// Note that this potentially reorders successors of b, so it
// must be used very carefully.
func (b *Block) removeEdge(i int) {
	e := b.Succs[i]
	c := e.b
	j := e.i

	// Adjust b.Succs
	b.removeSucc(i)

	// Adjust c.Preds
	c.removePred(j)

	// Remove phi args from c's phis.
	for _, v := range c.Values {
		if v.Op != OpPhi {
			continue
		}
		c.removePhiArg(v, j)