[Bug c++/102990] [9/10/11 Regression] ICE in tsubst_copy_and_build with NSDMI and double to int conversion

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102990

--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:6ba2a7e7474135b717c344030b114ffd6ad8ed7a

commit r11-9711-g6ba2a7e7474135b717c344030b114ffd6ad8ed7a
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Mar 22 18:42:27 2022 -0400

    c++: FIX_TRUNC_EXPR in tsubst [PR102990]

    This is a crash where a FIX_TRUNC_EXPR gets into tsubst_copy_and_build
    where it hits gcc_unreachable ().

    The history of tsubst_copy_and_build/FIX_TRUNC_EXPR is such that it
    was introduced in r181478, but it did the wrong thing, whereupon it
    was turned into gcc_unreachable () in r258821 (see this thread:
    <https://gcc.gnu.org/pipermail/gcc-patches/2018-March/495853.html>).

    In a template, we should never create a FIX_TRUNC_EXPR (that's what
    conv_unsafe_in_template_p is for).  But in this test we are NOT in
    a template when we call digest_nsdmi_init which ends up calling
    convert_like, converting 1.0e+0 to int, so convert_to_integer_1
    gives us a FIX_TRUNC_EXPR.

    But then when we get to parsing f's parameters, we are in a template
    when processing decltype(Helpers{}), and since r268321, when the
    compound literal isn't instantiation-dependent and the type isn't
    type-dependent, finish_compound_literal falls back to the normal
    processing, so it calls digest_init, which does fold_non_dependent_init
    and since the FIX_TRUNC_EXPR isn't dependent, we instantiate and
    therefore crash in tsubst_copy_and_build.

    The fateful call to fold_non_dependent_init comes from massage_init_elt,
    We shouldn't be calling f_n_d_i on the result of get_nsdmi.  This we can
    avoid by eschewing calling f_n_d_i on CONSTRUCTORs; their elements have
    already been folded.

            PR c++/102990

    gcc/cp/ChangeLog:

            * typeck2.c (massage_init_elt): Avoid folding CONSTRUCTORs.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/nsdmi-template22.C: New test.
            * g++.dg/cpp0x/nsdmi-template23.C: New test.

    (cherry picked from commit f0530882d99abc410bb080051aa04e5cea848f18)