[libcxx-commits] [libcxx] [libc++] Fix constexpr initialization of std::array<T, 0> (PR #74667)

[Mark de Wever via libcxx-commits]

================
@@ -0,0 +1,130 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <array>
+
+// template <class T, size_t N>
+// struct array
+
+// Make sure std::array<T, N> has the correct object size and alignment.
+// This test is mostly meant to catch subtle ABI-breaking regressions.
+
+// Ignore error about requesting a large alignment not being ABI compatible with older AIX systems.
+#if defined(_AIX)
+#  pragma clang diagnostic ignored "-Waix-compat"
+#endif
+
+#include <array>
+#include <cstddef>
+
+#include "test_macros.h"
+
+template <class T, std::size_t Size>
+struct MyArray {
+  T elems[Size];
+};
+
+template <class T>
+void test_type() {
+  {
+    static_assert(sizeof(std::array<T, 0>) == sizeof(T), "");
+    static_assert(alignof(std::array<T, 0>) == alignof(T), "");
+    static_assert(sizeof(std::array<T, 0>) == sizeof(T[1]), "");
+    static_assert(sizeof(std::array<T, 0>) == sizeof(MyArray<T, 1>), "");
+    static_assert(alignof(std::array<T, 0>) == alignof(MyArray<T, 1>), "");
+  }
+
+  {
+    static_assert(sizeof(std::array<T, 1>) == sizeof(T), "");
+    static_assert(alignof(std::array<T, 1>) == alignof(T), "");
+    static_assert(sizeof(std::array<T, 1>) == sizeof(T[1]), "");
+    static_assert(sizeof(std::array<T, 1>) == sizeof(MyArray<T, 1>), "");
+    static_assert(alignof(std::array<T, 1>) == alignof(MyArray<T, 1>), "");
+  }
+
+  {
+    static_assert(sizeof(std::array<T, 2>) == sizeof(T) * 2, "");
+    static_assert(alignof(std::array<T, 2>) == alignof(T), "");
+    static_assert(sizeof(std::array<T, 2>) == sizeof(T[2]), "");
+    static_assert(sizeof(std::array<T, 2>) == sizeof(MyArray<T, 2>), "");
+    static_assert(alignof(std::array<T, 2>) == alignof(MyArray<T, 2>), "");
+  }
+
+  {
+    static_assert(sizeof(std::array<T, 3>) == sizeof(T) * 3, "");
+    static_assert(alignof(std::array<T, 3>) == alignof(T), "");
+    static_assert(sizeof(std::array<T, 3>) == sizeof(T[3]), "");
+    static_assert(sizeof(std::array<T, 3>) == sizeof(MyArray<T, 3>), "");
+    static_assert(alignof(std::array<T, 3>) == alignof(MyArray<T, 3>), "");
+  }
+
+  {
+    static_assert(sizeof(std::array<T, 444>) == sizeof(T) * 444, "");
+    static_assert(alignof(std::array<T, 444>) == alignof(T), "");
+    static_assert(sizeof(std::array<T, 444>) == sizeof(T[444]), "");
+    static_assert(sizeof(std::array<T, 444>) == sizeof(MyArray<T, 444>), "");
+    static_assert(alignof(std::array<T, 444>) == alignof(MyArray<T, 444>), "");
+  }
+}
+
+struct Empty {};
+
+struct Aggregate {
+  int i;
+};
+
+struct WithPadding {
+  long double ld;
+  char c;
+};
+
+#if TEST_STD_VER >= 11
+struct alignas(alignof(std::max_align_t) * 2) Overaligned1 {};
+
+struct alignas(alignof(std::max_align_t) * 2) Overaligned2 {
+  char data[1000];
+};
+
+struct alignas(alignof(std::max_align_t)) Overaligned3 {
+  char data[1000];
+};
+
+struct alignas(8) Overaligned4 {
+  char c;
+};
+
+struct alignas(8) Overaligned5 {};
+#endif
+
+int main(int, char**) {
----------------
mordante wrote:

Maybe remain `main` to `test` since it's a compile only test.

https://github.com/llvm/llvm-project/pull/74667