From 1a78ae3c895d0520bbb8ad2f154e737d52fe7ae2 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Wed, 7 Feb 2018 23:50:25 +0000
Subject: [PATCH] Fix size and alignment of array<T, 0>.

An array T[1] isn't necessarily the same say when it's
a member of a struct. This patch addresses that problem and corrects
the tests to deal with it.

llvm-svn: 324545
---
 libcxx/include/__config                       |  1 +
 libcxx/include/array                          |  5 +++--
 .../array/size_and_alignment.pass.cpp         | 20 +++++++++++++++++--
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/libcxx/include/__config b/libcxx/include/__config
index a4acbcaf1ff0..cfe4ef08c94a 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -582,6 +582,7 @@ namespace std {
 #define __alignof__ __alignof
 #define _LIBCPP_NORETURN __declspec(noreturn)
 #define _ALIGNAS(x) __declspec(align(x))
+#define _ALIGNAS_TYPE(x) alignas(x)
 #define _LIBCPP_HAS_NO_VARIADICS
 
 #define _LIBCPP_BEGIN_NAMESPACE_STD namespace std {
diff --git a/libcxx/include/array b/libcxx/include/array
index 706e573dbed7..fdb1f9dae530 100644
--- a/libcxx/include/array
+++ b/libcxx/include/array
@@ -244,10 +244,11 @@ struct _LIBCPP_TEMPLATE_VIS array<_Tp, 0>
     typedef std::reverse_iterator<iterator>       reverse_iterator;
     typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
-
     typedef typename conditional<is_const<_Tp>::value, const char,
                                 char>::type _CharType;
-    _ALIGNAS(alignment_of<_Tp[1]>::value) _CharType __elems_[sizeof(_Tp[1])];
+
+    struct  _ArrayInStructT { _Tp __data_[1]; };
+    _ALIGNAS_TYPE(_ArrayInStructT) _CharType __elems_[sizeof(_ArrayInStructT)];
 
     // No explicit construct/copy/destroy for aggregate type
     _LIBCPP_INLINE_VISIBILITY void fill(const value_type&) {
diff --git a/libcxx/test/std/containers/sequences/array/size_and_alignment.pass.cpp b/libcxx/test/std/containers/sequences/array/size_and_alignment.pass.cpp
index d01e1ceb7922..966d063fe17a 100644
--- a/libcxx/test/std/containers/sequences/array/size_and_alignment.pass.cpp
+++ b/libcxx/test/std/containers/sequences/array/size_and_alignment.pass.cpp
@@ -21,12 +21,26 @@
 
 #include "test_macros.h"
 
+
+template <class T, size_t Size>
+struct MyArray {
+  T elems[Size];
+};
+
 template <class T, size_t Size>
 void test() {
   typedef T CArrayT[Size == 0 ? 1 : Size];
   typedef std::array<T, Size> ArrayT;
-  static_assert(sizeof(CArrayT) == sizeof(ArrayT), "");
-  static_assert(TEST_ALIGNOF(CArrayT) == TEST_ALIGNOF(ArrayT), "");
+  typedef MyArray<T, Size == 0 ? 1 : Size> MyArrayT;
+  static_assert(sizeof(ArrayT) == sizeof(CArrayT), "");
+  static_assert(sizeof(ArrayT) == sizeof(MyArrayT), "");
+  static_assert(TEST_ALIGNOF(ArrayT) == TEST_ALIGNOF(MyArrayT), "");
+#if defined(_LIBCPP_VERSION)
+  ArrayT a;
+  ((void)a);
+  static_assert(sizeof(ArrayT) == sizeof(a.__elems_), "");
+  static_assert(TEST_ALIGNOF(ArrayT) == __alignof__(a.__elems_), "");
+#endif
 }
 
 template <class T>
@@ -44,6 +58,8 @@ struct TEST_ALIGNAS(TEST_ALIGNOF(std::max_align_t) * 2) TestType2 {
   char data[1000];
 };
 
+//static_assert(sizeof(void*) == 4, "");
+
 int main() {
   test_type<char>();
   test_type<int>();