2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 % $Id: CgCase.lhs,v 1.63 2003/07/02 13:12:35 simonpj Exp $
6 %********************************************************
8 \section[CgCase]{Converting @StgCase@ expressions}
10 %********************************************************
13 module CgCase ( cgCase, saveVolatileVarsAndRegs,
14 mkRetDirectTarget, restoreCurrentCostCentre
17 #include "HsVersions.h"
19 import {-# SOURCE #-} CgExpr ( cgExpr )
25 import AbsCUtils ( mkAbstractCs, mkAbsCStmts, mkAlgAltsCSwitch, getAmodeRep )
26 import CgBindery ( getVolatileRegs, getArgAmodes,
27 bindNewToReg, bindNewToTemp,
29 rebindToStack, getCAddrMode, getCAddrModeIfVolatile,
30 buildContLivenessMask, nukeDeadBindings,
32 import CgCon ( bindConArgs, bindUnboxedTupleComponents )
33 import CgHeapery ( altHeapCheck, unbxTupleHeapCheck )
34 import CgRetConv ( dataReturnConvPrim, ctrlReturnConvAlg,
35 CtrlReturnConvention(..)
37 import CgStackery ( allocPrimStack, allocStackTop,
38 deAllocStackTop, freeStackSlots, dataStackSlots
40 import CgTailCall ( performTailCall )
41 import CgUsages ( getSpRelOffset )
42 import CLabel ( mkVecTblLabel, mkClosureTblLabel,
43 mkDefaultLabel, mkAltLabel, mkReturnInfoLabel
45 import ClosureInfo ( mkLFArgument )
46 import CmdLineOpts ( opt_SccProfilingOn )
47 import Id ( Id, idName, isDeadBinder )
48 import DataCon ( dataConTag, fIRST_TAG, ConTag )
49 import VarSet ( varSetElems )
50 import CoreSyn ( AltCon(..) )
51 import PrimOp ( primOpOutOfLine, PrimOp(..) )
52 import PrimRep ( getPrimRepSize, retPrimRepSize, PrimRep(..)
54 import TyCon ( TyCon, isEnumerationTyCon, tyConPrimRep )
55 import Unique ( Unique, Uniquable(..), newTagUnique )
57 import List ( sortBy )
63 = GCMayHappen -- The scrutinee may involve GC, so everything must be
64 -- tidy before the code for the scrutinee.
66 | NoGC -- The scrutinee is a primitive value, or a call to a
67 -- primitive op which does no GC. Hence the case can
68 -- be done inline, without tidying up first.
71 It is quite interesting to decide whether to put a heap-check
72 at the start of each alternative. Of course we certainly have
73 to do so if the case forces an evaluation, or if there is a primitive
74 op which can trigger GC.
76 A more interesting situation is this:
83 default -> !C!; ...C...
86 where \tr{!x!} indicates a possible heap-check point. The heap checks
87 in the alternatives {\em can} be omitted, in which case the topmost
88 heapcheck will take their worst case into account.
90 In favour of omitting \tr{!B!}, \tr{!C!}:
92 - {\em May} save a heap overflow test,
93 if ...A... allocates anything. The other advantage
94 of this is that we can use relative addressing
95 from a single Hp to get at all the closures so allocated.
97 - No need to save volatile vars etc across the case
101 - May do more allocation than reqd. This sometimes bites us
102 badly. For example, nfib (ha!) allocates about 30\% more space if the
103 worst-casing is done, because many many calls to nfib are leaf calls
104 which don't need to allocate anything.
106 This never hurts us if there is only one alternative.
119 Special case #1: case of literal.
122 cgCase (StgLit lit) live_in_whole_case live_in_alts bndr srt
123 alt_type@(PrimAlt tycon) alts
124 = bindNewToTemp bndr `thenFC` \ tmp_amode ->
125 absC (CAssign tmp_amode (CLit lit)) `thenC`
126 cgPrimAlts NoGC tmp_amode alts alt_type
129 Special case #2: scrutinising a primitive-typed variable. No
130 evaluation required. We don't save volatile variables, nor do we do a
131 heap-check in the alternatives. Instead, the heap usage of the
132 alternatives is worst-cased and passed upstream. This can result in
133 allocating more heap than strictly necessary, but it will sometimes
134 eliminate a heap check altogether.
137 cgCase (StgApp v []) live_in_whole_case live_in_alts bndr srt
138 alt_type@(PrimAlt tycon) alts
140 = -- Careful! we can't just bind the default binder to the same thing
141 -- as the scrutinee, since it might be a stack location, and having
142 -- two bindings pointing at the same stack locn doesn't work (it
143 -- confuses nukeDeadBindings). Hence, use a new temp.
144 getCAddrMode v `thenFC` \ amode ->
145 bindNewToTemp bndr `thenFC` \ tmp_amode ->
146 absC (CAssign tmp_amode amode) `thenC`
147 cgPrimAlts NoGC amode alts alt_type
148 -- TEMP Should be tmp_amode, not amode
149 -- but for line-by-line comparison with old stuff, we pass amode too
152 Special case #3: inline PrimOps.
155 cgCase (StgOpApp op@(StgPrimOp primop) args _)
156 live_in_whole_case live_in_alts bndr srt alt_type alts
157 | not (primOpOutOfLine primop)
158 = -- Get amodes for the arguments and results
159 getArgAmodes args `thenFC` \ arg_amodes ->
160 getVolatileRegs live_in_alts `thenFC` \ vol_regs ->
163 PrimAlt tycon -- PRIMITIVE ALTS
164 -> bindNewToTemp bndr `thenFC` \ tmp_amode ->
165 absC (COpStmt [tmp_amode] op arg_amodes vol_regs) `thenC`
166 -- Note: no liveness arg
167 cgPrimAlts NoGC tmp_amode alts alt_type
169 UbxTupAlt tycon -- UNBOXED TUPLE ALTS
170 -> -- No heap check, no yield, just get in there and do it.
171 -- NB: the case binder isn't bound to anything;
172 -- it has a unboxed tuple type
173 mapFCs bindNewToTemp res_ids `thenFC` \ res_tmps ->
174 absC (COpStmt res_tmps op arg_amodes vol_regs) `thenC`
177 [(_, res_ids, _, rhs)] = alts
179 AlgAlt tycon -- ENUMERATION TYPE RETURN
180 -> ASSERT( isEnumerationTyCon tycon )
181 do_enum_primop primop `thenFC` \ tag_amode ->
183 -- Bind the default binder if necessary
184 -- (avoiding it avoids the assignment)
185 -- The deadness info is set by StgVarInfo
186 (if (isDeadBinder bndr)
188 else bindNewToTemp bndr `thenFC` \ tmp_amode ->
189 absC (CAssign tmp_amode (tagToClosure tycon tag_amode))
193 cgAlgAlts NoGC (getUnique bndr)
194 Nothing{-cc_slot-} False{-no semi-tagging-}
195 (AlgAlt tycon) alts `thenFC` \ tagged_alts ->
198 absC (mkAlgAltsCSwitch tag_amode tagged_alts)
200 do_enum_primop :: PrimOp -> FCode CAddrMode -- Returns amode for result
201 do_enum_primop TagToEnumOp -- No code!
202 = returnFC (only arg_amodes)
204 do_enum_primop primop
205 = absC (COpStmt [tag_amode] op arg_amodes vol_regs) `thenC`
208 tag_amode = CTemp (newTagUnique (getUnique bndr) 'C') IntRep
209 -- Being a bit short of uniques for temporary variables here,
210 -- we use newTagUnique to generate a new unique from the case
211 -- binder. The case binder's unique will presumably have
212 -- the 'c' tag (generated by CoreToStg), so we just change
213 -- its tag to 'C' (for 'case') to ensure it doesn't clash with
215 -- We can't use the unique from the case binder, becaus e
216 -- this is used to hold the actual result closure
217 -- (via the call to bindNewToTemp)
219 other -> pprPanic "cgCase: case of primop has strange alt type" (ppr alt_type)
222 TODO: Case-of-case of primop can probably be done inline too (but
223 maybe better to translate it out beforehand). See
224 ghc/lib/misc/PackedString.lhs for examples where this crops up (with
227 Special case: scrutinising a non-primitive variable.
228 This can be done a little better than the general case, because
229 we can reuse/trim the stack slot holding the variable (if it is in one).
232 cgCase (StgApp fun args)
233 live_in_whole_case live_in_alts bndr srt alt_type alts
234 = getCAddrModeAndInfo fun `thenFC` \ (fun', fun_amode, lf_info) ->
235 getArgAmodes args `thenFC` \ arg_amodes ->
237 -- Nuking dead bindings *before* calculating the saves is the
238 -- value-add here. We might end up freeing up some slots currently
239 -- occupied by variables only required for the call.
240 -- NOTE: we need to look up the variables used in the call before
241 -- doing this, because some of them may not be in the environment
243 nukeDeadBindings live_in_alts `thenC`
244 saveVolatileVarsAndRegs live_in_alts
245 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
247 forkEval alts_eob_info
248 ( allocStackTop retPrimRepSize
249 `thenFC` \_ -> nopC )
250 ( deAllocStackTop retPrimRepSize `thenFC` \_ ->
251 cgEvalAlts maybe_cc_slot bndr srt alt_type alts )
252 `thenFC` \ scrut_eob_info ->
254 setEndOfBlockInfo (maybeReserveSeqFrame alt_type scrut_eob_info) $
255 performTailCall fun' fun_amode lf_info arg_amodes save_assts
258 Note about return addresses: we *always* push a return address, even
259 if because of an optimisation we end up jumping direct to the return
260 code (not through the address itself). The alternatives always assume
261 that the return address is on the stack. The return address is
262 required in case the alternative performs a heap check, since it
263 encodes the liveness of the slots in the activation record.
265 On entry to the case alternative, we can re-use the slot containing
266 the return address immediately after the heap check. That's what the
267 deAllocStackTop call is doing above.
269 Finally, here is the general case.
272 cgCase expr live_in_whole_case live_in_alts bndr srt alt_type alts
273 = -- Figure out what volatile variables to save
274 nukeDeadBindings live_in_whole_case `thenC`
276 saveVolatileVarsAndRegs live_in_alts
277 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
279 -- Save those variables right now!
280 absC save_assts `thenC`
282 -- generate code for the alts
283 forkEval alts_eob_info
284 (nukeDeadBindings live_in_alts `thenC`
285 allocStackTop retPrimRepSize -- space for retn address
288 (deAllocStackTop retPrimRepSize `thenFC` \_ ->
289 cgEvalAlts maybe_cc_slot bndr srt alt_type alts) `thenFC` \ scrut_eob_info ->
291 setEndOfBlockInfo (maybeReserveSeqFrame alt_type scrut_eob_info) $
295 There's a lot of machinery going on behind the scenes to manage the
296 stack pointer here. forkEval takes the virtual Sp and free list from
297 the first argument, and turns that into the *real* Sp for the second
298 argument. It also uses this virtual Sp as the args-Sp in the EOB info
299 returned, so that the scrutinee will trim the real Sp back to the
300 right place before doing whatever it does.
301 --SDM (who just spent an hour figuring this out, and didn't want to
304 Why don't we push the return address just before evaluating the
305 scrutinee? Because the slot reserved for the return address might
306 contain something useful, so we wait until performing a tail call or
307 return before pushing the return address (see
308 CgTailCall.pushReturnAddress).
310 This also means that the environment doesn't need to know about the
311 free stack slot for the return address (for generating bitmaps),
312 because we don't reserve it until just before the eval.
314 TODO!! Problem: however, we have to save the current cost centre
315 stack somewhere, because at the eval point the current CCS might be
316 different. So we pick a free stack slot and save CCCS in it. The
317 problem with this is that this slot isn't recorded as free/unboxed in
318 the environment, so a case expression in the scrutinee will have the
319 wrong bitmap attached. Fortunately we don't ever seem to see
320 case-of-case at the back end. One solution might be to shift the
321 saved CCS to the correct place in the activation record just before
325 (one consequence of the above is that activation records on the stack
326 don't follow the layout of closures when we're profiling. The CCS
327 could be anywhere within the record).
330 maybeReserveSeqFrame PolyAlt (EndOfBlockInfo args_sp (CaseAlts amode stuff _))
331 = EndOfBlockInfo (args_sp + retPrimRepSize) (CaseAlts amode stuff True)
332 maybeReserveSeqFrame other scrut_eob_info = scrut_eob_info
335 %************************************************************************
337 \subsection[CgCase-alts]{Alternatives}
339 %************************************************************************
341 @cgEvalAlts@ returns an addressing mode for a continuation for the
342 alternatives of a @case@, used in a context when there
343 is some evaluation to be done.
346 cgEvalAlts :: Maybe VirtualSpOffset -- Offset of cost-centre to be restored, if any
348 -> SRT -- SRT for the continuation
351 -> FCode Sequel -- Any addr modes inside are guaranteed
352 -- to be a label so that we can duplicate it
353 -- without risk of duplicating code
355 cgEvalAlts cc_slot bndr srt (UbxTupAlt _) [(con,args,_,rhs)]
356 = -- Unboxed tuple case
357 -- By now, the simplifier should have have turned it
358 -- into case e of (# a,b #) -> e
359 -- There shouldn't be a
360 -- case e of DEFAULT -> e
361 ASSERT2( case con of { DataAlt _ -> True; other -> False },
362 text "cgEvalAlts: dodgy case of unboxed tuple type" )
364 forkAbsC ( -- forkAbsC for the RHS, so that the envt is
365 -- not changed for the mkRetDirect call
366 restoreCurrentCostCentre cc_slot `thenC`
367 bindUnboxedTupleComponents args `thenFC` \ (live_regs, ptrs, nptrs, _) ->
368 -- Generate a heap check if necessary
369 unbxTupleHeapCheck live_regs ptrs nptrs AbsCNop $
370 -- And finally the code for the alternative
372 ) `thenFC` \ abs_c ->
373 mkRetDirectTarget bndr abs_c srt `thenFC` \ lbl ->
374 returnFC (CaseAlts lbl Nothing False)
376 cgEvalAlts cc_slot bndr srt alt_type@(PrimAlt tycon) alts
377 = forkAbsC ( -- forkAbsC for the RHS, so that the envt is
378 -- not changed for the mkRetDirect call
379 restoreCurrentCostCentre cc_slot `thenC`
380 bindNewToReg bndr reg (mkLFArgument bndr) `thenC`
381 cgPrimAlts GCMayHappen (CReg reg) alts alt_type
382 ) `thenFC` \ abs_c ->
383 mkRetDirectTarget bndr abs_c srt `thenFC` \ lbl ->
384 returnFC (CaseAlts lbl Nothing False)
386 reg = dataReturnConvPrim kind
387 kind = tyConPrimRep tycon
389 cgEvalAlts cc_slot bndr srt alt_type alts
390 = -- Algebraic and polymorphic case
391 -- Bind the default binder
392 bindNewToReg bndr node (mkLFArgument bndr) `thenC`
394 -- Generate sequel info for use downstream
395 -- At the moment, we only do it if the type is vector-returnable.
396 -- Reason: if not, then it costs extra to label the
397 -- alternatives, because we'd get return code like:
399 -- switch TagReg { 0 : JMP(alt_1); 1 : JMP(alt_2) ..etc }
401 -- which is worse than having the alt code in the switch statement
403 let ret_conv = case alt_type of
404 AlgAlt tc -> ctrlReturnConvAlg tc
405 PolyAlt -> UnvectoredReturn 0
407 use_labelled_alts = case ret_conv of
408 VectoredReturn _ -> True
411 semi_tagged_stuff = cgSemiTaggedAlts use_labelled_alts bndr alts
414 cgAlgAlts GCMayHappen (getUnique bndr)
415 cc_slot use_labelled_alts
416 alt_type alts `thenFC` \ tagged_alt_absCs ->
418 mkRetVecTarget bndr tagged_alt_absCs
419 srt ret_conv `thenFC` \ return_vec ->
421 returnFC (CaseAlts return_vec semi_tagged_stuff False)
425 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): If
426 we do an inlining of the case no separate functions for returning are
427 created, so we don't have to generate a GRAN_YIELD in that case. This info
428 must be propagated to cgAlgAltRhs (where the GRAN_YIELD macro might be
429 emitted). Hence, the new Bool arg to cgAlgAltRhs.
431 %************************************************************************
433 \subsection[CgCase-alg-alts]{Algebraic alternatives}
435 %************************************************************************
437 In @cgAlgAlts@, none of the binders in the alternatives are
438 assumed to be yet bound.
440 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): The
441 last arg of cgAlgAlts indicates if we want a context switch at the
442 beginning of each alternative. Normally we want that. The only exception
443 are inlined alternatives.
448 -> Maybe VirtualSpOffset
449 -> Bool -- True <=> branches must be labelled
450 -- (used for semi-tagging)
451 -> AltType -- ** AlgAlt or PolyAlt only **
452 -> [StgAlt] -- The alternatives
453 -> FCode [(AltCon, AbstractC)] -- The branches
455 cgAlgAlts gc_flag uniq restore_cc must_label_branches alt_type alts
456 = forkAlts [ cgAlgAlt gc_flag uniq restore_cc must_label_branches alt_type alt
460 -> Unique -> Maybe VirtualSpOffset -> Bool -- turgid state
461 -> AltType -- ** AlgAlt or PolyAlt only **
463 -> FCode (AltCon, AbstractC)
465 cgAlgAlt gc_flag uniq cc_slot must_label_branch
466 alt_type (con, args, use_mask, rhs)
467 = getAbsC (bind_con_args con args `thenFC` \ _ ->
468 restoreCurrentCostCentre cc_slot `thenC`
469 maybeAltHeapCheck gc_flag alt_type (cgExpr rhs)
470 ) `thenFC` \ abs_c ->
472 final_abs_c | must_label_branch = CCodeBlock lbl abs_c
475 returnFC (con, final_abs_c)
478 DataAlt dc -> mkAltLabel uniq (dataConTag dc)
479 DEFAULT -> mkDefaultLabel uniq
480 other -> pprPanic "cgAlgAlt" (ppr con)
482 bind_con_args DEFAULT args = nopC
483 bind_con_args (DataAlt dc) args = bindConArgs dc args
486 %************************************************************************
488 \subsection[CgCase-semi-tagged-alts]{The code to deal with sem-tagging}
490 %************************************************************************
492 Turgid-but-non-monadic code to conjure up the required info from
493 algebraic case alternatives for semi-tagging.
496 cgSemiTaggedAlts :: Bool -- True <=> use semitagging: each alt will be labelled
501 cgSemiTaggedAlts False binder alts
503 cgSemiTaggedAlts True binder alts
504 = Just ([st_alt con args | (DataAlt con, args, _, _) <- alts],
506 (DEFAULT, _, _, _) -> Just st_deflt
509 uniq = getUnique binder
512 (CCallProfCtrMacro FSLIT("RET_SEMI_BY_DEFAULT") [], -- ToDo: monadise?
513 mkDefaultLabel uniq))
515 st_alt con args -- Ha! Nothing to do; Node already points to the thing
517 (CCallProfCtrMacro FSLIT("RET_SEMI_IN_HEAP") -- ToDo: monadise?
518 [mkIntCLit (length args)], -- how big the thing in the heap is
522 con_tag = dataConTag con
523 join_label = mkAltLabel uniq con_tag
526 tagToClosure :: TyCon -> CAddrMode -> CAddrMode
527 -- Primops returning an enumeration type (notably Bool)
528 -- actually return an index into
529 -- the table of closures for the enumeration type
530 tagToClosure tycon tag_amode
531 = CVal (CIndex closure_tbl tag_amode PtrRep) PtrRep
533 closure_tbl = CLbl (mkClosureTblLabel tycon) PtrRep
536 %************************************************************************
538 \subsection[CgCase-prim-alts]{Primitive alternatives}
540 %************************************************************************
542 @cgPrimAlts@ generates suitable a @CSwitch@
543 for dealing with the alternatives of a primitive @case@, given an
544 addressing mode for the thing to scrutinise. It also keeps track of
545 the maximum stack depth encountered down any branch.
547 As usual, no binders in the alternatives are yet bound.
551 -> CAddrMode -- Scrutinee
552 -> [StgAlt] -- Alternatives
555 -- INVARIANT: the default binder is already bound
556 cgPrimAlts gc_flag scrutinee alts alt_type
557 = forkAlts (map (cgPrimAlt gc_flag alt_type) alts) `thenFC` \ tagged_absCs ->
559 ((DEFAULT, deflt_absC) : others) = tagged_absCs -- There is always a default
560 alt_absCs = [(lit,rhs) | (LitAlt lit, rhs) <- others]
562 absC (CSwitch scrutinee alt_absCs deflt_absC)
563 -- CSwitch does sensible things with one or zero alternatives
567 -> StgAlt -- The alternative
568 -> FCode (AltCon, AbstractC) -- Its compiled form
570 cgPrimAlt gc_flag alt_type (con, [], [], rhs)
571 = ASSERT( case con of { DEFAULT -> True; LitAlt _ -> True; other -> False } )
572 getAbsC (maybeAltHeapCheck gc_flag alt_type (cgExpr rhs)) `thenFC` \ abs_c ->
573 returnFC (con, abs_c)
577 %************************************************************************
579 \subsection[CgCase-tidy]{Code for tidying up prior to an eval}
581 %************************************************************************
586 -> AltType -- PolyAlt, PrimAlt, AlgAlt, but *not* UbxTupAlt
587 -> Code -- Continuation
589 maybeAltHeapCheck NoGC _ code = code
590 maybeAltHeapCheck GCMayHappen alt_type code
591 = -- HWL: maybe need yield here
592 -- yield [node] True -- XXX live regs wrong
593 altHeapCheck alt_type code
595 saveVolatileVarsAndRegs
596 :: StgLiveVars -- Vars which should be made safe
597 -> FCode (AbstractC, -- Assignments to do the saves
598 EndOfBlockInfo, -- sequel for the alts
599 Maybe VirtualSpOffset) -- Slot for current cost centre
601 saveVolatileVarsAndRegs vars
602 = saveVolatileVars vars `thenFC` \ var_saves ->
603 saveCurrentCostCentre `thenFC` \ (maybe_cc_slot, cc_save) ->
604 getEndOfBlockInfo `thenFC` \ eob_info ->
605 returnFC (mkAbstractCs [var_saves, cc_save],
610 saveVolatileVars :: StgLiveVars -- Vars which should be made safe
611 -> FCode AbstractC -- Assignments to to the saves
613 saveVolatileVars vars
614 = save_em (varSetElems vars)
616 save_em [] = returnFC AbsCNop
619 = getCAddrModeIfVolatile var `thenFC` \ v ->
621 Nothing -> save_em vars -- Non-volatile, so carry on
624 Just vol_amode -> -- Aha! It's volatile
625 save_var var vol_amode `thenFC` \ abs_c ->
626 save_em vars `thenFC` \ abs_cs ->
627 returnFC (abs_c `mkAbsCStmts` abs_cs)
629 save_var var vol_amode
630 = allocPrimStack (getPrimRepSize kind) `thenFC` \ slot ->
631 rebindToStack var slot `thenC`
632 getSpRelOffset slot `thenFC` \ sp_rel ->
633 returnFC (CAssign (CVal sp_rel kind) vol_amode)
635 kind = getAmodeRep vol_amode
638 ---------------------------------------------------------------------------
640 When we save the current cost centre (which is done for lexical
641 scoping), we allocate a free stack location, and return (a)~the
642 virtual offset of the location, to pass on to the alternatives, and
643 (b)~the assignment to do the save (just as for @saveVolatileVars@).
646 saveCurrentCostCentre ::
647 FCode (Maybe VirtualSpOffset, -- Where we decide to store it
648 AbstractC) -- Assignment to save it
650 saveCurrentCostCentre
651 = if not opt_SccProfilingOn then
652 returnFC (Nothing, AbsCNop)
654 allocPrimStack (getPrimRepSize CostCentreRep) `thenFC` \ slot ->
655 dataStackSlots [slot] `thenC`
656 getSpRelOffset slot `thenFC` \ sp_rel ->
658 CAssign (CVal sp_rel CostCentreRep) (CReg CurCostCentre))
660 restoreCurrentCostCentre :: Maybe VirtualSpOffset -> Code
661 restoreCurrentCostCentre Nothing = nopC
662 restoreCurrentCostCentre (Just slot)
663 = getSpRelOffset slot `thenFC` \ sp_rel ->
664 freeStackSlots [slot] `thenC`
665 absC (CCallProfCCMacro FSLIT("RESTORE_CCCS") [CVal sp_rel CostCentreRep])
666 -- we use the RESTORE_CCCS macro, rather than just
667 -- assigning into CurCostCentre, in case RESTORE_CCCS
668 -- has some sanity-checking in it.
671 %************************************************************************
673 \subsection[CgCase-return-vec]{Building a return vector}
675 %************************************************************************
677 Build a return vector, and return a suitable label addressing
681 mkRetDirectTarget :: Id -- Used for labelling only
682 -> AbstractC -- Return code
683 -> SRT -- Live CAFs in return code
684 -> FCode CAddrMode -- Emit the labelled return block,
685 -- and return its label
686 mkRetDirectTarget bndr abs_c srt
687 = buildContLivenessMask bndr `thenFC` \ liveness ->
688 getSRTInfo name srt `thenFC` \ srt_info ->
689 absC (CRetDirect uniq abs_c srt_info liveness) `thenC`
693 uniq = getUnique name
694 lbl = CLbl (mkReturnInfoLabel uniq) RetRep
698 mkRetVecTarget :: Id -- Just for its unique
699 -> [(AltCon, AbstractC)] -- Branch codes
700 -> SRT -- Continuation's SRT
701 -> CtrlReturnConvention
704 mkRetVecTarget bndr tagged_alt_absCs srt (UnvectoredReturn 0)
705 = ASSERT( null other_alts )
706 mkRetDirectTarget bndr deflt_absC srt
708 ((DEFAULT, deflt_absC) : other_alts) = tagged_alt_absCs
710 mkRetVecTarget bndr tagged_alt_absCs srt (UnvectoredReturn n)
711 = mkRetDirectTarget bndr switch_absC srt
713 -- Find the tag explicitly rather than using tag_reg for now.
714 -- on architectures with lots of regs the tag will be loaded
715 -- into tag_reg by the code doing the returning.
716 tag = CMacroExpr WordRep GET_TAG [CVal (nodeRel 0) DataPtrRep]
717 switch_absC = mkAlgAltsCSwitch tag tagged_alt_absCs
720 mkRetVecTarget bndr tagged_alt_absCs srt (VectoredReturn table_size)
721 = buildContLivenessMask bndr `thenFC` \ liveness ->
722 getSRTInfo name srt `thenFC` \ srt_info ->
724 ret_vector = CRetVector vtbl_lbl vector_table srt_info liveness
726 absC (mkAbstractCs alts_absCs `mkAbsCStmts` ret_vector) `thenC`
727 -- Alts come first, because we don't want to declare all the symbols
729 return (CLbl vtbl_lbl DataPtrRep)
731 tags = [fIRST_TAG .. (table_size+fIRST_TAG-1)]
732 vector_table = map mk_vector_entry tags
733 alts_absCs = map snd (sortBy cmp tagged_alt_absCs)
734 -- The sort is unnecessary; just there for now
735 -- to make the new order the same as the old
736 (DEFAULT,_) `cmp` (DEFAULT,_) = EQ
737 (DEFAULT,_) `cmp` _ = GT
738 (DataAlt d1,_) `cmp` (DataAlt d2,_) = dataConTag d1 `compare` dataConTag d2
739 (DataAlt d1,_) `cmp` (DEFAULT, _) = LT
743 uniq = getUnique name
744 vtbl_lbl = mkVecTblLabel uniq
746 deflt_lbl :: CAddrMode
747 deflt_lbl = case tagged_alt_absCs of
748 (DEFAULT, abs_c) : _ -> get_block_label abs_c
750 -- 'other' case: the simplifier might have eliminated a case
751 -- so we may have e.g. case xs of
753 -- In that situation the default should never be taken,
754 -- so we just use '0' (=> seg fault if used)
756 mk_vector_entry :: ConTag -> CAddrMode
758 = case [ absC | (DataAlt d, absC) <- tagged_alt_absCs, dataConTag d == tag ] of
759 -- The comprehension neatly, and correctly, ignores the DEFAULT
761 [abs_c] -> get_block_label abs_c
762 _ -> panic "mkReturnVector: too many"
764 get_block_label (CCodeBlock lbl _) = CLbl lbl CodePtrRep