2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
4 %********************************************************
6 \section[CgTailCall]{Tail calls: converting @StgApps@}
8 %********************************************************
11 #include "HsVersions.h"
16 mkStaticAlgReturnCode, mkDynamicAlgReturnCode,
21 -- and to make the interface self-sufficient...
25 import Pretty -- Pretty/Outputable: rm (debugging only) ToDo
32 import Type ( isPrimType, Type )
33 import CgBindery ( getAtomAmodes, getCAddrMode, getCAddrModeAndInfo )
34 import CgCompInfo ( oTHER_TAG, iND_TAG )
35 import CgRetConv ( dataReturnConvPrim, ctrlReturnConvAlg, dataReturnConvAlg,
37 CtrlReturnConvention(..), DataReturnConvention(..)
39 import CgStackery ( adjustRealSps, mkStkAmodes )
40 import CgUsages ( getSpARelOffset, getSpBRelOffset )
41 import CLabel ( CLabel, mkStdUpdCodePtrVecLabel, mkConUpdCodePtrVecLabel )
42 import ClosureInfo ( nodeMustPointToIt, getEntryConvention, EntryConvention(..) )
43 import CmdLineOpts ( GlobalSwitch(..) )
44 import Id ( getDataConTyCon, getDataConTag,
45 idType, getIdPrimRep, fIRST_TAG, Id,
48 import Maybes ( assocMaybe, maybeToBool, Maybe(..) )
49 import PrimRep ( retPrimRepSize )
53 %************************************************************************
55 \subsection[tailcall-doc]{Documentation}
57 %************************************************************************
60 cgTailCall :: StgArg -> [StgArg] -> StgLiveVars -> Code
63 Here's the code we generate for a tail call. (NB there may be no
64 arguments, in which case this boils down to just entering a variable.)
67 \item Adjust the stack ptr to \tr{tailSp + #args}.
68 \item Put args in the top locations of the resulting stack.
69 \item Make Node point to the function closure.
70 \item Enter the function closure.
73 Things to be careful about:
75 \item Don't overwrite stack locations before you have finished with
76 them (remember you need the function and the as-yet-unmoved
78 \item Preferably, generate no code to replace x by x on the stack (a
79 common situation in tail-recursion).
80 \item Adjust the stack high water mark appropriately.
83 Literals are similar to constructors; they return by putting
84 themselves in an appropriate register and returning to the address on
88 cgTailCall (StgLitArg lit) [] live_vars
89 = performPrimReturn (CLit lit) live_vars
92 Treat unboxed locals exactly like literals (above) except use the addr
93 mode for the local instead of (CLit lit) in the assignment.
95 Case for unboxed @Ids@ first:
97 cgTailCall atom@(StgVarArg fun) [] live_vars
98 | isPrimType (idType fun)
99 = getCAddrMode fun `thenFC` \ amode ->
100 performPrimReturn amode live_vars
103 The general case (@fun@ is boxed):
105 cgTailCall (StgVarArg fun) args live_vars = performTailCall fun args live_vars
108 %************************************************************************
110 \subsection[return-and-tail-call]{Return and tail call}
112 %************************************************************************
116 A quick bit of hacking to try to solve my void#-leaking blues...
118 I think I'm getting bitten by this stuff because code like
121 case ds.s12 :: IoWorld of {
122 -- lvs: [ds.s12]; rhs lvs: []; uniq: c0
123 IoWorld ds.s13# -> ds.s13#;
127 causes me to try to allocate a register to return the result in. The
128 hope is that the following will avoid such problems (and that Will
129 will do this in a cleaner way when he hits the same problem).
134 performPrimReturn :: CAddrMode -- The thing to return
138 performPrimReturn amode live_vars
140 kind = getAmodeRep amode
141 ret_reg = dataReturnConvPrim kind
143 assign_possibly = case kind of
145 kind -> (CAssign (CReg ret_reg) amode)
147 performReturn assign_possibly mkPrimReturnCode live_vars
149 mkPrimReturnCode :: Sequel -> Code
150 mkPrimReturnCode (UpdateCode _) = panic "mkPrimReturnCode: Upd"
151 mkPrimReturnCode sequel = sequelToAmode sequel `thenFC` \ dest_amode ->
152 absC (CReturn dest_amode DirectReturn)
153 -- Direct, no vectoring
155 -- All constructor arguments in registers; Node and InfoPtr are set.
156 -- All that remains is
157 -- (a) to set TagReg, if necessary
158 -- (b) to set InfoPtr to the info ptr, if necessary
159 -- (c) to do the right sort of jump.
161 mkStaticAlgReturnCode :: Id -- The constructor
162 -> Maybe CLabel -- The info ptr, if it isn't already set
163 -> Sequel -- where to return to
166 mkStaticAlgReturnCode con maybe_info_lbl sequel
167 = -- Generate profiling code if necessary
168 (case return_convention of
169 VectoredReturn sz -> profCtrC SLIT("VEC_RETURN") [mkIntCLit sz]
173 -- Set tag if necessary
174 -- This is done by a macro, because if we are short of registers
175 -- we don't set TagReg; instead the continuation gets the tag
176 -- by indexing off the info ptr
177 (case return_convention of
179 UnvectoredReturn no_of_constrs
181 -> absC (CMacroStmt SET_TAG [mkIntCLit zero_indexed_tag])
186 -- Generate the right jump or return
188 UpdateCode _ -> -- Ha! We know the constructor,
189 -- so we can go direct to the correct
190 -- update code for that constructor
192 -- Set the info pointer, and jump
194 getIntSwitchChkrC `thenFC` \ isw_chkr ->
195 absC (CJump (CLbl (update_label isw_chkr) CodePtrRep))
197 CaseAlts _ (Just (alts, _)) -> -- Ho! We know the constructor so
198 -- we can go right to the alternative
200 -- No need to set info ptr when returning to a
201 -- known join point. After all, the code at
202 -- the destination knows what constructor it
203 -- is going to handle.
205 case assocMaybe alts tag of
206 Just (alt_absC, join_lbl) -> absC (CJump (CLbl join_lbl CodePtrRep))
207 Nothing -> panic "mkStaticAlgReturnCode: default"
208 -- The Nothing case should never happen; it's the subject
209 -- of a wad of special-case code in cgReturnCon
211 other -> -- OnStack, or (CaseAlts) ret_amode Nothing)
212 -- Set the info pointer, and jump
214 sequelToAmode sequel `thenFC` \ ret_amode ->
215 absC (CReturn ret_amode return_info)
219 tag = getDataConTag con
220 tycon = getDataConTyCon con
221 return_convention = ctrlReturnConvAlg tycon
222 zero_indexed_tag = tag - fIRST_TAG -- Adjust tag to be zero-indexed
223 -- cf AbsCUtils.mkAlgAltsCSwitch
225 update_label isw_chkr
226 = case (dataReturnConvAlg isw_chkr con) of
227 ReturnInHeap -> mkStdUpdCodePtrVecLabel tycon tag
228 ReturnInRegs _ -> mkConUpdCodePtrVecLabel tycon tag
230 return_info = case return_convention of
231 UnvectoredReturn _ -> DirectReturn
232 VectoredReturn _ -> StaticVectoredReturn zero_indexed_tag
234 set_info_ptr = case maybe_info_lbl of
236 Just info_lbl -> absC (CAssign (CReg infoptr) (CLbl info_lbl DataPtrRep))
239 mkDynamicAlgReturnCode :: TyCon -> CAddrMode -> Sequel -> Code
241 mkDynamicAlgReturnCode tycon dyn_tag sequel
242 = case ctrlReturnConvAlg tycon of
245 profCtrC SLIT("VEC_RETURN") [mkIntCLit sz] `thenC`
246 sequelToAmode sequel `thenFC` \ ret_addr ->
247 absC (CReturn ret_addr (DynamicVectoredReturn dyn_tag))
249 UnvectoredReturn no_of_constrs ->
251 -- Set tag if necessary
252 -- This is done by a macro, because if we are short of registers
253 -- we don't set TagReg; instead the continuation gets the tag
254 -- by indexing off the info ptr
255 (if no_of_constrs > 1 then
256 absC (CMacroStmt SET_TAG [dyn_tag])
262 sequelToAmode sequel `thenFC` \ ret_addr ->
263 -- Generate the right jump or return
264 absC (CReturn ret_addr DirectReturn)
268 performReturn :: AbstractC -- Simultaneous assignments to perform
269 -> (Sequel -> Code) -- The code to execute to actually do
270 -- the return, given an addressing mode
271 -- for the return address
275 performReturn sim_assts finish_code live_vars
276 = getEndOfBlockInfo `thenFC` \ (EndOfBlockInfo args_spa args_spb sequel) ->
278 -- Do the simultaneous assignments,
279 doSimAssts args_spa live_vars sim_assts `thenC`
281 -- Adjust stack pointers
282 adjustRealSps args_spa args_spb `thenC`
285 finish_code sequel -- "sequel" is `robust' in that it doesn't
286 -- depend on stk-ptr values
290 performTailCall :: Id -- Function
295 performTailCall fun args live_vars
296 = -- Get all the info we have about the function and args and go on to
298 getCAddrModeAndInfo fun `thenFC` \ (fun_amode, lf_info) ->
299 getAtomAmodes args `thenFC` \ arg_amodes ->
302 fun fun_amode lf_info arg_amodes
303 live_vars AbsCNop {- No pending assignments -}
306 tailCallBusiness :: Id -> CAddrMode -- Function and its amode
307 -> LambdaFormInfo -- Info about the function
308 -> [CAddrMode] -- Arguments
309 -> StgLiveVars -- Live in continuation
311 -> AbstractC -- Pending simultaneous assignments
312 -- *** GUARANTEED to contain only stack assignments.
313 -- In ptic, we don't need to look in here to
314 -- discover all live regs
318 tailCallBusiness fun fun_amode lf_info arg_amodes live_vars pending_assts
319 = isSwitchSetC EmitArityChecks `thenFC` \ do_arity_chks ->
321 nodeMustPointToIt lf_info `thenFC` \ node_points ->
322 getEntryConvention fun lf_info
323 (map getAmodeRep arg_amodes) `thenFC` \ entry_conv ->
325 getEndOfBlockInfo `thenFC` \ (EndOfBlockInfo args_spa args_spb sequel) ->
329 = if node_points then
330 CAssign (CReg node) fun_amode
334 (arg_regs, finish_code)
339 CCallProfCtrMacro SLIT("ENT_VIA_NODE") [],
340 CAssign (CReg infoptr)
342 (CMacroExpr DataPtrRep INFO_PTR [CReg node]),
343 CJump (CMacroExpr CodePtrRep ENTRY_CODE [CReg infoptr])
345 StdEntry lbl Nothing -> ([], CJump (CLbl lbl CodePtrRep))
346 StdEntry lbl (Just itbl) -> ([], CAssign (CReg infoptr) (CLbl itbl DataPtrRep)
348 CJump (CLbl lbl CodePtrRep))
349 DirectEntry lbl arity regs ->
350 (regs, (if do_arity_chks
351 then CMacroStmt SET_ARITY [mkIntCLit arity]
353 `mkAbsCStmts` CJump (CLbl lbl CodePtrRep))
355 no_of_args = length arg_amodes
357 (reg_arg_assts, stk_arg_amodes)
358 = (mkAbstractCs (zipWithEqual assign_to_reg arg_regs arg_amodes),
359 drop (length arg_regs) arg_amodes) -- No regs, or
362 assign_to_reg reg_id amode = CAssign (CReg reg_id) amode
365 CJoinPoint join_spa join_spb -> -- Ha! A let-no-escape thingy
367 ASSERT(not (args_spa > join_spa) || (args_spb > join_spb))
368 -- If ASSERTion fails: Oops: the join point has *lower*
369 -- stack ptrs than the continuation Note that we take
370 -- the SpB point without the return address here. The
371 -- return address is put on by the let-no-escapey thing
374 mkStkAmodes join_spa join_spb stk_arg_amodes
375 `thenFC` \ (final_spa, final_spb, stk_arg_assts) ->
377 -- Do the simultaneous assignments,
378 doSimAssts join_spa live_vars
379 (mkAbstractCs [pending_assts, reg_arg_assts, stk_arg_assts])
383 adjustRealSps final_spa final_spb `thenC`
385 -- Jump to join point
388 _ -> -- else: not a let-no-escape (the common case)
390 -- Make instruction to save return address
391 loadRetAddrIntoRetReg sequel `thenFC` \ ret_asst ->
393 mkStkAmodes args_spa args_spb stk_arg_amodes
395 \ (final_spa, final_spb, stk_arg_assts) ->
397 -- The B-stack space for the pushed return addess, with any args pushed
398 -- on top, is recorded in final_spb.
400 -- Do the simultaneous assignments,
401 doSimAssts args_spa live_vars
402 (mkAbstractCs [pending_assts, node_asst, ret_asst,
403 reg_arg_assts, stk_arg_assts])
406 -- Final adjustment of stack pointers
407 adjustRealSps final_spa final_spb `thenC`
409 -- Now decide about semi-tagging
410 isSwitchSetC DoSemiTagging `thenFC` \ semi_tagging_on ->
411 case (semi_tagging_on, arg_amodes, node_points, sequel) of
414 -- *************** The semi-tagging case ***************
416 ( True, [], True, CaseAlts _ (Just (st_alts, maybe_deflt_join_details))) ->
418 -- Whoppee! Semi-tagging rules OK!
419 -- (a) semi-tagging is switched on
420 -- (b) there are no arguments,
421 -- (c) Node points to the closure
422 -- (d) we have a case-alternative sequel with
423 -- some visible alternatives
425 -- Why is test (c) necessary?
426 -- Usually Node will point to it at this point, because we're
427 -- scrutinsing something which is either a thunk or a
429 -- But not always! The example I came across is when we have
430 -- a top-level Double:
432 -- ... (case lit.3 of ...) ...
433 -- Here, lit.3 is built as a re-entrant thing, which you must enter.
434 -- (OK, the simplifier should have eliminated this, but it's
435 -- easy to deal with the case anyway.)
437 join_details_to_code (load_regs_and_profiling_code, join_lbl)
438 = load_regs_and_profiling_code `mkAbsCStmts`
439 CJump (CLbl join_lbl CodePtrRep)
441 semi_tagged_alts = [ (mkMachInt (toInteger (tag - fIRST_TAG)),
442 join_details_to_code join_details)
443 | (tag, join_details) <- st_alts
447 -- Enter Node (we know infoptr will have the info ptr in it)!
449 CCallProfCtrMacro SLIT("RET_SEMI_FAILED")
450 [CMacroExpr IntRep INFO_TAG [CReg infoptr]],
451 CJump (CMacroExpr CodePtrRep ENTRY_CODE [CReg infoptr]) ]
455 CAssign (CReg infoptr)
456 (CVal (NodeRel zeroOff) DataPtrRep),
458 case maybe_deflt_join_details of
460 CSwitch (CMacroExpr IntRep INFO_TAG [CReg infoptr])
464 CSwitch (CMacroExpr IntRep EVAL_TAG [CReg infoptr])
465 [(mkMachInt 0, enter_jump)]
467 (CMacroExpr IntRep INFO_TAG [CReg infoptr])
469 (join_details_to_code details))
473 -- *************** The non-semi-tagging case ***************
475 other -> absC finish_code
479 loadRetAddrIntoRetReg :: Sequel -> FCode AbstractC
481 loadRetAddrIntoRetReg InRetReg
482 = returnFC AbsCNop -- Return address already there
484 loadRetAddrIntoRetReg sequel
485 = sequelToAmode sequel `thenFC` \ amode ->
486 returnFC (CAssign (CReg RetReg) amode)
490 %************************************************************************
492 \subsection[doSimAssts]{@doSimAssts@}
494 %************************************************************************
496 @doSimAssts@ happens at the end of every block of code.
497 They are separate because we sometimes do some jiggery-pokery in between.
500 doSimAssts :: VirtualSpAOffset -- tail_spa: SpA as seen by continuation
501 -> StgLiveVars -- Live in continuation
505 doSimAssts tail_spa live_vars sim_assts
506 = -- Do the simultaneous assignments
507 absC (CSimultaneous sim_assts) `thenC`
509 -- Stub any unstubbed slots; the only live variables are indicated in
510 -- the end-of-block info in the monad
511 nukeDeadBindings live_vars `thenC`
512 getUnstubbedAStackSlots tail_spa `thenFC` \ a_slots ->
513 -- Passing in tail_spa here should actually be redundant, because
514 -- the stack should be trimmed (by nukeDeadBindings) to
515 -- exactly the tail_spa position anyhow.
517 -- Emit code to stub dead regs; this only generates actual
518 -- machine instructions in in the DEBUG version
519 -- *** NOT DONE YET ***
523 else profCtrC SLIT("A_STK_STUB") [mkIntCLit (length a_slots)] `thenC`
524 mapCs stub_A_slot a_slots
527 stub_A_slot :: VirtualSpAOffset -> Code
528 stub_A_slot offset = getSpARelOffset offset `thenFC` \ spa_rel ->
529 absC (CAssign (CVal spa_rel PtrRep)