gcc源代码分析，get_identifier ()函数分析，printf 产生标识符的过程

      if (value == IDENTIFIER)
    {
          yylval.ttype = get_identifier (token_buffer);
      lastiddecl = lookup_name (yylval.ttype);

      if (lastiddecl != 0 && TREE_CODE (lastiddecl) == TYPE_DECL)
        value = TYPENAME;
    }

  /* Search table for identifier */
  for (idp = hash_table[hi]; idp; idp = TREE_CHAIN (idp))
    if (IDENTIFIER_LENGTH (idp) == len
    && !strcmp (IDENTIFIER_POINTER (idp), text))
      return idp;        /* <-- return if found */

因为#include <stdio.h>文件中就有printf()函数的声明，所以到main中已经产生了一个tree节点。

printf
 <identifier_node 95540 printf permanent
 <function_decl 95740 printf
    type <function_type 956e8
        type <integer_type 824d0 int permanent SI
            size <integer_cst 8254c literal permanent 4
            align 32 size_unit 8 sep_unit 32 symtab 0
            sep <integer_cst 8251c literal permanent -2147483648 precision 32 min <integer_cst 8251c -2147483648>
            max <integer_cst 82534 literal permanent 2147483647
            pointer_to_this <pointer_type 88b4c> chain <integer_type 825bc* char>
        permanent EP
        size <integer_cst 82dd8 literal permanent 8
        align 32 size_unit 8 sep_unit 0 symtab 0
        arg-types <tree_list 95698 permanent value <pointer_type 9117c>
    external public permanent QI file /usr/include/stdio.h line 214
    align 1 size_unit 1 offset 0 chain <function_decl 954d8 ungetc>

(symbol_ref:SI ("printf"))

(mem:QI (symbol_ref:SI ("printf")))


printf
 <identifier_node 95540 printf public permanent
    global <function_decl 95740 printf
        type <function_type 956e8 type <integer_type 824d0* int>
            permanent EP
            size <integer_cst 82dd8 literal permanent 8
            align 32 size_unit 8 sep_unit 0 symtab 0
            arg-types <tree_list 95698 permanent value <pointer_type 9117c>
            chain <function_type 959b0>
        external public permanent QI file /usr/include/stdio.h line 214
        align 1 size_unit 1 offset 0
        chain <function_decl 954d8 ungetc type <function_type 8f4f0>
            external public permanent QI file /usr/include/stdio.h line 212
            align 1 size_unit 1 offset 0 chain <function_decl 95280 fputs>

经过下面的这句之后lastiddecl的值改变了

      lastiddecl = lookup_name (yylval.ttype);

 <function_decl 95740 printf
    type <function_type 956e8
        type <integer_type 824d0 int permanent SI
            size <integer_cst 8254c literal permanent 4
            align 32 size_unit 8 sep_unit 32 symtab 0
            sep <integer_cst 8251c literal permanent -2147483648 precision 32 min <integer_cst 8251c -2147483648>
            max <integer_cst 82534 literal permanent 2147483647
            pointer_to_this <pointer_type 88b4c> chain <integer_type 825bc* char>
        permanent EP
        size <integer_cst 82dd8 literal permanent 8
        align 32 size_unit 8 sep_unit 0 symtab 0
        arg-types <tree_list 95698 permanent value <pointer_type 9117c>
        chain <function_type 959b0>
    external public permanent used QI file /usr/include/stdio.h line 214
    align 1 size_unit 1 offset 0 chain <function_decl 954d8 ungetc>

c-parse.tab.y语法文件中有下面这句。

primary:
    IDENTIFIER
        { $$ = lastiddecl;

#define IDENTIFIER_GLOBAL_VALUE(NODE)    \
  (((struct lang_identifier *)(NODE))->global_value)