BTW, I am surprised that it is not easy to know which organizations exactly has signed such legal papers. It could happen (in big organizations) that such an assignment has been signed, and a putative minor contributor to GCC does not know about it yet.
There is a copyright list on gnu.org machines that people with accounts there have access to. It lists every person and organization with a copyright assignment. Personally, I think the list should be somewhere that *all* gcc maintainers have access to (not all of us have gnu.org accounts).
