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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-1573] libstdc++: Fix ambiguous expression in std::array<T, 0>::front() [PR110139] Date: Tue, 6 Jun 2023 11:45:47 +0000 (GMT) [thread overview] Message-ID: <20230606114547.E0B4B3858002@sourceware.org> (raw) https://gcc.gnu.org/g:56001fad4ecc32396beead6644906e3846244b67 commit r14-1573-g56001fad4ecc32396beead6644906e3846244b67 Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue Jun 6 11:38:42 2023 +0100 libstdc++: Fix ambiguous expression in std::array<T, 0>::front() [PR110139] For 32-bit targets using -pedantic (or using Clang) makes the expression _M_elems[0] ambiguous. The overloaded operator[] that we want to call has a size_t parameter, but 0 is type ptrdiff_t for many ILP32 targets, so using the implicit conversion from _M_elems to T* and then subscripting that is also viable. Change the 0 to (size_type)0 and also make the conversion to T* explicit, so that's it's not viable here. The latter change requires a static_cast in data() where we really do want to convert _M_elems to a pointer. libstdc++-v3/ChangeLog: PR libstdc++/110139 * include/std/array (__array_traits<T, 0>::operator T*()): Make conversion operator explicit. (array::front): Use size_type as subscript operand. (array::data): Use static_cast to make conversion explicit. * testsuite/23_containers/array/element_access/110139.cc: New test. Diff: --- libstdc++-v3/include/std/array | 10 +++++----- .../testsuite/23_containers/array/element_access/110139.cc | 5 +++++ 2 files changed, 10 insertions(+), 5 deletions(-) diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array index 27354d9e3fb..70280c1beeb 100644 --- a/libstdc++-v3/include/std/array +++ b/libstdc++-v3/include/std/array @@ -69,7 +69,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Conversion to a pointer produces a null pointer. __attribute__((__always_inline__)) - constexpr operator _Tp*() const noexcept { return nullptr; } + constexpr explicit operator _Tp*() const noexcept { return nullptr; } }; using _Is_swappable = true_type; @@ -240,7 +240,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION front() noexcept { __glibcxx_requires_nonempty(); - return _M_elems[0]; + return _M_elems[(size_type)0]; } [[__nodiscard__]] @@ -250,7 +250,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #if __cplusplus >= 201402L __glibcxx_requires_nonempty(); #endif - return _M_elems[0]; + return _M_elems[(size_type)0]; } [[__nodiscard__]] @@ -274,12 +274,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION [[__nodiscard__, __gnu__::__const__, __gnu__::__always_inline__]] _GLIBCXX17_CONSTEXPR pointer data() noexcept - { return _M_elems; } + { return static_cast<pointer>(_M_elems); } [[__nodiscard__]] _GLIBCXX17_CONSTEXPR const_pointer data() const noexcept - { return _M_elems; } + { return static_cast<const_pointer>(_M_elems); } }; #if __cpp_deduction_guides >= 201606 diff --git a/libstdc++-v3/testsuite/23_containers/array/element_access/110139.cc b/libstdc++-v3/testsuite/23_containers/array/element_access/110139.cc new file mode 100644 index 00000000000..6f09aacf0a7 --- /dev/null +++ b/libstdc++-v3/testsuite/23_containers/array/element_access/110139.cc @@ -0,0 +1,5 @@ +// { dg-options "-pedantic" } +// { dg-do compile { target c++11 } } +#include <array> +template class std::array<int, 0>; +// { dg-bogus "ambiguous overload" "" { target *-*-* } 0 }
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