libstdc++: Do not use list-initialization in std::span members [PR120997]
As the bug report shows, for span<const bool> the return statements of
the form `return {data(), count};` will use the new C++26 constructor,
span(initializer_list<element_type>).
Although the conversions from data() to bool and count to bool are
narrowing and should be ill-formed, in system headers the narrowing
diagnostics are suppressed. In any case, even if the compiler diagnosed
them as ill-formed, we still don't want the initializer_list constructor
to be used. We want to use the span(element_type*, size_t) constructor
instead.
Replace the braced-init-list uses with S(data(), count) where S is the
correct return type. We need to make similar changes in the C++26
working draft, which will be taken care of via an LWG issue.
libstdc++-v3/ChangeLog:
PR libstdc++/120997
* include/std/span (span::first, span::last, span::subspan): Do
not use braced-init-list for return statements.
* testsuite/23_containers/span/120997.cc: New test.
(cherry picked from commit a72d0e1a8bf0770ddf1d8d0ebe589f92a4fab4ef)
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index 49ab910..6f0213e 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -376,7 +376,7 @@
else
static_assert(_Count <= extent);
using _Sp = span<element_type, _Count>;
- return _Sp{ _SizedPtr{this->data()} };
+ return _Sp(_SizedPtr{this->data()});
}
[[nodiscard]]
@@ -384,7 +384,7 @@
first(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
- return { this->data(), __count };
+ return span<element_type>(this->data(), __count);
}
template<size_t _Count>
@@ -397,7 +397,7 @@
else
static_assert(_Count <= extent);
using _Sp = span<element_type, _Count>;
- return _Sp{ _SizedPtr{this->data() + (this->size() - _Count)} };
+ return _Sp(_SizedPtr{this->data() + (this->size() - _Count)});
}
[[nodiscard]]
@@ -405,7 +405,8 @@
last(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
- return { this->data() + (this->size() - __count), __count };
+ return span<element_type>(this->data() + (this->size() - __count),
+ __count);
}
template<size_t _Offset, size_t _Count = dynamic_extent>
@@ -424,7 +425,7 @@
using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
if constexpr (_Count == dynamic_extent)
- return _Sp{ this->data() + _Offset, this->size() - _Offset };
+ return _Sp(this->data() + _Offset, this->size() - _Offset);
else
{
if constexpr (_Extent == dynamic_extent)
@@ -437,7 +438,7 @@
static_assert(_Count <= extent);
static_assert(_Count <= (extent - _Offset));
}
- return _Sp{ _SizedPtr{this->data() + _Offset} };
+ return _Sp(_SizedPtr{this->data() + _Offset});
}
}
@@ -454,7 +455,7 @@
__glibcxx_assert(__count <= size());
__glibcxx_assert(__offset + __count <= size());
}
- return {this->data() + __offset, __count};
+ return span<element_type>(this->data() + __offset, __count);
}
private:
diff --git a/libstdc++-v3/testsuite/23_containers/span/120997.cc b/libstdc++-v3/testsuite/23_containers/span/120997.cc
new file mode 100644
index 0000000..fbf194c
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/120997.cc
@@ -0,0 +1,46 @@
+// { dg-do run { target c++26 } }
+
+#include <span>
+#include <testsuite_hooks.h>
+
+void
+test_first()
+{
+ bool arr[5];
+ std::span<const bool> s(arr);
+ std::span<const bool> s2 = s.first(5);
+ VERIFY( s2.data() == s.data() );
+ std::span<const bool> s3 = s.first<5>();
+ VERIFY( s3.data() == s.data() );
+}
+
+void
+test_last()
+{
+ bool arr[5];
+ std::span<const bool> s(arr);
+ std::span<const bool> s2 = s.last(5);
+ VERIFY( s2.data() == s.data() );
+ std::span<const bool> s3 = s.last<5>();
+ VERIFY( s3.data() == s.data() );
+}
+
+void
+test_subspan()
+{
+ bool arr[5];
+ std::span<const bool> s(arr);
+ std::span<const bool> s2 = s.subspan(0, 5);
+ VERIFY( s2.data() == s.data() );
+ std::span<const bool> s3 = s.subspan<0>();
+ VERIFY( s3.data() == s.data() );
+ std::span<const bool> s4 = s.subspan<0, 5>();
+ VERIFY( s4.data() == s.data() );
+}
+
+int main()
+{
+ test_first();
+ test_last();
+ test_subspan();
+}
