gcc研究笔记（一）tree是什么

         在gcc中，几乎所有的东西都是用树结构串起来的，从而形成抽象语法树。tree可以看作是指向树节点的指针，所有的树节点都有一个共同的基类：tree_common。

在文件coretypes.h中，tree的定义如下：

#ifndef USED_FOR_TARGET

...

typedef union tree_node *tree;

...

#else

...

#define tree union _dont_use_tree_here_ *

...

#endif

可见，当USED_FOR_TARGET宏未被定义的时候，tree是指向联合类型tree_node的指针类型；否则，tree是一个定义为union _dont_use_tree_here_ *的宏。

在tree.h中，可以找到union tree_node的定义：

union tree_node

{

 struct tree_common common;

 struct tree_int_cst int_cst;

 struct tree_real_cst real_cst;

 struct tree_vector vector;

 struct tree_string string;

 struct tree_complex complex;

 struct tree_identifier identifier;

 struct tree_decl_minimal decl_minimal;

 struct tree_decl_common decl_common;

 struct tree_decl_with_rtl decl_with_rtl;

 struct tree_decl_non_common decl_non_common;

 struct tree_parm_decl parm_decl;

 struct tree_decl_with_vis decl_with_vis;

 struct tree_var_decl var_decl;

 struct tree_field_decl field_decl;

 struct tree_label_decl label_decl;

 struct tree_result_decl result_decl;

 struct tree_const_decl const_decl;

 struct tree_type_decl type_decl;

 struct tree_function_decl function_decl;

 struct tree_type type;

 struct tree_list list;

 struct tree_vec vec;

 struct tree_exp exp;

 struct tree_ssa_name ssa_name;

 struct tree_phi_node phi;

 struct tree_block block;

 struct tree_binfo binfo;

 struct tree_statement_list stmt_list;

 struct tree_value_handle value_handle;

 struct tree_constructor constructor;

 struct tree_memory_tag mtag;

 struct tree_struct_field_tag sft;

 struct tree_omp_clause omp_clause;

};

 

同样，tree_common的定义也在tree.h中：

struct tree_common

{

 tree chain;

 tree type;

 union tree_ann_d *ann;

 ENUM_BITFIELD(tree_code) code : 8;

 unsigned side_effects_flag : 1;

 unsigned constant_flag : 1;

 unsigned addressable_flag : 1;

 unsigned volatile_flag : 1;

 unsigned readonly_flag : 1;

 unsigned unsigned_flag : 1;

 unsigned asm_written_flag: 1;

 unsigned nowarning_flag : 1;

 unsigned used_flag : 1;

 unsigned nothrow_flag : 1;

 unsigned static_flag : 1;

 unsigned public_flag : 1;

 unsigned private_flag : 1;

 unsigned protected_flag : 1;

 unsigned deprecated_flag : 1;

 unsigned invariant_flag : 1;

 unsigned lang_flag_0 : 1;

 unsigned lang_flag_1 : 1;

 unsigned lang_flag_2 : 1;

 unsigned lang_flag_3 : 1;

 unsigned lang_flag_4 : 1;

 unsigned lang_flag_5 : 1;

 unsigned lang_flag_6 : 1;

 unsigned visited : 1;

};