Reduced memory usage

src/build/scope/Variable.go

@@ -7,7 +7,7 @@ import (
 // Variable represents a named register.
 type Variable struct {
 	Name     string
-	Alive    int
+	Alive    uint8
 	Depth    uint8
 	Register cpu.Register
 }
@@ -19,9 +19,9 @@ func (v *Variable) IsAlive() bool {
 
 // Use reduces the lifetime counter by one.
 func (v *Variable) Use() {
-	v.Alive--
-
-	if v.Alive < 0 {
+	if v.Alive == 0 {
 		panic("incorrect number of variable use calls")
 	}
+
+	v.Alive--
 }