Re: [C++ PATCH] Incremental patch for -std=gnu++2a and -std=c++2a

[Jason Merrill <jason at redhat dot com>]

OK.

On Fri, Sep 15, 2017 at 8:49 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> On Thu, Sep 14, 2017 at 11:28:09PM +0200, Jakub Jelinek wrote:
>> > I'd be tempted to say leave all this, and march 1z -> 2a for the _next_ standard.  2020 or so is a good first stab at the date.
>>
>> I didn't want to add c++2a and gnu++2a in the same patch, it can be added
>> incrementally and readd the above wording.  Unless somebody else is planning
>> to do that, I can do that next.
>
> Here is so far untested incremental patch on top of the 1z -> 17 patch,
> mostly using Andrew's patch, but adjusted so that it applies and with
> various additions and small tweaks.
>
> 2017-09-15  Andrew Sutton  <andrew.n.sutton@gmail.com>
>             Jakub Jelinek  <jakub@redhat.com>
>
>         Add support for -std=c++2a.
>         * c-common.h (cxx_dialect): Add cxx2a as a dialect.
>         * opt.c: Add options for -std=c++2a and -std=gnu++2a.
>         * c-opts.c (set_std_cxx2a): New.
>         (c_common_handle_option): Set options when -std=c++2a is enabled.
>         (c_common_post_options): Adjust comments.
>         (set_std_cxx14, set_std_cxx17): Likewise.
>
>         * doc/cpp.texi (__cplusplus): Document value for -std=c++2a
>         or -std=gnu+2a.
>         * doc/invoke.texi: Document -std=c++2a and -std=gnu++2a.
>
>         * lib/target-supports.exp (check_effective_target_c++17): Return
>         1 also if check_effective_target_c++2a.
>         (check_effective_target_c++17_down): New.
>         (check_effective_target_c++2a_only): New.
>         (check_effective_target_c++2a): New.
>         * g++.dg/cpp2a/cplusplus.C: New.
>
>         * include/cpplib.h (c_lang): Add CXX2A and GNUCXX2A.
>         * init.c (lang_defaults): Add rows for CXX2A and GNUCXX2A.
>         (cpp_init_builtins): Set __cplusplus to 201709L for C++2a.
>
> --- gcc/c-family/c-common.h.jj  2017-09-14 22:53:34.977313456 +0200
> +++ gcc/c-family/c-common.h     2017-09-15 12:59:25.539053983 +0200
> @@ -703,7 +703,9 @@ enum cxx_dialect {
>    /* C++14 */
>    cxx14,
>    /* C++17 */
> -  cxx17
> +  cxx17,
> +  /* C++2a (C++20?) */
> +  cxx2a
>  };
>
>  /* The C++ dialect being used. C++98 is the default.  */
> --- gcc/c-family/c-opts.c.jj    2017-09-14 22:53:34.978313443 +0200
> +++ gcc/c-family/c-opts.c       2017-09-15 14:28:21.287595277 +0200
> @@ -111,6 +111,7 @@ static void set_std_cxx98 (int);
>  static void set_std_cxx11 (int);
>  static void set_std_cxx14 (int);
>  static void set_std_cxx17 (int);
> +static void set_std_cxx2a (int);
>  static void set_std_c89 (int, int);
>  static void set_std_c99 (int);
>  static void set_std_c11 (int);
> @@ -637,6 +638,12 @@ c_common_handle_option (size_t scode, co
>         set_std_cxx17 (code == OPT_std_c__17 /* ISO */);
>        break;
>
> +    case OPT_std_c__2a:
> +    case OPT_std_gnu__2a:
> +      if (!preprocessing_asm_p)
> +       set_std_cxx2a (code == OPT_std_c__2a /* ISO */);
> +      break;
> +
>      case OPT_std_c90:
>      case OPT_std_iso9899_199409:
>        if (!preprocessing_asm_p)
> @@ -938,7 +945,7 @@ c_common_post_options (const char **pfil
>         warn_narrowing = 1;
>
>        /* Unless -f{,no-}ext-numeric-literals has been used explicitly,
> -        for -std=c++{11,14,17} default to -fno-ext-numeric-literals.  */
> +        for -std=c++{11,14,17,2a} default to -fno-ext-numeric-literals.  */
>        if (flag_iso && !global_options_set.x_flag_ext_numeric_literals)
>         cpp_opts->ext_numeric_literals = 0;
>      }
> @@ -1589,7 +1596,7 @@ set_std_cxx14 (int iso)
>    flag_no_gnu_keywords = iso;
>    flag_no_nonansi_builtin = iso;
>    flag_iso = iso;
> -  /* C++11 includes the C99 standard library.  */
> +  /* C++14 includes the C99 standard library.  */
>    flag_isoc94 = 1;
>    flag_isoc99 = 1;
>    cxx_dialect = cxx14;
> @@ -1604,7 +1611,7 @@ set_std_cxx17 (int iso)
>    flag_no_gnu_keywords = iso;
>    flag_no_nonansi_builtin = iso;
>    flag_iso = iso;
> -  /* C++11 includes the C99 standard library.  */
> +  /* C++17 includes the C11 standard library.  */
>    flag_isoc94 = 1;
>    flag_isoc99 = 1;
>    flag_isoc11 = 1;
> @@ -1612,6 +1619,22 @@ set_std_cxx17 (int iso)
>    lang_hooks.name = "GNU C++17";
>  }
>
> +/* Set the C++ 202a draft standard (without GNU extensions if ISO).  */
> +static void
> +set_std_cxx2a (int iso)
> +{
> +  cpp_set_lang (parse_in, iso ? CLK_CXX2A: CLK_GNUCXX2A);
> +  flag_no_gnu_keywords = iso;
> +  flag_no_nonansi_builtin = iso;
> +  flag_iso = iso;
> +  /* C++17 includes the C11 standard library.  */
> +  flag_isoc94 = 1;
> +  flag_isoc99 = 1;
> +  flag_isoc11 = 1;
> +  cxx_dialect = cxx2a;
> +  lang_hooks.name = "GNU C++17"; /* Pretend C++17 until standardization.  */
> +}
> +
>  /* Args to -d specify what to dump.  Silently ignore
>     unrecognized options; they may be aimed at toplev.c.  */
>  static void
> --- gcc/c-family/c.opt.jj       2017-09-14 22:53:34.977313456 +0200
> +++ gcc/c-family/c.opt  2017-09-15 12:59:25.542053945 +0200
> @@ -1932,6 +1932,10 @@ std=c++17
>  C++ ObjC++
>  Conform to the ISO 2017 C++ standard.
>
> +std=c++2a
> +C++ ObjC++
> +Conform to the ISO 2020(?) C++ draft standard (experimental and incomplete support).
> +
>  std=c11
>  C ObjC
>  Conform to the ISO 2011 C standard.
> @@ -1990,6 +1994,10 @@ std=gnu++17
>  C++ ObjC++
>  Conform to the ISO 2017 C++ standard with GNU extensions.
>
> +std=gnu++2a
> +C++ ObjC++
> +Conform to the ISO 2020(?) C++ draft standard with GNU extensions (experimental and incomplete support).
> +
>  std=gnu11
>  C ObjC
>  Conform to the ISO 2011 C standard with GNU extensions.
> --- gcc/doc/cpp.texi.jj 2017-09-14 22:53:34.000000000 +0200
> +++ gcc/doc/cpp.texi    2017-09-15 14:23:32.394163061 +0200
> @@ -1877,7 +1877,10 @@ selected, the value of the macro is
>  @code{199711L} for the 1998 C++ standard,
>  @code{201103L} for the 2011 C++ standard,
>  @code{201402L} for the 2014 C++ standard,
> -@code{201703L} for the 2017 C++ standard.
> +@code{201703L} for the 2017 C++ standard,
> +or an unspecified value strictly larger than @code{201703L} for the
> +experimental languages enabled by @option{-std=c++2a} and
> +@option{-std=gnu++2a}.
>
>  @item __OBJC__
>  This macro is defined, with value 1, when the Objective-C compiler is in
> --- gcc/doc/invoke.texi.jj      2017-09-15 14:21:24.861740328 +0200
> +++ gcc/doc/invoke.texi 2017-09-15 14:22:04.607248773 +0200
> @@ -1879,6 +1879,16 @@ The name @samp{c++1z} is deprecated.
>  @itemx gnu++1z
>  GNU dialect of @option{-std=c++17}.
>  The name @samp{gnu++1z} is deprecated.
> +
> +@item c++2a
> +The next revision of the ISO C++ standard, tentatively planned for
> +2020.  Support is highly experimental, and will almost certainly
> +change in incompatible ways in future releases.
> +
> +@item gnu++2a
> +GNU dialect of @option{-std=c++2a}.  Support is highly experimental,
> +and will almost certainly change in incompatible ways in future
> +releases.
>  @end table
>
>  @item -fgnu89-inline
> --- gcc/testsuite/lib/target-supports.exp.jj    2017-09-14 22:53:35.000000000 +0200
> +++ gcc/testsuite/lib/target-supports.exp       2017-09-15 14:34:44.232867697 +0200
> @@ -7863,8 +7863,35 @@ proc check_effective_target_c++17_only {
>      }
>      return 0
>  }
> +
>  proc check_effective_target_c++17 { } {
> -    return [check_effective_target_c++17_only]
> +    if [check_effective_target_c++17_only] {
> +       return 1
> +    }
> +    return [check_effective_target_c++2a]
> +}
> +proc check_effective_target_c++17_down { } {
> +    if ![check_effective_target_c++] {
> +       return 0
> +    }
> +    return [expr ![check_effective_target_c++2a] ]
> +}
> +
> +proc check_effective_target_c++2a_only { } {
> +    global cxx_default
> +    if ![check_effective_target_c++] {
> +       return 0
> +    }
> +    if [check-flags { { } { } { -std=c++2a -std=gnu++2a } }] {
> +       return 1
> +    }
> +    if { $cxx_default == "c++20" && [check-flags { { } { } { } { -std=* } }] } {
> +       return 1
> +    }
> +    return 0
> +}
> +proc check_effective_target_c++2a { } {
> +    return [check_effective_target_c++2a_only]
>  }
>
>  # Check for C++ Concepts TS support, i.e. -fconcepts flag.
> --- gcc/testsuite/g++.dg/cpp2a/cplusplus.C.jj   2017-09-15 12:59:25.543053933 +0200
> +++ gcc/testsuite/g++.dg/cpp2a/cplusplus.C      2017-09-15 12:59:25.543053933 +0200
> @@ -0,0 +1,4 @@
> +// { dg-do compile }
> +// { dg-options "-std=c++2a" }
> +
> +static_assert(__cplusplus > 201703L);
> --- libcpp/include/cpplib.h.jj  2017-09-15 12:59:25.544053920 +0200
> +++ libcpp/include/cpplib.h     2017-09-15 13:01:03.516828002 +0200
> @@ -171,7 +171,8 @@ enum cpp_ttype
>  enum c_lang {CLK_GNUC89 = 0, CLK_GNUC99, CLK_GNUC11,
>              CLK_STDC89, CLK_STDC94, CLK_STDC99, CLK_STDC11,
>              CLK_GNUCXX, CLK_CXX98, CLK_GNUCXX11, CLK_CXX11,
> -            CLK_GNUCXX14, CLK_CXX14, CLK_GNUCXX17, CLK_CXX17, CLK_ASM};
> +            CLK_GNUCXX14, CLK_CXX14, CLK_GNUCXX17, CLK_CXX17,
> +            CLK_GNUCXX2A, CLK_CXX2A, CLK_ASM};
>
>  /* Payload of a NUMBER, STRING, CHAR or COMMENT token.  */
>  struct GTY(()) cpp_string {
> --- libcpp/init.c.jj    2017-09-15 12:59:25.545053908 +0200
> +++ libcpp/init.c       2017-09-15 13:00:43.267081384 +0200
> @@ -110,6 +110,8 @@ static const struct lang_flags lang_defa
>    /* CXX14    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    1,     1,     1,   0 },
>    /* GNUCXX17 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1 },
>    /* CXX17    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1 },
> +  /* GNUCXX2A */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1 },
> +  /* CXX2A    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1 },
>    /* ASM      */  { 0,  0,  1,  0,  0,  0,  0,   0,   0,   0,    0,     0,     0,   0 }
>  };
>
> @@ -497,7 +499,10 @@ cpp_init_builtins (cpp_reader *pfile, in
>
>    if (CPP_OPTION (pfile, cplusplus))
>      {
> -      if (CPP_OPTION (pfile, lang) == CLK_CXX17
> +      if (CPP_OPTION (pfile, lang) == CLK_CXX2A
> +         || CPP_OPTION (pfile, lang) == CLK_GNUCXX2A)
> +       _cpp_define_builtin (pfile, "__cplusplus 201709L");
> +      else if (CPP_OPTION (pfile, lang) == CLK_CXX17
>           || CPP_OPTION (pfile, lang) == CLK_GNUCXX17)
>         _cpp_define_builtin (pfile, "__cplusplus 201703L");
>        else if (CPP_OPTION (pfile, lang) == CLK_CXX14
>
>
>         Jakub