From 5467f5b5ca6f2302573649b4a4f897793a9a6e7f Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 22 Oct 2024 16:26:27 +0100
Subject: [PATCH] ginclude: stdalign.h should define __xxx_is_defined macros
for C++
The __alignas_is_defined macro has been required by C++ since C++11, and
C++ Library DR 4036 clarified that __alignof_is_defined should be
defined too. The whole <stdalign.h> header was deprecated for C++23 (see
LWG 3827) and is likely to be removed for C++26 (see P3348), but we can
deal with that later.
The macros alignas and alignof should not be defined, as they're
keywords in C++.
gcc/ChangeLog:
* ginclude/stdalign.h (__alignas_is_defined): Define for C++.
(__alignof_is_defined): Likewise.
libstdc++-v3/ChangeLog:
* testsuite/18_support/headers/cstdalign/macros.cc: New test.
---
gcc/ginclude/stdalign.h | 6 +++--
.../18_support/headers/cstdalign/macros.cc | 24 +++++++++++++++++++
2 files changed, 28 insertions(+), 2 deletions(-)
create mode 100644 libstdc++-v3/testsuite/18_support/headers/cstdalign/macros.cc
diff --git a/gcc/ginclude/stdalign.h b/gcc/ginclude/stdalign.h
index 5f82f2d68f27..980b1bba4e2c 100644
--- a/gcc/ginclude/stdalign.h
+++ b/gcc/ginclude/stdalign.h
@@ -26,12 +26,14 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
#ifndef _STDALIGN_H
#define _STDALIGN_H
-#if (!defined __cplusplus \
- && !(defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L))
+#if !(defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L)
+#ifndef __cplusplus
#define alignas _Alignas
#define alignof _Alignof
+#endif
+/* These are defined for C++, but deprecated in C++23. */
#define __alignas_is_defined 1
#define __alignof_is_defined 1
diff --git a/libstdc++-v3/testsuite/18_support/headers/cstdalign/macros.cc b/libstdc++-v3/testsuite/18_support/headers/cstdalign/macros.cc
new file mode 100644
index 000000000000..c50c921cd59a
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/headers/cstdalign/macros.cc
@@ -0,0 +1,24 @@
+// { dg-options "-D_GLIBCXX_USE_DEPRECATED=1 -Wno-deprecated" }
+// { dg-do preprocess { target c++11 } }
+
+#include <cstdalign>
+
+#ifndef __alignas_is_defined
+# error "The header <cstdalign> fails to define a macro named __alignas_is_defined"
+#elif __alignas_is_defined != 1
+# error "__alignas_is_defined is not defined to 1 in <cstdalign>"
+#endif
+
+#ifndef __alignof_is_defined
+# error "The header <cstdalign> fails to define a macro named __alignof_is_defined"
+#elif __alignof_is_defined != 1
+# error "__alignof_is_defined is not defined to 1 in <cstdalign>"
+#endif
+
+#ifdef alignas
+# error "The header <cstdalign> defines a macro named alignas"
+#endif
+
+#ifdef alignof
+# error "The header <cstdalign> defines a macro named alignof"
+#endif
--
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