diff options
| author | Jonathan Wakely <jwakely@redhat.com> | 2021-06-14 20:31:00 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-06-14 21:17:53 +0100 |
| commit | c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb (patch) | |
| tree | f038a183eb9ab811e71228d68a8e2ad8bf885cdc | |
| parent | 4986946f3b761dd4c3e0d79ca735c90e33f4bb83 (diff) | |
| download | gcc-c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb.zip gcc-c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb.tar.gz gcc-c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb.tar.bz2 | |
libstdc++: Fix common_reference for non-reference results [PR100894]
The result of COMMON-REF(A&, B&&) where they have no common reference
type should not be a reference. The implementation of COMMON-REF fails
to check that the result is a reference, so is well-formed when it
shouldn't be. This means that common_reference uses that result when it
shouldn't.
The fix is to reject the result of COMMON-REF(A, B) if it's not a
reference, so that common_reference falls through to the next case,
which uses COND-RES, which yields a non-reference result.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/100894
* include/std/type_traits (__common_ref_impl<X&, Y&>): Only
use the type if it's a reference.
* testsuite/20_util/common_reference/100894.cc: New test.
| -rw-r--r-- | libstdc++-v3/include/std/type_traits | 12 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/20_util/common_reference/100894.cc | 9 |
2 files changed, 18 insertions, 3 deletions
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index eaf06fc..d9068a0 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -3340,11 +3340,17 @@ template <typename _From, typename _To> template<typename _Ap, typename _Bp> using __common_ref = typename __common_ref_impl<_Ap, _Bp>::type; + // COND-RES(COPYCV(X, Y) &, COPYCV(Y, X) &) + template<typename _Xp, typename _Yp> + using __condres_cvref + = __cond_res<__copy_cv<_Xp, _Yp>&, __copy_cv<_Yp, _Xp>&>; + // If A and B are both lvalue reference types, ... template<typename _Xp, typename _Yp> - struct __common_ref_impl<_Xp&, _Yp&, - __void_t<__cond_res<__copy_cv<_Xp, _Yp>&, __copy_cv<_Yp, _Xp>&>>> - { using type = __cond_res<__copy_cv<_Xp, _Yp>&, __copy_cv<_Yp, _Xp>&>; }; + struct __common_ref_impl<_Xp&, _Yp&, __void_t<__condres_cvref<_Xp, _Yp>>> + : enable_if<is_reference_v<__condres_cvref<_Xp, _Yp>>, + __condres_cvref<_Xp, _Yp>> + { }; // let C be remove_reference_t<COMMON-REF(X&, Y&)>&& template<typename _Xp, typename _Yp> diff --git a/libstdc++-v3/testsuite/20_util/common_reference/100894.cc b/libstdc++-v3/testsuite/20_util/common_reference/100894.cc new file mode 100644 index 0000000..5e14476 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/common_reference/100894.cc @@ -0,0 +1,9 @@ +// { dg-options "-std=gnu++20" } +// { dg-do compile { target c++20 } } +// PR libstdc++/100894 - common_reference implementation seems to be wrong + +#include <type_traits> + +struct A {}; +struct B { B(A); }; +static_assert( std::is_same_v<std::common_reference_t<A&, B&&>, B> ); |