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 ( exprType, findDefault )
16 import CoreArity ( manifestArity )
25 import CostCentre ( noCCS )
28 import Maybes ( maybeToBool )
29 import Name ( getOccName, isExternalName, nameOccName )
30 import OccName ( occNameString, occNameFS )
31 import BasicTypes ( Arity )
38 import PrimOp ( PrimCall(..) )
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 :: PackageId -> [CoreBind] -> IO [StgBinding]
143 coreToStg this_pkg pgm
145 where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm
147 coreExprToStg :: CoreExpr -> StgExpr
149 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
154 -> IdEnv HowBound -- environment for the bindings
156 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
158 coreTopBindsToStg _ env [] = (env, emptyFVInfo, [])
159 coreTopBindsToStg this_pkg env (b:bs)
160 = (env2, fvs2, b':bs')
162 -- Notice the mutually-recursive "knot" here:
163 -- env accumulates down the list of binds,
164 -- fvs accumulates upwards
165 (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
166 (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs
171 -> FreeVarsInfo -- Info about the body
173 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
175 coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
177 env' = extendVarEnv env id how_bound
178 how_bound = LetBound TopLet $! manifestArity rhs
182 (stg_rhs, fvs') <- coreToTopStgRhs this_pkg body_fvs (id,rhs)
183 return (stg_rhs, fvs')
185 bind = StgNonRec id stg_rhs
187 ASSERT2(consistentCafInfo id bind, ppr id )
188 -- NB: previously the assertion printed 'rhs' and 'bind'
189 -- as well as 'id', but that led to a black hole
190 -- where printing the assertion error tripped the
192 (env', fvs' `unionFVInfo` body_fvs, bind)
194 coreTopBindToStg this_pkg env body_fvs (Rec pairs)
195 = ASSERT( not (null pairs) )
197 binders = map fst 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(consistentCafInfo (head binders) bind, ppr binders)
212 (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 -> GenStgBinding Var Id -> Bool
220 consistentCafInfo id bind
221 = WARN( not (exact || is_sat_thing) , ppr id )
224 safe = id_marked_caffy || not binding_is_caffy
225 exact = id_marked_caffy == binding_is_caffy
226 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
227 binding_is_caffy = stgBindHasCafRefs bind
228 is_sat_thing = occNameFS (nameOccName (idName id)) == fsLit "sat"
234 -> FreeVarsInfo -- Free var info for the scope of the binding
236 -> LneM (StgRhs, FreeVarsInfo)
238 coreToTopStgRhs this_pkg scope_fv_info (bndr, rhs)
239 = do { (new_rhs, rhs_fvs, _) <- coreToStgExpr rhs
240 ; lv_info <- freeVarsToLiveVars rhs_fvs
242 ; let stg_rhs = mkTopStgRhs this_pkg rhs_fvs (mkSRT lv_info) bndr_info new_rhs
243 stg_arity = stgRhsArity stg_rhs
244 ; return (ASSERT2( arity_ok stg_arity, mk_arity_msg stg_arity) stg_rhs,
247 bndr_info = lookupFVInfo scope_fv_info bndr
249 -- It's vital that the arity on a top-level Id matches
250 -- the arity of the generated STG binding, else an importing
251 -- module will use the wrong calling convention
252 -- (Trac #2844 was an example where this happened)
253 -- NB1: we can't move the assertion further out without
254 -- blocking the "knot" tied in coreTopBindsToStg
255 -- NB2: the arity check is only needed for Ids with External
256 -- Names, because they are externally visible. The CorePrep
257 -- pass introduces "sat" things with Local Names and does
258 -- not bother to set their Arity info, so don't fail for those
260 | isExternalName (idName bndr) = id_arity == stg_arity
262 id_arity = idArity bndr
263 mk_arity_msg stg_arity
265 ptext (sLit "Id arity:") <+> ppr id_arity,
266 ptext (sLit "STG arity:") <+> ppr stg_arity]
268 mkTopStgRhs :: PackageId -> FreeVarsInfo
269 -> SRT -> StgBinderInfo -> StgExpr
272 mkTopStgRhs _ rhs_fvs srt binder_info (StgLam _ bndrs body)
273 = StgRhsClosure noCCS binder_info
279 mkTopStgRhs this_pkg _ _ _ (StgConApp con args)
280 | not (isDllConApp this_pkg con args) -- Dynamic StgConApps are updatable
281 = StgRhsCon noCCS con args
283 mkTopStgRhs _ rhs_fvs srt binder_info rhs
284 = StgRhsClosure noCCS binder_info
292 -- ---------------------------------------------------------------------------
294 -- ---------------------------------------------------------------------------
299 -> LneM (StgExpr, -- Decorated STG expr
300 FreeVarsInfo, -- Its free vars (NB free, not live)
301 EscVarsSet) -- Its escapees, a subset of its free vars;
302 -- also a subset of the domain of the envt
303 -- because we are only interested in the escapees
304 -- for vars which might be turned into
305 -- let-no-escaped ones.
308 The second and third components can be derived in a simple bottom up pass, not
309 dependent on any decisions about which variables will be let-no-escaped or
310 not. The first component, that is, the decorated expression, may then depend
311 on these components, but it in turn is not scrutinised as the basis for any
312 decisions. Hence no black holes.
315 coreToStgExpr (Lit l) = return (StgLit l, emptyFVInfo, emptyVarSet)
316 coreToStgExpr (Var v) = coreToStgApp Nothing v []
318 coreToStgExpr expr@(App _ _)
319 = coreToStgApp Nothing f args
321 (f, args) = myCollectArgs expr
323 coreToStgExpr expr@(Lam _ _)
325 (args, body) = myCollectBinders expr
326 args' = filterStgBinders args
328 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
329 (body, body_fvs, body_escs) <- coreToStgExpr body
331 fvs = args' `minusFVBinders` body_fvs
332 escs = body_escs `delVarSetList` args'
333 result_expr | null args' = body
334 | otherwise = StgLam (exprType expr) args' body
336 return (result_expr, fvs, escs)
338 coreToStgExpr (Note (SCC cc) expr) = do
339 (expr2, fvs, escs) <- coreToStgExpr expr
340 return (StgSCC cc expr2, fvs, escs)
342 coreToStgExpr (Case (Var id) _bndr _ty [(DEFAULT,[],expr)])
343 | Just (TickBox m n) <- isTickBoxOp_maybe id = do
344 (expr2, fvs, escs) <- coreToStgExpr expr
345 return (StgTick m n expr2, fvs, escs)
347 coreToStgExpr (Note _ expr)
350 coreToStgExpr (Cast expr _)
353 -- Cases require a little more real work.
355 coreToStgExpr (Case scrut bndr _ alts) = do
356 (alts2, alts_fvs, alts_escs)
357 <- extendVarEnvLne [(bndr, LambdaBound)] $ do
358 (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
361 unionVarSets escs_s )
363 -- Determine whether the default binder is dead or not
364 -- This helps the code generator to avoid generating an assignment
365 -- for the case binder (is extremely rare cases) ToDo: remove.
366 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
367 | otherwise = bndr `setIdOccInfo` IAmDead
369 -- Don't consider the default binder as being 'live in alts',
370 -- since this is from the point of view of the case expr, where
371 -- the default binder is not free.
372 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
373 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
375 alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr
377 -- We tell the scrutinee that everything
378 -- live in the alts is live in it, too.
379 (scrut2, scrut_fvs, _scrut_escs, scrut_lv_info)
380 <- setVarsLiveInCont alts_lv_info $ do
381 (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
382 scrut_lv_info <- freeVarsToLiveVars scrut_fvs
383 return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
386 StgCase scrut2 (getLiveVars scrut_lv_info)
387 (getLiveVars alts_lv_info)
390 (mkStgAltType bndr alts)
392 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
393 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
394 -- You might think we should have scrut_escs, not
395 -- (getFVSet scrut_fvs), but actually we can't call, and
396 -- then return from, a let-no-escape thing.
399 vars_alt (con, binders, rhs)
400 = let -- Remove type variables
401 binders' = filterStgBinders binders
403 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
404 (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
406 -- Records whether each param is used in the RHS
407 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
409 return ( (con, binders', good_use_mask, rhs2),
410 binders' `minusFVBinders` rhs_fvs,
411 rhs_escs `delVarSetList` binders' )
412 -- ToDo: remove the delVarSet;
413 -- since escs won't include any of these binders
416 Lets not only take quite a bit of work, but this is where we convert
417 then to let-no-escapes, if we wish.
419 (Meanwhile, we don't expect to see let-no-escapes...)
421 coreToStgExpr (Let bind body) = do
422 (new_let, fvs, escs, _)
423 <- mfix (\ ~(_, _, _, no_binder_escapes) ->
424 coreToStgLet no_binder_escapes bind body
427 return (new_let, fvs, escs)
429 coreToStgExpr e = pprPanic "coreToStgExpr" (ppr e)
433 mkStgAltType :: Id -> [CoreAlt] -> AltType
434 mkStgAltType bndr alts
435 = case splitTyConApp_maybe (repType (idType bndr)) of
436 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
437 | isUnLiftedTyCon tc -> PrimAlt tc
438 | isHiBootTyCon tc -> look_for_better_tycon
439 | isAlgTyCon tc -> AlgAlt tc
440 | otherwise -> ASSERT2( _is_poly_alt_tycon tc, ppr tc )
445 _is_poly_alt_tycon tc
447 || isPrimTyCon tc -- "Any" is lifted but primitive
448 || isFamilyTyCon tc -- Type family; e.g. arising from strict
449 -- function application where argument has a
452 -- Sometimes, the TyCon is a HiBootTyCon which may not have any
453 -- constructors inside it. Then we can get a better TyCon by
454 -- grabbing the one from a constructor alternative
456 look_for_better_tycon
457 | ((DataAlt con, _, _) : _) <- data_alts =
458 AlgAlt (dataConTyCon con)
460 ASSERT(null data_alts)
463 (data_alts, _deflt) = findDefault alts
467 -- ---------------------------------------------------------------------------
469 -- ---------------------------------------------------------------------------
473 :: Maybe UpdateFlag -- Just upd <=> this application is
474 -- the rhs of a thunk binding
475 -- x = [...] \upd [] -> the_app
476 -- with specified update flag
478 -> [CoreArg] -- Arguments
479 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
482 coreToStgApp _ f args = do
483 (args', args_fvs) <- coreToStgArgs args
484 how_bound <- lookupVarLne f
487 n_val_args = valArgCount args
488 not_letrec_bound = not (isLetBound how_bound)
489 fun_fvs = singletonFVInfo f how_bound fun_occ
490 -- e.g. (f :: a -> int) (x :: a)
491 -- Here the free variables are "f", "x" AND the type variable "a"
492 -- coreToStgArgs will deal with the arguments recursively
494 -- Mostly, the arity info of a function is in the fn's IdInfo
495 -- But new bindings introduced by CoreSat may not have no
496 -- arity info; it would do us no good anyway. For example:
497 -- let f = \ab -> e in f
498 -- No point in having correct arity info for f!
499 -- Hence the hasArity stuff below.
500 -- NB: f_arity is only consulted for LetBound things
501 f_arity = stgArity f how_bound
502 saturated = f_arity <= n_val_args
505 | not_letrec_bound = noBinderInfo -- Uninteresting variable
506 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
507 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
510 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
511 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
512 -- saturated call doesn't escape
513 -- (let-no-escape applies to 'thunks' too)
515 | otherwise = unitVarSet f -- Inexact application; it does escape
517 -- At the moment of the call:
519 -- either the function is *not* let-no-escaped, in which case
520 -- nothing is live except live_in_cont
521 -- or the function *is* let-no-escaped in which case the
522 -- variables it uses are live, but still the function
523 -- itself is not. PS. In this case, the function's
524 -- live vars should already include those of the
525 -- continuation, but it does no harm to just union the
528 res_ty = exprType (mkApps (Var f) args)
529 app = case idDetails f of
530 DataConWorkId dc | saturated -> StgConApp dc args'
532 -- Some primitive operator that might be implemented as a library call.
533 PrimOpId op -> ASSERT( saturated )
534 StgOpApp (StgPrimOp op) args' res_ty
536 -- A call to some primitive Cmm function.
537 FCallId (CCall (CCallSpec (StaticTarget lbl (Just pkgId)) PrimCallConv _))
538 -> ASSERT( saturated )
539 StgOpApp (StgPrimCallOp (PrimCall lbl pkgId)) args' res_ty
541 -- A regular foreign call.
542 FCallId call -> ASSERT( saturated )
543 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
545 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
546 _other -> StgApp f args'
547 fvs = fun_fvs `unionFVInfo` args_fvs
548 vars = fun_escs `unionVarSet` (getFVSet args_fvs)
549 -- All the free vars of the args are disqualified
550 -- from being let-no-escaped.
552 -- Forcing these fixes a leak in the code generator, noticed while
553 -- profiling for trac #4367
554 app `seq` fvs `seq` seqVarSet vars `seq` return (
562 -- ---------------------------------------------------------------------------
564 -- This is the guy that turns applications into A-normal form
565 -- ---------------------------------------------------------------------------
567 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
569 = return ([], emptyFVInfo)
571 coreToStgArgs (Type _ : args) = do -- Type argument
572 (args', fvs) <- coreToStgArgs args
575 coreToStgArgs (arg : args) = do -- Non-type argument
576 (stg_args, args_fvs) <- coreToStgArgs args
577 (arg', arg_fvs, _escs) <- coreToStgExpr arg
579 fvs = args_fvs `unionFVInfo` arg_fvs
580 stg_arg = case arg' of
581 StgApp v [] -> StgVarArg v
582 StgConApp con [] -> StgVarArg (dataConWorkId con)
583 StgLit lit -> StgLitArg lit
584 _ -> pprPanic "coreToStgArgs" (ppr arg)
586 -- WARNING: what if we have an argument like (v `cast` co)
587 -- where 'co' changes the representation type?
588 -- (This really only happens if co is unsafe.)
589 -- Then all the getArgAmode stuff in CgBindery will set the
590 -- cg_rep of the CgIdInfo based on the type of v, rather
591 -- than the type of 'co'.
592 -- This matters particularly when the function is a primop
594 -- Wanted: a better solution than this hacky warning
596 arg_ty = exprType arg
597 stg_arg_ty = stgArgType stg_arg
598 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
599 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
600 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
601 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
602 -- we can treat an unlifted value as lifted. But the other way round
604 -- We also want to check if a pointer is cast to a non-ptr etc
606 WARN( bad_args, ptext (sLit "Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
607 return (stg_arg : stg_args, fvs)
610 -- ---------------------------------------------------------------------------
611 -- The magic for lets:
612 -- ---------------------------------------------------------------------------
615 :: Bool -- True <=> yes, we are let-no-escaping this let
616 -> CoreBind -- bindings
618 -> LneM (StgExpr, -- new let
619 FreeVarsInfo, -- variables free in the whole let
620 EscVarsSet, -- variables that escape from the whole let
621 Bool) -- True <=> none of the binders in the bindings
622 -- is among the escaping vars
624 coreToStgLet let_no_escape bind body = do
625 (bind2, bind_fvs, bind_escs, bind_lvs,
626 body2, body_fvs, body_escs, body_lvs)
627 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
629 -- Do the bindings, setting live_in_cont to empty if
630 -- we ain't in a let-no-escape world
631 live_in_cont <- getVarsLiveInCont
632 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
633 <- setVarsLiveInCont (if let_no_escape
636 (vars_bind rec_body_fvs bind)
639 extendVarEnvLne env_ext $ do
640 (body2, body_fvs, body_escs) <- coreToStgExpr body
641 body_lv_info <- freeVarsToLiveVars body_fvs
643 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
644 body2, body_fvs, body_escs, getLiveVars body_lv_info)
647 -- Compute the new let-expression
649 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
650 | otherwise = StgLet bind2 body2
653 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
656 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
658 real_bind_escs = if let_no_escape then
662 -- Everything escapes which is free in the bindings
664 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
666 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
669 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
671 -- Debugging code as requested by Andrew Kennedy
672 checked_no_binder_escapes
673 | debugIsOn && not no_binder_escapes && any is_join_var binders
674 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
676 | otherwise = no_binder_escapes
678 -- Mustn't depend on the passed-in let_no_escape flag, since
679 -- no_binder_escapes is used by the caller to derive the flag!
684 checked_no_binder_escapes
687 set_of_binders = mkVarSet binders
688 binders = bindersOf bind
690 mk_binding bind_lv_info binder rhs
691 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
693 live_vars | let_no_escape = addLiveVar bind_lv_info binder
694 | otherwise = unitLiveVar binder
695 -- c.f. the invariant on NestedLet
697 vars_bind :: FreeVarsInfo -- Free var info for body of binding
701 EscVarsSet, -- free vars; escapee vars
702 LiveInfo, -- Vars and CAFs live in binding
703 [(Id, HowBound)]) -- extension to environment
706 vars_bind body_fvs (NonRec binder rhs) = do
707 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
709 env_ext_item = mk_binding bind_lv_info binder rhs
711 return (StgNonRec binder rhs2,
712 bind_fvs, escs, bind_lv_info, [env_ext_item])
715 vars_bind body_fvs (Rec pairs)
716 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
718 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
719 binders = map fst pairs
720 env_ext = [ mk_binding bind_lv_info b rhs
723 extendVarEnvLne env_ext $ do
724 (rhss2, fvss, lv_infos, escss)
725 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
727 bind_fvs = unionFVInfos fvss
728 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
729 escs = unionVarSets escss
731 return (StgRec (binders `zip` rhss2),
732 bind_fvs, escs, bind_lv_info, env_ext)
735 is_join_var :: Id -> Bool
736 -- A hack (used only for compiler debuggging) to tell if
737 -- a variable started life as a join point ($j)
738 is_join_var j = occNameString (getOccName j) == "$j"
742 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
745 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
747 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
748 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
749 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
750 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
751 rhs_fvs, lv_info, rhs_escs)
753 bndr_info = lookupFVInfo scope_fv_info bndr
755 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
757 mkStgRhs _ _ _ (StgConApp con args) = StgRhsCon noCCS con args
759 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
760 = StgRhsClosure noCCS binder_info
765 mkStgRhs rhs_fvs srt binder_info rhs
766 = StgRhsClosure noCCS binder_info
772 SDM: disabled. Eval/Apply can't handle functions with arity zero very
773 well; and making these into simple non-updatable thunks breaks other
774 assumptions (namely that they will be entered only once).
776 upd_flag | isPAP env rhs = ReEntrant
777 | otherwise = Updatable
781 upd = if isOnceDem dem
782 then (if isNotTop toplev
783 then SingleEntry -- HA! Paydirt for "dem"
786 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
790 -- For now we forbid SingleEntry CAFs; they tickle the
791 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
792 -- and I don't understand why. There's only one SE_CAF (well,
793 -- only one that tickled a great gaping bug in an earlier attempt
794 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
795 -- specifically Main.lvl6 in spectral/cryptarithm2.
796 -- So no great loss. KSW 2000-07.
800 Detect thunks which will reduce immediately to PAPs, and make them
801 non-updatable. This has several advantages:
803 - the non-updatable thunk behaves exactly like the PAP,
805 - the thunk is more efficient to enter, because it is
806 specialised to the task.
808 - we save one update frame, one stg_update_PAP, one update
809 and lots of PAP_enters.
811 - in the case where the thunk is top-level, we save building
812 a black hole and futhermore the thunk isn't considered to
813 be a CAF any more, so it doesn't appear in any SRTs.
815 We do it here, because the arity information is accurate, and we need
816 to do it before the SRT pass to save the SRT entries associated with
819 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
821 arity = stgArity f (lookupBinding env f)
825 %************************************************************************
827 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
829 %************************************************************************
831 There's a lot of stuff to pass around, so we use this @LneM@ monad to
832 help. All the stuff here is only passed *down*.
835 newtype LneM a = LneM
836 { unLneM :: IdEnv HowBound
837 -> LiveInfo -- Vars and CAFs live in continuation
841 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
842 -- i.e. ones with a nested (non-top-level) binding
843 CafSet) -- Static live variables;
844 -- i.e. top-level variables that are CAFs or refer to them
846 type EscVarsSet = IdSet
850 = ImportBound -- Used only as a response to lookupBinding; never
851 -- exists in the range of the (IdEnv HowBound)
853 | LetBound -- A let(rec) in this module
854 LetInfo -- Whether top level or nested
855 Arity -- Its arity (local Ids don't have arity info at this point)
857 | LambdaBound -- Used for both lambda and case
860 = TopLet -- top level things
861 | NestedLet LiveInfo -- For nested things, what is live if this
862 -- thing is live? Invariant: the binder
863 -- itself is always a member of
864 -- the dynamic set of its own LiveInfo
866 isLetBound :: HowBound -> Bool
867 isLetBound (LetBound _ _) = True
870 topLevelBound :: HowBound -> Bool
871 topLevelBound ImportBound = True
872 topLevelBound (LetBound TopLet _) = True
873 topLevelBound _ = False
876 For a let(rec)-bound variable, x, we record LiveInfo, the set of
877 variables that are live if x is live. This LiveInfo comprises
878 (a) dynamic live variables (ones with a non-top-level binding)
879 (b) static live variabes (CAFs or things that refer to CAFs)
881 For "normal" variables (a) is just x alone. If x is a let-no-escaped
882 variable then x is represented by a code pointer and a stack pointer
883 (well, one for each stack). So all of the variables needed in the
884 execution of x are live if x is, and are therefore recorded in the
885 LetBound constructor; x itself *is* included.
887 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
891 emptyLiveInfo :: LiveInfo
892 emptyLiveInfo = (emptyVarSet,emptyVarSet)
894 unitLiveVar :: Id -> LiveInfo
895 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
897 unitLiveCaf :: Id -> LiveInfo
898 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
900 addLiveVar :: LiveInfo -> Id -> LiveInfo
901 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
903 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
904 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
906 mkSRT :: LiveInfo -> SRT
907 mkSRT (_, cafs) = SRTEntries cafs
909 getLiveVars :: LiveInfo -> StgLiveVars
910 getLiveVars (lvs, _) = lvs
914 The std monad functions:
916 initLne :: IdEnv HowBound -> LneM a -> a
917 initLne env m = unLneM m env emptyLiveInfo
921 {-# INLINE thenLne #-}
922 {-# INLINE returnLne #-}
924 returnLne :: a -> LneM a
925 returnLne e = LneM $ \_ _ -> e
927 thenLne :: LneM a -> (a -> LneM b) -> LneM b
928 thenLne m k = LneM $ \env lvs_cont
929 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
931 instance Monad LneM where
935 instance MonadFix LneM where
936 mfix expr = LneM $ \env lvs_cont ->
937 let result = unLneM (expr result) env lvs_cont
941 Functions specific to this monad:
944 getVarsLiveInCont :: LneM LiveInfo
945 getVarsLiveInCont = LneM $ \_env lvs_cont -> lvs_cont
947 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
948 setVarsLiveInCont new_lvs_cont expr
949 = LneM $ \env _lvs_cont
950 -> unLneM expr env new_lvs_cont
952 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
953 extendVarEnvLne ids_w_howbound expr
954 = LneM $ \env lvs_cont
955 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
957 lookupVarLne :: Id -> LneM HowBound
958 lookupVarLne v = LneM $ \env _lvs_cont -> lookupBinding env v
960 lookupBinding :: IdEnv HowBound -> Id -> HowBound
961 lookupBinding env v = case lookupVarEnv env v of
963 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
966 -- The result of lookupLiveVarsForSet, a set of live variables, is
967 -- only ever tacked onto a decorated expression. It is never used as
968 -- the basis of a control decision, which might give a black hole.
970 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
971 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
973 freeVarsToLiveVars' _env live_in_cont = live_info
975 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
976 lvs_from_fvs = map do_one (allFreeIds fvs)
978 do_one (v, how_bound)
980 ImportBound -> unitLiveCaf v -- Only CAF imports are
983 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
984 | otherwise -> emptyLiveInfo
986 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
987 -- (see the invariant on NestedLet)
989 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
992 %************************************************************************
994 \subsection[Free-var info]{Free variable information}
996 %************************************************************************
999 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
1000 -- The Var is so we can gather up the free variables
1003 -- The HowBound info just saves repeated lookups;
1004 -- we look up just once when we encounter the occurrence.
1005 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
1006 -- Imported Ids without CAF refs are simply
1007 -- not put in the FreeVarsInfo for an expression.
1008 -- See singletonFVInfo and freeVarsToLiveVars
1010 -- StgBinderInfo records how it occurs; notably, we
1011 -- are interested in whether it only occurs in saturated
1012 -- applications, because then we don't need to build a
1014 -- If f is mapped to noBinderInfo, that means
1015 -- that f *is* mentioned (else it wouldn't be in the
1016 -- IdEnv at all), but perhaps in an unsaturated applications.
1018 -- All case/lambda-bound things are also mapped to
1019 -- noBinderInfo, since we aren't interested in their
1022 -- For ILX we track free var info for type variables too;
1023 -- hence VarEnv not IdEnv
1027 emptyFVInfo :: FreeVarsInfo
1028 emptyFVInfo = emptyVarEnv
1030 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
1031 -- Don't record non-CAF imports at all, to keep free-var sets small
1032 singletonFVInfo id ImportBound info
1033 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
1034 | otherwise = emptyVarEnv
1035 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1037 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1038 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1040 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1041 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1043 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1044 minusFVBinders vs fv = foldr minusFVBinder fv vs
1046 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1047 minusFVBinder v fv = fv `delVarEnv` v
1048 -- When removing a binder, remember to add its type variables
1049 -- c.f. CoreFVs.delBinderFV
1051 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1052 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1054 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1055 -- Find how the given Id is used.
1056 -- Externally visible things may be used any old how
1058 | isExternalName (idName id) = noBinderInfo
1059 | otherwise = case lookupVarEnv fvs id of
1060 Nothing -> noBinderInfo
1061 Just (_,_,info) -> info
1063 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1064 allFreeIds fvs = ASSERT( all (isId . fst) ids ) ids
1066 ids = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs]
1068 -- Non-top-level things only, both type variables and ids
1069 getFVs :: FreeVarsInfo -> [Var]
1070 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1071 not (topLevelBound how_bound) ]
1073 getFVSet :: FreeVarsInfo -> VarSet
1074 getFVSet fvs = mkVarSet (getFVs fvs)
1076 plusFVInfo :: (Var, HowBound, StgBinderInfo)
1077 -> (Var, HowBound, StgBinderInfo)
1078 -> (Var, HowBound, StgBinderInfo)
1079 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1080 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1081 (id1, hb1, combineStgBinderInfo info1 info2)
1083 -- The HowBound info for a variable in the FVInfo should be consistent
1084 check_eq_how_bound :: HowBound -> HowBound -> Bool
1085 check_eq_how_bound ImportBound ImportBound = True
1086 check_eq_how_bound LambdaBound LambdaBound = True
1087 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1088 check_eq_how_bound _ _ = False
1090 check_eq_li :: LetInfo -> LetInfo -> Bool
1091 check_eq_li (NestedLet _) (NestedLet _) = True
1092 check_eq_li TopLet TopLet = True
1093 check_eq_li _ _ = False
1098 filterStgBinders :: [Var] -> [Var]
1099 filterStgBinders bndrs = filter isId bndrs
1104 -- Ignore all notes except SCC
1105 myCollectBinders :: Expr Var -> ([Var], Expr Var)
1106 myCollectBinders expr
1109 go bs (Lam b e) = go (b:bs) e
1110 go bs e@(Note (SCC _) _) = (reverse bs, e)
1111 go bs (Cast e _) = go bs e
1112 go bs (Note _ e) = go bs e
1113 go bs e = (reverse bs, e)
1115 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1116 -- We assume that we only have variables
1117 -- in the function position by now
1121 go (Var v) as = (v, as)
1122 go (App f a) as = go f (a:as)
1123 go (Note (SCC _) _) _ = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1124 go (Cast e _) as = go e as
1125 go (Note _ e) as = go e as
1127 | isTyCoVar b = go e as -- Note [Collect args]
1128 go _ _ = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1133 This big-lambda case occurred following a rather obscure eta expansion.
1134 It all seems a bit yukky to me.
1137 stgArity :: Id -> HowBound -> Arity
1138 stgArity _ (LetBound _ arity) = arity
1139 stgArity f ImportBound = idArity f
1140 stgArity _ LambdaBound = 0