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From: "serpent7776 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/104470] New: internal compiler error: Segmentation fault
 compiling std::variant with -std=c++20
Date: Wed, 09 Feb 2022 18:25:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104470

            Bug ID: 104470
           Summary: internal compiler error: Segmentation fault compiling
                    std::variant with -std=3Dc++20
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: serpent7776 at gmail dot com
  Target Milestone: ---

Created attachment 52396
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52396&action=3Dedit
Preprocessed source

I encountered an internal compiler error while compiling the following code=
 in
c++20 mode (no other flags are needed):

#include <variant>

template <typename T>
struct Foo
{
        T value;
};

template <typename T>
struct Bar
{
        T value;
};

template <typename T>
using V =3D std::variant<Foo<T>, Bar<T>>;

int main()
{
        V e =3D Foo("a");
}

When I switch to c++17 mode compiler does not crash.

I tested it on g++ 10.3.0 on FreeBSD 12.3-RELEASE-p1, but I can also reprod=
uce
it on trunk version here https://godbolt.org/z/vn5Ws14Ma

Full error:

# g++10 -std=3Dc++20 ice.ii
In file included from ice.cpp:1:
/usr/local/lib/gcc10/include/c++/variant: In substitution of 'template<class
... _Types> template<class _Tp, class> using __accepted_type =3D
std::variant<_Types>::__to_type<__accepted_index<_Tp> > [with _Tp =3D _Tp&&;
<template-parameter-2-2> =3D typename std::enable_if<std::variant<Foo<T>, B=
ar<T>
>::__not_self<_Tp&&>, void>::type; _Types =3D {Foo<T>, Bar<T>}]':
ice.cpp:20:15:   required from here
/usr/local/lib/gcc10/include/c++/variant:1335:36: internal compiler error:
Segmentation fault
 1335 |  using __accepted_type =3D __to_type<__accepted_index<_Tp>>;
      |                                    ^~~~~~~~~~~~~~~~~~~~
libbacktrace could not find executable to open=