A follow-up to this article has more explanation about those instructions:

http://www.os2museum.com/wp/curious-instructions/

This is also the post about the ZALLOC instruction that it mentions, where apparently someone who worked on the original P6 describes it:

https://groups.google.com/d/msg/comp.arch/-/h6uCzd3QQwUJ?hl=...

To save anyone else a moment, "LINK" is the Microsoft Visual C++ linker, "LINK.EXE".