[Sharlin]

Well, it is artificial in the sense that it's meant to be code emitted by the code generator of a compiler for a high-level language with very different idioms. And the architectures of these early microcomputers obviously don't exactly prioritize being easy compiler targets.

[userbinator]

Here's a sample of compiled Z80 code (the bootloader for one of these: https://en.wikipedia.org/wiki/S1_MP3_player ) generated by a C compiler --- of course, a commercial one and not a cheap one at that (IAR Embedded Workbench for Z80.) You can see that it has absolutely no problem using nearly all the registers:

https://pastebin.com/raw/f3919adf