[libcxx-commits] [libcxx] 7a1f6ad - [libc++] Simplify allocator propagation in vector assignments (#217635)

[via libcxx-commits]

Author: Nikolas Klauser
Date: 2026-09-02T16:22:46+02:00
New Revision: 7a1f6ad89e574d638e4618f41f243c63da76ce7b

URL: https://github.com/llvm/llvm-project/commit/7a1f6ad89e574d638e4618f41f243c63da76ce7b
DIFF: https://github.com/llvm/llvm-project/commit/7a1f6ad89e574d638e4618f41f243c63da76ce7b.diff

LOG: [libc++] Simplify allocator propagation in vector assignments (#217635)

We can just use `if constexpr` instead of dispatching based on type
traits. This will cause some more code generation in C++03, but I don't
think we should care at this point.

Added: 
    

Modified: 
    libcxx/include/__vector/vector.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 42c571ccbe323..99d86fbb63e90 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -270,7 +270,24 @@ class _LIBCPP_WARN_UNUSED vector {
       : __layout_(__a) {
     __init_with_size(__x.__layout_.__begin_ptr(), __x.__layout_.__end_ptr(), __x.size());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(const vector& __x);
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(const vector& __other) {
+    if (this == std::addressof(__other))
+      return *this;
+
+    if _LIBCPP_CONSTEXPR (__alloc_traits::propagate_on_container_copy_assignment::value) {
+      if (this->__layout_.__alloc() != __other.__layout_.__alloc()) {
+        clear();
+        __annotate_delete();
+        __alloc_traits::deallocate(this->__layout_.__alloc(), this->__layout_.__begin_ptr(), capacity());
+        __layout_.__reset_without_allocator();
+      }
+      this->__layout_.__alloc() = __other.__layout_.__alloc();
+    }
+
+    assign(__other.__layout_.__begin_ptr(), __other.__layout_.__end_ptr());
+    return *this;
+  }
 
 #ifndef _LIBCPP_CXX03_LANG
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector(initializer_list<value_type> __il) {
@@ -298,9 +315,22 @@ class _LIBCPP_WARN_UNUSED vector {
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20
   _LIBCPP_HIDE_FROM_ABI vector(vector&& __x, const __type_identity_t<allocator_type>& __a);
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(vector&& __x)
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(vector&& __other)
       _NOEXCEPT_(__noexcept_move_assign_container<_Allocator, __alloc_traits>::value) {
-    __move_assign(__x, integral_constant<bool, __alloc_traits::propagate_on_container_move_assignment::value>());
+    if _LIBCPP_CONSTEXPR (__alloc_traits::propagate_on_container_move_assignment::value) {
+      __vdeallocate();
+      __layout_.__alloc() = std::move(__other.__layout_.__alloc());
+    } else {
+      if (__layout_.__alloc() != __other.__layout_.__alloc()) {
+        typedef move_iterator<iterator> _Ip;
+        assign(_Ip(__other.begin()), _Ip(__other.end()));
+        return *this;
+      }
+      __vdeallocate();
+    }
+
+    __layout_.__move_assign_without_allocator(__other.__layout_);
     return *this;
   }
 
@@ -742,10 +772,6 @@ class _LIBCPP_WARN_UNUSED vector {
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
   __move_range(pointer __from_s, pointer __from_e, pointer __to);
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign(vector& __c, true_type)
-      _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value);
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign(vector& __c, false_type)
-      _NOEXCEPT_(__alloc_traits::is_always_equal::value);
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_end(pointer __new_last) _NOEXCEPT {
     size_type __old_size = size();
@@ -807,39 +833,10 @@ class _LIBCPP_WARN_UNUSED vector {
     _ConstructTransaction& operator=(_ConstructTransaction const&) = delete;
   };
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __copy_assign_alloc(const vector& __c) {
-    __copy_assign_alloc(__c, integral_constant<bool, __alloc_traits::propagate_on_container_copy_assignment::value>());
-  }
-
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(vector& __c)
-      _NOEXCEPT_(!__alloc_traits::propagate_on_container_move_assignment::value ||
-                 is_nothrow_move_assignable<allocator_type>::value) {
-    __move_assign_alloc(__c, integral_constant<bool, __alloc_traits::propagate_on_container_move_assignment::value>());
-  }
-
   [[__noreturn__]] _LIBCPP_HIDE_FROM_ABI static void __throw_length_error() { std::__throw_length_error("vector"); }
 
   [[__noreturn__]] _LIBCPP_HIDE_FROM_ABI static void __throw_out_of_range() { std::__throw_out_of_range("vector"); }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __copy_assign_alloc(const vector& __c, true_type) {
-    if (this->__layout_.__alloc() != __c.__layout_.__alloc()) {
-      clear();
-      __annotate_delete();
-      __alloc_traits::deallocate(this->__layout_.__alloc(), this->__layout_.__begin_ptr(), capacity());
-      __layout_.__reset_without_allocator();
-    }
-    this->__layout_.__alloc() = __c.__layout_.__alloc();
-  }
-
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __copy_assign_alloc(const vector&, false_type) {}
-
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(vector& __c, true_type)
-      _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value) {
-    this->__layout_.__alloc() = std::move(__c.__layout_.__alloc());
-  }
-
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(vector&, false_type) _NOEXCEPT {}
-
   template <class _Ptr = pointer, __enable_if_t<is_pointer<_Ptr>::value, int> = 0>
   static _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Ptr
   __add_alignment_assumption(_Ptr __p) _NOEXCEPT {
@@ -961,34 +958,6 @@ vector<_Tp, _Allocator>::vector(vector&& __x, const __type_identity_t<allocator_
   }
 }
 
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__move_assign(vector& __c, false_type)
-    _NOEXCEPT_(__alloc_traits::is_always_equal::value) {
-  if (this->__layout_.__alloc() != __c.__layout_.__alloc()) {
-    typedef move_iterator<iterator> _Ip;
-    assign(_Ip(__c.begin()), _Ip(__c.end()));
-  } else
-    __move_assign(__c, true_type());
-}
-
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__move_assign(vector& __c, true_type)
-    _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value) {
-  __vdeallocate();
-  __move_assign_alloc(__c); // this can throw
-  __layout_.__move_assign_without_allocator(__c.__layout_);
-}
-
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 inline _LIBCPP_HIDE_FROM_ABI vector<_Tp, _Allocator>&
-vector<_Tp, _Allocator>::operator=(const vector& __x) {
-  if (this != std::addressof(__x)) {
-    __copy_assign_alloc(__x);
-    assign(__x.__layout_.__begin_ptr(), __x.__layout_.__end_ptr());
-  }
-  return *this;
-}
-
 template <class _Tp, class _Allocator>
 template <class _Iterator, class _Sentinel>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void