Fixed incorrect register lifetime in for loops

tests/programs/fibonacci.q

@@ -0,0 +1,26 @@
+main() {
+	for i := 0..10 {
+		assert fib1(i) == fib2(i)
+	}
+}
+
+fib1(n int) -> int {
+	b := 0
+	c := 1
+
+	for 0..n {
+		a := b
+		b = c
+		c = a + b
+	}
+
+	return b
+}
+
+fib2(n int) -> int {
+	if n <= 1 {
+		return n
+	}
+
+	return fib2(n - 1) + fib2(n - 2)
+}

tests/programs_test.go

@@ -62,6 +62,7 @@ var programs = []struct {
 	{"loop-lifetime", 0},
 	{"loop-in-loop", 0},
 	{"for", 0},
+	{"fibonacci", 0},
 	{"memory-free", 0},
 	{"out-of-memory", 0},
 	{"index-static", 0},