A key objective of RISC-V was that every aspect of the ISA must be based on an expired patent. It was felt that this is the only truly reliable defense against patent lawsuits.
It is surprising that patents would cover architecture as opposed to implementation. Or rather, would be surprising if one had not seen even worse examples over the last couple of decades.
What aspects of microprocessor instruction set architecture (as opposed to implementation) have been patented? Including patents which have now expired.
I know some relatively recent CPUs have included hardware support for various compression and cryptography algorithms, which are patented. The intent of this question is to leave those out, and focus on things that could reasonably be considered part of a general-purpose instruction set.
I'm also, in this context, not so much focused on the mainframe computers of the 50s and 60s, as on microprocessors, since their invention in the early 70s.