Jakub Jelinek <jakub at gcc dot> changed:

           What    |Removed                     |Added
                 CC|                            |jakub at gcc dot

--- Comment #2 from Jakub Jelinek <jakub at gcc dot> ---
initialize_local_var has:
  /* Compute and store the initial value.  */
  already_used = TREE_USED (decl) || TREE_USED (type);
  if (TREE_USED (type))
    DECL_READ_P (decl) = 1;
  /* Set this to 0 so we can tell whether an aggregate which was
     initialized was ever used.  Don't do this if it has a
     destructor, so we don't complain about the 'resource
     allocation is initialization' idiom.  Now set
     attribute((unused)) on types so decls of that type will be
     marked used. (see TREE_USED, above.)  */
      && ! already_used
      && DECL_NAME (decl))
    TREE_USED (decl) = 0;
  else if (already_used)
    TREE_USED (decl) = 1;
And, for u TREE_USED (type) is set.
I'm afraid I have absolutely no idea how the fact whether type is used
(comes from:
#0  0x0000000000b1bf76 in maybe_record_typedef_use (t=<type_decl 0x7fffefc51000
U>) at ../../gcc/c-family/c-warn.c:1928
#1  0x000000000090ca8f in cp_parser_lookup_name (parser=0x7ffff7ff5bd0,
name=<identifier_node 0x7fffefc3ea80 U>, tag_type=none_type, 
    is_template=false, is_namespace=false, check_dependency=true,
ambiguous_decls=0x7fffffffd418, name_location=299520)
    at ../../gcc/cp/parser.c:25718
#2  0x0000000000904ec9 in cp_parser_class_name (parser=0x7ffff7ff5bd0,
typename_keyword_p=false, template_keyword_p=false, tag_type=none_type, 
    check_dependency_p=true, class_head_p=false, is_declaration=false,
enum_ok=false) at ../../gcc/cp/parser.c:21946
and then various copy_node) can affect whether a decl is used or not.

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