{-# LANGUAGE CPP, RecordWildCards #-} ----------------------------------------------------------------------------- -- -- Stg to C-- code generation: -- -- The types LambdaFormInfo -- ClosureInfo -- -- Nothing monadic in here! -- ----------------------------------------------------------------------------- module StgCmmClosure ( DynTag, tagForCon, isSmallFamily, ConTagZ, dataConTagZ, idPrimRep, isVoidRep, isGcPtrRep, addIdReps, addArgReps, argPrimRep, -- * LambdaFormInfo LambdaFormInfo, -- Abstract StandardFormInfo, -- ...ditto... mkLFThunk, mkLFReEntrant, mkConLFInfo, mkSelectorLFInfo, mkApLFInfo, mkLFImported, mkLFArgument, mkLFLetNoEscape, lfDynTag, maybeIsLFCon, isLFThunk, isLFReEntrant, lfUpdatable, -- * Used by other modules CgLoc(..), SelfLoopInfo, CallMethod(..), nodeMustPointToIt, isKnownFun, funTag, tagForArity, getCallMethod, -- * ClosureInfo ClosureInfo, mkClosureInfo, mkCmmInfo, -- ** Inspection closureLFInfo, closureName, -- ** Labels -- These just need the info table label closureInfoLabel, staticClosureLabel, closureSlowEntryLabel, closureLocalEntryLabel, -- ** Predicates -- These are really just functions on LambdaFormInfo closureUpdReqd, closureSingleEntry, closureReEntrant, closureFunInfo, isToplevClosure, blackHoleOnEntry, -- Needs LambdaFormInfo and SMRep isStaticClosure, -- Needs SMPre -- * InfoTables mkDataConInfoTable, cafBlackHoleInfoTable, indStaticInfoTable, staticClosureNeedsLink, ) where #include "../includes/MachDeps.h" #define FAST_STRING_NOT_NEEDED #include "HsVersions.h" import StgSyn import SMRep import Cmm import PprCmmExpr() import BlockId import CLabel import Id import IdInfo import DataCon import FastString import Name import Type import TypeRep import TcType import TyCon import BasicTypes import Outputable import DynFlags import Util ----------------------------------------------------------------------------- -- Data types and synonyms ----------------------------------------------------------------------------- -- These data types are mostly used by other modules, especially StgCmmMonad, -- but we define them here because some functions in this module need to -- have access to them as well data CgLoc = CmmLoc CmmExpr -- A stable CmmExpr; that is, one not mentioning -- Hp, so that it remains valid across calls | LneLoc BlockId [LocalReg] -- A join point -- A join point (= let-no-escape) should only -- be tail-called, and in a saturated way. -- To tail-call it, assign to these locals, -- and branch to the block id instance Outputable CgLoc where ppr (CmmLoc e) = ptext (sLit "cmm") <+> ppr e ppr (LneLoc b rs) = ptext (sLit "lne") <+> ppr b <+> ppr rs type SelfLoopInfo = (Id, BlockId, [LocalReg]) -- used by ticky profiling isKnownFun :: LambdaFormInfo -> Bool isKnownFun (LFReEntrant _ _ _ _) = True isKnownFun LFLetNoEscape = True isKnownFun _ = False ----------------------------------------------------------------------------- -- Representations ----------------------------------------------------------------------------- -- Why are these here? idPrimRep :: Id -> PrimRep idPrimRep id = typePrimRep (idType id) -- NB: typePrimRep fails on unboxed tuples, -- but by StgCmm no Ids have unboxed tuple type addIdReps :: [Id] -> [(PrimRep, Id)] addIdReps ids = [(idPrimRep id, id) | id <- ids] addArgReps :: [StgArg] -> [(PrimRep, StgArg)] addArgReps args = [(argPrimRep arg, arg) | arg <- args] argPrimRep :: StgArg -> PrimRep argPrimRep arg = typePrimRep (stgArgType arg) ----------------------------------------------------------------------------- -- LambdaFormInfo ----------------------------------------------------------------------------- -- 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. data LambdaFormInfo = LFReEntrant -- Reentrant closure (a function) TopLevelFlag -- True if top level !RepArity -- Arity. Invariant: always > 0 !Bool -- True <=> no fvs ArgDescr -- Argument descriptor (should really be in ClosureInfo) | 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 | LFCon -- A saturated constructor application DataCon -- The constructor | 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 -- The False case is good when we want to enter it, -- because then we know the entry code will do -- For a function, the entry code is the fast entry point | LFUnLifted -- A value of unboxed type; -- always a value, needs evaluation | LFLetNoEscape -- See LetNoEscape module for precise description ------------------------- -- StandardFormInfo tells whether this thunk has one of -- a small number of standard forms data StandardFormInfo = NonStandardThunk -- The usual case: not 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. RepArity -- Arity, n ------------------------------------------------------ -- Building LambdaFormInfo ------------------------------------------------------ mkLFArgument :: Id -> LambdaFormInfo mkLFArgument id | isUnLiftedType ty = LFUnLifted | might_be_a_function ty = LFUnknown True | otherwise = LFUnknown False where ty = idType id ------------- mkLFLetNoEscape :: LambdaFormInfo mkLFLetNoEscape = LFLetNoEscape ------------- 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 -> [Id] -> UpdateFlag -> LambdaFormInfo mkLFThunk thunk_ty top fvs upd_flag = ASSERT( not (isUpdatable upd_flag) || not (isUnLiftedType thunk_ty) ) 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 | UnaryRep rep <- repType ty , Just tc <- tyConAppTyCon_maybe rep , isDataTyCon tc = False | otherwise = True ------------- mkConLFInfo :: DataCon -> LambdaFormInfo mkConLFInfo con = LFCon con ------------- mkSelectorLFInfo :: Id -> Int -> Bool -> LambdaFormInfo mkSelectorLFInfo id offset updatable = LFThunk NotTopLevel False updatable (SelectorThunk offset) (might_be_a_function (idType id)) ------------- mkApLFInfo :: Id -> UpdateFlag -> Arity -> LambdaFormInfo mkApLFInfo id upd_flag arity = LFThunk NotTopLevel (arity == 0) (isUpdatable upd_flag) (ApThunk arity) (might_be_a_function (idType id)) ------------- mkLFImported :: Id -> LambdaFormInfo mkLFImported id | Just con <- isDataConWorkId_maybe id , isNullaryRepDataCon con = LFCon con -- An imported nullary constructor -- We assume that the constructor is evaluated so that -- the id really does point directly to the constructor | arity > 0 = LFReEntrant TopLevel arity True (panic "arg_descr") | otherwise = mkLFArgument id -- Not sure of exact arity where arity = idRepArity id ----------------------------------------------------- -- Dynamic pointer tagging ----------------------------------------------------- type ConTagZ = Int -- A *zero-indexed* contructor tag type DynTag = Int -- The tag on a *pointer* -- (from the dynamic-tagging paper) -- Note [Data constructor dynamic tags] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- The family size of a data type (the number of constructors -- or the arity of a function) can be either: -- * small, if the family size < 2**tag_bits -- * big, otherwise. -- -- Small families can have the constructor tag in the tag bits. -- Big families only use the tag value 1 to represent evaluatedness. -- We don't have very many tag bits: for example, we have 2 bits on -- x86-32 and 3 bits on x86-64. isSmallFamily :: DynFlags -> Int -> Bool isSmallFamily dflags fam_size = fam_size <= mAX_PTR_TAG dflags -- We keep the *zero-indexed* tag in the srt_len field of the info -- table of a data constructor. dataConTagZ :: DataCon -> ConTagZ dataConTagZ con = dataConTag con - fIRST_TAG tagForCon :: DynFlags -> DataCon -> DynTag tagForCon dflags con | isSmallFamily dflags fam_size = con_tag + 1 | otherwise = 1 where con_tag = dataConTagZ con fam_size = tyConFamilySize (dataConTyCon con) tagForArity :: DynFlags -> RepArity -> DynTag tagForArity dflags arity | isSmallFamily dflags arity = arity | otherwise = 0 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 ----------------------------------------------------------------------------- -- Observing LambdaFormInfo ----------------------------------------------------------------------------- ------------- maybeIsLFCon :: LambdaFormInfo -> Maybe DataCon maybeIsLFCon (LFCon con) = Just con maybeIsLFCon _ = Nothing ------------ isLFThunk :: LambdaFormInfo -> Bool isLFThunk (LFThunk {}) = True isLFThunk _ = False isLFReEntrant :: LambdaFormInfo -> Bool isLFReEntrant (LFReEntrant {}) = True isLFReEntrant _ = False ----------------------------------------------------------------------------- -- Choosing SM reps ----------------------------------------------------------------------------- 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" thunkClosureType :: StandardFormInfo -> ClosureTypeInfo thunkClosureType (SelectorThunk off) = ThunkSelector 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. ----------------------------------------------------------------------------- -- nodeMustPointToIt ----------------------------------------------------------------------------- nodeMustPointToIt :: DynFlags -> LambdaFormInfo -> Bool -- If nodeMustPointToIt is true, then the entry convention for -- this closure has R1 (the "Node" register) pointing to the -- closure itself --- the "self" argument 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 -- non-inherited (i.e. non-top-level) function. -- The isNotTopLevel test above ensures this is ok. nodeMustPointToIt dflags (LFThunk top no_fvs updatable NonStandardThunk _) = not no_fvs -- Self parameter || isNotTopLevel top -- Note [GC recovery] || updatable -- Need to push update frame || gopt Opt_SccProfilingOn dflags -- 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) ToDo: do we need this even for -- top-level thunks? If not, -- isNotTopLevel subsumes this nodeMustPointToIt _ (LFThunk {}) -- Node must point to a standard-form thunk = True 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 _ (LFUnknown _) = True nodeMustPointToIt _ LFUnLifted = False nodeMustPointToIt _ LFLetNoEscape = False {- Note [GC recovery] ~~~~~~~~~~~~~~~~~~~~~ If we a have a local let-binding (function or thunk) let f = <body> in ... AND <body> allocates, then the heap-overflow check needs to know how to re-start the evaluation. It uses the "self" pointer to do this. So even if there are no free variables in <body>, we still make nodeMustPointToIt be True for non-top-level bindings. Why do any such bindings exist? After all, let-floating should have floated them out. Well, a clever optimiser might leave one there to avoid a space leak, deliberately recomputing a thunk. Also (and this really does happen occasionally) let-floating may make a function f smaller so it can be inlined, so now (f True) may generate a local no-fv closure. This actually happened during bootsrapping GHC itself, with f=mkRdrFunBind in TcGenDeriv.) -} ----------------------------------------------------------------------------- -- getCallMethod ----------------------------------------------------------------------------- {- 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. Closure Node Argument Enter Characteristics Par Req'd Passing Via --------------------------------------------------------------------------- Unknown & no & yes & stack & node Known fun (>1 arg), no fvs & no & no & registers & fast entry (enough args) & slow entry (otherwise) Known fun (>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,selector & 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 (>1 arg), no fvs & yes & no & registers & fast entry (enough args) & slow entry (otherwise) Known fun (>1 arg), fvs & yes & yes & registers & node 0 arg, fvs \r,\s,selector & yes & yes & n/a & 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 When black-holing, single-entry closures could also be entered via node (rather than directly) to catch double-entry. -} data CallMethod = EnterIt -- No args, not a function | JumpToIt BlockId [LocalReg] -- A join point or a header of a local loop | ReturnIt -- It's a value (function, unboxed value, -- or constructor), so just return it. | SlowCall -- Unknown fun, or known fun with -- too few args. | DirectEntry -- Jump directly, with args in regs CLabel -- The code label RepArity -- Its arity getCallMethod :: DynFlags -> Name -- Function being applied -> Id -- Function Id used to chech if it can refer to -- CAF's and whether the function is tail-calling -- itself -> LambdaFormInfo -- Its info -> RepArity -- Number of available arguments -> CgLoc -- Passed in from cgIdApp so that we can -- handle let-no-escape bindings and self-recursive -- tail calls using the same data constructor, -- JumpToIt. This saves us one case branch in -- cgIdApp -> Maybe SelfLoopInfo -- can we perform a self-recursive tail call? -> CallMethod getCallMethod dflags _ id _ n_args _cg_loc (Just (self_loop_id, block_id, args)) | gopt Opt_Loopification dflags, id == self_loop_id, n_args == length args -- If these patterns match then we know that: -- * loopification optimisation is turned on -- * function is performing a self-recursive call in a tail position -- * number of parameters of the function matches functions arity. -- See Note [Self-recursive tail calls] in StgCmmExpr for more details = JumpToIt block_id args getCallMethod dflags _name _ lf_info _n_args _cg_loc _self_loop_info | nodeMustPointToIt dflags lf_info && gopt Opt_Parallel dflags = -- 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 dflags name id (LFReEntrant _ arity _ _) n_args _cg_loc _self_loop_info | n_args == 0 = ASSERT( arity /= 0 ) ReturnIt -- No args at all | n_args < arity = SlowCall -- Not enough args | otherwise = DirectEntry (enterIdLabel dflags name (idCafInfo id)) arity getCallMethod _ _name _ LFUnLifted n_args _cg_loc _self_loop_info = ASSERT( n_args == 0 ) ReturnIt getCallMethod _ _name _ (LFCon _) n_args _cg_loc _self_loop_info = ASSERT( n_args == 0 ) ReturnIt getCallMethod dflags name id (LFThunk _ _ updatable std_form_info is_fun) n_args _cg_loc _self_loop_info | 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 | updatable || gopt Opt_Ticky dflags -- to catch double entry {- OLD: || opt_SMP I decided to remove this, because in SMP mode it doesn't matter if we enter the same thunk multiple times, so the optimisation of jumping directly to the entry code is still valid. --SDM -} = EnterIt -- even a non-updatable selector thunk can be updated by the garbage -- collector, so we must enter it. (#8817) | SelectorThunk{} <- std_form_info = 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 | otherwise -- Jump direct to code for single-entry thunks = ASSERT( n_args == 0 ) DirectEntry (thunkEntryLabel dflags name (idCafInfo id) std_form_info updatable) 0 getCallMethod _ _name _ (LFUnknown True) _n_arg _cg_locs _self_loop_info = SlowCall -- might be a function getCallMethod _ name _ (LFUnknown False) n_args _cg_loc _self_loop_info = ASSERT2( n_args == 0, ppr name <+> ppr n_args ) EnterIt -- Not a function getCallMethod _ _name _ LFLetNoEscape _n_args (LneLoc blk_id lne_regs) _self_loop_info = JumpToIt blk_id lne_regs getCallMethod _ _ _ _ _ _ _ = panic "Unknown call method" ----------------------------------------------------------------------------- -- staticClosureRequired ----------------------------------------------------------------------------- {- staticClosureRequired is never called (hence commented out) SimonMar writes (Sept 07) It's an optimisation we used to apply at one time, I believe, but it got lost probably in the rewrite of the RTS/code generator. I left that code there to remind me to look into whether it was worth doing sometime {- 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. -} staticClosureRequired :: Name -> StgBinderInfo -> LambdaFormInfo -> Bool staticClosureRequired binder 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 binder other_binder_info other_lf_info = True -} ----------------------------------------------------------------------------- -- Data types for closure information ----------------------------------------------------------------------------- {- ClosureInfo: information about a binding We make a ClosureInfo for each let binding (both top level and not), but not bindings for data constructors: for those we build a CmmInfoTable directly (see mkDataConInfoTable). To a first approximation: ClosureInfo = (LambdaFormInfo, CmmInfoTable) A ClosureInfo has enough information a) to construct the info table itself, and build other things related to the binding (e.g. slow entry points for a function) b) to allocate a closure containing that info pointer (i.e. it knows the info table label) -} data ClosureInfo = ClosureInfo { closureName :: !Name, -- The thing bound to this closure -- we don't really need this field: it's only used in generating -- code for ticky and profiling, and we could pass the information -- around separately, but it doesn't do much harm to keep it here. closureLFInfo :: !LambdaFormInfo, -- NOTE: not an LFCon -- this tells us about what the closure contains: it's right-hand-side. -- the rest is just an unpacked CmmInfoTable. closureInfoLabel :: !CLabel, closureSMRep :: !SMRep, -- representation used by storage mgr closureProf :: !ProfilingInfo } -- | Convert from 'ClosureInfo' to 'CmmInfoTable'. mkCmmInfo :: ClosureInfo -> CmmInfoTable mkCmmInfo ClosureInfo {..} = CmmInfoTable { cit_lbl = closureInfoLabel , cit_rep = closureSMRep , cit_prof = closureProf , cit_srt = NoC_SRT } -------------------------------------- -- Building ClosureInfos -------------------------------------- mkClosureInfo :: DynFlags -> Bool -- Is static -> Id -> LambdaFormInfo -> Int -> Int -- Total and pointer words -> String -- String descriptor -> ClosureInfo mkClosureInfo dflags is_static id lf_info tot_wds ptr_wds val_descr = ClosureInfo { closureName = name , closureLFInfo = lf_info , closureInfoLabel = info_lbl -- These three fields are , closureSMRep = sm_rep -- (almost) an info table , closureProf = prof } -- (we don't have an SRT yet) where name = idName id sm_rep = mkHeapRep dflags is_static ptr_wds nonptr_wds (lfClosureType lf_info) prof = mkProfilingInfo dflags id val_descr nonptr_wds = tot_wds - ptr_wds info_lbl = mkClosureInfoTableLabel id lf_info -------------------------------------- -- Other functions over ClosureInfo -------------------------------------- -- Eager blackholing is normally disabled, but can be turned on with -- -feager-blackholing. When it is on, we replace the info pointer of -- the thunk with stg_EAGER_BLACKHOLE_info on entry. -- If we wanted to do eager blackholing with slop filling, -- we'd need to do it at the *end* of a basic block, otherwise -- we overwrite the free variables in the thunk that we still -- need. We have a patch for this from Andy Cheadle, but not -- incorporated yet. --SDM [6/2004] -- -- -- Previously, eager blackholing was enabled when ticky-ticky -- was on. But it didn't work, and it wasn't strictly necessary -- to bring back minimal ticky-ticky, so now EAGER_BLACKHOLING -- is unconditionally disabled. -- krc 1/2007 -- -- -- Static closures are never themselves black-holed. -- -- We also never black-hole non-updatable thunks. -- See Note [Black-holing non-updatable thunks] blackHoleOnEntry :: ClosureInfo -> Bool 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 _ _ -> updatable _other -> panic "blackHoleOnEntry" -- Should never happen {- Note [Black-holing non-updatable thunks] ========================================= We cannot black-hole non-updatable thunks otherwise we run into issues like Trac #10414. A single-entry (non-updatable) thunk can actually be entered more than once in a parallel program, if work is duplicated by two threads both entering the same updatable thunk before the other has blackholed it. So, we must not eagerly blackhole non-updatable thunks, or the second thread to enter one will become blocked indefinitely. (They are not blackholed by lazy blackholing either, since they have no associated update frame.) For instance, let's consider the following value (in pseudo-Core, example due to Reid Barton), x = \u [] concat [[1], []] with the following definitions, concat x = case x of [] -> [] (:) x xs -> (++) x (concat xs) (++) xs ys = case xs of [] -> ys (:) x rest -> (:) x ((++) rest ys) Where we use the syntax @\u []@ to denote an updatable thunk and @\s []@ to denote a single-entry (i.e. non-updatable) thunk. After a thread evaluates @x@ to WHNF and calls @(++)@ the heap will contain the following thunks, x = 1 : y y = \u [] (++) [] z z = \s [] concat [] Now that the stage is set, consider the follow evaluations by two racing threads A and B, 1. Both threads enter @y@ before either is able to replace it with an indirection 2. Thread A does the case analysis in @(++)@ and consequently enters @z@, replacing it with a black-hole 3. At some later point thread B does the same case analysis and also attempts to enter @z@. However, it finds that it has been replaced with a black-hole so it blocks. 4. Thread A eventually finishes evaluating @z@ (to @[]@) and updates @y@ accordingly. It does *not* update @z@, however, as it is single-entry. This leaves Thread B blocked forever on a black-hole which will never be updated. To avoid this sort of condition we never black-hole non-updatable thunks. -} isStaticClosure :: ClosureInfo -> Bool isStaticClosure cl_info = isStaticRep (closureSMRep cl_info) closureUpdReqd :: ClosureInfo -> Bool closureUpdReqd ClosureInfo{ closureLFInfo = lf_info } = lfUpdatable lf_info lfUpdatable :: LambdaFormInfo -> Bool lfUpdatable (LFThunk _ _ upd _ _) = upd lfUpdatable _ = False closureSingleEntry :: ClosureInfo -> Bool closureSingleEntry (ClosureInfo { closureLFInfo = LFThunk _ _ upd _ _}) = not upd closureSingleEntry _ = False closureReEntrant :: ClosureInfo -> Bool closureReEntrant (ClosureInfo { closureLFInfo = LFReEntrant _ _ _ _ }) = True closureReEntrant _ = False 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 funTag :: DynFlags -> ClosureInfo -> DynTag funTag dflags (ClosureInfo { closureLFInfo = lf_info }) = lfDynTag dflags lf_info isToplevClosure :: ClosureInfo -> Bool isToplevClosure (ClosureInfo { closureLFInfo = lf_info }) = case lf_info of LFReEntrant TopLevel _ _ _ -> True LFThunk TopLevel _ _ _ _ -> True _other -> False -------------------------------------- -- Label generation -------------------------------------- staticClosureLabel :: ClosureInfo -> CLabel staticClosureLabel = toClosureLbl . closureInfoLabel closureSlowEntryLabel :: ClosureInfo -> CLabel closureSlowEntryLabel = toSlowEntryLbl . closureInfoLabel closureLocalEntryLabel :: DynFlags -> ClosureInfo -> CLabel closureLocalEntryLabel dflags | tablesNextToCode dflags = toInfoLbl . closureInfoLabel | otherwise = toEntryLbl . closureInfoLabel mkClosureInfoTableLabel :: Id -> LambdaFormInfo -> CLabel mkClosureInfoTableLabel id lf_info = case lf_info of LFThunk _ _ upd_flag (SelectorThunk offset) _ -> mkSelectorInfoLabel upd_flag offset LFThunk _ _ upd_flag (ApThunk arity) _ -> mkApInfoTableLabel upd_flag arity LFThunk{} -> std_mk_lbl name cafs LFReEntrant{} -> std_mk_lbl name cafs _other -> panic "closureInfoTableLabel" where name = idName id std_mk_lbl | is_local = mkLocalInfoTableLabel | otherwise = mkInfoTableLabel cafs = idCafInfo id is_local = 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. thunkEntryLabel :: DynFlags -> Name -> CafInfo -> StandardFormInfo -> Bool -> CLabel -- thunkEntryLabel is a local help function, not exported. It's used from -- getCallMethod. thunkEntryLabel dflags _thunk_id _ (ApThunk arity) upd_flag = enterApLabel dflags upd_flag arity thunkEntryLabel dflags _thunk_id _ (SelectorThunk offset) upd_flag = enterSelectorLabel dflags upd_flag offset thunkEntryLabel dflags thunk_id c _ _ = enterIdLabel dflags thunk_id c enterApLabel :: DynFlags -> Bool -> Arity -> CLabel enterApLabel dflags is_updatable arity | tablesNextToCode dflags = mkApInfoTableLabel is_updatable arity | otherwise = mkApEntryLabel is_updatable arity enterSelectorLabel :: DynFlags -> Bool -> WordOff -> CLabel enterSelectorLabel dflags upd_flag offset | tablesNextToCode dflags = mkSelectorInfoLabel upd_flag offset | otherwise = mkSelectorEntryLabel upd_flag offset enterIdLabel :: DynFlags -> Name -> CafInfo -> CLabel enterIdLabel dflags id c | tablesNextToCode dflags = mkInfoTableLabel id c | otherwise = mkEntryLabel id c -------------------------------------- -- Profiling -------------------------------------- -- 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@. mkProfilingInfo :: DynFlags -> Id -> String -> ProfilingInfo mkProfilingInfo dflags id val_descr | not (gopt Opt_SccProfilingOn dflags) = NoProfilingInfo | otherwise = ProfilingInfo ty_descr_w8 val_descr_w8 where ty_descr_w8 = stringToWord8s (getTyDescription (idType id)) val_descr_w8 = stringToWord8s val_descr 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 -------------------------------------- -- CmmInfoTable-related things -------------------------------------- mkDataConInfoTable :: DynFlags -> DataCon -> Bool -> Int -> Int -> CmmInfoTable mkDataConInfoTable dflags data_con is_static ptr_wds nonptr_wds = CmmInfoTable { cit_lbl = info_lbl , cit_rep = sm_rep , cit_prof = prof , cit_srt = NoC_SRT } where name = dataConName data_con info_lbl | is_static = mkStaticInfoTableLabel name NoCafRefs | otherwise = mkConInfoTableLabel name NoCafRefs sm_rep = mkHeapRep dflags is_static ptr_wds nonptr_wds cl_type cl_type = Constr (dataConTagZ data_con) (dataConIdentity data_con) prof | not (gopt Opt_SccProfilingOn dflags) = NoProfilingInfo | otherwise = ProfilingInfo ty_descr val_descr ty_descr = stringToWord8s $ occNameString $ getOccName $ dataConTyCon data_con val_descr = stringToWord8s $ occNameString $ getOccName data_con -- We need a black-hole closure info to pass to @allocDynClosure@ when we -- want to allocate the black hole on entry to a CAF. cafBlackHoleInfoTable :: CmmInfoTable cafBlackHoleInfoTable = CmmInfoTable { cit_lbl = mkCAFBlackHoleInfoTableLabel , cit_rep = blackHoleRep , cit_prof = NoProfilingInfo , cit_srt = NoC_SRT } indStaticInfoTable :: CmmInfoTable indStaticInfoTable = CmmInfoTable { cit_lbl = mkIndStaticInfoLabel , cit_rep = indStaticRep , cit_prof = NoProfilingInfo , cit_srt = NoC_SRT } staticClosureNeedsLink :: Bool -> CmmInfoTable -> 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. -- -- At this point, the cit_srt field has not been calculated (that -- happens right at the end of the Cmm pipeline), but we do have the -- VarSet of CAFs that CoreToStg attached, and if that is empty there -- will definitely not be an SRT. -- staticClosureNeedsLink has_srt CmmInfoTable{ cit_rep = smrep } | isConRep smrep = not (isStaticNoCafCon smrep) | otherwise = has_srt -- needsSRT (cit_srt info_tbl)