Index: libcxx/include/__memory/unique_ptr.h
===================================================================
--- libcxx/include/__memory/unique_ptr.h
+++ libcxx/include/__memory/unique_ptr.h
@@ -47,10 +47,8 @@
                      0) _NOEXCEPT {}
 
   _LIBCPP_INLINE_VISIBILITY void operator()(_Tp* __ptr) const _NOEXCEPT {
-    static_assert(sizeof(_Tp) > 0,
-                  "default_delete can not delete incomplete type");
-    static_assert(!is_void<_Tp>::value,
-                  "default_delete can not delete incomplete type");
+    static_assert(sizeof(_Tp) >= 0, "cannot delete an incomplete type");
+    static_assert(!is_void<_Tp>::value, "cannot delete an incomplete type");
     delete __ptr;
   }
 };
@@ -78,10 +76,7 @@
   _LIBCPP_INLINE_VISIBILITY
   typename _EnableIfConvertible<_Up>::type
   operator()(_Up* __ptr) const _NOEXCEPT {
-    static_assert(sizeof(_Tp) > 0,
-                  "default_delete can not delete incomplete type");
-    static_assert(!is_void<_Tp>::value,
-                  "default_delete can not delete void type");
+    static_assert(sizeof(_Up) >= 0, "cannot delete an incomplete type");
     delete[] __ptr;
   }
 };
Index: libcxx/include/__ranges/access.h
===================================================================
--- libcxx/include/__ranges/access.h
+++ libcxx/include/__ranges/access.h
@@ -59,14 +59,14 @@
   struct __fn {
     template <class _Tp>
     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp (&__t)[]) const noexcept
-      requires (sizeof(_Tp) != 0)  // Disallow incomplete element types.
+      requires (sizeof(_Tp) >= 0)  // Disallow incomplete element types.
     {
       return __t + 0;
     }
 
     template <class _Tp, size_t _Np>
     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp (&__t)[_Np]) const noexcept
-      requires (sizeof(_Tp) != 0)  // Disallow incomplete element types.
+      requires (sizeof(_Tp) >= 0)  // Disallow incomplete element types.
     {
       return __t + 0;
     }
@@ -133,7 +133,7 @@
   public:
     template <class _Tp, size_t _Np>
     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp (&__t)[_Np]) const noexcept
-      requires (sizeof(_Tp) != 0)  // Disallow incomplete element types.
+      requires (sizeof(_Tp) >= 0)  // Disallow incomplete element types.
     {
       return __t + _Np;
     }
Index: libcxx/test/std/ranges/range.access/begin.sizezero.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/std/ranges/range.access/begin.sizezero.pass.cpp
@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: msvc
+
+// std::ranges::begin
+// std::ranges::cbegin
+//   Test the fix for https://llvm.org/PR54100
+
+#include <ranges>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A {
+  int m[0];
+};
+static_assert(sizeof(A) == 0); // an extension supported by GCC and Clang
+
+int main(int, char**)
+{
+  A a[10];
+  std::same_as<A*> auto p = std::ranges::begin(a);
+  assert(p == a);
+  std::same_as<const A*> auto cp = std::ranges::cbegin(a);
+  assert(cp == a);
+
+  return 0;
+}
Index: libcxx/test/std/ranges/range.access/end.sizezero.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/std/ranges/range.access/end.sizezero.pass.cpp
@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// 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: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: msvc
+
+// std::ranges::end
+// std::ranges::cend
+//   Test the fix for https://llvm.org/PR54100
+
+#include <ranges>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A {
+  int m[0];
+};
+static_assert(sizeof(A) == 0); // an extension supported by GCC and Clang
+
+int main(int, char**)
+{
+  A a[10];
+  std::same_as<A*> auto p = std::ranges::end(a);
+  assert(p == a + 10);
+  std::same_as<const A*> auto cp = std::ranges::cend(a);
+  assert(cp == a + 10);
+
+  return 0;
+}
Index: libcxx/test/std/utilities/smartptr/unique.ptr/unique.ptr.create/make_unique.sizezero.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/std/utilities/smartptr/unique.ptr/unique.ptr.create/make_unique.sizezero.pass.cpp
@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// This code triggers https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104568
+// UNSUPPORTED: gcc-11
+// UNSUPPORTED: msvc
+
+// Test the fix for https://llvm.org/PR54100
+
+#include <memory>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A {
+  int m[0];
+};
+static_assert(sizeof(A) == 0, "");  // an extension supported by GCC and Clang
+
+int main(int, char**)
+{
+  {
+    std::unique_ptr<A> p = std::unique_ptr<A>(new A);
+    assert(p != nullptr);
+  }
+  {
+    std::unique_ptr<A[]> p = std::unique_ptr<A[]>(new A[1]);
+    assert(p != nullptr);
+  }
+#if TEST_STD_VER > 11
+  {
+    std::unique_ptr<A> p = std::make_unique<A>();
+    assert(p != nullptr);
+  }
+  {
+    std::unique_ptr<A[]> p = std::make_unique<A[]>(1);
+    assert(p != nullptr);
+  }
+#endif
+  return 0;
+}