+ // If this is a block of pinned objects, we don't have to scan
+ // these objects, because they aren't allowed to contain any
+ // pointers. For these blocks, we skip the scavenge stage and put
+ // them straight on the scavenged_large_objects list.
+ if (bd->flags & BF_PINNED) {
+ ASSERT(get_itbl((StgClosure *)p)->type == ARR_WORDS);
+ if (new_gen != gen) { ACQUIRE_SPIN_LOCK(&new_gen->sync); }
+ dbl_link_onto(bd, &new_gen->scavenged_large_objects);
+ new_gen->n_scavenged_large_blocks += bd->blocks;
+ if (new_gen != gen) { RELEASE_SPIN_LOCK(&new_gen->sync); }
+ } else {
+ bd->link = ws->todo_large_objects;
+ ws->todo_large_objects = bd;
+ }
+
+ RELEASE_SPIN_LOCK(&gen->sync);
+}
+
+/* ----------------------------------------------------------------------------
+ Evacuate
+
+ This is called (eventually) for every live object in the system.
+
+ The caller to evacuate specifies a desired generation in the
+ gct->evac_gen 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_gen
+ if M > N do nothing
+ else evac to gen->to
+
+ if M < gct->evac_gen evac to gct->evac_gen, step 0
+
+ if the object is already evacuated, then we check which generation
+ it now resides in.
+
+ if M >= gct->evac_gen do nothing
+ if M < gct->evac_gen set gct->failed_to_evac flag to indicate that we
+ didn't manage to evacuate this object into gct->evac_gen.
+
+
+ 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 GNUC_ATTR_HOT void
+evacuate(StgClosure **p)
+{
+ bdescr *bd = NULL;
+ nat gen_no;
+ 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);
+
+ ASSERTM(LOOKS_LIKE_CLOSURE_PTR(q), "invalid closure, info=%p", q->header.info);
+
+ if (!HEAP_ALLOCED_GC(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 (*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_MARKED | 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->gen_no < gct->evac_gen_no) {
+ 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) {
+ evacuate_large((P_)q);
+ return;
+ }
+
+ /* If the object is in a gen that we're compacting, then we
+ * need to use an alternative evacuate procedure.
+ */
+ if (!is_marked((P_)q,bd)) {
+ mark((P_)q,bd);
+ push_mark_stack((P_)q);
+ }
+ return;
+ }
+
+ gen_no = bd->dest_no;
+
+ info = q->header.info;
+ if (IS_FORWARDING_PTR(info))
+ {
+ /* Already evacuated, just return the forwarding address.
+ * HOWEVER: if the requested destination generation (gct->evac_gen) 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. gen is the lowest generation that the
+ * current object would be evacuated to, so we only do the full
+ * check if gen is too low.
+ */
+ StgClosure *e = (StgClosure*)UN_FORWARDING_PTR(info);
+ *p = TAG_CLOSURE(tag,e);
+ if (gen_no < gct->evac_gen_no) { // optimisation
+ if (Bdescr((P_)e)->gen_no < gct->evac_gen_no) {
+ 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)),gen_no);
+ return;
+
+ // For ints and chars of low value, save space by replacing references to
+ // these with closures with references to common, shared ones in the RTS.
+ //
+ // * Except when compiling into Windows DLLs which don't support cross-package
+ // data references very well.
+ //
+ case CONSTR_0_1:
+ {
+#if defined(__PIC__) && defined(mingw32_HOST_OS)
+ copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen_no,tag);
+#else
+ 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,gen_no,tag);
+ }
+#endif
+ return;
+ }
+
+ case FUN_0_1:
+ case FUN_1_0:
+ case CONSTR_1_0:
+ copy_tag_nolock(p,info,q,sizeofW(StgHeader)+1,gen_no,tag);
+ return;
+
+ case THUNK_1_0:
+ case THUNK_0_1:
+ copy(p,info,q,sizeofW(StgThunk)+1,gen_no);
+ return;
+
+ case THUNK_1_1:
+ case THUNK_2_0:
+ case THUNK_0_2:
+#ifdef NO_PROMOTE_THUNKS
+#error bitrotted
+#endif
+ copy(p,info,q,sizeofW(StgThunk)+2,gen_no);
+ 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,gen_no,tag);
+ return;
+
+ case CONSTR_0_2:
+ copy_tag_nolock(p,info,q,sizeofW(StgHeader)+2,gen_no,tag);
+ return;
+
+ case THUNK:
+ copy(p,info,q,thunk_sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no);
+ return;
+
+ case FUN:
+ case IND_PERM:
+ case CONSTR:
+ copy_tag_nolock(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no,tag);
+ return;
+
+ case BLACKHOLE:
+ {
+ StgClosure *r;
+ const StgInfoTable *i;
+ r = ((StgInd*)q)->indirectee;
+ if (GET_CLOSURE_TAG(r) == 0) {
+ i = r->header.info;
+ if (IS_FORWARDING_PTR(i)) {
+ r = (StgClosure *)UN_FORWARDING_PTR(i);
+ i = r->header.info;
+ }
+ if (i == &stg_TSO_info
+ || i == &stg_WHITEHOLE_info
+ || i == &stg_BLOCKING_QUEUE_CLEAN_info
+ || i == &stg_BLOCKING_QUEUE_DIRTY_info) {
+ copy(p,info,q,sizeofW(StgInd),gen_no);
+ return;
+ }
+ ASSERT(i != &stg_IND_info);
+ }
+ q = r;
+ *p = r;
+ goto loop;
+ }
+
+ case BLOCKING_QUEUE:
+ case WEAK:
+ case PRIM:
+ case MUT_PRIM:
+ copy(p,info,q,sizeW_fromITBL(INFO_PTR_TO_STRUCT(info)),gen_no);
+ return;
+
+ case BCO:
+ copy(p,info,q,bco_sizeW((StgBCO *)q),gen_no);
+ return;
+
+ case THUNK_SELECTOR:
+ eval_thunk_selector(p, (StgSelector *)q, rtsTrue);
+ return;
+
+ case IND:
+ // 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 UNDERFLOW_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),gen_no);
+ return;
+
+ case AP:
+ copy(p,info,q,ap_sizeW((StgAP*)q),gen_no);
+ return;
+
+ case AP_STACK:
+ copy(p,info,q,ap_stack_sizeW((StgAP_STACK*)q),gen_no);
+ return;
+
+ case ARR_WORDS:
+ // just copy the block
+ copy(p,info,q,arr_words_sizeW((StgArrWords *)q),gen_no);
+ 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),gen_no);
+ return;
+
+ case TSO:
+ copy(p,info,q,sizeofW(StgTSO),gen_no);
+ return;
+
+ case STACK:
+ {
+ StgStack *stack = (StgStack *)q;
+
+ /* To evacuate a small STACK, we need to adjust the stack pointer
+ */
+ {
+ StgStack *new_stack;
+ StgPtr r, s;
+ rtsBool mine;
+
+ mine = copyPart(p,(StgClosure *)stack, stack_sizeW(stack),
+ sizeofW(StgStack), gen_no);
+ if (mine) {
+ new_stack = (StgStack *)*p;
+ move_STACK(stack, new_stack);
+ for (r = stack->sp, s = new_stack->sp;
+ r < stack->stack + stack->stack_size;) {
+ *s++ = *r++;
+ }
+ }
+ return;
+ }
+ }
+
+ case TREC_CHUNK:
+ copy(p,info,q,sizeofW(StgTRecChunk),gen_no);
+ return;
+
+ default:
+ barf("evacuate: strange closure type %d", (int)(INFO_PTR_TO_STRUCT(info)->type));
+ }
+
+ barf("evacuate");