2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
4 \section[CoreToStg]{Converts Core to STG Syntax}
6 And, as we have the info in hand, we may convert some lets to
10 module CoreToStg ( coreToStg, coreExprToStg ) where
12 #include "HsVersions.h"
15 import CoreUtils ( rhsIsStatic, manifestArity, exprType )
19 import TyCon ( isAlgTyCon )
21 import Var ( Var, globalIdDetails, idType )
22 import TyCon ( isUnboxedTupleTyCon, isPrimTyCon, isFunTyCon, isHiBootTyCon )
24 import MkId ( unsafeCoerceId )
28 import CostCentre ( noCCS )
31 import Maybes ( maybeToBool )
32 import Name ( getOccName, isExternalName, nameOccName )
33 import OccName ( occNameUserString, occNameFS )
34 import BasicTypes ( Arity )
35 import DynFlags ( DynFlags )
36 import StaticFlags ( opt_RuntimeTypes )
42 %************************************************************************
44 \subsection[live-vs-free-doc]{Documentation}
46 %************************************************************************
48 (There is other relevant documentation in codeGen/CgLetNoEscape.)
50 The actual Stg datatype is decorated with {\em live variable}
51 information, as well as {\em free variable} information. The two are
52 {\em not} the same. Liveness is an operational property rather than a
53 semantic one. A variable is live at a particular execution point if
54 it can be referred to {\em directly} again. In particular, a dead
55 variable's stack slot (if it has one):
58 should be stubbed to avoid space leaks, and
60 may be reused for something else.
63 There ought to be a better way to say this. Here are some examples:
70 Just after the `in', v is live, but q is dead. If the whole of that
71 let expression was enclosed in a case expression, thus:
73 case (let v = [q] \[x] -> e in ...v...) of
76 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
77 we'll return later to the @alts@ and need it.
79 Let-no-escapes make this a bit more interesting:
81 let-no-escape v = [q] \ [x] -> e
85 Here, @q@ is still live at the `in', because @v@ is represented not by
86 a closure but by the current stack state. In other words, if @v@ is
87 live then so is @q@. Furthermore, if @e@ mentions an enclosing
88 let-no-escaped variable, then {\em its} free variables are also live
91 %************************************************************************
93 \subsection[caf-info]{Collecting live CAF info}
95 %************************************************************************
97 In this pass we also collect information on which CAFs are live for
98 constructing SRTs (see SRT.lhs).
100 A top-level Id has CafInfo, which is
102 - MayHaveCafRefs, if it may refer indirectly to
104 - NoCafRefs if it definitely doesn't
106 The CafInfo has already been calculated during the CoreTidy pass.
108 During CoreToStg, we then pin onto each binding and case expression, a
109 list of Ids which represents the "live" CAFs at that point. The meaning
110 of "live" here is the same as for live variables, see above (which is
111 why it's convenient to collect CAF information here rather than elsewhere).
113 The later SRT pass takes these lists of Ids and uses them to construct
114 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
118 Interaction of let-no-escape with SRTs [Sept 01]
119 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
122 let-no-escape x = ...caf1...caf2...
126 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
127 build SRTs just as if x's defn was inlined at each call site, and
128 that means that x's CAF refs get duplicated in the overall SRT.
130 This is unlike ordinary lets, in which the CAF refs are not duplicated.
132 We could fix this loss of (static) sharing by making a sort of pseudo-closure
133 for x, solely to put in the SRTs lower down.
136 %************************************************************************
138 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
140 %************************************************************************
143 coreToStg :: DynFlags -> [CoreBind] -> IO [StgBinding]
146 where (_, _, pgm') = coreTopBindsToStg dflags emptyVarEnv pgm
148 coreExprToStg :: CoreExpr -> StgExpr
150 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
155 -> IdEnv HowBound -- environment for the bindings
157 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
159 coreTopBindsToStg dflags env [] = (env, emptyFVInfo, [])
160 coreTopBindsToStg dflags env (b:bs)
161 = (env2, fvs2, b':bs')
163 -- env accumulates down the list of binds, fvs accumulates upwards
164 (env1, fvs2, b' ) = coreTopBindToStg dflags env fvs1 b
165 (env2, fvs1, bs') = coreTopBindsToStg dflags env1 bs
171 -> FreeVarsInfo -- Info about the body
173 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
175 coreTopBindToStg dflags env body_fvs (NonRec id rhs)
177 env' = extendVarEnv env id how_bound
178 how_bound = LetBound TopLet (manifestArity rhs)
182 coreToTopStgRhs dflags body_fvs (id,rhs) `thenLne` \ (stg_rhs, fvs') ->
183 returnLne (stg_rhs, fvs')
186 bind = StgNonRec id stg_rhs
188 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
189 ASSERT2(consistentCafInfo id bind, ppr id)
190 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
191 (env', fvs' `unionFVInfo` body_fvs, bind)
193 coreTopBindToStg dflags env body_fvs (Rec pairs)
195 (binders, rhss) = unzip pairs
197 extra_env' = [ (b, LetBound TopLet (manifestArity rhs))
198 | (b, rhs) <- pairs ]
199 env' = extendVarEnvList env extra_env'
203 mapAndUnzipLne (coreToTopStgRhs dflags body_fvs) pairs
204 `thenLne` \ (stg_rhss, fvss') ->
205 let fvs' = unionFVInfos fvss' in
206 returnLne (stg_rhss, fvs')
209 bind = StgRec (zip binders stg_rhss)
211 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
212 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
213 (env', fvs' `unionFVInfo` body_fvs, bind)
216 -- Assertion helper: this checks that the CafInfo on the Id matches
217 -- what CoreToStg has figured out about the binding's SRT. The
218 -- CafInfo will be exact in all cases except when CorePrep has
219 -- floated out a binding, in which case it will be approximate.
220 consistentCafInfo id bind
221 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
224 = WARN (not exact, ppr id) safe
226 safe = id_marked_caffy || not binding_is_caffy
227 exact = id_marked_caffy == binding_is_caffy
228 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
229 binding_is_caffy = stgBindHasCafRefs bind
236 -> FreeVarsInfo -- Free var info for the scope of the binding
238 -> LneM (StgRhs, FreeVarsInfo)
240 coreToTopStgRhs dflags scope_fv_info (bndr, rhs)
241 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
242 freeVarsToLiveVars rhs_fvs `thenLne` \ lv_info ->
243 returnLne (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
245 bndr_info = lookupFVInfo scope_fv_info bndr
246 is_static = rhsIsStatic dflags rhs
248 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
251 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
252 = ASSERT( is_static )
253 StgRhsClosure noCCS binder_info
259 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
260 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
261 = StgRhsCon noCCS con args
263 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
264 = ASSERT2( not is_static, ppr rhs )
265 StgRhsClosure noCCS binder_info
273 -- ---------------------------------------------------------------------------
275 -- ---------------------------------------------------------------------------
280 -> LneM (StgExpr, -- Decorated STG expr
281 FreeVarsInfo, -- Its free vars (NB free, not live)
282 EscVarsSet) -- Its escapees, a subset of its free vars;
283 -- also a subset of the domain of the envt
284 -- because we are only interested in the escapees
285 -- for vars which might be turned into
286 -- let-no-escaped ones.
289 The second and third components can be derived in a simple bottom up pass, not
290 dependent on any decisions about which variables will be let-no-escaped or
291 not. The first component, that is, the decorated expression, may then depend
292 on these components, but it in turn is not scrutinised as the basis for any
293 decisions. Hence no black holes.
296 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
297 coreToStgExpr (Var v) = coreToStgApp Nothing v []
299 coreToStgExpr expr@(App _ _)
300 = coreToStgApp Nothing f args
302 (f, args) = myCollectArgs expr
304 coreToStgExpr expr@(Lam _ _)
306 (args, body) = myCollectBinders expr
307 args' = filterStgBinders args
309 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
310 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
312 fvs = args' `minusFVBinders` body_fvs
313 escs = body_escs `delVarSetList` args'
314 result_expr | null args' = body
315 | otherwise = StgLam (exprType expr) args' body
317 returnLne (result_expr, fvs, escs)
319 coreToStgExpr (Note (SCC cc) expr)
320 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
321 returnLne (StgSCC cc expr2, fvs, escs) )
324 -- For ILX, convert (__coerce__ to_ty from_ty e)
325 -- into (coerce to_ty from_ty e)
326 -- where coerce is real function
327 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
328 = coreToStgExpr (mkApps (Var unsafeCoerceId)
329 [Type from_ty, Type to_ty, expr])
332 coreToStgExpr (Note other_note expr)
335 -- Cases require a little more real work.
337 coreToStgExpr (Case scrut bndr _ alts)
338 = extendVarEnvLne [(bndr, LambdaBound)] (
339 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
342 unionVarSets escs_s )
343 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
345 -- Determine whether the default binder is dead or not
346 -- This helps the code generator to avoid generating an assignment
347 -- for the case binder (is extremely rare cases) ToDo: remove.
348 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
349 | otherwise = bndr `setIdOccInfo` IAmDead
351 -- Don't consider the default binder as being 'live in alts',
352 -- since this is from the point of view of the case expr, where
353 -- the default binder is not free.
354 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
355 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
358 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
360 -- We tell the scrutinee that everything
361 -- live in the alts is live in it, too.
362 setVarsLiveInCont alts_lv_info (
363 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
364 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
365 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
367 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
370 StgCase scrut2 (getLiveVars scrut_lv_info)
371 (getLiveVars alts_lv_info)
374 (mkStgAltType (idType bndr))
376 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
377 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
378 -- You might think we should have scrut_escs, not
379 -- (getFVSet scrut_fvs), but actually we can't call, and
380 -- then return from, a let-no-escape thing.
383 vars_alt (con, binders, rhs)
384 = let -- Remove type variables
385 binders' = filterStgBinders binders
387 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
388 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
390 -- Records whether each param is used in the RHS
391 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
393 returnLne ( (con, binders', good_use_mask, rhs2),
394 binders' `minusFVBinders` rhs_fvs,
395 rhs_escs `delVarSetList` binders' )
396 -- ToDo: remove the delVarSet;
397 -- since escs won't include any of these binders
400 Lets not only take quite a bit of work, but this is where we convert
401 then to let-no-escapes, if we wish.
403 (Meanwhile, we don't expect to see let-no-escapes...)
405 coreToStgExpr (Let bind body)
406 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
407 coreToStgLet no_binder_escapes bind body
408 ) `thenLne` \ (new_let, fvs, escs, _) ->
410 returnLne (new_let, fvs, escs)
414 mkStgAltType scrut_ty
415 = case splitTyConApp_maybe (repType scrut_ty) of
416 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
417 | isPrimTyCon tc -> PrimAlt tc
418 | isHiBootTyCon tc -> PolyAlt -- Algebraic, but no constructors visible
419 | isAlgTyCon tc -> AlgAlt tc
420 | isFunTyCon tc -> PolyAlt
421 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
426 -- ---------------------------------------------------------------------------
428 -- ---------------------------------------------------------------------------
432 :: Maybe UpdateFlag -- Just upd <=> this application is
433 -- the rhs of a thunk binding
434 -- x = [...] \upd [] -> the_app
435 -- with specified update flag
437 -> [CoreArg] -- Arguments
438 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
440 coreToStgApp maybe_thunk_body f args
441 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
442 lookupVarLne f `thenLne` \ how_bound ->
445 n_val_args = valArgCount args
446 not_letrec_bound = not (isLetBound how_bound)
448 = let fvs = singletonFVInfo f how_bound fun_occ in
449 -- e.g. (f :: a -> int) (x :: a)
450 -- Here the free variables are "f", "x" AND the type variable "a"
451 -- coreToStgArgs will deal with the arguments recursively
452 if opt_RuntimeTypes then
453 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
456 -- Mostly, the arity info of a function is in the fn's IdInfo
457 -- But new bindings introduced by CoreSat may not have no
458 -- arity info; it would do us no good anyway. For example:
459 -- let f = \ab -> e in f
460 -- No point in having correct arity info for f!
461 -- Hence the hasArity stuff below.
462 -- NB: f_arity is only consulted for LetBound things
463 f_arity = stgArity f how_bound
464 saturated = f_arity <= n_val_args
467 | not_letrec_bound = noBinderInfo -- Uninteresting variable
468 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
469 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
472 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
473 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
474 -- saturated call doesn't escape
475 -- (let-no-escape applies to 'thunks' too)
477 | otherwise = unitVarSet f -- Inexact application; it does escape
479 -- At the moment of the call:
481 -- either the function is *not* let-no-escaped, in which case
482 -- nothing is live except live_in_cont
483 -- or the function *is* let-no-escaped in which case the
484 -- variables it uses are live, but still the function
485 -- itself is not. PS. In this case, the function's
486 -- live vars should already include those of the
487 -- continuation, but it does no harm to just union the
490 res_ty = exprType (mkApps (Var f) args)
491 app = case globalIdDetails f of
492 DataConWorkId dc | saturated -> StgConApp dc args'
493 PrimOpId op -> ASSERT( saturated )
494 StgOpApp (StgPrimOp op) args' res_ty
495 FCallId call -> ASSERT( saturated )
496 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
497 _other -> StgApp f args'
502 fun_fvs `unionFVInfo` args_fvs,
503 fun_escs `unionVarSet` (getFVSet args_fvs)
504 -- All the free vars of the args are disqualified
505 -- from being let-no-escaped.
510 -- ---------------------------------------------------------------------------
512 -- This is the guy that turns applications into A-normal form
513 -- ---------------------------------------------------------------------------
515 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
517 = returnLne ([], emptyFVInfo)
519 coreToStgArgs (Type ty : args) -- Type argument
520 = coreToStgArgs args `thenLne` \ (args', fvs) ->
521 if opt_RuntimeTypes then
522 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
524 returnLne (args', fvs)
526 coreToStgArgs (arg : args) -- Non-type argument
527 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
528 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
530 fvs = args_fvs `unionFVInfo` arg_fvs
531 stg_arg = case arg' of
532 StgApp v [] -> StgVarArg v
533 StgConApp con [] -> StgVarArg (dataConWorkId con)
534 StgLit lit -> StgLitArg lit
535 _ -> pprPanic "coreToStgArgs" (ppr arg)
537 returnLne (stg_arg : stg_args, fvs)
540 -- ---------------------------------------------------------------------------
541 -- The magic for lets:
542 -- ---------------------------------------------------------------------------
545 :: Bool -- True <=> yes, we are let-no-escaping this let
546 -> CoreBind -- bindings
548 -> LneM (StgExpr, -- new let
549 FreeVarsInfo, -- variables free in the whole let
550 EscVarsSet, -- variables that escape from the whole let
551 Bool) -- True <=> none of the binders in the bindings
552 -- is among the escaping vars
554 coreToStgLet let_no_escape bind body
555 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
557 -- Do the bindings, setting live_in_cont to empty if
558 -- we ain't in a let-no-escape world
559 getVarsLiveInCont `thenLne` \ live_in_cont ->
560 setVarsLiveInCont (if let_no_escape
563 (vars_bind rec_body_fvs bind)
564 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
567 extendVarEnvLne env_ext (
568 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
569 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
571 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
572 body2, body_fvs, body_escs, getLiveVars body_lv_info)
575 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
576 body2, body_fvs, body_escs, body_lvs) ->
579 -- Compute the new let-expression
581 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
582 | otherwise = StgLet bind2 body2
585 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
588 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
590 real_bind_escs = if let_no_escape then
594 -- Everything escapes which is free in the bindings
596 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
598 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
601 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
604 -- Debugging code as requested by Andrew Kennedy
605 checked_no_binder_escapes
606 | not no_binder_escapes && any is_join_var binders
607 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
609 | otherwise = no_binder_escapes
611 checked_no_binder_escapes = no_binder_escapes
614 -- Mustn't depend on the passed-in let_no_escape flag, since
615 -- no_binder_escapes is used by the caller to derive the flag!
621 checked_no_binder_escapes
624 set_of_binders = mkVarSet binders
625 binders = bindersOf bind
627 mk_binding bind_lv_info binder rhs
628 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
630 live_vars | let_no_escape = addLiveVar bind_lv_info binder
631 | otherwise = unitLiveVar binder
632 -- c.f. the invariant on NestedLet
634 vars_bind :: FreeVarsInfo -- Free var info for body of binding
638 EscVarsSet, -- free vars; escapee vars
639 LiveInfo, -- Vars and CAFs live in binding
640 [(Id, HowBound)]) -- extension to environment
643 vars_bind body_fvs (NonRec binder rhs)
644 = coreToStgRhs body_fvs [] (binder,rhs)
645 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
647 env_ext_item = mk_binding bind_lv_info binder rhs
649 returnLne (StgNonRec binder rhs2,
650 bind_fvs, escs, bind_lv_info, [env_ext_item])
653 vars_bind body_fvs (Rec pairs)
654 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
656 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
657 binders = map fst pairs
658 env_ext = [ mk_binding bind_lv_info b rhs
661 extendVarEnvLne env_ext (
662 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
663 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
665 bind_fvs = unionFVInfos fvss
666 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
667 escs = unionVarSets escss
669 returnLne (StgRec (binders `zip` rhss2),
670 bind_fvs, escs, bind_lv_info, env_ext)
674 is_join_var :: Id -> Bool
675 -- A hack (used only for compiler debuggging) to tell if
676 -- a variable started life as a join point ($j)
677 is_join_var j = occNameUserString (getOccName j) == "$j"
681 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
684 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
686 coreToStgRhs scope_fv_info binders (bndr, rhs)
687 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
688 getEnvLne `thenLne` \ env ->
689 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
690 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
691 rhs_fvs, lv_info, rhs_escs)
693 bndr_info = lookupFVInfo scope_fv_info bndr
695 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
697 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
698 = StgRhsCon noCCS con args
700 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
701 = StgRhsClosure noCCS binder_info
706 mkStgRhs rhs_fvs srt binder_info rhs
707 = StgRhsClosure noCCS binder_info
713 SDM: disabled. Eval/Apply can't handle functions with arity zero very
714 well; and making these into simple non-updatable thunks breaks other
715 assumptions (namely that they will be entered only once).
717 upd_flag | isPAP env rhs = ReEntrant
718 | otherwise = Updatable
722 upd = if isOnceDem dem
723 then (if isNotTop toplev
724 then SingleEntry -- HA! Paydirt for "dem"
727 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
731 -- For now we forbid SingleEntry CAFs; they tickle the
732 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
733 -- and I don't understand why. There's only one SE_CAF (well,
734 -- only one that tickled a great gaping bug in an earlier attempt
735 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
736 -- specifically Main.lvl6 in spectral/cryptarithm2.
737 -- So no great loss. KSW 2000-07.
741 Detect thunks which will reduce immediately to PAPs, and make them
742 non-updatable. This has several advantages:
744 - the non-updatable thunk behaves exactly like the PAP,
746 - the thunk is more efficient to enter, because it is
747 specialised to the task.
749 - we save one update frame, one stg_update_PAP, one update
750 and lots of PAP_enters.
752 - in the case where the thunk is top-level, we save building
753 a black hole and futhermore the thunk isn't considered to
754 be a CAF any more, so it doesn't appear in any SRTs.
756 We do it here, because the arity information is accurate, and we need
757 to do it before the SRT pass to save the SRT entries associated with
760 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
762 arity = stgArity f (lookupBinding env f)
766 %************************************************************************
768 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
770 %************************************************************************
772 There's a lot of stuff to pass around, so we use this @LneM@ monad to
773 help. All the stuff here is only passed *down*.
776 type LneM a = IdEnv HowBound
777 -> LiveInfo -- Vars and CAFs live in continuation
780 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
781 -- i.e. ones with a nested (non-top-level) binding
782 CafSet) -- Static live variables;
783 -- i.e. top-level variables that are CAFs or refer to them
785 type EscVarsSet = IdSet
789 = ImportBound -- Used only as a response to lookupBinding; never
790 -- exists in the range of the (IdEnv HowBound)
792 | LetBound -- A let(rec) in this module
793 LetInfo -- Whether top level or nested
794 Arity -- Its arity (local Ids don't have arity info at this point)
796 | LambdaBound -- Used for both lambda and case
799 = TopLet -- top level things
800 | NestedLet LiveInfo -- For nested things, what is live if this
801 -- thing is live? Invariant: the binder
802 -- itself is always a member of
803 -- the dynamic set of its own LiveInfo
805 isLetBound (LetBound _ _) = True
806 isLetBound other = False
808 topLevelBound ImportBound = True
809 topLevelBound (LetBound TopLet _) = True
810 topLevelBound other = False
813 For a let(rec)-bound variable, x, we record LiveInfo, the set of
814 variables that are live if x is live. This LiveInfo comprises
815 (a) dynamic live variables (ones with a non-top-level binding)
816 (b) static live variabes (CAFs or things that refer to CAFs)
818 For "normal" variables (a) is just x alone. If x is a let-no-escaped
819 variable then x is represented by a code pointer and a stack pointer
820 (well, one for each stack). So all of the variables needed in the
821 execution of x are live if x is, and are therefore recorded in the
822 LetBound constructor; x itself *is* included.
824 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
828 emptyLiveInfo :: LiveInfo
829 emptyLiveInfo = (emptyVarSet,emptyVarSet)
831 unitLiveVar :: Id -> LiveInfo
832 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
834 unitLiveCaf :: Id -> LiveInfo
835 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
837 addLiveVar :: LiveInfo -> Id -> LiveInfo
838 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
840 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
841 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
843 mkSRT :: LiveInfo -> SRT
844 mkSRT (_, cafs) = SRTEntries cafs
846 getLiveVars :: LiveInfo -> StgLiveVars
847 getLiveVars (lvs, _) = lvs
851 The std monad functions:
853 initLne :: IdEnv HowBound -> LneM a -> a
854 initLne env m = m env emptyLiveInfo
858 {-# INLINE thenLne #-}
859 {-# INLINE returnLne #-}
861 returnLne :: a -> LneM a
862 returnLne e env lvs_cont = e
864 thenLne :: LneM a -> (a -> LneM b) -> LneM b
865 thenLne m k env lvs_cont
866 = k (m env lvs_cont) env lvs_cont
868 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
869 mapAndUnzipLne f [] = returnLne ([],[])
870 mapAndUnzipLne f (x:xs)
871 = f x `thenLne` \ (r1, r2) ->
872 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
873 returnLne (r1:rs1, r2:rs2)
875 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
876 mapAndUnzip3Lne f [] = returnLne ([],[],[])
877 mapAndUnzip3Lne f (x:xs)
878 = f x `thenLne` \ (r1, r2, r3) ->
879 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
880 returnLne (r1:rs1, r2:rs2, r3:rs3)
882 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
883 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
884 mapAndUnzip4Lne f (x:xs)
885 = f x `thenLne` \ (r1, r2, r3, r4) ->
886 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
887 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
889 fixLne :: (a -> LneM a) -> LneM a
890 fixLne expr env lvs_cont
893 result = expr result env lvs_cont
896 Functions specific to this monad:
899 getVarsLiveInCont :: LneM LiveInfo
900 getVarsLiveInCont env lvs_cont = lvs_cont
902 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
903 setVarsLiveInCont new_lvs_cont expr env lvs_cont
904 = expr env new_lvs_cont
906 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
907 extendVarEnvLne ids_w_howbound expr env lvs_cont
908 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
910 lookupVarLne :: Id -> LneM HowBound
911 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
913 getEnvLne :: LneM (IdEnv HowBound)
914 getEnvLne env lvs_cont = returnLne env env lvs_cont
916 lookupBinding :: IdEnv HowBound -> Id -> HowBound
917 lookupBinding env v = case lookupVarEnv env v of
919 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
922 -- The result of lookupLiveVarsForSet, a set of live variables, is
923 -- only ever tacked onto a decorated expression. It is never used as
924 -- the basis of a control decision, which might give a black hole.
926 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
927 freeVarsToLiveVars fvs env live_in_cont
928 = returnLne live_info env live_in_cont
930 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
931 lvs_from_fvs = map do_one (allFreeIds fvs)
933 do_one (v, how_bound)
935 ImportBound -> unitLiveCaf v -- Only CAF imports are
938 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
939 | otherwise -> emptyLiveInfo
941 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
942 -- (see the invariant on NestedLet)
944 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
947 %************************************************************************
949 \subsection[Free-var info]{Free variable information}
951 %************************************************************************
954 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
955 -- The Var is so we can gather up the free variables
958 -- The HowBound info just saves repeated lookups;
959 -- we look up just once when we encounter the occurrence.
960 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
961 -- Imported Ids without CAF refs are simply
962 -- not put in the FreeVarsInfo for an expression.
963 -- See singletonFVInfo and freeVarsToLiveVars
965 -- StgBinderInfo records how it occurs; notably, we
966 -- are interested in whether it only occurs in saturated
967 -- applications, because then we don't need to build a
969 -- If f is mapped to noBinderInfo, that means
970 -- that f *is* mentioned (else it wouldn't be in the
971 -- IdEnv at all), but perhaps in an unsaturated applications.
973 -- All case/lambda-bound things are also mapped to
974 -- noBinderInfo, since we aren't interested in their
977 -- For ILX we track free var info for type variables too;
978 -- hence VarEnv not IdEnv
982 emptyFVInfo :: FreeVarsInfo
983 emptyFVInfo = emptyVarEnv
985 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
986 -- Don't record non-CAF imports at all, to keep free-var sets small
987 singletonFVInfo id ImportBound info
988 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
989 | otherwise = emptyVarEnv
990 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
992 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
993 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
995 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
996 -- Type variables must be lambda-bound
998 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
999 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1001 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1002 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1004 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1005 minusFVBinders vs fv = foldr minusFVBinder fv vs
1007 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1008 minusFVBinder v fv | isId v && opt_RuntimeTypes
1009 = (fv `delVarEnv` v) `unionFVInfo`
1010 tyvarFVInfo (tyVarsOfType (idType v))
1011 | otherwise = fv `delVarEnv` v
1012 -- When removing a binder, remember to add its type variables
1013 -- c.f. CoreFVs.delBinderFV
1015 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1016 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1018 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1019 -- Find how the given Id is used.
1020 -- Externally visible things may be used any old how
1022 | isExternalName (idName id) = noBinderInfo
1023 | otherwise = case lookupVarEnv fvs id of
1024 Nothing -> noBinderInfo
1025 Just (_,_,info) -> info
1027 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1028 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1030 -- Non-top-level things only, both type variables and ids
1031 -- (type variables only if opt_RuntimeTypes)
1032 getFVs :: FreeVarsInfo -> [Var]
1033 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1034 not (topLevelBound how_bound) ]
1036 getFVSet :: FreeVarsInfo -> VarSet
1037 getFVSet fvs = mkVarSet (getFVs fvs)
1039 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1040 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1041 (id1, hb1, combineStgBinderInfo info1 info2)
1044 -- The HowBound info for a variable in the FVInfo should be consistent
1045 check_eq_how_bound ImportBound ImportBound = True
1046 check_eq_how_bound LambdaBound LambdaBound = True
1047 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1048 check_eq_how_bound hb1 hb2 = False
1050 check_eq_li (NestedLet _) (NestedLet _) = True
1051 check_eq_li TopLet TopLet = True
1052 check_eq_li li1 li2 = False
1058 filterStgBinders :: [Var] -> [Var]
1059 filterStgBinders bndrs
1060 | opt_RuntimeTypes = bndrs
1061 | otherwise = filter isId bndrs
1066 -- Ignore all notes except SCC
1067 myCollectBinders expr
1070 go bs (Lam b e) = go (b:bs) e
1071 go bs e@(Note (SCC _) _) = (reverse bs, e)
1072 go bs (Note _ e) = go bs e
1073 go bs e = (reverse bs, e)
1075 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1076 -- We assume that we only have variables
1077 -- in the function position by now
1081 go (Var v) as = (v, as)
1082 go (App f a) as = go f (a:as)
1083 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1084 go (Note n e) as = go e as
1085 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1089 stgArity :: Id -> HowBound -> Arity
1090 stgArity f (LetBound _ arity) = arity
1091 stgArity f ImportBound = idArity f
1092 stgArity f LambdaBound = 0