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
10 module CoreToStg ( coreToStg, coreExprToStg ) where
12 #include "HsVersions.h"
15 import CoreUtils ( rhsIsStatic, manifestArity, exprType )
19 import TyCon ( isAlgTyCon )
21 import Var ( Var, globalIdDetails, idType )
22 import TyCon ( isUnboxedTupleTyCon, isPrimTyCon, isFunTyCon, isHiBootTyCon )
24 import MkId ( unsafeCoerceId )
28 import CostCentre ( noCCS )
31 import Maybes ( maybeToBool )
32 import Name ( getOccName, isExternalName, nameOccName )
33 import OccName ( occNameUserString, occNameFS )
34 import BasicTypes ( Arity )
35 import CmdLineOpts ( DynFlags, opt_RuntimeTypes )
41 %************************************************************************
43 \subsection[live-vs-free-doc]{Documentation}
45 %************************************************************************
47 (There is other relevant documentation in codeGen/CgLetNoEscape.)
49 The actual Stg datatype is decorated with {\em live variable}
50 information, as well as {\em free variable} information. The two are
51 {\em not} the same. Liveness is an operational property rather than a
52 semantic one. A variable is live at a particular execution point if
53 it can be referred to {\em directly} again. In particular, a dead
54 variable's stack slot (if it has one):
57 should be stubbed to avoid space leaks, and
59 may be reused for something else.
62 There ought to be a better way to say this. Here are some examples:
69 Just after the `in', v is live, but q is dead. If the whole of that
70 let expression was enclosed in a case expression, thus:
72 case (let v = [q] \[x] -> e in ...v...) of
75 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
76 we'll return later to the @alts@ and need it.
78 Let-no-escapes make this a bit more interesting:
80 let-no-escape v = [q] \ [x] -> e
84 Here, @q@ is still live at the `in', because @v@ is represented not by
85 a closure but by the current stack state. In other words, if @v@ is
86 live then so is @q@. Furthermore, if @e@ mentions an enclosing
87 let-no-escaped variable, then {\em its} free variables are also live
90 %************************************************************************
92 \subsection[caf-info]{Collecting live CAF info}
94 %************************************************************************
96 In this pass we also collect information on which CAFs are live for
97 constructing SRTs (see SRT.lhs).
99 A top-level Id has CafInfo, which is
101 - MayHaveCafRefs, if it may refer indirectly to
103 - NoCafRefs if it definitely doesn't
105 The CafInfo has already been calculated during the CoreTidy pass.
107 During CoreToStg, we then pin onto each binding and case expression, a
108 list of Ids which represents the "live" CAFs at that point. The meaning
109 of "live" here is the same as for live variables, see above (which is
110 why it's convenient to collect CAF information here rather than elsewhere).
112 The later SRT pass takes these lists of Ids and uses them to construct
113 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
117 Interaction of let-no-escape with SRTs [Sept 01]
118 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
121 let-no-escape x = ...caf1...caf2...
125 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
126 build SRTs just as if x's defn was inlined at each call site, and
127 that means that x's CAF refs get duplicated in the overall SRT.
129 This is unlike ordinary lets, in which the CAF refs are not duplicated.
131 We could fix this loss of (static) sharing by making a sort of pseudo-closure
132 for x, solely to put in the SRTs lower down.
135 %************************************************************************
137 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
139 %************************************************************************
142 coreToStg :: DynFlags -> [CoreBind] -> IO [StgBinding]
145 where (_, _, pgm') = coreTopBindsToStg emptyVarEnv pgm
147 coreExprToStg :: CoreExpr -> StgExpr
149 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
153 :: IdEnv HowBound -- environment for the bindings
155 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
157 coreTopBindsToStg env [] = (env, emptyFVInfo, [])
158 coreTopBindsToStg env (b:bs)
159 = (env2, fvs2, b':bs')
161 -- env accumulates down the list of binds, fvs accumulates upwards
162 (env1, fvs2, b' ) = coreTopBindToStg env fvs1 b
163 (env2, fvs1, bs') = coreTopBindsToStg env1 bs
168 -> FreeVarsInfo -- Info about the body
170 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
172 coreTopBindToStg env body_fvs (NonRec id rhs)
174 env' = extendVarEnv env id how_bound
175 how_bound = LetBound TopLet (manifestArity rhs)
179 coreToTopStgRhs body_fvs (id,rhs) `thenLne` \ (stg_rhs, fvs') ->
180 returnLne (stg_rhs, fvs')
183 bind = StgNonRec id stg_rhs
185 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
186 ASSERT2(consistentCafInfo id bind, ppr id)
187 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
188 (env', fvs' `unionFVInfo` body_fvs, bind)
190 coreTopBindToStg env body_fvs (Rec pairs)
192 (binders, rhss) = unzip pairs
194 extra_env' = [ (b, LetBound TopLet (manifestArity rhs))
195 | (b, rhs) <- pairs ]
196 env' = extendVarEnvList env extra_env'
200 mapAndUnzipLne (coreToTopStgRhs body_fvs) pairs
201 `thenLne` \ (stg_rhss, fvss') ->
202 let fvs' = unionFVInfos fvss' in
203 returnLne (stg_rhss, fvs')
206 bind = StgRec (zip binders stg_rhss)
208 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
209 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
210 (env', fvs' `unionFVInfo` body_fvs, bind)
213 -- Assertion helper: this checks that the CafInfo on the Id matches
214 -- what CoreToStg has figured out about the binding's SRT. The
215 -- CafInfo will be exact in all cases except when CorePrep has
216 -- floated out a binding, in which case it will be approximate.
217 consistentCafInfo id bind
218 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
221 = WARN (not exact, ppr id) safe
223 safe = id_marked_caffy || not binding_is_caffy
224 exact = id_marked_caffy == binding_is_caffy
225 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
226 binding_is_caffy = stgBindHasCafRefs bind
232 :: FreeVarsInfo -- Free var info for the scope of the binding
234 -> LneM (StgRhs, FreeVarsInfo)
236 coreToTopStgRhs scope_fv_info (bndr, rhs)
237 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
238 freeVarsToLiveVars rhs_fvs `thenLne` \ lv_info ->
239 returnLne (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
241 bndr_info = lookupFVInfo scope_fv_info bndr
242 is_static = rhsIsStatic rhs
244 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
247 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
248 = ASSERT( is_static )
249 StgRhsClosure noCCS binder_info
255 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
256 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
257 = StgRhsCon noCCS con args
259 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
260 = ASSERT2( not is_static, ppr rhs )
261 StgRhsClosure noCCS binder_info
269 -- ---------------------------------------------------------------------------
271 -- ---------------------------------------------------------------------------
276 -> LneM (StgExpr, -- Decorated STG expr
277 FreeVarsInfo, -- Its free vars (NB free, not live)
278 EscVarsSet) -- Its escapees, a subset of its free vars;
279 -- also a subset of the domain of the envt
280 -- because we are only interested in the escapees
281 -- for vars which might be turned into
282 -- let-no-escaped ones.
285 The second and third components can be derived in a simple bottom up pass, not
286 dependent on any decisions about which variables will be let-no-escaped or
287 not. The first component, that is, the decorated expression, may then depend
288 on these components, but it in turn is not scrutinised as the basis for any
289 decisions. Hence no black holes.
292 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
293 coreToStgExpr (Var v) = coreToStgApp Nothing v []
295 coreToStgExpr expr@(App _ _)
296 = coreToStgApp Nothing f args
298 (f, args) = myCollectArgs expr
300 coreToStgExpr expr@(Lam _ _)
302 (args, body) = myCollectBinders expr
303 args' = filterStgBinders args
305 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
306 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
308 fvs = args' `minusFVBinders` body_fvs
309 escs = body_escs `delVarSetList` args'
310 result_expr | null args' = body
311 | otherwise = StgLam (exprType expr) args' body
313 returnLne (result_expr, fvs, escs)
315 coreToStgExpr (Note (SCC cc) expr)
316 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
317 returnLne (StgSCC cc expr2, fvs, escs) )
320 -- For ILX, convert (__coerce__ to_ty from_ty e)
321 -- into (coerce to_ty from_ty e)
322 -- where coerce is real function
323 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
324 = coreToStgExpr (mkApps (Var unsafeCoerceId)
325 [Type from_ty, Type to_ty, expr])
328 coreToStgExpr (Note other_note expr)
331 -- Cases require a little more real work.
334 coreToStgExpr (Case scrut bndr _ alts)
335 = extendVarEnvLne [(bndr, LambdaBound)] (
336 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
339 unionVarSets escs_s )
340 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
342 -- Determine whether the default binder is dead or not
343 -- This helps the code generator to avoid generating an assignment
344 -- for the case binder (is extremely rare cases) ToDo: remove.
345 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
346 | otherwise = bndr `setIdOccInfo` IAmDead
348 -- Don't consider the default binder as being 'live in alts',
349 -- since this is from the point of view of the case expr, where
350 -- the default binder is not free.
351 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
352 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
355 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
357 -- We tell the scrutinee that everything
358 -- live in the alts is live in it, too.
359 setVarsLiveInCont alts_lv_info (
360 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
361 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
362 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
364 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
367 StgCase scrut2 (getLiveVars scrut_lv_info)
368 (getLiveVars alts_lv_info)
371 (mkStgAltType (idType bndr))
373 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
374 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
375 -- You might think we should have scrut_escs, not
376 -- (getFVSet scrut_fvs), but actually we can't call, and
377 -- then return from, a let-no-escape thing.
380 vars_alt (con, binders, rhs)
381 = let -- Remove type variables
382 binders' = filterStgBinders binders
384 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
385 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
387 -- Records whether each param is used in the RHS
388 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
390 returnLne ( (con, binders', good_use_mask, rhs2),
391 binders' `minusFVBinders` rhs_fvs,
392 rhs_escs `delVarSetList` binders' )
393 -- ToDo: remove the delVarSet;
394 -- since escs won't include any of these binders
397 Lets not only take quite a bit of work, but this is where we convert
398 then to let-no-escapes, if we wish.
400 (Meanwhile, we don't expect to see let-no-escapes...)
402 coreToStgExpr (Let bind body)
403 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
404 coreToStgLet no_binder_escapes bind body
405 ) `thenLne` \ (new_let, fvs, escs, _) ->
407 returnLne (new_let, fvs, escs)
411 mkStgAltType scrut_ty
412 = case splitTyConApp_maybe (repType scrut_ty) of
413 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
414 | isPrimTyCon tc -> PrimAlt tc
415 | isHiBootTyCon tc -> PolyAlt -- Algebraic, but no constructors visible
416 | isAlgTyCon tc -> AlgAlt tc
417 | isFunTyCon tc -> PolyAlt
418 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
423 -- ---------------------------------------------------------------------------
425 -- ---------------------------------------------------------------------------
429 :: Maybe UpdateFlag -- Just upd <=> this application is
430 -- the rhs of a thunk binding
431 -- x = [...] \upd [] -> the_app
432 -- with specified update flag
434 -> [CoreArg] -- Arguments
435 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
437 coreToStgApp maybe_thunk_body f args
438 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
439 lookupVarLne f `thenLne` \ how_bound ->
442 n_val_args = valArgCount args
443 not_letrec_bound = not (isLetBound how_bound)
445 = let fvs = singletonFVInfo f how_bound fun_occ in
446 -- e.g. (f :: a -> int) (x :: a)
447 -- Here the free variables are "f", "x" AND the type variable "a"
448 -- coreToStgArgs will deal with the arguments recursively
449 if opt_RuntimeTypes then
450 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
453 -- Mostly, the arity info of a function is in the fn's IdInfo
454 -- But new bindings introduced by CoreSat may not have no
455 -- arity info; it would do us no good anyway. For example:
456 -- let f = \ab -> e in f
457 -- No point in having correct arity info for f!
458 -- Hence the hasArity stuff below.
459 -- NB: f_arity is only consulted for LetBound things
460 f_arity = stgArity f how_bound
461 saturated = f_arity <= n_val_args
464 | not_letrec_bound = noBinderInfo -- Uninteresting variable
465 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
466 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
469 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
470 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
471 -- saturated call doesn't escape
472 -- (let-no-escape applies to 'thunks' too)
474 | otherwise = unitVarSet f -- Inexact application; it does escape
476 -- At the moment of the call:
478 -- either the function is *not* let-no-escaped, in which case
479 -- nothing is live except live_in_cont
480 -- or the function *is* let-no-escaped in which case the
481 -- variables it uses are live, but still the function
482 -- itself is not. PS. In this case, the function's
483 -- live vars should already include those of the
484 -- continuation, but it does no harm to just union the
487 res_ty = exprType (mkApps (Var f) args)
488 app = case globalIdDetails f of
489 DataConWorkId dc | saturated -> StgConApp dc args'
490 PrimOpId op -> ASSERT( saturated )
491 StgOpApp (StgPrimOp op) args' res_ty
492 FCallId call -> ASSERT( saturated )
493 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
494 _other -> StgApp f args'
499 fun_fvs `unionFVInfo` args_fvs,
500 fun_escs `unionVarSet` (getFVSet args_fvs)
501 -- All the free vars of the args are disqualified
502 -- from being let-no-escaped.
507 -- ---------------------------------------------------------------------------
509 -- This is the guy that turns applications into A-normal form
510 -- ---------------------------------------------------------------------------
512 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
514 = returnLne ([], emptyFVInfo)
516 coreToStgArgs (Type ty : args) -- Type argument
517 = coreToStgArgs args `thenLne` \ (args', fvs) ->
518 if opt_RuntimeTypes then
519 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
521 returnLne (args', fvs)
523 coreToStgArgs (arg : args) -- Non-type argument
524 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
525 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
527 fvs = args_fvs `unionFVInfo` arg_fvs
528 stg_arg = case arg' of
529 StgApp v [] -> StgVarArg v
530 StgConApp con [] -> StgVarArg (dataConWorkId con)
531 StgLit lit -> StgLitArg lit
532 _ -> pprPanic "coreToStgArgs" (ppr arg)
534 returnLne (stg_arg : stg_args, fvs)
537 -- ---------------------------------------------------------------------------
538 -- The magic for lets:
539 -- ---------------------------------------------------------------------------
542 :: Bool -- True <=> yes, we are let-no-escaping this let
543 -> CoreBind -- bindings
545 -> LneM (StgExpr, -- new let
546 FreeVarsInfo, -- variables free in the whole let
547 EscVarsSet, -- variables that escape from the whole let
548 Bool) -- True <=> none of the binders in the bindings
549 -- is among the escaping vars
551 coreToStgLet let_no_escape bind body
552 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
554 -- Do the bindings, setting live_in_cont to empty if
555 -- we ain't in a let-no-escape world
556 getVarsLiveInCont `thenLne` \ live_in_cont ->
557 setVarsLiveInCont (if let_no_escape
560 (vars_bind rec_body_fvs bind)
561 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
564 extendVarEnvLne env_ext (
565 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
566 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
568 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
569 body2, body_fvs, body_escs, getLiveVars body_lv_info)
572 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
573 body2, body_fvs, body_escs, body_lvs) ->
576 -- Compute the new let-expression
578 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
579 | otherwise = StgLet bind2 body2
582 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
585 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
587 real_bind_escs = if let_no_escape then
591 -- Everything escapes which is free in the bindings
593 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
595 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
598 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
601 -- Debugging code as requested by Andrew Kennedy
602 checked_no_binder_escapes
603 | not no_binder_escapes && any is_join_var binders
604 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
606 | otherwise = no_binder_escapes
608 checked_no_binder_escapes = no_binder_escapes
611 -- Mustn't depend on the passed-in let_no_escape flag, since
612 -- no_binder_escapes is used by the caller to derive the flag!
618 checked_no_binder_escapes
621 set_of_binders = mkVarSet binders
622 binders = bindersOf bind
624 mk_binding bind_lv_info binder rhs
625 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
627 live_vars | let_no_escape = addLiveVar bind_lv_info binder
628 | otherwise = unitLiveVar binder
629 -- c.f. the invariant on NestedLet
631 vars_bind :: FreeVarsInfo -- Free var info for body of binding
635 EscVarsSet, -- free vars; escapee vars
636 LiveInfo, -- Vars and CAFs live in binding
637 [(Id, HowBound)]) -- extension to environment
640 vars_bind body_fvs (NonRec binder rhs)
641 = coreToStgRhs body_fvs [] (binder,rhs)
642 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
644 env_ext_item = mk_binding bind_lv_info binder rhs
646 returnLne (StgNonRec binder rhs2,
647 bind_fvs, escs, bind_lv_info, [env_ext_item])
650 vars_bind body_fvs (Rec pairs)
651 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
653 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
654 binders = map fst pairs
655 env_ext = [ mk_binding bind_lv_info b rhs
658 extendVarEnvLne env_ext (
659 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
660 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
662 bind_fvs = unionFVInfos fvss
663 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
664 escs = unionVarSets escss
666 returnLne (StgRec (binders `zip` rhss2),
667 bind_fvs, escs, bind_lv_info, env_ext)
671 is_join_var :: Id -> Bool
672 -- A hack (used only for compiler debuggging) to tell if
673 -- a variable started life as a join point ($j)
674 is_join_var j = occNameUserString (getOccName j) == "$j"
678 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
681 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
683 coreToStgRhs scope_fv_info binders (bndr, rhs)
684 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
685 getEnvLne `thenLne` \ env ->
686 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
687 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
688 rhs_fvs, lv_info, rhs_escs)
690 bndr_info = lookupFVInfo scope_fv_info bndr
692 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
694 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
695 = StgRhsCon noCCS con args
697 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
698 = StgRhsClosure noCCS binder_info
703 mkStgRhs rhs_fvs srt binder_info rhs
704 = StgRhsClosure noCCS binder_info
710 SDM: disabled. Eval/Apply can't handle functions with arity zero very
711 well; and making these into simple non-updatable thunks breaks other
712 assumptions (namely that they will be entered only once).
714 upd_flag | isPAP env rhs = ReEntrant
715 | otherwise = Updatable
719 upd = if isOnceDem dem
720 then (if isNotTop toplev
721 then SingleEntry -- HA! Paydirt for "dem"
724 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
728 -- For now we forbid SingleEntry CAFs; they tickle the
729 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
730 -- and I don't understand why. There's only one SE_CAF (well,
731 -- only one that tickled a great gaping bug in an earlier attempt
732 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
733 -- specifically Main.lvl6 in spectral/cryptarithm2.
734 -- So no great loss. KSW 2000-07.
738 Detect thunks which will reduce immediately to PAPs, and make them
739 non-updatable. This has several advantages:
741 - the non-updatable thunk behaves exactly like the PAP,
743 - the thunk is more efficient to enter, because it is
744 specialised to the task.
746 - we save one update frame, one stg_update_PAP, one update
747 and lots of PAP_enters.
749 - in the case where the thunk is top-level, we save building
750 a black hole and futhermore the thunk isn't considered to
751 be a CAF any more, so it doesn't appear in any SRTs.
753 We do it here, because the arity information is accurate, and we need
754 to do it before the SRT pass to save the SRT entries associated with
757 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
759 arity = stgArity f (lookupBinding env f)
763 %************************************************************************
765 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
767 %************************************************************************
769 There's a lot of stuff to pass around, so we use this @LneM@ monad to
770 help. All the stuff here is only passed *down*.
773 type LneM a = IdEnv HowBound
774 -> LiveInfo -- Vars and CAFs live in continuation
777 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
778 -- i.e. ones with a nested (non-top-level) binding
779 CafSet) -- Static live variables;
780 -- i.e. top-level variables that are CAFs or refer to them
782 type EscVarsSet = IdSet
786 = ImportBound -- Used only as a response to lookupBinding; never
787 -- exists in the range of the (IdEnv HowBound)
789 | LetBound -- A let(rec) in this module
790 LetInfo -- Whether top level or nested
791 Arity -- Its arity (local Ids don't have arity info at this point)
793 | LambdaBound -- Used for both lambda and case
796 = TopLet -- top level things
797 | NestedLet LiveInfo -- For nested things, what is live if this
798 -- thing is live? Invariant: the binder
799 -- itself is always a member of
800 -- the dynamic set of its own LiveInfo
802 isLetBound (LetBound _ _) = True
803 isLetBound other = False
805 topLevelBound ImportBound = True
806 topLevelBound (LetBound TopLet _) = True
807 topLevelBound other = False
810 For a let(rec)-bound variable, x, we record LiveInfo, the set of
811 variables that are live if x is live. This LiveInfo comprises
812 (a) dynamic live variables (ones with a non-top-level binding)
813 (b) static live variabes (CAFs or things that refer to CAFs)
815 For "normal" variables (a) is just x alone. If x is a let-no-escaped
816 variable then x is represented by a code pointer and a stack pointer
817 (well, one for each stack). So all of the variables needed in the
818 execution of x are live if x is, and are therefore recorded in the
819 LetBound constructor; x itself *is* included.
821 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
825 emptyLiveInfo :: LiveInfo
826 emptyLiveInfo = (emptyVarSet,emptyVarSet)
828 unitLiveVar :: Id -> LiveInfo
829 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
831 unitLiveCaf :: Id -> LiveInfo
832 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
834 addLiveVar :: LiveInfo -> Id -> LiveInfo
835 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
837 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
838 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
840 mkSRT :: LiveInfo -> SRT
841 mkSRT (_, cafs) = SRTEntries cafs
843 getLiveVars :: LiveInfo -> StgLiveVars
844 getLiveVars (lvs, _) = lvs
848 The std monad functions:
850 initLne :: IdEnv HowBound -> LneM a -> a
851 initLne env m = m env emptyLiveInfo
855 {-# INLINE thenLne #-}
856 {-# INLINE returnLne #-}
858 returnLne :: a -> LneM a
859 returnLne e env lvs_cont = e
861 thenLne :: LneM a -> (a -> LneM b) -> LneM b
862 thenLne m k env lvs_cont
863 = k (m env lvs_cont) env lvs_cont
865 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
866 mapAndUnzipLne f [] = returnLne ([],[])
867 mapAndUnzipLne f (x:xs)
868 = f x `thenLne` \ (r1, r2) ->
869 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
870 returnLne (r1:rs1, r2:rs2)
872 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
873 mapAndUnzip3Lne f [] = returnLne ([],[],[])
874 mapAndUnzip3Lne f (x:xs)
875 = f x `thenLne` \ (r1, r2, r3) ->
876 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
877 returnLne (r1:rs1, r2:rs2, r3:rs3)
879 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
880 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
881 mapAndUnzip4Lne f (x:xs)
882 = f x `thenLne` \ (r1, r2, r3, r4) ->
883 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
884 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
886 fixLne :: (a -> LneM a) -> LneM a
887 fixLne expr env lvs_cont
890 result = expr result env lvs_cont
893 Functions specific to this monad:
896 getVarsLiveInCont :: LneM LiveInfo
897 getVarsLiveInCont env lvs_cont = lvs_cont
899 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
900 setVarsLiveInCont new_lvs_cont expr env lvs_cont
901 = expr env new_lvs_cont
903 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
904 extendVarEnvLne ids_w_howbound expr env lvs_cont
905 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
907 lookupVarLne :: Id -> LneM HowBound
908 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
910 getEnvLne :: LneM (IdEnv HowBound)
911 getEnvLne env lvs_cont = returnLne env env lvs_cont
913 lookupBinding :: IdEnv HowBound -> Id -> HowBound
914 lookupBinding env v = case lookupVarEnv env v of
916 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
919 -- The result of lookupLiveVarsForSet, a set of live variables, is
920 -- only ever tacked onto a decorated expression. It is never used as
921 -- the basis of a control decision, which might give a black hole.
923 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
924 freeVarsToLiveVars fvs env live_in_cont
925 = returnLne live_info env live_in_cont
927 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
928 lvs_from_fvs = map do_one (allFreeIds fvs)
930 do_one (v, how_bound)
932 ImportBound -> unitLiveCaf v -- Only CAF imports are
935 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
936 | otherwise -> emptyLiveInfo
938 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
939 -- (see the invariant on NestedLet)
941 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
944 %************************************************************************
946 \subsection[Free-var info]{Free variable information}
948 %************************************************************************
951 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
952 -- The Var is so we can gather up the free variables
955 -- The HowBound info just saves repeated lookups;
956 -- we look up just once when we encounter the occurrence.
957 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
958 -- Imported Ids without CAF refs are simply
959 -- not put in the FreeVarsInfo for an expression.
960 -- See singletonFVInfo and freeVarsToLiveVars
962 -- StgBinderInfo records how it occurs; notably, we
963 -- are interested in whether it only occurs in saturated
964 -- applications, because then we don't need to build a
966 -- If f is mapped to noBinderInfo, that means
967 -- that f *is* mentioned (else it wouldn't be in the
968 -- IdEnv at all), but perhaps in an unsaturated applications.
970 -- All case/lambda-bound things are also mapped to
971 -- noBinderInfo, since we aren't interested in their
974 -- For ILX we track free var info for type variables too;
975 -- hence VarEnv not IdEnv
979 emptyFVInfo :: FreeVarsInfo
980 emptyFVInfo = emptyVarEnv
982 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
983 -- Don't record non-CAF imports at all, to keep free-var sets small
984 singletonFVInfo id ImportBound info
985 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
986 | otherwise = emptyVarEnv
987 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
989 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
990 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
992 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
993 -- Type variables must be lambda-bound
995 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
996 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
998 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
999 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1001 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1002 minusFVBinders vs fv = foldr minusFVBinder fv vs
1004 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1005 minusFVBinder v fv | isId v && opt_RuntimeTypes
1006 = (fv `delVarEnv` v) `unionFVInfo`
1007 tyvarFVInfo (tyVarsOfType (idType v))
1008 | otherwise = fv `delVarEnv` v
1009 -- When removing a binder, remember to add its type variables
1010 -- c.f. CoreFVs.delBinderFV
1012 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1013 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1015 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1016 -- Find how the given Id is used.
1017 -- Externally visible things may be used any old how
1019 | isExternalName (idName id) = noBinderInfo
1020 | otherwise = case lookupVarEnv fvs id of
1021 Nothing -> noBinderInfo
1022 Just (_,_,info) -> info
1024 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1025 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1027 -- Non-top-level things only, both type variables and ids
1028 -- (type variables only if opt_RuntimeTypes)
1029 getFVs :: FreeVarsInfo -> [Var]
1030 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1031 not (topLevelBound how_bound) ]
1033 getFVSet :: FreeVarsInfo -> VarSet
1034 getFVSet fvs = mkVarSet (getFVs fvs)
1036 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1037 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1038 (id1, hb1, combineStgBinderInfo info1 info2)
1041 -- The HowBound info for a variable in the FVInfo should be consistent
1042 check_eq_how_bound ImportBound ImportBound = True
1043 check_eq_how_bound LambdaBound LambdaBound = True
1044 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1045 check_eq_how_bound hb1 hb2 = False
1047 check_eq_li (NestedLet _) (NestedLet _) = True
1048 check_eq_li TopLet TopLet = True
1049 check_eq_li li1 li2 = False
1055 filterStgBinders :: [Var] -> [Var]
1056 filterStgBinders bndrs
1057 | opt_RuntimeTypes = bndrs
1058 | otherwise = filter isId bndrs
1063 -- Ignore all notes except SCC
1064 myCollectBinders expr
1067 go bs (Lam b e) = go (b:bs) e
1068 go bs e@(Note (SCC _) _) = (reverse bs, e)
1069 go bs (Note _ e) = go bs e
1070 go bs e = (reverse bs, e)
1072 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1073 -- We assume that we only have variables
1074 -- in the function position by now
1078 go (Var v) as = (v, as)
1079 go (App f a) as = go f (a:as)
1080 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1081 go (Note n e) as = go e as
1082 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1086 stgArity :: Id -> HowBound -> Arity
1087 stgArity f (LetBound _ arity) = arity
1088 stgArity f ImportBound = idArity f
1089 stgArity f LambdaBound = 0