Produce new-style Cmm from the Cmm parser
[ghc.git] / rts / sm / Evac.c
1 /* -----------------------------------------------------------------------------
2 *
3 * (c) The GHC Team 1998-2008
4 *
5 * Generational garbage collector: evacuation functions
6 *
7 * Documentation on the architecture of the Garbage Collector can be
8 * found in the online commentary:
9 *
10 * http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
11 *
12 * ---------------------------------------------------------------------------*/
13
14 #include "PosixSource.h"
15 #include "Rts.h"
16
17 #include "Evac.h"
18 #include "Storage.h"
19 #include "GC.h"
20 #include "GCThread.h"
21 #include "GCTDecl.h"
22 #include "GCUtils.h"
23 #include "Compact.h"
24 #include "MarkStack.h"
25 #include "Prelude.h"
26 #include "Trace.h"
27 #include "LdvProfile.h"
28
29 #if defined(PROF_SPIN) && defined(THREADED_RTS) && defined(PARALLEL_GC)
30 StgWord64 whitehole_spin = 0;
31 #endif
32
33 #if defined(THREADED_RTS) && !defined(PARALLEL_GC)
34 #define evacuate(p) evacuate1(p)
35 #define HEAP_ALLOCED_GC(p) HEAP_ALLOCED(p)
36 #endif
37
38 #if !defined(PARALLEL_GC)
39 #define copy_tag_nolock(p, info, src, size, stp, tag) \
40 copy_tag(p, info, src, size, stp, tag)
41 #endif
42
43 /* Used to avoid long recursion due to selector thunks
44 */
45 #define MAX_THUNK_SELECTOR_DEPTH 16
46
47 static void eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool);
48 STATIC_INLINE void evacuate_large(StgPtr p);
49
50 /* -----------------------------------------------------------------------------
51 Allocate some space in which to copy an object.
52 -------------------------------------------------------------------------- */
53
54 STATIC_INLINE StgPtr
55 alloc_for_copy (nat size, nat gen_no)
56 {
57 StgPtr to;
58 gen_workspace *ws;
59
60 /* Find out where we're going, using the handy "to" pointer in
61 * the gen of the source object. If it turns out we need to
62 * evacuate to an older generation, adjust it here (see comment
63 * by evacuate()).
64 */
65 if (gen_no < gct->evac_gen_no) {
66 if (gct->eager_promotion) {
67 gen_no = gct->evac_gen_no;
68 } else {
69 gct->failed_to_evac = rtsTrue;
70 }
71 }
72
73 ws = &gct->gens[gen_no]; // zero memory references here
74
75 /* chain a new block onto the to-space for the destination gen if
76 * necessary.
77 */
78 to = ws->todo_free;
79 ws->todo_free += size;
80 if (ws->todo_free > ws->todo_lim) {
81 to = todo_block_full(size, ws);
82 }
83 ASSERT(ws->todo_free >= ws->todo_bd->free && ws->todo_free <= ws->todo_lim);
84
85 return to;
86 }
87
88 /* -----------------------------------------------------------------------------
89 The evacuate() code
90 -------------------------------------------------------------------------- */
91
92 STATIC_INLINE GNUC_ATTR_HOT void
93 copy_tag(StgClosure **p, const StgInfoTable *info,
94 StgClosure *src, nat size, nat gen_no, StgWord tag)
95 {
96 StgPtr to, from;
97 nat i;
98
99 to = alloc_for_copy(size,gen_no);
100
101 from = (StgPtr)src;
102 to[0] = (W_)info;
103 for (i = 1; i < size; i++) { // unroll for small i
104 to[i] = from[i];
105 }
106
107 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
108 // __builtin_prefetch(to + size + 2, 1);
109 // }
110
111 #if defined(PARALLEL_GC)
112 {
113 const StgInfoTable *new_info;
114 new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, (W_)info, MK_FORWARDING_PTR(to));
115 if (new_info != info) {
116 return evacuate(p); // does the failed_to_evac stuff
117 } else {
118 *p = TAG_CLOSURE(tag,(StgClosure*)to);
119 }
120 }
121 #else
122 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
123 *p = TAG_CLOSURE(tag,(StgClosure*)to);
124 #endif
125
126 #ifdef PROFILING
127 // We store the size of the just evacuated object in the LDV word so that
128 // the profiler can guess the position of the next object later.
129 SET_EVACUAEE_FOR_LDV(from, size);
130 #endif
131 }
132
133 #if defined(PARALLEL_GC)
134 STATIC_INLINE void
135 copy_tag_nolock(StgClosure **p, const StgInfoTable *info,
136 StgClosure *src, nat size, nat gen_no, StgWord tag)
137 {
138 StgPtr to, from;
139 nat i;
140
141 to = alloc_for_copy(size,gen_no);
142
143 from = (StgPtr)src;
144 to[0] = (W_)info;
145 for (i = 1; i < size; i++) { // unroll for small i
146 to[i] = from[i];
147 }
148
149 // if somebody else reads the forwarding pointer, we better make
150 // sure there's a closure at the end of it.
151 write_barrier();
152 *p = TAG_CLOSURE(tag,(StgClosure*)to);
153 src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
154
155 // if (to+size+2 < bd->start + BLOCK_SIZE_W) {
156 // __builtin_prefetch(to + size + 2, 1);
157 // }
158
159 #ifdef PROFILING
160 // We store the size of the just evacuated object in the LDV word so that
161 // the profiler can guess the position of the next object later.
162 SET_EVACUAEE_FOR_LDV(from, size);
163 #endif
164 }
165 #endif
166
167 /* Special version of copy() for when we only want to copy the info
168 * pointer of an object, but reserve some padding after it. This is
169 * used to optimise evacuation of TSOs.
170 */
171 static rtsBool
172 copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve,
173 nat size_to_copy, nat gen_no)
174 {
175 StgPtr to, from;
176 nat i;
177 StgWord info;
178
179 #if defined(PARALLEL_GC)
180 spin:
181 info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
182 if (info == (W_)&stg_WHITEHOLE_info) {
183 #ifdef PROF_SPIN
184 whitehole_spin++;
185 #endif
186 goto spin;
187 }
188 if (IS_FORWARDING_PTR(info)) {
189 src->header.info = (const StgInfoTable *)info;
190 evacuate(p); // does the failed_to_evac stuff
191 return rtsFalse;
192 }
193 #else
194 info = (W_)src->header.info;
195 #endif
196
197 to = alloc_for_copy(size_to_reserve, gen_no);
198
199 from = (StgPtr)src;
200 to[0] = info;
201 for (i = 1; i < size_to_copy; i++) { // unroll for small i
202 to[i] = from[i];
203 }
204
205 write_barrier();
206 src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(to);
207 *p = (StgClosure *)to;
208
209 #ifdef PROFILING
210 // We store the size of the just evacuated object in the LDV word so that
211 // the profiler can guess the position of the next object later.
212 SET_EVACUAEE_FOR_LDV(from, size_to_reserve);
213 // fill the slop
214 if (size_to_reserve - size_to_copy > 0)
215 LDV_FILL_SLOP(to + size_to_copy, (int)(size_to_reserve - size_to_copy));
216 #endif
217
218 return rtsTrue;
219 }
220
221
222 /* Copy wrappers that don't tag the closure after copying */
223 STATIC_INLINE GNUC_ATTR_HOT void
224 copy(StgClosure **p, const StgInfoTable *info,
225 StgClosure *src, nat size, nat gen_no)
226 {
227 copy_tag(p,info,src,size,gen_no,0);
228 }
229
230 /* -----------------------------------------------------------------------------
231 Evacuate a large object
232
233 This just consists of removing the object from the (doubly-linked)
234 gen->large_objects list, and linking it on to the (singly-linked)
235 gen->new_large_objects list, from where it will be scavenged later.
236
237 Convention: bd->flags has BF_EVACUATED set for a large object
238 that has been evacuated, or unset otherwise.
239 -------------------------------------------------------------------------- */
240
241 STATIC_INLINE void
242 evacuate_large(StgPtr p)
243 {
244 bdescr *bd;
245 generation *gen, *new_gen;
246 nat gen_no, new_gen_no;
247 gen_workspace *ws;
248
249 bd = Bdescr(p);
250 gen = bd->gen;
251 gen_no = bd->gen_no;
252 ACQUIRE_SPIN_LOCK(&gen->sync);
253
254 // already evacuated?
255 if (bd->flags & BF_EVACUATED) {
256 /* Don't forget to set the gct->failed_to_evac flag if we didn't get
257 * the desired destination (see comments in evacuate()).
258 */
259 if (gen_no < gct->evac_gen_no) {
260 gct->failed_to_evac = rtsTrue;
261 TICK_GC_FAILED_PROMOTION();
262 }
263 RELEASE_SPIN_LOCK(&gen->sync);
264 return;
265 }
266
267 // remove from large_object list
268 if (bd->u.back) {
269 bd->u.back->link = bd->link;
270 } else { // first object in the list
271 gen->large_objects = bd->link;
272 }
273 if (bd->link) {
274 bd->link->u.back = bd->u.back;
275 }
276
277 /* link it on to the evacuated large object list of the destination gen
278 */
279 new_gen_no = bd->dest_no;
280
281 if (new_gen_no < gct->evac_gen_no) {
282 if (gct->eager_promotion) {
283 new_gen_no = gct->evac_gen_no;
284 } else {
285 gct->failed_to_evac = rtsTrue;
286 }
287 }
288
289 ws = &gct->gens[new_gen_no];
290 new_gen = &generations[new_gen_no];
291
292 bd->flags |= BF_EVACUATED;
293 initBdescr(bd, new_gen, new_gen->to);
294
295 // If this is a block of pinned objects, we don't have to scan
296 // these objects, because they aren't allowed to contain any
297 // pointers. For these blocks, we skip the scavenge stage and put
298 // them straight on the scavenged_large_objects list.
299 if (bd->flags & BF_PINNED) {
300 ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS);
301 if (new_gen != gen) { ACQUIRE_SPIN_LOCK(&new_gen->sync); }
302 dbl_link_onto(bd, &new_gen->scavenged_large_objects);
303 new_gen->n_scavenged_large_blocks += bd->blocks;
304 if (new_gen != gen) { RELEASE_SPIN_LOCK(&new_gen->sync); }
305 } else {
306 bd->link = ws->todo_large_objects;
307 ws->todo_large_objects = bd;
308 }
309
310 RELEASE_SPIN_LOCK(&gen->sync);
311 }
312
313 /* ----------------------------------------------------------------------------
314 Evacuate
315
316 This is called (eventually) for every live object in the system.
317
318 The caller to evacuate specifies a desired generation in the
319 gct->evac_gen thread-local variable. The following conditions apply to
320 evacuating an object which resides in generation M when we're
321 collecting up to generation N
322
323 if M >= gct->evac_gen
324 if M > N do nothing
325 else evac to gen->to
326
327 if M < gct->evac_gen evac to gct->evac_gen, step 0
328
329 if the object is already evacuated, then we check which generation
330 it now resides in.
331
332 if M >= gct->evac_gen do nothing
333 if M < gct->evac_gen set gct->failed_to_evac flag to indicate that we
334 didn't manage to evacuate this object into gct->evac_gen.
335
336
337 OPTIMISATION NOTES:
338
339 evacuate() is the single most important function performance-wise
340 in the GC. Various things have been tried to speed it up, but as
341 far as I can tell the code generated by gcc 3.2 with -O2 is about
342 as good as it's going to get. We pass the argument to evacuate()
343 in a register using the 'regparm' attribute (see the prototype for
344 evacuate() near the top of this file).
345
346 Changing evacuate() to take an (StgClosure **) rather than
347 returning the new pointer seems attractive, because we can avoid
348 writing back the pointer when it hasn't changed (eg. for a static
349 object, or an object in a generation > N). However, I tried it and
350 it doesn't help. One reason is that the (StgClosure **) pointer
351 gets spilled to the stack inside evacuate(), resulting in far more
352 extra reads/writes than we save.
353 ------------------------------------------------------------------------- */
354
355 REGPARM1 GNUC_ATTR_HOT void
356 evacuate(StgClosure **p)
357 {
358 bdescr *bd = NULL;
359 nat gen_no;
360 StgClosure *q;
361 const StgInfoTable *info;
362 StgWord tag;
363
364 q = *p;
365
366 loop:
367 /* The tag and the pointer are split, to be merged after evacing */
368 tag = GET_CLOSURE_TAG(q);
369 q = UNTAG_CLOSURE(q);
370
371 ASSERTM(LOOKS_LIKE_CLOSURE_PTR(q), "invalid closure, info=%p", q->header.info);
372
373 if (!HEAP_ALLOCED_GC(q)) {
374
375 if (!major_gc) return;
376
377 info = get_itbl(q);
378 switch (info->type) {
379
380 case THUNK_STATIC:
381 if (info->srt_bitmap != 0) {
382 if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
383 #ifndef THREADED_RTS
384 *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
385 gct->static_objects = (StgClosure *)q;
386 #else
387 StgPtr link;
388 link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
389 (StgWord)NULL,
390 (StgWord)gct->static_objects);
391 if (link == NULL) {
392 gct->static_objects = (StgClosure *)q;
393 }
394 #endif
395 }
396 }
397 return;
398
399 case FUN_STATIC:
400 if (info->srt_bitmap != 0 &&
401 *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
402 #ifndef THREADED_RTS
403 *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
404 gct->static_objects = (StgClosure *)q;
405 #else
406 StgPtr link;
407 link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
408 (StgWord)NULL,
409 (StgWord)gct->static_objects);
410 if (link == NULL) {
411 gct->static_objects = (StgClosure *)q;
412 }
413 #endif
414 }
415 return;
416
417 case IND_STATIC:
418 /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
419 * on the CAF list, so don't do anything with it here (we'll
420 * scavenge it later).
421 */
422 if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
423 #ifndef THREADED_RTS
424 *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
425 gct->static_objects = (StgClosure *)q;
426 #else
427 StgPtr link;
428 link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
429 (StgWord)NULL,
430 (StgWord)gct->static_objects);
431 if (link == NULL) {
432 gct->static_objects = (StgClosure *)q;
433 }
434 #endif
435 }
436 return;
437
438 case CONSTR_STATIC:
439 if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
440 #ifndef THREADED_RTS
441 *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
442 gct->static_objects = (StgClosure *)q;
443 #else
444 StgPtr link;
445 link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
446 (StgWord)NULL,
447 (StgWord)gct->static_objects);
448 if (link == NULL) {
449 gct->static_objects = (StgClosure *)q;
450 }
451 #endif
452 }
453 /* I am assuming that static_objects pointers are not
454 * written to other objects, and thus, no need to retag. */
455 return;
456
457 case CONSTR_NOCAF_STATIC:
458 /* no need to put these on the static linked list, they don't need
459 * to be scavenged.
460 */
461 return;
462
463 default:
464 barf("evacuate(static): strange closure type %d", (int)(info->type));
465 }
466 }
467
468 bd = Bdescr((P_)q);
469
470 if ((bd->flags & (BF_LARGE | BF_MARKED | BF_EVACUATED)) != 0) {
471
472 // pointer into to-space: just return it. It might be a pointer
473 // into a generation that we aren't collecting (> N), or it
474 // might just be a pointer into to-space. The latter doesn't
475 // happen often, but allowing it makes certain things a bit
476 // easier; e.g. scavenging an object is idempotent, so it's OK to
477 // have an object on the mutable list multiple times.
478 if (bd->flags & BF_EVACUATED) {
479 // We aren't copying this object, so we have to check
480 // whether it is already in the target generation. (this is
481 // the write barrier).
482 if (bd->gen_no < gct->evac_gen_no) {
483 gct->failed_to_evac = rtsTrue;
484 TICK_GC_FAILED_PROMOTION();
485 }
486 return;
487 }
488
489 /* evacuate large objects by re-linking them onto a different list.
490 */
491 if (bd->flags & BF_LARGE) {
492 evacuate_large((P_)q);
493 return;
494 }
495
496 /* If the object is in a gen that we're compacting, then we
497 * need to use an alternative evacuate procedure.
498 */
499 if (!is_marked((P_)q,bd)) {
500 mark((P_)q,bd);
501 push_mark_stack((P_)q);
502 }
503 return;
504 }
505
506 gen_no = bd->dest_no;
507
508 info = q->header.info;
509 if (IS_FORWARDING_PTR(info))
510 {
511 /* Already evacuated, just return the forwarding address.
512 * HOWEVER: if the requested destination generation (gct->evac_gen) is
513 * older than the actual generation (because the object was
514 * already evacuated to a younger generation) then we have to
515 * set the gct->failed_to_evac flag to indicate that we couldn't
516 * manage to promote the object to the desired generation.
517 */
518 /*
519 * Optimisation: the check is fairly expensive, but we can often
520 * shortcut it if either the required generation is 0, or the
521 * current object (the EVACUATED) is in a high enough generation.
522 * We know that an EVACUATED always points to an object in the
523 * same or an older generation. gen is the lowest generation that the
524 * current object would be evacuated to, so we only do the full
525 * check if gen is too low.
526 */
527 StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
528 *p = TAG_CLOSURE(tag,e);
529 if (gen_no < gct->evac_gen_no) { // optimisation
530 if (Bdescr((P_)e)->gen_no < gct->evac_gen_no) {
531 gct->failed_to_evac = rtsTrue;
532 TICK_GC_FAILED_PROMOTION();
533 }
534 }
535 return;
536 }
537
538 switch (INFO_PTR_TO_STRUCT(info)->type) {
539
540 case WHITEHOLE:
541 goto loop;
542
543 case MUT_VAR_CLEAN:
544 case MUT_VAR_DIRTY:
545 case MVAR_CLEAN:
546 case MVAR_DIRTY:
547 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no);
548 return;
549
550 // For ints and chars of low value, save space by replacing references to
551 // these with closures with references to common, shared ones in the RTS.
552 //
553 // * Except when compiling into Windows DLLs which don't support cross-package
554 // data references very well.
555 //
556 case CONSTR_0_1:
557 {
558 #if defined(COMPILING_WINDOWS_DLL)
559 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen_no,tag);
560 #else
561 StgWord w = (StgWord)q->payload[0];
562 if (info == Czh_con_info &&
563 // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
564 (StgChar)w <= MAX_CHARLIKE) {
565 *p = TAG_CLOSURE(tag,
566 (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
567 );
568 }
569 else if (info == Izh_con_info &&
570 (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
571 *p = TAG_CLOSURE(tag,
572 (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
573 );
574 }
575 else {
576 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen_no,tag);
577 }
578 #endif
579 return;
580 }
581
582 case FUN_0_1:
583 case FUN_1_0:
584 case CONSTR_1_0:
585 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen_no,tag);
586 return;
587
588 case THUNK_1_0:
589 case THUNK_0_1:
590 copy(p,info,q,sizeofW(StgThunk)+1,gen_no);
591 return;
592
593 case THUNK_1_1:
594 case THUNK_2_0:
595 case THUNK_0_2:
596 #ifdef NO_PROMOTE_THUNKS
597 #error bitrotted
598 #endif
599 copy(p,info,q,sizeofW(StgThunk)+2,gen_no);
600 return;
601
602 case FUN_1_1:
603 case FUN_2_0:
604 case FUN_0_2:
605 case CONSTR_1_1:
606 case CONSTR_2_0:
607 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,gen_no,tag);
608 return;
609
610 case CONSTR_0_2:
611 copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,gen_no,tag);
612 return;
613
614 case THUNK:
615 copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no);
616 return;
617
618 case FUN:
619 case IND_PERM:
620 case CONSTR:
621 copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no,tag);
622 return;
623
624 case BLACKHOLE:
625 {
626 StgClosure *r;
627 const StgInfoTable *i;
628 r = ((StgInd*)q)->indirectee;
629 if (GET_CLOSURE_TAG(r) == 0) {
630 i = r->header.info;
631 if (IS_FORWARDING_PTR(i)) {
632 r = (StgClosure *)UN_FORWARDING_PTR(i);
633 i = r->header.info;
634 }
635 if (i == &stg_TSO_info
636 || i == &stg_WHITEHOLE_info
637 || i == &stg_BLOCKING_QUEUE_CLEAN_info
638 || i == &stg_BLOCKING_QUEUE_DIRTY_info) {
639 copy(p,info,q,sizeofW(StgInd),gen_no);
640 return;
641 }
642 ASSERT(i != &stg_IND_info);
643 }
644 q = r;
645 *p = r;
646 goto loop;
647 }
648
649 case BLOCKING_QUEUE:
650 case WEAK:
651 case PRIM:
652 case MUT_PRIM:
653 copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no);
654 return;
655
656 case BCO:
657 copy(p,info,q,bco_sizeW((StgBCO *)q),gen_no);
658 return;
659
660 case THUNK_SELECTOR:
661 eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
662 return;
663
664 case IND:
665 // follow chains of indirections, don't evacuate them
666 q = ((StgInd*)q)->indirectee;
667 *p = q;
668 goto loop;
669
670 case RET_BCO:
671 case RET_SMALL:
672 case RET_BIG:
673 case UPDATE_FRAME:
674 case UNDERFLOW_FRAME:
675 case STOP_FRAME:
676 case CATCH_FRAME:
677 case CATCH_STM_FRAME:
678 case CATCH_RETRY_FRAME:
679 case ATOMICALLY_FRAME:
680 // shouldn't see these
681 barf("evacuate: stack frame at %p\n", q);
682
683 case PAP:
684 copy(p,info,q,pap_sizeW((StgPAP*)q),gen_no);
685 return;
686
687 case AP:
688 copy(p,info,q,ap_sizeW((StgAP*)q),gen_no);
689 return;
690
691 case AP_STACK:
692 copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),gen_no);
693 return;
694
695 case ARR_WORDS:
696 // just copy the block
697 copy(p,info,q,arr_words_sizeW((StgArrWords *)q),gen_no);
698 return;
699
700 case MUT_ARR_PTRS_CLEAN:
701 case MUT_ARR_PTRS_DIRTY:
702 case MUT_ARR_PTRS_FROZEN:
703 case MUT_ARR_PTRS_FROZEN0:
704 // just copy the block
705 copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),gen_no);
706 return;
707
708 case TSO:
709 copy(p,info,q,sizeofW(StgTSO),gen_no);
710 return;
711
712 case STACK:
713 {
714 StgStack *stack = (StgStack *)q;
715
716 /* To evacuate a small STACK, we need to adjust the stack pointer
717 */
718 {
719 StgStack *new_stack;
720 StgPtr r, s;
721 rtsBool mine;
722
723 mine = copyPart(p,(StgClosure *)stack, stack_sizeW(stack),
724 sizeofW(StgStack), gen_no);
725 if (mine) {
726 new_stack = (StgStack *)*p;
727 move_STACK(stack, new_stack);
728 for (r = stack->sp, s = new_stack->sp;
729 r < stack->stack + stack->stack_size;) {
730 *s++ = *r++;
731 }
732 }
733 return;
734 }
735 }
736
737 case TREC_CHUNK:
738 copy(p,info,q,sizeofW(StgTRecChunk),gen_no);
739 return;
740
741 default:
742 barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
743 }
744
745 barf("evacuate");
746 }
747
748 /* -----------------------------------------------------------------------------
749 Evaluate a THUNK_SELECTOR if possible.
750
751 p points to a THUNK_SELECTOR that we want to evaluate. The
752 result of "evaluating" it will be evacuated and a pointer to the
753 to-space closure will be returned.
754
755 If the THUNK_SELECTOR could not be evaluated (its selectee is still
756 a THUNK, for example), then the THUNK_SELECTOR itself will be
757 evacuated.
758 -------------------------------------------------------------------------- */
759 static void
760 unchain_thunk_selectors(StgSelector *p, StgClosure *val)
761 {
762 StgSelector *prev;
763
764 prev = NULL;
765 while (p)
766 {
767 ASSERT(p->header.info == &stg_WHITEHOLE_info);
768 // val must be in to-space. Not always: when we recursively
769 // invoke eval_thunk_selector(), the recursive calls will not
770 // evacuate the value (because we want to select on the value,
771 // not evacuate it), so in this case val is in from-space.
772 // ASSERT(!HEAP_ALLOCED_GC(val) || Bdescr((P_)val)->gen_no > N || (Bdescr((P_)val)->flags & BF_EVACUATED));
773
774 prev = (StgSelector*)((StgClosure *)p)->payload[0];
775
776 // Update the THUNK_SELECTOR with an indirection to the
777 // value. The value is still in from-space at this stage.
778 //
779 // (old note: Why not do upd_evacuee(q,p)? Because we have an
780 // invariant that an EVACUATED closure always points to an
781 // object in the same or an older generation (required by
782 // the short-cut test in the EVACUATED case, below).
783 if ((StgClosure *)p == val) {
784 // must be a loop; just leave a BLACKHOLE in place. This
785 // can happen when we have a chain of selectors that
786 // eventually loops back on itself. We can't leave an
787 // indirection pointing to itself, and we want the program
788 // to deadlock if it ever enters this closure, so
789 // BLACKHOLE is correct.
790
791 // XXX we do not have BLACKHOLEs any more; replace with
792 // a THUNK_SELECTOR again. This will go into a loop if it is
793 // entered, and should result in a NonTermination exception.
794 ((StgThunk *)p)->payload[0] = val;
795 write_barrier();
796 SET_INFO((StgClosure *)p, &stg_sel_0_upd_info);
797 } else {
798 ((StgInd *)p)->indirectee = val;
799 write_barrier();
800 SET_INFO((StgClosure *)p, &stg_IND_info);
801 }
802
803 // For the purposes of LDV profiling, we have created an
804 // indirection.
805 LDV_RECORD_CREATE(p);
806
807 p = prev;
808 }
809 }
810
811 static void
812 eval_thunk_selector (StgClosure **q, StgSelector * p, rtsBool evac)
813 // NB. for legacy reasons, p & q are swapped around :(
814 {
815 nat field;
816 StgInfoTable *info;
817 StgWord info_ptr;
818 StgClosure *selectee;
819 StgSelector *prev_thunk_selector;
820 bdescr *bd;
821 StgClosure *val;
822
823 prev_thunk_selector = NULL;
824 // this is a chain of THUNK_SELECTORs that we are going to update
825 // to point to the value of the current THUNK_SELECTOR. Each
826 // closure on the chain is a WHITEHOLE, and points to the next in the
827 // chain with payload[0].
828
829 selector_chain:
830
831 bd = Bdescr((StgPtr)p);
832 if (HEAP_ALLOCED_GC(p)) {
833 // If the THUNK_SELECTOR is in to-space or in a generation that we
834 // are not collecting, then bale out early. We won't be able to
835 // save any space in any case, and updating with an indirection is
836 // trickier in a non-collected gen: we would have to update the
837 // mutable list.
838 if (bd->flags & BF_EVACUATED) {
839 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
840 *q = (StgClosure *)p;
841 // shortcut, behave as for: if (evac) evacuate(q);
842 if (evac && bd->gen_no < gct->evac_gen_no) {
843 gct->failed_to_evac = rtsTrue;
844 TICK_GC_FAILED_PROMOTION();
845 }
846 return;
847 }
848 // we don't update THUNK_SELECTORS in the compacted
849 // generation, because compaction does not remove the INDs
850 // that result, this causes confusion later
851 // (scavenge_mark_stack doesn't deal with IND). BEWARE! This
852 // bit is very tricky to get right. If you make changes
853 // around here, test by compiling stage 3 with +RTS -c -RTS.
854 if (bd->flags & BF_MARKED) {
855 // must call evacuate() to mark this closure if evac==rtsTrue
856 *q = (StgClosure *)p;
857 if (evac) evacuate(q);
858 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
859 return;
860 }
861 }
862
863
864 // WHITEHOLE the selector thunk, since it is now under evaluation.
865 // This is important to stop us going into an infinite loop if
866 // this selector thunk eventually refers to itself.
867 #if defined(THREADED_RTS)
868 // In threaded mode, we'll use WHITEHOLE to lock the selector
869 // thunk while we evaluate it.
870 {
871 do {
872 info_ptr = xchg((StgPtr)&p->header.info, (W_)&stg_WHITEHOLE_info);
873 } while (info_ptr == (W_)&stg_WHITEHOLE_info);
874
875 // make sure someone else didn't get here first...
876 if (IS_FORWARDING_PTR(info_ptr) ||
877 INFO_PTR_TO_STRUCT((StgInfoTable *)info_ptr)->type != THUNK_SELECTOR) {
878 // v. tricky now. The THUNK_SELECTOR has been evacuated
879 // by another thread, and is now either a forwarding ptr or IND.
880 // We need to extract ourselves from the current situation
881 // as cleanly as possible.
882 // - unlock the closure
883 // - update *q, we may have done *some* evaluation
884 // - if evac, we need to call evacuate(), because we
885 // need the write-barrier stuff.
886 // - undo the chain we've built to point to p.
887 SET_INFO((StgClosure *)p, (const StgInfoTable *)info_ptr);
888 *q = (StgClosure *)p;
889 if (evac) evacuate(q);
890 unchain_thunk_selectors(prev_thunk_selector, (StgClosure *)p);
891 return;
892 }
893 }
894 #else
895 // Save the real info pointer (NOTE: not the same as get_itbl()).
896 info_ptr = (StgWord)p->header.info;
897 SET_INFO((StgClosure *)p,&stg_WHITEHOLE_info);
898 #endif
899
900 field = INFO_PTR_TO_STRUCT((StgInfoTable *)info_ptr)->layout.selector_offset;
901
902 // The selectee might be a constructor closure,
903 // so we untag the pointer.
904 selectee = UNTAG_CLOSURE(p->selectee);
905
906 selector_loop:
907 // selectee now points to the closure that we're trying to select
908 // a field from. It may or may not be in to-space: we try not to
909 // end up in to-space, but it's impractical to avoid it in
910 // general. The compacting GC scatters to-space pointers in
911 // from-space during marking, for example. We rely on the property
912 // that evacuate() doesn't mind if it gets passed a to-space pointer.
913
914 info = (StgInfoTable*)selectee->header.info;
915
916 if (IS_FORWARDING_PTR(info)) {
917 // We don't follow pointers into to-space; the constructor
918 // has already been evacuated, so we won't save any space
919 // leaks by evaluating this selector thunk anyhow.
920 goto bale_out;
921 }
922
923 info = INFO_PTR_TO_STRUCT(info);
924 switch (info->type) {
925 case WHITEHOLE:
926 goto bale_out; // about to be evacuated by another thread (or a loop).
927
928 case CONSTR:
929 case CONSTR_1_0:
930 case CONSTR_0_1:
931 case CONSTR_2_0:
932 case CONSTR_1_1:
933 case CONSTR_0_2:
934 case CONSTR_STATIC:
935 case CONSTR_NOCAF_STATIC:
936 {
937 // check that the size is in range
938 ASSERT(field < (StgWord32)(info->layout.payload.ptrs +
939 info->layout.payload.nptrs));
940
941 // Select the right field from the constructor
942 val = selectee->payload[field];
943
944 #ifdef PROFILING
945 // For the purposes of LDV profiling, we have destroyed
946 // the original selector thunk, p.
947 SET_INFO((StgClosure*)p, (StgInfoTable *)info_ptr);
948 OVERWRITING_CLOSURE((StgClosure*)p);
949 SET_INFO((StgClosure*)p, &stg_WHITEHOLE_info);
950 #endif
951
952 // the closure in val is now the "value" of the
953 // THUNK_SELECTOR in p. However, val may itself be a
954 // THUNK_SELECTOR, in which case we want to continue
955 // evaluating until we find the real value, and then
956 // update the whole chain to point to the value.
957 val_loop:
958 info_ptr = (StgWord)UNTAG_CLOSURE(val)->header.info;
959 if (!IS_FORWARDING_PTR(info_ptr))
960 {
961 info = INFO_PTR_TO_STRUCT((StgInfoTable *)info_ptr);
962 switch (info->type) {
963 case IND:
964 case IND_PERM:
965 case IND_STATIC:
966 val = ((StgInd *)val)->indirectee;
967 goto val_loop;
968 case THUNK_SELECTOR:
969 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
970 prev_thunk_selector = p;
971 p = (StgSelector*)val;
972 goto selector_chain;
973 default:
974 break;
975 }
976 }
977 ((StgClosure*)p)->payload[0] = (StgClosure *)prev_thunk_selector;
978 prev_thunk_selector = p;
979
980 *q = val;
981
982 // update the other selectors in the chain *before*
983 // evacuating the value. This is necessary in the case
984 // where the value turns out to be one of the selectors
985 // in the chain (i.e. we have a loop), and evacuating it
986 // would corrupt the chain.
987 unchain_thunk_selectors(prev_thunk_selector, val);
988
989 // evacuate() cannot recurse through
990 // eval_thunk_selector(), because we know val is not
991 // a THUNK_SELECTOR.
992 if (evac) evacuate(q);
993 return;
994 }
995
996 case IND:
997 case IND_PERM:
998 case IND_STATIC:
999 // Again, we might need to untag a constructor.
1000 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
1001 goto selector_loop;
1002
1003 case BLACKHOLE:
1004 {
1005 StgClosure *r;
1006 const StgInfoTable *i;
1007 r = ((StgInd*)selectee)->indirectee;
1008
1009 // establish whether this BH has been updated, and is now an
1010 // indirection, as in evacuate().
1011 if (GET_CLOSURE_TAG(r) == 0) {
1012 i = r->header.info;
1013 if (IS_FORWARDING_PTR(i)) {
1014 r = (StgClosure *)UN_FORWARDING_PTR(i);
1015 i = r->header.info;
1016 }
1017 if (i == &stg_TSO_info
1018 || i == &stg_WHITEHOLE_info
1019 || i == &stg_BLOCKING_QUEUE_CLEAN_info
1020 || i == &stg_BLOCKING_QUEUE_DIRTY_info) {
1021 goto bale_out;
1022 }
1023 ASSERT(i != &stg_IND_info);
1024 }
1025
1026 selectee = UNTAG_CLOSURE( ((StgInd *)selectee)->indirectee );
1027 goto selector_loop;
1028 }
1029
1030 case THUNK_SELECTOR:
1031 {
1032 StgClosure *val;
1033
1034 // recursively evaluate this selector. We don't want to
1035 // recurse indefinitely, so we impose a depth bound.
1036 if (gct->thunk_selector_depth >= MAX_THUNK_SELECTOR_DEPTH) {
1037 goto bale_out;
1038 }
1039
1040 gct->thunk_selector_depth++;
1041 // rtsFalse says "don't evacuate the result". It will,
1042 // however, update any THUNK_SELECTORs that are evaluated
1043 // along the way.
1044 eval_thunk_selector(&val, (StgSelector*)selectee, rtsFalse);
1045 gct->thunk_selector_depth--;
1046
1047 // did we actually manage to evaluate it?
1048 if (val == selectee) goto bale_out;
1049
1050 // Of course this pointer might be tagged...
1051 selectee = UNTAG_CLOSURE(val);
1052 goto selector_loop;
1053 }
1054
1055 case AP:
1056 case AP_STACK:
1057 case THUNK:
1058 case THUNK_1_0:
1059 case THUNK_0_1:
1060 case THUNK_2_0:
1061 case THUNK_1_1:
1062 case THUNK_0_2:
1063 case THUNK_STATIC:
1064 // not evaluated yet
1065 goto bale_out;
1066
1067 default:
1068 barf("eval_thunk_selector: strange selectee %d",
1069 (int)(info->type));
1070 }
1071
1072 bale_out:
1073 // We didn't manage to evaluate this thunk; restore the old info
1074 // pointer. But don't forget: we still need to evacuate the thunk itself.
1075 SET_INFO((StgClosure *)p, (const StgInfoTable *)info_ptr);
1076 // THREADED_RTS: we just unlocked the thunk, so another thread
1077 // might get in and update it. copy() will lock it again and
1078 // check whether it was updated in the meantime.
1079 *q = (StgClosure *)p;
1080 if (evac) {
1081 copy(q,(const StgInfoTable *)info_ptr,(StgClosure *)p,THUNK_SELECTOR_sizeW(),bd->dest_no);
1082 }
1083 unchain_thunk_selectors(prev_thunk_selector, *q);
1084 return;
1085 }