GCC主要数据结构之c_expr

/* Record parser information about an expression that is irrelevant
   for code generation alongside a tree representing its value.  */
struct c_expr
{
  /* The value of the expression.  */
  tree value;
  /* Record the original unary/binary operator of an expression, which may
     have been changed by fold, STRING_CST for unparenthesized string
     constants, C_MAYBE_CONST_EXPR for __builtin_constant_p calls
     (even if parenthesized), for subexpressions, and for non-constant
     initializers, or ERROR_MARK for other expressions (including
     parenthesized expressions).  */
  enum tree_code original_code;
  /* If not NULL, the original type of an expression.  This will
     differ from the type of the value field for an enum constant.
     The type of an enum constant is a plain integer type, but this
     field will be the enum type.  */
  tree original_type;
  /* The source range of this expression.  This is redundant
     for node values that have locations, but not all node kinds
     have locations (e.g. constants, and references to params, locals,
     etc), so we stash a copy here.  */
  source_range src_range;
  /* Access to the first and last locations within the source spelling
     of this expression.  */
  location_t get_start () const { return src_range.m_start; }
  location_t get_finish () const { return src_range.m_finish; }
  /* Set the value to error_mark_node whilst ensuring that src_range
     is initialized.  */
  void set_error ()
  {
    value = error_mark_node;
    src_range.m_start = UNKNOWN_LOCATION;
    src_range.m_finish = UNKNOWN_LOCATION;
  }
};

/* Type alias for struct c_expr. This allows to use the structure
   inside the VEC types.  */
typedef struct c_expr c_expr_t;