Add a new constructor to java_bytecode_parse_treet

Constructing a java_bytecode_parse_treet from an irep_idt avoids two uses of
short-lived local variables.

Author: tautschnig

jbmc/src/java_bytecode/java_bytecode_parse_tree.h

@@ -199,6 +199,11 @@ struct java_bytecode_parse_treet
   {
     classt() = default;
 
+    /// Create a class \p name.
+    explicit classt(const irep_idt &name) : name(name)
+    {
+    }
+
     // Disallow copy construction and copy assignment, but allow move
     // construction and move assignment.
     #ifndef _MSC_VER // Ommit this on MS VC2013 as move is not supported.
@@ -307,9 +312,14 @@ struct java_bytecode_parse_treet
   typedef std::set<irep_idt> class_refst;
   class_refst class_refs;
 
-  bool loading_successful;
+  bool loading_successful = false;
+
+  /// An empty bytecode parse tree, no class name set
+  java_bytecode_parse_treet() = default;
 
-  java_bytecode_parse_treet():loading_successful(false)
+  /// Create a blank parse tree for class \p class_name.
+  explicit java_bytecode_parse_treet(const irep_idt &class_name)
+    : parsed_class(class_name)
   {
   }
 };

jbmc/src/java_bytecode/java_class_loader.cpp

@@ -120,9 +120,7 @@ java_class_loadert::get_parse_tree(
   if(!class_loader_limit.load_class_file(class_name_to_jar_file(class_name)))
   {
     debug() << "not loading " << class_name << " because of limit" << eom;
-    java_bytecode_parse_treet parse_tree;
-    parse_tree.parsed_class.name = class_name;
-    parse_trees.push_back(std::move(parse_tree));
+    parse_trees.emplace_back(class_name);
     return parse_trees;
   }
 
@@ -179,9 +177,7 @@ java_class_loadert::get_parse_tree(
 
   // Not found or failed to load
   warning() << "failed to load class `" << class_name << '\'' << eom;
-  java_bytecode_parse_treet parse_tree;
-  parse_tree.parsed_class.name=class_name;
-  parse_trees.push_back(std::move(parse_tree));
+  parse_trees.emplace_back(class_name);
   return parse_trees;
 }