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attr
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EDIT :: noalias.h
#ifndef RBIMPL_ATTR_NOALIAS_H /*-*-C++-*-vi:se ft=cpp:*/ #define RBIMPL_ATTR_NOALIAS_H /** * @file * @author Ruby developers <ruby-core@ruby-lang.org> * @copyright This file is a part of the programming language Ruby. * Permission is hereby granted, to either redistribute and/or * modify this file, provided that the conditions mentioned in the * file COPYING are met. Consult the file for details. * @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are * implementation details. Don't take them as canon. They could * rapidly appear then vanish. The name (path) of this header file * is also an implementation detail. Do not expect it to persist * at the place it is now. Developers are free to move it anywhere * anytime at will. * @note To ruby-core: remember that this header can be possibly * recursively included from extension libraries written in C++. * Do not expect for instance `__VA_ARGS__` is always available. * We assume C99 for ruby itself but we don't assume languages of * extension libraries. They could be written in C++98. * @brief Defines #RBIMPL_ATTR_NOALIAS. * * ### Q&A ### * * - Q: There are seemingly similar attributes named #RBIMPL_ATTR_CONST, * #RBIMPL_ATTR_PURE, and #RBIMPL_ATTR_NOALIAS. What are the difference? * * - A: Allowed operations are different. * * - #RBIMPL_ATTR_CONST ... Functions attributed by this are not allowed to * read/write _any_ pointers at all (there are exceptional situations * when reading a pointer is possible but forget that; they are too * exceptional to be useful). Just remember that everything pointer- * related are NG. * * - #RBIMPL_ATTR_PURE ... Functions attributed by this can read any * nonvolatile pointers, but no writes are allowed at all. The ability * to read _any_ nonvolatile pointers makes it possible to mark ::VALUE- * taking functions as being pure, as long as they are read-only. * * - #RBIMPL_ATTR_NOALIAS ... Can both read/write, but only through * pointers passed to the function as parameters. This is a typical * situation when you create a C++ non-static member function which only * concerns `this`. No global variables are allowed to read/write. So * this is not a super-set of being pure. If you want to read something, * that has to be passed to the function as a pointer. ::VALUE -taking * functions thus cannot be attributed as such. */ #include "ruby/internal/compiler_since.h" #include "ruby/internal/has/declspec_attribute.h" /** Wraps (or simulates) `__declspec((noalias))` */ #if RBIMPL_COMPILER_BEFORE(Clang, 12, 0, 0) # /* # * `::llvm::Attribute::ArgMemOnly` was buggy before. Maybe because nobody # * actually seriously used it. It seems they somehow mitigated the situation # * in LLVM 12. Still not found the exact changeset which fiexed the # * attribute, though. # * # * :FIXME: others (armclang, xlclang, ...) can also be affected? # */ # define RBIMPL_ATTR_NOALIAS() /* void */ #elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noalias) # define RBIMPL_ATTR_NOALIAS() __declspec(noalias) #else # define RBIMPL_ATTR_NOALIAS() /* void */ #endif #endif /* RBIMPL_ATTR_NOALIAS_H */
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