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 )
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 $$ ppr rhs $$ ppr bind)
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)
465 fun_fvs = singletonFVInfo f how_bound fun_occ
466 -- e.g. (f :: a -> int) (x :: a)
467 -- Here the free variables are "f", "x" AND the type variable "a"
468 -- coreToStgArgs will deal with the arguments recursively
470 -- Mostly, the arity info of a function is in the fn's IdInfo
471 -- But new bindings introduced by CoreSat may not have no
472 -- arity info; it would do us no good anyway. For example:
473 -- let f = \ab -> e in f
474 -- No point in having correct arity info for f!
475 -- Hence the hasArity stuff below.
476 -- NB: f_arity is only consulted for LetBound things
477 f_arity = stgArity f how_bound
478 saturated = f_arity <= n_val_args
481 | not_letrec_bound = noBinderInfo -- Uninteresting variable
482 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
483 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
486 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
487 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
488 -- saturated call doesn't escape
489 -- (let-no-escape applies to 'thunks' too)
491 | otherwise = unitVarSet f -- Inexact application; it does escape
493 -- At the moment of the call:
495 -- either the function is *not* let-no-escaped, in which case
496 -- nothing is live except live_in_cont
497 -- or the function *is* let-no-escaped in which case the
498 -- variables it uses are live, but still the function
499 -- itself is not. PS. In this case, the function's
500 -- live vars should already include those of the
501 -- continuation, but it does no harm to just union the
504 res_ty = exprType (mkApps (Var f) args)
505 app = case globalIdDetails f of
506 DataConWorkId dc | saturated -> StgConApp dc args'
507 PrimOpId op -> ASSERT( saturated )
508 StgOpApp (StgPrimOp op) args' res_ty
509 FCallId call -> ASSERT( saturated )
510 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
511 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
512 _other -> StgApp f args'
516 fun_fvs `unionFVInfo` args_fvs,
517 fun_escs `unionVarSet` (getFVSet args_fvs)
518 -- All the free vars of the args are disqualified
519 -- from being let-no-escaped.
524 -- ---------------------------------------------------------------------------
526 -- This is the guy that turns applications into A-normal form
527 -- ---------------------------------------------------------------------------
529 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
531 = return ([], emptyFVInfo)
533 coreToStgArgs (Type ty : args) = do -- Type argument
534 (args', fvs) <- coreToStgArgs args
537 coreToStgArgs (arg : args) = do -- Non-type argument
538 (stg_args, args_fvs) <- coreToStgArgs args
539 (arg', arg_fvs, escs) <- coreToStgExpr arg
541 fvs = args_fvs `unionFVInfo` arg_fvs
542 stg_arg = case arg' of
543 StgApp v [] -> StgVarArg v
544 StgConApp con [] -> StgVarArg (dataConWorkId con)
545 StgLit lit -> StgLitArg lit
546 _ -> pprPanic "coreToStgArgs" (ppr arg)
548 -- WARNING: what if we have an argument like (v `cast` co)
549 -- where 'co' changes the representation type?
550 -- (This really only happens if co is unsafe.)
551 -- Then all the getArgAmode stuff in CgBindery will set the
552 -- cg_rep of the CgIdInfo based on the type of v, rather
553 -- than the type of 'co'.
554 -- This matters particularly when the function is a primop
556 -- Wanted: a better solution than this hacky warning
558 arg_ty = exprType arg
559 stg_arg_ty = stgArgType stg_arg
560 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
561 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
562 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
563 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
564 -- we can treat an unlifted value as lifted. But the other way round
566 -- We also want to check if a pointer is cast to a non-ptr etc
568 WARN( bad_args, ptext SLIT("Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
569 return (stg_arg : stg_args, fvs)
572 -- ---------------------------------------------------------------------------
573 -- The magic for lets:
574 -- ---------------------------------------------------------------------------
577 :: Bool -- True <=> yes, we are let-no-escaping this let
578 -> CoreBind -- bindings
580 -> LneM (StgExpr, -- new let
581 FreeVarsInfo, -- variables free in the whole let
582 EscVarsSet, -- variables that escape from the whole let
583 Bool) -- True <=> none of the binders in the bindings
584 -- is among the escaping vars
586 coreToStgLet let_no_escape bind body = do
587 (bind2, bind_fvs, bind_escs, bind_lvs,
588 body2, body_fvs, body_escs, body_lvs)
589 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
591 -- Do the bindings, setting live_in_cont to empty if
592 -- we ain't in a let-no-escape world
593 live_in_cont <- getVarsLiveInCont
594 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
595 <- setVarsLiveInCont (if let_no_escape
598 (vars_bind rec_body_fvs bind)
601 extendVarEnvLne env_ext $ do
602 (body2, body_fvs, body_escs) <- coreToStgExpr body
603 body_lv_info <- freeVarsToLiveVars body_fvs
605 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
606 body2, body_fvs, body_escs, getLiveVars body_lv_info)
609 -- Compute the new let-expression
611 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
612 | otherwise = StgLet bind2 body2
615 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
618 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
620 real_bind_escs = if let_no_escape then
624 -- Everything escapes which is free in the bindings
626 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
628 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
631 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
633 -- Debugging code as requested by Andrew Kennedy
634 checked_no_binder_escapes
635 | debugIsOn && not no_binder_escapes && any is_join_var binders
636 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
638 | otherwise = no_binder_escapes
640 -- Mustn't depend on the passed-in let_no_escape flag, since
641 -- no_binder_escapes is used by the caller to derive the flag!
646 checked_no_binder_escapes
649 set_of_binders = mkVarSet binders
650 binders = bindersOf bind
652 mk_binding bind_lv_info binder rhs
653 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
655 live_vars | let_no_escape = addLiveVar bind_lv_info binder
656 | otherwise = unitLiveVar binder
657 -- c.f. the invariant on NestedLet
659 vars_bind :: FreeVarsInfo -- Free var info for body of binding
663 EscVarsSet, -- free vars; escapee vars
664 LiveInfo, -- Vars and CAFs live in binding
665 [(Id, HowBound)]) -- extension to environment
668 vars_bind body_fvs (NonRec binder rhs) = do
669 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
671 env_ext_item = mk_binding bind_lv_info binder rhs
673 return (StgNonRec binder rhs2,
674 bind_fvs, escs, bind_lv_info, [env_ext_item])
677 vars_bind body_fvs (Rec pairs)
678 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
680 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
681 binders = map fst pairs
682 env_ext = [ mk_binding bind_lv_info b rhs
685 extendVarEnvLne env_ext $ do
686 (rhss2, fvss, lv_infos, escss)
687 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
689 bind_fvs = unionFVInfos fvss
690 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
691 escs = unionVarSets escss
693 return (StgRec (binders `zip` rhss2),
694 bind_fvs, escs, bind_lv_info, env_ext)
697 is_join_var :: Id -> Bool
698 -- A hack (used only for compiler debuggging) to tell if
699 -- a variable started life as a join point ($j)
700 is_join_var j = occNameString (getOccName j) == "$j"
704 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
707 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
709 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
710 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
712 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
713 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
714 rhs_fvs, lv_info, rhs_escs)
716 bndr_info = lookupFVInfo scope_fv_info bndr
718 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
720 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
721 = StgRhsCon noCCS con args
723 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
724 = StgRhsClosure noCCS binder_info
729 mkStgRhs rhs_fvs srt binder_info rhs
730 = StgRhsClosure noCCS binder_info
736 SDM: disabled. Eval/Apply can't handle functions with arity zero very
737 well; and making these into simple non-updatable thunks breaks other
738 assumptions (namely that they will be entered only once).
740 upd_flag | isPAP env rhs = ReEntrant
741 | otherwise = Updatable
745 upd = if isOnceDem dem
746 then (if isNotTop toplev
747 then SingleEntry -- HA! Paydirt for "dem"
750 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
754 -- For now we forbid SingleEntry CAFs; they tickle the
755 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
756 -- and I don't understand why. There's only one SE_CAF (well,
757 -- only one that tickled a great gaping bug in an earlier attempt
758 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
759 -- specifically Main.lvl6 in spectral/cryptarithm2.
760 -- So no great loss. KSW 2000-07.
764 Detect thunks which will reduce immediately to PAPs, and make them
765 non-updatable. This has several advantages:
767 - the non-updatable thunk behaves exactly like the PAP,
769 - the thunk is more efficient to enter, because it is
770 specialised to the task.
772 - we save one update frame, one stg_update_PAP, one update
773 and lots of PAP_enters.
775 - in the case where the thunk is top-level, we save building
776 a black hole and futhermore the thunk isn't considered to
777 be a CAF any more, so it doesn't appear in any SRTs.
779 We do it here, because the arity information is accurate, and we need
780 to do it before the SRT pass to save the SRT entries associated with
783 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
785 arity = stgArity f (lookupBinding env f)
789 %************************************************************************
791 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
793 %************************************************************************
795 There's a lot of stuff to pass around, so we use this @LneM@ monad to
796 help. All the stuff here is only passed *down*.
799 newtype LneM a = LneM
800 { unLneM :: IdEnv HowBound
801 -> LiveInfo -- Vars and CAFs live in continuation
805 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
806 -- i.e. ones with a nested (non-top-level) binding
807 CafSet) -- Static live variables;
808 -- i.e. top-level variables that are CAFs or refer to them
810 type EscVarsSet = IdSet
814 = ImportBound -- Used only as a response to lookupBinding; never
815 -- exists in the range of the (IdEnv HowBound)
817 | LetBound -- A let(rec) in this module
818 LetInfo -- Whether top level or nested
819 Arity -- Its arity (local Ids don't have arity info at this point)
821 | LambdaBound -- Used for both lambda and case
824 = TopLet -- top level things
825 | NestedLet LiveInfo -- For nested things, what is live if this
826 -- thing is live? Invariant: the binder
827 -- itself is always a member of
828 -- the dynamic set of its own LiveInfo
830 isLetBound (LetBound _ _) = True
831 isLetBound other = False
833 topLevelBound ImportBound = True
834 topLevelBound (LetBound TopLet _) = True
835 topLevelBound other = False
838 For a let(rec)-bound variable, x, we record LiveInfo, the set of
839 variables that are live if x is live. This LiveInfo comprises
840 (a) dynamic live variables (ones with a non-top-level binding)
841 (b) static live variabes (CAFs or things that refer to CAFs)
843 For "normal" variables (a) is just x alone. If x is a let-no-escaped
844 variable then x is represented by a code pointer and a stack pointer
845 (well, one for each stack). So all of the variables needed in the
846 execution of x are live if x is, and are therefore recorded in the
847 LetBound constructor; x itself *is* included.
849 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
853 emptyLiveInfo :: LiveInfo
854 emptyLiveInfo = (emptyVarSet,emptyVarSet)
856 unitLiveVar :: Id -> LiveInfo
857 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
859 unitLiveCaf :: Id -> LiveInfo
860 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
862 addLiveVar :: LiveInfo -> Id -> LiveInfo
863 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
865 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
866 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
868 mkSRT :: LiveInfo -> SRT
869 mkSRT (_, cafs) = SRTEntries cafs
871 getLiveVars :: LiveInfo -> StgLiveVars
872 getLiveVars (lvs, _) = lvs
876 The std monad functions:
878 initLne :: IdEnv HowBound -> LneM a -> a
879 initLne env m = unLneM m env emptyLiveInfo
883 {-# INLINE thenLne #-}
884 {-# INLINE returnLne #-}
886 returnLne :: a -> LneM a
887 returnLne e = LneM $ \env lvs_cont -> e
889 thenLne :: LneM a -> (a -> LneM b) -> LneM b
890 thenLne m k = LneM $ \env lvs_cont
891 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
893 instance Monad LneM where
897 instance MonadFix LneM where
898 mfix expr = LneM $ \env lvs_cont ->
899 let result = unLneM (expr result) env lvs_cont
903 Functions specific to this monad:
906 getVarsLiveInCont :: LneM LiveInfo
907 getVarsLiveInCont = LneM $ \env lvs_cont -> lvs_cont
909 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
910 setVarsLiveInCont new_lvs_cont expr
911 = LneM $ \env lvs_cont
912 -> unLneM expr env new_lvs_cont
914 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
915 extendVarEnvLne ids_w_howbound expr
916 = LneM $ \env lvs_cont
917 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
919 lookupVarLne :: Id -> LneM HowBound
920 lookupVarLne v = LneM $ \env lvs_cont -> lookupBinding env v
922 getEnvLne :: LneM (IdEnv HowBound)
923 getEnvLne = LneM $ \env lvs_cont -> env
925 lookupBinding :: IdEnv HowBound -> Id -> HowBound
926 lookupBinding env v = case lookupVarEnv env v of
928 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
931 -- The result of lookupLiveVarsForSet, a set of live variables, is
932 -- only ever tacked onto a decorated expression. It is never used as
933 -- the basis of a control decision, which might give a black hole.
935 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
936 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
938 freeVarsToLiveVars' env live_in_cont = live_info
940 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
941 lvs_from_fvs = map do_one (allFreeIds fvs)
943 do_one (v, how_bound)
945 ImportBound -> unitLiveCaf v -- Only CAF imports are
948 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
949 | otherwise -> emptyLiveInfo
951 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
952 -- (see the invariant on NestedLet)
954 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
957 %************************************************************************
959 \subsection[Free-var info]{Free variable information}
961 %************************************************************************
964 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
965 -- The Var is so we can gather up the free variables
968 -- The HowBound info just saves repeated lookups;
969 -- we look up just once when we encounter the occurrence.
970 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
971 -- Imported Ids without CAF refs are simply
972 -- not put in the FreeVarsInfo for an expression.
973 -- See singletonFVInfo and freeVarsToLiveVars
975 -- StgBinderInfo records how it occurs; notably, we
976 -- are interested in whether it only occurs in saturated
977 -- applications, because then we don't need to build a
979 -- If f is mapped to noBinderInfo, that means
980 -- that f *is* mentioned (else it wouldn't be in the
981 -- IdEnv at all), but perhaps in an unsaturated applications.
983 -- All case/lambda-bound things are also mapped to
984 -- noBinderInfo, since we aren't interested in their
987 -- For ILX we track free var info for type variables too;
988 -- hence VarEnv not IdEnv
992 emptyFVInfo :: FreeVarsInfo
993 emptyFVInfo = emptyVarEnv
995 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
996 -- Don't record non-CAF imports at all, to keep free-var sets small
997 singletonFVInfo id ImportBound info
998 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
999 | otherwise = emptyVarEnv
1000 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1002 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
1003 tyvarFVInfo tvs = emptyFVInfo -- Type variables are not recorded
1004 -- Old code recorded free tyvars for when we supported runtime types:
1005 -- foldVarSet add emptyFVInfo tvs
1007 -- add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1008 -- -- Type variables must be lambda-bound
1010 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1011 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1013 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1014 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1016 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1017 minusFVBinders vs fv = foldr minusFVBinder fv vs
1019 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1020 minusFVBinder v fv = fv `delVarEnv` v
1021 -- When removing a binder, remember to add its type variables
1022 -- c.f. CoreFVs.delBinderFV
1024 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1025 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1027 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1028 -- Find how the given Id is used.
1029 -- Externally visible things may be used any old how
1031 | isExternalName (idName id) = noBinderInfo
1032 | otherwise = case lookupVarEnv fvs id of
1033 Nothing -> noBinderInfo
1034 Just (_,_,info) -> info
1036 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1037 allFreeIds fvs = ASSERT( all (isId . fst) ids ) ids
1039 ids = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs]
1041 -- Non-top-level things only, both type variables and ids
1042 getFVs :: FreeVarsInfo -> [Var]
1043 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1044 not (topLevelBound how_bound) ]
1046 getFVSet :: FreeVarsInfo -> VarSet
1047 getFVSet fvs = mkVarSet (getFVs fvs)
1049 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1050 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1051 (id1, hb1, combineStgBinderInfo info1 info2)
1053 -- The HowBound info for a variable in the FVInfo should be consistent
1054 check_eq_how_bound ImportBound ImportBound = True
1055 check_eq_how_bound LambdaBound LambdaBound = True
1056 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1057 check_eq_how_bound hb1 hb2 = False
1059 check_eq_li (NestedLet _) (NestedLet _) = True
1060 check_eq_li TopLet TopLet = True
1061 check_eq_li li1 li2 = False
1066 filterStgBinders :: [Var] -> [Var]
1067 filterStgBinders bndrs = filter isId bndrs
1072 -- Ignore all notes except SCC
1073 myCollectBinders expr
1076 go bs (Lam b e) = go (b:bs) e
1077 go bs e@(Note (SCC _) _) = (reverse bs, e)
1078 go bs (Cast e co) = go bs e
1079 go bs (Note _ e) = go bs e
1080 go bs e = (reverse bs, e)
1082 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1083 -- We assume that we only have variables
1084 -- in the function position by now
1088 go (Var v) as = (v, as)
1089 go (App f a) as = go f (a:as)
1090 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1091 go (Cast e co) as = go e as
1092 go (Note n e) as = go e as
1093 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1097 stgArity :: Id -> HowBound -> Arity
1098 stgArity f (LetBound _ arity) = arity
1099 stgArity f ImportBound = idArity f
1100 stgArity f LambdaBound = 0