2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 % $Id: CgCase.lhs,v 1.22 1999/01/27 14:51:31 simonpj Exp $
6 %********************************************************
8 \section[CgCase]{Converting @StgCase@ expressions}
10 %********************************************************
13 module CgCase ( cgCase, saveVolatileVarsAndRegs, restoreCurrentCostCentre,
14 splitTyConAppThroughNewTypes ) where
16 #include "HsVersions.h"
18 import {-# SOURCE #-} CgExpr ( cgExpr )
24 import AbsCUtils ( mkAbstractCs, mkAbsCStmts, mkAlgAltsCSwitch,
25 getAmodeRep, nonemptyAbsC
27 import CoreSyn ( isDeadBinder )
28 import CgUpdate ( reserveSeqFrame )
29 import CgBindery ( getVolatileRegs, getArgAmodes,
30 bindNewToReg, bindNewToTemp,
32 rebindToStack, getCAddrMode,
33 getCAddrModeAndInfo, getCAddrModeIfVolatile,
34 buildContLivenessMask, nukeDeadBindings
36 import CgCon ( bindConArgs, bindUnboxedTupleComponents )
37 import CgHeapery ( altHeapCheck, yield )
38 import CgRetConv ( dataReturnConvPrim, ctrlReturnConvAlg,
39 CtrlReturnConvention(..)
41 import CgStackery ( allocPrimStack, allocStackTop,
42 deAllocStackTop, freeStackSlots
44 import CgTailCall ( tailCallFun )
45 import CgUsages ( getSpRelOffset, getRealSp )
46 import CLabel ( CLabel, mkVecTblLabel, mkReturnPtLabel,
47 mkDefaultLabel, mkAltLabel, mkReturnInfoLabel,
48 mkErrorStdEntryLabel, mkClosureTblLabel
50 import ClosureInfo ( mkLFArgument )
51 import CmdLineOpts ( opt_SccProfilingOn, opt_GranMacros )
52 import CostCentre ( CostCentre )
53 import Id ( Id, idPrimRep )
54 import DataCon ( DataCon, dataConTag, fIRST_TAG, ConTag,
55 isUnboxedTupleCon, dataConType )
56 import VarSet ( varSetElems )
57 import Const ( Con(..), Literal )
58 import PrimOp ( primOpOutOfLine, PrimOp(..) )
59 import PrimRep ( getPrimRepSize, retPrimRepSize, PrimRep(..)
61 import TyCon ( TyCon, isEnumerationTyCon, isUnboxedTupleTyCon,
62 isNewTyCon, isAlgTyCon, isFunTyCon, isPrimTyCon,
63 tyConDataCons, tyConFamilySize )
64 import Type ( Type, typePrimRep, splitAlgTyConApp, splitTyConApp_maybe,
65 splitFunTys, applyTys )
66 import Unique ( Unique, Uniquable(..) )
67 import Maybes ( maybeToBool )
73 = GCMayHappen -- The scrutinee may involve GC, so everything must be
74 -- tidy before the code for the scrutinee.
76 | NoGC -- The scrutinee is a primitive value, or a call to a
77 -- primitive op which does no GC. Hence the case can
78 -- be done inline, without tidying up first.
81 It is quite interesting to decide whether to put a heap-check
82 at the start of each alternative. Of course we certainly have
83 to do so if the case forces an evaluation, or if there is a primitive
84 op which can trigger GC.
86 A more interesting situation is this:
93 default -> !C!; ...C...
96 where \tr{!x!} indicates a possible heap-check point. The heap checks
97 in the alternatives {\em can} be omitted, in which case the topmost
98 heapcheck will take their worst case into account.
100 In favour of omitting \tr{!B!}, \tr{!C!}:
102 - {\em May} save a heap overflow test,
103 if ...A... allocates anything. The other advantage
104 of this is that we can use relative addressing
105 from a single Hp to get at all the closures so allocated.
107 - No need to save volatile vars etc across the case
111 - May do more allocation than reqd. This sometimes bites us
112 badly. For example, nfib (ha!) allocates about 30\% more space if the
113 worst-casing is done, because many many calls to nfib are leaf calls
114 which don't need to allocate anything.
116 This never hurts us if there is only one alternative.
119 *** NOT YET DONE *** The difficulty is that \tr{!B!}, \tr{!C!} need
120 to take account of what is live, and that includes all live volatile
121 variables, even if they also have stable analogues. Furthermore, the
122 stack pointers must be lined up properly so that GC sees tidy stacks.
123 If these things are done, then the heap checks can be done at \tr{!B!} and
124 \tr{!C!} without a full save-volatile-vars sequence.
136 Several special cases for inline primitive operations.
139 cgCase (StgCon (PrimOp op) args res_ty) live_in_whole_case live_in_alts bndr srt alts
140 | not (primOpOutOfLine op)
142 -- Get amodes for the arguments and results
143 getArgAmodes args `thenFC` \ arg_amodes ->
145 result_amodes = getPrimAppResultAmodes (getUnique bndr) alts
147 -- Perform the operation
148 getVolatileRegs live_in_alts `thenFC` \ vol_regs ->
150 absC (COpStmt result_amodes op
151 arg_amodes -- note: no liveness arg
154 -- Scrutinise the result
155 cgInlineAlts bndr alts
158 TODO: Case-of-case of primop can probably be done inline too (but
159 maybe better to translate it out beforehand). See
160 ghc/lib/misc/PackedString.lhs for examples where this crops up (with
163 Another special case: scrutinising a primitive-typed variable. No
164 evaluation required. We don't save volatile variables, nor do we do a
165 heap-check in the alternatives. Instead, the heap usage of the
166 alternatives is worst-cased and passed upstream. This can result in
167 allocating more heap than strictly necessary, but it will sometimes
168 eliminate a heap check altogether.
171 cgCase (StgApp v []) live_in_whole_case live_in_alts bndr srt
172 (StgPrimAlts ty alts deflt)
175 getCAddrMode v `thenFC` \amode ->
178 Careful! we can't just bind the default binder to the same thing
179 as the scrutinee, since it might be a stack location, and having
180 two bindings pointing at the same stack locn doesn't work (it
181 confuses nukeDeadBindings). Hence, use a new temp.
183 (if (isDeadBinder bndr)
185 else bindNewToTemp bndr `thenFC` \deflt_amode ->
186 absC (CAssign deflt_amode amode)) `thenC`
188 cgPrimAlts NoGC amode alts deflt []
191 Special case: scrutinising a non-primitive variable.
192 This can be done a little better than the general case, because
193 we can reuse/trim the stack slot holding the variable (if it is in one).
196 cgCase (StgApp fun args)
197 live_in_whole_case live_in_alts bndr srt alts@(StgAlgAlts ty _ _)
199 getCAddrModeAndInfo fun `thenFC` \ (fun_amode, lf_info) ->
200 getArgAmodes args `thenFC` \ arg_amodes ->
202 -- Squish the environment
203 nukeDeadBindings live_in_alts `thenC`
204 saveVolatileVarsAndRegs live_in_alts
205 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
207 allocStackTop retPrimRepSize `thenFC` \_ ->
209 forkEval alts_eob_info nopC (
210 deAllocStackTop retPrimRepSize `thenFC` \_ ->
211 cgEvalAlts maybe_cc_slot bndr srt alts)
212 `thenFC` \ scrut_eob_info ->
214 let real_scrut_eob_info =
216 then reserveSeqFrame scrut_eob_info
220 setEndOfBlockInfo real_scrut_eob_info (
221 tailCallFun fun fun_amode lf_info arg_amodes save_assts
225 not_con_ty = case (getScrutineeTyCon ty) of
230 Note about return addresses: we *always* push a return address, even
231 if because of an optimisation we end up jumping direct to the return
232 code (not through the address itself). The alternatives always assume
233 that the return address is on the stack. The return address is
234 required in case the alternative performs a heap check, since it
235 encodes the liveness of the slots in the activation record.
237 On entry to the case alternative, we can re-use the slot containing
238 the return address immediately after the heap check. That's what the
239 deAllocStackTop call is doing above.
241 Finally, here is the general case.
244 cgCase expr live_in_whole_case live_in_alts bndr srt alts
245 = -- Figure out what volatile variables to save
246 nukeDeadBindings live_in_whole_case `thenC`
248 saveVolatileVarsAndRegs live_in_alts
249 `thenFC` \ (save_assts, alts_eob_info, maybe_cc_slot) ->
251 -- Save those variables right now!
252 absC save_assts `thenC`
254 -- generate code for the alts
255 forkEval alts_eob_info
257 nukeDeadBindings live_in_alts `thenC`
258 allocStackTop retPrimRepSize -- space for retn address
261 (deAllocStackTop retPrimRepSize `thenFC` \_ ->
262 cgEvalAlts maybe_cc_slot bndr srt alts) `thenFC` \ scrut_eob_info ->
264 let real_scrut_eob_info =
266 then reserveSeqFrame scrut_eob_info
270 setEndOfBlockInfo real_scrut_eob_info (cgExpr expr)
273 not_con_ty = case (getScrutineeTyCon (alts_ty alts)) of
278 There's a lot of machinery going on behind the scenes to manage the
279 stack pointer here. forkEval takes the virtual Sp and free list from
280 the first argument, and turns that into the *real* Sp for the second
281 argument. It also uses this virtual Sp as the args-Sp in the EOB info
282 returned, so that the scrutinee will trim the real Sp back to the
283 right place before doing whatever it does.
284 --SDM (who just spent an hour figuring this out, and didn't want to
287 Why don't we push the return address just before evaluating the
288 scrutinee? Because the slot reserved for the return address might
289 contain something useful, so we wait until performing a tail call or
290 return before pushing the return address (see
291 CgTailCall.pushReturnAddress).
293 This also means that the environment doesn't need to know about the
294 free stack slot for the return address (for generating bitmaps),
295 because we don't reserve it until just before the eval.
297 TODO!! Problem: however, we have to save the current cost centre
298 stack somewhere, because at the eval point the current CCS might be
299 different. So we pick a free stack slot and save CCCS in it. The
300 problem with this is that this slot isn't recorded as free/unboxed in
301 the environment, so a case expression in the scrutinee will have the
302 wrong bitmap attached. Fortunately we don't ever seem to see
303 case-of-case at the back end. One solution might be to shift the
304 saved CCS to the correct place in the activation record just before
308 (one consequence of the above is that activation records on the stack
309 don't follow the layout of closures when we're profiling. The CCS
310 could be anywhere within the record).
313 alts_ty (StgAlgAlts ty _ _) = ty
314 alts_ty (StgPrimAlts ty _ _) = ty
317 %************************************************************************
319 \subsection[CgCase-primops]{Primitive applications}
321 %************************************************************************
323 Get result amodes for a primitive operation, in the case wher GC can't happen.
324 The amodes are returned in canonical order, ready for the prim-op!
326 Alg case: temporaries named as in the alternatives,
327 plus (CTemp u) for the tag (if needed)
330 This is all disgusting, because these amodes must be consistent with those
331 invented by CgAlgAlts.
334 getPrimAppResultAmodes
341 -- If there's an StgBindDefault which does use the bound
342 -- variable, then we can only handle it if the type involved is
343 -- an enumeration type. That's important in the case
349 -- The only reason for the restriction to *enumeration* types is our
350 -- inability to invent suitable temporaries to hold the results;
351 -- Elaborating the CTemp addr mode to have a second uniq field
352 -- (which would simply count from 1) would solve the problem.
353 -- Anyway, cgInlineAlts is now capable of handling all cases;
354 -- it's only this function which is being wimpish.
356 getPrimAppResultAmodes uniq (StgAlgAlts ty alts
357 (StgBindDefault rhs))
358 | isEnumerationTyCon spec_tycon = [tag_amode]
359 | otherwise = pprPanic "getPrimAppResultAmodes: non-enumeration algebraic alternatives with default" (ppr uniq <+> ppr rhs)
361 -- A temporary variable to hold the tag; this is unaffected by GC because
362 -- the heap-checks in the branches occur after the switch
363 tag_amode = CTemp uniq IntRep
364 (spec_tycon, _, _) = splitAlgTyConApp ty
367 If we don't have a default case, we could be scrutinising an unboxed
368 tuple, or an enumeration type...
371 getPrimAppResultAmodes uniq (StgAlgAlts ty alts other_default)
372 -- Default is either StgNoDefault or StgBindDefault with unused binder
374 | isEnumerationTyCon tycon = [CTemp uniq IntRep]
376 | isUnboxedTupleTyCon tycon =
378 [(con, args, use_mask, rhs)] ->
379 [ CTemp (getUnique arg) (idPrimRep arg) | arg <- args ]
380 _ -> panic "getPrimAppResultAmodes: case of unboxed tuple has multiple branches"
382 | otherwise = panic ("getPrimAppResultAmodes: case of primop has strange type: " ++ showSDoc (ppr ty))
384 where (tycon, _, _) = splitAlgTyConApp ty
387 The situation is simpler for primitive results, because there is only
391 getPrimAppResultAmodes uniq (StgPrimAlts ty _ _)
392 = [CTemp uniq (typePrimRep ty)]
396 %************************************************************************
398 \subsection[CgCase-alts]{Alternatives}
400 %************************************************************************
402 @cgEvalAlts@ returns an addressing mode for a continuation for the
403 alternatives of a @case@, used in a context when there
404 is some evaluation to be done.
407 cgEvalAlts :: Maybe VirtualSpOffset -- Offset of cost-centre to be restored, if any
409 -> SRT -- SRT for the continuation
411 -> FCode Sequel -- Any addr modes inside are guaranteed
412 -- to be a label so that we can duplicate it
413 -- without risk of duplicating code
415 cgEvalAlts cc_slot bndr srt alts
417 let uniq = getUnique bndr in
419 -- Generate the instruction to restore cost centre, if any
420 restoreCurrentCostCentre cc_slot `thenFC` \ cc_restore ->
422 -- get the stack liveness for the info table (after the CC slot has
423 -- been freed - this is important).
424 buildContLivenessMask uniq `thenFC` \ liveness_mask ->
428 -- algebraic alts ...
429 (StgAlgAlts ty alts deflt) ->
431 -- bind the default binder (it covers all the alternatives)
432 (if (isDeadBinder bndr)
434 else bindNewToReg bndr node mkLFArgument) `thenC`
436 -- Generate sequel info for use downstream
437 -- At the moment, we only do it if the type is vector-returnable.
438 -- Reason: if not, then it costs extra to label the
439 -- alternatives, because we'd get return code like:
441 -- switch TagReg { 0 : JMP(alt_1); 1 : JMP(alt_2) ..etc }
443 -- which is worse than having the alt code in the switch statement
445 let tycon_info = getScrutineeTyCon ty
446 is_alg = maybeToBool tycon_info
447 Just spec_tycon = tycon_info
450 -- deal with the unboxed tuple case
451 if is_alg && isUnboxedTupleTyCon spec_tycon then
453 [alt] -> let lbl = mkReturnInfoLabel uniq in
454 cgUnboxedTupleAlt lbl cc_restore True alt
456 getSRTLabel `thenFC` \srt_label ->
457 absC (CRetDirect uniq abs_c (srt_label, srt)
458 liveness_mask) `thenC`
459 returnFC (CaseAlts (CLbl lbl RetRep) Nothing)
460 _ -> panic "cgEvalAlts: dodgy case of unboxed tuple type"
462 -- normal algebraic (or polymorphic) case alternatives
464 ret_conv | is_alg = ctrlReturnConvAlg spec_tycon
465 | otherwise = UnvectoredReturn 0
467 use_labelled_alts = case ret_conv of
468 VectoredReturn _ -> True
472 = if use_labelled_alts then
473 cgSemiTaggedAlts bndr alts deflt -- Just <something>
475 Nothing -- no semi-tagging info
478 cgAlgAlts GCMayHappen uniq cc_restore use_labelled_alts (not is_alg)
479 alts deflt True `thenFC` \ (tagged_alt_absCs, deflt_absC) ->
481 mkReturnVector uniq tagged_alt_absCs deflt_absC srt liveness_mask
482 ret_conv `thenFC` \ return_vec ->
484 returnFC (CaseAlts return_vec semi_tagged_stuff)
487 (StgPrimAlts ty alts deflt) ->
489 -- Generate the switch
490 getAbsC (cgPrimEvalAlts bndr ty alts deflt) `thenFC` \ abs_c ->
492 -- Generate the labelled block, starting with restore-cost-centre
493 getSRTLabel `thenFC` \srt_label ->
494 absC (CRetDirect uniq (cc_restore `mkAbsCStmts` abs_c)
495 (srt_label,srt) liveness_mask) `thenC`
497 -- Return an amode for the block
498 returnFC (CaseAlts (CLbl (mkReturnPtLabel uniq) RetRep) Nothing)
508 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): If
509 we do an inlining of the case no separate functions for returning are
510 created, so we don't have to generate a GRAN_YIELD in that case. This info
511 must be propagated to cgAlgAltRhs (where the GRAN_YIELD macro might be
512 emitted). Hence, the new Bool arg to cgAlgAltRhs.
514 First case: primitive op returns an unboxed tuple.
517 cgInlineAlts bndr (StgAlgAlts ty [alt@(con,args,use_mask,rhs)] StgNoDefault)
518 | isUnboxedTupleCon con
519 = -- no heap check, no yield, just get in there and do it.
520 mapFCs bindNewToTemp args `thenFC` \ _ ->
524 = panic "cgInlineAlts: single alternative, not an unboxed tuple"
534 cgInlineAlts bndr (StgAlgAlts ty [] (StgBindDefault rhs))
535 = bindNewToTemp bndr `thenFC` \amode ->
537 (tycon, _, _) = splitAlgTyConApp ty
538 closure_lbl = CTableEntry (CLbl (mkClosureTblLabel tycon) PtrRep) amode PtrRep
540 absC (CAssign amode closure_lbl) `thenC`
544 Second case: algebraic case, several alternatives.
545 Tag is held in a temporary.
548 cgInlineAlts bndr (StgAlgAlts ty alts deflt)
549 = -- bind the default binder (it covers all the alternatives)
550 (if (isDeadBinder bndr)
552 else bindNewToReg bndr node mkLFArgument) `thenC`
554 cgAlgAlts NoGC uniq AbsCNop{-restore_cc-} False{-no semi-tagging-}
555 False{-not poly case-} alts deflt
556 False{-don't emit yield-} `thenFC` \ (tagged_alts, deflt_c) ->
559 absC (mkAlgAltsCSwitch tag_amode tagged_alts deflt_c)
561 -- A temporary variable to hold the tag; this is unaffected by GC because
562 -- the heap-checks in the branches occur after the switch
563 tag_amode = CTemp uniq IntRep
564 uniq = getUnique bndr
567 Third (real) case: primitive result type.
570 cgInlineAlts bndr (StgPrimAlts ty alts deflt)
571 = cgPrimInlineAlts bndr ty alts deflt
575 %************************************************************************
577 \subsection[CgCase-alg-alts]{Algebraic alternatives}
579 %************************************************************************
581 In @cgAlgAlts@, none of the binders in the alternatives are
582 assumed to be yet bound.
584 HWL comment on {\em GrAnSim\/} (adding GRAN_YIELDs for context switch): The
585 last arg of cgAlgAlts indicates if we want a context switch at the
586 beginning of each alternative. Normally we want that. The only exception
587 are inlined alternatives.
592 -> AbstractC -- Restore-cost-centre instruction
593 -> Bool -- True <=> branches must be labelled
594 -> Bool -- True <=> polymorphic case
595 -> [(DataCon, [Id], [Bool], StgExpr)] -- The alternatives
596 -> StgCaseDefault -- The default
597 -> Bool -- Context switch at alts?
598 -> FCode ([(ConTag, AbstractC)], -- The branches
599 AbstractC -- The default case
602 cgAlgAlts gc_flag uniq restore_cc must_label_branches is_fun alts deflt
603 emit_yield{-should a yield macro be emitted?-}
605 = forkAlts (map (cgAlgAlt gc_flag uniq restore_cc must_label_branches emit_yield) alts)
606 (cgAlgDefault gc_flag is_fun uniq restore_cc must_label_branches deflt emit_yield)
610 cgAlgDefault :: GCFlag
611 -> Bool -- could be a function-typed result?
612 -> Unique -> AbstractC -> Bool -- turgid state...
613 -> StgCaseDefault -- input
615 -> FCode AbstractC -- output
617 cgAlgDefault gc_flag is_fun uniq restore_cc must_label_branch StgNoDefault _
620 cgAlgDefault gc_flag is_fun uniq restore_cc must_label_branch
622 emit_yield{-should a yield macro be emitted?-}
624 = -- We have arranged that Node points to the thing
625 getAbsC (absC restore_cc `thenC`
626 (if opt_GranMacros && emit_yield
627 then yield [node] False
628 else absC AbsCNop) `thenC`
629 possibleHeapCheck gc_flag is_fun [node] [] Nothing (cgExpr rhs)
630 -- Node is live, but doesn't need to point at the thing itself;
631 -- it's ok for Node to point to an indirection or FETCH_ME
632 -- Hence no need to re-enter Node.
633 ) `thenFC` \ abs_c ->
636 final_abs_c | must_label_branch = CCodeBlock lbl abs_c
641 lbl = mkDefaultLabel uniq
643 -- HWL comment on GrAnSim: GRAN_YIELDs needed; emitted in cgAlgAltRhs
646 -> Unique -> AbstractC -> Bool -- turgid state
647 -> Bool -- Context switch at alts?
648 -> (DataCon, [Id], [Bool], StgExpr)
649 -> FCode (ConTag, AbstractC)
651 cgAlgAlt gc_flag uniq restore_cc must_label_branch
652 emit_yield{-should a yield macro be emitted?-}
653 (con, args, use_mask, rhs)
654 = getAbsC (absC restore_cc `thenC`
655 (if opt_GranMacros && emit_yield
656 then yield [node] True -- XXX live regs wrong
657 else absC AbsCNop) `thenC`
659 NoGC -> mapFCs bindNewToTemp args `thenFC` \_ -> nopC
660 GCMayHappen -> bindConArgs con args
662 possibleHeapCheck gc_flag False [node] [] Nothing (
664 ) `thenFC` \ abs_c ->
666 final_abs_c | must_label_branch = CCodeBlock lbl abs_c
669 returnFC (tag, final_abs_c)
672 lbl = mkAltLabel uniq tag
675 :: CLabel -- label of the alternative
677 -> Bool -- ctxt switch
678 -> (DataCon, [Id], [Bool], StgExpr) -- alternative
681 cgUnboxedTupleAlt lbl restore_cc emit_yield (con,args,use_mask,rhs)
683 absC restore_cc `thenC`
685 bindUnboxedTupleComponents args
686 `thenFC` \ (live_regs,tags,stack_res) ->
687 (if opt_GranMacros && emit_yield
688 then yield live_regs True -- XXX live regs wrong?
689 else absC AbsCNop) `thenC`
691 -- ToDo: could maybe use Nothing here if stack_res is False
692 -- since the heap-check can just return to the top of the
697 -- free up stack slots containing tags,
698 freeStackSlots (map fst tags) `thenC`
700 -- generate a heap check if necessary
701 possibleHeapCheck GCMayHappen False live_regs tags ret_addr (
703 -- and finally the code for the alternative
708 %************************************************************************
710 \subsection[CgCase-semi-tagged-alts]{The code to deal with sem-tagging}
712 %************************************************************************
714 Turgid-but-non-monadic code to conjure up the required info from
715 algebraic case alternatives for semi-tagging.
718 cgSemiTaggedAlts :: Id
719 -> [(DataCon, [Id], [Bool], StgExpr)]
720 -> GenStgCaseDefault Id Id
723 cgSemiTaggedAlts binder alts deflt
724 = Just (map st_alt alts, st_deflt deflt)
726 uniq = getUnique binder
728 st_deflt StgNoDefault = Nothing
730 st_deflt (StgBindDefault _)
732 (CCallProfCtrMacro SLIT("RET_SEMI_BY_DEFAULT") [], -- ToDo: monadise?
736 st_alt (con, args, use_mask, _)
737 = -- Ha! Nothing to do; Node already points to the thing
739 (CCallProfCtrMacro SLIT("RET_SEMI_IN_HEAP") -- ToDo: monadise?
740 [mkIntCLit (length args)], -- how big the thing in the heap is
744 con_tag = dataConTag con
745 join_label = mkAltLabel uniq con_tag
748 %************************************************************************
750 \subsection[CgCase-prim-alts]{Primitive alternatives}
752 %************************************************************************
754 @cgPrimEvalAlts@ and @cgPrimInlineAlts@ generate suitable @CSwitch@es
755 for dealing with the alternatives of a primitive @case@, given an
756 addressing mode for the thing to scrutinise. It also keeps track of
757 the maximum stack depth encountered down any branch.
759 As usual, no binders in the alternatives are yet bound.
762 cgPrimInlineAlts bndr ty alts deflt
763 = cgPrimAltsWithDefault bndr NoGC (CTemp uniq kind) alts deflt []
765 uniq = getUnique bndr
766 kind = typePrimRep ty
768 cgPrimEvalAlts bndr ty alts deflt
769 = cgPrimAltsWithDefault bndr GCMayHappen (CReg reg) alts deflt [reg]
771 reg = dataReturnConvPrim kind
772 kind = typePrimRep ty
774 cgPrimAltsWithDefault bndr gc_flag scrutinee alts deflt regs
775 = -- first bind the default if necessary
776 (if isDeadBinder bndr
778 else bindNewPrimToAmode bndr scrutinee) `thenC`
779 cgPrimAlts gc_flag scrutinee alts deflt regs
781 cgPrimAlts gc_flag scrutinee alts deflt regs
782 = forkAlts (map (cgPrimAlt gc_flag regs) alts)
783 (cgPrimDefault gc_flag regs deflt)
784 `thenFC` \ (alt_absCs, deflt_absC) ->
786 absC (CSwitch scrutinee alt_absCs deflt_absC)
787 -- CSwitch does sensible things with one or zero alternatives
791 -> [MagicId] -- live registers
792 -> (Literal, StgExpr) -- The alternative
793 -> FCode (Literal, AbstractC) -- Its compiled form
795 cgPrimAlt gc_flag regs (lit, rhs)
796 = getAbsC rhs_code `thenFC` \ absC ->
799 rhs_code = possibleHeapCheck gc_flag False regs [] Nothing (cgExpr rhs)
801 cgPrimDefault :: GCFlag
802 -> [MagicId] -- live registers
806 cgPrimDefault gc_flag regs StgNoDefault
807 = panic "cgPrimDefault: No default in prim case"
809 cgPrimDefault gc_flag regs (StgBindDefault rhs)
810 = getAbsC (possibleHeapCheck gc_flag False regs [] Nothing (cgExpr rhs))
814 %************************************************************************
816 \subsection[CgCase-tidy]{Code for tidying up prior to an eval}
818 %************************************************************************
821 saveVolatileVarsAndRegs
822 :: StgLiveVars -- Vars which should be made safe
823 -> FCode (AbstractC, -- Assignments to do the saves
824 EndOfBlockInfo, -- sequel for the alts
825 Maybe VirtualSpOffset) -- Slot for current cost centre
828 saveVolatileVarsAndRegs vars
829 = saveVolatileVars vars `thenFC` \ var_saves ->
830 saveCurrentCostCentre `thenFC` \ (maybe_cc_slot, cc_save) ->
831 getEndOfBlockInfo `thenFC` \ eob_info ->
832 returnFC (mkAbstractCs [var_saves, cc_save],
837 saveVolatileVars :: StgLiveVars -- Vars which should be made safe
838 -> FCode AbstractC -- Assignments to to the saves
840 saveVolatileVars vars
841 = save_em (varSetElems vars)
843 save_em [] = returnFC AbsCNop
846 = getCAddrModeIfVolatile var `thenFC` \ v ->
848 Nothing -> save_em vars -- Non-volatile, so carry on
851 Just vol_amode -> -- Aha! It's volatile
852 save_var var vol_amode `thenFC` \ abs_c ->
853 save_em vars `thenFC` \ abs_cs ->
854 returnFC (abs_c `mkAbsCStmts` abs_cs)
856 save_var var vol_amode
857 = allocPrimStack (getPrimRepSize kind) `thenFC` \ slot ->
858 rebindToStack var slot `thenC`
859 getSpRelOffset slot `thenFC` \ sp_rel ->
860 returnFC (CAssign (CVal sp_rel kind) vol_amode)
862 kind = getAmodeRep vol_amode
865 ---------------------------------------------------------------------------
867 When we save the current cost centre (which is done for lexical
868 scoping), we allocate a free stack location, and return (a)~the
869 virtual offset of the location, to pass on to the alternatives, and
870 (b)~the assignment to do the save (just as for @saveVolatileVars@).
873 saveCurrentCostCentre ::
874 FCode (Maybe VirtualSpOffset, -- Where we decide to store it
875 AbstractC) -- Assignment to save it
877 saveCurrentCostCentre
878 = if not opt_SccProfilingOn then
879 returnFC (Nothing, AbsCNop)
881 allocPrimStack (getPrimRepSize CostCentreRep) `thenFC` \ slot ->
882 getSpRelOffset slot `thenFC` \ sp_rel ->
884 CAssign (CVal sp_rel CostCentreRep) (CReg CurCostCentre))
886 restoreCurrentCostCentre :: Maybe VirtualSpOffset -> FCode AbstractC
888 restoreCurrentCostCentre Nothing
890 restoreCurrentCostCentre (Just slot)
891 = getSpRelOffset slot `thenFC` \ sp_rel ->
892 freeStackSlots [slot] `thenC`
893 returnFC (CCallProfCCMacro SLIT("RESTORE_CCCS") [CVal sp_rel CostCentreRep])
894 -- we use the RESTORE_CCCS macro, rather than just
895 -- assigning into CurCostCentre, in case RESTORE_CCC
896 -- has some sanity-checking in it.
899 %************************************************************************
901 \subsection[CgCase-return-vec]{Building a return vector}
903 %************************************************************************
905 Build a return vector, and return a suitable label addressing
909 mkReturnVector :: Unique
910 -> [(ConTag, AbstractC)] -- Branch codes
911 -> AbstractC -- Default case
912 -> SRT -- continuation's SRT
913 -> Liveness -- stack liveness
914 -> CtrlReturnConvention
917 mkReturnVector uniq tagged_alt_absCs deflt_absC srt liveness ret_conv
918 = getSRTLabel `thenFC` \srt_label ->
920 srt_info = (srt_label, srt)
922 (return_vec_amode, vtbl_body) = case ret_conv of {
924 -- might be a polymorphic case...
925 UnvectoredReturn 0 ->
926 ASSERT(null tagged_alt_absCs)
927 (CLbl ret_label RetRep,
928 absC (CRetDirect uniq deflt_absC (srt_label, srt) liveness));
930 UnvectoredReturn n ->
931 -- find the tag explicitly rather than using tag_reg for now.
932 -- on architectures with lots of regs the tag will be loaded
933 -- into tag_reg by the code doing the returning.
935 tag = CMacroExpr WordRep GET_TAG [CVal (nodeRel 0) DataPtrRep]
937 (CLbl ret_label RetRep,
938 absC (CRetDirect uniq
939 (mkAlgAltsCSwitch tag tagged_alt_absCs deflt_absC)
943 VectoredReturn table_size ->
945 (vector_table, alts_absC) =
946 unzip (map mk_vector_entry [fIRST_TAG .. (table_size+fIRST_TAG-1)])
948 ret_vector = CRetVector vtbl_label
950 (srt_label, srt) liveness
952 (CLbl vtbl_label DataPtrRep,
953 -- alts come first, because we don't want to declare all the symbols
954 absC (mkAbstractCs (mkAbstractCs alts_absC : [deflt_absC,ret_vector]))
959 returnFC return_vec_amode
963 vtbl_label = mkVecTblLabel uniq
964 ret_label = mkReturnInfoLabel uniq
967 case nonemptyAbsC deflt_absC of
968 -- the simplifier might have eliminated a case
969 Nothing -> CLbl mkErrorStdEntryLabel CodePtrRep
970 Just absC@(CCodeBlock lbl _) -> CLbl lbl CodePtrRep
972 mk_vector_entry :: ConTag -> (CAddrMode, AbstractC)
974 = case [ absC | (t, absC) <- tagged_alt_absCs, t == tag ] of
975 [] -> (deflt_lbl, AbsCNop)
976 [absC@(CCodeBlock lbl _)] -> (CLbl lbl CodePtrRep,absC)
977 _ -> panic "mkReturnVector: too many"
980 %************************************************************************
982 \subsection[CgCase-utils]{Utilities for handling case expressions}
984 %************************************************************************
986 @possibleHeapCheck@ tests a flag passed in to decide whether to do a
987 heap check or not. These heap checks are always in a case
988 alternative, so we use altHeapCheck.
993 -> Bool -- True <=> algebraic case
994 -> [MagicId] -- live registers
995 -> [(VirtualSpOffset,Int)] -- stack slots to tag
996 -> Maybe CLabel -- return address
997 -> Code -- continuation
1000 possibleHeapCheck GCMayHappen is_alg regs tags lbl code
1001 = altHeapCheck is_alg regs tags AbsCNop lbl code
1002 possibleHeapCheck NoGC _ _ tags lbl code
1006 splitTyConAppThroughNewTypes is like splitTyConApp_maybe except
1007 that it looks through newtypes in addition to synonyms. It's
1008 useful in the back end where we're not interested in newtypes
1011 Sometimes, we've thrown away the constructors during pruning in the
1012 renamer. In these cases, we emit a warning and fall back to using a
1013 SEQ_FRAME to evaluate the case scrutinee.
1016 getScrutineeTyCon :: Type -> Maybe TyCon
1017 getScrutineeTyCon ty =
1018 case (splitTyConAppThroughNewTypes ty) of
1021 if isFunTyCon tc then Nothing else -- not interested in funs
1022 if isPrimTyCon tc then Just tc else -- return primitive tycons
1023 -- otherwise (algebraic tycons) check the no. of constructors
1024 case (tyConFamilySize tc) of
1025 0 -> pprTrace "Warning" (hcat [
1026 text "constructors for ",
1028 text " not available.\n\tUse -fno-prune-tydecls to fix."
1032 splitTyConAppThroughNewTypes :: Type -> Maybe (TyCon, [Type])
1033 splitTyConAppThroughNewTypes ty
1034 = case splitTyConApp_maybe ty of
1036 | isNewTyCon tc -> splitTyConAppThroughNewTypes ty
1037 | otherwise -> Just (tc, tys)
1039 ([ty], _) = splitFunTys (applyTys (dataConType (head (tyConDataCons tc))) tys)