[PATCH] stdalign-tests: port to C23

[PATCH] stdalign-tests: port to C23

[Paul Eggert]

* tests/test-stdalign.c: Do not test __alignas_is_defined,
_Alignof, or _Alignas as they are obsolescent.
Do not use __alignas_is_defined in C23 or later (or C++11 or later),
as it’s removed in C23.
---
 ChangeLog                       |  8 ++++++++
 doc/posix-headers/stdalign.texi | 12 ++++++++----
 lib/alignof.h                   |  3 +--
 tests/test-stdalign.c           | 29 +++--------------------------
 4 files changed, 20 insertions(+), 32 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index d812e73f55..5013112632 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2022-09-13  Paul Eggert  <eggert@cs.ucla.edu>
+
+	stdalign-tests: port to C23
+	* tests/test-stdalign.c: Do not test __alignas_is_defined,
+	_Alignof, or _Alignas as they are obsolescent.
+	Do not use __alignas_is_defined in C23 or later (or C++11 or later),
+	as it’s removed in C23.
+
 2022-09-12  Bruno Haible  <bruno@clisp.org>
 
 	supersede: Avoid a failure when writing to /dev/null in Solaris zones.
diff --git a/doc/posix-headers/stdalign.texi b/doc/posix-headers/stdalign.texi
index 0f76bc90e6..4ed83bec3e 100644
--- a/doc/posix-headers/stdalign.texi
+++ b/doc/posix-headers/stdalign.texi
@@ -35,10 +35,9 @@ On most pre-C11 platforms, the operand of
 @code{alignof}/@code{_Alignof} cannot be a structure type containing a
 flexible array member.
 @item
-@code{_Alignas} and @code{alignas} are not always supported;
-on platforms lacking support, the
-macro @code{__alignas_is_defined} is not defined.
-Supported compilers include GCC, IBM C, Sun C 5.9 and later,
+@code{_Alignas} and @code{alignas} are not always supported.
+Supported compilers include any compiler supporting C11 or later,
+which includes GCC, IBM C, Sun C 5.9 and later,
 and MSVC 7.0 and later.
 @item
 Some compilers do not support alignment via
@@ -63,6 +62,11 @@ also known as Oracle Developer Studio 12.6.
 @code{<stdalign.h>} must be #included before @code{_Alignas} and
 @code{_Alignof} can be used.
 @item
+In C11 and C17, @code{<stdalign.h>} defines the macros
+@code{__alignas_is_defined} and
+@code{__alignof_is_defined} to 1.
+In C23, these macros are not defined.
+@item
 You cannot assume that @code{_Alignas} and @code{_Alignof} are reserved words;
 they might be macros.
 @end itemize
diff --git a/lib/alignof.h b/lib/alignof.h
index 3f4a54257d..41bab60378 100644
--- a/lib/alignof.h
+++ b/lib/alignof.h
@@ -22,8 +22,7 @@
 /* alignof_slot (TYPE)
    Determine the alignment of a structure slot (field) of a given type,
    at compile time.  Note that the result depends on the ABI.
-   This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
-   <stdalign.h> if __alignof_is_defined is 1.
+   This is the same as alignof (TYPE) and _Alignof (TYPE).
    Note: The result cannot be used as a value for an 'enum' constant,
    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
 #if defined __cplusplus
diff --git a/tests/test-stdalign.c b/tests/test-stdalign.c
index 85d23a6eda..69268b87b4 100644
--- a/tests/test-stdalign.c
+++ b/tests/test-stdalign.c
@@ -33,21 +33,12 @@ typedef struct { char a[2]; } struct2;
 typedef struct { char a[3]; } struct3;
 typedef struct { char a[4]; } struct4;
 
-verify (__alignof_is_defined == 1);
-#ifndef alignof
-# error "alignof is not a macro"
-#endif
-
-#if __alignas_is_defined
-verify (__alignas_is_defined == 1);
-# ifndef alignas
-#  error "alignas is not a macro"
-# endif
+#if (202311 <= __STDC_VERSION__ || __alignas_is_defined \
+     || 201103 <= __cplusplus)
 /* mingw can go up only to 8.  8 is all that GNU Emacs needs, so let's
    limit the test to 8 for now.  */
 # define TEST_ALIGNMENT 8
 #else
-# define _Alignas(alignment)
 # define alignas(alignment)
 # define TEST_ALIGNMENT 1
 #endif
@@ -55,10 +46,8 @@ verify (__alignas_is_defined == 1);
 #define CHECK_STATIC(type) \
   typedef struct { char slot1; type slot2; } type##_helper; \
   verify (alignof (type) == offsetof (type##_helper, slot2)); \
-  verify (_Alignof (type) == alignof (type)); \
   const int type##_alignment = alignof (type); \
-  type alignas (TEST_ALIGNMENT) static_##type##_alignas; \
-  type _Alignas (TEST_ALIGNMENT) static_##type##_Alignas
+  type alignas (TEST_ALIGNMENT) static_##type##_alignas
 
 #define CHECK_ALIGNED(var) ASSERT ((uintptr_t) &(var) % TEST_ALIGNMENT == 0)
 
@@ -96,31 +85,19 @@ main ()
   return 77;
 #else
   CHECK_ALIGNED (static_char_alignas);
-  CHECK_ALIGNED (static_char_Alignas);
   CHECK_ALIGNED (static_short_alignas);
-  CHECK_ALIGNED (static_short_Alignas);
   CHECK_ALIGNED (static_int_alignas);
-  CHECK_ALIGNED (static_int_Alignas);
   CHECK_ALIGNED (static_long_alignas);
-  CHECK_ALIGNED (static_long_Alignas);
 # ifdef INT64_MAX
   CHECK_ALIGNED (static_int64_t_alignas);
-  CHECK_ALIGNED (static_int64_t_Alignas);
 # endif
   CHECK_ALIGNED (static_float_alignas);
-  CHECK_ALIGNED (static_float_Alignas);
   CHECK_ALIGNED (static_double_alignas);
-  CHECK_ALIGNED (static_double_Alignas);
   /* CHECK_ALIGNED (static_longdouble_alignas); */
-  /* CHECK_ALIGNED (static_longdouble_Alignas); */
   CHECK_ALIGNED (static_struct1_alignas);
-  CHECK_ALIGNED (static_struct1_Alignas);
   CHECK_ALIGNED (static_struct2_alignas);
-  CHECK_ALIGNED (static_struct2_Alignas);
   CHECK_ALIGNED (static_struct3_alignas);
-  CHECK_ALIGNED (static_struct3_Alignas);
   CHECK_ALIGNED (static_struct4_alignas);
-  CHECK_ALIGNED (static_struct4_Alignas);
   return 0;
 #endif
 }
-- 
2.37.2

Re: [PATCH] stdalign-tests: port to C23

[Bruno Haible]

Paul Eggert wrote:
> _Alignof, or _Alignas as they are obsolescent.

_Alignas is obsolescent? Then we should better talk about 'alignas' instead.


2022-09-13  Bruno Haible  <bruno@clisp.org>

	Prefer talking about alignas than _Alignas.
	* m4/gnulib-common.m4 (gl_COMMON_BODY): Don't mention _Alignas in a
	comment.
	* m4/stdalign.m4 (gl_STDALIGN_H): Likewise.

diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index 8a5daa230e..d17cbec58c 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 73
+# gnulib-common.m4 serial 74
 dnl Copyright (C) 2007-2022 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -115,7 +115,7 @@ AC_DEFUN([gl_COMMON_BODY], [
 # define _GL_HAS_C_ATTRIBUTE(attr) 0
 #endif
 
-]dnl There is no _GL_ATTRIBUTE_ALIGNED; use stdalign's _Alignas instead.
+]dnl There is no _GL_ATTRIBUTE_ALIGNED; use stdalign's alignas instead.
 [
 /* _GL_ATTRIBUTE_ALLOC_SIZE ((N)) declares that the Nth argument of the function
    is the size of the returned memory block.
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
index 78577cb2ac..c3283760d5 100644
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -30,7 +30,7 @@ AC_DEFUN([gl_STDALIGN_H],
             char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
             char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
 
-            /* Test _Alignas only on platforms where gnulib can help.  */
+            /* Test alignas only on platforms where gnulib can help.  */
             #if \
                 ((defined __cplusplus && 201103 <= __cplusplus) \
                  || (__TINYC__ && defined __attribute__) \

Re: [PATCH] stdalign-tests: port to C23

[Paul Eggert]

On 9/13/22 15:19, Bruno Haible wrote:
> _Alignas is obsolescent?

Although it's still in the standard as of draft C23, it is to some 
extent deprecated as it is no longer necessarily a keyword (it might be 
a macro). My guess is that it will be obsoleted in some future version 
of the standard, if they keep producing new standards. As it's an 
unnecessary appendage at this point I think it's safe to call it 
obsolescent.

Similarly for other former keywords like _Bool and _Static_assert.