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 CmdLineOpts ( DynFlags, opt_RuntimeTypes )
41 %************************************************************************
43 \subsection[live-vs-free-doc]{Documentation}
45 %************************************************************************
47 (There is other relevant documentation in codeGen/CgLetNoEscape.)
49 The actual Stg datatype is decorated with {\em live variable}
50 information, as well as {\em free variable} information. The two are
51 {\em not} the same. Liveness is an operational property rather than a
52 semantic one. A variable is live at a particular execution point if
53 it can be referred to {\em directly} again. In particular, a dead
54 variable's stack slot (if it has one):
57 should be stubbed to avoid space leaks, and
59 may be reused for something else.
62 There ought to be a better way to say this. Here are some examples:
69 Just after the `in', v is live, but q is dead. If the whole of that
70 let expression was enclosed in a case expression, thus:
72 case (let v = [q] \[x] -> e in ...v...) of
75 (ie @alts@ mention @q@), then @q@ is live even after the `in'; because
76 we'll return later to the @alts@ and need it.
78 Let-no-escapes make this a bit more interesting:
80 let-no-escape v = [q] \ [x] -> e
84 Here, @q@ is still live at the `in', because @v@ is represented not by
85 a closure but by the current stack state. In other words, if @v@ is
86 live then so is @q@. Furthermore, if @e@ mentions an enclosing
87 let-no-escaped variable, then {\em its} free variables are also live
90 %************************************************************************
92 \subsection[caf-info]{Collecting live CAF info}
94 %************************************************************************
96 In this pass we also collect information on which CAFs are live for
97 constructing SRTs (see SRT.lhs).
99 A top-level Id has CafInfo, which is
101 - MayHaveCafRefs, if it may refer indirectly to
103 - NoCafRefs if it definitely doesn't
105 The CafInfo has already been calculated during the CoreTidy pass.
107 During CoreToStg, we then pin onto each binding and case expression, a
108 list of Ids which represents the "live" CAFs at that point. The meaning
109 of "live" here is the same as for live variables, see above (which is
110 why it's convenient to collect CAF information here rather than elsewhere).
112 The later SRT pass takes these lists of Ids and uses them to construct
113 the actual nested SRTs, and replaces the lists of Ids with (offset,length)
117 Interaction of let-no-escape with SRTs [Sept 01]
118 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
121 let-no-escape x = ...caf1...caf2...
125 where caf1,caf2 are CAFs. Since x doesn't have a closure, we
126 build SRTs just as if x's defn was inlined at each call site, and
127 that means that x's CAF refs get duplicated in the overall SRT.
129 This is unlike ordinary lets, in which the CAF refs are not duplicated.
131 We could fix this loss of (static) sharing by making a sort of pseudo-closure
132 for x, solely to put in the SRTs lower down.
135 %************************************************************************
137 \subsection[binds-StgVarInfo]{Setting variable info: top-level, binds, RHSs}
139 %************************************************************************
142 coreToStg :: DynFlags -> [CoreBind] -> IO [StgBinding]
145 where (_, _, pgm') = coreTopBindsToStg dflags emptyVarEnv pgm
147 coreExprToStg :: CoreExpr -> StgExpr
149 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
154 -> IdEnv HowBound -- environment for the bindings
156 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
158 coreTopBindsToStg dflags env [] = (env, emptyFVInfo, [])
159 coreTopBindsToStg dflags env (b:bs)
160 = (env2, fvs2, b':bs')
162 -- env accumulates down the list of binds, fvs accumulates upwards
163 (env1, fvs2, b' ) = coreTopBindToStg dflags env fvs1 b
164 (env2, fvs1, bs') = coreTopBindsToStg dflags env1 bs
170 -> FreeVarsInfo -- Info about the body
172 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
174 coreTopBindToStg dflags env body_fvs (NonRec id rhs)
176 env' = extendVarEnv env id how_bound
177 how_bound = LetBound TopLet (manifestArity rhs)
181 coreToTopStgRhs dflags body_fvs (id,rhs) `thenLne` \ (stg_rhs, fvs') ->
182 returnLne (stg_rhs, fvs')
185 bind = StgNonRec id stg_rhs
187 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
188 ASSERT2(consistentCafInfo id bind, ppr id)
189 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
190 (env', fvs' `unionFVInfo` body_fvs, bind)
192 coreTopBindToStg dflags env body_fvs (Rec pairs)
194 (binders, rhss) = unzip pairs
196 extra_env' = [ (b, LetBound TopLet (manifestArity rhs))
197 | (b, rhs) <- pairs ]
198 env' = extendVarEnvList env extra_env'
202 mapAndUnzipLne (coreToTopStgRhs dflags body_fvs) pairs
203 `thenLne` \ (stg_rhss, fvss') ->
204 let fvs' = unionFVInfos fvss' in
205 returnLne (stg_rhss, fvs')
208 bind = StgRec (zip binders stg_rhss)
210 ASSERT2(and [manifestArity rhs == stgRhsArity stg_rhs | (rhs,stg_rhs) <- rhss `zip` stg_rhss], ppr binders)
211 ASSERT2(consistentCafInfo (head binders) bind, ppr binders)
212 (env', fvs' `unionFVInfo` body_fvs, bind)
215 -- Assertion helper: this checks that the CafInfo on the Id matches
216 -- what CoreToStg has figured out about the binding's SRT. The
217 -- CafInfo will be exact in all cases except when CorePrep has
218 -- floated out a binding, in which case it will be approximate.
219 consistentCafInfo id bind
220 | occNameFS (nameOccName (idName id)) == FSLIT("sat")
223 = WARN (not exact, ppr id) safe
225 safe = id_marked_caffy || not binding_is_caffy
226 exact = id_marked_caffy == binding_is_caffy
227 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
228 binding_is_caffy = stgBindHasCafRefs bind
235 -> FreeVarsInfo -- Free var info for the scope of the binding
237 -> LneM (StgRhs, FreeVarsInfo)
239 coreToTopStgRhs dflags scope_fv_info (bndr, rhs)
240 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
241 freeVarsToLiveVars rhs_fvs `thenLne` \ lv_info ->
242 returnLne (mkTopStgRhs is_static rhs_fvs (mkSRT lv_info) bndr_info new_rhs, rhs_fvs)
244 bndr_info = lookupFVInfo scope_fv_info bndr
245 is_static = rhsIsStatic dflags rhs
247 mkTopStgRhs :: Bool -> FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr
250 mkTopStgRhs is_static rhs_fvs srt binder_info (StgLam _ bndrs body)
251 = ASSERT( is_static )
252 StgRhsClosure noCCS binder_info
258 mkTopStgRhs is_static rhs_fvs srt binder_info (StgConApp con args)
259 | is_static -- StgConApps can be updatable (see isCrossDllConApp)
260 = StgRhsCon noCCS con args
262 mkTopStgRhs is_static rhs_fvs srt binder_info rhs
263 = ASSERT2( not is_static, ppr rhs )
264 StgRhsClosure noCCS binder_info
272 -- ---------------------------------------------------------------------------
274 -- ---------------------------------------------------------------------------
279 -> LneM (StgExpr, -- Decorated STG expr
280 FreeVarsInfo, -- Its free vars (NB free, not live)
281 EscVarsSet) -- Its escapees, a subset of its free vars;
282 -- also a subset of the domain of the envt
283 -- because we are only interested in the escapees
284 -- for vars which might be turned into
285 -- let-no-escaped ones.
288 The second and third components can be derived in a simple bottom up pass, not
289 dependent on any decisions about which variables will be let-no-escaped or
290 not. The first component, that is, the decorated expression, may then depend
291 on these components, but it in turn is not scrutinised as the basis for any
292 decisions. Hence no black holes.
295 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
296 coreToStgExpr (Var v) = coreToStgApp Nothing v []
298 coreToStgExpr expr@(App _ _)
299 = coreToStgApp Nothing f args
301 (f, args) = myCollectArgs expr
303 coreToStgExpr expr@(Lam _ _)
305 (args, body) = myCollectBinders expr
306 args' = filterStgBinders args
308 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
309 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
311 fvs = args' `minusFVBinders` body_fvs
312 escs = body_escs `delVarSetList` args'
313 result_expr | null args' = body
314 | otherwise = StgLam (exprType expr) args' body
316 returnLne (result_expr, fvs, escs)
318 coreToStgExpr (Note (SCC cc) expr)
319 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
320 returnLne (StgSCC cc expr2, fvs, escs) )
323 -- For ILX, convert (__coerce__ to_ty from_ty e)
324 -- into (coerce to_ty from_ty e)
325 -- where coerce is real function
326 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
327 = coreToStgExpr (mkApps (Var unsafeCoerceId)
328 [Type from_ty, Type to_ty, expr])
331 coreToStgExpr (Note other_note expr)
334 -- Cases require a little more real work.
336 coreToStgExpr (Case scrut bndr _ alts)
337 = extendVarEnvLne [(bndr, LambdaBound)] (
338 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
341 unionVarSets escs_s )
342 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
344 -- Determine whether the default binder is dead or not
345 -- This helps the code generator to avoid generating an assignment
346 -- for the case binder (is extremely rare cases) ToDo: remove.
347 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
348 | otherwise = bndr `setIdOccInfo` IAmDead
350 -- Don't consider the default binder as being 'live in alts',
351 -- since this is from the point of view of the case expr, where
352 -- the default binder is not free.
353 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
354 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
357 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
359 -- We tell the scrutinee that everything
360 -- live in the alts is live in it, too.
361 setVarsLiveInCont alts_lv_info (
362 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
363 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
364 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
366 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
369 StgCase scrut2 (getLiveVars scrut_lv_info)
370 (getLiveVars alts_lv_info)
373 (mkStgAltType (idType bndr))
375 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
376 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
377 -- You might think we should have scrut_escs, not
378 -- (getFVSet scrut_fvs), but actually we can't call, and
379 -- then return from, a let-no-escape thing.
382 vars_alt (con, binders, rhs)
383 = let -- Remove type variables
384 binders' = filterStgBinders binders
386 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
387 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
389 -- Records whether each param is used in the RHS
390 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
392 returnLne ( (con, binders', good_use_mask, rhs2),
393 binders' `minusFVBinders` rhs_fvs,
394 rhs_escs `delVarSetList` binders' )
395 -- ToDo: remove the delVarSet;
396 -- since escs won't include any of these binders
399 Lets not only take quite a bit of work, but this is where we convert
400 then to let-no-escapes, if we wish.
402 (Meanwhile, we don't expect to see let-no-escapes...)
404 coreToStgExpr (Let bind body)
405 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
406 coreToStgLet no_binder_escapes bind body
407 ) `thenLne` \ (new_let, fvs, escs, _) ->
409 returnLne (new_let, fvs, escs)
413 mkStgAltType scrut_ty
414 = case splitTyConApp_maybe (repType scrut_ty) of
415 Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
416 | isPrimTyCon tc -> PrimAlt tc
417 | isHiBootTyCon tc -> PolyAlt -- Algebraic, but no constructors visible
418 | isAlgTyCon tc -> AlgAlt tc
419 | isFunTyCon tc -> PolyAlt
420 | otherwise -> pprPanic "mkStgAlts" (ppr tc)
425 -- ---------------------------------------------------------------------------
427 -- ---------------------------------------------------------------------------
431 :: Maybe UpdateFlag -- Just upd <=> this application is
432 -- the rhs of a thunk binding
433 -- x = [...] \upd [] -> the_app
434 -- with specified update flag
436 -> [CoreArg] -- Arguments
437 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
439 coreToStgApp maybe_thunk_body f args
440 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
441 lookupVarLne f `thenLne` \ how_bound ->
444 n_val_args = valArgCount args
445 not_letrec_bound = not (isLetBound how_bound)
447 = let fvs = singletonFVInfo f how_bound fun_occ in
448 -- e.g. (f :: a -> int) (x :: a)
449 -- Here the free variables are "f", "x" AND the type variable "a"
450 -- coreToStgArgs will deal with the arguments recursively
451 if opt_RuntimeTypes then
452 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (idType f))
455 -- Mostly, the arity info of a function is in the fn's IdInfo
456 -- But new bindings introduced by CoreSat may not have no
457 -- arity info; it would do us no good anyway. For example:
458 -- let f = \ab -> e in f
459 -- No point in having correct arity info for f!
460 -- Hence the hasArity stuff below.
461 -- NB: f_arity is only consulted for LetBound things
462 f_arity = stgArity f how_bound
463 saturated = f_arity <= n_val_args
466 | not_letrec_bound = noBinderInfo -- Uninteresting variable
467 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
468 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
471 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
472 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
473 -- saturated call doesn't escape
474 -- (let-no-escape applies to 'thunks' too)
476 | otherwise = unitVarSet f -- Inexact application; it does escape
478 -- At the moment of the call:
480 -- either the function is *not* let-no-escaped, in which case
481 -- nothing is live except live_in_cont
482 -- or the function *is* let-no-escaped in which case the
483 -- variables it uses are live, but still the function
484 -- itself is not. PS. In this case, the function's
485 -- live vars should already include those of the
486 -- continuation, but it does no harm to just union the
489 res_ty = exprType (mkApps (Var f) args)
490 app = case globalIdDetails f of
491 DataConWorkId dc | saturated -> StgConApp dc args'
492 PrimOpId op -> ASSERT( saturated )
493 StgOpApp (StgPrimOp op) args' res_ty
494 FCallId call -> ASSERT( saturated )
495 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
496 _other -> StgApp f args'
501 fun_fvs `unionFVInfo` args_fvs,
502 fun_escs `unionVarSet` (getFVSet args_fvs)
503 -- All the free vars of the args are disqualified
504 -- from being let-no-escaped.
509 -- ---------------------------------------------------------------------------
511 -- This is the guy that turns applications into A-normal form
512 -- ---------------------------------------------------------------------------
514 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
516 = returnLne ([], emptyFVInfo)
518 coreToStgArgs (Type ty : args) -- Type argument
519 = coreToStgArgs args `thenLne` \ (args', fvs) ->
520 if opt_RuntimeTypes then
521 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
523 returnLne (args', fvs)
525 coreToStgArgs (arg : args) -- Non-type argument
526 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
527 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
529 fvs = args_fvs `unionFVInfo` arg_fvs
530 stg_arg = case arg' of
531 StgApp v [] -> StgVarArg v
532 StgConApp con [] -> StgVarArg (dataConWorkId con)
533 StgLit lit -> StgLitArg lit
534 _ -> pprPanic "coreToStgArgs" (ppr arg)
536 returnLne (stg_arg : stg_args, fvs)
539 -- ---------------------------------------------------------------------------
540 -- The magic for lets:
541 -- ---------------------------------------------------------------------------
544 :: Bool -- True <=> yes, we are let-no-escaping this let
545 -> CoreBind -- bindings
547 -> LneM (StgExpr, -- new let
548 FreeVarsInfo, -- variables free in the whole let
549 EscVarsSet, -- variables that escape from the whole let
550 Bool) -- True <=> none of the binders in the bindings
551 -- is among the escaping vars
553 coreToStgLet let_no_escape bind body
554 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
556 -- Do the bindings, setting live_in_cont to empty if
557 -- we ain't in a let-no-escape world
558 getVarsLiveInCont `thenLne` \ live_in_cont ->
559 setVarsLiveInCont (if let_no_escape
562 (vars_bind rec_body_fvs bind)
563 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
566 extendVarEnvLne env_ext (
567 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
568 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
570 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
571 body2, body_fvs, body_escs, getLiveVars body_lv_info)
574 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
575 body2, body_fvs, body_escs, body_lvs) ->
578 -- Compute the new let-expression
580 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
581 | otherwise = StgLet bind2 body2
584 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
587 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
589 real_bind_escs = if let_no_escape then
593 -- Everything escapes which is free in the bindings
595 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
597 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
600 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
603 -- Debugging code as requested by Andrew Kennedy
604 checked_no_binder_escapes
605 | not no_binder_escapes && any is_join_var binders
606 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
608 | otherwise = no_binder_escapes
610 checked_no_binder_escapes = no_binder_escapes
613 -- Mustn't depend on the passed-in let_no_escape flag, since
614 -- no_binder_escapes is used by the caller to derive the flag!
620 checked_no_binder_escapes
623 set_of_binders = mkVarSet binders
624 binders = bindersOf bind
626 mk_binding bind_lv_info binder rhs
627 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
629 live_vars | let_no_escape = addLiveVar bind_lv_info binder
630 | otherwise = unitLiveVar binder
631 -- c.f. the invariant on NestedLet
633 vars_bind :: FreeVarsInfo -- Free var info for body of binding
637 EscVarsSet, -- free vars; escapee vars
638 LiveInfo, -- Vars and CAFs live in binding
639 [(Id, HowBound)]) -- extension to environment
642 vars_bind body_fvs (NonRec binder rhs)
643 = coreToStgRhs body_fvs [] (binder,rhs)
644 `thenLne` \ (rhs2, bind_fvs, bind_lv_info, escs) ->
646 env_ext_item = mk_binding bind_lv_info binder rhs
648 returnLne (StgNonRec binder rhs2,
649 bind_fvs, escs, bind_lv_info, [env_ext_item])
652 vars_bind body_fvs (Rec pairs)
653 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
655 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
656 binders = map fst pairs
657 env_ext = [ mk_binding bind_lv_info b rhs
660 extendVarEnvLne env_ext (
661 mapAndUnzip4Lne (coreToStgRhs rec_scope_fvs binders) pairs
662 `thenLne` \ (rhss2, fvss, lv_infos, escss) ->
664 bind_fvs = unionFVInfos fvss
665 bind_lv_info = foldr unionLiveInfo emptyLiveInfo lv_infos
666 escs = unionVarSets escss
668 returnLne (StgRec (binders `zip` rhss2),
669 bind_fvs, escs, bind_lv_info, env_ext)
673 is_join_var :: Id -> Bool
674 -- A hack (used only for compiler debuggging) to tell if
675 -- a variable started life as a join point ($j)
676 is_join_var j = occNameUserString (getOccName j) == "$j"
680 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
683 -> LneM (StgRhs, FreeVarsInfo, LiveInfo, EscVarsSet)
685 coreToStgRhs scope_fv_info binders (bndr, rhs)
686 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
687 getEnvLne `thenLne` \ env ->
688 freeVarsToLiveVars (binders `minusFVBinders` rhs_fvs) `thenLne` \ lv_info ->
689 returnLne (mkStgRhs rhs_fvs (mkSRT lv_info) bndr_info new_rhs,
690 rhs_fvs, lv_info, rhs_escs)
692 bndr_info = lookupFVInfo scope_fv_info bndr
694 mkStgRhs :: FreeVarsInfo -> SRT -> StgBinderInfo -> StgExpr -> StgRhs
696 mkStgRhs rhs_fvs srt binder_info (StgConApp con args)
697 = StgRhsCon noCCS con args
699 mkStgRhs rhs_fvs srt binder_info (StgLam _ bndrs body)
700 = StgRhsClosure noCCS binder_info
705 mkStgRhs rhs_fvs srt binder_info rhs
706 = StgRhsClosure noCCS binder_info
712 SDM: disabled. Eval/Apply can't handle functions with arity zero very
713 well; and making these into simple non-updatable thunks breaks other
714 assumptions (namely that they will be entered only once).
716 upd_flag | isPAP env rhs = ReEntrant
717 | otherwise = Updatable
721 upd = if isOnceDem dem
722 then (if isNotTop toplev
723 then SingleEntry -- HA! Paydirt for "dem"
726 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
730 -- For now we forbid SingleEntry CAFs; they tickle the
731 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
732 -- and I don't understand why. There's only one SE_CAF (well,
733 -- only one that tickled a great gaping bug in an earlier attempt
734 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
735 -- specifically Main.lvl6 in spectral/cryptarithm2.
736 -- So no great loss. KSW 2000-07.
740 Detect thunks which will reduce immediately to PAPs, and make them
741 non-updatable. This has several advantages:
743 - the non-updatable thunk behaves exactly like the PAP,
745 - the thunk is more efficient to enter, because it is
746 specialised to the task.
748 - we save one update frame, one stg_update_PAP, one update
749 and lots of PAP_enters.
751 - in the case where the thunk is top-level, we save building
752 a black hole and futhermore the thunk isn't considered to
753 be a CAF any more, so it doesn't appear in any SRTs.
755 We do it here, because the arity information is accurate, and we need
756 to do it before the SRT pass to save the SRT entries associated with
759 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
761 arity = stgArity f (lookupBinding env f)
765 %************************************************************************
767 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
769 %************************************************************************
771 There's a lot of stuff to pass around, so we use this @LneM@ monad to
772 help. All the stuff here is only passed *down*.
775 type LneM a = IdEnv HowBound
776 -> LiveInfo -- Vars and CAFs live in continuation
779 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
780 -- i.e. ones with a nested (non-top-level) binding
781 CafSet) -- Static live variables;
782 -- i.e. top-level variables that are CAFs or refer to them
784 type EscVarsSet = IdSet
788 = ImportBound -- Used only as a response to lookupBinding; never
789 -- exists in the range of the (IdEnv HowBound)
791 | LetBound -- A let(rec) in this module
792 LetInfo -- Whether top level or nested
793 Arity -- Its arity (local Ids don't have arity info at this point)
795 | LambdaBound -- Used for both lambda and case
798 = TopLet -- top level things
799 | NestedLet LiveInfo -- For nested things, what is live if this
800 -- thing is live? Invariant: the binder
801 -- itself is always a member of
802 -- the dynamic set of its own LiveInfo
804 isLetBound (LetBound _ _) = True
805 isLetBound other = False
807 topLevelBound ImportBound = True
808 topLevelBound (LetBound TopLet _) = True
809 topLevelBound other = False
812 For a let(rec)-bound variable, x, we record LiveInfo, the set of
813 variables that are live if x is live. This LiveInfo comprises
814 (a) dynamic live variables (ones with a non-top-level binding)
815 (b) static live variabes (CAFs or things that refer to CAFs)
817 For "normal" variables (a) is just x alone. If x is a let-no-escaped
818 variable then x is represented by a code pointer and a stack pointer
819 (well, one for each stack). So all of the variables needed in the
820 execution of x are live if x is, and are therefore recorded in the
821 LetBound constructor; x itself *is* included.
823 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
827 emptyLiveInfo :: LiveInfo
828 emptyLiveInfo = (emptyVarSet,emptyVarSet)
830 unitLiveVar :: Id -> LiveInfo
831 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
833 unitLiveCaf :: Id -> LiveInfo
834 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
836 addLiveVar :: LiveInfo -> Id -> LiveInfo
837 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
839 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
840 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
842 mkSRT :: LiveInfo -> SRT
843 mkSRT (_, cafs) = SRTEntries cafs
845 getLiveVars :: LiveInfo -> StgLiveVars
846 getLiveVars (lvs, _) = lvs
850 The std monad functions:
852 initLne :: IdEnv HowBound -> LneM a -> a
853 initLne env m = m env emptyLiveInfo
857 {-# INLINE thenLne #-}
858 {-# INLINE returnLne #-}
860 returnLne :: a -> LneM a
861 returnLne e env lvs_cont = e
863 thenLne :: LneM a -> (a -> LneM b) -> LneM b
864 thenLne m k env lvs_cont
865 = k (m env lvs_cont) env lvs_cont
867 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
868 mapAndUnzipLne f [] = returnLne ([],[])
869 mapAndUnzipLne f (x:xs)
870 = f x `thenLne` \ (r1, r2) ->
871 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
872 returnLne (r1:rs1, r2:rs2)
874 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
875 mapAndUnzip3Lne f [] = returnLne ([],[],[])
876 mapAndUnzip3Lne f (x:xs)
877 = f x `thenLne` \ (r1, r2, r3) ->
878 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
879 returnLne (r1:rs1, r2:rs2, r3:rs3)
881 mapAndUnzip4Lne :: (a -> LneM (b,c,d,e)) -> [a] -> LneM ([b],[c],[d],[e])
882 mapAndUnzip4Lne f [] = returnLne ([],[],[],[])
883 mapAndUnzip4Lne f (x:xs)
884 = f x `thenLne` \ (r1, r2, r3, r4) ->
885 mapAndUnzip4Lne f xs `thenLne` \ (rs1, rs2, rs3, rs4) ->
886 returnLne (r1:rs1, r2:rs2, r3:rs3, r4:rs4)
888 fixLne :: (a -> LneM a) -> LneM a
889 fixLne expr env lvs_cont
892 result = expr result env lvs_cont
895 Functions specific to this monad:
898 getVarsLiveInCont :: LneM LiveInfo
899 getVarsLiveInCont env lvs_cont = lvs_cont
901 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
902 setVarsLiveInCont new_lvs_cont expr env lvs_cont
903 = expr env new_lvs_cont
905 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
906 extendVarEnvLne ids_w_howbound expr env lvs_cont
907 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
909 lookupVarLne :: Id -> LneM HowBound
910 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
912 getEnvLne :: LneM (IdEnv HowBound)
913 getEnvLne env lvs_cont = returnLne env env lvs_cont
915 lookupBinding :: IdEnv HowBound -> Id -> HowBound
916 lookupBinding env v = case lookupVarEnv env v of
918 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
921 -- The result of lookupLiveVarsForSet, a set of live variables, is
922 -- only ever tacked onto a decorated expression. It is never used as
923 -- the basis of a control decision, which might give a black hole.
925 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
926 freeVarsToLiveVars fvs env live_in_cont
927 = returnLne live_info env live_in_cont
929 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
930 lvs_from_fvs = map do_one (allFreeIds fvs)
932 do_one (v, how_bound)
934 ImportBound -> unitLiveCaf v -- Only CAF imports are
937 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
938 | otherwise -> emptyLiveInfo
940 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
941 -- (see the invariant on NestedLet)
943 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
946 %************************************************************************
948 \subsection[Free-var info]{Free variable information}
950 %************************************************************************
953 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
954 -- The Var is so we can gather up the free variables
957 -- The HowBound info just saves repeated lookups;
958 -- we look up just once when we encounter the occurrence.
959 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
960 -- Imported Ids without CAF refs are simply
961 -- not put in the FreeVarsInfo for an expression.
962 -- See singletonFVInfo and freeVarsToLiveVars
964 -- StgBinderInfo records how it occurs; notably, we
965 -- are interested in whether it only occurs in saturated
966 -- applications, because then we don't need to build a
968 -- If f is mapped to noBinderInfo, that means
969 -- that f *is* mentioned (else it wouldn't be in the
970 -- IdEnv at all), but perhaps in an unsaturated applications.
972 -- All case/lambda-bound things are also mapped to
973 -- noBinderInfo, since we aren't interested in their
976 -- For ILX we track free var info for type variables too;
977 -- hence VarEnv not IdEnv
981 emptyFVInfo :: FreeVarsInfo
982 emptyFVInfo = emptyVarEnv
984 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
985 -- Don't record non-CAF imports at all, to keep free-var sets small
986 singletonFVInfo id ImportBound info
987 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
988 | otherwise = emptyVarEnv
989 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
991 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
992 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
994 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
995 -- Type variables must be lambda-bound
997 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
998 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1000 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1001 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1003 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1004 minusFVBinders vs fv = foldr minusFVBinder fv vs
1006 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1007 minusFVBinder v fv | isId v && opt_RuntimeTypes
1008 = (fv `delVarEnv` v) `unionFVInfo`
1009 tyvarFVInfo (tyVarsOfType (idType v))
1010 | otherwise = fv `delVarEnv` v
1011 -- When removing a binder, remember to add its type variables
1012 -- c.f. CoreFVs.delBinderFV
1014 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1015 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1017 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1018 -- Find how the given Id is used.
1019 -- Externally visible things may be used any old how
1021 | isExternalName (idName id) = noBinderInfo
1022 | otherwise = case lookupVarEnv fvs id of
1023 Nothing -> noBinderInfo
1024 Just (_,_,info) -> info
1026 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1027 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- varEnvElts fvs, isId id]
1029 -- Non-top-level things only, both type variables and ids
1030 -- (type variables only if opt_RuntimeTypes)
1031 getFVs :: FreeVarsInfo -> [Var]
1032 getFVs fvs = [id | (id, how_bound, _) <- varEnvElts fvs,
1033 not (topLevelBound how_bound) ]
1035 getFVSet :: FreeVarsInfo -> VarSet
1036 getFVSet fvs = mkVarSet (getFVs fvs)
1038 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1039 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1040 (id1, hb1, combineStgBinderInfo info1 info2)
1043 -- The HowBound info for a variable in the FVInfo should be consistent
1044 check_eq_how_bound ImportBound ImportBound = True
1045 check_eq_how_bound LambdaBound LambdaBound = True
1046 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1047 check_eq_how_bound hb1 hb2 = False
1049 check_eq_li (NestedLet _) (NestedLet _) = True
1050 check_eq_li TopLet TopLet = True
1051 check_eq_li li1 li2 = False
1057 filterStgBinders :: [Var] -> [Var]
1058 filterStgBinders bndrs
1059 | opt_RuntimeTypes = bndrs
1060 | otherwise = filter isId bndrs
1065 -- Ignore all notes except SCC
1066 myCollectBinders expr
1069 go bs (Lam b e) = go (b:bs) e
1070 go bs e@(Note (SCC _) _) = (reverse bs, e)
1071 go bs (Note _ e) = go bs e
1072 go bs e = (reverse bs, e)
1074 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1075 -- We assume that we only have variables
1076 -- in the function position by now
1080 go (Var v) as = (v, as)
1081 go (App f a) as = go f (a:as)
1082 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1083 go (Note n e) as = go e as
1084 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1088 stgArity :: Id -> HowBound -> Arity
1089 stgArity f (LetBound _ arity) = arity
1090 stgArity f ImportBound = idArity f
1091 stgArity f LambdaBound = 0