func (s *regAllocState) clobberRegs(m regMask) {
	m &= s.allocatable & s.f.Config.gpRegMask // only integer register can contain pointers, only clobber them
	for m != 0 {
		r := pickReg(m)
		m &^= 1 << r
		x := s.curBlock.NewValue0(src.NoXPos, OpClobberReg, types.TypeVoid)
		s.f.setHome(x, &s.registers[r])
	}
}

// setOrig records that c's original value is the same as
// v's original value.