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@kaizen_nagoya(Dr. Kiyoshi Ogawa)

C++ N4606 (84)7.6.3 Carries dependency attribute [dcl.attr.depend] p196

Last updated at Posted at 2018-04-17

#はじめに
N4606 Working Draft, Standard for Programming Language C++
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/#mailing2016-11
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

n4606は、ISO/IEC JTC1 SC22 WG21の作業原案(Working Draft)です。
公式のISO/IEC 14882原本ではありません。
ISO/IEC JTC1 SC22 WG21では、可能な限り作業文書を公開し、幅広い意見を求めています。
一連の記事はコード断片をコンパイルできる形にする方法を検討してコンパイル、リンク、実行して、規格案の原文と処理系(g++, Clang++)との違いを確認し、技術内容を検討し、ISO/IEC JTC1 SC22 WG21にフィードバックするために用います。
また、CERT C++, MISRA C++等のコーディング標準のコード断片をコンパイルする際の参考にさせていただこうと考えています。CERT C++, MISRA C++が標準化の動きとの時間的なずれがあれば確認できれば幸いです。また、boostライブラリとの関連、Linux OS, TOPPERSカーネル、g++(GCC), clang++(LLVM）との関係も調査中です。
何か、抜け漏れ、耳より情報がありましたらおしらせくださると幸いです。

##作業方針
１）コンパイルエラーを収集する。
２）コンパイルエラーをなくす方法を検討する。
コンパイルエラーになる例を示すだけが目的のコードは、コンパイルエラーをなくすのではなく、コンパイルエラーの種類を収集するだけにする。
文法を示すのが目的のコード場合に、コンパイルエラーをなくすのに手間がかかる場合は、順次作業します。
３）リンクエラーをなくす方法を検討する。
文法を示すのが目的のコード場合に、リンクエラーをなくすのに手間がかかる場合は、順次作業します。
４）意味のある出力を作る。
コンパイル、リンクが通っても、意味のある出力を示そうとすると、コンパイル・リンクエラーが出て収拾できそうにない場合がある。順次作業します。

１）だけのものから４）まで進んだものと色々ある状態です。一歩でも前に進むご助言をお待ちしています。「検討事項」の欄に現状を記録するようにしています。

list

N4606 Working Draft 2016, ISO/IEC 14882, C++ standard(1) coding list
https://qiita.com/kaizen_nagoya/items/df5d62c35bd6ed1c3d43/

Compiler

###clang++ --version
clang version 6.0.0 (tags/RELEASE_600/final)

###g++-7 --version
g++-7 (Homebrew GCC 7.3.0_1) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.

#(84)7.6.3 Carries dependency attribute [dcl.attr.depend]
p196

p196.cpp
// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p196.cpp(84)7.6.3 Carries dependency attribute [dcl.attr.depend]"

#include <iostream>
#include <atomic>
#include <thread>

/* Translation unit A. /
struct foo { int a; int* b; };
std::atomic foo_head[10];
int foo_array[10][10];
[[carries_dependency]] struct foo* f(int i) {
return foo_head[i].load(memory_order_consume);
}
int g(int* x, int* y [[carries_dependency]]) {
return kill_dependency(foo_array[x][*y]);
/ Translation unit A. /
struct foo { int a; int* b; };
std::atomic foo_head[10];
int foo_array[10][10];
[[carries_dependency]] struct foo* f(int i) {
return foo_head[i].load(memory_order_consume);
}
int g(int* x, int* y [[carries_dependency]]) {
return kill_dependency(foo_array[*x][*y]);

int main(){
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p196
$ clang++ p196.cpp
p196.cpp:11:21: error: cannot form array of deduced class template specialization type
std::atomic foo_head[10];
                    ^
p196.cpp:11:13: error: declaration of variable 'foo_head' with deduced type 'std::atomic [10]' requires an initializer
std::atomic foo_head[10];
            ^
p196.cpp:14:25: error: use of undeclared identifier 'memory_order_consume'; did you mean 'std::memory_order_consume'?
return foo_head[i].load(memory_order_consume);
                        ^~~~~~~~~~~~~~~~~~~~
                        std::memory_order_consume
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/atomic:583:27: note: 'std::memory_order_consume' declared here
    memory_order_relaxed, memory_order_consume, memory_order_acquire,
                          ^
p196.cpp:17:33: error: array subscript is not an integer
return kill_dependency(foo_array[x][*y]);
                                ^~
p196.cpp:20:21: error: cannot form array of deduced class template specialization type
std::atomic foo_head[10];
                    ^
p196.cpp:20:13: error: declaration of variable 'foo_head' with deduced type 'std::atomic [10]' requires an initializer
std::atomic foo_head[10];
            ^
p196.cpp:22:45: error: function definition is not allowed here
[[carries_dependency]] struct foo* f(int i) {
                                            ^
p196.cpp:25:46: error: function definition is not allowed here
int g(int* x, int* y [[carries_dependency]]) {
                                             ^
p196.cpp:31:2: error: expected '}'
}
 ^
p196.cpp:16:46: note: to match this '{'
int g(int* x, int* y [[carries_dependency]]) {
                                             ^
9 errors generated.

$ g++-7 p196.cpp
p196.cpp:11:1: error: template placeholder type 'atomic' must be followed by a simple declarator-id
 std::atomic foo_head[10];
 ^~~
In file included from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/atomic:41:0,
                 from p196.cpp:6:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/atomic_base.h:126:12: note: 'template<class _Tp> struct std::atomic' declared here
     struct atomic;
            ^~~~~~
p196.cpp:11:24: error: 'foo_head' declared as array of 'atomic'
 std::atomic foo_head[10];
                        ^
p196.cpp:13:43: warning: 'carries_dependency' attribute directive ignored [-Wattributes]
 [[carries_dependency]] struct foo* f(int i) {
                                           ^
p196.cpp: In function 'foo* f(int)':
p196.cpp:14:8: error: 'foo_head' was not declared in this scope
 return foo_head[i].load(memory_order_consume);
        ^~~~~~~~
p196.cpp:14:8: note: suggested alternative: 'foo_array'
 return foo_head[i].load(memory_order_consume);
        ^~~~~~~~
        foo_array
p196.cpp:14:25: error: 'memory_order_consume' was not declared in this scope
 return foo_head[i].load(memory_order_consume);
                         ^~~~~~~~~~~~~~~~~~~~
p196.cpp:14:25: note: suggested alternative:
In file included from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/atomic:41:0,
                 from p196.cpp:6:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/atomic_base.h:58:7: note:   'memory_order_consume'
       memory_order_consume,
       ^~~~~~~~~~~~~~~~~~~~
p196.cpp: At global scope:
p196.cpp:16:43: warning: 'carries_dependency' attribute directive ignored [-Wattributes]
 int g(int* x, int* y [[carries_dependency]]) {
                                           ^
p196.cpp: In function 'int g(int*, int*)':
p196.cpp:17:35: error: invalid types 'int [10][10][int*]' for array subscript
 return kill_dependency(foo_array[x][*y]);
                                   ^
p196.cpp:17:8: error: 'kill_dependency' was not declared in this scope
 return kill_dependency(foo_array[x][*y]);
        ^~~~~~~~~~~~~~~
p196.cpp:17:8: note: suggested alternative:
In file included from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/atomic:41:0,
                 from p196.cpp:6:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/atomic_base.h:111:5: note:   'std::kill_dependency'
     kill_dependency(_Tp __y) noexcept
     ^~~~~~~~~~~~~~~
p196.cpp:20:1: error: template placeholder type 'atomic' must be followed by a simple declarator-id
 std::atomic foo_head[10];
 ^~~
In file included from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/atomic:41:0,
                 from p196.cpp:6:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/atomic_base.h:126:12: note: 'template<class _Tp> struct std::atomic' declared here
     struct atomic;
            ^~~~~~
p196.cpp:20:24: error: 'foo_head' declared as array of 'atomic'
 std::atomic foo_head[10];
                        ^
p196.cpp:22:45: error: a function-definition is not allowed here before '{' token
 [[carries_dependency]] struct foo* f(int i) {
                                             ^
p196.cpp:25:43: warning: 'carries_dependency' attribute directive ignored [-Wattributes]
 int g(int* x, int* y [[carries_dependency]]) {
                                           ^
p196.cpp:25:46: error: a function-definition is not allowed here before '{' token
 int g(int* x, int* y [[carries_dependency]]) {
                                              ^
p196.cpp:31:1: error: expected '}' at end of input
 }
 ^

#検討事項
コンパイルエラーをなくす修正。

#参考資料

コンパイル用shell script C版(clangとgcc)とC++版(clang++とg++)
https://qiita.com/kaizen_nagoya/items/74220c0577a512c2d7da

Clang/Clang++(LLVM) gcc/g++(GNU) コンパイラ警告等比較
https://qiita.com/kaizen_nagoya/items/9a82b958cc3aeef0403f

Qiitaに投稿するCのStyle例(暫定)
https://qiita.com/kaizen_nagoya/items/946df1528a6a1ef2bc0d

MISRA C++ 5-0-16
https://qiita.com/kaizen_nagoya/items/7df2d4e05db724752a74

C++ Templates Part1 BASICS Chapter 3. Class Templates 3.2 Use of Class Template Stack stack1test.cpp
https://qiita.com/kaizen_nagoya/items/cd5fc49106fad5a4e9ed

ISO/IEC TS 17961:2013 C Secure Coding Rules(1) All list(to be confirmed)
https://qiita.com/kaizen_nagoya/items/54e056195c4f11b850a1

C言語（C++)に対する誤解、曲解、無理解、爽快。
https://qiita.com/kaizen_nagoya/items/3f3992c9722c1cee2e3a

C Puzzle Bookの有り難み5つ、C言語規格及びCコンパイラの特性を認識
https://qiita.com/kaizen_nagoya/items/d89a48c1536a02ecdec9

'wchar.h' file not found で困った clang++ macOS
https://qiita.com/kaizen_nagoya/items/de15cd46d657517fac11

Open POSIX Test Suiteの使い方を調べはじめました
https://qiita.com/kaizen_nagoya/items/644d5e407f5faf96e6dc

MISRA-C 2012 Referenceに掲載している文献の入手可能性を確認
https://qiita.com/kaizen_nagoya/items/96dc8b125e462d5575bb

どうやって MISRA Example Suiteをコンパイルするか
https://qiita.com/kaizen_nagoya/items/fbdbff5ff696e2ca7f00

MISRA C まとめ #include
https://qiita.com/kaizen_nagoya/items/f1a79a7cbd281607c7c9

#文書履歴
0.10 初稿 2080417

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