| Message ID | ZdaWtXmN6BoWPwfX@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] c++: implement [[gnu::non_owning]] [PR110358] | expand |
On 2/21/24 19:35, Marek Polacek wrote: > On Fri, Jan 26, 2024 at 04:04:35PM -0500, Jason Merrill wrote: >> On 1/25/24 20:37, Marek Polacek wrote: >>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? >>> >>> -- >8 -- >>> Since -Wdangling-reference has false positives that can't be >>> prevented, we should offer an easy way to suppress the warning. >>> Currently, that is only possible by using a #pragma, either around the >>> enclosing class or around the call site. But #pragma GCC diagnostic tend >>> to be onerous. A better solution would be to have an attribute. Such >>> an attribute should not be tied to this particular warning though. [*] >>> >>> The warning bogusly triggers for classes that are like std::span, >>> std::reference_wrapper, and std::ranges::ref_view. The common property >>> seems to be that these classes are only wrappers around some data. So >>> I chose the name non_owning, but I'm not attached to it. I hope that >>> in the future the attribute can be used for something other than this >>> diagnostic. >> >> You decided not to pursue Barry's request for a bool argument to the >> attribute? > > At first I thought it'd be an unnecessary complication but it was actually > pretty easy. Better to accept the optional argument from the get-go > otherwise people would have to add > GCC 14 checks. > >> Might it be more useful for the attribute to make reference_like_class_p >> return true, so that we still warn about a temporary of another type passing >> through it? > > Good point. Fixed. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > -- >8 -- > Since -Wdangling-reference has false positives that can't be > prevented, we should offer an easy way to suppress the warning. > Currently, that is only possible by using a #pragma, either around the > enclosing class or around the call site. But #pragma GCC diagnostic tend > to be onerous. A better solution would be to have an attribute. Such > an attribute should not be tied to this particular warning though. > > The warning bogusly triggers for classes that are like std::span, > std::reference_wrapper, and std::ranges::ref_view. The common property > seems to be that these classes are only wrappers around some data. So > I chose the name non_owning, but I'm not attached to it. I hope that > in the future the attribute can be used for something other than this > diagnostic. > > This attribute takes an optional bool argument to support cases like: > > template <typename T> > struct [[gnu::non_owning(std::is_reference_v<T>)]] S { > // ... > }; > > PR c++/110358 > PR c++/109642 > > gcc/cp/ChangeLog: > > * call.cc (non_owning_p): New. > (reference_like_class_p): Use it. > (do_warn_dangling_reference): Use it. Don't warn when the function > or its enclosing class has attribute gnu::non_owning. > * tree.cc (cxx_gnu_attributes): Add gnu::non_owning. > (handle_non_owning_attribute): New. > > gcc/ChangeLog: > > * doc/extend.texi: Document gnu::non_owning. > * doc/invoke.texi: Mention that gnu::non_owning disables > -Wdangling-reference. > > gcc/testsuite/ChangeLog: > > * g++.dg/ext/attr-non-owning1.C: New test. > * g++.dg/ext/attr-non-owning2.C: New test. > * g++.dg/ext/attr-non-owning3.C: New test. > * g++.dg/ext/attr-non-owning4.C: New test. > * g++.dg/ext/attr-non-owning5.C: New test. > * g++.dg/ext/attr-non-owning6.C: New test. > * g++.dg/ext/attr-non-owning7.C: New test. > * g++.dg/ext/attr-non-owning8.C: New test. > * g++.dg/ext/attr-non-owning9.C: New test. > --- > gcc/cp/call.cc | 38 ++++++++++-- > gcc/cp/tree.cc | 26 +++++++++ > gcc/doc/extend.texi | 25 ++++++++ > gcc/doc/invoke.texi | 21 +++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning1.C | 38 ++++++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning2.C | 29 +++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning3.C | 24 ++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning4.C | 14 +++++ > gcc/testsuite/g++.dg/ext/attr-non-owning5.C | 31 ++++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning6.C | 65 +++++++++++++++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning7.C | 31 ++++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning8.C | 30 ++++++++++ > gcc/testsuite/g++.dg/ext/attr-non-owning9.C | 25 ++++++++ > 13 files changed, 391 insertions(+), 6 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning1.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning2.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning3.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning4.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning5.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning6.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning7.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning8.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-non-owning9.C > > diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc > index 1dac1470d3b..e4bf9c963bd 100644 > --- a/gcc/cp/call.cc > +++ b/gcc/cp/call.cc > @@ -14033,11 +14033,7 @@ std_pair_ref_ref_p (tree t) > return true; > } > > -/* Return true if a class CTYPE is either std::reference_wrapper or > - std::ref_view, or a reference wrapper class. We consider a class > - a reference wrapper class if it has a reference member. We no > - longer check that it has a constructor taking the same reference type > - since that approach still generated too many false positives. */ > +/* Return true if a class T has a reference member. */ > > static bool > class_has_reference_member_p (tree t) > @@ -14061,12 +14057,41 @@ class_has_reference_member_p_r (tree binfo, void *) > ? integer_one_node : NULL_TREE); > } > > + > +/* Return true if T (either a class or a function) has been marked as > + non-owning. */ > + > +static bool > +non_owning_p (tree t) > +{ > + t = lookup_attribute ("non_owning", TYPE_ATTRIBUTES (t)); > + if (!t) > + return false; > + > + t = TREE_VALUE (t); > + if (!t) > + return true; > + > + t = build_converted_constant_bool_expr (TREE_VALUE (t), tf_warning_or_error); > + t = cxx_constant_value (t); > + return t == boolean_true_node; > +} > + > +/* Return true if a class CTYPE is either std::reference_wrapper or > + std::ref_view, or a reference wrapper class. We consider a class > + a reference wrapper class if it has a reference member. We no > + longer check that it has a constructor taking the same reference type > + since that approach still generated too many false positives. */ > + > static bool > reference_like_class_p (tree ctype) > { > if (!CLASS_TYPE_P (ctype)) > return false; > > + if (non_owning_p (ctype)) > + return true; > + > /* Also accept a std::pair<const T&, const T&>. */ > if (std_pair_ref_ref_p (ctype)) > return true; > @@ -14173,7 +14198,8 @@ do_warn_dangling_reference (tree expr, bool arg_p) > but probably not to one of its arguments. */ > || (DECL_OBJECT_MEMBER_FUNCTION_P (fndecl) > && DECL_OVERLOADED_OPERATOR_P (fndecl) > - && DECL_OVERLOADED_OPERATOR_IS (fndecl, INDIRECT_REF))) > + && DECL_OVERLOADED_OPERATOR_IS (fndecl, INDIRECT_REF)) > + || non_owning_p (TREE_TYPE (fndecl))) > return NULL_TREE; > > tree rettype = TREE_TYPE (TREE_TYPE (fndecl)); > diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc > index ad312710f68..017da7e294a 100644 > --- a/gcc/cp/tree.cc > +++ b/gcc/cp/tree.cc > @@ -47,6 +47,7 @@ static tree verify_stmt_tree_r (tree *, int *, void *); > static tree handle_init_priority_attribute (tree *, tree, tree, int, bool *); > static tree handle_abi_tag_attribute (tree *, tree, tree, int, bool *); > static tree handle_contract_attribute (tree *, tree, tree, int, bool *); > +static tree handle_non_owning_attribute (tree *, tree, tree, int, bool *); > > /* If REF is an lvalue, returns the kind of lvalue that REF is. > Otherwise, returns clk_none. */ > @@ -5102,6 +5103,8 @@ static const attribute_spec cxx_gnu_attributes[] = > handle_init_priority_attribute, NULL }, > { "abi_tag", 1, -1, false, false, false, true, > handle_abi_tag_attribute, NULL }, > + { "non_owning", 0, 1, false, true, false, false, > + handle_non_owning_attribute, NULL }, > }; > > const scoped_attribute_specs cxx_gnu_attribute_table = > @@ -5391,6 +5394,29 @@ handle_contract_attribute (tree *ARG_UNUSED (node), tree ARG_UNUSED (name), > return NULL_TREE; > } > > +/* Handle a "non_owning" attribute; arguments as in > + struct attribute_spec.handler. */ > + > +tree > +handle_non_owning_attribute (tree *node, tree name, tree args, int, > + bool *no_add_attrs) > +{ > + if (args && TREE_CODE (TREE_VALUE (args)) == STRING_CST) > + { > + error ("%qE attribute argument must be an expression that evaluates " > + "to true or false", name); > + *no_add_attrs = true; > + } > + else if (!FUNC_OR_METHOD_TYPE_P (*node) > + && !RECORD_OR_UNION_TYPE_P (*node)) > + { > + warning (OPT_Wattributes, "%qE attribute ignored", name); > + *no_add_attrs = true; > + } > + > + return NULL_TREE; > +} > + > /* Return a new PTRMEM_CST of the indicated TYPE. The MEMBER is the > thing pointed to by the constant. */ > > diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi > index 2135dfde9c8..9132add8267 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > @@ -29320,6 +29320,31 @@ Some_Class B __attribute__ ((init_priority (543))); > Note that the particular values of @var{priority} do not matter; only their > relative ordering. > > +@cindex @code{non_owning} type attribute > +@item non_owning > + > +This attribute can be applied on a class type, function, or member > +function and indicates that it does not own its associated data. For > +example, classes like @code{std::span} or @code{std::reference_wrapper} > +are considered non-owning. > + > +@smallexample > +class [[gnu::non_owning]] S @{ @dots{} @}; > +@end smallexample > + > +This attribute takes an optional argument, which must be an expression that > +evaluates to true or false: > + > +@smallexample > +template <typename T> > +struct [[gnu::non_owning(std::is_reference_v<T>)]] S @{ > + @dots{} > +@}; > +@end smallexample > + > +Currently, the only effect this attribute has is to suppress the > +@option{-Wdangling-reference} diagnostic. > + > @cindex @code{warn_unused} type attribute > @item warn_unused > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index b4e4ee9fb81..0df2e2ded34 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -3908,6 +3908,9 @@ const T& foo (const T&) @{ @dots{} @} > #pragma GCC diagnostic pop > @end smallexample > > +The @code{#pragma} can also surround the class; in that case, the warning > +will be disabled for all the member functions. > + > @option{-Wdangling-reference} also warns about code like > > @smallexample > @@ -3932,6 +3935,24 @@ struct Span @{ > as @code{std::span}-like; that is, the class is a non-union class > that has a pointer data member and a trivial destructor. > > +The warning can be disabled by using the @code{gnu::non_owning} attribute, > +which can be applied on the enclosing class type (in which case it disables > +the warning for all its member functions), member function, or a regular > +function. For example: Hmm, if we're also going to allow the attribute to be applied to a function, the name doesn't make so much sense. For a class, it says that the class refers to its initializer; for a function, it says that the function return value *doesn't* refer to its argument. If we want something that can apply to both classes and functions, we're probably back to an attribute that just suppresses the warning, with a different name. Or I guess we could have two attributes, but that seems like a lot. WDYT? Jason
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 1dac1470d3b..e4bf9c963bd 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -14033,11 +14033,7 @@ std_pair_ref_ref_p (tree t) return true; } -/* Return true if a class CTYPE is either std::reference_wrapper or - std::ref_view, or a reference wrapper class. We consider a class - a reference wrapper class if it has a reference member. We no - longer check that it has a constructor taking the same reference type - since that approach still generated too many false positives. */ +/* Return true if a class T has a reference member. */ static bool class_has_reference_member_p (tree t) @@ -14061,12 +14057,41 @@ class_has_reference_member_p_r (tree binfo, void *) ? integer_one_node : NULL_TREE); } + +/* Return true if T (either a class or a function) has been marked as + non-owning. */ + +static bool +non_owning_p (tree t) +{ + t = lookup_attribute ("non_owning", TYPE_ATTRIBUTES (t)); + if (!t) + return false; + + t = TREE_VALUE (t); + if (!t) + return true; + + t = build_converted_constant_bool_expr (TREE_VALUE (t), tf_warning_or_error); + t = cxx_constant_value (t); + return t == boolean_true_node; +} + +/* Return true if a class CTYPE is either std::reference_wrapper or + std::ref_view, or a reference wrapper class. We consider a class + a reference wrapper class if it has a reference member. We no + longer check that it has a constructor taking the same reference type + since that approach still generated too many false positives. */ + static bool reference_like_class_p (tree ctype) { if (!CLASS_TYPE_P (ctype)) return false; + if (non_owning_p (ctype)) + return true; + /* Also accept a std::pair<const T&, const T&>. */ if (std_pair_ref_ref_p (ctype)) return true; @@ -14173,7 +14198,8 @@ do_warn_dangling_reference (tree expr, bool arg_p) but probably not to one of its arguments. */ || (DECL_OBJECT_MEMBER_FUNCTION_P (fndecl) && DECL_OVERLOADED_OPERATOR_P (fndecl) - && DECL_OVERLOADED_OPERATOR_IS (fndecl, INDIRECT_REF))) + && DECL_OVERLOADED_OPERATOR_IS (fndecl, INDIRECT_REF)) + || non_owning_p (TREE_TYPE (fndecl))) return NULL_TREE; tree rettype = TREE_TYPE (TREE_TYPE (fndecl)); diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc index ad312710f68..017da7e294a 100644 --- a/gcc/cp/tree.cc +++ b/gcc/cp/tree.cc @@ -47,6 +47,7 @@ static tree verify_stmt_tree_r (tree *, int *, void *); static tree handle_init_priority_attribute (tree *, tree, tree, int, bool *); static tree handle_abi_tag_attribute (tree *, tree, tree, int, bool *); static tree handle_contract_attribute (tree *, tree, tree, int, bool *); +static tree handle_non_owning_attribute (tree *, tree, tree, int, bool *); /* If REF is an lvalue, returns the kind of lvalue that REF is. Otherwise, returns clk_none. */ @@ -5102,6 +5103,8 @@ static const attribute_spec cxx_gnu_attributes[] = handle_init_priority_attribute, NULL }, { "abi_tag", 1, -1, false, false, false, true, handle_abi_tag_attribute, NULL }, + { "non_owning", 0, 1, false, true, false, false, + handle_non_owning_attribute, NULL }, }; const scoped_attribute_specs cxx_gnu_attribute_table = @@ -5391,6 +5394,29 @@ handle_contract_attribute (tree *ARG_UNUSED (node), tree ARG_UNUSED (name), return NULL_TREE; } +/* Handle a "non_owning" attribute; arguments as in + struct attribute_spec.handler. */ + +tree +handle_non_owning_attribute (tree *node, tree name, tree args, int, + bool *no_add_attrs) +{ + if (args && TREE_CODE (TREE_VALUE (args)) == STRING_CST) + { + error ("%qE attribute argument must be an expression that evaluates " + "to true or false", name); + *no_add_attrs = true; + } + else if (!FUNC_OR_METHOD_TYPE_P (*node) + && !RECORD_OR_UNION_TYPE_P (*node)) + { + warning (OPT_Wattributes, "%qE attribute ignored", name); + *no_add_attrs = true; + } + + return NULL_TREE; +} + /* Return a new PTRMEM_CST of the indicated TYPE. The MEMBER is the thing pointed to by the constant. */ diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 2135dfde9c8..9132add8267 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -29320,6 +29320,31 @@ Some_Class B __attribute__ ((init_priority (543))); Note that the particular values of @var{priority} do not matter; only their relative ordering. +@cindex @code{non_owning} type attribute +@item non_owning + +This attribute can be applied on a class type, function, or member +function and indicates that it does not own its associated data. For +example, classes like @code{std::span} or @code{std::reference_wrapper} +are considered non-owning. + +@smallexample +class [[gnu::non_owning]] S @{ @dots{} @}; +@end smallexample + +This attribute takes an optional argument, which must be an expression that +evaluates to true or false: + +@smallexample +template <typename T> +struct [[gnu::non_owning(std::is_reference_v<T>)]] S @{ + @dots{} +@}; +@end smallexample + +Currently, the only effect this attribute has is to suppress the +@option{-Wdangling-reference} diagnostic. + @cindex @code{warn_unused} type attribute @item warn_unused diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index b4e4ee9fb81..0df2e2ded34 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -3908,6 +3908,9 @@ const T& foo (const T&) @{ @dots{} @} #pragma GCC diagnostic pop @end smallexample +The @code{#pragma} can also surround the class; in that case, the warning +will be disabled for all the member functions. + @option{-Wdangling-reference} also warns about code like @smallexample @@ -3932,6 +3935,24 @@ struct Span @{ as @code{std::span}-like; that is, the class is a non-union class that has a pointer data member and a trivial destructor. +The warning can be disabled by using the @code{gnu::non_owning} attribute, +which can be applied on the enclosing class type (in which case it disables +the warning for all its member functions), member function, or a regular +function. For example: + +@smallexample +class [[gnu::non_owning]] A @{ + int *p; + int &foo() @{ return *p; @} +@}; + +[[gnu::non_owning]] const int & +foo (const int &i) +@{ + @dots{} +@} +@end smallexample + This warning is enabled by @option{-Wall}. @opindex Wdelete-non-virtual-dtor diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning1.C b/gcc/testsuite/g++.dg/ext/attr-non-owning1.C new file mode 100644 index 00000000000..000f7f4019d --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning1.C @@ -0,0 +1,38 @@ +// { dg-do compile { target c++11 } } +// { dg-options "-Wdangling-reference" } + +int g = 42; + +struct [[gnu::non_owning]] A { + int *i; + int &foo() { return *i; } +}; + +struct A2 { + int *i; + [[gnu::non_owning]] int &foo() { return *i; } + [[gnu::non_owning]] static int &bar (const int &) { return *&g; } +}; + +union [[gnu::non_owning]] U { }; + +A a() { return A{&g}; } +A2 a2() { return A2{&g}; } + +class X { }; +const X x1; +const X x2; + +[[gnu::non_owning]] const X& get(const int& i) +{ + return i == 0 ? x1 : x2; +} + +void +test () +{ + [[maybe_unused]] const X& x = get (10); // { dg-bogus "dangling" } + [[maybe_unused]] const int &i = a().foo(); // { dg-bogus "dangling" } + [[maybe_unused]] const int &j = a2().foo(); // { dg-bogus "dangling" } + [[maybe_unused]] const int &k = a2().bar(10); // { dg-bogus "dangling" } +} diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning2.C b/gcc/testsuite/g++.dg/ext/attr-non-owning2.C new file mode 100644 index 00000000000..4d2037e8b78 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning2.C @@ -0,0 +1,29 @@ +// { dg-do compile { target c++11 } } +// Negative tests. + +struct [[non_owning]] A { // { dg-warning "ignored" } + [[non_owning]] int &foo (int &); // { dg-warning "ignored" } +}; + +[[non_owning]] int &bar (int &); // { dg-warning "ignored" } + +[[gnu::non_owning]] int i; // { dg-warning "ignored" } +[[gnu::non_owning]] double d; // { dg-warning "ignored" } +[[gnu::non_owning]] typedef int T; // { dg-warning "ignored" } + +[[gnu::non_owning()]] int &fn1 (int &); // { dg-error "parentheses" } +[[gnu::non_owning("a")]] int &fn2 (int &); // { dg-error "must be an expression" } +[[gnu::non_owning(true, true)]] int &fn3 (int &); // { dg-error "wrong number of arguments" } + +enum [[gnu::non_owning]] E { // { dg-warning "ignored" } + X [[gnu::non_owning]] // { dg-warning "ignored" } +}; + +[[gnu::non_owning]]; // { dg-warning "ignored" } + +void +g () +{ + goto L; +[[gnu::non_owning]] L:; // { dg-warning "ignored" } +} diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning3.C b/gcc/testsuite/g++.dg/ext/attr-non-owning3.C new file mode 100644 index 00000000000..81c6491643b --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning3.C @@ -0,0 +1,24 @@ +// { dg-do compile { target c++11 } } +// { dg-options "-Wdangling-reference" } + +template <typename T> +struct [[gnu::non_owning]] Span { + T* data_; + int len_; + // So that our heuristic doesn't suppress the warning anyway. + ~Span(); + + [[nodiscard]] constexpr auto operator[](int n) const noexcept -> T& { return data_[n]; } + [[nodiscard]] constexpr auto front() const noexcept -> T& { return data_[0]; } + [[nodiscard]] constexpr auto back() const noexcept -> T& { return data_[len_ - 1]; } +}; + +auto get() -> Span<int>; + +auto f() -> int { + int const& a = get().front(); // { dg-bogus "dangling" } + int const& b = get().back(); // { dg-bogus "dangling" } + int const& c = get()[0]; // { dg-bogus "dangling" } + + return a + b + c; +} diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning4.C b/gcc/testsuite/g++.dg/ext/attr-non-owning4.C new file mode 100644 index 00000000000..c50382c3e8f --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning4.C @@ -0,0 +1,14 @@ +// { dg-do compile { target c++11 } } + +#if !__has_attribute(non_owning) +#error unsupported +#endif + +#ifdef __has_cpp_attribute +# if !__has_cpp_attribute(non_owning) +# error non_owning +# endif +#endif + +struct [[gnu::non_owning]] S { }; +static_assert (__builtin_has_attribute (S, non_owning), ""); diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning5.C b/gcc/testsuite/g++.dg/ext/attr-non-owning5.C new file mode 100644 index 00000000000..d297bb615fe --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning5.C @@ -0,0 +1,31 @@ +// PR c++/110358 +// { dg-do compile { target c++20 } } +// { dg-options "-Wdangling-reference" } + +template <typename T> +struct Span { + T* data_; + int len_; + ~Span(); + + [[nodiscard]] constexpr auto operator[](int n) const noexcept -> T& { return data_[n]; } +}; + +template <> +struct [[gnu::non_owning]] Span<int> { + int* data_; + int len_; + ~Span(); + + [[nodiscard]] constexpr auto operator[](int n) const noexcept -> int& { return data_[n]; } +}; + +auto getch() -> Span<char>; +auto geti() -> Span<int>; + +void +f () +{ + [[maybe_unused]] const auto &a = getch()[0]; // { dg-warning "dangling reference" } + [[maybe_unused]] const auto &b = geti()[0]; // { dg-bogus "dangling reference" } +} diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning6.C b/gcc/testsuite/g++.dg/ext/attr-non-owning6.C new file mode 100644 index 00000000000..10ce1842852 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning6.C @@ -0,0 +1,65 @@ +// PR c++/110358 +// { dg-do compile { target c++20 } } +// { dg-options "-Wdangling-reference" } + +class X { }; +const X x1; +const X x2; + +constexpr bool val () { return true; } +struct ST { static constexpr bool value = true; }; +struct SF { static constexpr bool value = false; }; + +template<typename T> +[[gnu::non_owning(T::value)]] +const X& get (const int& i) +{ + return i == 0 ? x1 : x2; +} + +template<bool B = true> +[[gnu::non_owning(B)]] +const X& foo (const int& i) +{ + return i == 0 ? x1 : x2; +} + +[[gnu::non_owning(val ())]] +const X& bar (const int& i) +{ + return i == 0 ? x1 : x2; +} + +[[gnu::non_owning(!val ())]] +const X& baz (const int& i) +{ + return i == 0 ? x1 : x2; +} + +template <typename T> +struct [[gnu::non_owning(T::value)]] +Span { + T* data_; + int len_; + ~Span(); + + [[nodiscard]] constexpr auto operator[](int n) const noexcept -> T& { return data_[n]; } +}; + +auto geti() -> Span<ST>; +auto gety() -> Span<SF>; + +void +test () +{ + [[maybe_unused]] const X& x1 = get<ST> (10); // { dg-bogus "dangling" } + [[maybe_unused]] const X& x2 = get<SF> (10); // { dg-warning "dangling" } + [[maybe_unused]] const X& x3 = foo<true> (10); // { dg-bogus "dangling" } + [[maybe_unused]] const X& x4 = foo<false> (10); // { dg-warning "dangling" } + [[maybe_unused]] const X& x7 = foo<> (10); // { dg-bogus "dangling" } + [[maybe_unused]] const X& x5 = bar (10); // { dg-bogus "dangling" } + [[maybe_unused]] const X& x6 = baz (10); // { dg-warning "dangling" } + + [[maybe_unused]] const auto &b1 = geti()[0]; // { dg-bogus "dangling" } + [[maybe_unused]] const auto &b2 = gety()[0]; // { dg-warning "dangling" } +} diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning7.C b/gcc/testsuite/g++.dg/ext/attr-non-owning7.C new file mode 100644 index 00000000000..bba69871918 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning7.C @@ -0,0 +1,31 @@ +// PR c++/110358 +// { dg-do compile { target c++20 } } +// { dg-options "-Wdangling-reference" } + +class X { }; +const X x1; +const X x2; + +template<bool... N> +[[gnu::non_owning(N)]] const X& get(const int& i); // { dg-error "parameter packs not expanded" } + +template<typename T> +[[gnu::non_owning(T::x)]] // { dg-error "member" } +const X& foo(const int& i); + +bool val () { return true; } + +[[gnu::non_owning(val ())]] // { dg-error "call" } +const X& bar (const int& i); + +[[gnu::non_owning(20)]] const X& fn1 (const int &); + +void +test () +{ + [[maybe_unused]] const X& x1 = bar (10); // { dg-warning "dangling" } + [[maybe_unused]] const X& x2 = foo<int> (10); // { dg-error "no matching" } + [[maybe_unused]] const X& x3 // { dg-warning "dangling" } + = fn1 (10); // { dg-error "narrowing" } +} + diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning8.C b/gcc/testsuite/g++.dg/ext/attr-non-owning8.C new file mode 100644 index 00000000000..1bfed4ed33c --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning8.C @@ -0,0 +1,30 @@ +// PR c++/110358 +// { dg-do compile { target c++20 } } +// { dg-options "-Wdangling-reference" } + +template<class T> constexpr bool is_reference_v = false; +template<class T> constexpr bool is_reference_v<T&> = true; +template<class T> constexpr bool is_reference_v<T&&> = true; + +template <typename T> +struct [[gnu::non_owning(is_reference_v<T>)]] S { + int &foo (const int &); +}; + +template <typename T1, typename T2> +struct X { + template <typename U1 = T1, typename U2 = T2> + struct [[gnu::non_owning(is_reference_v<U1> && is_reference_v<U2>)]] Y { + int &foo (const int &); + }; +}; + +void +g () +{ + [[maybe_unused]] const int &x0 = S<int&>().foo (42); // { dg-bogus "dangling" } + [[maybe_unused]] const int &x1 = S<int>().foo (42); // { dg-warning "dangling" } + [[maybe_unused]] const auto &x2 = X<int, int&>::Y<>().foo (42); // { dg-warning "dangling" } + [[maybe_unused]] const auto &x3 = X<int&, int&>::Y<>().foo (42); // { dg-bogus "dangling" } +} + diff --git a/gcc/testsuite/g++.dg/ext/attr-non-owning9.C b/gcc/testsuite/g++.dg/ext/attr-non-owning9.C new file mode 100644 index 00000000000..6f6a72736ce --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-non-owning9.C @@ -0,0 +1,25 @@ +// PR c++/110358 +// { dg-do compile { target c++20 } } +// { dg-options "-Wdangling-reference" } + +template<bool B> +struct bool_constant { + static constexpr bool value = B; + constexpr operator bool() const { return value; } +}; + +using true_type = bool_constant<true>; +using false_type = bool_constant<false>; + +struct S { + template<bool B> + [[gnu::non_owning(B)]] int &foo (const int &); +}; + +void +g () +{ + [[maybe_unused]] const int &x0 = S().foo<false_type{}> (42); // { dg-warning "dangling" } + [[maybe_unused]] const int &x1 = S().foo<true_type{}> (42); // { dg-bogus "dangling" } +} +