pass: first attempt at register allocation

reg/set.go

@@ -1,7 +1,7 @@
 package reg
 
 // Set is a set of registers.
-type Set map[ID]Register
+type Set map[Register]bool
 
 // NewEmptySet builds an empty register set.
 func NewEmptySet() Set {
@@ -20,7 +20,7 @@ func NewSetFromSlice(rs []Register) Set {
 // Clone returns a copy of s.
 func (s Set) Clone() Set {
 	c := NewEmptySet()
-	for _, r := range s {
+	for r := range s {
 		c.Add(r)
 	}
 	return c
@@ -28,17 +28,17 @@ func (s Set) Clone() Set {
 
 // Add r to s.
 func (s Set) Add(r Register) {
-	s[r.ID()] = r
+	s[r] = true
 }
 
 // Discard removes r from s, if present.
 func (s Set) Discard(r Register) {
-	delete(s, r.ID())
+	delete(s, r)
 }
 
 // Update adds every register in t to s.
 func (s Set) Update(t Set) {
-	for _, r := range t {
+	for r := range t {
 		s.Add(r)
 	}
 }
@@ -52,7 +52,7 @@ func (s Set) Difference(t Set) Set {
 
 // DifferenceUpdate removes every element of t from s.
 func (s Set) DifferenceUpdate(t Set) {
-	for _, r := range t {
+	for r := range t {
 		s.Discard(r)
 	}
 }
@@ -62,10 +62,21 @@ func (s Set) Equals(t Set) bool {
 	if len(s) != len(t) {
 		return false
 	}
-	for _, r := range s {
-		if _, found := t[r.ID()]; !found {
+	for r := range s {
+		if _, found := t[r]; !found {
 			return false
 		}
 	}
 	return true
 }
+
+// OfKind returns the set of elements of s with kind k.
+func (s Set) OfKind(k Kind) Set {
+	t := NewEmptySet()
+	for r := range s {
+		if r.Kind() == k {
+			t.Add(r)
+		}
+	}
+	return t
+}