There was always one instruction that made r14 special: BL, branch with link. Both r13 and r14 are special for exception handling and SWI instructions, beca

There was always one instruction that made r14 special: BL, branch with link. Both r13 and r14 are special for exception handling and SWI instructions, because they have extra versions in the register banks, specifically for the supervisor mode stack pointer and exception return address.