diff options
Diffstat (limited to 'lib/attribute.h')
| -rw-r--r-- | lib/attribute.h | 108 |
1 files changed, 64 insertions, 44 deletions
diff --git a/lib/attribute.h b/lib/attribute.h index c85412d9..c50befdf 100644 --- a/lib/attribute.h +++ b/lib/attribute.h @@ -1,6 +1,6 @@ /* ATTRIBUTE_* macros for using attributes in GCC and similar compilers - Copyright 2020-2025 Free Software Foundation, Inc. + Copyright 2020-2026 Free Software Foundation, Inc. This file is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as @@ -89,7 +89,7 @@ _GL_ATTRIBUTE_NONNULL_IF_NONZERO, _GL_ATTRIBUTE_NONSTRING, _GL_ATTRIBUTE_NOTHROW, _GL_ATTRIBUTE_PACKED, _GL_ATTRIBUTE_PURE, _GL_ATTRIBUTE_REPRODUCIBLE, _GL_ATTRIBUTE_RETURNS_NONNULL, - _GL_ATTRIBUTE_SENTINEL, _GL_ATTRIBUTE_UNSEQUENCED. */ + _GL_ATTRIBUTE_SENTINEL, _GL_ATTRIBUTE_UNSEQUENCED, _GL_UNNAMED. */ #if !_GL_CONFIG_H_INCLUDED #error "Please include config.h first." #endif @@ -240,62 +240,68 @@ /* Applies to: functions. */ #define ATTRIBUTE_ALWAYS_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE -/* It is OK for a compiler to move calls to the function and to omit - calls to the function if another call has the same arguments or the - result is not used. - This attribute is safe for a function that neither depends on - nor affects state, and always returns exactly once - +/* It is OK for a compiler to move a call, or omit a duplicate call + and reuse a cached return value, even if the state changes between calls. + It is also OK to omit a call if the result is not used. + This attribute is safe if the function does not change observable state, + returns a value determined solely by its arguments' values + without examining state, and always returns exactly once - e.g., does not raise an exception, call longjmp, or loop forever. - (This attribute is stricter than ATTRIBUTE_PURE because the - function cannot observe state. It is stricter than UNSEQUENCED - because the function must return exactly once and cannot depend on - state addressed by its arguments.) */ + (This attribute is stricter than _GL_ATTRIBUTE_PURE because the + function cannot observe state. Unlike _GL_ATTRIBUTE_UNSEQUENCED + the function must return exactly once and cannot access state + addressed by its pointer arguments or that happens to have the same + value for all calls to the function, but the function is allowed to + return a pointer to storage that can be modified later. */ /* Applies to: functions. */ #define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST -/* It is OK for a compiler to move calls to the function and to omit duplicate - calls to the function with the same arguments, so long as the state - addressed by its arguments is the same. +/* It is OK for a compiler to move a call, or omit a duplicate call + and reuse a cached value returned either directly or indirectly via + a pointer, if the state addressed by its pointer arguments is the same; + however, pointer arguments cannot alias. 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 + stateless, and independent; see ISO C 23 § 6.7.13.8 for a definition of these terms. - (This attribute is stricter than REPRODUCIBLE because the function - must be stateless and independent. It is looser than ATTRIBUTE_CONST - because the function need not return exactly once and can depend - on state addressed by its arguments.) + (This attribute is stricter than _GL_ATTRIBUTE_REPRODUCIBLE because + the function must be stateless and independent. Unlike + _GL_ATTRIBUTE_CONST the function need not return exactly once, and + can depend on state accessed via its pointer arguments or that + happens to have the same value for all calls to the function, but + the function cannot return a pointer to storage whose contents + change later.) See also <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2956.htm> and - <https://stackoverflow.com/questions/76847905/>. - ATTENTION! Efforts are underway to change the meaning of this attribute. - See <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3424.htm>. */ + <https://stackoverflow.com/questions/76847905/>. */ /* Applies to: functions, pointer to functions, function type. */ #define UNSEQUENCED _GL_ATTRIBUTE_UNSEQUENCED -/* It is OK for a compiler to move calls to the function and to omit - calls to the function if another call has the same arguments or the - result is not used, and if observable state is the same. - 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 because the function - can depend on observable state. It is stricter than REPRODUCIBLE - because the function must return exactly once and cannot affect - state addressed by its arguments.) */ +/* It is OK for a compiler to move a call, or omit a duplicate call + and reuse a cached return value, if observable state is the same. + It is also OK to omit a call if the return value is not used. + This attribute is safe if the function does not change observable state, + returns a value determined solely by its arguments's values + together with observable state, and always returns exactly once. + (This attribute is looser than _GL_ATTRIBUTE_CONST because the function + can depend on observable state. + Unlike _GL_ATTRIBUTE_REPRODUCIBLE the function must return exactly + once and cannot change state addressed by its arguments, but the + function can return a pointer to storage whose contents change later.) */ /* Applies to: functions. */ #define ATTRIBUTE_PURE _GL_ATTRIBUTE_PURE -/* It is OK for a compiler to move calls to the function and to omit duplicate - calls to the function with the same arguments, so long as the state - addressed by its arguments is the same and is updated in time for - the rest of the program. - 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 because the function need - not be stateless and idempotent. It is looser than ATTRIBUTE_PURE - because the function need not return exactly once and can affect - state addressed by its arguments.) +/* It is OK for a compiler to move a call, or omit a duplicate call + and reuse a cached value returned either directly or indirectly via + a pointer, if other observable state is the same; + however, pointer arguments cannot alias. + This attribute is safe for a function that is effectless and idempotent; + see ISO C 23 § 6.7.13.8 for a definition of these terms. + (This attribute is looser than _GL_ATTRIBUTE_UNSEQUENCED because + the function need not be stateless or independent. + Unlike _GL_ATTRIBUTE_PURE the function need not return exactly once + and can change state addressed by its pointer arguments, but the + function cannot return a pointer to storage whose contents change later.) See also <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2956.htm> and - <https://stackoverflow.com/questions/76847905/>. - ATTENTION! Efforts are underway to change the meaning of this attribute. - See <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3424.htm>. */ + <https://stackoverflow.com/questions/76847905/>. */ /* Applies to: functions, pointer to functions, function type. */ #define REPRODUCIBLE _GL_ATTRIBUTE_REPRODUCIBLE @@ -328,4 +334,18 @@ #define ATTRIBUTE_MAY_ALIAS _GL_ATTRIBUTE_MAY_ALIAS +/* ==================== Unnamed function parameters ======================== */ + +/* Although UNNAMED is not an attribute, it is related to MAYBE_UNUSED + and so is defined here for convenience. */ + +/* UNNAMED (ID) is the "name" of an unnamed function parameter. + Each of the function's unnamed parameters should have a unique "name". + The "name" cannot be used. This ports both to C17 and earlier, which + lack unnamed parameters, and to C++ and later C, which have them. */ +/* Applies to: + - function parameters. */ +#define UNNAMED(id) _GL_UNNAMED (id) + + #endif /* _GL_ATTRIBUTE_H */ |