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Diffstat (limited to 'm4/stdalign.m4')
| -rw-r--r-- | m4/stdalign.m4 | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4 new file mode 100644 index 0000000..f49cf8e --- /dev/null +++ b/m4/stdalign.m4 @@ -0,0 +1,200 @@ +# Check for alignas and alignof that conform to C23. + +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. + +dnl Written by Paul Eggert and Bruno Haible. + +# Prepare for substituting <stdalign.h> if it is not supported. + +AC_DEFUN([gl_ALIGNASOF], +[ + AC_CACHE_CHECK([for alignas and alignof], + [gl_cv_header_working_stdalign_h], + [gl_save_CFLAGS=$CFLAGS + for gl_working in "yes, keywords" "yes, <stdalign.h> macros"; do + AS_CASE([$gl_working], + [*stdalign.h*], [CFLAGS="$gl_save_CFLAGS -DINCLUDE_STDALIGN_H"]) + AC_COMPILE_IFELSE( + [AC_LANG_PROGRAM( + [[#include <stdint.h> + #ifdef INCLUDE_STDALIGN_H + #include <stdalign.h> + #endif + #include <stddef.h> + + /* Test that alignof yields a result consistent with offsetof. + This catches GCC bug 52023 + <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. */ + #ifdef __cplusplus + template <class t> struct alignof_helper { char a; t b; }; + # define ao(type) offsetof (alignof_helper<type>, b) + #else + # define ao(type) offsetof (struct { char a; type b; }, b) + #endif + char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1]; + char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1]; + char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1]; + + /* Test alignas only on platforms where gnulib can help. */ + #if \ + ((defined __cplusplus && 201103 <= __cplusplus) \ + || (__TINYC__ && defined __attribute__) \ + || (defined __APPLE__ && defined __MACH__ \ + ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \ + : __GNUC__) \ + || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \ + || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__ \ + || 1300 <= _MSC_VER) + struct alignas_test { char c; char alignas (8) alignas_8; }; + char test_alignas[offsetof (struct alignas_test, alignas_8) == 8 + ? 1 : -1]; + #endif + ]])], + [gl_cv_header_working_stdalign_h=$gl_working], + [gl_cv_header_working_stdalign_h=no]) + + CFLAGS=$gl_save_CFLAGS + test "$gl_cv_header_working_stdalign_h" != no && break + done]) + + AS_CASE([$gl_cv_header_working_stdalign_h], + [yes*keyword*], + [AC_DEFINE([HAVE_C_ALIGNASOF], [1], + [Define to 1 if the alignas and alignof keywords work.])]) + + 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> +# endif + +/* ISO C23 alignas and alignof for platforms that lack it. + + References: + ISO C23 (latest free draft + <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n3047.pdf>) + sections 6.5.3.4, 6.7.5, 7.15. + C++11 (latest free draft + <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>) + section 18.10. */ + +/* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment + requirement of a structure member (i.e., slot or field) that is of + type TYPE, as an integer constant expression. + + This differs from GCC's and clang's __alignof__ operator, which can + yield a better-performing alignment for an object of that type. For + example, on x86 with GCC and on Linux/x86 with clang, + __alignof__ (double) and __alignof__ (long long) are 8, whereas + alignof (double) and alignof (long long) are 4 unless the option + '-malign-double' is used. + + The result cannot be used as a value for an 'enum' constant, if you + want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc. */ + +/* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023 + <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. + clang versions < 8.0.0 have the same bug. */ +# if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \ + || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \ + && !defined __clang__) \ + || (defined __clang__ && __clang_major__ < 8)) +# undef/**/_Alignof +# 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)) +# undef/**/alignof +# define alignof _Alignof +# endif + +/* alignas (A), also known as _Alignas (A), aligns a variable or type + to the alignment A, where A is an integer constant expression. For + example: + + int alignas (8) foo; + struct s { int a; int alignas (8) bar; }; + + aligns the address of FOO and the offset of BAR to be multiples of 8. + + A should be a power of two that is at least the type's alignment + and at most the implementation's alignment limit. This limit is + 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable + to MSVC through at least version 10.0, A should be an integer + constant, as MSVC does not support expressions such as 1 << 3. + To be portable to Sun C 5.11, do not align auto variables to + anything stricter than their default alignment. + + The following C23 requirements are not supported here: + + - If A is zero, alignas has no effect. + - alignas can be used multiple times; the strictest one wins. + - alignas (TYPE) is equivalent to alignas (alignof (TYPE)). + + */ +# if !HAVE_STDALIGN_H +# 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 +# endif + +# if _GL_STDALIGN_NEEDS_STDDEF +# include <stddef.h> +# endif +#endif]) +]) + +AC_DEFUN([gl_STDALIGN_H], +[ + AC_REQUIRE([gl_ALIGNASOF]) + if test "$gl_cv_header_working_stdalign_h" = no; then + GL_GENERATE_STDALIGN_H=true + else + GL_GENERATE_STDALIGN_H=false + fi + + gl_CHECK_NEXT_HEADERS([stdalign.h]) + if test $ac_cv_header_stdalign_h = yes; then + HAVE_STDALIGN_H=1 + else + HAVE_STDALIGN_H=0 + fi + AC_SUBST([HAVE_STDALIGN_H]) +]) |