (iBox scrut_discount)
where
- discount_for b
- | is_data && b `is_elem` cased_args = tyConFamilySize tycon
- | otherwise = 0
- where
- (is_data, tycon)
- = case (splitAlgTyConApp_maybe (idType b)) of
- Nothing -> (False, panic "discount")
- Just (tc,_,_) -> (True, tc)
-
- is_elem = isIn "calcUnfoldingGuidance" }
+ 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 :: Int# -- Bomb out if it gets bigger than this
-> [Id] -- Arguments; we're interested in which of these
-- get case'd
-> CoreExpr
-> ExprSize
-sizeExpr (I# bOMB_OUT_SIZE) args expr
+sizeExpr bOMB_OUT_SIZE top_args expr
= size_up expr
where
- size_up (Var v) = sizeZero
- size_up (Lit lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
- | otherwise = sizeZero
-
- size_up (SCC lbl body) = size_up body -- SCCs cost nothing
- size_up (Coerce _ _ body) = size_up body -- Coercions cost nothing
-
- size_up (App fun arg) = size_up fun `addSize` size_up_arg arg
- -- NB Zero cost for for type applications;
- -- others cost 1 or more
-
- size_up (Con con args) = conSizeN (numValArgs args)
- -- We don't count 1 for the constructor because we're
- -- quite keen to get constructors into the open
-
- size_up (Prim op args) = sizeN op_cost -- NB: no charge for PrimOp args
- where
- op_cost = if primOpCanTriggerGC op
- then uNFOLDING_DEAR_OP_COST
- -- these *tend* to be more expensive;
- -- number chosen to avoid unfolding (HACK)
- else uNFOLDING_CHEAP_OP_COST
-
- size_up expr@(Lam _ _)
- = let
- (tyvars, args, body) = collectBinders expr
- in
- size_up body `addSizeN` length args
+ size_up (Type t) = sizeZero -- Types cost nothing
+ size_up (Var v) = sizeOne
- size_up (Let (NonRec binder rhs) body)
- = nukeScrutDiscount (size_up rhs)
- `addSize`
- size_up body
- `addSizeN`
- 1 -- For the allocation
+ 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 (Let (Rec pairs) body)
- = nukeScrutDiscount (foldr addSize sizeZero [size_up rhs | (_,rhs) <- pairs])
- `addSize`
- size_up body
- `addSizeN`
- length pairs -- For the allocation
-
- size_up (Case scrut alts)
- = nukeScrutDiscount (size_up scrut)
- `addSize`
- arg_discount scrut
- `addSize`
- size_up_alts (coreExprType scrut) alts
- -- We charge for the "case" itself in "size_up_alts"
+ size_up (Note _ body) = size_up body -- Other notes cost nothing
- ------------
- -- In an application we charge 0 for type application
- -- 1 for most anything else
- -- N for norep_lits
- size_up_arg (LitArg lit) | isNoRepLit lit = sizeN uNFOLDING_NOREP_LIT_COST
- size_up_arg (TyArg _) = sizeZero
- size_up_arg other = sizeOne
+ size_up (App fun (Type t)) = size_up fun
+ size_up (App fun arg) = size_up_app fun [arg]
- ------------
- size_up_alts scrut_ty (AlgAlts alts deflt)
- = (foldr (addSize . size_alg_alt) (size_up_deflt deflt) alts)
- `addSizeN`
- alt_cost
- where
- size_alg_alt (con,args,rhs) = size_up rhs
- -- Don't charge for args, so that wrappers look cheap
-
- -- NB: we charge N for an alg. "case", where N is
- -- the number of constructors in the thing being eval'd.
- -- (You'll eventually get a "discount" of N if you
- -- think the "case" is likely to go away.)
- -- It's important to charge for alternatives. If you don't then you
- -- get size 1 for things like:
- -- case x of { A -> 1#; B -> 2#; ... lots }
-
- alt_cost :: Int
- alt_cost
- = case (splitAlgTyConApp_maybe scrut_ty) of
- Nothing -> 1
- Just (tc,_,_) -> tyConFamilySize tc
-
- size_up_alts _ (PrimAlts alts deflt)
- = foldr (addSize . size_prim_alt) (size_up_deflt deflt) alts
- -- *no charge* for a primitive "case"!
- where
- size_prim_alt (lit,rhs) = size_up rhs
+ size_up (Lit lit) = sizeN (litSize lit)
- ------------
- size_up_deflt NoDefault = sizeZero
- size_up_deflt (BindDefault binder rhs) = size_up rhs
+ size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
+ | otherwise = size_up e
- ------------
- -- We want to record if we're case'ing an argument
- arg_discount (Var v) | v `is_elem` args = scrutArg v
- arg_discount other = sizeZero
+ size_up (Let (NonRec binder rhs) body)
+ = nukeScrutDiscount (size_up rhs) `addSize`
+ size_up body `addSizeN`
+ (if isUnLiftedType (idType binder) then 0 else 1)
+ -- For the allocation
+ -- If the binder has an unlifted type there is no allocation
+
+ size_up (Let (Rec pairs) body)
+ = nukeScrutDiscount rhs_size `addSize`
+ size_up body `addSizeN`
+ length pairs -- For the allocation
+ where
+ rhs_size = foldr (addSize . size_up . snd) sizeZero pairs
+
+ size_up (Case (Var v) _ _ alts)
+ | v `elem` top_args -- We are scrutinising an argument variable
+ =
+{- I'm nuking this special case; BUT see the comment with case alternatives.
+
+ (a) It's too eager. We don't want to inline a wrapper into a
+ context with no benefit.
+ E.g. \ x. f (x+x) no point in inlining (+) here!
+
+ (b) It's ineffective. Once g's wrapper is inlined, its case-expressions
+ aren't scrutinising arguments any more
+
+ case alts of
+
+ [alt] -> size_up_alt alt `addSize` SizeIs 0# (unitBag (v, 1)) 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:
+ -- f x = g x x
+ -- h y = ...(f e)...
+ -- If we inline g's wrapper, f looks big, and doesn't get inlined
+ -- into h; if we inline f first, while it looks small, then g's
+ -- wrapper will get inlined later anyway. To avoid this nasty
+ -- ordering difference, we make (case a of (x,y) -> ...),
+ -- *where a is one of the arguments* look free.
+
+ other ->
+-}
+ alts_size (foldr addSize sizeOne alt_sizes) -- The 1 is for the scrutinee
+ (foldr1 maxSize 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
+ alt_sizes = map size_up_alt alts
+
+ -- 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
+ -- 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
+ alts_size tot_size _ = tot_size
+
+-- gaw 2004
+ size_up (Case e _ _ alts) = nukeScrutDiscount (size_up e) `addSize`
+ foldr (addSize . size_up_alt) sizeZero alts
+ -- We don't charge for the case itself
+ -- It's a strict thing, and the price of the call
+ -- is paid by scrut. Also consider
+ -- case f x of DEFAULT -> e
+ -- This is just ';'! Don't charge for it.
+
+ ------------
+ size_up_app (App fun arg) args
+ | isTypeArg arg = size_up_app fun args
+ | otherwise = size_up_app fun (arg:args)
+ size_up_app fun args = foldr (addSize . nukeScrutDiscount . size_up)
+ (size_up_fun fun args)
+ args
+
+ -- A function application with at least one value argument
+ -- so if the function is an argument give it an arg-discount
+ --
+ -- Also behave specially if the function is a build
+ --
+ -- Also if the function is a constant Id (constr or primop)
+ -- compute discounts specially
+ size_up_fun (Var fun) args
+ | fun `hasKey` buildIdKey = buildSize
+ | fun `hasKey` augmentIdKey = augmentSize
+ | otherwise
+ = case globalIdDetails fun of
+ DataConWorkId dc -> conSizeN dc (valArgCount args)
+
+ FCallId fc -> 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
+ -- is applied to one of the function's arguments, but it's
+ -- not good. At the moment, any unlifted-type arg gets a
+ -- 'True' for 'yes I'm evald', so we collect the discount even
+ -- 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`
+ (1 + length (filter (not . exprIsTrivial) args))
+ -- The 1+ is for the function itself
+ -- Add 1 for each non-trivial arg;
+ -- the allocation cost, as in let(rec)
+ -- Slight hack here: for constructors the args are almost always
+ -- trivial; and for primops they are almost always prim typed
+ -- 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_alt (con, bndrs, rhs) = size_up rhs
+ -- Don't charge for args, so that wrappers look cheap
+ -- (See comments about wrappers with Case)
- is_elem :: Id -> [Id] -> Bool
- is_elem = isIn "size_up_scrut"
+ ------------
+ -- 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
------------
-- These addSize things have to be here because
-- I don't want to give them bOMB_OUT_SIZE as an argument
- addSizeN TooBig _ = TooBig
- addSizeN (SizeIs n xs d) (I# m)
- | n_tot -# d <# bOMB_OUT_SIZE = SizeIs n_tot xs d
- | otherwise = TooBig
- where
- n_tot = n +# m
+ addSizeN TooBig _ = TooBig
+ addSizeN (SizeIs n xs d) m = mkSizeIs bOMB_OUT_SIZE (n +# iUnbox m) xs d
- addSize TooBig _ = TooBig
- addSize _ TooBig = TooBig
- addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
- | (n_tot -# d_tot) <# bOMB_OUT_SIZE = SizeIs n_tot xys d_tot
- | otherwise = TooBig
- where
- n_tot = n1 +# n2
- d_tot = d1 +# d2
- xys = xs ++ ys
-
-
+ addSize TooBig _ = TooBig
+ addSize _ TooBig = TooBig
+ addSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
+ = mkSizeIs bOMB_OUT_SIZE (n1 +# n2) (xs `unionBags` ys) (d1 +# d2)
\end{code}
Code for manipulating sizes
\begin{code}
-
data ExprSize = TooBig
- | SizeIs Int# -- Size found
- [Id] -- Arguments cased herein
- Int# -- Size to subtract if result is scrutinised
- -- by a case expression
-
-sizeZero = SizeIs 0# [] 0#
-sizeOne = SizeIs 1# [] 0#
-sizeN (I# n) = SizeIs n [] 0#
-conSizeN (I# n) = SizeIs n [] n
-scrutArg v = SizeIs 0# [v] 0#
-
+ | SizeIs FastInt -- Size found
+ (Bag (Id,Int)) -- Arguments cased herein, and discount for each such
+ FastInt -- Size to subtract if result is scrutinised
+ -- by a case expression
+
+-- 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 max n xs d | (n -# d) ># max = TooBig
+ | otherwise = SizeIs n xs d
+
+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)
+conSizeN dc n
+ | 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,
+ -- which is the same as a lone variable; and hence 'v' will
+ -- always be replaced by (iBox x), where v is bound to iBox x.
+ --
+ -- 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
+
+primOpSize op n_args
+ | not (primOpIsDupable op) = sizeN opt_UF_DearOp
+ | not (primOpOutOfLine op) = sizeN (2 - n_args)
+ -- Be very keen to inline simple primops.
+ -- We give a discount of 1 for each arg so that (op# x y z) costs 2.
+ -- We can't make it cost 1, else we'll inline let v = (op# x y z)
+ -- at every use of v, which is excessive.
+ --
+ -- A good example is:
+ -- let x = +# p q in C {x}
+ -- Even though x get's an occurrence of 'many', its RHS looks cheap,
+ -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
+ | otherwise = sizeOne
+
+buildSize = SizeIs (-2#) emptyBag 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
+ -- 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 = SizeIs (-2#) emptyBag 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
+
+-- 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
\end{code}
+
%************************************************************************
%* *
\subsection[considerUnfolding]{Given all the info, do (not) do the unfolding}
is more accurate (see @sizeExpr@ above for how this discount size
is computed).
-\begin{code}
-smallEnoughToInline :: Id -- The function (for trace msg only)
- -> [Bool] -- Evaluated-ness of value arguments
- -> Bool -- Result is scrutinised
- -> UnfoldingGuidance
- -> Bool -- True => unfold it
-
-smallEnoughToInline _ _ _ UnfoldAlways = True
-smallEnoughToInline _ _ _ UnfoldNever = False
-smallEnoughToInline id arg_is_evald_s result_is_scruted
- (UnfoldIfGoodArgs m_tys_wanted n_vals_wanted discount_vec size scrut_discount)
- = if enough_args n_vals_wanted arg_is_evald_s &&
- size - discount <= opt_UnfoldingUseThreshold
- then
- -- pprTrace "small enough" (ppr id <+> int size <+> int discount)
- True
- else
- False
- where
-
- enough_args n [] | n > 0 = False -- A function with no value args => don't unfold
- enough_args _ _ = True -- Otherwise it's ok to try
-
- -- 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 *efficiency*
- -- to be gained (e.g. beta reductions, case reductions) by inlining.
- discount :: Int
- discount = round (
- opt_UnfoldingKeenessFactor *
- fromInt (args_discount + result_discount)
- )
-
- args_discount = sum (zipWith arg_discount discount_vec arg_is_evald_s)
- result_discount | result_is_scruted = scrut_discount
- | otherwise = 0
-
- arg_discount no_of_constrs is_evald
- | is_evald = no_of_constrs * opt_UnfoldingConDiscount
- | otherwise = 0
-\end{code}
-
We use this one 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.
\begin{code}
-couldBeSmallEnoughToInline :: Id -> UnfoldingGuidance -> Bool
-couldBeSmallEnoughToInline id guidance = smallEnoughToInline id (repeat True) True guidance
-
-certainlySmallEnoughToInline :: Id -> UnfoldingGuidance -> Bool
-certainlySmallEnoughToInline id guidance = smallEnoughToInline id (repeat False) False guidance
+couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
+couldBeSmallEnoughToInline threshold rhs = case calcUnfoldingGuidance threshold rhs of
+ UnfoldNever -> False
+ other -> True
+
+certainlyWillInline :: Unfolding -> Bool
+ -- Sees if the unfolding is pretty certain to inline
+certainlyWillInline (CoreUnfolding _ _ _ is_cheap (UnfoldIfGoodArgs n_vals _ size _))
+ = is_cheap && size - (n_vals +1) <= opt_UF_UseThreshold
+certainlyWillInline other
+ = False
\end{code}
-Predicates
-~~~~~~~~~~
+%************************************************************************
+%* *
+\subsection{callSiteInline}
+%* *
+%************************************************************************
-@inlineUnconditionally@ decides whether a let-bound thing can
-*definitely* be inlined at each of its call sites. If so, then
-we can drop the binding right away. But remember, you have to be
-certain that every use can be inlined. So, notably, any ArgOccs
-rule this out. Since ManyOcc doesn't record FunOcc/ArgOcc
+This is the key function. It decides whether to inline a variable at a call site
-\begin{code}
-inlineUnconditionally :: Bool -> (Id,BinderInfo) -> Bool
+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
-inlineUnconditionally ok_to_dup (id, occ_info)
- | idMustNotBeINLINEd id = False
+\begin{code}
+callSiteInline :: DynFlags
+ -> Bool -- True <=> the Id can be inlined
+ -> Bool -- 'inline' note at call site
+ -> OccInfo
+ -> Id -- The Id
+ -> [Bool] -- One for each value arg; True if it is interesting
+ -> Bool -- True <=> continuation is interesting
+ -> Maybe CoreExpr -- Unfolding, if any
+
+
+callSiteInline dflags active_inline inline_call occ id arg_infos interesting_cont
+ = case idUnfolding id of {
+ NoUnfolding -> Nothing ;
+ OtherCon cs -> Nothing ;
+
+ CompulsoryUnfolding unf_template -> Just unf_template ;
+ -- CompulsoryUnfolding => there is no top-level binding
+ -- for these things, so we must inline it.
+ -- Only a couple of primop-like things have
+ -- compulsory unfoldings (see MkId.lhs).
+ -- We don't allow them to be inactive
+
+ CoreUnfolding unf_template is_top is_value is_cheap 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 = case occ of
+ IAmDead -> pprTrace "callSiteInline: dead" (ppr id) False
+ IAmALoopBreaker -> False
+ OneOcc in_lam _ _ -> (not in_lam || is_cheap) && consider_safe True
+ other -> is_cheap && consider_safe False
+ -- we consider even the once-in-one-branch
+ -- occurrences, because they won't all have been
+ -- caught by preInlineUnconditionally. In particular,
+ -- if the occurrence is once inside a lambda, and the
+ -- rhs is cheap but not a manifest lambda, then
+ -- pre-inline will not have inlined it for fear of
+ -- invalidating the occurrence info in the rhs.
+
+ consider_safe once
+ -- consider_safe decides whether it's a good idea to
+ -- inline something, given that there's no
+ -- work-duplication issue (the caller checks that).
+ | inline_call = True
+
+ | otherwise
+ = case guidance of
+ UnfoldNever -> False
+ UnfoldIfGoodArgs n_vals_wanted arg_discounts size res_discount
+
+ | 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
+
+ where
+ some_benefit = or arg_infos || really_interesting_cont ||
+ (not is_top && (once || (n_vals_wanted > 0 && enough_args)))
+ -- 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
+ -- really_interesting_cont tells if the result of the
+ -- call is in an interesting context.
+
+ small_enough = (size - discount) <= opt_UF_UseThreshold
+ discount = computeDiscount n_vals_wanted arg_discounts res_discount
+ arg_infos really_interesting_cont
+
+ in
+ if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "Considering inlining"
+ (ppr id <+> vcat [text "active:" <+> ppr active_inline,
+ text "occ info:" <+> ppr occ,
+ 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"])
+ result
+ else
+ result
+ }
- | isOneFunOcc occ_info
- && idMustBeINLINEd id = True
+computeDiscount :: Int -> [Int] -> Int -> [Bool] -> Bool -> Int
+computeDiscount n_vals_wanted arg_discounts res_discount arg_infos result_used
+ -- 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
+ -- *efficiency* to be gained (e.g. beta reductions, case reductions)
+ -- by inlining.
+
+ -- we also discount 1 for each argument passed, because these will
+ -- reduce with the lambdas in the function (we count 1 for a lambda
+ -- in size_up).
+ = 1 + -- Discount of 1 because the result replaces the call
+ -- so we count 1 for the function itself
+ length (take n_vals_wanted arg_infos) +
+ -- Discount of 1 for each arg supplied, because the
+ -- result replaces the call
+ round (opt_UF_KeenessFactor *
+ fromIntegral (arg_discount + result_discount))
+ where
+ arg_discount = sum (zipWith mk_arg_discount arg_discounts arg_infos)
- | isOneSafeFunOcc (ok_to_dup || idWantsToBeINLINEd id) occ_info
- = True
+ mk_arg_discount discount is_evald | is_evald = discount
+ | otherwise = 0
- | otherwise
- = False
+ -- 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}