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.
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 | isHiBootTyCon tc -> PolyAlt -- Algebraic, but no constructors visible
415 | isAlgTyCon tc -> AlgAlt tc
416 | isFunTyCon tc -> PolyAlt
417 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
422 -- ---------------------------------------------------------------------------
424 -- ---------------------------------------------------------------------------
428 :: Maybe UpdateFlag -- Just upd <=> this application is
429 -- the rhs of a thunk binding
430 -- x = [...] \upd [] -> the_app
431 -- with specified update flag
433 -> [CoreArg] -- Arguments
434 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
436 coreToStgApp maybe_thunk_body f args
437 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
438 lookupVarLne f `thenLne` \ how_bound ->
441 n_val_args = valArgCount args
442 not_letrec_bound = not (isLetBound how_bound)
444 = let fvs = singletonFVInfo f how_bound fun_occ in
445 -- e.g. (f :: a -> int) (x :: a)
446 -- Here the free variables are "f", "x" AND the type variable "a"
447 -- coreToStgArgs will deal with the arguments recursively
448 if opt_RuntimeTypes then
449 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
452 -- Mostly, the arity info of a function is in the fn's IdInfo
453 -- But new bindings introduced by CoreSat may not have no
454 -- arity info; it would do us no good anyway. For example:
455 -- let f = \ab -> e in f
456 -- No point in having correct arity info for f!
457 -- Hence the hasArity stuff below.
458 -- NB: f_arity is only consulted for LetBound things
459 f_arity = stgArity f how_bound
460 saturated = f_arity <= n_val_args
463 | not_letrec_bound = noBinderInfo -- Uninteresting variable
464 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
465 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
468 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
469 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
470 -- saturated call doesn't escape
471 -- (let-no-escape applies to 'thunks' too)
473 | otherwise = unitVarSet f -- Inexact application; it does escape
475 -- At the moment of the call:
477 -- either the function is *not* let-no-escaped, in which case
478 -- nothing is live except live_in_cont
479 -- or the function *is* let-no-escaped in which case the
480 -- variables it uses are live, but still the function
481 -- itself is not. PS. In this case, the function's
482 -- live vars should already include those of the
483 -- continuation, but it does no harm to just union the
486 res_ty = exprType (mkApps (Var f) args)
487 app = case globalIdDetails f of
488 DataConWorkId dc | saturated -> StgConApp dc args'
489 PrimOpId op -> ASSERT( saturated )
490 StgOpApp (StgPrimOp op) args' res_ty
491 FCallId call -> ASSERT( saturated )
492 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
493 _other -> StgApp f args'
498 fun_fvs `unionFVInfo` args_fvs,
499 fun_escs `unionVarSet` (getFVSet args_fvs)
500 -- All the free vars of the args are disqualified
501 -- from being let-no-escaped.
506 -- ---------------------------------------------------------------------------
508 -- This is the guy that turns applications into A-normal form
509 -- ---------------------------------------------------------------------------
511 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
513 = returnLne ([], emptyFVInfo)
515 coreToStgArgs (Type ty : args) -- Type argument
516 = coreToStgArgs args `thenLne` \ (args', fvs) ->
517 if opt_RuntimeTypes then
518 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
520 returnLne (args', fvs)
522 coreToStgArgs (arg : args) -- Non-type argument
523 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
524 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
526 fvs = args_fvs `unionFVInfo` arg_fvs
527 stg_arg = case arg' of
528 StgApp v [] -> StgVarArg v
529 StgConApp con [] -> StgVarArg (dataConWorkId con)
530 StgLit lit -> StgLitArg lit
531 _ -> pprPanic "coreToStgArgs" (ppr arg)
533 returnLne (stg_arg : stg_args, fvs)
536 -- ---------------------------------------------------------------------------
537 -- The magic for lets:
538 -- ---------------------------------------------------------------------------
541 :: Bool -- True <=> yes, we are let-no-escaping this let
542 -> CoreBind -- bindings
544 -> LneM (StgExpr, -- new let
545 FreeVarsInfo, -- variables free in the whole let
546 EscVarsSet, -- variables that escape from the whole let
547 Bool) -- True <=> none of the binders in the bindings
548 -- is among the escaping vars
550 coreToStgLet let_no_escape bind body
551 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
553 -- Do the bindings, setting live_in_cont to empty if
554 -- we ain't in a let-no-escape world
555 getVarsLiveInCont `thenLne` \ live_in_cont ->
556 setVarsLiveInCont (if let_no_escape
559 (vars_bind rec_body_fvs bind)
560 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
563 extendVarEnvLne env_ext (
564 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
565 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
567 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
568 body2, body_fvs, body_escs, getLiveVars body_lv_info)
571 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
572 body2, body_fvs, body_escs, body_lvs) ->
575 -- Compute the new let-expression
577 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
578 | otherwise = StgLet bind2 body2
581 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
584 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
586 real_bind_escs = if let_no_escape then
590 -- Everything escapes which is free in the bindings
592 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
594 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
597 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
600 -- Debugging code as requested by Andrew Kennedy
601 checked_no_binder_escapes
602 | not no_binder_escapes && any is_join_var binders
603 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
605 | otherwise = no_binder_escapes
607 checked_no_binder_escapes = no_binder_escapes
610 -- Mustn't depend on the passed-in let_no_escape flag, since
611 -- no_binder_escapes is used by the caller to derive the flag!
617 checked_no_binder_escapes
620 set_of_binders = mkVarSet binders
621 binders = bindersOf bind
623 mk_binding bind_lv_info binder rhs
624 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
626 live_vars | let_no_escape = addLiveVar bind_lv_info binder
627 | otherwise = unitLiveVar binder
628 -- c.f. the invariant on NestedLet
630 vars_bind :: FreeVarsInfo -- Free var info for body of binding
634 EscVarsSet, -- free vars; escapee vars
635 LiveInfo, -- Vars and CAFs live in binding
636 [(Id, HowBound)]) -- extension to environment
639 vars_bind body_fvs (NonRec binder rhs)
640 = coreToStgRhs body_fvs [] (binder,rhs)
641 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
643 env_ext_item = mk_binding bind_lv_info binder rhs
645 returnLne (StgNonRec binder rhs2,
646 bind_fvs, escs, bind_lv_info, [env_ext_item])
649 vars_bind body_fvs (Rec pairs)
650 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
652 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
653 binders = map fst pairs
654 env_ext = [ mk_binding bind_lv_info b rhs
657 extendVarEnvLne env_ext (
658 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
659 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
661 bind_fvs = unionFVInfos fvss
662 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
663 escs = unionVarSets escss
665 returnLne (StgRec (binders `zip` rhss2),
666 bind_fvs, escs, bind_lv_info, env_ext)
670 is_join_var :: Id -> Bool
671 -- A hack (used only for compiler debuggging) to tell if
672 -- a variable started life as a join point ($j)
673 is_join_var j = occNameUserString (getOccName j) == "$j"
677 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
680 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
682 coreToStgRhs scope_fv_info binders (bndr, rhs)
683 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
684 getEnvLne `thenLne` \ env ->
685 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
686 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
687 rhs_fvs, lv_info, rhs_escs)
689 bndr_info = lookupFVInfo scope_fv_info bndr
691 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
693 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
694 = StgRhsCon noCCS con args
696 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
697 = StgRhsClosure noCCS binder_info
702 mkStgRhs rhs_fvs srt binder_info rhs
703 = StgRhsClosure noCCS binder_info
709 SDM: disabled. Eval/Apply can't handle functions with arity zero very
710 well; and making these into simple non-updatable thunks breaks other
711 assumptions (namely that they will be entered only once).
713 upd_flag | isPAP env rhs = ReEntrant
714 | otherwise = Updatable
718 upd = if isOnceDem dem
719 then (if isNotTop toplev
720 then SingleEntry -- HA! Paydirt for "dem"
723 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
727 -- For now we forbid SingleEntry CAFs; they tickle the
728 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
729 -- and I don't understand why. There's only one SE_CAF (well,
730 -- only one that tickled a great gaping bug in an earlier attempt
731 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
732 -- specifically Main.lvl6 in spectral/cryptarithm2.
733 -- So no great loss. KSW 2000-07.
737 Detect thunks which will reduce immediately to PAPs, and make them
738 non-updatable. This has several advantages:
740 - the non-updatable thunk behaves exactly like the PAP,
742 - the thunk is more efficient to enter, because it is
743 specialised to the task.
745 - we save one update frame, one stg_update_PAP, one update
746 and lots of PAP_enters.
748 - in the case where the thunk is top-level, we save building
749 a black hole and futhermore the thunk isn't considered to
750 be a CAF any more, so it doesn't appear in any SRTs.
752 We do it here, because the arity information is accurate, and we need
753 to do it before the SRT pass to save the SRT entries associated with
756 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
758 arity = stgArity f (lookupBinding env f)
762 %************************************************************************
764 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
766 %************************************************************************
768 There's a lot of stuff to pass around, so we use this @LneM@ monad to
769 help. All the stuff here is only passed *down*.
772 type LneM a = IdEnv HowBound
773 -> LiveInfo -- Vars and CAFs live in continuation
776 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
777 -- i.e. ones with a nested (non-top-level) binding
778 CafSet) -- Static live variables;
779 -- i.e. top-level variables that are CAFs or refer to them
781 type EscVarsSet = IdSet
785 = ImportBound -- Used only as a response to lookupBinding; never
786 -- exists in the range of the (IdEnv HowBound)
788 | LetBound -- A let(rec) in this module
789 LetInfo -- Whether top level or nested
790 Arity -- Its arity (local Ids don't have arity info at this point)
792 | LambdaBound -- Used for both lambda and case
795 = TopLet -- top level things
796 | NestedLet LiveInfo -- For nested things, what is live if this
797 -- thing is live? Invariant: the binder
798 -- itself is always a member of
799 -- the dynamic set of its own LiveInfo
801 isLetBound (LetBound _ _) = True
802 isLetBound other = False
804 topLevelBound ImportBound = True
805 topLevelBound (LetBound TopLet _) = True
806 topLevelBound other = False
809 For a let(rec)-bound variable, x, we record LiveInfo, the set of
810 variables that are live if x is live. This LiveInfo comprises
811 (a) dynamic live variables (ones with a non-top-level binding)
812 (b) static live variabes (CAFs or things that refer to CAFs)
814 For "normal" variables (a) is just x alone. If x is a let-no-escaped
815 variable then x is represented by a code pointer and a stack pointer
816 (well, one for each stack). So all of the variables needed in the
817 execution of x are live if x is, and are therefore recorded in the
818 LetBound constructor; x itself *is* included.
820 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
824 emptyLiveInfo :: LiveInfo
825 emptyLiveInfo = (emptyVarSet,emptyVarSet)
827 unitLiveVar :: Id -> LiveInfo
828 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
830 unitLiveCaf :: Id -> LiveInfo
831 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
833 addLiveVar :: LiveInfo -> Id -> LiveInfo
834 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
836 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
837 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
839 mkSRT :: LiveInfo -> SRT
840 mkSRT (_, cafs) = SRTEntries cafs
842 getLiveVars :: LiveInfo -> StgLiveVars
843 getLiveVars (lvs, _) = lvs
847 The std monad functions:
849 initLne :: IdEnv HowBound -> LneM a -> a
850 initLne env m = m env emptyLiveInfo
854 {-# INLINE thenLne #-}
855 {-# INLINE returnLne #-}
857 returnLne :: a -> LneM a
858 returnLne e env lvs_cont = e
860 thenLne :: LneM a -> (a -> LneM b) -> LneM b
861 thenLne m k env lvs_cont
862 = k (m env lvs_cont) env lvs_cont
864 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
865 mapAndUnzipLne f [] = returnLne ([],[])
866 mapAndUnzipLne f (x:xs)
867 = f x `thenLne` \ (r1, r2) ->
868 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
869 returnLne (r1:rs1, r2:rs2)
871 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
872 mapAndUnzip3Lne f [] = returnLne ([],[],[])
873 mapAndUnzip3Lne f (x:xs)
874 = f x `thenLne` \ (r1, r2, r3) ->
875 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
876 returnLne (r1:rs1, r2:rs2, r3:rs3)
878 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
879 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
880 mapAndUnzip4Lne f (x:xs)
881 = f x `thenLne` \ (r1, r2, r3, r4) ->
882 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
883 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
885 fixLne :: (a -> LneM a) -> LneM a
886 fixLne expr env lvs_cont
889 result = expr result env lvs_cont
892 Functions specific to this monad:
895 getVarsLiveInCont :: LneM LiveInfo
896 getVarsLiveInCont env lvs_cont = lvs_cont
898 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
899 setVarsLiveInCont new_lvs_cont expr env lvs_cont
900 = expr env new_lvs_cont
902 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
903 extendVarEnvLne ids_w_howbound expr env lvs_cont
904 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
906 lookupVarLne :: Id -> LneM HowBound
907 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
909 getEnvLne :: LneM (IdEnv HowBound)
910 getEnvLne env lvs_cont = returnLne env env lvs_cont
912 lookupBinding :: IdEnv HowBound -> Id -> HowBound
913 lookupBinding env v = case lookupVarEnv env v of
915 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
918 -- The result of lookupLiveVarsForSet, a set of live variables, is
919 -- only ever tacked onto a decorated expression. It is never used as
920 -- the basis of a control decision, which might give a black hole.
922 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
923 freeVarsToLiveVars fvs env live_in_cont
924 = returnLne live_info env live_in_cont
926 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
927 lvs_from_fvs = map do_one (allFreeIds fvs)
929 do_one (v, how_bound)
931 ImportBound -> unitLiveCaf v -- Only CAF imports are
934 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
935 | otherwise -> emptyLiveInfo
937 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
938 -- (see the invariant on NestedLet)
940 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
943 %************************************************************************
945 \subsection[Free-var info]{Free variable information}
947 %************************************************************************
950 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
951 -- The Var is so we can gather up the free variables
954 -- The HowBound info just saves repeated lookups;
955 -- we look up just once when we encounter the occurrence.
956 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
957 -- Imported Ids without CAF refs are simply
958 -- not put in the FreeVarsInfo for an expression.
959 -- See singletonFVInfo and freeVarsToLiveVars
961 -- StgBinderInfo records how it occurs; notably, we
962 -- are interested in whether it only occurs in saturated
963 -- applications, because then we don't need to build a
965 -- If f is mapped to noBinderInfo, that means
966 -- that f *is* mentioned (else it wouldn't be in the
967 -- IdEnv at all), but perhaps in an unsaturated applications.
969 -- All case/lambda-bound things are also mapped to
970 -- noBinderInfo, since we aren't interested in their
973 -- For ILX we track free var info for type variables too;
974 -- hence VarEnv not IdEnv
978 emptyFVInfo :: FreeVarsInfo
979 emptyFVInfo = emptyVarEnv
981 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
982 -- Don't record non-CAF imports at all, to keep free-var sets small
983 singletonFVInfo id ImportBound info
984 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
985 | otherwise = emptyVarEnv
986 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
988 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
989 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
991 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
992 -- Type variables must be lambda-bound
994 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
995 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
997 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
998 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1000 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1001 minusFVBinders vs fv = foldr minusFVBinder fv vs
1003 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1004 minusFVBinder v fv | isId v && opt_RuntimeTypes
1005 = (fv `delVarEnv` v) `unionFVInfo`
1006 tyvarFVInfo (tyVarsOfType (idType v))
1007 | otherwise = fv `delVarEnv` v
1008 -- When removing a binder, remember to add its type variables
1009 -- c.f. CoreFVs.delBinderFV
1011 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1012 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1014 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1015 -- Find how the given Id is used.
1016 -- Externally visible things may be used any old how
1018 | isExternalName (idName id) = noBinderInfo
1019 | otherwise = case lookupVarEnv fvs id of
1020 Nothing -> noBinderInfo
1021 Just (_,_,info) -> info
1023 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1024 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1026 -- Non-top-level things only, both type variables and ids
1027 -- (type variables only if opt_RuntimeTypes)
1028 getFVs :: FreeVarsInfo -> [Var]
1029 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1030 not (topLevelBound how_bound) ]
1032 getFVSet :: FreeVarsInfo -> VarSet
1033 getFVSet fvs = mkVarSet (getFVs fvs)
1035 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1036 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1037 (id1, hb1, combineStgBinderInfo info1 info2)
1040 -- The HowBound info for a variable in the FVInfo should be consistent
1041 check_eq_how_bound ImportBound ImportBound = True
1042 check_eq_how_bound LambdaBound LambdaBound = True
1043 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1044 check_eq_how_bound hb1 hb2 = False
1046 check_eq_li (NestedLet _) (NestedLet _) = True
1047 check_eq_li TopLet TopLet = True
1048 check_eq_li li1 li2 = False
1054 filterStgBinders :: [Var] -> [Var]
1055 filterStgBinders bndrs
1056 | opt_RuntimeTypes = bndrs
1057 | otherwise = filter isId bndrs
1062 -- Ignore all notes except SCC
1063 myCollectBinders expr
1066 go bs (Lam b e) = go (b:bs) e
1067 go bs e@(Note (SCC _) _) = (reverse bs, e)
1068 go bs (Note _ e) = go bs e
1069 go bs e = (reverse bs, e)
1071 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1072 -- We assume that we only have variables
1073 -- in the function position by now
1077 go (Var v) as = (v, as)
1078 go (App f a) as = go f (a:as)
1079 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1080 go (Note n e) as = go e as
1081 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1085 stgArity :: Id -> HowBound -> Arity
1086 stgArity f (LetBound _ arity) = arity
1087 stgArity f ImportBound = idArity f
1088 stgArity f LambdaBound = 0