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 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 emptyVarEnv pgm
147 coreExprToStg :: CoreExpr -> StgExpr
149 = new_expr where (new_expr,_,_) = initLne emptyVarEnv (coreToStgExpr expr)
153 :: IdEnv HowBound -- environment for the bindings
155 -> (IdEnv HowBound, FreeVarsInfo, [StgBinding])
157 coreTopBindsToStg env [] = (env, emptyFVInfo, [])
158 coreTopBindsToStg env (b:bs)
159 = (env2, fvs2, b':bs')
161 -- env accumulates down the list of binds, fvs accumulates upwards
162 (env1, fvs2, b' ) = coreTopBindToStg env fvs1 b
163 (env2, fvs1, bs') = coreTopBindsToStg env1 bs
168 -> FreeVarsInfo -- Info about the body
170 -> (IdEnv HowBound, FreeVarsInfo, StgBinding)
172 coreTopBindToStg env body_fvs (NonRec id rhs)
174 env' = extendVarEnv env id how_bound
175 how_bound = LetBound TopLet (manifestArity rhs)
177 (stg_rhs, fvs', lv_info) =
179 coreToTopStgRhs body_fvs (id,rhs) `thenLne` \ (stg_rhs, fvs') ->
180 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
181 returnLne (stg_rhs, fvs', lv_info)
184 bind = StgNonRec (mkSRT lv_info) id stg_rhs
186 ASSERT2(manifestArity rhs == stgRhsArity stg_rhs, ppr id)
187 ASSERT2(consistentCafInfo id bind, ppr id)
188 -- WARN(not (consistent caf_info bind), ppr id <+> ppr cafs <+> ppCafInfo caf_info)
189 (env', fvs' `unionFVInfo` body_fvs, bind)
191 coreTopBindToStg env body_fvs (Rec pairs)
193 (binders, rhss) = unzip pairs
195 extra_env' = [ (b, LetBound TopLet (manifestArity rhs))
196 | (b, rhs) <- pairs ]
197 env' = extendVarEnvList env extra_env'
199 (stg_rhss, fvs', lv_info)
201 mapAndUnzipLne (coreToTopStgRhs body_fvs) pairs
202 `thenLne` \ (stg_rhss, fvss') ->
203 let fvs' = unionFVInfos fvss' in
204 freeVarsToLiveVars fvs' `thenLne` \ lv_info ->
205 returnLne (stg_rhss, fvs', lv_info)
208 bind = StgRec (mkSRT lv_info) (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 -- WARN(not (consistent caf_info bind), ppr binders <+> ppr cafs <+> ppCafInfo caf_info)
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")
222 = id_marked_caffy || not binding_is_caffy
224 = id_marked_caffy == binding_is_caffy
226 id_marked_caffy = mayHaveCafRefs (idCafInfo id)
227 binding_is_caffy = stgBindHasCafRefs bind
233 :: FreeVarsInfo -- Free var info for the scope of the binding
235 -> LneM (StgRhs, FreeVarsInfo)
237 coreToTopStgRhs scope_fv_info (bndr, rhs)
238 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, _) ->
239 returnLne (mkTopStgRhs upd rhs_fvs bndr_info new_rhs, rhs_fvs)
241 bndr_info = lookupFVInfo scope_fv_info bndr
243 upd | rhsIsNonUpd rhs = SingleEntry
244 | otherwise = Updatable
246 mkTopStgRhs :: UpdateFlag -> FreeVarsInfo -> StgBinderInfo -> StgExpr -> StgRhs
248 mkTopStgRhs upd rhs_fvs binder_info (StgLam _ bndrs body)
249 = StgRhsClosure noCCS binder_info
254 mkTopStgRhs upd rhs_fvs binder_info (StgConApp con args)
255 | not (isUpdatable upd) -- StgConApps can be updatable (see isCrossDllConApp)
256 = StgRhsCon noCCS con args
258 mkTopStgRhs upd rhs_fvs binder_info rhs
259 = StgRhsClosure noCCS binder_info
266 -- ---------------------------------------------------------------------------
268 -- ---------------------------------------------------------------------------
273 -> LneM (StgExpr, -- Decorated STG expr
274 FreeVarsInfo, -- Its free vars (NB free, not live)
275 EscVarsSet) -- Its escapees, a subset of its free vars;
276 -- also a subset of the domain of the envt
277 -- because we are only interested in the escapees
278 -- for vars which might be turned into
279 -- let-no-escaped ones.
282 The second and third components can be derived in a simple bottom up pass, not
283 dependent on any decisions about which variables will be let-no-escaped or
284 not. The first component, that is, the decorated expression, may then depend
285 on these components, but it in turn is not scrutinised as the basis for any
286 decisions. Hence no black holes.
289 coreToStgExpr (Lit l) = returnLne (StgLit l, emptyFVInfo, emptyVarSet)
290 coreToStgExpr (Var v) = coreToStgApp Nothing v []
292 coreToStgExpr expr@(App _ _)
293 = coreToStgApp Nothing f args
295 (f, args) = myCollectArgs expr
297 coreToStgExpr expr@(Lam _ _)
299 (args, body) = myCollectBinders expr
300 args' = filterStgBinders args
302 extendVarEnvLne [ (a, LambdaBound) | a <- args' ] $
303 coreToStgExpr body `thenLne` \ (body, body_fvs, body_escs) ->
305 fvs = args' `minusFVBinders` body_fvs
306 escs = body_escs `delVarSetList` args'
307 result_expr | null args' = body
308 | otherwise = StgLam (exprType expr) args' body
310 returnLne (result_expr, fvs, escs)
312 coreToStgExpr (Note (SCC cc) expr)
313 = coreToStgExpr expr `thenLne` ( \ (expr2, fvs, escs) ->
314 returnLne (StgSCC cc expr2, fvs, escs) )
317 -- For ILX, convert (__coerce__ to_ty from_ty e)
318 -- into (coerce to_ty from_ty e)
319 -- where coerce is real function
320 coreToStgExpr (Note (Coerce to_ty from_ty) expr)
321 = coreToStgExpr (mkApps (Var unsafeCoerceId)
322 [Type from_ty, Type to_ty, expr])
325 coreToStgExpr (Note other_note expr)
328 -- Cases require a little more real work.
330 coreToStgExpr (Case scrut bndr alts)
331 = extendVarEnvLne [(bndr, LambdaBound)] (
332 mapAndUnzip3Lne vars_alt alts `thenLne` \ (alts2, fvs_s, escs_s) ->
333 returnLne ( mkStgAlts (idType bndr) alts2,
335 unionVarSets escs_s )
336 ) `thenLne` \ (alts2, alts_fvs, alts_escs) ->
338 -- Determine whether the default binder is dead or not
339 -- This helps the code generator to avoid generating an assignment
340 -- for the case binder (is extremely rare cases) ToDo: remove.
341 bndr' | bndr `elementOfFVInfo` alts_fvs = bndr
342 | otherwise = bndr `setIdOccInfo` IAmDead
344 -- Don't consider the default binder as being 'live in alts',
345 -- since this is from the point of view of the case expr, where
346 -- the default binder is not free.
347 alts_fvs_wo_bndr = bndr `minusFVBinder` alts_fvs
348 alts_escs_wo_bndr = alts_escs `delVarSet` bndr
351 freeVarsToLiveVars alts_fvs_wo_bndr `thenLne` \ alts_lv_info ->
353 -- We tell the scrutinee that everything
354 -- live in the alts is live in it, too.
355 setVarsLiveInCont alts_lv_info (
356 coreToStgExpr scrut `thenLne` \ (scrut2, scrut_fvs, scrut_escs) ->
357 freeVarsToLiveVars scrut_fvs `thenLne` \ scrut_lv_info ->
358 returnLne (scrut2, scrut_fvs, scrut_escs, scrut_lv_info)
360 `thenLne` \ (scrut2, scrut_fvs, scrut_escs, scrut_lv_info) ->
363 StgCase scrut2 (getLiveVars scrut_lv_info)
364 (getLiveVars alts_lv_info)
368 scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
369 alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
370 -- You might think we should have scrut_escs, not
371 -- (getFVSet scrut_fvs), but actually we can't call, and
372 -- then return from, a let-no-escape thing.
375 vars_alt (con, binders, rhs)
376 = let -- Remove type variables
377 binders' = filterStgBinders binders
379 extendVarEnvLne [(b, LambdaBound) | b <- binders'] $
380 coreToStgExpr rhs `thenLne` \ (rhs2, rhs_fvs, rhs_escs) ->
382 -- Records whether each param is used in the RHS
383 good_use_mask = [ b `elementOfFVInfo` rhs_fvs | b <- binders' ]
385 returnLne ( (con, binders', good_use_mask, rhs2),
386 binders' `minusFVBinders` rhs_fvs,
387 rhs_escs `delVarSetList` binders' )
388 -- ToDo: remove the delVarSet;
389 -- since escs won't include any of these binders
392 Lets not only take quite a bit of work, but this is where we convert
393 then to let-no-escapes, if we wish.
395 (Meanwhile, we don't expect to see let-no-escapes...)
397 coreToStgExpr (Let bind body)
398 = fixLne (\ ~(_, _, _, no_binder_escapes) ->
399 coreToStgLet no_binder_escapes bind body
400 ) `thenLne` \ (new_let, fvs, escs, _) ->
402 returnLne (new_let, fvs, escs)
406 mkStgAlts scrut_ty orig_alts
407 | is_prim_case = StgPrimAlts (tyConAppTyCon scrut_ty) prim_alts deflt
408 | otherwise = StgAlgAlts maybe_tycon alg_alts deflt
410 is_prim_case = isUnLiftedType scrut_ty && not (isUnboxedTupleType scrut_ty)
412 prim_alts = [(lit, rhs) | (LitAlt lit, _, _, rhs) <- other_alts]
413 alg_alts = [(con, bndrs, use, rhs) | (DataAlt con, bndrs, use, rhs) <- other_alts]
416 = case orig_alts of -- DEFAULT is always first if it's there at all
417 (DEFAULT, _, _, rhs) : other_alts -> (other_alts, StgBindDefault rhs)
418 other -> (orig_alts, StgNoDefault)
420 maybe_tycon = case alg_alts of
421 -- Get the tycon from the data con
422 (dc, _, _, _) : _rest -> Just (dataConTyCon dc)
424 -- Otherwise just do your best
425 [] -> case splitTyConApp_maybe (repType scrut_ty) of
426 Just (tc,_) | isAlgTyCon tc -> Just tc
431 -- ---------------------------------------------------------------------------
433 -- ---------------------------------------------------------------------------
437 :: Maybe UpdateFlag -- Just upd <=> this application is
438 -- the rhs of a thunk binding
439 -- x = [...] \upd [] -> the_app
440 -- with specified update flag
442 -> [CoreArg] -- Arguments
443 -> LneM (StgExpr, FreeVarsInfo, EscVarsSet)
445 coreToStgApp maybe_thunk_body f args
446 = coreToStgArgs args `thenLne` \ (args', args_fvs) ->
447 lookupVarLne f `thenLne` \ how_bound ->
450 n_val_args = valArgCount args
451 not_letrec_bound = not (isLetBound how_bound)
453 = let fvs = singletonFVInfo f how_bound fun_occ in
454 -- e.g. (f :: a -> int) (x :: a)
455 -- Here the free variables are "f", "x" AND the type variable "a"
456 -- coreToStgArgs will deal with the arguments recursively
457 if opt_RuntimeTypes then
458 fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType (varType f))
461 -- Mostly, the arity info of a function is in the fn's IdInfo
462 -- But new bindings introduced by CoreSat may not have no
463 -- arity info; it would do us no good anyway. For example:
464 -- let f = \ab -> e in f
465 -- No point in having correct arity info for f!
466 -- Hence the hasArity stuff below.
467 -- NB: f_arity is only consulted for LetBound things
468 f_arity = stgArity f how_bound
469 saturated = f_arity <= n_val_args
472 | not_letrec_bound = noBinderInfo -- Uninteresting variable
473 | f_arity > 0 && saturated = stgSatOcc -- Saturated or over-saturated function call
474 | otherwise = stgUnsatOcc -- Unsaturated function or thunk
477 | not_letrec_bound = emptyVarSet -- Only letrec-bound escapees are interesting
478 | f_arity == n_val_args = emptyVarSet -- A function *or thunk* with an exactly
479 -- saturated call doesn't escape
480 -- (let-no-escape applies to 'thunks' too)
482 | otherwise = unitVarSet f -- Inexact application; it does escape
484 -- At the moment of the call:
486 -- either the function is *not* let-no-escaped, in which case
487 -- nothing is live except live_in_cont
488 -- or the function *is* let-no-escaped in which case the
489 -- variables it uses are live, but still the function
490 -- itself is not. PS. In this case, the function's
491 -- live vars should already include those of the
492 -- continuation, but it does no harm to just union the
495 res_ty = exprType (mkApps (Var f) args)
496 app = case globalIdDetails f of
497 DataConWorkId dc | saturated -> StgConApp dc args'
498 PrimOpId op -> ASSERT( saturated )
499 StgOpApp (StgPrimOp op) args' res_ty
500 FCallId call -> ASSERT( saturated )
501 StgOpApp (StgFCallOp call (idUnique f)) args' res_ty
502 _other -> StgApp f args'
507 fun_fvs `unionFVInfo` args_fvs,
508 fun_escs `unionVarSet` (getFVSet args_fvs)
509 -- All the free vars of the args are disqualified
510 -- from being let-no-escaped.
515 -- ---------------------------------------------------------------------------
517 -- This is the guy that turns applications into A-normal form
518 -- ---------------------------------------------------------------------------
520 coreToStgArgs :: [CoreArg] -> LneM ([StgArg], FreeVarsInfo)
522 = returnLne ([], emptyFVInfo)
524 coreToStgArgs (Type ty : args) -- Type argument
525 = coreToStgArgs args `thenLne` \ (args', fvs) ->
526 if opt_RuntimeTypes then
527 returnLne (StgTypeArg ty : args', fvs `unionFVInfo` tyvarFVInfo (tyVarsOfType ty))
529 returnLne (args', fvs)
531 coreToStgArgs (arg : args) -- Non-type argument
532 = coreToStgArgs args `thenLne` \ (stg_args, args_fvs) ->
533 coreToStgExpr arg `thenLne` \ (arg', arg_fvs, escs) ->
535 fvs = args_fvs `unionFVInfo` arg_fvs
536 stg_arg = case arg' of
537 StgApp v [] -> StgVarArg v
538 StgConApp con [] -> StgVarArg (dataConWorkId con)
539 StgLit lit -> StgLitArg lit
540 _ -> pprPanic "coreToStgArgs" (ppr arg)
542 returnLne (stg_arg : stg_args, fvs)
545 -- ---------------------------------------------------------------------------
546 -- The magic for lets:
547 -- ---------------------------------------------------------------------------
550 :: Bool -- True <=> yes, we are let-no-escaping this let
551 -> CoreBind -- bindings
553 -> LneM (StgExpr, -- new let
554 FreeVarsInfo, -- variables free in the whole let
555 EscVarsSet, -- variables that escape from the whole let
556 Bool) -- True <=> none of the binders in the bindings
557 -- is among the escaping vars
559 coreToStgLet let_no_escape bind body
560 = fixLne (\ ~(_, _, _, _, _, rec_body_fvs, _, _) ->
562 -- Do the bindings, setting live_in_cont to empty if
563 -- we ain't in a let-no-escape world
564 getVarsLiveInCont `thenLne` \ live_in_cont ->
565 setVarsLiveInCont (if let_no_escape
568 (vars_bind rec_body_fvs bind)
569 `thenLne` \ ( bind2, bind_fvs, bind_escs, bind_lv_info, env_ext) ->
572 extendVarEnvLne env_ext (
573 coreToStgExpr body `thenLne` \(body2, body_fvs, body_escs) ->
574 freeVarsToLiveVars body_fvs `thenLne` \ body_lv_info ->
576 returnLne (bind2, bind_fvs, bind_escs, getLiveVars bind_lv_info,
577 body2, body_fvs, body_escs, getLiveVars body_lv_info)
580 ) `thenLne` (\ (bind2, bind_fvs, bind_escs, bind_lvs,
581 body2, body_fvs, body_escs, body_lvs) ->
584 -- Compute the new let-expression
586 new_let | let_no_escape = StgLetNoEscape live_in_whole_let bind_lvs bind2 body2
587 | otherwise = StgLet bind2 body2
590 = binders `minusFVBinders` (bind_fvs `unionFVInfo` body_fvs)
593 = bind_lvs `unionVarSet` (body_lvs `delVarSetList` binders)
595 real_bind_escs = if let_no_escape then
599 -- Everything escapes which is free in the bindings
601 let_escs = (real_bind_escs `unionVarSet` body_escs) `delVarSetList` binders
603 all_escs = bind_escs `unionVarSet` body_escs -- Still includes binders of
606 no_binder_escapes = isEmptyVarSet (set_of_binders `intersectVarSet` all_escs)
609 -- Debugging code as requested by Andrew Kennedy
610 checked_no_binder_escapes
611 | not no_binder_escapes && any is_join_var binders
612 = pprTrace "Interesting! A join var that isn't let-no-escaped" (ppr binders)
614 | otherwise = no_binder_escapes
616 checked_no_binder_escapes = no_binder_escapes
619 -- Mustn't depend on the passed-in let_no_escape flag, since
620 -- no_binder_escapes is used by the caller to derive the flag!
626 checked_no_binder_escapes
629 set_of_binders = mkVarSet binders
630 binders = bindersOf bind
632 mk_binding bind_lv_info binder rhs
633 = (binder, LetBound (NestedLet live_vars) (manifestArity rhs))
635 live_vars | let_no_escape = addLiveVar bind_lv_info binder
636 | otherwise = unitLiveVar binder
637 -- c.f. the invariant on NestedLet
639 vars_bind :: FreeVarsInfo -- Free var info for body of binding
643 EscVarsSet, -- free vars; escapee vars
644 LiveInfo, -- Vars and CAFs live in binding
645 [(Id, HowBound)]) -- extension to environment
648 vars_bind body_fvs (NonRec binder rhs)
649 = coreToStgRhs body_fvs (binder,rhs)
650 `thenLne` \ (rhs2, bind_fvs, escs) ->
652 freeVarsToLiveVars bind_fvs `thenLne` \ bind_lv_info ->
654 env_ext_item = mk_binding bind_lv_info binder rhs
656 returnLne (StgNonRec (mkSRT bind_lv_info) binder rhs2,
657 bind_fvs, escs, bind_lv_info, [env_ext_item])
660 vars_bind body_fvs (Rec pairs)
661 = fixLne (\ ~(_, rec_rhs_fvs, _, bind_lv_info, _) ->
663 rec_scope_fvs = unionFVInfo body_fvs rec_rhs_fvs
664 binders = map fst pairs
665 env_ext = [ mk_binding bind_lv_info b rhs
668 extendVarEnvLne env_ext (
669 mapAndUnzip3Lne (coreToStgRhs rec_scope_fvs) pairs
670 `thenLne` \ (rhss2, fvss, escss) ->
672 bind_fvs = unionFVInfos fvss
673 escs = unionVarSets escss
675 freeVarsToLiveVars (binders `minusFVBinders` bind_fvs)
676 `thenLne` \ bind_lv_info ->
678 returnLne (StgRec (mkSRT bind_lv_info) (binders `zip` rhss2),
679 bind_fvs, escs, bind_lv_info, env_ext)
683 is_join_var :: Id -> Bool
684 -- A hack (used only for compiler debuggging) to tell if
685 -- a variable started life as a join point ($j)
686 is_join_var j = occNameUserString (getOccName j) == "$j"
690 coreToStgRhs :: FreeVarsInfo -- Free var info for the scope of the binding
692 -> LneM (StgRhs, FreeVarsInfo, EscVarsSet)
694 coreToStgRhs scope_fv_info (bndr, rhs)
695 = coreToStgExpr rhs `thenLne` \ (new_rhs, rhs_fvs, rhs_escs) ->
696 getEnvLne `thenLne` \ env ->
697 returnLne (mkStgRhs env rhs_fvs bndr_info new_rhs,
700 bndr_info = lookupFVInfo scope_fv_info bndr
702 mkStgRhs :: IdEnv HowBound -> FreeVarsInfo -> StgBinderInfo -> StgExpr -> StgRhs
704 mkStgRhs env rhs_fvs binder_info (StgConApp con args)
705 = StgRhsCon noCCS con args
707 mkStgRhs env rhs_fvs binder_info (StgLam _ bndrs body)
708 = StgRhsClosure noCCS binder_info
713 mkStgRhs env rhs_fvs binder_info rhs
714 = StgRhsClosure noCCS binder_info
720 SDM: disabled. Eval/Apply can't handle functions with arity zero very
721 well; and making these into simple non-updatable thunks breaks other
722 assumptions (namely that they will be entered only once).
724 upd_flag | isPAP env rhs = ReEntrant
725 | otherwise = Updatable
729 upd = if isOnceDem dem
730 then (if isNotTop toplev
731 then SingleEntry -- HA! Paydirt for "dem"
734 trace "WARNING: SE CAFs unsupported, forcing UPD instead" $
738 -- For now we forbid SingleEntry CAFs; they tickle the
739 -- ASSERT in rts/Storage.c line 215 at newCAF() re mut_link,
740 -- and I don't understand why. There's only one SE_CAF (well,
741 -- only one that tickled a great gaping bug in an earlier attempt
742 -- at ClosureInfo.getEntryConvention) in the whole of nofib,
743 -- specifically Main.lvl6 in spectral/cryptarithm2.
744 -- So no great loss. KSW 2000-07.
748 Detect thunks which will reduce immediately to PAPs, and make them
749 non-updatable. This has several advantages:
751 - the non-updatable thunk behaves exactly like the PAP,
753 - the thunk is more efficient to enter, because it is
754 specialised to the task.
756 - we save one update frame, one stg_update_PAP, one update
757 and lots of PAP_enters.
759 - in the case where the thunk is top-level, we save building
760 a black hole and futhermore the thunk isn't considered to
761 be a CAF any more, so it doesn't appear in any SRTs.
763 We do it here, because the arity information is accurate, and we need
764 to do it before the SRT pass to save the SRT entries associated with
767 isPAP env (StgApp f args) = listLengthCmp args arity == LT -- idArity f > length args
769 arity = stgArity f (lookupBinding env f)
773 %************************************************************************
775 \subsection[LNE-monad]{A little monad for this let-no-escaping pass}
777 %************************************************************************
779 There's a lot of stuff to pass around, so we use this @LneM@ monad to
780 help. All the stuff here is only passed *down*.
783 type LneM a = IdEnv HowBound
784 -> LiveInfo -- Vars and CAFs live in continuation
787 type LiveInfo = (StgLiveVars, -- Dynamic live variables;
788 -- i.e. ones with a nested (non-top-level) binding
789 CafSet) -- Static live variables;
790 -- i.e. top-level variables that are CAFs or refer to them
792 type EscVarsSet = IdSet
796 = ImportBound -- Used only as a response to lookupBinding; never
797 -- exists in the range of the (IdEnv HowBound)
799 | LetBound -- A let(rec) in this module
800 LetInfo -- Whether top level or nested
801 Arity -- Its arity (local Ids don't have arity info at this point)
803 | LambdaBound -- Used for both lambda and case
806 = TopLet -- top level things
807 | NestedLet LiveInfo -- For nested things, what is live if this
808 -- thing is live? Invariant: the binder
809 -- itself is always a member of
810 -- the dynamic set of its own LiveInfo
812 isLetBound (LetBound _ _) = True
813 isLetBound other = False
815 topLevelBound ImportBound = True
816 topLevelBound (LetBound TopLet _) = True
817 topLevelBound other = False
820 For a let(rec)-bound variable, x, we record LiveInfo, the set of
821 variables that are live if x is live. This LiveInfo comprises
822 (a) dynamic live variables (ones with a non-top-level binding)
823 (b) static live variabes (CAFs or things that refer to CAFs)
825 For "normal" variables (a) is just x alone. If x is a let-no-escaped
826 variable then x is represented by a code pointer and a stack pointer
827 (well, one for each stack). So all of the variables needed in the
828 execution of x are live if x is, and are therefore recorded in the
829 LetBound constructor; x itself *is* included.
831 The set of dynamic live variables is guaranteed ot have no further let-no-escaped
835 emptyLiveInfo :: LiveInfo
836 emptyLiveInfo = (emptyVarSet,emptyVarSet)
838 unitLiveVar :: Id -> LiveInfo
839 unitLiveVar lv = (unitVarSet lv, emptyVarSet)
841 unitLiveCaf :: Id -> LiveInfo
842 unitLiveCaf caf = (emptyVarSet, unitVarSet caf)
844 addLiveVar :: LiveInfo -> Id -> LiveInfo
845 addLiveVar (lvs, cafs) id = (lvs `extendVarSet` id, cafs)
847 unionLiveInfo :: LiveInfo -> LiveInfo -> LiveInfo
848 unionLiveInfo (lv1,caf1) (lv2,caf2) = (lv1 `unionVarSet` lv2, caf1 `unionVarSet` caf2)
850 mkSRT :: LiveInfo -> SRT
851 mkSRT (_, cafs) = SRTEntries cafs
853 getLiveVars :: LiveInfo -> StgLiveVars
854 getLiveVars (lvs, _) = lvs
858 The std monad functions:
860 initLne :: IdEnv HowBound -> LneM a -> a
861 initLne env m = m env emptyLiveInfo
865 {-# INLINE thenLne #-}
866 {-# INLINE returnLne #-}
868 returnLne :: a -> LneM a
869 returnLne e env lvs_cont = e
871 thenLne :: LneM a -> (a -> LneM b) -> LneM b
872 thenLne m k env lvs_cont
873 = k (m env lvs_cont) env lvs_cont
875 mapLne :: (a -> LneM b) -> [a] -> LneM [b]
876 mapLne f [] = returnLne []
878 = f x `thenLne` \ r ->
879 mapLne f xs `thenLne` \ rs ->
882 mapAndUnzipLne :: (a -> LneM (b,c)) -> [a] -> LneM ([b],[c])
884 mapAndUnzipLne f [] = returnLne ([],[])
885 mapAndUnzipLne f (x:xs)
886 = f x `thenLne` \ (r1, r2) ->
887 mapAndUnzipLne f xs `thenLne` \ (rs1, rs2) ->
888 returnLne (r1:rs1, r2:rs2)
890 mapAndUnzip3Lne :: (a -> LneM (b,c,d)) -> [a] -> LneM ([b],[c],[d])
892 mapAndUnzip3Lne f [] = returnLne ([],[],[])
893 mapAndUnzip3Lne f (x:xs)
894 = f x `thenLne` \ (r1, r2, r3) ->
895 mapAndUnzip3Lne f xs `thenLne` \ (rs1, rs2, rs3) ->
896 returnLne (r1:rs1, r2:rs2, r3:rs3)
898 fixLne :: (a -> LneM a) -> LneM a
899 fixLne expr env lvs_cont
902 result = expr result env lvs_cont
905 Functions specific to this monad:
908 getVarsLiveInCont :: LneM LiveInfo
909 getVarsLiveInCont env lvs_cont = lvs_cont
911 setVarsLiveInCont :: LiveInfo -> LneM a -> LneM a
912 setVarsLiveInCont new_lvs_cont expr env lvs_cont
913 = expr env new_lvs_cont
915 extendVarEnvLne :: [(Id, HowBound)] -> LneM a -> LneM a
916 extendVarEnvLne ids_w_howbound expr env lvs_cont
917 = expr (extendVarEnvList env ids_w_howbound) lvs_cont
919 lookupVarLne :: Id -> LneM HowBound
920 lookupVarLne v env lvs_cont = returnLne (lookupBinding env v) env lvs_cont
922 getEnvLne :: LneM (IdEnv HowBound)
923 getEnvLne env lvs_cont = returnLne env env lvs_cont
925 lookupBinding :: IdEnv HowBound -> Id -> HowBound
926 lookupBinding env v = case lookupVarEnv env v of
928 Nothing -> ASSERT2( isGlobalId v, ppr v ) ImportBound
931 -- The result of lookupLiveVarsForSet, a set of live variables, is
932 -- only ever tacked onto a decorated expression. It is never used as
933 -- the basis of a control decision, which might give a black hole.
935 freeVarsToLiveVars :: FreeVarsInfo -> LneM LiveInfo
936 freeVarsToLiveVars fvs env live_in_cont
937 = returnLne live_info env live_in_cont
939 live_info = foldr unionLiveInfo live_in_cont lvs_from_fvs
940 lvs_from_fvs = map do_one (allFreeIds fvs)
942 do_one (v, how_bound)
944 ImportBound -> unitLiveCaf v -- Only CAF imports are
947 | mayHaveCafRefs (idCafInfo v) -> unitLiveCaf v
948 | otherwise -> emptyLiveInfo
950 LetBound (NestedLet lvs) _ -> lvs -- lvs already contains v
951 -- (see the invariant on NestedLet)
953 _lambda_or_case_binding -> unitLiveVar v -- Bound by lambda or case
956 %************************************************************************
958 \subsection[Free-var info]{Free variable information}
960 %************************************************************************
963 type FreeVarsInfo = VarEnv (Var, HowBound, StgBinderInfo)
964 -- The Var is so we can gather up the free variables
967 -- The HowBound info just saves repeated lookups;
968 -- we look up just once when we encounter the occurrence.
969 -- INVARIANT: Any ImportBound Ids are HaveCafRef Ids
970 -- Imported Ids without CAF refs are simply
971 -- not put in the FreeVarsInfo for an expression.
972 -- See singletonFVInfo and freeVarsToLiveVars
974 -- StgBinderInfo records how it occurs; notably, we
975 -- are interested in whether it only occurs in saturated
976 -- applications, because then we don't need to build a
978 -- If f is mapped to noBinderInfo, that means
979 -- that f *is* mentioned (else it wouldn't be in the
980 -- IdEnv at all), but perhaps in an unsaturated applications.
982 -- All case/lambda-bound things are also mapped to
983 -- noBinderInfo, since we aren't interested in their
986 -- For ILX we track free var info for type variables too;
987 -- hence VarEnv not IdEnv
991 emptyFVInfo :: FreeVarsInfo
992 emptyFVInfo = emptyVarEnv
994 singletonFVInfo :: Id -> HowBound -> StgBinderInfo -> FreeVarsInfo
995 -- Don't record non-CAF imports at all, to keep free-var sets small
996 singletonFVInfo id ImportBound info
997 | mayHaveCafRefs (idCafInfo id) = unitVarEnv id (id, ImportBound, info)
998 | otherwise = emptyVarEnv
999 singletonFVInfo id how_bound info = unitVarEnv id (id, how_bound, info)
1001 tyvarFVInfo :: TyVarSet -> FreeVarsInfo
1002 tyvarFVInfo tvs = foldVarSet add emptyFVInfo tvs
1004 add tv fvs = extendVarEnv fvs tv (tv, LambdaBound, noBinderInfo)
1005 -- Type variables must be lambda-bound
1007 unionFVInfo :: FreeVarsInfo -> FreeVarsInfo -> FreeVarsInfo
1008 unionFVInfo fv1 fv2 = plusVarEnv_C plusFVInfo fv1 fv2
1010 unionFVInfos :: [FreeVarsInfo] -> FreeVarsInfo
1011 unionFVInfos fvs = foldr unionFVInfo emptyFVInfo fvs
1013 minusFVBinders :: [Id] -> FreeVarsInfo -> FreeVarsInfo
1014 minusFVBinders vs fv = foldr minusFVBinder fv vs
1016 minusFVBinder :: Id -> FreeVarsInfo -> FreeVarsInfo
1017 minusFVBinder v fv | isId v && opt_RuntimeTypes
1018 = (fv `delVarEnv` v) `unionFVInfo`
1019 tyvarFVInfo (tyVarsOfType (idType v))
1020 | otherwise = fv `delVarEnv` v
1021 -- When removing a binder, remember to add its type variables
1022 -- c.f. CoreFVs.delBinderFV
1024 elementOfFVInfo :: Id -> FreeVarsInfo -> Bool
1025 elementOfFVInfo id fvs = maybeToBool (lookupVarEnv fvs id)
1027 lookupFVInfo :: FreeVarsInfo -> Id -> StgBinderInfo
1028 -- Find how the given Id is used.
1029 -- Externally visible things may be used any old how
1031 | isExternalName (idName id) = noBinderInfo
1032 | otherwise = case lookupVarEnv fvs id of
1033 Nothing -> noBinderInfo
1034 Just (_,_,info) -> info
1036 allFreeIds :: FreeVarsInfo -> [(Id,HowBound)] -- Both top level and non-top-level Ids
1037 allFreeIds fvs = [(id,how_bound) | (id,how_bound,_) <- rngVarEnv fvs, isId id]
1039 -- Non-top-level things only, both type variables and ids
1040 -- (type variables only if opt_RuntimeTypes)
1041 getFVs :: FreeVarsInfo -> [Var]
1042 getFVs fvs = [id | (id, how_bound, _) <- rngVarEnv fvs,
1043 not (topLevelBound how_bound) ]
1045 getFVSet :: FreeVarsInfo -> VarSet
1046 getFVSet fvs = mkVarSet (getFVs fvs)
1048 plusFVInfo (id1,hb1,info1) (id2,hb2,info2)
1049 = ASSERT (id1 == id2 && hb1 `check_eq_how_bound` hb2)
1050 (id1, hb1, combineStgBinderInfo info1 info2)
1053 -- The HowBound info for a variable in the FVInfo should be consistent
1054 check_eq_how_bound ImportBound ImportBound = True
1055 check_eq_how_bound LambdaBound LambdaBound = True
1056 check_eq_how_bound (LetBound li1 ar1) (LetBound li2 ar2) = ar1 == ar2 && check_eq_li li1 li2
1057 check_eq_how_bound hb1 hb2 = False
1059 check_eq_li (NestedLet _) (NestedLet _) = True
1060 check_eq_li TopLet TopLet = True
1061 check_eq_li li1 li2 = False
1067 filterStgBinders :: [Var] -> [Var]
1068 filterStgBinders bndrs
1069 | opt_RuntimeTypes = bndrs
1070 | otherwise = filter isId bndrs
1075 -- Ignore all notes except SCC
1076 myCollectBinders expr
1079 go bs (Lam b e) = go (b:bs) e
1080 go bs e@(Note (SCC _) _) = (reverse bs, e)
1081 go bs (Note _ e) = go bs e
1082 go bs e = (reverse bs, e)
1084 myCollectArgs :: CoreExpr -> (Id, [CoreArg])
1085 -- We assume that we only have variables
1086 -- in the function position by now
1090 go (Var v) as = (v, as)
1091 go (App f a) as = go f (a:as)
1092 go (Note (SCC _) e) as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1093 go (Note n e) as = go e as
1094 go _ as = pprPanic "CoreToStg.myCollectArgs" (ppr expr)
1098 stgArity :: Id -> HowBound -> Arity
1099 stgArity f (LetBound _ arity) = arity
1100 stgArity f ImportBound = idArity f
1101 stgArity f LambdaBound = 0