#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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