A simple test for map compact.

test/cctest/test-mark-compact.cc

 // Copyright 2006-2008 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
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   obj_name = String::cast(Heap::LookupAsciiSymbol("theObject"));
   CHECK(Top::context()->global()->HasLocalProperty(obj_name));
   CHECK(Top::context()->global()->GetProperty(obj_name)->IsJSObject());
   obj = JSObject::cast(Top::context()->global()->GetProperty(obj_name));
   prop_name = String::cast(Heap::LookupAsciiSymbol("theSlot"));
   CHECK(obj->GetProperty(prop_name) == Smi::FromInt(23));
 }
 
 
+static Handle<Map> CreateMap() {
+  return Factory::NewMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
+}
+
+
+TEST(MapCompact) {
+  FLAG_max_map_space_pages = 16;
+  InitializeVM();
+
+  {
+    v8::HandleScope sc;
+    // keep allocating maps while pointers are still encodable and thus
+    // mark compact is permitted.
+    Handle<JSObject> root = Factory::NewJSObjectFromMap(CreateMap());
+    do {
+      Handle<Map> map = CreateMap();
+      map->set_prototype(*root);
+      root = Factory::NewJSObjectFromMap(map);
+    } while (Heap::map_space()->MapPointersEncodable());
+  }
+  // Now, as we don't have any handles to just allocated maps, we should
+  // be able to trigger map compaction.
+  // To give an additional chance to fail, try to force compaction which
+  // should be impossible right now.
+  Heap::CollectAllGarbage(true);
+  // And now map pointers should be encodable again.
+  CHECK(Heap::map_space()->MapPointersEncodable());
+}
+
+
 static int gc_starts = 0;
 static int gc_ends = 0;
 
 static void GCPrologueCallbackFunc() {
   CHECK(gc_starts == gc_ends);
   gc_starts++;
 }
 
 
 static void GCEpilogueCallbackFunc() {
@@ skipping 82 matching lines @@
     Object** g2_objects[] = { g2s1.location(), g2s2.location() };
     GlobalHandles::AddGroup(g1_objects, 2);
     GlobalHandles::AddGroup(g2_objects, 2);
   }
 
   CHECK(Heap::CollectGarbage(0, OLD_POINTER_SPACE));
 
   // All objects should be gone. 5 global handles in total.
   CHECK_EQ(5, NumberOfWeakCalls);
 }