Implement and enable zapping of code space while sweeping.

src/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3186 matching lines @@
   SWEEP_AND_VISIT_LIVE_OBJECTS
 };
 
 
 enum SkipListRebuildingMode {
   REBUILD_SKIP_LIST,
   IGNORE_SKIP_LIST
 };
 
 
+enum FreeSpaceTreatmentMode {
+  IGNORE_FREE_SPACE,
+  ZAP_FREE_SPACE
+};
+
+
 // Sweep a space precisely.  After this has been done the space can
 // be iterated precisely, hitting only the live objects.  Code space
 // is always swept precisely because we want to be able to iterate
 // over it.  Map space is swept precisely, because it is not compacted.
 // Slots in live objects pointing into evacuation candidates are updated
 // if requested.
-template<SweepingMode sweeping_mode, SkipListRebuildingMode skip_list_mode>
+template<SweepingMode sweeping_mode,
+         SkipListRebuildingMode skip_list_mode,
+         FreeSpaceTreatmentMode free_space_mode>
 static void SweepPrecisely(PagedSpace* space,
                            Page* p,
                            ObjectVisitor* v) {
   ASSERT(!p->IsEvacuationCandidate() && !p->WasSwept());
   ASSERT_EQ(skip_list_mode == REBUILD_SKIP_LIST,
             space->identity() == CODE_SPACE);
   ASSERT((p->skip_list() == NULL) || (skip_list_mode == REBUILD_SKIP_LIST));
 
   double start_time = 0.0;
   if (FLAG_print_cumulative_gc_stat) {
@@ skipping 13 matching lines @@
   }
 
   for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
     Address cell_base = it.CurrentCellBase();
     MarkBit::CellType* cell = it.CurrentCell();
     int live_objects = MarkWordToObjectStarts(*cell, offsets);
     int live_index = 0;
     for ( ; live_objects != 0; live_objects--) {
       Address free_end = cell_base + offsets[live_index++] * kPointerSize;
       if (free_end != free_start) {
+        if (free_space_mode == ZAP_FREE_SPACE) {
+          memset(free_start, 0xcc, static_cast<int>(free_end - free_start));
+        }
         space->Free(free_start, static_cast<int>(free_end - free_start));
 #ifdef ENABLE_GDB_JIT_INTERFACE
         if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
           GDBJITInterface::RemoveCodeRange(free_start, free_end);
         }
 #endif
       }
       HeapObject* live_object = HeapObject::FromAddress(free_end);
       ASSERT(Marking::IsBlack(Marking::MarkBitFrom(live_object)));
       Map* map = live_object->map();
@@ skipping 11 matching lines @@
           skip_list->AddObject(free_end, size);
           curr_region = new_region_end;
         }
       }
       free_start = free_end + size;
     }
     // Clear marking bits for current cell.
     *cell = 0;
   }
   if (free_start != p->area_end()) {
+    if (free_space_mode == ZAP_FREE_SPACE) {
+      memset(free_start, 0xcc, static_cast<int>(p->area_end() - free_start));
+    }
     space->Free(free_start, static_cast<int>(p->area_end() - free_start));
 #ifdef ENABLE_GDB_JIT_INTERFACE
     if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
       GDBJITInterface::RemoveCodeRange(free_start, p->area_end());
     }
 #endif
   }
   p->ResetLiveBytes();
   if (FLAG_print_cumulative_gc_stat) {
     space->heap()->AddSweepingTime(OS::TimeCurrentMillis() - start_time);
@@ skipping 225 matching lines @@
                  reinterpret_cast<intptr_t>(p));
         }
         PagedSpace* space = static_cast<PagedSpace*>(p->owner());
         p->ClearFlag(MemoryChunk::RESCAN_ON_EVACUATION);
 
         switch (space->identity()) {
           case OLD_DATA_SPACE:
             SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
             break;
           case OLD_POINTER_SPACE:
-            SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS, IGNORE_SKIP_LIST>(
+            SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
+                           IGNORE_SKIP_LIST,
+                           IGNORE_FREE_SPACE>(
                 space, p, &updating_visitor);
             break;
           case CODE_SPACE:
-            SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS, REBUILD_SKIP_LIST>(
-                space, p, &updating_visitor);
+            if (FLAG_zap_code_space) {
+              SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
+                             REBUILD_SKIP_LIST,
+                             ZAP_FREE_SPACE>(
+                  space, p, &updating_visitor);
+            } else {
+              SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
+                             REBUILD_SKIP_LIST,
+                             IGNORE_FREE_SPACE>(
+                  space, p, &updating_visitor);
+            }
             break;
           default:
             UNREACHABLE();
             break;
         }
       }
     }
   }
 
   GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_UPDATE_MISC_POINTERS);
@@ skipping 599 matching lines @@
           p->set_parallel_sweeping(MemoryChunk::PARALLEL_SWEEPING_PENDING);
           space->IncreaseUnsweptFreeBytes(p);
         }
         break;
       }
       case PRECISE: {
         if (FLAG_gc_verbose) {
           PrintF("Sweeping 0x%" V8PRIxPTR " precisely.\n",
                  reinterpret_cast<intptr_t>(p));
         }
-        if (space->identity() == CODE_SPACE) {
-          SweepPrecisely<SWEEP_ONLY, REBUILD_SKIP_LIST>(space, p, NULL);
+        if (space->identity() == CODE_SPACE && FLAG_zap_code_space) {
+          SweepPrecisely<SWEEP_ONLY, REBUILD_SKIP_LIST, ZAP_FREE_SPACE>(
+              space, p, NULL);
+        } else if (space->identity() == CODE_SPACE) {
+          SweepPrecisely<SWEEP_ONLY, REBUILD_SKIP_LIST, IGNORE_FREE_SPACE>(
+              space, p, NULL);
         } else {
-          SweepPrecisely<SWEEP_ONLY, IGNORE_SKIP_LIST>(space, p, NULL);
+          SweepPrecisely<SWEEP_ONLY, IGNORE_SKIP_LIST, IGNORE_FREE_SPACE>(
+              space, p, NULL);
         }
         pages_swept++;
         break;
       }
       default: {
         UNREACHABLE();
       }
     }
   }
 
@@ skipping 284 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal