[Bug c++/94592] [10 Regression] ICE in non-type template parameter with constexpr constructor

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94592

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:d419e176d74162af6513be0b3bc1031726543993

commit r10-7836-gd419e176d74162af6513be0b3bc1031726543993
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Apr 17 15:47:15 2020 -0400

    c++: Fix ICE with { } as template argument [PR94592]

    As an extension (there should be a CWG about this though), we support
    braced-init-list as a template argument, but convert_nontype_argument
    had trouble digesting them.  We ICEd because of the double coercion we
    perform for template arguments: convert_nontype_argument called from
    finish_template_type got a { }, and since a class type was involved and
    we were in a template, convert_like created an IMPLICIT_CONV_EXPR.  Then
    the second conversion of the same argument crashed in constexpr.c
    because the IMPLICIT_CONV_EXPR had gotten wrapped in a TARGET_EXPR.
    Another issue was that an IMPLICIT_CONV_EXPR leaked to constexpr.c when
    building an aggregate init.

    We should have instantiated the IMPLICIT_CONV_EXPR in the first call to
    convert_nontype_argument, but we didn't, because the call to
    is_nondependent_constant_expression returned false because it checks
    !BRACE_ENCLOSED_INITIALIZER_P.  Then non_dep was false even though the
    expression didn't contain anything dependent and we didn't instantiate
    it in convert_nontype_argument.  To fix this, check
    BRACE_ENCLOSED_INITIALIZER_P in cxx_eval_outermost_constant_expr rather
    than in is_nondependent_*.

            PR c++/94592
            * constexpr.c (cxx_eval_outermost_constant_expr): Return when T is
            a BRACE_ENCLOSED_INITIALIZER_P.
            (is_nondependent_constant_expression): Don't check
            BRACE_ENCLOSED_INITIALIZER_P.
            (is_nondependent_static_init_expression): Likewise.

            * g++.dg/cpp2a/nontype-class34.C: New test.
            * g++.dg/cpp2a/nontype-class35.C: New test.