On Wed, 26 Mar 2025 at 11:50, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> Because ranges can have any signed integer-like type as difference_type,
> it's not valid to use std::min(diff1, diff2). Instead of calling
> std::min with an explicit template argument, this adds a new __min
> helper that determines the common type and uses that with std::min.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/101587
> * include/bits/ranges_uninitialized.h (__detail::__min): New
> function object.
> (ranges::uninitialized_copy, ranges::uninitialized_copy_n)
> (ranges::uninitialized_move, ranges::uninitialized_move_n): Use
> __min instead of std::min.
> *
> testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc:
> Check ranges with difference difference types.
> *
> testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc:
> Likewise.
> ---
>
> Tested x86_64-linux.
>
> .../include/bits/ranges_uninitialized.h | 32 +++++++++++++++----
> .../uninitialized_copy/constrained.cc | 13 ++++++++
> .../uninitialized_move/constrained.cc | 13 ++++++++
> 3 files changed, 52 insertions(+), 6 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/ranges_uninitialized.h
> b/libstdc++-v3/include/bits/ranges_uninitialized.h
> index 990929efaa9..92a45e8fcff 100644
> --- a/libstdc++-v3/include/bits/ranges_uninitialized.h
> +++ b/libstdc++-v3/include/bits/ranges_uninitialized.h
> @@ -263,6 +263,26 @@ namespace ranges
> inline constexpr __uninitialized_value_construct_n_fn
> uninitialized_value_construct_n;
>
> + namespace __detail
> + {
> + // This is only intended for finding smaller iterator differences below,
> + // not as a general purpose replacement for std::min.
> + struct __min_fn
> + {
> + template<typename _Dp1, typename _Dp2>
> + common_type_t<_Dp1, _Dp2>
This needs to be constexpr.
> + operator()(_Dp1 __d1, _Dp2 __d2) const noexcept
> + {
> + // Every C++20 iterator I satisfies weakly_incrementable<I> which
> + // requires signed-integer-like<iter_difference_t<I>>.
> + static_assert(std::__detail::__is_signed_integer_like<_Dp1>);
> + static_assert(std::__detail::__is_signed_integer_like<_Dp2>);
> + return std::min<common_type_t<_Dp1, _Dp2>>(__d1, __d2);
> + }
> + };
> + inline constexpr __min_fn __min{};
> + }
> +
> template<typename _Iter, typename _Out>
> using uninitialized_copy_result = in_out_result<_Iter, _Out>;
>
> @@ -287,8 +307,8 @@ namespace ranges
> {
> auto __d1 = __ilast - __ifirst;
> auto __d2 = __olast - __ofirst;
> - return ranges::copy_n(std::move(__ifirst), std::min(__d1, __d2),
> - __ofirst);
> + return ranges::copy_n(std::move(__ifirst),
> + __detail::__min(__d1, __d2), __ofirst);
> }
> else
> {
> @@ -337,8 +357,8 @@ namespace ranges
> iter_reference_t<_Iter>>)
> {
> auto __d = __olast - __ofirst;
> - return ranges::copy_n(std::move(__ifirst), std::min(__n, __d),
> - __ofirst);
> + return ranges::copy_n(std::move(__ifirst),
> + __detail::__min(__n, __d), __ofirst);
> }
> else
> {
> @@ -381,7 +401,7 @@ namespace ranges
> auto __d2 = __olast - __ofirst;
> auto [__in, __out]
> = ranges::copy_n(std::make_move_iterator(std::move(__ifirst)),
> - std::min(__d1, __d2), __ofirst);
> + __detail::__min(__d1, __d2), __ofirst);
> return {std::move(__in).base(), __out};
> }
> else
> @@ -435,7 +455,7 @@ namespace ranges
> auto __d = __olast - __ofirst;
> auto [__in, __out]
> = ranges::copy_n(std::make_move_iterator(std::move(__ifirst)),
> - std::min(__n, __d), __ofirst);
> + __detail::__min(__n, __d), __ofirst);
> return {std::move(__in).base(), __out};
> }
> else
> diff --git
> a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
>
> b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
> index e0589e33f3d..af3b73364ec 100644
> ---
> a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
> +++
> b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
> @@ -175,6 +175,17 @@ test03()
> }
> }
>
> +void
> +test_pr101587()
> +{
> + short in[1];
> + __gnu_test::test_contiguous_range r(in); // difference_type is integer-like
> + long out[1];
> + std::span<long> o(out); // difference_type is ptrdiff_t
> + ranges::uninitialized_copy(r, o);
> + ranges::uninitialized_copy_n(ranges::begin(r), 0, o.begin(), o.end());
> +}
> +
> int
> main()
> {
> @@ -188,4 +199,6 @@ main()
>
> test02<false>();
> test02<true>();
> +
> + test_pr101587();
> }
> diff --git
> a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
>
> b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
> index 4c858e13704..fe82d1f156e 100644
> ---
> a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
> +++
> b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
> @@ -185,6 +185,17 @@ test03()
> }
> }
>
> +void
> +test_pr101587()
> +{
> + short in[1];
> + __gnu_test::test_contiguous_range r(in); // difference_type is integer-like
> + long out[1];
> + std::span<long> o(out); // difference_type is ptrdiff_t
> + ranges::uninitialized_move(r, o);
> + ranges::uninitialized_move_n(ranges::begin(r), 0, o.begin(), o.end());
> +}
> +
> int
> main()
> {
> @@ -198,4 +209,6 @@ main()
>
> test02<false>();
> test02<true>();
> +
> + test_pr101587();
> }
> --
> 2.49.0
>
