-calcU%
+%
% (c) The University of Glasgow 2006
% (c) The AQUA Project, Glasgow University, 1994-1998
%
Unfolding, UnfoldingGuidance, -- Abstract types
noUnfolding, mkImplicitUnfolding,
- mkTopUnfolding, mkUnfolding, mkCoreUnfolding,
- mkInlineRule, mkWwInlineRule,
+ mkUnfolding, mkCoreUnfolding,
+ mkTopUnfolding, mkSimpleUnfolding,
+ mkInlineUnfolding, mkInlinableUnfolding, mkWwInlineRule,
mkCompulsoryUnfolding, mkDFunUnfolding,
interestingArg, ArgSummary(..),
import DynFlags
import CoreSyn
import PprCore () -- Instances
+import TcType ( tcSplitSigmaTy, tcSplitDFunHead )
import OccurAnal
import CoreSubst hiding( substTy )
import CoreFVs ( exprFreeVars )
+import CoreArity ( manifestArity, exprBotStrictness_maybe )
import CoreUtils
import Id
import DataCon
import FastTypes
import FastString
import Outputable
-
+import Data.Maybe
\end{code}
%************************************************************************
\begin{code}
-mkTopUnfolding :: CoreExpr -> Unfolding
-mkTopUnfolding expr = mkUnfolding True {- Top level -} expr
+mkTopUnfolding :: Bool -> CoreExpr -> Unfolding
+mkTopUnfolding = mkUnfolding InlineRhs True {- Top level -}
mkImplicitUnfolding :: CoreExpr -> Unfolding
-- For implicit Ids, do a tiny bit of optimising first
-mkImplicitUnfolding expr = mkTopUnfolding (simpleOptExpr expr)
+mkImplicitUnfolding expr = mkTopUnfolding False (simpleOptExpr expr)
-- Note [Top-level flag on inline rules]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- top-level flag to True. It gets set more accurately by the simplifier
-- Simplify.simplUnfolding.
-mkUnfolding :: Bool -> CoreExpr -> Unfolding
-mkUnfolding top_lvl expr
- = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
- uf_src = InlineRhs,
- uf_arity = arity,
- uf_is_top = top_lvl,
- uf_is_value = exprIsHNF expr,
- uf_is_conlike = exprIsConLike expr,
- uf_expandable = exprIsExpandable expr,
- uf_is_cheap = is_cheap,
- uf_guidance = guidance }
- where
- is_cheap = exprIsCheap expr
- (arity, guidance) = calcUnfoldingGuidance is_cheap 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. And it should be rare, because large
- -- let-bound things that are dead are usually caught by preInlineUnconditionally
+mkSimpleUnfolding :: CoreExpr -> Unfolding
+mkSimpleUnfolding = mkUnfolding InlineRhs False False
-mkCoreUnfolding :: Bool -> UnfoldingSource -> CoreExpr
- -> Arity -> UnfoldingGuidance -> Unfolding
--- Occurrence-analyses the expression before capturing it
-mkCoreUnfolding top_lvl src expr arity guidance
- = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
- uf_src = src,
- uf_arity = arity,
- uf_is_top = top_lvl,
- uf_is_value = exprIsHNF expr,
- uf_is_conlike = exprIsConLike expr,
- uf_is_cheap = exprIsCheap expr,
- uf_expandable = exprIsExpandable expr,
- uf_guidance = guidance }
-
-mkDFunUnfolding :: DataCon -> [Id] -> Unfolding
-mkDFunUnfolding con ops = DFunUnfolding con (map Var ops)
+mkDFunUnfolding :: Type -> [CoreExpr] -> Unfolding
+mkDFunUnfolding dfun_ty ops
+ = DFunUnfolding dfun_nargs data_con ops
+ where
+ (tvs, theta, head_ty) = tcSplitSigmaTy dfun_ty
+ -- NB: tcSplitSigmaTy: do not look through a newtype
+ -- when the dictionary type is a newtype
+ (cls, _) = tcSplitDFunHead head_ty
+ dfun_nargs = length tvs + length theta
+ data_con = classDataCon cls
mkWwInlineRule :: Id -> CoreExpr -> Arity -> Unfolding
mkWwInlineRule id expr arity
- = mkCoreUnfolding True (InlineWrapper id)
+ = mkCoreUnfolding (InlineWrapper id) True
(simpleOptExpr expr) arity
(UnfWhen unSaturatedOk boringCxtNotOk)
mkCompulsoryUnfolding :: CoreExpr -> Unfolding
mkCompulsoryUnfolding expr -- Used for things that absolutely must be unfolded
- = mkCoreUnfolding True InlineCompulsory
+ = mkCoreUnfolding InlineCompulsory True
expr 0 -- Arity of unfolding doesn't matter
(UnfWhen unSaturatedOk boringCxtOk)
-mkInlineRule :: Bool -> CoreExpr -> Arity -> Unfolding
-mkInlineRule unsat_ok expr arity
- = mkCoreUnfolding True InlineRule -- Note [Top-level flag on inline rules]
- expr' arity
+mkInlineUnfolding :: Maybe Arity -> CoreExpr -> Unfolding
+mkInlineUnfolding mb_arity expr
+ = mkCoreUnfolding InlineStable
+ True -- Note [Top-level flag on inline rules]
+ expr' arity
(UnfWhen unsat_ok boring_ok)
where
expr' = simpleOptExpr expr
+ (unsat_ok, arity) = case mb_arity of
+ Nothing -> (unSaturatedOk, manifestArity expr')
+ Just ar -> (needSaturated, ar)
+
boring_ok = case calcUnfoldingGuidance True -- Treat as cheap
+ False -- But not bottoming
(arity+1) expr' of
(_, UnfWhen _ boring_ok) -> boring_ok
_other -> boringCxtNotOk
-- See Note [INLINE for small functions]
+
+mkInlinableUnfolding :: CoreExpr -> Unfolding
+mkInlinableUnfolding expr
+ = mkUnfolding InlineStable True is_bot expr'
+ where
+ expr' = simpleOptExpr expr
+ is_bot = isJust (exprBotStrictness_maybe expr')
\end{code}
+Internal functions
+
+\begin{code}
+mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr
+ -> Arity -> UnfoldingGuidance -> Unfolding
+-- Occurrence-analyses the expression before capturing it
+mkCoreUnfolding src top_lvl expr arity guidance
+ = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
+ uf_src = src,
+ uf_arity = arity,
+ uf_is_top = top_lvl,
+ uf_is_value = exprIsHNF expr,
+ uf_is_conlike = exprIsConLike expr,
+ uf_is_cheap = exprIsCheap expr,
+ uf_expandable = exprIsExpandable expr,
+ uf_guidance = guidance }
+
+mkUnfolding :: UnfoldingSource -> Bool -> Bool -> CoreExpr -> Unfolding
+-- Calculates unfolding guidance
+-- Occurrence-analyses the expression before capturing it
+mkUnfolding src top_lvl is_bottoming expr
+ = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr,
+ uf_src = src,
+ uf_arity = arity,
+ uf_is_top = top_lvl,
+ uf_is_value = exprIsHNF expr,
+ uf_is_conlike = exprIsConLike expr,
+ uf_expandable = exprIsExpandable expr,
+ uf_is_cheap = is_cheap,
+ uf_guidance = guidance }
+ where
+ is_cheap = exprIsCheap expr
+ (arity, guidance) = calcUnfoldingGuidance is_cheap (top_lvl && is_bottoming)
+ 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. And it should be rare, because large
+ -- let-bound things that are dead are usually caught by preInlineUnconditionally
+\end{code}
%************************************************************************
%* *
calcUnfoldingGuidance
:: Bool -- True <=> the rhs is cheap, or we want to treat it
-- as cheap (INLINE things)
+ -> Bool -- True <=> this is a top-level unfolding for a
+ -- diverging function; don't inline this
-> Int -- Bomb out if size gets bigger than this
-> CoreExpr -- Expression to look at
-> (Arity, UnfoldingGuidance)
-calcUnfoldingGuidance expr_is_cheap bOMB_OUT_SIZE expr
+calcUnfoldingGuidance expr_is_cheap top_bot bOMB_OUT_SIZE expr
= case collectBinders expr of { (bndrs, body) ->
let
val_bndrs = filter isId bndrs
= case (sizeExpr (iUnbox bOMB_OUT_SIZE) val_bndrs body) of
TooBig -> UnfNever
SizeIs size cased_bndrs scrut_discount
- | uncondInline n_val_bndrs (iBox size) && expr_is_cheap
- -> UnfWhen needSaturated boringCxtOk
+ | uncondInline n_val_bndrs (iBox size)
+ , expr_is_cheap
+ -> UnfWhen unSaturatedOk boringCxtOk -- Note [INLINE for small functions]
+ | top_bot -- See Note [Do not inline top-level bottoming functions]
+ -> UnfNever
| otherwise
-> UnfIfGoodArgs { ug_args = map (discount cased_bndrs) val_bndrs
a function call to account for. Notice also that constructor applications
are very cheap, because exposing them to a caller is so valuable.
-Note [Unconditional inlining]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We inline *unconditionally* if inlined thing is smaller (using sizeExpr)
-than the thing it's replacing. Notice that
+
+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 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:
+
+ * 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.
+ It's very important not to unconditionally replace a variable by
+ a non-atomic term.
+
+* 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.
+
+* However, when the function's arity > 0, we do insist that it
+ has at least one value argument at the call site. 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!
+
\begin{code}
uncondInline :: Arity -> Int -> Bool
-- Inline unconditionally if there no size increase
-- Size of call is arity (+1 for the function)
--- See Note [Unconditional inlining]
+-- See Note [INLINE for small functions]
uncondInline arity size
| arity == 0 = size == 0
| otherwise = size <= arity + 1
-- discounts even on nullary constructors
size_up (App fun (Type _)) = size_up fun
- size_up (App fun arg) = size_up_app fun [arg]
- `addSize` nukeScrutDiscount (size_up arg)
+ size_up (App fun arg) = size_up arg `addSizeNSD`
+ size_up_app fun [arg]
size_up (Lam b e) | isId b = lamScrutDiscount (size_up e `addSizeN` 1)
| otherwise = size_up e
size_up (Let (NonRec binder rhs) body)
- = nukeScrutDiscount (size_up rhs) `addSize`
- size_up body `addSizeN`
+ = size_up rhs `addSizeNSD`
+ 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
+ = foldr (addSizeNSD . size_up . snd)
+ (size_up body `addSizeN` length pairs) -- (length pairs) for the allocation
+ pairs
size_up (Case (Var v) _ _ alts)
| v `elem` top_args -- We are scrutinising an argument variable
- = alts_size (foldr1 addSize alt_sizes) -- The 1 is for the case itself
+ = alts_size (foldr1 addAltSize alt_sizes)
(foldr1 maxSize alt_sizes)
-- Good to inline if an arg is scrutinised, because
-- that may eliminate allocation in the caller
-- 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(2) +# tot -# max)) `unionBags` tot_disc) max_scrut
+ alts_size (SizeIs tot tot_disc tot_scrut) -- Size of all alternatives
+ (SizeIs max _ _) -- Size of biggest alternative
+ = SizeIs tot (unitBag (v, iBox (_ILIT(2) +# tot -# max)) `unionBags` tot_disc) 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
alts_size tot_size _ = tot_size
- size_up (Case e _ _ alts) = foldr (addSize . size_up_alt)
- (nukeScrutDiscount (size_up e))
- alts
+ size_up (Case e _ _ alts) = size_up e `addSizeNSD`
+ foldr (addAltSize . 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
-- size_up_app is used when there's ONE OR MORE value args
size_up_app (App fun arg) args
| isTypeArg arg = size_up_app fun args
- | otherwise = size_up_app fun (arg:args)
- `addSize` nukeScrutDiscount (size_up arg)
+ | otherwise = size_up arg `addSizeNSD`
+ size_up_app fun (arg:args)
size_up_app (Var fun) args = size_up_call fun args
size_up_app other args = size_up other `addSizeN` length args
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)
- = mkSizeIs bOMB_OUT_SIZE (n1 +# n2) (xs `unionBags` ys) (d1 +# d2)
+ -- addAltSize is used to add the sizes of case alternatives
+ addAltSize TooBig _ = TooBig
+ addAltSize _ TooBig = TooBig
+ addAltSize (SizeIs n1 xs d1) (SizeIs n2 ys d2)
+ = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
+ (xs `unionBags` ys)
+ (d1 +# 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 TooBig _ = TooBig
+ addSizeNSD _ TooBig = TooBig
+ addSizeNSD (SizeIs n1 xs _) (SizeIs n2 ys d2)
+ = mkSizeIs bOMB_OUT_SIZE (n1 +# n2)
+ (xs `unionBags` ys)
+ d2 -- Ignore d1
\end{code}
\begin{code}
conSize :: DataCon -> Int -> ExprSize
conSize dc n_val_args
- | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables
+ | n_val_args == 0 = SizeIs (_ILIT(0)) emptyBag (_ILIT(1)) -- Like variables
+
+-- See Note [Constructor size]
| isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (iUnbox n_val_args +# _ILIT(1))
- | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
- -- Treat a constructors application as size 1, 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.
- --
- -- 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
+-- See Note [Unboxed tuple result discount]
+-- | isUnboxedTupleCon dc = SizeIs (_ILIT(0)) emptyBag (_ILIT(0))
+
+-- See Note [Constructor size]
+ | otherwise = SizeIs (_ILIT(1)) emptyBag (iUnbox n_val_args +# _ILIT(1))
+\end{code}
+
+Note [Constructor size]
+~~~~~~~~~~~~~~~~~~~~~~~
+Treat a constructors application as size 1, 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.
+
+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.
+
+Note [Unboxed tuple result discount]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+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.
+
+\begin{code}
primOpSize :: PrimOp -> Int -> ExprSize
primOpSize op n_val_args
| not (primOpIsDupable op) = sizeN opt_UF_DearOp
-- Ditto (augment t (\cn -> e) ys) should cost only the cost of
-- e plus ys. The -2 accounts for the \cn
-nukeScrutDiscount :: ExprSize -> ExprSize
-nukeScrutDiscount (SizeIs n vs _) = SizeIs n vs (_ILIT(0))
-nukeScrutDiscount TooBig = TooBig
-
-- When we return a lambda, give a discount if it's used (applied)
lamScrutDiscount :: ExprSize -> ExprSize
lamScrutDiscount (SizeIs n vs _) = SizeIs n vs (iUnbox opt_UF_FunAppDiscount)
lamScrutDiscount TooBig = TooBig
\end{code}
+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 thesholds are defined in main/StaticFlags,
\begin{code}
couldBeSmallEnoughToInline :: Int -> CoreExpr -> Bool
couldBeSmallEnoughToInline threshold rhs
- = case calcUnfoldingGuidance False threshold rhs of
- (_, UnfNever) -> False
- _ -> True
+ = case sizeExpr (iUnbox threshold) [] body of
+ TooBig -> False
+ _ -> True
+ where
+ (_, body) = collectBinders rhs
----------------
smallEnoughToInline :: Unfolding -> Bool
NoUnfolding -> Nothing ;
OtherCon _ -> Nothing ;
DFunUnfolding {} -> Nothing ; -- Never unfold a DFun
- CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top, uf_is_value = is_value,
+ CoreUnfolding { uf_tmpl = unf_template, uf_is_top = is_top,
uf_is_cheap = is_cheap, uf_arity = uf_arity, uf_guidance = guidance } ->
-- uf_arity will typically be equal to (idArity id),
-- but may be less for InlineRules
interesting_saturated_call
= case cont_info of
- BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]
- CaseCtxt -> not (lone_variable && is_value) -- Note [Lone variables]
- ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt]
- ValAppCtxt -> True -- Note [Cast then apply]
+ BoringCtxt -> not is_top && uf_arity > 0 -- Note [Nested functions]
+ CaseCtxt -> not (lone_variable && is_cheap) -- Note [Lone variables]
+ ArgCtxt {} -> uf_arity > 0 -- Note [Inlining in ArgCtxt]
+ ValAppCtxt -> True -- Note [Cast then apply]
(yes_or_no, extra_doc)
= case guidance of
UnfNever -> (False, empty)
- UnfWhen unsat_ok boring_ok -> ( (unsat_ok || saturated)
- && (boring_ok || some_benefit)
- , empty )
- -- For the boring_ok part see Note [INLINE for small functions]
+ UnfWhen unsat_ok boring_ok
+ -> (enough_args && (boring_ok || some_benefit), empty )
+ where -- See Note [INLINE for small functions]
+ enough_args = saturated || (unsat_ok && n_val_args > 0)
UnfIfGoodArgs { ug_args = arg_discounts, ug_res = res_discount, ug_size = size }
-> ( is_cheap && some_benefit && small_enough
res_discount arg_infos cont_info
in
- if dopt Opt_D_dump_inlinings dflags then
+ if (dopt Opt_D_dump_inlinings dflags && dopt Opt_D_verbose_core2core dflags) then
pprTrace ("Considering inlining: " ++ showSDoc (ppr id))
(vcat [text "arg infos" <+> ppr arg_infos,
text "uf arity" <+> ppr uf_arity,
text "interesting continuation" <+> ppr cont_info,
text "some_benefit" <+> ppr some_benefit,
- text "is value:" <+> ppr is_value,
text "is cheap:" <+> ppr is_cheap,
text "guidance" <+> ppr guidance,
extra_doc,
{- 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.Bool.False -> y GHC.Bool.True -> x }) -}
+ 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 [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. (We do so if there is no INLINE
-pragma!)
-
-
Note [Things to watch]
~~~~~~~~~~~~~~~~~~~~~~
* { y = I# 3; x = y `cast` co; ...case (x `cast` co) of ... }
for the RHS of a 'let', we only profit from the inlining if we get a
CONLIKE thing (modulo lets).
-Note [Lone variables]
-~~~~~~~~~~~~~~~~~~~~~
+Note [Lone variables] See also Note [Interaction of exprIsCheap and lone variables]
+~~~~~~~~~~~~~~~~~~~~~ which appears below
The "lone-variable" case is important. I spent ages messing about
with unsatisfactory varaints, but this is nice. The idea is that if a
variable appears all alone
as scrutinee of a case CaseCtxt
as arg of a fn ArgCtxt
AND
- it is bound to a value
+ it is bound to a cheap expression
then we should not inline it (unless there is some other reason,
e.g. is is the sole occurrence). That is what is happening at
There's no advantage in inlining f here, and perhaps
a significant disadvantage. Hence some_val_args in the Stop case
+Note [Interaction of exprIsCheap and lone variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The lone-variable test says "don't inline if a case expression
+scrutines 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.
+
+I used to test is_value rather than is_cheap, which was utterly
+wrong, because the above expression responds True to exprIsHNF.
+
+This kind of thing can occur if you have
+
+ {-# INLINE foo #-}
+ foo = let x = e in (x,x)
+
+which Roman did.
+
\begin{code}
computeDiscount :: Int -> [Int] -> Int -> [ArgSummary] -> CallCtxt -> Int
computeDiscount n_vals_wanted arg_discounts res_discount arg_infos cont_info
go (Note _ a) n = go a n
go (Cast e _) n = go e n
go (Lam v e) n
- | isTyVar v = go e n
+ | isTyCoVar v = go e n
| n>0 = go e (n-1)
| otherwise = ValueArg
go (Let _ e) n = case go e n of { ValueArg -> ValueArg; _ -> NonTrivArg }
-- where t1..tk are the *universally-qantified* type args of 'dc'
exprIsConApp_maybe :: IdUnfoldingFun -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr])
-exprIsConApp_maybe id_unf (Note _ expr)
+exprIsConApp_maybe id_unf (Note note expr)
+ | notSccNote note
= exprIsConApp_maybe id_unf expr
- -- We ignore all notes. For example,
+ -- We ignore all notes except SCCs. For example,
-- case _scc_ "foo" (C a b) of
-- C a b -> e
- -- should be optimised away, but it will be only if we look
- -- through the SCC note.
+ -- should not be optimised away, because we'll lose the
+ -- entry count on 'foo'; see Trac #4414
exprIsConApp_maybe id_unf (Cast expr co)
= -- Here we do the KPush reduction rule as described in the FC paper
analyse (Var fun) args
| Just con <- isDataConWorkId_maybe fun
- , is_saturated
+ , count isValArg args == idArity fun
, let (univ_ty_args, rest_args) = splitAtList (dataConUnivTyVars con) args
= Just (con, stripTypeArgs univ_ty_args, rest_args)
-- Look through dictionary functions; see Note [Unfolding DFuns]
- | DFunUnfolding con ops <- unfolding
- , is_saturated
+ | DFunUnfolding dfun_nargs con ops <- unfolding
+ , let sat = length args == dfun_nargs -- See Note [DFun arity check]
+ in if sat then True else
+ pprTrace "Unsaturated dfun" (ppr fun <+> int dfun_nargs $$ ppr args) False
, let (dfun_tvs, _cls, dfun_res_tys) = tcSplitDFunTy (idType fun)
subst = zipOpenTvSubst dfun_tvs (stripTypeArgs (takeList dfun_tvs args))
= Just (con, substTys subst dfun_res_tys,
-- Look through unfoldings, but only cheap ones, because
-- we are effectively duplicating the unfolding
- | CoreUnfolding { uf_expandable = expand_me, uf_tmpl = rhs } <- unfolding
- , expand_me = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
- analyse rhs args
+ | Just rhs <- expandUnfolding_maybe unfolding
+ = -- pprTrace "expanding" (ppr fun $$ ppr rhs) $
+ analyse rhs args
where
- is_saturated = count isValArg args == idArity fun
- unfolding = id_unf fun -- Does not look through loop breakers
- -- ToDo: we *may* look through variables that are NOINLINE
- -- in this phase, and that is really not right
+ unfolding = id_unf fun
analyse _ _ = Nothing
-----------
- in_scope = mkInScopeSet (exprFreeVars expr)
-
- -----------
beta (Lam v body) pairs (arg : args)
| isTypeArg arg
= beta body ((v,arg):pairs) args
= Nothing
beta fun pairs args
- = case analyse (substExpr subst fun) args of
- Nothing -> -- pprTrace "Bale out! exprIsConApp_maybe" doc $
- Nothing
- Just ans -> -- pprTrace "Woo-hoo! exprIsConApp_maybe" doc $
- Just ans
+ = analyse (substExpr (text "subst-expr-is-con-app") subst fun) args
where
- subst = mkOpenSubst in_scope pairs
+ subst = mkOpenSubst (mkInScopeSet (exprFreeVars fun)) pairs
-- doc = vcat [ppr fun, ppr expr, ppr pairs, ppr args]
to the very same args as the dfun. It takes a little more work
to compute the type arguments to the dictionary constructor.
+Note [DFun arity check]
+~~~~~~~~~~~~~~~~~~~~~~~
+Here we check that the total number of supplied arguments (inclding
+type args) matches what the dfun is expecting. This may be *less*
+than the ordinary arity of the dfun: see Note [DFun unfoldings] in CoreSyn
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