[Bug c++/20408] Unnecessary code generated for empty structs

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-10 17:06 -------
>From call.c:
  /* Don't pass empty class objects by value.  This is useful
     for tags in STL, which are used to control overload resolution.
     We don't need to handle other cases of copying empty classes.  */
  if (! decl || ! DECL_BUILT_IN (decl))
    for (tmp = parms; tmp; tmp = TREE_CHAIN (tmp))
      if (is_empty_class (TREE_TYPE (TREE_VALUE (tmp)))
	  && ! TREE_ADDRESSABLE (TREE_TYPE (TREE_VALUE (tmp))))
	{
	  tree t = build0 (EMPTY_CLASS_EXPR, TREE_TYPE (TREE_VALUE (tmp)));
	  TREE_VALUE (tmp) = build2 (COMPOUND_EXPR, TREE_TYPE (t),
				     TREE_VALUE (tmp), t);
	}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20408