On Tue, Sep 17, 2024 at 05:16:47PM -0400, Jason Merrill wrote:
> Tested x86_64-pc-linux-gnu. Marek, any concerns?
LGTM, thanks. The ChangeLog may not pass the hook because it's
missing some entries.
> -- 8< --
>
> We can't have a dangling reference to an empty class unless it's
> specifically to that class or one of its bases. This was giving a
> false positive on the _ExtractKey pattern in libstdc++ hashtable.h.
>
> This also adjusts the order of arguments to reference_related_p, which
> is relevant for empty classes (unlike scalars).
>
> Several of the classes in the testsuite needed to gain data members to
> continue to warn.
>
> PR c++/115361
>
> gcc/cp/ChangeLog:
>
> * call.cc (do_warn_dangling_reference): Check is_empty_class.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/ext/attr-no-dangling6.C:
> * g++.dg/ext/attr-no-dangling7.C:
> * g++.dg/ext/attr-no-dangling8.C:
> * g++.dg/ext/attr-no-dangling9.C:
> * g++.dg/warn/Wdangling-reference1.C:
> * g++.dg/warn/Wdangling-reference2.C:
> * g++.dg/warn/Wdangling-reference3.C: Make classes non-empty.
> * g++.dg/warn/Wdangling-reference23.C: New test.
> ---
> gcc/cp/call.cc | 12 +++++++-----
> gcc/testsuite/g++.dg/ext/attr-no-dangling6.C | 6 +++---
> gcc/testsuite/g++.dg/ext/attr-no-dangling7.C | 6 +++---
> gcc/testsuite/g++.dg/ext/attr-no-dangling8.C | 2 ++
> gcc/testsuite/g++.dg/ext/attr-no-dangling9.C | 1 +
> gcc/testsuite/g++.dg/warn/Wdangling-reference1.C | 1 +
> gcc/testsuite/g++.dg/warn/Wdangling-reference2.C | 2 +-
> gcc/testsuite/g++.dg/warn/Wdangling-reference23.C | 14 ++++++++++++++
> gcc/testsuite/g++.dg/warn/Wdangling-reference3.C | 1 +
> 9 files changed, 33 insertions(+), 12 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference23.C
>
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index 664088eed9c..1ecf3aac705 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -14356,12 +14356,14 @@ do_warn_dangling_reference (tree expr, bool arg_p)
> if ((arg = do_warn_dangling_reference (arg, /*arg_p=*/true)))
> {
> /* If we know the temporary could not bind to the return type,
> - don't warn. This is for scalars only because for classes
> - we can't be sure we are not returning its sub-object. */
> - if (SCALAR_TYPE_P (TREE_TYPE (arg))
> + don't warn. This is for scalars and empty classes only
> + because for other classes we can't be sure we are not
> + returning its sub-object. */
> + if ((SCALAR_TYPE_P (TREE_TYPE (arg))
> + || is_empty_class (TREE_TYPE (arg)))
> && TYPE_REF_P (rettype)
> - && !reference_related_p (TREE_TYPE (arg),
> - TREE_TYPE (rettype)))
> + && !reference_related_p (TREE_TYPE (rettype),
> + TREE_TYPE (arg)))
> continue;
> return expr;
> }
> diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C
> b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C
> index 5b349e8e682..1fc426d20d3 100644
> --- a/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C
> +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C
> @@ -2,9 +2,9 @@
> // { dg-do compile { target c++20 } }
> // { dg-options "-Wdangling-reference" }
>
> -class X { };
> -const X x1;
> -const X x2;
> +class X { int i; };
> +const X x1 {};
> +const X x2 {};
>
> constexpr bool val () { return true; }
> struct ST { static constexpr bool value = true; };
> diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C
> b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C
> index a5fb809e6bd..04c6badf0b6 100644
> --- a/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C
> +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C
> @@ -2,9 +2,9 @@
> // { dg-do compile { target c++20 } }
> // { dg-options "-Wdangling-reference" }
>
> -class X { };
> -const X x1;
> -const X x2;
> +class X { int i; };
> +const X x1 {};
> +const X x2 {};
>
> template<bool... N>
> [[gnu::no_dangling(N)]] const X& get(const int& i); // { dg-error "parameter
> packs not expanded" }
> diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C
> b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C
> index 8208d751a4b..aa196315a38 100644
> --- a/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C
> +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C
> @@ -8,6 +8,7 @@ template<class T> constexpr bool is_reference_v<T&&> = true;
>
> template <typename T>
> struct [[gnu::no_dangling(is_reference_v<T>)]] S {
> + int i;
> int &foo (const int &);
> };
>
> @@ -15,6 +16,7 @@ template <typename T1, typename T2>
> struct X {
> template <typename U1 = T1, typename U2 = T2>
> struct [[gnu::no_dangling(is_reference_v<U1> && is_reference_v<U2>)]] Y {
> + int i;
> int &foo (const int &);
> };
> };
> diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C
> b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C
> index 65b4f7145a9..d7fd897de53 100644
> --- a/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C
> +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C
> @@ -12,6 +12,7 @@ using true_type = bool_constant<true>;
> using false_type = bool_constant<false>;
>
> struct S {
> + int i;
> template<bool B>
> [[gnu::no_dangling(B)]] int &foo (const int &);
> };
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C
> b/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C
> index 1718c28165e..a184317dd5c 100644
> --- a/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference1.C
> @@ -131,6 +131,7 @@ int n = 1;
> const int& refmax = max(n - 1, n + 1); // { dg-warning "dangling reference" }
>
> struct Y {
> + int i;
> operator int&();
> operator int&&();
> const int& foo(const int&);
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference2.C
> b/gcc/testsuite/g++.dg/warn/Wdangling-reference2.C
> index dafdb43f1b9..a3d5ad6d867 100644
> --- a/gcc/testsuite/g++.dg/warn/Wdangling-reference2.C
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference2.C
> @@ -3,7 +3,7 @@
> // { dg-options "-Wdangling-reference" }
>
> namespace std {
> -struct any {};
> +struct any { void *p; ~any(); };
> template <typename _ValueType> _ValueType any_cast(any &&);
> template <typename _Tp> struct remove_reference { using type = _Tp; };
> template <typename _Tp> _Tp forward(typename remove_reference<_Tp>::type);
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference23.C
> b/gcc/testsuite/g++.dg/warn/Wdangling-reference23.C
> new file mode 100644
> index 00000000000..e59ccc5057b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference23.C
> @@ -0,0 +1,14 @@
> +// PR c++/115361
> +// { dg-additional-options -Wdangling-reference }
> +
> +struct B { int i; };
> +
> +struct A {
> + const int & operator()(const B& b) { return b.i; }
> +};
> +
> +int main()
> +{
> + B b = {};
> + const int &r = A()(b);
> +}
> diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference3.C
> b/gcc/testsuite/g++.dg/warn/Wdangling-reference3.C
> index 4bc20c13b3f..7db1dc86855 100644
> --- a/gcc/testsuite/g++.dg/warn/Wdangling-reference3.C
> +++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference3.C
> @@ -18,6 +18,7 @@ struct G {
> };
>
> struct F {
> + int i;
> G& f();
> };
>
>
> base-commit: a9f9391e1eeccb9d062b9e73ef27ac577b23ed64
> --
> 2.46.0
>
Marek
