Further optimize visitRange by adding and using a "pushall"

src/gc/collector.cpp

@@ -55,11 +55,13 @@ void TraceStackGCVisitor::visit(void* p) {
 }
 
 void TraceStackGCVisitor::visitRange(void** start, void** end) {
-    stack->reserve(end-start);
+#ifndef NDEBUG
     while (start < end) {
-        _visit(*start);
+        assert(isValid(*start));
         start++;
     }
+#endif
+    stack->pushall(start, end);
 }
 
 void TraceStackGCVisitor::visitPotential(void* p) {

src/gc/collector.h

@@ -51,6 +51,10 @@ class TraceStack {
         std::vector<void*> v;
 
     public:
+        void pushall(void** start, void** end) {
+            v.insert(v.end(), start, end);
+        }
+
         void push(void* p) {
             v.push_back(p);
         }