2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 % $Id: CgCase.lhs,v 1.55 2001/12/05 17:35:13 sewardj Exp $
6 %********************************************************
8 \section[CgCase]{Converting @StgCase@ expressions}
10 %********************************************************
13 module CgCase ( cgCase, saveVolatileVarsAndRegs, restoreCurrentCostCentre
16 #include "HsVersions.h"
18 import {-# SOURCE #-} CgExpr ( cgExpr )
24 import AbsCUtils ( mkAbstractCs, mkAbsCStmts, mkAlgAltsCSwitch,
25 getAmodeRep, nonemptyAbsC
27 import CgUpdate ( reserveSeqFrame )
28 import CgBindery ( getVolatileRegs, getArgAmodes,
29 bindNewToReg, bindNewToTemp,
30 bindNewPrimToAmode, getCAddrModeAndInfo,
31 rebindToStack, getCAddrMode, getCAddrModeIfVolatile,
32 buildContLivenessMask, nukeDeadBindings,
34 import CgCon ( bindConArgs, bindUnboxedTupleComponents )
35 import CgHeapery ( altHeapCheck )
36 import CgRetConv ( dataReturnConvPrim, ctrlReturnConvAlg,
37 CtrlReturnConvention(..)
39 import CgStackery ( allocPrimStack, allocStackTop,
40 deAllocStackTop, freeStackSlots, dataStackSlots
42 import CgTailCall ( tailCallFun )
43 import CgUsages ( getSpRelOffset )
44 import CLabel ( mkVecTblLabel, mkClosureTblLabel,
45 mkDefaultLabel, mkAltLabel, mkReturnInfoLabel
47 import ClosureInfo ( mkLFArgument )
48 import CmdLineOpts ( opt_SccProfilingOn )
49 import Id ( Id, idPrimRep, isDeadBinder )
50 import DataCon ( DataCon, dataConTag, fIRST_TAG, ConTag )
51 import VarSet ( varSetElems )
52 import Literal ( Literal )
53 import PrimOp ( primOpOutOfLine, PrimOp(..) )
54 import PrimRep ( getPrimRepSize, retPrimRepSize, PrimRep(..)
56 import TyCon ( isEnumerationTyCon, isUnboxedTupleTyCon, tyConPrimRep )
57 import Unique ( Unique, Uniquable(..), newTagUnique )
58 import Maybes ( maybeToBool )
65 = GCMayHappen -- The scrutinee may involve GC, so everything must be
66 -- tidy before the code for the scrutinee.
68 | NoGC -- The scrutinee is a primitive value, or a call to a
69 -- primitive op which does no GC. Hence the case can
70 -- be done inline, without tidying up first.
73 It is quite interesting to decide whether to put a heap-check
74 at the start of each alternative. Of course we certainly have
75 to do so if the case forces an evaluation, or if there is a primitive
76 op which can trigger GC.
78 A more interesting situation is this:
85 default -> !C!; ...C...
88 where \tr{!x!} indicates a possible heap-check point. The heap checks
89 in the alternatives {\em can} be omitted, in which case the topmost
90 heapcheck will take their worst case into account.
92 In favour of omitting \tr{!B!}, \tr{!C!}:
94 - {\em May} save a heap overflow test,
95 if ...A... allocates anything. The other advantage
96 of this is that we can use relative addressing
97 from a single Hp to get at all the closures so allocated.
99 - No need to save volatile vars etc across the case
103 - May do more allocation than reqd. This sometimes bites us
104 badly. For example, nfib (ha!) allocates about 30\% more space if the
105 worst-casing is done, because many many calls to nfib are leaf calls
106 which don't need to allocate anything.
108 This never hurts us if there is only one alternative.
120 Special case #1: PrimOps returning enumeration types.
122 For enumeration types, we invent a temporary (builtin-unique 1) to
123 hold the tag, and cross our fingers that this doesn't clash with
124 anything else. Builtin-unique 0 is used for a similar reason when
125 compiling enumerated-type primops in CgExpr.lhs. We can't use the
126 unique from the case binder, because this is used to hold the actual
127 closure (when the case binder is live, that is).
129 There is an extra special case for
134 which generates no code for the primop, unless x is used in the
135 alternatives (in which case we lookup the tag in the relevant closure
136 table to get the closure).
138 Being a bit short of uniques for temporary variables here, we use
139 newTagUnique to generate a new unique from the case binder. The case
140 binder's unique will presumably have the 'c' tag (generated by
141 CoreToStg), so we just change its tag to 'C' (for 'case') to ensure it
142 doesn't clash with anything else.
145 cgCase (StgOpApp op args _)
146 live_in_whole_case live_in_alts bndr srt (StgAlgAlts (Just tycon) alts deflt)
147 | isEnumerationTyCon tycon
148 = getArgAmodes args `thenFC` \ arg_amodes ->
151 StgPrimOp TagToEnumOp -- No code!
152 -> returnFC (only arg_amodes) ;
154 _ -> -- Perform the operation
156 tag_amode = CTemp (newTagUnique (getUnique bndr) 'C') IntRep
158 getVolatileRegs live_in_alts `thenFC` \ vol_regs ->
159 absC (COpStmt [tag_amode] op arg_amodes vol_regs)
161 -- NB: no liveness arg
163 } `thenFC` \ tag_amode ->
166 closure = CVal (CIndex (CLbl (mkClosureTblLabel tycon) PtrRep)
171 -- Bind the default binder if necessary
172 -- The deadness info is set by StgVarInfo
173 (if (isDeadBinder bndr)
175 else bindNewToTemp bndr `thenFC` \ bndr_amode ->
176 absC (CAssign bndr_amode closure))
180 cgAlgAlts NoGC (getUnique bndr) Nothing{-cc_slot-} False{-no semi-tagging-}
181 False{-not poly case-} alts deflt
182 False{-don't emit yield-} `thenFC` \ (tagged_alts, deflt_c) ->
185 absC (mkAlgAltsCSwitch tag_amode tagged_alts deflt_c)
188 Special case #2: inline PrimOps.
191 cgCase (StgOpApp op@(StgPrimOp primop) args _)
192 live_in_whole_case live_in_alts bndr srt alts
193 | not (primOpOutOfLine primop)
195 -- Get amodes for the arguments and results
196 getArgAmodes args `thenFC` \ arg_amodes ->
197 getVolatileRegs live_in_alts `thenFC` \ vol_regs ->
200 StgPrimAlts tycon alts deflt -- PRIMITIVE ALTS
201 -> absC (COpStmt [CTemp (getUnique bndr) (tyConPrimRep tycon)]
203 arg_amodes -- note: no liveness arg
205 cgPrimInlineAlts bndr tycon alts deflt
207 StgAlgAlts (Just tycon) [(_, args, _, rhs)] StgNoDefault
208 | isUnboxedTupleTyCon tycon -- UNBOXED TUPLE ALTS
209 -> -- no heap check, no yield, just get in there and do it.
210 absC (COpStmt [ CTemp (getUnique arg) (idPrimRep arg) | arg <- args ]
212 arg_amodes -- note: no liveness arg
214 mapFCs bindNewToTemp args `thenFC` \ _ ->
217 other -> pprPanic "cgCase: case of primop has strange alts" (pprStgAlts alts)
220 TODO: Case-of-case of primop can probably be done inline too (but
221 maybe better to translate it out beforehand). See
222 ghc/lib/misc/PackedString.lhs for examples where this crops up (with
225 Another special case: scrutinising a primitive-typed variable. No
226 evaluation required. We don't save volatile variables, nor do we do a
227 heap-check in the alternatives. Instead, the heap usage of the
228 alternatives is worst-cased and passed upstream. This can result in
229 allocating more heap than strictly necessary, but it will sometimes
230 eliminate a heap check altogether.
233 cgCase (StgApp v []) live_in_whole_case live_in_alts bndr srt
234 (StgPrimAlts tycon alts deflt)
237 getCAddrMode v `thenFC` \amode ->
240 Careful! we can't just bind the default binder to the same thing
241 as the scrutinee, since it might be a stack location, and having
242 two bindings pointing at the same stack locn doesn't work (it
243 confuses nukeDeadBindings). Hence, use a new temp.
245 bindNewToTemp bndr `thenFC` \deflt_amode ->
246 absC (CAssign deflt_amode amode) `thenC`
248 cgPrimAlts NoGC amode alts deflt []
251 Special case: scrutinising a non-primitive variable.
252 This can be done a little better than the general case, because
253 we can reuse/trim the stack slot holding the variable (if it is in one).
256 cgCase (StgApp fun args)
257 live_in_whole_case live_in_alts bndr srt alts
258 = getCAddrModeAndInfo fun `thenFC` \ (fun', fun_amode, lf_info) ->
259 getArgAmodes args `thenFC` \ arg_amodes ->
261 -- Squish the environment
262 nukeDeadBindings live_in_alts `thenC`
263 saveVolatileVarsAndRegs live_in_alts
264 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
266 allocStackTop retPrimRepSize `thenFC` \_ ->
268 forkEval alts_eob_info nopC (
269 deAllocStackTop retPrimRepSize `thenFC` \_ ->
270 cgEvalAlts maybe_cc_slot bndr srt alts)
271 `thenFC` \ scrut_eob_info ->
273 setEndOfBlockInfo (maybeReserveSeqFrame alts scrut_eob_info) $
274 tailCallFun fun' fun_amode lf_info arg_amodes save_assts
277 Note about return addresses: we *always* push a return address, even
278 if because of an optimisation we end up jumping direct to the return
279 code (not through the address itself). The alternatives always assume
280 that the return address is on the stack. The return address is
281 required in case the alternative performs a heap check, since it
282 encodes the liveness of the slots in the activation record.
284 On entry to the case alternative, we can re-use the slot containing
285 the return address immediately after the heap check. That's what the
286 deAllocStackTop call is doing above.
288 Finally, here is the general case.
291 cgCase expr live_in_whole_case live_in_alts bndr srt alts
292 = -- Figure out what volatile variables to save
293 nukeDeadBindings live_in_whole_case `thenC`
295 saveVolatileVarsAndRegs live_in_alts
296 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
298 -- Save those variables right now!
299 absC save_assts `thenC`
301 -- generate code for the alts
302 forkEval alts_eob_info
303 (nukeDeadBindings live_in_alts `thenC`
304 allocStackTop retPrimRepSize -- space for retn address
307 (deAllocStackTop retPrimRepSize `thenFC` \_ ->
308 cgEvalAlts maybe_cc_slot bndr srt alts) `thenFC` \ scrut_eob_info ->
310 setEndOfBlockInfo (maybeReserveSeqFrame alts scrut_eob_info) $
314 There's a lot of machinery going on behind the scenes to manage the
315 stack pointer here. forkEval takes the virtual Sp and free list from
316 the first argument, and turns that into the *real* Sp for the second
317 argument. It also uses this virtual Sp as the args-Sp in the EOB info
318 returned, so that the scrutinee will trim the real Sp back to the
319 right place before doing whatever it does.
320 --SDM (who just spent an hour figuring this out, and didn't want to
323 Why don't we push the return address just before evaluating the
324 scrutinee? Because the slot reserved for the return address might
325 contain something useful, so we wait until performing a tail call or
326 return before pushing the return address (see
327 CgTailCall.pushReturnAddress).
329 This also means that the environment doesn't need to know about the
330 free stack slot for the return address (for generating bitmaps),
331 because we don't reserve it until just before the eval.
333 TODO!! Problem: however, we have to save the current cost centre
334 stack somewhere, because at the eval point the current CCS might be
335 different. So we pick a free stack slot and save CCCS in it. The
336 problem with this is that this slot isn't recorded as free/unboxed in
337 the environment, so a case expression in the scrutinee will have the
338 wrong bitmap attached. Fortunately we don't ever seem to see
339 case-of-case at the back end. One solution might be to shift the
340 saved CCS to the correct place in the activation record just before
344 (one consequence of the above is that activation records on the stack
345 don't follow the layout of closures when we're profiling. The CCS
346 could be anywhere within the record).
349 -- We need to reserve a seq frame for a polymorphic case
350 maybeReserveSeqFrame (StgAlgAlts Nothing _ _) scrut_eob_info = reserveSeqFrame scrut_eob_info
351 maybeReserveSeqFrame other scrut_eob_info = scrut_eob_info
354 %************************************************************************
356 \subsection[CgCase-alts]{Alternatives}
358 %************************************************************************
360 @cgEvalAlts@ returns an addressing mode for a continuation for the
361 alternatives of a @case@, used in a context when there
362 is some evaluation to be done.
365 cgEvalAlts :: Maybe VirtualSpOffset -- Offset of cost-centre to be restored, if any
367 -> SRT -- SRT for the continuation
369 -> FCode Sequel -- Any addr modes inside are guaranteed
370 -- to be a label so that we can duplicate it
371 -- without risk of duplicating code
373 cgEvalAlts cc_slot bndr srt alts
375 let uniq = getUnique bndr in
377 buildContLivenessMask uniq `thenFC` \ liveness_mask ->
381 -- algebraic alts ...
382 StgAlgAlts maybe_tycon alts deflt ->
384 -- bind the default binder (it covers all the alternatives)
385 bindNewToReg bndr node mkLFArgument `thenC`
387 -- Generate sequel info for use downstream
388 -- At the moment, we only do it if the type is vector-returnable.
389 -- Reason: if not, then it costs extra to label the
390 -- alternatives, because we'd get return code like:
392 -- switch TagReg { 0 : JMP(alt_1); 1 : JMP(alt_2) ..etc }
394 -- which is worse than having the alt code in the switch statement
396 let is_alg = maybeToBool maybe_tycon
397 Just spec_tycon = maybe_tycon
400 -- Deal with the unboxed tuple case
401 if is_alg && isUnboxedTupleTyCon spec_tycon then
402 -- By now, the simplifier should have have turned it
403 -- into case e of (# a,b #) -> e
404 -- There shouldn't be a
405 -- case e of DEFAULT -> e
406 ASSERT2( case (alts, deflt) of { ([_],StgNoDefault) -> True; other -> False },
407 text "cgEvalAlts: dodgy case of unboxed tuple type" )
410 lbl = mkReturnInfoLabel uniq
412 cgUnboxedTupleAlt uniq cc_slot True alt `thenFC` \ abs_c ->
413 getSRTInfo srt `thenFC` \ srt_info ->
414 absC (CRetDirect uniq abs_c srt_info liveness_mask) `thenC`
415 returnFC (CaseAlts (CLbl lbl RetRep) Nothing)
417 -- normal algebraic (or polymorphic) case alternatives
419 ret_conv | is_alg = ctrlReturnConvAlg spec_tycon
420 | otherwise = UnvectoredReturn 0
422 use_labelled_alts = case ret_conv of
423 VectoredReturn _ -> True
427 = if use_labelled_alts then
428 cgSemiTaggedAlts bndr alts deflt -- Just <something>
430 Nothing -- no semi-tagging info
433 cgAlgAlts GCMayHappen uniq cc_slot use_labelled_alts (not is_alg)
434 alts deflt True `thenFC` \ (tagged_alt_absCs, deflt_absC) ->
436 mkReturnVector uniq tagged_alt_absCs deflt_absC srt liveness_mask
437 ret_conv `thenFC` \ return_vec ->
439 returnFC (CaseAlts return_vec semi_tagged_stuff)
442 StgPrimAlts tycon alts deflt ->
444 -- Restore the cost centre
445 restoreCurrentCostCentre cc_slot `thenFC` \ cc_restore ->
447 -- Generate the switch
448 getAbsC (cgPrimEvalAlts bndr tycon alts deflt) `thenFC` \ abs_c ->
450 -- Generate the labelled block, starting with restore-cost-centre
451 getSRTInfo srt `thenFC` \srt_info ->
452 absC (CRetDirect uniq (cc_restore `mkAbsCStmts` abs_c)
453 srt_info liveness_mask) `thenC`
455 -- Return an amode for the block
456 returnFC (CaseAlts (CLbl (mkReturnInfoLabel uniq) RetRep) Nothing)
460 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): If
461 we do an inlining of the case no separate functions for returning are
462 created, so we don't have to generate a GRAN_YIELD in that case. This info
463 must be propagated to cgAlgAltRhs (where the GRAN_YIELD macro might be
464 emitted). Hence, the new Bool arg to cgAlgAltRhs.
466 %************************************************************************
468 \subsection[CgCase-alg-alts]{Algebraic alternatives}
470 %************************************************************************
472 In @cgAlgAlts@, none of the binders in the alternatives are
473 assumed to be yet bound.
475 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): The
476 last arg of cgAlgAlts indicates if we want a context switch at the
477 beginning of each alternative. Normally we want that. The only exception
478 are inlined alternatives.
483 -> Maybe VirtualSpOffset
484 -> Bool -- True <=> branches must be labelled
485 -> Bool -- True <=> polymorphic case
486 -> [(DataCon, [Id], [Bool], StgExpr)] -- The alternatives
487 -> StgCaseDefault -- The default
488 -> Bool -- Context switch at alts?
489 -> FCode ([(ConTag, AbstractC)], -- The branches
490 AbstractC -- The default case
493 cgAlgAlts gc_flag uniq restore_cc must_label_branches is_fun alts deflt
494 emit_yield{-should a yield macro be emitted?-}
496 = forkAlts (map (cgAlgAlt gc_flag uniq restore_cc must_label_branches emit_yield) alts)
497 (cgAlgDefault gc_flag is_fun uniq restore_cc must_label_branches deflt emit_yield)
501 cgAlgDefault :: GCFlag
502 -> Bool -- could be a function-typed result?
503 -> Unique -> Maybe VirtualSpOffset -> Bool -- turgid state...
504 -> StgCaseDefault -- input
506 -> FCode AbstractC -- output
508 cgAlgDefault gc_flag is_fun uniq cc_slot must_label_branch StgNoDefault _
511 cgAlgDefault gc_flag is_fun uniq cc_slot must_label_branch
513 emit_yield{-should a yield macro be emitted?-}
515 = -- We have arranged that Node points to the thing
516 restoreCurrentCostCentre cc_slot `thenFC` \restore_cc ->
517 getAbsC (absC restore_cc `thenC`
518 -- HWL: maybe need yield here
520 -- then yield [node] True
521 -- else absC AbsCNop) `thenC`
522 possibleHeapCheck gc_flag is_fun [node] [] Nothing (cgExpr rhs)
523 -- Node is live, but doesn't need to point at the thing itself;
524 -- it's ok for Node to point to an indirection or FETCH_ME
525 -- Hence no need to re-enter Node.
526 ) `thenFC` \ abs_c ->
529 final_abs_c | must_label_branch = CCodeBlock lbl abs_c
534 lbl = mkDefaultLabel uniq
536 -- HWL comment on GrAnSim: GRAN_YIELDs needed; emitted in cgAlgAltRhs
539 -> Unique -> Maybe VirtualSpOffset -> Bool -- turgid state
540 -> Bool -- Context switch at alts?
541 -> (DataCon, [Id], [Bool], StgExpr)
542 -> FCode (ConTag, AbstractC)
544 cgAlgAlt gc_flag uniq cc_slot must_label_branch
545 emit_yield{-should a yield macro be emitted?-}
546 (con, args, use_mask, rhs)
548 restoreCurrentCostCentre cc_slot `thenFC` \restore_cc ->
549 getAbsC (absC restore_cc `thenC`
550 -- HWL: maybe need yield here
552 -- then yield [node] True -- XXX live regs wrong
553 -- else absC AbsCNop) `thenC`
555 NoGC -> mapFCs bindNewToTemp args `thenFC` \_ -> nopC
556 GCMayHappen -> bindConArgs con args
558 possibleHeapCheck gc_flag False [node] [] Nothing (
560 ) `thenFC` \ abs_c ->
562 final_abs_c | must_label_branch = CCodeBlock lbl abs_c
565 returnFC (tag, final_abs_c)
568 lbl = mkAltLabel uniq tag
571 :: Unique -- unique for label of the alternative
572 -> Maybe VirtualSpOffset -- Restore cost centre
573 -> Bool -- ctxt switch
574 -> (DataCon, [Id], [Bool], StgExpr) -- alternative
577 cgUnboxedTupleAlt lbl cc_slot emit_yield (con,args,use_mask,rhs)
579 bindUnboxedTupleComponents args
580 `thenFC` \ (live_regs,tags,stack_res) ->
582 restoreCurrentCostCentre cc_slot `thenFC` \restore_cc ->
583 absC restore_cc `thenC`
585 -- HWL: maybe need yield here
587 -- then yield live_regs True -- XXX live regs wrong?
588 -- else absC AbsCNop) `thenC`
590 -- ToDo: could maybe use Nothing here if stack_res is False
591 -- since the heap-check can just return to the top of the
596 -- free up stack slots containing tags,
597 freeStackSlots (map fst tags) `thenC`
599 -- generate a heap check if necessary
600 possibleHeapCheck GCMayHappen False live_regs tags ret_addr (
602 -- and finally the code for the alternative
607 %************************************************************************
609 \subsection[CgCase-semi-tagged-alts]{The code to deal with sem-tagging}
611 %************************************************************************
613 Turgid-but-non-monadic code to conjure up the required info from
614 algebraic case alternatives for semi-tagging.
617 cgSemiTaggedAlts :: Id
618 -> [(DataCon, [Id], [Bool], StgExpr)]
619 -> GenStgCaseDefault Id Id
622 cgSemiTaggedAlts binder alts deflt
623 = Just (map st_alt alts, st_deflt deflt)
625 uniq = getUnique binder
627 st_deflt StgNoDefault = Nothing
629 st_deflt (StgBindDefault _)
631 (CCallProfCtrMacro SLIT("RET_SEMI_BY_DEFAULT") [], -- ToDo: monadise?
635 st_alt (con, args, use_mask, _)
636 = -- Ha! Nothing to do; Node already points to the thing
638 (CCallProfCtrMacro SLIT("RET_SEMI_IN_HEAP") -- ToDo: monadise?
639 [mkIntCLit (length args)], -- how big the thing in the heap is
643 con_tag = dataConTag con
644 join_label = mkAltLabel uniq con_tag
647 %************************************************************************
649 \subsection[CgCase-prim-alts]{Primitive alternatives}
651 %************************************************************************
653 @cgPrimEvalAlts@ and @cgPrimInlineAlts@ generate suitable @CSwitch@es
654 for dealing with the alternatives of a primitive @case@, given an
655 addressing mode for the thing to scrutinise. It also keeps track of
656 the maximum stack depth encountered down any branch.
658 As usual, no binders in the alternatives are yet bound.
661 cgPrimInlineAlts bndr tycon alts deflt
662 = cgPrimAltsWithDefault bndr NoGC (CTemp uniq kind) alts deflt []
664 uniq = getUnique bndr
665 kind = tyConPrimRep tycon
667 cgPrimEvalAlts bndr tycon alts deflt
668 = cgPrimAltsWithDefault bndr GCMayHappen (CReg reg) alts deflt [reg]
670 reg = WARN( case kind of { PtrRep -> True; other -> False },
671 text "cgPrimEE" <+> ppr bndr <+> ppr tycon )
672 dataReturnConvPrim kind
673 kind = tyConPrimRep tycon
675 cgPrimAltsWithDefault bndr gc_flag scrutinee alts deflt regs
676 = -- first bind the default if necessary
677 bindNewPrimToAmode bndr scrutinee `thenC`
678 cgPrimAlts gc_flag scrutinee alts deflt regs
680 cgPrimAlts gc_flag scrutinee alts deflt regs
681 = forkAlts (map (cgPrimAlt gc_flag regs) alts)
682 (cgPrimDefault gc_flag regs deflt)
683 `thenFC` \ (alt_absCs, deflt_absC) ->
685 absC (CSwitch scrutinee alt_absCs deflt_absC)
686 -- CSwitch does sensible things with one or zero alternatives
690 -> [MagicId] -- live registers
691 -> (Literal, StgExpr) -- The alternative
692 -> FCode (Literal, AbstractC) -- Its compiled form
694 cgPrimAlt gc_flag regs (lit, rhs)
695 = getAbsC rhs_code `thenFC` \ absC ->
698 rhs_code = possibleHeapCheck gc_flag False regs [] Nothing (cgExpr rhs)
700 cgPrimDefault :: GCFlag
701 -> [MagicId] -- live registers
705 cgPrimDefault gc_flag regs StgNoDefault
706 = panic "cgPrimDefault: No default in prim case"
708 cgPrimDefault gc_flag regs (StgBindDefault rhs)
709 = getAbsC (possibleHeapCheck gc_flag False regs [] Nothing (cgExpr rhs))
713 %************************************************************************
715 \subsection[CgCase-tidy]{Code for tidying up prior to an eval}
717 %************************************************************************
720 saveVolatileVarsAndRegs
721 :: StgLiveVars -- Vars which should be made safe
722 -> FCode (AbstractC, -- Assignments to do the saves
723 EndOfBlockInfo, -- sequel for the alts
724 Maybe VirtualSpOffset) -- Slot for current cost centre
727 saveVolatileVarsAndRegs vars
728 = saveVolatileVars vars `thenFC` \ var_saves ->
729 saveCurrentCostCentre `thenFC` \ (maybe_cc_slot, cc_save) ->
730 getEndOfBlockInfo `thenFC` \ eob_info ->
731 returnFC (mkAbstractCs [var_saves, cc_save],
736 saveVolatileVars :: StgLiveVars -- Vars which should be made safe
737 -> FCode AbstractC -- Assignments to to the saves
739 saveVolatileVars vars
740 = save_em (varSetElems vars)
742 save_em [] = returnFC AbsCNop
745 = getCAddrModeIfVolatile var `thenFC` \ v ->
747 Nothing -> save_em vars -- Non-volatile, so carry on
750 Just vol_amode -> -- Aha! It's volatile
751 save_var var vol_amode `thenFC` \ abs_c ->
752 save_em vars `thenFC` \ abs_cs ->
753 returnFC (abs_c `mkAbsCStmts` abs_cs)
755 save_var var vol_amode
756 = allocPrimStack (getPrimRepSize kind) `thenFC` \ slot ->
757 rebindToStack var slot `thenC`
758 getSpRelOffset slot `thenFC` \ sp_rel ->
759 returnFC (CAssign (CVal sp_rel kind) vol_amode)
761 kind = getAmodeRep vol_amode
764 ---------------------------------------------------------------------------
766 When we save the current cost centre (which is done for lexical
767 scoping), we allocate a free stack location, and return (a)~the
768 virtual offset of the location, to pass on to the alternatives, and
769 (b)~the assignment to do the save (just as for @saveVolatileVars@).
772 saveCurrentCostCentre ::
773 FCode (Maybe VirtualSpOffset, -- Where we decide to store it
774 AbstractC) -- Assignment to save it
776 saveCurrentCostCentre
777 = if not opt_SccProfilingOn then
778 returnFC (Nothing, AbsCNop)
780 allocPrimStack (getPrimRepSize CostCentreRep) `thenFC` \ slot ->
781 dataStackSlots [slot] `thenC`
782 getSpRelOffset slot `thenFC` \ sp_rel ->
784 CAssign (CVal sp_rel CostCentreRep) (CReg CurCostCentre))
786 restoreCurrentCostCentre :: Maybe VirtualSpOffset -> FCode AbstractC
787 restoreCurrentCostCentre Nothing = returnFC AbsCNop
788 restoreCurrentCostCentre (Just slot)
789 = getSpRelOffset slot `thenFC` \ sp_rel ->
790 freeStackSlots [slot] `thenC`
791 returnFC (CCallProfCCMacro SLIT("RESTORE_CCCS") [CVal sp_rel CostCentreRep])
792 -- we use the RESTORE_CCCS macro, rather than just
793 -- assigning into CurCostCentre, in case RESTORE_CCCS
794 -- has some sanity-checking in it.
797 %************************************************************************
799 \subsection[CgCase-return-vec]{Building a return vector}
801 %************************************************************************
803 Build a return vector, and return a suitable label addressing
807 mkReturnVector :: Unique
808 -> [(ConTag, AbstractC)] -- Branch codes
809 -> AbstractC -- Default case
810 -> SRT -- continuation's SRT
811 -> Liveness -- stack liveness
812 -> CtrlReturnConvention
815 mkReturnVector uniq tagged_alt_absCs deflt_absC srt liveness ret_conv
816 = getSRTInfo srt `thenFC` \ srt_info ->
818 (return_vec_amode, vtbl_body) = case ret_conv of {
820 -- might be a polymorphic case...
821 UnvectoredReturn 0 ->
822 ASSERT(null tagged_alt_absCs)
823 (CLbl ret_label RetRep,
824 absC (CRetDirect uniq deflt_absC srt_info liveness));
826 UnvectoredReturn n ->
827 -- find the tag explicitly rather than using tag_reg for now.
828 -- on architectures with lots of regs the tag will be loaded
829 -- into tag_reg by the code doing the returning.
831 tag = CMacroExpr WordRep GET_TAG [CVal (nodeRel 0) DataPtrRep]
833 (CLbl ret_label RetRep,
834 absC (CRetDirect uniq
835 (mkAlgAltsCSwitch tag tagged_alt_absCs deflt_absC)
839 VectoredReturn table_size ->
841 (vector_table, alts_absC) =
842 unzip (map mk_vector_entry [fIRST_TAG .. (table_size+fIRST_TAG-1)])
844 ret_vector = CRetVector vtbl_label vector_table srt_info liveness
846 (CLbl vtbl_label DataPtrRep,
847 -- alts come first, because we don't want to declare all the symbols
848 absC (mkAbstractCs (mkAbstractCs alts_absC : [deflt_absC,ret_vector]))
853 returnFC return_vec_amode
857 vtbl_label = mkVecTblLabel uniq
858 ret_label = mkReturnInfoLabel uniq
861 case nonemptyAbsC deflt_absC of
862 -- the simplifier might have eliminated a case
863 Nothing -> mkIntCLit 0 -- CLbl mkErrorStdEntryLabel CodePtrRep
864 Just absC@(CCodeBlock lbl _) -> CLbl lbl CodePtrRep
866 mk_vector_entry :: ConTag -> (CAddrMode, AbstractC)
868 = case [ absC | (t, absC) <- tagged_alt_absCs, t == tag ] of
869 [] -> (deflt_lbl, AbsCNop)
870 [absC@(CCodeBlock lbl _)] -> (CLbl lbl CodePtrRep,absC)
871 _ -> panic "mkReturnVector: too many"
874 %************************************************************************
876 \subsection[CgCase-utils]{Utilities for handling case expressions}
878 %************************************************************************
880 @possibleHeapCheck@ tests a flag passed in to decide whether to do a
881 heap check or not. These heap checks are always in a case
882 alternative, so we use altHeapCheck.
887 -> Bool -- True <=> algebraic case
888 -> [MagicId] -- live registers
889 -> [(VirtualSpOffset,Int)] -- stack slots to tag
890 -> Maybe Unique -- return address unique
891 -> Code -- continuation
894 possibleHeapCheck GCMayHappen is_alg regs tags lbl code
895 = altHeapCheck is_alg regs tags AbsCNop lbl code
896 possibleHeapCheck NoGC _ _ tags lbl code