The reason you do this is because you have an instruction that means nothing. You save space by recycling it. Why bother making a new instruction? That's agains

The reason you do this is because you have an instruction that means nothing. You save space by recycling it. Why bother making a new instruction? That's against the whole idea of RISC. It's not their problem if the compiler writer doesn't read the documentation. I mean, the documentation is literally written for them.