GCC-3.4.6源代码学习笔记（157）

来源：互联网发布：局域网传输软件编辑：程序博客网时间：2024/06/10 17:41

5.13.4.2. 迭代– 发布tinfo

现在所有需要代码发布的tinfo已经被串入unemitted_tinfo_decls中。接着在finish_file的2628行，emit_tinfo_decl确定decl的tinfo是否需要发布，如果需要，则返回true。下面，看到之前在finish_file的2571行调用的emit_support_tinfos中，doing_runtime被设为1。

那么在调用class_initializer这一点上（emit_tinfo_declàget_pseudo_ti_init），参数trail将是下图所示的树。注意到基类的tinfo的VAR_DECL已经产生了初始值（desc是当前类的tinfo的VAR_DECL）。

tmp

951 static tree

952 class_initializer(tree desc, tree target, tree trail) in rtti.c

953 {

954 tree init = tinfo_base_init(desc, target);

955

956 TREE_CHAIN (init) = trail;

957 init = build_constructor(NULL_TREE, init);

958 TREE_HAS_CONSTRUCTOR (init)= TREE_CONSTANT (init) = TREE_STATIC (init) = 1;

959 returninit;

960 }

看到在类type_info中，有一个“const char *”的域name，在745行开始的代码块为这个域产生修饰名及初始化代码。

738 static tree

739 tinfo_base_init(tree desc, tree target) in rtti.c

740 {

741 tree init = NULL_TREE;

742 tree name_decl;

743 tree vtable_ptr;

744

745 {

746 tree name_name;

747

748 /* Generate theNTBS array variable. */

749 tree name_type = build_cplus_array_type

750 (build_qualified_type(char_type_node, TYPE_QUAL_CONST),

751 NULL_TREE);

752 tree name_string = tinfo_name (target);

753

754 name_name = mangle_typeinfo_string_for_type(target);

755 name_decl = build_lang_decl(VAR_DECL, name_name, name_type);

756

757 DECL_ARTIFICIAL (name_decl) = 1;

758 TREE_READONLY (name_decl) = 1;

759 TREE_STATIC (name_decl) = 1;

760 DECL_EXTERNAL (name_decl) = 0;

761 TREE_PUBLIC (name_decl) = 1;

762 import_export_tinfo(name_decl, target, typeinfo_in_lib_p(target));

763 /* External nameof the string containing the type's name has a

764 specialname. */

765 SET_DECL_ASSEMBLER_NAME (name_decl,

766 mangle_typeinfo_string_for_type (target));

767 DECL_INITIAL (name_decl) = name_string;

768 mark_used(name_decl);

769 pushdecl_top_level_and_finish (name_decl,name_string);

770 }

771

772 vtable_ptr = TINFO_VTABLE_DECL (desc);

773 if (!vtable_ptr)

774 {

775 tree real_type;

776

777 push_nested_namespace(abi_node);

778 real_type = xref_tag(class_type, TINFO_REAL_NAME (desc),

779 true, false);

780 pop_nested_namespace (abi_node);

781

782 if (!COMPLETE_TYPE_P (real_type))

783 {

784 /* We never sawa definition of this type, so we need to

785 tell thecompiler that this is an exported class, as

786 indeed all ofthe __*_type_info classes are. */

787 SET_CLASSTYPE_INTERFACE_KNOWN(real_type);

788 CLASSTYPE_INTERFACE_ONLY (real_type) = 1;

789 }

790

791 vtable_ptr = get_vtable_decl(real_type, /*complete=*/1);

792 vtable_ptr = build_unary_op (ADDR_EXPR,vtable_ptr, 0);

793

794 /* We need topoint into the middle of the vtable. */

795 vtable_ptr = build

796 (PLUS_EXPR, TREE_TYPE (vtable_ptr),vtable_ptr,

797 size_binop (MULT_EXPR,

798 size_int (2 *TARGET_VTABLE_DATA_ENTRY_DISTANCE),

799 TYPE_SIZE_UNIT (vtable_entry_type)));

800 TREE_CONSTANT (vtable_ptr) = 1;

801

802 TINFO_VTABLE_DECL (desc) = vtable_ptr;

803 }

804

805 init = tree_cons (NULL_TREE, vtable_ptr,init);

806

807 init = tree_cons (NULL_TREE, decay_conversion(name_decl), init);

808

809 init = build_constructor(NULL_TREE, nreverse (init));

810 TREE_HAS_CONSTRUCTOR (init)= TREE_CONSTANT (init) = TREE_STATIC (init) = 1;

811 init = tree_cons (NULL_TREE, init,NULL_TREE);

812

813 return init;

814 }

注意在上面791行，get_vtable_decl的最后一个参数是1，该函数为这个类型的tinfo的vtable构建VAR_DECL，并把这个VRA_DECL标记为外部，但其中的cp_finish_decl不为其做任何事。

最后，在emit_tinfo_decl的1452行，var_init是如下的树。并且var_init将被用作这个tinfo的初始值。而在emit_tinfo_decl的1461行，decl是tinfo的VAR_DECL，正如我们在前面的章节所见，cp_finish_decl没有作任何事。

如果emit_tinfo_decl成功返回，这意味着正在处理的中间树发生了变化，强制再次迭代2573行的DO…WHILE循环。