Clean up unused template instantiation symbols

regression/cpp/Decltype3/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE
 main.cpp
 -std=c++11
 ^EXIT=0$

regression/cpp/Template_Instantiation4/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG
+CORE
 main.cpp
 
 ^EXIT=0$

src/cpp/cpp_typecheck.cpp

@@ -277,7 +277,12 @@ void cpp_typecheckt::clean_up()
     const symbolt &symbol=cur_it->second;
 
     // erase templates
-    if(symbol.type.get_bool(ID_is_template))
+    if(symbol.type.get_bool(ID_is_template) ||
+       // Remove all symbols that have not been converted.
+       //   In particular this includes symbols created for functions
+       //   during template instantiation that are never called,
+       //   and hence, their bodies have not been converted.
+       contains_cpp_name(symbol.value))
     {
       symbol_table.erase(cur_it);
       continue;
@@ -327,3 +332,13 @@ bool cpp_typecheckt::builtin_factory(const irep_idt &identifier)
 {
   return ::builtin_factory(identifier, symbol_table, get_message_handler());
 }
+
+bool cpp_typecheckt::contains_cpp_name(const exprt &expr)
+{
+  if(expr.id() == ID_cpp_name || expr.id() == ID_cpp_declaration)
+    return true;
+  forall_operands(it, expr)
+    if(contains_cpp_name(*it))
+      return true;
+  return false;
+}

src/cpp/cpp_typecheck.h

@@ -590,6 +590,8 @@ class cpp_typecheckt:public c_typecheck_baset
     exprt &new_expr,
     bool check_constantness=true);
 
+  bool contains_cpp_name(const exprt &expr);
+
 private:
   typedef std::list<irep_idt> dynamic_initializationst;
   dynamic_initializationst dynamic_initializations;