pub const fn reg_slot_or_ff(x: u8) -> u8Expand description
PVM2 GPR slot (0..=14) for x, or 0xFF if x has no slot — x0
(hardwired zero) or a reserved register (x16..x31). The gas
simulator reads 0xFF as “no dependency / no write”; both engines’ gas
paths use this (the recompiler via the const-folded REG_SLOT_LUT) so
gas agrees bit-for-bit. Note 0xFF conflates x0 with reserved — use
reg_is_reserved when that distinction matters.