https://gcc.gnu.org/g:47b205b4dcca8be98bff96ea6b6f80682c65a0b1
commit r14-10727-g47b205b4dcca8be98bff96ea6b6f80682c65a0b1
Author: Jason Merrill <ja...@redhat.com>
Date: Sun Sep 15 13:50:04 2024 +0200
c++: -Wdangling-reference and empty class [PR115361]
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.
Diff:
---
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(-)
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index a210ea5cd6ac..423285caada4 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -14291,12 +14291,14 @@ 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 5b349e8e6827..1fc426d20d3d 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 a5fb809e6bdb..04c6badf0b6f 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 8208d751a4bb..aa196315a38a 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 65b4f7145a92..d7fd897de539 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 1718c28165e9..a184317dd5c3 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 dafdb43f1b93..a3d5ad6d8676 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 000000000000..e59ccc5057bb
--- /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 4bc20c13b3f7..7db1dc86855d 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();
};
