On 10/23/24 10:39 AM, Jonathan Wakely wrote:
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 macros alignas and alignof should not be defined, as they're
keywords in C++.
Technically it's implementation-defined whether __STDC_VERSION__ is
defined by a C++ compiler, but G++ does not define it. Adjusting the
first #if this way works as intended: A C23 compiler will not enter the
outer if-group and so will not define any of the macros, a C17 compiler
will enter both if-groups and so define all the macros, and a C++
compiler will enter the outer if-group but not the inner if-group.
gcc/ChangeLog:
* ginclude/stdalign.h (__alignas_is_defined): Define for C++.
(__alignof_is_defined): Likewise.
Do we want to note somehow that these macros are deprecated since C++17?
libstdc++-v3/ChangeLog:
* testsuite/18_support/headers/cstdalign/macros.cc: New test.
---
The libc++ devs noticed recently that GCC's <stdalign.h> doesn't conform
to the C++ requirements.
Tested x86_64-linux.
OK for trunk?
gcc/ginclude/stdalign.h | 5 ++--
.../18_support/headers/cstdalign/macros.cc | 24 +++++++++++++++++++
2 files changed, 27 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 5f82f2d68f2..af73c322624 100644
--- a/gcc/ginclude/stdalign.h
+++ b/gcc/ginclude/stdalign.h
@@ -26,11 +26,12 @@ 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
#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 00000000000..c50c921cd59
--- /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>
Should there also/instead be a test with <stdalign.h>?
+
+#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
