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From: Jason Merrill <jason@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-1405] c-family: don't warn for [[maybe_unused]] on data member Date: Sat, 12 Jun 2021 16:46:51 +0000 (GMT) [thread overview] Message-ID: <20210612164652.016D83857C52@sourceware.org> (raw) https://gcc.gnu.org/g:c0f769fa3114ea852a26d93f0ee3f9595463de0b commit r12-1405-gc0f769fa3114ea852a26d93f0ee3f9595463de0b Author: Jason Merrill <jason@redhat.com> Date: Fri Jun 11 16:10:50 2021 -0400 c-family: don't warn for [[maybe_unused]] on data member 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. 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/ChangeLog: * doc/extend.texi (unused variable attribute): Applies to structure fields as well. Diff: --- 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(-) 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; };
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