[libcxx-commits] [libcxx] [libc++] Inline vector::__append into resize (PR #162086)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/162086

None

>From 1736b4a8757dce0346ba75bebc9ddc99cd0af0e9 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Mon, 6 Oct 2025 14:36:03 +0200
Subject: [PATCH] [libc++] Inline vector::__append into resize

---
 libcxx/include/__vector/vector.h | 71 ++++++++++++--------------------
 1 file changed, 26 insertions(+), 45 deletions(-)

diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 707aff3e7c3d3..11bbdf3dac582 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -664,9 +664,6 @@ class vector {
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
   __construct_at_end(_InputIterator __first, _Sentinel __last, size_type __n);
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __append(size_type __n);
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __append(size_type __n, const_reference __x);
-
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI iterator __make_iter(pointer __p) _NOEXCEPT {
 #ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_VECTOR
     // Bound the iterator according to the capacity, rather than the size.
@@ -971,36 +968,6 @@ vector<_Tp, _Allocator>::__construct_at_end(_InputIterator __first, _Sentinel __
   __tx.__pos_ = std::__uninitialized_allocator_copy(this->__alloc_, std::move(__first), std::move(__last), __tx.__pos_);
 }
 
-//  Default constructs __n objects starting at __end_
-//  throws if construction throws
-//  Postcondition:  size() == size() + __n
-//  Exception safety: strong.
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__append(size_type __n) {
-  if (static_cast<size_type>(this->__cap_ - this->__end_) >= __n)
-    this->__construct_at_end(__n);
-  else {
-    __split_buffer<value_type, allocator_type&> __v(__recommend(size() + __n), size(), this->__alloc_);
-    __v.__construct_at_end(__n);
-    __swap_out_circular_buffer(__v);
-  }
-}
-
-//  Default constructs __n objects starting at __end_
-//  throws if construction throws
-//  Postcondition:  size() == size() + __n
-//  Exception safety: strong.
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__append(size_type __n, const_reference __x) {
-  if (static_cast<size_type>(this->__cap_ - this->__end_) >= __n)
-    this->__construct_at_end(__n, __x);
-  else {
-    __split_buffer<value_type, allocator_type&> __v(__recommend(size() + __n), size(), this->__alloc_);
-    __v.__construct_at_end(__n, __x);
-    __swap_out_circular_buffer(__v);
-  }
-}
-
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 inline _LIBCPP_HIDE_FROM_ABI vector<_Tp, _Allocator>::vector(vector&& __x)
 #if _LIBCPP_STD_VER >= 17
@@ -1402,21 +1369,35 @@ vector<_Tp, _Allocator>::__insert_with_size(
 }
 
 template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::resize(size_type __sz) {
-  size_type __cs = size();
-  if (__cs < __sz)
-    this->__append(__sz - __cs);
-  else if (__cs > __sz)
-    this->__destruct_at_end(this->__begin_ + __sz);
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::resize(size_type __new_size) {
+  size_type __current_size = size();
+  if (__current_size < __new_size) {
+    if (__new_size <= capacity()) {
+      __construct_at_end(__new_size - __current_size);
+    } else {
+      __split_buffer<value_type, allocator_type&> __v(__recommend(__new_size), __current_size, __alloc_);
+      __v.__construct_at_end(__new_size - __current_size);
+      __swap_out_circular_buffer(__v);
+    }
+  } else if (__current_size > __new_size) {
+    this->__destruct_at_end(this->__begin_ + __new_size);
+  }
 }
 
 template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::resize(size_type __sz, const_reference __x) {
-  size_type __cs = size();
-  if (__cs < __sz)
-    this->__append(__sz - __cs, __x);
-  else if (__cs > __sz)
-    this->__destruct_at_end(this->__begin_ + __sz);
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::resize(size_type __new_size, const_reference __x) {
+  size_type __current_size = size();
+  if (__current_size < __new_size) {
+    if (__new_size <= capacity())
+      __construct_at_end(__new_size - __current_size, __x);
+    else {
+      __split_buffer<value_type, allocator_type&> __v(__recommend(__new_size), __current_size, __alloc_);
+      __v.__construct_at_end(__new_size - __current_size, __x);
+      __swap_out_circular_buffer(__v);
+    }
+  } else if (__current_size > __new_size) {
+    this->__destruct_at_end(this->__begin_ + __new_size);
+  }
 }
 
 template <class _Tp, class _Allocator>