[Git][ghc/ghc][master] 2 commits: Remove OneShotInfo field of LFReEntrant, document OneShotInfo
Marge Bot
gitlab at gitlab.haskell.org
Fri May 1 01:35:35 UTC 2020
Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
05b0a9fd by Ömer Sinan Ağacan at 2020-04-30T21:35:24-04:00
Remove OneShotInfo field of LFReEntrant, document OneShotInfo
The field is only used in withNewTickyCounterFun and it's easier to
directly pass a parameter for one-shot info to withNewTickyCounterFun
instead of passing it via LFReEntrant. This also makes !2842 simpler.
Other changes:
- New Note (by SPJ) [OneShotInfo overview] added.
- Arity argument of thunkCode removed as it's always 0.
- - - - -
a43620c6 by Ömer Sinan Ağacan at 2020-04-30T21:35:24-04:00
GHC.StgToCmm.Ticky: remove a few unused stuff
- - - - -
4 changed files:
- compiler/GHC/StgToCmm/Bind.hs
- compiler/GHC/StgToCmm/Closure.hs
- compiler/GHC/StgToCmm/Ticky.hs
- compiler/GHC/Types/Basic.hs
Changes:
=====================================
compiler/GHC/StgToCmm/Bind.hs
=====================================
@@ -111,7 +111,7 @@ cgTopRhsClosure dflags rec id ccs upd_flag args body =
(_, _, fv_details) = mkVirtHeapOffsets dflags header []
-- Don't drop the non-void args until the closure info has been made
; forkClosureBody (closureCodeBody True id closure_info ccs
- (nonVoidIds args) (length args) body fv_details)
+ args body fv_details)
; return () }
@@ -358,8 +358,8 @@ mkRhsClosure dflags bndr cc fvs upd_flag args body
-- forkClosureBody: (a) ensure that bindings in here are not seen elsewhere
-- (b) ignore Sequel from context; use empty Sequel
-- And compile the body
- closureCodeBody False bndr closure_info cc (nonVoidIds args)
- (length args) body fv_details
+ closureCodeBody False bndr closure_info cc args
+ body fv_details
-- BUILD THE OBJECT
-- ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
@@ -436,8 +436,7 @@ closureCodeBody :: Bool -- whether this is a top-level binding
-> Id -- the closure's name
-> ClosureInfo -- Lots of information about this closure
-> CostCentreStack -- Optional cost centre attached to closure
- -> [NonVoid Id] -- incoming args to the closure
- -> Int -- arity, including void args
+ -> [Id] -- incoming args to the closure
-> CgStgExpr
-> [(NonVoid Id, ByteOff)] -- the closure's free vars
-> FCode ()
@@ -452,31 +451,32 @@ closureCodeBody :: Bool -- whether this is a top-level binding
normal form, so there is no need to set up an update frame.
-}
-closureCodeBody top_lvl bndr cl_info cc _args arity body fv_details
- | arity == 0 -- No args i.e. thunk
+-- No args i.e. thunk
+closureCodeBody top_lvl bndr cl_info cc [] body fv_details
= withNewTickyCounterThunk
(isStaticClosure cl_info)
(closureUpdReqd cl_info)
(closureName cl_info) $
emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl [] $
- \(_, node, _) -> thunkCode cl_info fv_details cc node arity body
+ \(_, node, _) -> thunkCode cl_info fv_details cc node body
where
lf_info = closureLFInfo cl_info
info_tbl = mkCmmInfo cl_info bndr cc
-closureCodeBody top_lvl bndr cl_info cc args arity body fv_details
- = -- Note: args may be [], if all args are Void
- withNewTickyCounterFun
- (closureSingleEntry cl_info)
- (closureName cl_info)
- args $ do {
+closureCodeBody top_lvl bndr cl_info cc args@(arg0:_) body fv_details
+ = let nv_args = nonVoidIds args
+ arity = length args
+ in
+ -- See Note [OneShotInfo overview] in GHC.Types.Basic.
+ withNewTickyCounterFun (isOneShotBndr arg0) (closureName cl_info)
+ nv_args $ do {
; let
lf_info = closureLFInfo cl_info
info_tbl = mkCmmInfo cl_info bndr cc
-- Emit the main entry code
- ; emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl args $
+ ; emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl nv_args $
\(_offset, node, arg_regs) -> do
-- Emit slow-entry code (for entering a closure through a PAP)
{ mkSlowEntryCode bndr cl_info arg_regs
@@ -565,15 +565,15 @@ mkSlowEntryCode bndr cl_info arg_regs -- function closure is already in `Node'
-----------------------------------------
thunkCode :: ClosureInfo -> [(NonVoid Id, ByteOff)] -> CostCentreStack
- -> LocalReg -> Int -> CgStgExpr -> FCode ()
-thunkCode cl_info fv_details _cc node arity body
+ -> LocalReg -> CgStgExpr -> FCode ()
+thunkCode cl_info fv_details _cc node body
= do { dflags <- getDynFlags
; let node_points = nodeMustPointToIt dflags (closureLFInfo cl_info)
node' = if node_points then Just node else Nothing
; ldvEnterClosure cl_info (CmmLocal node) -- NB: Node always points when profiling
-- Heap overflow check
- ; entryHeapCheck cl_info node' arity [] $ do
+ ; entryHeapCheck cl_info node' 0 [] $ do
{ -- Overwrite with black hole if necessary
-- but *after* the heap-overflow check
; tickyEnterThunk cl_info
=====================================
compiler/GHC/StgToCmm/Closure.hs
=====================================
@@ -48,7 +48,7 @@ module GHC.StgToCmm.Closure (
-- ** Predicates
-- These are really just functions on LambdaFormInfo
- closureUpdReqd, closureSingleEntry,
+ closureUpdReqd,
closureReEntrant, closureFunInfo,
isToplevClosure,
@@ -201,7 +201,6 @@ argPrimRep arg = typePrimRep1 (stgArgType arg)
data LambdaFormInfo
= LFReEntrant -- Reentrant closure (a function)
TopLevelFlag -- True if top level
- OneShotInfo
!RepArity -- Arity. Invariant: always > 0
!Bool -- True <=> no fvs
ArgDescr -- Argument descriptor (should really be in ClosureInfo)
@@ -285,8 +284,7 @@ mkLFReEntrant :: TopLevelFlag -- True of top level
mkLFReEntrant _ _ [] _
= pprPanic "mkLFReEntrant" empty
mkLFReEntrant top fvs args arg_descr
- = LFReEntrant top os_info (length args) (null fvs) arg_descr
- where os_info = idOneShotInfo (head args)
+ = LFReEntrant top (length args) (null fvs) arg_descr
-------------
mkLFThunk :: Type -> TopLevelFlag -> [Id] -> UpdateFlag -> LambdaFormInfo
@@ -335,7 +333,7 @@ mkLFImported id
-- the id really does point directly to the constructor
| arity > 0
- = LFReEntrant TopLevel noOneShotInfo arity True (panic "arg_descr")
+ = LFReEntrant TopLevel arity True (panic "arg_descr")
| otherwise
= mkLFArgument id -- Not sure of exact arity
@@ -384,9 +382,9 @@ tagForArity dflags arity
lfDynTag :: DynFlags -> LambdaFormInfo -> DynTag
-- Return the tag in the low order bits of a variable bound
-- to this LambdaForm
-lfDynTag dflags (LFCon con) = tagForCon dflags con
-lfDynTag dflags (LFReEntrant _ _ arity _ _) = tagForArity dflags arity
-lfDynTag _ _other = 0
+lfDynTag dflags (LFCon con) = tagForCon dflags con
+lfDynTag dflags (LFReEntrant _ arity _ _) = tagForArity dflags arity
+lfDynTag _ _other = 0
-----------------------------------------------------------------------------
@@ -407,11 +405,11 @@ isLFReEntrant _ = False
-----------------------------------------------------------------------------
lfClosureType :: LambdaFormInfo -> ClosureTypeInfo
-lfClosureType (LFReEntrant _ _ arity _ argd) = Fun arity argd
-lfClosureType (LFCon con) = Constr (dataConTagZ con)
- (dataConIdentity con)
-lfClosureType (LFThunk _ _ _ is_sel _) = thunkClosureType is_sel
-lfClosureType _ = panic "lfClosureType"
+lfClosureType (LFReEntrant _ arity _ argd) = Fun arity argd
+lfClosureType (LFCon con) = Constr (dataConTagZ con)
+ (dataConIdentity con)
+lfClosureType (LFThunk _ _ _ is_sel _) = thunkClosureType is_sel
+lfClosureType _ = panic "lfClosureType"
thunkClosureType :: StandardFormInfo -> ClosureTypeInfo
thunkClosureType (SelectorThunk off) = ThunkSelector off
@@ -431,7 +429,7 @@ nodeMustPointToIt :: DynFlags -> LambdaFormInfo -> Bool
-- this closure has R1 (the "Node" register) pointing to the
-- closure itself --- the "self" argument
-nodeMustPointToIt _ (LFReEntrant top _ _ no_fvs _)
+nodeMustPointToIt _ (LFReEntrant top _ no_fvs _)
= not no_fvs -- Certainly if it has fvs we need to point to it
|| isNotTopLevel top -- See Note [GC recovery]
-- For lex_profiling we also access the cost centre for a
@@ -566,7 +564,7 @@ getCallMethod dflags _ id _ n_args v_args _cg_loc
-- self-recursive tail calls] in GHC.StgToCmm.Expr for more details
= JumpToIt block_id args
-getCallMethod dflags name id (LFReEntrant _ _ arity _ _) n_args _v_args _cg_loc
+getCallMethod dflags name id (LFReEntrant _ arity _ _) n_args _v_args _cg_loc
_self_loop_info
| n_args == 0 -- No args at all
&& not (gopt Opt_SccProfilingOn dflags)
@@ -811,11 +809,6 @@ lfUpdatable :: LambdaFormInfo -> Bool
lfUpdatable (LFThunk _ _ upd _ _) = upd
lfUpdatable _ = False
-closureSingleEntry :: ClosureInfo -> Bool
-closureSingleEntry (ClosureInfo { closureLFInfo = LFThunk _ _ upd _ _}) = not upd
-closureSingleEntry (ClosureInfo { closureLFInfo = LFReEntrant _ OneShotLam _ _ _}) = True
-closureSingleEntry _ = False
-
closureReEntrant :: ClosureInfo -> Bool
closureReEntrant (ClosureInfo { closureLFInfo = LFReEntrant {} }) = True
closureReEntrant _ = False
@@ -824,8 +817,8 @@ closureFunInfo :: ClosureInfo -> Maybe (RepArity, ArgDescr)
closureFunInfo (ClosureInfo { closureLFInfo = lf_info }) = lfFunInfo lf_info
lfFunInfo :: LambdaFormInfo -> Maybe (RepArity, ArgDescr)
-lfFunInfo (LFReEntrant _ _ arity _ arg_desc) = Just (arity, arg_desc)
-lfFunInfo _ = Nothing
+lfFunInfo (LFReEntrant _ arity _ arg_desc) = Just (arity, arg_desc)
+lfFunInfo _ = Nothing
funTag :: DynFlags -> ClosureInfo -> DynTag
funTag dflags (ClosureInfo { closureLFInfo = lf_info })
@@ -834,9 +827,9 @@ funTag dflags (ClosureInfo { closureLFInfo = lf_info })
isToplevClosure :: ClosureInfo -> Bool
isToplevClosure (ClosureInfo { closureLFInfo = lf_info })
= case lf_info of
- LFReEntrant TopLevel _ _ _ _ -> True
- LFThunk TopLevel _ _ _ _ -> True
- _other -> False
+ LFReEntrant TopLevel _ _ _ -> True
+ LFThunk TopLevel _ _ _ _ -> True
+ _other -> False
--------------------------------------
-- Label generation
=====================================
compiler/GHC/StgToCmm/Ticky.hs
=====================================
@@ -82,27 +82,22 @@ module GHC.StgToCmm.Ticky (
tickyHeapCheck,
tickyStackCheck,
- tickyUnknownCall, tickyDirectCall,
+ tickyDirectCall,
tickyPushUpdateFrame,
tickyUpdateFrameOmitted,
tickyEnterDynCon,
- tickyEnterStaticCon,
- tickyEnterViaNode,
tickyEnterFun,
- tickyEnterThunk, tickyEnterStdThunk, -- dynamic non-value
- -- thunks only
+ tickyEnterThunk,
tickyEnterLNE,
tickyUpdateBhCaf,
- tickyBlackHole,
tickyUnboxedTupleReturn,
tickyReturnOldCon, tickyReturnNewCon,
- tickyKnownCallTooFewArgs, tickyKnownCallExact, tickyKnownCallExtraArgs,
- tickySlowCall, tickySlowCallPat,
+ tickySlowCall
) where
import GHC.Prelude
@@ -276,10 +271,8 @@ tickyUpdateFrameOmitted = ifTicky $ bumpTickyCounter (fsLit "UPDF_OMITTED_ctr")
-- bump of name-specific ticky counter into. On the other hand, we can
-- still track allocation their allocation.
-tickyEnterDynCon, tickyEnterStaticCon, tickyEnterViaNode :: FCode ()
-tickyEnterDynCon = ifTicky $ bumpTickyCounter (fsLit "ENT_DYN_CON_ctr")
-tickyEnterStaticCon = ifTicky $ bumpTickyCounter (fsLit "ENT_STATIC_CON_ctr")
-tickyEnterViaNode = ifTicky $ bumpTickyCounter (fsLit "ENT_VIA_NODE_ctr")
+tickyEnterDynCon :: FCode ()
+tickyEnterDynCon = ifTicky $ bumpTickyCounter (fsLit "ENT_DYN_CON_ctr")
tickyEnterThunk :: ClosureInfo -> FCode ()
tickyEnterThunk cl_info
@@ -291,7 +284,7 @@ tickyEnterThunk cl_info
registerTickyCtrAtEntryDyn ticky_ctr_lbl
bumpTickyEntryCount ticky_ctr_lbl }
where
- updatable = closureSingleEntry cl_info
+ updatable = not (closureUpdReqd cl_info)
static = isStaticClosure cl_info
ctr | static = if updatable then fsLit "ENT_STATIC_THK_SINGLE_ctr"
@@ -299,16 +292,6 @@ tickyEnterThunk cl_info
| otherwise = if updatable then fsLit "ENT_DYN_THK_SINGLE_ctr"
else fsLit "ENT_DYN_THK_MANY_ctr"
-tickyEnterStdThunk :: ClosureInfo -> FCode ()
-tickyEnterStdThunk = tickyEnterThunk
-
-tickyBlackHole :: Bool{-updatable-} -> FCode ()
-tickyBlackHole updatable
- = ifTicky (bumpTickyCounter ctr)
- where
- ctr | updatable = (fsLit "UPD_BH_SINGLE_ENTRY_ctr")
- | otherwise = (fsLit "UPD_BH_UPDATABLE_ctr")
-
tickyUpdateBhCaf :: ClosureInfo -> FCode ()
tickyUpdateBhCaf cl_info
= ifTicky (bumpTickyCounter ctr)
=====================================
compiler/GHC/Types/Basic.hs
=====================================
@@ -243,13 +243,80 @@ instance Outputable Alignment where
************************************************************************
-}
+{-
+Note [OneShotInfo overview]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Lambda-bound Ids (and only lambda-bound Ids) may be decorated with
+one-shot info. The idea is that if we see
+ (\x{one-shot}. e)
+it means that this lambda will only be applied once. In particular
+that means we can float redexes under the lambda without losing
+work. For example, consider
+ let t = expensive in
+ (\x{one-shot}. case t of { True -> ...; False -> ... })
+
+Because it's a one-shot lambda, we can safely inline t, giving
+ (\x{one_shot}. case <expensive> of of
+ { True -> ...; False -> ... })
+
+Moving parts:
+
+* Usage analysis, performed as part of demand-analysis, finds
+ out whether functions call their argument once. Consider
+ f g x = Just (case g x of { ... })
+
+ Here 'f' is lazy in 'g', but it guarantees to call it no
+ more than once. So g will get a C1(U) usage demand.
+
+* Occurrence analysis propagates this usage information
+ (in the demand signature of a function) to its calls.
+ Example, given 'f' above
+ f (\x.e) blah
+
+ Since f's demand signature says it has a C1(U) usage demand on its
+ first argument, the occurrence analyser sets the \x to be one-shot.
+ This is done via the occ_one_shots field of OccEnv.
+
+* Float-in and float-out take account of one-shot-ness
+
+* Occurrence analysis doesn't set "inside-lam" for occurrences inside
+ a one-shot lambda
+
+Other notes
+
+* A one-shot lambda can use its argument many times. To elaborate
+ the example above
+ let t = expensive in
+ (\x{one-shot}. case t of { True -> x+x; False -> x*x })
+
+ Here the '\x' is one-shot, which justifies inlining 't',
+ but x is used many times. That's absolutely fine.
+
+* It's entirely possible to have
+ (\x{one-shot}. \y{many-shot}. e)
+
+ For example
+ let t = expensive
+ g = \x -> let v = x+t in
+ \y -> x + v
+ in map (g 5) xs
+
+ Here the `\x` is a one-shot binder: `g` is applied to one argument
+ exactly once. And because the `\x` is one-shot, it would be fine to
+ float that `let t = expensive` binding inside the `\x`.
+
+ But the `\y` is most definitely not one-shot!
+-}
+
-- | If the 'Id' is a lambda-bound variable then it may have lambda-bound
-- variable info. Sometimes we know whether the lambda binding this variable
--- is a \"one-shot\" lambda; that is, whether it is applied at most once.
+-- is a "one-shot" lambda; that is, whether it is applied at most once.
--
-- This information may be useful in optimisation, as computations may
-- safely be floated inside such a lambda without risk of duplicating
-- work.
+--
+-- See also Note [OneShotInfo overview] above.
data OneShotInfo
= NoOneShotInfo -- ^ No information
| OneShotLam -- ^ The lambda is applied at most once.
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/99ff8145044288a8a58c8028516903937ba3935c...a43620c621563deed76ba6b417e3a7a707c15d23
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/99ff8145044288a8a58c8028516903937ba3935c...a43620c621563deed76ba6b417e3a7a707c15d23
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