[PATCH 2/2] libstdc++: Some concat_view bugfixes [PR115215, PR115218, LWG 4082]
Patrick Palka
ppalka@redhat.com
Wed Mar 5 15:35:08 GMT 2025
On Mon, 17 Feb 2025, Patrick Palka wrote:
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>
> -- >8 --
>
> - Use __builtin_unreachable to suppress a false-positive "control
> reaches end of non-void function" warning in the recursive lambda
> (which the existing tests failed to notice since test01 wasn't
> being called at runtime)
> - Relax the constraints on views::concat in the single-argument case
> as per PR115215
> - Add an input_range requirement to that same case as per LWG 4082
> - In the const-converting constructor of concat_view's iterator,
> don't require the first iterator to be default constructible
>
> PR libstdc++/115215
> PR libstdc++/115218
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges
> (concat_view::iterator::_S_invoke_with_runtime_index): Use
> __builtin_unreachable in recursive lambda to certify it always
> exits via 'return'.
> (concat_view::iterator::iterator): In the const-converting
> constructor, direct initialize _M_it.
> (views::_Concat::operator()): Adjust constraints in the
> single-argument case as per LWG 4082.
> * testsuite/std/ranges/concat/1.cc (test01): Call it at runtime
> too.
> (test04): New test.
> ---
> libstdc++-v3/include/std/ranges | 28 +++++++++----------
> libstdc++-v3/testsuite/std/ranges/concat/1.cc | 16 +++++++++++
> 2 files changed, 30 insertions(+), 14 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 22e0c9cae44..a56dae43625 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -9919,6 +9919,7 @@ namespace ranges
> return __f.template operator()<_Idx>();
> if constexpr (_Idx + 1 < sizeof...(_Vs))
> return __self.template operator()<_Idx + 1>();
> + __builtin_unreachable();
> }.template operator()<0>();
> }
>
> @@ -9940,12 +9941,12 @@ namespace ranges
> constexpr
> iterator(iterator<!_Const> __it)
> requires _Const && (convertible_to<iterator_t<_Vs>, iterator_t<const _Vs>> && ...)
> - : _M_parent(__it._M_parent)
> - {
> - _M_invoke_with_runtime_index([this, &__it]<size_t _Idx>() {
> - _M_it.template emplace<_Idx>(std::get<_Idx>(std::move(__it._M_it)));
> - });
> - }
> + : _M_parent(__it._M_parent),
> + _M_it(_S_invoke_with_runtime_index([this, &__it]<size_t _Idx>() {
> + return __base_iter(in_place_index<_Idx>,
> + std::get<_Idx>(std::move(__it._M_it)));
> + }, __it._M_it.index()))
> + { }
>
> constexpr decltype(auto)
> operator*() const
> @@ -10179,16 +10180,15 @@ namespace ranges
>
> struct _Concat
> {
> - template<typename... _Ts>
> - requires __detail::__can_concat_view<_Ts...>
> + template<__detail::__can_concat_view... _Ts>
As pointed out by Tomasz, this change is incorrect and unnecessary.
The former checks __can_concat_view<_Ts...> whereas the latter checks
(__can_concat_view<Ts> && ...). Here's v2 with this change reverted:
-- >8 --
Subject: [PATCH v2] libstdc++: Some concat_view bugfixes [PR115215, PR115218, LWG
4082]
- Use __builtin_unreachable to suppress a false-positive "control
reaches end of non-void function" warning in the recursive lambda
(which the existing tests failed to notice since test01 wasn't
being called at runtime)
- Relax the constraints on views::concat in the single-argument case
as per PR115215
- Add an input_range requirement to that same case as per LWG 4082
- In the const-converting constructor of concat_view's iterator,
don't require the first iterator to be default constructible
PR libstdc++/115215
PR libstdc++/115218
libstdc++-v3/ChangeLog:
* include/std/ranges
(concat_view::iterator::_S_invoke_with_runtime_index): Use
__builtin_unreachable in recursive lambda to certify it always
exits via 'return'.
(concat_view::iterator::iterator): In the const-converting
constructor, direct initialize _M_it.
(views::_Concat::operator()): Adjust constraints in the
single-argument case as per LWG 4082.
* testsuite/std/ranges/concat/1.cc (test01): Call it at runtime
too.
(test04): New test.
---
libstdc++-v3/include/std/ranges | 25 ++++++++++---------
libstdc++-v3/testsuite/std/ranges/concat/1.cc | 16 ++++++++++++
2 files changed, 29 insertions(+), 12 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 6c65722b687..2228ab8c5ee 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -9919,6 +9919,7 @@ namespace ranges
return __f.template operator()<_Idx>();
if constexpr (_Idx + 1 < sizeof...(_Vs))
return __self.template operator()<_Idx + 1>();
+ __builtin_unreachable();
}.template operator()<0>();
}
@@ -9940,12 +9941,12 @@ namespace ranges
constexpr
_Iterator(_Iterator<!_Const> __it)
requires _Const && (convertible_to<iterator_t<_Vs>, iterator_t<const _Vs>> && ...)
- : _M_parent(__it._M_parent)
- {
- _M_invoke_with_runtime_index([this, &__it]<size_t _Idx>() {
- _M_it.template emplace<_Idx>(std::get<_Idx>(std::move(__it._M_it)));
- });
- }
+ : _M_parent(__it._M_parent),
+ _M_it(_S_invoke_with_runtime_index([this, &__it]<size_t _Idx>() {
+ return __base_iter(in_place_index<_Idx>,
+ std::get<_Idx>(std::move(__it._M_it)));
+ }, __it._M_it.index()))
+ { }
constexpr decltype(auto)
operator*() const
@@ -10183,12 +10184,12 @@ namespace ranges
requires __detail::__can_concat_view<_Ts...>
constexpr auto
operator() [[nodiscard]] (_Ts&&... __ts) const
- {
- if constexpr (sizeof...(_Ts) == 1)
- return views::all(std::forward<_Ts>(__ts)...);
- else
- return concat_view(std::forward<_Ts>(__ts)...);
- }
+ { return concat_view(std::forward<_Ts>(__ts)...); }
+
+ template<input_range _Range>
+ constexpr auto
+ operator() [[nodiscard]] (_Range&& __t) const
+ { return views::all(std::forward<_Range>(__t)); }
};
inline constexpr _Concat concat;
diff --git a/libstdc++-v3/testsuite/std/ranges/concat/1.cc b/libstdc++-v3/testsuite/std/ranges/concat/1.cc
index e5d10f476e9..16721912a37 100644
--- a/libstdc++-v3/testsuite/std/ranges/concat/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/concat/1.cc
@@ -85,10 +85,26 @@ test03()
VERIFY( ranges::equal(view2, std::vector{4, 5, 6, 1, 2, 3}) );
}
+void
+test04()
+{
+ // PR libstdc++/115215 - views::concat rejects non-movable reference
+ int x[] = {1,2,3};
+ struct nomove {
+ nomove() = default;
+ nomove(const nomove&) = delete;
+ };
+ auto v = x | views::transform([](int) { return nomove{}; });
+ using type = decltype(views::concat(v));
+ using type = decltype(v);
+}
+
int
main()
{
static_assert(test01());
+ test01();
test02();
test03();
+ test04();
}
--
2.49.0.rc0.57.gdb91954e18
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