diff mbox series

[pushed] c-family: don't warn for [[maybe_unused]] on data member

Message ID 20210612164527.1616742-1-jason@redhat.com
State New
Headers show
Series [pushed] c-family: don't warn for [[maybe_unused]] on data member | expand

Commit Message

Jason Merrill June 12, 2021, 4:45 p.m. UTC 
The C++17 standard (and C2x) says that [[maybe_unused]] may be applied to a
non-static data member, so we shouldn't warn about it.  And I don't see a
reason not to handle a FIELD_DECL the same as any other decl, by setting
TREE_USED on it.  It doesn't look like anything yet cares about that flag on a
FIELD_DECL, but setting it shouldn't hurt.

Tested x86_64-pc-linux-gnu, applying to trunk.

gcc/c-family/ChangeLog:

	* c-attribs.c (handle_unused_attribute): Handle FIELD_DECL.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/attrib62.C: No longer warn.
	* g++.dg/diagnostic/maybe_unused1.C: New test.
---
 gcc/doc/extend.texi                             |  6 +++---
 gcc/c-family/c-attribs.c                        |  1 +
 gcc/testsuite/g++.dg/diagnostic/maybe_unused1.C | 17 +++++++++++++++++
 gcc/testsuite/g++.dg/ext/attrib62.C             |  2 +-
 4 files changed, 22 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/diagnostic/maybe_unused1.C


base-commit: 08e1ff9d6e5a419d5b4a60c077df549e81601d9b
diff mbox series

Patch

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 408979b78af..8fc66d626d8 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -7516,9 +7516,9 @@  Not all targets support this attribute.
 
 @item unused
 @cindex @code{unused} variable attribute
-This attribute, attached to a variable, means that the variable is meant
-to be possibly unused.  GCC does not produce a warning for this
-variable.
+This attribute, attached to a variable or structure field, means that
+the variable or field is meant to be possibly unused.  GCC does not
+produce a warning for this variable or field.
 
 @item used
 @cindex @code{used} variable attribute
diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index 42026a811dd..6bf492afcc0 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -1568,6 +1568,7 @@  handle_unused_attribute (tree *node, tree name, tree ARG_UNUSED (args),
 	  || VAR_OR_FUNCTION_DECL_P (decl)
 	  || TREE_CODE (decl) == LABEL_DECL
 	  || TREE_CODE (decl) == CONST_DECL
+	  || TREE_CODE (decl) == FIELD_DECL
 	  || TREE_CODE (decl) == TYPE_DECL)
 	{
 	  TREE_USED (decl) = 1;
diff --git a/gcc/testsuite/g++.dg/diagnostic/maybe_unused1.C b/gcc/testsuite/g++.dg/diagnostic/maybe_unused1.C
new file mode 100644
index 00000000000..70a8ec937dd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/maybe_unused1.C
@@ -0,0 +1,17 @@ 
+/* [dcl.attr.unused] The attribute may be applied to the declaration of a
+   class, a typedef-name, a variable (including a structured binding
+   declaration), a non-static data member, a function, an enumeration, or an
+   enumerator.  */
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wunused -Wextra" }
+
+class [[maybe_unused]] Test {
+  [[maybe_unused]] int a_;
+  void b() {};
+};
+
+[[maybe_unused]] typedef Test Test2;
+
+[[maybe_unused]] int i;
+[[maybe_unused]] void f();
+enum [[maybe_unused]] E { e [[maybe_unused]] = 42 };
diff --git a/gcc/testsuite/g++.dg/ext/attrib62.C b/gcc/testsuite/g++.dg/ext/attrib62.C
index 116ee829a2d..d34cd2549de 100644
--- a/gcc/testsuite/g++.dg/ext/attrib62.C
+++ b/gcc/testsuite/g++.dg/ext/attrib62.C
@@ -3,5 +3,5 @@ 
 
 template<typename T> struct A
 {
-  T a, __attribute((unused)) b; // { dg-warning "attribute ignored" }
+  T a, __attribute((unused)) b;
 };