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 )
46 %************************************************************************
48 \subsection[live-vs-free-doc]{Documentation}
50 %************************************************************************
52 (There is other relevant documentation in codeGen/CgLetNoEscape.)
54 The actual Stg datatype is decorated with {\em live variable}
55 information, as well as {\em free variable} information. The two are
56 {\em not} the same. Liveness is an operational property rather than a
57 semantic one. A variable is live at a particular execution point if
58 it can be referred to {\em directly} again. In particular, a dead
59 variable's stack slot (if it has one):
62 should be stubbed to avoid space leaks, and
64 may be reused for something else.
67 There ought to be a better way to say this. Here are some examples:
74 Just after the `in', v is live, but q is dead. If the whole of that
75 let expression was enclosed in a case expression, thus:
77 case (let v = [q] \[x] -> e in ...v...) of
80 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
81 we'll return later to the @alts@ and need it.
83 Let-no-escapes make this a bit more interesting:
85 let-no-escape v = [q] \ [x] -> e
89 Here, @q@ is still live at the `in', because @v@ is represented not by
90 a closure but by the current stack state. In other words, if @v@ is
91 live then so is @q@. Furthermore, if @e@ mentions an enclosing
92 let-no-escaped variable, then {\em its} free variables are also live
95 %************************************************************************
97 \subsection[caf-info]{Collecting live CAF info}
99 %************************************************************************
101 In this pass we also collect information on which CAFs are live for
102 constructing SRTs (see SRT.lhs).
104 A top-level Id has CafInfo, which is
106 - MayHaveCafRefs, if it may refer indirectly to
108 - NoCafRefs if it definitely doesn't
110 The CafInfo has already been calculated during the CoreTidy pass.
112 During CoreToStg, we then pin onto each binding and case expression, a
113 list of Ids which represents the "live" CAFs at that point. The meaning
114 of "live" here is the same as for live variables, see above (which is
115 why it's convenient to collect CAF information here rather than elsewhere).
117 The later SRT pass takes these lists of Ids and uses them to construct
118 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
122 Interaction of let-no-escape with SRTs [Sept 01]
123 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
126 let-no-escape x = ...caf1...caf2...
130 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
131 build SRTs just as if x's defn was inlined at each call site, and
132 that means that x's CAF refs get duplicated in the overall SRT.
134 This is unlike ordinary lets, in which the CAF refs are not duplicated.
136 We could fix this loss of (static) sharing by making a sort of pseudo-closure
137 for x, solely to put in the SRTs lower down.
140 %************************************************************************
142 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
144 %************************************************************************
147 coreToStg :: PackageId -> [CoreBind] -> IO [StgBinding]
148 coreToStg this_pkg pgm
150 where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm
152 coreExprToStg :: CoreExpr -> StgExpr
154 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
159 -> IdEnv HowBound -- environment for the bindings
161 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
163 coreTopBindsToStg this_pkg env [] = (env, emptyFVInfo, [])
164 coreTopBindsToStg this_pkg env (b:bs)
165 = (env2, fvs2, b':bs')
167 -- env accumulates down the list of binds, fvs accumulates upwards
168 (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
169 (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs
175 -> FreeVarsInfo -- Info about the body
177 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
179 coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
181 env' = extendVarEnv env id how_bound
182 how_bound = LetBound TopLet $! manifestArity rhs
186 (stg_rhs, fvs') <- coreToTopStgRhs this_pkg body_fvs (id,rhs)
187 return (stg_rhs, fvs')
189 bind = StgNonRec id stg_rhs
191 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) )
192 ASSERT2(consistentCafInfo id bind, ppr id $$ ppr rhs $$ ppr bind)
193 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
194 (env', fvs' `unionFVInfo` body_fvs, bind)
196 coreTopBindToStg this_pkg env body_fvs (Rec pairs)
198 (binders, rhss) = unzip pairs
200 extra_env' = [ (b, LetBound TopLet $! manifestArity rhs)
201 | (b, rhs) <- pairs ]
202 env' = extendVarEnvList env extra_env'
206 (stg_rhss, fvss') <- mapAndUnzipM (coreToTopStgRhs this_pkg body_fvs) pairs
207 let fvs' = unionFVInfos fvss'
208 return (stg_rhss, fvs')
210 bind = StgRec (zip binders stg_rhss)
212 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
213 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
214 (env', fvs' `unionFVInfo` body_fvs, bind)
216 -- Assertion helper: this checks that the CafInfo on the Id matches
217 -- what CoreToStg has figured out about the binding's SRT. The
218 -- CafInfo will be exact in all cases except when CorePrep has
219 -- floated out a binding, in which case it will be approximate.
220 consistentCafInfo id bind
221 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
224 = WARN (not exact, ppr id) safe
226 safe = id_marked_caffy || not binding_is_caffy
227 exact = id_marked_caffy == binding_is_caffy
228 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
229 binding_is_caffy = stgBindHasCafRefs bind
235 -> FreeVarsInfo -- Free var info for the scope of the binding
237 -> LneM (StgRhs, FreeVarsInfo)
239 coreToTopStgRhs this_pkg scope_fv_info (bndr, rhs) = do
240 (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs
241 lv_info <- freeVarsToLiveVars rhs_fvs
242 return (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
244 bndr_info = lookupFVInfo scope_fv_info bndr
245 is_static = rhsIsStatic this_pkg rhs
247 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
250 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
251 = ASSERT( is_static )
252 StgRhsClosure noCCS binder_info
258 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
259 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
260 = StgRhsCon noCCS con args
262 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
263 = ASSERT2( not is_static, ppr rhs )
264 StgRhsClosure noCCS binder_info
272 -- ---------------------------------------------------------------------------
274 -- ---------------------------------------------------------------------------
279 -> LneM (StgExpr, -- Decorated STG expr
280 FreeVarsInfo, -- Its free vars (NB free, not live)
281 EscVarsSet) -- Its escapees, a subset of its free vars;
282 -- also a subset of the domain of the envt
283 -- because we are only interested in the escapees
284 -- for vars which might be turned into
285 -- let-no-escaped ones.
288 The second and third components can be derived in a simple bottom up pass, not
289 dependent on any decisions about which variables will be let-no-escaped or
290 not. The first component, that is, the decorated expression, may then depend
291 on these components, but it in turn is not scrutinised as the basis for any
292 decisions. Hence no black holes.
295 coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet)
296 coreToStgExpr (Var v) = coreToStgApp Nothing v []
298 coreToStgExpr expr@(App _ _)
299 = coreToStgApp Nothing f args
301 (f, args) = myCollectArgs expr
303 coreToStgExpr expr@(Lam _ _)
305 (args, body) = myCollectBinders expr
306 args' = filterStgBinders args
308 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
309 (body, body_fvs, body_escs) <- coreToStgExpr body
311 fvs = args' `minusFVBinders` body_fvs
312 escs = body_escs `delVarSetList` args'
313 result_expr | null args' = body
314 | otherwise = StgLam (exprType expr) args' body
316 return (result_expr, fvs, escs)
318 coreToStgExpr (Note (SCC cc) expr) = do
319 (expr2, fvs, escs) <- coreToStgExpr expr
320 return (StgSCC cc expr2, fvs, escs)
322 coreToStgExpr (Case (Var id) _bndr ty [(DEFAULT,[],expr)])
323 | Just (TickBox m n) <- isTickBoxOp_maybe id = do
324 (expr2, fvs, escs) <- coreToStgExpr expr
325 return (StgTick m n expr2, fvs, escs)
327 coreToStgExpr (Note other_note expr)
330 coreToStgExpr (Cast expr co)
333 -- Cases require a little more real work.
335 coreToStgExpr (Case scrut bndr _ alts) = do
336 (alts2, alts_fvs, alts_escs)
337 <- extendVarEnvLne [(bndr, LambdaBound)] $ do
338 (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
341 unionVarSets escs_s )
343 -- Determine whether the default binder is dead or not
344 -- This helps the code generator to avoid generating an assignment
345 -- for the case binder (is extremely rare cases) ToDo: remove.
346 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
347 | otherwise = bndr `setIdOccInfo` IAmDead
349 -- Don't consider the default binder as being 'live in alts',
350 -- since this is from the point of view of the case expr, where
351 -- the default binder is not free.
352 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
353 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
355 alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr
357 -- We tell the scrutinee that everything
358 -- live in the alts is live in it, too.
359 (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
360 <- setVarsLiveInCont alts_lv_info $ do
361 (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
362 scrut_lv_info <- freeVarsToLiveVars scrut_fvs
363 return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
366 StgCase scrut2 (getLiveVars scrut_lv_info)
367 (getLiveVars alts_lv_info)
370 (mkStgAltType bndr alts)
372 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
373 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
374 -- You might think we should have scrut_escs, not
375 -- (getFVSet scrut_fvs), but actually we can't call, and
376 -- then return from, a let-no-escape thing.
379 vars_alt (con, binders, rhs)
380 = let -- Remove type variables
381 binders' = filterStgBinders binders
383 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
384 (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
386 -- Records whether each param is used in the RHS
387 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
389 return ( (con, binders', good_use_mask, rhs2),
390 binders' `minusFVBinders` rhs_fvs,
391 rhs_escs `delVarSetList` binders' )
392 -- ToDo: remove the delVarSet;
393 -- since escs won't include any of these binders
396 Lets not only take quite a bit of work, but this is where we convert
397 then to let-no-escapes, if we wish.
399 (Meanwhile, we don't expect to see let-no-escapes...)
401 coreToStgExpr (Let bind body) = do
402 (new_let, fvs, escs, _)
403 <- mfix (\ ~(_, _, _, no_binder_escapes) ->
404 coreToStgLet no_binder_escapes bind body
407 return (new_let, fvs, escs)
411 mkStgAltType bndr alts
412 = case splitTyConApp_maybe (repType (idType bndr)) of
413 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
414 | isUnLiftedTyCon tc -> PrimAlt tc
415 | isHiBootTyCon tc -> look_for_better_tycon
416 | isAlgTyCon tc -> AlgAlt tc
417 | otherwise -> ASSERT( _is_poly_alt_tycon tc )
422 _is_poly_alt_tycon tc
424 || isPrimTyCon tc -- "Any" is lifted but primitive
425 || isOpenTyCon tc -- Type family; e.g. arising from strict
426 -- function application where argument has a
429 -- Sometimes, the TyCon is a HiBootTyCon which may not have any
430 -- constructors inside it. Then we can get a better TyCon by
431 -- grabbing the one from a constructor alternative
433 look_for_better_tycon
434 | ((DataAlt con, _, _) : _) <- data_alts =
435 AlgAlt (dataConTyCon con)
437 ASSERT(null data_alts)
440 (data_alts, _deflt) = findDefault alts
444 -- ---------------------------------------------------------------------------
446 -- ---------------------------------------------------------------------------
450 :: Maybe UpdateFlag -- Just upd <=> this application is
451 -- the rhs of a thunk binding
452 -- x = [...] \upd [] -> the_app
453 -- with specified update flag
455 -> [CoreArg] -- Arguments
456 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
459 coreToStgApp maybe_thunk_body f args = do
460 (args', args_fvs) <- coreToStgArgs args
461 how_bound <- lookupVarLne f
464 n_val_args = valArgCount args
465 not_letrec_bound = not (isLetBound how_bound)
467 = let fvs = singletonFVInfo f how_bound fun_occ in
468 -- e.g. (f :: a -> int) (x :: a)
469 -- Here the free variables are "f", "x" AND the type variable "a"
470 -- coreToStgArgs will deal with the arguments recursively
471 if opt_RuntimeTypes then
472 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
475 -- Mostly, the arity info of a function is in the fn's IdInfo
476 -- But new bindings introduced by CoreSat may not have no
477 -- arity info; it would do us no good anyway. For example:
478 -- let f = \ab -> e in f
479 -- No point in having correct arity info for f!
480 -- Hence the hasArity stuff below.
481 -- NB: f_arity is only consulted for LetBound things
482 f_arity = stgArity f how_bound
483 saturated = f_arity <= n_val_args
486 | not_letrec_bound = noBinderInfo -- Uninteresting variable
487 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
488 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
491 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
492 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
493 -- saturated call doesn't escape
494 -- (let-no-escape applies to 'thunks' too)
496 | otherwise = unitVarSet f -- Inexact application; it does escape
498 -- At the moment of the call:
500 -- either the function is *not* let-no-escaped, in which case
501 -- nothing is live except live_in_cont
502 -- or the function *is* let-no-escaped in which case the
503 -- variables it uses are live, but still the function
504 -- itself is not. PS. In this case, the function's
505 -- live vars should already include those of the
506 -- continuation, but it does no harm to just union the
509 res_ty = exprType (mkApps (Var f) args)
510 app = case globalIdDetails f of
511 DataConWorkId dc | saturated -> StgConApp dc args'
512 PrimOpId op -> ASSERT( saturated )
513 StgOpApp (StgPrimOp op) args' res_ty
514 FCallId call -> ASSERT( saturated )
515 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
516 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
517 _other -> StgApp f args'
521 fun_fvs `unionFVInfo` args_fvs,
522 fun_escs `unionVarSet` (getFVSet args_fvs)
523 -- All the free vars of the args are disqualified
524 -- from being let-no-escaped.
529 -- ---------------------------------------------------------------------------
531 -- This is the guy that turns applications into A-normal form
532 -- ---------------------------------------------------------------------------
534 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
536 = return ([], emptyFVInfo)
538 coreToStgArgs (Type ty : args) = do -- Type argument
539 (args', fvs) <- coreToStgArgs args
540 if opt_RuntimeTypes then
541 return (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
545 coreToStgArgs (arg : args) = do -- Non-type argument
546 (stg_args, args_fvs) <- coreToStgArgs args
547 (arg', arg_fvs, escs) <- coreToStgExpr arg
549 fvs = args_fvs `unionFVInfo` arg_fvs
550 stg_arg = case arg' of
551 StgApp v [] -> StgVarArg v
552 StgConApp con [] -> StgVarArg (dataConWorkId con)
553 StgLit lit -> StgLitArg lit
554 _ -> pprPanic "coreToStgArgs" (ppr arg)
556 -- WARNING: what if we have an argument like (v `cast` co)
557 -- where 'co' changes the representation type?
558 -- (This really only happens if co is unsafe.)
559 -- Then all the getArgAmode stuff in CgBindery will set the
560 -- cg_rep of the CgIdInfo based on the type of v, rather
561 -- than the type of 'co'.
562 -- This matters particularly when the function is a primop
564 -- Wanted: a better solution than this hacky warning
566 arg_ty = exprType arg
567 stg_arg_ty = stgArgType stg_arg
568 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
569 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
570 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
571 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
572 -- we can treat an unlifted value as lifted. But the other way round
574 -- We also want to check if a pointer is cast to a non-ptr etc
576 WARN( bad_args, ptext SLIT("Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
577 return (stg_arg : stg_args, fvs)
580 -- ---------------------------------------------------------------------------
581 -- The magic for lets:
582 -- ---------------------------------------------------------------------------
585 :: Bool -- True <=> yes, we are let-no-escaping this let
586 -> CoreBind -- bindings
588 -> LneM (StgExpr, -- new let
589 FreeVarsInfo, -- variables free in the whole let
590 EscVarsSet, -- variables that escape from the whole let
591 Bool) -- True <=> none of the binders in the bindings
592 -- is among the escaping vars
594 coreToStgLet let_no_escape bind body = do
595 (bind2, bind_fvs, bind_escs, bind_lvs,
596 body2, body_fvs, body_escs, body_lvs)
597 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
599 -- Do the bindings, setting live_in_cont to empty if
600 -- we ain't in a let-no-escape world
601 live_in_cont <- getVarsLiveInCont
602 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
603 <- setVarsLiveInCont (if let_no_escape
606 (vars_bind rec_body_fvs bind)
609 extendVarEnvLne env_ext $ do
610 (body2, body_fvs, body_escs) <- coreToStgExpr body
611 body_lv_info <- freeVarsToLiveVars body_fvs
613 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
614 body2, body_fvs, body_escs, getLiveVars body_lv_info)
617 -- Compute the new let-expression
619 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
620 | otherwise = StgLet bind2 body2
623 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
626 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
628 real_bind_escs = if let_no_escape then
632 -- Everything escapes which is free in the bindings
634 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
636 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
639 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
641 -- Debugging code as requested by Andrew Kennedy
642 checked_no_binder_escapes
643 | debugIsOn && not no_binder_escapes && any is_join_var binders
644 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
646 | otherwise = no_binder_escapes
648 -- Mustn't depend on the passed-in let_no_escape flag, since
649 -- no_binder_escapes is used by the caller to derive the flag!
654 checked_no_binder_escapes
657 set_of_binders = mkVarSet binders
658 binders = bindersOf bind
660 mk_binding bind_lv_info binder rhs
661 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
663 live_vars | let_no_escape = addLiveVar bind_lv_info binder
664 | otherwise = unitLiveVar binder
665 -- c.f. the invariant on NestedLet
667 vars_bind :: FreeVarsInfo -- Free var info for body of binding
671 EscVarsSet, -- free vars; escapee vars
672 LiveInfo, -- Vars and CAFs live in binding
673 [(Id, HowBound)]) -- extension to environment
676 vars_bind body_fvs (NonRec binder rhs) = do
677 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
679 env_ext_item = mk_binding bind_lv_info binder rhs
681 return (StgNonRec binder rhs2,
682 bind_fvs, escs, bind_lv_info, [env_ext_item])
685 vars_bind body_fvs (Rec pairs)
686 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
688 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
689 binders = map fst pairs
690 env_ext = [ mk_binding bind_lv_info b rhs
693 extendVarEnvLne env_ext $ do
694 (rhss2, fvss, lv_infos, escss)
695 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
697 bind_fvs = unionFVInfos fvss
698 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
699 escs = unionVarSets escss
701 return (StgRec (binders `zip` rhss2),
702 bind_fvs, escs, bind_lv_info, env_ext)
705 is_join_var :: Id -> Bool
706 -- A hack (used only for compiler debuggging) to tell if
707 -- a variable started life as a join point ($j)
708 is_join_var j = occNameString (getOccName j) == "$j"
712 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
715 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
717 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
718 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
720 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
721 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
722 rhs_fvs, lv_info, rhs_escs)
724 bndr_info = lookupFVInfo scope_fv_info bndr
726 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
728 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
729 = StgRhsCon noCCS con args
731 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
732 = StgRhsClosure noCCS binder_info
737 mkStgRhs rhs_fvs srt binder_info rhs
738 = StgRhsClosure noCCS binder_info
744 SDM: disabled. Eval/Apply can't handle functions with arity zero very
745 well; and making these into simple non-updatable thunks breaks other
746 assumptions (namely that they will be entered only once).
748 upd_flag | isPAP env rhs = ReEntrant
749 | otherwise = Updatable
753 upd = if isOnceDem dem
754 then (if isNotTop toplev
755 then SingleEntry -- HA! Paydirt for "dem"
758 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
762 -- For now we forbid SingleEntry CAFs; they tickle the
763 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
764 -- and I don't understand why. There's only one SE_CAF (well,
765 -- only one that tickled a great gaping bug in an earlier attempt
766 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
767 -- specifically Main.lvl6 in spectral/cryptarithm2.
768 -- So no great loss. KSW 2000-07.
772 Detect thunks which will reduce immediately to PAPs, and make them
773 non-updatable. This has several advantages:
775 - the non-updatable thunk behaves exactly like the PAP,
777 - the thunk is more efficient to enter, because it is
778 specialised to the task.
780 - we save one update frame, one stg_update_PAP, one update
781 and lots of PAP_enters.
783 - in the case where the thunk is top-level, we save building
784 a black hole and futhermore the thunk isn't considered to
785 be a CAF any more, so it doesn't appear in any SRTs.
787 We do it here, because the arity information is accurate, and we need
788 to do it before the SRT pass to save the SRT entries associated with
791 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
793 arity = stgArity f (lookupBinding env f)
797 %************************************************************************
799 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
801 %************************************************************************
803 There's a lot of stuff to pass around, so we use this @LneM@ monad to
804 help. All the stuff here is only passed *down*.
807 newtype LneM a = LneM
808 { unLneM :: IdEnv HowBound
809 -> LiveInfo -- Vars and CAFs live in continuation
813 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
814 -- i.e. ones with a nested (non-top-level) binding
815 CafSet) -- Static live variables;
816 -- i.e. top-level variables that are CAFs or refer to them
818 type EscVarsSet = IdSet
822 = ImportBound -- Used only as a response to lookupBinding; never
823 -- exists in the range of the (IdEnv HowBound)
825 | LetBound -- A let(rec) in this module
826 LetInfo -- Whether top level or nested
827 Arity -- Its arity (local Ids don't have arity info at this point)
829 | LambdaBound -- Used for both lambda and case
832 = TopLet -- top level things
833 | NestedLet LiveInfo -- For nested things, what is live if this
834 -- thing is live? Invariant: the binder
835 -- itself is always a member of
836 -- the dynamic set of its own LiveInfo
838 isLetBound (LetBound _ _) = True
839 isLetBound other = False
841 topLevelBound ImportBound = True
842 topLevelBound (LetBound TopLet _) = True
843 topLevelBound other = False
846 For a let(rec)-bound variable, x, we record LiveInfo, the set of
847 variables that are live if x is live. This LiveInfo comprises
848 (a) dynamic live variables (ones with a non-top-level binding)
849 (b) static live variabes (CAFs or things that refer to CAFs)
851 For "normal" variables (a) is just x alone. If x is a let-no-escaped
852 variable then x is represented by a code pointer and a stack pointer
853 (well, one for each stack). So all of the variables needed in the
854 execution of x are live if x is, and are therefore recorded in the
855 LetBound constructor; x itself *is* included.
857 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
861 emptyLiveInfo :: LiveInfo
862 emptyLiveInfo = (emptyVarSet,emptyVarSet)
864 unitLiveVar :: Id -> LiveInfo
865 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
867 unitLiveCaf :: Id -> LiveInfo
868 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
870 addLiveVar :: LiveInfo -> Id -> LiveInfo
871 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
873 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
874 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
876 mkSRT :: LiveInfo -> SRT
877 mkSRT (_, cafs) = SRTEntries cafs
879 getLiveVars :: LiveInfo -> StgLiveVars
880 getLiveVars (lvs, _) = lvs
884 The std monad functions:
886 initLne :: IdEnv HowBound -> LneM a -> a
887 initLne env m = unLneM m env emptyLiveInfo
891 {-# INLINE thenLne #-}
892 {-# INLINE returnLne #-}
894 returnLne :: a -> LneM a
895 returnLne e = LneM $ \env lvs_cont -> e
897 thenLne :: LneM a -> (a -> LneM b) -> LneM b
898 thenLne m k = LneM $ \env lvs_cont
899 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
901 instance Monad LneM where
905 instance MonadFix LneM where
906 mfix expr = LneM $ \env lvs_cont ->
907 let result = unLneM (expr result) env lvs_cont
911 Functions specific to this monad:
914 getVarsLiveInCont :: LneM LiveInfo
915 getVarsLiveInCont = LneM $ \env lvs_cont -> lvs_cont
917 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
918 setVarsLiveInCont new_lvs_cont expr
919 = LneM $ \env lvs_cont
920 -> unLneM expr env new_lvs_cont
922 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
923 extendVarEnvLne ids_w_howbound expr
924 = LneM $ \env lvs_cont
925 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
927 lookupVarLne :: Id -> LneM HowBound
928 lookupVarLne v = LneM $ \env lvs_cont -> lookupBinding env v
930 getEnvLne :: LneM (IdEnv HowBound)
931 getEnvLne = LneM $ \env lvs_cont -> env
933 lookupBinding :: IdEnv HowBound -> Id -> HowBound
934 lookupBinding env v = case lookupVarEnv env v of
936 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
939 -- The result of lookupLiveVarsForSet, a set of live variables, is
940 -- only ever tacked onto a decorated expression. It is never used as
941 -- the basis of a control decision, which might give a black hole.
943 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
944 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
946 freeVarsToLiveVars' env live_in_cont = live_info
948 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
949 lvs_from_fvs = map do_one (allFreeIds fvs)
951 do_one (v, how_bound)
953 ImportBound -> unitLiveCaf v -- Only CAF imports are
956 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
957 | otherwise -> emptyLiveInfo
959 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
960 -- (see the invariant on NestedLet)
962 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
965 %************************************************************************
967 \subsection[Free-var info]{Free variable information}
969 %************************************************************************
972 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
973 -- The Var is so we can gather up the free variables
976 -- The HowBound info just saves repeated lookups;
977 -- we look up just once when we encounter the occurrence.
978 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
979 -- Imported Ids without CAF refs are simply
980 -- not put in the FreeVarsInfo for an expression.
981 -- See singletonFVInfo and freeVarsToLiveVars
983 -- StgBinderInfo records how it occurs; notably, we
984 -- are interested in whether it only occurs in saturated
985 -- applications, because then we don't need to build a
987 -- If f is mapped to noBinderInfo, that means
988 -- that f *is* mentioned (else it wouldn't be in the
989 -- IdEnv at all), but perhaps in an unsaturated applications.
991 -- All case/lambda-bound things are also mapped to
992 -- noBinderInfo, since we aren't interested in their
995 -- For ILX we track free var info for type variables too;
996 -- hence VarEnv not IdEnv
1000 emptyFVInfo :: FreeVarsInfo
1001 emptyFVInfo = emptyVarEnv
1003 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
1004 -- Don't record non-CAF imports at all, to keep free-var sets small
1005 singletonFVInfo id ImportBound info
1006 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
1007 | otherwise = emptyVarEnv
1008 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1010 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
1011 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1013 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1014 -- Type variables must be lambda-bound
1016 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1017 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1019 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1020 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1022 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1023 minusFVBinders vs fv = foldr minusFVBinder fv vs
1025 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1026 minusFVBinder v fv | isId v && opt_RuntimeTypes
1027 = (fv `delVarEnv` v) `unionFVInfo`
1028 tyvarFVInfo (tyVarsOfType (idType v))
1029 | otherwise = fv `delVarEnv` v
1030 -- When removing a binder, remember to add its type variables
1031 -- c.f. CoreFVs.delBinderFV
1033 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1034 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1036 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1037 -- Find how the given Id is used.
1038 -- Externally visible things may be used any old how
1040 | isExternalName (idName id) = noBinderInfo
1041 | otherwise = case lookupVarEnv fvs id of
1042 Nothing -> noBinderInfo
1043 Just (_,_,info) -> info
1045 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1046 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1048 -- Non-top-level things only, both type variables and ids
1049 -- (type variables only if opt_RuntimeTypes)
1050 getFVs :: FreeVarsInfo -> [Var]
1051 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1052 not (topLevelBound how_bound) ]
1054 getFVSet :: FreeVarsInfo -> VarSet
1055 getFVSet fvs = mkVarSet (getFVs fvs)
1057 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1058 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1059 (id1, hb1, combineStgBinderInfo info1 info2)
1061 -- The HowBound info for a variable in the FVInfo should be consistent
1062 check_eq_how_bound ImportBound ImportBound = True
1063 check_eq_how_bound LambdaBound LambdaBound = True
1064 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1065 check_eq_how_bound hb1 hb2 = False
1067 check_eq_li (NestedLet _) (NestedLet _) = True
1068 check_eq_li TopLet TopLet = True
1069 check_eq_li li1 li2 = False
1074 filterStgBinders :: [Var] -> [Var]
1075 filterStgBinders bndrs
1076 | opt_RuntimeTypes = bndrs
1077 | otherwise = filter isId bndrs
1082 -- Ignore all notes except SCC
1083 myCollectBinders expr
1086 go bs (Lam b e) = go (b:bs) e
1087 go bs e@(Note (SCC _) _) = (reverse bs, e)
1088 go bs (Cast e co) = go bs e
1089 go bs (Note _ e) = go bs e
1090 go bs e = (reverse bs, e)
1092 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1093 -- We assume that we only have variables
1094 -- in the function position by now
1098 go (Var v) as = (v, as)
1099 go (App f a) as = go f (a:as)
1100 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1101 go (Cast e co) as = go e as
1102 go (Note n e) as = go e as
1103 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1107 stgArity :: Id -> HowBound -> Arity
1108 stgArity f (LetBound _ arity) = arity
1109 stgArity f ImportBound = idArity f
1110 stgArity f LambdaBound = 0