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e9fb2bc873
It is reported that on a system of i386 System V ABI, GCC returns 8 for __alignof__(double). OTOH the ABI defines alignments of double to be 4, and ISO/IEC 9899:2011 reads that _Alignof(double) shall return 4 on such machine. What we want in ruby is 4 instead of 8 there. We cannot use __alignof__. Additionally, both old GCC / old clang return 8 for _Alignof(double) on such platforms. They are their bugs, and already fixed in recent versions. But we have to support older compilers for a while. Shall check sanity of _Alignof.
132 lines
4.4 KiB
C++
132 lines
4.4 KiB
C++
#ifndef RBIMPL_STDALIGN_H /*-*-C++-*-vi:se ft=cpp:*/
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#define RBIMPL_STDALIGN_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_ALIGNAS / #RBIMPL_ALIGNOF
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*/
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#include "ruby/internal/config.h"
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#ifdef STDC_HEADERS
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# include <stddef.h>
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#endif
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#include "ruby/internal/attr/artificial.h"
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#include "ruby/internal/attr/const.h"
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#include "ruby/internal/attr/constexpr.h"
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#include "ruby/internal/attr/forceinline.h"
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#include "ruby/internal/compiler_is.h"
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#include "ruby/internal/has/attribute.h"
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#include "ruby/internal/has/declspec_attribute.h"
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#include "ruby/internal/has/extension.h"
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#include "ruby/internal/has/feature.h"
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/**
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* Wraps (or simulates) `alignas`. This is C++11's `alignas` and is _different_
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* from C11 `_Alignas`. For instance,
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*
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* ```CXX
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* typedef struct alignas(128) foo { int foo } foo;
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* ```
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*
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* is a valid C++ while
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*
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* ```C
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* typedef struct _Alignas(128) foo { int foo } foo;
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* ```
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*
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* is an invalid C because:
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*
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* - You cannot `struct _Alignas`.
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* - A `typedef` cannot have alignments.
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*/
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#if defined(__cplusplus) && RBIMPL_HAS_FEATURE(cxx_alignas)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__cplusplus) && (__cplusplus >= 201103L)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__INTEL_CXX11_MODE__)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__GXX_EXPERIMENTAL_CXX0X__)
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# define RBIMPL_ALIGNAS alignas
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#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(align)
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# define RBIMPL_ALIGNAS(_) __declspec(align(_))
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#elif RBIMPL_HAS_ATTRIBUTE(aliged)
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# define RBIMPL_ALIGNAS(_) __attribute__((__aligned__(_)))
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#else
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# define RBIMPL_ALIGNAS(_) /* void */
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#endif
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/**
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* Wraps (or simulates) `alignof`.
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*
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* We want C11's `_Alignof`. However in spite of its clear language, compilers
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* (including GCC and clang) tend to have buggy implementations. We have to
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* avoid such things to resort to our own version.
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*
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
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* @see https://bugs.llvm.org/show_bug.cgi?id=26547
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*/
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#if defined(__STDC_VERSION__) && defined(HAVE__ALIGNOF)
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# /* Autoconf detected availability of a sane `_Alignof()`. */
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# define RBIMPL_ALIGNOF(T) RB_GNUC_EXTENSION(_Alignof(T))
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#elif defined(__cplusplus)
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# /* C++11 `alignof()` can be buggy. */
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# /* see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 */
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# /* But don't worry, we can use templates and `constexpr`. */
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# define RBIMPL_ALIGNOF(T) ruby::rbimpl_alignof<T>()
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namespace ruby {
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template<typename T>
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RBIMPL_ATTR_CONSTEXPR(CXX11)
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RBIMPL_ATTR_ARTIFICIAL()
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RBIMPL_ATTR_FORCEINLINE()
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RBIMPL_ATTR_CONST()
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static size_t
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rbimpl_alignof()
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{
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typedef struct {
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char _;
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T t;
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} type;
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return offsetof(type, t);
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}
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}
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#elif RBIMPL_COMPILER_IS(MSVC)
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# /* Windows have no alignment glitch.*/
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# define RBIMPL_ALIGNOF __alignof
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#else
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# /* :BEWARE: It is an undefined behaviour to define a struct/union inside of
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# * `offsetof()`! This section is the last resort. If your compiler somehow
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# * supports querying alignment of a type please add your own definition of
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# * `RBIMPL_ALIGNOF` instead. */
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# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */
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# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t)
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#endif
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#endif /* RBIMPL_STDALIGN_H */
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