GC: rearrange storage to reduce memory accesses in the inner loop
[ghc-hetmet.git] / rts / sm / Scav.c
index 26b33f4..b22f244 100644 (file)
@@ -4,18 +4,26 @@
  *
  * Generational garbage collector: scavenging functions
  *
+ * Documentation on the architecture of the Garbage Collector can be
+ * found in the online commentary:
+ * 
+ *   http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC
+ *
  * ---------------------------------------------------------------------------*/
 
 #include "Rts.h"
+#include "RtsFlags.h"
 #include "Storage.h"
 #include "MBlock.h"
 #include "GC.h"
+#include "GCUtils.h"
 #include "Compact.h"
 #include "Evac.h"
 #include "Scav.h"
 #include "Apply.h"
 #include "Trace.h"
 #include "LdvProfile.h"
+#include "Sanity.h"
 
 static void scavenge_stack (StgPtr p, StgPtr stack_end);
 
@@ -23,6 +31,7 @@ static void scavenge_large_bitmap (StgPtr p,
                                   StgLargeBitmap *large_bitmap, 
                                   nat size );
 
+
 /* Similar to scavenge_large_bitmap(), but we don't write back the
  * pointers we get back from evacuate().
  */
@@ -39,7 +48,7 @@ scavenge_large_srt_bitmap( StgLargeSRT *large_srt )
     p      = (StgClosure **)large_srt->srt;
     for (i = 0; i < size; ) {
        if ((bitmap & 1) != 0) {
-           evacuate(*p);
+           evacuate(p);
        }
        i++;
        p++;
@@ -72,7 +81,7 @@ scavenge_srt (StgClosure **srt, nat srt_bitmap)
 
   while (bitmap != 0) {
       if ((bitmap & 1) != 0) {
-#ifdef ENABLE_WIN32_DLL_SUPPORT
+#if defined(__PIC__) && defined(mingw32_TARGET_OS)
          // Special-case to handle references to closures hiding out in DLLs, since
          // double indirections required to get at those. The code generator knows
          // which is which when generating the SRT, so it stores the (indirect)
@@ -82,12 +91,12 @@ scavenge_srt (StgClosure **srt, nat srt_bitmap)
          // If the SRT entry hasn't got bit 0 set, the SRT entry points to a
          // closure that's fixed at link-time, and no extra magic is required.
          if ( (unsigned long)(*srt) & 0x1 ) {
-             evacuate(*stgCast(StgClosure**,(stgCast(unsigned long, *srt) & ~0x1)));
+             evacuate(stgCast(StgClosure**,(stgCast(unsigned long, *srt) & ~0x1)));
          } else {
-             evacuate(*p);
+             evacuate(p);
          }
 #else
-         evacuate(*p);
+         evacuate(p);
 #endif
       }
       p++;
@@ -125,31 +134,47 @@ scavenge_fun_srt(const StgInfoTable *info)
 static void
 scavengeTSO (StgTSO *tso)
 {
+    rtsBool saved_eager;
+
+    if (tso->what_next == ThreadRelocated) {
+        // the only way this can happen is if the old TSO was on the
+        // mutable list.  We might have other links to this defunct
+        // TSO, so we must update its link field.
+        evacuate((StgClosure**)&tso->_link);
+        return;
+    }
+
+    saved_eager = gct->eager_promotion;
+    gct->eager_promotion = rtsFalse;
+
     if (   tso->why_blocked == BlockedOnMVar
        || tso->why_blocked == BlockedOnBlackHole
        || tso->why_blocked == BlockedOnException
-#if defined(PAR)
-       || tso->why_blocked == BlockedOnGA
-       || tso->why_blocked == BlockedOnGA_NoSend
-#endif
        ) {
-       tso->block_info.closure = evacuate(tso->block_info.closure);
+       evacuate(&tso->block_info.closure);
     }
-    tso->blocked_exceptions = 
-       (StgTSO *)evacuate((StgClosure *)tso->blocked_exceptions);
+    evacuate((StgClosure **)&tso->blocked_exceptions);
     
     // We don't always chase the link field: TSOs on the blackhole
     // queue are not automatically alive, so the link field is a
     // "weak" pointer in that case.
     if (tso->why_blocked != BlockedOnBlackHole) {
-       tso->link = (StgTSO *)evacuate((StgClosure *)tso->link);
+       evacuate((StgClosure **)&tso->link);
     }
 
     // scavange current transaction record
-    tso->trec = (StgTRecHeader *)evacuate((StgClosure *)tso->trec);
+    evacuate((StgClosure **)&tso->trec);
     
     // scavenge this thread's stack 
     scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
+
+    if (gct->failed_to_evac) {
+        tso->flags |= TSO_DIRTY;
+    } else {
+        tso->flags &= ~TSO_DIRTY;
+    }
+
+    gct->eager_promotion = saved_eager;
 }
 
 /* -----------------------------------------------------------------------------
@@ -181,7 +206,7 @@ scavenge_arg_block (StgFunInfoTable *fun_info, StgClosure **args)
     small_bitmap:
        while (size > 0) {
            if ((bitmap & 1) == 0) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
            p++;
            bitmap = bitmap >> 1;
@@ -199,7 +224,7 @@ scavenge_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
     StgWord bitmap;
     StgFunInfoTable *fun_info;
     
-    fun_info = get_fun_itbl(fun);
+    fun_info = get_fun_itbl(UNTAG_CLOSURE(fun));
     ASSERT(fun_info->i.type != PAP);
     p = (StgPtr)payload;
 
@@ -220,7 +245,7 @@ scavenge_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
     small_bitmap:
        while (size > 0) {
            if ((bitmap & 1) == 0) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
            p++;
            bitmap = bitmap >> 1;
@@ -234,495 +259,18 @@ scavenge_PAP_payload (StgClosure *fun, StgClosure **payload, StgWord size)
 STATIC_INLINE StgPtr
 scavenge_PAP (StgPAP *pap)
 {
-    pap->fun = evacuate(pap->fun);
+    evacuate(&pap->fun);
     return scavenge_PAP_payload (pap->fun, pap->payload, pap->n_args);
 }
 
 STATIC_INLINE StgPtr
 scavenge_AP (StgAP *ap)
 {
-    ap->fun = evacuate(ap->fun);
+    evacuate(&ap->fun);
     return scavenge_PAP_payload (ap->fun, ap->payload, ap->n_args);
 }
 
 /* -----------------------------------------------------------------------------
-   Scavenge a given step until there are no more objects in this step
-   to scavenge.
-
-   evac_gen is set by the caller to be either zero (for a step in a
-   generation < N) or G where G is the generation of the step being
-   scavenged.  
-
-   We sometimes temporarily change evac_gen back to zero if we're
-   scavenging a mutable object where early promotion isn't such a good
-   idea.  
-   -------------------------------------------------------------------------- */
-
-void
-scavenge(step *stp)
-{
-  StgPtr p, q;
-  StgInfoTable *info;
-  bdescr *bd;
-  nat saved_evac_gen = evac_gen;
-
-  p = stp->scan;
-  bd = stp->scan_bd;
-
-  failed_to_evac = rtsFalse;
-
-  /* scavenge phase - standard breadth-first scavenging of the
-   * evacuated objects 
-   */
-
-  while (bd != stp->hp_bd || p < stp->hp) {
-
-    // If we're at the end of this block, move on to the next block 
-    if (bd != stp->hp_bd && p == bd->free) {
-      bd = bd->link;
-      p = bd->start;
-      continue;
-    }
-
-    ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
-    info = get_itbl((StgClosure *)p);
-    
-    ASSERT(thunk_selector_depth == 0);
-
-    q = p;
-    switch (info->type) {
-
-    case MVAR:
-    { 
-       StgMVar *mvar = ((StgMVar *)p);
-       evac_gen = 0;
-       mvar->head = (StgTSO *)evacuate((StgClosure *)mvar->head);
-       mvar->tail = (StgTSO *)evacuate((StgClosure *)mvar->tail);
-       mvar->value = evacuate((StgClosure *)mvar->value);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable.
-       p += sizeofW(StgMVar);
-       break;
-    }
-
-    case FUN_2_0:
-       scavenge_fun_srt(info);
-       ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
-       ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
-       p += sizeofW(StgHeader) + 2;
-       break;
-
-    case THUNK_2_0:
-       scavenge_thunk_srt(info);
-       ((StgThunk *)p)->payload[1] = evacuate(((StgThunk *)p)->payload[1]);
-       ((StgThunk *)p)->payload[0] = evacuate(((StgThunk *)p)->payload[0]);
-       p += sizeofW(StgThunk) + 2;
-       break;
-
-    case CONSTR_2_0:
-       ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
-       ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
-       p += sizeofW(StgHeader) + 2;
-       break;
-       
-    case THUNK_1_0:
-       scavenge_thunk_srt(info);
-       ((StgThunk *)p)->payload[0] = evacuate(((StgThunk *)p)->payload[0]);
-       p += sizeofW(StgThunk) + 1;
-       break;
-       
-    case FUN_1_0:
-       scavenge_fun_srt(info);
-    case CONSTR_1_0:
-       ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
-       p += sizeofW(StgHeader) + 1;
-       break;
-       
-    case THUNK_0_1:
-       scavenge_thunk_srt(info);
-       p += sizeofW(StgThunk) + 1;
-       break;
-       
-    case FUN_0_1:
-       scavenge_fun_srt(info);
-    case CONSTR_0_1:
-       p += sizeofW(StgHeader) + 1;
-       break;
-       
-    case THUNK_0_2:
-       scavenge_thunk_srt(info);
-       p += sizeofW(StgThunk) + 2;
-       break;
-       
-    case FUN_0_2:
-       scavenge_fun_srt(info);
-    case CONSTR_0_2:
-       p += sizeofW(StgHeader) + 2;
-       break;
-       
-    case THUNK_1_1:
-       scavenge_thunk_srt(info);
-       ((StgThunk *)p)->payload[0] = evacuate(((StgThunk *)p)->payload[0]);
-       p += sizeofW(StgThunk) + 2;
-       break;
-
-    case FUN_1_1:
-       scavenge_fun_srt(info);
-    case CONSTR_1_1:
-       ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
-       p += sizeofW(StgHeader) + 2;
-       break;
-       
-    case FUN:
-       scavenge_fun_srt(info);
-       goto gen_obj;
-
-    case THUNK:
-    {
-       StgPtr end;
-
-       scavenge_thunk_srt(info);
-       end = (P_)((StgThunk *)p)->payload + info->layout.payload.ptrs;
-       for (p = (P_)((StgThunk *)p)->payload; p < end; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
-       }
-       p += info->layout.payload.nptrs;
-       break;
-    }
-       
-    gen_obj:
-    case CONSTR:
-    case WEAK:
-    case STABLE_NAME:
-    {
-       StgPtr end;
-
-       end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
-       for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
-       }
-       p += info->layout.payload.nptrs;
-       break;
-    }
-
-    case BCO: {
-       StgBCO *bco = (StgBCO *)p;
-       bco->instrs = (StgArrWords *)evacuate((StgClosure *)bco->instrs);
-       bco->literals = (StgArrWords *)evacuate((StgClosure *)bco->literals);
-       bco->ptrs = (StgMutArrPtrs *)evacuate((StgClosure *)bco->ptrs);
-       bco->itbls = (StgArrWords *)evacuate((StgClosure *)bco->itbls);
-       p += bco_sizeW(bco);
-       break;
-    }
-
-    case IND_PERM:
-      if (stp->gen->no != 0) {
-#ifdef PROFILING
-        // @LDV profiling
-        // No need to call LDV_recordDead_FILL_SLOP_DYNAMIC() because an 
-        // IND_OLDGEN_PERM closure is larger than an IND_PERM closure.
-        LDV_recordDead((StgClosure *)p, sizeofW(StgInd));
-#endif        
-        // 
-        // Todo: maybe use SET_HDR() and remove LDV_RECORD_CREATE()?
-        //
-       SET_INFO(((StgClosure *)p), &stg_IND_OLDGEN_PERM_info);
-
-        // We pretend that p has just been created.
-        LDV_RECORD_CREATE((StgClosure *)p);
-      }
-       // fall through 
-    case IND_OLDGEN_PERM:
-       ((StgInd *)p)->indirectee = evacuate(((StgInd *)p)->indirectee);
-       p += sizeofW(StgInd);
-       break;
-
-    case MUT_VAR_CLEAN:
-    case MUT_VAR_DIRTY: {
-       rtsBool saved_eager_promotion = eager_promotion;
-
-       eager_promotion = rtsFalse;
-       ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
-       eager_promotion = saved_eager_promotion;
-
-       if (failed_to_evac) {
-           ((StgClosure *)q)->header.info = &stg_MUT_VAR_DIRTY_info;
-       } else {
-           ((StgClosure *)q)->header.info = &stg_MUT_VAR_CLEAN_info;
-       }
-       p += sizeofW(StgMutVar);
-       break;
-    }
-
-    case CAF_BLACKHOLE:
-    case SE_CAF_BLACKHOLE:
-    case SE_BLACKHOLE:
-    case BLACKHOLE:
-       p += BLACKHOLE_sizeW();
-       break;
-
-    case THUNK_SELECTOR:
-    { 
-       StgSelector *s = (StgSelector *)p;
-       s->selectee = evacuate(s->selectee);
-       p += THUNK_SELECTOR_sizeW();
-       break;
-    }
-
-    // A chunk of stack saved in a heap object
-    case AP_STACK:
-    {
-       StgAP_STACK *ap = (StgAP_STACK *)p;
-
-       ap->fun = evacuate(ap->fun);
-       scavenge_stack((StgPtr)ap->payload, (StgPtr)ap->payload + ap->size);
-       p = (StgPtr)ap->payload + ap->size;
-       break;
-    }
-
-    case PAP:
-       p = scavenge_PAP((StgPAP *)p);
-       break;
-
-    case AP:
-       p = scavenge_AP((StgAP *)p);
-       break;
-
-    case ARR_WORDS:
-       // nothing to follow 
-       p += arr_words_sizeW((StgArrWords *)p);
-       break;
-
-    case MUT_ARR_PTRS_CLEAN:
-    case MUT_ARR_PTRS_DIRTY:
-       // follow everything 
-    {
-       StgPtr next;
-       rtsBool saved_eager;
-
-       // We don't eagerly promote objects pointed to by a mutable
-       // array, but if we find the array only points to objects in
-       // the same or an older generation, we mark it "clean" and
-       // avoid traversing it during minor GCs.
-       saved_eager = eager_promotion;
-       eager_promotion = rtsFalse;
-       next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
-       for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
-       }
-       eager_promotion = saved_eager;
-
-       if (failed_to_evac) {
-           ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_DIRTY_info;
-       } else {
-           ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
-       }
-
-       failed_to_evac = rtsTrue; // always put it on the mutable list.
-       break;
-    }
-
-    case MUT_ARR_PTRS_FROZEN:
-    case MUT_ARR_PTRS_FROZEN0:
-       // follow everything 
-    {
-       StgPtr next;
-
-       next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
-       for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
-       }
-
-       // If we're going to put this object on the mutable list, then
-       // set its info ptr to MUT_ARR_PTRS_FROZEN0 to indicate that.
-       if (failed_to_evac) {
-           ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN0_info;
-       } else {
-           ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN_info;
-       }
-       break;
-    }
-
-    case TSO:
-    { 
-       StgTSO *tso = (StgTSO *)p;
-       rtsBool saved_eager = eager_promotion;
-
-       eager_promotion = rtsFalse;
-       scavengeTSO(tso);
-       eager_promotion = saved_eager;
-
-       if (failed_to_evac) {
-           tso->flags |= TSO_DIRTY;
-       } else {
-           tso->flags &= ~TSO_DIRTY;
-       }
-
-       failed_to_evac = rtsTrue; // always on the mutable list
-       p += tso_sizeW(tso);
-       break;
-    }
-
-#if defined(PAR)
-    case RBH:
-    { 
-#if 0
-       nat size, ptrs, nonptrs, vhs;
-       char str[80];
-       StgInfoTable *rip = get_closure_info(p, &size, &ptrs, &nonptrs, &vhs, str);
-#endif
-       StgRBH *rbh = (StgRBH *)p;
-       (StgClosure *)rbh->blocking_queue = 
-           evacuate((StgClosure *)rbh->blocking_queue);
-       failed_to_evac = rtsTrue;  // mutable anyhow.
-       debugTrace(DEBUG_gc, "scavenge: RBH %p (%s) (new blocking_queue link=%p)",
-                  p, info_type(p), (StgClosure *)rbh->blocking_queue);
-       // ToDo: use size of reverted closure here!
-       p += BLACKHOLE_sizeW(); 
-       break;
-    }
-
-    case BLOCKED_FETCH:
-    { 
-       StgBlockedFetch *bf = (StgBlockedFetch *)p;
-       // follow the pointer to the node which is being demanded 
-       (StgClosure *)bf->node = 
-           evacuate((StgClosure *)bf->node);
-       // follow the link to the rest of the blocking queue 
-       (StgClosure *)bf->link = 
-           evacuate((StgClosure *)bf->link);
-       debugTrace(DEBUG_gc, "scavenge: %p (%s); node is now %p; exciting, isn't it",
-                  bf, info_type((StgClosure *)bf), 
-                  bf->node, info_type(bf->node)));
-       p += sizeofW(StgBlockedFetch);
-       break;
-    }
-
-#ifdef DIST
-    case REMOTE_REF:
-#endif
-    case FETCH_ME:
-       p += sizeofW(StgFetchMe);
-       break; // nothing to do in this case
-
-    case FETCH_ME_BQ:
-    { 
-       StgFetchMeBlockingQueue *fmbq = (StgFetchMeBlockingQueue *)p;
-       (StgClosure *)fmbq->blocking_queue = 
-           evacuate((StgClosure *)fmbq->blocking_queue);
-       debugTrace(DEBUG_gc, "scavenge: %p (%s) exciting, isn't it",
-                  p, info_type((StgClosure *)p)));
-       p += sizeofW(StgFetchMeBlockingQueue);
-       break;
-    }
-#endif
-
-    case TVAR_WATCH_QUEUE:
-      {
-       StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-       evac_gen = 0;
-       wq->closure = (StgClosure*)evacuate((StgClosure*)wq->closure);
-       wq->next_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->next_queue_entry);
-       wq->prev_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->prev_queue_entry);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTVarWatchQueue);
-       break;
-      }
-
-    case TVAR:
-      {
-       StgTVar *tvar = ((StgTVar *) p);
-       evac_gen = 0;
-       tvar->current_value = evacuate((StgClosure*)tvar->current_value);
-       tvar->first_watch_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)tvar->first_watch_queue_entry);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTVar);
-       break;
-      }
-
-    case TREC_HEADER:
-      {
-        StgTRecHeader *trec = ((StgTRecHeader *) p);
-        evac_gen = 0;
-       trec->enclosing_trec = (StgTRecHeader *)evacuate((StgClosure*)trec->enclosing_trec);
-       trec->current_chunk = (StgTRecChunk *)evacuate((StgClosure*)trec->current_chunk);
-       trec->invariants_to_check = (StgInvariantCheckQueue *)evacuate((StgClosure*)trec->invariants_to_check);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTRecHeader);
-        break;
-      }
-
-    case TREC_CHUNK:
-      {
-       StgWord i;
-       StgTRecChunk *tc = ((StgTRecChunk *) p);
-       TRecEntry *e = &(tc -> entries[0]);
-       evac_gen = 0;
-       tc->prev_chunk = (StgTRecChunk *)evacuate((StgClosure*)tc->prev_chunk);
-       for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
-         e->tvar = (StgTVar *)evacuate((StgClosure*)e->tvar);
-         e->expected_value = evacuate((StgClosure*)e->expected_value);
-         e->new_value = evacuate((StgClosure*)e->new_value);
-       }
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTRecChunk);
-       break;
-      }
-
-    case ATOMIC_INVARIANT:
-      {
-        StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-        evac_gen = 0;
-       invariant->code = (StgClosure *)evacuate(invariant->code);
-       invariant->last_execution = (StgTRecHeader *)evacuate((StgClosure*)invariant->last_execution);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgAtomicInvariant);
-        break;
-      }
-
-    case INVARIANT_CHECK_QUEUE:
-      {
-        StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-        evac_gen = 0;
-       queue->invariant = (StgAtomicInvariant *)evacuate((StgClosure*)queue->invariant);
-       queue->my_execution = (StgTRecHeader *)evacuate((StgClosure*)queue->my_execution);
-       queue->next_queue_entry = (StgInvariantCheckQueue *)evacuate((StgClosure*)queue->next_queue_entry);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgInvariantCheckQueue);
-        break;
-      }
-
-    default:
-       barf("scavenge: unimplemented/strange closure type %d @ %p", 
-            info->type, p);
-    }
-
-    /*
-     * We need to record the current object on the mutable list if
-     *  (a) It is actually mutable, or 
-     *  (b) It contains pointers to a younger generation.
-     * Case (b) arises if we didn't manage to promote everything that
-     * the current object points to into the current generation.
-     */
-    if (failed_to_evac) {
-       failed_to_evac = rtsFalse;
-       if (stp->gen_no > 0) {
-           recordMutableGen((StgClosure *)q, stp->gen);
-       }
-    }
-  }
-
-  stp->scan_bd = bd;
-  stp->scan = p;
-}    
-
-/* -----------------------------------------------------------------------------
    Scavenge everything on the mark stack.
 
    This is slightly different from scavenge():
@@ -730,15 +278,15 @@ scavenge(step *stp)
         doesn't need to advance the pointer on to the next object.
    -------------------------------------------------------------------------- */
 
-void
+static void
 scavenge_mark_stack(void)
 {
     StgPtr p, q;
     StgInfoTable *info;
-    nat saved_evac_gen;
+    step *saved_evac_step;
 
-    evac_gen = oldest_gen->no;
-    saved_evac_gen = evac_gen;
+    gct->evac_step = &oldest_gen->steps[0];
+    saved_evac_step = gct->evac_step;
 
 linear_scan:
     while (!mark_stack_empty()) {
@@ -748,52 +296,60 @@ linear_scan:
        info = get_itbl((StgClosure *)p);
        
        q = p;
-       switch (info->type) {
+        switch (((volatile StgWord *)info)[1] & 0xffff) {
            
-       case MVAR:
-       {
-           StgMVar *mvar = ((StgMVar *)p);
-           evac_gen = 0;
-           mvar->head = (StgTSO *)evacuate((StgClosure *)mvar->head);
-           mvar->tail = (StgTSO *)evacuate((StgClosure *)mvar->tail);
-           mvar->value = evacuate((StgClosure *)mvar->value);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable.
-           break;
-       }
+        case MVAR_CLEAN:
+        case MVAR_DIRTY:
+        { 
+            rtsBool saved_eager_promotion = gct->eager_promotion;
+            
+            StgMVar *mvar = ((StgMVar *)p);
+            gct->eager_promotion = rtsFalse;
+            evacuate((StgClosure **)&mvar->head);
+            evacuate((StgClosure **)&mvar->tail);
+            evacuate((StgClosure **)&mvar->value);
+            gct->eager_promotion = saved_eager_promotion;
+            
+            if (gct->failed_to_evac) {
+                mvar->header.info = &stg_MVAR_DIRTY_info;
+            } else {
+                mvar->header.info = &stg_MVAR_CLEAN_info;
+            }
+            break;
+        }
 
        case FUN_2_0:
            scavenge_fun_srt(info);
-           ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
-           ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
+           evacuate(&((StgClosure *)p)->payload[1]);
+           evacuate(&((StgClosure *)p)->payload[0]);
            break;
 
        case THUNK_2_0:
            scavenge_thunk_srt(info);
-           ((StgThunk *)p)->payload[1] = evacuate(((StgThunk *)p)->payload[1]);
-           ((StgThunk *)p)->payload[0] = evacuate(((StgThunk *)p)->payload[0]);
+           evacuate(&((StgThunk *)p)->payload[1]);
+           evacuate(&((StgThunk *)p)->payload[0]);
            break;
 
        case CONSTR_2_0:
-           ((StgClosure *)p)->payload[1] = evacuate(((StgClosure *)p)->payload[1]);
-           ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
+           evacuate(&((StgClosure *)p)->payload[1]);
+           evacuate(&((StgClosure *)p)->payload[0]);
            break;
        
        case FUN_1_0:
        case FUN_1_1:
            scavenge_fun_srt(info);
-           ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
+           evacuate(&((StgClosure *)p)->payload[0]);
            break;
 
        case THUNK_1_0:
        case THUNK_1_1:
            scavenge_thunk_srt(info);
-           ((StgThunk *)p)->payload[0] = evacuate(((StgThunk *)p)->payload[0]);
+           evacuate(&((StgThunk *)p)->payload[0]);
            break;
 
        case CONSTR_1_0:
        case CONSTR_1_1:
-           ((StgClosure *)p)->payload[0] = evacuate(((StgClosure *)p)->payload[0]);
+           evacuate(&((StgClosure *)p)->payload[0]);
            break;
        
        case FUN_0_1:
@@ -821,7 +377,7 @@ linear_scan:
            scavenge_thunk_srt(info);
            end = (P_)((StgThunk *)p)->payload + info->layout.payload.ptrs;
            for (p = (P_)((StgThunk *)p)->payload; p < end; p++) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
            break;
        }
@@ -835,17 +391,16 @@ linear_scan:
            
            end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
            for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
            break;
        }
 
        case BCO: {
            StgBCO *bco = (StgBCO *)p;
-           bco->instrs = (StgArrWords *)evacuate((StgClosure *)bco->instrs);
-           bco->literals = (StgArrWords *)evacuate((StgClosure *)bco->literals);
-           bco->ptrs = (StgMutArrPtrs *)evacuate((StgClosure *)bco->ptrs);
-           bco->itbls = (StgArrWords *)evacuate((StgClosure *)bco->itbls);
+           evacuate((StgClosure **)&bco->instrs);
+           evacuate((StgClosure **)&bco->literals);
+           evacuate((StgClosure **)&bco->ptrs);
            break;
        }
 
@@ -857,19 +412,18 @@ linear_scan:
 
        case IND_OLDGEN:
        case IND_OLDGEN_PERM:
-           ((StgInd *)p)->indirectee = 
-               evacuate(((StgInd *)p)->indirectee);
+           evacuate(&((StgInd *)p)->indirectee);
            break;
 
        case MUT_VAR_CLEAN:
        case MUT_VAR_DIRTY: {
-           rtsBool saved_eager_promotion = eager_promotion;
+           rtsBool saved_eager_promotion = gct->eager_promotion;
            
-           eager_promotion = rtsFalse;
-           ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
-           eager_promotion = saved_eager_promotion;
+           gct->eager_promotion = rtsFalse;
+           evacuate(&((StgMutVar *)p)->var);
+           gct->eager_promotion = saved_eager_promotion;
            
-           if (failed_to_evac) {
+           if (gct->failed_to_evac) {
                ((StgClosure *)q)->header.info = &stg_MUT_VAR_DIRTY_info;
            } else {
                ((StgClosure *)q)->header.info = &stg_MUT_VAR_CLEAN_info;
@@ -887,7 +441,7 @@ linear_scan:
        case THUNK_SELECTOR:
        { 
            StgSelector *s = (StgSelector *)p;
-           s->selectee = evacuate(s->selectee);
+           evacuate(&s->selectee);
            break;
        }
 
@@ -896,7 +450,7 @@ linear_scan:
        {
            StgAP_STACK *ap = (StgAP_STACK *)p;
            
-           ap->fun = evacuate(ap->fun);
+           evacuate(&ap->fun);
            scavenge_stack((StgPtr)ap->payload, (StgPtr)ap->payload + ap->size);
            break;
        }
@@ -920,21 +474,21 @@ linear_scan:
            // array, but if we find the array only points to objects in
            // the same or an older generation, we mark it "clean" and
            // avoid traversing it during minor GCs.
-           saved_eager = eager_promotion;
-           eager_promotion = rtsFalse;
+           saved_eager = gct->eager_promotion;
+           gct->eager_promotion = rtsFalse;
            next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
            for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
-           eager_promotion = saved_eager;
+           gct->eager_promotion = saved_eager;
 
-           if (failed_to_evac) {
+           if (gct->failed_to_evac) {
                ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_DIRTY_info;
            } else {
                ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
            }
 
-           failed_to_evac = rtsTrue; // mutable anyhow.
+           gct->failed_to_evac = rtsTrue; // mutable anyhow.
            break;
        }
 
@@ -946,12 +500,12 @@ linear_scan:
            
            next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
            for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-               *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+               evacuate((StgClosure **)p);
            }
 
            // If we're going to put this object on the mutable list, then
            // set its info ptr to MUT_ARR_PTRS_FROZEN0 to indicate that.
-           if (failed_to_evac) {
+           if (gct->failed_to_evac) {
                ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN0_info;
            } else {
                ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN_info;
@@ -961,92 +515,31 @@ linear_scan:
 
        case TSO:
        { 
-           StgTSO *tso = (StgTSO *)p;
-           rtsBool saved_eager = eager_promotion;
-
-           eager_promotion = rtsFalse;
-           scavengeTSO(tso);
-           eager_promotion = saved_eager;
-           
-           if (failed_to_evac) {
-               tso->flags |= TSO_DIRTY;
-           } else {
-               tso->flags &= ~TSO_DIRTY;
-           }
-           
-           failed_to_evac = rtsTrue; // always on the mutable list
+            scavengeTSO((StgTSO*)p);
+           gct->failed_to_evac = rtsTrue; // always on the mutable list
            break;
        }
 
-#if defined(PAR)
-       case RBH:
-       { 
-#if 0
-           nat size, ptrs, nonptrs, vhs;
-           char str[80];
-           StgInfoTable *rip = get_closure_info(p, &size, &ptrs, &nonptrs, &vhs, str);
-#endif
-           StgRBH *rbh = (StgRBH *)p;
-           bh->blocking_queue = 
-               (StgTSO *)evacuate((StgClosure *)bh->blocking_queue);
-           failed_to_evac = rtsTrue;  // mutable anyhow.
-           debugTrace(DEBUG_gc, "scavenge: RBH %p (%s) (new blocking_queue link=%p)",
-                      p, info_type(p), (StgClosure *)rbh->blocking_queue));
-           break;
-       }
-       
-       case BLOCKED_FETCH:
-       { 
-           StgBlockedFetch *bf = (StgBlockedFetch *)p;
-           // follow the pointer to the node which is being demanded 
-           (StgClosure *)bf->node = 
-               evacuate((StgClosure *)bf->node);
-           // follow the link to the rest of the blocking queue 
-           (StgClosure *)bf->link = 
-               evacuate((StgClosure *)bf->link);
-           debugTrace(DEBUG_gc, "scavenge: %p (%s); node is now %p; exciting, isn't it",
-                      bf, info_type((StgClosure *)bf), 
-                      bf->node, info_type(bf->node)));
-           break;
-       }
-
-#ifdef DIST
-       case REMOTE_REF:
-#endif
-       case FETCH_ME:
-           break; // nothing to do in this case
-
-       case FETCH_ME_BQ:
-       { 
-           StgFetchMeBlockingQueue *fmbq = (StgFetchMeBlockingQueue *)p;
-           (StgClosure *)fmbq->blocking_queue = 
-               evacuate((StgClosure *)fmbq->blocking_queue);
-           debugTrace(DEBUG_gc, "scavenge: %p (%s) exciting, isn't it",
-                      p, info_type((StgClosure *)p)));
-           break;
-       }
-#endif /* PAR */
-
        case TVAR_WATCH_QUEUE:
          {
            StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-           evac_gen = 0;
-            wq->closure = (StgClosure*)evacuate((StgClosure*)wq->closure);
-           wq->next_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->next_queue_entry);
-           wq->prev_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->prev_queue_entry);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+           gct->evac_step = 0;
+            evacuate((StgClosure **)&wq->closure);
+           evacuate((StgClosure **)&wq->next_queue_entry);
+           evacuate((StgClosure **)&wq->prev_queue_entry);
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
            break;
          }
          
        case TVAR:
          {
            StgTVar *tvar = ((StgTVar *) p);
-           evac_gen = 0;
-           tvar->current_value = evacuate((StgClosure*)tvar->current_value);
-           tvar->first_watch_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)tvar->first_watch_queue_entry);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+           gct->evac_step = 0;
+           evacuate((StgClosure **)&tvar->current_value);
+           evacuate((StgClosure **)&tvar->first_watch_queue_entry);
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
            break;
          }
          
@@ -1055,50 +548,50 @@ linear_scan:
            StgWord i;
            StgTRecChunk *tc = ((StgTRecChunk *) p);
            TRecEntry *e = &(tc -> entries[0]);
-           evac_gen = 0;
-           tc->prev_chunk = (StgTRecChunk *)evacuate((StgClosure*)tc->prev_chunk);
+           gct->evac_step = 0;
+           evacuate((StgClosure **)&tc->prev_chunk);
            for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
-             e->tvar = (StgTVar *)evacuate((StgClosure*)e->tvar);
-             e->expected_value = evacuate((StgClosure*)e->expected_value);
-             e->new_value = evacuate((StgClosure*)e->new_value);
+             evacuate((StgClosure **)&e->tvar);
+             evacuate((StgClosure **)&e->expected_value);
+             evacuate((StgClosure **)&e->new_value);
            }
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
            break;
          }
 
        case TREC_HEADER:
          {
            StgTRecHeader *trec = ((StgTRecHeader *) p);
-           evac_gen = 0;
-           trec->enclosing_trec = (StgTRecHeader *)evacuate((StgClosure*)trec->enclosing_trec);
-           trec->current_chunk = (StgTRecChunk *)evacuate((StgClosure*)trec->current_chunk);
-           trec->invariants_to_check = (StgInvariantCheckQueue *)evacuate((StgClosure*)trec->invariants_to_check);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+           gct->evac_step = 0;
+           evacuate((StgClosure **)&trec->enclosing_trec);
+           evacuate((StgClosure **)&trec->current_chunk);
+           evacuate((StgClosure **)&trec->invariants_to_check);
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
            break;
          }
 
         case ATOMIC_INVARIANT:
           {
             StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-            evac_gen = 0;
-           invariant->code = (StgClosure *)evacuate(invariant->code);
-           invariant->last_execution = (StgTRecHeader *)evacuate((StgClosure*)invariant->last_execution);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+            gct->evac_step = 0;
+           evacuate(&invariant->code);
+           evacuate((StgClosure **)&invariant->last_execution);
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
             break;
           }
 
         case INVARIANT_CHECK_QUEUE:
           {
             StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-            evac_gen = 0;
-           queue->invariant = (StgAtomicInvariant *)evacuate((StgClosure*)queue->invariant);
-           queue->my_execution = (StgTRecHeader *)evacuate((StgClosure*)queue->my_execution);
-            queue->next_queue_entry = (StgInvariantCheckQueue *)evacuate((StgClosure*)queue->next_queue_entry);
-           evac_gen = saved_evac_gen;
-           failed_to_evac = rtsTrue; // mutable
+            gct->evac_step = 0;
+           evacuate((StgClosure **)&queue->invariant);
+           evacuate((StgClosure **)&queue->my_execution);
+            evacuate((StgClosure **)&queue->next_queue_entry);
+           gct->evac_step = saved_evac_step;
+           gct->failed_to_evac = rtsTrue; // mutable
             break;
           }
 
@@ -1107,10 +600,10 @@ linear_scan:
                 info->type, p);
        }
 
-       if (failed_to_evac) {
-           failed_to_evac = rtsFalse;
-           if (evac_gen > 0) {
-               recordMutableGen((StgClosure *)q, &generations[evac_gen]);
+       if (gct->failed_to_evac) {
+           gct->failed_to_evac = rtsFalse;
+           if (gct->evac_step) {
+               recordMutableGen_GC((StgClosure *)q, gct->evac_step->gen);
            }
        }
        
@@ -1170,7 +663,7 @@ static rtsBool
 scavenge_one(StgPtr p)
 {
     const StgInfoTable *info;
-    nat saved_evac_gen = evac_gen;
+    step *saved_evac_step = gct->evac_step;
     rtsBool no_luck;
     
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
@@ -1178,15 +671,23 @@ scavenge_one(StgPtr p)
     
     switch (info->type) {
        
-    case MVAR:
+    case MVAR_CLEAN:
+    case MVAR_DIRTY:
     { 
+       rtsBool saved_eager_promotion = gct->eager_promotion;
+
        StgMVar *mvar = ((StgMVar *)p);
-       evac_gen = 0;
-       mvar->head = (StgTSO *)evacuate((StgClosure *)mvar->head);
-       mvar->tail = (StgTSO *)evacuate((StgClosure *)mvar->tail);
-       mvar->value = evacuate((StgClosure *)mvar->value);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable.
+       gct->eager_promotion = rtsFalse;
+       evacuate((StgClosure **)&mvar->head);
+       evacuate((StgClosure **)&mvar->tail);
+       evacuate((StgClosure **)&mvar->value);
+       gct->eager_promotion = saved_eager_promotion;
+
+       if (gct->failed_to_evac) {
+           mvar->header.info = &stg_MVAR_DIRTY_info;
+       } else {
+           mvar->header.info = &stg_MVAR_CLEAN_info;
+       }
        break;
     }
 
@@ -1201,7 +702,7 @@ scavenge_one(StgPtr p)
        
        end = (StgPtr)((StgThunk *)p)->payload + info->layout.payload.ptrs;
        for (q = (StgPtr)((StgThunk *)p)->payload; q < end; q++) {
-           *q = (StgWord)(StgPtr)evacuate((StgClosure *)*q);
+           evacuate((StgClosure **)q);
        }
        break;
     }
@@ -1225,7 +726,7 @@ scavenge_one(StgPtr p)
        
        end = (StgPtr)((StgClosure *)p)->payload + info->layout.payload.ptrs;
        for (q = (StgPtr)((StgClosure *)p)->payload; q < end; q++) {
-           *q = (StgWord)(StgPtr)evacuate((StgClosure *)*q);
+           evacuate((StgClosure **)q);
        }
        break;
     }
@@ -1233,13 +734,13 @@ scavenge_one(StgPtr p)
     case MUT_VAR_CLEAN:
     case MUT_VAR_DIRTY: {
        StgPtr q = p;
-       rtsBool saved_eager_promotion = eager_promotion;
+       rtsBool saved_eager_promotion = gct->eager_promotion;
 
-       eager_promotion = rtsFalse;
-       ((StgMutVar *)p)->var = evacuate(((StgMutVar *)p)->var);
-       eager_promotion = saved_eager_promotion;
+       gct->eager_promotion = rtsFalse;
+       evacuate(&((StgMutVar *)p)->var);
+       gct->eager_promotion = saved_eager_promotion;
 
-       if (failed_to_evac) {
+       if (gct->failed_to_evac) {
            ((StgClosure *)q)->header.info = &stg_MUT_VAR_DIRTY_info;
        } else {
            ((StgClosure *)q)->header.info = &stg_MUT_VAR_CLEAN_info;
@@ -1256,7 +757,7 @@ scavenge_one(StgPtr p)
     case THUNK_SELECTOR:
     { 
        StgSelector *s = (StgSelector *)p;
-       s->selectee = evacuate(s->selectee);
+       evacuate(&s->selectee);
        break;
     }
     
@@ -1264,7 +765,7 @@ scavenge_one(StgPtr p)
     {
        StgAP_STACK *ap = (StgAP_STACK *)p;
 
-       ap->fun = evacuate(ap->fun);
+       evacuate(&ap->fun);
        scavenge_stack((StgPtr)ap->payload, (StgPtr)ap->payload + ap->size);
        p = (StgPtr)ap->payload + ap->size;
        break;
@@ -1292,22 +793,22 @@ scavenge_one(StgPtr p)
        // array, but if we find the array only points to objects in
        // the same or an older generation, we mark it "clean" and
        // avoid traversing it during minor GCs.
-       saved_eager = eager_promotion;
-       eager_promotion = rtsFalse;
+       saved_eager = gct->eager_promotion;
+       gct->eager_promotion = rtsFalse;
        q = p;
        next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
        for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+           evacuate((StgClosure **)p);
        }
-       eager_promotion = saved_eager;
+       gct->eager_promotion = saved_eager;
 
-       if (failed_to_evac) {
+       if (gct->failed_to_evac) {
            ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_DIRTY_info;
        } else {
            ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
        }
 
-       failed_to_evac = rtsTrue;
+       gct->failed_to_evac = rtsTrue;
        break;
     }
 
@@ -1319,12 +820,12 @@ scavenge_one(StgPtr p)
       
        next = p + mut_arr_ptrs_sizeW((StgMutArrPtrs*)p);
        for (p = (P_)((StgMutArrPtrs *)p)->payload; p < next; p++) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+           evacuate((StgClosure **)p);
        }
 
        // If we're going to put this object on the mutable list, then
        // set its info ptr to MUT_ARR_PTRS_FROZEN0 to indicate that.
-       if (failed_to_evac) {
+       if (gct->failed_to_evac) {
            ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN0_info;
        } else {
            ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_FROZEN_info;
@@ -1334,106 +835,43 @@ scavenge_one(StgPtr p)
 
     case TSO:
     {
-       StgTSO *tso = (StgTSO *)p;
-       rtsBool saved_eager = eager_promotion;
-
-       eager_promotion = rtsFalse;
-       scavengeTSO(tso);
-       eager_promotion = saved_eager;
-
-       if (failed_to_evac) {
-           tso->flags |= TSO_DIRTY;
-       } else {
-           tso->flags &= ~TSO_DIRTY;
-       }
-
-       failed_to_evac = rtsTrue; // always on the mutable list
+       scavengeTSO((StgTSO*)p);
+       gct->failed_to_evac = rtsTrue; // always on the mutable list
        break;
     }
   
-#if defined(PAR)
-    case RBH:
-    { 
-#if 0
-       nat size, ptrs, nonptrs, vhs;
-       char str[80];
-       StgInfoTable *rip = get_closure_info(p, &size, &ptrs, &nonptrs, &vhs, str);
-#endif
-       StgRBH *rbh = (StgRBH *)p;
-       (StgClosure *)rbh->blocking_queue = 
-           evacuate((StgClosure *)rbh->blocking_queue);
-       failed_to_evac = rtsTrue;  // mutable anyhow.
-       debugTrace(DEBUG_gc, "scavenge: RBH %p (%s) (new blocking_queue link=%p)",
-                  p, info_type(p), (StgClosure *)rbh->blocking_queue));
-       // ToDo: use size of reverted closure here!
-       break;
-    }
-
-    case BLOCKED_FETCH:
-    { 
-       StgBlockedFetch *bf = (StgBlockedFetch *)p;
-       // follow the pointer to the node which is being demanded 
-       (StgClosure *)bf->node = 
-           evacuate((StgClosure *)bf->node);
-       // follow the link to the rest of the blocking queue 
-       (StgClosure *)bf->link = 
-           evacuate((StgClosure *)bf->link);
-       debugTrace(DEBUG_gc,
-                  "scavenge: %p (%s); node is now %p; exciting, isn't it",
-                  bf, info_type((StgClosure *)bf), 
-                  bf->node, info_type(bf->node)));
-       break;
-    }
-
-#ifdef DIST
-    case REMOTE_REF:
-#endif
-    case FETCH_ME:
-       break; // nothing to do in this case
-
-    case FETCH_ME_BQ:
-    { 
-       StgFetchMeBlockingQueue *fmbq = (StgFetchMeBlockingQueue *)p;
-       (StgClosure *)fmbq->blocking_queue = 
-           evacuate((StgClosure *)fmbq->blocking_queue);
-       debugTrace(DEBUG_gc, "scavenge: %p (%s) exciting, isn't it",
-                  p, info_type((StgClosure *)p)));
-       break;
-    }
-#endif
-
     case TVAR_WATCH_QUEUE:
       {
        StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-       evac_gen = 0;
-        wq->closure = (StgClosure*)evacuate((StgClosure*)wq->closure);
-        wq->next_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->next_queue_entry);
-        wq->prev_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)wq->prev_queue_entry);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
+       gct->evac_step = 0;
+        evacuate((StgClosure **)&wq->closure);
+        evacuate((StgClosure **)&wq->next_queue_entry);
+        evacuate((StgClosure **)&wq->prev_queue_entry);
+       gct->evac_step = saved_evac_step;
+       gct->failed_to_evac = rtsTrue; // mutable
        break;
       }
 
     case TVAR:
       {
        StgTVar *tvar = ((StgTVar *) p);
-       evac_gen = 0;
-       tvar->current_value = evacuate((StgClosure*)tvar->current_value);
-        tvar->first_watch_queue_entry = (StgTVarWatchQueue *)evacuate((StgClosure*)tvar->first_watch_queue_entry);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
+       gct->evac_step = 0;
+       evacuate((StgClosure **)&tvar->current_value);
+        evacuate((StgClosure **)&tvar->first_watch_queue_entry);
+       gct->evac_step = saved_evac_step;
+       gct->failed_to_evac = rtsTrue; // mutable
        break;
       }
 
     case TREC_HEADER:
       {
         StgTRecHeader *trec = ((StgTRecHeader *) p);
-        evac_gen = 0;
-       trec->enclosing_trec = (StgTRecHeader *)evacuate((StgClosure*)trec->enclosing_trec);
-       trec->current_chunk = (StgTRecChunk *)evacuate((StgClosure*)trec->current_chunk);
-        trec->invariants_to_check = (StgInvariantCheckQueue *)evacuate((StgClosure*)trec->invariants_to_check);
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
+        gct->evac_step = 0;
+       evacuate((StgClosure **)&trec->enclosing_trec);
+       evacuate((StgClosure **)&trec->current_chunk);
+        evacuate((StgClosure **)&trec->invariants_to_check);
+       gct->evac_step = saved_evac_step;
+       gct->failed_to_evac = rtsTrue; // mutable
         break;
       }
 
@@ -1442,38 +880,38 @@ scavenge_one(StgPtr p)
        StgWord i;
        StgTRecChunk *tc = ((StgTRecChunk *) p);
        TRecEntry *e = &(tc -> entries[0]);
-       evac_gen = 0;
-       tc->prev_chunk = (StgTRecChunk *)evacuate((StgClosure*)tc->prev_chunk);
+       gct->evac_step = 0;
+       evacuate((StgClosure **)&tc->prev_chunk);
        for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
-         e->tvar = (StgTVar *)evacuate((StgClosure*)e->tvar);
-         e->expected_value = evacuate((StgClosure*)e->expected_value);
-         e->new_value = evacuate((StgClosure*)e->new_value);
+         evacuate((StgClosure **)&e->tvar);
+         evacuate((StgClosure **)&e->expected_value);
+         evacuate((StgClosure **)&e->new_value);
        }
-       evac_gen = saved_evac_gen;
-       failed_to_evac = rtsTrue; // mutable
+       gct->evac_step = saved_evac_step;
+       gct->failed_to_evac = rtsTrue; // mutable
        break;
       }
 
     case ATOMIC_INVARIANT:
     {
       StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-      evac_gen = 0;
-      invariant->code = (StgClosure *)evacuate(invariant->code);
-      invariant->last_execution = (StgTRecHeader *)evacuate((StgClosure*)invariant->last_execution);
-      evac_gen = saved_evac_gen;
-      failed_to_evac = rtsTrue; // mutable
+      gct->evac_step = 0;
+      evacuate(&invariant->code);
+      evacuate((StgClosure **)&invariant->last_execution);
+      gct->evac_step = saved_evac_step;
+      gct->failed_to_evac = rtsTrue; // mutable
       break;
     }
 
     case INVARIANT_CHECK_QUEUE:
     {
       StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-      evac_gen = 0;
-      queue->invariant = (StgAtomicInvariant *)evacuate((StgClosure*)queue->invariant);
-      queue->my_execution = (StgTRecHeader *)evacuate((StgClosure*)queue->my_execution);
-      queue->next_queue_entry = (StgInvariantCheckQueue *)evacuate((StgClosure*)queue->next_queue_entry);
-      evac_gen = saved_evac_gen;
-      failed_to_evac = rtsTrue; // mutable
+      gct->evac_step = 0;
+      evacuate((StgClosure **)&queue->invariant);
+      evacuate((StgClosure **)&queue->my_execution);
+      evacuate((StgClosure **)&queue->next_queue_entry);
+      gct->evac_step = saved_evac_step;
+      gct->failed_to_evac = rtsTrue; // mutable
       break;
     }
 
@@ -1492,7 +930,7 @@ scavenge_one(StgPtr p)
        if (HEAP_ALLOCED(q) && Bdescr((StgPtr)q)->flags & BF_EVACUATED) {
            break;
        }
-       ((StgInd *)p)->indirectee = evacuate(q);
+       evacuate(&((StgInd *)p)->indirectee);
     }
 
 #if 0 && defined(DEBUG)
@@ -1526,8 +964,8 @@ scavenge_one(StgPtr p)
        barf("scavenge_one: strange object %d", (int)(info->type));
     }    
 
-    no_luck = failed_to_evac;
-    failed_to_evac = rtsFalse;
+    no_luck = gct->failed_to_evac;
+    gct->failed_to_evac = rtsFalse;
     return (no_luck);
 }
 
@@ -1547,7 +985,7 @@ scavenge_mutable_list(generation *gen)
 
     bd = gen->saved_mut_list;
 
-    evac_gen = gen->no;
+    gct->evac_step = &gen->steps[0];
     for (; bd != NULL; bd = bd->link) {
        for (q = bd->start; q < bd->free; q++) {
            p = (StgPtr)*q;
@@ -1564,6 +1002,10 @@ scavenge_mutable_list(generation *gen)
            case MUT_ARR_PTRS_FROZEN:
            case MUT_ARR_PTRS_FROZEN0:
                mutlist_MUTARRS++; break;
+           case MVAR_CLEAN:
+               barf("MVAR_CLEAN on mutable list");
+           case MVAR_DIRTY:
+               mutlist_MVARS++; break;
            default:
                mutlist_OTHERS++; break;
            }
@@ -1578,7 +1020,7 @@ scavenge_mutable_list(generation *gen)
            //
            switch (get_itbl((StgClosure *)p)->type) {
            case MUT_ARR_PTRS_CLEAN:
-               recordMutableGen((StgClosure *)p,gen);
+               recordMutableGen_GC((StgClosure *)p,gen);
                continue;
            case TSO: {
                StgTSO *tso = (StgTSO *)p;
@@ -1588,9 +1030,9 @@ scavenge_mutable_list(generation *gen)
                    // we don't want to have to mark a TSO dirty just
                    // because we put it on a different queue.
                    if (tso->why_blocked != BlockedOnBlackHole) {
-                       tso->link = (StgTSO *)evacuate((StgClosure *)tso->link);
+                       evacuate((StgClosure **)&tso->link);
                    }
-                   recordMutableGen((StgClosure *)p,gen);
+                   recordMutableGen_GC((StgClosure *)p,gen);
                    continue;
                }
            }
@@ -1601,13 +1043,13 @@ scavenge_mutable_list(generation *gen)
            if (scavenge_one(p)) {
                // didn't manage to promote everything, so put the
                // object back on the list.
-               recordMutableGen((StgClosure *)p,gen);
+               recordMutableGen_GC((StgClosure *)p,gen);
            }
        }
     }
 
     // free the old mut_list
-    freeChain(gen->saved_mut_list);
+    freeChain_sync(gen->saved_mut_list);
     gen->saved_mut_list = NULL;
 }
 
@@ -1619,25 +1061,38 @@ scavenge_mutable_list(generation *gen)
    remove non-mutable objects from the mutable list at this point.
    -------------------------------------------------------------------------- */
 
-void
+static void
 scavenge_static(void)
 {
-  StgClosure* p = static_objects;
+  StgClosure* p;
   const StgInfoTable *info;
 
   /* Always evacuate straight to the oldest generation for static
    * objects */
-  evac_gen = oldest_gen->no;
+  gct->evac_step = &oldest_gen->steps[0];
 
   /* keep going until we've scavenged all the objects on the linked
      list... */
-  while (p != END_OF_STATIC_LIST) {
 
+  while (1) {
+      
+    ACQUIRE_SPIN_LOCK(&static_objects_sync);
+    
+    /* get the next static object from the list.  Remember, there might
+     * be more stuff on this list after each evacuation...
+     * (static_objects is a global)
+     */
+    p = static_objects;
+    if (p == END_OF_STATIC_LIST) {
+         RELEASE_SPIN_LOCK(&static_objects_sync);
+         break;
+    }
+    
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
     info = get_itbl(p);
     /*
-    if (info->type==RBH)
-      info = REVERT_INFOPTR(info); // if it's an RBH, look at the orig closure
+       if (info->type==RBH)
+       info = REVERT_INFOPTR(info); // if it's an RBH, look at the orig closure
     */
     // make sure the info pointer is into text space 
     
@@ -1648,21 +1103,23 @@ scavenge_static(void)
     *STATIC_LINK(info,p) = scavenged_static_objects;
     scavenged_static_objects = p;
     
+    RELEASE_SPIN_LOCK(&static_objects_sync);
+    
     switch (info -> type) {
       
     case IND_STATIC:
       {
        StgInd *ind = (StgInd *)p;
-       ind->indirectee = evacuate(ind->indirectee);
+       evacuate(&ind->indirectee);
 
        /* might fail to evacuate it, in which case we have to pop it
         * back on the mutable list of the oldest generation.  We
         * leave it *on* the scavenged_static_objects list, though,
         * in case we visit this object again.
         */
-       if (failed_to_evac) {
-         failed_to_evac = rtsFalse;
-         recordMutableGen((StgClosure *)p,oldest_gen);
+       if (gct->failed_to_evac) {
+         gct->failed_to_evac = rtsFalse;
+         recordMutableGen_GC((StgClosure *)p,oldest_gen);
        }
        break;
       }
@@ -1682,7 +1139,7 @@ scavenge_static(void)
        next = (P_)p->payload + info->layout.payload.ptrs;
        // evacuate the pointers 
        for (q = (P_)p->payload; q < next; q++) {
-           *q = (StgWord)(StgPtr)evacuate((StgClosure *)*q);
+           evacuate((StgClosure **)q);
        }
        break;
       }
@@ -1691,13 +1148,7 @@ scavenge_static(void)
       barf("scavenge_static: strange closure %d", (int)(info->type));
     }
 
-    ASSERT(failed_to_evac == rtsFalse);
-
-    /* get the next static object from the list.  Remember, there might
-     * be more stuff on this list now that we've done some evacuating!
-     * (static_objects is a global)
-     */
-    p = static_objects;
+    ASSERT(gct->failed_to_evac == rtsFalse);
   }
 }
 
@@ -1715,7 +1166,7 @@ scavenge_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size )
     bitmap = large_bitmap->bitmap[b];
     for (i = 0; i < size; ) {
        if ((bitmap & 1) == 0) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+           evacuate((StgClosure **)p);
        }
        i++;
        p++;
@@ -1733,7 +1184,7 @@ scavenge_small_bitmap (StgPtr p, nat size, StgWord bitmap)
 {
     while (size > 0) {
        if ((bitmap & 1) == 0) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+           evacuate((StgClosure **)p);
        }
        p++;
        bitmap = bitmap >> 1;
@@ -1788,14 +1239,20 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
        // the indirection into an IND_PERM, so that evacuate will
        // copy the indirection into the old generation instead of
        // discarding it.
-       if (get_itbl(((StgUpdateFrame *)p)->updatee)->type == IND) {
+    {
+        nat type;
+        type = get_itbl(((StgUpdateFrame *)p)->updatee)->type;
+       if (type == IND) {
            ((StgUpdateFrame *)p)->updatee->header.info = 
                (StgInfoTable *)&stg_IND_PERM_info;
-       }
-       ((StgUpdateFrame *)p)->updatee 
-           = evacuate(((StgUpdateFrame *)p)->updatee);
+       } else if (type == IND_OLDGEN) {
+           ((StgUpdateFrame *)p)->updatee->header.info = 
+               (StgInfoTable *)&stg_IND_OLDGEN_PERM_info;
+        }            
+       evacuate(&((StgUpdateFrame *)p)->updatee);
        p += sizeofW(StgUpdateFrame);
        continue;
+    }
 
       // small bitmap (< 32 entries, or 64 on a 64-bit machine) 
     case CATCH_STM_FRAME:
@@ -1804,7 +1261,6 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
     case STOP_FRAME:
     case CATCH_FRAME:
     case RET_SMALL:
-    case RET_VEC_SMALL:
        bitmap = BITMAP_BITS(info->i.layout.bitmap);
        size   = BITMAP_SIZE(info->i.layout.bitmap);
        // NOTE: the payload starts immediately after the info-ptr, we
@@ -1822,7 +1278,7 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
        nat size;
 
        p++;
-       *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+       evacuate((StgClosure **)p);
        bco = (StgBCO *)*p;
        p++;
        size = BCO_BITMAP_SIZE(bco);
@@ -1833,7 +1289,6 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
 
       // large bitmap (> 32 entries, or > 64 on a 64-bit machine) 
     case RET_BIG:
-    case RET_VEC_BIG:
     {
        nat size;
 
@@ -1865,7 +1320,7 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
        
        // follow the ptr words
        for (size = RET_DYN_PTRS(dyn); size > 0; size--) {
-           *p = (StgWord)(StgPtr)evacuate((StgClosure *)*p);
+           evacuate((StgClosure **)p);
            p++;
        }
        continue;
@@ -1876,8 +1331,8 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
        StgRetFun *ret_fun = (StgRetFun *)p;
        StgFunInfoTable *fun_info;
 
-       ret_fun->fun = evacuate(ret_fun->fun);
-       fun_info = get_fun_itbl(ret_fun->fun);
+       evacuate(&ret_fun->fun);
+       fun_info = get_fun_itbl(UNTAG_CLOSURE(ret_fun->fun));
        p = scavenge_arg_block(fun_info, ret_fun->payload);
        goto follow_srt;
     }
@@ -1891,39 +1346,235 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
 /*-----------------------------------------------------------------------------
   scavenge the large object list.
 
-  evac_gen set by caller; similar games played with evac_gen as with
+  evac_step set by caller; similar games played with evac_step as with
   scavenge() - see comment at the top of scavenge().  Most large
-  objects are (repeatedly) mutable, so most of the time evac_gen will
+  objects are (repeatedly) mutable, so most of the time evac_step will
   be zero.
   --------------------------------------------------------------------------- */
 
-void
-scavenge_large(step *stp)
+static void
+scavenge_large (step_workspace *ws)
+{
+    bdescr *bd;
+    StgPtr p;
+
+    gct->evac_step = ws->stp;
+
+    bd = ws->todo_large_objects;
+    
+    for (; bd != NULL; bd = ws->todo_large_objects) {
+       
+       // take this object *off* the large objects list and put it on
+       // the scavenged large objects list.  This is so that we can
+       // treat new_large_objects as a stack and push new objects on
+       // the front when evacuating.
+       ws->todo_large_objects = bd->link;
+       
+       ACQUIRE_SPIN_LOCK(&ws->stp->sync_large_objects);
+       dbl_link_onto(bd, &ws->stp->scavenged_large_objects);
+       ws->stp->n_scavenged_large_blocks += bd->blocks;
+       RELEASE_SPIN_LOCK(&ws->stp->sync_large_objects);
+       
+       p = bd->start;
+       if (scavenge_one(p)) {
+           if (ws->stp->gen_no > 0) {
+               recordMutableGen_GC((StgClosure *)p, ws->stp->gen);
+           }
+       }
+    }
+}
+
+/* ----------------------------------------------------------------------------
+   Scavenge a block
+   ------------------------------------------------------------------------- */
+
+#define MINOR_GC
+#include "Scav.c-inc"
+#undef MINOR_GC
+#include "Scav.c-inc"
+
+/* ----------------------------------------------------------------------------
+   Find the oldest full block to scavenge, and scavenge it.
+   ------------------------------------------------------------------------- */
+
+static rtsBool
+scavenge_find_global_work (void)
 {
-  bdescr *bd;
-  StgPtr p;
+    bdescr *bd;
+    int s;
+    rtsBool flag;
+    step_workspace *ws;
+
+    flag = rtsFalse;
+    for (s = total_steps-1; s>=0; s--)
+    {
+        if (s == 0 && RtsFlags.GcFlags.generations > 1) { 
+            continue; 
+        }
+        ws = &gct->steps[s];
+
+        // If we have any large objects to scavenge, do them now.
+        if (ws->todo_large_objects) {
+            scavenge_large(ws);
+            flag = rtsTrue;
+        }
+
+        if ((bd = grab_todo_block(ws)) != NULL) {
+            // no need to assign this to ws->scan_bd, we're going
+            // to scavenge the whole thing and then push it on
+            // our scavd list.  This saves pushing out the
+            // scan_bd block, which might be partial.
+            if (N == 0) {
+                scavenge_block0(bd, bd->start);
+            } else {
+                scavenge_block(bd, bd->start);
+            }
+            push_scan_block(bd, ws);
+            return rtsTrue;
+        }
+
+        if (flag) return rtsTrue;
+    }
+    return rtsFalse;
+}
 
-  bd = stp->new_large_objects;
+/* ----------------------------------------------------------------------------
+   Look for local work to do.
 
-  for (; bd != NULL; bd = stp->new_large_objects) {
+   We can have outstanding scavenging to do if, for any of the workspaces,
 
-    /* take this object *off* the large objects list and put it on
-     * the scavenged large objects list.  This is so that we can
-     * treat new_large_objects as a stack and push new objects on
-     * the front when evacuating.
-     */
-    stp->new_large_objects = bd->link;
-    dbl_link_onto(bd, &stp->scavenged_large_objects);
+     - the scan block is the same as the todo block, and new objects
+       have been evacuated to the todo block.
 
-    // update the block count in this step.
-    stp->n_scavenged_large_blocks += bd->blocks;
+     - the scan block *was* the same as the todo block, but the todo
+       block filled up and a new one has been allocated.
+   ------------------------------------------------------------------------- */
 
-    p = bd->start;
-    if (scavenge_one(p)) {
-       if (stp->gen_no > 0) {
-           recordMutableGen((StgClosure *)p, stp->gen);
-       }
+static rtsBool
+scavenge_find_local_work (void)
+{
+    int s;
+    step_workspace *ws;
+    rtsBool flag;
+
+    flag = rtsFalse;
+    for (s = total_steps-1; s >= 0; s--) {
+        if (s == 0 && RtsFlags.GcFlags.generations > 1) { 
+            continue; 
+        }
+        ws = &gct->steps[s];
+
+        if (ws->todo_bd != NULL)
+        {
+            ws->todo_bd->free = ws->todo_free;
+        }
+        
+        // If we have a todo block and no scan block, start
+        // scanning the todo block.
+        if (ws->scan_bd == NULL && ws->todo_bd != NULL)
+        {
+            ws->scan_bd = ws->todo_bd;
+            ws->scan = ws->scan_bd->start;
+        }
+        
+        // If we have a scan block with some work to do,
+        // scavenge everything up to the free pointer.
+        if (ws->scan != NULL && ws->scan < ws->scan_bd->free)
+        {
+            if (N == 0) {
+                scavenge_block0(ws->scan_bd, ws->scan);
+            } else {
+                scavenge_block(ws->scan_bd, ws->scan);
+            }
+            ws->scan = ws->scan_bd->free;
+            flag = rtsTrue;
+        }
+        
+        if (ws->scan_bd != NULL && ws->scan == ws->scan_bd->free
+            && ws->scan_bd != ws->todo_bd)
+        {
+            // we're not going to evac any more objects into
+            // this block, so push it now.
+            push_scan_block(ws->scan_bd, ws);
+            ws->scan_bd = NULL;
+            ws->scan = NULL;
+            // we might be able to scan the todo block now.  But
+            // don't do it right away: there might be full blocks
+            // waiting to be scanned as a result of scavenge_block above.
+            flag = rtsTrue; 
+        }
+        
+        if (flag) return rtsTrue;
     }
-  }
+    return rtsFalse;
 }
 
+/* ----------------------------------------------------------------------------
+   Scavenge until we can't find anything more to scavenge.
+   ------------------------------------------------------------------------- */
+
+void
+scavenge_loop(void)
+{
+    rtsBool work_to_do;
+
+loop:
+    work_to_do = rtsFalse;
+
+    // scavenge static objects 
+    if (major_gc && static_objects != END_OF_STATIC_LIST) {
+       IF_DEBUG(sanity, checkStaticObjects(static_objects));
+       scavenge_static();
+    }
+    
+    // scavenge objects in compacted generation
+    if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
+       (mark_stack_bdescr != NULL && !mark_stack_empty())) {
+       scavenge_mark_stack();
+       work_to_do = rtsTrue;
+    }
+    
+    // Order is important here: we want to deal in full blocks as
+    // much as possible, so go for global work in preference to
+    // local work.  Only if all the global work has been exhausted
+    // do we start scavenging the fragments of blocks in the local
+    // workspaces.
+    if (scavenge_find_global_work()) goto loop;
+    if (scavenge_find_local_work())  goto loop;
+    
+    if (work_to_do) goto loop;
+}
+
+rtsBool
+any_work (void)
+{
+    int s;
+    step_workspace *ws;
+
+    write_barrier();
+
+    // scavenge static objects 
+    if (major_gc && static_objects != END_OF_STATIC_LIST) {
+       return rtsTrue;
+    }
+    
+    // scavenge objects in compacted generation
+    if (mark_stack_overflowed || oldgen_scan_bd != NULL ||
+       (mark_stack_bdescr != NULL && !mark_stack_empty())) {
+       return rtsTrue;
+    }
+    
+    // Check for global work in any step.  We don't need to check for
+    // local work, because we have already exited scavenge_loop(),
+    // which means there is no local work for this thread.
+    for (s = total_steps-1; s >= 0; s--) {
+        if (s == 0 && RtsFlags.GcFlags.generations > 1) { 
+            continue; 
+        }
+        ws = &gct->steps[s];
+        if (ws->todo_large_objects) return rtsTrue;
+        if (ws->stp->todos) return rtsTrue;
+    }
+
+    return rtsFalse;
+}