How to diagnose a false positive warning

g++ 16 ends up triggering a new false positive warning in some of my
code that didn't trigger in g++ 15.  An example of this warning:

In file included from /home/md5i/src/ipfix/master/tests/build.hpp:6,
                 from /home/md5i/src/ipfix/master/tests/read.cpp:7:
In function ‘void ipfix::convert::to_chunk_unsafe(auto:65&&, T) [with T = unsigned int; auto:65 = std::span<unsigned char>]’,
    inlined from ‘build::message& build::message::set_domain(build::u32)’ at /home/md5i/src/ipfix/master/tests/build.hpp:202:29,
    inlined from ‘virtual void ReadTest_EmptyMessages_Test::TestBody()’ at /home/md5i/src/ipfix/master/tests/read.cpp:262:19:
/home/md5i/src/ipfix/master/src/../include/detail/conversions.hpp:244:14: error: writing 4 bytes into a region of size 0 [-Werror=stringop-overflow=]
  244 |   std::memcpy(data(chunk), start, size(chunk));
      |   ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In member function ‘virtual void ReadTest_EmptyMessages_Test::TestBody()’:
cc1plus: note: destination object is likely at address zero

I'm fairly certain that this is a false positive, but the code is too
complex to reproduce here.  I started to work on a minimal reproducer,
but, again, the code is quite layered and complex.  I know I can ignore
the warning using diagnostic pragmas, but I prefer not to do that unless
completely necessary.  Can anyone recommend a way to debug why this
warning is triggered?

-- 
Michael Welsh Duggan
([email protected])