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From: "jbassett271 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/98367] New: ICE with CTAD non-type template parameter
Date: Fri, 18 Dec 2020 03:38:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98367

            Bug ID: 98367
           Summary: ICE with CTAD non-type template parameter
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jbassett271 at gmail dot com
  Target Milestone: ---

This ICEs the compiler with a segfault (see https://godbolt.org/z/ddceoM ):

template <typename A>
struct ctad_t {
    A a;
};

template <ctad_t T>
struct myclass {
};

template <typename Something>
constexpr auto myobject =3D ctad_t {Something::value};

template <typename Something>
using thing =3D myclass<myobject<Something>>;


Compiled with (grabbed from the Compiler Explorer link): g++ -g -o output.s
-masm=3Dintel -S -fdiagnostics-color=3Dalways -std=3Dc++2a example.cpp

I have also confirmed this on my own machine with gcc version 10.1.0.

Tested with GCC versions on Compiler Explorer:
 - gcc version 11.0.0 20201216 (experimental)
 - gcc version 10.2.0
 - gcc version 10.1.0
 - gcc version 9.3.0
 - gcc version 9.2.0
 - gcc version 9.1.0
 - gcc version 8.3.0
 - gcc version 8.2.0
 - gcc version 8.1.0

These also segfaulted with -std=3Dc++1z instead of -std=3Dc++2a:
 - gcc version 7.5.0
 - gcc version 7.4.0
 - gcc version 7.3.0
 - gcc version 7.2.0
 - gcc version 7.1.0

Earlier versions did not support CTAD.

Inlining the `object` variable does not segfault, but emits a message about
being unable to perform CTAD: https://godbolt.org/z/drWT6h=