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, isExternalName, isDllName )
34 import OccName ( occNameUserString )
35 import BasicTypes ( Arity )
36 import CmdLineOpts ( DynFlags, opt_RuntimeTypes )
37 import FastTypes hiding ( fastOr )
38 import Util ( listLengthCmp, mapAndUnzip )
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, upd) = 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 coreToTopStgRhs body_fvs ((id,rhs), upd) `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(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 extra_env = [ (b, LetBound (TopLet NoCafRefs) (manifestArity rhs))
204 env1 = extendVarEnvList env extra_env
205 (caf_infos, upd_flags) = mapAndUnzip (hasCafRefs env1) rhss
206 -- NB: use env1 not env'
208 -- If any has a CAF ref, they all do
209 caf_info | any mayHaveCafRefs caf_infos = MayHaveCafRefs
210 | otherwise = NoCafRefs
212 extra_env' = [ (b, LetBound (TopLet caf_info) arity)
213 | (b, LetBound _ arity) <- extra_env ]
214 env' = extendVarEnvList env extra_env'
216 (stg_rhss, fvs', lv_info)
218 mapAndUnzipLne (coreToTopStgRhs body_fvs)
219 (pairs `zip` upd_flags) `thenLne` \ (stg_rhss, fvss') ->
220 let fvs' = unionFVInfos fvss' in
221 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
222 returnLne (stg_rhss, fvs', lv_info)
225 bind = StgRec (mkSRT lv_info) (zip binders stg_rhss)
227 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
228 ASSERT2(consistent caf_info bind, ppr binders)
229 -- WARN(not (consistent caf_info bind), ppr binders <+> ppr cafs <+> ppCafInfo caf_info)
230 (env', fvs' `unionFVInfo` body_fvs, bind)
233 consistent caf_info bind = mayHaveCafRefs caf_info == stgBindHasCafRefs bind
238 :: FreeVarsInfo -- Free var info for the scope of the binding
239 -> ((Id,CoreExpr), UpdateFlag)
240 -> LneM (StgRhs, FreeVarsInfo)
242 coreToTopStgRhs scope_fv_info ((bndr, rhs), upd)
243 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
244 returnLne (mkTopStgRhs upd rhs_fvs bndr_info new_rhs, rhs_fvs)
246 bndr_info = lookupFVInfo scope_fv_info bndr
248 mkTopStgRhs :: UpdateFlag -> FreeVarsInfo -> StgBinderInfo
251 mkTopStgRhs upd rhs_fvs binder_info (StgLam _ bndrs body)
252 = StgRhsClosure noCCS binder_info
257 mkTopStgRhs ReEntrant rhs_fvs binder_info (StgConApp con args)
258 -- StgConApps can be Updatable: see isCrossDllConApp below
259 = StgRhsCon noCCS con args
261 mkTopStgRhs upd_flag rhs_fvs binder_info rhs
262 = StgRhsClosure noCCS binder_info
269 -- ---------------------------------------------------------------------------
271 -- ---------------------------------------------------------------------------
276 -> LneM (StgExpr, -- Decorated STG expr
277 FreeVarsInfo, -- Its free vars (NB free, not live)
278 EscVarsSet) -- Its escapees, a subset of its free vars;
279 -- also a subset of the domain of the envt
280 -- because we are only interested in the escapees
281 -- for vars which might be turned into
282 -- let-no-escaped ones.
285 The second and third components can be derived in a simple bottom up pass, not
286 dependent on any decisions about which variables will be let-no-escaped or
287 not. The first component, that is, the decorated expression, may then depend
288 on these components, but it in turn is not scrutinised as the basis for any
289 decisions. Hence no black holes.
292 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
293 coreToStgExpr (Var v) = coreToStgApp Nothing v []
295 coreToStgExpr expr@(App _ _)
296 = coreToStgApp Nothing f args
298 (f, args) = myCollectArgs expr
300 coreToStgExpr expr@(Lam _ _)
302 (args, body) = myCollectBinders expr
303 args' = filterStgBinders args
305 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
306 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
308 fvs = args' `minusFVBinders` body_fvs
309 escs = body_escs `delVarSetList` args'
310 result_expr | null args' = body
311 | otherwise = StgLam (exprType expr) args' body
313 returnLne (result_expr, fvs, escs)
315 coreToStgExpr (Note (SCC cc) expr)
316 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
317 returnLne (StgSCC cc expr2, fvs, escs) )
320 -- For ILX, convert (__coerce__ to_ty from_ty e)
321 -- into (coerce to_ty from_ty e)
322 -- where coerce is real function
323 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
324 = coreToStgExpr (mkApps (Var unsafeCoerceId)
325 [Type from_ty, Type to_ty, expr])
328 coreToStgExpr (Note other_note expr)
331 -- Cases require a little more real work.
333 coreToStgExpr (Case scrut bndr alts)
334 = extendVarEnvLne [(bndr, LambdaBound)] (
335 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
336 returnLne ( mkStgAlts (idType bndr) alts2,
338 unionVarSets escs_s )
339 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
341 -- Determine whether the default binder is dead or not
342 -- This helps the code generator to avoid generating an assignment
343 -- for the case binder (is extremely rare cases) ToDo: remove.
344 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
345 | otherwise = bndr `setIdOccInfo` IAmDead
347 -- Don't consider the default binder as being 'live in alts',
348 -- since this is from the point of view of the case expr, where
349 -- the default binder is not free.
350 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
351 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
354 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
356 -- We tell the scrutinee that everything
357 -- live in the alts is live in it, too.
358 setVarsLiveInCont alts_lv_info (
359 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
360 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
361 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
363 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
366 StgCase scrut2 (getLiveVars scrut_lv_info)
367 (getLiveVars alts_lv_info)
371 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
372 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
373 -- You might think we should have scrut_escs, not
374 -- (getFVSet scrut_fvs), but actually we can't call, and
375 -- then return from, a let-no-escape thing.
378 vars_alt (con, binders, rhs)
379 = let -- Remove type variables
380 binders' = filterStgBinders binders
382 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
383 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
385 -- Records whether each param is used in the RHS
386 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
388 returnLne ( (con, binders', good_use_mask, rhs2),
389 binders' `minusFVBinders` rhs_fvs,
390 rhs_escs `delVarSetList` binders' )
391 -- ToDo: remove the delVarSet;
392 -- since escs won't include any of these binders
395 Lets not only take quite a bit of work, but this is where we convert
396 then to let-no-escapes, if we wish.
398 (Meanwhile, we don't expect to see let-no-escapes...)
400 coreToStgExpr (Let bind body)
401 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
402 coreToStgLet no_binder_escapes bind body
403 ) `thenLne` \ (new_let, fvs, escs, _) ->
405 returnLne (new_let, fvs, escs)
409 mkStgAlts scrut_ty orig_alts
410 | is_prim_case = StgPrimAlts (tyConAppTyCon scrut_ty) prim_alts deflt
411 | otherwise = StgAlgAlts maybe_tycon alg_alts deflt
413 is_prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
415 prim_alts = [(lit, rhs) | (LitAlt lit, _, _, rhs) <- other_alts]
416 alg_alts = [(con, bndrs, use, rhs) | (DataAlt con, bndrs, use, rhs) <- other_alts]
419 = case orig_alts of -- DEFAULT is always first if it's there at all
420 (DEFAULT, _, _, rhs) : other_alts -> (other_alts, StgBindDefault rhs)
421 other -> (orig_alts, StgNoDefault)
423 maybe_tycon = case alg_alts of
424 -- Get the tycon from the data con
425 (dc, _, _, _) : _rest -> Just (dataConTyCon dc)
427 -- Otherwise just do your best
428 [] -> case splitTyConApp_maybe (repType scrut_ty) of
429 Just (tc,_) | isAlgTyCon tc -> Just tc
434 -- ---------------------------------------------------------------------------
436 -- ---------------------------------------------------------------------------
440 :: Maybe UpdateFlag -- Just upd <=> this application is
441 -- the rhs of a thunk binding
442 -- x = [...] \upd [] -> the_app
443 -- with specified update flag
445 -> [CoreArg] -- Arguments
446 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
448 coreToStgApp maybe_thunk_body f args
449 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
450 lookupVarLne f `thenLne` \ how_bound ->
453 n_val_args = valArgCount args
454 not_letrec_bound = not (isLetBound how_bound)
456 = let fvs = singletonFVInfo f how_bound fun_occ in
457 -- e.g. (f :: a -> int) (x :: a)
458 -- Here the free variables are "f", "x" AND the type variable "a"
459 -- coreToStgArgs will deal with the arguments recursively
460 if opt_RuntimeTypes then
461 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (varType f))
464 -- Mostly, the arity info of a function is in the fn's IdInfo
465 -- But new bindings introduced by CoreSat may not have no
466 -- arity info; it would do us no good anyway. For example:
467 -- let f = \ab -> e in f
468 -- No point in having correct arity info for f!
469 -- Hence the hasArity stuff below.
470 -- NB: f_arity is only consulted for LetBound things
471 f_arity = stgArity f how_bound
472 saturated = f_arity <= n_val_args
475 | not_letrec_bound = noBinderInfo -- Uninteresting variable
476 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
477 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
480 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
481 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
482 -- saturated call doesn't escape
483 -- (let-no-escape applies to 'thunks' too)
485 | otherwise = unitVarSet f -- Inexact application; it does escape
487 -- At the moment of the call:
489 -- either the function is *not* let-no-escaped, in which case
490 -- nothing is live except live_in_cont
491 -- or the function *is* let-no-escaped in which case the
492 -- variables it uses are live, but still the function
493 -- itself is not. PS. In this case, the function's
494 -- live vars should already include those of the
495 -- continuation, but it does no harm to just union the
498 res_ty = exprType (mkApps (Var f) args)
499 app = case globalIdDetails f of
500 DataConId dc | saturated -> StgConApp dc args'
501 PrimOpId op -> ASSERT( saturated )
502 StgOpApp (StgPrimOp op) args' res_ty
503 FCallId call -> ASSERT( saturated )
504 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
505 _other -> StgApp f args'
510 fun_fvs `unionFVInfo` args_fvs,
511 fun_escs `unionVarSet` (getFVSet args_fvs)
512 -- All the free vars of the args are disqualified
513 -- from being let-no-escaped.
518 -- ---------------------------------------------------------------------------
520 -- This is the guy that turns applications into A-normal form
521 -- ---------------------------------------------------------------------------
523 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
525 = returnLne ([], emptyFVInfo)
527 coreToStgArgs (Type ty : args) -- Type argument
528 = coreToStgArgs args `thenLne` \ (args', fvs) ->
529 if opt_RuntimeTypes then
530 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
532 returnLne (args', fvs)
534 coreToStgArgs (arg : args) -- Non-type argument
535 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
536 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
538 fvs = args_fvs `unionFVInfo` arg_fvs
539 stg_arg = case arg' of
540 StgApp v [] -> StgVarArg v
541 StgConApp con [] -> StgVarArg (dataConWrapId con)
542 StgLit lit -> StgLitArg lit
543 _ -> pprPanic "coreToStgArgs" (ppr arg)
545 returnLne (stg_arg : stg_args, fvs)
548 -- ---------------------------------------------------------------------------
549 -- The magic for lets:
550 -- ---------------------------------------------------------------------------
553 :: Bool -- True <=> yes, we are let-no-escaping this let
554 -> CoreBind -- bindings
556 -> LneM (StgExpr, -- new let
557 FreeVarsInfo, -- variables free in the whole let
558 EscVarsSet, -- variables that escape from the whole let
559 Bool) -- True <=> none of the binders in the bindings
560 -- is among the escaping vars
562 coreToStgLet let_no_escape bind body
563 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
565 -- Do the bindings, setting live_in_cont to empty if
566 -- we ain't in a let-no-escape world
567 getVarsLiveInCont `thenLne` \ live_in_cont ->
568 setVarsLiveInCont (if let_no_escape
571 (vars_bind rec_body_fvs bind)
572 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
575 extendVarEnvLne env_ext (
576 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
577 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
579 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
580 body2, body_fvs, body_escs, getLiveVars body_lv_info)
583 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
584 body2, body_fvs, body_escs, body_lvs) ->
587 -- Compute the new let-expression
589 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
590 | otherwise = StgLet bind2 body2
593 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
596 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
598 real_bind_escs = if let_no_escape then
602 -- Everything escapes which is free in the bindings
604 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
606 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
609 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
612 -- Debugging code as requested by Andrew Kennedy
613 checked_no_binder_escapes
614 | not no_binder_escapes && any is_join_var binders
615 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
617 | otherwise = no_binder_escapes
619 checked_no_binder_escapes = no_binder_escapes
622 -- Mustn't depend on the passed-in let_no_escape flag, since
623 -- no_binder_escapes is used by the caller to derive the flag!
629 checked_no_binder_escapes
632 set_of_binders = mkVarSet binders
633 binders = bindersOf bind
635 mk_binding bind_lv_info binder rhs
636 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
638 live_vars | let_no_escape = addLiveVar bind_lv_info binder
639 | otherwise = unitLiveVar binder
640 -- c.f. the invariant on NestedLet
642 vars_bind :: FreeVarsInfo -- Free var info for body of binding
646 EscVarsSet, -- free vars; escapee vars
647 LiveInfo, -- Vars and CAFs live in binding
648 [(Id, HowBound)]) -- extension to environment
651 vars_bind body_fvs (NonRec binder rhs)
652 = coreToStgRhs body_fvs (binder,rhs)
653 `thenLne` \ (rhs2, bind_fvs, escs) ->
655 freeVarsToLiveVars bind_fvs `thenLne` \ bind_lv_info ->
657 env_ext_item = mk_binding bind_lv_info binder rhs
659 returnLne (StgNonRec (mkSRT bind_lv_info) binder rhs2,
660 bind_fvs, escs, bind_lv_info, [env_ext_item])
663 vars_bind body_fvs (Rec pairs)
664 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
666 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
667 binders = map fst pairs
668 env_ext = [ mk_binding bind_lv_info b rhs
671 extendVarEnvLne env_ext (
672 mapAndUnzip3Lne (coreToStgRhs rec_scope_fvs) pairs
673 `thenLne` \ (rhss2, fvss, escss) ->
675 bind_fvs = unionFVInfos fvss
676 escs = unionVarSets escss
678 freeVarsToLiveVars (binders `minusFVBinders` bind_fvs)
679 `thenLne` \ bind_lv_info ->
681 returnLne (StgRec (mkSRT bind_lv_info) (binders `zip` rhss2),
682 bind_fvs, escs, bind_lv_info, env_ext)
686 is_join_var :: Id -> Bool
687 -- A hack (used only for compiler debuggging) to tell if
688 -- a variable started life as a join point ($j)
689 is_join_var j = occNameUserString (getOccName j) == "$j"
693 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
695 -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
697 coreToStgRhs scope_fv_info (bndr, rhs)
698 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
699 getEnvLne `thenLne` \ env ->
700 returnLne (mkStgRhs env rhs_fvs bndr_info new_rhs,
703 bndr_info = lookupFVInfo scope_fv_info bndr
705 mkStgRhs :: IdEnv HowBound -> FreeVarsInfo -> StgBinderInfo -> StgExpr -> StgRhs
707 mkStgRhs env rhs_fvs binder_info (StgConApp con args)
708 = StgRhsCon noCCS con args
710 mkStgRhs env rhs_fvs binder_info (StgLam _ bndrs body)
711 = StgRhsClosure noCCS binder_info
716 mkStgRhs env rhs_fvs binder_info rhs
717 = StgRhsClosure noCCS binder_info
721 upd_flag | isPAP env rhs = ReEntrant
722 | otherwise = Updatable
724 upd = if isOnceDem dem
725 then (if isNotTop toplev
726 then SingleEntry -- HA! Paydirt for "dem"
729 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
733 -- For now we forbid SingleEntry CAFs; they tickle the
734 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
735 -- and I don't understand why. There's only one SE_CAF (well,
736 -- only one that tickled a great gaping bug in an earlier attempt
737 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
738 -- specifically Main.lvl6 in spectral/cryptarithm2.
739 -- So no great loss. KSW 2000-07.
743 Detect thunks which will reduce immediately to PAPs, and make them
744 non-updatable. This has several advantages:
746 - the non-updatable thunk behaves exactly like the PAP,
748 - the thunk is more efficient to enter, because it is
749 specialised to the task.
751 - we save one update frame, one stg_update_PAP, one update
752 and lots of PAP_enters.
754 - in the case where the thunk is top-level, we save building
755 a black hole and futhermore the thunk isn't considered to
756 be a CAF any more, so it doesn't appear in any SRTs.
758 We do it here, because the arity information is accurate, and we need
759 to do it before the SRT pass to save the SRT entries associated with
763 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
765 arity = stgArity f (lookupBinding env f)
770 %************************************************************************
772 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
774 %************************************************************************
776 There's a lot of stuff to pass around, so we use this @LneM@ monad to
777 help. All the stuff here is only passed *down*.
780 type LneM a = IdEnv HowBound
781 -> LiveInfo -- Vars and CAFs live in continuation
784 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
785 -- i.e. ones with a nested (non-top-level) binding
786 CafSet) -- Static live variables;
787 -- i.e. top-level variables that are CAFs or refer to them
789 type EscVarsSet = IdSet
793 = ImportBound -- Used only as a response to lookupBinding; never
794 -- exists in the range of the (IdEnv HowBound)
796 | LetBound -- A let(rec) in this module
797 LetInfo -- Whether top level or nested
798 Arity -- Its arity (local Ids don't have arity info at this point)
800 | LambdaBound -- Used for both lambda and case
802 data LetInfo = NestedLet LiveInfo -- For nested things, what is live if this thing is live?
803 -- Invariant: the binder itself is always a member of
804 -- the dynamic set of its own LiveInfo
806 | TopLet CafInfo -- For top level things, is it a CAF, or can it refer to one?
808 isLetBound (LetBound _ _) = True
809 isLetBound other = False
811 topLevelBound ImportBound = True
812 topLevelBound (LetBound (TopLet _) _) = True
813 topLevelBound other = False
816 For a let(rec)-bound variable, x, we record LiveInfo, the set of
817 variables that are live if x is live. This LiveInfo comprises
818 (a) dynamic live variables (ones with a non-top-level binding)
819 (b) static live variabes (CAFs or things that refer to CAFs)
821 For "normal" variables (a) is just x alone. If x is a let-no-escaped
822 variable then x is represented by a code pointer and a stack pointer
823 (well, one for each stack). So all of the variables needed in the
824 execution of x are live if x is, and are therefore recorded in the
825 LetBound constructor; x itself *is* included.
827 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
831 emptyLiveInfo :: LiveInfo
832 emptyLiveInfo = (emptyVarSet,emptyVarSet)
834 unitLiveVar :: Id -> LiveInfo
835 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
837 unitLiveCaf :: Id -> LiveInfo
838 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
840 addLiveVar :: LiveInfo -> Id -> LiveInfo
841 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
843 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
844 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
846 mkSRT :: LiveInfo -> SRT
847 mkSRT (_, cafs) = SRTEntries cafs
849 getLiveVars :: LiveInfo -> StgLiveVars
850 getLiveVars (lvs, _) = lvs
854 The std monad functions:
856 initLne :: IdEnv HowBound -> LneM a -> a
857 initLne env m = m env emptyLiveInfo
861 {-# INLINE thenLne #-}
862 {-# INLINE returnLne #-}
864 returnLne :: a -> LneM a
865 returnLne e env lvs_cont = e
867 thenLne :: LneM a -> (a -> LneM b) -> LneM b
868 thenLne m k env lvs_cont
869 = k (m env lvs_cont) env lvs_cont
871 mapLne :: (a -> LneM b) -> [a] -> LneM [b]
872 mapLne f [] = returnLne []
874 = f x `thenLne` \ r ->
875 mapLne f xs `thenLne` \ rs ->
878 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
880 mapAndUnzipLne f [] = returnLne ([],[])
881 mapAndUnzipLne f (x:xs)
882 = f x `thenLne` \ (r1, r2) ->
883 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
884 returnLne (r1:rs1, r2:rs2)
886 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
888 mapAndUnzip3Lne f [] = returnLne ([],[],[])
889 mapAndUnzip3Lne f (x:xs)
890 = f x `thenLne` \ (r1, r2, r3) ->
891 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
892 returnLne (r1:rs1, r2:rs2, r3:rs3)
894 fixLne :: (a -> LneM a) -> LneM a
895 fixLne expr env lvs_cont
898 result = expr result env lvs_cont
901 Functions specific to this monad:
904 getVarsLiveInCont :: LneM LiveInfo
905 getVarsLiveInCont env lvs_cont = lvs_cont
907 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
908 setVarsLiveInCont new_lvs_cont expr env lvs_cont
909 = expr env new_lvs_cont
911 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
912 extendVarEnvLne ids_w_howbound expr env lvs_cont
913 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
915 lookupVarLne :: Id -> LneM HowBound
916 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
918 getEnvLne :: LneM (IdEnv HowBound)
919 getEnvLne env lvs_cont = returnLne env env lvs_cont
921 lookupBinding :: IdEnv HowBound -> Id -> HowBound
922 lookupBinding env v = case lookupVarEnv env v of
924 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
927 -- The result of lookupLiveVarsForSet, a set of live variables, is
928 -- only ever tacked onto a decorated expression. It is never used as
929 -- the basis of a control decision, which might give a black hole.
931 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
932 freeVarsToLiveVars fvs env live_in_cont
933 = returnLne live_info env live_in_cont
935 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
936 lvs_from_fvs = map do_one (allFreeIds fvs)
938 do_one (v, how_bound)
940 ImportBound -> unitLiveCaf v -- Only CAF imports are
942 LetBound (TopLet caf_info) _
943 | mayHaveCafRefs caf_info -> unitLiveCaf v
944 | otherwise -> emptyLiveInfo
946 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
947 -- (see the invariant on NestedLet)
949 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
952 %************************************************************************
954 \subsection[Free-var info]{Free variable information}
956 %************************************************************************
959 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
960 -- The Var is so we can gather up the free variables
963 -- The HowBound info just saves repeated lookups;
964 -- we look up just once when we encounter the occurrence.
965 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
966 -- Imported Ids without CAF refs are simply
967 -- not put in the FreeVarsInfo for an expression.
968 -- See singletonFVInfo and freeVarsToLiveVars
970 -- StgBinderInfo records how it occurs; notably, we
971 -- are interested in whether it only occurs in saturated
972 -- applications, because then we don't need to build a
974 -- If f is mapped to noBinderInfo, that means
975 -- that f *is* mentioned (else it wouldn't be in the
976 -- IdEnv at all), but perhaps in an unsaturated applications.
978 -- All case/lambda-bound things are also mapped to
979 -- noBinderInfo, since we aren't interested in their
982 -- For ILX we track free var info for type variables too;
983 -- hence VarEnv not IdEnv
987 emptyFVInfo :: FreeVarsInfo
988 emptyFVInfo = emptyVarEnv
990 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
991 -- Don't record non-CAF imports at all, to keep free-var sets small
992 singletonFVInfo id ImportBound info
993 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
994 | otherwise = emptyVarEnv
995 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
997 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
998 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1000 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1001 -- Type variables must be lambda-bound
1003 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1004 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1006 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1007 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1009 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1010 minusFVBinders vs fv = foldr minusFVBinder fv vs
1012 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1013 minusFVBinder v fv | isId v && opt_RuntimeTypes
1014 = (fv `delVarEnv` v) `unionFVInfo`
1015 tyvarFVInfo (tyVarsOfType (idType v))
1016 | otherwise = fv `delVarEnv` v
1017 -- When removing a binder, remember to add its type variables
1018 -- c.f. CoreFVs.delBinderFV
1020 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1021 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1023 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1024 -- Find how the given Id is used.
1025 -- Externally visible things may be used any old how
1027 | isExternalName (idName id) = noBinderInfo
1028 | otherwise = case lookupVarEnv fvs id of
1029 Nothing -> noBinderInfo
1030 Just (_,_,info) -> info
1032 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1033 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1035 -- Non-top-level things only, both type variables and ids
1036 -- (type variables only if opt_RuntimeTypes)
1037 getFVs :: FreeVarsInfo -> [Var]
1038 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1039 not (topLevelBound how_bound) ]
1041 getFVSet :: FreeVarsInfo -> VarSet
1042 getFVSet fvs = mkVarSet (getFVs fvs)
1044 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1045 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1046 (id1, hb1, combineStgBinderInfo info1 info2)
1049 -- The HowBound info for a variable in the FVInfo should be consistent
1050 check_eq_how_bound ImportBound ImportBound = True
1051 check_eq_how_bound LambdaBound LambdaBound = True
1052 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1053 check_eq_how_bound hb1 hb2 = False
1055 check_eq_li (NestedLet _) (NestedLet _) = True
1056 check_eq_li (TopLet _) (TopLet _) = True
1057 check_eq_li li1 li2 = False
1063 filterStgBinders :: [Var] -> [Var]
1064 filterStgBinders bndrs
1065 | opt_RuntimeTypes = bndrs
1066 | otherwise = filter isId bndrs
1071 -- Ignore all notes except SCC
1072 myCollectBinders expr
1075 go bs (Lam b e) = go (b:bs) e
1076 go bs e@(Note (SCC _) _) = (reverse bs, e)
1077 go bs (Note _ e) = go bs e
1078 go bs e = (reverse bs, e)
1080 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1081 -- We assume that we only have variables
1082 -- in the function position by now
1086 go (Var v) as = (v, as)
1087 go (App f a) as = go f (a:as)
1088 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1089 go (Note n e) as = go e as
1090 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1093 %************************************************************************
1095 \subsection{Figuring out CafInfo for an expression}
1097 %************************************************************************
1099 hasCafRefs decides whether a top-level closure can point into the dynamic heap.
1100 We mark such things as `MayHaveCafRefs' because this information is
1101 used to decide whether a particular closure needs to be referenced
1104 There are two reasons for setting MayHaveCafRefs:
1105 a) The RHS is a CAF: a top-level updatable thunk.
1106 b) The RHS refers to something that MayHaveCafRefs
1108 Possible improvement: In an effort to keep the number of CAFs (and
1109 hence the size of the SRTs) down, we could also look at the expression and
1110 decide whether it requires a small bounded amount of heap, so we can ignore
1111 it as a CAF. In these cases however, we would need to use an additional
1112 CAF list to keep track of non-collectable CAFs.
1115 hasCafRefs :: IdEnv HowBound -> CoreExpr -> (CafInfo, UpdateFlag)
1117 | is_caf || mentions_cafs = (MayHaveCafRefs, upd_flag)
1118 | otherwise = (NoCafRefs, ReEntrant)
1120 mentions_cafs = isFastTrue (cafRefs p expr)
1121 is_caf = not (rhsIsNonUpd p expr)
1122 upd_flag | is_caf = Updatable
1123 | otherwise = ReEntrant
1125 -- The environment that cafRefs uses has top-level bindings *only*.
1126 -- We don't bother to add local bindings as cafRefs traverses the expression
1127 -- because they will all be for LocalIds (all nested things are LocalIds)
1128 -- However, we must look in the env first, because some top level things
1129 -- might be local Ids
1132 = case lookupVarEnv p id of
1133 Just (LetBound (TopLet caf_info) _) -> fastBool (mayHaveCafRefs caf_info)
1134 Nothing | isGlobalId id -> fastBool (mayHaveCafRefs (idCafInfo id)) -- Imported
1135 | otherwise -> fastBool False -- Nested binder
1136 _other -> error ("cafRefs " ++ showSDoc (ppr id)) -- No nested things in env
1138 cafRefs p (Lit l) = fastBool False
1139 cafRefs p (App f a) = fastOr (cafRefs p f) (cafRefs p) a
1140 cafRefs p (Lam x e) = cafRefs p e
1141 cafRefs p (Let b e) = fastOr (cafRefss p (rhssOfBind b)) (cafRefs p) e
1142 cafRefs p (Case e bndr alts) = fastOr (cafRefs p e) (cafRefss p) (rhssOfAlts alts)
1143 cafRefs p (Note n e) = cafRefs p e
1144 cafRefs p (Type t) = fastBool False
1146 cafRefss p [] = fastBool False
1147 cafRefss p (e:es) = fastOr (cafRefs p e) (cafRefss p) es
1149 -- hack for lazy-or over FastBool.
1150 fastOr a f x = fastBool (isFastTrue a || isFastTrue (f x))
1153 rhsIsNonUpd :: IdEnv HowBound -> CoreExpr -> Bool
1154 -- True => Value-lambda, constructor, PAP
1155 -- This is a bit like CoreUtils.exprIsValue, with the following differences:
1156 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1158 -- b) (C x xs), where C is a contructors is updatable if the application is
1159 -- dynamic: see isDynConApp
1161 -- c) don't look through unfolding of f in (f x). I'm suspicious of this one
1163 -- This function has to line up with what the update flag
1164 -- for the StgRhs gets set to in mkStgRhs (above)
1166 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1167 -- them as making the RHS re-entrant (non-updatable).
1168 rhsIsNonUpd p (Lam b e) = isRuntimeVar b || rhsIsNonUpd p e
1169 rhsIsNonUpd p (Note (SCC _) e) = False
1170 rhsIsNonUpd p (Note _ e) = rhsIsNonUpd p e
1171 rhsIsNonUpd p other_expr
1172 = go other_expr 0 []
1174 go (Var f) n_args args = idAppIsNonUpd p f n_args args
1176 go (App f a) n_args args
1177 | isTypeArg a = go f n_args args
1178 | otherwise = go f (n_args + 1) (a:args)
1180 go (Note (SCC _) f) n_args args = False
1181 go (Note _ f) n_args args = go f n_args args
1183 go other n_args args = False
1185 idAppIsNonUpd :: IdEnv HowBound -> Id -> Int -> [CoreExpr] -> Bool
1186 idAppIsNonUpd p id n_val_args args
1187 | Just con <- isDataConId_maybe id = not (isCrossDllConApp con args)
1188 | otherwise = n_val_args < stgArity id (lookupBinding p id)
1190 stgArity :: Id -> HowBound -> Arity
1191 stgArity f (LetBound _ arity) = arity
1192 stgArity f ImportBound = idArity f
1193 stgArity f LambdaBound = 0
1195 isCrossDllConApp :: DataCon -> [CoreExpr] -> Bool
1196 isCrossDllConApp con args = isDllName (dataConName con) || any isCrossDllArg args
1197 -- Top-level constructor applications can usually be allocated
1198 -- statically, but they can't if
1199 -- a) the constructor, or any of the arguments, come from another DLL
1200 -- b) any of the arguments are LitLits
1201 -- (because we can't refer to static labels in other DLLs).
1202 -- If this happens we simply make the RHS into an updatable thunk,
1203 -- and 'exectute' it rather than allocating it statically.
1204 -- All this should match the decision in (see CoreToStg.mkStgRhs)
1207 isCrossDllArg :: CoreExpr -> Bool
1208 -- True if somewhere in the expression there's a cross-DLL reference
1209 isCrossDllArg (Type _) = False
1210 isCrossDllArg (Var v) = isDllName (idName v)
1211 isCrossDllArg (Note _ e) = isCrossDllArg e
1212 isCrossDllArg (Lit lit) = isLitLitLit lit
1213 isCrossDllArg (App e1 e2) = isCrossDllArg e1 || isCrossDllArg e2 -- must be a type app
1214 isCrossDllArg (Lam v e) = isCrossDllArg e -- must be a type lam