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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/113582] incorrect warning about unused label with `pragma
 GCC diagnostic` around the unused label
Date: Wed, 24 Jan 2024 22:59:44 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.2.1
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X-Bugzilla-Who: mpolacek at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113582

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 =3D finish_label_stmt (cp_parser_identifier (parser));
       if (label && TREE_CODE (label) =3D=3D LABEL_DECL)
-   FALLTHROUGH_LABEL_P (label) =3D fallthrough_p;
+   {
+     FALLTHROUGH_LABEL_P (label) =3D 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 =3D LABEL_EXPR_LABEL (t);
-   tree label;
-
-   label =3D finish_label_stmt (DECL_NAME (decl));
+   tree label =3D finish_label_stmt (DECL_NAME (decl));
    if (TREE_CODE (label) =3D=3D LABEL_DECL)
-     FALLTHROUGH_LABEL_P (label) =3D FALLTHROUGH_LABEL_P (decl);
+     {
+       FALLTHROUGH_LABEL_P (label) =3D FALLTHROUGH_LABEL_P (decl);
+       if (warning_suppressed_p (decl, OPT_Wunused_label))
+         TREE_USED (label) =3D true;
+     }
    if (DECL_ATTRIBUTES (decl) !=3D NULL_TREE)
      cplus_decl_attributes (&label, DECL_ATTRIBUTES (decl), 0);
       }=