[P2283R1] Implement constexpr specialized memory algorithms

Author: miscco

stl/inc/memory

@@ -1601,33 +1601,38 @@ namespace ranges {
     template <input_iterator _It, sentinel_for<_It> _Se, _No_throw_forward_iterator _Out,
         _No_throw_sentinel_for<_Out> _OSe>
         requires (constructible_from<iter_value_t<_Out>, iter_rvalue_reference_t<_It>>)
-    uninitialized_move_result<_It, _Out> _Uninitialized_move_unchecked(
+    _CONSTEXPR23 uninitialized_move_result<_It, _Out> _Uninitialized_move_unchecked(
         _It _IFirst, _Se _ILast, _Out _OFirst, _OSe _OLast) {
         // clang-format on
         constexpr bool _Is_sized1 = sized_sentinel_for<_Se, _It>;
         constexpr bool _Is_sized2 = sized_sentinel_for<_OSe, _Out>;
         if constexpr (_Iter_move_cat<_It, _Out>::_Bitcopy_constructible
                       && _Sized_or_unreachable_sentinel_for<_Se, _It> //
                       && _Sized_or_unreachable_sentinel_for<_OSe, _Out>) {
-            if constexpr (_Is_sized1 && _Is_sized2) {
-                return _Copy_memcpy_common(_IFirst, _RANGES next(_IFirst, _STD move(_ILast)), _OFirst,
-                    _RANGES next(_OFirst, _STD move(_OLast)));
-            } else if constexpr (_Is_sized1) {
-                return _Copy_memcpy_distance(_IFirst, _OFirst, _IFirst, _RANGES next(_IFirst, _STD move(_ILast)));
-            } else if constexpr (_Is_sized2) {
-                return _Copy_memcpy_distance(_IFirst, _OFirst, _OFirst, _RANGES next(_OFirst, _STD move(_OLast)));
-            } else {
-                _STL_ASSERT(false, "Tried to uninitialized_move two ranges with unreachable sentinels");
+#if _HAS_CXX23
+            if (!_STD is_constant_evaluated())
+#endif // _HAS_CXX23
+            {
+                if constexpr (_Is_sized1 && _Is_sized2) {
+                    return _Copy_memcpy_common(_IFirst, _RANGES next(_IFirst, _STD move(_ILast)), _OFirst,
+                        _RANGES next(_OFirst, _STD move(_OLast)));
+                } else if constexpr (_Is_sized1) {
+                    return _Copy_memcpy_distance(_IFirst, _OFirst, _IFirst, _RANGES next(_IFirst, _STD move(_ILast)));
+                } else if constexpr (_Is_sized2) {
+                    return _Copy_memcpy_distance(_IFirst, _OFirst, _OFirst, _RANGES next(_OFirst, _STD move(_OLast)));
+                } else {
+                    _STL_ASSERT(false, "Tried to uninitialized_move two ranges with unreachable sentinels");
+                }
             }
-        } else {
-            _Uninitialized_backout _Backout{_STD move(_OFirst)};
+        }
 
-            for (; _IFirst != _ILast && _Backout._Last != _OLast; ++_IFirst) {
-                _Backout._Emplace_back(_RANGES iter_move(_IFirst));
-            }
+        _Uninitialized_backout _Backout{_STD move(_OFirst)};
 
-            return {_STD move(_IFirst), _Backout._Release()};
+        for (; _IFirst != _ILast && _Backout._Last != _OLast; ++_IFirst) {
+            _Backout._Emplace_back(_RANGES iter_move(_IFirst));
         }
+
+        return {_STD move(_IFirst), _Backout._Release()};
     }
 } // namespace ranges
 #endif // __cpp_lib_concepts
@@ -1715,7 +1720,7 @@ _CONSTEXPR20 _NoThrowFwdIt _Uninitialized_copy_unchecked(_InIt _First, const _In
 }
 
 template <class _InIt, class _NoThrowFwdIt>
-_NoThrowFwdIt uninitialized_copy(const _InIt _First, const _InIt _Last, _NoThrowFwdIt _Dest) {
+_CONSTEXPR23 _NoThrowFwdIt uninitialized_copy(const _InIt _First, const _InIt _Last, _NoThrowFwdIt _Dest) {
     // copy [_First, _Last) to raw [_Dest, ...)
     _Adl_verify_range(_First, _Last);
     auto _UFirst      = _Get_unwrapped(_First);
@@ -1786,28 +1791,37 @@ _CONSTEXPR20 _Alloc_ptr_t<_Alloc> _Uninitialized_fill_n(
 }
 
 template <class _NoThrowFwdIt, class _Tval>
-void uninitialized_fill(const _NoThrowFwdIt _First, const _NoThrowFwdIt _Last, const _Tval& _Val) {
+_CONSTEXPR23 void uninitialized_fill(const _NoThrowFwdIt _First, const _NoThrowFwdIt _Last, const _Tval& _Val) {
     // copy _Val throughout raw [_First, _Last)
     _Adl_verify_range(_First, _Last);
     auto _UFirst      = _Get_unwrapped(_First);
     const auto _ULast = _Get_unwrapped(_Last);
     if constexpr (_Fill_memset_is_safe<_Unwrapped_t<const _NoThrowFwdIt&>, _Tval>) {
-        _Fill_memset(_UFirst, _Val, static_cast<size_t>(_ULast - _UFirst));
-    } else {
-        if constexpr (_Fill_zero_memset_is_safe<_Unwrapped_t<const _NoThrowFwdIt&>, _Tval>) {
+#if _HAS_CXX23
+        if (!_STD is_constant_evaluated())
+#endif // _HAS_CXX23
+        {
+            _Fill_memset(_UFirst, _Val, static_cast<size_t>(_ULast - _UFirst));
+            return;
+        }
+    } else if constexpr (_Fill_zero_memset_is_safe<_Unwrapped_t<const _NoThrowFwdIt&>, _Tval>) {
+#if _HAS_CXX23
+        if (!_STD is_constant_evaluated())
+#endif // _HAS_CXX23
+        {
             if (_Is_all_bits_zero(_Val)) {
                 _Fill_zero_memset(_UFirst, static_cast<size_t>(_ULast - _UFirst));
                 return;
             }
         }
+    }
 
-        _Uninitialized_backout<_Unwrapped_t<const _NoThrowFwdIt&>> _Backout{_UFirst};
-        while (_Backout._Last != _ULast) {
-            _Backout._Emplace_back(_Val);
-        }
-
-        _Backout._Release();
+    _Uninitialized_backout<_Unwrapped_t<const _NoThrowFwdIt&>> _Backout{_UFirst};
+    while (_Backout._Last != _ULast) {
+        _Backout._Emplace_back(_Val);
     }
+
+    _Backout._Release();
 }
 
 template <class _NoThrowFwdIt>
@@ -1849,19 +1863,24 @@ _CONSTEXPR20 _Alloc_ptr_t<_Alloc> _Uninitialized_value_construct_n(
 }
 
 template <class _NoThrowFwdIt, class _Diff>
-_NoThrowFwdIt _Uninitialized_value_construct_n_unchecked1(_NoThrowFwdIt _UFirst, _Diff _Count) {
+_CONSTEXPR23 _NoThrowFwdIt _Uninitialized_value_construct_n_unchecked1(_NoThrowFwdIt _UFirst, _Diff _Count) {
     // value-initialize all elements in [_UFirst, _UFirst + _Count_raw)
     _STL_INTERNAL_CHECK(_Count >= 0);
     if constexpr (_Use_memset_value_construct_v<_NoThrowFwdIt>) {
-        return _Zero_range(_UFirst, _UFirst + _Count);
-    } else {
-        _Uninitialized_backout<_NoThrowFwdIt> _Backout{_UFirst};
-        for (; 0 < _Count; --_Count) {
-            _Backout._Emplace_back();
+#if _HAS_CXX23
+        if (!_STD is_constant_evaluated())
+#endif // _HAS_CXX23
+        {
+            return _Zero_range(_UFirst, _UFirst + _Count);
         }
+    }
 
-        return _Backout._Release();
+    _Uninitialized_backout<_NoThrowFwdIt> _Backout{_UFirst};
+    for (; 0 < _Count; --_Count) {
+        _Backout._Emplace_back();
     }
+
+    return _Backout._Release();
 }
 
 #if _HAS_DEPRECATED_TEMPORARY_BUFFER

stl/inc/xmemory

@@ -295,6 +295,7 @@
 // P2136R3 invoke_r()
 // P2166R1 Prohibiting basic_string And basic_string_view Construction From nullptr
 // P2186R2 Removing Garbage Collection Support
+// P2283R2 constexpr Specialized Memory Algorithms
 
 // Parallel Algorithms Notes
 // C++ allows an implementation to implement parallel algorithms as calls to the serial algorithms.
@@ -620,6 +621,13 @@
 #define _CONSTEXPR20 inline
 #endif // ^^^ inline (not constexpr) in C++17 and earlier ^^^
 
+// Functions that became constexpr in C++23
+#if _HAS_CXX23
+#define _CONSTEXPR23 constexpr
+#else // ^^^ constexpr in C++23 and later / inline (not constexpr) in C++20 and earlier vvv
+#define _CONSTEXPR23 inline
+#endif // ^^^ inline (not constexpr) in C++20 and earlier ^^^
+
 // P0607R0 Inline Variables For The STL
 #if _HAS_CXX17
 #define _INLINE_VAR inline
@@ -1219,12 +1227,12 @@
 #ifndef _M_CEE
 #define __cpp_lib_parallel_algorithm 201603L
 #endif // _M_CEE
-#define __cpp_lib_raw_memory_algorithms 201606L
-#define __cpp_lib_sample                201603L
-#define __cpp_lib_scoped_lock           201703L
-#define __cpp_lib_shared_ptr_weak_type  201606L
-#define __cpp_lib_string_view           201803L
-#define __cpp_lib_to_chars              201611L
+
+#define __cpp_lib_sample               201603L
+#define __cpp_lib_scoped_lock          201703L
+#define __cpp_lib_shared_ptr_weak_type 201606L
+#define __cpp_lib_string_view          201803L
+#define __cpp_lib_to_chars             201611L
 #endif // _HAS_CXX17
 
 // C++20
@@ -1390,6 +1398,12 @@
 #define __cpp_lib_to_underlying               202102L
 #endif // _HAS_CXX23
 
+#if _HAS_CXX23
+#define __cpp_lib_raw_memory_algorithms 202106L
+#else // _HAS_CXX23
+#define __cpp_lib_raw_memory_algorithms 201606L
+#endif // _HAS_CXX23
+
 #define __cpp_lib_experimental_erase_if   201411L
 #define __cpp_lib_experimental_filesystem 201406L
 

stl/inc/yvals_core.h

@@ -452,6 +452,14 @@ tests\P1951R1_default_arguments_pair_forward_ctor
 tests\P2136R3_invoke_r
 tests\P2162R2_std_visit_for_derived_classes_from_variant
 tests\P2231R1_complete_constexpr_optional_variant
+tests\P2283R2_constexpr_uninitialized_copy
+tests\P2283R2_constexpr_uninitialized_copy_n
+tests\P2283R2_constexpr_uninitialized_fill
+tests\P2283R2_constexpr_uninitialized_fill_n
+tests\P2283R2_constexpr_uninitialized_move
+tests\P2283R2_constexpr_uninitialized_move_n
+tests\P2283R2_constexpr_uninitialized_value_construct
+tests\P2283R2_constexpr_uninitialized_value_construct_n
 tests\P2401R0_conditional_noexcept_for_exchange
 tests\P2415R2_owning_view
 tests\VSO_0000000_allocator_propagation

tests/std/test.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\concepts_latest_matrix.lst