{-# 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, coreExprToStg ) where #include "HsVersions.h" import CoreSyn import CoreUtils ( exprType, findDefault ) import CoreArity ( manifestArity ) import StgSyn import Type import RepType import TyCon import MkId ( coercionTokenId ) import Id import IdInfo import DataCon import CostCentre ( noCCS ) import VarSet import VarEnv import Module import Name ( getOccName, isExternalName, nameOccName ) import OccName ( occNameString, occNameFS ) import BasicTypes ( Arity ) import TysWiredIn ( unboxedUnitDataCon ) import Literal import Outputable import MonadUtils import FastString import Util import DynFlags import ForeignCall import Demand ( isUsedOnce ) import PrimOp ( PrimCall(..) ) import UniqFM import Data.Maybe (isJust, 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 [Collecting live CAF info] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- In this pass we also collect information on which CAFs are live. -- -- A top-level Id has CafInfo, which is -- -- - MayHaveCafRefs, if it may refer indirectly to -- one or more CAFs, or -- - NoCafRefs if it definitely doesn't -- -- The CafInfo has already been calculated during the CoreTidy pass. -- -- During CoreToStg, we then pin onto each binding and case expression, a -- list of Ids which represents the "live" CAFs at that point. The meaning -- of "live" here is the same as for live variables, see above (which is -- why it's convenient to collect CAF information here rather than elsewhere). -- -- The later SRT pass takes these lists of Ids and uses them to construct -- the actual nested SRTs, and replaces the lists of Ids with (offset,length) -- pairs. -- Note [What is a non-escaping let] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- -- 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 - it must have at least one parameter (see Note -- [Join point abstraction]); -- 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)... -- -------------------------------------------------------------- -- Setting variable info: top-level, binds, RHSs -- -------------------------------------------------------------- coreToStg :: DynFlags -> Module -> CoreProgram -> [StgBinding] coreToStg dflags this_mod pgm = pgm' where (_, _, pgm') = coreTopBindsToStg dflags this_mod emptyVarEnv pgm coreExprToStg :: CoreExpr -> StgExpr coreExprToStg expr = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr) coreTopBindsToStg :: DynFlags -> Module -> IdEnv HowBound -- environment for the bindings -> CoreProgram -> (IdEnv HowBound, FreeVarsInfo, [StgBinding]) coreTopBindsToStg _ _ env [] = (env, emptyFVInfo, []) coreTopBindsToStg dflags this_mod env (b:bs) = (env2, fvs2, b':bs') where -- Notice the mutually-recursive "knot" here: -- env accumulates down the list of binds, -- fvs accumulates upwards (env1, fvs2, b' ) = coreTopBindToStg dflags this_mod env fvs1 b (env2, fvs1, bs') = coreTopBindsToStg dflags this_mod env1 bs coreTopBindToStg :: DynFlags -> Module -> IdEnv HowBound -> FreeVarsInfo -- Info about the body -> CoreBind -> (IdEnv HowBound, FreeVarsInfo, StgBinding) coreTopBindToStg dflags this_mod env body_fvs (NonRec id rhs) = let env' = extendVarEnv env id how_bound how_bound = LetBound TopLet $! manifestArity rhs (stg_rhs, fvs') = initLne env $ do (stg_rhs, fvs') <- coreToTopStgRhs dflags this_mod body_fvs (id,rhs) return (stg_rhs, fvs') bind = 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', fvs' `unionFVInfo` body_fvs, bind) coreTopBindToStg dflags this_mod env body_fvs (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' (stg_rhss, fvs') = initLne env' $ do (stg_rhss, fvss') <- mapAndUnzipM (coreToTopStgRhs dflags this_mod body_fvs) pairs let fvs' = unionFVInfos fvss' return (stg_rhss, fvs') bind = StgRec (zip binders stg_rhss) in ASSERT2(consistentCafInfo (head binders) bind, ppr binders) (env', fvs' `unionFVInfo` body_fvs, 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 -> GenStgBinding Var Id -> 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 -> Module -> FreeVarsInfo -- Free var info for the scope of the binding -> (Id,CoreExpr) -> LneM (StgRhs, FreeVarsInfo) coreToTopStgRhs dflags this_mod scope_fv_info (bndr, rhs) = do { (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs ; let stg_rhs = mkTopStgRhs dflags this_mod rhs_fvs bndr bndr_info new_rhs stg_arity = stgRhsArity stg_rhs ; return (ASSERT2( arity_ok stg_arity, mk_arity_msg stg_arity) stg_rhs, rhs_fvs) } where bndr_info = lookupFVInfo scope_fv_info bndr -- 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] mkTopStgRhs :: DynFlags -> Module -> FreeVarsInfo -> Id -> StgBinderInfo -> StgExpr -> StgRhs mkTopStgRhs dflags this_mod = mkStgRhs' con_updateable -- Dynamic StgConApps are updatable where con_updateable con args = isDllConApp dflags this_mod con args -- --------------------------------------------------------------------------- -- Expressions -- --------------------------------------------------------------------------- coreToStgExpr :: CoreExpr -> LneM (StgExpr, -- Decorated STG expr FreeVarsInfo, -- Its free vars (NB free, not live) EscVarsSet) -- Its escapees, a subset of its free vars; -- also a subset of the domain of the envt -- because we are only interested in the escapees -- for vars which might be turned into -- let-no-escaped ones. -- 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 should be left by the time this is called. CorePrep -- should have converted them all to a real core representation. coreToStgExpr (Lit (LitInteger {})) = panic "coreToStgExpr: LitInteger" coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet) 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 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do (body, body_fvs, body_escs) <- coreToStgExpr body let fvs = args' `minusFVBinders` body_fvs escs = body_escs `delVarSetList` args' result_expr | null args' = body | otherwise = StgLam args' body return (result_expr, fvs, escs) coreToStgExpr (Tick tick expr) = do case tick of HpcTick{} -> return () ProfNote{} -> return () SourceNote{} -> return () Breakpoint{} -> panic "coreToStgExpr: breakpoint should not happen" (expr2, fvs, escs) <- coreToStgExpr expr return (StgTick tick expr2, fvs, escs) 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, alts_fvs, alts_escs) <- extendVarEnvLne [(bndr, LambdaBound)] $ do (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts return ( alts2, unionFVInfos fvs_s, unionVarSets escs_s ) let -- Determine whether the default binder is dead or not -- This helps the code generator to avoid generating an assignment -- for the case binder (is extremely rare cases) ToDo: remove. bndr' | bndr `elementOfFVInfo` alts_fvs = bndr | otherwise = bndr `setIdOccInfo` IAmDead -- Don't consider the default binder as being 'live in alts', -- since this is from the point of view of the case expr, where -- the default binder is not free. alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs alts_escs_wo_bndr = alts_escs `delVarSet` bndr -- We tell the scrutinee that everything -- live in the alts is live in it, too. (scrut2, scrut_fvs, _scrut_escs) <- coreToStgExpr scrut return ( StgCase scrut2 bndr' (mkStgAltType bndr alts) alts2, scrut_fvs `unionFVInfo` alts_fvs_wo_bndr, alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs -- You might think we should have scrut_escs, not -- (getFVSet scrut_fvs), but actually we can't call, and -- then return from, a let-no-escape thing. ) 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, rhs_fvs, rhs_escs) <- coreToStgExpr rhs ; return ((DEFAULT, [], rhs2), rhs_fvs, rhs_escs) } | otherwise = let -- Remove type variables binders' = filterStgBinders binders in extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs return ( (con, binders', rhs2), binders' `minusFVBinders` rhs_fvs, rhs_escs `delVarSetList` binders' ) -- ToDo: remove the delVarSet; -- since escs won't include any of these binders -- Lets not only take quite a bit of work, but this is where we convert -- then to let-no-escapes, if we wish. -- (Meanwhile, we don't expect to see let-no-escapes...) coreToStgExpr (Let bind body) = do (new_let, fvs, escs, _) <- mfix (\ ~(_, _, _, no_binder_escapes) -> coreToStgLet no_binder_escapes bind body ) return (new_let, fvs, escs) coreToStgExpr e = pprPanic "coreToStgExpr" (ppr e) mkStgAltType :: Id -> [CoreAlt] -> AltType mkStgAltType bndr alts = case repType (idType bndr) of UnaryRep rep_ty -> case tyConAppTyCon_maybe rep_ty of Just tc | isUnliftedTyCon tc -> PrimAlt tc | isAbstractTyCon tc -> look_for_better_tycon | isAlgTyCon tc -> AlgAlt tc | otherwise -> ASSERT2( _is_poly_alt_tycon tc, ppr tc ) PolyAlt Nothing -> PolyAlt MultiRep slots -> MultiValAlt (length slots) where _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 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet) coreToStgApp _ f args ticks = do (args', args_fvs, ticks') <- coreToStgArgs args how_bound <- lookupVarLne f let n_val_args = valArgCount args not_letrec_bound = not (isLetBound how_bound) fun_fvs = singletonFVInfo f how_bound fun_occ -- e.g. (f :: a -> int) (x :: a) -- Here the free variables are "f", "x" AND the type variable "a" -- coreToStgArgs will deal with the arguments recursively -- 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 fun_occ | not_letrec_bound = noBinderInfo -- Uninteresting variable | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call | otherwise = stgUnsatOcc -- Unsaturated function or thunk fun_escs | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly -- saturated call doesn't escape -- (let-no-escape applies to 'thunks' too) | otherwise = unitVarSet f -- Inexact application; it does escape -- At the moment of the call: -- either the function is *not* let-no-escaped, in which case -- nothing is live except live_in_cont -- or the function *is* let-no-escaped in which case the -- variables it uses are live, but still the function -- itself is not. PS. In this case, the function's -- live vars should already include those of the -- continuation, but it does no harm to just union the -- two regardless. 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' fvs = fun_fvs `unionFVInfo` args_fvs vars = fun_escs `unionVarSet` (getFVSet args_fvs) -- All the free vars of the args are disqualified -- from being let-no-escaped. tapp = foldr StgTick app (ticks ++ ticks') -- Forcing these fixes a leak in the code generator, noticed while -- profiling for trac #4367 app `seq` fvs `seq` seqVarSet vars `seq` return ( tapp, fvs, vars ) -- --------------------------------------------------------------------------- -- Argument lists -- This is the guy that turns applications into A-normal form -- --------------------------------------------------------------------------- coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo, [Tickish Id]) coreToStgArgs [] = return ([], emptyFVInfo, []) coreToStgArgs (Type _ : args) = do -- Type argument (args', fvs, ts) <- coreToStgArgs args return (args', fvs, ts) coreToStgArgs (Coercion _ : args) -- Coercion argument; replace with place holder = do { (args', fvs, ts) <- coreToStgArgs args ; return (StgVarArg coercionTokenId : args', fvs, ts) } coreToStgArgs (Tick t e : args) = ASSERT( not (tickishIsCode t) ) do { (args', fvs, ts) <- coreToStgArgs (e : args) ; return (args', fvs, t:ts) } coreToStgArgs (arg : args) = do -- Non-type argument (stg_args, args_fvs, ticks) <- coreToStgArgs args (arg', arg_fvs, _escs) <- coreToStgExpr arg let fvs = args_fvs `unionFVInfo` arg_fvs (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)) || (map typePrimRep (repTypeArgs arg_ty) /= map typePrimRep (repTypeArgs 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, fvs, ticks ++ aticks) -- --------------------------------------------------------------------------- -- The magic for lets: -- --------------------------------------------------------------------------- coreToStgLet :: Bool -- True <=> yes, we are let-no-escaping this let -> CoreBind -- bindings -> CoreExpr -- body -> LneM (StgExpr, -- new let FreeVarsInfo, -- variables free in the whole let EscVarsSet, -- variables that escape from the whole let Bool) -- True <=> none of the binders in the bindings -- is among the escaping vars coreToStgLet let_no_escape bind body = do (bind2, bind_fvs, bind_escs, body2, body_fvs, body_escs) <- mfix $ \ ~(_, _, _, _, rec_body_fvs, _) -> do ( bind2, bind_fvs, bind_escs, env_ext) <- vars_bind rec_body_fvs bind -- Do the body extendVarEnvLne env_ext $ do (body2, body_fvs, body_escs) <- coreToStgExpr body return (bind2, bind_fvs, bind_escs, body2, body_fvs, body_escs) -- Compute the new let-expression let new_let | let_no_escape = StgLetNoEscape bind2 body2 | otherwise = StgLet bind2 body2 free_in_whole_let = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs) real_bind_escs = if let_no_escape then bind_escs else getFVSet bind_fvs -- Everything escapes which is free in the bindings let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of -- this let(rec) no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs) -- Debugging code as requested by Andrew Kennedy checked_no_binder_escapes | debugIsOn && not no_binder_escapes && any is_join_var binders = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders) False | otherwise = no_binder_escapes -- Mustn't depend on the passed-in let_no_escape flag, since -- no_binder_escapes is used by the caller to derive the flag! return ( new_let, free_in_whole_let, let_escs, checked_no_binder_escapes ) where set_of_binders = mkVarSet binders binders = bindersOf bind mk_binding binder rhs = (binder, LetBound NestedLet (manifestArity rhs)) vars_bind :: FreeVarsInfo -- Free var info for body of binding -> CoreBind -> LneM (StgBinding, FreeVarsInfo, EscVarsSet, -- free vars; escapee vars [(Id, HowBound)]) -- extension to environment vars_bind body_fvs (NonRec binder rhs) = do (rhs2, bind_fvs, escs) <- coreToStgRhs body_fvs (binder,rhs) let env_ext_item = mk_binding binder rhs return (StgNonRec binder rhs2, bind_fvs, escs, [env_ext_item]) vars_bind body_fvs (Rec pairs) = mfix $ \ ~(_, rec_rhs_fvs, _, _) -> let rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs binders = map fst pairs env_ext = [ mk_binding b rhs | (b,rhs) <- pairs ] in extendVarEnvLne env_ext $ do (rhss2, fvss, escss) <- mapAndUnzip3M (coreToStgRhs rec_scope_fvs) pairs let bind_fvs = unionFVInfos fvss escs = unionVarSets escss return (StgRec (binders `zip` rhss2), bind_fvs, escs, env_ext) is_join_var :: Id -> Bool -- A hack (used only for compiler debuggging) to tell if -- a variable started life as a join point ($j) is_join_var j = occNameString (getOccName j) == "$j" coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding -> (Id,CoreExpr) -> LneM (StgRhs, FreeVarsInfo, EscVarsSet) coreToStgRhs scope_fv_info (bndr, rhs) = do (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs return (mkStgRhs rhs_fvs bndr bndr_info new_rhs, rhs_fvs, rhs_escs) where bndr_info = lookupFVInfo scope_fv_info bndr mkStgRhs :: FreeVarsInfo -> Id -> StgBinderInfo -> StgExpr -> StgRhs mkStgRhs = mkStgRhs' con_updateable where con_updateable _ _ = False mkStgRhs' :: (DataCon -> [StgArg] -> Bool) -> FreeVarsInfo -> Id -> StgBinderInfo -> StgExpr -> StgRhs mkStgRhs' con_updateable rhs_fvs bndr binder_info rhs | StgLam bndrs body <- rhs = StgRhsClosure noCCS binder_info (getFVs rhs_fvs) ReEntrant bndrs body | StgConApp con args _ <- unticked_rhs , not (con_updateable con args) = -- CorePrep does this right, but just to make sure ASSERT(not (isUnboxedTupleCon con || isUnboxedSumCon con)) StgRhsCon noCCS con args | otherwise = StgRhsClosure noCCS binder_info (getFVs rhs_fvs) 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 futhermore 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 little monad for this let-no-escaping pass -- --------------------------------------------------------------------------- -- There's a lot of stuff to pass around, so we use this LneM monad to -- help. All the stuff here is only passed *down*. newtype LneM a = LneM { unLneM :: IdEnv HowBound -> a } type EscVarsSet = IdSet 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) isLetBound :: HowBound -> Bool isLetBound (LetBound _ _) = True isLetBound _ = False topLevelBound :: HowBound -> Bool topLevelBound ImportBound = True topLevelBound (LetBound TopLet _) = True topLevelBound _ = False -- 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: initLne :: IdEnv HowBound -> LneM a -> a initLne env m = unLneM m env {-# INLINE thenLne #-} {-# INLINE returnLne #-} returnLne :: a -> LneM a returnLne e = LneM $ \_ -> e thenLne :: LneM a -> (a -> LneM b) -> LneM b thenLne m k = LneM $ \env -> unLneM (k (unLneM m env)) env instance Functor LneM where fmap = liftM instance Applicative LneM where pure = returnLne (<*>) = ap instance Monad LneM where (>>=) = thenLne instance MonadFix LneM where mfix expr = LneM $ \env -> let result = unLneM (expr result) env in result -- Functions specific to this monad: extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a extendVarEnvLne ids_w_howbound expr = LneM $ \env -> unLneM expr (extendVarEnvList env ids_w_howbound) lookupVarLne :: Id -> LneM HowBound lookupVarLne v = LneM $ \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 -- --------------------------------------------------------------------------- -- Free variable information -- --------------------------------------------------------------------------- type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo) -- The Var is so we can gather up the free variables -- as a set. -- -- The HowBound info just saves repeated lookups; -- we look up just once when we encounter the occurrence. -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids -- Imported Ids without CAF refs are simply -- not put in the FreeVarsInfo for an expression. -- See singletonFVInfo and freeVarsToLiveVars -- -- StgBinderInfo records how it occurs; notably, we -- are interested in whether it only occurs in saturated -- applications, because then we don't need to build a -- curried version. -- If f is mapped to noBinderInfo, that means -- that f *is* mentioned (else it wouldn't be in the -- IdEnv at all), but perhaps in an unsaturated applications. -- -- All case/lambda-bound things are also mapped to -- noBinderInfo, since we aren't interested in their -- occurrence info. -- -- For ILX we track free var info for type variables too; -- hence VarEnv not IdEnv emptyFVInfo :: FreeVarsInfo emptyFVInfo = emptyVarEnv singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo -- Don't record non-CAF imports at all, to keep free-var sets small singletonFVInfo id ImportBound info | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info) | otherwise = emptyVarEnv singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info) unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo minusFVBinders vs fv = foldr minusFVBinder fv vs minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo minusFVBinder v fv = fv `delVarEnv` v -- When removing a binder, remember to add its type variables -- c.f. CoreFVs.delBinderFV elementOfFVInfo :: Id -> FreeVarsInfo -> Bool elementOfFVInfo id fvs = isJust (lookupVarEnv fvs id) lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo -- Find how the given Id is used. -- Externally visible things may be used any old how lookupFVInfo fvs id | isExternalName (idName id) = noBinderInfo | otherwise = case lookupVarEnv fvs id of Nothing -> noBinderInfo Just (_,_,info) -> info -- Non-top-level things only, both type variables and ids getFVs :: FreeVarsInfo -> [Var] getFVs fvs = [id | (id, how_bound, _) <- nonDetEltsUFM fvs, -- It's OK to use nonDetEltsUFM here because we're not aiming for -- bit-for-bit determinism. -- See Note [Unique Determinism and code generation] not (topLevelBound how_bound) ] getFVSet :: FreeVarsInfo -> VarSet getFVSet fvs = mkVarSet (getFVs fvs) plusFVInfo :: (Var, HowBound, StgBinderInfo) -> (Var, HowBound, StgBinderInfo) -> (Var, HowBound, StgBinderInfo) plusFVInfo (id1,hb1,info1) (id2,hb2,info2) = ASSERT(id1 == id2 && hb1 == hb2) (id1, hb1, combineStgBinderInfo info1 info2) -- 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) myCollectArgs :: CoreExpr -> (Id, [CoreArg], [Tickish Id]) -- We assume that we only have variables -- in the function position by now 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