% % (c) The University of Glasgow 2006 % (c) The Univserity of Glasgow 1992-2004 % Data structures which describe closures, and operations over those data structures Nothing monadic in here Much of the rationale for these things is in the ``details'' part of the STG paper. \begin{code} {-# OPTIONS -fno-warn-tabs #-} -- The above warning supression flag is a temporary kludge. -- While working on this module you are encouraged to remove it and -- detab the module (please do the detabbing in a separate patch). See -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces -- for details module ClosureInfo ( ClosureInfo(..), LambdaFormInfo(..), -- would be abstract but StandardFormInfo(..), -- mkCmmInfo looks inside SMRep, ArgDescr(..), Liveness, C_SRT(..), needsSRT, mkLFThunk, mkLFReEntrant, mkConLFInfo, mkSelectorLFInfo, mkApLFInfo, mkLFImported, mkLFArgument, mkLFLetNoEscape, mkClosureInfo, mkConInfo, maybeIsLFCon, closureSize, ConTagZ, dataConTagZ, infoTableLabelFromCI, entryLabelFromCI, closureLabelFromCI, isLFThunk, closureUpdReqd, closureNeedsUpdSpace, closureIsThunk, closureSingleEntry, closureReEntrant, isConstrClosure_maybe, closureFunInfo, isKnownFun, funTag, funTagLFInfo, tagForArity, clHasCafRefs, enterIdLabel, enterReturnPtLabel, nodeMustPointToIt, CallMethod(..), getCallMethod, blackHoleOnEntry, staticClosureRequired, isToplevClosure, closureValDescr, closureTypeDescr, -- profiling isStaticClosure, cafBlackHoleClosureInfo, staticClosureNeedsLink, -- CgRep and its functions CgRep(..), nonVoidArg, argMachRep, primRepToCgRep, isFollowableArg, isVoidArg, isFloatingArg, is64BitArg, separateByPtrFollowness, cgRepSizeW, cgRepSizeB, retAddrSizeW, typeCgRep, idCgRep, tyConCgRep, ) where #include "../includes/MachDeps.h" #include "HsVersions.h" import StgSyn import SMRep import CLabel import Cmm import Unique import StaticFlags import Var import Id import IdInfo import DataCon import Name import Type import TypeRep import TcType import TyCon import BasicTypes import Outputable import FastString import Constants import DynFlags \end{code} %************************************************************************ %* * \subsection[ClosureInfo-datatypes]{Data types for closure information} %* * %************************************************************************ Information about a closure, from the code generator's point of view. A ClosureInfo decribes the info pointer of a closure. It has enough information a) to construct the info table itself b) to allocate a closure containing that info pointer (i.e. it knows the info table label) We make a ClosureInfo for - each let binding (both top level and not) - each data constructor (for its shared static and dynamic info tables) \begin{code} data ClosureInfo = ClosureInfo { closureName :: !Name, -- The thing bound to this closure closureLFInfo :: !LambdaFormInfo, -- NOTE: not an LFCon (see below) closureSMRep :: !SMRep, -- representation used by storage mgr closureSRT :: !C_SRT, -- What SRT applies to this closure closureType :: !Type, -- Type of closure (ToDo: remove) closureDescr :: !String, -- closure description (for profiling) closureInfLcl :: Bool -- can the info pointer be a local symbol? } -- Constructor closures don't have a unique info table label (they use -- the constructor's info table), and they don't have an SRT. | ConInfo { closureCon :: !DataCon, closureSMRep :: !SMRep } \end{code} %************************************************************************ %* * \subsubsection[LambdaFormInfo-datatype]{@LambdaFormInfo@: source-derivable info} %* * %************************************************************************ Information about an identifier, from the code generator's point of view. Every identifier is bound to a LambdaFormInfo in the environment, which gives the code generator enough info to be able to tail call or return that identifier. Note that a closure is usually bound to an identifier, so a ClosureInfo contains a LambdaFormInfo. \begin{code} data LambdaFormInfo = LFReEntrant -- Reentrant closure (a function) TopLevelFlag -- True if top level !Int -- Arity. Invariant: always > 0 !Bool -- True <=> no fvs ArgDescr -- Argument descriptor (should reall be in ClosureInfo) | LFCon -- A saturated constructor application DataCon -- The constructor | LFThunk -- Thunk (zero arity) TopLevelFlag !Bool -- True <=> no free vars !Bool -- True <=> updatable (i.e., *not* single-entry) StandardFormInfo !Bool -- True <=> *might* be a function type | LFUnknown -- Used for function arguments and imported things. -- We know nothing about this closure. Treat like -- updatable "LFThunk"... -- Imported things which we do know something about use -- one of the other LF constructors (eg LFReEntrant for -- known functions) !Bool -- True <=> *might* be a function type | LFLetNoEscape -- See LetNoEscape module for precise description of -- these "lets". !Int -- arity; | LFBlackHole -- Used for the closures allocated to hold the result -- of a CAF. We want the target of the update frame to -- be in the heap, so we make a black hole to hold it. ------------------------- -- StandardFormInfo tells whether this thunk has one of -- a small number of standard forms data StandardFormInfo = NonStandardThunk -- Not of of the standard forms | SelectorThunk -- A SelectorThunk is of form -- case x of -- con a1,..,an -> ak -- and the constructor is from a single-constr type. WordOff -- 0-origin offset of ak within the "goods" of -- constructor (Recall that the a1,...,an may be laid -- out in the heap in a non-obvious order.) | ApThunk -- An ApThunk is of form -- x1 ... xn -- The code for the thunk just pushes x2..xn on the stack and enters x1. -- There are a few of these (for 1 <= n <= MAX_SPEC_AP_SIZE) pre-compiled -- in the RTS to save space. Int -- Arity, n \end{code} %************************************************************************ %* * CgRep %* * %************************************************************************ An CgRep is an abstraction of a Type which tells the code generator all it needs to know about the calling convention for arguments (and results) of that type. In particular, the ArgReps of a function's arguments are used to decide which of the RTS's generic apply functions to call when applying an unknown function. It contains more information than the back-end data type MachRep, so one can easily convert from CgRep -> MachRep. (Except that there's no MachRep for a VoidRep.) It distinguishes pointers from non-pointers (we sort the pointers together when building closures) void from other types: a void argument is different from no argument All 64-bit types map to the same CgRep, because they're passed in the same register, but a PtrArg is still different from an NonPtrArg because the function's entry convention has to take into account the pointer-hood of arguments for the purposes of describing the stack on entry to the garbage collector. \begin{code} data CgRep = VoidArg -- Void | PtrArg -- Word-sized heap pointer, followed -- by the garbage collector | NonPtrArg -- Word-sized non-pointer -- (including addresses not followed by GC) | LongArg -- 64-bit non-pointer | FloatArg -- 32-bit float | DoubleArg -- 64-bit float deriving Eq instance Outputable CgRep where ppr VoidArg = ptext (sLit "V_") ppr PtrArg = ptext (sLit "P_") ppr NonPtrArg = ptext (sLit "I_") ppr LongArg = ptext (sLit "L_") ppr FloatArg = ptext (sLit "F_") ppr DoubleArg = ptext (sLit "D_") argMachRep :: CgRep -> CmmType argMachRep PtrArg = gcWord argMachRep NonPtrArg = bWord argMachRep LongArg = b64 argMachRep FloatArg = f32 argMachRep DoubleArg = f64 argMachRep VoidArg = panic "argMachRep:VoidRep" primRepToCgRep :: PrimRep -> CgRep primRepToCgRep VoidRep = VoidArg primRepToCgRep PtrRep = PtrArg primRepToCgRep IntRep = NonPtrArg primRepToCgRep WordRep = NonPtrArg primRepToCgRep Int64Rep = LongArg primRepToCgRep Word64Rep = LongArg primRepToCgRep AddrRep = NonPtrArg primRepToCgRep FloatRep = FloatArg primRepToCgRep DoubleRep = DoubleArg idCgRep :: Id -> CgRep idCgRep x = typeCgRep . idType $ x tyConCgRep :: TyCon -> CgRep tyConCgRep = primRepToCgRep . tyConPrimRep typeCgRep :: Type -> CgRep typeCgRep = primRepToCgRep . typePrimRep \end{code} Whether or not the thing is a pointer that the garbage-collector should follow. Or, to put it another (less confusing) way, whether the object in question is a heap object. Depending on the outcome, this predicate determines what stack the pointer/object possibly will have to be saved onto, and the computation of GC liveness info. \begin{code} isFollowableArg :: CgRep -> Bool -- True <=> points to a heap object isFollowableArg PtrArg = True isFollowableArg _ = False isVoidArg :: CgRep -> Bool isVoidArg VoidArg = True isVoidArg _ = False nonVoidArg :: CgRep -> Bool nonVoidArg VoidArg = False nonVoidArg _ = True -- isFloatingArg is used to distinguish @Double@ and @Float@ which -- cause inadvertent numeric conversions if you aren't jolly careful. -- See codeGen/CgCon:cgTopRhsCon. isFloatingArg :: CgRep -> Bool isFloatingArg DoubleArg = True isFloatingArg FloatArg = True isFloatingArg _ = False is64BitArg :: CgRep -> Bool is64BitArg LongArg = True is64BitArg _ = False \end{code} \begin{code} separateByPtrFollowness :: [(CgRep,a)] -> ([(CgRep,a)], [(CgRep,a)]) -- Returns (ptrs, non-ptrs) separateByPtrFollowness things = sep_things things [] [] -- accumulating params for follow-able and don't-follow things... where sep_things [] bs us = (reverse bs, reverse us) sep_things ((PtrArg,a):ts) bs us = sep_things ts ((PtrArg,a):bs) us sep_things (t :ts) bs us = sep_things ts bs (t:us) \end{code} \begin{code} cgRepSizeB :: CgRep -> ByteOff cgRepSizeB DoubleArg = dOUBLE_SIZE cgRepSizeB LongArg = wORD64_SIZE cgRepSizeB VoidArg = 0 cgRepSizeB _ = wORD_SIZE cgRepSizeW :: CgRep -> ByteOff cgRepSizeW DoubleArg = dOUBLE_SIZE `quot` wORD_SIZE cgRepSizeW LongArg = wORD64_SIZE `quot` wORD_SIZE cgRepSizeW VoidArg = 0 cgRepSizeW _ = 1 retAddrSizeW :: WordOff retAddrSizeW = 1 -- One word \end{code} %************************************************************************ %* * \subsection[ClosureInfo-construction]{Functions which build LFInfos} %* * %************************************************************************ \begin{code} mkLFReEntrant :: TopLevelFlag -- True of top level -> [Id] -- Free vars -> [Id] -- Args -> ArgDescr -- Argument descriptor -> LambdaFormInfo mkLFReEntrant top fvs args arg_descr = LFReEntrant top (length args) (null fvs) arg_descr mkLFThunk :: Type -> TopLevelFlag -> [Var] -> UpdateFlag -> LambdaFormInfo mkLFThunk thunk_ty top fvs upd_flag = ASSERT2( not (isUpdatable upd_flag) || not (isUnLiftedType thunk_ty), ppr thunk_ty $$ ppr fvs ) LFThunk top (null fvs) (isUpdatable upd_flag) NonStandardThunk (might_be_a_function thunk_ty) might_be_a_function :: Type -> Bool -- Return False only if we are *sure* it's a data type -- Look through newtypes etc as much as poss might_be_a_function ty = case tyConAppTyCon_maybe (repType ty) of Just tc -> not (isDataTyCon tc) Nothing -> True \end{code} @mkConLFInfo@ is similar, for constructors. \begin{code} mkConLFInfo :: DataCon -> LambdaFormInfo mkConLFInfo con = LFCon con maybeIsLFCon :: LambdaFormInfo -> Maybe DataCon maybeIsLFCon (LFCon con) = Just con maybeIsLFCon _ = Nothing mkSelectorLFInfo :: Id -> WordOff -> Bool -> LambdaFormInfo mkSelectorLFInfo id offset updatable = LFThunk NotTopLevel False updatable (SelectorThunk offset) (might_be_a_function (idType id)) mkApLFInfo :: Id -> UpdateFlag -> Int -> LambdaFormInfo mkApLFInfo id upd_flag arity = LFThunk NotTopLevel (arity == 0) (isUpdatable upd_flag) (ApThunk arity) (might_be_a_function (idType id)) \end{code} Miscellaneous LF-infos. \begin{code} mkLFArgument :: Id -> LambdaFormInfo mkLFArgument id = LFUnknown (might_be_a_function (idType id)) mkLFLetNoEscape :: Int -> LambdaFormInfo mkLFLetNoEscape = LFLetNoEscape mkLFImported :: Id -> LambdaFormInfo mkLFImported id = case idArity id of n | n > 0 -> LFReEntrant TopLevel n True (panic "arg_descr") -- n > 0 _ -> mkLFArgument id -- Not sure of exact arity \end{code} \begin{code} isLFThunk :: LambdaFormInfo -> Bool isLFThunk (LFThunk _ _ _ _ _) = True isLFThunk LFBlackHole = True -- return True for a blackhole: this function is used to determine -- whether to use the thunk header in SMP mode, and a blackhole -- must have one. isLFThunk _ = False \end{code} \begin{code} -- We keep the *zero-indexed* tag in the srt_len field of the info -- table of a data constructor. type ConTagZ = Int -- A *zero-indexed* contructor tag dataConTagZ :: DataCon -> ConTagZ dataConTagZ con = dataConTag con - fIRST_TAG \end{code} %************************************************************************ %* * Building ClosureInfos %* * %************************************************************************ \begin{code} mkClosureInfo :: Bool -- Is static -> Id -> LambdaFormInfo -> Int -> Int -- Total and pointer words -> C_SRT -> String -- String descriptor -> ClosureInfo mkClosureInfo is_static id lf_info tot_wds ptr_wds srt_info descr = ClosureInfo { closureName = name, closureLFInfo = lf_info, closureSMRep = sm_rep, closureSRT = srt_info, closureType = idType id, closureDescr = descr, closureInfLcl = isDataConWorkId id } -- Make the _info pointer for the implicit datacon worker binding -- local. The reason we can do this is that importing code always -- either uses the _closure or _con_info. By the invariants in CorePrep -- anything else gets eta expanded. where name = idName id sm_rep = mkHeapRep is_static ptr_wds nonptr_wds (lfClosureType lf_info) nonptr_wds = tot_wds - ptr_wds mkConInfo :: Bool -- Is static -> DataCon -> Int -> Int -- Total and pointer words -> ClosureInfo mkConInfo is_static data_con tot_wds ptr_wds = ConInfo { closureSMRep = sm_rep, closureCon = data_con } where sm_rep = mkHeapRep is_static ptr_wds nonptr_wds (lfClosureType lf_info) lf_info = mkConLFInfo data_con nonptr_wds = tot_wds - ptr_wds \end{code} %************************************************************************ %* * \subsection[ClosureInfo-sizes]{Functions about closure {\em sizes}} %* * %************************************************************************ \begin{code} closureSize :: ClosureInfo -> WordOff closureSize cl_info = heapClosureSize (closureSMRep cl_info) \end{code} \begin{code} -- we leave space for an update if either (a) the closure is updatable -- or (b) it is a static thunk. This is because a static thunk needs -- a static link field in a predictable place (after the slop), regardless -- of whether it is updatable or not. closureNeedsUpdSpace :: ClosureInfo -> Bool closureNeedsUpdSpace (ClosureInfo { closureLFInfo = LFThunk TopLevel _ _ _ _ }) = True closureNeedsUpdSpace cl_info = closureUpdReqd cl_info \end{code} %************************************************************************ %* * \subsection[SMreps]{Choosing SM reps} %* * %************************************************************************ \begin{code} lfClosureType :: LambdaFormInfo -> ClosureTypeInfo lfClosureType (LFReEntrant _ arity _ argd) = Fun (fromIntegral arity) argd lfClosureType (LFCon con) = Constr (fromIntegral (dataConTagZ con)) (dataConIdentity con) lfClosureType (LFThunk _ _ _ is_sel _) = thunkClosureType is_sel lfClosureType _ = panic "lfClosureType" thunkClosureType :: StandardFormInfo -> ClosureTypeInfo thunkClosureType (SelectorThunk off) = ThunkSelector (fromIntegral off) thunkClosureType _ = Thunk -- We *do* get non-updatable top-level thunks sometimes. eg. f = g -- gets compiled to a jump to g (if g has non-zero arity), instead of -- messing around with update frames and PAPs. We set the closure type -- to FUN_STATIC in this case. \end{code} %************************************************************************ %* * \subsection[ClosureInfo-4-questions]{Four major questions about @ClosureInfo@} %* * %************************************************************************ Be sure to see the stg-details notes about these... \begin{code} nodeMustPointToIt :: LambdaFormInfo -> Bool nodeMustPointToIt (LFReEntrant top _ no_fvs _) = not no_fvs || -- Certainly if it has fvs we need to point to it isNotTopLevel top -- If it is not top level we will point to it -- We can have a \r closure with no_fvs which -- is not top level as special case cgRhsClosure -- has been dissabled in favour of let floating -- For lex_profiling we also access the cost centre for a -- non-inherited function i.e. not top level -- the not top case above ensures this is ok. nodeMustPointToIt (LFCon _) = True -- Strictly speaking, the above two don't need Node to point -- to it if the arity = 0. But this is a *really* unlikely -- situation. If we know it's nil (say) and we are entering -- it. Eg: let x = [] in x then we will certainly have inlined -- x, since nil is a simple atom. So we gain little by not -- having Node point to known zero-arity things. On the other -- hand, we do lose something; Patrick's code for figuring out -- when something has been updated but not entered relies on -- having Node point to the result of an update. SLPJ -- 27/11/92. nodeMustPointToIt (LFThunk _ no_fvs updatable NonStandardThunk _) = updatable || not no_fvs || opt_SccProfilingOn -- For the non-updatable (single-entry case): -- -- True if has fvs (in which case we need access to them, and we -- should black-hole it) -- or profiling (in which case we need to recover the cost centre -- from inside it) nodeMustPointToIt (LFThunk _ _ _ _ _) = True -- Node must point to any standard-form thunk nodeMustPointToIt (LFUnknown _) = True nodeMustPointToIt LFBlackHole = True -- BH entry may require Node to point nodeMustPointToIt (LFLetNoEscape _) = False \end{code} The entry conventions depend on the type of closure being entered, whether or not it has free variables, and whether we're running sequentially or in parallel. \begin{tabular}{lllll} Closure Characteristics & Parallel & Node Req'd & Argument Passing & Enter Via \\ Unknown & no & yes & stack & node \\ Known fun ($\ge$ 1 arg), no fvs & no & no & registers & fast entry (enough args) \\ \ & \ & \ & \ & slow entry (otherwise) \\ Known fun ($\ge$ 1 arg), fvs & no & yes & registers & fast entry (enough args) \\ 0 arg, no fvs @\r,\s@ & no & no & n/a & direct entry \\ 0 arg, no fvs @\u@ & no & yes & n/a & node \\ 0 arg, fvs @\r,\s@ & no & yes & n/a & direct entry \\ 0 arg, fvs @\u@ & no & yes & n/a & node \\ Unknown & yes & yes & stack & node \\ Known fun ($\ge$ 1 arg), no fvs & yes & no & registers & fast entry (enough args) \\ \ & \ & \ & \ & slow entry (otherwise) \\ Known fun ($\ge$ 1 arg), fvs & yes & yes & registers & node \\ 0 arg, no fvs @\r,\s@ & yes & no & n/a & direct entry \\ 0 arg, no fvs @\u@ & yes & yes & n/a & node \\ 0 arg, fvs @\r,\s@ & yes & yes & n/a & node \\ 0 arg, fvs @\u@ & yes & yes & n/a & node\\ \end{tabular} When black-holing, single-entry closures could also be entered via node (rather than directly) to catch double-entry. \begin{code} data CallMethod = EnterIt -- no args, not a function | JumpToIt CLabel -- no args, not a function, but we -- know what its entry code is | ReturnIt -- it's a function, but we have -- zero args to apply to it, so just -- return it. | ReturnCon DataCon -- It's a data constructor, just return it | SlowCall -- Unknown fun, or known fun with -- too few args. | DirectEntry -- Jump directly, with args in regs CLabel -- The code label Int -- Its arity getCallMethod :: DynFlags -> Name -- Function being applied -> CafInfo -- Can it refer to CAF's? -> LambdaFormInfo -- Its info -> Int -- Number of available arguments -> CallMethod getCallMethod _ _ _ lf_info _ | nodeMustPointToIt lf_info && opt_Parallel = -- If we're parallel, then we must always enter via node. -- The reason is that the closure may have been -- fetched since we allocated it. EnterIt getCallMethod _ name caf (LFReEntrant _ arity _ _) n_args | n_args == 0 = ASSERT( arity /= 0 ) ReturnIt -- No args at all | n_args < arity = SlowCall -- Not enough args | otherwise = DirectEntry (enterIdLabel name caf) arity getCallMethod _ _ _ (LFCon con) n_args | opt_SccProfilingOn -- when profiling, we must always enter = EnterIt -- a closure when we use it, so that the closure -- can be recorded as used for LDV profiling. | otherwise = ASSERT( n_args == 0 ) ReturnCon con getCallMethod _dflags _name _caf (LFThunk _ _ _updatable _std_form_info is_fun) _n_args | is_fun -- it *might* be a function, so we must "call" it (which is -- always safe) = SlowCall -- We cannot just enter it [in eval/apply, the entry code -- is the fast-entry code] -- Since is_fun is False, we are *definitely* looking at a data value | otherwise = EnterIt -- We used to have ASSERT( n_args == 0 ), but actually it is -- possible for the optimiser to generate -- let bot :: Int = error Int "urk" -- in (bot `cast` unsafeCoerce Int (Int -> Int)) 3 -- This happens as a result of the case-of-error transformation -- So the right thing to do is just to enter the thing -- Old version: -- | updatable || doingTickyProfiling dflags -- to catch double entry -- = EnterIt -- | otherwise -- Jump direct to code for single-entry thunks -- = JumpToIt (thunkEntryLabel name caf std_form_info updatable) -- -- Now we never use JumpToIt, even if the thunk is single-entry, since -- the thunk may have already been entered and blackholed by another -- processor. getCallMethod _ _ _ (LFUnknown True) _ = SlowCall -- Might be a function getCallMethod _ name _ (LFUnknown False) n_args | n_args > 0 = WARN( True, ppr name <+> ppr n_args ) SlowCall -- Note [Unsafe coerce complications] | otherwise = EnterIt -- Not a function getCallMethod _ _ _ LFBlackHole _ = SlowCall -- Presumably the black hole has by now -- been updated, but we don't know with -- what, so we slow call it getCallMethod _ name _ (LFLetNoEscape 0) _ = JumpToIt (enterReturnPtLabel (nameUnique name)) getCallMethod _ name _ (LFLetNoEscape arity) n_args | n_args == arity = DirectEntry (enterReturnPtLabel (nameUnique name)) arity | otherwise = pprPanic "let-no-escape: " (ppr name <+> ppr arity) blackHoleOnEntry :: ClosureInfo -> Bool blackHoleOnEntry ConInfo{} = False blackHoleOnEntry cl_info | isStaticRep (closureSMRep cl_info) = False -- Never black-hole a static closure | otherwise = case closureLFInfo cl_info of LFReEntrant _ _ _ _ -> False LFLetNoEscape _ -> False LFThunk _ no_fvs _updatable _ _ -> not no_fvs -- to plug space-leaks. _other -> panic "blackHoleOnEntry" -- Should never happen isKnownFun :: LambdaFormInfo -> Bool isKnownFun (LFReEntrant _ _ _ _) = True isKnownFun (LFLetNoEscape _) = True isKnownFun _ = False \end{code} Note [Unsafe coerce complications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In some (badly-optimised) DPH code we see this Module X: rr :: Int = error Int "Urk" Module Y: ...((X.rr |> g) True) ... where g is an (unsafe) coercion of kind (Int ~ Bool->Bool), say It's badly optimised, because knowing that 'X.rr' is bottom, we should have dumped the application to True. But it should still work. These strange unsafe coercions arise from the case-of-error transformation: (case (error Int "foo") of { ... }) True ---> (error Int "foo" |> g) True Anyway, the net effect is that in STG-land, when casts are discarded, we *can* see a value of type Int applied to an argument. This only happens if (a) the programmer made a mistake, or (b) the value of type Int is actually bottom. So it's wrong to trigger an ASSERT failure in this circumstance. Instead we now emit a WARN -- mainly to draw attention to a probably-badly-optimised program fragment -- and do the conservative thing which is SlowCall. ----------------------------------------------------------------------------- SRT-related stuff \begin{code} staticClosureNeedsLink :: ClosureInfo -> Bool -- A static closure needs a link field to aid the GC when traversing -- the static closure graph. But it only needs such a field if either -- a) it has an SRT -- b) it's a constructor with one or more pointer fields -- In case (b), the constructor's fields themselves play the role -- of the SRT. staticClosureNeedsLink (ClosureInfo { closureSRT = srt }) = needsSRT srt staticClosureNeedsLink (ConInfo { closureSMRep = rep }) = not (isStaticNoCafCon rep) \end{code} Note [Entering error thunks] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this fail :: Int fail = error Int "Urk" foo :: Bool -> Bool foo True y = (fail `cast` Bool -> Bool) y foo False y = False This looks silly, but it can arise from case-of-error. Even if it does, we'd usually see that 'fail' is a bottoming function and would discard the extra argument 'y'. But even if that does not occur, this program is still OK. We will enter 'fail', which never returns. The WARN is just to alert me to the fact that we aren't spotting that 'fail' is bottoming. (We are careful never to make a funtion value look like a data type, because we can't enter a function closure -- but that is not the problem here.) Avoiding generating entries and info tables ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ At present, for every function we generate all of the following, just in case. But they aren't always all needed, as noted below: [NB1: all of this applies only to *functions*. Thunks always have closure, info table, and entry code.] [NB2: All are needed if the function is *exported*, just to play safe.] * Fast-entry code ALWAYS NEEDED * Slow-entry code Needed iff (a) we have any un-saturated calls to the function OR (b) the function is passed as an arg OR (c) we're in the parallel world and the function has free vars [Reason: in parallel world, we always enter functions with free vars via the closure.] * The function closure Needed iff (a) we have any un-saturated calls to the function OR (b) the function is passed as an arg OR (c) if the function has free vars (ie not top level) Why case (a) here? Because if the arg-satis check fails, UpdatePAP stuffs a pointer to the function closure in the PAP. [Could be changed; UpdatePAP could stuff in a code ptr instead, but doesn't seem worth it.] [NB: these conditions imply that we might need the closure without the slow-entry code. Here's how. f x y = let g w = ...x..y..w... in ...(g t)... Here we need a closure for g which contains x and y, but since the calls are all saturated we just jump to the fast entry point for g, with R1 pointing to the closure for g.] * Standard info table Needed iff (a) we have any un-saturated calls to the function OR (b) the function is passed as an arg OR (c) the function has free vars (ie not top level) NB. In the sequential world, (c) is only required so that the function closure has an info table to point to, to keep the storage manager happy. If (c) alone is true we could fake up an info table by choosing one of a standard family of info tables, whose entry code just bombs out. [NB In the parallel world (c) is needed regardless because we enter functions with free vars via the closure.] If (c) is retained, then we'll sometimes generate an info table (for storage mgr purposes) without slow-entry code. Then we need to use an error label in the info table to substitute for the absent slow entry code. \begin{code} staticClosureRequired :: Name -> StgBinderInfo -> LambdaFormInfo -> Bool staticClosureRequired _ bndr_info (LFReEntrant top_level _ _ _) -- It's a function = ASSERT( isTopLevel top_level ) -- Assumption: it's a top-level, no-free-var binding not (satCallsOnly bndr_info) staticClosureRequired _ _ _ = True \end{code} %************************************************************************ %* * \subsection[ClosureInfo-misc-funs]{Misc functions about @ClosureInfo@, etc.} %* * %************************************************************************ \begin{code} isStaticClosure :: ClosureInfo -> Bool isStaticClosure cl_info = isStaticRep (closureSMRep cl_info) closureUpdReqd :: ClosureInfo -> Bool closureUpdReqd ClosureInfo{ closureLFInfo = lf_info } = lfUpdatable lf_info closureUpdReqd ConInfo{} = False lfUpdatable :: LambdaFormInfo -> Bool lfUpdatable (LFThunk _ _ upd _ _) = upd lfUpdatable LFBlackHole = True -- Black-hole closures are allocated to receive the results of an -- alg case with a named default... so they need to be updated. lfUpdatable _ = False closureIsThunk :: ClosureInfo -> Bool closureIsThunk ClosureInfo{ closureLFInfo = lf_info } = isLFThunk lf_info closureIsThunk ConInfo{} = False closureSingleEntry :: ClosureInfo -> Bool closureSingleEntry (ClosureInfo { closureLFInfo = LFThunk _ _ upd _ _}) = not upd closureSingleEntry _ = False closureReEntrant :: ClosureInfo -> Bool closureReEntrant (ClosureInfo { closureLFInfo = LFReEntrant _ _ _ _ }) = True closureReEntrant _ = False isConstrClosure_maybe :: ClosureInfo -> Maybe DataCon isConstrClosure_maybe (ConInfo { closureCon = data_con }) = Just data_con isConstrClosure_maybe _ = Nothing closureFunInfo :: ClosureInfo -> Maybe (Int, ArgDescr) closureFunInfo (ClosureInfo { closureLFInfo = lf_info }) = lfFunInfo lf_info closureFunInfo _ = Nothing lfFunInfo :: LambdaFormInfo -> Maybe (Int, ArgDescr) lfFunInfo (LFReEntrant _ arity _ arg_desc) = Just (arity, arg_desc) lfFunInfo _ = Nothing funTag :: ClosureInfo -> Int funTag (ClosureInfo { closureLFInfo = lf_info }) = funTagLFInfo lf_info funTag _ = 0 -- maybe this should do constructor tags too? funTagLFInfo :: LambdaFormInfo -> Int funTagLFInfo lf -- A function is tagged with its arity | Just (arity,_) <- lfFunInfo lf, Just tag <- tagForArity arity = tag -- other closures (and unknown ones) are not tagged | otherwise = 0 tagForArity :: Int -> Maybe Int tagForArity i | i <= mAX_PTR_TAG = Just i | otherwise = Nothing clHasCafRefs :: ClosureInfo -> CafInfo clHasCafRefs (ClosureInfo {closureSRT = srt}) = case srt of NoC_SRT -> NoCafRefs _ -> MayHaveCafRefs clHasCafRefs (ConInfo {}) = NoCafRefs \end{code} \begin{code} isToplevClosure :: ClosureInfo -> Bool isToplevClosure (ClosureInfo { closureLFInfo = lf_info }) = case lf_info of LFReEntrant TopLevel _ _ _ -> True LFThunk TopLevel _ _ _ _ -> True _ -> False isToplevClosure _ = False \end{code} Label generation. \begin{code} infoTableLabelFromCI :: ClosureInfo -> CLabel infoTableLabelFromCI = fst . labelsFromCI entryLabelFromCI :: ClosureInfo -> CLabel entryLabelFromCI ci | tablesNextToCode = info_lbl | otherwise = entry_lbl where (info_lbl, entry_lbl) = labelsFromCI ci labelsFromCI :: ClosureInfo -> (CLabel, CLabel) -- (Info, Entry) labelsFromCI cl@(ClosureInfo { closureName = name, closureLFInfo = lf_info, closureInfLcl = is_lcl }) = case lf_info of LFBlackHole -> (mkCAFBlackHoleInfoTableLabel, mkCAFBlackHoleEntryLabel) LFThunk _ _ upd_flag (SelectorThunk offset) _ -> bothL (mkSelectorInfoLabel, mkSelectorEntryLabel) upd_flag offset LFThunk _ _ upd_flag (ApThunk arity) _ -> bothL (mkApInfoTableLabel, mkApEntryLabel) upd_flag arity LFThunk{} -> bothL std_mk_lbls name $ clHasCafRefs cl LFReEntrant _ _ _ _ -> bothL std_mk_lbls name $ clHasCafRefs cl _ -> panic "labelsFromCI" where std_mk_lbls = if is_lcl then (mkLocalInfoTableLabel, mkLocalEntryLabel) else (mkInfoTableLabel, mkEntryLabel) labelsFromCI cl@(ConInfo { closureCon = con, closureSMRep = rep }) | isStaticRep rep = bothL (mkStaticInfoTableLabel, mkStaticConEntryLabel) name $ clHasCafRefs cl | otherwise = bothL (mkConInfoTableLabel, mkConEntryLabel) name $ clHasCafRefs cl where name = dataConName con bothL :: (a -> b -> c, a -> b -> c) -> a -> b -> (c, c) bothL (f, g) x y = (f x y, g x y) -- ClosureInfo for a closure (as opposed to a constructor) is always local closureLabelFromCI :: ClosureInfo -> CLabel closureLabelFromCI cl@(ClosureInfo { closureName = nm }) = mkLocalClosureLabel nm $ clHasCafRefs cl closureLabelFromCI _ = panic "closureLabelFromCI" -- thunkEntryLabel is a local help function, not exported. It's used from both -- entryLabelFromCI and getCallMethod. {- UNUSED: thunkEntryLabel :: Name -> CafInfo -> StandardFormInfo -> Bool -> CLabel thunkEntryLabel _thunk_id _ (ApThunk arity) is_updatable = enterApLabel is_updatable arity thunkEntryLabel _thunk_id _ (SelectorThunk offset) upd_flag = enterSelectorLabel upd_flag offset thunkEntryLabel thunk_id caf _ _is_updatable = enterIdLabel thunk_id caf -} {- UNUSED: enterApLabel :: Bool -> Int -> CLabel enterApLabel is_updatable arity | tablesNextToCode = mkApInfoTableLabel is_updatable arity | otherwise = mkApEntryLabel is_updatable arity -} {- UNUSED: enterSelectorLabel :: Bool -> Int -> CLabel enterSelectorLabel upd_flag offset | tablesNextToCode = mkSelectorInfoLabel upd_flag offset | otherwise = mkSelectorEntryLabel upd_flag offset -} enterIdLabel :: Name -> CafInfo -> CLabel enterIdLabel id | tablesNextToCode = mkInfoTableLabel id | otherwise = mkEntryLabel id enterReturnPtLabel :: Unique -> CLabel enterReturnPtLabel name | tablesNextToCode = mkReturnInfoLabel name | otherwise = mkReturnPtLabel name \end{code} We need a black-hole closure info to pass to @allocDynClosure@ when we want to allocate the black hole on entry to a CAF. These are the only ways to build an LFBlackHole, maintaining the invariant that it really is a black hole and not something else. \begin{code} cafBlackHoleClosureInfo :: ClosureInfo -> ClosureInfo cafBlackHoleClosureInfo (ClosureInfo { closureName = nm, closureType = ty }) = ClosureInfo { closureName = nm, closureLFInfo = LFBlackHole, closureSMRep = blackHoleRep, closureSRT = NoC_SRT, closureType = ty, closureDescr = "", closureInfLcl = False } cafBlackHoleClosureInfo _ = panic "cafBlackHoleClosureInfo" \end{code} %************************************************************************ %* * \subsection[ClosureInfo-Profiling-funs]{Misc functions about for profiling info.} %* * %************************************************************************ Profiling requires two pieces of information to be determined for each closure's info table --- description and type. The description is stored directly in the @CClosureInfoTable@ when the info table is built. The type is determined from the type information stored with the @Id@ in the closure info using @closureTypeDescr@. \begin{code} closureValDescr, closureTypeDescr :: ClosureInfo -> String closureValDescr (ClosureInfo {closureDescr = descr}) = descr closureValDescr (ConInfo {closureCon = con}) = occNameString (getOccName con) closureTypeDescr (ClosureInfo { closureType = ty }) = getTyDescription ty closureTypeDescr (ConInfo { closureCon = data_con }) = occNameString (getOccName (dataConTyCon data_con)) getTyDescription :: Type -> String getTyDescription ty = case (tcSplitSigmaTy ty) of { (_, _, tau_ty) -> case tau_ty of TyVarTy _ -> "*" AppTy fun _ -> getTyDescription fun FunTy _ res -> '-' : '>' : fun_result res TyConApp tycon _ -> getOccString tycon ForAllTy _ ty -> getTyDescription ty LitTy n -> getTyLitDescription n } where fun_result (FunTy _ res) = '>' : fun_result res fun_result other = getTyDescription other getTyLitDescription :: TyLit -> String getTyLitDescription l = case l of NumTyLit n -> show n StrTyLit n -> show n \end{code}