[Bug c++/104284] [9/10/11/12 Regression] ICE: unexpected expression '<anonymous>' of kind implicit_conv_expr since r9-6073-ge8b3c1bc3ba22dcf

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104284

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:9fdac7e16c940fb6264e6ddaf99c761f1a64a054

commit r12-7805-g9fdac7e16c940fb6264e6ddaf99c761f1a64a054
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Mar 17 14:39:37 2022 -0400

    c++: ICE with template code in constexpr [PR104284]

    Since r9-6073 cxx_eval_store_expression preevaluates the value to
    be stored, and that revealed a crash where a template code (here,
    code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*.

    It happens because we're performing build_vec_init while processing
    a template, which calls get_temp_regvar which creates an INIT_EXPR.
    This INIT_EXPR's RHS contains an rvalue conversion so we create an
    IMPLICIT_CONV_EXPR.  Its operand is not type-dependent and the whole
    INIT_EXPR is not type-dependent.  So we call build_non_dependent_expr
    which, with -fchecking=2, calls fold_non_dependent_expr.  At this
    point the expression still has an IMPLICIT_CONV_EXPR, which ought to
    be handled in instantiate_non_dependent_expr_internal.  However,
    tsubst_copy_and_build doesn't handle INIT_EXPR; it will just call
    tsubst_copy which does nothing when args is null.  So we fail to
    replace the IMPLICIT_CONV_EXPR and ICE.

    The problem is that we call build_vec_init in a template in the
    first place.  We can avoid doing so by checking p_t_d before
    calling build_aggr_init in check_initializer.

            PR c++/104284

    gcc/cp/ChangeLog:

            * decl.cc (check_initializer): Don't call build_aggr_init in
            a template.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/constexpr-104284-1.C: New test.
            * g++.dg/cpp1y/constexpr-104284-2.C: New test.
            * g++.dg/cpp1y/constexpr-104284-3.C: New test.
            * g++.dg/cpp1y/constexpr-104284-4.C: New test.