Paul Eggert wrote in <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109914#c6>: > So my idea that "[[reproducible]] and __attribute__((pure)) are supposed to be > the same thing" is incorrect. Similarly, [[unsequenced]] and > __attribute__((const) are not the same thing. Oh well. We may need to change > Gnulib because of these discrepancies.
Here's a patch that adds macros REPRODUCIBLE and UNSEQUENCED to the 'attribute' module, as well as _GL_ prefixed macros for Gnulib-internal use. I consulted ISO C 23 and the standardization document <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2956.htm>. 2024-05-27 Bruno Haible <br...@clisp.org> attribute: Support ISO C 23 [[reproducible]] and [[unsequenced]]. * m4/gnulib-common.m4 (gl_COMMON_BODY): Define _GL_ATTR_reproducible, _GL_ATTR_unsequenced, _GL_ATTRIBUTE_REPRODUCIBLE, _GL_ATTRIBUTE_UNSEQUENCED. * lib/attribute.h (UNSEQUENCED, REPRODUCIBLE): New macros. diff --git a/lib/attribute.h b/lib/attribute.h index 710341ba41..a7076c8b7e 100644 --- a/lib/attribute.h +++ b/lib/attribute.h @@ -195,22 +195,50 @@ /* Applies to: function. */ #define ATTRIBUTE_ALWAYS_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE -/* It is OK for a compiler to omit duplicate calls with the same arguments. +/* It is OK for a compiler to omit duplicate calls to the function with the + same arguments. This attribute is safe for a function that neither depends on nor affects observable state, and always returns exactly once - e.g., does not loop forever, and does not call longjmp. - (This attribute is stricter than ATTRIBUTE_PURE.) */ + (This attribute is stricter than ATTRIBUTE_PURE. It is equivalent to + UNSEQUENCED for a function that has no pointer or array parameters.) */ /* Applies to: functions. */ #define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST -/* It is OK for a compiler to omit duplicate calls with the same +/* It is OK for a compiler to move calls to the function and to omit duplicate + calls to the function with the same arguments. + This attribute is safe for a function that is effectless, idempotent, + stateless, and independent; see ISO C 23 § 6.7.12.7 for a definition of + these terms. + (This attribute is stricter than REPRODUCIBLE. It is equivalent to + ATTRIBUTE_CONST for a function that has no pointer or array parameters.) + See also <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2956.htm> and + <https://stackoverflow.com/questions/76847905/>. */ +/* Applies to: functions. */ +#define UNSEQUENCED _GL_ATTRIBUTE_UNSEQUENCED + +/* It is OK for a compiler to omit duplicate calls to the function with the same arguments if observable state is not changed between calls. - This attribute is safe for a function that does not affect - observable state, and always returns exactly once. - (This attribute is looser than ATTRIBUTE_CONST.) */ + This attribute is safe for a function that does not affect observable state + and always returns exactly once. + (This attribute is looser than ATTRIBUTE_CONST. It is equivalent to + REPRODUCIBLE for a function for which all pointer or array parameters have + 'const'-qualified target types.) */ /* Applies to: functions. */ #define ATTRIBUTE_PURE _GL_ATTRIBUTE_PURE +/* It is OK for a compiler to omit duplicate calls to the function with the same + arguments if observable state is not changed between calls. + This attribute is safe for a function that is effectless and idempotent; see + ISO C 23 § 6.7.12.7 for a definition of these terms. + (This attribute is looser than UNSEQUENCED. It is equivalent to + ATTRIBUTE_PURE for a function for which all pointer or array parameters have + 'const'-qualified target types.) + See also <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2956.htm> and + <https://stackoverflow.com/questions/76847905/>. */ +/* Applies to: functions. */ +#define REPRODUCIBLE _GL_ATTRIBUTE_REPRODUCIBLE + /* The function is rarely executed. */ /* Applies to: functions. */ #define ATTRIBUTE_COLD _GL_ATTRIBUTE_COLD diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4 index cb73044950..044ecc93f1 100644 --- a/m4/gnulib-common.m4 +++ b/m4/gnulib-common.m4 @@ -1,5 +1,5 @@ # gnulib-common.m4 -# serial 93 +# serial 94 dnl Copyright (C) 2007-2024 Free Software Foundation, Inc. dnl This file is free software; the Free Software Foundation dnl gives unlimited permission to copy and/or distribute it, @@ -114,8 +114,10 @@ AC_DEFUN([gl_COMMON_BODY] # define _GL_ATTR_nothrow _GL_GNUC_PREREQ (3, 3) # define _GL_ATTR_packed _GL_GNUC_PREREQ (2, 7) # define _GL_ATTR_pure _GL_GNUC_PREREQ (2, 96) +# define _GL_ATTR_reproducible 0 /* not yet supported, as of GCC 14 */ # define _GL_ATTR_returns_nonnull _GL_GNUC_PREREQ (4, 9) # define _GL_ATTR_sentinel _GL_GNUC_PREREQ (4, 0) +# define _GL_ATTR_unsequenced 0 /* not yet supported, as of GCC 14 */ # define _GL_ATTR_unused _GL_GNUC_PREREQ (2, 7) # define _GL_ATTR_warn_unused_result _GL_GNUC_PREREQ (3, 4) # endif @@ -206,7 +208,9 @@ AC_DEFUN([gl_COMMON_BODY] This attribute is safe for a function that neither depends on nor affects observable state, and always returns exactly once - e.g., does not loop forever, and does not call longjmp. - (This attribute is stricter than _GL_ATTRIBUTE_PURE.) */ + (This attribute is stricter than _GL_ATTRIBUTE_PURE. It is equivalent to + _GL_ATTRIBUTE_UNSEQUENCED for a function that has no pointer or array + parameters.) */ /* Applies to: functions. */ #ifndef _GL_ATTRIBUTE_CONST # if _GL_HAS_ATTRIBUTE (const) @@ -505,9 +509,9 @@ AC_DEFUN([gl_COMMON_BODY] minimizing the memory required. */ /* Applies to: struct members, struct, union, in C++ also: class. */ +#ifndef _GL_ATTRIBUTE_PACKED /* Oracle Studio 12.6 miscompiles code with __attribute__ ((__packed__)) despite __has_attribute OK. */ -#ifndef _GL_ATTRIBUTE_PACKED # if _GL_HAS_ATTRIBUTE (packed) && !defined __SUNPRO_C # define _GL_ATTRIBUTE_PACKED __attribute__ ((__packed__)) # else @@ -515,12 +519,14 @@ AC_DEFUN([gl_COMMON_BODY] # endif #endif -/* _GL_ATTRIBUTE_PURE declares that It is OK for a compiler to omit duplicate +/* _GL_ATTRIBUTE_PURE declares that it is OK for a compiler to omit duplicate calls to the function with the same arguments if observable state is not changed between calls. - This attribute is safe for a function that does not affect - observable state, and always returns exactly once. - (This attribute is looser than _GL_ATTRIBUTE_CONST.) */ + This attribute is safe for a function that does not affect observable state + and always returns exactly once. + (This attribute is looser than _GL_ATTRIBUTE_CONST. It is equivalent to + _GL_ATTRIBUTE_REPRODUCIBLE for a function for which all pointer or array + parameters have 'const'-qualified target types.) */ /* Applies to: functions. */ #ifndef _GL_ATTRIBUTE_PURE # if _GL_HAS_ATTRIBUTE (pure) @@ -530,6 +536,23 @@ AC_DEFUN([gl_COMMON_BODY] # endif #endif +/* _GL_ATTRIBUTE_REPRODUCIBLE declares that it is OK for a compiler to omit + duplicate calls to the function with the same arguments if observable state + is not changed between calls. + This attribute is safe for a function that is effectless and idempotent; see + ISO C 23 § 6.7.12.7 for a definition of these terms. + (This attribute is looser than _GL_ATTRIBUTE_UNSEQUENCED. It is equivalent + to _GL_ATTRIBUTE_PURE for a function for which all pointer or array + parameters have 'const'-qualified target types.) */ +/* Applies to: functions. */ +#ifndef _GL_ATTRIBUTE_REPRODUCIBLE +# if _GL_HAS_ATTRIBUTE (reproducible) +# define _GL_ATTRIBUTE_REPRODUCIBLE [[reproducible]] +# else +# define _GL_ATTRIBUTE_REPRODUCIBLE +# endif +#endif + /* _GL_ATTRIBUTE_RETURNS_NONNULL declares that the function's return value is a non-NULL pointer. */ /* Applies to: functions. */ @@ -554,6 +577,24 @@ AC_DEFUN([gl_COMMON_BODY] # endif #endif +/* _GL_ATTRIBUTE_UNSEQUENCED declares that it is OK for a compiler to move + calls to the function and to omit duplicate calls to the function with the + same arguments. + This attribute is safe for a function that is effectless, idempotent, + stateless, and independent; see ISO C 23 § 6.7.12.7 for a definition of + these terms. + (This attribute is stricter than _GL_ATTRIBUTE_REPRODUCIBLE. It is + equivalent to _GL_ATTRIBUTE_CONST for a function that has no pointer or + array parameters.) */ +/* Applies to: functions. */ +#ifndef _GL_ATTRIBUTE_UNSEQUENCED +# if _GL_HAS_ATTRIBUTE (unsequenced) +# define _GL_ATTRIBUTE_UNSEQUENCED [[unsequenced]] +# else +# define _GL_ATTRIBUTE_UNSEQUENCED +# endif +#endif + /* A helper macro. Don't use it directly. */ #ifndef _GL_ATTRIBUTE_UNUSED # if _GL_HAS_ATTRIBUTE (unused)
