LibJS: Put zombie cell tracking code behind a compile-time flag

Since this is a debug-only feature, let's not have it impact GC marking
performance when you don't need it.

Userland/Libraries/LibJS/Heap/Cell.h

@@ -24,12 +24,18 @@ public:
     bool is_marked() const { return m_mark; }
     void set_marked(bool b) { m_mark = b; }
 
-    virtual void did_become_zombie() { }
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    virtual void did_become_zombie()
+    {
+    }
+#endif
 
     enum class State {
         Live,
         Dead,
+#ifdef JS_TRACK_ZOMBIE_CELLS
         Zombie,
+#endif
     };
 
     State state() const { return m_state; }

Userland/Libraries/LibJS/Heap/Heap.cpp

@@ -184,11 +184,13 @@ public:
             return;
         dbgln_if(HEAP_DEBUG, "  ! {}", &cell);
 
+#ifdef JS_TRACK_ZOMBIE_CELLS
         if (cell.state() == Cell::State::Zombie) {
             dbgln("BUG! Marking a zombie cell, {} @ {:p}", cell.class_name(), &cell);
             cell.vm().dump_backtrace();
             VERIFY_NOT_REACHED();
         }
+#endif
 
         cell.set_marked(true);
         cell.visit_edges(*this);
@@ -230,12 +232,16 @@ void Heap::sweep_dead_cells(bool print_report, const Core::ElapsedTimer& measure
                 dbgln_if(HEAP_DEBUG, "  ~ {}", cell);
                 if (should_store_swept_cells)
                     swept_cells.append(cell);
+#ifdef JS_TRACK_ZOMBIE_CELLS
                 if (m_zombify_dead_cells) {
                     cell->set_state(Cell::State::Zombie);
                     cell->did_become_zombie();
                 } else {
+#endif
                     block.deallocate(cell);
+#ifdef JS_TRACK_ZOMBIE_CELLS
                 }
+#endif
                 ++collected_cells;
                 collected_cell_bytes += block.cell_size();
             } else {

Userland/Libraries/LibJS/Heap/Heap.h

@@ -62,7 +62,12 @@ public:
     bool should_collect_on_every_allocation() const { return m_should_collect_on_every_allocation; }
     void set_should_collect_on_every_allocation(bool b) { m_should_collect_on_every_allocation = b; }
 
-    void set_zombify_dead_cells(bool b) { m_zombify_dead_cells = b; }
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    void set_zombify_dead_cells(bool b)
+    {
+        m_zombify_dead_cells = b;
+    }
+#endif
 
     void did_create_handle(Badge<HandleImpl>, HandleImpl&);
     void did_destroy_handle(Badge<HandleImpl>, HandleImpl&);
@@ -122,7 +127,10 @@ private:
     bool m_should_gc_when_deferral_ends { false };
 
     bool m_collecting_garbage { false };
+
+#ifdef JS_TRACK_ZOMBIE_CELLS
     bool m_zombify_dead_cells { false };
+#endif
 };
 
 }

Userland/Libraries/LibJS/Runtime/FinalizationRegistry.h

@@ -34,7 +34,13 @@ public:
 
 private:
     virtual void visit_edges(Visitor& visitor) override;
-    virtual void did_become_zombie() override { deregister(); }
+
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    virtual void did_become_zombie() override
+    {
+        deregister();
+    }
+#endif
 
     FunctionObject* m_cleanup_callback { nullptr };
 

Userland/Libraries/LibJS/Runtime/Shape.cpp

@@ -238,9 +238,11 @@ FLATTEN void Shape::add_property_without_transition(PropertyName const& property
     add_property_without_transition(property_name.to_string_or_symbol(), attributes);
 }
 
+#ifdef JS_TRACK_ZOMBIE_CELLS
 void Shape::did_become_zombie()
 {
     revoke_weak_ptrs();
 }
+#endif
 
 }

Userland/Libraries/LibJS/Runtime/Shape.h

@@ -88,7 +88,10 @@ public:
 private:
     virtual const char* class_name() const override { return "Shape"; }
     virtual void visit_edges(Visitor&) override;
+
+#ifdef JS_TRACK_ZOMBIE_CELLS
     virtual void did_become_zombie() override;
+#endif
 
     Shape* get_or_prune_cached_forward_transition(TransitionKey const&);
     Shape* get_or_prune_cached_prototype_transition(Object* prototype);

Userland/Libraries/LibJS/Runtime/WeakMap.h

@@ -30,7 +30,13 @@ public:
     virtual void remove_swept_cells(Badge<Heap>, Span<Cell*>) override;
 
 private:
-    virtual void did_become_zombie() override { deregister(); }
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    virtual void did_become_zombie() override
+    {
+        deregister();
+    }
+#endif
+
     void visit_edges(Visitor&) override;
 
     HashMap<Cell*, Value> m_values; // This stores Cell pointers instead of Object pointers to aide with sweeping

Userland/Libraries/LibJS/Runtime/WeakRef.h

@@ -31,7 +31,13 @@ public:
 
 private:
     virtual void visit_edges(Visitor&) override;
-    virtual void did_become_zombie() override { deregister(); }
+
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    virtual void did_become_zombie() override
+    {
+        deregister();
+    }
+#endif
 
     Object* m_value { nullptr };
     u32 m_last_execution_generation { 0 };

Userland/Libraries/LibJS/Runtime/WeakSet.h

@@ -30,7 +30,12 @@ public:
     virtual void remove_swept_cells(Badge<Heap>, Span<Cell*>) override;
 
 private:
-    virtual void did_become_zombie() override { deregister(); }
+#ifdef JS_TRACK_ZOMBIE_CELLS
+    virtual void did_become_zombie() override
+    {
+        deregister();
+    }
+#endif
 
     HashTable<Cell*> m_values; // This stores Cell pointers instead of Object pointers to aide with sweeping
 };