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.
12 module CgClosure ( cgTopRhsClosure,
18 #include "HsVersions.h"
20 import {-# SOURCE #-} CgExpr ( cgExpr )
51 %********************************************************
53 \subsection[closures-no-free-vars]{Top-level closures}
55 %********************************************************
57 For closures bound at top level, allocate in static space.
58 They should have no free variables.
62 -> CostCentreStack -- Optional cost centre annotation
67 -> FCode (Id, CgIdInfo)
69 cgTopRhsClosure id ccs binder_info upd_flag args body = do
70 { -- LAY OUT THE OBJECT
72 ; lf_info <- mkClosureLFInfo id TopLevel [] upd_flag args
73 ; srt_info <- getSRTInfo
74 ; mod_name <- getModuleName
75 ; let descr = closureDescription mod_name name
76 closure_info = mkClosureInfo True id lf_info 0 0 srt_info descr
77 closure_label = mkLocalClosureLabel name
78 cg_id_info = stableIdInfo id (mkLblExpr closure_label) lf_info
79 closure_rep = mkStaticClosureFields closure_info ccs True []
81 -- BUILD THE OBJECT, AND GENERATE INFO TABLE (IF NECESSARY)
82 ; emitDataLits closure_label closure_rep
83 ; forkClosureBody (closureCodeBody binder_info closure_info
86 ; returnFC (id, cg_id_info) }
89 %********************************************************
91 \subsection[non-top-level-closures]{Non top-level closures}
93 %********************************************************
95 For closures with free vars, allocate in heap.
100 -> CostCentreStack -- Optional cost centre annotation
106 -> [StgArg] -- payload
107 -> FCode (Id, CgIdInfo)
109 cgStdRhsClosure bndr cc bndr_info fvs args body lf_info payload
110 = do -- AHA! A STANDARD-FORM THUNK
111 { -- LAY OUT THE OBJECT
112 amodes <- getArgAmodes payload
113 ; mod_name <- getModuleName
114 ; let (tot_wds, ptr_wds, amodes_w_offsets)
115 = mkVirtHeapOffsets (isLFThunk lf_info) amodes
117 descr = closureDescription mod_name (idName bndr)
118 closure_info = mkClosureInfo False -- Not static
119 bndr lf_info tot_wds ptr_wds
120 NoC_SRT -- No SRT for a std-form closure
123 ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
126 ; heap_offset <- allocDynClosure closure_info use_cc blame_cc amodes_w_offsets
129 ; returnFC (bndr, heapIdInfo bndr heap_offset lf_info) }
132 Here's the general case.
136 -> CostCentreStack -- Optional cost centre annotation
142 -> FCode (Id, CgIdInfo)
144 cgRhsClosure bndr cc bndr_info fvs upd_flag args body = do
145 { -- LAY OUT THE OBJECT
146 -- If the binder is itself a free variable, then don't store
147 -- it in the closure. Instead, just bind it to Node on entry.
148 -- NB we can be sure that Node will point to it, because we
149 -- havn't told mkClosureLFInfo about this; so if the binder
150 -- _was_ a free var of its RHS, mkClosureLFInfo thinks it *is*
151 -- stored in the closure itself, so it will make sure that
152 -- Node points to it...
155 is_elem = isIn "cgRhsClosure"
156 bndr_is_a_fv = bndr `is_elem` fvs
157 reduced_fvs | bndr_is_a_fv = fvs `minusList` [bndr]
160 ; lf_info <- mkClosureLFInfo bndr NotTopLevel fvs upd_flag args
161 ; fv_infos <- mapFCs getCgIdInfo reduced_fvs
162 ; srt_info <- getSRTInfo
163 ; mod_name <- getModuleName
164 ; let bind_details :: [(CgIdInfo, VirtualHpOffset)]
165 (tot_wds, ptr_wds, bind_details)
166 = mkVirtHeapOffsets (isLFThunk lf_info) (map add_rep fv_infos)
168 add_rep info = (cgIdInfoArgRep info, info)
170 descr = closureDescription mod_name name
171 closure_info = mkClosureInfo False -- Not static
172 bndr lf_info tot_wds ptr_wds
175 -- BUILD ITS INFO TABLE AND CODE
176 ; forkClosureBody (do
178 let bind_fv (info, offset)
179 = bindNewToNode (cgIdInfoId info) offset (cgIdInfoLF info)
180 ; mapCs bind_fv bind_details
182 -- Bind the binder itself, if it is a free var
183 ; whenC bndr_is_a_fv (bindNewToReg bndr nodeReg lf_info)
186 ; closureCodeBody bndr_info closure_info cc args body })
190 to_amode (info, offset) = do { amode <- idInfoToAmode info
191 ; return (amode, offset) }
192 ; (use_cc, blame_cc) <- chooseDynCostCentres cc args body
193 ; amodes_w_offsets <- mapFCs to_amode bind_details
194 ; heap_offset <- allocDynClosure closure_info use_cc blame_cc amodes_w_offsets
197 ; returnFC (bndr, heapIdInfo bndr heap_offset lf_info) }
200 mkClosureLFInfo :: Id -- The binder
201 -> TopLevelFlag -- True of top level
203 -> UpdateFlag -- Update flag
205 -> FCode LambdaFormInfo
206 mkClosureLFInfo bndr top fvs upd_flag args
207 | null args = return (mkLFThunk (idType bndr) top fvs upd_flag)
208 | otherwise = do { arg_descr <- mkArgDescr (idName bndr) args
209 ; return (mkLFReEntrant top fvs args arg_descr) }
213 %************************************************************************
215 \subsection[code-for-closures]{The code for closures}
217 %************************************************************************
220 closureCodeBody :: StgBinderInfo
221 -> ClosureInfo -- Lots of information about this closure
222 -> CostCentreStack -- Optional cost centre attached to closure
228 There are two main cases for the code for closures. If there are {\em
229 no arguments}, then the closure is a thunk, and not in normal form.
230 So it should set up an update frame (if it is shared).
231 NB: Thunks cannot have a primitive type!
234 closureCodeBody binder_info cl_info cc [{- No args i.e. thunk -}] body = do
235 { body_absC <- getCgStmts $ do
236 { tickyEnterThunk cl_info
237 ; ldvEnter (CmmReg nodeReg) -- NB: Node always points when profiling
238 ; thunkWrapper cl_info $ do
239 -- We only enter cc after setting up update so
240 -- that cc of enclosing scope will be recorded
241 -- in update frame CAF/DICT functions will be
242 -- subsumed by this enclosing cc
243 { enterCostCentre cl_info cc body
247 ; emitClosureCodeAndInfoTable cl_info [] body_absC }
250 If there is /at least one argument/, then this closure is in
251 normal form, so there is no need to set up an update frame.
253 The Macros for GrAnSim are produced at the beginning of the
254 argSatisfactionCheck (by calling fetchAndReschedule). There info if
255 Node points to closure is available. -- HWL
258 closureCodeBody binder_info cl_info cc args body
259 = ASSERT( length args > 0 )
260 do { -- Get the current virtual Sp (it might not be zero,
261 -- eg. if we're compiling a let-no-escape).
263 ; let (reg_args, other_args) = assignCallRegs (addIdReps args)
264 (sp_top, stk_args) = mkVirtStkOffsets vSp other_args
266 -- Allocate the global ticky counter
267 ; let ticky_ctr_lbl = mkRednCountsLabel (closureName cl_info)
268 ; emitTickyCounter cl_info args sp_top
270 -- ...and establish the ticky-counter
271 -- label for this block
272 ; setTickyCtrLabel ticky_ctr_lbl $ do
274 -- Emit the slow-entry code
275 { reg_save_code <- mkSlowEntryCode cl_info reg_args
277 -- Emit the main entry code
279 mkFunEntryCode cl_info cc reg_args stk_args
280 sp_top reg_save_code body
281 ; emitClosureCodeAndInfoTable cl_info [] blks
286 mkFunEntryCode :: ClosureInfo
288 -> [(Id,GlobalReg)] -- Args in regs
289 -> [(Id,VirtualSpOffset)] -- Args on stack
290 -> VirtualSpOffset -- Last allocated word on stack
291 -> CmmStmts -- Register-save code in case of GC
294 -- The main entry code for the closure
295 mkFunEntryCode cl_info cc reg_args stk_args sp_top reg_save_code body = do
296 { -- Bind args to regs/stack as appropriate,
297 -- and record expected position of sps
298 ; bindArgsToRegs reg_args
299 ; bindArgsToStack stk_args
300 ; setRealAndVirtualSp sp_top
302 -- Enter the cost-centre, if required
303 -- ToDo: It's not clear why this is outside the funWrapper,
304 -- but the tickyEnterFun is inside. Perhaps we can put
306 ; enterCostCentre cl_info cc body
309 ; funWrapper cl_info reg_args reg_save_code $ do
310 { tickyEnterFun cl_info
315 The "slow entry" code for a function. This entry point takes its
316 arguments on the stack. It loads the arguments into registers
317 according to the calling convention, and jumps to the function's
318 normal entry point. The function's closure is assumed to be in
321 The slow entry point is used in two places:
323 (a) unknown calls: eg. stg_PAP_entry
324 (b) returning from a heap-check failure
327 mkSlowEntryCode :: ClosureInfo -> [(Id,GlobalReg)] -> FCode CmmStmts
328 -- If this function doesn't have a specialised ArgDescr, we need
329 -- to generate the function's arg bitmap, slow-entry code, and
330 -- register-save code for the heap-check failure
331 -- Here, we emit the slow-entry code, and
332 -- return the register-save assignments
333 mkSlowEntryCode cl_info reg_args
334 | Just (_, ArgGen _) <- closureFunInfo cl_info
335 = do { emitSimpleProc slow_lbl (emitStmts load_stmts)
336 ; return save_stmts }
337 | otherwise = return noStmts
339 name = closureName cl_info
340 slow_lbl = mkSlowEntryLabel name
342 load_stmts = mkStmts load_assts `plusStmts` mkStmts [stk_adj_pop, jump_to_entry]
343 save_stmts = oneStmt stk_adj_push `plusStmts` mkStmts save_assts
345 reps_w_regs :: [(CgRep,GlobalReg)]
346 reps_w_regs = [(idCgRep id, reg) | (id,reg) <- reverse reg_args]
347 (final_stk_offset, stk_offsets)
348 = mapAccumL (\off (rep,_) -> (off + cgRepSizeW rep, off))
351 load_assts = zipWithEqual "mk_load" mk_load reps_w_regs stk_offsets
352 mk_load (rep,reg) offset = CmmAssign (CmmGlobal reg)
353 (CmmLoad (cmmRegOffW spReg offset)
356 save_assts = zipWithEqual "mk_save" mk_save reps_w_regs stk_offsets
357 mk_save (rep,reg) offset = ASSERT( argMachRep rep == globalRegRep reg )
358 CmmStore (cmmRegOffW spReg offset)
359 (CmmReg (CmmGlobal reg))
361 stk_adj_pop = CmmAssign spReg (cmmRegOffW spReg final_stk_offset)
362 stk_adj_push = CmmAssign spReg (cmmRegOffW spReg (- final_stk_offset))
363 jump_to_entry = CmmJump (mkLblExpr (enterLocalIdLabel name)) []
367 %************************************************************************
369 \subsubsection[closure-code-wrappers]{Wrappers around closure code}
371 %************************************************************************
374 thunkWrapper:: ClosureInfo -> Code -> Code
375 thunkWrapper closure_info thunk_code = do
376 { let node_points = nodeMustPointToIt (closureLFInfo closure_info)
378 -- HWL: insert macros for GrAnSim; 2 versions depending on liveness of node
379 -- (we prefer fetchAndReschedule-style context switches to yield ones)
381 then granFetchAndReschedule [] node_points
382 else granYield [] node_points
384 -- Stack and/or heap checks
385 ; thunkEntryChecks closure_info $ do
386 { -- Overwrite with black hole if necessary
387 whenC (blackHoleOnEntry closure_info && node_points)
388 (blackHoleIt closure_info)
389 ; setupUpdate closure_info thunk_code }
390 -- setupUpdate *encloses* the thunk_code
393 funWrapper :: ClosureInfo -- Closure whose code body this is
394 -> [(Id,GlobalReg)] -- List of argument registers (if any)
395 -> CmmStmts -- reg saves for the heap check failure
396 -> Code -- Body of function being compiled
398 funWrapper closure_info arg_regs reg_save_code fun_body = do
399 { let node_points = nodeMustPointToIt (closureLFInfo closure_info)
401 -- Enter for Ldv profiling
402 ; whenC node_points (ldvEnter (CmmReg nodeReg))
404 -- GranSim yeild poin
405 ; granYield arg_regs node_points
407 -- Heap and/or stack checks wrap the function body
408 ; funEntryChecks closure_info reg_save_code
414 %************************************************************************
416 \subsubsubsection[update-and-BHs]{Update and black-hole wrappers}
418 %************************************************************************
422 blackHoleIt :: ClosureInfo -> Code
423 -- Only called for closures with no args
424 -- Node points to the closure
425 blackHoleIt closure_info = emitBlackHoleCode (closureSingleEntry closure_info)
427 emitBlackHoleCode :: Bool -> Code
428 emitBlackHoleCode is_single_entry
429 | eager_blackholing = do
430 tickyBlackHole (not is_single_entry)
431 stmtC (CmmStore (CmmReg nodeReg) (CmmLit (CmmLabel bh_lbl)))
435 bh_lbl | is_single_entry = mkRtsDataLabel SLIT("stg_SE_BLACKHOLE_info")
436 | otherwise = mkRtsDataLabel SLIT("stg_BLACKHOLE_info")
438 -- If we wanted to do eager blackholing with slop filling,
439 -- we'd need to do it at the *end* of a basic block, otherwise
440 -- we overwrite the free variables in the thunk that we still
441 -- need. We have a patch for this from Andy Cheadle, but not
442 -- incorporated yet. --SDM [6/2004]
444 -- Profiling needs slop filling (to support LDV profiling), so
445 -- currently eager blackholing doesn't work with profiling.
447 -- Previously, eager blackholing was enabled when ticky-ticky
448 -- was on. But it didn't work, and it wasn't strictly necessary
449 -- to bring back minimal ticky-ticky, so now EAGER_BLACKHOLING
450 -- is unconditionally disabled. -- krc 1/2007
452 eager_blackholing = False
456 setupUpdate :: ClosureInfo -> Code -> Code -- Only called for closures with no args
457 -- Nota Bene: this function does not change Node (even if it's a CAF),
458 -- so that the cost centre in the original closure can still be
459 -- extracted by a subsequent enterCostCentre
460 setupUpdate closure_info code
461 | closureReEntrant closure_info
464 | not (isStaticClosure closure_info)
465 = if closureUpdReqd closure_info
466 then do { tickyPushUpdateFrame; pushUpdateFrame (CmmReg nodeReg) code }
467 else do { tickyUpdateFrameOmitted; code }
469 | otherwise -- A static closure
470 = do { tickyUpdateBhCaf closure_info
472 ; if closureUpdReqd closure_info
473 then do -- Blackhole the (updatable) CAF:
474 { upd_closure <- link_caf closure_info True
475 ; pushUpdateFrame upd_closure code }
477 { -- krc: removed some ticky-related code here.
478 ; tickyUpdateFrameOmitted
483 -----------------------------------------------------------------------------
486 -- When a CAF is first entered, it creates a black hole in the heap,
487 -- and updates itself with an indirection to this new black hole.
489 -- We update the CAF with an indirection to a newly-allocated black
490 -- hole in the heap. We also set the blocking queue on the newly
491 -- allocated black hole to be empty.
493 -- Why do we make a black hole in the heap when we enter a CAF?
495 -- - for a generational garbage collector, which needs a fast
496 -- test for whether an updatee is in an old generation or not
498 -- - for the parallel system, which can implement updates more
499 -- easily if the updatee is always in the heap. (allegedly).
501 -- When debugging, we maintain a separate CAF list so we can tell when
502 -- a CAF has been garbage collected.
504 -- newCAF must be called before the itbl ptr is overwritten, since
505 -- newCAF records the old itbl ptr in order to do CAF reverting
506 -- (which Hugs needs to do in order that combined mode works right.)
509 -- ToDo [Feb 04] This entire link_caf nonsense could all be moved
510 -- into the "newCAF" RTS procedure, which we call anyway, including
511 -- the allocation of the black-hole indirection closure.
512 -- That way, code size would fall, the CAF-handling code would
513 -- be closer together, and the compiler wouldn't need to know
514 -- about off_indirectee etc.
516 link_caf :: ClosureInfo
517 -> Bool -- True <=> updatable, False <=> single-entry
518 -> FCode CmmExpr -- Returns amode for closure to be updated
519 -- To update a CAF we must allocate a black hole, link the CAF onto the
520 -- CAF list, then update the CAF to point to the fresh black hole.
521 -- This function returns the address of the black hole, so it can be
522 -- updated with the new value when available. The reason for all of this
523 -- is that we only want to update dynamic heap objects, not static ones,
524 -- so that generational GC is easier.
525 link_caf cl_info is_upd = do
526 { -- Alloc black hole specifying CC_HDR(Node) as the cost centre
527 ; let use_cc = costCentreFrom (CmmReg nodeReg)
529 ; hp_offset <- allocDynClosure bh_cl_info use_cc blame_cc []
530 ; hp_rel <- getHpRelOffset hp_offset
532 -- Call the RTS function newCAF to add the CAF to the CafList
533 -- so that the garbage collector can find them
534 -- This must be done *before* the info table pointer is overwritten,
535 -- because the old info table ptr is needed for reversion
536 ; emitRtsCallWithVols SLIT("newCAF") [(CmmReg nodeReg,PtrHint)] [node] False
537 -- node is live, so save it.
539 -- Overwrite the closure with a (static) indirection
540 -- to the newly-allocated black hole
541 ; stmtsC [ CmmStore (cmmRegOffW nodeReg off_indirectee) hp_rel
542 , CmmStore (CmmReg nodeReg) ind_static_info ]
546 bh_cl_info :: ClosureInfo
547 bh_cl_info | is_upd = cafBlackHoleClosureInfo cl_info
548 | otherwise = seCafBlackHoleClosureInfo cl_info
550 ind_static_info :: CmmExpr
551 ind_static_info = mkLblExpr mkIndStaticInfoLabel
553 off_indirectee :: WordOff
554 off_indirectee = fixedHdrSize + oFFSET_StgInd_indirectee*wORD_SIZE
558 %************************************************************************
560 \subsection[CgClosure-Description]{Profiling Closure Description.}
562 %************************************************************************
564 For "global" data constructors the description is simply occurrence
565 name of the data constructor itself. Otherwise it is determined by
566 @closureDescription@ from the let binding information.
569 closureDescription :: Module -- Module
570 -> Name -- Id of closure binding
572 -- Not called for StgRhsCon which have global info tables built in
573 -- CgConTbls.lhs with a description generated from the data constructor
574 closureDescription mod_name name
575 = showSDocDump (char '<' <>
576 (if isExternalName name
577 then ppr name -- ppr will include the module name prefix
578 else pprModule mod_name <> char '.' <> ppr name) <>
580 -- showSDocDump, because we want to see the unique on the Name.