[libc][type_traits] Add aligned_storage (#94074)

Author: PiJoules

libc/src/__support/CPP/CMakeLists.txt

@@ -111,6 +111,7 @@ add_header_library(
     type_traits/add_lvalue_reference.h
     type_traits/add_pointer.h
     type_traits/add_rvalue_reference.h
+    type_traits/aligned_storage.h
     type_traits/always_false.h
     type_traits/bool_constant.h
     type_traits/conditional.h

libc/src/__support/CPP/type_traits.h

@@ -12,6 +12,7 @@
 #include "src/__support/CPP/type_traits/add_lvalue_reference.h"
 #include "src/__support/CPP/type_traits/add_pointer.h"
 #include "src/__support/CPP/type_traits/add_rvalue_reference.h"
+#include "src/__support/CPP/type_traits/aligned_storage.h"
 #include "src/__support/CPP/type_traits/bool_constant.h"
 #include "src/__support/CPP/type_traits/conditional.h"
 #include "src/__support/CPP/type_traits/decay.h"

libc/src/__support/CPP/type_traits/aligned_storage.h

@@ -0,0 +1,27 @@
+//===-- aligned_storage type_traits    --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_ALIGNED_STORAGE_H
+#define LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_ALIGNED_STORAGE_H
+
+#include <stddef.h> // size_t
+
+namespace LIBC_NAMESPACE::cpp {
+
+template <size_t Len, size_t Align> struct aligned_storage {
+  struct type {
+    alignas(Align) unsigned char data[Len];
+  };
+};
+
+template <size_t Len, size_t Align>
+using aligned_storage_t = typename aligned_storage<Len, Align>::type;
+
+} // namespace LIBC_NAMESPACE::cpp
+
+#endif // LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_ALIGNED_STORAGE_H

libc/test/src/__support/CPP/type_traits_test.cpp

@@ -112,6 +112,15 @@ TEST(LlvmLibcTypeTraitsTest, add_rvalue_reference_void) {
                          const volatile void>));
 }
 
+TEST(LlvmLibcTypeTraitsTest, aligned_storage) {
+  struct S {
+    int a, b;
+  };
+  aligned_storage_t<sizeof(S), alignof(S)> buf;
+  EXPECT_EQ(alignof(buf), alignof(S));
+  EXPECT_EQ(sizeof(buf), sizeof(S));
+}
+
 TEST(LlvmLibcTypeTraitsTest, bool_constant) {
   EXPECT_TRUE((bool_constant<true>::value));
   EXPECT_FALSE((bool_constant<false>::value));