Function rv_slot_u8 

pub fn rv_slot_u8(r: u8) -> u8

PVM2 register → simulator slot (u8). 0xFF means “no register” — the simulator’s feed_direct interprets that as “skip dep / no write”. Single source: crate::regs::reg_slot_or_ff (the recompiler reads the same classification via REG_SLOT_LUT, so gas agrees bit-for-bit).