[Bug sanitizer/95693] [8/9 Regression] Incorrect error from undefined behavior sanitizer

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95693

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:a3458b238e1297ad7ab6f92ab1a00837f282691a

commit r8-10875-ga3458b238e1297ad7ab6f92ab1a00837f282691a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 22 19:03:23 2021 +0100

    c++: Fix up ubsan false positives on references [PR95693]

    Alex' 2 years old change to build_zero_init_1 to return NULL pointer with
    reference type for references breaks the sanitizers, the assignment of NULL
    to a reference typed member is then instrumented before it is overwritten
    with a non-NULL address later on.
    That change has been done to fix error recovery ICE during
    process_init_constructor_record, where we:
              if (TYPE_REF_P (fldtype))
                {
                  if (complain & tf_error)
                    error ("member %qD is uninitialized reference", field);
                  else
                    return PICFLAG_ERRONEOUS;
                }
    a few lines earlier, but then continue and ICE when build_zero_init returns
    NULL.

    The following patch reverts the build_zero_init_1 change and instead
creates
    the NULL with reference type constants during the error recovery.

    The pr84593.C testcase Alex' change was fixing still works as before.

    2021-01-22  Jakub Jelinek  <jakub@redhat.com>

            PR sanitizer/95693
            * init.c (build_zero_init_1): Revert the 2018-03-06 change to
            return build_zero_cst for reference types.
            * typeck2.c (process_init_constructor_record): Instead call
            build_zero_cst here during error recovery instead of
build_zero_init.

            * g++.dg/ubsan/pr95693.C: New test.

    (cherry picked from commit e5750f847158e7f9bdab770fd9c5fff58c5074d3)