[libcxx-commits] [libcxx] [libc++] Fix ABI break introduced by switching to _LIBCPP_COMPRESSED_PAIR (PR #154686)

Nikolas Klauser via libcxx-commits libcxx-commits at lists.llvm.org
Thu Aug 21 02:34:50 PDT 2025


https://github.com/philnik777 updated https://github.com/llvm/llvm-project/pull/154686

>From 2f00bcf71e52444f31faef9b3046d53c5e7bcd79 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Wed, 20 Aug 2025 17:29:17 +0200
Subject: [PATCH 1/2] [libc++] Add tests for the ABI break introduced by
 switching to [[no_unique_address]]

---
 .../associative/map/abi.compile.pass.cpp      | 161 ++++++++++++++++++
 .../associative/set/abi.compile.pass.cpp      | 159 +++++++++++++++++
 .../unord.map/abi.compile.pass.cpp            |  28 +++
 .../unord.set/abi.compile.pass.cpp            |  28 +++
 .../sequences/deque/abi.compile.pass.cpp      |  27 +++
 .../forwardlist/abi.compile.pass.cpp          | 115 +++++++++++++
 .../sequences/list/abi.compile.pass.cpp       |  28 +++
 .../vector.bool/abi.compile.pass.cpp          |  28 +++
 .../sequences/vector/abi.compile.pass.cpp     |  28 +++
 .../strings/basic.string/abi.compile.pass.cpp | 106 ++++++++++++
 10 files changed, 708 insertions(+)
 create mode 100644 libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
 create mode 100644 libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
 create mode 100644 libcxx/test/libcxx/containers/sequences/forwardlist/abi.compile.pass.cpp
 create mode 100644 libcxx/test/libcxx/containers/strings/basic.string/abi.compile.pass.cpp

diff --git a/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
new file mode 100644
index 0000000000000..ecb67621ddd38
--- /dev/null
+++ b/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
@@ -0,0 +1,161 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: libcpp-has-abi-fix-unordered-container-size-type, libcpp-abi-no-compressed-pair-padding
+
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
+
+#include <cstdint>
+#include <map>
+
+#include "min_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+template <class T>
+class small_pointer {
+  std::uint16_t offset;
+};
+
+template <class T>
+class small_iter_allocator {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::uint16_t;
+  using difference_type = std::int16_t;
+
+  small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  small_iter_allocator(small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(small_iter_allocator, small_iter_allocator) { return true; }
+  friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
+};
+
+template <class T>
+class final_small_iter_allocator final {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::uint16_t;
+  using difference_type = std::int16_t;
+
+  final_small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  final_small_iter_allocator(final_small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(final_small_iter_allocator, final_small_iter_allocator) { return true; }
+  friend bool operator!=(final_small_iter_allocator, final_small_iter_allocator) { return false; }
+};
+
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+};
+
+template <class T, class Alloc>
+using map_alloc = std::map<T, T, std::less<T>, Alloc>;
+
+struct user_struct {
+  map_alloc<int, common_base_allocator<std::pair<const int, int> > > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
+#if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
+
+static_assert(sizeof(map_alloc<int, std::allocator<std::pair<const int, int> > >) == 24, "");
+static_assert(sizeof(map_alloc<int, min_allocator<std::pair<const int, int> > >) == 24, "");
+static_assert(sizeof(map_alloc<int, test_allocator<std::pair<const int, int> > >) == 40, "");
+static_assert(sizeof(map_alloc<int, small_iter_allocator<std::pair<const int, int> > >) == 6, "");
+static_assert(sizeof(map_alloc<int, final_small_iter_allocator<std::pair<const int, int> > >) == 8, "");
+
+static_assert(sizeof(map_alloc<char, std::allocator<std::pair<const char, char> > >) == 24, "");
+static_assert(sizeof(map_alloc<char, min_allocator<std::pair<const char, char> > >) == 24, "");
+static_assert(sizeof(map_alloc<char, test_allocator<std::pair<const char, char> > >) == 40, "");
+static_assert(sizeof(map_alloc<char, small_iter_allocator<std::pair<const char, char> > >) == 6, "");
+static_assert(sizeof(map_alloc<char, final_small_iter_allocator<std::pair<const char, char> > >) == 8, "");
+
+static_assert(TEST_ALIGNOF(map_alloc<int, std::allocator<std::pair<const int, int> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, min_allocator<std::pair<const int, int> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, test_allocator<std::pair<const int, int> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, small_iter_allocator<std::pair<const int, int> > >) == 2, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, final_small_iter_allocator<std::pair<const int, int> > >) == 2, "");
+
+static_assert(TEST_ALIGNOF(map_alloc<char, std::allocator<std::pair<const char, char> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, min_allocator<std::pair<const char, char> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, test_allocator<std::pair<const char, char> > >) == 8, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, small_iter_allocator<std::pair<const char, char> > >) == 2, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, final_small_iter_allocator<std::pair<const char, char> > >) == 2, "");
+
+struct TEST_ALIGNAS(32) AlignedLess {};
+
+// This part of the ABI has been broken between LLVM 19 and LLVM 20.
+static_assert(sizeof(std::map<int, int, AlignedLess>) == 64, "");
+static_assert(TEST_ALIGNOF(std::map<int, int, AlignedLess>) == 32, "");
+
+#elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 16, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
+
+static_assert(sizeof(map_alloc<int, std::allocator<std::pair<const int, int> > >) == 12, "");
+static_assert(sizeof(map_alloc<int, min_allocator<std::pair<const int, int> > >) == 12, "");
+static_assert(sizeof(map_alloc<int, test_allocator<std::pair<const int, int> > >) == 24, "");
+static_assert(sizeof(map_alloc<int, small_iter_allocator<std::pair<const int, int> > >) == 6, "");
+static_assert(sizeof(map_alloc<int, final_small_iter_allocator<std::pair<const int, int> > >) == 6, "");
+
+static_assert(sizeof(map_alloc<char, std::allocator<std::pair<const char, char> > >) == 12, "");
+static_assert(sizeof(map_alloc<char, min_allocator<std::pair<const char, char> > >) == 12, "");
+static_assert(sizeof(map_alloc<char, test_allocator<std::pair<const char, char> > >) == 24, "");
+static_assert(sizeof(map_alloc<char, small_iter_allocator<std::pair<const char, char> > >) == 6, "");
+static_assert(sizeof(map_alloc<char, final_small_iter_allocator<std::pair<const char, char> > >) == 6, "");
+
+static_assert(TEST_ALIGNOF(map_alloc<int, std::allocator<std::pair<const int, int> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, min_allocator<std::pair<const int, int> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, test_allocator<std::pair<const int, int> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, small_iter_allocator<std::pair<const int, int> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<int, final_small_iter_allocator<std::pair<const int, int> > >) == 4, "");
+
+static_assert(TEST_ALIGNOF(map_alloc<char, std::allocator<std::pair<const char, char> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, min_allocator<std::pair<const char, char> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, test_allocator<std::pair<const char, char> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, small_iter_allocator<std::pair<const char, char> > >) == 4, "");
+static_assert(TEST_ALIGNOF(map_alloc<char, final_small_iter_allocator<std::pair<const char, char> > >) == 4, "");
+
+struct TEST_ALIGNAS(32) AlignedHash {};
+struct UnalignedEqualTo {};
+
+static_assert(sizeof(std::map<int, int, AlignedHash, UnalignedEqualTo>) == 64);
+static_assert(TEST_ALIGNOF(std::map<int, int, AlignedHash, UnalignedEqualTo>) == 32);
+
+#else
+#  error std::size_t has an unexpected size
+#endif
diff --git a/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
new file mode 100644
index 0000000000000..7e2f222146b69
--- /dev/null
+++ b/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
@@ -0,0 +1,159 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
+
+#include <cstdint>
+#include <set>
+
+#include "min_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+template <class T>
+class small_pointer {
+  std::uint16_t offset;
+};
+
+template <class T>
+class small_iter_allocator {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::uint16_t;
+  using difference_type = std::int16_t;
+
+  small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  small_iter_allocator(small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(small_iter_allocator, small_iter_allocator) { return true; }
+  friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
+};
+
+template <class T>
+class final_small_iter_allocator final {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::uint16_t;
+  using difference_type = std::int16_t;
+
+  final_small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  final_small_iter_allocator(final_small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(final_small_iter_allocator, final_small_iter_allocator) { return true; }
+  friend bool operator!=(final_small_iter_allocator, final_small_iter_allocator) { return false; }
+};
+
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+};
+
+template <class T, class Alloc>
+using set_alloc = std::set<T, std::less<T>, Alloc>;
+
+struct user_struct {
+  set_alloc<int, common_base_allocator<int> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
+#if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
+
+static_assert(sizeof(set_alloc<int, std::allocator<int> >) == 24, "");
+static_assert(sizeof(set_alloc<int, min_allocator<int> >) == 24, "");
+static_assert(sizeof(set_alloc<int, test_allocator<int> >) == 40, "");
+static_assert(sizeof(set_alloc<int, small_iter_allocator<int> >) == 6, "");
+static_assert(sizeof(set_alloc<int, final_small_iter_allocator<int> >) == 8, "");
+
+static_assert(sizeof(set_alloc<char, std::allocator<char> >) == 24, "");
+static_assert(sizeof(set_alloc<char, min_allocator<char> >) == 24, "");
+static_assert(sizeof(set_alloc<char, test_allocator<char> >) == 40, "");
+static_assert(sizeof(set_alloc<char, small_iter_allocator<char> >) == 6, "");
+static_assert(sizeof(set_alloc<char, final_small_iter_allocator<char> >) == 8, "");
+
+static_assert(TEST_ALIGNOF(set_alloc<int, std::allocator<int> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, min_allocator<int> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, test_allocator<int> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, small_iter_allocator<int> >) == 2, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, final_small_iter_allocator<int> >) == 2, "");
+
+static_assert(TEST_ALIGNOF(set_alloc<char, std::allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, min_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, test_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, small_iter_allocator<char> >) == 2, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, final_small_iter_allocator<char> >) == 2, "");
+
+struct TEST_ALIGNAS(32) AlignedLess {};
+
+// This part of the ABI has been broken between LLVM 19 and LLVM 20.
+static_assert(sizeof(std::set<int, AlignedLess>) == 64, "");
+static_assert(TEST_ALIGNOF(std::set<int, AlignedLess>) == 32, "");
+
+#elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 16, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
+
+static_assert(sizeof(set_alloc<int, std::allocator<int> >) == 12, "");
+static_assert(sizeof(set_alloc<int, min_allocator<int> >) == 12, "");
+static_assert(sizeof(set_alloc<int, test_allocator<int> >) == 24, "");
+static_assert(sizeof(set_alloc<int, small_iter_allocator<int> >) == 6, "");
+static_assert(sizeof(set_alloc<int, final_small_iter_allocator<int> >) == 6, "");
+
+static_assert(sizeof(set_alloc<char, std::allocator<char> >) == 12, "");
+static_assert(sizeof(set_alloc<char, min_allocator<char> >) == 12, "");
+static_assert(sizeof(set_alloc<char, test_allocator<char> >) == 24, "");
+static_assert(sizeof(set_alloc<char, small_iter_allocator<char> >) == 6, "");
+static_assert(sizeof(set_alloc<char, final_small_iter_allocator<char> >) == 6, "");
+
+static_assert(TEST_ALIGNOF(set_alloc<int, std::allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, min_allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, test_allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, small_iter_allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<int, final_small_iter_allocator<int> >) == 4, "");
+
+static_assert(TEST_ALIGNOF(set_alloc<char, std::allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, min_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, test_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, small_iter_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(set_alloc<char, final_small_iter_allocator<char> >) == 4, "");
+
+struct TEST_ALIGNAS(32) AlignedHash {};
+struct UnalignedEqualTo {};
+
+static_assert(sizeof(std::set<int, int, AlignedHash, UnalignedEqualTo>) == 64);
+static_assert(TEST_ALIGNOF(std::set<int, int, AlignedHash, UnalignedEqualTo>) == 32);
+
+#else
+#  error std::size_t has an unexpected size
+#endif
diff --git a/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
index 55d42a8d017e1..68ca174dba9c8 100644
--- a/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
@@ -66,10 +66,36 @@ class final_small_iter_allocator final {
   friend bool operator!=(final_small_iter_allocator, final_small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
 template <class T, class Alloc>
 using unordered_map_alloc = std::unordered_map<T, T, std::hash<T>, std::equal_to<T>, Alloc>;
 
+struct user_struct {
+  unordered_map_alloc<int, common_base_allocator<std::pair<const int, int> > > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
 #if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 48, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(unordered_map_alloc<int, std::allocator<std::pair<const int, int> > >) == 40, "");
 static_assert(sizeof(unordered_map_alloc<int, min_allocator<std::pair<const int, int> > >) == 40, "");
@@ -104,6 +130,8 @@ static_assert(sizeof(std::unordered_map<int, int, AlignedHash, UnalignedEqualTo>
 static_assert(TEST_ALIGNOF(std::unordered_map<int, int, AlignedHash, UnalignedEqualTo>) == 32, "");
 
 #elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 24, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
 
 static_assert(sizeof(unordered_map_alloc<int, std::allocator<std::pair<const int, int> > >) == 20, "");
 static_assert(sizeof(unordered_map_alloc<int, min_allocator<std::pair<const int, int> > >) == 20, "");
diff --git a/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
index bee2012bbea29..cbee8b157e474 100644
--- a/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
@@ -66,10 +66,36 @@ class final_small_iter_allocator final {
   friend bool operator!=(final_small_iter_allocator, final_small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
 template <class T, class Alloc>
 using unordered_set_alloc = std::unordered_set<T, std::hash<T>, std::equal_to<T>, Alloc>;
 
+struct user_struct {
+  unordered_set_alloc<int, common_base_allocator<int> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
 #if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 48, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(unordered_set_alloc<int, std::allocator<int> >) == 40, "");
 static_assert(sizeof(unordered_set_alloc<int, min_allocator<int> >) == 40, "");
@@ -103,6 +129,8 @@ static_assert(sizeof(std::unordered_set<int, AlignedHash, UnalignedEqualTo>) ==
 static_assert(TEST_ALIGNOF(std::unordered_set<int, AlignedHash, UnalignedEqualTo>) == 32, "");
 
 #elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 24, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
 
 static_assert(sizeof(unordered_set_alloc<int, std::allocator<int> >) == 20, "");
 static_assert(sizeof(unordered_set_alloc<int, min_allocator<int> >) == 20, "");
diff --git a/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
index 30586d8b2422c..16de9b4985948 100644
--- a/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
@@ -60,6 +60,25 @@ class final_small_iter_allocator final {
   friend bool operator!=(final_small_iter_allocator, final_small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
 #if __SIZE_WIDTH__ == 64
 
 static_assert(sizeof(std::deque<int>) == 48, "");
@@ -67,24 +86,28 @@ static_assert(sizeof(std::deque<int, min_allocator<int> >) == 48, "");
 static_assert(sizeof(std::deque<int, test_allocator<int> >) == 80, "");
 static_assert(sizeof(std::deque<int, small_iter_allocator<int> >) == 12, "");
 static_assert(sizeof(std::deque<int, final_small_iter_allocator<int> >) == 16, "");
+static_assert(sizeof(std::deque<int, common_base_allocator<int> >) == 56, "");
 
 static_assert(sizeof(std::deque<char>) == 48, "");
 static_assert(sizeof(std::deque<char, min_allocator<char> >) == 48, "");
 static_assert(sizeof(std::deque<char, test_allocator<char> >) == 80, "");
 static_assert(sizeof(std::deque<char, small_iter_allocator<char> >) == 12, "");
 static_assert(sizeof(std::deque<char, final_small_iter_allocator<char> >) == 16, "");
+static_assert(sizeof(std::deque<char, common_base_allocator<char> >) == 56, "");
 
 static_assert(TEST_ALIGNOF(std::deque<int>) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<int, min_allocator<int> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<int, test_allocator<int> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<int, small_iter_allocator<int> >) == 2, "");
 static_assert(TEST_ALIGNOF(std::deque<int, final_small_iter_allocator<int> >) == 2, "");
+static_assert(TEST_ALIGNOF(std::deque<int, common_base_allocator<int> >) == 8, "");
 
 static_assert(TEST_ALIGNOF(std::deque<char>) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<char, min_allocator<char> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<char, test_allocator<char> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<char, small_iter_allocator<char> >) == 2, "");
 static_assert(TEST_ALIGNOF(std::deque<char, final_small_iter_allocator<char> >) == 2, "");
+static_assert(TEST_ALIGNOF(std::deque<char, common_base_allocator<char> >) == 8, "");
 
 #elif __SIZE_WIDTH__ == 32
 
@@ -93,24 +116,28 @@ static_assert(sizeof(std::deque<int, min_allocator<int> >) == 24, "");
 static_assert(sizeof(std::deque<int, test_allocator<int> >) == 48, "");
 static_assert(sizeof(std::deque<int, small_iter_allocator<int> >) == 12, "");
 static_assert(sizeof(std::deque<int, final_small_iter_allocator<int> >) == 16, "");
+static_assert(sizeof(std::deque<int, common_base_allocator<int> >) == 28, "");
 
 static_assert(sizeof(std::deque<char>) == 24, "");
 static_assert(sizeof(std::deque<char, min_allocator<char> >) == 24, "");
 static_assert(sizeof(std::deque<char, test_allocator<char> >) == 48, "");
 static_assert(sizeof(std::deque<char, small_iter_allocator<char> >) == 12, "");
 static_assert(sizeof(std::deque<char, final_small_iter_allocator<char> >) == 16, "");
+static_assert(sizeof(std::deque<char, common_base_allocator<char> >) == 28, "");
 
 static_assert(TEST_ALIGNOF(std::deque<int>) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<int, min_allocator<int> >) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<int, test_allocator<int> >) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<int, small_iter_allocator<int> >) == 2, "");
 static_assert(TEST_ALIGNOF(std::deque<int, final_small_iter_allocator<int> >) == 2, "");
+static_assert(TEST_ALIGNOF(std::deque<int, common_base_allocator<int> >) == 4, "");
 
 static_assert(TEST_ALIGNOF(std::deque<char>) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<char, min_allocator<char> >) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<char, test_allocator<char> >) == 4, "");
 static_assert(TEST_ALIGNOF(std::deque<char, small_iter_allocator<char> >) == 2, "");
 static_assert(TEST_ALIGNOF(std::deque<char, final_small_iter_allocator<char> >) == 2, "");
+static_assert(TEST_ALIGNOF(std::deque<char, common_base_allocator<char> >) == 4, "");
 
 #else
 #  error std::size_t has an unexpected size
diff --git a/libcxx/test/libcxx/containers/sequences/forwardlist/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/forwardlist/abi.compile.pass.cpp
new file mode 100644
index 0000000000000..38bff22c55c11
--- /dev/null
+++ b/libcxx/test/libcxx/containers/sequences/forwardlist/abi.compile.pass.cpp
@@ -0,0 +1,115 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstdint>
+#include <forward_list>
+
+#include "min_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+template <class T>
+class small_pointer {
+  std::uint16_t offset;
+};
+
+template <class T>
+class small_iter_allocator {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::int16_t;
+  using difference_type = std::int16_t;
+
+  small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  small_iter_allocator(small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(small_iter_allocator, small_iter_allocator) { return true; }
+  friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
+};
+
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
+struct user_struct {
+  std::forward_list<int, common_base_allocator<int> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
+#if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 16, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
+
+static_assert(sizeof(std::forward_list<int>) == 8, "");
+static_assert(sizeof(std::forward_list<int, min_allocator<int> >) == 8, "");
+static_assert(sizeof(std::forward_list<int, test_allocator<int> >) == 24, "");
+static_assert(sizeof(std::forward_list<int, small_iter_allocator<int> >) == 2, "");
+
+static_assert(sizeof(std::forward_list<char>) == 8, "");
+static_assert(sizeof(std::forward_list<char, min_allocator<char> >) == 8, "");
+static_assert(sizeof(std::forward_list<char, test_allocator<char> >) == 24, "");
+static_assert(sizeof(std::forward_list<char, small_iter_allocator<char> >) == 2, "");
+
+static_assert(TEST_ALIGNOF(std::forward_list<int>) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, min_allocator<int> >) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, test_allocator<int> >) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, small_iter_allocator<int> >) == 2, "");
+
+static_assert(TEST_ALIGNOF(std::forward_list<char>) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, min_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, test_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, small_iter_allocator<char> >) == 2, "");
+
+#elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 8, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
+
+static_assert(sizeof(std::forward_list<int>) == 4, "");
+static_assert(sizeof(std::forward_list<int, min_allocator<int> >) == 4, "");
+static_assert(sizeof(std::forward_list<int, test_allocator<int> >) == 16, "");
+static_assert(sizeof(std::forward_list<int, small_iter_allocator<int> >) == 2, "");
+
+static_assert(sizeof(std::forward_list<char>) == 4, "");
+static_assert(sizeof(std::forward_list<char, min_allocator<char> >) == 4, "");
+static_assert(sizeof(std::forward_list<char, test_allocator<char> >) == 16, "");
+static_assert(sizeof(std::forward_list<char, small_iter_allocator<char> >) == 2, "");
+
+static_assert(TEST_ALIGNOF(std::forward_list<int>) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, min_allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, test_allocator<int> >) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<int, small_iter_allocator<int> >) == 2, "");
+
+static_assert(TEST_ALIGNOF(std::forward_list<char>) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, min_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, test_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(std::forward_list<char, small_iter_allocator<char> >) == 2, "");
+
+#else
+#  error std::size_t has an unexpected size
+#endif
diff --git a/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
index a16ae1d527921..440b1aeb710f7 100644
--- a/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
@@ -38,7 +38,33 @@ class small_iter_allocator {
   friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
+struct user_struct {
+  std::list<int, common_base_allocator<int> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
 #if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::list<int>) == 24, "");
 static_assert(sizeof(std::list<int, min_allocator<int> >) == 24, "");
@@ -61,6 +87,8 @@ static_assert(TEST_ALIGNOF(std::list<char, test_allocator<char> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::list<char, small_iter_allocator<char> >) == 2, "");
 
 #elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
 
 static_assert(sizeof(std::list<int>) == 12, "");
 static_assert(sizeof(std::list<int, min_allocator<int> >) == 12, "");
diff --git a/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
index cc6b0d94e7daf..2690e8e9f2d9b 100644
--- a/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
@@ -40,7 +40,33 @@ class small_iter_allocator {
   friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
+struct user_struct {
+  std::vector<bool, common_base_allocator<bool> > v;
+  [[no_unique_address]] common_base_allocator<bool> a;
+};
+
 #if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::vector<bool>) == 24, "");
 static_assert(sizeof(std::vector<bool, min_allocator<bool> >) == 24, "");
@@ -53,6 +79,8 @@ static_assert(TEST_ALIGNOF(std::vector<bool, test_allocator<bool> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::vector<bool, small_iter_allocator<bool> >) == 2, "");
 
 #elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 16, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
 
 static_assert(sizeof(std::vector<bool>) == 12, "");
 static_assert(sizeof(std::vector<bool, min_allocator<bool> >) == 12, "");
diff --git a/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
index 57684951c8e8e..96a924483d643 100644
--- a/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
@@ -46,7 +46,33 @@ class small_iter_allocator {
   friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
 };
 
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
+struct user_struct {
+  std::vector<int, common_base_allocator<int> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
 #if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::vector<int>) == 24, "");
 static_assert(sizeof(std::vector<int, min_allocator<int> >) == 24, "");
@@ -69,6 +95,8 @@ static_assert(TEST_ALIGNOF(std::vector<char, test_allocator<char> >) == 8, "");
 static_assert(TEST_ALIGNOF(std::vector<char, small_iter_allocator<char> >) == 2, "");
 
 #elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
 
 static_assert(sizeof(std::vector<int>) == 12, "");
 static_assert(sizeof(std::vector<int, min_allocator<int> >) == 12, "");
diff --git a/libcxx/test/libcxx/containers/strings/basic.string/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/strings/basic.string/abi.compile.pass.cpp
new file mode 100644
index 0000000000000..2cae1441252ab
--- /dev/null
+++ b/libcxx/test/libcxx/containers/strings/basic.string/abi.compile.pass.cpp
@@ -0,0 +1,106 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstdint>
+#include <string>
+
+#include "min_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+template <class T>
+class small_pointer {
+public:
+  using value_type        = T;
+  using difference_type   = std::int16_t;
+  using pointer           = small_pointer;
+  using reference         = T&;
+  using iterator_category = std::random_access_iterator_tag;
+
+private:
+  std::uint16_t offset;
+};
+
+template <class T>
+class small_iter_allocator {
+public:
+  using value_type      = T;
+  using pointer         = small_pointer<T>;
+  using size_type       = std::int16_t;
+  using difference_type = std::int16_t;
+
+  small_iter_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  small_iter_allocator(small_iter_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(small_iter_allocator, small_iter_allocator) { return true; }
+  friend bool operator!=(small_iter_allocator, small_iter_allocator) { return false; }
+};
+
+struct allocator_base {};
+
+template <class T>
+struct common_base_allocator : allocator_base {
+  using value_type      = T;
+
+  common_base_allocator() TEST_NOEXCEPT {}
+
+  template <class U>
+  common_base_allocator(common_base_allocator<U>) TEST_NOEXCEPT {}
+
+  T* allocate(std::size_t n);
+  void deallocate(T* p, std::size_t);
+
+  friend bool operator==(common_base_allocator, common_base_allocator);
+  friend bool operator!=(common_base_allocator, common_base_allocator);
+
+};
+
+template <class Alloc>
+using string_alloc = std::basic_string<char, std::char_traits<char>, Alloc>;
+
+struct user_struct {
+  string_alloc<common_base_allocator<char> > v;
+  [[no_unique_address]] common_base_allocator<int> a;
+};
+
+#if __SIZE_WIDTH__ == 64
+static_assert(sizeof(user_struct) == 32, "");
+static_assert(TEST_ALIGNOF(user_struct) == 8, "");
+
+static_assert(sizeof(string_alloc<std::allocator<char> >) == 24, "");
+static_assert(sizeof(string_alloc<min_allocator<char> >) == 24, "");
+static_assert(sizeof(string_alloc<test_allocator<char> >) == 32, "");
+static_assert(sizeof(string_alloc<small_iter_allocator<char> >) == 6, "");
+
+static_assert(TEST_ALIGNOF(string_alloc<std::allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(string_alloc<min_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(string_alloc<test_allocator<char> >) == 8, "");
+static_assert(TEST_ALIGNOF(string_alloc<small_iter_allocator<char> >) == 2, "");
+
+#elif __SIZE_WIDTH__ == 32
+static_assert(sizeof(user_struct) == 16, "");
+static_assert(TEST_ALIGNOF(user_struct) == 4, "");
+
+static_assert(sizeof(string_alloc<std::allocator<char> >) == 12, "");
+static_assert(sizeof(string_alloc<min_allocator<char> >) == 12, "");
+static_assert(sizeof(string_alloc<test_allocator<char> >) == 24, "");
+static_assert(sizeof(string_alloc<small_iter_allocator<char> >) == 6, "");
+
+static_assert(TEST_ALIGNOF(string_alloc<std::allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(string_alloc<min_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(string_alloc<test_allocator<char> >) == 4, "");
+static_assert(TEST_ALIGNOF(string_alloc<small_iter_allocator<char> >) == 2, "");
+
+#else
+#  error std::size_t has an unexpected size
+#endif

>From 6f3c37459b01e7a802cc7381ca2170ce40a34318 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Thu, 21 Aug 2025 09:26:19 +0200
Subject: [PATCH 2/2] [libc++] Fix ABI break introduced by switching to
 _LIBCPP_COMPRESSED_PAIR

---
 libcxx/include/__memory/compressed_pair.h     | 28 +++++++++++--------
 libcxx/include/string                         | 14 ++++++++--
 .../associative/map/abi.compile.pass.cpp      |  2 +-
 .../associative/set/abi.compile.pass.cpp      |  2 +-
 .../unord.map/abi.compile.pass.cpp            |  4 +--
 .../unord.set/abi.compile.pass.cpp            |  4 +--
 .../sequences/deque/abi.compile.pass.cpp      |  4 +--
 .../sequences/list/abi.compile.pass.cpp       |  2 +-
 .../vector.bool/abi.compile.pass.cpp          |  2 +-
 .../sequences/vector/abi.compile.pass.cpp     |  2 +-
 10 files changed, 39 insertions(+), 25 deletions(-)

diff --git a/libcxx/include/__memory/compressed_pair.h b/libcxx/include/__memory/compressed_pair.h
index fb7b7b7afcc8c..7f8de44204f9b 100644
--- a/libcxx/include/__memory/compressed_pair.h
+++ b/libcxx/include/__memory/compressed_pair.h
@@ -81,20 +81,24 @@ template <class _ToPad>
 class __compressed_pair_padding<_ToPad, true> {};
 
 #  define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)                                                  \
-    _LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>))) T1 Initializer1;    \
-    _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _);          \
-    _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2;                                                                         \
-    _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _)
+    struct {                                                                                                           \
+      _LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>))) T1 Initializer1;  \
+      _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _);        \
+      _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2;                                                                       \
+      _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _);        \
+    }
 
 #  define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3)                              \
-    _LIBCPP_NO_UNIQUE_ADDRESS                                                                                          \
-    __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>),                                                \
-                   __aligned__(::std::__compressed_pair_alignment<T3>))) T1 Initializer1;                              \
-    _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _);          \
-    _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2;                                                                         \
-    _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _);          \
-    _LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3;                                                                         \
-    _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _)
+    struct {                                                                                                           \
+      _LIBCPP_NO_UNIQUE_ADDRESS                                                                                        \
+      __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>),                                              \
+                     __aligned__(::std::__compressed_pair_alignment<T3>))) T1 Initializer1;                            \
+      _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _);        \
+      _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2;                                                                       \
+      _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _);        \
+      _LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3;                                                                       \
+      _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _);        \
+    }
 
 #else
 #  define _LIBCPP_COMPRESSED_PAIR(T1, Name1, T2, Name2)                                                                \
diff --git a/libcxx/include/string b/libcxx/include/string
index 3c1523eb5de33..1d197654b9fee 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -974,7 +974,12 @@ public:
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string()
       _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
-      : __rep_() {
+#  if _LIBCPP_STD_VER >= 20 // TODO(LLVM 23): Remove this condition; this is a workaround for https://llvm.org/PR154567
+      : __rep_(__short())
+#  else
+      : __rep_()
+#  endif
+  {
     __annotate_new(0);
   }
 
@@ -984,7 +989,12 @@ public:
 #  else
       _NOEXCEPT
 #  endif
-      : __rep_(), __alloc_(__a) {
+#  if _LIBCPP_STD_VER >= 20 // TODO(LLVM 23): Remove this condition; this is a workaround for https://llvm.org/PR154567
+      : __rep_(__short()),
+#  else
+      : __rep_(),
+#  endif
+        __alloc_(__a) {
     __annotate_new(0);
   }
 
diff --git a/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
index ecb67621ddd38..55ca67d35e3ce 100644
--- a/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/map/abi.compile.pass.cpp
@@ -89,7 +89,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 32, "");
+static_assert(sizeof(user_struct) == 24, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(map_alloc<int, std::allocator<std::pair<const int, int> > >) == 24, "");
diff --git a/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
index 7e2f222146b69..0f9ca9a8674fc 100644
--- a/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/set/abi.compile.pass.cpp
@@ -87,7 +87,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 32, "");
+static_assert(sizeof(user_struct) == 24, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(set_alloc<int, std::allocator<int> >) == 24, "");
diff --git a/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
index 68ca174dba9c8..f5cf0241ca5ed 100644
--- a/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/unord.map/abi.compile.pass.cpp
@@ -94,7 +94,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 48, "");
+static_assert(sizeof(user_struct) == 40, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(unordered_map_alloc<int, std::allocator<std::pair<const int, int> > >) == 40, "");
@@ -126,7 +126,7 @@ struct TEST_ALIGNAS(32) AlignedHash {};
 struct UnalignedEqualTo {};
 
 // This part of the ABI has been broken between LLVM 19 and LLVM 20.
-static_assert(sizeof(std::unordered_map<int, int, AlignedHash, UnalignedEqualTo>) == 64, "");
+static_assert(sizeof(std::unordered_map<int, int, AlignedHash, UnalignedEqualTo>) == 96, "");
 static_assert(TEST_ALIGNOF(std::unordered_map<int, int, AlignedHash, UnalignedEqualTo>) == 32, "");
 
 #elif __SIZE_WIDTH__ == 32
diff --git a/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
index cbee8b157e474..12e683e10b878 100644
--- a/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/associative/unord.set/abi.compile.pass.cpp
@@ -94,7 +94,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 48, "");
+static_assert(sizeof(user_struct) == 40, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(unordered_set_alloc<int, std::allocator<int> >) == 40, "");
@@ -125,7 +125,7 @@ struct TEST_ALIGNAS(32) AlignedHash {};
 struct UnalignedEqualTo {};
 
 // This part of the ABI has been broken between LLVM 19 and LLVM 20.
-static_assert(sizeof(std::unordered_set<int, AlignedHash, UnalignedEqualTo>) == 64, "");
+static_assert(sizeof(std::unordered_set<int, AlignedHash, UnalignedEqualTo>) == 96, "");
 static_assert(TEST_ALIGNOF(std::unordered_set<int, AlignedHash, UnalignedEqualTo>) == 32, "");
 
 #elif __SIZE_WIDTH__ == 32
diff --git a/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
index 16de9b4985948..8f4dfc509c098 100644
--- a/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/deque/abi.compile.pass.cpp
@@ -86,14 +86,14 @@ static_assert(sizeof(std::deque<int, min_allocator<int> >) == 48, "");
 static_assert(sizeof(std::deque<int, test_allocator<int> >) == 80, "");
 static_assert(sizeof(std::deque<int, small_iter_allocator<int> >) == 12, "");
 static_assert(sizeof(std::deque<int, final_small_iter_allocator<int> >) == 16, "");
-static_assert(sizeof(std::deque<int, common_base_allocator<int> >) == 56, "");
+static_assert(sizeof(std::deque<int, common_base_allocator<int> >) == 48, "");
 
 static_assert(sizeof(std::deque<char>) == 48, "");
 static_assert(sizeof(std::deque<char, min_allocator<char> >) == 48, "");
 static_assert(sizeof(std::deque<char, test_allocator<char> >) == 80, "");
 static_assert(sizeof(std::deque<char, small_iter_allocator<char> >) == 12, "");
 static_assert(sizeof(std::deque<char, final_small_iter_allocator<char> >) == 16, "");
-static_assert(sizeof(std::deque<char, common_base_allocator<char> >) == 56, "");
+static_assert(sizeof(std::deque<char, common_base_allocator<char> >) == 48, "");
 
 static_assert(TEST_ALIGNOF(std::deque<int>) == 8, "");
 static_assert(TEST_ALIGNOF(std::deque<int, min_allocator<int> >) == 8, "");
diff --git a/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
index 440b1aeb710f7..afe00cac5ce06 100644
--- a/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/list/abi.compile.pass.cpp
@@ -63,7 +63,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 32, "");
+static_assert(sizeof(user_struct) == 24, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::list<int>) == 24, "");
diff --git a/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
index 2690e8e9f2d9b..e724ae97c9e71 100644
--- a/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/vector.bool/abi.compile.pass.cpp
@@ -65,7 +65,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 32, "");
+static_assert(sizeof(user_struct) == 24, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::vector<bool>) == 24, "");
diff --git a/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp b/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
index 96a924483d643..854e122f8bcbe 100644
--- a/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
+++ b/libcxx/test/libcxx/containers/sequences/vector/abi.compile.pass.cpp
@@ -71,7 +71,7 @@ struct user_struct {
 };
 
 #if __SIZE_WIDTH__ == 64
-static_assert(sizeof(user_struct) == 32, "");
+static_assert(sizeof(user_struct) == 24, "");
 static_assert(TEST_ALIGNOF(user_struct) == 8, "");
 
 static_assert(sizeof(std::vector<int>) == 24, "");



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