summaryrefslogtreecommitdiff
path: root/compiler/GHC/CoreToIface.hs
blob: 2a4e6c9f331f15997e93342ac4a574ab08555419 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728

{-# LANGUAGE Strict #-} -- See Note [Avoiding space leaks in toIface*]

-- | Functions for converting Core things to interface file things.
module GHC.CoreToIface
    ( -- * Binders
      toIfaceTvBndr
    , toIfaceTvBndrs
    , toIfaceIdBndr
    , toIfaceBndr
    , toIfaceForAllBndr
    , toIfaceTyCoVarBinders
    , toIfaceTyVar
      -- * Types
    , toIfaceType, toIfaceTypeX
    , toIfaceKind
    , toIfaceTcArgs
    , toIfaceTyCon
    , toIfaceTyCon_name
    , toIfaceTyLit
      -- * Tidying types
    , tidyToIfaceType
    , tidyToIfaceContext
    , tidyToIfaceTcArgs
      -- * Coercions
    , toIfaceCoercion, toIfaceCoercionX
      -- * Pattern synonyms
    , patSynToIfaceDecl
      -- * Expressions
    , toIfaceExpr
    , toIfaceBang
    , toIfaceSrcBang
    , toIfaceLetBndr
    , toIfaceIdDetails
    , toIfaceIdInfo
    , toIfUnfolding
    , toIfaceTickish
    , toIfaceBind
    , toIfaceAlt
    , toIfaceCon
    , toIfaceApp
    , toIfaceVar
      -- * Other stuff
    , toIfaceLFInfo
    ) where

import GHC.Prelude

import GHC.StgToCmm.Types

import GHC.Core
import GHC.Core.TyCon hiding ( pprPromotionQuote )
import GHC.Core.Coercion.Axiom
import GHC.Core.DataCon
import GHC.Core.Type
import GHC.Core.Multiplicity
import GHC.Core.PatSyn
import GHC.Core.TyCo.Rep
import GHC.Core.TyCo.Tidy ( tidyCo )

import GHC.Builtin.Types.Prim ( eqPrimTyCon, eqReprPrimTyCon )
import GHC.Builtin.Types ( heqTyCon )
import GHC.Builtin.Names

import GHC.Iface.Syntax
import GHC.Data.FastString

import GHC.Types.Id
import GHC.Types.Id.Info
import GHC.Types.Id.Make ( noinlineIdName )
import GHC.Types.Literal
import GHC.Types.Name
import GHC.Types.Basic
import GHC.Types.Var
import GHC.Types.Var.Env
import GHC.Types.Var.Set
import GHC.Types.Tickish
import GHC.Types.Demand ( isTopSig )
import GHC.Types.Cpr ( topCprSig )

import GHC.Utils.Outputable
import GHC.Utils.Panic
import GHC.Utils.Misc
import GHC.Utils.Trace

import Data.Maybe ( catMaybes )

{- Note [Avoiding space leaks in toIface*]
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Building a interface file depends on the output of the simplifier.
If we build these lazily this would mean keeping the Core AST alive
much longer than necessary causing a space "leak".

This happens for example when we only write the interface file to disk
after code gen has run, in which case we might carry megabytes of core
AST in the heap which is no longer needed.

We avoid this in two ways.
* First we use -XStrict in GHC.CoreToIface which avoids many thunks
  to begin with.
* Second we define NFData instance for Iface syntax and use them to
  force any remaining thunks.

-XStrict is not sufficient as patterns of the form `f (g x)` would still
result in a thunk being allocated for `g x`.

NFData is sufficient for the space leak, but using -XStrict reduces allocation
by ~0.1% when compiling with -O. (nofib/spectral/simple, T10370).
It's essentially free performance hence we use -XStrict on top of NFData.

MR !1633 on gitlab, has more discussion on the topic.
-}

----------------
toIfaceTvBndr :: TyVar -> IfaceTvBndr
toIfaceTvBndr = toIfaceTvBndrX emptyVarSet

toIfaceTvBndrX :: VarSet -> TyVar -> IfaceTvBndr
toIfaceTvBndrX fr tyvar = ( occNameFS (getOccName tyvar)
                          , toIfaceTypeX fr (tyVarKind tyvar)
                          )

toIfaceTvBndrs :: [TyVar] -> [IfaceTvBndr]
toIfaceTvBndrs = map toIfaceTvBndr

toIfaceIdBndr :: Id -> IfaceIdBndr
toIfaceIdBndr = toIfaceIdBndrX emptyVarSet

toIfaceIdBndrX :: VarSet -> CoVar -> IfaceIdBndr
toIfaceIdBndrX fr covar = ( toIfaceType (idMult covar)
                          , occNameFS (getOccName covar)
                          , toIfaceTypeX fr (varType covar)
                          )

toIfaceBndr :: Var -> IfaceBndr
toIfaceBndr var
  | isId var  = IfaceIdBndr (toIfaceIdBndr var)
  | otherwise = IfaceTvBndr (toIfaceTvBndr var)

toIfaceBndrX :: VarSet -> Var -> IfaceBndr
toIfaceBndrX fr var
  | isId var  = IfaceIdBndr (toIfaceIdBndrX fr var)
  | otherwise = IfaceTvBndr (toIfaceTvBndrX fr var)

toIfaceTyCoVarBinder :: VarBndr Var vis -> VarBndr IfaceBndr vis
toIfaceTyCoVarBinder (Bndr tv vis) = Bndr (toIfaceBndr tv) vis

toIfaceTyCoVarBinders :: [VarBndr Var vis] -> [VarBndr IfaceBndr vis]
toIfaceTyCoVarBinders = map toIfaceTyCoVarBinder

{-
************************************************************************
*                                                                      *
        Conversion from Type to IfaceType
*                                                                      *
************************************************************************
-}

toIfaceKind :: Type -> IfaceType
toIfaceKind = toIfaceType

---------------------
toIfaceType :: Type -> IfaceType
toIfaceType = toIfaceTypeX emptyVarSet

toIfaceTypeX :: VarSet -> Type -> IfaceType
-- (toIfaceTypeX free ty)
--    translates the tyvars in 'free' as IfaceFreeTyVars
--
-- Synonyms are retained in the interface type
toIfaceTypeX fr (TyVarTy tv)   -- See Note [TcTyVars in IfaceType] in GHC.Iface.Type
  | tv `elemVarSet` fr         = IfaceFreeTyVar tv
  | otherwise                  = IfaceTyVar (toIfaceTyVar tv)
toIfaceTypeX fr ty@(AppTy {})  =
  -- Flatten as many argument AppTys as possible, then turn them into an
  -- IfaceAppArgs list.
  -- See Note [Suppressing invisible arguments] in GHC.Iface.Type.
  let (head, args) = splitAppTys ty
  in IfaceAppTy (toIfaceTypeX fr head) (toIfaceAppTyArgsX fr head args)
toIfaceTypeX _  (LitTy n)      = IfaceLitTy (toIfaceTyLit n)
toIfaceTypeX fr (ForAllTy b t) = IfaceForAllTy (toIfaceForAllBndrX fr b)
                                               (toIfaceTypeX (fr `delVarSet` binderVar b) t)
toIfaceTypeX fr (FunTy { ft_arg = t1, ft_mult = w, ft_res = t2, ft_af = af })
  = IfaceFunTy af (toIfaceTypeX fr w) (toIfaceTypeX fr t1) (toIfaceTypeX fr t2)
toIfaceTypeX fr (CastTy ty co)  = IfaceCastTy (toIfaceTypeX fr ty) (toIfaceCoercionX fr co)
toIfaceTypeX fr (CoercionTy co) = IfaceCoercionTy (toIfaceCoercionX fr co)

toIfaceTypeX fr (TyConApp tc tys)
    -- tuples
  | Just sort <- tyConTuple_maybe tc
  , n_tys == arity
  = IfaceTupleTy sort NotPromoted (toIfaceTcArgsX fr tc tys)

  | Just dc <- isPromotedDataCon_maybe tc
  , isBoxedTupleDataCon dc
  , n_tys == 2*arity
  = IfaceTupleTy BoxedTuple IsPromoted (toIfaceTcArgsX fr tc (drop arity tys))

  | tc `elem` [ eqPrimTyCon, eqReprPrimTyCon, heqTyCon ]
  , (k1:k2:_) <- tys
  = let info = mkIfaceTyConInfo NotPromoted sort
        sort | k1 `eqType` k2 = IfaceEqualityTyCon
             | otherwise      = IfaceNormalTyCon
    in IfaceTyConApp (IfaceTyCon (tyConName tc) info) (toIfaceTcArgsX fr tc tys)

    -- other applications
  | otherwise
  = IfaceTyConApp (toIfaceTyCon tc) (toIfaceTcArgsX fr tc tys)
  where
    arity = tyConArity tc
    n_tys = length tys

toIfaceTyVar :: TyVar -> FastString
toIfaceTyVar = occNameFS . getOccName

toIfaceCoVar :: CoVar -> FastString
toIfaceCoVar = occNameFS . getOccName

toIfaceForAllBndr :: (VarBndr TyCoVar flag) -> (VarBndr IfaceBndr flag)
toIfaceForAllBndr = toIfaceForAllBndrX emptyVarSet

toIfaceForAllBndrX :: VarSet -> (VarBndr TyCoVar flag) -> (VarBndr IfaceBndr flag)
toIfaceForAllBndrX fr (Bndr v vis) = Bndr (toIfaceBndrX fr v) vis

----------------
toIfaceTyCon :: TyCon -> IfaceTyCon
toIfaceTyCon tc
  = IfaceTyCon tc_name info
  where
    tc_name = tyConName tc
    info    = mkIfaceTyConInfo promoted sort
    promoted | isPromotedDataCon tc = IsPromoted
             | otherwise            = NotPromoted

    tupleSort :: TyCon -> Maybe IfaceTyConSort
    tupleSort tc' =
        case tyConTuple_maybe tc' of
          Just UnboxedTuple -> let arity = tyConArity tc' `div` 2
                               in Just $ IfaceTupleTyCon arity UnboxedTuple
          Just sort         -> let arity = tyConArity tc'
                               in Just $ IfaceTupleTyCon arity sort
          Nothing           -> Nothing

    sort
      | Just tsort <- tupleSort tc           = tsort

      | Just dcon <- isPromotedDataCon_maybe tc
      , let tc' = dataConTyCon dcon
      , Just tsort <- tupleSort tc'          = tsort

      | isUnboxedSumTyCon tc
      , Just cons <- tyConDataCons_maybe tc  = IfaceSumTyCon (length cons)

      | otherwise                            = IfaceNormalTyCon


toIfaceTyCon_name :: Name -> IfaceTyCon
toIfaceTyCon_name n = IfaceTyCon n info
  where info = mkIfaceTyConInfo NotPromoted IfaceNormalTyCon
  -- Used for the "rough-match" tycon stuff,
  -- where pretty-printing is not an issue

toIfaceTyLit :: TyLit -> IfaceTyLit
toIfaceTyLit (NumTyLit x) = IfaceNumTyLit x
toIfaceTyLit (StrTyLit x) = IfaceStrTyLit x
toIfaceTyLit (CharTyLit x) = IfaceCharTyLit x

----------------
toIfaceCoercion :: Coercion -> IfaceCoercion
toIfaceCoercion = toIfaceCoercionX emptyVarSet

toIfaceCoercionX :: VarSet -> Coercion -> IfaceCoercion
-- (toIfaceCoercionX free ty)
--    translates the tyvars in 'free' as IfaceFreeTyVars
toIfaceCoercionX fr co
  = go co
  where
    go_mco MRefl     = IfaceMRefl
    go_mco (MCo co)  = IfaceMCo $ go co

    go (Refl ty)            = IfaceReflCo (toIfaceTypeX fr ty)
    go (GRefl r ty mco)     = IfaceGReflCo r (toIfaceTypeX fr ty) (go_mco mco)
    go (CoVarCo cv)
      -- See [TcTyVars in IfaceType] in GHC.Iface.Type
      | cv `elemVarSet` fr  = IfaceFreeCoVar cv
      | otherwise           = IfaceCoVarCo (toIfaceCoVar cv)
    go (HoleCo h)           = IfaceHoleCo  (coHoleCoVar h)

    go (AppCo co1 co2)      = IfaceAppCo  (go co1) (go co2)
    go (SymCo co)           = IfaceSymCo (go co)
    go (TransCo co1 co2)    = IfaceTransCo (go co1) (go co2)
    go (NthCo _r d co)      = IfaceNthCo d (go co)
    go (LRCo lr co)         = IfaceLRCo lr (go co)
    go (InstCo co arg)      = IfaceInstCo (go co) (go arg)
    go (KindCo c)           = IfaceKindCo (go c)
    go (SubCo co)           = IfaceSubCo (go co)
    go (AxiomRuleCo co cs)  = IfaceAxiomRuleCo (coaxrName co) (map go cs)
    go (AxiomInstCo c i cs) = IfaceAxiomInstCo (coAxiomName c) i (map go cs)
    go (UnivCo p r t1 t2)   = IfaceUnivCo (go_prov p) r
                                          (toIfaceTypeX fr t1)
                                          (toIfaceTypeX fr t2)
    go (TyConAppCo r tc cos)
      | tc `hasKey` funTyConKey
      , [_,_,_,_, _] <- cos         = panic "toIfaceCoercion"
      | otherwise                =
        IfaceTyConAppCo r (toIfaceTyCon tc) (map go cos)
    go (FunCo r w co1 co2)   = IfaceFunCo r (go w) (go co1) (go co2)

    go (ForAllCo tv k co) = IfaceForAllCo (toIfaceBndr tv)
                                          (toIfaceCoercionX fr' k)
                                          (toIfaceCoercionX fr' co)
                          where
                            fr' = fr `delVarSet` tv

    go_prov :: UnivCoProvenance -> IfaceUnivCoProv
    go_prov (PhantomProv co)    = IfacePhantomProv (go co)
    go_prov (ProofIrrelProv co) = IfaceProofIrrelProv (go co)
    go_prov (PluginProv str)    = IfacePluginProv str
    go_prov (CorePrepProv b)    = IfaceCorePrepProv b

toIfaceTcArgs :: TyCon -> [Type] -> IfaceAppArgs
toIfaceTcArgs = toIfaceTcArgsX emptyVarSet

toIfaceTcArgsX :: VarSet -> TyCon -> [Type] -> IfaceAppArgs
toIfaceTcArgsX fr tc ty_args = toIfaceAppArgsX fr (tyConKind tc) ty_args

toIfaceAppTyArgsX :: VarSet -> Type -> [Type] -> IfaceAppArgs
toIfaceAppTyArgsX fr ty ty_args = toIfaceAppArgsX fr (typeKind ty) ty_args

toIfaceAppArgsX :: VarSet -> Kind -> [Type] -> IfaceAppArgs
-- See Note [Suppressing invisible arguments] in GHC.Iface.Type
-- We produce a result list of args describing visibility
-- The awkward case is
--    T :: forall k. * -> k
-- And consider
--    T (forall j. blah) * blib
-- Is 'blib' visible?  It depends on the visibility flag on j,
-- so we have to substitute for k.  Annoying!
toIfaceAppArgsX fr kind ty_args
  = go (mkEmptyTCvSubst in_scope) kind ty_args
  where
    in_scope = mkInScopeSet (tyCoVarsOfTypes ty_args)

    go _   _                   []     = IA_Nil
    go env ty                  ts
      | Just ty' <- coreView ty
      = go env ty' ts
    go env (ForAllTy (Bndr tv vis) res) (t:ts)
      = IA_Arg t' vis ts'
      where
        t'  = toIfaceTypeX fr t
        ts' = go (extendTCvSubst env tv t) res ts

    go env (FunTy { ft_af = af, ft_res = res }) (t:ts)
      = IA_Arg (toIfaceTypeX fr t) argf (go env res ts)
      where
        argf = case af of
                 VisArg   -> Required
                 InvisArg -> Inferred
                   -- It's rare for a kind to have a constraint argument, but
                   -- it can happen. See Note [AnonTCB InvisArg] in GHC.Core.TyCon.

    go env ty ts@(t1:ts1)
      | not (isEmptyTCvSubst env)
      = go (zapTCvSubst env) (substTy env ty) ts
        -- See Note [Care with kind instantiation] in GHC.Core.Type

      | otherwise
      = -- There's a kind error in the type we are trying to print
        -- e.g. kind = k, ty_args = [Int]
        -- This is probably a compiler bug, so we print a trace and
        -- carry on as if it were FunTy.  Without the test for
        -- isEmptyTCvSubst we'd get an infinite loop (#15473)
        warnPprTrace True (ppr kind $$ ppr ty_args) $
        IA_Arg (toIfaceTypeX fr t1) Required (go env ty ts1)

tidyToIfaceType :: TidyEnv -> Type -> IfaceType
tidyToIfaceType env ty = toIfaceType (tidyType env ty)

tidyToIfaceTcArgs :: TidyEnv -> TyCon -> [Type] -> IfaceAppArgs
tidyToIfaceTcArgs env tc tys = toIfaceTcArgs tc (tidyTypes env tys)

tidyToIfaceContext :: TidyEnv -> ThetaType -> IfaceContext
tidyToIfaceContext env theta = map (tidyToIfaceType env) theta

{-
************************************************************************
*                                                                      *
        Conversion of pattern synonyms
*                                                                      *
************************************************************************
-}

patSynToIfaceDecl :: PatSyn -> IfaceDecl
patSynToIfaceDecl ps
  = IfacePatSyn { ifName          = getName $ ps
                , ifPatMatcher    = to_if_pr (patSynMatcher ps)
                , ifPatBuilder    = fmap to_if_pr (patSynBuilder ps)
                , ifPatIsInfix    = patSynIsInfix ps
                , ifPatUnivBndrs  = map toIfaceForAllBndr univ_bndrs'
                , ifPatExBndrs    = map toIfaceForAllBndr ex_bndrs'
                , ifPatProvCtxt   = tidyToIfaceContext env2 prov_theta
                , ifPatReqCtxt    = tidyToIfaceContext env2 req_theta
                , ifPatArgs       = map (tidyToIfaceType env2 . scaledThing) args
                , ifPatTy         = tidyToIfaceType env2 rhs_ty
                , ifFieldLabels   = (patSynFieldLabels ps)
                }
  where
    (_univ_tvs, req_theta, _ex_tvs, prov_theta, args, rhs_ty) = patSynSig ps
    univ_bndrs = patSynUnivTyVarBinders ps
    ex_bndrs   = patSynExTyVarBinders ps
    (env1, univ_bndrs') = tidyTyCoVarBinders emptyTidyEnv univ_bndrs
    (env2, ex_bndrs')   = tidyTyCoVarBinders env1 ex_bndrs
    to_if_pr (name, _type, needs_dummy) = (name, needs_dummy)

{-
************************************************************************
*                                                                      *
        Conversion of other things
*                                                                      *
************************************************************************
-}

toIfaceBang :: TidyEnv -> HsImplBang -> IfaceBang
toIfaceBang _    HsLazy              = IfNoBang
toIfaceBang _   (HsUnpack Nothing)   = IfUnpack
toIfaceBang env (HsUnpack (Just co)) = IfUnpackCo (toIfaceCoercion (tidyCo env co))
toIfaceBang _   HsStrict             = IfStrict

toIfaceSrcBang :: HsSrcBang -> IfaceSrcBang
toIfaceSrcBang (HsSrcBang _ unpk bang) = IfSrcBang unpk bang

toIfaceLetBndr :: Id -> IfaceLetBndr
toIfaceLetBndr id  = IfLetBndr (occNameFS (getOccName id))
                               (toIfaceType (idType id))
                               (toIfaceIdInfo (idInfo id))
                               (toIfaceJoinInfo (isJoinId_maybe id))
  -- Put into the interface file any IdInfo that GHC.Core.Tidy.tidyLetBndr
  -- has left on the Id.  See Note [IdInfo on nested let-bindings] in GHC.Iface.Syntax

toIfaceIdDetails :: IdDetails -> IfaceIdDetails
toIfaceIdDetails VanillaId                      = IfVanillaId
toIfaceIdDetails (DFunId {})                    = IfDFunId
toIfaceIdDetails (RecSelId { sel_naughty = n
                           , sel_tycon = tc })  =
  let iface = case tc of
                RecSelData ty_con -> Left (toIfaceTyCon ty_con)
                RecSelPatSyn pat_syn -> Right (patSynToIfaceDecl pat_syn)
  in IfRecSelId iface n

  -- The remaining cases are all "implicit Ids" which don't
  -- appear in interface files at all
toIfaceIdDetails other = pprTrace "toIfaceIdDetails" (ppr other)
                         IfVanillaId   -- Unexpected; the other

toIfaceIdInfo :: IdInfo -> IfaceIdInfo
toIfaceIdInfo id_info
  = catMaybes [arity_hsinfo, caf_hsinfo, strict_hsinfo, cpr_hsinfo,
               inline_hsinfo,  unfold_hsinfo, levity_hsinfo]
               -- NB: strictness and arity must appear in the list before unfolding
               -- See GHC.IfaceToCore.tcUnfolding
  where
    ------------  Arity  --------------
    arity_info = arityInfo id_info
    arity_hsinfo | arity_info == 0 = Nothing
                 | otherwise       = Just (HsArity arity_info)

    ------------ Caf Info --------------
    caf_info   = cafInfo id_info
    caf_hsinfo = case caf_info of
                   NoCafRefs -> Just HsNoCafRefs
                   _other    -> Nothing

    ------------  Strictness  --------------
        -- No point in explicitly exporting TopSig
    sig_info = dmdSigInfo id_info
    strict_hsinfo | not (isTopSig sig_info) = Just (HsDmdSig sig_info)
                  | otherwise               = Nothing

    ------------  CPR --------------
    cpr_info = cprSigInfo id_info
    cpr_hsinfo | cpr_info /= topCprSig = Just (HsCprSig cpr_info)
               | otherwise             = Nothing
    ------------  Unfolding  --------------
    unfold_hsinfo = toIfUnfolding loop_breaker (realUnfoldingInfo id_info)
    loop_breaker  = isStrongLoopBreaker (occInfo id_info)

    ------------  Inline prag  --------------
    inline_prag = inlinePragInfo id_info
    inline_hsinfo | isDefaultInlinePragma inline_prag = Nothing
                  | otherwise = Just (HsInline inline_prag)

    ------------  Representation polymorphism  ----------
    levity_hsinfo | isNeverRepPolyIdInfo id_info = Just HsLevity
                  | otherwise                    = Nothing

toIfaceJoinInfo :: Maybe JoinArity -> IfaceJoinInfo
toIfaceJoinInfo (Just ar) = IfaceJoinPoint ar
toIfaceJoinInfo Nothing   = IfaceNotJoinPoint

--------------------------
toIfUnfolding :: Bool -> Unfolding -> Maybe IfaceInfoItem
toIfUnfolding lb (CoreUnfolding { uf_tmpl = rhs
                                , uf_src = src
                                , uf_guidance = guidance })
  = Just $ HsUnfold lb $
    case src of
        InlineStable
          -> case guidance of
               UnfWhen {ug_arity = arity, ug_unsat_ok = unsat_ok, ug_boring_ok =  boring_ok }
                      -> IfInlineRule arity unsat_ok boring_ok if_rhs
               _other -> IfCoreUnfold True if_rhs
        InlineCompulsory -> IfCompulsory if_rhs
        InlineRhs        -> IfCoreUnfold False if_rhs
        -- Yes, even if guidance is UnfNever, expose the unfolding
        -- If we didn't want to expose the unfolding, GHC.Iface.Tidy would
        -- have stuck in NoUnfolding.  For supercompilation we want
        -- to see that unfolding!
  where
    if_rhs = toIfaceExpr rhs

toIfUnfolding lb (DFunUnfolding { df_bndrs = bndrs, df_args = args })
  = Just (HsUnfold lb (IfDFunUnfold (map toIfaceBndr bndrs) (map toIfaceExpr args)))
      -- No need to serialise the data constructor;
      -- we can recover it from the type of the dfun

toIfUnfolding _ (OtherCon {}) = Nothing
  -- The binding site of an Id doesn't have OtherCon, except perhaps
  -- where we have called zapUnfolding; and that evald'ness info is
  -- not needed by importing modules

toIfUnfolding _ BootUnfolding = Nothing
  -- Can't happen; we only have BootUnfolding for imported binders

toIfUnfolding _ NoUnfolding = Nothing

{-
************************************************************************
*                                                                      *
        Conversion of expressions
*                                                                      *
************************************************************************
-}

toIfaceExpr :: CoreExpr -> IfaceExpr
toIfaceExpr (Var v)         = toIfaceVar v
toIfaceExpr (Lit (LitRubbish r)) = IfaceLitRubbish (toIfaceType r)
toIfaceExpr (Lit l)         = IfaceLit l
toIfaceExpr (Type ty)       = IfaceType (toIfaceType ty)
toIfaceExpr (Coercion co)   = IfaceCo   (toIfaceCoercion co)
toIfaceExpr (Lam x b)       = IfaceLam (toIfaceBndr x, toIfaceOneShot x) (toIfaceExpr b)
toIfaceExpr (App f a)       = toIfaceApp f [a]
toIfaceExpr (Case s x ty as)
  | null as                 = IfaceECase (toIfaceExpr s) (toIfaceType ty)
  | otherwise               = IfaceCase (toIfaceExpr s) (getOccFS x) (map toIfaceAlt as)
toIfaceExpr (Let b e)       = IfaceLet (toIfaceBind b) (toIfaceExpr e)
toIfaceExpr (Cast e co)     = IfaceCast (toIfaceExpr e) (toIfaceCoercion co)
toIfaceExpr (Tick t e)
  | Just t' <- toIfaceTickish t = IfaceTick t' (toIfaceExpr e)
  | otherwise                   = toIfaceExpr e

toIfaceOneShot :: Id -> IfaceOneShot
toIfaceOneShot id | isId id
                  , OneShotLam <- oneShotInfo (idInfo id)
                  = IfaceOneShot
                  | otherwise
                  = IfaceNoOneShot

---------------------
toIfaceTickish :: CoreTickish -> Maybe IfaceTickish
toIfaceTickish (ProfNote cc tick push) = Just (IfaceSCC cc tick push)
toIfaceTickish (HpcTick modl ix)       = Just (IfaceHpcTick modl ix)
toIfaceTickish (SourceNote src names)  = Just (IfaceSource src names)
toIfaceTickish (Breakpoint {})         = Nothing
   -- Ignore breakpoints, since they are relevant only to GHCi, and
   -- should not be serialised (#8333)

---------------------
toIfaceBind :: Bind Id -> IfaceBinding
toIfaceBind (NonRec b r) = IfaceNonRec (toIfaceLetBndr b) (toIfaceExpr r)
toIfaceBind (Rec prs)    = IfaceRec [(toIfaceLetBndr b, toIfaceExpr r) | (b,r) <- prs]

---------------------
toIfaceAlt :: CoreAlt -> IfaceAlt
toIfaceAlt (Alt c bs r) = IfaceAlt (toIfaceCon c) (map getOccFS bs) (toIfaceExpr r)

---------------------
toIfaceCon :: AltCon -> IfaceConAlt
toIfaceCon (DataAlt dc) = IfaceDataAlt (getName dc)
toIfaceCon (LitAlt l)   = assertPpr (not (isLitRubbish l)) (ppr l) $
                          -- assert: see Note [Rubbish literals] wrinkle (b)
                          IfaceLitAlt l
toIfaceCon DEFAULT      = IfaceDefault

---------------------
toIfaceApp :: Expr CoreBndr -> [Arg CoreBndr] -> IfaceExpr
toIfaceApp (App f a) as = toIfaceApp f (a:as)
toIfaceApp (Var v) as
  = case isDataConWorkId_maybe v of
        -- We convert the *worker* for tuples into IfaceTuples
        Just dc |  saturated
                ,  Just tup_sort <- tyConTuple_maybe tc
                -> IfaceTuple tup_sort tup_args
          where
            val_args  = dropWhile isTypeArg as
            saturated = val_args `lengthIs` idArity v
            tup_args  = map toIfaceExpr val_args
            tc        = dataConTyCon dc

        _ -> mkIfaceApps (toIfaceVar v) as

toIfaceApp e as = mkIfaceApps (toIfaceExpr e) as

mkIfaceApps :: IfaceExpr -> [CoreExpr] -> IfaceExpr
mkIfaceApps f as = foldl' (\f a -> IfaceApp f (toIfaceExpr a)) f as

---------------------
toIfaceVar :: Id -> IfaceExpr
toIfaceVar v
    | isBootUnfolding (idUnfolding v)
    = -- See Note [Inlining and hs-boot files]
      IfaceApp (IfaceApp (IfaceExt noinlineIdName)
                         (IfaceType (toIfaceType (idType v))))
               (IfaceExt name) -- don't use mkIfaceApps, or infinite loop

    | Just fcall <- isFCallId_maybe v = IfaceFCall fcall (toIfaceType (idType v))
                                      -- Foreign calls have special syntax

    | isExternalName name             = IfaceExt name
    | otherwise                       = IfaceLcl (getOccFS name)
  where name = idName v


---------------------
toIfaceLFInfo :: Name -> LambdaFormInfo -> IfaceLFInfo
toIfaceLFInfo nm lfi = case lfi of
    LFReEntrant top_lvl arity no_fvs _arg_descr ->
      -- Exported LFReEntrant closures are top level, and top-level closures
      -- don't have free variables
      assertPpr (isTopLevel top_lvl) (ppr nm) $
      assertPpr no_fvs (ppr nm) $
      IfLFReEntrant arity
    LFThunk top_lvl no_fvs updatable sfi mb_fun ->
      -- Exported LFThunk closures are top level (which don't have free
      -- variables) and non-standard (see cgTopRhsClosure)
      assertPpr (isTopLevel top_lvl) (ppr nm) $
      assertPpr no_fvs (ppr nm) $
      assertPpr (sfi == NonStandardThunk) (ppr nm) $
      IfLFThunk updatable mb_fun
    LFCon dc ->
      IfLFCon (dataConName dc)
    LFUnknown mb_fun ->
      IfLFUnknown mb_fun
    LFUnlifted ->
      IfLFUnlifted
    LFLetNoEscape ->
      panic "toIfaceLFInfo: LFLetNoEscape"

{- Note [Inlining and hs-boot files]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this example (#10083, #12789):

    ---------- RSR.hs-boot ------------
    module RSR where
      data RSR
      eqRSR :: RSR -> RSR -> Bool

    ---------- SR.hs ------------
    module SR where
      import {-# SOURCE #-} RSR
      data SR = MkSR RSR
      eqSR (MkSR r1) (MkSR r2) = eqRSR r1 r2

    ---------- RSR.hs ------------
    module RSR where
      import SR
      data RSR = MkRSR SR -- deriving( Eq )
      eqRSR (MkRSR s1) (MkRSR s2) = (eqSR s1 s2)
      foo x y = not (eqRSR x y)

When compiling RSR we get this code

    RSR.eqRSR :: RSR -> RSR -> Bool
    RSR.eqRSR = \ (ds1 :: RSR.RSR) (ds2 :: RSR.RSR) ->
                case ds1 of _ { RSR.MkRSR s1 ->
                case ds2 of _ { RSR.MkRSR s2 ->
                SR.eqSR s1 s2 }}

    RSR.foo :: RSR -> RSR -> Bool
    RSR.foo = \ (x :: RSR) (y :: RSR) -> not (RSR.eqRSR x y)

Now, when optimising foo:
    Inline eqRSR (small, non-rec)
    Inline eqSR  (small, non-rec)
but the result of inlining eqSR from SR is another call to eqRSR, so
everything repeats.  Neither eqSR nor eqRSR are (apparently) loop
breakers.

Solution: in the unfolding of eqSR in SR.hi, replace `eqRSR` in SR
with `noinline eqRSR`, so that eqRSR doesn't get inlined.  This means
that when GHC inlines `eqSR`, it will not also inline `eqRSR`, exactly
as would have been the case if `foo` had been defined in SR.hs (and
marked as a loop-breaker).

But how do we arrange for this to happen?  There are two ingredients:

    1. When we serialize out unfoldings to IfaceExprs (toIfaceVar),
    for every variable reference we see if we are referring to an
    'Id' that came from an hs-boot file.  If so, we add a `noinline`
    to the reference.

    2. But how do we know if a reference came from an hs-boot file
    or not?  We could record this directly in the 'IdInfo', but
    actually we deduce this by looking at the unfolding: 'Id's
    that come from boot files are given a special unfolding
    (upon typechecking) 'BootUnfolding' which say that there is
    no unfolding, and the reason is because the 'Id' came from
    a boot file.

Here is a solution that doesn't work: when compiling RSR,
add a NOINLINE pragma to every function exported by the boot-file
for RSR (if it exists).  Doing so makes the bootstrapped GHC itself
slower by 8% overall (on #9872a-d, and T1969: the reason
is that these NOINLINE'd functions now can't be profitably inlined
outside of the hs-boot loop.

-}