java_static_lifetime_init: Deterministic order of initialisation

Much like the C front-end, ensure that the collection of objects of
static lifetime is initialised in a fixed order, based on their names.
Previously, the (unspecified) order in an unordered set and unordered
map determined the sequence of instructions being generated, which
resulted in jdiff regression tests sometimes failing. Those failures
were caused by __CPROVER_initialize sometimes showing up among the list
of goto functions that differed.

Author: tautschnig

jbmc/src/java_bytecode/java_entry_point.cpp

@@ -259,34 +259,40 @@ void java_static_lifetime_init(
   // external. Iterate over a copy of the symtab, as its iterators are
   // invalidated by object_factory:
 
-  std::list<irep_idt> symbol_names;
+  // sort alphabetically for reproducible results
+  std::set<std::string> symbol_names;
   for(const auto &entry : symbol_table.symbols)
-    symbol_names.push_back(entry.first);
-
-  // Don't use a for-each loop here because the loop extends the list, and the
-  // for-each loop may only read `.end()` once.
-  for(
-    auto symbol_it = symbol_names.begin();
-    symbol_it != symbol_names.end();
-    ++symbol_it)
+    symbol_names.insert(id2string(entry.first));
+
+  std::set<std::string> additional_symbols;
+  while(!symbol_names.empty() || !additional_symbols.empty())
   {
-    const symbolt &sym = symbol_table.lookup_ref(*symbol_it);
-    if(should_init_symbol(sym))
+    if(!additional_symbols.empty())
+      symbol_names.swap(additional_symbols);
+
+    for(const auto &symbol_name : symbol_names)
     {
-      auto new_symbols = init_symbol(
-        sym,
-        code_block,
-        symbol_table,
-        source_location,
-        assume_init_pointers_not_null,
-        object_factory_parameters,
-        pointer_type_selector,
-        string_refinement_enabled,
-        message_handler);
-      symbol_names.insert(
-        symbol_names.end(), new_symbols.begin(), new_symbols.end());
+      const symbolt &sym = symbol_table.lookup_ref(symbol_name);
+      if(should_init_symbol(sym))
+      {
+        auto new_symbols = init_symbol(
+          sym,
+          code_block,
+          symbol_table,
+          source_location,
+          assume_init_pointers_not_null,
+          object_factory_parameters,
+          pointer_type_selector,
+          string_refinement_enabled,
+          message_handler);
+        for(const auto &new_symbol_name : new_symbols)
+          additional_symbols.insert(id2string(new_symbol_name));
+      }
     }
+
+    symbol_names.clear();
   }
+
   initialize_symbol.value = std::move(code_block);
 }