[libcxx-commits] [libcxx] [libc++] Destroy elements when exceptions are thrown in __construct_at_end (PR #167112)

[via libcxx-commits]

https://github.com/kisuhorikka updated https://github.com/llvm/llvm-project/pull/167112

>From 65cb17f3d14f30626b1c2690c8b9f56713d25b49 Mon Sep 17 00:00:00 2001
From: kisuhorikka <kisuhorikka at gmail.com>
Date: Mon, 15 Dec 2025 21:19:32 +0800
Subject: [PATCH] [libc++] Destroy elements when exceptions are thrown in
 __construct_at_end

---
 .../__memory/uninitialized_algorithms.h       | 26 +++++++++++++++++++
 libcxx/include/__vector/vector.h              | 10 ++-----
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/libcxx/include/__memory/uninitialized_algorithms.h b/libcxx/include/__memory/uninitialized_algorithms.h
index 34d065dc973e5..09a1b43e00f17 100644
--- a/libcxx/include/__memory/uninitialized_algorithms.h
+++ b/libcxx/include/__memory/uninitialized_algorithms.h
@@ -124,6 +124,18 @@ uninitialized_fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp&
 
 // uninitialized_fill_n
 
+template <class _Alloc, class _ForwardIterator, class _Size, class _Tp>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+__uninitialized_allocator_fill_n(_Alloc& __alloc, _ForwardIterator __first, _Size __n, const _Tp& __x) {
+  _ForwardIterator __idx = __first;
+  auto __guard           = std::__make_exception_guard([&] { std::__destroy(__first, __idx); });
+  for (; __n > 0; ++__idx, (void)--__n)
+    allocator_traits<_Alloc>::construct(__alloc, std::__to_address(__idx), __x);
+  __guard.__complete();
+
+  return __idx;
+}
+
 template <class _ValueType, class _ForwardIterator, class _Size, class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _ForwardIterator
 __uninitialized_fill_n(_ForwardIterator __first, _Size __n, const _Tp& __x) {
@@ -143,6 +155,20 @@ uninitialized_fill_n(_ForwardIterator __first, _Size __n, const _Tp& __x) {
   return std::__uninitialized_fill_n<_ValueType>(__first, __n, __x);
 }
 
+// __uninitialized_allocator_value_construct_n
+
+template <class _Alloc, class _ForwardIterator, class _Size>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
+__uninitialized_allocator_value_construct_n(_Alloc& __alloc, _ForwardIterator __first, _Size __n) {
+  auto __idx   = __first;
+  auto __guard = std::__make_exception_guard([&] { std::__destroy(__first, __idx); });
+  for (; __n > 0; ++__idx, (void)--__n)
+    allocator_traits<_Alloc>::construct(__alloc, std::__to_address(__idx));
+  __guard.__complete();
+
+  return __idx;
+}
+
 #if _LIBCPP_STD_VER >= 17
 
 // uninitialized_default_construct
diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 316d3a9d10eff..14c387414518e 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -941,10 +941,7 @@ vector<_Tp, _Allocator>::__recommend(size_type __new_size) const {
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__construct_at_end(size_type __n) {
   _ConstructTransaction __tx(*this, __n);
-  const_pointer __new_end = __tx.__new_end_;
-  for (pointer __pos = __tx.__pos_; __pos != __new_end; __tx.__pos_ = ++__pos) {
-    __alloc_traits::construct(this->__alloc_, std::__to_address(__pos));
-  }
+  __tx.__pos_ = std::__uninitialized_allocator_value_construct_n(this->__alloc_, this->__end_, __n);
 }
 
 //  Copy constructs __n objects starting at __end_ from __x
@@ -957,10 +954,7 @@ template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 inline void
 vector<_Tp, _Allocator>::__construct_at_end(size_type __n, const_reference __x) {
   _ConstructTransaction __tx(*this, __n);
-  const_pointer __new_end = __tx.__new_end_;
-  for (pointer __pos = __tx.__pos_; __pos != __new_end; __tx.__pos_ = ++__pos) {
-    __alloc_traits::construct(this->__alloc_, std::__to_address(__pos), __x);
-  }
+  __tx.__pos_ = std::__uninitialized_allocator_fill_n(this->__alloc_, this->__end_, __n, __x);
 }
 
 template <class _Tp, class _Allocator>