[Bug libstdc++/81173] New: bootstrap-ubsan errors in stl_bvector.h

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81173

            Bug ID: 81173
           Summary: bootstrap-ubsan errors in stl_bvector.h
           Product: gcc
           Version: 7.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

During bootstrap-ubsan I'm seeing hundreds of errors like:
.../gcc/obj16a/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/bits/stl_bvector.h:1132:18:
runtime error: null pointer passed as argument 1, which is declared to never be
null
This is from std::vector<bool>(0)
where it in the end calls
__builtin_memset(this->_M_impl._M_start._M_p, __x ? ~0 : 0,
(this->_M_impl._M_end_addr() - this->_M_impl._M_start._M_p)
* sizeof(_Bit_type));
and thus memset (NULL, 0, 0); which is UB.