1 files changed, 103 insertions, 18 deletions

diff --git a/gl/m4/stdalign.m4 b/gl/m4/stdalign.m4
index 20be01aa..dc297175 100644
--- a/gl/m4/stdalign.m4
+++ b/gl/m4/stdalign.m4
@@ -1,6 +1,6 @@
-# Check for stdalign.h that conforms to C11.
+# Check for alignas and alignof that conform to C23.
 
-dnl Copyright 2011-2013 Free Software Foundation, Inc.
+dnl Copyright 2011-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
@@ -9,16 +9,23 @@ dnl with or without modifications, as long as this notice is preserved.
 
 AC_DEFUN([gl_STDALIGN_H],
 [
-  AC_CACHE_CHECK([for working stdalign.h],
+  AC_CACHE_CHECK([for alignas and alignof],
     [gl_cv_header_working_stdalign_h],
-    [AC_COMPILE_IFELSE(
+    [gl_save_CFLAGS=$CFLAGS
+     for gl_working in "yes, keywords" "yes, <stdalign.h> macros"; do
+      AS_CASE([$gl_working],
+        [*stdalign.h*], [CFLAGS="$gl_save_CFLAGS -DINCLUDE_STDALIGN_H"])
+      AC_COMPILE_IFELSE(
        [AC_LANG_PROGRAM(
-          [[#include <stdalign.h>
+          [[#include <stdint.h>
+            #ifdef INCLUDE_STDALIGN_H
+             #include <stdalign.h>
+            #endif
             #include <stddef.h>
 
             /* Test that alignof yields a result consistent with offsetof.
                This catches GCC bug 52023
-               <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.  */
+               <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.  */
             #ifdef __cplusplus
                template <class t> struct alignof_helper { char a; t b; };
             # define ao(type) offsetof (alignof_helper<type>, b)
@@ -29,25 +36,103 @@ 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) \
-                 || __GNUC__ || __IBMC__ || __IBMCPP__ || __ICC \
-                 || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
+                 || (__TINYC__ && defined __attribute__) \
+                 || (defined __APPLE__ && defined __MACH__ \
+                     ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
+                     : __GNUC__) \
+                 || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
+                 || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__ \
+                 || 1300 <= _MSC_VER)
               struct alignas_test { char c; char alignas (8) alignas_8; };
               char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
                                 ? 1 : -1];
             #endif
           ]])],
-       [gl_cv_header_working_stdalign_h=yes],
-       [gl_cv_header_working_stdalign_h=no])])
+       [gl_cv_header_working_stdalign_h=$gl_working],
+       [gl_cv_header_working_stdalign_h=no])
+
+      CFLAGS=$gl_save_CFLAGS
+      test "$gl_cv_header_working_stdalign_h" != no && break
+     done])
+
+  GL_GENERATE_STDALIGN_H=false
+  AS_CASE([$gl_cv_header_working_stdalign_h],
+    [no],
+      [GL_GENERATE_STDALIGN_H=true],
+    [yes*keyword*],
+      [AC_DEFINE([HAVE_C_ALIGNASOF], [1],
+         [Define to 1 if the alignas and alignof keywords work.])])
 
-  if test $gl_cv_header_working_stdalign_h = yes; then
-    STDALIGN_H=''
-  else
-    STDALIGN_H='stdalign.h'
-  fi
+  AC_CHECK_HEADERS_ONCE([stdalign.h])
 
-  AC_SUBST([STDALIGN_H])
-  AM_CONDITIONAL([GL_GENERATE_STDALIGN_H], [test -n "$STDALIGN_H"])
+  dnl The "zz" puts this toward config.h's end, to avoid potential
+  dnl collisions with other definitions.
+  AH_VERBATIM([zzalignas],
+[#if !defined HAVE_C_ALIGNASOF && __cplusplus < 201103 && !defined alignof
+# if HAVE_STDALIGN_H
+#  include <stdalign.h>
+# else
+   /* Substitute.  Keep consistent with gnulib/lib/stdalign.in.h.  */
+#  ifndef _GL_STDALIGN_H
+#   define _GL_STDALIGN_H
+#   undef _Alignas
+#   undef _Alignof
+#   if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
+        || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
+            && !defined __clang__) \
+        || (defined __clang__ && __clang_major__ < 8))
+#    ifdef __cplusplus
+#     if (201103 <= __cplusplus || defined _MSC_VER)
+#      define _Alignof(type) alignof (type)
+#     else
+       template <class __t> struct __alignof_helper { char __a; __t __b; };
+#      define _Alignof(type) offsetof (__alignof_helper<type>, __b)
+#      define _GL_STDALIGN_NEEDS_STDDEF 1
+#     endif
+#    else
+#     if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
+#      define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
+#     else
+#      define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
+#      define _GL_STDALIGN_NEEDS_STDDEF 1
+#     endif
+#    endif
+#   endif
+#   if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
+#    define alignof _Alignof
+#   endif
+#   define __alignof_is_defined 1
+#   if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
+#    if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
+#     define _Alignas(a) alignas (a)
+#    elif (!defined __attribute__ \
+           && ((defined __APPLE__ && defined __MACH__ \
+                ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
+                : __GNUC__ && !defined __ibmxl__) \
+               || (4 <= __clang_major__) \
+               || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
+               || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
+#     define _Alignas(a) __attribute__ ((__aligned__ (a)))
+#    elif 1300 <= _MSC_VER
+#     define _Alignas(a) __declspec (align (a))
+#    endif
+#   endif
+#   if ((defined _Alignas \
+         && !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
+        || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
+#    define alignas _Alignas
+#   endif
+#   if (defined alignas \
+        || (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
+#    define __alignas_is_defined 1
+#   endif
+#   if _GL_STDALIGN_NEEDS_STDDEF
+#    include <stddef.h>
+#   endif
+#  endif /* _GL_STDALIGN_H */
+# endif
+#endif])
 ])