Since the manual is effectively a copy of the old (maybe dead) GMP online document, the x86 CPU supported are still things like Pentium or Pentium III that appears at the beginning of this century. So, how about today's CPU like Core i9 and Xeon W? Is it still the so-called generic assembly or MPIR has provided specific optimized code for these modern CPUs?
PS, I don't understand who is using Pentium nowadays. Even if someone is, I don't understand what he is doing arbitrary precision arithmetic for.