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Work around a bug in GCC 14 i386 C23 alignas

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Problem reported by Helmut Eller (bug#79886).
* src/lisp.h (USE_LSB_TAG): Adjust to alignas changes.
(alignas): For GCC and Clang, prefer __attribute__ ((__aligned__ (A)))
to alignas (A) even if the compiler claims to support the latter.
This works around a bug in GCC 14 i386 C23 alignas.
No need to worry about whether __alignas_is_defined is defined.
This commit is contained in:
Paul Eggert 2025-11-27 00:39:17 -08:00
parent 18a346da6a
commit 1ddc28997b
1 changed files with 11 additions and 7 deletions
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18
src/lisp.h
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@ -253,10 +253,10 @@ DEFINE_GDB_SYMBOL_END (INTTYPEBITS)
So, USE_LSB_TAG is true only on hosts where it might be useful. */
DEFINE_GDB_SYMBOL_BEGIN (bool, USE_LSB_TAG)
#if (ALIGNOF_EMACS_INT < IDEAL_GCALIGNMENT && !defined alignas \
&& ! (__GNUC__ || 4 <= __clang_major__) \
&& __STDC_VERSION__ < 202311 && __cplusplus < 201103) \
&& !defined WIDE_EMACS_INT \
&& !defined HAVE_STRUCT_ATTRIBUTE_ALIGNED \
&& !defined __alignas_is_defined \
&& __STDC_VERSION__ < 202311 && __cplusplus < 201103)
&& !defined HAVE_STRUCT_ATTRIBUTE_ALIGNED
#define USE_LSB_TAG 0
#else /* ALIGNOF_EMACS_INT >= IDEAL_GCALIGNMENT || defined alignas ... */
#define USE_LSB_TAG (VAL_MAX / 2 < INTPTR_MAX)
@ -268,10 +268,14 @@ DEFINE_GDB_SYMBOL_BEGIN (EMACS_INT, VALMASK)
# define VALMASK (USE_LSB_TAG ? - (1 << GCTYPEBITS) : VAL_MAX)
DEFINE_GDB_SYMBOL_END (VALMASK)
/* Ignore 'alignas' on compilers lacking it. */
#if (!defined alignas && !defined __alignas_is_defined \
&& __STDC_VERSION__ < 202311 && __cplusplus < 201103)
# define alignas(a)
/* Support 'alignas (A)' if possible, where A is an integer constant. */
#ifndef alignas
# if __GNUC__ || 4 <= __clang_major__
/* This is more reliable than the alignas operator, in GCC 14. */
# define alignas(a) __attribute__ ((__aligned__ (a)))
# elif __STDC_VERSION__ < 202311 && __cplusplus < 201103
# define alignas(a) /* not supported */
# endif
#endif
/* The minimum alignment requirement for Lisp objects that is imposed by the