s.startRegsMask &^= regMask(1) << r
		}
	}

	s.freeReg(r)
	s.usedSinceBlockStart |= regMask(1) << r
	return r
}

// makeSpill returns a Value which represents the spilled value of v.
// b is the block in which the spill is used.
func (s *regAllocState) makeSpill(v *Value, b *Block) *Value {
	vi := &s.values[v.ID]
	if vi.spill != nil {
		// Final block not known - keep track of subtree where restores reside.