[Bug c++/96873] New: Internal compiler error in alias_ctad_tweaks

[Bug c++/96873] New: Internal compiler error in alias_ctad_tweaks

[mateusz.pusz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

            Bug ID: 96873
           Summary: Internal compiler error in alias_ctad_tweaks
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mateusz.pusz at gmail dot com
  Target Milestone: ---

#include <cstdint>

template<typename CharT, std::size_t N>
struct basic_fixed_string {
  CharT data_[N + 1] = {};

  constexpr basic_fixed_string(CharT ch) noexcept { data_[0] = ch; }

  constexpr basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
  {
    if constexpr (N != 0)
      for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];
  }
};

template<typename CharT, std::size_t N>
basic_fixed_string(const CharT (&str)[N]) -> basic_fixed_string<CharT, N - 1>;

template<typename CharT>
basic_fixed_string(CharT) -> basic_fixed_string<CharT, 1>;

template<std::size_t N>
using fixed_string = basic_fixed_string<char, N>;

template<fixed_string>
struct X {};

X<"txt"> x;

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[mateusz.pusz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #1 from Mateusz Pusz <mateusz.pusz at gmail dot com> ---
Similar error but in a different line happens for:

```
#include <cstdint>

template<typename CharT, std::size_t N>
struct basic_fixed_string {
  CharT data_[N + 1] = {};

  constexpr basic_fixed_string(CharT ch) noexcept { data_[0] = ch; }

  constexpr basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
  {
    if constexpr (N != 0)
      for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];
  }

  [[nodiscard]] constexpr const CharT& operator[](std::size_t index) const
noexcept { return data_[index]; }
  [[nodiscard]] constexpr CharT operator[](std::size_t index) noexcept { return
data_[index]; }

  template<std::size_t N2>
  [[nodiscard]] constexpr friend basic_fixed_string<CharT, N + N2> operator+(
      const basic_fixed_string& lhs, const basic_fixed_string<CharT, N2>& rhs)
noexcept
  {
    CharT txt[N + N2 + 1] = {};

    for(std::size_t i = 0; i != N; ++i) txt[i] = lhs[i];
    for(std::size_t i = 0; i != N2; ++i) txt[N + i] = rhs[i];

    return basic_fixed_string<CharT, N + N2>(txt);
  }
};

template<typename CharT, std::size_t N>
basic_fixed_string(const CharT (&str)[N]) -> basic_fixed_string<CharT, N - 1>;

template<typename CharT>
basic_fixed_string(CharT) -> basic_fixed_string<CharT, 1>;

template<std::size_t N>
using fixed_string = basic_fixed_string<char, N>;

fixed_string txt = "txt";
```

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2020-08-31
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94691,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94560,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=93085
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed, but most likely a dup of one of the bugs in See Also.  The
backtraces aren't identical, but I'm sure these are all related.

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[mateusz.pusz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #3 from Mateusz Pusz <mateusz.pusz at gmail dot com> ---
Are there any chances for it to be fixed for gcc-11 or gcc-10.3? This feature
is essential for the Physical Units library for C++Next.

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Yeah, hopefully for both.

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[mateusz.pusz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #5 from Mateusz Pusz <mateusz.pusz at gmail dot com> ---
Thanks!

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |johelegp at gmail dot com

--- Comment #6 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Could this be a duplicate of Bug 95486?

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:1a19d334ce493ec2ce2daeac74beef63fd67e2bc

commit r11-8104-g1a19d334ce493ec2ce2daeac74beef63fd67e2bc
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Apr 9 18:02:38 2021 -0400

    c++: deduction guide using alias [PR99180]

    alias_ctad_tweaks was expecting that all deduction guides for the class
    would be suitable for deduction from the alias definition; in this case,
the
    deduction guide uses 'true' and the alias B uses 'false', so deduction
    fails.  But that's OK, we just don't use that deduction guide.  I also
    noticed that we were giving up on deduction entirely if substitution failed
    for some guide; we should only give up on that particular deduction guide.

    We ought to give a better diagnostic about this case when deduction fails,
    but that can wait.

    gcc/cp/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/99118
            PR c++/96873
            * pt.c (alias_ctad_tweaks): Handle failure better.

    gcc/testsuite/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias5.C: New test.
            * g++.dg/cpp2a/class-deduction-alias6.C: New test.
            * g++.dg/cpp2a/class-deduction-alias7.C: New test.
            * g++.dg/cpp2a/class-deduction-alias8.C: New test.

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |DUPLICATE
             Status|NEW                         |RESOLVED

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Dup.

*** This bug has been marked as a duplicate of bug 93295 ***

[Bug c++/96873] Internal compiler error in alias_ctad_tweaks

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96873

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:92e9b2a995f718f1c2ab1cd0840b439c24d3535f

commit r10-9852-g92e9b2a995f718f1c2ab1cd0840b439c24d3535f
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Apr 9 18:02:38 2021 -0400

    c++: deduction guide using alias [PR99180]

    alias_ctad_tweaks was expecting that all deduction guides for the class
    would be suitable for deduction from the alias definition; in this case,
the
    deduction guide uses 'true' and the alias B uses 'false', so deduction
    fails.  But that's OK, we just don't use that deduction guide.  I also
    noticed that we were giving up on deduction entirely if substitution failed
    for some guide; we should only give up on that particular deduction guide.

    We ought to give a better diagnostic about this case when deduction fails,
    but that can wait.

    gcc/cp/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/99118
            PR c++/96873
            * pt.c (alias_ctad_tweaks): Handle failure better.

    gcc/testsuite/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias5.C: New test.
            * g++.dg/cpp2a/class-deduction-alias6.C: New test.
            * g++.dg/cpp2a/class-deduction-alias7.C: New test.
            * g++.dg/cpp2a/class-deduction-alias8.C: New test.