A small GC optimisation
[ghc-hetmet.git] / rts / sm / Scav.c
index a2ee1ce..9ac152a 100644 (file)
@@ -46,30 +46,11 @@ static void scavenge_large_bitmap (StgPtr p,
    Scavenge a TSO.
    -------------------------------------------------------------------------- */
 
-STATIC_INLINE void
-scavenge_TSO_link (StgTSO *tso)
-{
-    // 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) {
-        evacuate((StgClosure **)&tso->_link);
-    }
-}
-
 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;
-    }
-
     debugTrace(DEBUG_gc,"scavenging thread %d",(int)tso->id);
 
     // update the pointer from the Task.
@@ -80,32 +61,33 @@ scavengeTSO (StgTSO *tso)
     saved_eager = gct->eager_promotion;
     gct->eager_promotion = rtsFalse;
 
-    if (   tso->why_blocked == BlockedOnMVar
-       || tso->why_blocked == BlockedOnBlackHole
-       || tso->why_blocked == BlockedOnException
-       ) {
-       evacuate(&tso->block_info.closure);
-    }
     evacuate((StgClosure **)&tso->blocked_exceptions);
+    evacuate((StgClosure **)&tso->bq);
     
     // scavange current transaction record
     evacuate((StgClosure **)&tso->trec);
-    
-    // scavenge this thread's stack 
-    scavenge_stack(tso->sp, &(tso->stack[tso->stack_size]));
 
-    if (gct->failed_to_evac) {
-        tso->dirty = 1;
-        scavenge_TSO_link(tso);
-    } else {
-        tso->dirty = 0;
-        scavenge_TSO_link(tso);
-        if (gct->failed_to_evac) {
-            tso->flags |= TSO_LINK_DIRTY;
-        } else {
-            tso->flags &= ~TSO_LINK_DIRTY;
-        }
+    evacuate((StgClosure **)&tso->stackobj);
+
+    evacuate((StgClosure **)&tso->_link);
+    if (   tso->why_blocked == BlockedOnMVar
+       || tso->why_blocked == BlockedOnBlackHole
+       || tso->why_blocked == BlockedOnMsgThrowTo
+        || tso->why_blocked == NotBlocked
+       ) {
+       evacuate(&tso->block_info.closure);
+    }
+#ifdef THREADED_RTS
+    // in the THREADED_RTS, block_info.closure must always point to a
+    // valid closure, because we assume this in throwTo().  In the
+    // non-threaded RTS it might be a FD (for
+    // BlockedOnRead/BlockedOnWrite) or a time value (BlockedOnDelay)
+    else {
+        tso->block_info.closure = (StgClosure *)END_TSO_QUEUE;
     }
+#endif
+
+    tso->dirty = gct->failed_to_evac;
 
     gct->eager_promotion = saved_eager;
 }
@@ -331,7 +313,7 @@ scavenge_srt (StgClosure **srt, nat srt_bitmap)
 
   while (bitmap != 0) {
       if ((bitmap & 1) != 0) {
-#if defined(__PIC__) && defined(mingw32_TARGET_OS)
+#if defined(__PIC__) && defined(mingw32_HOST_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)
@@ -380,11 +362,11 @@ scavenge_fun_srt(const StgInfoTable *info)
 /* -----------------------------------------------------------------------------
    Scavenge a block from the given scan pointer up to bd->free.
 
-   evac_gen is set by the caller to be either zero (for a step in a
+   evac_gen_no 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
+   We sometimes temporarily change evac_gen_no back to zero if we're
    scavenging a mutable object where eager promotion isn't such a good
    idea.  
    -------------------------------------------------------------------------- */
@@ -394,7 +376,6 @@ scavenge_block (bdescr *bd)
 {
   StgPtr p, q;
   StgInfoTable *info;
-  generation *saved_evac_gen;
   rtsBool saved_eager_promotion;
   gen_workspace *ws;
 
@@ -402,8 +383,7 @@ scavenge_block (bdescr *bd)
             bd->start, bd->gen_no, bd->u.scan);
 
   gct->scan_bd = bd;
-  gct->evac_gen = bd->gen;
-  saved_evac_gen = gct->evac_gen;
+  gct->evac_gen_no = bd->gen_no;
   saved_eager_promotion = gct->eager_promotion;
   gct->failed_to_evac = rtsFalse;
 
@@ -532,7 +512,7 @@ scavenge_block (bdescr *bd)
     gen_obj:
     case CONSTR:
     case WEAK:
-    case STABLE_NAME:
+    case PRIM:
     {
        StgPtr end;
 
@@ -554,23 +534,7 @@ scavenge_block (bdescr *bd)
     }
 
     case IND_PERM:
-      if (bd->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:
+    case BLACKHOLE:
        evacuate(&((StgInd *)p)->indirectee);
        p += sizeofW(StgInd);
        break;
@@ -589,10 +553,25 @@ scavenge_block (bdescr *bd)
        p += sizeofW(StgMutVar);
        break;
 
-    case CAF_BLACKHOLE:
-    case BLACKHOLE:
-       p += BLACKHOLE_sizeW();
-       break;
+    case BLOCKING_QUEUE:
+    {
+        StgBlockingQueue *bq = (StgBlockingQueue *)p;
+        
+       gct->eager_promotion = rtsFalse;
+        evacuate(&bq->bh);
+        evacuate((StgClosure**)&bq->owner);
+        evacuate((StgClosure**)&bq->queue);
+        evacuate((StgClosure**)&bq->link);
+       gct->eager_promotion = saved_eager_promotion;
+
+       if (gct->failed_to_evac) {
+           bq->header.info = &stg_BLOCKING_QUEUE_DIRTY_info;
+       } else {
+           bq->header.info = &stg_BLOCKING_QUEUE_CLEAN_info;
+       }
+        p += sizeofW(StgBlockingQueue);
+        break;
+    }
 
     case THUNK_SELECTOR:
     { 
@@ -666,48 +645,40 @@ scavenge_block (bdescr *bd)
 
     case TSO:
     { 
-       StgTSO *tso = (StgTSO *)p;
-        scavengeTSO(tso);
-       p += tso_sizeW(tso);
+        scavengeTSO((StgTSO *)p);
+        p += sizeofW(StgTSO);
        break;
     }
 
-    case TVAR_WATCH_QUEUE:
-      {
-       StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-       gct->evac_gen = 0;
-       evacuate((StgClosure **)&wq->closure);
-       evacuate((StgClosure **)&wq->next_queue_entry);
-       evacuate((StgClosure **)&wq->prev_queue_entry);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTVarWatchQueue);
-       break;
-      }
+    case STACK:
+    {
+        StgStack *stack = (StgStack*)p;
 
-    case TVAR:
-      {
-       StgTVar *tvar = ((StgTVar *) p);
-       gct->evac_gen = 0;
-       evacuate((StgClosure **)&tvar->current_value);
-       evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTVar);
-       break;
-      }
+        gct->eager_promotion = rtsFalse;
+
+        scavenge_stack(stack->sp, stack->stack + stack->stack_size);
+        stack->dirty = gct->failed_to_evac;
+        p += stack_sizeW(stack);
 
-    case TREC_HEADER:
+        gct->eager_promotion = saved_eager_promotion;
+        break;
+    }
+
+    case MUT_PRIM:
       {
-        StgTRecHeader *trec = ((StgTRecHeader *) p);
-        gct->evac_gen = 0;
-       evacuate((StgClosure **)&trec->enclosing_trec);
-       evacuate((StgClosure **)&trec->current_chunk);
-       evacuate((StgClosure **)&trec->invariants_to_check);
-       gct->evac_gen = saved_evac_gen;
+       StgPtr end;
+
+       gct->eager_promotion = rtsFalse;
+
+       end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
+       for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
+           evacuate((StgClosure **)p);
+       }
+       p += info->layout.payload.nptrs;
+
+       gct->eager_promotion = saved_eager_promotion;
        gct->failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgTRecHeader);
-        break;
+       break;
       }
 
     case TREC_CHUNK:
@@ -715,44 +686,19 @@ scavenge_block (bdescr *bd)
        StgWord i;
        StgTRecChunk *tc = ((StgTRecChunk *) p);
        TRecEntry *e = &(tc -> entries[0]);
-       gct->evac_gen = 0;
+       gct->eager_promotion = rtsFalse;
        evacuate((StgClosure **)&tc->prev_chunk);
        for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
          evacuate((StgClosure **)&e->tvar);
          evacuate((StgClosure **)&e->expected_value);
          evacuate((StgClosure **)&e->new_value);
        }
-       gct->evac_gen = saved_evac_gen;
+       gct->eager_promotion = saved_eager_promotion;
        gct->failed_to_evac = rtsTrue; // mutable
        p += sizeofW(StgTRecChunk);
        break;
       }
 
-    case ATOMIC_INVARIANT:
-      {
-        StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-        gct->evac_gen = 0;
-       evacuate(&invariant->code);
-       evacuate((StgClosure **)&invariant->last_execution);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgAtomicInvariant);
-        break;
-      }
-
-    case INVARIANT_CHECK_QUEUE:
-      {
-        StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-        gct->evac_gen = 0;
-       evacuate((StgClosure **)&queue->invariant);
-       evacuate((StgClosure **)&queue->my_execution);
-       evacuate((StgClosure **)&queue->next_queue_entry);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-       p += sizeofW(StgInvariantCheckQueue);
-        break;
-      }
-
     default:
        barf("scavenge: unimplemented/strange closure type %d @ %p", 
             info->type, p);
@@ -806,10 +752,10 @@ scavenge_mark_stack(void)
 {
     StgPtr p, q;
     StgInfoTable *info;
-    generation *saved_evac_gen;
+    rtsBool saved_eager_promotion;
 
-    gct->evac_gen = oldest_gen;
-    saved_evac_gen = gct->evac_gen;
+    gct->evac_gen_no = oldest_gen->no;
+    saved_eager_promotion = gct->eager_promotion;
 
     while ((p = pop_mark_stack())) {
 
@@ -822,8 +768,6 @@ scavenge_mark_stack(void)
         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);
@@ -906,7 +850,7 @@ scavenge_mark_stack(void)
        gen_obj:
        case CONSTR:
        case WEAK:
-       case STABLE_NAME:
+       case PRIM:
        {
            StgPtr end;
            
@@ -931,15 +875,13 @@ scavenge_mark_stack(void)
            // no "old" generation.
            break;
 
-       case IND_OLDGEN:
-       case IND_OLDGEN_PERM:
+       case IND:
+        case BLACKHOLE:
            evacuate(&((StgInd *)p)->indirectee);
            break;
 
        case MUT_VAR_CLEAN:
        case MUT_VAR_DIRTY: {
-           rtsBool saved_eager_promotion = gct->eager_promotion;
-           
            gct->eager_promotion = rtsFalse;
            evacuate(&((StgMutVar *)p)->var);
            gct->eager_promotion = saved_eager_promotion;
@@ -952,8 +894,25 @@ scavenge_mark_stack(void)
            break;
        }
 
-       case CAF_BLACKHOLE:
-       case BLACKHOLE:
+        case BLOCKING_QUEUE:
+        {
+            StgBlockingQueue *bq = (StgBlockingQueue *)p;
+            
+            gct->eager_promotion = rtsFalse;
+            evacuate(&bq->bh);
+            evacuate((StgClosure**)&bq->owner);
+            evacuate((StgClosure**)&bq->queue);
+            evacuate((StgClosure**)&bq->link);
+            gct->eager_promotion = saved_eager_promotion;
+            
+            if (gct->failed_to_evac) {
+                bq->header.info = &stg_BLOCKING_QUEUE_DIRTY_info;
+            } else {
+                bq->header.info = &stg_BLOCKING_QUEUE_CLEAN_info;
+            }
+            break;
+        }
+
        case ARR_WORDS:
            break;
 
@@ -986,13 +945,10 @@ scavenge_mark_stack(void)
        case MUT_ARR_PTRS_DIRTY:
            // follow everything 
        {
-           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 = gct->eager_promotion;
            gct->eager_promotion = rtsFalse;
 
             scavenge_mut_arr_ptrs((StgMutArrPtrs *)p);
@@ -1003,7 +959,7 @@ scavenge_mark_stack(void)
                 ((StgClosure *)q)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
             }
 
-           gct->eager_promotion = saved_eager;
+           gct->eager_promotion = saved_eager_promotion;
            gct->failed_to_evac = rtsTrue; // mutable anyhow.
            break;
        }
@@ -1032,81 +988,52 @@ scavenge_mark_stack(void)
            break;
        }
 
-       case TVAR_WATCH_QUEUE:
-         {
-           StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-           gct->evac_gen = 0;
-            evacuate((StgClosure **)&wq->closure);
-           evacuate((StgClosure **)&wq->next_queue_entry);
-           evacuate((StgClosure **)&wq->prev_queue_entry);
-           gct->evac_gen = saved_evac_gen;
-           gct->failed_to_evac = rtsTrue; // mutable
-           break;
-         }
-         
-       case TVAR:
-         {
-           StgTVar *tvar = ((StgTVar *) p);
-           gct->evac_gen = 0;
-           evacuate((StgClosure **)&tvar->current_value);
-           evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-           gct->evac_gen = saved_evac_gen;
-           gct->failed_to_evac = rtsTrue; // mutable
-           break;
-         }
-         
+        case STACK:
+        {
+            StgStack *stack = (StgStack*)p;
+
+            gct->eager_promotion = rtsFalse;
+
+            scavenge_stack(stack->sp, stack->stack + stack->stack_size);
+            stack->dirty = gct->failed_to_evac;
+
+            gct->eager_promotion = saved_eager_promotion;
+            break;
+        }
+
+        case MUT_PRIM:
+        {
+            StgPtr end;
+            
+            gct->eager_promotion = rtsFalse;
+            
+            end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
+            for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
+                evacuate((StgClosure **)p);
+            }
+            
+            gct->eager_promotion = saved_eager_promotion;
+            gct->failed_to_evac = rtsTrue; // mutable
+            break;
+        }
+
        case TREC_CHUNK:
          {
            StgWord i;
            StgTRecChunk *tc = ((StgTRecChunk *) p);
            TRecEntry *e = &(tc -> entries[0]);
-           gct->evac_gen = 0;
+           gct->eager_promotion = rtsFalse;
            evacuate((StgClosure **)&tc->prev_chunk);
            for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
              evacuate((StgClosure **)&e->tvar);
              evacuate((StgClosure **)&e->expected_value);
              evacuate((StgClosure **)&e->new_value);
            }
-           gct->evac_gen = saved_evac_gen;
-           gct->failed_to_evac = rtsTrue; // mutable
-           break;
-         }
-
-       case TREC_HEADER:
-         {
-           StgTRecHeader *trec = ((StgTRecHeader *) p);
-           gct->evac_gen = 0;
-           evacuate((StgClosure **)&trec->enclosing_trec);
-           evacuate((StgClosure **)&trec->current_chunk);
-           evacuate((StgClosure **)&trec->invariants_to_check);
-           gct->evac_gen = saved_evac_gen;
+           gct->eager_promotion = saved_eager_promotion;
            gct->failed_to_evac = rtsTrue; // mutable
            break;
          }
 
-        case ATOMIC_INVARIANT:
-          {
-            StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-            gct->evac_gen = 0;
-           evacuate(&invariant->code);
-           evacuate((StgClosure **)&invariant->last_execution);
-           gct->evac_gen = saved_evac_gen;
-           gct->failed_to_evac = rtsTrue; // mutable
-            break;
-          }
-
-        case INVARIANT_CHECK_QUEUE:
-          {
-            StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-            gct->evac_gen = 0;
-           evacuate((StgClosure **)&queue->invariant);
-           evacuate((StgClosure **)&queue->my_execution);
-            evacuate((StgClosure **)&queue->next_queue_entry);
-           gct->evac_gen = saved_evac_gen;
-           gct->failed_to_evac = rtsTrue; // mutable
-            break;
-          }
-
        default:
            barf("scavenge_mark_stack: unimplemented/strange closure type %d @ %p", 
                 info->type, p);
@@ -1114,8 +1041,8 @@ scavenge_mark_stack(void)
 
        if (gct->failed_to_evac) {
            gct->failed_to_evac = rtsFalse;
-           if (gct->evac_gen) {
-               recordMutableGen_GC((StgClosure *)q, gct->evac_gen->no);
+            if (gct->evac_gen_no) {
+                recordMutableGen_GC((StgClosure *)q, gct->evac_gen_no);
            }
        }
     } // while (p = pop_mark_stack())
@@ -1133,9 +1060,11 @@ static rtsBool
 scavenge_one(StgPtr p)
 {
     const StgInfoTable *info;
-    generation *saved_evac_gen = gct->evac_gen;
     rtsBool no_luck;
+    rtsBool saved_eager_promotion;
     
+    saved_eager_promotion = gct->eager_promotion;
+
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(p));
     info = get_itbl((StgClosure *)p);
     
@@ -1144,8 +1073,6 @@ scavenge_one(StgPtr p)
     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);
@@ -1190,6 +1117,7 @@ scavenge_one(StgPtr p)
     case CONSTR_0_2:
     case CONSTR_2_0:
     case WEAK:
+    case PRIM:
     case IND_PERM:
     {
        StgPtr q, end;
@@ -1204,7 +1132,6 @@ scavenge_one(StgPtr p)
     case MUT_VAR_CLEAN:
     case MUT_VAR_DIRTY: {
        StgPtr q = p;
-       rtsBool saved_eager_promotion = gct->eager_promotion;
 
        gct->eager_promotion = rtsFalse;
        evacuate(&((StgMutVar *)p)->var);
@@ -1218,10 +1145,25 @@ scavenge_one(StgPtr p)
        break;
     }
 
-    case CAF_BLACKHOLE:
-    case BLACKHOLE:
-       break;
-       
+    case BLOCKING_QUEUE:
+    {
+        StgBlockingQueue *bq = (StgBlockingQueue *)p;
+        
+        gct->eager_promotion = rtsFalse;
+        evacuate(&bq->bh);
+        evacuate((StgClosure**)&bq->owner);
+        evacuate((StgClosure**)&bq->queue);
+        evacuate((StgClosure**)&bq->link);
+        gct->eager_promotion = saved_eager_promotion;
+        
+        if (gct->failed_to_evac) {
+            bq->header.info = &stg_BLOCKING_QUEUE_DIRTY_info;
+        } else {
+            bq->header.info = &stg_BLOCKING_QUEUE_CLEAN_info;
+        }
+        break;
+    }
+
     case THUNK_SELECTOR:
     { 
        StgSelector *s = (StgSelector *)p;
@@ -1254,13 +1196,10 @@ scavenge_one(StgPtr p)
     case MUT_ARR_PTRS_CLEAN:
     case MUT_ARR_PTRS_DIRTY:
     {
-       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 = gct->eager_promotion;
        gct->eager_promotion = rtsFalse;
 
         scavenge_mut_arr_ptrs((StgMutArrPtrs *)p);
@@ -1271,7 +1210,7 @@ scavenge_one(StgPtr p)
            ((StgClosure *)p)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
        }
 
-       gct->eager_promotion = saved_eager;
+       gct->eager_promotion = saved_eager_promotion;
        gct->failed_to_evac = rtsTrue;
        break;
     }
@@ -1298,87 +1237,58 @@ scavenge_one(StgPtr p)
        break;
     }
   
-    case TVAR_WATCH_QUEUE:
-      {
-       StgTVarWatchQueue *wq = ((StgTVarWatchQueue *) p);
-       gct->evac_gen = 0;
-        evacuate((StgClosure **)&wq->closure);
-        evacuate((StgClosure **)&wq->next_queue_entry);
-        evacuate((StgClosure **)&wq->prev_queue_entry);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-       break;
-      }
+    case STACK:
+    {
+        StgStack *stack = (StgStack*)p;
 
-    case TVAR:
-      {
-       StgTVar *tvar = ((StgTVar *) p);
-       gct->evac_gen = 0;
-       evacuate((StgClosure **)&tvar->current_value);
-        evacuate((StgClosure **)&tvar->first_watch_queue_entry);
-       gct->evac_gen = saved_evac_gen;
+        gct->eager_promotion = rtsFalse;
+
+        scavenge_stack(stack->sp, stack->stack + stack->stack_size);
+        stack->dirty = gct->failed_to_evac;
+
+        gct->eager_promotion = saved_eager_promotion;
+        break;
+    }
+
+    case MUT_PRIM:
+    {
+       StgPtr end;
+        
+       gct->eager_promotion = rtsFalse;
+        
+       end = (P_)((StgClosure *)p)->payload + info->layout.payload.ptrs;
+       for (p = (P_)((StgClosure *)p)->payload; p < end; p++) {
+           evacuate((StgClosure **)p);
+       }
+
+       gct->eager_promotion = saved_eager_promotion;
        gct->failed_to_evac = rtsTrue; // mutable
        break;
-      }
 
-    case TREC_HEADER:
-      {
-        StgTRecHeader *trec = ((StgTRecHeader *) p);
-        gct->evac_gen = 0;
-       evacuate((StgClosure **)&trec->enclosing_trec);
-       evacuate((StgClosure **)&trec->current_chunk);
-        evacuate((StgClosure **)&trec->invariants_to_check);
-       gct->evac_gen = saved_evac_gen;
-       gct->failed_to_evac = rtsTrue; // mutable
-        break;
-      }
+    }
 
     case TREC_CHUNK:
       {
        StgWord i;
        StgTRecChunk *tc = ((StgTRecChunk *) p);
        TRecEntry *e = &(tc -> entries[0]);
-       gct->evac_gen = 0;
+       gct->eager_promotion = rtsFalse;
        evacuate((StgClosure **)&tc->prev_chunk);
        for (i = 0; i < tc -> next_entry_idx; i ++, e++ ) {
          evacuate((StgClosure **)&e->tvar);
          evacuate((StgClosure **)&e->expected_value);
          evacuate((StgClosure **)&e->new_value);
        }
-       gct->evac_gen = saved_evac_gen;
+       gct->eager_promotion = saved_eager_promotion;
        gct->failed_to_evac = rtsTrue; // mutable
        break;
       }
 
-    case ATOMIC_INVARIANT:
-    {
-      StgAtomicInvariant *invariant = ((StgAtomicInvariant *) p);
-      gct->evac_gen = 0;
-      evacuate(&invariant->code);
-      evacuate((StgClosure **)&invariant->last_execution);
-      gct->evac_gen = saved_evac_gen;
-      gct->failed_to_evac = rtsTrue; // mutable
-      break;
-    }
-
-    case INVARIANT_CHECK_QUEUE:
-    {
-      StgInvariantCheckQueue *queue = ((StgInvariantCheckQueue *) p);
-      gct->evac_gen = 0;
-      evacuate((StgClosure **)&queue->invariant);
-      evacuate((StgClosure **)&queue->my_execution);
-      evacuate((StgClosure **)&queue->next_queue_entry);
-      gct->evac_gen = saved_evac_gen;
-      gct->failed_to_evac = rtsTrue; // mutable
-      break;
-    }
-
     case IND:
         // IND can happen, for example, when the interpreter allocates
         // a gigantic AP closure (more than one block), which ends up
         // on the large-object list and then gets updated.  See #3424.
-    case IND_OLDGEN:
-    case IND_OLDGEN_PERM:
+    case BLACKHOLE:
     case IND_STATIC:
        evacuate(&((StgInd *)p)->indirectee);
 
@@ -1430,8 +1340,10 @@ void
 scavenge_mutable_list(bdescr *bd, generation *gen)
 {
     StgPtr p, q;
+    nat gen_no;
 
-    gct->evac_gen = gen;
+    gen_no = gen->no;
+    gct->evac_gen_no = gen_no;
     for (; bd != NULL; bd = bd->link) {
        for (q = bd->start; q < bd->free; q++) {
            p = (StgPtr)*q;
@@ -1440,7 +1352,7 @@ scavenge_mutable_list(bdescr *bd, generation *gen)
 #ifdef DEBUG       
            switch (get_itbl((StgClosure *)p)->type) {
            case MUT_VAR_CLEAN:
-               barf("MUT_VAR_CLEAN on mutable list");
+                // can happen due to concurrent writeMutVars
            case MUT_VAR_DIRTY:
                mutlist_MUTVARS++; break;
            case MUT_ARR_PTRS_CLEAN:
@@ -1466,12 +1378,12 @@ scavenge_mutable_list(bdescr *bd, generation *gen)
            //
            switch (get_itbl((StgClosure *)p)->type) {
            case MUT_ARR_PTRS_CLEAN:
-               recordMutableGen_GC((StgClosure *)p,gen->no);
+                recordMutableGen_GC((StgClosure *)p,gen_no);
                continue;
            case MUT_ARR_PTRS_DIRTY:
             {
-                rtsBool saved_eager;
-                saved_eager = gct->eager_promotion;
+                rtsBool saved_eager_promotion;
+                saved_eager_promotion = gct->eager_promotion;
                 gct->eager_promotion = rtsFalse;
 
                 scavenge_mut_arr_ptrs_marked((StgMutArrPtrs *)p);
@@ -1482,36 +1394,19 @@ scavenge_mutable_list(bdescr *bd, generation *gen)
                     ((StgClosure *)p)->header.info = &stg_MUT_ARR_PTRS_CLEAN_info;
                 }
 
-                gct->eager_promotion = saved_eager;
+                gct->eager_promotion = saved_eager_promotion;
                 gct->failed_to_evac = rtsFalse;
-               recordMutableGen_GC((StgClosure *)p,gen->no);
+                recordMutableGen_GC((StgClosure *)p,gen_no);
                continue;
             }
-           case TSO: {
-               StgTSO *tso = (StgTSO *)p;
-               if (tso->dirty == 0) {
-                    // Must be on the mutable list because its link
-                    // field is dirty.
-                    ASSERT(tso->flags & TSO_LINK_DIRTY);
-
-                    scavenge_TSO_link(tso);
-                    if (gct->failed_to_evac) {
-                        recordMutableGen_GC((StgClosure *)p,gen->no);
-                        gct->failed_to_evac = rtsFalse;
-                    } else {
-                        tso->flags &= ~TSO_LINK_DIRTY;
-                    }
-                   continue;
-               }
-           }
-           default:
+            default:
                ;
            }
 
            if (scavenge_one(p)) {
                // didn't manage to promote everything, so put the
                // object back on the list.
-               recordMutableGen_GC((StgClosure *)p,gen->no);
+                recordMutableGen_GC((StgClosure *)p,gen_no);
            }
        }
     }
@@ -1553,7 +1448,7 @@ scavenge_static(void)
 
   /* Always evacuate straight to the oldest generation for static
    * objects */
-  gct->evac_gen = oldest_gen;
+  gct->evac_gen_no = oldest_gen->no;
 
   /* keep going until we've scavenged all the objects on the linked
      list... */
@@ -1638,23 +1533,21 @@ scavenge_static(void)
 static void
 scavenge_large_bitmap( StgPtr p, StgLargeBitmap *large_bitmap, nat size )
 {
-    nat i, b;
+    nat i, j, b;
     StgWord bitmap;
     
     b = 0;
-    bitmap = large_bitmap->bitmap[b];
-    for (i = 0; i < size; ) {
-       if ((bitmap & 1) == 0) {
-           evacuate((StgClosure **)p);
-       }
-       i++;
-       p++;
-       if (i % BITS_IN(W_) == 0) {
-           b++;
-           bitmap = large_bitmap->bitmap[b];
-       } else {
+
+    for (i = 0; i < size; b++) {
+        bitmap = large_bitmap->bitmap[b];
+        j = stg_min(size-i, BITS_IN(W_));
+        i += j;
+        for (; j > 0; j--, p++) {
+            if ((bitmap & 1) == 0) {
+                evacuate((StgClosure **)p);
+            }
            bitmap = bitmap >> 1;
-       }
+        }            
     }
 }
 
@@ -1714,10 +1607,12 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
        // before GC, but that seems like overkill.
        //
        // Scavenging this update frame as normal would be disastrous;
-       // the updatee would end up pointing to the value.  So we turn
-       // the indirection into an IND_PERM, so that evacuate will
-       // copy the indirection into the old generation instead of
-       // discarding it.
+       // the updatee would end up pointing to the value.  So we
+       // check whether the value after evacuation is a BLACKHOLE,
+       // and if not, we change the update frame to an stg_enter
+       // frame that simply returns the value.  Hence, blackholing is
+        // compulsory (otherwise we would have to check for thunks
+        // too).
         //
         // Note [upd-black-hole]
         // One slight hiccup is that the THUNK_SELECTOR machinery can
@@ -1728,22 +1623,17 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
         // the updatee is never a THUNK_SELECTOR and we're ok.
         // NB. this is a new invariant: blackholing is not optional.
     {
-        nat type;
-        const StgInfoTable *i;
-        StgClosure *updatee;
-
-        updatee = ((StgUpdateFrame *)p)->updatee;
-        i = updatee->header.info;
-        if (!IS_FORWARDING_PTR(i)) {
-            type = get_itbl(updatee)->type;
-            if (type == IND) {
-                updatee->header.info = &stg_IND_PERM_info;
-            } else if (type == IND_OLDGEN) {
-                updatee->header.info = &stg_IND_OLDGEN_PERM_info;
-            }            
+        StgUpdateFrame *frame = (StgUpdateFrame *)p;
+        StgClosure *v;
+
+        evacuate(&frame->updatee);
+        v = frame->updatee;
+        if (GET_CLOSURE_TAG(v) != 0 ||
+            (get_itbl(v)->type != BLACKHOLE)) {
+            // blackholing is compulsory, see above.
+            frame->header.info = (const StgInfoTable*)&stg_enter_checkbh_info;
         }
-        evacuate(&((StgUpdateFrame *)p)->updatee);
-        ASSERT(GET_CLOSURE_TAG(((StgUpdateFrame *)p)->updatee) == 0);
+        ASSERT(v->header.info != &stg_TSO_info);
         p += sizeofW(StgUpdateFrame);
         continue;
     }
@@ -1752,6 +1642,7 @@ scavenge_stack(StgPtr p, StgPtr stack_end)
     case CATCH_STM_FRAME:
     case CATCH_RETRY_FRAME:
     case ATOMICALLY_FRAME:
+    case UNDERFLOW_FRAME:
     case STOP_FRAME:
     case CATCH_FRAME:
     case RET_SMALL:
@@ -1852,7 +1743,7 @@ scavenge_large (gen_workspace *ws)
     bdescr *bd;
     StgPtr p;
 
-    gct->evac_gen = ws->gen;
+    gct->evac_gen_no = ws->gen->no;
 
     bd = ws->todo_large_objects;