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0dea31c437
I observed CI failures. https://github.com/ruby/ruby/actions/runs/1240165911 It turns out that RBIMPL_ATTR_NOALIAS was not mature before. Skip using it for old clang, and everything work as expected.
69 lines
3.5 KiB
C++
69 lines
3.5 KiB
C++
#ifndef RBIMPL_ATTR_NOALIAS_H /*-*-C++-*-vi:se ft=cpp:*/
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#define RBIMPL_ATTR_NOALIAS_H
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/**
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* @file
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* @author Ruby developers <ruby-core@ruby-lang.org>
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* @copyright This file is a part of the programming language Ruby.
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* Permission is hereby granted, to either redistribute and/or
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* modify this file, provided that the conditions mentioned in the
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* file COPYING are met. Consult the file for details.
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* @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are
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* implementation details. Don't take them as canon. They could
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* rapidly appear then vanish. The name (path) of this header file
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* is also an implementation detail. Do not expect it to persist
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* at the place it is now. Developers are free to move it anywhere
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* anytime at will.
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* @note To ruby-core: remember that this header can be possibly
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* recursively included from extension libraries written in C++.
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* Do not expect for instance `__VA_ARGS__` is always available.
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* We assume C99 for ruby itself but we don't assume languages of
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* extension libraries. They could be written in C++98.
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* @brief Defines #RBIMPL_ATTR_NOALIAS.
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*
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* ### Q&A ###
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*
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* - Q: There are seemingly similar attributes named #RBIMPL_ATTR_CONST,
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* #RBIMPL_ATTR_PURE, and #RBIMPL_ATTR_NOALIAS. What are the difference?
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*
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* - A: Allowed operations are different.
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*
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* - #RBIMPL_ATTR_CONST ... Functions attributed by this are not allowed to
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* read/write _any_ pointers at all (there are exceptional situations
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* when reading a pointer is possible but forget that; they are too
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* exceptional to be useful). Just remember that everything pointer-
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* related are NG.
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*
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* - #RBIMPL_ATTR_PURE ... Functions attributed by this can read any
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* nonvolatile pointers, but no writes are allowed at all. The ability
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* to read _any_ nonvolatile pointers makes it possible to mark ::VALUE-
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* taking functions as being pure, as long as they are read-only.
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*
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* - #RBIMPL_ATTR_NOALIAS ... Can both read/write, but only through
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* pointers passed to the function as parameters. This is a typical
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* situation when you create a C++ non-static member function which only
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* concerns `this`. No global variables are allowed to read/write. So
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* this is not a super-set of being pure. If you want to read something,
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* that has to be passed to the function as a pointer. ::VALUE -taking
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* functions thus cannot be attributed as such.
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*/
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#include "ruby/internal/compiler_since.h"
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#include "ruby/internal/has/declspec_attribute.h"
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/** Wraps (or simulates) `__declspec((noalias))` */
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#if RBIMPL_COMPILER_BEFORE(Clang, 12, 0, 0)
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# /*
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# * `::llvm::Attribute::ArgMemOnly` was buggy before. Maybe because nobody
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# * actually seriously used it. It seems they somehow mitigated the situation
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# * in LLVM 12. Still not found the exact changeset which fiexed the
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# * attribute, though.
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# *
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# * :FIXME: others (armclang, xlclang, ...) can also be affected?
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# */
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# define RBIMPL_ATTR_NOALIAS() /* void */
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#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noalias)
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# define RBIMPL_ATTR_NOALIAS() __declspec(noalias)
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#else
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# define RBIMPL_ATTR_NOALIAS() /* void */
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#endif
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#endif /* RBIMPL_ATTR_NOALIAS_H */
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