2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[CoreToStg]{Converts Core to STG Syntax}
6 And, as we have the info in hand, we may convert some lets to
11 -- The above warning supression flag is a temporary kludge.
12 -- While working on this module you are encouraged to remove it and fix
13 -- any warnings in the module. See
14 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
17 module CoreToStg ( coreToStg, coreExprToStg ) where
19 #include "HsVersions.h"
22 import CoreUtils ( rhsIsStatic, manifestArity, exprType, findDefault )
28 import Var ( Var, globalIdDetails, idType )
31 import CostCentre ( noCCS )
34 import Maybes ( maybeToBool )
35 import Name ( getOccName, isExternalName, nameOccName )
36 import OccName ( occNameString, occNameFS )
37 import BasicTypes ( Arity )
38 import StaticFlags ( opt_RuntimeTypes )
44 %************************************************************************
46 \subsection[live-vs-free-doc]{Documentation}
48 %************************************************************************
50 (There is other relevant documentation in codeGen/CgLetNoEscape.)
52 The actual Stg datatype is decorated with {\em live variable}
53 information, as well as {\em free variable} information. The two are
54 {\em not} the same. Liveness is an operational property rather than a
55 semantic one. A variable is live at a particular execution point if
56 it can be referred to {\em directly} again. In particular, a dead
57 variable's stack slot (if it has one):
60 should be stubbed to avoid space leaks, and
62 may be reused for something else.
65 There ought to be a better way to say this. Here are some examples:
72 Just after the `in', v is live, but q is dead. If the whole of that
73 let expression was enclosed in a case expression, thus:
75 case (let v = [q] \[x] -> e in ...v...) of
78 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
79 we'll return later to the @alts@ and need it.
81 Let-no-escapes make this a bit more interesting:
83 let-no-escape v = [q] \ [x] -> e
87 Here, @q@ is still live at the `in', because @v@ is represented not by
88 a closure but by the current stack state. In other words, if @v@ is
89 live then so is @q@. Furthermore, if @e@ mentions an enclosing
90 let-no-escaped variable, then {\em its} free variables are also live
93 %************************************************************************
95 \subsection[caf-info]{Collecting live CAF info}
97 %************************************************************************
99 In this pass we also collect information on which CAFs are live for
100 constructing SRTs (see SRT.lhs).
102 A top-level Id has CafInfo, which is
104 - MayHaveCafRefs, if it may refer indirectly to
106 - NoCafRefs if it definitely doesn't
108 The CafInfo has already been calculated during the CoreTidy pass.
110 During CoreToStg, we then pin onto each binding and case expression, a
111 list of Ids which represents the "live" CAFs at that point. The meaning
112 of "live" here is the same as for live variables, see above (which is
113 why it's convenient to collect CAF information here rather than elsewhere).
115 The later SRT pass takes these lists of Ids and uses them to construct
116 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
120 Interaction of let-no-escape with SRTs [Sept 01]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
124 let-no-escape x = ...caf1...caf2...
128 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
129 build SRTs just as if x's defn was inlined at each call site, and
130 that means that x's CAF refs get duplicated in the overall SRT.
132 This is unlike ordinary lets, in which the CAF refs are not duplicated.
134 We could fix this loss of (static) sharing by making a sort of pseudo-closure
135 for x, solely to put in the SRTs lower down.
138 %************************************************************************
140 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
142 %************************************************************************
145 coreToStg :: PackageId -> [CoreBind] -> IO [StgBinding]
146 coreToStg this_pkg pgm
148 where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm
150 coreExprToStg :: CoreExpr -> StgExpr
152 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
157 -> IdEnv HowBound -- environment for the bindings
159 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
161 coreTopBindsToStg this_pkg env [] = (env, emptyFVInfo, [])
162 coreTopBindsToStg this_pkg env (b:bs)
163 = (env2, fvs2, b':bs')
165 -- env accumulates down the list of binds, fvs accumulates upwards
166 (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
167 (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs
173 -> FreeVarsInfo -- Info about the body
175 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
177 coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
179 env' = extendVarEnv env id how_bound
180 how_bound = LetBound TopLet $! manifestArity rhs
184 (stg_rhs, fvs') <- coreToTopStgRhs this_pkg body_fvs (id,rhs)
185 return (stg_rhs, fvs')
187 bind = StgNonRec id stg_rhs
189 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id $$ (ptext SLIT("rhs:")) <+> ppr rhs $$ (ptext SLIT("stg_rhs:"))<+> ppr stg_rhs $$ (ptext SLIT("Manifest:")) <+> (ppr $ manifestArity rhs) $$ (ptext SLIT("STG:")) <+>(ppr $ stgRhsArity stg_rhs) )
190 ASSERT2(consistentCafInfo id bind, ppr id)
191 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
192 (env', fvs' `unionFVInfo` body_fvs, bind)
194 coreTopBindToStg this_pkg env body_fvs (Rec pairs)
196 (binders, rhss) = unzip pairs
198 extra_env' = [ (b, LetBound TopLet $! manifestArity rhs)
199 | (b, rhs) <- pairs ]
200 env' = extendVarEnvList env extra_env'
204 (stg_rhss, fvss') <- mapAndUnzipM (coreToTopStgRhs this_pkg body_fvs) pairs
205 let fvs' = unionFVInfos fvss'
206 return (stg_rhss, fvs')
208 bind = StgRec (zip binders stg_rhss)
210 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
211 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
212 (env', fvs' `unionFVInfo` body_fvs, bind)
214 -- Assertion helper: this checks that the CafInfo on the Id matches
215 -- what CoreToStg has figured out about the binding's SRT. The
216 -- CafInfo will be exact in all cases except when CorePrep has
217 -- floated out a binding, in which case it will be approximate.
218 consistentCafInfo id bind
219 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
222 = WARN (not exact, ppr id) safe
224 safe = id_marked_caffy || not binding_is_caffy
225 exact = id_marked_caffy == binding_is_caffy
226 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
227 binding_is_caffy = stgBindHasCafRefs bind
233 -> FreeVarsInfo -- Free var info for the scope of the binding
235 -> LneM (StgRhs, FreeVarsInfo)
237 coreToTopStgRhs this_pkg scope_fv_info (bndr, rhs) = do
238 (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs
239 lv_info <- freeVarsToLiveVars rhs_fvs
240 return (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
242 bndr_info = lookupFVInfo scope_fv_info bndr
243 is_static = rhsIsStatic this_pkg rhs
245 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
248 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
249 = ASSERT( is_static )
250 StgRhsClosure noCCS binder_info
256 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
257 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
258 = StgRhsCon noCCS con args
260 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
261 = ASSERT2( not is_static, ppr rhs )
262 StgRhsClosure noCCS binder_info
270 -- ---------------------------------------------------------------------------
272 -- ---------------------------------------------------------------------------
277 -> LneM (StgExpr, -- Decorated STG expr
278 FreeVarsInfo, -- Its free vars (NB free, not live)
279 EscVarsSet) -- Its escapees, a subset of its free vars;
280 -- also a subset of the domain of the envt
281 -- because we are only interested in the escapees
282 -- for vars which might be turned into
283 -- let-no-escaped ones.
286 The second and third components can be derived in a simple bottom up pass, not
287 dependent on any decisions about which variables will be let-no-escaped or
288 not. The first component, that is, the decorated expression, may then depend
289 on these components, but it in turn is not scrutinised as the basis for any
290 decisions. Hence no black holes.
293 coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet)
294 coreToStgExpr (Var v) = coreToStgApp Nothing v []
296 coreToStgExpr expr@(App _ _)
297 = coreToStgApp Nothing f args
299 (f, args) = myCollectArgs expr
301 coreToStgExpr expr@(Lam _ _)
303 (args, body) = myCollectBinders expr
304 args' = filterStgBinders args
306 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
307 (body, body_fvs, body_escs) <- coreToStgExpr body
309 fvs = args' `minusFVBinders` body_fvs
310 escs = body_escs `delVarSetList` args'
311 result_expr | null args' = body
312 | otherwise = StgLam (exprType expr) args' body
314 return (result_expr, fvs, escs)
316 coreToStgExpr (Note (SCC cc) expr) = do
317 (expr2, fvs, escs) <- coreToStgExpr expr
318 return (StgSCC cc expr2, fvs, escs)
320 coreToStgExpr (Case (Var id) _bndr ty [(DEFAULT,[],expr)])
321 | Just (TickBox m n) <- isTickBoxOp_maybe id = do
322 (expr2, fvs, escs) <- coreToStgExpr expr
323 return (StgTick m n expr2, fvs, escs)
325 coreToStgExpr (Note other_note expr)
328 coreToStgExpr (Cast expr co)
331 -- Cases require a little more real work.
333 coreToStgExpr (Case scrut bndr _ alts) = do
334 (alts2, alts_fvs, alts_escs)
335 <- extendVarEnvLne [(bndr, LambdaBound)] $ do
336 (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
339 unionVarSets escs_s )
341 -- Determine whether the default binder is dead or not
342 -- This helps the code generator to avoid generating an assignment
343 -- for the case binder (is extremely rare cases) ToDo: remove.
344 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
345 | otherwise = bndr `setIdOccInfo` IAmDead
347 -- Don't consider the default binder as being 'live in alts',
348 -- since this is from the point of view of the case expr, where
349 -- the default binder is not free.
350 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
351 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
353 alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr
355 -- We tell the scrutinee that everything
356 -- live in the alts is live in it, too.
357 (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
358 <- setVarsLiveInCont alts_lv_info $ do
359 (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
360 scrut_lv_info <- freeVarsToLiveVars scrut_fvs
361 return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
364 StgCase scrut2 (getLiveVars scrut_lv_info)
365 (getLiveVars alts_lv_info)
368 (mkStgAltType bndr alts)
370 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
371 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
372 -- You might think we should have scrut_escs, not
373 -- (getFVSet scrut_fvs), but actually we can't call, and
374 -- then return from, a let-no-escape thing.
377 vars_alt (con, binders, rhs)
378 = let -- Remove type variables
379 binders' = filterStgBinders binders
381 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
382 (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
384 -- Records whether each param is used in the RHS
385 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
387 return ( (con, binders', good_use_mask, rhs2),
388 binders' `minusFVBinders` rhs_fvs,
389 rhs_escs `delVarSetList` binders' )
390 -- ToDo: remove the delVarSet;
391 -- since escs won't include any of these binders
394 Lets not only take quite a bit of work, but this is where we convert
395 then to let-no-escapes, if we wish.
397 (Meanwhile, we don't expect to see let-no-escapes...)
399 coreToStgExpr (Let bind body) = do
400 (new_let, fvs, escs, _)
401 <- mfix (\ ~(_, _, _, no_binder_escapes) ->
402 coreToStgLet no_binder_escapes bind body
405 return (new_let, fvs, escs)
409 mkStgAltType bndr alts
410 = case splitTyConApp_maybe (repType (idType bndr)) of
411 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
412 | isUnLiftedTyCon tc -> PrimAlt tc
413 | isHiBootTyCon tc -> look_for_better_tycon
414 | isAlgTyCon tc -> AlgAlt tc
415 | otherwise -> ASSERT( _is_poly_alt_tycon tc )
420 _is_poly_alt_tycon tc
422 || isPrimTyCon tc -- "Any" is lifted but primitive
423 || isOpenTyCon tc -- Type family; e.g. arising from strict
424 -- function application where argument has a
427 -- Sometimes, the TyCon is a HiBootTyCon which may not have any
428 -- constructors inside it. Then we can get a better TyCon by
429 -- grabbing the one from a constructor alternative
431 look_for_better_tycon
432 | ((DataAlt con, _, _) : _) <- data_alts =
433 AlgAlt (dataConTyCon con)
435 ASSERT(null data_alts)
438 (data_alts, _deflt) = findDefault alts
442 -- ---------------------------------------------------------------------------
444 -- ---------------------------------------------------------------------------
448 :: Maybe UpdateFlag -- Just upd <=> this application is
449 -- the rhs of a thunk binding
450 -- x = [...] \upd [] -> the_app
451 -- with specified update flag
453 -> [CoreArg] -- Arguments
454 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
457 coreToStgApp maybe_thunk_body f args = do
458 (args', args_fvs) <- coreToStgArgs args
459 how_bound <- lookupVarLne f
462 n_val_args = valArgCount args
463 not_letrec_bound = not (isLetBound how_bound)
465 = let fvs = singletonFVInfo f how_bound fun_occ in
466 -- e.g. (f :: a -> int) (x :: a)
467 -- Here the free variables are "f", "x" AND the type variable "a"
468 -- coreToStgArgs will deal with the arguments recursively
469 if opt_RuntimeTypes then
470 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
473 -- Mostly, the arity info of a function is in the fn's IdInfo
474 -- But new bindings introduced by CoreSat may not have no
475 -- arity info; it would do us no good anyway. For example:
476 -- let f = \ab -> e in f
477 -- No point in having correct arity info for f!
478 -- Hence the hasArity stuff below.
479 -- NB: f_arity is only consulted for LetBound things
480 f_arity = stgArity f how_bound
481 saturated = f_arity <= n_val_args
484 | not_letrec_bound = noBinderInfo -- Uninteresting variable
485 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
486 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
489 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
490 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
491 -- saturated call doesn't escape
492 -- (let-no-escape applies to 'thunks' too)
494 | otherwise = unitVarSet f -- Inexact application; it does escape
496 -- At the moment of the call:
498 -- either the function is *not* let-no-escaped, in which case
499 -- nothing is live except live_in_cont
500 -- or the function *is* let-no-escaped in which case the
501 -- variables it uses are live, but still the function
502 -- itself is not. PS. In this case, the function's
503 -- live vars should already include those of the
504 -- continuation, but it does no harm to just union the
507 res_ty = exprType (mkApps (Var f) args)
508 app = case globalIdDetails f of
509 DataConWorkId dc | saturated -> StgConApp dc args'
510 PrimOpId op -> ASSERT( saturated )
511 StgOpApp (StgPrimOp op) args' res_ty
512 FCallId call -> ASSERT( saturated )
513 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
514 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
515 _other -> StgApp f args'
519 fun_fvs `unionFVInfo` args_fvs,
520 fun_escs `unionVarSet` (getFVSet args_fvs)
521 -- All the free vars of the args are disqualified
522 -- from being let-no-escaped.
527 -- ---------------------------------------------------------------------------
529 -- This is the guy that turns applications into A-normal form
530 -- ---------------------------------------------------------------------------
532 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
534 = return ([], emptyFVInfo)
536 coreToStgArgs (Type ty : args) = do -- Type argument
537 (args', fvs) <- coreToStgArgs args
538 if opt_RuntimeTypes then
539 return (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
543 coreToStgArgs (arg : args) = do -- Non-type argument
544 (stg_args, args_fvs) <- coreToStgArgs args
545 (arg', arg_fvs, escs) <- coreToStgExpr arg
547 fvs = args_fvs `unionFVInfo` arg_fvs
548 stg_arg = case arg' of
549 StgApp v [] -> StgVarArg v
550 StgConApp con [] -> StgVarArg (dataConWorkId con)
551 StgLit lit -> StgLitArg lit
552 _ -> pprPanic "coreToStgArgs" (ppr arg)
554 -- WARNING: what if we have an argument like (v `cast` co)
555 -- where 'co' changes the representation type?
556 -- (This really only happens if co is unsafe.)
557 -- Then all the getArgAmode stuff in CgBindery will set the
558 -- cg_rep of the CgIdInfo based on the type of v, rather
559 -- than the type of 'co'.
560 -- This matters particularly when the function is a primop
562 -- Wanted: a better solution than this hacky warning
564 arg_ty = exprType arg
565 stg_arg_ty = stgArgType stg_arg
566 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
567 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
568 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
569 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
570 -- we can treat an unlifted value as lifted. But the other way round
572 -- We also want to check if a pointer is cast to a non-ptr etc
574 WARN( bad_args, ptext SLIT("Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
575 return (stg_arg : stg_args, fvs)
578 -- ---------------------------------------------------------------------------
579 -- The magic for lets:
580 -- ---------------------------------------------------------------------------
583 :: Bool -- True <=> yes, we are let-no-escaping this let
584 -> CoreBind -- bindings
586 -> LneM (StgExpr, -- new let
587 FreeVarsInfo, -- variables free in the whole let
588 EscVarsSet, -- variables that escape from the whole let
589 Bool) -- True <=> none of the binders in the bindings
590 -- is among the escaping vars
592 coreToStgLet let_no_escape bind body = do
593 (bind2, bind_fvs, bind_escs, bind_lvs,
594 body2, body_fvs, body_escs, body_lvs)
595 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
597 -- Do the bindings, setting live_in_cont to empty if
598 -- we ain't in a let-no-escape world
599 live_in_cont <- getVarsLiveInCont
600 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
601 <- setVarsLiveInCont (if let_no_escape
604 (vars_bind rec_body_fvs bind)
607 extendVarEnvLne env_ext $ do
608 (body2, body_fvs, body_escs) <- coreToStgExpr body
609 body_lv_info <- freeVarsToLiveVars body_fvs
611 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
612 body2, body_fvs, body_escs, getLiveVars body_lv_info)
615 -- Compute the new let-expression
617 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
618 | otherwise = StgLet bind2 body2
621 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
624 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
626 real_bind_escs = if let_no_escape then
630 -- Everything escapes which is free in the bindings
632 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
634 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
637 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
640 -- Debugging code as requested by Andrew Kennedy
641 checked_no_binder_escapes
642 | not no_binder_escapes && any is_join_var binders
643 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
645 | otherwise = no_binder_escapes
647 checked_no_binder_escapes = no_binder_escapes
650 -- Mustn't depend on the passed-in let_no_escape flag, since
651 -- no_binder_escapes is used by the caller to derive the flag!
656 checked_no_binder_escapes
659 set_of_binders = mkVarSet binders
660 binders = bindersOf bind
662 mk_binding bind_lv_info binder rhs
663 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
665 live_vars | let_no_escape = addLiveVar bind_lv_info binder
666 | otherwise = unitLiveVar binder
667 -- c.f. the invariant on NestedLet
669 vars_bind :: FreeVarsInfo -- Free var info for body of binding
673 EscVarsSet, -- free vars; escapee vars
674 LiveInfo, -- Vars and CAFs live in binding
675 [(Id, HowBound)]) -- extension to environment
678 vars_bind body_fvs (NonRec binder rhs) = do
679 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
681 env_ext_item = mk_binding bind_lv_info binder rhs
683 return (StgNonRec binder rhs2,
684 bind_fvs, escs, bind_lv_info, [env_ext_item])
687 vars_bind body_fvs (Rec pairs)
688 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
690 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
691 binders = map fst pairs
692 env_ext = [ mk_binding bind_lv_info b rhs
695 extendVarEnvLne env_ext $ do
696 (rhss2, fvss, lv_infos, escss)
697 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
699 bind_fvs = unionFVInfos fvss
700 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
701 escs = unionVarSets escss
703 return (StgRec (binders `zip` rhss2),
704 bind_fvs, escs, bind_lv_info, env_ext)
707 is_join_var :: Id -> Bool
708 -- A hack (used only for compiler debuggging) to tell if
709 -- a variable started life as a join point ($j)
710 is_join_var j = occNameString (getOccName j) == "$j"
714 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
717 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
719 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
720 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
722 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
723 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
724 rhs_fvs, lv_info, rhs_escs)
726 bndr_info = lookupFVInfo scope_fv_info bndr
728 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
730 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
731 = StgRhsCon noCCS con args
733 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
734 = StgRhsClosure noCCS binder_info
739 mkStgRhs rhs_fvs srt binder_info rhs
740 = StgRhsClosure noCCS binder_info
746 SDM: disabled. Eval/Apply can't handle functions with arity zero very
747 well; and making these into simple non-updatable thunks breaks other
748 assumptions (namely that they will be entered only once).
750 upd_flag | isPAP env rhs = ReEntrant
751 | otherwise = Updatable
755 upd = if isOnceDem dem
756 then (if isNotTop toplev
757 then SingleEntry -- HA! Paydirt for "dem"
760 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
764 -- For now we forbid SingleEntry CAFs; they tickle the
765 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
766 -- and I don't understand why. There's only one SE_CAF (well,
767 -- only one that tickled a great gaping bug in an earlier attempt
768 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
769 -- specifically Main.lvl6 in spectral/cryptarithm2.
770 -- So no great loss. KSW 2000-07.
774 Detect thunks which will reduce immediately to PAPs, and make them
775 non-updatable. This has several advantages:
777 - the non-updatable thunk behaves exactly like the PAP,
779 - the thunk is more efficient to enter, because it is
780 specialised to the task.
782 - we save one update frame, one stg_update_PAP, one update
783 and lots of PAP_enters.
785 - in the case where the thunk is top-level, we save building
786 a black hole and futhermore the thunk isn't considered to
787 be a CAF any more, so it doesn't appear in any SRTs.
789 We do it here, because the arity information is accurate, and we need
790 to do it before the SRT pass to save the SRT entries associated with
793 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
795 arity = stgArity f (lookupBinding env f)
799 %************************************************************************
801 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
803 %************************************************************************
805 There's a lot of stuff to pass around, so we use this @LneM@ monad to
806 help. All the stuff here is only passed *down*.
809 newtype LneM a = LneM
810 { unLneM :: IdEnv HowBound
811 -> LiveInfo -- Vars and CAFs live in continuation
815 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
816 -- i.e. ones with a nested (non-top-level) binding
817 CafSet) -- Static live variables;
818 -- i.e. top-level variables that are CAFs or refer to them
820 type EscVarsSet = IdSet
824 = ImportBound -- Used only as a response to lookupBinding; never
825 -- exists in the range of the (IdEnv HowBound)
827 | LetBound -- A let(rec) in this module
828 LetInfo -- Whether top level or nested
829 Arity -- Its arity (local Ids don't have arity info at this point)
831 | LambdaBound -- Used for both lambda and case
834 = TopLet -- top level things
835 | NestedLet LiveInfo -- For nested things, what is live if this
836 -- thing is live? Invariant: the binder
837 -- itself is always a member of
838 -- the dynamic set of its own LiveInfo
840 isLetBound (LetBound _ _) = True
841 isLetBound other = False
843 topLevelBound ImportBound = True
844 topLevelBound (LetBound TopLet _) = True
845 topLevelBound other = False
848 For a let(rec)-bound variable, x, we record LiveInfo, the set of
849 variables that are live if x is live. This LiveInfo comprises
850 (a) dynamic live variables (ones with a non-top-level binding)
851 (b) static live variabes (CAFs or things that refer to CAFs)
853 For "normal" variables (a) is just x alone. If x is a let-no-escaped
854 variable then x is represented by a code pointer and a stack pointer
855 (well, one for each stack). So all of the variables needed in the
856 execution of x are live if x is, and are therefore recorded in the
857 LetBound constructor; x itself *is* included.
859 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
863 emptyLiveInfo :: LiveInfo
864 emptyLiveInfo = (emptyVarSet,emptyVarSet)
866 unitLiveVar :: Id -> LiveInfo
867 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
869 unitLiveCaf :: Id -> LiveInfo
870 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
872 addLiveVar :: LiveInfo -> Id -> LiveInfo
873 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
875 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
876 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
878 mkSRT :: LiveInfo -> SRT
879 mkSRT (_, cafs) = SRTEntries cafs
881 getLiveVars :: LiveInfo -> StgLiveVars
882 getLiveVars (lvs, _) = lvs
886 The std monad functions:
888 initLne :: IdEnv HowBound -> LneM a -> a
889 initLne env m = unLneM m env emptyLiveInfo
893 {-# INLINE thenLne #-}
894 {-# INLINE returnLne #-}
896 returnLne :: a -> LneM a
897 returnLne e = LneM $ \env lvs_cont -> e
899 thenLne :: LneM a -> (a -> LneM b) -> LneM b
900 thenLne m k = LneM $ \env lvs_cont
901 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
903 instance Monad LneM where
907 instance MonadFix LneM where
908 mfix expr = LneM $ \env lvs_cont ->
909 let result = unLneM (expr result) env lvs_cont
913 Functions specific to this monad:
916 getVarsLiveInCont :: LneM LiveInfo
917 getVarsLiveInCont = LneM $ \env lvs_cont -> lvs_cont
919 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
920 setVarsLiveInCont new_lvs_cont expr
921 = LneM $ \env lvs_cont
922 -> unLneM expr env new_lvs_cont
924 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
925 extendVarEnvLne ids_w_howbound expr
926 = LneM $ \env lvs_cont
927 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
929 lookupVarLne :: Id -> LneM HowBound
930 lookupVarLne v = LneM $ \env lvs_cont -> lookupBinding env v
932 getEnvLne :: LneM (IdEnv HowBound)
933 getEnvLne = LneM $ \env lvs_cont -> env
935 lookupBinding :: IdEnv HowBound -> Id -> HowBound
936 lookupBinding env v = case lookupVarEnv env v of
938 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
941 -- The result of lookupLiveVarsForSet, a set of live variables, is
942 -- only ever tacked onto a decorated expression. It is never used as
943 -- the basis of a control decision, which might give a black hole.
945 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
946 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
948 freeVarsToLiveVars' env live_in_cont = live_info
950 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
951 lvs_from_fvs = map do_one (allFreeIds fvs)
953 do_one (v, how_bound)
955 ImportBound -> unitLiveCaf v -- Only CAF imports are
958 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
959 | otherwise -> emptyLiveInfo
961 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
962 -- (see the invariant on NestedLet)
964 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
967 %************************************************************************
969 \subsection[Free-var info]{Free variable information}
971 %************************************************************************
974 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
975 -- The Var is so we can gather up the free variables
978 -- The HowBound info just saves repeated lookups;
979 -- we look up just once when we encounter the occurrence.
980 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
981 -- Imported Ids without CAF refs are simply
982 -- not put in the FreeVarsInfo for an expression.
983 -- See singletonFVInfo and freeVarsToLiveVars
985 -- StgBinderInfo records how it occurs; notably, we
986 -- are interested in whether it only occurs in saturated
987 -- applications, because then we don't need to build a
989 -- If f is mapped to noBinderInfo, that means
990 -- that f *is* mentioned (else it wouldn't be in the
991 -- IdEnv at all), but perhaps in an unsaturated applications.
993 -- All case/lambda-bound things are also mapped to
994 -- noBinderInfo, since we aren't interested in their
997 -- For ILX we track free var info for type variables too;
998 -- hence VarEnv not IdEnv
1002 emptyFVInfo :: FreeVarsInfo
1003 emptyFVInfo = emptyVarEnv
1005 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
1006 -- Don't record non-CAF imports at all, to keep free-var sets small
1007 singletonFVInfo id ImportBound info
1008 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
1009 | otherwise = emptyVarEnv
1010 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1012 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
1013 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1015 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1016 -- Type variables must be lambda-bound
1018 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1019 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1021 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1022 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1024 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1025 minusFVBinders vs fv = foldr minusFVBinder fv vs
1027 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1028 minusFVBinder v fv | isId v && opt_RuntimeTypes
1029 = (fv `delVarEnv` v) `unionFVInfo`
1030 tyvarFVInfo (tyVarsOfType (idType v))
1031 | otherwise = fv `delVarEnv` v
1032 -- When removing a binder, remember to add its type variables
1033 -- c.f. CoreFVs.delBinderFV
1035 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1036 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1038 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1039 -- Find how the given Id is used.
1040 -- Externally visible things may be used any old how
1042 | isExternalName (idName id) = noBinderInfo
1043 | otherwise = case lookupVarEnv fvs id of
1044 Nothing -> noBinderInfo
1045 Just (_,_,info) -> info
1047 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1048 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1050 -- Non-top-level things only, both type variables and ids
1051 -- (type variables only if opt_RuntimeTypes)
1052 getFVs :: FreeVarsInfo -> [Var]
1053 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1054 not (topLevelBound how_bound) ]
1056 getFVSet :: FreeVarsInfo -> VarSet
1057 getFVSet fvs = mkVarSet (getFVs fvs)
1059 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1060 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1061 (id1, hb1, combineStgBinderInfo info1 info2)
1063 -- The HowBound info for a variable in the FVInfo should be consistent
1064 check_eq_how_bound ImportBound ImportBound = True
1065 check_eq_how_bound LambdaBound LambdaBound = True
1066 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1067 check_eq_how_bound hb1 hb2 = False
1069 check_eq_li (NestedLet _) (NestedLet _) = True
1070 check_eq_li TopLet TopLet = True
1071 check_eq_li li1 li2 = False
1076 filterStgBinders :: [Var] -> [Var]
1077 filterStgBinders bndrs
1078 | opt_RuntimeTypes = bndrs
1079 | otherwise = filter isId bndrs
1084 -- Ignore all notes except SCC
1085 myCollectBinders expr
1088 go bs (Lam b e) = go (b:bs) e
1089 go bs e@(Note (SCC _) _) = (reverse bs, e)
1090 go bs (Cast e co) = go bs e
1091 go bs (Note _ e) = go bs e
1092 go bs e = (reverse bs, e)
1094 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1095 -- We assume that we only have variables
1096 -- in the function position by now
1100 go (Var v) as = (v, as)
1101 go (App f a) as = go f (a:as)
1102 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1103 go (Cast e co) as = go e as
1104 go (Note n e) as = go e as
1105 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1109 stgArity :: Id -> HowBound -> Arity
1110 stgArity f (LetBound _ arity) = arity
1111 stgArity f ImportBound = idArity f
1112 stgArity f LambdaBound = 0