2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[CoreToStg]{Converts Core to STG Syntax}
6 And, as we have the info in hand, we may convert some lets to
10 module CoreToStg ( coreToStg, coreExprToStg ) where
12 #include "HsVersions.h"
15 import CoreUtils ( rhsIsStatic, manifestArity, exprType, findDefault )
19 import Coercion ( mkUnsafeCoercion )
20 import TyCon ( isAlgTyCon )
22 import Var ( Var, globalIdDetails, idType )
23 import TyCon ( isUnboxedTupleTyCon, isPrimTyCon, isFunTyCon, isHiBootTyCon )
26 import CostCentre ( noCCS )
29 import Maybes ( maybeToBool )
30 import Name ( getOccName, isExternalName, nameOccName )
31 import OccName ( occNameString, occNameFS )
32 import BasicTypes ( Arity )
33 import StaticFlags ( opt_RuntimeTypes )
34 import PackageConfig ( PackageId )
40 %************************************************************************
42 \subsection[live-vs-free-doc]{Documentation}
44 %************************************************************************
46 (There is other relevant documentation in codeGen/CgLetNoEscape.)
48 The actual Stg datatype is decorated with {\em live variable}
49 information, as well as {\em free variable} information. The two are
50 {\em not} the same. Liveness is an operational property rather than a
51 semantic one. A variable is live at a particular execution point if
52 it can be referred to {\em directly} again. In particular, a dead
53 variable's stack slot (if it has one):
56 should be stubbed to avoid space leaks, and
58 may be reused for something else.
61 There ought to be a better way to say this. Here are some examples:
68 Just after the `in', v is live, but q is dead. If the whole of that
69 let expression was enclosed in a case expression, thus:
71 case (let v = [q] \[x] -> e in ...v...) of
74 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
75 we'll return later to the @alts@ and need it.
77 Let-no-escapes make this a bit more interesting:
79 let-no-escape v = [q] \ [x] -> e
83 Here, @q@ is still live at the `in', because @v@ is represented not by
84 a closure but by the current stack state. In other words, if @v@ is
85 live then so is @q@. Furthermore, if @e@ mentions an enclosing
86 let-no-escaped variable, then {\em its} free variables are also live
89 %************************************************************************
91 \subsection[caf-info]{Collecting live CAF info}
93 %************************************************************************
95 In this pass we also collect information on which CAFs are live for
96 constructing SRTs (see SRT.lhs).
98 A top-level Id has CafInfo, which is
100 - MayHaveCafRefs, if it may refer indirectly to
102 - NoCafRefs if it definitely doesn't
104 The CafInfo has already been calculated during the CoreTidy pass.
106 During CoreToStg, we then pin onto each binding and case expression, a
107 list of Ids which represents the "live" CAFs at that point. The meaning
108 of "live" here is the same as for live variables, see above (which is
109 why it's convenient to collect CAF information here rather than elsewhere).
111 The later SRT pass takes these lists of Ids and uses them to construct
112 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
116 Interaction of let-no-escape with SRTs [Sept 01]
117 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
120 let-no-escape x = ...caf1...caf2...
124 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
125 build SRTs just as if x's defn was inlined at each call site, and
126 that means that x's CAF refs get duplicated in the overall SRT.
128 This is unlike ordinary lets, in which the CAF refs are not duplicated.
130 We could fix this loss of (static) sharing by making a sort of pseudo-closure
131 for x, solely to put in the SRTs lower down.
134 %************************************************************************
136 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
138 %************************************************************************
141 coreToStg :: PackageId -> [CoreBind] -> IO [StgBinding]
142 coreToStg this_pkg pgm
144 where (_, _, pgm') = coreTopBindsToStg this_pkg emptyVarEnv pgm
146 coreExprToStg :: CoreExpr -> StgExpr
148 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
153 -> IdEnv HowBound -- environment for the bindings
155 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
157 coreTopBindsToStg this_pkg env [] = (env, emptyFVInfo, [])
158 coreTopBindsToStg this_pkg env (b:bs)
159 = (env2, fvs2, b':bs')
161 -- env accumulates down the list of binds, fvs accumulates upwards
162 (env1, fvs2, b' ) = coreTopBindToStg this_pkg env fvs1 b
163 (env2, fvs1, bs') = coreTopBindsToStg this_pkg env1 bs
169 -> FreeVarsInfo -- Info about the body
171 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
173 coreTopBindToStg this_pkg env body_fvs (NonRec id rhs)
175 env' = extendVarEnv env id how_bound
176 how_bound = LetBound TopLet $! manifestArity rhs
180 coreToTopStgRhs this_pkg body_fvs (id,rhs) `thenLne` \ (stg_rhs, fvs') ->
181 returnLne (stg_rhs, fvs')
184 bind = StgNonRec id stg_rhs
186 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) )
187 ASSERT2(consistentCafInfo id bind, ppr id)
188 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
189 (env', fvs' `unionFVInfo` body_fvs, bind)
191 coreTopBindToStg this_pkg env body_fvs (Rec pairs)
193 (binders, rhss) = unzip pairs
195 extra_env' = [ (b, LetBound TopLet $! manifestArity rhs)
196 | (b, rhs) <- pairs ]
197 env' = extendVarEnvList env extra_env'
201 mapAndUnzipLne (coreToTopStgRhs this_pkg body_fvs) pairs
202 `thenLne` \ (stg_rhss, fvss') ->
203 let fvs' = unionFVInfos fvss' in
204 returnLne (stg_rhss, fvs')
207 bind = StgRec (zip binders stg_rhss)
209 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
210 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
211 (env', fvs' `unionFVInfo` body_fvs, bind)
214 -- Assertion helper: this checks that the CafInfo on the Id matches
215 -- what CoreToStg has figured out about the binding's SRT. The
216 -- CafInfo will be exact in all cases except when CorePrep has
217 -- floated out a binding, in which case it will be approximate.
218 consistentCafInfo id bind
219 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
222 = WARN (not exact, ppr id) safe
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
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 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
240 freeVarsToLiveVars rhs_fvs `thenLne` \ lv_info ->
241 returnLne (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) = returnLne (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' ] $
308 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
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 returnLne (result_expr, fvs, escs)
317 coreToStgExpr (Note (SCC cc) expr)
318 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
319 returnLne (StgSCC cc expr2, fvs, escs) )
321 coreToStgExpr (Note other_note expr)
324 coreToStgExpr (Cast expr co)
327 -- Cases require a little more real work.
329 coreToStgExpr (Case scrut bndr _ alts)
330 = extendVarEnvLne [(bndr, LambdaBound)] (
331 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
334 unionVarSets escs_s )
335 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
337 -- Determine whether the default binder is dead or not
338 -- This helps the code generator to avoid generating an assignment
339 -- for the case binder (is extremely rare cases) ToDo: remove.
340 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
341 | otherwise = bndr `setIdOccInfo` IAmDead
343 -- Don't consider the default binder as being 'live in alts',
344 -- since this is from the point of view of the case expr, where
345 -- the default binder is not free.
346 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
347 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
350 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
352 -- We tell the scrutinee that everything
353 -- live in the alts is live in it, too.
354 setVarsLiveInCont alts_lv_info (
355 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
356 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
357 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
359 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
362 StgCase scrut2 (getLiveVars scrut_lv_info)
363 (getLiveVars alts_lv_info)
366 (mkStgAltType (idType bndr) alts)
368 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
369 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
370 -- You might think we should have scrut_escs, not
371 -- (getFVSet scrut_fvs), but actually we can't call, and
372 -- then return from, a let-no-escape thing.
375 vars_alt (con, binders, rhs)
376 = let -- Remove type variables
377 binders' = filterStgBinders binders
379 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
380 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
382 -- Records whether each param is used in the RHS
383 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
385 returnLne ( (con, binders', good_use_mask, rhs2),
386 binders' `minusFVBinders` rhs_fvs,
387 rhs_escs `delVarSetList` binders' )
388 -- ToDo: remove the delVarSet;
389 -- since escs won't include any of these binders
392 Lets not only take quite a bit of work, but this is where we convert
393 then to let-no-escapes, if we wish.
395 (Meanwhile, we don't expect to see let-no-escapes...)
397 coreToStgExpr (Let bind body)
398 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
399 coreToStgLet no_binder_escapes bind body
400 ) `thenLne` \ (new_let, fvs, escs, _) ->
402 returnLne (new_let, fvs, escs)
406 mkStgAltType scrut_ty alts
407 = case splitTyConApp_maybe (repType scrut_ty) of
408 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
409 | isPrimTyCon tc -> PrimAlt tc
410 | isHiBootTyCon tc -> look_for_better_tycon
411 | isAlgTyCon tc -> AlgAlt tc
412 | isFunTyCon tc -> PolyAlt
413 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
417 -- Sometimes, the TyCon in the type of the scrutinee is an HiBootTyCon,
418 -- which may not have any constructors inside it. If so, then we
419 -- can get a better TyCon by grabbing the one from a constructor alternative
421 look_for_better_tycon
422 | ((DataAlt con, _, _) : _) <- data_alts =
423 AlgAlt (dataConTyCon con)
425 ASSERT(null data_alts)
428 (data_alts, _deflt) = findDefault alts
432 -- ---------------------------------------------------------------------------
434 -- ---------------------------------------------------------------------------
438 :: Maybe UpdateFlag -- Just upd <=> this application is
439 -- the rhs of a thunk binding
440 -- x = [...] \upd [] -> the_app
441 -- with specified update flag
443 -> [CoreArg] -- Arguments
444 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
446 coreToStgApp maybe_thunk_body f args
447 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
448 lookupVarLne f `thenLne` \ how_bound ->
451 n_val_args = valArgCount args
452 not_letrec_bound = not (isLetBound how_bound)
454 = let fvs = singletonFVInfo f how_bound fun_occ in
455 -- e.g. (f :: a -> int) (x :: a)
456 -- Here the free variables are "f", "x" AND the type variable "a"
457 -- coreToStgArgs will deal with the arguments recursively
458 if opt_RuntimeTypes then
459 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
462 -- Mostly, the arity info of a function is in the fn's IdInfo
463 -- But new bindings introduced by CoreSat may not have no
464 -- arity info; it would do us no good anyway. For example:
465 -- let f = \ab -> e in f
466 -- No point in having correct arity info for f!
467 -- Hence the hasArity stuff below.
468 -- NB: f_arity is only consulted for LetBound things
469 f_arity = stgArity f how_bound
470 saturated = f_arity <= n_val_args
473 | not_letrec_bound = noBinderInfo -- Uninteresting variable
474 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
475 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
478 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
479 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
480 -- saturated call doesn't escape
481 -- (let-no-escape applies to 'thunks' too)
483 | otherwise = unitVarSet f -- Inexact application; it does escape
485 -- At the moment of the call:
487 -- either the function is *not* let-no-escaped, in which case
488 -- nothing is live except live_in_cont
489 -- or the function *is* let-no-escaped in which case the
490 -- variables it uses are live, but still the function
491 -- itself is not. PS. In this case, the function's
492 -- live vars should already include those of the
493 -- continuation, but it does no harm to just union the
496 res_ty = exprType (mkApps (Var f) args)
497 app = case globalIdDetails f of
498 DataConWorkId dc | saturated -> StgConApp dc args'
499 PrimOpId op -> ASSERT( saturated )
500 StgOpApp (StgPrimOp op) args' res_ty
501 FCallId call -> ASSERT( saturated )
502 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
503 _other -> StgApp f args'
508 fun_fvs `unionFVInfo` args_fvs,
509 fun_escs `unionVarSet` (getFVSet args_fvs)
510 -- All the free vars of the args are disqualified
511 -- from being let-no-escaped.
516 -- ---------------------------------------------------------------------------
518 -- This is the guy that turns applications into A-normal form
519 -- ---------------------------------------------------------------------------
521 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
523 = returnLne ([], emptyFVInfo)
525 coreToStgArgs (Type ty : args) -- Type argument
526 = coreToStgArgs args `thenLne` \ (args', fvs) ->
527 if opt_RuntimeTypes then
528 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
530 returnLne (args', fvs)
532 coreToStgArgs (arg : args) -- Non-type argument
533 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
534 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
536 fvs = args_fvs `unionFVInfo` arg_fvs
537 stg_arg = case arg' of
538 StgApp v [] -> StgVarArg v
539 StgConApp con [] -> StgVarArg (dataConWorkId con)
540 StgLit lit -> StgLitArg lit
541 _ -> pprPanic "coreToStgArgs" (ppr arg)
543 returnLne (stg_arg : stg_args, fvs)
546 -- ---------------------------------------------------------------------------
547 -- The magic for lets:
548 -- ---------------------------------------------------------------------------
551 :: Bool -- True <=> yes, we are let-no-escaping this let
552 -> CoreBind -- bindings
554 -> LneM (StgExpr, -- new let
555 FreeVarsInfo, -- variables free in the whole let
556 EscVarsSet, -- variables that escape from the whole let
557 Bool) -- True <=> none of the binders in the bindings
558 -- is among the escaping vars
560 coreToStgLet let_no_escape bind body
561 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
563 -- Do the bindings, setting live_in_cont to empty if
564 -- we ain't in a let-no-escape world
565 getVarsLiveInCont `thenLne` \ live_in_cont ->
566 setVarsLiveInCont (if let_no_escape
569 (vars_bind rec_body_fvs bind)
570 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
573 extendVarEnvLne env_ext (
574 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
575 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
577 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
578 body2, body_fvs, body_escs, getLiveVars body_lv_info)
581 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
582 body2, body_fvs, body_escs, body_lvs) ->
585 -- Compute the new let-expression
587 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
588 | otherwise = StgLet bind2 body2
591 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
594 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
596 real_bind_escs = if let_no_escape then
600 -- Everything escapes which is free in the bindings
602 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
604 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
607 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
610 -- Debugging code as requested by Andrew Kennedy
611 checked_no_binder_escapes
612 | not no_binder_escapes && any is_join_var binders
613 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
615 | otherwise = no_binder_escapes
617 checked_no_binder_escapes = no_binder_escapes
620 -- Mustn't depend on the passed-in let_no_escape flag, since
621 -- no_binder_escapes is used by the caller to derive the flag!
627 checked_no_binder_escapes
630 set_of_binders = mkVarSet binders
631 binders = bindersOf bind
633 mk_binding bind_lv_info binder rhs
634 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
636 live_vars | let_no_escape = addLiveVar bind_lv_info binder
637 | otherwise = unitLiveVar binder
638 -- c.f. the invariant on NestedLet
640 vars_bind :: FreeVarsInfo -- Free var info for body of binding
644 EscVarsSet, -- free vars; escapee vars
645 LiveInfo, -- Vars and CAFs live in binding
646 [(Id, HowBound)]) -- extension to environment
649 vars_bind body_fvs (NonRec binder rhs)
650 = coreToStgRhs body_fvs [] (binder,rhs)
651 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
653 env_ext_item = mk_binding bind_lv_info binder rhs
655 returnLne (StgNonRec binder rhs2,
656 bind_fvs, escs, bind_lv_info, [env_ext_item])
659 vars_bind body_fvs (Rec pairs)
660 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
662 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
663 binders = map fst pairs
664 env_ext = [ mk_binding bind_lv_info b rhs
667 extendVarEnvLne env_ext (
668 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
669 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
671 bind_fvs = unionFVInfos fvss
672 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
673 escs = unionVarSets escss
675 returnLne (StgRec (binders `zip` rhss2),
676 bind_fvs, escs, bind_lv_info, env_ext)
680 is_join_var :: Id -> Bool
681 -- A hack (used only for compiler debuggging) to tell if
682 -- a variable started life as a join point ($j)
683 is_join_var j = occNameString (getOccName j) == "$j"
687 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
690 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
692 coreToStgRhs scope_fv_info binders (bndr, rhs)
693 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
694 getEnvLne `thenLne` \ env ->
695 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
696 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
697 rhs_fvs, lv_info, rhs_escs)
699 bndr_info = lookupFVInfo scope_fv_info bndr
701 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
703 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
704 = StgRhsCon noCCS con args
706 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
707 = StgRhsClosure noCCS binder_info
712 mkStgRhs rhs_fvs srt binder_info rhs
713 = StgRhsClosure noCCS binder_info
719 SDM: disabled. Eval/Apply can't handle functions with arity zero very
720 well; and making these into simple non-updatable thunks breaks other
721 assumptions (namely that they will be entered only once).
723 upd_flag | isPAP env rhs = ReEntrant
724 | otherwise = Updatable
728 upd = if isOnceDem dem
729 then (if isNotTop toplev
730 then SingleEntry -- HA! Paydirt for "dem"
733 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
737 -- For now we forbid SingleEntry CAFs; they tickle the
738 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
739 -- and I don't understand why. There's only one SE_CAF (well,
740 -- only one that tickled a great gaping bug in an earlier attempt
741 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
742 -- specifically Main.lvl6 in spectral/cryptarithm2.
743 -- So no great loss. KSW 2000-07.
747 Detect thunks which will reduce immediately to PAPs, and make them
748 non-updatable. This has several advantages:
750 - the non-updatable thunk behaves exactly like the PAP,
752 - the thunk is more efficient to enter, because it is
753 specialised to the task.
755 - we save one update frame, one stg_update_PAP, one update
756 and lots of PAP_enters.
758 - in the case where the thunk is top-level, we save building
759 a black hole and futhermore the thunk isn't considered to
760 be a CAF any more, so it doesn't appear in any SRTs.
762 We do it here, because the arity information is accurate, and we need
763 to do it before the SRT pass to save the SRT entries associated with
766 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
768 arity = stgArity f (lookupBinding env f)
772 %************************************************************************
774 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
776 %************************************************************************
778 There's a lot of stuff to pass around, so we use this @LneM@ monad to
779 help. All the stuff here is only passed *down*.
782 type LneM a = IdEnv HowBound
783 -> LiveInfo -- Vars and CAFs live in continuation
786 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
787 -- i.e. ones with a nested (non-top-level) binding
788 CafSet) -- Static live variables;
789 -- i.e. top-level variables that are CAFs or refer to them
791 type EscVarsSet = IdSet
795 = ImportBound -- Used only as a response to lookupBinding; never
796 -- exists in the range of the (IdEnv HowBound)
798 | LetBound -- A let(rec) in this module
799 LetInfo -- Whether top level or nested
800 Arity -- Its arity (local Ids don't have arity info at this point)
802 | LambdaBound -- Used for both lambda and case
805 = TopLet -- top level things
806 | NestedLet LiveInfo -- For nested things, what is live if this
807 -- thing is live? Invariant: the binder
808 -- itself is always a member of
809 -- the dynamic set of its own LiveInfo
811 isLetBound (LetBound _ _) = True
812 isLetBound other = False
814 topLevelBound ImportBound = True
815 topLevelBound (LetBound TopLet _) = True
816 topLevelBound other = False
819 For a let(rec)-bound variable, x, we record LiveInfo, the set of
820 variables that are live if x is live. This LiveInfo comprises
821 (a) dynamic live variables (ones with a non-top-level binding)
822 (b) static live variabes (CAFs or things that refer to CAFs)
824 For "normal" variables (a) is just x alone. If x is a let-no-escaped
825 variable then x is represented by a code pointer and a stack pointer
826 (well, one for each stack). So all of the variables needed in the
827 execution of x are live if x is, and are therefore recorded in the
828 LetBound constructor; x itself *is* included.
830 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
834 emptyLiveInfo :: LiveInfo
835 emptyLiveInfo = (emptyVarSet,emptyVarSet)
837 unitLiveVar :: Id -> LiveInfo
838 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
840 unitLiveCaf :: Id -> LiveInfo
841 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
843 addLiveVar :: LiveInfo -> Id -> LiveInfo
844 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
846 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
847 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
849 mkSRT :: LiveInfo -> SRT
850 mkSRT (_, cafs) = SRTEntries cafs
852 getLiveVars :: LiveInfo -> StgLiveVars
853 getLiveVars (lvs, _) = lvs
857 The std monad functions:
859 initLne :: IdEnv HowBound -> LneM a -> a
860 initLne env m = m env emptyLiveInfo
864 {-# INLINE thenLne #-}
865 {-# INLINE returnLne #-}
867 returnLne :: a -> LneM a
868 returnLne e env lvs_cont = e
870 thenLne :: LneM a -> (a -> LneM b) -> LneM b
871 thenLne m k env lvs_cont
872 = k (m env lvs_cont) env lvs_cont
874 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
875 mapAndUnzipLne f [] = returnLne ([],[])
876 mapAndUnzipLne f (x:xs)
877 = f x `thenLne` \ (r1, r2) ->
878 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
879 returnLne (r1:rs1, r2:rs2)
881 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
882 mapAndUnzip3Lne f [] = returnLne ([],[],[])
883 mapAndUnzip3Lne f (x:xs)
884 = f x `thenLne` \ (r1, r2, r3) ->
885 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
886 returnLne (r1:rs1, r2:rs2, r3:rs3)
888 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
889 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
890 mapAndUnzip4Lne f (x:xs)
891 = f x `thenLne` \ (r1, r2, r3, r4) ->
892 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
893 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
895 fixLne :: (a -> LneM a) -> LneM a
896 fixLne expr env lvs_cont
899 result = expr result env lvs_cont
902 Functions specific to this monad:
905 getVarsLiveInCont :: LneM LiveInfo
906 getVarsLiveInCont env lvs_cont = lvs_cont
908 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
909 setVarsLiveInCont new_lvs_cont expr env lvs_cont
910 = expr env new_lvs_cont
912 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
913 extendVarEnvLne ids_w_howbound expr env lvs_cont
914 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
916 lookupVarLne :: Id -> LneM HowBound
917 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
919 getEnvLne :: LneM (IdEnv HowBound)
920 getEnvLne env lvs_cont = returnLne env env lvs_cont
922 lookupBinding :: IdEnv HowBound -> Id -> HowBound
923 lookupBinding env v = case lookupVarEnv env v of
925 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
928 -- The result of lookupLiveVarsForSet, a set of live variables, is
929 -- only ever tacked onto a decorated expression. It is never used as
930 -- the basis of a control decision, which might give a black hole.
932 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
933 freeVarsToLiveVars fvs env live_in_cont
934 = returnLne live_info env live_in_cont
936 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
937 lvs_from_fvs = map do_one (allFreeIds fvs)
939 do_one (v, how_bound)
941 ImportBound -> unitLiveCaf v -- Only CAF imports are
944 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
945 | otherwise -> emptyLiveInfo
947 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
948 -- (see the invariant on NestedLet)
950 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
953 %************************************************************************
955 \subsection[Free-var info]{Free variable information}
957 %************************************************************************
960 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
961 -- The Var is so we can gather up the free variables
964 -- The HowBound info just saves repeated lookups;
965 -- we look up just once when we encounter the occurrence.
966 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
967 -- Imported Ids without CAF refs are simply
968 -- not put in the FreeVarsInfo for an expression.
969 -- See singletonFVInfo and freeVarsToLiveVars
971 -- StgBinderInfo records how it occurs; notably, we
972 -- are interested in whether it only occurs in saturated
973 -- applications, because then we don't need to build a
975 -- If f is mapped to noBinderInfo, that means
976 -- that f *is* mentioned (else it wouldn't be in the
977 -- IdEnv at all), but perhaps in an unsaturated applications.
979 -- All case/lambda-bound things are also mapped to
980 -- noBinderInfo, since we aren't interested in their
983 -- For ILX we track free var info for type variables too;
984 -- hence VarEnv not IdEnv
988 emptyFVInfo :: FreeVarsInfo
989 emptyFVInfo = emptyVarEnv
991 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
992 -- Don't record non-CAF imports at all, to keep free-var sets small
993 singletonFVInfo id ImportBound info
994 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
995 | otherwise = emptyVarEnv
996 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
998 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
999 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1001 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1002 -- Type variables must be lambda-bound
1004 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1005 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1007 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1008 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1010 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1011 minusFVBinders vs fv = foldr minusFVBinder fv vs
1013 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1014 minusFVBinder v fv | isId v && opt_RuntimeTypes
1015 = (fv `delVarEnv` v) `unionFVInfo`
1016 tyvarFVInfo (tyVarsOfType (idType v))
1017 | otherwise = fv `delVarEnv` v
1018 -- When removing a binder, remember to add its type variables
1019 -- c.f. CoreFVs.delBinderFV
1021 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1022 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1024 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1025 -- Find how the given Id is used.
1026 -- Externally visible things may be used any old how
1028 | isExternalName (idName id) = noBinderInfo
1029 | otherwise = case lookupVarEnv fvs id of
1030 Nothing -> noBinderInfo
1031 Just (_,_,info) -> info
1033 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1034 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1036 -- Non-top-level things only, both type variables and ids
1037 -- (type variables only if opt_RuntimeTypes)
1038 getFVs :: FreeVarsInfo -> [Var]
1039 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1040 not (topLevelBound how_bound) ]
1042 getFVSet :: FreeVarsInfo -> VarSet
1043 getFVSet fvs = mkVarSet (getFVs fvs)
1045 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1046 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1047 (id1, hb1, combineStgBinderInfo info1 info2)
1050 -- The HowBound info for a variable in the FVInfo should be consistent
1051 check_eq_how_bound ImportBound ImportBound = True
1052 check_eq_how_bound LambdaBound LambdaBound = True
1053 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1054 check_eq_how_bound hb1 hb2 = False
1056 check_eq_li (NestedLet _) (NestedLet _) = True
1057 check_eq_li TopLet TopLet = True
1058 check_eq_li li1 li2 = False
1064 filterStgBinders :: [Var] -> [Var]
1065 filterStgBinders bndrs
1066 | opt_RuntimeTypes = bndrs
1067 | otherwise = 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