sark_spoil.py

def spoils(f):
    """return the list of spoiled registers
    default is r0-r3
    not too smart, but safe - i.e. if list of spoiled registers is smaller than 4 - it's quite safe to assume only these registers are spoiled
    the opposite is false
    """
    spoiled = ['R0', 'R1', 'R2', 'R3']
    
    if any(f.xrefs_from):
        return spoiled
    regs = set()
    for l in f.lines:
        for op in l.insn.operands:
            regs.update(op.regs)
    if not regs.issubset(set(spoiled + ['LR', 'PC'])):
        return spoiled
    if all(reg in regs for reg in spoiled):
        return spoiled
    return list(regs)