Redundantly visit some fields of hidden classes that weren't visited.

Author: rudi-c

src/gc/collector.h

@@ -68,6 +68,7 @@ class GCVisitorNoRedundancy : public GCVisitor {
     virtual void visitRangeRedundant(void* const* start, void* const* end) { visitRange(start, end); }
     virtual void visitPotentialRedundant(void* p) { visitPotential(p); }
     virtual void visitPotentialRangeRedundant(void* const* start, void* const* end) { visitPotentialRange(start, end); }
+    virtual bool shouldVisitRedundants() { return true; }
 };
 }
 }

src/gc/gc.h

@@ -22,6 +22,10 @@
 // Files outside of the gc/ folder should only import gc.h or gc_alloc.h
 // which are the "public" memory management interface.
 
+// Some code is only useful towards an effort to implement a
+// moving gc, gate behind this flag for now.
+#define MOVING_GC 0
+
 #define GC_KEEP_ALIVE(t) asm volatile("" : : "X"(t))
 
 #define TRACE_GC_MARKING 0

src/runtime/hiddenclass.cpp

@@ -32,13 +32,23 @@ void HiddenClass::gc_visit(GCVisitor* visitor) {
     visitor->visitRange((void* const*)&children.vector()[0], (void* const*)&children.vector()[children.size()]);
     visitor->visit(attrwrapper_child);
 
-    // We don't need to visit the keys of the 'children' map, since the children should have those as entries
-    // in the attr_offssets map.
-    // Also, if we have any children, we can skip scanning our attr_offsets map, since it will be a subset
-    // of our child's map.
-    if (children.empty())
+    if (children.empty()) {
         for (auto p : attr_offsets)
             visitor->visit(p.first);
+    } else {
+#if MOVING_GC
+        // If we have any children, the attr_offsets map will be a subset of the child's map.
+        for (const auto& p : attr_offsets)
+            visitor->visitRedundant(p.first);
+#endif
+    }
+
+#if MOVING_GC
+    // The children should have the entries of the keys of the 'children' map in the attr_offsets map.
+    for (const auto& p : children) {
+        visitor->visitRedundant(p.first);
+    }
+#endif
 }
 
 void HiddenClass::appendAttribute(BoxedString* attr) {