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 )
43 %************************************************************************
45 \subsection[live-vs-free-doc]{Documentation}
47 %************************************************************************
49 (There is other relevant documentation in codeGen/CgLetNoEscape.)
51 The actual Stg datatype is decorated with {\em live variable}
52 information, as well as {\em free variable} information. The two are
53 {\em not} the same. Liveness is an operational property rather than a
54 semantic one. A variable is live at a particular execution point if
55 it can be referred to {\em directly} again. In particular, a dead
56 variable's stack slot (if it has one):
59 should be stubbed to avoid space leaks, and
61 may be reused for something else.
64 There ought to be a better way to say this. Here are some examples:
71 Just after the `in', v is live, but q is dead. If the whole of that
72 let expression was enclosed in a case expression, thus:
74 case (let v = [q] \[x] -> e in ...v...) of
77 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
78 we'll return later to the @alts@ and need it.
80 Let-no-escapes make this a bit more interesting:
82 let-no-escape v = [q] \ [x] -> e
86 Here, @q@ is still live at the `in', because @v@ is represented not by
87 a closure but by the current stack state. In other words, if @v@ is
88 live then so is @q@. Furthermore, if @e@ mentions an enclosing
89 let-no-escaped variable, then {\em its} free variables are also live
92 %************************************************************************
94 \subsection[caf-info]{Collecting live CAF info}
96 %************************************************************************
98 In this pass we also collect information on which CAFs are live for
99 constructing SRTs (see SRT.lhs).
101 A top-level Id has CafInfo, which is
103 - MayHaveCafRefs, if it may refer indirectly to
105 - NoCafRefs if it definitely doesn't
107 we collect the CafInfo first by analysing the original Core expression, and
108 also place this information in the environment.
110 During CoreToStg, we then pin onto each binding and case expression, a
111 list of Ids which represents the "live" CAFs at that point. The meaning
112 of "live" here is the same as for live variables, see above (which is
113 why it's convenient to collect CAF information here rather than elsewhere).
115 The later SRT pass takes these lists of Ids and uses them to construct
116 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
120 Interaction of let-no-escape with SRTs [Sept 01]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
124 let-no-escape x = ...caf1...caf2...
128 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
129 build SRTs just as if x's defn was inlined at each call site, and
130 that means that x's CAF refs get duplicated in the overall SRT.
132 This is unlike ordinary lets, in which the CAF refs are not duplicated.
134 We could fix this loss of (static) sharing by making a sort of pseudo-closure
135 for x, solely to put in the SRTs lower down.
138 %************************************************************************
140 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
142 %************************************************************************
145 coreToStg :: DynFlags -> [CoreBind] -> IO [StgBinding]
148 where (_, _, pgm') = coreTopBindsToStg emptyVarEnv pgm
150 coreExprToStg :: CoreExpr -> StgExpr
152 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
156 :: IdEnv HowBound -- environment for the bindings
158 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
160 coreTopBindsToStg env [] = (env, emptyFVInfo, [])
161 coreTopBindsToStg env (b:bs)
162 = (env2, fvs2, b':bs')
164 -- env accumulates down the list of binds, fvs accumulates upwards
165 (env1, fvs2, b' ) = coreTopBindToStg env fvs1 b
166 (env2, fvs1, bs') = coreTopBindsToStg env1 bs
171 -> FreeVarsInfo -- Info about the body
173 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
175 coreTopBindToStg env body_fvs (NonRec id rhs)
177 caf_info = hasCafRefs env rhs
178 env' = extendVarEnv env id how_bound
179 how_bound = LetBound (TopLet caf_info) (manifestArity rhs)
181 (stg_rhs, fvs', lv_info) =
183 coreToStgRhs body_fvs TopLevel (id,rhs) `thenLne` \ (stg_rhs, fvs', _) ->
184 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
185 returnLne (stg_rhs, fvs', lv_info)
188 bind = StgNonRec (mkSRT lv_info) id stg_rhs
190 ASSERT2(isLocalId id || idArity id == manifestArity rhs, ppr id)
191 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
192 ASSERT2(consistent caf_info bind, ppr id)
193 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
194 (env', fvs' `unionFVInfo` body_fvs, bind)
196 coreTopBindToStg env body_fvs (Rec pairs)
198 (binders, rhss) = unzip pairs
200 -- To calculate caf_info, we initially map
201 -- all the binders to NoCafRefs
202 env1 = extendVarEnvList env
203 [ (b, LetBound (TopLet NoCafRefs) (error "no arity"))
206 caf_info = hasCafRefss env1{-NB: not env'-} rhss
208 env' = extendVarEnvList env
209 [ (b, LetBound (TopLet caf_info) (manifestArity rhs))
212 (stg_rhss, fvs', lv_info)
214 mapAndUnzip3Lne (coreToStgRhs body_fvs TopLevel) pairs
215 `thenLne` \ (stg_rhss, fvss', _) ->
216 let fvs' = unionFVInfos fvss' in
217 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
218 returnLne (stg_rhss, fvs', lv_info)
221 bind = StgRec (mkSRT lv_info) (zip binders stg_rhss)
223 ASSERT2(and [isLocalId bndr || manifestArity rhs == idArity bndr | (bndr,rhs) <- pairs], ppr binders)
224 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
225 ASSERT2(consistent caf_info bind, ppr binders)
226 -- WARN(not (consistent caf_info bind), ppr binders <+> ppr cafs <+> ppCafInfo caf_info)
227 (env', fvs' `unionFVInfo` body_fvs, bind)
230 consistent caf_info bind = mayHaveCafRefs caf_info == stgBindHasCafRefs bind
235 :: FreeVarsInfo -- Free var info for the scope of the binding
238 -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
240 coreToStgRhs scope_fv_info top (binder, rhs)
241 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
242 returnLne (mkStgRhs top rhs_fvs binder_info new_rhs,
245 binder_info = lookupFVInfo scope_fv_info binder
247 mkStgRhs :: TopLevelFlag -> FreeVarsInfo -> StgBinderInfo
250 mkStgRhs top rhs_fvs binder_info (StgLam _ bndrs body)
251 = StgRhsClosure noCCS binder_info
256 mkStgRhs top rhs_fvs binder_info (StgConApp con args)
257 | isNotTopLevel top || not (isDllConApp con args)
258 = StgRhsCon noCCS con args
260 mkStgRhs top rhs_fvs binder_info rhs
261 = StgRhsClosure noCCS binder_info
266 updatable args body | null args && isPAP body = ReEntrant
267 | otherwise = Updatable
269 upd = if isOnceDem dem
270 then (if isNotTop toplev
271 then SingleEntry -- HA! Paydirt for "dem"
274 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
278 -- For now we forbid SingleEntry CAFs; they tickle the
279 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
280 -- and I don't understand why. There's only one SE_CAF (well,
281 -- only one that tickled a great gaping bug in an earlier attempt
282 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
283 -- specifically Main.lvl6 in spectral/cryptarithm2.
284 -- So no great loss. KSW 2000-07.
288 Detect thunks which will reduce immediately to PAPs, and make them
289 non-updatable. This has several advantages:
291 - the non-updatable thunk behaves exactly like the PAP,
293 - the thunk is more efficient to enter, because it is
294 specialised to the task.
296 - we save one update frame, one stg_update_PAP, one update
297 and lots of PAP_enters.
299 - in the case where the thunk is top-level, we save building
300 a black hole and futhermore the thunk isn't considered to
301 be a CAF any more, so it doesn't appear in any SRTs.
303 We do it here, because the arity information is accurate, and we need
304 to do it before the SRT pass to save the SRT entries associated with
308 isPAP (StgApp f args) = idArity f > length args
313 -- ---------------------------------------------------------------------------
315 -- ---------------------------------------------------------------------------
320 -> LneM (StgExpr, -- Decorated STG expr
321 FreeVarsInfo, -- Its free vars (NB free, not live)
322 EscVarsSet) -- Its escapees, a subset of its free vars;
323 -- also a subset of the domain of the envt
324 -- because we are only interested in the escapees
325 -- for vars which might be turned into
326 -- let-no-escaped ones.
329 The second and third components can be derived in a simple bottom up pass, not
330 dependent on any decisions about which variables will be let-no-escaped or
331 not. The first component, that is, the decorated expression, may then depend
332 on these components, but it in turn is not scrutinised as the basis for any
333 decisions. Hence no black holes.
336 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
337 coreToStgExpr (Var v) = coreToStgApp Nothing v []
339 coreToStgExpr expr@(App _ _)
340 = coreToStgApp Nothing f args
342 (f, args) = myCollectArgs expr
344 coreToStgExpr expr@(Lam _ _)
346 (args, body) = myCollectBinders expr
347 args' = filterStgBinders args
349 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
350 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
352 fvs = args' `minusFVBinders` body_fvs
353 escs = body_escs `delVarSetList` args'
354 result_expr | null args' = body
355 | otherwise = StgLam (exprType expr) args' body
357 returnLne (result_expr, fvs, escs)
359 coreToStgExpr (Note (SCC cc) expr)
360 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
361 returnLne (StgSCC cc expr2, fvs, escs) )
364 -- For ILX, convert (__coerce__ to_ty from_ty e)
365 -- into (coerce to_ty from_ty e)
366 -- where coerce is real function
367 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
368 = coreToStgExpr (mkApps (Var unsafeCoerceId)
369 [Type from_ty, Type to_ty, expr])
372 coreToStgExpr (Note other_note expr)
375 -- Cases require a little more real work.
377 coreToStgExpr (Case scrut bndr alts)
378 = extendVarEnvLne [(bndr, LambdaBound)] (
379 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
380 returnLne ( mkStgAlts (idType bndr) alts2,
382 unionVarSets escs_s )
383 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
385 -- Determine whether the default binder is dead or not
386 -- This helps the code generator to avoid generating an assignment
387 -- for the case binder (is extremely rare cases) ToDo: remove.
388 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
389 | otherwise = bndr `setIdOccInfo` IAmDead
391 -- Don't consider the default binder as being 'live in alts',
392 -- since this is from the point of view of the case expr, where
393 -- the default binder is not free.
394 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
395 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
398 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
400 -- We tell the scrutinee that everything
401 -- live in the alts is live in it, too.
402 setVarsLiveInCont alts_lv_info (
403 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
404 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
405 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
407 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
410 StgCase scrut2 (getLiveVars scrut_lv_info)
411 (getLiveVars alts_lv_info)
415 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
416 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
417 -- You might think we should have scrut_escs, not
418 -- (getFVSet scrut_fvs), but actually we can't call, and
419 -- then return from, a let-no-escape thing.
422 vars_alt (con, binders, rhs)
423 = let -- Remove type variables
424 binders' = filterStgBinders binders
426 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
427 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
429 -- Records whether each param is used in the RHS
430 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
432 returnLne ( (con, binders', good_use_mask, rhs2),
433 binders' `minusFVBinders` rhs_fvs,
434 rhs_escs `delVarSetList` binders' )
435 -- ToDo: remove the delVarSet;
436 -- since escs won't include any of these binders
439 Lets not only take quite a bit of work, but this is where we convert
440 then to let-no-escapes, if we wish.
442 (Meanwhile, we don't expect to see let-no-escapes...)
444 coreToStgExpr (Let bind body)
445 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
446 coreToStgLet no_binder_escapes bind body
447 ) `thenLne` \ (new_let, fvs, escs, _) ->
449 returnLne (new_let, fvs, escs)
453 mkStgAlts scrut_ty orig_alts
454 | is_prim_case = StgPrimAlts (tyConAppTyCon scrut_ty) prim_alts deflt
455 | otherwise = StgAlgAlts maybe_tycon alg_alts deflt
457 is_prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
459 prim_alts = [(lit, rhs) | (LitAlt lit, _, _, rhs) <- other_alts]
460 alg_alts = [(con, bndrs, use, rhs) | (DataAlt con, bndrs, use, rhs) <- other_alts]
463 = case orig_alts of -- DEFAULT is always first if it's there at all
464 (DEFAULT, _, _, rhs) : other_alts -> (other_alts, StgBindDefault rhs)
465 other -> (orig_alts, StgNoDefault)
467 maybe_tycon = case alg_alts of
468 -- Get the tycon from the data con
469 (dc, _, _, _) : _rest -> Just (dataConTyCon dc)
471 -- Otherwise just do your best
472 [] -> case splitTyConApp_maybe (repType scrut_ty) of
473 Just (tc,_) | isAlgTyCon tc -> Just tc
478 -- ---------------------------------------------------------------------------
480 -- ---------------------------------------------------------------------------
484 :: Maybe UpdateFlag -- Just upd <=> this application is
485 -- the rhs of a thunk binding
486 -- x = [...] \upd [] -> the_app
487 -- with specified update flag
489 -> [CoreArg] -- Arguments
490 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
492 coreToStgApp maybe_thunk_body f args
493 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
494 lookupVarLne f `thenLne` \ how_bound ->
497 n_val_args = valArgCount args
498 not_letrec_bound = not (isLetBound how_bound)
500 = let fvs = singletonFVInfo f how_bound fun_occ in
501 -- e.g. (f :: a -> int) (x :: a)
502 -- Here the free variables are "f", "x" AND the type variable "a"
503 -- coreToStgArgs will deal with the arguments recursively
504 if opt_RuntimeTypes then
505 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (varType f))
508 -- Mostly, the arity info of a function is in the fn's IdInfo
509 -- But new bindings introduced by CoreSat may not have no
510 -- arity info; it would do us no good anyway. For example:
511 -- let f = \ab -> e in f
512 -- No point in having correct arity info for f!
513 -- Hence the hasArity stuff below.
514 -- NB: f_arity is only consulted for LetBound things
515 f_arity = case how_bound of
516 LetBound _ arity -> arity
517 ImportBound -> idArity f
519 saturated = f_arity <= n_val_args
522 | not_letrec_bound = noBinderInfo -- Uninteresting variable
523 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
524 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
527 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
528 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
529 -- saturated call doesn't escape
530 -- (let-no-escape applies to 'thunks' too)
532 | otherwise = unitVarSet f -- Inexact application; it does escape
534 -- At the moment of the call:
536 -- either the function is *not* let-no-escaped, in which case
537 -- nothing is live except live_in_cont
538 -- or the function *is* let-no-escaped in which case the
539 -- variables it uses are live, but still the function
540 -- itself is not. PS. In this case, the function's
541 -- live vars should already include those of the
542 -- continuation, but it does no harm to just union the
545 res_ty = exprType (mkApps (Var f) args)
546 app = case globalIdDetails f of
547 DataConId dc | saturated -> StgConApp dc args'
548 PrimOpId op -> ASSERT( saturated )
549 StgOpApp (StgPrimOp op) args' res_ty
550 FCallId call -> ASSERT( saturated )
551 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
552 _other -> StgApp f args'
557 fun_fvs `unionFVInfo` args_fvs,
558 fun_escs `unionVarSet` (getFVSet args_fvs)
559 -- All the free vars of the args are disqualified
560 -- from being let-no-escaped.
565 -- ---------------------------------------------------------------------------
567 -- This is the guy that turns applications into A-normal form
568 -- ---------------------------------------------------------------------------
570 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
572 = returnLne ([], emptyFVInfo)
574 coreToStgArgs (Type ty : args) -- Type argument
575 = coreToStgArgs args `thenLne` \ (args', fvs) ->
576 if opt_RuntimeTypes then
577 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
579 returnLne (args', fvs)
581 coreToStgArgs (arg : args) -- Non-type argument
582 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
583 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
585 fvs = args_fvs `unionFVInfo` arg_fvs
586 stg_arg = case arg' of
587 StgApp v [] -> StgVarArg v
588 StgConApp con [] -> StgVarArg (dataConWrapId con)
589 StgLit lit -> StgLitArg lit
590 _ -> pprPanic "coreToStgArgs" (ppr arg)
592 returnLne (stg_arg : stg_args, fvs)
595 -- ---------------------------------------------------------------------------
596 -- The magic for lets:
597 -- ---------------------------------------------------------------------------
600 :: Bool -- True <=> yes, we are let-no-escaping this let
601 -> CoreBind -- bindings
603 -> LneM (StgExpr, -- new let
604 FreeVarsInfo, -- variables free in the whole let
605 EscVarsSet, -- variables that escape from the whole let
606 Bool) -- True <=> none of the binders in the bindings
607 -- is among the escaping vars
609 coreToStgLet let_no_escape bind body
610 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
612 -- Do the bindings, setting live_in_cont to empty if
613 -- we ain't in a let-no-escape world
614 getVarsLiveInCont `thenLne` \ live_in_cont ->
615 setVarsLiveInCont (if let_no_escape
618 (vars_bind rec_body_fvs bind)
619 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
622 extendVarEnvLne env_ext (
623 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
624 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
626 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
627 body2, body_fvs, body_escs, getLiveVars body_lv_info)
630 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
631 body2, body_fvs, body_escs, body_lvs) ->
634 -- Compute the new let-expression
636 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
637 | otherwise = StgLet bind2 body2
640 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
643 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
645 real_bind_escs = if let_no_escape then
649 -- Everything escapes which is free in the bindings
651 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
653 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
656 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
659 -- Debugging code as requested by Andrew Kennedy
660 checked_no_binder_escapes
661 | not no_binder_escapes && any is_join_var binders
662 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
664 | otherwise = no_binder_escapes
666 checked_no_binder_escapes = no_binder_escapes
669 -- Mustn't depend on the passed-in let_no_escape flag, since
670 -- no_binder_escapes is used by the caller to derive the flag!
676 checked_no_binder_escapes
679 set_of_binders = mkVarSet binders
680 binders = bindersOf bind
682 mk_binding bind_lv_info binder rhs
683 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
685 live_vars | let_no_escape = addLiveVar bind_lv_info binder
686 | otherwise = unitLiveVar binder
687 -- c.f. the invariant on NestedLet
689 vars_bind :: FreeVarsInfo -- Free var info for body of binding
693 EscVarsSet, -- free vars; escapee vars
694 LiveInfo, -- Vars and CAFs live in binding
695 [(Id, HowBound)]) -- extension to environment
698 vars_bind body_fvs (NonRec binder rhs)
699 = coreToStgRhs body_fvs NotTopLevel (binder,rhs)
700 `thenLne` \ (rhs2, bind_fvs, escs) ->
702 freeVarsToLiveVars bind_fvs `thenLne` \ bind_lv_info ->
704 env_ext_item = mk_binding bind_lv_info binder rhs
706 returnLne (StgNonRec (mkSRT bind_lv_info) binder rhs2,
707 bind_fvs, escs, bind_lv_info, [env_ext_item])
710 vars_bind body_fvs (Rec pairs)
711 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
713 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
714 binders = map fst pairs
715 env_ext = [ mk_binding bind_lv_info b rhs
718 extendVarEnvLne env_ext (
719 mapAndUnzip3Lne (coreToStgRhs rec_scope_fvs NotTopLevel) pairs
720 `thenLne` \ (rhss2, fvss, escss) ->
722 bind_fvs = unionFVInfos fvss
723 escs = unionVarSets escss
725 freeVarsToLiveVars (binders `minusFVBinders` bind_fvs)
726 `thenLne` \ bind_lv_info ->
728 returnLne (StgRec (mkSRT bind_lv_info) (binders `zip` rhss2),
729 bind_fvs, escs, bind_lv_info, env_ext)
733 is_join_var :: Id -> Bool
734 -- A hack (used only for compiler debuggging) to tell if
735 -- a variable started life as a join point ($j)
736 is_join_var j = occNameUserString (getOccName j) == "$j"
740 %************************************************************************
742 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
744 %************************************************************************
746 There's a lot of stuff to pass around, so we use this @LneM@ monad to
747 help. All the stuff here is only passed *down*.
750 type LneM a = IdEnv HowBound
751 -> LiveInfo -- Vars and CAFs live in continuation
754 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
755 -- i.e. ones with a nested (non-top-level) binding
756 CafSet) -- Static live variables;
757 -- i.e. top-level variables that are CAFs or refer to them
759 type EscVarsSet = IdSet
763 = ImportBound -- Used only as a response to lookupBinding; never
764 -- exists in the range of the (IdEnv HowBound)
766 | LetBound -- A let(rec) in this module
767 LetInfo -- Whether top level or nested
768 Arity -- Its arity (local Ids don't have arity info at this point)
770 | LambdaBound -- Used for both lambda and case
772 data LetInfo = NestedLet LiveInfo -- For nested things, what is live if this thing is live?
773 -- Invariant: the binder itself is always a member of
774 -- the dynamic set of its own LiveInfo
775 | TopLet CafInfo -- For top level things, is it a CAF, or can it refer to one?
777 isLetBound (LetBound _ _) = True
778 isLetBound other = False
780 topLevelBound ImportBound = True
781 topLevelBound (LetBound (TopLet _) _) = True
782 topLevelBound other = False
785 For a let(rec)-bound variable, x, we record LiveInfo, the set of
786 variables that are live if x is live. This LiveInfo comprises
787 (a) dynamic live variables (ones with a non-top-level binding)
788 (b) static live variabes (CAFs or things that refer to CAFs)
790 For "normal" variables (a) is just x alone. If x is a let-no-escaped
791 variable then x is represented by a code pointer and a stack pointer
792 (well, one for each stack). So all of the variables needed in the
793 execution of x are live if x is, and are therefore recorded in the
794 LetBound constructor; x itself *is* included.
796 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
800 emptyLiveInfo :: LiveInfo
801 emptyLiveInfo = (emptyVarSet,emptyVarSet)
803 unitLiveVar :: Id -> LiveInfo
804 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
806 unitLiveCaf :: Id -> LiveInfo
807 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
809 addLiveVar :: LiveInfo -> Id -> LiveInfo
810 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
812 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
813 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
815 mkSRT :: LiveInfo -> SRT
816 mkSRT (_, cafs) = SRTEntries cafs
818 getLiveVars :: LiveInfo -> StgLiveVars
819 getLiveVars (lvs, _) = lvs
823 The std monad functions:
825 initLne :: IdEnv HowBound -> LneM a -> a
826 initLne env m = m env emptyLiveInfo
830 {-# INLINE thenLne #-}
831 {-# INLINE returnLne #-}
833 returnLne :: a -> LneM a
834 returnLne e env lvs_cont = e
836 thenLne :: LneM a -> (a -> LneM b) -> LneM b
837 thenLne m k env lvs_cont
838 = k (m env lvs_cont) env lvs_cont
840 mapLne :: (a -> LneM b) -> [a] -> LneM [b]
841 mapLne f [] = returnLne []
843 = f x `thenLne` \ r ->
844 mapLne f xs `thenLne` \ rs ->
847 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
849 mapAndUnzipLne f [] = returnLne ([],[])
850 mapAndUnzipLne f (x:xs)
851 = f x `thenLne` \ (r1, r2) ->
852 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
853 returnLne (r1:rs1, r2:rs2)
855 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
857 mapAndUnzip3Lne f [] = returnLne ([],[],[])
858 mapAndUnzip3Lne f (x:xs)
859 = f x `thenLne` \ (r1, r2, r3) ->
860 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
861 returnLne (r1:rs1, r2:rs2, r3:rs3)
863 fixLne :: (a -> LneM a) -> LneM a
864 fixLne expr env lvs_cont
867 result = expr result env lvs_cont
870 Functions specific to this monad:
873 getVarsLiveInCont :: LneM LiveInfo
874 getVarsLiveInCont env lvs_cont = lvs_cont
876 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
877 setVarsLiveInCont new_lvs_cont expr env lvs_cont
878 = expr env new_lvs_cont
880 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
881 extendVarEnvLne ids_w_howbound expr env lvs_cont
882 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
884 lookupVarLne :: Id -> LneM HowBound
885 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
887 lookupBinding :: IdEnv HowBound -> Id -> HowBound
888 lookupBinding env v = case lookupVarEnv env v of
890 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
893 -- The result of lookupLiveVarsForSet, a set of live variables, is
894 -- only ever tacked onto a decorated expression. It is never used as
895 -- the basis of a control decision, which might give a black hole.
897 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
898 freeVarsToLiveVars fvs env live_in_cont
899 = returnLne live_info env live_in_cont
901 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
902 lvs_from_fvs = map do_one (allFreeIds fvs)
904 do_one (v, how_bound)
906 ImportBound -> unitLiveCaf v -- Only CAF imports are
908 LetBound (TopLet caf_info) _
909 | mayHaveCafRefs caf_info -> unitLiveCaf v
910 | otherwise -> emptyLiveInfo
912 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
913 -- (see the invariant on NestedLet)
915 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
918 %************************************************************************
920 \subsection[Free-var info]{Free variable information}
922 %************************************************************************
925 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
926 -- The Var is so we can gather up the free variables
929 -- The HowBound info just saves repeated lookups;
930 -- we look up just once when we encounter the occurrence.
931 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
932 -- Imported Ids without CAF refs are simply
933 -- not put in the FreeVarsInfo for an expression.
934 -- See singletonFVInfo and freeVarsToLiveVars
936 -- StgBinderInfo records how it occurs; notably, we
937 -- are interested in whether it only occurs in saturated
938 -- applications, because then we don't need to build a
940 -- If f is mapped to noBinderInfo, that means
941 -- that f *is* mentioned (else it wouldn't be in the
942 -- IdEnv at all), but perhaps in an unsaturated applications.
944 -- All case/lambda-bound things are also mapped to
945 -- noBinderInfo, since we aren't interested in their
948 -- For ILX we track free var info for type variables too;
949 -- hence VarEnv not IdEnv
953 emptyFVInfo :: FreeVarsInfo
954 emptyFVInfo = emptyVarEnv
956 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
957 -- Don't record non-CAF imports at all, to keep free-var sets small
958 singletonFVInfo id ImportBound info
959 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
960 | otherwise = emptyVarEnv
961 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
963 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
964 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
966 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
967 -- Type variables must be lambda-bound
969 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
970 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
972 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
973 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
975 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
976 minusFVBinders vs fv = foldr minusFVBinder fv vs
978 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
979 minusFVBinder v fv | isId v && opt_RuntimeTypes
980 = (fv `delVarEnv` v) `unionFVInfo`
981 tyvarFVInfo (tyVarsOfType (idType v))
982 | otherwise = fv `delVarEnv` v
983 -- When removing a binder, remember to add its type variables
984 -- c.f. CoreFVs.delBinderFV
986 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
987 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
989 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
990 -- Find how the given Id is used.
991 -- Externally visible things may be used any old how
993 | isExternallyVisibleName (idName id) = noBinderInfo
994 | otherwise = case lookupVarEnv fvs id of
995 Nothing -> noBinderInfo
996 Just (_,_,info) -> info
998 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
999 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1001 -- Non-top-level things only, both type variables and ids
1002 -- (type variables only if opt_RuntimeTypes)
1003 getFVs :: FreeVarsInfo -> [Var]
1004 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1005 not (topLevelBound how_bound) ]
1007 getFVSet :: FreeVarsInfo -> VarSet
1008 getFVSet fvs = mkVarSet (getFVs fvs)
1010 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1011 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1012 (id1, hb1, combineStgBinderInfo info1 info2)
1015 -- The HowBound info for a variable in the FVInfo should be consistent
1016 check_eq_how_bound ImportBound ImportBound = True
1017 check_eq_how_bound LambdaBound LambdaBound = True
1018 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1019 check_eq_how_bound hb1 hb2 = False
1021 check_eq_li (NestedLet _) (NestedLet _) = True
1022 check_eq_li (TopLet _) (TopLet _) = True
1023 check_eq_li li1 li2 = False
1029 filterStgBinders :: [Var] -> [Var]
1030 filterStgBinders bndrs
1031 | opt_RuntimeTypes = bndrs
1032 | otherwise = filter isId bndrs
1037 -- Ignore all notes except SCC
1038 myCollectBinders expr
1041 go bs (Lam b e) = go (b:bs) e
1042 go bs e@(Note (SCC _) _) = (reverse bs, e)
1043 go bs (Note _ e) = go bs e
1044 go bs e = (reverse bs, e)
1046 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1047 -- We assume that we only have variables
1048 -- in the function position by now
1052 go (Var v) as = (v, as)
1053 go (App f a) as = go f (a:as)
1054 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1055 go (Note n e) as = go e as
1056 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1059 %************************************************************************
1061 \subsection{Figuring out CafInfo for an expression}
1063 %************************************************************************
1065 hasCafRefs decides whether a top-level closure can point into the dynamic heap.
1066 We mark such things as `MayHaveCafRefs' because this information is
1067 used to decide whether a particular closure needs to be referenced
1070 There are two reasons for setting MayHaveCafRefs:
1071 a) The RHS is a CAF: a top-level updatable thunk.
1072 b) The RHS refers to something that MayHaveCafRefs
1074 Possible improvement: In an effort to keep the number of CAFs (and
1075 hence the size of the SRTs) down, we could also look at the expression and
1076 decide whether it requires a small bounded amount of heap, so we can ignore
1077 it as a CAF. In these cases however, we would need to use an additional
1078 CAF list to keep track of non-collectable CAFs.
1081 hasCafRefs :: IdEnv HowBound -> CoreExpr -> CafInfo
1082 -- Only called for the RHS of top-level lets
1083 hasCafRefss :: IdEnv HowBound -> [CoreExpr] -> CafInfo
1084 -- predicate returns True for a given Id if we look at this Id when
1085 -- calculating the result. Used to *avoid* looking at the CafInfo
1086 -- field for an Id that is part of the current recursive group.
1089 | isCAF expr || isFastTrue (cafRefs p expr) = MayHaveCafRefs
1090 | otherwise = NoCafRefs
1092 -- used for recursive groups. The whole group is set to
1093 -- "MayHaveCafRefs" if at least one of the group is a CAF or
1094 -- refers to any CAFs.
1096 | any isCAF exprs || isFastTrue (cafRefss p exprs) = MayHaveCafRefs
1097 | otherwise = NoCafRefs
1099 -- The environment that cafRefs uses has top-level bindings *only*.
1100 -- We don't bother to add local bindings as cafRefs traverses the expression
1101 -- because they will all be for LocalIds (all nested things are LocalIds)
1102 -- However, we must look in the env first, because some top level things
1103 -- might be local Ids
1106 = case lookupVarEnv p id of
1107 Just (LetBound (TopLet caf_info) _) -> fastBool (mayHaveCafRefs caf_info)
1108 Nothing | isGlobalId id -> fastBool (mayHaveCafRefs (idCafInfo id)) -- Imported
1109 | otherwise -> fastBool False -- Nested binder
1110 _other -> error ("cafRefs " ++ showSDoc (ppr id)) -- No nested things in env
1112 cafRefs p (Lit l) = fastBool False
1113 cafRefs p (App f a) = fastOr (cafRefs p f) (cafRefs p) a
1114 cafRefs p (Lam x e) = cafRefs p e
1115 cafRefs p (Let b e) = fastOr (cafRefss p (rhssOfBind b)) (cafRefs p) e
1116 cafRefs p (Case e bndr alts) = fastOr (cafRefs p e) (cafRefss p) (rhssOfAlts alts)
1117 cafRefs p (Note n e) = cafRefs p e
1118 cafRefs p (Type t) = fastBool False
1120 cafRefss p [] = fastBool False
1121 cafRefss p (e:es) = fastOr (cafRefs p e) (cafRefss p) es
1123 -- hack for lazy-or over FastBool.
1124 fastOr a f x = fastBool (isFastTrue a || isFastTrue (f x))
1126 isCAF :: CoreExpr -> Bool
1127 -- Only called for the RHS of top-level lets
1128 isCAF e = not (rhsIsNonUpd e)
1129 {- ToDo: check type for onceness, i.e. non-updatable thunks? -}
1132 rhsIsNonUpd :: CoreExpr -> Bool
1133 -- True => Value-lambda, constructor, PAP
1134 -- This is a bit like CoreUtils.exprIsValue, with the following differences:
1135 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1137 -- b) (C x xs), where C is a contructors is updatable if the application is
1138 -- dynamic: see isDynConApp
1140 -- c) don't look through unfolding of f in (f x). I'm suspicious of this one
1142 -- This function has to line up with what the update flag
1143 -- for the StgRhs gets set to in mkStgRhs (above)
1145 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1146 -- them as making the RHS re-entrant (non-updatable).
1147 rhsIsNonUpd (Lam b e) = isRuntimeVar b || rhsIsNonUpd e
1148 rhsIsNonUpd (Note (SCC _) e) = False
1149 rhsIsNonUpd (Note _ e) = rhsIsNonUpd e
1150 rhsIsNonUpd other_expr
1151 = go other_expr 0 []
1153 go (Var f) n_args args = idAppIsNonUpd f n_args args
1155 go (App f a) n_args args
1156 | isTypeArg a = go f n_args args
1157 | otherwise = go f (n_args + 1) (a:args)
1159 go (Note (SCC _) f) n_args args = False
1160 go (Note _ f) n_args args = go f n_args args
1162 go other n_args args = False
1164 idAppIsNonUpd :: Id -> Int -> [CoreExpr] -> Bool
1165 idAppIsNonUpd id n_val_args args
1166 | Just con <- isDataConId_maybe id = not (isCrossDllConApp con args)
1167 | otherwise = n_val_args < idArity id
1169 isCrossDllConApp :: DataCon -> [CoreExpr] -> Bool
1170 isCrossDllConApp con args = isDllName (dataConName con) || any isCrossDllArg args
1171 -- Top-level constructor applications can usually be allocated
1172 -- statically, but they can't if
1173 -- a) the constructor, or any of the arguments, come from another DLL
1174 -- b) any of the arguments are LitLits
1175 -- (because we can't refer to static labels in other DLLs).
1176 -- If this happens we simply make the RHS into an updatable thunk,
1177 -- and 'exectute' it rather than allocating it statically.
1178 -- All this should match the decision in (see CoreToStg.coreToStgRhs)
1181 isCrossDllArg :: CoreExpr -> Bool
1182 -- True if somewhere in the expression there's a cross-DLL reference
1183 isCrossDllArg (Type _) = False
1184 isCrossDllArg (Var v) = isDllName (idName v)
1185 isCrossDllArg (Note _ e) = isCrossDllArg e
1186 isCrossDllArg (Lit lit) = isLitLitLit lit
1187 isCrossDllArg (App e1 e2) = isCrossDllArg e1 || isCrossDllArg e2 -- must be a type app
1188 isCrossDllArg (Lam v e) = isCrossDllArg e -- must be a type lam