Merge pull request #1764 from smowton/smowton/feature/java-infer-opaque-type-fields-earlier

Java: infer opaque type fields before method conversion

Author: smowton

src/java_bytecode/java_bytecode_language.cpp

@@ -195,6 +195,67 @@ bool java_bytecode_languaget::parse(
   return false;
 }
 
+/// Infer fields that must exist on opaque types from field accesses against
+/// them. Note that we don't yet try to infer inheritence between opaque types
+/// here, so we may introduce the same field onto a type and its ancestor
+/// without realising that is in fact the same field, inherited from that
+/// ancestor. This can lead to incorrect results when opaque types are cast
+/// to other opaque types and their fields do not alias as intended.
+/// \param parse_tree: class parse tree
+/// \param symbol_table: global symbol table
+static void infer_opaque_type_fields(
+  const java_bytecode_parse_treet &parse_tree,
+  symbol_tablet &symbol_table)
+{
+  namespacet ns(symbol_table);
+  for(const auto &method : parse_tree.parsed_class.methods)
+  {
+    for(const auto &instruction : method.instructions)
+    {
+      if(instruction.statement == "getfield" ||
+         instruction.statement == "putfield")
+      {
+        const exprt &fieldref = instruction.args[0];
+        const symbolt *class_symbol =
+          symbol_table.lookup(fieldref.get(ID_class));
+        INVARIANT(
+          class_symbol != nullptr, "all field types should have been loaded");
+
+        const class_typet *class_type = &to_class_type(class_symbol->type);
+        irep_idt class_symbol_id = fieldref.get(ID_class);
+        const irep_idt &component_name = fieldref.get(ID_component_name);
+        while(!class_type->has_component(component_name))
+        {
+          if(class_type->get_bool(ID_incomplete_class))
+          {
+            // Accessing a field of an incomplete (opaque) type.
+            symbolt &writable_class_symbol =
+              symbol_table.get_writeable_ref(class_symbol_id);
+            auto &add_to_components =
+              to_struct_type(writable_class_symbol.type).components();
+            add_to_components.push_back(
+              struct_typet::componentt(component_name, fieldref.type()));
+            add_to_components.back().set_base_name(component_name);
+            add_to_components.back().set_pretty_name(component_name);
+            break;
+          }
+          else
+          {
+            // Not present here: check the superclass.
+            INVARIANT(
+              class_type->bases().size() != 0,
+              "class missing an expected field should have a superclass");
+            const symbol_typet &superclass_type =
+              to_symbol_type(class_type->bases()[0].type());
+            class_symbol_id = superclass_type.get_identifier();
+            class_type = &to_class_type(ns.follow(superclass_type));
+          }
+        }
+      }
+    }
+  }
+}
+
 bool java_bytecode_languaget::typecheck(
   symbol_tablet &symbol_table,
   const std::string &module)
@@ -248,6 +309,14 @@ bool java_bytecode_languaget::typecheck(
     }
   }
 
+  // Infer fields on opaque types based on the method instructions just loaded.
+  // For example, if we don't have bytecode for field x of class A, but we can
+  // see an int-typed getfield instruction referring to it, add that field now.
+  for(const auto &c : java_class_loader.class_map)
+  {
+    infer_opaque_type_fields(c.second, symbol_table);
+  }
+
   // Now incrementally elaborate methods
   // that are reachable from this entry point.
   if(lazy_methods_mode==LAZY_METHODS_MODE_CONTEXT_INSENSITIVE)

src/java_bytecode/java_bytecode_typecheck_expr.cpp

@@ -307,21 +307,6 @@ void java_bytecode_typecheckt::typecheck_expr_member(member_exprt &expr)
     struct_typet::componentst &components=
       struct_type.components();
 
-    if(struct_type.get_bool(ID_incomplete_class))
-    {
-      // member doesn't exist. In this case struct_type should be an opaque
-      // stub, and we'll add the member to it.
-      symbolt &symbol_table_type=symbol_table.get_writeable_ref(
-        "java::"+id2string(struct_type.get_tag()));
-      auto &add_to_components=
-        to_struct_type(symbol_table_type.type).components();
-      add_to_components
-        .push_back(struct_typet::componentt(component_name, expr.type()));
-      add_to_components.back().set_base_name(component_name);
-      add_to_components.back().set_pretty_name(component_name);
-      return;
-    }
-
     if(components.empty())
       break;