Reduction of parameterless tail-call to functions.

1. a0 (sum) is reduced, despite the complexity of the callee.

2. a1 (conflict) is not reduced, because the caller and callee have
   intersecting sets of labels.

3. a2 (usesResult) is not reduced, because it refers to a result variable.

-- go.mod --
module testdata
go 1.12

-- a/a0.go --
package a

func _() int {
	return sum(1, 2) //@ inline(re"sum", sum)
}

func sum(lo, hi int) int {
	total := 0
start:
	for i := lo; i <= hi; i++ {
		total += i
		if i == 6 {
			goto start
		} else if i == 7 {
			return -1
		}
	}
	return total
}

-- sum --
package a

func _() int {
	total := 0
start:
	for i := 1; i <= 2; i++ {
		total += i
		if i == 6 {
			goto start
		} else if i == 7 {
			return -1
		}
	}
	return total //@ inline(re"sum", sum)
}

func sum(lo, hi int) int {
	total := 0
start:
	for i := lo; i <= hi; i++ {
		total += i
		if i == 6 {
			goto start
		} else if i == 7 {
			return -1
		}
	}
	return total
}

-- a/a1.go --
package a

func _() int {
	hello:
	return conflict(1, 2) //@ inline(re"conflict", conflict)
	goto hello
}

func conflict(lo, hi int) int {
hello:
	return lo + hi
}

-- conflict --
package a

func _() int {
hello:
	return func() int {
	hello:
		return 1 + 2
	}() //@ inline(re"conflict", conflict)
	goto hello
}

func conflict(lo, hi int) int {
hello:
	return lo + hi
}

-- a/a2.go --
package a

func _() int {
	return usesResult(1, 2) //@ inline(re"usesResult", usesResult)
}

func usesResult(lo, hi int) (z int) {
	z = y + x
	return
}

-- usesResult --
package a

func _() int {
	return func() (z int) { z = y + x; return }() //@ inline(re"usesResult", usesResult)
}

func usesResult(lo, hi int) (z int) {
	z = y + x
	return
}