2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[CoreToStg]{Converts Core to STG Syntax}
6 And, as we have the info in hand, we may convert some lets to
11 -- The above warning supression flag is a temporary kludge.
12 -- While working on this module you are encouraged to remove it and fix
13 -- any warnings in the module. See
14 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
17 module CoreToStg ( coreToStg, coreExprToStg ) where
19 #include "HsVersions.h"
22 import CoreUtils ( rhsIsStatic, manifestArity, exprType, findDefault )
28 import Var ( Var, globalIdDetails, idType )
31 import CostCentre ( noCCS )
34 import Maybes ( maybeToBool )
35 import Name ( getOccName, isExternalName, nameOccName )
36 import OccName ( occNameString, occNameFS )
37 import BasicTypes ( Arity )
38 import StaticFlags ( opt_RuntimeTypes )
45 %************************************************************************
47 \subsection[live-vs-free-doc]{Documentation}
49 %************************************************************************
51 (There is other relevant documentation in codeGen/CgLetNoEscape.)
53 The actual Stg datatype is decorated with {\em live variable}
54 information, as well as {\em free variable} information. The two are
55 {\em not} the same. Liveness is an operational property rather than a
56 semantic one. A variable is live at a particular execution point if
57 it can be referred to {\em directly} again. In particular, a dead
58 variable's stack slot (if it has one):
61 should be stubbed to avoid space leaks, and
63 may be reused for something else.
66 There ought to be a better way to say this. Here are some examples:
73 Just after the `in', v is live, but q is dead. If the whole of that
74 let expression was enclosed in a case expression, thus:
76 case (let v = [q] \[x] -> e in ...v...) of
79 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
80 we'll return later to the @alts@ and need it.
82 Let-no-escapes make this a bit more interesting:
84 let-no-escape v = [q] \ [x] -> e
88 Here, @q@ is still live at the `in', because @v@ is represented not by
89 a closure but by the current stack state. In other words, if @v@ is
90 live then so is @q@. Furthermore, if @e@ mentions an enclosing
91 let-no-escaped variable, then {\em its} free variables are also live
94 %************************************************************************
96 \subsection[caf-info]{Collecting live CAF info}
98 %************************************************************************
100 In this pass we also collect information on which CAFs are live for
101 constructing SRTs (see SRT.lhs).
103 A top-level Id has CafInfo, which is
105 - MayHaveCafRefs, if it may refer indirectly to
107 - NoCafRefs if it definitely doesn't
109 The CafInfo has already been calculated during the CoreTidy pass.
111 During CoreToStg, we then pin onto each binding and case expression, a
112 list of Ids which represents the "live" CAFs at that point. The meaning
113 of "live" here is the same as for live variables, see above (which is
114 why it's convenient to collect CAF information here rather than elsewhere).
116 The later SRT pass takes these lists of Ids and uses them to construct
117 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
121 Interaction of let-no-escape with SRTs [Sept 01]
122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 let-no-escape x = ...caf1...caf2...
129 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
130 build SRTs just as if x's defn was inlined at each call site, and
131 that means that x's CAF refs get duplicated in the overall SRT.
133 This is unlike ordinary lets, in which the CAF refs are not duplicated.
135 We could fix this loss of (static) sharing by making a sort of pseudo-closure
136 for x, solely to put in the SRTs lower down.
139 %************************************************************************
141 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
143 %************************************************************************
146 coreToStg :: PackageId -> [CoreBind] -> IO [StgBinding]
147 coreToStg this_pkg pgm
149 where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm
151 coreExprToStg :: CoreExpr -> StgExpr
153 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
158 -> IdEnv HowBound -- environment for the bindings
160 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
162 coreTopBindsToStg this_pkg env [] = (env, emptyFVInfo, [])
163 coreTopBindsToStg this_pkg env (b:bs)
164 = (env2, fvs2, b':bs')
166 -- env accumulates down the list of binds, fvs accumulates upwards
167 (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
168 (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs
174 -> FreeVarsInfo -- Info about the body
176 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
178 coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
180 env' = extendVarEnv env id how_bound
181 how_bound = LetBound TopLet $! manifestArity rhs
185 (stg_rhs, fvs') <- coreToTopStgRhs this_pkg body_fvs (id,rhs)
186 return (stg_rhs, fvs')
188 bind = StgNonRec id stg_rhs
190 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id $$ (ptext SLIT("rhs:")) <+> ppr rhs $$ (ptext SLIT("stg_rhs:"))<+> ppr stg_rhs $$ (ptext SLIT("Manifest:")) <+> (ppr $ manifestArity rhs) $$ (ptext SLIT("STG:")) <+>(ppr $ stgRhsArity stg_rhs) )
191 ASSERT2(consistentCafInfo id bind, ppr id)
192 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
193 (env', fvs' `unionFVInfo` body_fvs, bind)
195 coreTopBindToStg this_pkg env body_fvs (Rec pairs)
197 (binders, rhss) = unzip pairs
199 extra_env' = [ (b, LetBound TopLet $! manifestArity rhs)
200 | (b, rhs) <- pairs ]
201 env' = extendVarEnvList env extra_env'
205 (stg_rhss, fvss') <- mapAndUnzipM (coreToTopStgRhs this_pkg body_fvs) pairs
206 let fvs' = unionFVInfos fvss'
207 return (stg_rhss, fvs')
209 bind = StgRec (zip binders stg_rhss)
211 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
212 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
213 (env', fvs' `unionFVInfo` body_fvs, bind)
215 -- Assertion helper: this checks that the CafInfo on the Id matches
216 -- what CoreToStg has figured out about the binding's SRT. The
217 -- CafInfo will be exact in all cases except when CorePrep has
218 -- floated out a binding, in which case it will be approximate.
219 consistentCafInfo id bind
220 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
223 = WARN (not exact, ppr id) safe
225 safe = id_marked_caffy || not binding_is_caffy
226 exact = id_marked_caffy == binding_is_caffy
227 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
228 binding_is_caffy = stgBindHasCafRefs bind
234 -> FreeVarsInfo -- Free var info for the scope of the binding
236 -> LneM (StgRhs, FreeVarsInfo)
238 coreToTopStgRhs this_pkg scope_fv_info (bndr, rhs) = do
239 (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs
240 lv_info <- freeVarsToLiveVars rhs_fvs
241 return (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
243 bndr_info = lookupFVInfo scope_fv_info bndr
244 is_static = rhsIsStatic this_pkg rhs
246 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
249 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
250 = ASSERT( is_static )
251 StgRhsClosure noCCS binder_info
257 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
258 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
259 = StgRhsCon noCCS con args
261 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
262 = ASSERT2( not is_static, ppr rhs )
263 StgRhsClosure noCCS binder_info
271 -- ---------------------------------------------------------------------------
273 -- ---------------------------------------------------------------------------
278 -> LneM (StgExpr, -- Decorated STG expr
279 FreeVarsInfo, -- Its free vars (NB free, not live)
280 EscVarsSet) -- Its escapees, a subset of its free vars;
281 -- also a subset of the domain of the envt
282 -- because we are only interested in the escapees
283 -- for vars which might be turned into
284 -- let-no-escaped ones.
287 The second and third components can be derived in a simple bottom up pass, not
288 dependent on any decisions about which variables will be let-no-escaped or
289 not. The first component, that is, the decorated expression, may then depend
290 on these components, but it in turn is not scrutinised as the basis for any
291 decisions. Hence no black holes.
294 coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet)
295 coreToStgExpr (Var v) = coreToStgApp Nothing v []
297 coreToStgExpr expr@(App _ _)
298 = coreToStgApp Nothing f args
300 (f, args) = myCollectArgs expr
302 coreToStgExpr expr@(Lam _ _)
304 (args, body) = myCollectBinders expr
305 args' = filterStgBinders args
307 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
308 (body, body_fvs, body_escs) <- coreToStgExpr body
310 fvs = args' `minusFVBinders` body_fvs
311 escs = body_escs `delVarSetList` args'
312 result_expr | null args' = body
313 | otherwise = StgLam (exprType expr) args' body
315 return (result_expr, fvs, escs)
317 coreToStgExpr (Note (SCC cc) expr) = do
318 (expr2, fvs, escs) <- coreToStgExpr expr
319 return (StgSCC cc expr2, fvs, escs)
321 coreToStgExpr (Case (Var id) _bndr ty [(DEFAULT,[],expr)])
322 | Just (TickBox m n) <- isTickBoxOp_maybe id = do
323 (expr2, fvs, escs) <- coreToStgExpr expr
324 return (StgTick m n expr2, fvs, escs)
326 coreToStgExpr (Note other_note expr)
329 coreToStgExpr (Cast expr co)
332 -- Cases require a little more real work.
334 coreToStgExpr (Case scrut bndr _ alts) = do
335 (alts2, alts_fvs, alts_escs)
336 <- extendVarEnvLne [(bndr, LambdaBound)] $ do
337 (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
340 unionVarSets escs_s )
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
354 alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr
356 -- We tell the scrutinee that everything
357 -- live in the alts is live in it, too.
358 (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
359 <- setVarsLiveInCont alts_lv_info $ do
360 (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
361 scrut_lv_info <- freeVarsToLiveVars scrut_fvs
362 return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
365 StgCase scrut2 (getLiveVars scrut_lv_info)
366 (getLiveVars alts_lv_info)
369 (mkStgAltType bndr alts)
371 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
372 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
373 -- You might think we should have scrut_escs, not
374 -- (getFVSet scrut_fvs), but actually we can't call, and
375 -- then return from, a let-no-escape thing.
378 vars_alt (con, binders, rhs)
379 = let -- Remove type variables
380 binders' = filterStgBinders binders
382 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
383 (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
385 -- Records whether each param is used in the RHS
386 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
388 return ( (con, binders', good_use_mask, rhs2),
389 binders' `minusFVBinders` rhs_fvs,
390 rhs_escs `delVarSetList` binders' )
391 -- ToDo: remove the delVarSet;
392 -- since escs won't include any of these binders
395 Lets not only take quite a bit of work, but this is where we convert
396 then to let-no-escapes, if we wish.
398 (Meanwhile, we don't expect to see let-no-escapes...)
400 coreToStgExpr (Let bind body) = do
401 (new_let, fvs, escs, _)
402 <- mfix (\ ~(_, _, _, no_binder_escapes) ->
403 coreToStgLet no_binder_escapes bind body
406 return (new_let, fvs, escs)
410 mkStgAltType bndr alts
411 = case splitTyConApp_maybe (repType (idType bndr)) of
412 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
413 | isUnLiftedTyCon tc -> PrimAlt tc
414 | isHiBootTyCon tc -> look_for_better_tycon
415 | isAlgTyCon tc -> AlgAlt tc
416 | otherwise -> ASSERT( _is_poly_alt_tycon tc )
421 _is_poly_alt_tycon tc
423 || isPrimTyCon tc -- "Any" is lifted but primitive
424 || isOpenTyCon tc -- Type family; e.g. arising from strict
425 -- function application where argument has a
428 -- Sometimes, the TyCon is a HiBootTyCon which may not have any
429 -- constructors inside it. Then we can get a better TyCon by
430 -- grabbing the one from a constructor alternative
432 look_for_better_tycon
433 | ((DataAlt con, _, _) : _) <- data_alts =
434 AlgAlt (dataConTyCon con)
436 ASSERT(null data_alts)
439 (data_alts, _deflt) = findDefault alts
443 -- ---------------------------------------------------------------------------
445 -- ---------------------------------------------------------------------------
449 :: Maybe UpdateFlag -- Just upd <=> this application is
450 -- the rhs of a thunk binding
451 -- x = [...] \upd [] -> the_app
452 -- with specified update flag
454 -> [CoreArg] -- Arguments
455 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
458 coreToStgApp maybe_thunk_body f args = do
459 (args', args_fvs) <- coreToStgArgs args
460 how_bound <- lookupVarLne f
463 n_val_args = valArgCount args
464 not_letrec_bound = not (isLetBound how_bound)
466 = let fvs = singletonFVInfo f how_bound fun_occ in
467 -- e.g. (f :: a -> int) (x :: a)
468 -- Here the free variables are "f", "x" AND the type variable "a"
469 -- coreToStgArgs will deal with the arguments recursively
470 if opt_RuntimeTypes then
471 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
474 -- Mostly, the arity info of a function is in the fn's IdInfo
475 -- But new bindings introduced by CoreSat may not have no
476 -- arity info; it would do us no good anyway. For example:
477 -- let f = \ab -> e in f
478 -- No point in having correct arity info for f!
479 -- Hence the hasArity stuff below.
480 -- NB: f_arity is only consulted for LetBound things
481 f_arity = stgArity f how_bound
482 saturated = f_arity <= n_val_args
485 | not_letrec_bound = noBinderInfo -- Uninteresting variable
486 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
487 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
490 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
491 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
492 -- saturated call doesn't escape
493 -- (let-no-escape applies to 'thunks' too)
495 | otherwise = unitVarSet f -- Inexact application; it does escape
497 -- At the moment of the call:
499 -- either the function is *not* let-no-escaped, in which case
500 -- nothing is live except live_in_cont
501 -- or the function *is* let-no-escaped in which case the
502 -- variables it uses are live, but still the function
503 -- itself is not. PS. In this case, the function's
504 -- live vars should already include those of the
505 -- continuation, but it does no harm to just union the
508 res_ty = exprType (mkApps (Var f) args)
509 app = case globalIdDetails f of
510 DataConWorkId dc | saturated -> StgConApp dc args'
511 PrimOpId op -> ASSERT( saturated )
512 StgOpApp (StgPrimOp op) args' res_ty
513 FCallId call -> ASSERT( saturated )
514 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
515 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
516 _other -> StgApp f args'
520 fun_fvs `unionFVInfo` args_fvs,
521 fun_escs `unionVarSet` (getFVSet args_fvs)
522 -- All the free vars of the args are disqualified
523 -- from being let-no-escaped.
528 -- ---------------------------------------------------------------------------
530 -- This is the guy that turns applications into A-normal form
531 -- ---------------------------------------------------------------------------
533 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
535 = return ([], emptyFVInfo)
537 coreToStgArgs (Type ty : args) = do -- Type argument
538 (args', fvs) <- coreToStgArgs args
539 if opt_RuntimeTypes then
540 return (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
544 coreToStgArgs (arg : args) = do -- Non-type argument
545 (stg_args, args_fvs) <- coreToStgArgs args
546 (arg', arg_fvs, escs) <- coreToStgExpr arg
548 fvs = args_fvs `unionFVInfo` arg_fvs
549 stg_arg = case arg' of
550 StgApp v [] -> StgVarArg v
551 StgConApp con [] -> StgVarArg (dataConWorkId con)
552 StgLit lit -> StgLitArg lit
553 _ -> pprPanic "coreToStgArgs" (ppr arg)
555 -- WARNING: what if we have an argument like (v `cast` co)
556 -- where 'co' changes the representation type?
557 -- (This really only happens if co is unsafe.)
558 -- Then all the getArgAmode stuff in CgBindery will set the
559 -- cg_rep of the CgIdInfo based on the type of v, rather
560 -- than the type of 'co'.
561 -- This matters particularly when the function is a primop
563 -- Wanted: a better solution than this hacky warning
565 arg_ty = exprType arg
566 stg_arg_ty = stgArgType stg_arg
567 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
568 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
569 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
570 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
571 -- we can treat an unlifted value as lifted. But the other way round
573 -- We also want to check if a pointer is cast to a non-ptr etc
575 WARN( bad_args, ptext SLIT("Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
576 return (stg_arg : stg_args, fvs)
579 -- ---------------------------------------------------------------------------
580 -- The magic for lets:
581 -- ---------------------------------------------------------------------------
584 :: Bool -- True <=> yes, we are let-no-escaping this let
585 -> CoreBind -- bindings
587 -> LneM (StgExpr, -- new let
588 FreeVarsInfo, -- variables free in the whole let
589 EscVarsSet, -- variables that escape from the whole let
590 Bool) -- True <=> none of the binders in the bindings
591 -- is among the escaping vars
593 coreToStgLet let_no_escape bind body = do
594 (bind2, bind_fvs, bind_escs, bind_lvs,
595 body2, body_fvs, body_escs, body_lvs)
596 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
598 -- Do the bindings, setting live_in_cont to empty if
599 -- we ain't in a let-no-escape world
600 live_in_cont <- getVarsLiveInCont
601 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
602 <- setVarsLiveInCont (if let_no_escape
605 (vars_bind rec_body_fvs bind)
608 extendVarEnvLne env_ext $ do
609 (body2, body_fvs, body_escs) <- coreToStgExpr body
610 body_lv_info <- freeVarsToLiveVars body_fvs
612 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
613 body2, body_fvs, body_escs, getLiveVars body_lv_info)
616 -- Compute the new let-expression
618 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
619 | otherwise = StgLet bind2 body2
622 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
625 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
627 real_bind_escs = if let_no_escape then
631 -- Everything escapes which is free in the bindings
633 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
635 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
638 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
640 -- Debugging code as requested by Andrew Kennedy
641 checked_no_binder_escapes
642 | debugIsOn && not no_binder_escapes && any is_join_var binders
643 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
645 | otherwise = no_binder_escapes
647 -- Mustn't depend on the passed-in let_no_escape flag, since
648 -- no_binder_escapes is used by the caller to derive the flag!
653 checked_no_binder_escapes
656 set_of_binders = mkVarSet binders
657 binders = bindersOf bind
659 mk_binding bind_lv_info binder rhs
660 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
662 live_vars | let_no_escape = addLiveVar bind_lv_info binder
663 | otherwise = unitLiveVar binder
664 -- c.f. the invariant on NestedLet
666 vars_bind :: FreeVarsInfo -- Free var info for body of binding
670 EscVarsSet, -- free vars; escapee vars
671 LiveInfo, -- Vars and CAFs live in binding
672 [(Id, HowBound)]) -- extension to environment
675 vars_bind body_fvs (NonRec binder rhs) = do
676 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
678 env_ext_item = mk_binding bind_lv_info binder rhs
680 return (StgNonRec binder rhs2,
681 bind_fvs, escs, bind_lv_info, [env_ext_item])
684 vars_bind body_fvs (Rec pairs)
685 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
687 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
688 binders = map fst pairs
689 env_ext = [ mk_binding bind_lv_info b rhs
692 extendVarEnvLne env_ext $ do
693 (rhss2, fvss, lv_infos, escss)
694 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
696 bind_fvs = unionFVInfos fvss
697 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
698 escs = unionVarSets escss
700 return (StgRec (binders `zip` rhss2),
701 bind_fvs, escs, bind_lv_info, env_ext)
704 is_join_var :: Id -> Bool
705 -- A hack (used only for compiler debuggging) to tell if
706 -- a variable started life as a join point ($j)
707 is_join_var j = occNameString (getOccName j) == "$j"
711 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
714 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
716 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
717 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
719 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
720 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
721 rhs_fvs, lv_info, rhs_escs)
723 bndr_info = lookupFVInfo scope_fv_info bndr
725 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
727 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
728 = StgRhsCon noCCS con args
730 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
731 = StgRhsClosure noCCS binder_info
736 mkStgRhs rhs_fvs srt binder_info rhs
737 = StgRhsClosure noCCS binder_info
743 SDM: disabled. Eval/Apply can't handle functions with arity zero very
744 well; and making these into simple non-updatable thunks breaks other
745 assumptions (namely that they will be entered only once).
747 upd_flag | isPAP env rhs = ReEntrant
748 | otherwise = Updatable
752 upd = if isOnceDem dem
753 then (if isNotTop toplev
754 then SingleEntry -- HA! Paydirt for "dem"
757 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
761 -- For now we forbid SingleEntry CAFs; they tickle the
762 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
763 -- and I don't understand why. There's only one SE_CAF (well,
764 -- only one that tickled a great gaping bug in an earlier attempt
765 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
766 -- specifically Main.lvl6 in spectral/cryptarithm2.
767 -- So no great loss. KSW 2000-07.
771 Detect thunks which will reduce immediately to PAPs, and make them
772 non-updatable. This has several advantages:
774 - the non-updatable thunk behaves exactly like the PAP,
776 - the thunk is more efficient to enter, because it is
777 specialised to the task.
779 - we save one update frame, one stg_update_PAP, one update
780 and lots of PAP_enters.
782 - in the case where the thunk is top-level, we save building
783 a black hole and futhermore the thunk isn't considered to
784 be a CAF any more, so it doesn't appear in any SRTs.
786 We do it here, because the arity information is accurate, and we need
787 to do it before the SRT pass to save the SRT entries associated with
790 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
792 arity = stgArity f (lookupBinding env f)
796 %************************************************************************
798 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
800 %************************************************************************
802 There's a lot of stuff to pass around, so we use this @LneM@ monad to
803 help. All the stuff here is only passed *down*.
806 newtype LneM a = LneM
807 { unLneM :: IdEnv HowBound
808 -> LiveInfo -- Vars and CAFs live in continuation
812 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
813 -- i.e. ones with a nested (non-top-level) binding
814 CafSet) -- Static live variables;
815 -- i.e. top-level variables that are CAFs or refer to them
817 type EscVarsSet = IdSet
821 = ImportBound -- Used only as a response to lookupBinding; never
822 -- exists in the range of the (IdEnv HowBound)
824 | LetBound -- A let(rec) in this module
825 LetInfo -- Whether top level or nested
826 Arity -- Its arity (local Ids don't have arity info at this point)
828 | LambdaBound -- Used for both lambda and case
831 = TopLet -- top level things
832 | NestedLet LiveInfo -- For nested things, what is live if this
833 -- thing is live? Invariant: the binder
834 -- itself is always a member of
835 -- the dynamic set of its own LiveInfo
837 isLetBound (LetBound _ _) = True
838 isLetBound other = False
840 topLevelBound ImportBound = True
841 topLevelBound (LetBound TopLet _) = True
842 topLevelBound other = False
845 For a let(rec)-bound variable, x, we record LiveInfo, the set of
846 variables that are live if x is live. This LiveInfo comprises
847 (a) dynamic live variables (ones with a non-top-level binding)
848 (b) static live variabes (CAFs or things that refer to CAFs)
850 For "normal" variables (a) is just x alone. If x is a let-no-escaped
851 variable then x is represented by a code pointer and a stack pointer
852 (well, one for each stack). So all of the variables needed in the
853 execution of x are live if x is, and are therefore recorded in the
854 LetBound constructor; x itself *is* included.
856 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
860 emptyLiveInfo :: LiveInfo
861 emptyLiveInfo = (emptyVarSet,emptyVarSet)
863 unitLiveVar :: Id -> LiveInfo
864 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
866 unitLiveCaf :: Id -> LiveInfo
867 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
869 addLiveVar :: LiveInfo -> Id -> LiveInfo
870 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
872 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
873 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
875 mkSRT :: LiveInfo -> SRT
876 mkSRT (_, cafs) = SRTEntries cafs
878 getLiveVars :: LiveInfo -> StgLiveVars
879 getLiveVars (lvs, _) = lvs
883 The std monad functions:
885 initLne :: IdEnv HowBound -> LneM a -> a
886 initLne env m = unLneM m env emptyLiveInfo
890 {-# INLINE thenLne #-}
891 {-# INLINE returnLne #-}
893 returnLne :: a -> LneM a
894 returnLne e = LneM $ \env lvs_cont -> e
896 thenLne :: LneM a -> (a -> LneM b) -> LneM b
897 thenLne m k = LneM $ \env lvs_cont
898 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
900 instance Monad LneM where
904 instance MonadFix LneM where
905 mfix expr = LneM $ \env lvs_cont ->
906 let result = unLneM (expr result) env lvs_cont
910 Functions specific to this monad:
913 getVarsLiveInCont :: LneM LiveInfo
914 getVarsLiveInCont = LneM $ \env lvs_cont -> lvs_cont
916 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
917 setVarsLiveInCont new_lvs_cont expr
918 = LneM $ \env lvs_cont
919 -> unLneM expr env new_lvs_cont
921 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
922 extendVarEnvLne ids_w_howbound expr
923 = LneM $ \env lvs_cont
924 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
926 lookupVarLne :: Id -> LneM HowBound
927 lookupVarLne v = LneM $ \env lvs_cont -> lookupBinding env v
929 getEnvLne :: LneM (IdEnv HowBound)
930 getEnvLne = LneM $ \env lvs_cont -> env
932 lookupBinding :: IdEnv HowBound -> Id -> HowBound
933 lookupBinding env v = case lookupVarEnv env v of
935 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
938 -- The result of lookupLiveVarsForSet, a set of live variables, is
939 -- only ever tacked onto a decorated expression. It is never used as
940 -- the basis of a control decision, which might give a black hole.
942 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
943 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
945 freeVarsToLiveVars' env live_in_cont = live_info
947 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
948 lvs_from_fvs = map do_one (allFreeIds fvs)
950 do_one (v, how_bound)
952 ImportBound -> unitLiveCaf v -- Only CAF imports are
955 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
956 | otherwise -> emptyLiveInfo
958 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
959 -- (see the invariant on NestedLet)
961 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
964 %************************************************************************
966 \subsection[Free-var info]{Free variable information}
968 %************************************************************************
971 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
972 -- The Var is so we can gather up the free variables
975 -- The HowBound info just saves repeated lookups;
976 -- we look up just once when we encounter the occurrence.
977 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
978 -- Imported Ids without CAF refs are simply
979 -- not put in the FreeVarsInfo for an expression.
980 -- See singletonFVInfo and freeVarsToLiveVars
982 -- StgBinderInfo records how it occurs; notably, we
983 -- are interested in whether it only occurs in saturated
984 -- applications, because then we don't need to build a
986 -- If f is mapped to noBinderInfo, that means
987 -- that f *is* mentioned (else it wouldn't be in the
988 -- IdEnv at all), but perhaps in an unsaturated applications.
990 -- All case/lambda-bound things are also mapped to
991 -- noBinderInfo, since we aren't interested in their
994 -- For ILX we track free var info for type variables too;
995 -- hence VarEnv not IdEnv
999 emptyFVInfo :: FreeVarsInfo
1000 emptyFVInfo = emptyVarEnv
1002 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
1003 -- Don't record non-CAF imports at all, to keep free-var sets small
1004 singletonFVInfo id ImportBound info
1005 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
1006 | otherwise = emptyVarEnv
1007 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1009 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
1010 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1012 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1013 -- Type variables must be lambda-bound
1015 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1016 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1018 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1019 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1021 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1022 minusFVBinders vs fv = foldr minusFVBinder fv vs
1024 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1025 minusFVBinder v fv | isId v && opt_RuntimeTypes
1026 = (fv `delVarEnv` v) `unionFVInfo`
1027 tyvarFVInfo (tyVarsOfType (idType v))
1028 | otherwise = fv `delVarEnv` v
1029 -- When removing a binder, remember to add its type variables
1030 -- c.f. CoreFVs.delBinderFV
1032 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1033 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1035 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1036 -- Find how the given Id is used.
1037 -- Externally visible things may be used any old how
1039 | isExternalName (idName id) = noBinderInfo
1040 | otherwise = case lookupVarEnv fvs id of
1041 Nothing -> noBinderInfo
1042 Just (_,_,info) -> info
1044 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1045 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1047 -- Non-top-level things only, both type variables and ids
1048 -- (type variables only if opt_RuntimeTypes)
1049 getFVs :: FreeVarsInfo -> [Var]
1050 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1051 not (topLevelBound how_bound) ]
1053 getFVSet :: FreeVarsInfo -> VarSet
1054 getFVSet fvs = mkVarSet (getFVs fvs)
1056 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1057 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1058 (id1, hb1, combineStgBinderInfo info1 info2)
1060 -- The HowBound info for a variable in the FVInfo should be consistent
1061 check_eq_how_bound ImportBound ImportBound = True
1062 check_eq_how_bound LambdaBound LambdaBound = True
1063 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1064 check_eq_how_bound hb1 hb2 = False
1066 check_eq_li (NestedLet _) (NestedLet _) = True
1067 check_eq_li TopLet TopLet = True
1068 check_eq_li li1 li2 = False
1073 filterStgBinders :: [Var] -> [Var]
1074 filterStgBinders bndrs
1075 | opt_RuntimeTypes = bndrs
1076 | otherwise = filter isId bndrs
1081 -- Ignore all notes except SCC
1082 myCollectBinders expr
1085 go bs (Lam b e) = go (b:bs) e
1086 go bs e@(Note (SCC _) _) = (reverse bs, e)
1087 go bs (Cast e co) = go bs e
1088 go bs (Note _ e) = go bs e
1089 go bs e = (reverse bs, e)
1091 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1092 -- We assume that we only have variables
1093 -- in the function position by now
1097 go (Var v) as = (v, as)
1098 go (App f a) as = go f (a:as)
1099 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1100 go (Cast e co) as = go e as
1101 go (Note n e) as = go e as
1102 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1106 stgArity :: Id -> HowBound -> Arity
1107 stgArity f (LetBound _ arity) = arity
1108 stgArity f ImportBound = idArity f
1109 stgArity f LambdaBound = 0