[guerrilla]

> * Adding logical registers breaks backwards compatibility, or at best means you get no speedup on things written (/compiled) for fewer logical registers. Adding physical registers lets you improve performance without recompiling.

> * Adding logical registers increases complexity for people writing assembly and/or compilers. Adding physical registers moves that complexity to people designing CPUs.

These two points are the same thing: compatibility and compatibility is what Intel and AMD have lived on from day one with x86. It's why we still live with this really weird instruction set with all of its historical oddities. Certain features of real mode weren't removed until long into the 64-bit era. Adding things isn't any better: If you wanted to add more add more registers, you'd have to change instruction encoding and the instruction space is finite (actually limited to 15 bytes.) That would be rather disruptive.