[libc][type_traits] Add aligned_storage

[PiJoules]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libc

Author: None (PiJoules)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/94074.diff

3 Files Affected:

• (modified) libc/src/__support/CPP/type_traits.h (+1)
• (added) libc/src/__support/CPP/type_traits/aligned_storage.h (+27)
• (modified) libc/test/src/__support/CPP/type_traits_test.cpp (+9)

diff --git a/libc/src/__support/CPP/type_traits.h b/libc/src/__support/CPP/type_traits.h
index 1494aeb905e093..d50b6612656dbb 100644
--- a/libc/src/__support/CPP/type_traits.h
+++ b/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"
diff --git a/libc/src/__support/CPP/type_traits/aligned_storage.h b/libc/src/__support/CPP/type_traits/aligned_storage.h
new file mode 100644
index 00000000000000..574b1146f6b2ad
--- /dev/null
+++ b/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
diff --git a/libc/test/src/__support/CPP/type_traits_test.cpp b/libc/test/src/__support/CPP/type_traits_test.cpp
index a2051f38027532..1c428e93a2fd8a 100644
--- a/libc/test/src/__support/CPP/type_traits_test.cpp
+++ b/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));

[michaelrj-google]

This patch has reminded me that I need to simplify the bazel a bit, so definitely don't land it before this patch lands: #94079

[lntue]

You'll need to add the new header to the type_traits target in src/__support/CPP/CMakeLists.txt

[PiJoules]

You'll need to add the new header to the type_traits target in src/__support/CPP/CMakeLists.txt

Done