2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[StgVarInfo]{Sets free/live variable info in STG syntax}
6 And, as we have the info in hand, we may convert some lets to
10 module StgVarInfo ( setStgVarInfo ) where
12 #include "HsVersions.h"
16 import Id ( setIdArity, getIdArity, Id )
20 import IdInfo ( ArityInfo(..), InlinePragInfo(..),
22 import Maybes ( maybeToBool )
23 import Name ( isLocallyDefined )
24 import BasicTypes ( Arity )
27 infixr 9 `thenLne`, `thenLne_`
30 %************************************************************************
32 \subsection[live-vs-free-doc]{Documentation}
34 %************************************************************************
36 (There is other relevant documentation in codeGen/CgLetNoEscape.)
38 March 97: setStgVarInfo guarantees to leave every variable's arity correctly
39 set. The lambda lifter makes some let-bound variables (which have arities)
40 and turns them into lambda-bound ones (which should not, else we get Vap trouble),
41 so this guarantee is necessary, as well as desirable.
43 The arity information is used in the code generator, when deciding if
44 a right-hand side is a saturated application so we can generate a VAP
47 The actual Stg datatype is decorated with {\em live variable}
48 information, as well as {\em free variable} information. The two are
49 {\em not} the same. Liveness is an operational property rather than a
50 semantic one. A variable is live at a particular execution point if
51 it can be referred to {\em directly} again. In particular, a dead
52 variable's stack slot (if it has one):
55 should be stubbed to avoid space leaks, and
57 may be reused for something else.
60 There ought to be a better way to say this. Here are some examples:
67 Just after the `in', v is live, but q is dead. If the whole of that
68 let expression was enclosed in a case expression, thus:
70 case (let v = [q] \[x] -> e in ...v...) of
73 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
74 we'll return later to the @alts@ and need it.
76 Let-no-escapes make this a bit more interesting:
78 let-no-escape v = [q] \ [x] -> e
82 Here, @q@ is still live at the `in', because @v@ is represented not by
83 a closure but by the current stack state. In other words, if @v@ is
84 live then so is @q@. Furthermore, if @e@ mentions an enclosing
85 let-no-escaped variable, then {\em its} free variables are also live
88 %************************************************************************
90 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
92 %************************************************************************
96 setStgVarInfo :: Bool -- True <=> do let-no-escapes
97 -> [StgBinding] -- input
98 -> [StgBinding] -- result
100 setStgVarInfo want_LNEs pgm
103 (pgm', _) = initLne want_LNEs (varsTopBinds pgm)
107 For top-level guys, we basically aren't worried about this
108 live-variable stuff; we do need to keep adding to the environment
109 as we step through the bindings (using @extendVarEnv@).
112 varsTopBinds :: [StgBinding] -> LneM ([StgBinding], FreeVarsInfo)
114 varsTopBinds [] = returnLne ([], emptyFVInfo)
115 varsTopBinds (bind:binds)
116 = extendVarEnvLne env_extension (
117 varsTopBinds binds `thenLne` \ (binds', fv_binds) ->
118 varsTopBind binders' fv_binds bind `thenLne` \ (bind', fv_bind) ->
119 returnLne ((bind' : binds'),
120 (fv_binds `unionFVInfo` fv_bind) `minusFVBinders` binders'
126 StgNonRec binder rhs -> [(binder,rhs)]
127 StgRec pairs -> pairs
129 binders' = [ binder `setIdArity` ArityExactly (rhsArity rhs)
130 | (binder, rhs) <- pairs
133 env_extension = binders' `zip` repeat how_bound
135 how_bound = LetrecBound
140 varsTopBind :: [Id] -- New binders (with correct arity)
141 -> FreeVarsInfo -- Info about the body
143 -> LneM (StgBinding, FreeVarsInfo)
145 varsTopBind [binder'] body_fvs (StgNonRec binder rhs)
146 = varsRhs body_fvs (binder,rhs) `thenLne` \ (rhs2, fvs, _) ->
147 returnLne (StgNonRec binder' rhs2, fvs)
149 varsTopBind binders' body_fvs (StgRec pairs)
150 = fixLne (\ ~(_, rec_rhs_fvs) ->
152 scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
154 mapAndUnzip3Lne (varsRhs scope_fvs) pairs `thenLne` \ (rhss2, fvss, _) ->
156 fvs = unionFVInfos fvss
158 returnLne (StgRec (binders' `zip` rhss2), fvs)
164 varsRhs :: FreeVarsInfo -- Free var info for the scope of the binding
166 -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
168 varsRhs scope_fv_info (binder, StgRhsCon cc con args)
169 = varsAtoms args `thenLne` \ (args', fvs) ->
170 returnLne (StgRhsCon cc con args', fvs, getFVSet fvs)
172 varsRhs scope_fv_info (binder, StgRhsClosure cc _ srt _ upd args body)
173 = extendVarEnvLne [ (zapArity a, LambdaBound) | a <- args ] (
174 do_body args body `thenLne` \ (body2, body_fvs, body_escs) ->
176 set_of_args = mkVarSet args
177 rhs_fvs = body_fvs `minusFVBinders` args
178 rhs_escs = body_escs `minusVarSet` set_of_args
179 binder_info = lookupFVInfo scope_fv_info binder
180 upd' | null args && isPAP body2 = ReEntrant
183 returnLne (StgRhsClosure cc binder_info srt (getFVs rhs_fvs) upd'
184 args body2, rhs_fvs, rhs_escs)
187 -- Pick out special case of application in body of thunk
188 do_body [] (StgApp f args) = varsApp (Just upd) f args
189 do_body _ other_body = varsExpr other_body
192 Detect thunks which will reduce immediately to PAPs, and make them
193 non-updatable. This has several advantages:
195 - the non-updatable thunk behaves exactly like the PAP,
197 - the thunk is more efficient to enter, because it is
198 specialised to the task.
200 - we save one update frame, one stg_update_PAP, one update
201 and lots of PAP_enters.
203 - in the case where the thunk is top-level, we save building
204 a black hole and futhermore the thunk isn't considered to
205 be a CAF any more, so it doesn't appear in any SRTs.
207 We do it here, because the arity information is accurate, and we need
208 to do it before the SRT pass to save the SRT entries associated with
212 isPAP (StgApp f args)
213 = case getIdArity f of
214 ArityExactly n -> n > n_args
215 ArityAtLeast n -> n > n_args
217 where n_args = length args
222 varsAtoms :: [StgArg]
223 -> LneM ([StgArg], FreeVarsInfo)
224 -- It's not *really* necessary to return fresh arguments,
225 -- because the only difference is that the argument variable
226 -- arities are correct. But it seems safer to do so.
229 = mapAndUnzipLne var_atom atoms `thenLne` \ (args', fvs_lists) ->
230 returnLne (args', unionFVInfos fvs_lists)
232 var_atom a@(StgConArg _) = returnLne (a, emptyFVInfo)
233 var_atom a@(StgVarArg v)
234 = lookupVarLne v `thenLne` \ (v', how_bound) ->
235 returnLne (StgVarArg v', singletonFVInfo v' how_bound stgArgOcc)
238 %************************************************************************
240 \subsection[expr-StgVarInfo]{Setting variable info on expressions}
242 %************************************************************************
244 @varsExpr@ carries in a monad-ised environment, which binds each
245 let(rec) variable (ie non top level, not imported, not lambda bound,
246 not case-alternative bound) to:
248 - its set of live vars.
249 For normal variables the set of live vars is just the variable
250 itself. For let-no-escaped variables, the set of live vars is the set
251 live at the moment the variable is entered. The set is guaranteed to
252 have no further let-no-escaped vars in it.
256 -> LneM (StgExpr, -- Decorated expr
257 FreeVarsInfo, -- Its free vars (NB free, not live)
258 EscVarsSet) -- Its escapees, a subset of its free vars;
259 -- also a subset of the domain of the envt
260 -- because we are only interested in the escapees
261 -- for vars which might be turned into
262 -- let-no-escaped ones.
265 The second and third components can be derived in a simple bottom up pass, not
266 dependent on any decisions about which variables will be let-no-escaped or
267 not. The first component, that is, the decorated expression, may then depend
268 on these components, but it in turn is not scrutinised as the basis for any
269 decisions. Hence no black holes.
272 varsExpr (StgApp f args) = varsApp Nothing f args
274 varsExpr (StgCon con args res_ty)
275 = getVarsLiveInCont `thenLne` \ live_in_cont ->
276 varsAtoms args `thenLne` \ (args', args_fvs) ->
277 returnLne (StgCon con args' res_ty, args_fvs, getFVSet args_fvs)
279 varsExpr (StgSCC label expr)
280 = varsExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
281 returnLne (StgSCC label expr2, fvs, escs) )
284 Cases require a little more real work.
286 varsExpr (StgCase scrut _ _ bndr srt alts)
287 = getVarsLiveInCont `thenLne` \ live_in_cont ->
288 extendVarEnvLne [(zapArity bndr, CaseBound)] (
289 vars_alts alts `thenLne` \ (alts2, alts_fvs, alts_escs) ->
290 lookupLiveVarsForSet alts_fvs `thenLne` \ alts_lvs ->
292 -- determine whether the default binder is dead or not
293 bndr'= if (bndr `elementOfFVInfo` alts_fvs)
294 then bndr `modifyIdInfo` (setInlinePragInfo NoInlinePragInfo)
295 else bndr `modifyIdInfo` (setInlinePragInfo IAmDead)
297 -- don't consider the default binder as being 'live in alts',
298 -- since this is from the point of view of the case expr, where
299 -- the default binder is not free.
300 live_in_alts = live_in_cont `unionVarSet`
301 (alts_lvs `minusVarSet` unitVarSet bndr)
303 -- we tell the scrutinee that everything live in the alts
304 -- is live in it, too.
305 setVarsLiveInCont live_in_alts (
307 ) `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
308 lookupLiveVarsForSet scrut_fvs `thenLne` \ scrut_lvs ->
310 live_in_whole_case = live_in_alts `unionVarSet` scrut_lvs
313 StgCase scrut2 live_in_whole_case live_in_alts bndr' srt alts2,
314 (scrut_fvs `unionFVInfo` alts_fvs)
315 `minusFVBinders` [bndr],
316 (alts_escs `unionVarSet` (getFVSet scrut_fvs))
317 `minusVarSet` unitVarSet bndr
321 vars_alts (StgAlgAlts ty alts deflt)
322 = mapAndUnzip3Lne vars_alg_alt alts
323 `thenLne` \ (alts2, alts_fvs_list, alts_escs_list) ->
325 alts_fvs = unionFVInfos alts_fvs_list
326 alts_escs = unionVarSets alts_escs_list
328 vars_deflt deflt `thenLne` \ (deflt2, deflt_fvs, deflt_escs) ->
330 StgAlgAlts ty alts2 deflt2,
331 alts_fvs `unionFVInfo` deflt_fvs,
332 alts_escs `unionVarSet` deflt_escs
335 vars_alg_alt (con, binders, worthless_use_mask, rhs)
336 = extendVarEnvLne [(zapArity b, CaseBound) | b <- binders] (
337 varsExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
339 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders ]
340 -- records whether each param is used in the RHS
343 (con, binders, good_use_mask, rhs2),
344 rhs_fvs `minusFVBinders` binders,
345 rhs_escs `minusVarSet` mkVarSet binders -- ToDo: remove the minusVarSet;
346 -- since escs won't include
347 -- any of these binders
350 vars_alts (StgPrimAlts ty alts deflt)
351 = mapAndUnzip3Lne vars_prim_alt alts
352 `thenLne` \ (alts2, alts_fvs_list, alts_escs_list) ->
354 alts_fvs = unionFVInfos alts_fvs_list
355 alts_escs = unionVarSets alts_escs_list
357 vars_deflt deflt `thenLne` \ (deflt2, deflt_fvs, deflt_escs) ->
359 StgPrimAlts ty alts2 deflt2,
360 alts_fvs `unionFVInfo` deflt_fvs,
361 alts_escs `unionVarSet` deflt_escs
364 vars_prim_alt (lit, rhs)
365 = varsExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
366 returnLne ((lit, rhs2), rhs_fvs, rhs_escs)
368 vars_deflt StgNoDefault
369 = returnLne (StgNoDefault, emptyFVInfo, emptyVarSet)
371 vars_deflt (StgBindDefault rhs)
372 = varsExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
373 returnLne ( StgBindDefault rhs2, rhs_fvs, rhs_escs )
376 Lets not only take quite a bit of work, but this is where we convert
377 then to let-no-escapes, if we wish.
379 (Meanwhile, we don't expect to see let-no-escapes...)
381 varsExpr (StgLetNoEscape _ _ _ _) = panic "varsExpr: unexpected StgLetNoEscape"
383 varsExpr (StgLet bind body)
384 = isSwitchSetLne {-StgDoLetNoEscapes-} `thenLne` \ want_LNEs ->
386 (fixLne (\ ~(_, _, _, no_binder_escapes) ->
388 non_escaping_let = want_LNEs && no_binder_escapes
390 vars_let non_escaping_let bind body
391 )) `thenLne` \ (new_let, fvs, escs, _) ->
393 returnLne (new_let, fvs, escs)
398 varsApp :: Maybe UpdateFlag -- Just upd <=> this application is
399 -- the rhs of a thunk binding
400 -- x = [...] \upd [] -> the_app
401 -- with specified update flag
403 -> [StgArg] -- Arguments
404 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
406 varsApp maybe_thunk_body f args
407 = getVarsLiveInCont `thenLne` \ live_in_cont ->
409 varsAtoms args `thenLne` \ (args', args_fvs) ->
411 lookupVarLne f `thenLne` \ (f', how_bound) ->
415 not_letrec_bound = not (isLetrecBound how_bound)
416 f_arity = getIdArity f'
417 fun_fvs = singletonFVInfo f' how_bound fun_occ
421 = NoStgBinderInfo -- Uninteresting variable
423 | otherwise -- Letrec bound; must have its arity
426 | n_args == 0 -> stgFakeFunAppOcc -- Function Application
427 -- with no arguments.
428 -- used by the lambda lifter.
429 | arity > n_args -> stgUnsatOcc -- Unsaturated
433 maybeToBool maybe_thunk_body -> -- Exactly saturated,
435 case maybe_thunk_body of
436 Just Updatable -> stgStdHeapOcc
437 Just SingleEntry -> stgNoUpdHeapOcc
438 other -> panic "varsApp"
440 | otherwise -> stgNormalOcc
441 -- Record only that it occurs free
443 myself = unitVarSet f'
445 fun_escs | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
446 | otherwise = case f_arity of -- Letrec bound, so must have its arity
448 | arity == n_args -> emptyVarSet
449 -- Function doesn't escape
450 | otherwise -> myself
451 -- Inexact application; it does escape
453 -- At the moment of the call:
455 -- either the function is *not* let-no-escaped, in which case
456 -- nothing is live except live_in_cont
457 -- or the function *is* let-no-escaped in which case the
458 -- variables it uses are live, but still the function
459 -- itself is not. PS. In this case, the function's
460 -- live vars should already include those of the
461 -- continuation, but it does no harm to just union the
466 -- = live_in_cont `unionVarSet` case how_bound of
467 -- LetrecBound _ lvs -> lvs `minusVarSet` myself
468 -- other -> emptyVarSet
472 fun_fvs `unionFVInfo` args_fvs,
473 fun_escs `unionVarSet` (getFVSet args_fvs)
474 -- All the free vars of the args are disqualified
475 -- from being let-no-escaped.
481 vars_let :: Bool -- True <=> yes, we are let-no-escaping this let
482 -> StgBinding -- bindings
484 -> LneM (StgExpr, -- new let
485 FreeVarsInfo, -- variables free in the whole let
486 EscVarsSet, -- variables that escape from the whole let
487 Bool) -- True <=> none of the binders in the bindings
488 -- is among the escaping vars
490 vars_let let_no_escape bind body
491 = fixLne (\ ~(_, _, _, rec_bind_lvs, _, rec_body_fvs, _, _) ->
493 -- Do the bindings, setting live_in_cont to empty if
494 -- we ain't in a let-no-escape world
495 getVarsLiveInCont `thenLne` \ live_in_cont ->
497 (if let_no_escape then live_in_cont else emptyVarSet)
498 (vars_bind rec_bind_lvs rec_body_fvs bind)
499 `thenLne` \ (bind2, bind_fvs, bind_escs, env_ext) ->
501 -- The live variables of this binding are the ones which are live
502 -- by virtue of being accessible via the free vars of the binding (lvs_from_fvs)
503 -- together with the live_in_cont ones
504 lookupLiveVarsForSet (bind_fvs `minusFVBinders` binders) `thenLne` \ lvs_from_fvs ->
506 bind_lvs = lvs_from_fvs `unionVarSet` live_in_cont
509 -- bind_fvs and bind_escs still include the binders of the let(rec)
510 -- but bind_lvs does not
513 extendVarEnvLne env_ext (
514 varsExpr body `thenLne` \ (body2, body_fvs, body_escs) ->
515 lookupLiveVarsForSet body_fvs `thenLne` \ body_lvs ->
517 returnLne (bind2, bind_fvs, bind_escs, bind_lvs,
518 body2, body_fvs, body_escs, body_lvs)
520 )) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
521 body2, body_fvs, body_escs, body_lvs) ->
524 -- Compute the new let-expression
526 new_let = if let_no_escape then
527 -- trace "StgLetNoEscape!" (
528 StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
534 = (bind_fvs `unionFVInfo` body_fvs) `minusFVBinders` binders
537 = bind_lvs `unionVarSet` (body_lvs `minusVarSet` set_of_binders)
539 real_bind_escs = if let_no_escape then
543 -- Everything escapes which is free in the bindings
545 let_escs = (real_bind_escs `unionVarSet` body_escs) `minusVarSet` set_of_binders
547 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
550 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
551 -- Mustn't depend on the passed-in let_no_escape flag, since
552 -- no_binder_escapes is used by the caller to derive the flag!
561 set_of_binders = mkVarSet binders
562 binders = case bind of
563 StgNonRec binder rhs -> [binder]
564 StgRec pairs -> map fst pairs
566 mk_binding bind_lvs (binder,rhs)
567 = (binder `setIdArity` ArityExactly (stgArity rhs),
568 LetrecBound False -- Not top level
572 live_vars = if let_no_escape then
573 extendVarSet bind_lvs binder
577 vars_bind :: StgLiveVars
578 -> FreeVarsInfo -- Free var info for body of binding
581 FreeVarsInfo, EscVarsSet, -- free vars; escapee vars
583 -- extension to environment
585 vars_bind rec_bind_lvs rec_body_fvs (StgNonRec binder rhs)
586 = varsRhs rec_body_fvs (binder,rhs) `thenLne` \ (rhs2, fvs, escs) ->
588 env_ext_item@(binder', _) = mk_binding rec_bind_lvs (binder,rhs)
590 returnLne (StgNonRec binder' rhs2, fvs, escs, [env_ext_item])
592 vars_bind rec_bind_lvs rec_body_fvs (StgRec pairs)
594 env_ext = map (mk_binding rec_bind_lvs) pairs
595 binders' = map fst env_ext
597 extendVarEnvLne env_ext (
598 fixLne (\ ~(_, rec_rhs_fvs, _, _) ->
600 rec_scope_fvs = unionFVInfo rec_body_fvs rec_rhs_fvs
602 mapAndUnzip3Lne (varsRhs rec_scope_fvs) pairs `thenLne` \ (rhss2, fvss, escss) ->
604 fvs = unionFVInfos fvss
605 escs = unionVarSets escss
607 returnLne (StgRec (binders' `zip` rhss2), fvs, escs, env_ext)
611 %************************************************************************
613 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
615 %************************************************************************
617 There's a lot of stuff to pass around, so we use this @LneM@ monad to
618 help. All the stuff here is only passed {\em down}.
621 type LneM a = Bool -- True <=> do let-no-escapes
622 -> IdEnv (Id, HowBound) -- Use the Id at all occurrences; it has correct
623 -- arity information inside it.
624 -> StgLiveVars -- vars live in continuation
632 Bool -- True <=> bound at top level
633 StgLiveVars -- Live vars... see notes below
635 isLetrecBound (LetrecBound _ _) = True
636 isLetrecBound other = False
639 For a let(rec)-bound variable, x, we record what varibles are live if
640 x is live. For "normal" variables that is just x alone. If x is
641 a let-no-escaped variable then x is represented by a code pointer and
642 a stack pointer (well, one for each stack). So all of the variables
643 needed in the execution of x are live if x is, and are therefore recorded
644 in the LetrecBound constructor; x itself *is* included.
646 The std monad functions:
648 initLne :: Bool -> LneM a -> a
649 initLne want_LNEs m = m want_LNEs emptyVarEnv emptyVarSet
651 {-# INLINE thenLne #-}
652 {-# INLINE thenLne_ #-}
653 {-# INLINE returnLne #-}
655 returnLne :: a -> LneM a
656 returnLne e sw env lvs_cont = e
658 thenLne :: LneM a -> (a -> LneM b) -> LneM b
659 thenLne m k sw env lvs_cont
660 = case (m sw env lvs_cont) of
661 m_result -> k m_result sw env lvs_cont
663 thenLne_ :: LneM a -> LneM b -> LneM b
664 thenLne_ m k sw env lvs_cont
665 = case (m sw env lvs_cont) of
666 _ -> k sw env lvs_cont
668 mapLne :: (a -> LneM b) -> [a] -> LneM [b]
669 mapLne f [] = returnLne []
671 = f x `thenLne` \ r ->
672 mapLne f xs `thenLne` \ rs ->
675 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
677 mapAndUnzipLne f [] = returnLne ([],[])
678 mapAndUnzipLne f (x:xs)
679 = f x `thenLne` \ (r1, r2) ->
680 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
681 returnLne (r1:rs1, r2:rs2)
683 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
685 mapAndUnzip3Lne f [] = returnLne ([],[],[])
686 mapAndUnzip3Lne f (x:xs)
687 = f x `thenLne` \ (r1, r2, r3) ->
688 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
689 returnLne (r1:rs1, r2:rs2, r3:rs3)
691 fixLne :: (a -> LneM a) -> LneM a
692 fixLne expr sw env lvs_cont = result
694 result = expr result sw env lvs_cont
695 -- ^^^^^^ ------ ^^^^^^
698 Functions specific to this monad:
700 isSwitchSetLne :: LneM Bool
701 isSwitchSetLne want_LNEs env lvs_cont
704 getVarsLiveInCont :: LneM StgLiveVars
705 getVarsLiveInCont sw env lvs_cont = lvs_cont
707 setVarsLiveInCont :: StgLiveVars -> LneM a -> LneM a
708 setVarsLiveInCont new_lvs_cont expr sw env lvs_cont
709 = expr sw env new_lvs_cont
711 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
712 extendVarEnvLne ids_w_howbound expr sw env lvs_cont
713 = expr sw (extendVarEnvList env [(id, pair) | pair@(id,_) <- ids_w_howbound]) lvs_cont
716 lookupVarLne :: Id -> LneM (Id, HowBound)
717 lookupVarLne v sw env lvs_cont
719 case (lookupVarEnv env v) of
721 Nothing -> --false:ASSERT(not (isLocallyDefined v))
725 -- The result of lookupLiveVarsForSet, a set of live variables, is
726 -- only ever tacked onto a decorated expression. It is never used as
727 -- the basis of a control decision, which might give a black hole.
729 lookupLiveVarsForSet :: FreeVarsInfo -> LneM StgLiveVars
731 lookupLiveVarsForSet fvs sw env lvs_cont
732 = returnLne (unionVarSets (map do_one (getFVs fvs)))
736 = if isLocallyDefined v then
737 case (lookupVarEnv env v) of
738 Just (_, LetrecBound _ lvs) -> extendVarSet lvs v
739 Just _ -> unitVarSet v
740 Nothing -> pprPanic "lookupVarEnv/do_one:" (ppr v)
746 %************************************************************************
748 \subsection[Free-var info]{Free variable information}
750 %************************************************************************
753 type FreeVarsInfo = IdEnv (Id, Bool, StgBinderInfo)
754 -- If f is mapped to NoStgBinderInfo, that means
755 -- that f *is* mentioned (else it wouldn't be in the
756 -- IdEnv at all), but only in a saturated applications.
758 -- All case/lambda-bound things are also mapped to
759 -- NoStgBinderInfo, since we aren't interested in their
762 -- The Bool is True <=> the Id is top level letrec bound
764 type EscVarsSet = IdSet
768 emptyFVInfo :: FreeVarsInfo
769 emptyFVInfo = emptyVarEnv
771 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
772 singletonFVInfo id ImportBound info = emptyVarEnv
773 singletonFVInfo id (LetrecBound top_level _) info = unitVarEnv id (id, top_level, info)
774 singletonFVInfo id other info = unitVarEnv id (id, False, info)
776 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
777 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
779 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
780 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
782 minusFVBinders :: FreeVarsInfo -> [Id] -> FreeVarsInfo
783 minusFVBinders fv ids = fv `delVarEnvList` ids
785 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
786 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
788 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
789 lookupFVInfo fvs id = case lookupVarEnv fvs id of
790 Nothing -> NoStgBinderInfo
791 Just (_,_,info) -> info
793 getFVs :: FreeVarsInfo -> [Id] -- Non-top-level things only
794 getFVs fvs = [id | (id,False,_) <- rngVarEnv fvs]
796 getFVSet :: FreeVarsInfo -> IdSet
797 getFVSet fvs = mkVarSet (getFVs fvs)
799 plusFVInfo (id1,top1,info1) (id2,top2,info2)
800 = ASSERT (id1 == id2 && top1 == top2)
801 (id1, top1, combineStgBinderInfo info1 info2)
805 rhsArity :: StgRhs -> Arity
806 rhsArity (StgRhsCon _ _ _) = 0
807 rhsArity (StgRhsClosure _ _ _ _ _ args _) = length args
810 zapArity id = id `setIdArity` UnknownArity