https://gcc.gnu.org/g:98847dc641b95a29fe470b90e4fec034daa4300b
commit r17-4727-g98847dc641b95a29fe470b90e4fec034daa4300b Author: Jonathan Wakely <[email protected]> Date: Fri Sep 25 10:00:35 2026 +0100 libstdc++: Enable dangling checks in std::pair and std::tuple [PR108822] In r13-6084-g916ce577ad109b I enabled the dangling-reference checks in std::pair unconditionally for C++20 (which was experimental at the time) but conditional on _GLIBCXX_DEBUG for C++17 and lower, saying: The pre-C++17 assertions are only enabled for Debug Mode, to avoid introducing a breaking change in Stage 4. We should consider enabling them by default in Stage 1 for GCC 14. In r14-7225-gf8a5298c97c460 I added the checks to std::tuple, again making them conditional on _GLIBCXX_DEBUG for C++17 and lower. We never revisited that during Stage 1 to remove the _GLIBCXX_DEBUG condition. I'm not aware of problems caused by making it ill-formed to create pairs and tuples with dangling references, so this commit removes the _GLIBCXX_DEBUG condition. This makes it ill-formed to create a std::pair or std::tuple that would have guaranteed UB if its element was accessed at runtime. Programs which use such types in code which is never executed should either remove the code, or use std::declval in unevaluated contexts, to avoid instantiating the ill-formed constructors. libstdc++-v3/ChangeLog: PR libstdc++/108822 * include/bits/stl_pair.h (__glibcxx_no_dangling_refs): Enable for normal mode, not only Debug Mode. * include/std/tuple (__glibcxx_no_dangling_refs): Likewise. Reviewed-by: Tomasz Kamiński <[email protected]> Diff: --- libstdc++-v3/include/bits/stl_pair.h | 3 +-- libstdc++-v3/include/std/tuple | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h index f08b2714a4fe..ccff86912067 100644 --- a/libstdc++-v3/include/bits/stl_pair.h +++ b/libstdc++-v3/include/bits/stl_pair.h @@ -726,8 +726,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// @cond undocumented // Error if construction from _U1 and _U2 would create a dangling ref. -#if __has_builtin(__reference_constructs_from_temporary) \ - && defined _GLIBCXX_DEBUG +#if __has_builtin(__reference_constructs_from_temporary) # define __glibcxx_no_dangling_refs(_U1, _U2) \ static_assert(!__reference_constructs_from_temporary(_T1, _U1) \ && !__reference_constructs_from_temporary(_T2, _U2), \ diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple index 63b4010c0b5e..d73cefcbca87 100644 --- a/libstdc++-v3/include/std/tuple +++ b/libstdc++-v3/include/std/tuple @@ -2096,8 +2096,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// @cond undocumented #undef __glibcxx_no_dangling_refs // Error if construction from _U1 and _U2 would create a dangling ref. -#if __has_builtin(__reference_constructs_from_temporary) \ - && defined _GLIBCXX_DEBUG +#if __has_builtin(__reference_constructs_from_temporary) # define __glibcxx_no_dangling_refs(_U1, _U2) \ static_assert(!__reference_constructs_from_temporary(_T1, _U1) \ && !__reference_constructs_from_temporary(_T2, _U2), \
