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Diffstat (limited to 'include/ruby/internal/attr/noalias.h')
| -rw-r--r-- | include/ruby/internal/attr/noalias.h | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/include/ruby/internal/attr/noalias.h b/include/ruby/internal/attr/noalias.h new file mode 100644 index 0000000000..0790ef60e5 --- /dev/null +++ b/include/ruby/internal/attr/noalias.h @@ -0,0 +1,69 @@ +#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 */ |