summaryrefslogtreecommitdiff
path: root/compiler/codeGen/StgCmmBind.hs
blob: fde662b31775f01d33e6e9fc3c021b0b2d4c2e16 (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
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
{-# LANGUAGE CPP #-}

-----------------------------------------------------------------------------
--
-- Stg to C-- code generation: bindings
--
-- (c) The University of Glasgow 2004-2006
--
-----------------------------------------------------------------------------

module StgCmmBind (
        cgTopRhsClosure,
        cgBind,
        emitBlackHoleCode,
        pushUpdateFrame, emitUpdateFrame
  ) where

#include "HsVersions.h"

import StgCmmExpr
import StgCmmMonad
import StgCmmEnv
import StgCmmCon
import StgCmmHeap
import StgCmmProf (curCCS, ldvEnterClosure, enterCostCentreFun, enterCostCentreThunk,
                   initUpdFrameProf)
import StgCmmTicky
import StgCmmLayout
import StgCmmUtils
import StgCmmClosure
import StgCmmForeign    (emitPrimCall)

import MkGraph
import CoreSyn          ( AltCon(..), tickishIsCode )
import SMRep
import Cmm
import CmmInfo
import CmmUtils
import CLabel
import StgSyn
import CostCentre
import Id
import IdInfo
import Name
import Module
import ListSetOps
import Util
import BasicTypes
import Outputable
import FastString
import DynFlags

import Control.Monad

import Prelude hiding ((<*>))

------------------------------------------------------------------------
--              Top-level bindings
------------------------------------------------------------------------

-- For closures bound at top level, allocate in static space.
-- They should have no free variables.

cgTopRhsClosure :: DynFlags
                -> RecFlag              -- member of a recursive group?
                -> Id
                -> CostCentreStack      -- Optional cost centre annotation
                -> StgBinderInfo
                -> UpdateFlag
                -> [Id]                 -- Args
                -> StgExpr
                -> (CgIdInfo, FCode ())

cgTopRhsClosure dflags rec id ccs _ upd_flag args body =
  let closure_label = mkLocalClosureLabel (idName id) (idCafInfo id)
      cg_id_info    = litIdInfo dflags id lf_info (CmmLabel closure_label)
      lf_info       = mkClosureLFInfo dflags id TopLevel [] upd_flag args
  in (cg_id_info, gen_code dflags lf_info closure_label)
  where
  -- special case for a indirection (f = g).  We create an IND_STATIC
  -- closure pointing directly to the indirectee.  This is exactly
  -- what the CAF will eventually evaluate to anyway, we're just
  -- shortcutting the whole process, and generating a lot less code
  -- (#7308)
  --
  -- Note: we omit the optimisation when this binding is part of a
  -- recursive group, because the optimisation would inhibit the black
  -- hole detection from working in that case.  Test
  -- concurrent/should_run/4030 fails, for instance.
  --
  gen_code dflags _ closure_label
    | StgApp f [] <- body, null args, isNonRec rec
    = do
         cg_info <- getCgIdInfo f
         let closure_rep   = mkStaticClosureFields dflags
                                    indStaticInfoTable ccs MayHaveCafRefs
                                    [unLit (idInfoToAmode cg_info)]
         emitDataLits closure_label closure_rep
         return ()

  gen_code dflags lf_info closure_label
   = do {     -- LAY OUT THE OBJECT
          let name = idName id
        ; mod_name <- getModuleName
        ; let descr         = closureDescription dflags mod_name name
              closure_info  = mkClosureInfo dflags True id lf_info 0 0 descr

              caffy         = idCafInfo id
              info_tbl      = mkCmmInfo closure_info -- XXX short-cut
              closure_rep   = mkStaticClosureFields dflags info_tbl ccs caffy []

                 -- BUILD THE OBJECT, AND GENERATE INFO TABLE (IF NECESSARY)
        ; emitDataLits closure_label closure_rep
        ; let fv_details :: [(NonVoid Id, VirtualHpOffset)]
              (_, _, fv_details) = mkVirtHeapOffsets dflags (isLFThunk lf_info)
                                               (addIdReps [])
        -- Don't drop the non-void args until the closure info has been made
        ; forkClosureBody (closureCodeBody True id closure_info ccs
                                (nonVoidIds args) (length args) body fv_details)

        ; return () }

  unLit (CmmLit l) = l
  unLit _ = panic "unLit"

------------------------------------------------------------------------
--              Non-top-level bindings
------------------------------------------------------------------------

cgBind :: StgBinding -> FCode ()
cgBind (StgNonRec name rhs)
  = do  { (info, fcode) <- cgRhs name rhs
        ; addBindC info
        ; init <- fcode
        ; emit init }
        -- init cannot be used in body, so slightly better to sink it eagerly

cgBind (StgRec pairs)
  = do  {  r <- sequence $ unzipWith cgRhs pairs
        ;  let (id_infos, fcodes) = unzip r
        ;  addBindsC id_infos
        ;  (inits, body) <- getCodeR $ sequence fcodes
        ;  emit (catAGraphs inits <*> body) }

{- Note [cgBind rec]

   Recursive let-bindings are tricky.
   Consider the following pseudocode:

     let x = \_ ->  ... y ...
         y = \_ ->  ... z ...
         z = \_ ->  ... x ...
     in ...

   For each binding, we need to allocate a closure, and each closure must
   capture the address of the other closures.
   We want to generate the following C-- code:
     // Initialization Code
     x = hp - 24; // heap address of x's closure
     y = hp - 40; // heap address of x's closure
     z = hp - 64; // heap address of x's closure
     // allocate and initialize x
     m[hp-8]   = ...
     m[hp-16]  = y       // the closure for x captures y
     m[hp-24] = x_info;
     // allocate and initialize y
     m[hp-32] = z;       // the closure for y captures z
     m[hp-40] = y_info;
     // allocate and initialize z
     ...

   For each closure, we must generate not only the code to allocate and
   initialize the closure itself, but also some initialization Code that
   sets a variable holding the closure pointer.

   We could generate a pair of the (init code, body code), but since
   the bindings are recursive we also have to initialise the
   environment with the CgIdInfo for all the bindings before compiling
   anything.  So we do this in 3 stages:

     1. collect all the CgIdInfos and initialise the environment
     2. compile each binding into (init, body) code
     3. emit all the inits, and then all the bodies

   We'd rather not have separate functions to do steps 1 and 2 for
   each binding, since in pratice they share a lot of code.  So we
   have just one function, cgRhs, that returns a pair of the CgIdInfo
   for step 1, and a monadic computation to generate the code in step
   2.

   The alternative to separating things in this way is to use a
   fixpoint.  That's what we used to do, but it introduces a
   maintenance nightmare because there is a subtle dependency on not
   being too strict everywhere.  Doing things this way means that the
   FCode monad can be strict, for example.
 -}

cgRhs :: Id
      -> StgRhs
      -> FCode (
                 CgIdInfo         -- The info for this binding
               , FCode CmmAGraph  -- A computation which will generate the
                                  -- code for the binding, and return an
                                  -- assignent of the form "x = Hp - n"
                                  -- (see above)
               )

cgRhs id (StgRhsCon cc con args)
  = withNewTickyCounterThunk False (idName id) $ -- False for "not static"
    buildDynCon id True cc con args

{- See Note [GC recovery] in compiler/codeGen/StgCmmClosure.hs -}
cgRhs name (StgRhsClosure cc bi fvs upd_flag _srt args body)
  = do dflags <- getDynFlags
       mkRhsClosure dflags name cc bi (nonVoidIds fvs) upd_flag args body

------------------------------------------------------------------------
--              Non-constructor right hand sides
------------------------------------------------------------------------

mkRhsClosure :: DynFlags -> Id -> CostCentreStack -> StgBinderInfo
             -> [NonVoid Id]                    -- Free vars
             -> UpdateFlag
             -> [Id]                            -- Args
             -> StgExpr
             -> FCode (CgIdInfo, FCode CmmAGraph)

{- mkRhsClosure looks for two special forms of the right-hand side:
        a) selector thunks
        b) AP thunks

If neither happens, it just calls mkClosureLFInfo.  You might think
that mkClosureLFInfo should do all this, but it seems wrong for the
latter to look at the structure of an expression

Note [Selectors]
~~~~~~~~~~~~~~~~
We look at the body of the closure to see if it's a selector---turgid,
but nothing deep.  We are looking for a closure of {\em exactly} the
form:

...  = [the_fv] \ u [] ->
         case the_fv of
           con a_1 ... a_n -> a_i

Note [Ap thunks]
~~~~~~~~~~~~~~~~
A more generic AP thunk of the form

        x = [ x_1...x_n ] \.. [] -> x_1 ... x_n

A set of these is compiled statically into the RTS, so we just use
those.  We could extend the idea to thunks where some of the x_i are
global ids (and hence not free variables), but this would entail
generating a larger thunk.  It might be an option for non-optimising
compilation, though.

We only generate an Ap thunk if all the free variables are pointers,
for semi-obvious reasons.

-}

---------- Note [Selectors] ------------------
mkRhsClosure    dflags bndr _cc _bi
                [NonVoid the_fv]                -- Just one free var
                upd_flag                -- Updatable thunk
                []                      -- A thunk
                expr
  | let strip = snd . stripStgTicksTop (not . tickishIsCode)
  , StgCase (StgApp scrutinee [{-no args-}])
         _ _ _ _   -- ignore uniq, etc.
         (AlgAlt _)
         [(DataAlt _, params, _use_mask, sel_expr)] <- strip expr
  , StgApp selectee [{-no args-}] <- strip sel_expr
  , the_fv == scrutinee                -- Scrutinee is the only free variable

  , let (_, _, params_w_offsets) = mkVirtConstrOffsets dflags (addIdReps params)
                                   -- Just want the layout
  , Just the_offset <- assocMaybe params_w_offsets (NonVoid selectee)

  , let offset_into_int = bytesToWordsRoundUp dflags the_offset
                          - fixedHdrSizeW dflags
  , offset_into_int <= mAX_SPEC_SELECTEE_SIZE dflags -- Offset is small enough
  = -- NOT TRUE: ASSERT(is_single_constructor)
    -- The simplifier may have statically determined that the single alternative
    -- is the only possible case and eliminated the others, even if there are
    -- other constructors in the datatype.  It's still ok to make a selector
    -- thunk in this case, because we *know* which constructor the scrutinee
    -- will evaluate to.
    --
    -- srt is discarded; it must be empty
    let lf_info = mkSelectorLFInfo bndr offset_into_int (isUpdatable upd_flag)
    in cgRhsStdThunk bndr lf_info [StgVarArg the_fv]

---------- Note [Ap thunks] ------------------
mkRhsClosure    dflags bndr _cc _bi
                fvs
                upd_flag
                []                      -- No args; a thunk
                (StgApp fun_id args)

  | args `lengthIs` (arity-1)
        && all (isGcPtrRep . idPrimRep . unsafe_stripNV) fvs
        && isUpdatable upd_flag
        && arity <= mAX_SPEC_AP_SIZE dflags
        && not (gopt Opt_SccProfilingOn dflags)
                                  -- not when profiling: we don't want to
                                  -- lose information about this particular
                                  -- thunk (e.g. its type) (#949)

                   -- Ha! an Ap thunk
  = cgRhsStdThunk bndr lf_info payload

  where
        lf_info = mkApLFInfo bndr upd_flag arity
        -- the payload has to be in the correct order, hence we can't
        -- just use the fvs.
        payload = StgVarArg fun_id : args
        arity   = length fvs

---------- Default case ------------------
mkRhsClosure dflags bndr cc _ fvs upd_flag args body
  = do  { let lf_info = mkClosureLFInfo dflags bndr NotTopLevel fvs upd_flag args
        ; (id_info, reg) <- rhsIdInfo bndr lf_info
        ; return (id_info, gen_code lf_info reg) }
 where
 gen_code lf_info reg
  = do  {       -- LAY OUT THE OBJECT
        -- If the binder is itself a free variable, then don't store
        -- it in the closure.  Instead, just bind it to Node on entry.
        -- NB we can be sure that Node will point to it, because we
        -- haven't told mkClosureLFInfo about this; so if the binder
        -- _was_ a free var of its RHS, mkClosureLFInfo thinks it *is*
        -- stored in the closure itself, so it will make sure that
        -- Node points to it...
        ; let
                is_elem      = isIn "cgRhsClosure"
                bndr_is_a_fv = (NonVoid bndr) `is_elem` fvs
                reduced_fvs | bndr_is_a_fv = fvs `minusList` [NonVoid bndr]
                            | otherwise    = fvs


        -- MAKE CLOSURE INFO FOR THIS CLOSURE
        ; mod_name <- getModuleName
        ; dflags <- getDynFlags
        ; let   name  = idName bndr
                descr = closureDescription dflags mod_name name
                fv_details :: [(NonVoid Id, ByteOff)]
                (tot_wds, ptr_wds, fv_details)
                   = mkVirtHeapOffsets dflags (isLFThunk lf_info)
                                       (addIdReps (map unsafe_stripNV reduced_fvs))
                closure_info = mkClosureInfo dflags False       -- Not static
                                             bndr lf_info tot_wds ptr_wds
                                             descr

        -- BUILD ITS INFO TABLE AND CODE
        ; forkClosureBody $
                -- forkClosureBody: (a) ensure that bindings in here are not seen elsewhere
                --                  (b) ignore Sequel from context; use empty Sequel
                -- And compile the body
                closureCodeBody False bndr closure_info cc (nonVoidIds args)
                                (length args) body fv_details

        -- BUILD THE OBJECT
--      ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
        ; let use_cc = curCCS; blame_cc = curCCS
        ; emit (mkComment $ mkFastString "calling allocDynClosure")
        ; let toVarArg (NonVoid a, off) = (NonVoid (StgVarArg a), off)
        ; let info_tbl = mkCmmInfo closure_info
        ; hp_plus_n <- allocDynClosure (Just bndr) info_tbl lf_info use_cc blame_cc
                                         (map toVarArg fv_details)

        -- RETURN
        ; return (mkRhsInit dflags reg lf_info hp_plus_n) }

-------------------------
cgRhsStdThunk
        :: Id
        -> LambdaFormInfo
        -> [StgArg]             -- payload
        -> FCode (CgIdInfo, FCode CmmAGraph)

cgRhsStdThunk bndr lf_info payload
 = do  { (id_info, reg) <- rhsIdInfo bndr lf_info
       ; return (id_info, gen_code reg)
       }
 where
 gen_code reg  -- AHA!  A STANDARD-FORM THUNK
  = withNewTickyCounterStdThunk False (idName bndr) $ -- False for "not static"
    do
  {     -- LAY OUT THE OBJECT
    mod_name <- getModuleName
  ; dflags <- getDynFlags
  ; let (tot_wds, ptr_wds, payload_w_offsets)
            = mkVirtHeapOffsets dflags (isLFThunk lf_info) (addArgReps payload)

        descr = closureDescription dflags mod_name (idName bndr)
        closure_info = mkClosureInfo dflags False       -- Not static
                                     bndr lf_info tot_wds ptr_wds
                                     descr

--  ; (use_cc, blame_cc) <- chooseDynCostCentres cc [{- no args-}] body
  ; let use_cc = curCCS; blame_cc = curCCS

  ; tickyEnterStdThunk closure_info

        -- BUILD THE OBJECT
  ; let info_tbl = mkCmmInfo closure_info
  ; hp_plus_n <- allocDynClosure (Just bndr) info_tbl lf_info
                                   use_cc blame_cc payload_w_offsets

        -- RETURN
  ; return (mkRhsInit dflags reg lf_info hp_plus_n) }


mkClosureLFInfo :: DynFlags
                -> Id           -- The binder
                -> TopLevelFlag -- True of top level
                -> [NonVoid Id] -- Free vars
                -> UpdateFlag   -- Update flag
                -> [Id]         -- Args
                -> LambdaFormInfo
mkClosureLFInfo dflags bndr top fvs upd_flag args
  | null args =
        mkLFThunk (idType bndr) top (map unsafe_stripNV fvs) upd_flag
  | otherwise =
        mkLFReEntrant top (map unsafe_stripNV fvs) args (mkArgDescr dflags args)


------------------------------------------------------------------------
--              The code for closures
------------------------------------------------------------------------

closureCodeBody :: Bool            -- whether this is a top-level binding
                -> Id              -- the closure's name
                -> ClosureInfo     -- Lots of information about this closure
                -> CostCentreStack -- Optional cost centre attached to closure
                -> [NonVoid Id]    -- incoming args to the closure
                -> Int             -- arity, including void args
                -> StgExpr
                -> [(NonVoid Id, ByteOff)] -- the closure's free vars
                -> FCode ()

{- There are two main cases for the code for closures.

* If there are *no arguments*, then the closure is a thunk, and not in
  normal form. So it should set up an update frame (if it is
  shared). NB: Thunks cannot have a primitive type!

* If there is *at least one* argument, then this closure is in
  normal form, so there is no need to set up an update frame.
-}

closureCodeBody top_lvl bndr cl_info cc _args arity body fv_details
  | arity == 0 -- No args i.e. thunk
  = withNewTickyCounterThunk (isStaticClosure cl_info) (closureName cl_info) $
    emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl [] $
      \(_, node, _) -> thunkCode cl_info fv_details cc node arity body
   where
     lf_info  = closureLFInfo cl_info
     info_tbl = mkCmmInfo cl_info

closureCodeBody top_lvl bndr cl_info cc args arity body fv_details
  = -- Note: args may be [], if all args are Void
    withNewTickyCounterFun (closureName cl_info) args $ do {

        ; let
             lf_info  = closureLFInfo cl_info
             info_tbl = mkCmmInfo cl_info

        -- Emit the main entry code
        ; emitClosureProcAndInfoTable top_lvl bndr lf_info info_tbl args $
            \(_offset, node, arg_regs) -> do
                -- Emit slow-entry code (for entering a closure through a PAP)
                { mkSlowEntryCode bndr cl_info arg_regs
                ; dflags <- getDynFlags
                ; let node_points = nodeMustPointToIt dflags lf_info
                      node' = if node_points then Just node else Nothing
                ; loop_header_id <- newLabelC
                -- Extend reader monad with information that
                -- self-recursive tail calls can be optimized into local
                -- jumps. See Note [Self-recursive tail calls] in StgCmmExpr.
                ; withSelfLoop (bndr, loop_header_id, arg_regs) $ do
                {
                -- Main payload
                ; entryHeapCheck cl_info node' arity arg_regs $ do
                { -- emit LDV code when profiling
                  when node_points (ldvEnterClosure cl_info (CmmLocal node))
                -- ticky after heap check to avoid double counting
                ; tickyEnterFun cl_info
                ; enterCostCentreFun cc
                    (CmmMachOp (mo_wordSub dflags)
                         [ CmmReg (CmmLocal node) -- See [NodeReg clobbered with loopification]
                         , mkIntExpr dflags (funTag dflags cl_info) ])
                ; fv_bindings <- mapM bind_fv fv_details
                -- Load free vars out of closure *after*
                -- heap check, to reduce live vars over check
                ; when node_points $ load_fvs node lf_info fv_bindings
                ; void $ cgExpr body
                }}}

  }

-- Note [NodeReg clobbered with loopification]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- Previously we used to pass nodeReg (aka R1) here. With profiling, upon
-- entering a closure, enterFunCCS was called with R1 passed to it. But since R1
-- may get clobbered inside the body of a closure, and since a self-recursive
-- tail call does not restore R1, a subsequent call to enterFunCCS received a
-- possibly bogus value from R1. The solution is to not pass nodeReg (aka R1) to
-- enterFunCCS. Instead, we pass node, the callee-saved temporary that stores
-- the original value of R1. This way R1 may get modified but loopification will
-- not care.

-- A function closure pointer may be tagged, so we
-- must take it into account when accessing the free variables.
bind_fv :: (NonVoid Id, ByteOff) -> FCode (LocalReg, ByteOff)
bind_fv (id, off) = do { reg <- rebindToReg id; return (reg, off) }

load_fvs :: LocalReg -> LambdaFormInfo -> [(LocalReg, ByteOff)] -> FCode ()
load_fvs node lf_info = mapM_ (\ (reg, off) ->
   do dflags <- getDynFlags
      let tag = lfDynTag dflags lf_info
      emit $ mkTaggedObjectLoad dflags reg node off tag)

-----------------------------------------
-- The "slow entry" code for a function.  This entry point takes its
-- arguments on the stack.  It loads the arguments into registers
-- according to the calling convention, and jumps to the function's
-- normal entry point.  The function's closure is assumed to be in
-- R1/node.
--
-- The slow entry point is used for unknown calls: eg. stg_PAP_entry

mkSlowEntryCode :: Id -> ClosureInfo -> [LocalReg] -> FCode ()
-- If this function doesn't have a specialised ArgDescr, we need
-- to generate the function's arg bitmap and slow-entry code.
-- Here, we emit the slow-entry code.
mkSlowEntryCode bndr cl_info arg_regs -- function closure is already in `Node'
  | Just (_, ArgGen _) <- closureFunInfo cl_info
  = do dflags <- getDynFlags
       let node = idToReg dflags (NonVoid bndr)
           slow_lbl = closureSlowEntryLabel  cl_info
           fast_lbl = closureLocalEntryLabel dflags cl_info
           -- mkDirectJump does not clobber `Node' containing function closure
           jump = mkJump dflags NativeNodeCall
                                (mkLblExpr fast_lbl)
                                (map (CmmReg . CmmLocal) (node : arg_regs))
                                (initUpdFrameOff dflags)
       tscope <- getTickScope
       emitProcWithConvention Slow Nothing slow_lbl
         (node : arg_regs) (jump, tscope)
  | otherwise = return ()

-----------------------------------------
thunkCode :: ClosureInfo -> [(NonVoid Id, ByteOff)] -> CostCentreStack
          -> LocalReg -> Int -> StgExpr -> FCode ()
thunkCode cl_info fv_details _cc node arity body
  = do { dflags <- getDynFlags
       ; let node_points = nodeMustPointToIt dflags (closureLFInfo cl_info)
             node'       = if node_points then Just node else Nothing
        ; ldvEnterClosure cl_info (CmmLocal node) -- NB: Node always points when profiling

        -- Heap overflow check
        ; entryHeapCheck cl_info node' arity [] $ do
        { -- Overwrite with black hole if necessary
          -- but *after* the heap-overflow check
        ; tickyEnterThunk cl_info
        ; when (blackHoleOnEntry cl_info && node_points)
                (blackHoleIt node)

          -- Push update frame
        ; setupUpdate cl_info node $
            -- We only enter cc after setting up update so
            -- that cc of enclosing scope will be recorded
            -- in update frame CAF/DICT functions will be
            -- subsumed by this enclosing cc
            do { tickyEnterThunk cl_info
               ; enterCostCentreThunk (CmmReg nodeReg)
               ; let lf_info = closureLFInfo cl_info
               ; fv_bindings <- mapM bind_fv fv_details
               ; load_fvs node lf_info fv_bindings
               ; void $ cgExpr body }}}


------------------------------------------------------------------------
--              Update and black-hole wrappers
------------------------------------------------------------------------

blackHoleIt :: LocalReg -> FCode ()
-- Only called for closures with no args
-- Node points to the closure
blackHoleIt node_reg
  = emitBlackHoleCode (CmmReg (CmmLocal node_reg))

emitBlackHoleCode :: CmmExpr -> FCode ()
emitBlackHoleCode node = do
  dflags <- getDynFlags

  -- Eager blackholing is normally disabled, but can be turned on with
  -- -feager-blackholing.  When it is on, we replace the info pointer
  -- of the thunk with stg_EAGER_BLACKHOLE_info on entry.

  -- If we wanted to do eager blackholing with slop filling, we'd need
  -- to do it at the *end* of a basic block, otherwise we overwrite
  -- the free variables in the thunk that we still need.  We have a
  -- patch for this from Andy Cheadle, but not incorporated yet. --SDM
  -- [6/2004]
  --
  -- Previously, eager blackholing was enabled when ticky-ticky was
  -- on. But it didn't work, and it wasn't strictly necessary to bring
  -- back minimal ticky-ticky, so now EAGER_BLACKHOLING is
  -- unconditionally disabled. -- krc 1/2007

  -- Note the eager-blackholing check is here rather than in blackHoleOnEntry,
  -- because emitBlackHoleCode is called from CmmParse.

  let  eager_blackholing =  not (gopt Opt_SccProfilingOn dflags)
                         && gopt Opt_EagerBlackHoling dflags
             -- Profiling needs slop filling (to support LDV
             -- profiling), so currently eager blackholing doesn't
             -- work with profiling.

  when eager_blackholing $ do
    emitStore (cmmOffsetW dflags node (fixedHdrSizeW dflags))
                  (CmmReg (CmmGlobal CurrentTSO))
    emitPrimCall [] MO_WriteBarrier []
    emitStore node (CmmReg (CmmGlobal EagerBlackholeInfo))

setupUpdate :: ClosureInfo -> LocalReg -> FCode () -> FCode ()
        -- Nota Bene: this function does not change Node (even if it's a CAF),
        -- so that the cost centre in the original closure can still be
        -- extracted by a subsequent enterCostCentre
setupUpdate closure_info node body
  | not (lfUpdatable (closureLFInfo closure_info))
  = body

  | not (isStaticClosure closure_info)
  = if not (closureUpdReqd closure_info)
      then do tickyUpdateFrameOmitted; body
      else do
          tickyPushUpdateFrame
          dflags <- getDynFlags
          let
              bh = blackHoleOnEntry closure_info &&
                   not (gopt Opt_SccProfilingOn dflags) &&
                   gopt Opt_EagerBlackHoling dflags

              lbl | bh        = mkBHUpdInfoLabel
                  | otherwise = mkUpdInfoLabel

          pushUpdateFrame lbl (CmmReg (CmmLocal node)) body

  | otherwise   -- A static closure
  = do  { tickyUpdateBhCaf closure_info

        ; if closureUpdReqd closure_info
          then do       -- Blackhole the (updatable) CAF:
                { upd_closure <- link_caf node True
                ; pushUpdateFrame mkBHUpdInfoLabel upd_closure body }
          else do {tickyUpdateFrameOmitted; body}
    }

-----------------------------------------------------------------------------
-- Setting up update frames

-- Push the update frame on the stack in the Entry area,
-- leaving room for the return address that is already
-- at the old end of the area.
--
pushUpdateFrame :: CLabel -> CmmExpr -> FCode () -> FCode ()
pushUpdateFrame lbl updatee body
  = do
       updfr  <- getUpdFrameOff
       dflags <- getDynFlags
       let
           hdr         = fixedHdrSize dflags
           frame       = updfr + hdr + sIZEOF_StgUpdateFrame_NoHdr dflags
       --
       emitUpdateFrame dflags (CmmStackSlot Old frame) lbl updatee
       withUpdFrameOff frame body

emitUpdateFrame :: DynFlags -> CmmExpr -> CLabel -> CmmExpr -> FCode ()
emitUpdateFrame dflags frame lbl updatee = do
  let
           hdr         = fixedHdrSize dflags
           off_updatee = hdr + oFFSET_StgUpdateFrame_updatee dflags
  --
  emitStore frame (mkLblExpr lbl)
  emitStore (cmmOffset dflags frame off_updatee) updatee
  initUpdFrameProf frame

-----------------------------------------------------------------------------
-- Entering a CAF
--
-- See Note [CAF management] in rts/sm/Storage.c

link_caf :: LocalReg           -- pointer to the closure
         -> Bool               -- True <=> updatable, False <=> single-entry
         -> FCode CmmExpr      -- Returns amode for closure to be updated
-- This function returns the address of the black hole, so it can be
-- updated with the new value when available.
link_caf node _is_upd = do
  { dflags <- getDynFlags
        -- Call the RTS function newCAF, returning the newly-allocated
        -- blackhole indirection closure
  ; let newCAF_lbl = mkForeignLabel (fsLit "newCAF") Nothing
                                    ForeignLabelInExternalPackage IsFunction
  ; bh <- newTemp (bWord dflags)
  ; emitRtsCallGen [(bh,AddrHint)] newCAF_lbl
      [ (CmmReg (CmmGlobal BaseReg),  AddrHint),
        (CmmReg (CmmLocal node), AddrHint) ]
      False

  -- see Note [atomic CAF entry] in rts/sm/Storage.c
  ; updfr  <- getUpdFrameOff
  ; let target = entryCode dflags (closureInfoPtr dflags (CmmReg (CmmLocal node)))
  ; emit =<< mkCmmIfThen
      (cmmEqWord dflags (CmmReg (CmmLocal bh)) (zeroExpr dflags))
        -- re-enter the CAF
       (mkJump dflags NativeNodeCall target [] updfr)

  ; return (CmmReg (CmmLocal bh)) }

------------------------------------------------------------------------
--              Profiling
------------------------------------------------------------------------

-- For "global" data constructors the description is simply occurrence
-- name of the data constructor itself.  Otherwise it is determined by
-- @closureDescription@ from the let binding information.

closureDescription :: DynFlags
           -> Module            -- Module
                   -> Name              -- Id of closure binding
                   -> String
        -- Not called for StgRhsCon which have global info tables built in
        -- CgConTbls.hs with a description generated from the data constructor
closureDescription dflags mod_name name
  = showSDocDump dflags (char '<' <>
                    (if isExternalName name
                      then ppr name -- ppr will include the module name prefix
                      else pprModule mod_name <> char '.' <> ppr name) <>
                    char '>')
   -- showSDocDump, because we want to see the unique on the Name.