Tighten up lazy loading for virtual functions implemented in base class

Previously we would load all base classes and all their methods.
However, we don't need this, we only need methods that aren't overridden
in the specific derived class we are trying to find virtual calls on.

Author: thk123

src/java_bytecode/gather_methods_lazily.cpp

@@ -297,13 +297,8 @@ void gather_methods_lazilyt::initialize_needed_classes_from_pointer(
 {
   const symbol_typet &class_type=to_symbol_type(pointer_type.subtype());
   const auto &param_classid=class_type.get_identifier();
-  std::vector<irep_idt> class_and_parents=
-    class_hierarchy.get_parents_trans(param_classid);
 
-  class_and_parents.push_back(param_classid);
-
-  for(const auto &classid : class_and_parents)
-    lazy_methods.add_needed_class(classid);
+  lazy_methods.add_needed_class(param_classid);
 
   gather_field_types(pointer_type.subtype(), ns, lazy_methods);
 }
@@ -360,6 +355,15 @@ void gather_methods_lazilyt::get_virtual_method_targets(
 
   auto old_size=needed_methods.size();
 
+  const irep_idt &self_method=
+    get_virtual_method_target(
+      needed_classes, call_basename, call_class, symbol_table);
+
+  if(!self_method.empty())
+  {
+    needed_methods.push_back(self_method);
+  }
+
   auto child_classes=class_hierarchy.get_children_trans(call_class);
   for(const auto &child_class : child_classes)
   {
@@ -373,36 +377,6 @@ void gather_methods_lazilyt::get_virtual_method_targets(
       needed_methods.push_back(child_method);
   }
 
-  irep_idt parent_class_id=call_class;
-  while(1)
-  {
-    auto parent_method=
-      get_virtual_method_target(
-        needed_classes,
-        call_basename,
-        parent_class_id,
-        symbol_table);
-    if(!parent_method.empty())
-    {
-      needed_methods.push_back(parent_method);
-      break;
-    }
-    else
-    {
-      auto findit=class_hierarchy.class_map.find(parent_class_id);
-      if(findit==class_hierarchy.class_map.end())
-        break;
-      else
-      {
-        const auto &entry=findit->second;
-        if(entry.parents.empty())
-          break;
-        else
-          parent_class_id=entry.parents[0];
-      }
-    }
-  }
-
   if(needed_methods.size()==old_size)
   {
     // Didn't find any candidate callee. Generate a stub.
@@ -494,9 +468,41 @@ irep_idt gather_methods_lazilyt::get_virtual_method_target(
   // Program-wide, is this class ever instantiated?
   if(!needed_classes.count(classname))
     return irep_idt();
-  auto methodid=id2string(classname)+"."+id2string(call_basename);
+  auto methodid=build_virtual_method_name(classname, call_basename);
   if(symbol_table.has_symbol(methodid))
     return methodid;
   else
+  {
+    // no method found for this specific classs, but a call to this class
+    // will be resolved in one of its base classes so we should work up the
+    // heirarchy to see if one resovles
+    class_hierarchyt::idst parent_classes=
+      class_hierarchy.get_parents_trans(classname);
+    for(const irep_idt &parent_class_id : parent_classes)
+    {
+      auto parent_method_id=
+        build_virtual_method_name(parent_class_id, call_basename);
+      if(symbol_table.has_symbol(parent_method_id))
+      {
+        return parent_method_id;
+      }
+    }
     return irep_idt();
+  }
+}
+
+
+/// Build a method name as found in a GOTO symbol table equivalent to the name
+/// of a concrete call of method component_method_name on class class_name
+/// \param component_method_name: The name of the function
+/// \param class_name: The class the implementation would be found on.
+/// \return A name for looking up in the symbol table for classes `class_name`'s
+///   implementation of `component_name`
+irep_idt gather_methods_lazilyt::build_virtual_method_name(
+  const irep_idt &class_name, const irep_idt &component_method_name)
+{
+  // Verify the parameters are called in the correct order.
+  PRECONDITION(id2string(class_name).find("::")!=std::string::npos);
+  PRECONDITION(id2string(component_method_name).find("(")!=std::string::npos);
+  return id2string(class_name)+'.'+id2string(component_method_name);
 }

src/java_bytecode/gather_methods_lazily.h

@@ -93,6 +93,10 @@ class gather_methods_lazilyt:public messaget
     const irep_idt &classname,
     const symbol_tablet &symbol_table);
 
+  static irep_idt build_virtual_method_name(
+    const irep_idt &class_name,
+    const irep_idt &component_method_name);
+
   class_hierarchyt class_hierarchy;
   const irep_idt main_class;
   const std::vector<irep_idt> main_jar_classes;