-/* -----------------------------------------------------------------------*-c-*-
- *
- * (c) The GHC Team 1998-2008
- *
- * Generational garbage collector: evacuation functions
- *
- * ---------------------------------------------------------------------------*/
-
-// We have two versions of evacuate(): one for minor GC, and one for
-// non-minor, parallel, GC. This file contains the code for both,
-// controllled by the CPP symbol MINOR_GC.
-
-#if defined(THREADED_RTS)
-# if !defined(PARALLEL_GC)
-# define copy(a,b,c,d,e) copy1(a,b,c,d,e)
-# define copy_tag(a,b,c,d,e,f) copy_tag1(a,b,c,d,e,f)
-# define copy_tag_nolock(a,b,c,d,e,f) copy_tag1(a,b,c,d,e,f)
-# define copyPart(a,b,c,d,e) copyPart1(a,b,c,d,e)
-# define evacuate(a) evacuate1(a)
-# endif
-#else
-# define copy_tag_nolock(a,b,c,d,e,f) copy_tag(a,b,c,d,e,f)
-#endif
-
-STATIC_INLINE void
-copy_tag(StgClosure **p, const StgInfoTable *info,
- StgClosure *src, nat size, step *stp, StgWord tag)
-{
- StgPtr to, from;
- nat i;
-
- to = alloc_for_copy(size,stp);
-
- TICK_GC_WORDS_COPIED(size);
-
- from = (StgPtr)src;
- to[0] = (W_)info;
- for (i = 1; i < size; i++) { // unroll for small i
- to[i] = from[i];
- }
-
-// if (to+size+2 < bd->start + BLOCK_SIZE_W) {
-// __builtin_prefetch(to + size + 2, 1);
-// }
-
-#if defined(PARALLEL_GC)
- {
- const StgInfoTable *new_info;
- new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, (W_)info, MK_FORWARDING_PTR(to));
- if (new_info != info) {
- return evacuate(p); // does the failed_to_evac stuff
- } else {
- *p = TAG_CLOSURE(tag,(StgClosure*)to);
- }
- }
-#else
- src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
- *p = TAG_CLOSURE(tag,(StgClosure*)to);
-#endif
-
-#ifdef PROFILING
- // We store the size of the just evacuated object in the LDV word so that
- // the profiler can guess the position of the next object later.
- SET_EVACUAEE_FOR_LDV(from, size);
-#endif
-}
-
-#if defined(PARALLEL_GC)
-STATIC_INLINE void
-copy_tag_nolock(StgClosure **p, const StgInfoTable *info,
- StgClosure *src, nat size, step *stp, StgWord tag)
-{
- StgPtr to, from;
- nat i;
-
- to = alloc_for_copy(size,stp);
- *p = TAG_CLOSURE(tag,(StgClosure*)to);
- src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
-
- TICK_GC_WORDS_COPIED(size);
-
- from = (StgPtr)src;
- to[0] = (W_)info;
- for (i = 1; i < size; i++) { // unroll for small i
- to[i] = from[i];
- }
-
-// if (to+size+2 < bd->start + BLOCK_SIZE_W) {
-// __builtin_prefetch(to + size + 2, 1);
-// }
-
-#ifdef PROFILING
- // We store the size of the just evacuated object in the LDV word so that
- // the profiler can guess the position of the next object later.
- SET_EVACUAEE_FOR_LDV(from, size);
-#endif
-}
-#endif
-
-/* Special version of copy() for when we only want to copy the info
- * pointer of an object, but reserve some padding after it. This is
- * used to optimise evacuation of BLACKHOLEs.
- */
-static void
-copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp)
-{
- StgPtr to, from;
- nat i;
- StgWord info;
-
-#if defined(PARALLEL_GC)
-spin:
- info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
- if (info == (W_)&stg_WHITEHOLE_info) {
-#ifdef PROF_SPIN
- whitehole_spin++;
-#endif
- goto spin;
- }
- if (IS_FORWARDING_PTR(info)) {
- src->header.info = (const StgInfoTable *)info;
- evacuate(p); // does the failed_to_evac stuff
- return ;
- }
-#else
- info = (W_)src->header.info;
-#endif
-
- to = alloc_for_copy(size_to_reserve, stp);
- *p = (StgClosure *)to;
-
- TICK_GC_WORDS_COPIED(size_to_copy);
-
- from = (StgPtr)src;
- to[0] = info;
- for (i = 1; i < size_to_copy; i++) { // unroll for small i
- to[i] = from[i];
- }
-
-#if defined(PARALLEL_GC)
- write_barrier();
-#endif
- src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(to);
-
-#ifdef PROFILING
- // We store the size of the just evacuated object in the LDV word so that
- // the profiler can guess the position of the next object later.
- SET_EVACUAEE_FOR_LDV(from, size_to_reserve);
- // fill the slop
- if (size_to_reserve - size_to_copy > 0)
- LDV_FILL_SLOP(to + size_to_copy - 1, (int)(size_to_reserve - size_to_copy));
-#endif
-}
-
-
-/* Copy wrappers that don't tag the closure after copying */
-STATIC_INLINE void
-copy(StgClosure **p, const StgInfoTable *info,
- StgClosure *src, nat size, step *stp)
-{
- copy_tag(p,info,src,size,stp,0);
-}
-
-/* ----------------------------------------------------------------------------
- Evacuate
-
- This is called (eventually) for every live object in the system.
-
- The caller to evacuate specifies a desired generation in the
- gct->evac_step thread-local variable. The following conditions apply to
- evacuating an object which resides in generation M when we're
- collecting up to generation N
-
- if M >= gct->evac_step
- if M > N do nothing
- else evac to step->to
-
- if M < gct->evac_step evac to gct->evac_step, step 0
-
- if the object is already evacuated, then we check which generation
- it now resides in.
-
- if M >= gct->evac_step do nothing
- if M < gct->evac_step set gct->failed_to_evac flag to indicate that we
- didn't manage to evacuate this object into gct->evac_step.
-
-
- OPTIMISATION NOTES:
-
- evacuate() is the single most important function performance-wise
- in the GC. Various things have been tried to speed it up, but as
- far as I can tell the code generated by gcc 3.2 with -O2 is about
- as good as it's going to get. We pass the argument to evacuate()
- in a register using the 'regparm' attribute (see the prototype for
- evacuate() near the top of this file).
-
- Changing evacuate() to take an (StgClosure **) rather than
- returning the new pointer seems attractive, because we can avoid
- writing back the pointer when it hasn't changed (eg. for a static
- object, or an object in a generation > N). However, I tried it and
- it doesn't help. One reason is that the (StgClosure **) pointer
- gets spilled to the stack inside evacuate(), resulting in far more
- extra reads/writes than we save.
- ------------------------------------------------------------------------- */
-
-REGPARM1 void
-evacuate(StgClosure **p)
-{
- bdescr *bd = NULL;
- step *stp;
- StgClosure *q;
- const StgInfoTable *info;
- StgWord tag;
-
- q = *p;
-
-loop:
- /* The tag and the pointer are split, to be merged after evacing */
- tag = GET_CLOSURE_TAG(q);
- q = UNTAG_CLOSURE(q);
-
- ASSERT(LOOKS_LIKE_CLOSURE_PTR(q));
-
- if (!HEAP_ALLOCED(q)) {
-
- if (!major_gc) return;
-
- info = get_itbl(q);
- switch (info->type) {
-
- case THUNK_STATIC:
- if (info->srt_bitmap != 0) {
- if (*THUNK_STATIC_LINK((StgClosure *)q) == NULL) {
-#ifndef THREADED_RTS
- *THUNK_STATIC_LINK((StgClosure *)q) = gct->static_objects;
- gct->static_objects = (StgClosure *)q;
-#else
- StgPtr link;
- link = (StgPtr)cas((StgPtr)THUNK_STATIC_LINK((StgClosure *)q),
- (StgWord)NULL,
- (StgWord)gct->static_objects);
- if (link == NULL) {
- gct->static_objects = (StgClosure *)q;
- }
-#endif
- }
- }
- return;
-
- case FUN_STATIC:
- if (info->srt_bitmap != 0 &&
- *FUN_STATIC_LINK((StgClosure *)q) == NULL) {
-#ifndef THREADED_RTS
- *FUN_STATIC_LINK((StgClosure *)q) = gct->static_objects;
- gct->static_objects = (StgClosure *)q;
-#else
- StgPtr link;
- link = (StgPtr)cas((StgPtr)FUN_STATIC_LINK((StgClosure *)q),
- (StgWord)NULL,
- (StgWord)gct->static_objects);
- if (link == NULL) {
- gct->static_objects = (StgClosure *)q;
- }
-#endif
- }
- return;
-
- case IND_STATIC:
- /* If q->saved_info != NULL, then it's a revertible CAF - it'll be
- * on the CAF list, so don't do anything with it here (we'll
- * scavenge it later).
- */
- if (((StgIndStatic *)q)->saved_info == NULL) {
- if (*IND_STATIC_LINK((StgClosure *)q) == NULL) {
-#ifndef THREADED_RTS
- *IND_STATIC_LINK((StgClosure *)q) = gct->static_objects;
- gct->static_objects = (StgClosure *)q;
-#else
- StgPtr link;
- link = (StgPtr)cas((StgPtr)IND_STATIC_LINK((StgClosure *)q),
- (StgWord)NULL,
- (StgWord)gct->static_objects);
- if (link == NULL) {
- gct->static_objects = (StgClosure *)q;
- }
-#endif
- }
- }
- return;
-
- case CONSTR_STATIC:
- if (*STATIC_LINK(info,(StgClosure *)q) == NULL) {
-#ifndef THREADED_RTS
- *STATIC_LINK(info,(StgClosure *)q) = gct->static_objects;
- gct->static_objects = (StgClosure *)q;
-#else
- StgPtr link;
- link = (StgPtr)cas((StgPtr)STATIC_LINK(info,(StgClosure *)q),
- (StgWord)NULL,
- (StgWord)gct->static_objects);
- if (link == NULL) {
- gct->static_objects = (StgClosure *)q;
- }
-#endif
- }
- /* I am assuming that static_objects pointers are not
- * written to other objects, and thus, no need to retag. */
- return;
-
- case CONSTR_NOCAF_STATIC:
- /* no need to put these on the static linked list, they don't need
- * to be scavenged.
- */
- return;
-
- default:
- barf("evacuate(static): strange closure type %d", (int)(info->type));
- }
- }
-
- bd = Bdescr((P_)q);
-
- if ((bd->flags & (BF_LARGE | BF_COMPACTED | BF_EVACUATED)) != 0) {
-
- // pointer into to-space: just return it. It might be a pointer
- // into a generation that we aren't collecting (> N), or it
- // might just be a pointer into to-space. The latter doesn't
- // happen often, but allowing it makes certain things a bit
- // easier; e.g. scavenging an object is idempotent, so it's OK to
- // have an object on the mutable list multiple times.
- if (bd->flags & BF_EVACUATED) {
- // We aren't copying this object, so we have to check
- // whether it is already in the target generation. (this is
- // the write barrier).
- if (bd->step < gct->evac_step) {
- gct->failed_to_evac = rtsTrue;
- TICK_GC_FAILED_PROMOTION();
- }
- return;
- }
-
- /* evacuate large objects by re-linking them onto a different list.
- */
- if (bd->flags & BF_LARGE) {
- info = get_itbl(q);
- if (info->type == TSO &&
- ((StgTSO *)q)->what_next == ThreadRelocated) {
- q = (StgClosure *)((StgTSO *)q)->_link;
- *p = q;
- goto loop;
- }
- evacuate_large((P_)q);
- return;
- }
-
- /* If the object is in a step that we're compacting, then we
- * need to use an alternative evacuate procedure.
- */
- if (bd->flags & BF_COMPACTED) {
- if (!is_marked((P_)q,bd)) {
- mark((P_)q,bd);
- if (mark_stack_full()) {
- mark_stack_overflowed = rtsTrue;
- reset_mark_stack();
- }
- push_mark_stack((P_)q);
- }
- return;
- }
- }
-
- stp = bd->step->to;
-
- info = q->header.info;
- if (IS_FORWARDING_PTR(info))
- {
- /* Already evacuated, just return the forwarding address.
- * HOWEVER: if the requested destination generation (gct->evac_step) is
- * older than the actual generation (because the object was
- * already evacuated to a younger generation) then we have to
- * set the gct->failed_to_evac flag to indicate that we couldn't
- * manage to promote the object to the desired generation.
- */
- /*
- * Optimisation: the check is fairly expensive, but we can often
- * shortcut it if either the required generation is 0, or the
- * current object (the EVACUATED) is in a high enough generation.
- * We know that an EVACUATED always points to an object in the
- * same or an older generation. stp is the lowest step that the
- * current object would be evacuated to, so we only do the full
- * check if stp is too low.
- */
- StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
- *p = TAG_CLOSURE(tag,e);
- if (stp < gct->evac_step) { // optimisation
- if (Bdescr((P_)e)->step < gct->evac_step) {
- gct->failed_to_evac = rtsTrue;
- TICK_GC_FAILED_PROMOTION();
- }
- }
- return;
- }
-
- switch (INFO_PTR_TO_STRUCT(info)->type) {
-
- case WHITEHOLE:
- goto loop;
-
- case MUT_VAR_CLEAN:
- case MUT_VAR_DIRTY:
- case MVAR_CLEAN:
- case MVAR_DIRTY:
- copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
- return;
-
- case CONSTR_0_1:
- {
- StgWord w = (StgWord)q->payload[0];
- if (info == Czh_con_info &&
- // unsigned, so always true: (StgChar)w >= MIN_CHARLIKE &&
- (StgChar)w <= MAX_CHARLIKE) {
- *p = TAG_CLOSURE(tag,
- (StgClosure *)CHARLIKE_CLOSURE((StgChar)w)
- );
- }
- else if (info == Izh_con_info &&
- (StgInt)w >= MIN_INTLIKE && (StgInt)w <= MAX_INTLIKE) {
- *p = TAG_CLOSURE(tag,
- (StgClosure *)INTLIKE_CLOSURE((StgInt)w)
- );
- }
- else {
- copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
- }
- return;
- }
-
- case FUN_0_1:
- case FUN_1_0:
- case CONSTR_1_0:
- copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,stp,tag);
- return;
-
- case THUNK_1_0:
- case THUNK_0_1:
- copy(p,info,q,sizeofW(StgThunk)+1,stp);
- return;
-
- case THUNK_1_1:
- case THUNK_2_0:
- case THUNK_0_2:
-#ifdef NO_PROMOTE_THUNKS
- if (bd->gen_no == 0 &&
- bd->step->no != 0 &&
- bd->step->no == generations[bd->gen_no].n_steps-1) {
- stp = bd->step;
- }
-#endif
- copy(p,info,q,sizeofW(StgThunk)+2,stp);
- return;
-
- case FUN_1_1:
- case FUN_2_0:
- case FUN_0_2:
- case CONSTR_1_1:
- case CONSTR_2_0:
- copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
- return;
-
- case CONSTR_0_2:
- copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,stp,tag);
- return;
-
- case THUNK:
- copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp);
- return;
-
- case FUN:
- case IND_PERM:
- case IND_OLDGEN_PERM:
- case CONSTR:
- copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
- return;
-
- case WEAK:
- case STABLE_NAME:
- copy_tag(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),stp,tag);
- return;
-
- case BCO:
- copy(p,info,q,bco_sizeW((StgBCO *)q),stp);
- return;
-
- case CAF_BLACKHOLE:
- case SE_CAF_BLACKHOLE:
- case SE_BLACKHOLE:
- case BLACKHOLE:
- copyPart(p,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
- return;
-
- case THUNK_SELECTOR:
- eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
- return;
-
- case IND:
- case IND_OLDGEN:
- // follow chains of indirections, don't evacuate them
- q = ((StgInd*)q)->indirectee;
- *p = q;
- goto loop;
-
- case RET_BCO:
- case RET_SMALL:
- case RET_BIG:
- case RET_DYN:
- case UPDATE_FRAME:
- case STOP_FRAME:
- case CATCH_FRAME:
- case CATCH_STM_FRAME:
- case CATCH_RETRY_FRAME:
- case ATOMICALLY_FRAME:
- // shouldn't see these
- barf("evacuate: stack frame at %p\n", q);
-
- case PAP:
- copy(p,info,q,pap_sizeW((StgPAP*)q),stp);
- return;
-
- case AP:
- copy(p,info,q,ap_sizeW((StgAP*)q),stp);
- return;
-
- case AP_STACK:
- copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),stp);
- return;
-
- case ARR_WORDS:
- // just copy the block
- copy(p,info,q,arr_words_sizeW((StgArrWords *)q),stp);
- return;
-
- case MUT_ARR_PTRS_CLEAN:
- case MUT_ARR_PTRS_DIRTY:
- case MUT_ARR_PTRS_FROZEN:
- case MUT_ARR_PTRS_FROZEN0:
- // just copy the block
- copy(p,info,q,mut_arr_ptrs_sizeW((StgMutArrPtrs *)q),stp);
- return;
-
- case TSO:
- {
- StgTSO *tso = (StgTSO *)q;
-
- /* Deal with redirected TSOs (a TSO that's had its stack enlarged).
- */
- if (tso->what_next == ThreadRelocated) {
- q = (StgClosure *)tso->_link;
- *p = q;
- goto loop;
- }
-
- /* To evacuate a small TSO, we need to relocate the update frame
- * list it contains.
- */
- {
- StgTSO *new_tso;
- StgPtr r, s;
-
- copyPart(p,(StgClosure *)tso, tso_sizeW(tso), sizeofW(StgTSO), stp);
- new_tso = (StgTSO *)*p;
- move_TSO(tso, new_tso);
- for (r = tso->sp, s = new_tso->sp;
- r < tso->stack+tso->stack_size;) {
- *s++ = *r++;
- }
- return;
- }
- }
-
- case TREC_HEADER:
- copy(p,info,q,sizeofW(StgTRecHeader),stp);
- return;
-
- case TVAR_WATCH_QUEUE:
- copy(p,info,q,sizeofW(StgTVarWatchQueue),stp);
- return;
-
- case TVAR:
- copy(p,info,q,sizeofW(StgTVar),stp);
- return;
-
- case TREC_CHUNK:
- copy(p,info,q,sizeofW(StgTRecChunk),stp);
- return;
-
- case ATOMIC_INVARIANT:
- copy(p,info,q,sizeofW(StgAtomicInvariant),stp);
- return;
-
- case INVARIANT_CHECK_QUEUE:
- copy(p,info,q,sizeofW(StgInvariantCheckQueue),stp);
- return;
-
- default:
- barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
- }
-
- barf("evacuate");
-}
-
-#undef copy
-#undef copy_tag
-#undef copy_tag_nolock
-#undef copyPart
-#undef evacuate