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 )
21 import MkId ( coercionTokenId )
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 <+> ppr id_marked_caffy <+> ppr binding_is_caffy )
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 []
317 coreToStgExpr (Coercion _) = coreToStgApp Nothing coercionTokenId []
319 coreToStgExpr expr@(App _ _)
320 = coreToStgApp Nothing f args
322 (f, args) = myCollectArgs expr
324 coreToStgExpr expr@(Lam _ _)
326 (args, body) = myCollectBinders expr
327 args' = filterStgBinders args
329 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $ do
330 (body, body_fvs, body_escs) <- coreToStgExpr body
332 fvs = args' `minusFVBinders` body_fvs
333 escs = body_escs `delVarSetList` args'
334 result_expr | null args' = body
335 | otherwise = StgLam (exprType expr) args' body
337 return (result_expr, fvs, escs)
339 coreToStgExpr (Note (SCC cc) expr) = do
340 (expr2, fvs, escs) <- coreToStgExpr expr
341 return (StgSCC cc expr2, fvs, escs)
343 coreToStgExpr (Case (Var id) _bndr _ty [(DEFAULT,[],expr)])
344 | Just (TickBox m n) <- isTickBoxOp_maybe id = do
345 (expr2, fvs, escs) <- coreToStgExpr expr
346 return (StgTick m n expr2, fvs, escs)
348 coreToStgExpr (Note _ expr)
351 coreToStgExpr (Cast expr _)
354 -- Cases require a little more real work.
356 coreToStgExpr (Case scrut bndr _ alts) = do
357 (alts2, alts_fvs, alts_escs)
358 <- extendVarEnvLne [(bndr, LambdaBound)] $ do
359 (alts2, fvs_s, escs_s) <- mapAndUnzip3M vars_alt alts
362 unionVarSets escs_s )
364 -- Determine whether the default binder is dead or not
365 -- This helps the code generator to avoid generating an assignment
366 -- for the case binder (is extremely rare cases) ToDo: remove.
367 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
368 | otherwise = bndr `setIdOccInfo` IAmDead
370 -- Don't consider the default binder as being 'live in alts',
371 -- since this is from the point of view of the case expr, where
372 -- the default binder is not free.
373 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
374 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
376 alts_lv_info <- freeVarsToLiveVars alts_fvs_wo_bndr
378 -- We tell the scrutinee that everything
379 -- live in the alts is live in it, too.
380 (scrut2, scrut_fvs, _scrut_escs, scrut_lv_info)
381 <- setVarsLiveInCont alts_lv_info $ do
382 (scrut2, scrut_fvs, scrut_escs) <- coreToStgExpr scrut
383 scrut_lv_info <- freeVarsToLiveVars scrut_fvs
384 return (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
387 StgCase scrut2 (getLiveVars scrut_lv_info)
388 (getLiveVars alts_lv_info)
391 (mkStgAltType bndr alts)
393 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
394 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
395 -- You might think we should have scrut_escs, not
396 -- (getFVSet scrut_fvs), but actually we can't call, and
397 -- then return from, a let-no-escape thing.
400 vars_alt (con, binders, rhs)
401 = let -- Remove type variables
402 binders' = filterStgBinders binders
404 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $ do
405 (rhs2, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
407 -- Records whether each param is used in the RHS
408 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
410 return ( (con, binders', good_use_mask, rhs2),
411 binders' `minusFVBinders` rhs_fvs,
412 rhs_escs `delVarSetList` binders' )
413 -- ToDo: remove the delVarSet;
414 -- since escs won't include any of these binders
417 Lets not only take quite a bit of work, but this is where we convert
418 then to let-no-escapes, if we wish.
420 (Meanwhile, we don't expect to see let-no-escapes...)
422 coreToStgExpr (Let bind body) = do
423 (new_let, fvs, escs, _)
424 <- mfix (\ ~(_, _, _, no_binder_escapes) ->
425 coreToStgLet no_binder_escapes bind body
428 return (new_let, fvs, escs)
430 coreToStgExpr e = pprPanic "coreToStgExpr" (ppr e)
434 mkStgAltType :: Id -> [CoreAlt] -> AltType
435 mkStgAltType bndr alts
436 = case splitTyConApp_maybe (repType (idType bndr)) of
437 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
438 | isUnLiftedTyCon tc -> PrimAlt tc
439 | isHiBootTyCon tc -> look_for_better_tycon
440 | isAlgTyCon tc -> AlgAlt tc
441 | otherwise -> ASSERT2( _is_poly_alt_tycon tc, ppr tc )
446 _is_poly_alt_tycon tc
448 || isPrimTyCon tc -- "Any" is lifted but primitive
449 || isFamilyTyCon tc -- Type family; e.g. arising from strict
450 -- function application where argument has a
453 -- Sometimes, the TyCon is a HiBootTyCon which may not have any
454 -- constructors inside it. Then we can get a better TyCon by
455 -- grabbing the one from a constructor alternative
457 look_for_better_tycon
458 | ((DataAlt con, _, _) : _) <- data_alts =
459 AlgAlt (dataConTyCon con)
461 ASSERT(null data_alts)
464 (data_alts, _deflt) = findDefault alts
468 -- ---------------------------------------------------------------------------
470 -- ---------------------------------------------------------------------------
474 :: Maybe UpdateFlag -- Just upd <=> this application is
475 -- the rhs of a thunk binding
476 -- x = [...] \upd [] -> the_app
477 -- with specified update flag
479 -> [CoreArg] -- Arguments
480 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
483 coreToStgApp _ f args = do
484 (args', args_fvs) <- coreToStgArgs args
485 how_bound <- lookupVarLne f
488 n_val_args = valArgCount args
489 not_letrec_bound = not (isLetBound how_bound)
490 fun_fvs = singletonFVInfo f how_bound fun_occ
491 -- e.g. (f :: a -> int) (x :: a)
492 -- Here the free variables are "f", "x" AND the type variable "a"
493 -- coreToStgArgs will deal with the arguments recursively
495 -- Mostly, the arity info of a function is in the fn's IdInfo
496 -- But new bindings introduced by CoreSat may not have no
497 -- arity info; it would do us no good anyway. For example:
498 -- let f = \ab -> e in f
499 -- No point in having correct arity info for f!
500 -- Hence the hasArity stuff below.
501 -- NB: f_arity is only consulted for LetBound things
502 f_arity = stgArity f how_bound
503 saturated = f_arity <= n_val_args
506 | not_letrec_bound = noBinderInfo -- Uninteresting variable
507 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
508 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
511 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
512 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
513 -- saturated call doesn't escape
514 -- (let-no-escape applies to 'thunks' too)
516 | otherwise = unitVarSet f -- Inexact application; it does escape
518 -- At the moment of the call:
520 -- either the function is *not* let-no-escaped, in which case
521 -- nothing is live except live_in_cont
522 -- or the function *is* let-no-escaped in which case the
523 -- variables it uses are live, but still the function
524 -- itself is not. PS. In this case, the function's
525 -- live vars should already include those of the
526 -- continuation, but it does no harm to just union the
529 res_ty = exprType (mkApps (Var f) args)
530 app = case idDetails f of
531 DataConWorkId dc | saturated -> StgConApp dc args'
533 -- Some primitive operator that might be implemented as a library call.
534 PrimOpId op -> ASSERT( saturated )
535 StgOpApp (StgPrimOp op) args' res_ty
537 -- A call to some primitive Cmm function.
538 FCallId (CCall (CCallSpec (StaticTarget lbl (Just pkgId)) PrimCallConv _))
539 -> ASSERT( saturated )
540 StgOpApp (StgPrimCallOp (PrimCall lbl pkgId)) args' res_ty
542 -- A regular foreign call.
543 FCallId call -> ASSERT( saturated )
544 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
546 TickBoxOpId {} -> pprPanic "coreToStg TickBox" $ ppr (f,args')
547 _other -> StgApp f args'
548 fvs = fun_fvs `unionFVInfo` args_fvs
549 vars = fun_escs `unionVarSet` (getFVSet args_fvs)
550 -- All the free vars of the args are disqualified
551 -- from being let-no-escaped.
553 -- Forcing these fixes a leak in the code generator, noticed while
554 -- profiling for trac #4367
555 app `seq` fvs `seq` seqVarSet vars `seq` return (
563 -- ---------------------------------------------------------------------------
565 -- This is the guy that turns applications into A-normal form
566 -- ---------------------------------------------------------------------------
568 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
570 = return ([], emptyFVInfo)
572 coreToStgArgs (Type _ : args) = do -- Type argument
573 (args', fvs) <- coreToStgArgs args
576 coreToStgArgs (Coercion _ : args) -- Coercion argument; replace with place holder
577 = do { (args', fvs) <- coreToStgArgs args
578 ; return (StgVarArg coercionTokenId : args', fvs) }
580 coreToStgArgs (arg : args) = do -- Non-type argument
581 (stg_args, args_fvs) <- coreToStgArgs args
582 (arg', arg_fvs, _escs) <- coreToStgExpr arg
584 fvs = args_fvs `unionFVInfo` arg_fvs
585 stg_arg = case arg' of
586 StgApp v [] -> StgVarArg v
587 StgConApp con [] -> StgVarArg (dataConWorkId con)
588 StgLit lit -> StgLitArg lit
589 _ -> pprPanic "coreToStgArgs" (ppr arg)
591 -- WARNING: what if we have an argument like (v `cast` co)
592 -- where 'co' changes the representation type?
593 -- (This really only happens if co is unsafe.)
594 -- Then all the getArgAmode stuff in CgBindery will set the
595 -- cg_rep of the CgIdInfo based on the type of v, rather
596 -- than the type of 'co'.
597 -- This matters particularly when the function is a primop
599 -- Wanted: a better solution than this hacky warning
601 arg_ty = exprType arg
602 stg_arg_ty = stgArgType stg_arg
603 bad_args = (isUnLiftedType arg_ty && not (isUnLiftedType stg_arg_ty))
604 || (typePrimRep arg_ty /= typePrimRep stg_arg_ty)
605 -- In GHCi we coerce an argument of type BCO# (unlifted) to HValue (lifted),
606 -- and pass it to a function expecting an HValue (arg_ty). This is ok because
607 -- we can treat an unlifted value as lifted. But the other way round
609 -- We also want to check if a pointer is cast to a non-ptr etc
611 WARN( bad_args, ptext (sLit "Dangerous-looking argument. Probable cause: bad unsafeCoerce#") $$ ppr arg )
612 return (stg_arg : stg_args, fvs)
615 -- ---------------------------------------------------------------------------
616 -- The magic for lets:
617 -- ---------------------------------------------------------------------------
620 :: Bool -- True <=> yes, we are let-no-escaping this let
621 -> CoreBind -- bindings
623 -> LneM (StgExpr, -- new let
624 FreeVarsInfo, -- variables free in the whole let
625 EscVarsSet, -- variables that escape from the whole let
626 Bool) -- True <=> none of the binders in the bindings
627 -- is among the escaping vars
629 coreToStgLet let_no_escape bind body = do
630 (bind2, bind_fvs, bind_escs, bind_lvs,
631 body2, body_fvs, body_escs, body_lvs)
632 <- mfix $ \ ~(_, _, _, _, _, rec_body_fvs, _, _) -> do
634 -- Do the bindings, setting live_in_cont to empty if
635 -- we ain't in a let-no-escape world
636 live_in_cont <- getVarsLiveInCont
637 ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext)
638 <- setVarsLiveInCont (if let_no_escape
641 (vars_bind rec_body_fvs bind)
644 extendVarEnvLne env_ext $ do
645 (body2, body_fvs, body_escs) <- coreToStgExpr body
646 body_lv_info <- freeVarsToLiveVars body_fvs
648 return (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
649 body2, body_fvs, body_escs, getLiveVars body_lv_info)
652 -- Compute the new let-expression
654 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
655 | otherwise = StgLet bind2 body2
658 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
661 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
663 real_bind_escs = if let_no_escape then
667 -- Everything escapes which is free in the bindings
669 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
671 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
674 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
676 -- Debugging code as requested by Andrew Kennedy
677 checked_no_binder_escapes
678 | debugIsOn && not no_binder_escapes && any is_join_var binders
679 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
681 | otherwise = no_binder_escapes
683 -- Mustn't depend on the passed-in let_no_escape flag, since
684 -- no_binder_escapes is used by the caller to derive the flag!
689 checked_no_binder_escapes
692 set_of_binders = mkVarSet binders
693 binders = bindersOf bind
695 mk_binding bind_lv_info binder rhs
696 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
698 live_vars | let_no_escape = addLiveVar bind_lv_info binder
699 | otherwise = unitLiveVar binder
700 -- c.f. the invariant on NestedLet
702 vars_bind :: FreeVarsInfo -- Free var info for body of binding
706 EscVarsSet, -- free vars; escapee vars
707 LiveInfo, -- Vars and CAFs live in binding
708 [(Id, HowBound)]) -- extension to environment
711 vars_bind body_fvs (NonRec binder rhs) = do
712 (rhs2, bind_fvs, bind_lv_info, escs) <- coreToStgRhs body_fvs [] (binder,rhs)
714 env_ext_item = mk_binding bind_lv_info binder rhs
716 return (StgNonRec binder rhs2,
717 bind_fvs, escs, bind_lv_info, [env_ext_item])
720 vars_bind body_fvs (Rec pairs)
721 = mfix $ \ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
723 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
724 binders = map fst pairs
725 env_ext = [ mk_binding bind_lv_info b rhs
728 extendVarEnvLne env_ext $ do
729 (rhss2, fvss, lv_infos, escss)
730 <- mapAndUnzip4M (coreToStgRhs rec_scope_fvs binders) pairs
732 bind_fvs = unionFVInfos fvss
733 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
734 escs = unionVarSets escss
736 return (StgRec (binders `zip` rhss2),
737 bind_fvs, escs, bind_lv_info, env_ext)
740 is_join_var :: Id -> Bool
741 -- A hack (used only for compiler debuggging) to tell if
742 -- a variable started life as a join point ($j)
743 is_join_var j = occNameString (getOccName j) == "$j"
747 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
750 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
752 coreToStgRhs scope_fv_info binders (bndr, rhs) = do
753 (new_rhs, rhs_fvs, rhs_escs) <- coreToStgExpr rhs
754 lv_info <- freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs)
755 return (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
756 rhs_fvs, lv_info, rhs_escs)
758 bndr_info = lookupFVInfo scope_fv_info bndr
760 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
762 mkStgRhs _ _ _ (StgConApp con args) = StgRhsCon noCCS con args
764 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
765 = StgRhsClosure noCCS binder_info
770 mkStgRhs rhs_fvs srt binder_info rhs
771 = StgRhsClosure noCCS binder_info
777 SDM: disabled. Eval/Apply can't handle functions with arity zero very
778 well; and making these into simple non-updatable thunks breaks other
779 assumptions (namely that they will be entered only once).
781 upd_flag | isPAP env rhs = ReEntrant
782 | otherwise = Updatable
786 upd = if isOnceDem dem
787 then (if isNotTop toplev
788 then SingleEntry -- HA! Paydirt for "dem"
791 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
795 -- For now we forbid SingleEntry CAFs; they tickle the
796 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
797 -- and I don't understand why. There's only one SE_CAF (well,
798 -- only one that tickled a great gaping bug in an earlier attempt
799 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
800 -- specifically Main.lvl6 in spectral/cryptarithm2.
801 -- So no great loss. KSW 2000-07.
805 Detect thunks which will reduce immediately to PAPs, and make them
806 non-updatable. This has several advantages:
808 - the non-updatable thunk behaves exactly like the PAP,
810 - the thunk is more efficient to enter, because it is
811 specialised to the task.
813 - we save one update frame, one stg_update_PAP, one update
814 and lots of PAP_enters.
816 - in the case where the thunk is top-level, we save building
817 a black hole and futhermore the thunk isn't considered to
818 be a CAF any more, so it doesn't appear in any SRTs.
820 We do it here, because the arity information is accurate, and we need
821 to do it before the SRT pass to save the SRT entries associated with
824 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
826 arity = stgArity f (lookupBinding env f)
830 %************************************************************************
832 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
834 %************************************************************************
836 There's a lot of stuff to pass around, so we use this @LneM@ monad to
837 help. All the stuff here is only passed *down*.
840 newtype LneM a = LneM
841 { unLneM :: IdEnv HowBound
842 -> LiveInfo -- Vars and CAFs live in continuation
846 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
847 -- i.e. ones with a nested (non-top-level) binding
848 CafSet) -- Static live variables;
849 -- i.e. top-level variables that are CAFs or refer to them
851 type EscVarsSet = IdSet
855 = ImportBound -- Used only as a response to lookupBinding; never
856 -- exists in the range of the (IdEnv HowBound)
858 | LetBound -- A let(rec) in this module
859 LetInfo -- Whether top level or nested
860 Arity -- Its arity (local Ids don't have arity info at this point)
862 | LambdaBound -- Used for both lambda and case
865 = TopLet -- top level things
866 | NestedLet LiveInfo -- For nested things, what is live if this
867 -- thing is live? Invariant: the binder
868 -- itself is always a member of
869 -- the dynamic set of its own LiveInfo
871 isLetBound :: HowBound -> Bool
872 isLetBound (LetBound _ _) = True
875 topLevelBound :: HowBound -> Bool
876 topLevelBound ImportBound = True
877 topLevelBound (LetBound TopLet _) = True
878 topLevelBound _ = False
881 For a let(rec)-bound variable, x, we record LiveInfo, the set of
882 variables that are live if x is live. This LiveInfo comprises
883 (a) dynamic live variables (ones with a non-top-level binding)
884 (b) static live variabes (CAFs or things that refer to CAFs)
886 For "normal" variables (a) is just x alone. If x is a let-no-escaped
887 variable then x is represented by a code pointer and a stack pointer
888 (well, one for each stack). So all of the variables needed in the
889 execution of x are live if x is, and are therefore recorded in the
890 LetBound constructor; x itself *is* included.
892 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
896 emptyLiveInfo :: LiveInfo
897 emptyLiveInfo = (emptyVarSet,emptyVarSet)
899 unitLiveVar :: Id -> LiveInfo
900 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
902 unitLiveCaf :: Id -> LiveInfo
903 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
905 addLiveVar :: LiveInfo -> Id -> LiveInfo
906 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
908 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
909 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
911 mkSRT :: LiveInfo -> SRT
912 mkSRT (_, cafs) = SRTEntries cafs
914 getLiveVars :: LiveInfo -> StgLiveVars
915 getLiveVars (lvs, _) = lvs
919 The std monad functions:
921 initLne :: IdEnv HowBound -> LneM a -> a
922 initLne env m = unLneM m env emptyLiveInfo
926 {-# INLINE thenLne #-}
927 {-# INLINE returnLne #-}
929 returnLne :: a -> LneM a
930 returnLne e = LneM $ \_ _ -> e
932 thenLne :: LneM a -> (a -> LneM b) -> LneM b
933 thenLne m k = LneM $ \env lvs_cont
934 -> unLneM (k (unLneM m env lvs_cont)) env lvs_cont
936 instance Monad LneM where
940 instance MonadFix LneM where
941 mfix expr = LneM $ \env lvs_cont ->
942 let result = unLneM (expr result) env lvs_cont
946 Functions specific to this monad:
949 getVarsLiveInCont :: LneM LiveInfo
950 getVarsLiveInCont = LneM $ \_env lvs_cont -> lvs_cont
952 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
953 setVarsLiveInCont new_lvs_cont expr
954 = LneM $ \env _lvs_cont
955 -> unLneM expr env new_lvs_cont
957 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
958 extendVarEnvLne ids_w_howbound expr
959 = LneM $ \env lvs_cont
960 -> unLneM expr (extendVarEnvList env ids_w_howbound) lvs_cont
962 lookupVarLne :: Id -> LneM HowBound
963 lookupVarLne v = LneM $ \env _lvs_cont -> lookupBinding env v
965 lookupBinding :: IdEnv HowBound -> Id -> HowBound
966 lookupBinding env v = case lookupVarEnv env v of
968 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
971 -- The result of lookupLiveVarsForSet, a set of live variables, is
972 -- only ever tacked onto a decorated expression. It is never used as
973 -- the basis of a control decision, which might give a black hole.
975 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
976 freeVarsToLiveVars fvs = LneM freeVarsToLiveVars'
978 freeVarsToLiveVars' _env live_in_cont = live_info
980 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
981 lvs_from_fvs = map do_one (allFreeIds fvs)
983 do_one (v, how_bound)
985 ImportBound -> unitLiveCaf v -- Only CAF imports are
988 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
989 | otherwise -> emptyLiveInfo
991 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
992 -- (see the invariant on NestedLet)
994 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
997 %************************************************************************
999 \subsection[Free-var info]{Free variable information}
1001 %************************************************************************
1004 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
1005 -- The Var is so we can gather up the free variables
1008 -- The HowBound info just saves repeated lookups;
1009 -- we look up just once when we encounter the occurrence.
1010 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
1011 -- Imported Ids without CAF refs are simply
1012 -- not put in the FreeVarsInfo for an expression.
1013 -- See singletonFVInfo and freeVarsToLiveVars
1015 -- StgBinderInfo records how it occurs; notably, we
1016 -- are interested in whether it only occurs in saturated
1017 -- applications, because then we don't need to build a
1019 -- If f is mapped to noBinderInfo, that means
1020 -- that f *is* mentioned (else it wouldn't be in the
1021 -- IdEnv at all), but perhaps in an unsaturated applications.
1023 -- All case/lambda-bound things are also mapped to
1024 -- noBinderInfo, since we aren't interested in their
1027 -- For ILX we track free var info for type variables too;
1028 -- hence VarEnv not IdEnv
1032 emptyFVInfo :: FreeVarsInfo
1033 emptyFVInfo = emptyVarEnv
1035 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
1036 -- Don't record non-CAF imports at all, to keep free-var sets small
1037 singletonFVInfo id ImportBound info
1038 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
1039 | otherwise = emptyVarEnv
1040 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1042 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1043 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1045 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1046 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1048 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1049 minusFVBinders vs fv = foldr minusFVBinder fv vs
1051 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1052 minusFVBinder v fv = fv `delVarEnv` v
1053 -- When removing a binder, remember to add its type variables
1054 -- c.f. CoreFVs.delBinderFV
1056 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1057 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1059 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1060 -- Find how the given Id is used.
1061 -- Externally visible things may be used any old how
1063 | isExternalName (idName id) = noBinderInfo
1064 | otherwise = case lookupVarEnv fvs id of
1065 Nothing -> noBinderInfo
1066 Just (_,_,info) -> info
1068 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1069 allFreeIds fvs = ASSERT( all (isId . fst) ids ) ids
1071 ids = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs]
1073 -- Non-top-level things only, both type variables and ids
1074 getFVs :: FreeVarsInfo -> [Var]
1075 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1076 not (topLevelBound how_bound) ]
1078 getFVSet :: FreeVarsInfo -> VarSet
1079 getFVSet fvs = mkVarSet (getFVs fvs)
1081 plusFVInfo :: (Var, HowBound, StgBinderInfo)
1082 -> (Var, HowBound, StgBinderInfo)
1083 -> (Var, HowBound, StgBinderInfo)
1084 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1085 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1086 (id1, hb1, combineStgBinderInfo info1 info2)
1088 -- The HowBound info for a variable in the FVInfo should be consistent
1089 check_eq_how_bound :: HowBound -> HowBound -> Bool
1090 check_eq_how_bound ImportBound ImportBound = True
1091 check_eq_how_bound LambdaBound LambdaBound = True
1092 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1093 check_eq_how_bound _ _ = False
1095 check_eq_li :: LetInfo -> LetInfo -> Bool
1096 check_eq_li (NestedLet _) (NestedLet _) = True
1097 check_eq_li TopLet TopLet = True
1098 check_eq_li _ _ = False
1103 filterStgBinders :: [Var] -> [Var]
1104 filterStgBinders bndrs = filter isId bndrs
1109 -- Ignore all notes except SCC
1110 myCollectBinders :: Expr Var -> ([Var], Expr Var)
1111 myCollectBinders expr
1114 go bs (Lam b e) = go (b:bs) e
1115 go bs e@(Note (SCC _) _) = (reverse bs, e)
1116 go bs (Cast e _) = go bs e
1117 go bs (Note _ e) = go bs e
1118 go bs e = (reverse bs, e)
1120 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1121 -- We assume that we only have variables
1122 -- in the function position by now
1126 go (Var v) as = (v, as)
1127 go (App f a) as = go f (a:as)
1128 go (Note (SCC _) _) _ = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1129 go (Cast e _) as = go e as
1130 go (Note _ e) as = go e as
1132 | isTyVar b = go e as -- Note [Collect args]
1133 go _ _ = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1138 This big-lambda case occurred following a rather obscure eta expansion.
1139 It all seems a bit yukky to me.
1142 stgArity :: Id -> HowBound -> Arity
1143 stgArity _ (LetBound _ arity) = arity
1144 stgArity f ImportBound = idArity f
1145 stgArity _ LambdaBound = 0