https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109642
Bug ID: 109642
Summary: False Positive -Wdangling-reference with
std::span-like classes
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: carlosgalvezp at gmail dot com
Target Milestone: ---
Hi,
We are bumping our GCC installation from
6910cad55ffc330dc9767d2c8e0b66ccfa4134af to
cc035c5d8672f87dc8c2756d9f8367903aa72d93 (GCC 13.1 release), and are now
getting a lot of False Positives from code that looks like this:
#include <iterator>
#include <span>
template <typename T>
struct MySpan
{
MySpan(T* data, std::size_t size) :
data_(data),
size_(size)
{}
T& operator[](std::size_t idx) { return data_[idx]; }
private:
T* data_;
std::size_t size_;
};
template <typename T, std::size_t n>
MySpan<T const> make_my_span(T const(&x)[n])
{
return MySpan(std::begin(x), n);
}
template <typename T, std::size_t n>
std::span<T const> make_span(T const(&x)[n])
{
return std::span(std::begin(x), n);
}
int main()
{
int x[10]{};
int const& y{make_my_span(x)[0]};
int const& y2{make_span(x)[0]};
}
Godbolt: https://godbolt.org/z/Pf6jsezoP
I.e. when using std::span, GCC is happy, but when using our own implementation
of span (since we can't enable C++20 yet in our project due to reasons), then
it complains about dangling reference. Clang trunk does not warn about this.
It warns both about non-const and const references.
