[Bug c++/113582] incorrect warning about unused label with `pragma GCC diagnostic` around the unused label

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113582

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Hack/fix:

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 3748ccd49ff..224d47f2f90 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -13093,7 +13093,11 @@ cp_parser_label_for_labeled_statement (cp_parser*
parser, tree attributes)
       /* Anything else must be an ordinary label.  */
       label = finish_label_stmt (cp_parser_identifier (parser));
       if (label && TREE_CODE (label) == LABEL_DECL)
-   FALLTHROUGH_LABEL_P (label) = fallthrough_p;
+   {
+     FALLTHROUGH_LABEL_P (label) = fallthrough_p;
+     if (!warning_enabled_at (input_location, OPT_Wunused_label))
+       suppress_warning (label, OPT_Wunused_label);
+   }
       break;
     }

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 74013533b0f..b6686d8543f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -18796,11 +18796,13 @@ tsubst_stmt (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
     case LABEL_EXPR:
       {
    tree decl = LABEL_EXPR_LABEL (t);
-   tree label;
-
-   label = finish_label_stmt (DECL_NAME (decl));
+   tree label = finish_label_stmt (DECL_NAME (decl));
    if (TREE_CODE (label) == LABEL_DECL)
-     FALLTHROUGH_LABEL_P (label) = FALLTHROUGH_LABEL_P (decl);
+     {
+       FALLTHROUGH_LABEL_P (label) = FALLTHROUGH_LABEL_P (decl);
+       if (warning_suppressed_p (decl, OPT_Wunused_label))
+         TREE_USED (label) = true;
+     }
    if (DECL_ATTRIBUTES (decl) != NULL_TREE)
      cplus_decl_attributes (&label, DECL_ATTRIBUTES (decl), 0);
       }