The getSrcFromCopy helper nowadays return a MachineOperand pointer,
so talking about zero_reg was incorrect as it nowadays return
a nullptr when not finding a copy like instruction.
}
// getSrcFromCopy - Get the original source register for a GPR64 <--> FPR64
-// copy instruction. Return zero_reg if the instruction is not a copy.
+// copy instruction. Return nullptr if the instruction is not a copy.
static MachineOperand *getSrcFromCopy(MachineInstr *MI,
const MachineRegisterInfo *MRI,
unsigned &SubReg) {