Message ID | ZeIS0IjmUuMN8v_b@redhat.com |
---|---|
State | New |
Headers | show |
Series | [v4] c++: implement [[gnu::non_owning]] [PR110358] | expand |
On 3/1/24 12:39, Marek Polacek wrote: > On Thu, Feb 29, 2024 at 07:30:02PM -0500, Jason Merrill wrote: >> On 2/29/24 19:12, Marek Polacek wrote: >>> On Wed, Feb 28, 2024 at 06:03:54PM -0500, Jason Merrill wrote: >>> >>>> 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. >>> >>> Yeah, that's a fair point; I guess "non_owning" would be too perplexing. >>> >>>> 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? >>> >>> I think we don't want two separate attributes, and we do want that one >>> attribute to apply to both fns and classes. We could implement something >>> like >>> >>> [[gnu::no_warning("Wdangling-reference")]] >>> [[gnu::no_warning("Wdangling-reference", bool)]] >>> >>> but first, that's a lot of typing, second, it would be confusing because >>> it wouldn't work for any other warning. We already have [[unused]] and >>> [[maybe_unused]] whose effect is to suppress a warning. It think our >>> best bet is to do the most straightforward thing: [[gnu::no_dangling]], >>> which this patch implements. I didn't call it no_dangling_reference in >>> the hope that it can, some day, be also used for some -Wdangling-pointer >>> purposes. >>> >>> >>> 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. >>> >>> To that end, this patch adds a new attribute, [[gnu::no_dangling]]. >>> This attribute takes an optional bool argument to support cases like: >>> >>> template <typename T> >>> struct [[gnu::no_dangling(std::is_reference_v<T>)]] S { >>> // ... >>> }; >>> >>> PR c++/110358 >>> PR c++/109642 >>> >>> gcc/cp/ChangeLog: >>> >>> * call.cc (no_dangling_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::no_dangling. >>> * tree.cc (cxx_gnu_attributes): Add gnu::no_dangling. >>> (handle_no_dangling_attribute): New. >>> >>> gcc/ChangeLog: >>> >>> * doc/extend.texi: Document gnu::no_dangling. >>> * doc/invoke.texi: Mention that gnu::no_dangling disables >>> -Wdangling-reference. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * g++.dg/ext/attr-no-dangling1.C: New test. >>> * g++.dg/ext/attr-no-dangling2.C: New test. >>> * g++.dg/ext/attr-no-dangling3.C: New test. >>> * g++.dg/ext/attr-no-dangling4.C: New test. >>> * g++.dg/ext/attr-no-dangling5.C: New test. >>> * g++.dg/ext/attr-no-dangling6.C: New test. >>> * g++.dg/ext/attr-no-dangling7.C: New test. >>> * g++.dg/ext/attr-no-dangling8.C: New test. >>> * g++.dg/ext/attr-no-dangling9.C: New test. >>> --- >>> gcc/cp/call.cc | 38 ++++++++++-- >>> gcc/cp/tree.cc | 26 ++++++++ >>> gcc/doc/extend.texi | 21 +++++++ >>> gcc/doc/invoke.texi | 21 +++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling1.C | 38 ++++++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling2.C | 29 +++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling3.C | 24 ++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling4.C | 14 +++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling5.C | 31 ++++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling6.C | 65 ++++++++++++++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling7.C | 31 ++++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling8.C | 30 +++++++++ >>> gcc/testsuite/g++.dg/ext/attr-no-dangling9.C | 25 ++++++++ >>> 13 files changed, 387 insertions(+), 6 deletions(-) >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling1.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling2.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling3.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling4.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling5.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling6.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling7.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling8.C >>> create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling9.C >>> >>> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc >>> index c40ef2e3028..9e4c8073600 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 >>> + not-dangling. */ >>> + >>> +static bool >>> +no_dangling_p (tree t) >>> +{ >>> + t = lookup_attribute ("no_dangling", 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 (no_dangling_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)) >>> + || no_dangling_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..e75be9a4e66 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_no_dangling_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 }, >>> + { "no_dangling", 0, 1, false, true, false, false, >>> + handle_no_dangling_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 "no_dangling" attribute; arguments as in >>> + struct attribute_spec.handler. */ >>> + >>> +tree >>> +handle_no_dangling_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 efd78014d1a..571655bf39a 100644 >>> --- a/gcc/doc/extend.texi >>> +++ b/gcc/doc/extend.texi >>> @@ -29317,6 +29317,27 @@ Some_Class B __attribute__ ((init_priority (543))); >>> Note that the particular values of @var{priority} do not matter; only their >>> relative ordering. >>> +@cindex @code{no_dangling} type attribute >>> +@item no_dangling >>> + >>> +This attribute can be applied on a class type, function, or member >>> +function. Entities marked with this attribute will have the >>> +@option{-Wdangling-reference} diagnostic suppressed. >>> + >>> +@smallexample >>> +class [[gnu::no_dangling]] 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::no_dangling(std::is_reference_v<T>)]] S @{ >>> + @dots{} >>> +@}; >>> +@end smallexample > >>> @cindex @code{warn_unused} type attribute >>> @item warn_unused >>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi >>> index 7862c751801..9022a413dd4 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::no_dangling} attribute, >> >> Can this be an xref, and put all the documentation for the usage and effect >> of the attribute in the attribute section? > > Yes. And I need an entry both for the type and function attribute. > >>> +which can be applied on the enclosing class type (in which case it disables >>> +the warning for all its member functions), >> >> I think this misrepresents the effect of putting the attribute on the class. >> Rather, it means that we won't warn about a dangling reference to the class. > > Updated, NFC: > > -- >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. > > To that end, this patch adds a new attribute, [[gnu::no_dangling]]. > This attribute takes an optional bool argument to support cases like: > > template <typename T> > struct [[gnu::no_dangling(std::is_reference_v<T>)]] S { > // ... > }; > > PR c++/110358 > PR c++/109642 > > gcc/cp/ChangeLog: > > * call.cc (no_dangling_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::no_dangling. > * tree.cc (cxx_gnu_attributes): Add gnu::no_dangling. > (handle_no_dangling_attribute): New. > > gcc/ChangeLog: > > * doc/extend.texi: Document gnu::no_dangling. > * doc/invoke.texi: Mention that gnu::no_dangling disables > -Wdangling-reference. > > gcc/testsuite/ChangeLog: > > * g++.dg/ext/attr-no-dangling1.C: New test. > * g++.dg/ext/attr-no-dangling2.C: New test. > * g++.dg/ext/attr-no-dangling3.C: New test. > * g++.dg/ext/attr-no-dangling4.C: New test. > * g++.dg/ext/attr-no-dangling5.C: New test. > * g++.dg/ext/attr-no-dangling6.C: New test. > * g++.dg/ext/attr-no-dangling7.C: New test. > * g++.dg/ext/attr-no-dangling8.C: New test. > * g++.dg/ext/attr-no-dangling9.C: New test. > --- > gcc/cp/call.cc | 38 ++++++++++-- > gcc/cp/tree.cc | 26 ++++++++ > gcc/doc/extend.texi | 51 +++++++++++++++ > gcc/doc/invoke.texi | 7 +++ > gcc/testsuite/g++.dg/ext/attr-no-dangling1.C | 38 ++++++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling2.C | 29 +++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling3.C | 24 ++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling4.C | 14 +++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling5.C | 31 ++++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling6.C | 65 ++++++++++++++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling7.C | 31 ++++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling8.C | 30 +++++++++ > gcc/testsuite/g++.dg/ext/attr-no-dangling9.C | 25 ++++++++ > 13 files changed, 403 insertions(+), 6 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling1.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling2.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling3.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling4.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling5.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling6.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling7.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling8.C > create mode 100644 gcc/testsuite/g++.dg/ext/attr-no-dangling9.C > > diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc > index c40ef2e3028..9e4c8073600 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 > + not-dangling. */ > + > +static bool > +no_dangling_p (tree t) > +{ > + t = lookup_attribute ("no_dangling", 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 (no_dangling_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)) > + || no_dangling_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..e75be9a4e66 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_no_dangling_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 }, > + { "no_dangling", 0, 1, false, true, false, false, > + handle_no_dangling_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 "no_dangling" attribute; arguments as in > + struct attribute_spec.handler. */ > + > +tree > +handle_no_dangling_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 6c2c7ae5d8a..5bd3933f011 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > @@ -4380,6 +4380,36 @@ visibility of their template. > If both the template and enclosing class have explicit visibility, the > visibility from the template is used. > > +@cindex @code{no_dangling} function attribute > +@item no_dangling > + > +The @code{gnu::no_dangling} attribute can be used to suppress the > +@option{-Wdangling-reference} diagnostic on a function or a member > +function. For example: > + > +@smallexample > +class A @{ > + int *p; > + [[gnu::no_dangling]] int &foo() @{ return *p; @} > +@}; > + > +[[gnu::no_dangling]] const int & > +foo (const int &i) > +@{ > + @dots{} > +@} > +@end smallexample > + > +This attribute takes an optional argument, which must be an expression that > +evaluates to true or false: > + > +@smallexample > +template <typename T> > +[[gnu::no_dangling(std::is_reference_v<T>)]] int foo (T& t) @{ > + @dots{} > +@}; > +@end smallexample > + > @cindex @code{warn_unused_result} function attribute > @item warn_unused_result > The @code{warn_unused_result} attribute causes a warning to be emitted > @@ -29327,6 +29357,27 @@ Some_Class B __attribute__ ((init_priority (543))); > Note that the particular values of @var{priority} do not matter; only their > relative ordering. > > +@cindex @code{no_dangling} type attribute > +@item no_dangling > + > +This attribute can be applied on a class type. Dangling references to > +classes marked with this attribute will have the @option{-Wdangling-reference} > +diagnostic suppressed. > + > +@smallexample > +class [[gnu::no_dangling]] 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::no_dangling(std::is_reference_v<T>)]] S @{ > + @dots{} > +@}; > +@end smallexample > + > @cindex @code{warn_unused} type attribute > @item warn_unused > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index dc5fd863ca4..0422b2c400a 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 +3935,10 @@ 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::no_dangling} attribute > +on a function (@pxref{Common Function Attributes}), or a class type > +(@pxref{C++ Attributes}). It seems surprising that one is in a generic attributes section and the other in the C++-specific section. Maybe both uses could be covered in the C++ attributes section? > This warning is enabled by @option{-Wall}. > > @opindex Wdelete-non-virtual-dtor > diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C > new file mode 100644 > index 00000000000..02eabbc5003 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C > @@ -0,0 +1,38 @@ > +// { dg-do compile { target c++11 } } > +// { dg-options "-Wdangling-reference" } > + > +int g = 42; > + > +struct [[gnu::no_dangling]] A { > + int *i; > + int &foo() { return *i; } > +}; > + > +struct A2 { > + int *i; > + [[gnu::no_dangling]] int &foo() { return *i; } > + [[gnu::no_dangling]] static int &bar (const int &) { return *&g; } > +}; > + > +union [[gnu::no_dangling]] U { }; > + > +A a() { return A{&g}; } > +A2 a2() { return A2{&g}; } > + > +class X { }; > +const X x1; > +const X x2; > + > +[[gnu::no_dangling]] 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" } > +} Do you want to add destructors to A/A2 like you did in other tests? > diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling2.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling2.C > new file mode 100644 > index 00000000000..4cdc97ea7c4 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling2.C > @@ -0,0 +1,29 @@ > +// { dg-do compile { target c++11 } } > +// Negative tests. > + > +struct [[no_dangling]] A { // { dg-warning "ignored" } > + [[no_dangling]] int &foo (int &); // { dg-warning "ignored" } > +}; > + > +[[no_dangling]] int &bar (int &); // { dg-warning "ignored" } > + > +[[gnu::no_dangling]] int i; // { dg-warning "ignored" } > +[[gnu::no_dangling]] double d; // { dg-warning "ignored" } > +[[gnu::no_dangling]] typedef int T; // { dg-warning "ignored" } > + > +[[gnu::no_dangling()]] int &fn1 (int &); // { dg-error "parentheses" } > +[[gnu::no_dangling("a")]] int &fn2 (int &); // { dg-error "must be an expression" } > +[[gnu::no_dangling(true, true)]] int &fn3 (int &); // { dg-error "wrong number of arguments" } > + > +enum [[gnu::no_dangling]] E { // { dg-warning "ignored" } > + X [[gnu::no_dangling]] // { dg-warning "ignored" } > +}; > + > +[[gnu::no_dangling]]; // { dg-warning "ignored" } > + > +void > +g () > +{ > + goto L; > +[[gnu::no_dangling]] L:; // { dg-warning "ignored" } > +} > diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C > new file mode 100644 > index 00000000000..764b104fd3c > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C > @@ -0,0 +1,24 @@ > +// { dg-do compile { target c++11 } } > +// { dg-options "-Wdangling-reference" } > + > +template <typename T> > +struct [[gnu::no_dangling]] 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-no-dangling4.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling4.C > new file mode 100644 > index 00000000000..e910723d985 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling4.C > @@ -0,0 +1,14 @@ > +// { dg-do compile { target c++11 } } > + > +#if !__has_attribute(no_dangling) > +#error unsupported > +#endif > + > +#ifdef __has_cpp_attribute > +# if !__has_cpp_attribute(no_dangling) > +# error no_dangling > +# endif > +#endif > + > +struct [[gnu::no_dangling]] S { }; > +static_assert (__builtin_has_attribute (S, no_dangling), ""); > diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling5.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling5.C > new file mode 100644 > index 00000000000..ec5075482c4 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling5.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::no_dangling]] 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-no-dangling6.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C > new file mode 100644 > index 00000000000..235a5fd86c5 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.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::no_dangling(T::value)]] > +const X& get (const int& i) > +{ > + return i == 0 ? x1 : x2; > +} > + > +template<bool B = true> > +[[gnu::no_dangling(B)]] > +const X& foo (const int& i) > +{ > + return i == 0 ? x1 : x2; > +} > + > +[[gnu::no_dangling(val ())]] > +const X& bar (const int& i) > +{ > + return i == 0 ? x1 : x2; > +} > + > +[[gnu::no_dangling(!val ())]] > +const X& baz (const int& i) > +{ > + return i == 0 ? x1 : x2; > +} > + > +template <typename T> > +struct [[gnu::no_dangling(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-no-dangling7.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C > new file mode 100644 > index 00000000000..3c392ed409f > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.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::no_dangling(N)]] const X& get(const int& i); // { dg-error "parameter packs not expanded" } > + > +template<typename T> > +[[gnu::no_dangling(T::x)]] // { dg-error "member" } > +const X& foo(const int& i); > + > +bool val () { return true; } > + > +[[gnu::no_dangling(val ())]] // { dg-error "call" } > +const X& bar (const int& i); > + > +[[gnu::no_dangling(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-no-dangling8.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C > new file mode 100644 > index 00000000000..8208d751a4b > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.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::no_dangling(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::no_dangling(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-no-dangling9.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C > new file mode 100644 > index 00000000000..65b4f7145a9 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.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::no_dangling(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" } > +} > + > > base-commit: 4894c82b0c3cf0d6ec4bc1e96709b6140ec11f6e
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index c40ef2e3028..9e4c8073600 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 + not-dangling. */ + +static bool +no_dangling_p (tree t) +{ + t = lookup_attribute ("no_dangling", 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 (no_dangling_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)) + || no_dangling_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..e75be9a4e66 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_no_dangling_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 }, + { "no_dangling", 0, 1, false, true, false, false, + handle_no_dangling_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 "no_dangling" attribute; arguments as in + struct attribute_spec.handler. */ + +tree +handle_no_dangling_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 6c2c7ae5d8a..5bd3933f011 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -4380,6 +4380,36 @@ visibility of their template. If both the template and enclosing class have explicit visibility, the visibility from the template is used. +@cindex @code{no_dangling} function attribute +@item no_dangling + +The @code{gnu::no_dangling} attribute can be used to suppress the +@option{-Wdangling-reference} diagnostic on a function or a member +function. For example: + +@smallexample +class A @{ + int *p; + [[gnu::no_dangling]] int &foo() @{ return *p; @} +@}; + +[[gnu::no_dangling]] const int & +foo (const int &i) +@{ + @dots{} +@} +@end smallexample + +This attribute takes an optional argument, which must be an expression that +evaluates to true or false: + +@smallexample +template <typename T> +[[gnu::no_dangling(std::is_reference_v<T>)]] int foo (T& t) @{ + @dots{} +@}; +@end smallexample + @cindex @code{warn_unused_result} function attribute @item warn_unused_result The @code{warn_unused_result} attribute causes a warning to be emitted @@ -29327,6 +29357,27 @@ Some_Class B __attribute__ ((init_priority (543))); Note that the particular values of @var{priority} do not matter; only their relative ordering. +@cindex @code{no_dangling} type attribute +@item no_dangling + +This attribute can be applied on a class type. Dangling references to +classes marked with this attribute will have the @option{-Wdangling-reference} +diagnostic suppressed. + +@smallexample +class [[gnu::no_dangling]] 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::no_dangling(std::is_reference_v<T>)]] S @{ + @dots{} +@}; +@end smallexample + @cindex @code{warn_unused} type attribute @item warn_unused diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index dc5fd863ca4..0422b2c400a 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 +3935,10 @@ 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::no_dangling} attribute +on a function (@pxref{Common Function Attributes}), or a class type +(@pxref{C++ Attributes}). + This warning is enabled by @option{-Wall}. @opindex Wdelete-non-virtual-dtor diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C new file mode 100644 index 00000000000..02eabbc5003 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling1.C @@ -0,0 +1,38 @@ +// { dg-do compile { target c++11 } } +// { dg-options "-Wdangling-reference" } + +int g = 42; + +struct [[gnu::no_dangling]] A { + int *i; + int &foo() { return *i; } +}; + +struct A2 { + int *i; + [[gnu::no_dangling]] int &foo() { return *i; } + [[gnu::no_dangling]] static int &bar (const int &) { return *&g; } +}; + +union [[gnu::no_dangling]] U { }; + +A a() { return A{&g}; } +A2 a2() { return A2{&g}; } + +class X { }; +const X x1; +const X x2; + +[[gnu::no_dangling]] 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-no-dangling2.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling2.C new file mode 100644 index 00000000000..4cdc97ea7c4 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling2.C @@ -0,0 +1,29 @@ +// { dg-do compile { target c++11 } } +// Negative tests. + +struct [[no_dangling]] A { // { dg-warning "ignored" } + [[no_dangling]] int &foo (int &); // { dg-warning "ignored" } +}; + +[[no_dangling]] int &bar (int &); // { dg-warning "ignored" } + +[[gnu::no_dangling]] int i; // { dg-warning "ignored" } +[[gnu::no_dangling]] double d; // { dg-warning "ignored" } +[[gnu::no_dangling]] typedef int T; // { dg-warning "ignored" } + +[[gnu::no_dangling()]] int &fn1 (int &); // { dg-error "parentheses" } +[[gnu::no_dangling("a")]] int &fn2 (int &); // { dg-error "must be an expression" } +[[gnu::no_dangling(true, true)]] int &fn3 (int &); // { dg-error "wrong number of arguments" } + +enum [[gnu::no_dangling]] E { // { dg-warning "ignored" } + X [[gnu::no_dangling]] // { dg-warning "ignored" } +}; + +[[gnu::no_dangling]]; // { dg-warning "ignored" } + +void +g () +{ + goto L; +[[gnu::no_dangling]] L:; // { dg-warning "ignored" } +} diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C new file mode 100644 index 00000000000..764b104fd3c --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling3.C @@ -0,0 +1,24 @@ +// { dg-do compile { target c++11 } } +// { dg-options "-Wdangling-reference" } + +template <typename T> +struct [[gnu::no_dangling]] 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-no-dangling4.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling4.C new file mode 100644 index 00000000000..e910723d985 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling4.C @@ -0,0 +1,14 @@ +// { dg-do compile { target c++11 } } + +#if !__has_attribute(no_dangling) +#error unsupported +#endif + +#ifdef __has_cpp_attribute +# if !__has_cpp_attribute(no_dangling) +# error no_dangling +# endif +#endif + +struct [[gnu::no_dangling]] S { }; +static_assert (__builtin_has_attribute (S, no_dangling), ""); diff --git a/gcc/testsuite/g++.dg/ext/attr-no-dangling5.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling5.C new file mode 100644 index 00000000000..ec5075482c4 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling5.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::no_dangling]] 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-no-dangling6.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.C new file mode 100644 index 00000000000..235a5fd86c5 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling6.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::no_dangling(T::value)]] +const X& get (const int& i) +{ + return i == 0 ? x1 : x2; +} + +template<bool B = true> +[[gnu::no_dangling(B)]] +const X& foo (const int& i) +{ + return i == 0 ? x1 : x2; +} + +[[gnu::no_dangling(val ())]] +const X& bar (const int& i) +{ + return i == 0 ? x1 : x2; +} + +[[gnu::no_dangling(!val ())]] +const X& baz (const int& i) +{ + return i == 0 ? x1 : x2; +} + +template <typename T> +struct [[gnu::no_dangling(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-no-dangling7.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.C new file mode 100644 index 00000000000..3c392ed409f --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling7.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::no_dangling(N)]] const X& get(const int& i); // { dg-error "parameter packs not expanded" } + +template<typename T> +[[gnu::no_dangling(T::x)]] // { dg-error "member" } +const X& foo(const int& i); + +bool val () { return true; } + +[[gnu::no_dangling(val ())]] // { dg-error "call" } +const X& bar (const int& i); + +[[gnu::no_dangling(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-no-dangling8.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.C new file mode 100644 index 00000000000..8208d751a4b --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling8.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::no_dangling(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::no_dangling(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-no-dangling9.C b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.C new file mode 100644 index 00000000000..65b4f7145a9 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/attr-no-dangling9.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::no_dangling(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" } +} +