> If the Zba extension is present, sh3add.uw is a single instruction for zero-extending idx from 32 bits to 64, multiplying it by sizeof(uint64_t), and adding it to slots.

Yay, we've got an equivalent of SIB byte but as three (six?) separate opcodes. Well, sub-opcodes.

It's a shame though that Zcmp extension didn't get into RVA23 even as an optional extension.