{-# LANGUAGE CPP #-} -- -- (c) The GRASP/AQUA Project, Glasgow University, 1993-1998 -- -------------------------------------------------------------- -- Converting Core to STG Syntax -------------------------------------------------------------- -- And, as we have the info in hand, we may convert some lets to -- let-no-escapes. module CoreToStg ( coreToStg ) where #include "HsVersions.h" import GhcPrelude import CoreSyn import CoreUtils ( exprType, findDefault, isJoinBind , exprIsTickedString_maybe ) import CoreArity ( manifestArity ) import StgSyn import Type import RepType import TyCon import MkId ( coercionTokenId ) import Id import IdInfo import DataCon import CostCentre import VarEnv import Module import Name ( isExternalName, nameOccName, nameModule_maybe ) import OccName ( occNameFS ) import BasicTypes ( Arity ) import TysWiredIn ( unboxedUnitDataCon, unitDataConId ) import Literal import Outputable import MonadUtils import FastString import Util import DynFlags import ForeignCall import Demand ( isUsedOnce ) import PrimOp ( PrimCall(..) ) import SrcLoc ( mkGeneralSrcSpan ) import Data.List.NonEmpty (nonEmpty, toList) import Data.Maybe (fromMaybe) import Control.Monad (liftM, ap) -- Note [Live vs free] -- ~~~~~~~~~~~~~~~~~~~ -- -- The two are not the same. Liveness is an operational property rather -- than a semantic one. A variable is live at a particular execution -- point if it can be referred to directly again. In particular, a dead -- variable's stack slot (if it has one): -- -- - should be stubbed to avoid space leaks, and -- - may be reused for something else. -- -- There ought to be a better way to say this. Here are some examples: -- -- let v = [q] \[x] -> e -- in -- ...v... (but no q's) -- -- Just after the `in', v is live, but q is dead. If the whole of that -- let expression was enclosed in a case expression, thus: -- -- case (let v = [q] \[x] -> e in ...v...) of -- alts[...q...] -- -- (ie `alts' mention `q'), then `q' is live even after the `in'; because -- we'll return later to the `alts' and need it. -- -- Let-no-escapes make this a bit more interesting: -- -- let-no-escape v = [q] \ [x] -> e -- in -- ...v... -- -- Here, `q' is still live at the `in', because `v' is represented not by -- a closure but by the current stack state. In other words, if `v' is -- live then so is `q'. Furthermore, if `e' mentions an enclosing -- let-no-escaped variable, then its free variables are also live if `v' is. -- Note [What are these SRTs all about?] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- Consider the Core program, -- -- fibs = go 1 1 -- where go a b = let c = a + c -- in c : go b c -- add x = map (\y -> x*y) fibs -- -- In this case we have a CAF, 'fibs', which is quite large after evaluation and -- has only one possible user, 'add'. Consequently, we want to ensure that when -- all references to 'add' die we can garbage collect any bit of 'fibs' that we -- have evaluated. -- -- However, how do we know whether there are any references to 'fibs' still -- around? Afterall, the only reference to it is buried in the code generated -- for 'add'. The answer is that we record the CAFs referred to by a definition -- in its info table, namely a part of it known as the Static Reference Table -- (SRT). -- -- Since SRTs are so common, we use a special compact encoding for them in: we -- produce one table containing a list of CAFs in a module and then include a -- bitmap in each info table describing which entries of this table the closure -- references. -- -- See also: Commentary/Rts/Storage/GC/CAFs on the GHC Wiki. -- Note [What is a non-escaping let] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- NB: Nowadays this is recognized by the occurrence analyser by turning a -- "non-escaping let" into a join point. The following is then an operational -- account of join points. -- -- Consider: -- -- let x = fvs \ args -> e -- in -- if ... then x else -- if ... then x else ... -- -- `x' is used twice (so we probably can't unfold it), but when it is -- entered, the stack is deeper than it was when the definition of `x' -- happened. Specifically, if instead of allocating a closure for `x', -- we saved all `x's fvs on the stack, and remembered the stack depth at -- that moment, then whenever we enter `x' we can simply set the stack -- pointer(s) to these remembered (compile-time-fixed) values, and jump -- to the code for `x'. -- -- All of this is provided x is: -- 1. non-updatable; -- 2. guaranteed to be entered before the stack retreats -- ie x is not -- buried in a heap-allocated closure, or passed as an argument to -- something; -- 3. all the enters have exactly the right number of arguments, -- no more no less; -- 4. all the enters are tail calls; that is, they return to the -- caller enclosing the definition of `x'. -- -- Under these circumstances we say that `x' is non-escaping. -- -- An example of when (4) does not hold: -- -- let x = ... -- in case x of ...alts... -- -- Here, `x' is certainly entered only when the stack is deeper than when -- `x' is defined, but here it must return to ...alts... So we can't just -- adjust the stack down to `x''s recalled points, because that would lost -- alts' context. -- -- Things can get a little more complicated. Consider: -- -- let y = ... -- in let x = fvs \ args -> ...y... -- in ...x... -- -- Now, if `x' is used in a non-escaping way in ...x..., and `y' is used in a -- non-escaping way in ...y..., then `y' is non-escaping. -- -- `x' can even be recursive! Eg: -- -- letrec x = [y] \ [v] -> if v then x True else ... -- in -- ...(x b)... -- Note [Cost-centre initialization plan] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- Previously `coreToStg` was initializing cost-centre stack fields as `noCCS`, -- and the fields were then fixed by a separate pass `stgMassageForProfiling`. -- We now initialize these correctly. The initialization works like this: -- -- - For non-top level bindings always use `currentCCS`. -- -- - For top-level bindings, check if the binding is a CAF -- -- - CAF: If -fcaf-all is enabled, create a new CAF just for this CAF -- and use it. Note that these new cost centres need to be -- collected to be able to generate cost centre initialization -- code, so `coreToTopStgRhs` now returns `CollectedCCs`. -- -- If -fcaf-all is not enabled, use "all CAFs" cost centre. -- -- - Non-CAF: Top-level (static) data is not counted in heap profiles; nor -- do we set CCCS from it; so we just slam in -- dontCareCostCentre. -- -------------------------------------------------------------- -- Setting variable info: top-level, binds, RHSs -- -------------------------------------------------------------- coreToStg :: DynFlags -> Module -> CoreProgram -> ([StgTopBinding], CollectedCCs) coreToStg dflags this_mod pgm = (pgm', final_ccs) where (_, (local_ccs, local_cc_stacks), pgm') = coreTopBindsToStg dflags this_mod emptyVarEnv emptyCollectedCCs pgm prof = WayProf `elem` ways dflags final_ccs | prof && gopt Opt_AutoSccsOnIndividualCafs dflags = (local_ccs,local_cc_stacks) -- don't need "all CAFs" CC | prof = (all_cafs_cc:local_ccs, all_cafs_ccs:local_cc_stacks) | otherwise = emptyCollectedCCs (all_cafs_cc, all_cafs_ccs) = getAllCAFsCC this_mod coreTopBindsToStg :: DynFlags -> Module -> IdEnv HowBound -- environment for the bindings -> CollectedCCs -> CoreProgram -> (IdEnv HowBound, CollectedCCs, [StgTopBinding]) coreTopBindsToStg _ _ env ccs [] = (env, ccs, []) coreTopBindsToStg dflags this_mod env ccs (b:bs) = (env2, ccs2, b':bs') where (env1, ccs1, b' ) = coreTopBindToStg dflags this_mod env ccs b (env2, ccs2, bs') = coreTopBindsToStg dflags this_mod env1 ccs1 bs coreTopBindToStg :: DynFlags -> Module -> IdEnv HowBound -> CollectedCCs -> CoreBind -> (IdEnv HowBound, CollectedCCs, StgTopBinding) coreTopBindToStg _ _ env ccs (NonRec id e) | Just str <- exprIsTickedString_maybe e -- top-level string literal -- See Note [CoreSyn top-level string literals] in CoreSyn = let env' = extendVarEnv env id how_bound how_bound = LetBound TopLet 0 in (env', ccs, StgTopStringLit id str) coreTopBindToStg dflags this_mod env ccs (NonRec id rhs) = let env' = extendVarEnv env id how_bound how_bound = LetBound TopLet $! manifestArity rhs (stg_rhs, ccs') = initCts env $ coreToTopStgRhs dflags ccs this_mod (id,rhs) bind = StgTopLifted $ StgNonRec id stg_rhs in ASSERT2(consistentCafInfo id bind, ppr id ) -- NB: previously the assertion printed 'rhs' and 'bind' -- as well as 'id', but that led to a black hole -- where printing the assertion error tripped the -- assertion again! (env', ccs', bind) coreTopBindToStg dflags this_mod env ccs (Rec pairs) = ASSERT( not (null pairs) ) let binders = map fst pairs extra_env' = [ (b, LetBound TopLet $! manifestArity rhs) | (b, rhs) <- pairs ] env' = extendVarEnvList env extra_env' -- generate StgTopBindings and CAF cost centres created for CAFs (ccs', stg_rhss) = initCts env' $ do mapAccumLM (\ccs rhs -> do (rhs', ccs') <- coreToTopStgRhs dflags ccs this_mod rhs return (ccs', rhs')) ccs pairs bind = StgTopLifted $ StgRec (zip binders stg_rhss) in ASSERT2(consistentCafInfo (head binders) bind, ppr binders) (env', ccs', bind) -- Assertion helper: this checks that the CafInfo on the Id matches -- what CoreToStg has figured out about the binding's SRT. The -- CafInfo will be exact in all cases except when CorePrep has -- floated out a binding, in which case it will be approximate. consistentCafInfo :: Id -> StgTopBinding -> Bool consistentCafInfo id bind = WARN( not (exact || is_sat_thing) , ppr id <+> ppr id_marked_caffy <+> ppr binding_is_caffy ) safe where safe = id_marked_caffy || not binding_is_caffy exact = id_marked_caffy == binding_is_caffy id_marked_caffy = mayHaveCafRefs (idCafInfo id) binding_is_caffy = topStgBindHasCafRefs bind is_sat_thing = occNameFS (nameOccName (idName id)) == fsLit "sat" coreToTopStgRhs :: DynFlags -> CollectedCCs -> Module -> (Id,CoreExpr) -> CtsM (StgRhs, CollectedCCs) coreToTopStgRhs dflags ccs this_mod (bndr, rhs) = do { new_rhs <- coreToStgExpr rhs ; let (stg_rhs, ccs') = mkTopStgRhs dflags this_mod ccs bndr new_rhs stg_arity = stgRhsArity stg_rhs ; return (ASSERT2( arity_ok stg_arity, mk_arity_msg stg_arity) stg_rhs, ccs') } where -- It's vital that the arity on a top-level Id matches -- the arity of the generated STG binding, else an importing -- module will use the wrong calling convention -- (Trac #2844 was an example where this happened) -- NB1: we can't move the assertion further out without -- blocking the "knot" tied in coreTopBindsToStg -- NB2: the arity check is only needed for Ids with External -- Names, because they are externally visible. The CorePrep -- pass introduces "sat" things with Local Names and does -- not bother to set their Arity info, so don't fail for those arity_ok stg_arity | isExternalName (idName bndr) = id_arity == stg_arity | otherwise = True id_arity = idArity bndr mk_arity_msg stg_arity = vcat [ppr bndr, text "Id arity:" <+> ppr id_arity, text "STG arity:" <+> ppr stg_arity] -- --------------------------------------------------------------------------- -- Expressions -- --------------------------------------------------------------------------- coreToStgExpr :: CoreExpr -> CtsM StgExpr -- The second and third components can be derived in a simple bottom up pass, not -- dependent on any decisions about which variables will be let-no-escaped or -- not. The first component, that is, the decorated expression, may then depend -- on these components, but it in turn is not scrutinised as the basis for any -- decisions. Hence no black holes. -- No LitInteger's or LitNatural's should be left by the time this is called. -- CorePrep should have converted them all to a real core representation. coreToStgExpr (Lit (LitNumber LitNumInteger _ _)) = panic "coreToStgExpr: LitInteger" coreToStgExpr (Lit (LitNumber LitNumNatural _ _)) = panic "coreToStgExpr: LitNatural" coreToStgExpr (Lit l) = return (StgLit l) coreToStgExpr (App (Lit LitRubbish) _some_unlifted_type) -- We lower 'LitRubbish' to @()@ here, which is much easier than doing it in -- a STG to Cmm pass. = coreToStgExpr (Var unitDataConId) coreToStgExpr (Var v) = coreToStgApp Nothing v [] [] coreToStgExpr (Coercion _) = coreToStgApp Nothing coercionTokenId [] [] coreToStgExpr expr@(App _ _) = coreToStgApp Nothing f args ticks where (f, args, ticks) = myCollectArgs expr coreToStgExpr expr@(Lam _ _) = let (args, body) = myCollectBinders expr args' = filterStgBinders args in extendVarEnvCts [ (a, LambdaBound) | a <- args' ] $ do body' <- coreToStgExpr body let result_expr = case nonEmpty args' of Nothing -> body' Just args'' -> StgLam args'' body' return result_expr coreToStgExpr (Tick tick expr) = do case tick of HpcTick{} -> return () ProfNote{} -> return () SourceNote{} -> return () Breakpoint{} -> panic "coreToStgExpr: breakpoint should not happen" expr2 <- coreToStgExpr expr return (StgTick tick expr2) coreToStgExpr (Cast expr _) = coreToStgExpr expr -- Cases require a little more real work. coreToStgExpr (Case scrut _ _ []) = coreToStgExpr scrut -- See Note [Empty case alternatives] in CoreSyn If the case -- alternatives are empty, the scrutinee must diverge or raise an -- exception, so we can just dive into it. -- -- Of course this may seg-fault if the scrutinee *does* return. A -- belt-and-braces approach would be to move this case into the -- code generator, and put a return point anyway that calls a -- runtime system error function. coreToStgExpr (Case scrut bndr _ alts) = do alts2 <- extendVarEnvCts [(bndr, LambdaBound)] (mapM vars_alt alts) scrut2 <- coreToStgExpr scrut return (StgCase scrut2 bndr (mkStgAltType bndr alts) alts2) where vars_alt (con, binders, rhs) | DataAlt c <- con, c == unboxedUnitDataCon = -- This case is a bit smelly. -- See Note [Nullary unboxed tuple] in Type.hs -- where a nullary tuple is mapped to (State# World#) ASSERT( null binders ) do { rhs2 <- coreToStgExpr rhs ; return (DEFAULT, [], rhs2) } | otherwise = let -- Remove type variables binders' = filterStgBinders binders in extendVarEnvCts [(b, LambdaBound) | b <- binders'] $ do rhs2 <- coreToStgExpr rhs return (con, binders', rhs2) coreToStgExpr (Let bind body) = do coreToStgLet bind body coreToStgExpr e = pprPanic "coreToStgExpr" (ppr e) mkStgAltType :: Id -> [CoreAlt] -> AltType mkStgAltType bndr alts | isUnboxedTupleType bndr_ty || isUnboxedSumType bndr_ty = MultiValAlt (length prim_reps) -- always use MultiValAlt for unboxed tuples | otherwise = case prim_reps of [LiftedRep] -> case tyConAppTyCon_maybe (unwrapType bndr_ty) of Just tc | isAbstractTyCon tc -> look_for_better_tycon | isAlgTyCon tc -> AlgAlt tc | otherwise -> ASSERT2( _is_poly_alt_tycon tc, ppr tc ) PolyAlt Nothing -> PolyAlt [unlifted] -> PrimAlt unlifted not_unary -> MultiValAlt (length not_unary) where bndr_ty = idType bndr prim_reps = typePrimRep bndr_ty _is_poly_alt_tycon tc = isFunTyCon tc || isPrimTyCon tc -- "Any" is lifted but primitive || isFamilyTyCon tc -- Type family; e.g. Any, or arising from strict -- function application where argument has a -- type-family type -- Sometimes, the TyCon is a AbstractTyCon which may not have any -- constructors inside it. Then we may get a better TyCon by -- grabbing the one from a constructor alternative -- if one exists. look_for_better_tycon | ((DataAlt con, _, _) : _) <- data_alts = AlgAlt (dataConTyCon con) | otherwise = ASSERT(null data_alts) PolyAlt where (data_alts, _deflt) = findDefault alts -- --------------------------------------------------------------------------- -- Applications -- --------------------------------------------------------------------------- coreToStgApp :: Maybe UpdateFlag -- Just upd <=> this application is -- the rhs of a thunk binding -- x = [...] \upd [] -> the_app -- with specified update flag -> Id -- Function -> [CoreArg] -- Arguments -> [Tickish Id] -- Debug ticks -> CtsM StgExpr coreToStgApp _ f args ticks = do (args', ticks') <- coreToStgArgs args how_bound <- lookupVarCts f let n_val_args = valArgCount args -- Mostly, the arity info of a function is in the fn's IdInfo -- But new bindings introduced by CoreSat may not have no -- arity info; it would do us no good anyway. For example: -- let f = \ab -> e in f -- No point in having correct arity info for f! -- Hence the hasArity stuff below. -- NB: f_arity is only consulted for LetBound things f_arity = stgArity f how_bound saturated = f_arity <= n_val_args res_ty = exprType (mkApps (Var f) args) app = case idDetails f of DataConWorkId dc | saturated -> StgConApp dc args' (dropRuntimeRepArgs (fromMaybe [] (tyConAppArgs_maybe res_ty))) -- Some primitive operator that might be implemented as a library call. PrimOpId op -> ASSERT( saturated ) StgOpApp (StgPrimOp op) args' res_ty -- A call to some primitive Cmm function. FCallId (CCall (CCallSpec (StaticTarget _ lbl (Just pkgId) True) PrimCallConv _)) -> ASSERT( saturated ) StgOpApp (StgPrimCallOp (PrimCall lbl pkgId)) args' res_ty -- A regular foreign call. FCallId call -> ASSERT( saturated ) StgOpApp (StgFCallOp call (idUnique f)) args' res_ty TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args') _other -> StgApp f args' tapp = foldr StgTick app (ticks ++ ticks') -- Forcing these fixes a leak in the code generator, noticed while -- profiling for trac #4367 app `seq` return tapp -- --------------------------------------------------------------------------- -- Argument lists -- This is the guy that turns applications into A-normal form -- --------------------------------------------------------------------------- coreToStgArgs :: [CoreArg] -> CtsM ([StgArg], [Tickish Id]) coreToStgArgs [] = return ([], []) coreToStgArgs (Type _ : args) = do -- Type argument (args', ts) <- coreToStgArgs args return (args', ts) coreToStgArgs (Coercion _ : args) -- Coercion argument; replace with place holder = do { (args', ts) <- coreToStgArgs args ; return (StgVarArg coercionTokenId : args', ts) } coreToStgArgs (Tick t e : args) = ASSERT( not (tickishIsCode t) ) do { (args', ts) <- coreToStgArgs (e : args) ; return (args', t:ts) } coreToStgArgs (arg : args) = do -- Non-type argument (stg_args, ticks) <- coreToStgArgs args arg' <- coreToStgExpr arg let (aticks, arg'') = stripStgTicksTop tickishFloatable arg' stg_arg = case arg'' of StgApp v [] -> StgVarArg v StgConApp con [] _ -> StgVarArg (dataConWorkId con) StgLit lit -> StgLitArg lit _ -> pprPanic "coreToStgArgs" (ppr arg) -- WARNING: what if we have an argument like (v `cast` co) -- where 'co' changes the representation type? -- (This really only happens if co is unsafe.) -- Then all the getArgAmode stuff in CgBindery will set the -- cg_rep of the CgIdInfo based on the type of v, rather -- than the type of 'co'. -- This matters particularly when the function is a primop -- or foreign call. -- Wanted: a better solution than this hacky warning let arg_ty = exprType arg stg_arg_ty = stgArgType stg_arg bad_args = (isUnliftedType arg_ty && not (isUnliftedType stg_arg_ty)) || (typePrimRep arg_ty /= typePrimRep stg_arg_ty) -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted), -- and pass it to a function expecting an HValue (arg_ty). This is ok because -- we can treat an unlifted value as lifted. But the other way round -- we complain. -- We also want to check if a pointer is cast to a non-ptr etc WARN( bad_args, text "Dangerous-looking argument. Probable cause: bad unsafeCoerce#" $$ ppr arg ) return (stg_arg : stg_args, ticks ++ aticks) -- --------------------------------------------------------------------------- -- The magic for lets: -- --------------------------------------------------------------------------- coreToStgLet :: CoreBind -- bindings -> CoreExpr -- body -> CtsM StgExpr -- new let coreToStgLet bind body = do (bind2, body2) <- do ( bind2, env_ext) <- vars_bind bind -- Do the body extendVarEnvCts env_ext $ do body2 <- coreToStgExpr body return (bind2, body2) -- Compute the new let-expression let new_let | isJoinBind bind = StgLetNoEscape noExtSilent bind2 body2 | otherwise = StgLet noExtSilent bind2 body2 return new_let where mk_binding binder rhs = (binder, LetBound NestedLet (manifestArity rhs)) vars_bind :: CoreBind -> CtsM (StgBinding, [(Id, HowBound)]) -- extension to environment vars_bind (NonRec binder rhs) = do rhs2 <- coreToStgRhs (binder,rhs) let env_ext_item = mk_binding binder rhs return (StgNonRec binder rhs2, [env_ext_item]) vars_bind (Rec pairs) = let binders = map fst pairs env_ext = [ mk_binding b rhs | (b,rhs) <- pairs ] in extendVarEnvCts env_ext $ do rhss2 <- mapM coreToStgRhs pairs return (StgRec (binders `zip` rhss2), env_ext) coreToStgRhs :: (Id,CoreExpr) -> CtsM StgRhs coreToStgRhs (bndr, rhs) = do new_rhs <- coreToStgExpr rhs return (mkStgRhs bndr new_rhs) -- Generate a top-level RHS. Any new cost centres generated for CAFs will be -- appended to `CollectedCCs` argument. mkTopStgRhs :: DynFlags -> Module -> CollectedCCs -> Id -> StgExpr -> (StgRhs, CollectedCCs) mkTopStgRhs dflags this_mod ccs bndr rhs | StgLam bndrs body <- rhs = -- StgLam can't have empty arguments, so not CAF ( StgRhsClosure noExtSilent dontCareCCS ReEntrant (toList bndrs) body , ccs ) | StgConApp con args _ <- unticked_rhs , -- Dynamic StgConApps are updatable not (isDllConApp dflags this_mod con args) = -- CorePrep does this right, but just to make sure ASSERT2( not (isUnboxedTupleCon con || isUnboxedSumCon con) , ppr bndr $$ ppr con $$ ppr args) ( StgRhsCon dontCareCCS con args, ccs ) -- Otherwise it's a CAF, see Note [Cost-centre initialization plan]. | gopt Opt_AutoSccsOnIndividualCafs dflags = ( StgRhsClosure noExtSilent caf_ccs upd_flag [] rhs , collectCC caf_cc caf_ccs ccs ) | otherwise = ( StgRhsClosure noExtSilent all_cafs_ccs upd_flag [] rhs , ccs ) where (_, unticked_rhs) = stripStgTicksTop (not . tickishIsCode) rhs upd_flag | isUsedOnce (idDemandInfo bndr) = SingleEntry | otherwise = Updatable -- CAF cost centres generated for -fcaf-all caf_cc = mkAutoCC bndr modl caf_ccs = mkSingletonCCS caf_cc -- careful: the binder might be :Main.main, -- which doesn't belong to module mod_name. -- bug #249, tests prof001, prof002 modl | Just m <- nameModule_maybe (idName bndr) = m | otherwise = this_mod -- default CAF cost centre (_, all_cafs_ccs) = getAllCAFsCC this_mod -- Generate a non-top-level RHS. Cost-centre is always currentCCS, -- see Note [Cost-centre initialzation plan]. mkStgRhs :: Id -> StgExpr -> StgRhs mkStgRhs bndr rhs | StgLam bndrs body <- rhs = StgRhsClosure noExtSilent currentCCS ReEntrant (toList bndrs) body | isJoinId bndr -- must be a nullary join point = ASSERT(idJoinArity bndr == 0) StgRhsClosure noExtSilent currentCCS ReEntrant -- ignored for LNE [] rhs | StgConApp con args _ <- unticked_rhs = StgRhsCon currentCCS con args | otherwise = StgRhsClosure noExtSilent currentCCS upd_flag [] rhs where (_, unticked_rhs) = stripStgTicksTop (not . tickishIsCode) rhs upd_flag | isUsedOnce (idDemandInfo bndr) = SingleEntry | otherwise = Updatable {- SDM: disabled. Eval/Apply can't handle functions with arity zero very well; and making these into simple non-updatable thunks breaks other assumptions (namely that they will be entered only once). upd_flag | isPAP env rhs = ReEntrant | otherwise = Updatable -- Detect thunks which will reduce immediately to PAPs, and make them -- non-updatable. This has several advantages: -- -- - the non-updatable thunk behaves exactly like the PAP, -- -- - the thunk is more efficient to enter, because it is -- specialised to the task. -- -- - we save one update frame, one stg_update_PAP, one update -- and lots of PAP_enters. -- -- - in the case where the thunk is top-level, we save building -- a black hole and furthermore the thunk isn't considered to -- be a CAF any more, so it doesn't appear in any SRTs. -- -- We do it here, because the arity information is accurate, and we need -- to do it before the SRT pass to save the SRT entries associated with -- any top-level PAPs. isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args where arity = stgArity f (lookupBinding env f) isPAP env _ = False -} {- ToDo: upd = if isOnceDem dem then (if isNotTop toplev then SingleEntry -- HA! Paydirt for "dem" else (if debugIsOn then trace "WARNING: SE CAFs unsupported, forcing UPD instead" else id) $ Updatable) else Updatable -- For now we forbid SingleEntry CAFs; they tickle the -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link, -- and I don't understand why. There's only one SE_CAF (well, -- only one that tickled a great gaping bug in an earlier attempt -- at ClosureInfo.getEntryConvention) in the whole of nofib, -- specifically Main.lvl6 in spectral/cryptarithm2. -- So no great loss. KSW 2000-07. -} -- --------------------------------------------------------------------------- -- A monad for the core-to-STG pass -- --------------------------------------------------------------------------- -- There's a lot of stuff to pass around, so we use this CtsM -- ("core-to-STG monad") monad to help. All the stuff here is only passed -- *down*. newtype CtsM a = CtsM { unCtsM :: IdEnv HowBound -> a } data HowBound = ImportBound -- Used only as a response to lookupBinding; never -- exists in the range of the (IdEnv HowBound) | LetBound -- A let(rec) in this module LetInfo -- Whether top level or nested Arity -- Its arity (local Ids don't have arity info at this point) | LambdaBound -- Used for both lambda and case deriving (Eq) data LetInfo = TopLet -- top level things | NestedLet deriving (Eq) -- For a let(rec)-bound variable, x, we record LiveInfo, the set of -- variables that are live if x is live. This LiveInfo comprises -- (a) dynamic live variables (ones with a non-top-level binding) -- (b) static live variabes (CAFs or things that refer to CAFs) -- -- For "normal" variables (a) is just x alone. If x is a let-no-escaped -- variable then x is represented by a code pointer and a stack pointer -- (well, one for each stack). So all of the variables needed in the -- execution of x are live if x is, and are therefore recorded in the -- LetBound constructor; x itself *is* included. -- -- The set of dynamic live variables is guaranteed ot have no further -- let-no-escaped variables in it. -- The std monad functions: initCts :: IdEnv HowBound -> CtsM a -> a initCts env m = unCtsM m env {-# INLINE thenCts #-} {-# INLINE returnCts #-} returnCts :: a -> CtsM a returnCts e = CtsM $ \_ -> e thenCts :: CtsM a -> (a -> CtsM b) -> CtsM b thenCts m k = CtsM $ \env -> unCtsM (k (unCtsM m env)) env instance Functor CtsM where fmap = liftM instance Applicative CtsM where pure = returnCts (<*>) = ap instance Monad CtsM where (>>=) = thenCts -- Functions specific to this monad: extendVarEnvCts :: [(Id, HowBound)] -> CtsM a -> CtsM a extendVarEnvCts ids_w_howbound expr = CtsM $ \env -> unCtsM expr (extendVarEnvList env ids_w_howbound) lookupVarCts :: Id -> CtsM HowBound lookupVarCts v = CtsM $ \env -> lookupBinding env v lookupBinding :: IdEnv HowBound -> Id -> HowBound lookupBinding env v = case lookupVarEnv env v of Just xx -> xx Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound getAllCAFsCC :: Module -> (CostCentre, CostCentreStack) getAllCAFsCC this_mod = let span = mkGeneralSrcSpan (mkFastString "<entire-module>") -- XXX do better all_cafs_cc = mkAllCafsCC this_mod span all_cafs_ccs = mkSingletonCCS all_cafs_cc in (all_cafs_cc, all_cafs_ccs) -- Misc. filterStgBinders :: [Var] -> [Var] filterStgBinders bndrs = filter isId bndrs myCollectBinders :: Expr Var -> ([Var], Expr Var) myCollectBinders expr = go [] expr where go bs (Lam b e) = go (b:bs) e go bs (Cast e _) = go bs e go bs e = (reverse bs, e) -- | Precondition: argument expression is an 'App', and there is a 'Var' at the -- head of the 'App' chain. myCollectArgs :: CoreExpr -> (Id, [CoreArg], [Tickish Id]) myCollectArgs expr = go expr [] [] where go (Var v) as ts = (v, as, ts) go (App f a) as ts = go f (a:as) ts go (Tick t e) as ts = ASSERT( all isTypeArg as ) go e as (t:ts) -- ticks can appear in type apps go (Cast e _) as ts = go e as ts go (Lam b e) as ts | isTyVar b = go e as ts -- Note [Collect args] go _ _ _ = pprPanic "CoreToStg.myCollectArgs" (ppr expr) -- Note [Collect args] -- ~~~~~~~~~~~~~~~~~~~ -- -- This big-lambda case occurred following a rather obscure eta expansion. -- It all seems a bit yukky to me. stgArity :: Id -> HowBound -> Arity stgArity _ (LetBound _ arity) = arity stgArity f ImportBound = idArity f stgArity _ LambdaBound = 0