[Bug c++/96282] [8/9 Regression] internal compiler error: in output_constructor_regular_field

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96282

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:fef6ee0790de58f16128a0de87571ba7e04b8320

commit r9-9455-gfef6ee0790de58f16128a0de87571ba7e04b8320
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Aug 5 15:05:30 2020 -0400

    c++: cxx_eval_vec_init after zero-initialization [PR96282]

    In the first testcase below, expand_aggr_init_1 sets up t's default
    constructor such that the ctor first zero-initializes the entire base b,
    followed by calling b's default constructor, the latter of which just
    default-initializes the array member b::m via a VEC_INIT_EXPR.

    So upon constexpr evaluation of this latter VEC_INIT_EXPR, ctx->ctor is
    nonempty due to the prior zero-initialization, and we proceed in
    cxx_eval_vec_init to append new constructor_elts to the end of ctx->ctor
    without first checking if a matching constructor_elt already exists.
    This leads to ctx->ctor having two matching constructor_elts for each
    index.

    This patch fixes this issue by truncating a zero-initialized array
    CONSTRUCTOR in cxx_eval_vec_init_1 before we begin appending array
    elements to it.  We propagate its zeroed out state during evaluation by
    clearing CONSTRUCTOR_NO_CLEARING on each new appended aggregate element.

    gcc/cp/ChangeLog:

            PR c++/96282
            * constexpr.c (cxx_eval_vec_init_1): Truncate ctx->ctor and
            then clear CONSTRUCTOR_NO_CLEARING on each appended element
            initializer if we're initializing a previously zero-initialized
            array object.

    gcc/testsuite/ChangeLog:

            PR c++/96282
            * g++.dg/cpp0x/constexpr-array26.C: New test.
            * g++.dg/cpp0x/constexpr-array27.C: New test.

    Co-authored-by: Jason Merrill <jason@redhat.com>
    (cherry picked from commit d21252de6c81ed236d8981d47b9a57dc4f1c6d57)