[libc++] LWG3187: P0591R4 reverted DR 2586 fixes to scoped_allocator_adaptor::construct()
#152424
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llvmbot
added
the
libc++
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@llvm/pr-subscribers-libcxx Author: A. Jiang (frederick-vs-ja) ChangesApplying it (adding missing Also
Fixes #100256. Full diff: https://github.com/llvm/llvm-project/pull/152424.diff 6 Files Affected:
diff --git a/libcxx/docs/Status/Cxx20Issues.csv b/libcxx/docs/Status/Cxx20Issues.csv
index 98b49f92bdf7a..7b5bcd69f6abd 100644
--- a/libcxx/docs/Status/Cxx20Issues.csv
+++ b/libcxx/docs/Status/Cxx20Issues.csv
@@ -151,7 +151,7 @@
"`LWG3184 <https://wg21.link/LWG3184>`__","Inconsistencies in ``bind_front``\ wording","2019-07 (Cologne)","|Complete|","13",""
"`LWG3185 <https://wg21.link/LWG3185>`__","Uses-allocator construction functions missing ``constexpr``\ and ``noexcept``\ ","2019-07 (Cologne)","|Complete|","16",""
"`LWG3186 <https://wg21.link/LWG3186>`__","``ranges``\ removal, partition, and ``partial_sort_copy``\ algorithms discard useful information","2019-07 (Cologne)","|Complete|","15",""
-"`LWG3187 <https://wg21.link/LWG3187>`__","`P0591R4 <https://wg21.link/p0591r4>`__ reverted DR 2586 fixes to ``scoped_allocator_adaptor::construct()``\ ","2019-07 (Cologne)","","",""
+"`LWG3187 <https://wg21.link/LWG3187>`__","`P0591R4 <https://wg21.link/p0591r4>`__ reverted DR 2586 fixes to ``scoped_allocator_adaptor::construct()``\ ","2019-07 (Cologne)","|Complete|","22",""
"`LWG3191 <https://wg21.link/LWG3191>`__","``std::ranges::shuffle``\ synopsis does not match algorithm definition","2019-07 (Cologne)","|Complete|","15",""
"`LWG3196 <https://wg21.link/LWG3196>`__","``std::optional<T>``\ is ill-formed is ``T``\ is an array","2019-07 (Cologne)","|Complete|","",""
"`LWG3198 <https://wg21.link/LWG3198>`__","Bad constraint on ``std::span::span()``\ ","2019-07 (Cologne)","|Complete|","",""
diff --git a/libcxx/include/__memory/allocator_arg_t.h b/libcxx/include/__memory/allocator_arg_t.h
index 31a73fc4557ef..a3dac879f45b6 100644
--- a/libcxx/include/__memory/allocator_arg_t.h
+++ b/libcxx/include/__memory/allocator_arg_t.h
@@ -14,6 +14,7 @@
#include <__memory/uses_allocator.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_constructible.h>
+#include <__type_traits/remove_cv.h>
#include <__type_traits/remove_cvref.h>
#include <__utility/forward.h>
@@ -40,34 +41,15 @@ constexpr allocator_arg_t allocator_arg = allocator_arg_t();
template <class _Tp, class _Alloc, class... _Args>
struct __uses_alloc_ctor_imp {
using _RawAlloc _LIBCPP_NODEBUG = __remove_cvref_t<_Alloc>;
- static const bool __ua = uses_allocator<_Tp, _RawAlloc>::value;
- static const bool __ic = is_constructible<_Tp, allocator_arg_t, _Alloc, _Args...>::value;
- static const int value = __ua ? 2 - __ic : 0;
+ static constexpr bool __ua = uses_allocator<__remove_cv_t<_Tp>, _RawAlloc>::value;
+ static constexpr bool __ic_head = is_constructible<_Tp, allocator_arg_t, const _RawAlloc&, _Args...>::value;
+ static constexpr bool __ic_tail = is_constructible<_Tp, _Args..., const _RawAlloc&>::value;
+ static constexpr int value = __ua ? (__ic_head ? 1 : __ic_tail ? 2 : -1) : 0;
};
template <class _Tp, class _Alloc, class... _Args>
struct __uses_alloc_ctor : integral_constant<int, __uses_alloc_ctor_imp<_Tp, _Alloc, _Args...>::value> {};
-template <class _Tp, class _Allocator, class... _Args>
-inline _LIBCPP_HIDE_FROM_ABI void
-__user_alloc_construct_impl(integral_constant<int, 0>, _Tp* __storage, const _Allocator&, _Args&&... __args) {
- new (__storage) _Tp(std::forward<_Args>(__args)...);
-}
-
-// FIXME: This should have a version which takes a non-const alloc.
-template <class _Tp, class _Allocator, class... _Args>
-inline _LIBCPP_HIDE_FROM_ABI void
-__user_alloc_construct_impl(integral_constant<int, 1>, _Tp* __storage, const _Allocator& __a, _Args&&... __args) {
- new (__storage) _Tp(allocator_arg, __a, std::forward<_Args>(__args)...);
-}
-
-// FIXME: This should have a version which takes a non-const alloc.
-template <class _Tp, class _Allocator, class... _Args>
-inline _LIBCPP_HIDE_FROM_ABI void
-__user_alloc_construct_impl(integral_constant<int, 2>, _Tp* __storage, const _Allocator& __a, _Args&&... __args) {
- new (__storage) _Tp(std::forward<_Args>(__args)..., __a);
-}
-
#endif // _LIBCPP_CXX03_LANG
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__memory/uses_allocator_construction.h b/libcxx/include/__memory/uses_allocator_construction.h
index 6733f5cf6fc35..55b634f5e7d0e 100644
--- a/libcxx/include/__memory/uses_allocator_construction.h
+++ b/libcxx/include/__memory/uses_allocator_construction.h
@@ -16,6 +16,7 @@
#include <__type_traits/enable_if.h>
#include <__type_traits/remove_cv.h>
#include <__utility/declval.h>
+#include <__utility/integer_sequence.h>
#include <__utility/pair.h>
#include <__utility/piecewise_construct.h>
#include <tuple>
@@ -29,6 +30,43 @@ _LIBCPP_PUSH_MACROS
_LIBCPP_BEGIN_NAMESPACE_STD
+// TODO: Guard this furtherly with _LIBCPP_STD_VER < 20 once P0591R4 is fully implemented.
+#if !defined(_LIBCPP_CXX03_LANG)
+
+template <class _Alloc, class... _Args, size_t... _Is>
+_LIBCPP_HIDE_FROM_ABI void __transform_tuple_using_allocator_impl(
+ integral_constant<int, -1>, const _Alloc&, tuple<_Args...>&&, __index_sequence<_Is...>) {
+ static_assert(false, "If uses_allocator_v<T, A> is true, T has to be allocator-constructible");
+}
+
+template <class _Alloc, class... _Args, size_t... _Is>
+_LIBCPP_HIDE_FROM_ABI tuple<_Args&&...> __transform_tuple_using_allocator_impl(
+ integral_constant<int, 0>, const _Alloc&, tuple<_Args...>&& __t, __index_sequence<_Is...>) {
+ return tuple<_Args&&...>(std::move(__t));
+}
+
+template <class _Alloc, class... _Args, size_t... _Is>
+_LIBCPP_HIDE_FROM_ABI tuple<allocator_arg_t, const _Alloc&, _Args&&...> __transform_tuple_using_allocator_impl(
+ integral_constant<int, 1>, const _Alloc& __a, tuple<_Args...>&& __t, __index_sequence<_Is...>) {
+ return tuple<allocator_arg_t, const _Alloc&, _Args&&...>(allocator_arg, __a, std::get<_Is>(std::move(__t))...);
+}
+
+template <class _Alloc, class... _Args, size_t... _Is>
+_LIBCPP_HIDE_FROM_ABI tuple<_Args&&..., const _Alloc&> __transform_tuple_using_allocator_impl(
+ integral_constant<int, 2>, const _Alloc& __a, tuple<_Args...>&& __t, __index_sequence<_Is...>) {
+ return tuple<_Args&&..., const _Alloc&>(std::get<_Is>(std::move(__t))..., __a);
+}
+
+template <class _Tp, class _Alloc, class... _Args>
+_LIBCPP_HIDE_FROM_ABI auto __transform_tuple_using_allocator(const _Alloc& __a, tuple<_Args...>&& __t)
+ -> decltype(std::__transform_tuple_using_allocator_impl(
+ __uses_alloc_ctor<_Tp, _Alloc, _Args>{}, __a, std::move(__t), __make_index_sequence<sizeof...(_Args)>{})) {
+ return std::__transform_tuple_using_allocator_impl(
+ __uses_alloc_ctor<_Tp, _Alloc, _Args>{}, __a, std::move(__t), __make_index_sequence<sizeof...(_Args)>{});
+}
+
+#endif // !defined(_LIBCPP_CXX03_LANG)
+
#if _LIBCPP_STD_VER >= 17
template <class _Tp>
diff --git a/libcxx/include/__memory_resource/polymorphic_allocator.h b/libcxx/include/__memory_resource/polymorphic_allocator.h
index 9a351199b5b16..ec38a3469675b 100644
--- a/libcxx/include/__memory_resource/polymorphic_allocator.h
+++ b/libcxx/include/__memory_resource/polymorphic_allocator.h
@@ -14,9 +14,15 @@
#include <__cstddef/byte.h>
#include <__cstddef/max_align_t.h>
#include <__fwd/pair.h>
+#include <__memory/allocator_arg_t.h>
+#include <__memory/uses_allocator.h>
+#include <__memory/uses_allocator_construction.h>
#include <__memory_resource/memory_resource.h>
#include <__new/exceptions.h>
#include <__new/placement_new_delete.h>
+#include <__type_traits/is_constructible.h>
+#include <__type_traits/remove_cv.h>
+#include <__utility/as_const.h>
#include <__utility/exception_guard.h>
#include <__utility/piecewise_construct.h>
#include <limits>
@@ -122,11 +128,18 @@ class _LIBCPP_AVAILABILITY_PMR polymorphic_allocator {
template <class _Tp, class... _Ts>
_LIBCPP_HIDE_FROM_ABI void construct(_Tp* __p, _Ts&&... __args) {
- std::__user_alloc_construct_impl(
- typename __uses_alloc_ctor<_Tp, polymorphic_allocator&, _Ts...>::type(),
- __p,
- *this,
- std::forward<_Ts>(__args)...);
+ if constexpr (!uses_allocator_v<remove_cv_t<_Tp>, polymorphic_allocator>) {
+ static_assert(is_constructible_v<_Tp, _Ts...>,
+ "If uses_allocator_v<T, polymorphic_allocator> is false, T has to be constructible from arguments");
+ ::new ((void*)__p) _Tp(std::forward<_Ts>(__args)...);
+ } else if constexpr (is_constructible_v<_Tp, allocator_arg_t, const polymorphic_allocator&, _Ts...>) {
+ ::new ((void*)__p) _Tp(allocator_arg, std::as_const(*this), std::forward<_Ts>(__args)...);
+ } else if constexpr (is_constructible_v<_Tp, _Ts..., const polymorphic_allocator&>) {
+ ::new ((void*)__p) _Tp(std::forward<_Ts>(__args)..., std::as_const(*this));
+ } else {
+ static_assert(
+ false, "If uses_allocator_v<T, polymorphic_allocator> is true, T has to be allocator-constructible");
+ }
}
template <class _T1, class _T2, class... _Args1, class... _Args2>
@@ -134,12 +147,8 @@ class _LIBCPP_AVAILABILITY_PMR polymorphic_allocator {
construct(pair<_T1, _T2>* __p, piecewise_construct_t, tuple<_Args1...> __x, tuple<_Args2...> __y) {
::new ((void*)__p) pair<_T1, _T2>(
piecewise_construct,
- __transform_tuple(typename __uses_alloc_ctor< _T1, polymorphic_allocator&, _Args1... >::type(),
- std::move(__x),
- make_index_sequence<sizeof...(_Args1)>()),
- __transform_tuple(typename __uses_alloc_ctor< _T2, polymorphic_allocator&, _Args2... >::type(),
- std::move(__y),
- make_index_sequence<sizeof...(_Args2)>()));
+ std::__transform_tuple_using_allocator<_T1>(*this, std::move(__x)),
+ std::__transform_tuple_using_allocator<_T2>(*this, std::move(__y)));
}
template <class _T1, class _T2>
@@ -193,26 +202,6 @@ class _LIBCPP_AVAILABILITY_PMR polymorphic_allocator {
# endif
private:
- template <class... _Args, size_t... _Is>
- _LIBCPP_HIDE_FROM_ABI tuple<_Args&&...>
- __transform_tuple(integral_constant<int, 0>, tuple<_Args...>&& __t, index_sequence<_Is...>) {
- return std::forward_as_tuple(std::get<_Is>(std::move(__t))...);
- }
-
- template <class... _Args, size_t... _Is>
- _LIBCPP_HIDE_FROM_ABI tuple<allocator_arg_t const&, polymorphic_allocator&, _Args&&...>
- __transform_tuple(integral_constant<int, 1>, tuple<_Args...>&& __t, index_sequence<_Is...>) {
- using _Tup = tuple<allocator_arg_t const&, polymorphic_allocator&, _Args&&...>;
- return _Tup(allocator_arg, *this, std::get<_Is>(std::move(__t))...);
- }
-
- template <class... _Args, size_t... _Is>
- _LIBCPP_HIDE_FROM_ABI tuple<_Args&&..., polymorphic_allocator&>
- __transform_tuple(integral_constant<int, 2>, tuple<_Args...>&& __t, index_sequence<_Is...>) {
- using _Tup = tuple<_Args&&..., polymorphic_allocator&>;
- return _Tup(std::get<_Is>(std::move(__t))..., *this);
- }
-
_LIBCPP_HIDE_FROM_ABI size_t __max_size() const noexcept {
return numeric_limits<size_t>::max() / sizeof(value_type);
}
diff --git a/libcxx/include/scoped_allocator b/libcxx/include/scoped_allocator
index 74effc547f3e2..d152a7ade498b 100644
--- a/libcxx/include/scoped_allocator
+++ b/libcxx/include/scoped_allocator
@@ -113,12 +113,15 @@ template <class OuterA1, class OuterA2, class... InnerAllocs>
# include <__cxx03/__config>
#else
# include <__config>
+# include <__memory/allocator_arg_t.h>
# include <__memory/allocator_traits.h>
+# include <__memory/uses_allocator.h>
# include <__memory/uses_allocator_construction.h>
# include <__type_traits/common_type.h>
# include <__type_traits/enable_if.h>
# include <__type_traits/integral_constant.h>
# include <__type_traits/is_constructible.h>
+# include <__type_traits/remove_cv.h>
# include <__type_traits/remove_reference.h>
# include <__utility/declval.h>
# include <__utility/forward.h>
@@ -421,23 +424,30 @@ public:
# else
template <class _Tp, class... _Args>
_LIBCPP_HIDE_FROM_ABI void construct(_Tp* __p, _Args&&... __args) {
- __construct(__uses_alloc_ctor<_Tp, inner_allocator_type&, _Args...>(), __p, std::forward<_Args>(__args)...);
+ using _OM = __outermost<outer_allocator_type>;
+ if constexpr (!uses_allocator<__remove_cv_t<_Type>, inner_allocator_type>::value) {
+ allocator_traits<typename _OM::type>::construct(_OM()(outer_allocator()), __p, std::forward<_Args>(__args)...);
+ } else if constexpr (is_constructible<_Type, allocator_arg_t, const inner_allocator_type&, _Args...>::value) {
+ allocator_traits<typename _OM::type>::construct(
+ _OM()(outer_allocator()), __p, allocator_arg, inner_allocator(), std::forward<_Args>(__args)...);
+ } else if constexpr (is_constructible<_Type, _Args..., const inner_allocator_type&>::value) {
+ allocator_traits<typename _OM::type>::construct(
+ _OM()(outer_allocator()), __p, std::forward<_Args>(__args)..., inner_allocator());
+ } else {
+ static_assert(false, "If uses_allocator_v<T, inner_allocator_type> is true, T has to be allocator-constructible");
+ }
}
template <class _T1, class _T2, class... _Args1, class... _Args2>
_LIBCPP_HIDE_FROM_ABI void
construct(pair<_T1, _T2>* __p, piecewise_construct_t, tuple<_Args1...> __x, tuple<_Args2...> __y) {
- typedef __outermost<outer_allocator_type> _OM;
+ using _OM = __outermost<outer_allocator_type>;
allocator_traits<typename _OM::type>::construct(
_OM()(outer_allocator()),
__p,
piecewise_construct,
- __transform_tuple(typename __uses_alloc_ctor< _T1, inner_allocator_type&, _Args1... >::type(),
- std::move(__x),
- __make_index_sequence<sizeof...(_Args1)>()),
- __transform_tuple(typename __uses_alloc_ctor< _T2, inner_allocator_type&, _Args2... >::type(),
- std::move(__y),
- __make_index_sequence<sizeof...(_Args2)>()));
+ std::__transform_tuple_using_allocator<_T1>(inner_allocator(), std::move(__x)),
+ std::__transform_tuple_using_allocator<_T2>(inner_allocator(), std::move(__y)));
}
template <class _T1, class _T2>
@@ -481,46 +491,6 @@ private:
_LIBCPP_HIDE_FROM_ABI explicit scoped_allocator_adaptor(
outer_allocator_type&& __o, inner_allocator_type&& __i) _NOEXCEPT : _Base(std::move(__o), std::move(__i)) {}
- template <class _Tp, class... _Args>
- _LIBCPP_HIDE_FROM_ABI void __construct(integral_constant<int, 0>, _Tp* __p, _Args&&... __args) {
- typedef __outermost<outer_allocator_type> _OM;
- allocator_traits<typename _OM::type>::construct(_OM()(outer_allocator()), __p, std::forward<_Args>(__args)...);
- }
-
- template <class _Tp, class... _Args>
- _LIBCPP_HIDE_FROM_ABI void __construct(integral_constant<int, 1>, _Tp* __p, _Args&&... __args) {
- typedef __outermost<outer_allocator_type> _OM;
- allocator_traits<typename _OM::type>::construct(
- _OM()(outer_allocator()), __p, allocator_arg, inner_allocator(), std::forward<_Args>(__args)...);
- }
-
- template <class _Tp, class... _Args>
- _LIBCPP_HIDE_FROM_ABI void __construct(integral_constant<int, 2>, _Tp* __p, _Args&&... __args) {
- typedef __outermost<outer_allocator_type> _OM;
- allocator_traits<typename _OM::type>::construct(
- _OM()(outer_allocator()), __p, std::forward<_Args>(__args)..., inner_allocator());
- }
-
- template <class... _Args, size_t... _Idx>
- _LIBCPP_HIDE_FROM_ABI tuple<_Args&&...>
- __transform_tuple(integral_constant<int, 0>, tuple<_Args...>&& __t, __index_sequence<_Idx...>) {
- return std::forward_as_tuple(std::get<_Idx>(std::move(__t))...);
- }
-
- template <class... _Args, size_t... _Idx>
- _LIBCPP_HIDE_FROM_ABI tuple<allocator_arg_t, inner_allocator_type&, _Args&&...>
- __transform_tuple(integral_constant<int, 1>, tuple<_Args...>&& __t, __index_sequence<_Idx...>) {
- using _Tup = tuple<allocator_arg_t, inner_allocator_type&, _Args&&...>;
- return _Tup(allocator_arg, inner_allocator(), std::get<_Idx>(std::move(__t))...);
- }
-
- template <class... _Args, size_t... _Idx>
- _LIBCPP_HIDE_FROM_ABI tuple<_Args&&..., inner_allocator_type&>
- __transform_tuple(integral_constant<int, 2>, tuple<_Args...>&& __t, __index_sequence<_Idx...>) {
- using _Tup = tuple<_Args&&..., inner_allocator_type&>;
- return _Tup(std::get<_Idx>(std::move(__t))..., inner_allocator());
- }
-
template <class...>
friend class __scoped_allocator_storage;
};
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index be30ab5b2173d..27c13fa63e0a9 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -382,6 +382,11 @@ public:
static_assert(!is_reference<_Hp>::value, "Attempted to default construct a reference element in a tuple");
}
+ template <class _Alloc, class... _Args>
+ _LIBCPP_HIDE_FROM_ABI __tuple_leaf(integral_constant<int, -1>, const _Alloc&, _Args&&...) {
+ static_assert(false, "If uses_allocator_v<T, A> is true, T has to be allocator-constructible");
+ }
+
template <class _Alloc>
_LIBCPP_HIDE_FROM_ABI constexpr __tuple_leaf(integral_constant<int, 0>, const _Alloc&) : __value_() {
static_assert(!is_reference<_Hp>::value, "Attempted to default construct a reference element in a tuple");
@@ -456,6 +461,11 @@ public:
_LIBCPP_HIDE_FROM_ABI constexpr __tuple_leaf() noexcept(is_nothrow_default_constructible<_Hp>::value) {}
+ template <class _Alloc, class... _Args>
+ _LIBCPP_HIDE_FROM_ABI __tuple_leaf(integral_constant<int, -1>, const _Alloc&, _Args&&...) {
+ static_assert(false, "If uses_allocator_v<T, A> is true, T has to be allocator-constructible");
+ }
+
template <class _Alloc>
_LIBCPP_HIDE_FROM_ABI constexpr __tuple_leaf(integral_constant<int, 0>, const _Alloc&) {}
|
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... `scoped_allocator_adaptor::construct()` Applying it (adding missing `const``) to pre-C++20 dispatching mechanisms. Also - make dispatch mechanisms in pre-C++20 `construct` more consistent, and - add fallback dispatching and overloads to emit better error messages.
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philnik777
requested changes
Aug 7, 2025
I found that there're some behavior differences introduced by P0591R4 and I'm not sure whether the C++20 behavior should be backported.
|
I think we should rather modify the utilities to have the required behaviour in C++17. Using them in these places was the original intent after all. Right now we don't fully implement P0591R4, since we never updated |
Oh, for |
Urgh. WDYT about implementing the |
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Applying it (adding missing
const) to pre-C++20 dispatching mechanisms.Also
constructmore consistent, andFixes #100256.