| `RISCVThreadStart                      -> (y_reg, y_sreg)
| `RISCVStopFetching                     -> (y_reg, y_sreg)

| `RISCVUTYPE (_, r0, _)                 -> fold_reg r0 (y_reg, y_sreg)
| `RISCVJAL (_, r0)                      -> fold_reg r0 (y_reg, y_sreg)
| `RISCVJALR (_, r0, r1)                 -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVBType (_, r0, r1, _)             -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVIType (_, r0, r1, _)             -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVShiftIop (_, r0, r1, _)          -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVRType (r0, r1, r2, _)            -> fold_reg r0 (fold_reg r1 (fold_reg r2 (y_reg, y_sreg)))
| `RISCVLoad (_, r0, r1, _, _, _, _)     -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVStore (_, r0, r1, _, _, _)       -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVADDIW (_, r0, r1)                -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVSHIFTW (_, r0, r1, _)            -> fold_reg r0 (fold_reg r1 (y_reg, y_sreg))
| `RISCVRTYPEW (r0, r1, r2, _)           -> fold_reg r0 (fold_reg r1 (fold_reg r2 (y_reg, y_sreg)))
| `RISCVFENCE (_, _)                     -> (y_reg, y_sreg)
| `RISCVFENCE_TSO (_, _)                 -> (y_reg, y_sreg)
| `RISCVFENCEI                           -> (y_reg, y_sreg)
| `RISCVLoadRes (_, _, rs1, _, rd)       -> fold_reg rs1 (fold_reg rd (y_reg, y_sreg))
| `RISCVStoreCon (_, _, rs2, rs1, _, rd) -> fold_reg rs2 (fold_reg rs1 (fold_reg rd (y_reg, y_sreg)))
| `RISCVAMO (_, _, _, rs2, rs1, _, rd)   -> fold_reg rs2 (fold_reg rs1 (fold_reg rd (y_reg, y_sreg)))