c++: #pragma doesn't disable -Wunused-label [PR113582]
Checks
Commit Message
Low prio and not a regression. Feel free to ignore till GCC 15.
Bootstrapped/regtested on x86_64-pc-linux-gnu.
-- >8 --
The PR complains that
void do_something(){
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-label"
start:;
#pragma GCC diagnostic pop
} #1
doesn't work. That's because we warn_for_unused_label only while we're
in finish_function, meaning we're at #1 where we're outside the #pragma
region. We can use suppress_warning + warning_suppressed_p to fix this.
Note that I'm not using TREE_USED. Propagating it in tsubst_stmt/LABEL_EXPR
from decl to label would mean that we don't warn in do_something2, but
I think we want the warning there: we're in a template and the goto is
a discarded statement.
PR c++/113582
gcc/c-family/ChangeLog:
* c-warn.cc (warn_for_unused_label): Don't warn if -Wunused-label has
been suppressed for the label.
gcc/cp/ChangeLog:
* parser.cc (cp_parser_label_for_labeled_statement): suppress_warning
if it's not enabled at input_location.
* pt.cc (tsubst_stmt): Call copy_warning.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wunused-label-4.C: New test.
---
gcc/c-family/c-warn.cc | 4 ++-
gcc/cp/parser.cc | 6 ++++-
gcc/cp/pt.cc | 9 ++++---
gcc/testsuite/g++.dg/warn/Wunused-label-4.C | 29 +++++++++++++++++++++
4 files changed, 42 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-label-4.C
base-commit: f22a7ae8a96f7e5e330b12bd5045424619aa4926
Comments
On 1/25/24 20:38, Marek Polacek wrote:
> Low prio and not a regression. Feel free to ignore till GCC 15.
OK for stage 1.
> Bootstrapped/regtested on x86_64-pc-linux-gnu.
>
> -- >8 --
> The PR complains that
>
> void do_something(){
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wunused-label"
> start:;
> #pragma GCC diagnostic pop
> } #1
>
> doesn't work. That's because we warn_for_unused_label only while we're
> in finish_function, meaning we're at #1 where we're outside the #pragma
> region. We can use suppress_warning + warning_suppressed_p to fix this.
>
> Note that I'm not using TREE_USED. Propagating it in tsubst_stmt/LABEL_EXPR
> from decl to label would mean that we don't warn in do_something2, but
> I think we want the warning there: we're in a template and the goto is
> a discarded statement.
>
> PR c++/113582
>
> gcc/c-family/ChangeLog:
>
> * c-warn.cc (warn_for_unused_label): Don't warn if -Wunused-label has
> been suppressed for the label.
>
> gcc/cp/ChangeLog:
>
> * parser.cc (cp_parser_label_for_labeled_statement): suppress_warning
> if it's not enabled at input_location.
> * pt.cc (tsubst_stmt): Call copy_warning.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Wunused-label-4.C: New test.
> ---
> gcc/c-family/c-warn.cc | 4 ++-
> gcc/cp/parser.cc | 6 ++++-
> gcc/cp/pt.cc | 9 ++++---
> gcc/testsuite/g++.dg/warn/Wunused-label-4.C | 29 +++++++++++++++++++++
> 4 files changed, 42 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wunused-label-4.C
>
> diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
> index 8168696fa45..fdb5338f6f6 100644
> --- a/gcc/c-family/c-warn.cc
> +++ b/gcc/c-family/c-warn.cc
> @@ -2186,7 +2186,9 @@ warn_for_unused_label (tree label)
> {
> if (!TREE_USED (label))
> {
> - if (DECL_INITIAL (label))
> + if (warning_suppressed_p (label, OPT_Wunused_label))
> + /* Don't warn. */;
> + else if (DECL_INITIAL (label))
> warning (OPT_Wunused_label, "label %q+D defined but not used", label);
> else
> warning (OPT_Wunused_label, "label %q+D declared but not defined", label);
> 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..af9fd8f6f03 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -18796,11 +18796,12 @@ 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);
> + copy_warning (label, decl);
> + }
> if (DECL_ATTRIBUTES (decl) != NULL_TREE)
> cplus_decl_attributes (&label, DECL_ATTRIBUTES (decl), 0);
> }
> diff --git a/gcc/testsuite/g++.dg/warn/Wunused-label-4.C b/gcc/testsuite/g++.dg/warn/Wunused-label-4.C
> new file mode 100644
> index 00000000000..d194f043d21
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wunused-label-4.C
> @@ -0,0 +1,29 @@
> +// PR c++/113582
> +// { dg-do compile { target c++17 } }
> +// { dg-options "-Wunused-label" }
> +
> +template<bool B> void
> +do_something ()
> +{
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wunused-label"
> +start:
> + if constexpr(B)
> + goto start;
> +#pragma GCC diagnostic pop
> +}
> +
> +template<bool B> void
> +do_something2 ()
> +{
> +start: // { dg-warning "defined but not used" }
> + if constexpr(B)
> + goto start;
> +}
> +
> +void
> +g ()
> +{
> + do_something<0>();
> + do_something2<0>();
> +}
>
> base-commit: f22a7ae8a96f7e5e330b12bd5045424619aa4926
@@ -2186,7 +2186,9 @@ warn_for_unused_label (tree label)
{
if (!TREE_USED (label))
{
- if (DECL_INITIAL (label))
+ if (warning_suppressed_p (label, OPT_Wunused_label))
+ /* Don't warn. */;
+ else if (DECL_INITIAL (label))
warning (OPT_Wunused_label, "label %q+D defined but not used", label);
else
warning (OPT_Wunused_label, "label %q+D declared but not defined", label);
@@ -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;
}
@@ -18796,11 +18796,12 @@ 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);
+ copy_warning (label, decl);
+ }
if (DECL_ATTRIBUTES (decl) != NULL_TREE)
cplus_decl_attributes (&label, DECL_ATTRIBUTES (decl), 0);
}
new file mode 100644
@@ -0,0 +1,29 @@
+// PR c++/113582
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wunused-label" }
+
+template<bool B> void
+do_something ()
+{
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-label"
+start:
+ if constexpr(B)
+ goto start;
+#pragma GCC diagnostic pop
+}
+
+template<bool B> void
+do_something2 ()
+{
+start: // { dg-warning "defined but not used" }
+ if constexpr(B)
+ goto start;
+}
+
+void
+g ()
+{
+ do_something<0>();
+ do_something2<0>();
+}