for i, v := range check.Args {
			if v != end {
				continue
			}

			check.SetArg(i, start)
			goto replacedEnd
		}
		panic(fmt.Sprintf("unreachable, ind: %v, start: %v, end: %v", ind, start, end))
	replacedEnd:

		for i, v := range ind.Args {
			if v != start {
				continue
			}

			ind.SetArg(i, end)
			goto replacedStart
		}

				// of a value so that a x.Uses==1 rule condition
				// fires reliably.
				for i, a := range v.Args {
					if a.Op != OpCopy {
						continue
					}
					aa := copySource(a)
					v.SetArg(i, aa)
					// If a, a copy, has a line boundary indicator, attempt to find a new value
					// to hold it.  The first candidate is the value that will replace a (aa),
					// if it shares the same block and line and is eligible.