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"
19 import TyCon ( isAlgTyCon )
22 import Var ( Var, globalIdDetails, varType )
24 import MkId ( unsafeCoerceId )
28 import CostCentre ( noCCS )
31 import DataCon ( dataConWrapId )
32 import Maybes ( maybeToBool )
33 import Name ( getOccName, isExternallyVisibleName, isDllName )
34 import OccName ( occNameUserString )
35 import BasicTypes ( TopLevelFlag(..), isNotTopLevel, Arity )
36 import CmdLineOpts ( DynFlags, opt_RuntimeTypes )
37 import FastTypes hiding ( fastOr )
38 import Util ( listLengthCmp )
44 %************************************************************************
46 \subsection[live-vs-free-doc]{Documentation}
48 %************************************************************************
50 (There is other relevant documentation in codeGen/CgLetNoEscape.)
52 The actual Stg datatype is decorated with {\em live variable}
53 information, as well as {\em free variable} information. The two are
54 {\em not} the same. Liveness is an operational property rather than a
55 semantic one. A variable is live at a particular execution point if
56 it can be referred to {\em directly} again. In particular, a dead
57 variable's stack slot (if it has one):
60 should be stubbed to avoid space leaks, and
62 may be reused for something else.
65 There ought to be a better way to say this. Here are some examples:
72 Just after the `in', v is live, but q is dead. If the whole of that
73 let expression was enclosed in a case expression, thus:
75 case (let v = [q] \[x] -> e in ...v...) of
78 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
79 we'll return later to the @alts@ and need it.
81 Let-no-escapes make this a bit more interesting:
83 let-no-escape v = [q] \ [x] -> e
87 Here, @q@ is still live at the `in', because @v@ is represented not by
88 a closure but by the current stack state. In other words, if @v@ is
89 live then so is @q@. Furthermore, if @e@ mentions an enclosing
90 let-no-escaped variable, then {\em its} free variables are also live
93 %************************************************************************
95 \subsection[caf-info]{Collecting live CAF info}
97 %************************************************************************
99 In this pass we also collect information on which CAFs are live for
100 constructing SRTs (see SRT.lhs).
102 A top-level Id has CafInfo, which is
104 - MayHaveCafRefs, if it may refer indirectly to
106 - NoCafRefs if it definitely doesn't
108 we collect the CafInfo first by analysing the original Core expression, and
109 also place this information in the environment.
111 During CoreToStg, we then pin onto each binding and case expression, a
112 list of Ids which represents the "live" CAFs at that point. The meaning
113 of "live" here is the same as for live variables, see above (which is
114 why it's convenient to collect CAF information here rather than elsewhere).
116 The later SRT pass takes these lists of Ids and uses them to construct
117 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
121 Interaction of let-no-escape with SRTs [Sept 01]
122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 let-no-escape x = ...caf1...caf2...
129 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
130 build SRTs just as if x's defn was inlined at each call site, and
131 that means that x's CAF refs get duplicated in the overall SRT.
133 This is unlike ordinary lets, in which the CAF refs are not duplicated.
135 We could fix this loss of (static) sharing by making a sort of pseudo-closure
136 for x, solely to put in the SRTs lower down.
139 %************************************************************************
141 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
143 %************************************************************************
146 coreToStg :: DynFlags -> [CoreBind] -> IO [StgBinding]
149 where (_, _, pgm') = coreTopBindsToStg emptyVarEnv pgm
151 coreExprToStg :: CoreExpr -> StgExpr
153 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
157 :: IdEnv HowBound -- environment for the bindings
159 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
161 coreTopBindsToStg env [] = (env, emptyFVInfo, [])
162 coreTopBindsToStg env (b:bs)
163 = (env2, fvs2, b':bs')
165 -- env accumulates down the list of binds, fvs accumulates upwards
166 (env1, fvs2, b' ) = coreTopBindToStg env fvs1 b
167 (env2, fvs1, bs') = coreTopBindsToStg env1 bs
172 -> FreeVarsInfo -- Info about the body
174 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
176 coreTopBindToStg env body_fvs (NonRec id rhs)
178 caf_info = hasCafRefs env rhs
179 env' = extendVarEnv env id how_bound
180 how_bound = LetBound (TopLet caf_info) (manifestArity rhs)
182 (stg_rhs, fvs', lv_info) =
184 coreToStgRhs body_fvs TopLevel (id,rhs) `thenLne` \ (stg_rhs, fvs', _) ->
185 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
186 returnLne (stg_rhs, fvs', lv_info)
189 bind = StgNonRec (mkSRT lv_info) id stg_rhs
191 ASSERT2(isLocalId id || idArity id == manifestArity rhs, ppr id)
192 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
193 ASSERT2(consistent caf_info bind, ppr id)
194 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
195 (env', fvs' `unionFVInfo` body_fvs, bind)
197 coreTopBindToStg env body_fvs (Rec pairs)
199 (binders, rhss) = unzip pairs
201 -- To calculate caf_info, we initially map
202 -- all the binders to NoCafRefs
203 env1 = extendVarEnvList env
204 [ (b, LetBound (TopLet NoCafRefs) (error "no arity"))
207 caf_info = hasCafRefss env1{-NB: not env'-} rhss
209 env' = extendVarEnvList env
210 [ (b, LetBound (TopLet caf_info) (manifestArity rhs))
213 (stg_rhss, fvs', lv_info)
215 mapAndUnzip3Lne (coreToStgRhs body_fvs TopLevel) pairs
216 `thenLne` \ (stg_rhss, fvss', _) ->
217 let fvs' = unionFVInfos fvss' in
218 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
219 returnLne (stg_rhss, fvs', lv_info)
222 bind = StgRec (mkSRT lv_info) (zip binders stg_rhss)
224 ASSERT2(and [isLocalId bndr || manifestArity rhs == idArity bndr | (bndr,rhs) <- pairs], ppr binders)
225 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
226 ASSERT2(consistent caf_info bind, ppr binders)
227 -- WARN(not (consistent caf_info bind), ppr binders <+> ppr cafs <+> ppCafInfo caf_info)
228 (env', fvs' `unionFVInfo` body_fvs, bind)
231 consistent caf_info bind = mayHaveCafRefs caf_info == stgBindHasCafRefs bind
236 :: FreeVarsInfo -- Free var info for the scope of the binding
239 -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
241 coreToStgRhs scope_fv_info top (binder, rhs)
242 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
243 returnLne (mkStgRhs top rhs_fvs binder_info new_rhs,
246 binder_info = lookupFVInfo scope_fv_info binder
248 mkStgRhs :: TopLevelFlag -> FreeVarsInfo -> StgBinderInfo
251 mkStgRhs top rhs_fvs binder_info (StgLam _ bndrs body)
252 = StgRhsClosure noCCS binder_info
257 mkStgRhs top rhs_fvs binder_info (StgConApp con args)
258 | isNotTopLevel top || not (isDllConApp con args)
259 = StgRhsCon noCCS con args
261 mkStgRhs top rhs_fvs binder_info rhs
262 = StgRhsClosure noCCS binder_info
267 updatable args body | null args && isPAP body = ReEntrant
268 | otherwise = Updatable
270 upd = if isOnceDem dem
271 then (if isNotTop toplev
272 then SingleEntry -- HA! Paydirt for "dem"
275 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
279 -- For now we forbid SingleEntry CAFs; they tickle the
280 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
281 -- and I don't understand why. There's only one SE_CAF (well,
282 -- only one that tickled a great gaping bug in an earlier attempt
283 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
284 -- specifically Main.lvl6 in spectral/cryptarithm2.
285 -- So no great loss. KSW 2000-07.
289 Detect thunks which will reduce immediately to PAPs, and make them
290 non-updatable. This has several advantages:
292 - the non-updatable thunk behaves exactly like the PAP,
294 - the thunk is more efficient to enter, because it is
295 specialised to the task.
297 - we save one update frame, one stg_update_PAP, one update
298 and lots of PAP_enters.
300 - in the case where the thunk is top-level, we save building
301 a black hole and futhermore the thunk isn't considered to
302 be a CAF any more, so it doesn't appear in any SRTs.
304 We do it here, because the arity information is accurate, and we need
305 to do it before the SRT pass to save the SRT entries associated with
309 isPAP (StgApp f args) = listLengthCmp args (idArity f) == LT -- idArity f > length args
314 -- ---------------------------------------------------------------------------
316 -- ---------------------------------------------------------------------------
321 -> LneM (StgExpr, -- Decorated STG expr
322 FreeVarsInfo, -- Its free vars (NB free, not live)
323 EscVarsSet) -- Its escapees, a subset of its free vars;
324 -- also a subset of the domain of the envt
325 -- because we are only interested in the escapees
326 -- for vars which might be turned into
327 -- let-no-escaped ones.
330 The second and third components can be derived in a simple bottom up pass, not
331 dependent on any decisions about which variables will be let-no-escaped or
332 not. The first component, that is, the decorated expression, may then depend
333 on these components, but it in turn is not scrutinised as the basis for any
334 decisions. Hence no black holes.
337 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
338 coreToStgExpr (Var v) = coreToStgApp Nothing v []
340 coreToStgExpr expr@(App _ _)
341 = coreToStgApp Nothing f args
343 (f, args) = myCollectArgs expr
345 coreToStgExpr expr@(Lam _ _)
347 (args, body) = myCollectBinders expr
348 args' = filterStgBinders args
350 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
351 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
353 fvs = args' `minusFVBinders` body_fvs
354 escs = body_escs `delVarSetList` args'
355 result_expr | null args' = body
356 | otherwise = StgLam (exprType expr) args' body
358 returnLne (result_expr, fvs, escs)
360 coreToStgExpr (Note (SCC cc) expr)
361 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
362 returnLne (StgSCC cc expr2, fvs, escs) )
365 -- For ILX, convert (__coerce__ to_ty from_ty e)
366 -- into (coerce to_ty from_ty e)
367 -- where coerce is real function
368 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
369 = coreToStgExpr (mkApps (Var unsafeCoerceId)
370 [Type from_ty, Type to_ty, expr])
373 coreToStgExpr (Note other_note expr)
376 -- Cases require a little more real work.
378 coreToStgExpr (Case scrut bndr alts)
379 = extendVarEnvLne [(bndr, LambdaBound)] (
380 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
381 returnLne ( mkStgAlts (idType bndr) alts2,
383 unionVarSets escs_s )
384 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
386 -- Determine whether the default binder is dead or not
387 -- This helps the code generator to avoid generating an assignment
388 -- for the case binder (is extremely rare cases) ToDo: remove.
389 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
390 | otherwise = bndr `setIdOccInfo` IAmDead
392 -- Don't consider the default binder as being 'live in alts',
393 -- since this is from the point of view of the case expr, where
394 -- the default binder is not free.
395 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
396 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
399 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
401 -- We tell the scrutinee that everything
402 -- live in the alts is live in it, too.
403 setVarsLiveInCont alts_lv_info (
404 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
405 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
406 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
408 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
411 StgCase scrut2 (getLiveVars scrut_lv_info)
412 (getLiveVars alts_lv_info)
416 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
417 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
418 -- You might think we should have scrut_escs, not
419 -- (getFVSet scrut_fvs), but actually we can't call, and
420 -- then return from, a let-no-escape thing.
423 vars_alt (con, binders, rhs)
424 = let -- Remove type variables
425 binders' = filterStgBinders binders
427 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
428 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
430 -- Records whether each param is used in the RHS
431 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
433 returnLne ( (con, binders', good_use_mask, rhs2),
434 binders' `minusFVBinders` rhs_fvs,
435 rhs_escs `delVarSetList` binders' )
436 -- ToDo: remove the delVarSet;
437 -- since escs won't include any of these binders
440 Lets not only take quite a bit of work, but this is where we convert
441 then to let-no-escapes, if we wish.
443 (Meanwhile, we don't expect to see let-no-escapes...)
445 coreToStgExpr (Let bind body)
446 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
447 coreToStgLet no_binder_escapes bind body
448 ) `thenLne` \ (new_let, fvs, escs, _) ->
450 returnLne (new_let, fvs, escs)
454 mkStgAlts scrut_ty orig_alts
455 | is_prim_case = StgPrimAlts (tyConAppTyCon scrut_ty) prim_alts deflt
456 | otherwise = StgAlgAlts maybe_tycon alg_alts deflt
458 is_prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
460 prim_alts = [(lit, rhs) | (LitAlt lit, _, _, rhs) <- other_alts]
461 alg_alts = [(con, bndrs, use, rhs) | (DataAlt con, bndrs, use, rhs) <- other_alts]
464 = case orig_alts of -- DEFAULT is always first if it's there at all
465 (DEFAULT, _, _, rhs) : other_alts -> (other_alts, StgBindDefault rhs)
466 other -> (orig_alts, StgNoDefault)
468 maybe_tycon = case alg_alts of
469 -- Get the tycon from the data con
470 (dc, _, _, _) : _rest -> Just (dataConTyCon dc)
472 -- Otherwise just do your best
473 [] -> case splitTyConApp_maybe (repType scrut_ty) of
474 Just (tc,_) | isAlgTyCon tc -> Just tc
479 -- ---------------------------------------------------------------------------
481 -- ---------------------------------------------------------------------------
485 :: Maybe UpdateFlag -- Just upd <=> this application is
486 -- the rhs of a thunk binding
487 -- x = [...] \upd [] -> the_app
488 -- with specified update flag
490 -> [CoreArg] -- Arguments
491 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
493 coreToStgApp maybe_thunk_body f args
494 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
495 lookupVarLne f `thenLne` \ how_bound ->
498 n_val_args = valArgCount args
499 not_letrec_bound = not (isLetBound how_bound)
501 = let fvs = singletonFVInfo f how_bound fun_occ in
502 -- e.g. (f :: a -> int) (x :: a)
503 -- Here the free variables are "f", "x" AND the type variable "a"
504 -- coreToStgArgs will deal with the arguments recursively
505 if opt_RuntimeTypes then
506 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (varType f))
509 -- Mostly, the arity info of a function is in the fn's IdInfo
510 -- But new bindings introduced by CoreSat may not have no
511 -- arity info; it would do us no good anyway. For example:
512 -- let f = \ab -> e in f
513 -- No point in having correct arity info for f!
514 -- Hence the hasArity stuff below.
515 -- NB: f_arity is only consulted for LetBound things
516 f_arity = case how_bound of
517 LetBound _ arity -> arity
518 ImportBound -> idArity f
520 saturated = f_arity <= n_val_args
523 | not_letrec_bound = noBinderInfo -- Uninteresting variable
524 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
525 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
528 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
529 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
530 -- saturated call doesn't escape
531 -- (let-no-escape applies to 'thunks' too)
533 | otherwise = unitVarSet f -- Inexact application; it does escape
535 -- At the moment of the call:
537 -- either the function is *not* let-no-escaped, in which case
538 -- nothing is live except live_in_cont
539 -- or the function *is* let-no-escaped in which case the
540 -- variables it uses are live, but still the function
541 -- itself is not. PS. In this case, the function's
542 -- live vars should already include those of the
543 -- continuation, but it does no harm to just union the
546 res_ty = exprType (mkApps (Var f) args)
547 app = case globalIdDetails f of
548 DataConId dc | saturated -> StgConApp dc args'
549 PrimOpId op -> ASSERT( saturated )
550 StgOpApp (StgPrimOp op) args' res_ty
551 FCallId call -> ASSERT( saturated )
552 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
553 _other -> StgApp f args'
558 fun_fvs `unionFVInfo` args_fvs,
559 fun_escs `unionVarSet` (getFVSet args_fvs)
560 -- All the free vars of the args are disqualified
561 -- from being let-no-escaped.
566 -- ---------------------------------------------------------------------------
568 -- This is the guy that turns applications into A-normal form
569 -- ---------------------------------------------------------------------------
571 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
573 = returnLne ([], emptyFVInfo)
575 coreToStgArgs (Type ty : args) -- Type argument
576 = coreToStgArgs args `thenLne` \ (args', fvs) ->
577 if opt_RuntimeTypes then
578 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
580 returnLne (args', fvs)
582 coreToStgArgs (arg : args) -- Non-type argument
583 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
584 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
586 fvs = args_fvs `unionFVInfo` arg_fvs
587 stg_arg = case arg' of
588 StgApp v [] -> StgVarArg v
589 StgConApp con [] -> StgVarArg (dataConWrapId con)
590 StgLit lit -> StgLitArg lit
591 _ -> pprPanic "coreToStgArgs" (ppr arg)
593 returnLne (stg_arg : stg_args, fvs)
596 -- ---------------------------------------------------------------------------
597 -- The magic for lets:
598 -- ---------------------------------------------------------------------------
601 :: Bool -- True <=> yes, we are let-no-escaping this let
602 -> CoreBind -- bindings
604 -> LneM (StgExpr, -- new let
605 FreeVarsInfo, -- variables free in the whole let
606 EscVarsSet, -- variables that escape from the whole let
607 Bool) -- True <=> none of the binders in the bindings
608 -- is among the escaping vars
610 coreToStgLet let_no_escape bind body
611 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
613 -- Do the bindings, setting live_in_cont to empty if
614 -- we ain't in a let-no-escape world
615 getVarsLiveInCont `thenLne` \ live_in_cont ->
616 setVarsLiveInCont (if let_no_escape
619 (vars_bind rec_body_fvs bind)
620 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
623 extendVarEnvLne env_ext (
624 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
625 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
627 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
628 body2, body_fvs, body_escs, getLiveVars body_lv_info)
631 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
632 body2, body_fvs, body_escs, body_lvs) ->
635 -- Compute the new let-expression
637 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
638 | otherwise = StgLet bind2 body2
641 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
644 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
646 real_bind_escs = if let_no_escape then
650 -- Everything escapes which is free in the bindings
652 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
654 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
657 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
660 -- Debugging code as requested by Andrew Kennedy
661 checked_no_binder_escapes
662 | not no_binder_escapes && any is_join_var binders
663 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
665 | otherwise = no_binder_escapes
667 checked_no_binder_escapes = no_binder_escapes
670 -- Mustn't depend on the passed-in let_no_escape flag, since
671 -- no_binder_escapes is used by the caller to derive the flag!
677 checked_no_binder_escapes
680 set_of_binders = mkVarSet binders
681 binders = bindersOf bind
683 mk_binding bind_lv_info binder rhs
684 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
686 live_vars | let_no_escape = addLiveVar bind_lv_info binder
687 | otherwise = unitLiveVar binder
688 -- c.f. the invariant on NestedLet
690 vars_bind :: FreeVarsInfo -- Free var info for body of binding
694 EscVarsSet, -- free vars; escapee vars
695 LiveInfo, -- Vars and CAFs live in binding
696 [(Id, HowBound)]) -- extension to environment
699 vars_bind body_fvs (NonRec binder rhs)
700 = coreToStgRhs body_fvs NotTopLevel (binder,rhs)
701 `thenLne` \ (rhs2, bind_fvs, escs) ->
703 freeVarsToLiveVars bind_fvs `thenLne` \ bind_lv_info ->
705 env_ext_item = mk_binding bind_lv_info binder rhs
707 returnLne (StgNonRec (mkSRT bind_lv_info) binder rhs2,
708 bind_fvs, escs, bind_lv_info, [env_ext_item])
711 vars_bind body_fvs (Rec pairs)
712 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
714 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
715 binders = map fst pairs
716 env_ext = [ mk_binding bind_lv_info b rhs
719 extendVarEnvLne env_ext (
720 mapAndUnzip3Lne (coreToStgRhs rec_scope_fvs NotTopLevel) pairs
721 `thenLne` \ (rhss2, fvss, escss) ->
723 bind_fvs = unionFVInfos fvss
724 escs = unionVarSets escss
726 freeVarsToLiveVars (binders `minusFVBinders` bind_fvs)
727 `thenLne` \ bind_lv_info ->
729 returnLne (StgRec (mkSRT bind_lv_info) (binders `zip` rhss2),
730 bind_fvs, escs, bind_lv_info, env_ext)
734 is_join_var :: Id -> Bool
735 -- A hack (used only for compiler debuggging) to tell if
736 -- a variable started life as a join point ($j)
737 is_join_var j = occNameUserString (getOccName j) == "$j"
741 %************************************************************************
743 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
745 %************************************************************************
747 There's a lot of stuff to pass around, so we use this @LneM@ monad to
748 help. All the stuff here is only passed *down*.
751 type LneM a = IdEnv HowBound
752 -> LiveInfo -- Vars and CAFs live in continuation
755 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
756 -- i.e. ones with a nested (non-top-level) binding
757 CafSet) -- Static live variables;
758 -- i.e. top-level variables that are CAFs or refer to them
760 type EscVarsSet = IdSet
764 = ImportBound -- Used only as a response to lookupBinding; never
765 -- exists in the range of the (IdEnv HowBound)
767 | LetBound -- A let(rec) in this module
768 LetInfo -- Whether top level or nested
769 Arity -- Its arity (local Ids don't have arity info at this point)
771 | LambdaBound -- Used for both lambda and case
773 data LetInfo = NestedLet LiveInfo -- For nested things, what is live if this thing is live?
774 -- Invariant: the binder itself is always a member of
775 -- the dynamic set of its own LiveInfo
776 | TopLet CafInfo -- For top level things, is it a CAF, or can it refer to one?
778 isLetBound (LetBound _ _) = True
779 isLetBound other = False
781 topLevelBound ImportBound = True
782 topLevelBound (LetBound (TopLet _) _) = True
783 topLevelBound other = False
786 For a let(rec)-bound variable, x, we record LiveInfo, the set of
787 variables that are live if x is live. This LiveInfo comprises
788 (a) dynamic live variables (ones with a non-top-level binding)
789 (b) static live variabes (CAFs or things that refer to CAFs)
791 For "normal" variables (a) is just x alone. If x is a let-no-escaped
792 variable then x is represented by a code pointer and a stack pointer
793 (well, one for each stack). So all of the variables needed in the
794 execution of x are live if x is, and are therefore recorded in the
795 LetBound constructor; x itself *is* included.
797 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
801 emptyLiveInfo :: LiveInfo
802 emptyLiveInfo = (emptyVarSet,emptyVarSet)
804 unitLiveVar :: Id -> LiveInfo
805 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
807 unitLiveCaf :: Id -> LiveInfo
808 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
810 addLiveVar :: LiveInfo -> Id -> LiveInfo
811 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
813 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
814 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
816 mkSRT :: LiveInfo -> SRT
817 mkSRT (_, cafs) = SRTEntries cafs
819 getLiveVars :: LiveInfo -> StgLiveVars
820 getLiveVars (lvs, _) = lvs
824 The std monad functions:
826 initLne :: IdEnv HowBound -> LneM a -> a
827 initLne env m = m env emptyLiveInfo
831 {-# INLINE thenLne #-}
832 {-# INLINE returnLne #-}
834 returnLne :: a -> LneM a
835 returnLne e env lvs_cont = e
837 thenLne :: LneM a -> (a -> LneM b) -> LneM b
838 thenLne m k env lvs_cont
839 = k (m env lvs_cont) env lvs_cont
841 mapLne :: (a -> LneM b) -> [a] -> LneM [b]
842 mapLne f [] = returnLne []
844 = f x `thenLne` \ r ->
845 mapLne f xs `thenLne` \ rs ->
848 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
850 mapAndUnzipLne f [] = returnLne ([],[])
851 mapAndUnzipLne f (x:xs)
852 = f x `thenLne` \ (r1, r2) ->
853 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
854 returnLne (r1:rs1, r2:rs2)
856 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
858 mapAndUnzip3Lne f [] = returnLne ([],[],[])
859 mapAndUnzip3Lne f (x:xs)
860 = f x `thenLne` \ (r1, r2, r3) ->
861 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
862 returnLne (r1:rs1, r2:rs2, r3:rs3)
864 fixLne :: (a -> LneM a) -> LneM a
865 fixLne expr env lvs_cont
868 result = expr result env lvs_cont
871 Functions specific to this monad:
874 getVarsLiveInCont :: LneM LiveInfo
875 getVarsLiveInCont env lvs_cont = lvs_cont
877 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
878 setVarsLiveInCont new_lvs_cont expr env lvs_cont
879 = expr env new_lvs_cont
881 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
882 extendVarEnvLne ids_w_howbound expr env lvs_cont
883 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
885 lookupVarLne :: Id -> LneM HowBound
886 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
888 lookupBinding :: IdEnv HowBound -> Id -> HowBound
889 lookupBinding env v = case lookupVarEnv env v of
891 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
894 -- The result of lookupLiveVarsForSet, a set of live variables, is
895 -- only ever tacked onto a decorated expression. It is never used as
896 -- the basis of a control decision, which might give a black hole.
898 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
899 freeVarsToLiveVars fvs env live_in_cont
900 = returnLne live_info env live_in_cont
902 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
903 lvs_from_fvs = map do_one (allFreeIds fvs)
905 do_one (v, how_bound)
907 ImportBound -> unitLiveCaf v -- Only CAF imports are
909 LetBound (TopLet caf_info) _
910 | mayHaveCafRefs caf_info -> unitLiveCaf v
911 | otherwise -> emptyLiveInfo
913 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
914 -- (see the invariant on NestedLet)
916 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
919 %************************************************************************
921 \subsection[Free-var info]{Free variable information}
923 %************************************************************************
926 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
927 -- The Var is so we can gather up the free variables
930 -- The HowBound info just saves repeated lookups;
931 -- we look up just once when we encounter the occurrence.
932 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
933 -- Imported Ids without CAF refs are simply
934 -- not put in the FreeVarsInfo for an expression.
935 -- See singletonFVInfo and freeVarsToLiveVars
937 -- StgBinderInfo records how it occurs; notably, we
938 -- are interested in whether it only occurs in saturated
939 -- applications, because then we don't need to build a
941 -- If f is mapped to noBinderInfo, that means
942 -- that f *is* mentioned (else it wouldn't be in the
943 -- IdEnv at all), but perhaps in an unsaturated applications.
945 -- All case/lambda-bound things are also mapped to
946 -- noBinderInfo, since we aren't interested in their
949 -- For ILX we track free var info for type variables too;
950 -- hence VarEnv not IdEnv
954 emptyFVInfo :: FreeVarsInfo
955 emptyFVInfo = emptyVarEnv
957 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
958 -- Don't record non-CAF imports at all, to keep free-var sets small
959 singletonFVInfo id ImportBound info
960 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
961 | otherwise = emptyVarEnv
962 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
964 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
965 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
967 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
968 -- Type variables must be lambda-bound
970 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
971 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
973 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
974 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
976 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
977 minusFVBinders vs fv = foldr minusFVBinder fv vs
979 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
980 minusFVBinder v fv | isId v && opt_RuntimeTypes
981 = (fv `delVarEnv` v) `unionFVInfo`
982 tyvarFVInfo (tyVarsOfType (idType v))
983 | otherwise = fv `delVarEnv` v
984 -- When removing a binder, remember to add its type variables
985 -- c.f. CoreFVs.delBinderFV
987 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
988 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
990 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
991 -- Find how the given Id is used.
992 -- Externally visible things may be used any old how
994 | isExternallyVisibleName (idName id) = noBinderInfo
995 | otherwise = case lookupVarEnv fvs id of
996 Nothing -> noBinderInfo
997 Just (_,_,info) -> info
999 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1000 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1002 -- Non-top-level things only, both type variables and ids
1003 -- (type variables only if opt_RuntimeTypes)
1004 getFVs :: FreeVarsInfo -> [Var]
1005 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1006 not (topLevelBound how_bound) ]
1008 getFVSet :: FreeVarsInfo -> VarSet
1009 getFVSet fvs = mkVarSet (getFVs fvs)
1011 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1012 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1013 (id1, hb1, combineStgBinderInfo info1 info2)
1016 -- The HowBound info for a variable in the FVInfo should be consistent
1017 check_eq_how_bound ImportBound ImportBound = True
1018 check_eq_how_bound LambdaBound LambdaBound = True
1019 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1020 check_eq_how_bound hb1 hb2 = False
1022 check_eq_li (NestedLet _) (NestedLet _) = True
1023 check_eq_li (TopLet _) (TopLet _) = True
1024 check_eq_li li1 li2 = False
1030 filterStgBinders :: [Var] -> [Var]
1031 filterStgBinders bndrs
1032 | opt_RuntimeTypes = bndrs
1033 | otherwise = filter isId bndrs
1038 -- Ignore all notes except SCC
1039 myCollectBinders expr
1042 go bs (Lam b e) = go (b:bs) e
1043 go bs e@(Note (SCC _) _) = (reverse bs, e)
1044 go bs (Note _ e) = go bs e
1045 go bs e = (reverse bs, e)
1047 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1048 -- We assume that we only have variables
1049 -- in the function position by now
1053 go (Var v) as = (v, as)
1054 go (App f a) as = go f (a:as)
1055 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1056 go (Note n e) as = go e as
1057 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1060 %************************************************************************
1062 \subsection{Figuring out CafInfo for an expression}
1064 %************************************************************************
1066 hasCafRefs decides whether a top-level closure can point into the dynamic heap.
1067 We mark such things as `MayHaveCafRefs' because this information is
1068 used to decide whether a particular closure needs to be referenced
1071 There are two reasons for setting MayHaveCafRefs:
1072 a) The RHS is a CAF: a top-level updatable thunk.
1073 b) The RHS refers to something that MayHaveCafRefs
1075 Possible improvement: In an effort to keep the number of CAFs (and
1076 hence the size of the SRTs) down, we could also look at the expression and
1077 decide whether it requires a small bounded amount of heap, so we can ignore
1078 it as a CAF. In these cases however, we would need to use an additional
1079 CAF list to keep track of non-collectable CAFs.
1082 hasCafRefs :: IdEnv HowBound -> CoreExpr -> CafInfo
1083 -- Only called for the RHS of top-level lets
1084 hasCafRefss :: IdEnv HowBound -> [CoreExpr] -> CafInfo
1085 -- predicate returns True for a given Id if we look at this Id when
1086 -- calculating the result. Used to *avoid* looking at the CafInfo
1087 -- field for an Id that is part of the current recursive group.
1090 | isCAF expr || isFastTrue (cafRefs p expr) = MayHaveCafRefs
1091 | otherwise = NoCafRefs
1093 -- used for recursive groups. The whole group is set to
1094 -- "MayHaveCafRefs" if at least one of the group is a CAF or
1095 -- refers to any CAFs.
1097 | any isCAF exprs || isFastTrue (cafRefss p exprs) = MayHaveCafRefs
1098 | otherwise = NoCafRefs
1100 -- The environment that cafRefs uses has top-level bindings *only*.
1101 -- We don't bother to add local bindings as cafRefs traverses the expression
1102 -- because they will all be for LocalIds (all nested things are LocalIds)
1103 -- However, we must look in the env first, because some top level things
1104 -- might be local Ids
1107 = case lookupVarEnv p id of
1108 Just (LetBound (TopLet caf_info) _) -> fastBool (mayHaveCafRefs caf_info)
1109 Nothing | isGlobalId id -> fastBool (mayHaveCafRefs (idCafInfo id)) -- Imported
1110 | otherwise -> fastBool False -- Nested binder
1111 _other -> error ("cafRefs " ++ showSDoc (ppr id)) -- No nested things in env
1113 cafRefs p (Lit l) = fastBool False
1114 cafRefs p (App f a) = fastOr (cafRefs p f) (cafRefs p) a
1115 cafRefs p (Lam x e) = cafRefs p e
1116 cafRefs p (Let b e) = fastOr (cafRefss p (rhssOfBind b)) (cafRefs p) e
1117 cafRefs p (Case e bndr alts) = fastOr (cafRefs p e) (cafRefss p) (rhssOfAlts alts)
1118 cafRefs p (Note n e) = cafRefs p e
1119 cafRefs p (Type t) = fastBool False
1121 cafRefss p [] = fastBool False
1122 cafRefss p (e:es) = fastOr (cafRefs p e) (cafRefss p) es
1124 -- hack for lazy-or over FastBool.
1125 fastOr a f x = fastBool (isFastTrue a || isFastTrue (f x))
1127 isCAF :: CoreExpr -> Bool
1128 -- Only called for the RHS of top-level lets
1129 isCAF e = not (rhsIsNonUpd e)
1130 {- ToDo: check type for onceness, i.e. non-updatable thunks? -}
1133 rhsIsNonUpd :: CoreExpr -> Bool
1134 -- True => Value-lambda, constructor, PAP
1135 -- This is a bit like CoreUtils.exprIsValue, with the following differences:
1136 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1138 -- b) (C x xs), where C is a contructors is updatable if the application is
1139 -- dynamic: see isDynConApp
1141 -- c) don't look through unfolding of f in (f x). I'm suspicious of this one
1143 -- This function has to line up with what the update flag
1144 -- for the StgRhs gets set to in mkStgRhs (above)
1146 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1147 -- them as making the RHS re-entrant (non-updatable).
1148 rhsIsNonUpd (Lam b e) = isRuntimeVar b || rhsIsNonUpd e
1149 rhsIsNonUpd (Note (SCC _) e) = False
1150 rhsIsNonUpd (Note _ e) = rhsIsNonUpd e
1151 rhsIsNonUpd other_expr
1152 = go other_expr 0 []
1154 go (Var f) n_args args = idAppIsNonUpd f n_args args
1156 go (App f a) n_args args
1157 | isTypeArg a = go f n_args args
1158 | otherwise = go f (n_args + 1) (a:args)
1160 go (Note (SCC _) f) n_args args = False
1161 go (Note _ f) n_args args = go f n_args args
1163 go other n_args args = False
1165 idAppIsNonUpd :: Id -> Int -> [CoreExpr] -> Bool
1166 idAppIsNonUpd id n_val_args args
1167 | Just con <- isDataConId_maybe id = not (isCrossDllConApp con args)
1168 | otherwise = n_val_args < idArity id
1170 isCrossDllConApp :: DataCon -> [CoreExpr] -> Bool
1171 isCrossDllConApp con args = isDllName (dataConName con) || any isCrossDllArg args
1172 -- Top-level constructor applications can usually be allocated
1173 -- statically, but they can't if
1174 -- a) the constructor, or any of the arguments, come from another DLL
1175 -- b) any of the arguments are LitLits
1176 -- (because we can't refer to static labels in other DLLs).
1177 -- If this happens we simply make the RHS into an updatable thunk,
1178 -- and 'exectute' it rather than allocating it statically.
1179 -- All this should match the decision in (see CoreToStg.coreToStgRhs)
1182 isCrossDllArg :: CoreExpr -> Bool
1183 -- True if somewhere in the expression there's a cross-DLL reference
1184 isCrossDllArg (Type _) = False
1185 isCrossDllArg (Var v) = isDllName (idName v)
1186 isCrossDllArg (Note _ e) = isCrossDllArg e
1187 isCrossDllArg (Lit lit) = isLitLitLit lit
1188 isCrossDllArg (App e1 e2) = isCrossDllArg e1 || isCrossDllArg e2 -- must be a type app
1189 isCrossDllArg (Lam v e) = isCrossDllArg e -- must be a type lam