2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[CgClosure]{Code generation for closures}
7 This module provides the support code for @StgToAbstractC@ to deal
8 with {\em closures} on the RHSs of let(rec)s. See also
9 @CgCon@, which deals with constructors.
13 -- The above warning supression flag is a temporary kludge.
14 -- While working on this module you are encouraged to remove it and fix
15 -- any warnings in the module. See
16 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
19 module CgClosure ( cgTopRhsClosure,
25 #include "HsVersions.h"
27 import {-# SOURCE #-} CgExpr ( cgExpr )
62 %********************************************************
64 \subsection[closures-no-free-vars]{Top-level closures}
66 %********************************************************
68 For closures bound at top level, allocate in static space.
69 They should have no free variables.
73 -> CostCentreStack -- Optional cost centre annotation
78 -> FCode (Id, CgIdInfo)
80 cgTopRhsClosure id ccs binder_info upd_flag args body = do
81 { -- LAY OUT THE OBJECT
83 ; lf_info <- mkClosureLFInfo id TopLevel [] upd_flag args
84 ; srt_info <- getSRTInfo
85 ; mod_name <- getModuleName
86 ; let descr = closureDescription mod_name name
87 closure_info = mkClosureInfo True id lf_info 0 0 srt_info descr
88 closure_label = mkLocalClosureLabel name
89 cg_id_info = stableIdInfo id (mkLblExpr closure_label) lf_info
90 closure_rep = mkStaticClosureFields closure_info ccs True []
92 -- BUILD THE OBJECT, AND GENERATE INFO TABLE (IF NECESSARY)
93 ; emitDataLits closure_label closure_rep
94 ; forkClosureBody (closureCodeBody binder_info closure_info
97 ; returnFC (id, cg_id_info) }
100 %********************************************************
102 \subsection[non-top-level-closures]{Non top-level closures}
104 %********************************************************
106 For closures with free vars, allocate in heap.
111 -> CostCentreStack -- Optional cost centre annotation
117 -> [StgArg] -- payload
118 -> FCode (Id, CgIdInfo)
120 cgStdRhsClosure bndr cc bndr_info fvs args body lf_info payload
121 = do -- AHA! A STANDARD-FORM THUNK
122 { -- LAY OUT THE OBJECT
123 amodes <- getArgAmodes payload
124 ; mod_name <- getModuleName
125 ; let (tot_wds, ptr_wds, amodes_w_offsets)
126 = mkVirtHeapOffsets (isLFThunk lf_info) amodes
128 descr = closureDescription mod_name (idName bndr)
129 closure_info = mkClosureInfo False -- Not static
130 bndr lf_info tot_wds ptr_wds
131 NoC_SRT -- No SRT for a std-form closure
134 ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
137 ; heap_offset <- allocDynClosure closure_info use_cc blame_cc amodes_w_offsets
140 ; returnFC (bndr, heapIdInfo bndr heap_offset lf_info) }
143 Here's the general case.
147 -> CostCentreStack -- Optional cost centre annotation
153 -> FCode (Id, CgIdInfo)
155 cgRhsClosure bndr cc bndr_info fvs upd_flag args body = do
156 { -- LAY OUT THE OBJECT
157 -- If the binder is itself a free variable, then don't store
158 -- it in the closure. Instead, just bind it to Node on entry.
159 -- NB we can be sure that Node will point to it, because we
160 -- havn't told mkClosureLFInfo about this; so if the binder
161 -- _was_ a free var of its RHS, mkClosureLFInfo thinks it *is*
162 -- stored in the closure itself, so it will make sure that
163 -- Node points to it...
166 is_elem = isIn "cgRhsClosure"
167 bndr_is_a_fv = bndr `is_elem` fvs
168 reduced_fvs | bndr_is_a_fv = fvs `minusList` [bndr]
171 ; lf_info <- mkClosureLFInfo bndr NotTopLevel fvs upd_flag args
172 ; fv_infos <- mapFCs getCgIdInfo reduced_fvs
173 ; srt_info <- getSRTInfo
174 ; mod_name <- getModuleName
175 ; let bind_details :: [(CgIdInfo, VirtualHpOffset)]
176 (tot_wds, ptr_wds, bind_details)
177 = mkVirtHeapOffsets (isLFThunk lf_info) (map add_rep fv_infos)
179 add_rep info = (cgIdInfoArgRep info, info)
181 descr = closureDescription mod_name name
182 closure_info = mkClosureInfo False -- Not static
183 bndr lf_info tot_wds ptr_wds
186 -- BUILD ITS INFO TABLE AND CODE
187 ; forkClosureBody (do
190 -- A function closure pointer may be tagged, so we
191 -- must take it into account when accessing the free variables.
192 mbtag = tagForArity (length args)
193 bind_fv (info, offset)
195 = bindNewToUntagNode (cgIdInfoId info) offset (cgIdInfoLF info) tag
197 = bindNewToNode (cgIdInfoId info) offset (cgIdInfoLF info)
198 ; mapCs bind_fv bind_details
200 -- Bind the binder itself, if it is a free var
201 ; whenC bndr_is_a_fv (bindNewToReg bndr nodeReg lf_info)
204 ; closureCodeBody bndr_info closure_info cc args body })
208 to_amode (info, offset) = do { amode <- idInfoToAmode info
209 ; return (amode, offset) }
210 ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
211 ; amodes_w_offsets <- mapFCs to_amode bind_details
212 ; heap_offset <- allocDynClosure closure_info use_cc blame_cc amodes_w_offsets
215 ; returnFC (bndr, heapIdInfo bndr heap_offset lf_info) }
218 mkClosureLFInfo :: Id -- The binder
219 -> TopLevelFlag -- True of top level
221 -> UpdateFlag -- Update flag
223 -> FCode LambdaFormInfo
224 mkClosureLFInfo bndr top fvs upd_flag args
225 | null args = return (mkLFThunk (idType bndr) top fvs upd_flag)
226 | otherwise = do { arg_descr <- mkArgDescr (idName bndr) args
227 ; return (mkLFReEntrant top fvs args arg_descr) }
231 %************************************************************************
233 \subsection[code-for-closures]{The code for closures}
235 %************************************************************************
238 closureCodeBody :: StgBinderInfo
239 -> ClosureInfo -- Lots of information about this closure
240 -> CostCentreStack -- Optional cost centre attached to closure
246 There are two main cases for the code for closures. If there are {\em
247 no arguments}, then the closure is a thunk, and not in normal form.
248 So it should set up an update frame (if it is shared).
249 NB: Thunks cannot have a primitive type!
252 closureCodeBody binder_info cl_info cc [{- No args i.e. thunk -}] body = do
253 { body_absC <- getCgStmts $ do
254 { tickyEnterThunk cl_info
255 ; ldvEnterClosure cl_info -- NB: Node always points when profiling
256 ; thunkWrapper cl_info $ do
257 -- We only enter cc after setting up update so
258 -- that cc of enclosing scope will be recorded
259 -- in update frame CAF/DICT functions will be
260 -- subsumed by this enclosing cc
261 { enterCostCentre cl_info cc body
265 ; emitClosureCodeAndInfoTable cl_info [] body_absC }
268 If there is /at least one argument/, then this closure is in
269 normal form, so there is no need to set up an update frame.
271 The Macros for GrAnSim are produced at the beginning of the
272 argSatisfactionCheck (by calling fetchAndReschedule). There info if
273 Node points to closure is available. -- HWL
276 closureCodeBody binder_info cl_info cc args body
277 = ASSERT( length args > 0 )
278 do { -- Get the current virtual Sp (it might not be zero,
279 -- eg. if we're compiling a let-no-escape).
281 ; let (reg_args, other_args) = assignCallRegs (addIdReps args)
282 (sp_top, stk_args) = mkVirtStkOffsets vSp other_args
284 -- Allocate the global ticky counter
285 ; let ticky_ctr_lbl = mkRednCountsLabel (closureName cl_info)
286 ; emitTickyCounter cl_info args sp_top
288 -- ...and establish the ticky-counter
289 -- label for this block
290 ; setTickyCtrLabel ticky_ctr_lbl $ do
292 -- Emit the slow-entry code
293 { reg_save_code <- mkSlowEntryCode cl_info reg_args
295 -- Emit the main entry code
297 mkFunEntryCode cl_info cc reg_args stk_args
298 sp_top reg_save_code body
299 ; emitClosureCodeAndInfoTable cl_info [] blks
304 mkFunEntryCode :: ClosureInfo
306 -> [(Id,GlobalReg)] -- Args in regs
307 -> [(Id,VirtualSpOffset)] -- Args on stack
308 -> VirtualSpOffset -- Last allocated word on stack
309 -> CmmStmts -- Register-save code in case of GC
312 -- The main entry code for the closure
313 mkFunEntryCode cl_info cc reg_args stk_args sp_top reg_save_code body = do
314 { -- Bind args to regs/stack as appropriate,
315 -- and record expected position of sps
316 ; bindArgsToRegs reg_args
317 ; bindArgsToStack stk_args
318 ; setRealAndVirtualSp sp_top
320 -- Enter the cost-centre, if required
321 -- ToDo: It's not clear why this is outside the funWrapper,
322 -- but the tickyEnterFun is inside. Perhaps we can put
324 ; enterCostCentre cl_info cc body
327 ; funWrapper cl_info reg_args reg_save_code $ do
328 { tickyEnterFun cl_info
333 The "slow entry" code for a function. This entry point takes its
334 arguments on the stack. It loads the arguments into registers
335 according to the calling convention, and jumps to the function's
336 normal entry point. The function's closure is assumed to be in
339 The slow entry point is used in two places:
341 (a) unknown calls: eg. stg_PAP_entry
342 (b) returning from a heap-check failure
345 mkSlowEntryCode :: ClosureInfo -> [(Id,GlobalReg)] -> FCode CmmStmts
346 -- If this function doesn't have a specialised ArgDescr, we need
347 -- to generate the function's arg bitmap, slow-entry code, and
348 -- register-save code for the heap-check failure
349 -- Here, we emit the slow-entry code, and
350 -- return the register-save assignments
351 mkSlowEntryCode cl_info reg_args
352 | Just (_, ArgGen _) <- closureFunInfo cl_info
353 = do { emitSimpleProc slow_lbl (emitStmts load_stmts)
354 ; return save_stmts }
355 | otherwise = return noStmts
357 name = closureName cl_info
358 slow_lbl = mkSlowEntryLabel name
360 load_stmts = mkStmts load_assts `plusStmts` mkStmts [stk_adj_pop, jump_to_entry]
361 save_stmts = oneStmt stk_adj_push `plusStmts` mkStmts save_assts
363 reps_w_regs :: [(CgRep,GlobalReg)]
364 reps_w_regs = [(idCgRep id, reg) | (id,reg) <- reverse reg_args]
365 (final_stk_offset, stk_offsets)
366 = mapAccumL (\off (rep,_) -> (off + cgRepSizeW rep, off))
369 load_assts = zipWithEqual "mk_load" mk_load reps_w_regs stk_offsets
370 mk_load (rep,reg) offset = CmmAssign (CmmGlobal reg)
371 (CmmLoad (cmmRegOffW spReg offset)
374 save_assts = zipWithEqual "mk_save" mk_save reps_w_regs stk_offsets
375 mk_save (rep,reg) offset = ASSERT( argMachRep rep == globalRegRep reg )
376 CmmStore (cmmRegOffW spReg offset)
377 (CmmReg (CmmGlobal reg))
379 stk_adj_pop = CmmAssign spReg (cmmRegOffW spReg final_stk_offset)
380 stk_adj_push = CmmAssign spReg (cmmRegOffW spReg (- final_stk_offset))
381 jump_to_entry = CmmJump (mkLblExpr (enterLocalIdLabel name)) []
385 %************************************************************************
387 \subsubsection[closure-code-wrappers]{Wrappers around closure code}
389 %************************************************************************
392 thunkWrapper:: ClosureInfo -> Code -> Code
393 thunkWrapper closure_info thunk_code = do
394 { let node_points = nodeMustPointToIt (closureLFInfo closure_info)
396 -- HWL: insert macros for GrAnSim; 2 versions depending on liveness of node
397 -- (we prefer fetchAndReschedule-style context switches to yield ones)
399 then granFetchAndReschedule [] node_points
400 else granYield [] node_points
402 -- Stack and/or heap checks
403 ; thunkEntryChecks closure_info $ do
404 { -- Overwrite with black hole if necessary
405 whenC (blackHoleOnEntry closure_info && node_points)
406 (blackHoleIt closure_info)
407 ; setupUpdate closure_info thunk_code }
408 -- setupUpdate *encloses* the thunk_code
411 funWrapper :: ClosureInfo -- Closure whose code body this is
412 -> [(Id,GlobalReg)] -- List of argument registers (if any)
413 -> CmmStmts -- reg saves for the heap check failure
414 -> Code -- Body of function being compiled
416 funWrapper closure_info arg_regs reg_save_code fun_body = do
417 { let node_points = nodeMustPointToIt (closureLFInfo closure_info)
420 -- Debugging: check that R1 has the correct tag
421 ; let tag = funTag closure_info
422 ; whenC (tag /= 0 && node_points) $ do
424 stmtC (CmmCondBranch (CmmMachOp mo_wordEq [cmmGetTag (CmmReg nodeReg),
425 CmmLit (mkIntCLit tag)]) l)
426 stmtC (CmmStore (CmmLit (mkWordCLit 0)) (CmmLit (mkWordCLit 0)))
430 -- Enter for Ldv profiling
431 ; whenC node_points (ldvEnterClosure closure_info)
433 -- GranSim yeild poin
434 ; granYield arg_regs node_points
436 -- Heap and/or stack checks wrap the function body
437 ; funEntryChecks closure_info reg_save_code
443 %************************************************************************
445 \subsubsubsection[update-and-BHs]{Update and black-hole wrappers}
447 %************************************************************************
451 blackHoleIt :: ClosureInfo -> Code
452 -- Only called for closures with no args
453 -- Node points to the closure
454 blackHoleIt closure_info = emitBlackHoleCode (closureSingleEntry closure_info)
456 emitBlackHoleCode :: Bool -> Code
457 emitBlackHoleCode is_single_entry = do
459 dflags <- getDynFlags
461 -- If we wanted to do eager blackholing with slop filling,
462 -- we'd need to do it at the *end* of a basic block, otherwise
463 -- we overwrite the free variables in the thunk that we still
464 -- need. We have a patch for this from Andy Cheadle, but not
465 -- incorporated yet. --SDM [6/2004]
467 -- Profiling needs slop filling (to support LDV profiling), so
468 -- currently eager blackholing doesn't work with profiling.
470 -- Previously, eager blackholing was enabled when ticky-ticky
471 -- was on. But it didn't work, and it wasn't strictly necessary
472 -- to bring back minimal ticky-ticky, so now EAGER_BLACKHOLING
473 -- is unconditionally disabled. -- krc 1/2007
475 let eager_blackholing = not opt_SccProfilingOn
476 && dopt Opt_EagerBlackHoling dflags
480 tickyBlackHole (not is_single_entry)
481 let bh_info = CmmReg (CmmGlobal EagerBlackholeInfo)
482 stmtC (CmmStore (CmmReg nodeReg) bh_info)
488 setupUpdate :: ClosureInfo -> Code -> Code -- Only called for closures with no args
489 -- Nota Bene: this function does not change Node (even if it's a CAF),
490 -- so that the cost centre in the original closure can still be
491 -- extracted by a subsequent enterCostCentre
492 setupUpdate closure_info code
493 | closureReEntrant closure_info
496 | not (isStaticClosure closure_info)
497 = if closureUpdReqd closure_info
498 then do { tickyPushUpdateFrame; pushUpdateFrame (CmmReg nodeReg) code }
499 else do { tickyUpdateFrameOmitted; code }
501 | otherwise -- A static closure
502 = do { tickyUpdateBhCaf closure_info
504 ; if closureUpdReqd closure_info
505 then do -- Blackhole the (updatable) CAF:
506 { upd_closure <- link_caf closure_info True
507 ; pushUpdateFrame upd_closure code }
509 { -- krc: removed some ticky-related code here.
510 ; tickyUpdateFrameOmitted
515 -----------------------------------------------------------------------------
518 -- When a CAF is first entered, it creates a black hole in the heap,
519 -- and updates itself with an indirection to this new black hole.
521 -- We update the CAF with an indirection to a newly-allocated black
522 -- hole in the heap. We also set the blocking queue on the newly
523 -- allocated black hole to be empty.
525 -- Why do we make a black hole in the heap when we enter a CAF?
527 -- - for a generational garbage collector, which needs a fast
528 -- test for whether an updatee is in an old generation or not
530 -- - for the parallel system, which can implement updates more
531 -- easily if the updatee is always in the heap. (allegedly).
533 -- When debugging, we maintain a separate CAF list so we can tell when
534 -- a CAF has been garbage collected.
536 -- newCAF must be called before the itbl ptr is overwritten, since
537 -- newCAF records the old itbl ptr in order to do CAF reverting
538 -- (which Hugs needs to do in order that combined mode works right.)
541 -- ToDo [Feb 04] This entire link_caf nonsense could all be moved
542 -- into the "newCAF" RTS procedure, which we call anyway, including
543 -- the allocation of the black-hole indirection closure.
544 -- That way, code size would fall, the CAF-handling code would
545 -- be closer together, and the compiler wouldn't need to know
546 -- about off_indirectee etc.
548 link_caf :: ClosureInfo
549 -> Bool -- True <=> updatable, False <=> single-entry
550 -> FCode CmmExpr -- Returns amode for closure to be updated
551 -- To update a CAF we must allocate a black hole, link the CAF onto the
552 -- CAF list, then update the CAF to point to the fresh black hole.
553 -- This function returns the address of the black hole, so it can be
554 -- updated with the new value when available. The reason for all of this
555 -- is that we only want to update dynamic heap objects, not static ones,
556 -- so that generational GC is easier.
557 link_caf cl_info is_upd = do
558 { -- Alloc black hole specifying CC_HDR(Node) as the cost centre
559 ; let use_cc = costCentreFrom (CmmReg nodeReg)
561 ; hp_offset <- allocDynClosure bh_cl_info use_cc blame_cc []
562 ; hp_rel <- getHpRelOffset hp_offset
564 -- Call the RTS function newCAF to add the CAF to the CafList
565 -- so that the garbage collector can find them
566 -- This must be done *before* the info table pointer is overwritten,
567 -- because the old info table ptr is needed for reversion
568 ; emitRtsCallWithVols (sLit "newCAF") [CmmKinded (CmmReg nodeReg) PtrHint] [node] False
569 -- node is live, so save it.
571 -- Overwrite the closure with a (static) indirection
572 -- to the newly-allocated black hole
573 ; stmtsC [ CmmStore (cmmRegOffW nodeReg off_indirectee) hp_rel
574 , CmmStore (CmmReg nodeReg) ind_static_info ]
578 bh_cl_info :: ClosureInfo
579 bh_cl_info = cafBlackHoleClosureInfo cl_info
581 ind_static_info :: CmmExpr
582 ind_static_info = mkLblExpr mkIndStaticInfoLabel
584 off_indirectee :: WordOff
585 off_indirectee = fixedHdrSize + oFFSET_StgInd_indirectee*wORD_SIZE
589 %************************************************************************
591 \subsection[CgClosure-Description]{Profiling Closure Description.}
593 %************************************************************************
595 For "global" data constructors the description is simply occurrence
596 name of the data constructor itself. Otherwise it is determined by
597 @closureDescription@ from the let binding information.
600 closureDescription :: Module -- Module
601 -> Name -- Id of closure binding
603 -- Not called for StgRhsCon which have global info tables built in
604 -- CgConTbls.lhs with a description generated from the data constructor
605 closureDescription mod_name name
606 = showSDocDump (char '<' <>
607 (if isExternalName name
608 then ppr name -- ppr will include the module name prefix
609 else pprModule mod_name <> char '.' <> ppr name) <>
611 -- showSDocDump, because we want to see the unique on the Name.