[Bug c++/93803] [10 Regression] ICE: segmentation fault with constant initialization of class having a [[no_unique_address]] field

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93803

--- Comment #3 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:d6ff22074126d38829f25981de9d6940cd2a234c

commit r10-6865-gd6ff22074126d38829f25981de9d6940cd2a234c
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Feb 24 09:19:01 2020 -0500

    c++: Fix ICE with constexpr init and [[no_unique_address]] [PR93803]

    Here we crash when constexpr-initializing a class member of empty class
    type with [[no_unique_address]].  Without the attribute we would have
    a ctor (that initializes bar) of the form

      { .D.2173 = { .x = {} } }

    but with the attribute reduced_constant_expression_p gets

      { .x = {} }

    That means that "idx != field" is true for the latter and we see that
    foo, the base class of bar, is an empty class, so we want to look at
    the next initializable field (since empty class fields may not have an
    initializer).  But in this case there are no more, therefore accessing
    DECL_CHAIN (field) crashes.  Long story short, we need to avoid a crash
    on a null field when we're initializing a class that only contains an
    empty base class.

    While poking into this I discovered c++/93898, but that's a different
    problem.

    2020-02-26  Marek Polacek  <polacek@redhat.com>

        PR c++/93803 - ICE with constexpr init and [[no_unique_address]].
        * constexpr.c (reduced_constant_expression_p): Don't crash on a null
        field.

        * g++.dg/cpp2a/constexpr-init16.C: New test.
        * g++.dg/cpp2a/constexpr-init17.C: New test.