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Subject: [Bug c++/94219] ICE in cxx_eval_bare_aggregate, at cp/constexpr.c:3790
Date: Sat, 04 Apr 2020 16:18:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94219

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:37244b217a7329792f4ec48027f63cf5010b0ea8

commit r10-7556-g37244b217a7329792f4ec48027f63cf5010b0ea8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 2 12:59:34 2020 -0400

    c++: Fix constexpr evaluation of self-modifying CONSTRUCTORs [PR94219]

    This PR reveals that cxx_eval_bare_aggregate and cxx_eval_store_express=
ion
do
    not anticipate that a constructor element's initializer could mutate the
    underlying CONSTRUCTOR.  Evaluation of the initializer could add new
elements to
    the underlying CONSTRUCTOR, thereby potentially invalidating any pointe=
rs
to
    or assumptions about the CONSTRUCTOR's elements, and so these routines
should be
    prepared for that.

    To fix this problem, this patch makes cxx_eval_bare_aggregate and
    cxx_eval_store_expression recompute the constructor_elt pointers through
which
    we're assigning, after it evaluates the initializer.  Care is taken to =
to
not
    slow down the common case where the initializer does not modify the
underlying
    CONSTRUCTOR.

    gcc/cp/ChangeLog:

            PR c++/94219
            PR c++/94205
            * constexpr.c (get_or_insert_ctor_field): Split out (while addi=
ng
            support for VECTOR_TYPEs, and optimizations for the common case)
            from ...
            (cxx_eval_store_expression): ... here.  Rename local variable
            'changed_active_union_member_p' to 'activated_union_member_p'.=
=20
Record
            the sequence of indexes into 'indexes' that yields the subobject
we're
            assigning to.  Record the integer offsets of the constructor
indexes
            we're assigning through into 'index_pos_hints'.  After evaluati=
ng
the
            initializer of the store expression, recompute 'valp' using
'indexes'
            and using 'index_pos_hints' as hints.
            (cxx_eval_bare_aggregate): Tweak comments.  Use
get_or_insert_ctor_field
            to recompute the constructor_elt pointer we're assigning through
after
            evaluating each initializer.

    gcc/testsuite/ChangeLog:

            PR c++/94219
            PR c++/94205
            * g++.dg/cpp1y/constexpr-nsdmi3.C: New test.
            * g++.dg/cpp1y/constexpr-nsdmi4.C: New test.
            * g++.dg/cpp1y/constexpr-nsdmi5.C: New test.
            * g++.dg/cpp1z/lambda-this5.C: New test.=