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, varType )
22 import TyCon ( isUnboxedTupleTyCon, isPrimTyCon, isFunTyCon )
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.
333 coreToStgExpr (Case scrut bndr alts)
334 = extendVarEnvLne [(bndr, LambdaBound)] (
335 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
338 unionVarSets escs_s )
339 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
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
354 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
356 -- We tell the scrutinee that everything
357 -- live in the alts is live in it, too.
358 setVarsLiveInCont alts_lv_info (
359 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
360 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
361 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
363 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
366 StgCase scrut2 (getLiveVars scrut_lv_info)
367 (getLiveVars alts_lv_info)
370 (mkStgAltType (idType bndr))
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'] $
384 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
386 -- Records whether each param is used in the RHS
387 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
389 returnLne ( (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)
402 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
403 coreToStgLet no_binder_escapes bind body
404 ) `thenLne` \ (new_let, fvs, escs, _) ->
406 returnLne (new_let, fvs, escs)
410 mkStgAltType scrut_ty
411 = case splitTyConApp_maybe (repType scrut_ty) of
412 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
413 | isPrimTyCon tc -> PrimAlt tc
414 | isAlgTyCon tc -> AlgAlt tc
415 | isFunTyCon tc -> PolyAlt
416 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
421 -- ---------------------------------------------------------------------------
423 -- ---------------------------------------------------------------------------
427 :: Maybe UpdateFlag -- Just upd <=> this application is
428 -- the rhs of a thunk binding
429 -- x = [...] \upd [] -> the_app
430 -- with specified update flag
432 -> [CoreArg] -- Arguments
433 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
435 coreToStgApp maybe_thunk_body f args
436 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
437 lookupVarLne f `thenLne` \ how_bound ->
440 n_val_args = valArgCount args
441 not_letrec_bound = not (isLetBound how_bound)
443 = let fvs = singletonFVInfo f how_bound fun_occ in
444 -- e.g. (f :: a -> int) (x :: a)
445 -- Here the free variables are "f", "x" AND the type variable "a"
446 -- coreToStgArgs will deal with the arguments recursively
447 if opt_RuntimeTypes then
448 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (varType f))
451 -- Mostly, the arity info of a function is in the fn's IdInfo
452 -- But new bindings introduced by CoreSat may not have no
453 -- arity info; it would do us no good anyway. For example:
454 -- let f = \ab -> e in f
455 -- No point in having correct arity info for f!
456 -- Hence the hasArity stuff below.
457 -- NB: f_arity is only consulted for LetBound things
458 f_arity = stgArity f how_bound
459 saturated = f_arity <= n_val_args
462 | not_letrec_bound = noBinderInfo -- Uninteresting variable
463 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
464 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
467 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
468 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
469 -- saturated call doesn't escape
470 -- (let-no-escape applies to 'thunks' too)
472 | otherwise = unitVarSet f -- Inexact application; it does escape
474 -- At the moment of the call:
476 -- either the function is *not* let-no-escaped, in which case
477 -- nothing is live except live_in_cont
478 -- or the function *is* let-no-escaped in which case the
479 -- variables it uses are live, but still the function
480 -- itself is not. PS. In this case, the function's
481 -- live vars should already include those of the
482 -- continuation, but it does no harm to just union the
485 res_ty = exprType (mkApps (Var f) args)
486 app = case globalIdDetails f of
487 DataConWorkId dc | saturated -> StgConApp dc args'
488 PrimOpId op -> ASSERT( saturated )
489 StgOpApp (StgPrimOp op) args' res_ty
490 FCallId call -> ASSERT( saturated )
491 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
492 _other -> StgApp f args'
497 fun_fvs `unionFVInfo` args_fvs,
498 fun_escs `unionVarSet` (getFVSet args_fvs)
499 -- All the free vars of the args are disqualified
500 -- from being let-no-escaped.
505 -- ---------------------------------------------------------------------------
507 -- This is the guy that turns applications into A-normal form
508 -- ---------------------------------------------------------------------------
510 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
512 = returnLne ([], emptyFVInfo)
514 coreToStgArgs (Type ty : args) -- Type argument
515 = coreToStgArgs args `thenLne` \ (args', fvs) ->
516 if opt_RuntimeTypes then
517 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
519 returnLne (args', fvs)
521 coreToStgArgs (arg : args) -- Non-type argument
522 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
523 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
525 fvs = args_fvs `unionFVInfo` arg_fvs
526 stg_arg = case arg' of
527 StgApp v [] -> StgVarArg v
528 StgConApp con [] -> StgVarArg (dataConWorkId con)
529 StgLit lit -> StgLitArg lit
530 _ -> pprPanic "coreToStgArgs" (ppr arg)
532 returnLne (stg_arg : stg_args, fvs)
535 -- ---------------------------------------------------------------------------
536 -- The magic for lets:
537 -- ---------------------------------------------------------------------------
540 :: Bool -- True <=> yes, we are let-no-escaping this let
541 -> CoreBind -- bindings
543 -> LneM (StgExpr, -- new let
544 FreeVarsInfo, -- variables free in the whole let
545 EscVarsSet, -- variables that escape from the whole let
546 Bool) -- True <=> none of the binders in the bindings
547 -- is among the escaping vars
549 coreToStgLet let_no_escape bind body
550 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
552 -- Do the bindings, setting live_in_cont to empty if
553 -- we ain't in a let-no-escape world
554 getVarsLiveInCont `thenLne` \ live_in_cont ->
555 setVarsLiveInCont (if let_no_escape
558 (vars_bind rec_body_fvs bind)
559 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
562 extendVarEnvLne env_ext (
563 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
564 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
566 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
567 body2, body_fvs, body_escs, getLiveVars body_lv_info)
570 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
571 body2, body_fvs, body_escs, body_lvs) ->
574 -- Compute the new let-expression
576 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
577 | otherwise = StgLet bind2 body2
580 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
583 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
585 real_bind_escs = if let_no_escape then
589 -- Everything escapes which is free in the bindings
591 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
593 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
596 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
599 -- Debugging code as requested by Andrew Kennedy
600 checked_no_binder_escapes
601 | not no_binder_escapes && any is_join_var binders
602 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
604 | otherwise = no_binder_escapes
606 checked_no_binder_escapes = no_binder_escapes
609 -- Mustn't depend on the passed-in let_no_escape flag, since
610 -- no_binder_escapes is used by the caller to derive the flag!
616 checked_no_binder_escapes
619 set_of_binders = mkVarSet binders
620 binders = bindersOf bind
622 mk_binding bind_lv_info binder rhs
623 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
625 live_vars | let_no_escape = addLiveVar bind_lv_info binder
626 | otherwise = unitLiveVar binder
627 -- c.f. the invariant on NestedLet
629 vars_bind :: FreeVarsInfo -- Free var info for body of binding
633 EscVarsSet, -- free vars; escapee vars
634 LiveInfo, -- Vars and CAFs live in binding
635 [(Id, HowBound)]) -- extension to environment
638 vars_bind body_fvs (NonRec binder rhs)
639 = coreToStgRhs body_fvs [] (binder,rhs)
640 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
642 env_ext_item = mk_binding bind_lv_info binder rhs
644 returnLne (StgNonRec binder rhs2,
645 bind_fvs, escs, bind_lv_info, [env_ext_item])
648 vars_bind body_fvs (Rec pairs)
649 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
651 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
652 binders = map fst pairs
653 env_ext = [ mk_binding bind_lv_info b rhs
656 extendVarEnvLne env_ext (
657 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
658 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
660 bind_fvs = unionFVInfos fvss
661 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
662 escs = unionVarSets escss
664 returnLne (StgRec (binders `zip` rhss2),
665 bind_fvs, escs, bind_lv_info, env_ext)
669 is_join_var :: Id -> Bool
670 -- A hack (used only for compiler debuggging) to tell if
671 -- a variable started life as a join point ($j)
672 is_join_var j = occNameUserString (getOccName j) == "$j"
676 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
679 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
681 coreToStgRhs scope_fv_info binders (bndr, rhs)
682 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
683 getEnvLne `thenLne` \ env ->
684 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
685 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
686 rhs_fvs, lv_info, rhs_escs)
688 bndr_info = lookupFVInfo scope_fv_info bndr
690 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
692 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
693 = StgRhsCon noCCS con args
695 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
696 = StgRhsClosure noCCS binder_info
701 mkStgRhs rhs_fvs srt binder_info rhs
702 = StgRhsClosure noCCS binder_info
708 SDM: disabled. Eval/Apply can't handle functions with arity zero very
709 well; and making these into simple non-updatable thunks breaks other
710 assumptions (namely that they will be entered only once).
712 upd_flag | isPAP env rhs = ReEntrant
713 | otherwise = Updatable
717 upd = if isOnceDem dem
718 then (if isNotTop toplev
719 then SingleEntry -- HA! Paydirt for "dem"
722 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
726 -- For now we forbid SingleEntry CAFs; they tickle the
727 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
728 -- and I don't understand why. There's only one SE_CAF (well,
729 -- only one that tickled a great gaping bug in an earlier attempt
730 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
731 -- specifically Main.lvl6 in spectral/cryptarithm2.
732 -- So no great loss. KSW 2000-07.
736 Detect thunks which will reduce immediately to PAPs, and make them
737 non-updatable. This has several advantages:
739 - the non-updatable thunk behaves exactly like the PAP,
741 - the thunk is more efficient to enter, because it is
742 specialised to the task.
744 - we save one update frame, one stg_update_PAP, one update
745 and lots of PAP_enters.
747 - in the case where the thunk is top-level, we save building
748 a black hole and futhermore the thunk isn't considered to
749 be a CAF any more, so it doesn't appear in any SRTs.
751 We do it here, because the arity information is accurate, and we need
752 to do it before the SRT pass to save the SRT entries associated with
755 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
757 arity = stgArity f (lookupBinding env f)
761 %************************************************************************
763 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
765 %************************************************************************
767 There's a lot of stuff to pass around, so we use this @LneM@ monad to
768 help. All the stuff here is only passed *down*.
771 type LneM a = IdEnv HowBound
772 -> LiveInfo -- Vars and CAFs live in continuation
775 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
776 -- i.e. ones with a nested (non-top-level) binding
777 CafSet) -- Static live variables;
778 -- i.e. top-level variables that are CAFs or refer to them
780 type EscVarsSet = IdSet
784 = ImportBound -- Used only as a response to lookupBinding; never
785 -- exists in the range of the (IdEnv HowBound)
787 | LetBound -- A let(rec) in this module
788 LetInfo -- Whether top level or nested
789 Arity -- Its arity (local Ids don't have arity info at this point)
791 | LambdaBound -- Used for both lambda and case
794 = TopLet -- top level things
795 | NestedLet LiveInfo -- For nested things, what is live if this
796 -- thing is live? Invariant: the binder
797 -- itself is always a member of
798 -- the dynamic set of its own LiveInfo
800 isLetBound (LetBound _ _) = True
801 isLetBound other = False
803 topLevelBound ImportBound = True
804 topLevelBound (LetBound TopLet _) = True
805 topLevelBound other = False
808 For a let(rec)-bound variable, x, we record LiveInfo, the set of
809 variables that are live if x is live. This LiveInfo comprises
810 (a) dynamic live variables (ones with a non-top-level binding)
811 (b) static live variabes (CAFs or things that refer to CAFs)
813 For "normal" variables (a) is just x alone. If x is a let-no-escaped
814 variable then x is represented by a code pointer and a stack pointer
815 (well, one for each stack). So all of the variables needed in the
816 execution of x are live if x is, and are therefore recorded in the
817 LetBound constructor; x itself *is* included.
819 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
823 emptyLiveInfo :: LiveInfo
824 emptyLiveInfo = (emptyVarSet,emptyVarSet)
826 unitLiveVar :: Id -> LiveInfo
827 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
829 unitLiveCaf :: Id -> LiveInfo
830 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
832 addLiveVar :: LiveInfo -> Id -> LiveInfo
833 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
835 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
836 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
838 mkSRT :: LiveInfo -> SRT
839 mkSRT (_, cafs) = SRTEntries cafs
841 getLiveVars :: LiveInfo -> StgLiveVars
842 getLiveVars (lvs, _) = lvs
846 The std monad functions:
848 initLne :: IdEnv HowBound -> LneM a -> a
849 initLne env m = m env emptyLiveInfo
853 {-# INLINE thenLne #-}
854 {-# INLINE returnLne #-}
856 returnLne :: a -> LneM a
857 returnLne e env lvs_cont = e
859 thenLne :: LneM a -> (a -> LneM b) -> LneM b
860 thenLne m k env lvs_cont
861 = k (m env lvs_cont) env lvs_cont
863 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
864 mapAndUnzipLne f [] = returnLne ([],[])
865 mapAndUnzipLne f (x:xs)
866 = f x `thenLne` \ (r1, r2) ->
867 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
868 returnLne (r1:rs1, r2:rs2)
870 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
871 mapAndUnzip3Lne f [] = returnLne ([],[],[])
872 mapAndUnzip3Lne f (x:xs)
873 = f x `thenLne` \ (r1, r2, r3) ->
874 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
875 returnLne (r1:rs1, r2:rs2, r3:rs3)
877 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
878 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
879 mapAndUnzip4Lne f (x:xs)
880 = f x `thenLne` \ (r1, r2, r3, r4) ->
881 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
882 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
884 fixLne :: (a -> LneM a) -> LneM a
885 fixLne expr env lvs_cont
888 result = expr result env lvs_cont
891 Functions specific to this monad:
894 getVarsLiveInCont :: LneM LiveInfo
895 getVarsLiveInCont env lvs_cont = lvs_cont
897 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
898 setVarsLiveInCont new_lvs_cont expr env lvs_cont
899 = expr env new_lvs_cont
901 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
902 extendVarEnvLne ids_w_howbound expr env lvs_cont
903 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
905 lookupVarLne :: Id -> LneM HowBound
906 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
908 getEnvLne :: LneM (IdEnv HowBound)
909 getEnvLne env lvs_cont = returnLne env env lvs_cont
911 lookupBinding :: IdEnv HowBound -> Id -> HowBound
912 lookupBinding env v = case lookupVarEnv env v of
914 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
917 -- The result of lookupLiveVarsForSet, a set of live variables, is
918 -- only ever tacked onto a decorated expression. It is never used as
919 -- the basis of a control decision, which might give a black hole.
921 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
922 freeVarsToLiveVars fvs env live_in_cont
923 = returnLne live_info env live_in_cont
925 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
926 lvs_from_fvs = map do_one (allFreeIds fvs)
928 do_one (v, how_bound)
930 ImportBound -> unitLiveCaf v -- Only CAF imports are
933 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
934 | otherwise -> emptyLiveInfo
936 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
937 -- (see the invariant on NestedLet)
939 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
942 %************************************************************************
944 \subsection[Free-var info]{Free variable information}
946 %************************************************************************
949 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
950 -- The Var is so we can gather up the free variables
953 -- The HowBound info just saves repeated lookups;
954 -- we look up just once when we encounter the occurrence.
955 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
956 -- Imported Ids without CAF refs are simply
957 -- not put in the FreeVarsInfo for an expression.
958 -- See singletonFVInfo and freeVarsToLiveVars
960 -- StgBinderInfo records how it occurs; notably, we
961 -- are interested in whether it only occurs in saturated
962 -- applications, because then we don't need to build a
964 -- If f is mapped to noBinderInfo, that means
965 -- that f *is* mentioned (else it wouldn't be in the
966 -- IdEnv at all), but perhaps in an unsaturated applications.
968 -- All case/lambda-bound things are also mapped to
969 -- noBinderInfo, since we aren't interested in their
972 -- For ILX we track free var info for type variables too;
973 -- hence VarEnv not IdEnv
977 emptyFVInfo :: FreeVarsInfo
978 emptyFVInfo = emptyVarEnv
980 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
981 -- Don't record non-CAF imports at all, to keep free-var sets small
982 singletonFVInfo id ImportBound info
983 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
984 | otherwise = emptyVarEnv
985 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
987 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
988 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
990 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
991 -- Type variables must be lambda-bound
993 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
994 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
996 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
997 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
999 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1000 minusFVBinders vs fv = foldr minusFVBinder fv vs
1002 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1003 minusFVBinder v fv | isId v && opt_RuntimeTypes
1004 = (fv `delVarEnv` v) `unionFVInfo`
1005 tyvarFVInfo (tyVarsOfType (idType v))
1006 | otherwise = fv `delVarEnv` v
1007 -- When removing a binder, remember to add its type variables
1008 -- c.f. CoreFVs.delBinderFV
1010 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1011 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1013 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1014 -- Find how the given Id is used.
1015 -- Externally visible things may be used any old how
1017 | isExternalName (idName id) = noBinderInfo
1018 | otherwise = case lookupVarEnv fvs id of
1019 Nothing -> noBinderInfo
1020 Just (_,_,info) -> info
1022 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1023 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1025 -- Non-top-level things only, both type variables and ids
1026 -- (type variables only if opt_RuntimeTypes)
1027 getFVs :: FreeVarsInfo -> [Var]
1028 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1029 not (topLevelBound how_bound) ]
1031 getFVSet :: FreeVarsInfo -> VarSet
1032 getFVSet fvs = mkVarSet (getFVs fvs)
1034 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1035 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1036 (id1, hb1, combineStgBinderInfo info1 info2)
1039 -- The HowBound info for a variable in the FVInfo should be consistent
1040 check_eq_how_bound ImportBound ImportBound = True
1041 check_eq_how_bound LambdaBound LambdaBound = True
1042 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1043 check_eq_how_bound hb1 hb2 = False
1045 check_eq_li (NestedLet _) (NestedLet _) = True
1046 check_eq_li TopLet TopLet = True
1047 check_eq_li li1 li2 = False
1053 filterStgBinders :: [Var] -> [Var]
1054 filterStgBinders bndrs
1055 | opt_RuntimeTypes = bndrs
1056 | otherwise = filter isId bndrs
1061 -- Ignore all notes except SCC
1062 myCollectBinders expr
1065 go bs (Lam b e) = go (b:bs) e
1066 go bs e@(Note (SCC _) _) = (reverse bs, e)
1067 go bs (Note _ e) = go bs e
1068 go bs e = (reverse bs, e)
1070 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1071 -- We assume that we only have variables
1072 -- in the function position by now
1076 go (Var v) as = (v, as)
1077 go (App f a) as = go f (a:as)
1078 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1079 go (Note n e) as = go e as
1080 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1084 stgArity :: Id -> HowBound -> Arity
1085 stgArity f (LetBound _ arity) = arity
1086 stgArity f ImportBound = idArity f
1087 stgArity f LambdaBound = 0